Cross-calibration, precision and patient dose measurements in preparation for clinical trials using dual energy X-ray absorptiometry of the lumbar spine.

Abstract

Large, multicentre clinical trials using DXA to monitor bone density following intervention are now common. At the same time, several different bone densitometers and calibration phantoms are currently in use. The aim of this study was to document the technical information required on cross-calibration of equipment, reproducibility and patient dose before commencing a multicentre clinical trial. To this end, we obtained an in vitro and in vivo cross-calibration of two machines (a Hologic QDR 2000 and a Lunar DPX-L) that were not significantly different. Interobserver and intraobserver precision, and radiation dose were also measured and three commonly used phantoms assessed for their usefulness in cross-calibration and quality assurance. Measured in vitro precision on the two machines (0.3-0.7%) was better than that specified by the manufacturers. In vivo precision was worse (1.4-2.1%), as might be expected in patients with reduced bone mass. Mean entrance skin radiation doses on each machine were 280 microSv for the QDR 2000 and 38 microSv for the DPX-L. No one phantom is ideal, but the European Spine Phantom or Lunar Aluminium Spine Phantom will provide an adequate cross-calibration for a clinical trial. This study demonstrates that an adequate cross-calibration can be obtained for use in groups of patients and that the equipment used is reproducible with a low radiation output.

Comparison of a GE Lunar DPX-IQ and a Norland XR-26 dual energy X-ray absorptiometry scanner for body composition measurements in pigs – <i>in vivo</i>

“…For bone mineral calibration Norland and Hologic use hydroxyapatite alone, whereas Lunar takes into account that bone contains also fat (TOTHILL 1995). Lunar devices appear to measure systematically higher values for BMC and BMD than Norland and Hologic devices (LASKEY et al 1991, MAZESS et al 1991, TOTHILL et al 1994a, CAWTE et al 1999. This was also demonstrated in the present study where Lunar yielded significantly larger BMD and BMC values.…”

“…Differences in the measurement of bone area are caused by the capability of a device to accurately detect the bone edge, including differences in the threshold value for bone detection. CAWTE et al (1999), comparing Lunar and Hologic devices, reported higher BMD values from Lunar and assumed that the edge detection algorithm of the Lunar device eliminated more low density bone than the Hologic device resulting in a smaller area and a consequently higher BMD. Comparing a fan beam with a pencil beam DXA device (Lunar), CRABTREE et al (2005) found a smaller bone area to be associated with a lower BMC in the fan beam device, but the resulting BMD was not different.…”

A Comparison of Phantoms for Cross-Calibration of Lumbar Spine DXA

“…There is about a 15% difference in BMD between Hologic and GE Lunar instruments [9] and the variation between DXA instruments from one manufacturer is of the order of a few percent in vivo and 1% in vitro [1][2][3]. This variation limits the applicability of standardized BMD [8].…”

“…The alternative is to use a cross-calibration phantom, and several have been produced over the years. All have some limitations [7,9]. The aim of this project was to compare the more recently available Bona Fide Phantom and two other phantoms used for cross-calibration (the European Spine Phantom and the GE Lunar Aluminum Spine Phantom) with an in vivo cross-calibration.…”

Comparison of quantitative computed tomography-based measures in predicting vertebral compressive strength

“…The current clinical standard, which is site-specific bone mineral density (BMD) assessment using dual energy x-ray aborptiometry (DXA) (1,4), is only moderately effective in predicting the occurrence of vertebral fractures (11). Numerous researchers have speculated that DXA is an inaccurate measure of vertebral fracture risk potential because it is structurally simplistic, i.e., it reflects only volume averaged material properties, and they have focused their efforts on developing more sophisticated mechanical models of vertebral body fractures (2,8,9,14,15,19,23,36).…”