A constant-perturbation saline phantom for electrical impedance tomography

In a phantom for electrical impedence tomography it is important to be able to change the electrical conductivity by a known factor, over a well defined region, to allow measurements of sensitivity and resolution. Saline phantoms have a number of advantages but it is difficult to introduce conductivity changes accurately. A device has been constructed which, when immersed in a saline phantom, causes an apparent change in conductivity by a factor which is very insensitive to the conductivity of the saline solution. The device is based on the theory of mixtures and consists of an array of beads suspended by nylon threads. Conducting and insulating beads were used to cause positive and negative perturbations in log conductivity: 0.17 and -0.09 in this study. The upper limits of the changes in these perturbations were only 6% and 14% over a factor of 56 in saline conductivity.