JP4316335B2 - X-ray scattered ray component correction method and program, and X-ray CT apparatus - Google Patents

Description

  The present invention relates to an X-ray scattered ray component correction method, a program therefor, and an X-ray CT apparatus. More specifically, the present invention includes an X-ray tube and an X-ray detector opposed to each other with a subject interposed therebetween. The present invention relates to a method of correcting an X-ray scattered ray component in an X-ray CT apparatus that reconstructs a CT tomographic image of a subject based on a signal, a program thereof, and an X-ray CT apparatus.

  In the X-ray C-cutter device, the X-ray scattered radiation component incident on each detection channel differs depending on the size of the subject (that is, the projection length of the X-ray transmitted through the subject). Even when scanning (acrylic phantom, water phantom, etc.), the uniformity of the reconstructed CT value may deteriorate. Therefore, it is necessary to appropriately correct the X-ray scattering component of each detection channel according to the size (body shape) of the subject.

Conventionally, for the purpose of correcting scattered X-rays generated from a subject, a multi-channel X-ray detector, means for logarithmically converting the detected signal intensity, and each projection angle j of the subject after logarithmic conversion A means for calculating an added value S _j obtained by adding projection data pro (i, j) for a specific one or a plurality of channels every time, and a material close to the X-ray absorption coefficient of the subject (water, polyethylene, acrylic, etc.) ), The scattered X-ray correction amount C in the linear region is determined from the values of the coefficients A and B and the added value S _j related to the scattered X-ray correction amount determined from several X-ray transmission images having different sizes obtained in advance. _sj
C _sj = A · S _j ^B
And the scattered X-ray correction amount C _sj is subtracted from the inverse logarithmically converted projection data obtained by inverse logarithmically transforming the projection data after logarithmic transformation of all channels for each projection angle j. There is known an X-ray CT apparatus that includes scattered radiation correction means and means for logarithmically converting the corrected measurement data to perform image reconstruction (Patent Document 1).
Japanese Patent Application Laid-Open No. 07-213517 (Claims).

  However, in the above-described conventional scattering component correction method, information on the body shape (subject size) that differs from patient to patient is not sufficiently reflected, so that appropriate correction data cannot be obtained.

  The present invention has been made in view of the above-mentioned problems of the prior art, and its object is to correct an X-ray scattering component that can correct an appropriate X-ray scattering component according to the body shape of the subject, and its It is to provide a program and an X-ray CT apparatus.

The above problem is solved by, for example, the configuration of FIG. That is, the X-ray scattering component correction method of the present invention (1) includes an X-ray tube and an X-ray detector facing each other across the subject, and the CT of the subject based on the detection signal of the X-ray detector. A method for correcting an X-ray scattering component in an X-ray CT apparatus for reconstructing a tomographic image, comprising a correction table defining a relationship between an X-ray projection length and an X-ray scattering component correction amount, and an object from at least one direction Based on the projection data of each channel obtained by the scout scan, extracting a plurality of projection data below a predetermined threshold, and the subject based on the extracted projection data and reference data representing the X-ray beam intensity A step of obtaining each X-ray projection length corresponding to each detection channel of the subject cross section using a predetermined X-ray attenuation coefficient preliminarily defined for each cross section, and a target based on the obtained data of each X-ray projection length. Sample cross-sectional shape A step of creating graphic data that can be generated and processed by a computer, and a cross section of a subject cross section at each view angle based on an intersection relationship between the created graphic data and a virtual X-ray beam corresponding to each view angle. A step of estimating an X-ray projection length corresponding to each detection channel, and a step of correcting an X-ray scattering component for projection data obtained by scanning the subject with reference to the correction table based on the estimated X-ray projection length Are provided.

