US 7929664 B2
CT scanning of transportation containers is performed by generating X-rays at various points at the opposite sides of the containers, detecting the X-rays passing through the containers, and analyzing the data received to determine the presence of contraband. The X-rays are generated by modulating a magnetic field through which a high-energy electron beam passes to deflect the beam successively to different targets positioned around the sides of the container, while the electron beam source remains stationary. The X-rays are detected by an array of cells using X-ray responsive storage phosphor material to emit light which is sent to analyzing and comparing equipment. The targets and detectors and the cargo container are moved relative to one another to scan a selected volume of the container.
1. A transportation container inspection system comprising
(a) a radiation scanner for scanning X-ray beams over a transportation container to be inspected, each of said beams having an energy level sufficient to penetrate said container,
(b) at least one X-ray sensor record member having a surface located at a distance from said container and positioned to receive transmitted X-ray radiation from said container, said record member being capable of storing energy corresponding to said transmitted X-ray radiation and being responsive to stimulating radiation to emit light corresponding in intensity to said stored energy,
(c) a detector for delivering stimulating radiation to said record member and detecting said light emitted by said record member, and
(d) computer analysis equipment for comparing said intensity of said emitted radiation with known reference values to determine the likely composition of a material in said container.
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7. An X-ray scanner including an X-ray generator, said generator comprising:
an electron beam source that generates an electron beam,
a target structure comprising a target for developing X-rays when struck by said beam, said target being spaced from said electron beam source with atmospheric air between said source and said target structure, said electron beam source being mounted to project an electron beam towards said target through said atmospheric air, and said target structure forming a plurality of spaced-apart target areas positioned at different angles relative to said beam source, and including
an electromagnetic field device for forming a magnetic field through which said beam passes, and
an electrical control device for varying said magnetic field so as to deflect said beam selectively towards different ones of said target areas and develop X-rays emitted from said target areas, and to scan said emitted X-rays across a body whose internal features are to be examined.
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10. A CT scanning system for transportation containers, said system comprising
(a) an X-ray scanner for projecting X-rays through said container from a plurality of positions around said container at a plurality of different angles,
(b) a detector structure positioned to detect those of said X-rays which have passed through said container,
(c) programmed computer equipment for comparing signals corresponding to the X-rays detected by said detector structure with known signals representing substances or objects being searched for and indicating a match,
(d) said X-ray scanner comprising at least one electron-beam source, a plurality of target areas spaced around said container, each target area radiating X-rays when hit by said electron-beam, and an electromagnetic field device for creating a magnetic field adjacent said electron beam source and modulating said field to deflect said beam to impinge upon each of said target areas sequentially.
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14. A method of scanning a body whose internal features are to be examined by projecting X-rays through said body at a plurality of different positions around said body and detecting said X-rays after they have passed through said body, said method comprising:
(a) providing an X-ray generator which generates X-rays by directing an electron beam through the ambient air towards a target which emits x-rays when it is hit by an electron beam,
(b) said target comprising a plurality of target areas extending partially around said body, each being made of a material which emits X-rays when struck by an electron beam,
(c) directing said electron beam to strike each of said target areas in succession,
(d) said target areas being positioned relative to said body and one another so that said target areas emit X-rays which pass through said body, and
(e) receiving said x-rays, which pass through said body in X-ray detectors positioned to detect X-rays transmitted through said body and adapted to produce signals indicating the strength of said X-rays passing through different locations in said body.
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22. A CT X-ray scanner for scanning a body whose internal features are to be examined, said scanner comprising
a support structure extending vertically on each of two opposite sides of said body,
two X-ray target members, each secured to said support structure on one of said opposite sides of said body,
each of said target members being curved at least part way around said body,
an electron beam source mounted below said target members,
said source including a controllable deflection system for deflecting one or more electron beams to sweep along said targets to generate X-rays at various points along the paths at which said electron beams strike said target member,
the position of said source, the curvature, dimensions and placement of said target members developing X-ray beams penetrating said body over an angle sufficient to provide a complete CT scan of said body.
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said deflection system being programmed to scan an electron beam along the length of first one and then the other of said target members.
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This patent application claims priority from U.S. provisional patent applications No. 60/901,065, filed Feb. 13, 2007, and 60/901,048, filed Feb. 13, 2007. The disclosures of those provisional patent applications hereby are incorporated herein by reference.
The present invention relates to apparatus and methods for computed tomography (“CT”) scanning.
More specifically, the present invention relates to CT X-ray scanners and methods for scanning relatively large objects or bodies; and to radiation detectors and detection methods for detecting X-ray and other radiation.
In particular, the invention relates to CT scanning and contraband detection in relatively large transportation containers such as standard sealed containers for transporting goods by ocean freight or air freight; land freight carrier containers such as truck bodies, railroad cars and the like; smaller cargo containers shipped on pallets or otherwise, and trunks and other baggage for ocean and airplane travelers, etc.
