JP4894359B2 - 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 and an X-ray tomographic imaging method for inspecting internal structure data of an object to be examined using X-rays or the like.

  Conventionally, non-destructive three-dimensional analysis is required in the field of research and development of semiconductor elements and the like in order to inspect cracks, breaks, and the like that exist inside a micro-inspection object. As one of the methods, there is a method using a computed tomography apparatus using X-rays (hereinafter referred to as an X-ray tomography apparatus).

  The X-ray tomographic imaging apparatus is, for example, an X-ray source (an X-ray generator configured by an X-ray tube or the like) and an X-ray focus from this X-ray source to irradiate a subject to be examined in the form of a cone beam. A two-dimensional detection means for detecting the detected X-ray, and a rotation axis orthogonal to the perpendicular line dropped from the X-ray focal point to the detection surface of the detection means while being placed between the detection means and the detection means It has a rotating base that rotates with an angular displacement based on it. The X-ray source irradiates the inspection object with X-rays, the transmission X-ray projection image of the inspection object is picked up by the two-dimensional detection means, processed as a plurality of digitized image data for each angle phase, and By reconstructing the internal structure data from the image data, it becomes easier to inspect and observe the inside of the inspection object.

  In the calculation for reconstructing the internal structure data described above, it is desirable that the projected image of the object to be inspected is within the width direction of the detection surface of the two-dimensional detection means. It is required to take an image by means.

  For example, there is a method as described in Patent Document 1 as means for artificially expanding the width of a finite two-dimensional detection means.

  An outline of a technique for artificially extending the width of the two-dimensional detection unit described in Patent Document 1 will be described with reference to FIGS. 8 and 9. FIG. 8 is a schematic diagram (bird's eye view) illustrating a method of imaging by moving a conventional X-ray two-dimensional detector in parallel. FIG. 9 is a top view of FIG.

  As shown in FIGS. 8 and 9, the initial position of the X-ray two-dimensional detector 102 (corresponding to the X-ray detector 101 described in Patent Document 1) is set as the X-ray tube 101 (X-ray described in Patent Document 1). (Corresponding to the tube 1) and the X-ray focal point passing through the rotation center of the inspection object 107 (corresponding to the subject 11 described in Patent Document 1) arranged between the X-ray focal point of the X-ray two-dimensional detector 102 To the position where the center of the X-ray two-dimensional detector 102 intersects with a perpendicular drawn to the detection surface of the X-ray two-dimensional detector 102. The X-ray two-dimensional detector 102 is translated in a plane parallel to the detection surface, such as positions 102a, 102b, and 102c, and a plurality of obtained projection images are synthesized to obtain a virtually wide projection image. .

JP 9-327453 A

  However, the X-ray two-dimensional detector 102 is placed in a device (shield cover) that prevents X-ray leakage, and the amount of parallel movement is largely limited by the size of the device. Further, when the amount of parallel movement of the X-ray two-dimensional detector 102 increases as in the positions 102a and 102c, the distance from the perpendicular drawn from the X-ray focal point to the X-ray two-dimensional detector 102 gradually increases, and the X-ray two-dimensional The projection image captured by the detector 102 cannot obtain sufficient brightness.

  The present invention has been made in view of such a point, and by using an X-ray two-dimensional detector placed in an apparatus having a limited space, it is possible to perform imaging while suppressing attenuation of luminance of a projected image. An object is to improve the magnification ratio of the obtained projection image.

