Department of Civil and Environmental Engineering, Vanderbilt University, Nashville, TN, USA.
Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA.
Ultrason Imaging. 2020 May;42(3):159-176. doi: 10.1177/0161734620917306. Epub 2020 May 3.
We perform finite element modeling of pulse-echo ultrasound of a hard inclusion in a soft tissue to gain a better understanding of B-mode image brightness characteristics. We simulate a pressure wave emitted by an ultrasound transducer through the inclusion-tissue medium by prescribing suitable boundary conditions, and collect the scattered wave response to simulate the behavior of the transducer array used for pulse-echo ultrasound. We form B-mode images from simulated channel data using standard delay and sum beamforming. We establish the accuracy of the finite element model by comparing the point spread function with that obtained from Field II ultrasound simulation program. We also demonstrate qualitative validation by comparing the brightness characteristics of rough and smooth surfaced circular inclusions with experimental images of a cylindrical metal tool immersed in a water tank. We next conduct simulation studies to evaluate changes in B-mode image brightness intensity and contrast related to different constitutive properties, namely, compressibility of the inclusion, impedance contrast between the host and inclusion, and surface roughness of the inclusion. We find that the intensity observed behind a hard inclusion in the axial direction is strongly affected by the compressibility and roughness of the inclusion. Also, the perceived width of the stone based on the intensity is greater for rougher stones. Our study indicates that imaging of compressible inclusions may benefit from targeted B-mode image forming algorithms. Our modeling framework can potentially be useful in differentiating hard inclusions from surrounding parenchyma, and for classifying kidney stones or gallstones.
我们对软组织中硬内含物的脉冲回波超声进行有限元建模，以更好地理解 B 模式图像的亮度特征。我们通过规定适当的边界条件来模拟超声换能器发出的压力波，通过包括组织介质中的内含物，并收集散射波响应来模拟用于脉冲回波超声的换能器阵列的行为。我们使用标准的延迟和求和波束形成技术从模拟通道数据形成 B 模式图像。我们通过将点扩散函数与 Field II 超声模拟程序获得的点扩散函数进行比较，来确定有限元模型的准确性。我们还通过将粗糙和光滑表面圆形内含物的亮度特征与圆柱形金属工具浸入水箱中的实验图像进行比较，进行定性验证。接下来，我们进行模拟研究，以评估与不同本构特性（即内含物的可压缩性、宿主与内含物之间的阻抗对比度以及内含物的表面粗糙度）相关的 B 模式图像亮度强度和对比度的变化。我们发现，在轴向方向观察到的硬内含物后面的强度强烈受到内含物的可压缩性和粗糙度的影响。此外，基于强度观察到的石头的感知宽度对于较粗糙的石头更大。我们的研究表明，对可压缩内含物的成像可能受益于有针对性的 B 模式图像形成算法。我们的建模框架有可能有助于将硬内含物与周围实质区分开来，并对肾结石或胆结石进行分类。
