Patent Publication Number: US-2023157655-A1

Title: X-ray diagnostic apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-190923, filed on Nov. 25, 2021; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an X-ray diagnostic apparatus. 
     BACKGROUND 
     Some X-ray diagnostic apparatus include an X-ray tube; an X-ray detector; and a C-arm or an Ω-arm that has the shape of a circular arc and that supports the X-ray tube and the X-ray detector to be at opposed positions. In such an X-ray diagnostic apparatus, the C-arm or the Ω-arm is made to perform a sliding movement in the circular arc direction around the subject, so that three-dimensional imaging can be performed. Herein, in order to perform three-dimensional imaging and collect three-dimensional image data, for example, it is desirable that the imaging range equal to or greater than 180° is secured around the subject. 
     Thus, in the X-ray diagnostic apparatus, it is necessary to secure a wide range (stroke) within which the arm is slidable. As a configuration satisfying such a requirement, for example, it is possible to think of an X-ray diagnostic apparatus that includes a plurality of arms (a first arm and a second arm) configured to be slidable in the same circular arm direction. In that case, the first arm is, for example, a C-arm that supports the X-ray tube and the X-ray detector and that performs the sliding movement in a circular arc direction. The second arm holds the first arm and performs the sliding movement in the same direction as the sliding direction of the first arm. With that, it becomes possible to widen the stroke of the C-arm, thereby enabling securing a wider imaging range. Meanwhile, in the present written description, the structure including such plurality of arms is called a double-slide structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram illustrating an exemplary configuration of an X-ray diagnostic apparatus according to a first embodiment; 
         FIG.  2    is a diagram for explaining a double-slide structure; 
         FIG.  3    is a diagram illustrating the movements occurring in the X-ray diagnostic apparatus according to the first embodiment; 
         FIGS.  4 A and  4 B  are cross-sectional views illustrating an exemplary structure of an imaging unit according to the first embodiment; 
         FIG.  5    is a diagram for explaining a roller unit according to the first embodiment; 
         FIG.  6    is a diagram illustrating a block and a rail according to the first embodiment; 
         FIG.  7    is a diagram for explaining the X-ray diagnostic apparatus according to a first modification example; 
         FIG.  8    is a diagram for explaining the X-ray diagnostic apparatus according to a second modification example; 
         FIG.  9    is a diagram for explaining a structure in which the size of a holder is increased and a plurality of wheels is included therein; and 
         FIG.  10    is a diagram illustrating an exemplary configuration of the imaging unit in the X-ray diagnostic apparatus according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An X-ray diagnostic apparatus according to an embodiment includes an arm, a first holder, a second holder, a driver, and a third holder. The arm has the shape of a circular arc; supports, at one end thereof, an X-ray tube which emits X-rays onto a subject; and supports, at the other end thereof, an X-ray detector which detects X-rays that have passed through the subject. The first holder grasps the arm in a movable manner in the circular arc direction. The second holder supports the first holder in a movable manner in the circular arc direction. The driver is disposed in the second holder; moves the first holder; and, at the same time, relatively moves the arm with respect to the first holder. The third holder is orthogonal to the rotation axis involved in the movement of the arm in the circular arc direction and holds the second holder in a rotatable manner with the axis substantially orthogonal to the vertical direction serving as the rotation axis. 
     Exemplary embodiments of an X-ray diagnostic apparatus are described below in detail with reference to the accompanying drawings. However, the X-ray diagnostic apparatus according to the application concerned is not limited by the embodiments described below. In the following explanation, identical constituent elements are referred to by the same reference numerals, and their explanation is not repeated. 
     First Embodiment 
       FIG.  1    is a block diagram illustrating an exemplary configuration of an X-ray diagnostic apparatus  1  according to a first embodiment. As illustrated in  FIG.  1   , the X-ray diagnostic apparatus  1  includes an imaging unit  10 , processing circuitry  20 , an input interface  21 , a display  22 , and memory circuitry  23 . The following explanation is given about an example in which the X-ray diagnostic apparatus  1  has a suspension mechanism (a suspended-type X-ray diagnostic apparatus) for keeping some part of the imaging unit  10  suspended from the ceiling. Moreover, the following explanation is given about an example in which the X-ray diagnostic apparatus  1  is of the single-plane type. However, the embodiments are not limited to that case, and alternatively the X-ray diagnostic apparatus  1  can be of the biplane type. 
     The imaging unit  10  includes an X-ray high-voltage generator  11 , an X-ray tube  12 , a couchtop  13 , an X-ray detector  14 , a C-arm  15 , roller units  16 , a holder  17 , a ceiling-type rotating arm  18 , and a ceiling-type rotating arm supporting member  19 . The imaging unit  10  emits X-rays onto a subject P, and detects the X-rays that have passed through the subject P. 
     The X-ray high-voltage generator  11  generates a high voltage under the control of the processing circuitry  20 , and applies the high voltage to the X-ray tube  12 . Based on the high voltage applied by the X-ray high-voltage generator  11 , the X-ray tube  12  emits X-rays toward the subject P who is present on the couchtop  13 . Moreover, in the X-ray tube  12 , an X-ray aperture (not illustrated) is included on the plane opposite to the subject P. Under the control of the processing circuitry  20 , the X-ray aperture opens and closes the aperture blade, and forms an exposure range (exposure field) of the X-rays emitted from the X-ray tube  12 . For example, the aperture blade is formed in the shape of a plate using an X-ray shielding material such as lead. The couchtop  13  is a bed on which the subject P is asked to lie down, and is placed on top of a couch (not illustrated). 
