Sound comparison of seven TMS coils at matched stimulation strength

• Published in: Brain stimulation Vol. 13; no. 3; pp. 873 - 880
• Main Authors: Koponen, Lari M., Goetz, Stefan M., Tucci, Debara L., Peterchev, Angel V.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.05.2020; Elsevier
• Subjects: Coil click; Female; Hearing - physiology; Hearing safety; Humans; Male; Sound; Stimulation strength; TMS; Transcranial magnetic stimulation; Transcranial Magnetic Stimulation - methods; Transcranial Magnetic Stimulation - standards; Stimulation strength; Sound; Transcranial magnetic stimulation; TMS; Hearing safety; Coil click
• ISSN: 1935-861X; 1876-4754; 1876-4754
• DOI: 10.1016/j.brs.2020.03.004

Accurate data on the sound emitted by transcranial magnetic stimulation (TMS) coils is lacking. We 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. Across 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. 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. •Coil click varies by over 20 dB between TMS coils at matched stimulation strength.•Close to a TMS coil, airborne sound pressure level may reach nearly 140 dB(Z).•During rTMS, continuous airborne sound level may exceed 110 dB(A).•Sound level of rTMS may exceed some standard safety limits for both subject and operator.