WO2012057022A1

WO2012057022A1 - Radiography system and radiography method

Info

Publication number: WO2012057022A1
Application number: PCT/JP2011/074293
Authority: WO
Inventors: 拓司多田
Original assignee: 富士フイルム株式会社
Priority date: 2010-10-27
Filing date: 2011-10-21
Publication date: 2012-05-03
Also published as: JP2014012029A

Abstract

The present invention prevents image quality from degrading even when misalignment occurs between the relative positions of gratings during fringe scanning. First and second absorptive gratings are disposed between an X-ray source and an X-ray image detector. While the relative positions of the first and second absorptive gratings are being incrementally varied, an image is taken by the X-ray image detector at each relative position. The relative positions are detected by a position sensor. A phase differential image generator generates, on the basis of the detection value of the position sensor, a phase differential image by computing the phase shift of an intensity modulation signal that indicates the intensity variation of pixel data for each pixel. A phase contrast image generator generates a phase contrast image by integrating the phase differential image in the direction of change of the relative positions.

Description

Radiographic system and radiographic method

The present invention relates to a radiation imaging system and a radiation imaging method for obtaining an image based on a phase change of radiation, and more particularly to a radiation imaging system and a radiation imaging method using a fringe scanning method.

Radiation, such as X-rays, has a characteristic that it is attenuated depending on the atomic number of elements constituting the substance and the density and thickness of the substance. Focusing on this characteristic, X-rays are used as a probe for seeing through the inside of a subject in fields such as medical diagnosis and nondestructive inspection.

In a general X-ray imaging apparatus, an object is placed between an X-ray source that emits X-rays and an X-ray image detector that detects X-rays, and X-rays transmitted through the object are imaged. Do. In this case, X-rays emitted from the X-ray source toward the X-ray image detector are absorbed and attenuated when passing through the subject, and then enter the X-ray image detector. As a result, an image based on an X-ray intensity change by the subject is detected by the X-ray image detector.

Since the X-ray absorption ability is lower with an element having a smaller atomic number, there is a problem that a change in X-ray intensity is small and a sufficient contrast cannot be obtained in an image in a soft body tissue or soft material. For example, most of the components of the cartilage portion constituting the joint of the human body and the joint fluid in the vicinity thereof are water, and the difference in the X-ray absorption capacity between them is small, so that it is difficult to obtain contrast.

Against the background of such problems, research on X-ray phase imaging that obtains an image (hereinafter referred to as a phase contrast image) based on the X-ray phase change by the subject instead of the X-ray intensity change by the subject has been conducted. It is actively done. X-ray phase imaging is a method of imaging the X-ray phase change based on the fact that the phase change of the X-ray incident on the subject is larger than the intensity change. A high-contrast image can be obtained. As a kind of X-ray phase imaging, an X-ray imaging system using two diffraction gratings and an X-ray image detector is known (see, for example, Patent Document 1 and Non-Patent Document 1).

In this X-ray imaging system, a first diffraction grating (grid) is disposed behind the subject as viewed from the X-ray source, and a second diffraction grating is disposed downstream from the first diffraction grating by a Talbot distance, It is configured by placing an X-ray image detector behind it. The Talbot distance is the distance at which X-rays that have passed through the first diffraction grating form a self-image (stripe image) due to the Talbot interference effect, and depends on the grating pitch of the first diffraction grating and the X-ray wavelength. . This self-image is modulated by the phase change of the X-rays caused by the subject and refraction. By detecting this modulation amount, the phase change of the X-ray is imaged.

The fringe scanning method is known as a method for detecting the modulation amount. In the fringe scanning method, one of the first and second diffraction gratings is intermittently moved N times by a predetermined pitch in a direction perpendicular to the grating lines, and the relative positions of the first and second diffraction gratings are changed. Then, X-ray imaging is performed immediately after each intermittent movement. A phase modulation signal representing the intensity change of the pixel data between the obtained N images is generated, and the phase shift amount of this phase modulation signal (the phase shift amount with and without the subject) is calculated. By calculating, a phase differential image representing the modulation amount is generated. A phase contrast image is obtained by integrating the phase differential image. This fringe scanning method is also used in an imaging device using laser light (see, for example, Non-Patent Document 2).

As described above, in the radiographic system using the fringe scanning method, if a positional deviation occurs in the relative positions of the first and second diffraction gratings during the fringe scanning, an error occurs in the calculation of the phase deviation amount of the phase modulation signal. There is a problem that the image quality of the differential image and the phase contrast image deteriorates. Accordingly, it has been proposed to detect the relative positions of the first and second diffraction gratings with a sensor and display a detection result to warn an operator when the detected value is outside a predetermined range (patent) Reference 2).

Japanese Patent No. 4445397 JP 2008-200320 A

However, in the radiation imaging system described in Patent Document 2, when a positional deviation exceeding a predetermined range occurs in the relative position, the operator is only warned, and the amount of phase deviation of the phase modulation signal is reduced. Calculation errors still occur. For this reason, in order to obtain a phase differential image and a phase contrast image with good image quality, it is necessary to perform imaging again after eliminating the cause of the positional deviation. When re-imaging is performed, the subject is unnecessarily exposed, and therefore it is desired to prevent image quality deterioration without performing re-imaging even when the relative position is displaced.

It is an object of the present invention to provide a radiation imaging system and a radiation imaging method that can prevent image quality deterioration even when a positional shift occurs in the relative position of a grating during fringe scanning.

