Elucidation of the mechanism on biological tissue injuries induced by shock waves

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1)Elucidation of physical phenomena in the focal region of the focused shock waves concerning the mechanism of biological tissue injuries.Focusing process of shock waves inside water was observed under an ultrasound diagnostic system. It was revealed that the hyperechoic region was induced around the focal region, and it moved distally , then, disappeared gradualy with elapsed time. This observation indicated that cavitation bubbles was responsible for generation of the hyperechoic region, and a fluid flow was induced at the time, Gene-ration and behavior of the liquid flow was simulated numerically by computer, and the results of simulation indicated that a direction of the fluid flow was not only parallel, but also radial to that of shock wave propagation. Consequently, besides the cavitation phenomena, the fluid flow was assumend to be an important factor causing tissue injury. In addition, it was observed on ultrasonic images that cavitation developed in wide range through the shock wave propagating path, from the prefocal region to the postfocal region. Tissue injuries through the path of shock wave propagation was confirmed by animal experiment. From considering aforementioned results, a new safer lithotriptor equipped anti-miss-shot device was developed and clinically used.2)Real-time observation on the tissue injury in the in situ rabbit auricular vessels was performed using high-speed video camera. Results indicated that the artery was injured following the vein, and during that process vasoconstiriction and vasodilation developed, suggesting that shock waves effected on autonomic nerves. If compared to the injury of kidney vessls in the previous experiments, the auricular vessels were relatively resistive to the shock wavaes. Therefore, sensitivity to shock wave injury was assumed to be influenced by the acoustic condition in various organs.