JP5635169B2 - Radiography system - Google Patents

Description

  The present invention relates to a radiation imaging system that images a subject with radiation such as X-rays, and more particularly to a radiation imaging system that performs X-ray phase imaging by arranging a grating between a radiation source and a radiation image detector.

  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 taken. In this case, the X-rays emitted from the X-ray source toward the X-ray image detector correspond to the difference in the characteristics (atomic number, density, thickness) of the substances existing on the path to the X-ray image detector. After receiving a certain amount of attenuation (absorption), it enters each pixel of the X-ray image detector. As a result, an 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 sufficient softness or contrast (contrast) of an X-ray absorption image cannot be obtained in a soft body tissue or soft material. 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 this background, in recent years, instead of X-ray intensity changes by the subject, an image based on the X-ray phase change (angle change) by the subject (hereinafter referred to as a phase contrast image) is obtained. Research on line phase imaging has been 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 X-ray phase imaging using a 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, an X-ray imaging system using an X-ray Talbot interferometer composed of an X-ray source, two transmission diffraction gratings, and an X-ray image detector has been devised ( For example, see Patent Document 1 and Non-Patent Document 1).

  The X-ray Talbot interferometer arranges the first diffraction grating from the X-ray source through the subject, and only the Talbot interference distance determined by the grating pitch of the first diffraction grating and the X-ray wavelength from the first diffraction grating. The second diffraction grating is disposed downstream, and an 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 of the first diffraction grating due to the Talbot interference effect. This self-image is modulated by the interaction (phase change) between the subject arranged between the X-ray source and the first diffraction grating and the X-ray.

  In the X-ray Talbot interferometer, the moiré fringes generated by the superposition (intensity modulation) of the first image of the first diffraction grating and the second diffraction grating are detected by the fringe scanning method. A phase contrast image of the subject is acquired. In the fringe scanning method, the second diffraction grating is substantially parallel to the surface of the first diffraction grating and substantially perpendicular to the grating direction (strip direction) of the first diffraction grating. In such a direction, a plurality of times of imaging are performed while translational movement (scanning) is performed at a scanning pitch obtained by equally dividing the grid pitch, and the phase shift of the intensity change with respect to the scanning of the pixel data of each pixel obtained by the X-ray image detector is performed. This is a method for acquiring a phase differential image (corresponding to the angular distribution of X-rays refracted by the subject) from the amount (the amount of phase shift between when the subject H is present and when it is absent). A phase contrast image of the subject is obtained by integrating the phase differential image along the fringe scanning direction. Since the pixel data is a signal whose intensity is periodically modulated with respect to the scan, the set of pixel data for the scan is hereinafter referred to as an “intensity modulation signal”. This fringe scanning method is also used in an imaging apparatus that uses laser light instead of X-rays (see, for example, Non-Patent Document 2).

  In an X-ray imaging system using an X-ray Talbot interferometer, a solid-state imaging device such as the FPD that can acquire pixel data as digital data is used as an X-ray image detector. Since such an X-ray image detector includes a large number of pixels, the occurrence of defective pixels is inevitable. Defective pixels include not only those caused by physical defects that occur during manufacturing, but also those in which the signal value becomes abnormal due to scratches on the detection surface, adhesion of dust, etc., although the pixels themselves are normal.

  As a method for dealing with defective pixels, a technique is known in which position information of defective pixels is acquired in advance and correction processing is performed on an X-ray image acquired by an X-ray image detector (for example, Patent Documents). 2 and 3).

JP 2008-200399 A JP 2008-079923 A JP 2002-197450 A

C. David, et al., Applied Physics Letters, Vol. 81, No. 17, October 2002, p. 3287 Hector Canabal, et al., Applied Optics, Vol.37, No.26, September 1998, 6227

  In the above X-ray imaging system, since the manufacturing error of the first and second diffraction gratings needs to be small and highly accurate, if a slight distortion occurs in the first and second diffraction gratings, A normal phase shift amount is not detected from the pixel corresponding to the distorted portion, and the pixel is substantially a defective pixel. However, conventionally, there is no known method for detecting a defective pixel due to such lattice distortion.

  Specifically, as the distortions of the first and second diffraction gratings, there can be considered grating pitch and aperture width unevenness, grating thickness unevenness, local inclination of the grating, and the like. Since these distortions affect not only the X-ray transmittance but also the intensity modulation signal obtained by relatively shifting the positions of the first diffraction grating and the second diffraction grating, the detection accuracy of the phase shift amount Deteriorate. For this reason, it is difficult to detect a defective pixel due to grating distortion based on an absorption image obtained by simply performing X-ray imaging of the first and second diffraction gratings. Patent Documents 2 and 3 do not relate to X-ray phase imaging, and do not disclose any method for detecting defective pixels caused by lattice distortion.

  In the X-ray imaging system, it is necessary to perform integration processing along the fringe scanning direction in order to obtain a phase contrast image from the phase differential image. When defective pixels occur, line-shaped artifacts along the fringe scanning direction are generated for each defective pixel, and it is particularly desired to detect defective pixels with high accuracy.

  The present invention has been made in view of the above problems, and an object thereof is to provide a radiation imaging system that can accurately detect defective pixels caused by lattice distortion.

In order to achieve the above object, the radiation imaging system of the present invention is different in phase from the first grating that generates a fringe image by passing radiation emitted from a radiation source, and the periodic pattern of the fringe image. 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 source not irradiated A first detection process for detecting defective pixels based on a dark image obtained by the radiation image detector in a state, and a plurality of fringe images acquired by the radiation image detector under radiation irradiation from the radiation source the basis, a second detection process of detecting a defective pixel based on the average value of the intensity modulated signal obtained for each pixel, based on the amplitude value of the intensity modulated signal obtained for each pixel And a defective pixel detecting means for performing Recessed and a third detection process of detecting a pixel, after the first detection process, the second and third detection process is performed.

  It is preferable that the third detection process is performed after the second detection process.