     The X-ray detector  14  is an X-ray flat plane detector (FPD) in which, for example, radiation detecting elements are arranged in a matrix. The X-ray detector  14  detects X-rays that, after being emitted from the X-ray tube  12 , have passed through the subject P; and outputs detection signals according to the detected X-ray dosage (i.e., outputs X-ray detection signals) to the processing circuitry  20 . 
     The C-arm  15  has the shape of a circular arc. At one end thereof, the C-arm  15  supports the X-ray tube  12 ; and, at the other end thereof, the C-arm  15  supports the X-ray detector  14 . Thus, the C-arm  15  supports the X-ray tube  12  and the X-ray detector  14  across the subject P. Moreover, the C-arm  15  supports the X-ray tube  12  and the X-ray detector  14  in an independently-rotatable manner. On the lateral face opposite to the inside face on which the X-ray tube and the X-ray detector  14  are disposed, the C-arm  15  includes U-shaped rails that move while making contact with wheels  161  of the roller units  16  (explained later). As a result, the C-arm  15  moves in a circular arc direction indicated by an arrow S 1  illustrated in  FIG.  1   . Herein, the C-arm  15  represents an example of an arm. 
     The roller units  16  grasp the C-arm  15  and enable the sliding movement of the C-arm  15  in the circular arc direction indicated by the arrow S 1  illustrated in  FIG.  1   . Moreover, the roller units  16  are supported by the holder  17 , and are capable of performing the sliding movement when a driving unit (explained later) runs them on the rails of the C-arm  15  in the circular arc direction indicated by an arrow S 2  illustrated in  FIG.  1   . The roller units  16  represent an example of a first holder. 
     The holder  17  has a driving unit installed therein, and supports the roller units  16  in a slidable manner in the circular arc direction illustrated by the arrow S 2 . Moreover, at the lower end of the ceiling-type rotating arm  18 , the holder  17  is pivotally supported to be rotatable around a rotation axis R 1  illustrated in  FIG.  1   . The holder  17  represents an example of a second holder. 
     The driving unit includes roller unit driving gears  31  (explained later), a timing belt driving pulley  32  (explained later), and a shaft  33  (explained later). The driving unit is disposed inside the holder  17  and, under the control of the processing circuitry  20  (explained later), drives the imaging unit  10  by transmitting power that comes from a power source such as a motor (not illustrated) or an actuator (not illustrated). For example, the driving unit causes the C-arm  15  and the roller units  16  to perform the sliding movement/rotation. The driving unit represents an example of a driver. 
     The rotation axis R 1  is positioned at the center of the holder  17  and at the lower end of the ceiling-type rotating arm  18 , and represents the rotation axis for the rotation of the holder  17  with respect to the ceiling-type rotating arm  18 . More particularly, the rotation axis R 1  is orthogonal to the rotation axis during the sliding movement of the C-arm  15 , and is also orthogonal to the vertical direction (gravity direction). When the holder  17  rotates around the rotation axis R 1 ; the roller units  16 , which are supported by the holder  17 , and the C-arm  15 , which is supported by the roller units  16 , rotate along with the holder  17  around the rotation axis R 1 . 
     The ceiling-type rotating arm  18  has the shape of a circular arc and, at the lower end thereof, supports the holder  17  in a rotatable manner around the rotation axis R 1 . Thus, the ceiling-type rotating arm  18  holds the holder  17  in a rotatable manner with the rotation axis R 1  serving as the rotation axis. Moreover, at the upper end thereof, the ceiling-type rotating arm  18  is supported by the ceiling-type rotating arm supporting member  19  in a gyratable manner around a rotation axis R 2 . The ceiling-type rotating arm  18  represents an example of a third holder. 
     The ceiling-type rotating arm supporting member  19  is installed on the ceiling of the inspection room. The ceiling-type rotating arm supporting member  19  supports the ceiling-type rotating arm  18  in a gyratable manner around the rotation axis R 2 . The rotation axis R 2  is orthogonal to the ceiling or the floor, and is also orthogonal to the rotation axis R 1 . 
     The processing circuitry  20  is configured using, for example, a processor. The processing circuitry  20  controls a control function  201  for controlling the entire X-ray diagnostic apparatus  1 . More particularly, the control function  201  supplies control signals to the X-ray high-voltage generator  11 , the X-ray tube  12 , the X-ray aperture, the couchtop  13 , the X-ray detector  14 , the C-arm  15 , the roller units  16 , the holder  17 , the ceiling-type rotating arm  18 , and the ceiling-type rotating arm supporting member  19 ; so that X-ray radiation is carried out. The control function  201  represents an example of a control unit. Regarding the control function  201 , the detailed explanation is given later. 
     The input interface  21  is configured using an input device that receives various input operations from the user. The input interface  21  receives an input operation from the user, and outputs an electrical signal corresponding to the received input operation to the processing circuitry  20 . For example, the input interface  21  includes a mouse, a keyboard, or a trackball. Alternatively, the input interface  21  includes a hand-switch (an exposure switch) or a foot-switch as an operation button for receiving an operation from the user. Still alternatively, the input interface  21  can be configured using a touchpad in which an input operation is performed by touching the operation screen; or using a contactless input circuit in which an optical sensor is used; or using a voice input circuit. The input interface  21  can also be configured using a tablet terminal capable of performing wireless communication with the device main body. Meanwhile, the input interface  21  is not limited to include a physical operation component such as a mouse or keyboard. That is, examples of the input interface  21  also include an electrical signal processing circuit that receives an electrical signal corresponding to an input operation from an external input device installed separately from the device, and that outputs the electrical signal to the processing circuitry  20 . 
