MRI method for B0-mapping

Patent metadata

Field	Value
Publication number	US-11474170-B2
Application number	US-201917256702-A
Country	US
Kind code	B2
Filing date	Jun 27, 2019
Priority date	Jul 3, 2018
Publication date	Oct 18, 2022
Grant date	Oct 18, 2022

Abstract

A B 0 -mapping method determines the spatial distribution of a static magnetic field in a pre-selected imaging zone comprising computation of the spatial distribution of a static magnetic field from a spatial distribution of spin-phase accruals between magnetic resonance echo signals from the imaging zone and an estimate of the proton density distribution in the imaging zone. The invention provides the field estimate also in cavities and outside tissue. Also the field estimate of the invention suffers less from so-called phase-wraps.

First claim

The invention claimed is:

1. A B 0 -mapping method for determining spatial distribution of a static magnetic field in a pre-selected imaging zone, the method comprising:
computing the spatial distribution of a static magnetic field from a spatial distribution of spin-phase accruals between magnetic resonance echo signals from the imaging zone; and
estimating a proton density distribution in the imaging zone by segmenting at least three components, wherein the segmenting involves at least components representing soft-tissue, interstitial voids and air.

2. The B 0 -mapping method of claim 1 , further comprising:
computing a phase-estimate magnetic susceptibility distribution that is consistent with a spin-phase accrual distribution;
computing a proton-estimate magnetic susceptibility distribution that is consistent with an estimated proton spin density distribution;
fitting a final magnetic susceptibility distribution to minimize differences both: (i) between the final magnetic susceptibility distribution and the phase-estimate magnetic susceptibility distribution; and (ii) between the final magnetic susceptibility distribution and the proton-estimate magnetic susceptibility distribution; and
computing a spatial distribution of a static magnetic field from the final magnetic susceptibility distribution.

3. The B 0 -mapping method of claim 2 , wherein
the computing of the final magnetic susceptibility distribution is done in an iterative procedure, and the iteration is done between constraints of:
a minimal difference between the final magnetic susceptibility distribution and the phase-estimate magnetic susceptibly distribution; and
a minimal difference between the final magnetic susceptibility distribution and the proton-estimate magnetic susceptibility distribution.

4. The B 0 -mapping method of claim 1 , wherein the segmenting includes components representing silicone, metal and ceramic.

5. The B 0 -mapping method as claimed in claim 3 , further comprising initializing the iterative procedure from an initial estimate of the spatial distribution of the static magnetic field and an accuracy of the spatial distribution of the static magnetic field.

6. The B 0 -mapping method of claim 3 , wherein a self-consistent minimization procedure minimizes differences both: (i) between the final magnetic susceptibility distribution and the phase-estimate magnetic susceptibility distribution; and (ii) between the final magnetic susceptibility distribution and the proton-estimate magnetic susceptibility distribution.

7. A magnetic resonance examination system, comprising:
a processor;
a tangible, non-transitory computer readable medium that stores instructions, which when executed by the processor, causes the processor to determine spatial distribution of a static magnetic field in a pre-selected imaging zone by:
computing the spatial distribution of a static magnetic field from a spatial distribution of spin-phase accruals between magnetic resonance echo signals from the imaging zone; and
estimating a proton density distribution in the imaging zone by segmenting at least three components, wherein the segmenting involves at least components representing soft-tissue, interstitial voids and air.

8. The magnetic resonance examination system of claim 7 , wherein the instructions further cause the processor to determine spatial distribution of a static magnetic field in a pre-selected imaging zone by:
computing a phase-estimate magnetic susceptibility distribution that is consistent with a spin-phase accrual distribution;
computing a proton-estimate magnetic susceptibility distribution that is consistent with an estimated proton spin density distribution,
fitting a final magnetic susceptibility distribution to minimize differences both: (i) between the final magnetic susceptibility distribution and the phase-estimate magnetic susceptibility distribution; and (ii) between the final magnetic susceptibility distribution and the proton-estimate magnetic susceptibility distribution; and
computing a spatial distribution of a static magnetic field from the final magnetic susceptibility distribution.

