JP2011206490A - Radiographic system and radiographic method - Google Patents

Abstract

In a radiation imaging system and a radiation imaging method for performing phase imaging of a subject, the imaging accuracy is improved.
A radiation imaging system includes an X-ray source, a first transmission type grating, a second transmission type grating, a scanning mechanism for moving the second transmission type grating, and a first transmission type. A flat panel detector 30 that detects X-rays transmitted through the first and second transmission gratings 31 and 32, and an operation for generating a phase contrast image of the subject based on a plurality of images acquired by the flat panel detector 30 The processing unit 22 has a subject-free state of the pixel 40 of the flat panel detector 30 corresponding to each pixel with respect to the pixel value of each pixel constituting the refraction angle distribution image. Thus, sensitivity correction is performed in accordance with the period of the signal obtained by scanning the second transmission grating 32.
[Selection] Figure 10

Description

  The present invention relates to a radiation imaging system and a radiation imaging method for imaging a subject using radiation such as X-rays.

  X-rays are used as a probe for seeing through the inside of a subject because they have characteristics such as attenuation depending on the atomic numbers of elements constituting the substance and the density and thickness of the substance. X-ray imaging is widely used in fields such as medical diagnosis and non-destructive inspection.

  In a general X-ray imaging system, a subject is placed between an X-ray source that emits X-rays and an X-ray image detector that detects X-rays, and a transmission image of the subject is captured. In this case, each X-ray emitted from the X-ray source toward the X-ray image detector is caused by a difference in characteristics (atomic number, density, thickness) of the substance existing on the path to the X-ray image detector. After receiving a corresponding amount of attenuation (absorption), it enters each pixel of the X-ray image detector. As a result, the X-ray absorption image of the subject is detected and imaged by the X-ray image detector. As an X-ray image detector, in addition to a combination of an X-ray intensifying screen and a film and a stimulable phosphor, a flat panel detector (FPD) using a semiconductor circuit is widely used.

  However, since the X-ray absorption ability is lower as a substance composed of an element having a smaller atomic number, a problem that a sufficient softness (contrast) of an X-ray absorption image cannot be obtained with a soft tissue or a soft material of a living body. There is. For example, most of the components of the cartilage part constituting the joint of the human body and the joint fluid in the vicinity thereof are water, and there is little difference in the amount of X-ray absorption between them, so that it is difficult to obtain a difference in light and shade.

  Against the background of such problems, in recent years, an X-ray phase for obtaining an image (hereinafter referred to as a phase contrast image) based on an X-ray phase change (angle change) by an object instead of an X-ray intensity change by an object. Imaging research is actively conducted. In general, it is known that when X-rays are incident on an object, the interaction is higher in phase than in X-ray intensity. For this reason, in the X-ray phase imaging using the phase difference, a high-contrast image can be obtained even for a weakly absorbing object having a low X-ray absorption capability. As a kind of such X-ray phase imaging, in recent years, an X-ray imaging system using an X-ray Talbot interferometer comprising two transmission diffraction gratings (phase grating and absorption grating) and an X-ray image detector has been proposed. It has been devised (for example, see Patent Document 1).

  In the X-ray Talbot interferometer, a first diffraction grating (phase type grating or absorption type grating) is arranged behind a subject, and a specific distance (Talbot interference distance) determined by the grating pitch of the first diffraction grating and the X-ray wavelength. The second diffraction grating (absorption type grating) is disposed only downstream, and the X-ray image detector is disposed behind the second diffraction grating. The Talbot interference distance is a distance at which X-rays that have passed through the first diffraction grating form a self-image due to the Talbot interference effect, and this self-image is between the X-ray source and the first diffraction grating. It is modulated by the interaction (phase change) between the arranged subject and the X-ray.

  In the X-ray Talbot interferometer, moire fringes generated by superimposing the first image of the first diffraction grating and the second diffraction grating are detected by a fringe scanning method, and the phase information of the subject is obtained from the change of the moire fringes caused by the subject. get. In the fringe scanning method, the second diffraction grating is substantially parallel to the surface of the first diffraction grating with respect to the first diffraction grating and substantially in the grating direction (strip direction) of the first diffraction grating. The angle of X-rays refracted by the subject from a change in the signal value of each pixel obtained by the X-ray image detector, which is taken multiple times while being translated in the vertical direction at a scanning pitch obtained by equally dividing the lattice pitch. A distribution (phase shift differential image) is obtained, and a phase contrast image of the subject is obtained based on this angular distribution.

  In the above-described fringe scanning method, the second diffraction grating is scanned with a very fine scanning pitch in the absence of a subject to perform imaging, and a change curve of an output signal of each pixel of the X-ray image detector is obtained in advance. In photographing an object, the second diffraction grating is scanned at several points, and the signal value of each pixel at that time is adapted to a change curve obtained in advance, so that the light is easily incident on each pixel. It has also been proposed to determine the phase of X-rays (see, for example, Patent Document 2).

  Note that phase imaging by image capturing using a Talbot interferometer has been devised before X-ray phase imaging for visible light (for example, a He-Ne laser) having high coherence like X-rays. (For example, refer nonpatent literature 1).

International Publication No. 04/058070 Special table 2008-545981

Hector Canabal and two others, “Improved phase-shifting method for automatic processing of moire deflectograms” , APPLIED OPTICS, September 1998, Vol.37, No.26, p.6227-6233

  In the above phase imaging, the signal value output from each pixel of the X-ray image detector obtained by translating the second diffraction grating at a predetermined scanning pitch is expressed by the following equation (1). Given in.

Here, A _k (k = 0, 1,...) Is a constant determined by the shape of the diffraction grating, d is the period of the grating pattern of the second diffraction grating, and δ (x, y) is the distortion and manufacturing error of the diffraction grating. Offset value caused by the arrangement error, Z is the distance between the first diffraction grating and the second diffraction grating, φ (x, y) is the X-ray refraction angle by the subject, and ξ is the translation of the second diffraction grating. The amount of movement.

  The self-image of the first diffraction grating is displaced by an amount corresponding to the refraction angle φ due to refraction of X-rays at the subject. Here, the refraction angle φ (x, y) is expressed by the following equation (2) using the X-ray wavelength λ and the phase shift distribution Φ (x, y) of the subject.

  As described above, the amount of displacement of the self-image of the first diffraction grating due to the refraction of X-rays at the subject is related to the phase shift distribution Φ (x, y) of the subject. With this displacement amount as Δ, the displacement amount Δ is obtained by scanning the second diffraction grating, and the phase shift amount ψ of the intensity modulation signal output from each pixel of the image detector (with or without the subject H) The phase shift amount of the intensity modulation signal of each pixel in each case is related to the following equation (3).

  When the subject is spherical, φ (x, y) at the edge portion is given by the following equation (4).