     The display  22  is configured using a display device that displays a variety of information. For example, the display  22  displays a graphical user interface (GUI) and collected X-ray images (fluoroscopic images or photographed images) of the subject P. 
     The memory circuitry  23  is configured using, for example, a semiconductor memory device such as a random access memory (RAM) or a flash memory; or a hard disk; or an optical disk. The memory circuitry  23  is used to store a variety of information used in or generated by the processing circuitry  20 . For example, the memory circuitry  23  is used to store a variety of information such as X-ray images of the subject P and a GUI. Moreover, the memory circuitry  23  is used to store a computer program that causes the processing circuitry  20  to function as the control function  201 . 
     Till now, the explanation was given about an exemplary configuration of the X-ray diagnostic apparatus  1  according to the first embodiment. With such a configuration, the X-ray diagnostic apparatus  1  enables expanding the slidable range of the arm while holding down an increase in the apparatus size. More particularly, in the X-ray diagnostic apparatus  1 , accompanying the sliding movement of the C-arm  15 , the roller units  16  made to slide in the same circular arc direction as the direction of the sliding movement of the C-arm  15 . With that, the stroke of the C-arm  15  can be widened while preventing an increase in the apparatus size. 
     In the X-ray diagnostic apparatus  1 , the X-ray tube  12  and the X-ray detector  14  are supported by the C-arm  15 , and the C-arm  15  is made to slide along a circular arc. With that, the X-ray tube  12  and the X-ray detector  14  are made to slide to the positions along the circular arc of the C-arm  15 . At that time, the X-ray diagnostic apparatus  1  can perform rotational transverse tomography in which images of the subject P are taken at every position (each photographing angle) along the circular arc of the C arm  15 . As a result, the X-ray diagnostic apparatus  1  can collect projection data at each photographing angle; perform three-dimensional reconstruction; and obtain three-dimensional images. However, in order to perform the three-dimensional reconstruction in an appropriate manner, the projection data needs to be collected at the photographing angles equal to or greater than 180° around the subject P. That is, an imaging system made up of the X-ray tube  12 , the X-ray detector  14 , and the C-arm  15  is required to be able to perform the sliding movement over 180° or more. 
     In that regard, in order to widen the stroke of the C-arm  15  that supports the X-ray tube  12  and the X-ray detector  14 , it is possible to think of an X-ray diagnostic apparatus that includes a plurality of arms capable of performing the sliding movement in the same circular arc direction.  FIG.  2    is a diagram illustrating an example of an X-ray diagnostic apparatus having the double-slide structure. With reference to  FIG.  2   , a suspended-type X-ray diagnostic apparatus includes a first arm D 1  and a second arm D 2 . The first arm D 1  supports an X-ray tube and an X-ray detector, and performs the sliding movement in the circular arc direction indicated by an arrow DS 1  illustrated in  FIG.  2   . The second arm D 2  holds the first arm D 1  via a holder D 3  provided for support at the lower end, and performs the sliding movement in the same direction as the direction of the sliding direction of the first arm D 1 . Moreover, the second arm D 2  is pivotally supported by a supporting member D 4  that is installed on the ceiling of the examination room. 
     However, the structure of the X-ray diagnostic apparatus as illustrated in  FIG.  2    may become large in size and complex. More particularly, in the case of using a plurality of sliding arms, as compared to an X-ray diagnostic apparatus that includes only a C-arm as a sliding arm, sometimes there is an increase in the overall size of the X-ray diagnostic apparatus in order to support the moment load during the sliding movement. Moreover, in the case of using a plurality of sliding arms, it may lead to an increase in the occupancy of the X-ray diagnostic apparatus in the examination room in which it is installed. Furthermore, in an X-ray diagnostic apparatus having the double-slide structure, a plurality of arms is made to slide in the same circular arc direction while supporting them. As a result, the internal structure becomes complex. 
     Moreover, it is possible to think that, when the apparatus structure becomes large and complex, it impairs the accessibility inside the examination room. For example, a situation may arise in which it is difficult to confirm the other devices, the subject, and the healthcare personnel present around the concerned device in the examination room. 
     In that regard, in the X-ray diagnostic apparatus  1  according to the first embodiment, accompanying the sliding movement of the C-arm  15 , the roller units  16  are made to slide in the same circular arc direction as the C-arm  15 . As a result, the stroke of the C-arm  15  can be widened while avoiding an increase in the size of the X-ray diagnostic apparatus  1 . 
       FIG.  3    is a diagram illustrating the movements occurring in the X-ray diagnostic apparatus  1  according to the first embodiment. In  FIG.  3    is illustrated the transition among three types of C-arm holding states in the X-ray diagnostic apparatus  1 . More particularly, in the central drawing in  FIG.  3   , a first holding state is illustrated in which the roller units  16  fit inside the holder  17  and in which the middle portion between the roller units  16  is coincident with the rotation axis R 1 . In the left-side drawing in  FIG.  3   , a second holding state is illustrated in which, with reference to the first holding state, the C-arm  15  and the roller units  16  are made to slide in the direction indicated by an arrow a 1 , so that the X-ray tube  12  moves away from the holder  17 . In the right-side drawing in  FIG.  3   , a third holding state is illustrated in which the C-arm  15  and the roller units  16  are made to slide in the direction indicated by an arrow a 2 , so that the X-ray tube  12  moves closer to the holder  17 . In the second holding state and the third holding state, the amount of sliding movement of the C-arm  15  and the roller units  16  is maximum. 
