Abstract:
A collimator comprises a pair of first plate members having X-ray absorbability and a pair of second plate members having X-ray absorbability. The pair of first plate members are movable in a direction parallel to surfaces thereof, and have respective end faces opposed to each other with an X-ray passing aperture being defined by a spacing between the opposed end faces of the first plate members. The pair of second plate members are capable of being folded in a zigzag fashion through hinges, and in order to intercept other X-rays than the X-ray passing through the aperture, each of the second plate members is connected at one end thereof to each end of the first plate members on the side opposite to the opposed end faces of the first plate members and is connected at the other end thereof to each of fixing portions.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to a collimator, an X-ray irradiator, and an X-ray apparatus. Particularly, the present invention is concerned with a collimator for defining an X-ray irradiation range, as well as an X-ray irradiator and an X-ray apparatus both provided with the collimator.  
         [0002]     In an X-ray irradiator there is used a collimator for defining an X-ray irradiation range. The collimator has an aperture which permits the passage of X-ray therethrough. The other portion than the aperture of the collimator does not permit the passage of X-ray. The degree of opening of the aperture is changeable, whereby the X-ray irradiation range can be adjusted.  
         [0003]     The collimator with such an adjustable aperture has movable plate members, i.e., blades, possessing X-ray absorbability. There are used a pair of blades having respective end faces opposed to each other. The pair of blades are movable in directions opposite to each other in a plane parallel to their surfaces. For widening the aperture, the pair of blades are moved in directions away from each other, while for narrowing the aperture, the pair of blades are moved toward each other.  
         [0004]     For reducing the collimator size without sacrificing the adjustable range of the aperture, there has been proposed an X-ray irradiator wherein blades are constructed of a flexible material and are wound onto drums to widen the aperture, while they are delivered from the drums to narrow the aperture (see, for example, Patent Document 1).  
         [0005]     [Patent Document] Japanese Published Unexamined Patent Application No. 2002-355242 (pages 2-3, FIGS. 1-2)  
         [0006]     In the above conventional collimator there is the problem that a special material which is flexible and superior in X-ray absorbability must be used as the blade material.  
       SUMMARY OF THE INVENTION  
       [0007]     Accordingly, it is an object of the present invention to provide a collimator which can be reduced in size without using any special material and without sacrificing an adjustable range of an aperture, as well as an X-ray irradiator and an X-ray apparatus both provided with such a collimator.  
         [0008]     (1) In one aspect of the present invention for solving the above-mentioned problem there is provided a collimator comprising: a pair of first plate members having X-ray absorbability, movable in a direction parallel to surfaces thereof, and having respective end faces opposed to each other, with an X-ray passing aperture being defined by a spacing between the opposed end faces of the first plate members; and a pair of second plate members each of which has X-ray absorbability, is capable of being folded in a zigzag fashion through hinges, and is connected at one end thereof to an end of each of the pair of first plate members on the side opposite to the opposed end faces of the first plate members and connected at the other end thereof to a fixing portion in order to intercept other X-rays than the X-ray passing through the aperture.  
         [0009]     (2) In another aspect of the present invention for solving the above-mentioned problem there is provided an X-ray irradiator comprising an X-ray tube and a collimator for collimating X-ray emitted from the X-ray tube. The collimator comprises: a pair of first plate members having X-ray absorbability, movable in a direction parallel to surfaces thereof, and having respective end faces opposed to each other, with an X-ray passing aperture being defined by a spacing between the opposed end faces of the first plate members; and a pair of second plate members each of which has X-ray absorbability, is capable of being folded in a zigzag fashion through hinges, and is connected at one end thereof to an end of each of the pair of first plate members on the side opposite to the opposed end faces of the first plate members and connected at the other end thereof to a fixing portion in order to intercept other X-rays than the X-ray passing through the aperture.  
