Experimental and Clinical Study of a Holmium: YAG Laser with Adjustable Pulse Duration

Background: The holmium:YAG laser is used for treatment of urolithiasis, transurethral laser ablation for benign prostate hypertrophy and bladder tumor. The pulse duration was fixed in the previous Ho:YAG laser systems. We have evaluated more practical pulse durations to disintegrate the stone. The SPHINX Ho40 (Heraeus Corporation) can change the pulse duration freely in the range from 150 microsec. to 800 microsec.

Materials And Methods: 1) We measured the total energy to perforate through stone models at three different pulse durations (150, 300, 600 microsec.). 2) We experimented with the energy of each single pulse and the power of the shock wave. 3) We observed thermogenesis during the lithotripsy for each pulse duration. 4) Disintegration effects of Ho:YAG are compared with other lithotripsy systems in clinical cases.

Results: 1) It was possible that the smallest amount of the total energy went through the fragment at the pulse duration 150 microsec. 2) The maximum amount of energy of the wave is higher when the pulse duration is short. Although the amount of energy was 12.6 V, the amounts of energy at 800 microsec decreased with a pulse duration 150 microsec. to 6.46 V which was about 40 % 3) The highest temperatures achieved when the irradiation of laser was started and finished were compared. The shorter the pulse duration was, the higher was the peak power. The shock wave was also more effective to disintegrate stones on using short pulse durations. 4) The individual clinical success rates are Ho:YAG (85.1 %), Alexandrite (80.6 %) and Lithoclast (74.5 %).