CT overcomes many problems faced by using conventional two-dimensional radiographs. CT does this by scanning thin slices of the body or other object with a narrow X-ray beam that rotates around the body or object. This produces an image of each slice as a cross section of the body, for example, and can thus show each of the tissues or objects in a slice of width ranging from 0.5 mm-10 mm, with 5 mm being typical.
In contrast to radiography, CT can also differentiate between tissues or objects of similar density because of the narrow x-ray beam and the use of “windowing.” In CT, information acquired can be stored on a digital computer as digital raw data and an image can, for example, be displayed on a video monitor or printed onto x-ray film. Such an image is made up of a matrix of thousands of tiny squares or pixels. A conventional single slice CT image has 262,144 pixels arranged in an array of 512×512 pixels, and 1,048,576 pixels (known as a “Megapixel”) arranged in an array of 1024×1024 pixels is fast becoming common.
The detection of contraband in transportation containers, and particularly in larger containers such as ocean freight cargo containers, air freight cargo containers, etc., presents a long-standing problem. Only a small percentage of such cargo containers are inspected for contraband, such as illegal drugs, explosive devices, illegal weapons, radioactive materials, etc. As a result, such containers present an inviting vehicle for the smuggling of contraband.
When such containers are inspected for contraband, it usually is very labor-intensive and time-consuming to do so. Therefore, it also is relatively expensive to do so. These factors are significant in limiting the amount of inspection which can be done at a tolerable cost.
Accordingly, one of the objects of the invention is to provide a system or device and method for inspecting transportation containers for contraband at a relatively modest cost.
CT scanners are used to perform the non-invasive inspection of objects such as luggage, bags, briefcases, cargo containers, vehicles and the like, to identify hidden contraband at airports, public buildings, roadways and other security checkpoints. The contraband may include hidden guns, knives, explosive devices and illegal drugs, for example.
Computed tomography (“CT”) enables the reconstruction of the cross-sectional images of the cargo contents being scanned, enabling identification of the items in the container. CT images have long attracted much attention in the field of medical diagnosis because they provide a sharp tomographic image of a soft tissue which could not be obtained using conventional X-ray films. CT images also provide higher resolution, better image contrast and greater sensitivity to characteristics of the object being scanned, than radiographs.
While the smuggling of contraband such as guns and explosives onto planes in carry-on bags and in luggage has been a well known, ongoing concern, another serious threat is the smuggling of contraband across land borders by concealment in trucks or automobiles and by boat in large cargo containers. Standard cargo containers are typically 20 to 50 feet (6 to 14 meters) long, 8 feet (2½ meters) high and 6 to 9 feet (6 to 14 meters) wide. Air cargo containers, which typically contain many pieces of luggage or other cargo to be stored in the body of an airplane, may range in size from about 35 by 21 by 21 (around less than 1 meter by 0.7 by 0.7 meter) inches up to about 240 by 118 by 96 inches (6 by 3 by 2½ meters).
Large collections of objects, such as, for example, many pieces of luggage, may also be supported on pallets. Pallets, which may have supporting side walls, may be of a size comparable to cargo containers.
Typical airport scanning systems for carry-on bags have tunnel entrances up to about 0.40×0.40 meters. Scanning systems for checked luggage have only slightly larger openings. Thus, such systems are insufficient to inspect cargo containers because only bags that are small enough to fit through the scanner's tunnel may be inspected. The relatively low energies used in typical X-ray luggage and baggage scanners usually are insufficient to enable the X-rays to pass through the much larger cargo containers. In addition, many such conventional systems operate too slowly to economically inspect larger objects, such as cargo containers. Thus, the art faces a problem in developing a system for scanning large objects efficiently and accurately.
Therefore, another object of the invention is to provide such a system or device and method which provides a relatively accurate and high quality inspection in a relatively short length of time.
A further object of the invention is to provide such a system or device and method which is relatively modest in manufacturing cost, and in costs to operate and maintain.
There have been numerous prior proposals for supplying equipment and methods to serve the same purpose as the present invention. However, it is believed that none of such prior proposals has been fully satisfactory, for a variety of reasons.
Some prior proposals involve the use of X-ray scanning and computer tomography to take many different images of the contents of a cargo container or the like and analyze the images to determine the composition of the materials at various locations within the container.
In one example, it has been proposed that a plurality of X-ray sources be moved on a semicircular track around a container to scan its contents, and that the X-rays passing through the container be detected. This proposal suffers from being very slow and expensive. The X-ray sources tend to be relatively heavy and difficult to move rapidly. Furthermore, because relatively high energy X-rays are required for inspecting large containers, the multiple X-ray sources can be very expensive.
Certain CT scanners have been proposed for producing scans of human patients by using a relatively large, arcuate sheet of phosphor material which records and stores X-radiation which it receives until stimulated by radiation such as laser beams to release visible light in proportion to the strength of the X-radiation received. However, such proposals have not met with wide acceptance for a variety of reasons.
