Hybrid magnetic apparatus for use in medical applications

• US 6,157,278 A
• Filed: 03/24/1999
• Issued: 12/05/2000
• Est. Priority Date: 07/23/1997
• Status: Expired due to Term

• Current Assignee: ODIN Technologies Limited
• Original Assignee: ODIN Technologies Limited
• Inventors: Rotem, Haim, Katznelson, Ehud, Zuk, Yuval
• Primary Examiner(s): Donovan, Lincoln
• Assistant Examiner(s): BARRERA, RAMON M
• Application Number:
  US09/274,671
• Time in Patent Office: 622 Days
• Field of Search: 335/216, 335/296-306, 324/318-320, 600/410, 600/407, 600/421, 600/422
• US Class Current: 335/296
• CPC Class Codes: G01R 33/3806 Open magnet assemblies for improved access to the sample, e.g. C-type or U-type magnets
• CPC Class Codes: G01R 33/383 using permanent magnets
• CPC Class Codes: H01F 7/0278 for generating uniform fields, focusing, deflecting electrically charged particles for magnetic separation by Lorentz force B03C1/023; specially adapted for NMR applications G01R33/383

Abstract

Permanent magnet assemblies and hybrid magnetic apparatus are disclosed for use in medical applications, particularly permanent magnet assemblies for use in Magnetic Resonance Imaging (MRI) and/or Magnetic Resonance Therapy (MRT) to produce a volume of substantially uniform magnetic field in a restricted part of the patient'"'"'s body in a region either adjacent to the surface of one permanent magnet assembly or between a set of a first and second permanent magnet assemblies, leaving open access to the patient'"'"'s body. The assemblies consist of a plurality of annular concentric magnets spaced-apart along their axis of symmetry. A method for constructing such annular permanent magnetic assemblies is disclosed, using equi-angular segments permanently magnetized. The hybrid magnetic apparatus includes an electromagnet flux generator for generating a first magnetic field in the volume, and permanent magnet assemblies for generating a second magnetic field superimposed on the first magnetic field for providing a substantially homogenous magnetic field having improved magnitude within the volume.

Claims

1. Open magnetic apparatus for use in an MRI or IMRI device to produce a predetermined volume of substantially uniform magnetic field directed parallel to an axis of symmetry of said volume, the apparatus comprising:

a first electromagnet assembly disposed at a first position along said axis, said first electromagnet assembly includes at least a first electromagnet coil, said at least first coil is radially symmetric with respect to said axis;

a second electromagnet assembly disposed at a second position spaced apart from said first position of said electromagnet assembly along said axis, said second electromagnet assembly includes at least a second electromagnet coil, said at least second coil is radially symmetric with respect to said axis, said at least first coil and said at least second coil are equidistant from the center of said volume, said first electromagnet assembly and said second electromagnetic assembly are adapted for generating a first magnetic field within said volume;

a first permanent magnet assembly positioned at a third position disposed between said first position and said second position along said axis, said first permanent magnet assembly has an inner surface facing said volume and an outer surface facing said first electromagnet assembly, said first permanent magnet assembly includes,

a first permanent magnet having an outer diameter, said first permanent magnet is radially symmetric with respect to said axis and has a first magnetization direction parallel to said axis,

at least a second annular permanent magnet coaxial with said first permanent magnet, said at least second permanent magnet has an inner diameter larger than said outer diameter of said first permanent magnet, said second permanent magnet is radially symmetric with respect to said axis and has a second magnetization direction parallel to said axis, and

a first low magnetic permeability frame for supporting said first permanent magnet and said at least second permanent magnet; and

a second permanent magnet assembly opposed to said first permanent magnet assembly, said second permanent magnet assembly is positioned at a fourth position spaced apart from said third position along said axis, said second permanent magnet assembly has an inner surface facing said volume and an outer surface facing said second electromagnet assembly, said second permanent magnet assembly includes,

a third permanent magnet having an outer diameters, said third permanent magnet is radially symmetric with respect to said axis and has a magnetization direction identical to said first magnetization direction,

at least a fourth permanent magnet coaxial with said third permanent magnet, said at least fourth permanent magnet has an inner diameter larger than said outer diameter of said third permanent magnet, said fourth permanent magnet is radially symmetric with respect to said axis and has a magnetization direction identical to said second magnetization direction, and

a second low magnetic permeability frame for supporting said third permanent magnet and said at least fourth permanent magnet,

wherein the inner surface of said first permanent magnet assembly and the inner surface of said second permanent magnet assembly define an open region therebetween, said volume is disposed within said open region, said third position of said first permanent magnetic assembly and said fourth position of second permanent magnetic assembly are equidistant along said axis from the center of said volume and wherein said first permanent magnetic assembly and said second permanent magnetic assembly are adapted to generate a second magnetic field superimposed on said first magnetic field to provide said substantially uniform magnetic field within said volume.

