JP4430987B2 - Radiation tomography apparatus, tomography method thereof, and correction data calculation method - Google Patents

Description

  The present invention relates to a radiation tomography apparatus, a tomography method and a correction data calculation method thereof, and more particularly to a radiation tomography apparatus and a tomography method for calculating correction data for correcting projection data of a subject in a slice thickness direction. The present invention relates to a correction data calculation method.

  As a radiation tomography 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 scans the periphery of the subject with the slice thickness direction of the subject as an axis, and irradiates the subject with X-rays from a plurality of view directions through the X-ray tube. Then, the X-rays irradiated by the X-ray tube are blocked by a collimator, and the X-rays are shaped so as to irradiate the imaging region of the subject. Then, based on projection data generated by detecting X-rays transmitted through the subject from a plurality of view directions via the collimator by the X-ray detector for each view direction, a tomographic image of the imaging region of the subject Is reconstructed and generated.

  The X-ray CT apparatus has diversified the imaging part of the subject and the purpose of imaging, and is required to improve the image quality such as resolution and to increase the imaging speed. 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. It is arranged. Here, in order to facilitate manufacture, the X-ray detector includes an X-ray detection module in which a plurality of detection elements for detecting X-rays are arranged in an array. The slice thickness direction and the channel direction perpendicular to the slice thickness direction are arranged adjacent to each other.

  In an X-ray detector in which a plurality of detection elements are arranged in an array, a plurality of detection elements are arranged close to each other, so that a part of the detection output generated by one detection element is close to each other. May flow out to other detection elements, and crosstalk may occur between the detection elements. For example, when the X-ray detector is a solid state detector, X-ray scattering between detection elements, charge leakage generated between photodiodes of the detection element, and light generated by the scintillator of the detection element Crosstalk occurs due to leakage of the detection element to the photodiode.

  When crosstalk occurs, a tomographic image is reconstructed based on projection data including the crosstalk, so that an artifact may occur in the tomographic image and image quality may deteriorate.

Conventionally, various methods have been proposed to prevent image quality deterioration due to crosstalk. For example, a crosstalk generation amount is obtained for each detection element in advance, and projection data is corrected using the obtained crosstalk generation amount (see, for example, Patent Document 1).
JP-A-2-13436

  However, in the past, since the phantom was scanned around the slice thickness direction, it was easy to determine the amount of crosstalk generated for each detection element in the channel direction. However, the crosstalk in the slice thickness direction was easy to obtain. It was difficult to determine the amount generated. For this reason, conventionally, it has been difficult to prevent deterioration in image quality due to crosstalk in the slice thickness direction. In particular, in the detection element of the X-ray detection module in the center in the channel direction, crosstalk in the slice thickness direction becomes significant, and artifacts are generated due to the projection data generated by this part of the detection element. In some cases, the image quality deteriorates significantly.

  Accordingly, an object of the present invention is to provide a radiation tomography apparatus, a tomographic imaging method thereof, and a correction data calculation method capable of preventing occurrence of artifacts in a tomographic image due to crosstalk and improving the image quality of the tomographic image. There is.

  In order to achieve the above object, in the radiation tomography apparatus of the present invention, an irradiation unit that irradiates radiation and a detection element that detects radiation irradiated from the irradiation unit are orthogonal to the slice thickness direction and the slice thickness direction. Detection units arranged in an array in the channel direction, and first projection data of the subject obtained by the detection unit detecting the radiation that is irradiated from the irradiation unit to the subject and transmitted through the subject A tomographic image generation unit that generates a tomographic image of the subject based on the correction data, a correction data calculation unit that calculates correction data for correcting crosstalk in the slice thickness direction of the first projection data, and A correction unit that corrects crosstalk of the first projection data based on the correction data calculated by the correction data calculation unit, and the correction data calculation unit has a conical shape. A slope phantom including a portion is disposed between the irradiation unit and the detection unit such that a circular center axis of the conical shape portion corresponds to the slice thickness direction, and the slope phantom is disposed on the slope phantom from the irradiation unit. A phantom tomographic image generation unit configured to generate a tomographic image of the slope phantom based on second projection data of the slope phantom obtained by irradiating the radiation and passing through the slope phantom and detected by the detection unit The correction data is calculated based on the slope phantom tomographic image generated by the phantom tomographic image generation unit.

