Technical Notes Errors in Longitudinal Measurements of Bone Mineral: Effect of Source Strength in Single and Dual Photon Absorptiometry

The effect of changing strength during the useful life of a radiation source was evaluated in studies performed on four dual photon (DPA) and two single photon (SPA) bone absorptiometry instruments. Two DPA units and one SPA unit did not show any systematic dependence of measured bone mineral content or bone mineral areal density (BMD) on source activity when evaluated over an entire source life. One DPA and one SPA instrument, however, showed significant time trends associated with source activity. The fourth DPA instrument had a significant linear decrease in BMD over a source life in the automatic mode but performed better in the manual mode. J NucÃ-Med 28:1751-1757,1987 ual photon absorptiometry (DPA) of the lumbar spine has evolved as a major technique for quantitation of mineral in the axial skeleton (7,2). When properly performed, this technique has acceptable precision, pro vides good discrimination between normal and osteo-porotic individuals, and is noninvasive with a low r