JP2014217398A - Radiographic apparatus and method of radiography - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent inhibition of imaging of a soft tissue due to an unwrapping error and reduce a level difference of data between OK regions in a phase differential image after off-set correction.SOLUTION: A radiographic apparatus generates image data by detecting an X-ray emitted from an X-ray source and passing through first and second gratings, generates a phase differential image on the basis of the image data, detects an NG region in which an unwrapping error is easily generated in the phase differential image generated at the time of main photographing in which a subject is arranged, detects other regions as an OK region, performs unwrapping processing only on the OK region with respect to the phase differential image, stores the phase differential image generated at the time of pre-photographing in which the subject is not arranged as an off-set image, performs unwrapping processing only on the OK region with respect to the off-set image, and performs off-set correction for subtracting the off-set image subjected to the unwrapping processing from the phase differential image subjected to the unwrapping processing.

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 one type 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 diffraction gratings and an X-ray image detector is known. (For example, refer to Patent Document 1).

  In this X-ray imaging apparatus, the first diffraction grating is disposed behind the subject as viewed from the X-ray source, and the second diffraction grating is disposed at a position separated from the first diffraction grating by the Talbot distance. An X-ray image detector is arranged behind. The Talbot distance is the distance at which the X-rays that have passed through the first diffraction grating form a self-image (striped image) of the first diffraction grating due to the Talbot effect, and the grating pitch of the first diffraction grating and the X-ray wavelength Depends on and. 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 diffraction grating is scanned with respect to the first diffraction grating in a direction parallel to the plane of the first diffraction grating and perpendicular to the grating line direction of the first diffraction grating. X-rays are radiated from the X-ray source at each scanning position while being translated (scanned) at a pitch, and the X-ray image passing through the subject and the first and second diffraction gratings is imaged by the X-ray image detector. Is the method. Calculating a phase shift amount (phase difference from an initial position when no subject exists) for a signal (intensity modulation signal) representing a change in the pixel value of each pixel obtained by the X-ray image detector with respect to the scanning. Thus, 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.

As shown in Patent Document 1, the phase shift amount is calculated using a function (arg [...]) for extracting a complex argument and an arctangent function (tan ^-1 [...]). . For this reason, the phase differential image is expressed by a value convolved (wrapped) in the range of the function (−π to + π or −π / 2 to + π / 2). In the phase differential image wrapped in this way, discontinuous points may occur at locations where the upper limit of the range changes to the lower limit or at locations where the lower limit changes to the upper limit. It is known to perform the unwrapping process (see, for example, Patent Document 2).

  This unwrapping process is also performed in the field of optical measurement or the like (see, for example, Patent Document 3). In general, unwrap processing is performed in order along a predetermined route from a starting point at a predetermined position in the image. When the discontinuous point is detected in the path, a value corresponding to the range of the function is uniformly added to or subtracted from data after the discontinuous point. Thereby, discontinuous points are eliminated and data is continuous.

  Further, in X-ray phase imaging, noise unevenness derived from a measurement system such as a diffraction grating appears in the phase differential image. In order to remove this noise unevenness, a phase differential image is acquired in the absence of the subject in advance, and this is stored as an offset image, and the offset image is obtained from the phase differential image acquired with the subject placed. Offset correction for subtraction is performed (see, for example, Patent Document 1).

WO2004 / 058070 JP 2011-045655 A JP 2008-082869 A

  However, when the subject includes a high-absorber having a high X-ray absorption capability such as a bone part, the X-ray is greatly attenuated in the high-absorber and the intensity and amplitude of the intensity modulation signal are reduced. Therefore, the calculation accuracy of the phase shift amount is lowered. Thereby, an unwrapping error is likely to occur in the high-absorber region of the phase differential image. In this unwrapping error, discontinuity occurs at a place that is not a discontinuous point and is considered as a discontinuous point. There are cases where the unwrapping process is not performed because it is not regarded as a discontinuous point.

  As shown in FIG. 19, when a starting point is set in the bone region that is a high-absorbent body and unwrap processing is performed along a path extending in one direction from the starting point, an unwrapping error is likely to occur in the bone region. Once an unwrap error occurs, an error value (a value corresponding to the value range of the function) is accumulated in the path after the location where the unwrap error has occurred. As a result, streaky noise along the path direction of the unwrapping process is generated in the phase differential image after the unwrapping process, and this noise overlaps a part of the cartilage part that is a soft tissue. There is a problem in that imaging of the soft tissue of the heart, which is a region, is hindered. Therefore, a method is conceivable in which an area where an unwrap error is likely to occur (NG area) is determined, and the other area (OK area) is unwrapped.

  However, if the phase differential image is divided into NG regions and a plurality of OK regions are generated, in order to remove the noise unevenness described above, the phase differential images obtained by performing unwrap processing on each OK region (FIG. 20A When the offset image (see FIG. 20B) that has been subjected to the unwrap process is subtracted from the entire image, the phase differential image after the offset process (see FIG. 20C) contains data between the OK regions. There arises a problem that a step is generated.

  The present invention has been made in view of the above problems, and prevents the inhibition of soft tissue imaging due to an unwrapping error, and reduces the data step between OK regions in the phase differential image after offset correction. An object of the present invention is to provide a radiation imaging apparatus and a radiation imaging method that enable this.

  In order to achieve the above object, a radiation imaging apparatus of the present invention includes a radiation detector that detects radiation emitted from a radiation source and transmitted through a subject to generate image data, and the radiation source and the radiation detector. A phase differential image generation unit that generates a phase differential image expressed by a value wrapped in a predetermined range based on the image data, and a state in which the subject is not arranged In the pre-imaging performed, in the main imaging performed in a state where the offset image storage unit that stores the phase differential image generated by the phase differential image generation unit as an offset image and the subject is arranged, the phase differential image An NG region where an unwrap error is likely to occur is detected from the phase differential image generated by the generation unit, and other regions are detected as OK regions. An OK / NG region detection unit, a first unwrap processing unit that unwraps only the OK region with respect to the phase differential image obtained by the main imaging, and a first unwrap processing unit that unwraps only the OK region with respect to the offset image. Offset correction for subtracting the offset image that has been unwrapped by the second unwrap processor from the phase differential image that has been unwrapped by the second unwrap processor and the first unwrap processor. And an offset processing unit to perform.

