Ictal MEG onset source localization compared to intracranial EEG and outcome: Improved epilepsy presurgical evaluation in pediatrics

Abstract

Summary Purpose Magnetoencephalography (MEG) has been shown a useful diagnostic tool for presurgical evaluation of pediatric medically intractable partial epilepsy as 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 ictal MEG onset source localization further improves results of interictal MEG in defining the SOZ. Methods We identified 20 pediatric patients with one habitual seizure during MEG recordings between October 2007 and April 2011. MEG was recorded with sampling rates of 600 Hz and 4000 Hz for 10 and 2 minutes respectively. Continuous head localization (CHL) was applied. 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. Key findings Eight patients met all inclusion criteria. 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. Significance Although the capture of seizures during MEG recording is challenging, the source localization for ictal MEG onset proved to be a useful tool for presurgical evaluation in our pediatric population with medically intractable epilepsy.

Magnetoencephalographic imaging of ictal high‐frequency oscillations (80‐200 Hz) in pharmacologically resistant focal epilepsy

“…However, recording and analysis of ictal MEG pose a significant challenge. 9 The present study recorded 67 seizures in 67 (9.7%) of 691 patients who were referred for MEG evaluation, but only 20 seizures in 20 (2.9%) of the 691 patients could be analyzed. There is very little literature that has studied HFOs during seizure activity.…”

“…34 Due to the low signal-to-noise ratio (SNR) of ictal rhythms, weak localization accuracy was reported in previous ictal MEG studies with ECD models. 9,35 Time-frequency analysis and source reconstruction with a spatial filter and current-density estimates are more accurate than ECD due to the advantage of analysis of a wide window rather than a single time point. However, previous studies had used either a manual selection of a particular period distinct from the BGA 36 or a wide time window.…”

“…None of the studies had evaluated ictal the MEG record for high-frequency oscillations (HFOs). Most of the studies 5,8,9 reported ictal localization using single equivalent current dipole (ECD) models, and few studies also reported poor localization in the ictal MEG record. 9 HFOs (80-200 Hz) are being recognized as EEG biomarkers for epileptogenicity.…”

“…Most of the studies 5,8,9 reported ictal localization using single equivalent current dipole (ECD) models, and few studies also reported poor localization in the ictal MEG record. 9 HFOs (80-200 Hz) are being recognized as EEG biomarkers for epileptogenicity. 10 The HFOs that happen during seizure onset can determine the EZ, which is useful for epilepsy surgery.…”

Multimodal investigation of epileptic networks

“…Owing to the relatively simpler physics of neural magnetic fields propagation, MEG is sensitive to smaller activated brain regions (4 cm 2 for MEG, Mikuni et al, 1997, 10 cm 2 for EEG, Grova et al, 2006). Source localization with DSM showed promising results for the presurgical workup of epilepsy, which led some authors to suggest that it could obviate icEEG investigations in some cases (Fujiwara et al, 2012).…”