JP6677263B2 - X-ray equipment - Google Patents

Description

  The present invention relates to an X-ray imaging apparatus, and more particularly to an X-ray imaging apparatus that captures an X-ray image using a grid that removes X-rays scattered by a subject.

  2. Description of the Related Art Conventionally, an X-ray imaging apparatus that captures an X-ray image using a grid has been known. Such an X-ray imaging apparatus is disclosed in, for example, JP-A-2002-152467.

  The X-ray imaging apparatus disclosed in Japanese Patent Application Laid-Open No. 2002-152467 includes an X-ray irradiator that irradiates the subject with X-rays, an X-ray detector that detects X-rays transmitted through the subject, and an X-ray detector. A grid disposed on the detection surface side of the line detection unit and removing scattered X-rays. The grid is a grid-like member in which linear shielding portions made of lead that absorb X-rays are arranged at a small interval (slit).

  When X-ray imaging is performed using a grid, a periodic moire pattern of a striped pattern appears due to a difference between the resolution (pixel pitch) of the X-ray detection unit and the pitch of the grid (interval between shielding units). . The X-ray imaging apparatus disclosed in Japanese Patent Application Laid-Open No. 2002-152467 performs a Fourier transform on an X-ray image to extract harmonic components of a moiré pattern, and removes the first to fourth harmonic components. The image processing unit includes an image processing unit that outputs an X-ray processed image from which the moiré pattern has been removed.

JP-A-2002-152467

  However, when removing the harmonic component of the moiré pattern, image components other than the moiré are also removed, which causes a problem that the resolution of the X-ray image is deteriorated.

  SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to unnecessarily degrade the resolution of an X-ray image by removing harmonic components of a moire pattern. An object of the present invention is to provide an X-ray imaging apparatus capable of suppressing the above.

In order to achieve the above object, an X-ray imaging apparatus according to one aspect of the present invention includes an X-ray irradiator that irradiates an X-ray to a subject, an X-ray detector that detects X-rays transmitted through the subject, , A grid arranged on the detection surface side of the X-ray detection unit to remove scattered X-rays, and a moire pattern removal process caused by the grid reflected in the X-ray image obtained by the X-ray detection unit, An image processing unit that outputs an X-ray processed image after the removal processing. The image processing unit extracts a harmonic component forming a moiré pattern from the X-ray image, and extracts a harmonic component as a first-order harmonic component. In accordance with the intensity of the second or third higher harmonic component higher than the first harmonic component, the intensity of the higher harmonic component is divided by the intensity of the frequency component near the higher harmonic component. When the calculated relative intensity has a peak equal to or greater than the threshold It is configured to change the contents of the removal process.

  In the X-ray imaging apparatus according to one aspect of the present invention, as described above, a harmonic component constituting a moiré pattern is extracted from an X-ray image, and a first harmonic component as a first harmonic component is extracted. Also, an image processing unit for changing the content of the removal processing is provided according to the intensity of the second or third higher harmonic component of the higher order. By taking into account the influence of the degradation of the resolution due to the removal of the second or third higher harmonic component and the influence of the deterioration of the image quality due to the reflection of the moiré pattern without removal, for example, Whether or not to remove the harmonic component can be changed according to the intensity of the higher harmonic component in each X-ray image. As a result, it becomes possible not to remove high-order harmonic components that do not need to be removed, so that it is possible to suppress unnecessary degradation of the resolution of the X-ray image due to removal of the harmonic components of the moire pattern. . It is not necessary to remove fourth-order or higher harmonic components because the influence of reflection is low in the first place.

  In the X-ray imaging apparatus according to the one aspect, preferably, the image processing unit generates a higher-order harmonic component and a higher-order harmonic component lower than the higher-order harmonic component according to the intensity of the higher-order harmonic component. It is configured to switch between a first removal process for removing and a second removal process for removing higher harmonic components lower than the higher harmonic components without removing the higher harmonic components. According to this structure, when the intensity of the high-order harmonic component is high, the high-order harmonic component can be removed by the first removal processing, and when the intensity of the high-order harmonic component is not high, the first removal process can be performed. High order harmonic components can be left by the 2 removal processing. Further, even in a configuration in which the removal processing is switched, higher-order harmonic components than lower-order harmonic components can be removed, so that reflection of a moire pattern can be effectively removed.

  In this case, preferably, the higher harmonic component is a third harmonic component, and the first removal process is a removal process for removing the first harmonic component, the second harmonic component, and the third harmonic component. The second removal process is a removal process for removing the first harmonic component and the second harmonic component without removing the third harmonic component. Here, the higher the harmonic component, the less the influence of the reflection. Therefore, while reliably removing the first harmonic component and the second harmonic component, which are relatively greatly affected by the reflection, whether or not the third harmonic component is removed on a case-by-case basis depending on the intensity. Can be selected, so that reflection of the moiré pattern can be effectively removed while effectively suppressing a decrease in resolution due to the moiré pattern removal processing.

  In the configuration in which the first removal processing and the second removal processing are switched in accordance with the intensity of the high-order harmonic component, preferably, the image processing unit includes a high-order harmonic component that is equal to or more than a threshold as compared with a nearby frequency component. The first removal processing is performed when the relative intensity has the peak of the relative intensity, and the second removal processing is performed when the high-order harmonic component has the relative intensity peak less than the threshold. With this configuration, the necessity of removal according to the intensity of the higher-order harmonic component can be easily determined using the threshold. Then, by setting an appropriate threshold value, it is possible to easily switch between the first removal processing for removing high-order harmonic components and the second removal processing for not removing high-order harmonic components as necessary. Becomes

  In this case, preferably, the image processing unit is configured to be able to change the set value of the threshold. Here, the threshold value for determining whether or not to remove high-order harmonic components differs depending on the device configuration of the X-ray imaging device (characteristics of the X-ray irradiator and X-ray detector, grid pitch, and the like). Therefore, by making the set value of the threshold value changeable, the image processing unit can be shared only by changing the set value of the threshold value, for example, when the apparatus configuration is changed or between X-ray imaging apparatuses having different specifications. In addition, the threshold value can be easily optimized.

