PRECISION OF DUAL X-RAY ABSORPTIOMETRY AND PERIPHERAL COMPUTED-TOMOGRAPHY USING MOBILE DENSITOMETRY UNITS

Irrespective of the method used for noninvasive bone mass determinatio n, data comparison between different centers is a major problem as sig nificant interunit variation may occur. We, therefore, have employed m obile densitometry units to reduce interunit variability in two large epidemiologic studies in Germany, Two cars were equipped with either t wo dual X-ray absorptiometry (DXA) instruments (QDR 1000 Hologic, USA) (car I) or a special purposed scanner for peripheral quantitative com puted tomography (pQCT) (XCT 900, Stratec, FRG) (car II). The cars wer e moved across Germany 11,090 km and 1651 km during the studies over a period of 30 and 7 months, respectively. Precision in vitro was deter mined using hydroxyapatite phantoms. Forty-eight patients underwent du plicate measurements at the lumbar spine (n = 22) and hip (n = 26) for assessing reproducibility in vivo. Between the two series of scans,th e car was moved 63 km. Long-term precision in vitro of the QDR 1000 in struments were 0.41% and 0.59% for BMD with no evidence of machine dri ft (rate of change per year 0.04% and 0.05%, respectively). Short-term reproducibility in vivo showed a coefficient of variation (cv) of 1.0 2% for spinal BMD (L2-L4) and 1.72% for femoral neck. Longterm precisi on in vitro of the pQCT scanner was 0.9%. Our study shows precision in vivo and in vitro and stability of the mobile densitometers similar t o that achieved with stationary equipment. In conclusion, mobile densi tometry may become a useful tool not only for epidemiologic surveys an d clinical trials but also for routine evaluation in less densely popu lated areas.