Abstract:
A mammographic apparatus for taking an image of a breast by detecting an X-ray radiated from an X-ray tube and transmitted a breast of a subject by means of an X-ray detector. The mammographic apparatus includes a column, a first support frame arranged, for rotation about a rotary axis, on the column and supporting the X-ray tube, a second support frame arranged, for rotation about the rotary axis, on the column and supporting the X-ray detector, and a mechanism for selectively switching over between a first mode that the second support frame is rotated by a rotation force of the first support frame and a second mode that the first support frame is rotated independently of the second support frame.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2006-023845, filed Jan. 31, 2006, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a mammographic apparatus for taking an image of a breast by detecting the X-ray radiated from an X-ray tube and transmitted through a breast of a subject by an X-ray detector. 
     2. Description of the Related Art 
     In the basic radiography with a mammographic apparatus, the X-ray tube T and the X-ray detector D are placed opposed to each other in taking an image at any angle, as shown in  FIGS. 10A ,  10 B and  10 C, for example. 
     Meanwhile, there is a tomosynthetic radiography (tomo-radiography) as means for obtaining a three-dimensional image by use of a mammographic apparatus. 
     In the tomosynthetic radiography, it is a practice to take an image while rotating the X-ray tube T relative to the breast in the state fixing the breast and the X-ray detector D, as shown in  FIG. 11 , as an example. 
     For this reason, the mammographic apparatus, capable of coping with the two radiographic schemes, is required to perform both operations of rotating the X-ray tube T and the X-ray detector D in a synchronous fashion and of rotating the X-ray tube T while placing the X-ray detector at rest. 
     In order to realize the operations, the X-ray tube T and the X-ray detector D are necessarily arranged on separate frames so that the frames can be rotated independently. 
     In this case, if desired to enhance the concentricity of rotation path between the X-ray tube T and the X-ray detector D, typically the frames are held for separate rotation about the common rotary axis. In this case, the frames are rotated by separate motors. 
     In such an arrangement, there is a need to synchronously control the two motors with accuracy in rotating the X-ray tube T and the X-ray detector D in a synchronous fashion. This, however, is not easy to realize. 
     Meanwhile, there is proposed a structure to move a frame fixed with an X-ray tube along an arcuate path (see JP-A 2003-305031, for example). However, with this structure, deterioration is encountered in the rotation-path concentricity of between the X-ray tube T and the X-ray detector D. 
     In this manner, there is conventionally a difficulty in implementing a synchronous rotation while enhancing the rotation-path concentricity of between the X-ray tube T and the X-ray detector D. 
     BRIEF SUMMARY OF THE INVENTION 
     In such situations, there is a desire for achieving well the concentricity and enabling a synchronous rotation with accuracy and easiness while enabling both operations of rotating the X-ray tube device and the detector unit in a synchronous fashion and of rotating the X-ray tube device with the detector unit placed at rest. 
     A mammographic apparatus according to a first aspect of the present invention is for taking an image of a breast by detecting an X-ray radiated from an X-ray tube and transmitted a breast of a subject by means of an X-ray detector, the mammographic apparatus comprising: a column; a first support frame arranged, for rotation about a rotary axis, on the column and supporting the X-ray tube; a second support frame arranged, for rotation about the rotary axis, on the column and supporting the X-ray detector; and a mechanism for selectively switching over between a first mode that the second support frame is rotated by a rotation force of the first support frame and a second mode that the first support frame is rotated independently of the second support frame. 
     Additional objects and advantages of the invention will be set forth in description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  is a view showing a construction of a mammographic apparatus according to a first embodiment of the present invention; 
         FIG. 2  is a perspective view showing a  FIG. 1  spur gear and arcuate gear with magnification; 
         FIG. 3  is a view showing a  FIG. 1  frame, by partly broken away, and an internal arrangement of a column unit; 
         FIG. 4  is a view showing a construction of a mammographic apparatus according to a second embodiment in a first status of operation; 
         FIG. 5  is a view showing the construction of the mammographic apparatus according to the second embodiment in a second status of operation; 
         FIG. 6  is an exploded view showing a structure of an electromagnetic brake of  FIGS. 4 and 5 ; 
         FIG. 7  is a view showing a concavo-convex formed in the  FIG. 6  clutch plates; 
         FIG. 8  is a view showing the electromagnetic brake in an open state; 
         FIG. 9  is a view showing the electromagnetic brake in an locked state; 
         FIGS. 10A ,  10 B and  10 C are views each showing a positional relationship of between an X-ray tube and an X-ray detector, in taking an image according to the basic radiography; and 
         FIG. 11  is a view showing a positional relationship of between the X-ray tube and the X-ray detector, in taking an image according to tomosynthetic radiography. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the drawings, explanation will now be made on embodiments. 
