Sponsored Links

 
Web LinkGrinder.com

Title: Methods and systems for the rapid detection of concealed objects

Abstract: The present invention provides for an improved scanning process having microwave arrays comprised of microwave transmitters in radiographic alignment with microwave receivers. The microwave array emits controllably directed microwave radiation toward an object under inspection. The object under inspection absorbs radiation in a manner dependent upon its metal content. The microwave radiation absorption can be used to generate a measurement of metal content. The measurement, in turn, can be used to calculate at least a portion of the volume and shape of the object under inspection. The measurement can be compared to a plurality of predefined threats. The microwave screening system can be used in combination with other screening technologies, such as NQR-based screening, X-ray transmission based screening, X-ray scattered based screening, or Computed Tomography based screening.

Patent Number: 7,417,440 Issued on 08/26/2008 to Peschmann,   et al.

Inventors: Peschmann; Kristian R. (Torrance, CA), Mann; Kenneth Robert (Caterham, GB)
Assignee: Rapiscan Security Products, Inc. (Torrance, CA)
Appl. No.: 10/952,665
Filed: September 29, 2004
Related U.S. Patent Documents
Application NumberFiling DatePatent NumberIssue Date
10662778Sep., 2003

Current U.S. Class: 324/637 ; 250/250; 324/639; 324/642; 340/540; 340/691.1; 343/853
Current International Class: G01R 29/08 (20060101); G08B 21/00 (20060101); H01Q 21/00 (20060101)
Field of Search: 324/637,639,642,638 34/638 250/582,250

References Cited [Referenced By]
U.S. Patent Documents
4975968 December 1990 Yukl
5642393 June 1997 Krug et al.
5689239 November 1997 Turner et al.
6026135 February 2000 McFee et al.
6184841 February 2001 Shober et al.
6188743 February 2001 Tybinkowski et al.
6216540 April 2001 Nelson et al.
6288676 September 2001 Maloney
6456093 September 2002 Merkel et al.
6480141 November 2002 Toth et al.
6768317 July 2004 Moller et al.
6876322 April 2005 Keller
6891381 May 2005 Bailey et al.
6894636 May 2005 Anderton et al.
2004/0077943 April 2004 Meaney et al.

Other References

Sheen, David, et al., "Three-Dimensional Millimeter-Wave Imaging for Concealed Weapon Detection", Sep. 2001, IEEE Transactions on Microwave Theory and Techniques, vol. 49, No. 9, pp. 1581-1592. cited by examiner.

Primary Examiner: Gutierrez; Diego
Assistant Examiner: Zhu; John
Attorney, Agent or Firm: PatentMetrix
Parent Case Text


CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation-in-part of U.S. patent application Ser. No. 10/662,778, filed on Sep. 15, 2003 now abandoned.
Claims


We claim:

1. A security scanning system, comprising: a housing; an inspection region located within said housing; a plurality of microwave arrays comprised of more than one microwave transmitters and more than one microwave receivers, wherein said array is in physical communication with said housing, wherein the microwave transmitters and microwave receivers are separated by said inspection region, wherein each of said microwave transmitters transmits microwave radiation to more than one microwave receivers; a data acquisition and imaging system that acquires data from said microwave receivers and generates an image of a concealed object within a container; and radiation shielding in physical communication with the housing, wherein said microwave transmitters emit controllably directed microwave radiation toward said container and wherein said container and its contents absorb radiation in a manner dependent upon their metal content, wherein said data comprises microwave radiation absorption data and wherein said data acquisition and imaging system outputs a measurement of metal content based upon said data.

2. The system of claim 1 wherein said data acquisition and imaging system outputs at least a portion of the volume and shape of the concealed object based upon said measurement.

3. The system of claim 2 wherein said data acquisition and imaging system compares a measurement of said volume and shape of the object to a plurality of predefined threats.

4. The system of claim 1 wherein said security scanning system identifies a container for additional screening if the measurement is different than a pre-defined value.

5. The system of claim 4 wherein the additional screening is selected from any one of NQR-based screening, X-ray transmission based screening, X-ray scattered based screening, or Computed Tomography based screening.

6. The system of claim 1 wherein said data acquisition and imaging system outputs a microwave image based upon the measurement.

7. The system of claim 1 wherein said data acquisition and imaging system outputs positional information of said metal content based upon the measurement.

8. The system of claim 7 wherein said data acquisition and imaging system directs an analysis from material specific detection technology based upon the positional information of metal content.

9. The system of claim 8 wherein said material specific detection technology is selected from any one of x-ray diffraction, thermal neutron analysis or pulsed fast neutron analysis.
Description


FIELD OF THE INVENTION

The present invention relates generally to a microwave imaging system that is compatible with X-ray and Nuclear Quadrupole Resonance (NQR) based methods and systems for detection of concealed threats, and threat resolution, and more specifically to improved methods and systems, using dual stage scanning to process luggage for faster inspection with reduced false alarm rate.

BACKGROUND OF THE INVENTION

Conventional X-ray systems produce radiographic projection images, which are then interpreted by an operator. These radiographs are often difficult to interpret because objects are superimposed. A trained operator must study and interpret each image to render an opinion on whether or not a target of interest, a threat, is present. With a large number of such radiographs to be interpreted, and with the implied requirement to keep the number of false alarms low, operator fatigue and distraction can compromise detection performance.

