基于有限元分析和集中参数模型微血管与超声微泡声学响应的模拟

摘要

背景：研究特定超声激励下微血管与内部单个微泡间的非线性声学响应，对于最大化超声能量的沉积，促进定量成像算法的发展，揭示损害机制或评价靶向治疗的效果，克服传统方法主要适用于大尺寸血管的局限性、测量微血管弹性意义重大。　　目的：构建微血管中超声微泡模型，揭示超声、微泡与血管、血流间的内在机制。　　方法：基于有限元分析和集中参数模型，在Comsol Multiphysics 3.5a平台上进行微血管中超声微泡三维模型构建和模拟仿真。　　结果与结论：①微泡径向运动因受近处血管壁面限制，移动速度较轴向小；而血管壁因与微泡振动耦合，近微泡的中心处位移和应力最大；②相同声压下，激励频率增加会减弱微血管的缩放且更快趋于稳定；在相同频率下，激励声压越大血管运动越强烈，振动传播产生的局部效应更持久；③微泡振动幅度随微血管壁杨氏模量的增加而降低，近似线性反比关系；振动频率则随血管壁杨氏模量的增加而增加；④结果表明，微血管尺寸越小，对微泡振动频率和幅值的限制越强烈，超声激励频率的增大会使微泡振动频率增大、幅值减小；声压对微泡和血管振动的影响则相反。此外，研究首次发现，血管壁弹性与微泡振动幅度呈近似线性正相关，说明利用微泡测定血管壁弹性是可能的。%BACKGROUND:Exploration on nonlinear acoustic response of the contrast agent microbubble contained in microvessel under ultrasound excitation is of great significance to maximizing ultrasonic energy deposition, promoting the development of quantitative imaging algorithm, revealing the damage mechanism or evaluating the targeted therapy, and overcoming the limitations of the traditional methods that are mainly used in large-size vessels, and measuring microvessel elasticity. OBJECTIVE:To build a microvessel containing an ultrasound microbubble, revealing the internal mechanism among ultrasound, microbubble, blood flow and microvessel. METHODS:Based on the finite element analysis and the lumped parameter model, three-dimensional microvessel containing microbubble model was built and simulated on Comsol Multiphysics 4.4 platform. RESULTS AND CONCLUSION:Microbubble exhibited slower radial motion compared with axial motion due to vascular wal limitation, but maximum displacement and stress were found near the microbubble center because of the oscil ation coupling of the microbubble with the vascular wal . Under the same ultrasound pressure, the excitation frequency increased, accompanied by decreased and stabilized microvessl constriction and dilation;under the same frequency, with the enhancement of ultrasound pressure, the local microbubble oscil ation lasted longer. With the increase of Young’s modulus of the microvessel wal , the frequency of microbubble oscil ation was reduced, while the amplitude increased. Al these findings indicate that the frequency of microbubble oscil ation increased with the reduction of microvessel size, while its amplitude decreased. The frequency of microbubble oscil ation increased with the enhancement of ultrasound excitation, while the amplitude decreased. On the contrary, ultrasound pressure affected the dynamic characteristics of microbubble and microvessel. In particular, it was the first to demonstrate that the elasticity of microvessel has approximate linear positive correlation with the amplitude of microbubble oscil ation, which reveals the relationship between microvessel elasticity and microbubble response so as to provide theoretical basis for indirect measurement of microvessel elasticity.