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Objectives: The Swedish CArdioPulmonary bioImage Study reexamination (SCAPIS reexamination) is the first population-based study to employ coronary CT angiography (CCTA) using photon-counting detector CT (PCD-CT). It includes 15,000 participants from SCAPIS baseline. This work aims to describe the PCD-CT protocol in SCAPIS reexamination, compare diagnostic image quality with energy-integrating detector CT (EID-CT) at SCAPIS baseline, and assess the comparability of Agatston scores and degree of stenosis between the studies.

Methods: The PCD-CT protocol in SCAPIS reexamination is provided. CCTA data from 1,147 participants in SCAPIS reexamination (51% women, age 65 [IQR 61–69]) and 29,554 participants in SCAPIS (52% women, age 58 [54–61]) were analyzed. The image quality in eleven proximal and middle coronary segments was compared, stratified by Agatston score. Agatston scores and stenosis degree were compared in age- and sex-matched samples.

Results: Full diagnostic image quality was more frequent in SCAPIS reexamination (1,036/1,147, 90%) compared with SCAPIS baseline (20,468/26,188, 78%), p < 0.001, despite a higher calcium burden (Agatston score 8 [0–106] vs. 0 [0–20]). Of participants with Agatston score > 400, 89/116, 77%, and 246/945, 26%, had full diagnostic image quality, respectively, p < 0.001. Agatston score distributions and stenosis ≥ 50% were similar in matched samples (p = 0.51 and p = 0.08). Of those with ≥ 50% stenosis at SCAPIS baseline, 30% (12/40) were reclassified to < 50% in SCAPIS reexamination.

Conclusion: The optimized PCD-CT protocol in SCAPIS reexamination provided high image quality, irrespective of Agatston scores, outperforming the EID-CT protocol used at SCAPIS baseline. Agatston scores were comparable, but potential differences in stenosis grading warrant further investigation.