Patent ID: 8610436

Claim:
A permanent magnet particularly for MRI scanners, which magnet has a tubular shape defined by a tube-like three-dimensional wall defining a longitudinal axis and a cross-section with respect to said longitudinal axis and wherein the cross-section has a closed annular shape, the tube-like three-dimensional wall being composed of a plurality of individual elements made of magnetized material having a longitudinal extension parallel to the axis of the tubular shape, said individual elements being arranged one after the other all the adjacent elements made of magnetized material or all of them except for two subsequent elements of magnetized material being provided one in contact to the other along at least a peripheral surface or a linear edge thereof having a longitudinal extension parallel to the axis of the tubular shape; wherein the magnetization of each said individual element made of magnetized material has a predetermined magnetization direction in a plane perpendicular to the longitudinal axis of the tube-like wall, said magnetization directions being defined so as to generate a uniform static magnetic field having a predetermined strength and a predetermined direction which field passes through a cavity delimited by the tube-like three-dimensional wall, wherein the magnetization direction of at least some individual elements is rotated in said plane perpendicular to the longitudinal axis of the tube-like three-dimensional wall with respect to a theoretical magnetization direction calculated on the basis of a two-dimensional (2D) magnet model corresponding to a cross-section of the tube-like three-dimensional wall of the magnet, while the remaining individual elements keep the theoretical magnetization direction calculated on the basis of said 2D magnet model, and wherein the at least some individual elements are rotated by a predetermined angle calculated such that differences of strength, direction and homogeneity parameters of a static magnetic field generated by a 3D model of the magnet and strength, direction and homogeneity parameters of an ideal static magnetic field according to the 2D magnet model are minimized.