A magnetic resonance imaging system (MRI) produces high acoustic noise levels during scanning. These systems use a strong static magnetic field in the order of a few Tesla. Additionally, these systems use a magnetic gradient field that varies in time. These gradient fields are created by means of a so-called gradient coil, in which electrical currents are used in the order of a few hundred amperes. Acoustic noise is generated due to the Lorentz forces acting upon the gradient coil and the main magnet outer vacuum chamber. The Lorentz forces on the main magnet outer vacuum chamber are generated by the eddy currents which are developed in the main magnet outer vacuum chamber as a result of the varying magnetic stray fields of the gradient coil. Combined with the strong magnetic field of the main magnet, large Lorentz forces are developed, resulting in vibrations and acoustic noise. The paper focuses upon the reduction of these eddy current induced vibrations and acoustic noise through magnetic shielding. Measurements on an experimental MRI system show a reduction up to 20 dB.
|Title of host publication||Proceedings of the Forum Acusticum 2005, 29 august-2 september 2005, Hungary, Budapest|
|Publication status||Published - 2005|