WO2009130829A1 - X線透視画像におけるモアレの除去方法、およびそれを用いたx線撮像装置 - Google Patents
X線透視画像におけるモアレの除去方法、およびそれを用いたx線撮像装置 Download PDFInfo
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- A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
- A61B6/52—Devices using data or image processing specially adapted for radiation diagnosis
- A61B6/5258—Devices using data or image processing specially adapted for radiation diagnosis involving detection or reduction of artifacts or noise
- A61B6/5282—Devices using data or image processing specially adapted for radiation diagnosis involving detection or reduction of artifacts or noise due to scatter
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Definitions
- the present invention relates to a moire removal method in which an X-ray grid, an array pattern, and a detection element array pattern of an FPD interfere with each other and appear in an X-ray fluoroscopic image, and an X-ray imaging apparatus using the method.
- the present invention relates to a technique for removing moire reflected in an included X-ray fluoroscopic image.
- An X-ray imaging apparatus that captures an X-ray fluoroscopic image of a subject includes an X-ray source that emits a cone-shaped X-ray beam and a flat panel detector (abbreviated as FPD) that detects the X-ray source. is there.
- the FPD has an X-ray detection surface on which X-ray detection elements are two-dimensionally arranged.
- the X-rays irradiated from the X-ray source are once scattered by the subject, and the scattered X-rays incident on the FPD cause deterioration of the contrast of the X-ray fluoroscopic image.
- the X-ray imaging apparatus is provided with a sheet-like X-ray grid in which strip-shaped metal foils are arranged so as to cover the X-ray detection surface of the FPD. .
- the arrangement pitch of the detection elements of the FPD and the arrangement pitch of the metal foil of the X-ray grid are not the same. Therefore, moire generated by interference of both pitches appears in the X-ray fluoroscopic image. Therefore, in the conventional X-ray imaging apparatus, in order to remove moire, the frequency analysis of the image is performed, the frequency component of moire is removed, and the image is reconstructed.
- a detection element that cannot detect X-rays may be generated on the detection surface of the FPD due to a defect in a semiconductor element or the like. Such a defect sometimes occurs due to a failure of a gate drive or a read transistor, so that it is impossible to detect all of the detection elements in series, and the X-ray fluoroscopic image has white or black defective pixels. A straight line appears. If the above-described moire removal calculation is performed on an X-ray fluoroscopic image having such a straight line, the regularity of moire fringes is disturbed by the defective pixels, so that the defective pixels are arranged in the image after the calculation. A straight line and a ghost in which the straight line spreads in the moire arrangement direction appear and the visibility of the X-ray fluoroscopic image is lowered.
- the defect region L when the defect region L extends in the moire stretching direction (y direction) (see FIG. 10B), the defect region L is ignored while ignoring the regularity of the moire fringes. It will be broken. Eventually, the regularity of moire fringes is disturbed by complementation of the defective pixels.
- statistical processing is performed on the left and right pixels E1 and E2 in series in the y direction in the defect region L to determine the most suitable pixel value.
- maximum likelihood estimation is performed in which pixel values in the left and right pixels E1 and E2 of the defective region L are tested and a pixel value most suitable for complementing the defective region L is estimated. This maximum likelihood estimation is simply performed based on pixel value variations. Naturally, the order of the pixels is ignored, and the regularity of moire fringes is not included in the processed image.
- the image values of the dark region D and the region L1 in which the missing pixels are complemented differ in the image after the image processing, and the regularity of the moire fringes is disturbed.
- the regularity of the moire fringes is disturbed, and as shown in FIG. A trace L2 of the pixel and a ghost L3 that spreads in the moire arrangement direction appear.
- An object of the present invention is to provide a method for removing moire in an X-ray fluoroscopic image in which a trace of a defective pixel and its ghost do not occur, and an X-ray imaging apparatus using the same.
- the present invention has the following configuration. That is, according to the first aspect of the present invention, in the method for removing moire in an X-ray fluoroscopic image, a moire frequency deriving step for obtaining the frequency of moire reflected in the X-ray fluoroscopic image, and one cycle of moire from the defective pixel.
- a missing pixel preliminary complementing step for forming a first intermediate image by complementing a missing pixel with reference to pixels separated by an integer multiple, a frequency analysis of the first intermediate image, and a moire reflected in the first intermediate image
- a moire removal step for removing and forming a second intermediate image
- an image smoothing step for performing image smoothing on the first intermediate image to form a third intermediate image
- a second intermediate image and a third intermediate image
- a deficient pixel recomplementing step for replenishing deficient pixels again by overlapping them.
- defective pixels are complemented without disturbing the regularity of moire fringes.
- the defective pixel preliminary complementing step in the present invention the defective pixel is complemented by referring to a pixel separated from the defective pixel by an integral multiple of one moire period. Therefore, the referred pixel has a moire stripe that should appear in the defective pixel. For example, when a defective pixel extends at a position where a moiré dark area appears, the referenced pixel is a moiré dark area. Further, for example, when a defective pixel extends at a position where a bright portion area of moiré appears, a pixel to be referred to is surely a bright portion area of moiré.
- the defective pixel can be reliably complemented.
- a pixel suitable for complementing a defective pixel is obtained by performing a smoothing process on an image in which the defective pixel is preliminarily supplemented. Therefore, even if a pixel adjacent to the defective pixel is a defective pixel.
- not only the pixel adjacent to the defective pixel but also the surrounding pixels are used to obtain a pixel suitable for complementing the defective pixel, so that the defective pixels appearing in the X-ray fluoroscopic image are formed in a row. Even if the defective pixel group is more complicated in shape, it is possible to provide a processed image from which moire has been removed while reliably complementing the defective pixel.
- the third intermediate image is formed from the first intermediate image that has not been subjected to the frequency filter yet and is obtained by only preliminarily complementing the missing pixels in the original image. That is, the third intermediate image is formed from an image that has not yet lost the same frequency component as the moire frequency. Therefore, the third intermediate image is more faithful to the original image, and if this is used to recomplement missing pixels, a processed image that more accurately represents the original image can be provided.
