JP4765354B2 - X-ray tomographic imaging apparatus and X-ray tomographic imaging method - Google Patents

Description

  The present invention relates to an X-ray tomographic imaging apparatus using an X-ray tube that generates an X-ray focal point having a micro size such as a submicrometer, and an X-ray tomographic imaging method performed by the apparatus.

Conventionally, in the field of research and development of semiconductor elements and the like, non-destructive three-dimensional analysis has been required in order to inspect cracks, disconnections, and the like that exist inside a minute object to be inspected. There is an X-ray tomographic imaging apparatus (also called an X-ray CT apparatus) that realizes the non-destructive three-dimensional analysis. This X-ray tomographic imaging apparatus detects an X-ray source (an X-ray generator configured by an X-ray tube or the like) and X-rays irradiated from the X-ray source through an X-ray focal point and transmitted through an object to be inspected. A detector is provided, and the object to be inspected placed between the X-ray source and the detector is rotated by a predetermined angular displacement, and the transmitted X-rays of each angular phase are imaged by the detector. Then, internal structure data is created by processing and reconstructing a plurality of captured images as image data, and the inside of the inspection object is inspected and observed (see, for example, Patent Document 1).
JP 2004-132931 A

  By the way, in an industrial X-ray tomographic imaging apparatus for inspecting a micro component such as a semiconductor element, cone beam (conical) X-rays are generally used. As the focal spot size of the cone-shaped X-ray is smaller, blurring of an edge (end) due to enlargement of the transmitted X-ray image is suppressed, and a more detailed projected image can be obtained. In recent years, an open X-ray tube has been developed as a microfocus X-ray source having a focal size of a micron unit or smaller, instead of a conventional sealed X-ray tube. Since this open X-ray tube has a very small focal size, a clear image with high resolution and no blur can be obtained. In addition, the X-ray tube has a feature such as high magnification.

FIG. 10 is a schematic cross-sectional view showing an example of a general open X-ray tube.
In an open X-ray tube (hereinafter simply referred to as “X-ray tube”) 100, a conical electron beam (electron stream) 102 emitted from a cathode 101 is guided to an electron converging cylinder 104 by a coil 103 or the like. . Then, when the electron beam 102, which has been narrowed to a predetermined diameter through the hole of the electron focusing tube 104, collides with the target 105 made of tungsten or the like, bremsstrahlung, that is, X-rays are emitted.

FIG. 11 shows an enlarged view of the main part of FIG.
In the case of an industrial X-ray tomography apparatus equipped with the open X-ray tube 100 as described above, bremsstrahlung is generated at the focal point 108 of the target 105 to form the first irradiation field 106 as shown in FIG. However, not only the bremsstrahlung generated at the focal point 108 but also the electron converging cylinder 104 that squeezes the electron beam 102 that exists behind the target 105 (cathode side) and is indispensable for controlling the designed focal point 108 to 1 μm or less. Since electrons collide with a metal member (such as molybdenum), it should be noted that weak bremsstrahlung is generated there.

FIG. 12 is a sectional view taken along line XX in FIG.
Although the latter weak bremsstrahlung is mostly absorbed by the electron converging cylinder member itself, as shown in FIG. 12, a thin hole (for example, φ1.0 mm to φ1. 5 mm) 110 is vacant, and bremsstrahlung 112 is emitted from the periphery 111 of the hole 110. As a result of the entire peripheral edge 111 of the hole of the electron converging cylinder 104 acting as if it is a donut-shaped X-ray focal point (pseudo-focus) 109, the thin, weak conical second bremsstrahlung passing through the thin hole 111 is obtained. An irradiation field (second irradiation field) 107 is formed.

Here, reconstructed images of the projection data of the inspected object imaged using the X-ray tube 100 will be described with reference to FIGS.
As shown in FIG. 13, first, the object to be inspected is disposed at a position 103 that is totally affected by the second irradiation field 107 of the X-rays emitted from the X-ray tube 100, and the two-dimensional detector is It arrange | positions in the position 102 orthogonal to the straight line which connects the focus 108 and the pseudo | simulation focus 109, and images a to-be-inspected object. Then, the projection data of the inspection object acquired by the two-dimensional detector is reconstructed and calculated.

  FIG. 14 is an example of a reconstructed image of the object to be inspected when the focal point 108 and the pseudo focal point 109 are on a straight line when viewed from the above-described two-dimensional detector, where A is a front view and B is a cross-sectional view. In the example of FIG. 14, a solid round bar of φ6 mm parallel pins is selected as an example of the object to be inspected. The projection of the solid round bar reflected in the projection data by the weak and thin second irradiation field 107 by the pseudo focus 109 behind the focus 108 has a magnification ratio smaller than the projection by the focus 108. When the projections by the two focal points 108 and the pseudo focal point 109 are reconstructed and the cross section is observed, as shown in FIG. 14A, another double bar 111 can be seen in the solid bar. Also in the cross-sectional view of FIG. 14B, the cross section 112 of another bar can be confirmed in the solid bar.

