Document Detail


Reducing the gradient artefact in simultaneous EEG-fMRI by adjusting the subject's axial position.
MedLine Citation:
PMID:  20932913     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Large artefacts that compromise EEG data quality are generated when electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) are carried out concurrently. The gradient artefact produced by the time-varying magnetic field gradients is the largest of these artefacts. Although average artefact correction (AAS) and related techniques can remove the majority of this artefact, the need to avoid amplifier saturation necessitates the use of a large dynamic range and strong low-pass filtering in EEG recording. Any intrinsic reduction in the gradient artefact amplitude would allow data with a higher bandwidth to be acquired without amplifier saturation, thus increasing the frequency range of neuronal activity that can be investigated using combined EEG-fMRI. Furthermore, gradient artefact correction methods assume a constant artefact morphology over time, so their performance is compromised by subject movement. Since the resulting, residual gradient artefacts can easily swamp signals from brain activity, any reduction in their amplitude would be highly advantageous for simultaneous EEG-fMRI studies. The aim of this work was to investigate whether adjustment of the subject's axial position in the MRI scanner can reduce the amplitude of the induced gradient artefact, before and after artefact correction using AAS. The variation in gradient artefact amplitude as a function of the subject's axial position was first investigated in six subjects by applying gradient pulses along the three Cartesian axes. The results of this study showed that a significant reduction in the gradient artefact magnitude can be achieved by shifting the subject axially by 4 cm towards the feet relative to the standard subject position (nasion at iso-centre). In a further study, the 4-cm shift was shown to produce a 40% reduction in the RMS amplitude (and a 31% reduction in the range) of the gradient artefact generated during the execution of a standard multi-slice, EPI sequence. By picking out signals occurring at harmonics of the slice acquisition frequency, it was also shown that the 4-cm shift led to a 36% reduction in the residual gradient artefact after AAS. Functional and anatomical MR data quality is not affected by the 4-cm shift, as the head remains in the homogeneous region of the static magnet field and gradients.
Authors:
Karen J Mullinger; Winston X Yan; Richard Bowtell
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2010-10-13
Journal Detail:
Title:  NeuroImage     Volume:  54     ISSN:  1095-9572     ISO Abbreviation:  Neuroimage     Publication Date:  2011 Feb 
Date Detail:
Created Date:  2010-12-21     Completed Date:  2011-03-31     Revised Date:  2013-07-03    
Medline Journal Info:
Nlm Unique ID:  9215515     Medline TA:  Neuroimage     Country:  United States    
Other Details:
Languages:  eng     Pagination:  1942-50     Citation Subset:  IM    
Copyright Information:
Copyright © 2010 Elsevier Inc. All rights reserved.
Affiliation:
Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, UK.
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MeSH Terms
Descriptor/Qualifier:
Algorithms
Artifacts*
Brain Mapping / methods
Computer Simulation
Electroencephalography / statistics & numerical data*
Humans
Image Processing, Computer-Assisted / methods*
Magnetic Resonance Imaging / statistics & numerical data*
Posture / physiology
Software
Grant Support
ID/Acronym/Agency:
G0901321//Medical Research Council; G0901321(46386)//Medical Research Council; G9900259//Medical Research Council
Comments/Corrections

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