Apparatus and method for x-ray scatter reduction and correction for fan beam CT and cone beam volume CT

• US 6,618,466 B1
• Filed: 02/21/2002
• Issued: 09/09/2003
• Est. Priority Date: 02/21/2002
• Status: Expired due to Term

• Current Assignee: University of Rochester
• Original Assignee: University of Rochester
• Inventors: Ning, Ruola
• Primary Examiner(s): BRUCE, DAVID VERNON
• Application Number:
  US10/078,529
• Time in Patent Office: 565 Days
• Field of Search: 378/4, 378/7, 378/15, 378/62, 378/98, 378/98.4, 378/901
• US Class Current: 378/62
• 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 6/4035 the source being combined with a filter or grating
• CPC Class Codes: A61B 6/4085 Cone-beams
• CPC Class Codes: A61B 6/4291 the detector being combined with a grid or grating
• CPC Class Codes: A61B 6/483 involving scattered radiation
• CPC Class Codes: A61B 6/508 for non-human patients
• CPC Class Codes: A61B 6/5235 combining images from the same or different ionising radiation imaging techniques, e.g. PET and CT
• CPC Class Codes: A61B 6/5282 due to scatter
• CPC Class Codes: A61B 6/583 using calibration phantoms
• 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 cone-beam volume computed tomography or similar imaging techniques, the effects of x-ray scatter are reduced through using a beam compensation filter (a bow tie filter), air gap technique, and an antiscatter grid and corrected through the use of a beam stop array combined with interpolation or convolution operation. Images are taken with the beam stop array, and a larger number of images are taken without the beam stop array. The images taken with the beam stop array are spatially interpolated to derive scatter information, which is then angularly interpolated to provide as many scatter images as there are images taken without the beam stop array. The interpolations are performed through cubic spline interpolation or any other interpolation techniques or low-pass filtering operation (convolution operation with a selected kernel). Each scatter image is subtracted from a corresponding one of the images taken without the beam stop array to provide a sequence of scatter-corrected images.

Claims

1. A method for imaging an object while correcting for scatter, the method comprising:

(a) providing a source of imaging radiation, a beam compensation filter, an antiscatter grid, a detector for the imaging radiation, an air gap between the object and the detector and a beam stop array;

(b) moving the source and the detector around the object;

(c) taking a first sequence of images of the object at selected different projection angles while the source and the detector are being moved around the object, to obtain samples of scatter distribution in each of the first sequence of images, by using the source, the beam compensation filter, the beam stop array, the air gap between the object and the detector, the antiscatter grid, and the detector, the first sequence of images comprising N′

images;

(d) taking a second sequence of images of the object at different projection angles by using the source and the detector without the beam stop array, the second sequence of images comprising N images, N≧

N′

;

(e) performing a projection angular interpolation on the first sequence of images of the object to obtain a sequence of scatter images, the sequence of scatter images comprising N images, each corresponding to one of the N images of the second sequence of images; and

(f) obtaining a sequence of primary images, the sequence of primary images comprising N images, each formed in accordance with a corresponding one of the N images of the second sequence of images and a corresponding one of the N images of the sequence of scatter images.

2. The method of claim 1, wherein step (e) comprises:

(i) recovering the scatter distribution in each of the first set of images so as to obtain a sequence of scatter sample images; and

(ii) performing the projection angular interpolation on the sequence of scatter sample images to obtain the sequence of scatter images.

3. The method of claim 2, wherein step (e)(i) comprises performing spatial interpolation on each of the first set of images of the object.

4. The method of claim 3, wherein each of the spatial interpolation and the projection angular interpolation comprises any interpolation methods including a cubic spline interpolation.

5. The method of claim 2, wherein step (e)(i) comprises performing a convolution operation on each of the first set of images of the object.

6. The method of claim 5, wherein the projection angular interpolation is performed through a convolution operation with a selected convolution kernel.

7. The method of claim 1, wherein step (f) comprises subtracting each of the N images of the sequence of scatter images from a corresponding one of the N images of the second sequence of images.

8. The method of claim 1, wherein the imaging radiation is x-ray radiation.

9. The method of claim 8, wherein the imaging radiation is a cone beam of said x-ray radiation.

10. The method of claim 9, further comprising (g) using the sequence of primary images to construct a cone-beam volume computed tomography image.

11. The method of claim 1, wherein N′

is equal or greater than 1.

