title: Stepping stone sampling for retrieving artifact-free electroencephalogram during functional magnetic resonance imaging.
abstract: Ballistocardiogram and imaging artifacts cause major interference with simultaneous electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) recording. In particular, the large amplitude of the imaging artifact precludes easy retrieval of EEG signals during fMRI scanning. Recording with 20,000-Hz digitization rate combined with 3000-Hz low-pass filter revealed the real waveform of the imaging artifact, in which it was elucidated that each artifact peak precisely corresponded to each gradient component and actually had differential waveforms of the original gradient pulses. Based on this finding, to retrieve EEG signal during fMRI acquisition, a blip-type echo planar sequence was modified so that EEG sampling might be performed at every 1000 micros (digitization rate 1000 Hz) exclusively in the period in which the artifact resided around the baseline level. This method, called "stepping stone sampling," substantially attenuated the amplitude of the imaging artifact. The remnant of the artifact was subtracted from the averaged artifact waveform. In human studies, alpha activity was successfully retrieved by inspection, and its attenuation/augmentation was observed during eyes open/closed periods. Fast Fourier transform analysis further revealed that even from DC up to 120 Hz, retrieved EEG data during scanning had very similar power distributions to the data retrieved during no scanning, implying the availability of the high-frequency band of the retrieved EEG signals, including even the gamma band.
authors.affiliation: Department of Psychiatry, National Center Hospital for Mental, Nervous, and Muscular Disorders, National Center of Neurology and Psychiatry, Tokyo 187-8551, Japan. anami@ncnpmusashi.gr.jp
authors.forename: Kimitaka
authors.initials: K
authors.lastname: Anami
authors.forename: Takeyuki
authors.initials: T
authors.lastname: Mori
authors.forename: Fumiko
authors.initials: F
authors.lastname: Tanaka
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Kawagoe
authors.forename: Jun
authors.initials: J
authors.lastname: Okamoto
authors.forename: Masaru
authors.initials: M
authors.lastname: Yarita
authors.forename: Takashi
authors.initials: T
authors.lastname: Ohnishi
authors.forename: Masato
authors.initials: M
authors.lastname: Yumoto
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Matsuda
authors.forename: Osamu
authors.initials: O
authors.lastname: Saitoh
mesh_terms: D000328:Adult; D000513:Alpha Rhythm; D016477:Artifacts; D001450:Ballistocardiography / Q000379:methods; D001931:Brain Mapping / Q000379:methods; D002540:Cerebral Cortex / Q000502:physiology*; D017352:Echo-Planar Imaging / Q000379:methods; D004569:Electroencephalography / Q000379:methods*; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D019047:Phantoms, Imaging; D012016:Reference Values