Skull Defects in Finite Element Head Models for Source Reconstruction from Magnetoencephalography Signals.
Magnetoencephalography (MEG) signals are influenced by skull defects. However, there is a lack of evidence of this influence during source reconstruction. Our objectives are to characterize errors in source reconstruction from MEG signals due to ignoring skull defects and to assess the ability of an exact finite element head model to eliminate such errors. A detailed finite element model of the head of a rabbit used in a physical experiment was constructed from magnetic resonance and co-registered computer tomography imaging that differentiated nine tissue types. Sources of the MEG measurements above intact skull and above skull defects respectively were reconstructed using a finite element model with the intact skull and one incorporating the skull defects. The forward simulation of the MEG signals reproduced the experimentally observed characteristic magnitude and topography changes due to skull defects. Sources reconstructed from measured MEG signals above intact skull matched the known physical locations and orientations. Ignoring skull defects in the head model during reconstruction displaced sources under a skull defect away from that defect. Sources next to a defect were reoriented. When skull defects, with their physical conductivity, were incorporated in the head model, the location and orientation errors were mostly eliminated. The conductivity of the skull defect material non-uniformly modulated the influence on MEG signals. We propose concrete guidelines for taking into account conducting skull defects during MEG coil placement and modeling. Exact finite element head models can improve localization of brain function, specifically after surgery.
Institute of Biomedical Engineering and Informatics, Technical University IlmenauIlmenau, Germany; Department of Neurology, Biomagnetic Center, University Hospital JenaJena, Germany; NeuroEngineering Laboratory, Department of Electrical and Electronic Engineering, University of MelbourneParkville, VIC, Australia; Centre for Neural Engineering, University of MelbourneParkville, VIC, Australia; Department of Medicine - St. Vincent's Hospital, University of MelbourneFitzroy, VIC, Australia.
Stephan
S
Lau
Medical Physics Group, Department of Diagnostic and Interventional Radiology, University Hospital Jena Jena, Germany.
Daniel
D
Güllmar
Department of Neurology, Biomagnetic Center, University Hospital Jena Jena, Germany.
Lars
L
Flemming
NeuroEngineering Laboratory, Department of Electrical and Electronic Engineering, University of MelbourneParkville, VIC, Australia; Centre for Neural Engineering, University of MelbourneParkville, VIC, Australia.
David B
DB
Grayden
Department of Medicine - St. Vincent's Hospital, University of Melbourne Fitzroy, VIC, Australia.
Mark J
MJ
Cook
Institute for Biomagnetism and Biosignalanalysis, Westfälische Wilhelms-Universität Münster Münster, Germany.
Carsten H
CH
Wolters
Institute of Biomedical Engineering and Informatics, Technical University Ilmenau Ilmenau, Germany.
Jens
J
Haueisen
electric conductivity; finite element analysis; magnetoencephalography; skull; source analysis; validation study