Abstract
The simultaneous transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) offers a unique opportunity to non-invasively stimulate brain circuits while simultaneously monitoring changes in brain activity. However, to take advantage of this multimodal technique, some technical issues need to be considered/addressed. In this work, we evaluated technical issues associated with the setup and utilization of this multimodal tool, such as the use of a large single-channel radio frequency (rf) coil, and the artifacts induced by TMS when interleaved with the echo-planar imaging (EPI) sequence. We demonstrated that good image quality can be achieved with this rf coil and that the adoption of axial imaging orientation in conjunction with a safe interval of 100 ms, between the TMS pulse and imaging acquisition, is a suitable combination to eliminate potential image artifacts when using the combined TMS-fMRI technique in 3-T MRI scanners.
Highlights
The concurrent transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging provides a non-invasive method for real-time evaluation of neuronal activity induced by TMS
A full assessment on passive and active image artifacts induced by TMS have been previously reported (Bestmann et al, 2003a), in which one of the first MRI compatible TMS coils, developed by Magstim, was used, and images were acquired on a 2-T scanner
A small decrease in tSNR for dt = 50 ms [low-frequency and high-frequency (5–10 Hz pulses/image)] was observed, with nearly no tSNR change for dt ≥ 100 ms, compared with the baseline, all observed tSNR differences were within the dispersion of the tSNR values inside the ROI (Figure 2H)
Summary
The concurrent transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) provides a non-invasive method for real-time evaluation of neuronal activity induced by TMS. A full assessment on passive (presence of a TMS coil) and active (during magnetic stimulation) image artifacts induced by TMS have been previously reported (Bestmann et al, 2003a), in which one of the first MRI compatible TMS coils, developed by Magstim, was used, and images were acquired on a 2-T scanner. New MRI-compatible TMS coils have been developed, 3-T scanners have become the primary imaging research tool, and imaging software and hardware have advanced significantly in recent years; only brief assessments have been reported lately on either passive (Bungert et al, 2012; Navarro de Lara et al, 2017) or Simultaneous TMS-fMRI: Technical Implementation Aspects active (Navarro de Lara et al, 2017) TMS-induced image artifacts. A comprehensive evaluation on the use of this multimodal tool in its current state is needed
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