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

Abstract

SummaryObjective: Specificity of ictal high-frequency oscillations (HFOs) in identifying epileptogenic abnormality is significant, compared to the spikes and interictal HFOs. The objectives of the study were to detect and to localize ictal HFOs by magnetoencephalography (MEG) for identifying the seizure onset zone (SOZ), evaluate the cortical excitability from preictal to ictal transition, and establish HFO concordance rates with other modalities and postsurgical resection. Methods: Sixty-seven patients with drug-resistant epilepsy had at least 1 spontaneous seizure each during MEG acquisition, and analysis was carried out on 20 seizures from 20 patients. Ictal MEG data were bandpass filtered (80-200 Hz) to visualize, review, and analyze the HFOs co-occurring with ictal spikes. Source montages were generated on both hemispheres, mean fast Fourier transform was computed on virtual time series for determining the preictal to ictal spectral power transition, and source reconstruction was performed with sLORETA and beamformers. The concordance rates of ictal MEG HFOs (SOZ) was estimated with 4 reference epileptogenic regions. Results: In each subject, transient bursts of high-frequency oscillatory cycles, distinct from the background activity, were observed in the periictal continuum.Time-frequency analysis showed significant spectral power surge (85-160 Hz) during ictal state (P < .05) compared to preictal state, but there was no variation in the peak HFO frequencies (P > .05) for each subgroup and at each source montage. HFO source localization was consistent between algorithms (k = 0.857 AE 0.138), with presumed epileptogenic zone (EZ) comparable to other modalities. In patients who underwent surgery (n = 6), MEG HFO SOZ was concordant with the presumed EZ and the surgical resection site (100%), and all were seizure-free during follow-up. Significance: HFOs could be detected in the MEG periictal state, and its sources were accurately localized. During preictal to ictal transition, HFOs exhibited

Localization of the Epileptogenic Zone Using High Frequency Oscillations

“…Using MSI, Miao et al (167) showed that ictal HFOs were spatially more refined than spikes and reliably localized a propagative pattern during absence seizures in childhood absence epilepsy (167, 168). Velmurugan et al (175) just recently demonstrated the benefit of MSI in a large sample of patients with drug-resistant focal epilepsy. They were able to localize the EZ using ictal HFOs concordantly with other modalities; surgery of this identified zone performed in six patients led to seizure freedom in all of these six patients.…”

Kurtosis and skewness of high-frequency brain signals are altered in paediatric epilepsy

“…Advances in magnetoencephalography (MEG) ( Migliorelli et al , 2017 ; Velmurugan et al , 2018 ; van Klink et al , 2019 ) and scalp EEG ( Kobayashi et al , 2010 ; Kramer et al , 2019 ) open a new window for the study of HFBS. The non-invasive nature of MEG and EEG enable the study of HFBS in both healthy subjects and patients ( Xiang et al , 2009 b ; Xiang et al , 2010 ; Tamilia et al , 2017 ).…”

“…Normative data may clarify the spatial variation of HFBS in the brain. For example, MEG and EEG methods, such as virtual electrodes (VE, or virtual sensors), can be used to assess brain activities at various brain areas ( Oishi et al , 2006 ; Velmurugan et al , 2018 ; van Klink et al , 2019 ). It has been shown that brain activities can be registered on to template MRI in common space, which can address the spatial variation and enable the direct comparison between patients and healthy subjects ( Douw et al , 2018 ).…”

Nonictal EEG biomarkers for diagnosis and treatment

“…Several studies have now reported the ability to record activity in the HFO frequency range from scalp electrodes, but it is unclear whether these events are the same as those recorded directly from the brain. Others have reported the ability to record HFOs with magnetoencephalography (MEG) . It is conceivable that interictal spikes associated with pHFOs will have a metabolic profile on functional magnetic resonance imaging (fMRI) that distinguishes them from interictal spikes without pHFOs, and some data are accumulating suggesting that fMRI may help to identify pHFOs noninvasively .…”

“…Others have reported the ability to record HFOs with magnetoencephalography (MEG). 31,32 It is conceivable that interictal spikes associated with pHFOs will have a metabolic profile on functional magnetic resonance imaging (fMRI) that distinguishes them from interictal spikes without pHFOs, and some data are accumulating suggesting that fMRI may help to identify pHFOs noninvasively. 33 Although we are close to accepting that pHFOs, recorded during chronic invasive monitoring, and intraoperatively, delineate the epileptogenic region for surgery, the clinical application of these EEG events for seizure diagnosis, treatment, and prediction, in the routine population of people with epilepsy, remains a hope for the future.…”