JP2010187827A - X-ray image processing method, x-ray image processor, program, and x-ray image capturing apparatus - Google Patents

Abstract

An X-ray image processing method, an X-ray image processing apparatus, a program, and an X-ray image photographing apparatus capable of removing unnecessary information from an X-ray image and creating an X-ray image that is more accurate and clear than before. To do.
A phase image and an absorption image of an X-ray image obtained by photographing the same part of a subject are acquired, and contour information of each part is extracted from the absorption image to create a first image. Subsequently, contour information that exists in common at the corresponding pixel positions of the phase image and the first image is specified, and the second image is created by removing the specified common contour information from the phase image. To do. Subsequently, a pixel having a pixel value equal to or less than the first threshold is removed from the second image to create a third image, and the absorption image and the third image are added to create a fourth image. .
[Selection] Figure 3

Description

  The present invention relates to an X-ray image processing method, an X-ray image processing apparatus, a program, and an X-ray image imaging apparatus for creating an X-ray image by combining an absorption image and a phase image of the same part obtained by X-ray imaging of a subject. Is.

  In an X-ray image captured image, conventionally, when X-rays pass through a subject such as a human body, an absorption image (by utilizing the X-ray dose absorbed depending on the density of each tissue (each part) of the subject varies). Absorption contrast image) (absorption imaging) has been the mainstream.

  On the other hand, in recent years, when X-rays pass through a subject, the X-rays are slightly refracted at a contour portion of each subject tissue (a boundary portion between tissues), for example, a boundary portion between cartilage and joint fluid. Thus, a phase image (phase contrast image) is created (phase imaging) by utilizing the phase change. Also, an X-ray image is created by combining an absorption image and a phase image.

  The phase image is an image in which the contour portion of each tissue of the subject is emphasized, and the soft tissue contour information that is difficult to draw in the absorption image, such as cartilage, breast, muscle, tendon, ligament, blood vessel, etc. And the outline of the surrounding tissue can be drawn clearly. Therefore, in a medical image, it is useful for diagnosis of a lesion site.

  The phase image includes not only information (contour information) on the contour portion of each tissue of the subject but also information on the absorption image, information on the skin surface, and the like. Here, the information on the absorption image is contour information obtained also in the absorption image, such as a boundary portion between a bone and a soft tissue. The information on the skin surface is unnecessary information in the contour information of the soft tissue, such as skin wrinkles (the boundary between the skin and air).

  For example, if the information on the skin surface included in the phase image is drawn while being superimposed on the soft tissue, there is a risk of misdiagnosis in the medical image. Therefore, it is not limited to information on the skin surface. For example, in the above-described medical image, by removing information unnecessary for diagnosis from the X-ray image and extracting only necessary information, images of bone tissue and soft tissue are extracted. It is desirable to create a more accurate and clear image.

  Here, there are Patent Documents 1 to 4 as prior art documents considered to be relevant to the present invention. Conventionally, extracting necessary information using a plurality of images has been performed as a temporal subtraction method (Patent Document 1) or an energy subtraction method (Patent Documents 2 and 3). Conventionally, it has been proposed to display an absorption image and a phase image so as to overlap each other, to replace at least a part of the absorption image with an image of a region of interest of the phase image, and the like (Patent Document 4).

JP 2001-8099 A JP-A-8-294054 JP 59-83147 A JP 2005-13572 A

  An object of the present invention is to remove an unnecessary information from an X-ray image and create an X-ray image processing method, X-ray image processing apparatus, program, and X-ray image photographing capable of creating an X-ray image that is more accurate and clear than before. To provide an apparatus.

In order to achieve the above object, the present invention acquires a phase image and an absorption image of an X-ray image obtained by photographing the same part of a subject,
Extracting the contour information of each part from the absorption image to create a first image,
Identifying contour information that exists in common at corresponding pixel positions of the phase image and the first image;
The second image is created by removing the specified common contour information from the phase image,
Removing a pixel having a pixel value equal to or less than a first threshold from the second image to create a third image;
The X-ray image processing method is characterized in that the fourth image is created by adding the absorption image and the third image.

  Here, it is preferable that the removal of the contour information is to delete the contour information included in the phase image.

  Alternatively, it is preferable that the removal of the contour information is to reduce a pixel value of a pixel included in the contour information included in the phase image to be equal to or less than a second threshold value. For example, pixels having a pixel value equal to or smaller than the second threshold value may be removed.

