Abstract
Ex vivo animal tissues (e.g., bovine liver) as well as water-agar gel are commonly used to simulate both experimentally and numerically the response of human tissues to cryoablation treatments. Data on the low temperature thermal properties of bovine liver are difficult to find in the literature and very often are not provided for the whole temperature range of interest. This article presents the thermal conductivity and thermal diffusivity measurements performed on ex-vivo bovine liver samples using the transient plane source method. Regression coefficients are provided to determine these properties in different temperature ranges except for the phase transition during which no results were obtained, which suggests an ad hoc calorimetric analysis. A quick procedure is also suggested to determine the water mass fraction in the tissue. Moreover, an attempt to estimate the liver density in the frozen state using measurements performed solely at room temperature is also presented. The measured thermal conductivity and thermal diffusivity values are compared with data reported in literature highlighting a spread up to 40%. Moreover, it emerges that water-agar gel usually made with 2% by weight of agar does not show the same thermal properties as the bovine liver.
Highlights
The use of cryosurgery has gained importance in the past for the treatment of malignant tumors, [1,2,3,4] for example, and more recently for treating atrial fibrillation by catheter ablation, [5,6,7,8] for example, some controversial aspects about the cooling/heating dynamics are not yet fully understood
The measured thermal conductivity and thermal diffusivity values are compared with data reported in literature highlighting a spread up to 40%
In addition to compare the experimental results obtained for the ex-vivo bovine liver and the water-agar gel, the paper aims to define a suitable experimental procedure to investigate the thermophysical properties of a massive biological material, including water content and density, over a wide temperature range
Summary
The use of cryosurgery has gained importance in the past for the treatment of malignant tumors, [1,2,3,4] for example, and more recently for treating atrial fibrillation by catheter ablation, [5,6,7,8] for example, some controversial aspects about the cooling/heating dynamics are not yet fully understood. In clinical applications of cryosurgery for the treatment of atrial fibrillation by catheter ablation, the cooling rate is typically high, close to 120 K/min [6], and the optimal ablation temperature required for long-term success is lower than −50 ◦ C [6,16] In these contexts, the knowledge of the heat diffusion properties of the frozen tissue becomes important to evaluate the thermal field inside it and to properly set the duration of the procedure to avoid collateral damage. Since in a previous work the authors presented the temperature dependence of the properties for water-agar gel (2% agar) [24], it is essential to understand whether this material really mimics the thermal behavior of an ex-vivo biological tissue in the temperature range of interest With this aim, it was decided to investigate the ex-vivo bovine liver, assuming that it is the tissue whose morphology and internal structure are best reproduced by the water-agar gel. In addition to compare the experimental results obtained for the ex-vivo bovine liver and the water-agar gel, the paper aims to define a suitable experimental procedure to investigate the thermophysical properties of a massive biological material, including water content and density, over a wide temperature range
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