Abstract:
There is provided a new X-ray imaging apparatus by the use of which X-ray CT and panoramic imaging can be effectively performed. In an X-ray imaging apparatus which rotates an X-ray generating section and an X-ray detecting section around an imaging object arranged between these X-ray generating section and the X-ray detecting section and also detects in the X-ray detecting section X-rays having been radiated from the X-ray generating section and transmitted through the imaging object to form an X-ray image, a panoramic imaging mode in which the X-ray generating section and the X-ray detecting section are driven to form a panoramic image of the imaging object and an offset scan/CT mode in which the X-ray generating section and the X-ray detecting section are driven to form a tomographic image of the imaging object are set, so as to selectively execute these two imaging modes. Consequently, the panoramic imaging mode and the offset scan/CT mode can be arbitrarily selected, thereby allowing formation of an X-ray imaged image that is optimum for treatment.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an X-ray computer tomography (CT) apparatus for dentistry or a jaw/face region. In particular, the present invention relates to an X-ray CT apparatus capable of performing local X-ray CT on a certain tooth or the like as an region of interest in dentistry or the jaw/face region, and performing panoramic X-ray imaging on a curved cross section of a dental arch, a jaw joint, and the like. 
   2. Description of the Related Art 
   The Japanese Patent Publication No. 10-225455 (A) discloses an X-ray CT apparatus for dental diagnosis. This X-ray CT apparatus is one having a local X-ray computer tomography (hereinafter referred to as “CT”) along with a panoramic X-ray imaging mode. This X-ray CT apparatus is capable of selecting the X-ray CT mode and the panoramic X-ray imaging mode, and characterized as follows: when the X-ray CT mode is selected, a rotational central axis is fixed onto a central axis of an region of interest, and when the panoramic X-ray imaging mode is selected, a rotational arm having an X-ray generator and an X-ray detector is rotationally moved while the rotational central axis moves along a locus for the panoramic X-ray imaging during imaging. 
   The Japanese Patent No. 3540916 (B) discloses a three-dimensional X-ray CT scanner, having in a hollow rotating body an X-ray generator and an X-ray detector which are opposed to each other with a horizontal central axis (rotational axis) provided therebetween. In this apparatus, while these X-ray generator and X-ray detector are rotated with respect to an imaging object positioned inside the rotating body, X-rays having been radiated from the X-ray generator and transmitted through the imaging object are detected in the X-ray detector, and using the X-ray image detected in the X-ray detector, a three-dimensional tomographic image can be reconstructed, so that an offset scan/CT method by which a three-dimensional CT image in a larger range than a visual field angle of a two-dimensional X-ray detector is obtained in addition to a so-called normal scan/CT method by which a CT image is obtained by irradiating the whole of the imaging object with X-rays. 
   This offset scan/CT method has the advantage of being capable of performing X-ray CT in a larger range than the visual field angle of the two-dimensional X-ray detector since part of the region of interest of the imaging object may be irradiated with X-rays at each time point during imaging, as compared with the normal scan/CT method of constantly irradiating the whole of the region of interest of the imaging object with X-rays at each time point during imaging. 
   SUMMARY OF THE INVENTION 
   There has been a problem with a conventional X-ray CT apparatus for jaw/face imaging in dentistry and the like in that, since the normal scan/CT method is a dominant method, in the case of performing CT by detecting a range not smaller than a visual field detectable by a two-dimensional X-ray sensor, a large-sized two-dimensional X-ray sensor is required, which causes a cost increase. 
   In view of the above situation, an object of the present invention is to provide a new X-ray imaging apparatus capable of performing CT on an region of interest such as a jaw/face by an offset scan/CT method using a relatively small two-dimensional X-ray sensor and also capable of performing panoramic X-ray imaging, and to provide a new X-ray imaging apparatus capable of switching the method to a normal scan/CT method in the case of the region of interest being smaller than a visual field angle of the X-ray two-dimensional sensor. 
   In order to achieve such an object, the present invention is an X-ray CT apparatus, which comprises an X-ray generating section that applies X-rays and an X-ray detecting section in opposing positions, and which rotates said X-ray generating section and X-ray detecting section with an imaging object arranged between said X-ray generating section and X-ray detecting section and also detects X-rays having been radiated from said X-ray generating section and transmitted through said imaging object in said X-ray detecting section to back-project X-ray CT data, so as to form a CT image, 
   wherein said apparatus comprises an imaging mode selecting device for selecting: 
   a panoramic imaging mode in which, during imaging, a rotational arm having said X-ray generating section and X-ray detecting section is rotationally driven while a rotational central axis of the rotational arm is moved, to form a panoramic image of said imaging object; and 
   an offset scan/CT mode in which a CT image of said imaging object is constructed on the basis of X-ray CT data obtained by rotating the rotational arm around a rotational central axis wherein the rotational arm is set in such a position as a part of a region of interest of said imaging object is constantly irradiated with a cone beam radiated from said X-ray generating section and detected in said X-ray detecting section. 
   An X-ray imaging apparatus in another aspect of the present invention including the imaging mode selecting means has a normal scan/CT mode in which a CT image of the imaging object is constructed on the basis of X-ray CT data obtained by rotating the rotational central axis of the rotational arm as the center that is provided in such a position as to constantly irradiate an region of interest of the imaging object with a cone beam radiated from the X-ray generating section and detected in the X-ray detecting section. 
   An X-ray imaging apparatus in another aspect of the present invention including a first slit which forms an X-ray beam, radiated from the X-ray generating section, into narrow strip shape to rotate a narrow beam toward said imaging object in accordance with said panoramic imaging mode; 
   a second slit which forms an X-ray beam, radiated from the X-ray generating section toward said imaging object, into a cone beam in accordance with at least either one of said offset scan/CT mode and said normal scan/CT mode; and 
   a slit moving device for selectively arranging said first slit and said second slit in said X-ray generating section. 
