Abstract
Background Accurate data on the sound emitted by various transcranial magnetic stimulation (TMS) coils is lacking.
Methods We recorded the coil sound waveforms of seven coils. We estimated the neural stimulation strength by measuring the induced electric field and applying a strength–duration model to account for different waveforms.
Results At typical resting motor threshold (RMT), sound pressure level (SPL) at a distance of 25 cm varied 87– 111 dB(Z) across coils and the sound duration ranged 1–16 ms. At maximum stimulator output and 5-cm distance, SPL is estimated to be 110–139 dB(Z), and a 10-Hz-train of repetitive TMS (rTMS) would produce a continuous sound level of 87–109 dB(A).
Conclusions The sound of all tested coils was below, but near, relevant safety limits. The safety standards may be inadequate for risks specific to TMS. Therefore, we recommend hearing protection during TMS.
Highlights
Coil click varies by 24 dB(Z) between different TMS coils for matched stimulation.
Sound pressure level can exceed 120 dB(Z) even at 25 cm from TMS coil.
Close to TMS coil, sound pressure level may reach nearly 140 dB(Z).
For rTMS, continuous sound level may reach nearly 110 dB(A).
Hearing protection is recommended during TMS, especially rTMS.
