Detecting explosives or other contraband by employing transmitted and scattered X-rays

• US 5,600,700 A
• Filed: 09/25/1995
• Issued: 02/04/1997
• Est. Priority Date: 09/25/1995
• Status: Expired due to Term

• Current Assignee: L-3 Communications Security and Detection Systems Corporation Delaware
• Original Assignee: Vivid Technologies, Inc. (Revvity, Inc.)
• Inventors: Stein, Jay A., Krug, Kristoph D., Eilbert, Richard F., Stillson, Jeffrey H., Aitkenhead, William F.
• Primary Examiner(s): Porta, David P.
• Application Number:
  US08/533,646
• Time in Patent Office: 498 Days
• Field of Search: 378/51, 378/53, 378/54, 378/56, 378/57, 378/62, 378/63, 378/86, 378/87, 378/88, 378/89, 378/90, 378/207
• US Class Current: 378/57
• CPC Class Codes: G01N 23/203 Measuring back scattering
• CPC Class Codes: G01N 23/207 Diffractometry using detectors, e.g. using a probe in a central position and one or more displaceable detectors in circumferential positions
• CPC Class Codes: G01V 5/222 measuring scattered radiation
• CPC Class Codes: G01V 5/224 Multiple energy techniques using one type of radiation, e.g. X-rays of different energies

Abstract

An X-ray inspection device for detecting a specific material of interest (typically contraband, for example, weapons, drugs, money, explosives) in items of various sizes and shapes includes an X-ray source system located at an inspection region and constructed to expose the examined item to at least one beam of X-ray radiation, one or more x-ray detection systems located at the inspection region and constructed to detect x-ray radiation modified by the examined item. The X-ray inspection device also includes one or more dimension detectors constructed to measure a selected dimension of the examined item, an interface system connected to receive X-ray data and dimension data, and a computer programmed to utilize the data for recognition of the specific material of interest and to indicate its presence in the examined item. The X-ray detection systems detect transmitted and/or scattered X-ray radiation utilizing several different geometries. There may be one or more X-ray back-scatter detection systems, or one or more X-ray forward-scatter detection systems detecting X-ray radiation scattered at different angles from different surfaces of the examined item. Each detection system includes one or more arrays of X-ray detectors arranged in a linear, circular or semi-spherical geometry. Each detection system also may be connected to a displacement unit constructed and arranged to move or rotate the detector array to a selected position relative to the inspection region and the examined item.

Claims

1. An X-ray inspection device for detecting a specific material of interest in items of baggage or packages, comprising:

a conveyor constructed and arranged to move items of baggage or packages to an inspection region;

an X-ray source system located at said inspection region and constructed to expose an examined item of baggage or package by a beam of X-ray radiation;

an x-ray detection system located at said inspection region and constructed to detect x-ray radiation modified by said examined item;

a dimension detector constructed to measure a selected dimension of said examined item;

an interface system connected to and receiving from said X-ray detection system X-ray data and from said dimension detector dimension data, said interface system constructed to order said X-ray data and said dimension data;

a computer operatively connected to and receiving from said interface system said ordered X-ray and dimension data, said computer programmed to utilize said data for recognition of said specific material of interest in said examined item; and

said computer further programmed to indicate presence of said specific material of interest.

2. The device of claim 1 wherein said dimension detector comprises

an optical source located near said inspection region and constructed to emit optical radiation in the ultraviolet to infrared range toward said examined item;

an optical detector located near said inspection region and constructed to detect said optical radiation; and

a processor connected to receive optical data from said optical detector and constructed to measure said selected dimension of said examined item.

3. The device of claim 1 wherein said dimension detector comprises

an array of optical sources located near said inspection region, each said optical source constructed to emit optical radiation toward said examined item;

an array of optical detectors located near said inspection region, each said optical detector constructed to detect said optical radiation reflected from a selected surface of said examined item; and

a processor connected to receive optical data from said array of optical detectors and constructed to measure said selected dimension of said examined item.

