Abstract:
A small-sized filter unit of a simple structure, as well as an X-ray tube unit and an X-ray imaging system both having the filter unit, are implemented. A filter unit in a first aspect of the present invention comprises a filter plate, the filter plate having a first filter, a second filter disposed in a first direction with respect to the first filter and a third filter disposed in a second direction having a predetermined angle from the first direction with respect to the first filter, a guide plate having a guide frame for movement of the filter plate in the first and second directions, and a drive device for moving the filter plate.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of Chinese Patent Application No. 200710102914.9 filed May 11, 2007, which is hereby incorporated by reference in its entirety. 
   BACKGROUND OF THE INVENTION 
   The subject matter disclosed herein relates to a filter unit for adjusting the energy spectrum of X-ray, as well as an X-ray tube unit and an X-ray imaging system both having the filter unit. Particularly, the embodiments described herein are concerned with a filter unit of low cost permitting replacement of plural filters, as well as an X-ray tube unit and an X-ray imaging system. 
   In an X-ray imaging system, X-ray is radiated to a subject after adjusting its energy spectrum with a filter. The filter is installed within a collimator box attached to an X-ray tube. In the invention of Japanese Unexamined Patent Publication No. 2006-226985, for obtaining a desired spectrum, the filter can be used by switching from one to another among plural filter plates secured to a rotary disc. 
   For radiating X-ray to a standing subject or to a subject who is lying down, it is necessary for an X-ray tube unit to direct its angle in an arbitrary direction. To meet this requirement it is necessary to reduce the size of the X-ray tube unit. An X-ray irradiation unit disclosed in the above-referenced patent publication permits adjustment in multiple stages, but the size of an X-ray tube unit used is large. Besides, if the X-ray tube unit is provided with plural drive devices such as motors, it becomes complicated in structure and gets out of order more frequently, with an increase of the manufacturing cost. 
   Accordingly, it is desirable to provide a filter unit simple in structure and small in size, as well as an X-ray tube unit and an X-ray imaging system both having the filter unit. 
   SUMMARY OF THE INVENTION 
   For solving the above-mentioned problems, a first aspect provides a filter unit comprising a filter plate, the filter plate having a first filter, a second filter disposed in a first direction with respect to the first filter and a third filter disposed in a second direction having a predetermined angle from the first direction with respect to the first filter, a guide plate having a guide frame for movement of the filter plate in the first and second directions, and a drive device for moving the filter plate. 
   According to this configuration, the filter plate having at least three filters can move in both first and second directions along the guide frame. Therefore, the filter unit of simple structure is provided. 
   In a filter unit according to a second aspect, the drive unit comprises a single motor and a rotary disc adapted to rotate by the drive motor. 
   According to this configuration, the filter plate can be moved in both first and second directions by a single drive motor. Since the filter plate can be moved in plural directions by a single drive motor, the filter unit is simple in structure and small-sized. 
   In a filter unit according to a third aspect, the rotary disc and the filter plate are connected with each other through a link member. 
   According to this configuration, since the rotary disc is connected to the filter plate through a link member, a rotational force of the rotary disc is applied to the filter plate. 
   In a filter unit according to a fourth aspect, a bushing is attached to the link member and is adapted to move along the guide frame. 
   According to this configuration, the bushing of the link member moves in the first and second directions along the guide frame. Consequently, a rotational force of the rotary disc is applied to the filter plate as a drive force acting in both first and second directions. 
   In a filter unit according to a fifth aspect, the guide plate is centrally provided with a first aperture, the rotary disc is centrally provided with a second aperture, and the guide plate and the rotary disc are superimposed one on the other. 
   According to this configuration, the filter plate rotates, centered at the first and second apertures. Besides, since the guide plate and the rotary disc are superimposed one on the other, a small space suffices and it is possible to attain the reduction in size of the filter unit. 
   In a filter unit according to a sixth aspect, the filter plate has a square outline and the first direction and the second direction are orthogonal to each other. 
   As can be seen from  FIG. 5 , if the filter plate has four filters, a square shape thereof is efficient and the filter unit can be constituted while saving space. 
