title: Reliability of MEG source imaging of anterior temporal spikes: analysis of an intracranially characterized spike focus.
abstract: OBJECTIVE
  To assess the reliability of MEG source imaging (MSI) of anterior temporal spikes through detailed analysis of the localization and orientation of source solutions obtained for a large number of spikes that were separately confirmed by intracranial EEG to be focally generated within a single, well-characterized spike focus.
  
  
  METHODS
  MSI was performed on 64 identical right anterior temporal spikes from an anterolateral temporal neocortical spike focus. The effects of different volume conductors (sphere and realistic head model), removal of noise with low frequency filters (LFFs) and averaging multiple spikes were assessed in terms of the reliability of the source solutions.
  
  
  RESULTS
  MSI of single spikes resulted in scattered dipole source solutions that showed reasonable reliability for localization at the lobar level, but only for solutions with a goodness-of-fit exceeding 80% using a LFF of 3 Hz. Reliability at a finer level of intralobar localization was limited. Spike averaging significantly improved the reliability of source solutions and averaging 8 or more spikes reduced dependency on goodness-of-fit and data filtering.
  
  
  CONCLUSIONS
  MSI performed on topographically identical individual spikes from an intracranially defined classical anterior temporal lobe spike focus was limited by low reliability (i.e., scattered source solutions) in terms of fine, sublobar localization within the ipsilateral temporal lobe. Spike averaging significantly improved reliability.
  
  
  CONCLUSIONS
  MSI performed on individual anterior temporal spikes is limited by low reliability. Reduction of background noise through spike averaging significantly improves the reliability of MSI solutions.
authors.affiliation: Krembil Neuroscience Centre, Division of Neurology, Toronto Western Hospital, University of Toronto, 399 Bathurst Street, Toronto, ON M5T 2S8, Canada. Electronic address: r.wennberg@utoronto.ca.
authors.forename: Richard
authors.initials: R
authors.lastname: Wennberg
authors.affiliation: Program in Neurosciences and Mental Health, Research Institute, The Hospital for Sick Children, University of Toronto, Toronto, ON M5G 1X8, Canada.
authors.forename: Douglas
authors.initials: D
authors.lastname: Cheyne
mesh_terms: D000465:Algorithms; D001931:Brain Mapping / Q000379:methods*; D004569:Electroencephalography / Q000379:methods*; D004833:Epilepsy, Temporal Lobe / Q000175:diagnosis* / Q000503:physiopathology*; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods*; D008959:Models, Neurological; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted; D013702:Temporal Lobe / Q000502:physiology / Q000503:physiopathology
keywords: Dipole mapping; Electroencephalography; Magnetoencephalography; Mesial temporal lobe epilepsy; Source localization; sLORETA