Device and method for inspection of baggage and other objects
First Claim
1. A device for detecting a specific material that may be present in an ensemble of objects comprisingan x-ray source adapted to expose an area of the ensemble to x-ray radiation of two substantially different energy bands,a detector, responsive to said source, adapted to detect radiation passing through said ensemble and to produce dual energy areal image information of said ensemble, anda computer adapted to process such dual energy information based on differences in attenuation between subareas of said exposed area to detect presence of said specific material by comparing selected subareas of said exposed area to other subareas in the vicinity of said selected subareas,said computer being capable of performing said comparison by computing for a selected test subarea of said exposed area the values (HT, LT) wherein HT is a function of the attenuation of said x-rays at the higher energy band at said test subarea and LT is a function of the attenuation of said x-rays at the lower energy band at said test subarea and computing for a subarea nearby said test subarea the values (HB, LB) wherein HB is a function of the attenuation of said x-rays at the higher energy band at said nearby subarea and LB is a function of the attenuation of said x-rays at the lower energy band at said nearby subarea, and employing said values (HT, LT) and (HB, LB) in determining the presence of said specific material.
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Accused Products
Abstract
A device and method is provided for finding a specific material superimposed on an unknown background when the locations of the specific material and the background are unknown, for example, inside an item of baggage. The invention comprises exposing an area of an item to be inspected to x-rays of two substanitally different energies, making effective use of the characteristic material specific differences in photoelectric effect scattering and Compton scattering, and comparing the pairwise differential attenuation of the x-rays at nearby exposed subareas to determine whether differences in attenuation can be attributed to the presence of different amounts of the specific material overlying the respective subareas. The most probable subareas are indicated on a standard image on a monitor as being the most likely location of the overlying specific material.
259 Citations
63 Claims
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1. A device for detecting a specific material that may be present in an ensemble of objects comprising
an x-ray source adapted to expose an area of the ensemble to x-ray radiation of two substantially different energy bands, a detector, responsive to said source, adapted to detect radiation passing through said ensemble and to produce dual energy areal image information of said ensemble, and a computer adapted to process such dual energy information based on differences in attenuation between subareas of said exposed area to detect presence of said specific material by comparing selected subareas of said exposed area to other subareas in the vicinity of said selected subareas, said computer being capable of performing said comparison by computing for a selected test subarea of said exposed area the values (HT, LT) wherein HT is a function of the attenuation of said x-rays at the higher energy band at said test subarea and LT is a function of the attenuation of said x-rays at the lower energy band at said test subarea and computing for a subarea nearby said test subarea the values (HB, LB) wherein HB is a function of the attenuation of said x-rays at the higher energy band at said nearby subarea and LB is a function of the attenuation of said x-rays at the lower energy band at said nearby subarea, and employing said values (HT, LT) and (HB, LB) in determining the presence of said specific material.
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2. A device for detecting an object of interest that may be present in a container of objects comprising
an x-ray source adapted to expose an area of said container to x-ray radiation of two substantially different energy bands, a detector, responsive to said source, adapted to detect radiation passing through said container and to produce dual energy areal image information of said container and its contents based on differences in absorption of said x-rays, and a computer adapted to process such dual energy information to detect said object of interest on the basis of comparisons of x-ray attenuation values (HT, LT) and (HB, LB) representing the substantially logarithmic dependence of x-rays absorption when passing through objects, wherein HT and HB represent the attenuation of said x-rays at the higher energy band at said test subarea and said nearby subarea, respectively, and LT and LB represent the attenuation of said x-rays at the lower energy band at said test subarea and said nearby subarea, respectively, said comparisons employing the (HT, LT) and (HB, LB) values of selected test subareas of said exposed area and other nearby subareas in the vicinity of said selected test subareas, respectively, to determine the presence of said object of interest.
- 3. A device for detecting a specific material that may be present in an ensemble of objects comprising means to expose an area of the ensemble to x-rays of at least two substantially different energy bands to produce dual energy image information of the ensemble and means to computer-process such dual energy information to detect said specific material on the basis of comparisons between attenuation image information from at least one of said energy bands and positionally corresponding image information of parameter P values derived from correlations of said dual energy image information with values in a predetermined lookup table reflecting attenuation at high and low energy bands over a range of thicknesses of a selected specific material and a range of thicknesses of a representative overlay material, with attenuation of a constant thickness of said overlay material and varying thicknesses of said specific material represented by said parameter P.
