JP2013042983A - Tomosynthesis imaging device and imaging method of tomosynthesis image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tomosynthesis imaging device and an imaging method of tomosynthesis image, capable of acquiring a high-quality phase image or differential phase image while suppressing deterioration in visibility of moire.SOLUTION: The tomosynthesis imaging device for acquiring internal depth information of an inspection object includes: a shield grid which is constituted by laminating at least two partial shield grids each having a transmissive portion and a shielding portion periodically aligned with a differed pitch of these portions; and a control means which moves the two partial shield grids in the direction of the pitch to control the overlapping state of each shielding portion between the partial shield grids by the lamination. The control means controls the overlapping state of each shielding portion according to the incident direction of an electromagnetic wave source by rotation of the electromagnetic wave source, and electromagnetic wave which is emitted from the electromagnetic wave source and transmitted by the transmissive portion of the shield grid suppresses the shielding by each shielding portion.

Description

  The present invention relates to a tomosynthesis imaging apparatus and a tomosynthesis image imaging method, and more particularly to a tomosynthesis imaging apparatus using a Talbot interferometer.

Talbot interferometry is a method for measuring the shape and composition of a subject using interference of electromagnetic waves of various wavelengths including light and X-rays. In general, an imaging apparatus including an electromagnetic wave source, a diffraction grating, and a detector is used. It is done.
Here, the principle of the Talbot interferometry will be briefly described.
First, a subject is irradiated with a coherent incident wave having a uniform phase wavefront from an electromagnetic wave source.
The wavefront of the electromagnetic wave transmitted through the subject changes depending on the shape and composition of the subject.
When the electromagnetic wave having this wavefront change is diffracted by the diffraction grating, an interference pattern is formed at a position away from the diffraction grating by a specific distance called a Talbot distance.
By detecting and analyzing the interference pattern with a detector, a phase wavefront (hereinafter referred to as a phase image) changed by the subject or a differential image of the phase wavefront (hereinafter referred to as a differential phase image) is obtained. Can do.

Moreover, as described in Patent Document 1, a moire is formed by arranging a shielding grid in which a transmission part that transmits an electromagnetic wave and a shielding part that shields it are periodically arranged at a position where an interference pattern occurs, There is also a method in which the moire is detected and analyzed to obtain a phase image or a differential phase image of the subject.
When this method is used, a detector having a spatial resolution larger than the period of the interference pattern can be used, so the Talbot interferometry using X-rays as electromagnetic waves (hereinafter referred to as X-ray Talbot interferometry) is used. It is often used in image pickup devices.
An interferometer provided with a light source grating that divides electromagnetic waves into a plurality of light sources is called a Talbot-Lau interferometer.

An X-ray imaging diagnostic apparatus has tomosynthesis as one of methods for acquiring depth information inside a subject, and has recently been put into practical use in a mammography apparatus or the like.
As described in Patent Document 2, tomosynthesis is different from CT (computer tomography) method in that only an X-ray tube or an X-ray tube and a detector need to be rotated about 50 degrees at maximum. Depth information inside the subject can be acquired without the need for an increase in size.

JP 2010-164373 A International Publication No. 93/22893 Pamphlet

When configuring a tomosynthesis imaging device using a Talbot interferometer, when the rotation angle of the electromagnetic wave source reaches a certain rotation angle or more, most of the electromagnetic waves incident on the shielding grid are shielded by the electromagnetic wave absorber of the shielding grid. End up.
As a result, the visibility calculated from the intensity distribution of the moire formed by the diffraction grating and the shielding grating is lowered, and the image quality of the obtained phase image and differential phase image may be lowered.

