Abstract:
The inventive body scanner is used to screen persons entering a security controlled area for the presence of security threats hidden under the clothing, such as guns, knifes, explosives and contraband. In one embodiment the body scanner consists of three joined modules, a front module located anterior to the person, a rear module located posterior to the person, and a base module upon which the person stands. The front and rear modules are significantly taller than they are wide, thereby allowing scanning of the full height of a person while providing a narrow-width apparatus. The inherent instability of the tall narrow-width package is overcome by rigidly joining the front and rear modules to the base module. Thus, the Intention provides for a body scanner that is significantly less wide than the prior art.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to the radiant energy imaging of humans to detect weapons, explosives, contraband, and other security threats hidden under the clothing. 
         [0002]    Criminals and terrorists frequently conceal security threats under their clothing, such as handguns, knifes, explosives and illicit drugs. These security threats must be detected on persons entering security controlled areas, such as prisons, airports, government buildings, nuclear power plants, military bases, and the like. Searching individuals by hand is time consuming, often ineffective, and objectionable to both the person being screened and the security officer performing the screening. Electronic imaging systems became commercially available in the  1990 s to facilitate this screening process. These include the model SECURE 1000, sold by Rapiscan Security Products; model SmartCheck, sold by American Science and Engineering; and model ProVision, sold by L3 Communications. These electronic imaging systems are commonly referred to as “body scanners.” 
         [0003]    Body scanners operate by exposing the person being screened to radiant energy, such as millimeter waves or x-rays. A portion of the radiant energy interacts with the person, their clothing, and any concealed objects they may be carrying. This interaction modulates the radiant energy that is reflected from, scattered by, or transmitted through the person. This reflected, scattered or transmitted radiant energy is collected by sensitive detectors, and the resulting electronic signals are routed to a digital computer. Software operating in the digital computer converts the electronic signals into digitally represented images of the person&#39;s body. In these images the clothing is essentially transparent, allowing the security officer to visualize any objects that are concealed under the clothing. 
         [0004]    Prior art body scanners are capable of detecting a wide range of objects concealed under the clothing. However, the human body is complex in shape, and the type of clothing worn by people is diverse and unpredictable. This results in areas of the body where prior art body scanners are ineffective in detecting objects. Of particular concern are the sides of the body and the shoes, where certain types of threats are likely to be missed by prior art systems. Further, prior art body scanners are physically large, and therefore difficult to incorporate into space-limited security checkpoints, such as airports. 
         [0005]      FIG. 1  depicts the operation of one type of prior art x-ray body scanner, such as described in U.S. Pat. Re. 28,544; 5,181,234; and 6,665,373. An x-ray source  10  produces an x-ray beam  11  that is directed at the examined person  12 . The cross-section of the x-ray beam  11  is typically about 6 mm×6 mm where it strikes the examined person  12 . One of three outcomes will be experienced by each individual x-ray in the x-ray beam  11 . First, the x-ray may interact with the body tissue through the photoelectric effect and be annihilated. Second, the x-ray may interact with the body tissue through Compton scattering, which alters its direction of propagation. X-rays that are scattered in the forward direction, that is, into the body, are not useful and are ignored. However, x-rays that scatter in the reverse or backward direction, called backscatter x-rays  20 , carry useful information. Third, an individual x-ray may pass completely through the examined person  12 , or pass around the examined person  12 , without interacting. These are called transmitted x-rays  15 , and also carry useful information. 
         [0006]    The backscatter x-rays  20  are detected by backscatter detector  30  to produce an electronic backscatter signal  35 . Likewise, the transmitted x-rays are detected by vertical transmission detector  18  and floor transmission detector  19 , thereby generating an electronic transmission signal  36 . Both the backscatter signal  35  and the transmission signal  36  are routed into digital computer  60 . As thus described, the instantaneous value of the backscatter signal  35  is a measurement of the backscattering properties of the examined person  12  at the location on the body where the x-ray beam  11  is incident. In a similar fashion, the instantaneous value of the transmission signal  36  is a measurement of the transmission properties of the examined person  12  at the location on the body where the x-ray beam  11  transits through the body. These instantaneous values of the signals are recorded by digital computer  60 . Subsequent measurements are made on all other locations on the body of the examined person  12  by redirecting the x-ray beam  11  to those locations, a technique known in the art as a “flying spot.” As disclosed in the above referenced U.S. patents, this flying spot scanning may be accomplished by a rotating chopper assembly for sweeping the x-ray beam in a horizontal arc, in conjunction with a vertical displacement or rotation of the x-ray source  10 . These apparatus and methods for steering the x-ray beam  11  are well known to those skilled in the art. A control signal  40  synchronizes the data collection of digital computer  60 , allowing it to format the measurements into electronic images. Specifically, the series of measurements appearing in the backscatter signal  35  is formatted into a backscatter image  50 . Likewise, the series of measurements appearing in the transmission signal  36  is formatted into a transmission image  70 . Accordingly, the backscatter image  50  is representative of the modulation produced by x-ray beam  11  being backscattered by the examined person  12 . Similarly, the transmission image  70  is representative of the modulation produced by the x-ray beam  11  being transmitted through the examined person  12 . 