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9. A device for detecting and indicating the probable presence of a specific material in an ensemble of objects, comprising
means for exposing said item to x-rays of at least two substantially different energy levels, means for generating for each subarea over the exposed area a set of data values representing logarithms of x-ray attenuation at said subarea at each of said energy levels, means for processing said data for said subarea to compute the values of (H,L) for said subarea, wherein H is the logarithm of the attenuation of said x-rays at said subarea at the higher energy level and L is the logarithm of the attenuation of said x-rays at said subarea at the lower energy level, and means for applying an edge finding or gradient evaluating operator such as a Sobel operator to image data of at least one energy level, means for generating gradient values HS for substantially all subareas, means for pruning to remove subareas with gradient values HS below a selected gradient threshold, means for determining for remaining subareas with gradient values HS above said selected gradient threshold parameter P values using a lookup table in computer storage reflecting x-ray attenuation at high and low energy bands over a range of thicknesses of said selected specific material and a range of thicknesses of a representative overlay material, with attenuation of a constant thickness of said overlay material and varying thicknesses of said specific material represented by said parameter P, means for applying said gradient evaluating operator to P image data formed using said parameter P values for said remaining subareas, means for generating gradient values PS for said remaining subareas, means for calculating a ratio HS /PS for said remaining subareas, means for raising said ratio to a power at least as large as unity to emphasize large values of said ratio, and means for storing said ratio HS /PS raised to said power for substantially all of said remaining subareas.
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11. A device for detecting and indicating the probable presence of a specific material in an ensemble of objects, comprising
means for exposing said item to x-rays of at least two substantially different energy levels, means for generating for each subarea over the exposed area a set of data values representing logarithms of x-ray attenuation at said subarea at each of said energy levels, means for filtering said data for said subarea, means for averaging said data for said subarea, means for processing said data for said subarea to compute the values of (H,L) for said test subarea, wherein H is the logarithm of the attenuation of said x-rays at said subarea at the higher energy level and L is the logarithm of the attenuation of said x-rays at said subarea at the lower energy level, and means for applying an edge finding or gradient evaluating operator such as a Sobel operator to image data of at least one energy level, means for generating gradient values HS for substantially all subareas, means for pruning to remove subareas with gradient values HS below a selected gradient threshold, means for determining for remaining subareas with gradient values HS above said selected gradient threshold parameter P values using a lookup table in computer storage reflecting x-ray attenuation at high and low energy bands over a range of thicknesses of said selected specific material and a range of thicknesses of a representative overlay material, with attenuation of a constant thickness of said overlay material and varying thicknesses of said specific material represented by said parameter P, means for applying said gradient evaluating operator to P image data formed using said parameter P values for said remaining subareas, means for generating gradient values PS for said remaining subareas, means for calculating a ratio HS /PS for said remaining subareas, means for raising said ratio to a power at least as large as unity to emphasize large values of said ratio, means for storing said ratio HS /PS raised to said power for substantially all of said remaining subareas, means for selecting an alarm threshold on said ratio HS /PS raised to said power so that subareas having said ratio HS /PS raised to said power above said alarm threshold are strongly indicative of presence of said specific material, means for applying a dilation algorithm using said H values and said L values for said image data, means for sounding an alarm if a certain number of subarea values are above said alarm threshold, means for applying an erosion algorithm to eliminate spurious noise in said image data, and means for displaying said image data with areas of particular interest highlighted.
- 12. A device for inspecting an ensemble of physical objects comprising means to expose an area of said ensemble to x-rays of at least two substantially different energy bands, detection means responsive to said x-rays passing through said ensemble to generate for subareas over said area respective sets of values representing the attenuation of said x-rays at each of said energy bands, comparison means operative on differences in attenuation between subareas in a neighborhood to determine the presence of a specific material in the neighborhood, and indicating means responsive to said comparisons for indicating presence of said specific material in said ensemble wherein said comparison means includes a lookup table reflecting attenuation at high and low energy bands over a range of thicknesses of a selected specific material and a range of thicknesses of a representative overlay material, with attenuation of a constant thickness of said overlay material and varying thicknesses of said specific material represented by a parameter P.