  The present invention has been made in view of the above problems, and provides a tomosynthesis imaging apparatus and a tomosynthesis image imaging method that can suppress a reduction in moire visibility and obtain a high-quality phase image or differential phase image. And

Tomosynthesis imaging apparatus of the present invention,
An electromagnetic wave source configured to be rotatable;
A diffraction grating for diffracting electromagnetic waves emitted from the electromagnetic wave source;
A shielding grating that blocks a part of the electromagnetic wave diffracted by the diffraction grating;
Detecting means for detecting an intensity distribution of the electromagnetic wave that has passed through the shielding grid;
A tomosynthesis imaging device for obtaining depth information inside the object to be inspected based on information detected by the detection means,
The shielding grating is composed of a stack of at least two partially shielding gratings in which a transmission part and a shielding part are periodically arranged, and these periods have different periods.
Control means for controlling the overlapping state of the shielding portions between the partial shielding gratings by the stack by moving the two partial shielding gratings in the direction of the period;
According to the incident direction of the electromagnetic wave source due to the rotation of the electromagnetic wave source, to control the overlapping state of the shielding portions by the control means,
The electromagnetic wave emitted from the electromagnetic wave source and transmitted through the transmission part of the shielding grid suppresses shielding by the shielding parts.
The tomosynthesis image capturing method of the present invention includes:
An electromagnetic wave source configured to be rotatable;
A diffraction grating for diffracting electromagnetic waves emitted from the electromagnetic wave source;
A shielding grating that blocks a part of the electromagnetic wave diffracted by the diffraction grating;
Detecting means for detecting an intensity distribution of the electromagnetic wave that has passed through the shielding grid;
A tomosynthesis image capturing method for obtaining depth information inside an object based on information detected by the detection means,
The tomosynthesis image is picked up by using a shielding grating composed of a stack of at least two partial shielding gratings, in which a transmission part and a shielding part are periodically arranged, and these periods have different periods. When doing
Rotating the electromagnetic wave source;
Controlling the attitude of the diffraction grating according to the rotation of the electromagnetic wave source;
According to the incident direction of the electromagnetic wave source, to control the overlapping state of the shielding portions,
Suppressing the electromagnetic wave emitted from the electromagnetic wave source and transmitted through the transmission part of the shielding grid from being shielded by the shielding parts;
Controlling the attitude of the detection means according to the rotation of the electromagnetic wave source;
It is characterized by having.

  According to the present invention, it is possible to realize a tomosynthesis imaging apparatus and a tomosynthesis image imaging method that can suppress a decrease in moire visibility and acquire a high-quality phase image and differential phase image.

It is a figure explaining the structural example of the X-ray tomosynthesis imaging device which concerns on embodiment of this invention. It is a figure explaining the two-dimensional diffraction grating which concerns on embodiment of this invention. It is a figure explaining the lamination | stacking state of the partial shielding grating which concerns on embodiment of this invention. It is a figure explaining the two-dimensional shielding grating which concerns on embodiment of this invention. It is a figure explaining the X-ray tomosynthesis imaging device in the typical rotation angle which concerns on embodiment of this invention.

