Total body bone mineral in vivo by dual photon absorptiometry. I. Measurement procedures.

A dual photon scanner using a 1 Ci 153Gd source, a NaI detector, traditional electronics and a desktop computer, was constructed. Software for the computation of the total body bone mineral (TBBM) was developed. Non-linear influences such as deadtime due to high count rates, patient scatter and Compton effects were investigated and correction algorithms were introduced in order to obtain exponential attenuation. System precision was measured on a bone-aluminium standard (CV = 2.6%) and system linearity was assessed on aluminium pieces (r = 0.999, SEE = 3.0%). Short-term precision in vivo was tested on 15 healthy subjects scanned twice with a 2-month interval (CV = 2.4%). Long-term reproducibility in vivo was tested on two healthy subjects scanned eight times with 1-month intervals (CV = 1.9% and 3.2%). The influence of patient orientation was investigated on two skeletons. No significant difference was found between anatomical and random orientation. It was concluded that the precision errors were small, therefore making the method applicable not only in cross-sectional studies but also in longitudinal studies designed to investigate the loss or gain of total bone mass in patients suffering from calcium metabolic disorders.