Method and apparatus for magnetic resonance imaging

Patent metadata

Field	Value
Publication number	US-9841476-B2
Application number	US-201615074250-A
Country	US
Kind code	B2
Filing date	Mar 18, 2016
Priority date	Mar 19, 2015
Publication date	Dec 12, 2017
Grant date	Dec 12, 2017

Abstract

To enable improved adjustment of at least one shim channel for magnetic resonance imaging of an examination region of an examination object by operation of a magnetic resonance apparatus that has a shim arrangement with a first shim channel volume having at least one first shim channel and a second shim channel volume having at least one second shim channel, the examination region is divided into multiple of sections, multiple first shim parameter sets are determined for the at least one first shim channel, with one first shim parameter set among the multiple first shim parameter sets being ascertained for each of the multiple sections, a second shim parameter set is ascertained for the at least one second shim channel, taking into account the ascertained multiple first shim parameter sets, and magnetic resonance image data of the examination region are acquired, but before this acquisition, the at least one second shim channel is adjusted using the second shim parameter set and the at least one first shim channel is adjusted for acquiring the magnetic resonance image data from a specific section of the multiple sections using a first shim parameter set ascertained for that specific section.

First claim

I claim as my invention:

1. A method for acquiring magnetic resonance (MR) data from an examination region of an examination object situated in an MR scanner that comprises a shim unit, said shim unit comprising a first shim channel volume having at least one first shim channel and a second shim channel volume having at least one second shim channel, said method comprising:
in a computer, dividing said examination region into multiple sections;
in said computer, determining a plurality of first shim parameter sets for said first shim channel, with one first shim channel parameter set among said plurality of first shim channel parameter sets being determined for each section among said multiple sections;
in said computer, determining a second shim parameter set for said second shim channel dependent on said plurality of determined first shim parameter sets;
before acquiring said magnetic resonance data from the examination region, adjusting said second shim channel using said second shim parameter set and adjusting said first shim channel for acquiring the magnetic resonance data from a specific section among said multiple sections using a first shim parameter set determined for that specific section; and
operating said MR scanner to acquire MR data from said specific section using the adjusted first shim channel and the adjusted second shim channel.

2. A method as claimed in claim 1 wherein said first shim channel volume and said second shim channel volume are disjunct.

3. A method as claimed in claim 1 comprising, before determining said plurality of first shim parameter sets, operating said MR scanner to acquire a first B0 field map that represents a basic magnetic field in said MR scanner, and determining said plurality of first shim parameter sets using said first B0 field map.

4. A method as claimed in claim 3 comprising acquiring said first B0 field map using raw data comprising at least three echo signals that are respectively acquired following an excitation of nuclear spins in the examination region.

5. A method as claimed in claim 3 comprising, in said computer, calculating a second B0 field map using said first B0 field map and said plurality of first shim parameter sets, and determining said second shim parameter set using said plurality of first shim parameter sets and said second B0 field map.

6. A method as claimed in claim 5 comprising calculating said second B0 field map using said first B0 field map and said plurality of first shim parameter sets by offsetting B0 field contributions, resulting from said plurality of first shim parameter sets, against said first B0 field map.

7. A method as claimed in claim 6 comprising, in said computer, offsetting a spatial portion of said first B0 field map against said B0 field contributions against a determined first shim parameter set among said plurality of first shim parameter sets that has been specifically determined for said section among said multiple sections, that corresponds to said spatial portion.

8. A method as claimed in claim 5 comprising, in said computer, calculating a third B0 field map using said first B0 field map and said second shim parameter set, and determining a plurality of adjusted first shim parameter sets for said first shim channel using said third B0 field map, with said first shim channel being adjusted using said plurality of adjusted first shim parameter sets for acquiring said MR data.

9. A method as claimed in claim 1 comprising operating said MR scanner to acquire said MR data by sequential steps comprising:
adjusting said second shim channel using said second shim parameter set;
thereafter adjusting said first shim channel using a first shim parameter set determined for a first section among said multiple sections;
thereafter acquiring MR data from said first section;
thereafter adjusting said first shim channel using a first shim parameter set determined for a second section among said multiple sections; and
thereafter acquiring MR data from said second section.

10. A method as claimed in claim 9 comprising operating said MR scanner to cause a second settling time to elapse between adjustment of said second shim channel and acquiring said MR data from said first section, and to cause a first settling time to elapse between adjusting said first shim channel using said first shim parameter set and acquiring the MR data from the first section, with said first settling time being shorter than said second settling time.

11. A method as claimed in claim 9 comprising, after adjusting said second shim channel, operating said MR scanner to acquire a fourth B0 field map, and determining a plurality of altered first shim parameter sets for said first shim channel using said fourth B0 field map and, during acquisition of said MR data, adjusting said first shim channel using said plurality of altered first shim parameter sets.

12. A magnetic resonance (MR) apparatus comprising:
an MR scanner comprising a shim unit, said shim unit comprising a first shim channel volume having at least one first shim channel and a second shim channel volume having at least one second shim channel;
a computer configured to divide an examination region of an examination subject into multiple sections;
said computer being configured to determine a plurality of first shim parameter sets for said first shim channel, with one first shim channel parameter set among said plurality of first shim channel parameter sets being determined for each section among said multiple sections;
said computer being configured to determine a second shim parameter set for said second shim channel dependent on said plurality of determined first shim parameter sets;
said computer being configured to adjust, before acquiring said magnetic resonance data from the examination region, said second shim channel using said second shim parameter set and to adjust said first shim channel for acquiring the magnetic resonance data from a specific section among said multiple sections using a first shim parameter set determined for that specific section; and
said computer being configured to operate said MR scanner to acquire MR data from said specific section using the adjusted first shim channel and the adjusted second shim channel.

13. A non-transitory, computer-readable data storage medium encoded with programming instructions for operating a magnetic resonance (MR) apparatus to acquire MR data from an examination region of an examination object situated in an MR scanner of the MR apparatus that comprises a shim unit, said shim unit comprising a first shim channel volume having at least one first shim channel and a second shim channel volume having at least one second shim channel, said MR apparatus comprising a control computer and said programming instructions causing said control computer to:
divide said examination region into multiple sections;
determine a plurality of first shim parameter sets for said first shim channel, with one first shim channel parameter set among said plurality of first shim channel parameter sets being determined for each section among said multiple sections;
determine a second shim parameter set for said second shim channel dependent on said plurality of determined first shim parameter sets;
before acquiring said magnetic resonance data from the examination region, adjust said second shim channel using said second shim parameter set and adjust said first shim channel for acquiring the magnetic resonance data from a specific section among said multiple sections using a first shim parameter set determined for that specific section; and
operate said MR scanner to acquire MR data from

Assignees

• Siemens Ag

Inventors

• Stemmer Alto

Classifications

• A61B5/055

  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging · CPC title

• G01R33/243

  Spatial mapping of the polarizing magnetic field · CPC title

• G01R33/3875 Primary

  using correction coil assemblies, e.g. active shimming · CPC title

• G01R33/56563

  caused by a distortion of the main magnetic field B0, e.g. temporal variation of the magnitude or spatial inhomogeneity of B0 (G01R33/56509, G01R33/56518, G01R33/56536 take precedence) · CPC title

• G01R33/543

  Control of the operation of the MR system, e.g. setting of acquisition parameters prior to or during MR data acquisition, dynamic shimming, use of one or more scout images for scan plane prescription (G01R33/546 takes precedence) · CPC title