JP2003018463A - X-ray inspection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray inspection apparatus that eliminates a scattered X-ray component included in an X-ray image so as to obtain the X-ray image with high quality. SOLUTION: An X-ray grid 3 is placed between an X-ray tube 1 being an X-ray source and a subject 6. The scattered ray component included in the X-ray tube is calculated and eliminated on the basis of the amplitude of the interference fringes included in the X-ray image. The X-ray inspection apparatus can obtain an X-ray image, an X-ray fluoroscopy and X-ray CT image or the like with high quality in spite of less exposed dose.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation inspection apparatus using radiation such as X-rays and γ-rays, and more particularly to a non-destructive inspection and medical X-ray inspection apparatus.

[0002]

2. Description of the Related Art Conventionally, methods and apparatuses for removing various scattered X-ray components have been reported. For example, an X-ray grid having a grid frequency that is the same as the detection pixel pitch of the X-ray detector or that is a fraction of an integer is formed on the X-ray detector surface, and a scattered radiation component obliquely incident on the detector surface. Has been reported (Prior Art 1: "JP-A-9-7533").
No. 2 publication ").

A method of removing scattered X-ray components using a deconvolution filter based on a point spread function of scattered X-rays measured in advance has been reported (Prior Art 2: "M. Honda. , et al., Med. Phys., 20
(1), 56-69 (1993) ").

Further, an apparatus has been reported which directly measures scattered X-ray components by scanning an X-ray slit arranged in front of an object and removes the scattered X-ray components (Prior Art 3: "K. Doi, et al., Radiology, 161, 513-518
(1986) ”).

Further, there has been reported a method of obtaining a high-quality reduced image without moire when wavelet transform is applied to original image data having a periodic structure to obtain a reduced image (Prior Art 4: "Special Features"). Kaihei 10-031737 publication ").

Furthermore, a method has been reported in which an X-ray grid is arranged between an X-ray tube and an object to correct the radiation angle dependence of the X-ray quality and dose (Prior Art 5: Japanese Patent Laid-Open No. 200-200).
0-245731 ”).

[0007]

The scattered X-ray component occupies 50% or more of the signal component of the detected X-ray transmission image depending on the case, and the inspection device for nondestructive inspection and the X-ray inspection device for medical use. Reduce the contrast of.

In the prior art 1, since the X-ray transmitting material forming the X-ray grid blocks not only scattered X-rays but also direct X-rays, the amount of signal detected by the X-ray detector decreases. It had a problem of being lost. In order to increase the detection signal amount, it is necessary to increase the X-ray dose incident on the subject, and as a result, there is a problem that the X-ray exposure amount of the subject increases. In addition, there is a problem that scattered X-rays having a small incident angle to the detector cannot be removed and it is difficult to form an X-ray grid on the front surface of the detector.

In the prior art 2, the scattered X-ray correction is performed by measuring the point spread function of the scattered X-rays in advance for a uniform subject with a constant tube voltage. Further, the scattered X-ray correction is performed under the assumption that the composition of the subject is uniform. However, in actual photographing, the composition and thickness of the subject change variously, and the tube voltage also changes variously. Therefore, there is a problem that the scattered X-ray component cannot be completely removed and the accuracy of correction is poor.

The prior art 3 has a problem that it is not possible to perform short-time photography or X-ray fluoroscopy because photography is performed while scanning the X-ray slit.

The prior art 4 obtains a high-quality reduced image for observation, but does not mention the removal of scattered X-ray components contained in the original image.

In the prior art 5, since the radiation angle dependence of X-rays emitted from the rotating anode X-ray tube is reduced, a homogeneous and high-quality X-ray image can be obtained, but scattered X-ray components There is no mention of removal.

An object of the present invention is to provide an X-ray inspection method and an X-ray inspection method capable of obtaining an X-ray image in which scattered X-ray components have been removed from an image of an X-ray transmission image of an inspection object detected by a two-dimensional X-ray detector. It is to provide a line inspection device.

Another object of the present invention is to provide an X-ray inspection method and an X-ray inspection apparatus capable of obtaining a high-quality X-ray image while reducing the X-ray exposure amount of the inspection object.

[0015]

In order to achieve the above object, in the present invention, an X-ray grid is arranged between an X-ray source and an inspection object, and an X-ray transmission image of the inspection object is detected by two-dimensional X-ray detection. To detect with a vessel. The X-rays incident on the inspection target are slit-shaped X-rays that have passed through the X-ray grid. The X-ray transmitted through the inspection object has a slit-shaped high frequency component (direct X-ray component),
The non-slit low frequency component (scattered X-ray component) scattered by the inspection target is included. When the X-ray transmission image of the inspection object is detected by the two-dimensional X-ray detector, the direct X-ray component is 2
Interference fringes occur between the dimensional X-ray detector and the X-ray grid, but scattered X-ray components do not.

Now, when the position of the X-ray grid is changed by a small distance in a direction substantially orthogonal to the direction connecting the focal point of the X-ray source and the center of the detection surface of the two-dimensional X-ray detector, the phase of the interference fringes is changed. Changes. At this time, the amplitude of the interference fringe directly reflects the X-ray component amount. That is, the signal component that changes with the change of the position of the X-ray grid is the direct line component, and the signal component that does not change corresponds to the scattered X-ray component.

From the above, a distribution image of scattered X-ray components included in the image of the X-ray transmission image of the inspection object (hereinafter, scattered X-ray distribution image) can be obtained from the amplitude of the interference fringes. Also,
The scattered X-ray distribution image can be subtracted from the X-ray transmission image to directly obtain the X-ray distribution image. Hereinafter, the operation of obtaining the direct X-ray distribution image will be referred to as scattered X-ray correction.

In order to obtain the amplitude of the interference fringe, it is necessary to separate the measurement image into an image of the interference fringe component (hereinafter, interference fringe image) and an image of other components (hereinafter, non-interference fringe image). is there. In order to obtain an interference fringe image, two X-ray transmission images in which interference fringes having phases different by approximately 180 ° appear are detected and a differential image of the two X-ray transmission images may be created.
On the other hand, in order to obtain a non-interference fringe image, the phase is almost 1
It suffices to create an added image of two X-ray transmission images different by 80 °. However, the phase is almost 1 between the two X-ray transmission images.
In order to produce interference fringes that differ by 80 °, it is necessary to accurately control minute changes in the position of the X-ray grid.

On the other hand, two Xs whose phases differ by approximately 180 °
The line transmission image can also be created by the following method. In the following description, the grid density of the X-ray grid is such that the direct X-ray component is
The value is set so that interference fringes generated between the two-dimensional X-ray detector and the X-ray grid are less likely to occur (not noticeable). Also,
The direction in which the slits in the X-ray grid are arranged is called the slit arrangement direction.

From the X-ray transmission image, 1 in the slit arrangement direction.
An image (hereinafter referred to as an extracted image) is created by thinning out pixels every pixel. By extracting every other pixel, interference fringes are generated in the extracted image. Two extracted images are created. However, the two extracted images are created by shifting the pixel extraction positions by one pixel in the slit arrangement direction. At this time, the interference fringes appearing in the two extracted images are almost 180
° Has different phases. Therefore, an interference fringe image can be created by taking the difference between these two extracted images. Also,
Scattered X-ray correction can be performed based on the interference fringe image.

In the scattered X-ray correction, the amount of X-ray component is directly obtained based on the amplitude of the interference fringe. The amplitude of the interference fringe is directly proportional to the amount of the X-ray component, and the ratio (hereinafter, amplitude ratio) is obtained by measurement in advance. The amplitude ratio is obtained using an air image obtained when the inspection target is not placed. Air image,
3 is one or more air images detected by a combination of one or more tube voltages of the X-ray tube and one or more X-ray grids with different scattered X-ray removal rates. An interference fringe image is created for each air image using the same method as above. At this time, the amplitude ratio is obtained as the ratio of the direct X-ray component amount to the interference fringe amplitude. However, the direct X-ray component amount can be obtained as the signal amount of the air image itself.

The amplitude ratio changes depending on the position in the air image. Therefore, the distribution of the amplitude ratio is created as a calibration image and stored in the memory. To create the calibration image, first, an interference fringe image is created for the air image. Next, an amplitude distribution image of interference fringes is created based on the interference fringe image. Finally, an image created by dividing each pixel value of the air image by the pixel value of the amplitude distribution image is used as a calibration image.

The procedure for performing scattered ray correction on an arbitrary X-ray transmission image using the calibration image is as follows. First, an interference fringe image is created for the X-ray transmission image (original image). Next, an amplitude distribution image of interference fringes is created based on the interference fringe image. Further, the calibration image is read from the memory, and the product of the calibration image and the amplitude distribution image is the X-ray transmission image (original image).
To obtain a scattered X-ray distribution image. Finally, the scattered X-ray distribution image is subtracted from the X-ray transmission image (original image) to directly create an X-ray distribution image.

