Heating and structural alterations in cartilage under laserradiation

摘要

The authors have developed a theoretical model to calculate thentemperature field and the spatial distribution of modified cartilagenfollowing laser irradiation. The model incorporates both thermal andnmass transfer in a tissue with bulk absorption of laser radiation, waternevaporation from the surfaces of a slab, and temperature dependence ofnthe diffusion coefficient. The authors propose that water undergoes anbound-to-free phase transition in cartilage heated to about 70°C andnthe mobility of proteoglycan units in the cartilage matrix increases.nMovement of the proteoglycan units takes place only when the temperaturenexceeds 70°C and results in tissue denaturation. Using their model,nthe authors show: (1) the maximal temperature is reached not on thensurface irradiated but rather at some distance below; (2) surfacentemperature reaches its asymptotic value quicker than the maximalntemperature; and (3) the depth of the denatured tissue volume stronglyndepends on laser fluency, wavelength, exposure time, and cartilagenthickness. The model allows for the prediction and control ofntemperature and depth of structural alterations during the course ofnlaser reshaping and treatment of cartilage