     For example, in the X-ray diagnostic apparatus  1 , as illustrated in the second holding state (the left-side drawing in  FIG.  3   ), during the sliding movement of the C-arm  15  in the direction of the arrow a 1 , the roller units  16  perform the sliding movement in the same direction (the direction indicated by the arrow a 1 ) up to the position of being pushed out from the holder  17 . As a result, in the X-ray diagnostic apparatus  1 , as compared to the case in which only the C-arm  15  performs the sliding movement in the same direction as explained above, regarding the sliding movement of the X-ray tube  12  in the direction away from the holder  17 , the stroke can be widened by the amount equivalent to the amount of sliding movement of the roller units  16 . Meanwhile, the roller units  16  perform the sliding movement due to the driving force transmitted thereto from a roller unit driving gear  31   a  that is disposed on the rotation axis R 1 . In this case, for the purpose of engaging with the roller unit driving gear  31   a,  the roller units  16  are provided with a gear on the side of the roller unit driving gear  31   a.  Thus, due to the driving force transmitted from the roller unit driving gear  31   a,  the roller units  16  perform the sliding movement. 
     In an identical manner, for example, in the X-ray diagnostic apparatus  1 , as illustrated in the third holding state (the right-side drawing in  FIG.  3   ), during the sliding movement of the C-arm  15  in the direction indicated by the arrow a 2 , the roller units  16  perform the sliding movement in the same direction (the direction indicated by the arrow a 2 ) up to the position of being pushed out from the holder  17 . As a result, in the X-ray diagnostic apparatus  1 , as compared to the case in which only the C-arm  15  performs the sliding movement in the same direction, regarding the sliding movement of the X-ray tube  12  in the direction toward the holder  17 , the stroke can be widened by the amount equivalent to the amount of sliding movement of the roller units  16 . Meanwhile, in an identical manner to the explanation given above, the roller units  16  perform the sliding movement due to the driving force transmitted thereto from the roller unit driving gear  31   a  disposed on the rotation axis R 1 . 
     As explained above, in the X-ray diagnostic apparatus  1 , the roller units  16  that grasp the C-arm  15  perform the sliding movement in the same direction as the direction of the sliding movement of the C-arm  15 . As a result, it becomes possible to widen the stroke. In that regard, in the X-ray diagnostic apparatus  1  according to the first embodiment, because of the structure of the imaging unit  10  explained below in detail, the sliding movement of the C-arm  15  and the sliding movement of the roller units  16  are driven using the same driving force. Given below is the detailed explanation of the structure of the imaging unit  10 .  FIGS.  4 A and  4 B  are cross-sectional views illustrating an exemplary structure of the imaging unit  10  according to the first embodiment. In  FIG.  4 A  is illustrated the cross-sectional surface in the axis direction of the rotation axis R 1  (i.e., an A-A cross-sectional surface). In  FIG.  4 B  is illustrated a B-B cross-sectional surface of  FIG.  4 A . 
     As illustrated in  FIG.  4 A , the holder  17  has blocks  171  fixed therein. Moreover, the holder  17  has the roller unit driving gear  31   a,  a roller unit driving gear  31   b,  the timing belt driving pulley  32 , and the shaft  33  are disposed therein. The roller unit driving gear  31   a,  the roller unit driving gear  31   b,  the timing belt driving pulley  32 , and the shaft  33  represent an example of a driving unit. Moreover, as illustrated in  FIGS.  4 A and  4 B , each roller unit  16  includes the wheels  161 , a rail  162 , a rack gear  163 , and a main body part  164 . Herein, two roller units are placed in bilateral symmetry with the center of the long axis direction of the shaft  33  serving as the axis of symmetry. The roller units  16  grasp the C-arm  15  when the rollers of the wheels  161  of each of the right and left roller units  16  engage with the U-shaped rails formed on the lateral faces of the C-arm  15 . 
     The shaft  33  is pivotally supported to be rotatable inside the holder  17 . According to the driving force transmitted from a driving source (not illustrated), the shaft  33  performs rotation with the long axis direction representing the rotation axis. Meanwhile, the driving source such as a motor need not be included in the holder  17 . 
     The timing belt driving pulley  32  is a pulley for transmitting the driving force to the C-arm  15 . The timing belt driving pulley  32  is fixed to the shaft  33 , and rotates accompanying the rotation of the shaft  33 . That is, the timing belt driving pulley  32  performs rotation with the shaft  33  representing the rotation axis, and transmits the driving force to the C-arm  15 . That results in the sliding movement of the C-arm  15 . 
     Given below is the explanation of a configuration of the imaging unit  10  involved in the sliding movement of the C-arm  15 . The C-arm  15  has the shape of a circular arc; and a timing belt (not illustrated) is stretched along the outer periphery, which represents the back surface of the inner surface on which the X-ray tube  12  and the X-ray detector  14  are disposed. The end portions of the timing belt are fixed to the end portions of the C-arm  15 , and are extended up to the timing belt driving pulley  32 . The timing belt driving pulley  32  is positioned away from the C-arm  15  at a predetermined distance, and is pivotally supported in a rotatable manner by the shaft  33 . On the outer surface of the timing belt driving pulley  32 , teeth are provided all around at the pitch for enabling engagement with the teeth of the timing belt. Moreover, the timing belt is pressed toward the outer periphery of the C-arm  15  by a timing belt roller (not illustrated). The timing belt roller is rotated by a driving source (not illustrated) according to the rotation of a rotation belt driving pulley  131 . 
     Given below is the explanation about the sliding movement of the C-arm  15 . For example, in the X-ray diagnostic apparatus  1 , the shaft  33  and the timing belt roller are rotated by a driving source. For example, in the second holding state (see the left-side drawing in  FIG.  3   ), during the sliding movement of the C-arm  15  in the direction indicated by the arrow a 1 , the timing belt is hauled in due to the rotation of the timing belt driving pulley  32  and the timing belt roller, and is carried in the direction indicated by the arrow a 1 . As a result, when the timing belt stretched along the outer periphery of the C-arm  15  gets pulled accompanying the rotation of the timing belt driving pulley  32 , the C-arm  15  performs the sliding movement in the direction indicated by the arrow a 1 . 
