Physics of Fluids Group, MIRA Institute of Biomedical Engineering and Technical Medicine, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands.
J Acoust Soc Am. 2011 Apr;129(4):1729-39. doi: 10.1121/1.3505116.
Oscillating phospholipid-coated ultrasound contrast agent microbubbles display a so-called "compression-only" behavior, where it is observed that the bubbles compress efficiently while their expansion is suppressed. Here, a theoretical understanding of the source of this nonlinear behavior is provided through a weakly nonlinear analysis of the shell buckling model proposed by Marmottant et al. [J. Acoust. Soc. Am. 118, 3499-3505 (2005)]. It is shown that the radial dynamics of the bubble can be considered as a superposition of a linear response at the fundamental driving frequency and a second-order nonlinear low-frequency response that describes the negative offset of the mean bubble radius. The analytical solution deduced from the weakly nonlinear analysis shows that the compression-only behavior results from a rapid change of the shell elasticity with bubble radius. In addition, the radial dynamics of single phospholipid-coated microbubbles was recorded as a function of both the amplitude and the frequency of the driving pressure pulse. The comparison between the experimental data and the theory shows that the magnitude of compression-only behavior is mainly determined by the initial phospholipids concentration on the bubble surface, which slightly varies from bubble to bubble.
振荡磷脂包覆的超声造影微泡表现出所谓的“仅压缩”行为，观察到微泡在高效压缩的同时抑制了膨胀。通过对 Marmottant 等人提出的壳层屈曲模型进行弱非线性分析，为这种非线性行为提供了理论理解[J. Acoust. Soc. Am. 118, 3499-3505 (2005)]。结果表明，微泡的径向动力学可以看作是在基本驱动频率下的线性响应和描述平均泡径负偏移的二阶非线性低频响应的叠加。从弱非线性分析中推导出的解析解表明，仅压缩行为是由于泡壳弹性随泡径的快速变化引起的。此外，还记录了单磷脂包覆微泡的径向动力学作为驱动压力脉冲幅度和频率的函数。实验数据与理论的比较表明，仅压缩行为的幅度主要取决于泡表面初始磷脂浓度，该浓度在不同泡之间略有变化。
