Abstract:
A personnel x-ray inspection system includes an electron source that provides a pencil beam of electrons. An electromagnet assembly receives the pencil beam of electrons and directs the beam of electrons along a line to form a scanning redirected beam under the control of a scan command signal. The scanning redirected beam strikes a target and generates a cone of x-rays that moves along a target line as a result of the scanning redirected beam. A collimator receives the scanning cone of x-rays and generates a collimated traveling pencil beam, which is directed to a person under inspection. A moving platform translates the person under inspection through the collimated traveling pencil beam. A backscatter detector detects backscattered x-rays, and provides a backscattered detected signal indicative thereof. A system controller provides the scan command signal, and also receives and processes the backscattered detected signal.

Description:
PRIORITY DATA 
     This application claims priority from provisional application designated Serial No. 60/337,299 filed Nov. 5, 2001 and entitled “Personnel Inspection System with X-Ray Line Source”, and is a continuation-in-part of utility patent application Ser. No. 09/897,715 entitled “Imaging With Digital Tomography and a Rapidly Moving X-ray Source”, filed Jul. 2, 2001, now U.S. Pat. No. 6,628,745. Both applications are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to the field of x-ray inspection systems, and in particular to an x-ray inspection for inspecting personnel. 
     The x-ray systems currently used to inspect people are based on using a scanning pencil beam of x-rays to produce an x-ray backscatter image. The pencil beam is formed by two collimators. The first collimator is a fixed slit and the second collimator is a rotating slit. As the rotating slit passes across the fixed slit, a single line of data is formed. For example, see U.S. Pat. No. 3,780,291 entitled “Radiant Energy Imaging With Scanning Pencil Beam” by Stein et al. Subsequent lines of data are produced by translating the entire pencil beam forming apparatus across the body of the person under inspection. These systems typically operate at 70-140 KV peak. 
     A problem with these systems is that they are rather large, and require an x-ray source that includes a rotating collimator. 
     Therefore, there is a need for an improved personnel x-ray inspection, including a personnel x-ray inspection system that includes an x-ray source which provides a collimated traveling pencil beam of x-rays without the need for a moving (e.g., rotating) collimator assembly. 
     SUMMARY OF THE INVENTION 
     Briefly, according to an aspect of the present invention, a personnel x-ray inspection system includes an electron source that provides a pencil beam of electrons. An electromagnet assembly receives the pencil beam of electrons and directs the beam of electrons along a straight line under the control of a scan command signal to form a scanning redirected beam. The scanning redirected beam strikes a target and generates a cone of x-rays that moves along a straight target line as a result of the scanning redirected beam. A collimator receives the scanning cone of x-rays and generates a collimated traveling pencil beam, which is directed to a person under inspection. A moving platform translates the person under inspection relative to the collimated traveling pencil beam. A backscatter detector detects backscattered x-rays, and provides a backscattered detected signal indicative thereof. A system controller provides the scan command signal, and also receives and processes the backscattered detected signal to provide an image signal indicative of the person under inspection. 
     In a first embodiment, the personnel x-ray inspection system includes a rotating base on which the person under inspection stands to rotate the person under inspection relative to the collimated traveling pencil beam of x-rays. In a second embodiment, the system includes a moving platform on which the person under inspection stands to translate the person under inspection longitudinally relative to the collimated traveling pencil beam of x-rays. In this second embodiment, the person is then turned around and translated again through the collimated traveling pencil beam of x-rays. 
     Advantageously, the personnel x-ray inspection system uses a scanning pencil beam, and produces a line of data without requiring any moving parts. In addition, subsequent lines of data are produced without moving the collimator. 
     The pencil beam preferably moves repetitively in a straight line that does not translate as the image is formed. The translation is produced by the motion of the person being inspected. This feature allows the use of a relatively narrow beam catcher for the x-rays. The beam catcher is mounted behind the person and may be a few inches wide by about six feet long. 
