Technical Performance of L3 Skeletal Muscle Index Assessment

This study is a technical report documenting the performance of the Skeletal Muscle Index at the L3 vertebra (L3SMI) as a reliable biomarker for assessing sarcopenia. The research utilized TotalSegmentator freeware to segment muscles in axial CT scans of 100 cancer patients, analyzing accuracy, reproducibility, and linearity against expert-segmented ground truth. A second dataset of 205 colorectal cancer patients was evaluated for repeatability in a test-retest setting. The study computed within Coefficient of Variation (wCV), performed Bland–Altman analysis for variability, and measured absolute and relative bias with confidence intervals. Results indicated intra and inter-reader variability of 5% and 7.6%, respectively, with a relative bias of -8.5% and an absolute bias of -11.3 cm². The findings suggest that L3SMI evaluations are reliable, although certain exclusion criteria were established for ill-positioned patients. The report emphasizes the importance of imaging in sarcopenia assessment and the potential of L3SMI in clinical applications.