Beckman Institute of Advanced Science and Technology, Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
J Acoust Soc Am. 2019 Jul;146(1):85. doi: 10.1121/1.5115355.
The backscatter coefficient (BSC) is a fundamental property of tissues and can be used to classify tissues. Two BSC calibration methods are the planar reflector method and the reference phantom method. In both methods, linear acoustic propagation is assumed. In this study, the calibration methods were evaluated when acoustic nonlinear distortion was present. Radio frequency data were acquired from two physical phantoms using a 5 MHz single-element transducer and low power (one excitation level) and high power (six increasing excitation levels) excitation signals. BSCs estimated from the high power settings were compared to the BSCs estimated using the low power by calculating the root mean square error (RMSE). The BSCs were parameterized by fitting the BSC curve to a power law and estimating the power law exponent and by estimating the effective scatterer diameter (ESD). When using the planar reflector method, estimates of the exponent were observed to monotonically increase in value versus increasing excitation level and the ESD decreased with increasing excitation level. The RMSE increased monotonically versus excitation level using the planar reflector method but did not increase using the reference phantom method. The results suggest that the effects of nonlinear distortion are minimized using the reference phantom method.
反向散射系数 (BSC) 是组织的基本特性，可以用于组织分类。有两种 BSC 校准方法，即平面反射器法和参考体模法。在这两种方法中，都假设声传播是线性的。在这项研究中，当存在声非线性失真时，评估了校准方法。使用 5MHz 单阵元换能器和低功率（一个激励水平）和高功率（六个递增激励水平）激励信号，从两个物理体模获取射频数据。通过计算均方根误差 (RMSE)，比较高功率设置下估计的 BSCs 与低功率设置下估计的 BSCs。通过将 BSC 曲线拟合为幂律并估计幂律指数，以及估计有效散射体直径 (ESD)，对 BSC 进行参数化。使用平面反射器方法时，观察到随着激励水平的增加，指数的估计值单调增加，而 ESD 随着激励水平的增加而减小。使用平面反射器方法时，RMSE 随着激励水平单调增加，但使用参考体模方法时，RMSE 并未增加。结果表明，参考体模法可最大限度地减少非线性失真的影响。
