Magnet and cryostat arrangement, and method for passive shimming

Patent metadata

Field	Value
Publication number	US-10060998-B2
Application number	US-201715587447-A
Country	US
Kind code	B2
Filing date	May 5, 2017
Priority date	May 6, 2016
Publication date	Aug 28, 2018
Grant date	Aug 28, 2018

Abstract

An arrangement for setting the spatial profile of a magnetic field in a working volume of a main field magnet ( 2 ), in particular a superconducting main field magnet, of a magnetic resonance installation. The main field magnet is arranged in a cryostat ( 1 ) and the spatial profile is set by a passive shim apparatus ( 3 ) with magnetic field forming elements which are arranged within the cryostat during operation and which have cryogenic temperatures. The magnetic resonance installation contains a room temperature tube ( 4 ), in which the sample volume is situated during operation. The passive shim apparatus is introduced into or removed from the cold region of the cryostat via a vacuum lock ( 5 ), without needing to ventilate the cold region of the cryostat. This provides a relatively simple, cost effective, and time-efficient method to carry out a stable field homogenization using a passive shim apparatus.

First claim

What is claimed is:

1. An arrangement for setting the spatial profile of a magnetic field in a working volume of a main field magnet of a magnetic resonance installation, comprising:
a main field magnet arranged in a cryostat having a cold region,
a passive shim apparatus for forming the spatial profile and comprising at least one magnetic field forming element arranged within the cryostat during operation and having a cryogenic temperature,
a room temperature tube, in which the sample volume is situated during the operation, and
a vacuum lock configured to introduce and/or remove at least parts of the passive shim apparatus into the cold region of the cryostat without needing to ventilate the cold region of the cryostat.

2. The arrangement as claimed in claim 1 , wherein the vacuum lock is configured to be mounted on or removed from the magnetic resonance installation, in an axial continuation of a room temperature bore that is configured to receive the room temperature tube during the operation.

3. The arrangement as claimed in claim 1 , wherein the vacuum lock comprises a first valve configured to hermetically seal the cryostat, a vacuum chamber, and a pump device which is configured to evacuate the vacuum chamber or to fill or to purge the chamber with fluid.

4. The arrangement as claimed in claim 1 , further comprising a displaceable ram arranged axially in a direction of an axis of a room temperature bore that contains the room temperature tube during the operation within the vacuum lock, wherein at least the parts of the passive shim apparatus are arranged to be moved by the ram.

5. The arrangement as claimed in claim 4 , wherein the cryostat comprises at least one radiation shield, and further comprising a cover apparatus for one-sided sealing of an opening on a side of the room temperature bore configured to attach to a magnet-side end of the ram.

6. The arrangement as claimed in claim 1 , wherein the cryostat comprises at least one radiation shield, and wherein at least parts of the passive shim apparatus are attached in a heat conducting manner to the at least one radiation shield.

7. The arrangement as claimed in claim 1 , wherein at least parts of the passive shim apparatus are attached in a heat conducting manner in a cold region of the cryostat on an outer side of a helium tank facing the room temperature tube during the operation of the magnetic resonance installation.

8. The arrangement as claimed in claim 1 , further comprising a centering device configured to optimize a spatial setting of an installation position of at least parts of the passive shim apparatus in a cold region of the cryostat.

9. The arrangement as claimed in claim 1 , further comprising an apparatus configured to measure the homogeneous magnetic field and arranged in the sample volume of the magnetic resonance installation, the apparatus being geometrically configured to be introduced as far as the sample volume through an open end of the room temperature bore.

10. The arrangement as claimed in claim 1 , further comprising a room temperature tube which is sealed on one side and which is configured to replace the room temperature tube which is open throughout and is installed during the operation of the magnetic resonance installation.

11. The arrangement as claimed in claim 10 , wherein spacer elements made of a material with a thermal conductivity of less than 0.3 W/(m·K) at 50 K spatially separate the room temperature tube by a predetermined distance from an external side of a helium tank facing the room temperature tube or from a radiation shield surrounding the helium tank.