  According to the above-described radiation tomography apparatus of the present invention, the slope phantom including the cone-shaped portion is disposed between the irradiation portion and the detection portion so that the circular central axis of the cone-shaped portion corresponds to the slice thickness direction, Generates a phantom tomographic image of the slope phantom based on the second projection data of the slope phantom obtained by irradiating the arranged slope phantom with radiation from the irradiation unit and transmitting through the slope phantom and detected by the detection unit Generated. Then, based on the slope phantom tomographic image generated by the phantom tomographic image generation unit, the correction data calculation unit calculates correction data for correcting crosstalk in the slice thickness direction of the first projection data. Then, based on the correction data calculated by the correction data calculation unit, the correction unit corrects the crosstalk in the slice thickness direction of the first projection data.

  In order to achieve the above object, a tomography method for a radiation tomography apparatus according to the present invention includes: an irradiation unit that irradiates radiation; and a detection element that detects radiation emitted from the irradiation unit includes: The detection unit is arranged in an array in a channel direction orthogonal to the direction, and is obtained by detecting the radiation irradiated from the irradiation unit to the subject and transmitted through the subject by the detection unit A tomography method for a radiation tomography apparatus for generating a tomographic image of a subject based on first projection data of the subject, wherein a slope phantom including a cone-shaped portion is placed in the slice thickness direction of the cone-shaped portion. A first step disposed between the irradiation unit and the detection unit so that a circle center axis corresponds, and the slope phantom disposed in the first step is released from the irradiation unit. A second step of generating a tomographic image of the slope phantom based on the second projection data of the slope phantom obtained by irradiating a line, passing through the slope phantom and detected by the radiation detected by the detection unit; Based on the tomographic image of the slope phantom generated in the second step, the third step for calculating correction data for correcting crosstalk in the slice thickness direction of the first projection data, and the third step And a fourth step of correcting crosstalk in the slice thickness direction of the first projection data based on the correction data calculated as described above.

  According to the tomography method of the radiation tomography apparatus of the present invention described above, in the first step, the slope phantom including the cone-shaped portion is connected to the irradiation unit so that the center axis of the cone-shaped portion corresponds to the slice thickness direction. It arrange | positions between detection parts. Then, in the second step, the first projection data of the slope phantom obtained by irradiating the slope phantom disposed in the first step from the irradiation unit and transmitting through the slope phantom and detected by the detection unit. Based on this, a tomographic image of the slope phantom is generated. In the third step, correction data for correcting crosstalk in the slice thickness direction of the first projection data is calculated based on the tomographic image of the slope phantom generated in the second step. In the fourth step, the crosstalk in the slice thickness direction of the first projection data is corrected based on the correction data calculated in the third step.

  In order to achieve the above object, according to the correction data calculation method of the present invention, an irradiation unit that irradiates radiation and a detection element that detects the radiation irradiated from the irradiation unit are orthogonal to the slice thickness direction and the slice thickness direction. A detection unit arranged in an array in the channel direction, and a first portion of the subject obtained by detecting the radiation that is irradiated from the irradiation unit to the subject and transmitted through the subject. Correction data calculation method for calculating correction data for correcting crosstalk of the first projection data in the slice thickness direction in a radiation tomography apparatus that generates a tomographic image of the subject based on one projection data A slope phantom including a cone-shaped portion is disposed between the irradiation unit and the detection unit such that a circular central axis of the cone-shaped portion corresponds to the slice thickness direction. The slope phantom obtained by irradiating radiation from the irradiation unit to the slope phantom arranged in the first step and passing through the slope phantom and detected by the detection unit A second step of generating a tomographic image of the slope phantom based on the second projection data, and a slice thickness direction of the first projection data based on the tomographic image of the slope phantom generated in the second step And a third step of calculating correction data for correcting crosstalk.

  According to the correction data calculation method of the present invention described above, in the first step, the slope phantom including the conical portion is arranged between the irradiation unit and the detection unit so that the circular central axis of the conical portion corresponds to the slice thickness direction. Place between. Then, in the second step, the first projection data of the slope phantom obtained by irradiating the slope phantom disposed in the first step from the irradiation unit and transmitting through the slope phantom and detected by the detection unit. Based on this, a tomographic image of the slope phantom is generated. In the third step, correction data for correcting crosstalk in the slice thickness direction of the first projection data is calculated based on the tomographic image of the slope phantom generated in the second step. In the fourth step, the crosstalk in the slice thickness direction of the first projection data is corrected based on the correction data calculated in the third step.

