JP2013063166A - Radiographic apparatus and image processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a phase differential image from which striped noises generated by an unwrapping error are removed.SOLUTION: A radiographic apparatus includes: a statistical operation processing unit 41 which applies statistical operation processing to actually-taken image data 52 obtained by stripe scanning; a phase differential image generating unit 40 which generates a differential image K1 of first phase having a pixel value superimposed on a range of a width α, on the basis of the actually-taken image data 52, and which generates a differential image K2 of second phase on the basis of the actually-taken image data 52 subjected to the statistical operation processing; an unwrapping processing unit 42 which applies unwrapping processing to the differential images K1 and K2 of first and second phases; and a corrective processing unit 44 which corrects an error in the unwrapping processing by calculating a difference Δ between the differential images K1 and K2 of first and second phases subjected to unwrapping processing, calculating an integer n, satisfying the inequality, nα-α/2≤Δ<nα+α/2, for each pixel, and subtracting the product of the integer n and the width α from the pixel value of each pixel of the differential image K1 of first phase after the unwrapping processing.

Description

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

  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).

  The unwrap process is performed in order along a predetermined path from a predetermined position in the image as a starting point. 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.

WO2004 / 058070 JP 2011-045655 A

  However, when the subject includes a high-absorber having a high X-ray absorption ability such as a bone part, the high-absorber greatly attenuates the X-ray, so that the intensity and amplitude of the intensity modulation signal are reduced. For this reason, in a region where there is a high absorber, the calculation accuracy of the phase shift amount is lowered, and an unwrapping error is likely to occur. There are two types of unwrapping errors: a case where discontinuity occurs at a location that is not a discontinuous point and the processing is considered as a discontinuous point. There is a case where unwrap processing is not performed because it is not regarded as a continuous point.

  For example, if there is a bone region on the path where unwrap processing is performed, once an unwrap error occurs on the bone region, an error value (a value corresponding to the range of the above function) is displayed on the path after the location where the unwrap error has occurred. Is accumulated. As a result, streak noise along the path direction of the unwrap process is generated in the phase differential image after the unwrap process. When this noise overlaps with a part of the cartilage part, which is a soft tissue, there is a problem in that imaging of the soft tissue of the heart, which is a region of interest in X-ray phase imaging, is hindered.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a radiographic imaging apparatus capable of obtaining a phase differential image from which streak noise caused by an unwrap error is removed by correcting the unwrap error. And It is another object of the present invention to provide an image processing method for correcting an unwrap error.

  The 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 a grating disposed between the radiation source and the radiation detector. A first phase differential image generation unit that generates a first phase differential image in which pixel values are convoluted in a predetermined range having a width α based on image data obtained by the radiation detector, and A statistical calculation processing unit that performs statistical calculation processing on the image data obtained by a radiation detector, and a predetermined range having a width α based on the image data that has been subjected to the statistical calculation processing by the statistical calculation processing unit A second phase differential image generation unit that generates a second phase differential image in which pixel values are convolved with each other, an unwrap processing unit that performs an unwrap process on the first phase differential image and the second phase differential image, and The difference Δ is calculated for each pixel by subtracting the second phase differential image after the unwrap processing from the first phase differential image after the unwrap processing, and an integer satisfying nα−α / 2 ≦ Δ <nα + α / 2 a correction processing unit that corrects an error of the unwrap processing by calculating n and subtracting a product of the integer n and the width α from a pixel value of each pixel of the first phase differential image after the unwrap processing; It is characterized by providing.

  The first phase differential image generation unit generates the first phase differential image, generates a phase differential image based on image data obtained in pre-imaging performed without placing the subject, and performs the unwrapping. The processing unit performs unwrap processing on the phase differential image generated by the pre-photographing together with the first phase differential image and the second phase differential image, and performs the unwrap processing on the phase differential image generated by the pre-photographing. An offset image storage unit that stores the applied image as an offset image; and the first phase differential image obtained by subtracting the offset image from the first phase differential image in which the error of the unwrap processing is corrected by the correction processing unit. And an offset processing unit that removes an offset component that is noise.

  The statistical calculation process performed by the statistical calculation process is preferably a noise reduction process for reducing noise in the image data.

  The noise reduction process is preferably a smoothing process for smoothing the image data.

  The smoothing process is preferably a moving average process that replaces the pixel value of each pixel of the image data with an average value of the pixel value of the pixel and the pixel values of surrounding pixels.

  The noise reduction process is a process in which a plurality of sets including a predetermined number of pixels of the image data are used, and an average value of pixel values of pixels belonging to each set is set as a new pixel value of all pixels of the set. Preferably there is.

  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.

  The scanning mechanism preferably moves the first grating or the second grating in a direction perpendicular to the grating lines.

  The scanning mechanism preferably moves the first grating or the second grating 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.

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

  It is preferable that 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.

