Improved thulium fiber laser vaporization of urinary stones using micro-pulse packets

The Thulium Fiber Laser (TFL) is being studied as an alternative to the Holmium:YAG (Ho:YAG) laser for lithotripsy. The diode-pumped TFL may be electronically modulated to operate with variable parameters for studying the influence of pulse train mode on stone ablation rates. In this study, the TFL was operated at 1908 nm, 35-mJ pulse energy, and 500-μs pulse duration, in a train of 5 micro-pulses, with macro-pulse rates of 10 Hz, compared with TFL operation at 10-50 Hz. TFL energy was delivered through 100-μm-core fibers in contact with human uric acid (UA) and calcium oxalate monohydrate (COM) stones. Mass removal rates, optical coherence tomography, and light microscopy were used to analyze ablation craters. Stone retropulsion and fiber tip degradation was also studied for these laser parameters. TFL operation in micro-pulse train (MPT) mode resulted in a two-fold increase in the ablation rate of 414 ± 94 μg/s and 122 ± 24 μg/s for the UA and COM stones, respectively, compared to 182 ± 69 μg/s and 60 ± 14 μg/s with standard pulse trains delivered at 50 Hz (P <0.05). Stone retropulsion remained minimal for both pulse modes. Fiber burnback was significant for both pulse modes and was higher for COM stones than UA stones. TFL operation in MPT mode results in increased stone ablation rates which, with further optimization, may approach rates comparable to Ho:YAG laser lithotripsy in the clinic.