4. The device of claim 3 wherein said dimension detector is further constructed to measure a dimension profile of at least a portion of said examined item.

5. The device of claim 4 wherein said dimension profile is a height profile of said item.

6. The device of claim 2 or 3 further comprising an dimension autocalibrator constructed to direct said dimension detector to perform an autocalibration sequence without an item of baggage or a package being in said inspection region and provide to said computer "air" dimension data.

7. The device of claim 2 or 3 further comprising a dimension autocalibrator including a factory calibration table, said factory calibration table includes data related to gain, offset, or geometry constants of said dimension detector.

8. The device of claim 1 wherein said X-ray source system, said X-ray detection system and said computer are further constructed and arranged to perform autocalibration sequences and acquire X-ray calibration data.

9. The device of claim 1 wherein said X-ray source system is further constructed to emit a fan beam of X-ray radiation of at least two substantially different energies.

10. The device of claim 9 wherein said x-ray detection system includes an array of X-ray transmission detectors constructed and positioned to detect x-ray radiation transmitted through said examined item.

11. The device of claim 10 wherein said array of transmission detectors is further constructed to detect separately X-ray radiation transmitted through said examined item at said two substantially different energies;

and said computer further constructed to receive separately a high energy transmission data and a low energy transmission data detected by said array.

12. The device of claim 11 wherein said array of X-ray transmission detectors is arranged to have an L-shaped form.

13. The device of claim 11 wherein each said X-ray transmission detector comprises an optical detector coupled to a scintillating material.

14. The device of claim 13 wherein said optical detector is a photodiode and said scintillating material is a sheet of GdOS coated paper.

15. The device of claim 10 further comprising an autocalibrator constructed to direct said X-ray source system, said X-ray transmission detection system and said computer to perform an autocalibration sequence wherein said X-ray transmission detectors provide to said computer "dark current" data while said X-ray source system emits no X-rays.

16. The device of claim 11 further comprising an autocalibrator constructed to direct said X-ray source system, said X-ray transmission detectors and said computer to perform an autocalibration sequence wherein said X-ray source system emits said X-ray radiation without an item of baggage or a package being in said inspection region and said X-ray transmission detectors provide to said computer "air" transmission data at each said energy.

17. The device of claim 10 further comprising an autocalibrator that includes a factory calibration table including "dark current" or "air" transmission data of at least one energy.

18. The device of claim 9 wherein said array of x-ray detection system includes an array of X-ray back-scatter detectors constructed and positioned to detect x-ray radiation back-scattered from said examined item to obtain x-ray back-scatter data of at least one energy.

19. The device of claim 18 further comprising a displacement unit connected to said array of back-scatter detectors and receiving data from said dimension detector, said displacement unit constructed and arranged to move said array of back-scatter detectors to a selected position based on data from said dimension detector.

20. The device of claim 18 or 19 further comprising an array of back-scatter collimators located in front of said array of X-ray back-scatter detectors, each said back-scatter collimator constructed and arranged to limit a view angle of the corresponding back-scatter detector to receive data back-scattered from the top surface of said item.

21. The device of claim 20 wherein said dimension detector is further constructed to measure distance data corresponding to positions of said back-scatter detectors, said distance data including distances from each said back-scatter detector to a surface of said examined item, said surface being within the corresponding detector'"'"'s view angle.

22. The device of claim 21 further comprising a back-scatter normalizer connected to receive said distance data from said dimension detector, said normalizer constructed and arranged to normalize X-ray back-scatter data utilizing said distance data.

23. The device of claim 22 wherein said back-scatter normalizer further includes a back-scatter normalization table, said normalizer being further constructed to normalize X-ray back-scatter data by utilizing data from said table.

24. The device of claim 22 wherein said back-scatter normalizer includes a look up table comprising distance data from each back-scatter detector to a surface of said examined item, said surface being within said view angle of the corresponding back-scatter detector.

