Dual photon absorptiometric measurements of bone mineral density increase with source life

Results from Dual Photon Absorptiometry, a common tool in the assessment of bone mass, vary as a function of source life, increasing by as much as 0.6% per month. This rate of increase may vary with source, and its cause is not clear. However, this long-term "drift" must be considered a significant problem for longitudinal studies and regular standardization of DPA equipment, in addition to calibration to machine standards, may be required for stringent quality control.