Usefulness of multiple frequency band source localizations in ictal MEG

•Source localization in the gamma band in a 10 s window before ictal onset showed the best concordance to the resection cavity among the tested frequencies and time windows.•A localization method using a 10 s time window does not require a subjective selection procedure; it would be both more convenient and more objective in a clinical setting.•Focal localization via a gamma band source predicts a seizure-free outcome, especially in patients with focal cortical dysplasia pathology.

ObjectiveWe evaluated the diagnostic value of multiple frequency band MEG source localization within a wide time window during the preictal period.MethodsData for 13 epilepsy patients who showed an ictal event during MEG were analyzed. Several seconds of preictal data were localized in the theta, alpha, beta, and gamma bands by using wavelet transformation and the sLORETA algorithm. The same analysis was performed with narrow time and frequency band. Localization concordances to the surgically resected area were compared.ResultsSource localization in the gamma band for a 10 s window before ictal onset showed best concordance to the resection cavity. Eight of 13 patients showed sub-lobar concordance in the 10 s gamma band localization, whereas 3 showed concordance in the narrow time and frequency analysis. Four of 7 patients with focal cortical dysplasia (FCD) achieved seizure-free outcome, and all 4 showed sub-lobar concordance.ConclusionsA 10 s time window gamma source localization method can be used to delineate the epileptogenic zone.SignificanceThe use of a long period during preictal gamma source localization has the potential to become a localizing biomarker of the epileptogenic zone in candidates for surgical intervention, especially in MRI-suspected FCD.