  The second unwrap processing unit unwraps only each OK region of the offset image when there are a plurality of the OK regions detected by the OK / NG region detection unit, and the OK region is 1 In the case of only one, it is preferable to unwrap the entire offset image.

  The second unwrap processing unit preferably performs the unwrap process by setting the same start point as the first unwrap processing unit.

  A difference in pixel value of the start point is calculated for the phase differential image that has been unwrapped by the first unwrap processor and the offset image that has been unwrapped by the second unwrap processor. It is preferable that a calibration processing unit that calibrates the OK region of the offset image based on the difference is provided.

  By fitting the noise remaining in the phase differential image that has been offset-corrected by the offset processing unit with a linear form or a polynomial, correction data representing a tendency of the noise is obtained, and the noise is calculated using the correction data. It is preferable to provide a correction processing unit to be removed.

  The unwrap processing unit sets a starting point group along a penetrating line that passes only through the OK region and penetrates the phase differential image in one direction, and follows a straight path perpendicular to the penetrating line from each starting point of the starting point group. It is preferable to perform unwrapping processing, unwrapping processing between adjacent starting points of the starting point group, and unwrapping processing for pixels in the OK region remaining behind the NG region when viewed from the starting point group.

  The grating unit partially shields the first periodic pattern image by passing the radiation from the radiation source to generate the first periodic pattern image, and displays the second periodic pattern image. It is preferable that the radiographic image detector generates the image data by detecting the second periodic pattern image.

  The grating unit includes a scanning mechanism that moves the first grating or the second grating at a predetermined scanning pitch and sequentially sets a plurality of scanning positions, and the radiological image detector includes the scanning mechanism at each scanning position. Preferably, the second periodic pattern image is detected to generate image data, and the phase differential image generation unit generates a phase differential image based on a plurality of image data generated by the radiation image detector. In this case, it is preferable that the scanning mechanism moves the first grating or the second grating in a direction orthogonal to the grating line. Further, the first grating or the second grating may be moved in a direction inclined with respect to the grating line.

  Preferably, the phase differential image generation unit generates the phase differential image based on single image data obtained by the radiation detector.

  It is preferable that the OK / NG area detection unit detects an NG area based on one or a combination of average intensity, amplitude, and visibility of an intensity modulation signal representing intensity change of a pixel value.

  It is preferable that an NG region image replacement unit that generates any one of an absorption image, a differential image of the absorption image, and a small angle scattered image and replaces the NG region of the phase differential image is provided.

  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 is preferably an absorption grating or a phase grating, and the first periodic pattern image is preferably generated by causing a Talbot effect to incident radiation.

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

  The radiography method of the present invention generates image data by detecting radiation emitted from a radiation source and passing through a lattice portion in a state where no subject is arranged, and is wrapped in a predetermined range based on the image data. In the pre-imaging process in which the phase differential image expressed by the measured value is generated and stored as an offset image, and the subject is disposed, the radiation source is emitted from the radiation source and passes through the subject and the lattice unit. A main imaging step of generating image data by detecting radiation and generating a phase differential image expressed by a value wrapped in a predetermined range based on the image data, and the phase generated in the main imaging step An OK / NG area detecting step of detecting an NG area where an unwrapping error is likely to occur from the differential image and detecting the other area as an OK area; A first unwrap processing step for unwrapping only the OK region with respect to the phase differential image generated in step 2 and a second unwrap processing for unwrapping only the OK region with respect to the offset image generated in the pre-imaging step. Offset processing step for performing offset correction for subtracting the offset image that has been unwrapped in the second unwrapping process from the phase differential image that has been unwrapped in the first unwrapping process And comprising.

  According to the present invention, only the OK region is unwrapped with respect to the phase differential image generated by the main photographing, and only the OK region is unwrapped with respect to the offset image generated by the pre-photographing, and then the phase differential is subjected to the unwrap processing. Since the offset image on which the unwrap processing has been performed is subtracted from the image, the inhibition of the soft tissue imaging due to the unwrap error is prevented, and the data level difference between the OK regions in the phase differential image after the offset correction is reduced. be able to.

It is a block 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 a graph which shows an intensity | strength modulation signal. It is a block diagram which shows the structure of an image process part. It is a flowchart explaining the flow of the unwrap processing method. It is a figure explaining the starting method of an unwrap process, and the setting method of a path | route. It is a figure explaining an unwrap process. It is a figure explaining the setting method of the starting point and path | route when a some OK area | region exists. It is a figure explaining the setting method of the starting point and path | route with respect to an offset image in case there is only one OK area | region. It is a flowchart explaining the effect | action of the X-ray imaging apparatus at the time of pre imaging | photography. It is a flowchart explaining the effect | action of the X-ray imaging apparatus at the time of this imaging | photography. It is explanatory drawing explaining offset correction. It is a block diagram which shows the structure of the image process part provided with the calibration process part. It is explanatory drawing explaining the effect | action of a calibration process part. It is a block diagram which shows the structure of the image process part provided with the calibration process part and the inclination correction process part. It is a figure explaining the example which performs an unwrap process in order for every pixel from one starting point. It is a block diagram which shows the structure of the image process part provided with the NG area | region image replacement part. It is explanatory drawing explaining the conventional unwrap process. It is explanatory drawing explaining the conventional offset correction.

  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. The X-ray source 11 includes, for example, a rotary anode type X-ray tube and a collimator that limits the X-ray irradiation field, and emits X-rays toward the subject H based on the control of the imaging control unit 17. To do.

  The grating unit 12 includes a first grating 21, a second grating 22, and a scanning mechanism 23. The first and second gratings 21 and 22 are disposed to face the X-ray source 11 with respect to the z direction that 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. The X-ray image detector 13 is, for example, a flat panel detector using a semiconductor circuit, and is arranged behind the second grating 22 so that the detection surface 13a is orthogonal to the z direction.

