Magnetic pull: biological effects or medical applications?

One of the questions on the IMS 2005 Quiz, is related to the magnetic fields used in magnetic resonance imaging (MRI) machines. In particular, it asked: an MRI (magnetic resonance imaging) machine uses: a) high-intensity static magnetic fields; b) time-varying magnetic fields in the kHz range; c) radio-frequency (RF) fields in the MHz range; and d) All of the above. The correct answer, d) All of the above, highlights the fact that an MRI machine employs all three types of fields in order to accomplish three-dimensional imaging for medical diagnostics. Therefore, in terms of safety, electromagnetic field exposure to patients and medical personnel needs to be assessed for all three types of fields. This is a much greater concern for open MRI systems, where the magnet surrounds the patient only partially in order to allow the medical personnel to perform procedures on the patient, guided by the MRI images. The IEEE Committee on Man and Radiation (COMAR) is in the final stages of preparing a technical information statement (TIS) on the subject.