title: Errors in dual-energy X-ray scanning of the hip because of nonuniform fat distribution.
abstract: The variable proportion of fat in overlying soft tissue is a potential source of error in dual-energy X-ray absorptiometry (DXA) measurements of bone mineral. The effect on spine scanning has previously been assessed from cadaver studies and from computed tomography (CT) scans of soft tissue distribution. We have now applied the latter technique to DXA hip scanning. The CT scans performed for clinical purposes were used to derive mean adipose tissue thicknesses over bone and background areas for total hip and femoral neck. The former was always lower. More importantly, the fat thickness differences varied among subjects. Errors because of bone marrow fat were deduced from CT measurements of marrow thickness and assumed fat proportions of marrow. The effect of these differences on measured bone mineral density was deduced from phantom measurements of the bone equivalence of fat. Uncertainties of around 0.06g/cm(2) are similar to those previously reported for spine scanning and the results from cadaver measurements. They should be considered in assessing the diagnostic accuracy of DXA scanning.
authors.affiliation: Department of Medical Physics, Western General Hospital, Edinburgh, UK. Electronic address: peter.tothill@ed.ac.uk.
authors.forename: Peter
authors.initials: P
authors.lastname: Tothill
authors.affiliation: Department of Medical Physics, Royal Infirmary, Edinburgh, UK.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Weir
authors.affiliation: Department of Medical Physics, Royal Infirmary, Edinburgh, UK.
authors.forename: John
authors.initials: J
authors.lastname: Loveland
mesh_terms: D015502:Absorptiometry, Photon; D000273:Adipose Tissue / Q000000981:diagnostic imaging; D050154:Adiposity; D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density; D003951:Diagnostic Errors; D005260:Female; D005272:Femur Neck / Q000000981:diagnostic imaging*; D006621:Hip Joint / Q000000981:diagnostic imaging*; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed
keywords: Dual-energy X-ray absorptiometry; fat; hip