3D-printed stand, timing interface, and coil localization tools for concurrent TMS-fMRI experiments

TL;DR

This paper introduces affordable, customizable tools including a 3D-printed stand, precise timing interface, and coil localization software to improve the reliability and accuracy of concurrent TMS-fMRI experiments.

Contribution

The authors present novel, cost-effective hardware and software solutions that address key challenges in implementing concurrent TMS-fMRI, enhancing precision and stability.

Findings

Enhanced coil positioning accuracy and stability.

Timing precision with under 1 ms variance.

Tools are freely available and easy to implement.

Abstract

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.