  In the X-ray imaging apparatus according to the one aspect, preferably, the image processing unit extracts a high-order harmonic component from the removed image from which a higher-order harmonic component lower than the higher-order harmonic component has been removed. Then, the content of the removal processing on the removed image is changed according to the intensity of the higher-order harmonic component. According to this structure, since the high-order harmonic components are extracted after removing the low-order harmonic components, a part of the low-order (first and second-order or first-order) harmonic components is removed. It is possible to suppress erroneous recognition as a higher-order harmonic component and omission of a higher-order harmonic component due to being mixed with a lower-order harmonic component. As a result, higher-order harmonic components can be more reliably extracted and appropriate removal processing can be performed.

  In the X-ray imaging apparatus according to the one aspect, preferably, the image processing unit is configured to extract the high-order harmonic component in a frequency range including the estimated value of the peak frequency of the high-order harmonic component, The processing unit is configured to be able to change the set value of the frequency range. Here, since there is an error in the grid pitch, the peak frequency of the higher-order harmonic component does not always match the estimated value. Therefore, by extracting the higher-order harmonic components in the frequency range including the estimated value of the peak frequency, the higher-order harmonic components can be more reliably extracted. Further, the frequency range for performing the extraction differs depending on the device configuration of the X-ray imaging device (the characteristics of the X-ray irradiator and the X-ray detector, the pitch of the grid, etc.). Therefore, by making the setting value of the frequency range changeable, the image processing unit can be changed only by changing the setting value of the frequency range, for example, when the apparatus configuration is changed or between X-ray imaging apparatuses having different specifications. Can be standardized.

  As described above, according to the present invention, it is possible to prevent the resolution of an X-ray image from being unnecessarily deteriorated due to removal of a harmonic component of a moiré pattern.

FIG. 1 is a schematic diagram illustrating an overall configuration of an X-ray imaging apparatus according to an embodiment of the present invention. FIG. 3 is a schematic diagram for explaining an X-ray image. 7 is a frequency spectrum showing an example of a Fourier transform result for an X-ray image. 9 is a frequency spectrum showing an example of a Fourier transform result for a removed image. FIG. 4 is a schematic diagram for explaining a first removal process and a second removal process by an image processing unit. FIG. 6 is a diagram illustrating an example 1 of spectrum intensity for each frequency division in a frequency range. FIG. 9 is a diagram illustrating a second example of the spectrum intensity for each frequency division in the frequency range. FIG. 9 is a schematic diagram for explaining a method of obtaining a luminance change amount of a target pixel. FIG. 9 is a schematic diagram for describing a method of acquiring a luminance change amount in units of a section area. FIG. 4 is a schematic diagram for explaining an X-ray processed image generated by a first removal process. 5 is a flowchart for explaining X-ray image processing of the X-ray imaging apparatus according to one embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Configuration of X-ray imaging apparatus)
First, an overall configuration of an X-ray imaging apparatus 100 according to an embodiment of the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the X-ray imaging apparatus 100 according to the present embodiment irradiates the subject P with X-rays and detects the X-rays transmitted through the subject P, thereby forming a transmitted image inside the subject P. This is an apparatus for capturing an X-ray image as a target. The X-ray imaging apparatus 100 according to the present embodiment is an X-ray diagnostic apparatus (medical X-ray apparatus) used for clinical diagnosis in the medical field. The subject P is mainly a human (patient).

  The X-ray imaging apparatus 100 includes an X-ray irradiator 1 that irradiates the subject P with X-rays, an X-ray detector 2 that detects X-rays transmitted through the subject P, and a detection surface side of the X-ray detector 2. And a grid 3 for removing scattered X-rays.

  The X-ray irradiator 1 and the X-ray detector 2 are arranged to face each other with the top plate 4 on which the subject P is placed interposed therebetween. The grid 3 is arranged at a position between the X-ray detector 2 and the top 4. The X-ray irradiator 1, the X-ray detector 2, and the grid 3 are movably supported by a moving mechanism 5. The top 4 can be moved in the horizontal direction by the top driving unit 6. The X-ray irradiator 1, the X-ray detector 2, the grid 3, and the top 4 are moved via the moving mechanism 5 and the top drive 6 so that the region of interest of the subject P can be imaged. The X-ray imaging apparatus 100 includes a control unit 7 that controls the moving mechanism 5 and the top driving unit 6.

  The X-ray irradiator 1 includes an X-ray tube 1a that generates X-rays by supplying power, and is connected to a high-voltage generator (not shown). The X-ray tube 1a is arranged with the X-ray emission direction facing the detection surface of the X-ray detection unit 2. The X-ray irradiator 1 is connected to the controller 7. The controller 7 controls the X-ray irradiator 1 according to preset imaging conditions such as a tube voltage, a tube current, and an X-ray irradiation time, and generates X-rays from the X-ray tube 1a.

  The X-ray detector 2 detects X-rays emitted from the X-ray irradiator 1 and transmitted through the subject P, and outputs a detection signal corresponding to the detected X-ray intensity. The X-ray detector 2 is configured by, for example, an FPD (Flat Panel Detector). Further, the X-ray imaging apparatus 100 includes an image processing unit 8 that acquires an X-ray detection signal from the X-ray detection unit 2 and generates an X-ray image 21 (see FIG. 2). The X-ray detection unit 2 outputs an X-ray image (detection signal) having a predetermined resolution to the image processing unit 8.

  The grid 3 is a grid-like member in which linear shielding portions made of lead that absorb X-rays are arranged at a minute interval (slit). The grid 3 is arranged such that, for example, the shielding portions extend in the vertical direction (Y direction in FIG. 2) of the X-ray image 21 and are arranged at a predetermined pitch in the horizontal direction.

