Evaluation of the elastic modulus of the arterial wall by accurate noninvasive measurement of change in its thickness

Diagnosis of early-stage atherosclerosis requires increase in spatial resolution to several millimeters, corresponding to the size of the macular lesions on the surface of the wall, when making a local evaluation of the acoustic characteristics of the arterial wall. Pulse wave velocity (PWV) ultrasound has been proposed for this purpose. The relation between PWV and Young's modulus in the circumferential direction of the artrial wall makes the noninvasive evaluation of the elastic characteristics of the arterial wall possible. Previously proposed methods do not provide sufficient spatial resolution. Here pulsive ultrasound is used to measure small vibration at the intima and the adventitia of the arterial wall from the surface of the skin accurately. Change in thickness of the arterial wall is obtained by integrating the difference between the two vibration signals at the intima and adventitia. The elastic modulus of the artrial wall is obtained by dividing the difference between systolic and diastolic blood pressure by the resultant change in thickness of the arterial wall, which is normalized by its thickness at diastole. Moreover, the proposed method is applied to evaluation of the elastic modulus of the human carotid artery in vivo.