  Here, D is the width of each pixel of the image detector in the scanning direction of the second diffraction grating, and Δn is the refractive index difference between the subject and the surrounding medium.

  From Equation (1) to Equation (4), when the refraction angle φ is obtained from the phase shift amount acquired from the intensity modulation signal of each pixel of the image detector, the period d of the grating pattern of the second diffraction grating. It is also affected by the distance Z between the first diffraction grating and the second diffraction grating and the width D of each pixel of the X-ray image detector.

  Regarding the period d of the grating pattern of the second diffraction grating, an error also occurs in the period d of the grating pattern due to distortion of the second diffraction grating and a manufacturing error, and the refraction angle φ changes due to the error of the period d. However, Patent Document 1 and Patent Document 2 do not consider any error in the period d of the grating pattern of the second diffraction grating. For this reason, in the phase contrast image generated based on the distribution of refraction angles, the contrast that should be originally formed is not formed.

  The present invention has been made in view of the above-described circumstances, and it is an object of the present invention to improve the accuracy of phase imaging in a radiation imaging system and a radiation imaging method for performing phase imaging of a subject.

(B) a radiation source that emits radiation; a first grating that generates a fringe image by passing the radiation; and a periodic pattern that substantially matches the periodic pattern of the fringe image. Intensity modulation means for applying intensity modulation to the fringe image in a plurality of relative positional relations having different phases with respect to the periodic pattern of the fringe image, and detecting the fringe image intensity-modulated based on the relative positional relations A distribution of refraction angles of radiation incident on the radiation image detector from a plurality of fringe images acquired by the radiation image detector, and a subject based on the distribution of refraction angles Calculating means for generating a phase contrast image of the pixel, and the calculating means for the pixel value of each pixel constituting the distribution image of the refraction angle by the intensity modulation means in the absence of a subject. When the intensity of the fringe image is modulated, sensitivity correction is performed according to the period of the output signal of the pixel of the radiation image detector corresponding to the pixel, and a phase contrast image is generated from the corrected distribution image of the refraction angle. A radiography system.
(B) Radiation is emitted from a radiation source to a subject, the radiation passes through a first grating to generate a fringe image, and a periodic pattern that substantially matches the periodic pattern of the fringe image has a period of the fringe image. Intensity modulation is applied to the fringe image in a plurality of relative positional relationships with different phases relative to the pattern, and the fringe image that has been intensity-modulated under each relative positional relationship is detected by a radiation image detector, and the radiation Radiation imaging that calculates a refraction angle distribution of radiation incident on the radiation image detector based on a plurality of fringe images acquired by an image detector and generates a phase contrast image of a subject based on the refraction angle distribution The pixel when the fringe image is intensity-modulated by the intensity modulation means in the absence of a subject with respect to the pixel value of each pixel constituting the distribution image of the refraction angle. A radiation imaging method for performing sensitivity correction according to a period of an output signal of a pixel of the radiological image detector corresponding to the above and generating a phase contrast image from the corrected distribution image of the refraction angle.

  According to the present invention, by looking at the period of the output signal of each pixel of the radiation image detector obtained when the intensity image is intensity-modulated by the intensity modulation means in the absence of a subject, the period of the pattern of the intensity modulation means is obtained. An error can be detected. Then, by performing sensitivity correction according to the period of the output signal of the pixel of the corresponding radiation image detector for the pixel value of each pixel constituting the distribution image of the refraction angle, the period of the pattern of the intensity modulation means A refraction angle distribution image reflecting an error can be obtained, and a phase contrast image can be generated from the refraction angle distribution image, thereby improving the accuracy of phase imaging.

It is a mimetic diagram showing the composition of an example of a radiography system for explaining the embodiment of the present invention. It is a block diagram which shows the control structure of the radiography system of FIG. It is a schematic diagram which shows the structure of a radiographic image detector. It is a perspective view which shows the structure of the 1st and 2nd transmissive | pervious grating | lattice. It is a side view which shows the structure of the 1st and 2nd transmissive | pervious grating | lattice. It is a schematic diagram which shows the mechanism for changing the period of a moire fringe by superimposition of the 1st and 2nd transmissive | pervious grating | lattice. It is a schematic diagram for demonstrating the refraction | bending of the radiation by a to-be-photographed object. It is a schematic diagram for demonstrating the fringe scanning method. It is a graph which shows the signal of the pixel of the radiographic image detector accompanying a fringe scanning. It is a schematic diagram for demonstrating the correction method of a phase contrast image. It is a mimetic diagram showing the composition of an example of a radiography system for explaining the embodiment of the present invention.

  An X-ray imaging system 10 shown in FIGS. 1 and 2 is an X-ray diagnostic apparatus that images a subject (patient) H in a standing position, and includes an X-ray source 11 that emits X-rays to the subject H, and an X-ray. An imaging unit 12 that is arranged to face the source 11 and detects X-rays transmitted through the subject H from the X-ray source 11 to generate image data, and an exposure operation and imaging of the X-ray source 11 based on the operation of the operator The console 12 is broadly classified into a console 13 that controls the photographing operation of the unit 12 and performs arithmetic processing on image data acquired by the photographing unit 12 to generate a phase contrast image.

  The X-ray source 11 is held movably in the vertical direction (x direction) by an X-ray source holding device 14 suspended from the ceiling. The photographing unit 12 is held by a standing stand 15 installed on the floor so as to be movable in the vertical direction.

  Based on the control of the X-ray source control unit 17, the X-ray source 11 is emitted from the X-ray tube 18 that generates X-rays according to the high voltage applied from the high voltage generator 16, and the X-ray tube 18. The X-ray includes a collimator unit 19 including a movable collimator 19a that limits an irradiation field so as to shield a portion that does not contribute to the inspection area of the subject H. The X-ray tube 18 is of an anode rotating type, and emits an electron beam from a filament (not shown) as an electron emission source (cathode) and collides with a rotating anode 18a rotating at a predetermined speed, thereby causing X-rays. Is generated. The colliding portion of the rotating anode 18a with the electron beam becomes the X-ray focal point 18b.

  The X-ray source holding device 14 includes a carriage portion 14a configured to be movable in a horizontal direction (z direction) by a ceiling rail (not shown) installed on the ceiling, and a plurality of support column portions 14b connected in the vertical direction. It consists of. A motor (not shown) that changes the position of the X-ray source 11 in the vertical direction is provided on the carriage unit 14 a by expanding and contracting the column unit 14 b.

  In the standing stand 15, a holding unit 15 b that holds the photographing unit 12 is attached to a main body 15 a installed on the floor so as to be movable in the vertical direction. The holding portion 15b is connected to an endless belt 15d that is suspended between two pulleys 15c that are spaced apart in the vertical direction, and is driven by a motor (not shown) that rotates the pulley 15c. The driving of the motor is controlled by the control device 20 of the console 13 described later based on the setting operation by the operator.

