Dual X-ray absorptiometry--cross-calibration and normative reference ranges for the spine: results of a European Community Concerted Action.

Bone density measurements by dual X-ray absorptiometry (DXA) of the spine can now be made precisely, but there is no uniformity in reporting results and in presenting reference data. A European Union Concerted Action therefore devised a uniform procedure for cross-calibrating and standardizing instruments, using the European spine phantom (ESP) prototype. This phantom differs in a number of respects from the final version of the ESP. Eighteen centers in nine countries obtained 1619 records (1035 women) from Caucasian subjects, aged 20-80 years, drawn from normal populations. The DXA machines used were made by the Hologic, Lunar, and Norland companies. Highly statistically significant differences were evident between populations, both in apparent rates of bone loss with age and in the spread of values about the age-adjusted means. There were small residual differences in the results obtained with the three machine brands which could have been due to the relatively large between-center population differences we observed. The alternative or additional explanation that they were attributable, in part, to the design differences between the ESP prototype and the definitive ESP, which became available after this study was completed, was shown to be a valid possibility. Results from postmenopausal women reported in relation to the years that have elapsed since menopause showed reduced population variance when compared with conventional reporting in relation to age. After cross-calibration, the center with the highest age-adjusted normal density value averaged 23% more than the center with the lowest. It is therefore crucially important to select appropriate reference data in clinical and epidemiological studies.(ABSTRACT TRUNCATED AT 250 WORDS

Dual X-ray absorptiometry--cross-calibration and normative reference ranges for the spine: results of a European Community Concerted Action.

Bone density measurements by dual X-ray absorptiometry (DXA) of the spine can now be made precisely, but there is no uniformity in reporting results and in presenting reference data. A European Union Concerted Action therefore devised a uniform procedure for cross-calibrating and standardizing instruments, using the European spine phantom (ESP) prototype. This phantom differs in a number of respects from the final version of the ESP. Eighteen centers in nine countries obtained 1619 records (1035 women) from Caucasian subjects, aged 20-80 years, drawn from normal populations. The DXA machines used were made by the Hologic, Lunar, and Norland companies. Highly statistically significant differences were evident between populations, both in apparent rates of bone loss with age and in the spread of values about the age-adjusted means. There were small residual differences in the results obtained with the three machine brands which could have been due to the relatively large between-center population differences we observed. The alternative or additional explanation that they were attributable, in part, to the design differences between the ESP prototype and the definitive ESP, which became available after this study was completed, was shown to be a valid possibility. Results from postmenopausal women reported in relation to the years that have elapsed since menopause showed reduced population variance when compared with conventional reporting in relation to age. After cross-calibration, the center with the highest age-adjusted normal density value averaged 23% more than the center with the lowest. It is therefore crucially important to select appropriate reference data in clinical and epidemiological studies.(ABSTRACT TRUNCATED AT 250 WORDS

European semi-anthropomorphic spine phantom for the calibration of bone densitometers: assessment of precision, stability and accuracy. The European Quantitation of Osteoporosis Study Group.