  The control unit 7 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The CPU executes a predetermined control program to control each unit of the X-ray imaging apparatus 100. Functions as a control unit for controlling. The control unit 7 controls the X-ray irradiation unit 1 and controls the driving of the moving mechanism 5 and the top plate driving unit 6.

  The X-ray imaging apparatus 100 includes a display unit 9, an operation unit 10, and a storage unit 11. The display unit 9 is a monitor such as a liquid crystal display. The operation unit 10 is configured to include, for example, a keyboard and a mouse, a touch panel, or another controller. The storage unit 11 is configured by a storage device such as a hard disk drive. The control unit 7 is configured to perform control for displaying the image generated by the image processing unit 8 on the display unit 9. The control unit 7 is configured to receive an input operation via the operation unit 10. The imaging conditions of the X-ray image 21 are preset in the control unit 7 before imaging by being read via the operation unit 10 or from the storage unit 11. Further, the control unit 7 is configured to cause the storage unit 11 to store image data, photographing conditions, and various setting values.

  The image processing unit 8 includes, for example, a CPU, a ROM, a RAM, and the like that are common to the control unit 7. That is, the image processing unit 8 is configured on software by causing the CPU to execute an image processing program. The image processing unit 8 may be configured by dedicated hardware (processor) separate from the control unit 7.

  As shown in FIG. 2, the image processing unit 8 performs a removal process of the moire pattern MP caused by the grid 3 reflected on the X-ray image 21 obtained by the X-ray detection unit 2, and the X-ray after the removal process It is configured to output the processed image 22 (see FIG. 5) to the control unit 7. The X-ray processed image 22 processed by the image processing unit 8 is displayed on the display unit 9 and stored in the storage unit 11.

(Moire pattern removal processing)
Hereinafter, the moire pattern removal processing by the image processing unit 8 will be described with reference to FIGS.

  In the present embodiment, as shown in FIG. 2, the image processing unit 8 extracts a harmonic component constituting the moiré pattern MP from the X-ray image 21. The moiré pattern MP is a periodic stripe pattern reflected on the X-ray image 21 due to the difference between the resolution (pixel pitch) of the X-ray detection unit 2 and the pitch of the grid 3 (interval between shielding portions).

  The moiré pattern MP is formed as a stripe pattern extending along the direction of the shielding portion of the grid 3 (Y direction in FIG. 2). The image processing unit 8 performs a one-dimensional Fourier transform on the X-ray image 21 on which the moiré pattern MP is reflected in the X direction orthogonal to the stripes of the moiré pattern MP. By the Fourier transform, a spectral intensity distribution of the X-ray image 21 as shown in FIG. 3 is obtained.

  The image processing unit 8 changes the content of the removal processing in accordance with the intensity of the second or third higher harmonic component higher than the first harmonic component 31 as the first harmonic component. Is configured. In the present embodiment, an example in which the image processing unit 8 is configured to change the content of the removal processing according to the intensity of the third harmonic component 33 will be described. The third harmonic component 33 is an example of the “higher harmonic component” in the claims.

  Hereinafter, each stage of the removal processing will be described in detail.

<Extraction of harmonic components>
The image processing unit 8 detects a harmonic component by detecting a peak of the spectrum. The image processing unit 8 extracts a first harmonic component 31, a second harmonic component 32, and a third harmonic component 33, respectively, as shown in FIG.

  As an example of the present embodiment, the resolution of the X-ray detector 2 has a pixel pitch of, for example, 139 μm, and the Nyquist frequency is about 3.6 [lp / mm]. The pitch of the grid 3 is, for example, 50 [lp / cm] = 5 [lp / mm]. In this case, the frequency component higher than the Nyquist frequency is folded around the Nyquist frequency (so-called aliasing), so that the peak of the first harmonic component 31 as the first harmonic component is 2.2 [lp / mm]. ] (That is, 3.6- (5.0-3.6) = 2.2 [lp / mm]).

  Since there is an error in the pitch of the grid 3, the first harmonic component 31 does not always appear exactly at 2.2 [lp / mm]. Therefore, the image processing unit 8 detects the peak of the first harmonic component 31 near the estimated value (2.2 [lp / mm]) from the spectral distribution. FIG. 3 shows an example in which the first harmonic component 31 appears at about 2.0 [lp / mm]. Since the second harmonic component 32 has twice the frequency of the first harmonic component 31, the image processing unit 8 similarly extracts the peak of the second harmonic component 32 near the estimated value. FIG. 3 shows an example in which the second harmonic component 32 appears at about 3.3 [lp / mm].

  The image processing unit 8 is configured to extract the third harmonic component 33 in a frequency range R including the estimated value E of the peak frequency of the third harmonic component 33. In the present embodiment, the first harmonic component 31 and the second harmonic component 32 are removed from the X-ray image 21 before the extraction of the third harmonic component 33, as described later.

  That is, the image processing unit 8 outputs the removed image 23 (see FIG. 5) from which the higher harmonic components (the first harmonic component 31 and the second harmonic component 32) lower than the third harmonic component 33 have been removed. On the other hand, the third harmonic component 33 is extracted. The image processing unit 8 performs the Fourier transform once again on the removed image 23 from which the first harmonic component 31 and the second harmonic component 32 have been removed, thereby changing the spectral intensity distribution of the removed image 23 shown in FIG. get. The image processing unit 8 extracts the third harmonic component 33 from the spectral intensity distribution of the removed image 23.

  The peak frequency of the third harmonic component 33 is three times the frequency of the first harmonic component 31. The image processing unit 8 calculates the peak frequency of the third harmonic component 33, and calculates the estimated value E in consideration of the aliasing at the Nyquist frequency. For example, in FIG. 3, since the frequency of the first harmonic component 31 is about 2.0 [lp / mm], the frequency of the third harmonic component 33 is about 6.0 [lp / mm]. Considering the return at the Nyquist frequency (approximately 3.6 [lp / mm]), the estimated value E = 3.6- (6.0-3.6) = 1.2 [lp / mm].

