title: Flexible head-casts for high spatial precision MEG.
abstract: In combination with magnetoencephalographic (MEG) data, accurate knowledge of the brain's structure and location provide a principled way of reconstructing neural activity with high temporal resolution. However, measuring the brain's location is compromised by head movement during scanning, and by fiducial-based co-registration with magnetic resonance imaging (MRI) data. The uncertainty from these two factors introduces errors into the forward model and limit the spatial resolution of the data.
  
  
  
  We present a method for stabilizing and reliably repositioning the head during scanning, and for co-registering MRI and MEG data with low error.
  
  
  
  Using this new flexible and comfortable subject-specific head-cast prototype, we find within-session movements of <0.25mm and between-session repositioning errors around 1mm.
  
  
  
  This method is an improvement over existing methods for stabilizing the head or correcting for location shifts on- or off-line, which still introduce approximately 5mm of uncertainty at best (Adjamian et al., 2004; Stolk et al., 2013; Whalen et al., 2008). Further, the head-cast design presented here is more comfortable, safer, and easier to use than the earlier 3D printed prototype, and give slightly lower co-registration errors (Troebinger et al., 2014b).
  
  
  
  We provide an empirical example of how these head-casts impact on source level reproducibility. Employment of the individual flexible head-casts for MEG recordings provide a reliable method of safely stabilizing the head during MEG recordings, and for co-registering MRI anatomical images to MEG functional data.
authors.affiliation: Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, London, UK. Electronic address: sofiemeyer@gmail.com.
authors.forename: Sofie S
authors.initials: SS
authors.lastname: Meyer
authors.affiliation: Sobell Department for Motor Neuroscience and Movement Disorders, University College London, London, UK.
authors.forename: James
authors.initials: J
authors.lastname: Bonaiuto
authors.affiliation: Chalk Studios Ltd, 14 Windsor St., N1 8QG, London, UK.
authors.forename: Mark
authors.initials: M
authors.lastname: Lim
authors.affiliation: Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, London, UK.
authors.forename: Holly
authors.initials: H
authors.lastname: Rossiter
authors.affiliation: Sobell Department for Motor Neuroscience and Movement Disorders, University College London, London, UK.
authors.forename: Sheena
authors.initials: S
authors.lastname: Waters
authors.affiliation: Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, London, UK.
authors.forename: David
authors.initials: D
authors.lastname: Bradbury
authors.affiliation: Sobell Department for Motor Neuroscience and Movement Disorders, University College London, London, UK.
authors.forename: Sven
authors.initials: S
authors.lastname: Bestmann
authors.affiliation: Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, UK.
authors.forename: Matthew
authors.initials: M
authors.lastname: Brookes
authors.affiliation: Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, London, UK.
authors.forename: Martina F
authors.initials: MF
authors.lastname: Callaghan
authors.affiliation: Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, London, UK; Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstrasse 1a, 04103 Leipzig, Germany.
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Weiskopf
authors.affiliation: Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, London, UK.
authors.forename: Gareth R
authors.initials: GR
authors.lastname: Barnes
mesh_terms: D000328:Adult; D004867:Equipment Design; D005260:Female; D006257:Head / Q000000981:diagnostic imaging; D019416:Head Movements; D006801:Humans; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography / Q000295:instrumentation*; D008297:Male; D008953:Models, Anatomic; D009038:Motion; D061214:Patient Safety; D015203:Reproducibility of Results
keywords: 3D printing; Head localization; Head movement minimization; Head-cast; MRI-MEG Co-registration; Magnetoencephalography; Spatial resolution