25. The device of claim 18 or 19 wherein said X-ray source system is further constructed to emit a fan beam of X-ray radiation of at least two substantially different energies.

26. The device of claim 25 wherein said array of back-scatter detectors is further constructed to detect separately X-ray radiation scattered from said examined item at said two substantially different energies;

and said computer further constructed to receive separately a high energy back-scatter data and a low energy back-scatter data detected by said array.

27. The device of claim 26 wherein each said X-ray back-scatter detector comprises an optical detector coupled to a scintillating material.

28. The device of claim 27 wherein said optical detector is a photomultiplier tube (PMT) and said scintillating material is a NaI crystal.

29. The device of claim 26 further comprising an autocalibrator constructed to direct said X-ray source system, said X-ray back-scatter detection system and said computer to perform an autocalibration sequence wherein said X-ray back-scatter detectors provide to said computer "dark current" data while said X-ray source system emits no X-rays.

30. The device of claim 26 further comprising an autocalibrator constructed to direct said X-ray source system, said X-ray back-scatter detection system and said computer to perform an autocalibration sequence wherein said X-ray source system emits said X-ray radiation without an item of baggage or a package being in said inspection region and said X-ray back-scatter detectors provide to said computer "air" back-scatter data at each said energy.

31. The device of claim 26 further comprising an autocalibrator that includes a factory calibration table including "dark current" back-scatter data or "air" back-scatter data of at least one energy.

32. The device of claim 26 wherein said computer is further programmed to calculate from said high energy back-scatter data or said low energy back-scatter data a selected signature of said specific material.

33. The device of claim 32 wherein said selected signature emphasizes relatively thin and highly scattering materials inside of said item.

34. The device of claim 9 wherein said array of x-ray detection system includes an array of X-ray forward-scatter detectors constructed and positioned to detect x-ray radiation forward-scattered from said examined item to obtain x-ray forward-scatter data of at least one energy.

35. The device of claim 34 further comprising a displacement unit connected to said array of forward-scatter detectors and receiving data from said dimension detector, said displacement unit constructed and arranged to move said array of forward-scatter detectors to a selected position based on data from said dimension detector.

36. The device of claim 34 or 35 further comprising an array of forward-scatter collimators located in front of said array of X-ray forward-scatter detectors, each said forward-scatter collimator constructed and arranged to limit a view angle of the corresponding forward-scatter detector to receive data forward-scattered from the forward-scattering surface of said item.

37. The device of claim 36 wherein said dimension detector is further constructed to measure distance data corresponding to positions of said forward-scatter detectors, said distance data including distances from each said forward-scatter detector to a surface of said examined item which is within the corresponding detector'"'"'s view angle.

38. The device of claim 37 further comprising a forward-scatter normalizer connected to receive said distance data from said dimension detector, said normalizer constructed and arranged to normalize X-ray forward-scatter data utilizing said distance data.

39. The device of claim 38 wherein said forward-scatter normalizer further includes a forward-scatter normalization table, said normalizer being further constructed to normalize X-ray forward-scatter data by utilizing data from said table.

40. The device of claim 38 wherein said forward-scatter normalizer includes a look up table comprising distance data from each forward-scatter detector to a surface of said examined item, said surface being within said view angle of the corresponding forward-scatter detector.

41. The device of claim 34 or 35 wherein said X-ray source system is further constructed to emit a fan beam of X-ray radiation of at least two substantially different energies.

42. The device of claim 41 wherein said array of forward-scatter detectors is further constructed to detect separately X-ray radiation scattered from said examined item at said two substantially different energies;

and said computer further constructed to receive a high energy forward-scatter data and a low energy forward-scatter data detected by said array.

43. The device of claim 42 wherein each said X-ray forward-scatter detector comprises an optical detector coupled to a scintillating material.

44. The device of claim 43 wherein said optical detector is a photomultiplier tube (PMT) and said scintillating material is a CdWO₄ crystal.

