title: Reference-free removal of EEG-fMRI ballistocardiogram artifacts with harmonic regression.
abstract: Combining electroencephalogram (EEG) recording and functional magnetic resonance imaging (fMRI) offers the potential for imaging brain activity with high spatial and temporal resolution. This potential remains limited by the significant ballistocardiogram (BCG) artifacts induced in the EEG by cardiac pulsation-related head movement within the magnetic field. We model the BCG artifact using a harmonic basis, pose the artifact removal problem as a local harmonic regression analysis, and develop an efficient maximum likelihood algorithm to estimate and remove BCG artifacts. Our analysis paradigm accounts for time-frequency overlap between the BCG artifacts and neurophysiologic EEG signals, and tracks the spatiotemporal variations in both the artifact and the signal. We evaluate performance on: simulated oscillatory and evoked responses constructed with realistic artifacts; actual anesthesia-induced oscillatory recordings; and actual visual evoked potential recordings. In each case, the local harmonic regression analysis effectively removes the BCG artifacts, and recovers the neurophysiologic EEG signals. We further show that our algorithm outperforms commonly used reference-based and component analysis techniques, particularly in low SNR conditions, the presence of significant time-frequency overlap between the artifact and the signal, and/or large spatiotemporal variations in the BCG. Because our algorithm does not require reference signals and has low computational complexity, it offers a practical tool for removing BCG artifacts from EEG data recorded in combination with fMRI.
authors.affiliation: Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA; Harvard-MIT Division of Health Sciences and Technology (HST), Cambridge, MA, USA. Electronic address: pavitrak@mit.edu.
authors.forename: Pavitra
authors.initials: P
authors.lastname: Krishnaswamy
authors.affiliation: Department of Radiology, Massachusetts General Hospital (MGH), Harvard Medical School, Boston, MA, USA; MGH/HST Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Bonmassar
authors.affiliation: Electrical Geodesics, Inc., Eugene, OR, USA.
authors.forename: Catherine
authors.initials: C
authors.lastname: Poulsen
authors.affiliation: Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Eric T
authors.initials: ET
authors.lastname: Pierce
authors.affiliation: MGH/HST Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA; Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Patrick L
authors.initials: PL
authors.lastname: Purdon
authors.affiliation: Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA; Harvard-MIT Division of Health Sciences and Technology (HST), Cambridge, MA, USA; Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA; Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, MA, USA. Electronic address: enb@neurostat.mit.edu.
authors.forename: Emery N
authors.initials: EN
authors.lastname: Brown
mesh_terms: D000465:Algorithms; D016477:Artifacts; D001450:Ballistocardiography; D004569:Electroencephalography; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging; D064847:Multimodal Imaging / Q000379:methods; D059906:Neuroimaging / Q000379:methods; D012815:Signal Processing, Computer-Assisted
keywords: Artifact removal; Ballistocardiogram; EEG-fMRI; Functional neuroimaging; Pulse artifact; Regression