Threshold Damage of In vivo Porcine Skin at 2000 nm Laser Irradiation

A series of experiments were conducted in vivo on female Yucatan mini-pigs to determine the ED50 damage thresholds for 2000 nm continuous wave laser irradiation. These results provide new information for refinement of Maximum Permissible Exposure (MPE). The study employed Gaussian laser beam exposures with spot diameters (1/e2) of 4.83 mm, 9.65 mm and 14.65 mm and exposure durations of 0.25 s, 0.5 s, 1.0 s and 2.5 seconds as a function of laser power. The effect of each irradiation was evaluated within one minute after irradiation and the final determination was made at 48 hours post exposure. Probit analysis was conducted to estimate the dose for 50% probability of laser-induced damage (ED50) defined as persistent redness at the site of irradiation for the mini-pig skin after 48 hours. Histopathologic procedures were used to determine the mechanisms of the laser effects in the skin and map the extent and severity of the lesions. The thresholds study shows that consideration for lowering the current Maximum Permissible Exposure (MPE) limits should be explored as the laser beam diameter becomes larger than 3.5 mm. Based on the limited experimental data, the duration and size dependences of the ED50 damage thresholds could be described by an empirical equation: Irradiance at the threshold[J/cm2] = (5.669 - 1.81 x spot diameter [cm]) x exposure duration[s] -0.794.
Published in Optical Interactions with Tissue and Cells XVII, Proceedings of SPIE, v6084, 60840C, 2006.