         [0010]     (3) In a further aspect of the present invention for solving the above-mentioned problem there is provided an X-ray apparatus comprising an X-ray tube, a collimator for collimating X-ray emitted from the X-ray tube and applying the collimated X-ray to an object to be radiographed, and a detector means for detecting the X-ray which has passed through the object to be radiographed. The collimator comprises: a pair of first plate members having X-ray absorbability, movable in a direction parallel to surfaces thereof, and having respective end faces opposed to each other, with an X-ray passing aperture being defined by a spacing between the opposed end faces of the first plate members; and a pair of second plate members each of which has X-ray absorbability, is capable of being folded in a zigzag fashion through hinges, and is connected at one end thereof to an end of each of the pair of first plate members on the side opposite to the opposed end faces of the first plate members and connected at the other end thereof to a fixing portion in order to intercept other X-rays than the X-ray passing through the aperture.  
         [0011]     In the above aspects of the present invention, since the second plate members which constitute blades together with the first plate members can be folded in a zigzag fashion through hinges, it is possible to reduce an external size of the collimator without using any special material such as a flexible X-ray absorbing material and without sacrificing an adjustable range of the aperture.  
         [0012]     In the above aspects of the present invention it is preferable, in point of defining an X-ray irradiation range in two directions perpendicular to each other, that the collimator further comprise: a pair of third plate members having X-ray absorbability, being movable in a direction parallel to surfaces thereof and perpendicular to the moving direction of the first plate members, and having respective end faces opposed to each other, with an X-ray passing aperture being defined by a spacing between the opposed end faces of the third plate members; and a pair of fourth plate members each of which has X-ray absorbability, is capable of being folded in a zigzag fashion through hinges, and is connected at one end thereof to and end of each of the third pair of plate members on the side opposite to the opposed end faces of the third plate members and connected at the other end thereof to a fixing portion in order to intercept other X-rays than the X-ray passing through the aperture.  
         [0013]     In point of increasing the degree of freedom in setting an irradiation range in the moving direction of the pair of first plate members, it is preferable that the pair of first plate members be movable independently of each other. Likewise, in point of increasing the degree of freedom in setting an irradiation range in the moving direction of the pair of third plate members, it is preferable that the pair of third plate members be movable independently of each other.  
         [0014]     According to the present invention, it is possible to provide a collimator capable of being reduced in size without using any special material and without sacrificing the aperture, as well as an X-ray irradiator and an X-ray apparatus provided with the collimator.  
         [0015]     Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  illustrates a schematic construction of an X-ray apparatus;  
         [0017]      FIG. 2  illustrates the construction of a principal portion of a collimating plate;  
         [0018]      FIG. 3  illustrates the construction of a drive mechanism;  
         [0019]      FIG. 4  illustrates the construction of a link mechanism; and  
         [0020]      FIG. 5  illustrates in what state an aperture is formed. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     An embodiment of the present invention will be described in detail hereinunder with reference to the accompanying drawings, provided the invention is not limited to the embodiment.  FIG. 1  illustrates a schematic construction of an X-ray apparatus according to an embodiment of the present invention. With the construction of this apparatus, there is shown a working example of the apparatus according to the present invention.  
         [0022]     In the X-ray apparatus, as shown in the same figure, X-ray emitted from an X-ray tube  1  is diaphragmed by an X-ray diaphragm  3  and is collimated by a collimating plate  500  disposed within a collimator  5 , then the collimated X-ray is directed to an object  7  to be radiographed and the X-ray which has passed through the object  7  is detected by a detector  9 . The X-ray tube  1  is a working example of the X-ray used in the present invention. The collimator  5  is a working example of the collimator used in the present invention. The detector  9  is a working example of the detector used in the present invention.  
         [0023]     The portion consisting of the X-ray tube  1 , X-ray diaphragm  3  and collimator  5  is a working example of the X-ray irradiator according to the present invention. With the construction of this portion there is shown a working example of the X-ray irradiator according to the present invention. The collimator  5  is a working example of the collimator used in the present invention. With the construction of the portion in question there is shown a working example of the collimator used in the present invention.  
