JP4602703B2 - Radiation imaging apparatus and image generation apparatus - Google Patents

Description

  The present invention relates to a radiation imaging apparatus and an image generation apparatus.

  As a radiation imaging apparatus, an X-ray CT (Computed Tomography) apparatus that generates an image of a tomographic plane of a subject using X-rays that are radiation is known. An X-ray CT apparatus uses a human body or an object as a subject, and is used in a wide range of applications such as medical use and industrial use.

The X-ray CT apparatus irradiates X-rays from an X-ray tube from a plurality of view directions around the subject with the slice thickness direction of the subject as an axis. Then, X-rays that pass through the subject from a plurality of view directions are detected by the X-ray detector for each view direction, and radiation projection data is generated. Then, the image generation apparatus included in the X-ray CT apparatus reconstructs and generates an image of the tomographic plane of the subject based on the radiation projection data. Then, image processing such as sharpening processing and smoothing processing is performed on the reconstructed subject image, and image quality corresponding to the imaging purpose is obtained (see, for example, Patent Document 1). ).
JP 2002-358517 A

  In the X-ray CT apparatus, the imaging region of the subject and the purpose of imaging have been diversified, and further improvement in image quality and speeding up of imaging are required. In order to meet such a demand, the X-ray detector of the X-ray CT apparatus has a plurality of detection elements arranged in an array so that a plurality of tomographic images can be obtained while scanning the periphery of the subject once. In order to obtain an image having a thin slice thickness, the detection elements are reduced in size and densified. For this reason, it is difficult to achieve both spatial resolution and density resolution of an image, and it has become difficult to improve image quality.

  In particular, when image processing such as sharpening or smoothing is performed on the reconstructed subject image, unnatural textures often occur due to overshoot or undershoot. It was difficult to improve.

  Further, when performing image reconstruction using a filter function corresponding to the imaging region of the subject at the time of image reconstruction, it is necessary to store a large amount of radiation projection data. Therefore, storage and management become difficult, and it is not easy to obtain image quality corresponding to the imaging region of the subject. In addition, in order to obtain image quality so as to correspond to the imaging region of the subject, the processing using the filter function may be performed a plurality of times, so that the operation efficiency may be reduced.

  Accordingly, an object of the present invention is to provide a radiation imaging apparatus and an image generation apparatus that can easily improve image quality and can improve operability.

  In order to achieve the above object, the radiographic apparatus of the present invention provides a radiographic image of the subject based on radiation projection data obtained by the detection unit detecting the radiation that is irradiated from the irradiation unit onto the subject and transmitted through the subject. A radiation imaging apparatus for generating an image, wherein a first filter processing is performed on the radiation projection data, and a first image is generated based on the radiation projection data subjected to the first filter processing. And a second image reconstruction unit that performs a second filter process different from the first filter process on the radiation projection data and generates a second image based on the radiation projection data subjected to the second filter process. A weighted addition unit that weights and adds the first image generated by the first image reconstruction unit and the second image generated by the second image reconstruction unit, and generates an image of the subject. .

  According to the above radiographic apparatus of the present invention, the first image reconstruction unit performs the first filter process on the radiation projection data from the subject, and based on the radiation projection data subjected to the first filter process. The first image is generated. Then, the second image reconstruction unit performs a second filter process different from the first filter process on the radiation projection data, and generates a second image based on the radiation projection data subjected to the second filter process. . Then, the image weighting addition unit weights and adds the first image generated by the first image reconstruction unit and the second image generated by the second image reconstruction unit, and generates an image of the subject.

  In order to achieve the above object, an image generation apparatus of the present invention is an image generation apparatus that generates an image of the subject based on radiation projection data obtained from the subject, and for the radiation projection data, A first image reconstruction unit that performs a first filter process and generates a first image based on the radiation projection data subjected to the first filter process; and a second different from the first filter process for the radiation projection data A second image reconstruction unit that performs a filtering process and generates a second image based on the radiation projection data that has been subjected to the second filter process; and the first image and the second image reconstruction unit that the first image reconstruction unit generates. And an image weighting addition unit that weights and adds the second image generated by the constituent unit and generates an image of the subject.

  According to the image generation apparatus of the present invention, the first image reconstruction unit performs the first filter process on the radiation projection data from the subject, and based on the radiation projection data subjected to the first filter process. The first image is generated. Then, the second image reconstruction unit performs a second filter process different from the first filter process on the radiation projection data, and generates a second image based on the radiation projection data subjected to the second filter process. . Then, the image weighting addition unit weights and adds the first image generated by the first image reconstruction unit and the second image generated by the second image reconstruction unit, and generates an image of the subject.

  According to the present invention, it is possible to provide a radiation imaging apparatus and an image generation apparatus that can easily improve image quality and can improve operability.

  Embodiments according to the present invention will be described below.

  FIG. 1 is a block diagram showing an overall configuration of an X-ray CT apparatus 1 as a radiation imaging apparatus according to an embodiment of the present invention, and FIG. 2 shows an X-ray CT as a radiation imaging apparatus according to an embodiment of the present invention. 2 is a configuration diagram showing a main part of the device 1. FIG.

