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 during laser irradiation by comparing calculated valueswith experimental measurements. Samples of normal human aorta, beef myocardium, and polyacrylamide gel were irradiated in air with an argon laser beam, while surfacetemperatures 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^°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^°C, however, the models greatly overestimated temperature rises in both cases. It was concluded that the discrepancies were mainly aresult of surface water vaporization, which was not considered in current models and which was by far the most significant surface-heat-loss mechanismfor laser irradiation in air. The inclusion of surface water vaporization in the mathematical models provided a much better match between predicted temperatures andexperimental results.