The FDA sets a maximum of 140 dB for an MR imaging system and a maximum of 99 dB for a patient with hearing protection (35). The majority of MR imaging unit noise originates from gradient coils because they are subject to rapid changes in current, which in turn interact with the main magnetic field through Lorentz forces. Pulse sequences that are gradient intensive, such as echo-planar imaging, are the loudest, but even these usually fall under the required maximum (36). Temporary hearing loss has been documented in patients who underwent routine MR imaging examinations without protective devices (37). It is common practice to require that patients use passive noise control, typically disposable earplugs or over-the-ear headphones, which can reduce noise levels by 10–30 dB. Newer-generation systems reduce noise levels by use of additional passive noise shields and active techniques such as noise-minimizing “silent” or
“quiet” pulse sequences (38).