Physical Sciences Platform, Sunnybrook Research Institute, Toronto, Canada. Department of Medical Biophysics, University of Toronto, Toronto, Canada.
Phys Med Biol. 2018 Nov 28;63(23):235017. doi: 10.1088/1361-6560/aaee91.
High intensity focused ultrasound (HIFU) can disintegrate blood clots through the generation and stimulation of bubble clouds within thrombi. This work examined the design of a device to image bubble clouds for monitoring cavitation-based HIFU treatments of deep vein thrombosis (DVT). Acoustic propagation simulations were carried out on multi-layered models of the human thigh using two patient data sets from the Visible Human Project. The design considerations included the number of receivers (32, 64, 128, 256, and 512), their spatial positioning, and the effective angular array aperture (100° and 180° about geometric focus). Imaging array performance was evaluated for source frequencies of 250, 750, and 1500 kHz. Receiver sizes were fixed relative to the wavelength (pistons, diameter = λ/2) and noise was added at levels that scaled with receiver area. With a 100° angular aperture the long axis size of the -3 dB main lobe was 1.2λ-i.e. on the order of the vessel diameter at 250 kHz (7 mm). Increasing the array aperture to span 180° about the geometric focus reduced the long axis by a factor of ~2. The smaller main lobe sizes achieved by imaging at higher frequencies came at the cost of increased levels of sensitivity to phase aberrations induced during acoustic propagation through the intervening soft tissue layers. With noise added to receiver signals, images could be reconstructed with peak sidelobe ratios < -3 dB using single-cycle integration times for source frequencies of 250 and 750 kHz (NRx ⩾ 128). At 1500 kHz, longer integration times and/or higher element counts were required to achieve similar peak sidelobe ratios. Our results suggest that a modest number of receivers(i.e. NRx = 128) arranged on a semi-cylindrical shell may be sufficient to enable passive acoustic imaging with single-cycle integration times (i.e. volumetric rates up to 0.75 MHz) for monitoring cavitation-based HIFU treatments of DVT.
高强度聚焦超声（HIFU）可以通过在血栓内产生和刺激气泡云来分解血块。这项工作研究了一种用于对基于空化的 HIFU 治疗深静脉血栓形成（DVT）的气泡云进行成像的设备的设计。使用来自可见人体项目的两个患者数据集，对人体大腿的多层模型进行了声学传播模拟。设计考虑因素包括接收器的数量（32、64、128、256 和 512）、它们的空间定位以及有效角阵列孔径（100°和 180°）。对于源频率为 250、750 和 1500 kHz 的成像阵列性能进行了评估。相对于波长（活塞，直径=λ/2）固定接收器的大小，并根据接收器面积按比例添加噪声。在 100°角孔径下，-3 dB 主瓣的长轴尺寸约为 1.2λ，即在 250 kHz 时约为血管直径（约 7mm）。将阵列孔径增加到跨越几何焦点的 180°会使长轴减小约 2 倍。在更高频率下进行成像获得的较小主瓣尺寸是以在通过中间软组织层传播期间引入的相位像差的灵敏度增加为代价的。向接收器信号添加噪声后，使用源频率为 250 和 750 kHz 的单周期积分时间，可以重建具有峰值旁瓣比<−3 dB 的图像（NRx≥128）。在 1500 kHz 时，需要更长的积分时间和/或更高的元素计数才能实现类似的峰值旁瓣比。我们的结果表明，在半圆柱壳上排列少量接收器（即 NRx=128）可能足以实现基于空化的 HIFU 治疗 DVT 的单周期集成时间的被动声学成像（即体积率高达 0.75 MHz）。
