Chapter 7 Appendix; Glossary - GE SIGNA Voyager Pre-Installation

Chapter 7 Appendix

1 Glossary

BB
Abbreviation for Broadband
Cryogen
A substance for producing low temperatures. Liquid helium is the cryogen used to cool the
magnet to approximately 4 Kelvin (-269°C or -452°F).
Cryostat
An apparatus maintaining a very low constant temperature. The cryostat consists of one
concentric, cylindrical container housed in an outer vacuum tight vessel. The main and bulking
coils are mounted in the inner container. The container is filled with liquid helium. The shields
surrounding the inner container are kept cold by a refrigeration device.
Dewar
A container with an evacuated space between two highly reflective walls used to keep low
temperature substances at near-constant temperatures. Liquid helium is usually stored and
shipped in dewars.
Exclusion Zone
Area where the magnetic flux density is greater than five gauss. Personnel with cardiac
pacemakers, neurostimulators and other biostimulation devices must NOT enter this zone.
Signs are posted outside the five gauss line alerting personnel of this requirement. Since the
magnetic field is three-dimensional, signs are also posted on floors above and below the
Magnet Room in which the five gauss line exists.
Ferrous Material
Any substance containing iron which is strongly attracted by a magnetic field.
Gauss (G)
A unit of magnetic flux density. The earth's magnetic field strength is approximately one half
gauss to one gauss depending on location. The internationally accepted unit is the tesla (1
Tesla = 10,000G and 1 milli Tesla = 10G).
Gradient
The amount and direction of the rate of change in space of the magnetic field strength. In the
magnetic resonance system, gradient amplifiers and coils are used to vary the magnetic field
strength in the x, y, and z planes.
Homogeneity
Uniformity. The homogeneity of the static magnetic field is an important quality of the magnet.
Isocenter
Center of the imaging volume ideally located at the magnet center.
Isogauss Line
An imaginary line or a line on a field plot connecting identical magnetic field strength points.
Chapter 7 Appendix
SIGNA Voyager Pre-Installation
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