  The image processing unit 8 extracts the third harmonic component 33 in a frequency range R set with a predetermined width on both sides of the estimated value E in the spectrum. In the present embodiment, the frequency range R is, for example, 1.0 [lp / mm] centered on a range of 0.2 [lp / mm] (1.2 [lp / mm]) on both sides of the estimated value E in the spectrum. ] To 1.4 [lp / mm] or less. In the present embodiment, the image processing unit 8 is configured to be able to change the set value of the frequency range R. The image processing unit 8 changes the set value of the frequency range R by, for example, inputting an operation via the operation unit 10 or reading a set value from the storage unit 11.

  The peak in the set frequency range R is detected as the third harmonic component 33. 3 and 4 show an example in which the third harmonic component 33 appears at about 1.29 [lp / mm].

<Harmonic component removal processing>
In the present embodiment, the image processing unit 8 is configured to switch between the first removal processing and the second removal processing according to the intensity of the higher-order harmonic component (the third harmonic component 33).

  The first removal processing is a removal processing for removing a higher-order harmonic component (third harmonic component 33) and a higher-order harmonic component lower than the higher-order harmonic component. That is, in the present embodiment, the first removal process is a removal process for removing the first harmonic component 31, the second harmonic component 32, and the third harmonic component 33.

  The second removal process is a removal process that removes a higher-order harmonic component lower than the higher-order harmonic component without removing the higher-order harmonic component (the third harmonic component 33). That is, in the present embodiment, the second removal process is a removal process for removing the first harmonic component 31 and the second harmonic component 32 without removing the third harmonic component 33.

  As described above, the image processing unit 8 removes the first harmonic component 31 and the second harmonic component 32 regardless of whether the first removal process or the second removal process is performed. When removing the first harmonic component 31 and the second harmonic component 32, the image processing unit 8 calculates the first harmonic component 31 and the second harmonic component from the Fourier transform result (spectral intensity distribution) shown in FIG. A filter corresponding to the spectrum of the component 32 is created. The image processing unit 8 extracts the first harmonic component 31 and the second harmonic component 32 using the created filter, and converts the extracted first harmonic component 31 and the second harmonic component 32 into the moire pattern MP. Is subtracted from the reflected X-ray image 21. As a result, the first harmonic component 31 and the second harmonic component 32 are removed from the X-ray image 21, and a removed image 23 from which the first harmonic component 31 and the second harmonic component 32 have been removed is obtained. Note that the extraction of the third harmonic component 33 is performed based on the Fourier transform result for the removed image 23 as described above.

  The image processing unit 8 removes the third harmonic component 33 in the first removal process and does not remove the third harmonic component 33 in the second removal process. Therefore, in the case of the second removal processing, the removed image 23 from which the first harmonic component 31 and the second harmonic component 32 have been removed is output as the X-ray processed image 22, as shown in FIG. The details of the first removal processing will be described later. Whether to perform the first removal processing or the second removal processing depends on the relative intensity of the peak of the third harmonic component 33 in the Fourier transform result (spectral intensity distribution).

  Specifically, the image processing unit 8 performs the first removal processing when the third harmonic component 33 has a relative intensity peak equal to or higher than the threshold TH (see FIG. 4) as compared with the nearby frequency component. , When the third harmonic component 33 has a peak of relative intensity less than the threshold value TH, the second removal processing is performed.

  For example, the image processing unit 8 divides the frequency range R from which the third harmonic component 33 has been extracted into a plurality of frequency sections, and acquires the spectrum intensity in each frequency section. Then, the image processing unit 8 determines whether or not the relative intensity of the spectrum with respect to the adjacent frequency division is equal to or more than the threshold value TH as a comparison with the nearby frequency component.

  In the example 1 shown in FIG. 6, the frequency range R is divided into eight sections from 1.00 [lp / mm] to 1.40 [lp / mm]. The number of sections may be a number other than eight. The image processing unit 8 calculates, as relative intensity, a ratio (percentage) between the spectrum intensity in the frequency segment of interest and the spectrum intensity in the adjacent (lower frequency) frequency segment among the frequency segments. Then, the image processing unit 8 performs the first removal processing if there is a section whose relative intensity is equal to or greater than the threshold TH among the frequency sections, and performs the second removal processing if there is no section whose relative intensity is equal to or greater than the threshold TH. I do.

  In the present embodiment, the threshold value TH of the relative intensity is set to, for example, 120%. In the present embodiment, the image processing unit 8 is configured to be able to change the set value of the threshold value TH. The image processing unit 8 changes the set value of the threshold value TH, for example, by an operation input via the operation unit 10 or by reading the set value from the storage unit 11.

  In Example 1 shown in FIG. 6, in the frequency division of 1.29 [lp / mm], the relative intensity is 146% (> 120%), and there is a division where the relative intensity is equal to or more than the threshold value TH. . Therefore, in the case of Example 1, the image processing unit 8 selects the first removal processing (see FIG. 5) for removing the third harmonic component 33. In Example 1, even if the first harmonic component 31 and the second harmonic component 32 are removed, it can be determined that the moire pattern MP caused by the third harmonic component 33 is reflected in the image. This corresponds to a case where it can be determined that removing the wave component 33 improves the visibility of the image.

  Note that, in Example 2 shown in FIG. 7, there is no section having a threshold value TH (120%) or more in any frequency section. Therefore, in the case of Example 2, the image processing unit 8 selects the second removal processing (see FIG. 5) that does not remove the third harmonic component 33. That is, the image processing unit 8 outputs the removed image 23 from which the first harmonic component 31 and the second harmonic component 32 have been removed as the X-ray processed image 22. Example 2 shows that the third harmonic component 33 does not have such an intensity that the visibility of the image when the X-ray processed image 22 is viewed is reduced. That is, in Example 2, since it can be determined that the moire pattern MP caused by the third harmonic component 33 is hardly reflected in the image, it is unnecessary to remove the third harmonic component 33, which is unnecessary with the removal processing. This corresponds to a case where it can be determined that the resolution degradation is suppressed. FIGS. 3 and 4 show an example in which the intensity of the third harmonic component 33 is large (corresponding to Example 1 in FIG. 6).