  In the case of the example in FIG. 14, a pseudo image of φ4.1 mm appears inside the φ6 mm parallel pin from the result of the reconstruction calculation. For example, if the distance from the X-ray focal point 108 to the object to be inspected is L1 = 20 mm, the position of the pseudo focal point 109 is 6 (mm) ÷ 4.1 (mm) × 20 (mm) = 29.27 (mm ) From the actual focal point 108 can be estimated to be 9.27 mm on the cathode side.

  In many cases, the double image by the pseudo-focus 109 can be ignored by setting the contrast when monitoring the reconstruction calculation result. However, for example, when the entire outer periphery of the object to be inspected is a metal case with a high absorption coefficient, and the inside is filled with an element having an extremely small absorption coefficient, a substance with a high absorption coefficient such as a metal case However, there is a case where double reconstruction calculation is performed in a reduced form from the reconstructed image by the focal point 108, which may cause serious trouble in nondestructive inspection.

  Further, as shown in FIG. 13, the object to be inspected is moved perpendicularly to the direction of the electron flow, and is disposed at a position 103 a that is partially affected by the second irradiation field 107 of the X-rays emitted from the X-ray tube 100. The two-dimensional detector has the same axis as the electron flow emitted from the cathode of the X-ray tube 100 so that the two-dimensional detector is at a position 102a orthogonal to a straight line connecting the focal point 108 and the object to be inspected after moving to the position 103a. Is rotated by an angle θ. At this time, the enlargement ratio L0 / L1 calculated from the ratio of the distance from the X-ray focal point 108 to the two-dimensional detector and the distance to the object to be inspected is the same as in the example of FIG.

FIG. 15 is an example of a reconstructed image of the inspection object when the inspection object and the two-dimensional detector are in the above-described positions, that is, when the focal point 108 and the pseudo-focus 109 are not on a straight line when viewed from the two-dimensional detector. Yes, A is a front view and B is a cross-sectional view. In the example of FIG. 15, a hollow stainless steel (SUS) thin tube is selected as the object to be inspected.
In this case, at the position of the two-dimensional detector and the inspection object, a part of the inspection object still covers the second irradiation field 107, and a white shadow 113 (see FIG. 15A) formed from the pseudo focus 109 is projected. A double image remained on the right side of the image, and a round image 114 (see FIG. 15B) appeared on the reconstructed cross section.

  The present invention has been made in view of such a point, and an object thereof is to prevent a double image due to a pseudo focus in a reconstructed image of acquired projection data.

In order to solve the above problems, the present invention provides an X-ray that forms a first irradiation field in a conical shape having a first focal point on a target as a vertex and a central axis substantially coaxial with an electron flow emitted from a cathode. An object to be inspected around a rotation axis of an object to be inspected that intersects perpendicularly to a two-dimensional detector with a detection surface substantially orthogonal to the electron flow emitted from the cathode from the first focal point of the source. When acquiring the projection data of the inspection object by rotating the inspection object placed on the rotation mechanism between the X-ray source and the two-dimensional detector, the two-dimensional detector in the initial posture from the first focus of the X-ray source The subject rotation axis is moved by a predetermined distance in a plane perpendicular to the first direction along the perpendicular line, and the perpendicular line is lowered from the X-ray focal point of the X-ray source to the inspection object rotation axis after the predetermined distance movement. The two-dimensional detector is tilted to form a right angle with the first focus of the X-ray source Ri electrons collide with the cathode to the electron converging tube is formed in the radiation to the first direction and on the same axis, with not influenced position of the second irradiation field according to the second focal point, the the first irradiation field A projection image of the whole inspection object or a specific part is acquired.

According to the above configuration, all or a specific portion of the object to be inspected collides with the electron converging cylinder at the cathode side of the first focus in the first irradiation field by the original X-ray focus (first focus). in a region where electrons are not affected by the second irradiation field by pseudo focal formed on the same and the direction along the perpendicular dropped to the two-dimensional detector axis of the initial attitude from the first focal point and the radiation (the second focal point) It can move and can acquire projection data of a to-be-inspected object in each angle phase.

  According to the present invention, since the projection image of the object to be inspected is picked up in the region not affected by the pseudo focus, there is an effect that no double image is generated in the reconstructed image. Furthermore, since the whole-body projection of the object to be inspected is acquired without loss, an extremely high-quality reconstructed image can be obtained.

  Examples of the best mode for carrying out the present invention will be described below, but the present invention is not limited to the following examples.

