Dual energy radiation scanning of contents of an object

• US 20080205594A1
• Filed: 08/13/2007
• Published: 08/28/2008
• Est. Priority Date: 03/01/2004
• Status: Active Grant

• Current Assignee: Varex Imaging Corporation
• Original Assignee: Varian Medical Systems Incorporated (Siemens AG)
• Inventors: Bjorkholm, Paul
• Granted Patent: US 7,636,417 B2
• Time in Patent Office: Days
• US Class Current: 378/53
• CPC Class Codes: G01N 23/04 and forming images of the material
• CPC Class Codes: G01T 3/00 Measuring neutron radiation G01T5/00 takes precedence
• CPC Class Codes: G01V 5/224 Multiple energy techniques using one type of radiation, e.g. X-rays of different energies
• CPC Class Codes: G01V 5/234 Measuring induced radiation, e.g. thermal neutron activation analysis
• CPC Class Codes: G01V 5/281 detecting special nuclear material [SNM], e.g. Uranium-235, Uranium-233 or Plutonium-239

Abstract

In one embodiment, a method of examining contents of an object is disclosed comprising scanning an object at first and second radiation energies, detecting radiation at the first and second energies, and calculating a function of the radiation detected at the first and second energies. The method further comprises calculating at least one second function based, at least in part, on at least some of the first functions, and determining whether the object at least potentially contains material in a class of materials based, at least in part, on the second function. The class of materials may be materials having an atomic number greater than the predetermined atomic number, for example. The second function may be compared to a criterion, which may be a threshold, for example. Systems are also disclosed.

Claims

1. A method of examining contents of an object, the method comprising:

scanning at least a portion of an object with a first radiation beam at a first energy and a second radiation beam at a second energy different from the first energy;

detecting first and second radiation after interaction of the first and second radiation beams with the at least a portion of the object, respectively;

calculating first functions of the radiation detected at the first and second energies;

calculating at least one second function based, at least in part, on at least some of the first functions; and

determining whether the object at least potentially contains material in a class of materials based, at least in part, on the at least one second function.

2. The method of claim 1, comprising determining whether the object at least potentially contains material in a class of material having an atomic number greater than a predetermined atomic number, based, at least in part, on the second function.

3. The method of claim 2, further comprising:

comparing the first functions to a criterion based, at least in part, on the predetermined atomic number, prior to calculating the second function;

wherein;

calculating the second function is based, at least in part, on the first functions meeting the criterion; and

determining whether the object at least potentially contains material in the class of materials having an atomic number greater than the predetermined atomic number based, at least in part, on the comparison.

4. The method of claim 3, wherein the predetermined atomic number is at least 26.

5. The method of claim 4, wherein the predetermined atomic number is at least 74.

6. The method of claim 1, further comprising:

comparing the second function to a predetermined criteria independent of the object; and

determining whether the object is in the class of materials based, at least in part, on the comparison.

7. The method of claim 1, comprising calculating the first functions for corresponding portions of the object.

8. The method of claim 7, wherein corresponding portions of the object overlap by at least one half.

9. The method of claim 1, further comprising:

comparing the first functions to a criterion;

wherein calculating the second function is based, at least in part, on the first functions meeting the criterion.

10. The method of claim 1, further comprising:

grouping first functions into at least one group; and

calculating the second function based on the first functions of the at least one group.

11. The method of claim 10, comprising:

grouping first functions into at least one examination window corresponding to at least a portion of the object, the window having a predetermined size;

calculating the second function by counting a number of first functions within the examination window meeting the criterion; and

comparing the counted number to a predetermined number to determine whether the object at least potentially contains a material in the class of materials.

12. The method of claim 11, wherein:

the predetermined number is based, at least in part, on a predetermined false positive rate.

13. The method of claim 10, comprising:

grouping first functions of contiguous portions of the object meeting the criterion;

calculating an area of the grouping; and

comparing the area with a predetermined area to determine whether the object at least potentially contains a material in the class of materials.

14. The method of claim 10, wherein the at least one grouping defines at least one matrix and the second function is an average, the method comprising:

calculating an average of the first functions for the plurality of corresponding pixels within the at least one matrix; and

comparing the average to the criterion to determine whether the object at least potentially contains a material in the class of materials.

15. The method of claim 3, wherein comparing the first functions to the criterion comprises:

comparing the first function to a threshold.

