The effect of argon gas pressure on ice ball size and rate of formation.

ABSTRACT

INTRODUCTION: Contemporary cryoablation technology utilizes the Joule-Thomson effect, defined as a change in temperature that results from expansion of a nonideal gas through an orifice or other restriction. We evaluated the effect of initial gas tank pressures on freezing dynamics in a single-probe model and in a multiprobe model using contemporary cryoablation technology. MATERIALS AND METHODS: Cryoablation trials were performed in a standardized system of transparent gelatin molds at 25°C. Two sets of trials were performed. The first trial evaluated temperature and ice ball size for a given tank pressure when a single needle was deployed. The second trial recorded ice ball temperatures for each probe when multiple probes were fired simultaneously. RESULTS: Trial 1 The rate of temperature change is directly related to the initial pressure of the gas being released, and the group with the highest starting pressures reached the lowest mean temperature and had the largest mean ice ball size (p < 0.01). Trail 2 Multiple-probe ablation did not affect the rate of temperature change or final temperature compared with firing a single probe (p > 0.7). CONCLUSIONS: In accordance with the Joule-Thomson effect, higher initial gas pressures used for cryoablation in a transparent gel model demonstrate statistically significant lower temperatures, faster decreases in temperature, and formation of larger ice balls than lower gas pressures do. With contemporary technology, multiple simultaneous cryoprobe deployment does not compromise individual probe efficacy. The use of higher initial tank pressures will theoretically help future cryoprobes be more effective, creating a greater volume of cell necrosis and a smaller indeterminate zone.