Abstract

Efforts to improve the effects transcranial magnetic stimulation (TMS) rely heavily on deciphering the underlying mechanisms. Neuroimaging has proven to be very useful in mapping the effects of TMS on brain activity at the systems level. It complements the knowledge, which can be gained from peripheral electrophysiology and behavioral measures. Neuroimaging methods are rapidly evolving, and the latest methodological and hardware developments allow achieving far more specific conclusions on the TMS effects. In this regard, magnetic resonance imaging (MRI) complements TMS in multiple ways:

(1) Anatomical images or fMRI acquired before TMS allows for structural/functional definition of stimulation targets (neuronavigation). (2) Offline imaging allows for the evaluation of lasting effects after TMS . (3) Finally, fMRI during TMS , i.e. concurrent TMS /fMRI measures the direct TMS -induced BOLD response.

However, classical TMS /fMRI setups based on large birdcage MR coils are characterised by low sensitivity at the stimulation target. Using an approach based on a dedicated multi-channel MR receive coil mounted underneath the MR-compatible TMS -coil, we show that it is possible to obtain high sensitivity functional imaging data that allows for assessing TMS -induced brain activity on an individual level. The new setup holds the advantage that image acceleration techniques like parallel imaging (GRAPPA, SENSE ) and multiband imaging (simultaneous multi-slice imaging, SMS ) can be used. Practical issues in applying this method and examples on how to overcome challenges including subject-motion will be discussed.