12. The method of claim 1, wherein the angular interval is no greater than 360 degrees.

13. The method of claim 1, wherein the beam compensation filter is a bow-tie filter.

14. A system for imaging an object while correcting for scatter, the system comprising:

a source of imaging radiation;

a beam compensation filter;

an antiscatter grid;

a detector for the imaging radiation, the detector being so located as to leave an air gap between the object and the detector;

a beam stop array for being placed, at selected times, in a path of the imaging radiation between the source and the detector;

a gantry frame for rotating the source and the detector around the object;

a control device for controlling the gantry, the source and the detector for;

(i) controlling the source and the detector to rotate around the object while taking a first sequence of images of the object at selected different projection angles by using the source, the detector and the beam stop array, the first sequence of images comprising N′

images;

(ii) controlling the source and the detector to rotate around the object while taking a second sequence of images of the object at different projections angles by using the source and the detector without the beam stop array, the second sequence of images comprising N images, N≧

N′

; and

an image processing device, receiving an output of the detector, for;

(i) performing an angular interpolation on the first sequence of images of the object to obtain a sequence of scatter images, the sequence of scatter images comprising N images, each corresponding to one of the N images of the second sequence of images; and

(ii) obtaining a sequence of primary images, the sequence of primary images comprising N images, each formed in accordance with a corresponding one of the N images of the second sequence of images and a corresponding one of the N images of the sequence of scatter images.

15. The system of claim 14, wherein the image processing device obtains the sequence of scatter images by recovering the scatter distribution in each of the first sequence of images to obtain a sequence of scatter sample images and performing the projection angular interpolation on the sequence of scatter sample images to obtain the sequence of scatter images.

16. The system of claim 15, wherein the image processing device recovers the scatter distribution by performing spatial interpolation on each of the first set of images of the object.

17. The system of claim 16, wherein each of the spatial interpolation and the angular interpolation comprises any interpolation methods include a cubic spline interpolation.

18. The system of claim 15, wherein the image processing device recovers the scatter distribution by performing a convolution operation on each of the first set of images of the object.

19. The system of claim 18, wherein the projection angular interpolation is performed through a convolution operation with a selected convolution kernel.

20. The system of claim 14, wherein the image processing device obtains the sequence of primary images by subtracting each of the N images of the sequence of scatter images form a corresponding one of the N images of the second sequence of images.

21. The system of claim 14, wherein the imaging radiation is x-ray radiation.

22. The system of claim 21, wherein the imaging radiation is a cone beam of said x-ray radiation and the detector is a two dimensional area detector.

23. The system of claim 22, wherein the image processing device uses the sequence of primary images to construct a cone-beam volume computed tomography image.

24. The system of claim 14, wherein N′

is equal to or greater than 1.

25. The system of claim 14, further comprising a rotatable gantry on which the source and the detector are mounted, and wherein the control device controls the rotatable gantry to move the source and the detector around the object to take the first sequence of images at an angular interval.

26. The system of claim 25, wherein the angular interval is no greater than 360 degrees.

27. The system of claim 14, wherein the beam compensation filter is a bow-tie filter.

28. A method for imaging an object while correcting for scatter, the method comprising:

(a) providing a source of imaging radiation, a detector for the imaging radiation, and a beam stop array;

(b) taking a first sequence of images of the object by using the source, the detector and the beam stop array, the first sequence of images comprising N′

images;

(c) taking a second sequence of images of the object by using the source and the detector without the beam stop array, the second sequence of images comprising N images, N>

N′

;

(d) performing a spatial interpolation on the first sequence of images of the object to obtain a sequence of scatter sample images;

(e) performing an angular interpolation on the sequence of scatter sample images to obtain a sequence of scatter images, the sequence of scatter images comprising N images, each corresponding to one of the N images of the second sequence of images; and

(f) obtaining a sequence of primary images, the sequence of primary images comprising N images, each formed in accordance with a corresponding one of the N images of the second sequence of images and a corresponding one of the N images of the sequence of scatter images.

29. The method of claim 28, wherein each of steps (d) and (e) is performed using cubic spline interpolation.

30. The method of claim 28, wherein each of steps (d) and (e) is performed using a convolution kernel.

31. The method of claim 28, wherein step (f) comprises subtracting each image of the sequence of scatter images from a corresponding image of the second sequence of images.

32. A system for imaging an object while correcting for scatter, the system comprising:

a source of imaging radiation;

a detector for the imaging radiation;

a beam stop array;

a gantry frame on which the source and the detector are mounted;

a control device for controlling the gantry frame, the source and the detector for;

(i) taking a first sequence of images of the object by using the source, the detector and the beam stop array, the first sequence of images comprising N′

images; and

(ii) taking a second sequence of images of the object by using the source and the detector without the beam stop array, the second sequence of images comprising N images, N>

N′

; and

an image processing device, receiving an output of the detector, for;

(i) performing a spatial interpolation on the first sequence of images of the object to obtain a sequence of scatter sample images;

(iii) performing an angular interpolation on the sequence of scatter sample images to obtain a sequence of scatter images, the sequence of scatter images comprising N images, each corresponding to one of the N images of the second sequence of images; and

(iii) obtaining a sequence of primary images, the sequence of primary images comprising N images, each formed in accordance with a corresponding one of the N images of the second sequence of images and a corresponding one of the N images of the sequence of scatter images.

33. The system of claim 32, wherein the image processing device performs the spatial interpolation and the angular interpolation using cubic spline interpolation.

34. The system of claim 32, wherein the image processing device performs the spatial interpolation and the angular interpolation using a convolution kernel.

35. The system of claim 32, wherein the image processing device obtains the primary images by subtracting each image of the sequence of scatter images from a corresponding image of the second sequence of images.