JP2005037193A - Imaging method and system for computerized tomography - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To propose an imaging technique for computerized tomography, which rapidly computes the optimal parameter used in a reconstruction computation process for internal structure data of a body to be inspected and can obtain the internal structure data with high sharpness by using the parameter. <P>SOLUTION: The system is provided with an X-ray source, a two-dimensional detecting means and a rotatable base section for the inspected body disposed between the X-ray source and the detecting means. The internal structure data are reconstructed from the projection images of the inspected body obtained at every angular displacement, and pixel data on a line perpendicular to the axis of the rotation of the inspected body are read from the projection images of the respective angular displacements, and an offset value of the rotation axis of the inspected body from the perpendicular line, which is dropped from the X-ray focal point to the detecting means, is set as the parameter used in the reconstruction computation process, and the pixel data at respective angular displacements are subjected to the reconstruction computation process while changing the parameter to obtain a plurality of images, and sharpness values are calculated respectively. When the maximum sharpness value is detected, the value of the parameter is specified as the optimal offset value of the rotation axis, and the internal structure data of the inspected body are reconstructed in consideration of the optimal offset value of the rotation axis. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a computer tomography method and apparatus for inspecting the internal structure of an object to be examined using X-rays or the like.
[0002]
[Prior art]
In the field of research and development such as semiconductor elements, non-destructive three-dimensional analysis is required to inspect cracks, disconnections, and the like that exist inside a minute 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).
[0003]
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 light-receiving surface of the detection means and placed between the detection means and the detection means A rotating base that rotates at an angular displacement based on the image, and a transmission X-ray projection image of the object to be inspected is picked up by a two-dimensional detection means and processed as a plurality of image data for each angle phase, By reconstructing the internal structure data from the image data, the inside of the inspection object can be easily inspected and observed.
[0004]
In the calculation for reconstructing the internal structure data described above, when the object to be inspected rotates around the rotation axis perpendicular to the perpendicular drawn from the X-ray focal point to the light receiving surface of the two-dimensional detection means, The internal structure data after the reconstruction calculation is blurred and the image quality is deteriorated. Therefore, the multiple projected images are divided into multiple parts, reconstructed and calculated, the images of the obtained partial projected images are compared, and the internal structure data is used using a set of projected images with higher sharpness. Has been proposed (see, for example, Patent Document 1).
[0005]
[Patent Document 1]
JP-A-2000-217810 [0006]
[Problems to be solved by the invention]
Further, when the internal structure data with higher sharpness is desired, the distance of the rotation center axis position of the object to be inspected with respect to the perpendicular drawn from the X-ray focal point to the light receiving surface of the two-dimensional detection means, that is, the deviation amount of the rotation center axis is calculated. Need to know exactly. If there is a difference between the rotation center axis deviation and the rotation center axis deviation given as a correction parameter during the actual reconstruction calculation, the internal structure data, which is the result of the reconstruction calculation, will be blurred, resulting in loss of clarity. This causes a problem that the image quality deteriorates. Possible causes of the above-described difference in rotational center axis deviation include mechanical position measurement errors and errors associated with X-ray focal point movement.
[0007]
As a method of calculating the rotation center axis deviation amount of the object to be inspected, for example, a standard inspection object (also referred to as a phantom model) such as a vertically attached thin wire is used as the object to be inspected. The rotation center axis deviation is calculated from the projection image obtained by imaging while rotating it, and this reference inspection object is replaced with the inspection object and imaged, and the rotation calculated by the reference inspection object There is a method of performing reconstruction calculation of internal structure data of an object to be inspected using the center axis deviation amount. However, there is a problem that it takes time to image the reference inspection object, and there is also an influence of a placement replacement error between the reference inspection object and the inspection object.
[0008]
In view of such a point, the present invention can calculate the optimum parameter at the time of reconstruction calculation of the internal structure data of the object to be inspected in a short time, and obtain the internal structure data with high sharpness using the parameter. We propose a computer tomography technique that can do this.