  The 1st grating | lattice 21 is an absorption type grating | lattice provided with the some X-ray absorption part 21a and X-ray transmission part 21b extended | stretched in the y direction which is one direction in the grating plane orthogonal to az direction. The X-ray absorption part 21a and the X-ray transmission part 21b are alternately arranged in the x direction orthogonal to the z direction and the y direction, and form a striped pattern. The second grating 22 is an absorption type grating having a plurality of X-ray absorbing portions 22a and X-ray transmitting portions 22b that are extended in the y direction and arranged alternately 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.

  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 scanning mechanism 23 translates the second grating 22 in the x direction, and sequentially changes the relative position of the second grating 22 with respect to the first grating 21. The scanning mechanism 23 is configured by a piezoelectric actuator or an electrostatic actuator, and is driven based on the control of the imaging control unit 17 in order to execute a fringe scanning described later. The memory 14 collectively stores image data obtained by the X-ray image detector 13 at each scanning position of fringe scanning.

  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 sets operation conditions such as setting of imaging conditions such as tube voltage, tube current, and irradiation time of the X-ray source 11, mode selection for main imaging or pre-imaging, and imaging execution instruction. Is possible. The main imaging is an imaging mode performed with the subject H placed between the X-ray source 11 and the first grating 21. Pre-imaging is an imaging mode performed without placing the subject H between the X-ray source 11 and the first grating 21. As will be described in detail later, the pre-photographing is used to acquire a background component caused by a manufacturing error or an arrangement error of the first and second gratings 21 and 22 as an offset image.

  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, an X-ray image detector 13 includes a pixel electrode 31 that collects charges generated in a semiconductor film (not shown) by incident X-rays, and a TFT (Thin for reading charges collected by the pixel electrode 31). A plurality of pixel portions 30 having a film transistor (32) are arranged in a two-dimensional manner. 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 JP-A-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. Further, the X-ray image detector 13 may be configured by combining a scintillator and a CMOS sensor.

  In FIG. 3, the X-rays emitted from the X-ray source 11 are cone beams having the X-ray focal point 11a as a light emission point. The 1st grating | lattice 21 is comprised so that the Talbot effect may not arise and the X-rays which passed X-ray transmissive part 21b may be projected geometrically. Specifically, the width of the X-ray transmission part 21b in the x direction is set to a value sufficiently larger than the peak 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 peak wavelength of the X-ray is about 0.4 mm. In this case, the width of the X-ray transmission part 21b may be about 1 to 10 μm.

  Thus, 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 related to the phase shift distribution Φ (x) by 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). Therefore, by detecting the displacement amount Δx by fringe scanning, which will be described later, a differential value of the phase shift distribution Φ (x) is obtained, and a phase differential image is generated.

In the fringe scanning, a value obtained by dividing the grating pitch p ₂ into M pieces (p ₂ / M) is used as a scanning pitch, and the second grating 22 is translated by the scanning mechanism 23 at this scanning pitch. Each time the image is translated, X-rays are emitted from the X-ray source 11 and a G2 image is captured by the X-ray image detector 13. M is an integer greater than or equal to 3, for example, it is preferable that M = 5.

If the above equation (1) is not satisfied slightly, or if rotation around the z direction or slight inclination with respect to the xy plane occurs between the first grating 21 and the second grating 22, G2 Moire fringes appear in the image. The moire fringes are moved along with the translational movement of the second grating 22, the moving distance in the x direction matches the original moiré fringe reaches the grating pitch p _2. By confirming the movement of the moire fringes, the translational movement amount of the second grating 22 can be verified.

M pixel values are obtained for each pixel unit 30 of the X-ray image detector 13 by the fringe scanning. As shown in FIG. 4, the M pixel values I _k periodically change with respect to the scanning position k of the second grating 22. The scanning position k is each position for each scanning pitch (p ₂ / M) when the second grating 22 is translated by one period. A signal indicating a change in the pixel value I _k with respect to the scanning position k is referred to as an intensity modulation signal.

  A broken line in the figure indicates an intensity modulation signal obtained in a state where the subject H is not arranged. On the other hand, a solid line indicates an intensity modulation signal in which the phase difference amount ψ (x) is generated by the subject H in a state where the subject H is arranged. This phase shift amount ψ (x) is in the relationship of the displacement amount Δx and the following equation (5).

Therefore, for each pixel unit 30, a phase differential image is obtained by obtaining the phase shift amount ψ (x) of the intensity modulation signal based on the M pixel values I _k obtained by the fringe scanning.

  Next, a method for calculating the phase shift amount ψ (x) will be described. The intensity modulation signal is generally expressed by the following formula (6).

Here, A ₀ represents the average intensity of the incident X-ray, A _n represents the amplitude of the intensity-modulated signal. n is a positive integer and i is an imaginary unit. As shown in FIG. 4, when the intensity modulation signal draws a sine wave, n = 1.

In the present embodiment, since the scanning pitch (p ₂ / M) is constant, the following expression (7) is established.

  When the above equation (7) is applied to the above equation (6), the phase shift amount ψ (x) is expressed by the following equation (8).

  Here, arg [...] is a function for extracting the argument of a complex number. Further, the phase shift amount ψ (x) can also be expressed by the following equation (9) using an arctangent function.

  Since the declination angle of the complex number ranges from −π to + π, when the phase shift amount ψ (x) is calculated based on the above equation (8), the phase shift amount ψ (x) is − Take a value that is convolved (wrapped) in the range of π to + π. On the other hand, the arc tangent function usually has a range of −π / 2 to + π / 2. Therefore, when the phase shift amount ψ (x) is calculated based on the above equation (9), The phase shift amount ψ (x) takes a value convoluted in a range of −π / 2 to + π / 2. In the above formula (9), by determining the denominator and the sign of the numerator in the arctangent function, the value range can be changed from −π to + π, and therefore the phase shift amount ψ ( It is also possible to calculate x).

