Objective
Time-temperature dependance of irreversible tissue damage during thermal treatments is often approximated by an Arrhenius first order kinetic model. This model requires only two parameters: the activation energy, ΔE, and the frequency factor, A. These parameters are determined experimentally. The Transition State Theory (TST) allows for similar rate calculations, but the material behavior is defined by two fundamental thermodynamic properties: the molar change in entropy, ΔS, and the molar change in enthalpy, ΔH. These parameters can be determined by measurement methods that are isolated from the thermal treatment protocol being modeled.

Methods
Differential Scanning Calorimetry (DSC) was used to determine the change in enthalpy in a tissue phase change corresponding to irreversible protein denaturation. This correlates ΔH with the heat flow into the system and the denaturation of proteins at critical temperatures. The heat capacity C_P, is calculated by dividing the molar enthalpy by the difference between the initial and final peak temperatures. ΔS is calculated by taking the natural log of the temperature difference and multiplying it by the heat capacity. Ten bovine liver samples were tested at each of four different heating rates (10° C to 50° C per minute) in order to determine the tissue variability and the heating rate dependence.

Results
The DSC values for ΔS and ΔH results are contrasted and compared with values of activation energy, ΔE, and frequency factor, A, that were determined using RF ablations created in ex vivo bovine liver.

Conclusions
The use of DSC to measure the thermodynamic properties of biological tissue allows one to employ damage rate equations based on TST. The advantage of using TST is parameter determination becomes a function of only target tissue, isolated from the other protocol parameters.