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Clin Neurophysiol. 2004 Sep;115(9):2181-92.

Removal of time-varying gradient artifacts from EEG data acquired during continuous fMRI.

Author information

  • 1Department of Diagnostic Radiology, Yale University School of Medicine, P.O. Box 208043, TAC Building MRRC Rm. N128, New Haven, CT 06520-8043, USA. michiro.negishi@yale.edu

Abstract

OBJECTIVE:

Recording low amplitude electroencephalography (EEG) signals in the face of large gradient artifacts generated by changing functional magnetic resonance imaging (fMRI) magnetic fields continues to be a challenge. We present a new method of removing gradient artifacts with time-varying waveforms, and evaluate it in continuous (non-interleaved) simultaneous EEG-fMRI experiments.

METHODS:

The current method consists of an analog filter, an EEG-fMRI timing error correction algorithm, and a temporal principal component analysis based gradient noise removal algorithm. We conducted a phantom experiment and a visual oddball experiment to evaluate the method.

RESULTS:

The results from the phantom experiment showed that the current method reduced the number of averaged samples required to obtain high correlation between injected and recovered signals, compared to a conventional average waveform subtraction method with adaptive noise cancelling. For the oddball experiment, the results obtained from the two methods were very similar, except that the current method resulted in a higher P300 amplitude when the number of averaged trials was small.

CONCLUSIONS:

The current method enabled us to obtain high quality EEGs in continuous simultaneous EEG-fMRI experiments.

SIGNIFICANCE:

Continuous simultaneous EEG-fMRI acquisition enables efficient use of data acquisition time and better monitoring of rare EEG events.

PMID:
15294222
[PubMed - indexed for MEDLINE]
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