  According to the present invention, it is possible to provide a radiation tomographic apparatus, a tomographic image capturing method thereof, and a correction data calculating method capable of preventing the occurrence of artifacts in a tomographic image due to crosstalk and improving the image quality of the tomographic image. it can.

  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 tomography apparatus according to an embodiment of the present invention, and FIG. 2 shows an X as a radiation tomography apparatus according to an embodiment of the present invention. 1 is a configuration diagram showing a main part of a line CT apparatus 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 provided for detecting X-rays emitted from the X-ray tube 20. 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 transmitted through the specimen 6 are detected by the X-ray detector 23 to generate 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 projection data of the subject 6 based on the X-rays detected by the 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 projection data by the detection element 23a of the X-ray detector 23 in accordance with the control signal CTL303 from the central processing unit 30, or adds a combination thereof, and the result is analog- Output to the digital converter 242. The analog-digital converter 242 converts the 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 it 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 projection data obtained by the detection element 23 a of the X-ray detector 23.

  The data processing unit 51 includes a subject tomographic image generation unit 52, a correction data calculation unit 53, and a correction unit 54.

  The subject tomographic image generation unit 52 converts the X-rays that are irradiated from the X-ray tube 20 to the subject 6 and transmitted through the subject 6 into the projection data of the subject 6 that can be detected by the X-ray detector according to the main scanning condition. Based on this, a tomographic image of the subject 6 is generated. For example, the subject tomographic image generation unit 52 generates a tomographic image of the subject 6 by performing image reconstruction on the projection data from a plurality of view directions by helical scanning, for example, by the filter-corrected back projection method. In the present embodiment, the subject tomographic image generation unit 52 generates a tomographic image of the subject 6 based on the projection data of the subject 6 corrected by the correction unit 54, as will be described later.

  The correction data calculation unit 53 calculates correction data for correcting crosstalk in the slice thickness direction of the projection data of the subject 6 obtained under the main scan conditions. The correction data calculation unit 53 includes a phantom tomographic image generation unit 53a as shown in FIG.

The phantom tomographic image generation unit 53a is disposed between the X-ray tube 20 and the X-ray detector 23 so that the circular central axis of the cone-shaped part corresponds to the slice thickness direction between the X-ray tube 20 and the X-ray detector 23. Based on the second projection data of the slope phantom P obtained by irradiating the arranged slope phantom P with X-rays from the X-ray tube 20, passing through the slope phantom P and detected by the X-ray detector 23. A tomographic image of the slope phantom P is generated.
For example, the phantom tomographic image generation unit 53a acquires the projection data of the slope phantom P from a plurality of view directions by, for example, a conventional scan based on the calibration scan condition, and regenerates the projection data by the filtered back projection method. A configuration is performed, and a tomographic image of the slope phantom P is generated.

  Then, the correction data calculating unit 53 calculates correction data based on the tomographic image of the slope phantom P generated by the phantom tomographic image generating unit 53a. For example, the correction data calculation unit 53 calculates difference data between the detection elements 23a based on pixel data corresponding to the detection elements 23a in the tomographic image of the slope phantom P generated by the phantom tomographic image generation unit 53a, Correction data is calculated based on the calculated difference value. Specifically, the correction data calculation unit 53 is an average value of pixel data corresponding to the detection elements 23a arranged in the X-ray detection module 23A in the tomographic image of the slope phantom P generated by the phantom tomographic image generation unit 53a. Is calculated for each X-ray detection module 23A. And in the average value calculated for every X-ray detection module, the difference between each X-ray detection module is calculated | required and it is set as average difference data. Then, correction data is calculated based on the calculated average difference data.

  The correction unit 54 corrects the crosstalk in the slice thickness direction of the projection data of the subject 6 based on the correction data calculated by the correction data calculation unit 53. The projection data of the subject 6 corrected by the correction unit 54 is output to the subject tomographic image generation unit 52, and the subject tomographic image generation unit 52 is based on the corrected projection data of the subject 6. 6 tomographic images are generated.

  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 to input various information such as imaging conditions such as calibration scan conditions and main scan conditions and information on the subject 6 to the central processing unit 30, for example.

  The display device 32 displays a tomographic image of the subject 6 generated by the subject tomographic image generation unit 52 and various other information based on a command from the central processing unit 30.

