Sound-level measurements and calculations of safe noise dosage during EPI at 3 T

This paper describes systematic methods for measuring and controlling sound levels within a magnetic resonance scanner. The methods are illustrated by application to the acoustic noise generated by a 3 T scanner during echopl anar imaging (EPI). Across five measurement sessions, sound pressure levels at the center of the head gradient coil ranged from 122 to 131 dB SPL [123 to 132 dB(A)]. For protection against damaging noise exposure, UK and US i ndustrial guidelines stipulate that the maximum permitted daily noise dosag e is equivalent to 90 dB(A) for 8 hours, where noise dosage is a function o f the level of an acoustic signal and the length of exposure to ft. Without hearing protection, this equivalent level would be exceeded by less than 5 seconds of exposure to the measured levels of scanner acoustic noise. Thes e findings highlight the importance of noise reduction and hearing protecti on for those exposed to the acoustic noise generated during EPI. (C) 2000 W iley-Liss, Inc.