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

  According to the image processing method of the present invention, a pixel value is set in a predetermined value range having a width α based on image data obtained by imaging a subject by arranging a grid portion between a radiation source and a radiation detector. Based on the first phase differential image generation step of generating a first phase differential image convolved with, a statistical calculation processing step of performing statistical calculation processing on the image data, and the image data subjected to the statistical calculation processing A second phase differential image generating step for generating a second phase differential image in which pixel values are convolved in a predetermined range having a width α, and an unwrapping process is performed on the first phase differential image and the second phase differential image. An unwrapping step, a difference calculating step for calculating a difference Δ between the first phase differential image and the second phase differential image subjected to the unwrapping process, and the difference Δ is nα−α / 2 ≦ Δ <. By calculating an integer n satisfying α + α / 2 for each pixel, an unwrap error cumulative number calculation step for calculating the number of unwrap errors accumulated in each pixel of the first phase differential image, and the unwrap processing after the unwrap processing, And a correction processing step of correcting an error in the unwrap processing by subtracting a product of the integer n and the width α from a pixel value of each pixel of the first phase differential image.

  According to the present invention, a phase differential image from which streak noise caused by an unwrap error is removed can be obtained.

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 explanatory drawing which shows the aspect of a moving average process. It is a figure explaining the starting method of an unwrap process, and the setting method of a path | route. It is explanatory drawing which shows the aspect of an unwrap process. It is explanatory drawing which shows the aspect which an unwrap error produces by an unwrap process. It is a flowchart which shows the correction process of an unwrapping error. 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 a figure which shows the aspect of a 1st phase differential image. It is a figure which shows the aspect of a 2nd phase differential image. It is explanatory drawing which shows the aspect by which an unwrap error is correct | amended. It is a figure which shows the phase differential image by which the unwrapping error was correct | amended. It is explanatory drawing which shows the other aspect of a moving average process.

  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 in which the phase shift amount ψ (x) calculated for each pixel unit 30 is a pixel value 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. Hereinafter, it is assumed that the pixel values of the phase differential image are wrapped in a predetermined value range having a width α (for example, a range from 0 to α).

  As shown in FIG. 5, the image processing unit 15 includes a phase differential image generation unit 40, a statistical calculation processing unit 41, an unwrap processing unit 42, an offset image storage unit 43, a correction processing unit 44, an offset processing unit 45, a phase contrast image. A generation unit 46 and the like are provided. The phase differential image generation unit 40 corresponds to a first phase differential image generation unit and a second phase differential image generation unit in claims.

  The phase differential image generation unit 40 uses the M image data (pre-photographed image data) 51 obtained by the X-ray image detector 13 in the pre-photographing fringe scanning, and uses the above equation (8) or the above equation (9). A phase differential image is generated by performing an operation based on the above.

  Similarly, the phase differential image generation unit 40 generates a phase differential image based on the M pieces of image data (main captured image data) 52 obtained by the X-ray image detector 13 by the main scanning fringe scanning. However, at the time of actual photographing, the phase differential image generation unit 40 generates two types of phase differential images, that is, a first phase differential image and a second phase differential image. The first phase differential image is a phase differential image that is directly generated from the actual captured image data 52, and the second phase differential image is obtained by using the actual captured image data 52 that has been subjected to statistical calculation processing by the statistical calculation processing unit 41. It is a phase differential image to generate.

  The phase differential image generation unit 40 generates the first phase differential image and the second phase differential image as described above. However, instead of the phase differential image generation unit 40, the phase differential image generation unit 40 receives input of the captured image data 52. Two types, a first phase differential image generation unit that generates a first phase differential image, and a second phase differential image generation unit that generates a second phase differential image in response to main shooting image data 52 subjected to statistical calculation processing. The phase differential image generation unit may be divided. In this case, the phase differential image at the time of pre-imaging may be generated by the first phase differential image generation unit.

  The statistical calculation processing unit 41 performs statistical calculation processing on the main captured image data 52 input at the time of main imaging, and inputs the statistical calculation processing to the phase differential image generation unit 40. The statistical calculation process is performed on each of the M actual captured image data 52. The statistical calculation process performed by the statistical calculation processing unit 41 on the actual captured image data 52 is a noise removal process that reduces noise in the actual captured image data 52, and is, for example, a smoothing process. More specifically, the statistical calculation processing unit 41 performs a so-called moving average process on the captured image data 52 as the above-described smoothing process (statistical calculation process).