[0009]
[Means for Solving the Problems]
The present invention places an X-ray source, a two-dimensional detection means for imaging a transmission X-ray of the inspection object, and an inspection object placed between the X-ray source and the two-dimensional detection means. A rotation base portion that rotates at a predetermined angular displacement, and reconstructs the internal structure data from the projected image of the object to be inspected at each angular displacement, and is a projected image captured at each angular displacement. The pixel data on a line orthogonal to the rotation axis of the object to be inspected is read, and the distance between the perpendicular drawn from the X-ray focal point of the X-ray source to the two-dimensional detection means and the rotation center axis position of the object to be inspected Is set as a parameter at the time of reconstruction calculation, the pixel data of each angular displacement is changed by this reconstruction parameter by the reconstruction means to calculate a plurality of cross-sectional images, Calculate the sharpness of each cross-sectional image, and this sharpness will be the maximum. Identified as the optimum rotation center axis shift amount parameter value when, to reconstruct the internal structure data of the inspection object by considering the optimum rotation center axis shift amount.
[0010]
According to the present invention, reconstruction is performed while changing the rotation center axis deviation amount as a parameter at the time of reconstruction calculation from pixel data for a certain line of the projection image of the object to be inspected imaged at each angular displacement. Calculate the cross-sectional image and specify the amount of rotation center axis deviation when the sharpness of the cross-section image is maximum as the optimum rotation center axis deviation amount. Can be obtained easily and simply.
[0011]
Further, in the above-described case, in the present invention, when pixel data on a line orthogonal to the rotation axis of the inspection object is obtained from the projection image of the inspection object captured at each angular displacement, the height of the line is obtained. By changing the position, from the relationship between the height position of this line and the optimum rotational center axis deviation amount calculated from this cross-sectional image at each line height position, the inspection object of this two-dimensional detection means An angular deviation amount with respect to the rotation center axis is calculated, and the internal structure data is reconstructed from the projection image of the inspection object in consideration of the angular deviation amount.
[0012]
According to the present invention, the height position of the line on the pixel data of the projection image is changed, and the height position of the line and the optimum rotation center axis deviation amount calculated from the cross-sectional images at the respective line height positions. From the relationship, the amount of angular deviation of the two-dimensional detection means relative to the rotation center axis of the object to be inspected is calculated, so that the inclination of the two-dimensional detection means can be corrected based on the amount of angular deviation.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example of an embodiment of a computer tomographic imaging apparatus to which the computer tomographic imaging method of the present invention is applied will be described with reference to FIGS.
[0014]
1A and 1B are schematic views of an example of an X-ray tomographic imaging apparatus used for industrial use, for example, nondestructive inspection for inspecting an internal structure of a micro-inspection object such as a semiconductor element. In the figure, reference numeral 1 denotes a known X-ray source (X-ray generator) that generates, for example, cone-beam X-rays and irradiates the entire inspection object 7, and is irradiated from the X-ray tube 1 of the X-ray generator. A projection image of the inspection object 7 is picked up by X-rays, and the transmission X-rays of the inspection object 7 are captured by the X-ray two-dimensional detector 2 as a two-dimensional detection means to obtain a projection image.
[0015]
The X-rays irradiated from the X-ray tube 1 are configured to form a minimal X-ray focal point having a focal size of 1 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 smaller because damage of a minute size or the like can be observed.
[0016]
The X-ray two-dimensional detector 2 is constituted by, for example, a flat panel detector (FPD), and X-ray two-dimensional detection is performed so that a perpendicular line dropped from the focal point of the X-ray is irradiated to the center of the X-ray two-dimensional detector 2. The Y / Z ′ axis drive mechanism 14 can adjust the left / right / up / down movement.
[0017]
The FPD is specifically disclosed as an example in JP-A-6-342098. X-rays transmitted through the object are absorbed by the photoconductive layer to generate charges according to the X-ray intensity, and the amount of charges is detected for each pixel. As an example of another type of FPD, as disclosed in JP-A-9-90048, X-rays are absorbed by a phosphor layer such as an intensifying screen to generate fluorescence, and the intensity of the fluorescence is photoelectrically converted. Some devices detect it. There are other methods for detecting fluorescence, such as a method using a CCD or C-MOS sensor.
[0018]
In particular, in the FPD of the method disclosed in the above-mentioned 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 of sharpness in the FPD and an image with excellent sharpness can be obtained. . As described above, the X-ray two-dimensional detector 2 of the present embodiment may be any device that can capture radiation such as X-rays and process it for each pixel by some means to obtain an image signal.