In order to solve the above problems, one aspect of an X-ray tomographic imaging apparatus according to the present invention includes an X-ray source and a two-dimensional detection that detects an X-ray transmitted through an object to be inspected and images a projection image of the object to be inspected. A vertical line arranged between the X-ray source and the X-ray focus of the X-ray source and the two-dimensional detection means, and the test object is placed on the detection surface of the two-dimensional detection means. Rotating means that rotates at an angular displacement set around an orthogonal rotation axis, and control means that performs control to reconstruct the internal structure data of the object to be inspected from the projected images imaged for each angular phase. Have.
The control means circumscribes a virtual cylindrical surface whose center plane is a straight line that passes through the X-ray focal point and is parallel to the rotation axis of the object to be inspected, and from the X-ray focal point, the two-dimensional detection unit First and second planes that are perpendicular to the detection surface at the initial position and that are symmetrical with respect to a plane parallel to the rotation axis at the initial position of the object to be inspected, with the side edges of the detection surface partially overlapping. The two-dimensional detection means is turned to a position by a turning mechanism, and a projected image of each angular phase is taken at each imaging position after turning,
Further, the portion that is not projected onto the detection surface of the object to be inspected at the first and / or second position is projected onto the detection surface at the first and / or second position. The rotating means is moved by the moving mechanism to the regions opposite to the first and / or second positions, respectively, across the surface while maintaining the same distance as the distance from the X-ray focal point to the rotation axis at the initial position, And the initial angle phase of the said rotation means is changed based on the moving amount | distance of the said rotation means, and the projection image of each angle phase of the said to-be-inspected object on the rotation means after the movement in the said 1st and 2nd position is obtained. Image
The projection image of each angular phase obtained at each imaging position is projected onto the virtual cylindrical surface, the reconstruction calculation is performed from the projection image obtained by the projection, and the internal structure data of the inspection object is reconstructed It is characterized by doing.

According to the above-described configuration, two-dimensional detection is performed along the inscribed circle (virtual cylindrical surface) as compared with a method in which a conventional two-dimensional detection means is translated to two or more imaging positions to synthesize a wide projection image. Since the means is moved, the moving distance can be reduced, and the shielding structure or the entire apparatus can be made compact.
Furthermore, the risk of the object to be inspected collides with the X-ray source is alleviated and the distance between the object to be inspected and the X-ray focal point can be further reduced, which is effective in improving the magnification of the object to be inspected.

  According to the present invention, an X-ray two-dimensional detector placed in an apparatus having a limited space is used to improve the magnification of a projected image obtained by imaging while suppressing the attenuation of the brightness of the projected image. Can be made.

  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. That is, an X-ray tomographic imaging apparatus that is widely used among tomographic imaging apparatuses will be described as an example. However, the present invention irradiates an object with X-rays and other radiations from multiple directions, and displays a projection image thereof. The present invention can be applied to a tomographic imaging apparatus that reconstructs internal structure data from a plurality of captured projection data.

A configuration of an X-ray tomographic imaging apparatus according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.
FIG. 1 is a schematic top view of an X-ray tomographic imaging apparatus according to an embodiment of the present invention. FIG. 2 is a schematic side view of the same X-ray tomographic imaging apparatus. The configurations shown in FIGS. 1 and 2 utilize the mechanism described in “Japanese Patent Laid-Open No. 2005-292047” previously filed by the present applicant, but are not limited to this example. Of course.

  The X-ray tomographic imaging apparatus shown in FIG. 1 and FIG. 2 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 entire inspection object 5. Irradiate the line. A desired projection image can be obtained by detecting the X-rays transmitted through the inspection object 5 by the two-dimensional detector 20 and converting it into an image signal. X-rays irradiated from the X-ray tube 1 are configured to form a very small X-ray focal point having a focal size of 5 μm or less, for example. Since the resolution of the X-ray tomographic imaging apparatus is determined by the focal size of the X-ray, it is preferable that this numerical value is small in order to observe a finer damage or the like.

  As shown in FIG. 2, the main body of the X-ray tube 1 has a structure in which 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 tube 1 near the X-ray focal point. 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. 2, the V block 8 is placed via a resilient body 9 on a V block pedestal 10 that can be rotated about a rotation fulcrum 11 on the bracket 7. 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.

  As shown in FIG. 1, the inspected object 5 is held on a rotating base 12 constituted by, for example, a drive motor and a bearing (not shown) for rotating the inspected object 5, and the X-ray tube 1 The X-ray focal point 2 rotates about a rotation axis that intersects at right angles with a perpendicular drawn 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 A linear motion guide portion 16 fixed to 34 constitutes a drive mechanism in the X-axis, Y-axis, and Z-axis directions. These mechanisms function as means for moving the object to be inspected (moving mechanism).

  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 composed of, for example, a flat panel detector (FPD), and can be adjusted to move left and right and up and down so that X-rays are irradiated at the center. An example of the FPD is specifically disclosed in JP-A-6-342098. The technique described in this patent publication absorbs X-rays transmitted through a subject with a photoconductive layer such as an a-Se layer to generate charges according to the X-ray intensity, and detects the amount of charges for each pixel. That's it. As an example of another type of FPD, for example, as disclosed in JP-A-9-90048, X-rays are absorbed in a phosphor layer such as an intensifying screen to generate fluorescence, and the intensity of the fluorescence Is detected by a photodetector such as a photodiode provided for each pixel. In addition, there is a method using a CCD (Charge Coupled Devices) or a C-MOS (Complementary Metal Oxide Semiconductor) sensor as a fluorescence detecting means.

