Objective: To assess the fiber-tissue interaction through ablation, coagulation, and carbonization characteristics of the Ho:YAG laser and super pulsed thulium fiber laser (TFL) in a nonperfused porcine kidney model. To assess the degradation of laser fibers during soft tissue treatment. Methods: A 50 W TFL generator was compared with a 120 W Ho:YAG laser. The laser settings that can be set identically between the two lasers (pulse energy and frequency), and clinically relevant for prostate laser enucleation, were identified and used for tissue incisions on fresh nonfrozen porcine kidneys. For each parameter, the short, medium, and long pulse durations for the Ho:YAG generator and the different peak powers 150, 250, and 500 W for the TFL generator were also tested. Laser incisions were performed with 550 μm stripped laser fiber fixed on a robotic arm at a distance of 0.1 mm with the tissue surface and at a constant speed of 10 mm/s. Histologic analysis was then performed, evaluating incision shape, incision depth and width, axial coagulation depth, and presence of carbonization. Degradation of the laser fiber was defined as reduction of laser fiber tip length after laser activation. Results: Incision depths and areas of coagulation were greater with the Ho:YAG laser than those with the TFL. Although no carbonization zone was found with the Ho:YAG laser, this was constant with the TFL. Although a fiber tip degradation was constantly observed with Ho:YAG laser, except in the case of a long pulse duration and low pulse energy (0.2 J), this was not the case with TFL. Conclusion: TFL appears to be an efficient alternative to Ho:YAG laser for soft tissue surgery. The histologic analysis found greater tissue penetration with the Ho:YAG laser and different coagulation properties between the two lasers. These results need to be investigated in vivo to assess the clinical impact of these differences and find the optimal settings for laser prostate enucleation.
Keywords: Ho:YAG laser; endourology; laser–tissue interactions; thulium fiber laser; tissue ablation.