Photon-Counting Detector CTA in Standard- and Ultrahigh-Resolution Modes for Diagnosing Coronary Artery Stenosis Using Invasive Angiography as the Reference: A Prospective Study

BACKGROUND. The literature reports excellent diagnostic performance of coronary CTA using photon-counting detector (PCD) CT, albeit obtained using various acquisition and reconstruction protocols. OBJECTIVE. The purpose of this study was to assess the diagnostic performance for detecting significant stenosis of coronary CTA performed by PCD CT with various standard-resolution (SR) and ultrahigh-resolution (UHR) protocols, using invasive coronary angiography (ICA) as the reference standard. METHODS. This prospective study enrolled inpatients undergoing coronary CTA between October 2023 and October 2024. Participants underwent coronary CTA by PCD CT, sequentially alternating between SR (collimation: 144 × 0.4 mm) and UHR (collimation: 120 × 0.2 mm) modes across participants. SR examinations were reconstructed into normal (SR_normal) and virtual noncalcium (SR_VNCa) image sets, both using 0.6-mm slice thickness and Bv40 kernel. UHR examinations were reconstructed into normal (UHR_normal [0.6-mm slice thickness, Bv40 kernel]) and thin (UHR_thin [0.2-mm slice thickness, Bv64 kernel]) image sets. Two radiologists independently measured the diameter of stenoses. The final analysis included patients who underwent ICA after CTA; a cardiologist reviewed the ICA images to determine the reference standard. Stenoses were considered significant at a threshold of 50% or greater. RESULTS. The SR group included 61 patients (mean age, 67 ± 9 [SD] years; 46 men, 15 women; 788 segments analyzed). The UHR group included 61 patients (67 ± 11 years; 43 men, 18 women; 825 segments analyzed). Per-segment sensitivity, specificity, and accuracy for reader 1 were 92.9%, 89.9%, and 90.5% for SR_normal, respectively; 92.9%, 91.6%, and 91.8% for SR_VNCa; 96.0%, 92.4%, and 93.0% for UHR_normal; and 100.0%, 98.6%, and 98.8% for UHR_thin; and for reader 2 were 92.9%, 88.8%, and 89.6% for SR_normal; 93.5%, 92.3%, and 92.5% for SR_VNCa; 96.0%, 91.6%, and 92.2% for UHR_normal; and 100.0%, 98.9%, and 99.0% for UHR_thin. Significant (p < .05) differences included SR_VNCa versus SR_normal for specificity for both readers and accuracy for reader 2; UHR_thin versus UHR_normal for sensitivity, specificity, and accuracy for both readers; and UHR_thin versus SR_VNCa for sensitivity, specificity, and accuracy for both readers. CONCLUSION. Coronary CTA performed by PCD CT achieved high diagnostic performance in the SR or UHR mode. Performance was higher for SR_VNCa than SR_normal and for UHR_thin than either UHR_normal or SR_VNCa. CLINICAL IMPACT. The findings will help to optimize protocols for coronary CTA performed by PCD CT.