In order to achieve the above object, a radiation imaging system of the present invention includes first and second gratings arranged opposite to a radiation source, and scanning in which the relative positions of the first and second gratings are changed stepwise. The radiation emitted from the radiation source at each relative position is detected by a plurality of pixels arranged two-dimensionally through the first and second gratings, and pixel data of each pixel is obtained. Based on a radiation image detector to be generated, a first position sensor that detects position information of the first and second gratings at each relative position, and position information detected by the first position sensor. A phase differential image generation unit that generates a phase differential image by calculating a phase shift amount of an intensity modulation signal that represents a change in intensity of pixel data for each pixel.

The phase differential image generation unit corrects each relative position based on each position information, creates the intensity modulation signal from the corrected relative position and pixel data, and performs a calculation based on the least square method. The phase shift amount is preferably calculated by

It is preferable that the apparatus further includes a phase contrast image generation unit that generates a phase contrast image by integrating the phase differential image generated by the phase differential image generation unit.

The first grating is an absorption grating, and it is preferable to project incident radiation onto the second grating geometrically. The first grating is preferably an absorption type grating or a phase type grating, and it is preferable that the incident radiation causes a Talbot interference effect to be projected onto the second grating.

A second position sensor for detecting position information of the radiation source; and the phase differential image generator generates a phase of the intensity modulation signal based on the position information detected by the first and second position sensors. It is preferable to calculate the amount of deviation.

It is preferable to further include a multi-slit that partially blocks the radiation emitted from the radiation source and disperses the focal point. In this case, the image sensor further includes a second position sensor that detects position information of the multi-slit, and the phase differential image generation unit is based on the position information detected by the first and second position sensors. It is preferable to calculate the phase shift amount of the intensity modulation signal.

The radiation imaging method of the present invention includes a step of changing the relative positions of the first and second gratings opposed to the radiation source in stages, and the radiation emitted from the radiation source at each relative position, Detecting a plurality of pixels arranged two-dimensionally through the first and second grids, and generating pixel data of each pixel; and at each relative position, the first and second are detected by a position sensor. Detecting the position information of the lattice of the image, and calculating the phase shift amount of the intensity modulation signal representing the intensity change of the pixel data for each pixel based on the position information detected by the position sensor, And a generating step.

According to the present invention, the position information of the first and second gratings is detected by the position sensor, and the phase shift amount of the intensity modulation signal representing the intensity change of the pixel data with respect to the relative position is calculated based on the position information. Even when the relative position is misaligned, it is possible to prevent the image quality from deteriorating.

It is explanatory drawing which shows the structure of a X-ray imaging system. It is a block diagram which shows the structure of a flat panel detector. It is explanatory drawing which shows the structure of a 1st and 2nd absorption type grating | lattice. It is explanatory drawing explaining a fringe scanning method. It is a graph which shows an intensity | strength modulation signal, (A) shows the intensity | strength modulation signal when there is no position shift from an appropriate relative position, and (B) shows the intensity modulation signal when a position deviation occurs from an appropriate relative position. It is explanatory drawing which shows the structure of the X-ray imaging system of 2nd Embodiment. It is description explaining the moving amount | distance of the G1 image accompanying the position shift of a X-ray focus. It is a perspective view which shows the structure of the X-ray imaging system of 3rd Embodiment. It is a perspective view which shows the structure of the X-ray imaging system of 4th Embodiment.

(First embodiment)
1, the X-ray imaging system 10 includes an X-ray source 11, an imaging unit 12, a memory 13, an image processing unit 14, an image recording unit 15, an imaging control unit 16, a console 17, and a system control unit 18. The X-ray source 11 irradiates the subject H with X-rays. The imaging unit 12 detects X-rays that have passed through the subject H based on the fringe scanning method, and generates a plurality of image data. The memory 13 stores a plurality of image data. The image processing unit 14 performs image processing on the plurality of image data stored in the memory 13 to generate a phase differential image and a phase contrast image. The image recording unit 15 records a phase contrast image. The imaging control unit 16 controls the X-ray source 11 and the imaging unit 12. The console 17 includes a known operation unit and monitor. The X-ray imaging system 10 comprehensively controls the entire X-ray imaging system 10 based on an operation signal input from the console 17.

As is well known, the X-ray source 11 includes a high voltage generator, an X-ray tube, a collimator (all not shown), and the like, and emits X-rays based on the control of the imaging control unit 16. The X-ray tube is of a rotary anode type, and generates X-rays by colliding an electron beam emitted from a filament with the rotary anode in accordance with a voltage applied from a high voltage generator. The rotating anode rotates to reduce deterioration due to the electron beam continuously hitting the fixed position. The collision portion between the rotating anode and the electron beam is an X-ray focal point that emits X-rays. The collimator limits the irradiation field so as to shield components other than the imaging range among the X-rays emitted from the X-ray tube.

The imaging unit 12 is provided with a flat panel detector (FPD) 20 composed of a semiconductor circuit, and first and

second absorption gratings

21 and 22 for detecting X-ray phase changes due to the subject H. ing. The FPD 20 is disposed so that the surface thereof is orthogonal to a direction along the optical axis LA of X-rays irradiated from the X-ray source 11 (hereinafter referred to as Z direction).

The first absorption type grating 21 has a plurality of X-ray absorption parts 21a extending in one direction (hereinafter referred to as Y direction) in a plane orthogonal to the Z direction, and a direction (hereinafter referred to as “Z direction”). the X that direction) in which are arranged at a predetermined pitch p _1. Similarly, the second absorption grating 22 has a plurality of X-ray absorbing portions 22a which extend in the Y direction, in which are arranged at a predetermined pitch p ₂ in the X direction. As a material of the

X-ray absorption parts

21a and 22a, a metal excellent in X-ray absorption is preferable, and for example, gold (Au) or platinum (Pt) is preferably used.

