Patent Publication Number: US-2009225955-A1

Title: X-ray ct apparatus collimator, method of manufacturing the x-ray ct apparatus collimator, and x-ray ct apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application a divisional of application Ser. No. 11/403,813, filed Apr. 14, 2006, and is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-118772, filed Apr. 15, 2005, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a collimator used for an X-ray CT (Computer Tomography) apparatus, a method of manufacturing the collimator, and an X-ray CT apparatus having the collimator. 
     2. Description of the Related Art 
     As is well known, an X-ray CT apparatus is designed to obtain an image (tomographic image) by calculating (reconstructing) the X-ray absorptance of tissue such as an organ as an index called a CT value with reference to the X-ray absorptance of water on the basis of the amount of X-rays absorbed by a subject. 
     This X-ray CT apparatus is provided with a collimator on, for example, the X-ray incident side of an X-ray detector to reshape the shape of an X-ray beam striking each X-ray detection element and to remove scattered X-rays.  FIG. 1A  shows an example of the arrangement of a conventional collimator having an integral structure (to be referred to as an “integral collimator” hereinafter). As shown in  FIG. 1A , the integral collimator has upper and lower arcuated supports arranged side by side in the slice direction along the body axis of a subject. Pairs of upper and lower grooves are formed in the upper and lower supports so as to allow the insertion of collimator plates therein such that the respective plates face an X-ray focal point (which is assumed to be the emission point of an X-ray source). Flattened collimator plates are inserted in these grooves. An adhesive is then applied to the portions of the plates which are inserted in the grooves and is cured, thereby forming a collimator as an integral structure. The collimator plates are supported by the grooves of the upper and lower supports, and reshape incident X-rays without degrading the warpage of each plate owing to its rigidity. 
     Assume that such an integral collimator comprises, for example, collimator plates each having a length of less than 100 mm in the slide direction in an X-ray CT apparatus. In this case, if flattening processing is performed for each collimator plate in advance, a collimator with little warpage on the 20 μm order can be formed with only the rigidity of each collimator plate. 
     The recent trend is to develop X-ray CT apparatuses with wider detection ranges in the slice direction. In an X-ray CT apparatus having  256  rows of multi-slice detectors which has currently been developed, the detection range in the slice direction is assumed to be about four times that in existing X-ray CT apparatuses. For this reason, according to the arrangement of a conventional integral collimator, it is difficult to maintain the flatness and warpage of each collimator plate with only the rigidity of each collimator plate. As a consequence, when each detector (detector unit) is to be mounted, alignment cannot be performed, and the solid angle of an X-ray beam striking each X-ray detection element cannot be properly limited, resulting in failure to acquire an appropriate tomographic image. 
     In order to solve this problem, for example, as shown in  FIG. 1B , there has been proposed a collimator having a module structure (to be referred to as a “module type collimator” hereinafter) which covers about 20 channels of a detector. As shown in  FIG. 1B , a plurality of such module type collimators are arranged to cover the entire detection surface of the X-ray detector along the channel direction. The module type collimator has front and rear supports, in each of which grooves in which collimator plates are to be inserted are formed. These grooves are formed in the front and rear supports at different pitches because collimator plates need to face the X-ray focal point. By inserting collimator plates in the pairs of grooves in the front and rear supports, the collimator plates form an arrangement widening toward the end. As a result, all the collimator plates are formed to face the X-ray focal point. 
     Such a module type collimator is assembled while adjusting the squareness with respect to an end face of each support or the reference surface of the central plate, thereby forming a module type collimator set at a correct position opposing the X-ray focal point. It has been confirmed that in even a region where the detection range of each collimator plate in the slice direction is about 200 mm or more and hence it is difficult to flatten collimator plates, warpage is corrected by inserting plates in the grooves formed in the front and rear supports in the slice direction, and a collimator which maintains flatness as in existing collimators can be formed. As a consequence, alignment with the detector can be done. 
     In the above module type collimator as well, for example, the following problem arises. 
     In the module type collimator, factors that unstabilize the mount surface of the detector module on which the collimator is mounted cannot be eliminated. Even if, for example, a dust particle on the 10 μm order exists on the mount surface, the X-ray focal point at the position about 10 μm ahead of the dust particle is enlarged and shifted. Therefore, steps are produced in continuity that connects the X-ray focal point at the joint portions between the module type collimators. As a consequence, when the polar response characteristic, i.e., the X-ray foal point, shifts over time, an impermissible unbalance amount, which cannot be neglected, is produced in variation components of shadow on the detector, resulting in the production of artifacts in an image. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention has been made in consideration of the above situation, and has as its object to provide an X-ray CT apparatus collimator, a method of manufacturing the collimator, and an X-ray CT apparatus which can realize proper X-ray collimation by maintaining the flatness of each collimator plate without losing the continuity of the X-ray focal point. 
     According to an aspect of the present invention, there is provided an X-ray CT apparatus which comprises: an X-ray exposing unit which exposes X-rays; an X-ray detection unit which is placed to face the X-ray exposing unit through a subject and detects X-rays incident to a detection surface; and a collimator unit ( 50 ) which is placed on the X-ray incident side of an X-ray detector to remove scattered X-rays and includes a plurality of collimator plates and a support unit, the plurality of collimator plates being arranged along a predetermined direction, and the support unit supporting at least three sides of each of the collimator plates such a manner that a surface of each of the collimator plates is substantially parallel to an X-ray incident direction from the X-ray exposing unit to the detection surface. 
     According to another aspect of the present invention, there is provided an X-ray CT apparatus collimator manufacturing method of manufacturing a collimator which is used for an X-ray CT apparatus comprising an X-ray exposing unit which exposes X-rays and an X-ray detection unit which is placed to face the X-ray exposing unit through a subject and detects X-rays striking a detection surface, and is provided on the detection surface to remove scattered X-rays, which comprises: assembling, by using side surface members, a first support unit including a plurality of first grooves formed along an X-ray incident direction from the X-ray exposing unit to the detection surface and a second support unit including a plurality of second grooves formed along the X-ray incident direction from the X-ray exposing unit to the detection surface so as to correspond to said plurality of first grooves; fixing, to the detection surface side of the first support unit and second support unit, a first support unit including a plurality of third grooves for fitting of peripheries of the collimator plates fitted in the first grooves and the second grooves which face each other which are located on the detection surface side; fitting collimator plates in the first grooves, the second grooves, and the third grooves which face each other; and bonding said each collimator plate to the first groove, the second groove, and the third groove which correspond to said each collimator plate. 
