Temperature Dependence of Thermal Properties of Ex Vivo Porcine Heart and Lung in Hyperthermia and Ablative Temperature Ranges

Abstract

This work proposes the characterization of the temperature dependence of the thermal properties of heart and lung tissues from room temperature up to > 90 °C. The thermal diffusivity (α), thermal conductivity (k), and volumetric heat capacity (Cv) of ex vivo porcine hearts and deflated lungs were measured with a dual-needle sensor technique. α and k associated with heart tissue remained almost constant until ~ 70 and ~ 80 °C, accordingly. Above ~ 80 °C, a more substantial variation in these thermal properties was registered: at 94 °C, α and k respectively experienced a 2.3- and 1.5- fold increase compared to their nominal values, showing average values of 0.346 mm2/s and 0.828 W/(m·K), accordingly. Conversely, Cv was almost constant until 55 °C and decreased afterward (e.g., Cv = 2.42 MJ/(m3·K) at 94 °C). Concerning the lung tissue, both its α and k were characterized by an exponential increase with temperature, showing a marked increment at supraphysiological and ablative temperatures (at 91 °C, α and k were equal to 2.120 mm2/s and 2.721 W/(m·K), respectively, i.e., 13.7- and 13.1-fold higher compared to their baseline values). Regression analysis was performed to attain the best-fit curves interpolating the measured data, thus providing models of the temperature dependence of the investigated properties. These models can be useful for increasing the accuracy of simulation-based preplanning frameworks of interventional thermal procedures, and the realization of tissue-mimicking materials.

Measurement of Thermal Conductivity and Thermal Diffusivity of Porcine and Bovine Kidney Tissues at Supraphysiological Temperatures up to 93 °C

“…The measurement of thermal properties was performed in steady-state conditions in a temperature-monitored environment by means of the transfer hot-wire technique employing a dual-needle probe. The measurement accuracy of the system was validated by our research group in previous studies [12,33,39], and its accurate reading capability has also been assessed in the present work by testing the measurement instrument on a polymeric standard material. The quantitative values of the measured thermal properties of biological tissues are presented, along with the estimation of the measurement uncertainty, the best-fit regression models interpolating the experimental data, and the analysis of the residual values.…”

“…s), and E i (−x) is the exponential integral, approximated using polynomials: in particular, for small arguments, it is approximated as the sum between the Euler-Mascheroni constant (γ ≈ 0.5772) and the natural logarithm of the argument, ln(x) [33,37,59].…”

“…Considering the high thermal gradients and temperature excursions to which the tissue may be exposed during thermal therapies [ 32 ], the temperature dependence of the thermal properties of biological tissue must be assessed in a wide thermal interval, ranging from nominal up to supraphysiological (i.e., hyperthermic and ablative) temperatures [ 9 , 12 , 21 , 33 ]. Different techniques have been adopted to characterize the thermal properties of biological media as a function of tissue temperature.…”

“…Self-heated thermistor probes have been utilized to measure the k and α of various human and animal tissues and assess their temperature dependence [ 34 , 35 , 36 ]. Moreover, in more recent years, the dual-needle technique based on the transient hot-wire method has been employed for the estimation of the thermal properties of porcine, bovine and ovine liver; muscle; porcine brain; pancreas; lung and heart [ 7 , 12 , 33 , 37 , 38 , 39 ].…”

Development of non-invasive flexible directional microwave ablation for central lung cancer: a simulation study

“…The tissue can be heated by both absorption of the microwave energy and thermal conduction according to the tissue properties, resulting in local tissue necrosis (i.e. an ablation zone) (Bianchi et al 2023, Farina et al 2023, Vidjak et al 2023.…”