Methods and apparatus for FOV-dependent aliasing artifact reduction

• US 20030031289A1
• Filed: 07/18/2001
• Published: 02/13/2003
• Est. Priority Date: 07/18/2001
• Status: Active Grant

• Current Assignee: GE Medical Systems Global Technology Company LLC (GE Healthcare Technologies, Inc.)
• Original Assignee: GE Medical Systems Global Technology Company LLC (GE Healthcare Technologies, Inc.)
• Inventors: Hsieh, Jiang
• Granted Patent: US 6,529,574 B1
• Time in Patent Office: Days
• US Class Current: 378/4
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: A61B 6/5258 involving detection or reduction of artifacts or noise
• 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 11/005 Specific pre-processing for tomographic reconstruction, e.g. calibration, source positioning, rebinning, scatter correction, retrospective gating
• CPC Class Codes: Y10S 378/901 Computer tomography program or processor

Abstract

In one aspect, there is provided a method for reducing aliasing artifacts in a computed tomography system. The method includes scanning an object with a computed tomography system to acquire a projection data set of measured views; synthesizing additional views of the projection data set utilizing view interpolation; and filtering and backprojecting the projection data set utilizing a weighting function dependent upon parameters R_f and R_t, where radius R_f around an isocenter of the CT imaging system is selected in accordance with a low artifact criterion and R_t is a parameter defining a transition region outside of radius R_f around the isocenter of the CT imaging system.

Claims

1. A method for reducing aliasing artifacts in a computed tomography system, said method comprising:

scanning an object with a computed tomography system to acquire a projection data set of measured views;

synthesizing additional views of the projection data set utilizing view interpolation; and

filtering and backprojecting the projection data set utilizing a weighting function dependent upon parameters R_f and R_t, where radius R_f around an isocenter of the CT imaging system is selected in accordance with a low artifact criterion and R_t is a parameter defining a transition region outside of radius R_f around the isocenter of the CT imaging system.

2. A method in accordance with claim 1 wherein the weighting function is different for the measured views and the synthesized views.

3. A method for reducing aliasing artifacts in a computed tomography system, said method comprising:

scanning an object with a computed tomography (CT) imaging system to acquire a projection data set of measured views;

reconstructing a first image utilizing the measured views to produce an image having a central, essentially artifact-free zone;

interpolating views between measured views to produce a projection data set having interpolated views;

reconstructing a second image utilizing both the interpolated views and the measured views; and

producing a blended image from the first image and the second image utilizing a weighting function selected to smoothly transition from the first image to the second image in a transition region surrounding an isocenter of the CT imaging system.

4. A method in accordance with claim 3 wherein the first image is written P₁ and the second image is written P₂, the first image and second image are combined using weighting functions w₁(i, j) and w₂(i, j), and the blended image P(i, j) is written:

P(i, j)=w₁ (i, j)P₁(i, j)+w₂ (i, j)P₂(i, j)

where;

w₁(i, j)=1−

w₂(i, j)

and

$w_2<br><br>\left(i,j\right)=\{\begin{array}{cc}0& r\le <br><br>R_f\\ \frac{r-R_f}{R_t-R_f}& R_f<<br><br>r\le <br><br>R_t\\ 1& r><br><br>R_t\end{array}.$

5. A method in accordance with claim 3 further comprising determining a radius R_f of the central, essentially artifact-free zone.

6. A method in accordance with claim 5 wherein the CT imaging system has a data acquisition system (DAS), and R_f is a function of a sampling rate of the DAS and a scan speed of the CT imaging system.

7. A method in accordance with claim 6 wherein R_f is a distance from the isocenter providing a sampling distance in an azimuthal direction of 50π

/984 cm.

8. A method in accordance with claim 3 wherein said interpolating views between measured views comprises synthesizing views uniformly in all directions.

