Variable pulsewidth Erbium: YAG laser ablation of the ureter and urethra in vitro and in vivo: Optimization of the laser fluence, pulse duration, and pulse repetition rate

Stricture recurrence frequently occurs due to mechanical or thermal insult during endourologic treatment of ureteral and urethral strictures. Optimization of the Er:YAG laser for precise incision of strictures was conducted using ureteral and urethral tissue samples, ex vivo, and a laparoscopic porcine ureteral model with exposed ureter, in vivo. Erbium:YAG laser radiation with a wavelength of 2.94 microns, pulse lengths of 8, 70, and 220 microseconds, output energies of 2-35 mJ, fluences of 1-25 J/cm ², and pulse repetition rates of 5-30 Hz, was delivered through germanium oxide optical fibers in contact with the tissue. Incision of the ureteral wall was achieved in vivo with less than 20 pulses at a laser fluence of 4 J/cm ². Thermal damage was reduced from 30-60 microns to 10-20 microns by shortening the laser pulse duration from 220 to 70 microseconds. Pulse repetition rates above 20 Hz resulted in larger thermal damage zones ranging from 60-120 microns. The Er:YAG laser, operating at a pulse duration of approximately 70 microseconds, a fluence of 4 J/cm ² or greater, and a repetition rate less than 20 Hz, is capable of rapidly incising urethral and ureteral tissues, in vivo, with minimal thermal and mechanical side-effects.