JP2013123460A - Radiographic apparatus, and radiographic method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely form a phase differential image by reducing the effect of linear flaws generated in image data.SOLUTION: This X-ray imaging apparatus includes a first lattice passing the radiation radiated from an X-ray source to form a first cycle pattern image, a second lattice for partially shielding the first cycle pattern image to form a second cycle pattern image having a Moire fringe formed thereto, an X-ray image detector for detecting the second cycle pattern image by a plurality of pixel parts two-dimensionally arranged along a line direction and the row direction crossing the line direction at the right angle to generate image data, and an image processing part for image-processing the image data. A predetermined number of pixel parts arranged in a direction reduced in the number of the linear flaws among the line and row directions are set to a first group Gr(x, n) and this group Gr(x, n) is successively set while altered by a predetermined pixel in the line and row directions. The phase shift quantity of an intensity modulation signal constituted of the pixel value contained in each of the groups Gr(x, n) is calculated to form the phase differential image.

Description

  The present invention relates to a radiation imaging apparatus and a radiation imaging method for detecting an image based on a phase change of radiation by a subject.

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

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

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

  Against this background, research on X-ray phase imaging that obtains an image based on the phase change of the X-ray by the subject instead of the change in the intensity of the X-ray by the subject has been actively conducted in recent years. X-ray phase imaging is a method of imaging the X-ray phase change based on the fact that the phase change of the X-ray incident on the subject is larger than the intensity change. A high-contrast image can be obtained. As a kind of X-ray phase imaging, an X-ray imaging apparatus that detects an X-ray phase change by configuring an X-ray Talbot interferometer using two gratings and an X-ray image detector is known. (For example, refer to Patent Documents 1 and 2).

  In this X-ray imaging apparatus, a first grating is arranged behind the subject as viewed from the X-ray source, a second grating is arranged at a position away from the first grating by a Talbot distance, and X A line image detector is arranged. The Talbot distance is a distance at which X-rays that have passed through the first grating form a self-image (stripe image) of the first grating by the Talbot effect. This self-image is modulated by refraction caused by the phase change of X-rays in the subject. By detecting this modulation amount, the phase change of the X-ray is imaged.

  A fringe scanning method is known as a method for detecting the modulation amount. In the fringe scanning method, the second grating is moved intermittently by a predetermined pitch with respect to the first grating, while X-rays are emitted from the X-ray source during each stop, the subject, the first And X-rays that have passed through the second grating are detected by a plurality of pixel units constituting the X-ray image detector. The moving direction of the second grating is a direction parallel to the plane of the first grating and perpendicular to the grating direction of the first grating.

  In the fringe scanning method, for each pixel portion of the X-ray image detector, an intensity modulation signal representing the intensity change of the pixel value with respect to the movement of the second grating is generated, and the phase shift amount of this intensity modulation signal (the subject exists) By calculating the phase difference from the initial position when not), an image related to the modulation amount is obtained. This image is an image reflecting the refractive index of the subject, and corresponds to the differential amount of the X-ray phase change (phase shift), and is called a phase differential image. By integrating the phase differential image, a phase contrast image representing the phase shift distribution is generated.

  However, in the fringe scanning method, since it is necessary to perform imaging a plurality of times (for example, 5 times) in order to acquire one phase contrast image, the image quality is deteriorated due to vibration of the apparatus or body movement of the subject. There's a problem. In addition, there is a problem that the exposure dose of the subject is large due to multiple imaging. Patent Document 1 describes that a phase differential image is generated from a single image data obtained by one imaging without moving the first and second gratings. Is not mentioned.

  Therefore, the present applicant proposes a specific method for generating a phase differential image from single image data obtained by one imaging without moving the first and second gratings in Japanese Patent Application No. 2010-265241. doing. In this method, a single image is obtained by an X-ray image detector in a state in which the second grating 22 is slightly inclined relative to the first grating in the grating plane direction to generate moire fringes. Get the data. Then, a predetermined number of pixel portions arranged in the direction crossing the moiré fringes are grouped into one group, and while changing this group, an intensity modulation signal is formed by pixel values of the pixel portions included in each group, and the phase of the intensity modulation signal A phase differential image is generated by calculating the amount of deviation.

JP 2008-200361 A International Publication No. 2008/102654

  However, as described in Patent Document 2, a linear defect in which abnormal pixel values are linearly generated may occur in image data obtained by an X-ray image detector. In the method described in Japanese Patent Application No. 2010-265241, the group for forming the intensity modulation signal extends in one direction. Therefore, when the direction of the linear defect and the extending direction of the group match, the group Are all abnormal pixel values, and a normal intensity modulation signal cannot be obtained. As a result, a linear defect corresponding to the linear defect of the image data is generated in the phase differential image.

  When a line defect is generated in the phase differential image as described above, the phase contrast image obtained by integrating the phase defect image has an effect of the defect on all pixels including part of the line defect in the integration region. As a result, the image quality deteriorates over a wide range.

  An object of the present invention is to provide a radiation imaging apparatus and a radiation imaging method capable of reducing the influence of linear defects generated in image data and generating a phase differential image with high accuracy.

  In order to achieve the above object, a radiation imaging apparatus according to the present invention includes a first grating that generates a first periodic pattern image by passing radiation emitted from a radiation source, and the first periodic pattern image. The second grating that generates a second periodic pattern image that is partially shielded and has moiré fringes, and a plurality of pixel portions that are two-dimensionally arranged along a row direction and a column direction perpendicular thereto. A radiation image detector that detects the second periodic pattern image to generate image data, and a predetermined number of the pixel units arranged in a first direction with few linear defects among the row direction and the column direction are 1 A group setting unit configured to set the group in order while changing the predetermined pixel in the first direction in each of the first direction; and calculating a phase shift amount of the intensity modulation signal configured by the pixel value included in each group Phase fine A differential phase image generator for generating an image, in which comprises a.

  The moire fringes are generated by arranging the second grating so as to be inclined relative to the first grating in the in-lattice direction, and the first and second gratings It is preferable to be substantially orthogonal to the lattice direction.