  Further, the standing stand 15 is provided with a position sensor (not shown) such as a potentiometer that detects the position of the photographing unit 12 in the vertical direction by measuring the movement amount of the pulley 15c or the endless belt 15d. . The detection value of this position sensor is supplied to the X-ray source holding device 14 by a cable or the like. The X-ray source holding device 14 moves the X-ray source 11 so as to follow the vertical movement of the imaging unit 12 by expanding and contracting the support column 14 b based on the supplied detection value.

  The console 13 is provided with a control device 20 including a CPU, a ROM, a RAM, and the like. The control device 20 includes an input device 21 through which an operator inputs an imaging instruction and the content of the instruction, an arithmetic processing unit 22 that performs arithmetic processing on the image data acquired by the imaging unit 12 and generates an X-ray image, and X A storage unit 23 for storing line images, a monitor 24 for displaying X-ray images and the like, and an interface (I / F) 25 connected to each unit of the X-ray imaging system 10 are connected via a bus 26. .

  As the input device 21, for example, a switch, a touch panel, a mouse, a keyboard, or the like can be used. By operating the input device 21, X-ray imaging conditions such as X-ray tube voltage and X-ray irradiation time, imaging timing, and the like. Is entered. The monitor 24 includes a liquid crystal display or the like, and displays characters such as X-ray imaging conditions and X-ray images under the control of the control device 20.

  The imaging unit 12 includes a flat panel detector (FPD) 30 made of a semiconductor circuit, a first transmissive grating 31 and a second transmissive grating 31 for detecting phase change (angle change) of X-rays by the subject H and performing phase imaging. The transmission type grating 32 is provided. The FPD 30 is disposed so that the detection surface is orthogonal to the optical axis A of the X-rays emitted from the X-ray source 11. Although described later in detail, the first and second transmission gratings 31 and 32 are disposed between the FPD 30 and the X-ray source 11. The imaging unit 12 also includes a scanning mechanism 33 that changes the relative positional relationship of the second transmissive grating 32 with respect to the first transmissive grating 31 by translating the second transmissive grating 32 in the vertical direction. Is provided. The scanning mechanism 33 is configured by an actuator such as a piezoelectric element, for example. The second transmission type grating 32 and the scanning mechanism 33 correspond to the intensity modulation means described in the claims.

  As shown in FIG. 3, the FPD 30 includes an image receiving unit 41 in which a plurality of pixels 40 that convert X-rays into electric charges and accumulate them in a two-dimensional array on the active matrix substrate, and an image from the image receiving unit 41. A scanning circuit 42 that controls the charge readout timing, a readout circuit 43 that reads out the charges accumulated in each pixel 40, converts the charges into image data and stores them, and the image data via the I / F 25 of the console 13. The data transmission circuit 44 is configured to transmit to the arithmetic processing unit 22. The scanning circuit 42 and each pixel 40 are connected by a scanning line 45 for each row, and the readout circuit 43 and each pixel 40 are connected by a signal line 46 for each column.

  Each pixel 40 directly converts X-rays into electric charges by a conversion layer (not shown) such as amorphous selenium, and stores the converted electric charges in a capacitor (not shown) connected to an electrode below the conversion layer. It can be configured as a direct conversion type element. A TFT switch (not shown) is connected to each pixel 40, and the gate electrode of the TFT switch is connected to the scanning line 45, the source electrode is connected to the capacitor, and the drain electrode is connected to the signal line 46. When the TFT switch is turned on by the drive pulse from the scanning circuit 42, the charge accumulated in the capacitor is read out to the signal line 46.

Each pixel 40 converts X-rays into visible light once with a scintillator (not shown) made of gadolinium oxide (Gd ₂ O ₃ ), cesium iodide (CsI), or the like, and converts the converted visible light into a photodiode. It is also possible to configure as an indirect conversion type X-ray detection element that converts the charges into charges (not shown) and accumulates them. The X-ray image detector is not limited to an FPD based on a TFT panel, and various X-ray image detectors based on a solid-state imaging device such as a CCD sensor or a CMOS sensor can also be used.

  The readout circuit 43 includes an integration amplifier circuit, an A / D converter, a correction circuit, and an image memory (all not shown). The integrating amplifier circuit integrates the charges output from each pixel 40 via the signal line 46, converts them into a voltage signal (image signal), and inputs it to the A / D converter. The A / D converter converts the input image signal into digital image data and inputs the digital image data to the correction circuit. The correction circuit performs offset correction, gain correction, and linearity correction on the image data, and stores the corrected image data in the image memory. As correction processing by the correction circuit, correction of X-ray exposure amount and exposure distribution (so-called shading) and pattern noise depending on FPD 30 control conditions (drive frequency and readout period) (for example, leak signal of TFT switch) May be included.

  As shown in FIGS. 4 and 5, the first transmissive grating 31 includes a substrate 31a and a plurality of X-ray shielding portions 31b arranged on the substrate 31a. Similarly, the second transmission type grating 32 includes a substrate 32a and a plurality of X-ray shielding portions 32b arranged on the substrate 32a. The substrates 31a and 31b are both made of an X-ray transparent member such as glass that transmits X-rays.

  Each of the X-ray shielding portions 31b and 32b is in one direction in a plane orthogonal to the optical axis A of the X-rays emitted from the X-ray source 11 (in the illustrated example, the y direction orthogonal to the x direction and the z direction). It is the linear member extended | stretched. As a material of each X-ray shielding part 31b, 32b, a material excellent in X-ray absorption is preferable, and for example, a metal such as gold, silver, or platinum is preferable. These X-ray shielding portions 31b and 32b can be formed by a metal plating method or a vapor deposition method.

The X-ray shielding portion 31b has a predetermined interval d _{1 with a} predetermined period p ₁ in a direction orthogonal to the one direction (x direction in the illustrated example) in a plane orthogonal to the optical axis A of the X-ray. Are arranged with a space between them. Similarly, X-ray shielding portion 32b, in the plane orthogonal to the optical axis A of the X-ray (in the present embodiments, x direction) direction perpendicular to the direction of constant at a period p _2, a predetermined one another They are arranged at intervals d _2. The first and second transmission gratings 31 and 32 do not give a phase difference to incident X-rays but give an intensity difference. Therefore, among the transmission gratings, particularly, an absorption grating or an amplitude. It is called a mold lattice. The slit portions (regions with the distances d ₁ and d ₂ ) may not be voids, and the voids may be filled with an X-ray low-absorbing material such as a polymer or light metal.

