Abstract:
A storage phosphor cassette for use in recording radiographic images of elongated objects. The cassette includes first and second storage phosphor plates having first and second length dimensions; a shell having first and second opposite open ends; a first assembly for detachably mounting the first storage phosphor plate in the shell from the first open end; and a second assembly for detachably mounting the second storage phosphor plate in the shell from the second open end, wherein the first and second storage phosphor plates are mounted in the shell such that they form a substantially continuous storage phosphor composite for recording an elongated radiographic image. An elongated ruler is located on the inside or outside of the cassette, the ruler being x-ray translucent and opaque to produce an image of the ruler in the first and second storage phosphor plates.

Description:
FIELD OF THE INVENTION 
     This invention relates in general to medical imaging and more particularly relates to the use in computed radiography (CR) of an elongated CR cassette for imaging elongated body regions, such as the full spine or the leg. 
     BACKGROUND OF THE INVENTION 
     Conventional size radiographic image acquisition units are limited in size and unsuitable for imaging elongated body regions such as the full spine or the leg. The largest conventional radiographic film and radiographic computed radiography plates used in chest radiography are 35×43 cm. (14×17 in.). When it is necessary to obtain a radiographic image of a full spine or leg, several approaches have been used. If film/screen technology is used, either an extra long, non-standard radiographic film is used, or as disclosed in U.S. Pat. No. 3,774,045, issued Nov. 20, 1973, inventor Trott and U.S. Pat. No. 3,725,703, issued Apr. 3, 1973, inventor Bucky, cassette or cart is provided for holding a plurality of overlapping conventional sized film cassettes or packs. In the case of a special elongated film, the cost of the film and its processing is substantially greater than the cost of the conventional sized film. In the case of multiple film solutions, the films must be taped together to obtain the full length radiographic image. This introduces overlap and alignment problems. 
     Similar solutions have been proposed when computed radiography plates are used. Thus, U.S. Pat. No. 5,130,541, issued Jul. 14, 1992, inventor Kawai discloses a self enclosed CR unit using elongated CR plates that are exposed, read, erased and reused within the unit. U.S. Pat. No. 5,111,045 discloses a self enclosed unit using conventional sized CR plates that are exposed, read, erased and reused within the unit. When an elongated body region is imaged, first and second overlapping CR plates are positioned at the exposure station, exposed and then processed. Both of these solutions are disadvantageous in the use of an expensive, heavy, self-enclosed unit that is unsuitable for use when a patient is unable to use the unit due to physical disability or when admitted to a hospital emergency room, intensive care unit or surgical suite. 
     EP Patent application EPO 919856A1, published Feb. 6,1999, inventor Dewaile et al. discloses an assembly for recording a radiographic image of an elongated body including a plurality of CR cassettes holding conventional sized CR plates that are held in staggered arrangement so that the length of the staggered arrangement is equal to at least the length of the elongated body. After exposure, the CR plates are read individually and the read electronic images are stitched together to form the entire image of the elongated body. This technique is disadvantageous in requiring the use of a special assembly to hold the CR cassettes. U.S. Pat. No. 5,986,279, issued Nov. 16, 1999, inventor Dewaile, discloses an elongated CR cassette holding a plurality of overlapping or non-overlapping CR screens. After exposure, the CR screens are removed from the elongated cassette, put into “normal” sized cassettes, and applied to a read out device that is able to read out normal sized cassettes. This technique is disadvantageous in the time and expense involved in loading and unloading the elongated cassette as well as in the subsequent handling of individual CR cassettes to enable CR screen readout. 
     It is also desirable that an effective and cost efficient process be provided to align read out sub-images for accurate composite image generation. 
     There is thus a need for a solution to these problems. 
     SUMMARY OF THE INVENTION 
     According to the present invention, there is provided a solution to the problems of the prior art. 