45. The device of claim 42 further comprising an autocalibrator constructed to direct said X-ray source system, said X-ray forward-scatter detectors and said computer to perform an autocalibration sequence wherein said X-ray forward-scatter detectors provide to said computer "dark current" data while said X-ray source system emits no X-rays.

46. The device of claim 42 further comprising an autocalibrator constructed to direct said X-ray source system, said X-ray forward-scatter detectors and said computer to perform an autocalibration sequence wherein said X-ray source system emits said X-ray radiation without an item of baggage or a package being in said inspection region and said X-ray forward-scatter detectors provide to said computer "air" forward-scatter data at each said energy.

47. The device of claim 42 further comprising an autocalibrator that includes a factory calibration table including "dark current" forward-scatter data or "air" forward-scatter data of at least one energy.

48. The device of claim 42 wherein said computer is further programmed to calculate from said high energy forward-scatter data or said low energy forward-scatter data a selected signature of said specific material.

49. The device of claim 48 wherein said selected signature emphasizes relatively thin and highly scattering materials inside of said item.

50. The device of claim 1 wherein said specific material of interest is shaped into a relatively thin sheet of material.

51. The device of claim 1 wherein said specific material of interest is an explosive material, currency, or drugs.

52. The device of claim 34 further comprising a second x-ray detection system that includes an array of X-ray transmission detectors constructed and positioned to detect x-ray radiation transmitted through said examined item.

53. The device of claim 52 further comprising an equalizer connected to receive X-ray transmission data from said array of X-ray transmission detectors, said equalizer constructed and arranged to equalize forward-scatter data by locating, from said transmission data, highly absorbing regions of said item and account for reduced values in said forward scatter data in said regions.

56. The device of claim 1 or 54 wherein said computer is operatively connected to a conveyor control system constructed to direct examined items identified as containing said specific material of interest to one destination and examined items identified as free of said specific material of interest to another destination.

58. The device of claim 1, 10, 18, 34 or 54 further comprising a display, operatively connected to said computer, constructed and arranged to display a selected image of data representing a selecting region of said item.

59. The device of claim 58 further comprising a user interface, operatively connected to said computer, constructed and arranged to enable an operator to obtain different images of said region of said item.

54. An X-ray inspection device for detecting a specific material of interest in items of baggage or packages, comprising:

a conveyor for sequentially moving items of baggage or packages through an inspection region;

a stationary X-ray source located at said inspection region and constructed to expose sequentially said items by a fan beam of X-ray radiation of at least two substantially different energies;

as X-ray detection system including

an array of X-ray transmission detectors constructed and positioned to detect X-ray radiation transmitted through said examined item,

an array of X-ray back-scatter detectors constructed and positioned to detect X-ray radiation back-scattered from said examined item relative to the incident X-ray beam,

an array of X-ray forward-scatter detectors constructed and positioned to detect X-ray radiation scattered forward from said examined item relative to the incident X-ray beam,

a interface system constructed and arranged to receive from said detection system X-ray data corresponding to the intensity of X-ray radiation at said energies detected by said arrays of detectors;

a computer operatively connected via said interface system to said detection system and programmed to correlate data detected by said transmission detectors and said scatter detectors and recognize said specific material of interest by effectively removing the effects of overlying or underlying materials in said examined item; and

said computer further programmed to automatically indicate presence of said specific material of interest while said item progresses on said conveyor.

55. The device of claim 54 further comprising a dimension detector constructed to measure a selected dimension of said examined item.

57. The device of claim I or 54 constructed to operate in conjunction with a CT scanner that further examines said item to provide information about density, texture, cross section or location of objects in said examined item.

