JP3114247B2 - Phase tomography device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tomography apparatus for reproducing a cross-sectional view of an object from projection images of the object from a plurality of different directions in order to non-destructively evaluate the inside of the object. In particular, the present invention relates to a tomography apparatus using energy waves such as X-rays, γ-rays, and neutron rays. In particular, it is effective for use in examining element distribution and density distribution inside organic materials and biological materials.

[0002]

2. Description of the Related Art Conventional tomography using X-rays, γ-rays, neutrons, etc. acquires transmission images of an object to be observed from a plurality of different directions using X-rays, γ-rays, neutrons, etc. A cross-sectional image of the object is reproduced by performing arithmetic processing on the acquired data. Here, transmission images are X-rays, γ-rays,
It indicates the absorption rate of the object to neutrons and the like,
The reproduced cross-sectional image shows the absorption rate distribution in the cross section.

When X-rays, γ-rays, neutrons and the like pass through an object, both the amplitude and the phase of the X-rays, γ-rays and neutrons change. It is generally known that a change in phase appears more remarkably than a change in amplitude. Therefore, an image having a higher contrast can be obtained by using the change in phase as the acquired data, rather than using the change in amplitude as the acquired data as in conventional tomography. The cross-sectional image reproduced in this case shows the refractive index distribution in the cross section. However, while the change in amplitude appears as absorption and is easily detected, the change in phase is not normally detected. A tomographic apparatus for measuring a phase change and reproducing a tomographic image has not been invented until now.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a tomography apparatus using X-rays, γ-rays, neutrons and the like to detect a change in the phase of the X-rays, γ-rays, and neutrons and to form a cross-sectional image. A device that introduces a reproduction method and adds a feature that a high-contrast cross-sectional image can be obtained in addition to the feature that a high-resolution cross-sectional image of a conventional tomography device using X-rays, γ-rays, and neutron beams can be obtained. It is to provide.

[0005]

In order to achieve the above object, it is necessary to introduce means for detecting a change in phase of X-rays, γ-rays, and neutrons. X-rays and gamma rays,
There is a method that utilizes the neutron beam interference phenomenon. That is, X-rays, γ-rays, and neutrons are separated into two propagation paths, and interfere with X-rays, γ-rays, and neutrons (hereinafter, referred to as signal waves) that pass through an object to generate interference fringes. An apparatus having a mechanism for forming X-rays, γ-rays, and neutron rays (hereinafter, referred to as reference waves) satisfies the above object.

In an embodiment of the present invention, a Bonze-Hart interferometer (Appl. Physics Letters, Vol. 6 (1965) No. 155, Appl. . Lett. 6 (1965) 1
55) "). In this interferometer, three thin crystal plates are cut out of one single crystal so as to be positioned at substantially equal intervals and almost in parallel, and the material is usually a silicon single crystal. X-rays, γ-rays, and neutrons are successively diffracted from three crystal plates in a Laue case (when a reflected diffraction wave is emitted in a direction transmitting a crystal). The X-rays, γ-rays, and neutrons separated by the first crystal (referred to as a beam splitter) into two propagation paths and separated in the respective propagation directions by the second crystal (referred to as a mirror) The lines are each diffracted and overlap at the location of the third crystal (called the analyzer), forming interference fringes. The fringe spacing of the interference fringes is the same as the lattice spacing of the crystal. When an object to be observed is inserted into one of the two propagation paths between the first crystal and the second crystal or between the second crystal and the third crystal, the X-ray or γ The phase of the neutron beam shifts slightly, and the position of the interference fringes slightly changes. The state of the interference of the energy wave by this object is such that the interval between the interference fringes is extremely narrow (the interval is several る の で because it is about the lattice interval of the crystal), and cannot be directly observed. The interference fringes overlap with the crystal lattice of the analyzer, and the pattern is observed as moiré fringes. The moiré fringes include information on the phase shift of X-rays, γ-rays, and neutrons. In order to extract phase information from moiré fringes, a method of deriving phase information from moiré fringes using amplitude information and a method of inserting a phase shifter into one propagation path are effective. A method of moving the analyzer in the direction of the diffraction vector is also possible.

