Multi-target X-ray tube for dynamic multi-spectral limited-angle CT imaging

• US 6,973,158 B2
• Filed: 06/25/2004
• Issued: 12/06/2005
• Est. Priority Date: 06/25/2003
• Status: Expired due to Fees

• Current Assignee: Forevision Imaging Technologies LLC
• Original Assignee: Guy M. Besson
• Inventors: Besson, Guy M.
• Primary Examiner(s): BRUCE, DAVID VERNON
• Application Number:
  US10/877,006
• Publication Number:
  US 20040264626A1
• Time in Patent Office: 529 Days
• Field of Search: 378/4, 378/5, 378/8, 378/15, 378/16, 378/19, 378/22, 378/901
• US Class Current: 378/16
• 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 6/0487 Motor-assisted positioning
• CPC Class Codes: A61B 6/06 Diaphragms
• CPC Class Codes: A61B 6/4028 resulting in acquisition of views from substantially different positions, e.g. EBCT
• CPC Class Codes: A61B 6/4035 the source being combined with a filter or grating
• CPC Class Codes: A61B 6/4042 K-edge filters
• CPC Class Codes: A61B 6/405 Source units specially adapted to modify characteristics of the beam during the data acquisition process A61B6/4021, A61B6/4035 take precedence
• 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 6/4275 using a detector unit almost surrounding the patient, e.g. more than 180°
• CPC Class Codes: A61B 6/4441 the rigid structure being a C-arm or U-arm
• CPC Class Codes: A61B 6/4488 Means for cooling A61B6/045 takes precedence
• 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 6/488 involving pre-scan acquisition
• CPC Class Codes: A61B 6/508 for non-human patients
• CPC Class Codes: A61B 6/5288 involving retrospective matching to a physiological signal
• CPC Class Codes: A61B 6/541 involving acquisition triggered by a physiological signal
• CPC Class Codes: A61B 6/542 involving control of exposure
• CPC Class Codes: A61B 6/563 : involving image data transmission via a network
• CPC Class Codes: A61B 6/583 : using calibration phantoms
• CPC Class Codes: G21K 1/10 : Scattering devices; Absorbing devices; Ionising radiation filters
• CPC Class Codes: Y10S 378/901 : Computer tomography program or processor

Abstract

A multispectral X-ray imaging system uses a wideband source and filtration assembly to select for M sets of spectral data. Spectral characteristics may be dynamically adjusted in synchrony with scan excursions where an X-ray source, detector array, or body may be moved relative to one another in acquiring T sets of measurement data. The system may be used in projection imaging and/or CT imaging. Processed image data, such as a CT reconstructed image, may be decomposed onto basis functions for analytical processing of multispectral image data to facilitate computer assisted diagnostics. The system may perform this diagnostic function in medical applications and/or security applications.

Claims

1. A method of imaging and determining constituents of a body, comprising the steps of:

(a) selecting a beam parameter from a set of beam parameters for use in generation of X-ray radiation to provide M sets of spectral characteristics;

(b) projecting a focused electron beam through a vacuum envelope towards a target, and scanning the focused electron beam onto the target in a directional sweep using the selected beam parameter;

(c) in consequence of the projecting step, producing X-ray radiation with a first spectrum according to electron beam parameters at a multiplicity of locations along the target, and directing said radiation through the body to the detectors by use of a collimator;

(d) filtering the radiation to refine the X-ray radiation;

(e) detecting the X-ray radiation energy after passage through the body by use of a detector array that contains multiple detectors to produce detection signals from the detectors, the detection signals being representative of the X-ray spectrum and body attenuation and defining a first set of X-ray projection paths and associated measurements sufficient for at least one of a projection image, a limited-angle CT reconstruction and tomosynthesis reconstruction of at least one slice through the body;

(e) iterating the steps above (a) through (e) to generate T electron beam sweeps along the targets for M sets of spectral characteristics, in synchrony with at least one of advancing the detector array, advancing the body, and electron-beam target selection or rotation, in such a manner that each X-ray radiation path through the body is sampled T times with M spectra to provide sufficient data for the at least one of the projection image, the limited-angle CT reconstruction and the tomosynthesis reconstruction of at least one slice through the body; and

(f) processing the data to produce a decomposition of reconstructed multi-spectral tomographic images onto a set of known basis functions representative of body constituents for the at least one slice through the body.

2. The method of claim 1, wherein the step of processing includes optimally reducing the T sets of data into M sets of data by signal processing methods, and utilizing a reconstruction technique selected from the group consisting of a multi-spectral limited-angle tomographic reconstruction and a multispectral tomosynthesis reconstruction for each of M resulting sweeps.