It is one of the further objects of the invention to utilize the beneficial properties of such phosphor material in improved scanning and computed tomography as applied to transportation containers. For such a purpose, a suitable detector has heretofore not been available.
Accordingly, it is another object of the invention to provide such a detector and a method of analyzing the data received by the detector to produce CT scanning of transportation containers.
A further problem with X-ray scanning of transportation containers for contraband is that the radiation used can be harmful to humans or living animals which might be present in the container. In addition, CT scanning usually will not detect radioactive material. Also, CT scanning of empty portions of containers should be avoided to prevent wasted CT scanning time. Therefore, it is an object of the invention to provide a system and method in which these drawbacks, as well as the others mentioned above are resolved.
In accordance with the present invention, the CT scanner generates and directs X-rays from a variety of different points around the circumference of a body whose internal features are to be examined. The X-rays are generated by use of an electron beam source, such as a linear accelerator, cyclotron, or the like, and a control system which guides the electron beam towards a series of target areas located in a path extending around a portion of the body to form X-ray beams at each target area. Those beams are directed at the body, and an array of detector cells is provided in a area where the X-ray beams emerge from the body.
Preferably, each of the detector cells includes a lens or other optical system which focuses light received from a radiation detection surface. The light is focused upon a fiber-optic conductor. The fiber-optic conductors deliver light from the cells to an array of electrical signal responsive devices such as CCD's each of which forms and stores a pixel of an image of the area through which the X-rays passed.
It also is preferred that stimulating radiation be developed to a storage phosphor detector element to read out the light corresponding to the energy stored in the phosphor, and that the stimulating radiation be delivered from a source such as a laser through a fiber-optic conductor to the focal point of the focusing device.
The light then travels through the focusing device such as a lens and is distributed to the surface of the phosphor material. Therefore, both the output and the input light signals flow through the same path.
Also, in accordance with the present invention, the CT scanner is used in detecting contraband in transportation containers by scanning them with high energy X-rays, detecting and analyzing the radiation transmitted through the containers by use of an array of detector cells and computer means to determine whether a particular area inside the container contains material identified as contraband. In effect, the system and method provides a CT analysis of the contents of the container.
The signals detected are compared by a computer with signals representing stored data. The data represents contraband substances such as illegal drugs, explosives, etc. When a match has been found, an alert signal is generated, and a computer image of the area in question is formed. This information is stored for every area of the cargo in which a match is found, and can be used later by inspection personnel to visually and personally inspect the cargo in the area identified by the contraband detection system and method
When one of the areas is detected as containing a material identified as contraband, authorities are notified. Preferably, then, and only then, an image of the area in which the contraband has been located is formed on a screen for use by human inspectors to investigate the potential contraband in person. The location information can be stored and used at a later time after the container has been removed from the CT scanning station so as not to delay the flow of containers through that station.
In one embodiment, discussed briefly above, the detector uses phosphor material which, in effect, stores signals corresponding to the X-radiation it receives. The detector system then delivers stimulating radiation to the phosphor material, which causes the material to emit light in an amount which is a function of the X-radiation it has received. Alternatively, scintillation crystals can be used to detect the X-radiation and emit corresponding amounts of light. The light then is transmitted by fiber optical conductors to the computer analysis equipment.
Preferably, the direction of the electron beam produced by the linear accelerator is controlled by modulating a variable magnetic field through which the beam passes as it emerges from the source. The electromagnetic field can be controlled so as to guide the electron beam successively towards each of a plurality of target areas extending around a part of the periphery of the body to be inspected, such as a cargo container. In effect, this scans the desired container volume without the use of a moving X-ray source, and allows the system to operate at a much higher speed than if the heavy X-ray source had to be moved in order to scan the X-ray beam across the cargo container.
Preferably, the electron beam target areas and detectors are mounted on a frame, which can be in the shape of an arch or other structure extending over and around the sides of the cargo container. The arch can be moved along a track in one direction while the cargo container is stationary. Alternatively, the arch and electron beam source remain stationary and the cargo container is moved through the arch. In either case, the container is scanned by moving the targets and detectors and the container relative to one another.
A separate conveyor or railcar system is provided for the cargo containers themselves to move them up to the scanning position and out of the scanning station when scanning has been completed, or to move them through the stationary arch.
The arch is moved by a pair of gear motors driving the arch structure along guide rails, or by another suitable drive and guidance system. Preferably, the instantaneous position of each end of the arch is sensed accurately by a position detector and the position signals are delivered to a computerized control system to control the position of the arch very accurately.
Similar means can be used to accurately and smoothly move the container through a stationary arch.
A computerized guidance system can be used to keep the electron beam aimed at the target areas, and to ensure that the X-rays are correctly directed to the detectors.
