Summary of the article: Non-invasive assessment of myocardial perfusion is done through: -Single-photon emission computed tomography is widely available and validated as well as being compatible with other stress modalities as exercise and dobutamine but with motion artifacts, radiation exposure Low sensitivity in detecting mild stenosis and sub endocardial perfusion defects -Myocardial contrast echocardiography offers better spatial resolution, as well no radiation dye, can be used along stress dobutamine but lower image quality and more artifacts and non |FDA approved dyes. -Positron emission tomography: better spatial resolution compared to SPECT, with less artifacts but much higher costs · Cardiac MRI: rapid test with high spatial resolution but with dye that may cause nephrogenic systemic sclerosis. · Cardiac CT: rapid with high spatial resolution but with high ionizing radiation dose.
Mohamed Ghanem
2 years ago
SPECT MPI :
Three radiotracers are commonly used clinically for SPECT MPI. Thallium-201, Tc-99m sestamibi and Tc-99m tetrofosmin
The first pass extraction of Tl-201, Tc-99m sestamibi, and Tc-99m tetrofosmin are 86%, 64%, and 54%, respectively, at resting flows. SPECT MPI Imaging Protocols:
With the same-day rest-stress protocol using a Tc99m-labeled perfusion agent
A typical Tl-201 technique might comprise injection during the maximum of the stress, imaging around 10 minutes later, and then obtaining a redistribution picture about 4 hours later
A dual-isotope protocol in which Tl-201 is used for the rest images and then a Tc-99m perfusion agent is used during stress soon thereafter. Advantages and Limitations of SPECT :
Advantages :
The widely used and well verified and readily available
compatible with a variety of stress modalities, including as exercise, dobutamine, or vasodilators
high temporal resolution is not as necessary, and signal-to-noise ratio (SNR) can be increased by accumulating data over a longer time
Limitations :
relatively long acquisition protocols and considerably poorer spatial resolution
, decrease detection of subendocardial perfusion defects
Sensitivity in diagnosing mild-to-moderate stenoses is limited by the roll-off of tracer uptake at greater myocardial blood flows
scatter and partial volume artefacts in the inferior wall owing to gut and biliary activity
variable attenuation artefacts resulting from breast or subdiaphragmatic attenuation
motion artefacts related to patient and respiratory movements
PET MPI : Advantages
Compared to SPECT, the spatial resolution of PET is better
PET tracers have significantly less roll-off of extraction at high flows as compared with Tc-99m– based SPECT agent
attenuation artifacts are less
The radiation dosages for PET are lower than for SPECT Limitations:
greater cost
For all imaging agents other than those tagged with F-18 or Rb-82, cyclotron requirements result in more restrictions
it is typically more difficult to detect motion artefacts during the scan, making it more difficult to assess how they affect the photos
Contrast Echocardiography Perfusion Techniques Advantages;
Ionizing radiation is absent.
increased spatial detail.
measurement of myocardial blood flow in absolute terms.
Accessibility and reasonably affordable price
Restrictions:
Motion-affected photography
Artifacts Pattern
Operator specific
No FDA approval
Theepa Mariamutu
2 years ago
Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected CAD.
Common Noninvasive myocardial perfusion test:
Single-photon emission computed tomography (SPECT) is most commonly used.
Myocardial contrast echocardiography (MCE).
Positron emission tomography (PET).
Cardiac MRI (CMR).
Cardiac computed tomography (CT).
Methods for Inducing Coronary Vasodilation:
Exercise induces coronary vasodilation.
Dipyridamole, adenosine, and regadenoson and Dobutamine,
SPECT MPI:
Radiotracers:
Thallium-201
Tc-99m sestamibi
Tc-99m tetrofosmin.
SPECT MPI Imaging Protocols:
Same-day rest-stress protocol: Tc99m-labeled perfusion.
First injection at rest is followed by imaging roughly 30 minutes later.
A second injection with 2 to 3 times the activity is administered during peak stress.
A typical Tl-201 protocol:
Injection during peak stress, then imaging roughly 10 minutes later, followed by a
redistribution image obtained roughly 4 hours later.
A dual-isotope protocol:
Tl-201 is used for the rest images and then a Tc-99m perfusion agent is used duringstress soon thereafter.
Advantages:
Widely available.
Extensively validated.
Compatible with multiple stress modalities
Less demand for high temporal resolution.
Limitation:
Long acquisition protocols.
Poorer spatial resolution limiting detection of sub endocardial perfusion defects.
Limited sensitivity in detecting mild-to-moderate stenosis.
Motion artifacts.
Reduced sensitivity for detecting left main disease.
Expose patients to radiation.
PET MPI:
PET Radiotracers:
N-13ammonia, Rubidium-82 (Rb-82), and O-15 water.
Imaging Protocol:
A bolus of the tracer is given and imaging usually commences between 90 to 120
seconds thereafter. ECG-gated PET acquisition is usually performed for 3 to 6 minutes for Rb-82 and 5 to 15 minutes for N-13 ammonia.
Stress imaging can be performed soon after rest imaging.
Advantages:
Improved spatial resolution.
PET tracers have significantly less roll-off of extraction.
Less artifacts.
More easily applied.
Less radiation.
High sensitivity.
Myocardial Contrast Echo Perfusion:
Still considered experimental.
Contrast Agents:
MCE contrast agents are small, gas-filled microbubbles (10 um) that compress and expand when exposed to an acoustic field and generate strong acoustic backscattering.
Contrast Echocardiography Perfusion Techniques:
Continuous infusion of microbubbles. When the microbubbles have reached steady state concentrations, a high mechanical index pulse is used to destroy the bubbles in the maging plane. The subsequent replenishment of microbubbles is related to myocardial perfusion. Areas that are hypo perfused will have a slower return of microbubbles,whereas areas that are well perfused will have a more rapid return of microbubbles.
Advantages;
No ionizing radiation.
Improved spatial resolution.
Perform absolute quantification of myocardial blood flow.
Availability and its relatively low cost.
Limitation:
Motion affect pictures.
Artifacts Formation.
Operator dependent.
No FDA-approved contras.
CMR Perfusion Imaging:
Contrast Agents gadolinium-DTPA c
Imaging Protocol:
Stress perfusion CMR is generally applied as part of a comprehensive study that
evaluates ventricular function, stress and rest perfusion.
Stress perfusion images are then obtained during infusion of 140 g/kg/min of Adenosine. 0.05 to 0.1mmol/kg gadolinium contrast.
Advantages:
High spatial resolution.
The ability to perform absolute quantification of perfusion.
Performed rapidly.
Has limited operator dependence.
Adequate spatial coverage and temporal resolution.
Limitations:
Artifact.
Nephrogenic systemic fibrosis.
CTA Perfusion Imaging:
Contrast Agents:
Iodinated contrast agents.
Advantages:
High spatial resolution.
Rapid data acquisition.
Combine information of coronary anatomy, ventricular function, and perfusion.
Widely available.
Enable dynamic analysis of perfusion with high temporal resolution.
Limitations
Heart rate with vasodilator stress may compromise image quality.
High doses of ionizing radiation
Artifacts.
Contrast induced nephropathy.
Fatima AlTaher
2 years ago
Normal physiological regulation of coronary artery flow.
In normal circumstances, coronary blood flow is tightly regulated process where blood flow mediate vascular endothelial relaxation and vasodilation .The earliest pathological changes in coronary vessels result from endothelial dysfunction where blood flow mediated VD is lost leading to reflex VC and decrease coronary blood flow and subsequent myocardial ischemia
Diagnosis and assessment of severity of CAD is very crucial for risk stratification in kidney recipients as CV diseases are the leading cause for death with functioning graft . One of the accurate and non invasive investigations for assessing myocardial functional status is myocardial perfusion imaging with SPECT being the most commonly used modality beside other modalities as cardiac MRI ,cardiac CT , PET scan and myocardial contrast echo.
Exercise MPI has a prognostic value as exercise tolerance correlates with patients survival and it depends on exercise induced coronary VD as exercise increase Coronary blood flow that in turn induce flow mediated vascular endothelial dilatation which is impaired or even lost in cases of severe CAD. Selecting the Ideal Perfusion Imaging Technique and Agent
The ideal perfusion agent should have high first myocardial uptake in relation to perfusion with minimal recirculation and back flow, rapid clearance from circulation , stable kinetics not affected by hypoxia While the ideal perfusion modality should have high sensitivity to small changes in coronary blood flow. Different modalities used in evaluating myocarditis perfusion
1- SPECT : is the most commonly used modality , can utilize 3 radiotracers..
1)T1 201 tracer that has short delayed redistribution so images must be taken with in 10-20 min after injection of the tracer.
2)Tc 99m sestamibi and Tc-99m tetrofosmin
Uptake of all SPECT tracers depends on myocardial cellular integrity and blood flow Image Analysis
Images are analyzed either qualitatively by visual analysis or semiquantitatively by differences between relative counts in both rest and stress compared to normal databases. Advantages of SPECT
1) widely available and have several modalities that can accurately diagnose multiple vessels affection. Limitations of SPECT
longer acquision protocol and poorer resolution compared with other modalities. 2)PET MPI
Was widely used previously but due to increased cost , lesser availability , it’s used has reduced.
Tracers that are used in PET MPI as N-13ammonia, Rubidium-82 (Rb-82), and O-15 water which have short redistribution time making them suitable for stress imaging. Advantages of PET
has better spatial resolution, lower dose of tracers us needed and lesser attenuation artifacts compared with SPECT. limitations of PET
Higher cost and need for cyclotron for tracers. Myocardial Contrast Echo Perfusion
Limited by lack of FDA approval of it’s contrast materials. CMR Perfusion Imaging
Limited by the use of godalinium as contrast as with the risk of nephrogenic systemic sclerosis Advantages
Rapid test , less operator dependant , not markedly affected by the patient body characteristics and highly sensitive for CAD and myocardial function diagnosis. Summary
Assessment of myocardial function is critical in kidney recipients and there are several techniques , each has its own advantages and limitations , so clinician should choose the most appropriate test based on his patient conditions.
Ahmed Omran
2 years ago
There is no gold standard procedure for noninvasive evaluation of myocardial perfusion. There are different modalities with advantages and disadvantages.
MPI relies on ability of modalities with stress to induce regional heterogenicity of coronary blood flow in case of coronary artery diseases. Exercise induce coronary VD. A Dipyridamole and adenosine are pharmacological vasodilators.
SPECT MPI is done using three radiotracers thaliem-201, Tc99m Sestamibi & Tc-99m Tetrosfosmin
SPECT MPI is compatible with many stress modalities but has long acquisition protocols and poor resolution compared with other modalities. SPECT MPI is easily available and has been significantly validated.
PET Radiotracers N-13ammonia,O-15 water and Rubidium-82 (Rb-82) are the PET tracers used for myocardial perfusion.
Myocardial contrast echo perfusion is suitable for evaluation ;exercise or dobutamine induced wall motion evaluation.
Contrast echocardiography perfusion technique evaluates myocardial perfusion with infusion of micro bubbles continuously.
CMR perfusion imaging: high spatial resolution but there is risk for nephrogenic systemic fibrosis.
CTA perfusion imaging
High spatial resolution: rapid data acquisition together with coronary anatomy delineation.
Risk of CIN in procedure using a contrast must be considered.
Asmaa Khudhur
2 years ago
Noninvasive Assessment of Myocardial Perfusion
The Ideal Perfusion Imaging Technique and Agent
both a perfusion imaging method and a perfusion imaging agent. High first-pass myocardial absorption proportional to perfusion, negligible back-diffusion and recirculation, quick clearance from the blood pool, and kinetics unaffected by factors like metabolism or hypoxia would all be characteristics of the ideal drug.
The ideal substance would not affect hemodynamics and would have a low volume in comparison to the volume of myocardial blood. Finally, the drug should be secure and have little adverse effects. High sensitivity to minute variations in coronary blood flow and a measurable correlation between signal intensity and perfusion would characterize the ideal perfusion imaging technique.
SPECT MPI :
Radiotracers
Three radiotracers are commonly used clinically for SPECT MPI:
Thallium-201 (Tl-201)
Tc-99m sestamibi
and Tc-99m tetrofosmin
Advantages and Limitations of SPECT:
Widely accessible and thoroughly validated, SPECT MPI. Exercise, dobutamine, and vasodilators are only a few examples of the various stress modalities that SPECT MPI is compatible with because the stress and imaging components are created separately. There is less need for high temporal resolution because the imaging does not take place during the first pass of a contrast agent, and the signal-to-noise ratio (SNR) can be increased by gathering data over a longer time frame.
The diagnosis of subendocardial perfusion abnormalities is hampered by the various constraints of SPECT MPI, including somewhat lengthy acquisition techniques and significantly lower spatial resolution than other current modalities. Furthermore, the sensitivity for diagnosing mild-to-moderate stenoses is limited by the roll-off of tracer uptake at greater myocardial blood flows.
The inferior wall’s dispersion and partial volume artifacts due to gastrointestinal and biliary activity, as well as variable attenuation artifacts brought on by breast or subdiaphragmatic attenuation, are additional constraints. The diagnostic value of the perfusion pictures may be diminished by these abnormalities. Motion correction techniques can be used in post-processing to correct motion artifacts. To identify attenuation artifacts from fixed perfusion deficiencies brought on by myocardial scar, ECG-gated scans that allow for assessment of regional myocardial function can be used.
PET MPI:
Although PET has been used for MPI for greater than 25 years, multiple factors including availability of scanners, increased cost, and reimbursement issues have limited wide- spread clinical application of PET.
PET Radiotracers:
N-13ammonia, Rubidium-82 (Rb-82), and O-15 water are the PET tracers typically used for myocardial perfusion.
Advantages and Limitations:
With a spatial resolution of 2 to 3 mm as opposed to the 6- to 8-mm resolution of traditional SPECT imaging, PET has better spatial resolution than SPECT. Comparing Tc-99m-based SPECT agents to PET tracers, the roll-off of extraction at high flows is substantially lower in the latter. Sadly, Rb-82 has the largest roll-off of the PET perfusion agents despite not requiring a cyclotron.
In addition, Rb-82 has a lesser spatial resolution and a larger dosage than N-15 ammunition due to its high positron emission energy and mean range of 5.5 mm. Attenuation artifacts are less of a problem with PET because attenuation correction for attenuation is a built-in feature of the technology. Additionally, dynamic scanning makes it easier to employ the tracers from PET to measure absolute perfusion levels.
With the most recent developments in PET/CT technology, it is now possible to combine anatomic imaging with PET and multimodality functional imaging of perfusion with CTA. PET agents get lower radiation doses than SPECT agents because of their short half-lives. The main drawbacks of PET are its higher price and the restrictions imposed by the requirement for a cyclotron for all imaging agents other than those tagged with Rb-82 or F-18.
It can be challenging to assess the effects of motion artifacts on images since they are typically difficult to see when the scan is in motion. Additionally, artifacts may be produced by registration errors between perfusion images and attenuation maps. Patients will likely be subjected to significantly higher radiation doses when PET and CTA are combined.
Myocardial Contrast Echo Perfusion:
MCE contrast agents are small, gas-filled microbubbles that compress and expand when exposed to an acoustic field and generate strong acoustic backscattering.
Advantages and Limitations:
MCE may be superior to other modalities in a variety of ways. Compared to SPECT, PET, and CT perfusion imaging, MCE has an advantage because it doesn’t employ ionizing radiation. MCE offers better spatial resolution than SPECT, making it possible to detect subendocardial ischemia. Absolute quantification of myocardial blood flow can also be done using MCE. Exercise or the use of inotropes or vasodilators during pharmacological stress can be used to perform imaging. The accessibility and affordability of echocardiography are two tangible benefits. The method has some drawbacks. Many individuals have sub-optimal imaging as a result of respiratory motion, body habit, or lung disease. The basal parts of the left ventricle may exhibit artifacts as a result of attenuation from the microbubbles. These variables may affect the ventricle’s geographic coverage and picture quality, which would increase variability and reduce repeatability. Additionally, there are several operator-dependent issues, such as preserving a steady image plane during microbubble replenishment. For MCE perfusion, there are no contrast agents that have received FDA approval.
CMR Perfusion Imaging:
Contrast Agents:
Most CMR studies of myocardial perfusion are based on the first-pass of a bolus of gadolinium-DTPA contrast agents.
Advantages and Limitations:
Cardiac MRI offers a number of advantages over other imaging modalities for perfusion stress testing, including excellent spatial resolution, the capacity to do absolute perfusion quantification, and the additional data that is offered in a thorough CMR investigation. The investigation can also be completed quickly, with little operator reliance, and with signal qualities that are generally independent of patient body habitus.
With future developments in parallel imaging techniques, CMR perfusion investigations continue to offer acceptable geographical coverage and temporal resolution. The “dark-rim” artifact present in current pulse sequences can be misinterpreted as a real perfusion problem. This artifact likely has multiple causes, such as myocardial motion during data acquisition, Gibbs ringing brought on by resolution issues, or susceptibility artifacts brought on by the passage of the contrast agents. When ventricular cavity enhancement reaches its height, this artifact typically only appears briefly in comparison to an actual perfusion anomaly.
CMR perfusion imaging is best compatible with vasodilator stress since imaging takes place during the first pass of a contrast agent. Gadolinium-DTPA is not the best contrast agent for a number of reasons. It features a nonlinear connection between signal intensity and perfusion and an intermediate extraction fraction during first-pass imaging. However, the combination of perfusion with delayed enhancement imaging enables accurate detection of myocardial infarction. Gadolinium has a slow washout in regions of infarction that alters the baseline signal intensity for the rest perfusion study.
Gadolinium contrast agents have recently been linked to nephrogenic systemic fibrosis, an uncommon but deadly illness that usually affects people who have significantly decreased creatinine clearance. Gadolinium-based contrast agents have a black-box warning from the FDA for individuals having a creatinine clearance of less than 30 mg/dL.
CTA Perfusion Imaging:
Myocardial perfusion imaging with CT is based on the intravenous injection of iodinated contrast agents that in- crease the absorption of x-rays in proportion to the concen- tration of iodine.
Advantages and Limitations:
High spatial resolution, quick data gathering, and the opportunity to incorporate data on coronary anatomy, ventricular function, and perfusion in one research are all benefits of MDCT. Furthermore, MDCT scanners are becoming more widely accessible due to the expansion of CTA. Although it has been shown to be possible for dynamic studies, absolute quantification of CT perfusion needs modeling of the effects of contrast diffusion into the extravascular space.
Additionally, the development of MDCT with 256 or 320 detectors may allow for high temporal resolution dynamic investigation of perfusion. However, there are a number of drawbacks to using MDCT for perfusion analysis. Since heart rate and picture quality are inversely correlated, the rise in heart rate brought on by vasodilator stress may reduce image quality. Additionally, the myocardium’s signal strength varies as a result of aberrations like beam-hardening, which makes it difficult to quantify perfusion.
The standard doses of contrast agents make it impossible to evaluate patients who have severe renal insufficiency. The biggest drawback of using MDCT to measure perfusion is the potential exposure to large amounts of ionizing radiation. The present coronary CTA radiation dose could possibly be doubled by protocols that involve doing CTA tests under stress and at rest. The radiation exposure for a dynamic perfusion analysis would likely be significantly higher. Additional research on perfusion with MDCT is necessary as the technology develops.
Wee Leng Gan
2 years ago
Non invasive Assessment of Myocardial Perfusion
SPECT MPI
SPECT MPI is widely available and has been extensively validated. It is compatible with multiple stress modalities including exercise, dobutamine, or vasodilators. The limitation includes relatively long acquisition protocols and considerably poorer spatial resolution than other available modalities, limiting detection of subendocardial perfusion defects. Furthermore, the roll-off of tracer uptake at higher myocardial blood flows limits sensitivity in detecting mild-to-moderate stenoses. Motion artifacts may decrease the diagnostic utility of the perfusion images. MPI has reduced sensitivity for detecting left main disease or 3-vessel disease related to balanced ischemia.
PET MPI
PET has improved spatial resolution as compared with SPECT. PET tracers have significantly less roll-off of extraction at high flows as compared with Tc-99m– based SPECT agents. Rb-82 in PET MPI has high positron emission energy and a mean range of 5.5 mm, resulting in a higher dose and lower spatial resolution than N-15 ammonia. The attenuation artifacts are less of an issue for PET. The major limitations to PET include higher costs and limitations imposed by the need for a cyclotron for all but Rb-82 imaging or imaging agents labelled with F-18. Artifacts from motion during the scan are frequently less apparent, making it harder to evaluate their effects on images. When PET is combined with CTA, patients probably will be exposed to even higher radiation doses.
Myocardial Contrast Echo ( MCE ) Perfusion Scan.
MCE does not involve ionizing radiation and enabling detection of subendocardial ischemia. MCE also has the ability to perform absolute quantification of myocardial blood flow. Imaging can be performed during pharmacological stress with inotropes or vasodilators or with exercise. It is wide availability and its relatively low cost.
MCE limitations include suboptimal images are obtained in a significant number of patients as the result of respiratory motion, body habitus, or lung disease. It is operator-dependent. Besides, there are no FDA-approved contrast agents for MCE perfusion.
Multidetector CT (MDCT)
MDCT has high spatial resolution, rapid data acquisition, and the ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in one study. The limitations include compromise of image quality when the heart increases. Artifacts such as beam-hardening result in variations of signal intensity within the myocardium, limiting the ability of quantitative assessment of perfusion. The main disadvantage of assessing perfusion with MDCT is the potentially high doses of ionizing radiation.
In my opinion, no single perfect non-invasive investigation to assess the myocardial perfusion. It depends on the health resources. As in my hospital with limited resources, we use only MCE as the invasive modality to assess cardiac perfusion status before kidney transplantation.
Hinda Hassan
2 years ago
Summarise this article
Non-invasive tools of assessing cardiovascular system are important in assessing CAD risk.They include single-photon emission computed tomography (SPECT), myocardial contrast echocardiography (MCE), positron emission tomography (PET), cardiac MRI (CMR), and cardiac computed tomography (CT) . SPECT MPI :
It is the most commonly used modality. Its advantages include doing the stress part and imaging part separately with less need for high temporal resolution. Disadvantages are low sensitivity, motion artifact, large radiation dose ,long period protocol and less resolution limiting the sub-endocardial perfusion defect detection when compared to other modalities. Studies revealed a sensitivity of 87-89% and specifity of 73-75% PET MPI:
It has higher resolution when compared to SPECT,cost effective less artifacts, easy performance and lower radiation dose.Limitations are the high cost, technical issues , artifacts and the high dose of radiation when combined with CTA. Studies revealed a sensitivity of 91-92% and specificity of 85-100 % for the detection of CAD. Myocardial Contrast Echo Perfusion:
FDA considers it to be an experimental procedure. The advantages are no ionizing radiation, available, less cost, better resolution for detection of sub-endocardial ischemia and can quantify myocardial blood flow. The limitations are suboptimal images, artifacts in the basal segments of the left ventricle, operator-dependent factors and no FDA-approved contrast agents for perfusion. The sensitivity is 82% and specificity is 80%. CMR Perfusion Imaging:
Cardiac MRI advantages are high spatial resolution, rapid procerdure, not dependent on the operator and patient body habitus, most compatible with vasodilator stress, can quantify the perfusion, and the additional information provided in a comprehensive CMR study. Disadvantages are the “dark-rim” artifact and the gadolinium associated nephrogenic systemic fibrosis, in patients with significant reductions in creatinine clearance.Sensitivity approaches 91 % and specificity is 81% CTA Perfusion Imagin:
Advantages include its high spatial resolution, wide availability, rapid data acquisition, and the ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in one study. Limitations are artifacts , poor quality with rapid heart rate during stress and high radiation dose
Since this article is addressing general population, please make refection on CKD patients SPECT MPI :
Has good classification potentials in CKD patients throughout the different stages. (1) PET MPI:
Shah and colleagues reported a higher all-cause mortality among patients with a reduced PET-and Charytan demonstrated similar results in patients with CKD and ESRD (2) Myocardial Contrast Echo Perfusion: Has good accuracy for ruling out the presence of a significant CAS in patients with ESRD.(3) CMR Perfusion Imaging:
Are cautiously used due to the concern of nephrogenic systemic fibrosis. Cardiovascular magnetic resonance spectroscopy has been studied to assess early cardiac dysfunction in pediatric population with advanced CKD . Dobutamine stress CMR was shown to be safe in the pre-renal transplant population .
1- Ahmed AM, Qureshi WT, O’Neal WT, Khalid F, Al-Mallah MH. Incremental prognostic value of SPECT-MPI in chronic kidney disease: A reclassification analysis. J Nucl Cardiol. 2018 Oct;25(5):1658-1673. doi: 10.1007/s12350-016-0756-0. Epub 2017 Jan 3. PMID: 28050863.
2- Vij, A., Doukky, R. The Prognostic Value of MPI in CKD: Can we do better?. J. Nucl. Cardiol.29, 155–157 (2022). https://doi.org/10.1007/s12350-021-02545-6
3- Sobkowicz B, Tomaszuk-Kazberuk A, Kralisz P, Malyszko J, Kalinowski M, Hryszko T, Malyszko J, Dobrzycki S, Musial WJ. Application of myocardial contrast echocardiography for the perfusion assessment in patients with end-stage renal failure–comparison with coronary
4- Parnham SF, Gleadle JM, De Pasquale CG, Selvanayagam JB. Myocardial Ischemia Assessment in Chronic Kidney Disease: Challenges and Pitfalls. Front Cardiovasc Med. 2014 Dec 19;1:13. doi: 10.3389/fcvm.2014.00013. PMID: 26664863; PMCID: PMC4668858.
Ahmed Abd El Razek
2 years ago
Summary
Noninvasive imaging techniques are gaining popularity in detection of occult CAD recently.
Coronary Physiology
Normal coronary physiology is maintained by intact endothelial function and nitric oxide release.
The primary change is the decreased perfusion before clinical manifestation of the disease and even preceding ECG changes. Significant stenosis exceeding 85 to 90 % impair myocardial oxygen supply.
Detection of abnormal coronary flow reserve with vasodilator stress in the absence of a marked coronary stenosis correlates to microvascular or endothelial dysfunction or even both.
Methods for Inducing Coronary Vasodilation
Myocardial perfusion imaging (MPI) depends on stress induction causing further heterogeneity of coronary artery blood flow in the setting of CAD.
On exercise, in the presence of CAD, perfusion reserve is impaired by the stenoses, endothelial dysfunction and adrenergic stimulation. Exercise is mainly associated with a 2- to 3-fold increase in myocardial blood flow, so it is considered as the preferred modality, as exercise capacity reflects an important prognostic value. Pharmacological agents causing arteriolar vasodilation by direct and endothelium-mediated mechanisms are being used to resemble exercise stress testing.
The Ideal Perfusion Imaging Technique and Agent
Criteria of ideal agent must include a high first-pass myocardial uptake proportional to perfusion. Also back-diffusion and recirculation would be insignificant. Provided that rapid clearance from the blood pool, as well as unaltered kinetics by other factors such as metabolism or hypoxia. Safety of the agent is a must with only minimal allowed side effects. High sensitivity to small changes in coronary blood flow with a quantifiable relationship between signal intensity and perfusion is required. Spatial resolution is beneficial in determining transmural differences in perfusion. The technique itself ought to be devoid of artifacts, easy to use, widely distributed, and cheap.
SPECT MPI
Commonly used radiotracers are Thallium-201, Tc-99m sestamibi and Tc-99m tetrofosmin. The uptake of the tracers is mainly dependent on myocardial cellular integrity besides blood flow.
Advantages and Limitations of SPECT
Being widely available, validated and compatible with multiple stress modalities including exercise, dobutamine, or vasodilators are considered various advantages. Whereas it has also some drawbacks as longer acquisition protocols as well as poorer spatial resolution compared to other available modalities, limiting detection of subendocardial perfusion defects. Limited sensitivity in detecting mild-to-moderate stenoses is also encountered due to roll off phenomenon. Also, various artifacts coexist affecting its accuracy as motion artifacts related to patient, respiratory motion, gut, biliary artifacts, as well as breast and sub diaphragmatic attenuation. Owing to the assessment of only relative perfusion is generally assessed, it has minimal sensitivity for detecting left main disease or triple vessel disease related to balanced ischemia. In addition to tracers expose patients to considerable radiation doses.
The diagnostic outcome can guide selective coronary angiography, reducing the cost associated with diagnosis and revascularization.
PET MPI
The limited availability of scanners and their increased cost restricts its use.
PET Radiotracers
The common available agents are N-13ammonia, Rubidium-82 (Rb-82), and O-15 water. The disadvantages include the presence of the roll-off phenomenon as well as the high radiation dose. Clinical studies with fluorine-18 (F-18) as a new promising tracer are progressing.
Advantages and Limitations
PET has better spatial resolution compared to SPECT. The PET tracers have significantly less roll-off of extraction at high flows in comparison to SPECT.it is regarded as a both sensitive and specific tool for the diagnosis of CAD.it is also a cost-effective measure compared to angiography, exercise ECG, and SPECT. It detects prevalence of CAD exceeding 70%.
Myocardial Contrast Echo Perfusion
Unfortunately, the lack of an FDA approved MCE contrast agent for perfusion hindered the widespread clinical application.
Advantages and Limitations
MCE potential advantages over other modalities is primarily lack of ionizing radiation, having better spatial resolution enabling detection of subendocardial ischemia and the ability to perform absolute quantification of myocardial blood flow. It is also widely available and of relatively lower cost. Drawbacks mainly being operator-dependent and its agents are not FDA-approved. It has comparable accuracy to SPECT for diagnosing CAD with sensitivity of 82% and specificity of 80% in addition to its prognostic value that was incremental to left ventricular ejection fraction.
CMR Perfusion Imaging
It is a gadolinium-DTPA contrast agent procedure whereas well perfused areas will reflect a shorter T1 and appear bright on heavily T1-weighted images, while hypoperfused regions will acquire longer T1 and appear as hypointense regions.
The use of nonselective saturation recovery (SR) pulse sequences which are more convenient for multislice imaging, insensitive to variations in heart rate, it also enables shorter preparation times as well as having less susceptibility induced image artifacts.
Stress perfusion CMR is helpful in evaluation of ventricular function, stress and rest perfusion, and viability/myocardial infarction. This technique has an estimated sensitivity and specificity of 89% and 87%, respectively, in detection of CAD. The high spatial resolution of CMR allows the detection of subendocardial ischemia clearly even in patients with triple vessel disease.
Advantages and Limitations
Cardiac MRI has unique advantages for perfusion stress testing:
High spatial resolution.
Absolute quantification of perfusion.
Can be performed rapidly.
Limited operator dependence.
The signal characteristics are not affected by the patient’s body habitus.
Disadvantages:
gadolinium-DTPA is not an ideal contrast agent correlated to nephrogenic systemic fibrosis disease.
The presence of an abnormal stress CMR was significantly predictive of MACE.
CTA Perfusion Imaging
It is based on the use of intravenous injection of iodinated contrast agents so, the main concern is contrast-induced nephropathy, especially in patients with renal impairment.
Accuracy was estimated by 72% sensitivity and 80% specificity for detecting a significant coronary stenosis.
Advantages and Limitations
Favorable advantages are: high spatial resolution, rapid data acquisition, and the ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in one study. They are also widely available. However, some disadvantages coexist as contrast induced nephropathy, high doses of radiation and the presence of artifacts.
Reflection on our centre practice is only dependent on echocardiography, dobutamine stress echocardiography, and coronary angiogram and stenting in high risk patients with high probability of renal replacement therapy in the form of haemodialysis. Magnetic resonance studies and computed tomography are not used for the fear of NSF and CIN AKI accompanied by high mortality and further required renal replacement therapies.
Alyaa Ali
2 years ago
Noninvasive assessment of myocardial perfusion is crucial in diagnosis and risk stratification of patients with known or suspected CAD.
Myocardial perfusion is a highly regulated process .Endothelial dysfunction plays a role in the development of CAD, AS it plays a role in epicardial and arteriolar vasodilatation.
Because perfusion is the early change in the ischaemic cascade , stress modalities that assess coronary perfusion reserve have a higher sensitivity in detecting flow limiting stenosis than analysis of stress induced wall motion abnormalities or ECG changes alone .
Attributes of an ideal perfusion agent and perfusion imaging modality
A) perfusion agent should be safe,easy to administer , its kinetics not altered by metabolism, low cost, with high first pass uptake and there is linear relationship between myocardial concentration and perfusion
B) imaging modality
_ high sensitivity, low cost , widely available, easy to use, high diagnostic utility, reproducible
_ quantifiable relationship between singal intensity and concentration of agent
_ high spatial/ temporal resolution
1) SPECT MPI
Three radiotracers are used Thallium-201 , Tc-99m sestamibi and Tc-99m tetrofosmin
Different imaging protocols
– same-day rest-stress protocol using a Tc 99m-labeled perfusion agent
– typical T1-201 protocol
– a dual isotope protocol in which T1-201 agent used during rest and Tc-99m used during stress
Advantages . It is widely available and compatible with multiple stress modalities
Limitations. Limited in detection of subendocardial perfusion defect , limited in detection of mild to moderate stenosis
Presence of motion artifacts related to patient and respiratory motion
Its sensitivity and specificity are 87% and 73% respectively.
2) PET MPI
N-13 ammonia, Rubidium-82 and 0-15 water are the PET tracer used for myocardial perfusion
Advantages.PET has improved spatial resolution as compared with SPECT. Attenuation artifacts are less of an issue for PET. The tracers used in PET are more easily applied in dynamic scanning to be used for absolute quantification of perfusion.
The short half-lives of the PET agents result in lower radiation does than SPECT
Major limitations include higher costs and limitations imposed by the need for a cyclotron for all .
Its sensitivity and specificity of 92% and 85% respectively.
3) Myocardial Contrast Echo Perfusion
MCE contrast agents are small, gas-filled microbubbles that compress and expand when exposed to an acoustic field and generate strong acoustic backscattering
Advantages. It doesn’t involve ionizing radiation, has improved spatial resolution enabling detection of subendocardial ischaemic, also has the ability to perform absolute quantification of myocardial blood flow ,wide variability and low cost
Limitations. Suboptimal images due to respiratory motion, body habits or lung disease, attenuation from microbubbles may result in artifacts in the basal segment of left ventricle. It is operator dependent
Its sensitivity and specificity 82 and 80 respectively
4) CMR perfusion imaging
Contrast agent . Gadolinium-DTPA
Stress perfusion CMR is applied as part of a comprehensive study that evaluates ventricular function
Advantages. High spatial resolution, the ability to perform absolute quantification of perfusion, the study can performed rapidly, has limited operator dependence
Limitations . In advanced CKD patients, it associated with nephrogenic systemic fibrosis.
Its sensitivity and specificity are 91% and 81% respectively
5) CTA perfusion imaging
Contrast agent. Nonionic Contrast agents with a high iodine concentration
Advantages. High spatial resolution, rapid data acquisition, the ability to combine information of coronary anatomy, ventricular function and perfusion in one study. Widely available.
Limitations. As image quality is inversely related to heart rate. The increase in heart rate with vasodilator stress may compromise image quality. Artifacts limit the ability of quantitative assessment of perfusion. High dose of ionizing radiation
In advanced kidney disease myocardial Contrast Echo Perfusion may be suitable tool
In other modalities we fear of Contrast
CMR is associated with nephrogenic systemic fibrosis
CARLOS TADEU LEONIDIO
2 years ago
Summarise this article
The article aims to make critical analyzes regarding the different methods for assessing myocardial perfusion. But first, we need to know the characteristics of Ideal Perfusion Imaging Technique and Agent.An ideal agent would have:
– a high first-pass myocardial uptake proportional to perfusion,
– a insignificant back-diffusion and recirculation,
– rapid clearance from the blood pool,
– kinetics that are not altered by factors such as metabolism or hypoxia
– be safe, with minimal side effects.
An ideal perfusion imagin Technique would have:
– a direct and quantifiable relationship between contrast agent concentration and myocardial perfusion,
– high sensitivity to small changes in coronary blood flow and a quantifiable relationship between signal intensity and perfusion.
– high spatial resolution so that transmural differences in perfusion could be detected
– be reproducible and have a high diagnostic utility and should be free of artifacts that would limit either;
– should be widely available, fast and easy to use, and cost-effective
Now, let’s go know the methods for assessing myocardial perfusion:
– SPECT:
Three types of tracers are commonly used: Tl-201, Tc-99m sestamibi, and Tc-99m, each with specific characteristics, interfering in the interpretation of results and thus requiring a type of protocol for each tracer.
As positive points: It’s compatible with multiple stress modalities including exercise, dobutamine, or vasodilators. There is an extensive literature evaluating the sensitivity and specificity of SPECT myocardial perfusion imaging for detecting CAD, one of the analyzes had demonstrated mean sensitivity and specificity of 87% and 73%, respectively, for exercise myocardial SPECT for detecting a greater than 50% stenosis.
As negative points: has multiple limitations, including relatively long acquisition protocols and considerably poorer spatial resolution than other available modalities, limiting detection of subendocardial perfusion defects. Additional limitations include motion artifacts related to patient and respiratory motion, scatter and partial volume artifacts in the inferior wall related to gut and biliary activity, and variable attenuation artifacts resulting from breast or subdiaphragmatic attenuation.
-PET:
N-13ammonia, Rubidium-82 (Rb-82), and O-15 water are the PET tracers typically used for myocardial perfusion.
As positive points: has improved spatial resolution as compared with SPECT, PET tracers have significantly less roll-off of extraction at high flows as compared with Tc-99m– based SPECT agentes, tracers used in PET are more easily applied in dynamic scanning to be used for absolute quantification of perfusion
– MYOCARDIAL CONTRAST ECHO PERFUSION:
This use microbubbles like a contrast agente.
As Limitations points: the sensitivity of wall motion analysis have led to the development of MCE techniques
– CMR PERFUSION IMAGING
It use gadolinium-DTPA contrast agentes that has interaction with water prótons.
As positive points: high spatial resolution, the ability to perform absolute quantification of perfusion, and the additional information provided in a comprehens, the study can be performed rapidly, has limited operator dependence, and the signal characteristics are largely independent of the patient’s body habitus.
As limitations points: gadolinium isn´t a an ideal contrast agente – In regions of infarction, gadolinium has a slow washout that changes the baseline signal intensity for the rest perfusion study; however, the combination of perfusion with delayed enhancement imaging enables accurate detection of myocardial infarction. Recently, gadolinium contrast agents have been associated with a rare but serious condition called nephrogenic systemic fibrosis, which primarily occurs in patients with significant reductions in creatinine clearance.
– CTA PERFUSION IMAGING:
Use intravenous injection of iodinated contrast agentes that are not hemodynamically inert and have an influence on coronary blood flow, inducing a reduction in coronary flow followed by a hyperemic response.
As positive points: high spatial resolution, rapid data acquisition, and the ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in one study
As limitations points: image quality is inversely related to heart rate, the increase in heart rate with vasodilator stress may compromise image quality. Furthermore, artifacts such as beam-hardening result in variations of signal intensity within the myocardium, limiting the ability of quantitative assessment of perfusion. The contrast agent doses typically used preclude evaluation of patients with significant renal insufficiency. The main disadvantage of assessing perfusion with MDCT is the potentially high doses of ionizing radiation.
Since this article is addressing general population, please make refection on CKD patients
These methods are likely to have greater sensitivity and specificity for patients with CKD, as they have a higher incidence of CAD, which increases their effectiveness. However, the importance of tracers and changes in their functionality should increase due to decreased renal function. Therefore, these methods should be revalidated for the CKD population.
Eusha Ansary
2 years ago
Summary:
There has been significant progress in the noninvasive evaluation of myocardial perfusion but yet to set a gold standard procedure. There are different modalities used with advantages and disadvantages.
MPI depends on ability of stress modalities to induce regional hetenogenicity of coronary arterial blood flow in case of coronary entry diseases. Exercise induce coronary vasodilation. In addition to that Dipyridamole, adenosine, and regadenoson are pharmacological vasodilators as well.
SPECT MPI clinically used three radiotracers thaliem-201, Tc99m sestamibi and Tc-99m tetrosfosmin
Spect MPI is compatible with multiple stress modalities but long acquisition protocols and poor resolution than other modalities. SPECT MPI is widely available and has been extensively validated.
PET Radiotracers N-13ammonia, Rubidium-82 (Rb-82), and O-15 water are the PET tracers typically used for myocardial perfusion.
Myocardial contrast echo perfusion is used for evaluation either exercise or dobutamine induced wall motion analysis.
Contrast echocardiography perfusion technique asses myocardial perfusion with continuous infusion of micro bubbles.
CMR perfusion imaging:
High spatial resolution but risk for nephrogenic systemic fibrosis.
CTA perfusion imaging
High spatial resolution, rapid data acquisition with coronary anatomy information
Refection on CKD patients:
Risk of CIN in the procedure using contrast.
Hamdy Hegazy
2 years ago
Summarize this article
Assessment of CAD can be done via different methods of MPI which include: 1- SPECT 2- MCE 3- PET 4- CMR 5- Cardiac CT SPECT-MPI: Radiotracers: Thallium 201, Tc99m Sestamibi, and Tc99m Tetrofosmin Sensitivity: 87% with exercise and 89% with vasodilators. Specificity: 73% with exercise and 75% with vasodilators. 3 different protocols: 1- Inject radiotracer (Technecium)-à imaging after 30 min, inject radiotracer again with during peak stress. 2- Inject Thallium radiotracer during peak stress-à imaging at 10 min and at 4 h. 3- Inject Thallium for rest image and Technecium for image during stress Advantages: stress compatible, lower need for high temporal resolution. Limitations: Time consuming, big radiation dose, low spatial resolution, multiple artefacts, less sensitive to detect sub-endocardial perfusion defects and significant coronary vessels stenosis. PET-MPI: Radiotracers: Rb-82, N13-ammonia, and 015 water. Sensitivity: 92%, Specificity: 85% Protocol: inject bolus of the radiotracer—-à imaging after 90-120 seconds because of short half life of radiotracers. Advantages: less dose of radiation, less attenuation artefacts, better spatial resolution. Limitations: High cost, cyclotron is needed, higher radiation when CT is used, and registration artefacts. MCE: Gas filled microbubbles are injected IV which acts as a contrast agent. It is not yet approved by FDA. Sensitivity: 82%, Specificity: 80%. Protocol: inject microbubbles—-à>images are taken in gated intermittent mode and in real time mode. Analysis can be done. Advantages: low price, no radiation, better spatial resolution, can detect subendocardial ischaemia Limitations: suboptimal images because of artefacts, operator dependent. Cardiac MRI: Gadolinium DTPA is the contrast agent to be used. Sensitivity: 91%, Specificity: 81% Protocol: different kind of images are needed, Cine image to evaluate ventricular function. Stress using Adenosine with gadolinium-à images at rest after a wash out period of 10 min. At the end take late gadolinium images. Advantages: high spatial resolution, can detect sub-endocardial ischaemia, quantification of perfusion can be done, rapid scan, not operator dependent. Limitations: not allowed if GFR below 30 CTA: Iodinated contrast agents are used. Sensitivity: 72%, specificity: 80% Protocol: CTA during adenosine stress and 20 min at rest. Advantages: high spatial resolution, rapid, can assess ventricular function, perfusion of coronaries. Limitations: risk of CIN, high dose of radiation, poor quality of images with fast HR.
Combined techniques of non-invasive MPI can achieve better assessment
Since this article is addressing general population, please make refection on CKD patients
In CKD patients cardiac MRI is avoided if GFR below 30. CKD patients are at higher risk for CIN with using CTA. Exercise MPS: CKD patients usually have low exercise tolerance and impaired chronotropic response.
Reem Younis
2 years ago
Summarise this article
-Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease (CAD). Although single-photon emission computed tomography (SPECT) is most commonly used, multiple modalities including myocardial contrast echocardiography (MCE), positron emission tomography (PET), cardiac MRI (CMR), and cardiac computed tomography (CT) have emerged as promising techniques. SPECT MPI Radiotracers
-Three radiotracers are commonly used clinically for SPECT MPI. SPECT MPI Imaging Protocols
-There are a number of SPECT MPI protocols available for the assessment of CAD. With the same-day rest-stress protocol using a Tc99m-labeled perfusion agent, a first injection at rest is followed by imaging roughly 30 minutes later. A second
injection with 2 to 3 times the activity is administered during peak stress to overcome the background signal from the rest images, and repeat imaging is performed.
-The radiation burden to the patient is higher with dual-isotope imaging (typically 24 mSv) than when using rest/stress Tc-99m sestamibi (typically 11 mSv) or Tc-99m– tetrofosmin (typically 8 mSv) alone. Advantages and Limitations of SPECT
– As the stress and imaging components are performed separately, SPECT MPI is compatible with multiple stress modalities including exercise, dobutamine, or vasodilators.
– SPECT MPI has multiple limitations, including relatively long acquisition
protocols and considerably poorer spatial resolution than other available modalities, limiting detection of subendocardial perfusion defects.
-Furthermore, the roll-off of tracer uptake at higher myocardial blood flows limits sensitivity indetecting mild-to-moderate stenoses.
-Additional limitations include motion artifacts related to patient and respiratory
motion, scatter and partial volume artifacts in the inferior wall related to gut and biliary activity, and variable attenuation artifacts resulting from breast or subdiaphragmatic attenuation. PET MPI
-Although PET has been used for MPI for greater than 25 years, multiple factors including availability of scanners,mincreased cost, and reimbursement issues have limited widespreadmclinical application of PET.31 However, the recent proliferation of hybrid PET-CT scanners may lead to an increasingly important clinical role. PET Radiotracers
N-13ammonia, Rubidium-82 (Rb-82), and O-15 water are the PET tracers typically used for myocardial perfusion. Imaging Protocol
Typically a resting perfusion image is acquired using either Rb-82 or N-13 ammonia. A bolus of the tracer is given and imaging usually commences between 90 to 120 seconds thereafter. ECG-gated PET acquisition is usually performed
for 3 to 6 minutes for Rb-82 and 5 to 15 minutes for N-13 ammonia, owing to their different half-lives. Advantages and Limitations
-PET has improved spatial resolution as compared with SPECT, with spatial resolution of 2 to 3 mm as compared with the 6- to 8-mm resolution of conventional SPECT imaging.PET tracers have significantly less roll-off of
extraction at high flows as compared with Tc-99m–based SPECT agents. Unfortunately, Rb-82, which does not require a cyclotron, has the most significant roll-off of the PET perfusion agents. Furthermore, Rb-82 has high positron
emission energy and a mean range of 5.5 mm, resulting in a higher dose and lower spatial resolution than N-15 ammonia.
– Because PET perfusion images are corrected for attenuation as an inherent component of the technology, attenuation artifacts are less of an issue for PET. Furthermore, the tracers used in PET are more easily applied in dynamic
scanning to be used for absolute quantification of perfusion.
-The short half-lives of the PET agents result in lower radiation doses than SPECT agents.
