Methods and systems to facilitate reducing cone beam artifacts in images

• US 7,573,973 B2
• Filed: 05/17/2005
• Issued: 08/11/2009
• Est. Priority Date: 05/17/2005
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Hsieh, Jiang, Tang, Xiangyang
• Primary Examiner(s): Glick; Edward J
• Assistant Examiner(s): Taningco; Alexander H
• Application Number:
  US11/130,769
• Publication Number:
  US 20060262893A1
• Time in Patent Office: 1,547 Days
• Field of Search: 378/420, 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 6/032 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 a cone-angle-and-image-plane-dependent view weighting, wherein the view weighting is at least partially defined by an orthogonal distance between an image plane and a central plane;

apply a Feldkamp, Davis, and Kress (FDK) algorithm with the cone-angle-and-image-plane-dependent view weighting to the set of projection data;

apply an FDK algorithm to a single circular source trajectory expressed as;

2. A computer in accordance with claim 1 wherein the 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|.

3. A computer in accordance with claim 1 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.

4. A computer in accordance with claim 1 wherein one of a ray passing through a pixel P and a conjugate of the ray impinge on a 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.

5. A computer in accordance with claim 1 wherein g(l) meets the following conditions:

g(l)≧

0, and

g(l₁)≦

g(l₂) while l₁≦

l₂.

6. A computer in accordance with claim 1 wherein ƒ

(ν

) and ƒ

(ν

_c) are defined as;

7. A computer in accordance with claim 6 wherein ƒ

′

(ν

) and ƒ

′

(ν

_c) are positive monotonous increasing functions of |ν

| and |ν

_c|.

8. A computer in accordance with claim 6 wherein ƒ

′

(ν

) and ƒ

′

(ν

_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|.

9. 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 a cone-angle-and-image-plane-dependent view weighting, wherein the view weighting is at least partially defined by an orthogonal distance between an image plane and a central plane;

apply an FDK algorithm to more than one circular source trajectory spaced apart in the z-direction that 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 the more than one circular source trajectory are expressed as;

10. 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 using a Feldkamp, Davis , and Kress (FDK) algorithm from the set of projection data using a cone-angle-and-image-plane-dependent view weighting, wherein the view weighting is at least partially defined by an orthogonal distance between an image plane and a central plane, wherein the FDK algorithm is applied to a single circular source trajectory expressed as;

11. A method in accordance claim 10 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|.

12. A method in accordance with claim 10 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.

13. A method in accordance with claim 10 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.

14. A method in accordance with claim 10 wherein g(l) meets the following conditions:

g(l)≧

0, and

g(l)≦

g(l₂) while l₁≦

l₂.

15. A method in accordance with claim 10 wherein ƒ

(ν

) and ƒ

(ν

_c) are defined as;

16. A method in accordance with claim 15 wherein ƒ

′

(ν

) and ƒ

′

(ν

_c) are positive monotonous increasing functions.

17. A method in accordance with claim 16 wherein ƒ

′

(ν

) and ƒ

′

(ν

_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|.

18. 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, wherein the view weighting is at least partially defined by an orthogonal distance between an image plane and a central plane wherein said cone-angle-and-image-plane-dependent view weighting function to the FDK algorithm is expressed as;

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

) meets conditions;

0≦

w(lα

)≦

1.0 and

w(l,α

₁)≧

w(l,α

₂) while |α

₁|≦

|α

₂|.

20. An imaging system in accordance with claim 18 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.

21. An imaging system in accordance with claim 18 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.

22. An imaging system in accordance with claim 18 wherein g(l) meets the following conditions:

g(l)≧

0, and

g(l₁)≦

g(l₂) while l₁≦

l₂.

23. An imaging system in accordance with claim 18 wherein ƒ

(ν

) and ƒ

(ν

_c) are defined as;

24. An imaging system in accordance with claim 23 wherein ƒ

′

(ν

) and ƒ

′

(ν

_c) are positive monotonous increasing functions.

25. An imaging system in accordance with claim 24 wherein ƒ

′

(ν

) and ƒ

′

(ν

_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|.