Chatterjee Dhiman, Sarkar Kausik
Department of Mechanical Engineering, University of Delaware, Newark, DE 19716, USA.
Ultrasound Med Biol. 2003 Dec;29(12):1749-57. doi: 10.1016/s0301-5629(03)01051-2.
A quantitative model of the dynamics of an encapsulated microbubble contrast agent will be a valuable tool in contrast ultrasound (US). Such a model must have predictive ability for widely varying frequencies and pressure amplitudes. We have developed a new model for contrast agents, and successfully investigated its applicability for a wide range of operating parameters. The encapsulation is modeled as a complex interface of an infinitesimal thickness. A Newtonian rheology with surface viscosities and interfacial tension is assumed for the interface, and a modified Rayleigh-Plesset equation is derived. The rheological parameters (surface tension and surface dilatational viscosity) for a number of contrast agents (Albunex, Optison and Quantison) are determined by matching the linearized model dynamics with experimentally obtained attenuation data. The model behavior for Optison (surface tension 0.9 N/m and surface dilatational viscosity 0.08 msP) was investigated in detail. Specifically, we have carried out a detailed interrogation of the model, fitted in the linear regime, for its nonlinear prediction. In contrast to existing models, the new model is found to capture the characteristic subharmonic emission of Optison observed by. A detailed parametric study of the bubble behavior was executed using the ratio of scattering to attenuation (STAR). It shows that the encapsulation drastically reduces the influence of resonance frequency on scattering cross-section, suggesting possible means of improvement in imaging at off-resonant frequencies. The predictive capability of the present model indicates that it can be used for characterizing different agents and designing new ones.
一种用于包裹型微泡造影剂动力学的定量模型将成为超声造影中的一种有价值的工具。这样的模型必须对广泛变化的频率和压力幅度具有预测能力。我们已经开发了一种新的造影剂模型，并成功研究了其在广泛的操作参数范围内的适用性。将包封建模为具有无限小厚度的复杂界面。假设该界面具有表面粘度和界面张力的牛顿流变学，并推导了修正的瑞利 - 普莱斯方程。通过将线性化模型动力学与实验获得的衰减数据相匹配，确定了多种造影剂（白蛋白微泡、Optison和Quantison）的流变学参数（表面张力和表面膨胀粘度）。详细研究了Optison（表面张力0.9 N/m和表面膨胀粘度0.08 mPa·s）的模型行为。具体而言，我们对在线性范围内拟合的模型进行了详细研究，以考察其非线性预测能力。与现有模型相比，发现新模型能够捕捉到Optison所观察到的特征性次谐波发射。使用散射与衰减比（STAR）对气泡行为进行了详细的参数研究。结果表明，包封大大降低了共振频率对散射截面的影响，这为在非共振频率下改善成像提供了可能的途径。本模型的预测能力表明它可用于表征不同的造影剂并设计新的造影剂。
