MR safety at high magnetic fields

MR imaging requires the exposure of human patients to magnetic fields that are much more intense than ever occur naturally. Under most circumstances, however, these fields do not appear to pose a health or safety risk even at levels well above those currently in clinical use. This margin of safety results from the extreme weakness of the diamagnetic interaction between human tissues and magnetic fields. Ferromagnetic materials, however, present either as implants within the patient or inadvertently introduced into the scanner environment, pose significant risks and must be scrupulously avoided. At very high field strengths, there is evidence for mild sensory effects, such as vertigo and metallic tastes, which do not appear to be harmful.