  The storage device 33 is configured by a memory, and stores various data such as image data of a tomographic image of the subject 6, a program, and the like. 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 tomography 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 X-ray detection module 23A corresponds to the detection module of the present invention. In the present embodiment, the detection element 23a corresponds to the detection element of the present invention. In the present embodiment, the tomographic image generation unit 52 corresponds to the tomographic image generation unit of the present invention. In the present embodiment, the correction data calculation unit 53 corresponds to the correction data calculation unit of the present invention. In the present embodiment, the phantom tomographic image generation unit 53a corresponds to the phantom tomographic image generation unit of the present invention. In the present embodiment, the correction unit 54 corresponds to the correction unit of the present invention. In the present embodiment, the slope phantom P corresponds to the slope phantom of the present invention.

  Hereinafter, a tomography method for generating a tomographic 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 the tomography method in the present embodiment.

  As shown in FIG. 7, first, a step of arranging a slope phantom is performed (S11).

  FIG. 8 is a diagram for explaining a state in which the slope phantom is arranged.

  As shown in FIG. 8, the slope phantom P is made of a single reference material, has a truncated cone shape, includes a cone shape, and has a thickness that is continuously inclined in one direction. The slope phantom P has a larger cross-sectional area in the slice thickness direction z when arranged as described above than the X-ray detection module A constituting the X-ray detector 23. As shown in FIG. 8, the slope phantom P is placed between the X-ray tube 20 and the X-ray detector 23 so that the central axis of the conical circle is parallel to the slice thickness direction z. Deploy. In this embodiment, when arranging the direction in which the thickness of the slope phantom P changes along the slice thickness direction z, the side opposite to the one side (z +) of the slice thickness direction z of the X-ray detector 23 (z +). Place it so that-) is thick.

  Next, a step of generating a phantom tomographic image is performed (S21).

  When taking a phantom tomographic image, the operator inputs each setting item of the calibration scan condition to the input device 31. For example, a calibration scan condition in which the slice thickness is 10 mm and the imaging method is a conventional scan is input to the input device 31. The calibration scan condition input to the input device 31 is output to the central processing unit 30.

  Based on the calibration scan condition input to the input device 31, 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. 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 41 outputs a control signal CTL 303 to the data collection unit 24 and controls to collect projection data obtained by the detection element 23 a of the X-ray detector 23.

  Based on the projection data of the slope phantom P obtained by irradiating the slope phantom P with X-rays from the X-ray tube 20 and passing through the slope phantom P and detected by the X-ray detector 23, The image generation unit 53a generates a tomographic image of the slope phantom P. The phantom tomographic image generation unit 53a generates a tomographic image of the slope phantom P by performing image reconstruction on the projection data of the slope phantom P from a plurality of view directions by a conventional scan by the filter-corrected back projection method.

  Next, a step of calculating correction data H for correcting the projection data of the subject 6 is performed (S31).

  FIG. 9 is a diagram for explaining the step of calculating the correction data H in the present embodiment.

In FIG. 9, FIG. 9A is a diagram of a tomographic image of the slope phantom P generated by the phantom tomographic image generation unit 53a. Further, in FIG. 9, FIG. 9B is a plan view schematically showing an enlarged part of the X-ray detector 23. FIG. 9B shows a portion where the X-ray detection modules 23A are arranged in the channel direction x. Here, the X-ray detector module _{23A X0} at the position of _{x 0} is disposed in the central portion _{x 0} of the channel direction x of the X-ray detector 23, X-ray detection module _23A is in the position of the _{x 0 X0} X-ray detection modules 23A _X1 and 23A _X-1 are disposed at the positions of x ₁ and x ₋₁ so that the end of the slope phantom P corresponds to x _i and x _−i . X-ray detection modules 23A _Xi and 23A _X-i are arranged at the positions.

The first region of interest ROI ₁ in FIG. 9 (a), the projection of the slope phantom P of the X-ray detector 23 obtained in X-ray detector module _{23A X0} at the position of _{x 0} shown in FIG. 9 (b) This corresponds to an area of an image generated by data. Further, the second region of interest ROI ₂ is obtained from the projection data of the slope phantom P obtained by the _X- ray detection modules 23A _X1 and A _X-1 at the positions of x ₁ and x ₋₁ in the X-ray detector 23. This corresponds to the area of the generated image. Although not shown in FIG. 9, the first region of interest ROI ₁ and the second region of interest ROI ₂ are the X-ray detection modules 23A _X0 , 23A _X1 , 23A _X− of the central portion of the X-ray detector 23. _1, the image of that portion becomes a band shape due to crosstalk, and the boundaries between the _X- ray detection modules 23A _X0 , 23A _X1 , and 23A _X-1 appear in the image.