In the first method, a means for blocking a reference wave is provided, and a projection image (moire fringe) having information on a phase distribution and a projection image showing an absorptivity distribution can be obtained by inserting and removing the means. To do. A projection image is obtained in the form of a phase shift distribution by calculation from the intensity distributions of both images.

A second method is to insert a phase shifter into one of the signal wave and the reference wave, and examine the displacement of the moire fringes while changing the thickness of the phase shifter. The phase shift at the position of the moiré fringes is an integral multiple of 2π without the phase shifter. Therefore, a distribution of the phase shift can be obtained from the position of the moire fringes. However, the phase shift between the stripes is not exactly known. Therefore, by inserting a phase shifter and moving the moiré fringes to the position where the phase shift is desired to be known, it is possible to know the phase shift at an arbitrary position. As a method of changing the thickness of the phase shifter, there is a method of inserting the phase shifter in a wedge shape into the propagation path and moving the phase shifter in a direction perpendicular to the propagation path.

In the second method, the analyzer may be moved in the direction of the diffraction vector instead of changing the thickness of the phase shifter. The movement is performed by a piezoelectric element. At this time, the analyzer is not separated from the whole interferometer, but a cut is made in a part of the base of the interferometer so that the analyzer can be moved by a very small distance. For example, the following two methods are available for monitoring the amount of movement of the analyzer. One is to attach a mirror to the analyzer and directly read the minute displacement using a laser interferometer. The other is to use X-ray or γ transmitted through the analyzer.
This method utilizes the fact that the intensity of the beam and neutron beam changes according to the amount of movement of the analyzer.

[0010]

When an X-ray, a γ-ray, a neutron beam or the like passes through an object, both the amplitude and the phase of the X-ray, a γ-ray, a neutron beam and the like change. The change in amplitude (attenuation) depends on the absorption rate of the object,
The change in phase depends on the refractive index of the object. It is generally known that a phase change appears more remarkably than an amplitude change. Since the phase tomography apparatus of the present invention uses the phase change as the acquired data, an image having a higher contrast can be obtained as compared with a conventional tomography apparatus using the amplitude change (absorption) as the acquired data. became. It should be noted that the conventional tomography apparatus reproduces a cross-sectional image in the form of an absorption distribution, whereas the phase tomography apparatus of the present invention reproduces a cross-sectional image in the form of a refractive index distribution. If a cross-sectional image is required in the form of an absorptivity distribution, it can be obtained by blocking the reference wave. Also, by combining images in various cross sections, a three-dimensional image can be finally obtained. Finally, X
When a ray, γ-ray, neutron ray or the like penetrates an object, the propagation path is slightly bent due to refraction. This limits the fundamental resolution of the present invention.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. Although each embodiment shows the case of X-rays, the same configuration can be applied to the case of γ-rays and neutron rays.

Embodiment 1 FIG. 1 is a diagram showing a configuration of an embodiment of a phase tomography apparatus according to the present invention. As shown in the figure, the phase tomography apparatus includes an X-ray source 20, a Bonze-Hart X-ray interferometer 1, a two-dimensional X-ray detector 11, a shutter 12, an object to be observed 10, a signal conversion device 31, It comprises a tomography signal processing device 30, a control device 41 and a display device 40. In the above configuration, the tomography signal processing device 30 used was that of a conventionally used tomography device. That is, the output signal of the signal conversion device 31 can be processed in the same manner as the signal processing of the transmission image of the object by the conventional tomography device. However, in FIG. 1, the signal conversion device 31 and the tomography signal processing device 30
Although the control device 41 and the control device 41 are shown as independent blocks, in an actual device, it is needless to say that these are constituted by a so-called microcomputer on which a predetermined program is mounted. This is the same in all the following embodiments.
Although the two-dimensional X-ray detector 11 is in close contact with the analyzer 5 in the same figure, in all of the following embodiments, if the distance is equal to or greater than a certain distance (l / cos θ: l is the beam width, θ is the incident angle). You may be away.