  As described above, in the present embodiment, the image processing unit 8 performs the first removal processing for removing the third harmonic component 33 and the removal of the third harmonic component 33 in accordance with the intensity of the third harmonic component 33. Is switched to the second removal processing that does not perform. In other words, the image processing unit 8 determines whether or not the moiré pattern MP caused by the third harmonic component 33 is reflected in the X-ray image 21 (removed image 23), and determines the third based on the presence or absence of the reflected light. It is configured to determine whether to remove the harmonic component 33.

  Next, the contents of the first removal processing will be described.

  The removal of the first harmonic component 31 and the second harmonic component 32 in the first removal processing is as described above. For the third harmonic component 33, the image processing unit 8 performs a different removal process from the first harmonic component 31 and the second harmonic component 32.

  Specifically, as shown in FIG. 2, the image processing unit 8 extracts a flat region 34 having a small luminance change from the removal image 23 and removes the third harmonic component 33 from the flat region 34. At the same time, in a region 35 (hatched portion) other than the flat region 34, a process for not removing the third harmonic component 33 is performed. That is, in the first removal processing, the first harmonic component 31, the second harmonic component 32, and the third harmonic component 33 are removed from a part (the flat region 34) of the removed image 23, and the remaining portion of the removed image 23 is removed. (The region 35 other than the flat region 34) is removed from the first harmonic component 31 and the second harmonic component 32, and the third harmonic component 33 is not removed. Although FIG. 2 shows the X-ray image 21, the flat region 34 and the region 35 are the same in the X-ray image 21 and the removed image 23.

  The reason why the third harmonic component 33 is partially (locally) removed is that the moire pattern MP is conspicuous in the flat region 34 where the luminance change is small, while the region 35 other than the flat region 34 (the luminance change is relatively large). This is because it is difficult to be recognized in the (area). As a result, even when the third harmonic component 33 is removed, degradation of the resolution (decrease in visibility) of the X-ray processed image 22 is reduced by performing the removal process only on a prominent portion (flat region 34) in the image. It is possible to suppress as much as possible. As an example, the region 35 where the luminance change is large is a region where a structure such as a bone is reflected, and the flat region 34 corresponds to a region where a flesh portion without a structure is reflected, for example.

  The image processing unit 8 outputs a third harmonic removal image 24 obtained by further removing the third harmonic component 33 from the removal image 23 for the flat region 34, and outputs the removal image 23 for the region 35 other than the flat region 34. Is created, and the created combined image is output as the X-ray processed image 22.

  The image processing unit 8 creates a filter corresponding to the spectrum of the third harmonic component 33 from the Fourier transform result (spectral intensity distribution) of the removed image 23 shown in FIG. The image processing unit 8 removes the third harmonic component 33 extracted from the removed image 23 by using the created filter to remove the third harmonic component 33 from the removed image 23. As a result, a third harmonic removal image 24 (see FIG. 5) is obtained.

  Further, the image processing unit 8 extracts the flat region 34. The image processing unit 8 calculates, for each pixel of the removed image 23, the amount of change in luminance between the target pixel 36 and the pixels surrounding the target pixel. For example, as shown in FIG. 8, the average value A of the luminance of the target pixel 36 and the surrounding (upper, lower, left and right) N pixels of the target pixel 36 is calculated, and the average value A is subtracted from the luminance B of the target pixel 36. By doing so, the luminance change amount F1 (= | B−A |) is obtained. The number N of surrounding pixels is, for example, about 10 pixels. The image processing unit 8 divides the obtained luminance change amount F1 by the luminance B of the target pixel 36 to obtain a normalized luminance change amount F2 (= | B−A | / B). As a result, the amount of change in luminance of each pixel can be evaluated based on a common standard. The image processing unit 8 acquires the luminance change amount F2 for each of all the pixels of the removed image 23.

  Further, as shown in FIG. 9, the image processing unit 8 divides the removed image 23 into a plurality of divided areas 37 and smoothes the value of the luminance change amount F2 of the pixels included in the divided areas 37. The size of the partition area 37 is not particularly limited, but is, for example, 16 × 16 pixels. The image processing unit 8 performs the averaging of the luminance change amount F2 of each pixel in the 16 × 16 pixel partitioned area 37 to obtain the averaging value F3. Then, the image processing unit 8 sets the luminance change amount of each pixel in the divided area 37 as an average value F3. That is, a common luminance change amount F3 is given to each pixel in the partition area 37 of 16 × 16 pixels. The luminance change amount F3 is obtained for each of the divided areas 37.

  The image processing unit 8 removes the third harmonic component 33 from the flat region 34 and the region 35 other than the flat region 34 (the third harmonic component 33 is removed) according to the luminance change amount F3 calculated for each of the divided regions 37. Area). That is, the image processing unit 8 sets the flat region 34 when the luminance change amount F3 is less than the change amount threshold, and sets the region 35 other than the flat region 34 when the luminance change amount F3 is equal to or more than the change amount threshold. Since the pixels in each of the divided areas 37 (16 × 16 pixels) have the common luminance change amount F3, the image processing unit 8 determines the threshold value of the luminance change amount F3 (the flat area 34 or Is determined). Note that the threshold determination may be performed on the luminance change amount F2 of each pixel of the removed image 23 without dividing the removed image 23 into the plurality of divided areas 37.

