Photon-counting CT iodine maps for late iodine enhancement: a retrospective feasibility study of image quality and reader confidence.

OBJECTIVE: Myocardial scar assessment is clinically relevant in advanced coronary artery disease, but late iodine enhancement (LIE) CT remains limited by image contrast and validation requirements. This study aimed to evaluate quantitative image quality and reader confidence of photon-counting detector computed tomography (PCD-CT)-derived iodine maps for ischemic-type LIE after coronary computed tomography angiography (CTA). MATERIALS AND METHODS: This is a retrospective single-center study including patients referred for work-up of coronary artery disease. LIE was acquired 5 min after contrast injection for coronary CTA (1.5 mL/kg bodyweight, 350 mg/mL iodine concentration). Iodine maps were reconstructed (Qr32, 4-mm slices). Contrast-to-noise ratios (CNR) were measured, including scar-myocardium CNR in patients with LIE. Eight readers rated image-quality-based confidence for assessing ischemic-type LIE at ≤ 25%, ≤ 50%, and > 50% transmural extent. Inter-reader agreement was assessed using ICC. RESULTS: Twenty-nine patients (13 women, age 73 ± 9 years, BMI 26.7 ± 6.6 kg/m2) were analyzed; LIE was present in 19/29 patients. Mean scar-myocardium contrast was 26.5 ± 9.8 HU. Median confidence increased with transmural extent: moderate for < 25% myocardium thickness (median 3, IQR 3-4), good for ≤ 50% (median 2, IQR 1-3) and high for > 50% (median 1, IQR 1-2, all p < 0.001). Inter-reader agreement was good across transmurality categories (ICC > 0.795, p < 0.001). CONCLUSION: PCD-CT iodine maps acquired 5 min after coronary CTA provided measurable scar conspicuity and high reader confidence for transmural LIE exceeding 50% wall thickness in this small, selected feasibility cohort. Diagnostic accuracy and clinical impact require prospective validation against LGE-MRI. KEY POINTS: Question: Delayed PCD-CT iodine maps acquired 5 min after coronary CTA provided interpretable late iodine enhancement images in selected patients. FINDINGS: In 29 patients, scar-myocardium CNR was 16.2 ± 7.3; reader confidence was high for enhancement involving 50% of myocardial wall thickness and lower for ≤ 25% involvement. RELEVANCE STATEMENT: These feasibility data support prospective validation of delayed iodine maps as a targeted adjunct when myocardial scar information is clinically relevant during cardiac CT work-up.