Bone mass measurements in the distal forearm using dual-energy x-ray absorptiometry and gamma-ray computed tomography: a longitudinal, in vivo comparative study.

Indices of bone mass were measured in 23 volunteers weekly over 14-16 weeks using dual-energy x-ray absorptiometry (DEXA) and special-purpose computed tomography (gamma-CT). In vitro, the precision for both systems was excellent (coefficient of variation less than 0.5%). Over 4 months, the precision in vivo (average CV for all subjects) for DEXA measures (BMD, g/cm2, and BMC, g/cm) varied between 0.6 and 1.1%; with gamma-CT it varied from 1.1% for TBD (g/cm3) to 2.2% for CBD (g/cm3). Correlation between the indices of bone mass measured using DEXA and gamma-CT at the ultradistal site was moderate, but these indices were not correlated at the distal third site. When BMD and BMC were derived from the CT index IBD, however, the correlation between these gamma-CT indices and the corresponding DEXA indices was high for both ultradistal and proximal radial sites.