- the image smoothing process in the above-described image smoothing step is a matrix operation using a predetermined matrix, and it is more desirable that the number of rows of the matrix is equal to or more than the number of pixels for one cycle of moire.
- the image smoothing process of the present invention is a matrix operation, and the number of rows of the matrix used for the operation is equal to or more than the number of pixels for one cycle of moire. That is, when such a matrix is used, the image is smoothed while the moire bright area and the dark area cancel each other. Therefore, the moire is erased from the third intermediate image.
- This image smoothing process is also effective for defective pixels in which all adjacent pixels are defective pixels.
- the moire frequency deriving step for obtaining the frequency of the moire reflected in the above-described X-ray fluoroscopic image, and complementing the defective pixel with reference to a pixel separated from the defective pixel by an integral multiple of one moire cycle
- a defective pixel preliminary complementing step for forming a first intermediate image, a frequency analysis of the first intermediate image, a moire removal step for removing a moire reflected in the first intermediate image to form a second intermediate image
- the intermediate image further includes a defective pixel recomplementation step of complementing the defective pixel supplemented by referring to a pixel adjacent to the defective pixel supplemented in the defective pixel preliminary complementing step.
- the defective pixels are complemented without disturbing the regularity of moire fringes.
- the defective pixel preliminary complementing step in the above configuration the defective pixel is supplemented with reference to a pixel separated from the defective pixel by an integral multiple of one moire period. Therefore, the referred pixel has a moire stripe that should appear in the defective pixel. For example, when a defective pixel extends at a position where a moiré dark area appears, the referenced pixel is a moiré dark area. Further, for example, when a defective pixel extends at a position where a bright portion area of moiré appears, a pixel to be referred to is surely a bright portion area of moiré.
- the regularity of the moire is not disturbed by the complement of the defective pixel, and when removing the moire reflected in the first intermediate image, the trace of the defective pixel and the moire ghosts that spread in the arrangement direction do not appear.
- the supplemented defective pixel is supplemented again with reference to the pixel adjacent to the supplemented defective pixel.
- the second intermediate image is obtained by removing moire from the first intermediate image that reproduces the moire fringes that should appear in the defective pixels. Therefore, the influence of moire does not appear in the second intermediate image.
- the missing pixel complemented in the second intermediate image is a pixel value replaced with reference to a pixel separated from the second intermediate image, the image of the subject reflected in the complemented missing pixel is It is different from the image of the subject that was supposed to be reflected in the pixels.
- the X-ray fluoroscopic image formed by the above configuration is suitable for diagnosis.
- an X-ray source that irradiates an X-ray beam
- an X-ray detection unit that detects an X-ray beam
- an X-ray detection unit An X-ray grid for removing scattered X-rays provided at a position where the X-ray source is interposed, a missing pixel preliminary complementing unit for performing a defective pixel preliminary complementing step, a moire removing unit for performing a moire removing step, and image smoothing
- image smoothing means for performing the conversion step and defective pixel recomplementation means for performing the defective pixel recomplementation step.
- the X-ray source for irradiating the X-ray beam the X-ray detection means for detecting the X-ray beam, the X-ray detection means, and the X-ray source are provided.
- An X-ray grid that removes scattered X-rays a defective pixel preliminary complementing unit that performs a defective pixel preliminary complementing step, a moire removing unit that performs a moire removing step, and a defective pixel recomplementing unit that performs a defective pixel recomplementing step. It is more desirable to have it.
- the present specification also describes the invention relating to the following radiation imaging apparatus.
- A X-ray source for irradiating an X-ray beam
- B X-ray detection means for detecting an X-ray beam
- C X-ray detection means, and scattering provided at a position where the X-ray source is interposed
- An X-ray grid for removing X-rays
- D moire frequency deriving means for obtaining the frequency of moire reflected in an X-ray fluoroscopic image
- E pixels spaced by an integral multiple of one moire period from the defective pixel
- F frequency analysis of the first intermediate image and removal of moire reflected in the first intermediate image by supplementing the defective pixel with reference to FIG.
- Moire removal means for forming a second intermediate image; (G) image smoothing means for performing image smoothing on the first intermediate image to form a third intermediate image; and (H) second intermediate image and third.
- the first missing pixel re-over which complements the missing pixel again by overlaying the intermediate image X-ray imaging apparatus characterized by comprising a complete unit.
- the image smoothing process performed by the above-described image smoothing means is a matrix operation using a predetermined matrix, and it is more desirable that the number of rows of the matrix is equal to or greater than the number of pixels for one cycle of moire.
- this specification also describes the invention relating to the following radiographic apparatus.
- A X-ray source for irradiating an X-ray beam
- B X-ray detection means for detecting an X-ray beam
- C X-ray detection means, and scattering provided at a position where the X-ray source is interposed
- An X-ray grid for removing X-rays
- D moire frequency deriving means for obtaining the frequency of moire reflected in an X-ray fluoroscopic image
- E pixels spaced by an integral multiple of one moire period from the defective pixel
- F frequency analysis of the first intermediate image and removal of moire reflected in the first intermediate image by supplementing the defective pixel with reference to FIG.
- Moiré removal means for forming a second intermediate image, and (I) a pixel value of a preliminarily complemented preliminary complementary pixel belonging to the first intermediate image is adjacent to a pixel at the same position as the preliminary complementary pixel in the second intermediate image
- an X-ray fluoroscopic image suitable for diagnosis can be obtained by reliably complementing the defective pixel while suppressing the occurrence of a ghost in which the defective pixel spreads and spreads.
- the X-ray grid for removing scattered X-rays is provided, the scattered X-rays are removed from the X-rays detected by the X-ray detection means. Therefore, the contrast of the finally obtained X-ray fluoroscopic image is high.
- the above configuration has moire removal means, moire is removed from the X-ray fluoroscopic image. And the said structure is provided with the defect pixel preliminary complement means.
- the above configuration includes a defective pixel recomplementing unit. Thereby, the pixel value of the defective pixel is changed to a more suitable one.
- the defective pixel is surely complemented while suppressing generation of a ghost in which the defective pixel spreads and is suitable for diagnosis.
- An X-ray imaging apparatus that forms an X-ray fluoroscopic image can be provided.
- defective pixels are complemented without disturbing the regularity of moire fringes.
