Patient-specific spectrum power determination for source localization of ictal MEG

Magnetoencephalography (MEG) has been shown to be a useful diagnostic tool for presurgical evaluation of pediatric medically intractable partial epilepsy. MEG source localization has been shown to improve the likelihood of seizure onset zone (SOZ) sampling during subsequent evaluation with intracranial EEG (ICEEG). We investigated whether frequency-dependent ictal MEG onset source localization further improves results of interictal MEG in defining the SOZ. Source localization analyses were applied using multiple algorithms, both at the beginning of ictal onset and for interictal MEG discharges. Ictal MEG onsets were identified by visual inspection and power spectrum using short-time Fourier transform (STFT). Source localizations were compared with ICEEG, surgical procedure and outcome. Eight patients were included in this study. Five of the 8 patients (63%) had concordant ictal MEG onset source localization and interictal MEG discharge source localizations in the same lobe, but the source of ictal MEG onset was closer to the SOZ defined by ICEEG. The source localization for the earliest ictal MEG onset with patient-specific frequency change proved to be a useful tool for presurgical evaluation in our pediatric population with medically intractable epilepsy.