Magnet assembly for use in NMR apparatus

Abstract

A magnet assembly (1) particularly for use in NMR apparatus comprises a first superconducting coil assembly (A,A'-C,C') for generating a first magnetic field; and a second superconducting coil assembly (D-F) for generating a second magnetic field. The second superconducting coil assembly (D-F) is electrically connected in series with the first superconducting coil assembly (A,A'-C,C'). Each coil assembly (A,A'-C,C'; D-F) generates magnetic fields where corresponding components are of substantially the same order of magnitude whereby a resultant, uniform magnetic field is generated in a working volume (3). The second magnetic field opposes the first magnetic field externally of the magnet assembly (1).

We claim: 
     
       1. A nuclear magnetic resonance magnet assembly comprising a first superconducting .Iadd.nuclear magnetic resonance .Iaddend.coil assembly .Iadd.having a first radius, .Iaddend.defining a working volume .Iadd.for human imaging having radial and axial dimensions .Iaddend.and adapted to generate a first magnetic field in said working volume; and a second superconducting .Iadd.nuclear magnetic resonance .Iaddend.coil assembly adapted to generate a second magnetic field, said second superconducting coil assembly .Iadd.having a second radius larger than the first radius and .Iaddend.being electrically connected in series with said first superconducting coil assembly, wherein said first and second superconducting coil assemblies are each adapted to generate magnetic fields whose corresponding components are of substantially the same order of magnitude, said .Iadd.coil .Iaddend.assemblies being arranged such that a resultant, uniform magnetic field .Iadd.with a uniformity equal to or better than approximately 400 parts per million .Iaddend.is generated in said working volume .Iadd.in the radial and axial dimensions, one of said coil assemblies having coils each with an independent position along an axis of the magnet and the coils being positioned as a group to provide the uniform field.Iaddend., and said second magnetic field opposes said first magnetic field externally of said magnet assembly. 
     
     
       2. .[.An.]. .Iadd.A magnet .Iaddend.assembly according to claim 1, wherein said .Iadd.magnet .Iaddend.assembly defines a mid-plane, said first superconducting coil assembly comprising a plurality of coaxial coils defining an axis and arranged symmetrically about said mid-plane of said magnet assembly normal to said axis. 
     
     
       3. .[.An.]. .Iadd.A magnet .Iaddend.assembly according to claim 1, wherein said .Iadd.magnet .Iaddend.assembly defines a mid-plane, said second superconducting coil assembly comprising a plurality of coaxial coils defining an axis and arranged symmetrically about said mid-plane of said magnet assembly normal to said axis. 
     
     
       4. .[.An.]. .Iadd.A magnet .Iaddend.assembly according to claim 1, wherein said .Iadd.magnet .Iaddend.assembly defines a mid-plane, said first superconducting coil assembly comprising a plurality of coaxial coils defining an axis and arranged symmetrically about said mid-plane of said magnet assembly normal to said axis and said second superconducting coil assembly comprising a plurality of coaxial coils defining an axis and arranged symmetrically about said mid-plane of said magnet assembly normal to said axis, wherein said axes of said coils of said first and second superconducting coil assemblies are coincident. 
     
     
       5. .[.An.]. .Iadd.A magnet .Iaddend.assembly according to claim 1, further comprising a shield of magnetic material arranged around at least said first superconducting coil assembly. 
     
     
       6. .[.An.]. .Iadd.A magnet .Iaddend.assembly according to claim 5, wherein said shield is made of iron. 
     
     
       7. .[.An.]. .Iadd.A magnet .Iaddend.assembly according to claim 5, further comprising a former supporting said second superconducting assembly; said shield being constituted by said former. 
     
     
       8. .[.An.]. .Iadd.A magnet .Iaddend.assembly according to claim 7, wherein said former is made of iron. 
     
     
       9. .[.An.]. .Iadd.A magnet .Iaddend.assembly according to claim 1, wherein said .Iadd.magnet .Iaddend.working volume defines opposed ends, said assembly further comprising a pair of additional coils positioned adjacent to each of said ends of said working volume and arranged to oppose the resultant magnet field generated by said first and second coil assemblies at these positions. 
     
