Spatially-selective excitation using tailored B-fields generated by a TMS coil for causal brain mapping applications

Motivation: MRI-compatible multichannel Transcranial Magnetic Stimulation (mTMS) arrays are being developed to enable concurrent stimulation and imaging. These coils can also be utilized as "miniature gradient coils" to perform signal encoding. Goal(s): We employed the TMS coils to perform selective excitation to avoid SAR trade-offs associated with traditional zoomed imaging. Approach: The MRI-compatible coils were coupled with custom-made low-power shim amplifiers. A 3D-GRE using an RF frequency offset without slab-selection was deployed with the TMS coil to enable spatial selection. Results: We demonstrate the capability of exciting target ROI using the hybrid TMS/MRI array and show sharp profiles without using SAR-intense zoom pulses. Impact: TMS coils can be utilized to reduce the field of view by exciting the part of the brain targeted only. This may offer improved capabilities for mapping of the TMS-induced brain activation more accurately.