Assessment of semi-automated CT myocardial tissue perfusion ratio (TPR) for identifying intermediate lesions in partial occlusion swine model

Background
Computed tomography myocardial perfusion (CTP) imaging is a promising application that combines coronary anatomy with assessment of ischemia. This additional capability is most needed in intermediate grade lesions.

Methods
Left anterior coronary artery (LAD) lesions ranging from 53-84% diameter stenosis were created by a pneumatic occlusion device implanted on the proximal to mid LAD in 10 female anesthetized swine (47.5±1.9 Kg). Occluder inflation pressures were adjusted to obtain stable fractional flow reserve (FFR = 74.3±1.7) during adenosine infusion (140ug/kg/min). Static CTP utilizing a stress-rest protocol with retrospective, ECG-gated acquisition was performed. Post-processing CTP analysis utilizing transmural perfusion (endocardial/epicardial flow) ratio (TPR) was performed utilizing semi-automated application software. This was compared to microsphere-derived TPR (TPRμ). TPR <0.60 during adenosine infusion was used to identify segmental perfusion defects with a modified 17 segment model and polar mapping.

Results
Intermediate lesions were verified by multiplanar coronary CT angiography (stress 77.5±10.1% vs rest 46.7±15.2%, P<0.001). During adenosine infusion perfusion defects (TPR <0.60) distal to the LAD occluder were identified in 9/60 (15%) segments by CTP and 17/60 (28.3%, P=0.076) by TPRμ with discordance noted between CTP and TPRμ defect locations. LAD distribution wall motion abnormalities were noted in 7/10 animals. Of these, 5/7 (71.4%) were associated with TPRμ < 0.60 compared with 2/7 by CTP (28.5%).

Conclusions
Although our study illustrated intermediate lesions by CTP TPR, disparity was noted with TPRμ measures of endocardial/epicardial blood flow and wall motion abnormalities suggesting further advance in analysis software may improve spatial localization of defects.