   An X-ray imaging apparatus in another aspect of the present invention is provided with a means of moving the first slit or the second slit arranged in the X-ray generating section to a direction orthogonal to the X-ray beam in accordance with a signal from the imaging mode selecting means. 
   An X-ray imaging apparatus in another aspect of the present invention includes a driving device for moving the rotational central axis of the rotational arm against the rotational arm to set in such a position as to constantly irradiate a part or the whole of a region of interest of said imaging object with said cone beam in accordance with at least one of said offset scan/CT mode and said normal scan/CT mode. 
   An X-ray imaging apparatus in another aspect of the present invention includes a driving device for moving said rotational central axis in accordance with a rotational angle of the rotational arm that holds said X-ray generating section and said X-ray detecting section. 
   According to the X-ray imaging apparatus (claim  1 ) of the present invention, a panoramic imaging mode or an offset scan/CT mode can be arbitrarily selected by the imaging mode selecting means of selecting the panoramic imaging mode or the offset scan/CT mode. It is thereby possible to perform panoramic imaging and offset scan/CT using a costless small two-dimensional X-ray sensor, and as necessary or upon request, it is possible to continuously acquire a panoramic image and an offset scan/CT image which are optimum for treatment. Accordingly, when an approximate position of an region of interest is obtained by panoramic imaging having a large imaging region and an imaging position is then set to perform the offset scan/CT on the region of interest, it is possible to perform CT in a larger range than a conventional range, so as to perform CT in a large range while holding down cost. 
   According to the X-ray imaging apparatus (claim  2 ) of the present invention, since the offset scan/CT mode and the normal scan/CT mode are selected as necessary, the convenience in CT increases, and hence with the use of CT, it is possible to acquire a CT image with even higher resolution. 
   According to the X-ray imaging apparatus (claim  3 ) of the present invention, a slit corresponding to the panoramic imaging mode or the CT mode is selectively arranged, and it is thereby possible to obtain the optimum X-ray beam required for each imaging mode. 
   According to the X-ray imaging apparatus (claim  4 ) of the present invention, the first or the second slit is adjusted to use only an X-ray inclined at a certain angle from the X-ray irradiation central axis, and it is thereby possible to efficiently obtain clear X-ray image data. 
   According to the X-ray imaging apparatus (claim  5 ,  6 ) of the present invention, the driving means is provided which moves the rotational central axis of the central arm in accordance with either the panoramic imaging mode or the CT mode selected by the imaging mode selecting means of selecting either mode, and it is thereby possible to obtain an arbitrary locus of the rotating means that is optimum for imaging. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an X-ray imaging apparatus of a first example according to the present invention; 
       FIG. 2  is a front view of the X-ray imaging apparatus of the first example according to the present invention; 
       FIG. 3  is a right side view of the X-ray imaging apparatus of the first example according to the present invention; 
       FIG. 4  is a left side view of the X-ray imaging apparatus of the first example according to the present invention; 
       FIG. 5  is a perspective view showing the X-ray imaging apparatus of the first example according to the present invention and a test object positioned therein; 
       FIG. 6  is a perspective view of a part cutting out from a rotational arm of the X-ray imaging apparatus of the first example shown in  FIG. 1 ; 
       FIG. 7  is a sectional view showing an XY movement mechanism of the rotational arm of the first example; 
       FIG. 8  is a view, seen from the below, of the XY movement mechanism of the rotational arm of the first example; 
       FIG. 9  is a sectional view showing an XY movement mechanism of an imaging object of a second example according to the present invention; 
       FIG. 10  is a sectional view of an X-ray generating section; 
       FIG. 11  is a perspective view showing a beam formation plate and the like which are built in the X-ray generating section; 
       FIG. 12  is a front view of a part cut out from the rotational arm has been cut out; 
       FIG. 13  is a perspective view of an X-ray detector; 
       FIG. 14  is a control block diagram for the X-ray imaging apparatus; 
       FIG. 15  is a flowchart showing a control program for the X-ray imaging apparatus; 
       FIG. 16  is a pattern view explaining an initial setting process for a reduced CT mode; 
       FIG. 17  is a pattern view showing an operation of the rotational arm in the reduced CT mode; 
       FIG. 18  is a pattern view explaining an initial setting process for an enlarged CT mode; and 
       FIG. 19  is a pattern view showing an operation of the rotational arm in the enlarged CT mode. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   With reference to the attached drawings, several embodiments of the X-ray imaging apparatus according to the present invention will be described below. It is to be noted that, although terms that mean a specific direction or a place (e.g. “upper”, “lower”, “left”, “right” and other terms including those terms) are used in the following description, these terms are used for the purpose of facilitating visual understanding of configurations represented in the drawings, and should not be used for defining a technical range of the invention. 
     FIGS. 1 to 5  show respective appearances of an X-ray CT apparatus according to one embodiment of the present invention. The X-ray CT apparatus is capable of performing three-dimensional computer X-ray tomography (Computer Tomography: hereinafter referred to as “CT”) in addition to a variety of imaging which are conventionally widely known in the dentistry field (e.g. panoramic imaging, linear tomography, linear scan imaging, scanogram imaging). It is to be noted that, although the X-ray CT apparatus of the embodiment is an X-ray CT apparatus for dentistry, application of the present invention is not restricted to the X-ray CT apparatus for dentistry, but the present invention is equally applicable to an X-ray CT apparatus for another sort of medical use. For example, although the X-ray CT apparatus shown in the figures is a vertical X-ray imaging apparatus and used with a test object in a standing state, the present invention is also applicable to a so-called lateral X-ray imaging apparatus which is used with a test object held in a horizontally lying state. 