The first and second transmission gratings 31 and 32 are configured to linearly project the X-rays that have passed through the slit portion regardless of the presence or absence of the Talbot interference effect. Specifically, by setting the distances d ₁ and d ₂ to a value sufficiently larger than the peak wavelength of X-rays emitted from the X-ray source 11, most of the X-rays included in the irradiated X-rays are slit at the slit portion. It is configured to pass through without being diffracted while maintaining straightness. For example, when tungsten is used as the rotary anode 18a described above and the tube voltage is 50 kV, the peak wavelength of the X-ray is about 0.4 mm. In this case, if the distances d ₁ and d ₂ are about ₁ to 10 μm, most of the X-rays are projected linearly without being diffracted by the slit portion.

The X-ray emitted from the X-ray source 11 is not a parallel beam but a cone beam having the X-ray focal point 18b as a light emitting point, and thus a projection image projected through the first transmission type grating 31 (hereinafter referred to as a projection image). The projection image is referred to as a G1 image) and is enlarged in proportion to the distance from the X-ray focal point 18b. The grating pitch p ₂ and the interval d ₂ of the second transmission type grating 32 are determined so that the slit portions thereof substantially coincide with the periodic pattern of the bright part of the G1 image at the position of the second transmission type grating 32. Yes. That is, when the distance from the X-ray focal point 18b to the first transmissive grating 31 is L ₁ and the distance from the first transmissive grating 31 to the second transmissive grating 32 is L ₂ , the grating pitch p ₂ and the interval d ₂ are determined so as to satisfy the relationship of the following expressions (5) and (6).

Distance L ₂ from the first transmission type grating 31 to the second transmission type grating 32, a Talbot interferometer, but is constrained to Talbot distance determined by the grating pitch and the X-ray wavelength of the first diffraction grating The imaging unit 12 of the X-ray imaging system 10 has a configuration in which the first transmission type grating 31 projects incident X-rays without diffracting, and the G1 image of the first transmission type grating 31 is the first. because in all the positions of the rear transmission type grating 31 similarly obtained, the distance L _2, can be set independently of the Talbot distance.

As described above, the imaging unit 12 does not constitute a Talbot interferometer, but the Talbot interference distance Z when it is assumed that X-rays are diffracted by the first transmission type grating 31 is the first transmission type grating. Using the lattice pitch p _{1 of} 31, the X-ray wavelength (peak wavelength) λ, and a positive integer m, it is expressed by the following equation (7).

In the present X-ray imaging system 10, the distance L ₂ is set to a value shorter than the minimum Talbot interference distance Z when m = 1 for the purpose of reducing the thickness of the imaging unit 12. That is, the distance L ₂ is set to a value in the range satisfying the following equation (8).

The X-ray shielding portions 31b and 32b preferably completely shield (absorb) X-rays in order to generate a periodic pattern image with high contrast, but the above-described materials (gold, silver) having excellent X-ray absorptivity. Even if platinum or the like is used, there are not a few X-rays that are transmitted without being absorbed. Therefore, in order to enhance the shielding of the X-rays, the X-ray shielding portion 31b, the respective thicknesses _h 1, _{h 2} of 32b, it is preferable to increase the thickness much as possible. For example, when the tube voltage of the X-ray tube 18 is 50 kV, it is preferable to shield 90% or more of the irradiated X-rays. In this case, the thicknesses h ₁ and h ₂ are 30 μm or more in terms of gold (Au). It is preferable that

On the other hand, if the thicknesses h ₁ and h ₂ of the X-ray shielding portions 31b and 32b are excessively increased, X-rays that enter the first and second transmission gratings 31 and 32 obliquely do not easily pass through the slit portion. There is a problem that so-called vignetting occurs and the effective visual field in the direction (x direction) orthogonal to the extending direction (strand direction) of the X-ray shielding portions 31b and 32b becomes narrow. Therefore, in view of the field of view secured to define the upper limit of the thickness _h 1, _{h 2.} In order to secure the effective field length V in the x direction on the detection surface of the FPD 30, assuming that the distance from the X-ray focal point 18 b to the detection surface of the FPD 30 is L, the thicknesses h ₁ and h ₂ are shown in FIG. It is necessary to set so that following Formula (9) and (10) may be satisfy | filled from a scientific relationship.

For example, when d ₁ = 2.5 μm and d ₂ = 3.0 μm, and assuming L = 2 m assuming a normal hospital examination, the effective visual field length V in the x direction is 10 cm. In order to ensure the length, the thickness h ₁ may be 100 μm or less and the thickness h ₂ may be 120 μm or less.

In the first and second transmission gratings 31 and 32 configured as described above, the G1 image of the first transmission grating 31 and the second transmission grating 32 when the subject H is not disposed. The image contrast is generated in the X-rays by superimposing the images, and this image contrast is captured by the FPD 30. The pattern period p ₁ ′ of the G1 image at the position of the second transmissive grating 32 and the substantial grating pitch p ₂ ′ (substantial pitch after production) of the second transmissive grating 32 are manufacturing errors. Some differences occur due to or placement errors. Among these, the arrangement error means that the substantial pitch in the x direction changes due to the relative inclination and rotation of the first and second transmission gratings 31 and 32 and the distance between the two changing. I mean.

Due to the minute difference between the pattern period p ₁ ′ of the G1 image and the grating pitch p ₂ ′, the image contrast becomes moire fringes. The period T of the moire fringes is expressed by the following equation (11).

  In order to detect the moire fringes with the FPD 30, the arrangement pitch P of the pixels 40 in the x direction needs to satisfy at least the following expression (12), and further preferably satisfies the following expression (13) (here , N is a positive integer).

  Expression (12) means that the arrangement pitch P is not an integral multiple of the moire period T, and it is possible in principle to detect moire fringes even when n ≧ 2. Expression (13) means that the arrangement pitch P is made smaller than the moire period T.

Since the arrangement pitch P of the pixels 40 of the FPD 30 is a value determined by design (generally about 100 μm) and is difficult to change, the magnitude relationship between the arrangement pitch P and the moire period T is adjusted. Adjusts the position of the first and second transmission gratings 31 and 32 and changes the moire period T by changing at least one of the pattern period p ₁ ′ and the grating pitch p ₂ ′ of the G1 image. It is preferable to do.

FIG. 6 shows a method of changing the moire cycle T. The moire period T can be changed by relatively rotating one of the first and second transmission type gratings 31 and 32 around the optical axis A. For example, a relative rotation mechanism 50 that rotates the second transmission type grating 32 relative to the first transmission type grating 31 about the optical axis A is provided. When the second transmission type grating 32 is rotated by the angle θ by the relative rotation mechanism 50, the substantial grating pitch in the x direction changes from “p ₂ ′” → “p ₂ ′ / cos θ”. As a result, the moire cycle T changes (FIG. 6A).

