Three-dimensional image reconstruction using transmission and scatter radiography methods

• US 10,416,098 B2
• Filed: 05/24/2017
• Issued: 09/17/2019
• Est. Priority Date: 05/26/2016
• Status: Active Grant

• Current Assignee: Loram Technologies Incorporated (Loram Maintenance of Way, Inc.), University of Florida Research Foundation, Incorporated (State University System of Florida)
• Original Assignee: Georgetown Rail Equipment Company (Loram Maintenance of Way, Inc.)
• Inventors: Liesenfelt, Michael John, Baciak, James Edward, Grissom, Gregory Thomas
• Primary Examiner(s): Song, Hoon K
• Application Number:
  US15/604,530
• Publication Number:
  US 20170343488A1
• Time in Patent Office: 846 Days
• Field of Search: None
• CPC Class Codes: G01N 2223/3302 object and detector fixed
• CPC Class Codes: G01N 2223/401 image processing
• CPC Class Codes: G01N 2223/646 flaws, defects
• CPC Class Codes: G01N 23/046 using tomography, e.g. computed tomography [CT]
• CPC Class Codes: G01N 23/203 Measuring back scattering
• CPC Class Codes: G01V 5/0016 Active interrogation, i.e. using an external radiation source, e.g. using pulsed, continuous or cosmic rays
• CPC Class Codes: G01V 5/22 Active interrogation, i.e. by irradiating objects or goods using external radiation sources, e.g. using gamma rays or cosmic rays
• 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 2211/424 Iterative
• CPC Class Codes: G06T 2211/436 Limited angle
• CPC Class Codes: G06T 7/0012 Biomedical image inspection

Abstract

A method for image reconstruction includes irradiating an object with a beam of radiation from a radiation source, measuring an attenuated portion of the beam, estimating a density of the object, determining a predicted attenuated portion of the beam using the density estimate, and iteratively adjusting the density estimate of the object. The predicted attenuated portion and the measured attenuated portion are compared to determine a signal difference. The density estimate of each portion of the object is adjusted by scaling the density estimate using the average signal differences of rays that intersect the portion of the object. The density estimate may be repeatedly adjusted until a difference between consecutive density estimates is below a selected threshold or a predetermined number of adjustments have been completed. The attenuated portion of the beam may include a scattered portion and a transmitted portion.

Claims

1. A penetrating radiation inspection system comprising:

at least one internal scanning subsystem having;

a radiation source configured to produce a beam of radiation, the beam having a plurality of rays, the radiation source positioned to direct the beam of radiation into an object for internal inspection during relative translational motion between the at least one internal scanning subsystem and the object; and

at least one detector positioned to at least partially measure an attenuated portion of the beam of radiation; and

a processor configured to convert an estimated density of a portion of the object to a corrected estimated density by;

determining a predicted attenuated portion using a density estimate;

comparing the predicted attenuated portion to the measured attenuated portion to determine a signal difference;

adjusting the density estimate of the portion of the object by scaling the density estimate using signal differences of rays that intersect the portion of the object; and

repeatedly adjusting the density estimate until a difference between consecutive density estimates is below a selected threshold or a predetermined number of adjustments have been completed.

2. The system of claim 1, wherein the system is stationary and further comprises a travel path through the system, wherein the object is translated through the system on the travel path.

3. The system of claim 1, further comprising a surface scanning subsystem configured to scan a surface of the object to produce a three-dimensional surface profile of the object, wherein the processor is configured to approximate a boundary of the object using the three-dimensional surface profile and initially estimate the density of a plurality of portions of the object within the boundary.

4. The system of claim 1, wherein the at least one internal scanning subsystem is configured to measure the attenuated portion of the beam of radiation without rotating around the object.

5. The system of claim 1, wherein the at least one internal scanning subsystem is a plurality of internal scanning subsystems, at least two of the internal scanning subsystems being oriented in different perspectives.

6. The system of claim 5, wherein the at least two of the internal scanning subsystems are offset.

7. The system of claim 1, wherein the beam of radiation comprises a plurality of energies.

8. The system of claim 1, wherein the beam of radiation is a collimated fan beam, a collimated cone beam, or a collimated pencil beam.