When reading the calibration image from the memory, the tube voltage when the X-ray transmission image is detected, X
A calibration image corresponding to the combination of line grids is read from memory.

When almost the same portion of the inspection object is continuously detected, the same scattering X is obtained at a specific time interval.
The scattered X-ray component can be removed from the images of the plurality of X-ray transmission images by using the line distribution image.

A parallel grid or a focused grid can be used as the X-ray grid used in the above description.
Further, two parallel grids or a cross grid in which focused grids are crossed and placed one on the other can be used.

As described above, according to the present invention, the scattered X-ray correction can be accurately executed by the simple arithmetic processing.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIG. 1 is a diagram for explaining the configuration of an X-ray inspection apparatus according to a first embodiment of the present invention. In FIG. 1, the horizontal direction in the plane of the paper is the y-axis, the vertical direction in the plane of the paper is the z-axis, and the direction perpendicular to the plane of the paper is the x-axis.

The X-ray inspection apparatus according to the first embodiment includes an X-ray tube 1, a collimator 2, an X-ray grid 3, a flat X-ray detector 4, a column 5, an object (inspection object) 6, and a bed top plate. 7, bed 8, monitor 9, console 10, clinical console 11,
Image memory 100, image processing means 101, calibration image storage memory 102, scattered radiation image storage memory 1
03 and the like. Known devices and mechanisms are used. Hereinafter, a system including the X-ray tube 1, the collimator 2, the X-ray grid 3, and the planar X-ray detector 4 is referred to as an imaging system.

The photographing system is fixed to the column 5. The column 5 can be tilted with respect to the bed top 7 by a tilting mechanism (not shown). However, the tilt direction is parallel to the yz plane. By inclining the pillar 5, the X-ray irradiation direction on the subject 6 can be freely changed. The bed 8 can move the position of the bed top 7 and the subject 6 placed on the bed top 7 in the x, y, and z directions by a known moving mechanism. X-ray grid 3
The position in the x, y and z directions with respect to the column 5 can be adjusted by a position adjusting device (not shown).

In FIG. 1, the distance between the X-ray generation point of the X-ray tube 1 and the input surface of the flat X-ray detector 4 is 100 cm. Moreover, the X-ray input surface of the flat panel X-ray detector 4 has two sides.
It is a square of 04.8 mm. The number of pixels of the flat panel X-ray detector 4 is 1024 × 1024 pixels, and each pixel has 1 pixel.
The side size is 200 μm. The typical frame rate of the flat panel X-ray detector 4 during X-ray fluoroscopy is 3
Although it is 0 [frame / second], it can be 7.5 or 15 [frame / second]. A known direct type X-ray detector or indirect type X-ray detector is used as the plane type X-ray detector 4. Representative examples of direct type detectors and indirect type detectors include “M. Choquette, et a
l., SPIE Vol.3977, 128-136 (2000) "(hereinafter referred to as reference 1)
And `` Tom JC Bruijns, et al., SPIE Vol.3977,
117-127 (2000) ”(hereinafter referred to as Reference 2).

The distance between the X-ray generation point of the X-ray tube 1 and the input surface of the X-ray grid 3 is 40 cm. The X-ray grid 3 is a known grid, and a large number of slits are formed by alternately arranging the X-ray absorbing material and the X-ray transmitting material. The slit direction of the X-ray grid 3 is formed in only one direction, and the X-ray grid 3 is arranged on the column 5 so that the slit direction is parallel to the y-axis. In the present X-ray grid 3, lead is used as the X-ray absorbing material and paper is used as the X-ray transmitting material, but the material is not limited to these materials and, for example, tungsten and aluminum may be used instead. . The grid ratio (lattice ratio) is 12:
1, grid density is 70 [lines / cm], lead foil thickness is 5
It is 0 [μm]. Further, the X-ray grid 3 has a focal point, and its focal length is 40 [cm].

Next, the operation of the X-ray inspection apparatus according to the first embodiment will be described. The X-ray inspection apparatus acquires an X-ray fluoroscopic image and an X-ray radiographic image of the subject 6, removes the scattered radiation components contained in these images, and then displays them on the monitor 9.
The procedure from the irradiation of X-rays during X-ray fluoroscopy and X-ray imaging to the display of the scattered radiation corrected image is as follows.

First, the inspector (operator) is the console 10
Alternatively, the start of X-ray fluoroscopy or imaging is instructed using the clinical console 11, and X-rays are emitted from the X-ray tube 1. Next, the X-rays transmitted through the subject 6 are detected by the flat panel X-ray detector 4 and immediately recorded in the image memory 100. Further, the image processing means 101 is configured to display the X stored in the image memory 100.
Only the scattered ray component in the transmitted ray image is extracted and stored in the scattered ray image storage memory 103. Finally, the subtractor 104 subtracts the scattered radiation component image stored in the scattered radiation image storage memory 103 from the X-ray transmission image stored in the image memory 100 to create a scattered radiation corrected image, and displays it on the monitor 9. . X
During fluoroscopy, the series of operations described above is repeated until the examiner gives an instruction to end fluoroscopy.

At this time, the scattered ray component image is stored in the image memory 1.
It may be created each time an X-ray fluoroscopic image is input to 00,
It may be created every few frames (usually 2 to 30 frames). If you want to create scattered ray component image every few frames,
Until the next scattered ray component image is created, scattered ray correction is approximately performed using the same scattered ray component image. In the following, such a near-term correction method during fluoroscopy is referred to as thinning correction. When the movement of the subject 6 is not so large with respect to the frame rate of the flat panel X-ray detector 4, thinning correction can be performed. By adopting the thinning-out correction, the processing speed required for the image processing means 101 can be reduced, so that the apparatus configuration can be simplified.

A calibration image stored in the calibration image storage memory 102 is used to extract the scattered radiation component. Details of the scattered radiation component extraction calculation by the image processing unit 101 and the calibration image will be described later.

FIG. 2 is a diagram for explaining the principle of removing scattered X-rays. Of these, FIG. 2 (A) is a diagram showing the relationship between the direct X-rays passing through the subject 6 and the flat panel X-ray detector 4, and FIG. 2 (B) is scattered inside the subject 6. It is a figure showing the relationship between the scattered X-rays and the flat panel X-ray detector 4.

First, in FIG. 2A, an X-ray generation point 2
A uniform X-ray 200 generated from 0 is generated by the X-ray grid 3
It is partially blocked by the X-ray absorbing material 21 inside. Therefore, the X-rays that have passed through the X-ray grid 3 become slit-shaped X-rays 201. Hereinafter, such a slit-shaped X-ray 201 is referred to as a modulated X-ray. The modulated X-ray 201 is a substantially rectangular X-ray beam, and has a high-frequency signal component itself. Therefore, the X-rays (direct X
The line) causes interference with the pixel 22 of the flat panel X-ray detector 4 to generate an interference fringe (moire). On the other hand, FIG.
In (B), the X-rays (scattered X-rays) 202 scattered inside the subject 6 do not generate interference fringes with the pixels 22 because high-frequency signal components are lost due to scattering.

From the above, it can be seen that the interference fringe reflects only the direct X-ray, and the amplitude of the interference fringe is proportional to the amount of the direct X-ray component. Therefore, by obtaining the amplitude of the interference fringes, the detection signal can be directly separated into the line component and the scattered line component to perform the scattered line correction. However, to perform scattered ray correction,
It is necessary to solve the following two problems. That is, to obtain the ratio of the amplitude of the interference fringe and the direct X-ray component (problem 1)
And to obtain the amplitude of the interference fringe (problem 2).

Regarding the problem 1, the ratio of the amplitude of the interference fringes to the direct line component (hereinafter referred to as the calibration ratio) is determined by using an X-ray transmission image (hereinafter referred to as an air image) detected in a state where the subject 6 is not placed. Can be asked. That is, since the signal included in the air image includes only the direct line component, if the amplitude of the interference fringe can be obtained, the calibration ratio can be easily obtained.

Regarding the problem 2, for example, the X-ray grid 3
The amplitude of the interference fringe can be obtained by observing the phase change of the interference fringe while slightly moving the position of in the horizontal direction. However, the above method involves a technical difficulty of moving the X-ray grid 3 at high speed and with high accuracy. For this reason, in the first embodiment, a method of measuring the amplitude of the interference fringes by thinning out pixels is adopted. Details of the thinning sampling will be described later.