The Bonze-Hart X-ray interferometer 1 is composed of an integral crystal cut out of a perfect silicon crystal, and comprises a sufficiently thick base 2, a beam splitter 3, a mirror 4, and an analyzer 5 (see FIG. 4). . As shown in the figure, the crystal orientation is <1, 0, 0> in the x-axis direction and <
1,1,0>, and the z-axis direction is <1, -1,0>. The thickness of the beam splitter 3, the mirror 4, and the analyzer 5 was 1 mm, and the distance between the beam splitter 3 and the mirror 4, and the distance between the mirror 4 and the analyzer 5 were both 15 mm. X-rays are diffracted in the Laue case on the (2,2,0) plane.

An X-ray 6 monochromatized in advance from an X-ray source 20 is incident on the beam splitter 3 at an angle θ that satisfies the Bragg diffraction condition, and is separated into a transmitted diffraction wave 7 and a reflected diffraction wave 8. The transmitted diffracted wave 7 and the reflected diffracted wave 8 are further diffracted by the mirror 4, become a signal wave 7 'and a reference wave 8', and interfere with each other. As a result, (2, 2,
0) has the same period as the surface period d ₂₂₀ (about 1.9 °),
Interference fringes 9 parallel to the (2, 2, 0) plane are generated on the surface of the analyzer 5. When the object 10 is placed on the propagation path of the signal wave 7 ', the phase of the signal wave 7' transmitted through the object 10 changes, and the interference fringe 9 on the surface of the analyzer 5 is displaced in accordance with the change. By examining the interference fringes 9, it is possible to know the phase shift. However, since the interval between the fringes is extremely narrow, direct observation is not possible. However, when the interference fringes 9 pass through the analyzer 5, the interference fringes 9 and (2,
Moire fringes can be observed at the position of the two-dimensional detector 11 due to the overlap with the (2, 0) plane. This moiré fringe is detected by the two-dimensional X-ray detector 11, converted into an electric signal, and sent to the signal converter 31 to convert the image of the moiré fringe into an image showing a phase shift based on the following principle and tomography. This is an input signal of the signal processing device 30. This signal conversion processing is performed by rotating the object 10 at a certain angle (for example, 1
This is performed on the projection image obtained while rotating it by 180 ° every other angle (°), and the tomographic signal processing device 30 reproduces a cross-sectional image and displays it on the display device 40. Here, the rotation axis of the object 10 is substantially perpendicular to the propagation path of the signal wave and substantially parallel to the plane containing the signal wave and the reference wave.
1 shows the content of the signal processing performed in step 1. The interference fringe 9 is represented by E (r) = A (r) exp (ik '· r) + exp (ik · r) (1). The first term indicates a signal wave, and the second term indicates a reference wave.
Here, r is a position vector, and k and k ′ are wave number vectors of a reference wave and a signal wave, respectively. i is an imaginary unit. A (r) is a term indicating a change due to transmission of the signal wave through the observed object 10. Signal wave change A (r)
Is a complex number, the absolute value of which indicates a change in amplitude (absorption), and the argument indicates a change of phase. The information I want to obtain in the end is A (r)
The image is reproduced using this information. When the complex refractive index of an object is represented by 1-δ-iβ, the absolute value of A (r) is exp (-2πβL / λ) and the argument is δL / λ, where L is the distance through which the X-ray passes through the object. It is. λ
Is the wavelength of the X-ray.

When the interference fringes 9 pass through the analyzer 5, moire fringes are observed at the position of the two-dimensional X-ray detector 11. When the back surface of the analyzer 5 or the incident surface of the two-dimensional X-ray detector 11 is represented by (y, z) coordinates, (the back surface of the analyzer 5 and the two-dimensional X
The incident surfaces of the line detectors 11 are in close contact with each other and are substantially the same. ), The intensity distribution I (y, z) of the moiré fringes can be expressed as I (y, z) = W (y) | E (0, y, z) | ² (2) Here, W (y) is a periodic function (period d ₂₂₀ ) indicating the distribution of the transmittance of the analyzer. Analyzer 5
The change A (r) of the signal wave on the surface of A is expressed as A (0, y, z) = A ₀ (y, z) exp {iΦ (y, z)} (3) _When expressed by ₀ (y, z) and the argument, that is, the phase shift Φ (y, z), the equation (2) uses the equation (1) to give I (y, z) = W (y) [{ _{a 0 (y, z)}} 2 + 1 + 2A 0 (y, z) cos {Φ (y, z) + 2πy / d 220}] can be represented as _{...... (4), a 0 (} y, If z) and W (y) are known, Φ (y, z) can be obtained.