[0019]
Reference numeral 3 denotes an entire rotation base (hereinafter referred to as a rotation base) composed of a rotation base on which the inspection object 7 is placed, a motor for rotating the rotation base, a bearing described later, and the like. The rotary base 3 is provided with a Z-axis drive mechanism 3a for moving the rotary base 3 in the direction parallel to the rotation axis of the rotary base 3, that is, in the Z-axis direction as shown in FIG. 1B. Moreover, the Y-axis drive mechanism 6 for moving the to-be-inspected object 7 to the Y-axis direction is provided. The inspected object 7 is held and fixed by a holding jig 8 on the rotary base.
[0020]
This rotary base 3 is supported by an air bearing described later, and is directly connected to the air bearing coaxially and has an angular positioning accuracy of 0.2 minutes or less, and a servo motor and a rotational phase detection means (not shown) At each angular displacement corresponding to the resolution of the servo motor and the rotational phase detection means, the servo motor is stationary in synchronism with the projection data capturing period necessary for reconstruction.
[0021]
Reference numeral 4 denotes a bearing of the inspection object rotation base. The axis of rotation of the bearing 4 is orthogonal to a perpendicular drawn from the focal point of the X-ray tube 1 to the vicinity of the center of the X-ray two-dimensional detector 2. In this example, the bearing 4 is composed of an air bearing capable of controlling the rotational base 3 with a minute angular displacement. However, the bearing 4 is not limited to this. That's fine.
[0022]
Reference numeral 5 denotes an XY table that mounts the X-ray tube 1 of the X-ray source and moves on a plane orthogonal to the rotation axis of the bearing 4. The turning radius of the inspected object 7 is appropriately fed back to the XY table 5, and projection data can be acquired in a state where the inspected object 7 and the XY table 5 are in close proximity as necessary. The top element that controls the enlargement factor is the distance between the X-ray focal point and the inspected object 7 held on the rotating base 3. If the enlargement factor is large, the internal structure of a finer part is analyzed. It becomes possible to do.
[0023]
Reference numeral 10 denotes an anti-vibration table on which all the devices, members, and the like that constitute the X-ray tomographic imaging apparatus described above are mounted and vibrations are removed so that no error occurs in the irradiation position. Reference numeral 11 denotes a shield cover made of lead or the like that covers the whole so that X-rays such as X-rays do not leak outside from the X-ray tomographic imaging apparatus.
[0024]
FIG. 2 is a configuration diagram of the X-ray tomographic imaging apparatus of this example. First, X-rays are irradiated from the X-ray tube 1 constituting the X-ray source to the object 7 to be inspected placed on the rotary base 3. The intensity, focus size, etc. of the X-rays irradiated at this time are controlled by a control console 22 as control operation means through an X-ray control unit 20 as X-ray control means.
[0025]
The position, rotation angle pitch, initial rotation angle, and the like of the rotation base 3 are controlled through a mechanism control unit 21 which is a mechanism control means for controlling the movement of the rotation base 3 and the XY stage 5 on which the X-ray source 1 is mounted. It is controlled by the desk 22. The inspected object 7 placed on the rotating base 3 is rotated by an angle designated by the control console 22, and the projected image is taken by the X-ray two-dimensional detector 2.
[0026]
The control console 22 is described later according to a GUI (Graphical User Interface) having input means such as a keyboard and a mouse, and display means for displaying device operation states and input values, information processing, and a program stored in a ROM (not shown). It comprises control means such as a processor for performing predetermined control. Information such as the X-ray intensity from the X-ray tube 1 is taken into the control console 22 and displayed on this display means, or an appropriate positioning of the object 7 to be inspected with respect to the rotating base 3 and the two-dimensional detector 2 is performed. Output commands.
[0027]
X-rays transmitted through the inspection object 7 are detected by an X-ray two-dimensional detector 2 such as an FPD. Then, the X-ray two-dimensional detector 2 supplies a projection image, which is detected X-ray information, to a projection image storage unit 23 as a projection image storage means, and this projection image is digitally transmitted according to an instruction from the control console 22. Projected projection data is stored in the projection image storage unit 23 composed of a large-capacity magnetic recording device or the like corresponding to information such as the rotation angle at the time of imaging, the initial rotation angle, and the X-ray intensity. The projection image storage means 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 means including removable recording media such as optical disks and semiconductor memories can be applied.
