JP2011206489A - Radiographic system and radiographic method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the accuracy of imaging in a radiographic system and a radiographic method for performing the phase imaging of a subject.SOLUTION: The radiographic system 10 includes an X-ray source 11, a first transmission type grating 31, a second transmission type grating 32, a scanning mechanism 33 for moving the second transmission type grating 32, a flat panel detector 30 for detecting X-rays which have transmitted through the first and second transmission type gratings 31, 32, and an arithmetic processing part 22 for generating the phase contrast image of a subject on the basis of a plurality of images acquired in the flat panel detector 30. The arithmetic processing part 22 executes sensitivity correction corresponding to an effective width D' to an incident radiation regarding the scanning direction of the second transmission type grating 32 of the pixel 40 of the flat panel detector 30 corresponding to the pixel, for the pixel value of each pixel configuring the distribution image of a refraction angle, and generates a phase contrast image on the basis of the corrected distribution image of the refraction angle.

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.

  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

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) And the phase shift amount of the intensity modulation signal of each pixel at (1) and (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 Equations (1) to (4), when the refraction angle φ is obtained from the phase shift amount ψ acquired from the intensity modulation signal of each pixel of the image detector, the period of the grating pattern of the second diffraction grating d, 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.

  Here, the X-ray emitted from the X-ray source is a cone beam, whereas the X-ray image detector is typically a plane. Therefore, the X-ray incident angle in each pixel of the X-ray image detector is different in each part of the X-ray image detector. When X-rays are incident substantially vertically on the central pixel of the X-ray image detector (X-ray incident angle is deep), the X-rays are inclined toward the periphery in the peripheral pixels (X Line incident angle becomes shallower). Therefore, the effective width of each pixel, that is, the projection width when each pixel is projected onto a plane orthogonal to the center line of the X-rays incident thereon is different in each part of the X-ray image detector.

  In Patent Document 1, the effective width of each pixel is not considered at all. However, as described above, the signal value of each pixel and the refraction angle acquired from the change in the signal value are the values of each pixel of the X-ray image detector. Depends on the width D. If the effective width of each pixel is different, the signal value of each pixel is different even if the phase shift of incident X-rays is the same, and useless contrast is 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 imaging in a radiation imaging system and a radiation imaging method for performing phase imaging of a subject.

(A) A radiation source that emits radiation; a first grating that generates a fringe image by passing the radiation; and an intensity of the fringe image at a plurality of relative positions that are different in phase from the periodic pattern of the fringe image. An intensity modulation unit that applies modulation; a radiation image detector that detects a fringe image intensity-modulated at each relative position by the intensity modulation unit; and a plurality of images acquired by the radiation image detector, Calculating a refraction angle distribution of the radiation incident on the detector, and generating a phase contrast image of the subject based on the refraction angle distribution, the calculation means including a refraction angle distribution image. With respect to the incident radiation with respect to the direction of movement of the pixel of the radiation image detector corresponding to the pixel with respect to the pixel value of each of the constituent elements, the moving direction when the intensity modulation unit takes the plurality of relative positions A radiation imaging system that performs sensitivity correction in accordance with all effective widths and generates a phase contrast image based on the corrected distribution image of the refraction angle.
(B) Radiation is radiated from a radiation source to a subject, the radiation passes through a first grating to generate a fringe image, and intensity modulation means at a plurality of relative positions whose phases are different from the periodic pattern of the fringe image By applying intensity modulation to the fringe image, the intensity modulation means detects the fringe image intensity-modulated at each relative position by a radiological image detector, and a plurality of fringe images acquired by the radiological image detector are detected. A radiation imaging method for calculating a refraction angle distribution of radiation incident on the radiation image detector and generating a phase contrast image of a subject based on the refraction angle distribution, and forming a refraction angle distribution image In relation to the pixel value of each pixel, the incident radiation with respect to the direction of movement of the pixel of the radiation image detector corresponding to the pixel when the intensity modulation means takes the plurality of relative positions. A radiation imaging method in which sensitivity correction is performed according to an effective width of the image and a phase contrast image is generated based on the corrected distribution image of the refraction angle.

  According to the present invention, by performing sensitivity correction on the pixel value of each pixel constituting the phase contrast image according to the effective width with respect to the incident radiation of the pixel of the radiation image detector corresponding to the pixel, Accuracy can be increased.