  The moire fringes are generated by adjusting the positional relationship in the opposing direction of the first and second gratings or the grating pitch of the first and second gratings. It may be substantially parallel to the lattice direction of the two lattices.

  The first direction is preferably substantially orthogonal to the moire fringes.

  The moire fringes are arranged such that the second grating is inclined relative to the first grating in the in-lattice direction, and the positional relationship between the first and second gratings is opposite to each other. Or it is produced | generated by adjusting the grating | lattice pitch of the said 1st and 2nd grating | lattice, and does not need to be orthogonal to the grating | lattice direction of the said 1st and 2nd grating | lattice, and it may not be parallel.

  A pixel defect information storage unit that stores map information of pixel defects of the radiation image detector; and an abnormal pixel value removal unit that removes abnormal pixel values from the pixel values in each group based on the map information. The phase differential image generation unit preferably calculates a phase shift amount of the intensity modulation signal based on normal pixel values other than the abnormal pixel values included in each group, and generates the phase differential image. .

  It is preferable that a normal pixel value counting unit that counts the number of normal pixel values in each group is provided. In this case, it is preferable to provide an error notification unit that performs error notification when there is a group in which the number of normal pixel values is smaller than a reference value.

  It is preferable that the number of the pixel parts constituting the group is equal to the number of the pixel parts included in an integer multiple of the period of the moire fringes.

  It is preferable to include a phase contrast image generating unit that generates a phase contrast image by integrating the phase differential image.

  Preferably, the first grating is an absorption grating, and the first periodic pattern image is generated by geometrically optically projecting incident radiation.

  The first grating may be an absorption grating or a phase grating, and may generate the first periodic pattern image by causing a Talbot effect to incident radiation.

  It is preferable to provide a multi slit that partially blocks the radiation emitted from the radiation source and disperses the focal point.

  In the radiographic method of the present invention, a step of generating a first periodic pattern image by passing radiation emitted from a radiation source through a first grating, and a part of the first periodic pattern image by a second grating. A second periodic pattern image in which moiré fringes are generated by shielding and a radiation image detector having a plurality of pixel portions arranged two-dimensionally along a row direction and a column direction orthogonal thereto A step of generating image data by detecting the second periodic pattern image, and a predetermined number of the pixel units arranged in a first direction with few linear defects in the row direction and the column direction are grouped. , Setting the groups in order while changing the predetermined pixels in the first direction, and calculating the phase shift amount of the intensity modulation signal formed by the pixel values included in each group Comprising the steps of: generating a phase differential image.

  According to the present invention, the predetermined number of the pixel units arranged in the first direction with few linear defects among the row direction and the column direction of the radiation image detector are grouped into one group, and this group is defined as the first direction. Since the pixels are sequentially set while being changed by predetermined pixels, it is possible to reduce the influence of linear defects generated in the image data and to generate a phase differential image with high accuracy.

It is a schematic diagram which shows the structure of an X-ray imaging apparatus. It is a schematic diagram which shows the structure of a X-ray image detector. It is explanatory drawing explaining the structure of the 1st and 2nd grating | lattice. It is explanatory drawing explaining the relationship between a pixel part and a moire fringe. It is explanatory drawing which shows the several pixel part contained in 1 group. It is a graph which shows an intensity | strength modulation signal. It is explanatory drawing explaining the relationship between a linear defect and a group. It is a block diagram which shows the structure of an image process part. It is explanatory drawing explaining the change method of a group. It is a graph which shows an intensity | strength modulation signal in case an abnormal pixel value exists. It is a flowchart explaining the effect | action of an X-ray imaging apparatus. It is a figure which shows the 1st modification of a group. It is a figure which shows the 2nd modification of a group. It is a figure which shows the 3rd modification of a group. It is explanatory drawing explaining the relationship between the pixel part in 2nd Embodiment, and a moire fringe. It is explanatory drawing explaining the change method of the group in 4th Embodiment. It is a flowchart explaining the procedure in the case of implementing update of map information, and offset correction.

(First embodiment)
In FIG. 1, an X-ray imaging apparatus 10 includes an X-ray source 11, a grating unit 12, an X-ray image detector 13, a memory 14, an image processing unit 15, an image recording unit 16, an imaging control unit 17, a console 18, and a system. A control unit 19 is provided. As is well known, the X-ray source 11 includes a rotary anode type X-ray tube (not shown) and a collimator (not shown) for limiting the X-ray irradiation field, and is controlled by the imaging control unit 17. Based on the above, X-rays are emitted toward the subject H.

  The lattice unit 12 includes a first lattice 21 and a second lattice 22. The first and second gratings 21 and 22 are disposed to face the X-ray source 11 in the Z direction, which is the X-ray irradiation direction. A space is provided between the X-ray source 11 and the first grating 21 so that the subject H can be arranged. As is well known, the X-ray image detector 13 is a flat panel detector using a semiconductor circuit, and is arranged in the vicinity of the back of the second grating 22. The detection surface 13a of the X-ray image detector 13 is orthogonal to the Z direction.

  The 1st grating | lattice 21 is an absorption type grating | lattice provided with several X-ray absorption part 21a and X-ray transmission part 21b extended | stretched in the Y direction in the lattice plane (XY plane) orthogonal to a Z direction. The X-ray absorption parts 21a and the X-ray transmission parts 21b are alternately arranged in the X direction (the direction orthogonal to the Z direction and the Y direction) to form a striped pattern. The second grating 22 is an absorption type grating having a plurality of X-ray absorbing portions 22 a and X-ray transmitting portions 22 b that are extended in the Y direction and alternately arranged in the X direction, like the first grating 21. is there. The X-ray absorbing portions 21a and 22a are formed of a material having X-ray absorption properties such as gold (Au) and platinum (Pt). The X-ray transmissive portions 21b and 22b are formed of a material having X-ray permeability such as silicon (Si) or resin or a gap.

