  We assessed the benefit of combining stress cardiac CT perfusion (CCTP)
myocardial blood flow (MBF) with coronary CT angiography (CCTA) using our
innovative CCTP software. By combining CCTA and CCTP, one can uniquely identify
a flow limiting stenosis (obstructive-lesion + low-MBF) versus MVD
(no-obstructive-lesion + low-MBF. We retrospectively evaluated 104 patients
with suspected CAD, including 18 with diabetes, who underwent CCTA+CCTP. Whole
heart and territorial MBF was assessed using our automated pipeline for CCTP
analysis that included beam hardening correction; temporal scan registration;
automated segmentation; fast, accurate, robust MBF estimation; and
visualization. Stenosis severity was scored using the CCTA
coronary-artery-disease-reporting-and-data-system (CAD-RADS), with obstructive
stenosis deemed as CAD-RADS>=3. We established a threshold MBF
(MBF=199-mL/min-100g) for normal perfusion. In patients with CAD-RADS>=3,
28/37(76%) patients showed ischemia in the corresponding territory. Two
patients with obstructive disease had normal perfusion, suggesting collaterals
and/or a hemodynamically insignificant stenosis. Among diabetics, 10 of 18
(56%) demonstrated diffuse ischemia consistent with MVD. Among non-diabetics,
only 6% had MVD. Sex-specific prevalence of MVD was 21%/24% (M/F). On a
per-vessel basis (n=256), MBF showed a significant difference between
territories with and without obstructive stenosis (165 +/- 61 mL/min-100g vs.
274 +/- 62 mL/min-100g, p <0.05). A significant and negative rank correlation
(rho=-0.53, p<0.05) between territory MBF and CAD-RADS was seen. CCTA in
conjunction with a new automated quantitative CCTP approach can augment the
interpretation of CAD, enabling the distinction of ischemia due to obstructive
lesions and MVD.
