The application of SAM virtual sensor method for analysis of epileptic discharges: comparison with simultaneously recorded ECoG

Abstract The synthetic aperture magnetometry (SAM) enables to display the regional currentodensitogram (CDG) of the arbitrary selected brain tissue as if depth electrodes were inserted. The sensitivity and directivity of this SAM virtual sensor (SAM-VS) method were investigated. MEG and ECoG were simultaneously measured in a patient with refractory temporal seizure from cortical dysplasia. The regional currentodensitogram from SAM-VSs, which were placed three-dimensionally covering over the temporal lobe, were computed and compared with ECoG on the same time axis. The epileptic discharges detected simultaneously by both method accounted for 60% of those by SAM-VS method, and for 27% of those by ECoG method. Analyzing the coincident discharges detected by both methods, the spatial position difference between sensors disclosed maximum amplitude was less than several millimeters. Thus, high directivity of SAM-VS method, comparable to the subdural electrodes, was suggested. This new functional imaging might eliminate the need for invasive intracranial electrodes by disclosing abnormal functional process in epileptic brain noninvasively.