  The first grating 21 partially passes X-rays emitted from the X-ray source 11 to generate a first periodic pattern image (hereinafter referred to as G1 image). The second grating 22 partially transmits the G1 image generated by the first grating 21 to generate a second periodic pattern image (hereinafter referred to as G2 image). When the subject H is not arranged, the G1 image substantially matches the lattice pattern of the second lattice 22. As will be described in detail later, the first grating 21 is slightly inclined around the Z axis (in the lattice plane direction) with respect to the second grating 22, and the G2 image has a period corresponding to the inclination angle. The moiré fringes it has have arisen.

  The X-ray image detector 13 detects the G2 image and generates image data. The memory 14 temporarily stores the image data read from the X-ray image detector 13. The image processing unit 15 generates a phase differential image based on the image data stored in the memory 14, and generates a phase contrast image based on the phase differential image. The image recording unit 16 records a phase differential image and a phase contrast image.

  The console 18 includes an operation unit 18a and a monitor 18b. The operation unit 18a includes a keyboard, a mouse, and the like, and enables setting of imaging conditions such as tube voltage, tube current, and irradiation time of the X-ray source 11, and operation input such as an imaging execution instruction.

  The monitor 18b displays photographing information such as photographing conditions and a phase differential image and a phase contrast image recorded in the image recording unit 16. The system control unit 19 comprehensively controls each unit according to a signal input from the operation unit 18a.

  In FIG. 2, the X-ray image detector 13, as is well known, reads out the charge collected by the pixel electrode 31 that collects charges generated in the semiconductor film (not shown) by incident X-rays, and the pixel electrode 31. A large number of pixel units 30 having TFTs (Thin Film Transistors) 32 are arranged in a two-dimensional lattice pattern. The semiconductor film is made of amorphous selenium, for example.

  The X-ray image detector 13 includes a gate scanning line 33, a scanning circuit 34, a signal line 35, and a readout circuit 36. The gate scanning line 33 is provided for each row of the pixel unit 30. The scanning circuit 34 applies a scanning signal for turning on / off the TFT 32 to each gate scanning line 33. The signal line 35 is provided for each column of the pixel unit 30. The readout circuit 36 reads out electric charges from the pixel unit 30 through the signal lines 35, converts them into image data, and outputs them. The detailed layer configuration of each pixel unit 30 is the same as the layer configuration described in Japanese Patent Application Laid-Open No. 2002-26300, for example.

  The readout circuit 36 includes an integration amplifier, an A / D converter, a correction circuit (none of which is shown), and the like. The integrating amplifier integrates the charges output from each pixel unit 30 via the signal line 35 to generate an image signal. The A / D converter converts the image signal generated by the integrating amplifier into digital image data. The correction circuit performs dark current correction, gain correction, linearity correction, and the like on the image data. The corrected image data is stored in the memory 14.

  The X-ray image detector 13 is not limited to the direct conversion type in which incident X-rays are directly converted into electric charges with a semiconductor film, and the incident X-rays are visible with a scintillator such as cesium iodide (CsI) or gadolinium oxysulfide (GOS). It may be an indirect conversion type that converts light into light and converts visible light into electric charge with a photodiode. Furthermore, the X-ray image detector 13 may be configured by combining a scintillator and a solid-state imaging device such as a CMOS sensor.

  The image data generated by the X-ray image detector 13 includes a direction along the signal line 35 (hereinafter referred to as a column direction) and a direction along the gate scanning line 33 (hereinafter referred to as “line direction”) due to abnormality of the signal line 35 and the gate scanning line 33. A linear defect in which a plurality of abnormal pixel values are arranged in the row direction may occur. The map information of the pixel defect including the linear defect is acquired in the inspection process at the final manufacturing stage of the X-ray image detector 13.

  The X-ray image detector 13 is arranged so that the direction of the linear defect does not coincide with the lattice direction (Y direction) of the first and second lattices 21 and 22. For example, when an abnormality occurs in the signal line 35 of the X-ray image detector 13 and a linear defect occurs along the column direction, the X-ray image detector 13 is arranged so that the row direction is along the Y direction. . When there are linear defects in both the column direction and the row direction, the X-ray image detector 13 is arranged so that the direction with few linear defects in the column direction and the row direction is along the Y direction. To do.

  In FIG. 3, X-rays radiated from the X-ray source 11 are cone beams having the X-ray focal point 11a as a light emission point. The first grating 21 is configured so as not to cause the Talbot effect and to project the X-rays that have passed through the X-ray transmission part 21b substantially geometrically. Specifically, the width of the X-ray transmission part 21b in the X direction is set to a value sufficiently larger than the effective wavelength of X-rays irradiated from the X-ray source 11, and most of the X-rays are diffracted by the X-ray transmission part 21b. It is realized by not doing. When tungsten is used as the rotating anode of the X-ray source 11 and the tube voltage is 50 kV, the effective wavelength of X-rays is about 0.4 mm. In this case, the width of the X-ray transmission part 21b may be about 1 to 10 μm.

  As a result, the G1 image is always a self-image of the first grating 21 regardless of the distance from the first grating 21 downstream in the Z direction. The G1 image is enlarged in proportion to the distance from the X-ray focal point 11a to the downstream in the Z direction.

As described above, the grating pitch p ₂ of the second grating 22 is set so that the grating pattern of the second grating 22 matches the G1 image at the position of the second grating 22. Specifically, the grating pitch _{p 2} of the second grating 22, the distance _{L 1} between the grating pitch _p 1, X-ray focal point 11a and the first grating 21 of the first grating 21, the first grating 21 and the distance L ₂ between the second grating 22, is set following equation (1) so as to satisfy substantially.

  The G1 image is modulated by being refracted by a phase change in the X-ray at the subject H. This modulation amount reflects the X-ray refraction angle φ (x) of the subject H. The figure illustrates an X-ray path that is refracted in accordance with a phase shift distribution Φ (x) representing a phase change of the X-ray in the subject H. Reference numeral X1 indicates a path along which the X-ray goes straight when the subject H does not exist, and reference numeral X2 indicates an X-ray path refracted by the subject H.