The first absorption type grating 21 transmits the X-rays irradiated from the X-ray source 11 to generate a first periodic pattern image (hereinafter referred to as a G1 image), and the second absorption type grating 22 is a G1 image. Is partially shielded (intensity modulated) to generate a second periodic pattern image (hereinafter referred to as G2 image).

Further, the imaging unit 12 scans to sequentially change the relative position of the second absorption type grating 22 with respect to the first absorption type grating 21 by intermittently moving the second absorption type grating 22 in the X direction. A mechanism 23 is provided. The scanning mechanism 23 has a piezoelectric actuator or an electrostatic actuator. The scanning mechanism 23 is driven based on the control of the imaging control unit 16 at the time of stripe scanning described later. The memory 13 stores image data generated by the FPD 20 at each scanning position.

Furthermore, the imaging unit 12 includes a position sensor 24 that detects position information regarding the X direction of the first and second

absorption type gratings

21 and 22. As the position sensor 24, for example, a laser displacement sensor is used. The detection value of the position sensor 24 is supplied to the image processing unit 14 via the imaging control unit 16 and the system control unit 18. In addition to the laser displacement sensor, an encoder, a potentiometer, a Hall element, an ultrasonic sensor, an acceleration sensor, or the like may be used as the position sensor 24.

The image processing unit 14 includes a phase differential image generation unit 14a and a phase contrast image generation unit 14b. The phase differential image generation unit 14 a generates a phase differential image based on a plurality of image data in which a G2 image is captured by the FPD 20 at each scanning position and stored in the memory 13. The phase differential image generation unit 14 a generates a phase differential image using the detection value supplied from the position sensor 24.

The phase contrast image generation unit 14b generates a phase contrast image by integrating the phase differential image generated by the phase differential image generation unit 14a along the scanning direction (X direction). The phase contrast image is recorded in the image recording unit 15 and then output to the console 17 and displayed on the monitor.

The operation unit of the console 17 makes it possible to input imaging conditions such as tube voltage, tube current, and X-ray irradiation time of the X-ray tube, and an imaging start instruction. For example, a switch, a touch panel, a mouse, a keyboard or the like is used as the operation unit. The monitor is composed of a liquid crystal display, a CRT display, or the like, and displays information such as photographing conditions and an image display such as a phase contrast image.

2, the FPD 20 includes an image receiving unit 31, a scanning circuit 32, and a reading circuit 33. The image receiving unit 31 includes a plurality of pixels 30 that convert X-rays into electric charges and accumulate them two-dimensionally on an active matrix substrate (not shown) along the X and Y directions. The scanning circuit 32 controls the timing for reading out charges from the pixels 30. The readout circuit 33 converts the charges read from the pixels 30 into image data and outputs the image data. The scanning circuit 32 and each pixel 30 are connected to each other by a scanning line 34 for each row. The readout circuit 33 and each pixel 30 are connected by a signal line 35 for each column. The arrangement pitch of the pixels 30 is about 100 μm in each of the X direction and the Y direction.

As is well known, the pixel 30 directly converts X-rays into charges by a conversion layer (not shown) such as amorphous selenium, and a capacitor (not shown) connected to the converted charge at the lower electrode of the conversion layer. ) Is a direct conversion type X-ray detection element. Each pixel 30 is provided with a TFT switch (not shown). The gate electrode of the TFT switch is connected to the scanning line 34, the source electrode is connected to the capacitor, and the drain electrode is connected to the signal line 35. When the TFT switch is turned on by the drive pulse applied from the scanning circuit 32, the charge accumulated in the capacitor is read out to the signal line 35.

The pixel 30 temporarily converts X-rays into visible light using a scintillator (not shown) formed of gadolinium oxide (Gd ₂ O ₃ ), cesium iodide (CsI), or the like, and converts the converted visible light to photo An indirect conversion type X-ray detection element that converts the charge into a charge by a diode (not shown) and stores the charge may be used. In this embodiment, an FPD based on a TFT panel is used as the radiation image detector. However, a radiation image detector based on a solid-state imaging device such as a CCD sensor or a CMOS sensor may be used.

The readout circuit 33 includes an integration amplifier, a correction circuit, an A / D converter (none of which are shown), and the like. The integrating amplifier integrates the charges output from the pixels 30 via the signal line 35 and converts them into a voltage signal (image signal). The A / D converter converts the image signal converted by the integrating amplifier into digital image data. The correction circuit performs dark current correction, gain correction, linearity correction, and the like on the image data, and inputs the corrected image data to the memory 13.

In FIG. 3, X-ray absorbing portion 21a of the first absorption grating 21, at a predetermined pitch p ₁ in the X direction, and are arranged at a predetermined interval d ₁ from each other. The portion of the spacing _{d 1,} is provided an X-ray transmitting portion 21b. Similarly, X-ray absorbing portion 22a of the second absorption-type grating 22, at a predetermined pitch p ₂ in the X direction, and are arranged at a predetermined interval d ₂ from each other. The portion of the spacing _{d 2,} is provided an X-ray transmitting portion 22b. The first and

second absorption gratings

21 and 22 are gratings that give an intensity difference to incident X-rays, and are also called amplitude gratings. The

X-ray transmission portions

21b and 22b are configured by an X-transmissive material such as silicon (Si) or a polymer, or a gap.