- 13. A device for inspecting an ensemble of physical objects comprising means to expose an area of said ensemble to x-rays of at least two substantially different energy bands, detection means responsive to said x-rays passing through said ensemble to generate for subareas over said area respective sets of values representing the attenuation of said x-rays at each of said energy bands, comparison means operative on differences in attenuation between subareas in a neighborhood to determine the presence of a specific material in the neighborhood, and indicating means responsive to said comparisons for indicating presence of said specific material in said ensemble wherein said comparison means include means to combine, according to a predetermined formula, values representing the attenuation of said x-rays for subareas in said neighborhood to provide an attenuation measure and means to compare said measure to a reference related to said specific material.
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14. A device for inspecting an ensemble of physical objects comprising means to expose an area of said ensemble to x-rays of at least two substantially different energy bands, detection means responsive to said x-rays passing through said ensemble to generate for subareas over said area respective sets of values representing the attenuation of said x-rays at each of said energy bands, comparison means operative on differences in attenuation between subareas in a neighborhood to determine the presence of a specific material in the neighborhood, and indicating means responsive to said comparisons for indicating presence of said specific material in said ensemble wherein said values generated representing the attenuation of said x-rays at said energy bands are logarithms of x-ray attenuation at each of said energy bands at each subarea.
- 24. A device for inspecting an ensemble of physical objects comprising means to expose an area of said ensemble to x-rays of at least two substantially different energy bands, detection means responsive to said x-rays passing through said ensemble to generate for subareas over said area respective sets of values representing the attenuation of said x-rays at each of said energy bands, comparison means operative on differences in attenuation between subareas in a neighborhood to determine the presence of a specific material in the neighborhood, and indicating means responsive to said comparisons for indicating presence of said specific material in said ensemble wherein said comparison means comprises means for computing for a selected test subarea of said area the values (HT,LT) wherein HT is the logarithm of the attenuation of said x-rays at said higher energy band at said test subarea and LT is the logarithm of the attenuation of said x-rays at said lower energy band at said test subarea, means for computing for a subarea nearby said test subarea the values (HB, LB) wherein HB is the logarithm of the attenuation of said x-rays at said higher energy band at said nearby subarea and LB is the logarithm of the attenuation of said x-rays at said lower energy band at said nearby subarea, said comparison means constructed to employ said values (HT, LT) and (HB, LB) in determining the presence of said specific material.
- 33. A device for inspecting an ensemble of physical objects comprising means to expose an area of said ensemble to x-rays of at least two substantially different energy bands, detection means responsive to said x-rays passing through said ensemble to generate for subareas over said area respective sets of values representing the attenuation of said x-rays at each of said energy bands, comparison means operative on differences in attenuation between subareas in a neighborhood to determine the presence of a specific material in the neighborhood, indicating means responsive to said comparisons for indicating presence of said specific material in said ensemble, and means for exposing selected numbers of samples of various known materials each of a range of different thicknesses to said x-rays of said different energy bands to measure the attenuation characteristic of the exposed samples to provide a reference for said comparison means.
- 36. A baggage inspection device for detecting and indicating the probable presence of a specific material in an item of baggage comprising means to expose an area of said item to x-rays of at least two substantially different energy bands, detection means responsive to said x-rays passing through said item to generate for subareas over said area respective sets of values representing the attenuation of said x-rays at each of said energy bands, comparison means operative on differences in attenuation between subareas in a neighborhood to determine the presence of a specific material in the neighborhood of said subareas, and indicating means responsive to said comparisons for indicating presence of said specific material in said item, said comparison means comprising means for computing for a selected test subarea of said area the values (HT,LT) wherein HT is the logarithm of the attenuation of said x-rays at said higher energy band at said test subarea and LT is the logarithm of the attenuation of said x-rays at said lower energy band at said test subarea, means for computing for a subarea nearby said test subarea the values (HB,LB ) wherein HB is the logarithm of the attenuation of said x-rays at said higher energy band at said nearby subarea and LB is the logarithm of the attenuation of said x-rays at said lower energy band at said nearby subarea, said comparison means constructed to employ said values (HT,LT) and (HB,LB) in determining the presence of said specific material.