3. The method of claim 2, wherein the reconstruction technique comprises at least one of a filtered-back-projection approach and an iterative approach.

4. The method of claim 1, wherein the step of processing includes performing at least one of a multi-spectral limited-angle tomographic reconstruction and a multispectral tomosynthesis reconstruction by averaging or combining the data from among a plurality of sweeps.

5. The method of claim 1, wherein the step of sampling each X-ray radiation path through the body T times with M spectra comprises sampling substantially the same X-ray radiation paths with a geometric error that results in small reconstructed images artifacts.

6. The method of claim 1, further comprising a step of presenting a different target and repeating the step of iterating.

7. The method of claim 6, wherein the step of presenting a different target includes rotating a rotor having a plurality of sides that contain different target materials.

8. The method of claim 7, wherein the rotor surfaces are geometrically defined so that for a given electron beam sweep velocity and a given rotor angular velocity, the local target surface hit by the focused electron beam remains at an angle that is substantially constant with respect to an orientation of the detector array.

9. The method of claim 1, wherein the beam parameter used in the step of selecting is selected from the group consisting of X-ray focal spot size, target angle with respect to the detector, peak tube kilovoltage, and tube current.

10. The method of claim 1, wherein the step of projecting includes using a feedback loop to maintain the respective phases of the rotor angle and the beam sweep in a pre-determined arrangement.

11. The method of claim 1, wherein the step of selecting includes changing the beam parameters and X-ray focal-spot geometric property by operation of electron-beam optics circuitry.

12. The method of claim 1, wherein the step of projecting operates on a hollow anode and includes using a cooling circuit that passes through the hollow anode and a heat exchanger to achieve active internal cooling of the hollow anode.

13. The method of claim 1, wherein the step of projecting includes cooling an external surface of a vacuum envelope on the anode side of the X-ray tube.

14. The method of claim 1, wherein the step of producing X-ray radiation includes facilitating heat exchange on an anode by action of a heat storage material.

15. The method of claim 1, wherein the heat storage material used in the step of producing X-ray radiation includes graphite.

16. The method of claim 1, wherein the step of producing X-ray radiation includes using an anode having a construction selected from the group consisting of an elongated cylinder, a solid-core cylinder, and a hollow-core cylinder, and where the target resides on the surface of the anode.

17. The method of claim 1, wherein the beam parameter selected in the step of selecting includes varying tube peak kilo-voltage in at least two of the iterations according to the step of iterating.

18. The method of claim 1, wherein the beam parameter selected in the step of selecting includes varying electron beam current in at least two of the iterations according to the step of iterating.

19. The method of claim 1, wherein the sweep in the step of projecting has a sweep direction and the synchrony of the iterating step occurs with at least one of advancing the detector array and advancing the body, the sweep direction is orthogonal to the detector or body advance direction.

20. The method of claim 1, wherein the body has an axis of elongation and including a step of presenting the body for imaging in a configuration where the axis of elongation is in an upright configuration.

21. The method of claim 1, wherein the body has an axis of elongation and including a step of presenting the body for imaging in a configuration where the axis of elongation is in a horizontal direction.

22. The method of claim 1, wherein the body presents an axis of elongation and the sweep in the step of projecting has a sweep direction, the synchrony of the iterating step occurring with both of the advancing the detector array in a detector advance direction and the advancing the body in a body advance direction, the sweep direction being parallel to one of the axis of elongation and the body advance direction, and the detector advance direction being orthogonal to the sweep direction.

23. The method of claim 1, wherein the body presents an axis of elongation and the sweep in the step of projecting has a sweep direction, the synchrony of the iterating step occurring with both of the advancing the detector array in a detector advance direction and the advancing the body in a body advance direction, the sweep direction being orthogonal to the axis of elongation and the body advance direction, and the detector advance direction being orthogonal to the sweep direction.

24. The method of claim 1, wherein the sweep in the step of projecting has a sweep direction along a vertical axis.

25. The method of claim 1, wherein the sweep in the step of projecting has a sweep direction and the step of filtering comprises advancing a filter sheet of spatially varying composition in front of the collimator in a direction orthogonal to the sweep direction.

26. The method of claim 1, wherein the sweep in the step of projecting has a sweep direction and the synchrony of the iterating step occurring with both of the advancing the detector array in a detector advance direction and the advancing the body in a body advance direction,

the step of filtering includes advancing a filter sheet of spatially varying composition in front of the detector in a direction parallel to at least one of the detector advance direction, the body advance direction, and in a direction orthogonal to the sweep direction.

27. The method of claim 1, wherein the step of processing comprises decomposing of each projection data on a multiplicity of spatial frequency bands.

