de Andrade Matheus Oliveira, Haqshenas Seyyed Reza, Pahk Ki Joo, Saffari Nader
UCL Mechanical Engineering, University College London, London WC1E 7JE, United Kingdom.
UCL Mechanical Engineering, University College London, London WC1E 7JE, United Kingdom.
Ultrason Sonochem. 2019 Jul;55:262-272. doi: 10.1016/j.ultsonch.2019.01.019. Epub 2019 Jan 18.
A phenomenological implementation of Classical Nucleation Theory (CNT) is employed to investigate the connection between high intensity focused ultrasound (HIFU) pressure and temperature fields with the energetic requirements of bubble nucleation. As a case study, boiling histotripsy in tissue-mimicking phantoms is modelled. The physics of key components in the implementation of CNT in HIFU conditions such as the derivation of nucleation pressure thresholds and approximations regarding the surface tension of the liquid are reviewed and discussed. Simulations show that the acoustic pressure is the ultimate trigger for millisecond bubble nucleation in boiling histotripsy, however, HIFU heat deposition facilitates nucleation by lowering nucleation pressure thresholds. Nucleation thus occurs preferentially at the regions of highest heat deposition within the HIFU field. This implies that bubble nucleation subsequent to millisecond HIFU heat deposition can take place at temperatures below 100 °C as long as the focal HIFU peak negative pressure exceeds the temperature-dependent nucleation threshold. It is also found that the magnitude of nucleation pressure thresholds decreases with decreasing frequencies. Overall, results indicate that it is not possible to separate thermal and mechanical effects of HIFU in the nucleation of bubbles for timescales of a few milliseconds. This methodology provides a promising framework for studying time and space dependencies of the energetics of bubble nucleation within a HIFU field.
采用经典成核理论（CNT）的唯象学方法来研究高强度聚焦超声（HIFU）压力场和温度场与气泡成核能量需求之间的联系。作为一个案例研究，对组织模拟体模中的沸腾组织粉碎术进行了建模。回顾并讨论了在HIFU条件下实施CNT时关键组件的物理原理，如成核压力阈值的推导以及关于液体表面张力的近似处理。模拟结果表明，声压是沸腾组织粉碎术中毫秒级气泡成核的最终触发因素，然而，HIFU热沉积通过降低成核压力阈值促进了成核。因此，成核优先发生在HIFU场内热沉积最高的区域。这意味着，只要聚焦HIFU峰值负压超过与温度相关的成核阈值，在毫秒级HIFU热沉积之后，气泡成核就可以在低于100°C的温度下发生。还发现，成核压力阈值的大小随频率降低而减小。总体而言，结果表明，在几毫秒的时间尺度内，不可能在气泡成核过程中将HIFU的热效应和机械效应分开。该方法为研究HIFU场内气泡成核能学的时间和空间依赖性提供了一个有前景的框架。
