Abstract:
Apparatus for reading information stored in a memory layer ( 15 ) which includes a shielding device ( 22 ), and an X-ray cassette and an X-ray table for use with the apparatus, are disclosed. The shielding device ( 22 ) serves to shield a reader device ( 10 ) from an information recording beam ( 25 ). The reader device ( 10 ) includes a receptor ( 12 ) to receive emission radiation ( 17 ) that contains an image of the information recorded in the memory layer ( 15 ). Instead of the shielding device ( 22 ), it is also possible to provide a converter ( 29 ) that serves to convert an information-recording beam ( 25 ) into converted radiation ( 28 ) that possesses less energy than the information recording beam ( 25 ).

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to apparatus for reading information recorded in a memory layer, such as an X-ray memory layer and an X-ray cassette and X-ray table for use with the apparatus.  
           [0002]    Particularly for medical purposes, an image of an object (such as a patient) is created using X-ray radiation that is recorded in a memory layer as a latent image. A phosphor film base is often used for this memory layer. In order to read the X-ray image recorded in the memory layer, the memory layer is excited using a radiation source. Because of this excitation, the memory layer radiates light of an intensity corresponding to the recorded X-ray image. The light emitted from the memory layer is received by a receptor and eventually converted into electrical signals so that the X-ray image recorded in the memory layer may then be made visible. The X-ray image may, for example, be displayed directly on a monitor or printed onto a special X-ray film suitable for X-ray images.  
           [0003]    Such a device used to read out information recorded in a memory layer is known, for example, from published International Patent Application No. WO 99/28765. In this known device, the memory layer is excited by rows by an exciter beam that is created by a radiation source. This radiation source may be a laser diode strip, for example. The light emitted because of excitation of the memory layer is received by a receptor. For this purpose, the receptor contains a number of light-sensitive surfaces that are arranged in adjacent rows. The radiation emitted from the memory layer is received by the light-sensitive surfaces. The receptor may be a Charge-Coupled Device (CCD) that contains a number of photo-detectors arranged in adjacent rows.  
           [0004]    In order to read the information recorded in the memory layer, the radiation source and receptor are moved over the memory layer by means of a linear motor.  
         SUMMARY OF THE INVENTION  
         [0005]    Based on the principle advanced by the aforementioned publication No. WO 99/28765, the principal objective of the present invention is to provide a simple and effective means to improve the quality of reproducing information recorded in a memory layer.  
           [0006]    This objective, as well as other objectives which will become apparent from the discussion that follows, are achieved, in accordance with the present invention, by providing apparatus for reading information stored in a memory layer which includes a reader device having a receptor to receive emission radiation that contains an image of the information recording on the memory layer. The apparatus also includes a shielding device, which serves to shield the reader device from an information recording beam. Alternatively or additionally, it is possible to provide a converter that serves to convert an information recording beam into converted radiation that possesses less energy than the information recording beam.  
           [0007]    As a result of the invention, impact of high-energy storage radiation on the reader may be avoided. The reader contains semiconductor components that are sensitive to the energy-rich recording radiation. As a result of the invention, it is possible to prevent, or at least reduce, the formation of grid error points within these semiconductor components. Such grid error points can cause alteration of the specific characteristics of the semiconductor components after cumulative irradiation from the recording beam. Specific characteristics of these semiconductor components may be altered by increasing levels of radiation exposure frequency by means of recording radiation. Aging symptoms may appear in these semiconductor components that then may lead to a negative effect on image quality during reproduction of the information recorded. The signal-to-noise ratio during reproduction of the information recorded is worsened. This is prevented by the invention.  
           [0008]    In an advantageous embodiment of the invention, the shielding device that shields the reader from storage radiation contains lead in order to prevent impact of the recording radiation on the reader. This allows shielding mainly against X-rays used as recording radiation in a simple and effective manner.  
           [0009]    In a further advantageous embodiment of the invention, the converter according to the invention used to convert the recording radiation into a beam that is of reduced energy with respect to its energy content also performs a wavelength conversion. Thus, for example, an X-ray beam may be transformed into a wavelength band that is located within the visible spectrum, particularly in the blue or ultra-violet range.  
