JP2008212524A - Radiographic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide radiographic equipment capable of removing high-frequency components even if executing a binning process to a radiographic image. <P>SOLUTION: Though a low-pass filter (LPF) 21 executes a process for removing high-frequency components from an X-ray image based on X rays detected through an X-ray grid, the process is executed previously to a binning process to be executed by a binning processing section 22. The high-frequency component removal process by the low-pass filter 21 is executed before the frequency characteristic change by the binning process so that, even if the binning process is executed to the X-ray image, the high-frequency component can be thus removed without changing the frequency characteristic. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radiation imaging apparatus that performs radiation imaging, and more particularly, to a technique for performing a binning process for collecting a plurality of pixels into one pixel on a radiation image.

  An X-ray imaging apparatus will be described as an example of the radiation imaging apparatus. In an X-ray imaging apparatus, X-rays are emitted from an X-ray tube toward a subject, X-rays transmitted through the subject are detected, and an X-ray image is obtained based on the detected X-rays. Take a picture. When X-rays pass through the subject, scattered rays are generated by the collision of the X-rays with the subject, and the image is blurred due to the scattered rays.

  Therefore, an X-ray grid is provided on the incident surface side of the X-ray detector in order to remove scattered radiation. The X-ray grid is configured by alternately arranging an absorber that absorbs X-rays (for example, lead) and a transmitter that transmits X-rays (for example, aluminum or air). When scattered rays are incident on the X-ray grid, they travel obliquely to the absorber and are absorbed and removed by the absorber. On the other hand, when X-rays other than scattered rays enter the X-ray grid, they travel substantially parallel to the transmissive body or absorber, and are transmitted through the transmissive body and incident on the X-ray detector for detection.

However, when an X-ray grid is used, the grid pattern appears in the X-ray image as a high frequency component. Therefore, conventionally, in order to remove high frequency components such as the grid frequency, a low-pass filter (LPF) is applied in a direction perpendicular to the grid pattern (that is, a direction perpendicular to the grid line). Alternatively, after extracting the grid frequency by applying a high-pass filter (HPF: High Pass Filter) in a direction that crosses the grid pattern vertically, the difference between the extracted grid frequency and the image reflected in the grid pattern is calculated. By removing the high frequency component. Further, the relationship between the Nyquist frequency f _n and the grid frequency f _g in the sampling process is such that m is an arbitrary positive integer, {(2m−4 / 3) ^* f _n } ≦ f _g ≦ {(2 m−2 / 3) There is also a method of setting so as to satisfy the conditional expression of ^* f _n } (excluding the case where m = 1 and f _g ≦ f _n ) (for example, see Patent Document 1).
JP 2000-316216 A (pages 1, 2, 5-8, FIGS. 1 and 2)

  However, if a binning process for combining a plurality of pixels into one pixel is performed on an X-ray image, the frequency characteristics change. Therefore, even if the grid pattern exists on the high frequency side in the X-ray image before the binning process, the grid pattern may appear on the low frequency side in the X-ray image after the binning process. In that case, if a conventional low-pass filter (LPF) that removes the grid pattern existing in the high frequency is performed, the grid pattern that appears on the low frequency side cannot be removed.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a radiation imaging apparatus capable of removing high-frequency components even when binning processing is performed on a radiation image. And

In order to achieve such an object, the present invention has the following configuration.
That is, the invention according to claim 1 includes radiation irradiating means for irradiating a subject with radiation, detects radiation transmitted through the subject, and obtains a radiation image based on the detected radiation. A radiation imaging apparatus that performs radiation imaging with a scattered radiation removing means for removing scattered radiation related to radiation, and a process for removing high-frequency components from a radiation image based on the radiation detected through the scattered radiation removing means A high-frequency component removal processing unit to perform, and a binning processing unit to perform a binning process for collecting a plurality of pixels into one pixel with respect to a radiographic image processed by the high-frequency component removal processing unit. is there.

