Actively shielded, cylindrical gradient coil system with passive RF shielding for NMR devices

Patent metadata

Field	Value
Publication number	US-9817096-B2
Application number	US-201414217557-A
Country	US
Kind code	B2
Filing date	Mar 18, 2014
Priority date	Mar 20, 2013
Publication date	Nov 14, 2017
Grant date	Nov 14, 2017

Abstract

A gradient coil system has a cylindrical section in a central region, which contains no conductor elements and has a maximum outer radius that is larger than a minimum inner radius of conductor elements of a main gradient coil. An outer radius of this cylindrical section is only insubstantially smaller or equal in size to a minimum inner radius of a shielding coil in this axial range. The free space in the center of the gradient coil system is used to insert a passive RF shield, whose radius in a central region becomes larger over a certain length than its radius in outer regions. The RF shield is constructed from at least three partial sections, which are electrically interconnected. The actively shielded gradient coil system maximizes the volume of the RF region without loss of gradient coil system performance.

First claim

I claim:

1. An actively shielded, cylindrical gradient coil system for use in an MR (=magnetic resonance) spectrometer, the spectrometer having a main field magnet, which generates a main magnet field aligned in a direction of a z-axis, wherein, when current flows, the gradient coil system generates a Z-gradient field in a measurement volume through which the z-axis passes whose zero crossing is located at a center of the measurement volume, the gradient system comprising:
at least one main gradient coil, said main gradient coil being constructed from at least two cylindrical partial coil systems, axially spaced from one another in the z-direction by a length L1 and symmetrically with respect to the center of the measurement volume, axes of said cylindrical partial coil systems being collinear with the z-axis, wherein said cylindrical partial coil systems are at least partially constructed from electrical conductor sections wound with a maximum outer radius R1gradient out max around the z-axis;
at least one active shielding coil, at least one of said at least one active shielding coil being constructed from electrical conductors on a minimum inner radius R1shield in min around the z-axis, with R1shield in min >R1gradient out max , wherein the gradient coil system has no electrical conductor elements disposed in a hollow cylindrical section along said axial length L1, symmetrically with respect to the center of the measurement volume in a radius range between a minimum inner radius R1gradient in min of the main gradient coil and R1shield in min ; and
a passive RF shield, said passive RF shield being constructed from at least three electrically interconnected partial sections, of which two partial sections are disposed around the z-axis with a maximum outer radius R1hf out max , wherein a third partial section with an axial length L2, a minimum inner radius R2hf in min and a maximum outer radius R2hf out max is disposed around the z-axis between said two partial sections, wherein R1hf out max <R1gradient in min , R1gradient out max <R2hf in min <R2hf out max and L2<L1.

2. The gradient coil system of claim 1 , wherein
R2hf out max <R1shield in min .

3. The gradient coil system of claim 1 , wherein
R2hf in min ≧1.1·R1gradient out max and R2hf out max ≧0.8·R1shield in min .

4. The gradient coil system of claim 1 , wherein
R2hf in min ≧R1gradient out max +3 mm and R2hf out max ≧R1shield in min −3 mm.

5. The gradient coil system of claim 1 , wherein electrical conductor sections wound around the z-axis are constructed from wire with a round cross section.

6. The gradient coil system of claim 1 , wherein electrical conductor sections wound around the z-axis are constructed from strip conductors.

7. The gradient coil system of claim 1 , wherein electrical conductor sections wound around the z-axis are constructed from electrically conductive layers coated on dielectric formers.

8. The gradient coil system of claim 1 , wherein at least two pairs of said axially spaced cylindrical partial coil systems of said main gradient coil have differing minimum inner radii.

9. The gradient coil system of claim 1 , wherein at least two partial sections of said passive RF shield have differing minimum inner radii.

10. The gradient coil system of claim 1 , wherein at least one of said cylindrical partial coil systems is constructed from a plurality of electrical conductor sections stacked in a radial direction.

11. The gradient coil system of claim 1 , wherein said cylindrical partial coil systems of said main gradient coil and at least one active shielding coil are completely enclosed by said passive RF shield with an exception of an incoming supply cable opening.

12. The gradient coil of claim 11 , wherein radial inner surfaces and the axial end faces of said cylindrical partial coil systems of said main gradient coil as well as radial outer surfaces and axial end faces of said at least one active shielding coil are enclosed by said passive RF shield.

13. The gradient coil system of claim 1 , wherein said passive RF shield is shaped to enclose a region of space that is impenetrable to RF radiation and from which RF radiation cannot escape.

14. The gradient coil system of claim 11 , wherein an RF impenetrability of said passive RF shield is achieved by capacitive overlapping elements of said passive RF shield, by soldering, by compression and/or by gluing with electrically conductive adhesive.

15. The gradient coil systems of claim 1 , wherein said passive RF shield is mounted on a substrate or is mounted on a substrate by vacuum deposition, sputtering, CVD, galvanic coating, printing, painting and/or gluing.

16. The gradient coil system of claim 1 , wherein at least two of said electrically interconnected partial sections of said passive RF shield are disposed cylindrically symmetrically around the z-axis with a maximum outer radius R1hf out max , wherein a third partial section with an axial length L2 and a minimum inner radius R2hf in min as well as a maximum outer radius R2hf out max is disposed around the z-axis between those two partial sections and that, between said third partial section and each of those two other partial sections, a transitional section is disposed, which interconnects partial sections disposed on different radii along an axial length L8.

17. The gradient coil system of claim 16 , wherein said transitional section comprises a conical element.

18. An MR spectrometer having the gradient coil system of claim 1 , further comprising an RF transmit and/or receive coil system which is disposed inside said radius R2hf in min along an axial length L3<L2 and symmetrically with respect to the center of the measurement volume.

Assignees

• Bruker Biospin Ag

Inventors

• Freytag Nicolas

Classifications

• G01R33/4215 Primary

  of the gradient magnetic field, e.g. using passive or active shielding of the gradient magnetic field · CPC title

• G01R33/3858

  Manufacture and installation of gradient coils, means for providing mechanical support to parts of the gradient-coil assembly (manufacture of inductances or coils in general H01F41/00) · CPC title