- the defective pixel preliminary complementing step in the present invention the defective pixel is complemented by referring to a pixel separated from the defective pixel by an integral multiple of one moire period. Therefore, the referred pixel has a moire stripe that should appear in the defective pixel. That is, according to the present invention, the moire is once surely removed from the image in which both the defective pixel and the moire overlap. That is, in the subsequent image processing, an operation for complementing the defective pixel may be executed. That is, the present invention has a configuration in which moire removal and replacement of defective pixels (recomplementation in the present invention) are sequentially performed on an image in which both defective pixels and moire overlap. Therefore, by replacing the defective pixel, the regularity of the moiré fringes is disturbed, and the trace of the defective pixel and the ghost in which it spreads do not appear in the finally formed X-ray fluoroscopic image.
- FIG. 3 is a functional block diagram for explaining a moire removal method in an X-ray fluoroscopic image according to Embodiment 1.
- FIG. It is a figure explaining the structure of FPD which concerns on Example 1.
- FIG. 3 is a flowchart for explaining the operation of the first embodiment.
- 3 is a schematic diagram illustrating an X-ray fluoroscopic image according to Embodiment 1.
- FIG. 6 is a schematic diagram for explaining an image smoothing step according to the first embodiment. 6 is a schematic diagram for explaining a defective pixel re-complementation step according to Embodiment 1.
- FIG. FIG. 10 is a diagram illustrating image processing according to a second embodiment.
- FIG. 10 is a functional block diagram illustrating a configuration of an X-ray imaging apparatus according to Embodiment 3.
- Moire frequency deriving section (moire frequency deriving means) 2 Deficient pixel preliminary complement part (Deficient pixel preliminary complement means) 3 Moire removal part (moire removal means) 4 Image smoothing unit (image smoothing means) 5 1st defective pixel recomplementation part (1st defective pixel recomplementation means) 24 second defective pixel recomplementation section (second defective pixel recomplementation means) P1 Preliminary complementary image (first intermediate image) P2 Moire removal image (second intermediate image) P3 Smoothed image (third intermediate image)
- FIG. 1 is a functional block diagram illustrating a method for removing moire in an X-ray fluoroscopic image according to the first embodiment.
- a moire frequency deriving unit 1 that obtains the frequency of moire from the original image P0 and pixels separated from the defective pixel by one cycle of moire.
- a defective pixel preliminary complement unit 2 that complements the defective pixel to form the preliminary complement image P1, a moire removal unit 3 that removes the moire reflected in the preliminary complement image P1 to form the moire removed image P2, and a preliminary complement image
- An image smoothing process is performed on P1
- an image smoothing unit 4 that forms a smoothed image P3, and a first defective pixel recompensation that complements the defective pixel again by superimposing the moire-removed image P2 and the smoothed image P3.
- a complementing unit 5 Note that the preliminary complement image P1, the moire-removed image P2, and the smoothed image P3 according to the first embodiment correspond to the first intermediate image, the second intermediate image, and the third intermediate image in the present invention, respectively.
- the moire frequency deriving unit corresponds to the moire frequency deriving unit of the present invention
- the defective pixel preliminary complementing unit corresponds to the defective pixel preliminary supplementing unit of the present invention.
- the moire removing unit corresponds to the moire removing unit of the present invention
- the image smoothing unit corresponds to the image smoothing unit of the present invention.
- the first missing pixel recomplementation unit corresponds to the first missing pixel recomplementation unit of the present invention.
- FIG. 2 is a diagram illustrating the configuration of the FPD according to the first embodiment.
- the FPD 10 that detects X-rays includes X-ray detection elements 10 a arranged in a matrix, a gate drive array 11 and an amplifier array 12 at the side ends of the detection element matrix. Missing pixels occur when any of these do not work at all.
- the gate drive elements 11a constituting the gate drive array 11 fails and all of the X-ray detection elements 10a driven by the failed gate drive element 11a do not operate, the X-ray fluoroscopic image is displayed. Shows a black straight line regardless of the object to be imaged. This is because the gate drive element 11a in the FPD 10 is configured to collectively drive the serial X-ray detection elements 10a.
- an X-ray imaging apparatus that captures an X-ray fluoroscopic image of a subject is irradiated with a cone-shaped X-ray beam from the X-ray source toward the subject, and transmitted X-rays transmitted through the subject are detected by the FPD 10.
- the FPD 10 There is something that is configured to.
- the X-ray imaging apparatus when X-rays pass through the subject, the X-rays are scattered in the subject and incident on the FPD 10, and this causes the contrast of the X-ray fluoroscopic image of the subject to increase. It becomes a factor to make it worse.
- an X-ray grid that absorbs scattered X-rays is provided so as to cover the X-ray detection surface of the FPD 10.
- the FPD 10 has a large number of semiconductor type X-ray detection elements 10a arranged in a matrix. Such an FPD 10 constructs an X-ray fluoroscopic image by discretely sampling the X-rays transmitted through the subject M by the arrayed X-ray detection elements 10a.
- the X-ray grid has a plurality of blades arranged in a blind shape. When the cone-shaped X-ray beam passes through the X-ray grid, a streak-like shadow is generated for each blade of the X-ray grid. If this shadow is seen in the whole X-ray grid, it becomes a striped X-ray shadow pattern, which is reflected in the FPD 10 arranged below the X-ray grid.
- This X-ray shadow pattern is discretely sampled by the X-ray detection elements 10a constituting the FPD 10, but the number of X-ray shadows reflected on each of the X-ray detection elements 10a is constant throughout the FPD 10. Don't be. This is because the arrangement pitch of the X-ray detection elements 10a and the arrangement pitch of the X-ray shadows do not match. In this way, interference fringes in which elongated dark areas where a large number of shadows are reflected and elongated light areas where a smaller number of shadows are alternately arranged appear in the X-ray fluoroscopic image.
- the detection element array pattern of the FPD 10 and the X-ray shadow pattern formed by the X-ray grid interfere with each other to generate moire and appear in the X-ray fluoroscopic image.
- the moire according to the present invention means this.
- the image from which all were removed from the X-ray fluoroscopic image in which the defective pixel and the moire were reflected simultaneously can be provided by image processing.