[0028]
The projection data stored in the projection image storage unit 23 is supplied to a reconstruction calculation computer 24 as reconstruction means connected thereto. The reconstruction calculation computer 24 reconstructs internal structure data from the input projection data, and the reconstructed internal structure data is stored in the projection image storage unit 23 or an external recording medium, and is not shown. The data is input to the reconstruction result display device 25 which is a display means via the display memory, and is displayed on a display such as a CRT monitor. The computer 24 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 22. Further, the display means of the reconstruction result display device 25 may be shared with the display means of the control console 22.
[0029]
With the configuration as described above, the internal structure data of the inspection object 7 is input to the reconstruction result display device 25 and the internal structure is displayed, and defects such as cracks and disconnection inside the inspection object such as minute electronic component elements are displayed. The presence or absence can be visually confirmed.
[0030]
In the calculation for reconstructing the internal structure data of the tomographic imaging process of the X-ray tomographic imaging apparatus described above, the rotation center axis of the inspected object 7 with respect to the perpendicular drawn from the X-ray focal point to the light receiving surface of the X-ray two-dimensional detector 2 The distance to the position, that is, the rotation center axis deviation amount (hereinafter referred to as deviation amount) will be described.
[0031]
3A is a diagram for explaining the amount of rotation center axis deviation of the inspection object 7 shown in FIG. 1, and FIG. 3B is an enlarged view of the main part of FIG. 3A. Reference numeral 30 denotes a rotation position region of the rotation center axis of the inspection object 7, in other words, an example of a range of rotation center axis deviation. As shown in the figure, on the plane perpendicular to the rotation center axis of the inspection object, the focal position of the X-rays irradiated from the X-ray source is Xs, and the inspection object 7 is irradiated with cone-beam X-rays. Thus, a projected image p (q, β) for each angular displacement of the inspection object 7 rotating around the point O is displayed on the X-ray two-dimensional detector 2 on the axis q. Β represents a rotation angle from the initial position at the start of imaging.
[0032]
In the reconstruction calculation for calculating the internal structure data of the inspection object from the projection image of the inspection object for each angular displacement, the focal position Xs of the X-ray source, the rotation center position O of the inspection object 7, and the two-dimensional X-ray Ideally, the point Q that is the position of the center position (q = 0) of the light receiving surface of the detector 2 is on a straight line (at this time, the straight line XsQ and the q axis are perpendicular to each other). If they are not aligned on a straight line due to a mechanical position accuracy error or the like, reconstruction calculation considering the deviation Δd from the ideal rotation center position O ′ of the object to be inspected shown in the enlarged view of the main part in FIG. 3B may be performed. .
[0033]
If the value of the deviation amount Δd is not accurately obtained, the resulting internal structure data of the inspected object will be blurred. Therefore, in this example, as shown in FIG. 4, the shift amount Δd is calculated from a pixel profile representing a transmission X-ray distribution for one line of the projected image (hatched portion) of the object to be inspected at each angular displacement. The reconstruction calculation is performed while changing the numerical value as a parameter for the reconstruction calculation.
[0034]
The principle of the computer tomography method of the present invention will be described with reference to FIG. As shown in FIG. 5A as an example of a screw, the inspection object 7 placed on the rotation base 3 is rotated, and the inspection object is irradiated with X-rays while rotating at a predetermined angular displacement, for example, at a pitch of 1 degree. Then, for example, 360 projection images for one rotation of the object to be inspected are acquired. Next, as shown in the left diagram of FIG. 5B, the line-shaped image data cut at a certain height of these 360 projected images is corrected by the shift amount Δd, and reconstructed and calculated. A cross-sectional image of the inspection object is calculated. Further, a plurality of cross-sectional images are obtained by changing the set value of the shift amount Δd, the degree of blur of each image is determined from the plurality of cross-sectional images, and when a shift amount that can obtain an image with the highest sharpness is found, the shift amount By reconstructing the internal structure data for the entire object to be inspected, optimum internal structure data with high sharpness can be obtained.
