Measurement of Ex Vivo Liver, Brain and Pancreas Thermal Properties as Function of Temperature

Abstract

The ability to predict heat transfer during hyperthermal and ablative techniques for cancer treatment relies on understanding the thermal properties of biological tissue. In this work, the thermal properties of ex vivo liver, pancreas and brain tissues are reported as a function of temperature. The thermal diffusivity, thermal conductivity and volumetric heat capacity of these tissues were measured in the temperature range from 22 to around 97 °C. Concerning the pancreas, a phase change occurred around 45 °C; therefore, its thermal properties were investigated only until this temperature. Results indicate that the thermal properties of the liver and brain have a non-linear relationship with temperature in the investigated range. In these tissues, the thermal properties were almost constant until 60 to 70 °C and then gradually changed until 92 °C. In particular, the thermal conductivity increased by 100% for the brain and 60% for the liver up to 92 °C, while thermal diffusivity increased by 90% and 40%, respectively. However, the heat capacity did not significantly change in this temperature range. The thermal conductivity and thermal diffusivity were dramatically increased from 92 to 97 °C, which seems to be due to water vaporization and state transition in the tissues. Moreover, the measurement uncertainty, determined at each temperature, increased after 92 °C. In the temperature range of 22 to 45 °C, the thermal properties of pancreatic tissue did not change significantly, in accordance with the results for the brain and liver. For the three tissues, the best fit curves are provided with regression analysis based on measured data to predict the tissue thermal behavior. These curves describe the temperature dependency of tissue thermal properties in a temperature range relevant for hyperthermia and ablation treatments and may help in constructing more accurate models of bioheat transfer for optimization and pre-planning of thermal procedures.

Fat Quantification Imaging and Biophysical Modeling for Patient-Specific Forecasting of Microwave Ablation Therapy

“…Literature values for thermal conductivity in healthy liver tissue range from 0.48-0.543 [W/(m•K)] (Valvano et al, 1985;Guntur et al, 2013;Kujawska et al, 2014;Mohammadi et al, 2021). Papers before 2005 reference thermal conductivity at approximately 0.48 [W/(m•K)], but these estimations were derived from tissue experiments at room temperature (25 • C) (Valvano et al, 1985).…”

“…Papers before 2005 reference thermal conductivity at approximately 0.48 [W/(m•K)], but these estimations were derived from tissue experiments at room temperature (25 • C) (Valvano et al, 1985). A study from Mohammadi et al (2021) describes thermal conductivity of ex vivo porcine liver as a function of temperature where the thermal conductivity was as high as 0.537 ± 0.009 [W/(m•K)] at body temperature (37 • C). Another study by Guntur et al (2013) calculated the thermal conductivity of ex vivo porcine liver at 37 • C to be approximately 0.520 [W/(m•K)].…”

Assessment and Modeling of Plasmonic Photothermal Therapy Delivered via a Fiberoptic Microneedle Device Ex Vivo

“…Moreover, the literature review revealed a gap in C p value (specific heat at constant pressure) for the porcine pancreas tissue. The specific heat for the porcine pancreas tissue at constant volume (C v ) was reported in recent literature [52] and used in this study with the assumption that, at low temperatures (22 • C), the difference between C p and C v was negligible. To assess the sensitivity of the model to this parameter, additional simulations were conducted using the C p value reported for the human pancreas by Agafonkina et al [53].…”

“…Here, h conv (5 Wm −2 •K −1 ) is the convection heat transfer coefficient, and T ∞ (295.15 K) is the ambient temperature. Furthermore, porcine pancreas tissue properties were obtained from both literature (e.g., ρ = 1040 kg•m −3 and C p = 3630 J•kg −1 •K −1 ) [39,52] and our team's previous work on characterization of tissue thermal and optical properties (e.g., k = 0.45 Wm −1 •K −1 , µ a , µ s , and R (detailed optical properties are shown in Table S1 of Supplementary Materials)) [40]. After setting up the equations and boundary conditions, two temperature probes were placed at 3 and 6 mm below the tissue's top surface and 2 mm away from the beam path to mimic the experimental setup described in Section 2.2 (Figure 4).…”

Recent Advances in Biomedical Photonic Sensors: A Focus on Optical-Fibre-Based Sensing

“…Finally, the strategy enabled the laser-induced temperature increase to be confined with higher accuracy in areas where sensors were located in the beam propagation direction [42]. In the context of laser ablation application, a different study reported the thermal properties of some ex vivo tissues (liver, brain, and pancreas) as a function of temperature [43]. Monitoring of respiratory rate is critical for the clinical care of patients, especially after surgery.…”