-The major limitations to PET include higher costs and limitations imposed by the need for a cyclotron for all but Rb-82 imaging or imaging agents labeled with F-18. Myocardial Contrast Echo Perfusion
-Although echocardiography for evaluation of exercise- or dobutamine-induced wall motion analysis is commonly used clinically, limitations of the sensitivity of wall motion analysis have led to the development of MCE techniques for
assessing perfusion. Unfortunately, the lack of an FDAapproved MCE contrast agent for perfusion has currently put limitations on its widespread clinical application. Contrast Echocardiography Perfusion Techniques
Myocardial perfusion can be assessed with continuous infusion of microbubbles. Advantages and Limitations
– MCE has an advantage over SPECT, PET, and CT perfusion imaging because it does not involve ionizing radiation. Compared with SPECT, MCE has improved spatial resolution, enabling detection of subendocardial ischemia.
MCE also has the ability to perform absolute quantification of myocardial blood flow. Imaging can be performed during pharmacological stress with inotropes or vasodilators or with exercise. Practical advantages of echocardiography include
its wide availability and its relatively low cost.
-The technique has some limitations. Suboptimal images are obtained in a
significant number of patients as the result of respiratory motion, body habitus, or lung disease.Attenuation from the microbubbles may result in artifacts in the basal segments of the left ventricle. These factors can limit image quality and
adequate spatial coverage of the ventricle, resulting in increased
variability and decreased reproducibility. Furthermore, there are some operator-dependent factors such as maintaining a constant image plane during replenishment of microbubbles. Finally, there are no FDA-approved contrast
agents for MCE perfusion. CMR Perfusion Imaging
-Over the last few years, improvements in hardware, pulse sequence development, and image reconstruction algorithms have enabled high-resolution imaging of first-pass myocardial perfusion with CMR. Advantages and Limitations
-Cardiac MRI has significant advantages for perfusion stress testing, including its high spatial resolution, the ability to perform absolute quantification of perfusion, and the additional information provided in a comprehensive CMR study.
-Furthermore, the study can be performed rapidly, has limited operator dependence, and the signal characteristics are largely independent of the patient’s body habitus. pass of a contrast agent, CMR perfusion imaging is most
compatible with vasodilator stress. CTA Perfusion Imaging
With the recent advances in multidetector CT (MDCT) and CT coronary angiography, there has been renewed interest in using CT to evaluate myocardial perfusion. Advantages and Limitations
-The advantages of MDCT include its high spatial resolution, rapid data acquisition, and the ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in one study. Furthermore, with the growth of CTA, MDCT scanners are becoming widely available. Absolute quantification of CT perfusion has been demonstrated for dynamic studies but requires modeling of the effects of contrast diffusion into the extravascular space. Furthermore, advancement of MDCT with 256 or 320 detectors may enable dynamic analysis of perfusion with high temporal resolution.
-However, the use of MDCT for perfusion analysis has multiple limitations. Because image quality is inversely related to heart rate, the increase in heart rate with vasodilator stress may compromise image quality. Furthermore, artifacts
such as beam-hardening result in variations of signal intensity within the myocardium, limiting the ability of quantitative assessment of perfusion. The contrast agent doses typically used preclude evaluation of patients with significant renal insufficiency.
-The main disadvantage of assessing perfusion with MDCT is the potentially high doses of ionizing radiation. Protocols that involve obtaining CTA studies at rest and stress would potentially double the current coronary CTA radiation dose. Dynamic perfusion analysis probably would have an even higher radiation dose.
Jamila Elamouri
2 years ago
NON-invasive assessment of myocardial perfusion is crucial. Known or suspected coronary artery disease (CAD). SPECT is most commonly used, but other techniques have emerged as (MEC) myocardial contrast echocardiography, (PET) positron emission tomography, (CMR) cardiac MRI, and (CT) cardiac computed tomography.
Coronary physiology:
Myocardial perfusion process includes epicardial vessels, resistance vessels, and the endothelium. Endothelial dysfunction occurs early insult in CAD. Under sympathetic stimulation nitric oxide from the endothelial cells released, resulting in vasodilation of the epicardial and arteriolar vessels in normal coronaries. In endothelial dysfunction; acetylcholine predominates; causes vasoconstriction and further perfusion defect.
Coronary autoregulation maintains an adequate myocardial oxygen supply by reducing the resistance of distal perfusion beds in case of coronary stenosis. However, maximal coronary flow has been shown to decrease with stenosis of 45%.
Clinically coronary perfusion reserve can be assessed using stress modalities, that have a higher sensitivity in the detecting flow-limiting stenosis, than analysis of stress-induced wall motion abnormalities or ECG changes alone. Abnormal coronary flow reserve with vasodilator stress in the absence of a significant coronary stenosis occurs and has been attributed to microvascular and/or endothelial dysfunction.
Methods for inducing coronary vasodilation:
1- Exercise induces coronary vasodilatation via an endothelial dependent process to meet the increased oxygen demand. Exercise is typically associated with a 2- to 3-fold increase in myocardial blood flow and is the preferred modality, as exercise capacity has important prognostic value.
2- Dipyridamole, adenosine, and regadenoson are pharmacological vasodilators that cause arteriolar vasodilation by both direct and endothelium-mediated mechanisms and are associated with a 3.5- to 4-fold increase in myocardial blood flow
3- Dobutamine, a synthetic 1- and 2-receptor agonist, typically produces a 2- to 3-fold increase in myocardial blood flow similar to exercise.
The Ideal Perfusion Imaging Technique and Agent
The ideal agent should have:
1- High first pass myocardia uptake proportional to perfusion.
2- Insignificant back-diffusion and recirculation.
3- Rapid clearance from the blood pool.
4- Kinetic that are not altered by metabolism or hypoxia.
5- Has no hemodynamic effect and it is a small in volume compared with the myocardial blood volume.
6- It should be safe, with minimal side effects.
The technique:
1- Has high spatial resolution.
2- The technique should be reproducible.
3- have a high diagnostic utility
4- should be free of artifact.
5- should be widely available, fast and easy to use, and cost-effective.
I. SPECT MPI
Radiotracers used are:
a- Thallium-201 (Tl-201) is suboptimal low energy and long half-life.
b- Tc-99m sestamibi
c- Tc-99m tetrofosmin
All of the agents have properties that allow the stress component and the imaging component to be separated in time and location, which is a significant advantage over other modalities.
SPECT MPI Imaging Protocols
1- The same day rest-stress protocol using a Tc99m-labeled perfusion agent.
2- A dual-isotope protocol in which Tl-201 is used for the rest images and then a Tc-99m perfusion agent is used during stress soon thereafter.
Image analysis using data base
Advantages and limitations of SPECT:
1- It is compatible to multiple stress modalities including exercise, dobutaminem or vasodilators.
2- there is less demand for high temporal resolution, and signal-to-noise ratio (SNR) can be improved by collecting data over a longer period of time.
Limitations:
1- long acquisition protocols.
2- Poor spatial resolution
3- Limited detection of subendocardial perfusion defects.
4- Limited sensitivity in detecting mild-to-moderate stenosis.
5- It has many artifacts related to motion, gut and biliary activity, and breast and subdiaphragmatic attenuations.
ECG-gated ecquisitions can be used to helop distinguish attenuation artifacts from fixed perfusion defects resulting from myocardial scar.
attenuation correction algorithms that use transmission as well as emission data are available and can improve the accuracy of SPECT MPI.
MPI has reduced sensitivity for detecting left main disease or 3-vessel disease related to balanced ischemia.
The diagnostic approach of SPECT MPI guiding selective coronary angiography reduces costs associated with both diagnosis and revascularization.
PET MPI
It has been widely used, although, availability of the scanners, increased cost, and reimbursement issues have limited wide use of PET.
Myocardial Contrast Echo Perfusion
Echocardiography used for evaluation of exercise- or dobutamine-induced wall motion analysis is widely used. Although limitations of the sensitivity of wall motion analysis have led to the development of MCE.
Contrast Echocardiography Perfusion Techniques
It is perfusion echocardiography has been performed with both vasodilator and inotropic pharmacological stress. It depends on detection of microbubbles after their destruction in the target area. Area of low perfusion the return of microbubbles will be slow while area of high perfusion will be high.
Advantage:
1- It does not involve ionizing radiation.
2- Compared with SPECT, MCE has improved spatial resolution, enabling detection of subendocardial ischemia.
3- MCE also has the ability to perform absolute quantification of myocardial blood flow.
4- Imaging can be performed during pharmacological stress with inotropes or vasodilators or with exercise.
5- wide availability and relatively low cost of the echocardiography.
Limitations:
1- Suboptimal images are obtained in a significant number of patients as the result of respiratory motion, body habitus, or lung disease.
2- Attenuation from the microbubbles may result in artifacts in the basal segments of the left ventricle.
3- some operator-dependent factors.
4- No FDA approved contrast agents for MCE
5- increased variability and decreased reproducibility.
According to literatures; MCE was shown to have prognostic value that was incremental to left ventricular ejection fraction.
CMR Perfusion Imaging
Most CMR studies of myocardial perfusion are based on the first-pass of a bolus of gadolinium-DTPA contrast agents.
Areas that are well perfused will have a shorter T1 and appear bright on heavily T1-weighted
images, whereas regions that are hypoperfused will have longer T1 and will appear hypointense.
This technique has an overall sensitivity and specificity of 89% and 87%, respectively, for detecting CAD.
Advantages:
1- its high spatial resolution, the ability to perform absolute quantification of perfusion.
2- the study can be performed rapidly, has limited operator dependence
3- the signal characteristics are largely independent of the patient’s body habitus.
Limitations:
1- Current pulse sequences suffer from a “dark-rim” artifact that can be mistaken for a true perfusion abnormality.
2- gadolinium-DTPA is not an ideal contrast agent.
3- gadolinium contrast agents have been associated with a rare, but serious condition called nephrogenic systemic sclerosis specially in with a creatinine clearance 30 mg/dL.
The diagnostic performance of perfusion CMR was superior as compared with the entire SPECT population in a study. But as it is new modality; limited data available.
CTA Perfusion Imaging
With the recent advances in multidetector CT (MDCT) and CT coronary angiography, there has been renewed interest in using CT to evaluate myocardial perfusion.
Advantages:
1- high spatial resolution, rapid data acquisition, and the ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in one study.
2- become widely available.
Limitations:
1- image quality is inversely related to heart rate, the increase in heart rate with vasodilator stress may compromise image quality.
2- limited ability of quantitative assessment of perfusion due to artefacts.
3- The contrast agent doses typically used preclude the evaluation of patients with significant renal insufficiency.
4- The main disadvantage of assessing perfusion with MDCT is the potentially high doses of ionizing radiation.
Myocardial contrast echocardiography (MEC), CT angiography (CTA), Myocardial perfusion scintigraphy (MPS), and cardiac MRI are all useful non-invasive modalities in the diagnosis of CAD in addition to street Echo.
CKD patients have a risk of contrast agents exposure during the test, which includes CIN, and gadolinium-induced nephrogenic systemic sclerosis.
so, stress echocardiography without contrast or gadolinium will be safe and good in CKD patients for diagnosis of CAD.
AMAL Anan
2 years ago
Summarise this article
Coronary physiology..
Highly regulated process which involves epicardial vessels, resistances vessels and endothelium.
Endothelial dysfunction here reflected on vascular diseases and coronary artery diseases
* methods for inducing coronary vasodilation :- MPI depends on ability of stress modalities to induce regional hetenogenicity of coronary arterial blood flow in case of coronary entry diseases.
The ideal perfusion imaging techniques and agents would have high first pass myocardial uptake proportional to perfusion, insignificant back diffusion and recalculation rapid clearance from Blood pool. Spect MPI clinically used three radiotracers thaliem-201, Tc99m sestamibi and Tc-99m tetrosfosmin
Spect MPI is compatible with multiple stress modalities but long acquisition protocols and poor resolution than other modalities.
Pet MPI for MPI more than 25 years.
Radio tracers: N-13 ammonia, Rubidium-82 and O-15 water for myocardial perfusion
It is improving spatial resolution in comparison to SPECT but costly. Myocardial contrast echo perfusion is used for evaluation either exercise or dobutamine induced wall motion analysis.
FDA give alarm for these with pulmonary hypertension or with disturbed Cardiopulmonary function Contrast echocardiography perfusion technique asses myocardial perfusion with continuous infusion of micro bubbles.
It is involved ionized radiation but there are increasing in variability while decreasing reproducibility CMR perfusion imaging:
High spatial resolution but risk for nephrogenic systemic fibrosis. CTA perfusion imaging
High spatial resolution, rapid data acquisition with coronary anatomy information
But there’s disability of quantitative assessment of perfusion
Since this article is addressing general population, please make refection on CKD patients
For chronic kidney discourse patient consider SPECT MPI and PET MPI
while contrast agent are not favourable carrying risk of contrast induce reptoropatly especially if not on dialysis or Nephrogenic systemic fibrosis.
Hoon Loi Chong
2 years ago
Summarise this article
Non-invasive assessment of myocardial perfusion can be done via different perfusion imaging modalities. This article gave a brief review of different perfusion imaging modalities, summarized as the table attached.
Since this article is addressing general population, please make refection on CKD patients
Primum non nocere, secundum cavere, tertium sanare. Imaging modalities such as stress echocardiography, myocardial contract echocardiography (MCE), CT angiography (CTA), myocardial perfusion scintigraphy (MPS) and cardiac MRI (CMR) are useful non-invasive clinical tools in the diagnosis of coronary artery disease (CAD). However, the clinical utility of MCE, CTA and CMR in advanced CKD patients in CAD diagnosis has been limited due to the concern of contrast-induced nephropathy (CIN) and nephrogenic systemic fibrosis (NSF), respectively. Hence, stress testing without contrast or gadolinium exposure will be a relatively safer and useful imaging modalities in CKD patients in detecting CAD. Robust studies have shown that stress echocardiography has a good performance in detecting CAD in CKD patients, with a sensitivity of 80% and specificity of 89%. Autonomic dysfunction is common in CKD hosts, and a blunted chronotropic response is expected during Dobutamine and Dipyridamole stress echocardiography (DSE) testing. Therefore, exercise stress echocardiography (ESE) will more ideal and useful clinically in the diagnosis of CAD in CKD hosts.
Dalia Ali
2 years ago
Noninvasive Assessment of Myocardial Perfusion
This article will critically evaluate the strengths and weakness of these modalities for evaluating myocardial perfusion
SPECT MPI
Protocol
There are a number of SPECT MPI protocols available for the assessment of CAD. With the same-day rest-stress protocol using a Tc99m-labeled perfusion agent, a first injection at rest is followed by imaging roughly 30 minutes later. A second injection with 2 to 3 times the activity is administered during peak stress to overcome the background signal from the rest images, and repeat imaging is performed.
Advantages and Limitations of SPECT SPECT MPI
Advantage
1- SPECT MPI is compatible with multiple stress modalities including exercise, dobutamine, or vasodilators.
2- less demand for high temporal resolution, and signal-to-noise ratio (SNR) can be improved by collecting data over a longer period of time.
Limitation
1- long acquisition protocols and considerably poorer spatial resolution than other available modalities
2- limiting detection of subendocardial perfusion defects
3- motion artifacts related to patient and respiratory motion, scatter and partial volume artifacts in the inferior wall related to gut and biliary activity, and variable attenuation artifacts resulting from breast or subdiaphragmatic attenuation. These artifacts can decrease the diagnostic utility of the perfusion images.
PET MPI
PET Radiotracers N-13ammonia, Rubidium-82 (Rb-82), and O-15 water are the PET tracers typically used for myocardial perfusion. O-15 water is freely diffusible and has a high first-pass extraction.15 The uptake is proportional to flow over the largest range of myocardial flows without significant roll-off.
Imaging Protocol Typically a resting perfusion image is acquired using either Rb-82 or N-13 ammonia. A bolus of the tracer is given and imaging usually commences between 90 to 120 seconds thereafter. ECG-gated PET acquisition is usually performed for 3 to 6 minutes for Rb-82 and 5 to 15 minutes for N-13 ammonia, owing to their different half-lives.
Advantages
1- spatial resolution of 2 to 3 mm as compared with the 6- to 8-mm resolution of conventional SPECT imaging.
2-PET tracers have significantly less roll-off of
extraction at high flows as compared with Tc-99m–based SPECT agents.
3-attenuation artifacts are less of an issue for PET.
4- PET are more easily applied in dynamic scanning to be used for absolute quantification of perfusion. With the recent advances in PET/CT technology
Limitations
1- the need for a cyclotron for all but Rb-82 imaging or imaging agents labeled with
2- Artifacts from motion during the scan are frequently less apparent, making it harder to evaluate their effects on images. Furthermore, registration artifacts between perfusion images and attenuation maps can result in artifacts.
3- If PET is combined with CTA, patients probably will be exposed to even higher radiation doses.
Myocardial Contrast Echo Perfusion
Contrast Agents MCE contrast agents are small, gas-filled microbubbles (⬍10 um) that compress and expand when exposed to an acoustic field and generate strong acoustic backscattering
Contrast Echocardiography Perfusion Techniques include continuous infusion of microbubbles. When the microbubbles have reached steady-state concentrations, a high mechanical index pulse is used to destroy the bubbles in the imaging plane. The subsequent replenishment of microbubbles is related to myocardial perfusion. Areas that are hypoperfused will have a slower return of microbubbles, whereas areas that are well perfused will have a more rapid return of microbubbles.
Advantages
1-it does not involve ionizing radiation.
2-Compared with SPECT, MCE has improved spatial resolution, enabling detection of subendocardial ischemia.
3-MCE also has the ability to perform absolute quantification of myocardial blood flow.
4- Imaging can be performed during pharmacological stress with inotropes or vasodilators or with exercise.
5-Practical advantages of echocardiography include
its wide availability and its relatively low cost.
limitations.
1-Suboptimal images are obtained in a significant number of patients as the result of respiratory motion, body habitus, or lung disease.
2-Attenuation from the microbubbles may result in artifacts in the basal segments of the left ventricle.
These factors can limit image quality and adequate spatial coverage of the ventricle, resulting in increased variability and decreased reproducibility.
CMR Perfusion Imaging
Contrast Agents Most CMR studies of myocardial perfusion are based on the first-pass of a bolus of gadolinium-DTPA contrast agents. Interactions between the unpaired electrons of paramagnetic gadolinium and water protons in close proximity result in more rapid relaxation of these water protons.
Protocol
Imaging Protocol Stress perfusion CMR is generally applied as part of a comprehensive study that evaluates ventricular function, stress and rest perfusion, and viability/myocardial infarction. Cine images to assess ventricular function are obtained generally in ⬍10 minutes. Stress perfusion images are then obtained during infusion of 140 g/kg/min of adenosine for 2 to 4 minutes.
Advantages
1- high spatial resolution
2- the ability to perform absolute quantification of perfusion
3- and the additional information provided in a comprehensive CMR study.
4- CMR perfusion studies have adequate spatial coverage and temporal resolution that continue to improve with further advances in parallel imaging techniques.
Limitations
1-operator dependence
2-the signal characteristics are largely independent of the patient’s body habitus.
CTA Perfusion Imaging
Contrast Agents Myocardial perfusion imaging with CT is based on the intravenous injection of iodinated contrast agents that increase the absorption of x-rays in proportion to the concentration of iodine.
Most of the agents used clinically are
nonionic contrast agents with a high iodine concentration.
Advantages
1-high spatial resolution
2-rapid data acquisition
3-the ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in 4-the growth of CTA, MDCT scanners are becoming widely available.
5-Absolute quantification of CT perfusion has been demonstrated for dynamic studies but requires modeling of the effects of contrast diffusion into the extravascular 6-advancement of MDCT with 256 or 320 detectors may enable dynamic analysis of perfusion with high temporal resolution.
limitations.
1-Because image quality is inversely related to heart rate, the increase in heart rate with vasodilator stress may compromise image quality.
2-The main disadvantage of assessing perfusion with MDCT is the potentially high doses of ionizing radiation. Protocols that involve obtaining CTA studies at rest and stress would potentially double the current coronary CTA radiation dose.
mai shawky
2 years ago
Non-invasive assessment of myocardial perfusion is important in screening for CAD for identification of high risk patients and their appropriate management.
The ideal agent should be safe, with minimal side effects, high sensitivity to small changes in coronary blood flow , widely available, fast and easy to use, and cost-effective.
v SPECT MPI:
ü is widely available, validated and has comparable efficacy with multiple stress modalities including exercise, dobutamine
ü however, it is time consuming, has poorer spatial resolution than other available modalities, limited ability to detect subendocardial perfusion defects.
ü Sensitivity 0.87 Specificity 0.73
v PET MPI:
ü better spatial resolution as compared with SPECT, easier 3. recent advances in PET/CT technology.
ü but less available, more expensive, higher dose of irradiation exposure.
ü Sensitivity 0.85 Specificity 0.87
v Myocardial Contrast Echo Perfusion:
ü wide availability and its relatively low cost
ü No ionizing radiation exposure.
ü detect the subendocardial ischemia
ü absolute quantification of myocardial blood flow.
ü however, like any US it is operator-dependent, affected by the respiratory motion, body habitus, or lung disease.
ü No FDA-approved contrast agents for MCE perfusion
v Cardiac MRI
ü High resolution, fast performance
ü not operator dependence.
ü however, not widely available , expensive ü Contraindicated if GFR less than 30, due to fear of nephrogenic systemic fibrosis
ü Sensitivity 0.91, Specificity 0.81
v CT coronary angiography
ü High resolution, fast performance
ü provides information about coronary anatomy, ventricular function, and perfusion in one study.
ü still, expensive, high dose of irradiation. ü can induce AKI in those with GFR < 60 In CKD Population:
ü – cardiac MRI is Contraindicated if GFR less than 30, due to fear of nephrogenic systemic fibrosis
ü CT coronary angiography can induce AKI in those with GFR < 60
Zahid Nabi
2 years ago
This article has discussed different modalities which can be used for non invasive detection of myocardial perfusion and also there limitations. 1- Single-photon emission computed tomography (SPECT) which is most commonly used. 2- Myocardial contrast echocardiography (MCE) 3- positron emission tomography (PET) 4- Cardiac MRI (CMR) 5- Cardiac computed tomography (CT)
Endothelial dysfunction is an early manifestation of vascular disease and plays a role in the development of CAD. Coronary autoregulation attempts to normalize myocardial blood flow even if stenosis exceeded 85% to 90%. However, under vasodilator stimulus, maximal coronary flow has been shown to decrease with stenosis of > 45%. Stress modalities are more sensitive assessing coronary perfusion than analysis of stress-induced wall motion abnormalities or ECG changes alone. SPECT In multicenter studies, it showed a sensitivity of 87% with a specificity of 73% and may have artifacts in which the associated ECG can help to differentiate. PET Has high sensitivity around 92% and specificity around 85%.Limitations include cost and unavailability of scanners. Myocardial Contrast Echo Perfusion:
Still experimental A meta-analysis of 18 studies of 1088 patients suggest sensitivity of 82% and specificity of 80%. Cardiac Magnetic Resonance (CMR) Perfusion imaging: This technique has overall sensitivity and specificity of 89% and 87%.It has limitation of use in CKD stage 4 and 5 i.e GFR less than 30ml/min. CTA perfusion imaging:The risk of contrast induced Nephropathy limits it’s judicial use Reflection on CKD patients I think all efforts should be made to diagnose myocardial perfusion defects in CKD patients non invasively however the current practice does not support use of these modalities for multiple reasons Like CIN with CT perfusion imaging
Risk of NSF with gadolinium based MRI which is not recommended in patients with GFR less than 30.
Rahul Yadav rahulyadavdr@gmail.com
2 years ago
Summarize this article
This article address non-invasive methods to diagnose significant Coronary artery disease by assessing myocardial perfusion and mentions critical appraisal of each method and helps in risk stratification of patients who underwent these non-invasive modalities with available studies in the literature.
Coronary Physiology relevant to the non-invasive modalities:
Coronary autoregulation is a regulated process to increase supply to myocardium at times of stress. When coronary artery stenosis leads to 85% to 90% occlusion of lumen, autoregulation fails to improve blood flow and significant reduction in flow occurs even at rest.
But during periods of exercise/Pharmacological stress, such autoregulation unable to cope with increasing demands of myocardium and maximum coronary flow starts reducing even at more than 45% stenosis in coronaries and can be diagnosed early.
Endothelial dysfunction and adrenergic stimulation also contribute to reduced coronary reserve at time of exercise apart from failure of autoregulation with increasing stenosis in coronaries.
Coronary/Myocardial flow increases variably with varying Pharmacological stress/exercise like Exercise, Dobutamine leading to 2-3-fold increase and Dipyridamole, Adenosine:3.5-to-4-fold increase.
Keeping in mind coronary physiology, various non-invasive tests exploit mechanisms of increase in myocardial blood flow to find out significant CAD.
Characteristics of an ideal Perfusion technique:
1. High First pass uptake in myocardium in proportion to perfusion
2. Should not alter hemodynamic and negligible volume to be required as compared to large myocardial blood flow
3. Safe and minimal side effects
4. Stable and low cost
Characteristics of an ideal imaging modality:
1. Highly sensitive
2. Relationship between signal intensity and concentration of agent should be quantifiable
3. Spatial/temporal resolution should be high
4. Should not be operator dependent, easy to use, low cost and widely available
5. High diagnostic yield
Various non-invasive modalities are:
1. SPECT MPI: Three radiotracers commonly used are Thallium 201(potassium analog taken by viable myocytes), Tc99 sestambi and tetrofosmin binds mitochondrial membrane with virtually no redistribution.
These agents have properties to allow imaging and stress component to be separated in time and location which is dependent on myocardial cellular integrity in addition to coronary flow and hence compatible with multiple stress modalities like exercise and pharmacological agents.
It has limitations like long acquisition time, poor spatial resolution limiting detection of subendocardial perfusion defects.
Roll off of tracer uptake at high myocardial flow limits detection of mild to moderate CAD.
Pooled diagnostic performance of SPECT MPI has moderate sensitivity and specificity.
2. PET MPI: N-13ammonia, Rubidium-82(Rb-82), and O-15 water are commonly used PET tracers for myocardium perfusion with varying pros and cons of each in terms of half-life, myocardial retention, roll off phenomenon, few requiring onsite cyclotron for synthesis.
Limitations includes cost and unavailability of scanners.
This modality can quantify myocardial perfusion in ml/min/g of tissue. PET has improved spatial resolution compared to SPECT (2-3mm versus 6-8mm) with less roll off and ability of absolute quantification of blood flow.
PET have high diagnostic accuracy (91% versus 76%) and higher specificity (100% versus 66%) comparing SPECT with coronary angiogram as gold standard in one study for detecting more than 50% stenosis.
Summed stress score had prognostic utility in suspected or known CAD and can be used in studies as a quantifiable measure.
3. Myocardial Contrast Echo Perfusion: Lack of FDA approved contrast agent for this technique limits its widespread clinical use and considered experimental.
Qualitative and quantitative analysis of myocardial blood flow can be possible with this modality.
It has an advantage of non-use of ionizing radiation compared with other techniques.
Compare to SPECT it has better spatial resolution enabling subendocardial defects.
A meta-analysis of 18 studies of 1088 patients suggest sensitivity of 82% and specificity of 80%
4. Cardiac Magnetic Resonance (CMR) Perfusion imaging: Based on first pass of bolus of gadolinium agent.
This technique has overall sensitivity and specificity of 89% and 87%.
High spatial resolution enables subendocardial ischemia and overall reduced perfusion in triple vessel disease which is not evident with PET and SPECT.
Ability to perform perfusion stress testing and absolute quantification of flow is another advantage.
Limitations include use of gadolinium and risk of NSF.
It has intermediate extraction fraction during first pass and non-linearity in relation between perfusion and signal intensity.
It has slow washout and perfusion with delayed enhancement enables accurate detection of myocardial infarction.
It has limitation of use in CKD stage 4 and 5 i.e GFR less than 30ml/min
5. CTA perfusion imaging: Iodinated contrast causes reduction in coronary flow followed by hyperemic response and is not hemodynamic inert.
During first pass there is significant diffusion in interstitial space and it is 33% at maximal flow and still higher with low flow.
Thus, for assessment, extravascular diffusion of agent to be taken in account.
Low osmolarity causes less hemodynamic changes but more extravascular diffusion and trade-off between various agents.
Black box warning of CIN with GFR less than 60.
High spatial resolution, rapid image acquisition, wide availability with moderate sensitivity and specificity are noted advantages of this modality.
All techniques have their weakness and strength, and no one has an unequivocal superiority.
Quantification methods need to be standardized keeping in mind current gold standard i.e coronary angiogram with all modalities in future.
Since this article is addressing general population, please make refection on CKD patients
SPECT MPI and PET MPI can be used to assess cardiovascular risk and prognosis in CKD patients. Radionuclide imaging can find relative flow difference between myocardium and can help in risk stratification and prognostication in CKD patients.
Myocardial contrast echo perfusion is currently experimental with non-availability of FDA approved contrast but at the same time can be employed in these subset of patients as it is free of ionizing radiation.
Toxicity of contrast microbubbles to be evaluated with further studies in CKD patients.
Few techniques can’t be used in CKD patients like CMR and CTA perfusion imaging due to risk of NSF and need for dialysis after contrast injection.
Ban Mezher
2 years ago
Non invasive techniques used in assessment of myocardial perfusion include SPECT, PET, CMR and cardiac CT which is important in diagnosis & risk assessment of patients with CAD.
Contrast agents should not change cardiac hemodynamics, small in volume, & safe with low incidence of side effects. Non invasive techniques should be available, easy, fast & cost-effective.
SPECT-MPI:
3 radio-tracer can be used with this test which have different half life, different first pass extraction. The result of image can be done by visual analysis or by differences in count between rest & stress.
Advantages:
widely available & validated, can use different stress modalities ( exercise, dobutamine, vasodilators)
low demand for high temporal resolution.
Limitations:
long acquisition protocol.
low resolution comparing to other techniques
detection of sub endothelial perfusion defects are limited.
limited sensitivity in mild to moderate coronary stenosis.
artefact
low sensitivity in detecting 3 vessels disease
exposure to radiation.
It is found that SPECT-MPI when used to select patients for coronary angiography associated with low cost associated with both diagnosis & re vascularization.
PET-MPI:
Tracers include: 0-15 water ( non approved by FDA), N-13 ammonia( good perfusion agent), Rb-82 (high radiation dose) & new agent fluorine -18. The image can be done qualitative or semi-quantitively.
Advantages:
higher spatial resolution than SPECT
tracers have less room-off of extraction
artefact
combination with CTA can be done
short half life of tracers result in lower radiation than SPECT
Limitation:
high cost
need for cyclotron
high radiation when used with CTA .
PET has higher sensitivity & specificity in diagnosis of >50% of stenosis than SPECT, & it can be cost effective when compared to angiography, exercise ECG, & SPECT.
Myocardial contrast ECHO perfusion:
This technique is limited by non FDA approval. The contrast agents are small, gas-filled micro bubbles which is not affect cardiac hemodynamics so it reflect directly myocardial blood flow. Hypo-perfused myocardial tissues show slow return of micro bubbles while good perfused tissues show rapid return of micro bubbles.
Advantages:
no ionizing radiation
can detect sub-endothelial ischemia.
quantify myocardial blood flow.
can be performed with pharmacological stress test or with exercise stress test
wide availability & low cost.
Limitations:
sub-optimal image due to respiratory movements, body habitus or lung diseases.
artefact
operator dependent factors
no FDA approved contrast.
Some studies show that MCE has sensitivity 82% & specificity 80%.
CMR perfusion image:
Use gadolinium-DTPA as contrast agent. Interaction between gadolinium & water proton can result in rapid relaxation of water proton. IN normal myocardial tissue with good perfusion has short T1 & looks bright on T1- weighted image but abnormal perfused tissues had long T1 & appear hypo-tense. Stress- perfusion CMR can evaluate ventricular function, myocardial perfusion both at rest & stress, and viability of myocardium. High resolution CMR can detect sub-endothelial ischemia.
Advantages:
high spatial resolution
absolute quantification of perfusion
rapid test
limited operator dependent
Limitations:
artefact.
gadolinium contraindicated if GFR <30.
CTA perfusion image:
Use iodinated contrast usually non ionic. It can affect coronary blood flow by hyperemic response which can be lessened by using low osmolar non ionic contrast. Combination of CT perfusion & angiography associated with increased sensitivity (86%) & specificity(92%( in detecting perfusion defects.
Advantages;
high spatial resolution
rapid data acquisition
assessment of ventricular function, coronary anatomy & myocardial perfusion in one technique .
Limitation:
compromisation of image quality during increased heart rate
artefact
high ionized radiation doses can preclude evaluation in renal impairment.
Stress techniques have low to moderate sensitivity in CKD patients due to poor exercise capacity & poor heart rate response to stress. CTA can cause contrast induced nephropathy when GFR < 60 & CMR associated with fatal condition (NSF) if gadolinium used when GFR<30.
Summarize this article
Coronary physiology:
In stress there is auto regulation to increase blood supply to myocardium also endothelium plays an important role as releasing NO causing vascular dilation.
The early stage of CAD is endothelial dysfunction
Significant stenosis if more than 80% of the lumen and in this level auto regulation fails to adequately supply myocardium.
Non invasive methods for diagnosis CAD :
A- SPECT MPI:
Using Thallium 201, Tc99 sestambi and tetrofosmin
It’s limitations : poor spatial resolution , long acquisition time
Has moderate sensitivity (76%) and specificity (66%)
B- PET MPI:
It’s limitation is very expensive and unavailable in all centers
PET have sensitivity of 91% and specificity 100%
C- Myocardial Contrast Echo Perfusion:
Considered experimental
D- Cardiac Magnetic Resonance (CMR) Perfusion imaging:
Has sensitivity 89% and specificity 87%
It’s limitation is using Gadolinium with risk of NSF with contraindication when eGFR less than 30%
E- CTA perfusion imaging:
High risk of CIN
Yashu Saini
2 years ago
Well this article explains about different non-invasive modalities of assessing the myocardial perfusion but. But it explains the pros and cons of each modality in quite detail and in terms of radio and nuclear physics which probably would be best understood by radiologists and nuclear medicine people.
I would still try to summarise it in very basic language it starts with explaining the basic corner of physiology and explains that dysfunction in endothelium is probably the earliest manifestation of vascular disease and his major determinant of developing coronary artery disease.
Changes in myocardial perfusion is probably the earliest change in the sequence of Ishmeet events and its sensitivity is much superior as compare to the modalities used for assessing slow limiting stenosis or motion abnormalities or ECG changes. Exercise induced Vassodilattors is the preferred modality as it is associated with significant increase in myocardial blood flow but this can also be achieved using pharmacological vasodilators.
The authors suggest the qualities of an ideal perfusion agent and imaging modality in very simple and tabular form but simultaneously suggest that none of the available imaging modalities is perfect and there is one or the other drawback of each of the imaging modalities including SPECT, PET, CARDIAC MRI, CT.
Each modality has been discussed in great detail including the advantages and disadvantages but the overall performance of the modalities discussed show that SPECT and PET have highest highest CADP prevalance of 76% and 77% respectively. Although sensitivity and specificity of cardiac MRI is highest among the discussed modalities but CAD prevalence is lowest in this to the tune of 57%.
Among all the discuss modalities appropriateness criteria for perfusion stress testing has been established for SPECT and CMR.
therefore with respect to evaluation of CKD patients being prepared for kidney transplant I would consider CMR as most superior modality in assessment of myocardial perfusion because not only its appropriateness criteria has been established, its sensitivity and specificity is also highest.
to conclude the authors suggest the need to develop further more advanced methodologies which adopt functional gold standard like fractional flow reserve to assess myocardial perfusion unlike the currently available radio nuclide techniques which only assess relative flow differences in different regions of myocardium
Manal Fatalla Malik
2 years ago
for clearfication Manal MALIK
Manal Fatahallah
2 years ago
Summary of Noninvasive Assessment of Myocardial PerfusionNon invasive tools of myocardial perfusion in diagnosid of CAD include single -photon emssion computed tomography(SPECT) is common use ,myocardial cpntrast ECHO(MCE),position emission tomography(PET),cardiac MRI(CMR),cardiac tomography(CT).
image analysed depend on difference between rest and stress as compred with normal data base.
Advantage of SPECT:
1-widely avaiable
2-extensively validated
3-comptable with multiple stress modilaties.
4-less demand for high temporal regulation
Limitation
1-long protocol.
2-poor spatial resoulation.
3-limiting detection of subendocardial perfusion defects.
4-limit sensitivity to detect mild to moderate stenosis.
5- motion artifacts and partial volume artifacts with inferior wall related to gut and biliary activity.
6- reduced sensitivity for detecting left main disease or 3-vessels disease related to balanced ischemia
7-expose patients to non trival radiation dose..
PET MPI
has limited clinical use of PET due to multiple factors
Advantages:
1-less roll-off of extraction at high flows as compered with TC-99m -based SPECT agents.
2-need higher doses and lower spatial resoulation.
3-less Artifacts
4-The tracers used in PET are more easily applied in dynamic scanning
5- lower radiation doses.
Limitation
1- higher costs
2- need for acycloton for all.
3-registration artifacts clinically.
when PETis combined with CTA patients will be exposed to even higher radiation doses.
Myocardial contrast ECHO Perfusion
is commonly used.
Limitation:
Sensitivity of wall motion analysis .
Advantages
1-not involve ionization radiation.
2-detect subendocardial ischemia.
3-ability to perform absolute quantification of myocardial blood flow.
4- imaging can be performed during pharmacological stress with intropes or vasodilators or with exercise.
5-wide availability.
6-low cost.
Limitation
1-suboptimal images as result of respiratory motion,body habitus or lung disease.
2-artifacts in the basal segment of the left ventricle.
3-variability and decreased reproducibility.
4-no FD approval contrast agents MCE perfusion.
CMR perfusion imaging
Advantage for perfusion stress testing ,including its high spatial resolution.
2- The ability to perform absolute quantification of perfusion.
3-added comprehensive CMRstudy.
4-can be perform rapidly .
Limitation :
1-operator dependence.
2- independent of the patients body habitus.
3- artifact can be mistaken for time perfusionabnormality .
4-can not be used in patients withegfr less than 30.
CTA Perfusion imaging:
Advantage of MDCT:1- high spatial resolution.
2-rapid data acquistion .
3- the ability to potentially combine information of coronary anatomy ,venticular function and perfusion in one study.
4-is widely available.
Limitation:
1- image quality is inversely related to heart rate.
2-artifacts result in variation of signal intensity with myocardium.
3- inability of quantitative assessment of perfusion .
4- can not be apply in patients with renal impairment.
5-high doses of ionizing radiation.
Summary
current available modalities have their advantages and limitation .
no technique has demonstrated unequivocal superiority.
The radionuclide techniques as used clinically only assess relative flow difference between regions of myocardium.
futures studies should adopt afunctional gold standard such as fractional flow reserve ,inaddition to the anatomic gold standard of coronary artery .
approproate criteria for perfusion stress testing have been established for SPECT and CMR and should be stablished for PET,contrast ECHO and CT perfusion .
cost effectiveness of the new technologist must be evualated
2-refection on CKD patients cardiac stress test is used widely in ckd pateints but low sensitivity in such group of paients due to abnormal base line ECG,more over the exercise capacity of patients with ckd is limited due to musle fatigue,anaemia ,peripheral vascular disease ,peripheral neuropathy,and other comorbidities.inaddition the sensitivity and specifity of exercise ECG in ck patients is poor.
CTAperfusion imaging and CMR perfuion
sensitivity and specificity of myocardial perfusion is highly variable
myocardial perfusion SPECT is based upon comparison of perfusion between myocardial segments ,balanced multivessel disease can result in false -negative SPECT.
stress ECHO this type of test is low sensitivity compared in non ckd pateints.
myocardial perfusion scintigraphy ,ckd and myocardial ischemia detected by stress are independent predictors offor cardiovascular events,coexistence of ckd and myocardial ischemias detect by stress MPIA is more useful for short -term risk stratification of cvs events,
Marius Badal
2 years ago
Summarise this article
The article was a bit challenging, but it is about the non-invasive assessment of myocardial perfusion and how it is important in the diagnosis and risk stratification of patients with possible coronary artery disease. It dealt with the evaluation of the strength and setback of the different modalities for the proper evaluation of myocardial perfusion. Some of the studies or modalities used in the studies were MCE, PET, CMR, and cardiac CT. Coronary physiology: myocardial perfusion is a highly regulated process that involves all the vessels and muscles. One of the fundamental early detections of cardiovascular dysfunction is endothelial dysfunction. With normal vessels, there is a balance of vasoconstriction and vasodilatation involving the sympathetic nervous system and the function of nitric oxide. However, when there are endothelial lesions or damage vasoconstriction is predominated decreasing normal blood flow. Also, atherosclerosis of the vessels plays a role in reducing blood flow and causing more damage to the myocardium. To better access myocardial perfusion, PET and MPI were done. So abnormal coronary flow reserve with vasodilator stress in the absence of significant coronary stenosis occurs and has been attributed to microvascular and or endothelial dysfunction. The methods for inducing coronary vasodilation. 1) Exercise induces coronary vasodilation via an endothelial-dependent flow-mediated process to meet the increased oxygen demand. It increases a 2-3-fold increase in myocardial blood flow and is the preferred modality. Also, medication like dobutamine increases myocardial blood flow by 2-3-fold. 2) Studies used: a) SPECT MPI radiotracers 1) these involve thallium 201 2) Tc 99m sestamibi 3) Tc 99m tetrofosmin The advantage of this study is that it is widely available, well-validated, compatible with other stress modalities, and less needed for high temporal resolution. The limitation of this study is that it requires long protocols, limited sensitivity in detecting mild to moderate stenosis, there are motion artifacts and exposes the patient to radiation. PET MPI: it is a study that has been around for years, but it has been modified for better results in this case the PET-CT scanners. The PET radiotracers which are made of N-13 ammonia, rubidium-82, and the O-15. Its advantage is that it improves spatial resolution, has fewer artifacts, is easily applied, and has high sensitivity. Myocardial contrast ECHO perfusion: It uses a small amount of contrast agent gas-filled microbubbles. It is a study that is not involved with ionizing radiation, it improves spatial resolution and also quantifies myocardial blood flow and it is cheap. It has its limitation like artifact formation, it depends on the operator and its motion can affect the picture. The CMR perfusion imaging is a contrast that is dependent on gadolinium DTPA c. It is very fast, doesn’t depend on the operator, has a high resolution, and had great spatial coverage. Its problem is the artifact seen and can cause nephrogenic systemic fibrosis. The CTA perfusion imaging is dependent on iodinated contrast. It has high spatial resolution with rapid data acquisition. It allows dynamic analysis of perfusion with temporal quality. As all studies have limitations, its limitation is the artifacts, can worsen kidney function by causing contrast-induced nephropathy and high dose of ionizing radiation.
Since this article is addressing the general population, please make refection to CKD patients
Patients with CKD as it relates to myocardial perfusion imaging stress echocardiogram may have a sensitivity of 80% and specificity of 89%. Stress ECHO will give details on cardiac motion, blood flow, dyskinesia, muscle size, thickness, etc but doesn’t give much detail in the microvascular of the heart and may miss disease in this specific area. CMR is contraindicated in patients with a GFR of less than 30 ml/min due to the possibility of nephrogenic systemic fibrosis. Patients on dialysis may perform the same but will need dialysis posteriorly. Contrast CTA, there is a high risk of CIN and will worsen kidney functions leading to needing RRT. Dobutamine and dipyridamole stress echo will detect inducible myocardial ischemia and also epicardial CAD but are limited to small vessel pathologies. Myocardial scintigraphy has its own limitation and it is similar to EST and ESE
Ghalia sawaf
2 years ago
SPECT Advantages of SPECT
,SPECT MPI is compatible with multiple stress modalities including exercise, dobutamine, or vasodilators.
less demand for high temporal resolution
signal-to-noise ratio (SNR) can be improved by collecting data over a longer period of time.
developments in novel imaging hardware and iterative reconstruction are leading to improved spatial resolution, contrast, and imaging speed for SPECT MPI.
Limitations SPECT
• relatively long acquisition protocols
• poorer spatial resolution than other available modalities,
• limiting detection of subendocardial perfusion defects
• limits sensitivity in detecting mild-to-moderate stenoses.
• motion artifacts related to patient and respiratory motion,
• volume artifacts in the inferior wall related to gut and biliary activity, attenuation artifacts resulting from breast or subdiaphragmatic attenuation.
Motion artifacts can be corrected in postprocessing with the use of motion correction algorithms.
19 ECG-gated acquisitions, which allow for assessment of regional myocardial function, can be used to help distinguish attenuation artifacts from fixed perfusion defects resulting from myocardial scar.
• MPI has reduced sensitivity for detecting left main disease or 3-vessel disease related to balanced ischemia.
• the tracers expose patients to nontrivial radiation doses
PET MPI Advantages
• PET has improved spatial resolution as compared with SPECT
• PET tracers have significantly less roll-off of extraction at high flows as compared with Tc-99m–based SPECT agents.
• Because PET perfusion images are corrected for attenuation as an inherent component of the technology, attenuation artifacts are less of an issue for PET.
• the tracers used in PET are more easily applied in dynamic scanning to be used for absolute quantification of perfusion.
• With the recent advances in PET/CT technology, multimodality functional imaging of perfusion with PET combined with anatomic imaging of computed tomographic angiography (CTA) is now possible.
• The short half-lives of the PET agents result in lower radiation doses than SPECT agents.
• increased cost, and reimbursement issues have limited widespread clinical application of PET
Limitations
• The major limitations to PET include higher costs and limitations imposed by the need for a cyclotron for all but Rb-82 imaging or imaging agents labeled with F-18.
• Artifacts from motion during the scan are frequently less apparent, making it harder to evaluate their effects on images.
• when PET is combined with CTA, patients probably will be exposed to even higher radiation doses.
Myocardial Contrast Echo Perfusion Advantages
• MCE has an advantage over SPECT, PET, and CT perfusion imaging because it does not involve ionizing radiation.
• Compared with SPECT, MCE has improved spatial resolution, enabling detection of subendocardial ischemia.
• MCE also has the ability to perform absolute quantification of myocardial blood flow.
• Imaging can be performed during pharmacological stress with inotropes or vasodilators or with exercise.
• Practical advantages of echocardiography include its wide availability and its relatively low cost.
Limitations
• Suboptimal images are obtained in a significant number of patients as the result of respiratory motion, body habitus, or lung disease.
• Attenuation from the microbubbles may result in artifacts in the basal segments of the left ventricle.
• These factors can limit image quality and adequate spatial coverage of the ventricle, resulting in increased variability and decreased reproducibility.
• there are no FDA-approved contrast agents for MCE perfusion.
CMR Perfusion Imaging Advantages
• Cardiac MRI has high spatial resolution
• the ability to perform absolute quantification of perfusion, and the additional information provided in a comprehensive CMR study.