The first and second

absorption type gratings

21 and 22 are configured to project X-rays that have passed through the

X-ray transmission parts

21b and 22b linearly (geometrically). Specifically, it is realized by setting the distances d ₁ and d ₂ to a value sufficiently larger than the peak wavelength of the X-rays irradiated from the X-ray source 11, and most of the X-rays included in the irradiated X-rays are diffracted. Without passing through, the

X-ray transmission parts

21b and 22b pass through while maintaining straightness. For example, when tungsten is used as the rotating anode of the aforementioned X-ray tube and the tube voltage is 50 kV, the peak wavelength of the X-ray is about 0.4 mm. In this case, the distances d ₁ and d ₂ may be about 1 μm to 10 μm. The grating pitches p ₁ and p ₂ are about 2 μm to 20 μm.

Since the X-ray irradiated from the X-ray source 11 is not a parallel beam but a cone beam having the X-ray focal point 11a as a light emitting point, the G1 image generated by the first absorption type grating 21 is an X-ray focal point. It is enlarged in proportion to the distance from 11a. The lattice pitch p ₂ and the interval d ₂ of the second absorption type grating 22 are set so that the pattern of the X-ray transmission part 22 b substantially matches the pattern of the bright part of the G1 image at the position of the second absorption type grating 22. Is set. When the distance from the X-ray focal point 11a to the first absorption-type grating 21 is L ₁ and the distance from the first absorption-type grating 21 to the second absorption-type grating 22 is L ₂ , the grating pitch p ₂ and distance d ₂ is set so as to satisfy substantially the relation of the following formula (1) and (2).

It is not always necessary to satisfy the formula (2), and the intervals d ₁ and d ₂ may be set independently.

The distance L ₂ from the first absorption type grating 21 to the second absorption type grating 22 is equal to the lattice pitch of the first absorption type grating 16 when the Talbot interference effect occurs in the first absorption type grating 21. While being constrained to Talbot distance determined by the X-ray wavelength, in the present embodiment, since the first absorption grating 21 is configured to geometrical optics projecting an incident X-ray, the distance L _2, and Talbot distance Can be set independently. This is because in this embodiment, the G1 image becomes a self-image of the first absorption type grating 21 at all positions downstream of the first absorption type grating 21.

Although the imaging unit 12 of the present embodiment does not constitute a Talbot interferometer, the Talbot distance Z _m when the Talbot interference effect is assumed to occur in the first absorption grating 21 is the first absorption. the grating pitch p ₁ of the type grating _21, the grating pitch p _2, X-ray wavelength (peak wavelength) lambda of the second absorption-type grating 22, and using the positive integer m, represented by the following formula (3).

Expression (3) is an expression representing the Talbot distance when the X-rays emitted from the X-ray source 11 are in the shape of a cone beam. “Atsushi Momose, et al., Japanese Journal of Applied Physics, Vol.47, No. 10, October 2008, 8077 ”.

In the present embodiment, it is possible to set the distance L ₂ as described above independently of the Talbot distance, for the purpose of thinning in the Z direction of the imaging unit 12, the distance L _2, in the case of m = 1 set to the minimum value shorter than a Talbot distance Z _1. That is, the distance L ₂ is set to a value in the range satisfying the following expression (4).

The

X-ray absorbers

21a and 22a preferably completely absorb (shield) X-rays in order to generate periodic pattern images (G1 image and G2 image) with high contrast. However, even if the above-described material having excellent X-ray absorption (gold, platinum, etc.) is used, there are not a few X-rays that are transmitted without being absorbed. For this reason, in order to increase the X-ray absorption, it is preferable to increase the thickness (thickness in the Z direction) of each of the

X-ray absorption portions

21a and 22a as much as possible (that is, increase the aspect ratio). For example, when the tube voltage of the X-ray tube is 50 kV, it is preferable to absorb 90% or more of the irradiated X-rays. The thickness of the

X-ray absorbing portions

21a and 22a is preferably in the range of 10 μm to 200 μm.

A G2 image generated by intensity-modulating the G1 image generated by the first absorption type grating 21 by the second absorption type grating 22 is photographed by the FPD 20. There may be a slight difference between the pattern period of the G1 image at the position of the second absorption grating 22 and the grating pitch p _{2 of} the second absorption grating 22 due to an arrangement error or the like. Causes moiré fringes in the G2 image. In addition, when one of the first and second

absorption type gratings

21 and 22 is rotated in the XY plane, a so-called rotational moire is generated in the G2 image. Even when moire fringes occur in the G2 image, there is no particular problem as long as the period of the moire fringes in the X direction or Y direction is larger than the arrangement pitch of the pixels 30.

When the subject H is disposed between the X-ray source 11 and the first absorption type grating 21, the G2 image detected by the FPD 20 is modulated by the subject H. This modulation amount is proportional to the angle of the X-ray deflected by the refraction effect by the subject H. Based on a plurality of image data obtained by the FPD 20, a phase differential image corresponding to the distribution of the X-ray refraction angles and a phase contrast image corresponding to a phase shift distribution described later are obtained.

Next, a method for generating a phase differential image and a phase contrast image will be described. Here, the coordinates in the X, Y, and Z directions are the x, y, and z coordinates. FIG. 3 illustrates one X-ray that is refracted according to the phase shift distribution Φ (x) in the X direction of the subject H. Reference numeral 40 indicates an X-ray path that goes straight when the subject H does not exist. X-rays traveling along the path 40 pass through the first and

second absorption gratings

21 and 22 and enter the FPD 20. Reference numeral 41 indicates an X-ray path refracted and deflected by the subject H when the subject H exists. X-rays traveling along this path 41 pass through the first absorption type grating 21 and are then absorbed by the X-ray absorption part 22 a of the second absorption type grating 22.

The phase shift distribution Φ (x) of the subject H is expressed by the following formula (5) using the refractive index distribution n (x, z) of the subject H. Here, the y-coordinate is omitted for simplification of description.