  It is preferable that a storage unit that stores position information of the defective pixel detected by the defective pixel detection unit is provided.

  The defective pixel detecting means distinguishes the position information of the defective pixel detected by the first detection process from the position information of the defective pixel detected by the second and third detection processes, so that the storage means can be identified. It is preferable to memorize.

The first detection process detects a pixel whose pixel data of the dark image is larger than an allowable value as a defective pixel, and the second detection process uses a pixel whose average value is outside a predetermined range as a defective pixel. Preferably, the third detection process detects a pixel having an amplitude value smaller than a predetermined value as a defective pixel.

  A phase for calculating a phase shift amount of an intensity modulation signal obtained for each pixel based on a plurality of fringe images acquired by the radiation image detector, and generating a phase differential image representing the phase shift amount as a phase differential value A differential image generation unit and a phase differential value of the phase differential image corresponding to each defective pixel detected by the defective pixel detection unit are calculated based on a phase differential value of an adjacent pixel adjacent to each defective pixel. It is preferable to include correction processing means for replacing with a correction value.

  It is preferable that the intensity modulating unit includes a second grating having a periodic pattern in the same direction as the fringe image, and a scanning unit that moves one of the first and second gratings at a predetermined pitch. .

  The first and second gratings are preferably absorption gratings, and the first grating projects the radiation from the radiation source onto the second grating as a fringe image.

  The first grating may be a phase-type grating, and the first grating may project radiation from the radiation source onto the second grating as a fringe image by a Talbot interference effect.

  The radiation imaging system of the present invention has a defect based on an average value and an amplitude value of an intensity modulation signal obtained for each pixel based on a plurality of fringe images obtained by a radiation image detector under radiation irradiation from a radiation source. Since the defective pixel detecting means for detecting the pixel is provided, it is possible to accurately detect the defective pixel caused by only the lattice. In particular, by performing defective pixel detection based on the average value and amplitude value of the intensity modulation signal, it is possible to detect defective pixels caused by lattice distortion with higher accuracy.

1 is a schematic diagram illustrating a configuration of an X-ray imaging system according to a first embodiment of the present invention. It is a schematic diagram which shows the structure of a flat panel detector. It is a schematic side view which shows the structure of the 1st and 2nd absorption type grating | lattice. It is explanatory drawing for demonstrating a fringe scanning method. It is a graph which illustrates pixel data (intensity modulation signal) which changes with fringe scanning. It is a flowchart explaining the correction process of a defective pixel. It is explanatory drawing about a point symmetrical pair. It is a flowchart explaining the detection process of a defective pixel. It is a graph explaining the average value and amplitude value of an intensity modulation signal. It is sectional drawing of the 1st absorption type grating explaining the type of defective pixel resulting from distortion. It is sectional drawing which shows the 1st absorption-type grating | lattice formed by joining several grating | lattices. It is a flowchart explaining the detection process of the defective pixel in 2nd Embodiment of this invention. It is a graph which illustrates the criterion based on the average value and amplitude value of an intensity modulation signal. It is a schematic diagram which shows the structure of the X-ray image detector used in 4th Embodiment of this invention.

(First embodiment)
In FIG. 1, an X-ray imaging system 10 according to the first embodiment of the present invention is disposed so as to face an X-ray source 11 that irradiates a subject H with X-rays, and is opposed to the X-ray source 11. An imaging unit 12 that detects X-rays transmitted through the specimen H and generates image data, a memory 13 that stores image data read from the imaging unit 12, and a plurality of image data stored in the memory 13 Image processing unit 14 for processing to generate a phase contrast image, image recording unit 15 for recording the phase contrast image generated by the image processing unit 14, and imaging control for controlling the X-ray source 11 and the imaging unit 12 Unit 16, a console 17 including an operation unit and a monitor, and a system control unit 18 that comprehensively controls the entire X-ray imaging system 10 based on an operation signal input from the console 17. That.

  The X-ray source 11 includes a high voltage generator, an X-ray tube, a collimator (all not shown), and the like, and irradiates the subject H with X-rays based on the control of the imaging control unit 16. For example, the X-ray tube is of a rotating anode type, emits an electron beam from a filament in accordance with a voltage from a high voltage generator, and collides the electron beam with a rotating anode rotating at a predetermined speed, thereby causing an X-ray. Is generated. The rotating anode rotates to reduce deterioration due to the electron beam continuously hitting the fixed position. The colliding part of the electron beam is an X-ray focal point that emits X-rays. The collimator limits the irradiation field so as to shield a portion of the X-ray emitted from the X-ray tube that does not contribute to the examination region of the subject H.

  The imaging unit 12 includes a flat panel detector (FPD) 20 made of a semiconductor circuit, a first absorption grating 21 for detecting phase change (angle change) of X-rays by the subject H, and performing phase imaging. Two absorption gratings 22 are provided. The FPD 20 is arranged so that the detection surface is orthogonal to a direction along the optical axis A of X-rays irradiated from the X-ray source 11 (hereinafter referred to as z direction).

The first absorption grating 21 has a plurality of X-ray shielding portions 21a extending in one direction in the plane orthogonal to the z direction (hereinafter referred to as the y direction), in a direction orthogonal to the z direction and the y direction (hereinafter referred to as the y direction). the x that direction) in which are arranged at a predetermined pitch p _1. Similarly, the second absorption grating 22 has a plurality of X-ray shielding portions 22a which extend in the y direction, in which are arranged at a predetermined pitch p ₂ in the x-direction. As a material of the X-ray shielding portions 21a and 22a, a metal excellent in X-ray absorption is preferable, and for example, gold, silver, platinum and the like are preferable.

