JP5487519B2 - Industrial X-ray CT apparatus and imaging method - Google Patents

Description

  The present invention relates to an industrial X-ray CT apparatus and imaging method for imaging a situation inside a subject in a non-destructive manner by measuring the amount of X-ray transmitted through the subject to be examined using X-rays. About.

  X-ray CT equipment 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 object. 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 focal spot size and detector size of the X-ray source strongly affect the spatial resolution of the image.

  Unlike medical applications, industrial X-ray CT apparatuses often have metallic objects as objects, 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). Increases to millimeter order. 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 a 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 imaging subject. The detector measures X-ray transmission amount integrated values on a straight line discretely arranged at regular intervals and connecting each detector element center from the X-ray source. In order to image the entire subject, the subject placed between the X-ray source and the detector is placed on a turntable and rotated to acquire projection data necessary to reconstruct the entire image (for example, Patent Document 1). Alternatively, the imaging subject is stopped, and the X-ray source and the detector are rotated around the subject to obtain necessary projection data.

JP 2008-96321 A

  In the internal measurement in the non-destructive inspection of the industrial product using the existing industrial X-ray CT apparatus as described in Patent Document 1, it is necessary to detect a defect having a size that affects the structural strength and performance characteristics of the object. . In the case of castings, these fatal casting defects can be detected with existing CT equipment, but to detect smaller defects around these defects, further resolution Improvement is needed. On the other hand, when a very small defect is detected compared to the overall size of the subject, enormous imaging time is required if the entire subject is imaged in accordance with the minimum size of these defects. Further, when image reconstruction of the entire subject is performed with the imaging spatial resolution matched to the minimum defect size, the image data becomes enormous, and enormous calculation time is required for the reconstruction calculation itself and data analysis after image creation.

  In addition, in the case of detecting a casting defect of a casting using X-ray CT, a portion where a defect is likely to occur three-dimensionally in the casting process can be narrowed down to some extent from casting simulation or existing destructive inspection. . In such a case, it is efficient to take an image with a high spatial resolution only for a portion where a casting defect is likely to occur. On the other hand, it is also important to image the entire region with a certain degree of spatial resolution and confirm the presence or absence of defects of a size that affects the structural strength and performance characteristics of the subject.

  In a conventional industrial X-ray CT apparatus, the X-ray source characteristics (focus size) and the detector size are set to constant values and do not change, so that the image resolution is constant in one apparatus. Therefore, when the resolution of the apparatus is increased, the imaging time and data processing time become enormous when imaging the entire subject.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an industrial X-ray CT apparatus and an imaging method capable of capturing an image with high spatial resolution only in an arbitrary designated specific region of an object to be imaged, and capable of easily and accurately synthesizing an image. There is to do.

(1) For the above purpose, the present invention is disposed between an X-ray source for irradiating X-rays, a detector for detecting X-rays transmitted through an object to be imaged, and an X-ray source and a detector. A driving mechanism that rotates and translates the subject to be imaged, a signal processing circuit that quantifies the amount of X-ray transmission measured by the detector, and image reconstruction that reconstructs an image based on a signal from the signal processing circuit. An X-ray CT apparatus comprising constituent means, the X-ray focus size adjusting means for changing the focus size of the X-ray beam emitted from the X-ray source, and the apparent size of each detection element of the detector Detector pixel integration processing means for making the size variable, control means for controlling the X-ray focus size adjustment means and the detector pixel integration processing means in conjunction with the X-ray focus size. Adjustment means and detector pixel integration processing means The focus size of the X-ray beam emitted from the X-ray source and each detector element size of the detector are set to a coarse resolution, and the entire subject is imaged with a coarse spatial resolution. The X-ray focus size adjusting means and the detector pixel integration processing means are controlled for a region designated as a part of the X-ray beam so that the X-ray beam focus size and each detector element size of the detector are finely resolved. And a composite image creating means for re-imaging only the specified specific area and further integrating and synthesizing fine image data of the specific specified area in the coarse image data of the entire area to form integrated image data. It is what I did.
With such a configuration, it is possible to capture an image with high spatial resolution only in an arbitrary designated specific region of the imaging target subject, and it is possible to easily synthesize an image with high accuracy.