As another example, the change in the moire period T is such that one of the first and second transmission gratings 31 and 32 is relatively centered about an axis perpendicular to the optical axis A and along the y direction. It can be performed by inclining. For example, a relative tilt mechanism 51 that tilts the second transmissive grating 32 relative to the first transmissive grating 31 with respect to an axis perpendicular to the optical axis A and along the y direction. Provide. When the second transmission type grating 32 is inclined by the angle α by the relative inclination mechanism 51, the substantial grating pitch in the x direction changes from “p ₂ ′” → “p ₂ ′ × cos α”. As a result, the moire cycle T changes (FIG. 6B).

As another example, the moire period T can be changed by relatively moving one of the first and second transmission gratings 31 and 32 along the direction of the optical axis A. For example, in order to change the distance L ₂ between the first transmission type grating 31 and the second transmission type grating 32, the second transmission type grating 32 is changed with respect to the first transmission type grating 31. A relative movement mechanism 52 that relatively moves along the direction of the optical axis A is provided. When the second transmission type grating 32 is moved by the movement amount δ to the optical axis A by the relative movement mechanism 52, the G1 image of the first transmission type grating 31 projected on the position of the second transmission type grating 32. The pattern period of “p ₁ ′” → “p ₁ ′ × (L ₁ + L ₂ + δ) / (L ₁ + L ₂ )” changes, and as a result, the moire period T changes (FIG. 6C).

In the X-ray imaging system 10, imaging unit 12 is not the Talbot interferometer as described above, since the distance L ₂ can be freely set, moire by changing the distance L ₂ as relative movement mechanism 52 A mechanism for changing the period T can be suitably employed. The change mechanism (relative rotation mechanism 50, relative tilt mechanism 51, and relative movement mechanism 52) of the first and second transmission gratings 31 and 32 for changing the moiré period T is constituted by an actuator such as a piezoelectric element. Is possible.

  When the subject H is disposed between the X-ray source 11 and the first transmission type grating 31, the moire fringes detected by the FPD 30 are 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. Therefore, the phase contrast image of the subject H can be generated by analyzing the moire fringes detected by the FPD 30.

  Next, a method for analyzing moire fringes will be described.

  FIG. 7 illustrates one X-ray refracted according to the phase shift distribution Φ (x) of the subject H in the x direction. Reference numeral 55 indicates an X-ray path that goes straight when the subject H does not exist. The X-ray that travels along this path 55 passes through the first and second transmission gratings 31 and 32 and enters the FPD 30. To do. Reference numeral 56 indicates an X-ray path refracted and deflected by the subject H when the subject H exists. X-rays traveling along the path 56 pass through the first transmission type grating 31 and are then shielded by the second transmission type grating 32.

  The phase shift distribution Φ (x) of the subject H is expressed by the following equation (14), where n (x, z) is the refractive index distribution of the subject H and z is the direction in which the X-rays travel.

  The G1 image projected from the first transmissive grating 31 to the position of the second transmissive grating 32 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. become. This amount of displacement Δx is approximately expressed by the following equation (15) based on the small X-ray refraction angle φ.

  Here, the refraction angle φ is expressed by the following equation (16) 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) of the subject H. This displacement amount Δx is the amount of phase shift ψ of the intensity modulation signal output from each pixel 40 of the FPD 30 (the amount of phase shift of the intensity modulation signal of each pixel 40 with and without the subject H). And the following equation (17).

  Accordingly, by obtaining the phase shift amount ψ of the intensity modulation signal of each pixel 40, the refraction angle φ is obtained from the equation (17), and the differential amount of the phase shift distribution Φ (x) is obtained using the equation (16). By integrating this with respect to x, the phase shift distribution Φ (x) of the subject H, that is, the phase contrast image of the subject H can be generated. In the present X-ray imaging system 10, the phase shift amount ψ is calculated using a fringe scanning method described below.

In the fringe scanning method, imaging is performed while one of the first and second transmission type gratings 31 and 32 is translated in a stepwise manner in the x direction relative to the other (that is, the phase of both grating periods is changed). Shoot while changing). In the X-ray imaging system 10, the second transmission type grating 32 is moved by the scanning mechanism 33 described above, but the first transmission type grating 31 may be moved. As the second transmission type grating 32 moves, the moire fringes move, and the translation distance (the amount of movement in the x direction) is one period of the grating period of the second transmission type grating 32 (grating pitch p ₂ ). (Ie, when the phase change reaches 2π), the moire fringes return to their original positions. With such a change in moire fringes, a fringe image is photographed by the FPD 30 while moving the second transmissive grating 32 by an integer of the grating pitch p ₂ , and each pixel 40 is taken out of the plural fringe images taken. By acquiring the intensity modulation signal and performing arithmetic processing by the arithmetic processing unit 22, the phase shift amount ψ of the intensity modulation signal of each pixel 40 is obtained.

FIG. 8 schematically shows how the second transmissive grating 32 is moved by the scanning pitch (p ₂ / M) obtained by dividing the grating pitch p ₂ into M (an integer of 2 or more). The scanning mechanism 33 translates the second transmissive grating 32 in order to M scanning positions of k = 0, 1, 2,..., M−1. In the figure, the initial position of the second transmissive grating 32 is substantially the same as the X-ray shielding part 32b in the dark portion of the G1 image at the position of the second transmissive grating 32 when the subject H is not present. The initial position is k = 0, 1, 2,..., M−1.

  First, at the position of k = 0, mainly X-rays that are not refracted by the subject H pass through the second transmission type grating 32. Next, when the second transmission type grating 32 is moved in order of k = 1, 2,..., X-rays passing through the second transmission type grating 32 are not refracted by the subject H. While the line component decreases, the X-ray component refracted by the subject H increases. In particular, at k = M / 2, mainly only X-rays refracted by the subject H pass through the second transmission type grating 32. When k = M / 2 is exceeded, the X-ray component that is refracted by the subject H decreases in the X-rays that pass through the second transmission type grating 32, while the X-ray that is not refracted by the subject H. The line component increases.

When imaging is performed by the FPD 30 at each position of k = 0, 1, 2,..., M−1, M pixel data are obtained for each pixel 40. Hereinafter, a method of calculating the phase shift amount ψ of the intensity modulation signal of each pixel 40 from the M pixel data will be described. When the pixel data (signal value) of each pixel 40 at the position k of the second transmission type grating 32 is denoted as I _k (x), I _k (x) is expressed by the following equation (18).

Here, x is a coordinate in the x direction of the pixel, A ₀ is the intensity of the incident X-ray, and _An is a value corresponding to the contrast of the intensity modulation signal (where n is a positive integer). is there). Φ (x) represents the refraction angle φ as a function of the coordinate x of the pixel 40.

  Next, using the relational expression of the following expression (19), the refraction angle φ (x) is expressed as the expression (20).

