Design of transcranial magnetic stimulation coils with optimal trade-off between depth, focality, and energy. (25th June 2018)

• Record Type: Journal Article
• Authors: Gomez, Luis J; Goetz, Stefan M; Peterchev, Angel V
• Is Part Of: Journal of neural engineering. Volume 15:Number 4(2018:Aug.)
• Publication Date: 2018-06-25
• Subjects: transcranial magnetic stimulation (TMS) -- coil -- focal -- deep -- minimum energy -- integer linear programming optimization; Neurosciences -- Periodicals; Biomedical engineering -- Periodicals; 612.8
• DOI: 10.1088/1741-2552/aac967
• Languages: English
• ISSNs: 1741-2560

Abstract

Abstract: Objective . Transcranial magnetic stimulation (TMS) is a noninvasive brain stimulation technique used for research and clinical applications. Existent TMS coils are limited in their precision of spatial targeting (focality), especially for deeper targets. This paper presents a methodology for designing TMS coils to achieve optimal trade-off between the depth and focality of the induced electric field (E-field), as well as the energy required by the coil. Approach . A multi-objective optimization technique is used for computationally designing TMS coils that achieve optimal trade-offs between E-field focality, depth, and energy (fdTMS coils). The fdTMS coil winding(s) maximize focality (minimize the volume of the brain region with E-field above a given threshold) while reaching a target at a specified depth and not exceeding predefined peak E-field strength and required coil energy. Spherical and MRI-derived head models are used to compute the fundamental depth–focality trade-off as well as focality–energy trade-offs for specific target depths. Main results . Across stimulation target depths of 1.0–3.4 cm from the brain surface, the suprathreshold volume can be theoretically decreased by 42%–55% compared to existing TMS coil designs. The suprathreshold volume of a figure-8 coil can be decreased by 36%, 44%, or 46%, for matched, doubled, or quadrupled energy. For matched focality and energy, the depth of a figure-8 coil can be increased by 22%. Significance . Computational design of TMS coils could enable more selective targeting of the induced E-field. The presented results appear to be the first significant advancement in the depth–focality trade-off of TMS coils since the introduction of the figure-8 coil three decades ago, and likely represent the fundamental physical limit.