Up to now it has not been possible to reliably cross-calibrate dual-energy X-ray absorptiometry (DXA) densitometry equipment made by different manufacturers so that a measurement made on an individual subject can be expressed in the units used with a different type of machine. Manufacturers have adopted various procedures for edge detection and calibration, producing various normal ranges which are specific to each individual manufacturer's brand of machine. In this study we have used the recently described European Spine Phantom (ESP, prototype version), which contains three semi-anthropomorphic "vertebrae" of different densities made of stimulated cortical and trabecular bone, to calibrate a range of DXA densitometers and quantitative computed tomography (QCT) equipment used in the measurement of trabecular bone density of the lumbar vertebrae. Three brands of QCT equipment and three brands of DXA equipment were assessed. Repeat measurements were made to assess machine stability. With the large majority of machines which proved stable, mean values were obtained for the measured low, medium and high density vertebrae respectively. In the case of the QCT equipment these means were for the trabecular bone density, and in the case of the DXA equipment for vertebral body bone density in the posteroanterior projection. All DXA machines overestimated the projected area of the vertebral bodies by incorporating variable amounts of transverse process. In general, the QCT equipment gave measured values which were close to the specified values for trabecular density, but there were substantial differences from the specified values in the results provided by the three DXA brands. For the QCT and Norland DXA machines (posteroanterior view), the relationships between specified densities and observed densities were found to be linear, whereas for the other DXA equipment (posteroanterior view), slightly curvilinear, exponential fits were found to be necessary to fit the plots of observed versus specified densities. From these plots, individual calibration equations were derived for each machine studied. For optimal cross-calibration, it was found to be necessary to use an individual calibration equation for each machine. This study has shown that it is possible to cross-calibrate DXA as well as QCT equipment for the measurement of axial bone density. This will be of considerable benefit for large-scale epidemiological studies as well as for multi-site clinical studies depending on bone densitometry

European semi-anthropomorphic phantom for the cross-calibration of peripheral bone densitometers: assessment of precision accuracy and stability.

A semi-anthropomorphic 'distal radius like' phantom, developed by Kalender and Ruegsegger for use in peripheral bone densitometry using single photon (DPA) dual X-ray (DXA) and quantitative computed tomography (QCT) machines, has been studied with a view to cross-calibrating different types and brands of densitometers in current use. In the context of an EU 'Concerted Action' (second Framework Programme) the phantom was repeatedly measured on six SPA machines, three DXA machines and nine QCT machines (545 measurements). Linear regression equations were derived, individual to each machine, which allowed the derivation of 'standardized densities'. In this way we converted measurements made by machines of the same modality to a common scale of measurements. Two machines (one DXA, one SPA) showed statistically significant instability over time emphasising the need for rigorous quality control in the application of densitometry. In other respects these results provide an encouraging basis for the derivation of standardized normative ranges and the more effective use of peripheral densitometry in future clinical and epidemiological studies

Poor correlation of mid-femoral measurements by CT and hip measurements by DXA in the elderly

Background and aims: Hip fracture is a devastating event in terms of outcome in the elderly, and the best predictor of hip fracture risk is hip bone density, usually measured by dual X-ray absorptiometry (DXA). However, bone density can also be ascertained from computerized tomography (CT) scans, and mid-thigh scans are frequently employed to assess the muscle and fat composition of the lower limb. Therefore, we examined if it was possible to predict hip bone density using mid-femoral bone density. Methods: Subjects were 803 ambulatory white and black women and men, aged 70-79 years, participating in the Health, Aging and Body Composition (Health ABC) Study. Bone mineral content (BMC, g) and volumetric bone mineral density (vBMD, mg/cm(3)) of the mid-femur were obtained by CT, whereas BMC and areal bone mineral density (aBMD, g/cm(2)) of the hip (femoral neck and trochanter) were derived from DXA. Results: In regression analyses stratified by race and sex, the coefficient of determination was low with mid-femoral BMC, explaining 6-27% of the variance in hip BMC, with a standard error of estimate (SEE) ranging from 16 to 22% of the mean. For mid-femur vBMD, the variance explained in hip aBMD was 2-17% with a SEE ranging from 15 to 18%. Adjusting aBMD to approximate volumetric density did not improve the relationships. In addition, the utility of fracture prediction was examined. Forty-eight subjects had one or more fractures (various sites) during a mean follow-up of 4.07 years. In logistic regression analysis, there was no association between mid-femoral vBMD and fracture (all fractures), whereas a 1 SD increase in hip BMD was associated with reduced odds for fracture of similar to60%. Conclusions: These results do not support the use of CT-derived mid-femoral vBMD or BMC to predict DXA-measured hip bone mineral status, irrespective of race or sex in older adults. Further, in contrast to femoral neck and trochanter BMD, mid-femur vBMD was not able to predict fracture (all fractures). (C) 2003, Editrice Kurtis