A phantom for assessing the performance of EIT systems

This paper describes a phantom built from 340 precision resistors on a printed circuit board (PCB) representing a circular homogeneous medium. Compared to other phantoms in the literature, this phantom generates very realistic signals while preserving the ability to produce localized perturbations for testing the imaging capabilities of an EIT system. Equivalent electrical models of the Ag/AgCl electrode impedances were integrated to the phantom. Parameters of the electrode models were fitted from impedance curves measured with an impedance analyzer. The technique used to build this phantom is general and applicable to phantoms of arbitrary shape and conductivity distribution. Assessing the performance of EIT systems usually requires a phantom for validation, calibration or comparison purposes. We describe some tests that can be performed with our phantom to measure signal-to-noise ratio, accuracy and modelling accuracy for every measurement of an EIT data frame. These tests were performed on four EIT systems: two of our own systems and two others that were made available to us. The performance of EIT systems is a function of frame rate, operating frequency, applied current intensity, measurement strategies and inter-modulation distortion when performing simultaneous measurements at several frequencies.