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The ferromagnetic pillow: a potential MR hazard not detectable by a hand-held magnet

Departments of ¹Clinical Physics and ²Neuroradiology, Institute of Neurological Sciences, 1345 Govan Road, Glasgow G51 4TF, UK

This paper describes an incident in which an apparently normal hospital pillow became a ferromagnetic missile when brought into the proximity of a 1.5 T MR system owing to a fine internal spring system within the pillow. Measurements revealed that the 1 kg pillow reached a maximum velocity of 33.7 km h^-1 after undergoing a maximum acceleration of 9.9g. Non-pathological cervical spines should sustain the measured forces and torques without significant injury. However, the effect could be injurious or even fatal to patients suffering from an existing cervical instability, for example due to rheumatoid arthritis. Of more general concern is the fact that the use of a powerful hand-held magnet did not reveal the presence of ferromagnetic components in this instance. Large objects containing sparsely distributed ferromagnetic materials may not be deflected by such a magnet but could still represent a hazard in the MR environment.