THE NOISE-LEVEL IN MAGNETIC STIMULATION

The noise generated by stimulating coils may jeopardize the hearing of the patients as well as the hearing of the examiner. To evaluate the potential risk caused by the impulse noise of stimulating coils, we ex amined the A-weighted peak sound pressure levels from five different t ypes of magnetic stimulator coils. At a distance of 10 cm, with 100% s timulation intensity, the coils with Dantec and Magstim stimulators cr eated maximum peak sound pressure levels of 110 dB. Correspondingly, C adwell MES-10 created maximum peak sound pressure levels of 132 dB. Th e decrease in the peak levels followed the distance rule quite closely . At a distance of 40 cm, the decrease in peak level was on average 14 dB (range -1-+1 dB). Based on American Conference of Governmental Ind ustrial Hygienists (ACGIH) threshold limits of impact noise, the permi tted maximum daily number of magnetic stimuli would be 1000 to 10 000. The permitted number of daily stimuli may be difficult to exceed in c linical practice. We consider the risk as small for the patients that are being examined and the operator using magnetic stimulation. The po tential risk can be further diminished by even very light weighted hea ring protectors providing proper attenuation to the coil impulses.