METHOD AND APPARATUS FOR MAGNETIC RESONANCE IMAGING

• US 20160274205A1
• Filed: 03/18/2016
• Published: 09/22/2016
• Est. Priority Date: 03/19/2015
• Status: Active Grant

• Current Assignee: Siemens Healthineers AG (Siemens AG)
• Original Assignee: Siemens AG
• Inventors: Stemmer, Alto
• Granted Patent: US 10,031,201 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: G01R 33/243 Spatial mapping of the polarizing magnetic field
• CPC Class Codes: G01R 33/3875 using correction coil assemblies, e.g. active shimming
• CPC Class Codes: G01R 33/543 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 Class Codes: G01R 33/56563 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

Abstract

To enable improved reconstruction of magnetic resonance (MR) image data from MR scan data acquired from an examination object using dynamic shimming in an MR scanner that has a shim unit with at least one shim channel, an examination region of the object is divided into multiple sections, a B0 field of the examination region is scanned, and a B0 field map is thereby generated, a number of shim parameter sets are determined for the shim channel using the B0 field map, with a first shim parameter set of the number of shim parameter sets being determined for a first section of the multiple sections, and a second shim parameter set of the multiple shim parameter sets is determined for a second section of the multiple sections. MR scan data of the examination region are acquired, but before acquiring the MR scan data from the first section, the shim channel is adjusted using the first shim parameter set and, before acquiring the MR scan data from the second section, the shim channel is adjusted using the second shim parameter set. MR image data are reconstructed from the MR scan data using the first B0 field map and the number of shim parameter sets.

Claims

1. A method for magnetic resonance (MR) imaging of an examination region of an examination object by operation of an MR scanner comprising a shim unit having at least one shim channel, said method comprising:

in a computer, dividing the examination region into multiple sections;

operating the MR scanner to scan a basic magnetic field of the examination region produced by the MR scanner, and generating a B0 field map in said computer from the scanned basic magnetic field;

in said computer, determining a plurality of shim parameter sets for said shim channel using said B0 field map, with a first shim parameter set among said plurality of shim parameter sets being determined for a first section of said multiple sections, and a second shim parameter set among said plurality of shim parameter sets being determined for a second section of said multiple sections;

operating the MR scanner to acquire MR scan data from the examination region but, before acquiring the MR scan data from the first section, adjusting said shim channel using said first shim parameter set and, before acquiring said MR scan data from the second section, adjusting said shim channel using said second shim parameter set; and

in said computer, reconstructing MR image data from the MR scan data using said B0 field map and said plurality of shim parameter sets, and making the reconstructed MR image data available from the computer in electronic form as a data file.

2. A method as claimed in claim 1 wherein said B0 field map is a first B0 field map, and comprising calculating a second B0 field map using said first B0 field map and said plurality of shim parameter sets, and reconstructing said MR image data from the MR scan data using said first B0 field map and said plurality of shim parameter sets and said second B0 field map.

3. A method as claimed in claim 2 comprising calculating said second B0 field map using said first B0 field map and said plurality of shim parameters by calculating a first spatial section of said second B0 field map using a first spatial section of said first B0 field map and said first shim parameter set and calculating a second spatial section of said second B0 field map using a second spatial section of said first B0 field map and said second shim parameter set.

4. A method as claimed in claim 3 comprising reconstructing said MR image data from said MR scan data by reconstructing a first image region of said MR image data using the first spatial section of the second B0 field map, and reconstructing a second image region of the MR image data using the second spatial section of the second B0 field map.

5. A method as claimed in claim 2 comprising calculating said second B0 field map using the first B0 field map and the plurality of shim parameter sets by offsetting B0 field contributions, which result from said plurality of shim parameter sets, against said first B0 field map.

6. A method as claimed in claim 5 comprising acquiring said MR scan data of the examination region by operating the MR scanner with an echo planar imaging method.

7. A method as claimed in claim 6 comprising, in said computer, converting said second B0 field map into a pixel shift map, and reconstructing said MR image data from said MR scan data using said pixel shift map.

8. A method as claimed in claim 7 comprising reconstructing said MR image data from said MR scan data in a first reconstruction step wherein provisional MR image data are reconstructed from the MR scan data, and in a second reconstruction step wherein said provisional MR image data are distortion-corrected using said pixel shift map.

9. A method as claimed in claim 6 comprising directly incorporating said second B0 field map into the reconstruction of the MR image data from the MR scan data.

10. A method as claimed in claim 1 comprising scanning said B0 field using raw data comprising at least three echo signals each acquired after an excitation of nuclear spins in the examination region.

11. A magnetic resonance (MR) for imaging of an examination region of an examination object, said MR apparatus comprising:

an MR scanner comprising a shim unit having at least one shim channel, and a basic field (B0 field) magnet that produces a basic magnetic field in the scanner;

a computer configured to divide the examination region into multiple sections;

said computer being configured to operate the MR scanner to scan the basic magnetic field in the examination region produced by the MR scanner, and to generate a B0 field map in said computer from the scanned basic magnetic field;

said computer being configured to determine a plurality of shim parameter sets for said shim channel using said B0 field map, with a first shim parameter set among said plurality of shim parameter sets being determined for a first section of said multiple sections, and a second shim parameter set among said plurality of shim parameter sets being determined for a second section of said multiple sections;

said computer being configured to operate the MR scanner to acquire MR scan data from the examination region but, before acquiring the MR scan data from the first section, to adjust said shim channel using said first shim parameter set and, before acquiring said MR scan data from the second section, to adjust said shim channel using said second shim parameter set; and

said computer being configured to reconstruct MR image data from the MR scan data using said B0 field map and said plurality of shim parameter sets, and to make the reconstructed MR image data available from the computer in electronic form as a data file.

12. A non-transitory, computer-readable data storage medium encoded with programming instructions for magnetic resonance (MR) imaging of an examination region of an examination object by operation of an MR scanner comprising a shim unit having at least one shim channel, said MR scanner being operated by a computer and said storage medium being loaded into the computer and the programming instructions causing said computer to:

divide the examination region into multiple sections;

operate the MR scanner to scan a basic magnetic field of the examination region produced by the MR scanner, and generate a B0 field map in said computer from the scanned basic magnetic field;

determine a plurality of shim parameter sets for said shim channel using said B0 field map, with a first shim parameter set among said plurality of shim parameter sets being determined for a first section of said multiple sections, and a second shim parameter set among said plurality of shim parameter sets being determined for a second section of said multiple sections;

operate the MR scanner to acquire MR scan data from the examination region but, before acquiring the MR scan data from the first section, adjust said shim channel using said first shim parameter set and, before acquiring said MR scan data from the second section, adjust said shim channel using said second shim parameter set; and

reconstruct MR image data from the MR scan data using said B0 field map and said plurality of shim parameter sets, and make the reconstructed MR image data available from the computer in electronic form as a data file.