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Image artifacts in concurrent transcranial magnetic stimulation (TMS) and fMRI caused by leakage currents: Modeling and compensation

  1. Nikolaus Weiskopf PhD1,*,
  2. Oliver Josephs MSc1,
  3. Christian C. Ruff PhD1,2,
  4. Felix Blankenburg MD1,2,3,
  5. Eric Featherstone BSc1,
  6. Anthony Thomas BSc4,
  7. Sven Bestmann PhD1,5,
  8. Jon Driver DPhil1,2,
  9. Ralf Deichmann PhD1,6

Article first published online: 22 APR 2009

DOI: 10.1002/jmri.21749

Issue

Journal of Magnetic Resonance Imaging

Journal of Magnetic Resonance Imaging

Volume 29, Issue 5, pages 1211–1217, May 2009

Additional Information

How to Cite

Weiskopf, N., Josephs, O., Ruff, C. C., Blankenburg, F., Featherstone, E., Thomas, A., Bestmann, S., Driver, J. and Deichmann, R. (2009), Image artifacts in concurrent transcranial magnetic stimulation (TMS) and fMRI caused by leakage currents: Modeling and compensation. J. Magn. Reson. Imaging, 29: 1211–1217. doi: 10.1002/jmri.21749

Author Information

  1. 1

    Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London, London, United Kingdom

  2. 2

    UCL Institute of Cognitive Neuroscience, University College London, London, United Kingdom

  3. 3

    Department of Neurology and Bernstein Center for Computational Neuroscience, Charité, Berlin, Germany

  4. 4

    The Magstim Company Limited, Whitland, Wales, United Kingdom

  5. 5

    Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, University College London, London, United Kingdom

  6. 6

    University Hospital, Brain Imaging Center, Frankfurt, Germany

*Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London, London, WC1N 3BG UK

Publication History

  1. Issue published online: 22 APR 2009
  2. Article first published online: 22 APR 2009
  3. Manuscript Accepted: 4 FEB 2009
  4. Manuscript Received: 25 OCT 2008

Funded by

  • Wellcome Trust supports the Wellcome Trust Centre for Neuroimaging
  • Wellcome Trust Programme
  • Medical Research Council (MRC)
  • Royal Society-Leverhulme Trust Senior Research Fellowship

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Keywords:

  • transcranial magnetic stimulation;
  • TMS;
  • functional magnetic resonance imaging;
  • fMRI;
  • MR artifacts;
  • leakage current

Abstract

Purpose

To characterize and eliminate a new type of image artifact in concurrent transcranial magnetic stimulation and functional MRI (TMS-fMRI) caused by small leakage currents originating from the high-voltage capacitors in the TMS stimulator system.

Materials and Methods

The artifacts in echo-planar images (EPI) caused by leakage currents were characterized and quantified in numerical simulations and phantom studies with different phantom-coil geometries. A relay-diode combination was devised and inserted in the TMS circuit that shorts the leakage current. Its effectiveness for artifact reduction was assessed in a phantom scan resembling a realistic TMS-fMRI experiment.

Results

The leakage-current-induced signal changes exhibited a multipolar spatial pattern and the maxima exceeded 1% at realistic coil-cortex distances. The relay-diode combination effectively reduced the artifact to a negligible level.

Conclusion

The leakage-current artifacts potentially obscure effects of interest or lead to false-positives. Since the artifact depends on the experimental setup and design (eg, amplitude of the leakage current, coil orientation, paradigm, EPI parameters), we recommend its assessment for each experiment. The relay-diode combination can eliminate the artifacts if necessary. J. Magn. Reson. Imaging 2009;29:1211–1217. © 2009 Wiley-Liss, Inc.

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