Myocardial iodine attenuation is associated with coronary artery stenosis severity: insights from photon-counting CT.

To investigate whether myocardial iodine attenuation and iodine/virtual non-contrast (VNC) ratios derived from photon-counting detector CT (PCCT) are associated with coronary artery stenosis severity as classified by CAD-RADS, and to evaluate their potential complementary value to anatomical grading. In this retrospective single-center study, 57 patients (42.1% women; mean age 64.2 ± 13.0 years) who underwent clinically indicated coronary CT angiography using PCCT were included if they had either no coronary atherosclerosis or a measurable atherosclerotic lesion involving the left main or left anterior descending coronary artery, allowing iodine assessment in the corresponding LAD myocardial territory. Myocardial iodine attenuation was quantified on iodine maps using three circular regions of interest placed in the anterior left ventricular wall on mid-ventricular multiplanar reconstructions. Mean iodine attenuation and iodine/VNC ratios were calculated per patient. Coronary artery disease severity was graded according to CAD-RADS 2.0. Associations were assessed using Spearman correlation and linear regression analyses adjusted for age, body mass index, and VNC attenuation. Mean myocardial iodine attenuation was 32.1 ± 18.5 HU, and the mean iodine/VNC ratio was 0.69 ± 0.52. Both metrics showed an overall decrease with increasing CAD-RADS category, with the lowest values observed in patients with CAD-RADS 4 (iodine attenuation 16.4 ± 12.9 HU; iodine/VNC ratio 0.24 ± 0.15). Significant inverse correlations were observed between CAD-RADS category and iodine attenuation (r = -0.54, p < 0.001) as well as iodine/VNC ratio (r = -0.70, p < 0.001). In multivariable analyses, CAD-RADS category remained independently associated with iodine attenuation (β = -8.61 HU per category increase, p < 0.001) and iodine/VNC ratio (β = -0.14, p = 0.003). Myocardial iodine attenuation and iodine/VNC ratios derived from photon-counting CT are associated with coronary artery stenosis severity, classified by CAD-RADS, and may serve as quantitative adjuncts to anatomical coronary assessment. Further validation against established functional reference standards is required.