  In the present embodiment, data obtained by calculating the phase shift amount ψ (x) for each pixel unit 30 is referred to as a phase differential image. Note that an image represented by data obtained by multiplying or adding a phase shift amount ψ (x) by a constant may be a phase differential image.

  In FIG. 5, the image processing unit 15 includes a phase differential image generation unit 40, an offset image storage unit 41, an OK / NG region detection unit 42, a first unwrap processing unit 43, a second unwrap processing unit 44, and an offset processing unit. 45 and a phase contrast image generation unit 46. The phase differential image generation unit 40 uses the image data for M sheets stored in the memory 14 as a result of performing the fringe scanning in the main photographing or the pre-photographing, and based on the above equation (8) or the above equation (9). A phase differential image is generated by performing an operation.

  The phase differential image generated by the phase differential image generation unit 40 during pre-photographing is stored in the offset image storage unit 41 as an offset image. The phase differential image generated by the phase differential image generation unit 40 during the main photographing is input to the first unwrap processing unit 43. In addition, when the offset image is input again from the phase differential image generation unit 40, the offset image storage unit 41 deletes the stored offset image and then stores the input offset image.

The OK / NG area detection unit 42 detects an area where an unwrap error is likely to occur in the phase differential image (hereinafter referred to as an NG area) based on the M pieces of image data stored in the memory 14, and detects an area other than the NG area. The area is detected as an OK area. OK / NG area detection unit 42, for each pixel unit 30, the average intensity _{A 0} is lower than the threshold region of the intensity modulated signal, domain amplitude _{A 1} is lower than the threshold value or visibility _A 1 / _{A 0} is lower than the threshold region, Is an NG region.

This NG region corresponds to a high-absorber region included in the subject H (when the subject H is a human body, a bone portion having a high X-ray absorption capability). This is based on the fact that the average intensity A ₀ , the amplitude A ₁ , or the visibility A ₁ / A ₀ decreases due to the X-rays being absorbed by the high absorber. The NG region may be detected by combining two or more of the average intensity A ₀ , the amplitude A ₁ , and the visibility A ₁ / A ₀ . Further, when the NG area is scattered and cannot be obtained as a gathering area having a certain size, the size of the NG area may be adjusted by changing the threshold value.

  The first unwrap processing unit 43 performs unwrap processing on the phase differential image input from the phase differential image generation unit 40 only for the OK region other than the NG region. The second unwrap processing unit 44 performs unwrap processing on the entire image or only the OK region on the offset image stored in the offset image storage unit 41.

  The offset processing unit 45 performs offset correction by subtracting the offset image subjected to the unwrap processing by the second unwrap processing unit 44 from the phase differential image subjected to the unwrap processing by the first unwrap processing unit 43. The phase contrast image generation unit 46 generates a phase contrast image representing the phase shift distribution by integrating the phase differential image after the offset correction along the x direction. The phase differential image after the offset correction and the phase contrast image are recorded in the image recording unit 16.

  Next, the unwrap processing method by the first unwrap processing unit 43 will be described in more detail with reference to FIGS. 6 and 7. First, the starting point for starting the unwrapping process is set in each row or each column of the phase differential image (step S10). These multiple starting points are called starting point groups.

  FIG. 7 shows the phase differential image as an image of 10 × 7 pixels for simplification of explanation, and the phase differential image shows the NG region detected by the OK / NG region detection unit 42. An area other than the NG area is an OK area. In step S10, a through line that passes only through the OK region and penetrates the phase differential image in the x direction or the y direction is searched, and a starting point group is set for one of the through lines. In the present embodiment, there are penetrating lines in each of the x direction and the y direction, but the starting point groups P0 to P6 are set along the penetrating lines along the shorter y direction. Here, the starting point groups P0 to P6 are set along end portions (short sides) in the x direction.

  After setting the starting point groups P0 to P6, linear straight paths R0 to R6 starting from the starting point groups P0 to P6 are set in the direction (x direction) orthogonal to the through line where the starting point groups P0 to P6 are set. Then, an unwrap process is executed along each straight path R0 to R6 (step S11). The straight paths R0 to R6 are not set in the NG area. For this reason, behind the NG area viewed from the starting point group P0 to P6, pixels that belong to the same OK area as the starting point groups P0 to P6 but do not have the straight paths R0 to R6 set remain.

  Specifically, in step S11, first, unwrap processing is performed in order along the straight line route R0 from the starting point P0, and when the unwrap processing of the straight line route R0 ends, the unwrapping processing of the starting point P1 is performed with reference to the starting point P0. Thereafter, the unwrapping process is sequentially performed from the starting point P1 along the straight path R1. Then, the unwrapping process is not performed on the pixels remaining behind the NG area in the same row as the straight line R1, and the unwrapping process of the starting point P2 is performed with the starting point P1 as a reference. Thereafter, the unwrapping process is performed in the same procedure, and when the unwrapping process for the straight line route R6 ends, the step S11 ends.

  Thereafter, a wraparound path is set for the pixels remaining behind the NG area, and a wraparound process is performed for performing an unwrap process along the wraparound path (step S12). Specifically, in step S12, the wraparound path WR0 is set for pixels remaining in the same row as the straight line route R1, and the wraparound path WR1 is set for pixels remaining in the same row as the straight line route R5. The wraparound path WR0 is unwrapped from the pixel on the adjacent straight path R0. The wraparound path WR1 is subjected to unwrap processing starting from a pixel on the adjacent straight path R6.

  As shown in FIG. 8, the unwrapping process on each path detects a discontinuous point DP that changes from the upper limit to the lower limit of the range of the function of the above equation (8) or the above equation (9), or from the lower limit to the upper limit. In this process, the data after the detected discontinuous point DP is uniformly added or subtracted with a value corresponding to the range to eliminate the discontinuous point DP and to make the data continuous.

