4703276 Permanent magnet ring assembly for NMR imaging system and method for using such assembly

Abstract

An NMR imaging system includes apparatus for producing a uniform magnetic field in a predetermined volume. Such apparatus includes a ring assembly having an axial extent L defined by a plurality of nonmagnetic rings, each having an axis and positioned side-by-side so that the axes of the rings are colinear and define the axis of the ring assembly. A plurality of discrete permanent magnet segments are angularly mounted within each ring for defining a central coaxial aperture. Each segment in a ring has a easy axis of magnetization whose orientation is functionally related to the angular position of the segment in the ring. Each segment has inner and outer edges that are nominally located at distances r 1 and r 2 , respectively, from the axis of the ring from which it is mounted. The inner free ends of the segments of all of the rings define a central aperture of length L within the ring assembly. Finally, an adjustment is provided for moving the segments in each ring such that the distance r 1 and r 2 of each segment are non-uniformly, but functionally related to the axial extent L of the assembly.