   As apparent from the figures, an X-ray CT apparatus (hereinafter simply referred to as “imaging apparatus”)  1  generally has a vertical column  2  fixed to a floor face; a lifting arm (first frame)  3  liftably provided along the vertical column  2  and a rotational arm (second frame)  4  rotatably coupled to the lifting arm  3  with a vertical rotational central axis (described later with reference to  FIGS. 6 to 8 ) as the center. 
   As shown in  FIGS. 3 and 4 , the lifting arm  3  as a whole has a substantially U shape, and roughly has a vertical arm section  5  liftably coupled to the vertical column  2 , and an upper arm section  6  and a lower arm section  7  respectively extending forward (toward the left side of  FIG. 3  and the right side of the  FIG. 4 ) from an upper end and a lower end of the vertical arm section  5 . As described later, the upper arm section  6  rotatably supports the rotational arm  4  arranged between the upper arm section  6  and the lower arm section  7 . As shown in  FIG. 5 , the lower arm section  7  has thereon a positioning mechanism  8  which positions a head of a person as an imaging object. For example, the positioning mechanism  8  of the X-ray CT apparatus  1  of the embodiment has a chin rest  9  which supports a jaw therefrom, a pair of lateral direction control member  10  which support the head of the test object as the imaging object from the right and left side thereof, and a pair of handles  11  held by the positioned person with his or her both hands so as to be kept stable. 
   As shown in  FIGS. 1 and 2 , the rotational arm  4  as a whole has a substantially inverted U shape, and roughly has: a horizontal arm section  12  which is rotatably suspendedly supported by the upper arm section  6  through a later-described coupling mechanism while suspendedly arranged under the upper arm section  6 ; and first and second suspending section  13  and  14  respectively extending downward from a right and left end of the horizontal arm section  12 . The first suspending section  13  shown on a right side of  FIG. 2  has an X-ray generating section  15 , and the second suspending section  14  shown on a left side of  FIG. 2  has an X-ray detecting section  16 . The X-ray generating section  15  and the X-ray detecting section  16  are opposed to each other with a prescribed spacing. A horizontal direction in which the X-ray generating section  15  and the X-ray detecting section  16  are opposed to each other is referred to as an “X-direction”, a horizontal direction orthogonal thereto is referred to as a “Y-direction”, and a height direction is referred to as a “Z-direction”. 
   The coupling mechanism (second coupling means) that couples the lifting arm  3  and the rotational arm  4  is described with reference to  FIGS. 6 to 8 . The coupling mechanism has an XY movement mechanism (first and second movement mechanisms)  18  housed in a rotational arm housing  17 . The XY movement mechanism  18  has a pair of Y-direction guide rails  19 Y fixed to the rotational arm housing  17  and extending in the Y-direction, a Y-direction moving frame  20 Y capable of reciprocating in the Y-direction along those Y-direction guide rails  19 Y, a pair of X-direction guide rails  20 X fixed to the Y-direction moving frames  20 Y and extending in the X-direction, and an X-direction moving frame  20 X capable of reciprocating in the X-direction along those X-direction guide rails  19 X. The Y-direction moving frame  20 Y is coupled to a Y-direction moving motor  23 Y fixed to the rotational arm housing  17  through an appropriate drive transmission mechanism (e.g. mechanism including a screw  24 Y drivingly coupled to the motor  23 Y and a nut  25 Y engaged therein and fixed to the frame  20 Y), so that the Y-direction moving frame  20 Y moves in the Y-direction on the basis of drive of the Y-direction moving motor  23 Y. Similarly, the X-direction moving frame  20 X is coupled to the X-direction moving motor  23 X fixed to the Y-direction moving frame  20 Y through an appropriate drive transmission mechanism (e.g., mechanism including a screw  24 X drivingly coupled to the motor  23 X and a nut  25 X engaged therein and fixed to the X-direction moving frame  20 X), so that the X-direction moving frame  20 X moves in the X-direction on the basis of drive of the X-direction moving motor  23 X. As thus described, in the XY movement mechanism  18 , the pair of Y-direction guide rails  19 Y, the Y-direction moving frame  20 Y, the Y-direction moving motor  23 Y, and the drive transmission mechanism therefor (screw  24 Y, nut  25 Y) constitute the Y-direction movement mechanism, and the pair of X-direction guide rails  19 X, the X-direction moving frame  20 X, the X-direction moving motor  23 X, and the drive transmission mechanism therefor (screw  24 X, nut  25 X) constitute the X-direction movement mechanism. Therefore, driving the moving motors  23 X and  23 Y can lead to arbitrary movement of the rotational central axis of the rotational arm. 
   A rotational central axis  29  in a cylindrical shape or a columnar shape coupling the lifting arm  3  and the rotational arm  4  is fixed to the X-direction moving frame  20 X at its upper end and rotatably supported by an axis bearing  31  (first coupling means) built in the rotational arm  4 . Further, a belt winding section  32  having a circular shape in its cross section is formed at a lower end of the rotational central axis  29 , and a belt  33  is wound around this belt winding section (pulley)  32 . The belt  33  is also drivingly coupled to another belt winding section  32  to which a rotational motor  34  built in the rotational arm  4  is drivingly coupled, so that the rotational central axis  29  and the rotational arm  4  fixed thereto are rotated on the basis of drive of the rotational motor  34 . These configurations are those having been used basically in the X-ray CT apparatus for dentistry. 
   Further, as shown in  FIG. 9 , in a second example according to the present invention, the rotational arm  4  is supported by columns  2   a ,  2   a  having high rigidity and an upper frame  2   b . The rotational arm  4  is uniaxially rotated, and the rotational central axis  29  is fixed. An region of interest is positioned by the positioning mechanism  8  having the XY movement mechanism  18 . 