         [0024]     The X-ray tube  1  has an anode  101  and a cathode  103 , and X-ray is emitted from a collision point (focal point) of electrons which are emitted from the cathode  103  toward the anode  101 . The X-ray thus emitted passes through the X-ray diaphragm  3  and the collimator  5  and is incident on an object to be radiographed. The X-ray diaphragm  3  is constructed of an X-ray absorbing material such as lead for example. The collimating plate  500  of the collimator  5  is also constructed of an X-ray absorbing material such as lead for example.  
         [0025]     The X-ray diaphragm  3  shapes the X-ray emitted from the X-ray tube  1  into a pyramidal beam with the X-ray focus on the anode  101  as a vertex. With an aperture formed by the collimating plate  500  of the collimator  5  there is defined an X-ray irradiation field. The aperture is changeable, whereby the X-ray irradiation field V is adjusted.  
         [0026]     A description will now be given of the collimating plate  500  in the collimator  5 .  FIG. 2  illustrates the construction of a principal portion of the collimating plate  500 . As shown in the same figure, the collimating plate  500  has an upper blade  510  and a lower blade  520  which are respectively disposed in two upper and lower stages. In the same figure, three directions perpendicular to one another are assumed to be x, y, and z, of which z represents the vertical direction. X-ray is radiated from above.  
         [0027]     The upper blade  510  has a pair of horizontal plates  512  and  512 ′. The horizontal plates  512  and  512 ′ are rectangular plates and are constructed of an X-ray absorbing material such as lead for example. The horizontal plates  512  and  512 ′ lie on one and same horizontal plane and their longs sides are parallel to each other, while their corresponding pairs of short sides each lie on one and same straight line. The horizontal plates  512  and  512 ′ are displaceable in the direction of their short sides (in x direction), whereby the distance “a” between their end faces opposed to each other can be adjusted. The horizontal plates  512  and  512 ′ are a working example of the first plate members used in the present invention.  
         [0028]     The horizontal plates  512  and  512 ′ are positionally adjustable each independently. An example of a drive mechanism which enables such a positional adjustment is shown in  FIG. 3 . As shown in the same figure, the horizontal plates  512  and  512 ′ are provided with arms  601  and  601 ′, respectively, which extend in y direction. End portions of the arms  601  and  601 ′ are engaged with shafts  603  and  603 ′, respectively.  
         [0029]     The shafts  603  and  603 ′ are parallel shafts extending in x direction and are spaced from each other through a predetermined spacing in z direction. The arm  601 ′ is bent in order to equalize the height in z direction of the horizontal plate  512 ′ to that of the horizontal plate  512 .  
         [0030]     The shafts  603  and  603 ′ are threaded throughout their overall lengths. The engaged portions of the arms  601  and  601 ′ with the shafts  603  and  603 ′ are internally threaded correspondingly. Motor  605  is mounted on one end of the shaft  603 , and a motor  605 ′ is mounted on one end of the shaft  603 ′. The motor  605  is capable of performing forward and reverse rotation. The motors  605  and  605 ′ are controlled each independently by control means (not shown).  
         [0031]     A pair of folding plates  514  and  514 ′ are connected to the horizontal plates  512  and  512 ′, respectively. One end of each of the folding plates  514  and  514 ′ is connected respectively to each end face of the horizontal plates  512  and  512 ′ on the side opposite to mutually opposed end faces of the horizontal plates, while the other end of each of the folding plates  514  and  514 ′ is connected respectively to a fixing portion.  
         [0032]     The pair of folding plates  514  and  514 ′ are also constructed of an X-ray absorbing material such as lead for example. For example, the folding plates  514  and  514 ′ are each constituted by a quadribent plate capable of being folded in a zigzag fashion. The number of bent portions is not limited to four, but may be any other appropriate number. The bent portions of the folding plates  514  and  514 ′ are constituted by hinges  516  and  516 ′. The hinges  516  and  516 ′ are also formed of such a material as lead, not permitting the passage of X-ray therethrough. The folding plates  514  and  514 ′ are a working example of the second plate members used in the present invention.  
         [0033]     The folding plates  514  and  514 ′ are provided with link mechanisms at both end faces of the hinges, an example of which is shown in  FIG. 4 . As shown in the same figure, link mechanisms  700  and  700 ′ are provided at one and opposite end faces of the folding plated  514  and  514 ′.  
