Magnetic resonance techniques are considered to be not harmful. The three electromagnetic fields used for MR - static magnetic field, switched gradient fields, and radio frequency field - interact with human tissue, but also with other materials exposed to these fields. The physical interactions with human tissue do not cause irreversible physiological effects, as long as certain limits are not exceeded. Concerning foreign material (e.g. implants), the physical effects of the applied fields may cause severe hazards for patients, staff, and material, if MR examinations are not performed properly.