  When calculating the correction data H, the correction data calculation unit 53 calculates the correction data H based on the tomographic image of the slope phantom P generated by the phantom tomographic image generation unit 53a. In the present embodiment, the correction data calculation unit 53 relatively compares pixel data corresponding to the detection element 23a in the tomographic image of the slope phantom P generated by the phantom tomographic image generation unit 53a, and compares the difference data S with the detection element. The correction data H is calculated based on the calculated difference data S.

  Specifically, the correction data calculation unit 53 first has pixel data corresponding to the detection elements 23a arranged in the X-ray detection module 23A in the tomographic image of the slope phantom P generated by the phantom tomographic image generation unit 53a. The average value A is calculated for each X-ray detection module 23A. In the present embodiment, CT values are used as pixel data corresponding to the detection elements 23a arranged in the X-ray detection module 23A.

Correction data calculating unit 53, for example, in the case where the average value _{A X0} of the pixel data in the X-ray detector module _{23A X0} at the position of _{x 0} corresponds to the X-ray detector module _{23A X0} at position _{x 0} An average value A _X0 is obtained using pixel data in the first region of interest ROI ₁ . Further, the correction data calculating section 53, the time for obtaining the average value _{A X1} of the pixel data in the X-ray detector module 23Ax _1, 23Ax _-1 at the position of the _{x 1} and _{x -1} are _{x 1} and _{x -1} The average value A _X1 is obtained using the pixel data in the _second region of interest ROI ₂ corresponding to the X-ray detection modules 23Ax ₁ and 23Ax ₋₁ at the positions. Similarly, the correction data calculating section 53, _{x i} and _x is in the position of the _-i X-ray detector module 23Ax _i, the average value _A Xi of the pixel data in 23Ax _-i, in when determining the _{A Xi} is An average value A _Xi is obtained using pixel data in the ( _{i + 1} ) -th region of interest ROI _{i + 1} corresponding to the X-ray detection modules 23Ax _i and 23Ax- _i at the positions of x _i and x _−i .

The average their respective average of the calculated pixel data values _{A X0, A X1, A Xi} and X-ray detection module _{23A X0, 23Ax 1, 23Ax -1} , 23Ax i, and relative comparison between 23Ax _-i The difference data S is calculated.

Here, the position _x i of the end _{side, x -i} is the X-ray detector module 23Ax _i, for the generation of crosstalk is small between the detecting elements 23a in 23Ax _-i, position _x i of the end side, The average of the pixel data corresponding to each X-ray detection module 23A _X0 , 23Ax ₁ , 23Ax ₋₁ with reference to the average value A _Xi of the pixel data corresponding to the X-ray detection modules 23Ax _i , 23Ax- _i in x _−i Differences from the values A _X0 , A _X1 , and A _Xi are calculated, and average difference data S _x0 , S _x1 , and S _x−1 are calculated. For example, the X-ray detection at the position x ₀ is detected from the average value A _Xi of the pixel data corresponding to the X-ray detection modules 23Ax _i and 23Ax _−i at the positions x _i and x _−i as shown in the equation (1). by subtracting the average value _{a x0} modules 23Ax _0, to calculate the average difference data _{S x0} corresponding to the X-ray detector module 23Ax ₀ at position _{x 0.} Then, as shown in Expression (2), the average value A _Xi of the pixel data corresponding to the X-ray detection modules 23Ax _i and 23Ax _−i at the positions x _i and x _−i is changed to the positions x _{1 and} x ₋₁ . by subtracting the average value _{a X1} of a X-ray detector module _23Ax 1, _{23Ax -1,} position _{x 1,} the average difference data _S x1 corresponding to the X-ray detector module _23Ax 1, _{23Ax -1} in the _{x -1, S x −1} is calculated.