The G1 image projected from the first absorption type grating 21 to the position of the second absorption type grating 22 is displaced in the X direction by an amount corresponding to the refraction angle φ due to refraction of X-rays at the subject H. . This displacement amount Δx is approximately expressed by the following equation (6) based on the fact that the refraction angle φ of X-rays is very small.

Here, the refraction angle φ is expressed by the following equation (7) using the X-ray wavelength λ and the phase shift distribution Φ (x) of the subject H.

Thus, the displacement amount Δx of the G1 image due to the refraction of X-rays at the subject H is related to the phase shift distribution Φ (x). This displacement amount Δx is the phase shift amount ψ of the intensity modulation signal representing the intensity change with respect to the scanning position of the pixel data of each pixel 30 detected by the FPD 20 (the phase with and without the subject H). (The amount of misalignment) is related to the following equation (8).

Accordingly, by obtaining the phase shift amount ψ of the intensity modulation signal of each pixel 30, the refraction angle φ is obtained from the equation (8), and the differential amount of the phase shift distribution Φ (x) is obtained using the equation (7). By integrating this with respect to x, a phase contrast image corresponding to the phase shift distribution Φ (x) can be generated.

Next, a fringe scanning method for obtaining the phase shift amount ψ will be described. In the fringe scanning method, one of the first and second

absorption type gratings

21 and 22 is intermittently moved by a predetermined pitch in the X direction with respect to the other (the phase of both grating periods is changed) and is stopped. Take a photo. In the present embodiment, the first absorption type grating 21 is fixed, and the second absorption type grating 22 is intermittently moved by the scanning mechanism 23. When moire fringes are generated in the G2 image, the moire fringes move with the movement of the second absorption type grating 22, and the movement distance in the X direction is 1 of the grating period of the second absorption type grating 22. When the period (grating pitch p ₂ ) is reached (when the phase change reaches 2π), the moire fringes match the original pattern.

Specifically, the second absorption grating 22, while intermittently moving by an integral fraction of the grating pitch p _2, taking a G2 image in FPD20 during the stop. The position sensor 24 described above detects the positions in the X direction by measuring the positions of the end faces of the first and

second absorption gratings

21 and 22.

FIG. 4 schematically shows how the second absorption type grating 22 is intermittently moved at a constant scanning pitch (p ₂ / M) obtained by dividing the grating pitch p ₂ into M pieces. The scanning mechanism 23 sequentially moves the second absorption type grating 22 to M relative positions of k = 0, 1, 2,..., M−1. M is an integer greater than or equal to 2, for example, M = 5.

First, at the position of k = 0, mainly the X-ray component (non-refractive component) that has not been refracted by the subject H passes through the second absorption grating 22. Next, when the second absorption type grating 22 is moved in order of k = 1, 2,..., X-rays passing through the second absorption type grating 22 are reduced in non-refractive components. The X-ray component (refractive component) refracted by the subject H increases. In particular, at the position of k = M / 2, almost only the refractive component passes through the second absorption type grating 22. When the position exceeds k = M / 2, the X-ray passing through the second absorption grating 22 decreases the refractive component while increasing the non-refractive component.

When photographing is performed by the FPD 20 at each relative position k = 0, 1, 2,..., M−1, M pixel data are obtained for each pixel 30. 5A and 5B exemplify intensity modulation signals in the case of M = 5. [delta] _k is the relative phase of the second absorption grating 22 relative to the first absorption grating 21 (hereinafter, referred to as relative phase) represents the, defined by the following equation (9).

Here, γ _k represents the amount of deviation from the appropriate relative phase (2πk / M) due to the first and second

absorption type gratings

21 and 22 being displaced from the appropriate relative position k. FIG. 6A shows pixel data I _k (x) when the first and

second absorption gratings

21 and 22 are not displaced from the appropriate relative position k, that is, when γ _k = 0. Show. On the other hand, FIG. 5B shows pixel data I _k (x) when the first and

second absorption gratings

21 and 22 are displaced from the appropriate relative position k.

The relative phase shift amount γ _k is expressed by the following formula (10), where α _k is the positional shift amount of the first absorption type grating 21 in the X direction and β _k is the positional shift amount of the second absorption type lattice 22 in the X direction. ). The positional shift amounts α _k and β _k are calculated based on the detection value of the position sensor 24.

Hereinafter, a method for calculating the phase shift amount ψ (x) of the intensity modulation signal by the subject H based on the M pieces of pixel data I _k (x) constituting the intensity modulation signal will be described. The pixel data I _k (x) is generally represented by the following expression (11).

Here, A ₀ represents the intensity of incident X-rays. _An is a value corresponding to the contrast of the intensity modulation signal (where n is a positive integer). I is an imaginary unit.

If high-order terms of n ≧ 2 in the equation (11) are ignored, the pixel data I _k (x) is expressed by the following equation (12) representing a sine wave.

Pixel data I _k (x) that satisfies Expression (12) is a theoretical value. On the other hand, the pixel data I _k (x) actually obtained by the FPD 20 includes an error, and a deviation occurs from the equation (12) by the error.

In order to calculate the phase shift amount ψ (x) from the actual measurement value of the pixel data I _k (x), first, the equation (12) is transformed as shown in the following equation (13).

Here, a ₀ , a ₁ , and a ₂ are represented by the following equations (14) to (16), respectively.

Then, if a ₀ , a ₁ , a ₂ are determined so as to minimize the difference between the theoretical value and the actual measurement value of the pixel data I _k (x) using the least square method or the like, the following equation (17) is obtained. As shown, the phase shift amount ψ (x) is obtained from a ₁ and a ₂ .