Advanced technologies, such as dual-energy projection imaging and Computed Tomography (CT), are being used for contraband detection, beyond conventional X-ray systems. In dual-energy imaging it is attempted to measure the effective atomic numbers of materials in containers such as luggage. However, the dual-energy method does not readily allow for the calculation of the actual atomic number of the concealed `threat` itself, but rather yields only an average atomic number that represents the mix of the various items falling within the X-ray beam path, as the contents of an actual luggage is composed of different items and rarely conveniently separated. Thus dual-energy analysis is often confounded. Even if the atomic number of an item could be measured, the precision of this measurement would be compromised by X-ray photon noise to the extent that many innocuous items would show the "same" atomic number as many threat substances, and therefore the atomic number in principle cannot serve as a sufficiently specific classifier for threat versus no threat.

In X-ray CT cross-sectional images of slices of an object are reconstructed by processing multiple attenuation measurements taken at various angles around an object. CT images do not suffer much from the super-positioning problem present in standard radiographs. However, conventional CT systems take considerable time to perform multiple scans, to capture data, and to reconstruct the images. The throughput of CT systems is generally low. Coupled with the size and expense of CT systems this limitation has hindered CT use in applications such as baggage inspection where baggage throughput is an important concern. In addition, CT alarms on critical mass and density of a threat, but such properties are not unique to explosives. CT based systems suffer from high false alarm rate. Any such alarm is then to be cleared or confirmed by an operator, again interpreting images, or hand searching.

Apart from X-ray imaging systems, detection systems based on X-ray diffraction, or coherent scatter are also known. Their primary purpose is not to acquire images but to obtain information about the molecular structure of the substances an object is composed of. The so-called diffraction or coherent scatter signature is based on BRAGG reflection, that is the interference pattern of X-ray light, which develops when X-rays are reflected by the molecular structure or electron density distribution of a substance.

Various inspection region geometries have been developed and disclosed. Kratky, in Austrian Patent No. 2003753 publishes a refined arrangement of circular concentric apertures combined with an X-ray source and a point detector, to gain the small angle diffraction signature of an object placed between the apertures. More recently Harding in U.S. Pat. No. 5,265,144, uses a similar geometry but replaces the point shaped detector aperture with an annular detector configurations. Both patents are incorporated herein by reference.

The resulting diffraction spectra can be analyzed to determine the molecular structure of the diffracting object, or at least to recognize similarity with any one of a number of spectra, which have previously been obtained from dangerous substances.

One approach to detecting explosives in luggage was disclosed in British patent No. 2,299,251 in which a device uses Bragg reflection from crystal structures to identify crystalline and poly-crystalline substances. Substances can be identified because the energy spectrum distribution of the polychromatic radiation reflected at selected angles is characteristic of the crystal structure of the substance reflecting the radiation.

U.S. Pat. Nos. 4,754,469, 4,956,856, 5,008,911, 5,265,144, 5,600,700 and 6,054,712 describe methods and devices for examining substances, from biological tissues to explosives in luggage, by recording the spectra of coherent radiation scattered at various angles relative to an incident beam direction. U.S. Pat. No. 5,265,144 describes a device using concentric detecting rings for recording the radiation scattered at particular angles. Each of the prior art systems and methods, however, suffer from low processing rates because the scatter interaction cross sections are relatively small and the exposure times required to obtain useful diffraction spectra are long, in the range of seconds and minutes. For security inspections, equipment performance has to combine high detection sensitivity and high threat specificity with high throughput, at the order of hundreds of bags per hour.

U.S. Pat. No. 5,182,764 discloses an apparatus for detecting concealed objects, such as explosives, drugs, or other contraband, using CT scanning. To reduce the amount of CT scanning required, a pre-scanning approach is disclosed. Based upon the pre-scan data, selected locations for CT scanning are identified and CT scanning is undertaken at the selected locations. The inventors claim the pre-scan step reduces the scanning time required for each scanned item, therefore increasing throughput. However, the use of CT scanning is still inefficient, not threat specific, and does not allow for rapid scanning of objects.

U.S. Pat. No. 5,642,393 discloses a multi-view X-ray inspection probe that employs X-ray radiation transmitted through or scattered from an examined item to identify a suspicious region inside the item. An interface is used to receive X-ray data providing spatial information about the suspicious region and to provide this information to a selected material sensitive probe. The material sensitive probe, such as a coherent scatter probe, then acquires material specific information about the previously identified suspicious region and provides it to a computer. The disclosed system does not, however, address critical problems that arise in the course of applying a scatter probe to a selected suspicious region, including the accurate identification of a suspicious region, correction of detected data, and the nature of processing algorithms used.

Nuclear quadrupole resonance (NQR) is a contraband material detection device, which has applications in security screening. This technology has shown potential for the detection of a range of materials, in particular it is very effective for the detection of the types of explosives which can be the most challenging to detect using x-rays or CT machines. One potential weakness of the technique is that, with carefully designed electromagnetic shielding, the materials which it is being used to detect can be rendered undetectable. This potential problem is mitigated by the fact that such shielding consists of conductive (typically metal) volumes that must completely encapsulate the item to be detected. Because the items being searched for typically have a size large in comparison with most metal clutter (i.e. keys, coins, zippers, etc) the counter measure can be detected using a variety of metal detection techniques. However, the presence of a conductive loop around luggage means that the simplest forms of inductive metal detector would have limited performance.

Accordingly, there is need for an improved automatic threat detection and resolution system that captures data through an X-ray system and utilizes this data to identify threat items in a rapid, yet accurate, manner. There is also a need for determining the presence of potential shields of explosive materials. There is additionally a need to determine the shielding's size, volume, and position. Furthermore, there is a need for such detection technology to operate within enclosed metallic tunnels. Additionally, the system should provide for greater accuracy in utilizing pre-scan data to identify an inspection region and in processing scan data.

