Thermal method for measuring perfusion in transplanted organs

Adequate blood flow to the graft kidney is critical in the postoperative care of the transplant patient. Many factors can lead to disturbance in blood flow to the kidney, including the various effects of medication or volume status of the patient. Current methods to monitor blood flow depend on either duplex ultrasound or nuclear medicine renal flow scan. These modalities do not provide continuous monitoring of renal blood flow.; A non-invasive technique to the organ is developed that will allow for the continuous qualitative and quantitative monitoring of blood perfusion in a kidney during postoperative periods utilizing an easily extracted thermistor probe. The continuous assessment of blood perfusion in the kidney may allow timely therapeutic maneuvers to correct any abnormality in blood flow and prevent graft thrombosis and loss.; The technique involves the use of a thermistor heating/measurement system. Results of the measurements are used with numerical calculations to infer qualitative levels of perfusion.; A two-dimensional axisymmetric finite difference model for predicting regional blood perfusion is presented. The system consists of two semi-infinite bodies, the kidney and a specified adjacent medium, and a spherical thermistor. The thermistor is treated as a point source and located adjacent to both media. The initial temperature of the system is taken as the baseline temperature. At t = 0+, the temperature of the thermistor is increased by 0.5°C of the baseline temperature and a transient, constant temperature heating is imposed at the heat source surface. Heating is induced for a predetermined amount of time and terminated. The system is allowed to return to baseline temperatures and the process is repeated. The “bioheat equation” is used in the development of the governing equations for the system. Different perfusion situations within the two media are simulated to assess the sensitivity of the technique to a variety of possibilities that might be found in actual surgery. The method yields temperature field distributions along with a qualitative and quantitative measurement of regional blood perfusion. Results of the numerical model are then validated with analytical and experimental results.