Abstract:
A multiview x-ray scanning system for inspecting the 3D volume of an object has been presented. The method uses multiple x-ray sources and multiple x-ray beams. The object to be inspected is interposed in the trajectory of these beams and moved relative to these beams. The x-ray beams after passing through the object are detected by detectors that are interleaved to realize a compact design. In order that the interleaved detectors do not intersect, the location of detectors and sources is adjusted. Further, the design of detectors is such that they can be placed in close proximity to each other in order to realize a small footprint scanner having a high resolution.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention describes a method of using x-rays to inspect an object or a parcel. 
     2. Description of the Related Art 
     X-ray scanners are used for baggage screening as at the airports, for inspection of parts in industrial use, for inspection of food cans by the food industry, and for any other inspection use. A simplified sketch of the conventional x-ray scanner is shown in FIG. l. It uses a single x-ray source  60  which is placed below and to one side of the tunnel  90  as shown. A fan beam  64  from the source  60  then passes through the object or baggage inside the tunnel and impinges on the “L” shaped detectors  611  and  612  which are housed in detector electronic boxes  613  and  614  respectively. The image produced by such a scanner is 2D and lacks the detail needed to inspect the 3D volume of the object. 
     Therefore, to inspect the 3D volume, CT (Computed Tomography) or CAT (Computed Axial Tomography) systems are used. However these systems are not in wide use, as they are large, expensive, consume large power and need heavy duty cabling to be first installed in the room, and are not portable. Therefore to fill the gap between 2D scanners and the 3D CT systems, multi view systems have been developed. 
     A simple multiview system with two views is shown in  FIG. 2 , and another system with two sources and six views as described in U.S. Pat. No. 7,319,737 B2 (Singh), is shown in  FIG. 3 . In  FIG. 2 , for the purposes of brevity, only the electronic boxes are shown. In comparison to  FIG. 1 , two additional boxes  513  and  514  are shown in  FIG. 2 . As is well known to a person skilled in the art, these would correspond to a second x-ray source placed on the other side of the tunnel across from the first source  50  of  FIG. 1 . The width  100  of the detector electronic boxes  613 ,  614 ,  513 ,  514  is usually in the range of twelve to fifteen inches. The addition of extra detector electronic boxes  513  and  514  makes the length  101  of the tunnel  90  longer. 
     Since the images produced from just two views is not sufficient to provide detailed information of a 3D object, more than two view systems have been developed. These multiview systems are three to five view systems. As would be apparent to a person skilled in the art, the addition of third or more views leads to adding more of detector electronic boxes to the system of  FIG. 2 . This leads to a large length of the tunnel which makes the system big. Such big systems are therefore not in use for the inspection of carry on baggage at check points in buildings or at airports where a small footprint is needed. 
     The problem becomes further worse for a system of  FIG. 3  which uses slant beams that require detector electronic boxes to be positioned at oblique angles and where the separation between two adjacent detectors may be much less than twelve or fifteen inches needed to accommodate such wide electronic boxes that the current technology offers. The system of  FIG. 3  uses two x-ray sources  50  and  60 . The beams  54 ,  55  and  56  are associated with the first source  50 , and are detected by detectors  51 ,  52  and  53  respectively. Likewise, the beams  64 ,  65  and  66  are associated with the second source  60 , and are detected by detectors  61 ,  62  and  63  respectively. If such a system were to use wide electronic boxes of  FIG. 1  or  FIG. 2 , the system of  FIG. 3  would become very large and impractical for use in office buildings or where smaller footprint is needed. 
     The objects of this invention are therefore to overcome some of the above problems and are listed next. 
     OBJECTS OF THE INVENTION 
     It is, accordingly, an object of the invention to build a small size, multi view x-ray scanner system for the inspection of objects. 
     It is also an object of this invention to build a compact size scanner with more than two or three views so that a higher resolution and higher performance can be achieved that is needed for 3D inspection of an object, or for explosives detection as required for baggage scanners used at airports. 
     These and other objects will become apparent in the description that follows. 
