Background/Objectives: Ventricular measurements from cardiac computed tomography (CCT) and cardiovascular magnetic resonance (CMR) may differ due to modality-specific, physiological, or observer-dependent reasons. We compared cross-modality disagreement with intra-modality interobserver variability. Methods: Fifty-four patients with CCT and CMR examinations within 36 months were retrospectively analyzed. Left ventricular (LV) end-diastolic volume (EDV), right ventricular (RV) EDV, and LV mass were measured on the same platform; 18 underwent independent second-observer measurements. The primary metric was the standard deviation of paired differences [SD(D)], with bootstrap 95% confidence intervals (CIs). Results: In the repeat-measurement subset, cross-modality SDs were 29.78 mL, 29.19 mL, and 16.72 g for LV EDV, RV EDV, and LV mass, versus 4.83, 7.33, and 6.71 within CCT and 3.57, 3.58, and 4.11 within CMR. Cross-modality variability was 6.16, 3.98, and 2.49 times the CCT and 8.34, 8.15, and 4.07 times the CMR interobserver variability; all 95% CIs exceeded 1. Examination-interval restriction did not materially reduce dispersion, and body-surface-area indexation changed scale but not relative disagreement. Conclusions: Under routine clinical conditions, cross-modality variability in EDV and LV mass exceeded interobserver variability by 2.5- to 8.3-fold. CCT-CMR differences are unlikely to reflect observer-related post-processing variability alone, and consistent modality selection appears preferable to interchanging quantitative thresholds.

Background and Objectives: Pericoronary adipose tissue (PCAT) attenuation measured on coronary CT angiography is a promising imaging biomarker of coronary inflammation; however, absolute values may be influenced by technical and inter-individual variability, and a standardized methodology for measurement has not been established. Our study aimed to evaluate the association between PCAT attenuation and CAC burden while comparing absolute attenuation values with normalized values to minimize these sources of variability. Materials and Methods: Two hundred patients undergoing cardiac CT were included and stratified into four CAC categories (0, 1–99, 100–299, ≥300). PCAT attenuation was measured at multiple locations on two main levels: aortic root level and four-chamber view level. Relative PCAT attenuation was calculated by subtracting subcutaneous fat attenuation from raw PCAT values. Group comparisons were performed using ANOVA or Kruskal–Wallis tests, and multivariable linear regression models were adjusted for age, sex, and body mass index. Results: In univariate analysis, relative PCAT attenuation differed significantly across CAC categories at the aortic-level right coronary artery (RCA) site (p = 0.007). In multivariable analysis, higher CAC categories were associated with increased relative PCAT attenuation at the aortic RCA (β = 8.56, p = 0.015 for CAC 100–299; β = 10.68, p = 0.005 for CAC ≥300), while associations at the left main coronary artery (LMCA) showed significance in low and moderate CAC categories (β = 6.91, p = 0.047 for CAC 1–99 and β = 8.57, p = 0.016 for CAC 100–299). No significant associations were observed between CAC and raw PCAT attenuation at the aortic level, while isolated and inconsistent findings were observed in other territories. Conclusions: Relative PCAT attenuation is independently associated with CAC severity and normalized values may reduce technical and biological variability, potentially enhancing the sensitivity and robustness of this CT-based biomarker.