title: Marker-based ballistocardiographic artifact correction improves spike identification in EEG-fMRI of focal epilepsy patients.
abstract: Ballistocardiographic (BCG) artifacts resemble interictal epileptic discharges (IEDs) and can lead to incorrect IED identification in EEG-fMRI. This study investigates IEDs marked in EEGs corrected using information from a moiré phase tracking (MPT) marker.
  
  
  
  EEG-fMRI from 18 patients was processed with conventional methods for BCG removal, while 9 patients used a MPT marker. IEDs were marked first without ECG information. In a second review, suspicious IEDs synchronous with the BCG were discarded. After each review, an event-related fMRI analysis was performed on the marked IEDs.
  
  
  
  No difference was found in the proportion of suspicious IEDs in the 2 patient groups. However, the distribution of IED timings was significantly related to the cardiac cycle in 11 of 18 patients recorded without MPT marker, but only 2 of 9 patients with marker. In patients recorded without marker, failing to discard suspicious IEDs led to more inaccurate fMRI maps and more distant activations.
  
  
  
  BCG artifact correction based on MPT recordings allowed a more straightforward identification of IEDs that did not require ECG information in the large majority of patients.
  
  
  
  Marker-based ballistocardiographic artifact correction greatly facilitates the study of the generators of interictal discharges with EEG-fMRI.
authors.affiliation: Dept. Neuropediatrics and Muscular Diseases, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Germany; Dept. Radiology, Medical Physics, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Germany. Electronic address: katharina.koerbl@gmx.de.
authors.forename: Katharina
authors.initials: K
authors.lastname: Körbl
authors.affiliation: Dept. Neuropediatrics and Muscular Diseases, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Germany; Epilepsy Center, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Jacobs
authors.affiliation: Dept. Radiology, Medical Physics, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Germany; Dept. Medicine, John A. Burns School of Medicine, University of Hawaii, Honolulu, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Herbst
authors.affiliation: Dept. Radiology, Medical Physics, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Germany.
authors.forename: Maxim
authors.initials: M
authors.lastname: Zaitsev
authors.affiliation: Epilepsy Center, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Schulze-Bonhage
authors.affiliation: Dept. Radiology, Medical Physics, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Hennig
authors.affiliation: Dept. Radiology, Medical Physics, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Germany.
authors.forename: Pierre
authors.initials: P
authors.lastname: LeVan
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001921:Brain / Q000000981:diagnostic imaging / Q000503:physiopathology*; D001931:Brain Mapping / Q000379:methods*; D002648:Child; D004569:Electroencephalography / Q000379:methods; D004828:Epilepsies, Partial / Q000000981:diagnostic imaging / Q000503:physiopathology*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D012815:Signal Processing, Computer-Assisted; D055815:Young Adult
keywords: Ballistocardiographic artifact correction; EEG-fMRI; Epileptic spike/IED; Fast fMRI; MPT marker; Optical tracking; Refractory epilepsy