A Cole phantom for EIT.

A phantom was designed for testing and comparing multifrequency EIT data collection systems. The phantom simulates a cylinder of homogeneous conductor with 16 drive and 16 receive electrodes interleaved. Combinations of resistors and capacitors were used to simulate the complex impedance, Z*, of a typical tissue in the frequency range 8-2048 kHz obeying the Cole equation Z* = Z infinity + (Z0 - Z infinity)/[1 + (if/fc)(1- alpha )] where Z* is the complex impedance at frequency f, Z0 and Z infinity are the limiting values of impedance at low and high frequencies, fc is the characteristic frequency and alpha is a constant. A practical phantom was then constructed on which four different sets of spectroscopic parameters could be selected: (i) alpha = 0.20, fc = 150 kHz, Z0/Z infinity = 3.31; (ii) alpha = 0, fc = 273 kHz, Z0/Z infinity = 2.64; (iii) alpha = 0, fc = 71.1 kHz, Z0/Z infinity = 1.36; and (iv) Z0/Z infinity = 1.00 with no dispersion.