60. An X-ray inspection method of detecting a specific material of interest in items of baggage or packages, comprising:

moving sequentially on a conveyor items of baggage or packages through an inspection region;

exposing sequentially, at said inspection region, one of said items by a beam of X-ray radiation;

detecting X-ray radiation modified by said examined item by an X-ray detection system;

measuring a selected dimension of said examined item by employing a dimension detector;

ordering X-ray data detected by said X-ray detection system and dimension data detected by said dimension detector;

recognizing by computer-processing said specific material of interest by utilizing said ordered X-ray data and said dimension data; and

indicating automatically presence of said specific material of interest in said examined item.

61. The X-ray inspection method of claim 60 further comprising the step of calculating, based on said dimension data, a distance from a surface of said item to a detector of said X-ray detection system viewing said surface.

62. The X-ray inspection method of claim 60 or 61 further comprising calibrating data of said dimension detector by performing an autocalibration sequence without an item of baggage or a package being in said inspection region by detecting "air" dimension data.

63. The X-ray inspection method of claim 60 wherein said exposing step includes emitting a fan beam of X-ray radiation of at least two substantially different energies.

64. The X-ray inspection method of claim 63 wherein said detecting step includes detecting X-ray radiation transmitted through said examined item to obtain X-ray transmission data of at least one energy.

65. The X-ray inspection method of claim 64 further comprising performing an autocalibration sequence by detecting "dark current" transmission data while said X-ray source system emits no X-rays.

66. The X-ray inspection method of claim 64 further comprising performing an autocalibration sequence by detecting "air" transmission data of at least one energy without an item of baggage or a package being in said inspection region.

67. The X-ray inspection method of claim 64 wherein said recognizing step includes calculating a selected signature of said specific material by utilizing said X-ray transmission data and said dimension data.

68. The X-ray inspection method of claim 63 wherein said detecting step includes detecting X-ray radiation back-scattered from said examined item to obtain X-ray back-scatter data of at least one energy.

69. The X-ray inspection method of claim 68 further comprising performing an autocalibration sequence by detecting "dark current" back-scatter data while said X-ray source system emits no X-rays.

70. The X-ray inspection method of claim 68 further comprising performing an autocalibration sequence by detecting "air" back-scatter data of at least one energy without an item of baggage or a package being in said inspection region.

71. The X-ray inspection method of claim 68 further comprising collimating said back-scattered X-ray radiation by placing an array of back-scatter collimators in front of said array of X-ray detectors.

72. The X-ray inspection method of claim 71 further comprising measuring distance data from each said back-scatter detector to a surface of said examined item being within the corresponding detector'"'"'s view angle.

73. The X-ray inspection method of claim 72 further comprising normalizing said X-ray back-scatter data utilizing said distance data.

74. The X-ray inspection method of claim 68 wherein said recognizing step includes identifying, from said back-scatter data, a sharp change in detected intensity.

75. The X-ray inspection method of claim 68 wherein said recognizing step includes calculating from said back-scatter data, over at least a selected region, a selected signature of said specific material.

76. The X-ray inspection method of claim 75 further including comparing said selected signature for different selected regions of said examined item.

77. The X-ray inspection method of claim 75 wherein said selected signature is a histogram.

78. The X-ray inspection method of claim 77 further including comparing said histogram to a histogram characteristic of said specific material.

79. The X-ray inspection method of claim 75 wherein said selected signature emphasizes relatively thin materials located inside of said examined item.

80. The X-ray inspection method of claim 75 wherein said selected signature is related to effective atomic number (Z_eff) of said specific material.

81. The X-ray inspection method of claim 75 wherein said selected signature is the ratio of high energy and low energy back-scatter data.

82. The X-ray inspection method of claim 75 wherein said selected signature is the sum of said high energy and said low energy forward-scatter data of each said detector.

83. The X-ray inspection method of claim 63 wherein said detecting step includes detecting X-ray radiation forward-scattered from said examined item to obtain X-ray forward-scatter data of at least one energy.

84. The X-ray inspection method of claim 83 further comprising performing an autocalibration sequence by detecting "dark current" forward-scatter data while said X-ray source system emits no X-rays.

