Use of Temperature as a Contrast Agent in Electrical Impedance Tomography

Abstract

Electrical Impedance Tomography (EIT) images conductivity changes within a body from electrical measurements at the body surface. There is significant interest in using EIT to measure cardiovascular parameters, such as blood perfusion. Currently, a hypertonic bolus of saline is injected into a central vein, producing an increase in conductivity which is visualized. Unfortunately, hypertonic saline has undesirable effects in large doses, and cannot be used for continuous monitoring. We propose the use of temperature contrasting isotonic saline as a new contrast agent for EIT, suitable for repeated measurements. The experiments were carried out on a cylindrical tank filled with a saline solution having a conductivity of 1 S/m and the temperature of 22.6 ◦C. A 280 ml saline bolus with the conductivity of 1 S/m and temperature difference ∆t was injected at the tank center. We selected 5 different temperatures for the bolus. Subsequent EIT image analysis demon- strated that the temperature contrast can be successfully reconstructed. A quantitative analy- sis revealed that reconstructed impedance values were correlating linearly with temperature. Our initial results show the suitability of EIT for real- time noninvasive temperature contrast imaging.