title: Comparison of three methods for localizing interictal epileptiform discharges with magnetoencephalography.
abstract: OBJECTIVE
  To compare three methods of localizing the source of epileptiform activity recorded with magnetoencephalography: equivalent current dipole, minimum current estimate, and dynamic statistical parametric mapping (dSPM), and to evaluate the solutions by comparison with clinical symptoms and other electrophysiological and neuroradiological findings.
  
  
  METHODS
  Fourteen children of 3 to 15 years were studied. Magnetoencephalography was collected with a whole-head 204-channel helmet-shaped sensor array. We calculated equivalent current dipoles and made minimum current estimate and dSPM movies to estimate the cortical distribution of interictal epileptiform discharges in these patients.
  
  
  RESULTS
  The results for four patients with localization-related epilepsy and one patient with Landau-Kleffner Syndrome were consistent among all the three analysis methods. In the rest of the patients, minimum current estimate and dSPM suggested multifocal or widespread activity; in these patients, the equivalent current dipole results were so scattered that interpretation of the results was not possible. For 9 patients with localization-related epilepsy and generalized epilepsy, the epileptiform discharges were wide spread or only slow waves, but dSPM suggested a possible propagation path of the interictal epileptiform discharges.
  
  
  CONCLUSIONS
  Minimum current estimate and dSPM could identify the propagation of epileptiform activity with high temporal resolution. The results of dSPM were more stable because the solutions were less sensitive to background brain activity.
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts, USA. siraisi@nmr.mgh.harvard.edu
authors.forename: Hideaki
authors.initials: H
authors.lastname: Shiraishi
authors.forename: Seppo P
authors.initials: SP
authors.lastname: Ahlfors
authors.forename: Steven M
authors.initials: SM
authors.lastname: Stufflebeam
authors.forename: Susanne
authors.initials: S
authors.lastname: Knake
authors.forename: Pål G
authors.initials: PG
authors.lastname: Larsson
authors.forename: Matti S
authors.initials: MS
authors.lastname: Hämäläinen
authors.forename: Kyoko
authors.initials: K
authors.lastname: Takano
authors.forename: Maki
authors.initials: M
authors.lastname: Okajima
authors.forename: Keisaku
authors.initials: K
authors.lastname: Hatanaka
authors.forename: Shinji
authors.initials: S
authors.lastname: Saitoh
authors.forename: Anders M
authors.initials: AM
authors.lastname: Dale
authors.forename: Eric
authors.initials: E
authors.lastname: Halgren
mesh_terms: D000293:Adolescent; D001921:Brain / Q000503:physiopathology*; D001931:Brain Mapping / Q000379:methods*; D058256:Brain Waves; D002648:Child; D002675:Child, Preschool; D004569:Electroencephalography; D004827:Epilepsy / Q000175:diagnosis* / Q000503:physiopathology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography / Q000379:methods*; D008297:Male; D015233:Models, Statistical; D011237:Predictive Value of Tests; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors