Precision of regional bone mineral measurements obtained from total-body scans

Newer bone densitometers using dual-photon absorptiometry (DPA) or dual energy x-ray absorptiometry (DEXA) are capable of measuring the total-body bone mineral; regional analysis of these scans would have significant utility if adequate precision were possible. This study investigated short term precision by weekly scanning (three to five times) normal subjects (total 48 scans) and long term precision by scanning a whole-body phantom 30 times over 15 mo. For the 30 phantom scans, a coefficient of variation (CV) of bone mineral content (BMC) and bone mineral density (BMD) was calculated for each region. Nonrandom changes were analyzed by plotting the phantom data with time and testing the slope of the fitted line for significance. Similarly for the subjects, a CV for each region and the mean value for all subjects was obtained. From this study we conclude (a) BMD is more precise than BMC, (b) long-term precision was poorer than short term, (c) long-term regional BMD precision (%) was: head, 3.2; arms, 2.8; legs, 1.6; ribs, 2.6; pelvis, 3.8; thoracic spine, 3.8; lumbar spine, 7.1; total spine, 2.4; trunk, 2.2; total body, 1.2.