EXPERIMENTAL EVALUATION OF 2 SIMPLE THERMAL MODELS USING HYPERTHERMIAIN MUSCLE IN-VIVO

The predictions from two simple field equation models for calculating temperature distributions in tissue, namely, the Pennes' bioheat trans fer equation (BHTE) and an effective thermal conductivity equation (ET CE), were compared to in vivo experimental temperature measurements ma de under hyperthermic conditions generated by scanned focused ultrasou nd. The models were kept simple (i.e. homogenous isotropic properties, no separate blood vessels included) in order to concentrate attention on the predictive abilities of these field equations using a minimum number of free parameters. Simulated results were fitted to the experi mental data (multiple, linear temperature profiles in the thigh muscle s of greyhound dogs) by minimizing a performance index using a golden section searth. This search determined a value for the single free par ameter in each model (blood perfusion in the BHTE, and effective therm al conductivity in the ETCE) which minimized the square error differen ce between the experimental and simulated temperatures. The results sh owed that (a) the simple BHTE model could qualitatively reproduce the major features of the temperature patterns seen experimentally better than the ETCE model could, and (b) the simple BHTE model produced bett er quantitative fits to the experimental data than did the simple ETCE model. In addition, blood perfusion predictions from the BHTE model c ompared well to measurements done with coloured microspheres. Finally, the experimental results showed that individual, large blood vessels appeared to have a major influence in producing asymmetries in the exp erimental data in 21 % of the measured temperature profiles.