  As shown in FIG. 1, the X-ray CT apparatus 1 of this embodiment includes a scanning gantry 2, an operation console 3, and an imaging table 4.

  The scanning gantry 2 includes an X-ray tube 20, an X-ray tube moving unit 21, a collimator 22, an X-ray detector 23, a data collection unit 24, an X-ray controller 25, a collimator controller 26, a rotation unit 27, and a rotation controller 28. . Here, the X-ray tube 20 and the X-ray detector 23 are disposed to face each other with the bore 29 interposed therebetween.

  The X-ray tube 20 is provided for irradiating X-rays. As shown in FIG. 2, the X-ray tube 20 irradiates the imaging region of the subject 6 with X-rays having a predetermined intensity via the collimator 22 based on a control signal CTL 251 from the X-ray controller 25.

  As shown in FIG. 2, the X-ray tube moving unit 21 places the radiation center of the X-ray tube 20 on the imaging table 4 in the bore 29 in the scanning gantry 2 based on the control signal CTL 252 from the X-ray controller 25. The object 6 to be placed is moved in the slice thickness direction z.

  As shown in FIGS. 1 and 2, the collimator 22 is disposed between the X-ray tube 20 and the X-ray detector 23. For example, as shown in FIG. 2, the collimator 22 is composed of two plates each provided in the channel direction x and the slice thickness direction z. Based on the control signal CTL 261 from the collimator controller 26, the collimator 22 moves the two plates provided in each direction independently, and blocks the X-rays emitted from the X-ray tube 20 in each direction. It is molded into a cone and the X-ray irradiation range is adjusted.

  The X-ray detector 23 is rotated together with the X-ray tube 20 by the rotating unit 27 about the slice thickness direction z, detects X-rays that pass through the subject for each of a plurality of view directions around the subject, and projects projection data. Is generated. As shown in FIG. 2, the X-ray detector 23 includes an X-ray detection module 23A, and a plurality of X-ray detection modules 23A are arranged along the channel direction x and the slice thickness direction z. ing. The X-ray detectors 23 are arranged such that, for example, J X-ray detection modules 23A are arranged in J in the channel direction x and I in the slice thickness direction z. That is, in the X-ray detector 23, the detection elements 23 a are arrayed in a channel direction x along the rotation direction by the rotation unit 27 and a slice thickness direction z that is a direction substantially perpendicular to the rotation direction by the rotation unit 27. Are two-dimensionally arranged.

  FIG. 3 is a configuration diagram showing the X-ray detection module 23 </ b> A constituting the X-ray detector 23. As shown in FIG. 3, in the X-ray detection module 23A, detection elements 23a for detecting X-rays are arranged in an array in the channel direction x and the slice thickness direction z. The plurality of detection elements 23a arranged two-dimensionally forms an X-ray incident surface curved in a cylindrical concave shape as a whole. Here, in the X-ray detection module 23A, for example, i detection elements 23a are arranged in the channel direction x, and j detection elements 23a are arranged in the slice thickness direction z.

  The detection element 23a includes, for example, a scintillator (not shown) that converts detected X-rays into light, and a photodiode (not shown) that converts light converted by the scintillator into charges. The X-ray detector 23 includes: It is configured as a solid state detector. The detection element 23a is not limited to this, and may be, for example, a semiconductor detection element using cadmium tellurium (CdTe) or the like, or an ionization chamber type detection element 23a using xenon (Xe) gas. Good.

  4 and 5 are diagrams showing the interrelationship among the X-ray tube 20, the collimator 22, and the X-ray detector 23. FIG. 4A is a diagram illustrating a state in which the slice thickness direction z is a line of sight, and FIG. 4B is a diagram illustrating a state in which the channel direction x is a line of sight. FIG. 5 is a diagram illustrating a state in which the subject 6 is imaged in a state where the line of sight is the channel direction x as in FIG. 4B.

  As shown in FIGS. 4A and 4B, the X-rays emitted from the X-ray tube 20 are formed into a cone shape by the collimator 22 and irradiated to the X-ray detector 23. When imaging the subject 6, the subject 6 is placed on the imaging table 4, and the placed subject 6 is carried into the bore 29. Then, as shown in FIG. 5, X-rays are irradiated from a plurality of view directions around the subject 6 with the slice thickness direction z of the subject 6 as an axis, and each subject view direction is viewed via the collimator 22. X-rays passing through the specimen 6 are detected by the X-ray detector 23 to generate radiation projection data of the subject.

