Erbium:YAG Laser Lithotripsy Using Hybrid Germanium/Silica Optical Fibers

Abstract

Previous studies have demonstrated that the erbium:YAG laser is two to three times more efficient for laser lithotripsy than the holmium:YAG laser. However, the lack of a suitable optical fiber delivery system remains a major obstacle to clinical application of Er:YAG laser lithotripsy. This paper describes the initial testing of a hybrid germanium oxide/silica optical fiber for potential endoscopic use with the Er:YAG laser. Er:YAG laser radiation with a wavelength of 2.94 microm, a pulse energy of 10 to 600 mJ, a pulse length of 220 microsec, and pulse-repetition rates of 3 to 10 Hz was focused into either 350- or 425- microm-core hybrid germanium/silica fibers in contact with human uric acid or calcium oxalate monohydrate stones. Average Er:YAG pulse energies of 157 +/- 46 mJ (66 J/cm(2)) (N = 8) were delivered at 10 Hz through the 425-microm hybrid fibers in contact with urinary stones before fiber damage was observed. A maximum pulse energy of 233 mJ (98 J/cm(2)) was also measured through the hybrid fiber in contact with the stones. These values are significantly greater than the stone ablation thresholds of 15 to 23 mJ (6-10 J/cm(2)) and the fiber damage thresholds measured for germanium oxide, 18 +/- 1 mJ (13 J/cm(2)), and sapphire, 73 mJ (51 J/cm(2)), optical fibers during Er:YAG laser lithotripsy (P < 0.05). A prototype hybrid germanium/silica optical fiber demonstrated better performance than both germanium oxide and sapphire fibers for transmission of Er:YAG laser radiation during in vitro lithotripsy.