[0035]
It can be seen that when the value of the shift amount Δd is changed, the calculated cross-sectional image becomes clear or blurred. FIG. 6 shows a cross-sectional image of a screw as an example of an object to be inspected. When Δd = 7.38 μm, the blur portion is small, and the blur portion increases as the value of Δd increases. Represents. The degree of blurring of the cross-sectional image is evaluated as the sharpness using, for example, the standard deviation value of the image, the deviation amount Δd and the sharpness are plotted, and the deviation amount when the sharpness is maximized (d is the optimum rotation center). The axis deviation amount is Δd _{0. When} the sharpness of the image is high, the standard deviation is large, and when the sharpness is low, the standard deviation is small.
[0036]
FIG. 7 shows the relationship between the rotation center axis deviation amount parameter (Δd) of each cross-sectional image of the internal structure data shown in FIG. 6 and the sharpness. In the example of FIG. 7, the sharpness becomes the highest when the value of the rotation center axis deviation amount is 7.38 μm, and this value is set as the optimum rotation center axis deviation amount Δd ₀ . In this example, the optimal rotation center axis deviation amount Δd ₀ is automatically calculated by the control means. For example, the control means approximates the numerical value of the rotation center axis deviation amount Δd from past statistical data. The optimum rotational center deviation amount Δd ₀ may be calculated by calculating the sharpness of the corresponding cross-sectional image while attaching the mark.
[0037]
After the value of the optimum rotation center axis deviation amount Δd ₀ is found, the internal structure data is reconstructed using the entire projection image for each angular displacement.
[0038]
FIG. 8 is a flowchart showing the flow of the computed tomography method using X-rays of this example. The rotation base 3 on which the inspection object 7 is placed is rotated, and a projection image of the inspection object 7 is captured by the X-ray two-dimensional detector 2 at every predetermined angular displacement, and stored in the projection image storage unit 23. A pixel profile for one line at a certain height is read from the obtained projection image for each angular displacement (step S1). The initial rotation center axis deviation is set to Δd (step S2).
[0039]
The initial rotation center axis deviation amount is a value calculated so that the focal position of the X-ray source, the rotation center of the inspection object 7 and the center position of the light receiving surface of the X-ray two-dimensional detector 2 are in a straight line. Although it is desirable in terms of shortening the time to convergence, Δd = 0 may also be used. The reconstruction calculation computer 24 performs reconstruction calculation using the initial rotation center axis deviation amount parameter Δd, generates a cross-sectional image (step S3), and calculates the sharpness of the cross-sectional image (step S4). Δd is changed (Step S6), and Steps S3 to S4 are repeated. When the sharpness reaches a maximum value that does not change any more, the rotation center axis deviation amount Δd at that time is determined as the optimum rotation center axis deviation amount. Δd ₀ is set (step S5), and the reconstruction calculation is performed with the Δd ₀ to generate internal structure data of the entire object to be inspected (step S7).
[0040]
As described above, the internal structure data of the inspection object 7 reconstructed based on the optimum rotation center axis deviation amount Δd ₀ is input to the reconstruction result display device 25 to display the internal structure with high sharpness. It is possible to visually confirm the presence or absence of defects such as cracks and disconnections inside the object to be inspected, such as minute electronic component elements.
[0041]
According to this example, the rotation center axis deviation amount is changed as a parameter at the time of reconstruction calculation from pixel data for one line of the projected image of the inspection object 7 imaged for each angular displacement. Since the configuration calculation is performed and the rotation center axis deviation amount when the sharpness is maximized is identified as the optimum rotation center axis deviation amount, the value of the optimum rotation center axis deviation amount can be obtained quantitatively. In addition, the internal structure data can be corrected in the calculation based on the value of the rotation center axis deviation amount. As a result, the internal structure data of the inspected object 7 can be reconstructed and the definition of the internal structure data of the inspected object 7 can be improved. Can be improved.
[0042]
The reconstruction calculation, for example, currently requires about 10 minutes to calculate the internal structure data of the inspected object having a size of (512 × 512 × 512), but calculates a cross-sectional image of (512 × 512). It takes about 20 seconds to do this. Therefore, it has become possible to calculate the optimum rotation center axis deviation amount Δd ₀ in a short time by a method of comparison using the sharpness of a plurality of cross-sectional images in which the rotation center axis deviation amount Δd is changed.
