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 'Shielded Gradient Coils' 
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Shielded Gradient CoilsInfoSheet: - Coils - 
Intro, 
Overview, 
etc.MRI Resource Directory:
 - Coils -
 
Current-carrying gradient coils with reduced gradient fringe field inside of the magnet cryostat structures like cryoshields and He-vessel. The shielding can be accomplished by secondary actively driven coils or by passive screens, which are inductively coupled to the gradient coils. In both cases eddy currents outside of the gradient system will be reduced.

See also Eddy Currents.
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Faraday's Law
   by hyperphysics.phy-astr.gsu.edu    
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Eddy Current ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.
 
Quick Overview
Artifact Information
NAME
Eddy current
DESCRIPTION
Image distortion
REASON
Induced by changes in a magnetic field
Eddy currents can cause artifacts in images and may seriously degrade overall magnet performance.
mri safety guidance
Image Guidance
Common uses to reduce the influence of eddy currents on gradient fields are eddy current compensation and shielded gradient coils (active or passive). If persistent, it must be addressed by a service representative to verify the magnet performance.

See also Eddy Current Compensation.
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Further Reading:
  Basics:
Generic Eddy Current Compensation for Rapid Magnetic Resonance Imaging(.pdf)
   by www.switt.ch    
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Eddy Current Compensation
 
Eliminate Gibb's artifact (Border ringing) for sharp images. Means of reducing the influence of eddy currents on pulsed gradient fields by employing an electrical preemphasis in the gradient amplifiers. Usually multiple time constants have to be used to correct for eddy current effects in various structures of the MR system such as the cryoshields and RF-shields.

See also Eddy Currents and Shielded Gradient Coils.
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Further Reading:
  Basics:
Generic Eddy Current Compensation for Rapid Magnetic Resonance Imaging(.pdf)
   by www.switt.ch    
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Eddy CurrentsForum -
related threadsInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.
 
Electric currents induced in a conductor by a changing magnetic field or by motion of the conductor through a magnetic field.
One of the sources of concern about a potential hazard to subjects in very high magnetic fields or rapidly varying gradient or main magnetic fields. Can be a practical problem in the cryostat of superconducting magnets. Eddy currents can cause artifacts in images and may seriously degrade overall magnet performance. Common means to reduce the influence of eddy currents on gradient fields are eddy current compensation and shielded gradient coils (active or passive).

See also Eddy Current Compensation.

See also the related poll result: 'Most outages of your scanning system are caused by failure of'
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Further Reading:
  Basics:
Electrical eddy currents in the human body: MRI scans and medical implants
   by www.phy.olemiss.edu    
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VISARTâ„¢InfoSheet: - Devices -
Intro, 
Types of Magnets, 
Overview, 
etc.MRI Resource Directory:
 - Devices -
 
http://www.medical.toshiba.com/clinical/radiology/15texcelart.htm From Toshiba America Medical Systems Inc.;
VISARTâ„¢ series is a 1.5 Tesla superconducting MRI system that has been designed to meet the expanding role of MRI in today's clinical environment. The system utilizes innovative technologies such as digital RF, high speed actively shielded gradients and optimized RF coils, which support a wide range of MRI developments. The Visart, an early type of Toshiba Medical Systems Inc., can be retrofitted or upgraded to the Excelart configuration.
Device Information and Specification
CLINICAL APPLICATION
Whole body
CONFIGURATION
Compact
Quadrature, solenoid and multi-channel configurations
SYNCHRONIZATION
ECG/peripheral optional, respiratory gating
PULSE SEQUENCES
SE, FE, IR, FastSE, FastIR, FastFLAIR, Fast STIR, FastFE, FASE, Hybrid EPI, Multi Shot EPI; Angiography: 2D(gate/non-gate)/3D TOF, SORS-STC
IMAGING MODES
Single, multislice, volume study
POWER REQUIREMENTS
380/400/415/440/480 V
COOLING SYSTEM TYPE
Closed-loop water-cooled
STRENGTH
25 mT/m
Passive, active
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Angio, cardiac imaging top list for MR and CT
1999   by www.diagnosticimaging.com    
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