  Here, arg [] means extraction of the declination and corresponds to the phase shift amount ψ of the intensity modulation signal of each pixel 40. Therefore, the refraction angle φ (x) is obtained by calculating the phase shift amount ψ of the intensity modulation signal of each pixel 40 from the M pixel data obtained in each pixel 40 based on the equation (20). .

Specifically, as shown in FIG. 9, the M pixel data obtained in each pixel 40 is periodically with a period of the grating pitch p _{2 with} respect to the position k of the second transmission type grating 32. Change. The broken line in the figure shows the change of the pixel data when the subject H does not exist, and the solid line in the figure shows the change of the pixel data when the subject H exists. The phase difference between the two waveforms corresponds to the phase shift amount ψ of the intensity modulation signal of each pixel 40.

  Since the refraction angle φ (x) is a value corresponding to the differential phase value as shown in the above equation (16), the phase shift is obtained by integrating the refraction angle φ (x) along the x-axis. A distribution Φ (x) is obtained.

Next, correction of the phase shift distribution Φ (x) reflecting the error of the grating pitch p ₂ of the second transmission type grating 32 will be described.

  First, in a state where there is no subject, photographing is performed while one of the first and second transmission gratings 31 and 32 is translated stepwise in the x direction relative to the other (that is, the first transmission grating). Photographing is performed while changing the phase of the periodic pattern of the G1 image of the mold grating 31 and the grating pattern of the second transmission grating 32), and pixel data of each pixel 40 of the FPD 30 in each step is acquired.

In the X-ray imaging system 10, the second transmission type grating 32 is moved by the scanning mechanism 33 described above, but the first transmission type grating 31 may be moved. The translation distance (movement amount in the x direction) of the second transmission type grating 32 is preferably one period (grating pitch p ₂ ) of the grating pattern of the second transmission type grating 32, and this distance is moved. The number of steps is not particularly limited as long as the period of variation of the pixel data of each pixel 40 can be known.

  Next, the phase change amount of the intensity modulation signal of each pixel 40 is obtained from the plurality of pixel data of each pixel 40 of the FPD 30 acquired. The calculation method of the phase change amount may be obtained, for example, by assuming that the acquired intensity modulation signal of each pixel 40 is a trigonometric function and applying least square fitting to a plurality of pixel data.

In FIG. 10, when the second transmissive grating 32 is translated by a grating pitch p ₂ corresponding to one period of the grating pattern for a predetermined time (the grating of the second transmissive grating 32 with respect to the periodic pattern of the G1 image). An example of the intensity modulation signal of the pixel 40 when the phase of the pattern is changed by 2π is shown.

In the second transmission type grating 32, when p _avg = p ₂ where p _avg is the actual average pitch of the portion that transmits the X-rays incident on the pixel 40 of interest, the phase of the intensity modulation signal of the pixel 40 is The initial phase is α and changes from α to α + m ₁ π, and the amount of change m ₁ π is 2π (FIG. 10A). When p _avg <p ₂ , the phase of the intensity modulation signal of the pixel 40 changes from α to α + m ₂ π, and the amount of change m ₂ π is greater than 2π (FIG. 10B). Further, the period T ₂ of the intensity modulation signal at this time is T ₂ <T ₁ , where T ₁ is the period of the intensity modulation signal of the pixel 40 when p _avg = p ₂ . When p _avg > p ₂ , the phase of the intensity modulation signal of the pixel 40 changes from α to α + m ₃ π, and the amount of change m ₃ π is smaller than 2π (FIG. 10C). Further, the period T ₃ of the intensity modulation signal at this time is T ₃ <T ₁ . In the example shown in the figure, the initial phase α is 0, but the initial phase α varies depending on the initial position of the second transmissive grating 32 when the second transmissive grating 32 is translated. To do.

  When the phase change amount of the intensity modulation signal of the pixel 40 is mπ, the following equation (21) is established.

When the phase of the grating pattern of the second transmission type grating 32 with respect to the periodic pattern of the G1 image is changed by 2π in the absence of the subject H, the phase change amount of the intensity modulation signal of the pixel 40 is mπ. From the equations (20) and (21), if the correction coefficient of the pixel 40 is 2 / m, the grating of the second transmission type grating 32 with respect to the refraction angle φ (x) (or the phase differential value). Correction that reflects the error of the pitch p ₂ can be performed. For example, the correction coefficient 2 / m of each pixel 40 is obtained and stored in the storage unit 23 as a sensitivity correction map. Then, shooting is performed with the subject placed, a distribution image of the refraction angle φ (x) is obtained from the obtained stripe image, and the pixel value of each pixel constituting this is stored in the storage unit 23. With reference to the sensitivity correction map, correction is performed by applying a correction coefficient 2 / m of the pixel 40 of the FPD 30 corresponding to the pixel. A phase contrast image is generated based on the distribution image of the refraction angle φ (x) obtained by this correction.

  In the above description, the y coordinate in the y direction of the pixel 40 is not considered. However, by performing the same calculation for each y coordinate, a two-dimensional phase shift distribution Φ (x, y in the x direction and the y direction is used. ) Is obtained.

  The above calculation is performed by the calculation processing unit 22, and the calculation processing unit 22 stores the corrected phase contrast image in the storage unit 23.

  The above-described fringe scanning and phase contrast image generation processing is performed automatically after the imaging instruction is given by the operator from the input device 21, and the respective units are linked and operated automatically under the control of the control device 20. The phase contrast image of the subject H is displayed on the monitor 24.

According to the X-ray imaging system 10 described above, the period p ₂ of the grating pattern of the second transmission type grating 32 can be obtained by looking at the period of the intensity modulation signal of the pixel 40 obtained by the step scanning without the subject. An error can be detected. Then, sensitivity correction is performed on the pixel value of each pixel constituting the distribution image of the refraction angle φ (x) (or the phase differential value) according to the above period of the corresponding pixel 40, so that the second A phase contrast image reflecting the error of the grating pattern period p ₂ of the transmissive grating 32 can be generated, and the accuracy of phase imaging can be improved.

According to the X-ray imaging system 10 described above, most of the X-rays are not diffracted by the first transmissive grating 31 and are linearly projected onto the second transmissive grating 32. High spatial coherence is not required, and a general X-ray source used in the medical field as the X-ray source 11 can be used. The distance L ₂ from the first transmission type grating 31 to the second transmission type grating 32 can be set to an arbitrary value, and the distance L ₂ is smaller than the minimum Talbot interference distance in the Talbot interferometer. Since it can be set, the photographing unit 12 can be downsized (thinned). Further, according to the X-ray imaging system 10, almost all wavelength components of irradiated X-rays contribute to the projected image (G1 image) from the first transmission type grating 31 and the contrast of moire fringes is improved. The detection sensitivity of the phase contrast image can be improved.

