SELF HEATED THERMISTORS TO QUANTIFY TISSUE PERFUSION

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The objective of this research is to combine the numerical, analytic, experimental, and medical expertise of the three investigators in order to produce an improved diagnostic technique for measuring thermal conductivity, thermal diffusivity, and perfusion using miniature self-heated thermistor probes. The proposed research will have four major efforts. The first task will use finite element numerical analysis to optimize the thermistor probe design, and measurement protocol. The second task will be an exhaustive experimental error analysis using an isolated rat liver preparation. The third task will be the collection of an in vitro thermal property data base. The thermal conductivity and diffusivity of human biopsy, and autopsy tissue will be measured. The fourth task will be to implement a clinical version of the existing microcomputer based instrument. Institutional Review Board approval of this instrument, with surface thermistor probes, will be requested in order to conduct future clinical studies. A combination of steady state and sinusoidal thermal power is delivered to a spherical thermistor positioned invasively within a tissue or noninvasively on the surface of a tissue. The heat is carried away from the probe into the tissue by thermal conduction, and perfusion. The finite element method is used to numerically solve the heat transfer between the heated thermistor and the perfused tissue. The electrical power and the resulting temperature rise are measured by the microcomputer instrument. These measurements are used to calculate the effective thermal conductivity which represents both the conductive and convective components of bioheat transfer. Because tissue blood flow strongly affects local heat transfer, the instrument is quite sensitive to perfusion. The funding of this proposal will translate into a long lasting improvement in patient care.