  Further, the above problem is solved by the configuration of FIG. In other words, the X-ray scattering component correction method of the present invention (2) includes an X-ray tube and an X-ray detector facing each other across the subject, and the CT of the subject based on the detection signal of the X-ray detector. A method for correcting an X-ray scattering component in an X-ray CT apparatus for reconstructing a tomographic image, comprising a correction table defining a relationship between an X-ray projection length and an X-ray scattering component correction amount, and obtained by scanning an object. Based on the projection data of each channel at each view angle, extracting a plurality of projection data below a predetermined threshold, and based on the extracted projection data and reference data representing the X-ray beam intensity, Estimating the X-ray projection length corresponding to each detection channel of the cross section of the subject at each view angle using a predetermined X-ray attenuation coefficient defined in advance, and based on the estimated X-ray projection length, Correction table Referring to, in which and a step of correcting the X-ray scattering component to the projection data obtained by scanning the subject.

  In the present invention (3), in the above-mentioned present invention (1) or (2), after the step of extracting a plurality of projection data lower than the predetermined threshold, each predetermined number of adjacent projection data extracted is extracted. A step of obtaining a plurality of average data by averaging, a step of interpolating and approximating between the obtained plurality of average data with a smooth curve, and a step of extracting a plurality of projection data based on the interpolated and approximated curve Is provided.

  The program of the present invention (4) is a computer-executable program for causing a computer to execute the X-ray scattering component correction method of the present invention (1) or (2).

  The X-ray CT apparatus of the present invention (5) includes an X-ray tube and an X-ray detector facing each other across the subject, and reconstructs a CT tomogram of the subject based on the detection signal of the X-ray detector. A predetermined threshold based on a correction table that defines the relationship between the X-ray projection length and the X-ray scattering component correction amount, and projection data of each channel obtained by scout scanning the subject from at least one direction. And a predetermined X-ray attenuation coefficient defined in advance for the cross section of the subject based on the extracted projection data and the reference data representing the X-ray beam intensity. Calculating means for obtaining each X-ray projection length corresponding to each detection channel of the subject cross-section, and graphic data representing the cross-sectional shape of the subject based on the obtained data of each X-ray projection length and generated by a computer ·place X-ray projection length corresponding to each detection channel of the cross section of the object at each view angle based on the crossing relationship between the creation means for creating a possible one and the created graphic data and the virtual X-ray beam corresponding to each view angle And an correcting means for correcting X-ray scattering components for projection data obtained by scanning the subject with reference to the correction table based on the estimated X-ray projection length.

  The X-ray CT apparatus of the present invention (6) includes an X-ray tube and an X-ray detector facing each other across the subject, and reconstructs a CT tomographic image of the subject based on the detection signal of the X-ray detector. In the X-ray CT apparatus to be configured, a predetermined threshold based on a correction table defining the relationship between the X-ray projection length and the X-ray scattering component correction amount, and projection data of each channel at each view angle obtained by scanning the subject And a predetermined X-ray attenuation coefficient defined in advance for the cross section of the subject based on the extracted projection data and the reference data representing the X-ray beam intensity. And an estimation means for estimating an X-ray projection length corresponding to each detection channel of the object cross section at each view angle, and a projection obtained by scanning the object with reference to the correction table based on the estimated X-ray projection length Against data In which and a correcting means for correcting that X-ray scattering component.

  In the present invention (7), a smooth curve is obtained between a plurality of average data obtained by averaging each predetermined number of adjacent projection data extracted by the extracting means in the present invention (5) or (6). And a second extraction means for extracting a plurality of projection data based on the interpolated and approximated curve.

  In the present invention (8), in the present invention (5) or (6), the correction table is detected and created for each detection channel in advance for a reference phantom having a uniform and different size.

  In the present invention (9), in the present invention (5) or (6), the reference phantom is made of an acrylic resin.

  According to the present invention (1), the cross-sectional shape at each view angle of the subject (that is, the X-ray projection length corresponding to each channel) can be appropriately estimated from the scout image data of the subject. It is possible to correct an appropriate X-ray scattering component according to the body shape.

  According to the present invention (2), it is possible to properly estimate the cross-sectional shape at each view angle of the subject (that is, the X-ray projection length corresponding to each channel) from the axial / helical scan data of the subject, Therefore, even when there is no scout image data, it is possible to correct an appropriate X-ray scattering component according to the body shape of the subject.

  Further, according to the present invention (3), the influence of bones and the like can be reduced by a configuration that interpolates / approximates a plurality of average data obtained by averaging each predetermined number of adjacent projection data in the extracted data. Reduced average data can be obtained, and projection data that more accurately reflects the cross-sectional shape of the subject can be generated and extracted based on the average data.

  Therefore, according to the present invention, required image quality can be ensured even when subjects having various body shapes are scanned.

  Hereinafter, a plurality of preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the same reference numerals denote the same or corresponding parts throughout the drawings.

  FIG. 1 is a block diagram of an X-ray CT apparatus according to an embodiment. The apparatus mounts a scanning gantry unit 30 that performs axial / helical scanning / reading of a subject 100 by an X-ray fan beam XLFB, and the subject 100. And an operation console unit 10 for performing remote control of the scanning gantry unit 30 and the imaging table 20 and for performing various settings and operations by an X-ray engineer or a doctor. .

  In the scanning gantry 30, 40 is a rotary anode type X-ray tube, 40 A is an X-ray tube controller for controlling the tube voltage kV, tube current mA, etc. of the X-ray tube, and 50 is a collimator for limiting the slice thickness of the X-ray. , 50A is a collimator control unit, 90 is an X-ray detector (multi-detector) in which a large number (n = 1000) of X-ray detection elements arranged in the channel CH direction are arranged in, for example, two rows L1 and L2 in the body axis CLb direction. ), 91 generates projection data g1 (X, θ), g2 (X, θ) of the subject 100 based on the detection signal of the X-ray detector 90 and collects them, and a data collecting unit (DAS) 35 collects these X A gantry 35A is a rotation control unit for the gantry 35. The gantry 35A is a gantry that rotatably supports each device related to the line imaging system around the body axis CLb.

  In the operation console unit 10, 11 is a central processing unit that performs main control and processing (scan control, correction of X-ray scattering components, and reconstruction of CT tomographic images) of the X-ray CT apparatus, 11a is its CPU, and 11b. Is a main memory (MM) composed of RAM, ROM, etc. used by the CPU 11a, 12 is an input device for commands and data including a keyboard and a mouse, 13 is a display for displaying various information related to scan plan information and CT tomograms. A device (CRT) 14 is a control interface for exchanging various control signals CS and monitor signals MS between the CPU 11a, the scanning gantry unit 30 and the imaging table 20, and 15 is a projection data from the data collection unit 91 temporarily. The data collection buffer 16 stores the scan (projection) data and CT tomogram data finally. While a secondary storage device that stores the data file or the like for various application programs and various arithmetic / correction required for the operation of the X-ray CT apparatus (hard disk drive, etc.).

  The operation of CT imaging is outlined. The X-ray fan beam XLFB from the X-ray tube 40 passes through the subject 100 and enters the detection rows L1 and L2 of the X-ray detector 90 all at once. The data collection unit 91 generates projection data g 1 (X, θ), g 2 (X, θ) corresponding to each detection output of the X-ray detector 90 and stores them in the data collection buffer 15. Here, X represents detection channels 1 to n of the X-ray detector 90, and θ represents a view angle 0 to 360 ° around the body axis CLb. Further, the projection similar to the above is performed at each view angle θ in which the gantry 35 is slightly rotated, and thus projection data for one rotation of the gantry is collected and accumulated. At the same time, the imaging table 20 is moved intermittently / continuously in the direction of the body axis CLb in accordance with the axial / helical scan method, and thus all projection data for the required imaging region of the subject 100 is collected and accumulated. Then, the CPU 11a reconstructs a CT tomogram of the subject 100 based on the obtained projection data after displaying all the scans or following (in parallel with) the scan execution, and displays this on the display device 13. .