The method of phase shift using the least square method is described in “Introduction to Applied Optical Measurement, Toyohiko Yadagai, Second Edition, published on February 15, 2005, Maruzen Co., Ltd. (pages 196 to 198)” Yes. In the present embodiment, a ₀ , a ₁ , and a ₂ are determined by solving the following determinant (18) based on the least square method.

Here, a, A (δ _k ), and B (δ _k ) are expressed by the following equations (19) to (21).

In the above description, the y coordinate of the pixel 30 is not taken into consideration. However, by performing the same calculation in consideration of the y coordinate of the pixel 30, a two-dimensional phase shift distribution ψ ( x, y) is obtained. This distribution ψ (x, y) is a phase differential image.

In the above description, higher-order terms of n ≧ 2 or more are ignored in equation (12). However, since terms of n ≧ 2 are also expressed by a linear combination, the terms of n ≧ 2 are included. Even in this case, equations (17) to (21) are established.

The phase differential image generation unit 14a applies a ₁ and a ₂ obtained by calculations based on the equations (18) to (21) for each pixel 30 to the equation (17), so that the phase differential image ψ (x, y) is generated. The phase contrast image generation unit 14 b generates a phase contrast image by performing integration processing along the X direction on the phase differential image ψ (x, y).

Next, the operation of the X-ray imaging system 10 configured as described above will be described. When an imaging start instruction is input from the console 17, the second absorption grating 22 is intermittently moved by a predetermined scanning pitch (p ₂ / M) by the scanning mechanism 23, and the relative position k is k = 0, 1, 2,..., M−1 in order, X-ray exposure by the X-ray source 11 and detection operation by the FPD 20 are performed at each relative position k.

As a result, M pieces of image data are generated by the FPD 20 and stored in the memory 13. At each relative position k, the position sensor 24 detects the positions of the first and

second absorption gratings

21 and 22 in the X direction, and the detection values are input to the image processing unit 14.

Next, the phase differential image generation unit 14a reads M pieces of image data from the memory 13, and performs calculations based on the equations (18) to (21) using the pixel data for each pixel 30. By applying a ₁ and a ₂ obtained by this calculation to Expression (17), a phase differential image ψ (x, y) is generated.

At the time of this calculation, the phase differential image generation unit 14a, based on the detection value input from the position sensor 24, shifts the position from the relative position k of the first and

second absorption gratings

21 and 22 in the X direction. The quantities α _k and β _k are calculated, and the above-described relative phase δ _k is obtained based on the equations (9) and (10), and this is applied to the equations (20) and (21). Note that using Equation (9) and Equation (10) corresponds to correcting the relative position k with the detection value of the position sensor 24.

After the phase differential image ψ (x, y) is generated, integration processing is performed by the phase contrast image generation unit 14b to generate a phase contrast image. The phase contrast image is recorded in the image recording unit 15 and then displayed on the monitor.

In the present embodiment, the positions of the first and

second absorption gratings

21 and 22 are detected by the position sensor 24. However, the positions of the first and

second absorption gratings

21 and 22 are individually detected. It may be detected by the position sensor. Moreover, a position sensor may be fixed to one of the 1st and 2nd absorption type | mold grating |

lattices

21 and 22, and both position may be detected by detecting the other position with this position sensor.

In the present embodiment, the initial position of the second absorption type grating 22 by the scanning mechanism 23 is a position where the dark part of the G1 image substantially coincides with the X-ray absorption part 22a when the subject H is not present (k = 0). However, the initial position is not limited to this, and any one of k = 0, 1, 2,..., M−1 may be selected.

In this embodiment, the phase contrast image is displayed on the monitor, but the phase differential image may be displayed on the monitor instead of the phase contrast image or together with the phase contrast image.

In the present embodiment, the two-dimensional distribution of the phase shift of the intensity modulation signal is a phase differential image. However, the differential value of the phase shift distribution Φ (x, y) is multiplied or added by a constant. If so, a two-dimensional distribution of any physical quantity such as the refraction angle φ may be used as the phase differential image.

In this embodiment, the subject H is arranged between the X-ray source 11 and the first absorption type grating 21, but the subject H is arranged with the first absorption type 21 and the second absorption type. You may arrange | position between the grating | lattices 22. FIG. In this case as well, a phase differential image and a phase contrast image can be similarly generated.

Hereinafter, other embodiments of the present invention will be described. In the following embodiments, the same reference numerals are used for the same configurations as those already described, and detailed description thereof is omitted.

(Second Embodiment)
In the first embodiment, the position of the first and second

absorption type gratings

21 and 22 is detected by the position sensor 24. In addition to this, the position of the X-ray source 11 is further detected, and the X-ray source 11 is detected. It may be configured to correct image quality deterioration due to the positional deviation.

As shown in FIG. 6, the X-ray imaging system 50 of the present embodiment includes a first position sensor 51 that detects position information about the X direction of the first and

second absorption gratings

21 and 22, and an X-ray. And a second position sensor 52 that detects position information regarding the X direction of the source 11. The first position sensor 51 has the same configuration as the position sensor 24 of the first embodiment.

As shown in FIG. 7, if the X-ray focal point 11a is moved by η _{k in the} X direction with the positional deviation of the X-ray source 11, the G1 image formed at the position of the second absorption grating 22 is , Move in the opposite direction. The movement amount ξ _k of the G1 image is expressed by the following equation (22) based on the geometric relationship.