It is within the scope of the invention also to provide an electron beam source which is stationary and whose beam is scanned both along an arc, and also in a longitudinal direction along the director of travel of the arch, to adjust for movement of the arch in scanning the container. Such longitudinal motion can be avoided by securing the electron beam source and the arch together.
Then, the electron beam source can be mounted to travel with the arch or remain stationary while the container moves past.
Although the electron beam can be directed to its targets through the ambient air without a vacuum chamber, a vacuum chamber can be used, or dual electron beam sources can be used, each with a vacuum chamber, to protect the beam from the elements and reduce attenuation.
The inspection station can include preliminary detectors to detect other kinds of problematic cargo in the containers. For example, at a first station, heat detectors can be used to determine whether live human beings or animals are present within the containers. If so, appropriate measures are taken to remove humans, and to remove the animals, if necessary to avoid potential damage by the high energy X-rays delivered at the inspection station.
At another preliminary inspection station, linear X-ray scans can be performed to determine where the empty spaces in the cargo container are so as to avoid CT scanning of areas of the containers which do not need such scanning.
Other preliminary inspection scans can be performed as needed. For example, at a third station, the detection of radioactive materials can be performed by the use of appropriate detection equipment.
The result of the invention is the provision of a CT scanning system and method, and a contraband detection system and method which solves or greatly alleviates many of the problems described above. Therefore, the invention admirably meets the objectives set forth above.
The CT scanning system can be modified and downsized to be used for extremely rapid CT scanning of smaller objects such as baggage and packages, and humans, by adding shielding and other protective structures to prevent deleterious contact between the subjects being analyzed and the electron beams, and reducing the energy levels of the X-rays produced.
The radiation detector, and particularly the one using a stimulatable storage phosphor, is highly advantageous for use with radiation detection in areas outside of CT scanning, and has general utility for that purpose.
The foregoing and other objects and advantages of the invention will be apparent from or explained in the following description and drawings.
The terminal 30 includes a conveyor system 36 with multiple conveyor belts 38, 40 and 42, drive rolls 44 and 46 and drive/idler rolls 48 along its length. The conveyor system is adapted to support and carry the containers 32, 34 from the right towards the left and through the inspection station 30.
A CT scanning station 50 is provided for the detailed scanning of the contents of each cargo container. Also provided are three preliminary scanning stations which are optional but recommended.
At the first preliminary scanning station 60, a thermal camera is provided to detect humans and animals which may be located in the containers. Such humans and animals can be stow-aways, farm animals, illegally captured wild animals, such as monkeys, parrots, etc. It is desired to detect such human and animal life in the containers to remove them and protect them from the high energy X-rays to which the container will be subjected at the CT scanning station 50.
At a second preliminary station 62, conventional X-rays can be used to perform a first scan of the cargo container to determine where the cargo might reside in the container, if it is not full, so as to avoid unnecessary scanning of empty space in the CT scanner, and also to detect potential problem areas for the CT scanner. The results of this preliminary scanning operation can be delivered to a human operator of the CT scanner to enable the operator to limit the area of the container scanned by the CT scanner, or a signal can be sent to the CT scanner to automatically limit the scan zone without human intervention.
At a third preliminary station 64, radiation detectors are provided for detecting radioactive materials in the containers so as to enable their removal, either immediately or later, after the CT scan.
The CT scanner 50 includes an arch 52 with a base support structure 54 or 56 at each of the lower ends of the arch. The arch 52 preferably moves forwardly and backwardly during CT scanning of a stationary container 32 or 34.
When the CT scan is finished, the container 34 moves to the left by means of the conveyor system and is removed to another location by means of a fork lift truck or other lifting and carrying mechanism.
If necessary, the container can be moved to one side out of the way of the other containers so it can be inspected by human inspectors, should the CT scan indicate the necessity for same. Thus, any container suspected of harboring contraband can be inspected without interrupting the flow and inspection of other containers.
If railroad cars are being inspected, tracks can be provided, as disclosed below, leading through the various stations so that the rail cars can simply roll into and out of the terminal on the tracks.
The height and length of the various transportation containers can differ significantly from one another. Accordingly, the CT scanner equipment preferably is made adjustable to accommodate a variety of different sizes of containers, as it will be made apparent in the disclosure to follow.
It should be understood that the structures shown in
The CT scanner 50 is shown schematically in some detail in
Referring first to
As it is shown in
Attached to the web 74 to one side of and parallel to the recess 76 is a strip 78 of metal such as lead or copper which serves as a target strip. As with the recess 76, there is a target strip 78 on each side of the arch 52, as it is shown in
The arch 52 is mounted to be movable along two pairs of guide rails 80, 82, and 84, 86. The support plates 54 and 56 are mounted to slide on the guide rails by means of ball-bearing sleeves 88 so that the arch 52 will move smoothly along the guide rails and will be supported against tipping backwardly or forwardly.