  The second threshold value is preferably given from the outside.

  Alternatively, it is preferable that the second threshold value is set according to the contrast of the entire X-ray image. For example, the difference between the maximum pixel value and the minimum pixel value in the X-ray image is d, and a coefficient for separating soft tissue contour information and unnecessary information as the soft tissue contour information is α. The threshold value of 2 may be set to the minimum pixel value + α × d.

  The first threshold value is preferably set to a value smaller than the pixel value of the pixel at the soft tissue boundary.

  Moreover, it is preferable to correct the distortion between the acquired absorption image and the phase image after acquiring the phase image and the absorption image.

Further, the present invention provides means for acquiring a phase image and an absorption image of an X-ray image obtained by photographing the same part of a subject,
Means for extracting the contour information of each part from the absorption image and creating a first image;
Means for identifying contour information that exists in common at corresponding pixel positions of the phase image and the first image;
Means for removing the identified common contour information from the phase image to create the second image;
Means for removing a pixel having a pixel value equal to or less than a first threshold from the second image to create a third image;
An X-ray image processing apparatus comprising: means for adding the absorption image and the third image to create a fourth image.

  Here, it is preferable that the removal of the contour information is to delete the contour information included in the phase image.

  Alternatively, it is preferable that the removal of the contour information is to reduce a pixel value of a pixel included in the contour information included in the phase image to be equal to or less than a second threshold value. For example, the removal of the contour information may be removal of a pixel having a pixel value equal to or less than the second threshold value.

  The second threshold is preferably given from the outside.

  Alternatively, it is preferable to further include means for setting the second threshold according to the contrast of the entire X-ray image. For example, the means for setting the second threshold value according to the contrast of the entire X-ray image includes d as a difference between the maximum pixel value and the minimum pixel value in the X-ray image, and contour information of the soft tissue and the soft part The second threshold value may be set to the minimum pixel value + α × d, where α is a coefficient for separating unnecessary information as tissue contour information.

  The first threshold value is preferably set to a value smaller than the pixel value of the pixel at the soft tissue boundary.

  Furthermore, it is preferable to have a means for correcting distortion between the acquired absorption image and phase image.

  The present invention also provides a program for causing a computer to execute any of the X-ray image processing methods described above.

The present invention also provides an X-ray imaging unit that images an object and outputs an X-ray image;
An X-ray image capturing apparatus according to any one of the above, comprising: an image processing unit that performs image processing on an X-ray image captured by the X-ray imaging unit. provide.

  In the present invention, unnecessary information is removed from the phase image, and the absorption image and the phase image are added. Therefore, according to the present invention, it is possible to create an X-ray image that is more accurate and clear than before. In particular, as medical images, it is possible to give accurate and clear outline information of soft tissues that were difficult to observe conventionally, so it is possible to grasp the state of bone tissue and soft tissues more accurately than before. This can improve the efficiency of diagnosis and prevent misdiagnosis.

  Hereinafter, an X-ray image processing method, an X-ray image processing apparatus, a program, and an X-ray image photographing apparatus of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

  FIG. 1 is a block diagram of an embodiment showing a configuration of an X-ray imaging apparatus according to the present invention. An X-ray imaging apparatus 10 shown in FIG. 1 creates an X-ray image by combining an absorption image and a phase image of the same part obtained by X-ray imaging of a subject such as a human body. The imaging apparatus 10 includes an X-ray imaging unit 12, an image processing unit 14 that is an image processing apparatus according to the present invention, a display unit 16, and an output unit 18.

  The X-ray imaging unit 12 captures an X-ray image of a subject, and as shown in FIG. 2, an X-ray source 20, an angle analyzer (angle analysis plate) 22 made of silicon single crystal, and two digital The X-ray image detectors 24a and 24b are configured. An analyzer 22 is disposed on the downstream side in the irradiation direction of X-rays irradiated (exposed) from the X-ray source 20, and detectors 24 a and 24 b are disposed on the downstream side of the analyzer 22.

  Although not shown in FIG. 2, the X-ray source 20 generates monochromatic parallel X-rays in a predetermined region from broad X-rays including X-rays having a wavelength in a predetermined band, and irradiates (exposes) the object 26. ) The X-rays emitted from the X-ray source 20 are directly incident on the analyzer 22 when the subject 26 is not present, and the X-rays transmitted through the subject 26 are incident on the analyzer 22 when the subject 26 is present.

