fig1 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 . fig2 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 fig1 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 . fig3 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 . fig4 is a simplified cross sectional illustration of the x - ray source 12 at time t 1 taken along line b — b in fig3 . 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 .) fig5 is a perspective view of the x - ray source illustrated in fig4 which illustrates the target line 51 along which the deflected electron beam 16 is controllably scanned . referring fig1 - 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 . fig6 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 fig1 - 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 . fig7 is a side view of the system illustrated in fig6 . as the person moves across the line of x - rays 28 as shown in fig6 and 7 , an image of one side of the person is formed . the person then turns around as shown in fig8 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 . fig9 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 fig6 . 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 . fig1 is a side view of the alternative embodiment personnel x - ray inspection system illustrated in fig9 taken along line a — a in fig9 . 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 .
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 .