  As a result of the above processing, the image processing unit 8 outputs the third harmonic removal image 24 in which the third harmonic component 33 has been removed from the removal image 23 for the flat region 34 in which the brightness variation F3 is less than the variation threshold. I do. For an area in which the luminance change amount F3 is equal to or larger than the change amount threshold (an area other than the flat area 34), the image processing unit 8 outputs the removed image 23 as it is. That is, as shown in FIG. 10, in the case of the first removal processing, the image processing unit 8 creates a composite image of the third harmonic removal image 24 (the flat region 34) and the removal image 23 (the region 35), The created composite image is output as the X-ray processed image 22. In this case, the moire pattern MP resulting from the third harmonic component 33 remains in the region 35, but has little effect on the visibility of the image because the amount of change in luminance is large as described above. In FIG. 10, for convenience, a dotted line portion indicating the moiré pattern MP slightly remaining due to the third harmonic component 33 is illustrated in the region 35.

(Processing operation of X-ray imaging apparatus)
Next, a processing operation of the X-ray imaging apparatus 100 will be described with reference to FIG.

  In step S1 of FIG. 11, an X-ray image 21 is obtained. First, the control unit 7 shown in FIG. 1 irradiates the subject P with X-rays from the X-ray irradiating unit 1 according to a preset imaging condition. The X-ray transmitted through the subject P is detected by the X-ray detection unit 2, and the image processing unit 8 acquires an X-ray image 21 (see FIG. 2) from the X-ray detection unit 2.

  In step S2, the image processing unit 8 performs one-dimensional Fourier transform on the X-ray image 21, and converts the first harmonic component 31 and the second harmonic component 32 from the obtained frequency spectrum (see FIG. 3). Extract.

  In step S3, the image processing unit 8 removes the extracted first harmonic component 31 and second harmonic component 32 from the X-ray image 21, and removes the first harmonic component 31 and the second harmonic component 32. The removed image 23 (see FIG. 5) is acquired.

  In parallel with step S3, the image processing unit 8 calculates an estimated value E of the peak frequency of the third harmonic component 33 based on the peak frequency of the first harmonic component 31 in step S4.

  Then, in step S5, one-dimensional Fourier transform is performed on the removed image 23, and in the frequency range R including the estimated value E in the obtained frequency spectrum (see FIG. 4), the third harmonic component 33 Perform strength judgment. That is, the image processing unit 8 determines whether or not the relative intensity of the spectrum with respect to adjacent frequency segments in the frequency range R is equal to or greater than the threshold value TH.

  In step S6, the image processing unit 8 determines whether to remove the third harmonic component 33 according to the intensity determination result of the third harmonic component 33. That is, the image processing unit 8 performs a first removal process for removing the third harmonic component 33 depending on whether the third harmonic component 33 has a peak of the relative intensity equal to or greater than the threshold value TH, It is determined whether to perform the second removal processing that does not remove the third harmonic component 33.

  When the third harmonic component 33 has a peak of the relative intensity equal to or larger than the threshold value TH, the image processing unit 8 removes the third harmonic component 33 in step S7. That is, the image processing unit 8 executes the first removal processing by removing the third harmonic component 33 from the removed image 23 from which the first harmonic component 31 and the second harmonic component 32 have been removed. I do.

  As described above, the image processing unit 8 obtains the third harmonic removal image 24 by subtracting the third harmonic component 33 from the removal image 23, and calculates the luminance change amount F3 from the removal image 23. The flat region 34 is extracted by performing a threshold determination of the luminance change amount F3. Then, the image processing unit 8 outputs the third harmonic-removed image 24 for the flat region 34, and outputs the removed image 23 for the region other than the flat region 34 as it is to the X-ray processed image 22 (FIG. 10). Reference).

  On the other hand, when the relative intensity of the third harmonic component 33 is less than the threshold value TH, the image processing unit 8 skips step S7 and proceeds to step S8. In this case, the image processing unit 8 sets the removed image 23 from which the first harmonic component 31 and the second harmonic component 32 have been removed as the X-ray processed image 22 (see FIG. 5). That is, when the relative intensity of the third harmonic component 33 is less than the threshold value TH, the image processing unit 8 skips step S7 to execute the second removal process that does not remove the third harmonic component 33. Become.

  In step S8, the image processing unit 8 displays (outputs) the created X-ray processed image 22 on the display unit 9 and stores it in the storage unit 11. When the image processing unit 8 executes step S7 (when the third harmonic component 33 has a peak of the relative intensity equal to or greater than the threshold value TH), the output X-ray processed image 22 includes the first harmonic component 31 and the The combined image is obtained by removing the second harmonic component 32 and removing the third harmonic component 33 from the flat region 34 (see FIG. 10). When the image processing unit 8 does not execute Step S7 (when the relative intensity of the third harmonic component 33 is less than the threshold), the output X-ray processed image 22 removes the third harmonic component 33. A removed image 23 from which the first harmonic component 31 and the second harmonic component 32 have been removed without performing.

(Effects of the embodiment)
In the present embodiment, the following effects can be obtained.

  In the present embodiment, as described above, the harmonic components constituting the moiré pattern MP are extracted from the X-ray image 21 and the third harmonic component 33 (third-order component) higher than the first harmonic component 31 is extracted. An image processing unit 8 that changes the content of the removal processing according to the intensity of the higher-order harmonic component of the image is provided. Thus, the third harmonic component 33 is removed in consideration of the influence of the degradation of the resolution due to the removal of the third harmonic component 33 and the degradation of the image quality due to the reflection of the moiré pattern MP when not removed. Whether or not to be removed can be changed according to the intensity of the third harmonic component 33 in each X-ray image 21. As a result, it becomes possible not to remove the third harmonic component 33 that does not need to be removed, so that it is possible to prevent the resolution of the X-ray image 21 from being unnecessarily deteriorated by removing the harmonic component of the moire pattern MP. be able to.