  As illustrated in FIG. 9, the phase differential image may be divided by the NG region, and a plurality of OK regions may be detected. In this case, the above steps S10 to S12 are individually executed for each OK area. The phase differential image shown in FIG. 2 includes first and second OK regions. In the first OK region, starting point groups P0a to P6a are set along the penetrating line penetrating in the y direction at the end in the x direction, and straight paths R0a to R6a are set from the starting point groups P0a to P6a in the y direction. Is done. And the unwrap process along each linear path | route R0a-R6a and the unwrap process between the adjacent starting points of the starting point groups P0a-P6a are performed.

  Similarly, in the second OK region, starting point groups P0b to P6b are set along penetrating lines penetrating in the y direction at the end in the x direction, and straight paths R0b to P6b from the starting point groups P0b to P6b in the y direction. R6b is set. And the unwrap process along each straight path R0b-R6b and the unwrap process between the adjacent starting points of the starting point groups P0b-P6b are performed. In addition, when it is necessary to set a wraparound path in the first and second OK regions, the setting is appropriately performed, and the unwrap process is performed along the set wraparound path.

  When the phase differential image is not divided by the NG region and only one OK region is detected, the second unwrap processing unit 44 applies the entire offset image regardless of the detection result of the NG region and the OK region. Perform unwrapping. Specifically, as illustrated in FIG. 10, the second unwrap processing unit 44 sets start point groups P0 to P6 along the y direction at the x direction end of the offset image, and from each of the start point groups P0 to P6. Straight lines R0 to R6 are set in the y direction, and an unwrap process along each straight path R0 to R6 and an unwrap process between adjacent start points of the start point groups P0 to P6 are performed. In this case, the starting point (starting point) P0 for starting the unwrapping process for the offset image and the starting point (starting point) P0 for starting the unwrapping process for the phase differential image are set to the same pixel position.

  In addition, the second unwrap processing unit 44 divides the phase differential image by the NG region, and when a plurality of OK regions are detected, the starting point group, straight path, and the like set by the first unwrap processing unit 43, The wraparound path is set at the same position with respect to the offset image, and unwrap processing is performed in the same order as the unwrap processing by the first unwrap processing unit 43.

  Next, the operation of the X-ray imaging apparatus 10 will be described with reference to the flowcharts shown in FIGS. When the shooting mode is selected using the operation unit 18a (step S20), it is determined whether or not the selected shooting mode is pre-shooting (step S21). If it is pre-photographing, a standby state for photographing instructions is entered (step S22). When an imaging instruction is given using the operation unit 18a (YES in step S22), the second grating 22 is translated by a predetermined scanning pitch by the scanning mechanism 23, and at each scanning position k by the X-ray source 11. X-ray irradiation and detection of the G2 image by the X-ray image detector 13 are performed (step S23). As a result of the fringe scanning, M pieces of image data are generated and stored in the memory 14.

  Thereafter, the M image data stored in the memory 14 is read by the image processing unit 15. In the image processing unit 15, a phase differential image is generated by the phase differential image generation unit 40 (step S24). This phase differential image is stored in the offset image storage unit 41 as an offset image (step S25). The pre-photographing operation ends here. Note that this pre-imaging may be performed at least once in a state in which the subject H is not disposed when the X-ray imaging apparatus 10 is started up, and need not be performed every time before the main imaging.

  Next, when the subject H is arranged and the main imaging is selected by selecting the imaging mode in step S20 (NO in step S21), the imaging instruction standby state is set (step S30). When a photographing instruction is given using the operation unit 18a (YES in step S30), the same stripe scanning as in step S23 is performed (step S31), and M pieces of image data are stored in the memory 14. Thereafter, similarly, the phase differential image is generated by the phase differential image generation unit 40 (step S32).

  Then, the OK / NG area detection unit 42 detects the NG area and the OK area based on the image data stored in the memory 14 (step S33). Based on the detection result, the first unwrap processing unit 43 unwraps only the OK region of the phase differential image generated in step S32 (step S34). Next, the second unwrap processing unit 44 performs unwrap processing on the offset image stored in the offset image storage unit 41. If there are a plurality of OK regions (YES in step S35), the offset image is displayed. Only the OK region is unwrapped in the same procedure as the first unwrapping processing unit 43 (step S36). On the other hand, when there is only one OK region (NO in step S35), unwrap processing is performed on the entire offset image (step S37).

  Thereafter, the offset correction unit 45 subtracts the offset image that has been unwrapped by the second unwrap processor 44 from the phase differential image that has been unwrapped by the first unwrap processor 43. Performed (step S38).

  The phase contrast image generation unit 46 integrates the phase differential image after the offset correction to generate a phase contrast image (step S39), and the phase differential image and the phase contrast image after the offset correction are stored in the image recording unit 16. After the recording, an image is displayed on the monitor 18b (step S40).

  As described above, in the unwrapping process by the first and second unwrapping processing units 43 and 44, the unwrapping process is performed only for the OK area other than the NG area where the unwrapping error is likely to occur. A phase differential image with less noise can be obtained. Since soft tissue (cartilage portion or the like), which is a region of interest in X-ray phase imaging, exists outside the NG region, it is prevented that imaging of the soft tissue is inhibited by noise due to unwrapping errors.

  The second unwrap processing unit 44 performs unwrap processing in the same procedure (the same start point and the same processing path) as the first unwrap processing unit 43 when there are a plurality of OK regions. As shown in FIGS. 13A and 13B, the noise unevenness included in the phase differential image is substantially the same as the noise unevenness of the offset image, and the phase differential image (difference image) after the offset correction is shown in FIG. As shown in (C), the data level difference between the OK regions hardly occurs or is reduced.

  In addition, when there are a plurality of OK regions as described above, even if the same unwrap processing is performed on each OK region by the first and second unwrap processing units 43 and 44, the phase differential image and the offset image If the pixel value of the start point P0 of each OK area does not match and there is a difference, this difference is reflected in the data in the same OK area of the difference image, and a slight level difference may occur. . For this reason, as shown in FIG. 14, it is preferable to provide a calibration processing unit 47 for calibrating the offset image in the preceding stage of the offset processing unit 45.

