Our laboratory is currently studying the Thulium fiber laser (TFL) as a potential alternative laser lithotripter to the
standard clinical Holmium:YAG laser. We have previously demonstrated efficient coupling of TFL energy into
fibers as small as 100-μm-core-diameter without damage to the proximal end. Although smaller fibers have greater
tendency to degrade at the distal tip during lithotripsy, fiber diameters (≤ 200 μm) have been shown to increase
saline irrigation rates through the working channel of a flexible ureteroscope, maximize ureteroscope deflection, and
reduce stone retropulsion during laser lithotripsy. In this study, a 50-μm-core-diameter, 85-μm-outer-diameter fiber
is characterized for TFL ablation of human calcium oxalate monohydrate urinary stones, ex vivo. The stone ablation
rate was measured to be 70 ± 22 μg/s for 35-mJ-pulse-energy, 500-μs-pulse-duration, and 50-Hz-pulse-rate. The ureteroscope working channel flow rate including the 50-μm fiber decreased by only 10% with no impairment of
ureteroscope deflection. The fiber delivered up to 15.4 ± 5.9 W under extreme bending (5-mm-radius) conditions.
Stone retropulsion and fiber burn-back averaged 201 ± 336 and 3000 ± 2600 μm, respectively, after 2 minutes. With further development, Thulium fiber laser lithotripsy using ultra-small, 50-μm-core fibers may introduce new integration and miniaturization possibilities and potentially provide an alternatiμe to conventional Holmium:YAG
laser lithotripsy using larger fibers.