Measurement of Change in Wall Thickness of Cylindrical Shell Due to Cyclic Remote Actuation for Assessment of Viscoelasticity of Arterial Wall

To characterize tissues in atherosclerotic plaques, we have developed a method, the phased tracking method , for measuring the strain (change in wall thickness) and elasticity of the arterial wall. However, some types of tissue, such as lipids and blood clots, cannot be discriminated from each other based only on elasticity because of the small difference in their elasticity. For more precise tissue characterization, we are attempting to measure the regional viscoelasticity. To determine viscoelastic properties, elastic moduli at multiple frequencies were obtained by generating the change in internal pressure due to remote cyclic actuation. From basic experiments using a silicone rubber tube, it was found that the change in internal pressure at the ultrasonic beam position (for measurement of the elastic modulus) can be generated by remotely applied actuation. Furthermore, from the resultant minute changes in wall thickness of less than 10 µm measured by the phased tracking method , elastic moduli were obtained at multiple actuation frequencies.