Health and safety risks in the design and construction of magnetic shielding for magnetic resonance imaging (MRI) suites

Price, Terence Raymond

Abstract

Once energised, and even when the equipment is not imaging, magnets used in magnetic resonance imaging will produce a static magnetic field that extends in three dimensions around the magnet. This static magnetic field is invisible; it is impossible to know that it is present or to be aware of it unless told. It is important to know the position and magnetic flux density of the static magnetic field because those persons having ferromagnetic material embedded within their bodies or their eyes (the result of a welding process for example), or fitted with electronic body implants, could suffer harm from the effects of the static magnetic field at relatively low levels. Those individuals fitted with some heart pacemakers could be affected at 0.5 mT.

The published literature relating to magnetic resonance imaging is, by its nature, restricted to the medico-technical-academic press and does not systematically appear in publications destined for construction professionals. There is no published literature relating to the design of magnetic shielding for MRI suites as it relates to health and safety risks to those exposed to the static magnetic field during the construction, maintenance and demolition phases of a magnetic resonance imaging project.

This thesis is progressive in its structure and fills gaps in knowledge by commencing with a study to determine if the requirements placed on duty holders as defined by The Construction (Design and Management) Regulations 2007 (CDM) and its antecedent regulations are understood by all those parties involved with the conception, design, construction and maintenance of an MRI suite. Several misconceptions are highlighted. A second study gave an evaluation of the availability of as-built drawings showing the position of the 0.5 mT footprint of the static magnetic field of the magnet and gives disappointing results. The third study was to assess the effectiveness of a retrofit installation of passive magnetic shielding and highlights some failings, with the fourth study to investigate if magnetic shielding had been installed to an operational MRI suite. The fifth study was to review if the client had considered the magnetic shielding design requirements of a magnet before it was installed.
Finally, the sixth case study was to evaluate if there was a clear understanding by designers of the function and attributes of RF shielding and of passive magnetic shielding to a Faraday cage. Examples, by the inclusion of annotated drawings, are given.
There was not a clear understanding by CDM duty-holders of responsibilities placed upon them under the CDM Regulations. The introduction of magnetic shielding into a magnetic resonance suite design can distort the symmetry of the 0.5 mT footprint of the static magnetic field, create areas of increased magnetic flux density and push parts of the 0.5 mT footprint to the outside of any designated controlled area. This will consequentially increase the risk of unscreened persons (both inside and outside the control of the employer) being exposed to the effects of the static magnetic field unless the magnitude and position of the 0.5 mT footprint is documented and disseminated to all those persons likely to come into contact with it. The incorporation of magnetic shielding as retrofit can result in leakages of magnetic flux at its joint with the finished floor and through any shielding fixing bolts.
This thesis could be useful to designers in developing risk management plans for MRI suite construction, maintenance and demolition. By making a synthesis that has not been made before, this thesis makes a contribution to knowledge by addressing these issues for the first time.

Citation

Price, T. R. Health and safety risks in the design and construction of magnetic shielding for magnetic resonance imaging (MRI) suites. (Thesis). Edinburgh Napier University. Retrieved from http://researchrepository.napier.ac.uk/id/eprint/5032

• Thesis Type: Thesis
• Deposit Date: Feb 28, 2012
• Peer Reviewed: Not Peer Reviewed
• Keywords: Magnetic resonance imaging; static magnetic field; RF shielding; magnetic flux density; rislk management
• Public URL: http://researchrepository.napier.ac.uk/id/eprint/5032
• Award Date: Feb 25, 2012