     According to yet another aspect of the present invention, there is provided an X-ray CT apparatus collimator manufacturing method of manufacturing a collimator which is used for an X-ray CT apparatus comprising an X-ray exposing unit which exposes X-rays and an X-ray detection unit which is placed to face the X-ray exposing unit through a subject and detects X-rays striking a detection surface, and is provided on the detection surface to remove scattered X-rays, which comprises: assembling, by using side surface members, a first support unit including a plurality of first grooves formed along an X-ray incident direction from the X-ray exposing unit to the detection surface and a second support unit including a plurality of second grooves formed along the X-ray incident direction from the X-ray exposing unit to the detection surface so as to correspond to said plurality of first grooves; fixing, to the detection surface side of the first support unit and second support unit, a first support unit including a plurality of third grooves for fitting of peripheries of the collimator plates fitted in the first grooves and the second grooves corresponding to each other which are located on the detection surface side; fixing the second support including slits which allow the collimator plates fitted in the first grooves and the second grooves which face each other to pass through the slits and support peripheries of the collimator plates which are on an X-ray incident side to the X-ray incident side of the first support unit and the second support unit; fitting collimator plates in the first grooves, the second grooves, and the third grooves which face each other upon making the collimator plates pass through the slits; and bonding the collimator plates to the first grooves, the second grooves, the third grooves, and the slits which correspond to each other. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1A  is a view for explaining the arrangement of a conventional integral collimator; 
         FIG. 1B  is a view for explaining the arrangement of a module type collimator; 
         FIG. 2A  is a block diagram showing the arrangement of an X-ray CT apparatus  10  according to an embodiment; 
         FIG. 2B  is a schematic view for explaining the layout of a detector-side collimator  50 ; 
         FIG. 3  is a view for explaining the arrangement of the detector-side collimator  50 ; 
         FIG. 4  is a view showing a form of supporting collimator plates  504  by using grooves  505  of upper and lower supports  500  and  501  and an abutment plate  503 ; 
         FIG. 5  is a view for explaining a method of forming grooves  506  in the abutment plate  503 ; 
         FIG. 6  is a view for explaining the shape of each groove  506  in a manufacturing process for the abutment plate  503 ; 
         FIG. 7  is a view for explaining the shape of each groove  506  at the time of assembly of the abutment plate  503  to the upper and lower supports  500  and  501 ; 
         FIG. 8  is a flowchart showing the flow of a manufacturing process for the detector-side collimator  50 ; 
         FIG. 9  is a view showing the arrangement of a detector-side collimator  50  according to the second embodiment; 
         FIG. 10A  is a perspective view showing the detector-side collimator  50  according to the second embodiment when viewed from the inner arcuated side,  FIG. 10B  is a view for explaining a method of manufacturing a guide plate  510 , and  FIG. 10C  is a sectional view of the flat guide plate  510  along slits  511 ; 
         FIG. 11  is a flowchart showing the flow of a manufacturing process for the detector-side collimator  50 ; 
         FIG. 12  is a view showing the arrangement of a detector-side collimator  50  possessed by an X-ray CT apparatus  10  according to the third embodiment; 
         FIG. 13  is a view for explaining a method of forming grooves  521  of internal diameter cover  520 ; 
         FIG. 14  is a view for explaining a method of forming grooves  521  of internal diameter cover  520 ; 
         FIG. 15  is a view for explaining a method of forming grooves  521  of internal diameter cover  520 ; 
         FIG. 16  is a flow chart showing the flow of a manufacturing process for the detector-side collimator  50  according to the third embodiment; 
         FIG. 17  is a view showing the arrangement of the detector-side collimator  50  according to a modified example of the third embodiment; 
         FIG. 18  is a view showing the arrangement of the detector-side collimator  50  according to a modified example of the third embodiment; 
         FIG. 19  is a flow chart showing the flow of a manufacturing process for the detector-side collimator  50  according to a modified example of the third embodiment; 
         FIG. 20A  is a view showing the arrangement of the detector-side collimator  50  possessed by the X-ray CT apparatus  10  according to a fourth embodiment; 
         FIG. 20B  is a view showing the arrangement of the detector-side collimator  50  possessed by the X-ray CT apparatus  10  according to the fourth embodiment; 
         FIG. 20C  is a view showing the arrangement of the detector-side collimator  50  possessed by the X-ray CT apparatus  10  according to the fourth embodiment; 
         FIG. 20D  is a view showing a modified example of the detector-side collimator  50  (detail description of the joint part between the neighboring internal diameter covers  530 ) according to the fourth embodiment; 
         FIG. 21  is a flow chart showing the flow of a manufacturing process for the detector-side collimator  50  according to the fourth embodiment; 
         FIG. 22  is a view showing the arrangement of the detector-side collimator  50  according to a modified example of the fourth embodiment; 
         FIG. 23  is a flow chart showing the flow of a manufacturing process for the detector-side collimator  50  according to a modified example of the fourth embodiment; 
         FIG. 24  is a view showing the arrangement of the detector-side collimator  50  possessed by the X-ray CT apparatus  10  according to a fifth embodiment; 
         FIG. 25A  is a view showing an aspect of an abutment plate  540  of the detector-side collimator  50  according to the fifth embodiment; 
         FIG. 25B  is a view showing an aspect of an abutment plate  540  of the detector-side collimator  50  according to the fifth embodiment; 
         FIG. 25C  is a view showing an aspect of an abutment plate  540  of the detector-side collimator  50  according to the fifth embodiment; 
         FIG. 26  is a flow chart showing the flow of a manufacturing process for the detector-side collimator  50  according to the fifth embodiment; 
         FIG. 27  is a view showing the arrangement of the detector-side collimator  50  according to a modified example of the fifth embodiment; 
         FIG. 28  is a flow chart showing the flow of a manufacturing process for the detector-side collimator  50  according to the modified example of the fifth embodiment; 
         FIG. 29  is a view showing the arrangement of the detector-side collimator  50  possessed by the X-ray CT apparatus  10  according to a sixth embodiment; 
         FIG. 30  is a flow chart showing the flow of a manufacturing process for the detector-side collimator  50  according to the sixth embodiment; 
         FIG. 31  is a view showing the arrangement of the detector-side collimator  50  according to a modified example of the sixth embodiment; 
         FIG. 32  is a view showing the arrangement of the detector-side collimator  50  according to the modified example of the sixth embodiment; 
         FIG. 33  is a flow chart showing the flow of a manufacturing process for the detector-side collimator  50  according to the modified example of the sixth embodiment; and 
         FIG. 34  is a view showing the arrangement of the detector-side collimator  50  according to another modified example of the sixth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The first and second embodiments of the present invention will be described below with reference to the views of the accompanying drawing. Note that the same reference numerals in the following description denote constituent elements having substantially the same functions and arrangements, and a repetitive description thereof will be made only when required. 
     First Embodiment 
       FIG. 2A  is a block diagram showing the arrangement of an X-ray CT apparatus  10  according to this embodiment. As shown in  FIG. 2A , the X-ray CT apparatus  10  comprises an imaging system A and a processing/display system B. The constituent elements of these systems will be described below. 
     The imaging system A acquires projection data (or raw data) by applying X-rays to a subject and detecting X-rays transmitted through the subject. Note that the imaging systems of X-ray CT apparatuses include various types, e.g., a rotate/rotate type in which an X-ray tube and a two-dimensional detector system rotate together around a subject, a stationary/rotate type in which many detection elements are arrayed in the form of a ring, and only an X-ray tube rotates around a subject, and a type which electronically moves the position of an X-ray source onto a target by deflecting an electron beam. The present invention can be applied to all types. In this case, the rotate/rotate type X-ray CT apparatus, which is currently the mainstream, will be exemplified. 