  As shown in FIG. 6, for example, the moving average process uses a pixel Q5 as a target pixel, and sets the pixel value to nine pixels of the target pixel Q5 and adjacent pixels Q1 to Q4 and Q6 to Q9 adjacent to the target pixel Q5. Replace with the average pixel value. The same applies to the other pixels, and each pixel is set as a target pixel, and an average value of nine pixel values of the target pixel and surrounding neighboring pixels is set as the pixel value of the target pixel. Here, for the sake of simplicity, an example has been described in which the average value of pixel values is calculated for 3 × 3 pixels centered on the pixel of interest, but the number of pixels for calculating the average value is arbitrary. However, if the number of pixels for which the average value is calculated in the moving average process is large, the resolution of the second phase differential image generated from the actual captured image data 52 that has been subjected to the moving average process is unnecessarily lowered. On the other hand, if the number of pixels for which the average value is calculated is small, there is an adverse effect that an unwrapping error occurs in the unwrapping process to be performed later. For this reason, when the statistical calculation processing unit 41 smoothes the captured image 52 by moving average processing, for example, it is preferable to obtain an average value of pixel values for 9 × 9 pixels centered on the target pixel. As will be described later, when the second phase differential image is unwrapped, an unwrapping error does not occur, and the decrease in resolution of the second phase differential image due to the smoothing of the actual captured image data 52 is minimized. This is the number of pixels that can be suppressed to the limit. When the number of pixels of the X-ray detector 13 is sufficiently large, an average value of a wider range of pixels such as a 16 × 16 pixel including the target pixel in the vicinity of the center or a range beyond that may be obtained. Further, the area for calculating the average value may not be a square, but may be a rectangle such as 9 × 10 pixels.

  In addition, although the statistical calculation process part 41 gave the example which performs a moving average process with respect to this picked-up image data 52, the statistical calculation process which the statistical calculation process part 41 performs with respect to this picked-up image data 52 is not restricted to a moving average process, Any process can be used as long as the captured image data 52 can be smoothed and noise can be reduced. For example, the statistical calculation processing unit 41 may perform median filter processing, mode value filtering processing, or the like on the actual captured image data 52. The median filter process is a process of replacing the pixel value of the pixel of interest (pixel Q5 in FIG. 6) with the median value of the pixel values in a predetermined range including the pixel (pixels Q1 to Q9 in FIG. 6). The mode value filter process is a process of replacing the pixel value of the target pixel with the mode value of the pixel values of pixels in a predetermined range including the target pixel value.

  The unwrap processing unit 42 (see FIG. 5) performs unwrap processing on the phase differential image input from the phase differential image generation unit 40. At the time of pre-photographing, the phase differential image generated based on the pre-photographed image data 51 is input from the phase differential image generation unit 40 to the unwrap processing unit 42. When the unwrap processing unit 42 performs an unwrap process on the phase differential image generated from the pre-captured image data 51, the unwrap processing unit 42 stores this in the offset image storage unit 43 as an offset image K0. Note that, when a new pre-shooting is performed and a new offset image K0 is input, the offset image storage unit 43 deletes the already stored offset image and then stores the newly input offset image K0. Remember.

  At the time of actual photographing, two types of phase differential images, that is, a first phase differential image and a second phase differential image are input from the phase differential image generation unit 40 to the unwrap processing unit 42. The unwrap processing unit 42 performs unwrap processing on the first phase differential image and the second phase differential image, respectively. Then, both the first phase differential image K1 subjected to the unwrap process and the second phase differential image K2 subjected to the unwrap process are input to the correction processing unit 44.

As shown in FIG. 7, the unwrap processing unit 42 sets the starting point SP ₁ for the pixel located at the end of each row or each column of the phase differential image 61, and performs the unwrapping process from the starting point SP ₁ along the path WR _1. After performing, unwrap processing is performed between the starting point SP ₁ and the starting point SP ₂ adjacent thereto, and the unwrap processing is performed from the starting point SP ₂ along the route WR _{2. The} starting point SP _n and the route WR _n are changed. Repeat in order. The phase differential image 61 shown here is one of a phase differential image generated during pre-imaging, a first phase differential image generated during main imaging, and a second phase differential image.

In the unwrap processing, as described above, a point that greatly changes (so-called phase jump) due to the pixel value of the phase differential image being wrapped in a predetermined value range is detected as a discontinuous point DP, and after the detected discontinuous point DP. In this process, the discontinuous point DP is eliminated by adding or subtracting the width α of the range to the pixel value on the path WR _n of FIG. The detection of the discontinuous point DP is performed by obtaining a location where the change amount of the pixel value is a predetermined amount (for example, α / 2) or more. As shown in FIG. 8, when the phase differential image is subjected to unwrapping processing, when only the discontinuous point DP due to the phase jump is detected on the path WR _n , the change in the pixel value is normally continued. .

On the other hand, as shown in FIG. 9, when there is a discontinuous point Err due to noise or the like on the path WR _{n as} well as a discontinuous point DPr due to noise or the like, the unwrap processing unit 42 causes the discontinuous point DP due to phase jump. And the discontinuous point Err due to noise or the like cannot be identified, and the range width α may be added to or subtracted from the discontinuous point Err. In this case, a gap having a width α occurs at the discontinuous point Err in the post-wrapping phase differential image. This gap is an unwrapping error.