The functional form of W (y) can be determined using a standard sample. The complex refractive index of an object with respect to X-rays can be measured by examining the reflectance and transmittance. Therefore, it is preferable that a substantially uniform object whose complex refractive index is measured in advance is processed into a wedge shape and used as a standard sample. A _0m (y,
Since z) and Φ _m (y, z) can be obtained by calculation from the shape of the standard sample, by measuring I _m (y, z) when the standard sample is inserted into the signal wave 7 ′, (4) W (y) can be obtained using the equation. The subscript m indicates that the value is obtained for the standard sample.

Next, when the reference wave 8 'is cut off while the object 10 is inserted, since the second term in equation (1) is equivalent to zero, the equation corresponding to equation (4) is obtained. Is I ′ (y, z) = W (y) {A ₀ (y, z)} ² …………… (5) Therefore, using W (y) obtained using the standard sample, A ₀ (y, z) can be obtained. That is, W (y)
And A ₀ (y, z) were obtained, and from equation (4), Φ (y,
z), that is, a phase shift distribution is obtained.

FIG. 2A shows a processing procedure for obtaining a sectional image of an object in the first embodiment. First, analyzer 5
Is determined using a standard sample (step 1). That is, the intensity distribution I _m (y, z) of the moire fringes is measured using a standard sample in which a uniform object whose refractive index to X-rays is measured in advance and processed into a wedge shape, and the intensity distribution _Im ( y, z), from A _0m (y, z) and Φ _m (y, z) obtained by calculation of a standard sample
W (y) is obtained based on equation (4). The object to be observed 10 is set (step 2). The shutter 12 is inserted, the propagation of the reference wave 8 'is cut off, and the intensity distribution I' (y, z) is measured by the two-dimensional X-ray detector 11 (step 3). With the shutter 12 retracted, the intensity distribution I of the moire fringes generated
(Y, z) is measured by the two-dimensional X-ray detector 11 (step 4). The data obtained by the above measurement, W (y),
A ₀ (y, z) is obtained from I ′ (y, z) by equation (5),
Using W (y), A ₀ (y, z) and I (y, z), (4)
Based on the equation, Φ (y, z) is obtained by calculation (step 5). The object 10 is rotated by a fixed angle (for example, 1 °), and the above steps 3 to 5 are repeated until the object 10 is rotated by 180 °, and Φ (y, z) in each rotation position, that is, in each projection direction is obtained. The data Φ (y, z) obtained by the above steps is sent to the tomography processing device 30 to reproduce a cross-sectional image of the object 10 and display it on the display device 40 (step 7). Further, similarly to the conventional apparatus, when obtaining an absorptance distribution image of the object 10, the processing procedure shown in FIG. 2B can be performed. Step 3 'obtained in the intensity distribution I'(y,
The image can be reproduced directly from step z) by the processing of step 7 '. The processing of steps 7 and 7 'is the same as the conventionally known method of reproducing an image from a projected image in tomography.

The control device 41 controls the operations of the signal conversion device 31 and the motor driving devices 51 and 53 according to the above-mentioned program given in advance by the operator. This also
The same applies to all the following embodiments.

Embodiment 2 FIG. 3 is a diagram showing a main configuration of a second embodiment of the phase tomography apparatus according to the present invention. As shown in the figure, the interferometer 1 used is the same as that of the first embodiment. Also,
FIG. 4 shows a perspective view. However, in the figure, parts other than the main body of the interferometer 1, the object 10, and the phase shifter 19 are omitted.

As can be seen from the above equation (4), the moiré fringes appear at every phase 2π, and the phase shift Φ (y, z) at the position of the moiré fringes, that is, the maximum intensity position, is 2nπ.
(N is an integer) even if A ₀ (y, z) is unknown. However, eventually all coordinates (y, z)
Needs to know the phase shift Φ (y, z) at the position between the moiré fringes. Hereinafter, A ₀ (y, z) without asking for [Phi (y,
z) is shown.

Here, it is assumed that a wedge-shaped phase shifter is inserted into at least one of the signal wave and the reference wave. In FIG. 3, a wedge-shaped phase shifter 19 is inserted in the signal wave.
In this case, the moire fringes captured by the two-dimensional X-ray detector are, for example, as shown in FIG. 5A when there is no object, and as shown in FIG. 5B when the object 10 is inserted. As described above, the phase shift Φ (y, z) is the same as that in FIG.
It can be obtained as the displacement from (a). FIG.
Assuming that the interval between the moiré fringes in FIG. 5A is a, the point P in FIG.
Is the displacement of the moiré fringe at f · a. As described above, the interval between moire fringes corresponds to a phase shift of 2π,
The displacement a corresponds to a phase shift of 2π. Therefore, the phase shift at the point P is 2πf. In this manner, the phase shift Φ at the position where the moiré fringe is located in FIG. 5B is obtained. The Φ at the position between the moiré fringes can be interpolated using the phase shift Φ at the position where the moiré fringe is located, or can be examined in more detail by the method described below.

The wedge-shaped phase shifter 19 shown in FIG. 3 is moved in parallel in the inclination direction of the wedge. Now, it is assumed that the user has moved by Δt. The moiré fringes observed at this time are shown in FIG.
(C) When the object 10 is inserted, the state becomes as shown in FIG. The thin lines in the figure are moiré fringes before moving the phase shifter 19, that is, FIGS. 5A and 5B.
Is the same as that shown in FIG. In short, the moiré fringes move, and the movement amount Δt. Therefore, for example, the moire fringes pass through the point Q in FIG. 5D, and the phase shift Φ at the point Q can be known. Thus, Φ (y, z) can be examined in detail by changing Δt from 0 to a. By repeating the above operation while rotating the object 10, a cross-sectional image can be obtained.

FIG. 6 shows a processing procedure up to section image reproduction. In a state where the object 10 is not present, the phase shifter 19 is inserted into one of the propagation paths to observe the moire fringes (step 1).
1). The object to be observed 10 is set (step 12). The moire fringes are observed (step 13). It is determined whether the phase shifter 19 is moved in the inclination direction of the wedge (step 1).
4). The phase shifter 19 is moved in the inclination direction of the wedge (step 15). Steps 3 and 5 are repeated as many times as necessary. For example, it repeats ten times with Δt set to a / 10. Using the data obtained in the above steps, a distribution image Φ (y, z) of the phase shift is obtained by arithmetic processing (step 16). The object 10 is rotated around the rotation axis 13 by a fixed angle (for example, 1 °).
Is repeated until it rotates 180 °, and each rotation position, that is,
In order to determine the phase shift Φ (y, z) in each projection direction, it is determined whether rotation is necessary (step 17). The data (y, z) of the phase shift Φ obtained in step 11-17 is sent to the tomography processing device 30 to reproduce a cross-sectional image of the object 10 and display it on the display device 40 (step 18).

Embodiment 3 In Embodiment 2, a method of moving the analyzer instead of the operation of moving the phase shifter will be described here. FIG.
Shows an interferometer configured so that the analyzer 5 can move. The notch 14 is formed in the base 2 so as to reach the back surface, and the analyzer 5 detects the diffraction vector (ie, y
(Axis). The driving at the time of movement is performed by applying a voltage to the piezoelectric element 15 inserted into the cut 14.

Before the analyzer 5 moves, the phase shift Φ
Coordinates (y, z) satisfying (y, z) = 2nπ (n is an integer)
Moire fringes appear at the position z). Now, assuming that the analyzer 5 has moved by Δy, Φ (y, z) = 2π (n + Δ
y / d ₂₂₀ ), the moire fringe moves to a position satisfying y / d ₂₂₀ ). Therefore, the phase shift Φ (y, z) can be examined in more detail by observing the displacement of the moire fringes when Δy is changed from 0 to d ₂₂₀ . Displacement Δ of analyzer 5
There are, for example, the following two methods for monitoring y.
One method is to attach a mirror 16 to the analyzer 5 and directly measure Δy using a laser interferometer 18. Another method is to measure the X-ray transmission intensity of the analyzer 5 at a coordinate position outside the image of the object 10. At this time, the transmission intensity oscillates sinusoidally with respect to Δy, and its cycle is d ₂₂₀ . Therefore, Δy can be known from the change in the X-ray transmission intensity. Other image reproducing operations are the same as those in the second embodiment.

[0027]

The present invention measures the phase change of X-rays, γ-rays, neutrons, etc., and introduces a tomography method so that an internal distribution image of the refractive index of the object can be obtained in a non-destructive manner. It was made. In general, X-rays, γ-rays, and neutrons have a more remarkable phase change due to transmission through an object than absorption, and a tomography for measuring a phase change shown in the present invention from a conventional tomography for measuring an absorptivity. A distribution image with higher contrast can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment.

FIGS. 2A and 2B are flow charts showing a signal processing procedure according to the first embodiment, wherein FIG. 2A shows a procedure for obtaining a cross-sectional image using a refractive index distribution, and FIG. 2B shows a procedure for obtaining a cross-sectional image using an absorptivity distribution.

FIG. 3 is a block diagram illustrating a configuration of a second embodiment.

FIG. 4 is a perspective view schematically showing a configuration of a part of an interferometer according to a second embodiment.

FIGS. 5A and 5B are examples of moiré fringes observed in Example 2; (a) when there is no object to be observed; (b) when there is an object to be observed;
The case where the wedge is moved without the object to be observed is shown. (D) The case where the wedge is moved with the object to be observed is shown. .

FIG. 6 is a flowchart illustrating a signal processing procedure according to the second embodiment.

FIG. 7 is a block diagram showing a configuration of a third embodiment.

[Explanation of symbols]

1. Bonse-Hart interferometer, 2. Interferometer base, 3.
Beam splitter, 4 ... Mirror, 5 ... Analyzer, 6 ...
Incident X-ray, 7: transmitted diffraction wave by beam splitter, 8
… Reflected and diffracted waves by the beam splitter, 7 ′: reflected and diffracted waves (signal waves) reflected by the mirror of wave 7, 8 ′: reflected and diffracted waves (reference waves) by the mirror of wave 8, 9: waves 7 ′ and 8 ′ Standing interference fringes, 10: object to be observed, 11: two-dimensional X-ray detector, 12: shutter, 14: cut, 15: piezoelectric element, 16: mirror, 17: laser beam, 18: laser interferometer, 19: phase Shifter, 20 X-ray source, 30 Tomography signal processing device, 31 Signal conversion device, 40 Display device, 41 Control device, 42 Power supply for piezoelectric element, 50 Motor for shutter drive, 51 Shutter drive Motor driver for 52, object rotating motor, 53 ... motor driver for object rotating, 54 ... linear motor for wedge movement, 55 ...
Linear motor driver for wedge movement.

Claims (9)

(57) [Claims] 1. An apparatus for irradiating an object with energy waves from a plurality of different directions and reproducing a cross-sectional image of the object from a projected image of the object obtained when the object is transmitted through the object, wherein the projected image is an energy wave. Is provided as one corresponding to the distribution of the phase shift of the energy wave generated when the energy wave passes through the object. 2. A phase tomography apparatus according to claim 1, wherein the distribution of the phase shift is obtained by using an interferometer. 3. An apparatus according to claim 1, wherein X-rays, γ-rays, or neutron rays are used as energy waves. 4. A phase tomography apparatus according to claim 2, wherein a Bonze-Hart interferometer is used. 5. An apparatus according to claim 4, wherein the projection images of the object from a plurality of different directions are obtained by rotating the object around a specific rotation axis while the energy wave source is fixed. A phase tomography apparatus characterized in that the rotation axis is selected so as to be substantially perpendicular to the traveling direction of the energy wave and substantially parallel to a plane including the signal wave and the reference wave of the Bonse-Hart interferometer. 6. The phase-type apparatus according to claim 4, wherein a shutter is provided for the purpose of selectively blocking a reference wave generated in the Bonse-Hart interferometer. Tomography device. 7. A phase shifter according to claim 4, wherein a phase shifter is inserted in at least one of a signal wave or a reference wave generated in the Bonse-Hart interferometer. Type tomography device. 8. An apparatus according to claim 7, wherein said phase shifter is wedge-shaped and made of a material having a substantially homogeneous composition. 9. An apparatus according to claim 4, wherein an analyzer that is part of the Bonse-Hart interferometer is movable relative to the entire interferometer. apparatus.