  [Operation / Effect] According to the invention described in claim 1, the high frequency component removal processing means performs the process of removing the high frequency component from the radiation image based on the radiation detected through the scattered radiation removal means. The processing is performed before the binning processing performed by the binning processing means. Then, the binning processing unit performs binning processing on the radiographic image processed by the high frequency component removal processing unit. Therefore, since the high frequency component removal processing by the high frequency component removal processing means is performed before the frequency characteristic change by the binning processing, the binning processing is performed in a state where the high frequency component can be removed without changing the frequency characteristics. It can be carried out. As a result, high-frequency components can be removed even when binning processing is performed on a radiographic image.

  In the above-described invention, an example of the process for removing the high-frequency component is a low-pass process for passing the low-frequency component, and the above-described high-frequency component removal processing means is a low-pass filter (claim 2). Described invention). By applying the low-pass filter, the low frequency component passes and the high frequency component is removed.

  In the above-described invention, another example of the process for removing the high-frequency component is to pass the high-frequency component due to the scattered radiation, extract the high-frequency component due to the scattered radiation, and then remove the extracted high-frequency component and the high-frequency component. The high-frequency component removal processing means described above is a process for obtaining a difference from the previous radiation image, and is a high-pass filter and a difference means for obtaining the difference described above (the invention according to claim 3). By applying the high-pass filter, the high-frequency component due to the scattered radiation is extracted, and the extracted high-frequency component is further removed by the difference means, so that the high-frequency component is removed.

  In addition to this, the processing for removing high-frequency components is not limited to the low-pass filter as in the invention of claim 2, the high-pass filter as in the invention of claim 3, and the differential processing. The difference between the extracted frequency component and the data before removing the frequency component after applying the band pass filter (BPF) after Fourier transform and extracting only the band of the frequency component due to scattered radiation As shown in the process of performing inverse Fourier transform, the process is not particularly limited as long as it is a process that removes a high-frequency component that is normally used.

  In these inventions described above, it is preferable to include selection means for selecting whether or not to perform binning processing (the invention according to claim 4). By including selection means for selecting whether or not to perform binning processing, it can be applied to an apparatus that does not perform binning processing, and versatility is enhanced.

  According to the radiation imaging apparatus of the present invention, the high-frequency component removal processing unit performs the process of removing the high-frequency component from the radiation image based on the radiation detected through the scattered radiation removal unit. This is performed prior to the binning process performed in (1). Therefore, since the high frequency component removal processing by the high frequency component removal processing means is performed before the frequency characteristic change by the binning processing, even when the binning processing is performed on the radiation image, the frequency characteristics are not changed. High frequency components can be removed.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram of an X-ray imaging apparatus according to an embodiment, FIG. 2 is a block diagram showing a specific configuration of an image processing unit used in the X-ray imaging apparatus, and FIG. FIG. 4 is a schematic diagram for explaining a grid frequency and its aliasing frequency, and FIG. 5 is an image in which a structure and a grid pattern having a high frequency component are reflected. FIG. In the present embodiment, an X-ray imaging apparatus will be described as an example of a radiation imaging apparatus.

  As shown in FIG. 1, the X-ray imaging apparatus includes a top plate 1 on which a subject M is placed, an X-ray tube 2 that irradiates the subject M with X-rays, and an X that passes through the subject M. A flat panel X-ray detector (hereinafter abbreviated as “FPD”) 3 for detecting a line. In addition to the FPD, the X-ray detector may be an image intensifier or an X-ray film. The X-ray tube 2 corresponds to the radiation irradiation means in this invention.

  In addition, the X-ray imaging apparatus also includes the top panel control unit 4 that controls the elevation and horizontal movement of the top panel 1, the FPD control unit 5 that controls the scanning of the FPD 3, and the tube voltage and tube current of the X-ray tube 2. An X-ray tube control unit 7 having a high voltage generation unit 6 to be generated, an A / D converter 8 that digitizes and extracts an X-ray detection signal that is a charge signal from the FPD 3, and an A / D converter 8 An image processing unit 9 that performs various processes based on the X-ray detection signal, a controller 10 that controls each of these components, a memory unit 11 that stores processed images, and an input that is input by an operator And a monitor 13 for displaying the processed image and the like.

