Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
IEEE Trans Ultrason Ferroelectr Freq Control. 2011 Apr;58(4):744-53. doi: 10.1109/TUFFC.2011.1867.
Although quantitative ultrasound imaging based on backscattering coefficients has proven potential for tissue characterization, the scattering models used in most studies assume distributions of identical scatterers. However, actual tissues may exhibit multiple levels of spatial scales. Therefore, the objective of the present study is to analyze the effects of scatterer size distributions when using a fluid-sphere model for estimating values of effective scatterer diameter (ESD) through both simulations and experiments. For simulations, ESD estimates were obtained at several analysis frequencies between 1 and 40 MHz from populations of scatterers with diameters ranging between 25 and 100 μm, 25 and 50 μm, 50 and 100 μm, and 50 and 75 μm. For sufficiently high analysis frequencies, the ESD estimates obtained through simulations were approximately inversely proportional to frequency and mostly independent of the underlying scatterer size distribution. Asymptotic expressions for the expected ESD estimates at low- and high-frequency limits were derived. Experiments were conducted using two gelatin phantoms with contrast agent spheres ranging in diameter from 30 to 140 μm and 70 to 140 μm, and 5-, 7.5-, 10-, and 13-MHz focused transducers. Not only was the asymptotic behavior of ESD versus frequency estimates observed experimentally, but also the experimental ESD estimates using the 10- and 13-MHz transducers were lower than the smallest scatterers present in the second phantom. These results may have a direct impact on how scatterer size estimates corresponding to specimens with different subresolution spatial scales should be interpreted.
虽然基于背向散射系数的定量超声成像已被证明具有组织特征化的潜力，但大多数研究中使用的散射模型假设具有相同散射体的分布。然而，实际的组织可能表现出多个空间尺度水平。因此，本研究的目的是分析在使用流体球模型估计有效散射体直径（ESD）值时，当散射体尺寸分布存在差异时会产生何种影响，通过模拟和实验进行分析。在模拟中，在 1 到 40 MHz 之间的几个分析频率下，从直径为 25 到 100 μm、25 到 50 μm、50 到 100 μm 和 50 到 75 μm 的散射体群体中获得了 ESD 估计值。在足够高的分析频率下，通过模拟获得的 ESD 估计值大约与频率成反比，且主要与底层散射体尺寸分布无关。推导出了低频和高频极限下预期 ESD 估计值的渐近表达式。实验使用两个含有对比剂球体的明胶体模进行，球体直径分别为 30 到 140 μm 和 70 到 140 μm，以及 5、7.5、10 和 13 MHz 的聚焦换能器。不仅在实验中观察到 ESD 与频率估计值的渐近行为，而且使用 10 和 13 MHz 换能器的实验 ESD 估计值也低于第二个体模中存在的最小散射体。这些结果可能会直接影响如何解释具有不同亚分辨率空间尺度的标本的散射体尺寸估计值。