• the study can be performed rapidly, has limited operator dependence, and the signal characteristics are largely independent of the patient’s body habitus.
• CMR perfusion studies have adequate spatial coverage and temporal resolution that continue to improve with further advances in parallel imaging techniques.
• CMR perfusion imaging is most compatible with vasodilator stress.
Limitations
• gadolinium-DTPA is not an ideal contrast agent
• intermediate extraction fraction during first-pass imaging and has nonlinearity in the relationship between signal intensity and perfusion.
• Recently, gadolinium contrast agents have been associated with a rare but serious condition called nephrogenic systemic fibrosis, which primarily occurs in patients with significant reductions in creatinine clearance in patients with a creatinine clearance 30 mg/dL.
CTA Perfusion Imaging Advantages
• high spatial resolution,
• rapid data acquisition,
• the ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in one study.
• with the growth of CTA, MDCT scanners are becoming widely available.
• Absolute quantification of CT perfusion has been demonstrated for dynamic studies but requires modeling of the effects of contrast diffusion into the extravascular space.
• advancement of MDCT with 256 or 320 detectors may enable dynamic analysis of perfusion with high temporal resolution.
limitations.
• Because image quality is inversely related to heart rate, the increase in heart rate with vasodilator stress may compromise image quality.
• artifacts such as beam-hardening result in variations of signal intensity within the myocardium, limiting the ability of quantitative assessment of perfusion.
• The contrast agent doses typically used preclude evaluation of patients with significant renal insufficiency.
• the potentially high doses of ionizing radiation.
For CKD patients CTA Perfusion Imaging
Produces contrast-induced nephropathy, especially in patients with reduced renal function (creatinine clearance 60).
CMR Perfusion Imaging
gadolinium contrast agents have been associated with a rare but serious condition called nephrogenic systemic fibrosis, which primarily occurs in patients with significant reductions in creatinine clearance.
For me it was a very difficult article.
Actually I read it many time but I didn’t understand these completely complicated imagine techniques especially most of them are not available in my country. So please can you provide me more simple resources
Mu'taz Saleh
2 years ago
summary :
Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease (CAD).
1- SPECT MPI Advantages:
Widely available.
Extensively validated.
Compatible with multiple stress modalities
Less demand for high temporal resolution.
Limitation:
Long acquisition protocols.
Poorer spatial resolution limiting detection of sub endocardial perfusion defects.
Limited sensitivity in detecting mild-to-moderate stenosis.
Motion artifacts.
Reduced sensitivity for detecting left main disease and 3 vessels disease due to balanced ischemia
Expose patients to radiation.
2- PET-MPI: Advantages:
Better spatial resolution and less artifacts.
Provide absolute quantification of perfusion.
Agents used result in lower radiation dose.
Limitations:
Higher cost,
some tracers need cyclotron
Studies showed that PET-MPI has higher diagnostic accuracy than SPECT and has a prognostic value.
Myocardial contrast echo perfusion
Its clinical use is limited as the contrast agent is not approved by FDA and is considered an experimental procedure.
CMR perfusion imaging: Advantages:
High spatial resolution with quantification of perfusion
Limited operator dependence and not affected by patient’s body habitus
Limitations:
Artifacts may be mistaken for perfusion abnormality
Gadolinium contrast agents may be associated with nephrogenic systemic fibrosis
FDA issued black-box warning for gadolinium contrast agent in patients with creatinine clearance <30mg/dl
Studies showed that adenosine stress cardiac MRI are sensitive and specific in detection of CAD
CTA perfusion imaging: Advantages:
MDCT provide high spatial resolution and information about coronary anatomy, ventricular function and perfusion.
Absolute quantification of CT perfusion
Limitations:
Image quality decrease with increased heart rate associated with vasodilator effect.
Limited use in patients with significant renal impairment
High doses of ionizing radiation compared to coronary CTA radiation dose.
In CKD patients:
SPECT:
high-false negative result from balanced ischemia.
CMR,
gadolinium contrast agent in patients with advanced kidney disease may lead to nephrogenic systemic fibrosis when eGFR less than 30
CT angiography,
increase risk of CIN
ESE :
Dobutamine and dipyridamole stress echocardiography (DSE) technique detects inducable myocardial ischemia based on detection of wall motion abnormalities, thus, would detect significant epicardial CAD, not microvascular disease myocardial perfusion scintigraphy MPS in the advanced CKD population has the same limitation as EST and ESE, i.e., related to the inadequate exercise performance and chronotropic incompetence
Huda Saadeddin
2 years ago
Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease (CAD).
Multiple modalities are used for evaluating myocardial perfusion
1 (SPECT) is most commonly used
2 myocardial contrast echocardiography (MCE)
3 positron emission tomography (PET)
4 cardiac MRI (CMR)
5 cardiac computed tomography (CT)
Generally The technique should be reproducible and have a high diagnostic utility and should be free of artifacts that would limit either. Finally, the technique should be widely available, fast and easy to use, and cost-effective.
currently available modalities each have their advantages and limitations, as described in this article, but no technique has demonstrated unequivocal superiority .
SPECT
SPECT MPI is widely available and has been extensively validated. As the stress and imaging components are performed separately, SPECT MPI is compatible with multiple stress modalities including exercise, dobutamine, or vasodilators.
SPECT MPI has multiple limitations, including relatively long acquisition protocols and considerably poorer spatial resolution than other available modalities, limiting detection of subendocardial perfusion defects. Furthermore, the roll-off of tracer uptake at higher myocardial blood flows limits sensitivity in detecting mild-to-moderate stenoses. Also
motion artifacts related to patient and respiratory motion, scatter and partial volume artifacts in the inferior wall related to gut and biliary activity, and variable attenuation artifacts resulting from breast or subdiaphragmatic attenuation.
PET MPI
Although PET has been used for MPI for greater than 25 years, multiple factors including availability of scanners, increased cost, and reimbursement issues have limited widespread clinical application of PET.
PET has improved spatial resolution as compared with SPECT
Contrast Echocardiography Perfusion Techniques
Myocardial perfusion can be assessed with continuous infusion of microbubbles.
MCE has an advantage over SPECT, PET, and CT perfusion imaging because it does not involve ionizing radiation. Compared with SPECT, MCE has improved spatial resolution, enabling detection of subendocardial ischemia. MCE also has the ability to perform absolute quantification of myocardial blood flow. Practical advantages of echocardiography include its wide availability and its relatively low cost.
Limitation there are some operator-dependent factors such as maintaining a constant image plane during replenishment of microbubbles. Finally, there are no FDA-approved contrast agents for MCE perfusion.
CMR Perfusion Imaging
Stress perfusion CMR is generally applied as part of a comprehensive study that evaluates ventricular function, stress and rest perfusion, and viability/myocardial infarction.
Cardiac MRI has significant advantages for perfusion stress testing, including its high spatial resolution, the ability to perform absolute quantification of perfusion, and the additional information provided in a comprehensive CMR study. Furthermore, the study can be performed rapidly, has limited operator dependence, and the signal characteristics are largely independent of the patient’s body habitus.
Recently, gadolinium contrast agents have been associated with a rare but serious condition called nephrogenic systemic fibrosis, which primarily occurs in patients with significant reductions in creatinine clearance 30 mg/dL.
CMR perfusion imaging is most compatible with vasodilator stress.
Adenosine stress cardiac MRI has been shown to be both sensitive and specific for detection of CAD.
CTA Perfusion Imaging
With the recent advances in multidetector CT (MDCT) and CT coronary angiography, there has been renewed interest in using CT to evaluate myocardial perfusion.
The advantages of MDCT include its high spatial resolution, rapid data acquisition, and the ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in one study. Furthermore, with the growth of CTA, MDCT scanners are becoming widely available.
The contrast agent doses typically used preclude evaluation of patients with significant renal insufficiency. The main disadvantage of assessing perfusion with MDCT is the potentially high doses of ionizing radiation. Protocols that involve obtaining CTA studies at rest and stress would potentially double the current coronary CTA radiation dose,with many artifacts.
—————————————-
in ckd
Exercise stress echocardiography and dobutamine stress echocardiographyExercise stress echocardiography (ESE) is better than the standard stress ECG in ruling in CAD . Its sensitivity has been reported ranging from 71 to 97% with specificity ranging from 64 to 90% (17). However, the utility of ESE in CKD population remains limited
The addition of echocardiography allows assessment of ventricular size and function, aortic and mitral valvular calcification, left ventricular hypertrophy (LVH), and potentially coronary flow reserve CFR. CFR measurement by Doppler echocardiography in the left anterior descending artery has been shown to be a determinant of cardiac events in CKD patients in the absence of obstructive epicardial CAD (18), although this is not performed routinely by many echocardiography laboratories due to technical difficulties.
Dobutamine and dipyridamole stress echocardiography (DSE) technique detects inducible myocardial ischemia based on detection of wall motion abnormalities, thus, would detect significant epicardial CAD, not microvascular disease. Abnormal DSE results in CKD patients have been associated with poorer prognosis for cardiac events and overall mortality
Exercise and pharmacological myocardial perfusion scintigraphy MPS in the advanced CKD population has the same limitation as EST and ESE, i.e., related to the inadequate exercise performance and chronotropic incompetence
Normal myocardial perfusion measured by SPECT may not be associated with excellent prognosis in CKD population unlike the normal population (30, 31), perhaps due to the high-false negative result from balanced ischemia. Cardiovascular magnetic resonance (CMR) with gadolinium contrast has not been widely utilized clinically in the CKD population due to the concern of nephrogenic systemic fibrosis (NSF) especially with creatinine clearance 30mg/dl
KAMAL ELGORASHI
2 years ago
Summary of the Assessment of myocardial perfusion;
Different study imaging used to evaluate, and assess myocardial perfusion and ischemia, all are using different study agent with variation in their analysis, advantages, and limitation.
Myocardial perfusion study , involves ; epicardial vesseles, resistance vessles, and endothelium assessment .
Endothelium dysfunction is an early manifestation of vascular diseases, in normal coronary artery, normal phisiological responses, to changes of haemodynamics and physilogical O2 demand of myocardium.
In atherosclerotic artery, if stenosis is more than 45%, the coronary blood flow will be affected even with maximal vasodilatory stimulant.
SPECT MPI imaging study : Rest and steress protocols is there, using Tc99m perfusion agent, first injection at rest fellowed by imaging after 30 minute, then second injection, during peak stress.
Other modality, Typical TI-201 protocol, is to inject during peak stress, then second image taken 10 min. later, and 3rd image taken after 4 hours.
Dual isotope protocol, using different agent (Tc99m,,TI-102), injection of TI-102 during rest , followed by Tc99m during stress, this modality give us more sensitivity in detecting perfusion defect, but more radiation burden to myocardium.
Image analysis involve; visual analsis, using qualitative method, or semiquantitative, using different rest, and stress results.
2.PET MPI:
used radiotracer N-13ammonia-Rubidium(Rb-82)0-15 water.
uptake is proportionate to the flow over the myocardium with serial imaging ,its semiquantitative study , with limition of use due to limitted availability of the scanner, and increasing cost of the study.
3.MCE: myocardium contrast Echocardiography study:
have some limitation because not yet approved by FDA.
safe agent, small volume , gas filled microbubbles, not affect cardiac haemodynamics,and directly reflect myocardium blood flow.
quantitatively and qualitatively analysis .
advantages over SPECT,PET,CT, is that , not using ionized radiation, improve spatial resolution , with ability to perform absolute quantitation of myocardium flow, either stress exercise or pharmacologiacl agent.
Limitation, suboptimal image if lung disease or motion with respiration.
4.CMR:
using contrast gadolinium-DTPA, evaluate ventricular function,rest and stress perfusion, have qualitatative visual analysis,
advantages: have high spatial resoluation, rapid study, and limited operator dependance.
5.CTA perfusion:
using iodinated ,non-ionic contrast, MPCT,CT angio.
Advantages, is doing many study in one , have high resolution , rapid data acqusition,ventricular function,and perfusion.
Disadvantages: high doses of ionizing radiation.
@ reflection of such studies in CKD patient:
As we know that CKD patient have some limitation of exercise capacity , that study may not give us the exact perfusion of myocardium, and the degree of ischemia , in the other hand the CKD patient with hypertension may have ECG changes from hypertension and thick myocardium , that lead to misinterpretation of the studies
Muntasir Mohammed
2 years ago
Article Summary
Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease (CAD).
Multiple modalities including myocardial contrast echocardiography (MCE), positron emission tomography (PET), cardiac MRI (CMR), and cardiac computed tomography (CT) have emerged as promising techniques. This article will critically evaluate the strengths and weakness of these modalities for evaluating myocardial perfusion.
Coronary Physiology
Myocardial perfusion is a highly regulated process that includes epicardial vessels, resistance vessels, and the endothelium. Endothelial dysfunction is an early manifestation of vascular disease and plays a role in the development of CAD. A stenosis must exceed 85% to 90% of luminal diameter before significant reductions
in resting blood flow occur. However, under vasodilator stimulus, maximal coronary flow has been shown to decrease with stenosis of _45%. This has been demonstrated clinically using quantitative PET myocardial perfusion imaging (MPI). Because perfusion is an early change in the ischemic cascade,7 stress modalities that assess coronary perfusion reserve have a higher sensitivity in detecting flow-limiting stenoses than analysis of stress-induced wall motion abnormalities or ECG changes alone. Methods for Inducing Coronary Vasodilation:
Exercise is typically associated with a 2- to 3-fold increase in myocardial blood flow and is the preferred
modality. Dipyridamole, adenosine, and regadenoson are pharmacological vasodilators that cause arteriolar vasodilation by both direct and endothelium-mediated mechanisms and are associated with a 3.5- to 4-fold increase in myocardial blood flow. Dobutamine typically produces a 2- to 3-fold increase in myocardial blood flow like exercise.
SPECT MPI: Radiotracers:
Three radiotracers are commonly used clinically for SPECT MPI:
Thallium-201 (Tl-201)
Tc-99m sestamibi
Tc-99m tetrofosmin Advantages: 1. Widely available. 2. Extensively validated. 3. Compatible with multiple stress modalities 4. Less demand for high temporal resolution. Limitation: 1. Long acquisition protocols. 2. Poorer spatial resolution limiting detection of sub endocardial perfusion defects. 3. Limited sensitivity in detecting mild-to-moderate stenosis. 4. Motion artifacts. 5. Reduced sensitivity for detecting left main disease. 6. Exposes patients to radiation. PET MPI:
Multiple factors including availability of scanners, increased cost, and reimbursement issues have limited widespread clinical application of PET.
PET Radiotracers: N-13ammonia, Rubidium-82 (Rb-82), and O-15 water. Advantages: 1. Improved spatial resolution. 2. PET tracers have significantly less roll-off of extraction. 3. Less artifacts. 4. More easily applied. 5. Less radiation. 6. High sensitivity. Myocardial Contrast Echo Perfusion:
Lack of an FDA approved MCE contrast agent for perfusion has currently put limitations on its widespread clinical application.
Contrast Agents: MCE contrast agents are small, gas-filled microbubbles (10 um) that compress and expand when exposed to an acoustic field and generate strong acoustic back scattering. Advantages; 1. No ionizing radiation. 2. Improved spatial resolution. 3. Perform absolute quantification of myocardial blood flow. 4. Availability and its relatively low cost. Limitation: 1. Motion affect pictures. 2. Artifacts Formation. 3. Operator dependent. 4. No FDA-approved contras. CMR Perfusion Imaging: Contrast Agents gadolinium-DTPA c Advantages: 1. High spatial resolution. 2. The ability to perform absolute quantification of perfusion. 3. Performed rapidly. 4. Has limited operator dependence. 5. Adequate spatial coverage and temporal resolution. Limitations: 1. Artifact. 2. Nephrogenic systemic fibrosis. CTA Perfusion Imaging: Contrast Agents: Iodinated contrast agents. Advantages: 1. High spatial resolution. 2. Rapid data acquisition. 3. Combine information of coronary anatomy, ventricular function, and perfusion. 4. Widely available. 5. Enable dynamic analysis of perfusion with high temporal resolution. Limitations 1. Heart rate with vasodilator stress may compromise image quality. 2. High doses of ionizing radiation. 3. Artifacts. 4. Contrast induced nephropathy. Since this article is addressing general population, please make refection on CKD patients. Cardiac stress test: Low sensitivity in CKD patient (36%) due to: 1. Deconditioning 2. Impaired heart rate response to exercise. 3. The frequently abnormal baseline ECG in CKD patient the interpretation of standard stress testing. 4. The ST segment changes at stress were shown to be not significantly different between non-severe CAD and severe CAD group. STRESS ECHOCARDIOGRAPHY: Most advanced CKD patients had a blunted chronotropic response, thus, did not achieve 85% maximal predicted heart rate. Thick myocardium due to LVH with small intracavitary volume, commonly found in CKD patients, obscures the detection of wall motion abnormality. MYOCARDIAL PERFUSION SCINTIGRAPHY: Exercise MPS in the advanced CKD population has the same limitation as EST and ESE, i.e., related to the inadequate exercise performance and chronotropic incompetence. High-false negative result from balanced ischemia. CTA Perfusion Imaging and CMR Perfusion Imaging: There is a risk of contrast nephropathy and nephrogenic systemic fibrosis in patient with CKD with e GFR <30ml/min.
Non invasive assessment of myocardial perfusion:
This article focus on the technique used to detect myocardial perfusion for CAD diagnosis and there strength and weakness.
First technique is myocardial perfusion imaging:
during exercise coronary blood flow increase to attempt adequate oxygen carrying by blood. In diseased coronary the reserve perfusion is reduced because of coronary vessels stenosis.
Exercise capacity are prognostic markers of CAD.
Pharmacologist vasodilator by dipyridamole or adenosine helping to increase blood flow to myocardium 3.5 to 4 fold similar to exercise.
SPECT MPI // used to assess of CAD
Radiotracers:
It’s has 3 methods
Thalium-201 (T1-201) is potassium analogous
Tc-99m sestamibi
Tc-99m tetroforsmin
Thalium-201 (T1-201) has significant delays redistribution more than 3-4hr, It’s help to distinguish ischemia from scar.
The uptake of all SPECT MPI tracer depend on myocardial cellular and integrity.
SPECT MPI protocol using to assess evidence of CAD.
Tc-99m labeled perfuse agents using at same day/ first injection at rest and fallow by imaging within 30min.
second injection with 2-3 times activity administered during peak of stress.
Typical T1-201 (inject during stress) and then imaging after 10min and then redistribution imaging obtained after 4hr.
Dull-isotope protocol:
T1-201 use for rest images and Tc-99m perfuse agent during stress, but radiation dose high with this protocol.
Images analysis: by visual analysis and difference in relative counting between rest and stress.
Advantage:
Widely used and low cost and easy.
Variable modalities by exercise and vasodilator.
Limitations:
Poor spatial resolution
limited in detecting sub endocardium perfusion defects.
roll off tracer uptake at high myocardial blood flow and limited in detecting mild stenosis.
Motion artificate due to the respiratory movement.
Scatter and partial volume artificat in inferior wall due to delay redistribution.
Those artificats reduce diagnostic utility of perfusion images.
But it’s can be corrected by correction algorithmic.
MPI is not sensitive to detect left main disease or 3 vessels disease.
MPI had sensitivity and specificity 87% and 73% respectively and detected more than 50% of coronary arteries stenosis.
PET-MPI :
It’s use of myocardial perfusion
radiotracer :
N-13 ammonia
Rubidrum-82
0-15 water
0-15 freely disfusable and high
first pass extraction
the uptake is proportional to blood flow. It’s has large uptake with high blood flow without roll off phenomenon. It’s has short half life and it has serial images
It’s still not approved by FDA.
N-13 ammonia//
It’s has myocardial retention and fast washout of blood pool which lead to good perfusion.
Disadvantage:
It’s has roll off uptake with high coronary blood flow
It’s radiation dose of N-13 ammonia is 2msv
Rb-82 is limited in use because of large roll off uptake and high radiation dose.
Recently Fluorine-18 has high cardiac uptake in proportional to blood flow with out significant roll off and good myocardial retention with out significant redistribution and has long half life.
Advantage//
PET more spatial resolution in comparison to SPECT
Less roll off
Limitations//
high cost
many artifacts especially during registration between cardiac perfusion and alternative map.
Myocardial contrast echo perfusion:
contrast used is small gas filled micro bubbles.
micro bubbles remain intravascular but not effect hemodynamic and directly reflects myocardial blood flow.
Ultrasound contrast agents are safe but need close monitoring in patients with cardi-pulmonary morbidity.
Advantage//
MCE not using ionizing radiation in comparison to other modalities.
Good spatial resolution.
Sensitive to detect subendocardial ischemia.
It’s has ability to quantify of myocardial blood flow
Images can be used with exercise and vasodilator agents.
Wide available and low cost.
Disadvantage//
Suboptimal in patients with cardiac and pulmonary disease.
micro bubbles may lead to artifact in base segment of left ventricle.
It’s still not approved by FDA
MCE has prognostic values in estimate LVEF.
CMR perfusion images//
It’s depend on gadolinium DTPS contrast agents.
It’s used to assess myocardial perfusion.
Area well perfused have short T1 and bright.
Hypoperfused area has long T1 and appears hypo intensity.
Recently first gadolinium based intravascular agents are approved for MRA.
CMR help to detect subendocardial ischemia especially with patients with 3 vessels disease.
Advantage//
It’s has high spatial resolution
Rapid procedure
High ability to perform absolute quantification of perfusion.
Disadvantage//
Many dark rim artifacts which may mistake by true perfusion.
Evidence of nephrogenic systemic fibrosis especially in patients with CKD.
Adenosine stress cardiac MRI is sensitive to detect CAD.
CTA perfusion images//
Multidetector CT and CT angiogram.
It’s depend on intravenous iodine contrast agents that increase absorption of X-ray in proportional to concentration of iodine.
Advantage//
High spatial resolutions
Rapid data aquarium
Helpful in formation of ventricle function and it’s perfusion
It’s widely available
Disadvantage//
High dose of radiation.
Q2// It’s reflection on CKD patients
MPI is not reliable and less diagnostic values
Cardiac MRI depend on gadolinium , So it’s not used in CKD patients because risk of nephrogenic systemic fibrosis
Coronary angiogram using in detect CAD but not used in CKD with Cr Cl less than 60ml/min to avoid need to dialysis because may lead to contrast induced nephropathy
Reflecting on CKD patients:
ECG:
To estimate any ischemic changes which may indicates presence of CAD.
ECHO:
Help to estimate LVEF and systolic/diastolic dysfunction and valvular abnormalities.
Exercise stress ECG and ECHO:
It’s has diagnostic element but limited in CKD with poor sensitivity 36%, because exercise intolerance and uncontrolled hypertension and chest pain due to increase oxygen demand in case of anemia of CKD patients.
Non invasive myocardial perfusion images:
it’s helping in detecting reversible perfusion defects or irreversible fixed perfusion defects ( myocardial ischemia), in CkD patients with sensitivity 86% and specificity 79%),
Stress SPECT -MPI is less diagnostic in CKD patients because:
Hemodynamic and anatomic abnormalities
Due to presence of LV hypertrophy.
Presence of chronic overload state and large left ventricle cavity due to presence in dialysis patients.
Hypertensive response may lead to perfusion defects in absence of CAD.
Endothelial dysfunction
Poor quality image because of overload lead to increase lung uptake of radioisotope.
Dobutamine stress ECHO:
It’s help in detecting abnormal wall motion with sensitivity 80% in CKD.
Positive DS ECHO associated with poor prognosis of cardiac events.
Negative DS ECHO associated with low incidence of cardiac events.
Coronary CT angiogram:
It’s non invasive testing to detect CAD with excellent negative predictive value in CKD with sensitivity 93% & specificity 63% and in ESRD have sensitivity 88% & specificity 53%.
It’s low specificity in patients with CKD because high level of calcium in coronary arteries. However it’s not significant in patients with calcified coronary arteries with out stenosis.
Invasive angiogram is gold standard diagnostic procedure but carrying risk of contrast induced nephropathy in CKD patients.
Cardio- pulmonary exercise test:
Its help in assess cardiac and lung and muscle and neuropsychology during exercise.
Gadolinium stress cardiac MRI:
It’s help to identify perfusion defects but contraindicated in patients with Cr Cl less than 30ml/min because risk of nephrogenic systemic fibrosis.
Coronary revascularization:
It’s carrying risk of cardio vascular events.
Wadia Elhardallo
2 years ago
Non-invasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease (CAD).
The ideal agent would not alter hemodynamics and would be small in volume compared with the myocardial blood volume, the agent should be safe, with minimal side effects. The ideal perfusion imaging modality would have a high sensitivity to small changes in coronary blood flow and a quantifiable relationship between signal intensity and perfusion. the technique should be widely available, fast and easy to use, and cost-effective.
SPECT MPI:
Advantages:
1. Availability
2. extensivelyvalidated.
3. SPECT MPI is compatible with multiplestress modalities including exercise, dobutamine, or vasodilators.
Limitations:
1. Time consuming
2. considerably poorer spatial resolution thanother available modalities
3. limiting detection of subendocardial perfusion defects.
4. the roll-off of traceruptake at higher myocardial blood flows limits sensitivity indetecting mild-to moderate stenoses.
1. improved spatial resolution as compared with SPECT
2. more easily applied in dynamic scanning to be used for absolute quantification of perfusion.
3. recent advances in PET/CT technology.
4. Because the imaging does not occur during first pass ofa contrast agent, there is less demand for high temporal resolution, and signal-to-noise ratio (SNR) can be improvedby collecting data over a longer period of time.
Limitations:
1. Limited availability
2. Higher cost
3. Combined CT modality will expose patients to higher radiation doses
3. The ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in one study.
Limitations:
1. High cost
2. image quality is inversely related to heart rate, the increase in heart rate with vasodilator stress may compromise image quality
3. Can cause contrast-induced nephropathy, especially in patients
with reduced renal function (creatinine clearance 60).87
In CKD Population:
MPI has relatively low diagnostic performance of in inESRD patients, as they have a predisposition for haemodynamic and anatomic abnormalities which could impair diagnostic accuracy.
Cardiac MRI:
Most CMR studies of myocardial perfusion are based on the gadolinium contrast agents , Gadolinium stress cardiac MRI can identify perfusion abnormalities. However, GBCAs are contraindicated in patients with impaired kidney function (eGFR <30 mL/min/m2).
Coronary CT Angiogram
has high negative predictive value makes it reliable in ruling out significant CAD in symptomatic patients
It has high sensitivity (93%) and moderate specificity (63%) in CKD for diagnosing obstructive CAD in RTCs.
The majorconcern is contrast-induced nephropathy, especially in patients
not on dialysis (generally creatinine clearance 60).
Thank You, Wadia, MPI is of moderate sensitivity and specificity, but it is an excellent negative test. I agree with the rest.
Huda Mazloum
2 years ago
This article assesses the strengths and weakness of modalities for evaluating myocardial perfusion
Coronary Physiology
A stenosis must exceed 85% to 90% of luminal diameter before significant reductions in resting blood flow occur.
under vasodilator stimulus, maximal coronary flow has been shown to decrease with stenosis of 45%
stress modalities that assess coronary perfusion reserve have a higher sensitivity in detecting flow-limiting stenoses than analysis of stress-induced wall motion abnormalities or ECG changes alone
Methods for Inducing Coronary Vasodilation
* Exercise and dobutamin is associated with a 2- to 3-fold increase in myocardial blood flow
* Dipyridamole, adenosine, and regadenoson are associated with a 3.5- to 4-fold increase in myocardial blood flow
The Ideal Perfusion Imaging Technique and Agent
An ideal agent
– High first-pass myocardial uptake
– Insignificant back-diffusion and recirculation
– Rapid clearance from the blood pool
– kinetics that are not altered by factors such as metabolism or hypoxia.
– Stable
– Low cost
– Safe
– Adirect relationship between contrast agent concentration and myocardial perfusion.
– Minimal side effects.
– Negligible volume
The ideal imaging modality
– High sensitivity
– Relationship between signal intensity and perfusion.
– High spatial/temporal resolution
– Adequate spatial coverage of the ventricle
Reproducible
– No operator dependence
– Fast and Easy to use
– Widely available
– Low cost
SPECT MPI
** Radiotracers : Thallium-201 , Tc-99m sestamibi, and Tc-99m tetrofosmin
** Protocols : rest-stress protocol using a Tc99m-labeled perfusion agent , A typical Tl-201 protocol , A dual-isotope with Tl-201 for the rest images and a Tc-99m during stress
** Advantages
widely available
multiple stress modalities including exercise, dobutamine, or vasodilators.
** limitations :
long acquisition protocols
poorer spatial resolution
limiting detection of subendocardial perfusion defects.
Low sensitivity in detecting mild-to-moderate stenoses.
artifacts due to patient and respiratory motion , gut and biliary activity , breast or subdiaphragmatic attenuation
** SPECT sensitivity and specificity is 87% and 73%, respectively
** exercise SPECT sensitivity and specificity of 89% and 75%, respectively
PET MPI
** Radiotracers : N-13ammonia, Rubidium-82, O-15 water , and fluorine-18 .
** Imaging Protocol
a resting perfusion image using eitherRb-82 or N-13 ammonia
stress imaging can be performed soon after rest imaging
dynamic scanning during first pass of thecontrast agent is performed
** Advantages
improved spatial resolution as compared with SPECT,
attenuation artifacts are less of an issue for PET
lower radiation doses than SPECT
It can do clmbind with CTA
** limitations
High cost
need for a cyclotron for all except Rb-82
Difficulty in evaluating the effect of motion
Resulting artifacts between perfusion images and attenuation maps
Higher radition doses when ia combined with CTA
** A sensitivity of 92 % and specificity of 85 % for the detection of CAD.
** In coparsion to SPECT , PET had a higher diagnostic accuracy(91% versus 76%) and higher specificity (100% versus 66%) for detection of a 50% or greater coronary artery stenosis
Myocardial Contrast Echo Perfusion
** Contrast agent : small, gas-filled microbubbles that compress and expand when exposed to an acoustic field and generate strong acoustic backscattering
FDA considers it to be an experimental procedure
Currently there are no ultrasound contrast agents approved for MCE perfusion imaging,
performed with both vasodilator and inotropic pharmacological stress.
** Advantages
MCE has an advantage over SPECT, PET, and CT perfusion imaging because it does not involve ionizing radiation
improved spatial resolution, enabling detection of subendocardial ischemia in comparsion to SPECT
has the ability to perform absolute quantification of myocardial blood flow
can be performed during pharmacological stress with inotropes or vasodilators or with exercise
wide availability and low cost
** limitations :
Suboptimal images as the result of respiratory motion, body habitus, or lung disease
artifacts in the basal segments of the left ventricle due to microbubbles
no FDA-approved contrast agents for MCE perfusion
** sensitivity of 82% and specificity of 80%
It has average concordance of 81% with SPECT
CMR Perfusion Imaging
** Contrast Agents : gadolinium-DTPA
areas that are perfused have a shorter T1 and appear bright on T1 whereas regions that are hypoperfused have longer T1 and appear hypointense.
sensitivity and specificity of 89% and 87%,
Imaging Protocol
Stress perfusion CMR to evaluates ventricular function ,stress and rest perfusion
CMR enables the detection of subendocardial ischemia which seen In a patiet has 3-vessel disease
** Advantages
high spatial resolution
perform absolute quantification of perfusion
little operator dependence
largely independent of the patient’s body habitus
** Limitations
A “dark-rim” artifact that can be mistaken for a true perfusion abnormality
nephrogenic systemic fibrosis in patients with a creatinine clearance30 mg/dL.
CTA Perfusion Imaging
** Contrast Agents
iodinated contrast agents
72% sensitivity and 80% specificity for detecting a significant coronary stenosis
** Advantages
high spatial resolution
rapid data acquisition
combine information of coronary anatomy , ventricular function, and perfusion
widely available
** limitations :
image quality is inversely related to heart rate, the increase in heart rate with vasodilator stress
artifacts limiting the ability of quantitative assessment of perfusion.
preclude evaluation of patients with significant renal insufficiency.
high doses of ionizing radiation.
higher radiation dose.
As for patients with CKD
SPECT MPI
PET MPI
Contrust agent imagining is not safe and need more studies in CKD patients
MRA has A risk of NSF
Thank you, but the reflection on CKD patients is more than this. Please write more
Abdullah hindawy
2 years ago
This article talks about different ways to assess myocardial perfusion ;with noninvasive procedure;which is too important in the diagnosis and risk stratification for patient with suspect coronary artery diseas.
Although the best and ideal perfusion imaging techniques and agents are also discussed in details.
Multiple methods,agents and drugs are used to induce coronary vasodilation
The ideal agent sould having the following:
1- high first pass
2-linear relation between myocardial concentration and perfusion.
3-no effect on hemodynamic
4-negligible volume
5-easy to administer and low cost.
The most important and used tests are the following :
1- Spect mpi imaging:
Have multiple protocol use different raditraces (thallium-201 ,tc-99m , tc 99m)
It is widely available and compatible with multiple stress modalities with less demand for high resolution, however it is of low sensitivity in detection of mild-mdoderate stenosis.
2-Pet mpi :
It uses N-13 ammonia,rubidium-82 and O-15 as tracers.
It is better than spect with spastial resoltion however it cost effective and the need for a cyclotron.
3-myocardial contrast echo perfusion :
It uses gas filled microbubbles .
It has the ability to perform absolute quantification of myocardial blood flow .
Doesn’t involve using of ionizing radiation.
It is operator dependent and have multiple artifact factors and no fda-approved for contrast agent.
4-cmr perfusion :
Depend on first pass of a bolus of gadolinium-dtpa contrast agent.
It has high spatial resolution and ability to perfome absolute of perfusion
It is however rapidly done, operator-dependent,
Problems with gadolinium decrease its use with some patient especially ckd patients.
5-CTa perfusion scan :
It depends on the intravenous injection of ionized or nonionic contrast agents.
Also it has high spatial resolution,rapid data acquisition, combine information of coronary anatomy, ventricular function and perfusion in one study ,however the test quality is inversely related to heart rate and multiple artifact factors are present.
The contrast agent needed for evaluation is high doses and contraindicated in ckd patients.
Since this article is addressing general population, please make refection on CKD patients.
Excersie depending tests are of low sensitivity in patients with ckd cause of multiple limitations in exercise tolerance in ckd patients .
Echocardiography depending also have multiple limitation due do ventricular channges in ckds patient
Gadolinium use are contraindicated in ckd patients with GFR less than 30% due to risk of nephrogenic systemic sclerosis.
Contrast agents are in past harmful for ckd patients but now multiple studies are done show that contrast agent could be used for ckd patient .
The term renalism is put to know the real harmfulness of contrast agents in ckd patients ,however multiple studies are needed to confirm the safety of using contrast in ckd patients .
Myocardial Perfusion Scintigraphy is the best obtion fo ckd patient with good sensivity but hogh prevelance of false negative result.
Coronary physiology: Endothelial dysfunction affects flow-mediated coronary vasodilation. Significant decrease in resting blood flow occurs only if the stenosis involves 85-90% of the coronary artery lumen diameter, but this decrease can be seen even with 45% stenosis by using vasodilators.
Methods for inducing coronary vasodilation leading to increased myocardial blood flow include exercise (2–3-time increase), vasodilator drugs like dipyridamole, adenosine and regadenoson (3.5-4-time increase) and intoropes like dobutamine (2-3-time increase).
SPECT-MPI
Sensitivity and specificity: 87% and 73% with exercise and 89% and 75% with vasodilators.
3 radiotracers, Thallium 201, Tc99m sestamibi and Tc 99 m tetrofosmin, are used, with maximum first pass extraction at resting flow 86%, 64% and 54% respectively.
Different protocols used include:
a) Tc99m injection followed by imaging at 30 minutes, then repeat imaging after second Tc99m injection with 2-3 times activity during peak stress.
b) Thallium 201 injection during peak stress followed by imaging at 10 minutes and at 4 hours (redistribution image)
c) Dual isotope protocol: Thallium 201 for rest image and Tc99m for image during stress. But it increases radiation dose.
Advantages of SPECT-MPI: compatible with multiple stress modalities and less demand for high temporal resolution
Limitations of SPECT-MPI: Poor spatial resolution, time consuming, high radiation dose, presence of various artifacts, poor sensitivity to detect subendocardial perfusion defects, mild to moderate stenosis and left main disease or triple vessel disease.
PET MPI
Sensitivity and specificity: 92% and 85%
3 radiotracers Rb-82 (Rubidium 82 – does not require on-site cyclotron), N13 ammonia and O15 water (both require on-site cyclotron), are used.
Protocol used: Resting image with N13 or Rb82 taken 90-120 seconds after giving the bolus. For ECG gated PET, imaging is performed for 3-6 minutes with Rb-82 and for 5-15 minutes with N-13. Due to low half life, stress imaging can be performed soon after rest imaging.
Qualitative, semiquantitative and quantitative analysis can be performed.
Advantages of PET-MPI: lower radiation dose, less roll-off of extraction at high flows, better spatial resolution and less attenuation artifacts.
Limitations of PET-MPI: high cost, need of cyclotron, high roll-off with Rb-82, increased radiation when used with CT and presence of registration artifacts.
MCE: Myocardial Contrast ECHO Perfusion
Sensitivity and specificity: 82% and 80%
Contrast agent used: intravascular small gas filled microbubbles (which compress and expand as per acoustic field) directly reflecting myocardial blood flow. But it has not been approved by FDA yet.
Protocol used: intravenous infusion of microbubbles, leading to a steady state followed by high mechanical index pulse leading to rupture of the bubbles and capturing the rate of replenishment (low in hypoperfused areas). Images can be taken in gated intermittent mode as well as real time mode.
Qualitative and quantitative analysis can be performed.
Advantages of MCE: No radiation, low cost, better spatial resolution, subendocardial ischemia can be detected, quantification of myocardial blood flow can be done, and the stress imaging can be performed with either of the 3 modalities (exercise, inotrope and vasodialtors).
Limitations of MCE: Artifacts lead to suboptimal imaging, operator dependent and FDA approved contrast media available.
Protocol used: Cine image to assess ventricular function, stress perfusion image using adenosine infusion with Gadolinium injection are taken and then perfusion images are taken at rest after a wash-out period of 10 minutes. Late gadolinium enhanced images are taken in the end.
Qualitative, semiquantitative and quantitative analysis can be performed.
Advantages of CMR: HIgh spatial resolution, subendocardial ischemia can be detected, absolute quantification of perfusion can be done, rapid, low operator dependence, most compatible with vasodilator stress.
Limitations of CMR: Artifacts, cannot be used in patient with GFR<30, can cause nephrogenic systemic fibrosis.
Protocol used: Contrast enhanced coronary CT angiography done during adenosine stress and then 20 minutes later at rest, assessing for areas of inducible ischemia.
Advantages of CTA: HIgh spatial resolution, rapid, combine information of coronary anatomy, perfusion and ventricular function.
Limitations of CTA: High radiation dose, presence of artifacts and image quality gets poorer with higher heart rates, contrast associated nephropathy can be seen in GFR less than 60.
With availability of these modalities, non-invasive assessment of myocardial perfusion can be performed, but combining 2 or more techniques will lead to better assessment.
Since this article is addressing general population, please make refection on CKD patients
In CKD patients, with respect to the myocardial perfusion imaging, stress Echocardiography (exercise induced or pharmacological stress) has sensitivity and specificity of 80% and 89%. With stress ECHO, there is blunted chronotropic response with reduced exercise capacity. Left ventricular hypertrophy will obscure wall motion abnormalities and microvascular disease can be missed.
SPECT-MPI may show false negative results in patients with triple vessel disease due to balanced ischemia (homogeneous tracer uptake). Exercise MPS has limitations due to inadequate exercise performance and chronotropic incompetence.
CMR cannot be done in patients with GFR less than 30 due to concerns regarding nephrogenic systemic fibrosis.
Contrast agent in CTA is associated with contrast induced nephropathy.
Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease.
There are many modalities, but we need an ideal modality with an ideal agent.
Characteristics of an ideal agent:
have a high first-pass myocardial uptake proportional to perfusion.
insignificant back-diffusion and recirculation.
rapid clearance from the blood pool.
kinetics that is not altered by factors such as metabolism or hypoxia.
would not alter hemodynamics.
would be small in volume compared with the myocardial blood volume.
the agent should be safe, with minimal side effects.
The ideal perfusion imaging modality would have a high sensitivity to small changes in coronary blood flow and a quantifiable relationship between signal intensity and perfusion.
The technique would have a high spatial resolution so that transmural differences in perfusion could be detected, should be reproducible and have a high diagnostic utility, and free of artefacts that would limit either, and should be widely available, fast and easy to use, and cost-effective.
SPECT MPI
Advantages:
widely available and extensively validated.
compatible with multiple stress modalities, including exercise, dobutamine, or vasodilators.
there is less demand for high temporal resolution, and the signal-to-noise ratio (SNR) can be improved by collecting data over a longer period of time.
Limitations:
relatively long acquisition protocols.
considerably poorer spatial resolution than other available modalities, limiting detection of subendocardial perfusion defects.
the roll-off of tracer uptake at higher myocardial blood flows limits sensitivity in detecting mild-to-moderate stenosis.
motion artefacts related to patient and respiratory motion, scatter and partial volume artefacts in the inferior wall related to gut and biliary activity, and variable attenuation artefacts resulting from breast or subdiaphragmatic attenuation.
reduced sensitivity for detecting left main disease or 3-vessel disease related to balanced ischemia.
tracers expose patients to nontrivial radiation doses.
Developments in novel imaging hardware and iterative reconstruction are leading to improved spatial resolution, contrast, and imaging speed for SPECT MPI.
PET MPI
Advantages:
improved spatial resolution as compared with SPECT.
PET tracers have significantly less roll-off of extraction at high flows as compared with Tc-99m– based SPECT agents.
attenuation artefacts are less of an issue for PET.
tracers used in PET are more easily applied in dynamic scanning to be used for absolute quantification of perfusion.
The short half-lives of the PET agents result in lower radiation doses than SPECT agents.
Limitations:
The major limitations to PET include higher costs.
the need for a cyclotron for all but Rb-82 imaging or imaging agents labelled with F-18.
Artifacts from motion during the scan are frequently less apparent, making it harder to evaluate their effects on images. Furthermore, registration artefacts between perfusion images and attenuation maps can result in artefacts.
when PET is combined with CTA, patients probably will be exposed to even higher radiation doses.
Myocardial Contrast Echo Perfusion:
limitations of the sensitivity of wall motion analysis by echocardiography have led to the development of MCE techniques. the lack of an FDA-approved MCE contrast agent for perfusion has currently put limitations on its widespread clinical application.
Advantages:
it does not involve ionizing radiation.
has improved spatial resolution, enabling detection of subendocardial ischemia.
has the ability to perform absolute quantification of myocardial blood flow.
Practical advantages of echocardiography include its wide availability and its relatively low cost.
Limitations:
Suboptimal images are obtained in a significant number of patients as the result of respiratory motion, body habitus, or lung disease.
Attenuation from the microbubbles may result in artefacts in the basal segments of the left ventricle.
there are some operator-dependent factors, such as maintaining a constant image plane during replenishment of microbubbles.
there are no FDA-approved contrast agents for MCE perfusion.
CMR Perfusion Imaging:
Most CMR studies of myocardial perfusion are based on the first pass of a bolus of gadolinium-DTPA contrast agents.
Advantages:
high spatial resolution.
the ability to perform absolute quantification of perfusion and the additional information provided in a comprehensive CMR study.
can be performed rapidly.
has limited operator dependence.
signal characteristics are largely independent of the patient’s body habitus.
have adequate spatial coverage and temporal resolution.
Limitation:
FDA has issued a black-box warning for gadolinium-based contrast agents in patients with a creatinine clearance of less than 30 mg/dL as it is associated with nephrogenic systemic sclerosis.
CTA Perfusion Imaging:
Myocardial perfusion imaging with CT is based on the intravenous injection of iodinated contrast agents that increase the absorption of x-rays in proportion to the concentration of iodine.
Advantages:
high spatial resolution.
rapid data acquisition.
the ability to potentially combine information on coronary anatomy, ventricular function, and perfusion in one study.
becoming widely available.
Limitations:
Because image quality is inversely related to heart rate, the increase in heart rate with vasodilator stress may compromise image quality.
artefacts such as beam-hardening result in variations of signal intensity within the myocardium, limiting the ability of quantitative assessment of perfusion.
The contrast agent doses typically used preclude the evaluation of patients with significant renal insufficiency.
the potentially high doses of ionizing radiation.
Since this article is addressing the general population, please make reflection on CKD patients
For CKD patients, the use of gadolinium is contraindicated if the GFR is below 30 ml/
min as there is a risk of nephrogenic systemic fibrosis.
Also, for CTA perfusion scanning, there is a high risk of ionizing radiation
Thank you, but the reflection on CKD patients is more than this. Please write more
Mohamad Habli
2 years ago
Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease (CAD).
Several non invasive modalities for assessment of pericardial perfusion are available, till now no ideal perfusion agent or imaging.
1- SPECT- MPI
Three radiotracers are commonly used clinically for SPECT MPI.
Radiotracers
• Thallium-201 (Tl-201)
• Tc-99m sestamibi
• Tc-99m tetrofosmin
– Thalium has longer half-life and higher first pass and more delayed redistribution when compared to Tc-99
– The uptake of all SPECT tracers is dependent on myocardial cellular integrity in addition to blood flow
Protocol
• Tl-201: injection at stress- image after 10 min then wait for 4 hours and do redistribution image
• Tc-99m : injection at rest-followed by imaging after 30 min(rest)- A second injection with 2 to 3 times the activity is administered and repeat image.
• Use of dual isotope tracers with different properties is associated with difficulties in interpretation and exposure the patient to more radiation (24 mSv vs 11 mSv or 8 mSv)
Advantages
• It is widely available
• Compatible with multiple stress modalities
• Extensively validated
• Sensitivity of 87% and specificity of 73% for detecting > 50 % stenosis
Limitations :
• It is time consuming because of long acquisition protocols
• Poor spatial resolution
• Limiting detection of subendocardial perfusion defects
• Motion artifact due to movement of the patient or respiratory motion
• Scatter and partial volume artifacts in the inferior wall related to gut and biliary activity
• Attenuation artifacts due to myocardial scar
2- PET
Radiotracers: Using 3 radiotracers
– N-13Ammonia
– Rubidium-82 (Rb-82)
– O-15 water – O-15 water is freely diffusible and has a high first-pass extraction. O-15 water has shorter half-life which makes it only compatible with imaging in stress
Protocol
• Injection of N-13 Ammonia or Rubidium-82 (Rb-82) at rest-image after 90 to 120 seconds. ECG-gated PET acquisition is usually performed for 3 to 6 minutes for Rb-82 and 5 to 15 minutes for N-13 ammonia. Stress imaging can be performed soon after rest imaging.
