J Korean Soc Magn Reson Med.  2013 Sep;17(3):169-180. 10.13104/jksmrm.2013.17.3.169.

A System for Concurrent TMS-fMRI and Evaluation of Imaging Effects

• Kim JC
• Kyeong S
• Lee JD
• Park HJ

• KMID: 2206915
• DOI: http://doi.org/10.13104/jksmrm.2013.17.3.169

Abstract

PURPOSE
The purpose of this study was to setup a concuurent transcranial magnetic stimulation (TMS)-functional MRI (fMRI) system for understanding causality of the functional brain network.
MATERIALS AND METHODS
We manufactured a TMS coil holder using nonmagnetic polyether ether ketone (PEEK). We simulated magnetic field distributions in the MR scanner according to TMS coil positions and angles. To minimize image distortions caused by TMS application, we controlled fMRI acquisition and TMS sequences to trigger TMS during inter-volume intervals.
RESULTS
Simulation showed that the magnetic field below the center of the coil was dramatically decreased with distance. Through the MR phantom study, we confirmed that TMS application around inter-volume acquisition time = 100 miliseconds reduced imaging distortion. Finally, the applicability of the concurrent TMS-fMRI was tested in preliminary studies with a healthy subject conducting a motor task within TMS-fMRI and passive motor movement induced by TMS in fMRI.
CONCLUSION
In this study, we confirmed that the developed system allows use of TMS inside an fMRI system, which would contribute to the research of brain activation changes and causality in brain connectivity.

Keyword

TMS; Concurrent TMS-fMRI

MeSH Terms

Brain
Ether, Ethyl
Magnetic Fields
Magnetic Resonance Imaging
Transcranial Magnetic Stimulation
Ether, Ethyl

Figure

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  Fig. 1 MR compatible figure-eight coil a. Magnetic field induced by transcranial magnetic stimulation (TMS) figure-eight coil. Red area is focal point of induced magnetic field. b. Specification of the figure-eight coil

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  Fig. 2 TMS coil holder. a. 3D graphic design of the prototype. b. TMS coil holder made from PEEK and polymer composites.

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  Fig. 3 (a) Task paradigm and (b) triggering system. a. The visual cue-based voluntary hand movement and concurrent TMS pulse. These voluntary hand movement and single shot TMS pulses are not periodic but randomly distributed. b. A scheme of a pilot study of concurrent TMS-fMRI experiment using our own TMS coil holder. Triggering system is based on TR signal from the MR scanner and E-prime software for minimizing TMS-induced artifact during interleaved experiment.

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  Fig. 4 (a) MR compatible coil holder setup and (b) neuronavigation system. a. MR-compatible holder setup for the MR phantom and healthy subject tasks. b. Neuronavigator (Brainsight2) guides the motor region. Activation map obtained from a simple motor task was overlaid on top of the individual's own structural image.

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  Fig. 5 Distribution of magnetic field induced by figure-eight coil and depending on distance from the coil: (a) at z=1 mm; (b) at z=10 mm; (c) at z=20 mm; (d) at z=30 mm. First and second column show the strength of magnetic field by color on x-y plane. The third column presents the magnetic field induced by every coil inside of the figure-eight coil Red spot is the most focused area.

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  Fig. 6 Distributions of TMS induced magnetic field - temporal dependency. The distribution of magnetic field induced by TMS coil (red curve) and summation of MR magnetic field (arrows in the yellow box): (a) TMS coil is perpendicular to the MR magnetic field; (b) -30 degree rotation; (c) +30 degree rotation.

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  Fig. 7 MR phantom EPI data. (a) without TMS coil, (b) with TMS shot, (c) 100ms after TMS shot and (d) difference between image (b) and (c). White arrows indicate positions of TMS coil. There is no image distortion in the absence of the TMS coil. A single shot TMS during scanning distorts the B0 field and disturbs EPI. This disturbance persists for at least 100 ms. The bottom image was acquired with optimized MR sequence and triggering system. There is no image distortion in the absence of the TMS coil.

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  Fig. 8 Activation maps during the task Activation maps of effects of (a) voluntary hand movement and (b) TMS (uncorrected p < 0.001)

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