  The data collection unit 24 is provided for collecting data based on radiation detected by the X-ray detector 23. The data collection unit 24 collects radiation projection data of the subject 6 based on the X-rays detected by the respective detection elements 23 a of the X-ray detector 23 and outputs the collected data to the operation console 3. As shown in FIG. 2, the data collection unit 24 includes a selection / addition switching circuit (MUX, ADD) 241 and an analog-digital converter (ADC) 242. The selection / addition switching circuit 241 selects the radiation projection data by the detection element 23a of the X-ray detector 23 according to the control signal CTL303 from the central processing unit 30, or adds the results by changing the combination. Output to digital converter 242. The analog-digital converter 242 converts the radiation projection data selected by the selection / addition switching circuit 241 or added in an arbitrary combination from an analog signal to a digital signal and outputs the digital signal to the central processing unit 30.

  As shown in FIG. 2, the X-ray controller 25 outputs a control signal CTL 251 to the X-ray tube 20 in accordance with a control signal CTL 301 from the central processing unit 30 to control X-ray irradiation. Further, the X-ray controller 25 outputs a control signal CTL252 to the X-ray tube moving unit 221 in response to the control signal CTL301 from the central processing unit 30, and moves the radiation center of the X-ray tube 20 in the slice thickness direction z. To control.

  As shown in FIG. 2, the collimator controller 26 outputs a control signal CTL 261 to the collimator 22 in response to the control signal CTL 302 from the central processing unit 30 to shape the X-rays emitted from the X-ray tube 20. 22 is controlled.

  As shown in FIG. 1, the rotating unit 27 rotates in a predetermined direction in response to a control signal CTL 28 from the rotation controller 28. The rotation unit 27 includes an X-ray tube 20, an X-ray tube moving unit 21, a collimator 22, an X-ray detector 23, a data collection unit 24, an X-ray controller 25, and a collimator controller 26, As the rotating unit 27 rotates, the position with respect to the subject 6 carried into the bore 29 changes. By rotating the rotating unit 27, X-rays are irradiated from a plurality of view directions with the slice thickness direction z of the subject 6 as an axis, and X-rays transmitted through the subject 6 are detected.

  As shown in FIG. 2, the rotation controller 28 outputs a control signal CTL 28 to the rotation unit 27 in accordance with a control signal CTL 304 from the central processing unit 30 of the operation console 3 and controls the rotation unit 27 to rotate.

  As shown in FIG. 1, the operation console 3 includes a central processing unit 30, an input device 31, a display device 32, and a storage device 33.

  FIG. 6 is a configuration diagram showing the configuration of the central processing unit 30 of the operation console 3.

  The central processing unit 30 is configured by a computer, for example, and includes a control unit 41 and a data processing unit 51 as shown in FIG.

  The control unit 41 irradiates the subject 6 with X-rays from the X-ray tube 20 based on the main scanning conditions for scanning the subject 6, and detects the X-rays transmitted through the subject 6 with the X-ray detector 23. In this way, each part is controlled to perform scanning. Specifically, the control unit 41 outputs a control signal CTL 30a to each unit based on the main scan condition to execute the main scan. For example, the control unit 41 outputs a control signal CTL 30 b to the imaging table 4, and causes the imaging table 4 to be carried into or out of the bore 29 of the scanning gantry 2. In addition, the control unit 41 outputs a control signal CTL 304 to the rotation controller 28 to rotate the rotation unit 27 of the scanning gantry 2. Further, the control unit 41 outputs a control signal CTL 301 to the X-ray controller 25 so that X-rays are emitted from the X-ray tube 20. And the control part 41 outputs the control signal CTL302 to the collimator controller 26, controls the collimator 22, and shape | molds X-ray | X_line. In addition, the control unit 42 outputs a control signal CTL 303 to the data collection unit 24 and controls to collect radiation projection data obtained by the detection element 23 a of the X-ray detector 23.

  The data processing unit 51 includes a first image reconstruction unit 61, a second image reconstruction unit 62, an image weighting addition unit 63, and an edge strength calculation unit 64.

The first image reconstruction unit 61 performs a first filter process on the radiation projection data collected by the data collection unit 24, and based on the radiation projection data subjected to the first filter process, the first image I ₁ (x , Y). That is, the first image reconstruction unit 61 reconstructs the first image I ₁ (x, y) by the filtered back projection method. Here, after performing preprocessing such as sensitivity correction and beam hardening correction, the first image reconstruction unit 61 performs processing for enhancing a high spatial frequency region as the first filter processing described above. The first image reconstruction unit 61 performs, for example, a back projection method after performing spatial integration processing on the radiation projection data from a plurality of view directions by a helical scan by superimposing and integrating with a filter function that emphasizes a high spatial frequency region. The first image I ₁ (x, y) corresponding to the tomographic plane of the subject 6 is reconstructed. As described above, the first image reconstruction unit 61 performs the filtering process, whereby the first image I ₁ (x, y) is sharpened.

