The Key Laboratory of Biomedical Information Engineering of the Ministry of Education, Department of Biomedical Engineering, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.
Institute of Artificial Intelligence and Robotics, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China; National Engineering Laboratory for Visual Information Processing and Applications, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.
Ultrason Sonochem. 2020 Jul;65:105060. doi: 10.1016/j.ultsonch.2020.105060. Epub 2020 Mar 9.
This work investigated and compared the dynamic cavitation characteristics between low and high boiling-point phase-shift nanodroplets (NDs) under physiologically relevant flow conditions during focused ultrasound (FUS) exposures at different peak rarefactional pressures. A passive cavitation detection (PCD) system was used to monitor cavitation activity during FUS exposure at various acoustic pressure levels. Root mean square (RMS) amplitudes of broadband noise, spectrograms of the passive cavitation detection signals, and normalized inertial cavitation dose (ICD) values were calculated. Cavitation activity of low-boiling-point perfluoropentane (PFP) NDs and high boiling-point perfluorohexane (PFH) NDs flowing at in vitro mean velocities of 0-15 cm/s were compared in a 4-mm diameter wall-less vessel in a transparent tissue-mimicking phantom. In the static state, both types of phase-shift NDs exhibit a sharp rise in cavitation intensity during initial FUS exposure. Under flow conditions, cavitation activity of the PFH NDs reached the steady state less rapidly compared to PFP NDs under the lower acoustic pressure (1.35 MPa); at the higher acoustic pressure (1.65 MPa), the RMS amplitude increased more sharply during the initial FUS exposure period. In particular, the RMS-time curves of the PFP NDs shifted upward as the mean flow velocity increased from 0 to 15 cm/s; the RMS amplitude of the PFH ND solution increased from 0 to 10 cm/s and decreased at 15 cm/s. Moreover, amplitudes of the echo signal for the low boiling-point PFP NDs were higher compared to the high boiling-point PFH NDs in the lower frequency range, whereas the inverse occurred in the higher frequency range. Both PFP and PFH NDs showed increased cavitation activity in the higher frequency under the flow condition compared to the static state, especially PFH NDs. At 1.65 MPa, normalized ICD values for PFH increased from 0.93 ± 0.03 to 0.96 ± 0.04 and from 0 to 10 cm/s, then decreased to 0.86 ± 0.05 at 15 cm/s. This work contributes to our further understanding of cavitation characteristics of phase-shift NDs under physiologically relevant flow conditions during FUS exposure. In addition, the results provide a reference for selecting suitable phase-shift NDs to enhance the efficiency of cavitation-mediated ultrasonic applications.
这项工作研究并比较了在不同的峰值稀疏压力下，在生理相关的流动条件下，低沸点和高沸点相移纳米液滴（NDs）之间的动态空化特性。在不同的声压水平下，使用被动空化检测（PCD）系统监测超声辐照过程中的空化活动。计算了宽带噪声的均方根（RMS）幅度、被动空化检测信号的频谱图和归一化惯性空化剂量（ICD）值。在透明组织模拟体模中的 4 毫米直径无壁容器中，比较了体外平均流速为 0-15cm/s 的低沸点全氟戊烷（PFP）NDs 和高沸点全氟己烷（PFH）NDs 的空化活性。在静态状态下，两种类型的相移 NDs 在初始超声辐照期间都表现出空化强度的急剧上升。在流动条件下，与低声压（1.35MPa）下的 PFP NDs 相比，PFH NDs 的空化活性达到稳定状态的速度较慢；在高声压（1.65MPa）下，在初始超声辐照期间，RMS 幅度增加更为剧烈。特别是，当平均流速从 0 增加到 15cm/s 时，PFP NDs 的 RMS-时间曲线向上移动；PFH ND 溶液的 RMS 幅度从 0 增加到 10cm/s，然后在 15cm/s 时减小。此外，与高沸点 PFH NDs 相比，低沸点 PFP NDs 的回波信号幅度在较低频率范围内较高，而在较高频率范围内则相反。与静态状态相比，在流动条件下，无论是 PFP 还是 PFH NDs，在较高频率下的空化活性都增加了，尤其是 PFH NDs。在 1.65MPa 时，PFH 的归一化 ICD 值从 0.93±0.03 增加到 0.96±0.04，从 0 增加到 10cm/s，然后在 15cm/s 时减小到 0.86±0.05。这项工作有助于我们进一步了解在超声辐照过程中生理相关流动条件下相移 NDs 的空化特性。此外，结果为选择合适的相移 NDs 以提高空化介导的超声应用效率提供了参考。
