Abstract
Abstract Event-related synthetic aperture magnetometry (erSAM) is a beamforming approach that allows measurement of instantaneous, time-locked source activity. Using erSAM, MEG data can be transformed into three-dimensional functional images and source locations of epileptiform discharges can be estimated. Both erSAM and the equivalent current dipole model (ECD) were used to analyze interictal spikes in three children with intractable partial epilepsy. We acquired MEG data using a whole-head 151-channel system (VSM MedTech Ltd, Coquitlam, Canada). We visually identified MEG spikes and applied markers at the peak of each spike. erSAM images with a spatial sampling resolution of 2 mm were computed for the whole head utilizing three different parameters: a single time point corresponding to ECD best fit utilizing band pass filters of a) 3–70 Hz and b) 20–70 Hz and c) mean power over a 50 ms time window of + 25 to − 25 ms from the ECD best fit with band pass filter 20–70 Hz. All three methods of erSAM analysis yielded concordant source localization results with the ECD in all three patients. The mean difference in source locations between erSAM and ECD ranged from 0.01 to 1.3 cm. erSAM presents an alternative accurate approach for source localization of epileptiform discharges.
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