  (2) In the above (1), preferably, imaging of the entire subject is performed only by rotating the subject, and re-imaging only of the specified specific region is performed using both rotation and translation of the subject. It is what I did.

(3) For the above purpose, the present invention is arranged between an X-ray source for irradiating X-rays, a detector for detecting X-rays transmitted through the subject to be imaged, and the X-ray source and detector. A driving mechanism that rotates and translates the subject to be imaged, a signal processing circuit that quantifies the amount of X-ray transmission measured by the detector, and image reconstruction that reconstructs an image based on a signal from the signal processing circuit. An X-ray CT imaging method using an X-ray CT apparatus comprising constituent means, wherein the focus size of the X-ray beam emitted from the X-ray source and the size of each detector element of the detector are set to a coarse resolution, After imaging the entire specimen with coarse spatial resolution, analyze the captured image, specify the area to be imaged with finer resolution, and reset the focus size of the X-ray beam and the size of each detector element to fine resolution. , Re-image only the specified specific area, and Fine image data of a specific designated area is incorporated into coarse image data and combined to obtain integrated image data.
With such a method, it is possible to image only a specified specific region of the imaging target subject with high spatial resolution, and it is possible to easily and highly accurately synthesize an image.

According to the present invention, it is possible to capture an image with high spatial resolution only in an arbitrary designated specific area of an imaging target object, and it is possible to easily and highly accurately synthesize an image.

It is an apparatus block diagram of the industrial X-ray CT apparatus by one Embodiment of this invention. It is a flowchart which shows the imaging method by the industrial X-ray CT apparatus by one Embodiment of this invention. 1 is a system configuration diagram of an industrial X-ray CT apparatus according to an embodiment of the present invention. It is explanatory drawing of the example of a display by the industrial X-ray CT apparatus by one Embodiment of this invention. It is explanatory drawing of the example of a display by the industrial X-ray CT apparatus by one Embodiment of this invention. It is explanatory drawing of the example of a display by the industrial X-ray CT apparatus by one Embodiment of this invention.

Hereinafter, the configuration and operation of an industrial X-ray CT apparatus according to an embodiment of the present invention will be described with reference to FIGS.
First, the overall configuration of the industrial X-ray CT apparatus according to the present embodiment will be described with reference to FIG.
FIG. 1 is an apparatus configuration diagram of an industrial X-ray CT apparatus according to an embodiment of the present invention.

  In the industrial X-ray CT apparatus of the present embodiment, an X-ray source 1 and a detector 2 are installed facing each other, a turntable 6 is placed between them, and an imaging object 8 is installed on the turntable 6. Is done. The turntable 6 is rotated within the paper surface by the driving means 15 and is movable in the vertical direction perpendicular to the paper surface.

  The X-ray 7 irradiated from the X-ray source 1 passes through the subject 8 and attenuates, and enters the detector 2 at the opposite position. For the detector 2, a compound semiconductor detector or a scintillator is used. These detectors 2 use a line array sensor in which the detector elements are arranged at regular intervals in the horizontal direction or a planar array sensor in which the detector elements are arranged at regular intervals in two dimensions in the horizontal and vertical directions. The X-rays incident on these detectors 2 are converted into electrical signals corresponding to the incident X-ray dose in the detector. The obtained electrical signals of the respective detector elements are subjected to addition processing for signals corresponding to the respective detector elements designated by the detector pixel integration processing mechanism 5. The processed signal is transmitted to the signal processing circuit 3, amplified and bit-converted, and then transmitted to the image reconstruction device 4. In order to reconstruct an image of the entire subject, the turntable 6 is rotated, and X-ray transmission amount data (projection data) detected by the detector 2 is collected for one rotation at a constant angle pitch. Projection data for each constant angle pitch is sequentially transmitted and stored in the image reconstruction device 3, and when one rotation is obtained, an image reconstruction operation is performed to obtain a reconstructed image. The obtained reconstructed image is transmitted to the CT image display device 11 and displayed on the display.

