title: Echo planar imaging at 4 Tesla with minimum acoustic noise.
abstract: OBJECTIVE
  To minimize the acoustic sound pressure levels of single-shot echo planar imaging (EPI) acquisitions on high magnetic field MRI scanners.
  
  
  METHODS
  The resonance frequencies of gradient coil vibrations, which depend on the coil length and the elastic properties of the materials in the coil assembly, were measured using piezoelectric transducers. The frequency of the EPI-readout train was adjusted to avoid the frequency ranges of mechanical resonances.
  
  
  RESULTS
  Our MRI system exhibited two sharp mechanical resonances (at 720 and 1220 Hz) that can increase vibrational amplitudes up to six-fold. A small adjustment of the EPI-readout frequency made it possible to reduce the sound pressure level of EPI-based perfusion and functional MRI scans by 12 dB.
  
  
  CONCLUSIONS
  Normal vibrational modes of MRI gradient coils can dramatically increase the sound pressure levels during echo planar imaging (EPI) scans. To minimize acoustic noise, the frequency of EPI-readout trains and the resonance frequencies of gradient coil vibrations need to be different.
authors.affiliation: Medical Department, Brookhaven National Laboratory, Upton, New York 11973, USA. Tomasi@bnl.gov
authors.forename: Dardo G
authors.initials: DG
authors.lastname: Tomasi
authors.forename: Thomas
authors.initials: T
authors.lastname: Ernst
mesh_terms: D000162:Acoustics; D017352:Echo-Planar Imaging / Q000295:instrumentation*; D009622:Noise; D012815:Signal Processing, Computer-Assisted; D014732:Vibration