Comparative assessment of abdominal and thigh muscle characteristics using CT-derived images

Objectives: The aim of this study was to compare the assessment of skeletal muscle area (SMA in cm²), skeletal muscle index (SMI in cm²/m²), and skeletal muscle density (SMD in HU) between third lumbar vertebra (L3) and thigh landmarks, and the agreement in diagnosing low muscle mass and low SMD (L3 as the reference method).

Methods: This was a multicenter, cross-sectional study including healthy individuals (≥18 y of age) of both sexes, who had an elective computed tomography exam including abdominal and pelvic regions. Computed tomography images were analyzed to evaluate SMA, SMI, and SMD. Muscle abnormalities (low SMA, SMI, and SMD) were defined as values below the fifth percentile from a subsample of healthy young individuals (n = 111; 18-39 y of age; 55.9% women). Correlation coefficients, Bland-Altman graphs, and receiver operating characteristic (ROC) curves were calculated for the total sample and stratified by sex and age.

Results: In all, 268 individuals (44.3 ± 15.2 y of age) were evaluated (53% women). Significant (P < 0.001 for all analysis) and strong correlations between SMA (r = 0.896), SMI (r= 0.853), and SMD (r= 0.864) compared with L3 and thigh landmarks were observed. For the ROC curves, similar areas under the curve values were obtained for men (0.981), women (0.895), younger (0.902), and older adults (0.894).

Conclusions: Muscle characteristics between L3and thigh landmarks have a strong correlation. This suggests that images of the thigh can be used to characterize muscle characteristics. Image acquisition and analysis of thigh region is simpler, with less radiation exposure, and consequently more appropriate for longitudinal analysis.