  When the discontinuous point Err due to noise or the like is composed of only one point of data, the unwrap processing is correctly performed as a result. This is because the difference between the discontinuous point Err and the previous data point exceeds a predetermined amount for detecting the discontinuous point, and the difference between the discontinuous point Err and the next data point also exceeds the predetermined amount. This is because an unwrap process for subtracting (adding) α and an unwrap process for adding (subtracting) α are performed, and the unwrap process at the discontinuous point Err is canceled. For this reason, the discontinuous point Err shown in FIG. 9 includes a plurality of data points. For example, the discontinuous point Err consists of two data points Err1 and Err2, the difference between the data point Err1 and the previous data point exceeds a predetermined amount, the difference between the data point Err1 and the data point Err2, and the data point Err2. And the next data point does not exceed a predetermined amount. In this case, the difference between the data point Err1 and the previous data point is detected and unwrapping is performed. The difference between the data point Err1 and the data point Err2 and the difference between the data point Err2 and the next data point are unwrapped. As a result, the unwrap process performed by detecting the difference between the data point Err1 and the immediately preceding data point remains as an unwrap error.

  Since the pre-imaging is an imaging performed without the subject H as described above, the pre-photographed image data 51 and the phase differential image generated from the pre-photographed image data 51 include discontinuous points DP due to phase jumps. The discontinuous point Err other than is basically not generated. For this reason, an unwrapping error does not occur even if an unwrapping process is performed on the phase differential image generated at the time of pre-shooting.

  Further, the second phase differential image K2 obtained at the time of the main imaging includes the subject H including a portion where noise is likely to appear in the bone portion or the like, but is subjected to moving average processing by the statistical calculation processing unit 42 and smoothed. Since it is generated based on the actual captured image data 51, no unwrapping error will occur even if the second phase differential image K2 is unwrapped. On the other hand, since the first phase differential image K1 obtained at the time of actual photographing is generated from the non-smoothed main photographed image data 51, an unwrapping error may occur when the first phase differential image K1 is subjected to unwrapping. .

  The correction processing unit 44 (see FIG. 5) corrects the unwrapping error that has occurred in the first phase differential image K1 based on the second phase differential image K2, and will describe the first phase differential image K1a in which the unwrapping error is corrected later. Input to the offset processing unit 45. The correction processing unit 44 performs correction of the unwrapping error in the first phase differential image K1 as described below.

As illustrated in FIG. 10, the correction processing unit 44 first sets the pixel coordinates of each phase differential image to (x, y) and the pixel value of each pixel of the first phase differential image K1 to ψ ₁ (x, y). The pixel value of each pixel of the second phase differential image K2 is ψ ₂ (x, y), and the pixel values of the first phase differential image K1 and the second phase differential image K2 are expressed as shown in the following equation (10). The difference Δ (x, y) is calculated (step S01). As shown in Expression (10), the difference Δ (x, y) calculated by the correction processing unit 44 is a difference based on the second phase differential image K2.

  Thereafter, for the calculated difference Δ (x, y), an integer n satisfying the following expression (11) is calculated for each pixel (step S02).

When no unwrapping error has occurred, there is almost no difference between the first phase differential image K1 (x, y) and the second phase differential image K2 (x, y), and the integer n satisfying equation (11) is 0. . On the other hand, when an unwrapping error occurs, n becomes an integer other than 0. For example, when an unwrap process is performed along the path WR _n for pixels where the integer n satisfying equation (11) is not 0, a gap due to an unwrap error for n times is accumulated to the pixel. Yes. Eventually, gaps due to unwrapping errors for n times accumulate as follows: when unwrapping errors occur n times in the same direction (positive or negative direction) and when there are a total of n or more unwrapping errors in the positive and negative directions In some cases, the gaps are partially offset and a gap corresponding to n unwrap errors is accumulated.

  In equation (11), the lower limit of the difference Δ includes an equal sign (≦) and the upper limit does not include an equal sign (<), but the position of the equal sign is arbitrary as long as the integer n can be uniquely determined. is there. That is, an equal sign may be included in the upper limit and no equal sign may be included in the lower limit (nα−α / 2 <Δ (x, y) ≦ nα + α / 2 (11 ′)).

The correction processing unit 44 uses the integer n satisfying the above-described equation (11), and as shown in the following equation (12), the pixel value of each pixel ψ ₁ (x, y) of the original first phase differential image K1. Are replaced with new pixel values ψ ₁ ′ (x, y), respectively (step S03).

The new pixel value ψ ₁ ′ (x, y) is subtracted from the original pixel value ψ ₁ (x, y) by the width α by the number of gaps due to unwrapping errors accumulated in the path to this pixel (n In the case of a negative value, the pixel value is substantially added). Therefore, by replacing the pixel value of each pixel in the entire first phase differential image K1 from ψ ₁ (x, y) to ψ ₁ ′ (x, y), the change in pixel value is substantially continuous.

