Probing deep tissues with laser-induced thermotherapy using near-infrared light

Abstract

Optically tunable gold nanoparticles have been widely used in research with near-infrared light as a means to enhance laser-induced thermal therapy since it capitalises on nanoparticles' plasmonic heating properties. There have been published several studies on numerical models replicating this therapy in such conditions. However, there are several limitations on some of the models which can render the model unfaithful to therapy simulations. In this paper, two techniques of simulating laser induced thermal therapy with a high absorbing localised region of interest inside a phantom are compared. To validate these models we conducted an experiment of an agar-agar phantom with an inclusion reproducing it with both models. The phantom was optically characterized by absorption and total attenuation. The first model is based on the macro perspective solution of the radiative transfer equation given by the diffusion equation, which is then coupled with the Pennes bioheat equation to obtain temperature. The second is a Monte Carlo model that considers a stochastic solution of the same equation and is also considered as input to the Pennes bioheat transfer equation which is then computed. The Monte Carlo is in good agreement with the experimental data having an average percentage difference of 4.5% and a correlation factor of 0.98, while the diffusion method comparison with experimental data is 61% and 0.95 respectively. The optical characterisation of the phantom and its inclusion were also validated indirectly since the Monte Carlo, which used those parameters, was also validated. While knowing the temperature in all points inside a body during photothermal therapy is important, one has to be mindful of the model which fit the conditions and properties. There are several reasons to justify the discrepancy of the diffusion method: low scattering conditions, absorption and reduced scattering are comparable. The error bars that are normally associated when characterizing an optical phantom can justify also a part of that uncertainty. For low size tumours in depth, one may have to increase the light dosage in photothermal therapies to have a more effective treatment.

Evaluation of Three Iterative Algorithms for Phase Modulation Regarding Their Application in Concentrating Light Inside Biological Tissues for Laser Induced Photothermal Therapy

“…In order to better target the tumor cells and protect the healthy surrounding cells, gold nanoparticles (GNP) have been studied [6,7]. These GNP are functionalized so they aggregate around tumors, and they have "tunable high-absorption properties in the NIR region that allow for local higher absorbed energy" [8]. This allows for them to be photo-induced in a determined wavelength to produce heat (through an effect called Surface Plasmon Resonance, SPR [9]) consequently leading to cytotoxic damage of the surrounding cells.…”