The arch can be moved forwardly and backwardly, by two separate reversible gear motors 90 and 92, one at each side of the arch By this means, the motors 90 and 92 can move the arch, the target strips 78 and the detector arrays back and forth past the container 34 to provide a CT scan of the contents.
Still referring to
It should be noted that preferably the arch 52 is mounted so as to be movable vertically in the directions indicated by the arrows 118 and 120 in
The electromagnetic field control section 96 provides a variable strength electromagnetic field through which the electron beam issuing from the linear accelerator 94 passes. The electromagnetic field can be modulated so as to deflect the beam in a controllable manner towards successive areas of the target strips 78.
Preferably, the linear accelerator issues an electron beam with relatively high energy, e.g. 8 mev to 18 mev, preferably around 9 mev. For example, the Linac Model 3000C linear accelerator sold by Varian Medical Systems can be used.
The target strips 78 are of moderate width and thickness, e.g., 5 cm wide and 1 to 2 cm thick. By making them continuous, rather than separate and discrete targets, different target areas can be selected to properly scan containers of different sizes and shapes.
Referring now to
The X-rays pass through the container 34 because they are of high enough intensity to pass through the metal or other materials of which the container is made, as well as the objects within the container. Some of the transmitted X-rays enter the vertical recesses 76 behind each of which is arranged a linear array 116 of detectors (
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Preferably, the pictures can be saved in computer storage and recalled later when the container has been pulled out of the inspection station and can be manually searched without delaying transit of other containers through the station.
It should be understood that the required angles A and B can be created by tilting the strip 78 as needed, or by positioning the arch 52 relative to the electron beam source appropriately.
It should be understood that several alternative structures and devices can be used instead of those described above.
Other relatively high-energy electron beam sources can be used instead of a linear accelerator. For example, a small cyclotron with magnetic field control; electrostatic accelerators; a betatron and other known accelerators can be used as the electron beam source.
Guide rail and drive structures other than those described above also can be used. For example, instead of the cylindrical guide rails 80, 82, 84, 86, two railroad rails can be used, together with appropriate modifications to the rolling support and drive structure, as it will be described below. Such rails usually are able to support larger loads, without excessive flexing, over longer distances than the cylindrical rails.
A conveyor belt support and drive system is another alternative. However, the conveyor should be carefully constructed to give minimal vibration, in view of the fact that X-rays will be projected as the conveyor moves continuously.
The preferred x-ray detector of the present invention is shown in greater detail in
First referring to
Secured to the inside surface of the thin aluminum web opposite the recess 76 is a sheet or a coating 146 of material containing an electron-trapping storage phosphor material such as one having a strontium sulfide base with one or more dopants such as either cesium or europium. This material has the property that, in reaction to the receipt of X-rays, it stores a signal in an amount proportional to the intensity of the X-rays it receives. Subsequently, when the material 146 is stimulated with radiation at an appropriate wavelength, the material 146 emits energy at a different wavelength, preferably in the form of visible light.
The lens 142 collects the visible light emitted by the material 146. The lens has a very short focal length which enables it to focus the light it receives on the ends of the optical fiber 156 to deliver a light signal to a CCD camera unit 160 and an analyzer unit 162 and a CPU 164 for analyzing the signal, together with others conducted in a similar fashion from the other detector cells that have been struck by an X-ray beam.
Preferably, in order to couple a maximum amount of light to the optical fiber, the divergence angle of the focused spot should be equal to the acceptance angle of the fiber. This means that the focus of the lens is given by the numerical aperture (NA) of the fiber.
The stimulating radiation is delivered by a laser source 158 through the fiber optic conductor 154, at a predetermined small time interval after the X-ray beam has been received.
Advantageously, the stimulating radiation signal is delivered to the focal point of the lens, and the stimulating signal passes through the lens 142 which spreads the beam and distributes the radiation over the surface of the phosphor material.
Preferably, the stimulating radiation is developed by a conventional, readily-available Nd:Yag laser whose output is centered at 1064 nm. Of course, it should be understood that other laser sources could be used instead. However, the wavelength of the excitation radiation should be well separated from the wavelength of the emitted radiation, and should be suited to the particular phosphors used in the sheet 146.
Precautions should be taken to be sure that only the desired radiation is processed. Thus, a filter should be used to eliminate the IR radiation provided by the Nd:YAG laser to stimulate the electron-trapping material (in some cases, the CCD cameras provides an IR filter). Alternatively, the optical fiber may have its maximum spectral response around the green light emitted from the electron trapping material, so the IR radiation is attenuated. Finally, the CCD cameras should operate well in the visible region and can be adjusted for integration times.
A preferred phosphor has the following active ingredients: Strontium sulfide (95.780%); lithium fluoride (4.205%); cerium sulfide (0.013%), and samarium oxide (0.003%). The remainder consists of inert ingredients. This phosphor reacts to both X-ray radiation and visible light. However, because each detector has an opaque metal housing, visible light is excluded and cannot reach the phosphor. There are other phosphors having characteristics like those described above and available for use in practicing the invention. These are well known and need not be listed here.