     First Embodiment 
       FIG. 1  is a view showing a construction of a mammographic apparatus according to a first embodiment. 
     The mammographic apparatus shown in  FIG. 1  includes a column unit  1  and a C-arm unit  2 . The C-arm unit  2  is mounted on a shaft  11  projecting from the column unit  1 . Thus, the column unit  1  supports the C-arm unit  2  rotatable about a rotary axis RA provided by the axis of the shaft  11 . 
     The C-arm unit  2  has two frames  21 ,  22  that constitute an arm body. The frames  21 ,  22  are supported by the column unit  1  so that they can separately rotate about the rotary axis RA. The frame  21  is arranged with an X-ray tube device  23 , a restriction  24 , a spur gear  25 , a motor  26  and a reduction gear  27 , as shown in  FIG. 1 . The frame  22  is arranged with a detector unit  28  and a pusher plate  29 , as shown in  FIG. 1 . Meanwhile, an arc gear  22   a  is provided on the frame  22 . 
     The X-ray tube device  23  incorporates an X-ray tube so that the X-ray tube can radiate an X-ray toward the detector unit  28 . The restriction  24  is to restrict the field-of-irradiation of the X-ray radiated from the X-ray tube device  23 . 
     The detector unit  28  is made flat in its upper surface as viewed in  FIG. 1 , which surface provides a photographic platform  28   a . The pusher plate  29  is arranged opposite to the photographic platform  28   a . The pusher plate  29  is variable in the spacing to the photographic platform  28   a , due to a movement mechanism built in the frame  22 . This allows the pusher plate  29  to depress a breast rested upon the photographic platform  28   a . The detector unit  28  incorporates an X-ray detector to detect an X-ray radiated from the X-ray tube device  23  and transmitted through the breast. The X-ray detector is to output an image signal in accordance with an X-ray image which the detected X-ray represents. 
       FIG. 2  is a perspective view showing a spur gear  25  and arc gear  22   a  with magnification. 
     The arc gear  22   a  is formed integral with the frame  22  in a state protruding from the frame  22 , as shown in  FIG. 2 . The arc gear  22   a  has a curved surface on the closer side to the rotary axis RA and extending along an arc about the rotary axis RA, thus being structured by forming grooves in the curved surface. The arc gear  22   a  is in mesh with the spur gear  25 . 
     The rotation force of the motor  26  is delivered to the spur gear  25  through the reduction gear  27 . The reduction gear  27  is to deliver the rotation force of the motor  26  to the spur gear  25  by increasing the torque through reducing the rotation plate thereof. The reduction gear  27  has a well-known self-locking function. Namely, the reduction gear  27  suppresses the spur gear  25  from rotating when the motor  26  is shut down. 
       FIG. 3  is a view showing the frame  21 , by partly broken away, and the internal arrangement of the column unit  1 . 
     The frame  21  is formed, at its end, with a through-hole in which a shaft  22   b  projecting from the frame  22  is inserted. The frame  21  is rotatable regardless of the shaft  22   b  by the well-known technique, e.g. arranging a bearing between the frame  21  and the shaft  22   b.    
     The shaft  22   b  is formed integral with the frame  22  or secured to the frame  22 . The shaft  22   b  is secured to the shaft  11  such that its axis is coincident with the rotary axis RA. 
     The shaft  11  is rotatably supported at the inside of the column unit  1 . In the column unit  1 , there are arranged a motor  12 , a gear  13  and a gear  14 . The gear  13  and the gear  14  are in mesh with each other. The gear  13  is attached to the motor  12 . The gear  14  is fixed on the shaft  11 . 