  In the imaging using the X-ray CT apparatus of the present embodiment, when the entire subject is initially imaged, the spatial resolution at the detection element size of the detector 2 is too fine, so the detector pixel integration processing mechanism 5 Addition processing is performed on signals from a plurality of adjacent detection elements. Thereby, the imaging time can be shortened and the image data after image reconstruction can be made compact. At this time, the X-ray source focal point size adjusting mechanism 9 provided in the X-ray source 1 changes the focal point size of the X-ray source in conjunction with the detector element size to be integrated.

  As an X-ray source focus size adjusting method by the X-ray source focus size adjusting mechanism 9, there is a method of installing a variable size collimator immediately after X-ray generation, although it differs depending on the type of X-ray source. In the case of a linear accelerator (LINAC), there is a method of adjusting the convergence size of an electron beam applied to a target for generating X-rays using an acceleration tube. There are types of X-ray tubes that can rotate the target, and the focus size can be variably adjusted by adjusting the thickness of the target in the direction of rotation. The focal spot size can be variably adjusted by installing an automatic target exchange mechanism even with an X-ray source using another method.

  In the present embodiment, the control means 20 performs the addition processing of the signals for the number of detector elements designated by the detector pixel integration processing mechanism 5 and the X-ray source focus size adjustment in conjunction with each other.

  In the present embodiment, after the entire object is imaged in the initial stage, the captured image is displayed on the CT image display device 11, and the defect occurrence probability obtained from the region where the defect occurrence frequency is high or the casting simulation is obtained from the entire object image. A high region is designated from the display using the input means 30 such as a mouse. After designating the region for performing the detailed imaging, the control means 20 uses the X-ray source focus size adjusting mechanism 9 provided in the X-ray source 1 and the detector pixel integration processing mechanism 5 to detect the focus size of the X-ray source and each detection. Sets the signal processing method for the number of elements. At this time, since it is an image of a part of the subject, the X-ray source focus size adjustment mechanism 9 is set so that the focus size becomes smaller, and the detector pixel integration processing mechanism 5 performs a plurality of additions. First, the detection signal of each detector element is output as it is. As a result, it is possible to perform imaging with a higher spatial resolution than during the entire imaging. After completing these settings, the imaging subject 8 on the turntable 6 is rotated to acquire projection data at each angle in the same manner as in the entire imaging, and an image of only the designated area is obtained.

  Here, for example, a specific example will be described. The detector 2 is a planar array sensor in which the detector elements are arranged at regular intervals in two dimensions in the horizontal direction and the vertical direction. Each detector element has a rectangular shape with a short side length of 0.4 mm and a long side length of 1.0 mm. A gap of 0.4 mm is formed between adjacent detector elements. Therefore, the pitch of detector elements adjacent in the short side direction is 0.8 mm. The pitch of detector elements adjacent in the long side direction is 1.4 mm. For example, the long side direction is a direction perpendicular to the paper surface of FIG. 1, and the short side direction is a direction parallel to the paper surface of FIG.

  When imaging the entire subject, the detector pixel integration processing mechanism 5 includes four detector elements adjacent in the short side direction and four detector elements adjacent in the long side direction, that is, a total of 16 detector elements. The output signals of the detector elements are integrated. Thereby, the apparent size of the detector element in the detector 2 is 4.4 mm in the short side direction (= the length of the short side of the detector element is 0.4 mm × 4 + the gap between adjacent detector elements is 0.4 mm). 4 mm × 3), and the long side direction is 4.8 mm (= the length of the long side of the detector element is 1.0 mm × 4 + the gap between adjacent detector elements is 0.4 mm × 2). Therefore, the spatial resolution is 1/12 when the signals are individually extracted from the detector elements, but the data amount in the signal processing circuit 3 and the image reconstruction device 4 is 1/12. At this time, the X-ray source focal point size adjusting mechanism 9 controls the X-ray source 1 to increase the opening angle of the emitted X-rays by 40 degrees. Thus, the drive mechanism 15 can irradiate the subject 8 placed on the turntable 6 with X-rays in the height direction at a time without moving the turntable 6 in translation. . Therefore, a CT image of the entire subject can be obtained only by rotating the turntable 6.