FIG. 3 is a diagram for explaining the positional relationship between the X-ray grid 3 and the planar X-ray detector 4. The distance from the X-ray generation point 20 to the input surface of the X-ray grid 3 is d,
The distance from the X-ray generation point 20 to the input surface of the flat panel X-ray detector 4 is represented by D. The value of d in the first embodiment is 40 [c
The values of m] and D are 100 [cm]. X-ray grid 3
The slit direction of is arranged so as to be parallel to the y-axis direction.

The X-ray detector 4 is arranged so that the pixel array is parallel to the x and y directions. Pixel array x
The positions in the and y directions are defined as the i and j directions, respectively, and the positions are expressed as (i, j) (i, j = 0, 1, ..., 1023). Also,
In the following description, an acrylic phantom 30 is used as the subject 6 for simplicity. However, acrylic phantom 3
0 is composed of an acrylic plate and a lead rod 31. Lead bar 31
Is arranged at the center of the acrylic plate such that its longitudinal direction is parallel to the y direction.

FIG. 4 is a diagram for explaining the detection pixel position in the detection of an X-ray transmission image by the flat panel X-ray detector 4. As shown in FIG. 4A, the X-ray detector 4
The pixel spacing in the i and j directions is indicated by Δd. However, this Example 1
In, Δd is 200 [μm]. During fluoroscopy and X-ray imaging, X-rays are detected at all pixel positions (i, j). An example of the profile of the detected image is shown in FIG.
It shows in (B). However, FIG. 4B shows the profile of the acrylic phantom 30 in the i direction.
At this time, if the specifications and the spatial arrangement of the X-ray grid 3 are properly set based on the method described later, FIG.
As shown in (B), the interference fringes generated in the profile in the i direction can be suppressed to be small. The signal shown in FIG. 4 (B) is obtained by simultaneously detecting the direct X-ray component as shown in FIG. 4 (C) and the scattered X-ray component as shown in FIG. 4 (D). The scattered radiation correction process is shown in FIG.
This corresponds to the process of extracting the direct X-ray component shown in FIG. 4C from the detection signal shown in FIG.

FIG. 5 is a diagram for explaining the relationship between the spatial frequency distribution of the direct X-ray component and the scattered X-ray component and the Nyquist frequency of the planar X-ray detector 4. The frequency component 500 of the direct X-ray includes the frequency characteristic of the modulated X-ray 201, the frequency characteristic of the direct X-ray passing through the subject 6, and the frequency response information of the flat panel X-ray detector 4. Generally, the frequency response of the flat panel X-ray detector 4 decreases as the frequency becomes higher. The frequency characteristic of the modulated X-ray 201 represents the structural information of the X-ray grid 3, and contains a lot of information about the grid period.

Now, assuming that the grid density is f _g [lines / cm], the projected grid density f _d projected on the plane of the flat panel X-ray detector 4 is expressed by the following equation.

[0047]

[Equation 1] (Equation 1) From (Equation 1), the value of f _d can be arbitrarily set by changing the values of f _g , d, and D. FIG. 5 shows an example in which the value of f _d is set slightly lower than the Nyquist frequency f _q of the detector. Frequency intensity 502 at frequency f _d
Becomes smaller as f _d approaches the Nyquist frequency f _q . This is due to the blurring of the flat panel X-ray detector 4, and periodic structure information of the X-ray grid 4 (hereinafter referred to as grid stripes).
Means to be unnoticeable. Where the difference between the Nyquist frequency f _q and the projected grid density f _d is the beat frequency
It is defined by the following formula as f _b .

[0048]

[Equation 2] ......... (number 2) That is, in order to obscure the grid pattern contained in the X-ray transmission image can be as small as possible f _b.
On the other hand, the frequency component 501 of the scattered X-ray contains only the information of the low frequency component.

FIG. 6 is a view for explaining thinning sampling for the detected X-ray transmission image. FIG. 7 is a diagram for explaining the relationship between the Nyquist frequency and the spatial frequency distribution of the direct X-ray component and the scattered X-ray component at the time of thinning sampling. As described in FIG. 4A, the X-ray transmission image is detected by using all the pixels of the flat panel X-ray detector 4. That is, if the signal amount detected at the pixel position (i, j) is f (i, j), the X-ray transmission image is f
It can be expressed as (i, j) (i, j = 0 to N-1). However,
N is the number of pixels of the planar X-ray detector 4 in the i and j directions. In the first embodiment, N = 1024. The thinning sampling is performed as shown in FIGS. 6 (A) and 6 (C).
This is a method of creating an image by extracting pixel values every other pixel in the i direction from j). At this time, the following two types of extracted images can be created depending on the extraction position of the pixel.

[0050]

[Equation 3] ……… (Equation 3)

[0051]

[Equation 4] ……… (Equation 4) Nyquist frequency f ′ in the m direction of f ₁ (m, n) and f ₂ (m, n)
_q (= 1 / (4Δd)) is the Nyquist frequency f of f (i, j)
It becomes half of _q (= 1 / (2Δd)). That is, _f'q = f
_q / 2. As shown in FIG. 7, the direct X-ray component 500 at the time of thinning sampling folds in line symmetry around f ′ _q to generate aliasing. In FIG. 7, 702 is the aliasing component of the direct X-ray component 500 due to aliasing, and 701 is the aliasing component of the scattered X-ray component 501 due to aliasing.

As a result, the component 50 of the projection grid density f _d
2 becomes the beat component 702 of the frequency f _b , appears on the low frequency side, and generates an interference fringe. Therefore, the extracted image f ₁ (m, n)
Interference fringes are included in the m-direction profile of f ₂ (m, n) (see FIGS. 6B and 6D).

As described above, in order to perform scattered radiation correction, the amplitude of the interference fringes may be measured. But the extracted image
Since f ₁ (m, n) and f ₂ (m, n) each include structural information of the subject 6 in addition to the interference fringe signal, the amplitude of the interference fringe component must be accurately extracted. Is difficult

In order to accurately extract the amplitude of the interference fringe component, the difference image s (m, n) of f ₁ (m, n) and f ₂ (m, n) is created by the following equation.

[0055]

[Equation 5] ... (Equation 5) As shown in (Equation 3) and (Equation 4), the sampling positions of f ₁ (m, n) and f ₂ (m, n) with respect to f (i, j) are i
They are offset from each other by one pixel. Therefore, f ₁ (m,
The interference fringes contained in n) and f ₂ (m, n) are 180 degrees out of phase with each other in the m direction. Therefore, the difference image s (m, n)
Includes only the interference fringe component as shown in FIG. 6E, so that the amplitude of the interference fringe can be easily obtained from s (m, n).

In the description using FIGS. 4 to 6, the projection grid density f _d is calculated from the Nyquist frequency f _q to the beat frequency.
It was set to a value lower by f _b (hereinafter referred to as non-aliasing setting). At this time, the frequency of the grid stripes appearing in the X-ray transmission image f (i, j) is f _d = (f _q −f _b ), and the extracted image f
The frequency of the interference fringes appearing in ₁ (m, n) and f ₂ (m, n) is f _b
Met. As mentioned above, it is necessary to make f _b as small as possible in order to make the grid stripes inconspicuous. However, at this time, the frequency f _{b of the} interference fringes is also reduced at the same time, and the position resolution is reduced. Thus, f _b must not be too large or too small. Usually f
_It is desirable to set _{b to} about 2 to 5 [lines / cm].

FIG. 8 is a diagram for explaining another method of setting the projection grid density. In the non-aliasing setting, the projection grid density f _d was set to a value lower than the Nyquist frequency f _q by the beat frequency f _b . On the other hand, a method of setting the projection grid density f _d to a value higher than the Nyquist frequency f _q by the beat frequency f _b (hereinafter referred to as aliasing setting) will be described below. When aliasing is set, aliasing also occurs in all pixel sampling. At this time, the frequency component 502 of the projection grid density f _d is a frequency (f _q −f _d ) due to aliasing.
The component 702 is observed (see FIG. 8A).

The value of frequency f _q −f _b is the same value as in the non-aliasing setting, but in the aliasing setting, grid fringes are observed as a folding component centered on f _q . The spectrum intensity is smaller than in the case of FIG. That is, by setting the aliasing, it is possible to make the grid stripes less noticeable than in the case of the non-aliasing setting.

On the other hand, also during thinning sampling, the frequency component 502 in the projection grid density f _d is observed as an interference fringe component of the frequency f _b by aliasing. However, since the spectrum intensity of this interference fringe component is also smaller than that in the case of non-aliasing setting, there is also a problem that the measurement accuracy of the interference fringe amplitude decreases. As mentioned above, the setting of the projection grid density gives priority to the suppression of grid stripes, or
The aliasing setting or the non-aliasing setting can be selected depending on whether the measurement accuracy of the interference fringe amplitude is prioritized.

