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Laser-induced thermotherapy
Laser-induced thermotherapy, also referred to as laser ablation, consists of tissue destruction, induced by a local increase of temperature by means of laser light energy transmission.
==Laser-tissue interactions==
The irreversible necrosis of tissue irradiated by laser energy occurs for a combination of the temperature rise produced locally and the exposure time: cell death occurs within few seconds for temperatures exceeding 60 °C, while for lower temperatures are necessary longer exposure time.
The advantage of using laser light for thermotherapy, compared to other methods, is its ability to deposit a precise amount of energy in a well defined region. Thanks to its characteristics of monochromatic light (waves of the same wavelength), coherent (waves in phase) and collimated (parallel waves) it is possible to induce lesions of reproducible size, transmitting large amounts of energy at long distances. All applications of laser thermotherapy occur within a range of wavelengths, called 'therapeutic window', in which the light has a good tissue penetration. The light produced by a Nd:YAG laser with a wavelength of 1064 nm represents an ideal compromise to obtain a safe penetration depth, inversely proportional to the frequency of the wave, and a sufficient tissue absorption, depending on the tissue optical properties.
Most of the absorbed light is converted into heat, which causes changes in optical properties of tissue. Coagulation is defined as the thermal damage of the tissue proteins at temperatures in the interval about 55 and 95 °C. Its extension region depends mainly on the time during which the temperatures remain within the range. The most obvious example of coagulation is boiling the white egg, where the medium changes from transparent to white. If the temperature exceeds 100 °C causes the vaporization of the water contained in the tissue, which leads to the formation of steam.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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