Graf et al reported that torque acting on metallic implants or instruments due to eddy current induction associated with MRI can be considerable. Larger implants such as orthopedic fixation devices made from well-conducting materials are especially affected. Gradient switching was shown to produce fast alternating torque. Significant vibrations at off-center positions of the metal parts may explain why some patients with metallic implants sometimes report feeling sensations of heating during MRI examinations.

Dr. Shellock is an adjunct clinical professor of radiology and medicine at the Keck School of Medicine and director of MRI studies of Biomimetic MicroElectronic Systems (BMES) Implants, National Science Foundation BMES Engineering Research Center, University of Southern California, and Institute for Magnetic Resonance Safety, Education, and Research.
www.MRIsafety.com
www.IMRSER.org

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