  The analyzer 22 has, for example, a rectangular plate shape, and its plate surface (X-ray light-receiving surface) is a surface perpendicular to the X-ray irradiation direction so that the maximum contrast can be obtained in a captured X-ray image. Is inclined at a predetermined angle in one direction. When the X-rays incident on the analyzer 22 pass through the inside of the analyzer 22, they are repeatedly reflected by a large number of crystal lattice planes in the silicon single crystal, and separated into X-rays of an absorption image and X-rays of a phase image. Details of the analyzer 22 are disclosed in, for example, Japanese Patent Application Laid-Open No. 2003-329617.

  The detectors 24a and 24b detect X-rays of the absorption image and X-rays of the phase image separated by the analyzer 22 and output digital image data of the phase image and digital image data of the absorption image, respectively. The absorption image and the phase image separated by the analyzer 22 are output from the analyzer 22 at a predetermined angle. The detectors 24a and 24b have their plate surfaces (X-ray light receiving surfaces) arranged in a direction perpendicular to the traveling directions of the phase image and the absorption image. An example of the detectors 24a and 24b is a flat panel (FPD) for X-ray detection.

  The X-ray imaging unit 12 irradiates X-rays toward the direction of the subject 26 (that is, the direction of the analyzer 22) positioned at a predetermined position between the X-ray source 20 and the analyzer 22 during X-ray imaging. An X-ray image of the subject 26 is taken. The photographed X-ray image includes an absorption image and a phase image. The X-ray imaging unit 12 outputs digital image data of a captured X-ray image, that is, digital image data of an absorption image and digital image data of a phase image.

  Here, the absorption image is an image generated based on the intensity information of the X-ray that has passed through the subject 26. On the other hand, the phase image is an image generated based on the phase information of the X-ray transmitted through the subject 26. FIG. 2 shows a graph of an absorption image and a phase image obtained by X-ray imaging. In these graphs, the vertical axis toward the detectors 24a and 24b represents the X-ray signal intensity, and the horizontal axis represents the positions of the detectors 24a and 24b.

  Subsequently, the image processing unit 14 performs predetermined image processing on the X-ray image captured by the X-ray imaging unit 12. For example, the computer and the X-ray image processing method according to the present invention are executed on the computer. It is comprised by the program for making it.

  In addition, the display unit 16 displays a photographed X-ray image, such as a liquid crystal display.

  The output unit 18 includes, for example, a thermal printer that prints out a captured X-ray image, a storage device that stores digital image data of the X-ray image, and the like.

  Next, an operation when X-ray imaging of a subject (for example, a human body) will be described.

  When X-ray imaging of the subject 26 is performed, a predetermined portion of the subject 26 to be X-rayed is positioned at a predetermined position between the X-ray source 20 and the analyzer 22 of the X-ray imaging unit 12. Thereafter, when X-rays are emitted from the X-ray source 20 toward the subject 26, the X-rays emitted from the X-ray source 20 pass through the subject 26 and are absorbed by the analyzer 22 with the phase image (X-rays). The image is separated into X-rays.

  The X-ray refracted by the subject 26 passes through the analyzer 22 and is detected by the detector 24a, and is output from the detector 24a as a phase image (digital image data thereof). On the other hand, X-rays that have not been refracted by the subject 26 (X-rays that have been absorbed by the subject and whose signal intensity has been weakened) pass through the analyzer 22 and are detected by the detector 24b, and are absorbed by the detector 24b. Image data).

  As shown in FIGS. 3 and 4, the image processing unit 14 performs image processing shown in steps S <b> 1 to S <b> 5 below using the phase image and the absorption image according to the X-ray image processing method according to the present invention.

  First, a phase image A (FIG. 4A) and an absorption image B (FIG. 4B) of an X-ray image obtained by X-ray imaging of the same portion of the subject 26 are acquired from the X-ray imaging unit 12 (S1). .

  In the following, the contour information of each tissue, in the example shown in FIG. 4B, is extracted from the absorption image B, and the contour information of the bone is extracted to create an image B ′ (not shown) (S2). Here, the method for extracting the contour information is not limited at all. For example, a method of applying a gradient filter, a sobel filter, a Laplacian filter, or the like can be used. Moreover, you may utilize the method disclosed by Unexamined-Japanese-Patent No. 2002-36661 regarding this applicant.