  The phase shift distribution Φ (x) is expressed by the following equation (2), where X-ray wavelength is λ and the refractive index distribution of the subject H is n (x, z).

  The refraction angle φ (x) is in the relationship of the phase shift distribution Φ (x) and the following equation (3).

  At the position of the second grating 22, the X-ray is displaced in the X direction by an amount corresponding to the refraction angle φ (x). This displacement amount Δx is approximately expressed by the following equation (4) based on the fact that the X-ray refraction angle φ (x) is very small.

  Thus, the displacement amount Δx is proportional to the differential value of the phase shift distribution Φ (x). The displacement amount Δx is expressed by a phase shift amount ψ (x) of the intensity modulation signal (phase shift amount of the intensity modulation signal with and without the subject H), which will be described later, and the following equation (5). Are related.

  From the above equations (3) to (5), it is understood that a phase differential image can be obtained by obtaining the phase shift amount ψ (x) of the intensity modulation signal. A phase differential image may be defined by multiplying or adding a constant to the phase shift amount ψ (x).

  In FIG. 4, the first grating 21 is inclined with respect to the second grating 22 by an angle θ around the Z axis so that the G1 image is slightly inclined with respect to the second grating 22 around the Z axis. Arranged. With this arrangement, a moiré fringe MS having a period T (hereinafter referred to as a moiré period T) represented by the following expression (6) is generated in the G2 image.

  The size in the X direction of the pixel portion 30 of the X-ray image detector 13 is assumed to be Dx (hereinafter referred to as a main pixel size Dx), and the size in the Y direction is referred to as Dy (hereinafter referred to as a subpixel size Dy). The inclination angle θ of the second grating 22 is set so that the moire period T is substantially an integral multiple of the sub-pixel size Dy. The main pixel size Dx is substantially the same as the subpixel size Dy.

  In FIG. 5, M pixel units 30 arranged along the Y direction are defined as one group Gr (x, n). Here, M and n are positive integers. n represents the y coordinate of the first pixel unit 30 in one group Gr (x, n). In the present embodiment, the number of pixels M in one group Gr (x, n) is made equal to the number of pixels ν (ν = 5 in the example of FIG. 4) included in one moire cycle T.

  I (x, y) indicates the pixel value of the pixel unit 30 at the coordinates x and y. Each pixel value I (x, y) is acquired from the image data stored in the memory 14. Pixel values I (x, n) to I (x, n + M−1) in one group Gr (x, n) constitute an intensity-modulated signal for one period as shown in FIG. This is because the degree of overlap between the G1 image and the second grating 22 in the X direction differs depending on the y coordinate of the pixel unit 30 within one moire period T, and the intensity modulation amount changes. Therefore, the intensity modulation signal formed by the pixel values I (x, n) to I (x, n + M−1) in one group Gr (x, n) is the first or second in the conventional fringe scanning method. This corresponds to an intensity modulation signal for one period acquired while intermittently moving the grating in a direction (X direction) substantially perpendicular to the grating direction.

  In the figure, ψ (x, n) indicates the phase shift amount of the intensity modulation signal (solid line) when the object H is arranged with respect to the intensity modulation signal (dashed line) when the object H is not arranged. ing.

  As described above, since the X-ray image detector 13 is arranged so that the direction with few linear defects in the column direction and the row direction is along the Y direction, the linear defects are as shown in FIG. It tends to occur along the X direction. Since the group Gr (x, n) is set to extend in the Y direction, the probability that all the pixel values in the group Gr (x, n) are abnormal pixel values is low.

  8, the image processing unit 15 includes a group setting unit 40, a pixel defect information storage unit 41, an abnormal pixel value removal unit 42, a phase differential image generation unit 43, a phase contrast image generation unit 44, and a normal pixel value counting unit 45. Have

  As shown in FIG. 9, the group setting unit 40 changes the leading coordinates of the group Gr (x, n) one pixel at a time in the Y direction for each column of the pixel units 30 arranged in the X direction (n is set to 1). The group Gr (x, n) is set in order until the last settable group is reached.

  As described above, the pixel defect information storage unit 41 stores pixel defect map information including linear defects acquired in the inspection process at the final manufacturing stage of the X-ray image detector 13. The abnormal pixel value removing unit 42 removes abnormal pixel values from the pixel values in each group Gr (x, n) based on the pixel defect map information stored in the pixel defect information storage unit 41.

  The phase differential image generation unit 43 configures an intensity modulation signal using only normal pixel values in each group Gr (x, n) from which abnormal pixel values have been removed, and a phase shift amount ψ (x , N) to generate a phase differential image. Specifically, the phase differential image generation unit 43 generates a phase differential image by a method similar to the fringe scanning method. This method is known, for example, from “Introduction to Applied Optical Measurement” by Toyohiko Yadagai, Maruzen Co., pp. 136-138

  The phase differential image generation unit 43 calculates the following simultaneous equations (7) to (9), and calculates the phase shift amount ψ (x, n) by applying the calculation result to the following equation (10).

Here, the reference phase δ _k is expressed by the following equation (11).

Note that the phase differential image generation unit 43 performs the calculation in the simultaneous equations (7) to (9) by excluding the term of the scanning position k corresponding to the abnormal pixel value from the sum of the left sides. Here, the term of the scanning position k corresponding to the abnormal pixel value is excluded, so that the reference phase δ _k becomes unequal. For example, as shown in FIG. 10, when the pixel value I (x, n + 1) is an abnormal pixel value, the k = 1 term is excluded from the sum of the left sides of the simultaneous equations (7) to (9). The calculation is performed using normal pixel values I (x, n) and I (x, n + 2) to I (x, n + M-1) corresponding to the non-equally spaced reference phases δ ₀ , δ _{2 to} δ _M−1. Done. This is because, as shown in the figure, only normal pixel values I (x, n), I (x, n + 2) to I (x, n + M−1) are fitted with sine waves, and the phase shift amount of this fitting waveform This corresponds to calculating ψ (x, n).