- the moire removal operation according to the first embodiment includes a moire frequency deriving step S1 performed by the moire frequency deriving unit 1 and a defective pixel preliminary complementing step S2 performed by the defective pixel preliminary complementing unit 2.
- a moire removal step S3 performed by the moire removal unit 3 an image smoothing step S4 performed by the image smoothing unit 4, and a defective pixel recomplementation step S5 performed by the first defective pixel recomplementation unit 5.
- the operation of each step will be described in order.
- FIG. 4 is a schematic diagram illustrating an X-ray fluoroscopic image according to the first embodiment.
- the X-ray fluoroscopic image (original image P0) acquired by FPD includes moire and defective pixels.
- the moire is obtained by arranging dark region D extending along the y direction at equal intervals in the x direction.
- the width of the dark area D of the moire is 1 pixel and the dark area D appears every 4 pixels in the x direction.
- the width and interval of the dark area D are limited to this. It is not something that can be done.
- the defective area La appears in the original image P0 as a black line in which the defective pixels are arranged in the y direction.
- the width of the defective region La is 1 pixel, but the present invention is not limited to this.
- the missing area La is present at the position where the moire dark area D appears in the original image P0, but the present invention is not limited to this. In the actual original image P0, the defect area La appears regardless of the moire phase.
- the moire frequency deriving unit 1 performs frequency analysis on the original image P0 and derives the moire frequency. By performing the frequency analysis, the original image P0 is converted into a frequency function, but the moire frequency component appears as a sharp peak in the frequency function. The maximum point of this peak is read to obtain the moire frequency ⁇ .
- the dark area D Since the dark area D is arranged at equal intervals in the x direction, assuming that the original image shown in FIG. 4A is 13 ⁇ 13 pixels, the dark area D appears at five locations. Clearly, in the example of FIG. 4A, since the defective region La extends in the region where the dark region D should appear, the number of moire dark region D is reduced by one. Note that the defect area La in the area where the dark area D should appear is merely an example, and in the present invention, the defect area La may extend to the area where the moire bright area should appear.
- the missing pixels are preliminarily complemented. Since the pixel value of the defective area La is extreme, if moiré is removed with the defective area La remaining, a ghost of the defective area La appears in the image. Therefore, prior to the removal of moire, the defective area La is replaced with a pixel in the vicinity thereof in advance. Specifically, as shown in FIG. 4B, in the moire stretching direction (y direction), it is at the same position as the defective pixel a and corresponds to one cycle of moire in the arrangement direction (x direction). The defective pixel a is replaced with the pixel b with reference to the pixel b separated from the defective pixel a by 4 pixels.
- the defective pixel is preliminarily supplemented by replacing the defective pixel with the pixel in the x direction.
- the defect area La is replaced with the preliminary complement area Lb
- the image obtained in step S2 is the preliminary complement image P1.
- FIG. 4B the complementary processing after the defective pixel a is not processed, but this is to emphasize the processing of the defective pixel a.
- defective pixels are replaced for the entire area of the original image P0. Note that 4 pixels corresponds to an integral multiple of one cycle of moire according to the present invention.
- pixels belonging to the preliminary complement region Lb are defined as preliminary complement pixels.
- the moire removing unit 3 performs frequency analysis on the above-described preliminary complement image P1, and removes the moire reflected in the preliminary complement image P1. Specifically, after performing a filtering process for removing the moire frequency ⁇ on the frequency function obtained by the frequency analysis on the preliminary complement image P1, it is converted again into an X-ray fluoroscopic image. Then, as shown in FIG. 4C, a moire-removed image P2 from which moire has been removed is obtained. As a result of this processing, it is assumed that the preliminary complement region Lb is a region Lc that does not include moire by removing the reflected moire.
- the moire has been removed, but the referenced pixels are separated in accordance with the moire cycle. That is, a pixel value that is not suitable due to the complement of the missing region La is used for the region Lc.
- the pixels belonging to the region Lc correspond to the defective pixels supplemented in the defective pixel preliminary complementing step of the present invention. In the following description, for the sake of convenience, it is referred to as a complemented defective pixel.
- FIG. 5 is a schematic diagram illustrating the image smoothing step according to the first embodiment.
- the smoothing of the preliminary complement image P1 is performed by a convolution filter using a convolution matrix having the same number of rows and columns of 5 ⁇ 5.
- the calculation performed on the pixel c belonging to the preliminary complement region Lb will be described.
- a rectangular area S is prepared so as to surround the pixel c.
- the rectangular area S is a 5 ⁇ 5 pixel square centered on the pixel c. That is, the rectangular area S has the same size as the convolution matrix. That is, the image smoothing process using the convolution matrix for the pixel c is performed using the 25 pixels belonging to the rectangular area S.
- the rectangular area S is larger than one cycle of moire.
- the number of rows is equal to or greater than the number of pixels of the moire.
- the image smoothing step S4 25 pixels belonging to the rectangular area S are weighted based on this convolution matrix, and a processed pixel value corresponding to the pixel c is calculated. This is performed at least over the entire preliminary complement region Lb to obtain a smoothed image P3. At this time, it is assumed that the preliminary complement region Lb in the preliminary complement image P1 is replaced with the smoothing processing region Ld in the smoothed image P3. In FIG. 5, the smoothing process after pixel c is unprocessed, but this is to emphasize the process of pixel c. In practice, the image is smoothed for the entire region of the preliminary complement image P1.
- the size of the convolution matrix is one or more periods of moire.
- the rectangular area S of the first embodiment is a 5 ⁇ 5 pixel square. Since the bright area B and the dark area D of moiré are mixed in this, if the preliminary complement image P1 is smoothed by the convolution filter, they will cancel each other. This is not limited to the pixel c, but the same cancellation occurs for all the pixels, so the moire is eliminated from the smoothed image P3.
- This convolution filter is also effective for a defective pixel in which all adjacent pixels are defective pixels.
- the missing pixels are not re-complemented based on the adjacent pixels, so that the defective pixel group formed by the continuous defective pixels appearing in the X-ray fluoroscopic image is more complicated. Even if it is a simple shape, a processed image from which moire has been removed is formed while reliably complementing missing pixels.