9. The system of claim 1, wherein the at least one detector is configured to integrate the energy of all of the measured attenuated portions of the beam of radiation.

10. The system of claim 1, wherein the at least one detector is configured to determine energy levels of the measured attenuated portion of the beam of radiation.

11. The system of claim 1, wherein the at least one detector is at least one transmission detector, the attenuated portion of the beam is a transmitted portion of the beam, and the predicted attenuated portion of the beam is a predicted transmitted portion of the beam.

12. The system of claim 1, wherein the at least one detector is at least one scatter detector, the attenuated portion of the beam is a scattered portion of the beam, and the predicted attenuated portion of the beam is a predicted scattered portion of the beam.

13. The system of claim 12, further comprising collimators associated with the at least one scatter detector, the collimators being configured to limit detection of scattered portions of the beam of radiation to a field of view.

14. The system of claim 1, wherein the at least one detector includes at least one scatter detector and at least one transmission detector, the attenuated portion of the beam includes a scattered portion of the beam and a transmitted portion of the beam, and the predicted attenuated portion of the beam includes a predicted scattered portion of the beam and a predicted transmitted portion of the beam.

15. The system of claim 14, further comprising a filter associated with at least one of the at least one scatter detector and at least one transmission detector, the filter being configured to filter lower energy photons.

16. The system of claim 1, wherein the radiation source is an X-ray, a gamma ray source, or a combination thereof.

17. A method for three-dimensional image reconstruction comprising:

translating at least one of an object and a radiation source;

irradiating the object with a beam of radiation from a radiation source, the beam having a plurality of rays;

measuring an attenuated portion of the beam with a first detector in a first perspective;

converting an estimated density of a plurality of portions of the object to a corrected estimated density of each portion of the object using a computer system by;

determining a predicted attenuated portion of the beam in the first perspective using a density estimate;

comparing the predicted attenuated portion in the first perspective to the measured attenuated portion in the first perspective to determine a signal difference of each ray in the first perspective;

adjusting the density estimate of the portion of the object by scaling the density estimate using signal differences of rays that intersect the portion of the object; and

repeatedly adjusting the density estimate until a difference between consecutive density estimates is below a selected threshold or a predetermined number of adjustments have been completed; and

generating a three-dimensional density array representing the object using the corrected estimated densities of the portions of the object.

18. The method of claim 17, wherein the attenuated portion of the beam is a scattered portion of the beam, the first detector is a scatter detector, and the predicted attenuated portion of the beam is a predicted scattered portion of the beam.

19. The method of claim 18, wherein the scatter detector has a plurality of detector elements, each detector element having a field of view, and the rays that intersect the portion of the object are rays that intersect the portion of the object and are within an intersecting field of view of the detector elements.

20. The method of claim 17, wherein the attenuated portion of the beam is a transmitted portion of the beam, the first detector is a transmission detector, and the predicted attenuated portion of the beam is a predicted transmitted portion of the beam.

21. The method of claim 17, further comprising:

irradiating the object with a second beam of radiation from a second radiation source, the second beam having a plurality of rays;

measuring an attenuated portion of the second beam with a second detector in a second perspective;

determining a predicted attenuated portion of the second beam in the second perspective using a density estimate; and

converting the estimated density of the plurality of portions of the object to a corrected estimated density of each portion of the object using an average signal difference of all the rays in the first and second perspectives that intersect the portion of the object.

22. The method of claim 21, wherein the attenuated portion of the beam is a transmitted portion of the second beam, the first detector is a transmission detector, and the predicted attenuated portion of the beam is a predicted transmitted portion of the beam.

23. The method of claim 22, wherein the attenuated portion of the second beam is a scattered portion of the second beam, the first detector is a scatter detector, and the predicted attenuated portion of the second beam is a predicted scattered portion of the second beam.

24. The method of claim 23, wherein the beam and the second beam are one beam.

25. The method of claim 21, wherein the second perspective is offset from the first perspective.

26. The method of claim 21, wherein the radiation source and the second radiation source are one radiation source.

27. The method of claim 17, wherein the beam of radiation from the radiation source has a plurality of energies.

28. The method of claim 17, further comprising:

approximating a boundary of the object using a three-dimensional surface scan; and

initially estimating a density of the portions of the object within the boundary.

