Measurements of occupational exposure to switched gradient and spatially-varying magnetic fields in areas adjacent to 1.5 T clinical MRI systems.
OBJECTIVE
To determine if magnetic field exposure close to two clinical 1.5 T magnetic resonance imaging (MRI) scanners during image acquisition and when moving in the spatially-varying static magnetic field is compliant with European Union (EU) Directive 2004/40/EC (the Directive).


METHODS
Using commercially available equipment we measured the magnetic flux density around the scanners during two clinical pulse sequences. The data was compared with frequency-dependent limits that will limit occupational exposure following transposition of the Directive into national law in 2008. The static magnetic field was measured around the scanners and the exposure from movement within this field was simulated.


RESULTS
The whole-body exposure experienced when standing close to the face of the magnet exceeds the limits in the Directive on the two scanners tested during clinical sequences. Simulation of movement toward the scanner shows that speeds must be restricted to 1/5 of normal walking speed to comply with the Directive.


CONCLUSIONS
EU Directive 2004/40/EC will have a major impact on the current use and future development of MRI due to limitations on exposure to time-varying gradient fields and movement within the spatially-varying static field. This will make interventional work impossible and routine MRI use impracticable in Europe.
Riches
Sophie F
SF
Cancer Research UK Clinical Magnetic Resonance Research Group, Royal Marsden NHS Trust and Institute of Cancer Research, Surrey, UK. sophie.riches@icr.ac.uk
Collins
David J
DJ
Charles-Edwards
Geoffrey D
GD
Shafford
Jonathan C
JC
Cole
Jonathan
J
Keevil
Stephen F
SF
Leach
Martin O
MO
D001822:Body Burden; D003198:Computer Simulation; D004574:Electromagnetic Fields; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008280:Magnetics / Q000295:instrumentation*; D008503:Medical Staff; D008954:Models, Biological; D016273:Occupational Exposure / Q000032:analysis*; D011829:Radiation Dosage; D011834:Radiation Monitoring / Q000379:methods; D012062:Relative Biological Effectiveness; D006113:United Kingdom; D014915:Whole-Body Counting / Q000379:methods*