Abstract:
A filter capable of adjusting spectrum in multiple stages and that capable of attaining the reduction of size, as well as an X-ray imaging system having such a filter, are provided. The filter, which is for adjusting the spectrum of passing radiation, comprises a support plate having an aperture for passage therethrough of radiation, plural filter plates supported by the filter plate and having mutually different filter characteristics, and moving device for moving the plural filter plates selectively to a position to close the aperture and a position to open the aperture.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Chinese Patent Application No. 200910118737.2 filed Jan. 24, 2009, which is hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     The embodiments described herein relate to a filter and an X-ray imaging system and, more particularly, to a filter for adjusting the spectrum of X-ray and an X-ray imaging system provided with such a filter. 
     In an X-ray imaging system, the spectrum of X-ray is adjusted by a filter and thereafter the X-ray is radiated to a subject. The filter is installed within a collimator box attached to an X-ray tube. In order to obtain a desired spectrum, plural filter plates of the filter, which are attached to a rotary disc, are used selectively (see, for example, Japanese Unexamined Patent Publication No. Hei 11 (1999)-76219 (Paragraph No. 0009, FIGS. 1 and 2)). 
     BRIEF DESCRIPTION OF THE INVENTION 
     It is desirable that the spectrum be adjustable in multiple stages. However, in the configuration wherein filter plates are switched over from one to another by device of a rotary disc, the adjustment is up to four stages at most. If an attempt is made to make adjustment possible in seven or more multiple stages in the rotary disc method, the rotary disc for the mounting of many filters becomes large-sized and thus such an attempt is not practical. 
     Accordingly, embodiments of the present invention provide a filter permitting the adjustment of spectrum in multiple stages and that permitting the reduction of size, as well as an X-ray imaging system provided with such a filter. 
     In a first aspect there is provided a filter for adjusting the spectrum of passing radiation, comprising: a support plate having an aperture for passage therethrough of radiation; a plurality of filter plates supported by the support plate and having mutually different filer characteristics; and moving device for moving the plural filter plates selectively to a position to close the aperture and a position to open the aperture. 
     In a second aspect there is provided, in accordance with the first aspect, a filter wherein the moving device comprises: spring device for operating the filter plates in a direction away from the aperture; a plurality of ratchets plates supported by the support plate in proximity to the filter plates and each having a notched portion; a first support point for supporting the filter plates pivotably on the support plate; a second support plate for supporting the ratchet plates pivotably on the support plate; a leaf spring connected to the filter plates and the ratchet plates, causing the filter plates and the ratchet plates to pivot interlockedly with each other; and a pawl engageable with the notched portions of the ratchet plates, the pawl being moved to pivot the ratchet plates, thereby making the filter plates movable to the position to close the aperture. 
     In a third aspect there is provided, in accordance with the first aspect, a filter wherein the support plate has a top layer and a bottom layer parallel to each other, and the filter plates are supported by the top layer and the bottom layer. 
     In a fourth aspect there is provided, in accordance with any of the first to the third aspects, a filter wherein the support plate is in the shape of disc and is formed with the apertures at a center thereof. 
     In a fifth aspect there is provided, in accordance with any of the first to the fourth aspects, a filter further comprising a ring capable of rotating along the circumference of the support plate, and the pawl is provided in the ring. 
     In a sixth aspect there is provided an X-ray imaging system for radiographing a subject with X-ray passing through a filter, the filter comprising: a support plate having an aperture for passage therethrough of radiation; a plurality of filter plates supported by the support plate and having mutually different filter characteristics; and moving device for moving the plural filter plates selectively to a position to close the aperture and a position to open the aperture. 
     In a seventh aspect there is provided, in accordance with the sixth aspect, an X-ray imaging system wherein the moving device comprises: spring device for operating the filter plates in a direction away from the aperture; a plurality of ratchet plates supported by the support plate in proximity to the filter plates and each having a notched portion; a first support point for supporting the filter plates pivotably on the support plate; a second support point for supporting the ratchet plates pivotably on the support plate; a leaf spring connected to the filter plates and the ratchet plates, causing the filter plates and the ratchet plates to pivot interlockedly with each other; and a pawl engageable with the notched portions of the ratchet plates, the pawl being moved to pivot the ratchet plates, thereby making the filter plates movable to the position to close the aperture. 
