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Magnetic ForcesMRI Resource Directory:
 - MRI Accidents -
 
Forces can result from the interaction of magnetic fields. Pulsed magnetic field gradients can interact with the main magnetic field during the MRI scan, to produce acoustic noise through the gradient coil.
Magnetic fields attract ferromagnetic objects with forces, which can be a lethal danger if one is hit by an unrestrained object in flight. One could also be trapped between the magnet and a large unrestrained ferromagnetic object or the object could damage the MRI machine.
Access control and personnel awareness are the best preventions of such accidents. The attraction mechanism for ferromagnetic objects is that the magnetic field magnetizes the iron. This induced magnetization reacts with the gradient of the magnetic field to produce an attraction toward the strongest area of the field. The details of this interaction are very dependent on the shape and composition of the attracted object. There is a very rapid increase of force as one approaches a magnet. There is also a torque or twisting force on objects, e.g. a long cylinder (such as a pen or an intracranial aneurysm clip) will tend to align along the magnet’s field lines. The torque increases with field strength while the attraction increases with field gradient.
Depending on the magnetic saturation of the object, attraction is roughly proportional to object mass. Motion of conducting objects in magnetic fields can induce eddy currents that can have the effect of opposing the motion.
See also Duty Cycle.

See also the related poll result: 'Most outages of your scanning system are caused by failure of'
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• For this and other aspects of MRI safety see our InfoSheet about MRI Safety.
• Patient-related information is collected in our MRI Patient Information.

 
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Further Reading:
  Basics:
How strong are magnets?
   by my.execpc.com    
Magnetic Field of the Strongest Magnet
2003   by hypertextbook.com    
  News & More:
Two stuck to MRI machine for 4 hrs
Tuesday, 11 November 2014   by www.mumbaimirror.com    
Technical Assessment of Artifact Production from Neuro Endovascular Coil At 3 Tesla MRI: An In Vitro Study
2012   by www.tmps.or.th    
Scientists improve MRI sensitivity
Wednesday, 28 January 2009   by news-service.stanford.edu    
Searchterm 'Magnetic Forces' was also found in the following service: 
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Radiology  (1) Open this link in a new window
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
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.comRadiation Safety,  Ionizing Radiation
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Radiology-tip.comUltrasound Safety,  Absorbed Dose
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• View the DATABASE results for 'MRI Safety' (42).Open this link in a new window


• 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    
Contrast Agents: Safety Profile
   by www.clinical-mri.com    
  News & More:
FDA Releases New Guidance On Establishing Safety, Compatibility Of Passive Implants In MR Environments
Tuesday, 16 December 2014   by www.meddeviceonline.com    
Newer Heart Devices Safe During MRI
Monday, 23 August 2004   by www.hospimedica.com    
Modern Implantable Heart Devices Safe For Use In MRI Scans
Wednesday, 16 March 2005   by www.sciencedaily.com    
MRI Safety Resources 
Safety Products - Claustrophobia - Cochlear Implant - Pacemaker - Stent
 
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.
Radiology-tip.comGamma Ray,  Electromagnetic Radiation
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Radiology-tip.comSonographic Features,  Echo
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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    
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TattoosMRI Resource Directory:
 - Safety -
 
Tattoos with metallic or ferromagnetic color ingredients can distort MR images. Skin irritations or burns caused by heating of the metallic particles due to the radio frequency pulse are also possible, but rare.
MRI Safety Guidance
Patients should be informed about the possible risk, and scanning should be stopped immediately if they feel heat. Metallic make-up can even be pulled into the eye by magnetic forces and should be removed previous to the MRI scan.
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Magnetic FieldForum -
related threads
 
(H) The region surrounding a magnet (or current carrying conductor) is equipped with certain properties like that a small magnet in such a region experiences a torque that tends to align it in a given direction. Magnetic field is a vector quantity; the direction of the field is defined as the direction that the north pole of the small magnet points when in equilibrium.


MRI Safety Guidance
A magnetic field produces a magnetizing force on a body within it. Although the dangers of large magnetic fields are largely hypothetical, this is an area of potential concern for safety limits. Formally, the forces experienced by moving charged particles, current carrying wires, and small magnets in the vicinity of magnet are due to magnetic induction (B), which includes the effect of magnetization, while the magnetic field (H) is defined so as not to include magnetization. However, both B and H are often loosely used to denote magnetic fields.
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Further Reading:
  Basics:
Magnet basics
   by my.execpc.com    
Magnetic Field
   by hyperphysics.phy-astr.gsu.edu    
Magnetic Field
   by en.wikipedia.org    
How strong are magnets?
   by my.execpc.com    
  News & More:
Two stuck to MRI machine for 4 hrs
Tuesday, 11 November 2014   by www.mumbaimirror.com    
Commission proposes to revamp rules to protect EU workers from harmful electromagnetic fields
Tuesday, 14 June 2011   by finchannel.com    
Magnetic fields drive drug-loaded nanoparticles to reduce blood vessel blockages in an animal study
Monday, 19 April 2010   by www.eurekalert.org    
MRI Resources 
Abdominal Imaging - Education - Cochlear Implant - MRI Technician and Technologist Career - Supplies - Nerve Stimulator
 
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