Comparison of detachable and tapered fiber optic tips for use in thulium fiber laser lithotripsy

The Thulium fiber laser (TFL) has recently been proposed as an alternative to the Holmium:YAG laser for lithotripsy. The TFL's Gaussian spatial beam profile provides higher power transmission through smaller optical fibers with reduced proximal fiber tip damage, and improved saline irrigation and flexibility through the ureteroscope. However, distal fiber tip damage may still occur during stone fragmentation, resulting in disposal of the entire fiber after the procedure. A novel design for a short, detachable, distal fiber tip that can fit into an ureteroscope's working channel is proposed. A prototype, twist-lock, spring-loaded mechanism was constructed using micromachining methods, mating a 150-μm-core trunk fiber to 300-μm-core fiber tip. Optical transmission measuring 80% was observed using a 30 mJ pulse energy and 500 μs pulse duration. Ex vivo human calcium oxalate monohydrate urinary stones were vaporized at an average rate of 187 μg/s using 20 Hz modulated 50% duty cycle five pulse packets. The highest stone ablation rates corresponded to highest fiber tip degradation, thus providing motivation for use of detachable and disposable distal fiber tips during lithotripsy. The 1-mm-outer-diameter prototype functioned comparable to previously tested tapered fiber tips, and the novel design shows promise for potential integration into miniaturized flexible ureteroscopes.