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 detection element 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.

  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.

  Next, correction of the phase shift distribution Φ (x, y) considering the effective width of each pixel 40 will be described.

FIG. 10 shows an example of correction. First, the X-ray shielding plate 60 provided with the pinhole 61 is arranged so that the pinhole 61 is positioned on the optical axis (center X-ray) of the X-ray emitted from the X-ray source 11. In this state, X-rays are emitted from the X-ray source 11 and the X-rays that have passed through the pinhole 61 are imaged by the FPD 30. From the image position of the X-rays passing through the pinhole 61, obtains the arrival position _{P 0} of the center X-rays in FPD 30. For example, among the pixels 40 that have detected X-rays that have passed through the pinhole 61, the position of the pixel 40 having the largest signal value or the position of the pixel 40 that is the center of the X-ray image is determined as the arrival position P _{0 of the} center X-ray. (FIG. 10A).

Next, a sample 62 formed of a material having excellent X-ray absorption is set at the arrival position P ₀ of the central X-ray in the FPD 30. Although the shape of the sample 62 is not specifically limited, For example, a rod-shaped thing can be used. The X-ray shielding plate 60 is removed, X-rays are emitted from the X-ray source 11 and photographed with the FPD 30, and an X-ray absorption image I of the sample 62 is acquired (FIG. 10B).

Next, the X-ray incident angle θ ₀ and the X-ray incident direction at the arrival position P ₀ of the center X-ray are obtained from the acquired X-ray absorption image. For example, the X-ray absorption image of the sample 62 at each incident angle is changed in various ways, the X-ray absorption image of the sample 62 is stored in advance in the storage unit 23 of the X-ray imaging system 10, and a number of X-ray absorptions stored in the storage unit 23 are stored. An image comparison between the image and the acquired X-ray absorption image can be performed to estimate the incident angle θ ₀ . As for the incident direction, in the case of the rod-shaped sample 62, the X-ray absorption image extends.

Next, a projection position O obtained by projecting the X-ray source 11 (specifically, the X-ray focal point 18 b) perpendicularly to the image receiving surface of the FPD 30 is obtained. Distance R ₀ between the arrival position P ₀ of the center X-rays from the X-ray incident angle theta ₀ and the projection position O in the arrival position P ₀ of the center X-ray is obtained by the following equation (21), the projection position O, the distance R ₀ and the X-ray incident direction at the arrival position P ₀ of the central X-ray (FIG. 10C).

  Here, L is the distance between the X-ray source 11 and the FPD 30.

  Then, the X-ray incident angle θ in the x direction (scanning direction of the second transmissive grating 32) in each pixel 40 is geometrically determined by the following equation (22) (FIG. 10C).

  Here, R is the distance in the x direction from the projection position O of the X-ray source 11 to each pixel 40 and is obtained from the pixel pitch in the x direction of the FPD 30.

  The effective width D ′ in the x direction of each pixel 40 is expressed by the following equation (23) from the X-ray incident angle θ in the x direction in each pixel 40.

  From Expressions (4) and (23), if the correction coefficient of each pixel 40 is √cos θ, the refraction angle φ (x, y) (or the differential amount of the phase shift distribution Φ (x, y)) is obtained. The correction according to the effective width D ′ of each pixel 40 can be performed. For example, the correction coefficient √cos θ of each pixel 40 is obtained and stored in the storage unit 23 as a sensitivity correction map. Then, with respect to the pixel value of each pixel constituting the distribution image of the refraction angle φ (x, y), referring to the sensitivity correction map stored in the storage unit 23, the correction of the pixel 40 of the FPD 30 corresponding to the pixel is performed. Correct by multiplying coefficient √cosθ. Then, the corrected refraction angle φ (x, y) is integrated in the x and y directions to obtain a phase shift distribution Φ (x, y), which is converted into a phase contrast image. Although the change in the effective width in the y direction of each pixel 40 is not taken into account, when the second transmission type grating 32 is scanned in the x direction, anisotropy occurs in the intensity modulation signal of the pixel 40, and While it changes rapidly in the x direction, it changes slowly in the y direction. For this reason, when the effective width of the pixel 40 in the x direction changes, the obtained refraction angle φ also undergoes large fluctuations, but the change in the effective width of the pixel 40 in the y direction has little effect on the refraction angle φ. Therefore, it is practically sufficient to perform correction according to the effective width of the pixel 40 in the x direction.