Advantages
• Better spatial resolution when compared to SPECT
• Significantly less roll-off of extraction at high flows as compared with Tc-99m– based SPECT agents
• Tracers are more easily applied in dynamic scanning to be used for absolute quantification of perfusion
• Lower radiation dose
• Less attenuation artifact
• Sensitivity of 91% and specificity of 100% for detecting > 50 % stenosis
Limitations
• Higher costs
• The need for a cyclotron for all but Rb-82 imaging or imaging agents labeled with F-18
• Motion artifacts are difficult to be assessed
3- Myocardial Contrast Echo Perfusion
Contrast agent: Gas filled microbubbles that compress and expand when exposed to an acoustic field and generate strong acoustic backscattering
Technique
• Myocardial perfusion can be assessed with continuous infusion of microbubbles then ECHO is performed. The real-time technique allows simultaneous assessment of both perfusion and wall motion but has a lower sensitivity for microbubble detection.
Advantages
• Availability
• lower cost
• Good spatial resolution
• No ionizing radiation exposure
• Can be used with physical or pharmacological stress
• Can be used to quantify myocardial blood flow
• Sensitivity of 82% and specificity of 80% for detecting of CAD
Limitations
• The lack of an FDA approved MCE contrast agent for perfusion has currently put limitations on its widespread clinical application
• Respiratory motion, body habitus, or lung disease can result in suboptimal images
• Attenuation from the microbubbles may result in artifacts in the basal segments of the left ventricle
4- CMR Perfusion Imaging
• Stress perfusion CMR is generally applied as part of a comprehensive study that evaluates ventricular function, stress and rest perfusion, and viability/myocardial infarction.
Contrast agent
• Most studies are based on the administration of gadolinium-DTPA
Protocol
• Cine images to assess ventricular function are obtained generally in 10 minutes.
• Stress perfusion images are obtained after injection of adenosine for 2-4 min- 3-4 short axis perfusion images are obtained.
• Forty to 60 image frames are usually obtained. After a 10-minute contrast washout period, perfusion images are obtained at rest using the same imaging protocol
Advantages
• Availability
• Perfect spatial resolution
• The ability to perform absolute quantification of perfusion
• No exposure to radiation
• Rapid method
• Sensitivity of 91% and specificity of 81% for detecting of CAD
Limitations :
• Dark-rim artifact which can be mistaken for a true perfusion abnormality
• The risk of Nephrogenic systemic sclerosis if given in patient with GFR < 30
5- CTA Perfusion Imaging
Contrast agent
Iodinated contrast agents
Protocol
CTA protocols during adenosine stress and 20 minutes later at rest and visually assessed for areas of inducible ischemia
Advantages
• Availability
• Perfect spatial resolution
• Rapid data acquisition
• Dynamic analysis of perfusion with high temporal resolution
• Sensitivity of 72% and specificity of 80% for detecting of significant CAD
Summarise this article
*Non invasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease (CAD).
# Single-photon emission computed tomography (SPECT) is commonly applied
# Others promising techniques including:
* Myocardial contrast echocardiography (MCE).
*Positron emission tomography (PET).
*Cardiac MRI (CMR).
*Cardiac computed tomography (CT)
***This article will importantly investigate the advantages and disadvantages of these modalities for evaluating myocardial perfusion.
# Coronary Physiology
*Myocardial perfusion is a controlled mechanism that includes epicardial vessels, resistance vessels, and the endothelium.
*Endothelial disorder is an early sign of vascular disease that plays a role in the development of CAD.
*In normal coronaries, sympathetic stimulation leads to epicardial and arteriolar vasodilation. With endothelial dysfunction, vasoconstriction from acetylcholine predominates, so coronary arteries narrowed by atherosclerotic disease, coronary autoregulation attempts to normalize myocardial blood flow by reducing the resistance of distal perfusion beds to preserve adequate myocardial oxygen supply.
*The stenosis must be above 85% to 90% of luminal diameter prior to significant reductions in resting blood flow, but under vasodilator stimulus, maximal flow reduce with stenosis of 45%.
# Methods for Inducing Coronary Vasodilation
*Exercise result in coronary vasodilation by an endothelium-dependent flow-mediated mechanism to overcome the requirement of high oxygen demand. It is associated with a 2- to 3- high fold myocardial blood flow and is the best modality, because the exercise capacity has important prognostic value.
*Dipyridamole, adenosine, and regadenoson are pharmacological vasodilators that cause arteriolar vasodilation by both direct and endothelium-mediated mechanisms and are associated with a 3.5- to 4-fold increase in myocardial blood flow
# The Ideal Perfusion Imaging Technique and Agent
*An ideal agent would have a high first-pass myocardial uptake proportional
to perfusion.
*Insignificant back diffusion and recirculation.
*Rapid clearance from the blood pool, and kinetics that are not altered by factors.
*For imaging during first pass, there should be a direct and quantifiable relationship between contrast agent concentration
and myocardial perfusion.
*The contrast agent concentration should be proportional to perfusion over
a large range of coronary flows.
*The ideal agent would not alter hemodynamics and would be small in volume compared with the myocardial blood volume.
*The agent should be safe, with minimal side effects.
*I T should have a high sensitivity to small changes in coronary blood flow and a quantifiable relationship between signal intensity and perfusion.
*The technique should be widely available, fast and easy to use, and cost-effective.
# SPECT MPI
*Three radiotracers are mainly used for SPECT MPI: Thallium-201 (Tl-201) ,Tc-99m sestamibi and Tc-99m tetrofosmin bind mitochondrial membranes.
*All the agents have characteristics to permit the stress and the imaging components to be separated in time and location, and the uptake of all SPECT tracers is dependent on myocardial cellular integrity and blood flow.
SPECT MPI Imaging Protocols
*Tc99m is a same-day rest-stress protocol, the first injection at rest followed by imaging after 1/2 hour. A second injection with 2 to 3 times the activity is administered during peak stress and repeat imaging is performed.
*Tl-201 protocol would involve injection during peak stress, then imaging roughly 10 minutes later, followed by a redistribution image obtained roughly 4 hours later.
*A dual-isotope protocol in which Tl-201 is used for the rest images and then a Tc-99m perfusion agent is used during stress soon thereafter.
*Advantages of SPECT
-SPECT MPI is widely available.
-Extensively validated.
-Compatible with multiple stress modalities including exercise, dobutamine, or vasodilators.
*Limitations
-Long acquisition protocols
-Poorer spatial resolution than other available modalities.
-Limiting detection of subendocardial perfusion defects.
-Limits sensitivity in detecting mild-to-moderate stenoses.
-Motion artifacts related to patient and respiratory motion
-Reduced sensitivity for detecting left main or 3-vessel disease related to balanced ischemia.
-Radiation exposure risk.
# PET MPI
*N-13ammonia, Rubidium-82 (Rb-82), and O-15 water are the PET tracers typically used for myocardial perfusion.
* A bolus of the tracer is given and imaging usually commences between 90 to 120 seconds there after.
* ECG-gated PET acquisition is usually performed for 3 to 6 minutes for Rb-82 and 5 to 15 minutes for N-13 ammonia, owing to their different half-lives then stress imaging can be performed soon after rest imaging.
*Advantages
-PET has improved spatial resolution as compared with SPECT
-PET tracers have significantly less roll-off compared with Tc-99m–based
SPECT agents.
-Attenuation artifacts are less of an issue for PET.
-The tracers used in PET are more easily applied in dynamic scanning to be used for absolute quantification of perfusion.
-With the recent advances in PET/CT technology, multimodality functional imaging of perfusion with PET combinend with anatomic imaging of (CTA) is now possible.
*Limitations
-Higher costs.
-Need for a cyclotron.
-When PET is combined with CTA, patients need high radiation doses.
# Myocardial Contrast Echo Perfusion
*MCE contrast agents are small, gas-filled microbubbles (_10 um) that compress and expand when exposed to an acoustic field and generate strong acoustic backscattering.
*The sensitivity of 82% and specificity of 80%.
*MCE was shown to have prognostic value that was incremental to left ventricular
ejection fraction.
*Advantages
– MCE has an advantage over SPECT, PET, and CT perfusion imaging because it does not involve ionizing radiation.
-MCE has improved spatial resolution, enabling detection of subendocardial ischemia.
-Has the ability to perform absolute quantification of myocardial blood flow.
-Imaging can be performed during pharmacological stress with inotropes , vasodilators and exercise.
-Wide availability and its relatively low cost.
*Limitations
-Suboptimal images are obtained in a significant number of patients as the result of respiratory
motion, body habitus, or lung disease.
-Attenuation from the microbubbles may result in artifacts in the basal segments of the left ventricle
-Some operator-dependent factors.
-Not FDA-approved contrast agents for MCE perfusion.
# CMR Perfusion Imaging
*Based on the first-pass of a bolus of gadolinium-DTPA contrast agents.
*Advantages
-Cardiac MRI has significant advantages of high spatial resolution, the ability to perform absolute quantification of perfusion
-The study can be performed rapidly, has limited operator dependence, and the signal characteristics are largely independent of the patient’s body habitus.
*Limitations
Gadolinium-DTPA is not an ideal contrast agent and associated with nephrogenic systemic fibrosis.
# CTA Perfusion Imaging
Based on the intravenous injection of iodinated contrast agents that increase the absorption of x-rays in proportion to the concentration of iodine.
*Advantages
High spatial resolution, rapid data acquisition, and the ability to potentially combine
information of coronary anatomy, ventricular function, and
perfusion in one study. Furthermore, with the growth of CTA,
MDCT scanners are becoming widely available.
* Limitations
Image quality is inversely related to the increase in heart rate with vasodilator stress .
Limit the ability of quantitative assessment of perfusion.
The contrast agent doses typically used preclude evaluation of patients with significant renal
insufficiency.
High doses of ionizing radiation.
# Since this article is addressing general population, please make refection on CKD patients
*EST is limited in the advanced CKD, with poor sensitivity of 36% , as deconditioning leads to reduced exercise capacity. Impaired heart rate response to exercise. Frequently abnormal baseline ECG hampers the interpretation of standard stress testing. ST segment changes at stress were not different between non-severe CAD and severe CAD.
*Exercise Stress ECHO Cardiography and Dobutamine stress Echocardiography:
Is superior to the ordinary stress ECG in ruling in or out CAD; with sensitivity (71-97%) and specificity (64 -90%).But still limited for the same physical reasons. The addition of echocardiography give more benefit in evaluation of ventricular size and function ,aortic and mitral valvular calcification, left ventricular hypertrophy(LVH),and potentially coronary flow reserve (CFR).
* Dobutamine and dipyridamole stress echocardiography (DSE):
Detects inducible myocardial ischemia based on detection of wall motion abnormalities, thus, would detect significant epicardial CAD, not microvascular disease
* Myocardial Perfusion Scintigraphy:
Exercise and pharmacological myocardial perfusion scintigraphy (MPS) with sensitivity (87 -89%) and specificity (73 – 75%), in detecting >50% coronary artery stenosis in non advanced CKD. Exercise MPS in the advanced CKD has the same limitation as EST and ESE. MPS has high false negative result in detecting ischemia in people with significant triple vessel CAD, in CKD due to “balanced ischemia”
* Cardiovascular Magnetic Resonance (CMR):
With gadolinium contrast has not been used in the CKD patients for the risk of nephrogenic systemic fibrosis.
Summaries this article
This article reviews the available noninvasive myocardial perfusion tests that would help in the diagnosis of CAD and addresses their benefits and restrictions Introduction
Cardiac perfusion is structured by epicardial vessels, vascular resistance, and endothelium. The endothelial dysfunction and perfusion defects are considered early changes in IHD.
Stress tests are very sensitive modalities to assess coronary perfusion reserve and flow-limiting stenosis compared to stress-induced wall motion abnormalities or ECG changes alone.
Endothelial dysfunction and microvascular disease can occur in the absence of significant Coronary stenosis and can be confirmed by abnormal coronary flow reserve, and perfusion defect as early changes in ischemic cascades and can be assessed by different quantitative noninvasive MPI images. exercise-induced coronary vasodilation which is through endothelial-dependent flow in order to meet the o2 demand and can be increased 2-3 times the myocardial flow capacity while in the case of CAD the perfusion flow reserve is diminished by flow-limiting coronary stenosis, endothelial dysfunction, and adrenergic stimulant.
The Ideal Perfusion Imaging Technique and Agent characteristics include the following:
1. Use of gents with High first pass uptake compared to perfusion
2. Insignificant back-diffusion flow and recirculation.
3. Safe, small volume, and Rapid clearance and not altered the hemodynamics with fewer side effects
4. kinetics that does not change by the effects of metabolism or hypoxia.
5. High sensitivity for small changes in coronary flow. quantifiable and reproducible with good diagnostic quality (not operator dependent).
6.fast, easy, and cost-effective
SPECT-MPI is of noninvasive stress test
Widely used and well-validated stress test available with easy access with different modalities including exercise dobutamine, vasodilator, its use limited by long protocol with poor spatial resolution, limitation in the detection of subendocardial perfusion defect, lower sensitivity in detecting mild to moderate stenosis, triple vessel disease due to balanced ischemia and lt the main disease its diagnostic utility can be affected by variable attenuation artifacts related to motion, respiratory, volume artifact and this can be improved by using attenuation correction algorithm However its diagnostic approach use, especially in severe CKD, DM patients can help in selective use of CAG and revascularization therapy with cost-effectiveness PET -MPI
have been used for more than 25 years and are cost-effective compared to CAG, stress test, with more superior diagnostic accuracy compared to SPECT, PET scan more sensitivity, and specificity for the diagnosis of CAD, BY using N13- ammonia and Rb 82 is a perfusion agent and it’s more accurate and superior to SPECT for the diagnosis of > 50% coronary artery stenosis with 91% accuracy and 100% specificity. Its clinical use is limited by the availability of the scanner and increased cost, also more radiation risk with RB82, a new agent fluorine-based (F-18) with less radiation risk and more cardiac uptake and less roll off and good myocardial retention with less redistribution effect, in addition, it’s compatible with many stresses imaging protocols and a long half-life
The new innovation of PET/CTA modality for both functional perfusion imaging by PET scan and anatomical imaging by CT angiogram but with the cost of more radiation.
Myocardial contrast echo (MCE). Contain both quantitative and qualitative analysis by looking at the rate or amount of the contrast replenishment
Superior to PET, SPECT, and CT as no exposure to radiation, more accurate for detection of subendocardial ischemia, and able to quantify the myocardial blood flow, the test can be performed with exercise or pharmacological agents like inotrope, vasodilators, available with low cost
Limitation, suboptimal images in obese, respiratory distress, lung disease, attenuation from microbubbles, operator dependent, FDA not yet approved contrast agents for MCE perfusion. with limitation of its use for patients with severe PHT and unstable cardiopulmonary disease and should be used with intensive monitoring Contrast Echocardiography Perfusion Techniques:
By using continuous infusion of microbubbles contrast and the area of hypoperfusion have a slower return of microbubbles compared to the well-perfused area with a more rapid return of the microbubbles contrast, in real-time techniques can evaluate both the perfusion and wall motion with lower sensitivity to microbubbles detections CMR Perfusion images Using first pass gadolinium -DPTA contrast agent with the high-resolution test for assessment of myocardial perfusion, bright and heavily T1 with shorter T1 reflect the areas of good perfusion while longer and hypointenseT1 indicate the area of perfusion defect, highly sensitive and specific for the detection of CAD with late gadolinium enhanced defect indicate previous MI while stressing CMR for inducible reversible ischemia. Also, for subendocardial ischemia in patients with diffuse triple vessel disease.
Advantage
High-resolution quantitative perfusion analysis.
Limitation, operator dependent, gadolinium use is associated with rare irreversible NSF (nephrogenic systemic fibrosis), and its use is not preferred in patients with GFR < 30ML/MIN. CTA Perfusion Imaging
MDCT (multidetector CT), is high resolution and very informative for dynamic perfusion studies anatomy and ventricular function, limitation, invasive, radiation, contrast-induced nephropathy
Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk
stratification of patients with known or suspected CAD.
Common Noninvasive myocardial perfusion test:
Single-photon emission computed tomography (SPECT) is most commonly used.
Myocardial contrast echocardiography (MCE).
Positron emission tomography (PET).
Cardiac MRI (CMR).
Cardiac computed tomography (CT).
Advantages:
#High spatial resolution.
#The ability to perform absolute quantification of perfusion.
#Performed rapidly.
#Has limited operator dependence.
#Adequate spatial coverage and temporal resolution.
Since this article is addressing general population, please make refection on CKD patients
Cardiac stress test:
Low sensitivity in CKD patient.
STRESS ECHOCARDIOGRAPHY. MYOCARDIAL PERFUSION SCINTIGRAPHY:
Exercise MPS in the advanced CKD population has the same limitation as EST and ESE, CTA Perfusion Imaging and CMR Perfusion Imaging:
Risk of contrast nephropathy.
Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease (CAD). There are multiple modalities used for evaluating myocardial perfusion which include:
1- single-photon emission computed tomography (SPECT) which is most commonly used.
2- myocardial contrast echocardiography (MCE)
3- positron emission tomography (PET)
4- cardiac MRI (CMR)
5- cardiac computed tomography (CT)
Coronary physiology: Endothelial dysfunction is an early manifestation of vascular disease and plays a role in the development of CAD. Coronary autoregulation attempts to normalize myocardial blood flow even if stenosis exceeded 85% to 90%. However, under vasodilator stimulus, maximal coronary flow has been shown to decrease with stenosis of > 45%. Stress modalities are more sensitive assessing coronary perfusion than analysis of stress-induced wall motion abnormalities or ECG changes alone. Methods for Inducing Coronary Vasodilation include exercise, pharmacological (Dipyridamole, adenosine, and regadenoson) & Dobutamine. The Ideal Perfusion Imaging Technique and Agent have special characteristics such as being safe, stable and easy to administer with low cost (for the agent) and being reproducible, with high sensitivity and widely available (for the imaging modality).
SPECT MPI
There are multiples protocol using different radiotracers as (Thallium-201 (Tl-201), Tc-99m sestamibi and Tc-99m tetrofosmin) including same-day rest-stress protocol and a dual-isotope protocol.
Advantages:
· Widely available & extensively validated.
· Compatible with multiple stress modalities.
· Less demand for high temporal resolution.
Limitations:
· Long acquisition protocols.
· Poorer spatial resolution limiting detection of subendocardial perfusion defects.
· Limited sensitivity in detecting mild-to-moderate stenosis.
· Motion, volume & attenuation artifacts which can decrease the diagnostic utility of the perfusion images.
· Reduced sensitivity for detecting left main disease or 3-vessle disease.
· Expose patients to nontrivial radiation doses
PET MPI PET Radiotracers include N-13ammonia, Rubidium-82 (Rb-82), and O-15 water. Imaging Protocol: A bolus of the tracer is given, and imaging usually commences between 90 to 120 seconds. ECG-gated PET acquisition is usually performed for 3 to 6 minutes for Rb-82 and 5 to 15 minutes for N-13 ammonia. Stress imaging can be performed soon after rest imaging.
Advantages:
· Improved spatial resolution as compared with SPECT.
· PET tracers have significantly less roll-off of extraction.
· Less attenuation artifacts.
· Easily applied.
· Lower radiation doses than SPECT.
Limitations:
· Higher cost.
· The need for a cyclotron for all but Rb-82 imaging, or imaging agents labeled with F-18.
Myocardial Contrast Echo Perfusion Contrast Agents: MCE contrast agents are small, gas-filled microbubbles (10 um) that compress and expand when exposed to an acoustic field and generate strong acoustic backscattering. However, it lacks FDA approval. Contrast Echocardiography Perfusion Techniques: can be assessed with continuous infusion
of microbubbles. When the microbubbles have reached steady-state concentrations, a high mechanical index pulse is used to destroy the bubbles in the imaging plane. The subsequent replenishment of microbubbles is related to myocardial perfusion. Areas that are hypoperfused will have a slower return of microbubbles, whereas areas that are well perfused will have a more rapid return of microbubbles.
Advantages:
· No ionizing radiation.
· Improved spatial resolution detecting sub-endocardial ischemia.
· Perform absolute quantification of myocardial blood flow.
· Exercise and pharmacological stress can be used.
· Wide availability and relatively low cost.
Limitations:
· Suboptimal images due to body habits or respiratory movement.
· Attenuation artifacts from the microbubbles.
· Operator-dependent factors
· No FDA approval for contrast agents.
CMR Perfusion Imaging Contrast Agents: gadolinium-DTPA c Imaging Protocol: Stress perfusion CMR is generally applied as part of a comprehensive study thatevaluates ventricular function, stress and rest perfusion, and viability/myocardial infarction.Cine images are obtained in <10 minutes. Stress perfusion images are then obtained during infusion of 140 g/kg/min of Adenosine for 2-4 mins. The study takes approximately 45 to 60 minutes with gadolinium used as a contrast.
Advantages:
· High spatial resolution.
· The ability to perform absolute quantification of perfusion.
· Can be performed rapidly.
· Has limited operator dependence.
· Adequate spatial coverage and temporal resolution.
Limitations:
· Artifacts
· Intermediate extraction fraction during first-pass imaging.
· Risk of nephrogenic systemic fibrosis in Create clearance < 30ml/min.
Advantages:
· High spatial resolution.
· Rapid data acquisition.
· Combine information of coronary anatomy, ventricular function, and perfusion in one study.
· Widely available.
· Enable dynamic analysis of perfusion with high temporal resolution.
Limitations:
· The increase in heart rate with vasodilator stress may compromise image quality.
· Artifacts.
· High doses of ionizing radiation.
· Rik of Contrast induced nephropathy.
Since this article is addressing general population, please make reflection on CKD patients.
The following stress tests are used in CKD but with certain limitations:
EXERCISE STRESS ECG: Its limitations in CKD population include reduced exercise capacity due to deconditioning factors, impaired chronotropic response & abnormal baseline ECG and left ventricular hypertrophy.
EXERCISE STRESS ECHOCARDIOGRAPHY: Though it is better than the standard exercise stress ECG, but it has the same limitations. One of the advantages of this modality is the assessment of ventricular size and function, aortic and mitral valvular calcification, left ventricular hypertrophy (LVH), and potentially CFR.
DOBUTAMINE STRESS ECHOCARDIOGRAPHY: detects inducible myocardial ischemia based on the detection of wall motion abnormalities, thus, would detect significant epicardial CAD, but not the microvascular disease.
MYOCARDIAL PERFUSIONSCINTIGRAPHY: Exercise MPS in the advanced CKD population has the same limitation as EST and ESE, i.e., related to the inadequate exercise performance and Chronotropic incompetence.
CARDIOVASCULAR MAGNETIC RESONANCE: Has not been widely utilized clinically in the CKD population due to the concern of nephrogenic systemic fibrosis. Dobutamine stress CMR was shown to be safe in the pre-renal transplant population.
CTA PERFUSION IMAGING: Risk of contrast induced nephropathy.
Various modalities are available for diagnosis and assessment of CAD.
Coronary autoregulation can keep adequate oxygen supply to the myocardium with no decrease in resting blood flow despite 85-90% stenosis of the coronaries but under the effect of vasodilators, coronary flow decrease with stenosis >45% and can be detected using quantitative myocardial perfusion imaging.
Coronary perfusion imaging by stress methods is more sensitive than detection of stress induced regional wall motion abnormalities or ECG changes. Methods for inducing coronary vasodilatation include exercise, pharmacological vasodilators (dipyridamole, adenosine) and dobutamine. SPECT-MPI:
Advantages:
Available, different stress modalities can be used.
Limitations:
Subendocardial perfusion defects are not well detected.
Low sensitivity in mild to moderate stenosis and in detection of left main disease and 3 vessel disease.
Several artifacts limit its diagnostic ability.
Exposure to nontrivial radiation dose.
Studies showed that it provides important prognostic information
PET-MPI:
Advantages:
Better spatial resolution and less artifacts.
Provide absolute quantification of perfusion.
Agents used result in lower radiation dose.
Limitations:
Higher cost, some tracers need cyclotron
Studies showed that PET-MPI has higher diagnostic accuracy than SPECT and has a prognostic value.
Myocardial contrast echo perfusion
Its clinical use is limited as the contrast agent is not approved by FDA and is considered an experimental procedure. CMR perfusion imaging:
Advantages:
High spatial resolution with quantification of perfusion
Limited operator dependence and not affected by patient’s body habitus
Limitations:
Artifacts may be mistaken for perfusion abnormality
Gadolinium contrast agents may be associated with nephrogenic systemic fibrosis (rare condition but serious in patients with advanced kidney disease)
FDA issued black-box warning for gadolinium contrast agent in patients with creatinine clearance <30mg/dl
Studies showed that adenosine stress cardiac MRI are sensitive and specific in detection of CAD
CTA perfusion imaging:
Advantages:
MDCT provide high spatial resolution and information about coronary anatomy, ventricular function and perfusion.
Absolute quantification of CT perfusion
Limitations:
Image quality decrease with increased heart rate associated with vasodilator effect.
Limited use in patients with significant renal impairment
High doses of ionizing radiation compared to coronary CTA radiation dose. No technique shows superiority in the evaluation of myocardial perfusion. In CKD patients: SPECT:
CKD patients have higher levels of baseline adenosine which attenuate the detection of induced perfusion abnormalities, correction of attenuation leads to poor quality images. CMR, gadolinium contrast agent in patients with advanced kidney disease may lead to nephrogenic systemic fibrosis CT angiography, contrast agents are associated with an increased risk of contrast induced nephropathy.
Gadolinium shouldn’t be used in CKD patients with eGFR <30 but if no other alternative diagnostic test is available, it should be administered with precautions.
Schieda N, Blaichman JI, Costa AF, Glikstein R, Hurrell C, James M, Jabehdar Maralani P, Shabana W, Tang A, Tsampalieros A, van der Pol CB. Gadolinium-based contrast agents in kidney disease: a comprehensive review and clinical practice guideline issued by the Canadian Association of Radiologists. Canadian journal of kidney health and disease. 2018 Jun 11;5:2054358118778573.
Dr. Tufayel Chowdhury
2 years ago
Summery:
All the modalities have some advantages and disadvantages with no superiority.Radionuclide techniques are used to assess flow differences of myocardium.SPECT and CMR have established criteria, however, PET , contrast echocardiography, CT perfusion criteria yet to be established.
SPECT -MPI has imperfectb diagnostic accuracy in ESRD patients, but still a valuable modality in cardiovascular risk assessment.
Summarize this article
This article is talking about the non-invasive methods of assessing myocardial perfusion. The coronary physiology of myocardial perfusion is highly regulated and is dependent on:
Epicardial vessels
Resistance vessels
Endothelium
In normal coronaries, sympathetic stimulation causes a flow-mediated endothelium-dependent release of NO resulting in epicardial and arteriolar vasodilation. With endothelial dysfunction, vasoconstriction from Each predominated, resulting in attenuation or absence of the normal flow mediated vasodilation. When coronary arteries are narrowed by atherosclerotic disease, coronary autoregulation attempts to normalize the myocardial blood flow by reducing the resistance of the distal perfusion to preserve adequate myocardial oxygen supply. Under vasodilator stimulus, maximal coronary flow has been shown to decrease with stenosis of > 45%.
The myocardial perfusion modalities assess the coronary perfusion reserve by using stressors like vasodilators, dobutamine or exercise.
Exercise is typically associated with a 2- to 3- fold increase in myocardial blood flow and is the preferred modality as exercise capacity has an important prognostic value.
Dipyridamole, adenosine and regadenason are pharmacologic vasodilators that cause arteriolar vasodilation by both direct and endothelium-mediated mechanisms and are are associated with a 3.5-4 fold increase in myocardial blood flow.
Dobutamine, a synthetic beta 1 and beta 2 receptor agonist, typically produces a 2-3 fold increase in myocardial blood flow
The principle of the MPI is to have a perfusion agent that should have a high first pass myocardial uptake with insignificant back diffusion and recirculation with rapid clearance from the blood pool and an imaging modality that is highly sensitive to small changes in coronary blood and a quantifiable relationship between signal intensity and perfusion.
SPECT MPI
Uses TI-201, Tc-99 sestamibi or Tc-99 tetrofosmin as the radio tracers. TI-201 has a low energy and a long half life and hence, is sub-optimal for perfusion imaging. The first pass extraction is highest for TI-201 than the other 2. SPECT has several advantages including:
It is widely used and has been extensively validated
As the stress and imaging components are performed separately, SPECT MPI is compatible with multiple stress modalities
Because the imaging does not occur during first pass of a contrast agent, there is less demand for a high temporal resolution.
It also has several limitations:
Relatively long acquisition protocols
Considerably poorer spatial resolution than other available modalities limiting detection of subendocardial perfusion defects
The roller-off of tracer uptake at high myocardial blood flows limits sensitivity in detecting mild to moderate stenosis
Motion artifacts related to patient and respiratory motion
Has reduced sensitivity for detecting left main due or triple vessel due due to balanced ischemia
Exercise SPECT MPI has a high sensitivity and specificity of 87% and 73% respectively for detecting stenosis of > 50%. Vasodilator SPECT MPI has a sensitivity of 89% and specificity of 75%. It also provides important prognostic information. However, its sensitivity and specificity is lower in patients with advanced CKD.
PET MPI
It has been used for > 25 years. The main limiting factors for its widespread use are cost, and availability of scanners.
The PET radio tracers include N-13 ammonia, Rubidium-82 and O-15 water. O-15 water is not FDA approved. N-13 ammonia and O-15 water require an onsite cyclotron for synthesis. Rb-82 can be eluted from a generator and does not require a cyclotron. A new agent, fluorine-18 (F-18) has been developed which has a long half life and good cardiac uptake and is currently undergoing evaluation.
PET has improved spatial resolution as compared to SPECT. PET tracers have significantly less roll-off of extraction at high flows as compared with Tc-99. The short half lives of the PET agents results in lower radiation than SPECT
PET MPI has a high sensitivity and specificity of 92% and 85% respectively. When PET MPI was compared to SPECT, it had a higher diagnostic accuracy (91% vs 76%) and higher specificity (100% vs 66%).
Myocardial Contrast Echo (MCE)
MCE contrast agents are small gas-filled micro bubbles (<10 um) that compress and expand when exposed to an acoustic field and generate strong acoustic backscattering. At certain acoustic pressures they undergo non-linear oscillations that result in generation of harmonic frequencies that can be used to distinguish the signal of the micro bubbles from the surrounding tissue. The micro bubbles remain intravascular as they transit the myocardial capillary bed and do not affect cardiac hemodynamics and thus directly reflect myocardial blood flow. Unfortunately, the lack an FDA approved MCE contrast agent for perfusion has currently put limitations on its widespread clinical application.
MCE has a number of potential advantages over other modalities. SPECT, PET and CT perfusion imaging use ionizing radiation while MCE does not. Compared with SPECT, MCE has improved spatial resolution, enabling detection of subendocardial ischemia. . MCE also has the ability of to perform absolute quantification of myocardial blood flow.
It also some limitations. Attenuation from the micro bubbles may result in artifacts in basal segments of the LV. Suboptimal images are obtained in a significant no of patients as the result of respiratory motion, body habits or lung disease.
A no of studies have demonstrated a high concordance of MCE with SPECT. the overall sensitivity and specificity of MCE is 82% and 80% respectively
Cardiac MR Perfusion Imaging
Most CMR studies of myocardial perfusion are based on the first-pass of a bolus of gadolinium contrast agents. Interactions between the unpaired electrons of the paramagnetic gadolinium and water protons in close proximity result in more rapid relaxation of these water protons. Thus, the gadolinium is being indirectly detected via its effects on the relaxation of protons. The T1 and T2 relaxation times of stare protons are inversely proportional to the local gadolinium concentration. Therefore, the areas that are well perfused will have a shorter T1 and appear bright on heavily weighted T1 images, whereas regions that are hypo-refused will have longer T1 and will appear hypointense
Stress perfusion CMR is generally applied as part of a comprehensive study that evaluated ventricular function, stress and rest perfusion and viability/myocardial infarction.
Cardiac MRI has significant advantages for perfusion stress testing including high spatial resolution, the ability to perform absolute quantification of perfusion, and the additional information like size and thickness of the LV. The study can be performed rapidly and has less operator dependance and the signal characteristics re largely independent of the patients body habits.
The FDA has issued a blackbox warning for use of gadolinium-based contrast agents in patients with an eGFR of <30 mls/min due to the risk of developing nephrogenic systemic fibrosis.
Adenosine stress CMR has a sensitivity of 91% and a specificity of 81%
CT Perfusion Imaging
MPI with CT imaging is based o the IV injection of iodinated contrast agents that increase the absorption of x-rays in proportion to the concentration of iodine. Iodinated contrast agents are not hemodynamically inert and have an influence on coronary blood flow. They can induce a reduction in coronary flow followed by a hyperemic response. During first-pass, there is also significant diffusion of the contrast agents into the interstitial space, particularly for the non-ionic and low molecular weight compounds.
Multiple studies have evaluated perfusion in MI, but to date there are only a few published studies that have evaluated myocardial perfusion to detect inducible ischemia with vasodilator stress. One study showed that it as a sensitivity of 72% and specificity of 80% for detecting a significant coronary stenosis. Adenosine stress CT perfusion imaging and angiography in 40 pts by George et al detected perfusion abnormalities with a sensitivity of 86% and a specificity of 92%.
The advantages of MDCT include its high spatial resolution, rapid data acquisition and the ability to potentially combine information of coronary anatomy, ventricular function and perfusion in one study. The advancement of MDCT with 256 or 320 slice detectors may enable dynamic analysis of perfusion with high temporal resolution.
Its image quality may be limited by the increase in heart rate which happens with vasodilator stress. Artifacts within the myocardium limit the ability of quantitative assessment of perfusion. It precludes patients with advanced CKD due to the contrast. It also uses high dose ionizing radiation
Since this article is addressing general population, please make reflection on CKD patients
The SPECT MPI has been shown to have a lower sensitivity and specificity in advanced CKD patients as compared to non-CKD patients
There is no absolute contraindication for PET MPI in patients with advanced CKD although ESKD have been excluded in the few trials that looked at PET MPI
There are very few studies on MCE due to FDA blackbox warning on the bubble contrast so it can’t be used to asses perfusion
Cardiac MR – In patients with advanced CKD, the use of gadolinium is contraindicated due to the risk of developing NSF
CT perfusion imaging – The use of iodinated-contrast is not recommended in patients with CKD
Excellent Dr Hussein Regarding Gadolinium, any cut-off eGFR below which we should not use it in CKD patients?
ISAAC BUSAYO ABIOLA
2 years ago
Noninvasive assessment of myocardia perfusion is a critical tool in the diagnosis and prognostication of patient with suspected or known with coronary artery disease (CAD). However, non of this tool is without it advantages or disadvantages, but they have all emerged as a good promising tool.
SPECT MPI: This form of noninvasive assessment of myocardia perfusion has three types of radiotracer; Thalium-201, Tc – 99m sestamibi, and Tc – 99m tetrofosmin all having different perfusion ability through the my0cardium and half life. They also have different properties that allow both stress and imagine component to be separated in time and location which is not seen in other form of diagnostic tool. Although SPECT MPI is widely available and has been validated but has some limitation like ; relative long acquisition protocols and poor spatial resolution, the role over of tracer uptake at high myocardia flow limit sensitivity in detecting mild to moderate stenosis. Analysis of a study showed sensitivity and specificity of 87% & 73% to detecting myocardia stenosis of greater than 50%
PET MPI: The commonly used radiotracers for the procedure are; N-13 ammonia, Rubidium-82, and 0-15 water with different half life and radiation dose. New radiotracer is Flourine-18. PET has an improved spatial resolution compared to SPECT, the tracers have significant less roll-off of extraction at high flow compared to Tc-99m of SPECT, and the tracers used in PET are more easily applied in dynamic scanning are some of the advantages of this diagnostic tool. PET has a higher diagnostic accuracy (91% vs 76% ) and specificity (100% vs 66%) in detecting greater than 50% coronary artery stenosis compared to SPECT.
Myocardia Contrast Echo Perfusion: It wide use has been limited by non approval of it contrast agent by the FDA, nevertheless it has some advantages over SPET and PET modalities. First, it does not have an ionizing agent, has improved spatial resolution over SPECT in detecting subendocardial ischemia, also it has absolute quantification of myocardial blood flow and wide availability of echocardiography has helped it use. However, it has some limitations like, suboptimal images are obtained in a number of patient because of respiratory motion, body habitus and lung disease. MCE has a sensitivity and specificity of 82% and 80% respectively.
CMR Perfusion Imaging: Myocardial perfusion is based on first pass effect of bolus of Gadolinium-DTPA which is not an ideal physiologic contrast. This test can be done rapidly and less dependent on the operator and because the imaging occur at first pass, it is best suited for vasodilator stress test
CTA Perfusion Imaging: Operation mechanism is based on injection of iodinated contrast that enhance absorptions of the x -ray in proportion to the concentration of iodine in the myocardium. Among the advantages of CTA perfusion imagine are; high spatial resolution, rapid data acquisition, and the ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in one study. This tool is not without some limitation like, increase in heart rate with vasodilator stress may compromise image quality and the present of artifact can limit the ability for adequate perfusion of the myocardium
All the above investigation will help in early diagnosis and prognostication of CAD among CKD patient because it is the commonest cause of morbidity and mortality. Also, because myocardial infarction is the commonest CAD among patient with CKD, all the above investigation will help in higher sensitivity and specificity.
Thanks Prof Halawa, i action mean to write ESKD patient been work up for kidney transplant that those investigation will be helpful among them
Rihab Elidrisi
2 years ago
Noninvasive Assessment of Myocardial Perfusion
Summarise this article
Since this article is addressing general population, please make refection on CKD patients
Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease (CAD).
Normal coronary physiology depends:
sympathetic still,ulation causes a flow mediated endothelium release of N.O which will improve the epicardial and arteriolar vasodilatation.
Coronary artery has been affected by atherosclerotic changes which will affect the preserve for mycordail o2 supply.
A stenosis must reach 85% to 90 % of the luminal diameter before significant reduction in resting blood flow occur.
How to detect ischemia in MPI;
By inducing coronary vasodilation which creat hetrogencicity area in CAD patient .
exercise cause coronary vasodilation via an endothelium-dependent flow-mediated process to meet the increased oxygen demand.
Exercise is the preferred modality and is associated with a 2- to 3-fold increase in myocardial blood flow.
SPECT MPI.
There are multiples protocol using different radiotracers as (Thallium-201 (Tl-201) , Tc-99m sestamibi and Tc-99m tetrofosmin) sometimes a dual-isotope protocol is used.
With images taken during rest and stress time and analysis of myocardial perfusion done with using visual analysis or semi-quantitatively using differences in relative counts.
=Advantages .
–Guiding selective coronary angiography reduces costs associated with both diagnosis and revascularization. =Limitations of SPECT.
–Patient exposed to high radiation doses.
–Motion artifacts.
–Less sensitivity in detecting mild-to-moderate stenosis due to roll-off of tracer uptake.
–Limiting detection of sub endocardial perfusion defects.
PET MPI.
Has high sensitivity 92% around and specificity around 85%
Depend on N-13ammonia, Rubidium-82 (Rb-82), and O-15 water are the PET tracers which most of them has short half-life and CT scanners used in rest and with stress by exercise or pharmacologically, analysis of myocardial perfusion done with using visual analysis or semi-quantitatively using differences in relative counts. =Advantages and Limitations
-High spatial resolution as compared with SPECT.
– PET tracers have significantly less roll-off.
– lower radiation doses than SPECT.
-But, costly and also there is artifact.
Myocardial Contrast Echo Perfusion.
Using ECHO with contrast (gas-filled microbubbles) to assess myocardial perfusion with vasodilator and inotropic pharmacological stress. but still not fully approved by FDA .
Areas that are hypo-perfused will have a slower return of microbubbles, whereas areas that are well perfused will have a more rapid return of microbubbles.
MCE showed a sensitivity of 82% and specificity of 80%. =Advantages:
–No ionizing radiation.
–Can detect of sub-endocardial ischemia.
–Exercise and pharmacological stress can be used.
–Low cost. =Limitation:
–Suboptimal images due to body habits or respiratory movement.
–Artifact from bubbles Attenuation.
–Still no FDA approval.
CMR Perfusion Imaging.
Study done with in 45-60 mints with based gadolinium as based contrast with pharmacological stress material as adenosine .
Can detect ventricular function, stress and rest perfusion, and viability/myocardial infarction.
Technique has a sensitivity and specificity of 89% and 87%, respectively, for detecting CAD. =Advantages.
–Rapid technique.
–High spatial resolution.
–Has limited operator dependence. = Limitations
–Intermediate extraction fraction during first-pass imaging.
–Risk of nephrogenic systemic fibrosis.
CTA Perfusion Imaging.
Nonionic contrast agents with a high iodine concentration mostly used nowadays but Contrast induced nephropathy should be in mind specially with CKD old patient.
Give us information about coronary anatomy, ventricular function, and perfusion. =Advantages:
–Rapid test.
–High spatial resolution.
–Allow dynamic analysis of perfusion with high temporal resolution. =Limitation:
–Image quality affected by heart rate.
–Contrast side effects.
–High dose of radiation if frequently done.
Finally, Diagnostic Performance of Perfusion Imaging Techniques is variable and each one has their upsides and downsides and we should choose our modality according to patient criteria and hospital facilities.
Stress Echo cardiography:
Is considered to be a good choice for cardiac assessment, with sensitivity around 80% and detects wall motion abnormalities on stress indicating myocardial ischemia.
Coronary CT Angiogram:
Has high sensitivity > 90% for diagnosing obstructive CAD ,but calcium deposition still challenges for detection of CAD and is high risk of CIN in CKD patients.
Cardiac MRI:
Can detect ventricular function, stress and rest perfusion with high sensitivity and specificity but it still Gadolinium based and risk of nephrogenic systemic fibrosis appear .
== Reflection on CKD patients:
CKD patients is higher risk than general populations regards CAD as our patients have multiple co-morbidities as (HTN, DM, Dyslipidemia ,CKD-MBD, Volume overload & etc.).
Many factors interprets sensitivity and specificity of diagnostic tests, so need high suspicion and good selection of the test.
Filipe prohaska Batista
2 years ago
This study evaluates non-invasive modalities in myocardial perfusion, evaluating specificity and sensitivity as well as the advantages and disadvantages of each procedure.
Considering the perfusion agents and imaging modality, several factors were considered in an attempt to establish the best model to be used. First-pass absorption, myocardial concentration and perfusion, volume, hemodynamic effects, stability, safety, ease of administration, pharmacokinetics, and pharmacodynamics, and finally, cost-effectiveness.
Adding stress modalities (dipyridamole, adenosine, regadenoson, dobutamine) can detect coronary dysfunction earlier and with more sensitivity than static methods due to the possibility of evaluating endothelial and/or microvascular dysfunction.
SPECT
The radiopharmaceuticals used are Thallium (Tl-201) and Technetium (Tc-99m), the former is not available in Brazil. Rest and post injections vary by isotope and protocol being used. The quality of marker absorption is dependent on myocardial cell integrity plus blood flow. In multicenter studies, it showed a sensitivity of 87% with a specificity of 73% and may have artifacts in which the associated ECG can help to differentiate. Its ability to assess subendocardial perfusion left heart disease, or 3-vessel disease may be underestimated, especially when there is an inflammatory biliary activity or other artifacts.
PET MPI
Availability of equipment, high cost, need for cyclotrons to produce radioisotopes; as well as its transport, storage, and half-life; limit their use more often. Radioisotopes such as Rubidium (Rb-82), Ammonia (N-13), Water O-15, and Fluorine (F-18) can be used in different ways depending on the half-life of each. It can provide more complete images when compared to SPECT, especially when image reconstruction is combined with computed tomography, raising its sensitivity to 92% and specificity to 85%.
Despite the complex structure, it can be cost-effective when compared to angiography.
Myocardial Contrast Echo Perfusion
The use of microbubbles as a contrasting agent and the generated acoustic shield helps to understand blood flow without altering cardiac hemodynamics, helping to assess myocardial blood flow in real-time. The quality of the microbubbles is important to reflect the perfusion, without the need for ionizing radiation, and can even assess subendocardial ischemia. Although low cost and widely available, it is extremely operator-dependent. When well performed by trained people, it has 82% sensitivity and 80% specificity.
CMR Perfusion Imaging
The use of gadolinium (DTPA) in the first pass makes a myocardial assessment with intensity reproduction on T1 in magnetic resonance inversely proportional to the degree of ischemia. Techniques such as FLASH (low-angle shot), echoplanar imaging, and SSFP (steady-state free precession) are protocols to optimize and improve the interpretation of results, being able to add adenosine for stress perfusion increasing sensitivity to 91% and specificity to 81%. Unlike SPECT, it assesses myocardial ischemia and 3-vessel disease well. Avoid using gadolinium in patients with creatinine clearance less than 30 due to the risk of nephrogenic systemic fibrosis.
Unfortunately, due to the risk of renal fibrosis, this method cannot be used in patients with end-stage renal disease.
CTA Perfusion Imaging
Iodinated contrasts can increase the intensity of images on computed tomography, assessing coronary flow and having a sensitivity of 72% and specificity of 80%. Unfortunately, iodinated contrast agents can cause significant nephropathy, especially when the creatinine clearance is less than 60. It is able to simultaneously assess anatomy, ventricular function and perfusion, especially when associated with a second method (coronary angiography, for example).
Conclusions
Individualization and the need for a multidisciplinary team to define the best combination of diagnostic methods is essential. The cost effectiveness must be considered, as well as the limitations of each patient with a given method. Unfortunately, contrast agents (iodine and gadolinium) can bring harm to patients with end-stage renal disease or close to it.
The best exam is still the one available, affordable cost, minimizing damage and getting results.
This article critically evaluates the strengths and weaknesses of these modalities for assessing myocardial perfusion.
Coronary Physiology;
Myocardial perfusion is regulated by:
1- Epicardial vessels,
2- Resistance vessels,
3- Endothelium. Endothelial dysfunction plays a role in the development of CAD.
Sympathetic stimulation causes vasoconstriction from acetylcholine. As a result, coronary arteries are narrowed by atherosclerotic disease, and coronary autoregulation normalizes myocardial blood flow by decreasing the resistance of distal perfusion beds to preserve adequate myocardial oxygen supply.
Stenosis is more than 85% to 90% of luminal diameter before significant reductions in resting blood flow occur.
Under vasodilator stimulus, the maximal coronary flow has been shown to decrease with stenosis of _45%
Methods for Inducing Coronary Vasodilation:
Exercisecause coronary vasodilation via an endothelium-dependent flow-mediated process to meet the increased oxygen demand.
Exercise is the preferred modality and is associated with a 2- to 3-fold increase in myocardial blood flow.
The Ideal Perfusion Imaging Technique and Agent:
The best perfusion imaging modality would be highly sensitive to small changes in coronary blood flow.