Note that, as shown in Expression (12), in a pixel where the integer n satisfying Expression (11) is 0, the original pixel value ψ ₁ (x, y) and the new pixel value ψ ₁ ′ (x, y) are equal. The pixel value is not replaced. A pixel whose integer n is 0 is a pixel in which no unwrapping error has occurred until this pixel, or a pixel in which the number of additions / subtractions of the range α is equal and the gap due to the unwrapping error is offset. unnecessary.

  The offset processing unit 45 (see FIG. 5) performs offset correction on the first differential phase image K1a in which the unwrapping error is corrected by the correction processing unit 44 as described above. The offset correction is a correction process for subtracting noise superimposed as a background on the first phase differential image K1a by subtracting the offset image K0 from the first phase differential image K1a in which the unwrapping error is corrected. Here, the noise component removed as an offset is a noise component superimposed as a background, for example, due to distortion or slight positional deviation (including rotation or inclination) of the first grating 21 or the second grating 22. It is.

  The phase contrast image generation unit 46 (see FIG. 5) integrates the first phase differential image K1b from which the offset has been removed from the first phase differential image K1a along the x direction, thereby expressing the phase contrast representing the phase shift distribution. Generate an image. The first phase differential image K1b and the phase contrast image after the offset correction are recorded in the image recording unit 16.

  Hereinafter, the operation of the X-ray imaging apparatus 10 will be described. When imaging the subject H using the X-ray imaging apparatus 10, pre-imaging is performed before imaging the subject H as shown in FIG. When the pre-shooting mode is selected as the shooting mode using the operation unit 18a (step S10), the camera enters a shooting instruction input standby state (step S11). When an imaging instruction is input using the operation unit 18a, the second grating 22 is translated by a predetermined scanning pitch by the scanning mechanism 23, and X-ray irradiation by the X-ray source 11 and X at each scanning position k are performed. The G2 image is detected by the line image detector 13 (step S12). As a result of the fringe scanning, M pieces of pre-captured image data 51 are generated and stored in the memory 14.

  The pre-captured image data 51 is read out to the image processing unit 15. In the image processing unit 15, a phase differential image is generated from the pre-captured image data 51 by the phase differential image generation unit 40 (step S13). This phase differential image is stored in the offset image storage unit 41 as an offset image after being unwrapped (step S14). 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, as shown in FIG. 12, the subject H is arranged and the main imaging is performed. When performing the main shooting, the main shooting mode is selected as the shooting mode using the operation unit 18a (step S20). When the main shooting mode is selected, a shooting instruction standby state is set (step S21). When a shooting instruction is given using the operation unit 18a, stripe scanning is performed (step S22), and M main captured image data 52 are stored in the memory 14.

  Thereafter, the actual captured image data 52 is read by the image processing unit 15. In the image processing unit 15, the phase differential image generation unit 40 generates a first phase differential image K1 from the actual captured image data 52 (step S23), and the unwrap processing unit 42 performs unwrap processing (step S24).

  On the other hand, at the same time as the first differential phase image K1 is generated as described above, the actual captured image data 52 is input to the statistical calculation processing unit 41. The above-mentioned moving average processing is performed on each of the M actual captured image data 52 input to the statistical calculation processing unit 41 by the statistical calculation processing unit 41 (step S25). Then, the actual captured image data 52 that has been subjected to the moving average process is input to the phase differential image generation unit 40, and a second phase differential image K2 is generated from the actual captured image data 52 that has been subjected to the moving average process. (Step S26) Unwrap processing is performed (Step S27).

  Here, since the first phase differential image K1 and the second phase differential image K2 are used for the correction processing to be performed later, the first phase differential image K1 and the second phase differential image K2 are generated and unwrapped at the same time. Although an example has been described, the generation and unwrapping of the first phase differential image K1 and the second phase differential image K2 do not have to be performed strictly at the same time. After performing the generation and unwrapping processing of the first phase differential image K1, the moving average processing to the actual captured image data 52 by the statistical calculation processing unit 42 and the generation and unwrapping processing of the second phase differential image K2 may be performed. On the contrary, after performing the moving average process to the actual captured image data 52 and the generation and unwrapping process of the second phase differential image K2 by the statistical calculation processing unit 42, the generation and unwrapping process of the first phase differential image K1 are performed. Also good. Further, after generating the first phase differential image K1 and the second phase differential image K2, respectively, the first phase differential image K1 and the second phase differential image K2 may be unwrapped.

  As described above, when the first phase differential image K1 and the second phase differential image K2 are generated and the unwrapping process is performed, the correction processing unit 44 performs the first phase differential image based on the second phase differential image K2. A correction process for correcting the unwrapping error of K1 is performed (step S28).

  The first phase differential image K1a in which the unwrapping error is corrected is further offset-corrected by the offset processing unit 44 to remove the offset (step S29). Further, the phase contrast image generation unit 46 integrates the first phase differential image K1b from which the offset is removed, thereby generating a phase contrast image representing the phase shift distribution (step S30), and the first phase differential image K1b. And a phase contrast image are recorded in the image recording unit 16. Thereafter, the first phase differential image K1b and the phase contrast image are displayed on the monitor 18b (step S31).

