Method and system for in-phase and out-of-phase magnetic resonance imaging

Patent metadata

Field	Value
Publication number	US-11474179-B2
Application number	US-202117149040-A
Country	US
Kind code	B2
Filing date	Jan 14, 2021
Priority date	Jan 16, 2020
Publication date	Oct 18, 2022
Grant date	Oct 18, 2022

Abstract

In a method for MRI of an object, spins of a first material and spins of a second material are excited. An in-phase echo signal is acquired when the spins are in-phase and an out-of-phase echo signal is acquired, when the spins are out of phase. A first image for the first material and/or a second image for the second material is generated by a computing unit depending on the in-phase echo signal and the out-of-phase echo signal. For acquiring the out-of-phase echo signal, a momentum space is sampled asymmetrically in a read-out direction.

First claim

The invention claimed is:

1. A method for magnetic resonance (MR) imaging of an object, comprising:
exciting spins of a first material of the object and spins of a second material of the object;
acquiring an in-phase echo signal in response to the excited spins of the first material and the excited spins of the second material being in phase;
acquiring an out-of-phase echo signal in response to the excited spins of the first material and the excited spins of the second material being out-of-phase, the acquiring of the out-of-phase echo signal including sampling k-space asymmetrically in a read-out direction; and
generating a first image for the first material and/or a second image for the second material based on the in-phase echo signal and the out-of-phase echo signal.

2. A magnetic resonance imaging system comprising:
a magnetic resonance imaging scanner; and
a controller configured to:
control the magnetic resonance imaging scanner to:
apply an excitation pulse to excite spins of a first material of an object and spins of a second material of the object;
acquire an in-phase echo signal in response to the excited spins of the first material and the spins of the second material being in phase; and
acquire an out-of-phase echo signal in response to the spins of the first material and the excited spins of the second material being out-of-phase, the acquiring of the out-of-phase echo signal including sampling k-space asymmetrically in a read-out direction; and

generate a first image for the first material and/or a second image for the second material based on the in-phase echo signal and the out-of-phase echo signal.

3. The method according to claim 1 , wherein:
an excitation pulse is applied to excite the spins of the first and the second materials;
after the excitation pulse, a pre-phasing gradient lobe is applied; and
after the pre-phasing gradient lobe, a first read-out gradient lobe is applied to acquire the out-of-phase echo signal, the momentum change due to the pre-phasing gradient lobe and a momentum change due to the first read-out gradient lobe causing the asymmetric sampling.

4. The method according to claim 3 , wherein the momentum change due to the pre-phasing gradient lobe is smaller than one half of the momentum change due to the first read-out gradient lobe.

5. The method according to claim 3 , wherein after the first read-out gradient lobe, a second read-out gradient lobe is applied to acquire the in-phase echo signal.

6. The method according to claim 3 , wherein:
after applying the excitation pulse, a refocusing pulse is applied;
the pre-phasing gradient lobe is applied between the excitation pulse and the refocusing pulse; and
the first read-out gradient lobe is applied after the refocusing pulse.

7. The method according to claim 6 , wherein the pre-phasing gradient lobe and the first read-out gradient lobe have a same polarity.

8. The method according to claim 6 , wherein the method is based on a spin echo acquisition technique or a turbo spin echo acquisition technique.

9. The method according to claim 3 , wherein the pre-phasing gradient lobe and the first read-out gradient lobe have opposite polarities.

10. The method according to claim 9 , wherein the method is based on a gradient echo acquisition technique.

11. The method according to claim 1 , further comprising acquiring a further out-of-phase echo signal in response to the spins of the first material and the spins of the second material being out-of-phase, wherein k-space is sampled asymmetrically in the read-out direction for acquiring the further out-of-phase echo signal.

12. The method according to claim 11 , further comprising:
generating a phase-difference map based on the out-of-phase echo signal and on the further out-of-phase echo signal, wherein the first image and/or the second image is generated based on the phase-difference map.

13. The method according to claim 1 , further comprising:
generating an out-of-phase map based on the out-of-phase echo signal;
generating an in-phase map based on the in-phase echo signal; and
superimposing the in-phase map and the out-of-phase map to generate the first image and/or the second image.

14. The method according to claim 1 , wherein k-space is sampled symmetrically in the read-out direction to acquire the in-phase echo signal.

15. A non-transitory computer program product which includes a program and is directly loadable into a memory of a MR imaging device, when executed by a processor of the MR imaging device, causes the processor to perform the method as claimed in claim 1 .

16. A non-transitory computer-readable storage medium with an executable program stored thereon, that when executed, instructs a processor to perform the method of claim 1 .

17. The method according to claim 1 , wherein the in-phase echo signal and the out-of-phase echo signal are acquired based on a same excitation pulse with no refocusing pulse applied between a first read-out gradient lobe and a second read-out gradient lobe.

18. The method according to claim 1 , wherein sampling k-space asymmetrically in the read-out direction comprises sampling only a portion of k-space in the read-out direction.

19. The method according to claim 1 , wherein sampling k-space asymmetrically in the read-out direction comprises sampling only a portion of k-space on a side of positive momenta or a side of negative momenta, in the read-out direction.

Assignees

• Siemens Healthcare Gmbh

Inventors

• Dispenza Nadine
• Paul Dominik
• Stich Manuel
• Zeller Mario

Classifications

• G01R33/4828 Primary

  Resolving the MR signals of different chemical species, e.g. water-fat imaging · CPC title

• G01R33/561

  by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences · CPC title

• G01R33/4818

  MR characterised by data acquisition along a specific k-space trajectory or by the temporal order of k-space coverage, e.g. centric or segmented coverage of k-space · CPC title

• G01R33/485

  based on chemical shift information {[CSI] or spectroscopic imaging, e.g. to acquire the spatial distributions of metabolites} · CPC title

• G01R33/5615

  Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE] · CPC title