Padilla F, Jenson F, Bousson V, Peyrin F, Laugier P
CNRS, UMR7623 LIP, Paris, F-75006 France.
Bone. 2008 Jun;42(6):1193-202. doi: 10.1016/j.bone.2007.10.024. Epub 2007 Nov 17.
The present study was designed to assess the relationships between QUS parameters and bone density or microarchitecture on samples of human femoral trabecular bone. The normalized slope of the frequency-dependent attenuation (nBUA), the speed of sound (SOS) and the broadband ultrasound backscatter coefficient (BUB) were measured on 37 specimens of pure trabecular bones removed from upper parts of fresh human femurs. Bone mineral density (BMD) was assessed using a clinical scanner. Finally, 8 mm diameter cylindrical cores were extracted from the specimens and their microarchitecture was reconstructed after synchrotron radiation microtomography experiments (isotropic resolution of 10 microm). A large number of microarchitectural parameters were computed, describing morphology, connectivity and geometry of the specimens. BMD correlated with all the microarchitectural parameters and the number of significant correlations was found among the architectural parameters themselves. All QUS parameters were significantly correlated to BMD (R=0.83 for nBUA, R=0.81 for SOS and R=0.69 for BUB) and to microarchitectural parameters (R=-0.79 between nBUA and Tb.Sp, R=-0.81 between SOS and Tb.Sp, R=-0.65 between BUB and BS/BV). Using multivariate model, it was found that microstructural parameters adds 10%, 19%, and 4% to the respective BMD alone contribution for the three variables BUA, SOS and BUB. Moreover, the RMSE was reduced by up to 50% for SOS, by up to 21% for nBUA and up to 11% when adding structural variables to BMD in explaining QUS results. Given the sample, which is not osteoporosis-enriched, the added contribution is quite substantial. The variability of SOS was indeed completely explained by a multivariate model including BMD and independent structural parameters (R(2)=0.94). The inverse problem on the data presented here has been addressed using simple and multiple linear regressions. It was shown that the predictions (in terms of R(2) or RMSE) of microarchitectural parameters was not enhanced when combining 2 or 3 QUS in multiple linear regressions compared to the prediction obtained with one QUS parameter alone. The best model was found for the prediction of Tb.Th() from BUA (R(2)=0.58, RMSE=17 microm). Given the high values of RMSE, these linear models appear of limited clinical value, suggesting that appropriate models have to be derived in order to solve the inverse problem. In this regard, a very interesting multivariate model was found for nBUA and BUB with Tb.Th and Tb.N, in agreement with single scattering theories by random medium. However, the source of residual variability of nBUA and BUB (15% and 45% respectively) remained unexplained.
本研究旨在评估定量超声（QUS）参数与人类股骨小梁骨样本的骨密度或微观结构之间的关系。在从新鲜人股骨上部取出的37个纯小梁骨标本上，测量了频率依赖性衰减的归一化斜率（nBUA）、声速（SOS）和宽带超声背向散射系数（BUB）。使用临床扫描仪评估骨矿物质密度（BMD）。最后，从标本中提取直径8毫米的圆柱形芯，并在同步辐射显微断层扫描实验（各向同性分辨率为10微米）后重建其微观结构。计算了大量描述标本形态、连通性和几何形状的微观结构参数。BMD与所有微观结构参数相关，并且在结构参数之间发现了大量显著相关性。所有QUS参数均与BMD显著相关（nBUA的R = 0.83，SOS的R = 0.81，BUB的R = 0.69），也与微观结构参数相关（nBUA与骨小梁间距（Tb.Sp）之间的R = -0.79，SOS与Tb.Sp之间的R = -0.81，BUB与骨表面积与骨体积比（BS/BV）之间的R = -0.65）。使用多变量模型发现，对于三个变量BUA、SOS和BUB，微观结构参数分别为单独的BMD贡献增加了10%、19%和4%。此外，在解释QUS结果时，将结构变量添加到BMD中，SOS的均方根误差（RMSE）最多降低50%，nBUA最多降低21%，最多降低11%。鉴于该样本并非富含骨质疏松症患者，这种额外贡献相当可观。实际上，SOS的变异性完全由包含BMD和独立结构参数的多变量模型解释（R² = 0.94）。这里呈现的数据的逆问题已通过简单和多元线性回归解决。结果表明，与仅使用一个QUS参数获得的预测相比，在多元线性回归中组合2个或3个QUS时，微观结构参数的预测（就R²或RMSE而言）并未得到增强。从BUA预测骨小梁厚度（Tb.Th）时发现了最佳模型（R² = 0.58，RMSE = 17微米）。鉴于RMSE值较高，这些线性模型的临床价值有限，这表明必须推导合适的模型来解决逆问题。在这方面，发现了一个关于nBUA和BUB与Tb.Th和骨小梁数量（Tb.N）的非常有趣的多变量模型，这与随机介质的单次散射理论一致。然而，nBUA和BUB的残余变异性来源（分别为15%和%）仍无法解释。
