JP4239878B2 - Two-dimensional radiation detector and manufacturing method thereof - Google Patents

Description

  The present invention relates to a two-dimensional radiation detector used in a medical radiography apparatus and the like, and a manufacturing method thereof.

  An intensifying screen-film system having a structure in which an intensifying screen and a film are in close contact with each other is known as an apparatus for taking a radiographic image. In this method, X-rays transmitted through a subject are converted into low-energy light by an intensifying screen, and the film exposed to the light is developed to visualize the X-ray absorption characteristics of the subject on the film. Is the method. However, this method cannot obtain image information as an electrical signal. In order to take out the image information of the subject carried on the film as an electric signal, it is necessary to separately digitize the film with a film digitizer or the like, which is very troublesome. In addition, since the latitude of the film is narrow, there is a drawback that there is a high risk of underexposure and overexposure due to shooting failure.

  CR (Computed Radiography) is well known as an imaging apparatus that can directly extract X-ray image information transmitted through a subject as a digital signal. In this apparatus, the energy of X-rays transmitted through the subject is temporarily accumulated in the stimulable phosphor, and this is excited by laser light to output stimulated emission proportional to the accumulated X-ray energy. Light emission can be extracted as an electrical signal by a photoelectric conversion element such as a photomultiplier. This method has a drawback that it takes time to read out the photostimulated luminescence. In addition, a mechanism for scanning with laser light is required and the apparatus is expensive, and there are also disadvantages that it tends to cause a malfunction of the mechanical part.

  Therefore, in recent years, a solid-state imaging device called a flat panel detector (FPD) has attracted attention. In this method, X-ray energy is directly converted into electric charge, and this electric charge is read as an electric signal by a reading element such as a TFT, and the X-ray energy is converted into light by a scintillator or the like, and this converted photoelectric conversion element is used. An indirect type FPD that converts charges into electric charges and reads out the electric charges as electric signals by a reading element such as a TFT is known. In either method, the subject information collected on the detector surface is read as spatially sampled information according to the pitch of the reading elements (hereinafter referred to as detector pitch).

  As shown in FIG. 1, when X-rays 102 are exposed to the subject 101, some X-rays 103 are absorbed by the subject 101, but the remaining X-rays are absorbed by the subject 101 as transmitted X-rays 104. It reaches the detector 112 without. On the other hand, in addition to the transmitted X-rays 104 that pass through the subject 101, noise components called scattered rays 105 are emitted from the subject 101. In order to reduce the S / N ratio and contrast of the image information of the subject 101 carried by the transmitted X-rays 104, the scattered radiation 105 has a method of removing the scattered radiation component as much as possible by using the normal grid 111.

  The grid 111 has a structure in which the X-ray shielding materials 1 are arranged at regular intervals in a stripe shape with the intermediate substance 2 interposed therebetween. Since the scattered radiation 105 is absorbed by the X-ray shielding material 1, it does not reach the detector 112. Therefore, the SN ratio and contrast of the image information can be remarkably improved (Patent Document 1: FIG. 7, paragraph number 0012).

  In general, there are a grid ratio and a grid density as values representing the scattered radiation removal ability of the grid, and these are determined by the thickness and height of the X-ray shielding material and the thickness and height of the intermediate substance. The figure is shown in FIG. It is determined by the grid ratio r = h / t2 and grid density N = 1 / (t1 + t2), and these values are selected according to the type of detector and the intended use.

  There are two types of grids: moving grids and fixed grids. The moving grid is a method that prevents the fixed pattern of the grid from being imaged in the image by moving the grid in the direction perpendicular to the direction of the grid stripes in synchronization with the X-ray exposure. The fixed grid is a method of shooting with the grid fixed to the detector. When a fixed grid is used in the shooting method using the grid, grid stripes are fixed in the subject information that reaches the detector. A pattern will be included.

  When a moving grid is used, a fixed pattern of grid stripes is not included, but there is a problem in that the X-ray shielding material causes a cut-off when moving and the X-ray dose is insufficient and the image quality is deteriorated. Further, since a mechanism for mechanically moving the grid is required, the apparatus is increased in size and disadvantageous in cost. In addition, there is a problem that the image is greatly adversely affected by vibration during movement and electrical noise such as a motor required for movement.