In the first embodiment, the grid density f _{g is set} to 7
0 [lines / cm], X-ray generation point-grid distance d is 40
[Cm], X-ray generation point-detector distance D is 100 [cm]
Therefore, the projection grid density f _d is 28 [lines /
cm]. On the other hand, since the pixel interval Δd is 200 [μm], the Nyquist frequency f _q is 25 [lines / cm]. Therefore, the projection grid density is set to alias, and its beat frequency is 3 [lines / cm]. In order to set the projection grid density f _d to non-aliasing, for example, d may be 31.4 [cm] in the above setting. At this time, the projection grid density f _d is 22 [lines /
cm], and similarly interference fringes having a beat frequency of 3 [lines / cm] are generated.

FIG. 9 is a diagram for explaining a method for deriving the spatial distribution of the interference fringe amplitude based on the interference fringe image.
Difference image s (m, n) (m = 0 to N / 2-
1 and n = 0 to N-1) is an interference fringe image 9 including only interference fringe components.
It is 0 ((a) in FIG. 9). The interference fringe amplitude distribution calculation means 1104 is a means for obtaining the interference fringe amplitude distribution image 95 based on the interference fringe image 90, and comprises the following calculation procedure.

First, the interference fringe peak detecting means 91 detects the interference fringe 99 with respect to the profile of the interference fringe image 90 in the m direction.
The peak position (maximum value and minimum value) of is detected (Fig. 9
(B)). The peak detection in the above m direction is performed for all n (=
0 to N-1) position. Next, the peak-to-peak pixel interpolating means 92 connects the maximum values and the minimum values that are adjacent to each other in the m direction with a straight line to obtain an upper limit envelope 96 and a lower limit envelope 97 of the interference fringe 99 ((c) in FIG. 9). ).

Further, the above-mentioned interpolated value is obtained by pixel position m (= 0 to N /
2-1) Not only at the points above, but also at the intermediate position of pixels adjacent in the m direction. By obtaining the interpolated value at the intermediate position of the pixels, the number of pixels in the m direction, which was N / 2 after thinning sampling, can be returned to N again. The above interpolation is performed for all n (= 0 to N-1) positions. Since the position in the n direction coincides with the position in the j direction of all sampled images, the pixel matrix is re- (i, j) at the end of interpolation.
It can be returned to (i, j = 0 to N-1). Upper envelope 96
And the difference 98 between the lower limit envelope 97 and the lower limit envelope 97 corresponds to the amplitude of the interference fringe 99.

Therefore, the amplitude calculating means 93 then finds the difference 98 at all positions (i, j) (i, j = 0 to N-1) to obtain the interference fringe amplitude distribution at each position (in FIG. 9). (D)). However, since the interference fringe distribution includes high-frequency components generated by the linear interpolation, the two-dimensional LPF
High frequency components are removed using the (Low Pass Filter) 94 to obtain a final amplitude distribution image A (i, j) ((e) in FIG. 9). As an example of the two-dimensional LPF 94, known moving average processing (pixel area for moving average: 2 × 2 pixels to 5 ×
5 pixels) or the like.

FIG. 10 is a diagram for explaining another sampling method in thinning sampling. In FIG. 6, a method of extracting pixels every other pixel in the i direction as the thinning sampling is shown, but the extraction interval may be generally expanded every k pixels (1 ≦ k). As an example, FIG. 10 shows an example in which every two pixels are extracted. In this case, there are three kinds of extraction methods as shown in FIGS. 10A to 10C, and every time the sampling position is shifted by one pixel in the i direction, the phase shift of the interference fringes generated by the thinning sampling is 120. Change.

That is, the phase shift of the interference fringes between FIGS. 10A and 10B and between FIGS. 10B and 10C is 120 degrees. Further, the phase shift of the interference fringes between FIGS. 10A and 10C is 240 degrees. In either case, when the difference image of both images is created, the structural information of the subject in the signal can be removed and only the interference fringes can be extracted.

The phase of the interference fringes extracted changes according to the phase shift amount between the images for which the difference is taken, but the amplitude distribution does not change. That is, FIG. 10A to FIG.
Even if the difference image is created for any combination of (C), the interference fringe amplitude distribution calculation means 1 in FIG. 11 described later.
Amplitude distribution image A (i, j) finally obtained by 104
Does not make a big difference. However, in order to accurately remove the structural information of the subject by the difference, the pixel extraction positions between the difference images should be as close as possible. That is, it is desirable to perform the difference using two extracted images whose pixel extraction positions are adjacent to each other. In general, if thinning sampling is performed every k pixels, the phase shift amount q between two extracted images whose pixel extraction positions are adjacent to each other is expressed by the following equation.

[0068]

[Equation 6] (Equation 6) X-ray quantum noise is included in the difference image, which may deteriorate the measurement accuracy of the interference fringe amplitude. Therefore, the original image f (i, j) (i, j = 0
~ N-1) may be subjected to moving average processing to reduce quantum noise. If the number of pixels for moving average in the i and j directions is 2I + 1 and 2J + 1 (I, J = 0, 1, 2, ...),
The image f _m (i, j) after the moving average is calculated by the following equation.

[0069]

[Equation 7] (Equation 7) However, when the moving average in the i direction is performed, the high frequency component decreases, and the interference fringe strength in the thinned image decreases. For this reason,
Generally, moving average in the i direction is not performed. On the other hand, j
A moving average is usually taken in the range of I = 5-10.

The moving average processing, thinning sampling processing, and amplitude distribution image deriving processing have been described on the assumption that the slit direction of the X-ray grid 3 is perpendicular to the j direction. On the other hand, when the slit direction of the X-ray grid 3 is arranged in the i direction, the i direction and j
You can change the direction. Further, when the X-ray grid 3 having a grid-like slit is used, all of the above processes may be performed in both the i direction and the j direction.

Although the amplitude distribution image of the interference fringes is shown by using the thinning sampling as described above, a method of performing scattered ray correction using the amplitude distribution image will be described below.

A pixel value f (i, j) (I = 0 in the X-ray transmission image)
~ N-1) Let f _d (i, j) be the amount of direct line components contained in f
_d (i, j) is proportional to the amplitude A (i, j) of the interference fringe at the same position. Therefore, the direct line distribution image f _d (i, j) can be obtained by previously obtaining the ratio (calibration ratio) of the amplitude of the interference fringe and the direct line component amount.

The calibration ratio can be obtained using an air image. Generally, the calibration ratio is slightly different depending on the detection position on the flat panel X-ray detector 4, and therefore its distribution is obtained as a calibration image. Now, when the calibration image is represented by r (i, j), r (i, j) is obtained by the following equation.

[0074]

[Equation 8] (Equation 8) However, f _air (i, j) is an air image measured without placing the subject 6, and A _{a ir} (i, j) is relative to f _air (i, j). It is the amplitude distribution image obtained by.

At this time, the direct line component amount of an arbitrary X-ray transmission image f (i, j) can be roughly calculated by the following equation.

[0076]

[Equation 9] … (Equation 9) Here, the reason why the calculation result of (Equation 9) is used as the approximate value of the direct line component is that the high frequency component is lacking in f _d '(i, j). . It should be noted that the lack of the above high frequency component is due to the amplitude distribution image.
The lack of high frequency components in A (i, j) is due to the lack of high frequency components in A (i, j) due to the interpolation processing by the peak-to-peak pixel interpolating means 92. In order to obtain an accurate direct line distribution image f _d (i, j) from the direct line component approximate value f _d '(i, j), first obtain the scattered line distribution image f _s (i, j), and then Original image f (i, j) to f
Subtract _s (i, j). The scattered radiation distribution image is obtained by the following equation.

[0077]

[Equation 10] (Equation 10) However, g (i, j) is a two-dimensional LPF (Low Pass Filter), and calculation ** represents a two-dimensional convolution integral.
In (Equation 10), the calculation result in the right side {} includes the scattered radiation component and the high frequency component of the direct radiation. Therefore, LPF
To remove the high frequency component (direct ray component) and extract only the scattered ray component. As the LPF, an ordinary digital filter or moving average processing is used. If the scattered ray distribution image f _s (i, j) is obtained, the direct ray distribution image f _d (i, j)
Can be calculated by the following equation.

[0078]

[Equation 11] (Equation 11) The method of performing scattered radiation correction using the calibration image has been described above. If the change in the calibration ratio in the calibration image is relatively small, r (i, j) = ro may be approximated. In this case r
For o, for example, the average value of r (i, j) is used. Also, r
The value of (i, j) or ro changes somewhat depending on the tube voltage of the X-ray tube 1. Therefore, for several tube voltages, r
(i, j) or ro may be measured in advance and selected according to the tube voltage at the time of photographing or fluoroscopy.

