Wu Qiang, Gray Michael, Smith Cameron A B, Bau Luca, Cleveland Robin O, Coussios Constantin, Stride Eleanor
Institute of Biomedical Engineering, Department of Engineering Science, University of Oxford, Oxford, United Kingdom.
Botnar Institute for Musculoskeletal Sciences, University of Oxford, Oxford, United Kingdom.
J Acoust Soc Am. 2024 Nov 1;156(5):3608-3620. doi: 10.1121/10.0034426.
Both the biological effects and acoustic emissions generated by cavitation are functions of bubble dynamics. Monitoring of acoustic emissions is therefore desirable to improve treatment safety and efficacy. The relationship between the emission spectra and bubble dynamics is, however, complex. The aim of this study was to characterise this relationship for single microbubbles using simultaneous ultra-high-speed optical imaging and passive acoustic mapping of cavitation emissions. As expected, both the number of discrete harmonics and broadband content in the emissions increased with increasing amplitude of bubble oscillation, but the spectral content was also dependent upon other variables, including the frequency of bubble collapse and receiving transducer characteristics. Moreover, phenomena, such as fragmentation and microjetting, could not be distinguished from spherical oscillations when using the full duration acoustic waveform to calculate the emission spectra. There was also no correlation between the detection of broadband noise and widely used thresholds for distinguishing bubble dynamics. It is therefore concluded that binary categorisations, such as stable and inertial cavitation, should be avoided, and different types of bubble behavior should not be inferred on the basis of frequency content alone. Treatment monitoring criteria should instead be defined according to the relevant bioeffect(s) for a particular application.
空化产生的生物效应和声发射都是气泡动力学的函数。因此，监测声发射有助于提高治疗的安全性和有效性。然而，发射光谱与气泡动力学之间的关系很复杂。本研究的目的是通过同时进行超高速光学成像和空化发射的被动声学映射来表征单个微气泡的这种关系。正如预期的那样，发射中离散谐波的数量和宽带含量都随着气泡振荡幅度的增加而增加，但光谱含量也取决于其他变量，包括气泡崩溃的频率和接收换能器的特性。此外，当使用整个持续时间的声学波形来计算发射光谱时，诸如破碎和微喷射等现象无法与球形振荡区分开来。宽带噪声的检测与用于区分气泡动力学的广泛使用的阈值之间也没有相关性。因此得出结论，应避免使用诸如稳定空化和惯性空化之类的二元分类，并且不应仅根据频率含量来推断不同类型的气泡行为。相反，治疗监测标准应根据特定应用的相关生物效应来定义。
