title: Artifact reduction for EEG/fMRI recording: nonlinear reduction of ballistocardiogram artifacts.
abstract: OBJECTIVE
  We present a new method of effectively removing the ballistocardiogram artifacts (BAs) of electroencephalography (EEG), recorded inside a 1.5 T static magnetic field scanner with no fMRI scanning, which conserves the time and frequency features of event-related EEG activity.
  
  
  METHODS
  The BAs are approximated as deterministically chaotic dynamics. A Wavelet-based nonlinear noise reduction (WNNR) method consisting of: (a) wavelet transformation, (b) nonlinear noise reduction and (c) spatial average subtraction, is developed to effectively reduce the BAs so that the residual artifacts are smaller than the EEG signals.
  
  
  RESULTS
  The effectiveness of the WNNR method to remove the BAs with conservation of the temporal EEG signals is evaluated by simulations and experiments inside a 1.5 T static magnetic field, with the visual evoked EEG dynamics. The WNNR method is also demonstrated to effectively retrieve alpha waves while the subjects' eyes are closed.
  
  
  CONCLUSIONS
  The WNNR method has the abilities to effectively remove the BAs and conserve the time-frequency features of EEG activity.
  
  
  CONCLUSIONS
  The WNNR method provides us a significant technique to obtain clean temporal EEG signals during recording with MRI, especially for the event-related EEG dynamics. Notably, it might work effectively at higher field strengths as well. Moreover, it can be also used to process many other biological data contaminated by the cardiac pulses.
authors.affiliation: Advanced Science and Technology of Materials NICHe, Tohoku University, Aobaku, Sendai 980-8579, Japan. xwan@idac.tohoku.ac.jp
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Wan
authors.forename: Kazuki
authors.initials: K
authors.lastname: Iwata
authors.forename: Jorge
authors.initials: J
authors.lastname: Riera
authors.forename: Torh
authors.initials: T
authors.lastname: Ozaki
authors.forename: Masaharu
authors.initials: M
authors.lastname: Kitamura
authors.forename: Ryuta
authors.initials: R
authors.lastname: Kawashima
mesh_terms: D000328:Adult; D016477:Artifacts; D001450:Ballistocardiography; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping; D004569:Electroencephalography; D005074:Evoked Potentials, Visual / Q000502:physiology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D017711:Nonlinear Dynamics; D010775:Photic Stimulation / Q000379:methods; D012815:Signal Processing, Computer-Assisted