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In 2075 (after about 100 years of ...) the MRI scan will be :
obsolete 
done with handheld probe 
done at home (app, ...) 
a 3 second walk through 
daily done 
replaced by something much ... 




 
MRI Safety
Safety Rules
 
 
  • Safety Rules
 
 
Radiology Safety Open this link in a new window
'Safety' in MRI News (61) and in MRI Resources (43) 
Legal Requirements 


MRI Safety Guidance
The owner of MRI equipment has to ensure that the equipment does fulfill the local requirements.
In some countries, the requirements are more stringent than in others; in other countries, they are nonexistent.
The user in general is unable to check power output, gradient strength, or even field strength. The manufacturer has to cover authorized hardware and software updates after the initial installation and has to give guarantee for the requirements. Specially designed computer programs usually supervise the power output of MRI devices and will not allow or will interrupt any imaging or spectroscopy procedure exceeding those limits considered safe.

See also European Medicines Agency, FDA information:
www.fda.gov/cdrh/safety/mrisafety.html

• View the DATABASE results for 'Legal Requirements' (3).Open this link in a new window

 
Further Reading:
  News & More:
A Primer on Medical Device Interactions with Magnetic Resonance Imaging Systems
   by govpulse.us    
Specific Absorption Rate 

(SAR) The Specific Absorption Rate is defined as the RF power absorbed per unit of mass of an object, and is measured in watts per kilogram (W/kg).
The SAR describes the potential for heating of the patient's tissue due to the application of the RF energy necessary to produce the MR signal. Inhomogeneity of the RF field leads to a local exposure where most of the absorbed energy is applied to one body region rather than the entire person, leading to the concept of a local SAR. Hot spots may occur in the exposed tissue, to avoid or at least minimize effects of such theoretical complications, the frequency and the power of the radio frequency irradiation should be kept at the lowest possible level. Averaging over the whole body leads to the global SAR.
It increases with field strength, radio frequency power and duty cycle, transmitter-coil type and body size. The doubling of the field strength from 1.5 Tesla (1.5T) to 3 Tesla (3T) leads to a quadrupling of SAR. In high and ultrahigh fields, some of the multiple echo, multiple-slice pulse sequences may create a higher SAR than recommended by the agencies. SAR can be reduced by lower flip angle and longer repetition times, which could potentially affect image contrast.
Normally no threatening increase in temperature could be shown. Even in high magnetic fields, the local temperature increases not more than 1°C. 2.1°C is the highest measured increase in skin temperature. Eddy currents may heat up implants and thus may cause local heating.

FDA SAR limits:
Whole body: 4W/kg/15-minute exposure averaged;
Head: 3W/kg/10-minute exposure averaged;
Head or torso: 8W/kg/5 minute exposure per gram of tissue;
Extremities: 12W/kg/5 minute exposure per gram of tissue.
IEC (International Electrotechnical Commission) SAR limits of some European countries:
All limits are averaged over 6 minutes.
Level 0 (normal operating mode): Whole body 2W/kg; Head 3.2W/kg; Head or Torso (local) 10W/kg; Extremities (local) 20W/kg;
Level I (first level controlled operating mode): Whole body 4W/kg; Head 3.2W/kg; Head or Torso (local) 10W/kg; Extremities (local) 20W/kg;
Level II (second level controlled operating mode): All values are over Level I values.
(For more details: IEC 60601-2-33 (2002))

In most countries standard MRI systems are limited to a maximum SAR of 4 W/kg, so most scanning in level II is impossible.
For Level I, in addition to routine monitoring, particular caution must be exercised for patients who are sensitive to temperature increases or to RF energy.
For Japan different SAR limits are valid.

• View the NEWS results for 'Specific Absorption Rate' (1).Open this link in a new window.

• View the DATABASE results for 'Specific Absorption Rate' (8).Open this link in a new window

 
Further Reading:
  Basics:
Numerical investigations of MRI RF field induced heating for external fixation devices
Thursday, 7 February 2013   by 7thspace.com    
Evaluation of Specific Absorption Rate as a Dosimeter of MRI-Related Implant Heating
2004   by www.imrser.org    
  News & More:
Specific Absorption Rate: A Specious Dosimetric Means of Characterizing MRI-Related Implant Heating?
Wednesday, 3 December 2003   by rsna2003.rsna.org    
Accounting for biological aggregation in heating and imaging of magnetic nanoparticles
Tuesday, 2 September 2014   by www.ecnmag.com    
Commission delays electromagnetic fields legislation
Monday, 29 October 2007   by cordis.europa.eu:80    
Guidance for Industry and FDA Staff, Criteria for Significant Risk Investigations of Magnetic Resonance Diagnostic Devices
Monday, 14 July 2003   by www.fda.gov    
5 Gauss Limit 

The national regulatory boards decided to limit the threshold for access to MRI areas to 5 gauss.


MRI Safety Guidance
It is of special interest for the observer of bureaucratic procedures that the 5 gauss safety limit is ten times higher than the average earth magnetic field, but lower than the magnetic field in electric trains such as subways (up to 7 gauss). For example, the fields measured on the surface of the receiver of a telephone are 35 gauss and of an audio headset 100 gauss.

