Magnetic Stray Field
Most MR instruments are equipped with superconducting magnets designed in ultra-shielded magnet technology to minimize the magnetic flux density of the static magnetic field around the magnet (stray field). Nevertheless, in the vicinity of the magnet, a remaining stray field exists which decreases with increasing distance to the magnet center.
The contours of the magnetic flux density of the static magnetic field around the magnet (stray field) are shown in the diagrams below. According to the Directive 2013/35/EU of the European Parliament on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (electromagnetic fields), the following two Action levels (ALs) are outlined:
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- 0.5 mT: Interference with active implanted devices, e.g. cardiac pacemakers
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- 3 mT: Attraction and projectile risk in the fringe field of high field strength
The risks arising from this magnetic field and the establishment of a controlled access area are discussed in the chapters Safety of the User Documentation and System Owner Manual.
The following figures provide contours of equal field strength (magnetic flux density expressed in Tesla and Gauss) of the magnetic stray field surrounding the magnet and the operation area. These data can be used to
- 1.
- Define the controlled access area around the MR instrument
- 2.
- Define operation procedures that are consistent with the regulations given by occupational standards
- 3.
- Evaluate the MR compatibility of non-Bruker MR products with the MR instrument. The system owner has to ensure that the use of non-Bruker MR products in the vicinity of the magnet does not conflict with the functions of the MR instrument and vice versa.
In principle MR instruments may be used only together with MR-compatible equipment. MR compatible1) equipment is MR safe2) and has additionally no significant influence on the quality of information of the MR instrument. Furthermore the characteristics of the MR compatible equipment are not affected by the MR instrument.
The MR instrument or equipment should not be used adjacent to other equipment. If adjacent or beside use is required, the equipment or the MR instrument should be observed to verify normal operation in the configuration in which it will be used.
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1) The MR conditions under which the equipment was tested must be specified. Since a equipment which is specified to be MR safe or MR compatible under one set of MR-conditions, eventually may not be so under a more extreme MR condition.
2) An MR safe equipment in use does not generates an additional risk in the MR environment neither for the user nor for the sample under investigation. However, it may affect the quality of the data from MR instrument
Further information