     SUMMARY OF THE INVENTION 
     A x-ray scanning system for 3D inspection of an object is presented. The system described in this invention is a multiview system that is compact in size and hence would be useful as a check point security scanner for carry on baggage at airports, office buildings, etc. At present, there are no such compact multiview systems and most of the scanners in use today use the old technology that produces 2D images which are not good enough for detecting explosives or object of threats. In order to make a compact multiview system, the preferred embodiment of this invention uses two sources placed on two opposing sides of and below a tunnel through which the object or bag under inspection is conveyed. Each x-ray source emits three fan beams, one beam is perpendicular to the direction in which the bag or object is moved or conveyed through the tunnel, and two other beams are slanting, one towards and one away from the direction of conveyance of the object. In order to make the system compact, the two sources are located such that their beams interleave as they pass through the tunnel. Further, the detectors that detect these beams is such that the position of these detectors is interleaved. In order to realize such a system where the detectors for the various beam do not intersect, the angle of the beams and the vertical distance of the x-ray source beneath the tunnel are adjusted. 
     The existing multiview scanners are extremely large and not used at check points. When the size of the system is scaled down to make a small footprint scanner, the geometries and the spacing of detectors also scale down. This leads to a requirement that the detector electronic boxes needed to detect the various beams be placed with in a few inches of each other. To realize such a system, a new method of detector and electronic assembly is described wherein the electronic cards housing the preamplifiers are placed vertically with respect to the detector. This allows for very narrow detector electronic boxes of two to three inches width compared to the usual twelve to fifteen inches currently used. 
     There are several embodiments, objects and advantages to this invention that will be apparent to one skilled in the art. The accompanying figures and description herein should be considered illustrative only and not limiting or restricting the scope of invention, the scope being indicated by the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the simplified view of a conventional x-ray scanner that produces 2D images. 
         FIG. 2  shows the detector electronics box placement for a two view system. 
         FIG. 3  shows a multi view system with 6 views and 2 sources as described in U.S. Pat. No. 7,319,737 B2 (Singh). 
         FIG. 4  shows a simplified sketch of the system as per one embodiment of this invention. 
         FIG. 5  shows the detector placement on the top of the tunnel for the embodiment shown in  FIG. 4   
         FIG. 6  shows the detector detail within any of the L shaped detector of  FIG. 4 . 
         FIG. 7  shows the novel arrangement of detector and preamplifier electronics that reduces the width of the detector electronics box. 
         FIG. 8  shows the location of three x-ray sources in an alternate embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In describing the preferred embodiment and its alternatives, specific terminology will be used for the sake of clarity. However, the invention is not limited to the specific terms so used, and it should be understood that each specific term includes all its technical equivalents which operate in a similar manner to accomplish similar purpose. 
     A simplified sketch of the preferred embodiment of the invention is shown in  FIG. 4 . An object or bag under inspection,  80 , is moved in the direction  81 , through a tunnel  90  comprising of walls  901 ,  902 ,  903  and  904 . Two x-ray or radiation sources, a first radiation source  50  and a second radiation source  60  are shown located below and on the opposite sides of the tunnel  90 . The x-ray source  50  emits a first radiation comprising of three radiation or fan beams  54 ,  55  and  56  that comprise a first set of beams. These radiation beams are incident on a first set of detectors  51 ,  52  and  53  and their paths of travel from the source to detectors constitute the first set of paths. Further, the beams  54 ,  55 , and  56  are angularly spaced with respect to each other and are detected by the first set of detectors  51 ,  52  and  53  respectively. 
     As shown in  FIG. 4 , the location and orientation of second source  60  are such that its radiation is directed or oriented at an angle with respect to the first radiation from the first source  50 . The three angularly spaced beams  64 ,  65  and  66  comprising the second radiation from the second source  60  are detected by a second set of detectors  61 ,  62  and  63  respectively. The radiation beams emitting from source  60  and incident on detectors  61 ,  62  and  63  constitute a second set of beams and their paths of travel from the source to detectors constitute a second set of paths. As shown in  FIG. 4 , the detectors are placed such that they receive radiation from their associated radiation source along paths that are oriented at different angles. The paths of radiation for detectors  51  and  61  make an angle of 90 degrees with the horizontal since their associated beams  54  and  64  are in the vertical planes. The direction of radiation beams for detectors  52 ,  53 ,  62  and  63  are slanted on either side of the vertical, the magnitude of the angles they make with the vertical may or may not be the same. 