28. The method of claim 27, wherein the step of processing includes a step of reconstructing low- and mid-spatial frequency projection bands for any missing projection data to accommodate the step of decomposing.

29. The method of claim 27, wherein the step of processing comprises completing truncated projections by a technique selected from the group consisting of fitting, interpolating and extrapolating low- and mid-spatial frequency bands.

30. The method of claim 1, wherein the step of processing includes decomposing a line integral function onto a plurality of known basis functions, and performing an analysis of the decomposed line integral data to produce analytical results, and performing a reconstruction for each basis function.

31. The method of claim 1, wherein the step of processing includes using the detection signals to prepare an image of the body and mapping the analytical results onto the image.

32. The method of claim 31, wherein the step of processing includes using techniques of data pre-processing, signal extraction, feature analysis;

using a multivariate model to process multispectral projection data;

processing reconstructed and decomposed images of the body; and

mapping analytical detection, characterization, and classification results onto the images.

33. The method of claim 1, wherein the step of detecting includes positioning part of the detector array with respect to a primary beam projection to detect scattered X-ray radiation outside the projected primary beam.

34. The method of claim 31, wherein the step of detecting includes detecting Compton scattered X-ray radiation as input for the step of processing.

35. The method of claim 31, wherein the step of detecting includes detecting Rayleigh scattered X-ray radiation as input for the step of processing.

36. The method of claim 31, wherein the step of detecting includes detecting X-rays that have been scattered a multiplicity of times as input for the step of processing.

37. The method of claim 1, wherein the body is a living body.

38. The method of claim 1, wherein the body is an inanimate object.

39. The method of claim 1, wherein the body is a tissue sample.

40. A system for imaging and determining constituents of a body, comprising:

selecting a beam parameter from a set of beam parameters for use in generation of X-ray radiation according to provide M sets of spectral characteristics;

(b) projecting a focused electron beam through a vacuum envelope towards a target, and scanning the focused electron beam onto the target in a directional sweep using the selected beam parameter;

(c) in consequence of the projecting step, producing X-ray radiation with a first spectrum according to electron beam parameters at a multiplicity of locations along the target, and directing said radiation through the body to the detectors by use of a collimator;

(d) means for filtering the radiation to refine the X-ray radiation;

(e) means for detecting the X-ray radiation energy after passage through the body by use of a detector array that contains multiple detectors to produce detection signals from the detectors, the detection signals being representative of the X-ray spectrum and body attenuation and defining a first set of X-ray projection paths and associated measurements sufficient for at least one of a projection image, a limited-angle CT reconstruction and tomosynthesis reconstruction of at least one slice through the body;

(f) means for iterating through use of the above means (a) through (e) to generate T electron beam sweeps along the targets for M sets of spectral characteristics, in synchrony with at least one of advancing the detector array, for advancing the body, and electron-beam target selection or rotation in such a manner that each X-ray radiation path through the body is sampled T times with M spectra to provide sufficient data for the at least one of the multispectral projection image, the multispectral limited-angle CT reconstruction and the multispectral tomosynthesis reconstruction of at least one slice through the body; and

(g) means for processing the data to produce a decomposition of reconstructed multi-spectral tomographic images onto a set of known basis functions representative of body constituents for the at least one slice through the body.

41. The system of claim 40, wherein the means for processing further includes means for performing multi-spectral tomographic reconstructions for each sweep.

42. The system of claim 40, wherein the means for processing further includes means for optimally reducing the T sets of data into M sets of data by signal processing means and performing multi-spectral tomographic reconstruction for the resulting set of sweeps.

43. The system of claim 42, wherein the means for performing multispectral reconstructions includes means for implementing at least one of a filtered-backprojection reconstruction approach and an iterative technique.

44. The system of claim 42, wherein the means for performing multispectral tomographic reconstruction includes means for implementing at least one of a filtered-backprojection reconstruction approach and an iterative technique.

45. The system of claim 40, wherein the means for selecting includes means for presenting a selectably different target to the electron beam.

46. The system of claim 45, wherein the means for presenting includes deflecting the electron beam to a different segment of the anode track that contains a different target material.

47. The system of claim 45, wherein the means for presenting includes a rotor having a plurality of sides that contain different target material.

48. The system of claim 47, where the rotor has surfaces that are geometrically defined for a selected electron beam sweep velocity and a given rotor angular velocity, such that the local target surface receiving the electron beam remains at an angle that is substantially constant with respect to a surface of the detector array.

49. The system of claim 45, wherein the means for selecting includes means for adjusting the beam parameter as X-ray focal spot size and target angle with respect to the detector.

50. The system of claim 47, further comprising a feedback loop to maintain an anode rotation angle and a beam sweep cycle at a fixed, pre-determined phase arrangement with respect to one another.