  In particular, in the FPD of the method disclosed in the above Japanese Patent Laid-Open No. 6-342098, the X-ray dose is directly converted into the charge amount for each pixel, so that there is little deterioration in sharpness in the FPD and an image with excellent sharpness is obtained. It is done. In this example, the two-dimensional detector 20 is configured by an FPD. However, any device can be used as long as it can detect transmitted X-rays of an object to be inspected and process each pixel to obtain an image signal.

  The two-dimensional detector 20 is installed such that its detection surface is 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 by the support 21. The support 21 includes a drive mechanism that allows the two-dimensional detector 20 to move in the vertical (Z-axis) direction. 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 linearly slid in the X-axis direction on the turning guide unit 25 provided on the detector base 28. The mounted two-dimensional detector 20 can be rotated 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 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 turning the two-dimensional detector (turning mechanism). The support base 29 supports the entire drive mechanism of 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. This is done using a mechanism.

  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.

  With such a configuration, for example, as shown in FIG. 3, the two-dimensional detector 20 includes a perpendicular drawn from the X-ray focal point 2 to the detection surface 20 a at the initial position (Pos0) of the two-dimensional detector 20. 5 can be moved to imaging positions Pos1, 2, 3, and 4 at even-numbered positions that are plane-symmetric with respect to a plane parallel to the rotational axis at the initial position.

  The entire mechanism on the surface plate 34 is covered with an ionizing radiation shielding box (shield cover) (not shown).

  Next, an example of a block configuration of the above-described X-ray tomographic imaging apparatus will be described with reference to FIG.

  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 position, rotation angle displacement, initial angle phase, and the like of the rotary base 12 on which the inspection object 5 is placed are controlled through a mechanism control unit 42 that functions as a mechanism control means for controlling the position and movement of the rotary 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 two-dimensional detector 2.

  The control console 44 is an example of a control means. For example, a personal computer (hereinafter referred to as a keyboard) and other display means for displaying a GUI (Graphical User Interface) screen, a reconstruction result of a subject image, and the like are connected. And PC). A processor (arithmetic processing unit) mounted on a personal computer performs calculation and control of an X-ray tomographic imaging process, which will be described later, according to a program stored in a non-volatile memory (not shown) such as a ROM (Read Only Memory). In addition, the personal computer displays information such as the X-ray intensity of the X-rays emitted from the X-ray tube 1 on the display means, or causes the X-ray control unit 41 to display information based on an operation signal input via the input means. On the other hand, a control command is output, or a command for appropriately positioning the object to be inspected 5 is output to the rotating base 12. Further, a command is issued to the two-dimensional detector 20 through the mechanism control unit 43 to control the inclination angle (rotation angle), movement in the X-axis direction, and the like.

  X-rays that have passed through the inspection object 5 are captured and detected by the two-dimensional detector 20. The two-dimensional detector 20 supplies a projection image, which is detected X-ray information, to a projection image storage unit 45 serving as a projection image storage unit. This projection image is stored in the projection image storage unit 45 as digitized projection data in association with the angle phase at the time of imaging in accordance with an instruction from the control console 44. The projection image storage unit 45 is not limited to this as long as it has a capacity capable of recording projection data, and includes a large-capacity magnetic recording device, a removable recording medium such as an optical recording medium or a semiconductor memory, etc. Various things can be applied. Further, the projection data supplied from the two-dimensional detector 20 may be stored in the projection image storage unit 45 in association with information such as the angle phase, angle displacement, initial angle phase, and X-ray intensity at the time of imaging.

  The projection data stored in the projection image storage unit 45 is supplied to a reconstruction calculation computer 46 that functions as reconstruction means connected thereto. The reconstruction calculation computer 46 reconstructs the internal structure data of the inspected object 5 from the input projection data. The reconstructed internal structure data (reconstruction data) is stored in the projection image storage unit 45 or another recording medium, and is also input to the reconstruction result display device 47 as 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 have an arithmetic processing capability capable of collecting input projection data and reconstructing internal structure data, and may be shared with the control means of the control console 44. The reconstruction result display device 47 may be shared with the display means of the control console 44.

