Pulsed photothermal radiometry of surgical laser-tissue interaction

Abstract

Achievements and prospects of PPTR-method for monitoring Icontrol of laser treatment in surgery purposes are presented. Connection of output laser parameters and ones of irradiated zone in tissue with parameters of measured thermal emission from irradiated tissue are analysed. There are presented the results of investigations of the high power laser-tissue interaction and of the processes of tissue destruction stimulated by middle-infrared-range pulsed lasers radiation in different sorts of tissues carried out by PPTR-technique. PPTR and Laser Mass-Spectrometry are united in study of evolution of tissue destruction under action of power CO2 laser. The evolution of thermal signal and, correspondingly, temperature in tissue under single laser pulse treatment with rise of energy density are obtained. Method of the temperature stroboscopy which allows to see very fast tissue heating stimulated by pulsed laser treatment more elaborate are presented.

Influence of tissue desiccation on critical temperature for thermal damage during Er:YAG laser skin treatments

“…In this study, skin characteristics following irradiations by Er:YAG laser pulses were measured using a technique commonly known as OTR (opto-thermal radiometry), or OTTER (opto-thermal transient emission radiometry). 15,19,34 As opposed to most of the previously published studies, a fast thermal camera was used instead of a single wavelength infrared detector.…”

“…In the third step, the hottest part of the tissue close to the surface is ablated, in effect reducing the depth of the thermally affected skin layer. Ablation temperatures substantially above 100°C [14][15][16] indicate that the Er:YAG laser ablation of human tissues is based on a microexplosion mechanism. 17 As the bound tissue water trapped within the microscopic cavities within the tissue absorbs the laser radiation, its temperature increases until the boiling point (T ≈ 100°C) is reached.…”

“…Micro-explosive removal of tissue starts when the pressure exceeds the ultimate tensile strength of the tissue, which for soft tissue occurs at water vapor temperatures of about 250°C. 15,17,18 The above process describes what happens with the bound water. On the other hand, the free water can evaporate from the tissue sooner during the heating phase, that is, before the tissue reaches the ablation temperature.…”

“…As the vapor cannot expand freely, pressure in the cavity rises and exerts force on the cavity wall. Micro‐explosive removal of tissue starts when the pressure exceeds the ultimate tensile strength of the tissue, which for soft tissue occurs at water vapor temperatures of about 250°C 15,17,18 …”

Applications of fiber optic pulsed photothermal radiometry

“…The PPTR method was used in medical applications to distinguish between normal and diseased biological tissues [9][10][11][12] and to assist in laser surgery. 13 In most of the work done to date, the delivery of the laser radiation and the collection of thermal radiation was done by standard optical elements such as lenses or mirrors, in the absence of optical fibers for the mid IR.…”