     The roller unit driving gear  31   a  is fixed to the shaft  33 , and rotates accompanying the rotation of the shaft  33 . That is, the roller unit driving gear  31   a  rotates along with the shaft  33 . The roller unit driving gear  31   a  engages with the rack gear  163  that is fixed to one of the two roller units  16  which are in bilateral symmetry with the center of the long axis direction of the shaft  33  serving as the axis of symmetry. Then, the roller unit driving gear  31   a  rotates accompanying the rotation of the shaft  33 , and transmits the driving force to the corresponding roller unit  16 . 
     The roller unit driving gear  31   b  is fixed to the shaft  33 , and rotates accompanying the rotation of the shaft  33 . That is, the roller unit driving gear  31   b  rotates along with the shaft  33 . The roller unit driving gear  31   b  engages with the rack gear  163  that is fixed to the other of the two roller units  16  which are in bilateral symmetry with the center of the long axis direction of the shaft  33  serving as the axis of symmetry. Then, the roller unit driving gear  31   b  rotates accompanying the rotation of the shaft  33 , and transmits the driving force to the corresponding roller unit  16 . 
     As explained above, the roller unit driving gears  31   a  and  31   b  that are fixed to the shaft  33  transmit the driving force to the respective roller units  16  accompanying the rotation of the shaft  33 . With that, the two roller units  16  perform the sliding movement in synchronization. Given below is the explanation of a configuration of the imaging unit  10  involved in the sliding movement of the roller units  16 .  FIG.  5    is a diagram illustrating a roller unit according to the first embodiment from an identical viewpoint to  FIG.  4 B . In  FIG.  5    are illustrated the wheels of one of the two roller units  16  that are disposed in bilateral symmetry in the holder  17 . The main body part  164  represents the main body part of the concerned roller unit  16 , and has the shape of a circular arc running along the circular arc of the C-arm  15 . For example, the main body part  164  includes two wheels  161  along the circular arc direction. Each wheel  161  includes a plurality of cylindrical rollers that run on the corresponding rail of the C-arm  15 . Some part of the wheel  161  is pivotally supported by the main body part  164  to be rotatable up to a predetermined rotation angle. 
     The rail  162  is fixed to the main body part  164  of the corresponding roller unit  16 . The rail  162  fits in the block  171  that is fixed to the holder  17 , and is thus supported by the block  171 . That is, since the rail  162  is supported by the block  171 , the roller unit  16  is also supported by the holder  17 . The rail  162  and the block  171  constitute a linear guide.  FIG.  6    is a diagram illustrating the rail  162  and the block  171  according to the first embodiment. As illustrated in  FIG.  4 B , the rail  162  is formed along the circular arc shape of the main body part  164 , and has a U-shaped groove formed on each lateral face thereof. Accompanying the movement of the roller unit  16 , the rail  162  moves with respect to the block  171  in the directions indicated by the arrows illustrated in  FIG.  6   . As a result, accompanying the movement of the roller unit  16 , the rail  162  performs the sliding movement in such a way that the position at which it is supported by the block  171  changes. The block  171  represents an example of a supporter. 
     In  FIG.  6    is illustrated an internal structure of the block  171 . The block  171  is a housing that fits with the rail  162  via a plurality of internal spherical objects strung together like beads. The block  171  causes the spherical objects to roll so as to enable the sliding movement of the rail  162 . Moreover, the block  171  has through holes formed therein as the paths for circulating the spherical objects accompanying the rolling motion. As a result, the block  171  enables a smooth sliding movement of the rail  162 . Moreover, regarding the moment load attributed to the projection of the imaging system that occurs accompanying the sliding movement of the rail  162 , the block  171  becomes able to resist the moment load with excellent rigidity. 
     The rack gear  163  is fixed to the roller unit  16 , and engages with corresponding the roller unit driving gear  31 . More particularly, the rack gear  163  is formed along the circular arc shape of the main body part  164  as illustrated in  FIG.  4 B , and is disposed on the back surface of the main body part  164 . Moreover, in the rack gear  163 , teeth are provided at the pitch for enabling engagement with the teeth of the corresponding roller unit driving gear  31 . With such a configuration, the rack gear  163  receives the transmission of the driving force from the corresponding roller unit driving gear  31 . As a result, the roller unit  16  receives, from the corresponding roller unit driving gear  31 , the driving force attributed to the rotation of the shaft  33 , and accordingly performs the sliding movement. 
     Herein, the number of teeth of each roller unit driving gear  31  is set according to the velocity ratio between the C-arm  15  and the corresponding roller unit  16 , and according to the number of teeth of the timing belt driving pulley  32 . The velocity ratio is set in advance according to the relationship between the maximum movement distance of the C-arm  15  and the maximum movement distance of the roller unit  16 . The maximum movement distance represents the maximum value of the distance of the path at the time of performing the movement along a circular arc. For example, the maximum movement distance represents the movement distance for performing the movement along a circular arc at the time of transition from the second holding state to the third holding state. More particularly, the maximum movement distance of the C-arm  15  represents the distance of the path followed during the sliding movement of the C-arm  15  from the second holding state to the third holding state (or from the third holding state to the second holding state). In an identical manner, the maximum movement distance of each roller unit  16  represents the distance of the path followed during the sliding movement of the roller unit  16  from the second holding state to the third holding state (or from the third holding state to the second holding state). 
