A feasibility study for imaging of epileptic seizures by EIT using a realistic FEM of the head 12th Conf. on Biomedical Application of EIT (Seoul, Korea)

Electrical Impedance Tomography could be used to image the source of epileptic seizures, by measuring voltages on the scalp due to internal brain conductivity changes. The purpose of this study was to model the magnitude of the boundary voltage changes resulting from focal seizures at 7 frequencies from 5 Hz-4MHz, using a realistic 3D finite element model of the human head and 31 scalp electrodes. The conductivity change was simulated as decrease of 3 – 16% for seizures in the right hippocampus (2.5 cm3), right parahippocampal structures (6 cm3) and right temporal lobe (18 cm3). Estimates of the boundary voltage changes were made for 100µA at all frequencies or increasing by 100µA*f(kHz) above 1 kHz as in IEC601-1 safety regulations. The highest 1% percent of the boundary voltage changes for lateral temporal lobe perturbation were at 5–50 Hz - 0.8% (1.5µV) and 0.6% (0.5µV) for real and imaginary part respectively. Using higher currents for f>1kHz the largest changes were at 50 kHz - 0.97% (21µV) and 1.4% (20µV). Peak changes for the smaller and deeper seizures were up to 10x smaller. These changes are of the order of the noise in EIT measurements so work is in progress to attempt to diminish the electronic and physiological noise to below this level.