SUMMARY OF THE INVENTION

One object of the present invention is to provide for an improved scanning process having a first stage to pre-select the locations of potential threats and a second stage to accurately identify the nature of the threat. The improved scanning process increases throughput by limiting the detailed inspection to a small fraction of the total bag volume, and it decreases the frequency of false alarms by applying threat specific analysis.

Another object of the invention is to provide for improved processing techniques performed in association with various scanning systems. The improved processing techniques enable the substantially automated detection of threats and decrease the dependence on operator skill and performance.

Another object of the invention is to provide for a method and system to screen for relatively small amounts of threat material.

Another object of the invention is to provide for an improved method and system for screening for metal.

It is an object of the present invention to have a system that is relatively immune interference from metallic clutter items which are typical in bags and packages.

Yet another object of the present invention is to provide a system that is compact and compatible with being built into the structures typical for housing NQR equipment and X-ray or CT equipment.

A further object of the present invention is to provide a conductive volume imaging and detection system which is relatively insensitive to distortions in the image, owing largely to cross talk between different transmit and receive antenna pairs or microwave reflections caused by the presence of metallic clutter or reflections from the equipment housing the system.

A still further object of the present invention is to provide a system that uses an appropriate frequency of operation such that penetration is sufficient for the detection and imaging of objects within typical packages and bags but with a minimal amount of inaccuracies being introduced due to items with high dielectric loss being present within a bag.

A further object of the invention is to provide a system which will provide information which, either alone, or in conjunction with other metal detection techniques can be used to calculate the volume of any region encapsulated by conductive material.

A yet further object of the present invention is to provide a microwave detection and imaging system that can generate metal information in one, two or three axes for display. Images may be displayed for the microwave imaging system alone or overlaid with images from different imaging technologies such as computed tomography x-rays or transmission x-ray imaging systems.

A further object of the invention is a system that provides 3-dimensional positional information, which can be transmitted to complementary detection sensors that can be targeted at volumes within an object that cannot be screened effectively using NQR.

Accordingly, one embodiment of the present invention provides an apparatus for identifying an object concealed within a container. These objects may be considered threats, such as metal, an illegal drug, an explosive material, or a weapon. One embodiment is directed toward an integrated security scanning system, comprising a plurality of microwave arrays comprised of microwave transmitters in radiographic alignment with a plurality of microwave receivers, wherein said array is in physical communication with a housing and radiation shielding in physical communication with the housing. The microwave array emits controllably directed microwave radiation toward an object under inspection wherein said object under inspection absorbs radiation in a manner dependent upon its metal content. The microwave radiation absorption can be used to generate a measurement of metal content. The measurement, in turn, can be used to calculate at least a portion of the volume and shape of the object under inspection. The measurement can also be compared to a plurality of predefined threats.

In one embodiment, if the measurement is different than a pre-defined value, the object under inspection can be ignored by a system operator. Alternatively, if the measurement is different than a pre-defined value, the object under inspection can be selected for additional screening, such as NQR-based screening, X-ray transmission based screening, X-ray scattered based screening, or Computed Tomography based screening.

Optionally, the measurement can be used to generate a microwave image. The microwave image can be combined with an image produced by a technology selected from any one of NQR-based screening, X-ray transmission based screening, X-ray scattered based screening, or Computed Tomography based screening. The measurement can be used to generate positional information of metal content in the object under inspection. The positional information of metal content can be used to direct an analysis from material specific detection technology, such as X-ray diffraction, thermal neutron analysis or pulsed fast neutron analysis.

Optionally, the microwave transmitters and microwave receivers are configured in a plurality of different configurations, such as in a manner that replicates X-ray beam fan beam geometry, X-ray beam folded array geometry, or Computed Tomography array geometry. Optionally, the microwave transmitters are broad beam transmit antennas and microwave receivers are narrow band receive antennas. The broad beam transmit antennas are configured in parallel with said narrow band receive antennas. The broad beam transmit antennas are configured in parallel with said narrow band receive antennas and switched such that each transmit antenna transmits to several receive antennas. The switching occurs to move an illumination point around a region.

The present invention is also directed toward a method of scanning an object comprising the steps of subjecting the object to a first screening system comprising microwave arrays having at least one microwave transmitter in radiographic alignment with at least one microwave receiver and subjecting the object to a second screening system selected from any one of NQR-based screening, X-ray transmission based screening, X-ray scattered based screening, or Computed Tomography based screening. Optionally, first screening system operates concurrent with said second screening system or the first screening system operates serially with respect to said second screening system.

The present invention is also directed toward an integrated security scanning system, comprising a first screening system comprising microwave arrays having at least one microwave transmitter in radiographic alignment with at least one microwave receiver and a second screening system selected from any one of NQR-based screening, X-ray transmission based screening, X-ray scattered based screening, or Computed Tomography based screening. Optionally, the first screening system operates concurrent with said second screening system or the first screening system operates serially with respect to said second screening system.

The aforementioned and other embodiments of the present invention shall be described in greater depth in the drawings and detailed description provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will be appreciated, as they become better understood by reference to the following Detailed Description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic view of one embodiment of the dual stage X-ray scanning system;

FIG. 2 is a schematic view of one embodiment of an X-ray scanning system for the first stage scanning system;

FIG. 3 is a schematic view of one embodiment of the first stage of the X-ray scanning system for identifying a target region;

FIG. 3a depicts exemplary images for identifying the location of an item within a container;

FIG. 4 is a schematic diagram of a cross-section of one embodiment of a preferred beam delivery system for use in a second stage scanning system;

FIG. 5 is a schematic diagram of one embodiment of the beam delivery system of the second stage scanning system;

FIG. 6 is a schematic diagram of an exemplary look up source for transmission spectra;

FIG. 7 is a schematic representation of a beam delivery system having multiple energy dispersive detectors;

FIG. 8 is a graphical representation of an artificial neural network;

FIG. 9 is a flow diagram describing a plurality of steps for practicing one embodiment of the present invention; and

FIG. 10 is a flowchart depicting a process of training the neural network.

