Image artifacts in concurrent transcranial magnetic stimulation (TMS) and fMRI caused by leakage currents: Modeling and compensation
Article first published online: 22 APR 2009
Copyright © 2009 Wiley-Liss, Inc.
Journal of Magnetic Resonance Imaging
Volume 29, Issue 5, pages 1211–1217, May 2009
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
- Issue published online: 22 APR 2009
- Article first published online: 22 APR 2009
- Manuscript Accepted: 4 FEB 2009
- Manuscript Received: 25 OCT 2008
- Wellcome Trust supports the Wellcome Trust Centre for Neuroimaging
- Wellcome Trust Programme
- Medical Research Council (MRC)
- Royal Society-Leverhulme Trust Senior Research Fellowship
- transcranial magnetic stimulation;
- functional magnetic resonance imaging;
- MR artifacts;
- leakage current
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.
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.
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.