[0043]
Next, as shown in FIG. 9A using a screw as an object to be inspected, for example, the height position of the line for acquiring the pixel profile of the projection image for each angular displacement is set to h1, h2, h3 from the upper side of the projection image, for example. Then, the height position of the plurality of lines and the change of the optimum rotation center axis deviation amount calculated by the reconstruction calculation from the pixel profile acquired at each height position are plotted.
[0044]
Originally, the straight line from the X-ray focal point passing through the rotation center axis of the object to be inspected to the X-ray two-dimensional detector is vertical, so it can be calculated at any height position on the projection image. The optimum center axis deviation to be performed should be constant, but may vary depending on the height position of the line.
[0045]
FIG. 9B shows the relationship between the height position of the line on the projection image and the optimum rotation center axis deviation amount. In this example, when the height position of the line on the projected image was changed by 1000 pixels to h1, h2, and h3, the optimum rotation center axis deviation amount changed by about 0.25 μm. This is considered to be caused by the fact that the X-ray two-dimensional detector 2 is inclined with respect to the rotation center axis of the inspection object 7. For example, in this example, since the magnification of the projected image at this time is 200 times and the size per pixel of the X-ray two-dimensional detector 2 is 200 μm, the X-ray two-dimensional detector 2 is 2.5. It turned out that it inclined about x10 < ^-4 > rad. By correcting this inclination mechanically, artifacts generated during reconstruction calculation could be reduced.
[0046]
In this example, the projection image for each angular displacement is used to obtain the optimum rotation center axis deviation amount Δd ₀ , but the image is taken with one rotation of the object to be inspected for the purpose of shortening the time for generating the cross-sectional image. For example, a total of 360 projected images may be 180, and the number of projected images may be thinned out. However, there is a possibility that an error may occur more than when the value of the optimum rotation center axis deviation amount Δd ₀ is calculated without thinning out. Therefore, a method is also conceivable in which a rough rotation center axis deviation amount Δd ₀ is obtained from the thinned projection image, and then the calculation is performed without thinning out to calculate the value of the optimum rotation center axis deviation amount Δd ₀ .
[0047]
In the above-described example, the computer tomography method and apparatus using X-rays have been described. However, the present invention is not limited to X-rays, and other radiation that forms a micro focus is applied to an inspection body and transmitted through the inspection body. The present invention can be applied to a method for reconstructing internal structure data from a plurality of projection images picked up in this manner and an apparatus in which the method is used.
[0048]
Further, the present invention is not limited to the above-described embodiments, and various other configurations can be taken without departing from the gist of the present invention.
[0049]
【The invention's effect】
According to the present invention, the rotation center axis deviation amount is estimated from the pixel data for one line of the projection image of the object to be inspected imaged at each angular displacement, and is changed as a parameter at the time of reconstruction calculation. Reconstruction calculation is performed, and the rotation center axis deviation when the cross-sectional image has the maximum sharpness is specified as the optimum rotation center axis deviation. Therefore, the accurate rotation center axis deviation can be quantitatively and easily determined. Can be obtained. Therefore, correction is made based on the calculated value of the optimum rotation center axis deviation, and the reconstructed calculation of the internal structure data of the object to be inspected becomes clearer, improving the definition of the internal structure data of the object to be inspected. it can.
[0050]
Further, the height position of the line on the pixel data of the projection image is changed, and from the relationship between the height position of this line and the optimum rotation center axis deviation amount calculated from the cross-sectional image at each line height position, this When the amount of angular deviation of the two-dimensional detection means with respect to the rotation center axis of the object to be inspected is calculated, the inclination of the two-dimensional detection means can be corrected based on the amount of angular deviation. Therefore, in combination with the above-described optimum rotation center axis deviation amount, further refinement of the internal structure data of the object to be inspected can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic view of an X-ray tomographic imaging apparatus as an example of an embodiment of a computer tomographic imaging apparatus of the present invention, in which A is a top view and B is a side view.
FIG. 2 is a configuration diagram of the X-ray tomographic imaging apparatus of the present example.
FIG. 3 is a diagram for explaining rotation center deviation.
FIG. 4 is a diagram showing an example of a projected image and a pixel profile.
FIG. 5 is a diagram for explaining one embodiment of the present invention.
FIG. 6 is an example of a sectional view in the height direction of internal structure data.
