Optimization, implementation, and performance of TMS coils with maximum focality and various stimulation depths

Area of Science:

• Neuroscience
• Biomedical Engineering
• Medical Devices

Background:

• Conventional transcranial magnetic stimulation (TMS) coils produce diffuse electric fields (E-fields), limiting spatial targeting precision.
• Previous theoretical work established a methodology for designing TMS coils with maximal focality and minimal energy requirements.

Purpose of the Study:

• To practically design, implement, and characterize novel focal-deep TMS (fdTMS) coils based on theoretical optimization.
• To evaluate the focality, energy efficiency, and practical performance of fdTMS coils compared to conventional designs.

Main Methods:

• Designed a curved 'hat' former and optimized partial-multi-layer windings to enhance energy efficiency and coil placement flexibility.
• Utilized spherical and realistic head models for electromagnetic simulations to benchmark fdTMS E-field focality and energy requirements.
• Implemented prototype fdTMS coils and conducted experimental validation using robotic probes and human motor mapping studies.

Main Results:

• Simulations and robotic measurements confirmed a more compact E-field generated by fdTMS coils compared to conventional figure-8 coils.
• Human subject testing demonstrated improved focality with fdTMS coils, albeit with increased E-field spread and heating due to design constraints.
• fdTMS coils showed enhanced precision for motor mapping applications.

Conclusions:

• The developed fdTMS coils offer improved spatial targeting for TMS applications.
• The design framework provides a foundation for future optimization of TMS coils for precise brain mapping and therapeutic interventions.