EXPERIMENTAL EVALUATION OF 2 SIMPLE THERMAL MODELS USING TRANSIENT TEMPERATURE ANALYSIS

Thermal models are used to predict temperature distributions of heated tissues during thermal therapies. Recent interest in short duration h igh temperature therapeutic procedures necessitates the accurate model ling of transient temperature profiles in heated tissues. Blood flow p lays an important role in tissue heat transfer and the resultant tempe rature distribution. This work examines the transient predictions of t wo simple mathematical models of heat transfer by blood flow (the bioh eat transfer equation model and the effective thermal conductivity equ ation model) and compares their predictions to measured transient temp erature data. Large differences between the two models are predicted i n the tissue temperature distribution as a function of blood flow for a short heat pulse. In the experiments a hot water needle, similar to 30 degrees C above ambient, delivered a 20 s heating pulse to an excis ed fixed porcine kidney that was used as a Bow model. Temperature prof iles of a thermocouple that primarily traversed the kidney cortex were examined. Kidney locations with large vessels were avoided in the tem perature profile analysis by examination of the vessel geometry using high resolution computed tomography angiography and the detection of t he characteristic large vessel localized cooling or heating patterns i n steady-state temperature profiles. It was found that for regions wit hout large vessels, predictions of the Pennes bioheat transfer equatio n were in much better agreement with the experimental data when compar ed to predictions of the scalar effective thermal conductivity equatio n model. For example, at a location r similar to 2 mm away from the so urce, the measured delay time was 10.6 +/- 0.5 s compared to predictio ns of 9.4 s and 5.4 s of the BHTE and ETCE models, respectively. Howev er, for the majority of measured locations, localized cooling and heat ing effects were detected close to large vessels when the kidney was p erfused. Finally, it is shown that increasing Bow in regions without l arge vessels minimally perturbs temperature profiles for short exposur e times; regions with large vessels still have a significant effect.