For the purpose of use in the cargo scanner 50, each cell preferably has an outside dimension of one centimeter. The octagonal exterior shape for the cell housing facilitates aligning and mounting the cells in arrays with numerous rows and columns of cells, if desired.
Smaller cells would be advantageous where greater resolution is needed, such as in medical or baggage scanners.
In a typical installation, there will be two arrays of detector cells, one on each side of the arch 52. Each array covers an angle of 90 degrees plus 15 degrees or 105 degrees total. The total angle D (
It is also possible to have multiple columns of cells side by side, as shown in dashed outline at 166 in
Instead of using the phosphor member 146 as a detector element, it would be possible to use known scintillation crystals to detect the x-rays and emit visible light signals in response. Such crystals do not need simulating radiation to operate. However, the phosphor sheet or coating 146 has the advantage that it stores the signals and will permit delayed retrieval of the light signals, if necessary, and can be much less costly than the crystals. Furthermore, the stimulation signals can be, and are used to enable the detectors at precise instants of time while not having to turn the X-ray generator off and on frequently.
Securing the sheet or coating 146 to the thin aluminum web portion 76 has advantages over mounting it by other means. In
Stimulation signals are delivered over one of the optical fibers 306 or 316 to read out the stored signals, and the light signals read out are delivered over the other set of optical fibers to a CCD array or other utilization means.
If the phosphor used is sensitive to visible light as well as X-rays, the top surface should have an opaque cover over it (also covering the scanning mechanism to prevent false readings due to stray visible light).
Alternatively, the phosphor can be one of the many known phosphors which is sensitive to X-rays but not to visible light.
The detectors shown in
The transverse electromagnetic field bends the electron beam and deflects it to control the direction.
The device shown in
Preferably, the intensity of the beam can be controlled to keep the beam intensity constant, or adjust it to compensate for unwanted deviations.
Preferably, the detectors are computer controlled in accordance with a program that enables the detectors to sample the X-rays transmitted through the cargo container once during each small time interval during each sweep of the electron beam so as to provide, in effect, a rotating X-ray beam source which sweeps the entire cargo container in well under one second. The program adjusts the signals stored in the CCD devices in accordance with variations in the strength of the X-rays due to varying distances of the target areas from the electron beam source, etc., in order to correct for such variations.
The horizontal scale is in milliseconds, and the field varies in strength and polarity from positive to negative and back again to positive.
At the start of a first sweep, at time zero, the field strength at point 192 is at its maximum value, and the electron beam is at its position farthest to the left in
The field strength decreases in curved segment 194 until the beam sweeps to a point represented at 196 where it is about to strike the cargo container.
Since there is no need to move the electron beam slowly over the cargo, in segment 198 the field strength decreases as rapidly as possible and reverses polarity to point 200 at which the beam has been swept to a position where it just misses the right-hand lower corner of the cargo container 34, and then drops at a much slower rate until it reaches the maximum negative value at 202. At this point, the electron beam reverses its path, swinging from right to left, until, at 204, the beam again encounters the right-hand lower corner of the cargo container and increases as rapidly as possible over the segment 206 to the point 208 where it reaches the left-hand lower corner of the cargo container. Thereafter, the field strength increases at a slower rate until the beam reaches the starting position at 210. At this point, the cycle is repeated with the beam sweeping again from left to right. This is repeated as many times as necessary to scan the entire volume of the cargo container.
As it can be seen, the horizontal axis for the graph 188 is divided into segments, each of which is ten milliseconds in width. It is at each of these ten millisecond time intervals that it is desired to sample the X-rays transmitted through the cargo container.
Preferably, the signals 212 and 214 are delayed before operating at point 200 if the transition between point 196 and point 200 requires more than ten milliseconds.
As stated above, the CCD array is programmed to normalize the X-ray signal strength to compensate for varying distances between the beam source and the target areas being scanned.
It should be understood that the time interval and the scan sweep speed can be determined to meet criteria other than those given by way of example here. For example, the time interval of ten milliseconds between sequential samples can be reduced or increased, as needed and desired.
As it is shown in
With the timing illustrated in
Ideally, the cross-section of the electron beam is circular. Preferably, the diameter of the circle is substantially less than the width of the target strip so that the beam produces a maximum intensity of X-radiation at all times.
One problem with such an electron beam is that the electron concentration in the center of the cross-section often is relatively much lower than in the outer portions. In order to make the electron beam density more uniform, it is known practice to vibrate the beam slightly so as to scan it over a very short distance sufficient to spread the electron density more evenly over the cross-section. It is preferred that this vibration be provided for the electron beam used in the present invention.