FIGS. 11(a), 11(b) and 11(c) are projection drawings depicting a resonator body in a preferred NQR security system as used in the present invention;

FIG. 11(d) depicts a perspective view of the resonator body of the NQR security system in FIGS. 11(a), 11(b), and 11(c);

FIG. 12(a) illustrates the layout of an enclosed resonator probe in a preferred NQR security system as used in the present invention;

FIG. 12(b) is a drawing depicting the inspection volume or cutaway of the enclosed resonator probe in a preferred NQR security system as used in the present invention;

FIG. 12(c) is a drawing illustrating the coil cross-section and shows the magnetic flux path within the resonator body of the NQR system of the present invention;

FIG. 12(d) depicts the equivalent circuit diagram of an enclosed resonator probe in a preferred NQR security system as used in the present invention;

FIG. 13 is a drawing depicting the layout of a NQR baggage scanner having single resonator coil in another preferred embodiment of the NQR system of the present invention;

FIG. 14 is a diagram showing a single tuning mechanism for controlling tuning vanes of two or more resonator probes, in another preferred embodiment of the NQR system of the present invention;

FIG. 15 is a diagram depicting the layout of a dual coil NQR baggage scanner with single tuning mechanism, in another preferred embodiment of the NQR system of the present invention;

FIG. 16 illustrates pathways of transmit/receive pairs in one embodiment of a microwave imaging system of the present invention;

FIG. 17 depicts microwave antenna arrays housed in a system with a complimentary security technology, including, but not limited to an NQR shielding waveguide, X-ray tunnel, or CT tunnel;

FIG. 18 depicts a preferred configuration of multiple antenna arrays in a two-dimensional imaging system;

FIG. 19 illustrates a combined image derived from the image of the microwave imaging system and the image from an X-ray system, in another preferred embodiment of the present invention;

FIG. 20 is an isometric sketch depicting microwave antenna arrays housed in a system with a complimentary security technology, as in FIG. 17;

FIG. 21 is a diagram showing a baggage scanner configured to comprise two novel resonator probes and a transmission X-ray system in another embodiment of the present invention;

FIG. 22 depicts one embodiment of shielding for probes that have a thinned section of conductive material;

FIG. 23 illustrates a transmitted microwave fan beam and a folded array of detectors in a geometry typical of security line scan x-ray systems; and

FIG. 24 depicts an exemplary configuration of transmit/receive antennas used to collect data producing CT images of conductive objects.

DETAILED DESCRIPTION OF THE INVENTION

I. Introduction

The methods and systems described herein are directed towards finding, locating, and confirming threat items and substances. Such threats may comprise explosives such as C4, RDX, Semtex, Seismoplast, PE4, TNT, dynamite, PETN, ANFO among others, as well as other contraband such as drugs. Although the embodiments have been described in the context of a baggage inspection system, it should be evident to persons of ordinary skill in the art that items other than luggage such as other packages, mail, and cargo-containers, or even processed food stuffs, can also be analyzed and screened or graded and that the descriptions are exemplary and are not restrictive of the invention. Further, while the invention is described as a dual-stage system and method, the processing techniques discussed herein can be applied to each of the individual scanning stages.

II. An Overview of the Dual Stage System

Referring to FIG. 1, a dual stage scanning system 100 comprises a housing 130, which encompasses a conveyor system 115 for moving containers, baggage, luggage, or similar object 110 through a plurality of scanning stages 150, 155. A sensor system 165 is connected at the entrance to determine when an object being scanned 110 enters the scan field and communicates with a controller [not shown] to activate or deactivate an X-ray radiation source, 170, 172, as needed. A lead lined tunnel 180 surrounds the conveyor to reduce radiation leakage outside the equipment. At least one radiation source is not expressly depicted in FIG. 1 and would be visible if the system were viewed from the opposite side.

III. A Preferred Embodiment of the Dual Stage System of the Present Invention

a. A Preferred First Stage

Referring to FIG. 2, the first stage 150, comprises two X-ray cameras held together by a support structure 220, such as a frame or yoke, for stability. Each camera consists of an X-ray source 170, 171, a X-ray focusing means, such as a collimating 5 slit comprised of a radio-opaque material, for example lead (not shown), and an array of detectors, 200, 201. In one embodiment, it is preferred that the detectors are configured into a L-shape in order to save space. One of ordinary skill in the art would appreciate that other folded configurations may be acceptable, provided that the detectors are appropriately positioned relative to the inspection region and X-ray source.

Behind each slit collimator, a thin sheet of X-rays 210 is formed. Within the sheet, a fan of pencil beams can be defined, shown as dashed lines in FIG. 2, by connecting lines between the stationary focus, not shown, and channels in the detector array. Between focus and detector is a tunnel 180 through which the luggage is transported or moved using any means known in the art, including, for example, a conveyor 115, the surface of which is depicted in FIG. 2. Wherever in the system radiation has to be transmitted from X-ray sources 170, 171 and through the region defined by tunnel 180, the conveyor belt support structure as well as the tunnel has windows constructed from materials essentially translucent to X-rays. The collimating slits and detector arrays are oriented so that the radiation-fans intersect the main conveyor surface within a few degrees of perpendicular relative to the conveyor surface. The two X-ray sources and their fans point in different directions.