  The top board control unit 4 horizontally moves the top board 1 to accommodate the subject M up to the imaging position, moves the top and bottom, rotates and horizontally moves the subject M to a desired position, or horizontally moves the subject M. Then, the image is picked up, or the image is moved horizontally after the image pickup is finished, and the control is performed to retract from the image pickup position. The FPD control unit 5 performs control related to scanning by moving the FPD 3 horizontally or rotating around the body axis of the subject M. The high voltage generation unit 6 generates a tube voltage and a tube current for irradiating X-rays and applies them to the X-ray tube 2. The X-ray tube control unit 7 moves the X-ray tube 2 horizontally, Control relating to scanning by rotating around the axis of the body axis of M, control of the setting of the irradiation field of the collimator (not shown) on the X-ray tube 2 side, and the like are performed. When scanning the X-ray tube 2 or the FPD 3, the X-ray tube 2 and the FPD 3 move while facing each other so that the FPD 3 can detect the X-rays emitted from the X-ray tube 2.

  The A / D converter 8 converts the charge signal output from the FPD 3 from analog to digital, and outputs a digitized X-ray detection signal. The controller 10 is configured by a central processing unit (CPU) and the like, and the memory unit 11 is configured by a storage medium represented by ROM (Read-only Memory), RAM (Random-Access Memory), and the like. Yes. The input unit 12 includes a pointing device represented by a mouse, a keyboard, a joystick, a trackball, a touch panel, and the like. In the X-ray imaging apparatus, the FPD 3 detects X-rays transmitted through the subject M, and the image processing unit 9 performs image processing based on the detected X-rays, thereby imaging the subject M.

  In order to remove scattered radiation, an X-ray grid 14 is provided on the incident surface side of the FPD 3. The X-ray grid 14 is configured by, for example, alternately arranging lead and aluminum. When scattered rays are incident on the X-ray grid 14, they travel obliquely to lead and are absorbed and removed by lead. On the other hand, when X-rays other than scattered rays enter the X-ray grid 14, the X-rays travel almost parallel to aluminum or lead, so that they pass through the aluminum and enter the FPD 3 to be detected. The X-ray grid 14 corresponds to the scattered radiation removing means in this invention.

  As shown in FIG. 2, the image processing unit 9 includes a low-pass filter 21 (denoted by “LPF” in FIG. 2), a selection unit 22 that selects whether or not to perform binning processing to be described later, and binning processing. Unit 23, a high-pass filter 24 (indicated as “HPF” in FIG. 2), a low-pass filter 25 (indicated as “LPF” in FIG. 2), and a subtractor 26. Yes. The low-pass filter 21 corresponds to the high-frequency component removal processing means in this invention, the selection unit 22 corresponds to the selection means in this invention, and the binning processing unit 23 corresponds to the binning processing means in this invention.

The low-pass filter 21 removes high-frequency components such as the grid frequency from the X-ray image based on the X-rays detected through the X-ray grid 14 in a direction that crosses the grid pattern vertically (that is, the grid). The low frequency component is passed in the direction perpendicular to the eyes. The binning processing unit 23 performs binning processing on the X-ray image processed by the low-pass filter 21 to combine a plurality of pixels into one pixel. For example, as shown in FIG. 3 (a), a total of four pixels P _A Aspect 2 × 2, as shown in FIG. 3 (b), into one pixel P _B. By combining the pixels into one pixel, for example, as shown in FIG. 3A, an X-ray image composed of 1024 × 1024 pixels can be obtained from 512 × 512 pixels as shown in FIG. 3B. An X-ray image is obtained. When combining into one pixel, the pixel values of each pixel may be added, and the added pixel value may be used as the pixel value after binning processing, or the average of the pixel values of each pixel (arithmetic average) may be calculated. The obtained pixel value may be used as the pixel value after the binning process.

