Adjustment of Optical Fiber Position Using Laser-induced Bubble Dynamics Change Near a Thrombus

Abstract

In the treatment of acute cerebral infarction, it is important to remove the thrombus quickly without causing side effects such as intracranial hemorrhage. A new laser treatment system for acute cerebral infarction has been developed to address certain weaknesses of current treatment methods such as catheter devices and drugs. This laser system uses a 532nm pulsed laser to remove thrombus without damaging the vessel wall, but it is difficult to adjust the position of the catheter tip to a clot within an effective range. We then developed a real-time monitoring function to evaluate the distance between the thrombus and the catheter tip. In the real-time monitoring function, we used 785nm CW laser added to 532nm pulsed laser, evaluated the 785nm laser reflected from 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. As a result of evaluation of in vitro studies, it turned out that how its change is affected by the distance between the thrombus and the tip of the catheter. When the area around the catheter tip is filled with fluid, the signal disappears quickly and easily, and when there is a blood clot, it disappears less easily. These results suggest that it may be possible to adjust the position of the optical fiber by evaluating the change in Fresnel reflection after pulsed laser irradiation.