  As described above, when the X-ray imaging apparatus 10 generates the phase differential image in the main imaging, the first phase differential image K1 directly generated from the main imaging image data 52 based on the main imaging image data 51 and Two types of phase differential images of the second phase differential image K2 generated from the actual captured image data 52 subjected to the moving average process are generated, and the first and second phase differential images K1 and K2 are used to generate the first phase differential image K2. An unwrapping error that occurs when the unwrapping process is performed on the one-phase differential image K1 is corrected. Thereby, the X-ray imaging apparatus 10 can generate and display the first phase differential image K1b and the phase contrast image without an unwrapping error.

The X-ray imaging apparatus 10 corrects the unwrapping error of the first phase differential image K1, and this unwrapping error correction processing is based on the pixel value ψ ₂ (x, y) of the second phase differential image K2. Thus, the location where the unwrap error has occurred and the substantial cumulative number of gaps due to the unwrap error are detected, and only the gap caused by the unwrap error is corrected. Compared with correction processing (for example, correction processing performed by interpolation, fitting, etc.) that corrects the pixel value ψ ₁ (x, y) in which the unwrap error has occurred to an approximate value and simply makes the unwrap error inconspicuous, this X-ray imaging The unwrapping error correction process performed by the apparatus 10 has an advantage that the unwrapping error can be accurately corrected without losing any information or resolution of the image of the subject H.

  Furthermore, as a comparative example, for example, from the phase differential image before unwrapping, a region where unwrapping can be normally performed and a region where an unwrapping error can occur are extracted in advance, and unwrapping is performed only on regions where unwrapping can be performed normally. It is conceivable that an unwrapping error will not occur by selecting a starting point or a route for unwrapping processing. However, if the unwrapping error of the first phase differential image K1 is corrected on the basis of the second phase differential image K2 as in the above-described embodiment, the extraction or starting point of the region where the unwrap processing can be normally performed as in the comparative example, Complicated processing such as route setting is not required, and unwrapping errors can be corrected with simple processing.

  Hereinafter, a mode in which the unwrapping error is corrected by the correction processing unit 44 will be described more specifically.

For example, as shown in FIG. 13, the subject H has a bone 66 that is low in contrast and easily generates noise due to its high X-ray absorption ability, and a soft tissue 67 that is a main region of interest for imaging by the X-ray imaging apparatus 10. (Cartilage, synovial fluid, etc.) Since the bone portion 66 has a low contrast and an unwrapping error is likely to occur, in the phase differential image K1 directly generated from the actual captured image data 52, streak noise due to the unwrapping error along the path WR _n passing through the bone portion 66. 67 may occur. As in a region 68 indicated by a broken line, at a place where the noise 67 is superimposed on the soft tissue 67, the observation of the soft tissue 67 that is the region of interest is hindered.

  On the other hand, as shown in FIG. 14, since the second phase differential image K2 is generated and unwrapped from the main image data 52 that has been subjected to moving average processing and smoothed, the first phase differential image is obtained. An unwrapping error does not occur even if the unwrapping process is performed as in K1. In addition, the second phase differential image K2 has a slightly blurred outline of the soft tissue 67 as compared to the first phase differential image K1, but the image of the subject H that is substantially the same as the first phase differential image K1 is displayed. It is. For this reason, the corresponding pixels of the first phase differential image K1 and the second phase differential image K2 are data of substantially the same portion of the subject H.

As shown in FIG. 15, a pixel value ψ ₁ (x, y) on a certain path WR _{n in} which an unwrapping error has occurred in the first phase differential image K1 is converted into a corresponding pixel value ψ ₂ (x , Y), in both the first phase differential image K1 and the second phase differential image K2, the discontinuous points DP1 and DP2 due to the phase jump are connected by the unwrap process and are made continuous.

At the discontinuous point Err due to noise or the like, in the case of the first phase differential image K1, an unwrap error in which the range width α is added by the unwrap process occurs. Therefore, the range E1 from the starting point SP _n of unwrapping to discontinuity Err due to noise or the like, the pixel values ψ _{1 (x,} y) but are smoothly connected by the unwrapping, the width α in the discontinuity Err This gap is also reflected in the region E2 after the discontinuous point Err in the form of adding the gap due to this unwrapping error. On the other hand, since the second phase differential image K2 is generated after smoothing the actual captured image data 52, there is no discontinuity point Err due to noise or the like in the original actual captured image data 52, and after the unwrap processing. no gap is on the route WR _n.

Thus, the first differential phase image K1 difference delta (x, y) of the second differential phase image K2 calculating the until discontinuity Err due to noise or the like from the starting point SP _n of unwrapping the first differential phase image K1 In the area E1, the difference Δ (x, y) is almost 0 (Δ (x, y) ≈0). On the other hand, in the region E2 after the discontinuous point Err, the difference Δ (x, y) is approximately the width α (Δ (x, y) ≈α). Therefore, when the integer n satisfying the above-described equation (11) is calculated, n = 0 in the region E1 and n = 1 in the region E2.