     FIRST MODIFICATION EXAMPLE 
     In the first embodiment described above, the explanation is given about the structure in which the suspended-type X-ray diagnostic apparatus  1  includes the C-arm  15 . However, the first embodiment is not limited to that structure. Alternatively, the X-ray diagnostic apparatus  1  can include an Ω-arm  24 .  FIG.  7    is a diagram for explaining the imaging unit  10  and the movements therein according to a first modification example. As illustrated in  FIG.  7   , the X-ray diagnostic apparatus  1  includes the Ω-arm  24  that corresponds to the C-arm  15  illustrated in  FIG.  1   . In  FIG.  7    is illustrated the transition among three types of Ω-arm holding states occurring in the suspended-type X-ray diagnostic apparatus  1  including an Ω-arm. More particularly, in the central drawing in  FIG.  7    is illustrated a first Ω-arm holding state that corresponds to the first holding state illustrated in  FIG.  3   . In an identical manner, the left-side drawing and the right-side drawing in  FIG.  7    correspond to the second holding state and the third holding state, respectively, illustrated in  FIG.  3   . In the left-side drawing illustrated in  FIG.  7   , a second Ω-arm holding state is illustrated that is attained when the Ω-arm  24  and the roller units  16  are made to slide in the direction indicated by an arrow b 1  from the first Ω-arm holding state, so that the X-ray tube  12  moves away from the holder  17 . In the right-side drawing in  FIG.  7   , a third Ω-arm holding state is illustrated that is attained when the Ω-arm  24  and the roller units  16  are made to slide in the direction indicated by an arrow b 2 , so that the X-ray tube  12  moves closer to the holder  17 . 
     For example, as illustrated in the second Ω-arm holding state (the left-side drawing in  FIG.  7   ), during the sliding movement of the Ω-arm  24  in the direction indicated by the arrow a 1 , the roller units  16  perform the sliding movement in the same direction (the direction indicated by the arrow b 1 ) up to the position of being pushed out from the holder  17 . In an identical manner, as illustrated in the third Ω-arm holding state (the right-side drawing in  FIG.  7   ), the roller units  16  perform the sliding movement in the same direction (the direction indicated by the arrow b 2 ) up to the position of being pushed out from the holder  17 . As a result, in the X-ray diagnostic apparatus  1 , as compared to the case in which only the Ω-arm  24  performs the sliding movement in the same direction as explained above, during the sliding movement in which the X-ray tube  12  moves away from the holder  17 , the stroke can be widened by the amount equivalent to the amount of sliding movement of the roller units  16 . 
     SECOND MODIFICATION EXAMPLE 
     In the first embodiment described above, the explanation is given about the case in which the X-ray diagnostic apparatus  1  is of the suspended type. However, the embodiment is not limited to that case. Alternatively, the imaging unit  10  can be of the floor-standing type in which the support is provided by the floor.  FIG.  8    is a diagram for explaining the imaging unit  10  and the movements therein according to a second modification example. As illustrated in  FIG.  8   , the floor-standing X-ray diagnostic apparatus  1  includes a stand  25  that is installed on the floor and that supports the holder  17 . The upper portion of the stand  25  (the portion supporting the holder  17 ) is pivotally supported around a rotation axis R 3  in a rotatable manner. Moreover, the lower portion of the stand  25  (the portion in contact with the floor surface) is pivotally supported around a rotation axis R 4  in a rotatable manner, and causes gyration of the stand  25  and the holder  17  in an integrated manner on the floor surface. In  FIG.  8   , the holding state of the C-arm  15  corresponds to the first holding state illustrated in  FIG.  3   . 
     Given below is the explanation of the movements occurring in the floor-standing X-ray diagnostic apparatus  1 . In an identical manner to the suspended-type X-ray diagnostic apparatus  1  according to the first embodiment, the roller units  16  that hold the C-arm  15  perform the sliding movement in the same direction as the direction of the sliding movement of the C-arm  15 . With that, in the floor-standing X-ray diagnostic apparatus  1 , the stroke of the C-arm can be widened. More particularly, due to the same driving force, the C-arm  15  and the roller unit  16  perform the sliding movement in circular arc directions indicated by arrows S 1  and S 2 , respectively, illustrated in  FIG.  8   ; so that either the X-ray tube  12  or the X-ray detector  14  moves away from the holder  17 . As a result, in an identical manner to the suspended-type X-ray diagnostic apparatus  1 , in the floor-standing X-ray diagnostic apparatus  1  too, as compared to the case in which only the C-arm  15  performs the sliding movement in the same direction as explained above, the stroke can be widened by the amount equivalent to the amount of sliding movement of the roller unit  16 . 
     As explained above, according to the first embodiment described above, the C-arm  15  has the shape of a circular arc. The C-arm  15  supports, at one end thereof, the X-ray tube  12  that emits X-rays onto the subject; and supports, at the other end thereof, the X-ray detector  14  that detects the X-rays which have passed through the subject. The roller units  16  grasp the C-arm  15  in a movable manner in the circular direction arc. The holder  17  supports the roller units  16  in a movable manner in the circular arc direction of the C-arm  15 . The driving unit is disposed in the holder  17 . The driving unit causes the roller units  16  to move, and causes the C-arm  15  to relatively move with respect to the roller units  16 . The ceiling-type rotating arm  18  is orthogonal to the rotation axis involved in the movement of the C-arm  15  in the circular arc direction, and rotatably holds the holder  17  with the axis substantially orthogonal to the vertical direction serving as the rotation axis. As a result, in addition to implementing the sliding movement of the C-arm  15 , the sliding movement of the roller units  16  is also implemented. That is, the stroke of the C-arm  15  can be widened by the amount equivalent to the amount of sliding movement of the roller units  16 . That enables achieving expansion in the slidable range of the C-arm  15 . 
