JP2006288465A - Device for x-ray image radiographing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems that, while image processing is executed so as to eliminate inappropriate grid stripes from radiation images, when an angle / position deviation of a certain value or more in which the arrangement of pixels of an X-ray image detection panel and the stripes of a grid for eliminating scattered X-rays are not parallel is caused, moire stripes are generated in diagnostic images to be obstructive during observations, the number of lines for performing image processing increases and the time required for the image processing increases. <P>SOLUTION: By providing a means for adjusting the relative position / angle of an X-ray detector and the grid for eliminating the X-ray scattered radiation, this X-ray image radiographing device suppresses the influence of grid cutoff and the generation of the moire stripes to be harmful in terms of diagnosing. Thus, the time required for the image processing is reduced and excellent images are efficiently obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an X-ray imaging apparatus using a flat detector provided with a detachable scattered X-ray removal grid.

  Conventionally, the most common imaging method for X-ray imaging is a film / screen method, which is a method of imaging by combining a photosensitive film and a phosphor having sensitivity to X-rays. As a second imaging method, a method called a computed radiography (CR) method has been put into practical use. In this method, an X-ray transmission image is temporarily stored as a latent image in a phosphor, and the latent image is read by irradiating excitation light later.

  Further, with recent progress in semiconductor process technology, an apparatus for taking an X-ray image similarly using a semiconductor sensor has been developed as a third imaging method. This type of system has the advantage that an image of an extremely wide X-ray exposure area can be recorded as compared with a conventional X-ray photography system using a silver salt photograph. That is, X-rays in a wide dynamic range are read by photoelectric conversion means and converted into electrical signals, and then X-ray images are visualized on recording materials such as photographic photosensitive materials and display devices such as CRTs using the electrical signals. As a result, it is possible to obtain an X-ray image that is hardly affected by fluctuations in the amount of X-ray exposure.

  FIG. 9 shows a schematic diagram of an X-ray imaging system using the above-described semiconductor sensor. The X-ray imaging apparatus 3 includes an X-ray having a detection surface in which a plurality of photoelectric conversion elements are two-dimensionally arranged. A detection sensor 4 is built in, the X-ray emitted from the X-ray generator 1 is irradiated onto the subject 2, and the X-ray transmitted through the subject 2 is detected by the X-ray detection sensor 4. The image signal output from the X-ray detection sensor 4 is subjected to digital image processing in the image processing means 5 and displayed as an X-ray image of the subject 2 on the monitor 6. Such an X-ray detection sensor is called a flat detector, a flat panel, or the like because of its shape.

  In order to enable imaging of a wide range of parts more quickly with an apparatus using the X-ray detection sensor, a portable imaging apparatus called an electronic cassette having excellent operability has been proposed (for example, (See Patent Document 1 and Patent Document 2.)

  In addition, there is an imaging method using a scattered X-ray removal grid for the purpose of improving the contrast of the X-ray image. This is for irradiating X-rays and removing scattered X-rays generated by internal transmission of the subject, and this scattered X-ray removing grid is arranged between the X-ray tube and the X-ray image detector. And take a picture.

  This scattered X-ray removal grid is composed of a plurality of foils made of lead or the like having a high X-ray absorption rate as an X-ray absorption member, aluminum, paper, wood, synthetic resin, carbon fiber reinforced resin having a low X-ray absorption rate, etc. The intermediate material made of is alternately laminated and covered with a cover member made of aluminum or the like. In this case, since X-rays are incident from a direction along the surface of the foil, scattered X-rays enter the foil at a certain angle and are absorbed by the foil. Since the X-ray primary light transmitted through the subject is incident in parallel to the foil, it passes through the intermediate material portion and passes through the grid. Therefore, the scattered X-rays scattered in the subject can be absorbed by the foil, and a reduction in resolution due to the scattered X-rays can be prevented.

  FIG. 10 is a longitudinal sectional view of a schematic configuration of an imaging apparatus using a conventional X-ray flat panel detector, and FIG. 12 is an example of a transverse sectional view.

  This X-ray imaging apparatus includes a phosphor 14a that converts X-rays into visible light, an imaging device 14 that includes a substrate 14c on which the photoelectric conversion element 14b is formed, and a base that supports the substrate 14c. 13, a circuit board 16 on which a circuit board on which an electronic component for processing an electric signal from the photoelectric conversion element 14b is mounted, and a wiring 15 and a photoelectric conversion element for electrically connecting the photoelectric conversion element 14b and the circuit board 16 are mounted. 14b and a power supply circuit 17 for supplying power to the circuit board 16, power supply wiring, a spacer 12 for fixing the base 13, and a casing 11 for storing them.

  Further, a detachable grid unit 20 is provided on the X-ray input surface side of the housing 11. The grid unit 20 includes a grid fixing frame 19 provided with an opening 19 ′ and a grid fixing frame 19. It consists of a grid 18 for removing scattered X-rays.

FIG. 11 is a plan view of the scattered X-ray removal grid 18 as viewed from the X-ray incident direction. A line drawn in parallel in this figure means a line schematically representing the laminated state of the foil 18b having a depth perpendicular to the paper surface and the intermediate substance inside the scattered X-ray removal grid 18. The center line 18a of the scattered X-ray removal grid 18 is parallel to the illustrated stacking direction of the foil 18b. In the case of a so-called focusing grid having a focal point at the center of the X-ray tube, the center line 18a is a line aligned with the center of the tube, so the foil 19b near the center line 18a Although it is parallel, it becomes the structure parallel to the X-ray irradiation angle as it leaves | separates gradually from the centerline 18a.
JP 55-12429 A JP-A-56-11395

  The X-ray image detector composed of semiconductor pixels as in the above-described conventional example has the directionality of the pixels distributed two-dimensionally as shown in FIG. 12, and the X-ray absorbing members are arranged in a band shape or a lattice shape. Primary X-rays if the relative relationship is not appropriate when the X-ray absorbing member arranged in a grid or a band is used together with the scattered X-ray removing means composed of a converging grid inclined at the periphery so as to face the X-ray source The X-ray image captured due to the loss of light causes unevenness in brightness and darkness as a whole, and inappropriate grid stripes are superimposed on the radiographic image due to aliasing and setting of the sampling period.

  Image processing is performed in order to remove such inappropriate grid stripes from the radiographic image. The parallel lines 14d of the pixels of the X-ray image detector and the grid 18 of the scattered X-ray removing means are used. If the center line 18a has an angle greater than a certain value that is not parallel, various obstacles occur.

  First, the generation of moire fringes becomes a problem. When the number of foils per 1 cm of the grid 18 is expressed as a grid density (lines / cm), the normal grid density is about 30 to 60 (lines / cm). Accordingly, the spatial frequency of the stripes of the grid 18 is 3 to 6 lp / mm. On the other hand, the pitch of the pixels of the semiconductor sensor used for X-ray imaging is usually in the range of 200 to 50 μm because the effective range of the sensor is large. Therefore, the resolution of the sensor is 2.5 to 10 lp / mm, which approximates the spatial frequency of the stripes of the grid 18, and when both overlap with a certain angle, interference occurs and moire fringes are generated, It becomes an obstacle when observing minute lesions in diagnosis using X-ray images.

  Second, there is a problem in image processing. When some image processing is performed on the stripes of the grid 18, if the stripes of the grid 18 are inclined with respect to the pixel arrangement, how many stripes are there? There is a problem that the number of lines for image processing increases and the time required for image processing increases because the pixel line is straddled.

  Therefore, an object of the present invention is to solve the above-described problems in order to provide an X-ray imaging apparatus capable of efficiently obtaining a good image.

  In order to achieve the above object, the present invention according to claim 1 is directed to an X-ray image detector that detects an intensity distribution of X-rays transmitted through a subject, a housing that contains the X-ray image detector, The scattered X-ray removing means that can be detachably attached to the X-ray incident surface of the body, and the relative relationship between the X-ray image detector and the scattered X-ray removing means with respect to an axis perpendicular to the X-ray incident surface of the housing It is an X-ray imaging apparatus characterized by having means for regulating and adjusting a typical angular position.

  The X-ray imaging apparatus according to the present invention can perform alignment with a simple method even if there is a variation in the component accuracy between the X-ray detector and the X-ray scattered radiation removal grid, and has a grid cutoff that is harmful to diagnosis. The influence and the generation of moire fringes can be suppressed. In addition, since the number of image reading lines where the grid images intersect is restricted, the range of image processing for performing grid removal or the like is reduced, and the calculation time can be shortened.

  The present invention will be described in detail based on the embodiment shown in FIGS. In the following embodiment, as an example of the X-ray imaging apparatus of the present invention, a medical imaging apparatus (X-ray imaging apparatus) that images a subject using X-rays will be described. It is also possible to apply the invention to an X-ray image photographing apparatus for photographing another subject or an imaging apparatus using other X-rays.

  FIG. 1 is a longitudinal sectional view illustrating a schematic configuration of the X-ray imaging apparatus of the first embodiment, and FIG. 2 is a transverse sectional view of FIG.

  The configuration of the first embodiment will be described with reference to FIG.

  This X-ray imaging apparatus includes a phosphor 14a that converts X-rays into visible light, an image sensor 114 that includes a substrate 114c on which the photoelectric conversion element 114b is formed, and a base that points to the substrate 114c. 113, a circuit board 116 on which a circuit board on which an electronic component for processing an electric signal from the photoelectric conversion element 114b is mounted, a wiring 115 for electrically connecting the photoelectric conversion element 114b and the circuit board 116, and the photoelectric conversion element 114b and a power supply circuit 117 for supplying power to the circuit board 116, power supply wiring (not shown), a spacer 112 for fixing the base 113, and a casing 111 for storing them.

  Specific examples of the power supply circuit 117 include a combination of a battery and a DC / DC power supply circuit, or a DC / DC power supply that generates various voltages by being supplied with a predetermined voltage from an external power cable (not shown). .

  Further, a detachable grid unit 120, a grid adjustment unit 121, a grid holding unit 122, and a grid cover 123 covering these are configured on the X-ray incident surface side of the housing 111. An opening 123 'is provided in the grid cover.

  The grid unit 120 includes a scattered X-ray removal grid 118 and a grid frame 119 attached to the edge of the grid unit 119. Further, the grid frame 119 is provided with a V-groove 119 ′ on the entire periphery.

  As shown in FIG. 2, a grid adjustment unit 121 and a grid holding unit 122 are disposed and attached to the housing 111 at opposing positions. The grid adjustment part 121 is provided with a pin part 121 ′ whose protrusion amount can be adjusted, and is connected from the inside of the casing 111 by a signal line and a power source not shown. The grid holding part 122 includes a pin 122c, a spring 122a, and a housing 122b that contains them.

  The grid cover 123 is fixed to the housing 111 by a hooking portion (not shown). By removing the grid cover 123, the grid unit 120, the grid adjustment unit 121, and the grid holding unit 122 can be detached from the housing 111. It has become. By removing these, it is possible to perform imaging without using the scattered X-ray removal grid.

  FIG. 3 is a schematic enlarged view of a vertical section of the grid unit, the grid holding unit 122, and the grid adjustment unit 121. The tips of the grid adjustment pin portion 121 ′ and the grid holding portion 122 c are spherical, and the grid unit is held by being fitted into the grid frame V groove portion 119 ′ in the grid unit 120. When the pin portion 121 ′ of the grid adjustment 121 moves with a value input by an input means (not shown), the grid unit 120 follows and moves by the grid holding spring portion 122 b provided on the opposite side.

  When the value is input from the input means based on the value calculated by the control means (not shown), the grid is changed by changing the pin protrusion amount of the grid adjustment unit 121 installed on the two sides as shown in FIG. It is moved so that it is as close as possible to 0 degree which is the ideal value of the line 118x parallel to the stripes of the grid 118 and the parallel line 114x of the pixels of the photoelectric conversion element 114b of the X-ray image detector.

  FIG. 5 is an explanatory view schematically showing a state in which the grid 118 is sampled. In FIG. 5A, a portion indicated by S indicates a sampling interval. If the sampling interval SP and the grid 118S are accurately aligned, the striped pattern is stably observed, does not disturb the observer, and is filtered. It is easy to remove even image processing such as. However, as shown in FIG. 5B, when the grid 118S is inclined with respect to the sampling interval SP, strong low-frequency moire fringes are observed in an oblique direction, which is extremely disturbing for an observer, and is an image obtained by filtering or the like. Removal by processing becomes difficult.

FIG. 6 is a graph showing a state of sampling at a spatial frequency. The vertical axis represents the vertical frequency, the horizontal axis represents the horizontal frequency, the frequency fg represents the grid frequency, and the frequency fs represents the sampling frequency. Generally, the observed fringe frequency is equal to or lower than the Nyquist frequency, which is half of the sampling frequency, and the observed fringe frequency fm is modulated with the sampling frequency fs, and therefore can be calculated by the following equation.
fm = | fgn · fg |; fm ≦ fs / 2 (where n is a positive natural number)

  In the case of FIG. 6A showing a state in which the grid mounting angle is parallel to the X-ray image detection panel, the grid frequency fg is larger than the sampling frequency fs. A fringe having a fringe frequency fm is generated at a point-symmetrical position. In this case, the frequency component in the vertical direction does not appear.

  However, in the case of FIG. 6B in which the grid mounting angle is inclined by θ, the fringe frequency fm appears at a point-symmetrical position with respect to the sampling frequency fs as in FIG. 6A. The angle of the fringe frequency fm is not an attachment angle, but a fringe having an angle θ0 larger in the opposite direction appears. This angle θ0 is the moire fringe observed in FIG. From the results of various experiments, if the mounting angle is 0.5 degrees or more, the observation is hindered, and removal by image processing also increases the processing time and becomes difficult.

  Therefore, in the embodiment of the present invention, the grid adjustment unit 121 adjusts the mounting angle of the grid 118 as close as possible to parallel to the arrangement of the pixels of the photoelectric conversion element 114b of the X-ray image detector. It is easy or unnecessary to remove the stripe pattern.

  FIG. 7 is a longitudinal sectional view illustrating a schematic configuration of the X-ray imaging apparatus according to the second embodiment.

  A grid holding part 122 and a grid adjustment part 121 are attached to a grid cover 131 having an opening 131 ′ on the X-ray incident and emission surface, and a grid unit and a grid frame 119 are assembled to the grid unit 131. To do. The grid cover 131 is provided with an opening 131 ′ on the X-ray incident and emission surface, and a grid unit is inserted into a guide rail 132 provided inside the housing from a housing side opening (not shown). It is a configured form.

  FIG. 8 is a plan view for explaining an application example of the first embodiment.

  By providing an index 111m indicating the center of the X-ray image detector in the casing 111 and an index 119m indicating the center of the grid 118 in the grid frame 119, and using it as a position guide when assembling the grid unit 120 to the casing 111, The amount of adjustment can be reduced.

  Note that the X-ray imaging apparatus of the above-described embodiment is not limited to these examples, and it goes without saying that various modifications can be made without departing from the scope of the claims.

It is a longitudinal cross-sectional view explaining schematic structure of the X-ray imaging device of 1st Embodiment. 1 is a plan view illustrating a schematic configuration of an X-ray imaging apparatus according to a first embodiment. It is a fragmentary sectional view explaining the grid holding part and grid adjustment part of the X-ray imaging device of a 1st embodiment. 1 is a cross-sectional view illustrating a schematic configuration of an X-ray imaging apparatus according to a first embodiment. It is a schematic diagram explaining a moire fringe. It is a schematic graph explaining the sampling in a spatial frequency. It is a longitudinal cross-sectional view explaining schematic structure of the X-ray imaging device of 2nd Embodiment. It is a top view explaining the schematic structure of the modification of 1st Embodiment. It is explanatory drawing of the conventional X-ray imaging system. It is a longitudinal cross-sectional view explaining schematic structure of the conventional X-ray imaging apparatus. It is a top view explaining the grid for the conventional scattered X-ray removal. It is a cross-sectional view illustrating a schematic configuration of a conventional X-ray imaging apparatus.

Explanation of symbols

111 Housing 113 Base 114 X-ray detection panel 114a Phosphor 114b Photoelectric conversion element 114c Substrate 115 Wiring 116 Circuit board 118 Scattered X-ray removal grid 119 Grid frame 120 Grid unit cover 121 Grid adjustment unit 122 Grid holding unit 122a Holding case Body 122b Spring 122c Holding pin 123 Grid unit

Claims (10)

  An X-ray image detector that detects the intensity distribution of X-rays transmitted through the subject, a housing that contains the X-ray image detector, and scattered X-rays that can be detachably attached to the X-ray input surface of the housing Removing means, and means for regulating and adjusting a relative angular position between the X-ray image detector and the scattered X-ray removing means with respect to an axis perpendicular to the X-ray incident surface of the housing. A featured X-ray imaging apparatus.   The right and left and upper and lower relative positions are regulated and adjusted so that the centers of the X-ray image detector and the scattered X-ray removal means on the surface parallel to the X-ray incident surface of the housing are substantially matched. The X-ray imaging apparatus according to claim 1, further comprising: means.   The X-ray imaging apparatus according to claim 1, wherein the adjustment unit is detachable as an independent part or / and provided in the casing or / and the radiation removing unit.   The X-ray imaging apparatus according to claim 3, further comprising a restricting unit for ensuring relative attachment position accuracy between the X-ray image detector or the scattered radiation removing unit and the adjusting unit. .   A control unit that calculates a deviation amount between the X-ray image detector and the scattered X-ray removal unit based on image information acquired by X-ray imaging and drives the adjustment unit to adjust the position. Item 3. The X-ray imaging apparatus according to Item 1 or 2.   The X-ray imaging apparatus according to claim 5, further comprising an input unit that inputs a control amount to the control unit.   The X-ray imaging apparatus according to claim 1, wherein an index representing a center is provided in the casing and the scattered X-ray removing unit.   3. The relative angle error between the X-ray detector and the scattered X-ray removal means with respect to an axis perpendicular to the X-ray input surface is adjusted within 0.5 degrees. X-ray imaging apparatus.   The X-ray imaging apparatus according to claim 1, wherein the scattered X-ray removing unit has a structure in which X-ray absorbing members are arranged in a band shape or a lattice shape.   The X-ray imaging apparatus according to claim 2, wherein the scattered X-ray removing means is a convergent grid whose periphery is inclined so that the X-ray absorbing member arranged in a strip shape faces the X-ray source.

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