The second image reconstruction unit 62 performs a second filter process different from the first filter process on the radiation projection data collected by the data collection unit 24, and based on the radiation projection data subjected to the second filter process. To reconstruct the second image I ₂ (x, y). That is, the second image reconstruction unit 62 reconstructs the second image I ₂ (x, y) by the filtered back projection method. Here, the second image reconstruction unit 62 performs preprocessing such as sensitivity correction and beam hardening correction, and then, as the above-described second filter processing, performs processing that emphasizes a lower spatial frequency region than the first filter processing. carry out. The second image reconstruction unit 62 integrates and integrates the same radiation projection data as the radiation projection data reconstructed by the first image reconstruction unit 61 with a filter function that emphasizes the low spatial frequency region. After the spatial filter processing, reconstruction is performed by the back projection method, and the second image I ₂ (x, y) corresponding to the tomographic plane of the subject 6 is reconstructed. As described above, the second image reconstruction unit 62 performs the filtering process, whereby the second image I ₂ (x, y) is smoothed. Note that the second image _I 1 (x, y) first image _I 1 to (x, y) and the second image reconstructing section 62 to the first image reconstructing section 61 reconstructs the reconstitution, the storage device It is output to 33 and stored.

The image weighting addition unit 63 includes a first image I ₁ (x, y) reconstructed by the first image reconstruction unit 61 and a second image I ₂ (x, y reconstructed by the second image reconstruction unit 62. ) Are weighted and added to generate an image I (x, y) of the subject 6. Here, the image weighting addition unit 63 weights and adds the first image I ₁ (x, y) and the second image I ₂ (x, y) stored in the storage device 33, and the image I of the subject 6 ( x, y) is generated. The image weighting addition unit 63 also uses the first image I ₁ (x, y) and the second image I ₂ (x, y) based on the edge strength β (x, y) calculated by the edge strength calculation unit 64. The weighting coefficient α (x, y) for weighting and adding is calculated, and the first image I ₁ (x, y) and the second image I ₂ (x, y) are calculated based on the calculated weighting coefficient α (x, y). y) is weighted and added to generate an image I (x, y) corresponding to the tomographic plane of the subject 6.

The edge strength calculation unit 64 includes a first image I ₁ (x, y) generated by the first image reconstruction unit 61, and a second image I ₂ (x, y) generated by the second image reconstruction unit 62. The edge strength β (x, y) of at least one of the images is calculated. Here, the edge strength indicates the difference in contrast of the edge portion of the image and the degree of change in the inclination of the edge. Edge strength calculating unit 64, for example, the target pixel in the first image (i, j) pixel values _I 1 (i, j) with, neighboring pixel (i-1 of the target pixel (i, j), j- 1), (i, j-1), (i + 1, j-1), (i-1, j), (i + 1, j), (i-1, j + 1), (i, j + 1), (i + 1, j + 1) pixel values I ₁ (i−1, j−1), I ₁ (i, j−1), I ₁ (i + 1, j−1), I ₁ (i−1, j), I ₁ ( i + 1, j), I ₁ (i−1, j + 1), I ₁ (i, j + 1), I ₁ (i + 1, j + 1), and the edge intensity β (i, j) for the target pixel (i, j) ) Is calculated.

  The input device 31 of the operation console 3 is composed of input devices such as a keyboard and a mouse, for example. The input device 31 is provided, for example, for inputting imaging conditions such as main scanning conditions and various types of information such as information about the subject 6 to the central processing unit 30.

  The display device 32 displays an image of the subject 6 generated by weighted addition by the image weighting addition unit 63 and other various information based on a command from the central processing unit 30.

The storage device 33 is configured by a memory, and a first image I ₁ (x, y) reconstructed by the first image reconstruction unit 61 and a second image I reconstructed by the second image reconstruction unit 62. ₂ Various data such as (x, y) and programs are stored. In the storage device 33, the stored data is accessed to the central processing unit 30 as necessary.

  The imaging table 4 is configured by a table on which the subject 6 to be imaged is placed. The imaging table 4 carries the subject 6 in or out of the bore 29 of the scanning gantry 2 based on a control signal from the operation console 3.

  In the present embodiment, the X-ray CT apparatus 1 corresponds to the radiation imaging apparatus of the present invention. In the present embodiment, the X-ray tube corresponds to the irradiation unit of the present invention. In the present embodiment, the X-ray detector 23 corresponds to the detection unit of the present invention. In the present embodiment, the storage device 33 corresponds to the storage unit of the present invention. In the present embodiment, the data processing unit 51 corresponds to the image generation device of the present invention. In the present embodiment, the first image reconstruction unit 61 corresponds to the first image reconstruction unit of the present invention. In the present embodiment, the second image reconstruction unit 62 corresponds to the second image reconstruction unit of the present invention. In the present embodiment, the image weighting addition unit 63 corresponds to the image weighting addition unit of the present invention. In the present embodiment, the edge strength calculation unit 64 corresponds to the edge strength calculation unit of the present invention.

  Hereinafter, an image generation method for generating an image of the subject 6 using the X-ray CT apparatus 1 of the present embodiment will be described.

  FIG. 7 is a flowchart showing an image generation method according to this embodiment.

  As shown in FIG. 7, first, radiation projection data is collected (S11).