  Next, an X-ray scattering component correction table used in the present embodiment will be described. FIG. 7 is a flowchart of an X-ray scattering component correction table creation process according to the embodiment, and FIG. 8 is an image diagram of the process. X-ray projection length-X-ray scattering component correction data using a reference phantom 61 of various sizes in advance. This shows the process of creating a conversion table. This process does not need to be performed for each X-ray CT apparatus, and a table created before shipment for a certain X-ray CT apparatus can be used for other X-ray CT apparatuses of the same type.

  In FIG. 7, in step S <b> 81, the reference phantom 61 is attached to the distal end portion of the imaging table (cradle) 20. The image is shown in FIG. The phantom 61 is made of, for example, a columnar body made of a homogeneous acrylic resin (PPMA: polymethylmethacrylate), and its diameter φ1 is φ1 = 16 cm which represents a typical head size of the subject. Further, the diameter φ2 of the other phantom is φ = 32 cm which represents a typical body size of the subject. Further, when a phantom having a large diameter φ3 can be used, this is used. In this embodiment, since the linear attenuation coefficient μa of acrylic resin is close to a human tissue (excluding bones), it is adopted as a reference phantom. However, the present invention is not limited to this. In addition, a standard phantom made of water or polyethylene can be used.

  In step S82, scanning of the reference phantom 61 (acquisition of projection data for at least a certain view angle) is performed. In step S83, an X-ray scattering component at that time is detected and stored in the memory. The X-ray scattering component can be detected by a known method in which, for example, a grid or a filter that detects the X-ray scattering component is provided on the X-ray detection surface of each channel. In step S84, it is determined whether or not an X-ray scattering component has been detected for all available size reference phantoms. If NO, the process returns to step S81, and detection processing similar to that described above is performed for reference phantoms of other sizes. If YES, in step S85, a table of X-ray projection length-X-ray scattering component correction data corresponding to each channel is created and stored in the memory.

  FIG. 8B shows a graph of projection data and X-ray scattering data corresponding to the reference phantom 61 of each size φ1, φ2, and φ3. The horizontal axis represents X-ray detection channels CH1 to CHn, and the vertical axis represents projection data (solid line) and X-ray scattering data (one-dot chain line). Since the reference phantom 61 is homogeneous, the projection data is a smooth graph corresponding to the phantom shape and attenuates according to the X-ray projection length through which the X-rays are transmitted.

  On the other hand, as for the X-ray scattering component, generally, the longer the X-ray projection length, the more scattered rays gather in the path direction. Therefore, it is known that the longer the X-ray projection length, the larger the scattering data. . That is, in the phantom having the same diameter, the scattered data of the central detection channel CHc tends to be larger than the scattered data of each of the surrounding channels. However, when the phantom diameter is large, the scattering component is also attenuated, so that the scattered data is relatively small as compared with the case where the phantom diameter is small.

  FIG. 8C shows a graph of X-ray projection length-correction data corresponding to each channel. The horizontal axis is the X-ray projection length, and the vertical axis is the correction data. For the center detection channel CHc, correction data corresponding to the three X-ray projection lengths φ1, φ2, and φ3 are generated based on the graph of FIG. 8B. That is, each correction data is obtained as a value that cancels the scattered component. Furthermore, values (graphs) that fill between these sample points can be interpolated and approximated by a linear or quadratic or higher curve by the least square method or the like. On the other hand, for the peripheral detection channel CHi, for example, correction data corresponding to two X-ray projection lengths φ1 and φ2 are generated based on the graph of FIG. 8B. In this case, the graph in the range exceeding φ2 can be statistically generated by referring to the physical property of the scattering component and the graph with respect to the detection channel CHc in the center. This is indicated by the dotted line in the figure. In this way, a table of X-ray projection length-correction data is obtained for each detection channel.

