A comparison of two EIT systems suitable for imaging impedance changes in epilepsy.

Electrical impedance tomography (EIT) has the potential to produce functional images of the conductivity changes associated with epilepsy to help localization of epileptic foci. Scalp voltage changes associated with internal conductivity changes due to focal seizures have been shown at the limit of detectability for present EIT systems. The performances of two EIT systems, which may be employed in clinical recordings during presurgical assessment of intractable epilepsy, were compared. Those were the 32-channel serial UCH Mk2.5 and the 16-channel semi-parallel KHU Mk1. Images of three conductivity perturbations, simulating epileptic foci, in a head-shaped saline tank without and with a real human skull were recorded using 31-channel and 16-channel protocols with the UCH Mk2.5, while only 16-channel protocols with the KHU Mk1. The UCH Mk2.5 employing the 31-channel protocol had better overall performance with a localization error of 12.7% of the tank diameter, which would be sufficient for lateralization of the epileptic activity. More blurred images, but with similar localization, were obtained using 16 electrodes.