9. The magnetic resonance examination system of claim 8 , wherein the computing of the final magnetic susceptibility distribution is done in an iterative procedure, and the iteration is done between constraints of:
a minimal difference between the final magnetic susceptibility distribution and the phase-estimate magnetic susceptibly distribution; and
a minimal difference between the final magnetic susceptibility distribution and the proton-estimate magnetic susceptibility distribution.

10. The magnetic resonance examination system of claim 7 , wherein the segmenting includes components representing silicone, metal and ceramic.

11. The magnetic resonance examination system of claim 9 , wherein the instructions further cause the processor to determine spatial distribution of a static magnetic field in a pre-selected imaging zone by:
initializing the iterative procedure from an initial estimate of the spatial distribution of the static magnetic field and an accuracy of the spatial distribution of the static magnetic field.

12. A B 0 -mapping method for determining spatial distribution of a static magnetic field in a pre-selected imaging zone, the method comprising:
computing the spatial distribution of a static magnetic field from a spatial distribution of spin-phase accruals between magnetic resonance echo signals from the imaging zone;
estimating a proton density distribution in the imaging zone;

computing a phase-estimate magnetic susceptibility distribution that is consistent with a spin-phase accrual distribution;
computing a proton-estimate magnetic susceptibility distribution that is consistent with an estimated proton spin density distribution;
fitting a final magnetic susceptibility distribution to minimize differences both: (i) between the final magnetic susceptibility distribution and the phase-estimate magnetic susceptibility distribution; and (ii) between the final magnetic susceptibility distribution and the proton-estimate magnetic susceptibility distribution; and
computing a spatial distribution of a static magnetic field from the final magnetic susceptibility distribution.

13. The B 0 -mapping method of claim 12 , wherein the computing of the final magnetic susceptibility distribution is done in an iterative procedure, and the iteration is done between constraints of:
a minimal difference between the final magnetic susceptibility distribution and the phase-estimate magnetic susceptibly distribution; and
a minimal difference between the final magnetic susceptibility distribution and the proton-estimate magnetic susceptibility distribution.

14. The B 0 -mapping method of claim 12 , wherein the estimating the proton density distribution comprises segmenting at most components representing soft-tissue, interstitial voids and air.

15. The B 0 -mapping method as claimed in claim 13 , further comprising initializing the iterative procedure from an initial estimate of the spatial distribution of the static magnetic field and an accuracy of the spatial distribution of the static magnetic field.

16. The B 0 -mapping method of claim 13 , wherein a self-consistent minimization procedure minimizes differences both: (i) between the final magnetic susceptibility distribution and the phase-estimate magnetic susceptibility distribution; and (ii) between the final magnetic susceptibility distribution and the proton-estimate magnetic susceptibility distribution.

17. A magne

Assignees

• Koninklijke Philips Nv

Inventors

• Fuderer Miha

Classifications

• G01R33/5608

  Data processing and visualization specially adapted for MR, e.g. for feature analysis and pattern recognition on the basis of measured MR data, segmentation of measured MR data, edge contour detection on the basis of measured MR data, for enhancing measured MR data in terms of signal-to-noise ratio by means of noise filtering or apodization, for enhancing measured MR data in terms of resolution by means for deblurring, windowing, zero filling, or generation of gray-scaled images, colour-coded images or images displaying vectors instead of pixels (image data processing or generation, in general G06T) · CPC title

• G01R33/448

  Relaxometry, i.e. quantification of relaxation times or spin density (G01R33/50 takes precedence) · CPC title

• G01R33/243 Primary

  Spatial mapping of the polarizing magnetic field · CPC title

• G01R33/443

  Assessment of an electric or a magnetic field, e.g. spatial mapping, determination of a B0 drift or dosimetry · 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