In one preferred embodiment, the detector arrays are mounted on printed circuit boards with a vector positioned normal to their surfaces directed to the X-ray focus. An exemplary printed circuit board has a capacity of 64 channels, and the boards are physically arranged in Venetian blind configuration. The detector arrays consist of linear arrays of silicon photodiodes that are covered with scintillation material, which produces light when exposed to X-rays. The light is detected by the photodiodes that produce corresponding photo current signals. The detectors measure to what degree the X-ray signal has attenuated due to passing through a defined inspection volume. Specifically, the detected data are converted to digital format, corrected for detector gain and offset, and then stored. The required processor means may comprise computing hardware, firmware and/or software known to persons of ordinary skill in the art. When a container under inspection is moving through the tunnel and passing through the X-ray projections, both detector arrays are being sampled repetitively between 50 and 500 times per second. Displaying the line projections on a monitor renders the projection X-ray image.

While a conventional line scan system could be used as the first stage scanning system, it is preferred to use the system as described herein. More specifically, the present invention provides for the placement of at least two X-ray sources such that the directions of the X-ray projections emanating from the sources are mirrored relative to the central vertical plane. Therefore, from the perspective of a view along the path of conveyance through the first stage scanning system, at least one X-ray generator is mounted at a five o'clock position and at least one X-ray generator is mounted at the 7 o'clock position.

One of ordinary skill in the art would appreciate that the first stage scanning system is not limited to the specific embodiments described above and that other variations are included within the scope of this invention. In one alternative embodiment, detector arrays are expanded from a single array to multiple parallel arrays of detectors. In a second alternative embodiment, X-ray projections are taken using two-dimensional pixellated detector planes, without requiring the use of a conveyance means. It should be appreciated that, while the present invention will be further described using a description of the invention based on using the line scan configuration of single stationary foci and single line detector arrays in conjunction with a means of conveyance, the present invention includes other systems and methods that generate X-ray projection images and that such systems and methods can be used in the novel dual stage scanning system disclosed herein.

An alternative embodiment uses dual energy imaging. Dual energy imaging can be utilized to display an image where materials of a metallic constituency are suppressed (not displayed) or materials of an organic constituency are suppressed. Having the ability to selectively display certain materials within images helps reduce image clutter. For example, when inspecting containers for masses or explosives, which have little or no metallic component, the "organic materials only" display is preferred. The dual energy approach can be further refined to automatically discriminate between similar materials of higher and lower relative atomic numbers, such as between a plastic comprised of more lower atomic number atoms like hydrogen and carbon and a plastic comprised of more higher atomic number elements like oxygen and nitrogen; or between aluminum (atomic number 13) and steel (atomic number 26).

In one embodiment, dual energy data is generated by using an X-ray tube with extended spectral emission, which is standard, in conjunction with arrays of stacked detectors, where the first detector is positioned to detect more of the lower energy, or so-called softer X-ray photons, and the second detector is positioned to detect the balance of the energy, namely the higher energy, or so-called harder, photons. The second detector is typically positioned behind the first detector. The low energy and high energy measurements are combined in a suitable way using a series of calibration measurements derived from dual energy measurements taken of identified organic and metallic materials of known thicknesses and result in the display of images, including organic only or metal only images. One of ordinary skill in the art would appreciate that various dual energy line scan systems are commercially available.

It is preferred to use projection imaging as the first stage scanning step in this invention. Features shown in the projection images can be used by an operator to make a final decision on whether items identified in a container represent a threat of some type. Additionally, by taking projections from at least two different angles, it is possible to triangulate the location of a potential threat relative to the physical coordinates of the system and use those coordinates to perform a more specific and focused second stage scan. The triangulation process localizes certain items that generate features of interest in the images and identifies their location in the form of system coordinates.

To perform the triangulation process, the images that form the basis of the triangulation process and that are used to identify a target region are first identified. In one embodiment, the images are analyzed by an operator who visually and approximately determines a plurality of X-ray image characteristics, such as degree of attenuation and projected area, associated with mass, atomic number (identified using image color coding), and shape. Operators also use contextual information, such as an X-ray opaque organic mass in a transistor radio or a suspiciously thick suitcase wall. The analytical process is known to those of ordinary skill in the art and includes the interpretation of X-ray image characteristics.

In another embodiment, images are identified by determining the target regions automatically. For example, where the screening target is a mass of plastic explosive, known algorithms, working on dual energy X-ray projection image data, can be combined to automatically find such target. Examples for such algorithm components include, but are not limited to, edge detection, watershed, and connected component labeling.

Referring to FIG. 3, a container 110 is moved on a conveyor 115 through a tunnel 180 in x-direction, perpendicular to the plane of the Figure. A first X-ray generator 170, C1, with an X-ray emitting focus projects a fan of X-rays 300 through a slit collimator onto an array of detectors mounted on printed circuit boards 200. One of ordinary skill in the art would appreciate that only a small sampling of detectors are shown in FIG. 3 and that a typical system would have a far greater number of detectors, preferably 700 to 800, more preferably 740. As shown, the orientation of the fan plane is perpendicular to the conveyor surface. While a container is being moved along the conveyor surface, the detectors are read out repeatedly, and their signals are converted into digital format by detector electronics that are also mounted on the detector boards 200. The data are being processed and sorted further and stored in a computer [not shown] for display on a monitor [not shown]. Each horizontal line on the monitor corresponds to one particular detector in the array. Therefore, in a system using 740 detectors, the full image is composed of 740 lines.

