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Laser Micro/Nano Fabrication Lab.

Research

Low Level Laser Treatment

Low Level Laser treatment

Over the past decades, the application of low-level laser therapy (LLLT) has been expanded to various areas of treatment such as nerve regeneration, wound healing, pain relief, anti-inflammation, etc. For LLLT, visible or near infrared (NIR) lasers (600–1,064 nm) at the intensity level of about 0.001–5 W/cm2 were typically used with an irradiation time of a few seconds or longer. Despite many reports with positive results, the efficacy of LLLT is still under controversy. This is partially because the mechanism of laser-tissue interaction during LLLT is not well understood and also the optimal treatment parameters of LLLT were not systematically established yet.

Effects of temperature-dependent optical properties on the fluence rate and temperature of biological tissue during low-level laser therapy

In this work, the effects of temperature-dependent optical properties on fluence rate and tissue temperature were investigated by both experimental and numerical methods. In experiments, the fluence rate and temperature of low-level laser irradiated porcine skin were measured for varying durations of laser irradiation. Also, the variations of optical properties of porcine skin with respect to increasing temperature up to 40 °C were measured and utilized in the numerical model. Using a mathematical model that included temperature dependency of optical properties, the variations of fluence rate and temperature distribution were calculated and compared with the measured data. Numerical simulations for human skin were also carried out to investigate the influence of temperature dependent optical properties on LLLT.

Fig. 1 Schematic diagram of the experimental setup for a fluence rate and b optical property measurements.

Fig. 2 Measured absorption coefficient (μa) and reduced scattering coefficient (μs′ ) of porcine skin at varying tissue temperatures.


Fig. 3 Effects of temperature-dependent optical properties of human skin on a fluence rate profile (t=2 s), b heat generation profile (t=2 s), and c surface temperature increase.

In this work, the effects of temperature-dependent optical properties on fluence rate and tissue temperature were investigated by both experimental and numerical methods. In experiments, the fluence rate and temperature of low-level laser irradiated porcine skin were measured for varying durations of laser irradiation. Also, the variations of optical properties of porcine skin with respect to increasing temperature up to 40 °C were measured and utilized in the numerical model. Using a mathematical model that included temperature dependency of optical properties, the variations of fluence rate and temperature distribution were calculated and compared with the measured data. Numerical simulations for human skin were also carried out to investigate the influence of temperature dependent optical properties on LLLT.

Soogeun Kim and Sungho Jeong, "Effects of temperature-dependent optical properties on the fluence rate and temperature of biological tissue during low-level"

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