Even if the high frequency component is removed, as shown in FIG. 4, the folded frequency component f _g ′ of the high frequency component due to the scattered radiation appears on the lower frequency side than the grid frequency f _g which is the high frequency component. That is, this aliasing frequency component is a grid pattern that appears on the low frequency side. Therefore, in order to remove the aliasing frequency component, it is preferable to include the above-described high-pass filter 24 and subtractor 26 (both refer to FIG. 2). Specifically, as shown in FIG. 5, the high-pass filter 24 vertically crosses the grid pattern _Pg with respect to the X-ray image binned by the binning processing unit 23 (that is, the grid eye and the grid eye). vertically) P _x, is passed through a high-frequency component is a folding frequency component extracting aliasing frequency components. Therefore, the subtractor 26 takes the difference between the extracted folding frequency component (grid pattern P _g ) and the X-ray image binned by the binning processing unit 23, whereby the folding frequency component of the high-frequency component due to the scattered radiation. Can be removed.

As shown in FIG. 5, when the structure P ₁ having a high frequency component is reflected in the image, the structure P together with the aliasing frequency component by the above-described high-pass filter 24 (see FIG. 2). will be extracted to _1, the subtractor 26 (see Figure 2), there is a possibility that up structure P ₁ is removed together with the folding frequency component. Therefore, in order to remove the image structure P ₁ at the time of extraction, the low-pass filter 25 (see FIG. 2) performs an operation on the image having the aliasing frequency component extracted by the high-pass filter 24. as shown in FIG. 5, in a direction parallel to P _y grid pattern P _g, it passes a low frequency component.

That is, the aliasing frequency component naturally has a low frequency with respect to the parallel direction P _y of the grid pattern P _g , but the structure P ₁ often crosses the grid pattern P _g instead of being parallel. Therefore, by performing a low-pass filter 25, the frequency components of the structure P ₁ only the structure P ₁ is regarded as a high-frequency component is removed, with respect to a direction parallel P _y grid pattern P _g The folding frequency component which is a low frequency component can be passed. As a result, the difference between the aliasing frequency component (grid pattern) processed by the low-pass filter 25 and from which the image structure is removed and the X-ray image binned by the binning processor 23 is subtracted. By taking 26, it is possible to remove the aliasing frequency component of the high frequency component caused by the scattered radiation while leaving the structure of the image.

  Next, a series of image processing by the image processing unit 9 will be described with reference to the flowchart of FIG. FIG. 6 is a flowchart showing a series of image processing.

(Step S1) Collection of original image on X-ray grid X-ray irradiated from the X-ray tube 2 toward the subject M and transmitted through the subject M is converted into a flat panel X-ray detector (FPD) 3 Will detect. Scattered rays are removed by transmitting through the X-ray grid 14 before entering the FPD 3. Thereby, an original image in which a grid pattern by the X-ray grid 14 is reflected is collected.

(Step S2) LPF Processing Low-pass processing (LPF processing) by the low-pass filter 21 in the direction perpendicular to the grid pattern (that is, the direction perpendicular to the grid eyes) with respect to the original image collected in step S1. The low frequency component is allowed to pass through. By performing the LPF process, a high frequency component such as a grid frequency is removed from the X-ray image. When the selection unit 22 selects to perform the binning process in the binning processing unit 23, the process proceeds to the next step S3.

(Step S <b> 3) 2 × 2 Pixel Binning Processing The binning processing unit 23 performs binning processing that combines a plurality of pixels into one pixel for the X-ray image processed by the low-pass filter 21 in step S <b> 2. . In the present embodiment, as described above, a binning process is performed in which a total of 4 pixels of 2 × 2 in length and width are combined into one pixel.

