Simulations and experiments for tracking lethal temperature isotherm in single cryoprobe freezing process

Among the various minimally invasive treatments, cryosurgery has been considered a potential methodology to treat solid cancerous tumors. The treatment involves using cryogenic temperatures to decrease the temperature of cancer tissues in order to destroy them. Low-pressure liquid nitrogen cooled cryoprobes have been employed to bring the temperature of tumor tissues below the lethal temperature (223 K). Experiments were performed with a liquid nitrogen cooled cryoprobe inserted in the biogel medium to simulate a single-cryoprobe freezing situation. The transient evolution of the freezing front was tracked using field-intensity maps obtained through processing the digital holograms. The longitudinal temperature along the cryoprobe tip was measured using three thermocouples. The recorded temperatures were used in the numerical simulations as a forcing function to simulate the freezing process. The freezing front (273 K) tracked using numerical simulations was observed to agree well with intensity-based experimental data. Upon realizing the accuracy of the numerical simulation, the transient temperature distribution was used to track the clinically significant lethal temperature isotherm and the region engulfed in it. Further, the experiments were repeated for higher operating pressures, viz., 3, 3.5, and 4 atm, and the effect of operating pressure on the advancement of lethal temperature isotherm is investigated. It was concluded that the cooldown time was reduced by 2 to 3 times with higher tank operating pressure. The investigation pertaining to the advancement of lethal temperature isotherm could assist the clinician in deciding the optimum operating pressure and operation time, thus increasing the efficacy of cryosurgical planning. (author)