Magnetic Resonance - Technology Information Portal Welcome to MRI Technology


The impact of TTIP/TPP on the MRI scanner market will bring :
more variety 
better scanners 
more risk 
less regulation 
cheaper scanners 
Lost in Translation 
no change at all 

MRI Safety
  • Intro
Radiology Safety Open this link in a new window
'Safety' in MRI News (62) and in MRI Resources (43) 
MRI 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.

• View the NEWS results for 'MRI Safety' (13).Open this link in a new window.

• View the DATABASE results for 'MRI Safety' (42).Open this link in a new window

Further Reading:
MRI Safety
2001   by    
Contrast Agents: Safety Profile
  News & More:
Implantable Infusion Pumps in the Magnetic Resonance (MR) Environment: FDA Safety Communication - Important Safety Precautions
Wednesday, 11 January 2017   by    
FDA Releases New Guidance On Establishing Safety, Compatibility Of Passive Implants In MR Environments
Tuesday, 16 December 2014   by    
Newer Heart Devices Safe During MRI
Monday, 23 August 2004   by    
Modern Implantable Heart Devices Safe For Use In MRI Scans
Wednesday, 16 March 2005   by    
MRI Risks 

The subacute risks and side effects of magnetic and RF fields (for patients and staff) have been intensively examined for a long time, but there have been no long-term studies following persons who have been exposed to the static magnetic fields used in MRI. However, no permanent hazardous effects of a static magnetic field exposure upon human beings have yet been demonstrated.
Temporary possible side effects of high magnetic and RF fields:
Varying magnetic fields can induce so-called magnetic phosphenes that occur when an individual is subject to rapid changes of 2–5 T/s, which can produce a flashing sensation in the eyes. This temporary side effect does not seem to damage the eyes. Static field strengths used for clinical MRI examinations vary between 0.2 and 3.0 tesla;; field changes during the MRI scan vary in the dimension of mT/s. Experimental imaging units can use higher field strengths of up to 14.0 T, which are not approved for human use.
The Radio frequency pulses mainly produce heat, which is absorbed by the body tissue. If the power of the RF radiation is very high, the patient may be heated too much. To avoid this heating, the limit of RF exposure in MRI is up to the maximum specific absorption rate (SAR) of 4 W/kg whole body weight (can be different from country to country). For MRI safety reasons, the MRI machine starts no sequence, if the SAR limit is exceeded.
Very high static magnetic fields are needed to reduce the conductivity of nerves perceptibly. Augmentation of T waves is observed at fields used in standard imaging but this side effect in MRI is completely reversible upon removal from the magnet. Cardiac arrhythmia threshold is typically set to 7–10 tesla. The magnetohydrodynamic effect, which results from a voltage occurring across a vessel in a magnetic field and percolated by a saline solution such as blood, is irrelevant at the field strengths used.
The results of some animal and cellular studies suggest the possibility that electromagnetic fields may act as co-carcinogens or tumor promoters, but the data are inconclusive. Up to 45 tesla, no important effects on enzyme systems have been observed. Neither changes in enzyme kinetics, nor orientation changes in macromolecules have been conclusively demonstrated.
There are some publications associating an increase in the incidence of leukemia with the location of buildings close to high-current power lines with extremely low-frequency (ELF) electromagnetic radiation of 50-60 Hz, and industrial exposure to electric and magnetic fields but a transposition of such effects to MRI or MRS seems unlikely.
Under consideration of the MRI safety guidelines, real dangers or risks of an exposure with common MRI field strengths up to 3 tesla as well as the RF exposure during the MRI scan, are not to be expected.
For more MRI safety information see also Nerve Conductivity, Contraindications, Pregnancy and Specific Absorption Rate.

See also the related poll result: 'In 2010 your scanner will probably work with a field strength of'

• View the NEWS results for 'MRI Risks' (3).Open this link in a new window.

• View the DATABASE results for 'MRI Risks' (9).Open this link in a new window

Further Reading:
Working with MRI machines may cause vertigo: Study
Wednesday, 25 June 2014   by    
Physics of MRI Safety
Specific Absorption Rate: A Specious Dosimetric Means of Characterizing MRI-Related Implant Heating?
Wednesday, 3 December 2003   by    
  News & More:
Commission delays electromagnetic fields legislation
Monday, 29 October 2007   by    
MagnaSafe Registry: Risks of MRI at 1.5 Tesla For Patients With Non-MRI Conditional Pacemakers and ICDs
Tuesday, 18 November 2014   by    
Magnetic Forces 

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'

• View the DATABASE results for 'Magnetic Forces' (4).Open this link in a new window

Further Reading:
How strong are magnets?
Magnetic Field of the Strongest Magnet
2003   by    
  News & More:
Two stuck to MRI machine for 4 hrs
Tuesday, 11 November 2014   by    
Technical Assessment of Artifact Production from Neuro Endovascular Coil At 3 Tesla MRI: An In Vitro Study
2012   by    
Scientists improve MRI sensitivity
Wednesday, 28 January 2009   by    
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'

• View the DATABASE results for 'Magnetic Shielding' (11).Open this link in a new window

Further Reading:
Faraday's Law
  News & More:
Magnetic Sensitivity of MRI Systems to External Iron: The Design Process
  Hazards, Risks and Side Effects top
Radiology Safety Open this link in a new window
Thus the metric system did not really catch on in the States, unless you count the increasing popularity of the nine-millimeter bullet.
- Dave Barry
Share This Page

Forgot your UserID/Password ?  


Magnetic Resonance - Technology Information Portal
Member of SoftWays' Medical Imaging Group - MR-TIP • Radiology-TIP • US-TIP • The-Medical-Market
Copyright © 2003 - 2016 SoftWays. All rights reserved. [ 24 February 2017]
Terms of Use | Privacy Policy | Advertising
 [last update: 2017-02-21 00:45:00]