  The phase contrast image generation unit 44 generates a phase contrast image representing the phase shift distribution by integrating the phase differential image generated by the phase differential image generation unit 43 along the X direction.

  The normal pixel value counting unit 45 counts the number of normal pixel values other than the abnormal pixel value removed by the abnormal pixel value removing unit 42 for each group Gr (x, n). The system control unit 19 determines whether or not there is a group Gr (x, n) in which the normal pixel value count C is smaller than a predetermined reference value S (for example, 3). When there is a group Gr (x, n) in which the count number C is smaller than the reference value S, the phase shift amount ψ (x, n) of the intensity modulation signal corresponding to the group Gr (x, n) is accurate. Since it is not calculated, the system control unit 19 controls the monitor 18b to display an error message indicating that an abnormality has occurred (error notification). Here, the system control unit 19 and the monitor 18b constitute an error notification unit. Note that this error notification may be performed by voice or lighting of a lamp.

As can be seen from the fact that there are three parameters a ₀ , a ₁ , and a ₂ in the simultaneous equations (7) to (9), the calculation of the phase shift amount ψ (x, y) is normal. At least three pixel values are required. For this reason, it is preferable to set the reference value S to “3”. Further, in order to satisfy the so-called sampling theorem, the number of normal pixel values needs to be at least four. Therefore, it is preferable to set the reference value S to “4” more strictly.

  Next, the operation of the X-ray imaging apparatus 10 will be described along the flowchart shown in FIG. When the subject H is placed and an imaging instruction is given by the operation unit 18a (YES in step S10), X-rays are emitted from the X-ray source 11, and the subject H, the first and second gratings 21 and 22 are passed through. The G2 image generated via the X-ray image detector 13 is detected and image data is generated (step S11).

  When the image data is stored in the memory 14, the group Gr (x, n) is set by the group setting unit 40 (step S 13), and is stored in the pixel defect information storage unit 41 by the abnormal pixel value removal unit 42. The abnormal pixel value is removed from the pixel values in the group Gr (x, n) based on the map information of the pixel defect thus made (step S14). When the abnormal pixel value is removed, the normal pixel value counting unit 45 counts the number of normal pixel values in the group Gr (x, n) (step S15).

  The system control unit 19 determines whether or not the count number C of normal pixel values in the group Gr (x, n) is smaller than a predetermined reference value S (step S16), and the count number C is smaller than the reference value S. In that case (YES in step S16), an error message is displayed on the monitor 18b (step S17). In this case, the operation ends without generating the phase differential image and the phase contrast image.

  On the other hand, when the count number C is greater than or equal to the reference value S (NO in step S16), only normal pixel values in each group Gr (x, n) from which the abnormal pixel values have been removed by the phase differential image generation unit 43. Is used to construct an intensity modulation signal, and its phase shift amount ψ (x, n) is calculated (step S18).

  Then, it is determined whether or not the group Gr (x, n) set in step S13 is the final group (step S19). If it is not the final group (NO in step S19), the group setting unit 40 causes the group The first coordinate of Gr (x, n) is changed by one pixel in the Y direction (step S20), and a new group Gr (x, n) is set (step S13). In step S20, when the group Gr (x, n) is changed in the Y direction and the final group that can be set in the Y direction is reached, the group Gr (x, n) is similarly applied to pixel columns adjacent in the X direction. n) is set.

  As described above, steps S13 to S19 are repeatedly executed while the group Gr (x, n) is changed. When the group Gr (x, n) reaches the final group (YES in step S19), a phase differential image is generated based on the calculation result of the phase shift amount ψ (x, n) for one screen ( Step S21).

  Then, the phase contrast image generation unit 44 performs an integration process on the phase differential image to generate a phase contrast image (step S22). A phase differential image and a phase contrast image are displayed on the monitor 18b (step S23). As described above, since the abnormal pixel value is removed from the image data and the phase shift amount ψ (x, n) is calculated, the phase differential image and the phase contrast image are generated with high accuracy.

  In the above embodiment, as shown in FIG. 5, the number of pixels M in one group Gr (x, n) is the same as the number of pixels ν included in one moire period T, but as shown in FIG. In addition, the number of pixels M in one group Gr (x, n) may be the same as N times the number of pixels ν included in one moire period T (where N is an integer of 2 or more).

  Further, as shown in FIG. 13, the number M of pixels in one group Gr (x, n) may not match the number of pixels ν included in one moire period T or N times the number. Furthermore, as shown in FIG. 14, the number of pixels M in one group Gr (x, n) may be smaller than the number of pixels ν included in one moire period T.

  In the above embodiment, the group setting unit 40 changes the group Gr (x, n) one pixel at a time in the Y direction as shown in FIG. 9, but the group Gr (x, n) is changed to Y The direction may be changed in units of two or more pixels.

  Moreover, in the said embodiment, the extending | stretching direction of the X-ray absorption part 22a of the 2nd grating | lattice 22 is made into a Y direction, and the extending | stretching direction of the X-ray absorption part 21a of the 1st grating | lattice 21 is made to incline by angle (theta) with respect to this. However, conversely, the extending direction of the X-ray absorbing portion 21a of the first grating 21 is defined as the Y direction, and the extending direction of the X-ray absorbing portion 22a of the second grating 22 is inclined by an angle θ. May be. Furthermore, the extending direction of the X-ray absorbing portion 21a of the first grating 21 and the extending direction of the X-ray absorbing portion 22a of the second grating 22 are inclined in the opposite direction with respect to the y direction, and both are angled. You may make it make (theta).

  In the above-described embodiment, when the count number C is smaller than the reference value S, the operation is finished without generating the phase differential image and the phase contrast image. May be terminated without generating the phase differential image and the phase contrast image. In addition, without performing these end operations, only a group having a count C smaller than the reference value S may be detected to generate a phase differential image and a phase contrast image. In this case, after generating the phase differential image, the pixels corresponding to the group having the count number C smaller than the reference value S may be interpolated using the pixel values of the peripheral pixels.