SPECT MPI:
There are three radiotracers are commonly used clinically for SPECT MPI.:
Several SPECT MPI protocols are available using a Tc99m-labeled perfusion agent; the first injection at rest is followed by imaging about 30 minutes then .
A second injection with 2 to 3 times the activity during peak stress to signal from the rest images and repeat imaging is performed.
can be corrected in postprocessingwith the use of motion correction algorithms.19 ECG-gated acquisitions
4- limiting detection of sub-endocardial perfusion defects.
MPI has reduced sensitivity for detecting left central disease or 3-vessel disease related to balanced ischemia
PET MPI: Advantages:
PET has been used for MPI for greater than 25 years,
Limitation:
1-availability
2- increased cost, and reimbursement issues
PET Radiotracers:
PET tracers:
1- N-13ammonia,
2- Rubidium-82 (Rb-82),
3- O-15 water.
Imaging Protocol:
Typically a resting perfusion image uses Rb-82 or N-13 ammonia.
As described above, mages may be analyzed qualitatively and semi-quantitatively for SPECT imaging.
Advantages and Limitations:
1-PET has improved spatial resolution as compared with SPECT.
2-PET PET is costly
Compared with angiography, exercise ECG, and SPECT in terms of quality of life-years, the prevalence of CAD _is 70%.43 Initial studies have begun to assess the potential of hybrid PET-CT imaging protocols.44 tracers have significantly less roll-off of extraction
Myocardial Contrast Echo Perfusion:
Advantages
1-evaluation of exercise-
2-dobutamine-induced wall motion analysis
limitations of the sensitivity of wall motion
CMR Perfusion Imaging
image reconstruction algorithms are enabled high-resolution imaging of first-pass myocardial
perfusion with CMR.
Contrast Agents:
Most CMR studies of myocardial perfusion are based on the first pass of a bolus of gadolinium-DTPA contrast agents.
Data Acquisition Pulse Sequences
first-pass CMR perfusion imaging pulse sequence includes substantial T1 weighting to impart contrast related to the contrast agent concentration, rapid data acquisition to images at multiple slice locations per R-R interval, an adequate spatial resolution to detect subendocardial perfusion abnormalities, and minimal artifacts to maximize
diagnostic utility. The disadvantages
of SR are its reduced dynamic range compared to IR preparation.
Cardiac MRI has advantages for perfusion stress testing, including its high spatial resolution, the ability to perform absolute quantification of perfusion, and information provided in a comprehensive CMR study.
Furthermore, the study can be performed rapidly,
Many investigators performed perfusion studies at 3 T and improved SNR and CNR.67 Recently, 3D encoding methods are combined with
imaging to improve spatial coverage using either 3D SSFP or 3D FLASH
no technique has demonstrated unequivocal superiority Advances in quantitative methods are continuing to improve diagnostic accuracy
the radionuclide techniques are used clinically, only assessing relative flow differences between regions of the myocardium.
Since this article is addressing the general population, please make refection on CKD patients:
Cardiovascular disease is the primary cause of morbidity and mortality in CKD patients.
The noninvasive modality is used in CKD patients, .but it has a limitation, a contrast agent not be used.
Summary of the article:
Non-invasive assessment of myocardial perfusion is done through:
-Single-photon emission computed tomography is widely available and validated as well as being compatible with other stress modalities as exercise and dobutamine but with motion artifacts, radiation exposure Low sensitivity in detecting mild stenosis and sub endocardial perfusion defects
-Myocardial contrast echocardiography offers better spatial resolution, as well no radiation dye, can be used along stress dobutamine but lower image quality and more artifacts and non |FDA approved dyes.
-Positron emission tomography: better spatial resolution compared to SPECT, with less artifacts but much higher costs
· Cardiac MRI: rapid test with high spatial resolution but with dye that may cause nephrogenic systemic sclerosis.
· Cardiac CT: rapid with high spatial resolution but with high ionizing radiation dose.
SPECT MPI :
Three radiotracers are commonly used clinically for SPECT MPI. Thallium-201, Tc-99m sestamibi and Tc-99m tetrofosmin
The first pass extraction of Tl-201, Tc-99m sestamibi, and Tc-99m tetrofosmin are 86%, 64%, and 54%, respectively, at resting flows.
SPECT MPI Imaging Protocols:
With the same-day rest-stress protocol using a Tc99m-labeled perfusion agent
A typical Tl-201 technique might comprise injection during the maximum of the stress, imaging around 10 minutes later, and then obtaining a redistribution picture about 4 hours later
A dual-isotope protocol in which Tl-201 is used for the rest images and then a Tc-99m perfusion agent is used during stress soon thereafter.
Advantages and Limitations of SPECT :
Advantages :
The widely used and well verified and readily available
compatible with a variety of stress modalities, including as exercise, dobutamine, or vasodilators
high temporal resolution is not as necessary, and signal-to-noise ratio (SNR) can be increased by accumulating data over a longer time
Limitations :
relatively long acquisition protocols and considerably poorer spatial resolution
, decrease detection of subendocardial perfusion defects
Sensitivity in diagnosing mild-to-moderate stenoses is limited by the roll-off of tracer uptake at greater myocardial blood flows
scatter and partial volume artefacts in the inferior wall owing to gut and biliary activity
variable attenuation artefacts resulting from breast or subdiaphragmatic attenuation
motion artefacts related to patient and respiratory movements
PET MPI :
Advantages
Compared to SPECT, the spatial resolution of PET is better
PET tracers have significantly less roll-off of extraction at high flows as compared with Tc-99m– based SPECT agent
attenuation artifacts are less
The radiation dosages for PET are lower than for SPECT
Limitations:
greater cost
For all imaging agents other than those tagged with F-18 or Rb-82, cyclotron requirements result in more restrictions
it is typically more difficult to detect motion artefacts during the scan, making it more difficult to assess how they affect the photos
Contrast Echocardiography Perfusion Techniques
Advantages;
Ionizing radiation is absent.
increased spatial detail.
measurement of myocardial blood flow in absolute terms.
Accessibility and reasonably affordable price
Restrictions:
Motion-affected photography
Artifacts Pattern
Operator specific
No FDA approval
Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected CAD.
Common Noninvasive myocardial perfusion test:
Methods for Inducing Coronary Vasodilation:
Exercise induces coronary vasodilation.
Dipyridamole, adenosine, and regadenoson and Dobutamine,
SPECT MPI:
Radiotracers:
SPECT MPI Imaging Protocols:
Same-day rest-stress protocol: Tc99m-labeled perfusion.
First injection at rest is followed by imaging roughly 30 minutes later.
A second injection with 2 to 3 times the activity is administered during peak stress.
A typical Tl-201 protocol:
Injection during peak stress, then imaging roughly 10 minutes later, followed by a
redistribution image obtained roughly 4 hours later.
A dual-isotope protocol:
Tl-201 is used for the rest images and then a Tc-99m perfusion agent is used duringstress soon thereafter.
Advantages:
Limitation:
PET MPI:
Imaging Protocol:
A bolus of the tracer is given and imaging usually commences between 90 to 120
seconds thereafter. ECG-gated PET acquisition is usually performed for 3 to 6 minutes for Rb-82 and 5 to 15 minutes for N-13 ammonia.
Stress imaging can be performed soon after rest imaging.
Advantages:
Myocardial Contrast Echo Perfusion:
Contrast Echocardiography Perfusion Techniques:
Continuous infusion of microbubbles. When the microbubbles have reached steady state concentrations, a high mechanical index pulse is used to destroy the bubbles in the maging plane. The subsequent replenishment of microbubbles is related to myocardial perfusion. Areas that are hypo perfused will have a slower return of microbubbles,whereas areas that are well perfused will have a more rapid return of microbubbles.
Advantages;
Limitation:
CMR Perfusion Imaging:
Contrast Agents gadolinium-DTPA c
Imaging Protocol:
Advantages:
Limitations:
Contrast Agents:
Iodinated contrast agents.
Advantages:
Limitations
Normal physiological regulation of coronary artery flow.
In normal circumstances, coronary blood flow is tightly regulated process where blood flow mediate vascular endothelial relaxation and vasodilation .The earliest pathological changes in coronary vessels result from endothelial dysfunction where blood flow mediated VD is lost leading to reflex VC and decrease coronary blood flow and subsequent myocardial ischemia
Diagnosis and assessment of severity of CAD is very crucial for risk stratification in kidney recipients as CV diseases are the leading cause for death with functioning graft . One of the accurate and non invasive investigations for assessing myocardial functional status is myocardial perfusion imaging with SPECT being the most commonly used modality beside other modalities as cardiac MRI ,cardiac CT , PET scan and myocardial contrast echo.
Exercise MPI has a prognostic value as exercise tolerance correlates with patients survival and it depends on exercise induced coronary VD as exercise increase Coronary blood flow that in turn induce flow mediated vascular endothelial dilatation which is impaired or even lost in cases of severe CAD.
Selecting the Ideal Perfusion Imaging Technique and Agent
The ideal perfusion agent should have high first myocardial uptake in relation to perfusion with minimal recirculation and back flow, rapid clearance from circulation , stable kinetics not affected by hypoxia While the ideal perfusion modality should have high sensitivity to small changes in coronary blood flow.
Different modalities used in evaluating myocarditis perfusion
1- SPECT : is the most commonly used modality , can utilize 3 radiotracers..
1)T1 201 tracer that has short delayed redistribution so images must be taken with in 10-20 min after injection of the tracer.
2)Tc 99m sestamibi and Tc-99m tetrofosmin
Uptake of all SPECT tracers depends on myocardial cellular integrity and blood flow
Image Analysis
Images are analyzed either qualitatively by visual analysis or semiquantitatively by differences between relative counts in both rest and stress compared to normal databases.
Advantages of SPECT
1) widely available and have several modalities that can accurately diagnose multiple vessels affection.
Limitations of SPECT
longer acquision protocol and poorer resolution compared with other modalities.
2)PET MPI
Was widely used previously but due to increased cost , lesser availability , it’s used has reduced.
Tracers that are used in PET MPI as N-13ammonia, Rubidium-82 (Rb-82), and O-15 water which have short redistribution time making them suitable for stress imaging.
Advantages of PET
has better spatial resolution, lower dose of tracers us needed and lesser attenuation artifacts compared with SPECT.
limitations of PET
Higher cost and need for cyclotron for tracers.
Myocardial Contrast Echo Perfusion
Limited by lack of FDA approval of it’s contrast materials.
CMR Perfusion Imaging
Limited by the use of godalinium as contrast as with the risk of nephrogenic systemic sclerosis
Advantages
Rapid test , less operator dependant , not markedly affected by the patient body characteristics and highly sensitive for CAD and myocardial function diagnosis.
Summary
Assessment of myocardial function is critical in kidney recipients and there are several techniques , each has its own advantages and limitations , so clinician should choose the most appropriate test based on his patient conditions.
There is no gold standard procedure for noninvasive evaluation of myocardial perfusion. There are different modalities with advantages and disadvantages.
MPI relies on ability of modalities with stress to induce regional heterogenicity of coronary blood flow in case of coronary artery diseases. Exercise induce coronary VD. A Dipyridamole and adenosine are pharmacological vasodilators.
SPECT MPI is done using three radiotracers thaliem-201, Tc99m Sestamibi & Tc-99m Tetrosfosmin
SPECT MPI is compatible with many stress modalities but has long acquisition protocols and poor resolution compared with other modalities. SPECT MPI is easily available and has been significantly validated.
PET Radiotracers N-13ammonia,O-15 water and Rubidium-82 (Rb-82) are the PET tracers used for myocardial perfusion.
Myocardial contrast echo perfusion is suitable for evaluation ;exercise or dobutamine induced wall motion evaluation.
Contrast echocardiography perfusion technique evaluates myocardial perfusion with infusion of micro bubbles continuously.
CMR perfusion imaging: high spatial resolution but there is risk for nephrogenic systemic fibrosis.
CTA perfusion imaging
High spatial resolution: rapid data acquisition together with coronary anatomy delineation.
Risk of CIN in procedure using a contrast must be considered.
Noninvasive Assessment of Myocardial Perfusion
The Ideal Perfusion Imaging Technique and Agent
both a perfusion imaging method and a perfusion imaging agent. High first-pass myocardial absorption proportional to perfusion, negligible back-diffusion and recirculation, quick clearance from the blood pool, and kinetics unaffected by factors like metabolism or hypoxia would all be characteristics of the ideal drug.
The ideal substance would not affect hemodynamics and would have a low volume in comparison to the volume of myocardial blood. Finally, the drug should be secure and have little adverse effects. High sensitivity to minute variations in coronary blood flow and a measurable correlation between signal intensity and perfusion would characterize the ideal perfusion imaging technique.
SPECT MPI :
Radiotracers
Three radiotracers are commonly used clinically for SPECT MPI:
Thallium-201 (Tl-201)
Tc-99m sestamibi
and Tc-99m tetrofosmin
Advantages and Limitations of SPECT:
Widely accessible and thoroughly validated, SPECT MPI. Exercise, dobutamine, and vasodilators are only a few examples of the various stress modalities that SPECT MPI is compatible with because the stress and imaging components are created separately. There is less need for high temporal resolution because the imaging does not take place during the first pass of a contrast agent, and the signal-to-noise ratio (SNR) can be increased by gathering data over a longer time frame.
The diagnosis of subendocardial perfusion abnormalities is hampered by the various constraints of SPECT MPI, including somewhat lengthy acquisition techniques and significantly lower spatial resolution than other current modalities. Furthermore, the sensitivity for diagnosing mild-to-moderate stenoses is limited by the roll-off of tracer uptake at greater myocardial blood flows.
The inferior wall’s dispersion and partial volume artifacts due to gastrointestinal and biliary activity, as well as variable attenuation artifacts brought on by breast or subdiaphragmatic attenuation, are additional constraints. The diagnostic value of the perfusion pictures may be diminished by these abnormalities. Motion correction techniques can be used in post-processing to correct motion artifacts. To identify attenuation artifacts from fixed perfusion deficiencies brought on by myocardial scar, ECG-gated scans that allow for assessment of regional myocardial function can be used.
PET MPI:
Although PET has been used for MPI for greater than 25 years, multiple factors including availability of scanners, increased cost, and reimbursement issues have limited wide- spread clinical application of PET.
PET Radiotracers:
N-13ammonia, Rubidium-82 (Rb-82), and O-15 water are the PET tracers typically used for myocardial perfusion.
Advantages and Limitations:
With a spatial resolution of 2 to 3 mm as opposed to the 6- to 8-mm resolution of traditional SPECT imaging, PET has better spatial resolution than SPECT. Comparing Tc-99m-based SPECT agents to PET tracers, the roll-off of extraction at high flows is substantially lower in the latter. Sadly, Rb-82 has the largest roll-off of the PET perfusion agents despite not requiring a cyclotron.
In addition, Rb-82 has a lesser spatial resolution and a larger dosage than N-15 ammunition due to its high positron emission energy and mean range of 5.5 mm. Attenuation artifacts are less of a problem with PET because attenuation correction for attenuation is a built-in feature of the technology. Additionally, dynamic scanning makes it easier to employ the tracers from PET to measure absolute perfusion levels.
With the most recent developments in PET/CT technology, it is now possible to combine anatomic imaging with PET and multimodality functional imaging of perfusion with CTA. PET agents get lower radiation doses than SPECT agents because of their short half-lives. The main drawbacks of PET are its higher price and the restrictions imposed by the requirement for a cyclotron for all imaging agents other than those tagged with Rb-82 or F-18.
It can be challenging to assess the effects of motion artifacts on images since they are typically difficult to see when the scan is in motion. Additionally, artifacts may be produced by registration errors between perfusion images and attenuation maps. Patients will likely be subjected to significantly higher radiation doses when PET and CTA are combined.
Myocardial Contrast Echo Perfusion:
MCE contrast agents are small, gas-filled microbubbles that compress and expand when exposed to an acoustic field and generate strong acoustic backscattering.
Advantages and Limitations:
MCE may be superior to other modalities in a variety of ways. Compared to SPECT, PET, and CT perfusion imaging, MCE has an advantage because it doesn’t employ ionizing radiation. MCE offers better spatial resolution than SPECT, making it possible to detect subendocardial ischemia. Absolute quantification of myocardial blood flow can also be done using MCE. Exercise or the use of inotropes or vasodilators during pharmacological stress can be used to perform imaging. The accessibility and affordability of echocardiography are two tangible benefits. The method has some drawbacks. Many individuals have sub-optimal imaging as a result of respiratory motion, body habit, or lung disease. The basal parts of the left ventricle may exhibit artifacts as a result of attenuation from the microbubbles. These variables may affect the ventricle’s geographic coverage and picture quality, which would increase variability and reduce repeatability. Additionally, there are several operator-dependent issues, such as preserving a steady image plane during microbubble replenishment. For MCE perfusion, there are no contrast agents that have received FDA approval.
CMR Perfusion Imaging:
Contrast Agents:
Most CMR studies of myocardial perfusion are based on the first-pass of a bolus of gadolinium-DTPA contrast agents.
Advantages and Limitations:
Cardiac MRI offers a number of advantages over other imaging modalities for perfusion stress testing, including excellent spatial resolution, the capacity to do absolute perfusion quantification, and the additional data that is offered in a thorough CMR investigation. The investigation can also be completed quickly, with little operator reliance, and with signal qualities that are generally independent of patient body habitus.
With future developments in parallel imaging techniques, CMR perfusion investigations continue to offer acceptable geographical coverage and temporal resolution. The “dark-rim” artifact present in current pulse sequences can be misinterpreted as a real perfusion problem. This artifact likely has multiple causes, such as myocardial motion during data acquisition, Gibbs ringing brought on by resolution issues, or susceptibility artifacts brought on by the passage of the contrast agents. When ventricular cavity enhancement reaches its height, this artifact typically only appears briefly in comparison to an actual perfusion anomaly.
CMR perfusion imaging is best compatible with vasodilator stress since imaging takes place during the first pass of a contrast agent. Gadolinium-DTPA is not the best contrast agent for a number of reasons. It features a nonlinear connection between signal intensity and perfusion and an intermediate extraction fraction during first-pass imaging. However, the combination of perfusion with delayed enhancement imaging enables accurate detection of myocardial infarction. Gadolinium has a slow washout in regions of infarction that alters the baseline signal intensity for the rest perfusion study.
Gadolinium contrast agents have recently been linked to nephrogenic systemic fibrosis, an uncommon but deadly illness that usually affects people who have significantly decreased creatinine clearance. Gadolinium-based contrast agents have a black-box warning from the FDA for individuals having a creatinine clearance of less than 30 mg/dL.
CTA Perfusion Imaging:
Myocardial perfusion imaging with CT is based on the intravenous injection of iodinated contrast agents that in- crease the absorption of x-rays in proportion to the concen- tration of iodine.
Advantages and Limitations:
High spatial resolution, quick data gathering, and the opportunity to incorporate data on coronary anatomy, ventricular function, and perfusion in one research are all benefits of MDCT. Furthermore, MDCT scanners are becoming more widely accessible due to the expansion of CTA. Although it has been shown to be possible for dynamic studies, absolute quantification of CT perfusion needs modeling of the effects of contrast diffusion into the extravascular space.
Additionally, the development of MDCT with 256 or 320 detectors may allow for high temporal resolution dynamic investigation of perfusion. However, there are a number of drawbacks to using MDCT for perfusion analysis. Since heart rate and picture quality are inversely correlated, the rise in heart rate brought on by vasodilator stress may reduce image quality. Additionally, the myocardium’s signal strength varies as a result of aberrations like beam-hardening, which makes it difficult to quantify perfusion.
The standard doses of contrast agents make it impossible to evaluate patients who have severe renal insufficiency. The biggest drawback of using MDCT to measure perfusion is the potential exposure to large amounts of ionizing radiation. The present coronary CTA radiation dose could possibly be doubled by protocols that involve doing CTA tests under stress and at rest. The radiation exposure for a dynamic perfusion analysis would likely be significantly higher. Additional research on perfusion with MDCT is necessary as the technology develops.
Non invasive Assessment of Myocardial Perfusion
SPECT MPI
SPECT MPI is widely available and has been extensively validated. It is compatible with multiple stress modalities including exercise, dobutamine, or vasodilators. The limitation includes relatively long acquisition protocols and considerably poorer spatial resolution than other available modalities, limiting detection of subendocardial perfusion defects. Furthermore, the roll-off of tracer uptake at higher myocardial blood flows limits sensitivity in detecting mild-to-moderate stenoses. Motion artifacts may decrease the diagnostic utility of the perfusion images. MPI has reduced sensitivity for detecting left main disease or 3-vessel disease related to balanced ischemia.
PET MPI
PET has improved spatial resolution as compared with SPECT. PET tracers have significantly less roll-off of extraction at high flows as compared with Tc-99m– based SPECT agents. Rb-82 in PET MPI has high positron emission energy and a mean range of 5.5 mm, resulting in a higher dose and lower spatial resolution than N-15 ammonia. The attenuation artifacts are less of an issue for PET. The major limitations to PET include higher costs and limitations imposed by the need for a cyclotron for all but Rb-82 imaging or imaging agents labelled with F-18. Artifacts from motion during the scan are frequently less apparent, making it harder to evaluate their effects on images. When PET is combined with CTA, patients probably will be exposed to even higher radiation doses.
Myocardial Contrast Echo ( MCE ) Perfusion Scan.
MCE does not involve ionizing radiation and enabling detection of subendocardial ischemia. MCE also has the ability to perform absolute quantification of myocardial blood flow. Imaging can be performed during pharmacological stress with inotropes or vasodilators or with exercise. It is wide availability and its relatively low cost.
MCE limitations include suboptimal images are obtained in a significant number of patients as the result of respiratory motion, body habitus, or lung disease. It is operator-dependent. Besides, there are no FDA-approved contrast agents for MCE perfusion.
Multidetector CT (MDCT)
MDCT has high spatial resolution, rapid data acquisition, and the ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in one study. The limitations include compromise of image quality when the heart increases. Artifacts such as beam-hardening result in variations of signal intensity within the myocardium, limiting the ability of quantitative assessment of perfusion. The main disadvantage of assessing perfusion with MDCT is the potentially high doses of ionizing radiation.
In my opinion, no single perfect non-invasive investigation to assess the myocardial perfusion. It depends on the health resources. As in my hospital with limited resources, we use only MCE as the invasive modality to assess cardiac perfusion status before kidney transplantation.
Non-invasive tools of assessing cardiovascular system are important in assessing CAD risk.They include single-photon emission computed tomography (SPECT), myocardial contrast echocardiography (MCE), positron emission tomography (PET), cardiac MRI (CMR), and cardiac computed tomography (CT) .
SPECT MPI :
It is the most commonly used modality. Its advantages include doing the stress part and imaging part separately with less need for high temporal resolution. Disadvantages are low sensitivity, motion artifact, large radiation dose ,long period protocol and less resolution limiting the sub-endocardial perfusion defect detection when compared to other modalities. Studies revealed a sensitivity of 87-89% and specifity of 73-75%
PET MPI:
It has higher resolution when compared to SPECT,cost effective less artifacts, easy performance and lower radiation dose.Limitations are the high cost, technical issues , artifacts and the high dose of radiation when combined with CTA. Studies revealed a sensitivity of 91-92% and specificity of 85-100 % for the detection of CAD.
Myocardial Contrast Echo Perfusion:
FDA considers it to be an experimental procedure. The advantages are no ionizing radiation, available, less cost, better resolution for detection of sub-endocardial ischemia and can quantify myocardial blood flow. The limitations are suboptimal images, artifacts in the basal segments of the left ventricle, operator-dependent factors and no FDA-approved contrast agents for perfusion. The sensitivity is 82% and specificity is 80%.
CMR Perfusion Imaging:
Cardiac MRI advantages are high spatial resolution, rapid procerdure, not dependent on the operator and patient body habitus, most compatible with vasodilator stress, can quantify the perfusion, and the additional information provided in a comprehensive CMR study. Disadvantages are the “dark-rim” artifact and the gadolinium associated nephrogenic systemic fibrosis, in patients with significant reductions in creatinine clearance.Sensitivity approaches 91 % and specificity is 81%
CTA Perfusion Imagin:
Advantages include its high spatial resolution, wide availability, rapid data acquisition, and the ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in one study. Limitations are artifacts , poor quality with rapid heart rate during stress and high radiation dose
Since this article is addressing general population, please make refection on CKD patients
SPECT MPI :
Has good classification potentials in CKD patients throughout the different stages. (1)
PET MPI:
Shah and colleagues reported a higher all-cause mortality among patients with a reduced PET-and Charytan demonstrated similar results in patients with CKD and ESRD (2)
Myocardial Contrast Echo Perfusion:
Has good accuracy for ruling out the presence of a significant CAS in patients with ESRD.(3)
CMR Perfusion Imaging:
Are cautiously used due to the concern of nephrogenic systemic fibrosis. Cardiovascular magnetic resonance spectroscopy has been studied to assess early cardiac dysfunction in pediatric population with advanced CKD . Dobutamine stress CMR was shown to be safe in the pre-renal transplant population .
1- Ahmed AM, Qureshi WT, O’Neal WT, Khalid F, Al-Mallah MH. Incremental prognostic value of SPECT-MPI in chronic kidney disease: A reclassification analysis. J Nucl Cardiol. 2018 Oct;25(5):1658-1673. doi: 10.1007/s12350-016-0756-0. Epub 2017 Jan 3. PMID: 28050863.
2- Vij, A., Doukky, R. The Prognostic Value of MPI in CKD: Can we do better?. J. Nucl. Cardiol. 29, 155–157 (2022). https://doi.org/10.1007/s12350-021-02545-6
3- Sobkowicz B, Tomaszuk-Kazberuk A, Kralisz P, Malyszko J, Kalinowski M, Hryszko T, Malyszko J, Dobrzycki S, Musial WJ. Application of myocardial contrast echocardiography for the perfusion assessment in patients with end-stage renal failure–comparison with coronary
4- Parnham SF, Gleadle JM, De Pasquale CG, Selvanayagam JB. Myocardial Ischemia Assessment in Chronic Kidney Disease: Challenges and Pitfalls. Front Cardiovasc Med. 2014 Dec 19;1:13. doi: 10.3389/fcvm.2014.00013. PMID: 26664863; PMCID: PMC4668858.
Summary
Noninvasive imaging techniques are gaining popularity in detection of occult CAD recently.
Coronary Physiology
Normal coronary physiology is maintained by intact endothelial function and nitric oxide release.
The primary change is the decreased perfusion before clinical manifestation of the disease and even preceding ECG changes. Significant stenosis exceeding 85 to 90 % impair myocardial oxygen supply.
Detection of abnormal coronary flow reserve with vasodilator stress in the absence of a marked coronary stenosis correlates to microvascular or endothelial dysfunction or even both.
Methods for Inducing Coronary Vasodilation
Myocardial perfusion imaging (MPI) depends on stress induction causing further heterogeneity of coronary artery blood flow in the setting of CAD.
On exercise, in the presence of CAD, perfusion reserve is impaired by the stenoses, endothelial dysfunction and adrenergic stimulation. Exercise is mainly associated with a 2- to 3-fold increase in myocardial blood flow, so it is considered as the preferred modality, as exercise capacity reflects an important prognostic value. Pharmacological agents causing arteriolar vasodilation by direct and endothelium-mediated mechanisms are being used to resemble exercise stress testing.
The Ideal Perfusion Imaging Technique and Agent
Criteria of ideal agent must include a high first-pass myocardial uptake proportional to perfusion. Also back-diffusion and recirculation would be insignificant. Provided that rapid clearance from the blood pool, as well as unaltered kinetics by other factors such as metabolism or hypoxia. Safety of the agent is a must with only minimal allowed side effects. High sensitivity to small changes in coronary blood flow with a quantifiable relationship between signal intensity and perfusion is required. Spatial resolution is beneficial in determining transmural differences in perfusion. The technique itself ought to be devoid of artifacts, easy to use, widely distributed, and cheap.
SPECT MPI
Commonly used radiotracers are Thallium-201, Tc-99m sestamibi and Tc-99m tetrofosmin. The uptake of the tracers is mainly dependent on myocardial cellular integrity besides blood flow.
Advantages and Limitations of SPECT
Being widely available, validated and compatible with multiple stress modalities including exercise, dobutamine, or vasodilators are considered various advantages. Whereas it has also some drawbacks as longer acquisition protocols as well as poorer spatial resolution compared to other available modalities, limiting detection of subendocardial perfusion defects. Limited sensitivity in detecting mild-to-moderate stenoses is also encountered due to roll off phenomenon. Also, various artifacts coexist affecting its accuracy as motion artifacts related to patient, respiratory motion, gut, biliary artifacts, as well as breast and sub diaphragmatic attenuation. Owing to the assessment of only relative perfusion is generally assessed, it has minimal sensitivity for detecting left main disease or triple vessel disease related to balanced ischemia. In addition to tracers expose patients to considerable radiation doses.
The diagnostic outcome can guide selective coronary angiography, reducing the cost associated with diagnosis and revascularization.
PET MPI
The limited availability of scanners and their increased cost restricts its use.
PET Radiotracers
The common available agents are N-13ammonia, Rubidium-82 (Rb-82), and O-15 water. The disadvantages include the presence of the roll-off phenomenon as well as the high radiation dose. Clinical studies with fluorine-18 (F-18) as a new promising tracer are progressing.
Advantages and Limitations
PET has better spatial resolution compared to SPECT. The PET tracers have significantly less roll-off of extraction at high flows in comparison to SPECT.it is regarded as a both sensitive and specific tool for the diagnosis of CAD.it is also a cost-effective measure compared to angiography, exercise ECG, and SPECT. It detects prevalence of CAD exceeding 70%.
Myocardial Contrast Echo Perfusion
Unfortunately, the lack of an FDA approved MCE contrast agent for perfusion hindered the widespread clinical application.
Advantages and Limitations
MCE potential advantages over other modalities is primarily lack of ionizing radiation, having better spatial resolution enabling detection of subendocardial ischemia and the ability to perform absolute quantification of myocardial blood flow. It is also widely available and of relatively lower cost. Drawbacks mainly being operator-dependent and its agents are not FDA-approved. It has comparable accuracy to SPECT for diagnosing CAD with sensitivity of 82% and specificity of 80% in addition to its prognostic value that was incremental to left ventricular ejection fraction.
CMR Perfusion Imaging
It is a gadolinium-DTPA contrast agent procedure whereas well perfused areas will reflect a shorter T1 and appear bright on heavily T1-weighted images, while hypoperfused regions will acquire longer T1 and appear as hypointense regions.
The use of nonselective saturation recovery (SR) pulse sequences which are more convenient for multislice imaging, insensitive to variations in heart rate, it also enables shorter preparation times as well as having less susceptibility induced image artifacts.
Stress perfusion CMR is helpful in evaluation of ventricular function, stress and rest perfusion, and viability/myocardial infarction. This technique has an estimated sensitivity and specificity of 89% and 87%, respectively, in detection of CAD. The high spatial resolution of CMR allows the detection of subendocardial ischemia clearly even in patients with triple vessel disease.
Advantages and Limitations
Cardiac MRI has unique advantages for perfusion stress testing:
High spatial resolution.
Absolute quantification of perfusion.
Can be performed rapidly.
Limited operator dependence.
The signal characteristics are not affected by the patient’s body habitus.
Disadvantages:
gadolinium-DTPA is not an ideal contrast agent correlated to nephrogenic systemic fibrosis disease.
The presence of an abnormal stress CMR was significantly predictive of MACE.
CTA Perfusion Imaging
It is based on the use of intravenous injection of iodinated contrast agents so, the main concern is contrast-induced nephropathy, especially in patients with renal impairment.
Accuracy was estimated by 72% sensitivity and 80% specificity for detecting a significant coronary stenosis.
Advantages and Limitations
Favorable advantages are: high spatial resolution, rapid data acquisition, and the ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in one study. They are also widely available. However, some disadvantages coexist as contrast induced nephropathy, high doses of radiation and the presence of artifacts.
Reflection on our centre practice is only dependent on echocardiography, dobutamine stress echocardiography, and coronary angiogram and stenting in high risk patients with high probability of renal replacement therapy in the form of haemodialysis. Magnetic resonance studies and computed tomography are not used for the fear of NSF and CIN AKI accompanied by high mortality and further required renal replacement therapies.
Noninvasive assessment of myocardial perfusion is crucial in diagnosis and risk stratification of patients with known or suspected CAD.
Myocardial perfusion is a highly regulated process .Endothelial dysfunction plays a role in the development of CAD, AS it plays a role in epicardial and arteriolar vasodilatation.
Because perfusion is the early change in the ischaemic cascade , stress modalities that assess coronary perfusion reserve have a higher sensitivity in detecting flow limiting stenosis than analysis of stress induced wall motion abnormalities or ECG changes alone .
Attributes of an ideal perfusion agent and perfusion imaging modality
A) perfusion agent should be safe,easy to administer , its kinetics not altered by metabolism, low cost, with high first pass uptake and there is linear relationship between myocardial concentration and perfusion
B) imaging modality
_ high sensitivity, low cost , widely available, easy to use, high diagnostic utility, reproducible
_ quantifiable relationship between singal intensity and concentration of agent
_ high spatial/ temporal resolution
1) SPECT MPI
Three radiotracers are used Thallium-201 , Tc-99m sestamibi and Tc-99m tetrofosmin
Different imaging protocols
– same-day rest-stress protocol using a Tc 99m-labeled perfusion agent
– typical T1-201 protocol
– a dual isotope protocol in which T1-201 agent used during rest and Tc-99m used during stress
Advantages . It is widely available and compatible with multiple stress modalities
Limitations. Limited in detection of subendocardial perfusion defect , limited in detection of mild to moderate stenosis
Presence of motion artifacts related to patient and respiratory motion
Its sensitivity and specificity are 87% and 73% respectively.
2) PET MPI
N-13 ammonia, Rubidium-82 and 0-15 water are the PET tracer used for myocardial perfusion
Advantages.PET has improved spatial resolution as compared with SPECT. Attenuation artifacts are less of an issue for PET. The tracers used in PET are more easily applied in dynamic scanning to be used for absolute quantification of perfusion.
The short half-lives of the PET agents result in lower radiation does than SPECT
Major limitations include higher costs and limitations imposed by the need for a cyclotron for all .
Its sensitivity and specificity of 92% and 85% respectively.
3) Myocardial Contrast Echo Perfusion
MCE contrast agents are small, gas-filled microbubbles that compress and expand when exposed to an acoustic field and generate strong acoustic backscattering
Advantages. It doesn’t involve ionizing radiation, has improved spatial resolution enabling detection of subendocardial ischaemic, also has the ability to perform absolute quantification of myocardial blood flow ,wide variability and low cost
Limitations. Suboptimal images due to respiratory motion, body habits or lung disease, attenuation from microbubbles may result in artifacts in the basal segment of left ventricle. It is operator dependent
Its sensitivity and specificity 82 and 80 respectively
4) CMR perfusion imaging
Contrast agent . Gadolinium-DTPA
Stress perfusion CMR is applied as part of a comprehensive study that evaluates ventricular function
Advantages. High spatial resolution, the ability to perform absolute quantification of perfusion, the study can performed rapidly, has limited operator dependence
Limitations . In advanced CKD patients, it associated with nephrogenic systemic fibrosis.
Its sensitivity and specificity are 91% and 81% respectively
5) CTA perfusion imaging
Contrast agent. Nonionic Contrast agents with a high iodine concentration
Advantages. High spatial resolution, rapid data acquisition, the ability to combine information of coronary anatomy, ventricular function and perfusion in one study. Widely available.
Limitations. As image quality is inversely related to heart rate. The increase in heart rate with vasodilator stress may compromise image quality. Artifacts limit the ability of quantitative assessment of perfusion. High dose of ionizing radiation
In advanced kidney disease myocardial Contrast Echo Perfusion may be suitable tool
In other modalities we fear of Contrast
CMR is associated with nephrogenic systemic fibrosis
The article aims to make critical analyzes regarding the different methods for assessing myocardial perfusion. But first, we need to know the characteristics of Ideal Perfusion Imaging Technique and Agent.An ideal agent would have:
– a high first-pass myocardial uptake proportional to perfusion,
– a insignificant back-diffusion and recirculation,
– rapid clearance from the blood pool,
– kinetics that are not altered by factors such as metabolism or hypoxia
– be safe, with minimal side effects.
An ideal perfusion imagin Technique would have:
– a direct and quantifiable relationship between contrast agent concentration and myocardial perfusion,
– high sensitivity to small changes in coronary blood flow and a quantifiable relationship between signal intensity and perfusion.
– high spatial resolution so that transmural differences in perfusion could be detected
– be reproducible and have a high diagnostic utility and should be free of artifacts that would limit either;
– should be widely available, fast and easy to use, and cost-effective
Now, let’s go know the methods for assessing myocardial perfusion:
– SPECT:
Three types of tracers are commonly used: Tl-201, Tc-99m sestamibi, and Tc-99m, each with specific characteristics, interfering in the interpretation of results and thus requiring a type of protocol for each tracer.
As positive points: It’s compatible with multiple stress modalities including exercise, dobutamine, or vasodilators. There is an extensive literature evaluating the sensitivity and specificity of SPECT myocardial perfusion imaging for detecting CAD, one of the analyzes had demonstrated mean sensitivity and specificity of 87% and 73%, respectively, for exercise myocardial SPECT for detecting a greater than 50% stenosis.
As negative points: has multiple limitations, including relatively long acquisition protocols and considerably poorer spatial resolution than other available modalities, limiting detection of subendocardial perfusion defects. Additional limitations include motion artifacts related to patient and respiratory motion, scatter and partial volume artifacts in the inferior wall related to gut and biliary activity, and variable attenuation artifacts resulting from breast or subdiaphragmatic attenuation.
-PET:
N-13ammonia, Rubidium-82 (Rb-82), and O-15 water are the PET tracers typically used for myocardial perfusion.
As positive points: has improved spatial resolution as compared with SPECT, PET tracers have significantly less roll-off of extraction at high flows as compared with Tc-99m– based SPECT agentes, tracers used in PET are more easily applied in dynamic scanning to be used for absolute quantification of perfusion
– MYOCARDIAL CONTRAST ECHO PERFUSION:
This use microbubbles like a contrast agente.
As Limitations points: the sensitivity of wall motion analysis have led to the development of MCE techniques
– CMR PERFUSION IMAGING
It use gadolinium-DTPA contrast agentes that has interaction with water prótons.
As positive points: high spatial resolution, the ability to perform absolute quantification of perfusion, and the additional information provided in a comprehens, the study can be performed rapidly, has limited operator dependence, and the signal characteristics are largely independent of the patient’s body habitus.
As limitations points: gadolinium isn´t a an ideal contrast agente – In regions of infarction, gadolinium has a slow washout that changes the baseline signal intensity for the rest perfusion study; however, the combination of perfusion with delayed enhancement imaging enables accurate detection of myocardial infarction. Recently, gadolinium contrast agents have been associated with a rare but serious condition called nephrogenic systemic fibrosis, which primarily occurs in patients with significant reductions in creatinine clearance.
– CTA PERFUSION IMAGING:
Use intravenous injection of iodinated contrast agentes that are not hemodynamically inert and have an influence on coronary blood flow, inducing a reduction in coronary flow followed by a hyperemic response.
As positive points: high spatial resolution, rapid data acquisition, and the ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in one study
As limitations points: image quality is inversely related to heart rate, the increase in heart rate with vasodilator stress may compromise image quality. Furthermore, artifacts such as beam-hardening result in variations of signal intensity within the myocardium, limiting the ability of quantitative assessment of perfusion. The contrast agent doses typically used preclude evaluation of patients with significant renal insufficiency. The main disadvantage of assessing perfusion with MDCT is the potentially high doses of ionizing radiation.
These methods are likely to have greater sensitivity and specificity for patients with CKD, as they have a higher incidence of CAD, which increases their effectiveness. However, the importance of tracers and changes in their functionality should increase due to decreased renal function. Therefore, these methods should be revalidated for the CKD population.
Summary:
There has been significant progress in the noninvasive evaluation of myocardial perfusion but yet to set a gold standard procedure. There are different modalities used with advantages and disadvantages.
MPI depends on ability of stress modalities to induce regional hetenogenicity of coronary arterial blood flow in case of coronary entry diseases. Exercise induce coronary vasodilation. In addition to that Dipyridamole, adenosine, and regadenoson are pharmacological vasodilators as well.
SPECT MPI clinically used three radiotracers thaliem-201, Tc99m sestamibi and Tc-99m tetrosfosmin
Spect MPI is compatible with multiple stress modalities but long acquisition protocols and poor resolution than other modalities. SPECT MPI is widely available and has been extensively validated.
PET Radiotracers N-13ammonia, Rubidium-82 (Rb-82), and O-15 water are the PET tracers typically used for myocardial perfusion.
Myocardial contrast echo perfusion is used for evaluation either exercise or dobutamine induced wall motion analysis.
Contrast echocardiography perfusion technique asses myocardial perfusion with continuous infusion of micro bubbles.
CMR perfusion imaging:
High spatial resolution but risk for nephrogenic systemic fibrosis.
CTA perfusion imaging
High spatial resolution, rapid data acquisition with coronary anatomy information
Refection on CKD patients:
Risk of CIN in the procedure using contrast.
Assessment of CAD can be done via different methods of MPI which include:
1- SPECT
2- MCE
3- PET
4- CMR
5- Cardiac CT
SPECT-MPI:
Radiotracers: Thallium 201, Tc99m Sestamibi, and Tc99m Tetrofosmin
Sensitivity: 87% with exercise and 89% with vasodilators. Specificity: 73% with exercise and 75% with vasodilators.
3 different protocols:
1- Inject radiotracer (Technecium)-à imaging after 30 min, inject radiotracer again with during peak stress.
2- Inject Thallium radiotracer during peak stress-à imaging at 10 min and at 4 h.
3- Inject Thallium for rest image and Technecium for image during stress
Advantages: stress compatible, lower need for high temporal resolution.
Limitations: Time consuming, big radiation dose, low spatial resolution, multiple artefacts, less sensitive to detect sub-endocardial perfusion defects and significant coronary vessels stenosis.
PET-MPI:
Radiotracers: Rb-82, N13-ammonia, and 015 water.
Sensitivity: 92%, Specificity: 85%
Protocol: inject bolus of the radiotracer—-à imaging after 90-120 seconds because of short half life of radiotracers.
Advantages: less dose of radiation, less attenuation artefacts, better spatial resolution.
Limitations: High cost, cyclotron is needed, higher radiation when CT is used, and registration artefacts.
MCE:
Gas filled microbubbles are injected IV which acts as a contrast agent. It is not yet approved by FDA.
Sensitivity: 82%, Specificity: 80%.
Protocol: inject microbubbles—-à>images are taken in gated intermittent mode and in real time mode. Analysis can be done.
Advantages: low price, no radiation, better spatial resolution, can detect subendocardial ischaemia
Limitations: suboptimal images because of artefacts, operator dependent.
Cardiac MRI:
Gadolinium DTPA is the contrast agent to be used.
Sensitivity: 91%, Specificity: 81%
Protocol: different kind of images are needed, Cine image to evaluate ventricular function.
Stress using Adenosine with gadolinium-à images at rest after a wash out period of 10 min.
At the end take late gadolinium images.
Advantages: high spatial resolution, can detect sub-endocardial ischaemia, quantification of perfusion can be done, rapid scan, not operator dependent.
Limitations: not allowed if GFR below 30
CTA:
Iodinated contrast agents are used.
Sensitivity: 72%, specificity: 80%
Protocol: CTA during adenosine stress and 20 min at rest.
Advantages: high spatial resolution, rapid, can assess ventricular function, perfusion of coronaries.
Limitations: risk of CIN, high dose of radiation, poor quality of images with fast HR.
Combined techniques of non-invasive MPI can achieve better assessment
In CKD patients cardiac MRI is avoided if GFR below 30.
CKD patients are at higher risk for CIN with using CTA.
Exercise MPS: CKD patients usually have low exercise tolerance and impaired chronotropic response.
Summarise this article
-Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease (CAD). Although single-photon emission computed tomography (SPECT) is most commonly used, multiple modalities including myocardial contrast echocardiography (MCE), positron emission tomography (PET), cardiac MRI (CMR), and cardiac computed tomography (CT) have emerged as promising techniques.
SPECT MPI
Radiotracers
-Three radiotracers are commonly used clinically for SPECT MPI.
SPECT MPI Imaging Protocols
-There are a number of SPECT MPI protocols available for the assessment of CAD. With the same-day rest-stress protocol using a Tc99m-labeled perfusion agent, a first injection at rest is followed by imaging roughly 30 minutes later. A second
injection with 2 to 3 times the activity is administered during peak stress to overcome the background signal from the rest images, and repeat imaging is performed.
-The radiation burden to the patient is higher with dual-isotope imaging (typically 24 mSv) than when using rest/stress Tc-99m sestamibi (typically 11 mSv) or Tc-99m– tetrofosmin (typically 8 mSv) alone.
Advantages and Limitations of SPECT
– As the stress and imaging components are performed separately, SPECT MPI is compatible with multiple stress modalities including exercise, dobutamine, or vasodilators.
– SPECT MPI has multiple limitations, including relatively long acquisition
protocols and considerably poorer spatial resolution than other available modalities, limiting detection of subendocardial perfusion defects.
-Furthermore, the roll-off of tracer uptake at higher myocardial blood flows limits sensitivity indetecting mild-to-moderate stenoses.
-Additional limitations include motion artifacts related to patient and respiratory
motion, scatter and partial volume artifacts in the inferior wall related to gut and biliary activity, and variable attenuation artifacts resulting from breast or subdiaphragmatic attenuation.
PET MPI
-Although PET has been used for MPI for greater than 25 years, multiple factors including availability of scanners,mincreased cost, and reimbursement issues have limited widespreadmclinical application of PET.31 However, the recent proliferation of hybrid PET-CT scanners may lead to an increasingly important clinical role.
PET Radiotracers
N-13ammonia, Rubidium-82 (Rb-82), and O-15 water are the PET tracers typically used for myocardial perfusion.
Imaging Protocol
Typically a resting perfusion image is acquired using either Rb-82 or N-13 ammonia. A bolus of the tracer is given and imaging usually commences between 90 to 120 seconds thereafter. ECG-gated PET acquisition is usually performed
for 3 to 6 minutes for Rb-82 and 5 to 15 minutes for N-13 ammonia, owing to their different half-lives.
Advantages and Limitations
-PET has improved spatial resolution as compared with SPECT, with spatial resolution of 2 to 3 mm as compared with the 6- to 8-mm resolution of conventional SPECT imaging.PET tracers have significantly less roll-off of
extraction at high flows as compared with Tc-99m–based SPECT agents. Unfortunately, Rb-82, which does not require a cyclotron, has the most significant roll-off of the PET perfusion agents. Furthermore, Rb-82 has high positron
emission energy and a mean range of 5.5 mm, resulting in a higher dose and lower spatial resolution than N-15 ammonia.
