title: Time-frequency analysis of resting state and evoked EEG data recorded at higher magnetic fields up to 9.4 T.
abstract: BACKGROUND
  Combining both high temporal and spatial resolution by means of simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) is of relevance to neuroscientists. This combination, however, leads to a distortion of the EEG signal by the so-called cardio-ballistic artefacts. The aim of the present study was developing an approach to restore meaningful physiological EEG data from recordings at different magnetic fields.
  
  
  METHODS
  The distortions introduced by the magnetic field were corrected using a combination of concepts from independent component analysis (ICA) and mutual information (MI). Thus, the components were classified as either related to the cardio-ballistic artefacts or to the signals of interest. EEG data from two experimental paradigms recorded at different magnetic field strengths up to 9.4 T were analyzed: (i) spontaneous activity using an eyes-open/eyes-closed alternation, and (ii) responses to auditory stimuli, i.e. auditory evoked potentials.
  
  
  RESULTS
  Even at ultra-high magnetic fields up to 9.4 T the proposed artefact rejection approach restored the physiological time-frequency information contained in the signal of interest and the data were suitable for subsequent analyses.
  
  
  METHODS
  Blind source separation (BSS) has been used to retrieve information from EEG data recorded inside the MR scanner in previous studies. After applying the presented method on EEG data recorded at 4 T, 7 T, and 9.4 T, we could retrieve more information than from data cleaned with the BSS method.
  
  
  CONCLUSIONS
  The present work demonstrates that EEG data recorded at ultra-high magnetic fields can be used for studying neuroscientific research question related to oscillatory activity.
authors.affiliation: Institute of Neuroscience and Medicine, INM-4, Forschungszentrum Jülich, Jülich, Germany; Institute of Clinical Neuroscience and Medical Psychology, Medical Faculty, Heinrich Heine University Düsseldorf, Düsseldorf, Germany; Department of Medical Engineering, Ruhr-Universität Bochum, Bochum, Germany. Electronic address: omid.abbasi@med.uni-duesseldorf.de.
authors.forename: Omid
authors.initials: O
authors.lastname: Abbasi
authors.affiliation: Institute of Neuroscience and Medicine, INM-4, Forschungszentrum Jülich, Jülich, Germany. Electronic address: j.dammers@fz-juelich.de.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Dammers
authors.affiliation: Institute of Neuroscience and Medicine, INM-4, Forschungszentrum Jülich, Jülich, Germany; Department of Psychiatry, Psychotherapy and Psychosomatics, RWTH Aachen University, Aachen, Germany. Electronic address: j.arrubla@fz-juelich.de.
authors.forename: Jorge
authors.initials: J
authors.lastname: Arrubla
authors.affiliation: Institute of Neuroscience and Medicine, INM-4, Forschungszentrum Jülich, Jülich, Germany. Electronic address: t.warbrick@fz-juelich.de.
authors.forename: Tracy
authors.initials: T
authors.lastname: Warbrick
authors.affiliation: Institute of Clinical Neuroscience and Medical Psychology, Medical Faculty, Heinrich Heine University Düsseldorf, Düsseldorf, Germany. Electronic address: markus.butz@hhu.de.
authors.forename: Markus
authors.initials: M
authors.lastname: Butz
authors.affiliation: Institute of Neuroscience and Medicine, INM-4, Forschungszentrum Jülich, Jülich, Germany; Department of Psychiatry, Psychotherapy and Psychosomatics, RWTH Aachen University, Aachen, Germany; JARA-BRAIN-Translational Medicine, RWTH Aachen University, Aachen, Germany. Electronic address: i.neuner@fz-juelich.de.
authors.forename: Irene
authors.initials: I
authors.lastname: Neuner
authors.affiliation: Institute of Neuroscience and Medicine, INM-4, Forschungszentrum Jülich, Jülich, Germany; Department of Psychiatry, Psychotherapy and Psychosomatics, RWTH Aachen University, Aachen, Germany; Department of Neurology, RWTH Aachen University, Aachen, Germany. Electronic address: n.j.shah@fz-juelich.de.
authors.forename: N Jon
authors.initials: NJ
authors.lastname: Shah
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D000513:Alpha Rhythm; D016477:Artifacts; D001307:Auditory Perception / Q000502:physiology; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000295:instrumentation / Q000379:methods*; D004569:Electroencephalography / Q000379:methods*; D005072:Evoked Potentials, Auditory; D005260:Female; D006801:Humans; D007257:Information Theory; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D008297:Male; D064847:Multimodal Imaging / Q000295:instrumentation / Q000379:methods*; D012146:Rest; D012815:Signal Processing, Computer-Assisted; D014796:Visual Perception / Q000502:physiology
keywords: Cardio-ballistic artefact; EEG; Hybrid imaging; Independent component analysis; Mutual information; Time-frequency analysis; Ultra-high field MR