  The calibration processing unit 47 calculates a pixel value difference at the start point P0 between the phase differential image after the unwrap processing and the offset image, and calibrates the pixel value in the OK region including the start point P0 of the offset image. Specifically, for each OK region, as shown in FIGS. 15A and 15B, a difference δ of the pixel value at the start point P0 of the offset image with respect to the pixel value at the start point P0 of the phase differential image is set. Then, as shown in FIG. 15C, the difference δ is added to the pixel value in the OK region of the offset image, thereby matching the noise unevenness between the two. Thereafter, offset correction is performed by the offset processing unit 45, thereby eliminating the data level difference due to the pixel value mismatch at the start point P0.

  In addition, when the slope of noise unevenness in the xy plane (the increase / decrease rate of the pixel value in the x direction and the y direction) differs between the phase differential image and the offset image after the unwrap processing, the difference image after the offset correction is displayed. It is conceivable that noise having an inclination remains. For this reason, as shown in FIG. 16, it is preferable to further provide an inclination correction processing unit 48 subsequent to the offset processing unit 45. The inclination correction processing unit 48 performs a two-dimensional correction representing the inclination tendency in the xy plane by fitting each OK region of the difference image after the offset correction in the x direction and the y direction with a linear form or a polynomial. The inclination is removed by obtaining data and subtracting the correction data from the difference image. As a result, a phase differential image from which noise due to a difference in noise unevenness is removed is obtained.

  In the above embodiment, the second unwrap processing unit 44 performs the unwrap processing on the entire offset image when there is one OK region. However, even when there is only one OK region, the OK region Similarly to the case where there are a plurality of unwrapped areas, unwrapping may be performed only on the OK area.

  Moreover, in the said embodiment, whenever it unwraps one linear path | route among several linear path | route R0-R6 in the unwrap process by the 1st and 2nd unwrap process parts 43 and 44, the starting point of the straight line path | route The unwrap processing with the starting point with the next straight path is performed, but before the unwrap processing with the straight paths R0 to R6, the starting point groups P0 to P6 are first unwrapped, and each starting point group P0 after the unwrapping process is performed. Each of the straight paths R0 to R6 may be unwrapped from ~ P6.

  Conversely, after unwrapping each straight line route R0 to R6, each starting point group P0 to P6 is unwrapped, and the data of each straight line route R0 to R6 after the unwrapping process is obtained as each starting point group P0 after the unwrapping process. You may shift according to the data of -P6.

  Moreover, in the said embodiment, in the unwrap process by the 1st and 2nd unwrap process parts 43 and 44, when a penetration line exists in each of the x direction and the y direction, the y direction is given priority in the y direction. Although the starting point group is set so as to be along, the starting point group may be set so as to be along the x direction with priority on the x direction.

  Further, whether to set the starting point group in the y direction or the x direction may be determined based on the shape of the NG region. For example, the direction of the starting point group is determined so that the number of wraparound processes performed on the pixels remaining behind the NG area is reduced. As shown in FIG. 7, when the starting point group is set in the y direction, the wrapping process is required for two lines (lines including the starting points P1 and P5) along the x direction. It is. On the other hand, when the starting point group is set in the x direction, the wraparound process is required for six lines along the y direction, so the number of wraparound processes is six. Therefore, in the case of the shape of the NG area shown in the figure, the y direction in which the number of wraparound processes is reduced is determined as the direction of the starting point group.

  In the above embodiment, in the unwrap processing by the first and second unwrap processing units 43 and 44, the starting point group is set at the end of the OK region in the x direction or the y direction, but the starting point group is not necessarily x. It is not necessary to set the end in the direction or the y direction.

  Moreover, in the said embodiment, in the unwrap process by the 1st and 2nd unwrap process parts 43 and 44, a starting point is set to each column or each row so that an unwrap process may be performed for every column or each row of a phase differential image. However, instead of this, one starting point (starting point) may be set in the OK region, and adjacent pixels from this starting point may be unwrapped in order.

  For example, as shown in FIG. 17A, a start point P0 is set in the OK region, and pixels adjacent in the x direction and the y direction from this start point P0 are unwrapped. Next, as shown in FIG. 17B, the pixels adjacent in the x direction and the y direction are unwrapped from each unwrapped pixel. At this time, if the adjacent pixel is a pixel belonging to the NG area, it is not considered and the unwrapping process is not performed. Further, when the adjacent pixel is an adjacent pixel of another pixel that has been unwrapped, priority is given to one of them. Here, the adjacent pixels in the x direction have priority over the adjacent pixels in the y direction. Thereafter, the unwrapping process may be advanced in the same manner.

  In the above-described embodiment, the OK / NG region detection unit 42 detects an NG region in which an unwrapping error is likely to occur based on the average intensity, amplitude, or visibility of the intensity modulation signal. Is not limited to this, and an area where variation between pixels of the average intensity of the intensity modulation signal (that is, dispersion between pixels of the absorption image) or dispersion between pixels of the phase differential image is larger than a predetermined value is detected as an NG area. May be. In addition, it is preferable that the dispersion | variation between the pixels of this phase differential image is a dispersion | variation in the direction (x direction) orthogonal to the lattice line of the 1st and 2nd grating | lattices 21 and 22. FIG.

  In addition, an absolute value is taken for each pixel of the phase differential image, and an edge portion of the superabsorbent region can be detected by detecting a portion where the absolute value exceeds a predetermined value. The region may be detected as an NG region.

  Alternatively, an area where the average intensity or the maximum intensity of the intensity modulation signal is larger than a predetermined value and the intensity modulation signal is saturated may be detected as an NG area. This saturation of the intensity modulation signal is likely to occur in a pixel region (elementary region) that is directly transmitted to the X-ray image detector 13 through the first and second gratings 21 and 22 without passing through the subject H. When the intensity modulation signal is saturated, the phase shift amount ψ (x) cannot be obtained accurately, and this unaccompanied region is also a region where unwrapping errors are likely to occur. You may combine the above detection criteria suitably.

