"Development of ultrasonic diagnosis system for early-stage arteriosclerosis using impulsive actuator"

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In this research, we have developed a new method to measure local pulse wave velocity, which is an index of the hardness in the range of several millimeters on the aortic wall. In the standard method, the pulse wave velocity (PWV) is obtained from the difference in arrival time of pressure waves propagating from the carotid artery to the femoral artery. In this method, the measurable points are limited to those where the aorta exists near the skin surface and the distance between such points is considerable long, i. e., several hundred millimeters. It is important for early diagnosis, however, to measure the local hardness of the surface of the arterial wall. To increase the spatial resolution, it is necessary to measure vibrations due to pulse waves with frequency components up to about 50 Hz.Therefore, we have developed a new system to noninvasively measure small vibration signals on the heart wall or the aortic wall from the surface of the skin based on the ultrasonic Doppler effect. By this system, small vibrations with amplitudes of 10-100mum on the motion due to heart beat with the large amplitude of 10 mm are successfully detected in the frequency range up to 1 kHz continuously for more than ten beat periods from the chest.To improve the spatial resolution in the local velocity measurement of vibration propagating on the arterial wall, this research also developed a new method to actuate impulsive wave with higher frequency components until 1 kHz from the backbone and transcutaneously measure the transit delay time of the impulsive wave propagating two proximate points on the aortic wall. The method offers potential for research in acoustical diagnosis of arteriosclerosis.