Fabrication of an MRI Model Magnet With an Off-Centered Distribution of Homogeneous Magnetic Field Zone

Magnetic resonance imaging (MRI) requires a highly homogenous magnetic field zone which usually appears at the center of the MRI magnet coil. If this homogeneous zone is allowed to occur at an off-centered position along the coil axis, quite new applications of MRI may be possible. In order to examine this idea, we fabricate a model magnet consisting of several NbTi coils and generating a vertical magnetic field of 0.77 T; coil outer diameter is 307 mm, coil length 191 mm, designed field homogeneity 5 ppm @ 35 mm DSV, and the location of homogeneous field zone 29.4 mm off-centered along the vertical coil axis. As an example of application of this type of MRI, we will discuss about a functional-MRI-based Benton visual retention test which is currently adopted on dementia. This test requires patients to carry out some work like drawing, so that they need some field of vision while sitting in the magnet. The off-centered homogeneous field zone is expected to provide the necessary field of vision.