Patent Publication Number: US-2002003220-A1

Title: Image information reading apparatus

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to an image information reading apparatus for reading radiation image information recorded on a double-sided stimulable phosphor sheet which emits light from both sides thereof when exciting light is applied to a recording surface thereof.  
       [0003] 2. Description of the Related Art  
       [0004] A system is known for recording radiation image information of a subject such as a human body with a stimulable phosphor, and reproducing the recorded radiation image information on a photosensitive medium such as a photographic film, or displaying the recorded radiation image information on a display device such as a CRT or the like.  
       [0005] When a radiation energy such as X-rays, α-rays, γ-rays, electron beams, ultraviolet radiation, or the like is applied to a certain phosphor, it stores part of the applied radiation energy. When exciting light such as visible light is subsequently applied to the phosphor, the phosphor emits light depending upon the stored radiation energy. Such a phosphor is referred to as a stimulable phosphor. A stimulable phosphor is usually used in the form of a sheet which is referred to as a stimulable phosphor sheet.  
       [0006] The above known system includes an image information reading apparatus which comprises a reading unit for reading image information recorded on a stimulable phosphor sheet, and an erasing assembly for erasing remaining image information from the stimulable phosphor sheet after the recorded image information has been read. In the image information reading apparatus, a cassette housing a stimulable phosphor sheet which bears radiation image information of a subject recorded by an external exposure device is inserted into a loading unit.  
       [0007] Thereafter, the lid of the cassette is opened, and then the stimulable phosphor sheet is taken out of the cassette by a sheet feeding mechanism. The stimulable phosphor sheet is delivered to the reading unit by a sheet delivering mechanism. In the reading unit, the recorded image information is read from the stimulable phosphor sheet, and then remaining image information is erased from the stimulable phosphor sheet in the erasing assembly, after which the stimulable phosphor sheet is placed into the cassette which has been disposed in the loading unit.  
       [0008] It has been desired to efficiently read the energy that has been stored in the stimulable phosphor sheet as in the field of mammography. To meet such a demand, there has been an attempt to use a transparent base in the stimulable phosphor sheet. When the exciting light is applied to the stimulable phosphor sheet from the side of a phosphor layer (recording surface) thereof, the stimulable phosphor sheet emits light from the base (reverse surface) as well as the phosphor layer. Therefore, the reading unit has two light guiding means disposed respectively on both sides of the stimulable phosphor sheet for guiding the light emitted therefrom.  
       [0009] The reading unit has a structure with roller pairs for gripping and feeding the stimulable phosphor sheet while holding the reverse surface thereof in contact with guide means in order to read the recorded radiation image information highly accurately. The guide means comprises a plurality of separate guide means at the position where the exciting light is applied to the stimulable phosphor sheet, for guiding the emitted light to the guiding means that is disposed on the side of the reverse surface of the stimulable phosphor sheet.  
       [0010] When the stimulable phosphor sheet is transferred from one of the guide means to the other guide means in the vicinity of the position where the exciting light is applied to the stimulable phosphor sheet, the stimulable phosphor sheet is brought into direct contact with the other guide means comprising, for example, a glass guide, possibly resulting in damage caused to the reverse surface of the stimulable phosphor sheet. Another problem is that, when the leading end of the stimulable phosphor sheet abuts against the other guide means, the stimulable phosphor sheet is caused to flutter, and the image read therefrom suffers undesirable irregularities.  
       SUMMARY OF THE INVENTION  
       [0011] It is a major object of the present invention to provide an image information reading apparatus which is capable of reading a recorded image highly accurately from a double-sided stimulable phosphor sheet without causing damage thereto.  
       [0012] The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0013]FIG. 1 is a schematic vertical cross-sectional view of an image information reading apparatus according to the present invention;  
     [0014]FIG. 2 is a fragmentary exploded perspective view of a reading unit of the image information reading apparatus shown in FIG. 1;  
     [0015]FIG. 3 is a front elevational view, partly in cross section, of the reading unit shown in FIG. 2; and  
     [0016]FIG. 4 is a view showing parameters to set up a condition for preventing a laser beam from straying. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0017]FIG. 1 shows in schematic vertical cross section an image information reading apparatus  10  according to the present invention. shown in FIG. 1, the image information reading apparatus  10  has an apparatus housing  12  including a front wall (control wall) which supports on its upper portion a touch panel  14  that functions as controls and a display monitor. The apparatus housing  12  accommodates therein a cassette loading region  20  for removably holding a cassette  18 . The cassette loading region  20  is disposed below the touch panel  14 .  
     [0018] The cassette  18  comprises a casing  24  for housing a stimulable phosphor sheet  22  and a lid  28  by which an opening  26  in the casing  24  is openably closed. The stimulable phosphor sheet  22  comprises a double-sided stimulable phosphor sheet having a transparent base with a recording surface thereon, and emits light bearing recorded radiation image information from both sides thereof when irradiated with exciting light.  