   A seventh aspect of the present invention provides an X-ray tube unit having an X-ray tube, a collimator and a filter unit, the filter unit comprising a filter plate, the filter plate having a first filter, a second filter disposed in a first direction with respect to the first filter and a third filter disposed in a second direction having a predetermined angle from the first direction with respect to the first filter, a guide plate having a guide frame for movement of the filter plate in the first and second directions, and a drive device for moving the filter plate. 
   The filter plate has a first aperture formed centrally of the guide plate and a second aperture formed centrally of a rotary disc, the first aperture and the second aperture being in alignment with an axis joining an X-ray tube and an aperture of a collimator. 
   In an X-ray tube unit according to an eighth aspect, the filter plate has a first aperture formed centrally of the guide plate and a second aperture formed centrally of a rotary disc, the first aperture and the second aperture being in alignment with an axis joining an X-ray tube and an aperture of a collimator. 
   Further, such an X-ray tube unit is employable in an X-ray imaging system. 
   According to such a configuration it is possible to provide an X-ray tube unit simple in structure and small-sized, and an X-ray imaging system using the X-ray tube unit can be reduced in cost. Besides, since the first and second apertures being in alignment with an axis joining the X-ray tube and the collimator aperture, an X-ray beam emitted from the X-ray tube is not obstructed halfway. 
   According to the embodiments described herein, a filter unit having at least three filters can be provided in a simple structure and reduced size. Therefore, it is possible to implement a small-sized X-ray tube unit and an X-ray imaging system having such an X-ray tube unit. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram showing the configuration of an X-ray imaging system  100  for obtaining an X-ray radioscopic image of a subject. 
       FIG. 2(   a ) is a perspective view showing a filter unit  12  that may be used with the X-ray imaging system shown in  FIG. 1  and  FIG. 2(   b ) is an exploded view thereof. 
       FIG. 3  is a sectional view of the filter unit  12 . 
       FIG. 4(   a ) is a plan view of the filter unit  12  and  FIG. 4(   b ) is a drive explaining diagram equivalent to the filter unit  12 . 
       FIGS. 5(   a )- 5 ( f ) are operation diagrams showing in what manner beam attenuating filters are switched one after another from F 1  to F 4  with use of drive explaining diagrams equivalent to the filter unit  12 . 
       FIG. 6(   a ) illustrates a filter plate  121  of a regular triangle and  FIG. 6(   b ) illustrates a filter plate  121  of a regular hexagon. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The best mode for carrying out the present invention will be described in detail hereinunder with reference to the drawings. The present invention is not limited to the best mode for carrying out the invention. 
   Entire Configuration of X-ray Imaging System.  FIG. 1  is a block diagram showing the configuration of an X-ray imaging system (CR: Computed Radiography)  100  for obtaining an X-ray transmitted image of a subject. 
   System  100  includes an X-ray tube  10  for emitting X-ray, a stand  32  for radiographing a subject in a stand-up state, a table  36  on which the subject is to lie down, and an operator console  80 . Flat panel detectors  34  for detecting X-ray after passing through the subject are attached to the stand  32  and the table  36  respectively. The operator console  80  has an X-ray data collector  86  for collecting image data transferred from the flat panel detectors  34 . The image data collected and stored by the X-ray data collector  86  are subjected to image processing in an image processor  87  and an X-ray radioscopic image resulting from the image processing is displayed on a display  81 . 
   The X-ray tube unit  10  is suspended from the ceiling in a diagnostic room through a support post  23  which is extended and contracted with a motor (not shown). The X-ray tube unit  10  and the support post  23  are connected with each other by a ball joint structure and the X-ray tube unit  10  is rotatable in any direction. Therefore, X-ray can be radiated in any direction in accordance with a portion to be radiographed of the subject. The X-ray tube unit  10  may be mounted to a movable stand disposed on a floor. 
