Proposal for a permanent magnet system with a constant gradient mechanically adjustable in direction and strength

A design for a permanent magnet system is proposed that generates spatially homogeneous, constant magnetic field gradients, thus creating conditions suitable for MRI without gradient coils and amplifiers. This is achieved by superimposing a weak Halbach quadrupole on a strong Halbach dipole. Rotation of either the quadrupole or the entire magnet assembly can be used to generate two-dimensional images via filtered backprojection. Additionally, the mutual rotation of two quadrupoles can be used to scale the resulting gradient. If both gradients have identical strength the gradient can even be made to vanish. The concept is demonstrated by analytical considerations and FEM simulations. However, a demonstration on a working prototype is still pending. (c) 2016 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 46B: 41-48, 2016