Interaction of Er:YAG laser radiation with ureter tissue

The aim of the work was to investigate the possibility of the ureter wall perforation by Er:YAG laser radiation and to explore the basic interaction characteristics for ureter surface and its deep structures. For these experiments Er:YAG laser system (wavelength 2.94 μm) working in free-running and Q-switched regime was utilized. Laser radiation was delivered to the investigated tissue by a special waveguide system. The basic part was a cyclic olefin polymer-coated silver hollow glass waveguide (inner/outer diameter 700/850/μm or 320/450/μm). Sealed cap of the waveguide was used for contact treatment. Maximum interaction pulse energy and length for free-running Er:YAG I laser with the 700 μm waveguide were 100 mJ and 200 μs, respectively (corresponding intensity was 130kW/cm²). Similarly the maximum interaction pulse energy and length for free-running Er:YAG II laser with the 320 um waveguide were 80 mJ and 200 μs, respectively (corresponding intensity was 500kW/cm²). Maximum interaction pulse energy and length in Q-switched regime were 17 mJ and 70ns, respectively (corresponding intensity 63MW/cm²). The number of pulses needed to perforate the ureter wall tissue (thickness ∼ 1 mm) for using long 200 μs Er:YAG pulses (thermal ablation) and short 70 ns Er:YAG pulses (photoablation) was found. From the histological evaluation it follows that the application of Q-switched Er:YAG laser radiation on ureteral tissue resulted in minimum adjacent tissue alteration (up to 50 μm from the surface) without any influence on the deeper layers.