Patent Publication Number: US-2005133748-A1

Title: Raster scanning system for scanning photo-stimulatable radiographic media

Description:
FIELD OF THE INVENTION  
      This invention relates in general to radiography and in particular to scanning a computer radiographic phosphor plate having a latent image to generate a digital image file by means of a scanning apparatus having a modulated flying spot scanning beam and CCD sensor array.  
     BACKGROUND OF THE INVENTION  
      In a photo-stimulatable phosphor imaging system, as described in U.S. Patent No. RE 31,847, a photo-stimulatable phosphor sheet is exposed to an image wise pattern of short wavelength radiation, such as x-radiation, to record a latent image pattern in the photo-stimulatable phosphor sheet. The latent image is read out by stimulating the phosphor with a relatively long wavelength stimulating radiation such as red or infrared light. Upon stimulation, the photo-stimulatable phosphor releases emitted radiation of an intermediate wavelength such as blue or violet light in proportion to the quantity of short wavelength radiation that was received. To produce a signal useful in electronic image processing, the photo-stimulatable phosphor sheet is scanned in a raster pattern by a beam of light to produced emitted radiation, which is sensed by a photo-detector such as a photo-multiplier tube to produce the electronic image signal. The signal is then transmitted to a separate device, a film writer, which reproduces the scanned image.  
      While the above system works well a need exists to improve image quality along with scanning rates.  
     SUMMARY OF THE INVENTION  
      Briefly, according to one aspect of the present invention a raster scanning system for scanning photo-stimulatable radiographic media comprises a flying spot light source adapted to fire a beam at a rotating mirror to form a stimulated area of radiographic media generating emitted light. Collection optics collect the emitted light and reflected light from the radiographic media. A filter permits the emitted light to pass to a charge coupled detector (CCD). An analog to digital converter receives the signal from the CCD. A control process unit (CPU) receives the converted signal. An output device processes the signal from the CPU.  
      The invention and its objects and advantages will become more apparent in the detailed description of the preferred embodiment presented below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter of the present invention, it is believed that the invention will be better understood from the following description when taken in conjunction with accompanying drawings.  
       FIG. 1  is a single scan embodiment of the present invention;  
       FIG. 2  is a perspective view of  FIG. 1 ;  
       FIG. 3  is a schematic view of a dual scanning system of the present invention with a single source of stimulation; and  
       FIG. 4  is a schematic view of a dual scanning system of the present invention with a dual side stimulation of the radiographic media. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The present invention will be directed in particular to elements forming part of, or in cooperation more directly with the apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art.  
      Referring now to  FIGS. 1 and 2  is a system includes a raster scanning system for scanning photo-stimulatable radiographic media  14 . It uses a flying spot light source  10  adapted to fire a beam  11  at a rotating mirror  12  to form a stimulated area  13  of radiographic media  14  generating emitted light  15 . Collection optics  16  which can be an optical lens system to collect emitted light  15  and the reflected light  17  from the radiographic media. The collection optics  16  are elliptical in one embodiment. A blue filter  18  permits the emitted light  15  to pass to a charge coupled detector (CCD)  20 . The filter does not permit the reflected light to pass to the CCD. An analog to digital converter  22  receives the signal from the CCD. A control processing unit (CPU)  24  receives the converted signal from the analog to digital converter  22 . An output device  26  is in communication with the CPU for processing the signal. While scanning, the radiographic media  14  moves along axis  28  to allow scanning of larger portions, and up to the entire sheet of radiographic media.  
      The radiographic media  14  has a first side  100  and a second side  101 . The area  13  to be stimulated can be a series of stimulated areas. The radiographic media can be a phosphor sheet. The media is a sheet, a screen, a plate, or combinations thereof.  
      In a preferred embodiment, the mirror rotates at a rate of between 4,000 rpm and 30,000 rpm.  
      The laser can be a flying spot light source such as a laser which is a single mode or a multiple mode laser. Preferably, the multimode laser is a 635 nanometer, 100 mW laser. Preferably the single mode laser is a 635 nanometer 100 mW laser.  
      The collection optics are preferably a chamber comprising a reflective surface, such as a mirrored surface.  
      The invention provides a set of collection optics which provide a reflectivity between 80 and 95%.  
      In a preferred embodiment, the output device is a filmwriter, a printer or a display.  
      In another embodiment of the invention, as shown in  FIG. 3 , is a scanning system for scanning photo-stimulatable radiographic media from a first side  100  and a second side  101  of the radiographic media  14 .  
      It involves a flying spot light source  10  adapted to fire a beam  11  at a rotating mirror  12  to stimulate an area  13  of radiographic media  14  generating emitted light  15  and second emitted light  115 . The first emitted light  15  and reflected light  17  are collected by the first collection optics  16  and the second emitted light is collected by the second collection optics  116  which is on the side of media opposite the first collection optics  16 .  
      The second collection optics  116  communicates with a second CCD  200  which then generates a second signal and then transmits that second signal to the analog to digital converter  22 .  
      A blue filter  18  permits the emitted light  15  to pass to the first charge coupled detector (CCD)  20  without passing the reflected light  17 . The analog to digital converter  22  receives the signals from the first and second CCDs and transmits the signal to a control CPU  24  for receiving and compiling the converted signals. An output device communicates with the CPU for processing the signal from the CPU to a filmwriter or it can be a display.  
       FIG. 4  shows another embodiment of the present invention. In this version, radiographic media  14  has a first and second side  100  and  101  respectively. This embodiment has all the elements shown in  FIG. 1 , but additionally has, on the second side of the radiographic media, a second flying spot light source  202  which provides a second beam  204  to a second rotating mirror  206 . This second beam  204  stimulates a second area  207  causing a second emitted light  115  from the radiographic media. Second reflected light  208  is reflected from the surface of the radiographic media and both the second reflected light and the second emitted light are collected by second collection optics  116 . A second filter  210  communicates with the second collection optics to stop the second reflected light from passing to a second CCD  200 . Preferably the second filter is a blue filter as in  FIG. 1 . Light in the second CCD is converted to a signal which is transmitted to the analog to digital converter  22 . As in  FIG. 1 , the signal is converted to a digital signal and then transmitted to a CPU  24  which compiles and stores the signals. The signals can be transferred to an output device, such as filmwriter  26 . It is contemplated that more than one output device can be used in the scope of this invention.  
      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 scope of the invention.  
     Parts List  
     
         
           10  flying spot light source  
           11  beam  
           12  rotating mirror  
           13  stimulated area  
           14  radiographic media  
           15  emitted light from stimulated area  
           16  first collection optics  
           17  reflected light  
           18  blue filter  
           20  first charge coupled detector (CCD)  
           22  analog to digital converter  
           24  control processing unit (CPU)  
           26  output device  
           28  axis  
           100  first side of radiographic media  
           101  second side of radiographic media  
           115  second emitted light  
           116  second collection optics  
           200  second charge coupled detector (CCD)  
           202  second flying spot light source  
           204  second beam  
           206  second rotating mirror  
           207  second stimulated area  
           208  second reflected light  
           210  second filter