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Regarding permanent and resistive magnets: a. Permanent magnets used in MRI are often manufactured from ferrite b. Resistive magnets usually contain an iron yolk c. Typical strengths of the produced magnetic field are 0.2–0.3 T for permanent magnets and up to 1 T for resistive magnets d. At similar field strengths, the fringe field is more extensive in permanent than in resistive magnets e. The main use of permanent and resistive magnets is in open MRI systems |
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Answer» a. False. They are usually made from rare earth materials – typically neodymium-iron-boron (NIB) or samarium cobalt (SmCo). b. True. Old air-cored designs are no longer in use. c. False. The value for permanent magnets is correct; however, currently available iron-cored resistive magnets give field strengths of up to 0.6 T only. d. False. In permanent magnets, the fringe field is almost entirely contained within the magnet. e. True. |
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