     In an eighth aspect there is provided, in accordance with the sixth aspect, an X-ray imaging system wherein the support plate has a top layer and a bottom layer parallel to each other, and the filter plates are supported by the top layer and the bottom layer. 
     In a ninth aspect of the present invention there is provided, in accordance with any of the sixth to eighth aspects, an X-ray imaging system wherein the support plate is in the shape of a disc and is formed with the aperture at a center thereof. 
     In a tenth aspect there is provided, in accordance with any of the sixth to ninth aspects, an X-ray imaging system wherein the filter further comprises a ring capable of rotating along the circumference of the support plate, and the pawl is provided in the ring. 
     According some embodiments, since the filter for adjusting the spectrum of passing radiation comprises: a support plate having an aperture for passage therethrough of radiation; a plurality of filter plates supported by the support plate and having mutually different filter characteristics; and moving device for moving the plural filter plates selectively to a position to close the aperture and a position to open the aperture, it is possible to realize a filter capable of adjusting the spectrum in multiple stages and capable of attaining the reduction of size, as well as an X-ray imaging system provided with such a filter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing the configuration of an X-ray imaging system as an example of the best mode for carrying out the invention. 
         FIG. 2  is a diagram showing a schematic configuration of a filter. 
         FIG. 3  is a diagram showing a schematic configuration of the filter. 
         FIG. 4  is an exploded diagram showing the configuration of the filter. 
         FIGS. 5A and 5B  are diagrams showing the configuration and operation of parallel links 
         FIGS. 6A ,  6 B, and  6 C are diagrams showing the configuration and operation of the parallel links. 
         FIG. 7  is a diagram showing the configuration of a pawl. 
         FIG. 8  is a diagram showing an operating condition of the filter. 
         FIG. 9  is a diagram showing a further operating condition of the filter. 
         FIG. 10  is a diagram showing a still further operating condition of the filter. 
         FIG. 11  is a diagram showing a still further operating condition of the filter. 
         FIG. 12  is a diagram showing a still further operating condition of the filter. 
         FIG. 13  is a diagram showing a still further operating condition of the filter. 
         FIG. 14  is a diagram showing a still further operating condition of the filter. 
         FIG. 15  is a diagram showing a still further operating condition of the filter. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention will be described in detail hereinunder with reference to the drawings. The present invention is not limited to the embodiments described herein. 
       FIG. 1  shows a schematic configuration of an X-ray imaging system. 
     AS shown in the same figure, this system includes an X-ray irradiator  10 , an X-ray detector  20  and an operator console  30 . The X-ray irradiator  10  and the X-ray detector  20  are opposed to each other with a subject  40  therebetween. 
     The X-ray irradiator  10  includes an X-ray tube  12  and a collimator box  14 . A filter  16  and a collimator  18  are accommodated within the collimator box  14 . The filter  16  is an example of the best mode for carrying out the invention. With the configuration of the filter  16  there is shown an example of the best mode for carrying out the invention with respect to the filter. 
     X-ray emitted from the X-ray tube  12  is adjusted its spectrum by the filter  16  and is then radiated to the subject  40  through an aperture of the collimator  18 . The filter  16  is a spectrum variable filter. The collimator  18  is an aperture variable collimator. 
     The X-ray which has passed through the subject  40  is detected by the X-ray detector  20  and is inputted to the operator console  30 . On the basis of the inputted signal the operator console  30  reconstructs a radioscopic image of the subject  40 . The reconstructed image is displayed on a display  32  of the operator console  30 . 
     The operator console  30  controls the X-ray irradiator  10 . Control of the filer  16  and that of the collimator  18  are included in the control of the X-ray irradiator  10  made by the operator console  30 . Where required, the filter  16  and the collimator  18  can be adjusted manually. 
       FIG. 2  shows the configuration of the filter  16  schematically. As shown in  FIG. 2 , the filter  16  is of a two-layer structure comprising a top layer  100  and a bottom layer  200 . The top layer  100  has an aperture  102  and the bottom layer  200  has an aperture  202 . The apertures  102  and  202  are concentric and equal in size and X-ray passes through the apertures  102  and  202 . 
