DUAL-ENERGY X-RAY ABSORPTIOMETRY MEASUREMENTS OF BODY-COMPOSITION - EFFECTS OF DEPTH AND TISSUE THICKNESS, INCLUDING COMPARISONS WITH DIRECT ANALYSIS

1. There are few data regarding the accuracy of Hologic QDR-1000W dual -energy X-ray absorptiometry for the measurement of body composition. In two studies, one in an in vitro experimental system using oil and w ater mixtures and the other in samples of pork meat, the effect of dep th and tissue thickness on the measured composition was assessed. In t he latter study the measured fat mass was compared with that measured by direct analysis. 2. All data indicated a trend in the measured fat mass with depth, such that more fat was measured at extremes of depth (< 10 cm and > 25 cm) than at intermediate depths. 3. In samples of me at weighing approximately 55 kg, dual X-ray absorptiometry significant ly underestimated the absolute fat mass compared with direct analysis (mean 20.4 +/- 1.65%) by 5-8% or 1-4 kg of fat. 4. These findings are of direct relevance to both clinical and research work using this tech nique to measure body composition, in particular in circumstances in w hich changes in body composition and/or tissue thickness are anticipat ed.