Comparative study of the performances of X-ray and gadolinium 153 bone densitometers at the level of the spine, femoral neck and femoral shaft.

We investigated the precision of gadolinium 153 dual photon absorptiometry (DPA) and quantitative digital radiography (QDR) bone densitometers by determining in vitro and in vivo coefficients of variation (CV) of bone mineral density (BMD). In vitro, the long-term CV of spine phantom BMD measured weekly for 40 weeks was 1.2% and 0.7% for DPA and QDR, respectively. Stimulating soft-tissue thickness with water, the CV of 6 repeat measurements of spine phantom at depths from 0 to 27 cm in 1 cm steps (a total of 168 measurements) increased from 0.1% at 0 cm of water to 2.5% at 27 cm for DPA, and from 0.2% at 0 cm to 1.4% at 27 cm for QDR; mean CV of the 28 series (0-27 cm) was higher for DPA (1.2% +/- 0.8%, mean +/- SD) than for QDR (0.7% +/- 0.6%; P less than 0.001). With the hip phantom, femoral neck BMD was determined, and the CV was also dependent on water thickness; mean CV of the 20 series (0-10 cm) was 2.1% +/- 1.2% for DPA and 1.3% +/- 0.9% for QDR (not significant). In vivo, at the spine level, with DPA, mean CV of BMD measured 6 times after repositioning in 6 healthy volunteers was 3.8% +/- 1.9% and 2.1% +/- 0.7% with 153 Gd activity of 0.46 Ci and 1 Ci, respectively (BMD range: 0.796-1.247 g/cm2, no significant difference between the two groups).(ABSTRACT TRUNCATED AT 250 WORDS)