A MULTICENTER COMPARISON OF DUAL-ENERGY X-RAY ABSORPTIOMETERS - IN-VIVO AND IN-VITRO SOFT-TISSUE MEASUREMENT

Objective: To assess intra- and inter-site soft tissue variability by dual energy X-ray absorptiometry (DXA). Design: Cross-sectional trial. Setting: Three medical research institutions. Subjects: Five humans ( in vivo) and four phantoms (in vitro), configured from two whole body phantoms with artificial skeletons and thickness overlays. Interventio ns: Duplicate total-body DXA scans were performed on all subjects at e ach institution within a 15 d period. Results: All intra-site coeffici ents of variation (CV) were < 0.5% for total tissue mass, but in vitro and in vivo Cvs were 7.2% and 2.3% for fat mass (FM) and 2.5% and 0.9 % for lean mass (LM), respectively. Several total-body and regional FM and LM measurements were significantly different between sites (P < 0 .05), with percent differences between sites ranging from 2.6-13.3% fo r FM and from 1.6-13.6% for LM. Site 2 was consistently lower for FM a nd Site 3 was consistently lower for LM. Conclusions: These results st ress the need for both rigorous and standardized cross-calibration pro cedures for soft tissue measurement by DXA.