9. A method for reducing aliasing artifacts in a computed tomography system, said method comprising:

scanning an object with a computed tomography (CT) imaging system to acquire a projection data set of measured views;

reconstructing a first image utilizing the projection data of measured views set to produce an image having a central, essentially artifact-free zone;

interpolating views between the measured views to produce a projection data set having interpolated views;

reconstructing a second image utilizing the interpolated views; and

producing a blended image from the first image and the second image utilizing a weighting function selected to smoothly transition from the first image to the second image in a transition region surrounding an isocenter of the CT imaging system;

and further wherein the first image is written P₁(i, j), the second image is written P₂(i, j), pixel (i, j) is a distance r from the isocenter, and images P₁(i, j) and P₂(i, j) are combined by weighting P₁(i, j) and P₂(i, j) with weights w₁(i, j) and w₂ (i, j), respectively, where a sum of weights w₁(i, j) and w₂ (i, j) is a constant, and w₂ (i, j) increases in magnitude relative to w₁(i, j) at least within a transition region in a vicinity of a radius R_f of the central, essentially artifact-free zone.

10. A method in accordance with claim 9 wherein

11. A computed tomographic (CT) imaging system having a rotating gantry, a detector array on said rotating gantry, and a radiation source on said rotating gantry configured to project a beam of radiation towards said detector array through an object to be imaged;

said system configured to;

scan an object to acquire a projection data set of measured views;

synthesize additional views of said projection data set utilizing view interpolation; and

filter and backproject said projection data set utilizing a weighting function dependent upon parameters R_f and R_t, where radius R_f around an isocenter of said CT imaging system is selected in accordance with a low artifact criterion and R_t is a parameter defining a transition region outside of radius R_f around said isocenter of said CT imaging system.

12. A system in accordance with claim 11 wherein said weighting function is different for said measured views and said synthesized views.

13. A computed tomographic (CT) imaging system having a rotating gantry, a detector array on said rotating gantry, and a radiation source on said rotating gantry configured to project a beam of radiation towards said detector array through an object to be imaged;

said system configured to;

scan an object to acquire a projection data set of measured views;

reconstruct a first image utilizing said measured views to produce an image having a central, essentially artifact-free zone;

interpolate views between measured views to produce a projection data set having both interpolated views and said measured views;

reconstruct a second image utilizing both said interpolated views and said measured views; and

produce a blended image from said first image and said second image utilizing a weighting function selected to smoothly transition from said first image to said second image in a transition region surrounding an isocenter of said CT imaging system.

14. A system in accordance with claim 13 wherein said first image is written P₁ and said second image is written P₂, said first image and said second image are combined using weighting functions w₁(i, j) and w₂(i, j), and said blended image P(i, j) is written:

P(i, j)=w₁(i, j)P₁(i, j)+w₂(i, j)P₂(i, j)

where;

w₁(i, j)=1−

w₂(i, j)

and

$w_2<br><br>\left(i,j\right)=\{\begin{array}{cc}0& r\le <br><br>R_f\\ \frac{r-R_f}{R_t-R_f}& R_f<<br><br>r\le <br><br>R_t\\ 1& r><br><br>R_t\end{array}.$

15. A system in accordance with claim 13 further configured to determine a radius R_f of the central, essentially artifact-free zone.

16. A system in accordance with claim 15 wherein said CT imaging system has a data acquisition system (DAS), and R_f is a function of a sampling rate of said DAS and a scan speed of said CT imaging system.

17. A system in accordance with claim 16 wherein R_f is a distance from said isocenter providing a sampling distance in an azimuthal direction of 50π

/984 cm.

18. A system in accordance with claim 13 wherein to interpolate said views between said measured views, said system is configured to synthesize views uniformly in all directions.