  Subsequently, contour information that exists in common at corresponding pixel positions in the phase image A and the image B ′ is specified (S3), and the specified common contour information is removed from the phase image A to obtain the image C. (FIG. 4C) is created (S4). Thereby, contour information included only in the phase image A (contour information not included in the absorption image B) is obtained. At this time, it is not always necessary to match the contrast of the phase image A and the image B ′.

  Here, the removal of the contour information is performed by deleting the contour information included in the phase image A (the pixel value of the pixel included in the contour information is set to zero) or by setting the pixel value of the pixel included in the contour information to a predetermined value. The threshold value (second threshold value) (for example, a value that cannot be visually recognized) is reduced to a value equal to or lower than the threshold value.

  Here, the second threshold value may be given from the outside, or may be automatically set by the image processing unit 14 in accordance with the contrast of the entire X-ray image. When the image processing unit 14 automatically determines the second threshold value, the difference between the maximum pixel value and the minimum pixel value in the image is set to d, and the second threshold value is set to the minimum pixel value + α × d. Here, α is a coefficient for separating the outline information of the soft tissue drawn with a strong contrast and the information unnecessary for the outline information of the soft tissue drawn with a weak contrast, and may be set as appropriate. However, for example, a numerical value such as 0.5 is set. Further, for example, a pixel having a pixel value equal to or smaller than the second threshold may be removed (the pixel value is set to zero).

  Subsequently, an image D (FIG. 4D) is created by removing pixels having a pixel value equal to or smaller than a predetermined threshold from the image C (S5). The image C includes unnecessary information including information on the skin surface and the like, but this unnecessary information is smaller in contrast than the soft tissue boundary as compared with the pixel value of the pixel at the soft tissue boundary. A threshold value (first threshold value) may be set. By step S5, unnecessary information including information on the skin surface and the like can be removed, and only necessary information can be left.

  Subsequently, the absorption image B and the image D are added (the pixel values of the corresponding pixels are added) to create an image E (FIG. 4E) (S6). Image D includes, in addition to absorption image B, contour information included only in phase image A (contour information not included in absorption image B), and unnecessary information including skin surface information and the like. Is removed. Therefore, in step S6, it is possible to create an X-ray image that is more accurate and clear than before.

  When the image processing by the image processing unit 14 ends, the X-ray image E after the image processing is displayed on the display unit 16. If necessary, the image is printed on a recording medium such as a thermal film by a thermal printer and stored in a storage medium such as a database (S7).

  The X-ray image created by the imaging apparatus 10 can provide diagnostically useful information as a medical image that cannot be obtained only by the absorption image by combining the absorption image and the phase image from which unnecessary information is removed. In particular, by providing contour information of soft tissue that has been difficult to observe as a medical image, it is possible to grasp the state of bone tissue and soft tissue more accurately than before, making diagnosis more efficient, Effects such as prevention of misdiagnosis can be obtained.

  In addition, when distortion such as local deformation due to misalignment, magnification (enlargement / reduction), rotation, heartbeat, or the like occurs between the phase image A and the absorption image B, before starting image processing. It is desirable to correct (calibrate) this distortion. Note that the distortion correction method is not limited.

  In the imaging apparatus 10, the configurations of the X-ray imaging unit 12, the image processing unit 14, the display unit 16, and the output unit 18 are not limited at all, and various configurations that perform similar functions can be used. Moreover, the display part 16 and the output part 18 are not an essential component, and should just be provided suitably as needed. That is, step S7 is not an essential step, and may be appropriately performed as necessary.

  The present invention uses a phase image and an absorption image as the X-ray image, but the method for acquiring these images is not limited at all. The example of FIG. 2 applies the dark field method to obtain an absorption image and a phase image at the same time. However, for example, other methods and means including the Talbot method can be applied to obtain a phase image. Although it is desirable to simultaneously acquire the absorption image and the phase image by one X-ray imaging, the absorption image and the phase image may be acquired separately by performing X-ray imaging twice.

  In addition, it is not essential that the X-ray imaging unit 12 captures an absorption image and a phase image. For example, a designated absorption image and phase image are selected from X-ray images that are captured in advance and stored in a database. It is also possible to obtain and subject to image processing.

The present invention is basically as described above.
Although the present invention has been described in detail above, the present invention is not limited to the above-described embodiment, and it is needless to say that various improvements and modifications may be made without departing from the gist of the present invention.