  With the configuration as described above, the internal structure data of the inspection object 5 is obtained in the reconstruction result display device 47, and the internal structure of the inspection object 5 is displayed. The operator (operator) visually recognizes the presence and state 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. In the present embodiment, as shown in FIG. 3, the inspected object 5 includes a vertical line that drops the two-dimensional detector 20 from the X-ray focal point 2 to the detection surface 20 a at the initial position (Pos0) of the two-dimensional detector 20. Are moved to even-numbered positions that are plane-symmetric with respect to the plane parallel to the rotation axis at the initial position, and the projected images of the respective angular phases are captured at the respective imaging positions after the movement. At this time, in order to keep the enlargement ratio constant, as shown in FIG. 5, a virtual surface with the detection surface 20 a of the two-dimensional detector 20 parallel to the rotation axis of the object to be inspected 5 and passing through the X-ray focal point 2 is the central axis. The two-dimensional detector 20 is turned by a turning mechanism so as to circumscribe the cylindrical surface and partially overlap the side end portion of the detection surface 20a at each position.

  The two-dimensional detector 20 captures projection images of each angular phase for each predetermined angular displacement at each imaging position Pos1, 2, 3, and 4 after turning, and the projection image storage unit 45 stores data of each captured partial projection image. To remember. Then, the reconstruction calculation computer 46 synthesizes the partial projection images to create an entire projection image, performs reconstruction calculation using the entire projection image, and reconstructs the internal structure data of the inspection object 5. .

According to such an imaging method, an inscribed circle (virtual circle) is compared to a method (see FIGS. 8 and 9) in which the two-dimensional detector 20 is translated to two or more imaging positions to synthesize a wide projection image. Since the two-dimensional detector 20 is moved along the cylindrical surface 60), the shielding structure or the entire apparatus can be made compact.
In addition, when the projection image captured by the two-dimensional detector 20 is projected onto the virtual cylindrical surface 60, the distance difference between the actual two-dimensional detection surface 20a and the virtual cylindrical surface 60 is projected onto the virtual plane. A smaller image with less conversion error can be obtained.
Furthermore, when trying to obtain a wide projection image by the conventional method, the farther the pixel on the detection surface is away from the straight line connecting the X-ray source 1 and the center (rotation axis) of the inspection object 5, Although the distance between the X-ray source 1 and the two-dimensional detector 20 is increased and the brightness of the projection image is attenuated, in the present embodiment, the distance between the X-ray source 1 and the two-dimensional detector 20 is constant. There is no problem, and a projection image with a constant luminance can be obtained at either the central portion or the peripheral portion of the detection surface.

  Next, another example of imaging processing by the X-ray tomographic imaging apparatus described above will be described. In this example, only the imaging positions Pos2 and Pos3 are selected from the even-numbered imaging positions shown in FIG. 5, and the high-magnification partial projection of the inspection object 5 is performed at the initial position (−S, 0) of the inspection object 5. To get. Then, the partial projection of the inspected object projection to be imaged at the imaging position Pos1 that is beyond the imaging position (not projected onto the detection surface), and the rotation base of the two-dimensional detector 20 remains at the imaging position Pos2. When the 12 rotation axes are moved to the coordinates of the position A (-Scos α, Ssin α) by the rotation base moving mechanism, and the object angular phase is further offset by α degrees, the projection data is geometrically congruent with the imaging position Pos1. Can be obtained.

  Similarly, the projection data to be imaged at the imaging position Pos4 that protrudes at the imaging position Pos3, the position of the two-dimensional detector remains at the imaging position Pos3, and the inspection object rotation base 12 is moved to the coordinates of B (-Scosα, -Ssinα). It is possible to obtain the object by shifting the position and further offsetting the inspection object angle phase by -α degrees. The concept of this imaging method can also be applied to divided imaging at even locations exceeding 4 (not shown).

  Here, a method for capturing a projection image by moving the object to be inspected without turning the two-dimensional detector 20 to Pos 1 and 4 will be described more specifically. FIG. 6 is an enlarged view (top view) of a main part of the X-ray tomographic imaging apparatus shown in FIG.