In accordance with the integer n satisfying the equation (11) calculated in this way, the correction processing unit 44 subtracts the total amount nα of gaps caused by the unwrap error, as shown in the equation (12), and the pixel value ψ ₁ ′ (x , Y) is a new pixel value of the first phase differential image K1. As a result, as shown in FIG. 15, the new pixel value ψ ₁ ′ (x, y) substantially coincides with the second phase differential image ψ ₂ (x, y), is smoothly connected, and an unwrapping error occurs. It will be resolved.

  As shown in FIG. 16, the first phase differential image K1a in which the unwrapping error has been corrected in this way has no streak noise and a clear outline of the soft tissue 67 that is the region of interest.

  Since the unwrap process is a process of adding / subtracting the range width α, the unwrap error is also a gap between pixel values in units of the width α. Therefore, the difference Δ (x, y) between the first differential phase image K1 and the second differential phase image K2 is also basically a value with the width α as a unit. Therefore, if n satisfying the difference Δ (x, y) ≈nα is calculated, the total amount of gaps due to unwrapping errors accumulated in this pixel can be detected. However, since the second phase differential image K2 is generated from the actual captured image data 52 smoothed by the moving average process, it is strictly different from the first phase differential image K1 instead of causing no unwrapping error. It becomes a pixel value. For this reason, in the above equation (11), an integer n that simply satisfies the difference Δ (x, y) = nα in consideration of the difference due to the generation process of the first phase differential image K1 and the second phase differential image K2. Is not calculated, but a range having a range width of ± α / 2 (the total width is α) centering on the gap amount nα caused by the unwrapping error is used.

  As can be seen from this, when the difference due to the difference in the generation process of the first phase differential image K1 and the second phase differential image K2 can be reduced by adjusting the number of pixels to be averaged during the moving average process, the expression (11) It is also conceivable to make the range width smaller than ± α / 2, such as ± α / 4. However, the range width specified by Expression (11) cannot be larger than ± α / 2. If the range width specified by Expression (11) is larger than ± α / 2, overlap occurs in each range centered on the gap amount nα caused by the unwrap error, and the integer n cannot be calculated uniquely. is there.

  Further, when the range width of the expression (11) is made smaller than ± α / 2, since the respective ranges centered on the gap amount nα caused by the unwrap error are not continuous, the integer n may not be calculated. For example, when the range width of Expression (11) is ± α / 4, if the difference Δ (x, y) is −α / 4 ≦ Δ (x, y) <+ α / 4, the integer n is 0 and α + α If n / 4 ≦ Δ (x, y) <α + α / 4, the integer n is 1. However, if α / 4 ≦ Δ (x, y) <α + α / 4, the integer n cannot be calculated. For this reason, it is preferable that the width of each range centered on the gap amount nα is ± α / 2 and the range specified for each gap amount nα is continuous as shown in the equation (11).

  In the above-described embodiment, as an example of the statistical calculation process performed by the statistical calculation processing unit 41, the moving average process in which the pixel value of each pixel is replaced with the average value with the surrounding pixel values is taken as an example. The moving average process performed by the processing unit 41 may be a moving average process corresponding to a so-called binning process in an aspect described below.

  As shown in FIG. 17, for example, the pixels of the actual captured image data 52 are divided into 3 × 3 areas. For example, in the 3 × 3 area 81a, the pixel values of all the pixels Q1 to Q9 are replaced with the average value of the pixel values in the area 81a ((Q1 + Q2 +... + Q8 + Q9) / 9). Similarly, in the region 81b, the pixel values of all the pixels Q11 to Q19 are replaced with the average value ((Q11 + Q12 +... + Q18 + Q19) / 9) of the pixel values in the region 81b. As described above, the moving average process in which the pixel values in each of the regions 81a and 81b and the like are all replaced with the average value of the pixels in the same region makes each of the regions 81a and 81b one large pixel. Equivalent to.

  When the moving average processing for increasing the pixels is performed in this way, the light intensity of each large pixel (regions 81a, 81b, etc.) increases compared to each pixel of the original actual captured image data 52, and S / N ratio is improved. For this reason, the contrast of the intensity modulation signal is improved, the phase shift amount ψ (x) can be accurately calculated, and noise that causes an unwrapping error in the second phase differential image K2 does not occur.

  In addition, although the example which forms a large pixel by 3x3 pixel was demonstrated here, the size of a large pixel is arbitrary. As described above, in order to prevent an unwrapping error from occurring in the second phase differential image K2 and to minimize a decrease in resolution of the second phase differential image K2, about 9 × 9 pixels are set as one large pixel. It is preferable. Here, an example has been described in which the pixel value of the large pixel is the average value of the original pixels, but the total value of each pixel may be simply set as the pixel value of the large pixel.