     According to a feature of the present invention, there is provided a storage phosphor cassette for use in recording radiographic images of elongated objects comprising: first and second storage phosphor plates having first and second length dimensions; a shell having first and second opposite open ends, a first assembly for detachably mounting said first storage phosphor plate in said shell from said first open end; a second assembly for detachably mounting said second storage phosphor plate in said shell from said second open end, wherein said first and second storage phosphor plates are mounted in said shell such that they form a substantially continuous storage phosphor composite for recording an elongated radiographic image; and an elongated ruler located on the inside or outside of said cassette, said ruler being x-ray translucent/opaque to produce an image of said ruler in said first and second storage phosphor plates. 
     ADVANTAGEOUS EFFECT OF THE INVENTION 
     The invention has the following advantages. 
     1. Radiographic images of an elongated object can be made in a single exposure using conventional size CR plates. 
     2. The CR plates are exposed to a radiographic image in the same plane, obviating the need for stacking multiple cassettes and performing complex corrections or multi-plane images. 
     3. The CR plates are not handled manually and are read automatically thus minimizing degradation of the CR plate and resultant image degradation. 
     4. A process is provided for aligning sub-images for accurate composite image generation. 
     5. The composite image can be constructed automatically without human intervention. The composite image construction software only requires a prior knowledge that a scoliosis/elongated body image should be generated. Providing to the image processing software the exam information is consistent with current CR image processing algorithms. In the prior art, a technologist is required to interact with the image processing software via a workstation user interface to select and sequence the images that are to be digitally stitched into a composite. 
     6. Embedded in the composite image is a human readable reference for distance that can be used by the radiologist or clinician for qualitative assessments, which provides absolute distance measurement and is invariant to image viewing methods. 
     7. Because the image is at most 2× size of a standard 2500 pixel×2000 pixel image, the composite image can be automatically routed and printed on a single sheet of film at full resolution using a standard 5K×4K laser printer, e.g., Kodak 2180 Laser Printer. However, the image will not be printed at true size. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic view of a CR cassette according to the present invention. 
     FIG. 2 is a diagrammatic view of a radiographic image system using the present invention. 
     FIG. 3 is a diagrammatic view showing a storage phosphor assembly partially detached from the cassette. 
     FIG. 4 is a partial cross-sectional view of a cassette. 
     FIG. 5 is a diagrammatic view showing a radiographic imaging system. 
     FIG. 6 is a partial perspective view showing a storage phosphor cassette containing a storage phosphor plate assembly. 
     FIG. 7 is a partial perspective view showing a storage phosphor cassette. 
     FIG. 8 is a partial perspective view showing a storage phosphor plate assembly. 
     FIG. 9 is a diagrammatic perspective view of a storage phosphor reader. 
     FIGS. 10 and 11 are perspective views showing steps in unlatching of a storage phosphor plate assembly from a cassette. 
     FIG. 12 is a diagrammatic plan view showing partial removal of a storage phosphor plate assembly from a cassette. 
     FIG. 13 is a diagrammatic plan view showing complete removal of a storage phosphor plate assembly form the cassette. 
     FIG. 14 is a diagrammatic view of an elongated cassette containing contiguous storage phosphor plates. 
     FIGS. 15 a  and  15   b  are diagrammatic views of two embodiments of alignment rulers. 
     FIG. 16 is a block diagram of a CR imaging system incorporating the present invention. 
     FIG. 17 is a flow diagram of a method of the invention. 
     FIGS. 18 a - 18   d  are diagrammatic views useful in illustrating the present invention. 
     FIG. 19 is a side elevational view of another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In general, the present invention relates to the radiographic imaging of an elongate object such as the full spine (for diagnosing scoliosis, for example) or leg of a human subject. 
     Two contiguous CR plates contained in an elongated cassette are exposed to a radiographic image of an elongate object to produce a latent image stored in the CR plates. The CR plates are removably mounted in the cassette and are sequentially fed to a CR reader where the latent radiographic images are converted to two electronic images which are combined to form an elongated image. The elongate image can be displayed on an electronic display or printed out on hard copy media. 
