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：

---

多普勒无源声映射

在使用微泡的治疗性超声中，至关重要的是将微泡驱动到正确的活动类型和正确的位置，以产生所需的生物学反应。尽管无源声学映射（PAM）能够定位产生微泡活动的位置，但众所周知，微泡在超声束内快速移动。我们提出了一种技术，该技术可以通过估计微气泡在焦点体积内的速度来成像。使用1 MHz聚焦超声对嵌入组织模拟材料的无壁通道内的微气泡进行超声处理。由微气泡产生的声发射被线性阵列（L7-4）捕获。具有强大Capon波束成形的PAM用于定位微泡声发射。我们从频谱上分析了每个位置的时间轨迹，并隔离了高次谐波。从声波过程中不同时间点的位置相关多普勒频移构建微气泡速度图。由于主要的声辐射力，微气泡主要以1 m / s的速度从换能器移开，从而产生与时间有关的速度分布。我们检测到微气泡运动既向接收阵列又向接收阵列方向移动，揭示了超声辐射对声辐射力和流体运动的影响。高速光学图像确认了声学测量的微气泡速度。多普勒PAM能够被动估计微气泡运动，可能在治疗应用中有用，例如跨血脑屏障的药物输送，声穿孔，声溶栓，