Methods and systems to facilitate reducing cone beam artifacts in images

• US 20060262893A1
• Filed: 05/17/2005
• Published: 11/23/2006
• Est. Priority Date: 05/17/2005
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Hsieh, Jiang, Tang, Xiangyang
• Granted Patent: US 7,573,973 B2
• Time in Patent Office: Days
• 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 6/032 Transmission computed tomography [CT]
• CPC Class Codes: A61B 6/4085 Cone-beams
• 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 2211/421 Filtered back projection [FBP]

Abstract

Methods and systems for generating images from a set of projection data acquired during a CT scan is provided. The system includes a computer programmed to utilize at least one of a cone angle dependent view weighting and an image plane dependent view weighting to generate an image.

Claims

1. A computer programmed to generate computed tomographic (CT) images from a set of projection data acquired during a CT scan, said computer programmed to perform at least one of a cone angle dependent view weighting and an image plane dependent view weighting.

2. A computer in accordance with claim 1 further programmed to apply a Feldkamp, Davis, and Kress (FDK) algorithm with at least one of a cone angle dependent view weighting and an image plane dependent view weighting to the set of projection data.

3. A computer in accordance with claim 2 further programmed to apply an FDK algorithm to a single circular source trajectory expressed as:

4. A computer in accordance with claim 3 wherein cone-angle-and-image-plane-dependent view weighting function w(l,α

) meets conditions;

0≦

w(l,α

)≦

1.0 and
w(l,α

₁)≦

w(l,α

₂) while α

₁≦

α

₂.

5. A computer in accordance with claim 3 wherein conjugate rays are rays that are 180°

apart in view angle, said computer further programmed to weight a first ray associated with a relatively larger cone angle less than a second ray associated with a relatively smaller cone angle, the rays being conjugates with respect to each other.

6. A computer in accordance with claim 3 wherein one of a ray passing through a pixel P and a conjugate of the ray impinge on the detector, said computer further programmed to weight the ray impinging the detector relatively greater than the ray not impinging the detector when reconstructing pixel P.

7. A computer in accordance with claim 3 wherein the cone-angle-and-image-plane-dependent view weighting function is expressed as:

8. A computer in accordance with claim 7 wherein g(l) meets the following conditions:

g(l)≧

2 , and
g(l)≦

g(l₂) while l₁≦

l₂.

9. A computer in accordance with claim 3 wherein the cone-angle-and-image-plane-dependent view weighting function is expressed as:

10. A computer in accordance with claim 9 wherein ƒ

(ν

) and ƒ

(ν

_c) are defined as;

11. A computer in accordance with claim 10 wherein ƒ

′

(ν

) and ƒ

′

(ν

_c) are positive monotonous increasing functions.

12. A computer in accordance with claim 11 wherein ƒ

′

(ν

) and ƒ

′

(ν

hd c) meet the conditions;

ƒ

′

(ν

₁)≦

ƒ

′

(ν

₂) while ν

₁≦

ν

₂, and
ƒ

′

(ν

_cl)≦

ƒ

′

(ν

_c2) while ν

_c1≦

ν

_c2.

13. A computer in accordance with claim 3 wherein more than one circular source trajectories spaced apart in the z-direction define respective central planes such that a distance between the image plane and a first trajectory is l, and a distance between the IP and a second trajectory is L-l and wherein for each trajectory, the cone-angle-and-image-plane-dependent view weighting function is expressed as:

14. A method for producing a cross-sectional image of an object by using a computed tomography imaging system, which includes a source of a conical beam of radiation and a multi-row detector array arranged on opposite sides of an axis of rotation, said method comprising:

rotating the source and detector array about the axis of rotation;

while rotating, collecting x-ray attenuation data samples from the multi-row detector array at a plurality of projection angles to produce a set of projection data measured with a circular orbit of the x-ray source; and

generating an image from the set of projection data using at least one of a cone angle dependent view weighting and an image plane dependent view weighting.

15. A method in accordance with claim 14 wherein a Feldkamp, Davis, and Kress (FDK) algorithm is utilized in generating the image.

16. A method in accordance with claim 15 wherein the FDK algorithm utilizes a cone angle dependent view weighting in generating the image.

17. A method in accordance with claim 15 wherein the FDK algorithm utilizes an FDK algorithm applied to a single circular source trajectory expressed as:

18. A method in accordance with claim 17 wherein cone-angle-and-image-plane-dependent view weighting function w(l,α

) meets conditions;

0≦

w(l,α

)≦

1.0 and
w(l,α

₁)≦

w(l,α

₂) while α

₁≦

α

₂.

