[Measurement of lumbar bone mineral density by biphoton absorptiometry. Methodology. Reproductibility. Normal values].

Measurements were made with a DPA apparatus (Novo Lab 22a) on different phantoms and on volunteers in an attempt to evaluate the system precision. The reproductibility was found in the range of 0.98 to 4.10% in the case of in vitro measurements, depending on the geometry of the phantoms used, and in the range of 1.6 to 2.94% for volunteers after repositioning. Secondly, the BMD in the lumbar spine of normal women and normal men was estimated. In control females, the BMD is well fitted to the age by a cubic regression. The maximum value of the BMD is found in this case at the age of 31.5 and the maximum rate of bone loss takes place at 57. Total bone loss between 31.5 and the elderly is about 32%. In control males, results are more scattered and are represented by a simple linear regression. The average mineral loss between 30 and 80 years is 11.5% in this area of measurement.