- FIG. 6 is a schematic diagram illustrating the defective pixel recomplementation step according to the first embodiment. As shown in FIG. 6, the pixel value of each pixel constituting the region Lc of the moire-removed image P2 is replaced with the pixel value of each pixel of the smoothing region Ld in the smoothed image P3 corresponding thereto.
- the smoothing region Ld of the smoothed image P3 is more suitable for complementing the defect region La than the region Lc of the moire removal image P2.
- the region Lc is obtained by applying the pixel values of the pixels separated from the defective region La.
- the smoothing region Ld is acquired with reference to pixels around the defect region La.
- the moire is erased from the smoothing region Ld. Therefore, if the region Lc of the moire-removed image P2 is replaced with the smoothing region Ld of the smoothed image P3, X-ray fluoroscopy in which moire is removed and a more appropriate pixel value is applied to complement the missing region La An image will be formed.
- the defect region La is complemented without disturbing the regularity of the moire fringes.
- the missing pixel preliminary complementing step S2 in the first embodiment the missing pixel a is complemented with reference to the pixel b separated from the missing area La by one moiré cycle. Therefore, the pixel b referred to has a moire stripe that should appear in the defective pixel a.
- the pixel to be referred to is the dark area D of the moire.
- the pixel referred to is surely the bright area B of the moiré.
- the regularity of the moire fringes is not disturbed by the complement of the defect area La, and the moire reflected in the preliminary complement image P1 is removed in the moire removal step S3.
- the preliminary complement region Lb that is the complemented region and the ghost that spreads in the moire arrangement direction (x direction) do not appear.
- the defective pixel can be reliably complemented.
- a pixel suitable for complementing a defective pixel is obtained by performing a smoothing process on an image in which the defective pixel is preliminarily supplemented. Therefore, even if a pixel adjacent to the defective pixel is a defective pixel.
- the smoothed image P3 is formed from a preliminary complement image P1 that is not yet subjected to a frequency filter, and is obtained by only preliminary complementing missing pixels in the original image P0.
- the smoothed image P3 is formed from an image that has not yet lost the frequency component before the moire is removed. Therefore, the smoothed image P3 is more faithful to the original image, and if this is used to recomplement the missing pixels, a processed image that more accurately represents the original image P0 can be provided.
- moire is reflected in the preliminary complement region Lb, moire cannot be confirmed in the smoothed image P3 formed in the image smoothing step S4. This is because the size of the convolution matrix is one or more periods of moire. Since the moire bright area B and the dark area D are mixed in the area S defined by the convolution matrix, if the preliminary complement image P1 is smoothed by the convolution filter, they will cancel each other. Moreover, since such cancellation occurs for all the pixels in the smoothed image P3, the moire is erased from the smoothed image P3.
- FIG. 7A is a functional block diagram illustrating a method for removing moire in an X-ray fluoroscopic image according to the second embodiment.
- the moire frequency deriving unit 21 for obtaining the frequency of moire from the original image P0 is separated from the defective pixel by one cycle of moire.
- a defective pixel preliminary complement unit 22 that complements the defective pixel from the completed pixels to form the preliminary complement image P1
- a moire removal unit 23 that removes the moire reflected in the preliminary complement image P1 and forms the moire removal image P2
- a second missing pixel re-complementing unit 24 that complements the missing pixel complemented with reference to the pixel in the moiré-removed image P2.
- the preliminary complement image P1 and the moire-removed image P2 according to the second embodiment correspond to the first intermediate image and the second intermediate image in the present invention, respectively.
- the second defective pixel recomplementation unit corresponds to the second defective pixel recomplementation unit of the present invention.
- the moire removal operation according to the second embodiment includes a moire frequency deriving step S1 performed by the moire frequency deriving unit 21, and a defective pixel preliminary complementing step S2 performed by the defective pixel preliminary complementing unit 22.
- a moire removing step S3 performed by the moire removing unit 23 and a defective pixel recomplementing step T4 performed by the second defective pixel recomplementing unit 24.
- steps S1 to S3 are the same as in the first embodiment. Therefore, these descriptions are omitted.
- FIG. 7B is a schematic diagram illustrating the defective pixel recomplementation step according to the second embodiment. As shown in FIG. 7B, in the defective pixel recomplementation step T4, an operation of replacing the pixel value of the preliminarily supplemented defective pixel g with reference to the pixel h that does not belong to the region Lc in the moire removal image P2. Done.
- a pixel that does not belong to the region Lc is defined as a pixel h, and the pixel value of this pixel h is read and pre-complemented.
- the pixel value of the defective pixel g is changed to this.
- an X-ray fluoroscopic image in which the preliminarily complemented defective pixel g is recomplemented is formed. That is, the second missing pixel re-complementation unit 24 sets the pixel value of the preliminary complement missing pixel g (preliminary complement pixel) belonging to the preliminary complement image P1 on the moire removal image P2 at the same position as the missing pixel g.
- the preliminarily complemented defective pixel g of the preparatory complement image P1 is complemented again.
- the defective pixel a is complemented without disturbing the regularity of the moire fringes.
- the missing pixel is complemented with reference to the pixel b that is separated from the missing pixel a by one time the number of pixels for one moire period. Therefore, the pixel b referred to has a moire stripe that should appear in the defective pixel a. That is, according to the configuration of the second embodiment, the regularity of the moire is not disturbed by the complement of the defective pixel a, and when removing the moire reflected in the preliminary complement image P1, A ghost that spreads and spreads in the direction of the moire arrangement does not appear.
- the preliminarily complemented missing pixel g in the moiré-removed image P2 is a pixel value replaced with reference to the pixel b separated from the moire-removed image P2, it appears in the preliminarily complemented missing pixel g.
- the image of the subject is different from the image of the subject that should have appeared in the defective pixel a. Even if this is the case, according to the configuration of the second embodiment, the subject that should have been reflected in the pre-complemented missing pixel g with reference to the pixel h adjacent to the pre-complemented missing pixel g It is configured to reproduce as much as possible. Therefore, the X-ray fluoroscopic image formed by the configuration of Example 2 is suitable for diagnosis.