         [0007]    As thus described, the prior art body scanner depicted in  FIG. 1  acquires a backscatter image  50  and a transmission image  70  from a single viewpoint on the anterior or front side of the examined person. That is, the depicted body scanner would be said to be a “single-view, dual mode” system, acquiring a front-backscatter image and a front-transmission image. An important aspect of the prior art body scanner depicted in  FIG. 1 , as it pertains to the present Invention, is that the x-ray source  10  is physically positioned between and/or behind the x-ray detectors  30 . An attribute of this prior art embodiment is that both the transmission image  70  and the backscatter image  50  have a complete field-of-view. That is, the entire examined person  12  appears in the images  50   70  from head to toe, with no regions missing from the image acquisition. In addition, this embodiment operates with stationary detectors  18   19 , thereby avoiding the problem of moving sensitive electronics during the image acquisition. 
         [0008]    A limitation of the prior art embodiment of  FIG. 1  is that the examined person  12  must turn their body to obtain a rear scan. Another limitation of this embodiment is that the shoes are examined with the same apparatus that scans the whole body. That is, the shoes are portrayed in the same backscatter image  50  and transmission image  70  as the front of the body, and not otherwise examined. However, these images of the prior art are not sufficient to detect security threats in the shoes for two important reasons. First, the backscatter image  50  is only a view from an angle generally above and in front of the shoes, and cannot visualize concealed objects hidden underneath the foot, or concealed within the sole and heal of the shoes. Second, the spatial resolution of the transmission x-ray image  70  is too low to adequately inspect the shoes. As known in the art, the spatial resolution of a flying spot imaging system is determined by the cross-section of the x-ray beam  11  where it strikes the examined person  12 . For prior art body scanners this is typically about  6  mm, which is insufficient to resolve the bones in the feet of the examined person  12 . In turn, the insufficiently resolved bones in the feet produce an image clutter that drastically interferes with the visualization of concealed objects. Put in other words, the task of the security operator viewing the image is to discriminate between the normal anatomy of the feet and non-anatomic objects contained in the shoes. If the operator cannot clearly identify the complex pattern of bones in the feet, they cannot distinguish these bones from hidden objects. 
         [0009]    These limitations and attributes of the prior art depicted in  FIG. 1  can be compared with a second embodiment of the prior art.  FIG. 2  is a depiction of another prior art body scanner geometry, in accordance with U.S. Patent Application 2009/0116617. This consists of a front scanner  8  and a rear scanner  7 , which are essentially identical in physical structure. This front-back symmetry allows both backscatter and transmission images to be acquired from both the anterior and posterior viewpoints. For the posterior or rear scanning cycle, rear carriage assembly  80  emits an x-ray beam  11  horizontally, striking examined person  12 . As previously explained, a portion of the x-ray beam  11  will become backscatter x-rays  20 , and a portion will become transmitted x-rays  15 . The backscatter x-rays  20  are detected by a rear-upper detector  31  and a rear-lower detector  32 , and used to create a rear-backscatter image. The transmitted x-rays  15  are detected by a front-upper detector  33 , and used to create a rear-transmission image. As known in the art and disclosed in the above referenced document, the x-ray beam  11  is scanned horizontally in an arc to acquire one line in both the backscatter and transmission images. To complete the vertical component of the raster scan, rear carriage  80  and front carriage  81  move vertically in synchronization, maintaining alignment of the transmitted x-rays  15  with the front-upper detector  33 . 
         [0010]    Because the front scanner  8  and the rear scanner  7  are identical in physical structure, the above operation can be repeated in a mirror image fashion. That is, a front-backscatter image is acquired by emitting an x-ray beam from the front carriage  81 , and detecting backscatter x-rays with front-upper detector  33  and front-lower detector  34 . Likewise, a front-transmission image is simultaneously acquired by detecting transmitted x-rays with upper-rear detector  31 . Accordingly, the prior art body scanner depicted in  FIG. 2  acquires both transmission and backscatter images from both the front (anterior to the examined person  12 ) and rear (posterior to the examined person  12 ), and therefore would generally be called a “dual-view dual mode”system. However, this prior art system does not fully meet this classification, since transmission images from both the front and rear cannot be obtained of the lower legs and feet. The lowermost location on the examined person  12  that will appear in the transmission image is limited by the physical size of the front carriage  80  and the rear carriage  81 . That is, when the carriages  80   81  are in their lowermost position, their respective x-ray beams will be some distance above the ground. Tilting the x-ray beams toward the ground allows for acquisition of complete backscatter images, including the feet. However, no detector is present that is capable of detecting x-rays that are transmitted through the lower legs and feet. In a practical embodiment the lower 12″ to 18″ of the legs will not appear in the images. As before, an important aspect of the prior art body scanner depicted in  FIG. 2 , as it pertains to the present Invention, is that the x-ray source is physically positioned between and/or behind the x-ray detectors. 
