Optical fiber tip damage by sparks in holmium:YAG laser lithotripsy

Abstract

Laser lithotripsy disintegrates urinary stones using laser pulses delivered to the stone via an optical fiber. The fiber tip is frequently damaged during the procedure, but the mechanism of damage is not understood. Here we show that the free-running long-pulse (>150 μs) infrared holmium:YAG lasers that currently are most often used for laser lithotripsy can produce sparks and shock waves, which is an unexpected result as the optical breakdown is typically observed with more powerful Q-switched lasers. We used an ultrahigh-speed camera Shimadzu HPV-X2 at frame rate up to 10 million frames per second to record single laser pulses with 242-μm glass-core-diameter fibers in contact with whole surgically retrieved urinary stones, BegoStones, and hydroxyapatite-coated glass slides in air and water. Fiber-tip damage occurred even without cavitation and was greater at 1.0 J than at 0.6 J (p = 0.010). No fiber-tip damage occurred without sparks (1.0 J, 500 pulses, water). Shock waves produced by sparks and subsequent collapses of vapor bubbles could break optical fiber tip in a single laser pulse. These observations suggest that the previously unappreciated optical breakdown with the free-running holmium:YAG lasers can be responsible for fiber-tip damage in laser procedures. [Work supported by NIDDK of NIH under award R43DK129104.]