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Result : Searchterm 'Second' found in 1 term [] and 82 definitions []
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Magnetic Shielding
 
Means to confine the region of strong magnetic field surrounding a magnet; most commonly the use of material with high permeability (passive shielding) or by employing secondary counteracting coils outside of the primary coils (active shielding). The high permeability material can be employed in the form of a yoke immediately surrounding the magnet (self-shielding) or installed in the walls of a room as full or partial room-shielding. Unlike shielding ionizing radiation, for example, magnetic shielding can only be accomplished by forcing the unavoidable magnetic return flux through more confined areas or structures, not by absorbing it.

See also Radio Frequency Shielding Radio Frequency Shielding, and Faraday cage.

See also the related poll result: 'Most outages of your scanning system are caused by failure of'
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• Related Searches:
    • Self Shielding
    • Passive Shielding
    • Room Shielding
    • Radio Frequency Shielding
    • Permanent Magnet
 
Further Reading:
  Basics:
Faraday's Law
   by hyperphysics.phy-astr.gsu.edu    
  News & More:
Magnetic Sensitivity of MRI Systems to External Iron: The Design Process
   by www.integratedsoft.com    
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Magnetism
 
Magnetic forces are fundamental forces that arise due to the movement of electrical charge. Maxwell's equations describe the origin and behavior of the fields that govern these forces. Thus, magnetism is seen whenever electrically charged particles are in motion. This can arise either from movement of electrons in an electric current, resulting in 'electromagnetism', or from the quantum-mechanical orbital motion (there is no orbital motion of electrons around the nucleus like planets around the sun, but there is an 'effective electron velocity') and spin of electrons, resulting in what are known as 'permanent magnets'.
The physical cause of the magnetism of objects, as distinct from electrical currents, is the atomic magnetic dipole. Magnetic dipoles, or magnetic moments, result on the atomic scale from the two kinds of movement of electrons. The first is the orbital motion of the electron around the nucleus this motion can be considered as a current loop, resulting in an orbital dipole magnetic moment along the axis of the nucleus. The second, much stronger, source of electronic magnetic moment is due to a quantum mechanical property called the spin dipole magnetic moment.
Gauss (G) and tesla (T) are units to define the intensity of magnetic fields. One tesla is equivalent to 10 000 gauss.
Typically, the field strength of MRI scanners is between 0.15 T and 3 T.

See also Diamagnetism, Paramagnetism, Superparamagnetism, and Ferromagnetism.
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Further Reading:
  Basics:
Magnet basics
   by my.execpc.com    
  News & More:
What affects the strength of a magnet?
   by my.execpc.com    
MRI Resources 
General - Implant and Prosthesis - Lung Imaging - Chemistry - DICOM - Mobile MRI Rental
 
Matching Network
 
An arrangement of reactive elements (inductors and capacitors) used to transform an input impedance of a given value to an output impedance of a second value. Such circuits are used in interfacing high impedance RF coils to low impedance (usually 50 ohms) transmission lines that feed RF energy to the coil or send the MR signal to an MR preamplifier.
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MeterForum -
related threads
 
(m) The SI base unit of distance.
Definition: 1983 defined as the distance traveled by light in a vacuum during the time interval of 1/299 792 458 of a second.
The speed of light in a vacuum, c, is one of the fundamental constants of nature.

1 meter (m) is equal to approximately 39.370 079 inches (in)
1 meter is equal to approximately 3.280 840 feet (ft)
1 meter is equal to approximately 1.093 613 3 yard (yd)
1 square meter (m2) is equal to approximately 10.763911 square feet (ft2)
1 inch = 2.54 centimeters
Smaller or larger units are, e.g.:
1 (m) = 1 000 millimeter (mm)
1 kilometer (km) = 1 000 (m)
1 kilometer (km) = 0.62137 (statute) miles (mi)
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Further Reading:
  Basics:
How Many? A Dictionary of Units of Measurement © Russ Rowlett and the University of North Carolina at Chapel Hill
Wednesday, 21 March 2001   by www.unc.edu    
  News & More:
Welcome to NODC Unit Conversion Guide
Monday, 4 August 2003   by www.nodc.noaa.gov    
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Motion Compensation Pulse SequencesInfoSheet: - Sequences - 
Intro, 
Overview, 
Types of, 
etc.MRI Resource Directory:
 - Sequences -
 
Pulse sequences, designed to be insensitive to flow, e.g. at every even echo, a spin echo sequence is not flow sensitive. Velocity compensation is achieved by using gradients, which are either symmetrical around a 180° pulse and switched on twice as is the case for motion compensated spin echo pulse sequences, or two antisymmetrical gradient lobes without 180° pulse, which is the way to produce a velocity compensated gradient echo pulse sequence.
The signal of the second echo (and all other even echoes) is independent of the velocity of the object. Thus, velocity-based motion effects stemming from the entire voxel or from spins within a voxel (intravoxel incoherent motion) are suppressed with such pulse sequences.
If higher order motion is relevant, as it may be in turbulent jets across valves, acceleration and jerk effects can also be compensated for by the use of appropriate combinations of gradient- and radio frequency pulses.
With the increasingly stronger gradients, echo times in MR systems can be shortened to the point at which effects other than velocity effects hardly ever become relevant.
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Further Reading:
  News & More:
Patient movement during MRI: Additional points to ponder
Tuesday, 5 January 2016   by www.healthimaging.com    
Motion-compensation of Cardiac Perfusion MRI using a Statistical Texture Ensemble(.pdf)
June 2003   by www.imm.dtu.dk    
MRI Resources 
Pacemaker - Portals - Bioinformatics - Raman Spectroscopy - Image Quality - Guidance
 
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