         [0011]    As thus described, prior art body scanners are limited in their ability to search persons entering security controlled areas by the number of images they can acquire of each person. At most, prior art systems acquire dual-view dual-mode images, with the transmission images being only partial images. This results in blind areas in detection on the body of the person being screened. Further, the prior art apparatus has a physically large footprint, and therefore is not able to be installed in security checkpoints where floor space is limited. For instance, the apparatus in  FIG. 2  is approximately nine feet wide, with three feet for the width of the rear scanner  7 , three feet for the positioning of the examined person  12 , and three feet for the width of the front scanner  8 . Further, prior art body scanners can scan a person without the person turning their body, as depicted in  FIG. 2 , or they can create complete transmission images of the entire person&#39;s body, as depicted in  FIG. 1 . However, no prior art body scanner can do both in a single apparatus. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    The present Invention overcomes these limitations of the prior art by providing an apparatus and method capable of acquiring improved digital images of the person being screened. In one embodiment this is achieved by viewing the person with radiant energy from three directions: from the person&#39;s anterior side (i.e., the front), from the person&#39;s posterior side (i.e., the rear), and from beneath the person&#39;s feet in the standing position. Further, the present Invention views the person with two modalities ofradiant energy modulation: backscatter and transmission. These tri-view and dual-mode features of the present invention, operating separately or preferably in combination, eliminate the critical blind areas of prior art systems. In one preferred embodiment the present Invention acquires six distinct and complete x-ray images of the person being examined: front- backscatter, rear-backscatter, feet-backscatter, front-transmission, rear-transmission, and feet- transmission. Further, the present Invention achieves this improvement while reducing the physical size of the apparatus compared with the prior art. 
         [0013]    It is therefore the goal of the present Invention to provide an improved method and apparatus for detecting security threats concealed under the clothing of a person entering a security controlled area. Another goal of the invention is to provide additional images of the person being examined to eliminate blind spots where security threats may be concealed. Yet another goal is to provide complete images of the entire body, thereby further eliminating blind spots. Still another goal is to more throughly inspect the shoes worn by the person. A further goal is to provide a physically compact apparatus that occupies less floor space in the security checkpoint. Yet another goal is to obtain anterior and posterior images in rapid succession, with complete a complete field of view on both the backscatter and transmission images. Still another goal is to provide a body scanner with stationary detectors, while not requiring the person to turn their body during the examination. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a depiction of the prior art. 
           [0015]      FIG. 2  is a depiction of the prior art. 
           [0016]      FIG. 3  is a depiction in accordance with the physical structure of the present Invention. 
           [0017]      FIG. 4A  and  FIG. 4B  are depictions in accordance with the present Invention. 
           [0018]      FIG. 5  is a depiction in accordance with the transmission image of the present invention. 
           [0019]      FIG. 6A  and  FIG. 6B  are depictions in accordance with the operation of the present invention. 
           [0020]      FIG. 7A ,  FIG. 7B ,  FIG. 7C , and  FIG. 7D  are depictions in accordance with the operation of the present invention. 
           [0021]      FIG. 8  is a depiction in accordance with one aspect of the present invention. 
           [0022]      FIG. 9A ,  FIG. 9B ,  FIG. 9C , and  FIG. 9D  are depictions in accordance with one aspect of the present Invention. 
           [0023]      FIG. 10  is a depiction in accordance with one aspect of the present invention. 
           [0024]      FIG. 11  is a depiction in accordance with one aspect of the present invention. 
           [0025]      FIG. 12  is a depiction in accordance with one aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]      FIG. 3  depicts the overall physical structure of a preferred embodiment of the present Invention. The body scanner  100  generally comprises a base assembly  200  measuring approximately 60″ by 60″ by 4″; a front assembly  300  measuring approximately 13″ by 60″ by 9 6 ″ inches; and a rear assembly  400  measuring approximately 13″ by 60″ by 96″. The examined person  12  stands on the base assembly  200  centered between the front assembly  300  and the rear assembly  400 . The front assembly  300  is joined with the base assembly  200  by front connection  309 . Likewise, the rear assembly  400  is joined with the base assembly  200  by rear connection  409 . The front and rear connections  309   409  are preferably removable fasteners that can be connected or disconnected at will, such as bolts, clamps and tie downs known in the art. This facilitates movement of the body scanner  100  from one location to another by disassembly into three easily transported assemblies  200   300   400 . 