FIG. 11 is a block diagram for explaining the procedure for obtaining the calibration image. The calibration image is created by first capturing an air image.
By capturing the air image, the air image is stored in the image memory 100.
f _air (i, j) is secured. Next, the moving average calculation means 11
00 is used to perform a moving average in the i and j directions. In addition, the calculation of the moving average uses (Equation 7).

Next, the extracted images f ₁ (m, n) and f ₂ (m, n) are created using the thinned-out image creating means 1101 and 1102, respectively. In addition, (Formula 3) and (Formula 4) are used to create the extracted image. Next, the subtractor 1103 calculates the difference between the extracted images f ₁ (m, n) and f ₂ (m, n),
A difference image s (m, n) is created. Next, the interference fringe amplitude distribution calculation means 1104 creates an amplitude distribution image A _air (i, j) for the air image. The calculation by the interference fringe amplitude distribution calculating means 1104 has been described in detail with reference to FIG.

Next, the amplitude distribution image is obtained by the divider 1105.
The ratio of A _air (i, j) and f _air (i, j) is calculated, and the calibration image r (i, j) is created. Finally, the calibration image r (i, j) is stored in the calibration image storage memory 102 together with the tube voltage information input from the console 10.

FIG. 12 is a block diagram for explaining the procedure for obtaining the scattered radiation distribution image based on the calibration image. First, an X-ray fluoroscopic image or radiographic image f (i, j)
Are secured in the image memory 100. Moving average calculation means 1100 to interference fringe amplitude distribution calculation means 1 to be performed subsequently
The process up to 104 is the same as that of the calibration image creating means shown in FIG. Through the above process, the amplitude distribution image A (i, j) is created.

Next, the integrator 1200 outputs the amplitude distribution image A
(i, j) and the calibration image r (i, j) stored in the calibration image storage memory 102 are integrated,
Create a direct line component approximate image _f'd (i, j). The main integration corresponds to the calculation of (Equation 9). In addition, in the above integration, the calibration image r (i, j) created with the tube voltage closest to the tube voltage when the original image f (i, j) was created.
Is selected. Next, the subtractor 1201 uses the original image f (i, j)
The direct line component approximate image f ′ _d (i, j) is subtracted from this, and the LPF 1202 subsequently cuts off the high frequency component of the subtracted image to create a scattered line component image f _s (i, j). A series of operations by the subtractor 1201 and the LPF 1202 corresponds to (Equation 10). Finally, the scattered radiation component image f _s (i, j) is stored in the scattered radiation image storage memory 103.

As described above, in the first embodiment, the amplitude distribution of the interference fringes is measured based on the two extracted images created by the thinning sampling, and the scattered radiation correction is performed. Since the interference fringes can be obtained accurately from one X-ray transmission image, high-speed and highly accurate scattered radiation correction can be performed.

(Embodiment 2) FIG. 13 is a diagram for explaining the structure of an X-ray inspection apparatus according to a second embodiment of the present invention.

Only the differences from the X-ray inspection apparatus according to the first embodiment will be described below. In the X-ray inspection apparatus according to the first embodiment, the X-ray tube 1, the collimator 2, and the X-ray grid 3 are the object 6 to be examined. On the other hand, in the X-ray inspection apparatus according to the second embodiment, the X-ray tube 1, the collimator 2, and the X-ray grid 3 are all arranged on the upper surface of the bed. 7 is placed on the bottom surface (hereinafter,
Under tube configuration).

In the case of the overtube structure, there is a problem that the subject 6 is likely to accidentally contact the X-ray grid 3 because the distance between the X-ray grid 3 and the subject 6 is small. With the tube configuration, it is possible to avoid the risk of the X-ray grid 3 accidentally coming into contact with the subject 6.

(Embodiment 3) FIG. 14 is a diagram for explaining the configuration of an X-ray inspection apparatus according to a third embodiment of the present invention. In the third embodiment, the interference fringe amplitude distribution is measured without using thinning sampling. Only the differences from the X-ray inspection apparatus according to the first embodiment will be described below.

The X-ray inspection apparatus according to the third embodiment has a grid position controller 1400. Grid position controller 14
00 can change the position of the X-ray grid 3 at high speed in the x-axis direction by using a position changing mechanism (not shown). X
The grid ratio of the line grid 3 is 12: 1, the grid density is 117.5 [lines / cm], and the thickness of the lead foil is 40 [μm]. The position changing mechanism is realized by using a piezoelectric material or the like.

During X-ray photography, pulsed X-rays are emitted twice with a time interval Δt. In addition, the flat panel X-ray detector 4 detects two X-ray imaged images in synchronization with the above-described two emission of pulse X-rays. On the other hand, during X-ray fluoroscopy, pulsed X-rays are continuously emitted at every time interval Δt. Further, the X-ray fluoroscopic image is continuously detected by the flat panel X-ray detector 4 in synchronization with the emission of the pulsed X-rays. A typical example of the X-ray pulse interval Δt in the above imaging and fluoroscopy is 33.3.
Although it is [ms], it can be 66.6 [ms].

The grid position controller 1400 synchronizes with the emission of the pulsed X-rays at the time of photographing and fluoroscopy, and X
The position of the line grid 3 in the x-axis direction is changed. The amount of fluctuation at this time will be described later.

FIG. 15 is a diagram for explaining the relationship between the projection grid density and the Nyquist frequency of the flat panel X-ray detector 4 in the third embodiment of the present invention. In the X-ray inspection apparatus according to the third embodiment, interference fringes are generated on the X-ray transmission image itself. Therefore, the projection grid density f _d is set so as to approach a value twice the Nyquist frequency f _q . Now, 'when the _b, the frequency f by aliasing in X-ray transmission image' the difference between the 2f _q and f _d f interference fringe component 702 _b is generated.

In the third embodiment, the grid density of the X-ray grid 3 is 117.5 [lines / cm], the X-ray generation point-grid distance d is 40 [cm], the X-ray generation point-detector. The distance D was set to 100 [cm]. Therefore, from (Equation 1), the projection grid density f _d is 47 [lines / cm]. On the other hand, since the pixel interval Δd is 200 [μm], the Nyquist frequency f _q is 25 [lines / cm]. From the above, X
Frequency f _'b of the interference fringes generated during linear transmission image is 3 [present / c
m].

FIG. 16 is a diagram for explaining minute fluctuations of the X-ray grid in the third embodiment of the present invention. As described above, in the X-ray inspection apparatus according to the third embodiment, the X-ray grid 3 is slightly moved in the x-axis direction during the X-ray pulse interval Δt. The amount of movement is defined by the period Δh of the X-ray absorbing material 21 forming the X-ray grid 3.

First, at the time of photographing, the X-ray pulse is emitted twice, and two photographed images are measured. At this time, the grid position controller 1400 controls the position of the X-ray grid 3 so that the position of the X-ray grid 3 shifts by Δh / 2 in the x-axis direction between the two imagings. That is, the position of the X-ray grid 3 at the time of the first imaging is shown in FIG.
Assuming (A), the position of the X-ray grid at the time of the second imaging is shown in FIG. 16 (B).

On the other hand, during fluoroscopy, X-ray pulses are continuously generated. Therefore, the grid position controller 140
0 vibrates the X-ray grid so that the position of the X-ray grid 3 becomes as shown in FIG. 16 (A) → (B) → (A) → (B) → ... Every time an X-ray pulse is generated.

As the position of the X-ray grid 3 changes, X
The phase of the interference fringes generated in the line transmission image is shifted by 180 degrees in the x direction. Therefore, two X-ray transmission images having interference fringes whose phases are different by 180 degrees can be obtained. The method of extracting the interference fringes and performing the scattered ray correction by using the difference image of these two X-ray transmission images is the same as the method described in the first embodiment, and thus the description thereof is omitted. In addition, in order to remove the interference fringe component in the X-ray transmission image, an addition image of the two X-ray transmission images may be created. By this addition, the interference fringes included in the X-ray transmission image can be canceled and removed. Scattered ray correction is performed on the added image.

(Embodiment 4) FIG. 17 is a diagram for explaining the configuration of an X-ray inspection apparatus according to a fourth embodiment of the present invention. In the fourth embodiment, the scattered radiation correction method based on the thinning sampling described in the first embodiment is applied to X-ray CT. Therefore, the scattered radiation correction processing after the X-ray transmission image acquisition is the same as the method shown in the first embodiment, and therefore its explanation is omitted, and only the differences in the apparatus configuration and the imaging method will be described.