  On the other hand, when a fixed grid is used, when an image including a fixed pattern of grid stripes is digitized, a non-existent stripe pattern called a moire stripe is formed according to the relationship between the sampling frequency determined by the detector pitch and the grid frequency. May appear. Moire fringes become noise with respect to the image information of the subject and significantly impede the doctor's diagnosis. In order to avoid moire fringes, it is conceivable to use a grid having a frequency that is an integral multiple of the sampling frequency. However, in the conventional technique, a manufacturing error always occurs, and this causes moire fringes.

  Further, the grid improves the S / N ratio and contrast of the image information by absorbing the scattered radiation 105 in the X-ray shielding material 1, but reduces the X-ray dose reaching the detector 112, so that the image quality deteriorates. There was a problem to do. Therefore, it is also conceivable that the X-ray shielding material 1 is vertical in the central portion immediately below the X-ray source and tilted in the direction of the X-ray source toward the periphery (Patent Document 1: FIG. 7). , Paragraph number 0014).

JP 2002-71815 A

  However, in this way, a grid is produced in which the X-ray shielding material 1 is accurately provided at a frequency interval that is an integral multiple of the sampling frequency (detector pitch) and is precisely arranged so that each tilts in the direction of the X-ray source. It was very difficult to manufacture. The present invention provides a method by which such a grid can be manufactured easily and accurately.

  The method for manufacturing a two-dimensional radiation detector according to the present invention is characterized by a method for producing a grid. The grid is configured by alternately arranging an intermediate substance that transmits X-rays and an X-ray shielding material, and is strictly configured so that the interval between the X-ray shielding materials is an integral multiple of the detector pitch. An assembly jig for producing a plurality of modules in which a plurality of intermediate substances and X-ray shielding materials are bonded one by one or alternately, and at least one of the intermediate substances or the X-ray shielding materials protrudes from another material. It is a fitting part with the groove. On the other hand, the assembly jig is formed with a plurality of grooves to be fitted with the fitting portions, and each groove has an inclination angle toward the focal direction of the X-ray source. The fitting part of each module is fitted in the groove of the assembly jig, each module is joined, and then each fitting part is cut to produce a grid. Using the grid thus produced, two-dimensional radiation detection is performed. Manufacture equipment.

  In the two-dimensional radiation detector of the present invention, since the grid is assembled as described above, the interval between the X-ray shielding materials can be easily manufactured with high accuracy and the generation of moire fringes can be satisfactorily suppressed. It can be. In addition, the direction of the X-ray shielding material can be accurately directed to the focal direction of the X-ray source, and the reduction of the incident dose to the detector can be prevented.

  FIG. 10 is a diagram showing a schematic configuration of the radiation imaging apparatus. A control circuit 209 provided in the radiation imaging apparatus of this embodiment controls all the apparatuses and circuits in this figure. When an X-ray generation command is issued by the X-ray generation control device 201, X-rays are emitted toward the subject 101 by the X-ray source 202. The X-ray generation command of the X-ray generation control device 201 is input to the control circuit 209, and other circuits are controlled in synchronization with the generation of X-rays.

  The X-rays that have passed through the subject 101 pass through the grid 111 to reduce the amount of scattered rays. Image information of the subject 101 whose scattered radiation has been reduced by the grid 111 is detected as an electrical signal by the detector 112. The detector 112 may be either a direct FPD or an indirect FPD.

(First Embodiment) The first embodiment relates to a method of manufacturing a two-dimensional radiation detector. FIG. 1 is a view showing a cross section of a grid 111 and a detector 112 of the two-dimensional radiation detector according to the first embodiment of the present invention. The X-ray shielding material 1 looks at the focal point F of the X-ray tube and is arranged at a pitch that matches an integer multiple of the arrangement of each pixel on the detector 112 surface. In the case of the embodiment of FIG. 1, the X-ray shielding material 1 is arranged at a pitch twice that of the arrangement of each pixel on the detector 112 surface. Here, the section of the detector 112 does not actually have a partition as shown in the figure, but the detector pitch is determined by the pitch of the TFT elements and is shown for convenience. The X-ray shielding material 1 and the intermediate substance 2 are supported at their upper and lower end surfaces by a covering material 3 and a covering material 4, and between the edge portions of the covering material 3 and the covering material 4 are supported by a spacer 5 and a spacer 6. ing.

