Myocardial Assessment with Cardiac CT: Ischemic Heart Disease and Beyond

Figures

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  Fig. 1. Graphical representation of two of the most common CTP protocols used. a Rest-stress protocol—standard patient preparation for CCTA is recommended prior to the acquisition of rest images. Vasodilator infusion can be started within the last 3–5 min of the washout phase to facilitate throughput. Finally, a 5–15-min delay is standard prior to prospective ECG-triggered acquisition for DE assessment. Total time protocol time is approximately 20–40 min. b Stress-rest protocol—vasodilator stress agent is given upfront followed by retrospective ECG-gated acquisition (may vary based on scanner platform). Adenosine is preferred given its short half-life, preventing carryover hyperemia and hemodynamic changes into the rest acquisition. After a 5–15-min delay, DE images can be obtained (IV nodal blocking agents can be given prior to acquisition if needed). Finally, additional nodal blockers are administered followed by nitroglycerin prior to ECG-triggered prospective rest series acquisition

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  Fig. 2. The left-sided images depict a thick-slab three-chamber average attenuation reconstruction (WW/WL 300/150) with a segment of the apical septal wall segment magnified to better demonstrate where epicardial (epi) and subendocardial (endo) regions of interest (ROI) would be drawn. TPR is calculated by obtaining the average Hounsfield unit (HU) attenuation from a ROI within the endo (HUendo) and dividing by the average HU derived from a ROI within the epi (HUepi) within the same wall segment. A ratio < 1.0 is abnormal and ratios ≤ 0.75 are highly suggestive of ischemia. The right-sided image represents available postprocessing application software available through various vendors that allow for semiautomated calculation of TPR throughout the entire myocardium. Color overlay can be added to assist with visual assessment of ischemia. In the presented image, there is evidence of ischemia in the LAD distribution. Of note, the apparent perfusion defect in the inferolateral wall segment represents a common artifact observed in CTP and not true ischemia in the left circumflex distribution

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  Fig. 3. Representation of currently available vendor-specific dual-energy CT (DECT) solutions available to date

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  Fig. 4. Thick-slab average HU short-axis projection demonstrating a perfusion defect in the LAD territory (black arrows). In the visual assessment of ischemia with CTP imaging, windowing at the 3D workstation is vital to maximize visual discrimination between ischemic myocardium (HU attenuation between 30 and 70) and normal myocardium (HU attenuation ~ 100). As is commonly observed, a hypoattenuation artifact is present in the inferolateral wall segment secondary to beam hardening from the descending thoracic aorta (*) mimicking a perfusion defect in this territory

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  Fig. 5. Thin-slab two-chamber projection demonstrating isolated LV apical hypertrophy (*) in a patient with the apical variant of hypertrophic cardiomyopathy. The white arrow denotes a small apical aneurysm/pouch, which is commonly observed in this variant of HCM and easily appreciated on CCT