The X-ray imaging system 10 described above performs a fringe scan on the projection image of the first transmission type grating 31 to calculate the refraction angle φ and the phase shift distribution Φ. Although the second transmission type gratings 31 and 32 have been described as being absorption type gratings, the present invention is not limited to this. As described above, when the refraction angle φ is calculated by performing fringe scanning on the Talbot interference image, the refraction angle φ depends on the period p ₂ of the grating pattern of the second transmission type grating 32. The invention is useful. Therefore, the first transmission type grating 31 is not limited to the absorption type grating but may be a phase type grating.

  Further, when the distance from the X-ray source 11 to the FPD 30 is increased, the blur of the G1 image due to the focal size of the X-ray focal point 18b (generally about 0.1 mm to 1 mm) is affected, and the image quality of the phase contrast image is affected. Since there is a risk of lowering, a multi-slit (source grid) may be arranged immediately after the X-ray focal point 18b.

  The multi-slit is an absorption type grating having a configuration similar to that of the first and second transmission type gratings 31 and 32, and a plurality of X-rays extending in one direction (in the X-ray imaging system 10 described above, the y direction). The shielding portions are periodically arranged in the same direction as the X-ray shielding portions 31b and 32b of the first and second transmission gratings 31 and 32 (in the X-ray imaging system 10 described above, the x direction). . This multi-slit partially shields X-rays from the X-ray source 11 to reduce the effective focal size in the x direction, and forms a large number of point light sources (dispersed light sources) in the x direction. Suppresses the blur of the G1 image.

  Further, in the X-ray imaging system 10 described above, the subject H is disposed between the X-ray source 11 and the first absorption grating 31, but the subject H is arranged with the first transmission grating 31 and the second absorption grating 31. A phase contrast image can also be generated in the same manner when it is arranged between the transmission type grating 32.

  In the X-ray imaging system 10 described above, the second transmission type grating 32 is used as the intensity modulation means. However, by using the X-ray image detector having the configuration disclosed in Japanese Patent Application Laid-Open No. 2009-133823, the Two transmission gratings 32 can be eliminated. This X-ray image detector is a direct conversion type X-ray image detector including a conversion layer that converts X-rays into electric charges and a charge collection electrode that collects electric charges converted in the conversion layer. The charge collection electrode is configured by arranging a plurality of linear electrode groups formed by electrically connecting linear electrodes arranged at a constant period so that the phases thereof are different from each other.

  FIG. 11 illustrates the configuration of the above X-ray image detector (FPD). The pixels 70 are two-dimensionally arranged at a constant pitch along the x and y directions, and each pixel 70 has a charge collection for collecting the charges converted by the conversion layer that converts X-rays into charges. An electrode 71 is formed. The charge collection electrode 71 is composed of first to sixth linear electrode groups 72 to 77, and the phase of the arrangement period of the linear electrodes of each linear electrode group is shifted by π / 3. Specifically, when the phase of the first linear electrode group 72 is 0, the phase of the second linear electrode group 73 is π / 3, the phase of the third linear electrode group 74 is 2π / 3, The phase of the fourth linear electrode group 75 is π, the phase of the fifth linear electrode group 76 is 4π / 3, and the phase of the sixth linear electrode group 77 is 5π / 3. Charges in the y direction of the pixels 70 are stored through the linear electrode groups 72 to 77, respectively.

  Further, each pixel 70 is provided with a switch group 78 for reading out charges collected by the charge collecting electrode 71. The switch group 78 includes TFT switches provided in each of the first to sixth linear electrode groups 72 to 77. By collecting the charges collected by the first to sixth linear electrode groups 72 to 77 individually by controlling the switch group 78, six types of fringe images having different phases can be obtained by one imaging. A phase contrast image can be generated based on these six types of fringe images. That is, the charge collection electrode 71 constitutes the intensity modulation means described in the claims.

  In the X-ray imaging system 10 described above, by using the X-ray image detector having the above-described configuration instead of the FPD 30, the second transmission type grating 32 is not required from the imaging unit 12. Can be realized. Further, in the present embodiment, it is possible to acquire a plurality of fringe images that have been intensity-modulated at different phases by one shooting, so that physical scanning for fringe scanning becomes unnecessary, and the above scanning is performed. The mechanism 33 can be eliminated. Instead of the charge collection electrode 71, it is possible to use a charge collection electrode having another configuration described in Japanese Patent Laid-Open No. 2009-133823.

  Furthermore, as another embodiment when the second transmission type grating 32 is not disposed, the fringe image (G1 image) obtained by the X-ray image detector is periodically sampled while changing the phase by signal processing. Thus, it is also possible to apply intensity modulation to the fringe image.

  The X-ray imaging apparatus 10 described above is an application of the present invention to an apparatus for medical diagnosis. However, the present invention is not limited to medical diagnosis applications, and may be applied to other radiation detection apparatuses for industrial use. Is also possible.

  As described above, the present specification substantially matches the periodic pattern of the fringe image, the radiation source that emits radiation, the first grating that generates the fringe image by passing the radiation. Intensity modulation means for providing intensity modulation to the fringe image by placing the periodic pattern in a plurality of relative positional relationships having phases different from each other with respect to the periodic pattern of the fringe image, and based on each relative positional relationship From the radiation image detector that detects the fringe image intensity-modulated at a plurality of fringe images obtained by the radiation image detector, the distribution of the refraction angle of the radiation incident on the radiation image detector is calculated, Computing means for generating a phase contrast image of the subject based on the refraction angle distribution, the computing means having no subject for the pixel value of each pixel constituting the refraction angle distribution image. In the state, when the intensity image is intensity-modulated by the intensity modulation means, sensitivity correction is performed according to the period of the output signal of the pixel of the radiation image detector corresponding to the pixel, and the distribution of the corrected refraction angle is performed. A radiography system for generating a phase contrast image from an image is disclosed.

  Further, in the radiographic system disclosed in this specification, when the calculation unit intensity-modulates the fringe image by the intensity modulation unit in a state where there is no subject for each pixel constituting the refraction angle distribution image. The ratio of the phase change amount of the periodic pattern of the intensity modulation means to the periodic pattern of the fringe image and the phase change amount of the output signal obtained from the pixel of the radiation image detector corresponding to the pixel, Sensitivity correction is performed by setting the sensitivity correction coefficient of the pixel and multiplying the pixel value of the pixel by the sensitivity correction coefficient.

  The radiation imaging system disclosed in the present specification includes a storage unit that stores a sensitivity correction map that holds the sensitivity correction coefficient of each pixel constituting the refraction angle distribution image, and the calculation unit includes the calculation unit Sensitivity correction is performed with reference to the sensitivity correction map stored in the storage unit.

