Errors due to non-uniform distribution of fat in dual X-ray absorptiometry of the lumbar spine.
Errors in spinal dual X-ray absorptiometry (DXA) were studied by analysing X-ray CT scans taken for diagnostic purposes on 20 patients representing a wide range of fat content. The mean difference between the fat thickness over the vertebral bodies and that over a background area in antero-posterior (AP) scanning was 6.7 +/- 8.1 mm for men and 13.4 +/- 4.7 mm for women. For lateral scanning the mean fat thickness difference was only 4 mm for both sexes, but the dispersion was greater, with a standard deviation of 15 mm. To relate these differences to errors in bone mineral, measurements were made of the bone mineral equivalence of fat-equivalent materials on DXA machines from three manufacturers. 10 mm of adipose tissue was equivalent to -0.043 g/cm2 of hydroxyapatite. For AP scanning a non-uniform fat distribution leads to a mean overestimate of 0.029 g/cm2 for men and 0.057 g/cm2 for women. The error exceeded 0.1 g/cm2 in 10% of slices. For lateral scanning the error exceeded 0.1 g/cm2 (about 15% of normal) in a quarter of slices.
Tothill
P
P
Department of Medical Physics and Medical Engineering, Western General Hospital, Edinburgh, UK.
Pye
D W
DW
D015502:Absorptiometry, Photon; D000273:Adipose Tissue / Q000000981:diagnostic imaging; D015519:Bone Density; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000737:chemistry* / Q000000981:diagnostic imaging; D008297:Male; D012737:Sex Factors; D014057:Tomography, X-Ray Computed