(Step S4) HPF Processing With respect to the X-ray image binned by the binning processing unit 23 in step S3, the high-pass filter 24 increases the height in the direction perpendicular to the grid pattern (that is, the direction perpendicular to the grid eyes). By applying the band-pass process (HPF process), the high-frequency component that is the aliasing frequency component is passed and the aliasing frequency component is extracted. At this time, when a structure having a high frequency component is reflected in the image, the structure is extracted together with the folding frequency component as described above.

(Step S5) LPF Processing Therefore, the low-pass processing by the low-pass filter 25 is performed in the direction parallel to the grid pattern on the image having the aliasing frequency component extracted by the high-pass filter 24 in step S4. By applying (LPF processing), the low frequency component is passed. Only the structure is removed by performing the LPF process.

(Step S6) Difference between Images The aliasing frequency component (grid pattern) from which the structure of the image has been removed by the low-pass filter 25 in step S5, and the X-ray image binned by the binning processing unit 23 in step S3 The subtractor 26 takes the difference between the high-frequency component and the aliasing frequency component due to the scattered radiation while the image structure remains.

  According to the X-ray imaging apparatus according to the present embodiment, the low-pass filter (LPF) 21 performs the process of removing the high-frequency component from the X-ray image based on the X-rays detected through the X-ray grid 14. However, the process is performed before the binning process performed by the binning processing unit 22. Then, the binning processing unit 22 performs a binning process on the X-ray image processed by the low-pass filter 21. Therefore, since the high-frequency component removal processing by the low-pass filter 21 is performed before the frequency characteristic change by the binning processing, the binning processing can be performed in a state where the high-frequency components can be removed without changing the frequency characteristics. It can be performed. As a result, high-frequency components can be removed even when binning processing is performed on an X-ray image.

  In the present embodiment, as an example of the process for removing the high frequency component, a low-pass process for passing the low frequency component is described as an example. That is, the high-frequency component removal processing means in the present invention is the low-pass filter 21, and by applying the low-pass filter 21, the low-frequency component passes and the high-frequency component is removed.

  Moreover, it is preferable to provide the selection part 22 which selects whether a binning process is performed like a present Example. By including the selection unit 22 that selects whether or not to perform binning processing, it can be applied to an apparatus that does not perform binning processing, and versatility is enhanced.

  The present invention is not limited to the above-described embodiment, and can be modified as follows.

  (1) In the above-described embodiments, an X-ray imaging apparatus has been described as an example of a radiation imaging apparatus. However, an ECT (Emission) represented by a PET (Positron Emission Tomography) apparatus, a SPECT (Single Photon Emission CT) apparatus, or the like. Applied to radiation imaging devices that perform radiation imaging by detecting radiation other than X-rays (γ rays in the case of PET devices) and obtaining radiation images based on the detected radiation, such as computed tomography devices May be.

  (2) In the above-described embodiment, the X-ray imaging apparatus as shown in FIG. 1 has been described as an example. However, the present invention is also applied to, for example, an X-ray imaging apparatus disposed on a C-arm. Also good. The present invention may also be applied to an X-ray CT apparatus.

  (3) In the above-described embodiment, the low-pass filter 21 is described as an example of the high-frequency component removal processing means in the present invention, but the high-frequency component removal processing means is not limited to this. For example, as shown in FIG. 7, the high-frequency component removal processing unit may include a high-pass filter 31 (indicated as “HPF” in FIG. 7) and a subtractor 32. Since the block diagram subsequent to the subtracter 32 has the same configuration as that of the image processing unit 9 of the embodiment, the description thereof is omitted. The high-pass filter 31 has a grid frequency in a direction perpendicular to the grid pattern (that is, a direction perpendicular to the grid eyes) with respect to an X-ray image based on the X-rays detected through the X-ray grid 14. Such a high-frequency component is passed and the high-frequency component is extracted. The subtractor 32 takes the difference between the extracted high frequency component and the original image before removing the high frequency component. That is, as a process for removing the high-frequency component, the high-frequency component due to the scattered radiation is passed through the high-pass filter 31 to extract the high-frequency component due to the scattered radiation, and then the extracted high-frequency component and the high-frequency component are removed. The subtracter 32 takes the difference from the previous radiation image. By applying the high-pass filter 31, the high frequency component due to the scattered radiation is extracted, and the extracted high frequency component is further removed by the subtractor 32. As a result, the high frequency component is removed. The subtractor 32 corresponds to the difference means in this invention.

