CT systems with oblique image planes

• US 6,178,220 B1
• Filed: 10/18/1999
• Issued: 01/23/2001
• Est. Priority Date: 11/28/1996
• Status: Expired due to Fees

• Current Assignee: Marconi Medical Systems Israel Ltd (Koninklijke Philips N.V.)
• Original Assignee: Marconi Medical Systems Israel Ltd (Koninklijke Philips N.V.)
• Inventors: Ruimi, David, Zaslavsky, Alex, Freundlich, David
• Primary Examiner(s): BRUCE, DAVID VERNON
• Application Number:
  US09/319,062
• Time in Patent Office: 463 Days
• Field of Search: 378/4, 378/15, 378/17, 378/20, 378/901, 382/131
• US Class Current: 378/4
• CPC Class Codes: A61B 6/027 characterised by the use of a particular data acquisition trajectory, e.g. helical or spiral
• CPC Class Codes: G06T 11/003 Reconstruction from projections, e.g. tomography

Abstract

A method for reconstructing one or more non-axial image slices in a CT scanner, comprising: acquiring X-ray attenuation data over an axial range; and processing the attenuation data to determine CT values at a plurality of points along one or more surface corresponding respectively to each one or more non-axial image slices, wherein processing the attenuation data comprises back-projecting the data directly to the plurality of points along each of the one or more surfaces.

Claims

1. A method for reconstructing one or more non-axial image slices in a CT scanner, comprising:

reconstructing the one or more oblique or non-planar image slices, by processing X-ray attenuation data acquired over an axial range, to determine CT values at a plurality of points along one or more surfaces corresponding respectively to each of one or more oblique or non-planar image slices; and

removing ring artifacts from the reconstructed images,

wherein processing the attenuation data comprises back-projecting the data directly to the plurality of points along each of the one or more surfaces.

2. A method according to claim 1, the data is acquired over a range defined by an axial extent of the one or more oblique or non-planar image slices.

3. A method according to claim 1 wherein back-projecting the data comprises back-projecting the data to determine CT values substantially only at or in the vicinity of the plurality of points in each of the one or more oblique or non-planar slices.

4. A method according to claim 1, wherein the X-ray attenuation data is acquired along a spiral scan path traversing the range.

5. A method according to claim 1 wherein the reconstructed slices are curved non-planar slices constructed over one or more curved surfaces and wherein reconstructing the attenuation data to determine CT values along the one or more slices comprises processing the data to determine CT values at points along the curved surfaces.

6. A method according to claim 1, wherein the reconstructed slices are oblique image slices, oriented obliquely relative to an axis of the scanner, and wherein processing the attenuation data to determine CT values along the one or more slices comprises processing the data to determine CT values at points in one or more oblique planes defined by the image oblique slices.

7. A method according to claim 6 wherein the ring artifacts are detected and corrected on the reconstructed oblique image.

8. A method according to claim 7 wherein said ring artifacts are detected in the one or more oblique image slices by identifying at least a portion of an ellipse in at least one of the oblique image slices.

9. A method according to claim 8, wherein identifying at least a portion of the ellipse comprises finding an ellipse having a known ratio of major to minor axes.

10. A method according to claim 8, wherein identifying at least a portion of the ellipse comprises finding an ellipse having a known angular orientation of its axes in the plane of one of the one or more oblique image slices.

11. A method according to claim 5 or claim 6 wherein removing ring artifacts comprises:

selecting a plurality of axial planes, which define a plurality of lines at the respective intersections of the axial planes with the one or more oblique or non-planar slices, along which lines the CT values are determined; and

processing the X-ray attenuation data to determine CT values at additional points in a vicinity of one or more of the lines in at least one of the axial planes.

12. A method according to claim 11 wherein removing ring artifacts includes detecting artifacts in the at least one of the axial planes using the CT values at the additional points.

13. A method according to claim 1, wherein processing the attenuation data to determine CT values comprises pre-processing the attenuation data during a CT scan, storing the pre-processed data, and processing the stored data to determine the CT values.

14. A method for reconstructing one or more oblique or non-planar image slices in a CT scanner, comprising:

selecting a plurality of axial planes, having a predetermined axial spacing therebetween, thereby defining a plurality of lines at the intersections of the planes with the one or more non-axial image slices;

acquiring X-ray attenuation data along a spiral scan path having a known pitch traversing an axial range defined by the plurality of axial planes; and

processing the X-ray attenuation data to determine CT values directly only at a plurality of points along the plurality of lines and in the axial planes only in a vicinity of the lines.

15. A method according to claim 14 wherein processing the attenuation data comprises filtering the attenuation data before back-projecting the data, and wherein data that are not used to determine the CT values along the plurality of lines or their vicinity are eliminated from the filtering operation.

16. A method according to claim 14, wherein processing the attenuation data comprises interpolating the attenuation data to find effective attenuation values in the plurality of axial planes.

17. A method according to claim 14, wherein selecting the plurality of axial planes comprises selecting axial planes mutually spaced by a distance substantially less than the thickness of an axial image slice corresponding to one of the axial planes.

18. A method according to claim 17, wherein selecting axial planes mutually spaced by a distance substantially less than or equal to the thickness of the axial image slice corresponding to one of the axial planes comprises selecting axial planes mutually spaced by a distance less than or equal to half the thickness of the axial image slice.

19. A method according to claim 18, wherein selecting axial planes mutually spaced by a distance substantially equal to or less than half the thickness of the axial image slice corresponding to one of the axial planes comprises selecting axial planes mutually spaced by a distance less than or equal to one third the thickness of the axial image slice.

20. A method for reconstructing a plurality of non-axial image slices in a CT scanner, comprising:

selecting a position and an orientation for each of the plurality of oblique or non-planar slices; and

reconstructing each of the slices according to the method of claim 14, wherein selecting the plurality of axial planes comprises selecting at least one common axial plane for reconstructing at least a portion of each of two of the plurality of oblique or non-planar slices.

21. A method according to claim 20, wherein slices are oblique slices, and wherein selecting the position and the orientation for each of the plurality of oblique slices comprises selecting a common orientation for at least two of the oblique slices.

22. A method according to claim 21, wherein selecting the position and orientation for each of the plurality of oblique slices comprises selecting a common orientation for a group of at least three of the oblique slices and selecting the positions of the slices so that the slices in the group are evenly spaced.

23. A method according to claim 21, and comprising fusing at least two of the commonly-oriented oblique slices to produce an oblique sum slice.

24. A method according to claim 23, wherein fusing the at least two commonly-oriented oblique slices to produce an oblique sum slice comprises producing a sum slice having angle-independent resolution.

25. A method according to claim 24, wherein selecting the position and orientation for each of the plurality of oblique slices comprises selecting a common orientation for a group of at least three of the oblique slices and selecting the positions of the slices so that the slices in the group are unequally spaced.

26. A method according to claim 20, wherein selecting the position and orientation for each of the plurality of slices comprises selecting different orientations for at least two of the slices.

27. A method according to claim 14 wherein processing the X-ray attenuation data comprises fusing attenuation data from multiple, mutually-adjacent planes among the plurality of axial planes to produce sum data, and wherein back-projecting the attenuation data comprises back-projecting the sum data.

28. A method according to claim 14, wherein processing the attenuation data to determine CT values comprises pre-processing the attenuation data during a CT scan, storing the pre-processed data, and processing the stored data to determine the CT values.

29. A method according to claim 28, wherein pre-processing the data comprises filtering the data.