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Identifying the sources of the pulse artefact in EEG recordings made inside an MR scanner

Mullinger, Karen J.; Havenhand, Jade; Bowtell, Richard W.

Authors

Karen J. Mullinger karen.mullinger@nottingham.ac.uk

Jade Havenhand

Richard W. Bowtell richard.bowtell@nottingham.ac.uk



Abstract

EEG recordings made during concurrent fMRI are confounded by the pulse artefact (PA), which although smaller than the gradient artefact is often more problematic because of its variability over multiple cardiac cycles. A better understanding of the PA is needed in order to generate improved methods for reducing its effect in EEG-fMRI experiments. Here we performed a study aimed at identifying the relative contributions of three putative sources of the PA (cardiac-pulse-driven head rotation, the Hall effect due to pulsatile blood flow and pulse-driven expansion of the scalp) to its amplitude and variability. EEG recordings were made from 6 subjects lying in a 3T scanner. Accelerometers were fixed on the forehead and temple to monitor head motion. A bite-bar and vacuum cushion were used to restrain the head, thus greatly attenuating the contribution of cardiac-driven head rotation to the PA, while an insulating layer placed between the head and the EEG electrodes was used to eliminate the Hall voltage contribution. Using the root mean square (RMS) amplitude of the PA averaged over leads and time as a measure of the PA amplitude, we found that head restraint and insulating layer reduced the PA by 61% and 42%, respectively, when compared with the PA induced with the subject relaxed, indicating that cardiac-pulse-driven head rotation is the dominant source of the PA. With both the insulating layer and head restraint in place, the PA was reduced in RMS amplitude by 78% compared with the relaxed condition, the remaining PA contribution resulting from scalp expansion or residual head motion. The variance of the PA across cardiac cycles was more strongly reduced by the insulating layer than the head restraint, indicating that the flow-induced Hall voltage makes a larger contribution than pulse-driven head rotation to the variability of the PA.

Journal Article Type Article
Publication Date May 1, 2013
Journal NeuroImage
Print ISSN 1053-8119
Electronic ISSN 1053-8119
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 71
Issue 1
APA6 Citation Mullinger, K. J., Havenhand, J., & Bowtell, R. W. (2013). Identifying the sources of the pulse artefact in EEG recordings made inside an MR scanner. NeuroImage, 71(1), doi:10.1016/j.neuroimage.2012.12.070
DOI https://doi.org/10.1016/j.neuroimage.2012.12.070
Keywords EEG–fMRI, Pulse artefact, Artefact reduction
Publisher URL http://www.sciencedirect.com/science/article/pii/S1053811913000098
Copyright Statement Copyright information regarding this work can be found at the following address: http://creativecommons.org/licenses/by/4.0

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Copyright Statement
Copyright information regarding this work can be found at the following address: http://creativecommons.org/licenses/by/4.0





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