2. The magnetic apparatus according to claim 1, wherein said first magnetization direction is oriented parallel to said second magnetization direction.

3. The magnetic apparatus according to claim 1, wherein said first magnetization direction is oriented anti-parallel to said second magnetization direction.

4. The magnetic apparatus according to claim 1, wherein said at least first electromagnet coil and said at least second electromagnet coil are operatively arranged as a Helmholtz pair.

5. The magnetic apparatus according to claim 1, wherein said first low magnetic permeability frame is adapted for varying the position of at least said first permanent magnet along said axis, and said second low magnetic permeability frame is adapted for varying the position of at least said third permanent magnet along said axis.

6. The magnetic apparatus according to claim 1, wherein said first low magnetic permeability frame is adapted for varying the tilt angle of at least said first permanent magnet with respect to said axis, and said second low magnetic permeability frame is adapted for varying the tilt angle of at least said third permanent magnet with respect said axis.

7. The magnetic apparatus according to claim 1, wherein said at least first electromagnet coil and said at least second electromagnet coil are resistive electromagnet coils.

8. The magnetic apparatus according to claim 1, wherein said at least first electromagnet coil and said at least second electromagnet coil are superconducting electromagnet coils.

9. The magnetic apparatus according to claim 1, further including a first gradient coil assembly disposed between said outer surface of said first permanent magnet assembly and said first electromagnet assembly, and a second gradient coil assembly disposed between said outer surface of said second permanent magnet assembly and said second electromagnet assembly.

10. The magnetic apparatus according to claim 9, wherein each of said first gradient coil assembly and said second gradient coil assembly includes one or more gradient coils selected from an x-gradient coil, a y-gradient coil, a z-gradient coil and any combination thereof.

11. The magnetic apparatus according to claim 10, wherein each of said first gradient coil assembly and said second gradient coil assembly is a multi-layer printed circuit assembly, and wherein at least one of said x-gradient coil, y-gradient coil and z-gradient coil of each of said first gradient coil assembly and said second gradient coil assembly is a substantially planar printed circuit coil.

12. The magnetic apparatus according to claim 1, wherein said first and said third permanent magnets are selected from a disc-like permanent magnet having a circular cross section in a plane perpendicular to said axis, a regular right polygonal prism-like permanent magnet having a regular polygonal cross-section in a plane perpendicular to said axis and having N sides, a ring-like annular permanent magnet and a annular right regular polygonal permanent magnet having N sides.

13. The magnetic apparatus according to claim 12, wherein N is equal to or larger than eight.

14. The magnetic apparatus according to claim 1, wherein said at least second and said at least fourth permanent magnets are selected from a ring-like annular permanent magnet and an annular right regular polygonal permanent magnet having N sides.

15. The magnetic apparatus according to claim 14, wherein N is equal to or larger than eight.

16. The magnetic apparatus according to claim 1, wherein said at least first electromagnet coil and said at least second electromagnet coil are selected from a circular coil and a regular polygonal shaped coil having N sides.

17. The magnetic apparatus according to claim 16, wherein N is equal to or larger than eight.

18. The magnetic apparatus according to claim 1, wherein said first permanent magnet and said third permanent magnet comprise a plurality of permanently magnetized segments attached to adjacent segments using a non-conductive adhesive, so as to reduce eddy currents.

19. The magnetic apparatus according to claim 18, wherein said segments are equi-angular segments.

20. The magnetic apparatus according to claim 1, wherein said at least second annular permanent magnet and said at least fourth annular permanent magnet comprise a plurality of permanently magnetized segments attached to adjacent segments using a non-conductive adhesive, so as to reduce eddy currents.

21. The magnetic apparatus according to claim 20, wherein said segments are equi-angular segments.

22. A method for constructing an open magnetic apparatus for use in an MRI or IMRI device to produce a predetermined volume of substantially uniform magnetic field directed parallel to an axis of symmetry of said volume, the method comprising the steps of:

providing a first electromagnet assembly disposed at a first position along said axis, said first electromagnet assembly includes at least a first electromagnet coil, said at least first coil is radially symmetric with respect to said axis;

providing a second electromagnet assembly disposed at a second position spaced apart from said first position of said electromagnet assembly along said axis, said second electromagnet assembly includes at least a second electromagnet coil, said at least second coil is radially symmetric with respect to said axis, said at least first coil and said at least second coil are equidistant from the center of said volume, said first electromagnet assembly and said second electromagnetic assembly are adapted for generating a first magnetic field within said volume;

