Device and method for inspection of baggage and other objects

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 (H.sub.T, L.sub.T) and (H.sub.B, L.sub.B) representing the substantially logarithmic dependence of x-rays absorption when passing through objects, wherein H.sub.T and H.sub.B represent the attenuation of said x-rays at the higher energy band at said test subarea and said nearby subarea, respectively, and L.sub.T and L.sub.B 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 (H.sub.T, L.sub.T) and (H.sub.B, L.sub.B) 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.

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 H.sub.S for substantially all subareas,
• means for pruning to remove subareas with gradient values H.sub.S below a selected gradient threshold,
• means for determining for remaining subareas with gradient values H.sub.S 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 P.sub.S for said remaining subareas,
• means for calculating a ratio H.sub.S /P.sub.S 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 H.sub.S /P.sub.S raised to said power for substantially all of said remaining subareas.

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 H.sub.S for substantially all subareas,
• means for pruning to remove subareas with gradient values H.sub.S below a selected gradient threshold,
• means for determining for remaining subareas with gradient values H.sub.S 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 P.sub.S for said remaining subareas,
• means for calculating a ratio H.sub.S /P.sub.S 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 H.sub.S /P.sub.S raised to said power for substantially all of said remaining subareas,
• means for selecting an alarm threshold on said ratio H.sub.S /P.sub.S raised to said power so that subareas having said ratio H.sub.S /P.sub.S 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.

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 (H.sub.T,L.sub.T) wherein H.sub.T is the logarithm of the attenuation of said x-rays at said higher energy band at said test subarea and L.sub.T 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 (H.sub.B, L.sub.B) wherein H.sub.B is the logarithm of the attenuation of said x-rays at said higher energy band at said nearby subarea and L.sub.B 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 (H.sub.T, L.sub.T) and (H.sub.B, L.sub.B) in determining the presence of said specific material.

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 (H.sub.T,L.sub.T) wherein H.sub.T is the logarithm of the attenuation of said x-rays at said higher energy band at said test subarea and L.sub.T 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 (H.sub.B,L.sub.B ) wherein H.sub.B is the logarithm of the attenuation of said x-rays at said higher energy band at said nearby subarea and L.sub.B 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 (H.sub.T,L.sub.T) and (H.sub.B,L.sub.B) in determining the presence of said specific material.

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 (H.sub.T, L.sub.T) wherein H.sub.T is a function of the attenuation of said x-rays at the higher energy band at said test subarea and L.sub.T 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 (H.sub.B, L.sub.B) wherein H.sub.B is a function of the attenuation of said x-rays at the higher energy band at said nearby subarea and L.sub.B is a function of the attenuation of said x-rays at the lower energy band at said nearby subarea, and employing said values (H.sub.T, L.sub.T) and (H.sub.B, L.sub.B) in determining the presence of said specific material.

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 (H.sub.T,L.sub.T) for said test subarea, wherein H.sub.T is the logarithm of the attenuation of said x-rays at said test subarea at the higher energy level and L.sub.T 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 (H.sub.B,L.sub.B) for said background subarea, wherein H.sub.B is the logarithm of the attenuation of said x-rays at said background subarea at the higher energy level and L.sub.B is the logarithm of the attenuation of said x-rays at said background subarea at the lower energy level, and
• computing the value of K.sub.TB =(H.sub.T -H.sub.B)/(L.sub.T -L.sub.B), and
• comparing said value of K.sub.TB to the value of K.sub.MAT, wherein K.sub.MAT =.mu..sub.H (H.sub.T,L.sub.T,H.sub.B,L.sub.B)/.mu..sub.L (H.sub.T,L.sub.T,H.sub.B,L.sub.B) wherein .mu..sub.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 .mu..sub.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, and
• ascertaining whether said value of K.sub.TB is within a selected window of values of K.sub.MAT, incrementing a respective counter if said value of K.sub.TB 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.

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 (H.sub.T,L.sub.T) for said test subarea, wherein H.sub.T is the logarithm of the attenuation of said x-rays at said test subarea at the higher energy level and L.sub.T 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 (H.sub.B,L.sub.B) for said background subarea, wherein H.sub.B is the logarithm of the attenuation of said x-rays at said background subarea at the higher energy level and L.sub.B 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 P.sub.T with said values (H.sub.T,L.sub.T) wherein said p-value P.sub.T is proportional to the thickness of overlying materials at said test subarea,
• associating a p-value P.sub.B with said values (H.sub.B,L.sub.B) wherein said p-value P.sub.B is proportional to the thickness of overlying materials at said nearby subarea,
• computing the value of .vertline.(H.sub.T -H.sub.B)/(P.sub.T -P.sub.B).vertline.=.DELTA.H/.DELTA.P,
• associating .DELTA.H/.DELTA.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.

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 H.sub.S for substantially all subareas,
• pruning to remove subareas with gradient values H.sub.S below a selected gradient threshold,
• determining for remaining subareas with gradient values H.sub.S 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 P.sub.S for said remaining subareas,
• calculating a ratio H.sub.S /P.sub.S 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 H.sub.S /P.sub.S raised to said power for substantially all of said remaining subareas,
• selecting an alarm threshold on said ratio H.sub.S /P.sub.S raised to said power so that subareas having said ratio H.sub.S /P.sub.S 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.

A device for detecting a specific material of interest in a package or suitcase comprising:

• 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.