Measurements of bone mineral density of the proximal femur by two commercially available dual energy X-ray absorptiometric systems

Abstract

Two dual energy X-ray absorptiometric (DXA) instruments have recently become commercially available for local bone densitometry: the QDR-1000 (Hologic Inc.) and the DPX (Lunar Radiation Corp.). We report the precision, influence of femoral rotation, correlation and agreement of bone mineral measurements of the proximal femur by these two instruments. In vitro (femur phantom) short-term precision was 1.1%-3.5%, and the long-term precision was 1.2%-3.8%. In vivo (groups of 10 premenopausal and 10 post-menopausal women) short-term precision of duplicate measurements was 1.6%-4.7%, and long-term precision was 1.9%-5.5%. Overall, the precision for Ward's triangle was over 3% and that for the femoral neck and trochanter, 2%-3%. Rotation of a femur phantom produced a statistically significant change in the bone mineral density (BMD) of the femoral neck. Within a clinically relevant range of femoral rotation (20 degrees inward rotation +/- 5 degrees) the coefficient of variation (CV%) increased by a mean factor of 1.1-1.4. Although the correlation (r less than 0.9) between BMD measurements of the proximal femur by the DPX and QDR-1000 in 30 postmenopausal women was high, there was lack of agreement between the two instruments. We found no statistically significant differences between the right and left femur in 30 postmenopausal women. A bilateral femur scan took a mean total time of about 22 min. We conclude that with the introduction of DXA instruments, the precision of bone mineral measurements of the proximal femur has improved. However, for comparability between commercially available DXA instruments, it might be advantageous if units were standardized.

European semi-anthropomorphic spine phantom for the calibration of bone densitometers: Assessment of precision, stability and accuracy the European quantitation of osteoporosis study group

“…These include both photon flux and photon energy, particularly with respect to the low-energy beam in DXA systems, and repositioning, which in patient measurement of the proximal femur can have a substantial influence on the BMD results obtained [8]. Differences in rotation were minimized with the ESP because of its fiat bottom and standardized respositioning procedure.…”

“…At the time this study was initiated it was not possible to reliably convert measurements made, for example, on the spine of an individual subject using one manufacturer's DXA machine and interpret the results in the context of the reference ranges and spread of pathological values seen in contemporary studies conducted with machines made by other manufacturers [8][9][10][11][12]. This has hindered the development of protocols for multi-centre studies.…”

Relationship between calcaneal quantitative ultrasound and hip dual energy X-ray absorptiometry in young healthy men

“…This system has been previously used in the study of BMD in young men [30,31] and offers acceptable precision; coefficient of variation is below 1.5% for neck of femur in vitro repeat measurements, whilst in vivo the overall precision for the femoral neck and trochanter is 2-3% and that for Ward's triangle over 3% [32,33]. Effective subject radiation dose is 0.07 mSv.…”

Follow-up of Individual Patients on Two DXA Scanners of the Same Manufacturer

“…It is an accurate and reproducible technique [1]. Devices of different manufacturers give different results [2,3] while those of the same manufacturer give more or less comparable results [4,5]. Nevertheless, slight and unpredictable differences may occur that can be great enough to be clinically relevant [6,7].…”