Frequency Analysis of Strain of Cylindrical Shell for Assessment of Viscosity

Abstract

For tissue characterization of atherosclerotic plaque, we have developed a method, namely, the phased tracking method, [H. Kanai et al.: IEEE Trans. Ultrason. Ferroelectr. Freq. Control 43 (1996) 791] to measure the regional strain (change in wall thickness) and elasticity of the arterial wall. In addition to the regional elasticity, we are attempting to measure the regional viscosity for a more precise tissue characterization. Previously, we showed that the viscosity can be obtained by measuring the frequency dependence of the elastic modulus using remote actuation [H. Hasegawa et al.: Jpn. J. Appl. Phys. 43 (2004) 3197]. However, in this method, we need to apply external actuation to the subject. To simplify the measurement, we instead to obtain the frequency dependence of the elastic modulus from the change in arterial wall thickness spontaneously caused by the heartbeat because this change in thickness consists of frequency components up to 20–30 Hz. In this paper, the frequency dependence of the elastic modulus of a silicone rubber tube was investigated by applying frequency analysis to the change in wall thickness caused by the change in internal pressure simulating the actual arterial blood pressure.