   The XY movement mechanism  18  has the pair of Y-direction guide rails  19 Y fixed to a seat  8   aa  of a chair  8   a  and extending in the Y-direction, the Y-direction moving frame  20 Y capable of reciprocating in the Y-direction along those Y-direction guide rails  19 Y, the pair of X-direction guide rails  19 X fixed to a base  8   ab  of the chair  8   a  and extending in the X-direction, and the X-direction moving frame  20 X capable of reciprocating in the X-direction along those X-direction guide rails  19 X. The Y-direction moving frame  20 Y is coupled to the Y-direction moving motor  23 Y fixed to the chair  8   a  through an appropriate drive transmission mechanism (e.g., mechanism including the screw  24 Y drivingly coupled to the motor  23 Y and the nut  25 Y engaged therein and fixed to frame  20 Y), so that the Y-direction moving frame  20 Y moves in the Y-direction on the basis of drive of the Y-direction moving motor  23 Y. Similarly, the X-direction moving frame  20 X is coupled to the X-direction moving motor  23 X fixed to the chair  8   a  through an appropriate drive transmission mechanism (e.g., mechanism including the screw  24 X drivingly coupled to the motor  23 X and the nut  25 X engaged therein and fixed to the X-direction moving frame  20 X), so that the X-direction moving frame  20 X moves in the X-direction on the basis of drive of the X-direction moving motor  23 X. As thus described, in the XY movement mechanism  18 , the pair of Y-direction guide rails  19 Y, the Y-direction moving frame  20 Y, the Y-direction moving motor  23 Y, and the drive transmission mechanism therefor (screw  24 Y, nut  25 Y) constitute the Y-direction movement mechanism, and the pair of X-direction guide rails  19 X, the X-direction moving frame  20 X, the X-direction moving motor  23 X, and the drive transmission mechanism therefor (screw  24 X, nut  25 X) constitute the X-direction movement mechanism. Therefore, driving the moving motors  23 X and  23 Y can lead to arbitrary movement of the rotational central axis of the central axis. 
   It is to be noted that in the second example, the height (Z-direction) can also be adjusted by the chair  8   a . Similarly to the X-direction movement mechanism and the Y-direction movement mechanism, a Z-direction movement mechanism is made up of a Z-direction moving motor  23 Z and its drive transmission mechanism (nut  24 Z, the nut  25 Z), and capable of arbitrarily moving the height of the region of interest of the imaging object. 
   Further, the first example and the second example may be combined so as to provide respective XY movement mechanisms on the sides adjacent the rotational arm  4  and the chair  8   a.    
   As shown in  FIG. 10 , the X-ray generating section  15  has an X-ray generating section housing  35  having various sorts of configurations described below. The X-ray generating section housing  35  is coupled to the rotational arm housing  17  through the X-ray generating section rotating mechanism  36 . Specifically, in the X-ray imaging apparatus of the embodiment, an X-ray generating section rotating mechanism  36  has an X-ray generating section rotating motor  37  fixed to the inside of the rotational arm housing  17 , a vertical axis  38  rotatably attached to the rotational arm housing  17 , a gear mechanism  39  drivingly coupling the X-ray generating section rotating motor  37  and the vertical axis  38 , and a fixed member  40  fixed to the X-ray generating section housing  35  and the vertical axis  38 , such that the X-ray generating section housing  35  rotates with the vertical axis  38  as the center on the basis of drive of the X-ray generating section rotating motor  37 . The X-ray generating section housing  35  is horizontally rotated for turning the X-ray generating section toward a head fixing apparatus for cephalometric imaging, not shown, in cephalometric imaging. 
   An X-ray tube (X-rays generator)  41  as an X-ray generating source is housed inside the X-ray generating section housing  35 . The X-ray tube  41  is surrounded by an X-ray blocking case  42  except for a region (region on the left side of  FIG. 9 ) opposed to the X-ray detecting section  16 . The X-ray blocking case  42  has a beam formation plate  50  in the region opposed to the X-ray detecting section  16 , and a beam forming mechanism  44  is arranged on this beam formation plate  50 . As shown in  FIG. 11 , the beam forming mechanism  44  has a support frame or a block  47  which is liftably supported along a plurality of vertical guide rails  46  through the plurality of guide rollers  45 . The block  47  has an X-ray passage aperture  48  (see  FIG. 10 ) which guides X-rays radiated from the X-ray tube  41  toward the X-ray detecting section  16 , and is coupled to a block lifting motor  49  fixed to the X-ray generating section housing  35  through, for example, a spring mechanism, to allow up and down movement of an irradiation angle of X-rays on the basis of drive of the block lifting motor  49  so that a variety of angles and places can be imaged. It is thereby possible to move the irradiation angle of the X-rays up and down without up and down movement of the X-ray generating section  15 . 
   At this time, imaging can be performed by enlarging an X-ray detecting device  71  shown in  FIG. 13 . Further, though not shown, with the use of a mechanism of moving the X-ray detecting device  71  up and down inside the X-ray detector  64 , imaging can be performed even with a small X-ray detecting device. 
   A beam formation plate  50 , having a plurality of beam formation slits as beam forming means of forming an X-ray beam radiated from the X-ray tube  41 , is arranged in front of the block  47  and in particular, the outside of the X-ray passage aperture  48 . The beam formation plate  50  is supported by a slit moving means which is horizontally movable by a plurality of guiding roller  51  fixed to the front face of the block  47 . The slit moving means has a coupling arm  52  coupled to a beam formation plate  50 , a nut  53  fixed to the coupling arm  52  is engaged in a horizontal screw axis  54  rotatably supported by the block  47 , and further, the horizontal screw axis  54  is coupled to a beam formation plate moving motor  55  fixed to the block  47 . Therefore, the beam formation plate  50  is capable of moving the front of the block  47  right and left, so as to apply a desired X-ray beam. 
