Method and apparatus for reconstruction of magnetic resonance image data for multiple chemical substances in multi-echo imaging

1. A method for reconstructing image data for at least two chemical substance types in a defined region of an examination object, comprising:

providing a processor with raw magnetic resonance data acquired from a defined region in an examination object at different echo times in a magnetic resonance scan, said defined region comprising at least two different chemical substance types, and said raw magnetic resonance data comprising signal contributions from all of said chemical substance types;

in said computer, executing a reconstruction algorithm to reconstruct image data from said raw magnetic resonance data, by first applying a target function to said raw magnetic resonance data that produces said image data with signal contributions from all of said chemical substance types, said target function comprising a regularization term that correlates the image data at the different echo times, and then separating the image data produced by said target function with said regularization term with respect to said at least two different chemical substance types, in order to produce a reconstructed image of the region in which at least one of said two different chemical substance types is represented; and

making the reconstructed image available from the computer in electronic form.

2. A method as claimed in claim 1 comprising, in said reconstruction algorithm, formulating said regularization term based on a correlation matrix that takes into account sought image data values at different echo times and at different image points.

3. A method as claimed in claim 2 comprising applying said reconstruction algorithm to said raw data by optimizing the target function dependent on a condition selected from the group consisting of said correlation matrix having a low rank, and the correlation matrix has a rank that matches the number of said chemical substance types.

4. A method as claimed in claim 3 comprising optimizing said target function iteratively.

5. A method as claimed in claim 3 comprising selecting said local region to cause a phase error in said local region to be approximately constant.

6. A method as claimed in claim 5 wherein said local region is comprised of 10×10×10 image points.

7. A method as claimed in claim 5 wherein said local region comprises 5×5×5 image points.

8. A method as claimed in claim 1 comprising, in said reconstruction algorithm, formulating said regularization term based on a nuclear norm of a local correlation matrix that takes into account sought image data values at different echo times and at different image points of a local region.

9. A method as claimed in claim 1 comprising, in said reconstruction algorithm, formulating said regularization term based on a total of a plurality of nuclear norms respectively for a plurality of local correlation matrices, wherein each local correlation matrix takes into account sought image data values at different echo times and at different image points of a local region.

10. A method as claimed in claim 1 comprising acquiring said raw data from said defined region during at least four different echo times.

11. A method as claimed in claim 1 comprising applying a Dixon method to separate image data of said different chemical substances in said image reconstruction algorithm.

12. An image processor for reconstructing image data for at least two chemical substance types in a defined region of an examination object, comprising:

a computer having an input via which the computer receives raw magnetic resonance data acquired from a defined region in an examination object at different echo times in a magnetic resonance scan, said defined region comprising at least two different chemical substance types, and said raw magnetic resonance data comprising signal contributions from all of said chemical substance types;

said computer being configured to execute a reconstruction algorithm to reconstruct image data from said raw magnetic resonance data, by first applying a target function to said raw magnetic resonance data that produces said image data with signal contributions from all of said chemical substance types, said target function comprising a regularization term that correlates the image data at the different echo times, and then separating the image data produced by said target function with said regularization term with respect to said at least two different chemical substance types, in order to produce a reconstructed image of the region in which at least one of said two different chemical substance types is represented; and

said computer being configured to make the reconstructed image available from the computer in electronic form.

13. A magnetic resonance (MR) apparatus comprising:

an MR scanner adapted to receive an examination object therein;

a computer configured to operate the MR scanner to acquire raw magnetic resonance data from a defined region in an examination object at different echo times in a magnetic resonance scan, said defined region comprising at least two different chemical substance types, and said raw magnetic resonance data comprising signal contributions from all of said chemical substance types;

said computer being configured to execute a reconstruction algorithm to reconstruct image data from said raw magnetic resonance data, by first applying a target function to said raw magnetic resonance data that produces said image data with signal contributions from all of said chemical substance types, said target function comprising a regularization term, that correlates the image data at the different echo times, and then separating the image data produced by said target function with said regularization term, with respect to said at least two different chemical substance types, in order to produce a reconstructed image of the region in which at least one of said two different chemical substance types is represented; and

said computer being configured to make the reconstructed image available from the computer in electronic form.

14. A non-transitory, computer-readable data storage medium encoded with programming instructions, said storage medium being loaded into a processor of a magnetic resonance apparatus, and said programming instructions causing said processor to:

receive raw magnetic resonance data acquired from a defined region in an examination object at different echo times in a magnetic resonance scan, said defined region comprising at least two different chemical substance types, and said raw magnetic resonance data comprising signal contributions from all of said chemical substance types;

execute a reconstruction algorithm to reconstruct image data from said raw magnetic resonance data, by first applying a target function to said raw magnetic resonance data that produces said image data with signal contributions from all of said chemical substance types, said target function comprising a regularization term that correlates image data of the different echo times, and then separate the image data produced by said target function with said regularization term, with respect to said at least two different chemical substance types, in order to produce a reconstructed image of the region in which at least one of said two different chemical substance types are represented; and

make the reconstructed image available from the computer in electronic form.