- 45. A device for detecting a specific material that may be present in an ensemble of objects comprising means to expose an area of the ensemble to x-ray energies to produce dual energy image information of the ensemble, means to computer-process such dual energy information to detect said specific material on the basis of comparisons of selected subareas of said exposed area to other subareas in the vicinity of said selected subareas, means for locating edges in the exposed area where one material overlaps another, means for choosing subareas in close proximity to said edges to be said selected subareas, and means for assigning to said selected subareas a relative probability for the presence of said specific materials at said subareas based upon said comparisons with other subareas in the vicinity, and indicating means responsive to said relative probability assignment.
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46. A device for inspecting an ensemble of physical objects comprising means to expose an area of said ensemble to x-rays of at least two substantially different energy bands, detection means responsive to said x-rays passing through said ensemble to generate for subareas over said area respective sets of values representing the attenuation of said x-rays at each of said energy bands, comparison means operative on differences in attenuation between subareas in a neighborhood to determine the presence of a specific material in the neighborhood, indicating means responsive to said comparisons for indicating presence of said specific material in said ensemble, means for locating edges in the exposed area where one material overlaps another, means for choosing subareas in close proximity to said edges to be said selected subareas, and means for assigning to said selected subareas a relative probability for the presence of said specific materials at said subareas based upon comparisons with other subareas in the neighborhood, said indicating means being responsive to said relative probability assignment.
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48. A method of detecting a specific material that may be present in an ensemble of objects comprising the steps of
exposing an area of the ensemble to x-ray radiation of two substantially different energy bands, detecting radiation passing through the ensemble and producing dual energy areal image information of said exposed ensemble, and processing such dual energy information based on differences in attenuation between subareas of said exposed area to detect presence of said specific material by comparing selected subareas of said exposed area to other subareas in the vicinity of said selected subareas, said processing further including performing said comparison by computing for a selected test subarea of said exposed area the values (HT, LT) wherein HT is a function of the attenuation of said x-rays at the higher energy band at said test subarea and LT is a function of the attenuation of said x-rays at the lower energy band at said test subarea and computing for a subarea nearby said test subarea the values (HB, LB) wherein HB is a function of the attenuation of said x-rays at the higher energy band at said nearby subarea and LB is a function of the attenuation of said x-rays at the lower energy band at said nearby subarea, and employing said values (HT, LT) and (HB, LB) in determining the presence of said specific material.
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49. A method of detecting an object of interest that may be present in a container of objects comprising the steps of
exposing an area of the container to x-ray radiation of two substantially different energy bands, detecting radiation passing through the ensemble and producing dual energy areal image information of said exposed ensemble, and processing such dual energy information to detect said object of interest on the basis of comparisons of x-ray attenuation values (HT, LT) and (HB, LB) representing the substantially logarithmic dependence of absorption of x-rays passing through objects, wherein HT and HB represent the attenuation of said x-rays at the higher energy band at said test subarea and said nearby subarea, respectively, and LT and LB represent the attenuation of said x-rays at the lower energy band at said test subarea and said nearby subarea, respectively, said comparisons employing the (HT, LT) and (HB, LB) values of selected test subareas of said exposed area and other nearby subareas in the vicinity of said selected test subareas, respectively, to determine the presence of said object of interest.
