MEDRADSC 2Z03 Lecture Notes - Lecture 13: Ionizing Radiation, Ferromagnetism, Radiography
29 Jun 2016
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Document Summary
Mri is generally considered a safe, non-invasive imaging modality. It does not involve harmful ionising radiation like x-rays (ct) or radioisotopes (pet). There are no known permanent biological effects of short term exposure to high static magnetic fields. Another infrequent side effect is peripheral nerve stimulation, an effect caused by rapidly switching and alternating pulsed field gradients that induce currents in the body, causing muscles to twitch. While potentially uncomfortable or even painful, these effects are not harmful in short exposure. The major dangers involved with mri arise from the presence of the field itself, and the potential for heating of tissue by rf energy. By their nature, strong magnets attract ferromagnetic objects, whether they be within the human body or outside it. The fringe field of a magnet rapidly drops off with distance from the magnet, but strong fields can exist up to a few metres from the magnet.