FIG. 1 is a schematic diagram showing the concept of an X-ray tomographic imaging method according to the present invention. As described with reference to FIGS. 10 to 12, the open X-ray tube 1 has an X-ray focal point 2 on the target as an apex, and its central axis (conical rotation axis) is emitted from the cathode. The first irradiation field 2a is formed in a conical shape substantially coaxial with the flow (in the optical axis main line direction 4). At this time, the second focal field 3a narrower than the first radiation field 2a is formed by the pseudo focal point 3 generated on the cathode side from the focal point 2. Therefore, in the present invention, all or a specific part of the inspection object 5 is moved between the first irradiation field 2a and the second irradiation field 3a which are not affected by the second irradiation field 3a, and the inspection object in each angle phase is performed. The projection data of the body 5 is acquired, and the acquired projection data is subjected to reconstruction calculation to obtain a reconstructed image.
The present invention is applied to an X-ray tomographic imaging apparatus that uses an X-ray tube that generates a micro focus on the order of microns or less, such as a microfocus X-ray tube, and generates a double image due to the structure of an electron focusing cylinder. Is done.

  In this example, the first irradiation field 2a is about 120 °, for example, and the second irradiation field 3a is narrower than the first irradiation field 2a, for example, about 15 ° to 20 °. The angle range of the first irradiation field and the second irradiation field is not limited to this example.

Next, the configuration of an X-ray tomographic imaging apparatus according to an embodiment of the present invention will be described with reference to FIGS.
FIG. 2 is a schematic top view of an X-ray tomographic imaging apparatus according to an embodiment of the present invention. FIG. 3 is a schematic side view of the same X-ray tomographic imaging apparatus. 2 and 3, the mechanism described in “Japanese Patent Application No. 2004-110306” previously filed by the present applicant can be used as it is.

  The X-ray tomographic imaging apparatus shown in FIGS. 2 and 3 is broadly transmitted through the X-ray tube 1, the rotating base 12 on which the inspection object 5 to be irradiated with X-rays is placed, and the inspection object 5. The two-dimensional detector 20 having an X-ray detection surface, each drive mechanism supporting and moving these elements, and a surface plate 34 on which all of them are mounted and provided with a vibration removing function.

  The X-ray tube 1 is a well-known microfocus X-ray source that generates, for example, a cone-shaped (cone beam-shaped) X-ray. The X-ray tube 1 emits a cone-shaped X-ray from the X-ray tube 1 to the object 5 to be inspected. The whole inspection object 5 is irradiated with X-rays. As shown in FIG. 3, the main body of the X-ray tube 1 is configured such that a front housing 1a and a rear housing 1b are connected by a hinge 6, and an L-shaped bracket 7 and an X-ray near the X-ray focal point. The tube 1 is supported on the surface plate 34 by the V block 8 provided immediately below the weight center of gravity 1c and on the horizontal surface of the bracket 7.

  As shown in FIG. 3, the V block 8 is placed on the V block cradle 10 that can rotate about the rotation fulcrum 11 on the bracket 7 via an elastic body 9. By placing the V block 8 immediately below the bracket 7 and the center of gravity 1c in this way, not only the positioning of the cathode (not shown) of the X-ray tube 1 is facilitated, but also the connection by the hinge 6 is released and the vacuum is released. When the cathode is replaced, the rear housing 1b of the X-ray tube 1 is supported by elastic force, so that precise mechanical work such as cathode coordinate adjustment becomes easy even in a horizontal position. The rotation axis of the hinge 6 of the X-ray tube 1 main body connecting portion and the rotation fulcrum 11 of the V block cradle 10 are arranged substantially coaxially.

  2 is held on a rotation base 12 configured by, for example, a drive motor and a bearing (not shown) for rotating the inspection object 5, and the X-ray of the X-ray tube 1 It rotates around a rotation axis that intersects perpendicularly with a perpendicular drawn from the focal point 2 to a detection surface of a two-dimensional detector 20 described later. Also, a Z-axis movable part 13 that is fastened to the rotary base 12 and is movable in the Z-axis direction, a Y-axis movable part 14 that is movable in the Y-axis direction, an X-axis movable part 15 that is movable in the X-axis direction, and a surface plate The linear motion guide portion 16 fixed to 34 constitutes a drive mechanism in the Z-axis direction and a drive mechanism in the Y-axis direction, and the object to be inspected 5 placed on the Z-axis movable portion 13 is in the Z-axis direction. Configured to be movable in the direction and the Y-axis direction. These mechanisms function as means for moving the object to be inspected.

  Further, the rotary base 12 is supported by, for example, an air bearing (not shown), and is directly coupled coaxially to the air bearing and has a servo motor (not shown) having an angular positioning accuracy of, for example, 0.2 minutes or less, and a rotation phase. The detecting means (not shown) is stationary in synchronism with the projection data capturing period necessary for reconstruction at each angular displacement corresponding to the resolution of the servo motor and the rotational phase detecting means. The rotation axis of the bearing of the rotation base 12 is orthogonal to the perpendicular line dropped from the focal point of the X-ray tube 1 to the detection surface of the two-dimensional detector 20. In this example, the rotary base 12 is composed of an air bearing capable of controlling the fine angular displacement. However, the present invention is not limited to this, and any structure may be used as long as the rotary base 12 is supported and smoothly rotated to control the fine angular displacement.

