title: Improving the excess kurtosis (g2) method for localizing epileptic sources in magnetoencephalographic recordings.
abstract: OBJECTIVE
  To suggest ways to apply the excess kurtosis estimator g2, in the detection of epileptic activity with magnetoencephalography, while avoiding its bias towards detecting high-amplitude, infrequent events.
  
  
  METHODS
  Synthetic aperture magnetometry (SAM), combined with g2, was applied using window lengths ranging from 0.125 s to 32 s and with sum and maximum metrics on simulated data and recordings of two focal epilepsy patients.
  
  
  RESULTS
  Comparing sources with different spike rates (two per second and one per 2s), the sum metric was most efficient when using a window of 0.25s. Simulations showed that the sum metric is insensitive to spike frequency when the window includes more than one spike. SAM(g2) images from long segments with maximum metric resulted in misleading images, showing the strongest activity away from the lesions.
  
  
  CONCLUSIONS
  Using a sliding window and the sum metric is beneficial when imaging interictal spikes and status epilepticus. Windows should be short enough not to include more than one interictal event. For continuous events such as electrographic seizures windows should contain baseline data and the epileptic event.
  
  
  CONCLUSIONS
  The sliding window and metric should be set according to the suggested guidelines when using SAM(g2) for presurgical evaluation.
authors.affiliation: Gonda Brain Research Center, Bar-Ilan University, Ramat-Gan, Israel. Electronic address: Yuval.Harpaz@biu.ac.il.
authors.forename: Yuval
authors.initials: Y
authors.lastname: Harpaz
authors.affiliation: MEG Core Facility, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA.
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Robinson
authors.affiliation: Brain Function Imaging Unit, Tel-Aviv Sourasky Medical Center, Tel-Aviv, Israel; BioMag Laboratory, Helsinki University Central Hospital, Helsinki, Finland.
authors.forename: Mordekhay
authors.initials: M
authors.lastname: Medvedovsky
authors.affiliation: Gonda Brain Research Center, Bar-Ilan University, Ramat-Gan, Israel; Department of Psychology, Bar-Ilan University, Ramat-Gan, Israel.
authors.forename: Abraham
authors.initials: A
authors.lastname: Goldstein
mesh_terms: D000293:Adolescent; D004828:Epilepsies, Partial / Q000175:diagnosis* / Q000503:physiopathology*; D005260:Female; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods* / Q000592:standards; D008297:Male; D013226:Status Epilepticus / Q000175:diagnosis* / Q000503:physiopathology*
keywords: Beamforming; Epilepsy; Kurtosis; Source localization; Spike