Method and apparatus of spectral differential phase-contrast cone-beam CT and hybrid cone-beam CT

• US 9,364,191 B2
• Filed: 03/15/2013
• Issued: 06/14/2016
• Est. Priority Date: 02/11/2013
• Status: Active Grant

• Current Assignee: University of Rochester
• Original Assignee: University of Rochester
• Inventors: Ning, Ruola, Cai, Weixing
• Primary Examiner(s): Midkiff, Anastasia
• Application Number:
  US13/843,508
• Publication Number:
  US 20140226783A1
• Time in Patent Office: 1,187 Days
• Field of Search: 378 4- 20, 378/37, 378/51, 378/62, 378/98, 378/98.2, 378/98.8, 378/98.9, 378/98.12, 378/204, 378/210, 378/901, 257/414, 257/428, 257/429, 257/E27.14, 257/E27.146
• US Class Current: 1/1
• 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 6/4241 using energy resolving detectors, e.g. photon counting
• CPC Class Codes: A61B 6/4291 the detector being combined with a grid or grating
• CPC Class Codes: A61B 6/482 involving multiple energy imaging
• CPC Class Codes: A61B 6/484 involving phase contrast X-ray imaging
• CPC Class Codes: A61B 6/502 for diagnosis of breast, i.e. mammography
• 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: G01N 23/087 using polyenergetic X-rays
• CPC Class Codes: G01N 23/20091 Measuring the energy-dispersion spectrum [EDS] of diffracted radiation
• 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: G06T 2207/10081 Computed x-ray tomography [CT]
• CPC Class Codes: G06T 2207/20212 Image combination

Abstract

DPC (differential phase contrast) images are acquired for each photon energy channel, which are called spectral DPC images. The final DPC image can be computed by summing up these spectral DPC images or just computed using certain ‘color’ representation algorithms to enhance desired features. In addition, with quasi-monochromatic x-ray source, the required radiation dose is substantially reduced, while the image quality of DPC images remains acceptable.

Claims

1. A method for cone beam CT imaging of an object, the method comprising:

(a) acquiring projection images of the object taken at different view angles by using an imaging process that uses a polychromatic x-ray source, an energy-resolving detector having a plurality of energy channels, and a grating system;

(b) said acquiring comprising acquiring, for each of the plurality of energy channels of the detector, a respective plurality of the projection images taken at different view angles;

(c) performing three-dimensional (3D) computed tomography reconstructions of the object for each of the plurality of energy channels to produce a respective plurality of 3D reconstruction images; and

(d) processing the plurality of 3D reconstruction images for each of the plurality of energy channels to produce one or more images of the object, wherein step (d) comprises assigning different weights to the images acquired from different energy channels.

2. The method of claim 1, wherein the object is a human breast being imaged using a half-cone geometry in which x-ray radiation from the x-ray source radiates the breast only without penetrating chest cavity or other body parts of the patient.

3. The method of claim 1, wherein step (d) comprises assigning different colors to weighted averages of images acquired from different energy channels.

5. The method of claim 1, wherein the image is a matrix of a 3D distribution of phase coefficients.

6. The method of claim 1, wherein the image is a matrix of a 3D distribution of attenuation coefficients.

8. The method of claim 1, wherein the grating system comprises a steppable mechanism to perform phase-stepping use a source grating, a phase grating and an analyzer grating.

9. The method of claim 8, wherein the steppable mechanism comprises a linear stage that carries the source grating, the phase grating or the analyzer grating.

10. The method of claim 8, wherein the steppable mechanism has a plurality of branches where each branch has a grating set of a phase grating and an analyzer grating with a displacement corresponding to a successive set of phase steps.

11. The method of claim 8, wherein the steppable mechanism has a plurality of branches where each branch has a source grating that can be aligned to an optical axis through the object, with a displacement corresponding to a successive set of phase steps.

12. The method of claim 8, wherein the steppable mechanism produces a plurality of phase steps within one period and an intensity image is acquired at each phase step.

13. The method of claim 12, wherein a differential phase contrast image is computed from a plurality of the intensity images.

14. The method of claim 12, wherein an attenuation image is computed from the plurality of intensity images.

15. The method of claim 12, wherein a dark-field image is computed from the plurality of intensity images.

16. The method of claim 1, wherein the grating system comprises phase and analyzer gratings that are misaligned to produce a moire pattern.

17. The method of claim 16, wherein a differential phase contrast image is computed from the moire pattern.

18. The method of claim 17, wherein an attenuation image is computed from the moire pattern.

19. The method of claim 18, wherein a dark-field image is computed from the moire pattern.

20. The method of claim 1, further comprising, before step (a):

(i) imaging the object with an imaging process different from the imaging process of step (a)-(d) to determine a region of interest in the object; and

(ii) positioning the object so that the region of interest is positioned for steps (a)-(d).

21. The method of claim 20, wherein the imaging process different from the imaging process of steps (a)-(d) is computed tomography.