- FIG. 8 is a functional block diagram illustrating the configuration of the X-ray imaging apparatus according to the third embodiment. As illustrated in FIG. 8, the X-ray imaging apparatus 30 according to the third embodiment is provided on the top plate 31 on which the subject M is placed, the FPD 32 provided at the lower portion of the top plate 31, and the upper portion of the top plate.
- An X-ray tube 33 that irradiates the FPD 32 with a cone-shaped X-ray beam, and a position where the FPD 32 and the X-ray tube 33 are interposed, and a scattering X provided so as to cover the X-ray detection surface of the FPD 32
- a defective pixel preliminary complement unit 42 that preliminarily complements the pixel values of the first pixel value to form a preliminary complement image P1, a
- the X-ray imaging apparatus 30 When the configuration of the first embodiment is adopted, the X-ray imaging apparatus 30 according to the third embodiment includes an image smoothing unit 44 that forms a smoothed image P3 by performing a smoothing process on the preliminary complement image P1. ing. This configuration is not necessarily required when the configuration of the second embodiment is adopted.
- the X-ray imaging apparatus 30 also includes a main control unit 47 that controls each of the control units 35, 37, and 39 in an integrated manner.
- the main control unit 47 is constituted by a CPU, and realizes the control units 35, 37, and 39 by executing various programs.
- the X-ray tube 33 and the FPD 32 correspond to the X-ray source and the X-ray detection means of the present invention.
- each of the moire frequency deriving unit, the defective pixel preliminary complementing unit, the moire removing unit, the image smoothing unit, and the defective pixel recomplementing unit includes a moire frequency deriving unit, a defective pixel preliminary complementing unit, a moire removing unit, and an image smoothing. Corresponds to each of the means and the defective pixel re-complementing means.
- the subject M is first placed on the top plate 31. Then, the FPD 32 and the X-ray tube 33 are moved to a position sandwiching the region of interest of the subject M.
- the X-ray tube 33 is controlled so as to emit a cone-shaped X-ray beam. Note that the cone-shaped X-ray beam has a pulse shape.
- the X-ray transmitted through the subject M passes through the X-ray grid 34 and enters the FPD 32.
- moire generated by interference between the arrangement pitch of the detection elements of the FPD 32 and the arrangement pitch of the metal foil of the X-ray grid 34 is reflected.
- the original image P0 includes a moire frequency deriving step S1 performed by the moire frequency deriving unit 41, a defective pixel preliminary complementing step S2 performed by the defective pixel preliminary complementing unit 42, a moire removing step S3 performed by the moire removing unit 43, and an image smoothing.
- an image smoothing step S4 performed by the conversion unit 44 and the defective pixel re-complementation step performed by the defective pixel re-complementing unit 45, moire is removed and converted into an X-ray fluoroscopic image suitable for diagnosis. Since this image processing has been described in detail in each of the above-described embodiments, description thereof will be omitted. Thus, the acquisition of the X-ray fluoroscopic image by the X-ray imaging apparatus using the moire removal method described in the first and second embodiments is completed.
- the operation of the defective pixel re-complementing unit 45 performs the operation of step S5 described in the first embodiment.
- the operation of the defective pixel re-complementing unit 45 performs the operation of step T4 described in the second embodiment.
- the defective pixel a is included in the FPD 32, the defective pixel a is reliably complemented while suppressing the occurrence of a ghost in which the defective pixel a is spread and spread.
- An X-ray imaging apparatus 30 that forms an X-ray fluoroscopic image suitable for diagnosis can be provided.
- the X-ray grid 34 for removing scattered X-rays is provided, the scattered X-rays are removed from the X-rays detected by the FPD 32. Therefore, the contrast of the finally obtained X-ray fluoroscopic image is high.
- the configuration of the third embodiment includes the moire removing unit 43, moire is removed from the X-ray fluoroscopic image.
- the configuration of the third embodiment includes a defective pixel preliminary complement unit 42. Thereby, the regularity of the moire fringes is reproduced in the defective pixel. Further, the third embodiment includes a defective pixel recomplementation unit 45. Thereby, the pixel value of the defective pixel a is changed to a suitable value. As described above, according to the configuration of the third embodiment, even when the defective pixel a is included in the FPD 32, the defective pixel a is reliably complemented while suppressing the occurrence of a ghost in which the defective pixel spreads and spreads. An X-ray imaging apparatus 30 that forms a suitable X-ray fluoroscopic image can be provided.
- the present invention is not limited to the above embodiments, and can be modified as follows.
- the defective pixel is referred to by referring to a pixel separated from the defective pixel by 4 pixels corresponding to one moire period in the moire arrangement direction (x direction).
- the present invention is not limited to this.
- the pixel values of a plurality of pixels b1 and b2 separated from the missing pixel by 4 pixels in the x direction may be referred to and the average value may be used as the missing pixel a.
- the pixel b referred to when complementing the defective pixel a is at the same position as the defective pixel a in the moire stretching direction (y direction).
- the present invention is not limited to this.
- a pixel separated by one pixel in the moire arrangement direction (y direction) from the defective pixel a may be referred to.
- the separation distance in the y direction can be freely set.
- the pixel b referred to when complementing the defective pixel a is from the defective pixel a by one period of moire in the moire arrangement direction (x direction).
- the present invention is not limited to this.
- pixels separated from the defective pixel a by two moire cycles may be referred to. That is, in the present invention, the separation distance in the x direction can be an integral multiple of one cycle of moire.
- the preliminarily supplemented defective pixel g is recomplemented with reference to the pixel h, but the present invention is not limited thereto.
- the replenishment of the preliminarily supplemented defective pixel g may be performed with reference to a plurality of pixels adjacent to the preliminarily supplemented defective pixel g.
- the present invention is suitable for the medical field.
