Visible lesion thresholds with pulse duration, spot size dependency, and model predictions for 1.54-μm, near-infrared laser pulses penetrating porcine skin

Abstract

Er:glass lasers have been in operation with both long pulses (hundreds of microseconds) and Q-switched pulses (50 to 100 ns) for more than 35 yr. The ocular hazards of this laser were reported early, and it was determined that damage to the eye from the 1.54-microm wavelength occurred mainly in the cornea where light from this wavelength is highly absorbed. Research on skin hazards has been reported only in the past few years because of limited pulse energies from these lasers. Currently, however, with pulse energies in the hundreds of joules, these lasers may be hazardous to the skin in addition to being eye hazards. We report our minimum visible lesion (MVL) threshold measurements for two different pulse durations and three different spot sizes for the 1.54-microm wavelength using porcine skin as an in vivo model. We also compare our measurements to results from our model, based on the heat transfer equation and the rate process equation. Our MVL-ED50 thresholds for the long pulse (600 micros) at 24 h postexposure were measured to be 20, 8.1, and 7.4 J cm(-2) for spot diameters of 0.7, 1.0, and 5 mm, respectively. Q-switched laser pulses of 31 ns had lower ED50 (estimated dose for a 50% probability of laser-induced damage) thresholds of 6.1 J cm(-2) for a 5-mm-diam, top-hat spatial profile laser pulse.

Injury thresholds for topical-cream-coated skin of hairless guinea pigs ( cavia porcellus ) in the near-infrared region

“…3 Many of these lasers are used in military settings and are capable of producing high peak-power with short pulses. 2 This type of exposure has proved to cause more extensive damage than continuous wave lasers. The reflectance of the skin plays a vital role in determining how much radiation will be absorbed.…”

“…The ED 50 is compared to a similar study done using Yucatan minipigs. 2 The Yorkshire and Yucatan mini-pig are commonly used as in vivo skin models for damage threshold determination for national laser safety standards used in the ANSI Z.136.1-2000. 6 Of the two, the Yucatan mini-pig has been deemed the more applicable animal model for laser-induced skin injury investigations.…”

Thermal effects of white light illumination during microsurgery: clinical pilot study on the application safety of surgical microscopes

“…4,5 Several studies provide data about damage thresholds or maximum permissible exposure ͑MPE͒ values, but they are related to laser irradiation. [6][7][8] MPE values for skin, as listed in the International Electrotechnical Commission ͑IEC͒ or the American National Standards Institute ͑ANSI͒ safety standards for incoherent ͑lamp͒ or coherent ͑laser͒ irradiation ͑see Sec. 4͒, provide a basis to estimate limits for safe use.…”

Modeling of surface thermodynamics and damage thresholds in the IR and THz regime

“…Recently, we have focused on revisions of ANSI infrared exposure limits to more accurately reflect the trends in biological response. [7][8][9] This has led to a need for close examination of strongly absorbed frequencies both in the infrared (IR) and the terahertz (THz) region 10 of the electromagnetic spectrum. 7,11,12 In these regions, absorption depth of the incident radiation can be extremely shallow.'…”

“…[7][8][9] This has led to a need for close examination of strongly absorbed frequencies both in the infrared (IR) and the terahertz (THz) region 10 of the electromagnetic spectrum. 7,11,12 In these regions, absorption depth of the incident radiation can be extremely shallow.' 3 We have speculated that boundary conditions must be accurately represented in order to correctly predict the temperature response, and subsequent damage thresholds.…”