• View the DATABASE results for '5 Gauss Limit' (3).Open this link in a new window

 
Further Reading:
  Basics:
Magnetic Sensitivity of MRI Systems to External Iron: The Design Process
   by www.integratedsoft.com    
  News & More:
A Primer on Medical Device Interactions with Magnetic Resonance Imaging Systems
   by govpulse.us    
Modern Implantable Heart Devices Safe For Use In MRI Scans
Wednesday, 16 March 2005   by www.sciencedaily.com    
5 Gauss Line 

This line specifies the perimeter around a MR scanner within which the static magnetic fields are higher than five gauss. Five gauss and below are considered 'safe' levels of static magnetic field exposure for the general public.
Portable devices requiring a separation distance between the device and the MR magnet, should not be considered 'MR Safe', 'MR Compatible', or intended for use in the MR environment. Typically the 5 gauss line is the only location where the static magnetic field strength is specified around a MR scanner. Therefore, labeling specifying a separation distance between the MR magnet and the device to ensure safe or proper operation of the device should be avoided.

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

• View the DATABASE results for '5 Gauss Line' (6).Open this link in a new window

 
Further Reading:
  News & More:
Boston Scientific and Biophan in MRI Collaboration
Friday, 21 November 2003   by www.medimaging.net    
MR Compatibility 


MRI Safety Guidance
If a device is to be labeled MR Safe, the following information should be provided:
Data demonstrating that when the device is introduced or used in the MRI environment (i.e. the MRI scan room) it does not pose an increased safety risk to the patient or other personnel,
a scientifically-based rationale for why data are not necessary to prove the safety of the device in the MR environment (for example, a passive device made entirely of a polymer known to be nonreactive in strong magnetic fields).
If a device is to be labeled MR Compatible, the following information should be provided:
Data demonstrating that when the device is introduced or used in the MRI environment, it is MR safe that it performs its intended function without performance degradation, and that it does not adversely affect the function of the MRI scanner (e.g. no significant image artifacts or noise). Any image artifact or noise due to the medical device should be quantified (e.g., % volume affected, signal to noise ratio),
a scientifically-based rationale for why data are not necessary to prove the compatibility of the device in the MRI environment.
Test Conditions:
The static magnetic field strength (Gauss (G) or Tesla (T)) to which the device was tested and demonstrated to be MRI 'safe', 'compatible', or 'intended for use in' should be related to typical machine ratings (e.g. 0.5 T, 1.5 T, 2.0 T, and shielded or unshielded magnet, etc).
The same conditions should be used for the spatial gradient (field strength per unit distance (i.e., G/cm)) in which the device was tested and demonstrated to be 'safe', 'compatible', or 'intended for use in'.
Also the RF transmitter power used during testing of the device, should be related to this typical machine ratings.

• View the NEWS results for 'MR Compatibility' (2).Open this link in a new window.

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

 
Further Reading:
  Basics:
Newer Heart Devices Safe During MRI
Monday, 23 August 2004   by www.hospimedica.com    
  News & More:
Boston Scientific and Biophan in MRI Collaboration
Friday, 21 November 2003   by www.medimaging.net    
MRI safety targeted as new group offers credentialing test
Monday, 12 January 2015   by www.modernhealthcare.com    
FDA Releases New Guidance On Establishing Safety, Compatibility Of Passive Implants In MR Environments
Tuesday, 16 December 2014   by www.meddeviceonline.com    
Pregnancy 

MRI can be indicated for use in pregnant women if other forms of diagnostic imaging are inadequate or require exposure to ionizing radiation such as X-ray or CT.
As a safety precaution, MR scanning should be avoided in the first three months of pregnancy.
Similar considerations hold for pregnant staff of a magnetic resonance department. An epidemiological study (by Kanal, et al.) concluded that data collected from MRI technologists were negative with respect to any statistically significant elevations in the rates of spontaneous abortion, infertility and premature delivery.
However, also for psychological reasons, it might be a wise precaution that pregnant staff members do not remain in the scan room during actual scanning.
There have been several reports (results could not be reproduced) that static magnetic fields may provoke genetic mutations, changes in growth rate and leukocyte count and other effects. No reports have been published that persons exposed to magnetic fields, including staff at MR departments, have a higher incidence of genetic damage to their children than found in the average population.
This research needs further investigation and for this purpose pregnancy should be considered a relative contraindication for MR spectroscopy and MRI procedures.
Taking into account that clinical MR imaging devices operate at field strengths of between 0.2 and 2.0 T, higher field strengths need more investigation.


MRI Safety Guidance
Today, there is no sign that MR can harm the fetus or embryo (MRI is used for fetal MRI - fetography). However, if a MRI examination is ordered, there should be a strict indication for this examination.

See also the related poll result: 'MRI will have replaced 50% of x-ray exams by'

• View the NEWS results for 'Pregnancy' (1).Open this link in a new window.

• View the DATABASE results for 'Pregnancy' (5).Open this link in a new window

 
Further Reading:
  News & More:
MRI rules out appendicitis during pregnancy
Wednesday, 1 March 2006   by www.medicineonline.com    
  Contraindications top
Radiology Safety Open this link in a new window
When choosing between two evils, I always like to try the one I've never tried before.
- Mae West
 
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