Microsurgery of ureteral strictures using pulsed mid-IR lasers

Efficiency and precision of intraluminal laser incisions of soft tissue were investigated particularly for reopening ureteral strictures. We used mid-IR laser radiation and an application system which nearly tangentially performed the contact incision via a low-OH quartz fiber to achieve a longitudinal cut through the whole ureter wall up to the periureteral fat tissue. With pulsed Holmium and Thulium laser radiation we investigated in vitro (using the model of pig ureters) the cutting efficiency and coagulation zone with respect to laser power, pulse length, cutting speed and fiber diameter. The thermo-mechanical mechanism of tissue ablation was evaluated by fast flash photography showing a growing influence of the cavitation bubble towards shorter pulse lengths. In a first clinical study 14 patients underwent the laser therapy. We used the Holmium laser in the free running mode at a pulse repetition rate of 10 Hz and with an average power of 3 W at the end of a 300 micrometers fiber. The reopening of the stenoses took about 19 min. with an average laser energy of 819 J applied. The whole procedure was observed by videoscopy. No bleeding could be seen and no complications during the laser treatment occurred.