In therapeutic ultrasound using microbubbles, it is essential to drive the microbubbles into the correct type of activity and the correct location to produce the desired biological response. Although passive acoustic mapping (PAM) is capable of locating where microbubble activities are generated, it is well known that microbubbles rapidly move within the ultrasound beam. We propose a technique that can image microbubble movement by estimating their velocities within the focal volume. Microbubbles embedded within a wall-less channel of a tissue-mimicking material were sonicated using 1-MHz focused ultrasound. The acoustic emissions generated by the microbubbles were captured with a linear array (L7-4). PAM with robust Capon beamforming was used to localize the microbubble acoustic emissions. We spectrally analyzed the time trace of each position and isolated the higher harmonics. Microbubble velocity maps were constructed from the position-dependent Doppler shifts at different time points during sonication. Microbubbles moved primarily away from the transducer at velocities on the order of 1 m/s due to primary acoustic radiation forces, producing a time-dependent velocity distribution. We detected microbubble motion both away and toward the receiving array, revealing the influence of acoustic radiation forces and fluid motion due to the ultrasound exposure. High-speed optical images confirmed the acoustically measured microbubble velocities. Doppler PAM enables passive estimation of microbubble motion and may be useful in therapeutic applications, such as drug delivery across the blood-brain barrier, sonoporation, sonothrombolysis, and drug release.

中文翻译：

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采用 MEMS 铸造工艺的晶圆上微矩形同轴延迟线


在使用微泡的超声治疗中，必须将微泡驱动到正确的活动类型和正确的位置以产生所需的生物反应。尽管被动声学测绘 (PAM) 能够定位微泡活动产生的位置，但众所周知，微泡在超声波束内快速移动。我们提出了一种技术，可以通过估计焦点体积内微泡的速度来对微泡运动进行成像。使用 1 MHz 聚焦超声波对嵌入组织模拟材料的无壁通道内的微泡进行超声处理。微泡产生的声发射被线性阵列（L7-4）捕获。使用具有强大 Capon 波束成形功能的 PAM 来定位微泡声发射。我们对每个位置的时间轨迹进行了频谱分析并隔离了高次谐波。微泡速度图是根据超声处理过程中不同时间点的位置相关多普勒频移构建的。由于主要声辐射力，微泡主要以 1 m/s 量级的速度远离换能器，产生与时间相关的速度分布。我们检测到微泡远离和朝向接收阵列的运动，揭示了超声波暴露造成的声辐射力和流体运动的影响。高速光学图像证实了声学测量的微泡速度。多普勒 PAM 能够被动估计微泡运动，并可用于治疗应用，例如穿过血脑屏障的药物输送、声孔作用、声波溶解和药物释放。