The configuration example of the tomosynthesis imaging apparatus according to the embodiment of the present invention will be described below.
The tomosynthesis imaging apparatus of the present embodiment includes an electromagnetic wave source configured to be rotatable, a diffraction grating that diffracts an electromagnetic wave emitted from the electromagnetic wave source, and a shielding grating that blocks a part of the electromagnetic wave diffracted by the diffraction grating. And comprising.
And the intensity distribution of the said electromagnetic wave which passed this shielding grid is detected by a detection means, and it is comprised so that the depth information inside a to-be-inspected object may be acquired based on this detected information.
These will be described with reference to the drawings. In each of the drawings described below, the same members are denoted by the same reference numerals, and redundant descriptions are omitted.
In this embodiment, a case where the present invention is applied to an X-ray tomosynthesis imaging apparatus using the X-ray Talbot interferometry will be described.
FIG. 1 is a diagram illustrating a configuration example of an X-ray tomosynthesis imaging apparatus according to the present embodiment.
The X-ray tomosynthesis imaging apparatus shown in FIG. 1 includes an X-ray source 110, a diffraction grating 130 that diffracts X-rays from the X-ray source, and a shielding grating that shields part of the X-rays diffracted by the diffraction grating 130. 150 and a detector (detection means) 170 for detecting X-rays that have passed through the shielding grid.
The shielding grating 150 is composed of at least two partial shielding gratings 301 (see FIG. 3).
Furthermore, a calculation device 180 that performs calculation based on the detection result of the detector, and a control unit (control means) 190 that controls the posture of the X-ray source 110, the diffraction grating 130, the shielding grating 150, and the partial shielding grating 301 are provided. Yes.
For example, according to the rotation of the electromagnetic wave source, the control unit controls the posture of the grating surface of the shielding grating and the grating surface of the diffraction grating in parallel, and in the grating surface direction of the diffraction grating with respect to the incident direction of the electromagnetic wave. The attitude can be controlled.
Further, the attitude of the diffraction grating can be controlled so that the grating surface of the diffraction grating is perpendicular to the electromagnetic wave incident direction according to the rotation of the electromagnetic wave source.
Then, the imaging apparatus of the present embodiment images the phase information of the subject (inspected object) 120 as moire.

Hereinafter, each of the above-described configurations will be described more specifically.
The imaging apparatus of this embodiment includes an X-ray source 110 as an electromagnetic wave source.
When the X-ray 111 generated from the X-ray source 110 passes through the subject 120, a change in phase and absorption occur in the X-ray 111 according to the composition and shape of the subject 120.
As the X-ray source, an X-ray source that generates continuous X-rays or an X-ray source that generates characteristic X-rays may be used.
The wavelength is appropriately selected from those having a wavelength of 0.1 to 5 mm.
Further, on the path of the X-rays emitted from the X-ray source 110, a wavelength selection filter and a light source grating for the source for dividing the X-rays into thin beams may be provided as appropriate.

In addition, the diffraction grating 130 has a phase advancer 131 and a phase delayer 132 periodically arranged, and diffracts the X-ray 111 to form an interference pattern 140 having a bright part and a dark part.
In FIG. 1, the diffraction grating 130 is disposed between the subject 120 and the shielding grating 150, but may be disposed between the X-ray source and the subject.
When the diffraction grating 130 is disposed between the subject 120 and the shielding grating 150, an X-ray whose phase wavefront has changed by the subject is diffracted, thereby forming an interference pattern having the phase information of the subject.
On the other hand, when a diffraction grating is disposed between the X-ray source and the subject, an X-ray phase wavefront diffracted by the diffraction grating changes depending on the subject, thereby forming an interference pattern having the phase information of the subject. .

The phase advancer 131 and the phase delay unit 132 may be formed so as to have a phase difference with respect to the transmitted X-ray.
Generally, the phase difference between the X-ray transmitted through the phase delay unit 132 and the X-ray transmitted through the phase advance unit 131 is π or π / 2. The former is sometimes called a π diffraction grating and the latter is called a π / 2 diffraction grating.
However, the phase difference between the X-rays transmitted through the phase delay unit 132 and the X-rays transmitted through the phase advancer 131 may be constant within the region where X-rays are diffracted, even if it is not π or π / 2. For example, the phase difference of transmitted X-rays may be π / 3.

The phase advancing unit 131 and the phase delay unit 132 may be arranged so as to have a one-dimensional period, or may be arranged so as to have a two-dimensional period.
As an example in which the phase advancer 131 and the phase delay unit 132 are arranged so as to have a two-dimensional period, the phase advancer 220 and the phase delay unit 210 are arranged in a checkered pattern as shown in FIG. The diffraction grating 201 is mentioned.
In addition, there is a diffraction grating 201 in which a phase advancement unit 220 and a phase delay unit 210 as shown in FIG.
However, the arrangement method and shape of the phase advancer 131 and the phase delay unit 132 are not limited to these. For example, the phase advancer 131 and the phase delay unit 132 can be used as a diffraction grating even if the outer edge of the phase advancer or the phase delay unit is circular. Is possible.

When the diffraction grating 130 has a one-dimensional period, only the phase gradient information of the subject 120 in the one-dimensional direction can be acquired.
However, when the diffraction grating 130 has a two-dimensional period, the phase gradient information in the two-dimensional direction can be acquired, so that the phase information of the subject can be obtained more accurately.
Note that the material constituting the diffraction grating 130 is preferably a substance that transmits X-rays, and for example, silicon or the like can be used.

The interference pattern formed by diffracting the X-rays onto the diffraction grating 130 has a distance Z ₁ from the diffraction grating 130 of the following formula (1), where Z ₀ is the distance between the X-ray source 110 and the diffraction grating 130. ) Appears most clearly at the position where
In Equation (1), λ is the wavelength of X-rays, and d is the grating period of the diffraction grating 130.

N is a different value depending on the form of the diffraction grating, and is a real number that can be expressed as follows. Note that n is a natural number.
One-dimensional array of π diffraction gratings: N = n / 4−1 / 8
One-dimensional array of π / 2 diffraction grating: N = n−1 / 2
Two-dimensional checkered pattern π diffraction grating: N = n / 4−1 / 8
Two-dimensional checkered pattern π / 2 diffraction grating: N = n / 2−1 / 4
The shielding grating of this embodiment is configured by a stack of at least two partial shielding gratings in which a transmission part and a shielding part are periodically arranged, and these periods have different periods.
Specifically, the shielding grating 150 includes a transmission part 151 and a shielding part 152, and includes at least two partial shielding gratings 301. The partial shielding grating 301 includes a transmission part 350 and a shielding part 360 that are periodically arranged, and forms a moire by shielding a part of a bright part of the interference pattern 140.
Therefore, it is preferably provided at a position away from the diffraction grating 130 by the distance Z _1, but a moire can be formed even if the arrangement position of the shielding grating is deviated as long as the manufacturing error is about.
In FIG. 1, for convenience of explanation, the interference pattern 140 and the shielding grating 150 are illustrated separately.

As shown in FIG. 3, the partially shielded grating can correspond to a spherical wave emitted from the X-ray source by having different grating periods.
When one side of the lattice plane of the partial shielding grating is L, the period of the first partial shielding grating 301 is p1, and the period of the second partial shielding grating 310 is p2, the following conditional expression (2) needs to be satisfied. is there.

However, this is not the case when the area of the X-ray absorber portion is smaller than the area of the X-ray transmission portion.
Note that the transmission part 151 of the shielding grid is not limited as long as a part of the X-rays can be transmitted, and the opening does not need to pass therethrough.
Further, the shielding part 152 of the shielding grid may shield X-rays to such an extent that moire is generated when the shielding grating is arranged at the position where the interference pattern 140 is formed, and may not completely shield the X-rays. For example, gold can be used as a material constituting the shielding portion 152.

The period of the shielding grating 150 is the same as or slightly different from the interference pattern.
When a shielding grid having the same period as the interference pattern is used, moire is generated by in-plane rotation of the shielding grid with respect to the interference pattern.
Assuming that the period of the interference pattern is D and the angle between the light and dark period directions of the interference pattern and the period direction of the shielding grating is θ (where θ << 1 radians), the moire period Dm is D / θ.
On the other hand, when a shield grating having a slightly different period from the interference pattern is used, moire occurs without in-plane rotation of the shield grating.
If the period of the shielding grating is Da = D + δ (where δ << D), the moire period Dm is D ² / δ.

The partially shielded gratings can move in the periodic direction within a period of one cycle according to the rotation angle of the X-ray source in the X-ray tomosynthesis imaging apparatus.
As the partial shielding grating moves, the shielding portions in which the shielding portions of the partial shielding grating are stacked are arranged on a straight line in the X-ray incident direction.
In the shielding grid 150, the transmission part 151 and the shielding part 152 may be arranged periodically in a one-dimensional manner, or may be arranged in a two-dimensional manner.
For example, in the case of the checkered grating-like diffraction grating shown in FIG. 2A and using a π diffraction grating, the transmission part 420 and the shielding part 410 are two-dimensionally shown in FIG. The arrayed grid-like shielding grid 401 can be used.
Further, in the case of using the sigma lattice π / 2 diffraction grating shown in FIG. 2B, the transmission part 420 and the shielding part 410 are two-dimensionally arranged as shown in FIG. 4B. A checkered grid 401 can be used.
The above combination is an example, and various combinations of the diffraction grating and the shielding grating are possible.

The X-ray interference pattern information transmitted through the shielding grating 150 is detected by the X-ray detector 170 as a moire intensity distribution.
The X-ray detector 170 is an image sensor that can image X-ray moire.
As the detector, for example, an FPD (Flat Panel Detector) that can be converted into a digital signal can be used.

The control unit of the present embodiment controls the overlapping state of the shielding units between the partial shielding gratings by moving the two partial shielding gratings in the periodic direction.
At that time, according to the incident direction of the electromagnetic wave source due to the rotation of the electromagnetic wave source, the control means controls the overlapping state of the shielding parts, and the electromagnetic waves emitted from the electromagnetic wave source and transmitted through the transmission part of the shielding grid are transmitted to the shielding parts. It is comprised so that shielding by may be suppressed.
Specifically, the control unit of the present embodiment controls the postures of the diffraction grating, the shielding grating, and the detector according to the rotation of the X-ray source that rotates about the subject (inspection object).
The maximum rotation angle about the subject of the X-ray source is 20 degrees to the left and right, and imaging is performed by controlling the posture by 2 degrees within this range, for a total of 11 times.
The rotation angle around the subject of the X-ray source is θ, the distance from the X-ray source to the center of the subject at the normal position (when the X-ray source is perpendicular to the detector surface) is a, the subject When the distance from the center of the specimen to the diffraction grating surface is b, and the distance from the diffraction grating surface to the shielding grating surface is c,
The amount of control of the attitude of the diffraction grating, shielding grating, and detector by the rotation of the X-ray source is as follows.
The amount of translation along the grating plane of the diffraction grating is b tan θ, and the amount of translation along the detector plane of the shielding grating and detector is (b + c) tan θ.
However, the shielding grid and the detector are arranged at extremely close positions.
For example, as shown in FIG. 5, the distance from the X-ray source to the subject center is 1350 mm, the distance from the subject center to the diffraction grating surface is 10 mm, and the distance from the diffraction grating surface to the shielding grating surface is 125 mm. To do.
Then, control amounts of the attitudes of the diffraction grating, the shielding grating, and the detector due to the rotation of the X-ray source when the positive position is rotated 15 degrees in the positive direction and 15 degrees in the negative direction are calculated.
The diffraction grating has a translation amount of 2.7 mm along the grating surface, and a translation amount of 36 mm along the shielding grating and the detector surface of the detector.

The arithmetic device 180 calculates a spatial frequency spectrum by Fourier transforming the intensity distribution of the moire detected by the detector 170.
Next, phase recovery processing is performed using a spectrum corresponding to the frequency of the fundamental period component (hereinafter referred to as carrier frequency), and a differential phase image and a phase image are obtained. The arithmetic device 180 has, for example, a CPU.
Although the X-ray imaging apparatus of this embodiment has a calculation unit, if the Fourier transform and the phase recovery process can be performed based on information detected by the detector, the calculation apparatus and the X-ray imaging apparatus are provided separately. May be.
As the phase recovery method, the fringe scanning recovery method described in Patent Document 1 may be used.

