Multi-Frequency Current Source for Varying Loads in Electrical Impedance Tomography Systems

摘要

A current source plays a vital role in electrical impedance tomography (EIT) systems. EIT is a 2D medical imaging technique that uses alternating current injection along a pair of electrodes and measuring the corresponding voltages across the remaining electrodes. Thus, it provides an information about the variation of the conductivity for a given system. A constant, sinusoidal current is usually required for EIT studies. An enhanced Howland current circuit is developed along with a compensator circuit to eliminate the effects of stray capacitances. Three operational amplifiers (IC AD8041, IC TL082, and IC μA741) were considered. The tests included current measurements at different frequencies and at different loads: without a compensator circuit and with a compensator circuit. Results show that IC TL082 op-amp delivers a stable current around 2.21 mA even without a compensator circuit in the frequency range from 1 kHz to 1 MHz for a load of up to 2 kΩ and hence could be suitable for EIT studies.