A second X-ray camera, C2, consisting of X-ray generator 171, slit collimator (not shown) and detector array 201 is mounted in a different orientation, and offset in conveyor direction, by typically 100 mm. The detectors aligned with this camera are sampled essentially simultaneously with the detectors of the first camera and produce a second image displayed on a monitor.

Operationally, an item 340 located within the container 110 is recognized in the course of the first stage scan using a detection algorithm or by operator analysis, depending upon the system mode chosen. With the item 340 identified, the approximate centerline X-ray projections 330, 331 that pass through the object can be determined. Each of the centerlines 330, 331 is associated with a certain detector channel, 310 and 311 respectively in each view.

Referring to FIG. 3a, once the detector channels have been determined, the location of the associated item 340 can be found in the y-z coordinate system. Two images 380, 381 corresponding to the two views are shown. With knowledge of the detectors associated with the centerlines 331, 330 and the range of detectors, 308 to 314, defined, the y and z coordinates of the item 340 can be derived. The x-coordinate is defined by the direction of conveyor motion and is known because the conveyor motion control system, timing of X-ray exposure, and the fixed offset of the two scan planes are known. The x-coordinate can, for example, be referenced to the beginning, or leading edge of the container, which can be detected by a light curtain or similar position-detecting device. In particular, the two images are referenced to each other precisely in the x-coordinate direction.

The purpose of this triangulation or localization of identified items in a container is to generate control commands that can be used to position and focus the inspection region or inspection volume of the second stage scanning system on the identified item. Therefore, the first inspection stage quickly locates potential threats and determines their coordinates, as referenced to the system, while the second stage focuses on better determining the nature of the identified potential threat. It should be appreciated that, because the first stage characterization of a threat is loosely based on features in X-ray images, it will locate, find, and label, as a potential threat, items which are innocuous, in addition to real threats. Therefore, the performance of a detection system based only on the first stage, as described, suffers from a high false alarm rate.

One of ordinary skill in the art would also appreciate that other elements of the first stage scanning system are not depicted in FIG. 1 but would be included in an implementation of the system. For example, a shielding curtain is positioned at both the entrance and exit of the system 100 to protect against radiation leakage to the surrounding environment. The system 100 is controlled by a data interface system and computer system that is capable of rapid, high data rate processing, is in data communication with storage media for the storage of scan data and retrieval of reference libraries, and outputs to a monitor having a graphics card capable of presenting images.

It should also be appreciated that a second stage scan may not be required. In one embodiment, radiographic images from the first stage scan are displayed on a computer monitor for visual inspection with target regions or potential threats identified. An operator may dismiss some of the identified regions or threats based on context, observation, or other analytical tools. If no threats are identified, the container is cleared to exit the inspection system without subjecting it to the second stage of scanning. However, if the operator is unable to resolve an area as being a non-threat, the area is identified as a target region.

b. The Second Stage

The second stage inspection or scanning system closely inspects the identified target locations by deriving more specific information, or a signature, and confirming the first stage threat alarm only if the obtained signature matches the signature of a threat substance or threat item. An alarm confirmed by the second stage system are then taken seriously by operators and indicate the need for further inspection, including, but not limited to, operator image interpretation, additional scanning, and/or hand searching the container.

In a preferred embodiment, the second stage scanning system uses diffracted or scattered radiation to determine the properties of a material, obtain a signature, and, accordingly, identify a threat. Diffracted or scattered radiation comprises photons that have experienced an interaction with the object under investigation. In the special case of small angle scattering, the majority of interactions are elastic or energy-conserving; specifically, the diffracted photon has the same energy as it had before the interaction, just its direction of propagation has changed. If the energy distribution of the scattered photons is being analyzed by an energy-dispersive detector system, which is commercially available, certain properties of the material causing the scatter are being encoded in the signature. Photons scattered under small angles are scattered selectively due to interference effects. Since the process does not change the energy of the photons the signal also contains the distribution of the primary radiation in a simply multiplicative way. The incoming primary radiation, as well as the scattered radiation, encounter further spectral modifications due to other types of interactions, such as Compton scatter and photoelectric absorption, which are not energy preserving. If one wants to view the characteristics of the scattering material, other distracting spectral effects have to be removed.

The detected signature of a threat is therefore a combination of X-ray properties. One important property is a BRAGG diffraction spectrum, observed at small diffraction angles between 2 and 8 degrees, with a preferred value around 3 degrees.

FIG. 4 shows schematically a cross section of a preferred beam delivery system used to obtain BRAGG spectra at small angles. Other beam delivery systems can also be used in the present invention, including those disclosed by Kratky, et al. in Austrian Patent No. 2003753 and Harding in U.S. Pat. No. 5,265,144. The preferred system depicted in FIG. 4 further includes a transmission detector.

A beam delivery system separates the photon radiation emitted by the focus 400 of the X-ray source 404 into a plurality of beams. A beam 401 is formed by passing through apertures 410 and is directly detected by detectors 402, which are within the beam's direct line-of sight. These beams are referred to as transmission beams. Scatter interactions are detected by blocking direct line-of-sight detection through the use of ring apertures 410, 411 and exposing the associated detector 420 only to scattered radiation 492. Therefore, scatter radiation, generated when certain beams interact with an inspection region or volume 445, can be detected in the same apparatus as transmission radiation.

The choice of ring aperture diameters, distance to focus, and distance to detector determines the effective scatter angle 430 of the photons falling on the detector. In one embodiment, the scatter angle 430 is approximately the same for substantially all photons detected by the detector of the scattered radiation. It is preferred to configure the beam delivery system to establish an effective scatter angle of between two and 8 degrees. It is more preferable to have a scatter angle at or about 3 degrees. Using a beam delivery system having a circular symmetry has the advantage of obtaining a scatter contribution from a larger volume of the material being inspected, thereby increasing the inherently weak scatter signal. Additionally, the scatter spectrum can be cost efficiently detected using only a single detector channel 420 with an entrance aperture in the shape of a hole 421.