  On the other hand, when imaging a specified region rather than the entire subject, the detector pixel integration processing mechanism 5 does not integrate the output signals from the individual detector elements, and outputs from the individual detector elements. Are sent to the signal processing circuit 3 and the image reconstruction device 4 independently. At this time, since the designated area is smaller than the whole subject, the data amount does not increase extremely. At this time, the X-ray source focal point size adjusting mechanism 9 controls the X-ray source 1 to increase the opening angle of the emitted X-rays by 20 degrees. Therefore, a CT image with high spatial resolution can be obtained. In this case, since X-rays cannot be irradiated at once in the height direction of the subject, the drive mechanism 15 needs to rotate the turntable 6 and also use translational movement.

Next, the imaging method by the industrial X-ray CT apparatus according to the present embodiment will be described with reference to FIG.
FIG. 2 is a flowchart showing an imaging method using an industrial X-ray CT apparatus according to an embodiment of the present invention.

  In step S10, initial imaging conditions such as the X-ray source focus size, detector pitch, and image pixel size are set. Next, in step S20, imaging is performed under this imaging condition, and in step S30, image reconstruction of the entire subject is performed from the obtained projection data. In this whole imaging, a method is used in which imaging is performed only by rotating the subject.

  Next, in step S40, a detailed imaging region is set based on the entire subject imaging result. In step S50, the imaging conditions of the X-ray source focus size, detector pitch, and image pixel size are reset for the set area. Thereafter, in step S60, only the designated area is re-imaged under this imaging condition. In the imaging of the designated area, an imaging method is used in which the subject is rotated and translated. In step S70, when there are a plurality of designated areas, the resetting of the imaging conditions and the re-imaging of the designated areas are repeated for all the designated areas.

  Next, in step S80, the detailed imaging data of these designated areas is reconstructed for all areas, and in step S90, the CT image data obtained by the entire imaging and the detailed image data of the designated area are integrated. Make it.

Next, the system configuration of the industrial X-ray CT apparatus according to the present embodiment will be described with reference to FIG.
FIG. 3 is a system configuration diagram of an industrial X-ray CT apparatus according to an embodiment of the present invention. The same reference numerals as those in FIG. 1 indicate the same parts.

  Here, the correspondence between FIG. 1 and FIG. 3 will be described.

  Whole imaging condition specifying means 30A, X-ray focus size specifying means 30B, detector pixel size condition specifying means 30C, image reconstruction calculation condition specifying means 30D, composite image creation condition specifying means 30E, and X-ray irradiation conditions shown in FIG. The correction means 30F and the reconstruction calculation condition correction means 30GB are provided in the input means 30 of FIG. The input unit 30 includes a mouse and a keyboard.

  The whole imaging condition storage means 40A, X-ray source irradiation condition data storage means 40B, projection data storage means 40C, reconstructed image data storage means 40D, and composite image storage means 40E shown in FIG. 3 are stored in the storage means 40 of FIG. Is provided.

  3A is provided in the image reconstruction unit 4 shown in FIG. 1. The composite image creation unit 4A for the partial region reconstruction image shown in FIG. The image reconstruction projection data creation means 3A shown in FIG. 3 is provided in the signal processing circuit 3 of FIG.

  The entire imaging condition specifying means 30A, the X-ray source focus size specifying means 30B, the detector pixel size specifying means 30C, the image reconstruction calculation condition specifying means 30D, and the composite image condition specifying means 30E9 of the input means 30 are used for each processing process. Enter the necessary conditions.

  2, the entire imaging condition D3 (imaging area size data, irradiation condition data, detector size data) specified by the entire imaging condition specifying unit 30A is stored in the entire imaging condition storage unit 40A. .

