Abstract
ObjectiveKurtosis beamforming is a useful technique for analysing magnetoencephalograpy (MEG) data containing epileptic spikes. However, the implementation varies and few studies measure concordance with subsequently resected areas. We evaluated kurtosis beamforming as a means of localizing spikes in drug-resistant epilepsy patients. MethodsWe retrospectively applied kurtosis beamforming to MEG recordings of 22 epilepsy patients that had previously been analysed using equivalent current dipole (ECD) fitting. Virtual electrodes were placed in the kurtosis volumetric peaks and visually inspected to select a candidate source. The candidate sources were compared to the ECD localizations and resection areas. ResultsThe kurtosis beamformer produced interpretable localizations in 18/22 patients, of which the candidate source coincided with the resection lobe in 9/13 seizure-free patients and in 3/5 patients with persistent seizures. The sublobar accuracy of the kurtosis beamformer with respect to the resection zone was higher than ECD (56% and 50%, respectively), however, ECD resulted in a higher lobar accuracy (75%, 67%). ConclusionsKurtosis beamforming may provide additional value when spikes are not clearly discernible on the sensors and support ECD localizations when dipoles are scattered. SignificanceKurtosis beamforming should be integrated with existing clinical protocols to assist in localizing the epileptogenic zone.
Highlights
The aim of epilepsy surgery is to remove the epileptogenic zone (EZ), i.e. the region whose removal ensures postoperative seizure freedom (Engel, 1996, Lüders et al, 2006)
For the seizure-free patients, in whom the resection cavity corresponds to the epileptogenic zone, the kurtosis beamformer overlapped with the resection cavity in 9/13 patients (69%) (6 direct overlap and 3 partial overlap)
Our results show that kurtosis beamforming performs comparably to equivalent current dipole (ECD) but with fewer subjective steps and without the need of a priori information to guide the analysis
Summary
The aim of epilepsy surgery is to remove the epileptogenic zone (EZ), i.e. the region whose removal ensures postoperative seizure freedom (Engel, 1996, Lüders et al , 2006). The underlying hypothesis is that regions containing spikes will have increased kurtosis values relative to regions with normal brain activity. Studies evaluating this method have demonstrated a good level of concordance with other inverse models (Kirsch et al, 2006; de Gooijer-van de Groep et al, 2013) and seizure onset zones identified by iEEG (de Gooijer-van de Groep et al, 2013; Rose et al , 2013)
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