Several international organizations establish minimum safety standards to ensure that workers and the general
population are protected against adverse health effects associated with electromagnetic radiation. Suitable standards are
typically defined using published experimental data. To date, few experimental studies have been conducted at Terahertz
(THz) frequencies, and as a result, current THz standards have been defined using extrapolated estimates from
neighboring spectral regions. In this study, we used computational modeling and experimental approaches to determine
tissue-damage thresholds at THz frequencies. For the computational modeling efforts, we used the Arrhenius damage
integral to predict damage-thresholds. We determined thresholds experimentally for both long (minutes) and short
(seconds) THz exposures. For the long exposure studies, we used an in-house molecular gas THz laser (υ= 1.89 THz,
189.92 mW/cm2, 10 minutes) and excised porcine skin. For the short exposure studies, we used the Free Electron Laser
(FEL) at Jefferson Laboratory (υ= 0.1-1.0 THz, 2.0-14.0 mW/cm2, 2 seconds) and wet chamois cloths. Thresholds were
determined using conventional damage score determination and probit analysis techniques, and tissue temperatures were
measured using infrared thermographic techniques. We found that the FEL was ideal for tissue damage studies, while
our in-house THz source was not suitable to determine tissue damage thresholds. Using experimental data, the tissue
damage threshold (ED50) was determined to be 7.16 W/cm2. This value was in well agreement with that predicted using
our computational models. We hope that knowledge of tissue-damage thresholds at THz frequencies helps to ensure the
safe use of THz radiation.
Historically, safety analyses for radio frequency emission and optical laser exposures have been designed to define the threshold level for tissue damage. To date, no experimental studies have documented damage thresholds to living tissues in the terahertz (THz) range of electromagnetic frequencies (0.1 - 10 THz). Exposure limits exist as extrapolated estimates at the extreme bounds of current occupational safety standards for lasers and radio frequency sources. Therefore, due to the lack of published data on the safety of terahertz emissions, an understanding of the bioeffects of tissue exposures to terahertz beams is necessary. The terahertz frequency band represents an intermediate range in which both optical and radiofrequency methods of theory and experimentation can be selectively employed and compared for consistency. We report on work recently completed to reconcile the theoretical methods of optical and radio-frequency radiative transport modeling, while additionally discussing preliminary theoretical estimates of damage thresholds to skin tissue from terahertz energy and work planned to validate these findings experimentally.
Conference Committee Involvement (1)
Optical Interactions with Tissue and Cells XIX
21 January 2008 | San Jose, California, United States
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