51. The system of claim 40, wherein the means for selecting includes electron beam optics for adjusting an the X-ray focal spot geometric parameter between successive iterations.

52. The system of claim 40, including a cooling circuit and heat exchanger to achieve active internal cooling of a hollow anode proximate the target.

53. The system of claim 40, including a cooling circuit for use cooling an external surface of a vacuum envelope on an anode side of the X-ray tube vacuum envelope.

54. The system of claim 40, including an anode proximate the target, the anode design including a core of a heat storage material.

55. The system of claim 54, wherein the heat storage material comprises graphite.

56. The system of claim 40, including an anode proximate the target, wherein the anode is formed as one of an elongated cylinder, a solid-core cylinder, and a hollow-core cylinder, the anode having surfaces that lie on one of the surface of the cylinder and on a multiplicity of facet surfaces.

57. The system of claim 40, wherein the means for selecting includes means for changing tube peak kilo-voltage between iterations.

58. The system of claim 40, wherein the means for selecting includes means for changing electron beam current between iterations.

59. The system of claim 40, wherein the means for projecting advances the sweep in a sweep direction and the synchrony of the iterating step occurs with at least one of advancing the detector array and advancing the body, the sweep direction being orthogonal to the detector or body advance direction.

60. The system of claim 40, wherein the body has an axis of elongation and including means for presenting the body for imaging in a configuration where the axis of elongation is in an upright configuration.

61. The system of claim 40, wherein the body has an axis of elongation and including a means for presenting the body for imaging in a configuration where the axis of elongation is in a horizontal direction.

62. The system of claim 40, wherein the body presents an axis of elongation and the means for projecting advances the sweep in a sweep direction, the synchrony of the means for iterating step occurs with both of the advancing the detector array in a detector advance direction and the advancing the body in a body advance direction, the sweep direction being parallel to one of the axis of elongation and the body advance direction, and the detector advance direction being orthogonal to the sweep direction.

63. The system of claim 40, wherein the body presents an axis of elongation and the means for projecting advances the sweep in a sweep direction, the synchrony of the means for iterating occurs with both of the advancing the detector array in a detector advance direction and the advancing the body in a body advance direction, the sweep direction being orthogonal to the axis of elongation and the body advance direction, and the detector advance direction being orthogonal to the sweep direction.

64. The system of claim 40, wherein the means for projecting advances the sweep in a sweep direction along a vertical axis.

65. The system of claim 40, wherein the means for projecting advances the sweep in a sweep direction and the means for filtering comprises means for advancing a filter sheet of spatially varying composition in front of the collimator in a direction orthogonal to the sweep direction.

66. The system of claim 40, wherein the means for projecting advances the sweep in a sweep direction and the synchrony of the means for iterating occurs with both of the advancing the detector array in a detector advance direction and the advancing the body in a body advance direction, and

the means for filtering includes means for advancing a filter sheet of spatially varying composition in front of the detector in a direction parallel to at least one of the detector advance direction, the body advance direction, and in a direction orthogonal to the sweep direction.

67. The system of claim 40, wherein the means for processing includes means for decomposing each projection data on a multiplicity of spatial frequency bands.

68. The system of claim 67, wherein the means for processing includes program instructions for reconstructing low- and mid-spatial frequency projection bands with respect to missing projection data to accommodate the step of decomposing.

69. The system of claim 67, wherein the means for processing includes program instructions for completing truncated projections by a technique selected from the group consisting of fitting, interpolating and extrapolating low- and mid-spatial frequency bands.

70. The system of claim 40, wherein the means for processing includes program instructions configured to decompose a line integral function onto a plurality of known basis functions, to perform an analysis of the decomposed line integral data to produce analytical results, and to perform a reconstruction for each basis function.

71. The system of claim 40, wherein the means for processing includes program instructions configured to use the detection signals to prepare an image of the body and map the analytical results onto the image.

72. The system of claim 71, wherein the program instructions implement techniques including data pre-processing, signal extraction, and feature analysis;

use a multivariate model to process multispectral projection data;

process reconstructed and decomposed images of the body; and

map analytical detection, characterization, and classification results onto the images.

73. The system of claim 40, wherein the means for detecting includes means for positioning part of the detector array with respect to a primary beam projection to detect scattered X-ray radiation outside the projected primary beam.

74. The system of claim 73, wherein the means for detecting includes means for detecting Compton scattered X-ray radiation as input to the means for processing.

75. The system of claim 73, wherein the means for detecting includes means for detecting Rayleigh scattered X-ray radiation as input to the means for processing.

76. The system of claim 73, wherein the means for detecting includes means for detecting X-rays that have been scattered a multiplicity of times as input to the means for processing.