  In the above example, the arrival position of the central X-ray in the FPD 30 is obtained using the X-ray shielding plate 60 provided with the pinhole 61, and the X-ray incident angle at the arrival position of the central X-ray is obtained using the sample 62. Although the X-ray incident direction is obtained, the X-ray incident angle at the arrival position of the central X-ray may be obtained by another method. For example, using a measuring device such as a laser displacement meter, or providing an acceleration sensor in the X-ray source 11 to measure the relative position of the X-ray source 11 with respect to the XFPD 30, and providing an acceleration sensor in the X-ray source 11, By measuring the attitude of the X-ray source 11 with respect to the FPD 30, the arrival position of the central X-ray in the FPD 30, the X-ray incident angle at the arrival position of the central X-ray, and the X-ray incident direction can also be 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, with respect to the pixel value of each pixel constituting the refraction angle distribution image, the x direction (second transmission type) of the pixel 40 of the FPD 30 corresponding to the pixel with respect to the incident radiation. By performing sensitivity correction in accordance with the effective width D ′ in the scanning direction of the grating 32, the imaging accuracy can be increased.

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. Therefore, the first and second transmission types are used. Although the gratings 31 and 32 have been described as both absorbing gratings, the present invention is not limited to this. As described above, also when the refraction angle φ is calculated by performing fringe scanning on the Talbot interference image, the refraction angle φ depends on the effective width D ′ in the scanning direction of each pixel 40 of the FPD 30 and the refraction angle φ. However, the present invention for performing correction according to the effective width D ′ of each pixel 40 in the scanning direction 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 arranged between the X-ray source 11 and the first transmission type grating 31, but the subject H is arranged with the first transmission type grating 31 and the second transmission type 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 the 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, in the present specification, the phase of the radiation source that emits radiation, the first grating that generates the fringe image by passing the radiation, and the periodic pattern of the fringe image are different. Obtained by intensity modulation means for applying intensity modulation to the fringe image at a plurality of relative positions, a radiation image detector for detecting the fringe image intensity-modulated at each relative position by the intensity modulation means, and the radiation image detector A calculation means for calculating a refraction angle distribution of radiation incident on the radiation image detector from a plurality of images, and generating a phase contrast image of a subject based on the distribution of refraction angles, The arithmetic means moves the pixel of the radiation image detector corresponding to the pixel value of each pixel constituting the refraction angle distribution image when the intensity modulating means takes the plurality of relative positions. Relates direction, performs a sensitivity correction in accordance with the effective width of the relative incident radiation, a radiation imaging system that generates a phase contrast image based on the distribution image of the corrected refraction angles is disclosed.

  Further, in the radiation imaging system disclosed in the present specification, the calculation unit is configured to detect a pixel value of each pixel constituting the refraction angle distribution image in a pixel of the radiation image detector corresponding to the pixel. Sensitivity correction is performed by applying a sensitivity correction coefficient represented by √cos θ, where θ is the radiation incident angle in the moving direction when the intensity modulating means takes the plurality of relative positions.

  The radiation imaging system disclosed in the present specification further includes a position detection unit that detects a vertical projection position of the radiation source on an image receiving surface of the radiological image detector, and the calculation unit includes: The distance to the vertical projection position of the radiation source detected by the position detection means, and the intensity modulation from the vertical projection position of the radiation source detected by the position detection means to each pixel of the radiation image detector. Based on the distance along the moving direction when the means takes the plurality of relative positions, the radiation incident angle θ at the pixel is geometrically calculated.

  Further, in the radiation imaging system disclosed in this specification, the calculation unit stores a sensitivity correction map in which the sensitivity correction coefficient for the pixel value of each pixel constituting the refraction angle distribution image is held for all pixels. And a 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 radiographic system disclosed in this specification, the radiological image detector includes, for each pixel, a conversion layer that converts radiation into charges and a charge collection electrode that collects charges converted in the conversion layer. The charge collection electrode is formed by arranging a plurality of linear electrode groups having a periodic pattern in the same direction as the fringe image so that their phases are different from each other. The charge collecting electrode is used.