  FIG. 2 is a flowchart of the X-ray CT imaging process according to the embodiment. In step S11, the engineer sets scan parameters (tube voltage kV, tube current mA, etc.) for the scout scan of the subject. Usually the default value is used. In step S12, a scout scan of the subject 100 is performed. FIG. 4A shows an image of scout scanning. In the scout scan, while the gantry 35 is fixed at a predetermined view angle (for example, θ = 0 °), the imaging table 20 is moved at a constant speed in the direction of the subject body axis CLb, and a fluoroscopic image of the subject 100 ( That is, it refers to a scan for obtaining an X-ray image. In step S13, the obtained scout image is displayed on the screen. FIG. 4B shows an example scout image.

  In step S14, the engineer sets parameters (such as localization) for the subsequent axial / helical scan while referring to the scout image on the screen. In step S15, it is determined whether or not the setting is confirmed (CONFIRM). If not confirmed, the process returns to step S14. Thus, when the setting confirmation button is pressed, an axial / helical scan of the subject is performed in step S16, and projection data is collected and accumulated in step S17. In step S18, it is determined whether or not all scans in the predetermined imaging area are complete. If not, the process returns to step S16.

  Thus, when all the scans are completed, an X-ray projection length estimation process, which will be described later, is performed in step S19. In step S20, the correction table of FIG. 8C is referred to according to the calculated X-ray projection length, and X-ray scattering component correction processing is performed corresponding to each detection channel. Although not shown, other various correction processes (channel sensitivity correction, reference correction, etc.) are also performed. In step S21, back projection (CT reconstruction) processing is performed using the corrected projection data. In step S22, the obtained CT tomographic image is displayed on the screen.

Next, X-ray projection length estimation processing according to the embodiment will be described. FIG. 3 is a flowchart of the X-ray projection length estimation processing according to the first embodiment, and estimates the cross-sectional size (X-ray projection length) of the subject using projection data obtained by the scout scan of the subject. Shows when to do. In step S31, the projection data is read from the memory, and in step S32, the projection data Ij (= 1 to m) of the portion below the predetermined threshold value TH is extracted. FIG. 4C shows line data with a scout image. The horizontal axis represents the detection channels CH1 to CHn, and the vertical axis represents the projection data g (X, θ = 0). Through the process in step S32, projection data Ij (= 1 to m) of a portion corresponding to the subject cross section is extracted.

  In step S33, projection data for a plurality of adjacent channels is averaged to obtain average data for every predetermined number of channels. In general, because there are bones etc. on the path of a certain detection channel, the obtained line data is not always smooth, but by averaging the projection data for multiple channels, projection data by bones etc. Can reduce the impact on Furthermore, smooth line data can be obtained by interpolating and approximating each average data with a smooth curve. This line data reflects more parts of tissues (organs, fat bones, etc.) in which the influence of the subject's bones, etc. has been reduced, and more accurately represents the body shape of the subject.

  In step S34, an X-ray projection length tj corresponding to each channel is obtained based on the interpolated / approximate line data. That is, now, the j-th projection data Ij of the subject is expressed by equation (1),

here,
I ₀ : X-ray emission intensity (reference data)
μc: X-ray attenuation count representing the subject (for example, substantially acrylic X-ray attenuation count μa)
tj: Expressed by X-ray projection length. Solving the above equation (1) for the X-ray projection length tj, equation (2),

Is obtained. FIG. 4D shows a profile of the subject cross section represented by a series of height tj.

  In step S35, graphic data representing the cross-sectional shape of the subject based on the obtained X-ray projection length tj, which can be generated and processed by a computer, is created and stored in a memory. In general, such graphic data is called computer aided design (CAD) data, and this graphic data preferably represents a cross-sectional shape of the subject by a computer (ie, each X-ray projection length). The graphic data is automatically generated so as to surround (tj), and the rotation conversion processing of the graphic data is automatically performed corresponding to each view angle. Hereinafter, this graphic data is referred to as CAD data.