   In the embodiment, the beam formation plate  50  has three beam forming slits (slit for primary formation). Specifically, these three beam forming slits include a beam forming transmission aperture  56  (first slit) for CT in a rectangular or a square shape (e.g. 120 mm in length and 120 mm in breadth), a beam forming transmission aperture  57  (second slit) for panoramic imaging which is vertically oriented (e.g. 150 mm in length and 6 mm in breadth), and a beam forming transmission aperture  58  for cephalometric imaging which is also vertically oriented (e.g. 22 mm in length and 6 mm in breadth). Therefore, in a state where the beam forming transmission aperture  56  for CT is opposed to the X-ray tube  41  through the X-ray passage aperture  48 , an X-ray cone beam extending in a pyramid shape is radiated from the X-ray generating section  15  toward the X-ray detecting section  16 . In the case of using such a cone beam for CT, it is possible to perform CT for example in a range with a diameter of the order of 60 mm and a height of the order of 60 mm as an imaging region. 
   In the embodiment, since the length and breadth of the beam forming transmission aperture  56  for CT are the same, the cross section of the X-ray beam which is orthogonal to a traveling direction has a square shape. In a state where the beam forming transmission aperture  57  for panoramic imaging or the beam forming transmission aperture  58  for cephalometric imaging is opposed to the X-ray tube  41  through the X-ray passage aperture  48 , an X-ray narrow beam is radiated from the X-ray generating section  15  toward the X-ray detecting section  16  in a long flat plate shape having a cross section with its longitudinal length larger than its lateral length, though strictly in the pyramid shape. 
   As shown in  FIG. 12 , the X-ray detecting section  16  has an X-ray detecting section housing  59  surrounding a variety of configurations which are described below. 
   In the inside of the X-ray detecting section housing  59 , a detector holder  65  is provided for housing an X-ray detector (X-ray detecting section)  64  having a solid-state image sensing device (CCD) configured by arranging semiconductor image pickup devices in the longitudinal and lateral directions. The detector holder  65  is movably supported in the horizontal direction along a holder guide rail  66  and coupled to the X-ray detecting section moving motor  67  fixed to the X-ray detecting section housing  59 , so as to move in the horizontal direction on the basis of drive of the X-ray detecting section moving motor  67 . The CCD is not necessarily applied to the X-ray detecting section, but a flat panel detector (FPD) such as a MOS sensor, and an X-ray fluorescent multiplier tube (XII) may be applied. 
   As shown in  FIG. 13 , the detector holder  65  has a plurality of beam formation slits (slit for secondary formation)  68 ,  69 ,  70  in shapes corresponding to the forgoing plurality of beam forming transmission apertures  56 ,  57 ,  58  in the X-ray generating section  15 , and on the basis of drive of the X-ray detecting section moving motor  67  according to the imaging mode, the beam formation slit  68 ,  69  or  70  in the X-ray detecting section  16  which correspond to the beam forming transmission aperture in the X-ray generating section  15  is positioned in extension of the X-ray tube  41  and the beam forming transmission apertures  56 ,  57  or  58  in the X-ray generating section  15  in accordance with a selection signal of the imaging mode selecting means. The X-ray detector  64  has: an X-ray detecting device  71  obtained by arranging image pickup devices in almost square shape corresponding to the beam formation slit  68  in almost square shape; and an X-ray detecting device  72  obtained by arranging image pickup devices in a shape vertically oriented corresponding to the vertically oriented beam formation slits  69  and  70 . The X-ray detector  64  is inserted into a slot  73  formed in the detector holder  65 . The X-ray detecting device  71  is arranged behind the beam formation slit  68  in X-ray CT, and the X-ray detecting device  72  is arranged behind the beam formation slits  69  and  70  in panoramic imaging or in cephalometric imaging. 
     FIG. 14  is a control block diagram of a plurality of motors and the like included in the X-ray CT apparatus  1 . As shown in the figure, the X-ray imaging apparatus has a controller (CPU)  94 . The CPU  94  is connected with the foregoing plurality of motors, namely, the Y-direction moving motor, the X-direction moving motor  26 , the rotational motor  34 , the X-ray generating section rotating motor  37 , the block lifting motor  49 , the beam formation plate moving motor  55 , and the X-ray detecting section moving motor  67 . These motors are connected to corresponding rotational amount detecting sensors (e.g. encoder)  81  to  88  for the purpose of detecting rotational amounts thereof and controlling drive of the motors on the basis of the detected rotational amounts, and outputs of these sensors  81  to  88  are connected to the CPU  94 . 
   The CPU  94  is also connected with the X-ray tube  41  and a plurality of storage sections. The storage sections have movement locus data (Read Only Memory: ROM)  95 , and an X-ray image storing section (Random Access Memory: RAM)  96 . The ROM  95  stores the following information during imaging (including processes before and after imaging) in accordance with each image mode described later, a movement amount in an XY direction of the rotational central axis  29 , rotation of the rotational central axis  29  (rotational angle of the rotational arm  4 ), rotational angles of the X-ray generating section housing  35  and the X-ray detecting section housing  59  against the rotational arm  4 , a moving amount in the up-and-down direction and the horizontal direction of the block  47  and a movement amount in the horizontal direction of the beam formation plate  50  in the X-ray generating section  15 , and movement amounts in the horizontal direction of the X-ray detector  64  and the detector holder  65  in the X-ray detecting section  16 . In particular, the movement amount of the rotational central axis  29  and the movement amount of the rotational arm  4  are defined by data with parameters being time and a coordinate value of an XY coordinate system made up of axes in two orthogonal directions (e.g., a back and forth direction in which the upper and lower arm sections  6  and  7  project in the lifting arm  3  and a horizontal direction orthogonal thereto) on the horizontal plane. The coordinate value may be given by a polar coordinate instead of the XY coordinate system. 