22. The method of claim 21, wherein the computed tomography is cone-beam computed tomography.

23. The method of claim 1, wherein step (b) comprises moving the x-ray source, the grating system and the detector relative to the object to define a data acquisition geometry.

4. A method for cone beam CT imaging of an object, the method comprising:

(a) acquiring projection images of the object taken at different view angles by using an imaging process that uses a polychromatic x-ray source, an energy-resolving detector having a plurality of energy channels, and a grating system;

(b) said acquiring comprising acquiring, for each of the plurality of energy channels of the detector, a respective plurality of the projection images taken at different view angles;

(c) performing three-dimensional (3D) computed tomography reconstructions of the object for each of the plurality of energy channels to produce a respective plurality of 3D reconstruction images; and

(d) processing the plurality of 3D reconstruction images for each of the plurality of energy channels to produce one or more images of the object, wherein step (d) comprises assigning different colors to weighted averages of images acquired from different energy channels, and wherein the different colors are assigned to the energy channels through a two-dimensional matrix of color weighting coefficients.

7. A method for cone beam CT imaging of an object, the method comprising:

(a) acquiring projection images of the object taken at different view angles by using an imaging process that uses a polychromatic x-ray source, an energy-resolving detector having a plurality of energy channels, and a grating system;

(b) said acquiring comprising acquiring, for each of the plurality of energy channels of the detector, a respective plurality of the projection images taken at different view angles;

(c) performing three-dimensional (3D) computed tomography reconstructions of the object for each of the plurality of energy channels to produce a respective plurality of 3D reconstruction images; and

(d) processing the plurality of 3D reconstruction images for each of the plurality of energy channels to produce one or more images of the object, wherein step (d) comprises assigning different colors to weighted averages of images acquired from different energy channels;

wherein the image is a matrix of a 3D distribution of a density of sub-micron structures.

24. A method for cone beam CT imaging of an object, the method comprising:

(a) acquiring projection images of the object at different view angles by using an imaging process that uses an x-ray source, a detector, a grating system and an x-ray beam filter;

(b) said acquiring comprising producing, with the beam filter, a quasi-monochromatic x-ray spectrum for differential phase contrast imaging; and

(c) performing three-dimensional (3D) computed tomography reconstructions using said projection images to produce one or more reconstruction images of the object wherein the reconstructed image is a matrix of a 3D distribution of a density of sub-micron structures.

25. The method of claim 24, wherein the object is a human breast being imaged using a half-cone geometry in which x-ray radiation from the x-ray source radiates the breast only without penetrating chest cavity or other body p arts of the patient.

26. The method of claim 24, wherein the reconstructed image is a matrix of a 3D distribution of phase coefficients.

27. The method of claim 24, wherein the reconstructed image is a matrix of a 3D distribution of attenuation coefficients.

28. The method of claim 24, wherein the grating system comprises a steppable mechanism to perform phase-stepping of a source grating, a phase grating and an analyzer grating.

29. The method of claim 28, wherein the steppable mechanism comprises a linear stage that carries the source grating, the phase grating or the analyzer grating.

30. The method of claim 28, wherein the steppable mechanism has a plurality of branches where each branch has a grating set of a phase grating and an analyzer grating with a displacement corresponding to a successive set of phase steps.

31. The method of claim 28, wherein the steppable mechanism has a plurality of branches where each branch has a source grating that can be aligned to an optical axis through the object, with a displacement corresponding to a successive set of phase steps.

32. The method of claim 28, wherein the steppable mechanism produces a plurality of phase steps within one period and an intensity image is acquired at each step.

33. The method of claim 32, wherein a differential phase contrast image is computed from a plurality of the intensity images.

34. The method of claim 32, wherein an attenuation image is computed from the plurality of intensity images.

35. The method of claim 32, wherein a dark-field image is computed from the plurality of intensity images.

36. The method of claim 32, wherein the grating system comprises phase and analyzer gratings that are misaligned to produce a moire pattern.

37. The method of claim 36, wherein the differential phase contrast images are computed from the moire pattern.

38. The method of claim 36, wherein an attenuation image is computed from the moire pattern.

39. The method of claim 36, wherein a dark-field image is computed from the moire pattern.

40. The method of claim 24, further comprising, before step (a):

(i) imaging the object with an imaging process different from the imaging process of steps (a) and (c) to determine a region of interest in the object; and

(ii) positioning the object so that the region of interest is positioned for steps (a) and (c).

41. The method of claim 40, wherein the imaging process different from the imaging process of steps (a) and (c) is computed tomography.

42. The method of claim 41, wherein the computed tomography is cone-beam computed tomography.

43. The method of claim 24, wherein step (a) comprises moving the x-ray source, the gratings and the detector relative to the object to define a data acquisition geometry.

44. The method of claim 24, wherein compared to a polychromatic spectrum, the quasi-monochromatic spectrum can reduce x-ray exposure to obtain the same image quality.