Bolotin H H, Sievänen H, Grashuis J L
School of Medical Sciences, RMIT University, Bundoora, Victoria, Australia.
J Bone Miner Res. 2003 Jun;18(6):1020-7. doi: 10.1359/jbmr.2003.18.6.1020.
Nonuniform extraosseous fat is shown to raise the magnitude of inaccuracies in DXA in vivo BMD measurements into the range of 20-50% in clinically relevant cases. Hence, DXA-based bone fragility diagnoses/ prognoses and evaluations of bone responsiveness to treatment can be unreliable. Patient-specific DXA in vivo bone mineral areal density (BMD) measurements have been demonstrated to be inherently inaccurate even when extraosseous fat (F) and lean muscle tissue (L) are uniformly distributed throughout the scan region of interest (ROI). The present work extends these investigations to quantitative evaluation of the extent to which clinically realistic soft tissue inhomogeneities external to the bone within the DXA scan ROI affect patient-specific in vivo BMD measurement inaccuracies. The results are particularly relevant to patient-specific lumbar vertebral and proximal femoral sites. Norland, Hologic, and Lunar DXA scans and corresponding DXA simulation studies of the same set of 225 different phantom arrays were carried out. The phantoms were specially fabricated absorptiometric replications of bone mineral material (B), red marrow (RM), and yellow marrow (YM) mixtures, and extraosseous F and L combinations spanning the anthropometric ranges encountered clinically. The three different DXA scanners yielded BMD results that effectively coincided, were in excellent agreement with the findings of the present corresponding DXA-simulation studies in each case, and confirmed the validity of the DXA BMD inaccuracy analysis formalism. It was found that only relatively small extraosseous soft tissue inhomogeneities within the ROI of DXA BMD scans can increase substantially the already sizable BMD inaccuracies shown earlier to pertain for uniformly distributed extraosseous soft tissues. The extent of these in vivo BMD inaccuracies (%) are shown to depend on the mean extraosseous F-to-L areal density ratio and its degree of nonuniformity within the local bone scan ROI, the marrow thickness and specific composition, and the actual BMD in any given case. It was found that patient-specific DXA-measured in vivo BMD inaccuracies can, in many clinically encountered cases, be as large as 20-50%, particularly so for osteopenic, osteoporotic, and elderly patients. It is concluded that, because these DXA in vivo BMD inaccuracies are unavoidable and clinically unpredictable, diagnoses/ prognoses of bone fragility and evaluations of bone responsiveness to treatment of individual patients based mainly on DXA in vivo BMD measurements can be unreliable.
在临床相关案例中，已表明非均匀性骨外脂肪会使双能X线吸收法（DXA）活体骨密度（BMD）测量的误差幅度提高到20%-50%。因此，基于DXA的骨脆性诊断/预后以及对骨对治疗反应性的评估可能不可靠。即使骨外脂肪（F）和瘦肌肉组织（L）在整个感兴趣扫描区域（ROI）均匀分布，特定患者的DXA活体骨矿物质面密度（BMD）测量也已被证明本质上是不准确的。本研究将这些调查扩展到定量评估DXA扫描ROI内骨外部临床上现实的软组织不均匀性对特定患者活体BMD测量误差的影响程度。结果与特定患者的腰椎和股骨近端部位特别相关。对同一组225个不同的体模阵列进行了Norland、Hologic和Lunar DXA扫描以及相应的DXA模拟研究。这些体模是专门制作的骨矿物质材料（B）、红骨髓（RM）和黄骨髓（YM）混合物以及跨越临床遇到的人体测量范围的骨外F和L组合的吸收测定复制品。三种不同的DXA扫描仪得出的BMD结果有效吻合，在每种情况下都与当前相应DXA模拟研究的结果高度一致，并证实了DXA BMD误差分析形式的有效性。研究发现，在DXA BMD扫描的ROI内，只有相对较小的骨外软组织不均匀性就能大幅增加先前已表明与均匀分布的骨外软组织相关的相当大的BMD误差。这些活体BMD误差的程度（%）显示取决于局部骨扫描ROI内骨外F与L的平均面密度比及其不均匀程度、骨髓厚度和具体成分以及任何给定案例中的实际BMD。研究发现，在许多临床遇到的案例中，特定患者DXA测量的活体BMD误差可能高达20%-50%，骨质疏松、骨质疏松症和老年患者尤其如此。得出的结论是，由于这些DXA活体BMD误差是不可避免且临床不可预测的，主要基于DXA活体BMD测量对个体患者的骨脆性诊断/预后以及骨对治疗反应性的评估可能不可靠。