     The top layer  100  and the bottom layer  200  each have on the outer periphery thereof such a ring as will be described later. The rings are integrally driven by a motor  300  via a gear  302  so as to be rotatable reversibly in clockwise and counterclockwise directions. 
       FIG. 3  shows a ring-detached state and a ring-attached state with respect to the top layer  100  and the bottom layer  200 . As shown in  FIG. 3 , the top layer  100  and the bottom layer  200  include disc-like top support  104  and bottom support  204  assembled together in facing relation to each other, as well as rings  106  and  206  attached respectively to their outer peripheries in a rotatable manner. 
     The top support  104  and the bottom support  204  do not rotate and are formed with the apertures  102  and  202  respectively at their centers. The rings  106  and  206  are integrally driven by the motor  300  via the gear  302  and are adapted to rotate along the circumference of the top support  104  and that of the bottom support  204  respectively. 
       FIG. 4  shows a disassembled state of the filter  16  into the top layer  100  and the bottom layer  200 .  FIG. 4  shows a state in which the top support  104  and the bottom support  204  are opened to both right and left at the confronting portion thereof. 
     The top support  104  and the bottom support  204  are coupled together by three holes  108   a ,  108   b ,  108   c  formed in the top support  104  and three studs  208   a ,  208   b ,  208   c  formed on the bottom support  104 . 
     The rings  106  and  206  are coupled together by three holes  109   a ,  109   b ,  109   c  formed in the ring  106  and three studs  209   a ,  209   b ,  209   c  formed on the ring  206 . 
     The top support  104  has three filter plates  110 ,  120  and  130  on an inner surface thereof, i.e., on its surface confronting the bottom support  204 . The filter plates  110 ,  120  and  130  comprise three steel plates or the like different in thickness and supported by a support frame. For example, the three steel plates or the like are 0.1, 0.2 and 0.3 mm, respectively, in thickness. 
     The filter plates  110 ,  120  and  130  constitute a part of three parallel link mechanisms, and with operation of the parallel links, the filter plates are adapted to advance and retreat to a position to close the aperture  120  and a position to open the same aperture. 
     The three parallel links are driven in order by a pawl  140  which rotates together with the ring  106 . Here there is shown a state in which with operation of the pawl  140  the filter plate  110  has advanced to the position to close the aperture  102 , while the filter plates  120  and  130  have retreated to the position to open the aperture  102 . 
     The bottom support  204  has three filter plates  210 ,  220  and  230  on an inner surface thereof, i.e., on its surface confronting the top support  104 . The filter plates  210 ,  220  and  230  comprise three steel plates or the like different in thickness and supported by a support frame. For example, the three steel plates or the like are 0.6, 0.9 and 1.5 mm, respectively, in thickness. 
     The filter plates  210 ,  220  and  230  constitute a part of the three parallel links, and with operation of the parallel links, the filter plates are adapted to advance and retreat to a position to close the aperture  202  and a position to open the same aperture. 
     The three parallel links are driven in order by a pawl  240  which rotates together with the ring  206 . Here there is shown a state in which with operation of the pawl  240  the filter plate  210  has advanced to the position to close the aperture  202 , while the filter plates  220  and  230  have advanced to the position to open the aperture  202 . 
       FIGS. 5A and 5B  show the configuration and operation of parallel links with respect to the filter plate  110 . Also as to the other filter plates  120  to  230 , the configuration and operation of parallel links are the same. As shown in  FIGS. 5A and 5B , the parallel links are made up of links A, B, C, D and joints a, b, c, d. The link A is a fixed link, the link B is a driving link, the link C is a parallel moving link, and the link D is a driven link. 
     The driven link D is constituted by the filter plate  110  and the driving link B is constituted by a ratchet plate  112 . The filter plate  110  is rotatable about the joint a, the ratchet plate  112  is rotatable about the joint b, and both are connected together at the joints c and d through the link C. 
