Comparison of two Hologic DXA systems (QDR 1000 and QDR 4500/A).

Abstract

Bone mineral content is reliably measured by dual energy X-ray absorptiometry (DXA), if manufacturers' recommendations and quality control (QC) procedures are followed. Several phantoms (Hologic anthropomorphic spine phantom, the Groupe de Recherche et d'Informations sur les Osteoporoses (GRIO) test objects and the European semi-anthropomorphic phantoms) were used to evaluate reproducibility, linearity, accuracy and spatial resolution of two DXA devices in vitro. These parameters were also evaluated in vivo from measurements performed on 120 volunteer patients. It was found that when one device (a single beam monodetector QDR 1000) is replaced by another (a fan beam multidetector QDR 4500/A), the novel combination of procedures described here, ensures that the accuracy of DXA study results is maintained when both devices are used in succession for the same patient. To study the possible responses in clinical situations, the influence of bone environment (soft and adipose tissues) was also evaluated. In both systems, similar performances (in vitro coefficients of variation of 0.5%) were established. At extreme bone density values, slight differences in linearity were found, as well as differences in accuracy and spatial resolution. Lumbar spine and femoral neck measurements were performed with both systems in 120 volunteers, both measurements being made on the same day. The corresponding bone mineral density (BMD) values were highly correlated (r2 = 0.985 for lumbar spine and 0.948 for the femoral neck), and the mean BMD differences were 0.68% and 0.37% for each anatomical site, respectively. Although small, these differences add to the precision error of the method, which is near 1%. A calibration curve has to be obtained in order that both devices can be equally used in regular clinical study. We concluded that when a DXA system is replaced by a new one, appropriate QC procedures must be strictly observed.

Cross-calibration of GE/Lunar pencil and fan-beam dual energy densitometers—bone mineral density and body composition studies

“…Recent studies have also shown similar differences when pencil-and fan-beam DXA machines from the same manufacturer are compared (Blake et al, 1993;Faulkner et al, 1993;Abrahamsen et al, 1995;Franck et al, 1995;Bouyoucef et al, 1996;Barthe et al, 1997;Ellis & Shypailo, 1998;Ruetsche et al, 2000;Kolta et al, 2000;Tothill et al, 2001).…”

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 main manufacturers, however, calibrate their instruments to different standards, use different methodologies, with different software for bone edge detection and different assumptions about fat distribution. Not only this, but there is a significant variation between instruments from the same manufacturer, comparable with the rate of bone loss per annum in postmenopausal women [1][2][3][4]. It is generally agreed that an in vivo cross calibration is the best [5][6][7][8], but there are many situations where this is impractical, particularly in multicenter clinical trials.…”

Axial and Total-Body Bone Densitometry Using a Narrow-Angle Fan-Beam

“…Mean values for BMD obtained on the PRODIGY were within 1% of DPX values both in vitro and in vivo. This is noteworthy because previous studies have shown systematic differences of from 1% to 4% between the pencil-beam QDR-1000 and fan-beam QDR-2000, or QDR-4500 [7][8][9][10][11]21,22]. The PRODIGY results for BMD on the ESP phantom, like the DPX results, were linear, but overestimated the nominal BMD (Table 3).…”