– Because PET perfusion images are corrected for attenuation as an inherent component of the technology, attenuation artifacts are less of an issue for PET. Furthermore, the tracers used in PET are more easily applied in dynamic
scanning to be used for absolute quantification of perfusion.
-The short half-lives of the PET agents result in lower radiation doses than SPECT agents.
-The major limitations to PET include higher costs and limitations imposed by the need for a cyclotron for all but Rb-82 imaging or imaging agents labeled with F-18.
Myocardial Contrast Echo Perfusion
-Although echocardiography for evaluation of exercise- or dobutamine-induced wall motion analysis is commonly used clinically, limitations of the sensitivity of wall motion analysis have led to the development of MCE techniques for
assessing perfusion. Unfortunately, the lack of an FDAapproved MCE contrast agent for perfusion has currently put limitations on its widespread clinical application.
Contrast Echocardiography Perfusion Techniques
Myocardial perfusion can be assessed with continuous infusion of microbubbles.
Advantages and Limitations
– MCE has an advantage over SPECT, PET, and CT perfusion imaging because it does not involve ionizing radiation. Compared with SPECT, MCE has improved spatial resolution, enabling detection of subendocardial ischemia.
MCE also has the ability to perform absolute quantification of myocardial blood flow. Imaging can be performed during pharmacological stress with inotropes or vasodilators or with exercise. Practical advantages of echocardiography include
its wide availability and its relatively low cost.
-The technique has some limitations. Suboptimal images are obtained in a
significant number of patients as the result of respiratory motion, body habitus, or lung disease.Attenuation from the microbubbles may result in artifacts in the basal segments of the left ventricle. These factors can limit image quality and
adequate spatial coverage of the ventricle, resulting in increased
variability and decreased reproducibility. Furthermore, there are some operator-dependent factors such as maintaining a constant image plane during replenishment of microbubbles. Finally, there are no FDA-approved contrast
agents for MCE perfusion.
CMR Perfusion Imaging
-Over the last few years, improvements in hardware, pulse sequence development, and image reconstruction algorithms have enabled high-resolution imaging of first-pass myocardial perfusion with CMR.
Advantages and Limitations
-Cardiac MRI has significant advantages for perfusion stress testing, including its high spatial resolution, the ability to perform absolute quantification of perfusion, and the additional information provided in a comprehensive CMR study.
-Furthermore, the study can be performed rapidly, has limited operator dependence, and the signal characteristics are largely independent of the patient’s body habitus. pass of a contrast agent, CMR perfusion imaging is most
compatible with vasodilator stress.
CTA Perfusion Imaging
With the recent advances in multidetector CT (MDCT) and CT coronary angiography, there has been renewed interest in using CT to evaluate myocardial perfusion.
Advantages and Limitations
-The advantages of MDCT include its high spatial resolution, rapid data acquisition, and the ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in one study. Furthermore, with the growth of CTA, MDCT scanners are becoming widely available. Absolute quantification of CT perfusion has been demonstrated for dynamic studies but requires modeling of the effects of contrast diffusion into the extravascular space. Furthermore, advancement of MDCT with 256 or 320 detectors may enable dynamic analysis of perfusion with high temporal resolution.
-However, the use of MDCT for perfusion analysis has multiple limitations. Because image quality is inversely related to heart rate, the increase in heart rate with vasodilator stress may compromise image quality. Furthermore, artifacts
such as beam-hardening result in variations of signal intensity within the myocardium, limiting the ability of quantitative assessment of perfusion. The contrast agent doses typically used preclude evaluation of patients with significant renal insufficiency.
-The main disadvantage of assessing perfusion with MDCT is the potentially high doses of ionizing radiation. Protocols that involve obtaining CTA studies at rest and stress would potentially double the current coronary CTA radiation dose. Dynamic perfusion analysis probably would have an even higher radiation dose.
NON-invasive assessment of myocardial perfusion is crucial. Known or suspected coronary artery disease (CAD). SPECT is most commonly used, but other techniques have emerged as (MEC) myocardial contrast echocardiography, (PET) positron emission tomography, (CMR) cardiac MRI, and (CT) cardiac computed tomography.
Coronary physiology:
Myocardial perfusion process includes epicardial vessels, resistance vessels, and the endothelium. Endothelial dysfunction occurs early insult in CAD. Under sympathetic stimulation nitric oxide from the endothelial cells released, resulting in vasodilation of the epicardial and arteriolar vessels in normal coronaries. In endothelial dysfunction; acetylcholine predominates; causes vasoconstriction and further perfusion defect.
Coronary autoregulation maintains an adequate myocardial oxygen supply by reducing the resistance of distal perfusion beds in case of coronary stenosis. However, maximal coronary flow has been shown to decrease with stenosis of 45%.
Clinically coronary perfusion reserve can be assessed using stress modalities, that have a higher sensitivity in the detecting flow-limiting stenosis, than analysis of stress-induced wall motion abnormalities or ECG changes alone. Abnormal coronary flow reserve with vasodilator stress in the absence of a significant coronary stenosis occurs and has been attributed to microvascular and/or endothelial dysfunction.
Methods for inducing coronary vasodilation:
1- Exercise induces coronary vasodilatation via an endothelial dependent process to meet the increased oxygen demand. Exercise is typically associated with a 2- to 3-fold increase in myocardial blood flow and is the preferred modality, as exercise capacity has important prognostic value.
2- Dipyridamole, adenosine, and regadenoson are pharmacological vasodilators that cause arteriolar vasodilation by both direct and endothelium-mediated mechanisms and are associated with a 3.5- to 4-fold increase in myocardial blood flow
3- Dobutamine, a synthetic 1- and 2-receptor agonist, typically produces a 2- to 3-fold increase in myocardial blood flow similar to exercise.
The Ideal Perfusion Imaging Technique and Agent
The ideal agent should have:
1- High first pass myocardia uptake proportional to perfusion.
2- Insignificant back-diffusion and recirculation.
3- Rapid clearance from the blood pool.
4- Kinetic that are not altered by metabolism or hypoxia.
5- Has no hemodynamic effect and it is a small in volume compared with the myocardial blood volume.
6- It should be safe, with minimal side effects.
The technique:
1- Has high spatial resolution.
2- The technique should be reproducible.
3- have a high diagnostic utility
4- should be free of artifact.
5- should be widely available, fast and easy to use, and cost-effective.
I. SPECT MPI
Radiotracers used are:
a- Thallium-201 (Tl-201) is suboptimal low energy and long half-life.
b- Tc-99m sestamibi
c- Tc-99m tetrofosmin
All of the agents have properties that allow the stress component and the imaging component to be separated in time and location, which is a significant advantage over other modalities.
SPECT MPI Imaging Protocols
1- The same day rest-stress protocol using a Tc99m-labeled perfusion agent.
2- A dual-isotope protocol in which Tl-201 is used for the rest images and then a Tc-99m perfusion agent is used during stress soon thereafter.
Image analysis using data base
Advantages and limitations of SPECT:
1- It is compatible to multiple stress modalities including exercise, dobutaminem or vasodilators.
2- there is less demand for high temporal resolution, and signal-to-noise ratio (SNR) can be improved by collecting data over a longer period of time.
Limitations:
1- long acquisition protocols.
2- Poor spatial resolution
3- Limited detection of subendocardial perfusion defects.
4- Limited sensitivity in detecting mild-to-moderate stenosis.
5- It has many artifacts related to motion, gut and biliary activity, and breast and subdiaphragmatic attenuations.
ECG-gated ecquisitions can be used to helop distinguish attenuation artifacts from fixed perfusion defects resulting from myocardial scar.
attenuation correction algorithms that use transmission as well as emission data are available and can improve the accuracy of SPECT MPI.
MPI has reduced sensitivity for detecting left main disease or 3-vessel disease related to balanced ischemia.
The diagnostic approach of SPECT MPI guiding selective coronary angiography reduces costs associated with both diagnosis and revascularization.
PET MPI
It has been widely used, although, availability of the scanners, increased cost, and reimbursement issues have limited wide use of PET.
Myocardial Contrast Echo Perfusion
Echocardiography used for evaluation of exercise- or dobutamine-induced wall motion analysis is widely used. Although limitations of the sensitivity of wall motion analysis have led to the development of MCE.
Contrast Echocardiography Perfusion Techniques
It is perfusion echocardiography has been performed with both vasodilator and inotropic pharmacological stress. It depends on detection of microbubbles after their destruction in the target area. Area of low perfusion the return of microbubbles will be slow while area of high perfusion will be high.
Advantage:
1- It does not involve ionizing radiation.
2- Compared with SPECT, MCE has improved spatial resolution, enabling detection of subendocardial ischemia.
3- MCE also has the ability to perform absolute quantification of myocardial blood flow.
4- Imaging can be performed during pharmacological stress with inotropes or vasodilators or with exercise.
5- wide availability and relatively low cost of the echocardiography.
Limitations:
1- Suboptimal images are obtained in a significant number of patients as the result of respiratory motion, body habitus, or lung disease.
2- Attenuation from the microbubbles may result in artifacts in the basal segments of the left ventricle.
3- some operator-dependent factors.
4- No FDA approved contrast agents for MCE
5- increased variability and decreased reproducibility.
According to literatures; MCE was shown to have prognostic value that was incremental to left ventricular ejection fraction.
CMR Perfusion Imaging
Most CMR studies of myocardial perfusion are based on the first-pass of a bolus of gadolinium-DTPA contrast agents.
Areas that are well perfused will have a shorter T1 and appear bright on heavily T1-weighted
images, whereas regions that are hypoperfused will have longer T1 and will appear hypointense.
This technique has an overall sensitivity and specificity of 89% and 87%, respectively, for detecting CAD.
Advantages:
1- its high spatial resolution, the ability to perform absolute quantification of perfusion.
2- the study can be performed rapidly, has limited operator dependence
3- the signal characteristics are largely independent of the patient’s body habitus.
Limitations:
1- Current pulse sequences suffer from a “dark-rim” artifact that can be mistaken for a true perfusion abnormality.
2- gadolinium-DTPA is not an ideal contrast agent.
3- gadolinium contrast agents have been associated with a rare, but serious condition called nephrogenic systemic sclerosis specially in with a creatinine clearance 30 mg/dL.
The diagnostic performance of perfusion CMR was superior as compared with the entire SPECT population in a study. But as it is new modality; limited data available.
CTA Perfusion Imaging
With the recent advances in multidetector CT (MDCT) and CT coronary angiography, there has been renewed interest in using CT to evaluate myocardial perfusion.
Advantages:
1- high spatial resolution, rapid data acquisition, and the ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in one study.
2- become widely available.
Limitations:
1- image quality is inversely related to heart rate, the increase in heart rate with vasodilator stress may compromise image quality.
2- limited ability of quantitative assessment of perfusion due to artefacts.
3- The contrast agent doses typically used preclude the evaluation of patients with significant renal insufficiency.
4- The main disadvantage of assessing perfusion with MDCT is the potentially high doses of ionizing radiation.
Myocardial contrast echocardiography (MEC), CT angiography (CTA), Myocardial perfusion scintigraphy (MPS), and cardiac MRI are all useful non-invasive modalities in the diagnosis of CAD in addition to street Echo.
CKD patients have a risk of contrast agents exposure during the test, which includes CIN, and gadolinium-induced nephrogenic systemic sclerosis.
so, stress echocardiography without contrast or gadolinium will be safe and good in CKD patients for diagnosis of CAD.
Coronary physiology..
Highly regulated process which involves epicardial vessels, resistances vessels and endothelium.
Endothelial dysfunction here reflected on vascular diseases and coronary artery diseases
* methods for inducing coronary vasodilation :-
MPI depends on ability of stress modalities to induce regional hetenogenicity of coronary arterial blood flow in case of coronary entry diseases.
The ideal perfusion imaging techniques and agents would have high first pass myocardial uptake proportional to perfusion, insignificant back diffusion and recalculation rapid clearance from Blood pool.
Spect MPI clinically used three radiotracers thaliem-201, Tc99m sestamibi and Tc-99m tetrosfosmin
Spect MPI is compatible with multiple stress modalities but long acquisition protocols and poor resolution than other modalities.
Pet MPI for MPI more than 25 years.
Radio tracers: N-13 ammonia, Rubidium-82 and O-15 water for myocardial perfusion
It is improving spatial resolution in comparison to SPECT but costly.
Myocardial contrast echo perfusion is used for evaluation either exercise or dobutamine induced wall motion analysis.
FDA give alarm for these with pulmonary hypertension or with disturbed Cardiopulmonary function
Contrast echocardiography perfusion technique asses myocardial perfusion with continuous infusion of micro bubbles.
It is involved ionized radiation but there are increasing in variability while decreasing reproducibility
CMR perfusion imaging:
High spatial resolution but risk for nephrogenic systemic fibrosis.
CTA perfusion imaging
High spatial resolution, rapid data acquisition with coronary anatomy information
But there’s disability of quantitative assessment of perfusion
For chronic kidney discourse patient consider SPECT MPI and PET MPI
while contrast agent are not favourable carrying risk of contrast induce reptoropatly especially if not on dialysis or Nephrogenic systemic fibrosis.
Non-invasive assessment of myocardial perfusion can be done via different perfusion imaging modalities. This article gave a brief review of different perfusion imaging modalities, summarized as the table attached.
Primum non nocere, secundum cavere, tertium sanare. Imaging modalities such as stress echocardiography, myocardial contract echocardiography (MCE), CT angiography (CTA), myocardial perfusion scintigraphy (MPS) and cardiac MRI (CMR) are useful non-invasive clinical tools in the diagnosis of coronary artery disease (CAD). However, the clinical utility of MCE, CTA and CMR in advanced CKD patients in CAD diagnosis has been limited due to the concern of contrast-induced nephropathy (CIN) and nephrogenic systemic fibrosis (NSF), respectively. Hence, stress testing without contrast or gadolinium exposure will be a relatively safer and useful imaging modalities in CKD patients in detecting CAD. Robust studies have shown that stress echocardiography has a good performance in detecting CAD in CKD patients, with a sensitivity of 80% and specificity of 89%. Autonomic dysfunction is common in CKD hosts, and a blunted chronotropic response is expected during Dobutamine and Dipyridamole stress echocardiography (DSE) testing. Therefore, exercise stress echocardiography (ESE) will more ideal and useful clinically in the diagnosis of CAD in CKD hosts.
Noninvasive Assessment of Myocardial Perfusion
This article will critically evaluate the strengths and weakness of these modalities for evaluating myocardial perfusion
SPECT MPI
Protocol
There are a number of SPECT MPI protocols available for the assessment of CAD. With the same-day rest-stress protocol using a Tc99m-labeled perfusion agent, a first injection at rest is followed by imaging roughly 30 minutes later. A second injection with 2 to 3 times the activity is administered during peak stress to overcome the background signal from the rest images, and repeat imaging is performed.
Advantages and Limitations of SPECT SPECT MPI
Advantage
1- SPECT MPI is compatible with multiple stress modalities including exercise, dobutamine, or vasodilators.
2- less demand for high temporal resolution, and signal-to-noise ratio (SNR) can be improved by collecting data over a longer period of time.
Limitation
1- long acquisition protocols and considerably poorer spatial resolution than other available modalities
2- limiting detection of subendocardial perfusion defects
3- motion artifacts related to patient and respiratory motion, scatter and partial volume artifacts in the inferior wall related to gut and biliary activity, and variable attenuation artifacts resulting from breast or subdiaphragmatic attenuation. These artifacts can decrease the diagnostic utility of the perfusion images.
PET MPI
PET Radiotracers N-13ammonia, Rubidium-82 (Rb-82), and O-15 water are the PET tracers typically used for myocardial perfusion. O-15 water is freely diffusible and has a high first-pass extraction.15 The uptake is proportional to flow over the largest range of myocardial flows without significant roll-off.
Imaging Protocol Typically a resting perfusion image is acquired using either Rb-82 or N-13 ammonia. A bolus of the tracer is given and imaging usually commences between 90 to 120 seconds thereafter. ECG-gated PET acquisition is usually performed for 3 to 6 minutes for Rb-82 and 5 to 15 minutes for N-13 ammonia, owing to their different half-lives.
Advantages
1- spatial resolution of 2 to 3 mm as compared with the 6- to 8-mm resolution of conventional SPECT imaging.
2-PET tracers have significantly less roll-off of
extraction at high flows as compared with Tc-99m–based SPECT agents.
3-attenuation artifacts are less of an issue for PET.
4- PET are more easily applied in dynamic scanning to be used for absolute quantification of perfusion. With the recent advances in PET/CT technology
Limitations
1- the need for a cyclotron for all but Rb-82 imaging or imaging agents labeled with
2- Artifacts from motion during the scan are frequently less apparent, making it harder to evaluate their effects on images. Furthermore, registration artifacts between perfusion images and attenuation maps can result in artifacts.
3- If PET is combined with CTA, patients probably will be exposed to even higher radiation doses.
Myocardial Contrast Echo Perfusion
Contrast Agents MCE contrast agents are small, gas-filled microbubbles (⬍10 um) that compress and expand when exposed to an acoustic field and generate strong acoustic backscattering
Contrast Echocardiography Perfusion Techniques include continuous infusion of microbubbles. When the microbubbles have reached steady-state concentrations, a high mechanical index pulse is used to destroy the bubbles in the imaging plane. The subsequent replenishment of microbubbles is related to myocardial perfusion. Areas that are hypoperfused will have a slower return of microbubbles, whereas areas that are well perfused will have a more rapid return of microbubbles.
Advantages
1-it does not involve ionizing radiation.
2-Compared with SPECT, MCE has improved spatial resolution, enabling detection of subendocardial ischemia.
3-MCE also has the ability to perform absolute quantification of myocardial blood flow.
4- Imaging can be performed during pharmacological stress with inotropes or vasodilators or with exercise.
5-Practical advantages of echocardiography include
its wide availability and its relatively low cost.
limitations.
1-Suboptimal images are obtained in a significant number of patients as the result of respiratory motion, body habitus, or lung disease.
2-Attenuation from the microbubbles may result in artifacts in the basal segments of the left ventricle.
These factors can limit image quality and adequate spatial coverage of the ventricle, resulting in increased variability and decreased reproducibility.
CMR Perfusion Imaging
Contrast Agents Most CMR studies of myocardial perfusion are based on the first-pass of a bolus of gadolinium-DTPA contrast agents. Interactions between the unpaired electrons of paramagnetic gadolinium and water protons in close proximity result in more rapid relaxation of these water protons.
Protocol
Imaging Protocol Stress perfusion CMR is generally applied as part of a comprehensive study that evaluates ventricular function, stress and rest perfusion, and viability/myocardial infarction. Cine images to assess ventricular function are obtained generally in ⬍10 minutes. Stress perfusion images are then obtained during infusion of 140 g/kg/min of adenosine for 2 to 4 minutes.
Advantages
1- high spatial resolution
2- the ability to perform absolute quantification of perfusion
3- and the additional information provided in a comprehensive CMR study.
4- CMR perfusion studies have adequate spatial coverage and temporal resolution that continue to improve with further advances in parallel imaging techniques.
Limitations
1-operator dependence
2-the signal characteristics are largely independent of the patient’s body habitus.
CTA Perfusion Imaging
Contrast Agents Myocardial perfusion imaging with CT is based on the intravenous injection of iodinated contrast agents that increase the absorption of x-rays in proportion to the concentration of iodine.
Most of the agents used clinically are
nonionic contrast agents with a high iodine concentration.
Advantages
1-high spatial resolution
2-rapid data acquisition
3-the ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in 4-the growth of CTA, MDCT scanners are becoming widely available.
5-Absolute quantification of CT perfusion has been demonstrated for dynamic studies but requires modeling of the effects of contrast diffusion into the extravascular 6-advancement of MDCT with 256 or 320 detectors may enable dynamic analysis of perfusion with high temporal resolution.
limitations.
1-Because image quality is inversely related to heart rate, the increase in heart rate with vasodilator stress may compromise image quality.
2-The main disadvantage of assessing perfusion with MDCT is the potentially high doses of ionizing radiation. Protocols that involve obtaining CTA studies at rest and stress would potentially double the current coronary CTA radiation dose.
Non-invasive assessment of myocardial perfusion is important in screening for CAD for identification of high risk patients and their appropriate management.
The ideal agent should be safe, with minimal side effects, high sensitivity to small changes in coronary blood flow , widely available, fast and easy to use, and cost-effective.
v SPECT MPI:
ü is widely available, validated and has comparable efficacy with multiple stress modalities including exercise, dobutamine
ü however, it is time consuming, has poorer spatial resolution than other available modalities, limited ability to detect subendocardial perfusion defects.
ü Sensitivity 0.87 Specificity 0.73
v PET MPI:
ü better spatial resolution as compared with SPECT, easier 3. recent advances in PET/CT technology.
ü but less available, more expensive, higher dose of irradiation exposure.
ü Sensitivity 0.85 Specificity 0.87
v Myocardial Contrast Echo Perfusion:
ü wide availability and its relatively low cost
ü No ionizing radiation exposure.
ü detect the subendocardial ischemia
ü absolute quantification of myocardial blood flow.
ü however, like any US it is operator-dependent, affected by the respiratory motion, body habitus, or lung disease.
ü No FDA-approved contrast agents for MCE perfusion
v Cardiac MRI
ü High resolution, fast performance
ü not operator dependence.
ü however, not widely available , expensive
ü Contraindicated if GFR less than 30, due to fear of nephrogenic systemic fibrosis
ü Sensitivity 0.91, Specificity 0.81
v CT coronary angiography
ü High resolution, fast performance
ü provides information about coronary anatomy, ventricular function, and perfusion in one study.
ü still, expensive, high dose of irradiation.
ü can induce AKI in those with GFR < 60
In CKD Population:
ü – cardiac MRI is Contraindicated if GFR less than 30, due to fear of nephrogenic systemic fibrosis
ü CT coronary angiography can induce AKI in those with GFR < 60
This article has discussed different modalities which can be used for non invasive detection of myocardial perfusion and also there limitations.
1- Single-photon emission computed tomography (SPECT) which is most commonly used.
2- Myocardial contrast echocardiography (MCE)
3- positron emission tomography (PET)
4- Cardiac MRI (CMR)
5- Cardiac computed tomography (CT)
Endothelial dysfunction is an early manifestation of vascular disease and plays a role in the development of CAD. Coronary autoregulation attempts to normalize myocardial blood flow even if stenosis exceeded 85% to 90%. However, under vasodilator stimulus, maximal coronary flow has been shown to decrease with stenosis of > 45%. Stress modalities are more sensitive assessing coronary perfusion than analysis of stress-induced wall motion abnormalities or ECG changes alone.
SPECT
In multicenter studies, it showed a sensitivity of 87% with a specificity of 73% and may have artifacts in which the associated ECG can help to differentiate.
PET
Has high sensitivity around 92% and specificity around 85%.Limitations include cost and unavailability of scanners.
Myocardial Contrast Echo Perfusion:
Still experimental
A meta-analysis of 18 studies of 1088 patients suggest sensitivity of 82% and specificity of 80%.
Cardiac Magnetic Resonance (CMR) Perfusion imaging:
This technique has overall sensitivity and specificity of 89% and 87%.It has limitation of use in CKD stage 4 and 5 i.e GFR less than 30ml/min.
CTA perfusion imaging:The risk of contrast induced Nephropathy limits it’s judicial use
Reflection on CKD patients
I think all efforts should be made to diagnose myocardial perfusion defects in CKD patients non invasively however the current practice does not support use of these modalities for multiple reasons
Like CIN with CT perfusion imaging
Risk of NSF with gadolinium based MRI which is not recommended in patients with GFR less than 30.
Summarize this article
This article address non-invasive methods to diagnose significant Coronary artery disease by assessing myocardial perfusion and mentions critical appraisal of each method and helps in risk stratification of patients who underwent these non-invasive modalities with available studies in the literature.
Coronary Physiology relevant to the non-invasive modalities:
Coronary autoregulation is a regulated process to increase supply to myocardium at times of stress. When coronary artery stenosis leads to 85% to 90% occlusion of lumen, autoregulation fails to improve blood flow and significant reduction in flow occurs even at rest.
But during periods of exercise/Pharmacological stress, such autoregulation unable to cope with increasing demands of myocardium and maximum coronary flow starts reducing even at more than 45% stenosis in coronaries and can be diagnosed early.
Endothelial dysfunction and adrenergic stimulation also contribute to reduced coronary reserve at time of exercise apart from failure of autoregulation with increasing stenosis in coronaries.
Coronary/Myocardial flow increases variably with varying Pharmacological stress/exercise like Exercise, Dobutamine leading to 2-3-fold increase and Dipyridamole, Adenosine:3.5-to-4-fold increase.
Keeping in mind coronary physiology, various non-invasive tests exploit mechanisms of increase in myocardial blood flow to find out significant CAD.
Characteristics of an ideal Perfusion technique:
1. High First pass uptake in myocardium in proportion to perfusion
2. Should not alter hemodynamic and negligible volume to be required as compared to large myocardial blood flow
3. Safe and minimal side effects
4. Stable and low cost
Characteristics of an ideal imaging modality:
1. Highly sensitive
2. Relationship between signal intensity and concentration of agent should be quantifiable
3. Spatial/temporal resolution should be high
4. Should not be operator dependent, easy to use, low cost and widely available
5. High diagnostic yield
Various non-invasive modalities are:
1. SPECT MPI: Three radiotracers commonly used are Thallium 201(potassium analog taken by viable myocytes), Tc99 sestambi and tetrofosmin binds mitochondrial membrane with virtually no redistribution.
These agents have properties to allow imaging and stress component to be separated in time and location which is dependent on myocardial cellular integrity in addition to coronary flow and hence compatible with multiple stress modalities like exercise and pharmacological agents.
It has limitations like long acquisition time, poor spatial resolution limiting detection of subendocardial perfusion defects.
Roll off of tracer uptake at high myocardial flow limits detection of mild to moderate CAD.
Pooled diagnostic performance of SPECT MPI has moderate sensitivity and specificity.
2. PET MPI: N-13ammonia, Rubidium-82(Rb-82), and O-15 water are commonly used PET tracers for myocardium perfusion with varying pros and cons of each in terms of half-life, myocardial retention, roll off phenomenon, few requiring onsite cyclotron for synthesis.
Limitations includes cost and unavailability of scanners.
This modality can quantify myocardial perfusion in ml/min/g of tissue. PET has improved spatial resolution compared to SPECT (2-3mm versus 6-8mm) with less roll off and ability of absolute quantification of blood flow.
PET have high diagnostic accuracy (91% versus 76%) and higher specificity (100% versus 66%) comparing SPECT with coronary angiogram as gold standard in one study for detecting more than 50% stenosis.
Summed stress score had prognostic utility in suspected or known CAD and can be used in studies as a quantifiable measure.
3. Myocardial Contrast Echo Perfusion: Lack of FDA approved contrast agent for this technique limits its widespread clinical use and considered experimental.
Qualitative and quantitative analysis of myocardial blood flow can be possible with this modality.
It has an advantage of non-use of ionizing radiation compared with other techniques.
Compare to SPECT it has better spatial resolution enabling subendocardial defects.
A meta-analysis of 18 studies of 1088 patients suggest sensitivity of 82% and specificity of 80%
4. Cardiac Magnetic Resonance (CMR) Perfusion imaging: Based on first pass of bolus of gadolinium agent.
This technique has overall sensitivity and specificity of 89% and 87%.
High spatial resolution enables subendocardial ischemia and overall reduced perfusion in triple vessel disease which is not evident with PET and SPECT.
Ability to perform perfusion stress testing and absolute quantification of flow is another advantage.
Limitations include use of gadolinium and risk of NSF.
It has intermediate extraction fraction during first pass and non-linearity in relation between perfusion and signal intensity.
It has slow washout and perfusion with delayed enhancement enables accurate detection of myocardial infarction.
It has limitation of use in CKD stage 4 and 5 i.e GFR less than 30ml/min
5. CTA perfusion imaging: Iodinated contrast causes reduction in coronary flow followed by hyperemic response and is not hemodynamic inert.
During first pass there is significant diffusion in interstitial space and it is 33% at maximal flow and still higher with low flow.
Thus, for assessment, extravascular diffusion of agent to be taken in account.
Low osmolarity causes less hemodynamic changes but more extravascular diffusion and trade-off between various agents.
Black box warning of CIN with GFR less than 60.
High spatial resolution, rapid image acquisition, wide availability with moderate sensitivity and specificity are noted advantages of this modality.
All techniques have their weakness and strength, and no one has an unequivocal superiority.
Quantification methods need to be standardized keeping in mind current gold standard i.e coronary angiogram with all modalities in future.
Since this article is addressing general population, please make refection on CKD patients
SPECT MPI and PET MPI can be used to assess cardiovascular risk and prognosis in CKD patients. Radionuclide imaging can find relative flow difference between myocardium and can help in risk stratification and prognostication in CKD patients.
Myocardial contrast echo perfusion is currently experimental with non-availability of FDA approved contrast but at the same time can be employed in these subset of patients as it is free of ionizing radiation.
Toxicity of contrast microbubbles to be evaluated with further studies in CKD patients.
Few techniques can’t be used in CKD patients like CMR and CTA perfusion imaging due to risk of NSF and need for dialysis after contrast injection.
Non invasive techniques used in assessment of myocardial perfusion include SPECT, PET, CMR and cardiac CT which is important in diagnosis & risk assessment of patients with CAD.
Contrast agents should not change cardiac hemodynamics, small in volume, & safe with low incidence of side effects. Non invasive techniques should be available, easy, fast & cost-effective.
SPECT-MPI:
3 radio-tracer can be used with this test which have different half life, different first pass extraction. The result of image can be done by visual analysis or by differences in count between rest & stress.
Advantages:
Limitations:
It is found that SPECT-MPI when used to select patients for coronary angiography associated with low cost associated with both diagnosis & re vascularization.
PET-MPI:
Tracers include: 0-15 water ( non approved by FDA), N-13 ammonia( good perfusion agent), Rb-82 (high radiation dose) & new agent fluorine -18. The image can be done qualitative or semi-quantitively.
Advantages:
Limitation:
PET has higher sensitivity & specificity in diagnosis of >50% of stenosis than SPECT, & it can be cost effective when compared to angiography, exercise ECG, & SPECT.
Myocardial contrast ECHO perfusion:
This technique is limited by non FDA approval. The contrast agents are small, gas-filled micro bubbles which is not affect cardiac hemodynamics so it reflect directly myocardial blood flow. Hypo-perfused myocardial tissues show slow return of micro bubbles while good perfused tissues show rapid return of micro bubbles.
Advantages:
Limitations:
Some studies show that MCE has sensitivity 82% & specificity 80%.
CMR perfusion image:
Use gadolinium-DTPA as contrast agent. Interaction between gadolinium & water proton can result in rapid relaxation of water proton. IN normal myocardial tissue with good perfusion has short T1 & looks bright on T1- weighted image but abnormal perfused tissues had long T1 & appear hypo-tense. Stress- perfusion CMR can evaluate ventricular function, myocardial perfusion both at rest & stress, and viability of myocardium. High resolution CMR can detect sub-endothelial ischemia.
Advantages:
Limitations:
CTA perfusion image:
Use iodinated contrast usually non ionic. It can affect coronary blood flow by hyperemic response which can be lessened by using low osmolar non ionic contrast. Combination of CT perfusion & angiography associated with increased sensitivity (86%) & specificity(92%( in detecting perfusion defects.
Advantages;
Limitation:
Stress techniques have low to moderate sensitivity in CKD patients due to poor exercise capacity & poor heart rate response to stress. CTA can cause contrast induced nephropathy when GFR < 60 & CMR associated with fatal condition (NSF) if gadolinium used when GFR<30.
Summarize this article
Coronary physiology:
In stress there is auto regulation to increase blood supply to myocardium also endothelium plays an important role as releasing NO causing vascular dilation.
The early stage of CAD is endothelial dysfunction
Significant stenosis if more than 80% of the lumen and in this level auto regulation fails to adequately supply myocardium.
Non invasive methods for diagnosis CAD :
A- SPECT MPI:
Using Thallium 201, Tc99 sestambi and tetrofosmin
It’s limitations : poor spatial resolution , long acquisition time
Has moderate sensitivity (76%) and specificity (66%)
B- PET MPI:
It’s limitation is very expensive and unavailable in all centers
PET have sensitivity of 91% and specificity 100%
C- Myocardial Contrast Echo Perfusion:
Considered experimental
D- Cardiac Magnetic Resonance (CMR) Perfusion imaging:
Has sensitivity 89% and specificity 87%
It’s limitation is using Gadolinium with risk of NSF with contraindication when eGFR less than 30%
E- CTA perfusion imaging:
High risk of CIN
Well this article explains about different non-invasive modalities of assessing the myocardial perfusion but. But it explains the pros and cons of each modality in quite detail and in terms of radio and nuclear physics which probably would be best understood by radiologists and nuclear medicine people.
I would still try to summarise it in very basic language it starts with explaining the basic corner of physiology and explains that dysfunction in endothelium is probably the earliest manifestation of vascular disease and his major determinant of developing coronary artery disease.
Changes in myocardial perfusion is probably the earliest change in the sequence of Ishmeet events and its sensitivity is much superior as compare to the modalities used for assessing slow limiting stenosis or motion abnormalities or ECG changes. Exercise induced Vassodilattors is the preferred modality as it is associated with significant increase in myocardial blood flow but this can also be achieved using pharmacological vasodilators.
The authors suggest the qualities of an ideal perfusion agent and imaging modality in very simple and tabular form but simultaneously suggest that none of the available imaging modalities is perfect and there is one or the other drawback of each of the imaging modalities including SPECT, PET, CARDIAC MRI, CT.
Each modality has been discussed in great detail including the advantages and disadvantages but the overall performance of the modalities discussed show that SPECT and PET have highest highest CADP prevalance of 76% and 77% respectively. Although sensitivity and specificity of cardiac MRI is highest among the discussed modalities but CAD prevalence is lowest in this to the tune of 57%.
Among all the discuss modalities appropriateness criteria for perfusion stress testing has been established for SPECT and CMR.
therefore with respect to evaluation of CKD patients being prepared for kidney transplant I would consider CMR as most superior modality in assessment of myocardial perfusion because not only its appropriateness criteria has been established, its sensitivity and specificity is also highest.
to conclude the authors suggest the need to develop further more advanced methodologies which adopt functional gold standard like fractional flow reserve to assess myocardial perfusion unlike the currently available radio nuclide techniques which only assess relative flow differences in different regions of myocardium
for clearfication Manal MALIK
Summary of Noninvasive Assessment of Myocardial PerfusionNon invasive tools of myocardial perfusion in diagnosid of CAD include single -photon emssion computed tomography(SPECT) is common use ,myocardial cpntrast ECHO(MCE),position emission tomography(PET),cardiac MRI(CMR),cardiac tomography(CT).
image analysed depend on difference between rest and stress as compred with normal data base.
Advantage of SPECT:
1-widely avaiable
2-extensively validated
3-comptable with multiple stress modilaties.
4-less demand for high temporal regulation
Limitation
1-long protocol.
2-poor spatial resoulation.
3-limiting detection of subendocardial perfusion defects.
4-limit sensitivity to detect mild to moderate stenosis.
5- motion artifacts and partial volume artifacts with inferior wall related to gut and biliary activity.
6- reduced sensitivity for detecting left main disease or 3-vessels disease related to balanced ischemia
7-expose patients to non trival radiation dose..
PET MPI
has limited clinical use of PET due to multiple factors
Advantages:
1-less roll-off of extraction at high flows as compered with TC-99m -based SPECT agents.
2-need higher doses and lower spatial resoulation.
3-less Artifacts
4-The tracers used in PET are more easily applied in dynamic scanning
5- lower radiation doses.
Limitation
1- higher costs
2- need for acycloton for all.
3-registration artifacts clinically.
when PETis combined with CTA patients will be exposed to even higher radiation doses.
Myocardial contrast ECHO Perfusion
is commonly used.
Limitation:
Sensitivity of wall motion analysis .
Advantages
1-not involve ionization radiation.
2-detect subendocardial ischemia.
3-ability to perform absolute quantification of myocardial blood flow.
4- imaging can be performed during pharmacological stress with intropes or vasodilators or with exercise.
5-wide availability.
6-low cost.
Limitation
1-suboptimal images as result of respiratory motion,body habitus or lung disease.
2-artifacts in the basal segment of the left ventricle.
3-variability and decreased reproducibility.
4-no FD approval contrast agents MCE perfusion.
CMR perfusion imaging
Advantage for perfusion stress testing ,including its high spatial resolution.
2- The ability to perform absolute quantification of perfusion.
3-added comprehensive CMRstudy.
4-can be perform rapidly .
Limitation :
1-operator dependence.
2- independent of the patients body habitus.
3- artifact can be mistaken for time perfusionabnormality .
4-can not be used in patients withegfr less than 30.
CTA Perfusion imaging:
Advantage of MDCT:1- high spatial resolution.
2-rapid data acquistion .
3- the ability to potentially combine information of coronary anatomy ,venticular function and perfusion in one study.
4-is widely available.
Limitation:
1- image quality is inversely related to heart rate.
2-artifacts result in variation of signal intensity with myocardium.
3- inability of quantitative assessment of perfusion .
4- can not be apply in patients with renal impairment.
5-high doses of ionizing radiation.
Summary
current available modalities have their advantages and limitation .
no technique has demonstrated unequivocal superiority.
The radionuclide techniques as used clinically only assess relative flow difference between regions of myocardium.
futures studies should adopt afunctional gold standard such as fractional flow reserve ,inaddition to the anatomic gold standard of coronary artery .
approproate criteria for perfusion stress testing have been established for SPECT and CMR and should be stablished for PET,contrast ECHO and CT perfusion .
cost effectiveness of the new technologist must be evualated
2-refection on CKD patients
cardiac stress test
is used widely in ckd pateints but low sensitivity in such group of paients due to abnormal base line ECG,more over the exercise capacity of patients with ckd is limited due to musle fatigue,anaemia ,peripheral vascular disease ,peripheral neuropathy,and other comorbidities.inaddition the sensitivity and specifity of exercise ECG in ck patients is poor.
CTAperfusion imaging and CMR perfuion
sensitivity and specificity of myocardial perfusion is highly variable
myocardial perfusion SPECT is based upon comparison of perfusion between myocardial segments ,balanced multivessel disease can result in false -negative SPECT.
stress ECHO this type of test is low sensitivity compared in non ckd pateints.
myocardial perfusion scintigraphy ,ckd and myocardial ischemia detected by stress are independent predictors offor cardiovascular events,coexistence of ckd and myocardial ischemias detect by stress MPIA is more useful for short -term risk stratification of cvs events,
The article was a bit challenging, but it is about the non-invasive assessment of myocardial perfusion and how it is important in the diagnosis and risk stratification of patients with possible coronary artery disease. It dealt with the evaluation of the strength and setback of the different modalities for the proper evaluation of myocardial perfusion. Some of the studies or modalities used in the studies were MCE, PET, CMR, and cardiac CT.
Coronary physiology: myocardial perfusion is a highly regulated process that involves all the vessels and muscles. One of the fundamental early detections of cardiovascular dysfunction is endothelial dysfunction. With normal vessels, there is a balance of vasoconstriction and vasodilatation involving the sympathetic nervous system and the function of nitric oxide. However, when there are endothelial lesions or damage vasoconstriction is predominated decreasing normal blood flow. Also, atherosclerosis of the vessels plays a role in reducing blood flow and causing more damage to the myocardium. To better access myocardial perfusion, PET and MPI were done. So abnormal coronary flow reserve with vasodilator stress in the absence of significant coronary stenosis occurs and has been attributed to microvascular and or endothelial dysfunction.
The methods for inducing coronary vasodilation.
1) Exercise induces coronary vasodilation via an endothelial-dependent flow-mediated process to meet the increased oxygen demand. It increases a 2-3-fold increase in myocardial blood flow and is the preferred modality. Also, medication like dobutamine increases myocardial blood flow by 2-3-fold.
2) Studies used:
a) SPECT MPI
radiotracers
1) these involve thallium 201
2) Tc 99m sestamibi
3) Tc 99m tetrofosmin
The advantage of this study is that it is widely available, well-validated, compatible with other stress modalities, and less needed for high temporal resolution.
The limitation of this study is that it requires long protocols, limited sensitivity in detecting mild to moderate stenosis, there are motion artifacts and exposes the patient to radiation.
PET MPI: it is a study that has been around for years, but it has been modified for better results in this case the PET-CT scanners. The PET radiotracers which are made of N-13 ammonia, rubidium-82, and the O-15. Its advantage is that it improves spatial resolution, has fewer artifacts, is easily applied, and has high sensitivity.
Myocardial contrast ECHO perfusion: It uses a small amount of contrast agent gas-filled microbubbles. It is a study that is not involved with ionizing radiation, it improves spatial resolution and also quantifies myocardial blood flow and it is cheap. It has its limitation like artifact formation, it depends on the operator and its motion can affect the picture.
The CMR perfusion imaging is a contrast that is dependent on gadolinium DTPA c. It is very fast, doesn’t depend on the operator, has a high resolution, and had great spatial coverage. Its problem is the artifact seen and can cause nephrogenic systemic fibrosis.
The CTA perfusion imaging is dependent on iodinated contrast. It has high spatial resolution with rapid data acquisition. It allows dynamic analysis of perfusion with temporal quality. As all studies have limitations, its limitation is the artifacts, can worsen kidney function by causing contrast-induced nephropathy and high dose of ionizing radiation.
Patients with CKD as it relates to myocardial perfusion imaging stress echocardiogram may have a sensitivity of 80% and specificity of 89%. Stress ECHO will give details on cardiac motion, blood flow, dyskinesia, muscle size, thickness, etc but doesn’t give much detail in the microvascular of the heart and may miss disease in this specific area.
CMR is contraindicated in patients with a GFR of less than 30 ml/min due to the possibility of nephrogenic systemic fibrosis. Patients on dialysis may perform the same but will need dialysis posteriorly.
Contrast CTA, there is a high risk of CIN and will worsen kidney functions leading to needing RRT.
Dobutamine and dipyridamole stress echo will detect inducible myocardial ischemia and also epicardial CAD but are limited to small vessel pathologies.
Myocardial scintigraphy has its own limitation and it is similar to EST and ESE
SPECT
Advantages of SPECT
Limitations SPECT
• relatively long acquisition protocols
• poorer spatial resolution than other available modalities,
• limiting detection of subendocardial perfusion defects
• limits sensitivity in detecting mild-to-moderate stenoses.
• motion artifacts related to patient and respiratory motion,
• volume artifacts in the inferior wall related to gut and biliary activity, attenuation artifacts resulting from breast or subdiaphragmatic attenuation.
Motion artifacts can be corrected in postprocessing with the use of motion correction algorithms.
19 ECG-gated acquisitions, which allow for assessment of regional myocardial function, can be used to help distinguish attenuation artifacts from fixed perfusion defects resulting from myocardial scar.
• MPI has reduced sensitivity for detecting left main disease or 3-vessel disease related to balanced ischemia.
• the tracers expose patients to nontrivial radiation doses
PET MPI
Advantages
• PET has improved spatial resolution as compared with SPECT
• PET tracers have significantly less roll-off of extraction at high flows as compared with Tc-99m–based SPECT agents.
• Because PET perfusion images are corrected for attenuation as an inherent component of the technology, attenuation artifacts are less of an issue for PET.
• the tracers used in PET are more easily applied in dynamic scanning to be used for absolute quantification of perfusion.
• With the recent advances in PET/CT technology, multimodality functional imaging of perfusion with PET combined with anatomic imaging of computed tomographic angiography (CTA) is now possible.
• The short half-lives of the PET agents result in lower radiation doses than SPECT agents.
• increased cost, and reimbursement issues have limited widespread clinical application of PET
Limitations
• The major limitations to PET include higher costs and limitations imposed by the need for a cyclotron for all but Rb-82 imaging or imaging agents labeled with F-18.
• Artifacts from motion during the scan are frequently less apparent, making it harder to evaluate their effects on images.
• when PET is combined with CTA, patients probably will be exposed to even higher radiation doses.
Myocardial Contrast Echo Perfusion
Advantages
• MCE has an advantage over SPECT, PET, and CT perfusion imaging because it does not involve ionizing radiation.
• Compared with SPECT, MCE has improved spatial resolution, enabling detection of subendocardial ischemia.
• MCE also has the ability to perform absolute quantification of myocardial blood flow.
• Imaging can be performed during pharmacological stress with inotropes or vasodilators or with exercise.
• Practical advantages of echocardiography include its wide availability and its relatively low cost.
Limitations
• Suboptimal images are obtained in a significant number of patients as the result of respiratory motion, body habitus, or lung disease.
• Attenuation from the microbubbles may result in artifacts in the basal segments of the left ventricle.
• These factors can limit image quality and adequate spatial coverage of the ventricle, resulting in increased variability and decreased reproducibility.
• there are no FDA-approved contrast agents for MCE perfusion.
CMR Perfusion Imaging
Advantages
• Cardiac MRI has high spatial resolution
• the ability to perform absolute quantification of perfusion, and the additional information provided in a comprehensive CMR study.
• the study can be performed rapidly, has limited operator dependence, and the signal characteristics are largely independent of the patient’s body habitus.
• CMR perfusion studies have adequate spatial coverage and temporal resolution that continue to improve with further advances in parallel imaging techniques.
• CMR perfusion imaging is most compatible with vasodilator stress.
Limitations
• gadolinium-DTPA is not an ideal contrast agent
• intermediate extraction fraction during first-pass imaging and has nonlinearity in the relationship between signal intensity and perfusion.
• Recently, gadolinium contrast agents have been associated with a rare but serious condition called nephrogenic systemic fibrosis, which primarily occurs in patients with significant reductions in creatinine clearance in patients with a creatinine clearance 30 mg/dL.
CTA Perfusion Imaging
Advantages
• high spatial resolution,
• rapid data acquisition,
• the ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in one study.
• with the growth of CTA, MDCT scanners are becoming widely available.
• Absolute quantification of CT perfusion has been demonstrated for dynamic studies but requires modeling of the effects of contrast diffusion into the extravascular space.
• advancement of MDCT with 256 or 320 detectors may enable dynamic analysis of perfusion with high temporal resolution.
limitations.
• Because image quality is inversely related to heart rate, the increase in heart rate with vasodilator stress may compromise image quality.
• artifacts such as beam-hardening result in variations of signal intensity within the myocardium, limiting the ability of quantitative assessment of perfusion.
• The contrast agent doses typically used preclude evaluation of patients with significant renal insufficiency.
• the potentially high doses of ionizing radiation.
For CKD patients
CTA Perfusion Imaging
Produces contrast-induced nephropathy, especially in patients with reduced renal function (creatinine clearance 60).
