Inertial Cavitation Behaviors Induced by Nonlinear Focused Ultrasound Pulses.
Inertial Cavitation Behaviors Induced by Nonlinear Focused Ultrasound Pulses.
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非线性聚焦超声脉冲诱导的惯性空化行为。
DOI：
10.1109/tuffc.2021.3073347
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发表时间：
2021-09
期刊：
影响因子：
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通讯作者：
Khokhlova TD
中科院分区：
文献类型：
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作者：
Bawiec CR;Rosnitskiy PB;Peek AT;Maxwell AD;Kreider W;Haar GRT;Sapozhnikov OA;Khokhlova VA;Khokhlova TD
由脉冲高强度聚焦超声（pHIFU）诱导的惯性空化先前已被证明成功地渗透肿瘤组织并增强化疗药物摄取。除了HIFU频率、峰值稀疏压力（p-）和脉冲持续时间外，最近还将空化诱导生物效应的阈值与非线性传播、衍射和焦点波形中冲击形成引起的非对称失真相关，因此与换能器F数相关。为了将先前观察到的生物效应与气泡动力学及其伴随的物理机制联系起来，使用高速摄影和被动空化检测（PCD）在透明琼脂糖凝胶模型中研究了惯性空化行为对冲击形成的依赖性。浓度范围为1.5-5%的琼脂糖幻影暴露于1毫秒脉冲使用三个换能器相同的孔径，但不同的焦距（F-数为0.77，1.02，和1.52）。脉冲的中心频率为1 MHz、1.5 MHz或1.9 MHz，焦点处的p−范围为1-18 MPa。随着声功率的增加，观察到三种不同类别的气泡行为：单个气泡的静止近球形振荡、多个气泡沿着pHIFU束轴的增殖以及朝向换能器的扇出增殖。只有在强非线性或冲击形成条件下，无论频率如何，并且只有当气泡达到一定的阈值尺寸范围时，才能观察到膨胀气泡。在具有较高琼脂糖浓度的较硬凝胶中，观察到相同的空化行为模式，但增殖云的尺寸较小。这些观察结果表明，可能参与气泡增殖的机制：增强冲击形成条件下的气泡生长，随后从凝胶-气泡界面的冲击散射，导致由声波产生的重复张力增加，并在近端方向出现新的生长气泡。不同的行为对应于PCD信号中的特定光谱特性：在所有情况下的宽带噪声，在静止气泡的情况下的背散射谐波的窄峰，以及在增殖气泡的情况下的加宽的、移位的谐波峰。谐波峰的偏移可以解释为来自以高达2 m/s的速度移动的目标的多普勒偏移，其对应于观察到的气泡增殖速度。
Inertial cavitation induced by pulsed high intensity focused ultrasound (pHIFU) has previously been shown to successfully permeabilize tumor tissue and enhance chemotherapeutic drug uptake. In addition to HIFU frequency, peak rarefactional pressure (p−), and pulse duration, the threshold for cavitation-induced bioeffects has recently been correlated with asymmetric distortion caused by nonlinear propagation, diffraction and formation of shocks in the focal waveform, and therefore with the transducer F-number. To connect previously observed bioeffects with bubble dynamics and their attendant physical mechanisms, the dependence of inertial cavitation behavior on shock formation was investigated in transparent agarose gel phantoms using high-speed photography and passive cavitation detection (PCD). Agarose phantoms with concentrations ranging from 1.5–5% were exposed to 1-ms pulses using three transducers of the same aperture but different focal distances (F-numbers of 0.77, 1.02, and 1.52). Pulses had central frequencies of 1 MHz, 1.5 MHz, or 1.9 MHz and a range of p− at the focus varying within 1–18 MPa. Three distinct categories of bubble behavior were observed as the acoustic power increased: stationary near-spherical oscillation of individual bubbles, proliferation of multiple bubbles along the pHIFU beam axis, and fanned-out proliferation towards the transducer. Proliferating bubbles were only observed under strongly nonlinear or shock-forming conditions regardless of frequency, and only where the bubbles reached a certain threshold size range. In stiffer gels with higher agarose concentrations, the same pattern of cavitation behavior was observed, but the dimensions of proliferating clouds were smaller. These observations suggest mechanisms that may be involved in bubble proliferation: enhanced growth of bubbles under shock-forming conditions, subsequent shock scattering from the gel-bubble interface, causing an increase in the repetitive tension created by the acoustic wave and the appearance of a new growing bubble in the proximal direction. Different behaviors corresponded to specific spectral characteristics in the PCD signals: broadband noise in all cases, narrow peaks of backscattered harmonics in the case of stationary bubbles, and broadened, shifted harmonic peaks in the case of proliferating bubbles. The shift in harmonic peaks can be interpreted as a Doppler shift from targets moving at speeds of up to 2 m/s, which correspond to the observed bubble proliferation speeds.