Interaction of shock waves with cavitation bubble: Application of Ho:YAG pulse laser irradiation for cerebral thrombolysis

Abstract

This paper reports on the application of underwater shock waves and vapor cavities for cerebral thrombolysis. The energy source was a Q-switched Ho:YAG laser (Nippon Infrared Industries Co., Ltd.) with 91 and 140 mJ/pulse energy measured at the end of a 0.60-mm-diam glass optical fiber, pulse duration of 200 ns, and wavelength of 2100 nm. The whole sequences of the shock-wave propagation and growth of the cavitation bubbles from the end of the optical fiber were visualized by high-speed photography using an Imacon 468 camera (Hadland Photonics Ltd.). The shock-wave generation was associated with the laser breakdown in the water. The laser interaction produced a microplasma and heated the liquid in front of the fiber. The plasma drove spherical shock wave in water, followed by the formation of a high-temperature vapor cavity. Collapse of the cavity produced a secondary spherical shock wave in water. Successive generation and collapse of the bubbles were visualized. Pressure histories were measured by PVDF needle hydrophones. The underwater shock waves and the vapor cavities were successfully applied for disruption of artificial thrombosis. The result clearly shows potential extension of this method to precise medical treatment for revascularization in neurosurgery.