Shpak Oleksandr, Verweij Martin, de Jong Nico, Versluis Michel
Physics of Fluids Group, MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, 217, Enschede, 7500 AE, The Netherlands.
Acoustic Wavefield Imaging, Delft University of Technology, Delft, 2600 GA, The Netherlands.
Adv Exp Med Biol. 2016;880:157-74. doi: 10.1007/978-3-319-22536-4_9.
The interaction of droplets and bubbles with ultrasound has been studied extensively in the last 25 years. Microbubbles are broadly used in diagnostic and therapeutic medical applications, for instance, as ultrasound contrast agents. They have a similar size as red blood cells, and thus are able to circulate within blood vessels. Perfluorocarbon liquid droplets can be a potential new generation of microbubble agents as ultrasound can trigger their conversion into gas bubbles. Prior to activation, they are at least five times smaller in diameter than the resulting bubbles. Together with the violent nature of the phase-transition, the droplets can be used for local drug delivery, embolotherapy, HIFU enhancement and tumor imaging. Here we explain the basics of bubble dynamics, described by the Rayleigh-Plesset equation, bubble resonance frequency, damping and quality factor. We show the elegant calculation of the above characteristics for the case of small amplitude oscillations by linearizing the equations. The effect and importance of a bubble coating and effective surface tension are also discussed. We give the main characteristics of the power spectrum of bubble oscillations. Preceding bubble dynamics, ultrasound propagation is introduced. We explain the speed of sound, nonlinearity and attenuation terms. We examine bubble ultrasound scattering and how it depends on the wave-shape of the incident wave. Finally, we introduce droplet interaction with ultrasound. We elucidate the ultrasound-focusing concept within a droplets sphere, droplet shaking due to media compressibility and droplet phase-conversion dynamics.
在过去25年里，液滴和气泡与超声的相互作用已得到广泛研究。微泡广泛应用于医学诊断和治疗领域，例如作为超声造影剂。它们的大小与红细胞相似，因此能够在血管内循环。全氟化碳液滴可成为新一代潜在的微泡剂，因为超声能促使其转变为气泡。在激活之前，它们的直径至少比生成的气泡小五倍。连同相变的剧烈特性，这些液滴可用于局部药物递送、栓塞治疗、高强度聚焦超声（HIFU）增强及肿瘤成像。在此，我们解释由瑞利 - 普莱斯方程描述的气泡动力学基础、气泡共振频率、阻尼和品质因数。我们通过对方程进行线性化展示了小振幅振荡情况下上述特性的精确计算。还讨论了气泡涂层和有效表面张力的作用及重要性。我们给出了气泡振荡功率谱的主要特性。在介绍气泡动力学之前，先引入超声传播。我们解释了声速、非线性和衰减项。我们研究了气泡超声散射及其如何依赖于入射波的波形。最后，我们介绍液滴与超声的相互作用。我们阐明了液滴球体内的超声聚焦概念、由于介质可压缩性导致的液滴振荡以及液滴相变动力学。
