Department of Biomedical Engineering, University of Michigan, Ann Arbor, United States of America.
Phys Med Biol. 2022 Jul 19;67(15). doi: 10.1088/1361-6560/ac7d90.
. Soft tissue phase aberration may be particularly severe for histotripsy due to large aperture and low-number transducer geometries. This study investigated how phase aberration from human abdominal tissue affects focusing of a large, strongly curved histotripsy transducer.A computational model (k-Wave) was experimentally validated withporcine abdominal tissue and used to simulate focusing a histotripsy transducer (radius: 14.2 cm,-number: 0.62, central frequency: 750 kHz) through the human abdomen. Abdominal computed tomography images from 10 human subjects were segmented to create three-dimensional acoustic property maps. Simulations were performed focusing at 3 target locations in the liver of each subject with ideal phase correction, without phase correction, and after separately matching the sound speed of water and fat to non-fat soft tissue.Experimental validation in porcine abdominal tissue showed that simulated and measured arrival time differences agreed well (average error, ∼0.10 acoustic cycles at). In simulations with human tissue, aberration created arrival time differences of 0.65s (∼0.5 cycles) at the target and shifted the focus from the target by 6.8 mm (6.4 mm pre-focally along depth direction), on average. Ideal phase correction increased maximum pressure amplitude by 95%, on average. Matching the sound speed of water and fat to non-fat soft tissue decreased the average pre-focal shift by 3.6 and 0.5 mm and increased pressure amplitude by 2% and 69%, respectively.Soft tissue phase aberration of large aperture, low-number histotripsy transducers is substantial despite low therapeutic frequencies. Phase correction could potentially recover substantial pressure amplitude for transabdominal histotripsy. Additionally, different heterogeneity sources distinctly affect focusing quality. The water path strongly affects the focal shift, while irregular tissue boundaries (e.g. fat) dominate pressure loss.
软组织相位像差可能在 histotripsy 中特别严重，因为孔径较大且换能器数量较少。本研究探讨了人腹部组织的相位像差如何影响大曲率 histotripsy 换能器的聚焦。采用（k-Wave）计算模型对猪腹部组织进行了实验验证，并用于模拟通过人体腹部聚焦 histotripsy 换能器（半径：14.2cm，-数：0.62，中心频率：750kHz）。从 10 名人类受试者的腹部计算机断层扫描图像中分割出三维声特性图。在每个受试者的肝脏中，在 3 个目标位置进行了模拟，分别进行了理想相位校正、无相位校正以及分别将水和脂肪的声速与非脂肪软组织匹配的模拟。在猪腹部组织中的实验验证表明，模拟和测量的到达时间差吻合较好（平均误差，在）。在具有人体组织的模拟中，像差导致的到达时间差为 0.65s（约 0.5 个周期）在目标处，焦点平均偏移 6.8mm（沿深度方向 6.4mm 前焦点）。理想相位校正平均使最大压力幅度增加了 95%。将水和脂肪的声速与非脂肪软组织匹配分别使平均前焦点偏移减小了 3.6mm 和 0.5mm，压力幅度分别增加了 2%和 69%。尽管治疗频率较低，但大孔径、低数量 histotripsy 换能器的软组织相位像差仍然很大。相位校正有可能为经腹 histotripsy 恢复相当大的压力幅度。此外，不同的异质性源明显影响聚焦质量。水程强烈影响焦点偏移，而不规则的组织边界（如脂肪）主导压力损失。