  In FIG. 6, the focus position of the X-ray tube 1 is set as the origin O, and the X axis and the Y axis are set. If the distance from the X-ray focal point 2 of the X-ray tube 1 to the center point at the initial position of the inspection object 5 is S, the position of the inspection object 5 is expressed as (−S, 0).

  First, the detection surface 20a of the two-dimensional detector 20 circumscribes the virtual cylindrical surface 60 having a straight line passing through the X-ray focal point 2 parallel to the rotation axis of the object 5 to be inspected and Pos2 and Pos2 are arranged so as to be plane symmetric with respect to a plane parallel to the initial position rotation axis of the object 5 to be inspected, including a perpendicular line dropped on the initial position detection surface of the dimension detector 20, and so that the side end portions of the detection surface 20a partially overlap. The two-dimensional detector 20 is turned by the turning mechanism to the position of Pos3, and a projected image of each angle phase is taken at each imaging position after the turning.

  Further, the rotation base 12 is rotated with the X-ray focal point 2 and the initial position so that a portion that is not projected onto the detection surface 20a of the inspection object 5 at the Pos2 imaging position is projected onto the detection surface 20a at the Pos2 position. While keeping the distance from the axis constant, the axis is moved to the position 5a in the opposite region of Pos2 across the symmetry axis (plane) 51, and rotated based on the movement amount (movement angle) α of the rotating base 12. The initial angle phase of the base 12 is changed. That is, the center of the inspection object 5 is moved to the position A (−Scos θ, Ssin θ), and the angular phase of the inspection object 5 is offset by α degrees. And after moving the to-be-inspected object 5 to the position 5a, the projection image of each angle phase is imaged in each imaging position. By such a method, the projection image captured at the position 5a of the inspection object 5 can obtain a projection image substantially the same as the projection image captured at Pos1.

  As shown in FIG. 6, the offset of this angle phase shift is such that a straight line passing through the X-ray focal point 2 and the center of the inspection object 5 is a reference point 5b1 on the inspection object 5 after the inspection object 5 is moved to the position 5a. This can be done by rotating the object 5 so as to pass through.

  Similarly, at the imaging position Pos3 of the two-dimensional detector 20, when there is a portion that is not projected onto the detection surface 20a of the inspection object 5, the center of the inspection object 5 is moved to the position B (−Scos θ, −Ssin θ). Further, the angle phase of the object to be inspected 5 is offset by -α degrees. And after moving the to-be-inspected object 5 to the position 5b, the projection image of each angle phase is imaged in each imaging position. By such a method, the projection image captured at the position 5a of the inspection object 5 can obtain a projection image substantially the same as the projection image captured at Pos4.

  The computer 46 for reconstruction calculation is an overall projection image obtained by synthesizing each partial projection image captured at each position before and after the movement of the inspection object 5 with respect to each imaging position of the two-dimensional detector 20 described above. Is used to reconstruct the internal structure data of the inspected object 5.

  Usually, the highest element that controls the magnification of the projected image is the relationship between the distance between the X-ray focal point 2 and the object 5 to be inspected held on the rotary base 12. In FIG. 5, the magnification is dOF. / DFD. With a finite device size (shielding structure), it is necessary to reduce dOF as the enlargement ratio increases. If an attempt is made to acquire a projection image of the entire object to be inspected with a high magnification ratio in order to obtain a high-definition reconstructed image with a finite detector size, the number of partial imagings for partial projection increases. Here, in order to obtain the geometric congruence only by moving the inspected object rotation base 12, the partial projection to be imaged at the imaging position Pos1 or Pos4 while keeping the coordinates of the initial position Pos0 on the two-dimensional detector 20. In FIG. 5, it is necessary to turn the object to be inspected 5 by a predetermined angle β. However, if α is an angle formed by adjacent imaging positions and β is an angle formed by the initial positions Pos0 and Pos4, the risk of the object 5 to be inspected colliding with the tip of the X-ray tube 1 is increased since α <β. it is obvious. Therefore, having a drive mechanism that moves the two-dimensional detector 20 to the coordinates Pos2 and Pos3 in FIG. 5 is beneficial in avoiding the risk of collision.

  According to the above other embodiment examples, the same effects as the above embodiment examples are obtained, and the following effects are newly obtained.