     
       10. NMR imaging apparatus incorporating a magnet assembly comprising a first superconducting .Iadd.NMR .Iaddend.coil assembly .Iadd.having a first radius, .Iaddend.defining a working volume .Iadd.for human imaging having radial and axial dimensions .Iaddend.and adapted to generate a first magnetic field in said working volume; and a second superconducting .Iadd.NMR .Iaddend.coil assembly .Iadd.having a second radius larger than the first radius and .Iaddend.adapted to generate a second magnetic field, said second superconducting coil assembly being electrically connected in series with said first superconducting coil assembly, wherein said first and second superconducting coil assemblies are each adapted to generate magnetic fields whose corresponding components are of substantially the same order of magnitude, said .Iadd.coil .Iaddend.assemblies being arranged such that a resultant, uniform magnetic field .Iadd.with a uniformity equal to or better than approximately 400 parts per million .Iaddend.is generated in said working volume, .Iadd.in the radial and axial dimensions, one of said coil assemblies having coils each with an independent position along an axis of the magnet and the coils being positioned as a group to provide the uniform field .Iaddend.and said second magnetic field opposes said first magnetic field externally of said magnet assembly; a power supply for activating said first and second superconducting coil assemblies; and control means for controlling operation of the apparatus. .Iadd. 
     
     
       11.  A nuclear magnetic resonance magnet assembly defining a mid-plane and comprising a first superconducting nuclear magnetic resonance coil assembly having a first radius, defining a working volume for human imaging having radial and axial dimensions, adapted to generate a first magnetic field in said working volume and comprising a plurality of coaxial coils defining an axis and arranged symmetrically about said mid-plane of said magnet assembly normal to said axis; and a second superconducting nuclear magnetic resonance coil assembly having a second radius larger than the first radius and adapted to generate a second magnetic field, said second superconducting coil assembly being electrically connected in series with said first superconducting coil assembly, wherein said first and second superconducting coil assemblies are each adapted to generate magnetic fields whose corresponding components are of substantially the same order of magnitude, said coil assemblies being arranged surrounding said working volume such that a resultant, uniform magnetic field with a uniformity equal to or better than approximately 400 parts per million is generated in said working volume in the radial and axial dimensions, the coils each having an independent position along the axis of the magnet and the coils being positioned as a group to provide the uniform field, and said second magnetic field opposes said first magnetic field externally of said magnet assembly. .Iaddend..Iadd. 
     