  When collecting the radiation projection data of the subject 6, the operator inputs each setting item of the main scan condition to the input device 31 and outputs it to the central processing unit 30. For example, as the main scan conditions, the slice thickness, the number of slices, and other imaging methods such as conventional scan and helical scan are input to the input device 31 by the operator. Then, the control unit 41 of the central processing unit 30 outputs control signals CTL 30 a and CTL 30 b to the scanning gantry 2 and the imaging table 4. As a result, the control unit 41 outputs the control signal CTL 30 b to the imaging table 4 and causes the imaging table 4 to be carried into or out of the bore 29 of the scanning gantry 2. Then, the control unit 41 outputs a control signal CTL 304 to the rotation controller 28 to rotate the rotation unit 27 of the scanning gantry 2. Further, the control unit 41 outputs a control signal CTL 301 to the X-ray controller 25 so that X-rays are emitted from the X-ray tube 20. And the control part 41 outputs the control signal CTL302 to the collimator controller 26, controls the collimator 22, and shape | molds X-ray | X_line. Further, the control unit 41 outputs a control signal CTL 303 to the data collection unit 24 and controls to collect radiation projection data obtained by the detection element 23a of the X-ray detector 23.

Next, the first image I ₁ (x, y) and the second image I ₂ (x, y) of the subject 6 are reconstructed based on the collected radiation projection data (S21).

When the first image I ₁ (x, y) of the subject 6 is reconstructed, the first image reconstruction unit 61 performs a first filter process on the radiation projection data collected by the data collection unit 24. Then, the first image I ₁ (x, y) is reconstructed based on the first filtered radiation projection data. The first image reconstruction unit 61 performs, for example, spatial projection processing of radiation projection data from a plurality of view directions by a helical scan by a filter function that emphasizes a high spatial frequency region, and then performs reconstruction by a back projection method, A first image I ₁ (x, y) corresponding to the tomographic plane of the subject 6 is reconstructed. Thereby, the first image reconstruction unit 61 reconstructs the sharpened first image I ₁ (x, y).

Then, when the second image I ₂ (x, y) of the subject 6 is reconstructed, the second image reconstructing unit 62 performs the above-described first reconfiguration on the radiation projection data collected by the data collecting unit 24. A second filter process different from the one filter process is performed, and the second image I ₂ (x, y) is reconstructed based on the radiation projection data subjected to the second filter process. The second image reconstruction unit 62 spatially filters the same radiation projection data as the radiation projection data reconstructed by the first image reconstruction unit 61 with a filter function that emphasizes the low spatial frequency region. Reconstruction is performed by the back projection method, and the second image I ₂ (x, y) corresponding to the tomographic plane of the subject 6 is reconstructed. Thereby, the second image reconstruction unit 62 reconstructs the smoothed second image I ₂ (x, y).

Then, the first image _I 1 (x, y) and the second image _I 1 (x, y) of the second image reconstructing section 62 reconstructs the first image reconstructing section 61 reconstructs a storage device It outputs to 33 and memorize | stores it.

Next, the edge intensity β (x, y) of the first image I ₁ (x, y) is calculated for each pixel (S31). As described above, the edge intensity β (x, y) of the second image I ₂ (x, y) may be calculated for each pixel.

FIG. 8 is a diagram illustrating a part of the pixels of the first image I ₁ (x, y). FIG. 8 shows a 3 × 3 pixel matrix, and there are eight neighboring pixels (i−1) in the vicinity of the square target pixel (i, j) in the first image I ₁ (x, y). , J−1), (i, j−1), (i + 1, j−1), (i−1, j), (i + 1, j), (i−1, j + 1), (i, j + 1), It indicates that there is (i + 1, j + 1).

In calculating the edge intensity β (x, y) of the first image I ₁ (x, y) for each pixel, the edge intensity calculating unit 64, for example, in the first image I ₁ (x, y) pixel values _I 1 (i, j) of the pixel (i, j) and its target pixel (i, j) neighboring pixels (i-1, j-1 ), (i, j-1), (i + 1 , J−1), (i−1, j), (i + 1, j), (i−1, j + 1), (i, j + 1), (i + 1, j + 1) pixel values I ₁ (i−1, j) −1), I ₁ (i, j−1), I ₁ (i + 1, j−1), I ₁ (i−1, j), I ₁ (i + 1, j), I ₁ (i−1, j + 1) ), I ₁ (i, j + 1) and I ₁ (i + 1, j + 1) are used to calculate the edge strength β (i, j) for the target pixel (i, j). In the present embodiment, the CT value is used as the pixel value, and the edge strength β is calculated.

  First, the edge intensity calculation unit 64 first calculates the absolute value Ex of the difference in the pixel values of the rows in the row direction x in the neighboring neighboring pixels sandwiching the target pixel (i, j) as shown in Equation (1). Further, as shown in Equation (2), the absolute value Ey of the difference in the pixel values in the column in the column direction y is calculated in the neighboring neighboring pixels sandwiching the target pixel (i, j). Then, among the neighboring neighboring pixels sandwiching the target pixel (i, j), among the absolute value Ex of the difference in the pixel value of the row in the row direction x and the absolute value Ey of the difference in the pixel value of the column in the column direction y, The larger value is extracted as the first edge strength component E1.

