Department of Mathematics, University College London, Gower Street, London WC1E 6BT, United Kingdom.
J Acoust Soc Am. 2013 Aug;134(2):1416-27. doi: 10.1121/1.4812860.
Interest in coated microbubbles as agents for therapeutic and quantitative imaging applications in biomedical ultrasound has increased the need for their accurate theoretical characterization. Effects such as gas diffusion, variation in the properties of the coating and the resulting changes in bubble behavior under repeated exposure to ultrasound pulses are, however, still not well understood. In this study, a revised equation for microbubble motion is proposed that includes the effects of gas diffusion, as well as adsorption, desorption and shedding of a surfactant from the bubble surface. This is incorporated into a nonlinear wave propagation model to account for these additional time dependent effects in the response of microbubble populations. The results from the model indicate there can be significant changes in both bubble behavior and the propagated pulse over time. This is in agreement with existing experimental data but is not predicted by existing propagation models. The analysis indicates that changes in bubble dynamics are dominated by surfactant shedding on the timescale of a diagnostic ultrasound pulse and gas diffusion over the timescale of the pulse repetition frequency. The implications of these results for the development of more accurate algorithms for quantitative imaging and for therapeutic applications are discussed.
人们对涂层微泡作为医学超声治疗和定量成像应用的试剂越来越感兴趣，这增加了对其进行准确理论描述的需求。然而，气体扩散、涂层性质的变化以及微泡在重复超声脉冲作用下的行为变化等影响仍然没有得到很好的理解。在这项研究中，提出了一个修正的微泡运动方程，其中包括气体扩散以及气泡表面上的表面活性剂吸附、解吸和脱落的影响。这被纳入一个非线性波传播模型中，以解释微泡群体响应中这些附加的时变效应。模型的结果表明，在时间上，气泡行为和传播的脉冲都可能发生显著变化。这与现有的实验数据一致，但现有的传播模型无法预测。分析表明，气泡动力学的变化主要由诊断超声脉冲时间尺度上的表面活性剂脱落和脉冲重复频率时间尺度上的气体扩散决定。这些结果对开发更精确的定量成像和治疗应用算法的意义进行了讨论。
