Design of Mechanical Durable TMS Coils for Safe Operation in High-Field MRI Environments

<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Objective:</i> Interleaving transcranial magnetic stimulation with magnetic resonance imaging (TMS–MRI) is a promising tool for neuroscience. However, its development is limited by the strong interactions between the TMS current pulse and the high magnetic field present within the MRI environment. The objective of this study is to develop methodologies for designing TMS coils that can operate safely inside MRI scanners. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Methods:</i> By using an inverse boundary element method design framework, we study the effects of controlling different norms of the Lorentz force in the design process to produce more durable TMS coils. We apply this method to design rodent–specific TMS coils capable of withstanding the high static magnetic fields present in small animal MRI scanners. The performance of the proposed TMS coils is validated under realistic simulations using practical coil plate materials and pulses in the COMSOL Multiphysics software. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Results:</i> The numerical simulations indicate that minimising the maximum magnitude (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$l^{\infty}$</tex-math></inline-formula> norm) of the Lorentz force distribution produces TMS coils with improved mechanical behaviour when operating within an MRI environment. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Significance:</i> The proposed design strategy offers an effective solution for producing TMS coils with enhanced mechanical durability. This improvement may be particularly valuable to address the current challenges faced in interleaved TMS–MRI applications.