Development and experimental in vivo validation of mathematical modeling of laser coagulation

Abstract

Most clinical procedures using the laser are based on thermal laser-tissue interactions. The treatment often consists of inducing damage of given degree and extent by heating the tissue. The aim of this study was to develop a model called HELIOS. The ability of HELIOS to predict thermal coagulation was evaluated by comparison with in vivo experimental results. Conversion of laser light in tissue was studied using the beam-broadening model. Temperature was described by the heat conduction equation solved using the finite difference method. The tissue denaturation was modeled by the Henriques equation leading to the determination of the damage coefficient omega. For a given set of laser and tissue parameters, HELIOS makes a graphic representation of coagulation necrosis and temperature evolution in tissue. HELIOS was validated by experimental studies in vivo on rat liver using a CW Nd:YAG laser, a CO2 laser, and an argon laser. For given sets of laser parameters, temperature measurements were performed using an infrared camera. Histological examinations were carried out on samples to quantify the depth of coagulation necrosis. Experimental data obtained in vivo were compared with those calculated using HELIOS and similar sets of parameters. The difference between the predicted temperature evolution on tissue surface and that measured by the infrared camera was < 5 degrees C in all cases. The difference between the predicted coagulation necrosis depth and the corresponding experimental one was < 10%. In conclusion, HELIOS allows good prediction of tissue temperature and coagulation necrosis.

Temperature dependent change in equilibrium elastic modulus after thermally induced stress relaxation in porcine septal cartilage

“…Numerical modeling of the optical and thermal lasertissue interactions has proven to be a useful tool for the planning and optimization of many clinical procedures involving laser energy [10,[18][19][20]. However, simulation of the relatively new LCR procedures goes well beyond the scope of traditional opto-thermal models and requires consideration of thermally induced changes in the tissue mechanical state.…”

Nd:YAG laser combined with IPL treatment improves clinical results in non‐ablative photorejuvenation

“…Beacco et al confirmed these observations by mathematical modelling. [11][12][13][14] Advantages of the combined energy of these two wavelengths are currently being seen in our patients at a clinical level because of the higher temperatures accumulating in the dermis, but without damaging the overlying epidermis. When the Nd:YAG laser is applied to IPLirradiated tissue, the process of tissue denaturation has already taken place, which occurs at temperatures in the range 50-65 ‡C and involves thermal breaking of the heatlabile hydrogen bonds between collagen fibrils caused by the IPL pulse in the dermal tissue.…”

Influence of pulsatile blood flow and heating scheme on the temperature distribution during hyperthermia treatment

“…Its objective is to raise the temperature of pathological tissues above cytotoxic temperatures (41-45°C) without overexposing healthy tissues [1][2][3][4]. Although difficult to achieve and maintain in a clinical setting, uniform temperature distributions, are significant during hyperthermia treatment [5] since the use of temperatures above 55°C may directly destroy tissues through thermal coagulation, as was illustrated by Beacco et al [6]. Temperature variations, which may be associated with the mechanisms of heat removal by the body and may sometimes be caused by inadequate heating technologies, are often heterogeneous, and can lead to defectively heated tissues, hot spots and potential burning.…”