S _x0 = A _Xi −A _X0 (1)

S _x1 = S _x−1 = A _Xi −A _X1 (2)

Then, based on the average difference data S _x0 , S _x1 , S _x−1 calculated as described above, the correction coefficient α is determined for each X-ray detection module 23A _X0 , 23Ax ₁ , 23Ax _−1. 53 is calculated. The correction data calculation unit 53 calculates correction coefficients α _x0 , α _x1 , α _x−1 in the range of 0 to 1 based on the absolute values of the average difference data S _x0 , S _x1 , S _x−1 . For example, as shown in Equation (3), the absolute value of the average difference data S _X0 of the X-ray detection module 23Ax _{0 at} the position x ₀ is converted by the conversion constants k ₁ and k _{2 and} is at the position x ₀ . A correction coefficient α _x0 in the X-ray detection module 23Ax ₀ is calculated. Further, as shown in Expression (4), the absolute values of the average difference data S _x1 and S _x-1 of the X-ray detection modules 23Ax _1, 23Ax _{-1 at} the positions x _1, x _-1 are converted into the conversion constant k _1. , K ₂ , and correction coefficients α _x1 and α _x−1 in the X-ray detection modules 23Ax _{1 and} 23Ax _{−1 at} the positions x _{1 and} x ₋₁ are calculated. Here, k ₁ and k ₂ in the formulas (3) and (4) are constants, and the absolute values of the average difference data S _x0 , S _x1 and S _x−1 are corrected within the range of 0 to 1. The coefficients α _x0 , α _x1 , and α _x−1 are set to be converted.

α _x0 = k ₁ · | S _X0 | + k ₂ (3)

α _x1 = α _x−1 = k ₁ · | S _X1 | + k ₂ = k ₁ · | S _X−1 | + k ₂ (4)

Then, the correction data calculation unit 53 sets the positive / negative sign of the average difference data S and the value of the correction coefficient α as correction data H and outputs the correction data H to the correction unit 54. The correction data calculation unit 53 uses, as the correction data H, the positive / negative sign of the average difference data S _x0 , S _x1 , S _x−1 for each of the X-ray detection modules 23A _X0 , 23Ax ₁ , 23Ax ₋₁ and the correction coefficient α _x0. , Α _x1 , α _x-1 and the correction data H _X0 , H _X1 , H _X-1 corresponding to the respective X-ray detection modules 23A _X0 , 23Ax ₁ , 23Ax ₋₁ are generated, and the correction unit To 54.

  Next, a step of correcting the projection data of the subject 6 is performed (S41).

  When correcting the projection data of the subject 6, first, the projection data of the subject 6 is collected. When collecting projection data of the subject 6, each setting item of the main scan condition is input to the input device 31 by the operator and output 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 projection data obtained by the detection element 23a of the X-ray detector 23.

  After collecting the projection data of the subject 6 under the main scan conditions, the correction unit 54 corrects the projection data of the subject 6 in the slice thickness direction based on the correction data H calculated by the correction data calculation unit 53.

  FIG. 10 is a diagram for explaining the correction of the projection data of the subject 6.

In Figure 10, and FIG. 9 (b) in which an enlarged view of the X-ray detection module _{23A X0} at the position of _{x 0,} two so as to sandwich the detecting elements 23a ₀ of center detection elements _23a 1, _{23a -1} Indicates a portion arranged in the slice thickness direction z. Moreover, the arrow shown in FIG. 10 has shown the crosstalk between each detection element 23a, and when the magnitude | size of the arrow is large, it has shown that the amount of crosstalk is large.

For example, in the correction data H generated in the above step, when the sign of the average difference data S _x0 of the X-ray detection module 23A _X0 at the position of x ₀ is positive, the correction data H is arranged as shown in FIG. The amount of crosstalk is larger in the thin direction (Z−) than in the direction (Z +) where the thickness of the slope phantom P is thick.

In this case, the projection data _{P 0} according to the detection elements 23a ₀ in the center in FIG. 10, relatively would have crosstalk only the detection element 23a ₁ of the Z + side. For this reason, the correction unit 54 uses the correction coefficient α _x0 to return the data for the crosstalk from the projection data P ₁ by the detection element 23a ₁ on the Z + side as shown in Expression (5), and the corrected projection data c_P ₀ is obtained.

c_P ₀ = (1−α _x0 ) · P ₀ + α _x0 · P ₁ (5)

On the other hand, in the correction data H generated in the above-described step, when the sign of the average difference data S _x0 of the X-ray detection module 23A _X0 at the position of x ₀ is negative, contrary to the case shown in FIG. The amount of crosstalk is greater in the thicker direction (Z +) than in the thinner direction (Z−) of the arranged slope phantom P.

In this case, the projection data _{P 0} according to the detection elements 23a ₀ in the center in FIG. 10, relatively would have crosstalk only the detection element 23a ₁ of the Z- side. For this reason, the correction unit 54 uses the correction coefficient α _x0 to return the crosstalk data from the projection data P ₋₁ by the Z− side detection element 23a ₋₁ as shown in Equation (6), and after correction. Projection data c_P ₀ is obtained.

c_P ₀ = (1−α _x0 ) · P ₀ + α _x0 · P ₋₁ (6)

  As described above, the correction unit 54 corrects the projection data of the subject 6 based on the correction data H.

  Then, the projection data of the subject 6 corrected by the correction unit 54 is output to the subject tomographic image generation unit 52, and the subject tomographic image generation unit 52 based on the corrected projection data of the subject 6. A tomographic image of the subject 6 is generated. The subject tomographic image generation unit 52 reconstructs the projection data corrected by the correction unit 54 by, for example, a filter-corrected back projection method, and generates a tomographic image of the subject 6. The tomographic image of the subject 6 generated by the subject tomographic image generation unit 52 is output to the display device 32 and displayed.

  As described above, according to the X-ray CT apparatus of the present embodiment, the slope phantom P including the cone-shaped portion has the slice central axis between the X-ray tube 20 and the X-ray detector 23 and the circular central axis of the cone-shaped portion. Slope obtained by X-rays arranged so as to correspond to the direction z, irradiating the arranged slope phantom P with X-rays from the X-ray tube 20, passing through the slope phantom P and detected by the X-ray detector 23 Based on the projection data of the phantom P, the phantom tomographic image generation unit 53a generates a tomographic image of the slope phantom P. Then, based on the slope phantom tomographic image generated by the phantom tomographic image generation unit 53a, the correction data calculation unit 53 calculates correction data for correcting the projection data of the subject 6 in the slice thickness direction z. . Based on the correction data calculated by the correction data calculation unit 53, the correction unit 54 corrects the crosstalk in the slice thickness direction z of the projection data of the subject 6.

  For this reason, according to this embodiment, it is possible to prevent occurrence of artifacts in the tomographic image due to crosstalk, and to improve the image quality of the tomographic image.

  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-described embodiment, an example is described in which projection data of a subject is acquired using X-rays as radiation and a tomographic image is generated. However, radiation is not limited to X-rays. Such radiation may be used.

  In the above-described embodiment, the correction data calculation unit calculates the average difference data based on the average value of the pixel data corresponding to the detection module at the end side position. For example, separately from the slope phantom, a tomographic image of a cylindrical phantom having the same diameter at the slice thickness center is generated, and the pixel data of the cylindrical phantom tomographic image is averaged based on the average value Difference data may be calculated.

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 the tomography method in the embodiment according to the present invention. FIG. 8 is a view for explaining a state in which the phantoms according to the embodiment of the present invention are arranged. FIG. 9 is a diagram for explaining the step of calculating correction data in the embodiment according to the invention. FIG. 10 is a diagram for explaining correction of the projection data of the subject in the embodiment according to the invention.

Explanation of symbols

1 X-ray CT apparatus (radiation tomography 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 (detection module),
23a ... detection element (detection 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,
41. Control unit,
51: Data processing unit,
52. Subject tomographic image generation unit,
53. Correction data calculation unit,
53a ... Phantom tomographic image generator,
54. Correction unit,
P ... Slope phantom

Claims (9)