   The RAM  96  temporarily stores necessary information. For example, as shown in the figure, the X-ray detector  64  is electrically connected to the CPU  94  while being in the state of being mounted on the X-ray detecting section  16 , and image data acquired in the X-ray detector  64  by X-ray imaging is temporarily stored into the RAM  96 . 
   The CPU  94  is further connected with an imaging start switch  90  for starting X-ray imaging, an imaging mode selecting switch  91  for switching an imaging mode, such as the normal scan/CT mode, the offset scan/CT mode, the panoramic X-ray imaging mode, and the cephalometric imaging mode, a changing-over switch  93  for making switching between a reduced (wide area) imaging mode in which a wide area of an imaging object is imaged and an enlarged (narrow) imaging mode in which a narrow area of the imaging object is enlarged and imaged, and a communication section  97  for performing communication with a computer, not shown. 
   A basic operation of the X-ray imaging apparatus having such a configuration is described with reference to the block diagram of  FIG. 14  and a flowchart of  FIG. 15 . First, as shown in  FIGS. 5 and 9 , the imaging object is positioned in the X-ray CT apparatus  1  by the positioning mechanism  8  prior to imaging. At this time, in the first example shown in  FIG. 5 , the imaging object stands in front of the lower arm section  7  of the lifting arm  3 , holds the handles  11  with his or her both hands, and puts his or her jaw on the chin rest  9  while a right-and-left movement of his or her head is in the state of being restricted by the right and left lateral direction control member  10 . Further, in the second example shown in  FIG. 9 , the imaging object sits on the chair  8   a  while his or her head is in the state of being restricted so as to remain still by a head fixing apparatus  8   b.    
   An operator operates the imaging mode selecting switch  91  to select an imaging mode (panoramic imaging, CT or the like). Further, when the CT mode has been selected, a normal scan/CT-offset scan/CT mode selecting switch  92  is operated to select either the normal scan/CT mode or the offset scan/CT mode. It is to be noted that the normal scan/CT mode is a mode in which the rotational arm  4  is rotated with the rotational central axis  29  as the center, and X-rays having been radiated from the X-ray generating section  15  and transmitted through the whole of the region of interest  105  of the imaging object are detected in the X-ray detecting section  16 , and on the basis of information included in the X-rays having transmitted through the whole of the region of interest  105  of the imaging object and been detected in the X-ray detecting section  16 , a tomographic image of an imaging object arranged between the X-ray generating section  15  and the X-ray detecting section  16  is constructed. Further, the offset scan/CT mode is a mode in which the rotational arm  4  is rotated with the rotational central axis  29  as the center, and X-rays having been radiated from the X-ray generating section  15  and transmitted through part of the region of interest  105  of the imaging object are detected in the X-ray detecting section  16 , and on the basis of information included in the X-rays having transmitted through the part of the region of interest  105  of the imaging object and been detected in the X-ray detecting section  16 , a tomographic image of the imaging object arranged between the X-ray generating section  15  and the X-ray detecting section  16  is constructed. In the present embodiment, in the normal scan/CT mode, a CT image of the imaging object is constructed on the basis of X-ray imaging data obtained by arranging a center  100  of the region of interest  105  of the imaging object which radiated from the X-ray generating section  15  and detected in the X-ray detecting section  16  on the same axis as the rotational central axis  29  and rotating the center. 
   In the normal scan/CT mode, since imaging is performed while the region of interest  105  is constantly present in a cone beam  104  irrespective of the rotational angle of the rotational arm  4 , an image can be reconstructed on the basis of X-ray transmission information obtained during rotation of the rotational arm of 180 degrees. Further, the rotational arm is more favorably rotated 360 degrees for reconstitution of a fine image. Imaging can be performed in a wide area in the offset scan/CT mode as compared with the normal scan/CT mode. 
   Moreover, according to the offset scan/CT mode, for example when an FPD with a size of 120 mm×120 mm of the present example is used, imaging can be performed in a range with a diameter of the order of 120 mm and a height of the order of 60 mm, whereas in the normal scan/CT mode, imaging can be performed only in a range with a diameter of the order of 60 mm and a height of the order of 60 mm. 
   When the panoramic imaging mode has been selected, the CPU  94  reads a program (not shown) in accordance with the panoramic imaging mode from the ROM  95 , and drives, if necessary, one or more than one of the Y-direction moving motor  23 Y, the X-direction moving motor  23 X and the rotational motor  34  simultaneously or sequentially on the basis of the read program, to move the rotational arm  4 , the X-ray generating section  15  and the X-ray detecting section  16  to initial imaging positions (Step # 2 ). Further, the CPU  94  drives the beam formation plate moving motor  55 , to make the beam forming transmission aperture  57  for panoramic imaging in accordance with the selected panoramic imaging mode opposed to the X-ray tube  41 . 
   After completion of the above-mentioned preparation, when a command to start panoramic imaging is inputted by operation of the imaging start switch  90  (Step # 3 ), the CPU  94  drives the Y-direction moving motor  23 Y, the X-direction moving motor  23 X, the rotational motor  34  and the like on the basis of a program read from the ROM  95 , and also activates the X-ray tube  41  to generate X-rays (Step # 5 ). As a result, while the rotational arm  4 , the X-ray generating section  15  and the X-ray detecting section  16  move along loci indicated by the program, the X-rays radiated from the X-ray tube  41  are applied to the imaging object through the X-ray passage aperture  48  of the block  47  and the beam forming transmission aperture  57  for panoramic imaging of the beam formation plate  50 . The X-rays having transmitted through the imaging object are detected by the X-ray detector  64  through the beam formation slit for panoramic imaging of the X-ray detector  64  in the X-ray detecting section  16 . The X-ray detecting section  16  transmits data corresponding to the detected X-ray image to the RAM  96  at regular time intervals or after completion of imaging. The image data stored in the RAM  96  is transmitted to a computer through the communication section  97 , and objected to a necessary process therein, to be displayed on a display, not shown. A typical imaging process in panoramic X-ray imaging is a known process, namely an imaging process of laminating frame images with displacement of a prescribed amount. Further, panoramic X-ray imaging can be performed prior to CT, to set an region of interest to be objected to CT. 