           [0010]    In a further particularly advantageous embodiment of the invention, the shielding device or conversion device is arranged above the resting position of the reader. Thus, the size of the shielding device or conversion device may be limited. Further, a fixed position is assigned to the shielding device or conversion device within the apparatus according to the invention. It is thereby ensured that the reader is protected from the high-energy recording beam during downloading of information in the memory layer.  
           [0011]    Advantageously the reader device, shielded by the shielding device or conversion device, also contains a radiation source to excite the memory layer. This radiation source with the receptor is therefore simultaneously shielded from the recording beam.  
           [0012]    For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a perspective, phantom view of a preferred embodiment of the X-ray cassette based on the invention.  
         [0014]    [0014]FIG. 2 is a schematic representation of the preferred embodiment of the X-ray cassette during readout of recorded information.  
         [0015]    [0015]FIG. 3 is a further schematic representation of the preferred embodiment of the X-ray cassette during recording of an X-ray radiation image.  
         [0016]    [0016]FIG. 4 is a schematic representation of another preferred embodiment of the X-ray cassette based on the invention with a conversion device during irradiation.  
         [0017]    [0017]FIG. 5 is a preferred embodiment of the X-ray table with an X-ray cassette.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    The preferred embodiments of the present invention will now be described with reference to FIGS.  1 - 5  of the drawings. Identical elements in the various figures are designated with the same reference numerals.  
         [0019]    [0019]FIG. 1 shows a preferred embodiment of an X-ray cassette  1 . This X-ray cassette  1  contains a memory layer  15 . The memory layer  15  here is a phosphor plate. X-ray radiation images may be recorded within the phosphor plate  15 . The X-ray cassette  1  contains a reader head  10  used to read the X-ray radiation images recorded in the phosphor plate  15 . The reader head  10  may be transported over the surface of the phosphor plate  15  in direction A along two guide rails using a drive  27 . The drive  27  may be a linear motor, for example. A deleting lamp  19  is mounted behind the reader head  10 . The deleting lamp  19  is firmly connected to the reader head  10 , and can be transported over the surface of the phosphor plate  15  in direction A with reader head  10 . The deleting lamp  19  serves to erase the information stored in the phosphor plate  15  that remains stored within the phosphor plate  15  after the reader head  10  reads the X-ray radiation image. The deleting lamp  19  and the reader head  10  extend along direction B across the entire width of the phosphor plate  15 . The row direction B is perpendicular to movement direction A.  
         [0020]    The X-ray cassette  1  further contains a control device  13  by means of which the components within the X-ray cassette  1  may be controlled. The reader head  10 , the deleting lamp  19 , and the control device  13  are arranged within the X-ray cassette to the right, adjacent to the phosphor plate  15 , as shown in FIG. 1. The reader head  10 , the deleting lamp  19 , and the control device  13  are shown in the rest position  26 . In this rest position  26 , the reader head  10  and the deleting lamp  19  are not propelled across the surface of the phosphor plate  15  by the drive  27 . A shielding device  22  is located above the rest position  26 . In this embodiment, the shielding device  22  is a lead shield. The reader head  10 , the deleting lamp  19 , and the control device  13  are shielded from X-rays directed toward the X-ray cassette  1  by means of this lead shielding device  22 . The lead shield  22  blocks such X-ray radiation. The lead shield  22  is firmly attached to the upper side (cover) of the housing of the X-ray cassette  1 . It is also possible not to connect the lead shield  22  to the housing of the X-ray cassette  1 , but rather to the transportable unit containing the reader head  10 , the deleting lamp  19 , and the control device  13 . The control device  13  may be firmly fixed within the X-ray cassette  1 . It is not necessary that the control device  13  be transported across the surface of the phosphor plate  15  along with the reader head  10  and the deleting lamp  19  by means of the drive  27 . Suitable wire connection between the control device  13  on the one end and the reader head  10  and the deleting lamp  19  on the other would allow control of the reader head  10  and the deleting lamp  19  if a readout of the information stored within the phosphor layer  15  results. Instead of the lead shielding  22 , other materials may also be used to shield the reader head  10 , the deleting lamp  19 , and the control device  13 . It is possible to employ a conversion device instead of the shielding device  22  by means of which the high-energy recording beam (X-ray radiation) is reduced in energy.  
