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Porcine skin ED 50 damage thresholds for 2,000 nm laser irradiation
Author(s) -
Chen Bo,
O'Dell Daniel C.,
Thomsen Sharon L.,
Rockwell Benjamin A.,
Welch Ashley J.
Publication year - 2005
Publication title -
lasers in surgery and medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 112
eISSN - 1096-9101
pISSN - 0196-8092
DOI - 10.1002/lsm.20243
Subject(s) - irradiation , laser , laser safety , irradiance , continuous wave , exposure duration , materials science , optics , nuclear medicine , medicine , toxicology , physics , biology , nuclear physics
Background and Objectives To gain refinement in safe‐exposure limits, indicated by the maximum permissible exposure (MPE) limits, the minimum visible lesion thresholds for three spot sizes (5–15 mm) and four exposure durations (0.25–2.5 seconds) were determined for the skin at 2,000 nm continuous wave laser irradiation. Study Design/Materials and Methods A series of experiments were conducted in vivo on female Yucatan mini‐pigs to determine the ED 50 damage thresholds for 2,000 nm continuous wave laser irradiation. The study employed Gaussian laser beam exposures with spot diameters (1/ e 2 ) of 4.83, 9.65, and 14.65 mm and exposure durations of 0.25, 0.5, 1.0, and 2.5 seconds as a function of laser power. The effect of each irradiation was evaluated within 1 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 (ED 50 ), defined as persistent redness at the site of irradiation for the mini‐pig skin after 48 hours. Results The MPE spot size and exposure duration trends for 2,000 nm laser exposure is consistent for exposure diameters less than 3.5 mm. However, for larger exposure diameters of 4.83, 9.65, and 14.65 mm and exposure duration longer than 0.25 second, the current MPEs are bigger than one tenth of our damage thresholds. For Gaussian laser profile, which is common for many laser output irradiance distributions, lower energy is required to generate a lesion on skin for smaller spot sizes and shorter exposure duration. On the other hand, for spot sizes greater than 4.83 mm and exposure duration over 0.25 second, the average radiant exposure at threshold is inversely proportional to spot size. The irradiance‐time and temperature‐time power law at the threshold were investigated as well and showed that the irradiance‐time power law was a close approximation to estimate laser irradiance at ED 50 damage threshold. Conclusions The thresholds study shows that consideration for lowering the MPE standards 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 ED 50 damage thresholds could be described by an empirical equation: Irradiance at the threshold = (5.669−1.81×spot diameter)×exposure duration −0.794 . Lasers Surg. Med. 37:373–381, 2005. © 2005 Wiley‐Liss, Inc.