  Further, in the present embodiment, as described above, the third harmonic component 33 and the lower harmonic components lower than the third harmonic component 33 depend on the intensity of the third harmonic component 33 (higher harmonic component). A first removal process for removing wave components (a first harmonic component 31 and a second harmonic component 32), and a lower harmonic than the third harmonic component 33 without removing the third harmonic component 33 Switching between the second removal processing for removing components is performed. Thus, when the intensity of the third harmonic component 33 is high, the third harmonic component 33 can be removed by the first removal processing, and when the intensity of the third harmonic component 33 is not high, the second harmonic component can be removed. The third harmonic component 33 can be left by the removal processing. Further, even in a configuration in which the removal processing is switched, higher-order harmonic components lower than the third harmonic component 33 can be removed, so that reflection of the moiré pattern MP can be effectively removed.

  Further, with the above-described configuration, the first harmonic component 31 and the second harmonic component 32, which are relatively greatly affected by the reflection, are reliably removed, and the third harmonic component 33 is changed depending on the intensity. It is possible to select whether or not to remove the case. As a result, it is possible to effectively suppress the reflection of the moiré pattern MP while effectively suppressing the reduction in resolution due to the removal processing of the moiré pattern MP.

  In particular, since the low frequency component contains more original image information other than the moiré pattern MP than the high frequency component, the third harmonic component 33 (approximately 1.29) as illustrated in the above embodiment. [Lp / mm]) appears in a frequency region lower than the first harmonic component 31 (approximately 2.0 [lp / mm]), the resolution is significantly reduced when the third harmonic component 33 is removed. . For this reason, by selecting whether or not to remove the third harmonic component 33 in accordance with the intensity, the resolution is effectively suppressed from lowering as compared with a configuration in which the third harmonic component 33 is uniformly removed. It is possible to do.

  Further, in the present embodiment, as described above, when the third harmonic component 33 has a peak of the relative intensity equal to or larger than the threshold value TH as compared with the nearby frequency component, the first removal processing is performed and the third harmonic component is removed. When the wave component 33 has a peak of relative intensity less than the threshold value TH, the second removal processing is performed. Thus, the necessity of removal according to the intensity of the third harmonic component 33 can be easily determined using the threshold value TH. Then, by setting an appropriate threshold value TH, the first removal processing for removing the third harmonic component 33 and the second removal processing for not removing the third harmonic component 33 are easily switched as necessary. It becomes possible.

  In the present embodiment, as described above, the image processing unit 8 is configured so that the set value of the threshold value TH can be changed. Thus, for example, even when the apparatus configuration is changed, or between X-ray imaging apparatuses 100 having different specifications, the image processing unit 8 can be shared by only changing the set value of the threshold value TH. It is easy to optimize TH.

  Further, in the present embodiment, as described above, the removed image 23 from which the higher harmonic components (the first harmonic component 31 and the second harmonic component 32) lower than the third harmonic component 33 are removed is used. Then, the image processing unit 8 is configured to extract the third harmonic component 33 and change the content of the removal processing on the removed image 23 according to the intensity of the third harmonic component 33. As a result, the third harmonic component 33 is extracted after removing the low-order harmonic component, so that a part of the low-order harmonic component is erroneously recognized as the third harmonic component 33, And that the third harmonic component 33 is overlooked due to being mixed by the higher harmonic component. As a result, it is possible to more reliably extract the third harmonic component 33 and execute an appropriate removal process.

  Further, in the present embodiment, as described above, the image processing unit 8 is configured to extract the third harmonic component 33 in the frequency range R including the estimated value E of the peak frequency of the third harmonic component 33. , The set value of the frequency range R can be changed. Thereby, even when there is an error in the pitch of the grid 3, the third harmonic component 33 is extracted more reliably in the frequency range R including the estimated value E of the peak frequency, so that the third harmonic component 33 is more reliably extracted. Be able to extract. Further, by making the set value of the frequency range R changeable, for example, even when the apparatus configuration is changed or between X-ray imaging apparatuses having different specifications, the image can be changed only by changing the set value of the frequency range R. The processing unit 8 can be shared.

(Modification)
It should be understood that the embodiments disclosed this time are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description of the embodiments, and includes all modifications (modifications) within the meaning and scope equivalent to the terms of the claims.

  For example, in the above embodiment, the example in which the subject is a person has been described, but the present invention is not limited to this. In the present invention, the subject may be an organism other than a human or an object. For example, the X-ray imaging apparatus of the present invention may be used for industrial equipment such as an X-ray inspection apparatus (non-destructive inspection apparatus) other than medical equipment such as an X-ray apparatus. Further, the X-ray imaging apparatus of the present invention may be used for an analytical instrument or the like.

  Further, in the above-described embodiment, an example in which the lying subject is imaged has been described, but the present invention is not limited to this. In the present invention, a subject in an awake state (upright position) may be imaged.

  Further, in the above-described embodiment, an example of the configuration in which the content of the removal processing is changed according to the intensity of the third harmonic component 33 which is the third higher harmonic component has been described, but the present invention is not limited to this. I can't. In the present invention, the content of the removal processing may be changed according to the intensity of the second harmonic component 32, which is the second higher harmonic component. In that case, the second harmonic component 32 is an example of a “higher harmonic component” in the claims. Since the reflection of the moiré pattern differs depending on the device configuration of the X-ray imaging apparatus 100, it may be better to determine whether to remove the second harmonic component 32 according to the intensity on a case-by-case basis. . This is a case where the reflection of the moire pattern is weaker than the case described in the above embodiment, and the third harmonic component 33 can be ignored. In this case, a series of processes in the above embodiment may be applied to the second harmonic component 32. That is, in the above embodiment, the “third harmonic component 33” may be replaced with the “second harmonic component 32”, and the removed image 23 may be an image from which only the first harmonic component 31 has been removed.

  Further, in the above embodiment, the third harmonic component 33 (higher harmonic component) is extracted, and the third harmonic component 33 is removed by subtracting the extracted third harmonic component 33 from the removal image 23. However, the present invention is not limited to this. In the present invention, for example, the third harmonic component 33 may be only partially removed (suppressed) by reducing the peak intensity of the extracted third harmonic component 33 in the frequency spectrum.

