Magnetic Field (B)
A condition in a region of space established by the presence of a magnet and characterized by
the presence of a detectable magnetic force at every point in the region. A magnetic field exists
in the space around a magnet (or current carrying conductor) and can produce a magnetizing
force on a body within it.
Magnetic Resonance (MR)
The absorption or emission of electromagnetic energy by nuclei in a static magnetic field, after
excitation by a suitable radio frequency field.
Magnetic Sheilding
Using material (e.g. steel) to redistribute a magnetic field , usually to reduce fringe fields.
NB
Abbreviation for Narrow Band
Quench
Condition when a superconducting magnet becomes resistive thus rapidly boiling off liquid
helium. The magnetic field reduces rapidly after a quench.
Radio Frequency (RF)
Frequency intermediate between audio frequency and infrared frequencies. Used in magnetic
resonance systems to excite nuclei to resonance. Typical frequency range for magnetic
resonance systems is 5-130 Mhz.
Radio Frequency Shielding
Using material (e.g. copper, aluminium, or steel) to reduce interference from external radio
frequencies. A radio frequency shielded room usually encloses the entire magnet room.
Resonance
A large amplitude vibration caused by a relative small periodic stimulus of the same or nearly
the same period as the natural vibration period of the system. In magnetic resonance imaging,
the radio frequency pulses are the periodic stimuli which are at the same vibration period as the
hydrogen nuclei being imaged.
Security Zone
Area within the Magnet Room where the magnet is located. Signs are posted outside the
Magnet Room warning personnel of the high magnetic field existing in the Magnet Room and
the possibility of ferrous objects becoming dangerous projectiles within this zone.
Shield Cooler Coldhead
An external refrigeration device which maintains the shields inside the cryostat at a constant
temperature.
Shimming
Correction of inhomogeneity of the main magnetic field due to imperfections in the magnet or to
the presence of external ferromagnetic objects.
SIGNA Voyager Pre-Installation
Direction 5680008–1EN, Revision 2
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1 Glossary