The X-ray inspection apparatus according to the fourth embodiment includes the X-ray tube 1, the X-ray filter 12, the collimator 2, the X-ray grid 3, the X-ray solid state detector 4, the subject 6, the bed top 7, and the rotation. Board 1701, gantry 1700, monitor 9, console 1
0, an image memory 100, an image processing unit 101, a calibration image storage memory 102, a scattered ray image storage memory 103, an image reconstruction unit 1702, and the like.
Known devices and mechanisms are used.

In the following, the X-ray tube 1, the X-ray filter 12,
A system including the collimator 2, the X-ray grid 3, and the X-ray detector 4 is called an imaging system. Rotating plate 1701
And is rotated by a known drive motor (not shown). In the following, the rotation axis of the rotary plate 1701 is the Z axis. Further, horizontal and vertical coordinate axes having the origin of rotation O as the origin are defined as the X axis and the Y axis, respectively. Rotating plate 17
The entire 01 is supported by the gantry 1700.

In FIG. 17, the distance between the X-ray generation point 20 and the rotation center O of the rotary plate 1701 is 69 [cm], and the distance between the X-ray generation point 20 and the input surface of the X-ray grid 3 is 32 [c].
m], the distance between the X-ray generation point 20 and the input surface of the X-ray detector 4 is 107 [cm], the effective field of view centering on the rotation center O of the X-ray detector 4 is 48 [cm] in diameter, and the opening is The diameter of 1703 is 70 [cm]. A typical example of the time required to scan the rotary plate 1701 for one rotation is 0.6 seconds. The X-ray detector 4 is a solid-state detector composed of ceramic scintillator elements, and has 896 channels in the XY plane direction and 64 channels in the Z axis direction. The size of each element in the XY plane direction and the Z axis direction is 1 [m
m]. In addition, each element is arranged on an arc that is substantially equidistant from the X-ray generation point S. A typical example of the number of images photographed in one rotation of the rotary plate 1701 is 900.
One shot is taken for every 0.4 degree of rotation.

At the time of photographing, photographed images photographed by the X-ray detector 4 are sequentially stored in the image memory 100 through a known slip ring mechanism (not shown). Image memory 10
The X-ray image recorded at 0 is input to the image reconstructing unit 1702 after the scattered radiation correction is performed using the same method as that described in the first embodiment. Image reconstruction means 170
2 is the subject 6 using a known image reconstruction algorithm.
A CT tomographic image is created and displayed on the monitor 9.

FIG. 18 is a diagram for explaining the positional relationship between the X-ray grid 3 and the X-ray detector 4 of the X-ray inspection apparatus according to the fourth embodiment of the present invention. In the X-ray grid 3, the X-ray absorbing material and the X-ray transmitting material are alternately arranged on an arc centered on the X-ray generation point 20 to form a slit. Further, the slits are arranged in a direction parallel to the Z axis.
Although lead is used as the X-ray absorbing material of the present X-ray grid 3 and paper is used as the X-ray transmitting material, the present invention is not limited to these materials and, for example, tungsten and aluminum may be used instead. Good. X-ray grid 3 has a grid ratio of 1
The grid density is 4: 1, the grid density is 27 [lines / cm], and the thickness of the lead foil is 100 [μm]. Further, the X-ray grid 3 has a focal point, and its focal length is 40 [cm]. X
The pixels of the line detector 4 have a position i in the direction of the rotation plane and a rotation axis (Z
They are arranged in a matrix whose position in the (axis) direction is j. The slits of the X-ray grid 3 are projected in the j direction and generate interference fringes in the i axis direction.

In the fourth embodiment, the grid density fg is set to 70.
[Lines / cm], X-ray generation point-grid distance d is 32 [c
m] and the X-ray generation point-detector distance D is 107 [cm], the projection grid density f _d is 8 [lines / c from (Equation 1).
m]. On the other hand, since the pixel interval Δd is 1 [mm], the Nyquist frequency f _q is 5 [lines / cm]. Therefore, the projection grid density is set to aliasing,
The beat frequency is 3 [lines / cm]. Using this interference fringe component waveform, scattered ray correction can be performed using the thinning sampling described in the first embodiment.

The present invention has been specifically described above based on the first to fourth embodiments. In the conventional X-ray grid method, which is a scattered ray correction method, it is physically difficult to produce an X-ray grid with a large grid ratio (lattice ratio), so scattered X-rays are not completely removed. It was As an example, using an X-ray grid having a grid density of 60 [lines / cm], a grid ratio of 10: 1, and a lead foil thickness of 50 [μm], a thickness of 30
When X-ray photography of a tank of [cm] is performed (tube voltage 120
[KV]), and the ratio of scattered X-ray components to the detected X-ray signals (scattered-ray component ratio) was about 50%.

On the other hand, when the present invention is used, the scattered radiation component ratio can be suppressed to about 5%, so that the image quality of the X-ray transmission image can be greatly improved. Further, in the conventional X-ray grid method, since the X-ray grid is arranged between the X-ray detector and the subject, there is a problem that ineffective exposure of the subject occurs. On the other hand, in this method, since the X-ray grid is arranged between the X-ray source and the subject, the above-mentioned ineffective exposure is eliminated, and the exposure dose of the subject is reduced by 30 to 40% as compared with the X-ray grid method. It is possible to

It is needless to say that the present invention is not limited to the above Examples 1 to 4 and can be variously modified without departing from the gist thereof.

For example, although an X-ray tube is used as the X-ray source in this embodiment, synchrotron radiation may be used instead. Further, the method may be applied to radiation other than X-rays, visible light, ultraviolet rays, infrared rays and the like. Furthermore, the present invention provides an X-ray C
It is also possible to apply to an X-ray non-destructive inspection device, an X-ray baggage inspection device, etc. in addition to the T device and the X-ray fluoroscopic imaging device.

