A MULTICENTER COMPARISON OF DUAL-ENERGY X-RAY ABSORPTIOMETERS - IN-VIVO AND IN-VITRO MEASUREMENTS OF BONE-MINERAL CONTENT AND DENSITY

As part of a multicenter research project, we compared dual-energy X-r ay absorptiometry (CXA) instruments at three research centers (sites 1 , 2, and 3) to determine both intra- and intersite variability of bone mineral content (BMC), bone mineral density (BMD), and bone area (BA) , Scans of the total body and lumbar spine were performed in duplicate on five humans (in vivo), and scans of the total body were performed on two whole body phantoms with artificial skeletons and thickness ove rlays (in vitro) at all sites over 15 days, The average intrasite vari ability in two consecutive total body BMD measurements, expressed as a percent difference, was significantly higher in vitro) 1.74 +/- 1.97% , than in vivo, 0.71 +/- 038% (p < 0.05), Average intrasite variabilit y of the in vivo lumbar spine BMD was 1.08 +/- 1.12%, The intersite co efficients of variation for all BMD, BMC, and BA measurements were < 2 .0%. The total body BMD from site 2 was systematically lower than at s ites 1 and 3 both in vivo and in vitro (p < 0.05) with no differences in BMC and Bk Although significant, the total body BMD differences bet ween sites were small (< 1.2%) in vivo compared with in vitro (< 2.6%) and are encouraging for the comparison and pooling of human data from multicenter trials, provided that appropriate standardized cross-cali bration and analysis procedures are applied.