Open architecture magnetic resonance imaging passively shimmed superconducting magnet assembly

Claim 1

An open architecture magnetic resonance imaging magnet utilizing a separated pair of superconducting magnet coil assemblies positioned about the axis thereof and forming an axial bore to receive patients, and providing open radial space between the magnet coil assemblies to minimize confinement to the patient within the axial bore and to maximize access to the patient in the open radial space comprising: a first annular superconducting magnet assembly positioned about said axis including a first axially extending central opening; a second annular superconducting magnet assembly positioned about said axis, and spaced from and substantially parallel to said first magnet assembly including a second axially extending central opening; said bore formed by said central axially extending openings of said first and second magnet assemblies about said axis; a plurality of spacers extending between said first magnet coil assembly and said second magnet coil assembly; each of said magnet assemblies including at least one superconducting magnet coil in a housing and means to cool the interior of said housing and said magnet coil to superconducting temperatures to provide a magnetic field within said bore; said magnet assemblies being configured and positioned to preclude a negative Z2 component of said magnetic field and providing a substantial positive Z2 magnetic field in the central patient imaging region in the axial space of the bore between and outside the bores of the superconducting magnet coil assemblies; and a passive magnetic shim assembly positioned substantially within and contiguous to at least one of said axially extending central openings of said housing without axially extending through the region between said housings, and including a plurality of magnetic shim members selectively positionable on said passive shim assembly and about said axis to improve the magnetic homogeneity in said central opening of said bore between said magnet coil assemblies; whereby said patient imaging region between said housings is substantially free of magnetic shim members and whereby said magnetic coil assemblies provide an inhomogeneous magnetic field in said central patient imaging region therebetween which said shim members improve.