Coronary Artery Calcium Scoring with Photon-Counting Detector CT: Ultra-Low-Dose Scan Versus Coronary CT Angiography-Derived Images.
PURPOSE To compare coronary artery calcium (CAC) scores from ultra-low-dose true non-contrast (TNC), virtual non-contrast (VNC), and virtual non-iodine (VNI) images with standard TNC on a dual-source photon-counting detector CT (PCD-CT). METHODS In this prospective single-center study (January 2025-March 2026), patients underwent standard TNC (sequential, 120 kVp), ultra-low-dose TNC (high-pitch helical, tin-filtered 100 kVp), and coronary CT angiography (CCTA); VNC and VNI images were generated from CCTA. CAC scores and burden categories were evaluated. Correlation and agreement with standard TNC were assessed using Pearson coefficients with Williams' test, Bland-Altman plots, and weighted Cohen's kappa. RESULTS Seventy-one patients (median age, 75 years; 52 men) were evaluated. Median dose-length product was 7.98, 71.8, and 428 mGy cm for ultra-low-dose TNC, standard TNC, and CCTA, respectively. Ultra-low-dose TNC showed the strongest correlation with standard TNC (r = 0.996), superior to VNI (r = 0.976, P < 0.001) and VNC (r = 0.900, P < 0.001). Agreement in CAC burden categorization was excellent for ultra-low-dose TNC (κ = 0.932) and good for VNI (κ = 0.827), whereas VNC showed moderate agreement (κ = 0.424). VNI had minimal bias (mean difference, -3.9) but wider limits of agreement than ultra-low-dose TNC (-356.5 to 348.6 vs. -163.2 to 105.9). VNC underestimated CAC scores (mean bias, -442.0). CONCLUSION Ultra-low-dose TNC with dual-source PCD-CT showed excellent agreement with standard TNC while reducing radiation by nearly 90%. VNI was acceptable but less robust, whereas VNC substantially underestimated CAC scores. Ultra-low-dose TNC is a reliable, dose-efficient alternative to standard TNC for CAC scoring.