   An X-ray power supply unit  84  is provided within the operator console  80  to supply electric power to the X-ray tube unit via an X-ray controller  82 . The X-ray tube unit  10  houses therein an X-ray tube  11 , a filter unit  12  and a collimator  13 . The X-ray tube  11  emits X-ray at voltage and current controlled by the X-ray controller  82 . The X-ray emitted from the X-ray tube  11  is adjusted its energy spectrum by the filter unit  12 . The collimator  13  has an aperture whose area is changeable and X-ray having been adjusted to an appropriate irradiation area is radiated to a subject through the aperture. The filter unit  12  has plural filters so that the energy spectrum can be changed. 
   In the X-ray tube unit  10  there is provided a drive motor  21  so that the plural filters in the filter unit  12  can be switched from one to another. The drive motor  21  is driven through a motor driver  89  under control by the X-ray controller  82 . 
   Configuration of Filter Unit  12 .  FIG. 2(   a ) is a perspective view showing the filter unit  12  according to an embodiment of the present invention and  FIG. 2(   b ) is an exploded view thereof  FIG. 3  illustrates the X-ray tube  10 , including sectional views of the X-ray tube  11 , filter unit  12  and collimator  13 . 
   The filter unit  12  includes a filter plate  121  having four filters, a guide plate  122  for guiding a moving route of the filter plate  121 , and a drive plate  123  for moving the filter plate  121  in a predetermined direction. 
   The filter plate  121  is provided with, for example, a beam attenuating filter F 1  of approximately 0.0 millimeters (mm), a beam attenuating filter F 2  of approximately 0.1 mm, a beam attenuating filter F 3  of approximately 0.2 mm and a beam attenuating filter F 4  of approximately 0.3 mm. By the beam attenuating filter F 1  of approximately 0.0 mm is meant a filter-free state with only the frame of the filter plate  121  being present. With respect to the beam attenuating filter F 1 , the beam attenuating filter F 2  is disposed in a first direction of the beam attenuating filter F 1  and the beam attenuating filter F 4  is disposed in a second direction orthogonal to the first direction. The beam attenuating filter F 3  is disposed in the second direction with respect to the beam attenuating filter F 2 . The filters are not limited to beam attenuating filters, but may be any other filters insofar as they change the characteristics of X-ray. One of the filters may be a light shielding filter as a substitute for a light shielding shutter and a metallic sheet having a percentage light shielding of 100% may also be used as one filter. 
   The filter plate  121  is centrally formed with a hole for passing therethrough of a pin  125 - a  of a link bar  125  which will be described later. The filters F 1  to F 4  are square in shape and the size of each filter is between approximately 10.0 square centimeters (cm 2 ) and approximately 15.0 cm 2 . The filters F 1  to F 4  may be circular. The filter plate  121  is square in shape and its size is between approximately 20.0 cm 2  and approximately 35.0 cm 2 . The material of the filter plate  121  is, for example, light-weight aluminum. 
   The filter plate  121  is provided with, for example, a beam attenuating filter F 1  of approximately 0.0 millimeters (mm), a beam attenuating filter F 2  of approximately 0.1 mm, a beam attenuating filter F 3  of approximately 0.2 mm and a beam attenuating filter F 4  of approximately 0.3 mm. By the beam attenuating filter F 1  of approximately 0.0 mm is meant a filter-free state with only the frame of the filter plate  121  being present. 
   The filters are not limited to beam attenuating filters, but may be any other filters insofar as they change the characteristics of X-ray. 
   For guiding a moving route of the filter plate  121 , the guide plate  122  is formed with a guide groove  122 - 3  between an outer guide plate  122 - 1  and an inner guide plate  122 - 2 . A bushing  127  is inserted into the guide groove  122 - 3 . A through hole is formed in the bushing  127  and a pin  125 - a  of a link bar  125  to be described later passes through the through hole. The bushing  127  is circular or square in shape so as to be movable along the guide groove  122 - 3 . The guide groove  122 - 3  is formed in conformity with the layout of the filters F 1  to F 4 . One side of the guide groove  122 - 3  extends in the first direction and the other side thereof extends in the second direction. 