     [0019] The cassette loading region  20  has a support base  30  for placing the cassette  18  thereon, and a shutter  32  for blocking light against entry into the apparatus housing  12 . The cassette loading region  20  also has a sheet feeder  36  for removing the stimulable phosphor sheet  22  from the cassette  18  and returning the stimulable phosphor sheet  22  into the cassette  18  after recorded radiation image information has been read from the stimulable phosphor sheet  22  into and after remaining radiation image information has been erased from the stimulable phosphor sheet  22 . The sheet feeder  36  has suction cups  40   a ,  40   b  that are movable into the cassette  18  whose lid  28  is opened in the cassette loading region  20 .  
     [0020] The apparatus housing  12  houses therein an erasing device  44  and a reading unit  46  which are disposed below the sheet feeder  36  with a feed system  42  interposed therebetween. The feed system  42  has a plurality of roller pairs  48  making up a vertical feed path, with the erasing device  44  disposed on one side thereof. The erasing assembly  44  comprises an erasing assembly  50  disposed on the side of the recording surface of the stimulable phosphor sheet  22 . The erasing assembly  50  comprises a vertical array of erasing light sources  52 .  
     [0021] The roller pairs  48  also make up a horizontal feed path, with the reading unit  46  disposed on one side thereof. The reading unit  46  comprises an auxiliary scanning feeding mechanism  54  for delivering the stimulable phosphor sheet  22  taken from the cassette  18  in an auxiliary scanning direction indicated by the arrow A, a laser beam applying means (exciting light applying means)  56  for applying a laser beam L as it is deflected in a main scanning direction (substantially perpendicular to the auxiliary scanning direction) to the recording surface of the stimulable phosphor sheet  22  as it is delivered in the auxiliary canning direction, and first and second light guiding systems (light guiding means)  58   a ,  58   b  for photoelectrically reading light which is emitted from the stimulable phosphor sheet  22  when the stimulable phosphor sheet  22  is exposed to the laser beam L.  
     [0022] The auxiliary scanning feeding mechanism  54  has first and second roller pairs  60 ,  62  rotatable in synchronism with each other. The first and second roller pairs  60 ,  62  have drive rollers  60   a ,  62   a  and nip rollers  60   b ,  62   b  that can be moved toward and away from the drive rollers  60   a ,  62   a.    
     [0023] The first light guiding system  58   a  comprises a first light guide  64   a  extending along a main scanning line in the position over the recording surface of the stimulable phosphor sheet  22  where the laser beam L is applied, and a first photomultiplier  66   a  mounted on an upper end of the first light guide  64   a . The second light guiding system  58   b  is disposed on the side of the reverse surface of the stimulable phosphor sheet  22 , and comprises a second light guide  64   b  extending along a main scanning line over the reverse surface of the stimulable phosphor sheet  22 , and a second photomultiplier  66   b  mounted on a lower end of the second light guide  64   b.    
     [0024] As shown in FIGS. 2 and 3, the reading unit  46  comprises first and second guide members (first guide means)  70 ,  72  disposed on the side of the reverse surface of the stimulable phosphor sheet  22 , for guiding the stimulable phosphor sheet  22  in the direction indicated by the arrow A, and a light-transmissive guide member (second guide means), e.g., a glass guide  74 , disposed between the first and second guide members  70 ,  72  and located in the position over the recording surface of the stimulable phosphor sheet  22  where the laser beam L is applied. The first and second guide members  70 ,  72  and the glass guide  74  are integrally held by a guide mount  76 .  
     [0025] The guide mount  76  is elongate in the main scanning direction of the laser beam L, and has an opening  78  defined therein along the main scanning line of the laser beam L. The opening  78  is of a width that is large enough to allow the second light guide  64   b  of the second light guiding system  58   b  to pass therethrough. The guide mount  76  has on its upper end first and second mount surfaces  80 ,  82  on which the first and second guide members  70 ,  72  are mounted, and third and fourth mount surfaces  84   a ,  84   b  on which the glass guide  74  is mounted. The first and second mount surfaces  80 ,  82  have a plurality of screw holes  86  and small-diameter screw holes  87  that are defined therein at spaced intervals.  
     [0026] The first guide member  70  extends fully across the stimulable phosphor sheet  22  along the main scanning direction and from a position upstream of the first roller pair  60  to a position near the main scanning line. The first guide member  70  has a plurality of openings  90  defined therein which receive respective roller surfaces  88  of the drive roller  60   a  of the first roller pair  60 . The first guide member  70  comprises a plate  92  and a damper  94  on the upper surface of the plate  92  for contact with the stimulable phosphor sheet  22 . The damper  94  is made of woven or nonwoven fabric of polyester or the like, and extends from the upper surface of the plate  92  along an end face juxtaposed to the glass guide  74  to an opposite lower surface of the plate  92 .  