         [0021]    [0021]FIG. 2 shows a more detailed view of the X-ray cassette  1  shown in FIG. 1. This shows a reader head  10  that contains a radiation source  11 . The radiation source  11  here is a strip of laser diodes with a number of adjacent laser diodes. The strip of laser diodes  11  may produce excitation radiation  16  that serves to excite the phosphor plate  15 . In this embodiment, the phosphor plate  15  is configured in rows. The phosphor plate  15  emits an emission radiation  17  because of the excitation radiation  16 . This emission radiation  17  is displayed by an optical projection device  14  (that may contain micro-lenses, for example) onto a CCD row  12 . The CCD row  12  contains a number of adjacent light-sensitive surfaces  10 . Thus, an image of the information stored in a row of the phosphor plate  15  may be detected by the CCD row  12  and converted into electrical signals. These signals created by the CCD row  12  are forwarded to the control device  13  that is connected with the reader head  10  and particularly with the CCD row  12  for this purpose.  
         [0022]    In the embodiment according to FIG. 2, the reader head  10  is driven by the drive  27  in order to read the information stored in the phosphor plate  15 . As shown in FIG. 2, the reader head  10  is not located at its rest position  26 . Instead, the reader head  10  is located to the left of the rest position  26  that is shielded by the lead shield  22 . New information is not simultaneously recorded into the phosphor plate  15  during reading of the information stored in the phosphor plate  15 .  
         [0023]    [0023]FIG. 3 shows the aforementioned embodiment of the X-ray cassette  1  according to the invention during the storage of information in the phosphor plate  15 . For this purpose, an X-ray beam  25  from an X-ray radiation source (not shown) is emitted in the direction of the X-ray cassette. This X-ray beam  25  basically impacts on the overall extent of the X-ray cassette  1 . The function of the lead shield  22  is clear from the example shown in FIG. 3. The X-ray beam  25  striking the lead shield  22  is deflected, and thus cannot strike the reader head  10  and the control device  13 . The high-energy X-ray beam  25  does not irradiate the components within the reader head  10  and the control device  13 .  
         [0024]    [0024]FIG. 4 shows another embodiment of the X-ray cassette  1  according to the invention. Instead of the lead shield  22 , the X-ray cassette  1  here contains a conversion device  29 . This device  29  converts the X-ray beam  25  into a converted radiation  28 . The converted radiation  28  has an energy level that is markedly lower than that of the X-ray beam  25 . The conversion device  29  may, for example, be a so-called scintillation layer as is known from the German Patent No. DE 195 05 729 C1. Such a scintillation layer  29  can transform the wavelength of the excitation beam  25 . The wavelength of the converted radiation  28  is approximately in the blue or ultra-violet range of the visible spectrum because of the wavelength energy transformation performed by the conversion device  29 .  
         [0025]    [0025]FIG. 5 shows a preferred embodiment of an X-ray table  20  into which the X-ray cassette  1  previously described is inserted. The X-ray table  20  contains an X-ray base  23  in which the X-ray cassette  1  is located, and a supporting surface  24  positioned on the X-ray base  23 . Patients are positioned on this supporting surface  24  for X-ray exposures. An X-ray source  21  is positioned above the X-ray table  20  with the supporting surface  24  and the X-ray base  23  containing the X-ray cassette  1 . The X-ray source  21  emits the X-ray beam  25  toward the supporting surface  24  to record the X-ray image.  
         [0026]    There has thus been shown and described a novel apparatus for reading information recorded in a memory layer and an X-ray cassette and X-ray table for use with the apparatus which fulfills all the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is to be limited only by the claims which follow.