Determining and correcting for phase jumps

• US 4,797,615 A
• Filed: 09/30/1987
• Issued: 01/10/1989
• Est. Priority Date: 09/30/1987
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: Elscint Limited (Elbit Imaging Limited)
• Inventors: Rotem, Haim, Goldberg, Shmuel, Shimoni, Yair
• Primary Examiner(s): Tokar, Michael J.
• Application Number:
  US07/103,012
• Time in Patent Office: 468 Days
• Field of Search: 364/413, 128/653, 324/300, 324/307, 324/309, 324/312
• US Class Current: 324/309
• CPC Class Codes: G01R 33/565 Correction of image distortions, e.g. due to magnetic field inhomogeneities
• CPC Class Codes: G01R 33/56527 due to chemical shift effects
• CPC Class Codes: G01R 33/56563 caused by a distortion of the main magnetic field B0, e.g. temporal variation of the magnitude or spatial inhomogeneity of B0 G01R33/56509, G01R33/56518, G01R33/56536 take precedence

Abstract

A continuous phase magnetic field map is provided by dividing the field map of elements into regions; determining discontinuities in the regions and adding a constant modulo 2π to the phase values of each element of the region which results in a minimum difference between adjacent elements of the region. Then similarly joining the continuous regions to form continuous sections and the continuous sections to form continuous zones until substantially continuous phase magnetic field maps are obtained.

Claims

1. A method of providing a continuous magnetic field map for magnetic resonance systems, said method including the steps of:

acquiring a phase image comprising a plurality of elements corresponding to pixels,

dividing the phase image into a plurality of subimages each comprising a plurality of said elements wherein the sizes of the subimages are sufficiently small to limit the phase spread of each of the subimages to being no more than 2π

, and

phase unwrapping in each subimage by adding a selected modulo 2π

constant to each element of the subimage to provide said continuous map of the magnetic field.

2. The method of claim 1 including the step of connecting two unwrapped subimages to form a section.

3. The method of claim 2 including the step of joining two sections to form zones.

4. The method of claim 3 including the step of connecting two or more zones together to form a substantially continuous image.

5. The method of claim 4 wherein the step of connecting together continuous subimages includes the step of connecting the subimages in a first direction along an orthogonal axis of orthogonal axes.

6. The method of claim 5 wherein the step of connecting two or more sections together comprises connecting the sections together in a second direction along another of said orthogonal axes.

7. The method of claim 6 including reversing the first direction and the second direction.

8. The method of claim 7 wherein the step of joining the zones together comprises determining at which of said elements the zones are juxtaposed and joining the zones together at the juxtaposed elements having the least phase value.

9. A system for providing a continous magnetic field map for magnetic resonance systems, said system including:

means for acquiring a phase image comprising a plurality of elements corresponding to pixels,

means for dividing the phase image into a plurality of subimages each comprising a plurality of said elements wherein the sizes of the subimages are sufficiently small to limit the phase spread of each of the subimages to being no more than 2π

, and

means for phase unwrapping each subimage by adding a selected modulo 2π

constant to each element of the subimage to provide said continuous map of the magnetic field.

10. The system of claim 9 including:

means for connecting two unwrapped subimages to form a section.

11. The system of claim 10 including means for joining two sections to form zones.

12. The system of claim 11 including the step of connecting two or more zones together to form a substantially continuous image.

13. The system of claim 12 wherein the means for connecting together continuous subimages includes means for connecting the subimages in a first direction along an orthogonal axis of orthogonal axes.

14. The system of claim 13 wherein the means for connecting two or more sections together comprises means for connecting the sections together in a second direction along another of said orthogonal axes.

15. The system of claim 14 including means for reversing in the first direction and the second direction.

16. The system of claim 15 wherein said means for joining the zones together comprises means for determining at which of said elements the zones are juxtaposed and joining the zones together at the juxtaposed elements having the least phase value.