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Abstract
Description
すなわち、請求項1に記載の発明は、X線透視画像におけるモアレの除去方法において、X線透視画像に写り込んでいるモアレの周波数を求めるモアレ周波数導出ステップと、欠損画素からモアレ1周期分の整数倍だけ離間した画素を参照して欠損画素を補完することにより第1中間画像を形成する欠損画素予備補完ステップと、第1中間画像を周波数解析し、第1中間画像に写り込んだモアレを除去して第2中間画像を形成するモアレ除去ステップと、第1中間画像に画像平滑化処理を行い、第3中間画像を形成する画像平滑化ステップと、第2中間画像と第3中間画像とを重ね合わせて欠損画素を再び補完する欠損画素再補完ステップとを備えることを特徴とするものである。
(A)X線ビームを照射するX線源と、(B)X線ビームを検出するX線検出手段と、(C)X線検出手段と、X線源の介在する位置に設けられた散乱X線を除去するX線グリッドと、(D)X線透視画像に写り込んでいるモアレの周波数を求めるモアレ周波数導出手段と、(E)欠損画素からモアレ1周期分の整数倍だけ離間した画素を参照して欠損画素を補完することにより第1中間画像を形成する欠損画素予備補完手段と、(F)第1中間画像を周波数解析し、第1中間画像に写り込んだモアレを除去して第2中間画像を形成するモアレ除去手段と、(G)第1中間画像に画像平滑化処理を行い、第3中間画像を形成する画像平滑化手段と、(H)第2中間画像と第3中間画像とを重ね合わせて欠損画素を再び補完する第1欠損画素再補完手段とを備えることを特徴とするX線撮影装置。
(A)X線ビームを照射するX線源と、(B)X線ビームを検出するX線検出手段と、(C)X線検出手段と、X線源の介在する位置に設けられた散乱X線を除去するX線グリッドと、(D)X線透視画像に写り込んでいるモアレの周波数を求めるモアレ周波数導出手段と、(E)欠損画素からモアレ1周期分の整数倍だけ離間した画素を参照して欠損画素を補完することにより第1中間画像を形成する欠損画素予備補完手段と、(F)第1中間画像を周波数解析し、第1中間画像に写り込んだモアレを除去して第2中間画像を形成するモアレ除去手段と、(I)第1中間画像に属する予備的に補完された予備補完画素の画素値を第2中間画像における予備補完画素と同一位置にある画素に隣接する隣接画素の画素値に置き換えることにより、第1中間画像の予備補完画素を再び補完する第2欠損画素再補完手段とを備えることを特徴とするX線撮影装置。
2 欠損画素予備補完部(欠損画素予備補完手段)
3 モアレ除去部(モアレ除去手段)
4 画像平滑化部(画像平滑化手段)
5 第1欠損画素再補完部(第1欠損画素再補完手段)
24 第2欠損画素再補完部(第2欠損画素再補完手段)
P1 予備補完画像(第1中間画像)
P2 モアレ除去画像(第2中間画像)
P3 平滑化画像(第3中間画像)
図4は、実施例1に係るX線透視画像を表す模式図である。FPDによって取得されたX線透視画像(元画像P0)は、モアレと、欠損画素を含んでいる。図4(a)に示すように、モアレは、y方向に沿って伸びた暗部領域Dが、x方向に等間隔に配列したものである。なお、説明の便宜上、モアレの暗部領域Dの幅は1ピクセルとし、x方向に暗部領域Dが4ピクセルごとに表れているものとするが、この暗部領域Dの幅と間隔は、これに限られるものではない。一方、欠損領域Laは、欠損画素がy方向に配列した黒い線として元画像P0に表れている。なお、説明の便宜上、欠損領域Laの幅は1ピクセルとするが、本発明はこれに限られるものではない。また、欠損領域Laは、元画像P0において、ちょうどモアレの暗部領域Dが現れる位置に存しているが、本発明はこれに限られない。実際の元画像P0においては、モアレの位相と関係なく欠損領域Laが出現している。
次に、欠損画素を予備的に補完する。欠損領域Laの画素値は、極端なものとなっているので、欠損領域Laを残した状態でモアレの除去を行ってしまうと、欠損領域Laのゴーストが画像に表れてしまう。そこで、モアレの除去に先駆けて、予め欠損領域Laをその近傍の画素に置換する。具体的には、図4(b)に示すように、モアレの延伸方向(y方向)において、欠損画素aと同一位置であるとともに、配列方向(x方向)にモアレの1周期分に相当する4ピクセル分だけ欠損画素aから離間した画素bを参照して、欠損画素aを、画素bに置換する。この様に、実施例1に係る欠損画素予備補完ステップS2では、欠損画素をx方向の画素に置換することで、欠損画素の予備補完を行う。なお、この置き換えによって、欠損領域Laは、予備補完領域Lbに代えられるものとし、このステップS2によって得られる画像を予備補完画像P1とする。また、図4(b)においては、欠損画素a以降の補完処理は、未処理となっているが、これは、欠損画素aの処理を強調するためである。実際は、元画像P0の全領域について欠損画素の置き換えが行われる。なお、4ピクセル分は、本発明に係るモアレ1周期分の整数倍に相当する。なお、本発明においては、この予備補完領域Lbに属する画素を予備補完画素と定義する。
そして、モアレ除去部3において、上述の予備補完画像P1に対して周波数解析を行い、予備補完画像P1に写り込んだモアレを除去する。具体的には、予備補完画像P1に対する周波数解析によって取得した周波数関数に対してモアレの周波数ωを除去するフィルタリング処理を行った後、それを再びX線透視画像へと変換する。すると、図4(c)に示すように、モアレが除去されたモアレ除去画像P2が得られる。この処理によって、予備補完領域Lbは、写り込んだモアレが除去されてモアレを含まない領域Lcとなったものとする。この領域Lcに注目すれば、モアレは除去されてはいるものの、参照した画素はモアレの周期に対応して離間したものとなっている。つまり領域Lcには、欠損領域Laの補完により適さない画素値が使用されていることになる。なお、この領域Lcに属する画素は、本発明の欠損画素予備補完ステップにおいて補完した欠損画素に相当する。以降の説明においては便宜上、補完した欠損画素と呼ぶ。