   The bushing  127  is made up of a small-diameter bushing  127 - a  getting into the guide groove  123 - 3  and a large-diameter bushing  127 - b  put in contact with a surface of the outer guide plate  122 - 1  and that of the inner guide plate  122 - 2 . Consequently, as can be seen from  FIG. 3 , the bushing  127  can move in a plane in contact with the guide plate  122 . To prevent the bushing  127  from falling off the guide groove  122 - 3 , a side face of the outer guide plate  122 - 1  and that of the inner guide plate  122 - 2  may be formed in such a structure as sandwiches the bushing  127 . 
   The guide plate  122  is fixed to a fixed portion of the X-ray tube unit  10  and is disposed in a fixed positional relation to the X-ray tube  11 . That is, the outer guide plate  122 - 1  is fixed to a housing of the X-ray tube unit  10 . Although in  FIG. 2  the inner guide plate  122 - 2  is floating in the air, the inner guide plate  122 - 2  is connected in at least one position to the outer guide plate  122 - 1  or to another member. Centrally of the guide plate  122  is formed a first square aperture  122 - 4  for radiation of an X-ray beam emitted from the X-ray tube  11 . Of course, the aperture  122 - 4  may be a circular aperture. 
   The drive plate  123  is for moving the bushing  127  along the guide groove  122 - 3 . An outer periphery gear is formed on an outer periphery of the drive plate  123  and it is in mesh with a driving gear  124 . The driving gear  124  is connected to the drive motor  21 . A link bar  125  capable of rotating 360° is secured to a certain position of the drive plate  123 . The link bar  125  has a predetermined length and a pin  125 - a  is provided at one end of the link bar  125 . A front end portion of the pin  125 - a  is threaded and passes through the through hole of the bushing  127 , further through the central hole of the filter plate  121 , then comes into engagement with a nut  126 . Without specially providing the bushing  127 , the thickness of the pin  125 - a  may be made equal to the width of the guide groove  122 - 3 , thereby allowing the pin  125 - a  to fulfill the same function as the bushing  127 . 
   The drive plate  123  is fixed to the fixed portion of the X-ray tube unit  10  via a bearing (not shown) and is disposed in a fixed positional relation to the X-ray tube  11 . Centrally of the drive plate  123  is formed a second circular aperture  123 - 1  for radiation of an X-ray beam emitted from the X-ray tube  11 . Of course, the aperture  123 - 1  may be a square aperture. Although reference has been made above to an example in which the outer periphery gear is formed on the outer periphery of the drive plate  123 , the outer periphery gear may be substituted by an inner periphery gear formed on an inner periphery of the drive plate  123 . 
   As shown in  FIG. 3 , the guide plate  122  and the drive plate  123  are disposed in such a manner that the center of the first square aperture  122 - 4  and that of the second circular aperture  123 - 1  are coincident with an axis joining the center of the X-ray tube  11  and that of the collimator  13 . That is, the X-ray beam emitted from the X-ray tube  11  passes through the filter F in the filter plate  121  and then passes through the first square aperture  122 - 4 . Further, the X-ray beam passes through the second square aperture  123 - 1 , then through the collimator  13  and irradiates a subject (not shown). The filter unit  12  may be reversed right and left in  FIG. 3 , thereby allowing the X-ray beam to pass through the second circular aperture  123 - 1 , then through the first square aperture  122 - 4  and thereafter through the filter F in the filer plate  121 . 
   Operation of Filter Unit  12 .  FIG. 4(   a ) is a plan view of the filter unit  12  and  FIG. 4(   b ) is a drive explaining diagram equivalent to the filter unit  12 . 
   In  FIG. 4(   a ), upon rotation of the drive motor  21 , the drive gear  124  rotates and so does the drive plate  123 . With rotation of the drive plate  123 , the link bar  125  moves. The pin  125 - a  of the link bar  125  is connected to the bushing  127  and the bushing  127  moves along the guide groove  122 - 3 , so that the link bar  125  rotates with respect to the drive plate  123 . 
   Since the guide plate  122  is fixed, the filter plate  121  moves along the guide groove  122 - 3 . In the state of  FIG. 4(   a ), an intermediate position between the beam attenuating filters F 1  and F 2  lies in the central square aperture of the guide plate  122  and the central circular aperture of the drive plate  123 . When the drive motor  21  rotates, the filter plate  121  moves along the guide groove  122 - 3  with respect to the central square aperture of the guide plate  122  and the central circular aperture of the drive plate  123 . 