  The two-dimensional detector 20 is a flat panel detector (hereinafter referred to as “FPD”) used to detect X-rays transmitted through the object 5 and acquire projection data, and in this example, for example, a detection surface. Is an area larger than the A4 size, the pixel size is 120 μm × 120 μm or more, and the tube voltage range of the detectable X-ray tube 1 is 40 to 150 kV. In this example, the two-dimensional detector 20 is configured by an FPD. However, any device may be used as long as it can detect an X-ray using a known technique and process it for each pixel to obtain an image signal.

  The detection surface of the two-dimensional detector 20 is installed by the support 21 so as to be perpendicular to the straight line passing through the approximate center of the inspection object 5 from the X-ray focal point 2 of the X-ray tube 1, and the support 21 is a two-dimensional detector. The drive mechanism which enables 20 to move to a perpendicular direction is provided. Further, the horizontal movable portion 22 constituting the linear motion mechanism fastened to the support 21 moves on the linear motion guide portion 23 in the horizontal direction, thereby moving the two-dimensional detector 20 in the horizontal direction parallel to the detection surface. be able to.

  Further, a convex portion (cam follower) 27 is provided in the vicinity of the end portion of the lower surface of the linear motion guide portion 23 used for moving the two-dimensional detector 20 in the horizontal direction. The engaging member 26 is engaged with the engaging member 26, and the engaging member 26 is slid linearly on the turning guide unit 25 provided on the detector base 28, thereby being mounted on the linear guide unit 23. The dimension detector 20 can be pivoted integrally with the linear motion guide unit 23, for example, about an axis parallel to the rotation axis of the rotary base 12 at an angle of less than about ± 30 ° with respect to the Y axis. The turning angle at this time is controlled based on the indicated value of the encoder 30 directly connected to the rotating shaft 24. These mechanisms function as means for moving the two-dimensional detector. The support base 29 supports the entire mechanism relating to the two-dimensional detector 20.

  In this example, the turning drive of the two-dimensional detector 20 is not performed by a conventionally used direct drive motor (index motor), for example, ball screw drive (linear motion) is easy to obtain angle accuracy and there is no fear of collision or runaway. A mechanism is used for the turning drive system.

  The detector base 28 on which these two-dimensional detectors 20 are mounted can move on the rail 31 via the drive shaft 33 in the X-axis direction (optical axis main line direction) by driving the drive unit 32. Therefore, the distance from the X-ray focal point 2 to the two-dimensional detector 20 can be adjusted.

  FIG. 4 is a block diagram of an X-ray tomographic imaging apparatus according to an embodiment of the present invention. As described above, the X-ray tube 1 irradiates the inspection object 5 placed on the rotating base 12 with X-rays. The intensity and quality of the X-rays irradiated at this time are controlled by the control console 44 through the X-ray control unit 41 which is an X-ray control means.

  The XYZ position, rotation angle displacement, initial angle phase, and the like of the rotation base 12 on which the inspection object 5 is placed are controlled through a mechanism control unit 42 that is a mechanism control means for controlling the position and movement of the rotation base 12. It is controlled by the console 44. The inspection object 5 placed on the rotating base 12 is rotated by the angular displacement designated by the control signal from the control console 44, and the projection image is taken by the X-ray two-dimensional detector 2.

The control console 44 is connected to input means such as a keyboard and a mouse, and display means (not shown) having a GUI (Graphical User Interface) for displaying device operation states, input values, and the like. Also, a control composed of a processor or the like that performs processing of input operation signals from the input means and arithmetic / control of imaging processing described later in accordance with a program stored in a non-volatile memory (not shown) such as a ROM (Read Only Memory). Means.
Further, the control console 44 captures and displays information such as the X-ray intensity of the X-rays emitted from the X-ray tube 1 on the display means, and a mechanism control unit for appropriately positioning the object 5 to be inspected. A command is issued to the rotary base 12 through 4221.

  X-rays that have passed through the inspection object 5 are detected by the two-dimensional detector 20. The two-dimensional detector 20 converts the projection image, which is detected X-ray information, into digital data, and the projection data of the digital data is stored in a projection image storage unit 45 that is composed of a large-capacity magnetic recording device or the like and functions as an imaging storage unit. Send it out. Control of the tilt angle (rotation angle) and movement of the two-dimensional detector 20 in the X-axis direction is performed from the control console 44 through the mechanism control unit 43.