An irradiation unit for irradiating radiation;
A detection unit in which detection elements for detecting radiation irradiated from the irradiation unit are arranged in an array in a slice thickness direction and a channel direction orthogonal to the slice thickness direction,
Subject tomography that generates a tomographic image of the subject based on first projection data of the subject obtained by the detection unit detecting the radiation that is irradiated to the subject from the irradiation unit and transmitted through the subject An image generator;
A correction data calculation unit for calculating correction data for correcting crosstalk in the slice thickness direction of the first projection data;
A correction unit that corrects crosstalk of the first projection data based on the correction data calculated by the correction data calculation unit;
The correction data calculation unit
A slope phantom including a cone-shaped portion is disposed between the irradiation unit and the detection unit so that a circular center axis of the cone-shaped portion corresponds to the slice thickness direction, and the irradiation of the slope phantom is performed A phantom tomographic image generation unit that generates a tomographic image of the slope phantom based on second projection data of the slope phantom obtained by irradiating radiation from the unit and passing through the slope phantom and detected by the detection unit Including
A radiation tomography apparatus that calculates the correction data based on a tomographic image of a slope phantom generated by the phantom tomographic image generation unit. The correction data calculation unit calculates difference data between the detection elements based on pixel data corresponding to the detection elements in the tomographic image of the slope phantom generated by the phantom tomographic image generation unit, and the calculated The radiation tomography apparatus according to claim 1, wherein the correction data is calculated based on a difference value. The detection unit includes a plurality of detection modules in which the detection elements are arranged in an array in the slice thickness direction and the channel direction, and the plurality of detection modules are arranged at least along the channel direction. ,
The correction data calculation unit calculates, for each detection module, an average value of pixel data corresponding to the detection elements arranged in the detection module in the slope phantom tomographic image generated by the phantom tomographic image generation unit. The average data calculated as the difference between the detection modules of the average value calculated for each detection module is calculated later, and the correction data is calculated based on the calculated average difference data. Radiation tomography equipment. An irradiation unit that irradiates radiation, and a detection unit in which detection elements that detect radiation emitted from the irradiation unit are arranged in an array in a slice thickness direction and a channel direction orthogonal to the slice thickness direction. And generating a tomographic image of the subject based on the first projection data of the subject obtained by detecting the radiation irradiated to the subject from the irradiation unit and transmitted through the subject by the detection unit. A tomography method for a radiation tomography apparatus,
A first step of disposing a slope phantom including a conical portion between the irradiation unit and the detection unit such that a circular central axis of the conical portion corresponds to the slice thickness direction;
Based on second projection data of the slope phantom obtained by irradiating the slope phantom arranged in the first step from the irradiation unit and transmitting the radiation through the slope phantom and detected by the detection unit. A second step of generating a tomographic image of the slope phantom;
A third step of calculating correction data for correcting crosstalk in the slice thickness direction of the first projection data based on the tomographic image of the slope phantom generated in the second step;
A tomography method for a radiation tomography apparatus, comprising: a fourth step of correcting crosstalk in the slice thickness direction of the first projection data based on the correction data calculated in the third step. In the third step, difference data between the detection elements is calculated based on pixel data corresponding to the detection elements in the tomographic image of the slope phantom generated in the second step, and the calculated difference The tomography method for a radiation tomography apparatus according to claim 4, wherein the correction data is calculated based on data. In the radiation tomography apparatus, the detection unit includes a plurality of detection modules in which the detection elements are arranged in an array in the slice thickness direction and the channel direction, and the plurality of detection modules are at least in the channel direction. Are arranged along the
In the third step, in the tomographic image of the slope phantom generated in the second step, after calculating an average value of pixel data corresponding to the detection elements arranged in the detection module for each detection module The radiation according to claim 5, wherein average difference data that is a difference between the detection modules of an average value calculated for each detection module is calculated, and the correction data is calculated based on the calculated average difference data. A tomography method of a tomography apparatus. An irradiation unit that irradiates radiation, and a detection unit in which detection elements that detect radiation emitted from the irradiation unit are arranged in an array in a slice thickness direction and a channel direction orthogonal to the slice thickness direction. And generating a tomographic image of the subject based on the first projection data of the subject obtained by detecting the radiation irradiated to the subject from the irradiation unit and transmitted through the subject by the detection unit. A correction data calculation method for calculating correction data for correcting crosstalk of the first projection data in the slice thickness direction in a radiation tomography apparatus,
A first step of disposing a slope phantom including a conical portion between the irradiation unit and the detection unit such that a circular central axis of the conical portion corresponds to the slice thickness direction;
Based on second projection data of the slope phantom obtained by irradiating the slope phantom arranged in the first step from the irradiation unit and transmitting the radiation through the slope phantom and detected by the detection unit. A second step of generating a tomographic image of the slope phantom;
A third step of calculating correction data for correcting crosstalk in the slice thickness direction of the first projection data based on the tomographic image of the slope phantom generated in the second step. Method. In the third step, difference data between the detection elements is calculated based on pixel data corresponding to the detection elements in the tomographic image of the slope phantom generated in the second step, and the calculated difference The correction data calculation method according to claim 7, wherein the correction data is calculated based on data. In the radiation tomography apparatus, the detection unit includes a plurality of detection modules in which the detection elements are arranged in an array in the slice thickness direction and the channel direction, and the plurality of detection modules are at least in the channel direction. Are arranged along the
In the third step, in the tomographic image of the slope phantom generated in the second step, after calculating an average value of pixel data corresponding to the detection elements arranged in the detection module for each detection module The correction according to claim 8, wherein average difference data that is a difference between the detection modules of an average value calculated for each detection module is calculated, and the correction data is calculated based on the calculated average difference data. Data calculation method.

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