Department of Medical Physics, Western General Hospital, Edinburgh, UK.
Department of Medical Physics, Royal Infirmary, Edinburgh, UK.
J Clin Densitom. 2014 Jan-Mar;17(1):91-6. doi: 10.1016/j.jocd.2013.02.008. Epub 2013 Mar 21.
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.
软组织上层脂肪比例的变化是双能 X 射线吸收法（DXA）测量骨矿物质时的一个潜在误差源。此前，已经从尸体研究和软组织分布的计算机断层扫描（CT）评估了其对脊柱扫描的影响。我们现在将后一种技术应用于 DXA 髋关节扫描。为临床目的而进行的 CT 扫描用于得出总髋关节和股骨颈骨和背景区域的平均脂肪组织厚度。前者总是较低。更重要的是，脂肪厚度差异在受试者之间有所不同。由于骨髓脂肪引起的误差是从骨髓厚度的 CT 测量和假设的骨髓脂肪比例推导出来的。这些差异对测量骨矿物质密度的影响是从脂肪的骨等效性的体模测量中推断出来的。大约 0.06g/cm(2)的不确定度与之前报道的脊柱扫描和尸体测量结果相似。在评估 DXA 扫描的诊断准确性时，应考虑这些不确定度。