12. The arrangement as claimed in claim 1 , wherein the passive shim apparatus comprises a field forming element with an integral design, wherein the field forming element is constructed from a film and/or sheet, wherein the field forming element comprises recesses which are selected in terms of form, position and size such that the form and amount of the remaining ferromagnetic material leads to a desired spatial profile of the magnetic field in the sample volume of the main field magnet in response to appropriate positioning of the film and/or of the sheet relative to the sample volume of the main field magnet.

13. A vacuum lock for use in an arrangement as claimed in claim 1 , wherein the vacuum lock is configured such that at least parts of the passive shim apparatus can be introduced into or removed from the cold region of the cryostat after removal of the room temperature tube which is open throughout by way of the vacuum lock, without having to ventilate the cold region of the cryostat.

14. A method for setting the spatial profile of a magnetic field in a sample volume of a superconducting main field magnet in an arrangement as claimed in claim 1 , comprising:
(a) measuring the magnetic field in the sample volume;
(b) introducing or replacing at least parts of the passive shim apparatus, the geometry of which is based on the result of the field measurement in step (a), into or from the cold region of the cryostat through the vacuum lock; and
(c) again measuring the magnetic field in the sample volume.

15. The method as claimed in claim 14 ,
wherein the arrangement comprises a room temperature tube which is sealed on one side and which is configured to replace the room temperature tube which is open throughout and is installed during the operation of the magnetic resonance installation,
wherein, during the operating phases of the magnetic resonance installation, the room temperature tube which is open throughout is inserted into the room temperature bore of the cryostat and
wherein a room temperature tube which is sealed on one side is introduced into the room temperature bore of the cryostat prior to a testing phase of the magnet.

16. The arrangement as claimed in claim 1 , wherein the main field magnet is a superconducting main field magnet.

17. The arrangement as claimed in claim 3 , wherein the vacuum lock comprises a second valve configured to evacuate the vacuum chamber.

18. The arrangement as claimed in claim 5 , wherein the cryostat comprises a plurality of radially nested radiation shields, and wherein the cover apparatus for the one-sided sealing of the opening on the side of the room temperature bore configured to attach to a magnet-side end of the ram for one-sided sealing of a radially innermost radiation shield arranged adjacent to the room temperature tube.

19. The arrangement as claimed in claim 6 , wherein the cryostat comprises a plurality of radially nested radiation shields, and wherein at least parts of the passive shim apparatus are configured to attach to a radially innermost radiation shield adjacent to the room temperature tube on a side facing the room temperature tube during the operation of the magnetic resonance installation.

20. The arrangement as claimed in claim 9 , wherein the apparatus is configured to measure the magnetic field gradient.

21. The arrangement as claimed in claim 1 , wherein the passive shim apparatus comprises a single field forming element with an integral design, wherein the single field forming element is constructed from a film and/or sheet, wherein the single field forming element comprises recesses which are selected in terms of form, position and size such that the form and amount of a remaining ferromagnetic material leads to a desired spatial profile of the magnetic field in the sample volume of the main field magnet in response to appropriate positioning of the film and/or of

Assignees

• Bruker Biospin Gmbh

Inventors

• Wikus Patrick
• Niemann Volker
• Frantz Wolfgang
• Dumm Michael
• Wagenknecht Michael
• Bonn Steffen

Classifications

• G01R33/3815

  with superconducting coils, e.g. power supply therefor · CPC title

• G01R33/3804

  Additional hardware for cooling or heating of the magnet assembly, for housing a cooled or heated part of the magnet assembly or for temperature control of the magnet assembly · CPC title

• G01R33/3873 Primary

  using ferromagnetic bodies {; Passive shimming} · CPC title

• G01R33/28

  Details of apparatus provided for in groups G01R33/44 - G01R33/64 · CPC title