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Bone Mineral and Body Composition Measurements: Cross‐Calibration of Pencil‐Beam and Fan‐Beam Dual‐Energy X‐Ray Absorptiometers
Author(s) -
Ellis Kenneth J.,
Shypailo Roman J.
Publication year - 1998
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1359/jbmr.1998.13.10.1613
Subject(s) - dual energy , beam (structure) , pencil (optics) , x ray , calibration , optics , bone mineral content , materials science , bone mineral , physics , medicine , osteoporosis , quantum mechanics
Pencil‐beam dual‐energy X‐ray absorptiometers (DXA) are being replaced with instruments that rely solely on fan‐beam technology. However, information has been lacking regarding the translation of bone mineral and body composition data between the two devices. We have compared total body scans using pencil‐beam (Hologic QDR‐2000W) and fan‐beam (Hologic QDR‐4500A) instruments for 33 children (ages 3–18 years) and 14 adults. Bone mineral content (BMC), bone mineral density (BMD), fat, lean, and body fatness (%fat) values were highly correlated ( r 2 = 0.984–0.998) between the two DXA instruments. The mean differences between the paired measurements were: ΔBMC = 7.5 ± 73.6 g, ΔBMD = 0.0074 ± 0.0252 g/cm 2 , Δlean = 1.05 ± 1.8 kg, Δfat = −0.77 ± 1.7 kg, and Δ%fat = −0.94% ± 2.5%. The BMC and BMD values were not statistically different, whereas the differences for the body composition values were significant ( p < 0.02–0.005). Regression equations are provided for conversion of bone and body composition data between pencil‐beam and fan‐beam values for the whole body. To test the performance of these equations for a second group (23 subjects), predicted values were compared with the measured data obtained using the fan‐beam instrument. The mean differences were −1.0% to 1.4%, except for body fat mass, where the difference was 6.4%. For cross‐sectional studies, the two DXA technologies can be considered equivalent after using the translational equations provided. For longitudinal studies in which small changes in body composition for the individual are to be detected, we recommend that the same DXA instrument be used whenever possible. For example, transition from a pencil‐beam to a fan‐beam instrument could, in extreme cases, result in differences as large as 19% for the estimate of body fat mass.