As it has been noted above, it also is possible for a beam to be deflected out of its intended path slightly or varied in intensity due to changing ambient conditions. This can be corrected by varying the signal delivered to the field producing coils, especially those in the
One preferred mechanism is shown in
The calibrating device is a conventional and well known device used in hospitals, usually once a day, to calibrate X-ray equipment used in the hospital. The calibration unit sends a signal 85 to the control system for the magnetic fields controlling the electron beam and the linear accelerator producing the electron beam to compensate for deviations from the desired standard set earlier in the day. The difference is, however, that the calibration routine can be performed easily and automatically more than once a day. In fact, the routine can be performed for every different cargo container being scanned, and even once at the end of every scan back-and-forth across the arch so as to provide for prompt correction of errors as they may occur.
Another calibration device like device 81 can be positioned adjacent the bottom edge of the left-hand side of the arch 52 as shown in
A second electron beam deflector device is illustrated schematically in
It should be understood that the two sets of coils shown in
Even where the electron beam source travels with the arch, as shown in
By sweeping the electron beam across the targets instead of moving multiple X-ray sources, a large amount of weight is removed from the portions of the scanner which must be moved. This increases the potential speed of operation of the scanner very considerably.
An alternative arrangement for moving the electron beam source as the arch moves is shown in
Still another means for moving the electron beam to accommodate longitudinal movement of the arch 52 is to mount the electron beam source 94, 96 on an axis 95 (
In scanning a desired volume of the shipping container 34 the following method is used.
First, it should be noted that each of the gear motors 90 and 92 has a drive gear 126 (see
Preferably, a shaft position encoder wheel 128 is attached to the output shaft of each motor. The output signals from the encoders are delivered over a line 130 to appropriate servo control equipment so as to provide a very accurate indication of the location of each of the drive motors, and correspondingly accurate control of the speed of movement. Thus, the operation of the two drive motors can be synchronized and controlled very accurately to accurately position the arch 52 and control its speed.
In starting a scan, the drive motors are started and preferably run continuously until the end of a fairly lengthy section of the container has been scanned. This is greatly preferred to stopping and starting the arch structure once for every scan. This eliminates the adverse effects of most of the stopping and starting inertia, reduces vibration, and promotes smooth, rapid scanning operation. If the electron beam source 94, 96 is to be rotated about its axis 95, that also can be done by a suitable drive motor with accurate position indication.
As the arch is moving continuously, the electron beam produced by the source 94 is continuously swept back and forth from one side of the arch to the other, while remaining aimed accurately at the target strip 78. If necessary, electronic tracking devices in common used for tracking moving objects can be used to ensure that the electron beam remains in contact with the moving strips 78 during each sweep.
If a single row of detector cells is used, there is one sweep of the beam from one side of the arch to the other for every centimeter of length moved by the scanning mechanism. The results of these sweeps produce signals representing pixels of images of objects in the cargo container.
After the arch has moved by a predetermined distance, say two or three meters, it is stopped. Then, if it has completed the scanning of a given container, it stops and waits for the next container to be moved into position for scanning. If it has not finished the scan of the first container, but has reached the limit of its motion (such as might be dictated by the maximum angle C permissible as shown in
In this embodiment of the invention, it is preferred that the cargo container be completely stationary while it is being scanned.
An alternative embodiment of the invention is shown schematically in
In order to facilitate this embodiment, means are provided for moving the cargo container 34 in the direction of the arrow 238 shown in
The flatbed rail car can be driven by any of a number of well known drive mechanisms. One such mechanism which is believed to be suitable is that shown in
The cog wheel 228 and the cog rail 236 are shown to one side of the flatbed rail car 220, for simplicity of illustration.
The arch 52 is mounted on a plate 54 which is bolted to a concrete mounting block 218 buried beneath the surface of the earth, as is illustrated in
Another feature is illustrated in
It also should be evident that the railroad tracks 234 can be used to carry standard railroad cars through the arch for inspection as well.
The strength of the flatbed rail car 220 should be sufficient to hold the maximum load expected. Cargo containers typically weigh anywhere from 1 ton to 40 tons.
It also should be understood that the tracks 234 extend well outside of the building 212 in which the inspection equipment is housed. Thus, the flatbed rail car, after passing through the arch and outwardly through the doors 214 on the track 234 can have its cargo container 34 lifted by means of a crane, which then can load the container onto a nearby ship, or otherwise position it for further processing.
If potential contraband has been detected, the crane can move the container 34 to a different location to await actual inspection by inspectors who are guided to look for specific objects in specific areas within the containers. A special siding with tracks branching off from the tracks 234 can be provided for storing containers to be inspected, with the tracks 234 continuing to a station where the containers can be loaded onto a ship. Multiple flatbed cars can be provided for carrying the cargo containers. Also, preliminary inspection stations can be provided as shown and described in connection with
The building 212 housing the inspection station equipment preferably has climate control equipment for controlling the temperature, air pressure, and humidity inside the building.