     Referring now to FIGS. 1 and 2, there is shown an embodiment of the present invention. As shown, storage phosphor cassette  10  includes an elongate rectangular shell  12  having first and second open ends  14  and  16 . A first storage phosphor plate assembly  18  is detachably mounted in shell  12  from the first open end  14 . A second storage phosphor plate assembly  20  is detachably mounted on shell  12  from the second open end  16 . Each assembly  18 ,  20  includes a storage phosphor plate  22 ,  24  and a support and latching assembly  26 ,  28 . Plates  22 ,  24  are butt joined or overlapped in the central region  29  of shell  12 . Shell  12  includes upper and lower members  30 ,  32  and side extrusions  34 ,  36  which together form a rectangular shell. 
     FIG. 3 shows first storage phosphor assembly  18  partially detached from cassette  10  at a reading device (not shown). 
     FIG. 4 shows a cross-section of cassette  10  showing upper and lower members  30 ,  32  having respective opposed inner surfaces  40 ,  42  including deflectors  44 ,  46  extending therefrom for guiding the inner ends of assemblies  18 ,  20  to overlap. This results in an overlapping of storage phosphor plates  22  and  24  to form a composite storage phosphor plate for elongate radiographic images, such as the human spine and leg. 
     FIG. 5 shows a radiographic imaging system using the elongated storage phosphor cassette of the present invention. As shown, cassette  10  is mounted on support  50 . Patient  52  is positioned between cassette  10  and a source  54  of X-rays. An X-ray beam  56  from source  54  penetrates the torso region  58  of patient  52  to record a latent radiographic image thereof in the composite storage phosphor plates of cassette  10 . The cassette  10  is removed and the first storage phosphor assembly placed in a reading device (described later). The first plate is read and the first electronic image stored. The cassette is removed from the reading device, inverted and the second storage phosphor assembly is placed in the reading device. The second storage phosphor plate is read and the second electronic image is stored. The two images can then be processed into a single image if so desired. 
     FIGS. 6,  7  and  8  show in greater detail the components of storage phosphor cassette  10 . As shown, cassette  10  is viewed from one end showing first storage phosphor assembly  18 . It will be understood that the other end of cassette  10  is similar in structure but showing storage phosphor assembly  20 . Storage phosphor plate assembly  18  has a storage phosphor plate  22  including an aluminum support plate  60  carrying a storage phosphor screen  62 . Plate  22  is cantilevered from assembly  26  which has a plurality of openings  64  and an opening  68  to be explained later (FIG.  8 ). Shell  12  has a lower member  32  having notches  66  with set back portions  70  at each open end  14 ,  16 . A locking mechanism in assembly  26  locks storage phosphor plate assembly  18  into shell  12 . 
     Referring now to FIGS. 9-13, there is shown a reader device for reading a storage phosphor plate assembly. As shown, storage phosphor reading device  100  includes a cassette receiving station  102  for receiving a cassette  103  containing a storage phosphor plate that stores a latent radiographic image. Station  102  has clamps  104 ,  106  for clamping the end of cassette  103 . Extractor bar assembly  108  includes hooks  110  for removing and replacing a storage phosphor assembly relative to cassette  103 . Assembly  108  is mounted on stage  112  for movement in opposite directions  114 . Stage  112  is mounted for movement in opposite directions  116  on rails  118 ,  120  on support  122 . 
     As shown in FIGS. 10 and 11, the lower member  130  of cassette  103  has cut-outs  132  with slots  134 . The support and latch assembly  136  of the storage phosphor plate assembly contained in cassette  103  has a front wall  138  with openings  140  through which hooks  110  project. Assembly  136  has a latch  142  with cutouts  144  and angled tabs  146 . In FIG. 10, the storage phosphor plate assembly is locked in cassette  103  by the mating of tabs  146  of latch  142  with slots  134  of cutouts  132 . In FIG. 11, hooks  110  with bearing portion  110   a  of extractor bar assembly  108  have been moved to the left to unlatch latch  142  from lower member  130  of cassette  103 . Hooks  110  grab front wall  138  of the storage phosphor plate assembly to allow removal of the assembly from cassette  103 . 
