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      Identification of EEG events in the MR scanner: the problem of pulse artifact and a method for its subtraction.

      1 , , , ,
      NeuroImage
      Elsevier BV

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          Abstract

          Triggering functional MRI (fMRI) image acquisition immediately after an EEG event can provide information on the location of the event generator. However, EEG artifact associated with pulsatile blood flow in a subject inside the scanner may obscure EEG events. This pulse artifact (PA) has been widely recognized as a significant problem, although its characteristics are unpredictable. We have investigated the amplitude, distribution on the scalp, and frequency of occurrence of this artifact. This showed large interindividual variations in amplitude, although PA is normally largest in the frontal region. In five of six subjects, PA was greater than 50 microV in at least one of the temporal, parasagittal, and central channels analyzed. Therefore, we developed and validated a method for removing PA. This subtracts an averaged PA waveform calculated for each electrode during the previous 10 s. Particular attention has been given to reliable ECG peak detection and ensuring that the average PA waveform is free of other EEG artifacts. Comparison of frequency spectra for EEG recorded outside and inside the scanner, with and without PA subtraction, showed a clear reduction in artifact after PA subtraction for all four frequency ranges analyzed. As further validation, lateralized epileptiform spikes were added to recordings from inside and outside the scanner: PA subtraction significantly increased the proportion of these spikes that were correctly identified and decreased the number of false spike detections. We conclude that in some subjects, EEG/fMRI studies will be feasible only using PA subtraction.

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          Author and article information

          Journal
          Neuroimage
          NeuroImage
          Elsevier BV
          1053-8119
          1053-8119
          Oct 1998
          : 8
          : 3
          Affiliations
          [1 ] Department of Clinical Neurophysiology, The National Hospital for Neurology and Neurosurgery, Queen Square, London, UK.
          Article
          S1053-8119(98)90361-5
          10.1006/nimg.1998.0361
          9758737
          6748e7f9-3547-47a0-9a1d-18c8d89b1767
          Copyright 1998 Academic Press.
          History

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