Database of 25 validated coil models for electric field simulations for TMS

Area of Science:

• Neuroscience
• Biomedical Engineering
• Medical Physics

Background:

• Transcranial magnetic stimulation (TMS) efficacy relies on coil design, leading to variable stimulation properties across vendors.
• Inconsistent coil characteristics hinder the comparability of TMS study results.

Purpose of the Study:

• To systematically compare commercial TMS coils for focality, stimulation depth, and efficacy.
• To provide validated coil models for accurate electric field simulations.

Main Methods:

• Magnetic vector potentials of 25 commercial TMS coils were reconstructed from magnetic field measurements.
• Electric fields were simulated in a spherical head model using reconstructed potentials.
• Motor thresholds were estimated using simulated fields, pulse waveforms, and a neural membrane model.

Main Results:

• A trade-off between coil focality and relative stimulation depth was confirmed.
• Peak field strength and estimated motor thresholds showed weak correlation with focality and depth, requiring further investigation.

Conclusions:

• Comprehensive characterization enables objective comparison of TMS coils from different vendors.
• Provided models and data support SimNIBS simulations, aiding informed coil selection and reducing uncertainty in TMS applications.