First, the method of imaging by moving the position of the subject 5 while reducing the amount of rotation of the two-dimensional detector 20 simplifies the structure of the X-ray tomographic imaging apparatus, and is large even in quadrant imaging. Since a depth shielding structure including approximately two detectors can be regarded as a sufficient space, the apparatus size can be made compact.
The symmetrical even-division imaging method can utilize data acquired more efficiently than odd-division imaging when an imaging method that performs reconstruction calculation using projection data of only one of the symmetry planes is selected.
Some of the two-dimensional detectors 20 need to be calibrated based on a white image or a black image in which nothing is reflected, and this calibration is performed by adjusting the focal position of the X-ray source. And the two-dimensional detector 20 must be changed each time the positional relationship changes. However, in the above-described other embodiment examples, it is possible to take an image without changing the position of the two-dimensional detector 20, so that it is possible to take an image at each position (imaging position) only by performing calibration once. .
In addition, since the imaging can be performed with the two-dimensional detector 20 fixed, it is easy to maintain the geometric positional relationship without bending the surface plate, and more accurate imaging can be realized. The configuration of the imaging device is also simplified.

  In general, an imaging method known as an offset scan known in the field of examination using an X-ray tomographic imaging apparatus and acquisition of a tomographic image of an object to be inspected are only at the two imaging positions Pos1 and Pos2 shown in FIG. This is performed using projection data that has been picked up and combined, or projection data that has been picked up and combined at only two positions of image pickup positions Pos3 and Pos4. In the case of two-division imaging, either Pos2 or Pos3 projection may be used. Symmetrical (symmetrical) division imaging at an even number exceeding 4 with a plane parallel to the inspection object rotation axis and including a perpendicular drawn from the X-ray focal point to the two-dimensional detector 20 at the initial position Pos0. In this case, by using projection data on either the Pos2 side or the Pos3 side with the symmetry plane as a boundary, the concept of the offset scan method can be applied as in the case of imaging at two or four points.

  Next, with reference to FIG. 7, a method for projective transformation of the projected image captured by the two-dimensional detector 20 to the virtual cylindrical surface 60 inscribed therein will be described. In FIG. 7, the virtual cylindrical surface 60 is assumed to contact at a midpoint that bisects 2 × G (= even) horizontal total pixels in the horizontal direction of the two-dimensional detector 20. Half of the area is shown. Further, the horizontal line on the detection surface 20a including the midpoint that bisects the total horizontal pixels of the two-dimensional detector 20 includes a perpendicular line dropped from the X-ray focal point 2 to the two-dimensional detector 20, as shown in FIG. Cross in position. In this example, the G pixel information of the two-dimensional detector 20 is projectively transformed while weighting the G pixel information (the same number as the two-dimensional detector 20) of the virtual cylindrical surface 60.

Here, L is the size of the detection surface 20a divided in two in the horizontal direction, R is the distance from the X-ray focal point O to the contact point between the detection surface 20a of the two-dimensional detector 20 and the virtual cylindrical surface 60, and the virtual cylindrical surface 60 If the angle θ of the detection surface is δ, the pixel pitch (pixel size) in the horizontal direction of the detection surface 20a is δ, and the angle between adjacent pixels in the horizontal direction of the virtual cylindrical surface 60 is Δθ, ,
L = G × δ,
θ = arctan (L / R),
Δθ = θ / G (assuming θ <45 °)
It is.

  The distance from the X-ray focal point O to the contact point between the detection surface 20a of the two-dimensional detector 20 and the virtual cylindrical surface 60 is R, the horizontal pixel pitch of the detection surface 20a is δ, and the horizontal angle of the virtual cylindrical surface 60 is equal. The pixel value of the nth pixel from the contact point in the horizontal pixel of the detection surface 20a is Pn, and the pixel value of the nth pixel from the contact point in the horizontal pixel of the virtual cylindrical surface 60 is Tn. Then, a calculation formula for projectively transforming the horizontal projection image obtained by the two-dimensional detector 20 onto the virtual cylindrical surface 60 is obtained as follows.

First, in the horizontal direction of the two-dimensional detector 20, the distances Ln and Ln−1 from the contact point to the nth pixel are:
Ln = R × tan (n × Δθ)
Ln−1 = R × tan {(n−1) × Δθ}
It is represented by

  From these definitions and calculation formulas, the pixel information on the n-th two-dimensional detector 20 from the middle point (contact point) on the two-dimensional detector 20 is Pn, and the virtual cylindrical surface 60 with the same total number of pixels in the horizontal direction with the same angular pitch is also the same. Assuming that the nth pixel information from the midpoint is Tn, when θ is 45 degrees and G = 10, a unique value that considers weighting on and near the plane that includes the perpendicular and is orthogonal to the rotation axis of the inspection object The general relationship is expressed as follows.

