Simulation of ultrasonic pulse propagation through the abdominal wall
Simulation of ultrasonic pulse propagation through the abdominal wall
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DOI：
10.1121/1.421015
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发表时间：
1997-08-01
影响因子：
2.4
通讯作者：
Waag, RC
中科院分区：
文献类型：
--
作者：
Mast, TD;Hinkelman, LM;Waag, RC
采用二维模型模拟了超声脉冲在人体腹壁中的传播，离散了变声速、变密度介质中波传播的时域方程，得到了一组耦合的有限差分方程组，并用空间四阶精度和时间二阶精度的两步MacCormack格式进行了数值求解。腹壁的不均匀组织用声速和密度的二维矩阵表示。这些值是通过处理腹壁横截面的扫描图像来确定的，这些图像被染色以识别结缔组织、肌肉和脂肪，假设每种组织都具有恒定的声速和密度，选择计算配置来模拟在相同样本上进行的波前失真测量。这些测量结果与目前的计算结果在定性上是一致的，表明计算模型正确地描述了活体超声波前失真的显著特征。然而，定量的一致性受到计算的二维性和缺乏详细的组织微结构的限制，使用渐近直射线近似进行的计算与全波方法预测的时移像差显示出很好的一致性，但不能解释在实验和全波计算中发现的幅度波动和波形失真。计算的组织横截面内波传播的可视化表明，在通过腹壁的超声传播中观察到的幅度波动和波形失真与内部不均匀的散射有关，例如皮下脂肪内的隔膜。这些观测以及对计算和观测的幅度波动的统计分析表明，弱波动模型不能完全描述由腹壁引起的超声波波前失真。(C)1997年美国声学学会。
Ultrasonic pulse propagation through the human abdominal wall has been simulated using a model for two-dimensional propagation through anatomically realistic tissue cross sections, The time-domain equations for wave propagation in a medium of variable sound speed and density were discretized to obtain a set of coupled finite-difference equations, These difference equations were solved numerically using a two-step MacCormack scheme that is fourth-order accurate in space and second-order accurate in time. The inhomogeneous tissue of the abdominal wall was represented by two-dimensional matrices of sound speed and density values. These values were determined by processing scanned images of abdominal wall cross sections stained to identify connective tissue, muscle, and fat, each of which was assumed to have a constant sound speed and density, The computational configuration was chosen to simulate that of wavefront distortion measurements performed on the same specimens. Qualitative agreement was found between those measurements and the results of the present computations, indicating that the computational model correctly depicts the salient characteristics of ultrasonic wavefront distortion in vivo. However, quantitative agreement was limited by the two-dimensionality of the computation and the absence of detailed tissue microstructure, Calculations performed using an asymptotic straight-ray approximation showed good agreement with time-shift aberrations predicted by the full-wave method, but did not explain the amplitude fluctuations and waveform distortion found in the experiments and the full-wave calculations. Visualization of computed wave propagation within tissue cross sections suggests that amplitude fluctuations and waveform distortion observed in ultrasonic propagation through the abdominal wall are associated with scattering from internal inhomogeneities such as septa within the subcutaneous fat. These observations, as well as statistical analysis of computed and observed amplitude fluctuations, suggest that weak fluctuation models do not fully describe ultrasonic wavefront distortion caused by the abdominal wall. (C) 1997 Acoustical Society of America.