Gradient field structure and method for use with magnetic resonance imaging apparatus

In a magnetic imaging apparatus, an electromagnet providing an opening for receiving the object to be imaged, said electromagnet having first and second coil assemblies providing a main magnetic field in the opening and first and second spaced apart substantially planar gradient field structures providing a set of three two-dimensional quadrupole fields in the opening, said gradient field structures comprising arrays of conductors having substantially rectangular geometries lying in planes, the conductors having being distributed in space in each plane with respect to each other to provide a desired current distribution in each plane, each of said gradient field structures including an x gradient coil, a y gradient coil and a z gradient coil, each of said gradient field structures also including a plurality of trim coils, each of said x, y and z coils and said trim coils being provided in separate superposed sheets, the x and y coils each being carried by a sheet of non-conducting material, a plurality of spaced parallel conductors carried by the sheet of non-conducting material in such a manner so that the current flow in the conductors is in the same direction.

In a method for creating an image of an object disposed in a space by the use of magnetic resonance, creating a main magnetic field in the space, creating a set of three two-dimensional quadrupole fields in the space, each of the two dimensional quadrupole fields being formed by a plurality of substantially parallel current paths arranged in a substantially rectangular geometry lying in a plane to provide a sheet-like current distribution.

In a magnetic resonance imaging apparatus for imaging an object, an electromagnet providing an opening forming a space having a central axis for receiving the object to be imaged and providing a main magnetic field in the opening, first and second gradient field structures lying in spaced apart planes and providing a set of three two-dimensional magnetic fields having approximately quadrupole symmetry near the central axis to produce approximately linear gradients in the main field in each of three orthogonal directions and, means linearly combining the three two-dimensional fields to superimpose upon the main magnetic field a single substantially linear gradient oriented in any desired arbitrary direction in the space formed by the opening.

In a magnetic resonance imaging apparatus for imaging an object, an electromagnet providing an opening forming a space having a central axis for receiving the object to be imaged and providing a main magnetic field in the opening and first and second gradient field structures providing a set of two-dimensional quadrupole magnetic fields having approximately quadrupole symmetry near the central axis to produce approximately linear gradients in the main field in each of three orthogonal directions whereby a linear combination of the three fields can be created to superimpose upon the main magnetic field a single substantially linear gradient oriented in any desired arbitrary direction in the space formed by the opening, each of the gradient field structures being comprised of a plurality of arrays of conductors lying in substantially parallel planes, the conductors in each plane having at least portions thereof spaced apart and parallel to each other to form current sheets.

In a magnetic resonance imaging apparatus for imaging an object, an electromagnet providing an opening forming a space having a central axis for receiving the object to be imaged and providing a main magnetic field in the opening, first and second gradient field structures lying in spaced apart planes and providing a set of three two-dimensional magnetic fields having approximately quadrupole symmetry near the central axis to produce approximately linear gradients in the main field in each of three orthogonal directions, and means linearly combining the three two-dimensional fields to superimpose upon the main magnetic field a single substantially linear gradient oriented in any desired arbitrary direction in the space formed by the opening, the gradient field structures being comprised of planar sheet-like structures, each of the sheet-like structures including an array of conductors lying in a substantially parallel plane and wherein at least portions of the conductors are spaced apart and parallel to each other.

In a magnetic resonance imaging apparatus for imaging an object, an electromagnet providing an opening forming a space having a central axis for receiving the object to be imaged and providing a main magnetic field in the opening and first and second gradient field structures providing a set of two-dimensional quadrupole magnetic fields having approximately quadrupole symmetry near the central axis to produce approximately linear gradients in the main field in each of three orthogonal directions whereby a linear combination of the three fields can be created to superimpose upon the main magnetic field a single substantial linear gradient oriented in any desired arbitrary direction in the space formed by the opening, the gradient field structures being positioned so that the forces introduced by the interaction of the gradient fields with the main field are in the planes of the gradient field structures.

In a method for magnetic resonance imaging of an object in a space defined by an opening, creating a main magnetic field in the space, creating a set of three quadrupole fields to establish approximately linear gradients in the main field in each of three orthogonal directions and combining the three quadrupole fields linearly to create a substantially linear gradient on the main field which can be oriented in any desired arbitrary direction in the space.

In a magnetic resonance imaging apparatus for imaging an object, an electromagnet providing an opening forming a space having a central axis for receiving the object to be imaged and providing a main magnetic field in the opening, first and second gradient field structures lying in spaced apart planes and providing a set of three two-dimensional magnetic fields having approximately quadrupole symmetry near the central axis to produce approximately linear gradients in the main field in each of three orthogonal directions and means linearly combining the three two-dimensional fields to superimpose upon the main magnetic field a single substantially linear gradient oriented in any desired arbitrary direction in the space formed by the opening, each of the gradient field structures being formed in sections and each being electrically excited independently to facilitate trimming of the main field.