Thulium fiber laser ablation of kidney stones using a 50-μm-core silica optical fiber

Our laboratory is currently studying the experimental thulium fiber laser (TFL) as a potential alternative laser lithotripter to the gold standard, clinical Holmium: YAG laser. We have previously demonstrated the efficient coupling of TFL energy into fibers as small as 100-mu m-core-diameter without damage to the proximal end. Although smaller fibers have a greater tendency to degrade at the distal tip during lithotripsy, fiber diameters (<= 200 mu m) have been shown to increase the saline irrigation rates through the working channel of a flexible ureteroscope, to maximize the ureteroscope deflection, and to reduce the stone retropulsion during laser lithotripsy. In this study, a 50-mu m-core-diameter, 85-mu m-outer-diameter, low-OH silica fiber is characterized for TFL ablation of human calcium oxalate monohydrate urinary stones, ex vivo. The 50-mu m-core fiber consumes approximately 30 times less cross-sectional area inside the single working channel of a ureteroscope than the standard 270-mu m-core fiber currently used in the clinic. The ureteroscope working channel flow rate, including the 50-mu m fiber, decreased by only 10% with no impairment of ureteroscope deflection. The fiber delivered up to 15.4 +/- 5.9 Wunder extreme bending (5-mm-radius) conditions. The stone ablation rate measured 70 +/- 22 mu g/s for 35-mJ-pulse-energy, 500-mu s-pulse-duration, and 50-Hz-pulse-rate. Stone retropulsion and fiber burnback averaged 201 +/- 336 and 3000 +/- 2600 m, respectively, after 2 min. With further development, thulium fiber laser lithotripsy using ultra-small, 50-mu m-core fibers may introduce new integration and miniaturization possibilities and potentially provide an alternative to conventional Holmium: YAG laser lithotripsy using larger fibers. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)