title: Noise in magnetic resonance imaging: no risk for sensorineural function but increased amplitude variability of otoacoustic emissions.
abstract: OBJECTIVE
  Objectives were to perform exact measurements of the noise exposure in a magnetic resonance imager and to investigate the effects of magnetic resonance imaging (MRI) noise on hearing sensitivity, which are still controversial, in a large number of patients.
  
  
  METHODS
  Prospective trial.
  
  
  METHODS
  Acoustic noise during seven different MRI sequences was measured using a custom-made microphone containing no ferromagnetic parts. In 244 ears of 126 patients, pure-tone audiometry was performed once before and once after MRI noise, and distortion product otoacoustic emissions were measured once before and three times after MRI.
  
  
  RESULTS
  The sound pressure level (SPL) at the patient's ear (with consideration of the sound-damping effect of the head support) ranged from 79.5 to 86.5 dB (A), depending on the MRI sequence, with brief sound pressure peaks up to 120 dB SPL. No significant incidence of temporary threshold shift and no reduction of mean distortion product otoacoustic emission amplitude were apparent. However, a significant increase in distortion product otoacoustic emission amplitude variability after noise exposure with equal distribution of increased and decreased amplitudes was observed. This variability showed a maximum at 15 minutes after noise, as demonstrated by continuous measurements.
  
  
  CONCLUSIONS
  First, MRI noise does not impose a risk to hearing function under the measurement condition of a sound-damping head support or ear protectors. Second, a subtle effect is demonstrated by increased distortion product otoacoustic emission amplitude variability. Third, the increased otoacoustic emission amplitude variability is an audiometric parameter that is extremely sensitive to effects of acoustic stimulation, indicating more discrete changes in cochlear activity than pure-tone audiometry or otoacoustic emission amplitude reduction. A shift of the operation point (OP) of the outer hair cell (OHC) between basilar membrane and tectorial membrane is suggested as underlying cause.
authors.affiliation: Department of Otorhinolaryngology, University of Tübingen, Elfriede-Aulhorn-Strasse 5, 72076 Tübingen, Germany. w.wagner@med.uni-tuebingen.de
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wagner
authors.forename: Irene
authors.initials: I
authors.lastname: Staud
authors.forename: Gerhard
authors.initials: G
authors.lastname: Frank
authors.forename: Florian
authors.initials: F
authors.lastname: Dammann
authors.forename: Stefan
authors.initials: S
authors.lastname: Plontke
authors.forename: Peter K
authors.initials: PK
authors.lastname: Plinkert
mesh_terms: D001301:Audiometry, Pure-Tone; D001309:Auditory Threshold; D006257:Head; D006309:Hearing; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000009:adverse effects; D009622:Noise / Q000009:adverse effects; D017084:Otoacoustic Emissions, Spontaneous; D011446:Prospective Studies; D013018:Sound Spectrography