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]; <i>P</i> < .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; <i>P</i> < .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; <i>P</i> = .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; <i>P</i> = .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. © RSNA, 2025 <i>Supplemental material is available for this article.</i>