If the flatbed cars are used to carry motor trucks through the inspection station, the trucks either can be lifted onto the raised flatbed of the rail car by means of a crane, or they can be driven up a ramp and onto the flatbed and rest on the tires of the truck. This is described as an alternative to the system shown in
In another embodiment of the invention, it may be possible to integrate the inspection equipment with a ship loading crane which has equipment for picking up the cargo container and lifting it onto the ship. In this embodiment, it is preferred to move the arch past the stationary cargo container because there is little room to move the container past a stationary arch. Therefore, the invention can make good use of either type of motion.
Although, in the embodiments described above, a single electron beam source sends an electron beam through open air to a target and scans the beam along the target to produce X-rays, it may be preferable to house the target and the electron beam in a vacuum chamber so as to protect the target and the electron beam from the elements and minimize corrections needed. In addition, it may be preferred to use an electron beam scanning system in which neither the arch nor the electron beam source need be raised or lowered to accommodate cargo containers of different sizes.
Referring first to
It should be understood that the arch 256 also could be mounted in a stationary position with a rail system for moving the cargo container 34 through the arch instead, if preferred.
In accordance with one feature of this embodiment, two electron beam sources 262 and 264 are provided, each with a controllable magnetic field structure for scanning an electron beam 274 or 276 along a curved target strip 270 or 272 mounted in a vacuum chamber 266 or 268 formed by an air-tight housing 286 or 288. Each of the electron beam sources and vacuum chambers is secured to one of the upright beams 258 or 260. The lower end of each electron beam source moves in a trench 263 or 265, at least partly below ground.
The two electron beam sources operate in sequence to produce X-ray beams impinging first against the target strip 270 and then against the target strip 272 to form X-rays which scan the cargo container 34 in the manner described above.
Two separate electron beam sources are used instead of one for several reasons.
One reason is that a vacuum chamber for the single electron beam source shown in
A second reason for providing two electron beam sources is that, by so doing, there is no need for the electron beam to clear the body of the cargo container on its way to one of the target strips, as is the case in
Third, it may be possible to reduce the required energy output from each of the electron beam sources by the use of vacuum chambers, and by the constructions used, so that lower power output and hence less expensive electron beam sources can be used.
The use of the vacuum chambers can reduce the attenuation or disturbance of the electron beam by air puffs, etc., on its way to the target.
It should be understood that other structures and electron beam device arrangements can be used to advantage if a vacuum chamber is acceptable and otherwise desirable.
It should be noted that the front panel 287 (see
The construction shown in
As it can be seen in
It should be readily understood by those skilled in the art that the electron beam traveling through air from the linear accelerator to the targets 78 will suffer a substantial amount of attenuation. It can be assured that, even under the worst circumstances, there will be sufficient power to deliver usable X-rays. This is done by the simple expedient of ensuring that the electron beam is of sufficiently high energy. It is believed that the 8 to 18 mev energy levels identified above will be sufficient to give this assurance.
Some variation in the level of energy delivered to the target area from the electron beam may result from changes in the pressure, temperature or humidity of the air in which the CT scanner is operated. These factors can be controlled, to a large extent, by housing the terminal in an air-conditioned, climate-controlled enclosure, and by the use of automatic, frequent re-calibration of the device by the means described above.
To the extent that such control is not completely possible, or in case of variations in power delivered to the targets for other reasons, the power levels, measured in terms of x-ray radiation produced, can be sensed by one or more of the detectors in a given test scan, and control of the energy delivered by the electron beam accelerator can be corrected to compensate for such changes, if necessary.
Alternatively, the computer program analyzing the data detected by scanning the container can be modified to correct for the variations in power level. These correction features can be implemented easily by those skilled in the art.
The CT analysis software used in the invention is readily available to the public and can be freely downloaded from the worldwide web. The only modifications needed are to adapt the software to the system disclosed. Data bases needed for comparison purposes to identify contraband typically are developed for each new item of contraband as it is detected. Some such data bases already are available and can be used in the invention. These uses and developments can be made readily, without undue experimentation, by those skilled in the art.
Programming the computerized beam scanning and control; arch or cargo container movement, automatic calibration and correction features described above also are well within the skill of trained programmers and will not be described in detail herein.
As a result of the invention, CT scanning of transportation containers can be done within a reasonable length of time, and even relatively quickly so as to greatly increase the attractiveness of using the technique to detect contraband. Furthermore, the equipment used is relatively simple and less expensive than equipment previously proposed to be used for the same purpose. Therefore, the invention facilitates a trend towards 100% inspection of cargos before they are loaded on ships, or when they are received, or when they are in transit from one place to another to reduce the use of transportation containers as convenient, relatively safe conveyors of contraband.
The above description of the invention is intended to be illustrative and not limiting. Variations, changes or modifications to the embodiments described may occur to those skilled in the art. These can be made without departing from the spirit or scope of the invention.