title: Ballistocardiogram artifact correction taking into account physiological signal preservation in simultaneous EEG-fMRI.
abstract: The ballistocardiogram (BCG) artifact is currently one of the most challenging in the EEG acquired concurrently with fMRI, with correction invariably yielding residual artifacts and/or deterioration of the physiological signals of interest. In this paper, we propose a family of methods whereby the EEG is decomposed using Independent Component Analysis (ICA) and a novel approach for the selection of BCG-related independent components (ICs) is used (PROJection onto Independent Components, PROJIC). Three ICA-based strategies for BCG artifact correction are then explored: 1) BCG-related ICs are removed from the back-reconstruction of the EEG (PROJIC); and 2-3) BCG-related ICs are corrected for the artifact occurrences using an Optimal Basis Set (OBS) or Average Artifact Subtraction (AAS) framework, before back-projecting all ICs onto EEG space (PROJIC-OBS and PROJIC-AAS, respectively). A novel evaluation pipeline is also proposed to assess the methods performance, which takes into account not only artifact but also physiological signal removal, allowing for a flexible weighting of the importance given to physiological signal preservation. This evaluation is used for the group-level parameter optimization of each algorithm on simultaneous EEG-fMRI data acquired using two different setups at 3T and 7T. Comparison with state-of-the-art BCG correction methods showed that PROJIC-OBS and PROJIC-AAS outperformed the others when priority was given to artifact removal or physiological signal preservation, respectively, while both PROJIC-AAS and AAS were in general the best choices for intermediate trade-offs. The impact of the BCG correction on the quality of event-related potentials (ERPs) of interest was assessed in terms of the relative reduction of the standard error (SE) across trials: 26/66%, 32/62% and 18/61% were achieved by, respectively, PROJIC, PROJIC-OBS and PROJIC-AAS, for data collected at 3T/7T. Although more significant improvements were achieved at 7T, the results were qualitatively comparable for both setups, which indicate the wide applicability of the proposed methodologies and recommendations.
authors.affiliation: Institute for Systems and Robotics and Department of Bioengineering, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal. Electronic address: rodolfo.abreu@ist.utl.pt.
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Abreu
authors.affiliation: Institute for Systems and Robotics and Department of Bioengineering, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal; Department of Clinical and Experimental Epilepsy, University College London Institute of Neurology, Queen Square, London, WC1N 3BG, UK; The Wellcome Trust Centre for Neuroimaging, University College London Institute of Neurology, Queen Square, London, WC1N 3BG, UK.
authors.forename: Marco
authors.initials: M
authors.lastname: Leite
authors.affiliation: Institute for Systems and Robotics and Department of Bioengineering, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal; Laboratory for Functional and Metabolic Imaging, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
authors.forename: João
authors.initials: J
authors.lastname: Jorge
authors.affiliation: Biomedical Imaging Research Center (CIBM), Department of Radiology and Medical Informatics, Geneva, University Hospital, University of Geneva, Geneva, Switzerland.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Grouiller
authors.affiliation: Biomedical Imaging Research Center (CIBM), École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
authors.forename: Wietske
authors.initials: W
authors.lastname: van der Zwaag
authors.affiliation: Centro de Investigação e Intervenção Social and Department of Neurophysiology, Centro Hospitalar Psiquiátrico de Lisboa, Lisbon, Portugal.
authors.forename: Alberto
authors.initials: A
authors.lastname: Leal
authors.affiliation: Institute for Systems and Robotics and Department of Bioengineering, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal.
authors.forename: Patrícia
authors.initials: P
authors.lastname: Figueiredo
mesh_terms: D000465:Algorithms; D016477:Artifacts; D001450:Ballistocardiography / Q000379:methods*; D001931:Brain Mapping / Q000379:methods*; D055424:Cardiac-Gated Imaging Techniques / Q000379:methods; D002648:Child; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D004569:Electroencephalography / Q000379:methods*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D009038:Motion; D064847:Multimodal Imaging / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D055815:Young Adult
keywords: Ballistocardiogram; Electroencephalography; Independent Component Analysis; fMRI