  The sent projection image (according to an instruction from the control console 44) is stored in the projection image storage unit 45 in correspondence with information such as the angle phase, angular displacement, initial angle phase, and X-ray intensity at the time of imaging. The The projection image storage unit 45 is not limited to this as long as it has a recording capacity capable of recording projection data, and various types of projection image storage unit 45 including an optical recording medium and a removable recording medium such as a semiconductor memory are applied. be able to.

  And the projection data memorize | stored in the projection image memory | storage part 45 are sent out to the computer 46 for a reconstruction calculation which functions as a reconstruction means connected with this. The reconstruction calculation computer 46 reconstructs the internal structure data of the inspection object 5 from the input projection data, and stores the reconstructed internal structure data (reconstruction data) in the projection image storage unit 45 or an external recording medium. Remember. Further, it is output to a reconstruction result display device 47 as a display means via a display memory (not shown) and displayed on a display such as a CRT (Cathode Ray Tube) monitor.

  The computer 46 for reconstruction calculation only needs to be able to collect projection data and reconstruct the internal structure data and have a calculation / control capability for performing predetermined control, and stores it in the control console 44 together with the projection image storage unit 45. May be. The reconstruction result display device 47 may be shared with the display means of the control console 44.

  With the configuration described above, the internal structure data of the device under test 5 is input to the reconstruction result display device 47 and the internal structure is displayed. The operator (operator) visually recognizes the presence or absence of defects such as cracks and breaks in the inspected object such as multilayer film plates and minute electronic component elements by the internal structure displayed on the reconstruction result display device 47. Can be confirmed.

Next, imaging processing by the above-described X-ray tomographic imaging apparatus will be described.
First, as an embodiment of the present invention, referring to FIGS. 5 to 7, the entire imaging region of the object to be inspected is not affected by the second irradiation field 3 a by the pseudo-focus 3. A case where the projection data of the object to be inspected is acquired by moving between the first irradiation field 3a and the second irradiation field 3a will be described.

  As shown in FIG. 5, the X-ray tube 1 has an X-ray focal point 2 on the target as an apex, and its central axis (conical rotation axis) is substantially coaxial (X axis) with the thermoelectron flow emitted from the cathode. The first X-ray irradiation field 2a is formed in a conical shape. When the rotation axis of the inspection object 5 and the two-dimensional detector 20 are at the positions 103 and 102 before the movement, that is, conventionally, from the focal point 2 of the X-ray tube 1, the thermoelectron flow emitted from the cathode of the X-ray tube 1 ( Placed on the inspection object rotation mechanism centering on the rotation axis (initial rotation axis) of the inspection object 5 that intersects at right angles to the perpendicular drawn to the two-dimensional detector 20 having the detection surface substantially orthogonal to the X axis) as the initial posture. The to-be-inspected object 5 is rotated between the X-ray tube 1 and the two-dimensional detector 20, and the enlarged projection data is acquired. In this case, the projected image of the inspection object 5 is affected by the second irradiation field by the pseudo focal point 3.

  FIG. 6 shows an example of a reconstructed image sectional view. As shown in FIG. 6, when the rotation axis of the object to be inspected 5 and the two-dimensional detector 20 are at the positions 103 and 102, a double image is generated in the reconstructed image section.

  In this example, the rotation axis of the object to be inspected 5 is a minute distance to the position 5a in a plane perpendicular to the X axis in the Y axis direction perpendicular to the flow of the thermoelectron flow (X axis) emitted from the cathode of the X-ray tube 1. The two-dimensional detector 20 is tilted by an angle θ and moved to a position 20a so as to make a right angle to a perpendicular line dropped from the X-ray focal point 2 of the X-ray tube 1 to the rotation axis 5 of the object to be inspected after the minute movement. Accordingly, the cone-shaped second irradiation field 3a of weak and thin bremsstrahlung by the pseudo focal point 3 formed on the cathode side (rear side) and substantially coaxial with the X axis on the cathode side (rear side) on the X-ray tube 1 target member 2 is formed. Even if the dimension detector 20 completely avoids or the end of the two-dimensional detector 20 enters the thin second irradiation field 3a, the object under inspection does not interfere with the area occupied by the projection 51 of the object under inspection 5. Full-body projection data can be acquired without loss. Then, the acquired projection image for each angular displacement is reconstructed to obtain a reconstructed image of the object to be inspected.

  In this way, the rotational axis of the object to be inspected 5 is moved at right angles (Y axis direction) to the thermal electron flow (X axis) emitted from the cathode of the X-ray tube 1, and the two-dimensional detector 20 is focused on the focal point 2. And the object to be inspected 5 are inclined so as to be orthogonal to the straight line connecting the rotation axes, and the region between the first irradiation field 2a and the second irradiation field 3a is not affected by the second irradiation field 3a by the pseudo-focus 3 Thus, the whole-body projection 51 of the subject 5 can be accommodated in the two-dimensional detector 20. As a result, the object to be inspected is completely detached from the second irradiation field 3a and the influence thereof is completely eliminated, so that the double image disappears as shown in FIG. 7, and a reconstructed image with extremely high quality can be obtained. .