Ex = | (I ₁ (i−1, j−1) + I ₁ (i, j−1), I ₁ (i + 1, j−1)) / 3− (I ₁ (i−1, j + 1) + I ₁ (I, j + 1) + I ₁ (i + 1, j + 1)) / 3 | (1)

Ey = | (I ₁ (i−1, j−1) + I ₁ (i−1, j), I ₁ (i−1, j + 1)) / 3− (I ₁ (i + 1, j−1) + I ₁ (I + 1, j) + I ₁ (i + 1, j + 1)) / 3 | (2)

Then, the edge strength calculating unit 64, as shown in Equation (3), from twice the value of the pixel values _I 1 of the pixel (i, j) (i, j), the pixel (i, j ) In the row direction x, the absolute value F1 of the value obtained by subtracting the pixel values I ₁ (i−1, j) and I ₁ (i + 1, j) of neighboring pixels (i−1, j) and (i + 1, j). Is calculated. Similarly, the edge intensity calculation unit 64 calculates the target pixel (i) from a value twice the pixel value I ₁ (i, j) of the target pixel (i, j) as shown in Equation (4). , J) is a value obtained by subtracting the pixel values I ₁ (i, j−1) and I ₁ (i, j−1) of neighboring pixels (i, j−1) and (i, j + 1) sandwiching the column direction x. The absolute value F2 is calculated. Similarly, the edge intensity calculation unit 64 has a value twice as large as the pixel value I ₁ (i, j) of the target pixel (i, j) as shown in Expression (5) and Expression (6). From pixel values I ₁ (i−1, j−1), I of neighboring pixels (i−1, j−1) and (i + 1, j + 1) sandwiching the target pixel (i, j) in one diagonal direction. The absolute value F3 of the value obtained by subtracting ₁ (i + 1, j + 1) is calculated, and neighboring pixels (i-1, j-1), (i + 1, j + 1) sandwiching the target pixel (i, j) in one diagonal direction The absolute value F4 of the value obtained by subtracting the pixel values I ₁ (i−1, j−1) and I ₁ (i + 1, j + 1) is calculated. As described above, the edge intensity calculation unit 64 calculates the target from the value twice the pixel value I ₁ (i, j) of the target pixel (i, j) in the first image I ₁ (x, y). Neighboring pixels (i−1, j−1), (i, j−1), (i + 1, j−1), (i−1, j), (i + 1) in a region extending in a predetermined direction centering on the pixel , J), (i−1, j + 1), (i, j + 1), (i + 1, j + 1), the pixel values I ₁ (i−1, j−1), I ₁ (i, j−1), I _{1 (i + 1, j-1} ), I 1 (i-1, j), I 1 (i + 1, j), I 1 (i-1, j + 1), I 1 (i, j + 1), I 1 (i + 1, j + 1 ), The absolute values F1, F2, F3, and F4 are calculated. Then, in the first image I ₁ (x, y), an area extending in a predetermined direction centering on the target pixel from a value twice the pixel value I ₁ (i, j) of the target pixel (i, j) Neighboring pixels (i−1, j−1), (i, j−1), (i + 1, j−1), (i−1, j), (i + 1, j), (i−1, j + 1) ), (I, j + 1), (i + 1, j + 1), pixel values I ₁ (i−1, j−1), I ₁ (i, j−1), I ₁ (i + 1, j−1), I ₁ Calculated by subtracting the pixel values of (i−1, j), I ₁ (i + 1, j), I ₁ (i−1, j + 1), I ₁ (i, j + 1), I ₁ (i + 1, j + 1) The maximum value is extracted as the second edge intensity component E2 from the absolute values F1, F2, F3, and F4.

F1 = | (2 · I ₁ (i, j) −I ₁ (i−1, j) −I ₁ (i + 1, j) | (3)

F2 = | (2 · I ₁ (i, j) −I ₁ (i, j−1) −I ₁ (i, j + 1) | (4)

F3 = | (2 · I ₁ (i, j) −I ₁ (i−1, j−1) −I ₁ (i + 1, j + 1) |) (5)

F4 = | (2 · I ₁ (i, j) −I ₁ (i−1, j + 1) −I ₁ (i + 1, j−1) | (6)

  The edge strength calculation unit 64 then sets the square root of the value obtained by multiplying the first edge strength component E1 and the second edge strength component E2 as edge strength β (i, j) as shown in Equation (7). calculate.

  β (i, j) = √ (E1 × E2) (7)

  The edge strength calculation unit 64 calculates the edge strength β (x, y) corresponding to each pixel as described above.

Next, the first image I ₁ (x, y) and the second image I ₂ (x, y) are weighted and added to generate the image I (x, y) of the subject 6 (S41).

In weighted addition of the first image I ₁ (x, y) and the second image I ₂ (x, y), based on the edge strength β (x, y) calculated by the edge strength calculation unit 64, The image weighting addition unit 63 calculates a weighting coefficient α (x, y) for weighted addition of the first image I ₁ (x, y) and the second image I ₂ (x, y). In the present embodiment, the weighting factor alpha (x, y) is the image i (x, y) first image _I 1 (x, y) in the subject 6 shows the percentage of using, from 0 to 1 Set by range. Since the first filter process performs high frequency region enhancement, the first image tends to include an edge. For this reason, it is better to detect the edge in the first image.

  FIG. 9 is a diagram showing the relationship between the edge strength β (x, y) and the weighting coefficient α (x, y).

As shown in FIG. 9, the edge intensity beta (x, y) if the increase, the first image I _{1 (x,} y) weighting coefficients such ratio is increased using alpha (x, y) image weighting addition Set by the unit 63. For example, the image weighting addition unit 63 sets the weighting coefficient α (x, y) to 0 when the edge strength β (x, y) is less than 10, and within the range where the edge strength β (x, y) is 10 or more and 300 or less. The weight coefficient α (x, y) is set so as to increase exponentially, and when the edge strength β (x, y) exceeds 300, the weight coefficient α (x, y) is set to 1. .

Then, as shown in Expression (8), the image weighting addition unit 63 uses the first image I ₁ (x, y) and the second image I ₂ ( x, y) is weighted and added to generate an image I (x, y) corresponding to the tomographic plane of the subject 6.

I (x, y) = α (x, y) · I ₁ (x, y) + (1−α (x, y)) · I ₂ (x, y) (8)

  Then, the image I (x, y) of the subject 6 generated by weighted addition by the image weighted addition unit 63 is output to the display device 32 and displayed.

As described above, according to the present embodiment, the first image reconstruction unit 61 performs the first filter process on the radiation projection data from the subject 6, and the radiation projection data subjected to the first filter process. To reconstruct the first image I ₁ (x, y). Then, the second image reconstruction unit 62 performs a second filter process different from the first filter process on the radiation projection data, and the second image I ₂ based on the radiation projection data subjected to the second filter process. Reconstruct (x, y). Then, the image weighting addition unit 63 includes the first image I ₁ (x, y) reconstructed by the first image reconstruction unit and the second image I ₂ (x, y) reconstructed by the second image reconstruction unit. Are weighted and added to generate an image I (x, y) of the subject 6.

  Here, the first image reconstruction unit 61 performs a process of enhancing a high spatial frequency region as the first filter process, and the second image reconstruction unit 62 is lower than the first filter process as the second filter process. A process for enhancing the spatial frequency domain is performed.

Further, according to the present embodiment, the first image I ₁ (x, y) generated by the first image reconstruction unit 61 and the second image I ₂ (x, y) generated by the second image reconstruction unit 62 are used. Is stored in the storage device 33. Then, the image weighting addition unit 63 weights and adds the first image I ₁ (x, y) and the second image I ₂ (x, y) stored in the storage device 33, and the image I (( x, y) is generated.

And, according to this embodiment, the first image I _{1 (x,} y) of the first image reconstructing section 61 reconstructs the second image I _{2 (x} of the second image reconstructing section 62 reconstructs, The edge strength calculation unit 64 calculates the edge strength β (x, y) of at least one of the images y). Then, the image weighting addition unit 63 determines the first image I ₁ (x, y) and the second image I ₂ (x, y) based on the edge strength β (x, y) calculated by the edge strength calculation unit 64. The weighting coefficient α (x, y) for weighted addition is calculated, and the first image I ₁ (x, y) and the second image I ₂ (x, y) are calculated based on the calculated weighting coefficient α (x, y). ) And weighted addition.

For this reason, this embodiment can easily achieve both spatial resolution and density resolution of an image, and can improve image quality. In addition, since the first image I ₁ (x, y) and the second image I ₂ (x, y) are reconstructed by the filter functions having different characteristics at the time of reconstruction, and they are weighted and added, Since there is no need to store radiation projection data, a large-capacity recording medium is unnecessary, and storage and management are facilitated, and operation efficiency can be improved. As described above, according to the present embodiment, it is easy to improve image quality, and operability can be improved.

  In implementing the present invention, the present invention is not limited to the above-described embodiment, and various modifications can be employed.

  For example, in the above embodiment, an example has been described in which radiation projection data of a subject is acquired using X-rays as radiation, and an image of the subject is generated. However, radiation is not limited to X-rays. For example, radiation such as gamma rays may be used.

  For example, in the above embodiment, the image weighting addition unit calculates a weighting factor for weighting and adding the first image and the second image based on the edge strength calculated by the edge strength calculation unit, and calculates the weighting factor. However, the present invention is not limited to this, and has a weighting factor input unit for inputting a weighting factor by an operator, and is based on the weighting factor set by the operator. Thus, the image weight addition unit may be configured to perform weight addition of the first image and the second image.

