Optimization of the Erbium:YAG laser for precise incision of ureteral and urethral tissues: In vitro and in vivo results

Background and Objectives: Tissue damage during endoscopic treatment of urethral and ureteral strictures may result in stricture recurrence. The Erbium:YAG laser ablates soft tissues with minimal peripheral damage and may be a promising alternative to cold knife and Holmium:YAG laser for precise incision of urological strictures. Study Design/Materials and Methods: Optimization of the Er:YAG laser was conducted using ex vivo porcine ureteral and canine urethral tissues. Preliminary in vivo studies were also performed in a laparoscopic porcine ureteral model with exposed ureter. Laser radiation with a wavelength of 2.94 μm, pulse lengths of 8, 70, and 220 micro-seconds, output energies of 2-35 mJ, fluences of 1-25 J/cm², and pulse repetition rates of 5-30 Hz, was delivered through 250-μm and 425-μm core germanium oxide optical fibers in direct contact with tissue. Results: Ex vivo perforation thresholds measured 2-4 J/cm², with ablation rates of 50 μm/pulse at fluences of 6-11 J/cm². In vivo perforation thresholds were approximately 1.8 J/cm², with the ureter perforated in less than 20 pulses at fluences greater than 3.6 J/cm². Peripheral thermal damage in tissue decreased from 30 to 60 μm to 10-20 μm as the laser pulse length decreased from 220 to 8 microseconds. Mechanical tissue damage was observed at the 8 microseconds pulse duration. Conclusions: The Er:YAG laser, operating at a pulse duration of ∼70 microseconds, a fluence greater than ∼4 J/cm², and a repetition rate less than 20 Hz, is capable of rapidly incising urethral and ureteral tissues with minimal thermal and mechanical side-effects.