     Meanwhile, other than the configuration of the X-ray diagnostic apparatus  1  according to the first embodiment, it is also possible to think of a structure in which the size of the holder is increased so that the number of wheels fixed inside the holder can be increased and it becomes possible to transfer the C-arm on the wheels. However, that structure may lead to an increase in the size of the X-ray diagnostic apparatus. In  FIG.  9    is illustrated an example of an X-ray diagnostic apparatus having the structure in which the size of the holder is increased and a plurality of wheels is included therein. As illustrated in  FIG.  9   , a C-arm E1 performs the sliding movement in the direction indicated by an arrow ES 1  and on four wheels included in a holder E 4 . In contrast to this structure, in the first embodiment, the holder is prevented from increasing in size, thereby enabling prevention of an increase in the size of the X-ray diagnostic apparatus. 
     Moreover, according to the first embodiment described above, the driving unit drives the movement of the C-arm  15  and the movement of the roller units  16  with the same driving force. That eliminates the need to install separate driving sources for moving the C-arm  15  and moving the roller units  16 . Thus, the configuration of the X-ray diagnostic apparatus  1  enables avoiding complexity of the internal structure of the imaging unit  10 . That enables achieving expansion of the stroke of the C-arm while holding down an increase in the size of the X-ray diagnostic apparatus  1 . 
     Furthermore, according to the first embodiment described above, the rotation axis of the timing belt driving pulley  32  using which the driving unit transmits the driving force to the C-arm  15  is formed on the same axis as the rotation axis of the roller unit driving gears  31  using which the driving unit transmits the driving force to the roller units  16 . As a result, the driving force that is transmitted to the shaft  33  can be transmitted to the C-arm  15  and the roller units  16 . Thus, in the X-ray diagnostic apparatus  1 , the structure regarding the driving of the roller units  16  is disposed to be linked with the driving of the C-arm  15 . Hence, it becomes possible to further avoid complexity in the internal structure of the imaging unit  10 . In turn, it becomes possible to hold down an increase in the size of the X-ray diagnostic apparatus  1 . 
     Moreover, according to the first embodiment, the driving unit moves the C-arm  15  and the roller units  16  at the velocity ratio corresponding to the relationship between the maximum movement distance of the C-arm  15  and the maximum movement distance of the roller units  16 . Hence, in the X-ray diagnostic apparatus  1 , the C-arm  15  and the roller units  16  can be made to slide in a coordinated manner, while catering to the respective movement distances different from each other. Thus, in the X-ray diagnostic apparatus  1 , the C-arm  15  and the roller units  16  can be made to slide in an appropriately coordinated manner. 
     Furthermore, according to the first embodiment, the driving unit transmits the driving force to the C-arm  15  and moves the C-arm  15 ; as well as transmits the driving force to the roller units  16  via the roller unit driving gears  31 , which have teeth in proportion to the velocity ratio, and accordingly moves the roller units  16 . As a result, in tandem with the sliding movement of the C-arm  15 , the roller units  16  can perform the sliding movement according to the rotation of the roller unit driving gears  31 . Thus, in the X-ray diagnostic apparatus  1 , an appropriately coordinated movement of the C-arm  15  and the roller units  16  can be achieved with ease. 
     Moreover, according to the first embodiment, the holder  17  includes a supporting member. The roller units  16  have rails in the shape of a circular arc, and the rails are supported by the supporting member. The position at which the rails are supported by the supporting member changes accompanying the movement of the roller units  16 . Hence, in regard to the sliding movement of the C-arm  15  and the roller units  16 , the load created as a result of pushing out the imaging system from the holder  17  is supported by the slidable engagement of the rails  162  and the block  171 . That enables achieving a smooth sliding movement. For that reason, it becomes possible to reduce the vibrations of the imaging system attributed to the sliding movement, while eliminating the need to add a complex internal structure for holding down the vibrations of the imaging system. Thus, it becomes possible to hold down an increase in the size of the X-ray diagnostic apparatus  1 . 
     Other Embodiment 
     In the first embodiment, the explanation is given for the case in which the C-arm  15  and the roller units  16  perform the sliding movement in the same circular arc direction. However, the embodiment is not limited to that case. Alternatively, the C-arm  15  and the roller units  16  can independently perform the sliding movement in circular arc directions.  FIG.  10    is a diagram illustrating an exemplary configuration of the imaging unit  10  in the X-ray diagnostic apparatus  1  according to another embodiment. In the X-ray diagnostic apparatus  1  according to the other embodiment, as compared to the first embodiment, the control performed by the control function  201  in the processing circuitry  20  is different and the driving unit is also different. The following explanation is focused on those differences. 
     In addition to having the control function  201  according to the first embodiment, the control function  201  according to the other embodiment also has a function for setting up the amount of movement of the roller units  16  based on the positional relationship between the C-arm  15  and the roller units  16 . The amount of movement represents the distance of the path followed during the sliding movement along a circular arc. Moreover, regarding the control function  201 , in addition to calculating the amount of movement based on the positional relationship between the C-arm  15  and the roller units  16 , the control function  201  can also change the calculated amount of movement in response to an operation performed by the user via the input interface  21 . Alternatively, the user can set, in advance, a rough indication of the amount of movement; so that the control function  201  can calculate the amount of movement based on the preset amount. 
