Method and apparatus for magnetic resonance imaging

Patent metadata

Field	Value
Publication number	US-9453896-B2
Application number	US-201213649326-A
Country	US
Kind code	B2
Filing date	Oct 11, 2012
Priority date	Oct 11, 2011
Publication date	Sep 27, 2016
Grant date	Sep 27, 2016

Abstract

In a method and apparatus for magnetic resonance (MR) imaging, a magnetization of nuclear spins in a subject is prepared in multiple preparation modules of an acquisition sequence. MR signals are acquired with at least one imaging module of the sequence. Spoiler gradient fields are generated in the multiple preparation modules in order to affect a transverse magnetization of the spins. The spoiler gradient fields that are applied in at least two different preparation modules are spatially varied along different directions. Spoiler gradient moments of the spoiler gradient fields are selected so that, for at least one of three orthogonal spatial directions, a weighted sum of the spoiler gradient moments that are applied along this spatial direction satisfies a threshold condition.

First claim

We claim as our invention:

1. A method for acquiring magnetic resonance (MR) imaging data, comprising:
operating a magnetic resonance data acquisition unit, with an examination subject therein, with an imaging data acquisition sequence comprising multiple preparation modules and at least one imaging module, with each of said multiple preparation modules preparing a magnetization of nuclear spins in the examination subject and wherein magnetic resonance signals, originating from said nuclear spins, are acquired in said at least one imaging module;
in the respective multiple preparation modules, generating spoiler gradient magnetic fields that produce a transverse magnetization of said nuclear spins in the examination subject, with a spoiler gradient magnetic field generated in one of said preparation modules being spatially variable along a first spatial direction among three orthogonal spatial directions, and, in another of said preparation modules, generating a spoiler gradient magnetic field that is spatially variable along a direction among three orthogonal spatial directions that is different from said first spatial direction;
generating said spoiler gradient magnetic fields with respective spoiler gradient moments that cause, for at least one of said three orthogonal spatial directions, a weighted sum of the spoiler gradient moments along said at least one of said three orthogonal spatial directions to satisfy a threshold condition; and
entering said acquired magnetic resonance signals into a data file, and making said data file available in electronic form.

2. A method as claimed in claim 1 comprising selecting said spoiler gradient moments by establishing respective spoiler gradient moments for the multiple preparation modules in an iterative method.

3. A method as claimed in claim 2 comprising, in one iteration of said iterative method, generating a spoiler gradient magnetic field along a first spatial direction among said three orthogonal spatial directions dependent on a second maximum of spoiler gradient moments that are generated along a second spatial direction among said three orthogonal spatial directions, that is different from said first spatial direction, said second maximum being a maximum of the spoiler gradient moments established in iterations in said iterative method preceding said one of said iterations.

4. A method as claimed in claim 3 comprising, in said one of said iterations, establishing said spoiler gradient moment along said first of said spatial directions dependent on a first maximum of spoiler gradient moments along said first spatial direction established in said iterations preceding said one of said iterations.

5. A method as claimed in claim 4 comprising comparing twice said first maximum with said second maximum, and establishing said gradient moment along said first of said spatial directions dependent on a result of said comparison.

6. A method as claimed in claim 2 comprising, in said iterative method, sequentially filling a multi-dimensional population matrix, in a spoiler gradient moment domain, with values of said spoiler gradient moments established in successive iterations.

7. A method as claimed in claim 6 comprising excluding fields in said population matrix dependent on said threshold condition.

8. A method as claimed in claim 1 comprising, in said one of said preparation modules, generating said spoiler gradient magnetic field along said one of said directions as a first spoiler gradient field having a spoiler gradient moment that is a whole-number multiple of a first threshold, and generating said spoiler gradient magnetic field along said another direction as a second spoiler gradient field having a spoiler gradient moment that is a whole number multiple of a second threshold.

9. A method as claimed in claim 8 wherein said first threshold and said second threshold are different from each other.

10. A method as claimed in claim 8 comprising setting said first threshold dependent on an extent of an imaging voxel in said one of said three orthogonal spatial directions, and setting said second threshold dependent on an extent of an imaging voxel in said another of said three orthogonal spatial directions.

11. A method as claimed in claim 1 comprising, in said at least one of said preparation modules, generating a both a first spoiler gradient magnetic field that is spatially variable in said one of said spatial directions, and generating a second spoiler gradient magnetic field that is spatially variable along said another of said spatial directions of said three orthogonal spatial directions.

12. A method as claimed in claim 1 wherein said three orthogonal spatial directions correspond to a phase coding direction, a frequency coding direction, and a slice coding direction for said sequence.

13. A method as claimed in claim 1 comprising:
selecting the spoiler gradient moments of the spoiler gradient fields so that, for each N th set of coefficients {f 1 , f 2 , . . . , f N } that is not equal to {0, 0, . . . , 0} and in which each coefficient f i (with 1 ≦i ≦N) is selected from the group {−1; 0; 1}, wherein N designates a number of said preparation modules the following condition is satisfied for at least one spatial direction (Dir) of the three orthogonal spatial directions:
|Σ i=1 . . . N f i ·M i Dir |≧M S Dir ,

wherein
i is an index for respective preparation modules,
Dir is selected from a phase coding direction, a frequency coding direction and a slice selection direction,
M i Dir is a threshold associated with the corresponding spatial direction; and
M S Dir is a threshold associated with the corresponding spatial direction.

14. A method as claimed in claim 13 comprising selecting the respective spoiler gradient moments to cause said condition to be satisfied for more than one of said three orthogonal spatial directions.

15. A method as claimed in claim 13 , comprising:
setting the threshold to be
M S Dir =2·π/(γ·d Dir ),

wherein γ is a gyromagnetic ratio of a kernel, and d Dir is an extent of an imaging voxel in the direction Dir.

16. A method as claimed in claim 1 comprising selecting the respective spoiler gradient moments of the spoiler gradient magnetic fields dependent on an imaging gradient moment generated in said imaging modules.

17. A method as claimed in claim 16 , comprising:
selecting the spoiler gradient moments of the spoiler gradient fields so that for each N th set of coefficients {f 1 , f 2 , . . . , f N } that is not equal to {0, 0, . . . , 0} and in which each coefficient f i (with 1 <i <N) is selected from a group {−1; 0; 1 }, wherein N designates a number of said preparation modules, and
for each K-tuple of coefficients {g 1 , g 2 , . . . , g K } in which each coefficient g j (with 1 ≦j ≦K) is selected from the group {−1; 0; 1}, wherein K designates a number of imaging modules, the following condition is satisfied for at least one spatial direction (Dir) of the three orthogonal spatial directions:
|(Σ i=1 . . . N f i ·M i Dir )+(Σ j=1 . . . K g j ·M B Dir )|≧ M S Dir ,

wherein
i is an index for respective preparation modules,
j is an index for respective imaging modules,
Dir is selected from a phase coding direction, a frequency coding direction and a slice selection direction,
M i Dir is a spoiler gradient moment along the corresponding spatial direction in the i-th preparation module,
M B Dir is an imaging gradient moment along the corresponding spatial direction in the imaging modules,
M S

Assignees

• Feiweier Thorsten
• Kuehn Bernd
• Siemens Ag

Inventors

• Feiweier Thorsten
• Kuehn Bernd

Classifications

• G01R33/5607

  by reducing the NMR signal of a particular spin species, e.g. of a chemical species for fat suppression, or of a moving spin species for black-blood imaging · CPC title

• G01R33/4838 Primary

  using spatially selective suppression or saturation of MR signals · CPC title