85. The X-ray inspection method of claim 83 further comprising performing an autocalibration sequence by detecting "air" forward-scatter data of at least one energy without an item of baggage or a package being in said inspection region.

86. The X-ray inspection method of claim 83 further comprising collimating said forward-scattered X-ray radiation by placing an array of forward-scatter collimators in front of said array of X-ray detectors.

87. The X-ray inspection method of claim 86 further comprising measuring distance data from each said forward-scatter detector to a surface of said examined item being within the corresponding detector'"'"'s view angle.

88. The X-ray inspection method of claim 87 further comprising normalizing said X-ray forward-scatter data utilizing said distance data.

89. The X-ray inspection method of claim 83 wherein said recognizing step includes identifying, from said forward-scatter data, a sharp change in detected intensity.

90. The X-ray inspection method of claim 83 wherein said recognizing step includes calculating from said forward-scatter data, over at least a selected region, a selected signature of said specific material.

91. The X-ray inspection method of claim 90 further including comparing said selected signature for different selected regions of said examined item.

92. The X-ray inspection method of claim 90 wherein said selected signature is a histogram.

93. The X-ray inspection method of claim 92 further including comparing said histogram to a histogram characteristic of said specific material.

94. The X-ray inspection method of claim 90 wherein said selected signature emphasizes relatively thin materials located inside of said examined item.

95. The X-ray inspection method of claim 90 wherein said selected signature is related to effective atomic number (Z_eff) of said specific material.

96. The X-ray inspection method of claim 90 wherein said selected signature is the ratio of high energy and low energy forward-scatter data.

97. The X-ray inspection method of claim 90 wherein said selected signature is the sum of said high energy and said low energy forward-scatter data of each said detector.

98. The X-ray inspection method of claim 68 further comprising detecting X-ray radiation forward-scattered from said examined item to obtain X-ray forward-scatter data.

99. The X-ray inspection method of claim 98 wherein said recognizing step includes calculating from said back-scatter data and said forward-scatter data, over at least a selected region, a second selected signature of said specific material.

100. The X-ray inspection method of claim 99 wherein said second selected signature is the gradient of said forward-scatter low energy data and said back-scatter low energy data squared.

101. The X-ray inspection method of claim 99 wherein said second selected signature is the difference between said forward-scatter data and said back-scatter data of at least one energy.

102. An X-ray inspection method of detecting a specific material of interest in items of baggage or packages, comprising:

moving sequentially on a conveyor items of baggage or packages through an inspection region;

exposing sequentially, at said inspection region, one of said items by a beam of X-ray radiation;

detecting X-ray radiation transmitted through said examined item by an X-ray transmission detection system to create X-ray transmission data;

detecting X-ray radiation back-scattered from said examined item by an X-ray back-scatter detection system to create X-ray back-scatter data;

detecting X-ray radiation forward-scattered from said examined item by an X-ray forward-scatter detection system to create X-ray forward-scatter data;

ordering X-ray data detected by said X-ray detection systems;

recognizing, by computer-processing said ordered X-ray data, said specific material of interest by effectively removing the effects of overlying or underlying materials in said examined item; and

indicating automatically presence of said specific material of interest in said examined item.

103. The X-ray inspection method of claim 102 further comprising measuring a selected dimension of said examined item by employing a dimension detector.

104. The X-ray inspection method of claim 60 or 102 operating in conjunction with a conveyor control system directing examined items identified as containing said specific material of interest to one destination and examined items identified as free of said specific material of interest to another destination.

105. The X-ray inspection method of claim 60 or 102 operating in conjunction with a CT scanner further comprising CT scanning said item to provide information about density, texture, cross section or location of objects in said examined item.

106. The X-ray inspection method of claim 60, 64, 68, 83 or 102 further comprising displaying a selected image of data representing a selecting region of said item.

107. The X-ray inspection method of claim 106 further comprising obtaining different images of said region of said item.