Foreign body lesions in MR tomography

The hazard involved in MR tomography if there are foreign parts in the body made of metal, is assessed. There are certain hazard-influencing factors. As far as the foreign body is concerned, these are: ability to become magnetised, size, length, elasticity, sharp edges or ends, and sharp surfaces. In the human body itself, risk factors are determined by the position of the foreign body in or near sensitive organs such as cerebrum, nerves, vessels, lungs, eyes, ears and the heart; other factors are the fixation to bones or lack of fixation in hollow organs. One should assume when assessing the risk that the foreign body consists of iron that is capable of complete magnetisation. In that case the attacking forces will not exceed the 25 to 36 fold value of the foreign body's own weight. It is thus possible to predict with some measure of probability whether the position of the foreign body will shift during MR examination and whether the examination can result in injury. (orig.)