Neck-to-knee dixon MRI thigh volume as a superior mass biomarker for Sarcopenia: evidence from the UK biobank

Sarcopenia assessment requires biomarkers capturing muscle-specific strength beyond single-slice measurements. We developed an automated MRI framework segmenting 27 pelvic-thigh musculoskeletal structures to investigate muscle distribution as functional biomarkers. Among 37,004 UK Biobank participants (64.5 ± 7.9 years), transformer-based segmentation achieved Dice similarity coefficient of 0.896. Dixon MRI-derived thigh muscle volume showed exceptional DEXA concordance (r = 0.936). Posterior/anterior (P/A) muscle ratio independently predicted adverse outcomes: weak grip strength (OR 1.60, 95%CI 1.45-1.77), sarcopenia (OR 1.42, 95%CI 1.13-1.78), mortality (OR 1.49, 95%CI 1.23-1.81), and falls (OR 1.12, 95%CI 1.05-1.20), all p < 0.005, while left/right asymmetry showed no associations. Automated MRI phenotyping reveals muscle distribution patterns, particularly reduced anterior compartment volume, predict functional decline independent of total muscle mass, supporting evolution toward composition-aware sarcopenia criteria.