Rapid computation of TMS-induced E-fields using a dipole-based magnetic stimulation profile approach

Area of Science:

• Neuroscience
• Biomedical Engineering
• Computational Electromagnetics

Background:

• Transcranial magnetic stimulation (TMS) neuronavigation aims for improved targeting and dosing.
• Current commercial TMS solutions utilize simplified approximations for electric field (E-field) calculations.
• Limitations exist in achieving accurate, real-time E-field visualization for TMS guidance.

Purpose of the Study:

• To develop a near real-time method for approximating TMS-induced E-fields.
• To utilize subject-specific, high-resolution, surface-based head models for accurate TMS navigation.
• To enhance the precision of TMS targeting and dosing through improved E-field approximation.

Main Methods:

• A Magnetic Stimulation Profile (MSP) approach using magnetic dipoles on a surface enclosing an MRI-based head model.
• Basis functions were defined for incident and total E-fields.
• Near real-time computation achieved by relating total E-field to incident E-field and conductivity boundaries.

Main Results:

• The MSP approximation showed high agreement with an established TMS solver.
• E-field amplitude error was approximately 5%, with spatial distribution correlation >98%.
• E-field computation on a 120k facet cortical surface mesh took ~100 ms.

Conclusions:

• The MSP approximation method offers numerical accuracy and speed.
• Suitable for interactive planning, targeting, dosing, and visualization of intracranial E-fields.
• Enables near real-time guidance for TMS coil positioning.