Next, a method for manufacturing the grid of the two-dimensional radiation detector of the present invention will be described.
First, as shown in FIG. 2, a module 11 is manufactured by bonding a plurality of intermediate substances 2 and X-ray shielding materials 1 each having a thickness corresponding to an X-ray transmitting portion one by one or alternately. The X-ray shielding material 1 and the intermediate substance 2 are set at the same height. The module 11 produces the quantity necessary for constructing the grid. At least one of the intermediate substances 2 constituting the module 11 is an intermediate substance 12 with a fitting portion having a fitting portion with a groove 22 (see FIGS. 3 and 5) of the assembly jig 21. Or higher than the X-ray shielding material 1. The X-ray shielding material 1, the intermediate material 2, and the intermediate material 12 with a fitting portion are bonded together with one surface in the longitudinal direction aligned. Here, in the present embodiment, the intermediate substance 2 (including the intermediate substance 12 with the fitting portion) is composed of three sheets and the X-ray shielding material 1 is composed of three sheets, but the number of sheets can be appropriately selected. Further, when the X-ray shielding material 1 is a plate having hardness, a fitting portion may be formed on the X-ray shielding material 1. For bonding the intermediate substance 2 and the X-ray shielding material 1, a thin double-sided adhesive tape having a thickness accuracy can be used.

  The X-ray shielding material 1 is made of a material having a large atomic number and a large X-ray absorption, such as molybdenum, tungsten, lead, an alloy containing molybdenum as a main component, an alloy containing tungsten as a main component, and an alloy containing lead as a main component. Must be selected. On the other hand, the intermediate substance 2 and the intermediate substance 12 with a fitting portion have a small X-ray absorption, can provide a thickness accuracy, and can be easily subjected to wire electric discharge machining or the like in a cutting process to be described later, such as aluminum or aluminum alloy. Is desirable.

  Next, about the completed module 11, the groove | channel 22 of the assembly jig 21 which consists of the groove plate 23 shown in FIG. 3 and the intermediate substance 12 with a fitting part are fitted and arrange | positioned. The assembly jig 21 connects the detector side end and the focal point F of the X-ray source so that the flat surfaces of the X-ray shielding materials 1 after the grid assembly are directed to the focal point F of the X-ray source. A plurality of predetermined grooves 22 are formed so as to be inclined and aligned along a straight line. As a method for producing the assembly jig 21, there is a method in which the groove 22 is formed by a wire electric discharge machine, a dicing machine, or the like.

  As another form of the assembly jig 21, the groove plate 23 is divided as shown in FIG. 4, and the grooves 22 are formed by a wire electric discharge machine, a dicing machine, etc., and arranged and fixed so that the grooves coincide with each other. Also good. In this case, since the length of the groove can be relatively short, even a grid with a large area such as a 450 mm square size can be used.

  FIG. 5 is a cross-sectional view of a part of the module 11 in which the intermediate substance 12 with the fitting portion is fitted in the groove 22 of the assembly jig 21. Here, a state where only five modules 11 are fitted is shown.

  As shown in FIG. 5, the groove depth is set so that a clearance 24 is formed between the module 11 and the assembly jig 21. This is used in the separation process from the groove of the later assembly jig. Further, the groove depth and the groove width are set so that the intermediate substance 12 with the fitting portion is inserted and fixed at a predetermined position. The grooves 22 are arranged at a pitch that matches the integer multiple of the detector pitch, that is, the integer multiple of the arrangement interval of each pixel on the detector 112 surface shown in FIG. 1, with the X-ray shielding material 1 looking at the focal point F of the X-ray tube. To be set.

  Here, as apparent from FIG. 5, only the intermediate substance 12 with one fitting portion is actually fitted in the groove 22, and the other three X-ray shielding materials 1 and 2 are fitted. The position of the intermediate substance 2 is not guaranteed. However, the fact that there is no problem in practice will be explained by considering the ideal shape.

FIG. 6 shows a schematic cross-sectional view of an ideal shape for the right half of the grid. The figure shows an ideal-shaped grid when the X-ray shielding material 1 is arranged at a pitch twice that of the arrangement of each pixel on the detector 112 surface. The X-ray shielding material 1 is arranged with a certain thickness, and the shape of the intermediate substance 2 is determined so as to come to an ideal position. Here, the thickness of the upper surface of the intermediate substance 2 in the ideal shape is d1, and the thickness of the lower surface is d2. Here, as an example of actual values, detector pitch: 0.15 mm, X-ray shielding material thickness: 0.03 mm, grid thickness: 2.7 mm, grid area: 450 mm × 450 mm, focal point F—grid top surface distance: 1200 mm The distance between the grid bottom surface and the detector is 3 mm.
FIG. 7 shows the ideal values of d1 and d2 calculated from these values at each position from the center. According to this, the difference between d1 and d2 at the same distance from the center is only about 0.6 μm. Further, even when d2 at the center position where the difference is the largest and d1 at the end on the far side are compared, the difference is about 5.6 μm. Considering that the detector pitch is 0.15 mm, these values are within an allowable error range, and the thickness of the intermediate material 2 is d1, and the intermediate material 2 (intermediate material 12 with a fitting portion is defined as in this embodiment). 3) and three X-ray shielding materials 1 constitute the X-ray shielding material module 11, that is, every third intermediate substance 2 is guaranteed by the groove 22 in position. Therefore, it can be seen that there is no problem in position accuracy. Furthermore, when actually used, a sensitivity correction is performed by combining the grid 111 and the detector 112 in advance, and a method of correcting the image based on the data is used to prevent sensitivity unevenness. There is no.

Next, in a state where the required number of intermediate materials 12 with fitting portions of the module 11 are fitted in the grooves 22 of the assembly jig 21, the integral covering material 3 is bonded to the upper end portion of the module 11 (FIG. 8).
Then, in order to separate the X-ray shielding material module 11 from the groove 22 of the assembly jig 21, only the intermediate substance 12 with a fitting portion that is fitted to the groove 22 by wire electric discharge machining is removed from the X-ray shielding material 1. And it cuts so that the height with intermediate substance 2 may become the same. The cross section after cutting is shown in FIG. Here, the wire electric discharge machining cuts only the intermediate substance 2, and as described above, when the material of the intermediate substance 2 is aluminum or an aluminum alloy, the machining is easy and takes less time, which is advantageous in terms of cost. If the height of the intermediate substance 12 with the fitting portion does not match the X-ray shielding material 1 and the intermediate substance 2, the height may be adjusted by polishing appropriately.

Finally, as shown in FIG. 9, the spacer 5 and the spacer 6 are bonded to the side ends, and the integral covering material 4 is bonded to the lower end of the module 11 and the opposite surface of the spacer 5 and the spacer 6. And
The covering material 3 and the covering material 4 have a low X-ray absorption, and in order to maintain dimensional accuracy, it is necessary to select a material that is stable against temperature changes, has a small thermal expansion coefficient, and has excellent strength. In order to satisfy these conditions, it is desirable to select so-called CFRP (carbon fiber reinforced plastics) or the like for the covering material 3 and the covering material 4.

  As described above, the present invention is suitable for medical and industrial radiation imaging apparatuses.

It is a figure which shows one Example of the two-dimensional radiation detector which concerns on 1st Embodiment of this invention. It is a figure which shows an example of a module. It is a figure which shows an example of the assembly jig of a module. It is a figure which shows an example of the assembly jig of a module. It is a figure which shows an example of the manufacture process of a grid. It is state explanatory drawing of a grid. It is a figure which shows the ideal thickness of the intermediate substance in each position from the center of a grid. It is a figure which shows an example of the manufacture process of a grid. It is a figure which shows an example of the finished product of a grid. It is a figure which shows schematic structure of a radiography apparatus. It is a figure which shows description of the principle of a grid.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... X-ray shielding material 2 ... Intermediate substance 11 ... Module 12 ... Intermediate substance with a fitting part 21 ... Assembly jig 22 ... Groove 23 ... Groove plate 24 ... Clearance 105 ... Scattered ray 111 ... Grid 112 ... Detector

Claims (2)

  Subject information obtained by transmitting X-rays generated from an X-ray source through a subject is two-dimensionally arranged through a grid in which intermediate substances and X-ray shielding materials that transmit X-rays are alternately arranged. A method of manufacturing a two-dimensional radiation detector that obtains an electrical signal by a detector arranged on the grid, wherein the grid is configured such that an interval between X-ray shielding materials is an integral multiple of a detector pitch, and the intermediate A fitting portion with a groove of an assembly jig having a length protruding at least one of the intermediate substance or the X-ray shielding material to be bonded one by one or alternately a plurality of substances and X-ray shielding materials. A plurality of modules were produced, and the fitting portions of the modules were fitted into grooves of an assembly jig in which a plurality of grooves having inclination angles toward the focal direction of the X-ray source were formed, and the modules were joined. rear, Method for producing a two-dimensional radiation detector, characterized in that those made by cutting the serial fitting portion.   A two-dimensional radiation detector manufactured by the manufacturing method according to claim 1.

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