     
       12.  A nuclear magnetic resonance magnet assembly comprising a first superconducting nuclear magnetic resonance coil assembly having a first radius, defining a working volume for human imaging having radial and axial dimensions and adapted to generate a first magnetic field in said working volume; and a second superconducting nuclear magnetic resonance coil assembly having a second radius larger than the first radius and adapted to generate a second magnetic field, said second superconducting coil assembly being electrically connected in series with said first superconducting coil assembly, wherein said first and second superconducting coil assemblies are each adapted to generate magnetic fields whose corresponding components are of substantially the same order of magnitude, said coil assemblies being arranged concentrically with respect to said working volume such that a resultant, uniform magnetic field with a uniformity equal to or better than approximately 400 parts per million is generated in said working volume in the radial and axial dimensions, one of said coil assemblies having coils each with an independent position along an axis of the magnet and the coils being positioned as a group to provide the uniform field, and said second magnetic field opposes said first magnetic field externally of said magnet assembly. .Iaddend..Iadd.13. A nuclear magnetic resonance magnet assembly comprising a first superconducting nuclear magnetic resonance coil assembly having a first radius, defining a working volume for human imaging having radial and axial dimensions and adapted to generate a first magnetic field in said working volume; and a second superconducting nuclear magnetic resonance coil assembly having a second radius larger than the first radius and adapted to generate a second magnetic field, said second superconducting coil assembly being electrically connected in series with said first superconducting coil assembly, wherein said first and second superconductor coil assemblies are each adapted to generate magnetic fields whose corresponding components are of substantially the same order of magnitude, said coil assemblies being arranged with respect to said working volume such that a resultant, uniform magnetic field with a uniformity equal to or better than approximately 400 parts per million is generated in said working volume in the radial and axial dimensions sufficient for nuclear magnetic resonance, one of said coil assemblies having coils each with an independent position along an axis of the magnet and the coils being positioned as a group to provide the uniform field, and said second magnetic field opposes said first magnetic field externally of said magnet assembly. .Iaddend..Iadd.14. A nuclear magnetic resonance magnet assembly comprising a first superconducting nuclear magnetic resonance coil assembly having a first radius, defining a working volume for human imaging having radial and axial dimensions and adapted to generate a first magnetic field in said working volume; and a second superconducting nuclear magnetic resonance coil assembly having a second radius larger than the first radius and adapted to generate a second magnetic field, said second superconducting coil assembly being electrically connected in series with said first superconducting coil assembly, wherein said first and second superconducting coil assemblies are each adapted to generate magnetic fields whose corresponding components are of substantially the same order of magnitude, said coil assemblies comprising coils defining a mid-plane and an axis in said working volume, and being arranged at radial and axial positions with respect to the axis and at positions with respect to each other as a group to generate a resultant, uniform magnetic field with a uniformity equal to or better than 400 parts per million in said working volume in the radial and axial dimensions, and to generate opposing fields externally of said magnet assembly. .Iaddend..Iadd.15. A nuclear magnetic resonance magnet assembly comprising a first superconducting nuclear magnetic resonance coil assembly having a first radius, defining a working volume for human imaging having radial and axial dimensions and adapted to generate a first uniform, magnetic field in said working volume; and a second superconducting nuclear magnetic resonance coil assembly having a second radius larger than the first radius and adapted to generate a second uniform magnetic field, said second superconducting coil assembly being electrically connected in series with said first superconducting coil assembly, wherein said first and second superconducting coil assemblies are each adapted to generate magnetic fields whose corresponding components are of substantially the same order of magnitude, said coil assemblies being arranged with respect to said working volume such that a resultant, uniform magnetic field with a uniformity equal to or better than approximately 400 parts per million and combining said first and second uniform magnetic fields is generated in said working volume one of said coil assemblies having coils each with an independent position along an axis of the magnet and the coils being positioned as a group to provide the uniform field, and said second magnetic field opposes said first 
     
     
        magnetic field externally of said magnet assembly. .Iaddend..Iadd.16.  A nuclear magnetic resonance magnet assembly comprising a first superconducting nuclear magnetic resonance coil assembly having a first radius, defining a working volume for human imaging having radial and axial dimensions and adapted to generate a first non-uniform, magnetic field in said working volume; and a second superconducting nuclear magnetic resonance coil assembly having a second radius larger than the first radius and adapted to generate a second non-uniform, magnetic field, said second superconducting coil assembly being electrically connected in series with said first superconducting coil assembly, wherein said first and second superconducting coil assemblies are each adapted to generate magnetic field whose corresponding components are of substantially the same order of magnitude, said coil assemblies being arranged with respect to said working volume such that a resultant, uniform magnetic field, with a uniformity equal to or better than 400 parts per million and combining said first and second non-uniform magnetic fields, is generated in said working volume in the radial and axial dimensions, said coil assemblies comprising coils each having an independent position along an axis of the magnet and the coils being positioned as a group to provide the uniform field and said second magnetic field opposes said first magnetic field externally of said magnet assembly. .Iaddend..Iadd.17. A magnet assembly according to claim 1, 10, 11, 12, 13, 14, 15 or 16, further comprising a protective resistance connected in parallel to said first and second 
     
     
        superconducting coil assemblies. .Iaddend..Iadd.18.  A nuclear resonance magnet, comprising: a first nuclear magnetic resonance coil assembly defining a working volume for human imaging having radial and axial dimensions, said first assembly having an axis and a first radius and having first coils positioned at independent positions along the axis, the first coils generating a first non-uniform magnetic field having a first magnitude; and   a second nuclear magnetic resonance coil assembly having a second radius larger than the first radius, said second assembly electrically connected in series with said first assembly and having coils positioned at independent positions along the axis, the second coils generating a second non-uniform magnetic field opposing the first field and having a second magnitude of substantially the same order as the first magnitude, the first and second coils being positioned at the independent positions producing a resultant uniform field having the radial and axial dimensions of the working volume the uniform field having a uniformity equal to or better than 400 parts per million, and the first coils being positioned at the positions also suppressing the first non-uniform magnetic field externally of the magnet and shielding objects external of the magnet from magnetic influence of the magnet. .Iaddend.