Thulium Fiber Laser Lithotripsy using Small, Medium, and Large Muzzle Brake Fiber Optic Tips

Previous Thulium fiber laser (TFL) studies using fiber optic muzzle brake tips reported reduced stone retropulsion and distal fiber tip degradation. This study compares muzzle brake tips of various dimensions using the TFL at 1908 and 1940 nm wavelengths in terms of stone phantom retropulsion displacement using a pendulum setup, needle hydrophone pressure transient measurements, and uric acid (UA) stone ablation rates. Low and high TFL pulse energies of 35 and 140 mJ, 500 mu s pulse duration, and pulse rates up to 300 Hz were used with 100- and 200-mu m-core optical fibers. "Small", "medium", and "large" muzzle brake tips dimensions measured 180/340, 360/560, and 550/710 mu m inner/outer diameter, respectively, with a porthole positioned 500 mu m from distal muzzle brake end. Pendulum displacement measured 50%, 200%, and 50% of bare trunk fibers for small, medium and large muzzle tips, respectively, in optimal configuration. Needle hydrophone pressures measured 300%, 20%, and 50% of bare trunk fiber for small, medium and large muzzle tips, respectively, in optimal configuration. Stone ablation rates at low pulse energy (35 mJ) were maintained for medium muzzle brake tips while small and large muzzle brake tips performed about 10 and 7.5 times worse than bare fibers. At high pulse energy (140 mJ), the large muzzle tip performed similar to a bare 200-mu m-core fiber with 100%, 50%, and 100% the displacement, pressure, and ablation rate. These studies show feasibility of modifying muzzle brake tip dimensions to obtain comparative ablation rates and minimal stone retropulsion for lithotripsy.