Volumetric localization of epileptic activity using wavelet-based synthetic aperture magnetometry

To go beyond using magnetoencephalography (MEG) for visual identification of epileptic spikes, this study was to quantitatively estimate epileptic spectral power and volumetrically localize the neuromagnetic activity associated with epilepsy. MEG data were recorded from 16 patients with epilepsy using a whole-cortex MEG system. Focal increases of spectral power were identified using wavelet; the three-dimensional neuromagnetic distributions of the focal increases of spectral power were estimated using synthetic aperture magnetometry (SAM). SAM images and dipoles pointed to a same area in 12 patients (75% 12/16), SAM revealed focal epileptic activity but dipole modelling failed in 2 patients (12.5%, 2/16), and SAM detected more epileptic foci than dipole modelling did in 2 patients (12.5%, 2/16). Interestingly, spectrogram revealed focal increases of spectral power just before magnetic spikes; and SAM peaks were close to the dipoles of the initial portion of the spikes. The results suggest that wavelet-based SAM analysis has the potential to localize the onset of epileptic seizures, and seems superior to dipole modelling for estimation of multiple epileptic foci. In comparison to the conventional visual identification of spike, wavelet-based SAM analysis is objective and quantitative. Thus, wavelet-based SAM analysis has the potential to be extremely useful for clinical management of epilepsy.