  Furthermore, when a defect occurs in the X-ray image detector 13, the first grating 21, or the second grating 22, or dust or the like adheres, the pixel value of the predetermined pixel unit 30 is always high, or May be lower. The region where such a pixel defect occurs is a region where an unwrapping error is likely to occur because the average intensity, amplitude, or visibility of the intensity modulation signal indicates an abnormal value. Such a pixel defect region can also be detected as an NG region by appropriately combining the above detection criteria.

  In the above embodiment, since the unwrapping process is not performed in the NG area, the NG area of the phase differential image that is finally recorded in the image recording unit 16 and displayed on the monitor 18b is a noise in which discontinuous points remain. Therefore, as shown in FIG. 18, an NG region image replacement unit 50 may be provided in the image processing unit 15.

  Moreover, in the said embodiment, although the 1st and 2nd unwrap process parts 43 and 44 are provided as a separate process part, respectively, these are integrated as a single process part and the phase obtained by this imaging | photography The process of the first unwrap processing unit 43 described above may be performed on the differential image, and the process of the second unwrap processing unit 44 described above may be performed on the offset image.

  The NG region image replacement unit 50 generates an absorption image, a differential image of the absorption image, or a small-angle scattered image based on the M image data stored in the memory 14 at the time of the main photographing, and corresponds to the NG region of the image. The portion to be replaced is inserted into the NG area of the phase differential image after offset correction. Similarly, the NG area of the phase contrast image may be replaced. The absorption image is generated by imaging the average intensity of the intensity modulation signal. The differential image of the absorption image is generated by differentiating the absorption image in a predetermined direction (for example, the x direction). The small angle scattered image is generated by imaging the amplitude of the intensity modulation signal.

  In the above-described embodiment, the subject H is disposed between the X-ray source 11 and the first grating 21, but the subject H is disposed between the first grating 21 and the second grating 22. You may arrange.

  Moreover, in the said embodiment, although the 2nd grating | lattice 22 is moved to the direction (x direction) orthogonal to a grating | lattice line at the time of fringe scanning, as filed as Japanese Patent Application No. 2011-097090 by this applicant. The second grating 22 may be moved in a direction inclined with respect to the grid line (a direction not orthogonal to the x direction and the y direction in the xy plane). In this case, the scanning position k may be set based on the x-direction component of the movement of the second grating 22. By moving the second grating 22 in a direction inclined with respect to the grating lines, the stroke (movement distance) required for one period of the fringe scanning is increased, and there is an advantage that the movement accuracy is improved.

  Moreover, in the said embodiment, although the 2nd grating | lattice 22 is moved at the time of fringe scanning, it replaces with the 2nd grating | lattice 22, and the 1st grating | lattice 21 is moved to the direction orthogonal to the grid line, or the direction which inclines. May be.

In the first embodiment, 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. 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 .

Moreover, in the said embodiment, the X-rays inject | emitted from the X-ray source 11 are made to inject into the 1st grating | lattice 21, and although the X-ray source 11 is a single focus, immediately after the emission side of the X-ray source 11 The X focus may be dispersed by providing a multi slit (radiation source lattice) described in WO 2006/131235. As a result, it becomes possible to use a high-power X-ray source and the X-ray dose is improved, so that the image quality of the phase differential image is improved. In this case, the pitch p _{0 of the} multi-slit needs to satisfy the following formula (10). In this case, the distance L ₁ represents the distance from the multi slit to the first grating 21.

  Moreover, in the said embodiment, although the 1st grating | lattice 21 is comprised so that incident X-ray may be projected geometrically optically, as known in WO2004 / 058070 etc., the 1st grating | lattice 21 is comprised. 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 light source or the multi-slit may be used so as to enhance the spatial coherence of X-rays.

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. the distance _{L 2} from the first grid 21 to the second grid 22 is required to be 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 (11). Here, m is a positive integer.

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 And expressed by the following formula (12). Here, m is 0 or a positive integer.

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 (13). Here, m is 0 or a positive integer.

The first grating 21 is absorption grating, if X-rays emitted from the X-ray source 11 is a parallel beam shape, Talbot distance Z _m is represented by the following formula (14). Here, m is a positive integer.

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 (15). Here, m is 0 or a positive integer.

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 (16). Here, m is 0 or a positive integer.

  In the above embodiment, the grating portion 12 is provided with the two gratings of the first and second gratings 21 and 22. However, the second grating 22 may be omitted and only the first grating 21 may be used. Is possible.

  For example, by using an X-ray image detector described in Japanese Patent Application Laid-Open No. 2009-133823, the second grating 22 can be omitted and only the first grating 21 can be used. 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 includes a plurality of linear electrode groups. One linear electrode group is obtained by electrically connecting linear electrodes arranged at a constant period, and is arranged so that the phases thereof are different from those of other linear electrode groups. This linear electrode group functions as the second grating 22, and the presence of a plurality of linear electrode groups allows detection of a plurality of G2 images having different phases in one imaging. Therefore, in this configuration, the scanning mechanism 23 can be omitted.

  Further, there is a method of omitting the scanning mechanism 23 and generating a phase differential image based on single image data obtained by the X-ray image detector 13 via the first and second gratings 21 and 22. As this method, there is a pixel division method filed as Japanese Patent Application No. 2010-256241 by the present applicant. In this pixel division method, the first grating 21 and the second grating 22 are slightly rotated around the z direction, and moire fringes having a period in the y direction are generated in the G2 image. A single image data obtained by the X-ray image detector 13 is divided into groups of pixel rows (pixels arranged in the x direction) having different phases from each other with respect to the moire fringes. A phase differential image is generated in the same procedure as the above-described fringe scanning method, assuming that the images are based on a plurality of different G2 images by fringe scanning. In this pixel division method, the intensity modulation signal described above is expressed as a change in intensity of pixel values for one cycle of moire fringes generated in single image data.

