Method and magnetic resonance system for time-dependent intensity correction of diffusion-weighted MR images

Patent metadata

Field	Value
Publication number	US-9632161-B2
Application number	US-201314043985-A
Country	US
Kind code	B2
Filing date	Oct 2, 2013
Priority date	Oct 2, 2012
Publication date	Apr 25, 2017
Grant date	Apr 25, 2017

Abstract

In a method and magnetic resonance (MR) apparatus for time-dependent intensity correction of diffusion-weighted MR images that are acquired with a sequence of different diffusion gradient fields, different diffusion gradient fields are associated with at least one group, with the association with groups being established so that the diffusion gradient fields that are associated with the same group satisfy an orthogonality criterion. For each group, an MR result image is created from the MR images associated with the group, such that the MR result image has a suppressed direction dependency of the diffusion weighting in comparison to the constituent MR images. An intensity correction can be made based on the multiple MR result images and used to correct the constituent MR images.

First claim

We claim as our invention:

1. A method for time-dependent intensity correction of diffusion-weighted magnetic resonance (MR) images, comprising:
operating an MR data acquisition unit to acquire data representing a plurality of diffusion-weighted MR images, with a sequence of diffusion gradient fields having respectively different directions, each of said diffusion-weight MR images being comprised of image points;
entering said plurality of diffusion-weighted MR images on an input into a processor and, in said processor for each image point of each diffusion-weighted MR image, estimating a diffusion tensor based on the MR images and based on a model of a time dependency of intensity;
in said processor, determining an intensity correction based on said model of said time dependency;
in said processor, applying the intensity correction to said MR images to obtain corrected MR images; and
making the corrected MR images available at an output of said processor in electronic form, as respective data files.

2. A method as claimed in claim 1 comprising using, as said model of time dependency, a model that is at least partially predetermined, and, from said processor, accessing said at least partially predetermined model.

3. A method as claimed in claim 1 comprising generating said model to embody at least one of a time-dependent heating of gradient coils in said MR data acquisition unit, a polynomial dependency of intensity on time, a trigonometric dependency of intensity on time, and a spatial dependency between different image points.

4. A method as claimed in claim 1 comprising determining said model of time dependency according to a spatial dependency used as boundary condition with respect to adjacent image points.

5. A method as claimed in claim 1 comprising determining said model of time dependency using a polynomial dependency as a series expansion up to a predetermined order.

6. A method as claimed in claim 1 comprising determining said model of time dependency using a trigonometric dependency as a series expansion up to a predetermined order.

7. A method as claimed in claim 1 wherein at least some successive diffusion gradient fields in said sequence have respectively different b-values.

8. A method as claimed in claim 1 wherein a spatial derivative of successive diffusion gradient fields in said sequence assumes a value that is greater than a predetermined change threshold.

9. A method for time-dependent intensity correction of diffusion-weighted magnetic resonance (MR) images, comprising:
operating an MR data acquisition unit to acquire data representing a plurality of diffusion-weighted MR images with a sequence of diffusion gradient fields, respectively activated in different directions;
entering said plurality of diffusion-weighted MR images on an input into a processor and, in said processor, automatically associating diffusion gradient fields among said plurality of different diffusion gradient fields, that have respective directions that satisfy an orthogonality criterion into at least one subset of said plurality of diffusion gradient fields;
in said processor, for each set of diffusion gradient fields, generating an MR result image from respective MR constituent images formed by data acquired with diffusion weighting produced by the diffusion gradient field in each subset, thereby giving said MR result image a suppressed direction dependency of said diffusion weighting in comparison to said MR constituent images;
from the respective MR result images created for each subset, determining an intensity correction in said processor;
in said processor, applying said intensity correction to the constituent MR images to produce intensity-corrected MR images; and
making the intensity-corrected MR images available at an output of said processor in electronic form, as respective data files.

10. A method as claimed in claim 9 wherein each of said intensity-corrected MR images is comprised of image points, with each image point having an intensity associated therewith, and wherein said method comprises, for each of said image points of each of said intensity-corrected MR images, iteratively:
estimating a diffusion tensor based on the intensity-corrected MR images;
determining an additional intensity correction from the estimated diffusion tensor and the intensity-corrected MR images;
applying the additional intensity correction to the intensity-corrected MR images; and
terminating iteration when a predetermined convergence criterion is satisfied.

11. A method as claimed in claim 10 comprising estimating said diffusion tensor by:
adapting image point values of the diffusion tensor based on image point values of the respective image points of the intensity-corrected MR image, and based on b-values of the diffusion gradient fields.

12. A method as claimed in claim 9 comprising creating the MR result image from the constituent MR images in a respective subset by calculating a geometric mean of said constituent MR images in the respective group.

13. A method as claimed in claim 9 comprising associating said different diffusion gradient fields into respective subsets according to at least one further criterion selected from the group of criteria consisting of:
a predetermined number of successive diffusion gradient fields;
no diffusion gradient field is commonly associated with successive subsets;
no more than one diffusion gradient field is commonly associated with successive subsets;
no more than two diffusion gradient fields are commonly associated with successive subsets;
diffusion gradient fields associated with a same subset exhibit respectively different directions having an angle, with respect to 90°, that is less than a predetermined angle threshold; or
diffusion gradient fields associated with a same subset have same b-values.

14. A method as claimed in claim 13 wherein said predetermined number is 3.

15. A method as claimed in claim 9 wherein said constituent MR images and said MR result image are each comprised of image points, and comprising intensity-correcting said constituent MR images by, for each image point thereof:
determining a temporal scaling of the intensity from the MR result images; and
applying the intensity correction to each image point by normalizing the intensity of the MR images to a reference intensity value based on said determined temporal scaling.

16. A method as claimed in claim 9 comprising determining said intensity correction by at least one of:
low-pass filtering a spatial frequency domain representation of the MR result images;
suppressing background noise in the MR result images; and
for different image points in said MR result imaging, determining a fraction of an intensity value with respect to a reference intensity value of that image point, as the intensity correction.

17. A magnetic resonance (MR) apparatus for time-dependent intensity correction of diffusion-weighted MR images, comprising:
an MR data acquisition unit;
a control computer configured to operate the MR data acquisition unit to acquire data representing a plurality of diffusion-weighted MR images with a sequence of diffusion gradient fields, respectively activated in different directions;
a processor that receives said plurality of diffusion-weighted MR images and that is configured to associate diffusion gradient fields among said plurality of different diffusion gradient fields, that have respective directions that satisfy an orthogonality criterion into at least one subset of said plurality of diffusion gradient fields;

Assignees

• Huwer Stefan
• Porter David Andrew
• Siemens Ag

Inventors

• Huwer Stefan
• Porter David Andrew

Classifications

• G01R33/56 Primary

  Image enhancement or correction, e.g. subtraction or averaging techniques {, e.g. improvement of signal-to-noise ratio and resolution} · CPC title

• G01R33/56341 Primary

  Diffusion imaging · CPC title

• G01R33/5659

  caused by a distortion of the RF magnetic field, e.g. spatial inhomogeneities of the RF magnetic field (G01R33/56509, G01R33/56518, G01R33/56536 take precedence) · CPC title