19. A method in accordance with claim 17 wherein conjugate rays are rays that are 180°

apart in view angle, said method further comprising weighting a first ray associated with a relatively larger cone angle less than a second ray associated with a relatively smaller cone angle, the rays being conjugates with respect to each other.

20. A method in accordance with claim 17 wherein one of a ray passing through a pixel P and a conjugate of the ray impinge on the detector, said method further comprising weighting the ray impinging the detector relatively greater than the ray not impinging the detector when reconstructing pixel P.

21. A method in accordance with claim 17 wherein the cone-angle-and-image-plane-dependent view weighting function is expressed as:

22. A method in accordance with claim 21 wherein g(l) meets the following conditions:

g(l)≧

0, and
g(l₁)≦

g(l₂) while l₁≦

l₂.

23. A method in accordance with claim 17 wherein the cone-angle-and-image-plane-dependent view weighting function is expressed as:

24. A method in accordance with claim 23 wherein ƒ

(ν

) and ƒ

(ν

_c) are defined as;

25. A method in accordance with claim 24 wherein ƒ

′

(v) and ƒ

′

(v_c) are positive monotonous increasing functions.

26. A method in accordance with claim 25 wherein ƒ

′

(v) and ƒ

′

(v_c) meet the conditions;

ƒ

′

(v₁)≦

ƒ

′

(ν

₂) while ν

₁≦

ν

₂, and
ƒ

′

(ν

_cl)≦

ƒ

′

(ν

_c2) while ν

_c1≦

ν

_c2.

27. A method in accordance with claim 17 wherein more than one circular source trajectories spaced apart in the z-direction define respective central planes such that a distance between the image plane and a first trajectory is l, and a distance between the IP and a second trajectory is L-l and wherein for each trajectory, the cone-angle-and-image-plane-dependent view weighting function is expressed as:

28. A computed tomographic (CT) imaging system for reconstructing an image of an object, said imaging system comprising:

a detector array;

at least one radiation source; and

a computer coupled to said detector array and said radiation source, said computer configured to utilize a cone-angle-and-image-plane-dependent view weighting function to generate three dimensional images from cone-beam projections measured with a circular orbit of the radiation source.

29. An imaging system in accordance with claim 28 wherein said computer is further configured to apply a cone-angle-and-image-plane-dependent view weighting function to a Feldkamp, Davis, and Kress (FDK) algorithm.

30. An imaging system in accordance with claim 28 wherein said computer is further configured to apply a cone-angle-and-image-plane-dependent view weighting function to the FDK algorithm expressed as:

31. A computer in accordance with claim 30 wherein cone-angle-and-image-plane-dependent view weighting function w(l,α

) meets conditions;

0≦

w(l,α

)≦

1.0 and
w(l,α

₁)≦

w(l,α

₂) while α

₁≦

α

₂.

32. An imaging system in accordance with claim 30 wherein conjugate rays are rays that are 180°

apart in view angle, said computer further configured to weight a first ray associated with a relatively larger cone angle less than a second ray associated with a relatively smaller cone angle, the rays being conjugates with respect to each other.

33. An imaging system in accordance with claim 30 wherein one of a ray passing through a pixel P and a conjugate of the ray impinge on the detector, said computer further configured to weight the ray impinging the detector relatively greater than the ray not impinging the detector when reconstructing pixel P.

34. An imaging system in accordance with claim 30 wherein the cone-angle-and-image-plane-dependent view weighting function is expressed as:

35. An imaging system in accordance with claim 34 wherein g(l) meets the following conditions:

g(l)≧

2, and
g(l₁)≦

g(l₂) while l₁≦

l₂.

36. An imaging system in accordance with claim 30 wherein the cone-angle-and-image-plane-dependent view weighting function is expressed as:

37. An imaging system in accordance with claim 36 wherein f(v) and ƒ

(ν

_c) are defined as;

38. An imaging system in accordance with claim 37 wherein ƒ

′

(v) and ƒ

′

(v_c) are positive monotonous increasing functions.

39. An imaging system in accordance with claim 38 wherein ƒ

′

(v) and ƒ

′

(v_c) meet the conditions;

ƒ

′

(ν

₁)≦

ƒ

′

(ν

₂) while ν

₁≦

ν

₂ and
ƒ

′

(ν

_c1)≦

ƒ

′

(ν

_c2) while ν

_c1≦

ν

_c2.

40. An imaging system in accordance with claim 30 wherein more than one circular source trajectories spaced apart in the z-direction define respective central planes such that a distance between the image plane and a first trajectory is l, and a distance between the IP and a second trajectory is L-l and wherein for each trajectory the imaging system is further configured to express the cone-angle-and-image-plane-dependent view weighting function as: