Measuring leg muscle and fat mass in humans: comparison of CT and dual-energy X-ray absorptiometry

Dual-energy X-ray absorptiometry (DEXA) is reported to be inferior to compu ted tomography (CT) to measure changes in appendicular soft tissue composit ion. We compared CT- and DEXA-measured thigh muscle and fat mass to evaluat e the random and systematic discrepancies between these two methods. Thigh skeletal muscle area (single-slice CT) was suboptimally (r(2) = 0.74, P < 0 .0001) related to DEXA-measured thigh fat-free mass (FFM). In contrast, thi gh muscle and adipose tissue volumes (multislice CT) were highly related to DEXA-measured thigh FFM and fat; (both r(2) = 0.90, P < 0.0001). DEXA-meas ured leg fat was significantly less than multislice-CT-measured leg adipose tissue volume, whereas multislice-CT-measured leg muscle mass was less (P < 0.0001) than DEXA-measured leg FFM. The systematic discrepancies between the two approaches were consistent with the 10-15% nonfat components of adi pose tissue. In conclusion, CT and DEXA measures of appendicular soft tissu e are highly related. Systematic differences between DEXA and CT likely rel ate to the underlying principles of the techniques.