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Radio Frequency Shielding
 
Radio frequency shielding includes the construction of enclosures for the purpose of reducing the transmission of electric or magnetic fields from one space to another (Faraday cage, Faraday shield). Electrically conducted shielding is designed to isolate MRI systems from its environment at the resonant frequencies.
All electronic and computer systems radiate certain frequencies of radio and magnetic waves. They can interfere with other equipment in the vicinity. Magnetic shielding enclosures are used to reduce the levels of RF radiation that enters or leaves the shielded room.
Copper shielding enclosures are designed to filter a range of frequencies under specified conditions. One of the characteristics of copper is its high electrical conductivity. Also its other physical properties like ductility, malleability, and ease of soldering, make it an ideal material for radio frequency shielding. Sheet copper can be formed into any shape and size, and electrically connected to a grounding system to provide an effective RF shielding.

See also MRI Safety
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MRI Resources 
PACS - MRI Training Courses - Open Directory Project - Mass Spectrometry - Raman Spectroscopy - Safety Products
 
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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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    
MRI Resources 
Musculoskeletal and Joint MRI - Journals - Absorption and Emission - Distributors - IR - Breast MRI
 
Zipper ArtifactInfoSheet: - Artifacts - 
Case Studies, 
Reduction Index, 
etc.MRI Resource Directory:
 - Artifacts -
 
Quick Overview
Artifact Information
NAME
Zipper, star
DESCRIPTION
Bands through image center
REASON
Hardware or software problems
HELP
Larger FOV, oversampling
Zipper artifacts appear as dashed lines. There are various causes for this MRI artifact.
Most of zipper artifacts result from inhomogeneities of the magnetic field caused by interferences with radio frequency from various sources ('your radio is working in the scanner room means your shielding is not working'). Software and equipment problems can also cause zipper lines in both directions.
mri safety guidance
Image Guidance
Scanning room door during the acquisition of images is closed, shielding is working, and all disturbing devices are removed?

See also Room Shielding, Active Shielding, Radio Frequency Shielding.
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MRI SafetyMRI Resource Directory:
 - Safety -
 
There are different types of contraindications that would prevent a person from being examined with an MRI scanner. MRI systems use strong magnetic fields that attract any ferromagnetic objects with enormous force. Caused by the potential risk of heating, produced from the radio frequency pulses during the MRI procedure, metallic objects like wires, foreign bodies and other implants needs to be checked for compatibility. High field MRI requires particular safety precautions. In addition, any device or MRI equipment that enters the magnet room has to be MR compatible. MRI examinations are safe and harmless, if these MRI risks are observed and regulations are followed.

Safety concerns in magnetic resonance imaging include:
•
the magnetic field strength;
•
possible 'missile effects' caused by magnetic forces;
•
the potential for heating of body tissue due to the application of the radio frequency energy;
•
the effects on implanted active devices such as cardiac pacemakers or insulin pumps;
•
magnetic torque effects on indwelling metal (clips, etc.);
•
the audible acoustic noise;
•
danger due to cryogenic liquids;
•
the application of contrast medium;
mri safety guidance
MRI Safety Guidance
It is important to remember when working around a superconducting magnet that the magnetic field is always on. Under usual working conditions the field is never turned off. Attention must be paid to keep all ferromagnetic items at an adequate distance from the magnet. Ferromagnetic objects which came accidentally under the influence of these strong magnets can injure or kill individuals in or nearby the magnet, or can seriously damage every hardware, the magnet itself, the cooling system, etc.. See MRI resources Accidents.
The doors leading to a magnet room should be closed at all times except when entering or exiting the room. Every person working in or entering the magnet room or adjacent rooms with a magnetic field has to be instructed about the dangers. This should include the patient, intensive-care staff, and maintenance-, service- and cleaning personnel, etc..
The 5 Gauss limit defines the 'safe' level of static magnetic field exposure. The value of the absorbed dose is fixed by the authorities to avoid heating of the patient's tissue and is defined by the specific absorption rate. Leads or wires that are used in the magnet bore during imaging procedures, should not form large-radius wire loops. Leg-to-leg and leg-to-arm skin contact should be prevented in order to avoid the risk of burning due to the generation of high current loops if the legs or arms are allowed to touch. The patient's skin should not be in contact with the inner bore of the magnet.
The outflow from cryogens like liquid helium is improbable during normal operation and not a real danger for patients.
The safety of MRI contrast agents is tested in drug trials and they have a high compatibility with very few side effects. The variations of the side effects and possible contraindications are similar to X-ray contrast medium, but very rare. In general, an adverse reaction increases with the quantity of the MRI contrast medium and also with the osmolarity of the compound.

See also 5 Gauss Fringe Field, 5 Gauss Line, Cardiac Risks, Cardiac Stent, dB/dt, Legal Requirements, Low Field MRI, Magnetohydrodynamic Effect, MR Compatibility, MR Guided Interventions, Claustrophobia, MRI Risks and Shielding.
Radiology-tip.comradRadiation Safety,  Ionizing Radiation
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Medical-Ultrasound-Imaging.comUltrasound Safety,  Absorbed Dose
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• View the NEWS results for 'MRI Safety' (13).Open this link in a new window.
 
Further Reading:
  Basics:
MRI Safety
2001   by www.fda.gov    
What MRI Sequences Produce the Highest Specific Absorption Rate (SAR), and Is There Something We Should Be Doing to Reduce the SAR During Standard Examinations?
Thursday, 16 April 2015   by www.ajronline.org    
Contrast Agents: Safety Profile
   by www.clinical-mri.com    
  News & More:
How safe is 7T MRI for patients with neurosurgical implants?
Thursday, 17 November 2022   by healthimaging.com    
Newer Heart Devices Safe During MRI
Monday, 23 August 2004   by www.hospimedica.com    
Study: Face Masks Unsafe in MRI Machines
Wednesday, 13 July 2022   by www.laboratoryequipment.com    
COVID-19: Attention shifts to MRI infection control
Thursday, 9 July 2020   by https://www.auntminnieeurope.com/index.aspx?sec=ser§sub=def§pag=dis§ItemID=619012    
FDA Releases New Guidance On Establishing Safety, Compatibility Of Passive Implants In MR Environments
Tuesday, 16 December 2014   by www.meddeviceonline.com    
Modern Implantable Heart Devices Safe For Use In MRI Scans
Wednesday, 16 March 2005   by www.sciencedaily.com    
MRI Resources 
MRA - Patient Information - Examinations - Health - Mass Spectrometry - Blood Flow Imaging
 
Faraday Shield
 
In electromagnetism, the Faraday cage or shield is an application of Gauss's law, one of Maxwell's equations. Gauss's law describes the distribution of electrical charge on a conducting form, such as a sphere, a plane, a torus, etc. Intuitively, since like charges repel each other, charge will "migrate" to the surface of the conducting form, as described below. The application is named after physicist Michael Faraday, who built the first Faraday cage in 1836, to demonstrate his finding. A Faraday shield is used generally for any kind of electrostatic shielding.
In MRI, one use of the Faraday shield is the shielding of the scanning room, to block incoming radio frequency (RF) signals which would contaminate the send and received signals of the MRI scanner, and it suppresses RF signals, which would else pollute the environment around.
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Further Reading:
  Basics:
Faraday's Law
   by hyperphysics.phy-astr.gsu.edu    
Faraday_shield
   by en.wikipedia.org    
  News & More:
Electrical eddy currents in the human body: MRI scans and medical implants
   by www.phy.olemiss.edu    
MRI Resources 
MR Guided Interventions - MRI Technician and Technologist Schools - Corporations - Guidance - - Shoulder MRI
 
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