     As shown in FIG. 12, extractor bar assembly  108  has engaged storage phosphor plate assembly  150  of cassette  103  and unlatched assembly  150  from cassette shell  152  of cassette  103 . In FIG. 13, extractor bar assembly  108  has completely removed storage phosphor plate assembly  150  from shell  152  of cassette  103 . Assembly  108  and assembly  150  are then moved in the direction  116  so that a laser scanner (not shown) reads the latent radiographic image stored in the storage phosphor screen  154  of storage phosphor plate assembly  150 . U.S. Pat. No. 5,276,333, issued Jan. 4, 1994, inventor Robertson, discloses an exemplary X-ray cassette having a single removable storage phosphor assembly. U.S. Pat. No. 5,330,309, issued Jul. 19, 1994, inventors Brahm et al., discloses an exemplary reader having cassette locating and unlatching mechanism. 
     It will be understood that the present invention includes other types of elongated cassettes having removable storage phosphor plate assemblies. Thus, as shown in FIG. 19, this cassette shell  190  could have a three-sided, U shaped with an open bottom in which the storage phosphor plate assemblies  192  close off the open bottom. Other type of latching mechanisms can also be used. 
     According to another feature of the present invention there is provided one or more x-ray translucent/opaque rulers attached to the inside or outside of the elongated cassette. As shown in FIG. 14, elongated cassette  200  contains contiguous storage phosphor plates  202  and  204 . Associated with cassette  200  are x-ray transparent/opaque alignment rulers  206  and  208  (meter, inches). Rulers  206  and  208  have regular markings which during exposure imposes a shadow of the ruler on plates  202  and  204 . The regular marking are illustrated in FIGS. 15 a  and  15   b  as regularly spaced metric or inches lines or circles. Rulers  206  and  208  are preferably made of a metal substance such as lead of different densities or of any other x-ray translucent/opaque material or combination of materials that impose sufficient latent contrast of the ruler markings on plates  202  and  204 . 
     Referring now to FIG. 16, there is shown an imaging system incorporating the present invention. As shown, system  220  includes x-ray exposure assembly  222  (such as shown in FIG.  2 ); CR reader  224 , image processor  226 , and output  228 . FIG. 17 shows the flow of operations of system  220 . During exposure, a shadow of the ruler is imposed as a latent image on the storage phosphor plates (box  230 ). The exposed storage phosphor plates are then scanned (box  232 ) using a computed radiography storage phosphor reader  224  resulting in two digital radiographic images, each containing an image of a portion of the ruler. In preferred embodiment of the present invention, the storage phosphor reader  224  will be informed, e.g., via keyboard entry by a radiographic technologist, or electronically via the radiology information system, that a composite image should be generated. Reference markings on the ruler are then automatically recognized from each of the digital images by the image processing software ( 226 ) using a standard pattern recognition method to determine the top and bottom images and left versus right orientation (box  234 ). The rulers also provide an indication of any missing image data that may be caused by a small physical gap between the two storage phosphor plates inside the extended length cassette. The exact amount of missing data is determined by calculating the portion of the center of the ruler that is missing from each of the sub-images. Both the top and bottom images are then digitally re-sampled using interpolation (such as bilinear, cubic spine etc) (box  236 ) to align the rulers across the two storage phosphor plates. Any residual missing pixel data in the composite image caused by a gap between top and bottom images is then filled-in using digital interpolation or using a predetermined constant pixel value. 
     The final composite image is then stored, printed or displayed (box  238 -output  228 ). 
     FIGS. 18 a - 18   d  are a graphical illustration of the processing steps required to automatically construct the composite image from the two seamed sub-images. FIG. 18 a  depicts each storage phosphor plate being independently scanned. The scanning direction may not be exactly aligned with the edge of the plate causing the rulers to be offset between the two images. FIG. 18 b  shows the effect on the captured image of imperfect scanning of the top and bottom storage phosphor plates. FIG. 18 c  shows realignment of the top and bottom images to the known dimensions and positions since the rulers have known truth dimensions and positional relationships between the top and bottom plates. FIG. 18 d  shows filling in any missing image data using digital interpolation to construct the final composite image. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 PARTS LIST 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  10 
                 storage phosphor cassette 
               