         [0027]      FIG. 4A  and  FIG. 4B  are a more detailed depiction of a preferred embodiment of body scanner  100 . Front assembly  300  comprises a front x-ray detector  320 , which is stationary, and a front x-ray source  310 , which translates in the vertical direction during the front scanning cycle  610 . Likewise, rear assembly  400  comprises a rear x-ray detector  420 , which is stationary, and a rear x-ray source  410 , which translates in the vertical direction during the rear scanning cycle  620 . The base assembly  200  comprises a base x-ray detector  220  and a base x-ray source  210 , both of which translate horizontally during the base scanning cycle  630 . 
         [0028]    As depicted in  FIG. 4B , the screening of the examined person  12  comprises three scanning cycles executed sequentially. In one embodiment the sequence starts  600  by executing a front scanning cycle  610 . At the beginning of the front scanning cycle  610  the front x-ray source  310  is at its lowermost position within the front assembly  300 . During the scanning cycle  610 , lasting about  3  seconds in a preferred embodiment, the front x-ray source  310  translates from its lowermost to its uppermost position within the front assembly  300 . At the beginning of this motion the front x-ray source  310  starts emission of a front x-ray beam  301 . As previously described and known in the art, the front x-ray beam  301  is a flying spot configuration. That is, front x-ray beam  301  is a narrow beam of x-rays that are swept in a horizontal arc. A portion of the front x-ray beam  301  will interact with the body of examined person  12  and become the front-backscatter x-rays  302 . These front-backscatter x-rays are detected by front x-ray detector  320  and the information used to create the front-backscatter image  370 . A portion of front x-ray beam  301  is transmitted through examined person  12  where it is detected by rear detector  420 , and the information used to create the front transmission image  380 . The rear scanning cycle  620  begins at the completion of the front- scanning cycle  610  and is essentially a mirror image. That is, the rear x-ray source  410  moves from its lowermost to uppermost position within rear assembly  400  while emitting a rear x-ray beam  401 . Rear-backscatter x-rays  402  from the rear x-ray beam  401  are detected by rear detector  420  and the information used to create rear-backscatter image  470 . Likewise, the portion of the rear x- ray beam  401  that is transmitted through the examined person  12  strikes the front x-ray detector  320 , and is used to create the rear-transmission image  480 . 
         [0029]    The base scanning cycle  630  begins at the completion of the rear scanning cycle  620 . During the base scanning cycle  630  the base x-ray source  210  moves horizontally within the base assembly  200  from a position behind the examined person  12  to a position in front of the examined person  12 . Concurrently, the base x-ray source  210  emits a base x-ray beam  201 , upward through the shoes and feet of the examined person  12 , at an angle of approximately  45  degrees with the vertical. Base-backscatter x-rays  202 , which are scattered from the base x-ray beam  201  by the shoe and/or foot of examined person  12 , are detected by base detector  220 , and the information used to create the base backscatter image  270 . The portion of the base x-ray beam  201  that is transmitted through the shoes and feet of the examined person  12  is detected by the front detector  320 , and the information used to create base transmission image  280 . The scanning sequence ends  640  at the completion of the base scanning cycle  630 . 
         [0030]      FIG. 4A  depicts an important advantage of the present Invention over the prior art: a comprehensive inspection of the shoes of the examined person  12 . This is critically important since the shoes are a common hiding place for weapons, explosives, contraband, and the like. The preferred embodiment of the present Invention provides images of the feet within all four of the main body images: front-backscatter  370 , front-transmission  380 , rear-backscatter  470 , and rear transmission  480 . However, the inspection of the shoes in these images may not be adequate for all security inspection applications, for the same reasons described for the prior art configuration depicted in  FIG. 1 . A significant advantage of one embodiment of the present Invention is the inclusion of a dedicated scanner to examine the shoes for concealed objects. Base-backscatter image  270  is obtained from beneath the shoes, thereby detecting security threats hidden underneath the foot, in the soles of the shoes, and in the heals of the shoes. Further, because of the close proximity of the base x-ray source  210  to the shoes, the cross section of the base x-ray beam  201  is only about 1.5 mm×1.5 mm where it intersects the shoes. This results in a 1.5 mm spacial resolution in both the base backscatter image  270  and the base transmission image  280 . This factor of four improvement in spacial resolution, compared to any of the images in the prior art, enables discrimination between the bones in the feet and concealed objects in the shoes. That is, the close placement of the base x-ray source to the shoes overcomes the inadequacies of the prior art. 