  Thus, if the angle θ of the virtual cylindrical surface 60 and the number of pixels G of the two-dimensional detector 20 are determined, a unique relational expression similar to the expression (1) is obtained for each.

  By the way, other than the method of assuming that the total number of pixels in the horizontal direction of the virtual cylindrical surface 60 with equal angular pitch is equal to the total number of pixels equally spaced in the horizontal direction of the two-dimensional detector 20, for example, the pixel sizes of both are equal and equal. A projective transformation method to a virtual cylindrical surface with an angular pitch is also conceivable. However, in the case of divided imaging where part of the side edges of the detection surface of the two-dimensional detector overlap each other, when combining the partial projections projected onto the virtual cylindrical surface, pasting with half-end pixel coordinates on the cylindrical surface is performed. If you try to avoid alignment, the calculation of the bonding position on the two-dimensional detector side that actually exists due to the reaction will be complicated and disadvantageous (demerit) will become complicated, as shown in FIGS. Since this is shorter than the two-dimensional detector, there is a demerit that reduces the amount of projection information obtained by the original two-dimensional detector.

  On the other hand, according to the above-described embodiment, by performing the projective transformation by defining the total number of horizontal pixels of the virtual cylindrical surface 60 as being equal to the total number of horizontal pixels of the two-dimensional detector 20, the post-projection transformation is performed. In addition, the information amount of the projection image captured by the original two-dimensional detector 20 is not impaired, and the complexity of pasting the divided projection images can be reduced.

  In the claims and the specification of the present application, each process (step) for realizing the X-ray tomographic imaging method is not necessarily performed in time series according to the described order, but is necessarily performed in time series. Even if it is not, it includes processing executed in parallel or individually.

  In the above-described embodiment, the rotation angle of the rotation base 3 is not necessarily 360 °, and may be 270 °, for example.

  The means for capturing the projected image of the object to be inspected is not limited to the X-ray two-dimensional detector, but may be a one-dimensional detector such as a line sensor.

  Moreover, the numerical conditions such as the materials used, the amount thereof, the processing time, and the dimensions mentioned in the above description are only suitable examples, and the dimensional shapes and arrangement relationships in the drawings used for the description are also schematic. That is, the present invention is not limited to this embodiment.

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. It is a figure which shows the example which moved the two-dimensional detector to the imaging position of the even number place of plane symmetry. 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 the X-ray tomographic imaging method of this invention. It is a figure which shows an example of the principal part of the X-ray tomographic imaging apparatus shown in FIG. It is a figure where it uses for description of the projective transformation which concerns on this invention. It is the schematic (bird's-eye view) explaining the method to translate and image the conventional X-ray two-dimensional detector. It is the schematic (top view) explaining the method to translate and image the conventional X-ray two-dimensional detector.

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 (X axis), 5 ... Test object, 5a, 5b ... Cover The moving position of the test object, 12: Rotation base, 20 ... Two-dimensional detector, 20a ... Detection surface, 42, 43 ... Mechanism control unit, 44 ... Control console, 45 ... Projection image storage unit, 46 ... Reconstruction calculation Computer 47: Reconstruction result display device 50 ... Inspected object initial position 51 ... Symmetry axis (plane) 60 ... Virtual cylindrical surface Pos 1, 2, 3, 4 ... Moving position of two-dimensional detector

Claims (4)