  Further, similarly to the pixel division method, the scanning mechanism 23 is omitted, and the phase differential image is obtained based on the single image data obtained by the X-ray image detector 13 via the first and second gratings 21 and 22. As a generation method, a Fourier transform method described in WO2010 / 050484 is known. This Fourier transform method obtains a Fourier spectrum by performing a Fourier transform on the single image data, separates a spectrum corresponding to a carrier frequency (a spectrum carrying phase information) from the Fourier spectrum, and then reverses the spectrum. This is a method of generating a phase differential image by performing Fourier transform. In this Fourier transform method, the intensity modulation signal described above is expressed as a change in intensity of pixel values for one cycle of moire fringes generated in a single image data, as in the case of the pixel division method.

  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 Grating part 20 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 31 Pixel electrode 33 Gate scanning line 35 Signal line

Claims (17)

A radiation detector that detects radiation emitted from the radiation source and transmitted through the subject to generate image data; and
A grating portion disposed between the radiation source and the radiation detector;
Based on the image data, a phase differential image generation unit that generates a phase differential image expressed by a value wrapped in a predetermined range;
In pre-imaging performed without placing the subject, an offset image storage unit that stores the phase differential image generated by the phase differential image generation unit as an offset image;
In main imaging performed with the subject placed, an NG region that is likely to cause an unwrapping error is detected from the phase differential image generated by the phase differential image generation unit, and other regions are detected as OK regions. An OK / NG region detection unit to perform,
A first unwrap processing unit that unwraps only the OK region with respect to the phase differential image obtained by the main photographing;
A second unwrap processing unit that unwraps only the OK region for the offset image;
An offset processing unit that performs offset correction to subtract the offset image that has been unwrapped by the second unwrapping unit from the phase differential image that has been unwrapped by the first unwrapping unit;
A radiation imaging apparatus comprising:   The second unwrap processing unit unwraps only each OK region of the offset image when there are a plurality of the OK regions detected by the OK / NG region detection unit, and the OK region is 1 The radiation imaging apparatus according to claim 1, wherein when there is only one, the entire image of the offset image is unwrapped.   The radiation imaging apparatus according to claim 1, wherein the second unwrap processing unit performs unwrap processing by setting the same start point as the first unwrap processing unit.   A difference in pixel value of the start point is calculated for the phase differential image that has been unwrapped by the first unwrap processor and the offset image that has been unwrapped by the second unwrap processor. The radiation imaging apparatus according to claim 3, further comprising a calibration processing unit configured to calibrate the OK region of the offset image based on the difference.   By fitting the noise remaining in the phase differential image that has been offset-corrected by the offset processing unit with a linear form or a polynomial, correction data representing a tendency of the noise is obtained, and the noise is calculated using the correction data. The radiation imaging apparatus according to claim 4, further comprising a correction processing unit to be removed.   The unwrap processing unit sets a starting point group along a penetrating line that passes only through the OK region and penetrates the phase differential image in one direction, and follows a straight path perpendicular to the penetrating line from each starting point of the starting point group. The unwrap processing, unwrap processing between adjacent starting points of the starting point group, and unwrapping processing for pixels in the OK region remaining behind the NG region when viewed from the starting point group are performed. Item 6. The radiographic apparatus according to any one of Items 1 to 5. The grating unit partially shields the first periodic pattern image by passing the radiation from the radiation source to generate the first periodic pattern image, and displays the second periodic pattern image. A second grid to generate,
The radiation imaging apparatus according to claim 1, wherein the radiation image detector detects the second periodic pattern image to generate image data. The grating unit includes a scanning mechanism that moves the first grating or the second grating at a predetermined scanning pitch and sequentially sets a plurality of scanning positions.
The radiation image detector detects the second periodic pattern image at each scanning position to generate image data;
The radiographic apparatus according to claim 7, wherein the phase differential image generation unit generates a phase differential image based on a plurality of image data generated by the radiological image detector.   The radiation imaging apparatus according to claim 8, wherein the scanning mechanism moves the first grating or the second grating in a direction orthogonal to the grating line.   The radiation imaging apparatus according to claim 8, wherein the scanning mechanism moves the first grating or the second grating in a direction inclined with respect to a grating line.   The radiation imaging apparatus according to claim 7, wherein the phase differential image generation unit generates the phase differential image based on single image data obtained by the radiation detector.   9. The OK / NG area detecting unit detects an NG area based on one or a combination of an average intensity, an amplitude, and a visibility of an intensity modulation signal representing an intensity change of a pixel value. 11. The radiographic apparatus according to any one of 11 to 11.   13. An NG region image replacement unit that generates any one of an absorption image, a differential image of an absorption image, and a small-angle scattered image and replaces the NG region of the phase differential image. The radiation imaging apparatus according to item 1.   The said 1st grating | lattice is an absorption type grating | lattice, The said 1st periodic pattern image is produced | generated by projecting the incident radiation geometrically optically, The any one of Claim 7 to 13 characterized by the above-mentioned. The radiation imaging apparatus described.   The first grating is an absorption grating or a phase grating, and generates the first periodic pattern image by causing a Talbot effect to incident radiation. The radiographic apparatus according to the item.   The radiation imaging apparatus according to claim 1, further comprising a multi-slit that partially shields radiation emitted from the radiation source and disperses the focal point. In a state in which the subject is not arranged, the radiation that has been emitted from the radiation source and passed through the grating portion is detected to generate image data, and based on this image data, a phase derivative expressed by a value wrapped in a predetermined range A pre-shooting step of generating an image and storing it as an offset image;
In the state in which the subject is arranged, image data is generated by detecting radiation emitted from the radiation source and passing through the subject and the lattice unit, and based on this image data, a value wrapped in a predetermined range is used. A main photographing process for generating a expressed phase differential image;
An OK / NG region detecting step of detecting an NG region in which an unwrapping error is likely to occur from the phase differential image generated in the main photographing step, and detecting other regions as OK regions;
A first unwrapping step of unwrapping only the OK region for the phase differential image generated in the main photographing step;
A second unwrap processing step of unwrapping only the OK region for the offset image generated in the pre-shooting step;
An offset processing step for performing offset correction for subtracting the offset image that has been unwrapped in the second unwrapping step from the phase differential image that has been unwrapped in the first unwrapping step; and
A radiation imaging method comprising:

Images