A porous medium approach to thermal analysis of focused ultrasound for treatment of thyroid nodules

Abstract

Focused ultrasound (FU) is a hyperthermia-induced method for the treatment of thyroid tumors. FU has the privilege of ablating the cancer tissue, while preserving the healthy tissue from undesired damage. Inaccuracies in the temperature evaluation reduces the treatment effectiveness; therefore, the present study through experimental and numerical analysis of FU presents a new approach to increase the accuracy of temperature estimation. Our study encompasses novelty by conducting a thermal analysis based on the porous structure of thyroid nodule. The thyroid tumor specimens are exposed to the ultrasound wave irradiation while the temperature elevation is accurately monitored and measured at the focal point. To numerically model the problem, the thyroid tumors are considered as porous media. The sample porosities are determined using Field Emission Scanning Electron Microscopy (FESEM) imaging system. The thermal properties are averaged over vascular and extravascular regions as the fluid and solid phases, respectively. It is observed that the focal point temperature can be predicted numerically with results being within 0.06% of those measured experimentally. The use of classical bio-heat transfer model, to predict the focal point temperature, has also been tested with results within 0.39% of the experimental data. The structural-based bio-heat transfer model is used to determine the extent of the necrotic area at different transducer powers. Results show that based on a porous medium approach, an irreversible necrosis does not occur at 5 W ultrasound power, while more than half of the thyroid tumor would be destructed when the power is increased to 10 W.