title: Identification of epileptic high frequency oscillations in the time domain by using MEG beamformer-based virtual sensors.
abstract: OBJECTIVE
  High frequency oscillations (HFOs, >80Hz) are biomarkers for epileptogenic cortex in invasive and non-invasive electroencephalography (EEG). Identification of HFOs in magnetoencephalography (MEG) is hindered by noise. Computing spatial filters using beamforming to reconstruct time series for selected brain regions, so-called virtual sensors (VS), can increase the signal-to-noise ratio. We identified HFOs in MEG in time domain using VS.
  
  
  METHODS
  Fifteen minutes of MEG data were selected from 12 patients. VS were placed around the epileptic spikes (affected region) and in the contralateral hemisphere. VS and physical sensors were reviewed for HFOs and spikes. HFO locations were compared to spikes and other clinical parameters.
  
  
  RESULTS
  Eight patients showed 78 time points with 575 HFOs in VS, 513 were in the affected region. HFOs could not be identified in physical sensors for 61 of the 78 VS time points. HFOs overlapped with presumed epileptogenic areas and were also visible in unfiltered VS signals.
  
  
  CONCLUSIONS
  Beamformer-based VS analysis can help to identify epileptic HFOs that are not discernable in physical MEG sensors.
  
  
  CONCLUSIONS
  This approach can be extended to enable localization of non-invasively recorded HFOs. This would help surgical planning and reduce the need for invasive diagnostics.
authors.affiliation: Brain Center Rudolf Magnus, Department of Neurology and Neurosurgery, University Medical Center Utrecht, The Netherlands. Electronic address: n.vanklink-2@umcutrecht.nl.
authors.forename: Nicole
authors.initials: N
authors.lastname: van Klink
authors.affiliation: Department of Clinical Neurophysiology and Magnetoencephalography Center, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Arjan
authors.initials: A
authors.lastname: Hillebrand
authors.affiliation: Brain Center Rudolf Magnus, Department of Neurology and Neurosurgery, University Medical Center Utrecht, The Netherlands; SEIN - Stichting Epilepsy Instellingen Nederland, Heemstede, The Netherlands.
authors.forename: Maeike
authors.initials: M
authors.lastname: Zijlmans
mesh_terms: D000200:Action Potentials; D000293:Adolescent; D000328:Adult; D002648:Child; D004827:Epilepsy / Q000175:diagnosis*; D005260:Female; D006801:Humans; D015225:Magnetoencephalography / Q000295:instrumentation / Q000379:methods*; D008297:Male
keywords: Beamforming; Epilepsy; High frequency oscillations; Magnetoencephalography; Virtual electrodes