  In this example, since the inspection object 5 is moved between the first irradiation field 2a and the second irradiation field 3a that are not affected by the second irradiation field 3a due to the pseudo focal point 3, the projection of the inspection object 5 is performed. In order to fit the entire image on the detection surface of the two-dimensional detector 20, the distance between the object to be inspected 5 and the focal point 2 needs to be larger than the value 20 mm before the movement. Therefore, before and after the movement, the magnification ratio of the projected image becomes (602 mm / 20 mm)> (610 mm / 44 mm), and the magnification ratio of the projected image after the movement may decrease.

  Next, as another embodiment of the present invention, when the projection of the object to be inspected 5 is divided into two at a position where the object to be inspected 5 is not affected by the second irradiation field 3a, and an enlarged projection is obtained. Will be described with reference to FIG.

The drive mechanism for moving the rotary base 12 shown in FIGS. 2 to 4 and the drive mechanism for turning or moving the two-dimensional detector 20 are used to divide and image the region of the inspection object 5. Thus, the specific part can be observed with high spatial resolution (see Japanese Patent Application No. 2003-197383).
For example, according to “Japanese Patent Application No. 2003-197383” filed earlier by the present applicant, the position of the rotary base and / or the two-dimensional detector is set so that a part of the inspected object is projected onto the two-dimensional detector. Adjusting and imaging a part of the object to be inspected for each angle phase to obtain a partial projection image group of the left half, for example, and then rotating the base so that the remaining part of the object to be inspected is projected onto the two-dimensional detector And / or adjusting the position of the two-dimensional detector, and imaging the remaining part of the object to be inspected for each displacement to obtain a right half partial projection image group, from these left half and right half partial projection image groups. Thus, it is possible to calculate the enlarged internal structure data of the entire object to be inspected, which is about twice as large as the projection image that is normally captured.
Note that the enlarged internal structure data having an enlargement ratio of about 4 times can be obtained by projecting a captured image in which the left and right halves are further divided and the object to be inspected is divided into four, instead of dividing the left and right halves into two.

  As described above, when it is attempted to avoid the influence of the pseudo focal point 3 on the projection data and to obtain the projection of the inspection object 5 at a desired magnification, the whole-body projection data of the inspection object 5 is converted into the two-dimensional detector 20. It may not fit in one piece. Therefore, the above-described method of imaging the subject to be divided into two parts is applied.

  As shown in FIG. 8, two points on the Y axis are in a plane perpendicular to the X axis that is line symmetric with respect to the X axis and the test object 5 completely leaves the thin second irradiation field 3a by the pseudo focal point 3. The rotation axis of the inspection object 5 is moved to the coordinates 61a and 61b. Next, the two-dimensional detector 20 is inclined at an angle θ so as to intersect at right angles to the perpendiculars 63a and 63b dropped from the X-ray main focal point 2 to the rotation axis of the inspection object 5 at the respective positions, and the two positions 62a and 62b. Move to. Then, after inspecting object 5 projection data including the rotation axis of the inspecting object 5 at each position is obtained in two parts, they are combined to obtain a single inspecting object 5 whole body projection data. Then, a composite projection image for each angular displacement is reconstructed to obtain a reconstructed image of the object to be inspected.

As shown in FIG. 8, only the half area of the object to be inspected 5 needs to be obtained, so the distance dOF1 from the focal point 2 to the axis of rotation of the object to be inspected 5 after movement can be shortened. Accordingly, since the magnification ratio before and after the movement of the inspection object 5 is (dFD / dOF) <(dFD1 / dOF1), the magnification ratio of the projected image after the movement is increased.
Therefore, according to this example, it is possible to obtain enlarged internal structure data of the entire object to be inspected that is approximately twice that of a normally captured projection image. In this example as well, as in Japanese Patent Application No. 2003-197383, it is possible to obtain enlarged internal structure data with an enlargement ratio of about 4 times by taking a projection image obtained by further dividing the left and right halves and dividing the object to be inspected into four. It is.

  Next, as still another embodiment of the present invention, an imaging method in a case where a little less than 50% of the projection of the inspection object 5 does not include the inspection object rotation axis is affected by the second irradiation field 3a. This will be described with reference to FIG.