         [0034]     The link mechanisms  700  and  700 ′ have bent portions symmetric with respect to the bent portions of the folding plates  514  and  514 ′ and are mounted to the end faces of the folding plates  514  and  514 ′ through rotary shafts  718  and  718 ′ so as to be bent through the hinges  716  and  716 ′. With such link mechanisms  700  and  700 ′, intermediate portions of the folding plates  514  and  514 ′ are prevented from sagging.  
         [0035]     The lower blade  520  also has the same construction as the upper blade  510 . That is, the lower blade  520  has a pair of rectangular, horizontal plates  522  and  522 ′ constructed of an X-ray absorbing material such as lead for example. The horizontal plates  522  and  522 ′ lie on one and same horizontal plate and their long sides are parallel to each other, while their corresponding pairs of short sides each lie on one and same straight line.  
         [0036]     The horizontal plane where the horizontal plates  522  and  522 ′ are present underlies the horizontal plane where the horizontal plates  512  and  512 ′ of the upper blade  510  are present. The direction of long sides of the horizontal plates  522  and  522 ′ is perpendicular to the direction of long sides of the horizontal plates  512  and  512 ′ of the upper blade  510 .  
         [0037]     The horizontal plates  522  and  522 ′ are displaceable in their short side direction (y direction), whereby the distance “b” between their mutually opposed end faces can be adjusted. A positional adjustment for the horizontal plates  522  and  522 ′ is done by a drive mechanism similar to that shown in  FIG. 3 . The horizontal plates  522  and  522 ′ are a working example of the third plate members used in the present invention.  
         [0038]     A pair of folding plates  524  and  524 ′ are connected to the horizontal plates  522  and  522 ′, respectively. More specifically, one end of each of the folding plates  524  and  524 ′ is connected to an end face of each of the horizontal plates  522  and  522 ′ on the side opposite to the mutually opposed end faces of the horizontal plates, while the other end of each of the folding plates  524  and  524 ′ is connected respectively to a fixing portion.  
         [0039]     The pair of folding plates  524  and  524 ′ are also formed of an X-ray absorbing material such as lead for example. The folding plates  524  and  524 ′ are constituted, for example, by a quadribent plate capable of being folded in a zigzag fashion. The number of such bent portions is not limited to four, but may be any other appropriate number. The bent portions of the folding plates  524  and  524 ′ are constituted by hinges  526  and  526 ′. The hinges  526  and  526 ′ are also formed of an X-ray absorbing material such as lead for example, not permitting the passage of X-ray therethrough. The folding plates  524  and  524 ′ are a working example of the fourth plate members used in the present invention. The folding plates  524  and  524 ′ are provided at both end faces of the hinges with link mechanisms similar to those shown in  FIG. 4  to prevent sagging of their intermediate portions.  
         [0040]     With the collimating plate  500  of the above construction, such a quadrangular aperture having a size of “a×b” as shown in  FIG. 5  is formed for the X-ray emitted from the X-ray tube  1 . Since the positions of the four horizontal plates  512 ,  512 ′,  522 , and  522 ′ can be changed each independently, the sizes a and b in both directions of the aperture can be adjusted each independently and a two-dimensional position of the aperture is also adjustable as desired.  
         [0041]     In this case, since the folding plates  514 ,  514 ′,  524 , and  524 ′ are adapted to expand and contract according to the positions of the horizontal plates  512 ,  512 ′,  522 , and  522 ′, an external size of the collimating plate  500  does not increase even if the aperture is widened, thus permitting the reduction in size of the collimator. Besides, since the horizontal plates  512 ,  512 ′,  522 ,  522 ′ and the folding plates  514 ,  514 ′,  524 ,  524 ′ can both be fabricated by lead plates for example, there is not required any special material. In the case either the aperture size a or b may always be a fixed value, the plates on that side may be constituted, for example, by lead plates which define a fixed aperture.  
         [0042]     Many widely different embodiments of the invention may be configured without departing from the spirit and the scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in the specification, except as defined in the appended claims.