To the Editor. —
The Food and Drug Administration1 recently reclassified the magnetic resonance imaging (MRI) scanner from a class III to a class II device and issued revised guidelines for the safe clinical use of this imaging modality. Along with the reclassification, the previously recommended conservative levels of exposure to the electromagnetic fields required for MRI were relaxed significantly.The new recommended safe levels of exposure are as follows: static magnetic fields, 2 T; gradient magnetic fields, 6 T/s or less; and radiofrequency magnetic fields, exposure should not produce a core temperature increase in excess of 1°C or localized heating to greater than 38°C in the head, 39°C in the trunk, or 40°C in the extremities.No long-lasting, hazardous biologic effects have been observed, and none are anticipated from acute or short-term exposures of humans to the static magnetic fields currently used in commercially available MRI scanners.2-4
Shellock FG, Bierman H. The Safety of MRI. JAMA. 1989;261(23):3412. doi:10.1001/jama.1989.03420230064024
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