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Design of TMS coils with reduced Lorentz forces: application to concurrent TMS-fMRI
Clemente Cobos Sánchez1,2, Miguel Ruiz Cabello3, Ángel Quirós Olozábal1
1Departamento Ingeniería de Sistemas y Electrónica, Avenida de la Universidad, 10, E-11519, Puerto Real (Cádiz), Spain.
Journal of Neural Engineering
|February 13, 2020
Summary
This study presents a new method for designing transcranial magnetic stimulation (TMS) coils that reduces forces within MRI scanners. This innovation aims to overcome technical limitations for interleaved TMS-fMRI studies of brain connectivity.
Area of Science:
- Neuroimaging
- Biomedical Engineering
- Electromagnetism
Background:
- Interleaving transcranial magnetic stimulation (TMS) with functional Magnetic Resonance Imaging (fMRI) is a powerful technique for investigating human brain functional connectivity.
- Current technical limitations, particularly the interaction between TMS current pulses and MRI magnetic fields, hinder the development of interleaved TMS-fMRI.
- These interactions generate Lorentz forces that can compromise the mechanical stability and performance of TMS coils within the MRI environment.
Purpose of the Study:
- To present a novel TMS coil design methodology that incorporates control over Lorentz forces.
- To enhance the mechanical stability of TMS coils for use in conjunction with MRI scanners.
- To facilitate the advancement of interleaved TMS-fMRI techniques by addressing key technical challenges.
Main Methods:
- The study adapted an existing inverse boundary element method (IBEM) for TMS coil design.
- New electromagnetic computational models were integrated to specifically account for and control Lorentz forces during the coil design process.
- The method was applied to design and simulate TMS coils on various surfaces, including rectangular flat, spherical, and hemispherical.
Main Results:
- The developed TMS coil design method successfully produced coils with reduced Lorentz forces within the static magnetic field of an MRI scanner.
- Simulations demonstrated improved mechanical stability for TMS coils designed using this approach.
- A trade-off was observed, where reducing Lorentz forces impacted other coil performance parameters.
Conclusions:
- The proposed coil design approach offers an effective tool for creating TMS stimulators with enhanced mechanical stability across diverse coil geometries.
- This methodology is crucial for overcoming existing limitations in interleaved TMS-fMRI.
- The ability to control Lorentz forces paves the way for more robust and reliable combined TMS-fMRI investigations of brain function.
