Artifacts caused by transcranial magnetic stimulation coils and EEG electrodes in T2∗-weighted echo-planar imaging

Abstract

We investigated the effects of transcranial magnetic stimulation (TMS) coils and electroencephalographic (EEG) electrodes on T2∗-weighted echo-planar images (EPI) at 2.0 T (gradient-echo EPI, mean TE = 53 ms, 2 × 2 × 4 mm3). In comparison with anatomic gradient-echo images (3D FLASH, TE = 4 ms, 1 × 1 × 1 mm3), T2∗-weighted EPI acquisitions of a water-filled spherical phantom revealed severe signal losses and geometric distortions in the vicinity of TMS coils. Even remote effects were observed for image orientations perpendicular to the coil plane. EEG electrodes and the fixation gel caused milder localized distortions. In humans, complications were avoided by the large distance between the TMS coil and the cortical surface and when using an EPI orientation parallel to the plane of the coil. It is concluded that T2∗-weighted EPI studies of human brain function may be performed without distortions caused by TMS coils and EEG electrodes.