  When the detailed area is set by the process of step 40 of FIG. 2, the X-ray source focus size and the X-ray source irradiation condition storage means 40A set by the X-ray source focus size changing means 30B are stored by the process of step s50. The irradiated irradiation condition data D10 is input to the X-ray source focal point size changing unit 9, and the X-ray source focal point size changing unit 9 changes the irradiation condition of the X-ray source 1 based on the input irradiation condition data D10. . The X-ray irradiation condition D4 is stored in the X-ray source irradiation condition data storage unit 40B.

  The image reconstruction projection data creation means 3A is designated by the detector pixel size condition designation means 30C by the X-ray irradiation condition D4 stored in the X-ray source irradiation condition data storage means 40B and the processing of step s50 in FIG. Based on the detector pixel size condition D11 and the X-ray irradiation condition corrected by the X-ray irradiation condition correcting means 30F, image reconstruction projection data D5 is created. The created image reconstruction projection data is stored in the projection data storage means C6.

  The image reconstruction unit 4 stores the X-ray irradiation condition D4 stored in the X-ray source irradiation condition data storage unit 40B and the projection data storage unit 40C by the processing in step S30 in FIG. 2 or the processing in step S80. Based on the image reconstruction projection data D5, the image reconstruction calculation condition D12 specified by the image reconstruction calculation condition specifying means 30D, and the reconstruction calculation condition D17 corrected by the reconstruction calculation condition correcting means 30G, the image Data D6 is created. The created image data D6 is stored in the reconstructed image data storage means 40D.

  As described above, the entire captured image in step S20 in FIG. 2 is obtained according to the entire imaging condition, and the detailed captured image of the designated region in step S60 in FIG. 2 is obtained by changing the X-ray source focal point size and the detector pixel size. It is done.

  The composite image creation means 4A for the partial area reconstructed image is obtained by combining the entire captured image stored in the reconstructed image data storage means 40D and the detailed captured image D6 of the designated area with the composite image creation condition by the processing in step S90 of FIG. Based on the composite image creation condition D13 designated by the designation unit 30E, the composite image data D7 is stored in the composite image storage unit 40E.

  Each condition D3 and data D4, D5, D6, and D7 stored in the X-ray source irradiation condition data storage means 40B, projection data storage means 40C, reconstructed image data storage means 40D, and composite image storage means 40E are displayed as CT images. It is displayed on the device 11.

Next, display examples by the industrial X-ray CT apparatus according to the present embodiment will be described with reference to FIGS.
4-6 is explanatory drawing of the example of a display by the industrial X-ray CT apparatus by one Embodiment of this invention.

  FIG. 4 is a display example of the entire image displayed on the CT image display device 11. The display means 11 is provided with a display area designation frame 24, and designation of “entire area” and “partial area:” is possible on the display. A designation area list display frame 25 is provided for designation of the partial area. Set and select a plurality of designated areas (for example, area a, area b, and area c) For example, after selecting area a in the designated area list display frame 25, two diagonal lines are displayed on the image display screen 26. By designating with a mouse or the like, the area a is displayed.

  The illustrated display example is, for example, a cast two-cylinder engine block. Two large circles near the center are the cylinder gaps. An arc-shaped ellipse around the cylinder is a gap in the cooling water passage.

  FIG. 5 is a display example when a detailed image is displayed on the image display screen 26. When the area b is selected in the designated area list display frame 25, an enlarged image of the area b is displayed. Here, as in the region b, a void is likely to occur in the peripheral portion, and the void D1 is displayed in the Kakuda image.

  FIG. 6 shows an example in which the entire image and the detailed image are combined and displayed on the image display screen 26 by the process of step S90 of FIG. By synthesizing the detailed image with the entire image, it can be displayed even in the cast hole D1.

