A multi-sensor array to measure anisotropic thermal conductivity of tissue

Recent advances in the theory of bioheat transfer suggest that perfused tissue might be modeled best by a thermally conductive solid with a perfusion-dependent conductivity. The blood perfusion is believed to enhance the conductivity anisotropically in the direction of thermally significant counter current blood vessels. Traditionally, heat transfer in tissue has been modeled as an isotropic heat sink. Due to the directional nature of recent theory, single point probes cannot adequately quantify the thermal characteristics of tissue. The theoretical analysis and hardware design of a multiple sensor probe that can be used to determine the coefficients of the thermal conductivity tensor are presented. The probe consists of an array of thermistors with the central thermistor acting as a heat source and the surrounding thermistors as temperature sensors. The system is computer-controlled and heating is done either in a pulse-decay mode or as a step input of power. Results of model calculations and of tests on a prototype are presented