Finally, the X-ray inspection method according to the present invention will be described below. (1) According to the X-ray inspection method of the present invention, an X-ray grid is arranged between an X-ray source that generates X-rays and an inspection target, and the inspection target is irradiated with the X-ray to transmit the inspection target. A step of detecting the image by a two-dimensional X-ray detector, and a pixel from the image of the transmission image in a direction in which the X-ray absorber grids of the X-ray grid are arranged at a sampling frequency with a predetermined number of pixels spaced. And extracting two extracted images in which interference fringes having different phases by a predetermined angle respectively appear, and an amplitude distribution representing the distribution of the amplitude of the interference fringes from the difference in pixel value between the two extracted images. A step of obtaining an image, a step of obtaining a scattered X-ray distribution image representing a distribution of scattered X-ray components contained in the image of the transmission image using the amplitude distribution image, and the scattering from the pixel value of the image of the transmission image. Reduce the pixel value of X-ray distribution image To have a step of removing the scattered X-ray component from the image of the transmitted image. (2) (1) In the X-ray inspection method, an estimated image obtained in advance for estimating the distribution of direct X-ray components included in the image of the transmission image is stored from the pixel value of the image of the transmission image. And subtracting the product of the pixel value of the estimated image and the pixel value of the amplitude distribution image read from the memory, the scattering X representing the distribution of the scattered X-ray component contained in the image of the transmission image.
The method includes a step of obtaining a line distribution image and a step of subtracting a pixel value of the scattered X-ray distribution image from a pixel value of the image of the transmission image, and removing the scattered X-ray component from the image of the transmission image. (3) In the X-ray inspection method of (2), an X-ray tube is used as the X-ray source, and it corresponds to a combination of the tube voltage of the X-ray tube and the X-ray grid when the transmission image is detected. Reading the estimated image from the memory,
Remove line components. (4) In the X-ray inspection method according to (2), the inspection target is not placed in the direction in which the X-ray absorber grids are arranged at the sampling frequency with the predetermined number of pixels spaced from each other. Extracting pixels from the detected air image to obtain two air extraction images in which interference fringes having different phases by the predetermined angle respectively appear, and from the difference in pixel value between the two air extraction images Obtaining an air amplitude distribution image representing the amplitude distribution of interference fringes, and pixels of the air amplitude distribution image having pixel values of the air distribution image representing the distribution of direct X-ray components passing through the X-ray grid of the air image. Determining the estimated image having a ratio to a value as a pixel value, and storing the estimated image in the memory. (5) In the X-ray inspection method of (2), an X-ray tube is used as the X-ray source, and one or more tube voltages and one or more X-ray grids having different scattered X-ray removal rates are used. 1 detected by the combination without the inspection target placed
Or, with respect to a plurality of air images, at the sampling frequency spaced by the predetermined number of pixels, in the direction in which the X-ray absorber grid is arranged, pixels are extracted from the air image to obtain the predetermined angle. A step of obtaining two air extraction images in which interference fringes each having a different phase appear respectively,
Obtaining an air amplitude distribution image representing the amplitude distribution of interference fringes from the difference in pixel values between the two air extracted images; and direct X-ray passing through the X-ray grid of the air image.
Determining the estimated image having as a pixel value the ratio of the pixel value of the air distribution image representing the distribution of the line component to the pixel value of the air amplitude distribution image, and performing each of the air images. The estimated image for the air image is stored in memory. (6) The X-ray inspection method according to (2), wherein the predetermined number is 1, 2, or 3. (7) In the X-ray inspection method of (2), the predetermined angles are 90 °, 120 °, 180 °, 240 °, 270 °.
Is an angle in the vicinity of any of. (8) In the X-ray inspection method of (2), the scattered X-ray component is removed from the images of the plurality of transmission images by using the same estimated image obtained in advance. (9) In the X-ray inspection method of (2), the difference between the spatial frequency of the array of the X-ray absorber grids on the detection surface of the two-dimensional X-ray detector and the sampling frequency is greater than the sampling frequency. Is also small. (10) In the X-ray inspection method of (2), the two-dimensional X
The space so that the difference between the spatial frequency of the array of X-ray absorber grids on the detection surface of the X-ray detector and the Nyquist frequency of the X-ray detector is smaller than half the Nyquist frequency. The frequency is set and / or the position where the X-ray grid is arranged is set. (11) In the X-ray inspection method of (2), from the added image obtained by adding the pixel values of a plurality of pixels adjacent to the pixels of the transmission image in the direction in which the X-ray absorber grids are arranged, There is a step of obtaining the extracted image by extracting pixels at the sampling frequency spaced by a predetermined number of pixels. (12) According to the X-ray inspection method of the present invention, an X-ray grid is arranged between an X-ray source that generates X-rays and an inspection target, and the inspection target is irradiated with the X-ray to transmit the inspection target. A step of detecting an image by a two-dimensional X-ray detector, and extracting an image from the image of the transmission image in the direction in which the X-ray absorber grids of the X-ray grid are arranged, and interference fringes having different phases by a predetermined angle. Of the scattered X-ray components contained in the image of the transmission image, using the step of obtaining two extracted images in which each appears and the amplitude distribution image showing the distribution of the amplitude of the interference fringes obtained from the two extracted images. A step of obtaining a scattered X-ray distribution image representing the above, and a step of subtracting the pixel value of the scattered X-ray distribution image from the pixel value of the image of the transmission image to remove the scattered X-ray component from the image of the transmission image. Have and. (13) According to the X-ray inspection method of the present invention, an X-ray grid is arranged between an X-ray source that generates X-rays and an inspection target, and the inspection target is irradiated with the X-ray to transmit the inspection target. A step of detecting an image by a two-dimensional X-ray detector, and n being an integer,
At the spatial sampling frequency of (1 / n) of the spatial sampling frequency of the two-dimensional X-ray detector, the pixel data of the image of the transmission image is sampled, and interference fringes having a predetermined inversion phase respectively appear 2 Obtaining two extracted images, obtaining an amplitude distribution image representing the amplitude distribution of interference fringes by the difference in pixel value between the two extracted images, and using the amplitude distribution image, an image of the transmission image From the image of the transmission image by subtracting the pixel value of the distribution image of the scattered X-ray from the pixel value of the image of the transmission image, The scattered X-ray component is removed. (14) In the X-ray inspection method of (13), n is 2,
It is either 3 or 4. (15) The X-ray inspection method of the present invention comprises the step of irradiating the inspection target with the X-rays through an X-ray grid arranged between an X-ray source that generates X-rays and the inspection target, and the X-rays. A step of detecting a transmission image of the inspection object obtained by irradiation with an X-ray detector, and a scattered X-ray component included in the transmission image based on the amplitude of interference fringes generated in the transmission image of the inspection object. Extracting and removing.

The above X-ray inspection method can be applied to a non-destructive inspection method such as a medical X-ray inspection method in which the inspection object is the human body, and a baggage inspection method in which general inspection objects other than the human body are targeted. Needless to say.

[0111]

According to the present invention, since the scattered ray component contained in the X-ray transmission image is directly extracted based on the amplitude of the interference fringes and then removed, highly accurate scattered ray correction can be performed. Further, since the X-ray grid is arranged between the X-ray source and the subject, ineffective exposure of the subject is eliminated and the exposure dose can be suppressed.

As described above, a high-quality X-ray radiographic image, X-ray fluoroscopic image, X-ray CT image, etc. can be obtained with a small exposure dose.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the configuration of an X-ray inspection apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the principle of scattered X-ray removal.

FIG. 3 is a diagram for explaining a positional relationship between an X-ray grid and a flat panel X-ray detector.

FIG. 4 is a diagram for explaining detection pixel positions in the detection of an X-ray transmission image by a flat panel X-ray detector.

FIG. 5 is a diagram for explaining a relationship between a spatial frequency distribution of a direct X-ray component and a scattered X-ray component and a Nyquist frequency of a flat panel X-ray detector.

FIG. 6 is a diagram for explaining thinning-out sampling for a detected X-ray transmission image.

FIG. 7 is a diagram for explaining the relationship between the Nyquist frequency and the spatial frequency distribution of direct X-ray components and scattered X-ray components during thinning sampling.

FIG. 8 is a diagram for explaining another setting method of the projection grid density.

FIG. 9 is a diagram for explaining a method of deriving a spatial distribution of interference fringe amplitude based on an interference fringe image.

FIG. 10 is a diagram for explaining another sampling method in thinning sampling.

FIG. 11 is a block diagram for explaining a procedure for obtaining a calibration image.

FIG. 12 is a block diagram for explaining a procedure for obtaining a scattered radiation distribution image based on a calibration image.

FIG. 13 is a diagram for explaining the configuration of an X-ray inspection apparatus according to a second embodiment of the present invention.

FIG. 14 is a diagram for explaining the configuration of an X-ray inspection apparatus according to a third embodiment of the present invention.

FIG. 15 is a diagram for explaining the relationship between the projection grid density and the Nyquist frequency of the flat panel X-ray detector in the third embodiment of the present invention.

FIG. 16 is a diagram for explaining minute fluctuations of the X-ray grid in the third embodiment of the present invention.

FIG. 17 is a diagram for explaining the configuration of an X-ray inspection apparatus according to a fourth embodiment of the present invention.

FIG. 18 is a diagram for explaining the positional relationship between the X-ray grid and the X-ray detector of the X-ray inspection apparatus according to the fourth embodiment of the present invention.

[Explanation of symbols]

1 ... X-ray tube, 2 ... Collimator, 3 ... X-ray grid, 4 ...
Flat type X-ray detector, 5 ... Support, 6 ... Subject, 7 ... Bed top, 8 ... Bed, 9 ... Monitor, 10 ... Console, 11 ...
Clinical console, 100 ... Image memory, 101 ... Image processing means, 102 ... Calibration image storage memory,
103 ... Scattered ray image storage memory, 1700 ... Gantry,
1701 ... Rotating plate, 1702 ... Image reconstructing means, 170
3 ... Aperture.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G21K 1/02 G21K 5/02 X 5/02 G01T 1/161 D // G01T 1/161 A61B 6/00 350S F-term (reference) 2G001 AA01 AA02 BA11 BA14 CA01 CA02 DA09 FA01 FA06 GA07 GA13 HA01 HA07 HA13 JA04 JA11 KA03 LA01 SA01 SA04 SA14 2G088 EE01 EE29 FF02 FF04 JJ05 JJ12 AZ12A34 A05 A29A34 A01 A29 A34 A21 A29 A29 A34 A21 A29 A34 A21 A29 A29 A29 A22 A29 A29 A22 A34 A21 A29 A29 A22 A29 A29 A22 A29 A22 A29 A22 A34 A02 A34 A22 A29 A29 A22 A34 A02 A34 A02 A34 A02 A34 A01 A22 A34 A01 A22 A34 A01 A22 A23 A01 A02 A11 A01 A02 A11 A11 A01 A02 A11 A11 A01 A02 A11 A11 A02 A11 A01 A06 EA20 EB17 EB22 EB24 EC13 EC22 ED01 EE01 FA11 FC16 FD05 FD07 FD12 FF01 FF34 FF36 FF50 FH02 GA02 GA06 5B057 AA08 BA03 CA12 CA16 CB12 CB16 CE02 CH01 DA16

Claims (15)