  (4) In the embodiment described above, the low-pass filter 21 is described as an example of the high-frequency component removal processing means in the present invention, and in the above-described modification (3), the high-pass filter 31 and The difference means (the subtractor 32 in FIG. 7) has been described as an example, but is not particularly limited as long as it is a process for removing a high-frequency component that is normally used. For example, after applying a band pass filter (BPF) after Fourier transform and extracting only the frequency component band due to scattered radiation, the extracted frequency component and the data before removing the frequency component A high frequency component may be removed by taking the difference and performing inverse Fourier transform.

  (5) In the above-described embodiment, the selection unit 22 that selects whether or not to perform binning processing is provided. However, if it is applied only to an apparatus that performs binning processing, the selection unit 32 is not necessarily provided.

  (6) In the above-described embodiment, the high-pass filter 24 and the subtractor 26 are provided in order to remove the aliasing frequency component of the high-frequency component caused by the scattered radiation. However, the aliasing frequency component is not taken into account or the aliasing is not considered. If the influence of the frequency component on the image is small, the high-pass filter 24 and the subtractor 26 are not necessarily provided.

  (7) In the above-described embodiment, when a grid pattern (including a grid pattern with a folded frequency component) is extracted, a low-pass signal is passed in the parallel direction of the grid pattern in order to leave a structure with a high frequency component. By applying the mold filter 25, the low-frequency component is allowed to pass and the structure is removed at the time of extraction. Finally, a structure having a high frequency component is left, but the structure is not taken into account, or the structure is a frequency component. In the case of low, it is not always necessary to provide the low-pass filter 25.

1 is a block diagram of an X-ray imaging apparatus according to an embodiment. It is the block diagram which showed the specific structure of the image process part used for X-ray imaging apparatus. It is a schematic diagram of the image used for description of a binning process. It is a schematic diagram with which it uses for description of a grid frequency and its folding frequency. It is a schematic diagram of the image in which the structure and grid pattern with a high frequency component were reflected. It is a flowchart which shows a series of image processing. It is the block diagram which showed the specific structure of the image process part which concerns on a modification.

Explanation of symbols

2 ... X-ray tube 14 ... X-ray grid 21 ... Low-pass filter (LPF)
22 ... Selection unit 23 ... Binning processing unit M ... Subject

Claims (4)

  A radiation imaging apparatus that includes radiation irradiating means for irradiating radiation toward a subject, detects radiation transmitted through the subject, and obtains a radiation image based on the detected radiation to perform radiation imaging. A scattered radiation removing means for removing scattered radiation related to radiation, a high frequency component removing processing means for performing a process of removing a high frequency component from a radiation image based on the radiation detected through the scattered radiation removing means, and the high frequency component A radiation imaging apparatus comprising: binning processing means for performing binning processing for collecting a plurality of pixels into one pixel for a radiation image processed by the removal processing means.   2. The radiation imaging apparatus according to claim 1, wherein the process of removing the high-frequency component is a low-pass process that passes a low-frequency component, and the high-frequency component removal processing unit is a low-pass filter. A radiation imaging apparatus.   2. The radiation imaging apparatus according to claim 1, wherein the process of removing the high-frequency component passes the high-frequency component due to the scattered radiation and extracts the high-frequency component due to the scattered radiation, and then extracts the extracted high-frequency component and the high-frequency component. A radiation imaging apparatus, wherein the high-frequency component removal processing means is a high-pass filter and a difference means for taking the difference, which is a process for taking a difference from a radiation image before removing a component.   4. The radiation imaging apparatus according to claim 1, further comprising a selection unit that selects whether or not to perform the binning process. 5.

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