  In addition, the imaging unit 12 translates the second absorption type grating 22 in a direction (x direction) orthogonal to the grating direction, so that the first absorption type grating 21 and the second absorption type grating 22 can be translated. A scanning mechanism 23 for changing the relative position is provided. The scanning mechanism 23 is configured by an actuator such as a piezoelectric element. The scanning mechanism 23 is driven based on the control of the imaging control unit 16 at the time of stripe scanning described later. As will be described in detail later, the memory 13 stores image data obtained by the photographing unit 12 at each scanning step of fringe scanning. The second absorption type grating 22 and the scanning mechanism 23 constitute the intensity modulation means described in the claims.

  The image processing unit 14 detects a defective pixel of the FPD 20 from image data obtained during the calibration operation, and creates a defect map (defective pixel position information) and a defective pixel detection unit 30. A defect map storage unit 31 for storing the defect map. The defective pixel detection unit 30 operates during the calibration operation and creates a defect map. When there is an existing defect map in the defect map storage unit 31, the existing defect map is overwritten and updated with the created defect map.

  The image processing unit 14 includes a phase differential image generation unit 32 that generates a phase differential image based on a plurality of image data captured by the imaging unit 12 and stored in the memory 13 at each scanning step of fringe scanning, and a defect. Based on the defect map stored in the map storage unit 31, a correction processing unit 33 that performs defect pixel correction on the phase differential image, and integrating the corrected phase differential image along the x direction allows phase contrast. A phase contrast image generation unit for generating an image; The phase contrast image generated by the phase contrast image generation unit 34 is recorded in the image recording unit 15 and then output to the console 17 and displayed on a monitor (not shown). Instead of the phase contrast image, it is also possible to record a phase differential image on the image recording unit 15 and display the phase differential image on a monitor.

  In addition to the monitor, the console 17 includes an input device (not shown) through which an operator inputs a shooting instruction and the content of the instruction. As this input device, for example, a switch, a touch panel, a mouse, a keyboard or the like is used, and an X-ray imaging condition such as a tube voltage of the X-ray tube or an X-ray irradiation time, an imaging timing, etc. are input by operation of the input device. The The monitor is composed of a liquid crystal display or a CRT display, and displays characters such as X-ray imaging conditions and the phase contrast image.

  2, the FPD 20 includes an image receiving unit 41 in which a plurality of pixels 40 that convert X-rays into electric charges and accumulate them two-dimensionally on the active matrix substrate along the x direction and the y direction, and the image receiving unit 41. The scanning circuit 42 controls the readout timing of the charge from the pixel, and the readout circuit 43 reads the charge accumulated in each pixel 40, converts the charge into image data, and stores it. The scanning circuit 42 and each pixel 40 are connected by a scanning line 44 for each row, and the readout circuit 43 and each pixel 40 are connected by a signal line 45 for each column. The arrangement pitch of the pixels 40 is about 100 μm in each of the x direction and the y direction.

  The pixel 40 directly converts X-rays into charges by a conversion layer (not shown) such as amorphous selenium, and directly stores the converted charges in a capacitor (not shown) connected to an electrode below the conversion layer. It is configured as a conversion type X-ray detection 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 44, the source electrode is connected to the capacitor, and the drain electrode is connected to the signal line 45. 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 45.

Note that the pixel 40 temporarily converts X-rays into visible light using 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 into electric charge and accumulates it (not shown). In this embodiment, an FPD based on a TFT panel is used as a radiation image detector. However, the present invention is not limited to this, and various types of radiation image detectors based on a solid-state imaging device such as a CCD sensor or a CMOS sensor. It is also possible to use.

  The readout circuit 43 includes an integration amplifier, a correction circuit, an A / D converter (all not shown), and the like. The integrating amplifier integrates the charges output from each pixel 40 via the signal line 45 and converts them into a voltage signal (image signal). The A / D converter converts the image signal converted by the integrating amplifier into digital image data. The correction circuit performs offset correction, gain correction, linearity correction, and the like on the image data, and inputs the corrected image data to the memory 13.

In FIG. 3, X-ray shielding portion 21a of the first absorption grating 21, at a predetermined pitch p ₁ in the x direction, and are arranged at a predetermined interval d ₁ from each other. Similarly, X-rays shielding portions 22a of the second absorption-type grating 22, at a predetermined pitch p ₂ in the x direction, and are arranged at a predetermined interval d ₂ from each other. The X-ray shielding portions 21a and 22a are each disposed on an X-ray transmissive substrate (not shown) (for example, a glass substrate). The first and second absorption gratings 21 and 22 do not give a phase difference to incident X-rays but give an intensity difference, and are also called amplitude gratings. Incidentally, (a region of the interval d _1, d ₂₎ slit portion may not be a void, X-rays low absorption material such as a polymer or light metal may be filled.

The first and second absorption type gratings 21 and 22 are configured to linearly project 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 rotating anode of the aforementioned X-ray tube and the tube voltage is 50 kV, the peak wavelength of the X-ray is about 0.4 mm. In this case, if the distances d ₁ and d ₂ are about ₁ μm to 10 μm, most of the X-rays are projected linearly without being diffracted by the slit portion. In this case, the lattice pitches p ₁ and p ₂ are about ₂ μm to 20 μm.

The X-ray irradiated from the X-ray source 11 is not a parallel beam but a cone beam having the X-ray focal point 11a as a light emission point, and therefore a projected image projected through the first absorption grating 21 (hereinafter referred to as a projection image). The projection image is referred to as a G1 image or a fringe image) and is enlarged in proportion to the distance from the X-ray focal point 11a. The grating pitch p ₂ and the interval d ₂ of the second absorption type grating 22 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 absorption type grating 22. Yes. That is, when the distance from the X-ray focal point 11a to the first absorption-type grating 21 is L ₁ and the distance from the first absorption-type grating 21 to the second absorption-type grating 22 is L ₂ , the grating pitch p ₂ and the distance d ₂ are determined so as to satisfy the relationship of the following expressions (1) and (2).

