Experimental evaluation of mathematical models for predicting the thermal response of tissue to laser irradiation.

We investigated the ability of mathematical models to predict temperature rises in biological tissue duringlaser irradiation by comparing calculated values with experimental measurements. Samples of normal human aorta, beef myocardium, and polyacrylamide gel were irradiated in air with an argon laser beam, while surface temperatures were monitored with an IR camera. The effects of different surface boundary conditions in the model predictions were examined and compared with the experimental data. It was observed that, before a temperature of 60 degrees C was reached, the current mathematical models were capable of predicting tissue-surface temperature rises with an accuracy of 90% for a purely absorbing medium and with an accuracy of 75% for biological tissue (a scattering medium). Above 60 degrees C, however, the models greatly overestimated temperature rises in both cases. It was concluded that the discrepancieswere mainly a result of surface water vaporization, which was not considered in current models and which was by far the most significant surface-heat-loss mechanism for laser irradiation in air. The inclusion of surface water vaporization in the mathematical models provided a much better match between predicted temperatures and experimental results.