IMAGING OF CORTICAL SPREADING DEPRESSION OF EIT - IMPLICATIONS FOR LOCALIZATION OF ELIEPTIC FOCI

Severe epileptics may require curative neurosurgery. Sometimes focus l ocalization requires recording with electrodes inserted deep into the brain, which may cause death or permanent neurological damage. Since e pileptic seizures are associated with marked changes in cerebral imped ance, we propose that EIT With sub-dural electrodes (inserted between the brain and skull) could provide a superior and less dangerous metho d for the localization of epileptic foci. The purpose of these experim ents was to determine whether EIT could be used to localize the origin of seizure activity. In terms of impedance characteristics, an approp riate model is cortical spreading depression in the animal brain. Six rabbits were anaesthetized and paralysed and the brain exposed. Err im ages and DC potentials were recorded from an array of 16 electrodes on the brain during cortical spreading depression induced by DC stimulus . Cortical spreading depression could be localized by EIT with an accu racy of 8.7% +/- 6.4% (mean +/- SD) of electrode array diameter. The e rrors in localization appeared to be distributed randomly. In a phanto m of similar geometry, the error was 5% after correction for a systema tic component. Results are sufficiently encouraging that we intend to extend this study to human patients.