MRI MAGNET Flashcards
is any object that produces its own magnetic field that interacts with other magnetic fields
Magnet
Three principal types of magnets:
– Natural - Earth
– Permanent
– Electromagnet
are distinguished from permanent magnets by their ability to generate magnetic fields when electric current
flows through them. current to generate magnetism.
Electromagnets
usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in the hole in the center of the coil
Electromagnets
TYPES OF MAGNETS USED IN MRI
Superconducting Magnets
Resistive Magnets
Permanent Magnets
- commonly used magnet nowadays. This magnets operate near absolute zero temperature. Magnetic field above 0.5Tesla. (1-3Tesla)
Superconducting Magnets
- similar to superconductive but wires are not cooled. Magnetic field not higher than 0.6Tesla.
Resistive Magnets
– operate to magnetic fields up to 0.4 Tesla. (.15-4T)
Permanent Magnets
Types of magnets in terms of
field strengths
Ultrahigh field
High field
Midfield
Low field
Ultralow field
(4-7 Tesla)- used for research
Ultrahigh field
(1.5-3 Tesla)
High field
(0.5-1.4 Tesla)
Midfield
(0.2-0.4 Tesla)
Low field
(<0.2 Tesla)
Ultralow field
Magnetic Susceptibility
– Diamagnetic
– Ferromagnetic
– Paramagnetic
-substances have no unpaired orbital electrons. Weakly repelled by either
magnetic poles. Ex. Water and plastic
Diamagnetic
- strongly magnetized by a magnet and usually can be permanently magnetized by exposure to a magnetic field. Ex. Alnico
Ferromagnetic
- materials lie somewhere between ferromagnetic and nonmagnetic
Paramagnetic
Weakly repelled from both poles of a magnetic field.
Example:GoldDiamondsLeadSilver
Diamagnetic
Weakly attracted to both poles of a magnetic field.Example:Gadolinium (excellent contrast agent for
MRI)TungstenAluminum
Paramagnetic
Can be strongly magnetized
Example:IronNickel
Ferromagnetic
the unit of the strength of a magnetic field.
Gauss & Tesla
is the smaller unit of measurement
compared with tesla.1 tesla is equals to
10,000 Gauss
Gauss
The earth’s magnetic field is about
0.5Gauss
Is a highly developed innovative technique that provide anatomic images in multiple planes and allows information on tissue characterization.
Magnetic resonance imaging
–is a vector quantity consisting
of both a north and south pole.
Magnetic field
– a magnetic field characterized by its own magnetic north and south poles separated by a finite distance
Dipole
– the amount of magnetic flux in a unit area perpendicular to the direction of magnetic flow.
Magnetic intensity
- a device that attracts iron and
produces a magnetic field. The biggest and the most important part of the MRI system.
Magnet
– precesses or tumble
Spin
– the phenomenon of magnetic field spinning or gyrating around imaginary axis of its own creation.
Precession
- is the rate at which the
nuclei complete a revolution about the
precessional path. (megahertz or millions of
cycle per second
Frequency precession
– the ratio between magnetic
moment and angular momentum.
Gyromagnetic ratio
- the angle formed between a
precessing object and its imaginary axis.
Angular momentum
– is ideal for MRI because its
nucleus has a single proton and a large magnetic moment.
Hydrogen atom
- refers to spinning motion of
positive protons and the negative electrons that create a small magnetic field about the atom
Magnetic moment
- refers to that portion of
the electromagnetic spectrum in which
electromagnetic waves can be generated by alternating current fed to an antenna.
Radiofrequency Pulse
- phenomenon resulting in the
absorption and/or emission of electromagnetic energy by nuclei or electrons in a static magnetic field, after excitation by a suitable magnetic field.
Resonance
- specific frequency of resonance.
Larmor Frequency