  As described above, when it is attempted to avoid the influence of the pseudo focal point 3 on the projection data and to obtain the projection of the inspection object 5 at a desired magnification, the whole-body projection data of the inspection object 5 is converted into the two-dimensional detector 20. It may not fit in one piece. Therefore, on the Y axis in the plane orthogonal to the X axis, which is axisymmetric with respect to the X axis and at least 50% or more including the rotation axis of the inspection object 5 leaves the thin second irradiation field 3a by the pseudo focal point 3. Two-dimensional detection is performed so that the rotation axis of the inspection object 5 is moved to two coordinates 71a and 71b, and perpendicular lines 73a and 73b dropped from the X-ray focal point 2 to the inspection object 5 rotation axis at the respective positions. The container 20 is moved to the two positions 72a and 72b by inclining the angle θ.

  Then, after the inspected object 5 projection data including the rotation axis of the inspected object 5 at each position is obtained in two parts, the projection of the part not affected by the thin second irradiation field 3a by the pseudo focal point 3a among them is obtained. Only the data is cut out and combined to obtain a single inspected object 5 whole body projection data. That is, perpendicular lines 73a and 73b dropped from the X-ray focal point 2 to the rotation axis of the inspection object 5 at each position, and projections 74a and 74b near the end of the two-dimensional detector 20 of the inspection object 5 at each position. Projection data of the sandwiched area is acquired. Then, a composite projection image for each angular displacement is reconstructed to obtain a reconstructed image of the object to be inspected.

  Also in the example of FIG. 9, the distance dOF1 from the focal point 2 to the rotation axis of the inspection object 5 after the movement can be shortened, so that the enlargement ratio before and after the movement of the inspection object 5 is (dFD / dOF) <(dFD1 / dOF1). Thus, the same effect as in the example of FIG. 8 can be obtained. Furthermore, the example of FIG. 9 has an advantage that the inclination angle of the two-dimensional detector 20 is smaller than that of FIG.

  In the example of FIG. 9, the projection on the opposite side of 180 degrees of the inspected object 5 shown in FIG. 8 is not affected by the second irradiation field 3a. The synthesis method in the example of FIG. 8 can be applied mutatis mutandis.

According to the above-described embodiment, for example, when the case portion of the object to be inspected is a metal having a high absorption coefficient and the inside thereof is filled with a light element, the X-ray tube that generates a micro focus is mounted. In the X-ray tomography apparatus, the double image by the pseudo focus makes the non-destructive analysis very difficult. This is an obvious demerit when using an X-ray tube, for example, an open X-ray tube, which has a focal size of, for example, submicrometer and can obtain a reconstructed image with high spatial resolution.
However, according to the imaging method of the present invention, this problem can be completely solved because it is not affected by the X-ray irradiation field due to the pseudo focus. In addition, since the imaging method can be obtained in a straightforward manner without losing the whole-body projection of the object to be inspected, a reconstructed image with extremely high quality can be obtained.

  Note that the present invention is not limited to the above-described embodiments, and various modifications and changes can be made without departing from the scope of the present invention.

It is a schematic diagram showing the concept of the present invention. 1 is a schematic top view of an X-ray tomographic imaging apparatus according to an embodiment of the present invention. 1 is a schematic side view of an X-ray tomographic imaging apparatus according to an embodiment of the present invention. 1 is a block configuration diagram of an X-ray tomographic imaging apparatus according to an embodiment of the present invention. It is a figure where it uses for description of one embodiment of this invention. It is the figure which showed an example of the conventional reconstruction Z-axis cross section. It is the figure which showed an example of the reconstruction Z-axis cross section by the example of 1 embodiment of this invention. It is a figure where it uses for description of the other embodiment of this invention. It is a figure where it uses for description of the further another example of embodiment of this invention. It is a schematic sectional drawing of an example of an X-ray tube. It is an enlarged view of the principal part of FIG. It is sectional drawing which follows the XX line of FIG. It is a figure where it uses for description of a prior art example. A and B are diagrams showing examples of images when a focal point and a pseudo focal point according to a conventional imaging method are on a straight line. A and B are diagrams illustrating an example of an image when the focus and the pseudo focus by the conventional imaging method are not on a straight line.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... X-ray tube, 2 ... Focus, 2a ... 1st irradiation field, 3 ... Pseudo-focus, 3a ... 2nd irradiation field, 4 ... Conical center axis | shaft (X axis), 5 ... Test object, 12 ... Rotation base , 20 ... Two-dimensional detector, 42, 43 ... Mechanism control unit, 44 ... Control console, 45 ... Projection image storage unit, 46 ... Computer for reconstruction calculation, 47 ... Reconstruction result display device

Claims (6)