         [0031]      FIG. 5  depicts the characteristics of the front and rear transmission images  380   480 . The transmission background  555  corresponds to the region around the examined person  12  where no objects exist in the imaging area. In this region the x-ray beams  301   401  propagate unaffected from the x-ray sources  310   410  to the x-ray detectors,  420   320 , respectively. The presence of this region in the transmission images  380   480  is important because it informs the security officer inspecting the image that no security threats reside in this area. As known in the art, this information cannot always be obtained from the backscatter images  370   470  due to an ambiguity related to the physics of backscatter x-rays. In particular, this area around the body in backscatter images  370   470  appears black because there is no material to scatter the x-rays. Likewise, metal objects appear black in backscatter images  370   470  because the high atomic number material strongly absorbs x-rays by the photoelectric effect. This results in both metal and the background appearing black, with little or no ability to discriminate between the two. However, the background  555  of the transmission images  380   480  has no such ambiguity, and allows full detection of metal objects. 
         [0032]    The region representing the examined person  12  in the transmission images  380   480  can be divided into two sections. The first consists of areas on the body where the x-ray beams  301   401  encounter less than a few inches of tissue on their path through the body of the examined person  12 . This includes the feet  551 , the forearms  552 , and about one-half inch around the periphery of the body  553 . The second is those areas on the body where the x-ray beams  301   401  encounter more than a few inches of tissue on their path through the body, that is, highly attenuated areas  550 . As known in the art, the signal-to-noise ratio of a transmitted x-ray beam is greatly diminished when the beam becomes highly attenuated. Unlike medical radiography where the allowable incident radiation levels are quite high, body scanners must use a minuscule level of radiation for the upmost safety. Therefore, even though the x-ray beams  301   401  do penetrate the highly attenuated areas  550  to some extent, the signal-to-noise ratio of the respective detected signals is too low to create a usable image. This results in the highly attenuated areas  550  of the transmission images being of little use for detecting concealed objects. However, this is of little consequence, since this is exactly the region where the backscatter images  370   470  excel in concealed object detection. This illustrates a fundamental strategy and advantage of the present Invention: images are acquired from up to three views with two modalities such that the relative limitations of any one image are overlapped and overcome by the relative strengths of another image. As known in the art, the dividing line between the highly attenuated areas  550  and the remainder of the image is not abrupt, but gradual in nature. The distinctness of the border depicted in  FIG. 5  is for explanatory purposes only, and those skilled in the art of x-ray imaging clearly understand the nature of this transition. 
         [0033]    In comparison, the feet  551 , the forearms  552 , and the periphery of the body  553  are regions of the body where backscatter images  370   470  often fail to detect concealed objects. This failure occurs for a variety of reason. One reason is the ambiguity between background and metal previously discussed, since the periphery of the body  553  is adjacent to the transmission background  555 . Another reason is that small objects can be concealed in the closed hands, under the soles of the feet, or within the structure of the shoes. Still another reason is the ability to conceal objects in an arm pit or between the arm and the side of the body. In all of these cases the concealed object is hidden from backscatter inspection by an inch or two of overlaying body tissue. In summary, the transmission images  380   480  excel at detection of concealed security threats in the transmission background  555 , the hands and forearms  552 , and the periphery of the body  553 . On the other hand, the transmission images provide little or no detection capability in the highly attenuated areas  550 , and only partial capability in the shoes and feet  551 . In comparison, the backscatter images provide excellent detection in the highly attenuated areas  555 , but generally poor detection everywhere else. Lastly, the base transmission image  280  and the base backscatter image  270  close the remaining gap in detection, providing high resolutions images of the feet and shoes. 
         [0034]      FIG. 6A  and  FIG. 6B  depict top views of one preferred embodiment of the present Invention. As previously described, prior art body scanners have their x-ray sources located between and/or behind their detectors. In contrast, one preferred embodiment of the present Invention employs a unique positioning of x-ray sources and detectors to achieve a number of advantages. As depicted in  FIG. 6A  and  FIG. 6B , this unique positioning involves five objects, the examined person  12 , the front x-ray source  310 , the rear x-ray source  410 , the front x-ray detector  320 , and the rear x-ray detector  420 . The front x-ray source  310  and the rear x-ray source  410  being jointly referred to as the x-ray source pair  310   410 . Likewise, the front x-ray detector  320  and the rear x-ray detector  420  are referred to jointly as the x-ray detector pair  320   420 . The unique positioning being the x-ray source pair  310   410  being horizontally located between the x-ray detector pair  320   420 , and the examined person  12  being horizontally located between the x-ray source pair  310   410 . Described in other words, the location of the five objects, in order from the posterior to the anterior sides of the examined person  12 , are: rear x-ray detector  420 , rear x-ray source  410 , examined person  12 , front x-ray source  310 , and the front x-ray detector  320 . 
         [0035]    In one preferred embodiment, as depicted in  FIG. 6A  and  FIG. 6B , the x-ray detectors  320   420  are wider on the sides of the x-ray sources  310   410 , and become narrower behind them. In another preferred embodiment the detectors  320   420  are the same width their entire length, essentially the same width as depicted in  FIG. 6A  and  FIG. 6B  behind the x-ray sources  310   410 . The distinction in these two cases being the particular internal construction of the x-ray detectors  320   420 . For instance, as known in the art, x-ray detectors can be formed from a light tight enclosure lined with fluorescent screens, with large diameter photomultiplier tubes mounted on the interior. The wider part of the x-ray detectors  320   420 , as shown in  FIG. 6A  and  FIG. 6B , are useful to enclose the photomultiplier tubes in this particular detector construction. Alternatively, as known in the prior art, x-ray detectors  320   420  can be constructed from sheets of plastic scintillator with smaller diameter photomultiplers mounted on the ends. In this construction the x-ray detectors  320   420  are a uniform width as needed to house the plastic scintilator sheet, typically a few inches. The important point being that the x-ray detectors  320   420  extend behind, i.e., outside of, the x-ray sources  310   410 , as depicted in  FIG. 6A  and  FIG. 6B . 
         [0036]    The front scanning cycle  610  of the preferred embodiment is further explained in  FIG. 6A . X-ray source  310  emits a front x-ray beam  301 , in the direction of the examined person  12 . Interaction of the front x-ray beam  301  with the body of the examined person  12  results in front-backscattered x-rays  302 , which are detected by front x-ray detector  320 . The portion of the front x-ray beam  301  that is transmitted through the examined person  12  is detected by rear x-ray detector  420 . During the front scanning cycle  610 , the front x-ray beam  301  is repeatedly swept in an arc  306 , as depicted by the front x-ray beam  301  successively moving to a second position  303 , a third position  304  and a fourth position  305 . As known in the art, this beam sweeping motion provides the horizontal component of the flying spot raster scan. During the front scanning cycle  610 , x-ray source  310  moves from a lowermost position to an uppermost position, thereby providing the vertical component of the flying spot raster scan. The information from the front x-ray detector  320  and the rear x-ray detector  420  is used to create the front-backscatter image  370  and the front-transmission image  380 , respectively. In one preferred embodiment, during the front scanning cycle  610  the rear x-ray source  410  is positioned above the head of the examined person  12 , thereby placing it out of the field-of-view of the front backscatter image and the rear backscatter image. In this manner the front scanned images have a complete field of view with no missing regions. 
         [0037]    As depicted in  FIG. 6B , the rear scanning cycle  620  is carried out in a mirror image fashion to that of the front scanning cycle  610 . The rear x-ray source  410  emits a rear x-ray beam  401  that sweeps in an arc  406  as represented by a second position  403 , a third position  404  and fourth position  405 . The rear-backscatter x-rays  402  are detected by rear x-ray detector  420 , and the information used to create rear-backscatter image  470 . The portion of the rear x-ray beam  401  that is transmitted through the examined person is detected by front x-ray detector  320 , and the information is used to create the rear-transmission image  480 . As previously described, the sweeping motion of the rear x-ray beam provides the horizontal component of the raster scan of the flying spot, and the vertical motion of the rear x-ray source  410  provides the vertical component. As generally explained above, in one preferred embodiment the front x-ray source  310  is located above the head of the examined subject  12  during the rear scanning cycle  620 , thereby allowing the rear transmission image  480  and the rear backscatter image  470  to have a complete field-of-view. 
         [0038]    The unique positioning of the x-ray sources  310   410 , x-ray detectors  320   420 , and the examined person  12 , depicted in  FIG. 6A  and  FIG. 6B , has numerous advantages over the prior art. First, the apparatus is extremely compact, with a front-to-back width of only about five feet, compared with approximately nine feet in the prior art. This width reduction allows the present Invention to be used in security checkpoints with limited floor space, whereas the prior art body scanners simply would not fit. Second, it enables scanning of both the anterior and posterior sides of a stationary person, while obtaining a complete field-of-view on both the backscatter and transmission images. As previously discussed, prior art systems are unable to achieve both of these advantages in a single embodiment. Third, the overall placement of the components facilitates the incorporation of a base assembly  200 , containing a shoe scanner. 