That is, the movement of the X-ray focal point 11a by η _{k in the} X direction corresponds to the movement of the second absorption grating 22 by ξ _{k in the} same direction. The shift amount γ _k ′ of the relative phase between the second absorption type grating 22 and the G1 image corresponding to the movement amount ξ _k is expressed by the following equation (23).

Therefore, in the present embodiment, the phase differential image generation unit 14a obtains the shift amount γ _k by the following equation (24) instead of the above equation (10), and thereafter performs the same calculation to obtain the first and first values. The positional shift of the two

absorption gratings

21 and 22 and the X-ray source 11 is corrected. Other configurations and operations are the same as those of the first embodiment.

In the present embodiment, the positions of the first and

second absorption gratings

21 and 22 and the X-ray source 11 are individually detected, but a position sensor is fixed to one of these, The position sensor may be configured to detect the other two positions.

(Third embodiment)
In the first embodiment, when the distance from the X-ray source 11 to the FPD 20 is increased, the blur of the G1 image due to the focal spot size (generally about 0.1 mm to 1 mm) of the X-ray focal spot 11a affects the phase contrast. There is a risk of degrading the image quality. Therefore, as a third embodiment of the present invention, as shown in FIG. 8, a multi slit (ray source grid) 60 is arranged on the emission side of the X-ray source 11. The X-ray imaging system of the present embodiment has the same configuration as that of the first embodiment except that the multi-slit 60 is provided.

The multi-slit 60 is an absorption-type grating having the same configuration as the first and second absorption-

type gratings

21 and 22, and a plurality of X-ray absorption parts 61 extending in the Y direction are periodically arranged in the X direction. It is a thing. The multi-slit 60 partially shields the X-rays from the X-ray source 11 to disperse the X-ray focus in the X direction and reduce the size of each effective X-ray focus in the X direction. Therefore, the blur of the G1 image is suppressed. Similarly, an X-ray transmission part (not shown) is provided between the X-ray absorption parts 61 adjacent in the X direction.

In the present embodiment, the slit position of the multi-slit 60 becomes the X-ray focal point, and therefore the distance from the multi-slit 60 to the first absorption grating 21 corresponds to the distance L ₁ of the first embodiment. In the present embodiment, it is possible to correct image quality degradation due to the movement of the X-ray focal point, as in the second embodiment, by detecting position information regarding the X direction of the multi-slit 60 with a position sensor. The amount of movement of the multi slit 60 in the X direction may be the amount of movement η _k in the above equation (22). If the arrangement pitch in the X direction of the X-ray absorber 61 is p ₀ , it is necessary to satisfy the relationship of p ₀ = p ₂ L ₁ / L ₂ from the geometrical relationship. Other configurations and operations are the same as those of the first embodiment.

(Fourth embodiment)
In each of the above embodiments, the first absorption type grating 21 or the second absorption type grating 22 is moved in the fringe scanning. However, when the multi-slit 60 is provided, the first and second absorption type gratings are provided. It is possible to perform fringe scanning by moving the multi slit 60 while 21 and 22 are fixed.

In FIG. 9, the X-ray imaging system 70 of this embodiment includes a multi-slit 60 between the X-ray source 11 and the first absorption grating 21. The multi slit 60 is moved in the X direction by the scanning mechanism 71. In the present embodiment, similarly to the third embodiment, the distance L ₁ is a distance from the multi slit 60 to the first absorption type grating 21. The arrangement pitch p _{0 in} the X direction of the X-ray absorber 61 satisfies the relationship p ₀ = p ₂ L ₁ / L ₂ .

The scanning mechanism 71 intermittently moves the multi-slit 60 using a value obtained by dividing the arrangement pitch p ₀ by M as a scanning pitch. As a result, the relative position k of the multi-slit 60 with respect to the first and second

absorption type gratings

21 and 22 is sequentially changed to k = 0, 1, 2,..., M−1.

The X-ray imaging system 70 includes a position sensor 72 that detects the positions of the multi-slit 60 and the second absorption grating 22 in the X direction at each relative position k. In the present embodiment, since the multi slit 60 corresponds to the X-ray focal point, the amount of positional deviation in the X direction of the multi slit 60 corresponds to η _k of the second embodiment.

Therefore, the phase differential image generation unit 14a obtains the shift amount γ _k after setting α _k = 0 in the above equation (24), and performs the same calculation, whereby the multi-slit 60 and the second absorption type grating are obtained. 22 position shift is corrected. Other configurations and operations are the same as those of the first embodiment.

In the present embodiment, the position sensor 72 detects the positions of the multi-slit 60 and the second absorption grating 22, but in addition to this, the position of the first absorption grating 21 may be detected. Good. In this case, the phase differential image generation unit 14a obtains the shift amount γ _k using the above equation (24). Moreover, you may detect each of the multi slit 60, the 1st absorption-type grating | lattice 21, and the 2nd absorption-type grating | lattice 22 with an individual position sensor. In addition, a position sensor is fixed to any one of the multi slit 60, the first absorption type grating 21, and the second absorption type grating 22, and the other two positions are detected by the position sensor. It may be configured.

Furthermore, since the cause of the vibration is different between the multi-slit 60 and the first and second

absorption type gratings

21, 22, it is considered that the multi-slit 60 only vibrates. Therefore, a position sensor is provided only in the multi-slit 60. May be. In this case, the phase differential image generation unit 14a obtains the shift amount γ _k after setting α _k = β _k = 0 in the above equation (24), and performs the same calculation, whereby the multi-slit 60 Correct the misalignment.

