ESTIMATION OF SHEAR ELASTICITY OF BIOTISSUES USING SURFACE WAVES

进行了一项高贵的实验，旨在利用表面声波测量生物组织和凝胶等软材料的剪切弹性。在生物组织中进行了广泛的超声波研究。然而，有关剪切弹性的研究报道甚少。在本研究中，测量了纤维组织、鸡胸肌和牛心肌的表面波速度和吸收。由表面波性质得出的剪切弹性沿纤维结构表现出很大的方向依赖性。这与超声性质表现出很小的方向依赖性形成了鲜明的对比。在这些组织中测定了弹性刚度张量。在表面张力和弹性都作为恢复力的情况下，表面波的传播尚不清楚。我和明治大学的Y.Onodera教授推导了色散方程，发现有两种表面波模能够在凝胶态中传播：瑞利型表面波和泄漏表面张力波。后者是第一次被预测的。明胶溶胶和凝胶的表面波测量表明，这两种模式都是存在的。本研究为研究软材料的弹性提供了一种新的工具。

A noble experiment was made, aiming to measure shear elasticity in soft materials such as biotissues and gels using suf ace acoustic waves. Extensive ultrasonic studies have been made in biotissues. However, very few studies on shear elasticity have been reported. In the present study surface wave velocity and absorption were measured in fibrous tissues, chicken breast muscle and bovine myocardium. The shear elasticity derived from the surface wave properties showed large direction dependence along the fibrous structure. This is marked contrast with the ultrasonic properties which showed small direction dependence. Elastic stiffness tensors were determined in these tissues.Propagation of surface waves has not been clarified in the case that both surface tension and elasticity are operating as a restoring force. I and Prof.Y.Onodera of meiji University have derived the dispersion equation and have found that two kinds of surface wave modes are able to propagate in a gel state : Rayleigh type surface waves and leaky surface tension waves. The latter was predicted for the first time. The surface wave measurementsin gelatin sol and gel showed the exsitence of the two modes. The present study provides a new tool for investigating elasticity in soft materials.