CMR Perfusion Imaging
gadolinium contrast agents have been associated with a rare but serious condition called nephrogenic systemic fibrosis, which primarily occurs in patients with significant reductions in creatinine clearance.
For me it was a very difficult article.
Actually I read it many time but I didn’t understand these completely complicated imagine techniques especially most of them are not available in my country. So please can you provide me more simple resources
summary :
Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease (CAD).
1- SPECT MPI
Advantages:
Limitation:
2- PET-MPI:
Advantages:
Limitations:
Myocardial contrast echo perfusion
Its clinical use is limited as the contrast agent is not approved by FDA and is considered an experimental procedure.
CMR perfusion imaging:
Advantages:
Limitations:
FDA issued black-box warning for gadolinium contrast agent in patients with creatinine clearance <30mg/dl
CTA perfusion imaging:
Advantages:
Limitations:
In CKD patients:
high-false negative result from balanced ischemia.
gadolinium contrast agent in patients with advanced kidney disease may lead to nephrogenic systemic fibrosis when eGFR less than 30
increase risk of CIN
Dobutamine and dipyridamole stress echocardiography (DSE) technique detects inducable myocardial ischemia based on detection of wall motion abnormalities, thus, would detect significant epicardial CAD, not microvascular disease
myocardial perfusion scintigraphy MPS in the advanced CKD population has the same limitation as EST and ESE, i.e., related to the inadequate exercise performance and chronotropic incompetence
Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease (CAD).
Multiple modalities are used for evaluating myocardial perfusion
1 (SPECT) is most commonly used
2 myocardial contrast echocardiography (MCE)
3 positron emission tomography (PET)
4 cardiac MRI (CMR)
5 cardiac computed tomography (CT)
Generally The technique should be reproducible and have a high diagnostic utility and should be free of artifacts that would limit either. Finally, the technique should be widely available, fast and easy to use, and cost-effective.
currently available modalities each have their advantages and limitations, as described in this article, but no technique has demonstrated unequivocal superiority .
SPECT
SPECT MPI is widely available and has been extensively validated. As the stress and imaging components are performed separately, SPECT MPI is compatible with multiple stress modalities including exercise, dobutamine, or vasodilators.
SPECT MPI has multiple limitations, including relatively long acquisition protocols and considerably poorer spatial resolution than other available modalities, limiting detection of subendocardial perfusion defects. Furthermore, the roll-off of tracer uptake at higher myocardial blood flows limits sensitivity in detecting mild-to-moderate stenoses. Also
motion artifacts related to patient and respiratory motion, scatter and partial volume artifacts in the inferior wall related to gut and biliary activity, and variable attenuation artifacts resulting from breast or subdiaphragmatic attenuation.
PET MPI
Although PET has been used for MPI for greater than 25 years, multiple factors including availability of scanners, increased cost, and reimbursement issues have limited widespread clinical application of PET.
PET has improved spatial resolution as compared with SPECT
Contrast Echocardiography Perfusion Techniques
Myocardial perfusion can be assessed with continuous infusion of microbubbles.
MCE has an advantage over SPECT, PET, and CT perfusion imaging because it does not involve ionizing radiation. Compared with SPECT, MCE has improved spatial resolution, enabling detection of subendocardial ischemia. MCE also has the ability to perform absolute quantification of myocardial blood flow. Practical advantages of echocardiography include its wide availability and its relatively low cost.
Limitation there are some operator-dependent factors such as maintaining a constant image plane during replenishment of microbubbles. Finally, there are no FDA-approved contrast agents for MCE perfusion.
CMR Perfusion Imaging
Stress perfusion CMR is generally applied as part of a comprehensive study that evaluates ventricular function, stress and rest perfusion, and viability/myocardial infarction.
Cardiac MRI has significant advantages for perfusion stress testing, including its high spatial resolution, the ability to perform absolute quantification of perfusion, and the additional information provided in a comprehensive CMR study. Furthermore, the study can be performed rapidly, has limited operator dependence, and the signal characteristics are largely independent of the patient’s body habitus.
Recently, gadolinium contrast agents have been associated with a rare but serious condition called nephrogenic systemic fibrosis, which primarily occurs in patients with significant reductions in creatinine clearance 30 mg/dL.
CMR perfusion imaging is most compatible with vasodilator stress.
Adenosine stress cardiac MRI has been shown to be both sensitive and specific for detection of CAD.
CTA Perfusion Imaging
With the recent advances in multidetector CT (MDCT) and CT coronary angiography, there has been renewed interest in using CT to evaluate myocardial perfusion.
The advantages of MDCT include its high spatial resolution, rapid data acquisition, and the ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in one study. Furthermore, with the growth of CTA, MDCT scanners are becoming widely available.
The contrast agent doses typically used preclude evaluation of patients with significant renal insufficiency. The main disadvantage of assessing perfusion with MDCT is the potentially high doses of ionizing radiation. Protocols that involve obtaining CTA studies at rest and stress would potentially double the current coronary CTA radiation dose,with many artifacts.
—————————————-
in ckd
Exercise stress echocardiography and dobutamine stress echocardiographyExercise stress echocardiography (ESE) is better than the standard stress ECG in ruling in CAD . Its sensitivity has been reported ranging from 71 to 97% with specificity ranging from 64 to 90% (17). However, the utility of ESE in CKD population remains limited
The addition of echocardiography allows assessment of ventricular size and function, aortic and mitral valvular calcification, left ventricular hypertrophy (LVH), and potentially coronary flow reserve CFR. CFR measurement by Doppler echocardiography in the left anterior descending artery has been shown to be a determinant of cardiac events in CKD patients in the absence of obstructive epicardial CAD (18), although this is not performed routinely by many echocardiography laboratories due to technical difficulties.
Dobutamine and dipyridamole stress echocardiography (DSE) technique detects inducible myocardial ischemia based on detection of wall motion abnormalities, thus, would detect significant epicardial CAD, not microvascular disease.
Abnormal DSE results in CKD patients have been associated with poorer prognosis for cardiac events and overall mortality
Exercise and pharmacological myocardial perfusion scintigraphy MPS in the advanced CKD population has the same limitation as EST and ESE, i.e., related to the inadequate exercise performance and chronotropic incompetence
Normal myocardial perfusion measured by SPECT may not be associated with excellent prognosis in CKD population unlike the normal population (30, 31), perhaps due to the high-false negative result from balanced ischemia.
Cardiovascular magnetic resonance (CMR) with gadolinium contrast has not been widely utilized clinically in the CKD population due to the concern of nephrogenic systemic fibrosis (NSF) especially with creatinine clearance 30mg/dl
Summary of the Assessment of myocardial perfusion;
Different study imaging used to evaluate, and assess myocardial perfusion and ischemia, all are using different study agent with variation in their analysis, advantages, and limitation.
Myocardial perfusion study , involves ; epicardial vesseles, resistance vessles, and endothelium assessment .
Endothelium dysfunction is an early manifestation of vascular diseases, in normal coronary artery, normal phisiological responses, to changes of haemodynamics and physilogical O2 demand of myocardium.
In atherosclerotic artery, if stenosis is more than 45%, the coronary blood flow will be affected even with maximal vasodilatory stimulant.
Other modality, Typical TI-201 protocol, is to inject during peak stress, then second image taken 10 min. later, and 3rd image taken after 4 hours.
Dual isotope protocol, using different agent (Tc99m,,TI-102), injection of TI-102 during rest , followed by Tc99m during stress, this modality give us more sensitivity in detecting perfusion defect, but more radiation burden to myocardium.
Image analysis involve; visual analsis, using qualitative method, or semiquantitative, using different rest, and stress results.
2.PET MPI:
used radiotracer N-13ammonia-Rubidium(Rb-82)0-15 water.
uptake is proportionate to the flow over the myocardium with serial imaging ,its semiquantitative study , with limition of use due to limitted availability of the scanner, and increasing cost of the study.
3.MCE: myocardium contrast Echocardiography study:
have some limitation because not yet approved by FDA.
safe agent, small volume , gas filled microbubbles, not affect cardiac haemodynamics,and directly reflect myocardium blood flow.
quantitatively and qualitatively analysis .
advantages over SPECT,PET,CT, is that , not using ionized radiation, improve spatial resolution , with ability to perform absolute quantitation of myocardium flow, either stress exercise or pharmacologiacl agent.
Limitation, suboptimal image if lung disease or motion with respiration.
4.CMR:
using contrast gadolinium-DTPA, evaluate ventricular function,rest and stress perfusion, have qualitatative visual analysis,
advantages: have high spatial resoluation, rapid study, and limited operator dependance.
5.CTA perfusion:
using iodinated ,non-ionic contrast, MPCT,CT angio.
Advantages, is doing many study in one , have high resolution , rapid data acqusition,ventricular function,and perfusion.
Disadvantages: high doses of ionizing radiation.
@ reflection of such studies in CKD patient:
As we know that CKD patient have some limitation of exercise capacity , that study may not give us the exact perfusion of myocardium, and the degree of ischemia , in the other hand the CKD patient with hypertension may have ECG changes from hypertension and thick myocardium , that lead to misinterpretation of the studies
Article Summary
Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease (CAD).
Multiple modalities including myocardial contrast echocardiography (MCE), positron emission tomography (PET), cardiac MRI (CMR), and cardiac computed tomography (CT) have emerged as promising techniques. This article will critically evaluate the strengths and weakness of these modalities for evaluating myocardial perfusion.
Coronary Physiology
Myocardial perfusion is a highly regulated process that includes epicardial vessels, resistance vessels, and the endothelium. Endothelial dysfunction is an early manifestation of vascular disease and plays a role in the development of CAD. A stenosis must exceed 85% to 90% of luminal diameter before significant reductions
in resting blood flow occur. However, under vasodilator stimulus, maximal coronary flow has been shown to decrease with stenosis of _45%. This has been demonstrated clinically using quantitative PET myocardial perfusion imaging (MPI). Because perfusion is an early change in the ischemic cascade,7 stress modalities that assess coronary perfusion reserve have a higher sensitivity in detecting flow-limiting stenoses than analysis of stress-induced wall motion abnormalities or ECG changes alone.
Methods for Inducing Coronary Vasodilation:
Exercise is typically associated with a 2- to 3-fold increase in myocardial blood flow and is the preferred
modality. Dipyridamole, adenosine, and regadenoson are pharmacological vasodilators that cause arteriolar vasodilation by both direct and endothelium-mediated mechanisms and are associated with a 3.5- to 4-fold increase in myocardial blood flow. Dobutamine typically produces a 2- to 3-fold increase in myocardial blood flow like exercise.
SPECT MPI:
Radiotracers:
Three radiotracers are commonly used clinically for SPECT MPI:
Thallium-201 (Tl-201)
Tc-99m sestamibi
Tc-99m tetrofosmin
Advantages:
1. Widely available.
2. Extensively validated.
3. Compatible with multiple stress modalities
4. Less demand for high temporal resolution.
Limitation:
1. Long acquisition protocols.
2. Poorer spatial resolution limiting detection of sub endocardial perfusion defects.
3. Limited sensitivity in detecting mild-to-moderate stenosis.
4. Motion artifacts.
5. Reduced sensitivity for detecting left main disease.
6. Exposes patients to radiation.
PET MPI:
Multiple factors including availability of scanners, increased cost, and reimbursement issues have limited widespread clinical application of PET.
PET Radiotracers:
N-13ammonia, Rubidium-82 (Rb-82), and O-15 water.
Advantages:
1. Improved spatial resolution.
2. PET tracers have significantly less roll-off of extraction.
3. Less artifacts.
4. More easily applied.
5. Less radiation.
6. High sensitivity.
Myocardial Contrast Echo Perfusion:
Lack of an FDA approved MCE contrast agent for perfusion has currently put limitations on its widespread clinical application.
Contrast Agents:
MCE contrast agents are small, gas-filled microbubbles (10 um) that compress and expand when exposed to an acoustic field and generate strong acoustic back scattering.
Advantages;
1. No ionizing radiation.
2. Improved spatial resolution.
3. Perform absolute quantification of myocardial blood flow.
4. Availability and its relatively low cost.
Limitation:
1. Motion affect pictures.
2. Artifacts Formation.
3. Operator dependent.
4. No FDA-approved contras.
CMR Perfusion Imaging:
Contrast Agents gadolinium-DTPA c
Advantages:
1. High spatial resolution.
2. The ability to perform absolute quantification of perfusion.
3. Performed rapidly.
4. Has limited operator dependence.
5. Adequate spatial coverage and temporal resolution.
Limitations:
1. Artifact.
2. Nephrogenic systemic fibrosis.
CTA Perfusion Imaging:
Contrast Agents:
Iodinated contrast agents.
Advantages:
1. High spatial resolution.
2. Rapid data acquisition.
3. Combine information of coronary anatomy, ventricular function, and perfusion.
4. Widely available.
5. Enable dynamic analysis of perfusion with high temporal resolution.
Limitations
1. Heart rate with vasodilator stress may compromise image quality.
2. High doses of ionizing radiation.
3. Artifacts.
4. Contrast induced nephropathy.
Since this article is addressing general population, please make refection on CKD patients.
Cardiac stress test:
Low sensitivity in CKD patient (36%) due to:
1. Deconditioning
2. Impaired heart rate response to exercise.
3. The frequently abnormal baseline ECG in CKD patient the interpretation of standard stress testing.
4. The ST segment changes at stress were shown to be not significantly different between non-severe CAD and severe CAD group.
STRESS ECHOCARDIOGRAPHY:
Most advanced CKD patients had a blunted chronotropic response, thus, did
not achieve 85% maximal predicted heart rate.
Thick myocardium due to LVH with small intracavitary volume, commonly found in CKD
patients, obscures the detection of wall motion abnormality.
MYOCARDIAL PERFUSION SCINTIGRAPHY:
Exercise MPS in the advanced CKD population has the same limitation as EST and ESE,
i.e., related to the inadequate exercise performance and chronotropic incompetence.
High-false negative result from balanced ischemia.
CTA Perfusion Imaging and CMR Perfusion Imaging:
There is a risk of contrast nephropathy and nephrogenic systemic fibrosis in patient with CKD with e GFR <30ml/min.
Thank You, well done
Non invasive assessment of myocardial perfusion:
This article focus on the technique used to detect myocardial perfusion for CAD diagnosis and there strength and weakness.
First technique is myocardial perfusion imaging:
during exercise coronary blood flow increase to attempt adequate oxygen carrying by blood. In diseased coronary the reserve perfusion is reduced because of coronary vessels stenosis.
Exercise capacity are prognostic markers of CAD.
Pharmacologist vasodilator by dipyridamole or adenosine helping to increase blood flow to myocardium 3.5 to 4 fold similar to exercise.
SPECT MPI // used to assess of CAD
Radiotracers:
It’s has 3 methods
Thalium-201 (T1-201) is potassium analogous
Tc-99m sestamibi
Tc-99m tetroforsmin
Thalium-201 (T1-201) has significant delays redistribution more than 3-4hr, It’s help to distinguish ischemia from scar.
The uptake of all SPECT MPI tracer depend on myocardial cellular and integrity.
SPECT MPI protocol using to assess evidence of CAD.
Tc-99m labeled perfuse agents using at same day/ first injection at rest and fallow by imaging within 30min.
second injection with 2-3 times activity administered during peak of stress.
Typical T1-201 (inject during stress) and then imaging after 10min and then redistribution imaging obtained after 4hr.
Dull-isotope protocol:
T1-201 use for rest images and Tc-99m perfuse agent during stress, but radiation dose high with this protocol.
Images analysis: by visual analysis and difference in relative counting between rest and stress.
Advantage:
Widely used and low cost and easy.
Variable modalities by exercise and vasodilator.
Limitations:
Poor spatial resolution
limited in detecting sub endocardium perfusion defects.
roll off tracer uptake at high myocardial blood flow and limited in detecting mild stenosis.
Motion artificate due to the respiratory movement.
Scatter and partial volume artificat in inferior wall due to delay redistribution.
Those artificats reduce diagnostic utility of perfusion images.
But it’s can be corrected by correction algorithmic.
MPI is not sensitive to detect left main disease or 3 vessels disease.
MPI had sensitivity and specificity 87% and 73% respectively and detected more than 50% of coronary arteries stenosis.
PET-MPI :
It’s use of myocardial perfusion
radiotracer :
N-13 ammonia
Rubidrum-82
0-15 water
0-15 freely disfusable and high
first pass extraction
the uptake is proportional to blood flow. It’s has large uptake with high blood flow without roll off phenomenon. It’s has short half life and it has serial images
It’s still not approved by FDA.
N-13 ammonia//
It’s has myocardial retention and fast washout of blood pool which lead to good perfusion.
Disadvantage:
It’s has roll off uptake with high coronary blood flow
It’s radiation dose of N-13 ammonia is 2msv
Rb-82 is limited in use because of large roll off uptake and high radiation dose.
Recently Fluorine-18 has high cardiac uptake in proportional to blood flow with out significant roll off and good myocardial retention with out significant redistribution and has long half life.
Advantage//
PET more spatial resolution in comparison to SPECT
Less roll off
Limitations//
high cost
many artifacts especially during registration between cardiac perfusion and alternative map.
Myocardial contrast echo perfusion:
contrast used is small gas filled micro bubbles.
micro bubbles remain intravascular but not effect hemodynamic and directly reflects myocardial blood flow.
Ultrasound contrast agents are safe but need close monitoring in patients with cardi-pulmonary morbidity.
Advantage//
MCE not using ionizing radiation in comparison to other modalities.
Good spatial resolution.
Sensitive to detect subendocardial ischemia.
It’s has ability to quantify of myocardial blood flow
Images can be used with exercise and vasodilator agents.
Wide available and low cost.
Disadvantage//
Suboptimal in patients with cardiac and pulmonary disease.
micro bubbles may lead to artifact in base segment of left ventricle.
It’s still not approved by FDA
MCE has prognostic values in estimate LVEF.
CMR perfusion images//
It’s depend on gadolinium DTPS contrast agents.
It’s used to assess myocardial perfusion.
Area well perfused have short T1 and bright.
Hypoperfused area has long T1 and appears hypo intensity.
Recently first gadolinium based intravascular agents are approved for MRA.
CMR help to detect subendocardial ischemia especially with patients with 3 vessels disease.
Advantage//
It’s has high spatial resolution
Rapid procedure
High ability to perform absolute quantification of perfusion.
Disadvantage//
Many dark rim artifacts which may mistake by true perfusion.
Evidence of nephrogenic systemic fibrosis especially in patients with CKD.
Adenosine stress cardiac MRI is sensitive to detect CAD.
CTA perfusion images//
Multidetector CT and CT angiogram.
It’s depend on intravenous iodine contrast agents that increase absorption of X-ray in proportional to concentration of iodine.
Advantage//
High spatial resolutions
Rapid data aquarium
Helpful in formation of ventricle function and it’s perfusion
It’s widely available
Disadvantage//
High dose of radiation.
Q2// It’s reflection on CKD patients
MPI is not reliable and less diagnostic values
Cardiac MRI depend on gadolinium , So it’s not used in CKD patients because risk of nephrogenic systemic fibrosis
Coronary angiogram using in detect CAD but not used in CKD with Cr Cl less than 60ml/min to avoid need to dialysis because may lead to contrast induced nephropathy
Reflecting on CKD patients:
ECG:
To estimate any ischemic changes which may indicates presence of CAD.
ECHO:
Help to estimate LVEF and systolic/diastolic dysfunction and valvular abnormalities.
Exercise stress ECG and ECHO:
It’s has diagnostic element but limited in CKD with poor sensitivity 36%, because exercise intolerance and uncontrolled hypertension and chest pain due to increase oxygen demand in case of anemia of CKD patients.
Non invasive myocardial perfusion images:
it’s helping in detecting reversible perfusion defects or irreversible fixed perfusion defects ( myocardial ischemia), in CkD patients with sensitivity 86% and specificity 79%),
Stress SPECT -MPI is less diagnostic in CKD patients because:
Dobutamine stress ECHO:
It’s help in detecting abnormal wall motion with sensitivity 80% in CKD.
Positive DS ECHO associated with poor prognosis of cardiac events.
Negative DS ECHO associated with low incidence of cardiac events.
Coronary CT angiogram:
It’s non invasive testing to detect CAD with excellent negative predictive value in CKD with sensitivity 93% & specificity 63% and in ESRD have sensitivity 88% & specificity 53%.
It’s low specificity in patients with CKD because high level of calcium in coronary arteries. However it’s not significant in patients with calcified coronary arteries with out stenosis.
Invasive angiogram is gold standard diagnostic procedure but carrying risk of contrast induced nephropathy in CKD patients.
Cardio- pulmonary exercise test:
Its help in assess cardiac and lung and muscle and neuropsychology during exercise.
Gadolinium stress cardiac MRI:
It’s help to identify perfusion defects but contraindicated in patients with Cr Cl less than 30ml/min because risk of nephrogenic systemic fibrosis.
Coronary revascularization:
It’s carrying risk of cardio vascular events.
Non-invasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease (CAD).
The ideal agent would not alter hemodynamics and would be small in volume compared with the myocardial blood volume, the agent should be safe, with minimal side effects. The ideal perfusion imaging modality would have a high sensitivity to small changes in coronary blood flow and a quantifiable relationship between signal intensity and perfusion. the technique should be widely available, fast and easy to use, and cost-effective.
SPECT MPI:
Advantages:
1. Availability
2. extensively validated.
3. SPECT MPI is compatible with multiple stress modalities including exercise, dobutamine, or vasodilators.
Limitations:
1. Time consuming
2. considerably poorer spatial resolution than other available modalities
3. limiting detection of subendocardial perfusion defects.
4. the roll-off of tracer uptake at higher myocardial blood flows limits sensitivity in detecting mild-to moderate stenoses.
*Sensitivity 0.87 (0.86–0.88) Specificity 0.73 (0.70–0.76)
PET MPI:
Advantages:
1. improved spatial resolution as compared with SPECT
2. more easily applied in dynamic scanning to be used for absolute quantification of perfusion.
3. recent advances in PET/CT technology.
4. Because the imaging does not occur during first pass of a contrast agent, there is less demand for high temporal resolution, and signal-to-noise ratio (SNR) can be improved by collecting data over a longer period of time.
Limitations:
1. Limited availability
2. Higher cost
3. Combined CT modality will expose patients to higher radiation doses
*Sensitivity 0.85 (0.79–0.90) Specificity 0.87 (0.84–0.90)
Myocardial Contrast Echo Perfusion:
Advantages:
1. wide availability and its relatively low cost
2. No ionizing radiation.
3. Compared with SPECT, MCE has improved spatialresolution, enabling detection of subendocardial ischemia
4. has the ability to perform absolute quantification of
myocardial blood flow.
5. Imaging can be performed during pharmacological stress with inotropes or vasodilators or with exercise.
Limitations:
1. Operator-dependent factors
2. Suboptimal images are obtained due to respiratory motion, body habitus, or lung disease.
3. Attenuation from the microbubbles may result in artifacts
4. No FDA-approved contrast agents for MCE perfusion
*Sensitivity 0.82 (0.76–0.88) Specificity 0.80 (0.73–0.87)
Cardiac MRI
Advantages:
1. High spatial resolution
2. The study can be performed rapidly
3. Has limited operator dependence
4. The signal characteristics are largely independent of the patient’s body habitus.
Limitations:
1. Limited availability
2. High cost
3. False positive: Current pulse sequences suffer from a “dark-rim” artifact that can be mistaken for a true perfusion abnormality.
4. Gadolinium contrast agents have been associated with a rare but serious condition called nephrogenic systemic fibrosis, which primarily occurs in
patients with significant reductions in creatinine clearance < 30.
*Sensitivity 0.91 (0.88–0.94) Specificity 0.81 (0.77–0.85)
CT coronary angiography
Advantages:
1. High spatial resolution
2. Rapid relatively
3. The ability to potentially combine information of coronary anatomy, ventricular function, and perfusion in one study.
Limitations:
1. High cost
2. image quality is inversely related to heart rate, the increase in heart rate with vasodilator stress may compromise image quality
3. Can cause contrast-induced nephropathy, especially in patients
with reduced renal function (creatinine clearance 60).87
In CKD Population:
MPI has relatively low diagnostic performance of in in ESRD patients, as they have a predisposition for haemodynamic and anatomic abnormalities which could impair diagnostic accuracy.
Cardiac MRI:
Most CMR studies of myocardial perfusion are based on the gadolinium contrast agents , Gadolinium stress cardiac MRI can identify perfusion abnormalities. However, GBCAs are contraindicated in patients with impaired kidney function (eGFR <30 mL/min/m2).
Coronary CT Angiogram
has high negative predictive value makes it reliable in ruling out significant CAD in symptomatic patients
It has high sensitivity (93%) and moderate specificity (63%) in CKD for diagnosing obstructive CAD in RTCs.
The major concern is contrast-induced nephropathy, especially in patients
not on dialysis (generally creatinine clearance 60).
Thank You, Wadia, MPI is of moderate sensitivity and specificity, but it is an excellent negative test.
I agree with the rest.
This article assesses the strengths and weakness of modalities for evaluating myocardial perfusion
Coronary Physiology
A stenosis must exceed 85% to 90% of luminal diameter before significant reductions in resting blood flow occur.
under vasodilator stimulus, maximal coronary flow has been shown to decrease with stenosis of 45%
stress modalities that assess coronary perfusion reserve have a higher sensitivity in detecting flow-limiting stenoses than analysis of stress-induced wall motion abnormalities or ECG changes alone
Methods for Inducing Coronary Vasodilation
* Exercise and dobutamin is associated with a 2- to 3-fold increase in myocardial blood flow
* Dipyridamole, adenosine, and regadenoson are associated with a 3.5- to 4-fold increase in myocardial blood flow
The Ideal Perfusion Imaging Technique and Agent
An ideal agent
– High first-pass myocardial uptake
– Insignificant back-diffusion and recirculation
– Rapid clearance from the blood pool
– kinetics that are not altered by factors such as metabolism or hypoxia.
– Stable
– Low cost
– Safe
– Adirect relationship between contrast agent concentration and myocardial perfusion.
– Minimal side effects.
– Negligible volume
The ideal imaging modality
– High sensitivity
– Relationship between signal intensity and perfusion.
– High spatial/temporal resolution
– Adequate spatial coverage of the ventricle
Reproducible
– No operator dependence
– Fast and Easy to use
– Widely available
– Low cost
SPECT MPI
** Radiotracers : Thallium-201 , Tc-99m sestamibi, and Tc-99m tetrofosmin
** Protocols : rest-stress protocol using a Tc99m-labeled perfusion agent , A typical Tl-201 protocol , A dual-isotope with Tl-201 for the rest images and a Tc-99m during stress
** Advantages
widely available
multiple stress modalities including exercise, dobutamine, or vasodilators.
** limitations :
long acquisition protocols
poorer spatial resolution
limiting detection of subendocardial perfusion defects.
Low sensitivity in detecting mild-to-moderate stenoses.
artifacts due to patient and respiratory motion , gut and biliary activity , breast or subdiaphragmatic attenuation
** SPECT sensitivity and specificity is 87% and 73%, respectively
** exercise SPECT sensitivity and specificity of 89% and 75%, respectively
PET MPI
** Radiotracers : N-13ammonia, Rubidium-82, O-15 water , and fluorine-18 .
** Imaging Protocol
a resting perfusion image using eitherRb-82 or N-13 ammonia
stress imaging can be performed soon after rest imaging
dynamic scanning during first pass of thecontrast agent is performed
** Advantages
improved spatial resolution as compared with SPECT,
attenuation artifacts are less of an issue for PET
lower radiation doses than SPECT
It can do clmbind with CTA
** limitations
High cost
need for a cyclotron for all except Rb-82
Difficulty in evaluating the effect of motion
Resulting artifacts between perfusion images and attenuation maps
Higher radition doses when ia combined with CTA
** A sensitivity of 92 % and specificity of 85 % for the detection of CAD.
** In coparsion to SPECT , PET had a higher diagnostic accuracy(91% versus 76%) and higher specificity (100% versus 66%) for detection of a 50% or greater coronary artery stenosis
Myocardial Contrast Echo Perfusion
** Contrast agent : small, gas-filled microbubbles that compress and expand when exposed to an acoustic field and generate strong acoustic backscattering
FDA considers it to be an experimental procedure
Currently there are no ultrasound contrast agents approved for MCE perfusion imaging,
performed with both vasodilator and inotropic pharmacological stress.
** Advantages
MCE has an advantage over SPECT, PET, and CT perfusion imaging because it does not involve ionizing radiation
improved spatial resolution, enabling detection of subendocardial ischemia in comparsion to SPECT
has the ability to perform absolute quantification of myocardial blood flow
can be performed during pharmacological stress with inotropes or vasodilators or with exercise
wide availability and low cost
** limitations :
Suboptimal images as the result of respiratory motion, body habitus, or lung disease
artifacts in the basal segments of the left ventricle due to microbubbles
no FDA-approved contrast agents for MCE perfusion
** sensitivity of 82% and specificity of 80%
It has average concordance of 81% with SPECT
CMR Perfusion Imaging
** Contrast Agents : gadolinium-DTPA
areas that are perfused have a shorter T1 and appear bright on T1 whereas regions that are hypoperfused have longer T1 and appear hypointense.
sensitivity and specificity of 89% and 87%,
Imaging Protocol
Stress perfusion CMR to evaluates ventricular function ,stress and rest perfusion
CMR enables the detection of subendocardial ischemia which seen In a patiet has 3-vessel disease
** Advantages
high spatial resolution
perform absolute quantification of perfusion
little operator dependence
largely independent of the patient’s body habitus
** Limitations
A “dark-rim” artifact that can be mistaken for a true perfusion abnormality
nephrogenic systemic fibrosis in patients with a creatinine clearance30 mg/dL.
CTA Perfusion Imaging
** Contrast Agents
iodinated contrast agents
72% sensitivity and 80% specificity for detecting a significant coronary stenosis
** Advantages
high spatial resolution
rapid data acquisition
combine information of coronary anatomy , ventricular function, and perfusion
widely available
** limitations :
image quality is inversely related to heart rate, the increase in heart rate with vasodilator stress
artifacts limiting the ability of quantitative assessment of perfusion.
preclude evaluation of patients with significant renal insufficiency.
high doses of ionizing radiation.
higher radiation dose.
As for patients with CKD
SPECT MPI
PET MPI
Contrust agent imagining is not safe and need more studies in CKD patients
MRA has A risk of NSF
Thank you, but the reflection on CKD patients is more than this. Please write more
This article talks about different ways to assess myocardial perfusion ;with noninvasive procedure;which is too important in the diagnosis and risk stratification for patient with suspect coronary artery diseas.
Although the best and ideal perfusion imaging techniques and agents are also discussed in details.
Multiple methods,agents and drugs are used to induce coronary vasodilation
The ideal agent sould having the following:
1- high first pass
2-linear relation between myocardial concentration and perfusion.
3-no effect on hemodynamic
4-negligible volume
5-easy to administer and low cost.
The most important and used tests are the following :
1- Spect mpi imaging:
Have multiple protocol use different raditraces (thallium-201 ,tc-99m , tc 99m)
It is widely available and compatible with multiple stress modalities with less demand for high resolution, however it is of low sensitivity in detection of mild-mdoderate stenosis.
2-Pet mpi :
It uses N-13 ammonia,rubidium-82 and O-15 as tracers.
It is better than spect with spastial resoltion however it cost effective and the need for a cyclotron.
3-myocardial contrast echo perfusion :
It uses gas filled microbubbles .
It has the ability to perform absolute quantification of myocardial blood flow .
Doesn’t involve using of ionizing radiation.
It is operator dependent and have multiple artifact factors and no fda-approved for contrast agent.
4-cmr perfusion :
Depend on first pass of a bolus of gadolinium-dtpa contrast agent.
It has high spatial resolution and ability to perfome absolute of perfusion
It is however rapidly done, operator-dependent,
Problems with gadolinium decrease its use with some patient especially ckd patients.
5-CTa perfusion scan :
It depends on the intravenous injection of ionized or nonionic contrast agents.
Also it has high spatial resolution,rapid data acquisition, combine information of coronary anatomy, ventricular function and perfusion in one study ,however the test quality is inversely related to heart rate and multiple artifact factors are present.
The contrast agent needed for evaluation is high doses and contraindicated in ckd patients.
Since this article is addressing general population, please make refection on CKD patients.
Excersie depending tests are of low sensitivity in patients with ckd cause of multiple limitations in exercise tolerance in ckd patients .
Echocardiography depending also have multiple limitation due do ventricular channges in ckds patient
Gadolinium use are contraindicated in ckd patients with GFR less than 30% due to risk of nephrogenic systemic sclerosis.
Contrast agents are in past harmful for ckd patients but now multiple studies are done show that contrast agent could be used for ckd patient .
The term renalism is put to know the real harmfulness of contrast agents in ckd patients ,however multiple studies are needed to confirm the safety of using contrast in ckd patients .
Myocardial Perfusion Scintigraphy is the best obtion fo ckd patient with good sensivity but hogh prevelance of false negative result.
Thank you, but the reflection on CKD patients is more than this. Please write more
Myocardial perfusion imaging (MPI) in a suspected coronary artery disease (CAD) patient can be assessed by:
1) SPECT: Single-photon emission computed tomography
2) MCE: myocardial contrast echocardiography
3) PET: positron emission tomography
4) CMR: cardiac MRI
5) CCT: cardiac CT
Coronary physiology: Endothelial dysfunction affects flow-mediated coronary vasodilation. Significant decrease in resting blood flow occurs only if the stenosis involves 85-90% of the coronary artery lumen diameter, but this decrease can be seen even with 45% stenosis by using vasodilators.
Methods for inducing coronary vasodilation leading to increased myocardial blood flow include exercise (2–3-time increase), vasodilator drugs like dipyridamole, adenosine and regadenoson (3.5-4-time increase) and intoropes like dobutamine (2-3-time increase).
SPECT-MPI
Sensitivity and specificity: 87% and 73% with exercise and 89% and 75% with vasodilators.
3 radiotracers, Thallium 201, Tc99m sestamibi and Tc 99 m tetrofosmin, are used, with maximum first pass extraction at resting flow 86%, 64% and 54% respectively.
Different protocols used include:
a) Tc99m injection followed by imaging at 30 minutes, then repeat imaging after second Tc99m injection with 2-3 times activity during peak stress.
b) Thallium 201 injection during peak stress followed by imaging at 10 minutes and at 4 hours (redistribution image)
c) Dual isotope protocol: Thallium 201 for rest image and Tc99m for image during stress. But it increases radiation dose.
Advantages of SPECT-MPI: compatible with multiple stress modalities and less demand for high temporal resolution
Limitations of SPECT-MPI: Poor spatial resolution, time consuming, high radiation dose, presence of various artifacts, poor sensitivity to detect subendocardial perfusion defects, mild to moderate stenosis and left main disease or triple vessel disease.
PET MPI
Sensitivity and specificity: 92% and 85%
3 radiotracers Rb-82 (Rubidium 82 – does not require on-site cyclotron), N13 ammonia and O15 water (both require on-site cyclotron), are used.
Protocol used: Resting image with N13 or Rb82 taken 90-120 seconds after giving the bolus. For ECG gated PET, imaging is performed for 3-6 minutes with Rb-82 and for 5-15 minutes with N-13. Due to low half life, stress imaging can be performed soon after rest imaging.
Qualitative, semiquantitative and quantitative analysis can be performed.
Advantages of PET-MPI: lower radiation dose, less roll-off of extraction at high flows, better spatial resolution and less attenuation artifacts.
Limitations of PET-MPI: high cost, need of cyclotron, high roll-off with Rb-82, increased radiation when used with CT and presence of registration artifacts.
MCE: Myocardial Contrast ECHO Perfusion
Sensitivity and specificity: 82% and 80%
Contrast agent used: intravascular small gas filled microbubbles (which compress and expand as per acoustic field) directly reflecting myocardial blood flow. But it has not been approved by FDA yet.
Protocol used: intravenous infusion of microbubbles, leading to a steady state followed by high mechanical index pulse leading to rupture of the bubbles and capturing the rate of replenishment (low in hypoperfused areas). Images can be taken in gated intermittent mode as well as real time mode.
Qualitative and quantitative analysis can be performed.
Advantages of MCE: No radiation, low cost, better spatial resolution, subendocardial ischemia can be detected, quantification of myocardial blood flow can be done, and the stress imaging can be performed with either of the 3 modalities (exercise, inotrope and vasodialtors).
Limitations of MCE: Artifacts lead to suboptimal imaging, operator dependent and FDA approved contrast media available.
Cardiac MRI: CMR
Sensitivity and specificity: 91% and 81%
Contrast agent used: Intravascular Gadolinium DTPA
Protocol used: Cine image to assess ventricular function, stress perfusion image using adenosine infusion with Gadolinium injection are taken and then perfusion images are taken at rest after a wash-out period of 10 minutes. Late gadolinium enhanced images are taken in the end.
Qualitative, semiquantitative and quantitative analysis can be performed.
Advantages of CMR: HIgh spatial resolution, subendocardial ischemia can be detected, absolute quantification of perfusion can be done, rapid, low operator dependence, most compatible with vasodilator stress.
Limitations of CMR: Artifacts, cannot be used in patient with GFR<30, can cause nephrogenic systemic fibrosis.
CT Angiography: CTA
Sensitivity and specificity: 72% and 80%
Contrast agent used: Intravascular iodinated contrast agents
Protocol used: Contrast enhanced coronary CT angiography done during adenosine stress and then 20 minutes later at rest, assessing for areas of inducible ischemia.
Advantages of CTA: HIgh spatial resolution, rapid, combine information of coronary anatomy, perfusion and ventricular function.
Limitations of CTA: High radiation dose, presence of artifacts and image quality gets poorer with higher heart rates, contrast associated nephropathy can be seen in GFR less than 60.
With availability of these modalities, non-invasive assessment of myocardial perfusion can be performed, but combining 2 or more techniques will lead to better assessment.
In CKD patients, with respect to the myocardial perfusion imaging, stress Echocardiography (exercise induced or pharmacological stress) has sensitivity and specificity of 80% and 89%. With stress ECHO, there is blunted chronotropic response with reduced exercise capacity. Left ventricular hypertrophy will obscure wall motion abnormalities and microvascular disease can be missed.
SPECT-MPI may show false negative results in patients with triple vessel disease due to balanced ischemia (homogeneous tracer uptake). Exercise MPS has limitations due to inadequate exercise performance and chronotropic incompetence.
CMR cannot be done in patients with GFR less than 30 due to concerns regarding nephrogenic systemic fibrosis.
Contrast agent in CTA is associated with contrast induced nephropathy.
Thank you, EXCELLENT reflection on CKD patients
Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease.
There are many modalities, but we need an ideal modality with an ideal agent.
Characteristics of an ideal agent:
The ideal perfusion imaging modality would have a high sensitivity to small changes in coronary blood flow and a quantifiable relationship between signal intensity and perfusion.
The technique would have a high spatial resolution so that transmural differences in perfusion could be detected, should be reproducible and have a high diagnostic utility, and free of artefacts that would limit either, and should be widely available, fast and easy to use, and cost-effective.
SPECT MPI
Advantages:
Limitations:
Developments in novel imaging hardware and iterative reconstruction are leading to improved spatial resolution, contrast, and imaging speed for SPECT MPI.
PET MPI
Advantages:
Limitations:
Myocardial Contrast Echo Perfusion:
limitations of the sensitivity of wall motion analysis by echocardiography have led to the development of MCE techniques. the lack of an FDA-approved MCE contrast agent for perfusion has currently put limitations on its widespread clinical application.
Advantages:
Limitations:
CMR Perfusion Imaging:
Most CMR studies of myocardial perfusion are based on the first pass of a bolus of gadolinium-DTPA contrast agents.
Advantages:
Limitation:
FDA has issued a black-box warning for gadolinium-based contrast agents in patients with a creatinine clearance of less than 30 mg/dL as it is associated with nephrogenic systemic sclerosis.
CTA Perfusion Imaging:
Myocardial perfusion imaging with CT is based on the intravenous injection of iodinated contrast agents that increase the absorption of x-rays in proportion to the concentration of iodine.
Advantages:
Limitations:
For CKD patients, the use of gadolinium is contraindicated if the GFR is below 30 ml/
min as there is a risk of nephrogenic systemic fibrosis.
Also, for CTA perfusion scanning, there is a high risk of ionizing radiation
Thank you, but the reflection on CKD patients is more than this. Please write more
Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease (CAD).
Several non invasive modalities for assessment of pericardial perfusion are available, till now no ideal perfusion agent or imaging.
1- SPECT- MPI
Three radiotracers are commonly used clinically for SPECT MPI.
Radiotracers
• Thallium-201 (Tl-201)
• Tc-99m sestamibi
• Tc-99m tetrofosmin
– Thalium has longer half-life and higher first pass and more delayed redistribution when compared to Tc-99
– The uptake of all SPECT tracers is dependent on myocardial cellular integrity in addition to blood flow
Protocol
• Tl-201: injection at stress- image after 10 min then wait for 4 hours and do redistribution image
• Tc-99m : injection at rest-followed by imaging after 30 min(rest)- A second injection with 2 to 3 times the activity is administered and repeat image.
• Use of dual isotope tracers with different properties is associated with difficulties in interpretation and exposure the patient to more radiation (24 mSv vs 11 mSv or 8 mSv)
Advantages
• It is widely available
• Compatible with multiple stress modalities
• Extensively validated
• Sensitivity of 87% and specificity of 73% for detecting > 50 % stenosis
Limitations :
• It is time consuming because of long acquisition protocols
• Poor spatial resolution
• Limiting detection of subendocardial perfusion defects
• Motion artifact due to movement of the patient or respiratory motion
• Scatter and partial volume artifacts in the inferior wall related to gut and biliary activity
• Attenuation artifacts due to myocardial scar
2- PET
Radiotracers: Using 3 radiotracers
– N-13Ammonia
– Rubidium-82 (Rb-82)
– O-15 water – O-15 water is freely diffusible and has a high first-pass extraction. O-15 water has shorter half-life which makes it only compatible with imaging in stress
Protocol
• Injection of N-13 Ammonia or Rubidium-82 (Rb-82) at rest-image after 90 to 120 seconds. ECG-gated PET acquisition is usually performed for 3 to 6 minutes for Rb-82 and 5 to 15 minutes for N-13 ammonia. Stress imaging can be performed soon after rest imaging.
Advantages
• Better spatial resolution when compared to SPECT
• Significantly less roll-off of extraction at high flows as compared with Tc-99m– based SPECT agents
• Tracers are more easily applied in dynamic scanning to be used for absolute quantification of perfusion
• Lower radiation dose
• Less attenuation artifact
• Sensitivity of 91% and specificity of 100% for detecting > 50 % stenosis
Limitations
• Higher costs
• The need for a cyclotron for all but Rb-82 imaging or imaging agents labeled with F-18
• Motion artifacts are difficult to be assessed
3- Myocardial Contrast Echo Perfusion
Contrast agent: Gas filled microbubbles that compress and expand when exposed to an acoustic field and generate strong acoustic backscattering
Technique
• Myocardial perfusion can be assessed with continuous infusion of microbubbles then ECHO is performed. The real-time technique allows simultaneous assessment of both perfusion and wall motion but has a lower sensitivity for microbubble detection.
Advantages
• Availability
• lower cost
• Good spatial resolution
• No ionizing radiation exposure
• Can be used with physical or pharmacological stress
• Can be used to quantify myocardial blood flow
• Sensitivity of 82% and specificity of 80% for detecting of CAD
Limitations
• The lack of an FDA approved MCE contrast agent for perfusion has currently put limitations on its widespread clinical application
• Respiratory motion, body habitus, or lung disease can result in suboptimal images
• Attenuation from the microbubbles may result in artifacts in the basal segments of the left ventricle
4- CMR Perfusion Imaging
• Stress perfusion CMR is generally applied as part of a comprehensive study that evaluates ventricular function, stress and rest perfusion, and viability/myocardial infarction.
Contrast agent
• Most studies are based on the administration of gadolinium-DTPA
Protocol
• Cine images to assess ventricular function are obtained generally in 10 minutes.
• Stress perfusion images are obtained after injection of adenosine for 2-4 min- 3-4 short axis perfusion images are obtained.
• Forty to 60 image frames are usually obtained. After a 10-minute contrast washout period, perfusion images are obtained at rest using the same imaging protocol
Advantages
• Availability
• Perfect spatial resolution
• The ability to perform absolute quantification of perfusion
• No exposure to radiation
• Rapid method
• Sensitivity of 91% and specificity of 81% for detecting of CAD
Limitations :
• Dark-rim artifact which can be mistaken for a true perfusion abnormality
• The risk of Nephrogenic systemic sclerosis if given in patient with GFR < 30
5- CTA Perfusion Imaging
Contrast agent
Iodinated contrast agents
Protocol
CTA protocols during adenosine stress and 20 minutes later at rest and visually assessed for areas of inducible ischemia
Advantages
• Availability
• Perfect spatial resolution
• Rapid data acquisition
• Dynamic analysis of perfusion with high temporal resolution
• Sensitivity of 72% and specificity of 80% for detecting of significant CAD
Thank you, but WHERE IS YOUR reflection on CKD?
Summarise this article
*Non invasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease (CAD).
# Single-photon emission computed tomography (SPECT) is commonly applied
# Others promising techniques including:
* Myocardial contrast echocardiography (MCE).
*Positron emission tomography (PET).
*Cardiac MRI (CMR).
*Cardiac computed tomography (CT)
***This article will importantly investigate the advantages and disadvantages of these modalities for evaluating myocardial perfusion.
# Coronary Physiology
*Myocardial perfusion is a controlled mechanism that includes epicardial vessels, resistance vessels, and the endothelium.
*Endothelial disorder is an early sign of vascular disease that plays a role in the development of CAD.
*In normal coronaries, sympathetic stimulation leads to epicardial and arteriolar vasodilation. With endothelial dysfunction, vasoconstriction from acetylcholine predominates, so coronary arteries narrowed by atherosclerotic disease, coronary autoregulation attempts to normalize myocardial blood flow by reducing the resistance of distal perfusion beds to preserve adequate myocardial oxygen supply.
*The stenosis must be above 85% to 90% of luminal diameter prior to significant reductions in resting blood flow, but under vasodilator stimulus, maximal flow reduce with stenosis of 45%.
# Methods for Inducing Coronary Vasodilation
*Exercise result in coronary vasodilation by an endothelium-dependent flow-mediated mechanism to overcome the requirement of high oxygen demand. It is associated with a 2- to 3- high fold myocardial blood flow and is the best modality, because the exercise capacity has important prognostic value.
*Dipyridamole, adenosine, and regadenoson are pharmacological vasodilators that cause arteriolar vasodilation by both direct and endothelium-mediated mechanisms and are associated with a 3.5- to 4-fold increase in myocardial blood flow
# The Ideal Perfusion Imaging Technique and Agent
*An ideal agent would have a high first-pass myocardial uptake proportional
to perfusion.