From the first focal point of the X-ray source that forms the first irradiation field in a conical shape whose apex is the first focal point on the target and whose central axis is substantially coaxial with the electron flow emitted from the cathode, from the cathode A test object placed on a test object rotation mechanism centered on a test object rotation axis that intersects with a perpendicular line perpendicular to a two-dimensional detector whose initial position is a detection surface substantially orthogonal to the emitted electron flow. In an X-ray tomographic imaging apparatus that rotates between an X-ray source and a two-dimensional detector and acquires projection data of the inspection object,
Inspected object moving means for moving the inspected object rotation axis by a predetermined distance in a plane orthogonal to the first direction along the perpendicular line drawn from the first focus of the X-ray source to the two-dimensional detector in the initial posture;
A two-dimensional detector moving means for tilting and moving the two-dimensional detector so as to form a right angle with a perpendicular drawn to the rotation axis of the inspection object after moving a predetermined distance from the first focal point of the X-ray source;
The electrons collide with the electron converging tube at the first focal point than the cathode side of the X-ray source is formed by radiating the first direction and on the same axis, it is not affected by the second irradiation field according to the second focal point An X-ray tomographic imaging apparatus that obtains a projection image of all or a specific portion of the subject to be inspected by the first irradiation field at a position. The inspected object moving means is line-symmetric with respect to the first direction, and the inspected object leaves the second irradiation field by the second focus, and is in a second direction within a plane orthogonal to the first direction. Move the object rotation axis to two coordinates,
Further, the two-dimensional detector moving means moves the two-dimensional detector at two positions so as to intersect at right angles to the perpendicular line dropped from the first focus to the inspection object rotation axis at each position with respect to the inspection object at each position. Tilt and move at the position
2. The projection data of the object to be inspected including the rotation axis of the object to be inspected at each position is obtained in two divisions, and then the two divided projection data are combined to form one piece of object inspection data. X-ray tomographic imaging apparatus according to claim 1. The inspected object moving means is configured such that at least 50% or more of projections including line symmetry with respect to the first direction and including the inspected object rotation axis leave the second irradiation field by the second focus. The test object rotation axis is moved to two coordinates on the second direction in a plane perpendicular to the direction,
The two-dimensional detector moving means tilts and moves the two-dimensional detector at two positions so as to intersect at right angles to a perpendicular line dropped from the first focal point to the rotation axis of the inspection object at each position.
After the projection data of the inspection object including the rotation axis of the inspection object at each position is obtained in two parts, only the projection data of the part not affected by the second irradiation field by the second focus is extracted. The X-ray tomographic imaging apparatus according to claim 1, wherein the X-ray tomographic imaging apparatus is synthesized and used as a single inspected object projection data. It is emitted from the cathode from the focal point of the X-ray source that forms the first irradiation field in a conical shape having the first focal point on the target as the apex and the central axis of which is substantially coaxial with the electron flow emitted from the cathode. X-rays of the inspection object placed on the inspection object rotation mechanism centering on the inspection object rotation axis that intersects perpendicularly with the perpendicular drawn to the two-dimensional detector whose initial posture is the detection surface substantially orthogonal to the electron flow. In an X-ray tomographic imaging method of rotating between a source and a two-dimensional detector and acquiring projection data of the inspection object,
Moving the rotation axis of the object to be inspected by a predetermined distance in a plane perpendicular to the first direction along the perpendicular line dropped from the first focus of the X-ray source to the two-dimensional detector in the initial posture;
Further, the two-dimensional detector is tilted and moved so as to form a right angle with a perpendicular drawn from the first focal point of the X-ray source to the rotation axis of the inspection object after moving a predetermined distance,
Then, the electrons collide with the electron converging tube at the first focal point than the cathode side of the X-ray source is formed by radiating the first direction and on the same axis, the influence of the second irradiation field according to the second focal point An X-ray tomographic imaging method for acquiring a projection image of all or a specific portion of the subject to be inspected by the first irradiation field at a position not received. Inspected to two coordinates in the second direction within a plane orthogonal to the first direction, the line to be inspected being symmetrical with respect to the first direction, and leaving the second irradiation field by the second focus. Move the rotation axis,
In addition, the two-dimensional detector is tilted and moved at two positions so as to intersect at right angles to the perpendicular drawn from the first focal point to the test object rotation axis at each position with respect to the test object at each position,
5. The projection data of the object to be inspected including the rotation axis of the object to be inspected at each position is obtained in two parts, and then the two divided projection data are synthesized to form one piece of object data to be inspected. An X-ray tomographic imaging method according to claim 1. A projection in the plane perpendicular to the first direction in which at least 50% or more of the projections that are line-symmetric with respect to the first direction and include the rotation axis of the inspection object leave the second irradiation field by the second focus. The test object rotation axis is moved to two coordinates in two directions,
In addition, the two-dimensional detector is tilted and moved at two positions so as to intersect at right angles to the perpendicular line dropped from the first focal point to the rotation axis of the inspection object at each position,
After the projection data of the inspection object including the rotation axis of the inspection object at each position is obtained in two parts, only the projection data of the part not affected by the second irradiation field by the second focus is extracted and combined. The X-ray tomographic imaging method according to claim 4, wherein one piece of inspected object projection data is used.