title: Fetal MEG redistribution by projection operators.
abstract: The fetal magnetoencephalogram (fMEG) is measured in the presence of large interference from the maternal and fetal magnetocardiograms. This interference can be efficiently attenuated by orthogonal projection of the corresponding spatial vectors. However, the projection operators redistribute the fMEG signal among sensors. Although redistribution can be readily accounted for in the forward solution, visual interpretation of the fMEG signal topography is made difficult. We have devised a general, model-independent method for correction of the redistribution effect that utilizes the assumption that we know in which channels the fMEG should be negligible (such channels are distant from the known fetal head position). In a simplified case where the fMEG can be explained by equivalent current dipoles, the correction can also be obtained from fitting the dipoles to the fMEG signal. The corrected fMEG signal topography then corresponds to the dipole forward solution, but without orthogonal projection. We illustrate the redistribution correction on an example of experimentally measured flash evoked fMEG.
authors.affiliation: VSM MedTech Ltd., Coquitlam, BC, Canada, V3K 7B2. jvrba@vsmmedtech.com
authors.forename: Jiri
authors.initials: J
authors.lastname: Vrba
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Robinson
authors.forename: Jack
authors.initials: J
authors.lastname: Mccubbin
authors.forename: Curtis L
authors.initials: CL
authors.lastname: Lowery
authors.forename: Hari
authors.initials: H
authors.lastname: Eswaran
authors.forename: James D
authors.initials: JD
authors.lastname: Wilson
authors.forename: Pamela
authors.initials: P
authors.lastname: Murphy
authors.forename: Hubert
authors.initials: H
authors.lastname: Preissl
mesh_terms: D000465:Algorithms; D016477:Artifacts; D001921:Brain / Q000196:embryology* / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods; D003198:Computer Simulation; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D005074:Evoked Potentials, Visual / Q000502:physiology; D005323:Fetal Monitoring / Q000379:methods*; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods*; D008959:Models, Neurological; D015233:Models, Statistical