It is a block diagram of one embodiment showing composition of an X-ray imaging device concerning the present invention. It is a conceptual diagram showing the structure of the X-ray imaging part shown in FIG. It is a flowchart showing operation | movement of the X-ray imaging apparatus shown in FIG. (A)-(E) are the conceptual diagrams showing the image AE created by the image processing part shown in FIG.

DESCRIPTION OF SYMBOLS 10 X-ray imaging device 12 X-ray imaging part 14 Image processing part 16 Display part 18 Output part 20 X-ray source 22 Angle analyzer (angle analysis board)
24a, 24 Digital X-ray image detector 26 Subject

Claims (20)

Obtain a phase image and an absorption image of an X-ray image of the same part of the subject,
Extracting the contour information of each part from the absorption image to create a first image,
Identifying contour information that exists in common at corresponding pixel positions of the phase image and the first image;
The second image is created by removing the specified common contour information from the phase image,
Removing a pixel having a pixel value equal to or less than a first threshold from the second image to create a third image;
An X-ray image processing method comprising: adding the absorption image and the third image to create a fourth image.   The X-ray image processing method according to claim 1, wherein the removal of the contour information is to delete the contour information included in the phase image.   The X-ray image processing method according to claim 1, wherein the removal of the contour information is to reduce a pixel value of a pixel included in the contour information included in the phase image to a second threshold value or less.   The X-ray image processing method according to claim 3, wherein a pixel having a pixel value equal to or less than the second threshold is removed.   5. The X-ray image processing method according to claim 3, wherein the second threshold value is given from the outside.   The X-ray image processing method according to claim 3, wherein the second threshold value is set according to a contrast of the entire X-ray image.   The difference between the maximum pixel value and the minimum pixel value in the X-ray image is d, the coefficient for separating the soft tissue contour information and unnecessary information as the soft tissue contour information is α, and the second The X-ray image processing method according to claim 6, wherein the threshold is set to a minimum pixel value + α × d.   The X-ray image processing method according to claim 1, wherein the first threshold value is set to a value smaller than a pixel value of a pixel at a soft tissue boundary.   The X-ray image processing method according to claim 1, wherein after acquiring the phase image and the absorption image, distortion between the acquired absorption image and the phase image is corrected. Means for acquiring a phase image and an absorption image of an X-ray image obtained by imaging the same part of the subject;
Means for extracting the contour information of each part from the absorption image and creating a first image;
Means for identifying contour information that exists in common at corresponding pixel positions of the phase image and the first image;
Means for removing the identified common contour information from the phase image to create the second image;
Means for removing a pixel having a pixel value equal to or less than a first threshold from the second image to create a third image;
An X-ray image processing apparatus comprising: means for adding the absorption image and the third image to create a fourth image.   The X-ray image processing apparatus according to claim 10, wherein the removal of the contour information is to delete the contour information included in the phase image.   The X-ray image processing apparatus according to claim 10, wherein the removal of the contour information is to reduce a pixel value of a pixel included in the contour information included in the phase image to a second threshold value or less.   13. The X-ray image processing apparatus according to claim 12, wherein the removal of the contour information is to remove pixels having a pixel value equal to or less than the second threshold value.   The X-ray image processing apparatus according to claim 12, wherein the second threshold is given from outside.   The X-ray image processing apparatus according to claim 12, further comprising means for setting the second threshold according to a contrast of the entire X-ray image.   The means for setting the second threshold according to the contrast of the entire X-ray image is d for the difference between the maximum pixel value and the minimum pixel value in the X-ray image, and contour information of the soft tissue and the soft tissue 16. The X-ray image processing apparatus according to claim 15, wherein the second threshold is set to a minimum pixel value + α × d, where α is a coefficient for separating unnecessary information as contour information.   The X-ray image processing apparatus according to claim 10, wherein the first threshold value is set to a value smaller than a pixel value of a pixel at a soft tissue boundary.   The X-ray image processing apparatus according to claim 10, further comprising means for correcting distortion between the acquired absorption image and phase image.   A program for causing a computer to execute the X-ray image processing method according to claim 1. An X-ray imaging unit that images a subject and outputs an X-ray image;
The X-ray image processing apparatus according to claim 10, further comprising an image processing unit that performs image processing on the X-ray image captured by the X-ray imaging unit. Image shooting device.

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