  Further, in the above embodiment, when removing the third harmonic component 33 (higher harmonic component), the third harmonic component 33 is removed from the flat region 34 of the removed image 23 where the luminance change is small. Although an example of the configuration has been described, the present invention is not limited to this. In the present invention, when removing the third harmonic component 33 (higher harmonic component), the third harmonic component 33 may be removed from the entire removed image 23 at once.

  Further, in the above embodiment, the first removal processing for removing the first harmonic component 31, the second harmonic component 32, and the third harmonic component 33, and the first removal processing without removing the third harmonic component 33, are performed. Although the example of the configuration for switching between the wave component 31 and the second removal process for removing the second harmonic component 32 has been described, the present invention is not limited to this. In the present invention, for example, the first removal processing for completely removing the third harmonic component 33 and the second removal processing for reducing the peak intensity of the third harmonic component 33 may be switched. Further, a removal process other than the first removal process and the second removal process may be further added, and switching may be performed between three or more removal processes.

  Further, in the above-described embodiment, when the third harmonic component 33 (higher harmonic component) has a peak of relative intensity equal to or higher than the threshold value TH as compared with a nearby frequency component, the third harmonic component 33 is removed. However, the present invention is not limited to this. In the present invention, the third harmonic component 33 may be removed when the peak intensity (absolute intensity) of the third harmonic component 33 instead of the relative intensity is equal to or greater than a predetermined threshold.

  Further, in the above-described embodiment, an example of the configuration in which the third harmonic component 33 (higher harmonic component) is extracted and removed from the removed image 23 has been described, but the present invention is not limited to this. . In the present invention, the third harmonic component 33 may be extracted from the X-ray image 21 instead of the removed image 23. That is, the first harmonic component 31, the second harmonic component 32, and the third harmonic component 33 are extracted from the X-ray image 21 collectively, and a removal process corresponding to the intensity of the third harmonic component 33 is performed. It may be performed together with the removal processing of the first harmonic component 31 and the second harmonic component 32.

  Further, in the above-described embodiment, an example has been described in which the set value of the frequency range R for extracting the third harmonic component 33 (higher harmonic component) can be changed, but the present invention is not limited to this. I can't. In the present invention, the set value of the frequency range R may be a fixed value.

  Further, in the above-described embodiment, an example has been described in which the set value of the threshold value TH of the relative intensity of the third harmonic component 33 (higher harmonic component) is changeable, but the present invention is not limited to this. In the present invention, the set value of the threshold value TH may be a fixed value.

  Further, in the above-described embodiment, for convenience of explanation, the processing of the X-ray imaging apparatus of the present invention has been described using the flow-driven flowchart in which the processing is sequentially performed along the processing flow, but the present invention is not limited thereto. Absent. In the present invention, the processing operation may be performed by event-driven (event-driven) processing that executes processing in event units. In this case, it may be performed in a completely event-driven manner, or may be performed in a combination of event-driven and flow-driven.

DESCRIPTION OF SYMBOLS 1 X-ray irradiation part 2 X-ray detection part 3 Grid 8 Image processing part 21 X-ray image 22 X-ray processing image 23 Removal image 31 1st harmonic component 32 2nd harmonic component (higher harmonic component)
33 Third harmonic component (higher harmonic component)
100 X-ray imaging apparatus E Estimated peak frequency MP Moiré pattern P Subject R Frequency range TH threshold

Claims (7)

An X-ray irradiator that irradiates the subject with X-rays;
An X-ray detector that detects X-rays transmitted through the subject;
A grid disposed on the detection surface side of the X-ray detection unit and removing scattered X-rays;
An image processing unit that performs a moire pattern removal process caused by the grid reflected in the X-ray image obtained by the X-ray detection unit, and outputs an X-ray processed image after the removal process;
The image processing unit extracts a harmonic component constituting the moiré pattern from the X-ray image, and extracts a higher-order second or third-order component than a first harmonic component as a first-order harmonic component. According to the intensity of the higher harmonic component, the relative intensity that is a ratio calculated by dividing the intensity of the higher harmonic component by the intensity of the frequency component near the higher harmonic component is equal to or greater than a threshold. An X-ray imaging apparatus configured to change the content of the removal processing when a peak is present . The image processing unit, according to the intensity of the higher harmonic components,
A first removal process for removing higher-order harmonic components and lower-order harmonic components than the higher-order harmonic components;
2. The X-ray according to claim 1, wherein the X-ray is configured to switch between a second removal process that removes a higher-order harmonic component lower than the higher-order harmonic component without removing the higher-order harmonic component. 3. Shooting equipment. The higher harmonic component is a third harmonic component;
The first removal processing is a removal processing for removing a first harmonic component, a second harmonic component, and a third harmonic component,
The X-ray imaging apparatus according to claim 2, wherein the second removal processing is a removal processing for removing the first harmonic component and the second harmonic component without removing the third harmonic component. The image processing unit,
When the high-order harmonic component has a peak of the relative intensity of greater than or equal to the threshold value as compared to the frequency component near performs the first removing process,
4. The X-ray imaging apparatus according to claim 2, wherein the second removal processing is performed when the higher-order harmonic component has a peak of relative intensity less than the threshold. 5.   The X-ray imaging apparatus according to claim 4, wherein the image processing unit is configured to change a set value of the threshold.   The image processing unit extracts the high-order harmonic component from the removed image from which the higher-order harmonic component lower than the higher-order harmonic component has been removed, and reduces the intensity of the higher-order harmonic component. The X-ray imaging apparatus according to claim 1, wherein the X-ray imaging apparatus is configured to change the content of the removal processing on the removed image in response to the change. The image processing unit is configured to extract the high-order harmonic component in a frequency range including an estimated value of the peak frequency of the high-order harmonic component,
The X-ray imaging apparatus according to claim 1, wherein the image processing unit is configured to change a set value of the frequency range.

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