title: Magnetoencephalography signals are influenced by skull defects.
abstract: OBJECTIVE
  Magnetoencephalography (MEG) signals had previously been hypothesized to have negligible sensitivity to skull defects. The objective is to experimentally investigate the influence of conducting skull defects on MEG and EEG signals.
  
  
  METHODS
  A miniaturized electric dipole was implanted in vivo into rabbit brains. Simultaneous recording using 64-channel EEG and 16-channel MEG was conducted, first above the intact skull and then above a skull defect. Skull defects were filled with agar gels, which had been formulated to have tissue-like homogeneous conductivities. The dipole was moved beneath the skull defects, and measurements were taken at regularly spaced points.
  
  
  RESULTS
  The EEG signal amplitude increased 2-10 times, whereas the MEG signal amplitude reduced by as much as 20%. The EEG signal amplitude deviated more when the source was under the edge of the defect, whereas the MEG signal amplitude deviated more when the source was central under the defect. The change in MEG field-map topography (relative difference measure, RDM(∗)=0.15) was geometrically related to the skull defect edge.
  
  
  CONCLUSIONS
  MEG and EEG signals can be substantially affected by skull defects.
  
  
  CONCLUSIONS
  MEG source modeling requires realistic volume conductor head models that incorporate skull defects.
authors.affiliation: Institute of Biomedical Engineering and Informatics, Ilmenau University of Technology, P.O. Box 100565, D-98684 Ilmenau, Germany; Biomagnetic Center, Department of Neurology, Jena University Hospital, Erlanger Allee 101, D-07747 Jena, Germany; NeuroEngineering Laboratory, Department of Electrical & Electronic Engineering, The University of Melbourne, Parkville 3010, Australia; Department of Medicine - St. Vincent's Hospital, The University of Melbourne, Fitzroy 3057, Australia. Electronic address: stephan.lau@tu-ilmenau.de.
authors.forename: S
authors.initials: S
authors.lastname: Lau
authors.affiliation: Biomagnetic Center, Department of Neurology, Jena University Hospital, Erlanger Allee 101, D-07747 Jena, Germany; Department of Traumatology and Orthopedics, Robert-Koch-Hospital, Jenaer Straße 66, D-99510 Apolda, Germany.
authors.forename: L
authors.initials: L
authors.lastname: Flemming
authors.affiliation: Institute of Biomedical Engineering and Informatics, Ilmenau University of Technology, P.O. Box 100565, D-98684 Ilmenau, Germany; Biomagnetic Center, Department of Neurology, Jena University Hospital, Erlanger Allee 101, D-07747 Jena, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Haueisen
mesh_terms: D000362:Agar; D000818:Animals; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000295:instrumentation / Q000379:methods*; D004553:Electric Conductivity; D004567:Electrodes, Implanted; D004569:Electroencephalography / Q000295:instrumentation; D015225:Magnetoencephalography / Q000295:instrumentation*; D008422:Materials Testing; D023421:Models, Animal; D008954:Models, Biological; D011817:Rabbits; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D012867:Skin; D012886:Skull / Q000033:anatomy & histology / Q000473:pathology* / Q000502:physiology*
chemical_list: D000362:Agar
keywords: Biomagnetism; Breach rhythm; Electroencephalography; Magnetoencephalography; Skull hole; Volume conduction