     [0027] The first guide member  70  has holes  96  defined therein in alignment with the screw holes  86  defined in the guide mount  76 , and is fastened to the guide mount  76  by screws  98  that are threaded through the holes  96  into the screw holes  86 . The first guide member  70  has recesses  99  defined in opposite ends thereof over which glass guide holders  100  are positioned. When screws  102  are threaded through the glass guide holders  100  into the screw holes  87 , the glass guide  74  is fastened to the guide mount  76 . The second guide member  72  is of a structure identical to the first guide member  70 . Those parts of the second guide member  72  which are identical to those of the first guide member  70  are denoted by identical reference characters, and will not be described in detail below.  
     [0028] The glass guide  74  has an antireflection coating on its reverse surface that faces the second light guide  64   b  for reducing reflections of the laser beam L and increasing the transmittance of the light emitted from the stimulable phosphor sheet  22 . The glass guide  74  has a beveled corner  104  that is used to distinguish the face side from the reverse side of the glass guide  74 .  
     [0029] As shown in FIG. 3, with the first and second guide members  70 ,  72  and the glass guide  74  being mounted on the guide mount  76 , the surface of the damper  94  of each of the first and second guide members  70 ,  72  is closer to the stimulable phosphor sheet  22  than the surface of the glass guide  74  by a distance H ranging from 0.1 mm to 0.2 mm.  
     [0030] Operation of the image information reading apparatus  12  thus constructed will be described below.  
     [0031] A cassette  18  which stores a stimulable phosphor sheet  22  which carries radiation image information of a subject such as a human body recorded by an exposure device (not shown) is introduced into the apparatus housing  12  along the support base  30  of the cassette loading region  20 . As the cassette  18  is introduced, the leading end of the cassette  18  pushes open the shutter  32  and enters the interior space of the apparatus housing  12 , opening the lid  28  to a certain angular position.  
     [0032] The suction cups  40   a ,  40   b  of the sheet feeder  36  then move along a path extending from an upper position downwardly obliquely toward the base of the stimulable phosphor sheet  22  in the cassette  18 . When the suction cups  40   a ,  40   b  attracts the base of the stimulable phosphor sheet  22 , the suction cups  40   a ,  40   b  move out of the cassette  18  toward the feed system  42  until the leading end of the stimulable phosphor sheet  22  is gripped by the first roller pair  48  of the feed system  42 . As the roller pairs  48  rotate, the stimulable phosphor sheet  22  is fed horizontally and then vertically downwardly through the erasing assembly  44 , after which the stimulable phosphor sheet  22  is fed horizontally to the reading unit  46 .  
     [0033] In the reading unit  46 , the stimulable phosphor sheet  22  is fed in the auxiliary scanning direction indicated by the arrow A by the first and second roller pairs  60 ,  62  of the auxiliary scanning feeding mechanism  54 . At the same time, the laser beam L emitted from the laser beam applying means  56  is applied to the recording surface of the stimulable phosphor sheet  22  while it is being deflected in the main scanning direction.  
     [0034] Light emitted from the recording surface of the stimulable phosphor sheet  22  is photoelectrically read by the first light guiding system  58   a , and light emitted from the reverse surface of the stimulable phosphor sheet  22  is photoelectrically read by the second light guiding system  58   b . Accordingly, the recorded radiation image information can be read with increased accuracy. The reading unit  46  which operates in the manner described above is effectively suitable for achieving a high level of image quality such as in the field of mammography.  
     [0035] The stimulable phosphor sheet  22  from which the desired radiation image information has been read is switched back in the auxiliary scanning feeding mechanism  54 , and fed vertically upwardly through the erasing unit  50  of the erasing assembly  50  of the erasing assembly  44  to the sheet feeder  36 . In the erasing assembly  50 , the erasing light sources  52  of the erasing unit  50  are energized to apply erasing light to both surfaces of the stimulable phosphor sheet  22 , erasing remaining radiation image information from the stimulable phosphor sheet  22 . The stimulable phosphor sheet  22  is then returned into the empty cassette  18  by the suction cups  40   a ,  40   b  of the sheet feeder  36 .  
     [0036] As shown in FIG. 3, the glass guide  74  is disposed in the position where the laser beam L is applied, and the first and second guide members  70 ,  72  are disposed near the opposite ends of the glass guide  74 . Therefore, the light emitted from the reverse surface of the stimulable phosphor sheet  22  passes through the glass guide  74  and is reliably applied to the second light guide  64   b . Consequently, the radiation image information recorded in the stimulable phosphor sheet  22  is read with increased accuracy.  