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

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

  Further, in the present specification, radiation is emitted from a radiation source to a subject, the radiation is passed through a first grating to generate a fringe image, and a plurality of relative phases having different phases with respect to the periodic pattern of the fringe image are provided. Intensity modulation is applied to the fringe image by an intensity modulation means at a position, and the fringe image intensity-modulated at each relative position by the intensity modulation means is detected by a radiation image detector, and acquired by the radiation image detector. A radiation imaging method for calculating a refraction angle distribution of radiation incident on the radiation image detector based on a plurality of fringe images and generating a phase contrast image of a subject based on the refraction angle distribution, comprising: With respect to the pixel value of each pixel constituting the distribution image, the pixel of the radiation image detector corresponding to that pixel is related to the moving direction when the intensity modulation means takes the plurality of relative positions. Performs sensitivity correction in accordance with the effective width of the relative incident radiation, a radiation imaging method for generating a phase contrast image based on the distribution image of the corrected refraction angles is disclosed.

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 First transmission type grating 32 Second transmission type grating (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;
Intensity modulation means for applying intensity modulation to the fringe image at a plurality of relative positions different in phase with respect to the periodic pattern of the stripe image;
A radiation image detector for detecting a fringe image intensity-modulated at each relative position by the intensity modulation means;
An operation for calculating a refraction angle distribution of radiation incident on the radiation image detector from a plurality of images acquired by the radiation image detector and generating a phase contrast image of the subject based on the refraction angle distribution. Means,
With
When the intensity modulation unit of the pixel of the radiation image detector corresponding to the pixel has a plurality of relative positions with respect to the pixel value of each pixel constituting the refraction angle distribution image, A radiation imaging system that performs sensitivity correction according to an effective width for incident radiation with respect to a moving direction, and generates a phase contrast image based on the corrected distribution image of the refraction angle. The radiation imaging system according to claim 1,
When the intensity modulating means takes the plurality of relative positions in the pixel of the radiation image detector corresponding to the pixel value of each pixel constituting the distribution image of the refraction angle. Radiation imaging system that performs sensitivity correction by applying a sensitivity correction coefficient represented by √cosθ, where θ is the radiation incident angle in the moving direction of. The radiographic system according to claim 2,
A position detecting means for detecting a vertical projection position of the radiation source onto the image receiving surface of the radiation image detector;
The calculation means is configured to detect the radiation image detector from the distance from the radiation source to the vertical projection position of the radiation source detected by the position detection means and the vertical projection position of the radiation source detected by the position detection means. A radiation imaging system that geometrically calculates a radiation incident angle θ at each pixel based on a distance along the moving direction when the intensity modulation means takes the plurality of relative positions. The radiation imaging system according to any one of claims 1 to 3,
The calculation means has a storage unit that stores a sensitivity correction map that holds the sensitivity correction coefficient for all the pixels for the pixel value of each pixel constituting the refraction angle distribution image, and stores the storage unit in the storage unit. A radiation imaging system that performs sensitivity correction with reference to the sensitivity correction map. The radiographic system according to any one of claims 1 to 4,
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 radiographic system according to any one of claims 1 to 4,
The radiological image detector is a radiological image detector comprising 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 in the same direction as the fringe image are arranged in different phases.
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 projects the radiation from the radiation source onto the intensity modulation unit as a periodic pattern. The radiation imaging system according to any one of claims 1 to 6,
The first grating is a phase-type grating, and projects a radiation pattern from the radiation source onto the intensity modulation unit as a periodic pattern 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;
Applying intensity modulation to the fringe image by intensity modulation means at a plurality of relative positions having different phases with respect to the periodic pattern of the stripe image,
The fringe image intensity-modulated at each relative position by the intensity modulation means 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,
With respect to the pixel value of each pixel constituting the distribution image of the refraction angle, the incident of the pixel of the radiation image detector corresponding to the pixel with respect to the moving direction when the intensity modulation means takes the plurality of relative positions. A radiation imaging method for performing sensitivity correction in accordance with an effective width for radiation and generating a phase contrast image based on the corrected distribution image of the refraction angle.

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