     In this arrangement, when the motor  12  is rotated in a state the motor  26  is shut down, the rotation force of the motor  12  is delivered through the gears  13 ,  14  to thereby rotate the shafts  11 ,  22   b . As a result, the frame  22  is rotated. Due to the rotation of the frame  22 , the arc gear  22   a  is caused to move. Because the arc gear  22   a  is in mesh with the spur gear  25  while the reduction gear  27  is self-locked, the moving force of the arc gear  22   a  is directly delivered to the reduction gear  27  through the spur gear  25 . Consequently, the frame  21  is pushed by means of the reduction gear  27 , thus causing the frame  21  to rotate. Namely, in this state, the frames  21 ,  22  rotate periodically. In this case, because both the frames  21 ,  22  rotate about the rotary axis RA, concentricity is achieved well. Meanwhile, because the frames  21 ,  22  are rotated only based on the rotation force of the motor  12 , there is no need to control a plurality of motors synchronously. Accordingly, the frames  21 ,  22  can be rotated in a synchronous fashion with accuracy. 
     Meanwhile, when the motor  26  is rotated in a state the motor  12  is shut down, the spur gear  25  rotates. In this case, because the frame  22  remains in the current position due to the shutdown of the motor  12 , the spur gear  25  moves along the curved surface of the arc gear  22   a  through the meshing of between the arc gear  22   a  and the spur gear  25 . The moving force of the spur gear  25  is directly conveyed to the reduction gear  27 . Consequently, the frame  21  is pushed by means of the reduction gear  27 , to rotate the frame  21 . Namely, in this state, the frame  21  rotates relatively to the frame  22  being at rest. 
     In this manner, the first embodiment allows for achieving well the concentricity and enabling a synchronous rotation with accuracy and easiness while enabling both operations of rotating the X-ray tube device  23  and the detector unit  28  in a synchronous fashion and of rotating the X-ray tube device  23  with the detector unit  28  placed at rest. 
     Second Embodiment 
       FIG. 4  is a view showing a construction of a mammographic apparatus according to a second embodiment. Note that, in  FIG. 4 , the corresponding elements to those of  FIGS. 1 to 3  are attached with the identical reference numerals, to omit the detailed explanation thereof. 
     The mammographic apparatus shown in  FIG. 4  includes a C-arm unit  2  and a column unit  3 . Namely, the mammographic apparatus in the second embodiment is provided with the column unit  3  in place of the column unit  1  of the mammographic apparatus of the first embodiment. Incidentally,  FIG. 4  shows a frame  21  partly broken away, together with the internal arrangement of the column unit  1 . 
     The C-arm unit  2  is attached to a shaft  31  projecting from the column unit  3 . The shaft  31  includes an outer part  31   a  and an inner part  31   b . The outer and inner parts  31   a ,  31   b  are both formed cylindrical thus being coincident at the axes thereof. The outer part  31   a  is made rotatable regardless of the inner part  31   b  by the well-known technique, e.g. arranging a bearing between the outer part  31   a  and the inner part  31   b.    
     The outer part  31   a  has one end secured to the frame  21 . The other end of the outer part  31   a  is secured to the gear  32 . The inner part  31   b  has one end secured to the frame  22 . A tooth clutch  33  is firmly fixed on the inner part  31   b  at an intermediate portion thereof. The tooth clutch  33  is arranged in a position close to the gear  32 . 
     The gear  32  is in mesh with the gear  13 , by means of the teeth formed in the peripheral surface thereof. The gear  32  is formed with teeth, for meshing with the tooth clutch  33 , on a surface opposite to the side the outer part  31   a  is secured. The tooth clutch  33  has a part allowed to move reciprocally in a direction along the rotary axis RA. The movable portion has a tip formed with teeth for meshing with the teeth provided in the gear  32 . 
     The inner part  31   b  has an end, on the opposite side to the end to which the frame  22  is secured, where a clutch plate  35  is fixed. In the vicinity of the clutch plate  35 , an electromagnetic brake  34  is arranged opposite to the clutch plate  35 . 
     In the state shown in  FIG. 4 , the tooth clutch  33  is locked while the electromagnetic brake  34  is open. In the case the motor  12  is rotated in such a state, the rotation force of the motor  12  is conveyed through the gears  13 ,  32 , to thereby rotate the outer part  31   a . As a result, the frame  21  is caused to rotate. Meanwhile, because the tooth clutch  33  is being in mesh with the gear  32 , the rotation force of the motor  12  is conveyed through the gears  13 ,  32  and the tooth clutch  33 . Because the electromagnetic brake  34  is not locking the clutch plate  35 , the inner part  31   b  is also rotated with a result that the frame  22  is rotated. Namely, in this state, the frames  21 ,  22  rotate in a synchronous fashion. In this case, because both the frames  21 ,  22  rotate about the rotary axis RA, concentricity is achieved well. Meanwhile, because the frames  21 ,  22  are rotated only by the rotation force of the motor  12 , there is no need to control a plurality of motors synchronously. Accordingly, the frames  21 ,  22  can be rotated in a synchronous fashion with accuracy. 