     As shown in  FIG. 2A , the imaging system A has an X-ray tube  101 , rotating ring  102 , two-dimensional detector system  103 , data acquisition circuit (DAS)  104 , non-contact data transmission device  105 , gantry driving unit  107 , slip ring  108 , X-ray tube side collimator (not shown in  FIG. 2A ), and X-ray detector-side collimator (not shown in  FIG. 1 ). 
     The X-ray tube  101  is a vacuum tube which generates X-rays, and is amounted on the rotating ring  102 . Power (a tube current or tube voltage) required for the emission of X-rays is supplied from a high voltage generator  109  to the X-ray tube  101  through the slip ring  108 . The X-ray tube  101  exposes X-rays to a subject placed in an effective field of view FOV by accelerating electrons using the applied high voltage and making them collide with the target. 
     An X-ray tube side collimator (not shown) which reshapes an X-ray beam exposed from the X-ray tube  101  into a cone shape (quadrangular pyramidal shape) or a fan beam shape is provided between the X-ray tube  101  and the subject. 
     The two-dimensional detector system  103  is a detector system which detects X-rays transmitted through the subject, and is mounted on the rotating ring  102  to face the X-ray tube  101 . In the two-dimensional detector system  103 , a plurality of detection elements comprising combinations of scintillators and photodiodes form a detection surface, and are arrayed in the form of a matrix in the body axis direction of the subject (slice direction) and the channel direction perpendicular thereto. 
     As schemes of converting incident X-rays into electric charges in each detection element, a direct conversion scheme and an indirect conversion scheme are available. This embodiment is not limited to either of the schemes. 
     The X-ray tube  101  and the detector system  103  are mounted on the rotating ring  102 . The rotating ring  102  is driven by the gantry driving unit  107  and rotates around the subject at a high speed of one rotation per second. 
     The data acquisition circuit (DAS)  104  has a plurality of data acquisition element rows on which DAS chips are arrayed. The data acquisition circuit (DAS)  104  receives an enormous amount of data (M×N-channel data per view will be referred to as “raw data” hereinafter) associated with all M×N channels, which are detected by the two-dimensional detector system  103 , performs amplification processing, A/D conversion processing, and the like, and transmits the resultant data altogether to a data processing unit on the fixed side through the non-contact data transmission device  105  using optical communication. 
     The X-ray detector-side collimator reshapes an X-ray beam striking each detection element of the two-dimensional detector system  103 , and is provided on the X-ray incident side of the two-dimensional detector system  103 . 
     The processing/display system B will be described next. The processing/display system B comprises a pre-processing device  106 , the high voltage generator  109 , a host controller  110 , a storage device  111 , a reconstruction device  114 , an input device  115 , a display device  116 , an image processing unit  118 , a network communication device  119 , and a data/control bus  300 . 
     The pre-processing device  106  receives raw data from the DAS  104  through the non-contact data transmission device  105 , and executes sensitivity correction and X-ray intensity correction. Note that the raw data pre-processed by the pre-processing device  106  will be referred to as “projection data”. 
     The gantry driving unit  107  performs, for example, driving control to rotate the X-ray tube  101  and the two-dimensional detector system  103  together around a central axis parallel to the body axis direction of the subject inserted in the opening for diagnosis. 
     The high voltage generator  109  is a device which supplies power necessary for the emission of X-rays to the X-ray tube  101  through the slip ring  108 , and comprises a high voltage transformer, filament heating converter, rectifier, high voltage switch, and the like. The high voltage generator  109  applies a high voltage to the X-ray tube  101  through the slip ring  108 . 
     The host controller  110  performs overall control associated with various kinds of processing, e.g., imaging processing, data processing, and image processing. 
     The storage device  111  stores image data such as acquired raw data, projection data, and CT image data. 
     The reconstruction device  114  generates reconstructed image data corresponding to a predetermined number of slices by performing reconstruction processing for projection data on the basis of predetermined reconstruction parameters (e.g., a reconstruction area size, a reconstruction matrix size, and a threshold for the extraction of a region of interest). In general, reconstruction processing includes cone beam reconstruction (the Feldkamp method, ASSR method, and the like) and fan beam reconstruction. Any technique can be implemented. 
     The input device  115  is a device which comprises a keyboard, various kinds of switches, a mouse, and the like, and can input various kinds of scan conditions such as a slice thickness and the number of slices through an operator. 
     The image processing unit  118  performs image processing for display, e.g., window conversion and RGB processing, for the reconstructed image data generated by the reconstruction device  114 , and outputs the resultant data to the display device  116 . The image processing unit  118  generates a so-called pseudo three-dimensional image such as a tomographic image of an arbitrary slice, a projection image from an arbitrary direction, or a three-dimensional surface image on the basis of an instruction from the operator, and outputs the generated image data to the display device  116 . The output image data is displayed as an X-ray CT image on the display device  116 . 
     The network communication device  119  transmits/receives various kinds of data to/from another device or a network system such as an RIS (Radiology Information System) through a network. 
     The data/control bus  300  is a signal line for connecting the respective units to each other and transmitting/receiving various kinds of data, control signals, address information, and the like. 
     (Collimator) 
     The details of the X-ray detector-side collimator will be described next. This X-ray detector-side collimator has a structure which ensures to maintain the continuity of an X-ray focal point and the flatness of each collimator plate even if the detection range is relatively large in the slice direction. 
       FIG. 2B  is a view for explaining an outline of a form of installing an X-ray detector-side collimator  50 . As shown in  FIG. 2B , the X-ray detector-side collimator  50  is installed along the shape of the two-dimensional detector system  103  (i.e., in an arcuated shape) on the X-ray incident side of the two-dimensional detector system  103 . 
       FIG. 3  is a view for explaining the arrangement of the X-ray detector-side collimator  50 . As shown in  FIG. 3 , the X-ray detector-side collimator  50  has an upper support  500 , a lower support  501 , side surface members  502 , an abutment plate  503 , and collimator plates  504 . Note that with regard to the supports  500  and  501 , the terms “upper” and “lower” are defined with reference to the upper and lower sides of a subject placed along the slice direction. These terms are defined for the sake of convenience, and hence the distinction between the terms “upper” and “lower” concerning the supports is not essential. 
     The upper support  500  and the lower support  501  each are formed into an arcuated shape corresponding to the shape of the two-dimensional detector system  103 , and have grooves  505  for the insertion of the collimator plates  504 . The grooves  505  are formed at the same pitch along the X-ray incident direction such that an X-ray focal point exists in a plane including the inserted collimator plates. The upper support  500  and the lower support  501  are fixed side by side with the side surface members  502  so as to make the corresponding grooves  505  face each other. 
