Safety in Simultaneous Ultra-Low-Field MRI and MEG: Forces Exerted on Magnetizable Objects by Magnetic Fields

摘要

Ultra-low-field magnetic resonance imaging (ULF-MRI) and magnetoencephalography (MEG) can be combined to a unified imaging modality (MEG-MRI). To enhance the ULF-MR image quality in MEG-MRI, it is necessary to apply a prepolarization field of the order of 1-100 millitesla. When constructing the ULF-MRI apparatus, the effects of the prepolarization field and its gradients need to be considered as to what kinds of magnetizable objects are safe in their vicinity. The shape of the objects plays a role in the forces induced on them. Also, magnetized objects within the body may be subject to a torque that may press the tissue. These effects are investigated in this work.