  Even in conventional imaging, it was possible to image a CT apparatus with a high X-ray source energy level and an apparatus with a low X-ray source energy level but high spatial resolution for a single subject. A CT apparatus with a low energy level of the X-ray source has a low X-ray transmission capability, so the entire subject cannot be imaged, and it is necessary to physically cut out only a portion of interest and decompose it into small sizes. It was. In addition, in order to synthesize the entire imaging data and the detailed imaging data of the part that is physically cut out, it is necessary to perform positioning with high accuracy, and imaging and image data processing are very difficult. On the other hand, in the present embodiment, since the entire imaging and the detailed imaging are performed with the same object position in the same apparatus, there is no positioning problem at the time of imaging and image data synthesis, and it is simple and highly accurate. With this, image composition can be performed.

As described above, according to the present embodiment, by providing an apparatus and an imaging method capable of imaging only a specified specific region of an imaging target subject with high spatial resolution in an industrial X-ray CT apparatus, The entire target object can be imaged with coarse spatial resolution and only the necessary area can be imaged with high resolution, and the imaging data that can be imaged in a short time that can realize high-resolution imaging is also suppressed to the minimum required size. Calculation and analysis time can be shortened.

DESCRIPTION OF SYMBOLS 1 ... X-ray source 2 ... Detector 3 ... Signal processing circuit 4 ... Image reconstruction apparatus 5 ... Detector pixel integration processing mechanism 6 ... Turntable 7 ... X-ray 8 ... Subject to be imaged 9 ... X-ray source focus size adjustment Mechanism 10 ... Signal transmission circuit 11 ... CT image display device 15 ... Driving means 20 ... Control means 24 ... Display area designation frame 25 ... Designated area list display frame 26 ... Image display screen 30 ... Input means 40 ... Storage device

Claims (3)

An X-ray source that emits X-rays;
A detector for detecting X-rays transmitted through the subject to be imaged;
A drive mechanism that rotates and translates the subject to be imaged disposed between the X-ray source and the detector;
A signal processing circuit for digitizing the amount of X-ray transmission measured by the detector;
An X-ray CT apparatus comprising image reconstruction means for reconstructing an image based on a signal from the signal processing circuit,
X-ray focus size adjusting means for changing the focus size of the X-ray beam emitted from the X-ray source;
Detector pixel integration processing means for varying the apparent size of each detector element size of the detector;
Control means for controlling in conjunction with the X-ray focus size adjusting means and the detector pixel integration processing means,
The control unit controls the X-ray focal point size adjusting unit and the detector pixel integration processing unit to coarsen the focal point size of the X-ray beam emitted from the X-ray source and each detector element size of the detector. The resolution is set, the entire subject is imaged with a rough spatial resolution, and the X-ray focal point size adjusting means and the detector pixel integration processing means are applied to a region designated as a part of the subject. Control, reset the focus size of the X-ray beam and each detector element size of the detector to a fine resolution, re-image only the specified specific area,
An X-ray CT apparatus, further comprising: composite image creating means for incorporating and synthesizing fine image data of a specific designated area into image data having a rough entire area and combining them into integrated image data. The X-ray CT apparatus according to claim 1,
An X-ray CT apparatus characterized in that imaging of the entire subject is performed only by rotating the subject, and re-imaging only of a specified specific region is performed using both rotation and translation of the subject. An X-ray source for irradiating X-rays, a detector for detecting X-rays transmitted through the object to be imaged, and a drive mechanism for rotating and translating the object to be imaged disposed between the X-ray source and the detector; X-ray using an X-ray CT apparatus comprising a signal processing circuit for digitizing the amount of X-ray transmission measured by a detector and an image reconstruction means for reconstructing an image based on a signal from the signal processing circuit CT imaging method comprising:
The focus size of the X-ray beam emitted from the X-ray source and the size of each detector element of the detector are set to coarse resolution, and the entire subject is imaged with coarse spatial resolution, and then the captured image is analyzed to obtain finer details. Specify the area to be imaged with resolution, reset the focus size of the X-ray beam and each detector element size of the detector to fine resolution, re-image only the specified specific area,
Further, an X-ray CT imaging method characterized in that fine image data of a specific designated area is combined and synthesized into image data with a coarse entire area to form integrated image data.

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