In the above-described embodiment, the X-ray image detector 13 is disposed close to the back of the second grating 22 and detects the G2 image generated by the second grating 22 at substantially the same magnification. A space may be provided between the X-ray image detector 13 and the second grating 22. When an X-ray image detector 13 spacing in the Z direction between the second grid 22 and L _3, G2 image is enlarged at a magnification R of the formula (12) is detected by the X-ray image detector 13 .

  In this case, the moire fringe period T ′ detected by the X-ray image detector 13 is R times the moire period T expressed by the above equation (6) (that is, T ′ = RT). For this reason, the group Gr (x, n) may be similarly set based on the moire cycle T ′.

(Second Embodiment)
In the first embodiment, moire fringes are generated in the G2 image by the relative inclination of the first and second gratings 21 and 22 in the lattice plane direction. In the present embodiment, the first and first gratings are generated. The positional relation (distance L ₁ , L ₂ ) of the first and second gratings 21 and 22 or the first so as to slightly break the relation of the above formula (1) without tilting the two gratings 21 and 22. Further, by adjusting the grating pitches p ₁ and p ₂ of the second gratings 21 and 22, moiré fringes MS having a period in the X direction are generated in the G2 image as shown in FIG.

The pattern period p _{3 in} the X direction of the G1 image at the position of the second grating 22 is slightly shifted from the grating pitch p ₂ of the second grating 22. Moire fringes MS have a period T expressed by the following expression (13) in the X direction.

  In the present embodiment, the X-ray image detector 13 is arranged so that the direction of the linear defect does not coincide with the direction (X direction) orthogonal to the lattice direction of the first and second lattices 21 and 22. For example, when an abnormality occurs in the signal line 35 of the X-ray image detector 13 and a linear defect occurs along the column direction, the X-ray image detector 13 is arranged so that the row direction is along the X direction. . When there are linear defects in both the column direction and the row direction, the X-ray image detector 13 is arranged so that the direction with few linear defects in the column direction and the row direction is along the X direction. To do.

  In the present embodiment, as shown in FIG. 16, the group setting unit 40 changes the leading coordinates of the group Gr (n, y) one pixel at a time in the X direction for each row of the pixel units 30 arranged in the Y direction. The group Gr (n, y) is sequentially set until reaching the final settable group (while changing n by 1). The abnormal pixel value removing unit 42 removes abnormal pixel values from the pixel values in each group Gr (n, y) based on the pixel defect map information stored in the pixel defect information storage unit 41.

  As described above, since the X-ray image detector 13 is arranged so that the direction with few linear defects in the column direction and the row direction is along the X direction, the linear defects are along the Y direction. Prone to occur. Since the group Gr (n, y) is set to extend in the X direction, the probability that all the pixel values in the group Gr (n, y) are abnormal pixel values is low.

  The phase differential image generation unit 43 configures an intensity modulation signal using only normal pixel values in each group Gr (n, y) from which abnormal pixel values have been removed, and the phase shift amount ψ (n) of each intensity modulation signal , Y) to generate a phase differential image. The method of calculating the phase shift amount ψ (n, y) is the same as in the first embodiment. Specifically, the following simultaneous equations (14) to (16) may be calculated, and the calculation result may be applied to the following expression (17).

In the simultaneous equations (14) to (16), the phase differential image generation unit 43 performs the calculation by excluding the term of the scanning position k corresponding to the abnormal pixel value from the sum of the left sides. Here, the term of the scanning position k corresponding to the abnormal pixel value is excluded, so that the reference phase δ _k becomes unequal.

In this embodiment as well, an interval L ₃ may be provided between the X-ray image detector 13 and the second grating 22. In this case, the group Gr (n, y) is set based on the moire cycle T ′ obtained by multiplying the moire cycle T represented by the above equation (13) by the magnification R represented by the above equation (12). That's fine.

  Also in this embodiment, as in the first embodiment, the number of pixels M in one group Gr (n, y) may not match the number of pixels ν included in one moire period T or N times that number. Further, the group resetting unit 61 may change the group Gr (n, y) in units of two or more pixels in the X direction. Other configurations and operations of the X-ray imaging apparatus of the present embodiment are the same as those of the first embodiment, and thus the description thereof is omitted.

  Note that the relative inclination of the first and second gratings 21 and 22 in the first embodiment to the in-lattice direction and the first and second gratings 21 and 22 shown in the second embodiment are the same. When the positional relationship or the lattice pitch shifts simultaneously, moire fringes having a period in a direction not parallel to either the X direction or the Y direction may occur in the G2 image. In this case, since the moire fringes have components in the X direction and the Y direction, a phase differential image can be generated by using any one of the methods of the first and second embodiments. In this case, it is also possible to form a group by a plurality of pixel units 30 arranged in an oblique direction not parallel to either the X direction or the Y direction, and similarly generate a phase differential image.

(Third embodiment)
In the first and second embodiments, after the first and second gratings 21 and 22 are set, X-rays are reduced so that the number of linear defects that coincide with the periodic direction of moire fringes (the extending direction of the group) decreases. The direction of the image detector 13 is set. In the present embodiment, conversely, after setting the direction of the X-ray image detector 13, the relative inclination angle θ of the first and second gratings 21 and 22 in the lattice plane direction, and the first and second By adjusting the positional relationship of the second gratings 21 and 22 in the Z direction, the period direction of the moire fringes is set so that the number of linear defects that coincide with the period direction of the moire fringes (the extending direction of the group) is reduced. To do. Other configurations and operations of the X-ray imaging apparatus of the present embodiment are the same as those of the first or second embodiment, and thus the description thereof is omitted.

  It should be noted that the extending direction of the moire fringe periodic direction group does not necessarily match, and may be adjusted so that the extending direction of the group does not match the linear defect as much as possible. By doing so, all pixel values in the group do not become abnormal pixel values, and a phase differential image can be generated with high accuracy.