In the present embodiment, since the distance L ₁ is usually larger than the distance L ₂ and the arrangement pitch p ₀ is relatively larger than the arrangement pitches p ₁ and p ₂ , the movement accuracy of the multi-slit 60 by the scanning mechanism 71 is There is an advantage that it may be lower than when the first absorption type grating 21 or the second absorption type grating 22 is moved. Further, since the multi-slit 60 is disposed near the X-ray source 11, the multi-slit 60 may be smaller than the first and second

absorption type gratings

21 and 22, and has an advantage that it can be easily moved.

(Fifth embodiment)
In each of the above embodiments, the X-rays incident on the first absorption type grating 21 are configured to be geometrically optically projected onto the second absorption type grating 22, but instead of this, Patent No. 4445977 As described in US Pat. No. 7,180,796, etc., the X-rays incident on the first grating form a self-image by the Talbot interference effect and are projected onto the position of the second grating. Also good. In this case, it is necessary to set the distance between the first and second gratings to the Talbot distance.

In this case, the first grating may be a phase grating instead of the absorption grating. The thickness of the X-ray absorption part and the X-ray transmission part is such that a phase difference of “π” or “π / 2” is generated in the X-ray between the X-ray absorption part and the X-ray transmission part. It is configured by setting materials.

The above embodiments may be combined with each other within a consistent range. The present invention can be applied to other radiographic systems such as industrial and nondestructive inspections, in addition to radiographic systems for medical diagnosis. The present invention can also be applied to a radiographic imaging system that uses gamma rays or the like in addition to X-rays.

Further, in the present specification, the following configuration related to the fourth embodiment is disclosed.
[Configuration 1]
First and second gratings disposed opposite the radiation source;
A multi-slit disposed between the radiation source and the first grating and partially shielding the radiation emitted from the radiation source to disperse the focal point;
A scanning mechanism that changes the relative position of the multi slit with respect to the first and second gratings in stages;
Radiation that detects radiation radiated from the radiation source at each relative position by a plurality of pixels arranged two-dimensionally via the first and second gratings and generates pixel data of each pixel. An image detector;
A position sensor for detecting position information with the multi-slit at each relative position;
Based on each position information detected by the position sensor, a phase differential image generation unit that generates a phase differential image by calculating a phase shift amount of an intensity modulation signal representing an intensity change of pixel data for each pixel;
A radiation imaging system comprising:
[Configuration 2]
The radiation imaging system according to Configuration 1, wherein the position sensor further detects position information of at least one of the first grating and the second grating.
[Configuration 3]
The radiation imaging system according to Configuration 1, wherein the position sensor further detects position information of each of the first grating and the second grating.
[Configuration 4]
The phase differential image generation unit corrects each relative position based on each position information, creates the intensity modulation signal from the corrected relative position and pixel data, and performs a calculation based on the least square method. The radiation imaging system according to any one of configurations 1 to 3, wherein the phase shift amount is calculated by:
[Configuration 5]
5. The configuration according to claim 1, further comprising: a phase contrast image generation unit that generates a phase contrast image by integrating the phase differential image generated by the phase differential image generation unit. Radiography system.

DESCRIPTION OF SYMBOLS 10 X-ray imaging system 20 Flat panel detector 21 1st absorption grating 21a X-ray absorption part 21b X-ray transmission part 22 2nd absorption type grating 22a X-ray absorption part 22b X-ray transmission part

Claims

First and second gratings disposed opposite the radiation source;
A scanning mechanism that changes the relative positions of the first and second gratings in stages;
Radiation that detects radiation radiated from the radiation source at each relative position by a plurality of pixels arranged two-dimensionally via the first and second gratings and generates pixel data of each pixel. An image detector;
A first position sensor for detecting position information of the first and second gratings at each relative position;
A phase differential image generation unit configured to generate a phase differential image by calculating a phase shift amount of an intensity modulation signal representing an intensity change of pixel data for each pixel based on each position information detected by the first position sensor; ,
A radiation imaging system comprising:
The phase differential image generation unit corrects each relative position based on each position information, creates the intensity modulation signal from the corrected relative position and pixel data, and performs a calculation based on the least square method. The radiation imaging system according to claim 1, wherein the phase shift amount is calculated by:
3. The phase contrast image generation unit according to claim 1, further comprising a phase contrast image generation unit that generates a phase contrast image by integrating the phase differential image generated by the phase differential image generation unit. The radiation imaging system described.
The first grating according to any one of claims 1 to 3, wherein the first grating is an absorptive grating, and projects incident radiation onto the second grating geometrically. Radiography system.
4. The first to third aspects according to claim 1, wherein the first grating is an absorption type grating or a phase type grating, and causes a Talbot interference effect on incident radiation to be projected onto the second grating. The radiation imaging system according to any one of Items.
A second position sensor for detecting position information of the radiation source;
The phase differential image generation unit calculates a phase shift amount of the intensity modulation signal based on position information detected by the first and second position sensors. 6. The radiographic system according to item 5.
The radiation imaging system according to claim 1, further comprising a multi-slit that partially shields radiation emitted from the radiation source and disperses the focal point.
A second position sensor for detecting position information of the multi-slit;
8. The phase differential image generation unit according to claim 7, wherein the phase differential image generation unit calculates a phase shift amount of the intensity modulation signal based on position information detected by the first and second position sensors. Radiography system.
Changing the relative positions of the first and second gratings opposed to the radiation source in stages;
Detecting radiation emitted from the radiation source at each relative position by a plurality of pixels arranged two-dimensionally via the first and second gratings, and generating pixel data of each pixel; ,
Detecting position information of the first and second gratings by a position sensor at each relative position;
Calculating a phase shift amount of an intensity modulation signal representing intensity change of pixel data for each pixel based on each position information detected by the position sensor, and generating a phase differential image;
A radiation imaging method characterized in that