Conducting interslice stimulation for concurrent TMS-fMRI.

Area of Science:

• Neuroimaging
• Neuroscience
• Biomedical Engineering

Background:

• Concurrent Transcranial Magnetic Stimulation (TMS) and functional Magnetic Resonance Imaging (fMRI) enable causal inference in brain-behavior relationships.
• TMS pulses can introduce artifacts into fMRI data, necessitating artifact mitigation strategies.
• Interslice TMS-fMRI, where TMS pulses are delivered during MRI slice acquisition gaps, offers a potential solution.

Purpose of the Study:

• To provide guidance on the required interslice gap for artifact-free TMS-fMRI.
• To develop a framework and code for researchers to test their TMS-fMRI protocols.
• To quantify the impact of TMS pulses on fMRI data quality.

Main Methods:

• TMS-fMRI data were collected using a Siemens 3T Prismafit scanner with a multiband sequence (factor=2).
• Signal dropout and temporal signal-to-noise ratio were quantified using a spherical phantom with TMS pulses delivered at varying timings relative to slice excitation (-100 ms to +100 ms).
• Experiments included interslice gaps of 37.5 ms/100 ms, up to 3 pulses per volume, and TMS-dedicated surface coils, with a subset repeated on a human participant.

Main Results:

• Minimal fMRI data contamination was observed when TMS pulses were applied at least -20 ms/ +50 ms from slice excitation.
• The interslice TMS-fMRI approach was confirmed to be compatible with 10 Hz TMS.
• Data quality was influenced by stimulator intensity, slice orientation, and the number of TMS pulses.

Conclusions:

• A 10 Hz TMS interslice protocol is viable with minimal data contamination.
• Stimulation frequencies exceeding 10 Hz would necessitate shorter interslice gaps or slice acquisition times.
• Researchers must consider stimulator intensity, slice orientation, and pulse number for optimal TMS-fMRI protocol design.