In the case of a Talbot interferometer, the distance L ₂ from the first absorption type grating 21 to the second absorption type grating 22 is limited to the Talbot interference distance determined by the grating pitch of the first diffraction grating and the X-ray wavelength. However, in the imaging unit 12 of the present embodiment, the first absorption type grating 21 projects the incident X-rays without diffracting, and the G1 image of the first absorption type grating 21 is the first one. because at every position of the rear absorption gratings 21 of similarly obtained, the distance L _2, can be set independently of the Talbot distance.

As described above, the imaging unit 12 of the present embodiment does not constitute a Talbot interferometer, but it is assumed that X-ray diffraction occurs in the first absorption grating 21 and a Talbot interference effect is generated. the Talbot interference distance Z, the grating pitch p ₁ of the first absorption-type grating _21, the grating pitch p _2, X-ray wavelength of the second absorption-type grating 22 (peak wavelength) lambda, and using the positive integer m Is expressed by the following equation (3).

  Equation (3) is an equation representing the Talbot interference distance when the X-rays emitted from the X-ray source 11 are cone beams. “Atsushi Momose, et al., Japanese Journal of Applied Physics, Vol. 47, No. 10, October 2008, p. 8077 ”.

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

  The X-ray shielding parts 21a and 22a preferably completely shield (absorb) X-rays in order to generate a periodic pattern image with high contrast, but the above-described materials (gold, silver) that are excellent in X-ray absorption Even if platinum or the like is used, there are not a few X-rays that are transmitted without being absorbed. For this reason, in order to improve the shielding property of X-rays, it is preferable to increase the thickness of each of the X-ray shielding portions 21a and 22a (thickness in the z direction) as much as possible (that is, increase the aspect ratio). For example, when the tube voltage of the X-ray tube is 50 kV, it is preferable to shield 90% or more of the irradiated X-rays. In this case, the thicknesses of the X-ray shielding portions 21a and 22a are calculated in terms of gold (Au). It is preferable that it is 30 micrometers or more.

In the first and second absorption-type gratings 21 and 22 configured as described above, intensity modulation is performed by superimposing the G1 image (stripe image) of the first absorption-type grating 21 and the second absorption-type grating 22. The striped image is captured by the FPD 20. There is a slight difference between the pattern period of the G1 image at the position of the second absorption type grating 22 and the grating pitch p _{2 of} the second absorption type grating 22 due to manufacturing errors and arrangement errors. Thus, moire fringes are generated in the intensity-modulated fringe image. Further, when an error occurs in the lattice arrangement direction of the first and second absorption type gratings 21 and 22, and the arrangement directions are not the same, so-called rotational moire occurs. However, even when such moire fringes occur in the fringe image, there is no particular problem as long as the period of the moire fringes in the x direction or y direction is larger than the arrangement pitch of the pixels 40. Ideally, it is preferable not to generate moire fringes, but the moire fringes can be used to confirm the scanning amount of the fringe scanning (translation distance of the second absorption grating 22), as will be described later. .

  When the subject H is disposed between the X-ray source 11 and the first absorption type grating 21, the fringe image detected by the FPD 20 is modulated by the subject H. This modulation amount is proportional to the angle of the X-ray deflected by the refraction effect by the subject H. Therefore, a phase contrast image of the subject H can be generated by analyzing the fringe image detected by the FPD 20.

  Next, a fringe image analysis method will be described. In the drawing, one X-ray path refracted according to the phase shift distribution Φ (x) in the x direction of the subject H is illustrated. Reference numeral 50 indicates an X-ray path that goes straight when the subject H does not exist. X-rays traveling along the path 50 pass through the first and second absorption gratings 21 and 22 and enter the FPD 20. Reference numeral 51 indicates an X-ray path refracted and deflected by the subject H when the subject H exists. X-rays traveling along the path 51 pass through the first absorption type grating 21 and are then shielded by the X-ray shielding part 22 a of the second absorption type grating 22.

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

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

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

  Thus, the displacement amount Δx of the G1 image due to X-ray refraction 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 of each pixel 40 detected by the FPD 20 (the amount of phase shift of the intensity modulation signal of each pixel 40 with and without the subject H). ) Is related to the following equation (8).

  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 (8), and the differential amount of the phase shift distribution Φ (x) is obtained using the equation (7). By integrating this with respect to x, 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 embodiment, the phase shift amount ψ is calculated using the fringe scanning method shown below.

In the fringe scanning method, imaging is performed while one of the first and second absorption type gratings 21 and 22 is translated in the x direction relative to the other (that is, while changing the phase of the grating period of both). Take a picture). In the present embodiment, the second absorption type grating 22 is moved by the scanning mechanism 23 described above. As the second absorption type grating 22 moves, the moiré fringes move, and the translation distance (the amount of movement in the x direction) is one period of the grating period of the second absorption type grating 22 (grating pitch p ₂ ). (Ie, when the phase change reaches 2π), the moire fringes return to their original positions. In this way, while moving the second absorption type grating 22 by an integer of the grating pitch p ₂ , a fringe image is taken with the FPD 20, and an intensity modulation signal of each pixel is acquired from the taken plural stripe images. Then, the phase differential image generation unit 32 in the image processing unit 14 performs arithmetic processing to obtain the phase shift amount ψ of the intensity modulation signal of each pixel. This two-dimensional distribution of the phase shift amount ψ corresponds to a phase differential image.

FIG. 4 schematically shows how the second absorption type grating 22 is moved by the scanning pitch (p ₂ / M) obtained by dividing the grating pitch p ₂ into M (integers of 2 or more). The scanning mechanism 23 sequentially translates the second absorption type grating 22 to each of M scanning positions k = 0, 1, 2,..., M−1. In this figure, the initial position of the second absorption type grating 22 is set such that the dark part of the G1 image at the position of the second absorption type grating 22 when the subject H is not present is almost at the X-ray shielding part 22a. Although the matching position (k = 0) is assumed, this initial position may be any position among k = 0, 1, 2,..., M−1.

