Patent ID: 6313634
Filing Date: 2001-11-06
Classification: G01R

Abstract:
Device to homogenize a magnetic field created in a working volume by a main magnet of a magnetic resonance apparatus, the device essentially surrounding the working volume and comprising a multitude of ferromagnetic platelets (shims) mounted in stacks of predetermined numbers at fixed positions into one or more support structures removably attached to the main magnet wherein the fixed positions, numbers of platelets at these positions and magnetization strength of the platelets are chosen such that in combination they essentially cancel field inhomogenities of the main magnet across the working volume, and further comprising means, to which at least some of the shim stacks are mounted, for moving said at least some shim stacks about their fixed positions with small amplitudes along at least one direction for an actual fine correction, wherein the means for moving comprised piezo translators that are mounted to the support structures and that carry the shim stacks.