Solenoidal, octopolar, transverse gradient coils

Claims

I claim:

1. A non-ferromagnetic transverse gradient coil system having a central axis, said system comprising:

an even number of solenoidal-like central axial coils having a major diameter wound on rigid coilforms having axial coil axes parallel to said central axis and positioned such that the distance between said central axis and each said axial coil axis is greater than the major diameter of said axial coils, the coils arranged in two groups, the groups substantially symmetrical to each other with respect to 180.degree. rotation about the central axis, the coils being substantially symmetrical with respect to reflection through a plane perpendicular to said central axis.

2. The coil system of claim 1 wherein each of said axial coils further characterized by having turns density at symmetrical non-central locations greater than the turns density near its center.

3. The coil system of claim 1 wherein each of the groups of coils further comprises a pair of saddle coils symmetrically disposed one near a first end of the axial coils and the other near the other end of the axial coils, said saddle coils having axes aligned substantially radially from said central axis.

4. The coil system of claim 1 in which each axial coil further comprises end coils coaxial with the central coil thereof and symmetrically secured beyond the end of said central coil.

5. The coil system of claim 1 further comprising a metallic shield cylinder having electrical conductivity less than 30 nano-ohm-meters symmetrically surrounding said coil system.

6. The coil system of claim 1 in which said rigid coilforms are made from a nonmetallic material have elastic modulus greater than 12 GPa and density greater than 2 g/cm.sup.3.

7. The coil system of claim 1 in which said central coils are further characterized by having windings inclined with respect to the coil axis.

8. The coil system of claim 1 in which said rigid coilforms have substantially trapezoidal cross-section.

9. The coil system of claim i further comprising a plurality of cross coils disposed at each end of said central coils, said cross coils having axes aligned substantially radially.

10. The coil system of claim 9 in which said axial coils generate a transverse gradient field and in which said saddle coils, when energized, generate a transverse quadrupolar field such that said transverse gradient field is increased in said central region.

11. The coil system of claim 10 in which said end coils and said central coils, when energized, generate a magnetic field with a substantial axial quadrupolar component.

12. The coil system of claim 1 in which said rigid coilforms have substantially round cross-section.

13. The coil system of claim 1 in which said coilform made from a material selected from the set consisting of alumina, silicon nitride, zirconia, alumina-silica-boria glasses, borosilicate glasses, machinable glasses, plastic composites having at least 10% carbon fiber content, plastic composites having more than 25% ceramic fiber content, and plastic composites having density greater than 2.0 g/cm.sup.3.

14. An x-y gradient coil system comprising first and second non-ferromagnetic transverse gradient coil systems, each transverse gradient coil system being substantially symmetrical with respect to 180.degree. rotation about a central axis and substantially symmetrical with respect to reflection through a plane perpendicular to said central axis, each said transverse gradient coil system comprising an even number of solenoidal-like central axial coils having a major diameter wound on rigid coilforms having axial coil axes parallel to said central axis and positioned such that the distance between said central axis and each said axial coil axis is greater than the major diameter of said axial coils, each of said axial coils further characterized by having turns density at symmetrical non-central locations greater than the turns density near its center, the central axes of the transverse gradient coil systems being coincident, the transverse gradient coil systems being oriented orthogonally to each other, whereby said x-y coil system is capable of producing transverse gradients in the central axial field in two orthogonal directions.

15. The coil system of claim 14 in which said central axial coils are substantially round in cross section.

16. The coil system of claim 14 in which said central axial coils are substantially trapezoidal in cross section.

17. A gradient coil system for use in magnetic resonance imaging employing a superconducting magnet to establish a magnetic field B.sub.Z, said coil system comprising:

current conducting elements disposed to generate a transverse gradient in B.sub.z, said conducting elements arranged such that they are substantially nonparallel to B.sub.z over more than 80% of their total length;

a rigid form to support said conducting elements; and

said conducting elements further comprising:

a plurality of loops having dipole moment parallel to B.sub.Z ;

a plurality of loops having dipole moment perpendicular to B.sub.Z ;

said loops arranged substantially symmetrically with respect to a 180.degree. rotation about the z axis and substantially symmetrically with respect to a reflection through a plane perpendicular to said axis.

18. The coil system of claim 17 in which said loops having dipole moment parallel to B.sub.Z are substantially round.

19. The coil system of claim 17 in which said loops having dipole moment parallel to B.sub.Z are substantially trapezoidal.

20. A non-ferromagnetic elongate U-coil for producing an external localized flux region, said U-coil comprising:

a central substantially solenoidal coil wound on a coilform of length h.sub.S and major diameter d.sub.S and having a mean first axis of symmetry;

two transverse coils, one disposed at each end of said central solenoidal coil, having axes perpendicular to said first axis, and having outside diameter d.sub.T and axial length h.sub.T such that h.sub.T is less than d.sub.S.

21. The U-coil of claim 20 in which each said transverse coil comprises a cross coil, each said cross coil wound on the coilform.

22. The U-coil of claim 20 in which each said transverse coil comprises a saddle coil portion, said saddle coil portion comprising conductors threaded through transverse holes in the coilform.

23. The U-coil of claim 20 in which said central solenoidal coil is substantially round in cross section.

24. The U-coil of claim 20 in which said central solenoidal coil is substantially trapezoidal in cross section.

25. The U-coil of claim 20 in which said coilform is made from a material selected from the set consisting of alumina, silicon nitride, zirconia, alumina-silica-boria glasses, borosilicate glasses, machinable glasses, plastic composites having at least 10% carbon fiber content, plastic composites having more than 25% ceramic fiber content, and plastic composites having density greater than 2.0 g/cm.sup.3.

26. A gradient coil system comprising a plurality of U-coils, each U-coil comprising a central substantially solenoidal coil wound on a coilform of length h.sub.S and major diameter d.sub.S