Sound comparison of seven TMS coils at matched stimulation strength

Lari M Koponen,Stefan M Goetz,Debara L Tucci,Angel V Peterchev

doi:10.1016/j.brs.2020.03.004

Lari M Koponen, Stefan M Goetz + Show 2 more

Open Access

https://doi.org/10.1016/j.brs.2020.03.004

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Journal: Brain Stimulation	Publication Date: Mar 12, 2020
Citations: 34	License type: cc-by

Affiliation: Duke University

Abstract

BackgroundAccurate data on the sound emitted by transcranial magnetic stimulation (TMS) coils is lacking. MethodsWe recorded the sound waveforms of seven coils with high bandwidth. We estimated the neural stimulation strength by measuring the induced electric field and applying a strength–duration model to account for different waveforms. ResultsAcross coils, at maximum stimulator output and 25 cm distance, the sound pressure level (SPL) was 98–125 dB(Z) per pulse and 76–98 dB(A) for a 20 Hz pulse train. At 5 cm distance, these values were estimated to increase to 112–139 dB(Z) and 90–112 dB(A), respectively. ConclusionsThe coils’ airborne sound can exceed some exposure limits for TMS subjects and, in some cases, for operators. These findings are consistent with the current TMS safety guidelines that recommend the use of hearing protection.

Highlights

Transcranial magnetic stimulation (TMS) activates cortical neurons by electromagnetically inducing an electric field (E-field) pulse with a coil placed on the subject’s scalp
Specific stimulatorecoil combinations have been evaluated with hearing safety measurements [6,7], and a comparison between coils has been published [2,12]. We extend this previous work by quantifying the impulse characteristics of the airborne transcranial magnetic stimulation (TMS) sound and comparing the measurements of seven coils at normalized stimulation strengths
The peak E-field at 100% MSO varied between 140 and 260 V/m across the tested coils, and it had nearly linear relationship to the stimulator output setting for all coils (Fig. 1A)

Summary

Introduction

Transcranial magnetic stimulation (TMS) activates cortical neurons by electromagnetically inducing an electric field (E-field) pulse with a coil placed on the subject’s scalp. The sound pulse can potentially cause hearing loss [3,4]. This risk can be mitigated with adequate hearing protection [5e7]. Accurate data on the sound emitted by transcranial magnetic stimulation (TMS) coils is lacking. Conclusions: The coils’ airborne sound can exceed some exposure limits for TMS subjects and, in some cases, for operators. These findings are consistent with the current TMS safety guidelines that recommend the use of hearing protection

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Results

Discussion

Conclusion