  First, at the position of k = 0, mainly the X-rays that are not refracted by the subject H pass through the second absorption type grating 22. Next, when the second absorption type grating 22 is moved in order of k = 1, 2,..., The X-rays passing through the second absorption type grating 22 were not refracted by the subject H. While the X-ray component decreases, the X-ray component refracted by the subject H increases. In particular, at the position of k = M / 2, mainly only the X-rays refracted by the subject H pass through the second absorption type grating 22. When the position of k = M / 2 is exceeded, the X-ray component passing through the second absorption grating 22 is refracted by the subject H while the X-ray component refracted by the subject H decreases. The X-ray component that has not been increased.

When photographing is performed by the FPD 20 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. The pixel data I _k (x) of each pixel 40 at the position k of the second absorption type grating 22 is expressed by the following equation (9).

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 (10), the refraction angle φ (x) is expressed as the expression (11).

  Here, arg [] means extraction of the declination and corresponds to the phase shift amount ψ of the intensity modulation signal of each pixel. Therefore, by calculating the phase shift amount ψ from the M pieces of pixel data (intensity modulation signal) obtained from each pixel 40 based on the equation (11), the refraction angle φ (x) is obtained, and the phase shift distribution is obtained. The differential amount of Φ (x) is obtained.

Specifically, as shown in FIG. 5, 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 absorption type grating 22. Change. A broken line in the figure indicates a change in pixel data when the subject H does not exist, and a solid line indicates a change in 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.

  In the above description, the y coordinate in the y direction of the pixel 40 is not taken into consideration. However, by performing the same calculation for each y coordinate, a two-dimensional phase shift distribution ψ (x, y) is obtained. This phase shift distribution ψ (x, y) corresponds to the phase differential image. Since the refraction angle φ and the phase shift amount ψ are in a proportional relationship as shown in the above formula (7), both are physical quantities corresponding to the differential amount of the phase shift distribution Φ (x).

  Next, the correction process of defective pixels by the correction processing unit 33 will be described. The correction processing unit 33 performs correction processing on the phase differential image (phase shift distribution ψ (x, y)) calculated by the phase differential image generation unit 32 based on the above principle according to the flowchart shown in FIG. Do. First, the correction processing unit 33 selects one defective pixel from the defect map stored in the defect map storage unit 31 (step S1). Next, the correction processing unit 33, based on the phase differential image input from the phase differential image generation unit 32, phase differential values (phase shift amount ψ) corresponding to the eight adjacent pixels adjacent to the defective pixel selected in step S1. Is extracted (step S2).

  Next, as shown in FIG. 7, the correction processing unit 33 converts the eight adjacent pixels adjacent to the defective pixel into four types of point symmetric pairs I, II, III, A difference in phase differential value is calculated for each IV (step S3). When two or more defective pixels are adjacent to each other, the adjacent pixels include defective pixels. In this case, the point symmetry pair including the defective pixel is excluded from the calculation target of the phase differential value difference.

  And the correction | amendment process part 33 specifies the point symmetrical pair with the smallest absolute value of the difference of a phase differential value (step S4), calculates the average value of the phase differential value of the selected point symmetrical pair (step S5), Using the calculated average value as a correction value, the phase differential value of the defective pixel is replaced (step S6).

  Thereafter, it is determined whether or not the selected defective pixel is the final defective pixel (step S7). If the selected defective pixel is not the final defective pixel (step S7: NO determination), the process returns to step S1 again and is in the defect map. Other defective pixels are selected, and steps S2 to S6 are executed in the same manner. As a result, correction processing is performed for all defective pixels in the defect map.

  The phase differential image subjected to the correction processing as described above is input to the phase contrast image generation unit 34. The phase contrast image generation unit 34 integrates the input phase differential image along the x axis to generate a phase shift distribution Φ (x, y) of the subject H, and records this as a phase contrast image. Part 15 is recorded.

  Next, the defective pixel detection process executed by the defective pixel detection unit 30 during the calibration operation will be described based on the flowchart shown in FIG. The calibration operation is executed by the system control unit 18 controlling each unit based on an instruction from the console 17 by the operator.

  When there is an instruction for calibration (step S10: YES determination), the system control unit 18 causes the FPD 20 to perform an imaging operation in a state where X-ray irradiation (exposure) from the X-ray source 11 is prohibited. (Hereinafter, the image data obtained without X-ray irradiation is referred to as “dark image”) is stored in the memory 13 (step S11).

  The dark image stored in the memory 13 is read out by the defective pixel detection unit 30, and the defective pixel detection unit 30 determines that the pixel data of the dark image (that is, the noise value of the pixel) is larger than the allowable value as defective pixels. (Step S12). Thereby, a pixel in which a large dark current (leakage current) is generated due to a defect such as a TFT switch is determined as a defective pixel.

  Next, the system control unit 18 does not place the subject H between the X-ray source 11 and the FPD 20, and irradiates the X-ray with a predetermined intensity from the X-ray source 11 with the scanning mechanism 23. Are moved to the respective scanning positions of k = 0, 1, 2,..., M−1, while the FPD 20 performs photographing operations (hereinafter referred to as “stripe scanning photographing”). The image data obtained at each scanning position is stored in the memory 13 (step S13).

The plurality of image data stored in the memory 13 is read by the defective pixel detection unit 30, and the defective pixel detection unit 30 calculates an average value of the pixel data (intensity modulation signal) for each pixel (step S14). Specifically, as shown in FIG. 9, the average value is obtained by averaging pixel data I _k (x) obtained for each scanning position k. Note that fewer scanning position k, in the case where the simple average of the pixel data I _{k (x)} can not obtain an average value, obtains a sine wave that best fit to the resulting pixel data I _{k (x)} What is necessary is just to obtain | require the average value of this sine wave.

