Bone mineral and fat measurement with a novel dual photon absorptiometer.

The authors have produced an original dual-photon absorptiometer, with specific algorithms, permitting real-time automatic bone recognition, to reduce examination time (to 5 min). It permits the simultaneous measurement of the mineral density of an area of bone (BMD), the fat percentage of the soft tissues (PFST) that surround it, and the variation in this percentage. It visually represents, on one and the same picture, freely defined in terms of dimension and definition, bone mineral distribution and fat mass distribution. The performances are analysed, using phantoms and taking ten control subjects, in the region of the femoral neck. The variations in PFST in the control subjects are compared with the measurements carried out in MRI in the same region. In all these control subjects, there is a regular decrease in PFST in this region along an upper external/lower internal axis. This decrease has been likened to a regression line, the slope of which, representing between -0.16 per cent of fat per cm and -1.7 per cent per cm, has a mean value of -0.81 per cent per cm. The BMD is thus reduced by 0-2.5 per cent, depending on the subjects.