Threshold-automated CT measurements of muscle size and radiological attenuation in multiple lower-extremity muscles of older individuals

Muscle atrophy and fat infiltration, two indicators of deconditioning and weakness in elderly frail patients, are typically assessed by means of manual image analysis from computed tomography (CT) scans. As this time-consuming image analysis limits its wider use in clinical studies, the use of tissue thresholds to semi-automatically assess muscle composition has been suggested. Here, we aimed to investigate the relationship between manual and semi-automated analysis of both cross-sectional area (CSA) and radiological attenuation (RA), in multiple muscles of the lower extremities in aged (77 +/- 6 years) sedentary individuals (n = 40). The participants underwent CT scans of their lower limbs, including hip, thigh and calf muscles. The subsequent analysis of CSA and RA was conducted using both manual segmentation and semi-automatic thresholds (-30 to +150 Hounsfield units). Automated measurements were generally strongly correlated with manually encircled CSA in all muscle groups (R = 0.79-0.99, p < .05) and shortened the analysis time by 70% (p < .05). In m. iliopsoas, however, the CSA became overestimated (15%, p < .05) with thresholded measurements, while the assessment of both CSA and RA was underestimated in muscles with high-fat content (i.e., the gluteal muscles) and in individuals with high-fat infiltration. In conclusion, using the semi-automated technique with conventional thresholds is a time-saving method that delivers accurate gross size of the muscle groups, particularly in the thigh. However, caution should be exercised when using semi-automated techniques for assessing CSA and fat infiltration in muscles with high-fat content.