  Next, the defective pixel detection unit 30 determines that a pixel whose average value calculated in step S14 is outside the predetermined range is a defective pixel (step S15). This average value is obtained by multiplying the X-ray transmittance for the first and second absorption type gratings 21 and 22 (the transmittance for the first absorption type grating 21 and the transmittance for the second absorption type grating 22). Value). That is, this average value reflects the thickness (length in the z direction) and the width (length in the x direction) of the first and second absorption type gratings 21 and 22. In addition, defective pixels due to thickness unevenness and width unevenness of the X-ray shielding portions 21a and 22a are detected. For example, when the thickness and width of the X-ray shielding portions 21a and 22a are distorted, the X-ray shielding performance decreases (leakage increases), and the average value of the intensity modulation signal increases. If it exceeds the upper limit of the predetermined range, it is determined as a defective pixel. On the contrary, when the thickness and width of the X-ray shielding portions 21a and 22a are distorted, the X-ray shielding performance increases, so that the average value of the intensity modulation signal decreases, and the lower limit of the predetermined range is reduced. If it falls below, it is determined as a defective pixel.

Next, the defective pixel detection unit 30 calculates the amplitude value of the pixel data (intensity modulation signal) for each pixel (step S16). Specifically, the amplitude value is obtained by calculating the difference between the maximum value and the minimum value of the pixel data I _k (x) obtained for each scanning position k. Note that fewer scanning position k, if it is not possible to obtain the amplitude value by the maximum and minimum values of the pixel data I _{k (x),} is the most fitting to the obtained pixel data I _{k (x)} sine What is necessary is just to obtain | require a wave and to obtain | require the amplitude value of this sine wave.

  Next, the defective pixel detection unit 30 determines that a pixel whose amplitude value calculated in step S16 is smaller than a predetermined value is a defective pixel (step S17). This amplitude value represents the difference (that is, contrast) of the signal value when the phase difference between the grating periods of the first and second absorption gratings 21 and 22 is “0” and “π”. Yes. If either of the first and second absorption type gratings 21 and 22 has a nonuniformity in the grating pitch or aperture width, the amplitude value of the intensity modulation signal of the pixel corresponding to that part decreases and falls below a predetermined value. If it is, the pixel is determined as a defective pixel.

  Then, the defective pixel detection unit 30 integrates the defective pixel information obtained in step S15 and step S17, creates a defect map representing the position information of the defective pixel, and inputs this to the defect map storage unit 31. (Step S18). At this time, if a defect map already exists in the defect map storage unit 31, it is updated (overwritten) to the newly input defect map.

  Next, the operation of the X-ray imaging system 10 configured as described above will be described. When an instruction for calibration is input from the console 17 by the operator, the respective units of the X-ray imaging system 10 operate in cooperation to execute the above-described calibration operation, and the defective pixel detection unit 30 performs defective pixel detection processing. The defect map created based on the detected defective pixels is stored in the defect map storage unit 31.

  Next, when an imaging instruction is input from the console 17 while the subject H is disposed between the X-ray source 11 and the FPD 20, the respective units of the X-ray imaging system 10 operate in cooperation with each other to perform the above imaging. The operation is executed, a phase differential image (phase shift distribution ψ (x, y)) is generated, defect pixel correction based on the defect map is performed, and then a phase contrast image is generated and displayed on the monitor.

  Next, the types of defective pixels caused by lattice distortion detected by the defective pixel detection process will be described. FIGS. 10A to 10C illustrate the types of strain generated in the first absorption type grating 21. Here, the X-ray shielding part 21a forms a groove 62 in a laminated body 61 such as a resist film laminated on an X-ray transparent substrate 60 made of glass or the like, and X-ray high absorption of Au or the like is formed in the groove 62. It is formed by filling a material.

FIG. 5A shows the distortion caused by the local variation in the thickness of the X-ray shielding part 21a. The portion surrounded by a broken line, for example, by filling the X-ray high-absorbing material is insufficient, the thickness of the X-ray shielding portion 21a is lower than the design thickness h _1. In this portion, the X-ray transmittance is increased and the average value of the intensity modulation signal is increased. Therefore, the pixel corresponding to this portion is determined as a defective pixel in step S15. However, since this increase in transmittance has a considerable influence on the amplitude value of the intensity modulation signal, it may be determined as a defective pixel in step S17.

FIG. 4B shows distortion caused by the local fluctuation of the width of the X-ray shielding part 21a. The portion surrounded by a broken line, for example, larger width of the X-ray shielding portion 21a in the formation error of the grooves 62, the pitch and opening width is different from the design pitch p ₁ and width d _1. In this portion, mismatching occurs with the second absorption type grating 22 and the amplitude value of the intensity modulation signal is lowered. Therefore, the pixel corresponding to this portion is determined as a defective pixel in step S17. The However, since the variation in the pitch and the opening width has a considerable influence on the average value of the intensity modulation signal, it may be determined as a defective pixel in step S15.

  FIG. 3C shows the distortion caused by the local inclination of the X-ray shielding part 21a. This inclination is likely to occur when the stacked body 61 is formed of a relatively soft resist material. In the portion surrounded by the broken line, the X-ray shielding portion 21a is inclined, causing X-ray vignetting, and the pitch and the opening width are substantially changed. For this reason, the pixel corresponding to this portion is determined as a defective pixel in step S17 as in the example shown in FIG. Similarly, since the inclination of the X-ray shielding part 21a has a considerable influence on the average value of the intensity modulation signal, it may be determined as a defective pixel in step S15.

  In the above examples, the case where any one of the X-ray shielding portions 21a is distorted is shown. However, in reality, the plurality of X-ray shielding portions 21a are often distorted in groups. In this case, the average value and the amplitude value of the intensity modulation signal fluctuate more significantly. The same applies when distortion occurs in the second absorption type grating 22.

  Incidentally, in the X-ray imaging system 10 of the present embodiment, in order to increase the field of view of the imaging region, the first and second absorption type gratings 21 and 22 need to be enlarged, as shown in FIG. The first absorption type grating 21 can be enlarged by joining the plurality of first absorption type gratings 21 to each other. Similarly, the second absorption type grating 22 can be enlarged by joining a plurality of second absorption type gratings 22 to each other.

