  Concurrent TMS-fMRI involves administrating TMS while subjects are inside an
MRI scanner and allows the study of the effects of neurostimulation on
simultaneous brain activity. Despite its high promise, the technique has proven
challenging to implement for at least three reasons. First, it is difficult to
position and stabilize the TMS coil inside the MRI scanner in a way that
precisely targets a pre-specified brain region. Second, standard
task-presentation software suffers from imprecise timing, which can lead to TMS
causing large image artifacts. Third, it is difficult to verify the exact TMS
coil position during scanning. In this paper, we describe solutions to all
three of these challenges. First, we develop a 3D-printed TMS stand that is
fully adjustable and can reach most areas of the scalp. The stand is compatible
with various MR coils and features an adjustable mirror holder. Second, we
create an interface that can precisely time the TMS pulses with respect to the
fMRI image acquisition with a variance of under 1 ms. Third, we develop
software for precisely determining the TMS coil position inside the MRI scanner
and computing the location of maximal stimulation. All three tools are either
free or inexpensive. We provide detailed instructions for building and
implementing these tools to facilitate an efficient and reliable concurrent
TMS-fMRI setup.
