A finite element solution to conjugated heat transfer in tissue using magnetic resonance angiography to measure the in vitro velocity field.
AuthorDutton, Andrew William.
Committee ChairRoemer, Robert
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PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractIn this research a combined numerical and experimental system for tissue heat transfer analysis was developed. The goal was to develop an integrated set of tools for studying the problem of providing accurate temperature estimation for use in hyperthermia treatment planning in a clinical environment. The completed system combines 1) Magnetic Resonance Angiography (MRA) to non-destructively measure the velocity field in situ, 2) the Streamwisc Upwind Petrov-Galerkin finite element solution to the 3D steady state convective energy equation (CEE), 3) a medical image based automatic 3D mesh generator, and 4) a Gaussian type estimator to determine unknown thermal model parameters such as thermal conductivity, blood perfusion, and blood velocities from measured temperature data. The system was capable of using any combination of three thermal models: 1) the Convective Energy Equation (CEE), 2) the Bioheat Transfer Equation (BHTE), and 3) the Effective Thermal Conductivity Equation (ETCE). Incorporation of the theoretically correct CEE was a significant theoretical advance over approximate models made possible by the use of MRA to directly measure the 3D velocity field in situ. Experiments were carried out in a perfused alcohol fixed canine liver with hyperthermia induced through scanned focussed ultrasound. Velocity fields were measured using Phase Contrast Angiography. The complete system was then used to 1) develop a 3D finite element model based upon user traced outlines over a series of MR images of the liver and 2) simulate temperatures at steady state using the CEE, BHTE, and ETCE thermal models in conjunction with the gauss estimator. Results of using the system on an in vitro liver preparation indicate the need for improved accuracy in the MRA scans and accurate spatial registration between the thermocouple junctions, the measured velocity field, and the scanned ultrasound power. No individual thermal model was able to meet the desired accuracy of 0.5 °C, the resolution desired for prognostic evaluation of a treatment. However the CEE model did produce the expected asymmetric results while the BHTE and ETCE, used in their simplest forms of homogenous properties, produced symmetric results. Experimental measurements tended to show marked asymmetries which suggests further development of the CEE thermal model to be the most promising.
Degree ProgramAerospace and Mechanical Engineering