Comparison of MR coil options for concurrent TMS-fMRI

Abstract Concurrent transcranial magnetic stimulation (TMS) with functional magnetic resonance imaging (fMRI) is increasingly being used to study how TMS affects neural processing in local and remote connected brain regions. However, there are many technical challenges that arise when operating this unique combination of techniques. One such challenge is MR head coil compatibility and the image resolution that can be achieved. Here we compare the temporal-signal-to noise-ratio (tSNR) between 3 different MR head coils that can be used with TMS. We show that the 7-channel TMS-dedicated surface coils result in a very high tSNR directly under the TMS and the supplementary coil in comparison to the TxRx and the Magnetica. However, there is low tSNR elsewhere. This field inhomogeneity may not be suitable for all research questions, for example where the aim is to look at distributed neural responses. In these cases, an MR coil with a more homogeneous tSNR such as the Magnetica, may be more appropriate.