Coronary plaque quantification with ultrahigh-spatial-resolution photon-counting detector CT: intraindividual comparison with energy-integrating detector CT

Background: Other than enhancing the accuracy of stenosis measurements, the improved spatial resolution of photon-counting detector (PCD) CT may have an impact on quantitative plaque assessment at coronary CT angiography (CCTA). Purpose: To evaluate the effect of PCD CT on coronary plaque quantification and characterization compared with that of energy-integrating detector (EID) CT. Materials and Methods: Consecutive participants undergoing clinically indicated CCTA at EID CT (192 × 0.6-mm collimation) were enrolled to undergo ultrahigh-spatial-resolution (UHR) PCD CT (120 × 0.2-mm collimation) within 30 days. PCD CT was performed using equivalent or lower CT dose index and equivalent contrast media volume as the clinical scan. Total, calcified, fibrotic, and low-attenuation coronary plaque volumes were quantified and compared between scanners. Intra- and interreader reproducibility was assessed for both systems. Results: A total of 164 plaques from 48 participants were segmented on both scans. Total plaque volume was lower at PCD CT compared with EID CT (723.5 mm3 [IQR, 500.6–1184.7 mm3] vs 1084.7 mm3 [IQR, 710.7–1609.8 mm3]; P < .001). UHR-based segmentations produced lower fibrotic (325.4 mm3 [IQR, 151.7–519.2 mm3] vs 627.7 mm3 [IQR, 385.8–795.1 mm3], respectively; P < .001) and higher low-attenuation plaque volumes (72.1 mm3 [IQR, 38.6–161.9 mm3] vs 58.1 mm3 [IQR, 23.4–102.3 mm3], respectively; P = .004) than EID CT–based measurements. Calcified plaque volumes did not differ significantly between PCD CT and EID CT (344.5 mm3 [IQR, 174.3–605.7 mm3] vs 342.1 mm3 [IQR, 180.4–607.5 mm3], respectively; P = .13). Total, calcified, and fibrotic plaque volumes demonstrated excellent agreement between repeated measurements and between readers for both PCD CT and EID CT (all intraclass correlation coefficients [ICCs] > 0.90). Whereas low-attenuation plaque volume had strong intrareader (ICC, 0.84; 95% CI: 0.57, 0.94) and interreader (ICC, 0.92; 95% CI: 0.81, 0.97) agreements for PCD CT, EID CT showed only moderate (ICC, 0.62; 95% CI: 0.11, 0.86) and poor (ICC, 0.47; 95% CI: 0.01, 0.79) intrareader and interreader reproducibility. Conclusion: Compared with EID CT, PCD CT UHR imaging reduced segmented coronary plaque volume by nearly one-third and improved reproducibility of low-attenuation plaque measurements.