FIG. 7 is a diagram showing a relationship between a rotation center deviation amount parameter and sharpness.
FIG. 8 is a flowchart for explaining the computed tomography method of the present invention.
FIG. 9 is a diagram showing an example of a relationship with the line height optimum rotation center axis deviation amount on the projected image.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... X-ray tube, 2 ... X-ray two-dimensional detector, 3 ... Rotary base part, 3a ... Z-axis drive mechanism, 4 ... Bearing, 5 ... XY table, 6 ... Y-axis drive mechanism, 7 ... Inspected object, 8 ... holding jig, 10 ... vibration isolation table, 11 ... shield cover, 14 ... X-ray two-dimensional detector Y'Z 'axis drive mechanism, 20 ... X-ray control unit, 21 ... mechanism control unit, 22 ... Control console, 23 ... Projected image storage unit, 24 ... Computer for reconstruction calculation, 25 ... Reconstruction result display device

Claims (4)

An X-ray source, a two-dimensional detection means for imaging a transmitted X-ray of the object to be inspected, and the object to be inspected disposed between the X-ray source and the two-dimensional detection means are placed at a predetermined angular displacement. A computerized tomography method for reconstructing internal structure data from a projected image of the object to be inspected for each angular displacement,
Read pixel data on a line perpendicular to the rotation axis of the object to be inspected from the projection image captured for each angular displacement,
A rotation center axis deviation amount, which is a distance between a perpendicular drawn from the X-ray focal point of the X-ray source to the two-dimensional detection means and the rotation center axis position of the object to be inspected, is set as a parameter at the time of reconstruction calculation;
A plurality of cross-sectional images are calculated by reconstructing the pixel data of each angular displacement by the reconstruction means while changing the parameters.
Calculating the sharpness of each of the plurality of cross-sectional images;
Specify the parameter value when the sharpness is maximum as the optimum rotation center axis deviation amount,
A computer tomography method characterized in that the internal structure data of the object to be inspected is reconstructed in consideration of the optimum rotation center axis deviation amount. The computer tomography method according to claim 1,
When obtaining pixel data on a line orthogonal to the rotation axis of the inspection object from the projection image of the inspection object captured at each angular displacement, the height position of the line is changed by changing the height position of the line. An angular deviation amount with respect to the rotation center axis of the object to be inspected by the two-dimensional detection means is calculated from the relationship between the vertical position and the optimum rotation center axis deviation amount calculated from the cross-sectional image at each line height position. ,
A computer tomography method characterized in that internal structure data is reconstructed from a projection image of the inspection object in consideration of the amount of angular deviation. An X-ray source, a two-dimensional detection means for imaging a transmitted X-ray of the object to be inspected, and the object to be inspected disposed between the X-ray source and the two-dimensional detection means are placed at a predetermined angular displacement. A computerized tomography apparatus for reconstructing internal structure data from a projected image of the object to be inspected for each angular displacement,
The pixel data on a line orthogonal to the rotation axis of the object to be inspected is read from the projection image picked up at each angular displacement, the perpendicular line dropped from the X-ray focal point of the X-ray source to the two-dimensional detection means, and the object to be detected. The rotation center axis deviation amount, which is the distance from the rotation center axis position of the inspection object, is set as a parameter at the time of reconstruction calculation, and the pixel data of each angular displacement is reconstructed by changing the parameter by the reconstruction means. Calculating a plurality of cross-sectional images, calculating the sharpness of each image of the plurality of cross-sectional images, comprising a control means for specifying a parameter value when the sharpness is maximized as an optimum rotation center axis deviation amount,
A computer tomography apparatus characterized in that the internal structure data of the object to be inspected is reconstructed in consideration of the optimum rotation center axis deviation amount. The computed tomography apparatus according to claim 3.
When obtaining pixel data on a line orthogonal to the rotation axis of the inspection object from the projection image of the inspection object imaged for each angular displacement, the control means changes the height position of the line, By changing the height position of the line, the relationship between the height position of the line and the optimum rotation center axis deviation amount calculated from the cross-sectional image at each line height position, the two-dimensional detection means Calculate the amount of angular deviation with respect to the rotation center axis of the inspection object,
A computed tomography apparatus which reconstructs internal structure data from a projection image of the object to be examined in consideration of the angular deviation amount.

Images