[Claims] 1. An X-ray source for generating X-rays, a two-dimensional X-ray detector for irradiating an inspection target with the X-rays to detect a transmission image of the inspection target, the X-ray source and the inspection target. An X-ray grid disposed between the two-dimensional X-ray detectors and an arithmetic processing means for performing arithmetic processing on the output of the two-dimensional X-ray detector, wherein the arithmetic processing means performs sampling with a predetermined number of pixel intervals. Pixels are extracted from the image of the transmission image at a frequency in the direction in which the X-ray absorber grids of the X-ray grid are arranged, and interference fringes having different phases by a predetermined angle respectively appear 2
An operation of obtaining one extracted image, an operation of obtaining an amplitude distribution image representing an amplitude distribution of interference fringes from a difference in pixel value between the two extracted images, and an image of the transmission image using the amplitude distribution image. The calculation for obtaining the scattered X-ray distribution image representing the distribution of the included scattered X-ray components, the pixel value of the scattered X-ray distribution image is subtracted from the pixel value of the image of the transmission image, and An X-ray inspection apparatus, which performs a calculation for removing scattered X-ray components. 2. The X-ray inspection apparatus according to claim 1, wherein
The arithmetic processing unit has a memory that stores a calibration image that is obtained in advance to extract the distribution of the direct X-ray components included in the image of the transmission image, and the arithmetic processing unit determines from the pixel values of the image of the transmission image. , A scattered X-ray distribution image representing the distribution of scattered X-ray components contained in the image of the transmission image by subtracting the product of the pixel value of the calibration image read from the memory and the pixel value of the amplitude distribution image And a calculation for subtracting the pixel value of the scattered X-ray distribution image from the pixel value of the image of the transmission image to remove the scattered X-ray component from the image of the transmission image. X-ray inspection device. 3. The X-ray inspection apparatus according to claim 2,
An X-ray tube is used as the X-ray source, and the arithmetic processing means includes a tube voltage of the X-ray tube when the transmission image is detected,
An X-ray inspection apparatus, wherein the calibration image corresponding to the combination of the X-ray grids is read out from the memory, and an operation for removing the scattered X-ray component is performed. 4. The X-ray inspection apparatus according to claim 2, wherein
The arithmetic processing means includes pixels from an air image detected in a state in which the inspection target is not placed in the direction in which the X-ray absorber grid is arranged, at the sampling frequency at which the predetermined number of pixels are arranged. To obtain two air extracted images in which interference fringes having phases different from each other by the predetermined angle appear, and the amplitude distribution of the interference fringes is calculated from the difference in pixel value between the two air extracted images. The calculation for obtaining the represented air amplitude distribution image and the X of the air image
The calibration image having the pixel value of the ratio of the pixel value of the air distribution image representing the distribution of the direct X-ray component passing through the line grid to the pixel value of the air amplitude distribution image is calculated, and the calibration image is obtained. Is stored in the memory. 5. The X-ray inspection apparatus according to claim 2, wherein
The calculation processing means uses an X-ray tube as the X-ray source, and the inspection target is determined by a combination of one or more tube voltages and one or more X-ray grids having different scattered X-ray removal rates. From the air image, in the direction in which the X-ray absorber grids are arranged, at the sampling frequency spaced by the predetermined number of pixels, with respect to the one or more air images detected in the non-placed state. Calculation of extracting two pixels and obtaining two air-extracted images in which interference fringes having different phases by the predetermined angle respectively appear, and the distribution of the amplitude of the interference fringes from the difference in pixel value between the two air-extracted images. And calculating the ratio of the pixel value of the air distribution image representing the distribution of the direct X-ray component passing through the X-ray grid of the air image to the pixel value of the air amplitude distribution image. And a calculation for obtaining the calibration image with a value, the performed for each air image, X-rays inspection apparatus characterized by having a memory for storing said calibration image for each air image. 6. The X-ray inspection apparatus according to claim 2,
The arithmetic processing means performs an arithmetic operation to remove the scattered X-ray component from the plurality of transmission image images by using the same scattered X-ray distribution image obtained in advance. apparatus. 7. The X-ray inspection apparatus according to claim 2,
The difference between the spatial frequency of the array of X-ray absorber grids on the detection surface of the two-dimensional X-ray detector and the Nyquist frequency of the two-dimensional X-ray detector is smaller than half the Nyquist frequency. An X-ray inspection apparatus characterized in that 8. The X-ray inspection apparatus according to claim 2, wherein
The difference between the spatial frequency of the array of X-ray absorber grids on the detection surface of the two-dimensional X-ray detector and the Nyquist frequency of the two-dimensional X-ray detector is smaller than half the Nyquist frequency. The X-ray inspection apparatus is characterized in that the spatial frequency is set and / or the position where the X-ray grid is arranged is set. 9. The X-ray inspection apparatus according to claim 2, wherein
The arithmetic processing unit calculates the predetermined number of pixels from the added image obtained by adding the pixel values of a plurality of pixels adjacent to the pixels of the transmission image in the direction in which the X-ray absorber grids are arranged. An X-ray inspection apparatus, characterized in that the pixels are extracted at the sampling frequencies with intervals to obtain the extracted image. 10. An X-ray source for generating X-rays, a two-dimensional X-ray detector for irradiating the inspection object with the X-rays to detect a transmission image of the inspection object, the X-ray source and the inspection object. An X-ray grid disposed between the X-ray grid and an X-ray absorber grid of the X-ray grid. Pixels are extracted from the image of the transmission image in the arrangement direction, and interference fringes having different phases by a predetermined angle respectively appear 2
Scattered X-rays representing the distribution of scattered X-ray components contained in the image of the transmission image by using the calculation for obtaining two extracted images and the amplitude distribution image representing the distribution of the amplitudes of the interference fringes obtained from the two extracted images. A calculation for obtaining a distribution image and a calculation for removing the scattered X-ray component from the image of the transmission image by subtracting the pixel value of the scattered X-ray distribution image from the pixel value of the image of the transmission image. Characteristic X-ray inspection device. 11. An X-ray source for generating X-rays, and a two-dimensional X-ray detector for irradiating the inspection object with the X-rays and detecting a transmission image of the inspection object at a preset spatial sampling frequency. It has an X-ray grid arranged between the X-ray source and the inspection object, and an arithmetic processing means for performing arithmetic processing of the output of the two-dimensional X-ray detector, wherein the arithmetic processing means makes n an integer. As a spatial sampling frequency of (1 / n) of the spatial sampling frequency of the two-dimensional X-ray detector,
The pixel data of the image of the transmission image is sampled to obtain two extracted images in which interference fringes each having a predetermined reverse phase appear, and the interference fringes are determined by the difference in pixel value between the two extracted images. A calculation for obtaining an amplitude distribution image showing the distribution of amplitude, a calculation for obtaining a scattered X-ray distribution image showing the distribution of scattered X-ray components contained in the image of the transmission image, using the amplitude distribution image, and the transmission image. And subtracting the pixel value of the scattered X-ray distribution image from the pixel value of the image, and performing an operation of removing the scattered X-ray component from the image of the transmission image. 12. The X-ray inspection apparatus according to claim 11, wherein n is 2, 3, or 4.
Line inspection equipment. 13. An X-ray source for generating X-rays, a two-dimensional X-ray detector for irradiating the inspection object with the X-rays to detect a transmission image of the inspection object, and an inspection object for supporting the inspection object. It has a supporting means and an arithmetic processing means for performing arithmetic processing of the output of the two-dimensional X-ray detector, the inspection object is arranged on the upper surface of the inspection object supporting means, and the X element is on the lower surface of the inspection object supporting means. An X-ray inspection apparatus, in which a X-ray source is disposed, and an X-ray grid is disposed between the X-ray source and the lower surface of the inspection target support means. 14. An X-ray source for generating X-rays, a two-dimensional X-ray detector for irradiating an inspection object with the X-rays to detect a transmission image of the inspection object, the X-ray source and the two-dimensional image. The X-ray source includes an imaging system rotating unit that rotates an imaging system composed of a pair of X-ray detectors around the inspection target, and an arithmetic processing unit that performs arithmetic processing of the output of the two-dimensional detector. An X-ray grid is disposed between the X-ray grid and the inspection target, and the imaging system rotation unit rotates the imaging system while maintaining the position of the X-ray grid with respect to the imaging system substantially constant. An X-ray inspection apparatus, wherein a plurality of X-ray transmission images are photographed from a plurality of directions to generate and display an X-ray tomographic image of the inspection target. 15. An X-ray source for generating X-rays, an X-ray detector for irradiating the inspection object with the X-rays to detect a transmission image of the inspection object, the X-ray source and the inspection object. And an X-ray grid arranged in between, and is configured to extract and remove a scattered X-ray component included in the transmission image based on the amplitude of interference fringes generated in the transmission image of the inspection target. An X-ray inspection apparatus characterized in that