Between the X-ray source, a two-dimensional detector means for capturing a projection image of the detection to obtaining step body transmitted X-rays the object to be inspected, the X-ray focal point of the X-ray source and the two-dimensional detector rotating means for rotating at arranged the inspection object placed to perpendicular to that rotation axis set angular displacement about the the perpendicular dropped from the X-ray focal point to the test exit face of the two-dimensional detecting unit to , an X-ray tomographic imaging apparatus and a control means for controlling to reconstruct the internal structure data of the test subject than the projected image captured in each angular phase,
The control means circumscribes a virtual cylindrical surface whose center plane is a straight line that passes through the X-ray focal point and is parallel to the rotation axis of the object to be inspected, and from the X-ray focal point, the two-dimensional detection unit said it includes perpendicular dropped to the detection surface in the initial position a plane symmetrical with respect to a plane parallel to the rotational axis in the initial position of the device under test, the detection surface side end portion first and second overlapping part of the The two-dimensional detection means is turned to a position by a turning mechanism, and a projected image of each angular phase is taken at each imaging position after turning,
Further, the portion that is not projected onto the detection surface of the object to be inspected at the first and / or second position is projected onto the detection surface at the first and / or second position. The rotating means is moved by the moving mechanism to the regions opposite to the first and / or second positions, respectively, across the surface while maintaining the same distance as the distance from the X-ray focal point to the rotation axis at the initial position, And the initial angle phase of the said rotation means is changed based on the moving amount | distance of the said rotation means, and the projection image of each angle phase of the said to-be-inspected object on the rotation means after the movement in the said 1st and 2nd position is obtained. Image
The projection image of each angular phase obtained at each imaging position is projected onto the virtual cylindrical surface, the reconstruction calculation is performed from the projection image obtained by the projection , and the internal structure data of the inspection object is reconstructed you
X- ray tomographic imaging apparatus. The control means uses a projection image obtained by imaging an object to be inspected at each angle phase at each imaging position obtained by a horizontal pixel of the two-dimensional detection means as a rotation axis of the object to be inspected. has a straight line passing through the X-ray focal point parallel to the central axis, and the horizontal pixel total number on the two-dimensional detecting unit to the imaginary cylindrical surface is equal to the total number of pixels in the horizontal direction of the two-dimensional detector Project one or more equivalent pixel information while sampling well.
Reconfigures calculated using the projected shadow image which is obtained by combining the projected shadow image which is the projection, to reconstruct the internal structure data of the object to be inspected
X-ray tomographic imaging apparatus according to 請 Motomeko 1. Between the X-ray source, a two-dimensional detector means for capturing a projection image of the detection to obtaining step body transmitted X-rays the object to be inspected, the X-ray focal point of the X-ray source and the two-dimensional detector rotating means for rotating at arranged the inspection object placed to perpendicular to that rotation axis set angular displacement about the the perpendicular dropped from the X-ray focal point to the test exit face of the two-dimensional detecting unit to An X-ray tomographic imaging method for an X-ray tomographic imaging apparatus, comprising: a control unit that performs control to reconstruct the internal structure data of the object to be inspected from projection images captured for each angular phase;
The control means circumscribes the virtual cylindrical surface whose center plane is a straight line passing through the X-ray focal point and parallel to the rotation axis of the object to be inspected, and from the X-ray focal point to the two-dimensional detection unit said it includes perpendicular dropped to the detection surface in the initial position a plane symmetrical with respect to a plane parallel to the rotational axis in the initial position of the device under test, the detection surface side end portion first and second overlapping part of the Turning the two-dimensional detection means to a position by a turning mechanism;
Capturing a projected image of each angular phase at each imaging position after turning;
The rotating means so that a portion of the object to be inspected that is not projected onto the detection surface at the first and / or second position is projected onto the detection surface at the first and / or second position. Are moved by a moving mechanism to the regions opposite to the first and / or second positions, respectively, with the surface being held while maintaining the same distance as the distance from the X-ray focal point to the rotation axis at the initial position;
Changing the initial angle phase of the rotating means based on the amount of movement of the rotating means;
Capturing a projected image of each angular phase of the object to be inspected on the rotating means after movement at the first and second positions;
The projection image of each angular phase obtained at each imaging position is projected onto the virtual cylindrical surface, the reconstruction calculation is performed from the projection image obtained by the projection , and the internal structure data of the inspection object is reconstructed the method comprising the steps of,
X-ray tomographic imaging method that have a. A projection image obtained by imaging the object to be inspected at each angular phase at each imaging position obtained by the control means on the pixels in the horizontal direction of the two-dimensional detection means is used as a rotation axis of the object to be inspected. A parallel straight line passing through the X-ray focal point is a central axis, and the total number of pixels in the horizontal direction is equal to the total number of pixels in the horizontal direction of the two-dimensional detection unit on the two-dimensional detection unit. Project one or more equivalent pixel information while sampling well.
Reconstruction calculation is performed using the projection images obtained by combining the projected images, and the internal structure data of the object to be inspected is reconstructed.
The X-ray tomographic imaging method according to claim 3.

Images