title: Event-related beamforming: a robust method for presurgical functional mapping using MEG.
abstract: OBJECTIVE
  We describe the application of a new spatial filtering technique--event-related beamforming (ERB)--for presurgical functional mapping of primary sensory areas using MEG. This method provides an alternative to equivalent current dipole (ECD) modeling that potentially eliminates problems of intracranial magnetic artifacts due to movement of ferromagnetic materials (e.g., orthodontic braces) or eye movements.
  
  
  METHODS
  We compared localization results for ERB and ECD localization of primary somatosensory (M20) and auditory (M100) evoked responses in 12 healthy control subjects and four subjects with metallic dental implants. Data were recorded with a 151-channel CTF MEG system using standard presurgical mapping protocols.
  
  
  RESULTS
  We found a high level of agreement between the two methods in control subjects (overall localization difference was 5.9+/-2.2 mm for M20 and 10.4+/-5.6 mm for M100). Subjects with dental implants showed severely distorted evoked responses that could not be analyzed using ECD, whereas the ERB method localized sources to expected anatomical locations.
  
  
  CONCLUSIONS
  MEG functional mapping may be carried out without removal of orthodontic or other metallic implants using event-related beamformer analysis.
  
  
  CONCLUSIONS
  Spatial filtering methods can overcome some of the limitations associated with MEG expanding its applicability, particularly in pediatric clinical environments.
authors.affiliation: Program in Neurosciences and Mental Health, Hospital for Sick Children Research Institute, and Department of Medical Imaging, University of Toronto, Ontario, Canada. douglas.cheyne@utoronto.ca
authors.forename: Douglas
authors.initials: D
authors.lastname: Cheyne
authors.forename: Andreea C
authors.initials: AC
authors.lastname: Bostan
authors.forename: William
authors.initials: W
authors.lastname: Gaetz
authors.forename: Elizabeth W
authors.initials: EW
authors.lastname: Pang
mesh_terms: D000328:Adult; D016477:Artifacts; D001303:Auditory Cortex / Q000502:physiology*; D001921:Brain / Q000601:surgery; D015921:Dental Implants; D005072:Evoked Potentials, Auditory; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods*; D008297:Male; D008670:Metals; D008875:Middle Aged; D011300:Preoperative Care / Q000379:methods; D013003:Somatosensory Cortex / Q000502:physiology*
chemical_list: D015921:Dental Implants; D008670:Metals