Bossy Emmanuel, Laugier Pascal, Peyrin Françoise, Padilla Frédéric
Laboratoire Photons et Matière, ESPCI, CNRS UPR 5, F-75005 France.
J Acoust Soc Am. 2007 Oct;122(4):2469-75. doi: 10.1121/1.2766779.
Numerical simulations (finite-difference time domain) are compared to experimental results of ultrasound wave propagation through human trabecular bones. Three-dimensional high-resolution microcomputed tomography reconstructions served as input geometry for the simulation. The numerical simulation took into account scattering, but not absorption. Simulated and experimental values of the attenuation coefficients (alpha, dB/cm) and the normalized broadband ultrasound attenuation (nBUA, dB/cm/MHz) were measured and compared on a set of 28 samples. While experimental and simulated nBUA values were highly correlated (R(2)=0.83), and showed a similar dependence with bone volume fraction, the simulation correctly predicted experimental nBUA values only for low bone volume fraction (BV/TV). Attenuation coefficients were underestimated by the simulation. The absolute difference between experimental and simulated alpha values increased with both BV/TV and frequency. As a function of frequency, the relative difference between experimental and simulated alpha values decreased from 60% around 400 kHz to 30% around 1.2 MHz. Under the assumption that the observed discrepancy expresses the effect of the absorption, our results suggests that nBUA and its dependence on BV/TV can be mostly explained by scattering, and that the relative contribution of scattering to alpha increases with frequency, becoming predominant (>50 %) over absorption for frequencies above 600 kHz.
将数值模拟（时域有限差分法）与超声波在人体小梁骨中传播的实验结果进行了比较。三维高分辨率微型计算机断层扫描重建结果用作模拟的输入几何模型。数值模拟考虑了散射，但未考虑吸收。在一组28个样本上测量并比较了衰减系数（α，dB/cm）和归一化宽带超声衰减（nBUA，dB/cm/MHz）的模拟值和实验值。虽然实验和模拟的nBUA值高度相关（R² = 0.83），并且与骨体积分数表现出相似的依赖性，但模拟仅在低骨体积分数（BV/TV）时才正确预测了实验nBUA值。模拟低估了衰减系数。实验值与模拟α值之间的绝对差异随BV/TV和频率的增加而增大。作为频率的函数，实验值与模拟α值之间的相对差异从400 kHz左右的60%降至1.2 MHz左右的30%。在观察到的差异表示吸收效应的假设下，我们的结果表明，nBUA及其对BV/TV的依赖性主要可以用散射来解释，并且散射对α的相对贡献随频率增加，在频率高于600 kHz时超过吸收成为主要因素（>50%）。
