title: Simultaneous EEG-fMRI at ultra-high field: artifact prevention and safety assessment.
abstract: The simultaneous recording of scalp electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) can provide unique insights into the dynamics of human brain function, and the increased functional sensitivity offered by ultra-high field fMRI opens exciting perspectives for the future of this multimodal approach. However, simultaneous recordings are susceptible to various types of artifacts, many of which scale with magnetic field strength and can seriously compromise both EEG and fMRI data quality in recordings above 3T. The aim of the present study was to implement and characterize an optimized setup for simultaneous EEG-fMRI in humans at 7 T. The effects of EEG cable length and geometry for signal transmission between the cap and amplifiers were assessed in a phantom model, with specific attention to noise contributions from the MR scanner coldheads. Cable shortening (down to 12 cm from cap to amplifiers) and bundling effectively reduced environment noise by up to 84% in average power and 91% in inter-channel power variability. Subject safety was assessed and confirmed via numerical simulations of RF power distribution and temperature measurements on a phantom model, building on the limited existing literature at ultra-high field. MRI data degradation effects due to the EEG system were characterized via B0 and B1(+) field mapping on a human volunteer, demonstrating important, although not prohibitive, B1 disruption effects. With the optimized setup, simultaneous EEG-fMRI acquisitions were performed on 5 healthy volunteers undergoing two visual paradigms: an eyes-open/eyes-closed task, and a visual evoked potential (VEP) paradigm using reversing-checkerboard stimulation. EEG data exhibited clear occipital alpha modulation and average VEPs, respectively, with concomitant BOLD signal changes. On a single-trial level, alpha power variations could be observed with relative confidence on all trials; VEP detection was more limited, although statistically significant responses could be detected in more than 50% of trials for every subject. Overall, we conclude that the proposed setup is well suited for simultaneous EEG-fMRI at 7 T.
authors.affiliation: Institute for Systems and Robotics and Department of Bioengineering, Instituto Superior Técnico, University of Lisbon, Lisbon, Portugal; Laboratory for Functional and Metabolic Imaging, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland. Electronic address: joao.jorge@epfl.ch.
authors.forename: João
authors.initials: J
authors.lastname: Jorge
authors.affiliation: Biomedical Imaging Research Center, Geneva University Hospital, University of Geneva, Geneva, Switzerland.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Grouiller
authors.affiliation: Biomedical Imaging Research Center-Animal Imaging and Technology, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
authors.forename: Özlem
authors.initials: Ö
authors.lastname: Ipek
authors.affiliation: Brain Products, GmbH, Gilching, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Stoermer
authors.affiliation: Department of Fundamental Neurosciences, University of Geneva, Geneva, Switzerland.
authors.forename: Christoph M
authors.initials: CM
authors.lastname: Michel
authors.affiliation: Institute for Systems and Robotics and Department of Bioengineering, Instituto Superior Técnico, University of Lisbon, Lisbon, Portugal.
authors.forename: Patrícia
authors.initials: P
authors.lastname: Figueiredo
authors.affiliation: Biomedical Imaging Research Center-Animal Imaging and Technology, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
authors.forename: Wietske
authors.initials: W
authors.lastname: van der Zwaag
authors.affiliation: Laboratory for Functional and Metabolic Imaging, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; Department of Radiology, University of Lausanne, Lausanne, Switzerland; Department of Radiology, University of Geneva, Geneva, Switzerland.
authors.forename: Rolf
authors.initials: R
authors.lastname: Gruetter
mesh_terms: D016477:Artifacts; D004569:Electroencephalography / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D008297:Male; D012815:Signal Processing, Computer-Assisted; D014793:Visual Cortex / Q000502:physiology; D055815:Young Adult
keywords: Alpha wave; Electromagnetic simulation; Simultaneous EEG–fMRI; Ultra-high field; Visual evoked potential