Some factors which influence the evaluation of a dual photon measurement of lumbar spine bone mineral mass.

The accuracy of a commercial dual photon densitometer was found to be within 3.0% of true values when measured using a cadaver spine. The precision, the ratio of standard deviation to mean derived from repeated measurements of a tissue-equivalent phantom spine, was 1.6%. Patient size and the age of the radioisotope source had no discernable effect upon bone mineral mass measurements. The intervention of the technologist during data analysis can influence the determination of bone mineral mass in approximately 40% of measurements. When a lumbar spine phantom was measured on six different densitometers manufactured by three different companies, within-manufacturer variations of between 4% and 7% were found. Bone mineral densities differed by up to 30% between manufacturers. Values of lumbar spine mineral mass were measured for 206 apparently normal women. The resultant normal range was similar to others documented by the manufacturer. The differences between these studies and a published study of 892 normal women can best be explained on the basis of intermanufacturer differences.