(Other embodiments)
In each of the embodiments described above, the size of the group set by the group setting unit 40 is constant, but the number of normal pixel values included in the group when the number of normal pixel values included in the group is less than a predetermined number. The size of the group may be expanded so that the number exceeds a predetermined number.

  In each of the above embodiments, the pixel defect map information to be stored in the pixel defect information storage unit 41 is obtained in the inspection process at the final stage of manufacture of the X-ray image detector 13, but the map information is stored in the X-ray imaging apparatus 10. The map information may be acquired after the X-ray image detector 13 is manufactured. Further, the map information may be appropriately updated when the X-ray imaging apparatus 10 is used.

  In each of the above embodiments, imaging is performed only in a state where the subject H is arranged. However, by performing imaging in the same manner without arranging the subject H, a phase differential image is generated, and this is used as an offset image. May be stored, and offset correction may be performed by subtracting the offset image from the phase differential image generated when the subject H is placed and imaging is performed. Thus, the present invention can also be applied to imaging (pre-imaging) performed without arranging the subject H.

  When updating map information and offset correction, for example, each process is executed according to the procedure shown in the flowchart of FIG. First, the map information in the pixel defect information storage unit 41 is updated (step S30), and the X-ray image detector 13 and the first and second grids are arranged so that the extending direction of the group and the linear defect do not coincide as much as possible. The positions 21 and 22 are adjusted (step S31). Thereafter, pre-imaging (step S32) performed without arranging the subject H and main imaging (step S33) performed with the subject H being performed are sequentially executed.

  When the main photographing is completed, offset correction is performed by subtracting the offset image obtained by the pre-photographing from the phase differential image obtained by the main photographing (step S34). Then, the phase differential image after the offset correction is integrated by the phase contrast image generation unit 44, and a phase contrast image is generated (step S35). As described above, when the positions of the X-ray image detector 13 and the first and second gratings 21 and 22 are adjusted, it is preferable to perform pre-imaging thereafter to obtain an offset image. Note that the order of the pre-photographing and the main photographing may be reversed.

  In each of the above embodiments, the subject H is arranged between the X-ray source 11 and the first grating 21, but the subject H is located between the first grating 21 and the second grating 22. You may arrange in.

In each of the above embodiments, the X-ray source 11 that emits cone-beam X-rays emitted from the X-ray source 11 is used. However, an X-ray source that emits parallel-beam X-rays is used. It is also possible. In this case, instead of the above equation (1), the first and second gratings 21 and 22 may be configured so as to substantially satisfy p ₂ = p ₁ .

In each of the above embodiments, X-rays emitted from the X-ray source 11 are incident on the first grating 21 and the X-ray source 11 has a single focal point, but immediately after the emission side of the X-ray source 11. In addition, the X focus may be dispersed by providing a multi slit (line source grid) described in WO2006 / 131235. The multi-slit lattice line extends in the Y direction and is parallel to at least one of the first and second lattices 21 and 22. In this case, the lattice pitch p _{0 in} the X direction of the multi-slit needs to satisfy the following formula (18). Here, the distance L ₀ represents the distance in the Z direction from the multi slit to the first grating 21.

About another structure and effect | action, it is the same as said each embodiment. In the present embodiment, since the position of the multi slit is the position of the X-ray focal point, the distance L ₁ may be replaced with the distance L ₀ in the above equation (1).

Even when the multi-slit is provided as described above, the interval L ₃ may be provided between the X-ray image detector 13 and the second grating 22. In this case, the group Gr (x) is based on the moire cycle T ′ obtained by multiplying the moire cycle T represented by the above equation (6) or the above equation (13) by the magnification R represented by the above equation (12). , N) or group Gr (n, y) may be set. Even when the multi-slit 23 is provided, the G2 image generated by the second grating 22 has the X-ray focal point 11a of the X-ray source 11 as the origin and the distance from the X-ray focal point 11a to the X-ray image detector 20. to be enlarged in proportion to, the magnification R of G2 image, (without replacing the distance L ₁ at a distance L ₀₎ above equation (14) as it may be used.

  Further, in each of the above embodiments, the first grating 21 is configured to project incident X-rays geometrically, but the first grating 21 is known as disclosed in WO 2004/058070 and the like. 21 may be configured to generate the Talbot effect. In order to generate the Talbot effect in the first grating 21, a small-focus X-ray source may be used or the focus may be reduced using the multi-slit so as to enhance the spatial coherence of X-rays. Further, when the Talbot effect is generated in the first grating 21, the first grating 21 can be a phase grating instead of the absorption grating.

When the Talbot effect is generated in the first grating 21, the self-image (G1 image) of the first grating 21 is generated at a position away from the first grating 21 by the Talbot distance Z _m downstream in the Z direction. it is necessary to set the distance L ₂ from the first grid 21 to the second grating 22 on the Talbot distance Z _m.

Talbot distance Z _m is dependent on the beam shape of the structure and the X-ray of the first grating 21. An absorption grating first grating 21, when X-rays emitted from the X-ray source 11 is a cone beam shape, Talbot distance Z _m is represented by the following formula (19). Here, m is a positive integer. In this case, the grating pitches p ₁ and p ₂ are set so as to substantially satisfy the above formula (1) (however, when a multi-slit is used, the distance L ₁ is replaced with the distance L ₀ ).

Further, when the first grating 21 is a phase-type grating that applies phase modulation of π / 2 to the X-ray, and the X-ray emitted from the X-ray source 11 has a cone beam shape, the Talbot distance Z _m is Is represented by the following formula (20). Here, m is 0 or a positive integer. In this case, the grating pitches p ₁ and p ₂ are set so as to substantially satisfy the above formula (1) (however, when a multi-slit is used, the distance L ₁ is replaced with the distance L ₀ ).

