2009/04/22 by Nikolaus Weiskopf, Oliver Josephs, Christian C. Ruff +6 · 2 citations
Medicine · Neuroscience · #Advanced MRI Techniques and Applications #Functional Brain Connectivity Studies #Transcranial Magnetic Stimulation Studies
paper · pdf · doi:10.1002/jmri.21749
openalex publication_date 2009/04/22 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/29
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.