     Note that each of the grooves  505 , as shown in  FIG. 4 , is triangular shape in the view of y-direction (channel direction). Each groove is formed in this shape in consideration of convenience in inserting the collimator plate  504  into the groove  505 . However, the shape of each groove  505  is not limited to this and may have any shape as long as it can support the collimator plate  504 . 
     The abutment plate  503  is a plate formed into an arcuated shape corresponding to the shape of the two-dimensional detector system  103  (i.e., the shapes of the upper support  500  and lower support  501 ), and has grooves  506  formed at the same pitch as that of the grooves  505  which the upper support  500  and the lower support  501  have. The abutment plate  503  is made of a material exhibiting high X-ray resistance, processability, X-ray transparency, and mechanical structural strength, e.g., polyethylene terephthalate, an epoxy resin, or a carbon fiber resin. The abutment plate  503  is fixed to the arcuated outside portions of the upper support  500  and lower support  501  (on the outside arcuated side, i.e., the detection surface side of the X-ray detector) such that the grooves  506  correspond to the grooves  505  of the upper support  500  and lower support  501 . 
     The collimator plate  504  is made of a metal exhibiting excellent rigidity, X-ray shielding property, and mechanical structure strength, e.g., tungsten or molybdenum. As shown in  FIG. 4 , the collimator plates  504  are inserted into the grooves  505  of the upper support  500  and lower support  501  and the grooves  506  of the abutment plate  503 , with each being supported at its three sides, and are arranged along a direction almost perpendicular to the slice direction. Note that the collimator plates  504  are fixed in the grooves  505  and  506  with an adhesive. 
     (Method of Forming Grooves in Abutment Plate) 
     A method of forming the grooves  506  in the abutment plate  503  will be described next. 
       FIG. 5  is a view for explaining the method of forming the grooves  506  in the abutment plate  503 . Referring to  FIG. 5 , first of all, a CFRP plate  51  having the same shape and size as those of the abutment plate  503  (without any groove  506 ) by using a material exhibiting a high X-ray transmittance such as carbon fiber reinforced plastic (CFRP resin) with a thickness of about 2 to 3 mm. 
     The grooves  506  are then formed in the CFRP plate  51  along the slice direction by using a blade  52  having a thickness equivalent to the width of the groove  506  in the channel direction. At this time, as shown in  FIG. 6 , each groove  506  is tapered in the thickness direction of the CFRP plate  51  so as to satisfy A&gt;a where A is the groove width on the insertion side (X-ray tube side) of the collimator plate  504  and a is the groove width on the abutment side (X-ray detector side) of the collimator plate  504 . Each groove  506  is formed in such a shape so as to make the groove width A almost equal to the groove width a and set the collimator plate  504  to be almost perpendicular to the abutment plate  503  when the abutment plate  503  is deformed into an arcuated shape to be fixed on the arcuated surfaces of the upper support  500  and lower support  501 , as shown in  FIG. 7 . 
     In order to make the groove width A almost equal to the groove width a in a state wherein the abutment plate  503  is fixed to the upper support  500  and the lower support  501  (i.e., the state shown in  FIG. 7 ), the value of the groove width A is preferably determined on the basis of the curvature of the abutment plate  503  and the groove width a in the fixed state. 
     Alternatively, this apparatus may have an arrangement in which each groove  506  is formed to satisfy groove width A &gt;&gt;groove width a (i.e., the groove width A is clearly larger than the groove width a) in the state shown in  FIG. 6  so as to satisfy groove width A&gt;groove width a while the abutment plate  503  is fixed to the upper support  500  and lower support  501 . With this arrangement, the groove  506  has a tapered shape even in the state wherein the abutment plate  503  is fixed to the upper support  500  and the lower support  501 . This makes it easy to insert each collimator plate  504  and makes it possible to realize self-alignment of each collimator plate. 
     In this embodiment, the abutment plate  503  is formed as an integral part which covers the upper support  500  and the lower support  501  (see  FIG. 3 ). However, the present invention is not limited to this. In consideration of, for example, limitations in terms of groove processing, this apparatus may have a split structure which covers the upper support  500  and the lower support  501  with a plurality of abutment plates. If a split arrangement is to be used, the joint portions are preferably tapered to overlap each other or placed at the shadows of the collimator plates. This makes it possible to avoid the influence of the joint portions. 
     (Collimator Manufacturing Method) 
     A method of manufacturing the X-ray detector-side collimator  50  according to the first embodiment will be described next. 
       FIG. 8  is a flowchart showing the flow of a manufacturing process for the X-ray detector-side collimator  50 . As shown in  FIG. 8 , first of all, the upper support  500 , lower support  501 , and side surface member  502  are assembled together to form the outer frame of the X-ray detector-side collimator  50  (step S 1 ). 
     An adhesive is applied to the grooves  505  formed in the upper support  500  and lower support  501  (step S 2 ). The abutment plate  503  is then elastically deformed into an arcuated shape and fixed to the arcuated side surfaces on the outer periphery sides of the upper support  500  and lower support  501  with screws or the like (step S 3 ). 
     An adhesive is applied to the grooves  506  of the abutment plate  503  (step S 4 ). The collimator plates  504  are then inserted into the grooves  505  of the upper support  500  and lower support  501  and the grooves  506  of the abutment plate  503  (step S 5 ). 
     The resultant structure is then placed in a curing oven to cure the adhesive to complete the X-ray detector-side collimator  50  with the three sides of each collimator plate  504  being supported by the grooves  505  and  506  (step S 6 ). 
     According to the above arrangement, the following effects can be obtained. 
     This detector-side collimator has an integral structure, and the angle of each collimator plate with respect to the X-ray focal point is determined by the corresponding grooves formed in the upper and lower supports. This prevents the occurrence of deviation of the X-ray focal point among a plurality of modules as in conventional module type collimators, and makes it possible to ensure the continuity of the X-ray focal point. As a consequence, proper X-ray collimation can be realized. 
     In addition, since this detector-side collimator has an integral structure, no alignment is required between a plurality of models as in conventional module type collimators. This makes it possible to reduce work load in installing and maintaining the X-ray CT apparatus. 
     Furthermore, this detector-side collimator is configured to support each collimator plate at three sides. Therefore, as compared with a collimator configured to support each collimator plate at two sides, the flatness of each collimator plate can be properly maintained. As a consequence, there is no need to perform maintenance for correcting the warpage of each collimator plate. This makes it possible to reduce the work load and realize proper X-ray collimation in imaging operation for X-ray CT images. 
     Second Embodiment 
     A detector-side collimator  50  according to the second embodiment of the present invention will be described next. The second embodiment is directed to further ensure the maintenance of the flatness of each collimator plate as compared with the first embodiment. 
       FIG. 9  is a view showing the arrangement of the detector-side collimator  50  which an X-ray CT apparatus  10  according to the second embodiment has. As shown in  FIG. 9 , the detector-side collimator  50  according to this embodiment further comprises a guide plate  510  on the arcuated side surfaces on the inner periphery side in addition to the arrangement shown in  FIG. 3 . 
     The guide plate  510  is a plate formed into an arcuated shape corresponding to the shape of the detector-side collimator  50  (i.e., the shapes of an upper support  500  and lower support  501 ), and has slits  511  formed at the same pitch as that of grooves  505  and  506 . Each slit  511  has a width and height that at least allow a corresponding collimator plate  504  to pass through the slit. 
     Like the abutment plate  503 , the guide plate  510  is made of a material exhibiting high X-ray resistance, processability, X-ray transparency, and mechanical structural strength, e.g., polyethylene terephthalate, an epoxy resin, or a carbon fiber resin. The guide plate  510  is fixed to the arcuated inside portions (inner arcuated sides) of the upper support  500  and lower support  501  such that the slits  511  correspond to the grooves  505  and  506 , as shown in  FIG. 10A . 
     The guide plate  510  can be manufactured as follows. As shown in  FIG. 10B , a CFRP plate  53  having the same shape and size as those of the guide plate  510  (without any slit  511 ) is formed by using a material having a high X-ray transmittance such as carbon fiber reinforced plastic (CFRP resin). 
     The slits  511  are then formed in the CFRP plate  53  along the slice direction by using a blade  54  having a thickness equivalent to the width of the slits  511  in the channel direction, thereby manufacturing the guide plate  510 . Note that  FIG. 10C  is a sectional view of the guide plate  510  in a plane along the slits  511 . 
     (Collimator Manufacturing Method) 
     A method of manufacturing the detector-side collimator  50  according to the second embodiment will be described next. 
       FIG. 11  is a flowchart showing the flow of a manufacturing process for the detector-side collimator  50 . The process from steps S 11  to S 14  in  FIG. 11  is the same as the process from steps S 1  to S 4  shown in  FIG. 8 , and hence a description thereof will be omitted. 
     After an adhesive is applied to the grooves  506  of the abutment plate  503 , the guide plate  510  with slits is assembled to the upper support  500  and the lower support  501  (step S 15 ). After this assembly, the collimator plates  504  are inserted into the grooves  505  of the upper support  500  and lower support  501  and the grooves  506  of the abutment plate  503  through the slits  511  of the guide plate  510  (step S 16 ). 
     After an adhesive is applied to the slits  511  (step S 17 ), the resultant structure is placed in a curing oven to cure the adhesive, thereby completing the detector-side collimator  50  with the four sides of each collimator plate  504  being supported by the groove  505 , groove  506 , and slit  511  (step S 18 ). 
     According to the above arrangement, in addition to the effects described in the first embodiment, the flatness of each collimator plate can be maintained with higher accuracy. Even if, therefore, the detection range in the slice direction is wider, the flatness of each collimator plate can be properly maintained. 
     Third Embodiment 
     A detector-side collimator according to the third embodiment of the present invention, and an X-ray CT apparatus comprising such collimator will be described. The present detector-side collimator has a structure in which each collimator plate is supported by four sides, with an upper support, a lower support, an integral abutment plate and an integral internal diameter cover. 
       FIG. 12  is a view showing the arrangement of a detector-side collimator  50  possessed by an X-ray CT apparatus  10  according to the third embodiment. As illustrated, the detector-side collimator  50  according to the present embodiment comprises an upper support  500 , a lower support  501 , side surface members  502 , an abutment plate  503 , an integral internal diameter cover  520  and a plurality of collimator plates  504 . 
     The abutment plate  503  is in an integral structure and has grooves  506  so as to insert one side of the collimator plate  504 . 
     The internal diameter cover  520  is a plate formed in a shape of the upper support  500  and the lower support  501  (i.e. in an arcuated shape). The internal diameter cover  520  which is a cover to support the collimator plate  504  from the internal diameter-side of the upper support  500  and the lower support  501  has grooves  521  to insert one side of each collimator plate  504 . Likewise the abutment plate  503 , this internal diameter cover  520  is made of a material exhibiting high X-ray resistance, processability, X-ray transparency, and mechanical structural strength, e.g., polyethylene terephthalate, an epoxy resin, or a carbon fiber resin. 
       FIG. 13  is a view for explaining a method of forming grooves  521  of the internal diameter cover  520 . As illustrated, first, a CFRP plate  55  bearing the shape and size of the internal diameter cover  520  (without any groove  521 ) is formed by using a material having a high X-ray transmittance such as carbon fiber reinforced plastic (CFRP resin) in the thickness of about 2 to 3 mm. 
     The grooves  521  are then formed on the CFRP plate  55  along the slice direction by using a blade  52  having a thickness equivalent to the width of the grooves  521  in the channel direction. At this time, as shown in  FIG. 14 , each groove  521  is tapered in the thickness direction of the CFRP plate  55  so as to satisfy groove widths B&gt;b where B is the groove width on the insertion side (X-ray detector-side) of the collimator plate  504  and b is the groove width on the abutment side (X-ray tube-side) of the collimator plate  504 . Each groove  521  is formed in such a shape so as to make the groove width B almost equal to the groove width b and set the collimator plate  504  almost perpendicular to the internal diameter cover  520  when deforming the internal diameter cover  520  into an arcuated shape to be fixed along the arcuated surfaces of the upper support  500  and lower support  501 , as shown in  FIG. 15 . 
     In order to make the groove width B almost equal to the groove width b in a state where the internal diameter cover  520  is fixed to the upper support  500  and the lower support  501  (i.e., the state shown in  FIG. 15 ), the value of the groove width B is preferably determined on the basis of the curvature of the internal diameter cover  520  and the groove width b in such fixed state. 
     (Collimator Manufacturing Method) 
     A method of manufacturing the detector-side collimator  50  according to the present embodiment will be described next. 
       FIG. 16  is a flowchart showing the flow of a manufacturing process for the detector-side collimator  50 . The process from steps S 21  to S 24  in  FIG. 16  is approximately the same as the process from steps S 1  to S 4  shown in  FIG. 8 , and hence a description thereof will be omitted. 
     After an adhesive is applied to grooves  506  of the abutment plate  503 , the collimator plates  504  are inserted in grooves  505  of the upper support  500  and the lower support  501  and the grooves  506  of the abutment plate  503  (step S 25 ). 
     Then, after an adhesive is applied to the grooves  521  of the internal diameter cover  520  (step S 26 ), the internal diameter cover  520  is fixed on the upper support  500 , the lower support  501 , and the side surface members  502  while inserting each collimator plate  504  into each groove  521 , (step S 27 ). In addition, when inserting each collimator plate  504  into each groove  521 , the internal diameter cover  520  may also be pressed along the inserting direction, or may be pressed while causing either one of the collimator plate  504 -side and the internal diameter cover  520  to vibrate, if needed. 
     The collimator  50  is then placed in a curing oven to cure the adhesive (step S 28 ). As a result of each process above, the detector-side collimator  50  in which the four sides of each collimator plate  504  are supported by the grooves  505 ,  506  and  521  is completed. 
     Further, the adhesive for grooves  505 ,  506  and  521  is not mandatory. For example, if each collimator plate  504  can be supported sufficiently without an adhesive, it is fine to omit the application of adhesives on at least one or all grooves. The same applies to other embodiments in this regard. 
     (Modified Examples) 
     Next, modified examples of the present embodiment will be explained. A detector-side collimator  50  according to the present modified example supports one side among the four sides of a collimator signal plate  504  by an internal diameter cover which does not have groove  521 . 
       FIG. 17  is a view showing the arrangement of a detector-side collimator  50  according to the present modified example. As illustrated, the detector-side collimator  50  is provided with an internal diameter cover  525 , which is integral and does not have grooves for inserting the collimator plates  504 . 
     Except for the point that there is no groove  521  formed on the internal diameter cover  525 , it has the same structure as the internal diameter cover  520 . As shown in  FIG. 18 , this internal diameter cover  525  is fixed on the upper support  500 , lower support  501  and side surface members  502  in a manner that would press one side of each collimator plate  504  (i.e., one side of the X-ray tube  101 -side). Pressed by the internal diameter cover  525 , the collimator plate  504  is supported by one side. 
     (Collimator Manufacturing Method) 
     A method of manufacturing the detector-side collimator  50  according to the present modified example will be described next. 
       FIG. 19  is a flowchart showing the flow of a manufacturing process for the detector-side collimator  50 . The process from steps S 31  to S 35  shown in  FIG. 19  is basically the same as the process from steps S 21  to S 25  shown in  FIG. 16 , and hence a description thereof will be omitted. 
     After inserting the collimator plates  504 , the internal diameter cover  525  is fixed on the upper support  500 , lower support  501  and side surface members  502  in a manner that would press one side of the X-ray tube  101 -side of each collimator plate  504  (step S 36 ). 
     The collimator  50  is then placed in a curing oven to cure the adhesive (step S 37 ). As a result of each process above, the detector-side collimator  50  in which the four sides of each collimator plate  504  are supported by the grooves  505  and  506  and the internal diameter  525  is completed. 
     According to the above arrangement, in addition to the effects described in the first embodiment, a next new effect can be realized. 
     In the present detector-side collimator, each collimator plate is supported by four sides. Accordingly, in comparison to the case of the conventional two sides support and the three sides support, it is possible to realize a detector-side collimator with high flatness in the collimator plates. As a result, it is possible to realize an ideal collimation. Particularly, even if the detection range in the slice direction is wider, the flatness of each collimator plate can be properly maintained. 
     Further, as the collimator plates are supported equally by four sides. For this reason, the collimator plates can maintain high rigidity even when the detector side collimator is rotated with a central focus on the body axis of a subject at a high speed of one second or less per rotation. As a result, the operation of restoring flatness of the collimator plates upon maintenance can be reduced. 
     Fourth Embodiment 
     A detector-side collimator according to the fourth embodiment of the present invention, and an X-ray CT apparatus comprising such collimator will be described. The present detector-side collimator has a structure in which each collimator plate is supported by four sides, with an upper support, a lower support, an integral abutment plate and a module type internal diameter cover. 
       FIG. 20A  is a view showing the arrangement of a detector-side collimator  50  possessed by an X-ray CT apparatus  10  according to the fourth embodiment. As illustrated, the detector-side collimator  50  according to the present embodiment comprises an upper support  500 , a lower support  501 , side surface members  502 , an abutment plate  503 , a module type internal diameter cover  530  and a plurality of collimator plates  504 . 
     The abutment plate  503  is in an integral structure and has grooves  506  so as to insert one side of the collimator plate  504 . 
     The internal diameter cover  530  is a plate bearing an arcuated shape corresponding to the curvature (i.e., the curvature of an arc) of the upper support  500  and the lower support  501  in the channel direction, and is arranged plurally along the channel direction. The internal diameter cover  530  is a cover that supports the collimator plate  504  from the internal diameter-side of the upper support  500  and the lower support  501 , and has a groove  531  for inserting one side of the collimator plate  504 . Likewise the abutment plate  503 , this internal diameter cover  530  is made of a material exhibiting high X-ray resistance, processability, X-ray transparency, and mechanical structural strength, such as polyethylene terephthalate, an epoxy resin, or a carbon fiber resin. 
     Further, the internal diameter cover  530  has groove  532 , which is different from groove  531 . When arranging a plurality of internal diameter covers  530  along the channel direction, the grooves  532  of the neighboring internal diameter covers  530  form a groove  531  for inserting the collimator plate  504  as shown in  FIGS. 20B and 20C . By inserting the collimator plates  504  in the grooves  531  formed by the grooves  532  of the neighboring internal diameter covers  530  in this manner, an effect on the X-ray detection caused by the joint of the internal diameter cover  530  can be circumvented. 
     In addition, the internal diameter cover  530  can be arranged either in the channel direction with a certain space d as in  FIG. 20B  or in the channel direction that enables the neighbors to come in contact as in  FIG. 20D . In either arrangement, the width of groove  532  in the channel direction is designed to form a groove  533  by the grooves  532  of the neighboring internal diameter covers  530 . 
     Such internal diameter cover  530  can be produced by the means almost similar to the internal diameter cover  520  according to the third embodiment. 
     (Collimator Manufacturing Method) 
     A method of manufacturing the detector-side collimator  50  according to the present embodiment will be described next. 
       FIG. 21  is a flowchart showing the flow of a manufacturing process for the detector-side collimator  50 . The process from steps S 41  to S 45  shown in  FIG. 21  is basically the same as the process from steps S 31  to S 35  shown in  FIG. 19 , and hence a description thereof will be omitted. 
     After inserting the collimator plates  504 , an adhesive is applied to the grooves  531  and the grooves  532  of each modularized internal diameter cover  530  (step S 46 ), which is then fixed on the upper support  500 , lower support  501  and side surface members  502  while inserting each collimator plate  504  in each groove  531  (step S 47 ). Meanwhile, when inserting each collimator plate  504  in each groove  531  and groove  532 , the internal diameter cover  530  may be pressed along the inserting direction, or may be pressed while causing at least either one of the collimator plate  504 -side and the internal diameter cover  530  to vibrate, according to need. 
     The collimator  50  is then placed in a curing oven to cure the adhesive (step S 48 ). As a result of each process above, the detector-side collimator  50  in which the four sides of each collimator plate  504  is being supported by the grooves  505 ,  506  and  521  is completed. 
     (Modified Example) 
     Next, modified examples of the present embodiment will be explained. A detector-side collimator  50  according to the present modified example supports one side among the four sides of a collimator signal plate  504  by a modularized internal diameter cover, which does not have grooves  532 . 
       FIG. 22  is a view showing the arrangement of the detector-side collimator  50  according to the present modified example. As illustrated, the detector-side collimator  50  comprises an internal diameter cover  533 , which is modularized and does not have grooves for inserting collimator plates  504 . 
     Except for the point that there is no groove  531  formed on the internal diameter cover  533 , it has the same arrangement as the internal diameter cover  530 . Likewise the example shown in  FIG. 18 , each internal diameter cover  533  is fixed on the upper support  500 , lower support  501  and side surface members  502  in a manner that presses one side of each collimator plate  504  (i.e., one side of the X-ray tube  101 -side). Pressed by the internal diameter cover  533 , the collimator plate  504  is supported by one side. 
     (Collimator Manufacturing Method) 
     A method of manufacturing the detector-side collimator  50  according to the present modified example will be described next. 
       FIG. 23  is a flowchart showing the flow of a manufacturing process for the detector-side collimator  50 . Since the process from steps S 51  to S 55  is basically the same as the process from steps S 41  to S 45  shown in  FIG. 21 , description thereof will be omitted. 
     After inserting the collimator plates  504 , the internal diameter cover  533  is fixed on the upper support  500 , lower support  501  and side surface members  502  in a manner that presses one side of the X-ray tube  101 -side of each collimator plate  504  (step S 56 ). 
     The collimator  50  is then placed in a curing oven to cure the adhesive (step S 57 ). As a result of each process above, the detector-side collimator  50  in which the four sides of each collimator plate  504  is being supported by the grooves  505  and  506  and the internal diameter cover  533  is completed. 
     According to the above arrangement, the next new effect can be realized in addition to the effect described in the third embodiment. In other words, being modularized, the internal diameter cover supporting one side of the collimator plate can be partially disassembled. Accordingly, when there is need to, for example, adjust or change a portion of the collimator plate, this may be done by simply removing the internal diameter cover supporting such collimator plate. Consequently, this can reduce operation loads and expenses upon maintenance. 
     Fifth Embodiment 
     A detector-side collimator according to the fifth embodiment of the present invention, and an X-ray CT apparatus comprising such collimator will be described. The present detector-side collimator has a structure in which each collimator plate is supported by four sides, with an upper support, a lower support, an integral internal diameter cover and a module type abutment plate. 
       FIG. 24  is a view showing the arrangement of a detector-side collimator  50  possessed by an X-ray CT apparatus  10  according to the fifth embodiment. As illustrated, the detector-side collimator  50  according to the present embodiment comprises an upper support  500 , a lower support  501 , side surface members  502 , a modularized abutment plate  540 , an integral internal diameter cover  520  and a plurality of collimator plates  504 . 
       FIG. 25A  is a view showing an aspect of an abutment plate  540 . As illustrated, a plurality of abutment plates  540  is arranged along the channel direction. The abutment plate  540  has a groove  541  to insert one side of the collimator plate  504 . Likewise the abutment plate  503 , this abutment plate  540  is made of a material exhibiting high X-ray resistance, processability, X-ray transparency, and mechanical structural strength, e.g., polyethylene terephthalate, an epoxy resin, or a carbon fiber resin. Again, the abutment plate  540  can be made by almost the same method as for the abutment plate  503  (see  FIGS. 13 ,  14  and  15 ). 
     Further, the abutment plate  540  has a groove  542 , which is different from the groove  541 . As illustrated in  FIGS. 25A and 25B , when arranging a plurality of abutment plates  540  in a channel direction, the grooves  542  of the neighboring abutment plates  540  form a groove  543  for inserting the collimator plate  504 . By inserting the collimator plates  504  in the grooves  543  formed by the grooves  542  of the neighboring abutment plates  540  in this manner, an effect on the X-ray detection caused by the joint of the abutment plate  540  can be circumvented. 
     In addition, the abutment plate  540  can be arranged either in the channel direction with a certain space d as in  FIG. 25A  or in the channel direction which the neighbors come in contact as in  FIG. 25C . In either arrangement, the width of the groove  542  in the channel direction is designed to form a groove  543  by the grooves  542  of the neighboring abutment plates  540 . 
     (Collimator Manufacturing Method) 
     A method of manufacturing the detector-side collimator  50  according to the present embodiment will be described next. 
       FIG. 26  is a flowchart showing the flow of a manufacturing process for the detector-side collimator  50 . As illustrated, first, the upper support  500 , lower support  501  and side surface members  502  are assembled to form an outer frame of the X-ray detector-side collimator  50  (step S 61 ). Then, an adhesive is applied to grooves  505  formed respectively on the upper support  500  and lower support  501  (step S 62 ), and each modularized abutment plate  540  is resiliently deformed in a circular arc shape and assembled by, for example, a screw clamp on the arcuated side surface of the circumference-side of the upper support  500  and the lower support  501  (step S 63 ). 
     An adhesive is then applied to the grooves  541  and  542  of each abutment plate  540  (step S 64 ), and the collimator plates  504  are inserted in the grooves  505  of the upper support  500  and the lower support  501  and the grooves  541  of each abutment plate  540  (step S 65 ). 
     Then, after an adhesive is applied to the grooves  521  of the internal diameter cover  520  (step S 66 ), the internal diameter cover  520  is fixed on the upper support  500 , the lower support  501  and the side surface members  502  while inserting each collimator plate  504  into each groove  521  (step S 67 ). In addition, when inserting each collimator plate  504  into each groove  521 , the internal diameter cover  520  may be pressed along the inserting direction, or may be pressed while causing at least either one of the collimator plate  504 -side and the internal diameter cover  520  to vibrate, according to need. 
     The collimator  50  is then placed in a curing oven to cure the adhesive (step S 68 ). As a result of each process above, the detector-side collimator  50  in which the four sides of each collimator plate  504  is being supported by the grooves  505 ,  521 ,  541  and  542  is completed. 
     (Modified Examples) 
     Next, modified examples of the present embodiment will be explained. A detector-side collimator  50  according to the present modified example supports one side among the four sides of a collimator signal plate  504  by an internal diameter cover  525 , which does not have grooves  521 . 
       FIG. 27  is a view showing the arrangement of the detector-side collimator  50  according to the present modified example. As illustrated, the detector-side collimator  50  comprises a modularized abutment plate  540  and an internal diameter cover  525 , which is integral and does not have grooves for inserting collimator plates  504 . 
     (Collimator Manufacturing Method) 
     A method of manufacturing the detector-side collimator  50  according to the present modified example will be described next. 
       FIG. 28  is a flowchart showing the flow of a manufacturing process for the detector-side collimator  50 . Since the process from steps S 71  to S 75  is basically the same as the process from steps S 61  to S 65  shown in  FIG. 26 , description thereof will be omitted. 
     After the collimator plates  504  are inserted, the internal diameter cover  525  is fixed on the upper support  500 , lower support  501  and side surface members  502  in a manner which presses one side of the X-ray tube  101 -side of each collimator plate  504  (step S 76 ). 
     The collimator  50  is then placed in a curing oven to cure the adhesive (step S 77 ). As a result of each process above, the detector-side collimator  50  in which the four sides of each collimator plate  504  is being supported by the grooves  505  and  541  and the internal diameter cover  525  is completed. 
     According to the above arrangement, the next new effect can be realized in addition to the effect described in the third embodiment. In other words, being modularized, the abutment plate supporting one side of the collimator plate can be partially disassembled. Accordingly, when there is need to, for example, adjust or change a portion of the collimator plate, this may be done by only removing the abutment plate supporting such collimator plate. Consequently, this can reduce operation loads and expenses upon maintenance. 
     Sixth Embodiment 
     A detector-side collimator according to the sixth embodiment of the present invention, and an X-ray CT apparatus comprising such collimator will be described. The present detector-side collimator has a structure in which each collimator plate is supported by four sides, with an upper support, a lower support, an abutment plate and upper and lower internal diameter covers. 
       FIG. 29  is a view showing the arrangement of a detector-side collimator  50  possessed by an X-ray CT apparatus  10  according to the sixth embodiment. As illustrated, the detector-side collimator  50  according to the present embodiment comprises an upper support  500 , a lower support  501 , side surface members  502 , an abutment plate  503 , an integral upper internal diameter cover  550 , an integral lower internal diameter cover  551  and a plurality of collimator plates  504 . 
     The upper internal diameter cover  550  and the lower internal diameter cover  551  are plates which each bears an arcuated shape corresponding to the curvature (i.e., the curvature of an arc) of the upper support  500  and the lower support  501  in the channel direction. The upper internal diameter cover  550  is a cover that supports the collimator plate  504  from the internal diameter side of the upper support  500  and has a groove  552  to insert one side of the collimator plate  504 . Likewise the abutment plate  503 , the upper internal diameter cover  550  and lower internal diameter cover  551  are made of a material exhibiting high X-ray resistance, processability, X-ray transparency, and mechanical structural strength, such as polyethylene terephthalate, an epoxy resin, or a carbon fiber resin. 
     In addition, the upper internal diameter cover  550  and the lower internal diameter cover  551  can be made by basically the same method as for making the internal diameter cover  520  according to the third embodiment. 
     (Collimator Manufacturing Method) 
     A method of manufacturing the detector-side collimator  50  according to the present embodiment will be described next. 
       FIG. 30  is a flowchart showing the flow of a manufacturing process for the detector-side collimator  50 . The process from steps S 81  to S 85  is basically the same as the process from steps S 21  to S 25  shown in  FIG. 16 , and hence a description thereof will be omitted. 
     After inserting the collimator plates  504 , an adhesive is applied to grooves  552  on the upper internal diameter cover  550  (step S 86 ), which is then fixed on the upper support  500  and side surface members  502  while inserting each collimator plate  504  in each groove  552 . Further, an adhesive is applied to grooves  552  on the lower internal diameter cover  551 , which is then fixed on the lower support  501  and side surface members  502  while inserting each collimator plate  504  in each groove  552  (step S 87 ). Meanwhile, when inserting each collimator plate  504  in each groove  552 , the upper internal diameter cover  550  (lower internal diameter cover  551 ) may be pressed along the inserting direction or may be pressed while causing at least either one of the collimator plate  504 -side and the internal diameter cover  550  to vibrate, according to need. 
     The collimator  50  is then placed in a curing oven to cure the adhesive (step S 88 ). As a result of each process above, the detector-side collimator  50  in which the four sides of each collimator plate  504  is supported by the grooves  505 ,  506  and  552  is completed. 
     (Modified Examples) 
     Next, modified examples of the present embodiment will be explained. A detector-side collimator  50  according to the present modified example supports one side among the four sides of a collimator signal plate  504  by an upper internal diameter cover  555  and a lower internal diameter cover  556  which do not have grooves  552 . 
       FIG. 31  is a view showing the arrangement of the detector-side collimator  50  according to the present modified example. As illustrated, the detector-side collimator  50  comprises an upper internal diameter cover  555  and lower internal diameter cover  556 , which do not have grooves for inserting collimator plates  504 . 
     Except for the point that there are no grooves  552  formed on the upper internal diameter cover  555  and lower internal diameter cover  556 , they have the same structures as the upper internal diameter cover  550  and the lower internal diameter cover  551 . Likewise the example shown in  FIG. 32 , the upper internal diameter cover  555  and lower internal diameter cover  556  are fixed on the upper support  500  and so forth in a manner that presses one side of each collimator plate  504  (i.e., one side of the X-ray tube  101 -side). Pressed by the upper internal diameter cover  555  and the lower internal diameter cover  556 , the collimator plate  504  has the one side supported. 
     (Collimator Manufacturing Method) 
     A method of manufacturing the detector-side collimator  50  according to the present modified example will be described next. 
       FIG. 33  is a flowchart showing the flow of a manufacturing process for the detector-side collimator  50 . Since the process from steps S 91  to S 95  is basically the same as the process from steps S 81  to S 85  shown in  FIG. 30 , description thereof will be omitted. 
     After inserting the collimator plates  504 , the upper internal diameter cover  555  is fixed on the upper support  500  and side surface members  502  so as to press one side of the X-ray tube  101 -side of each collimator plate  504 . Further, the lower internal diameter cover  556  is fixed on the lower support  501  and side surface members  502  so as to press one side of the X-ray tube  101 -side of each collimator plate  504  (step S 96 ). 
     The collimator  50  is then placed in a curing oven to cure the adhesive (step S 97 ). As a result of each process above, the detector-side collimator  50  in which the four sides of each collimator plate  504  is supported by the grooves  505  and  506 , the upper internal diameter cover  555  and lower internal diameter cover  556  is completed. 
     According to the above arrangement, an effect equivalent to the third embodiment can be realized. 
     Note that the present invention is not limited to the above embodiments, and constituent elements can be modified and embodied in the execution stage within the spirit and scope of the invention. 
     (1) The guide plate  510  described in the second embodiment comprises the integral member which covers the upper support  500  and the lower support  501  (see  FIGS. 9 and 10 ). However, the present invention is not limited to this. In consideration of, for example, limitations in terms of groove processing, this guide plate may have a split structure which covers the upper support  500  and the lower support  501  with a plurality of plates. If a split arrangement is to be used, the joint portions are preferably tapered to overlap each other or placed at the shadows of the collimator plates as in the case of the abutment plate  503 . 
     (2) The abutment plate  503  and guide plate  510  described in each embodiment may be applied to a module type collimator. This makes it possible to maintain the flatness of each collimator plate in a module type collimator with higher accuracy than in the prior art. 
     (3) The detector-side collimator described in each embodiment may comprise a plurality of (e.g., three or four) collimator units ( 50 ) coupled to each other instead of a completely integral structure. In this case, the arrangements described in the respective embodiments and modifications (1) and (2) can be applied to each collimator unit ( 50 ). 
     (4) The detector-side collimator according to the sixth embodiment may be arranged to modularize at least either one of the upper internal diameter cover and the lower internal diameter cover as shown, for example, in  FIG. 34 . 
     In addition, various inventions can be formed by proper combinations of a plurality of constituent elements disclosed in the above embodiments. For example, several constituent elements may be omitted from all the constituent elements disclosed in the above embodiments. Furthermore, constituent elements in the different embodiments may be properly combined.