    
    
     These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of preferred embodiments thereof, as illustrated in the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a top view of a personnel x-ray inspection system; 
     FIG. 2 is a cross sectional illustration of the collimator; 
     FIG. 3 is a side view of the personnel x-ray inspection system illustrated in FIG. 1; and 
     FIG. 4 is a sectional view taken along line B—B in FIG. 3 to illustrate the x-ray source; 
     FIG. 5 is a perspective view of the x-ray source illustrated in FIG. 4; 
     FIG. 6 illustrates a top view of an alternative embodiment personnel x-ray inspection system; and 
     FIG. 7 illustrates a side view of the embodiment illustrated in FIG. 6; 
     FIG. 8 illustrates the alternative embodiment personnel x-ray inspection system of FIG. 7, with the person under inspection turned around with respect to his position illustrated in FIG. 7; 
     FIG. 9 is a top view of yet another alternative embodiment personnel x-ray inspection system; and 
     FIG. 10 is a side view of the alternative embodiment personnel x-ray inspection system illustrated in FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a top view of a personnel x-ray inspection  10 . The system includes an x-ray source  12 , which includes an electron accelerator  14  that provides a mono-energetic electron beam  16 , for example in the range of about 70 to 200 KeV (preferably 70-150 KeV), which enters a vacuum chamber  18  that includes an electromagnet assembly  20 . The electron beam  16  is deflected across an x-ray anode  22  (e.g., tungsten, gold, et cetera), preferably by an electric field established by the electromagnet assembly  20  operating under the control of a system controller  24 . As the deflected electron beam  16  strikes the target  22  along a straight line, a cone of x-rays is formed that travels rapidly along a straight line. The cone of x-rays is input to slit collimator  26 , which provides a collimated traveling pencil beam of x-rays  28 . 
     FIG. 2 is a cross sectional illustration of the collimator  26 . The collimator includes a row of small holes  27  in a bar (e.g., tungsten, iron or lead) thick enough to absorb the x-ray beam in the area between the holes  27 . In addition, the holes must be deep enough so that the x-rays that are not normal to the collimator  26  do not pass through the adjacent holes (i.e., only one hole in the collimator allows x-rays to pass through the collimator at any time). These holes/slots may be about one (1) mm square. 
     Referring again to FIG. 1, the system  10  also includes an x-ray backscatter detector  30 , arranged adjacent to the collimator  26 . The x-ray backscatter detector  30  preferably includes a scintillating material (e.g., plastic scintillating material) and plurality of x-ray detector elements, such as for example photomultipliers, photodiodes, et cetera. The traveling pencil beam  28  strikes the person under inspection, and backscattered x-rays  31  are detected by the backscatter detectors. As shown, in one embodiment, the backscatter detector  30  is arranged in a semi-cylindrical shape, and a vertical slit  32  bisects the backscatter detector to allow the collimated traveling pencil beam  28  to pass. The backscatter detector  30  provides electrical signals  34  indicative of the detected backscattered x-rays to the system controller  24 , which forms an image. The image may be presented on a display  36  to a system operator. The system  10  also includes a beam catcher  38  positioned to capture x-rays that pass through the person under inspection. 
     The system produces a line of image data along the entire height of the person being inspected. Subsequent lines of data are produced by rotating the body of the person, who is standing on a rotating base  40 , and rescanning the electron beam along the target line to form the vertically traveling pencil beam. The time for a single line of data is approximately 5 milliseconds, so 1000 lines will be produced in 5 seconds. Approximately 500 slots are sampled twice each to form 1000 independent pixels (Nyquist Theorem). The backscatter x-ray image is preferably a “development” of the surface of the human body. Thus, the image is preferably not a picture of the subject, but rather a detailed “map” of the surface of the body. The image is therefore not an invasion of privacy. 
     FIG. 3 is a side view of the personnel inspection system  10 . At time t 1 , the collimated traveling pencil beam  28  strikes the person under inspection at a first position  44 , and at time t 2  the collimated traveling pencil beam  28  strikes the person under inspection at a second position  46 . In general, the electron beam is scanned along a vertical line on the anode  22 . FIG. 4 is a simplified cross sectional illustration of the x-ray source  12  at time t 1  taken along line B—B in FIG.  3 . As shown, electromagnets  48 ,  50  deflect the electron beam  16  such that it strikes the anode  22  (at time t 1  at location  52 ) to generate the cone of x-rays that is collimated to generate the pencil beam  28 . Deflecting the electron beam in a controlled manner so it vertically scans along the vertically arranged target  22  and collimating the resultant cone of x-rays results in the collimated traveling pencil beam  28 . Magnetic steering of an electron beam to generate a scanning x-ray beam to generate a scanning x-ray beam is known (e.g., U.S. Pat. No. 6,009,146 entitled “MEVSCAN Transmission X-ray and X-ray System Utilizing a Stationary Collimator Method and Apparatus” by Adler et al., which is incorporated herein by reference.) 
     FIG. 5 is a perspective view of the x-ray source illustrated in FIG. 4, which illustrates the target line  51  along which the deflected electron beam  16  is controllably scanned. 
