QUANTIFICATION OF TISSUE PERFUSION BY SIMULTANEOUS MEASUREMENT OF INTRINSIC AND EFFECTIVE THERMAL CONDUCTIVITY

The purpose of this research is to develop a technique to quantify perfusion using sinusoidally heated thermistors. A limitation of previous thermal techniques applied to perfusion measurement has been the inability to distinguish conductive transport from thermal transport associated with perfusion. Previous techniques require that blood flow be interrupted to determine intrinsic thermal conductivity.; In this technique, two miniature thermistors are inserted into tissue. A combination of steady-state and sinusoidal thermal perturbations is applied to perfused tissue. Power is applied to one thermistor using a sinusoidal voltage source, and the other thermistor monitors surrounding tissue temperature. The power and measured temperature response are both characterized by an average value and a sinusoidal amplitude. The average values are indicative of total thermal transport. The sinusoidal signal components are primarily determined by intrinsic conductivity. The probe is calibrated empirically for temperature thermal conductivity, and perfusion measurements.; Instrumentation was developed using a floppy disk-based microcomputer system, including analog instrumentation, digital hardware, and data acquisition software.; A numerical model has been solved using a finite element method. Solutions were used to verify the dependence between measured parameters and thermal properties. The effect of heating the sensing thermistor by the heating thermistor was analyzed using analytical results obtained in the literature. A tradeoff was found between signal magnitude and the sensor's capability to cancel the effects of spatial temperature gradients. The accuracy of the thermal conductivity measurements has been evaluated using mixtures of glycerol and agar-gelled water. Average accuracy of the conductivity measurement is 2%.; An alcohol-fixed canine kidney perfusion model was used for testing this technique to allow careful control of temperature and perfusion. Perfused kidney experiments have been conducted to investigate the relationships between perfusion parameters, total flow and pressure, and thermal measurements, effective thermal conductivity and intrinsic thermal conductivity. The principal challenge has been the independent determination of perfusion in the measurement volume surrounding the heated thermistor. The approach taken has been to use an independent thermal washout technique, and a dye injection technique combined with total flow measurements. The average perfusion accuracy was 16% of full scale.