16. The method of claim 15, further comprising:

calculating the threshold, at least in part, by;

scanning at least a portion of a second object comprising material in the class, with third and fourth radiation beams at the first energy and the second energy, respectively;

detecting third and fourth radiation after interaction of the third and fourth radiation beams with the at least a portion of the second object; and

calculating the first function of the radiation detected at the third and fourth energies.

17. The method of claim 16, wherein scanning at least a portion of the second object comprises:

scanning at least a portion of a second object comprising a material having an atomic number less than an atomic number of uranium.

18. The method of claim 17, comprising:

scanning at least a portion of a second object comprising a material having an atomic number less than an atomic number of lead.

19. The method of claim 16, comprising:

scanning a plurality of objects comprising a plurality of different materials to calculate a plurality of thresholds; and

selecting a threshold for use as the criterion based, at least in part, on the expected contents of the object.

20. The method of claim 1, wherein:

calculating the first function comprises dividing the first detected radiation by the second detected radiation.

21. The method of claim 1, further comprising:

selecting a threshold based on radiation detected at least one of the first radiation and the second radiation.

22. A system for examining contents of an object, the system method comprising:

means for scanning at least a portion of the object with a first radiation beam at a first energy and a second radiation beam at a second energy different from the first energy;

means for detecting first and second radiation after interaction of the first and second radiation beams with the at least a portion of the object, respectively;

means for calculating first functions of the radiation detected at the first and second energies;

means for calculating at least one second function based, at least in part, on at least some of the first functions; and

means for determining whether the object at least potentially contains material in a class of material.

23. A system for examining contents of an object, the system comprising:

at least one radiation source to scan at least a portion of an object with first and second radiation beams at first and second radiation energies, respectively, wherein the first radiation energy is different than the second radiation energy;

at least one detector positioned to detect radiation at the first and second radiation energies after interaction with the object;

at least one processor coupled to the detector, the at least one processor being configured to;

calculate first functions of the radiation detected at the first and second energies;

calculate at least one second function based, at least in part, on at least some of the first functions; and

determine whether the object at least potentially contains material in a class of materials based, at least in part, on the at least one second function.

24. The system of claim 23, wherein the processor is configured to:

determine whether the object at least potentially contains material in a class of materials having an atomic number greater than a predetermined atomic number, based, at least in part, on the second function.

25. The system of claim 24, wherein the processor is configured to:

compare the first functions to a criterion based, at least in part, on the predetermined atomic number, prior to calculating the second function;

wherein calculating the second function is based, at least in part, on the first functions meeting the criterion.

26. The system of claim 25, wherein the predetermined atomic number is at least 26.

27. The system of claim 26, wherein the predetermined atomic number is at least 74.

28. The system of claim 23, wherein the processor is further configured to:

compare the second function to a predetermined criterion independent of the object; and

determine whether the object is in the class of materials based, at least in part, on the comparison.

29. The system of claim 23, wherein the processor is configured to calculate the first functions for corresponding portions of the object.

30. The system of claim 29, wherein corresponding portions of the object overlap by at least one half.

31. The system of claim 23, wherein the processor is further configured to:

compare the first functions to a criterion;

wherein calculating the second function is based, at least in part, on the first functions meeting the criterion.

32. The method of claim 31, wherein the processor is configured to compare the first functions to the criterion by:

comparing the first function to a threshold.

34. The system of claim 23, wherein the processor is further configured to:

group first functions into at least one group; and

calculate the second function based on the first functions of the at least one group.

35. The system of claim 34, wherein the processor is further configured to:

group first functions into at least one examination window corresponding to at least a portion of the object, the window having a predetermined size;

calculate the second function by counting a number of first functions within the examination window meeting the criterion; and

compare the counted number to a predetermined number to determine whether the object at least potentially contains a material in the class of materials.

36. The system of claim 35, wherein:

the predetermined number is based, at least in part, on a predetermined false positive rate.

37. The method of claim 34, wherein the processor is further configured to:

group first functions of contiguous portions of the object meeting the criterion;

calculate an area of the grouping; and

compare the area with a predetermined area to determine whether the object at least potentially contains a material in the class of materials.

38. The method of claim 34, wherein the at least one grouping defines at least one matrix and the second function is an average, the processor being further configured to:

calculate an average of the first functions for the plurality of corresponding pixels within the at least one matrix; and

compare the average to the criterion to determine whether the object at least potentially contains a material in the class of materials.

39. The system of claim 23, wherein the processor is further configured to:

calculate the threshold based, at least in part, on detected radiation after scanning a test material in the class.

33. The system of claim 33, wherein the at least one processor is further configured to:

select the threshold for use in the criterion based, at least in part, on expected contents of the object.