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In the treatment of acute cerebral infarction, it is important to remove the thrombus quickly without side effects such as intracranial hemorrhage. We have been developing a new therapy way of acute cerebral infraction using laser to solve some weaknesses of current devices and medicines. We use 532nm pulsed laser to remove clot without damage of vessel wall, but it is difficult to adjust position of the tip of catheter to a clot within an effective range. Then, we developed real time monitoring function to evaluate it. In a real-time monitoring function, we used 785nm CW laser added on 532nm pulsed laser, evaluated the 785nm laser which is reflected the tip of the optical fiber. A power of the reflected 785nm is based on the Fresnel equations, and time change levels of reflected 785nm reflects how bubbles generated by pulsed lasers disappear. In the result of evaluation of in vitro studies, it turned out that how its change is affected by the surrounding environment (e.g., hardness and viscosity around the catheter tip). If the area around the catheter tip is filled with liquid, the signal will disappear quickly and simply, and if there is a blood clot, it will be less likely to disappear and its shape is more complex and the key to these phenomena is how the shock generated by the pulsed laser propagates, and we hypothesize that it is a type of rebound due to cavitation.
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