Repeatability, reproducibility, and observer variability of body composition assessment with single-slice lumbar MRI

The single-slice MRI at the third lumbar vertebra (L3) offers an efficient way to assess body composition but evidence on the reliability of this method is scarce. This study evaluates the accuracy and precision of the single-slice L3 method for adipose and muscle tissue measurements. The technical performance of single-slice (L3) MRI body composition measurements was assessed in a prospective, single-center study of 12 participants, focusing on scan-rescan repeatability, cross-scanner reproducibility, and analyst variability. Participants were scanned using Philips 1.5 T (reference scanner) and Philips 3 T scanners. Additionally, retrospective data from multiple imaging centers from 36 participants were analyzed to evaluate inter-device and inter-observer (analyst vs. radiologist) variability across a wide range of body types, scanner manufacturers (Siemens, Philips, GE) and field strengths (1.5 T and 3 T). Blinded analyses were performed for visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) cross-sectional areas (CSA), VAT and SAT indices, VAT/SAT ratio, skeletal muscle CSA, skeletal muscle index (SMI), psoas muscle CSA, and psoas muscle index. Single-slice MRI-based body composition measurements showed high scan-rescan repeatability (CoV: 1.5%–7.9%, ICC: 0.97–1.0), with low repeatability coefficients (RC) across key metrics, including 12 cm2 for SAT CSA, 15 cm2 for VAT CSA, 5 cm2 for skeletal muscle CSA, and 1.4 cm2 for psoas muscle CSA. Cross-scanner reproducibility was consistent (CoV: 2.3%–15%, ICC: 0.90–1.0). Inter- and intra-analyst variability was minimal (CoV: 0.5%–5.0%, ICC: 0.98–1.0). Analyst-radiologist comparisons showed near-perfect correlations (r = 0.97–1.00, p < 0.001) and excellent reliability (ICC: 0.96–1.0). The results demonstrate that the MRI-based single-slice method at the L3 vertebral level provides accurate, repeatable, and reproducible measurements of adipose and muscle tissue across diverse body types, consistent between trained analysts and experienced radiologists. This study establishes technical validity of the single-slice L3 method and supports its potential for use in clinical and research settings.