Bone mass measurement by DXA: Influence of analysis procedures and interunit variation

Abstract

Interunit variability among bone densitometers is due to different factors, including different calibration procedures and algorithms and variability in photon source energies and/or intensities. Other factors, such as the choice of scan parameters or the analysis procedures, can also introduce variability. The new generation of dual-energy x-ray absorptiometry (DXA) has partially improved this situation. The aim of this study was to investigate the operator-dependent analysis procedures that can affect scan results and to evaluate the phantom and in vivo interunit variation of some DXA instruments. Four DXA instruments (QDR 1000 and 1000/W, Hologic, Inc.) were used. Potential sources of variability in the analysis procedures of anteroposterior lumbar spine and hip scans were considered: in most cases these procedures significantly influenced scan results. On lumbar spine, an enlargement of the scan window of less than 3 cm was responsible for an average increase in bone mineral density (BMD) of about 3%. On the hip, lowering the scan window by about 1 cm accounted for an increase in the whole-segment BMD of about 4%. After standardization of analysis procedures, interunit and intraunit coefficients of variation and percentage differences among instruments were less than 1% for all the parameters considered (area and bone mineral content and density) with both an anatomic and a geometric phantom, and in nine subjects scanned by two different devices the percentage difference in BMD was greater than 2%. This study shows that present interunit variability allows comparisons among laboratories, but only if highly standardized analysis procedures are used.

Radiofrequency echographic multispectrometry compared with dual X-ray absorptiometry for osteoporosis diagnosis on lumbar spine and femoral neck

“…On the other hand, to the best of our knowledge, there are no reported studies actually quantifying the repeatability of BMD measurements obtained through anteroposterior DXA measurements on living subjects. Among the literature-available papers, those closest to the mentioned topic are the following three: Trevisan et al [38] evaluated the inter-device variability, reporting a CV higher than 2% for BMD measurements on volunteers; Larnach et al [39] assessed the inter-operator repeatability of lateral spinal scans, reporting CV = 3.8% for BMD measurements; Raffan et al [40] evaluated the interoperator variability of body composition measurements performed on canine cadavers, reporting CVs variable in a wide range (from 0.04 to 1.6%) as a function of the considered tissue.…”

Result of Proficiency Test and Comparison of Accuracy Using a European Spine Phantom among the Three Bone Densitometries

“…[5] The European Spine Phantom (ESP) had been developed as a universal standard for instruments measuring bone density. The ESP is composed of three semi-anthropomorphic hydroxyapatite vertebrae of varying densities surrounded by soft tissue equivalent plastic designed to resemble human bone and soft tissue when scanned on bone densitometers.…”

Tibial subchondral bone mineral density: sources of variability and reproducibility

“…Scans were considered as acceptable when the entire bone map was recognized, with no holes. The size of the window and, consequently, the scan length are determinant for bone mass precision as previously observed for lumbar spine and hip DXA assessment 27 . Each image must include at least: tibial tuberosity, femoral condyles and the patella.…”