A pulsed holmium laser (wavelength 2.1 μm, pulse duration 250 μs) was used to ablate rabbit liver, stomach, and colon in vivo. Microscopic examination of the tissues revealed zones of thermal damage extending 0.5-1.0 mm from ablation sites. In addition, ablation rates were measured using a mass loss technique and found to increase linearly with delivered radiant exposure. The threshold radiant exposure for ablation was calculated to be 50 J/cm2 with a heat of ablation of 7000 J/cm3. Because the holmium laser produces less thermal necrosis than current endoscopic laser systems, such as the continuous-wave neodymium: YAG laser, and because the ablation rate can be precisely controlled, the holmium laser shows promise as an alternative method for endoscopic removal of tissue.
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