29. The method of claim 17, wherein the radiation source does not rotate around the object.

30. A method for three-dimensional image reconstruction comprising:

obtaining a measured attenuated portion of each of at least one beam of radiation, the at least one beam having a plurality of rays, the at least one beam of radiation being from a radiation source and having been attenuated by interaction with an object;

converting an estimated density of a plurality of portions of the object to a corrected estimated density of each portion of the object using a computer system by;

determining a predicted attenuated portion of the at least one beam using a density estimate;

comparing the predicted attenuated portion to the measured attenuated portion to determine a signal difference;

adjusting the density estimate of the portion of the object by scaling the density estimate using signal differences of rays that intersect the portion of the object; and

repeatedly adjusting the density estimate until a difference between consecutive density estimates is below a selected threshold or a predetermined number of adjustments have been completed; and

generating a three-dimensional density array representing the object using the corrected estimated densities of the portions of the object.

31. The method of claim 30, wherein the at least one beam of radiation is a plurality of beams of radiation oriented in different perspectives.

32. The method of claim 30, wherein:

the measured attenuated portion of each of at least one beam of radiation comprises a measured transmitted portion of a first beam of the at least one beam and a measured scattered portion of a second beam of the at least one beam;

determining a predicted attenuated portion of the at least one beam using the density estimate comprises determining a predicted transmitted portion of the first beam using a density estimate and determining a predicted scattered portion of the second beam using a density estimate;

the signal difference includes a transmitted signal difference and a scattered signal difference; and

comparing the predicted attenuated portion to the measured attenuated portion to determine a signal difference comprises comparing the predicted transmitted portion to the measured transmitted portion to determine a transmitted signal difference and comparing the predicted scattered portion to the measured scattered portion to determine a scattered signal difference.

33. The method of claim 32, wherein adjusting the density estimate of the portion of the object by scaling the density estimate using signal differences of rays that intersect the portion of the object comprises adjusting the density estimate of the portion of the object by scaling the density estimate using transmitted signal differences of rays that intersect the portion of the object.

34. The method of claim 32, wherein adjusting the density estimate of the portion of the object by scaling the density estimate using signal differences of rays that intersect the portion of the object comprises adjusting the density estimate of the portion of the object by scaling the density estimate using scattered signal differences of rays that intersect the portion of the object.

35. The method of claim 32, wherein adjusting the density estimate of the portion of the object by scaling the density estimate using signal differences of rays that intersect the portion of the object comprises:

making an adjustment of the density estimate of the portion of the object by scaling the density estimate using scattered signal differences of rays that intersect the portion of the object; and

making another adjustment of the density estimate of the portion of the object by scaling the density estimate using transmitted signal differences of rays that intersect the portion of the object.

36. The method of claim 32, wherein the first beam and the second beam are one beam.

37. The method of claim 32, wherein the first beam and the second beam are oriented in different perspectives.

38. The method of claim 30, wherein the measured attenuated portion is a measured transmitted portion and the predicted attenuated portion is a predicted transmitted portion.

39. The method of claim 30, wherein the measured attenuated portion is a measured scattered portion and the predicted attenuated portion is a predicted scattered portion.

40. The method of claim 30, wherein the at least one beam of radiation from the radiation source has a plurality of energies.

41. The method of claim 30, further comprising:

approximating a boundary of the object using a three-dimensional surface scan; and

initially estimating the density of the portions of the object within the boundary.

42. A method for three-dimensional image reconstruction comprising:

obtaining a measured attenuated portion of a beam of radiation, the beam having been attenuated by interaction with an object;

determining a predicted attenuated portion of the beam of radiation using a density estimate;

iteratively adjusting the density estimate of the object by comparing the predicted attenuated portion and the measured attenuated portion, wherein the predicted attenuated portion is re-determined once the density estimate is adjusted; and

generating a three-dimensional density array representing the object using the adjusted density estimate.

43. The method of claim 42, wherein the density estimate is iteratively updated until a difference between consecutive density estimates is below a selected threshold.

44. The method of claim 42, wherein the measured attenuated portion of the beam includes a measured scattered portion and a measured transmitted portion, and the predicted attenuated portion of the beam includes a predicted scattered portion and a predicted transmitted portion.