*Insignificant back diffusion and recirculation.
*Rapid clearance from the blood pool, and kinetics that are not altered by factors.
*For imaging during first pass, there should be a direct and quantifiable relationship between contrast agent concentration
and myocardial perfusion.
*The contrast agent concentration should be proportional to perfusion over
a large range of coronary flows.
*The ideal agent would not alter hemodynamics and would be small in volume compared with the myocardial blood volume.
*The agent should be safe, with minimal side effects.
*I T should have a high sensitivity to small changes in coronary blood flow and a quantifiable relationship between signal intensity and perfusion.
*The technique should be widely available, fast and easy to use, and cost-effective.
# SPECT MPI
*Three radiotracers are mainly used for SPECT MPI: Thallium-201 (Tl-201) ,Tc-99m sestamibi and Tc-99m tetrofosmin bind mitochondrial membranes.
*All the agents have characteristics to permit the stress and the imaging components to be separated in time and location, and the uptake of all SPECT tracers is dependent on myocardial cellular integrity and blood flow.
SPECT MPI Imaging Protocols
*Tc99m is a same-day rest-stress protocol, the first injection at rest followed by imaging after 1/2 hour. A second injection with 2 to 3 times the activity is administered during peak stress and repeat imaging is performed.
*Tl-201 protocol would involve injection during peak stress, then imaging roughly 10 minutes later, followed by a redistribution image obtained roughly 4 hours later.
*A dual-isotope protocol in which Tl-201 is used for the rest images and then a Tc-99m perfusion agent is used during stress soon thereafter.
*Advantages of SPECT
-SPECT MPI is widely available.
-Extensively validated.
-Compatible with multiple stress modalities including exercise, dobutamine, or vasodilators.
*Limitations
-Long acquisition protocols
-Poorer spatial resolution than other available modalities.
-Limiting detection of subendocardial perfusion defects.
-Limits sensitivity in detecting mild-to-moderate stenoses.
-Motion artifacts related to patient and respiratory motion
-Reduced sensitivity for detecting left main or 3-vessel disease related to balanced ischemia.
-Radiation exposure risk.
# PET MPI
*N-13ammonia, Rubidium-82 (Rb-82), and O-15 water are the PET tracers typically used for myocardial perfusion.
* A bolus of the tracer is given and imaging usually commences between 90 to 120 seconds there after.
* ECG-gated PET acquisition is usually performed for 3 to 6 minutes for Rb-82 and 5 to 15 minutes for N-13 ammonia, owing to their different half-lives then stress imaging can be performed soon after rest imaging.
*Advantages
-PET has improved spatial resolution as compared with SPECT
-PET tracers have significantly less roll-off compared with Tc-99m–based
SPECT agents.
-Attenuation artifacts are less of an issue for PET.
-The tracers used in PET are more easily applied in dynamic scanning to be used for absolute quantification of perfusion.
-With the recent advances in PET/CT technology, multimodality functional imaging of perfusion with PET combinend with anatomic imaging of (CTA) is now possible.
*Limitations
-Higher costs.
-Need for a cyclotron.
-When PET is combined with CTA, patients need high radiation doses.
# Myocardial Contrast Echo Perfusion
*MCE contrast agents are small, gas-filled microbubbles (_10 um) that compress and expand when exposed to an acoustic field and generate strong acoustic backscattering.
*The sensitivity of 82% and specificity of 80%.
*MCE was shown to have prognostic value that was incremental to left ventricular
ejection fraction.
*Advantages
– MCE has an advantage over SPECT, PET, and CT perfusion imaging because it does not involve ionizing radiation.
-MCE has improved spatial resolution, enabling detection of subendocardial ischemia.
-Has the ability to perform absolute quantification of myocardial blood flow.
-Imaging can be performed during pharmacological stress with inotropes , vasodilators and exercise.
-Wide availability and its relatively low cost.
*Limitations
-Suboptimal images are obtained in a significant number of patients as the result of respiratory
motion, body habitus, or lung disease.
-Attenuation from the microbubbles may result in artifacts in the basal segments of the left ventricle
-Some operator-dependent factors.
-Not FDA-approved contrast agents for MCE perfusion.
# CMR Perfusion Imaging
*Based on the first-pass of a bolus of gadolinium-DTPA contrast agents.
*Advantages
-Cardiac MRI has significant advantages of high spatial resolution, the ability to perform absolute quantification of perfusion
-The study can be performed rapidly, has limited operator dependence, and the signal characteristics are largely independent of the patient’s body habitus.
*Limitations
Gadolinium-DTPA is not an ideal contrast agent and associated with nephrogenic systemic fibrosis.
# CTA Perfusion Imaging
Based on the intravenous injection of iodinated contrast agents that increase the absorption of x-rays in proportion to the concentration of iodine.
*Advantages
High spatial resolution, rapid data acquisition, and the ability to potentially combine
information of coronary anatomy, ventricular function, and
perfusion in one study. Furthermore, with the growth of CTA,
MDCT scanners are becoming widely available.
* Limitations
Image quality is inversely related to the increase in heart rate with vasodilator stress .
Limit the ability of quantitative assessment of perfusion.
The contrast agent doses typically used preclude evaluation of patients with significant renal
insufficiency.
High doses of ionizing radiation.
# Since this article is addressing general population, please make refection on CKD patients
*EST is limited in the advanced CKD, with poor sensitivity of 36% , as deconditioning leads to reduced exercise capacity. Impaired heart rate response to exercise. Frequently abnormal baseline ECG hampers the interpretation of standard stress testing. ST segment changes at stress were not different between non-severe CAD and severe CAD.
*Exercise Stress ECHO Cardiography and Dobutamine stress Echocardiography:
Is superior to the ordinary stress ECG in ruling in or out CAD; with sensitivity (71-97%) and specificity (64 -90%).But still limited for the same physical reasons. The addition of echocardiography give more benefit in evaluation of ventricular size and function ,aortic and mitral valvular calcification, left ventricular hypertrophy(LVH),and potentially coronary flow reserve (CFR).
* Dobutamine and dipyridamole stress echocardiography (DSE):
Detects inducible myocardial ischemia based on detection of wall motion abnormalities, thus, would detect significant epicardial CAD, not microvascular disease
* Myocardial Perfusion Scintigraphy:
Exercise and pharmacological myocardial perfusion scintigraphy (MPS) with sensitivity (87 -89%) and specificity (73 – 75%), in detecting >50% coronary artery stenosis in non advanced CKD. Exercise MPS in the advanced CKD has the same limitation as EST and ESE. MPS has high false negative result in detecting ischemia in people with significant triple vessel CAD, in CKD due to “balanced ischemia”
* Cardiovascular Magnetic Resonance (CMR):
With gadolinium contrast has not been used in the CKD patients for the risk of nephrogenic systemic fibrosis.
Thank you, EXCELLENT reflection on CKD patients
Summaries this article
This article reviews the available noninvasive myocardial perfusion tests that would help in the diagnosis of CAD and addresses their benefits and restrictions
Introduction
Cardiac perfusion is structured by epicardial vessels, vascular resistance, and endothelium. The endothelial dysfunction and perfusion defects are considered early changes in IHD.
Stress tests are very sensitive modalities to assess coronary perfusion reserve and flow-limiting stenosis compared to stress-induced wall motion abnormalities or ECG changes alone.
Endothelial dysfunction and microvascular disease can occur in the absence of significant Coronary stenosis and can be confirmed by abnormal coronary flow reserve, and perfusion defect as early changes in ischemic cascades and can be assessed by different quantitative noninvasive MPI images. exercise-induced coronary vasodilation which is through endothelial-dependent flow in order to meet the o2 demand and can be increased 2-3 times the myocardial flow capacity while in the case of CAD the perfusion flow reserve is diminished by flow-limiting coronary stenosis, endothelial dysfunction, and adrenergic stimulant.
The Ideal Perfusion Imaging Technique and Agent characteristics include the following:
1. Use of gents with High first pass uptake compared to perfusion
2. Insignificant back-diffusion flow and recirculation.
3. Safe, small volume, and Rapid clearance and not altered the hemodynamics with fewer side effects
4. kinetics that does not change by the effects of metabolism or hypoxia.
5. High sensitivity for small changes in coronary flow. quantifiable and reproducible with good diagnostic quality (not operator dependent).
6.fast, easy, and cost-effective
SPECT-MPI is of noninvasive stress test
Widely used and well-validated stress test available with easy access with different modalities including exercise dobutamine, vasodilator, its use limited by long protocol with poor spatial resolution, limitation in the detection of subendocardial perfusion defect, lower sensitivity in detecting mild to moderate stenosis, triple vessel disease due to balanced ischemia and lt the main disease its diagnostic utility can be affected by variable attenuation artifacts related to motion, respiratory, volume artifact and this can be improved by using attenuation correction algorithm However its diagnostic approach use, especially in severe CKD, DM patients can help in selective use of CAG and revascularization therapy with cost-effectiveness
PET -MPI
have been used for more than 25 years and are cost-effective compared to CAG, stress test, with more superior diagnostic accuracy compared to SPECT, PET scan more sensitivity, and specificity for the diagnosis of CAD, BY using N13- ammonia and Rb 82 is a perfusion agent and it’s more accurate and superior to SPECT for the diagnosis of > 50% coronary artery stenosis with 91% accuracy and 100% specificity. Its clinical use is limited by the availability of the scanner and increased cost, also more radiation risk with RB82, a new agent fluorine-based (F-18) with less radiation risk and more cardiac uptake and less roll off and good myocardial retention with less redistribution effect, in addition, it’s compatible with many stresses imaging protocols and a long half-life
The new innovation of PET/CTA modality for both functional perfusion imaging by PET scan and anatomical imaging by CT angiogram but with the cost of more radiation.
Myocardial contrast echo (MCE). Contain both quantitative and qualitative analysis by looking at the rate or amount of the contrast replenishment
Superior to PET, SPECT, and CT as no exposure to radiation, more accurate for detection of subendocardial ischemia, and able to quantify the myocardial blood flow, the test can be performed with exercise or pharmacological agents like inotrope, vasodilators, available with low cost
Limitation, suboptimal images in obese, respiratory distress, lung disease, attenuation from microbubbles, operator dependent, FDA not yet approved contrast agents for MCE perfusion. with limitation of its use for patients with severe PHT and unstable cardiopulmonary disease and should be used with intensive monitoring
Contrast Echocardiography Perfusion Techniques:
By using continuous infusion of microbubbles contrast and the area of hypoperfusion have a slower return of microbubbles compared to the well-perfused area with a more rapid return of the microbubbles contrast, in real-time techniques can evaluate both the perfusion and wall motion with lower sensitivity to microbubbles detections
CMR Perfusion images
Using first pass gadolinium -DPTA contrast agent with the high-resolution test for assessment of myocardial perfusion, bright and heavily T1 with shorter T1 reflect the areas of good perfusion while longer and hypointenseT1 indicate the area of perfusion defect, highly sensitive and specific for the detection of CAD with late gadolinium enhanced defect indicate previous MI while stressing CMR for inducible reversible ischemia. Also, for subendocardial ischemia in patients with diffuse triple vessel disease.
Advantage
High-resolution quantitative perfusion analysis.
Limitation, operator dependent, gadolinium use is associated with rare irreversible NSF (nephrogenic systemic fibrosis), and its use is not preferred in patients with GFR < 30ML/MIN.
CTA Perfusion Imaging
MDCT (multidetector CT), is high resolution and very informative for dynamic perfusion studies anatomy and ventricular function, limitation, invasive, radiation, contrast-induced nephropathy
Thank you, but WHERE IS YOUR reflection on CKD?
Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk
stratification of patients with known or suspected CAD.
Common Noninvasive myocardial perfusion test:
Single-photon emission computed tomography (SPECT) is most commonly used.
Myocardial contrast echocardiography (MCE).
Positron emission tomography (PET).
Cardiac MRI (CMR).
Cardiac computed tomography (CT).
Advantages:
#High spatial resolution.
#The ability to perform absolute quantification of perfusion.
#Performed rapidly.
#Has limited operator dependence.
#Adequate spatial coverage and temporal resolution.
Cardiac stress test:
Low sensitivity in CKD patient.
STRESS ECHOCARDIOGRAPHY.
MYOCARDIAL PERFUSION SCINTIGRAPHY:
Exercise MPS in the advanced CKD population has the same limitation as EST and ESE,
CTA Perfusion Imaging and CMR Perfusion Imaging:
Risk of contrast nephropathy.
Thank you, but WHERE IS YOUR reflection on CKD?
Summarise this article
Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease (CAD). There are multiple modalities used for evaluating myocardial perfusion which include:
1- single-photon emission computed tomography (SPECT) which is most commonly used.
2- myocardial contrast echocardiography (MCE)
3- positron emission tomography (PET)
4- cardiac MRI (CMR)
5- cardiac computed tomography (CT)
Coronary physiology: Endothelial dysfunction is an early manifestation of vascular disease and plays a role in the development of CAD. Coronary autoregulation attempts to normalize myocardial blood flow even if stenosis exceeded 85% to 90%. However, under vasodilator stimulus, maximal coronary flow has been shown to decrease with stenosis of > 45%. Stress modalities are more sensitive assessing coronary perfusion than analysis of stress-induced wall motion abnormalities or ECG changes alone.
Methods for Inducing Coronary Vasodilation include exercise, pharmacological (Dipyridamole, adenosine, and regadenoson) & Dobutamine.
The Ideal Perfusion Imaging Technique and Agent have special characteristics such as being safe, stable and easy to administer with low cost (for the agent) and being reproducible, with high sensitivity and widely available (for the imaging modality).
SPECT MPI
There are multiples protocol using different radiotracers as (Thallium-201 (Tl-201), Tc-99m sestamibi and Tc-99m tetrofosmin) including same-day rest-stress protocol and a dual-isotope protocol.
Advantages:
· Widely available & extensively validated.
· Compatible with multiple stress modalities.
· Less demand for high temporal resolution.
Limitations:
· Long acquisition protocols.
· Poorer spatial resolution limiting detection of subendocardial perfusion defects.
· Limited sensitivity in detecting mild-to-moderate stenosis.
· Motion, volume & attenuation artifacts which can decrease the diagnostic utility of the perfusion images.
· Reduced sensitivity for detecting left main disease or 3-vessle disease.
· Expose patients to nontrivial radiation doses
PET MPI
PET Radiotracers include N-13ammonia, Rubidium-82 (Rb-82), and O-15 water.
Imaging Protocol: A bolus of the tracer is given, and imaging usually commences between 90 to 120 seconds. ECG-gated PET acquisition is usually performed for 3 to 6 minutes for Rb-82 and 5 to 15 minutes for N-13 ammonia. Stress imaging can be performed soon after rest imaging.
Advantages:
· Improved spatial resolution as compared with SPECT.
· PET tracers have significantly less roll-off of extraction.
· Less attenuation artifacts.
· Easily applied.
· Lower radiation doses than SPECT.
Limitations:
· Higher cost.
· The need for a cyclotron for all but Rb-82 imaging, or imaging agents labeled with F-18.
Myocardial Contrast Echo Perfusion
Contrast Agents: MCE contrast agents are small, gas-filled microbubbles (10 um) that compress and expand when exposed to an acoustic field and generate strong acoustic backscattering. However, it lacks FDA approval.
Contrast Echocardiography Perfusion Techniques: can be assessed with continuous infusion
of microbubbles. When the microbubbles have reached steady-state concentrations, a high mechanical index pulse is used to destroy the bubbles in the imaging plane. The subsequent replenishment of microbubbles is related to myocardial perfusion. Areas that are hypoperfused will have a slower return of microbubbles, whereas areas that are well perfused will have a more rapid return of microbubbles.
Advantages:
· No ionizing radiation.
· Improved spatial resolution detecting sub-endocardial ischemia.
· Perform absolute quantification of myocardial blood flow.
· Exercise and pharmacological stress can be used.
· Wide availability and relatively low cost.
Limitations:
· Suboptimal images due to body habits or respiratory movement.
· Attenuation artifacts from the microbubbles.
· Operator-dependent factors
· No FDA approval for contrast agents.
CMR Perfusion Imaging
Contrast Agents: gadolinium-DTPA c
Imaging Protocol: Stress perfusion CMR is generally applied as part of a comprehensive study that evaluates ventricular function, stress and rest perfusion, and viability/myocardial infarction. Cine images are obtained in <10 minutes. Stress perfusion images are then obtained during infusion of 140 g/kg/min of Adenosine for 2-4 mins. The study takes approximately 45 to 60 minutes with gadolinium used as a contrast.
Advantages:
· High spatial resolution.
· The ability to perform absolute quantification of perfusion.
· Can be performed rapidly.
· Has limited operator dependence.
· Adequate spatial coverage and temporal resolution.
Limitations:
· Artifacts
· Intermediate extraction fraction during first-pass imaging.
· Risk of nephrogenic systemic fibrosis in Create clearance < 30ml/min.
CTA Perfusion Imaging
Contrast Agents: Iodinated contrast agents.
Advantages:
· High spatial resolution.
· Rapid data acquisition.
· Combine information of coronary anatomy, ventricular function, and perfusion in one study.
· Widely available.
· Enable dynamic analysis of perfusion with high temporal resolution.
Limitations:
· The increase in heart rate with vasodilator stress may compromise image quality.
· Artifacts.
· High doses of ionizing radiation.
· Rik of Contrast induced nephropathy.
Since this article is addressing general population, please make reflection on CKD patients.
The following stress tests are used in CKD but with certain limitations:
Thank you, this is an EXCELLENT REFLECTION; well done.
Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk
stratification of patients with known or suspected CAD.
Common Noninvasive myocardial perfusion test:
Single-photon emission computed tomography (SPECT) is most commonly used.
Myocardial contrast echocardiography (MCE).
Positron emission tomography (PET).
Cardiac MRI (CMR).
Cardiac computed tomography (CT).
Methods for Inducing Coronary Vasodilation:
Exercise induces coronary vasodilation.
Dipyridamole, adenosine, and regadenoson and Dobutamine,
SPECT MPI:
Radiotracers:
Thallium-201
Tc-99m sestamibi
Tc-99m tetrofosmin.
SPECT MPI Imaging Protocols:
Same-day rest-stress protocol: Tc99m-labeled perfusion.
First injection at rest is followed by imaging roughly 30 minutes later.
A second injection with 2 to 3 times the activity is administered during peak stress.
A typical Tl-201 protocol:
Injection during peak stress, then imaging roughly 10 minutes later, followed by a
redistribution image obtained roughly 4 hours later.
A dual-isotope protocol:
Tl-201 is used for the rest images and then a Tc-99m perfusion agent is used during
stress soon thereafter.
Advantages:
Widely available.
Extensively validated.
Compatible with multiple stress modalities
Less demand for high temporal resolution.
Limitation:
Long acquisition protocols.
Poorer spatial resolution limiting detection of sub endocardial perfusion defects.
Limited sensitivity in detecting mild-to-moderate stenosis.
Motion artifacts.
Reduced sensitivity for detecting left main disease.
Expose patients to radiation.
PET MPI:
PET Radiotracers:
N-13ammonia, Rubidium-82 (Rb-82), and O-15 water.
Imaging Protocol:
A bolus of the tracer is given and imaging usually commences between 90 to 120
seconds thereafter. ECG-gated PET acquisition is usually performed for 3 to 6 minutes
for Rb-82 and 5 to 15 minutes for N-13 ammonia.
Stress imaging can be performed soon after rest imaging.
Advantages:
Improved spatial resolution.
PET tracers have significantly less roll-off of extraction.
Less artifacts.
More easily applied.
Less radiation.
High sensitivity.
Myocardial Contrast Echo Perfusion:
Still considered experimental.
Contrast Agents:
MCE contrast agents are small, gas-filled microbubbles (10 um) that compress and
expand when exposed to an acoustic field and generate strong acoustic backscattering.
Contrast Echocardiography Perfusion Techniques:
Continuous infusion of microbubbles. When the microbubbles have reached steady-
state concentrations, a high mechanical index pulse is used to destroy the bubbles in the
imaging plane. The subsequent replenishment of microbubbles is related to myocardial
perfusion. Areas that are hypo perfused will have a slower return of microbubbles,
whereas areas that are well perfused will have a more rapid return of microbubbles.
Advantages;
No ionizing radiation.
Improved spatial resolution.
Perform absolute quantification of myocardial blood flow.
Availability and its relatively low cost.
Limitation:
Motion affect pictures.
Artifacts Formation.
Operator dependent.
No FDA-approved contras.
CMR Perfusion Imaging:
Contrast Agents gadolinium-DTPA c
Imaging Protocol:
Stress perfusion CMR is generally applied as part of a comprehensive study that
evaluates ventricular function, stress and rest perfusion.
Stress perfusion images are then obtained during infusion of 140 g/kg/min of Adenosine.
0.05 to 0.1mmol/kg gadolinium contrast.
Advantages:
High spatial resolution.
The ability to perform absolute quantification of perfusion.
Performed rapidly.
Has limited operator dependence.
Adequate spatial coverage and temporal resolution.
Limitations:
Artifact.
Nephrogenic systemic fibrosis.
CTA Perfusion Imaging:
Contrast Agents:
Iodinated contrast agents.
Advantages :
High spatial resolution.
Rapid data acquisition.
Combine information of coronary anatomy, ventricular function, and perfusion.
Widely available.
Enable dynamic analysis of perfusion with high temporal resolution.
Limitations
Heart rate with vasodilator stress may compromise image quality.
High doses of ionizing radiation.
Artifacts.
Contrast induced nephropathy.
patients.
Cardiac stress test:
Low sensitivity in CKD patient (36%) due to:
· Deconditioning .
· Impaired heart rate response to exercise.
· The frequently abnormal baseline ECG in CKD patient the interpretation of
standard stress testing.
· The ST segment changes at stress were shown to be not significantly different
between non-severe CAD and severe CAD group.
STRESS ECHOCARDIOGRAPHY:
The majority of advanced CKD patients had a blunted chronotropic response, thus, did
not achieve 85% maximal predicted heart rate.
Thick myocardium due to LVH with small intracavitary volume, commonly found in CKD
patients, obscures the detection of wall motion abnormality.
MYOCARDIAL PERFUSION SCINTIGRAPHY:
Exercise MPS in the advanced CKD population has the same limitation as EST and ESE,
i.e., related to the inadequate exercise performance and chronotropic incompetence.
High-false negative result from balanced ischemia.
CTA Perfusion Imaging and CMR Perfusion Imaging:
There’s risk of contrast nephropathy and nephrogenic systemic fibrosis.
Excellent
Various modalities are available for diagnosis and assessment of CAD.
Coronary autoregulation can keep adequate oxygen supply to the myocardium with no decrease in resting blood flow despite 85-90% stenosis of the coronaries but under the effect of vasodilators, coronary flow decrease with stenosis >45% and can be detected using quantitative myocardial perfusion imaging.
Coronary perfusion imaging by stress methods is more sensitive than detection of stress induced regional wall motion abnormalities or ECG changes.
Methods for inducing coronary vasodilatation include exercise, pharmacological vasodilators (dipyridamole, adenosine) and dobutamine.
SPECT-MPI:
Available, different stress modalities can be used.
Subendocardial perfusion defects are not well detected.
Low sensitivity in mild to moderate stenosis and in detection of left main disease and 3 vessel disease.
Several artifacts limit its diagnostic ability.
Exposure to nontrivial radiation dose.
PET-MPI:
Better spatial resolution and less artifacts.
Provide absolute quantification of perfusion.
Agents used result in lower radiation dose.
Higher cost, some tracers need cyclotron
Myocardial contrast echo perfusion
Its clinical use is limited as the contrast agent is not approved by FDA and is considered an experimental procedure.
CMR perfusion imaging:
High spatial resolution with quantification of perfusion
Limited operator dependence and not affected by patient’s body habitus
Artifacts may be mistaken for perfusion abnormality
Gadolinium contrast agents may be associated with nephrogenic systemic fibrosis (rare condition but serious in patients with advanced kidney disease)
FDA issued black-box warning for gadolinium contrast agent in patients with creatinine clearance <30mg/dl
CTA perfusion imaging:
MDCT provide high spatial resolution and information about coronary anatomy, ventricular function and perfusion.
Absolute quantification of CT perfusion
Image quality decrease with increased heart rate associated with vasodilator effect.
Limited use in patients with significant renal impairment
High doses of ionizing radiation compared to coronary CTA radiation dose.
No technique shows superiority in the evaluation of myocardial perfusion.
In CKD patients:
SPECT:
CKD patients have higher levels of baseline adenosine which attenuate the detection of induced perfusion abnormalities, correction of attenuation leads to poor quality images.
CMR, gadolinium contrast agent in patients with advanced kidney disease may lead to nephrogenic systemic fibrosis
CT angiography, contrast agents are associated with an increased risk of contrast induced nephropathy.
Excellent
Regarding Gadolinium, any cut-off eGFR below which we should not use it in CKD patients?
Gadolinium shouldn’t be used in CKD patients with eGFR <30 but if no other alternative diagnostic test is available, it should be administered with precautions.
Schieda N, Blaichman JI, Costa AF, Glikstein R, Hurrell C, James M, Jabehdar Maralani P, Shabana W, Tang A, Tsampalieros A, van der Pol CB. Gadolinium-based contrast agents in kidney disease: a comprehensive review and clinical practice guideline issued by the Canadian Association of Radiologists. Canadian journal of kidney health and disease. 2018 Jun 11;5:2054358118778573.
Summery:
All the modalities have some advantages and disadvantages with no superiority.Radionuclide techniques are used to assess flow differences of myocardium.SPECT and CMR have established criteria, however, PET , contrast echocardiography, CT perfusion criteria yet to be established.
SPECT -MPI has imperfectb diagnostic accuracy in ESRD patients, but still a valuable modality in cardiovascular risk assessment.
Thank you for your reply, please expand more
Summarize this article
This article is talking about the non-invasive methods of assessing myocardial perfusion. The coronary physiology of myocardial perfusion is highly regulated and is dependent on:
In normal coronaries, sympathetic stimulation causes a flow-mediated endothelium-dependent release of NO resulting in epicardial and arteriolar vasodilation. With endothelial dysfunction, vasoconstriction from Each predominated, resulting in attenuation or absence of the normal flow mediated vasodilation. When coronary arteries are narrowed by atherosclerotic disease, coronary autoregulation attempts to normalize the myocardial blood flow by reducing the resistance of the distal perfusion to preserve adequate myocardial oxygen supply. Under vasodilator stimulus, maximal coronary flow has been shown to decrease with stenosis of > 45%.
The myocardial perfusion modalities assess the coronary perfusion reserve by using stressors like vasodilators, dobutamine or exercise.
Exercise is typically associated with a 2- to 3- fold increase in myocardial blood flow and is the preferred modality as exercise capacity has an important prognostic value.
Dipyridamole, adenosine and regadenason are pharmacologic vasodilators that cause arteriolar vasodilation by both direct and endothelium-mediated mechanisms and are are associated with a 3.5-4 fold increase in myocardial blood flow.
Dobutamine, a synthetic beta 1 and beta 2 receptor agonist, typically produces a 2-3 fold increase in myocardial blood flow
The principle of the MPI is to have a perfusion agent that should have a high first pass myocardial uptake with insignificant back diffusion and recirculation with rapid clearance from the blood pool and an imaging modality that is highly sensitive to small changes in coronary blood and a quantifiable relationship between signal intensity and perfusion.
SPECT MPI
Uses TI-201, Tc-99 sestamibi or Tc-99 tetrofosmin as the radio tracers. TI-201 has a low energy and a long half life and hence, is sub-optimal for perfusion imaging. The first pass extraction is highest for TI-201 than the other 2. SPECT has several advantages including:
It also has several limitations:
Exercise SPECT MPI has a high sensitivity and specificity of 87% and 73% respectively for detecting stenosis of > 50%. Vasodilator SPECT MPI has a sensitivity of 89% and specificity of 75%. It also provides important prognostic information. However, its sensitivity and specificity is lower in patients with advanced CKD.
PET MPI
It has been used for > 25 years. The main limiting factors for its widespread use are cost, and availability of scanners.
The PET radio tracers include N-13 ammonia, Rubidium-82 and O-15 water. O-15 water is not FDA approved. N-13 ammonia and O-15 water require an onsite cyclotron for synthesis. Rb-82 can be eluted from a generator and does not require a cyclotron. A new agent, fluorine-18 (F-18) has been developed which has a long half life and good cardiac uptake and is currently undergoing evaluation.
PET has improved spatial resolution as compared to SPECT. PET tracers have significantly less roll-off of extraction at high flows as compared with Tc-99. The short half lives of the PET agents results in lower radiation than SPECT
PET MPI has a high sensitivity and specificity of 92% and 85% respectively. When PET MPI was compared to SPECT, it had a higher diagnostic accuracy (91% vs 76%) and higher specificity (100% vs 66%).
Myocardial Contrast Echo (MCE)
MCE contrast agents are small gas-filled micro bubbles (<10 um) that compress and expand when exposed to an acoustic field and generate strong acoustic backscattering. At certain acoustic pressures they undergo non-linear oscillations that result in generation of harmonic frequencies that can be used to distinguish the signal of the micro bubbles from the surrounding tissue. The micro bubbles remain intravascular as they transit the myocardial capillary bed and do not affect cardiac hemodynamics and thus directly reflect myocardial blood flow. Unfortunately, the lack an FDA approved MCE contrast agent for perfusion has currently put limitations on its widespread clinical application.
MCE has a number of potential advantages over other modalities. SPECT, PET and CT perfusion imaging use ionizing radiation while MCE does not. Compared with SPECT, MCE has improved spatial resolution, enabling detection of subendocardial ischemia. . MCE also has the ability of to perform absolute quantification of myocardial blood flow.
It also some limitations. Attenuation from the micro bubbles may result in artifacts in basal segments of the LV. Suboptimal images are obtained in a significant no of patients as the result of respiratory motion, body habits or lung disease.
A no of studies have demonstrated a high concordance of MCE with SPECT. the overall sensitivity and specificity of MCE is 82% and 80% respectively
Cardiac MR Perfusion Imaging
Most CMR studies of myocardial perfusion are based on the first-pass of a bolus of gadolinium contrast agents. Interactions between the unpaired electrons of the paramagnetic gadolinium and water protons in close proximity result in more rapid relaxation of these water protons. Thus, the gadolinium is being indirectly detected via its effects on the relaxation of protons. The T1 and T2 relaxation times of stare protons are inversely proportional to the local gadolinium concentration. Therefore, the areas that are well perfused will have a shorter T1 and appear bright on heavily weighted T1 images, whereas regions that are hypo-refused will have longer T1 and will appear hypointense
Stress perfusion CMR is generally applied as part of a comprehensive study that evaluated ventricular function, stress and rest perfusion and viability/myocardial infarction.
Cardiac MRI has significant advantages for perfusion stress testing including high spatial resolution, the ability to perform absolute quantification of perfusion, and the additional information like size and thickness of the LV. The study can be performed rapidly and has less operator dependance and the signal characteristics re largely independent of the patients body habits.
The FDA has issued a blackbox warning for use of gadolinium-based contrast agents in patients with an eGFR of <30 mls/min due to the risk of developing nephrogenic systemic fibrosis.
Adenosine stress CMR has a sensitivity of 91% and a specificity of 81%
CT Perfusion Imaging
MPI with CT imaging is based o the IV injection of iodinated contrast agents that increase the absorption of x-rays in proportion to the concentration of iodine. Iodinated contrast agents are not hemodynamically inert and have an influence on coronary blood flow. They can induce a reduction in coronary flow followed by a hyperemic response. During first-pass, there is also significant diffusion of the contrast agents into the interstitial space, particularly for the non-ionic and low molecular weight compounds.
Multiple studies have evaluated perfusion in MI, but to date there are only a few published studies that have evaluated myocardial perfusion to detect inducible ischemia with vasodilator stress. One study showed that it as a sensitivity of 72% and specificity of 80% for detecting a significant coronary stenosis. Adenosine stress CT perfusion imaging and angiography in 40 pts by George et al detected perfusion abnormalities with a sensitivity of 86% and a specificity of 92%.
The advantages of MDCT include its high spatial resolution, rapid data acquisition and the ability to potentially combine information of coronary anatomy, ventricular function and perfusion in one study. The advancement of MDCT with 256 or 320 slice detectors may enable dynamic analysis of perfusion with high temporal resolution.
Its image quality may be limited by the increase in heart rate which happens with vasodilator stress. Artifacts within the myocardium limit the ability of quantitative assessment of perfusion. It precludes patients with advanced CKD due to the contrast. It also uses high dose ionizing radiation
Since this article is addressing general population, please make reflection on CKD patients
Excellent Dr Hussein
Regarding Gadolinium, any cut-off eGFR below which we should not use it in CKD patients?
Noninvasive assessment of myocardia perfusion is a critical tool in the diagnosis and prognostication of patient with suspected or known with coronary artery disease (CAD). However, non of this tool is without it advantages or disadvantages, but they have all emerged as a good promising tool.
All the above investigation will help in early diagnosis and prognostication of CAD among CKD patient because it is the commonest cause of morbidity and mortality. Also, because myocardial infarction is the commonest CAD among patient with CKD, all the above investigation will help in higher sensitivity and specificity.
Thank you, Issac
Please expand more on CKD
Thanks Prof Halawa, i action mean to write ESKD patient been work up for kidney transplant that those investigation will be helpful among them
Noninvasive Assessment of Myocardial Perfusion
Noninvasive assessment of myocardial perfusion is important in the diagnosis and risk stratification of patients with known or suspected coronary artery disease (CAD).
Non invasive modalities include:
1- single-photon emission computed tomography (SPECT) i
2- myocardial contrast echocardiography (MCE),
3- positron emission tomography (PET),
4- cardiac MRI (CMR
5- cardiac computed tomography (CT)
Normal coronary physiology depends:
sympathetic still,ulation causes a flow mediated endothelium release of N.O which will improve the epicardial and arteriolar vasodilatation.
Coronary artery has been affected by atherosclerotic changes which will affect the preserve for mycordail o2 supply.
A stenosis must reach 85% to 90 % of the luminal diameter before significant reduction in resting blood flow occur.
How to detect ischemia in MPI;
By inducing coronary vasodilation which creat hetrogencicity area in CAD patient .
exercise cause coronary vasodilation via an endothelium-dependent flow-mediated process to meet the increased oxygen demand.
Exercise is the preferred modality and is associated with a 2- to 3-fold increase in myocardial blood flow.
SPECT MPI.
There are multiples protocol using different radiotracers as (Thallium-201 (Tl-201) , Tc-99m sestamibi and Tc-99m tetrofosmin) sometimes a dual-isotope protocol is used.
With images taken during rest and stress time and analysis of myocardial perfusion done with using visual analysis or semi-quantitatively using differences in relative counts.
=Advantages .
–Guiding selective coronary angiography reduces costs associated with both diagnosis and revascularization.
=Limitations of SPECT.
–Patient exposed to high radiation doses.
–Motion artifacts.
–Less sensitivity in detecting mild-to-moderate stenosis due to roll-off of tracer uptake.
–Limiting detection of sub endocardial perfusion defects.
PET MPI.
Has high sensitivity 92% around and specificity around 85%
Depend on N-13ammonia, Rubidium-82 (Rb-82), and O-15 water are the PET tracers which most of them has short half-life and CT scanners used in rest and with stress by exercise or pharmacologically, analysis of myocardial perfusion done with using visual analysis or semi-quantitatively using differences in relative counts.
=Advantages and Limitations
-High spatial resolution as compared with SPECT.
– PET tracers have significantly less roll-off.
– lower radiation doses than SPECT.
-But, costly and also there is artifact.
Myocardial Contrast Echo Perfusion.
Using ECHO with contrast (gas-filled microbubbles) to assess myocardial perfusion with vasodilator and inotropic pharmacological stress. but still not fully approved by FDA .
Areas that are hypo-perfused will have a slower return of microbubbles, whereas areas that are well perfused will have a more rapid return of microbubbles.
MCE showed a sensitivity of 82% and specificity of 80%.
=Advantages:
–No ionizing radiation.
–Can detect of sub-endocardial ischemia.
–Exercise and pharmacological stress can be used.
–Low cost.
=Limitation:
–Suboptimal images due to body habits or respiratory movement.
–Artifact from bubbles Attenuation.
–Still no FDA approval.
CMR Perfusion Imaging.
Study done with in 45-60 mints with based gadolinium as based contrast with pharmacological stress material as adenosine .
Can detect ventricular function, stress and rest perfusion, and viability/myocardial infarction.
Technique has a sensitivity and specificity of 89% and 87%, respectively, for detecting CAD.
=Advantages.
–Rapid technique.
–High spatial resolution.
–Has limited operator dependence.
= Limitations
–Intermediate extraction fraction during first-pass imaging.
–Risk of nephrogenic systemic fibrosis.
CTA Perfusion Imaging.
Nonionic contrast agents with a high iodine concentration mostly used nowadays but Contrast induced nephropathy should be in mind specially with CKD old patient.
Give us information about coronary anatomy, ventricular function, and perfusion.
=Advantages:
–Rapid test.
–High spatial resolution.
–Allow dynamic analysis of perfusion with high temporal resolution.
=Limitation:
–Image quality affected by heart rate.
–Contrast side effects.
–High dose of radiation if frequently done.
Finally, Diagnostic Performance of Perfusion Imaging Techniques is variable and each one has their upsides and downsides and we should choose our modality according to patient criteria and hospital facilities.
Stress Echo cardiography:
Is considered to be a good choice for cardiac assessment, with sensitivity around 80% and detects wall motion abnormalities on stress indicating myocardial ischemia.
Coronary CT Angiogram:
Has high sensitivity > 90% for diagnosing obstructive CAD ,but calcium deposition still challenges for detection of CAD and is high risk of CIN in CKD patients.
Cardiac MRI:
Can detect ventricular function, stress and rest perfusion with high sensitivity and specificity but it still Gadolinium based and risk of nephrogenic systemic fibrosis appear .
== Reflection on CKD patients:
CKD patients is higher risk than general populations regards CAD as our patients have multiple co-morbidities as (HTN, DM, Dyslipidemia ,CKD-MBD, Volume overload & etc.).
Many factors interprets sensitivity and specificity of diagnostic tests, so need high suspicion and good selection of the test.
This study evaluates non-invasive modalities in myocardial perfusion, evaluating specificity and sensitivity as well as the advantages and disadvantages of each procedure.
Considering the perfusion agents and imaging modality, several factors were considered in an attempt to establish the best model to be used. First-pass absorption, myocardial concentration and perfusion, volume, hemodynamic effects, stability, safety, ease of administration, pharmacokinetics, and pharmacodynamics, and finally, cost-effectiveness.
Adding stress modalities (dipyridamole, adenosine, regadenoson, dobutamine) can detect coronary dysfunction earlier and with more sensitivity than static methods due to the possibility of evaluating endothelial and/or microvascular dysfunction.
SPECT
The radiopharmaceuticals used are Thallium (Tl-201) and Technetium (Tc-99m), the former is not available in Brazil. Rest and post injections vary by isotope and protocol being used. The quality of marker absorption is dependent on myocardial cell integrity plus blood flow. In multicenter studies, it showed a sensitivity of 87% with a specificity of 73% and may have artifacts in which the associated ECG can help to differentiate. Its ability to assess subendocardial perfusion left heart disease, or 3-vessel disease may be underestimated, especially when there is an inflammatory biliary activity or other artifacts.
PET MPI
Availability of equipment, high cost, need for cyclotrons to produce radioisotopes; as well as its transport, storage, and half-life; limit their use more often. Radioisotopes such as Rubidium (Rb-82), Ammonia (N-13), Water O-15, and Fluorine (F-18) can be used in different ways depending on the half-life of each. It can provide more complete images when compared to SPECT, especially when image reconstruction is combined with computed tomography, raising its sensitivity to 92% and specificity to 85%.
Despite the complex structure, it can be cost-effective when compared to angiography.
Myocardial Contrast Echo Perfusion
The use of microbubbles as a contrasting agent and the generated acoustic shield helps to understand blood flow without altering cardiac hemodynamics, helping to assess myocardial blood flow in real-time. The quality of the microbubbles is important to reflect the perfusion, without the need for ionizing radiation, and can even assess subendocardial ischemia. Although low cost and widely available, it is extremely operator-dependent. When well performed by trained people, it has 82% sensitivity and 80% specificity.
CMR Perfusion Imaging
The use of gadolinium (DTPA) in the first pass makes a myocardial assessment with intensity reproduction on T1 in magnetic resonance inversely proportional to the degree of ischemia. Techniques such as FLASH (low-angle shot), echoplanar imaging, and SSFP (steady-state free precession) are protocols to optimize and improve the interpretation of results, being able to add adenosine for stress perfusion increasing sensitivity to 91% and specificity to 81%. Unlike SPECT, it assesses myocardial ischemia and 3-vessel disease well. Avoid using gadolinium in patients with creatinine clearance less than 30 due to the risk of nephrogenic systemic fibrosis.
Unfortunately, due to the risk of renal fibrosis, this method cannot be used in patients with end-stage renal disease.
CTA Perfusion Imaging
Iodinated contrasts can increase the intensity of images on computed tomography, assessing coronary flow and having a sensitivity of 72% and specificity of 80%. Unfortunately, iodinated contrast agents can cause significant nephropathy, especially when the creatinine clearance is less than 60. It is able to simultaneously assess anatomy, ventricular function and perfusion, especially when associated with a second method (coronary angiography, for example).
Conclusions
Individualization and the need for a multidisciplinary team to define the best combination of diagnostic methods is essential. The cost effectiveness must be considered, as well as the limitations of each patient with a given method. Unfortunately, contrast agents (iodine and gadolinium) can bring harm to patients with end-stage renal disease or close to it.
The best exam is still the one available, affordable cost, minimizing damage and getting results.
Thank you
Please expand more on CKD
Noninvasive Assessment of Myocardial Perfusion
Summary :
Noninvasive assessment of myocardial perfusion is essential for diagnosing patients with known or suspected coronary artery disease (CAD).
Multiple modalities include:
1- single-photon emission computed tomography (SPECT) i
2- myocardial contrast echocardiography (MCE),
3- positron emission tomography (PET),
4- cardiac MRI (CMR
5- cardiac computed tomography (CT)
This article critically evaluates the strengths and weaknesses of these modalities for assessing myocardial perfusion.
Coronary Physiology;
Myocardial perfusion is regulated by:
1- Epicardial vessels,
2- Resistance vessels,
3- Endothelium. Endothelial dysfunction plays a role in the development of CAD.
Sympathetic stimulation causes vasoconstriction from acetylcholine. As a result, coronary arteries are narrowed by atherosclerotic disease, and coronary autoregulation normalizes myocardial blood flow by decreasing the resistance of distal perfusion beds to preserve adequate myocardial oxygen supply.
Stenosis is more than 85% to 90% of luminal diameter before significant reductions in resting blood flow occur.
Under vasodilator stimulus, the maximal coronary flow has been shown to decrease with stenosis of _45%
Methods for Inducing Coronary Vasodilation:
Exercisecause coronary vasodilation via an endothelium-dependent flow-mediated process to meet the increased oxygen demand.
Exercise is the preferred modality and is associated with a 2- to 3-fold increase in myocardial blood flow.
The Ideal Perfusion Imaging Technique and Agent:
The best perfusion imaging modality would be highly sensitive to small changes in coronary blood flow.
SPECT MPI:
There are three radiotracers are commonly used clinically for SPECT MPI.:
1- Thallium-201 (Tl-201)
2- Tc-99m sestamibi
3-Tc-99m tetrofosmin binds mitochondrial membranes
SPECT MPI Imaging Protocols:
Several SPECT MPI protocols are available using a Tc99m-labeled perfusion agent; the first injection at rest is followed by imaging about 30 minutes then .
A second injection with 2 to 3 times the activity during peak stress to signal from the rest images and repeat imaging is performed.
Image Analysis:
1-Qualitatively
2-Semiquantitatively
1-Advantages and Limitations of SPECT:
Advantages:
1- SPECT MPI is widely available
2- Validated
Limitation :
1 long acquisition protocol.
2- considerably poorer spatial resolution
3-motion artifacts
can be corrected in postprocessingwith the use of motion correction algorithms.19 ECG-gated acquisitions
4- limiting detection of sub-endocardial perfusion defects.
MPI has reduced sensitivity for detecting left central disease or 3-vessel disease related to balanced ischemia
PET MPI:
Advantages:
PET has been used for MPI for greater than 25 years,
Limitation:
1-availability
2- increased cost, and reimbursement issues
PET Radiotracers:
PET tracers:
1- N-13ammonia,
2- Rubidium-82 (Rb-82),
3- O-15 water.
Imaging Protocol:
Typically a resting perfusion image uses Rb-82 or N-13 ammonia.
As described above, mages may be analyzed qualitatively and semi-quantitatively for SPECT imaging.
Advantages and Limitations:
1-PET has improved spatial resolution as compared with SPECT.
2-PET PET is costly
Compared with angiography, exercise ECG, and SPECT in terms of quality of life-years, the prevalence of CAD _is 70%.43 Initial studies have begun to assess the potential of hybrid PET-CT imaging protocols.44 tracers have significantly less roll-off of extraction
Myocardial Contrast Echo Perfusion:
Advantages
1-evaluation of exercise-
2-dobutamine-induced wall motion analysis
limitations of the sensitivity of wall motion
CMR Perfusion Imaging
image reconstruction algorithms are enabled high-resolution imaging of first-pass myocardial
perfusion with CMR.
Contrast Agents:
Most CMR studies of myocardial perfusion are based on the first pass of a bolus of gadolinium-DTPA contrast agents.
Data Acquisition Pulse Sequences
first-pass CMR perfusion imaging pulse sequence includes substantial T1 weighting to impart contrast related to the contrast agent concentration, rapid data acquisition to images at multiple slice locations per R-R interval, an adequate spatial resolution to detect subendocardial perfusion abnormalities, and minimal artifacts to maximize
diagnostic utility. The disadvantages
of SR are its reduced dynamic range compared to IR preparation.
Cardiac MRI has advantages for perfusion stress testing, including its high spatial resolution, the ability to perform absolute quantification of perfusion, and information provided in a comprehensive CMR study.
Furthermore, the study can be performed rapidly,
Many investigators performed perfusion studies at 3 T and improved SNR and CNR.67 Recently, 3D encoding methods are combined with
imaging to improve spatial coverage using either 3D SSFP or 3D FLASH
no technique has demonstrated unequivocal superiority Advances in quantitative methods are continuing to improve diagnostic accuracy
the radionuclide techniques are used clinically, only assessing relative flow differences between regions of the myocardium.
Since this article is addressing the general population, please make refection on CKD patients:
Cardiovascular disease is the primary cause of morbidity and mortality in CKD patients.
The noninvasive modality is used in CKD patients, .but it has a limitation, a contrast agent not be used.
Thank you
Please expand more on CKD