title: 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.
authors: Istituto di Scienze Mediche, Università degli Studi di Milano, Italy.
authors: C
authors: C
authors: Trevisan
authors: G G
authors: GG
authors: Gandolini
authors: P
authors: P
authors: Sibilla
authors: M
authors: M
authors: Penotti
authors: M P
authors: MP
authors: Caraceni
authors: S
authors: S
authors: Ortolani
mesh_terms: D015502:Absorptiometry, Photon / Q000295:instrumentation / Q000592:standards; D015519:Bone Density; D005269:Femur; D006801:Humans; D008159:Lumbar Vertebrae; D008953:Models, Anatomic; D015203:Reproducibility of Results