A 3-axis coil design for multichannel TMS arrays.

Area of Science:

• Neuroscience
• Biomedical Engineering
• Medical Devices

Background:

• Multichannel transcranial magnetic stimulation (mTMS) allows for simultaneous or sequential stimulation at multiple brain sites.
• Current mTMS systems often require complex coil repositioning.
• Novel coil designs are needed to enhance the efficiency and scalability of mTMS arrays.

Purpose of the Study:

• To design and characterize a modular 3-axis TMS coil for use in large-scale mTMS arrays.
• To evaluate the coil's performance, including magnetic field generation, cooling efficiency, and element coupling.
• To assess the suitability of the 3-axis coil for effective brain stimulation.

Main Methods:

• Fabrication of a modular 3-axis TMS coil.
• Measurement of induced magnetic field (dB/dt) using a custom stimulator.
• Thermal performance assessment via temperature measurements.
• Inductance measurements to quantify mutual and self-coupling between coil elements.
• Electromagnetic simulations for stimulation intensity and focality analysis.

Main Results:

• Experimental dB/dt values validated computational models, confirming coil and stimulator functionality.
• The integrated air-cooling system effectively managed heat during various stimulation protocols.
• Electromagnetic simulations indicated comparable stimulation intensity to conventional TMS coils.
• Measured and calculated coil coupling between elements was minimal (< 3.4%).

Conclusions:

• A novel, air-cooled 3-axis TMS coil suitable for mTMS arrays was successfully developed and characterized.
• The coil's design meets specifications, with negligible inductive coupling between elements.
• The 3-axis coil is a promising component for advancing multichannel TMS technology.