Cross Calibration of Hologic QDR2000 and GE Lunar Prodigy for Forearm Bone Mineral Density Measurements

doi:10.1016/j.jocd.2007.05.003

Journal of Clinical Densitometry

Volume 10, Issue 3, July–September 2007, Pages 306-311

https://doi.org/10.1016/j.jocd.2007.05.003 Get rights and content

Abstract

The purpose of this study was to carry out an in vivo cross calibration for forearm bone mineral density (BMD) between a Hologic QDR2000 (Hologic Inc., Bedford MA, USA) and Lunar Prodigy (GE Healthcare, Madison WI, USA) during equipment upgrade. Nineteen subjects (17 females and 2 males, mean age 57 yr, range: 42–79 yr) attending for routine dual energy X-ray absorptiometry scanning were recruited. BMD of the nondominant forearm was measured on both instruments. Cross-calibration equations were derived for total forearm, ultradistal radius and ulna, and 33% radius and ulna. A Bland & Altman plot was used to calculate the mean difference and limits of agreement between instruments. There were significant differences in BMD at all sites. The Prodigy BMD was 15% higher at the total forearm and 20–25% higher in the cortical regions of the 33% ulna and 33% radius. The differences are smaller in the ultradistal regions, as it appears that the Prodigy underestimates BMD at low BMD. The standard error of estimate about the cross calibration was such that it cannot be used to transfer individual patients between instruments, but could be applied to clinical trial data.

Introduction

The International Society for Clinical Densitometry (ISCD) recommends the use of forearm dual energy X-ray absorptiometry (DXA) scans when hip and/or spine cannot be measured or interpreted for technical reasons (e.g., the presence of osteophytes or implants), when the subject has hyperparathyroidism, where there is a reduction in the cortical thickness of bone, and in very obese patients who are over the weight limit for DXA table 1, 2. The ISCD recommends the use of the 33% radius (or one-third radius) region of interest (ROI) on the nondominant forearm for the diagnosis of osteoporosis, because it is the ROI that is at almost the same site when measured on instruments from different manufacturers (3). The site also predicts fracture as well as the more distal ROIs (3), which are less consistently placed by different manufacturers. Forearm bone mineral density (BMD) is useful in studies of bone growth (4), in investigating the effects of exercise (5) and in clinical trials, where the differential effect of new therapies on cortical and trabecular bone is of interest 6, 7.

There are very few studies that have considered cross calibration of forearm DXA scans 8, 9, 10, 11, 12. Most have dealt with comparisons between instruments from the same manufacturers and only 3 have compared equipment from different manufacturers 8, 11, 12. The purpose of this study was to carry out an in vivo cross calibration for forearm BMD between an Hologic QDR2000 (Hologic Inc., Bedford MA, USA) and Lunar Prodigy (GE Healthcare, Madison WI, USA) during equipment upgrade.

Section snippets

Methods

Nineteen subjects attending for routine bone densitometry were recruited to the study. Ethical approval for the study was obtained from the Nottingham Research Ethics Committee 2. Forearm BMD of the nondominant forearm was measured on a Hologic QDR2000 (QDR2000) in array mode and a Lunar Prodigy (Prodigy). BMD results were derived for the total forearm ROI and the 33% radius, ultradistal radius, 33% ulna, and the ultradistal ulna (Fig. 1). During the period of the study, daily quality control

Results

Nineteen subjects (17 females and 2 males, mean age 57 yr, range: 42–79 yr) were recruited. Figure 1 shows the positioning and definition of the forearm ROIs for the same subject on the 2 DXA instruments. Table 1 summarizes the BMD data and the mean difference and limits of agreement from the Bland & Altman plots. Figure 2 shows a typical Bland & Altman plot for the 33% radius BMD.

Figure 3 shows the in vivo cross calibrations for radius BMD. Both the 33% and ultradistal regions are shown. There

Discussion

As expected, there are systematic differences in BMD between the QDR2000 and the Prodigy (Table 1). The BMD measured on the Prodigy is 15% higher in the total forearm in common with the difference in BMD between Hologic and Lunar instruments at other sites (16). The difference in BMD is correlated with the BMD (Fig. 2) so is 20–25% higher in the cortical regions of the 33% ulna and 33% radius and smaller in the ultradistal ROIs, where the BMD is lower. The fact that a single cross-calibration

Conclusions

There are systematic differences in forearm BMD between scanners. At low BMD, the Prodigy appears to underestimate forearm BMD. The standard error of estimate about the in vivo cross calibration is such that it cannot be used to transfer individual patients between instruments, but could be applied to clinical trial data. Spine phantoms do not provide an adequate cross calibration for forearm BMD.

Acknowledgments

We would like to acknowledge the grant funding to support this work from Bio-Imaging Technologies Inc and NPS Pharmaceuticals. We also gratefully acknowledge the support and review of this work from Dr Colin Miller from Bio-Imaging and Dr Stuart Jackson.

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Original ArticleCross Calibration of Hologic QDR2000 and GE Lunar Prodigy for Forearm Bone Mineral Density Measurements

Abstract

Introduction

Section snippets

Methods

Results

Discussion

Conclusions

Acknowledgments

Bone

Am J Clin Nutr

J Clin Densitom

Bone

Bone

J Clin Densitom

J Clin Densitom

J Clin Densitom

Bone Miner

Which central dual X-ray absorptiometry skeletal sites and regions of interest should be used to determine the diagnosis of osteoporosis?

J Clin Densitom

Original Article
Cross Calibration of Hologic QDR2000 and GE Lunar Prodigy for Forearm Bone Mineral Density Measurements