  Further, in the radiation imaging system disclosed in this specification, the intensity modulation unit includes a second grating having a periodic pattern substantially matching the periodic pattern of the fringe image, and the first and second gratings. Scanning means for moving any one of them at a predetermined pitch.

  In the radiation imaging system disclosed in this specification, the intensity modulation unit moves one of the first grating and the second grating by one period of the grating pitch.

  Further, in the radiation imaging system disclosed in this specification, the radiological image detector includes, for each pixel, a conversion layer that converts radiation into electric charge, and a charge collection electrode that collects electric charge converted in the conversion layer. The charge collection electrode includes a plurality of linear electrode groups having a periodic pattern that substantially matches the periodic pattern of the fringe image, arranged in such a manner that their phases are different from each other. The intensity modulating means is constituted by the charge collecting electrode.

  In the radiation imaging system disclosed in this specification, the first grating is an absorption grating, and the radiation from the radiation source is projected onto the intensity modulation unit as a fringe image.

  In the radiation imaging system disclosed in this specification, the first grating is a phase grating, and the radiation from the radiation source is projected onto the intensity modulation unit as a fringe image by a Talbot interference effect.

  Further, in the present specification, a periodic pattern substantially matching the periodic pattern of the fringe image is generated by radiating radiation from a radiation source to a subject, causing the radiation to pass through a first grating to generate a fringe image. The fringe image is subjected to intensity modulation on the fringe image in a plurality of relative positional relations having phases different from each other with respect to the periodic pattern, and the intensity-modulated fringe image based on the relative positional relation is obtained by a radiation image detector. Based on the plurality of fringe images detected and acquired by the radiation image detector, the refraction angle distribution of the radiation incident on the radiation image detector is calculated, and the phase contrast image of the subject is calculated based on the refraction angle distribution. In the radiation imaging method for generating the image, the intensity modulation of the fringe image is performed by the intensity modulation means in a state where there is no subject with respect to the pixel value of each pixel constituting the distribution image of the refraction angle. A radiation imaging method is disclosed in which sensitivity correction is performed in accordance with a period of an output signal of a pixel of the radiation image detector corresponding to the pixel, and a phase contrast image is generated from the corrected distribution image of the refraction angle. Yes.

10 X-ray imaging system (radiography system)
11 X-ray source (radiation source)
DESCRIPTION OF SYMBOLS 12 Imaging | photography part 13 Console 14 X-ray source holding | maintenance apparatus 15 Standing stand 16 High voltage generator 17 X-ray source control part 18 X-ray tube 19 Collimator unit 20 Control apparatus 21 Input device 22 Arithmetic processing part 23 Storage part 24 Monitor 25 I / F
30 Flat panel detector (radiation image detector)
31 1st grating | lattice 32 2nd grating | lattice (intensity modulation means)
33 Scanning mechanism (intensity modulation means)
40 pixels

Claims (9)

A radiation source that emits radiation; and
A first grating that passes the radiation to generate a fringe image;
An intensity that has a periodic pattern that substantially matches the periodic pattern of the fringe image, and that applies intensity modulation to the fringe image by placing the periodic pattern in a plurality of relative positional relationships with respect to the periodic pattern of the fringe image. Modulation means;
A radiation image detector for detecting the fringe image intensity-modulated under each relative positional relationship;
A distribution of refraction angles of radiation incident on the radiation image detector is calculated from a plurality of fringe images acquired by the radiation image detector, and a phase contrast image of a subject is generated based on the distribution of refraction angles. Computing means;
With
The calculation means is the radiation image corresponding to the pixel when the intensity image is intensity-modulated by the intensity modulation means with no subject for the pixel value of each pixel constituting the distribution image of the refraction angle. A radiation imaging system that performs sensitivity correction according to a period of an output signal of a pixel of a detector and generates a phase contrast image from the corrected distribution image of the refraction angle. The radiation imaging system according to claim 1,
The calculation means includes: the intensity modulation means for the periodic pattern of the fringe image when the intensity modulation means is intensity-modulated by the intensity modulation means for each pixel constituting the distribution image of the refraction angle without a subject. The ratio between the phase change amount of the periodic pattern and the phase change amount of the output signal obtained by the pixel of the radiation image detector corresponding to the pixel is used as the sensitivity correction coefficient of the pixel, and the sensitivity correction coefficient is the pixel. Radiation imaging system that corrects sensitivity by applying to the pixel value of. The radiographic system according to claim 2,
A storage unit that stores a sensitivity correction map that holds the sensitivity correction coefficient of each pixel constituting the refraction angle distribution image;
The calculation means is a radiation imaging system that performs sensitivity correction with reference to the sensitivity correction map stored in the storage unit. The radiation imaging system according to any one of claims 1 to 3,
The intensity modulation means includes a second grating having a periodic pattern substantially matching the periodic pattern of the fringe image, and scanning means for moving one of the first and second gratings at a predetermined pitch. A radiography system comprising: The radiation imaging system according to claim 4,
The intensity modulation means is a radiation imaging system that moves one of the first grating and the second grating by one period of the grating pitch. The radiation imaging system according to any one of claims 1 to 3,
The radiological image detector is a radiological image detector provided with a conversion layer for converting radiation into electric charge and a charge collecting electrode for collecting electric charge converted in the conversion layer for each pixel,
The charge collection electrodes are arranged such that a plurality of linear electrode groups having a periodic pattern substantially coinciding with the periodic pattern of the fringe image are arranged in different phases from each other.
The intensity modulation means is a radiographic system comprising the charge collection electrode. The radiation imaging system according to any one of claims 1 to 6,
The first grating is an absorption grating, and the radiation imaging system projects the radiation from the radiation source onto the intensity modulation unit as a fringe image. The radiation imaging system according to any one of claims 1 to 6,
The first grating is a phase-type grating, and projects the radiation from the radiation source as a fringe image onto the intensity modulation means by a Talbot interference effect. Radiation from the radiation source to the subject,
Causing the radiation to pass through a first grating to produce a fringe image;
Providing a periodic pattern substantially coincident with the periodic pattern of the fringe image in a plurality of relative positional relationships different from each other in phase with respect to the periodic pattern of the fringe image, and applying intensity modulation to the fringe image;
The fringe image intensity-modulated under each relative positional relationship is detected by a radiation image detector,
Based on the plurality of fringe images acquired by the radiation image detector, a refraction angle distribution of the radiation incident on the radiation image detector is calculated, and a phase contrast image of the subject is generated based on the refraction angle distribution. A radiography method,
The pixel of the radiation image detector corresponding to the pixel value of each pixel constituting the distribution image of the refraction angle when the fringe image is intensity-modulated by the intensity modulation means in a state where there is no subject. A radiation imaging method for performing sensitivity correction in accordance with the period of the output signal and generating a phase contrast image from the corrected distribution image of the refraction angle.

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