As shown in the figure, when the first absorption type grating 21 is enlarged, the interval between the X-ray shielding portions 21a is increased in the joint portion surrounded by the broken line, and the pitch and the opening width are substantially increased. This is different from the design pitch p ₁ and width d ₁ . The same applies to the second absorption type grating 22.

  In the defective pixel detection process, a pixel corresponding to such a joint is also detected as a defective pixel, and correction processing is performed. Therefore, the defective pixel detection processing according to the present invention is also suitable for an X-ray imaging system using a large grating produced by joining a plurality of gratings to each other as described above.

In the above embodiment, the defective pixel is detected using the amplitude value and the average value as the characteristic value of the intensity modulation signal, but instead of the amplitude value, the maximum value, the minimum value, the variance value, the standard deviation, Any of the sharpness levels may be used. These are values that change according to the contrast of the intensity modulation signal. Here, the sharpness is a value represented by (I _max −I _min ) / (I _max + I _min ) where I _{max is} the maximum value of the intensity modulation signal and I _min is the minimum value.

Further, the defective pixel may be detected using the period of the intensity modulation signal as the characteristic value of the intensity modulation signal. The period of the intensity modulation signal varies depending on the fluctuation of the grating pitches p ₁ and p ₂ of the first and second absorption gratings 21 and 22.

  In the above embodiment, when the distance from the X-ray source 11 to the FPD 20 is increased, the blur of the G1 image due to the focus size of the X-ray focus 11a (generally about 0.1 mm to 1 mm) affects the phase. Since there is a risk of degrading the image quality of the contrast image, a multi slit (ray source grid) may be arranged immediately after the X-ray focal point 11a.

  The multi-slit is an absorption type grating having a configuration similar to that of the first and second absorption type gratings 21 and 22, and a plurality of X-ray shielding portions extending in one direction (in this embodiment, y direction) The first and second absorption type gratings 21 and 22 are periodically arranged in the same direction (in the present embodiment, the x direction) as the X-ray shielding portions 21a and 22a. 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.

In the above embodiment, the first and second absorption type gratings 21 and 22 are configured to linearly project the X-rays that have passed through the slit portion, but the present invention is limited to this configuration. Instead of this, it is also possible to adopt a configuration in which a so-called Talbot interference effect is generated by diffracting X-rays at the slit portion (configuration described in International Publication WO 2004/058070). However, in this case, it is necessary to set the distance L ₂ between the first and second absorption gratings 21 and 22 to the Talbot distance. In this case, a phase type grating (phase type diffraction grating) can be used in place of the first absorption type grating 21. The phase type grating used instead of the first absorption type grating 21 projects a fringe image (self-image) generated by the Talbot interference effect onto the second absorption type grating 22.

  The difference between the phase type grating and the absorption type grating is only the thickness of the X-ray high absorption material (X-ray shielding part), and the thickness of the X-ray shielding part is about 30 μm in terms of Au in the case of the absorption type grating. On the other hand, in the case of a phase type grating, it is set to about 1 μm to 5 μm. The phase-type grating generates a Talbot interference effect by applying a predetermined amount (preferably π or π / 2) of phase modulation to the radiation irradiated from the X-ray source 11 by the X-ray high absorption material. Thus, a fringe image (self-image) is generated. Accordingly, if the thickness or pitch of the X-ray high-absorbing material locally varies in the phase type grating, the fringe image of that portion will be deteriorated, so that the corresponding portion of the pixel needs to be detected as a defective pixel. . According to the defective pixel detection processing of the present invention, it is possible to detect defective pixels in the same manner even when a phase type grating is used instead of the first absorption type grating 21.

  Further, in the above embodiment, the subject H is disposed between the X-ray source 11 and the first absorption type grating 21, but the subject H is arranged with the first absorption type grating 21 and the second absorption type. A phase contrast image can be generated in the same manner when it is disposed between the grating 22 and the grating 22.

(Second Embodiment)
Next, as a second embodiment of the present invention, a modified example of the defective pixel detection processing by the defective pixel detection unit 30 will be described. In the present embodiment, the correction processing unit 33 performs detection processing according to the flowchart shown in FIG.

  First, as in the first embodiment, when there is an instruction for calibration (step S20: YES determination), image data is displayed by the FPD 20 in a state where X-ray irradiation (exposure) from the X-ray source 11 is prohibited. (Dark image) is acquired and stored in the memory 13 (step S21). The dark image stored in the memory 13 is read by the defective pixel detection unit 30, and the defective pixel detection unit 30 determines that a pixel whose pixel data (pixel noise value) is larger than an allowable value is a defective pixel (step). S22).

  Next, without scanning the subject H between the X-ray source 11 and the FPD 20, stripe scanning imaging is performed in a state where X-rays are irradiated from the X-ray source 11 with a predetermined intensity, and at each scanning position. The obtained image data is stored in the memory 13 (step S23). The plurality of image data stored in the memory 13 is read out by the defective pixel detection unit 30, and the defective pixel detection unit 30 calculates the average value and the amplitude value of the pixel data (intensity modulation signal) for each pixel. The calculation is performed in the same procedure as in the first embodiment (step S24).

  Next, the defective pixel detection unit 30 performs defective pixel determination for each pixel using a determination criterion that depends on the average value and the amplitude value of the intensity modulation signal as shown in FIG. 13 (step S25). The determination criterion shown in FIG. 6 is almost inversely proportional to both the average value and the amplitude value, and the defective pixel detection unit 30 determines a pixel whose average value and amplitude value are lower than the determination criterion as a defective pixel. Note that this criterion is set in advance in the defective pixel detection unit 30. The determination criteria are set in the form of a function or a matrix table.

  Then, the defective pixel detection unit 30 integrates the defective pixel information obtained in step S22 and step S25, creates a defect map representing the position information of the defective pixel, and inputs this to the defect map storage unit 31. (Step S26).