The scatter signal is generated by positioning the target region 445, identified in the first stage scan, between the beam forming apertures, irradiating that region 445 using the conical beam 442, and making sure scatter radiation from the target region 445 can be detected by the scatter detector. The target region 445, often contained within a container 450, is in the shape of a tube or ring 445 and is referred to as the inspection volume or inspection region. The length, diameter, and wall thickness of the inspection volume depends on the particular shape of the elements of the beam delivery system, including focus size, ring aperture diameter and width, detector opening and overall distance. In a preferred embodiment for the inspection of large luggage, the inspection volume is at or about 60 cubic centimeters.

In a preferred embodiment, as shown in FIG. 5, the components of the beam delivery system are mounted to the open ends of a rigid support structure 500 formed in the shape of a C (referred to herein as a C-arm) and aligned with a tolerance of at or about 0.1 millimeters. A first arm of the C-arm comprises a X-ray tube with X-ray focus 172, a beam limiting aperture hole mounted to the tube head 401, and a ring-shaped aperture 410. A second arm holds comprises a transmission detector array 402, a second ring aperture 411, and an energy dispersive detector 420, equipped with an aperture hole.

The energy dispersive detector 420 is positioned to receive scattered radiation from a target object placed on the conveyor running between the arms of the C-arm support structure where a first arm is above the conveyor and a second arm is below the conveyor. The transmission detector is positioned to receive radiation attenuated by the same target object. It is preferable for the C-arm to be mobile and capable of moving in the x-direction along the length of the conveyor. Therefore, the C-arm with tube and detectors can be re-positioned along the length of the conveyor.

In a preferred embodiment, the scatter detector 420 is comprised of cadmium telluride or cadmium zinc telluride and is operated at room temperature, or approximate to room temperature, An exemplary embodiment is available from the e-V Products Company, Saxonburg, Pa. This type of detector has a spectral resolution performance that is well matched to the limited angular requirements of this application, and therefore the limited spectral resolution of the beam delivery system.

In one mode of operation, the potential threat locations inside a container are found automatically by the first stage, and, based upon the physical coordinates obtained through triangulation, the second stage scanning system is automatically positioned to generate an inspection region that substantially overlaps with the identified target region. Where multiple threat locations are identified, the second stage scanning system is sequentially repositioned to focus on each subsequent target region. To scan each target region, the second stage X-ray source is activated and the scatter detector and transmission detector are sampled simultaneously. In a preferred embodiment, a transmission spectrum associated with the detected transmission data is characterized using a look up reference, figure, table, or chart, and the scatter spectrum is normalized using that identified transmission spectrum.

In another mode of operation, an operator actively identifies images that he or she believes corresponds to a potential threat. X-ray images from the first inspection stage are displayed to the operator, and the operator points to a suspicious object as it appears in both views. To support this functionality, operators use a computer system, comprising a mouse and monitor, to position cross hairs over the areas of interest on each of the images. Using coordinate data generated through triangulation, the second stage scanning system automatically positions itself such that an inspection region overlaps with the target region, activates the X-ray source and simultaneously samples the scatter detector and transmission detector. In a preferred embodiment, a transmission spectrum associated with the detected transmission data is characterized using a look up reference, figure, table, or chart, and the scatter spectrum is normalized using that identified transmission spectrum.

c. The Transmission Detectors

As discussed above, a transmission detector is integrally formed with the beam delivery system, as shown in FIGS. 4 and 5. A preferred transmission detector comprises a 16 channel array of dual energy detectors. The detector array further comprises pairs of detectors, including a low energy channel that receives and measures a first amount of radiation first (low energy) and a high energy channel that receives and measures a substantial portion of the balance of radiation (high energy). Dual energy detection has been described in connection with the linear scan arrays of the first inspection stage and is known to persons of ordinary skill in the art.

The low energy and high energy detectors measure a plurality of low energy and high energy values that can be used to characterize the material being scanned. In a preferred embodiment, low energy and high energy data are used to reference a look up reference, figure, table, or chart (referred to as a look up source) which contains transmission spectra arranged in accordance with corresponding high and low energy values. The look up source is constructed with high energy values on one axis (i.e. the x-axis), and low energy values on a second axis (i.e. the y-axis). Referring to FIG. 6, an exemplary look up source 600 is shown. The source 600 is a graph with high energy values on the x-axis 605 and low energy values on the y-axis 610. Points 615 corresponding to measured spectra 620 are positioned on the graph according to certain linear combinations of the measured high and low dual energy detector signals on the x and y axis.

The transmission spectra used to normalize scatter data is therefore identified by obtaining high energy and low energy data values, identifying the point on the graph corresponding to the detected high and low energy values, and looking up the spectrum associated with that point. Where the detected high and low energy values yield a point on a graph that corresponds to an intermediate point 630 proximate to pre-established points 635, 615, a corresponding transmission spectra 645 can be calculated by performing a two-dimensional interpolation of the spectra 640, 620 associated with the pre-established points 635, 615.