The above phase recovery processing calculation is performed for each step according to the rotation of the X-ray source, and the tomosynthesis image is reconstructed by the shift addition method.
The shift addition method is a method of forming an image of an arbitrary cross section by shifting an appropriate amount of each image in the scanning direction with respect to a series of captured images and superimposing the images.
In addition, an X-ray imaging system may be configured by connecting an arithmetic device and a display unit.
However, in this specification, an X-ray imaging apparatus including an arithmetic device and a display unit that displays an image based on the arithmetic result of the arithmetic device are collectively referred to as an X-ray imaging system. According to the configuration of the present embodiment described above, it is possible to obtain a high-quality phase image and a differential phase image by controlling the attitude of at least one of the partial shielding gratings constituting the shielding grating. .

110: X-ray source 111: X-ray 120: Subject (inspection object)
130: diffraction grating 131: phase advancing unit 132: phase delay unit 140: interference pattern 150: shielding grating 151: transmission unit 152: shielding unit 170: detector (detecting means)
180: arithmetic device 190: control unit (control means)

Claims (6)

An electromagnetic wave source configured to be rotatable;
A diffraction grating for diffracting electromagnetic waves emitted from the electromagnetic wave source;
A shielding grating that blocks a part of the electromagnetic wave diffracted by the diffraction grating;
Detecting means for detecting an intensity distribution of the electromagnetic wave that has passed through the shielding grid;
A tomosynthesis imaging device for obtaining depth information inside the object to be inspected based on information detected by the detection means,
The shielding grating is composed of a stack of at least two partially shielding gratings in which a transmission part and a shielding part are periodically arranged, and these periods have different periods.
Control means for controlling the overlapping state of the shielding portions between the partial shielding gratings by the stack by moving the two partial shielding gratings in the direction of the period;
According to the incident direction of the electromagnetic wave source due to the rotation of the electromagnetic wave source, to control the overlapping state of the shielding portions by the control means,
The tomosynthesis imaging apparatus, wherein an electromagnetic wave emitted from the electromagnetic wave source and transmitted through a transmission part of the shielding grating suppresses shielding by the shielding parts.   The imaging apparatus according to claim 1, further comprising: a light source grid that divides electromagnetic waves emitted from the electromagnetic wave source.   The control means controls the posture of the grating surface of the shielding grating and the grating surface of the diffraction grating in parallel according to the rotation of the electromagnetic wave source, and the grating surface of the diffraction grating with respect to the incident direction of the electromagnetic wave The tomosynthesis imaging apparatus according to claim 1, wherein the posture is controlled in a direction.   2. The control unit according to claim 1, wherein the control unit controls the attitude of the diffraction grating so that a grating surface of the diffraction grating is perpendicular to an electromagnetic wave incident direction according to rotation of the electromagnetic wave source. Item 3. The tomosynthesis imaging apparatus according to Item 2.   The tomosynthesis imaging apparatus according to any one of claims 1 to 4, wherein the electromagnetic wave is an X-ray. An electromagnetic wave source configured to be rotatable;
A diffraction grating for diffracting electromagnetic waves emitted from the electromagnetic wave source;
A shielding grating that blocks a part of the electromagnetic wave diffracted by the diffraction grating;
Detecting means for detecting an intensity distribution of the electromagnetic wave that has passed through the shielding grid;
A tomosynthesis image capturing method for obtaining depth information inside an object based on information detected by the detection means,
The tomosynthesis image is picked up by using a shielding grating composed of a stack of at least two partial shielding gratings, in which a transmission part and a shielding part are periodically arranged, and these periods have different periods. When doing
Rotating the electromagnetic wave source;
Controlling the attitude of the diffraction grating according to the rotation of the electromagnetic wave source;
According to the incident direction of the electromagnetic wave source, to control the overlapping state of the shielding portions,
Suppressing the electromagnetic wave emitted from the electromagnetic wave source and transmitted through the transmission part of the shielding grid from being shielded by the shielding parts;
Controlling the attitude of the detection means according to the rotation of the electromagnetic wave source;
A tomosynthesis image capturing method characterized by comprising:

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