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50. A method of baggage inspection for detecting and indicating the probable presence of a specific material in an item of baggage, comprising the steps of
exposing said item to x-rays of at least two substantially different energy levels, generating for each subarea over the exposed area a set of data values representing logarithms of x-ray attenuation at said subarea at each of said energy levels, choosing a test subarea, filtering said data for said test subarea, averaging said data for said test subarea, processing said data for said test subarea to compute the values of (HT,LT) for said test subarea, wherein HT is the logarithm of the attenuation of said x-rays at said test subarea at the higher energy level and LT is the logarithm of the attenuation of said x-rays at said test subarea at the lower energy level, and choosing a background subarea, filtering said data for said background subarea, averaging said data for said background subarea, processing said data for said background subarea to compute the values of (HB,LB) for said background subarea, wherein HB is the logarithm of the attenuation of said x-rays at said background subarea at the higher energy level and LB is the logarithm of the attenuation of said x-rays at said background subarea at the lower energy level, and computing the value of KTB =(HT -HB)/(LT -LB), and comparing said value of KTB to the value of KMAT, wherein KMAT =μ -
H (HT,LT,HB,LB)/μ
L (HT,LT,HB,LB) wherein μ
H, an attenuation coefficient of a specific material exposed to said higher energy x-rays, is a function of the logarithms of the attenuation of said x-rays at said test subarea and at said background subarea, wherein μ
L, an attenuation coefficient of said specific material exposed to said lower energy x-rays, is a function of the logarithms of the attenuation of said x-rays at said test subarea and at said background subarea, andascertaining whether said value of KTB is within a selected window of values of KMAT, incrementing a respective counter if said value of KTB is within said window, choosing another background subarea, and iterating the steps from filtering said data for said background subarea to choosing another background subarea until a substantial number of background subareas have been so examined, and choosing another test subarea, and iterating the steps from filtering said data for said test subarea to choosing another test subarea until substantially all subareas have been so tested, and examining said subarea counters, producing values for each subarea indicative of the relative probability of matching said specific material, and displaying subareas over said area, and highlighting those subareas having a probability greater than or equal to a selected threshold value of matching said specific material.
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H (HT,LT,HB,LB)/μ
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51. A method of baggage inspection for detecting and indicating the probable presence of a specific material in an item of baggage, comprising the steps of
exposing said item to x-rays of at least two substantially different energy levels, generating for each subarea over the exposed area a set of data values representing logarithms of x-ray attenuation at said subarea at each of said energy levels, choosing a test subarea, filtering said data for said test subarea, averaging said data for said test subarea, processing said data for said test subarea to compute the values of (HT,LT) for said test subarea, wherein HT is the logarithm of the attenuation of said x-rays at said test subarea at the higher energy level and LT is the logarithm of the attenuation of said x-rays at said test subarea at the lower energy level, and choosing a background subarea, filtering said data for said background subarea, averaging said data for said background subarea, processing said data for said background subarea to compute the values of (HB,LB) for said background subarea, wherein HB is the logarithm of the attenuation of said x-rays at said background subarea at the higher energy level and LB is the logarithm of the attenuation of said x-rays at said background subarea at the lower energy level, and providing p-values P representing attenuation characteristics of various overlying materials, associating a p-value PT with said values (HT,LT) wherein said p-value PT is proportional to the thickness of overlying materials at said test subarea, associating a p-value PB with said values (HB,LB) wherein said p-value PB is proportional to the thickness of overlying materials at said nearby subarea, computing the value of |(HT -HB)/(PT -PB)|=Δ - H/Δ
P,associating Δ
H/Δ
P with a relative probability measure for the presence of said specific material at respective subareas,storing said probability measure, choosing another background subarea, and iterating the steps from filtering said data for said background subarea to choosing another background subarea until a substantial number of background subareas have been so examined, and choosing another test subarea, and iterating the steps from filtering said data for said test subarea to choosing another test subarea until substantially all subareas have been so tested, and examining said subarea probability measure stores, producing values for each subarea indicative of the relative probability of matching said specific material, and displaying subareas over said area, and highlighting those subareas having a probability greater than or equal to a selected threshold value of matching said specific material.
- H/Δ
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52. A method of detecting a specific material that may be present in an ensemble of objects comprising the steps of
exposing an area of the ensemble to x-rays of at least two substantially different energy bands to produce dual energy image information of the ensemble, and computer-processing such dual energy information to detect said specific material on the basis of comparisons between attenuation image information from at least one of said energy bands and positionally corresponding image information of parameter P values derived from correlations of said dual energy image information with values in a predetermined lookup table reflecting attenuation at high and low energy bands over a range of thicknesses of a selected specific material and a range of thicknesses of a representative overlay material, with attenuation of a constant thickness of said overlay material and varying thicknesses of said specific material represented by said parameter P.