               
                   
                  12 
                 elongated rectangular shell 
               
               
                   
                  14 
                 first open end 
               
               
                   
                  16 
                 second open end 
               
               
                   
                  18 
                 first phosphor plate assembly 
               
               
                   
                  20 
                 second phosphor plate assembly 
               
               
                   
                  22, 24 
                 storage phosphor plate 
               
               
                   
                  26, 28 
                 latching assembly 
               
               
                   
                  29 
                 central region 
               
               
                   
                  30, 32 
                 upper and lower members 
               
               
                   
                  34, 36 
                 side extrusions 
               
               
                   
                  40, 42 
                 inner surfaces 
               
               
                   
                  44, 46 
                 deflectors 
               
               
                   
                  50 
                 support 
               
               
                   
                  52 
                 patient 
               
               
                   
                  54 
                 source 
               
               
                   
                  56 
                 X-ray beam 
               
               
                   
                  58 
                 torso region 
               
               
                   
                  60 
                 aluminum support plate 
               
               
                   
                  62 
                 storage phosphor assembly 
               
               
                   
                  64 
                 openings 
               
               
                   
                  66 
                 notches 
               
               
                   
                  68 
                 opening 
               
               
                   
                  70 
                 back portions 
               
               
                   
                 100 
                 storage phosphor reading device 
               
               
                   
                 102 
                 cassette receiving station 
               
               
                   
                 103 
                 cassette 
               
               
                   
                 104, 106 
                 clamps 
               
               
                   
                 108 
                 assembly 
               
               
                   
                 110, 110a 
                 hooks 
               
               
                   
                 112 
                 stage 
               
               
                   
                 114 
                 opposite direction 
               
               
                   
                 116 
                 opposite direction 
               
               
                   
                 118, 120 
                 rails 
               
               
                   
                 122 
                 support 
               
               
                   
                 130 
                 lower member 
               
               
                   
                 132 
                 cutouts 
               
               
                   
                 134 
                 slots 
               
               
                   
                 136 
                 assembly 
               
               
                   
                 138 
                 front wall 
               
               
                   
                 140 
                 openings 
               
               
                   
                 142 
                 unlatch latch 
               
               
                   
                 144 
                 cutouts 
               
               
                   
                 146 
                 angled tabs 
               
               
                   
                 150 
                 plate assembly 
               
               
                   
                 152 
                 cassette shell 
               
               
                   
                 154 
                 screen 
               
               
                   
                 190 
                 cassette shell 
               
               
                   
                 192 
                 storage phosphor plate assembly 
               
               
                   
                 200 
                 elongated cassette 
               
               
                   
                 202, 204 
                 phosphor plates 
               
               
                   
                 206, 208 
                 rulers 
               
               
                   
                 220 
                 system 
               
               
                   
                 222 
                 exposure assembly 
               
               
                   
                 224 
                 CR reader 
               
               
                   
                 226 
                 image processor 
               
               
                   
                 228 
                 output 
               
               
                   
                 230 
                 exposure storage 
               
               
                   
                 232 
                 scan storage 
               
               
                   
                 234 
                 construct composite 
               
               
                   
                 236 
                 interpolate over image data