New coil positioning method for interleaved transcranial magnetic stimulation (TMS)/functional MRI (fMRI) and its validation in a motor cortex study

Purpose

To develop and test a novel method for coil placement in interleaved transcranial magnetic stimulation (TMS)/functional MRI (fMRI) studies.

Materials and Methods

Initially, a desired TMS coil position at the subject's head is recorded using a neuronavigation system. Subsequently, a custom‐made holding device is used for coil placement inside the MR scanner. The parameters of the device corresponding to the prerecorded position are automatically determined from a fast structural image acquired directly before the experiment. The spatial accuracy of our method was verified on a phantom. Finally, in a study on five subjects, the coil was placed above the cortical representation of a hand muscle in M1 and the blood oxygenation level‐dependent (BOLD) responses to short repetitive TMS (rTMS) trains were assessed using echo‐planar imaging (EPI) recordings.

Results

The spatial accuracy of our method is in the range of 2.9 ± 1.3 (SD) mm. Motor cortex stimulation resulted in robust BOLD activations in motor‐ and auditoryrelated brain areas, with the activation in M1 being localized in the hand knob.

Conclusion

We present a user‐friendly method for TMS coil positioning in the MR scanner that exhibits good spatial accuracy and speeds up the setup of the experiment. The motor‐cortex study proves the viability of the approach and validates our interleaved TMS/fMRI setup. J. Magn. Reson. Imaging 2009;29:189–197. © 2008 Wiley‐Liss, Inc.