   When the CT mode has been selected by the imaging mode selecting switch  91 , the CPU  94  determines either the normal scan/CT mode (first imaging mode) or the offset scan/CT mode (second imaging mode) has been selected on the basis of a signal from the normal scan/CT-offset scan/CT mode selecting switch  93  (Step # 6 ). 
   When the normal scan/CT mode has been selected, the CPU  94  drives the beam formation plate moving motor  55  to make the beam forming transmission aperture  56  for CT in accordance with the selected CT mode opposed to the X-ray tube  41 . Next, the CPU  94  reads a program (not shown) in accordance with the selected normal scan/CT mode from the ROM  95 , and drives, if necessary, one or more than one of the Y-direction moving motor  23 Y, the X-direction moving motor  23 X and the rotational motor  34  simultaneously or sequentially on the basis of the read program, to move the rotational arm  4  to the initial imaging position (Step # 7 ). Typically, in this state, the center of the driving axis  30  is placed on a line linking the X-ray generating section  15  (center of the X-ray tube  41 ) and the X-ray detecting section  16  (center of the X-ray detecting device  71 ). 
   Subsequently, when a command to start imaging is inputted by operation of the imaging start switch  90  (Step # 8 ), the CPU  94  activates the X-ray tube  41  to generate X-rays, also drives a necessary motor in accordance with the foregoing program (Step # 9 ). At this time, the rotational amount of each motor is detected by the corresponding sensors  81  to  88 , and using this detection result, the rotational amount of each motor is feedback-controlled. The X-rays radiated from the X-ray tube  41  are applied to the imaging object through the X-ray passage aperture  48  of the block  47  and the beam forming transmission aperture  56  for CT of the beam formation plate  50 . The X-rays having transmitted through the imaging object are detected by the X-ray detector  64  through the beam formation slit for panoramic imaging of the X-ray detector  64  in the X-ray detecting section  16 . The X-ray detecting section  16  stores data corresponding to the detected X-ray image into the RAM  96  at regular time intervals. The image data stored in the RAM  96  is transmitted to the computer through the communication section  97 , and objected to a necessary process therein, to be displayed on the display, not shown. At this time, a necessary image is reconstructed through the use of image data obtained by detecting X-rays having transmitted through both side regions sandwiching the rotational central axis  29 . 
   When the offset scan/CT mode has been selected, the CPU  94  drives the beam formation plate moving motor  55  to make the beam forming transmission aperture  56  for CT in accordance with the selected CT mode opposed to the X-ray tube  41 . At this time, if necessary, the block  47  is moved in a rotational direction relatively to the beam formation plate  50  in the X-ray generating section  15 , and meanwhile, the detector holder  65  is moved in the rotational direction in the X-ray detecting section  16 . Further, the CPU  94  reads a program (not shown) in accordance with the selected offset scan/CT mode from the ROM  95 , and drives, if necessary, one or more than one of the Y-direction moving motor  23 Y, the X-direction moving motor  23 X and the rotational motor  34  simultaneously or sequentially on the basis of the read program, to move the rotational arm  4  to the initial imaging position (Step # 10 ). 
   Subsequently, when a command to start imaging is inputted by operation of the imaging start switch  90  (Step # 11 ), the CPU  94  activates the X-ray tube  41  to generate the X-ray tube  41 , and also drives a necessary motor in accordance with the foregoing program (Step # 12 ). At this time, the rotational amount of each motor is detected by the corresponding sensors  81  to  88 , and on the basis of this detection result, the rotational amount of each motor is feedback-controlled. The X-rays radiated from the X-ray tube  41  are applied to the imaging object through the X-ray passage aperture  48  of the block  47  and the beam forming transmission aperture  56  for CT of the beam formation plate  50 . The X-rays having transmitted through the imaging object are detected by the X-ray detector  64  through the beam formation slit for CT of the X-ray detector  64  in the X-ray detecting section  16 . The X-ray detecting section  16  stores data corresponding to the detected X-ray image to the RAM  96  at regular time intervals. The image data stored in the RAM  96  is transmitted to the computer through the communication section  97 , and objected to a necessary process therein, to be displayed on the display, not shown. At this time, a necessary image is reconstructed through the use of image data obtained by detecting X-rays having transmitted through one of both side regions sandwiching the rotational central axis  29 . 
   An initial setting process in the case where the offset scan/CT mode has been selected is described with reference to  FIG. 15 . It is assumed here that in the state prior to the initial setting process, the rotational central axis  29  of the X-ray CT apparatus  1  is located at a center  100  of an imaging region  101  (region surrounded by an outer circle out of double circles) of the imaging object which is positioned by the positioning mechanism  8  of the imaging object. As shown in the figure, in this state, the imaging region  101  of the imaging object is not completely included in an X-ray irradiating region (region surrounded by outer edges  102  and  103  indicated by the two dotted lines)  104  detected in the X-ray detecting section  16  out of X-rays radiated from the X-ray generating section  15 , and only an region of interest (region surrounded by an inner circle out of the double circles)  105  inside the imaging region  101  of the imaging object can be imaged. 