19. A computed tomographic (CT) imaging system having a rotating gantry, a detector array on said rotating gantry, and a radiation source on said rotating gantry configured to project a beam of radiation towards said detector array through an object to be imaged;

said system configured to;

scan an object to acquire a projection data set of measured views;

reconstruct a first image utilizing said measured views to produce an image having a central, essentially artifact-free zone;

interpolate views between said measured views to produce a projection data set of interpolated views;

reconstruct a second image utilizing said interpolated views; and

produce a blended image from said first image and said second image utilizing a weighting function selected to smoothly transition from said first image to said second image in a transition region surrounding an isocenter of said CT imaging system;

and further wherein said first image is written P₁(i, j), said second image is written P₂(i, j), pixel (i, j) is a distance r from said isocenter, and said system is configured to combine said images P₁(i, j) and P₂(i, j) by weighting P₁(i, j) and P₂(i, j) with weights w₁(i, j) and w₂ (i, j), respectively, where a sum of said weights w₁(i, j) and w₂(i, j) is a constant, and w₂ (i, j) increases in magnitude relative to w₁(i, j) at least within a transition region in a vicinity of a radius R_f of said central, essentially artifact-free zone.

20. A system in accordance with claim 19 wherein

21. A computer configured to:

read a projection data set of measured views obtained by scanning an object with a computed tomographic (CT) imaging system;

synthesize additional views of the projection data set utilizing view interpolation; and

filter and backproject the projection data set utilizing a weighting function dependent upon parameters R_f and R_t, where radius R_f around an isocenter of the CT imaging system is selected in accordance with a low artifact criterion and R_t is a parameter defining a transition region outside of radius R_f around the isocenter of said CT imaging system.

22. A system in accordance with claim 21 wherein said weighting function is different for said measured views and said synthesized views.

23. A computer configured to:

read a projection data set of measured views obtained by scanning an object with a computed tomographic imaging system;

reconstruct a first image utilizing the measured views to produce an image having a central, essentially artifact-free zone;

interpolate views between the measured views to produce a projection data set having interpolated views;

reconstruct a second image utilizing said interpolated views; and

produce a blended image from said first image and said second image utilizing a weighting function selected to smoothly transition from said first image to said second image in a transition region surrounding an isocenter of the CT imaging system.

24. A computer in accordance with claim 23 wherein to reconstruct said second image, said computer is configured to utilize the measured views in addition to said interpolated views;

and

said first image is written P₁ and said second image is written P₂, said first image and said second image are combined using weighting functions w₁(i, j) and w₂(i, j), and said blended image P(i, j) is written;

P(i, j)=w₁(i, j)P₁(i, j)+w₂(i, j)P₂(i, j)

where;

w₁(i, j)=1−

w₂(i, j)

and

$w_2<br><br>\left(i,j\right)=\{\begin{array}{cc}0& r\le <br><br>R_f\\ \frac{r-R_f}{R_t-R_f}& R_f<<br><br>r\le <br><br>R_t\\ 1& r><br><br>R_t\end{array}.$

25. A computer in accordance with claim 23 further configured to determine a radius R_f of the central, essentially artifact-free zone.

26. A computer in accordance with claim 25 wherein the CT imaging system has a data acquisition system (DAS), and said computer is configured to determine R_f as a function of a sampling rate of the DAS and a scan speed of the CT imaging system.

27. A computer in accordance with claim 26 wherein R_f is a distance from the isocenter providing a sampling distance in an azimuthal direction of 50π

/984 cm.

28. A computer in accordance with claim 23 wherein to interpolate said views between the measured views, said computer is configured to synthesize views uniformly in all directions.

29. A computer in accordance with claim 23 wherein said first image is written P₁(i, j), said second image is written P₂(i, j), pixel (i, j) is a distance r from the isocenter, and wherein said computer is configured to combine said images P₁(i, j) and P₂(i, j) by weighting P₁(i, j) and P₂(i, j) with weights w₁(i, j) and w₂ (i, j), respectively, where a sum of said weights w₁ (i, j) and w₂(i, j) is a constant, and w₂(i, j) increases in magnitude relative to w₁(i, j) at least within a transition region in a vicinity of a radius R_f of said central, essentially artifact-free zone.