     With such an operation of the parallel links, the filter plate  110  assumes either such a retreated state as  FIG. 5A  or such an advanced state as  FIG. 5B . The filter plate  110 , in its retreated state  FIG. 5A , opens the aperture  102 , while in its advanced state  FIG. 5B  it closes the aperture  102 . 
     As shown in  FIGS. 6A ,  6 B, and  6 C, a tensile force induced by a spring  114  acts on the filter plate  110  constantly. Consequently, while the parallel links are not in operation, the filter plate  110  is in abutment against a stop pin  116 , as shown in  FIG. 6A . 
     The parallel links operate when the ratchet plate  112  is pushed up by the pawl  140 . The pawl  140  rotates while describing a circular path together with the ring  106  and pushes up the ratchet plate  112  when it rotates in the counterclockwise direction, thereby causing rotation of the ratchet plate  112 . As a result, the parallel links operate and the filter plate  110  advances to the position to close the aperture  102 , as shown in  FIG. 6B . The engagement between the ratchet plate  112  and the pawl  140  in this state is as shown on a larger scale in  FIG. 6C . 
     As shown in  FIG. 7 , the pawl  140  is attached to the ring  106  rotatably with a shaft  142 . A rotating force is applied in the counterclockwise direction in the figure by means of a coil spring  144  mounted on the shaft  142  and the pawl  140  is in an abutted state against a stop pin  146 . One end of the coil spring  144  is fixed to the pawl  140  and an opposite end thereof is fixed to a pin  148 . 
     When the pawl  140  stays at the position b as shown in  FIGS. 6A ,  6 B, and  6 C, the filter plate  110  stays at its advanced position. As the pawl  140  further moves in the counterclockwise direction from this state, the pawl  140  passes while pushing aside the ratchet plate  112 . At this time, with the restoring force of the spring  114 , the filter plate  110  retreats and the aperture  102  is opened. 
     When the ring  106  rotates in the clockwise direction, the pawl  140  cannot push up the ratchet plate  112 , so that the ratchet plate  112  is not actuated and hence the parallel links do not operate. 
     A description will now be given about a synthetic operation of the filter  16  thus constructed. Behaviors of the filter plates with rotation of the pawls  140  and  240  are shown in order in  FIGS. 8 to 14 .  FIGS. 8 to 14  are diagrams in which the top layer  100  and the bottom layer  200  are seen in an X-ray irradiating direction. 
       FIG. 8  shows an initial state of both top layer  100  and bottom layer  200 . In the initial state, none of the filter plates close the apertures  102  and  202 . This corresponds to the state in which a filter plate having a thickness of zero has been inserted into the apertures  102  and  202 . 
     With counterclockwise rotation of the rings  106  and  206  and with drive by the pawl  140 , filter plates 0.1, 0.2 and 0.3 located on the top player  100  side advance in order to the position to close the aperture  102 , as shown in  FIGS. 9 ,  10  and  11 . In this way X-ray spectrum is adjusted by each of the filter plates. During this period, on the bottom layer  200  side, all the filter plates stay in their retreated positions because the pawl  240  passes while stroking all the ratchet plates. 
     With clockwise rotation of the rings  106  and  206  and with drive by the pawl  240 , filter plates 0.6, 0.9 and 1.5 located on the bottom layer  200  side advance in order to the position to close the aperture  202 , as shown in  FIGS. 12 ,  13  and  14 . In this way X-ray spectrum is adjusted by each of the filter plates. During this period, on the top layer  100  side, all the filter plates stay in their retreated positions because the pawl  140  passes while stroking all the ratchet plates. 
     In this way it is possible to obtain the filter  16  whose filter plate thickness changes in seven stages. The filter  16  has a two-layer structure of both top layer  100  and bottom layer  200 , and each layer has three filter plates driven by parallel links, thus facilitating reduction of the entire size. 
     Two pawls for actuating parallel links may be provided for each layer as in  FIG. 15 . With two pawls  140   a  and  140   b  and  240   a  and  240   b , it is possible to shorten the time for access to the filter plate located at the remotest position from the current position of each pawl. 
     When the number of switching stages of filter plates may be four, the filter  16  may be of a single-layer structure of either the top layer  100  or the bottom layer  200 . Further, the number of filter plates per layer is not limited to three, but may be any other suitable number.