Guidelines on Exposure to Electromagnetic Fields from Magnetic Resonance Clinical Systems - Safety Code 26

5. Guidance on Exposures

5.1 Patients

Exposures in MR systems which do not exceed the following limits are considered of minimal, if any, health hazard:

1. the static magnetic field: 2 T,
2. the rate of time change of the magnetic field: 3 T/s (rms),
3. RF field which does not cause an increase of body temperature (core or rectal temperature) of more than 0.5oC, and of any part of the body of more than 1oC. These limits are expected to be satisfied, if the specific absorption rates (SARs) do not exceed 1 W/kg as averaged over any 25% of the whole-body mass for exposures of durations longer than 15 min, and 2 W/kg as averaged over any 25% of the whole-body mass for exposures of durations of up to 15 min, where for the balance of the hour the person is not exposed to RF fields produced by the MR device.

Exposures in MR systems which exceed the limits specified are not necessarily hazardous, but a careful, individual evaluation should be done, as the presently available scientific data are not sufficient for providing general recommendations.

5.2 Operators

Operators of MR devices should not be continuously exposed to a magnetic flux density exceeding 0.01 T during the working day. Exposures to higher flux densities are permitted for short-time durations (about 10 minutes per hour); their number and duration should be minimized.

5.3 Special Considerations

Because of potential health hazards, as outlined in Section 4, special consideration should be given and precautionary measures employed when the following categories of patients are examined in MR systems:

1. cardiac pacemaker bearers,
2. persons with metallic clips and other metallic implants,
3. pregnant women.

In cases where cardiac pacemaker bearers are examined in MR devices, continuous medical surveillance and corrective procedures should be available during the examination. However, since many cardiac resuscitation devices do not operate properly in fields above about 10 mT, they have to be used and the patient transferred outside the room where the MR device is located.

For persons with metallic clips and other metallic implants, an individual assessment of suitability for MR examination should be made: In cases where persons having large metallic implants are subjected to MR examination, they should be continuously monitored, and when discomfort is experienced around the site of the implant the exposure should be stopped immediately. Small metallic implants such as tooth fillings are not a problem in MR exposures.

There is no scientific basis to believe than an examination in a MR device that does not exceed the limits specified in paragraph 5.1 is hazardous to a pregnant woman. However, in view of the relatively limited experience with this clinical diagnostic modality, an individual assessment should be made for each pregnant patient.