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53. A method of detecting and indicating the probable presence of a specific material in an ensemble of objects, comprising the steps of
exposing said item to x-rays of at least two substantially different energy levels, generating for each subarea over the exposed area a set of data values representing logarithms of x-ray attenuation at said subarea at each of said energy levels, filtering said data for said subarea, averaging said data for said subarea, processing said data for said subarea to compute the values of (H,L) for said test subarea, wherein H is the logarithm of the attenuation of said x-rays at said subarea at the higher energy level and L is the logarithm of the attenuation of said x-rays at said subarea at the lower energy level, and applying an edge finding or gradient evaluating operator such as a Sobel operator to image data of at least one energy level, generating gradient values HS for substantially all subareas, pruning to remove subareas with gradient values HS below a selected gradient threshold, determining for remaining subareas with gradient values HS above said selected gradient threshold parameter P values using a lookup table in computer storage reflecting x-ray attenuation at high and low energy bands over a range of thicknesses of said selected specific material and a range of thicknesses of a representative overlay material, with attenuation of a constant thickness of said overlay material and varying thicknesses of said specific material represented by said parameter P, applying said gradient evaluating operator to P image data formed using said parameter P values for said remaining subareas, generating gradient values PS for said remaining subareas, calculating a ratio HS /PS for said remaining subareas, raising said ratio to a power at least as large as unity to emphasize large values of said ratio, storing said ratio HS /PS raised to said power for substantially all of said remaining subareas, selecting an alarm threshold on said ratio HS /PS raised to said power so that subareas having said ratio HS /PS raised to said power above said alarm threshold are strongly indicative of presence of said specific material, applying a dilation algorithm using said H values and said L values for said image data, sounding an alarm if a certain number of subarea values are above said alarm threshold, applying an erosion algorithm to eliminate spurious noise in said image data, and displaying said image data with areas of particular interest highlighted.
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55. A device for detecting a specific material of interest in a package or suitcase comprising:
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means to acquire x-ray transmission data through many spatially adjacent points of a package or suitcase at least at two substantially different energies, and means to computer process the x-ray data which include; treating the data spatially as numerous "object" regions and neighboring background regions, where each "object" region is taken as having substantially the same x-ray attenuating properties as a neighboring background region except for the addition of a thickness of unknown material, processing the data in numerous "object" regions and respective neighboring background regions to characterize the x-ray properties of the assumed thickness of unknown material of the "object" regions with the contribution of background removed, and comparing the determined x-ray properties of the thickness of unknown material in the "object" regions to the properties of the specific material of interest to determine if the "object" regions are likely to contain the specific material of interest. - View Dependent Claims (56, 57, 58, 59, 60)
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61. A device for detecting a specific material that may be present in an ensemble of objects comprising means to expose an area of the ensemble to x-ray energies to produce dual energy image information of the ensemble, means to computer-process such dual energy information to detect said specific material on the basis of comparisons of selected subareas of said exposed area to other subareas in the vicinity of said selected subareas, and means for dilating indications of subareas over regions whose edges have been determined to indicate the presence of said specific material, wherein said dilation makes said regions more prominently noticeable to an operator of said device, and wherein said dilation enhances indication of presence of said specific material.
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62. A device for inspecting an ensemble of physical objects comprising means to expose an area of said ensemble to x-rays of at least two substantially different energy bands, detection means responsive to said x-rays passing through said ensemble to generate for subareas over said area respective sets of values representing the attenuation of said x-rays at each of said energy bands, comparison means operative on differences in attenuation between subareas in a neighborhood to determine the presence of a specific material in the neighborhood, indicating means responsive to said comparisons for indicating presence of said specific material in said ensemble, and means for dilating indications of subareas over regions whose edges have been determined to indicate the presence of said specific material, wherein said dilation makes said regions more prominently noticeable to an operator of said device, and wherein said dilation enhances indication of presence of said specific material.
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63. A device for detecting a specific material of interest in a package or suitcase comprising:
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x-ray source adapted to expose a package or suitcase to x-ray radiation of at least two substantially different energy bands, detector, responsive to said source, adapted to acquire x-ray transmission data through many spatially adjacent points of said package or suitcase at said energy bands, computer adapted to treat said x-ray data spatially as numerous "object" regions and neighboring background regions, where each "object" region is taken as having substantially the same x-ray attenuating properties as a neighboring background region except for the additional presence of unknown material, to process said x-ray data in numerous "object" regions and respective neighboring background regions to characterize at least one x-ray property of the assumed unknown material of the "object" regions with the contribution of background removed, and to compare the determined x-ray property of said unknown material in the "object" regions to the corresponding property of the specific material of interest to determine if the "object" regions are likely to contain the specific material of interest.
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Specification