     The driving unit applies different driving forces for causing the sliding movement of the C-arm  15  and for causing the sliding movement of the roller units  16 , and thus implements independent sliding movements. For example, the timing belt driving pulley  32 , which is involved in the driving of the C-arm  15 , and the roller unit driving gears  31 , which are involved in the driving of the roller units  16 , are not driven by the same driving force, and perform rotation after independently receiving the transmission of a driving force. As a result, the roller units  16  become able to perform the sliding movement in a different direction than the direction of the sliding movement of the C-arm  15 . 
     For example, the control function  201  controls the driving unit that applies a driving force to the C-arm  15 , and causes the C-arm  15  to perform the sliding movement in the direction indicated by an arrow c 1  illustrated in  FIG.  10   . Then, the control function  201  controls the driving unit that applies a driving force to the roller units  16 , and causes the roller units  16  to perform the sliding movement in the direction indicated by an arrow c 2  illustrated in  FIG.  10   . For example, when the sliding movement causes the X-ray tube  12  to move away from the holder  17 , the X-ray tube  12  might have a large mass thereby resulting in a large moment load. In that case, the control function  201  collects the positional relationship between the C-arm  15  and the roller units  16 , and decides on the amount of sliding movement of the roller units  16  in the direction indicated by the arrow c 2 . Then, the driving unit causes the roller units  16  to perform the sliding movement in the direction indicated by the arrow c 2  according to the decided amount of sliding movement of the roller units  16 . As a result, in the X-ray diagnostic apparatus  1 , the moment load of the X-ray tube  12  gets supported. 
     Herein, the explanation is given about the case in which the direction of the sliding movement of the C-arm  15  and the direction of the sliding movement of the roller units  16  are opposite directions as indicated by the arrows cl and c 2  illustrated in  FIG.  10   . However, the embodiment is not limited to that case. Alternatively, the C-arm  15  and the roller units  16  can perform the sliding movement in the same direction. In that case, the C-arm  15  and the roller units  16  can perform the sliding movement with different amounts of movement without any coordination therebetween. For example, the driving unit causes the roller units  16  to perform the sliding movement in the direction indicated by the arrow c 1  and according to the amount of sliding movement decided by the control function  201 . As a result, in the X-ray diagnostic apparatus  1 , it becomes possible to resist the moment load, which is generated in the imaging unit  10 , in an excellent manner. 
     As explained above, according to the other embodiment, the driving unit moves the roller units  16  independently from the movement of the C-arm  15  and with a different driving force than the driving force applied for the sliding movement of the C-arm  15 . As a result, the moment load generated in the imaging system due to the movement of the C-arm  15  can be resisted in an excellent manner because of the independent movement of the roller units  16 . Thus, in the X-ray diagnostic apparatus  1 , the support balance of the imaging unit  10  in regard to the sliding movement of the C-arm  15  can be maintained in a better way, thereby making it possible to easily expand the slidable range of the C-arm  15 . 
     Moreover, according to the other embodiment, based on the positional relationship between the C-arm  15  and the roller units  16 , the control function  201  sets up the amount of movement of the roller units  16 . As a result, the roller units  16  can be moved to arbitrary positions, thereby making it possible to resist the moment load generated in the imaging system due to the movement of the C-arm  15 . Thus, in the X-ray diagnostic apparatus  1 , the support balance of the imaging unit  10  in regard to the sliding movement of the C-arm  15  can be maintained in a better way, thereby making it possible to easily expand the slidable range of the C-arm  15 . 
     Meanwhile, the term “processor” used in the description of the embodiments implies, for example, a central processing unit (CPU), or a graphics processing unit (GPU), or an application specific integrated circuitry (ASIC), or a programmable logic device (such as a simple programmable logic device (SPLD), or a complex programmable logic device (CPLD), or a field programmable gate array (FPGA)). Moreover, instead of storing a computer program in the memory circuitry  23 , it can be directly incorporated into the circuitry of a processor. In that case, the processor reads the computer program incorporated in the circuitry and executes it so that the functions get implemented. Meanwhile, the processors according to the embodiments are not limited to be configured using a single circuitry on a processor-by-processor basis. Alternatively, a single processor can be configured by combining a plurality of independent circuitries, and the corresponding functions can be implemented. 
     A computer program executed by a processor is stored in advance in a read only memory (ROM) or a memory circuit. Alternatively, the computer program can be recorded as an installable file or an executable file in a non-transitory computer-readable recording medium such as a compact disk read only memory (CD-ROM), a flexible disk (FD), a compact disk recordable (CD-R), or a digital versatile disk (DVD). Still alternatively, the computer program can be stored in a downloadable manner in a computer that is connected to a network such as the Internet. For example, the computer program is configured using modules of the processing functions explained above. As far as the actual hardware is concerned, a CPU reads the computer program from a memory medium such as a ROM and executes it, so that the modules get loaded and generated in a main memory device. 
     In the embodiments and the modification examples described above, the constituent elements of the device illustrated in the drawings are merely conceptual, and need not be physically configured as illustrated. The constituent elements, as a whole or in part, can be separated or integrated either functionally or physically based on various types of loads or use conditions. The processing functions implemented by the device are entirely or partially implemented by the CPU or by computer programs that are analyzed and executed by the CPU, or are implemented as hardware by wired logic. 
     Of the processes described in the embodiments, all or part of the processes explained as being performed automatically can be performed manually. Similarly, all or part of the processes explained as being performed manually can be performed automatically by a known method. The processing procedures, the control procedures, specific names, various data, and information including parameters described in the embodiments or illustrated in the drawings can be changed as required unless otherwise specified. 
     According to at least one of the embodiments described above, it is possible to expand the slidable range of the arm while holding down an increase in the apparatus size. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.