     It should be noted that as shown in  FIG. 4 , the detectors belonging to the first set of detectors are interleaved with those in the second set of detectors. Likewise the first set of beams from the first source  50 , are interleaved with the beams from the second source  60 . 
     As shown in  FIG. 4 , each of the detectors  51 ,  52 ,  53 ,  61 ,  62 , and  63  is like “L” shaped. Each of the “L” shaped detector has a horizontal part which lies on the top surface  901  of the tunnel  90 , and a vertical part that is along the vertical side  902  or  904  of the tunnel as shown in  FIG. 4 . The vertical parts of  51 ,  52  and  53  are along the vertical wall  904  of the tunnel  90 , and the vertical parts of  61 ,  62  and  63  are along the vertical wall  902  of the tunnel. As is well known to a person skilled in the art, each of the detectors is in fact an array of smaller detectors that are oriented towards the x-ray source that is emitting fan beams directed to these detectors. Also not shown to avoid the clutter in the drawings but well known to a person skilled in the art, are the conveyor belt, the rollers, the motors, various other mechanical details, the data acquisition electronics, the computer or image display system and other details required to build such a system. As is well known to a person skilled in the art, the relative translation between the said object and said radiation beams allows one to generate scanned pictures, further the use of multiple beams leads to a generation of multiple views of the object  80  from different angles or orientations, these scanned pictures or multiple views can then be analyzed in order to inspect the object. 
     The arrangement of the horizontal parts of the detectors is illustrated in  FIG. 5 . The horizontal parts of the detectors  51 ,  52  and  53  of  FIG. 4  are shown as  511 ,  521  and  531  respectively in  FIG. 5 . Likewise the horizontal parts of detectors  61 ,  62  and  63  of  FIG. 4  are shown as  611 ,  621  and  631  respectively in  FIG. 5 . It should be noted that for x-ray source  50 , the arrangement of detectors  51 ,  52  and  53  in the first set of detectors is such that they are not parallel to each other. Likewise, for x-ray source  60 , the arrangement of detectors  61 ,  62  and  63  in the second set of detectors is such that they are not parallel to each other. With reference to  FIG. 5 , it is seen that only  511  and  611  are parallel and perpendicular to the sides of the tunnel  90 , these correspond to the central beams  54  and  64  that rise up in vertical planes from sources  50  and  60  respectively as shown in  FIG. 4 . 
     The angular width of the fan beams used in ordinary x-ray scanners is of the order of 60 degrees. With such a wide beam, the vertical height  57  of source  50  in  FIG. 4  is usually in the range 10-15 inches below the belt. For such small distances of sources  50  and  60  below the belt, and the use of such a wide angled beams, the interleaving of beams from two sources as shown in  FIG. 4 , would lead to the intersection of some of the detectors  51 ,  52  and  53  with some of detectors  61 ,  62  and  63 . Therefore in accordance with this invention, the distances  57  of source  50 , and likewise of source  60 , are increased such that for the chosen angles of the slant beams  55 ,  56  or  64 ,  66 , the detectors do not intersect or are too close to each other. It should be noted that by adjusting or varying the distance  57 , in essence the distance between the source  50  and its associated detectors  51 ,  52  and  53  is being changed. Therefore this distance between the source and detectors must not be too small to avoid the intersection of detectors for a two source system of  FIG. 4 . Adjusting the distance between sources and detectors, in such a way to prevent the intersection of detectors, leads to a compact multiview system with a small footprint. 
     Not shown for clarity of the drawings are the collimators associated with each of the detectors. As is well known to a person skilled in the art, these collimators are used to receive beams only from the desired direction, in this case the source the detector is associated with. Collimators are useful in that they eliminate the stray and back scattered x-rays coming from other than the direction of the source and hence lead to higher resolution images. 
     The detail of any one detector is similar to that shown in  FIG. 6  for the detector  51  associated with beam  54  coming from source  50  in  FIG. 4 . The horizontal part  511  of detector  51  is shown to be made of multiple smaller arrays,  5111 ,  5112 ,  5113  and  5114 , each of which is oriented towards the source  50  to maximize the reception or the sensitivity of the detected signal. Likewise, the vertical part  512  of detector  51  has been shown to be comprising of multiple small sized arrays  5121  and  5122 . 
