Mold for bonding MRI pole piece tiles and method of making the mold

• US 20010005165A1
• Filed: 12/18/2000
• Published: 06/28/2001
• Est. Priority Date: 11/24/1998
• Status: Active Grant

• Current Assignee: Bulent Aksel, Evangelos T. Laskaris, Johannes M Van Oort, Michele D. Ogle, Paul S. Thompson, William D. Barber
• Original Assignee: Bulent Aksel, Evangelos T. Laskaris, Johannes M Van Oort, Michele D. Ogle, Paul S. Thompson, William D. Barber
• Inventors: Barber, William D., van Oort, Johannes M., Aksel, Bulent, Thompson, Paul S., Laskaris, Evangelos T., Ogle, Michele D.
• Granted Patent: US 6,429,761 B2
• Time in Patent Office: Days
• US Class Current: 335/299
• 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
• CPC Class Codes: Y10S 29/001 Method or apparatus involving adhesive
• CPC Class Codes: Y10T 29/4902 Electromagnet, transformer or inductor
• CPC Class Codes: Y10T 29/49075 including permanent magnet or core
• CPC Class Codes: Y10T 29/49078 Laminated

Abstract

A laminate tile pole piece for an MRI, a method and a mold for manufacturing laminate tile metal pole pieces for an MRI. Each laminate tile has a trapezoidal or annular sector shape. The trapezoidal shape allows the tiles to be attached side by side to form a multiple concentric annular array pole piece without using oddly shaped edge filler tiles needed to fill a circular pole piece with square tiles. The pole piece is made by placing a plurality of tiles into a mold and filling the mold with an adhesive substance to bind the plurality of tiles into a unitary tile body. The unitary tile body is then removed from the mold and attached to a pole piece base to form the pole piece. The mold cavity surface preferably has a non-uniform contour. The bottom surface of the unitary tile body forms a substantially inverse contour of the mold cavity surface contour.

Claims

1. A pole piece for a magnetic resonance imaging (MRI) system, comprising a plurality of trapezoid or annular sector shaped tiles arranged in a plurality of concentric annular arrays.

2. The pole piece of

claim 1

, wherein the tiles comprise a plurality of laminated layers.

3. The pole piece of

claim 1

, wherein the height of a first concentric annular array is greater than a height of a second concentric annular array.

4. The pole piece of

claim 3

, wherein the surface contour of the plurality of concentric annular arrays forms a substantially inverse contour of a non-uniform mold cavity surface.

5. The pole piece of

claim 1

, wherein the plurality of concentric annular arrays comprise a unitary tile body.

6. The pole piece of

claim 1

, wherein a first tile is separated from a second tile by an adhesive layer.

7. The pole piece of

claim 2

, wherein the laminating direction of the tile layers is parallel to a plane of each concentric annular array.

8. The pole piece of

claim 2

, wherein the laminating direction of the tile layers perpendicular to a plane of each concentric annular array.

9. The pole piece of

claim 2

, further comprising a first tile containing laminated layers attached over a second tile containing laminated layers to form a combined laminate tile.

10. The pole piece of

claim 9

, wherein the layer laminating direction of the first tile is perpendicular to the layer laminating direction of the second tile.

11. The pole piece of

claim 1

, wherein at least one tile contains a cavity in the tile face.

12. The pole piece of

claim 11

, wherein at least one cavity is filled by a shim or an auxiliary magnet.

13. The pole piece of

claim 1

, further comprising:

a yoke;

a first magnet containing a first side attached to a first portion of the yoke and a second side attached to the laminate tile pole piece;

a second magnet attached to a second portion of the yoke; and

a second pole piece comprising a plurality of second tiles attached to the second magnet and facing the laminate tile pole piece.

14. A method of making a pole piece comprising the steps of:

placing a plurality of tiles into a mold cavity;

filling the mold cavity with an adhesive substance to bind the plurality of tiles into a unitary body;

removing the unitary body from the mold cavity; and

attaching a second surface of the unitary body to a pole piece base to form a first pole piece.

15. The method of

claim 14

, wherein:

the mold contains a non-uniform cavity surface contour; and

a first surface of the unitary body forms a substantially inverse contour of the non-uniform mold cavity surface.

16. The method of

claim 15

, further comprising the steps of:

attaching the first pole piece to a first surface of a first magnet;

attaching the second surface of the first magnet to a first portion of a yoke;

attaching a second surface of a second magnet to a second portion of the yoke; and

attaching a second pole piece to a first surface of the second magnet.

17. The method of

claim 16

, further comprising the steps of:

performing a simulation of magnetic flux density between the first magnet and the second magnet;

determining an optimum contour of the first surface of the pole piece based on an optimum value of the magnetic flux density between the first magnet and the second magnet; and

forming the mold cavity surface contour as a substantial inverse of the contour of the first surface of the pole piece.

18. The method of

claim 17

, wherein:

the non-uniform mold cavity surface comprises a plurality of spacers of different height; and

wherein the top surface of the spacers forms the non-uniform mold cavity surface contour.

19. The method of

claim 18

, wherein the spacers comprise cylindrical spacers.

20. The method of

claim 18

, further comprising the steps of:

pressing the unitary body against the spacers; and

forming a plurality of cavities in the unitary body.

21. The method of

claim 14

, further comprising the step of arranging the tiles in a concentric annular array in the mold.

22. The method of

claim 21

, wherein the tiles comprise laminate tiles.

23. The method of

claim 14

, further comprising the step of covering the mold with a cover plate prior to filling the mold with adhesive.

24. The method of

claim 23

, further comprising the step of placing a plurality of tiles into the mold until a top surface of the tiles is substantially even with a top of the mold prior to covering the mold with the cover plate.

25. The method of

claim 14

, further comprising the steps of:

placing a first side of an adhesive tape in contact with a portion of a first tile; and

placing a second side of the adhesive tape in contact with the mold cavity surface.

26. The method of

claim 14

, wherein the adhesive substance comprises epoxy.

27. A mold containing an non-uniform cavity surface for forming a laminate tile pole piece for an MRI system, made by the method of:

performing a simulation of magnetic flux density between a first magnet of the MRI system and a second magnet of the MRI system;

determining an optimum contour of a first surface of the pole piece based on an optimum value of the magnetic flux density between the first magnet and the second magnet; and

forming the mold cavity surface contour as a substantial inverse of the optimum contour of the first surface of the pole piece.

28. The mold of

claim 27

, wherein the non-uniform cavity surface comprises a plurality of cylindrical spacers of non-uniform height.

29. A method of making a mold containing an non-uniform cavity surface, for forming a laminate tile pole piece for an MRI system, comprising:

performing a simulation of magnetic flux density between a first magnet of the MRI system and a second magnet of the MRI system;

determining an optimum contour of a first surface of the pole piece based on an optimum value of the magnetic flux density between the first magnet and the second magnet; and

forming the mold cavity surface contour as a substantial inverse of the optimum contour of the first surface of the pole piece.

30. The mold of

claim 29

, wherein forming the bottom mold surface comprises placing a plurality of cylindrical spacers of non-uniform height into the mold.