Thermal processes during local laser heating of biological tissues

Abstract

Introduction. Lasers in medicine are currently widely used for both diagnosis and treatment. Studies of the thermal processes that occur when a person is exposed to laser radiation have made it possible to developinnovative methods of treating many diseases. Purpose: to study thermal processes in biological tissues during their local laser heating (mathematical model and experiment). Materials and methods. Using the developed mathematical model of the process of local heating of a certain region inside biological tissue, we studied the process of heating the environment by continuous and pulsed laser radiation using infrared light with a wavelength of 0.98 μm, red light with a wavelength of 0.65 μm, green light with a wavelength 0.5 microns and blue light with a wavelength of 0.435 microns. Results. The sizes of the heated region, the time of establishment and decrease in temperature are determined. The calculation results are in good agreement with the obtained experimental data. Findings. The mode of heating biological tissue with laser radiation depends on the wavelength. The maximum heating temperature of the irradiated section with a radiation pulse duration much shorter than the thermal time constant is independent of the shape and duration of the pulse and is determined only by the energy of the absorbed radiation. The distribution of heat into the medium during the duration of the pulse is determined by its duration and thermal diffusivity of the tissue. To reduce the heating of the surrounding tissue, it is necessary to use short radiation pulses. The progress of tissue heating by a sequence of radiation pulses depends on the relationship between the duration of the pulses, the period of their repetition, and the thermal time constant of the medium. The average (smoothed) temperature is the same as when heated with continuous power equal to the average power of the pulse-modulated radiation.