     In the state shown in  FIG. 5 , the tooth clutch  33  is open while the electromagnetic brake  34  is locked. In the case the motor  12  is rotated in this state, the rotation force of the motor  12  is conveyed through the gears  13 ,  32 , to thereby rotate the outer part  31   a . As a result, the frame  21  is rotated. However, because the tooth clutch  33  is not being in mesh with the gear  32 , the rotation force of the motor  12  is not conveyed to the inner part  31   b . Moreover, the electromagnetic brake  34  locks the clutch plate  35 . Accordingly, the inner part  31   b  is not rotated and hence the frame  22  is not rotated. Namely, in this state, the frame  21  rotates relative to the frames  22  being at rest. 
       FIG. 6  is an exploded view showing a structure of the electromagnetic brake  34 . 
     The electromagnetic brake  34  includes a base plate  341 , an electromagnet unit  342 , a plurality of springs  343  and a clutch plate  344 , as shown in  FIG. 6 . In  FIG. 6 , the base plate  341  and the electromagnet unit  342  are shown by broken away. 
     The base plate  341  is secured to a housing or the like of the column unit  3 . The base plate  341  is formed with a plurality of holes  341   a  nearly parallel with the rotary axis RA. 
     The electromagnet unit  342  is structured by receiving an electromagnet  342   b  in a cylindrical case  342   a . The case  342   a  is formed with a plurality of holes  342   c  nearly parallel with the rotary axis RA. The electromagnet unit  342  is attached to the base plate  341  in a state the plurality of holes  342   c  respectively communicate with the plurality of holes  341   a.    
     The plurality of springs  343  are arranged respectively in the plurality of holes  342   c.    
     The clutch plate  344  is formed of metal and arranged oppositely to the clutch plate  35 . The clutch plate  344  has a plurality of pins  344   a  projecting nearly vertically from a surface thereof oppositely to the surface facing to the clutch plate  35 . The plurality of pins  344   a  are inserted in the plurality of holes  341   a  through the interiors of the plurality of springs  343  arranged in the plurality of holes  342   c , respectively. 
     In each of the clutch plate  344 ,  35 , there is formed a concavo-convex for meshing as shown in  FIG. 7 . The concavo-convex is provided in a manner to suppress the clutch plate  35  from rotating when placed in meshing with each other. 
       FIG. 8  shows a view illustrating the electromagnetic brake  34  being open. 
     In the open state, the electromagnet  342   b  is energized as shown in  FIG. 8 . Consequently, the clutch plate  344  is magnetically attracted by the electromagnet  342   b , thus being detached from the clutch plate  35 . In this state, the clutch plate  344  and the clutch plate  35  are not placed in engagement with each other at their concavo-convexes, thus allowing the clutch plate  35  and hence the inner part  31   b  of the shaft  31  to rotate. 
       FIG. 9  shows a view illustrating the electromagnetic brake  34  being locked. 
     In the locking state, the electromagnet  342   b  is not energized as shown in  FIG. 9 . Consequently, the clutch plate  344  is urged on the clutch plate  35  by means of the springs  343 . In this state, the clutch plate  344  and the clutch plate  35  are placed in engagement with each other at their concavo-convexes, thus preventing the clutch plate  35  and hence the inner part  31   b  of the shaft  31  from rotating. 
     In this manner, the second embodiment allows for achieving well the concentricity and enabling a synchronous rotation with accuracy and easiness while enabling both operations of rotating the X-ray tube device  23  and the detector unit  28  in a synchronous fashion and of rotating the X-ray tube device  23  with the detector unit  28  placed at rest. 
     Meanwhile, the second embodiment can reduce the number of the components to be arranged to the frame  21  as compared to those of the first embodiment. As a result, the second embodiment can reduce the rotation torque for the frame  21  as compared to that of the first embodiment, thus relieving the motor  12  of load. Meanwhile, the second embodiment can reduce the size of the C-arm unit as compared to that of the first embodiment, thus enabling to lessen the suppression feeling to the subject. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.