Methods and devices for CT reconstruction using a grangeat approach

• US 6,983,034 B2
• Filed: 02/17/2004
• Issued: 01/03/2006
• Est. Priority Date: 02/14/2003
• Status: Expired due to Fees

• Current Assignee: University of Iowa Research Foundation
• Original Assignee: University of Iowa Research Foundation
• Inventors: Lee, Seung Wook, Wang, Ge
• Primary Examiner(s): Glick, Edward J.
• Assistant Examiner(s): KEANEY, ELIZABETH MARIE
• Application Number:
  US10/780,916
• Publication Number:
  US 20040240604A1
• Time in Patent Office: 686 Days
• Field of Search: 378/4, 378/15, 378/19, 378/901
• 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: A61B 6/583 using calibration phantoms
• CPC Class Codes: G01N 2223/419 computed tomograph
• CPC Class Codes: G01N 23/046 using tomography, e.g. computed tomography [CT]
• CPC Class Codes: G06T 11/006 Inverse problem, transformation from projection-space into object-space, e.g. transform methods, back-projection, algebraic methods
• CPC Class Codes: G06T 2211/436 Limited angle
• CPC Class Codes: Y10S 378/901 Computer tomography program or processor

Abstract

An image of an object is reconstructed in a three-dimensional coordinate system in an x-ray computed tomography system. A partial scan of the object is performed by rotating an x-ray beam having a cone beam geometry around a portion of the object or rotating the object in the cone-beam. The x-ray beam forms on a scanning trajectory through a plurality of projection lines from a plurality of successive focal point locations. The scanning trajectory may be substantially circular, helical, spiral, or spiral-like. The x-ray beam, attenuated by the object during the spiral scan, is detected to produce detector values. The detector values are integrated along straight lines on the detector plane to obtain intermediate data. Three-dimensional Radon values representing approximate plane integrals of the object are calculated from the intermediate data using a Grangeat relationship or a modified or extended version or the Grangeat relationship. The calculated and estimated Radon values are then reconstructed into an image volume according to the Radon inversion formula.

Claims

1. A method for reconstructing an image of an object in a three-dimensional coordinate system with an x-ray computed tomography system, the method comprising the steps of:

conducting a partial scan of the object by rotating an x-ray beam having a cone beam geometry around a portion of the object or rotating the object in the x-ray beam, the x-ray beam forming a scanning trajectory through a plurality of projection lines from a plurality of successive focal point locations;

detecting the x-ray beam, attenuated by the object during the scan, to produce detector values;

integrating the detector values along the projection lines to obtain intermediate data; and

calculating three-dimensional Radon values representing substantially accurate or approximate plane integrals of the object from the intermediate data using a Grangeat relationship.

2. The method of claim 1, wherein the step of conducting a partial scan includes rotating the x-ray beam around the object continuously or piece-wise continuously.

3. The method of claim 1, wherein the scanning trajectory is substantially circular.

4. The method of claim 1, wherein the scanning trajectory is substantially helical, spiral, or spiral-like.

5. The method of claim 1, wherein the step of integrating is performed explicitly.

6. The method of claim 1, wherein the step of integrating is performed implicitly.

7. The method of claim 1, wherein the step of calculating three-dimensional radon values uses a modified or extended version of the Grangeat relationship.

8. The method of claim 7, wherein in the modified or extended version of the Grangeat relationship comprising:

a mosaic of truncated fan-beams used to cover a plane and estimate the radon value as the plane integral.

9. The method of claim 7, wherein in the modified or extended version of the Grangeat algorithm comprising:

each characteristic point in the radon space categorized into singly, doubly, triply sampled, and shadow regions.

10. The method of claim 9, wherein each characteristic point is weighted appropriately to suppress image artifacts.

11. The method of claim 1, further comprising using at least one smooth weighting function to suppress data inconsistencies and associated image artifacts.

12. The method of claim 9, wherein the shadow regions are estimated by interpolation or extrapolation to remove artifacts due to missing information.

13. The method of claim 1, wherein the object is a short object.

14. The method of claim 1, wherein the object is a long object.

15. The method of claim 1, wherein the partial scan is less than 360 degrees.

16. A device for reconstructing an image of an object in a three-dimensional coordinate system with an x-ray computed tomography system, the device comprising:

a scanner for conducting a partial scan of the object by rotating an x-ray beam having a cone beam geometry around a portion of the object or rotating the object in the x-ray beam, the x-ray beam forming a scanning trajectory through a plurality of projection lines from a plurality of successive focal point locations;

detectors for detecting the x-ray beam, attenuated by the object during the scan, to produce detector values; and

a processor for integrating the detector values along the projection lines to obtain intermediate data and calculating three-dimensional Radon values representing approximate or substantially accurate plane integrals of the object from the intermediate data using a Grangeat relationship.

17. The device of claim 16, wherein the scanner rotates the x-ray beam around the object continuously or piece-wise continuously.

18. The device of claim 16, wherein the scanning trajectory is substantially circular.

19. The device of claim 16, wherein the scanning trajectory is substantially helical, spiral, or spiral-like.

20. The device of claim 16, wherein the processor performs integration explicitly.

21. The device of claim 16, wherein the processor performs integration implicitly.

22. The device of claim 16, wherein the processor calculates three-dimensional Radon values using a modified or extended version of the Grangeat relationship.

23. The device of claim 22, wherein in the modified or extended version of the Grangeat relationship comprising:

a mosaic of truncated fan-beams used to cover a plane and estimate the radon value as the plane integral.

24. The device of claim 22, wherein in the modified or extended version of the Grangeat algorithm comprising:

each characteristic point in the radon space is categorized into singly, doubly, triply sampled, and shadow regions.

25. The device of claim 24, wherein each characteristic point is weighted appropriately to suppress image artifacts.

26. The device of claim 16, wherein the processor uses at least one smooth weighting function to suppress data inconsistencies and associated image artifacts.

27. The device of claim 24, wherein the shadow regions are estimated by interpolation or extrapolation to remove artifacts due to missing information.

28. The device of claim 16, wherein the object is a short object.

29. The device of claim 16, wherein the object is a long object.

30. The device of claim 16, wherein the scan is less than 360 degrees.