Gradient coils for magnetic resonance meeting

• US 6,144,204 A
• Filed: 11/28/1998
• Issued: 11/07/2000
• Est. Priority Date: 11/28/1997
• Status: Expired due to Fees

• Current Assignee: Picker Nordstar Oy
• Original Assignee: Picker Nordstar Oy
• Inventors: Sementchenko, Mikhail G.
• Primary Examiner(s): ARANA, LOUIS M
• Application Number:
  US09/200,405
• Time in Patent Office: 710 Days
• Field of Search: 324/318, 324/319, 324/320, 324/321, 324/322, 324/307, 324/309
• US Class Current: 324/318
• CPC Class Codes: G01R 33/385 using gradient magnetic field coils
• CPC Class Codes: G01R 33/3856 Means for cooling the gradient coils or thermal shielding of the gradient coils
• CPC Class Codes: G01R 33/4215 of the gradient magnetic field, e.g. using passive or active shielding of the gradient magnetic field

Abstract

Shielded gradient coils are adapted for use in an MR imaging apparatus having spaced apart pole pieces. The x, y, and z coils each include a active and shield layers. The x-active and shield layers are interconnected by a plurality of vertical electrical connections extending around the periphery of the coil. The y-active and shield layers are similarly connected. The z-active and shield layers each have a generally spiral conductor pattern.

Claims

1. An apparatus for use in magnetic resonance imaging comprising:

a magnet which includes first and second pole pieces disposed on opposite sides of and generating a main magnetic field within an examination region;

a generally planar first gradient coil for generating a first gradient magnetic field within the examination region, the first gradient coil disposed between the first pole piece and the examination region and having an outer perimeter, the first gradient coil including;

first and second active layers; and

a shield layer disposed between an active layer and the first pole piece, the active and shield layers being electrically connected at a plurality of locations along the outer perimeter of the gradient coil.

2. The apparatus of claim 1 wherein the active and shield layers arc electrically connected so as to form a squirrel cage structure.

3. The apparatus of claim 2 wherein the first and second active layers are substantially mirror images of one another.

4. The apparatus of claim 3 wherein the shield layer includes first and second shield layers which are substantially mirror images of one another.

5. The apparatus of claim 1 wherein the first gradient coil generates a first gradient magnetic field in a direction orthogonal to the main magnetic field and wherein the apparatus further includes a generally planar second gradient coil for generating a second gradient magnetic field in a direction orthogonal to the main magnetic field, the second gradient coil disposed between the first pole piece and the examination region and having an outer perimeter, the second gradient coil including:

first and second active layers; and

a shield layer disposed between the active layers and the first pole piece, the active and shield layers being electrically connected at a plurality of locations along outer perimeter of the gradient coil.

6. The apparatus of claim 5 wherein the active layer of the second gradient coil is disposed between an active layer of the first gradient coil and the first pole piece.

7. The apparatus of claim 6 wherein the shield layer of the second gradient coil is disposed between the shield layer of the first gradient coil and the first pole piece.

8. The apparatus of claim 7 further including a third gradient coil for generating a third gradient magnetic field in a direction parallel to the main magnetic field, the third gradient coil being disposed between the active layer of the second gradient coil and the shield layer of the first gradient coil.

9. An apparatus for use in magnetic resonance imaging comprising:

a magnet which includes first and second pole pieces disposed on opposite sides of and generating a main magnetic field within an examination region;

a generally planar first gradient coil for generating a first gradient magnetic field within the examination region, the first gradient coil disposed between the first pole piece and the examination region and having an outer perimeter, the first gradient coil including;

an active layer; and

a shield layer disposed between the active layer and the first pole piece, the active and shield layers being electrically connected at a plurality of locations along the outer perimeter of the gradient coil, wherein the average current in the plane of the gradient coil along the outer perimeter of the gradient coil is substantially zero.

10. The apparatus of claim 9 wherein the active and shield layers each comprise a plurality of generally planar conductors, the conductors having slits extending therethrough, whereby eddy currents generated by magnetic flux having a component perpendicular to the plane of the gradient coil are reduced.

11. The apparatus of claim 9 wherein the active layer includes first and second active layers which are substantially mirror images of one another.

12. The apparatus of claim 11 wherein the shield layer includes first and second shield layers which are substantially mirror images of one another.

13. A magnetic resonance imaging apparatus comprising:

a magnet which includes first and second pole pieces disposed on opposite sides of and generating a main magnetic field within an examination region;

generally planar first, second, and third gradient coils for generating gradient magnetic fields in orthogonal directions, the first and second gradient coils each including

an active layer disposed between the first pole piece and the examination region and having a first plurality of conductors; and

a shield layer disposed between the first pole piece and the active layer and having a second plurality of conductors, each of the conductors in the shield layer being connected electrically in series with a conductor in the active layer such that an average current in the plane of the coil at the perimeter of the coil is substantially zero.

14. The apparatus of claim 13 wherein the shield layer of the second gradient coil, the shield layer of the first gradient coil, the active layer of the second gradient coil, and the active layer of the first gradient coil are disposed in sequence between the first pole piece and the examination region.

15. The apparatus of claim 14 wherein the third gradient coil is disposed between the shield layer of the first gradient coil and the active layer of the second gradient coil.

16. The apparatus of claim 13 wherein the electrical connections between the active and shield layers of the first gradient coil include electrical conductors located at the perimeter of the gradient coil.

17. The apparatus of claim 16 wherein the electrical conductors are parallel to the main magnetic field.

18. The apparatus of claim 16 wherein the electrical conductors include a first electrical conductor portion integral with an active layer conductor and a second electrical conductor portion integral with a shield layer conductor, the first and second conductor portions being electrically connected.

19. The apparatus of claim 13 wherein the spacing between the active and shield layers of the first gradient coil is equal to the spacing between the active and shield layers of the second gradient coil.