Active resistive shimming for MRI devices

Patent metadata

Field	Value
Publication number	US-9599687-B2
Application number	US-201514658079-A
Country	US
Kind code	B2
Filing date	Mar 13, 2015
Priority date	Dec 13, 2011
Publication date	Mar 21, 2017
Grant date	Mar 21, 2017

Abstract

Active resistive shim coil assemblies may be used in magnetic resonance imaging (MRI) systems to reduce in-homogeneity of the magnetic field in the imaging volume. Disclosed embodiments may be used with continuous systems, gapped cylindrical systems, or vertically gapped systems. Disclosed embodiments may also be used with an open MRI system and can be used with an instrument placed in the gap of the MRI system. An exemplary embodiment of the active resistive shim coil assembly of the present disclosure includes active resistive shim coils each operable to be energized by separate currents through a plurality of power channels. In some embodiments, the disclosed active resistive shim coil assemblies allow for various degrees of freedom to shim out field in-homogeneity.

First claim

What is claimed is:

1. A system comprising:
an active resistive shim coil assembly configured to be disposed outside of a first magnet of a magnetic resonance imaging system and proximate to a first gradient coil of the magnetic resonance imaging system, the first gradient coil being disposed between the first magnet and a longitudinal axis extending through a bore of the first magnet, the longitudinal axis parallel to a main magnetic field generated by the first magnet of the magnetic resonance imaging system, the active resistive shim coil assembly comprising:
a plurality of shim coils; and
a plurality of connections configured to connect each of the plurality of shim coils to a plurality of power channels, the plurality of shim coils being operable to be energized by separate currents through the plurality of power channels.

2. The system of claim 1 , wherein the magnetic resonance imaging system further comprises a second magnet spaced apart from the first magnet by a gap configured to receive an instrument, wherein the first gradient coil is a split gradient coil and the plurality of shim coils are split shim coils.

3. The system of claim 1 , wherein at least one of the plurality of shim coils comprises a split resistive shim coil comprising four quadrants, wherein a first pair of the four quadrants of the split resistive shim coil are disposed symmetrically about a central plane and a second pair of the four quadrants of the split resistive shim coil are disposed symmetrically about the central plane.

4. The system of claim 1 , wherein at least one of the plurality of shim coils comprises a split resistive shim coil comprising a pair of halves disposed symmetrically about a central plane.

5. The MRI system of claim 1 , wherein the plurality of shim coils comprises an X-shim coil, a Y-shim coil, and a Z-shim coil.

6. The system of claim 5 , wherein the plurality of shim coils further comprise a zero-order shim coil.

7. The system of claim 5 , wherein the X-shim coil comprises four quadrants operable to be energized by currents from four respective power channels, the Y-shim coil comprises four quadrants operable to be energized by currents from four respective power channels, and the Z-shim coil comprises two halves operable to be energized by currents from two respective power channels.

8. The system of claim 5 , wherein the active X-shim coil comprises four quadrants, the active Y-shim coil comprises four quadrants, and the Z-shim coil comprises two halves, and wherein two pairs of the quadrants of the active X-shim coil are operable to be energized by currents from two respective power channels of the plurality of power channels, two pairs of the quadrants of the active Y-shim coil are operable to be energized by currents from two respective power channels of the plurality of power channels, and the two halves of the active Z-shim coil are operable to be energized by currents from two respective power channels of the plurality of power channels.

9. The system of claim 1 , further comprising a passive shimming device.

10. The system of claim 1 , further comprising the first gradient coil, and wherein the active resistive shim coil assembly and the first gradient coil are disposed inside a single module.

11. The system of claim 1 , wherein the active resistive shim coil assembly is configured to be disposed between the first magnet and the first gradient coil.

12. The system of claim 1 , wherein the active resistive shim coil assembly is configured to be disposed between the first gradient coil and the longitudinal axis.

13. An active resistive shim coil assembly comprising:
a resistive Z2-shim coil;
a resistive ZX shim coil comprising two halves separated by 180 degrees in an azimuthal direction;
a resistive ZY shim coil comprising another two halves rotated from the resistive ZX shim coil by 90 degrees, wherein the ZX and ZY resistive shim coils are disposed symmetrically about a central plane;
a resistive XZ shim coil comprising two sets of four quadrants positioned symmetrically about the central plane and separated by 90 degrees in the azimuthal direction;
a resistive X2-Y2 shim coil comprising another two sets of four quadrants positioned symmetrically about the central plane and rotated from the YZ resistive shim coil by 90 degrees;
resistive Z2-shim, ZX-shim, ZY-shim, XZ-shim, and X2-Y2 shim coils are each operable to be energized by separate currents through a plurality of power channels.

14. The active resistive shim coil assembly of claim 13 , wherein the two halves of the ZX-shim coil and the other two halves of the ZY-shim coil are operable to be energized by currents from separate power channels to allow for two degrees of freedom for each of the ZX-shim coil and the ZY-shim coil.

15. The active resistive shim coil assembly of claim 13 , wherein first and second quadrants of the X-shim coil are connected in series and operable to be energized by a current from a first power channel and third and fourth quadrants of the X-shim coil are connected in series and operable to be energized by a current from a second power channel.

16. The active resistive shim coil assembly of claim 13 , wherein the two sets of four quadrants of the XY-shim coil and the other two sets of four quadrants of the X2-Y2-shim coil are operable to be energized by currents from separate power channels to allow for eight degrees of freedom for each of the XY-shim coil and the X2-Y2-shim coil.

17. The system of claim 1 , wherein the plurality of shim coils are each configured to be energized by independent currents through the plurality of power channels.

18. A method comprising:
determining currents to be provided to shim coils of an active resistive shim coil assembly disposed outside of a magnet of a magnetic resonance imaging system and proximate to a gradient coil of the magnetic resonance imaging system, the currents comprising first currents being operable to shim out at least some field inhomogeneity of the magnetic resonance imaging system, each of the shim coils comprising a plurality of coils;
applying the first currents to the shim coils of the active resistive shim coil assembly to shim out the at least some field inhomogeneity;
determining that the first currents do not allow a desired level of field homogeneity of the magnetic resonance imaging system;
applying additional currents to the to the shim coils of the active resistive shim coil assembly to further improve the field homogeneity of the magnetic resonance imaging system; and
wherein the first currents and the additional currents comprise a plurality of independent currents for each of the plurality of coils.

19. The method of claim 18 , wherein the determining of the currents to be provided to the shim coils of the active resistive shim coil assembly comprises mathematically determining a magnetic field in an imaging volume of the magnetic resonance imaging system.

20. The method of claim 19 , wherein the mathematically determining comprises receiving data from one or more sensors of a magnetic camera and quantifying the magnetic field over a surface of the magnetic camera using one or more processors.

21. The method of claim 18 , further comprising shimming out residual in-homogeneity by adjusting one or more passive shims.

Assignees

• Viewray Incorporated
• Viewray Tech Inc

Inventors

• Shvartsman Shmaryu M
• Dempsey James F

Classifications

• G01R33/4808

  Multimodal MR, e.g. MR combined with positron emission tomography [PET], MR combined with ultrasound or MR combined with computed tomography [CT] · CPC title

• G01R33/385

  using gradient magnetic field coils · CPC title

• G01R33/481

  MR combined with positron emission tomography [PET] or single photon emission computed tomography [SPECT] · CPC title

• G01R33/3806

  Open magnet assemblies for improved access to the sample, e.g. C-type or U-type magnets · CPC title

• G01R33/4814

  MR combined with ultrasound · CPC title