Investigation of thermal damage of tissues embedded with large blood vessels during plasmonic photo-thermal heating (PPTH)

The large blood vessels (LBV) would act as a heat sink and hence play a significant role during photo-thermal therapy. Gold nanoshell was considered as a high-heat absorbing agent in photo-thermal heating to reduce the cooling effect of LBV. The heat sink effect of LBV results in insignificant irreversible tissue thermal damage. The paper aims to discuss these issues.

In this paper, the thermal history of tissue embedded with LBV during photo-thermal heating were calculated using finite element-based simulation technique. A volumetric laser source term based on modified Beer-Lambert law was introduced to model laser heating. The numerically predicted temperature drop was validated against that of previously performed experiments by the authors on tissue mimic embedded with simulated blood vessels. In the later part of the study, Arrhenius equation was coupled with the energy equation to investigate and report the irreversible thermal damage to the bio-tissues.

The results obtained conclude that tissue with different orientation of blood vessels results in different thermal response at the tissue surface. Gold nanoshells were introduced into the laser irradiated tissue to overcome the cooling effect of LBV during plasmonic photo-thermal heating. The effect of size and concentration of nanoparticles on tissue heating were analyzed. The predicted damage parameter was much lower in case of tissue embedded with blood vessel than that predicted in case of bare tissue, which results in incomplete tissue necrosis. Finally, the effects of laser specification, blood vessel specification and blood perfusion on the tissue thermal damage were examined.

The conjugate energy equations in conjunction with Arrhenius equation were solved numerically to predict the tissue irreversible damage embedded with LBV.