         [0039]      FIGS. 7A-D  further explain the operation of one preferred embodiment of the present Invention.  FIG. 7A  depicts the location of the front x-ray source  310  at the initiation of the front scanning cycle  610 . The front x-ray source  310  is at its lowermost position within the front assembly  300 , with a rotation  571  that directs the front x-ray beam  301  downward at an approximate  45  degree angle with respect to the vertical. At this initial location, the portion of the front x-ray beam  301  that passes through the feet and shoes of the examined person  12  is detected by the base detector  220 . As the front scanning cycle proceeds, as depicted in  FIG. 7B , the front x-ray source  310  moves upward  570  and rotates  571 , while the base detector  220  move horizontally  572 . These motions  570   571   572  are synchronized such that the front x-ray beam  301  is continually detected by the base detector  220 .  FIG. 7C  depicts that the detection of the front x-ray beam  301  is transferred from base detector  220  to rear detector  420  during the scanning cycle  610 .  FIG. 7D  depicts the location of the front x-ray source  310  at a time later in the front scanning cycle  610 , where the rotation  571  has place the front x-ray beam  301  essentially horizontal. For the remainder of the front scanning cycle  610  the front x-ray beam  301  remains essentially horizontal. In one preferred embodiment shown in  FIG. 7  A-D, during the course of the front scanning cycle  610  the rear x-ray source  410  is positioned above the head of the examined person  12 , such that it does not interfere with the front transmission image  380  or the front backscatter image  370 . During the subsequent rear scanning cycle  620 , the operations described for the front scanning cycle  610  are duplicated in a mirror image fashion. 
         [0040]      FIG. 8  depicts a top view of another embodiment of the present Invention. The base detector  220  moves a shorter distance in this embodiment, about  14  inches, being just long enough to acquire a base-backscatter image  270  and a base-transmission image  280  of the shoes. A base rear detector  430  is mounted within the base assembly  200  between the most rearward position of the base detector  220  and the rear detector  420 . Acting together, these three detectors  420   430   220  detect the complete field-of-view for the front transmission image  380 . Likewise, a base front detector  330  is provided to obtain a complete rear transmission image  480 , acting in conjunction with the base x-ray detector  220  and the front x-ray detector  320 . 
         [0041]      FIG. 9  A-D depicts another preferred embodiment where two shoe scanners are provided, one for each of the two shoes worn by the examined person  12 . The base scanning cycle  630  of this embodiment begins with both the left shoe x-ray source  230  and the right shoe x-ray source  231  in the rear position, as depicted in  FIG. 9A . The left shoe x-ray source  230  emits a left shoe x-ray beam  260  upward in the same geometry as previously described in  FIG. 4  for base x-ray source  210  and base x-ray beam  210 . In accordance with the flying spot technique previously described, the left shoe x-ray beam is repeatedly swept in an arc  206 , depicted by a second position  261 , a third position  262 , and a fourth position  263  of the x-ray beam  260 . Left shoe x-ray source  230  is simultaneously moved horizontally  207 , as depicted in  FIG. 9B , thereby mapping out a left shoe field-of-view  290 . In the second portion of the base scanning cycle  630 , as depicted in  FIG. 9C  and  FIG. 9D , the right x-ray source repeats this process. That is, the right shoe x-ray beam  265  is swept in an arc depicted by second  266 , third  267  and fourth positions  268 , while the right shoe x-ray source  231  is moved  209  from back to front thereby defining a right shoe field-of-view  291 . During both the left and right portions of the base scanning cycle  630 , the front detector  320  detects transmitted x-rays and the base detector  220  detects backscatter x-rays as previously described. 
         [0042]      FIG. 10  depicts another preferred embodiment of the present Invention. Front detector  320  comprises a front-left detector  321  and a front-right detector  322 . Likewise, rear detector  420  comprises a rear-left detector  421  and a rear-right detector  422 . A front connecting member  351  rigidly connects the front x-ray source  310  with a front vertical motion actuator  350 . Likewise, a rear connecting member  451  rigidly connects the rear x-ray source  410  with a rear vertical motion actuator  450 . X-ray sources used in the art typically weight about 30 pounds, requiring the front and rear connecting members  351   451  to preferably be steel or aluminum bars of about 0.25″ thickness. Therefore, the gap between the front-left detector  321  and the front-right detector  322 , and the gap between the rear-left detector  421  and the rear-right detector  422 , is preferably about 0.75″, providing sufficient clearance for the vertical movement of the components. That is, the front vertical motion actuator  350  provides support and vertical motion to the front x-ray source  310  through front connecting member  351 . Likewise, the rear vertical motion actuator  450  provides support and vertical motion to the rear x-ray source  410  through rear connecting member  451 . In this embodiment, the front beam emission centerline  355  has a front horizontal offset  357  from the examined person centerline  590 , by about 0.5 inches. Likewise, the rear beam emission centerline  455  has a rear horizontal offset  457  from the examined person centerline  590 , by about 0.5 inches. That is, the front image acquisition is shifted about 0.5 inches to the examined person&#39;s right, while the rear image acquisition is shifted about 0.5 inches to the examined person&#39;s left. 
