Effective thermal penetration depth in photo-irradiated Ex vivo human tissues

Objective: In this work, a model of bioheat distribution is discussed for ex vivo human tissue samples, and the thermal penetration depth measurements performed on several tissues are presented. Background data: Optical radiation is widely applied in the treatment and diagnosis of different pathologies. A power density of incident light at 100 mW/cm² is sufficiently high enough to induce a temperature increase of >5°C in irradiated human tissue. In this case, knowledge of the thermal properties of the tissue is needed to achieve a better understanding of the therapeutic effects. Method: The application of the diffusion approximation of the radiative transfer equation for the distribution of optical radiation, the experimental setup, and the results thereof are presented and discussed. Results: The effective thermal penetration depth in the studied tissues has been determined to be in the range of 4.3-7.0 mm. Conclusions: The effective thermal penetration depth has been defined, and this could be useful for developing models to describe the thermal effects with a separate analysis of the tissue itself and the blood that irrigates it.