Evaluation of differences between fan-beam and pencil-beam densitometers

We compared the bone and body composition results in vivo on two bone densi tometers using fan-beam geometry (EXPERT and PRODIGY) with those using penc il-beam geometry (DPX). Measurements were made on large groups of adults ra nging in weight from about 50 to 120 kg. Both spine and femur neck BMD on t he fan-beam densitometers averaged within 1% of the pencil-beam results, an d there was no magnitude dependence of the results by Bland-Altman analysis . Total body BMC and BMD on the PRODIGY and DPX were congruent, but on the EXPERT, BMC was about 2% lower and BMD 2% higher than corresponding values on the DPX. Soft-tissue composition was closely congruent for the PRODIGY a nd DPX; the comparable EXPERT-DPX differences showed greater scatter but no significant magnitude dependence. The smaller fan-angle of the PRODIGY (4 degrees) probably contributed to its better congruence to pencil-beam resul ts compared with the EXPERT (12 degrees).