To create the look up source, an exemplary approach places various materials of known composition and thickness, exposes them to X-ray sources, measures the resulting high and low energy data values, and uses the scatter detector to measure the corresponding transmission spectrum. More specifically, the beam path of the beam delivery system is modified to allow a direct beam from the focus through the pinhole to fall on the energy dispersive scatter detector. To further reduce the photon flux into a range that can be tolerated for energy-dispersive measurement, the current of the X-ray source is preferably reduced by a large factor, e.g. 100. Under these parameters, the scatter detector can be used to measure the transmission spectrum. Materials of known composition and thickness are placed in the beam path. The materials are exposed to X-ray radiation. Dual energy measurements are made using the dual energy detectors and a transmission spectrum is obtained using the scatter detector. Through this approach, for each material composition and thickness, a transmission spectrum is obtained and correlated with discrete pairs of dual energy transmission detector readings. This information is then arranged on a chart with the high energy value of the dual energy detector measurement on the x-axis, and the low energy value on the y-axis.

It should be appreciated that, in the disclosed embodiment, the spectra are the looked-up objects of the look up source. Instead of the spectra, however, the look up source can alternatively consist of spectral attenuation functions related to the attenuation of the materials placed in the beam when the look up source is being generated. The spectrum can then be obtained by multiplying one fixed spectrum, for example the spectrum measured without the material placed into the beam, with the spectral attenuation function retrieved from the look up source. Alternatively, the look-up source can contain numbers that are the parameters of analytical expressions, e.g. polynomials, which are formed to describe the attenuation functions in a parametric way.

The presently described approach is preferred because it enables the construction of a transmission detector array from lower cost materials, as opposed to constructing the array using more expensive energy dispersive detectors and support electronics. Moreover, it also addresses the difficult problem of using energy dispersive detectors to measure transmission spectra at the high flux rates that are experienced at the location of the transmission detector in the given configuration and at the same time at which the scatter data are recorded. The required strong attenuation of the transmission beams is a difficult problem that is avoided using the present invention. The look up table is an important element because the preferred dual energy detectors used in the transmission detector cannot deliver spectra directly.

As discussed, transmission spectra are being used to correct the scatter spectra that are being recorded by the energy dispersive detector. Normalizing scatter spectra with transmission spectra corrects for the confounding effects introduced by the specific spectral distribution of the primary radiation, as emitted from the X-ray source, as well as by spectrum-distorting effects known as beam hardening. To correct the scatter spectra, the detected scatter spectra are divided by the looked-up transmission spectra.

A normalized scatter spectrum exhibits a plurality of features. A first feature is that the location of the peaks and valleys of the spectrum are determined by the molecular structure of the materials located in the probe region. A second unrelated feature is that the average spectral signal of the normalized scatter signal, which can be of varying intensity, is linearly related to the gravimetric density of the material in the probe region. This can be used for threat discrimination since most explosives, particularly military explosives, have a density range above that of most other plastic or food items in suitcases.

In one embodiment, the normalized scatter signal is used to identify a threat item by comparing the obtained normalized scatter spectrum and/or spectral signal with a library of scatter signals from known threat items. This comparison can occur automatically by using a processor to compare a library of threat items, stored in a memory, with the obtained scatter signals. Such a library is developed by measuring the normalized scatter signatures of known threat items. In addition to using the transmission detector to generate data used to identify reference spectra, the transmission detector can function in a plurality of other ways. In one embodiment, the transmission detector acts as a position sensor. The transmission beam is interrupted or attenuated momentarily when an object on the conveyor crosses it. Tracking the moment of interruption can provide information on the physical position of the container on the conveyor and be used to appropriately position the beam delivery system or container.

In a second embodiment, the transmission detector array functions as an imaging detector to provide precise attenuation data for certain areas in containers, like container wall areas, where contraband can be hidden. When the circular beam is centered on an edge of a container, the edge of the container can be imaged in good detail, and can help analyze the edges for concealed threats.

In a third embodiment, transmission detector measurements can be used to determine whether the inspection region is, in fact, the same target region previously identified in the first stage scan. If the transmission data correlates with X-ray characteristics different than those obtained in the first stage scan, the relative positioning of the second stage scanning system and the object under inspection may be modified until the transmission data correlates with the same material characteristics that was identified in the first stage scan.

In a fourth embodiment, transmission detector data are also being used to simplify the algorithm-training procedure of the system, as described below, in particular the collection of threat material properties with irregularly shaped threat samples, like sticks of dynamite.

It should be noted that it would appear because the scatter radiation path and transmission path differ downstream from the scatter volume, there would be inconsistencies in the data when scatter and transmission data are combined. This inconsistency is one example of a number of partial volume effects, solutions for which are addressed herein. However, the inconsistencies are not significant and can be tolerated without encountering significant performance degradation of the system as a whole. As shown, FIG. 4 is not an isometric schematic and, in reality, the scatter angle is preferably about 3 degrees, and the real path differences are comparatively smaller.

d. Positioning Inspection Regions

As previously discussed, the second stage scanning system positions an inspection region to physically coincide with the target region identified in the first stage scan. The positioning means may be achieved using any method known in the art. In one embodiment, a plural





DISCLAIMER

Snappy Quick is a free service that searches the Internet and indexes all files found so that you may search quickly and easily for shared files. These files are created and made available individually by users whose identity we are not aware of and who we have no control over. In essence we function like a search engine tool; these files ARE NOT STORED OR SERVED BY OUR NETWORK. We are not responsible for any materials obtained by using our service. We do not monitor any of the contents of these files. These files may contain viruses, illegal materials, materials inappropriate for minors, offensive files and the like. BY USING OUR SERVICE, YOU ASSUME FULL RESPONSIBILITY FOR DOWNLOADING THESE MATERIALS AND WILL INDEMNIFY US FOR ANY DAMAGES THAT MAY BE INCURRED.

For More Specific Information VIEW OUR TERMS OF SERVICE.

Thank you and Enjoy!