Ischemia Imaging With CT Perfusion Introduction Coronary CT angiography (CTA) is excellent for anatomical depiction and has high negative predictive value to exclude obstructive coronary artery disease (CAD) in low- to intermediate-risk populations. However, coronary CTA alone has limited ability to estimate the hemodynamic significance of a stenotic lesion. CT perfusion (CTP) is one of the CT techniques that can provide noninvasive hemodynamic information, which helps in selecting patients that may benefit from further intervention or surgery. CTP evaluates the perfusion by the attenuation differences induced in myocardium during the first pass of intravenously injected iodinated contrast material. Technique & Protocol There are multiple, heterogeneous CTP techniques and protocols. Static snapshot technique is the most commonly used acquisition type, which involves a single acquisition in one point of time, typically 8 to 16 seconds after peak aortic attenuation. This provides only qualitative and semi-quantitative information, which can be performed rapidly. In the dynamic technique, myocardium is sampled at multiple time points to generate a time attenuation curve. This allows quantitative evaluation but is associated with higher radiation dose and spatial misregistration. CTP can be performed using either single-energy or dual-energy techniques. Dual-energy technique offers higher sensitivity and specificity, although it is not widely available. Sensitivity is increased due to improved lesion conspicuity in iodine maps and virtual monoenergetic images. Specificity is improved due to lower beam hardening artifacts in high-energy virtual monoenergetic images. Perfusion can be quantified using iodine maps. Stress is induced using pharmacological agents such as adenosine and regadenoson. Some centers do stress scan first followed by a rest acquisition, which doubles as a coronary CTA study, whereas other centers do rest first. Some centers also do a delayed iodine enhancement acquisition in 10-15 minutes to look for myocardial scar similar to MR, but this technique is limited by poor contrast-to-noise ratio. Interpretation of Findings Qualitative analysis shows perfusion defect as a subendocardial or transmural hypoattenuating area in a vascular distribution. Ischemic defect is seen only at stress, whereas infarct is seen both in stress and rest images. Qualitative analysis is not sensitive for the detection of balanced ischemia in all three vascular territories since this technique relies on relative myocardial attenuation differences. Semi-quantitative analysis includes transmural perfusion ratio. Quantitative analysis can be performed only in dynamic acquisition and can quantify myocardial blood flow (MBF) and coronary flow reserve (CFR). False-positive result is seen due to beam hardening artifact. This artifact is due to preferential initial attenuation of low-energy photons of a polyenergetic beam and manifests as a dark subendocardial defect adjacent to dense contrast in the ventricular blood pool. The use of high-energy x-ray or high-energy virtual monoenergetic images of dual-energy CT can decrease this artifact and improve specificity of CTP. Current Evidence CTP has higher accuracy than SPECT for predicting obstructive CAD (> 50%) on invasive coronary angiography (ICA). CTA + CTP have pooled per-vessel specificity of 93% and sensitivity of 85% for diagnosis of stenosis > 50% in ICA. CTP has been validated against nuclear medicine, MR, coronary angiography and invasive fractional flow reserve (FFR) for evaluation of hemodynamically significant stenosis. On a per-vessel basis, CTP has a specificity of 84% and positive predictive value (PPV) of 82% with invasive FFR as the gold standard for ischemia. CTP improves the PPV and pooled specificity for lesion-specific ischemia when compared to coronary CTA alone (0.77 vs. 0.43). CTP perfusion defect and CTA stenosis > 50% is 98% specific for ischemia. A normal CTP perfusion with CTA stenosis < 50% is 100% specific for excluding ischemia. This makes CT an effective gatekeeper for ICA, with per-patient negative likelihood ratio of 0.12, which is superior to SPECT and echo and comparable to MR and PET. CTA + CTP has higher customer satisfaction than either CTA, CTP, MR, or SPECT alone. CTP has also been shown to be more cost effective than SPECT, with incremental cost effective ratio per quality-adjusted life year of $3,191 for CTP compared to $3,357 for SPECT. CTP also adds an incremental prognostic value over CTA for major adverse cardiovascular events (MACE). The presence and number of perfusion defects is associated with higher risk of MACE. There is 5x reduction in downstream invasive angiography and revascularization and low 1-year MACE by using CTP along with CTA. CTP has a higher pooled specificity than CT-FFR (0.86 vs. 0.78), both higher than CTA (0.61). CTP + CTA was shown to improve the diagnostic performance of these two individual techniques, whereas CT-FFR results in only small and insignificant improvement over CTA. CTP + CT-FFR can provide complementary information, with accuracy of 78% for the combination compared to 70% for individual tests. Specifically, CTP improves the the accuracy of CT-FFR in intermediate range values between 0.74 and 0.85. CTP can be done in patients with heavy calcium or stents, which are typically not evaluable by CT-FFR. Only gold members can continue reading. 