  In this embodiment, since defective pixel detection is performed using the determination criteria depending on the average value and the amplitude value as described above, “pixels with a small average value but a large amplitude value” and “amplitude value are It is not necessary to determine that the “small pixel with a large average value” is a defective pixel. That is, if either one of the average value and the amplitude value is large, the above-described phase shift may be identified. Therefore, such a pixel is not determined as a defective pixel, and contributes to generation of a phase contrast image. be able to.

  In addition, it is also preferable to store a plurality of the determination criteria in the defective pixel detection unit 30 so that the determination criteria can be appropriately selected by operating the console 17 or the like. For example, when the X-ray imaging system 10 is applied for medical diagnosis, it is preferable to change the determination criterion according to selection of imaging conditions (selection of an affected area or the like to be imaged) by the console 17. Each criterion may be determined in advance by clinical research or the like.

  The defective pixel information obtained in step S22 is due to the defect of the FPD 20, and the defective pixel information obtained in step S25 is due to the defect of the first and second absorption type gratings 21 and 22. For this reason, when the defect map storage unit 31 stores the defect, it is preferable that the defect is caused to be identifiable. For example, defect information is stored in different storage areas (sectors) in the defect map storage unit 31 according to the cause of the defect. By reading the defect information from the defect map storage unit 31 at the time of maintenance, it becomes easy to identify the cause of the defect, so that maintainability is improved.

  In this embodiment, defective pixel information caused by the FPD 20 is detected by a dark image, but in addition to this, the first and second absorption gratings 21, between the X-ray source 11 and the FPD 20, It is also preferable to detect defective pixel information caused by the FPD 20 on the basis of a uniform absorption image obtained by retracting 22 and making uniform X-rays incident on the FPD 20.

(Third embodiment)
In each of the above embodiments, the second absorption type grating 22 is provided independently of the FPD 20. However, by using an X-ray image detector having a configuration disclosed in Japanese Patent Laid-Open No. 2009-133823. The second absorption type grating 22 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 are different from each other. Constitutes the intensity modulating means described in the claims.

  FIG. 14 illustrates the configuration of the X-ray image detector (FPD) of this embodiment. 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. In this way, the charges generated in the pixel 70 are stored through the linear electrode groups 72 to 77.

  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.

  By using the X-ray image detector having the above configuration in place of the FPD 20, the second absorption type grating 22 is not required from the imaging unit 12, so that the cost can be reduced and the thickness can be further reduced. 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 23 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 absorption type grating 22 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.

In each of the above embodiments, the case of using the X-ray source 11 that emits cone-beam X-rays is illustrated, but an X-ray source that emits parallel X-rays can also be used. In this case, the above formulas (1) to (4) are transformed into the following formulas (12) to (15), respectively.

  Each embodiment described above can be applied not only to a radiographic system for medical diagnosis but also to other radiographic systems for industrial use and nondestructive inspection. In addition to X-rays, gamma rays or the like can be used as radiation.

10 X-ray imaging system 11 X-ray source (radiation source)
11a X-ray focus 20 Flat panel detector (FPD)
DESCRIPTION OF SYMBOLS 21 1st absorption-type grating | lattice 21a X-ray shielding part 22 2nd absorption-type grating | lattice 22a X-ray shielding part 60 Line | wire transparent substrate 61 Laminated body 62 Groove 70 Pixel 71 Charge collection electrode 72-77 1st-6th line Electrode group 78 switch group

Claims (9)

A first grating for generating a fringe image by passing radiation emitted from a radiation source;
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 fringe image;
A radiation image detector for detecting a fringe image intensity-modulated at each relative position by the intensity modulation means;
A first detection process for detecting defective pixels based on a dark image obtained by the radiation image detector in a state in which the radiation source is not irradiated; and under radiation irradiation from the radiation source, the radiation image detector. Based on a second detection process for detecting a defective pixel based on an average value of intensity modulation signals obtained for each pixel based on a plurality of obtained fringe images, and on the amplitude value of the intensity modulation signal obtained for each pixel Defective pixel detection means for performing a third detection process for detecting defective pixels
With
The radiation imaging system, wherein the second and third detection processes are performed after the first detection process.   The radiation imaging system according to claim 1, wherein the third detection process is performed after the second detection process.   The radiation imaging system according to claim 1, further comprising a storage unit that stores position information of the defective pixel detected by the defective pixel detection unit.   The defective pixel detecting means distinguishes the position information of the defective pixel detected by the first detection process from the position information of the defective pixel detected by the second and third detection processes, so that the storage means can be identified. The radiation imaging system according to claim 3, wherein the radiation imaging system is stored. The first detection process detects a pixel whose pixel data of the dark image is larger than an allowable value as a defective pixel, and the second detection process uses a pixel whose average value is outside a predetermined range as a defective pixel. 5. The radiation imaging system according to claim 1, wherein the third detection process detects a pixel having an amplitude value smaller than a predetermined value as a defective pixel. 6. A phase for calculating a phase shift amount of an intensity modulation signal obtained for each pixel based on a plurality of fringe images acquired by the radiation image detector, and generating a phase differential image representing the phase shift amount as a phase differential value Differential image generation means;
Correction for replacing the phase differential value of the phase differential image corresponding to each defective pixel detected by the defective pixel detection means with a correction value calculated based on the phase differential value of an adjacent pixel adjacent to each defective pixel Processing means;
The radiation imaging system according to claim 1, further comprising:   The intensity modulation means includes a second grating having a periodic pattern in the same direction as the fringe image, and a scanning means for moving one of the first and second gratings at a predetermined pitch. The radiation imaging system according to any one of claims 1 to 6.   The first and second gratings are absorption gratings, and the first grating projects radiation from the radiation source onto the second grating as a fringe image. Item 8. The radiographic system according to Item 7.   The first grating is a phase-type grating, and the first grating projects radiation from the radiation source as a fringe image onto the second grating by a Talbot interference effect. The radiation imaging system according to claim 7.

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