  In the above-described embodiment, the example in which the phase differential image and the phase contrast image are generated has been described. However, the absorption image, the differential image of the absorption image, or the small-angle scattering image is obtained from the pre-captured image data 51 and the main captured image data 52. It may be generated. 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.

  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, etc. of the intensity modulation signal show abnormal values. Thus, the present invention is also effective when the unwrapping error is caused by a pixel defect, and the unwrapping error can be corrected.

  The unwrapping error due to the pixel defect described above also occurs during pre-photographing. For this reason, in the above-described embodiment, the example in which the unwrapping error correction process is performed only during the main photographing has been described. Is preferred. The mode of correcting the unwrapping error at the time of pre-shooting is the same as in the case of the main shooting described in the above-described embodiment. A second phase differential image may be generated from the pre-captured image data 51 that has been subjected to the moving average processing, and the correction processing unit 44 may perform unwrapping error correction processing using these.

  In the above 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). This moving direction may be any direction as long as it is within the xy plane and other than the y direction. 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, a high-power X-ray source can be used, 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 (13). 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 (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 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 (15). 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 (16). 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 (17). 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 (18). 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 equation (19). 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 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 (15)

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;
A first phase differential image generation unit that generates a first phase differential image in which pixel values are convoluted into a predetermined value range having a width α based on image data obtained by the radiation detector;
A statistical calculation processing unit that performs statistical calculation processing on the image data obtained by the radiation detector;
Second phase differential image generation for generating a second phase differential image in which pixel values are convoluted into a predetermined value range having a width α based on the image data subjected to the statistical calculation processing by the statistical calculation processing unit And
An unwrap processing unit that performs unwrap processing on the first phase differential image and the second phase differential image;
The difference Δ is calculated for each pixel by subtracting the second phase differential image after the unwrap processing from the first phase differential image after the unwrap processing, and satisfies nα−α / 2 ≦ Δ <nα + α / 2. A correction processing unit that calculates an integer n and corrects an error in the unwrap process by subtracting a product of the integer n and the width α from a pixel value of each pixel of the first phase differential image after the unwrap process. When,
A radiation imaging apparatus comprising: The first phase differential image generation unit generates the first phase differential image and generates a phase differential image based on image data obtained in pre-imaging performed in a state where the subject is not disposed,
The unwrap processing unit performs unwrap processing on the phase differential image generated by the pre-photographing together with the first phase differential image and the second phase differential image,
An offset image storage unit that stores an image obtained by performing the unwrap processing on the phase differential image generated by the pre-photographing, as an offset image;
An offset processing unit that subtracts the offset image from the first phase differential image in which the error of the unwrap processing is corrected by the correction processing unit;
The radiation imaging apparatus according to claim 1, further comprising:   The radiation imaging apparatus according to claim 1, wherein the statistical calculation process performed by the statistical calculation process is a noise reduction process for reducing noise of the image data.   The radiation imaging apparatus according to claim 3, wherein the noise reduction process is a smoothing process for smoothing the image data.   The smoothing process is a moving average process in which the pixel value of each pixel of the image data is replaced with an average value of the pixel value of the pixel and the pixel values of surrounding pixels. Radiography equipment.   The noise reduction process is a process in which a plurality of sets including a predetermined number of pixels of the image data are used, and an average value of pixel values of pixels belonging to each set is set as a new pixel value of all pixels of the set. The radiation imaging apparatus according to claim 3, wherein the radiation imaging apparatus is provided. 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 and generates 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 a grating line.   9. 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 the grating line.   The radiographic 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.   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 Claims 7-11 characterized by the above-mentioned. The radiation imaging apparatus described in 1.   The said 1st grating | lattice is an absorption-type grating | lattice or a phase-type grating | lattice, The Talbot effect is produced in the incident radiation, The said 1st periodic pattern image is produced | generated, The one of Claims 7-11 characterized by the above-mentioned. The radiation imaging apparatus according to item 1.   The radiation imaging 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. A first phase in which pixel values are convoluted into a predetermined value range having a width α based on image data obtained by imaging a subject with a grating portion disposed between a radiation source and a radiation detector. A first phase differential image generation step for generating a differential image;
A statistical calculation processing step for performing statistical calculation processing on the image data;
A second phase differential image generation step of generating a second phase differential image in which a pixel value is convolved with a predetermined value range having a width α based on the image data subjected to the statistical calculation processing;
An unwrap processing step of applying unwrap processing to the first phase differential image and the second phase differential image;
A difference calculating step of calculating a difference Δ between the first phase differential image and the second phase differential image subjected to the unwrapping process;
An unwrap error for calculating the number of unwrap errors accumulated in each pixel of the first phase differential image by calculating an integer n for each pixel where the difference Δ satisfies nα−α / 2 ≦ Δ <nα + α / 2. A cumulative number calculation step;
A correction processing step of correcting an error of the unwrap processing by subtracting a product of the integer n and the width α from a pixel value of each pixel of the first phase differential image after the unwrap processing;
An image processing method comprising: