The invention relates to a magnetic resonance imaging (MRI) system (1)
comprising an examination volume (11) in which a patient to be examined
can be accommodated, a main magnet system (3) for generating a magnetic
field having a main field portion (17) in the examination volume with a
substantially constant magnetic field strength (B0), and a gradient
magnet system (13) for generating gradients of the main field portion.
The MRI system further comprises a damping member (25, 27) which is
mounted to a part (5) of the MRI system susceptible to vibrations
relative to the magnetic field during operation. Said damping member
comprises an electrically conductive member (29, 35, 37) which is present
in the magnetic field and in which eddy currents are generated as a
result of said vibrations. According to the invention, the conductive
member (29, 35, 37) is arranged in a secondary portion of the magnetic
field at a distance from the main field portion (17), which secondary
portion has a magnetic field strength which differs by more than 25% from
the magnetic field strength (B0) of the main field portion. In this
manner, the distance between the conductive member and the main field
portion is sufficiently large to prevent the eddy currents in the
conductive member from causing unacceptable distortions of the main field
portion, while, on the other hand, the magnetic field strength in said
secondary portion is still sufficiently large to provide an adequate
damping effect of the damping member (25, 27). The damping member (25,
27) can for example be mounted to a housing (5) of the main magnet system
(3). Alternatively, the damping member (139, 141) can be mounted to the
gradient magnet system (127). In another embodiment the damping member
(27) is mounted to a rigid portion of the MRI system (1), for example to
the supporting member (21), which does hardly vibrate during operation.
In this embodiment, the damping member (27) is used to damp the
vibrations of the magnetic field generating portions (9) of the main
magnet system (3).