     [0037] Each of the first and second guide members  70 ,  72  has the damper  94  on its surface for contact with the base of the stimulable phosphor sheet  22 , and the surface of the glass guide  74  facing the stimulable phosphor sheet  22  is spaced from the stimulable phosphor sheet  22  by the distance H. Consequently, the reverse surface of the stimulable phosphor sheet  22  is not damaged by contact with the first and second guide members  70 ,  72 , and is not damaged by the glass guide  74  as it is held out of contact with the glass guide  74 . The leading end of the stimulable phosphor sheet  22  is prevented from being caught by the glass guide  74  when it is transferred from the first guide member  70  across the glass guide  74  to the second guide member  72 .  
     [0038] The stimulable phosphor sheet  22  is thus smoothly transferred from the first guide member  70  across the glass guide  74  to the second guide member  72 . Since the stimulable phosphor sheet  22  is prevented from fluttering at this time, the image read from the stimulable phosphor sheet  22  is free of undesired irregularities.  
     [0039] The damper  94  extends from the upper surface of the plate  92  so as to cover the end face thereof which is juxtaposed to the glass guide  74 . Therefore, when the stimulable phosphor sheet  22  is transferred from the first guide member  70  across the glass guide  74  to the second guide member  72 , the leading end of the stimulable phosphor sheet  22  is prevented from being caught by the edges of the plates  92 . Thus, the stimulable phosphor sheet  22  can be fed smoothly and highly accurately in the auxiliary scanning direction indicated by the arrow A.  
     [0040] As shown in FIG. 2, the first and second guide members  70 ,  72  are placed on and fastened to the first and second mount surfaces  80 ,  82  of the guide mount  76  by the screws  98 . The glass guide  74  is placed on the third mount surfaces  84   a ,  84   b  of the guide mount  76 , and has its opposite ends fixed in position by the respective glass guide holders  100 . Accordingly, the first and second guide members  70 ,  72  and the glass guide  74  can reliably be held in their relative positions depending on the machining accuracy of the guide mount  76 . The first and second guide members  70 ,  72  and the glass guide  74  can thus be positioned with high accuracy by the simple structure.  
     [0041] A condition may be set up to prevent a regularly reflected component of the laser beam L from returning to the optical system of the reading unit  46  when the leading end of the stimulable phosphor sheet  22  enters the boundary between the glass guide  74  and the second guide member  72 . Specifically, as shown in FIG. 4, it is assumed that the glass guide  74  has a width W, the laser beam L is applied to the stimulable phosphor sheet  22  at an incident angle θ (which is positive in a clockwise direction in FIG. 4), and the distance from the surface of the first and second guide members  70 ,  72  for guiding the stimulable phosphor sheet  22  to the surface of the glass guide  74  is represented by H.  
     [0042] If the incident angle θ of the laser beam L is in the rang of 0≦θ≦tan −1  (H/W), then when the leading end of the stimulable phosphor sheet  22  flexes over the glass guide  74  in front of the second guide member  72 , the laser beam L may be applied perpendicularly to the stimulable phosphor sheet  22 . At this time, a regularly reflected component of the laser beam L from the stimulable phosphor sheet  22  returns as a stray beam in the direction in which the laser beam L is applied to the stimulable phosphor sheet  22 . The stray beam thus traveling back in the optical system tends to disturb the oscillating state of the laser oscillator and also to disturb the controlling operation of APC and ACC circuits, causing the amount of light of the laser beam L to vary unexpectedly to introduce noise in the image read from the stimulable phosphor sheet  22 .  
     [0043] In the present embodiment, the above shortcomings can effectively be avoided if the incident angle θ of the laser beam L is in the range of θ&gt;tan −1  (H/W) or θ&lt;0.  
     [0044] In the above embodiment, the light-transmissive guide member comprises the glass guide  74 . However, the light-transmissive guide member may be made of a relatively less damageable material such as an acrylic resin or the like. In the auxiliary scanning feeding mechanism  54 , the first and second guide members  70 ,  72  and the glass guide  74  are shown as being flat for feeding the stimulable phosphor sheet  22  along a flat feed path. However, if the auxiliary scanning feeding mechanism  54  provides a curved feed path, the first and second guide members  70 ,  72  and the glass guide  74  may be of a curved shape.  
     [0045] In the image information reading apparatus according to the present invention, since the guide members and the light-transmissive guide member are disposed on the side of the reverse surface of the stimulable phosphor sheet, with the light-transmissive guide member being disposed in the position where the exciting light is applied to the stimulable phosphor sheet, light emitted from the reverse surface of the stimulable phosphor sheet is reliably guided through the light-transmissive guide member. Thus, the radiation image information recorded on the stimulable phosphor sheet can be read highly accurately with a simple arrangement.  
     [0046] Although a certain preferred embodiment of the present invention has been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.