         [0043]      FIG. 11  depicts another aspect of this preferred embodiment. During the front scanning cycle  610 , depicted in the right half of  FIG. 11 , the front x-ray source  310  moves upward in the front assembly  300 , as previously described. In this embodiment, the rear x-ray source  410  is positioned vertically such that there is a first controlled vertical height  390  where the front x-ray beam  301  passes the rear x-ray source  410 . Likewise, during the rear scanning cycle  620 , depicted in the left half of  FIG. 11 , the front x-ray source  310  is positioned vertically such that there is second controlled vertical height  490  where the rear x-ray beam  401  passes the front x-ray source  310 . The vertical distance between the first and second controlled vertical heights  390   490  being a vertical scanning offset  580 . 
         [0044]      FIG. 12  depicts the purpose and advantage of the described vertical and horizontal offsets. The right half of  FIG. 12  depicts the front-transmission image  380  while the left half shows the rear- transmission image  480 . The gap between rear-left detector  421  and rear-right detector  422  appears in the front transmission image  380  as a front-blind-vertical-region  379 , where no image information has been obtained. Likewise, the gap between front-left detector  321  and front-right detector  322  appears in the rear transmission image  480  as a rear-blind-vertical-region  479 , where no image information has been obtained. For positional reference, the examined person&#39;s centerline  590  appears in the transmission images  380   480  at the centerline-imaged-position  592 . The left side of the examined person  12  appears in the transmission images  380   480  as denoted by the upper case “L”  392   492 , and the right side by the upper case “R”  393   493 , respectively. In the front transmission image  380 , the front horizontal offset  357  causes the front-blind-vertical-region  379  to be offset  376  from the centerline-imaged-position  592 . Likewise, in the rear transmission image  480 , the rear horizontal offset  457  causes the rear-blind-vertical-region  479  to be offset  476  from the centerline-imaged-position  592 . That is, the horizontal offsets  357   457  in the imaging apparatus result in corresponding offsets  376   476  in the images  380   480 , respectively. However, the offsets  376   476  in these two image  380   480  occur in opposite directions from the centerline-imaged- position  592 . That is, one is to the examined person&#39;s left  392   492 , and one to the examined person&#39;s right  393   493 . In a front transmission image  380 , the rear x-ray source  410  appears as a first blind area  372  at a first image height  371  that corresponds to the first controlled vertical height  390 . Likewise, in the rear transmission image  480 , the front x-ray source  310  appears as a second blind area  472  at a second image height  471  that corresponds to the second controlled vertical height  490 . 
         [0045]    The horizontal vertical offset  581  being the difference between these two, and corresponding to the vertical scanning offset  580 . 
         [0046]    Near the horizontal center of the transmitted images  380   480 , the front x-ray beam  301  and the rear x-ray beam  401  transverse approximately the same path through the imaging area, but in opposite directions. Therefore, the front and rear transmitted images  380   480  contain essentially the same information near their horizontal centers. As depicted in  FIG. 12 , the blind areas  372   379  of the front transmission image  380  occupy a different region than the blind areas  472   479  of the rear transmission image. Therefore, the combination of the two transmission images  380   480  contains full and complete information, just as if the blind areas  372   379   472   479  did not exist. In other words, this embodiment of the present Invention provides for small gaps between the detectors, and also provides for the non-imaging x-ray source to be within the field-of-view, while still obtaining full and complete transmission image information. 
         [0047]    Although particular embodiments of the Invention have been described in detail for the purpose of illustration, various other modifications may be made without departing from the spirit and scope of the present Invention. The radiant energy emission, typified by they use of x-rays, may be other forms of radiant energy, such a gamma rays, millimeter waves, terahertz waves, charged and uncharged particles, acoustic waves, and so on. The detectors may be constructed with scintillator materials and light detectors; ionization chambers; solid state devices such as germanium and cadmium zinc telluride; and other detector technologies known in the art. Generation of the flying spot beam may be accomplished by rotating disks or drums, other forms of movable apertures, moving focal spot x-ray tubes, or other methods of controlling radiant energy known to those skilled in the art. The front, rear and base scanning cycles may be conducted in different sequential orders. Acquisition and manipulation of the various electronic images is in accordance with the broad fields of analog electronics, digital electronics, and digital image processing, with many known techniques and methods that one skilled in the art will recognize as being within the spirit and scope of the present Invention.