     Referring FIGS. 1-5, advantageously the x-ray source  12  is much closer to the subject under inspection than in the prior art. This allows a smaller source strength because of the inverse square law. In addition, the fixed collimator  26  can be placed very close to the subject, which improves the spatial resolution of the image, allowing about a 1 mm resolution. In the prior art, the spatial resolution is of the order of a few mm or more because of the limited strength of the x-ray source. In addition, the maximum exposure to the subject, by FDA rule, is 10 micro-Roentgens, so that the image can only be improved by improving the spatial resolution at the maximum allowed x-ray exposure. 
     An additional advantage is that the x-ray anode  22  requires no cooling because the large area of the target and because the “dwell time” of the electron beam at each point on the target is only about 10 micro-seconds. Furthermore, the solid angle subtended by the backscatter detector 30 is much larger than in the prior art, because of the wrap around geometry, not possible in the prior art. This larger solid angle allows more data to be collected for a given x-ray exposure. 
     Because of the improved design the inspection time can be reduced to about 5 seconds/inspection. 
     While the subject is being rotated, other modes of inspection can be employed via other slits. 
     A problem with the rotating platform  40  is that the radiation exposure to different parts of the body will be different, depending upon the distance from the center of rotation to the surface of the body. In fact the radiation exposure is inversely proportional to this distance. Thus the exposure to the neck will be greater than the exposure to the midsection of the person, and a thin person will receive a larger dose than a fat person. 
     FIG. 6 illustrates a top view of an alternate embodiment personnel x-ray inspection system  70 . The system  70  is substantially the same as the system illustrated in FIGS. 1-5, with the principal exception that the alternative embodiment system  70  employs a moving (i.e., translating) platform  71  that carries the person under inspection across the line of x-rays  28 . The movement of the platform  71  is into and out of the paper. The system  70  also includes a backscatter detector  73 . In this alternative embodiment personnel x-ray inspection system  70  the backscatter detectors  73  are flat to allow passage of the person. The backscatter detectors  73  are preferably arranged on adjacent sides of the passage through which the x-ray pencil beams pass  28 . FIG. 7 is a side view of the system illustrated in FIG.  6 . As the person moves across the line of x-rays  28  as shown in FIGS. 6 and 7, an image of one side of the person is formed. The person then turns around as shown in FIG. 8, and the platform  71  reverses direction to image the other side of the person. Other views, such as a side image can also be taken. 
     The personnel inspection systems of the present invention can be used to uniquely identify a person. The identification techniques may include, for example, measuring a distance between anatomical markers such as width of head or distance between the eyes, and storing an x-ray image of the person in memory and use it as a template for future identification of the person. A person would find it almost impossible to change enough of his anatomy to defeat the system. 
     FIG. 9 is a top view of yet another alternative embodiment personnel x-ray inspection  100 . This system includes first x-ray imaging system  102  and a second x-ray imaging system  104 . The first and second imaging systems  102 ,  104  are positioned on opposite sides of a pathway  105 , and each of the first and second imaging systems is preferably substantially similar to the system illustrated in FIG.  6 . However, in this embodiment, the person to be inspected can walk through the inspection system and be completely imaged, without having to be turned around and reinspected to image other side of the person under inspection. Significantly, a first side  106  of the person to be inspected is imaged by a first scanning pencil beam  108 , while a second side  109  of the person to be inspected is imaged by a second scanning pencil beam  110 . Scattered x-rays  112  associated with the first scanning pencil beam  108  are detected by a first detector  114 , and scattered x-rays associated with the second scanning pencil beam  110  are detected by a second detector  116 . The detectors  114 ,  116  provide electrical signals to the system controller, which provides first and second images, respectively, for display to a system operator. That is, the first image is associated with the first side  106  of the person, while the second image is associated with the second side  109  of the person. The person can walk through and be x-rayed with or without his knowledge. In this embodiment, the translation of the body is accomplished as the person walks by the x-ray scanning pencil beam. Although the translation motion is not as uniform as in the case of a moving platform, a usable image for the purpose of detecting contraband is produced. 
     FIG. 10 is a side view of the alternative embodiment personnel x-ray inspection system illustrated in FIG. 9 taken along line A—A in FIG.  9 . 
     Although the present invention has been shown and described with respect to several preferred embodiments thereof, various changes, omissions and additions to the form and detail thereof, may be made therein, without departing from the spirit and scope of the invention.