Observer-Related Versus Cross-Modality Variability in Ventricular Quantification by Cardiac CT and Cardiovascular Magnetic Resonance

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.