     Also not shown for clarity of the drawings are the detector electronic boxes similar to the ones shown in  FIG. 1  that go along with each of the detectors. These boxes house the preamplifiers and associated electronics that amplify and process the signal sensed by the detectors. The detector electronic boxes currently used are wide flat boxes as shown in  FIG. 1  and  FIG. 2 . Their widths are usually in the range of 12 to 15 inches. However, the distances  85 ,  86  or  87  in  FIG. 5  would only be a few inches for a small footprint scanner and this would make the system of  FIG. 4  unrealizable if such wide detector electronic boxes were to be used. Therefore, this invention presents yet another novel feature of detector and electronics assembly that makes the detector electronic boxes narrow which leads to compact size of the overall system. 
     The novel arrangement of detector and preamplifier electronics, shown in  FIG. 7 , constitutes a novel detector device. In accordance with this invention, the novel detector device comprises of a detector  74  supported on a printed circuit board  71  hereafter called the detector board. The novel detector device further includes at least one preamplifier electronics board. These electronics boards are needed to amplify and further process the signal sensed by the detectors. In  FIG. 7  are shown two preamplifier electronics boards,  72  and  73 . These boards are placed vertically over the detector board  71 . This vertical arrangement of electronics boards over the detector board leads to a very small width dimension  102  of only about a couple of inches or so compared to the 12 to 15 inches of the usual boxes currently being used. The narrow width of the detector electronic boxes thus achieved by this invention, therefore allows the detectors to be placed in close proximity to one another. This allows one to realize the system where the detectors are placed according to  FIG. 4  and  FIG. 5  which in turn leads to a very compact system of high resolution. It should be noted that in the novel detector device of  FIG. 7 , two electronic cards have been shown, but only one or more than two electronic cards can be used. Further, the electronics and detector can be mounted on one flexible board instead and the board bent at right angles so as to make the detectors at right angle to the electronics. Alternatively, the detector and electronics could be mounted on one rigid board such that the plane of electronics is vertical or parallel to the incident radiation beam and the detectors are held by a means such that the detectors are oriented towards the incident radiation beam. It should be noted that the main feature of the novelty is that electronics is arranged or assembled over a plane that is essentially parallel to the incident radiation beam where as in the prior art they were arranged orthogonal or at right angles to the incident radiation. It is however not necessary that the electronics be parallel to or make a zero degree angle to the incident radiation beam, it could make a 45 degree angle to the incident radiation beam thereby realizing half the shrinkage in width of the detector electronic box as this may be acceptable in some situations. This is the same as saying that electronic boards or the plane of electronics should be at an angle substantially different from 90 degrees to the incident radiation beam, the desired angle being zero. 
     It should be noted that it is not necessary to house the detectors in boxes that are arranged in “L” shaped configuration. Instead of two detector electronic boxes, three or more boxes can be used and arranging them such that the detectors are oriented towards the source they are detecting the radiation from. 
     In the preceding discussion, only two sources each with three beams have been used. However, as would be apparent to a person skilled in the art, several variations are possible. One such alternate embodiment uses a third source  70  shown in the end view of the tunnel in  FIG. 8 . As shown, the direction of radiation of the third source is substantially horizontal. The location of the third source can be different from that shown, what is important is that its radiation is directed such that it makes a substantial angle to both the radiation from the first source  50  and that from the second source  60 . Further, instead of 3 beams per source, fewer or more beams can be used. 
     As is well known to a person skilled in the art the data, obtained from the various detectors as described in this invention, leads to generation of views of the object from different angles. These views can be analyzed or combined including the method of laminography or tomography or computer reconstruction to analyze the object under inspection. 
     The foregoing description of the invention and its embodiments should be considered as illustrative only of the concept and principles of the invention. The invention may be configured in a variety of ways, shapes and sizes and is not limited to the description above. Numerous applications of the present invention will readily occur to those skilled in the art. Therefore, it is desired that the scope of the present invention not be limited by the description above but by the claims presented herein.