Electric field depth–focality tradeoff in transcranial magnetic stimulation: simulation comparison of 50 coil designs

By Zhi-De Deng, Sarah H. Lisanby, Angel V. Peterchev. Brain Stimulation, 2012

942 citations recorded by the source corpus.

Background Various transcranial magnetic stimulation (TMS) coil designs are available or have been proposed. However, key coil characteristics such as electric field focality and attenuation in depth have not been adequately compared. Knowledge of the coil focality and depth characteristics can help TMS researchers and clinicians with coil selection and interpretation of TMS studies. Objective To quantify the electric field focality and depth of penetration of various TMS coils. Methods The electric field distributions induced by 50 TMS coils were simulated in a spherical human head model using the finite element method. For each coil design, we quantified the electric field penetration by the half-value depth, d1/2, and focality by the tangential spread, S1/2, defined as the half-value volume (V1/2) divided by the half-value depth, S1/2 = V1/2/d1/2. Results The 50 TMS coils exhibit a wide range of electric field focality and depth, but all followed a depth–focality tradeoff: coils with larger half-value depth cannot be as focal as more superficial coils. The ranges of achievable d1/2 are similar between coils producing circular and figure-8 electric field patterns, ranging 1.0–3.5 cm and 0.9–3.4 cm, respectively. However, figure-8 field coils are more focal, having S1/2 as low as 5 cm2 compared to 34 cm2 for circular field coils. Conclusions For any coil design, the ability to directly stimulate deeper brain structures is obtained at the expense of inducing wider electrical field spread. Novel coil designs should be benchmarked against comparison coils with consistent metrics such as d1/2 and S1/2.

Subfields: Biophysics, Neurology, Radiology, Nuclear Medicine and Imaging

View Paper: https://www.semanticscholar.org/paper/0d15c9ff58443c564c84f1ab21732d1f52b7cf6a

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Citations in the corpus

Safety and recommendations for TMS use in healthy subjects and patient populations, with updates on training, ethical and regulatory issues: Expert Guidelines (2020, positive): “Several of these studies have used randomized double-blinded controlled trials to compare the side effects of ECT versus MST (Fitzgerald et al., 2013; Kayser et al., 2011; Lisanby et al., 2003).”
Safety of transcranial Direct Current Stimulation: Evidence Based Update 2016 (2016, background): “However, in contrast to TMS, electric fields produced by tDCS in the brain are static not pulsed, and are two orders of magnitude below those employed in rTMS [12], [147].”
Identification of reproducible individualized targets for treatment of depression with TMS based on intrinsic connectivity (2012, neutral): “It is important to note that accurately modeling the volume of TMS-induced changes in neuronal activity is complicated and depends on the specific stimulation coil, intensity, coil orientation, underlying anatomy, and assumed neuronal depolarization function (Deng et al., 2012; Wagner et al., 2007).”
Temporal Interference Stimulation Enhances Neural Regeneration (2026, unknown): “However, the use of these modalities induces stronger stimulation of the overlying cortical areas, pushing the limits of safety guidelines [ 45 ] and making the spatial precision of DBS a key feature to target cell transplants and neurogenic niches.”
A guide for concurrent TMS-fMRI to investigate functional brain networks (2022, background): “Transcranial magnetic stimulation (TMS) allows for direct causal manipulation of the cerebral cortex by inducing an electric field in a focal region of the brain near the scalp (Thielscher et al., 2011; Deng et al., 2013; Siebner et al., 2022).”
Working Memory and Transcranial-Alternating Current Stimulation—State of the Art: Findings, Missing, and Challenges (2022, background): “, 2015; Reinhart and Nguyen, 2019) with minimal side effects (Thut et al., 2011b; Deng et al., 2013) and reduce the heterogeneity of results due to the inter-individual variability (section “tACS and Working Memory”).”