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Ischemia Imaging With CT Perfusion Introduction Coronary CT angiography (CTA) is excellent for anatomical depiction and has high negative predictive value to exclude obstructive coronary artery disease (CAD) in low- to intermediate-risk populations. However, coronary CTA alone has limited ability to estimate the hemodynamic significance of a stenotic lesion. CT perfusion (CTP) is one of the CT techniques that can provide noninvasive hemodynamic information, which helps in selecting patients that may benefit from further intervention or surgery. CTP evaluates the perfusion by the attenuation differences induced in myocardium during the first pass of intravenously injected iodinated contrast material. Technique & Protocol There are multiple, heterogeneous CTP techniques and protocols. Static snapshot technique is the most commonly used acquisition type, which involves a single acquisition in one point of time, typically 8 to 16 seconds after peak aortic attenuation. This provides only qualitative and semi-quantitative information, which can be performed rapidly. In the dynamic technique, myocardium is sampled at multiple time points to generate a time attenuation curve. This allows quantitative evaluation but is associated with higher radiation dose and spatial misregistration. CTP can be performed using either single-energy or dual-energy techniques. Dual-energy technique offers higher sensitivity and specificity, although it is not widely available. Sensitivity is increased due to improved lesion conspicuity in iodine maps and virtual monoenergetic images. Specificity is improved due to lower beam hardening artifacts in high-energy virtual monoenergetic images. Perfusion can be quantified using iodine maps. Stress is induced using pharmacological agents such as adenosine and regadenoson. Some centers do stress scan first followed by a rest acquisition, which doubles as a coronary CTA study, whereas other centers do rest first. Some centers also do a delayed iodine enhancement acquisition in 10-15 minutes to look for myocardial scar similar to MR, but this technique is limited by poor contrast-to-noise ratio. Interpretation of Findings Qualitative analysis shows perfusion defect as a subendocardial or transmural hypoattenuating area in a vascular distribution. Ischemic defect is seen only at stress, whereas infarct is seen both in stress and rest images. Qualitative analysis is not sensitive for the detection of balanced ischemia in all three vascular territories since this technique relies on relative myocardial attenuation differences. Semi-quantitative analysis includes transmural perfusion ratio. Quantitative analysis can be performed only in dynamic acquisition and can quantify myocardial blood flow (MBF) and coronary flow reserve (CFR). False-positive result is seen due to beam hardening artifact. This artifact is due to preferential initial attenuation of low-energy photons of a polyenergetic beam and manifests as a dark subendocardial defect adjacent to dense contrast in the ventricular blood pool. The use of high-energy x-ray or high-energy virtual monoenergetic images of dual-energy CT can decrease this artifact and improve specificity of CTP. Current Evidence CTP has higher accuracy than SPECT for predicting obstructive CAD (> 50%) on invasive coronary angiography (ICA). CTA + CTP have pooled per-vessel specificity of 93% and sensitivity of 85% for diagnosis of stenosis > 50% in ICA. CTP has been validated against nuclear medicine, MR, coronary angiography and invasive fractional flow reserve (FFR) for evaluation of hemodynamically significant stenosis. On a per-vessel basis, CTP has a specificity of 84% and positive predictive value (PPV) of 82% with invasive FFR as the gold standard for ischemia. CTP improves the PPV and pooled specificity for lesion-specific ischemia when compared to coronary CTA alone (0.77 vs. 0.43). CTP perfusion defect and CTA stenosis > 50% is 98% specific for ischemia. A normal CTP perfusion with CTA stenosis < 50% is 100% specific for excluding ischemia. This makes CT an effective gatekeeper for ICA, with per-patient negative likelihood ratio of 0.12, which is superior to SPECT and echo and comparable to MR and PET. CTA + CTP has higher customer satisfaction than either CTA, CTP, MR, or SPECT alone. CTP has also been shown to be more cost effective than SPECT, with incremental cost effective ratio per quality-adjusted life year of $3,191 for CTP compared to $3,357 for SPECT. CTP also adds an incremental prognostic value over CTA for major adverse cardiovascular events (MACE). The presence and number of perfusion defects is associated with higher risk of MACE. There is 5x reduction in downstream invasive angiography and revascularization and low 1-year MACE by using CTP along with CTA. CTP has a higher pooled specificity than CT-FFR (0.86 vs. 0.78), both higher than CTA (0.61). CTP + CTA was shown to improve the diagnostic performance of these two individual techniques, whereas CT-FFR results in only small and insignificant improvement over CTA. CTP + CT-FFR can provide complementary information, with accuracy of 78% for the combination compared to 70% for individual tests. Specifically, CTP improves the the accuracy of CT-FFR in intermediate range values between 0.74 and 0.85. CTP can be done in patients with heavy calcium or stents, which are typically not evaluable by CT-FFR. Only gold members can continue reading. Log In or Register to continue Share this:Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window) Related posts: page 2: CORONARY ARTERY DISEASE 7: CONGENITAL HEART DISEASE Approach to Venous Disease INDEX Approach to Heart Failure Stay updated, free articles. Join our Telegram channel Join