30. A computer in accordance with claim 29 wherein

31. A computer readable medium having instructions recorded thereon configured to instruct a computer to:

read a projection data set of measured views obtained by scanning an object with a computed tomographic (CT) imaging system;

synthesize additional views of the projection data set utilizing view interpolation; and

filter and backproject the projection data set utilizing a weighting function dependent upon parameters R_f and R_t, where radius R_f around an isocenter of the CT imaging system is selected in accordance with a low artifact criterion and R_t is a parameter defining a transition region outside of radius R_f around the isocenter of said CT imaging system.

32. A computer readable medium in accordance with claim 31 wherein said weighting function is different for said measured views and said synthesized views.

33. A computer readable medium having instructions recorded thereon configured to instruct a computer to:

read a projection data set of measured views obtained by scanning an object with a computed tomographic imaging system;

reconstruct a first image utilizing the measured views to produce an image having a central, essentially artifact-free zone;

interpolate views between the measured views to produce an projection data set having interpolated views;

reconstruct a second image utilizing said interpolated views; and

produce a blended image from said first image and said second image utilizing a weighting function selected to smoothly transition from said first image to said second image in a transition region surrounding an isocenter of the CT imaging system.

34. A computer readable medium in accordance with claim 33 where to reconstruct a second image, said computer readable medium has recorded thereon instructions configured to instruct the computer to utilize the measured views in addition to said interpolated views;

and wherein said first image is written P₁ and said second image is written P₂, said first image and said second image are combined using weighting functions w₁ (i, j) and w₂(i, j), and said blended image P(i, j) is written;

P(i, j)=w₁(i, j)P₁(i, j)+w₂(i, j)P₂(i, j)

where;

w₁(i, j)=1−

w₂(i, j)

and

$w_2<br><br>\left(i,j\right)=\{\begin{array}{cc}\text{\hspace{1em}<br><br>}<br><br>0& \text{\hspace{1em}<br><br>}<br><br>r\le <br><br>R_f\\ \frac{r-R_f}{R_i-R_f}& R_f<<br><br>r\le <br><br>R_i\\ \text{\hspace{1em}<br><br>}<br><br>1& \text{\hspace{1em}<br><br>}<br><br>r><br><br>R_i\end{array}.$

35. A computer readable medium in accordance with claim 33 further having instructions recorded thereon configured to instruct a computer to determine a radius R_f of the central, essentially artifact-free zone.

36. A computer readable medium in accordance with claim 35 wherein the CT imaging system has a data acquisition system (DAS), and said computer readable medium further has instructions recorded thereon configured to instruct a computer to determine R_f as a function of a sampling rate of the DAS and a scan speed of the CT imaging system.

37. A computer readable medium in accordance with claim 36 wherein R_f is a distance from the isocenter providing a sampling distance in an azimuthal direction of 50π

/984 cm.

38. A computer readable medium in accordance with claim 33 wherein to interpolate said views between the measured views, said computer readable medium has instructions recorded thereon configured to instruct a computer to synthesize views uniformly in all directions.

39. A computer readable medium in accordance with claim 33 wherein said first image is written P₁(i, j), said second image is written P₂(i, j), pixel (i, j) is a distance r from the isocenter, and wherein said computer readable medium has recorded thereon instructions configured to instruct the computer to combine said images P₁ (i, j) and P₂(i, j) by weighting P₁(i, j) and P₂(i, j) with weights w₁(i, j) and w₂(i, j), respectively, where a sum of said weights w₁(i, j) and w₂(i, j) is a constant, and w₂(i, j) increases in magnitude relative to w₁(i, j) at least within a transition region in a vicinity of a radius R_f of said central, essentially artifact-free zone.

40. A computer readable medium in accordance with claim 39 wherein w₁(i, j)=1−

w₂(i, j) and