   For briefly explaining the operation of the filter plate  121 , reference is here made to the drive explaining diagram of  FIG. 4(   b ) equivalent to the plan view of  FIG. 4(   a ). 
   The guide groove  122 - 3 , the drive plate  123 , and the link bar  125 , shown in  FIG. 4(   a ), are equivalent to an imaginary guide groove  222 - 3 , an imaginary bar  223 , and an imaginary drive member  224 , respectively, in  FIG. 4(   b ). Likewise, the link bar  125  and the bushing  127  in  FIG. 4(   a ) are equivalent to an imaginary link bar  225  and an imaginary bushing  227 , respectively, in  FIG. 4(   b ). 
     FIG. 5  comprises operation diagrams showing in what manner the beam attenuation filters are switched one after another from F 1  to F 4  with use of drive explaining diagrams equivalent to the filter unit  12 . 
     FIG. 5(   a ) shows a state in which the beam attenuating filter F 1  in the filter plate  121  is disposed in both the central square aperture of the guide plate  122  and the central circular aperture of the drive plate  123 . With rotation of the drive motor  21 , the filter unit  12  moves and, as shown in  FIG. 5(   b ), the beam attenuating filter F 2  is disposed in the central square aperture of the guide plate  122 . As the drive motor  21  further rotates, the filter unit  12  moves and a shift is made from the beam attenuating filter F 2  to the beam attenuating filter F 3 .  FIG. 5(   c ) shows this shifting state. 
     FIG. 5(   d ) shows a state in which a shift has been made to the beam attenuating filter F 3  with movement of the filter unit  12 . As the drive motor  21  further rotates, a shift is made from the beam attenuating filter F 3  to the beam attenuating filter F 4 .  FIG. 5(   e ) shows this shifting state. As the filter unit  12  further moves, a shift is made to the state of  FIG. 5(   f ) in which the beam attenuating filter F 4  is disposed in the central square aperture of the guide plate  122  and the central circular aperture of the drive plate  123 . 
   When the drive motor  21  is rotated reverse from its state shown in  FIG. 5(   f ), a shift is made from the beam attenuating filter F 4  and through the beam attenuating filters F 3  and F 2 , then the beam attenuating filter F 1  returns to the central square aperture of the guide plate  122 , as shown in  FIG. 5(   a ). In such an operation of the filter unit  12 , the bushing  127  does not pass a hatched portion S of the guide groove  122 - 3 . Therefore, in the hatched portion S it suffices for both outer guide plate  122 - 1  and inner guide plate  122 - 2  to be connected with each other. 
     FIG. 6  illustrate filter plates of other shapes with use of explanatory diagrams equivalent to the filter unit  12 . 
     FIG. 6(   a ) illustrates a filter plate  121  of a regular triangle and  FIG. 6(   b ) illustrates a filter plate  121  of a regular hexagon. The filter plate  121  of a regular triangle has three circular beam attenuating filters F 1  to F 3 . The filter plate  121  of a regular hexagon has six circular beam attenuating filters F 1  to F 6 . 
   As shown in  FIGS. 6(   a ) and  6 ( b ), there are formed imaginary guide grooves  222 - 3  of a regular triangle and a regular hexagon, and as imaginary bushings  227  move along the imaginary guide grooves  222 - 3 , the filter plates  121  of a regular triangle and a regular hexagon move and it is possible to replace beam attenuating filters one after another. Thus, as described above in connection with  FIGS. 2 to 5 , the shape of the filter plate  121  need not be limited to the square shape. 
   The filter unit  12  may be constructed so as to omit the drive motor  21  and instead permit manual adjustment where required. 
   Although the construction of the present invention has been described above in terms of an X-ray imaging system for obtaining an X-ray radioscopic image of a subject, the present invention is applicable also to an X-ray tube unit used for example in X-ray tomographic imaging apparatus. Moreover, the present invention is applicable to an industrial X-ray inspection apparatus using X-ray radiation. Further, the present invention is applicable not only to digital X-ray apparatus but also to X-ray apparatus for film.