そこで、領域Lcの画素値をより好適なものとするため、欠損領域Laの補完にふさわしい画素値を画像平滑化処理によって取得する。画像平滑化部4においては、欠損画素予備補完ステップS2で得られた予備補完画像P1に画像平滑化処理を行うことで、平滑化画像P3を構築する。図5は、実施例1に係る画像平滑化ステップを説明する模式図である。予備補完画像P1の平滑化は、行数と列数が同一の5×5となっているコンボリューション行列を用いたコンボリューションフィルタによって行われる。ここで、予備補完領域Lbに属する画素cで行われる演算について説明する。まず、画素cを囲むように矩形領域Sが用意される。この矩形領域Sは、画素cを中心とする5×5ピクセルの正方形をしている。つまり、矩形領域Sは、コンボリューション行列と同様の大きさとなっている。つまり、この矩形領域Sに属する25個の画素を使って画素cに対するコンボリューション行列を用いた画像平滑化処理が行われることになる。
最後に、モアレ除去画像P2の領域Lcを平滑化画像P3の平滑処理領域Ldに置換するる欠損画素の再補完が第1欠損画素再補完部5で行われる。図6は、実施例1に係る欠損画素再補完ステップを説明する模式図である。図6に示すように、モアレ除去画像P2の領域Lcを構成する各画素の画素値をそれに対応する平滑化画像P3における平滑処理領域Ldの各画素の画素値に置換する。
実施例2の特徴的なステップである欠損画素再補完ステップT4の説明をする。図7(b)は、実施例2に係る欠損画素再補完ステップの説明をする模式図である。図7(b)に示すように、欠損画素再補完ステップT4では、モアレ除去画像P2における領域Lcに属しない画素hを参照して、予備補完された欠損画素gの画素値を置換する操作が行われる。具体的には、再補完の対象となる予備補完された欠損画素gを取り囲む画素のうち、領域Lcに属していない画素を画素hとし、この画素hの画素値を読み出して、予備補完された欠損画素gの画素値をこれに変更する。こうして、予備補完された欠損画素gが再補完されたX線透視画像が形成される。つまり、第2欠損画素再補完部24は、予備補完画像P1に属する予備補完された欠損画素g(予備補完画素)の画素値をこの欠損画素gと同一位置となっているモアレ除去画像P2上の画素に隣接する画素hの画素値に置き換えることにより、予備補完画像P1の予備補完された欠損画素gを再び補完するのである。
Claims (6)
- X線透視画像におけるモアレの除去方法において、
X線透視画像に写り込んでいるモアレの周波数を求めるモアレ周波数導出ステップと、
欠損画素から前記モアレ1周期分の整数倍だけ離間した画素を参照して前記欠損画素を補完することにより第1中間画像を形成する欠損画素予備補完ステップと、
前記第1中間画像を周波数解析し、前記第1中間画像に写り込んだモアレを除去して第2中間画像を形成するモアレ除去ステップと、
前記第1中間画像に画像平滑化処理を行い、第3中間画像を形成する画像平滑化ステップと、
前記第2中間画像と前記第3中間画像とを重ね合わせて前記欠損画素を再び補完する欠損画素再補完ステップとを備えることを特徴とするX線透視画像におけるモアレの除去方法。 - 請求項1に記載のX線透視画像におけるモアレの除去方法において、
前記画像平滑化ステップの画像平滑化処理は、所定の行列を用いた行列演算であり、前記行列の行数は、モアレの1周期分の画素数以上であることを特徴とするX線透視画像におけるモアレの除去方法。 - X線透視画像におけるモアレの除去方法において、
X線透視画像に写り込んでいるモアレの周波数を求めるモアレ周波数導出ステップと、
欠損画素から前記モアレ1周期分の整数倍だけ離間した画素を参照して前記欠損画素を補完することにより、第1中間画像を形成する欠損画素予備補完ステップと、
前記第1中間画像を周波数解析し、前記第1中間画像に写り込んだモアレを除去して第2中間画像を形成するモアレ除去ステップと、
前記第2中間画像において、前記欠損画素予備補完ステップにおいて補完した欠損画素に隣接する画素を参照してさらに前記補完した欠損画素を補完する欠損画素再補完ステップとを備えることを特徴とするX線透視画像におけるモアレの除去方法。 - (A)X線ビームを照射するX線源と、
(B)前記X線ビームを検出するX線検出手段と、
(C)前記X線検出手段と、前記X線源の介在する位置に設けられた散乱X線を除去するX線グリッドと、
(D)X線透視画像に写り込んでいるモアレの周波数を求めるモアレ周波数導出手段と、
(E)欠損画素から前記モアレ1周期分の整数倍だけ離間した画素を参照して前記欠損画素を補完することにより第1中間画像を形成する欠損画素予備補完手段と、
(F)前記第1中間画像を周波数解析し、前記第1中間画像に写り込んだモアレを除去して第2中間画像を形成するモアレ除去手段と、
(G)前記第1中間画像に画像平滑化処理を行い、第3中間画像を形成する画像平滑化手段と、
(H)前記第2中間画像と前記第3中間画像とを重ね合わせて前記欠損画素を再び補完する第1欠損画素再補完手段とを備えることを特徴とするX線撮像装置。 - 請求項4に記載のX線透視画像において、
(G1)前記画像平滑化手段が行う画像平滑化処理は、所定の行列を用いた行列演算であり、前記行列の行数は、モアレの1周期分の画素数以上であることを特徴とするX線撮像装置。 - (A)X線ビームを照射するX線源と、
(B)前記X線ビームを検出するX線検出手段と、
(C)前記X線検出手段と、前記X線源の介在する位置に設けられた散乱X線を除去するX線グリッドと、
(D)X線透視画像に写り込んでいるモアレの周波数を求めるモアレ周波数導出手段と、
(E)欠損画素から前記モアレ1周期分の整数倍だけ離間した画素を参照して前記欠損画素を補完することにより第1中間画像を形成する欠損画素予備補完手段と、
(F)前記第1中間画像を周波数解析し、前記第1中間画像に写り込んだモアレを除去して第2中間画像を形成するモアレ除去手段と、
(I)前記第1中間画像に属する予備的に補完された予備補完画素の画素値を前記第2中間画像における前記予備補完画素と同一位置にある画素に隣接する隣接画素の画素値に置き換えることにより、前記第1中間画像の予備補完画素を再び補完する第2欠損画素再補完手段とを備えることを特徴とするX線撮像装置。
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