FIG. 1 is a block diagram showing an overall configuration of an X-ray CT apparatus according to an embodiment of the present invention. FIG. 2 is a configuration diagram showing a main part of the X-ray CT apparatus in the embodiment according to the present invention. FIG. 3 is a configuration diagram showing an X-ray detection module constituting the X-ray detector in the embodiment according to the present invention. FIG. 4 is a diagram showing the interrelationship among the X-ray tube, the collimator, and the X-ray detector in the embodiment according to the present invention. FIG. 5 is a diagram showing the interrelationship among the X-ray tube, the collimator, and the X-ray detector in the embodiment according to the present invention. FIG. 6 is a configuration diagram showing the configuration of the central processing unit of the operation console in the embodiment according to the present invention. FIG. 7 is a flowchart showing an image generation method according to the embodiment of the present invention. FIG. 8 is a diagram illustrating a part of the pixels of the first image in the embodiment according to the invention. FIG. 9 is a diagram showing the relationship between the edge strength and the weighting coefficient in the embodiment according to the present invention.

Explanation of symbols

1 ... X-ray CT apparatus (radiation imaging apparatus),
2 ... Scanning gantry,
3. Operation console,
4 ... Shooting table,
6 ... Subject,
20 ... X-ray tube (irradiation part),
21 ... X-ray tube moving part,
22 ... Collimator,
23 ... X-ray detector (detector),
23A ... X-ray detection module,
23a ... detecting element,
24 ... Data collection unit,
241 ... Selection / addition switching circuit,
242 ... Analog-to-digital converter,
25 ... X-ray controller,
26 ... Collimator controller,
27 ... rotating part,
28 ... Rotation controller,
29 ... Boa,
30 ... Central processing unit,
31 ... Input device,
32 ... display device,
33 ... Storage device (storage unit)
41. Control unit,
51. Data processing unit (image generating device),
61 ... 1st image reconstruction part (1st image reconstruction part),
62 ... 2nd image reconstruction part (2nd image reconstruction part),
63 ... Image weighting addition unit (image weighting addition unit),
64... Edge strength calculator (edge strength calculator)

Claims (6)

A radiation imaging apparatus that generates an image of the subject based on radiation projection data obtained by the detection unit detecting the radiation irradiated to the subject from an irradiation unit and transmitted through the subject,
To the radiation projection data, a high spatial frequency domain performed first filtering emphasizes, first image reconstruction unit which reconstructs a first image based on the first filtered radiation projection data ,
A second filter process different from the first filter process for emphasizing a low spatial frequency region lower than the first filter process is performed on the radiation projection data, and based on the radiation projection data subjected to the second filter process A second image reconstruction unit for reconstructing the second image;
The first image reconstructed by the first image reconstruction unit and the second image reconstructed by the second image reconstruction unit are weighted using a weighting coefficient obtained based on the edge intensity for each pixel. A radiation imaging apparatus comprising: an image weighting addition unit that adds and generates an image of the subject. A storage unit for storing the first image reconstructed by the first image reconstruction unit and the second image reconstructed by the second image reconstruction unit;
The image weighting addition unit weights and adds the first image and the second image stored in the storage unit using a weighting coefficient obtained for each pixel to generate an image of the subject. Item 2. The radiographic apparatus according to Item 1 . An edge strength calculation unit that calculates edge strength for each pixel of at least one of the first image reconstructed by the first image reconstruction unit and the second image reconstructed by the second image reconstruction unit; Have
The image weighting addition unit calculates, for each pixel, a weighting coefficient for weighting and adding the first image and the second image based on the edge strength for each pixel calculated by the edge strength calculation unit, the radiographic apparatus according to claim 1 or 2 weighted summing said first image and the second image based on the weighting factor. An image generating device that generates an image of the subject based on radiation projection data obtained from the subject,
To the radiation projection data, a high spatial frequency domain performed first filtering emphasizes, first image reconstruction unit which reconstructs a first image based on the first filtered radiation projection data ,
The radiation projection data is subjected to a second filtering process different from the first filtering process for emphasizing a low spatial frequency region lower than the first filtering process, and a second filtering process is performed based on the radiation filtering data subjected to the second filtering process. A second image reconstruction unit for reconstructing two images;
The first image reconstructed by the first image reconstruction unit and the second image reconstructed by the second image reconstruction unit are weighted using a weighting coefficient obtained based on the edge intensity for each pixel. An image generation apparatus comprising: an image weighting addition unit that adds and generates an image of the subject. A storage unit for storing the first image reconstructed by the first image reconstruction unit and the second image reconstructed by the second image reconstruction unit;
The image weighting addition unit weights and adds the first image and the second image stored in the storage unit using a weighting coefficient obtained for each pixel to generate an image of the subject. Item 5. The image generation device according to Item 4 . An edge strength calculation unit that calculates edge strength for each pixel of at least one of the first image reconstructed by the first image reconstruction unit and the second image reconstructed by the second image reconstruction unit; Have
The image weighting addition unit calculates, for each pixel, a weighting coefficient for weighting and adding the first image and the second image based on the edge strength for each pixel calculated by the edge strength calculation unit, The image generation apparatus according to claim 4, wherein the first image and the second image are weighted and added based on the weighting factor obtained.

Images