Safety of strong, static magnetic fields

Issues associated with the exposure of patients to strong, static magnetic fields during magnetic resonance imaging (MRI) are reviewed and discussed. The history of human exposure to magnetic fields is reviewed, and the contr adictory nature of the literature regarding effects on human health is desc ribed. In the absence of ferromagnetic foreign bodies, there is no replicat ed scientific study showing a health hazard associated with magnetic field exposure and no evidence for hazards associated with cumulative exposure to these fields. The very high degree of patient safety in strong magnetic fi elds is attributed to the small value of the magnetic susceptibility of hum an tissues and to the lack of ferromagnetic components in these tissues. Th e wide range of susceptibility values between magnetic materials and human tissues is shown to lead to qualitatively differing behaviors of these mate rials when they are exposed to magnetic fields. Mathematical expressions ar e provided for the calculation of forces and torques. (C) 2000 Wiley-Liss, Inc.