In addition, when the first grating 21 is a phase-type grating that imparts π phase modulation to X-rays and the X-rays emitted from the X-ray source 11 have a cone beam shape, the Talbot distance Z _m is as follows. It is represented by Formula (21). Here, m is 0 or a positive integer. In this case, since the pattern period of the G1 image is ½ times the grating period of the first grating 21, the grating pitches p ₁ and p ₂ are set so as to substantially satisfy the following expression (22). (However, when using a multi-slit, the distance _{L 1} is replaced by a distance _{L 0).}

Further, when the first grating 21 is an absorption grating and the X-rays emitted from the X-ray source 11 have a parallel beam shape, the Talbot distance Z _m is expressed by the following equation (23). Here, m is a positive integer. In this case, the lattice pitches p ₁ and p ₂ are set so as to substantially satisfy the relationship of p ₂ = p ₁ .

Further, when the first grating 21 is a phase-type grating that applies phase modulation of π / 2 to X-rays, and the X-rays emitted from the X-ray source 11 are parallel beams, the Talbot distance Z _m is Is represented by the following formula (24). Here, m is 0 or a positive integer. In this case, the lattice pitches p ₁ and p ₂ are set so as to substantially satisfy the relationship of p ₂ = p ₁ .

When the first grating 21 is a phase type grating that imparts π phase modulation to X-rays, and the X-rays emitted from the X-ray source 11 are parallel beams, the Talbot distance Z _m is It is represented by Formula (25). Here, m is 0 or a positive integer. In this case, since the pattern period of the G1 image is ½ times the grating period of the first grating 21, the grating pitches p ₁ and p ₂ almost satisfy the relationship of p ₂ = p _1/2. Set to

  The above embodiments may be combined with each other within a consistent range. The present invention can be applied to an industrial radiography apparatus and the like in addition to a radiography apparatus for medical diagnosis. In addition to X-rays, gamma rays or the like can be used as radiation.

DESCRIPTION OF SYMBOLS 10 X-ray imaging apparatus 12 Lattice part 13 X-ray image detector 21 1st grating | lattice 21a X-ray absorption part 21b X-ray transmission part 22 2nd grating | lattice 22a X-ray absorption part 22b X-ray transmission part 30 Pixel part 31 Pixel electrode 33 Gate scanning line 35 Signal line

Claims (14)

A first grating for generating a first periodic pattern image by passing radiation emitted from a radiation source;
A second grating that partially shields the first periodic pattern image to generate a second periodic pattern image in which moire fringes are generated;
A radiation image detector that generates image data by detecting the second periodic pattern image by a plurality of pixel units arranged two-dimensionally along a row direction and a column direction orthogonal to the row direction;
Among the row direction and the column direction, a predetermined number of the pixel portions arranged in the first direction with few linear defects are set as one group, and the groups are sequentially set while changing the predetermined pixel by one in the first direction. A group setting section;
A phase differential image generation unit that generates a phase differential image by calculating a phase shift amount of an intensity modulation signal configured by pixel values included in each group; and
A radiation imaging apparatus comprising:   The moire fringes are generated by arranging the second grating so as to be inclined relative to the first grating in the in-lattice direction, and the first and second gratings The radiation imaging apparatus according to claim 1, wherein the radiation imaging apparatus is substantially orthogonal to the lattice direction.   The moire fringes are generated by adjusting the positional relationship in the opposing direction of the first and second gratings or the grating pitch of the first and second gratings. The radiation imaging apparatus according to claim 1, wherein the radiation imaging apparatus is substantially parallel to a grating direction of the two gratings.   The radiation imaging apparatus according to claim 1, wherein the first direction is substantially orthogonal to the moire fringes.   The moire fringes are arranged such that the second grating is inclined relative to the first grating in the in-lattice direction, and the positional relationship between the first and second gratings is opposite to each other. Or it is produced | generated by adjusting the grating | lattice pitch of the said 1st and 2nd grating | lattice, It is not orthogonal to the grating | lattice direction of the said 1st and 2nd grating | lattice, It is characterized by the above-mentioned. Item 2. The radiographic apparatus according to Item 1. A pixel defect information storage unit that stores map information of pixel defects of the radiation image detector; and an abnormal pixel value removal unit that removes abnormal pixel values from the pixel values in each group based on the map information. ,
The phase differential image generation unit calculates a phase shift amount of the intensity modulation signal based on normal pixel values other than the abnormal pixel values included in each group, and generates the phase differential image. The radiation imaging apparatus according to any one of claims 1 to 5.   The radiation imaging apparatus according to claim 6, further comprising a normal pixel value counting unit that counts the number of normal pixel values in each group.   The radiation imaging apparatus according to claim 7, further comprising an error notification unit that performs error notification when there is a group in which the number of normal pixel values is smaller than a reference value.   9. The radiographic apparatus according to claim 1, wherein the number of the pixel units constituting the group is equal to the number of the pixel units included in an integer multiple of the period of the moire fringes. .   The radiation imaging apparatus according to claim 1, further comprising a phase contrast image generation unit that generates a phase contrast image by integrating the phase differential image.   The said 1st grating | lattice is an absorption-type grating | lattice, and produces | generates a said 1st periodic pattern image by projecting the incident radiation geometrically optically, The any one of Claim 1 to 10 characterized by the above-mentioned. The radiation imaging apparatus described.   11. The first periodic pattern image is generated by generating a Talbot effect on incident radiation and generating the first periodic pattern image. The radiographic apparatus according to the item.   13. The radiographic apparatus according to claim 1, further comprising a multi-slit that partially blocks the radiation emitted from the radiation source and disperses the focal point. Passing the radiation emitted from the radiation source through the first grating to generate a first periodic pattern image;
Generating a second periodic pattern image in which moire fringes are generated by partially shielding the first periodic pattern image with a second grating;
Detecting the second periodic pattern image by a radiation image detector having a plurality of pixel portions arranged two-dimensionally in a row direction and a column direction orthogonal thereto, and generating image data;
Among the row direction and the column direction, a predetermined number of the pixel portions arranged in the first direction with few linear defects are set as one group, and the groups are sequentially set while changing the predetermined pixel by one in the first direction. Steps,
Generating a phase differential image by calculating a phase shift amount of an intensity modulation signal composed of pixel values included in each group;
A radiation imaging method comprising: