Abstract:
With a view to providing an X-ray irradiator capable of detecting a relative rotational angle of a collimator box with respect to an X-ray tube, the X-ray irradiator comprises: an X-ray tube having a flange formed around an X-ray output window; a collimator box having an entry plate formed with an X-ray incidence window, the collimator box accommodating a collimator in the interior thereof; a ring provided on the entry plate so as to surround the X-ray incidence window, the ring receiving therein the flange of the X-ray tube and having a plurality of slots formed radially through the ring; a plurality of tongue pieces being inserted through the slots from outside to inside of the ring and holding down a back side of the flange; and sensor device provided inside the flange to detect a relative rotational angle of the collimator box with respect to the flange.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to an X-ray irradiator and an X-ray imaging apparatus. Particularly, the present invention is concerned with an X-ray irradiator for irradiation of X-rays from an X-ray tube through a collimator, as well as an X-ray imaging apparatus using the X-ray irradiator.  
         [0002]     In an X-ray imaging apparatus, X-rays are radiated to a subject while limiting an irradiation field by means of a collimator. The collimator is housed within a collimator box attached to an X-ray tube (see, for example, Patent Literature 1).  
         [0003]     [Patent Literature 1] Japanese Unexamined Patent Publication No. 2003-61941 (page 3, FIG. 1)  
         [0004]     A certain object requires to be photographed in an appropriately rotated state of a collimator box relative to an X-ray tube. When the collimator box is rotated, a frame of a display image also rotates. For correcting this state to obtain an erected image frame constantly, it is necessary to detect a rotational angle of the collimator box.  
       SUMMARY OF THE INVENTION  
       [0005]     Therefore, it is an object of the present invention to provide an X-ray irradiator capable of detecting a relative rotational angle of a collimator box with respect to an X-ray tube, as well as an X-ray imaging apparatus using such an X-ray irradiator.  
         [0006]     In one aspect of the present invention for achieving the above-mentioned object there is provided an X-ray irradiator comprising: an X-ray tube having a flange formed so as to surround an X-ray output window; a collimator box having an entry plate formed with an X-ray incidence window, the collimator box accommodating a collimator in the interior thereof; a ring provided on the entry plate so as to surround the X-ray incidence window, the ring receiving therein the flange of the X-ray tube and having a plurality of slots formed radially through the ring; a plurality of tongue pieces being inserted through the slots from outside to inside of the ring and holding down a back side of the flange; and a sensor means provided inside the flange to detect a relative rotational angle of the collimator box with respect to the flange.  
         [0007]     In another aspect of the present invention for achieving the above-mentioned object there is provided an X-ray imaging apparatus having an X-ray irradiator and an X-ray detector both opposed to each other, the X-ray irradiator comprising: an X-ray tube having a flange formed so as to surround an X-ray output window; a collimator box having an entry plate formed with an X-ray incidence window, the collimator box accommodating a collimator in the interior thereof; a ring provided on the entry plate so as to surround the X-ray incidence window, the ring receiving therein the flange of the X-ray tube and having a plurality of slots formed radially through the ring; a plurality of tongue pieces being inserted through the slots from outside to inside of the ring and holding down a back side of the flange; and a sensor means provided inside the flange so as to detect a relative rotational angle of the collimator box with respect to the flange.  
         [0008]     For making non-contact detection possible, it is preferable that the sensor means be an optical sensor means.  
         [0009]     For detecting a relative rotational angle properly, it is preferable for the optical sensor means to have an optical pattern provided on the flange side and an optical sensor provided on the entry plate side.  
         [0010]     For obtaining a continuous pattern free of a break, it is preferable that the optical pattern form a ring along an inner periphery of the flange.  
         [0011]     For facilitating the detection of an angle, it is preferable for the optical pattern to be a comb teeth-like pattern.  
         [0012]     For making an angle original clear, it is preferable that the comb teeth-like pattern have a notch for an angle origin.  
         [0013]     For preventing an excessive rotation, it is preferable for the X-ray irradiator to be provided with a limiting means for limiting a maximum rotational angle of the collimator box.  
         [0014]     For the simplification of construction, it is preferable that the limiting means have a pin provided on the entry plate side and an arcuate slot provided on the flange side so as to engage the pin.  
         [0015]     According to the present invention it is possible to provide an X-ray irradiator comprising: an X-ray tube having a flange formed so as to surround an X-ray output window; a collimator box having an entry plate formed with an X-ray incidence window, the collimator box accommodating a collimator in the interior thereof; a ring provided on the entry plate so as to surround the X-ray incidence window, the ring receiving therein the flange of the X-ray tube and having a plurality of slots formed radially through the ring; a plurality of tongue pieces being inserted through the slots form outside to inside of the ring and holding down a back side of the flange; and a sensor means provided inside the flange to detect a relative rotational angle of the collimator box with respect to the flange, and is possible to provide an X-ray imaging apparatus using the X-ray irradiator.  
         [0016]     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  
       [0017]      FIG. 1  shows a schematic construction of an X-ray imaging apparatus.  
         [0018]      FIG. 2  shows an appearance of a collimator box.  
         [0019]      FIG. 3  is a plan view of a flange of an X-ray tube.  
         [0020]      FIG. 4  is an elevation thereof.  
         [0021]      FIG. 5  shows the construction of a collimator box mounting mechanism.  
         [0022]      FIG. 6  shows in what state the flange is held down.  
         [0023]      FIG. 7  shows a released state of the flange.  
         [0024]      FIG. 8  shows a removed state of the collimator box from the flange.  
         [0025]      FIG. 9  shows the flange as seen obliquely from below.  
         [0026]      FIG. 10  shows a ring alone provided inside the flange.  
         [0027]      FIG. 11  shows the collimator box.  
         [0028]      FIG. 12  shows the flange as seen obliquely from below. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]     The best mode for carrying out the present invention will be described hereinunder with reference to the drawings. The present invention is not limited to the best mode.  FIG. 1  shows a schematic construction of an X-ray imaging apparatus. This apparatus is an embodiment of the present invention. With the construction of this apparatus, there is shown an embodiment of the X-ray imaging apparatus of the present invention.  
         [0030]     As shown in the same figure, this apparatus 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 sensor  20  are opposed to each other with a subject  40  therebetween. The X-ray irradiator  10  is an embodiment of the present invention. With the construction of this device, there is shown an embodiment of the X-ray irradiator of the present invention.  
         [0031]     The X-ray irradiator  10  includes an X-ray tube  12  and a collimator box  14 . A collimator  16  is housed within the collimator box  14 . X-rays emitted from the X-ray tube  12  are radiated to the subject  40  through an aperture of the collimator  16 . The aperture of the collimator  16  is variable so that the X-ray irradiation field can be adjusted. A relative rotational angle of the collimator box  14  with respect to the X-ray tube  12  can be adjusted.  
         [0032]     The X-rays which have passed through the subject  40  is detected by the X-ray detector  20  and the detected signal is inputted to the operator console  30 . In accordance with the inputted signal the operator console  30  reconstruct a radioscopic image of the subject  40 . The radioscopic image thus reconstructed is displayed on a display  32  disposed on the operator console  30 . Further, the operator console  30  controls the X-ray irradiator  10 .  
         [0033]     A rotational angle is inputted from the collimator box  14  to the operator console  30 . In accordance with the inputted angular signal the operator console  30  corrects the rotation of the frame of the display image so that the image frame is erected constantly irrespective of rotation of the collimator box  14 .  
         [0034]      FIG. 2  shows the appearance of the collimator box  14  together with a flange  200  of the X-ray tube  12  attached thereto. The X-ray tube  12  lies on the flange  200  and is rendered integral with the flange. Thus, the flange  200  is a part of the X-ray tube  12 .  
         [0035]     As shown in the same figure, the collimator box  14  is a box of a generally rectangular parallelepiped and houses the collimator  16  therein. A front side of the collimator box  14  is formed as an interface  400  which is used for an operator to adjust the aperture of the collimator  16 . An indicator  402 , buttons  404 , and controls  406 , are provided on the interface  400 .  
         [0036]     An upper surface of the entry plate  14  is constituted by an entry plate  500 . The entry plate  500  has an X-ray incidence window  502 . A mounting mechanism  600  for mounting the collimator box  14  to the flange  200  of the X-ray tube  12  is provided around the X-ray incidence window  502 .  
         [0037]      FIGS. 3 and 4  are a plan view and an elevation of the flange  200 . As shown in the same figure, the flange  200  is a stepped disc having a central aperture  202 . The central aperture  202  serves as an X-ray output window.  
         [0038]     A large-diameter portion  204  of the disc has four notches  242  formed in the edge of the disc at equal intervals in the circumferential direction. The notch  242  is a V-shaped notch. A divergent angle of V is, for example, 90°. Four holes  262  for screwing the disc to the body of the X-ray tube are formed in a small-diameter portion  206  of the disc at equal intervals in the circumferential direction and in parallel with the axis of the disc. A pair of parallel surfaces  264  for indicating a reference direction are formed sideways of the small-diameter portion  206 .  
         [0039]      FIG. 5  shows a close-up of the entry plate  500  having the mounting mechanism  600 , together with the flange  200 . As shown in the same figure, the mounting mechanism  600  has a ring  610 . The ring  610  is mounted on the entry plate  500  so as to be concentric with the X-ray incidence window  502 . Mounting of the ring  610  to the entry plate  500  is performed with screws or the like from the back side for example. The ring  610  has an inside diameter conforming to the outside diameter of the large-diameter portion  204  of the flange  200 . As a result, the flange  200  can be received in a fitted state within the ring  610 .  
         [0040]     The ring  610  has five slots to be described later which extend radially through the ring, and five tongue pieces  621 - 625  are inserted through those slots from outside to inside of the ring  610 .  
         [0041]     The tip of one tongue piece  621  is adapted to fit in a notch  242  formed in the flange  200 . The tongue piece  621  is pushed out from a sheath  630  located outside the ring  610  by means of a spring. A lock screw  632  is provided on the sheath  630  so that it can lock the tongue piece  621 .  
         [0042]     The tongue piece  621  biased by the spring constitutes a click mechanism together with the notches  242 . Since there are four notches  242  at equal intervals along the circumference of the flange  200 , the click mechanism can restrict the rotational angle of the collimator box  14 , i.e., the rotational angle of the X-ray irradiation field in 90° step. The number and spacing of the notches  242  may be determined suitably in accordance with a desired rotational angle step. Further, the rotational angle of the collimator box  14  may be set at an arbitrary angle intermediate the click position.  
         [0043]     The rotational position of the collimator box  14  is fixed by locking the tongue piece  621  with the lock screw  632 . With the lock screw  632 , it is possible to lock and unlock the tongue piece  621  easily.  
         [0044]     The remaining four tongue pieces  622  to  625  hold down the back side of the large-diameter portion  204  of the flange  200  from above at four equally spaced positions, whereby the collimator box  14  is clamped to the X-ray tube  12 .  
         [0045]     Since the four tongue pieces  622 - 625  hold down the back side of the large-diameter portion  204  of the flange  200  along the circumference at four equally spaced positions, the flange can be held down uniformly. The number of tongue pieces for holding down the flange  200  may be three or five or more.  
         [0046]     A pair of semicircular rings  640  and  640 ′ each take a partial charge of holding the tongue pieces  622 - 625  outside the ring  610 . More specifically, the tongue pieces  622  and  623  are held by the semicircular ring  640 , while the tongue pieces  624  and  625  are held by the semicircular ring  640 ′.  
         [0047]     Mounting of the tongue pieces  622 - 625  to the semicircular rings  640  and  640 ′ is performed by screwing from the back side of the semicircular rings  640  and  640 ′. By so doing, in an assembled state of the mounting mechanism, it becomes impossible to make access to the screw head and thus there is no fear of loosening the screw by mistake which would lead to fall-off of the collimator box  14 .  
         [0048]      FIG. 6  shows in what state the flange  200  is held down by the tongue piece  622 .  FIG. 6  corresponds to a sectional view taken on line A-A in  FIG. 5 . As shown in  FIG. 6 , the tongue piece  622  held by the semicircular ring  640  is inserted from the outside to the inside through a slot  612  formed in the ring  610  and holds down the back side of the large-diameter portion  204  of the flange  200 . As a result, the large-diameter portion  204  of the flange  200  is sandwiched in between the tongue piece  622  and the entry plate  500 . This is also the case with the other tongue pieces  623 - 625 .  
         [0049]     The semicircular rings  640  and  640 ′ are disposed so that their one ends are opposed to each other and so are their opposite ends to surround the ring  610 . The respective one ends of the semicircular rings  640  and  640 ′ are connected together by a connecting means  642 . For example, the connecting means  642  comprises a pair of nuts  644  and  644 ′ fixed to one ends of the semicircular rings  640  and  640 ′ respectively and a bolt  646  which connect those nuts with each other.  
         [0050]     The other ends of the semicircular rings  640  and  640 ′ are mounted to the entry plate  500  with pins  648  and  648 ′ respectively. The semicircular rings  640  and  640 ′ are rotatable about the pins  648 ,  648 ′ and along the surface of the entry plate  500 . Therefore, when the connection by the connecting means is released, the semicircular rings  640  and  640 ′ can be rotated in opposite directions, i.e., in an opening direction.  
         [0051]     This state is shown in  FIG. 7 , in which the illustration of the tongue piece  621 , sheath  630  and lock screw  632  is omitted. As shown in the same figure, the semicircular rings  640  and  640 ′ are widely open on their one end sides and the four tongue pieces  622 - 625  are disengaged from the slots  612 - 615 . In this state, the flange  200  is no longer held down by the tongue pieces  622 - 625 , so that the collimator box  14  can be taken out from the X-ray tube  12 .  
         [0052]     For mounting the collimator box  14  to the X-ray tube  12 , the semicircular rings  640  and  640 ′ are kept open and the flange  200  of the X-ray tube  12  is fitted in the ring  610 , then the semicircular rings  640  and  640 ′ are closed and their one ends are connected together by the connecting means  642 .  
         [0053]      FIG. 8  shows a removed state of the collimator box  14  from the flange  200 . As shown in the same figure, a pair of sensors  504  and  504 ′ are provided on the entry plate  500  of the collimator box  14  at positions inside the ring  610 . The sensors  504  and  504 ′ are symmetric with respect to the center of the ring  610 . The sensors  504  and  504 ′ are each an optical sensor having a light emitting portion and a light receiving portion.  
         [0054]      FIG. 9  shows the flange  200  as seen obliquely from below. As shown in the same figure, the inside of the flange  200  is scooped out concentrically and a ring  270  is provided therein concentrically.  
         [0055]      FIG. 10  shows the ring  270  alone. As shown in a partially enlarged manner in (b) of the same figure, the ring  270  has a comb teeth-like structural portion  272 . The comb teeth-like structural portion  272  is provided on one side of the ring  270  and along the whole circumference so as to project axially of the ring. A notch  274  able to make distinction from the other portion is formed in one position of the comb teeth-like structural portion  272 .  
         [0056]     When the collimator box  14  is mounted to the flange  200 , the sensors  504  and  504 ′ are opposed to the comb teeth-like structural portion  272  at positions inside the flange  200 . The sensors  504  and  504 ′ each radiate light to the comb teeth-like structural portion  272  and receive reflected light.  
         [0057]     The comb teeth-like structural portions  272  form optical patterns of alternately arranged teeth and gaps. Therefore, when the collimator box  14  is rotated with respect to the flange  200 , the reflected light undergoes strong and weak pulses. Accordingly, a rotational angle can be measured on the basis of the number of such pulses.  
         [0058]     If the phase of the photo-detection by the sensors  504  and  504 ′ is made different by only half of the comb teeth pitch, it becomes possible to perform the detection of angle with a resolving power twice as high as the resolving power determined by the comb teeth pitch. When the comb teeth pitch is very small, there may be used only one of the sensors  504  and  504 ′.  
         [0059]     Thus, the portion comprising the sensors  504 ,  504 ′ and the ring  270  constitutes an optical angle encoder. The notch  274  formed at one position of the comb teeth-like structural portion  272  determines an origin of the angle encoding.  
         [0060]     Since such an angle encoder is incorporated in the flange  200 , a rotational angle of the collimator box  14  can be fed back to the operator console  30  from the X-ray irradiator  10 . Then, the operator console  30  can correct the angle of the image frame in accordance with the rotational angle of the collimator box  14 .  
         [0061]     The portion comprising the sensors  504 ,  504 ′ and the ring  270  is an example of the sensor means in the present invention. Since the sensor means is an optical sensor means, it is possible to make a non-contact angle detection. Further, since the optical sensor means has an optical pattern provided on the flange side and an optical sensor provided on the entry plate side so as to be opposed to the optical pattern, a relative rotational angle can be detected properly.  
         [0062]     Since the optical pattern forms a ring along the inner periphery of the flange, it is possible to obtain a continuous pattern free of a break. Since the optical pattern is a comb teeth-like pattern, the detection of an angle is easy. Moreover, since the comb teeth-like pattern has a notch for an angle origin, it is possible to make an angle origin clear.  
         [0063]     As shown in  FIG. 11 , if a pin  506  is provided on the entry plate  500  and an arcuate slot  280  is formed correspondingly in an end face of the flange  200  as in  FIG. 12 , a maximum rotational angle value of the collimator box  14  can be limited by the length of the slot  280  when engaged with the pin  506 . The portion comprising the pin  506  and the slot  280  is an example of the limiting means in the present invention.  
         [0064]     By thus using the limiting means for limiting the maximum rotational angle of the collimator box, it is possible to prevent an excessive rotation of the collimator box. Since the limiting means has the pin provided on the entry plate side and the arcuate slot provided on the flange side, it is possible to simplify the construction.  
         [0065]     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.