providing a first permanent magnet assembly positioned at a third position disposed between said first position and said second position along said axis, said first permanent magnet assembly has an inner surface facing said volume and an outer surface facing said first electromagnet assembly, said first permanent magnet assembly includes,

a first permanent magnet having an outer diameter, said first permanent magnet is radially symmetric with respect to said axis and has a first magnetization direction parallel to said axis,

at least a second annular permanent magnet coaxial with said first permanent magnet, said at least second permanent magnet has an inner diameter larger than said outer diameter of said first permanent magnet, said second permanent magnet is radially symmetric with respect to said axis and has a second magnetization direction parallel to said axis, and

a first low magnetic permeability frame for supporting said first permanent magnet and said at least second permanent magnet; and

providing a second permanent magnet assembly opposed to said first permanent magnet assembly, said second permanent magnet assembly is positioned at a fourth position spaced apart from said third position along said axis, said second permanent magnet assembly has an inner surface facing said volume and an outer surface facing said second electromagnet assembly, said second permanent magnet assembly includes,

a third permanent magnet having an outer diameter, said third permanent magnet is radially symmetric with respect to said axis and has a magnetization direction identical to said first magnetization direction,

at least a fourth permanent magnet coaxial with said third permanent magnet, said at least fourth permanent magnet has an inner diameter larger than said outer diameter of said third permanent magnet, said fourth permanent magnet is radially symmetric with respect to said axis and has a magnetization direction identical to said second magnetization direction, and

a second low magnetic permeability frame for supporting said third permanent magnet and said at least fourth permanent magnet,

wherein the inner surface of said first permanent magnet assembly and the inner surface of said second permanent magnet assembly define an open region therebetween, said volume is disposed within said open region, said third position of said first permanent magnetic assembly and said fourth position of second permanent magnetic assembly are equidistant along said axis from the center of said volume and wherein said first permanent magnetic assembly and said second permanent magnetic assembly are adapted to generate a second magnetic field superimposed on said first magnetic field to provide said substantially uniform magnetic field within said volume.

23. A method for providing a substantially homogenous magnetic field within a volume disposed in an open region within a magnetic apparatus the method comprising the steps of:

providing a first electromagnet assembly disposed at a first position along said axis, said first electromagnet assembly includes at least a first electromagnet coil, said at least first coil is radially symmetric with respect to said axis, and a second electromagnet assembly disposed at a second position spaced apart from said first position of said electromagnet assembly along said axis, said second electromagnet assembly includes at least a second electromagnet coil, said at least second coil is radially symmetric with respect to said axis, said at least first coil and said at least second coil are equidistant from the center of said volume;

providing a first permanent magnet assembly positioned at a third position disposed between said first position and said second position along said axis, said first permanent magnet assembly has an inner surface facing said volume and an outer surface facing said first electromagnet assembly, said first permanent magnet assembly includes,

a first permanent magnet having an outer diameter, said first permanent magnet is radially symmetric with respect to said axis and has a first magnetization direction parallel to said axis,

at least a second annular permanent magnet coaxial with said first permanent magnet, said at least second permanent magnet has an inner diameter larger than said outer diameter of said first permanent magnet, said second permanent magnet is radially symmetric with respect to said axis and has a second magnetization direction parallel to said axis, and

a first low magnetic permeability frame for supporting said first permanent magnet and said at least second permanent magnet, and

a second permanent magnet assembly opposed to said first permanent magnet assembly, said second permanent magnet assembly is positioned at a fourth position spaced apart from said third position along said axis, said second permanent magnet assembly has an inner surface facing said volume and an outer surface facing said second electromagnet assembly, said second permanent magnet assembly includes,

a third permanent magnet having an outer diameter, said third permanent magnet is radially symmetric with respect to said axis and has a magnetization direction identical to said first magnetization direction,

at least a fourth permanent magnet coaxial with said third permanent magnet, said at least fourth permanent magnet has an inner diameter larger than said outer diameter of said third permanent magnet, said fourth permanent magnet is radially symmetric with respect to said axis and has a magnetization direction identical to said second magnetization direction, and

a second low magnetic permeability frame for supporting said third permanent magnet and said at least fourth permanent magnet,

wherein the inner surface of said first permanent magnet assembly and the inner surface of said second permanent magnet assembly define an open region therebetween, said volume is disposed within said open region, said third position of said first permanent magnet assembly and said fourth position of second permanent magnetic assembly are equidistant along said axis from the center of said volume, and wherein said first permanent magnetic assembly and said second permanent magnetic assembly generate a first permanent magnetic field in said volume;

electrically energizing said first electromagnet assembly and said second electromagnetic assembly to provide a second magnetic field within said volume, wherein said second magnetic field is superimposed on said first permanent magnetic field to provide said substantially uniform magnetic field within said volume.