   From this state, with the position of the imaging object in a fixed state, the CPU  94  drives the X-direction moving motor  23 X of the XY movement mechanism  18  to move the rotational arm  4  in the X-direction (direction to the right, direction of the arrow in the shown example) by a prescribed distance from the position of  FIG. 16A , while locating the rotational central axis  29  at the center of the imaging region  101  of the imaging object from the position of  FIG. 16A  (see  FIG. 16B ). Subsequently, while keeping the rotational central axis  29  located at the center of the imaging region  101  of the imaging object, the CPU  94  moves the rotational arm  4  in the Y-direction (direction upward, direction of the arrow in the shown example) to bring the X-ray detecting section  16  closer to the imaging region  101  of the imaging object so as to locate the outer edge  102  or  103  of the cone beam  104  at the center of the imaging region  101  (see  FIG. 16C ). At this time, the outer edge  102  or  103  of the cone beam  104  is not necessarily at the center of the imaging region  101  of the imaging object, but at least the center of the imaging region  101  needs to be located inside the cone beam  104 . As shown in the figure, in this state, half of the imaging region  101  of the imaging object is completely included in the cone beam  104 . 
   Subsequently, as shown in  FIG. 17 , the CPU  94  drives the rotational motor  34  to rotate the rotational arm  4  in a clockwise direction as indicated by the arrows. As a result, although the cone beam  104  covers only half of the imaging region  101  of the imaging object at each time point during imaging, when the rotational arm  4  rotates completely (360 degrees), the imaging region  101  of the imaging object is entirely scanned by the cone beam  104 . This can result in subsequent reconstruction of X-ray imaged image data detected in the X-ray detecting section  16 , thereby allowing reconstruction of a desired image of the entire imaging region  101  of the imaging object. Such imaging is called offset scan/CT, which can be performed in a wider range than the normal scan/CT. 
   The initial setting process in a case where the enlarged (narrow) mode has been selected is described with reference to  FIG. 18 . Similarly to what was described above, it is assumed that in the state prior to the initial setting process, the rotational central axis  29  of the X-ray CT apparatus  1  is located at the center of the imaging region  101  (region surrounded by an outer circle out of double circles) of the imaging object which is positioned by the positioning mechanism  8  of the imaging object. As shown in the figure, in this state, the imaging region  101  of the imaging object is not completely included in the X-ray irradiating region (region surrounded by the outer edges  102  and  103  indicated by the two dotted lines)  104  detected in the X-ray detecting section  16  out of X-rays radiated from the X-ray generating section  15 , and only the region of interest (region surrounded by an inner circle out of the double circles)  105  inside the imaging region  101  of the imaging object can be imaged. 
   From this state, the CPU  94  drives the X-direction moving motor  23 X of the XY movement mechanism  18  to move the rotational arm  4  in the X-direction (direction to the right, direction of the arrow in the shown example) by a prescribed distance, while locating the rotational central axis  29  at the center of the imaging region  101 . Subsequently, while keeping the rotational central axis  100  located at the center of the imaging region  101  of the imaging object, the CPU  94  moves the rotational arm  4  in the Y-direction (direction downward, direction of the arrow in the shown example) to bring the imaging region  101  of the imaging object closer to the X-ray generating section  15  so as to locate the outer edge  102  or  103  of the cone beam  104  at the center of the imaging region  101 . At this time, the outer edge  102  or  103  of the cone beam  104  is not necessarily at the center of the imaging region  101  of the imaging object, but at least the center of the imaging region  101  needs to be located inside the cone beam  104 . As shown in the figure, in this state, half of the imaging region  101  of the imaging object is completely included in the cone beam  104 . 
   Subsequently, as shown in  FIG. 19 , the CPU  94  drives the rotational motor  34  to rotate the rotational arm  4  in a clockwise direction as indicated by the arrows As a result, although the cone beam  104  covers only half of the imaging region  101  of the imaging object at each time point during imaging, when the rotational arm  4  rotates 360 degrees, the imaging region  101  of the imaging object is entirely scanned by the cone beam  104 . This can result in subsequent reconstruction of X-ray imaged image data detected in the X-ray detecting section  16 , thereby allowing reconstruction of a desired image of the entire imaging region  101  of the imaging object. By performing imaging in such a manner, a projected image can be enlarged and imaged since the distance between the X-ray source and the imaging object is shorter than in the case of  FIG. 16 . 
   In these preferred embodiments, An imaging region at normal scan/CT mode is defined as a region of interest as an example. 
   The imaging region at normal scan/CT mode is a region like the region of circle  105  in  FIG. 16A  or  FIG. 18A . 
   And an imaging region at offset scan/CT mode is for example an region includes the imaging region at normal scan/CT mode and the region around the imaging region at normal scan/CT mode like the region of circle  101  in  FIG. 16A  or  FIG. 18A . 
   Therefore the maximum region of the imaging region at offset scan/CT mode is defined by outer edges  102  or  103  of conebeam  104 . 
   In  FIG. 16A  to C,  FIG. 18A  to C the imaging region  101  is indicated as an example smaller than the maximum region of the imaging region above mentioned considering the convenience for understanding. 
   It is to be noted that, although the rotational arm  4  was first moved in the X-direction and then moved in the Y-direction in the above description, this order may be reversed, or the rotational arm  4  may be moved all at once in an oblique direction obtained by synthesizing those movements in the two directions. 
   The X-direction movement mechanism provided in the rotational arm  4  is particularly effective in the X-ray imaging apparatus having the offset scan/CT mode, as described above. For example, the cone beam need to be moved to the direction orthogonal to the X-ray applying direction in the offset scan/CT method, but the movement amount thereof can be adjusted in a wider range. Further, an enlargement ratio of an image imaged in the X-ray detecting section of limited size can be adjusted in a large scale as compared with a constitution where the rotational arm is simply moved in the Y-direction. 
   In addition, the cone beam refers to an X-ray beam that narrows X-rays so as to apply X-rays within a certain region. In the above examples, the beam forming transmission aperture for CT was in almost square shape and the cone beam in the pyramid shape was applied from the X-ray generating section toward the X-ray detecting section. However, a shape of the beam forming transmission aperture for CT is not restricted to this, but a cone beam in cone shape can be formed when the beam forming transmission aperture is formed into circular or oval shape.