JP2013108776A - X-ray detector and industrial x-ray ct apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance spatial resolution of a CT image in an industrial x-ray CT apparatus, and to provide x-ray detectors contributing to the enhancement of spatial resolution.SOLUTION: The x-ray CT apparatus includes: an x-ray source for irradiating x-rays to an analyte; a linear array sensor configured by arranging a plurality of x-ray detectors 2 for detecting x-rays transmitted through the analyte like an array; a turntable arranged between the x-ray source and the x-ray detectors 2 to horizontally rotate the analyte; a signal processing circuit for numerizing x-ray transmission amounts measured by the x-ray detectors 2; and an arithmetic unit for reconstituting signals to an original image. Each x-ray detector 2 includes a semiconductor member 12 for detecting x-rays, a base plate 18 in which the semiconductor member 12 is buried and a shield plate 14 attached only to a one-side face of arrayed arrangement direction side out of faces of the semiconductor member 12 to shield leaked electrons.

Description

  The present invention relates to an industrial X-ray CT apparatus that images the state inside a subject in a non-destructive manner by measuring the amount of X-ray transmitted through the subject, and an X-ray detector suitable for use therein. .

  The X-ray CT system is widely used as a medical human body internal measuring device. However, even in industrial applications, the internal state of cast parts can be measured because the internal state can be measured without cutting the specimen. It is used for many purposes as non-destructive inspection such as measurement.

  In an X-ray CT apparatus, an imaging subject is placed between an X-ray source and a detector, and the amount of X-ray transmitted after the X-ray irradiated from the X-ray source passes through the subject and attenuates is measured by the detector. The image inside the subject is reconstructed from the X-ray transmission amount distribution. Therefore, the X-ray detector size strongly affects the spatial resolution of the image.

  Unlike medical applications, industrial X-ray CT apparatuses for industrial use often have a metal object as an industrial product, and require X-ray energy having a higher transmission capability than the human body. As an X-ray source for generating X-rays, an X-ray tube can be used up to 800 kv, and an X-ray source by a linear accelerator is required at an energy level in the MV region.

  In an X-ray tube, an X-ray source with a focus size of micron order exists in a low energy level region (˜225 kV), but a thick metal object cannot be imaged because of its low transmission capability.

  Further, in an X-ray tube having a relatively high energy level (320 kV to 800 kV), the transmission capability increases, but the focal point size of the X-ray generation source increases from submillimeter to millimeter order.

  In a linear accelerator that can obtain an X-ray energy level in the MV region, the transmission capability is further increased, and the focal point size of the X-ray source is from submillimeters as in an X-ray tube in a region with a relatively high energy level (320 kV to 800 kV). Grows on the order of millimeters.

  From these X-ray tubes and linear accelerators, X-rays are usually irradiated in a cone shape and collimated immediately after X-ray generation and in a fan shape.

  A radiation detector such as a scintillator or a compound semiconductor is used as an X-ray detector that measures the amount of attenuation of X-rays irradiated from the X-ray source and attenuated inside the imaging subject. These detectors are installed at positions facing the X-ray source across the subject to be imaged.

  The X-ray detectors are discretely arranged at regular intervals, and measure X-ray transmission amount integrated values on a straight line connecting the X-ray detector element centers from the X-ray source.

  In order to image the entire subject, the subject placed between the X-ray source and the X-ray detector is placed on a turntable and rotated to acquire projection data necessary for reconstructing the entire image. Alternatively, the imaging subject is fixed on a turntable, and an X-ray source and an X-ray detector are rotated around the subject to obtain necessary projection data.

  In this way, the subject is rotated relative to the X-ray source and the X-ray detector, and the radiation dose of the incident X-rays is measured by all the X-ray detectors at each rotation angle pitch. Projection data. Image reconstruction is performed by a typical FBP method using projection data for each rotation angle at the time of imaging.

Miyai H, Satoh K, Kitaguchi H, Izumi S. A high energy X-ray computed tomography using silicon semiconductor detectors.In: 1996 Nuclear Science Symposium Conference Record, vol.2, 1997.p.81621.

  In the internal measurement in the non-destructive inspection of an industrial product using the above-described existing industrial X-ray CT apparatus, it is necessary to detect a defect having a size that affects the structural strength and performance characteristics of the industrial product that is the subject.

  When targeting industrial castings, these fatal casting defects can be detected with existing CT equipment, but to detect smaller defects around these defects, Further improvement in resolution is required.

  In a conventional industrial X-ray CT apparatus, a radiation detector such as a scintillator or a compound semiconductor has been used as an X-ray detector. In particular, as shown in Non-Patent Document 1, a semiconductor compound material is used. The X-ray detector using is highly sensitive to high energy X-rays and can be made thinner than a scintillator.

  Therefore, when a detector array is constructed using an X-ray detector using a semiconductor compound material, the detector interval can be set narrow. By narrowing the detector interval, the sampling interval of projection data for image generation is reduced, and a high-resolution image is obtained.

  On the other hand, in the X-ray detector using the semiconductor compound material shown in Non-Patent Document 1, in addition to the semiconductor member for detecting the transmitted X-ray, leakage electrons (crosstalk) between the detectors are suppressed. A shielding plate was installed. For this reason, there is a limit to the densification of the detector array by reducing the thickness of the detector, and there is a limit to improving the resolution of the X-ray CT apparatus.

  In order to make the X-ray detectors in the detector array denser than at present, it is necessary to make the X-ray sensitive part thinner or to remove the shielding plate. When the X-ray sensitive part is thinned, the incident X-ray dose is decreased from before the thinning, so that the SN ratio is lowered and the image resolution is deteriorated.

  On the other hand, when the shielding plate is removed, leakage radiation is generated in the X-ray detector adjacent to the target detector due to Compton scattering of X-rays incident on the target detector and generation of electron pairs. These leaked radiation doses act as noise signals for the original X-ray measurement values for adjacent detectors, and when imaged using an existing image reconstruction technique, the boundary of the imaging subject is blurred, Image resolution is reduced.

  Accordingly, a first object of the present invention is to provide an X-ray detector capable of reducing the amount of radiation leaking to an adjacent detector simultaneously with a dense arrangement. The second object is to provide an industrial X-ray CT apparatus capable of performing imaging with improved spatial resolution by densifying the arrangement of X-ray detectors, further reducing the amount of radiation leaking to adjacent detectors and suppressing noise. There is.

  Means for achieving the first object includes a semiconductor member that receives X-rays, a substrate on which an electrode of the semiconductor member is mounted, and a shielding member that shields leakage electrons from the semiconductor member. In the X-ray detector, the base plate in which the semiconductor member is embedded is mounted on the substrate and the shielding member.

  Preferably, the substrate is disposed around the shielding member and attached to the base plate.

  More preferably, in the base plate, an opening is formed at a site where X-rays to be detected enter the semiconductor member, and the semiconductor member faces the opening.

  More preferably, the shielding member is preferably arranged so as to cover only one surface in the array arrangement direction of the X-ray detectors.

  Moreover, the shielding member is preferably a metal provided on the surface of the semiconductor portion by vapor deposition or bonding.

  Means for achieving the second object includes an X-ray source for irradiating X-rays and a plurality of X-ray detectors arranged and arrayed so as to detect X-rays transmitted through the subject. A drive mechanism that changes the relative position of the subject with respect to the X-ray source and the X-ray detector, and a signal processing circuit that digitizes the amount of X-ray transmission measured by the X-ray detector And an industrial X-ray CT apparatus comprising an arithmetic unit that reconstructs an image based on a signal from the signal processing circuit, as an X-ray detector described as means for achieving the first object. It is an industrial X-ray CT apparatus provided with any X-ray detector.

  According to the X-ray detector of the present invention, a thin X-ray detector can be configured despite the fact that a semiconductor member is embedded in a base plate and a shielding member is provided. When used, the X-ray detectors can be densely arranged and the amount of radiation leaking to adjacent X-ray detectors can be reduced by shielding with a shielding plate, so that X-ray imaging with high resolution can be achieved. An X-ray detector that can contribute can be provided.

  Moreover, according to the industrial X-ray CT apparatus of the present invention, the arrangement of the X-ray detectors of the industrial X-ray CT apparatus is densified, and further, the amount of radiation leaking to the adjacent detector is reduced to suppress the noise. An industrial X-ray CT apparatus capable of obtaining an X-ray imaging result with improved resolution can be provided.

It is a figure showing the industrial X-ray CT apparatus by one Example of this invention. The figure shows an example of the structure of an X-ray detector used in a conventional X-ray CT apparatus, where (a) is an overall perspective view of the X-ray detector, and (b) is (a). It is the figure which looked at what arranged the X-ray detector of FIG. FIG. 1 is a diagram showing an example of the structure of an X-ray detector used in the X-ray CT apparatus of FIG. 1, and (a) is a partially exploded view of the X-ray detector, (b) FIG. (A) is the perspective view showing the whole after the assembly of the X-ray detector of (a) figure, (c) figure is X-ray incident direction which arranged the X-ray detector of (b) figure side by side, and made an array It is the figure seen from. FIG. 1A is a diagram showing another example of the structure of the X-ray detector used in the X-ray CT apparatus of FIG. 1, and FIG. 1A is a partially exploded view of the X-ray detector; ) Is a perspective view showing the entire assembly of the X-ray detector of FIG. (A), and FIG. (C) is an X-ray array of the X-ray detectors of FIG. It is the figure seen from the incident direction. It is the figure which showed an example of the image reconstruction system in the X-ray CT apparatus of FIG.

  In an embodiment of the present invention, an X-ray source 1 that irradiates X-rays 7, an X-ray detector 2 that detects X-rays transmitted through a subject 8 to be imaged, an X-ray source 1 and an X-ray detector 2. A drive mechanism (turntable 6) for rotating and translating the subject 8 to be imaged disposed between the signal processing circuit 3 and the signal processing circuit 3 for converting the X-ray transmission amount measured by the X-ray detector 2 into numerical values. An image reconstruction device 4 having an arithmetic device for reconstructing an image based on a signal is provided, and a semiconductor member 12 for detecting X-rays transmitted through the X-ray detector 2 and the semiconductor member 12 on the inside are supported. An industrial X-ray CT apparatus in which a plurality of thin X-ray detectors 2 each having an integral structure of a base plate 18 and a radiation shielding plate 14 are arranged and arranged at regular intervals in a horizontal plane direction to obtain a tomographic image; The structure of the thin X-ray detector 2 used for it is shown.

  In another embodiment of the present invention, an X-ray source 1 that irradiates X-rays 7, an X-ray detector 2 that detects X-rays transmitted through a subject 8 to be imaged, and an X-ray source 1 and X-ray detection. A drive mechanism (turn table 6) for rotating and translating the subject 8 to be imaged disposed between the detectors 2, and a signal processing circuit 3 for digitizing the X-ray transmission amount measured by the X-ray detector 2. An image reconstruction device 4 having an arithmetic device for reconstructing an image based on these signals is provided, and a semiconductor member 12 for detecting X-rays transmitted to the X-ray detector 2 and an inside thereof are provided. A thin X-ray detector 2 is constructed by providing a base plate 18 to be supported and a metal part having a radiation shielding function deposited or bonded on the surface of the semiconductor member 12 and integrating them with each other. A plurality of 2 are arranged at regular intervals in the horizontal plane direction for acquiring a tomographic image. And industrial X-ray CT apparatus Bei, there is shown the structure of the X-ray detector 2 thin used therein.

  In each embodiment of the present invention, in the image reconstruction process in the industrial X-ray CT apparatus of either of the above-described embodiments of the present invention, projection data obtained by each X-ray detector in each imaging section is used. Using X-ray CT imaging method that performs the process of removing noise components due to crosstalk through a signal processing process that corrects each projection data for each detector, the resolution can be improved by reducing noise in signal processing. I am trying.

  Each example will be described below with reference to the drawings.

  An industrial X-ray CT apparatus according to an embodiment of the present invention is shown in FIG. As shown in FIG. 1, in an industrial X-ray CT apparatus, an X-ray source 1 and a plurality of X-ray detectors 2 are installed on both sides of a turntable 6.

  The turntable 6 is employed as a drive mechanism that changes the relative position of the subject 8 with respect to the X-ray source 1 and the X-ray detector 2 to change the X-ray irradiation position.

  For the X-ray detector 2, a compound semiconductor detector or a scintillator is used. A plurality of X-ray detectors 2 are employed, and each X-ray detector 2 is arranged as a line array sensor as shown in FIG. Each detector element is arranged in a two-dimensional manner in the horizontal direction and in the vertical direction at a constant interval to form an array as a planar array sensor.

  The subject 8 is placed as an imaging target on the turntable 6 so as to be positioned between the X-ray source 1 and the plurality of X-ray detectors 2. The subject 8 is a metal industrial product.

  In this industrial X-ray CT apparatus, the X-rays 7 irradiated from the X-ray source 1 are transmitted through the subject 8 and attenuated, and enter the X-ray detector 2 at the opposing position. The X-rays incident on these X-ray detectors 2 are converted into electric signals corresponding to the incident X-ray dose (X-ray transmission amount) in the X-ray detector, and are generated as electric signals of each detector element. .

  The electrical signals of the respective detector elements obtained in this way are transmitted to the detector pixel integration processing mechanism 5 and are subjected to addition processing for the number of detector elements designated by the detector pixel integration processing mechanism 5.

  The added electric signal is transmitted from the detector pixel integration processing mechanism 5 to the signal processing circuit 3, amplified and bit-converted, and then transmitted from the signal processing circuit 3 to the image reconstruction device 4.

  In order to reconstruct the entire image of the subject 8, the turntable 6 is rotated, and an electrical signal (referred to as projection data) corresponding to the X-ray transmission amount detected by all the X-ray detectors 2 at a constant angle pitch. ) Is collected for one rotation.

  Projection data for each constant angle pitch is sequentially processed by the detector pixel integration processing mechanism 5 and the signal processing circuit 3 and transmitted to and stored in the image reconstruction device 4. An image reconstruction operation is executed based on the projection data in the reconstruction device 4 to obtain reconstructed image data.

  The obtained reconstructed image data is transmitted to the CT image display device 11 and displayed on the display of the CT image display device 11.

  Moreover, the X-ray detector 2 used for the industrial X-ray CT apparatus of a present Example is shown in FIG. For comparison, the structure of a conventional X-ray detector is shown in FIG. In a conventional X-ray detector, a semiconductor member 12 for detecting X-rays is mounted on an FPC board 13 and a shielding plate 14 is provided on them. FIG. 2A shows one X-ray detector 2, and FIG. 2B shows the X-ray detection of the line array sensor 16 in which these X-ray detectors are arranged at regular intervals in the horizontal direction. The vessel arrangement is shown.

  In the X-ray detector 2 employed in this embodiment shown in FIG. 3, the semiconductor member 12 that is a detector element for detecting X-rays is embedded so as to be inserted into the concave portion of the U-shaped base plate 18. Provided.

  Furthermore, the shield plate 14 is embedded in the concave portion of the U-shaped FPC board 13 and provided. Therefore, as shown in FIG. 3C, the shielding plate 14 is incorporated from the FPC board 13 and the semiconductor member 12 is incorporated from the base plate 18 so as not to protrude in the direction in which the X-ray detectors 2 are arranged.

  As for the protrusion, it is preferable that the protrusion does not completely protrude, but it does not have to be complete. Only a part of the shielding plate 14 is in the recess of the FPC board 13 and a part of the semiconductor member 12 is in the base plate 18. A partially embedded state may be embedded in the recess.

  The FPC board 13 to which the shielding plate 14 is attached is bonded to the base plate 18 to which the semiconductor member 12 is attached. In this way, the shielding plate 14, the FPC board 13, the semiconductor member 12, and the base plate 18 are integrated to form one X-ray detector 2, and the shielding plate 14, the FPC board 13, and the semiconductor member 12 are combined. It is supported by the base plate 18.

  When the FPC board 13 is bonded to the base plate 18, the shielding plate 14 is positioned so as to cover one surface of the semiconductor member 12 as shown in FIG. This makes it possible to block the entry and exit of the semiconductor member 12 inside and outside the semiconductor member 12 between adjacent X-ray detectors.

  3 (a) and 3 (b) show one X-ray detector 2, and FIG. 2 (c) shows a line array sensor in which these X-ray detectors 2 are arranged at regular intervals in the horizontal direction. Sixteen X-ray detector arrays were shown.

  As shown in FIG. 3C, in the structure of the X-ray detector 2 of the present embodiment, since the shielding plate 14 is embedded in the FPC board 13, the thickness of the X-ray detector 2 can be reduced in the arrangement direction. This is possible, and when the X-ray detectors 2 are arranged to form an array, the interval in the arrangement direction of the X-ray detectors 2 can be made dense.

  In the second embodiment of the present invention, the X-ray detector 2 in the first embodiment is changed, and the other contents are the same as those in the first embodiment. Therefore, in the following, the changed X-ray detector 2 will be described.

  The X-ray detector 2 of the second embodiment is shown in FIG. In this embodiment, as shown in FIG. 4A, the base plate 18 and the FPC board 13 of the X-ray detector 2 are U-shaped. The base plate 18 is mounted so that the semiconductor member 12 is embedded in a recess formed by making the base plate 18 U-shaped.

  Further, the surface of one side of the semiconductor member 12 of the X-ray detector 2, that is, the surface of one side in the arrangement direction of the X-ray detector 2 of the linear array sensor 16 as shown in FIG. A metal part 17 (gold, silver, copper, etc.) equivalent to the shielding plate 14 is attached and integrated by vapor deposition or bonding.

  The FPC board 13 is attached to and integrated with the base plate 18 so that the metal part 17 fits in the recess. In this way, the semiconductor member 12, the FPC board 13, the shielding plate 17, and the base plate 18 are integrated.

  As in the first embodiment, the X-ray detector 2 configured in this way is arranged in a horizontal direction at a constant interval in the horizontal plane for acquiring a tomographic image as shown in FIG. A line array sensor 16 having a line detector array is used and incorporated in an industrial X-ray CT apparatus.

  In the structure of the X-ray detector 2 of the present embodiment, the semiconductor member 12, the FPC board 13, the shielding plate 17, and the base plate 18 are in an integrated state as in the first embodiment. Since the metal portion 17 serving as a shielding material for radiation or the like has the same layout as that embedded in the FPC board 13, the thickness of the X-ray detector 2 can be reduced, and the X-ray detector 2 is arranged. Thus, the array interval of the X-ray detectors 2 can be made dense.

  As shown in FIG. 4C, the metal part 17 is not projected from the FPC board 13 and the semiconductor member 12 is projected from the base plate 18 in the direction in which the X-ray detectors 2 are arranged. However, it is not necessary for the metal part 17 to be completely protruded, only a part of the metal part 17 is in the concave part of the FPC board 13, and a part of the semiconductor member 12 is in the concave part of the base plate 18. A partially embedded state may be used.

  In any of the above-described embodiments, in the system of the industrial X-ray CT apparatus, a noise component due to crosstalk from projection data obtained as a result of detection by each X-ray detector 2 in each imaging section in image reconstruction processing. A reconstructed image with less noise can be obtained in combination with noise suppression by blocking the entrance and exit of noise such as radiation between the X-ray detectors 2 by the shielding plate 14 and the metal part 17. . The data processing process for these is shown in FIG.

  In each of the first and second embodiments, the CT process imaging by the industrial X-ray CT apparatus using the X-ray detector 2 is realized by adopting the processing process shown in FIG.

  In the processing process, the conditions required for each processing process are input from the input means C15 as the whole imaging condition specifying means C9, the noise correction condition specifying means C10, the detector pixel size specifying means C11, and the image reconstruction calculation condition specifying. Input to each processing process by means C12.

  The overall imaging conditions are stored in the overall imaging condition storage means C2, and after passing through the noise correction conditions and X-ray source irradiation condition storage means C4 set by the noise correction condition setting means C3, and the projection data storage means C6 by actual imaging, An image is created by the image reconstruction means C7. Finally, a reconstructed image D6 is obtained, recorded in the reconstructed image storage means C8, and displayed on the display means C16.

  In any of the embodiments of the present invention, in an industrial X-ray CT apparatus, the thickness of the X-ray detector can be reduced, and the array can be densified when the X-ray detector is arrayed. By using an X-ray detector structure that reduces the radiation dose, an industrial X-ray CT apparatus having high resolution can be provided.

  The X-ray detector of the present invention is applicable to industrial and medical X-ray CT apparatuses.

DESCRIPTION OF SYMBOLS 1 X-ray source 2 X-ray detector 3 Signal processing circuit 4 Image reconstruction apparatus 5 Detector pixel integration processing mechanism 6 Turntable 7 X-ray 8 Subject 9 X-ray source focus size adjustment mechanism 10 Signal transmission circuit 11 Image display apparatus 12 Semiconductor member 13 FPC board 14 Shield plate 15 Electrode 16 Line array sensor 17 Metal part 18 Base plate

Claims (6)

  An X-ray detector comprising: a semiconductor member that receives X-rays; a substrate on which an electrode of the semiconductor member is mounted; and a shielding member that shields leaked electrons from the semiconductor member. A base in which the semiconductor member is embedded An X-ray detector formed by mounting the substrate and the shielding member on a plate.   The X-ray detector according to claim 1, wherein the substrate is disposed around the shielding member and attached to the base plate.   The X-ray detection according to claim 1, wherein the base plate has an opening formed at a site where X-rays to be detected enter the semiconductor member, and the semiconductor member faces the opening. vessel.   4. The X-ray detector according to claim 1, wherein the shielding member is disposed so as to cover a surface on one side in the arraying arrangement direction of the X-ray detector. 5.   The X-ray detector according to claim 4, wherein the shielding member is a metal provided on the surface of the semiconductor portion by vapor deposition or bonding.   An X-ray source for irradiating X-rays, a plurality of X-ray detectors arranged in an array so as to detect X-rays transmitted through the subject, and the X-ray source and the X-ray detector On the other hand, a drive mechanism that changes the relative position of the subject, a signal processing circuit that quantifies the amount of X-ray transmission measured by the X-ray detector, and an image based on a signal from the signal processing circuit An industrial X-ray CT apparatus comprising an arithmetic unit to be reconfigured includes the X-ray detector according to any one of claims 1 to 5 as the X-ray detector. X-ray CT system.