Mid-infrared pulsed laser lithotripsy using an Er:YAG laser and a difference frequency generation laser

Abstract

We conducted fundamental research on a novel lithotripsy technique using mid-infrared pulsed lasers. We irradiated gallstones extracted from the common bile duct using two mid-infrared lasers, namely, a difference-frequency generation (DFG) laser tunable within a wavelength range of 5.5-10 μm and an Er:YAG laser with a 2.94 μm wavelength, and then examined the depth and dimension of the crater formed. Some of the gallstones were continuously wet with distilled water during laser irradiation. The absorption spectrum of the gallstones was measured using a Fourier transform infrared spectrometer. The gallstones showed a strong peak around the wavelengths of 2.94 and 6.83 μm. In the case of DFG laser irradiation, the wavelength used was 6.83 μm and the average power density range of the laser was about 2-52 W/cm². After irradiation, a relatively small hole with a depth range of 0.1-0.2 mm and a dimension within 0.01-0.04 mm² was created. On the other hand, in the case of Er:YAG laser irradiation, the average power density range was about 0.20-0.78 kW/cm². As the result, a large hole was made and the mass of 0.4-1.6 mg was removed. In conclusion, wet gallstones were more decomposed than dry gallstones in both cases of laser irradiation, and these techniques proved to be effective for gallstone lithotripsy.