ESTIMATION OF SHEAR ELASTICITY OF BIOTISSUES USING SURFACE WAVES

利用表面声波测量生物组织和凝胶等软质材料的剪切弹性，进行了一项高尚的实验。在生物组织中进行了广泛的超声研究。然而，关于剪切弹性的研究报道很少。本研究测定了纤维组织、鸡胸肌和牛心肌的表面波速度和吸收。由表面波性质导出的剪切弹性沿纤维结构表现出较大的方向依赖性。这与表现出小方向依赖性的超声特性形成鲜明对比。测定这些组织的弹性刚度张量。在表面张力和弹性都作为恢复力的情况下，表面波的传播还没有得到澄清。我和明治大学的onodera教授推导出色散方程，发现两种表面波模式能够在凝胶状态下传播：瑞利型表面波和泄漏表面张力波。后者是首次被预测到。明胶溶胶和凝胶的表面波测量表明了这两种模式的存在。本研究为研究软质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.