This CAD data can be generated as a closed figure of the cross section of the subject surrounding the line segment of each X-ray projection length. By creating CAD data, rotation processing according to the view angle of the subject cross section can be easily performed. In step S36, the X-ray projection length corresponding to each view angle is estimated based on the generated CAD data and stored in the memory. The X-ray projection length estimation image corresponding to the view angle (45 °) in FIG. For example, when the CAD data 100b of the subject cross section is rotated by 45 °, the relationship shown in the figure is obtained. If X-rays are irradiated vertically, each virtual X-ray projection length extracted from the cross relationship between the two is tj (j = 1 to k). The same processing can be performed for other view angles. It goes without saying that the X-ray irradiation angle may be rotated instead of rotating the CAD data 100b. In step S37, it is determined whether or not the X-ray projection length for all slice positions and all view angles to be reconstructed has been estimated. If NO, the process returns to step S36. And if it becomes YES eventually, this process will be exited.

  FIG. 5 is a flowchart of the X-ray projection length estimation process according to the second embodiment, and shows a case where the X-ray projection length is obtained directly from the axial scan data of the subject. According to this method, it is possible to appropriately correct the X-ray scattering component even when the scout scan is not performed in advance. In step S41, projection data corresponding to a certain view angle is read from the scan data stored in the memory. FIG. 6A shows line data g (X, θ = 0) in the case of the view angle (= 0 °). In step S42, projection data Ij (= 1 to m) of a portion below a predetermined threshold TH is extracted. In step S43, projection data for a plurality of channels are averaged to obtain average data for every predetermined number of channels. Furthermore, smooth line data can be obtained by interpolating and approximating each average data with a smooth curve. This line data reflects more parts of tissues (organs, fat bones, etc.) in which the influence of the subject's bones, etc. has been reduced, and more accurately represents the body shape of the subject. In step S44, the X-ray projection length tj is obtained corresponding to each channel based on the interpolated / approximate line data and stored in the memory. FIG. 6A shows a profile of each X-ray projection length tj (j = 1 to m) estimated based on the line data g (X, θ = 0) at the view angle (= 0 °).

  In step S45, it is determined whether or not the X-ray projection lengths for all slice positions and all view angles have been obtained. If NO, the process returns to step S41 and the same processing as described above is performed. FIG. 6B shows the profile of the line data g (X, θ = 45) in the case of the view angle (= 45 °) and each X-ray projection length tj (j = 1 to k) estimated based on the line data g (X, θ = 45). Indicates. FIG. 6C shows the line data g (X, θ = 95) in the case of the view angle (= 90 °) and the X-ray projection lengths tj (j = 1 to p) estimated based on the line data g (X, θ = 95). Shows the profile. In this way, when the total X-ray projection length is obtained in the determination in step S45, the process is exited.

  In the case of helical scan, the axial data can be generated by interpolation, and then the X-ray projection length can be generated by the same method as described above.

  Moreover, although several embodiment suitable for the said invention was described, it cannot be overemphasized that the structure of each part, a control, a process, and these combinations can be variously changed within the range which does not deviate from this invention. .

1 is a block diagram of an X-ray CT apparatus according to an embodiment. It is a flowchart of the X-ray CT imaging process by embodiment. It is a flowchart of the X-ray projection length estimation process by 1st Embodiment. It is an image figure of the X-ray projection length estimation process by 1st Embodiment. It is a flowchart of the X-ray projection length estimation process by 2nd Embodiment. It is an image figure of the X-ray projection length estimation process by 2nd Embodiment. It is a flowchart of the X-ray scattering component correction table creation process by embodiment. It is an image figure of the X-ray-scattering component correction table creation process by embodiment.

Explanation of symbols

10 Operation console 11 Central processing unit 11a CPU
11b Main memory (MM)
12 Input device 13 Display device (CRT)
14 Control Interface 15 Data Collection Buffer 16 Secondary Storage Device (Hard Disk Device etc.)
20 Imaging table 30 Scanning gantry section 35 Gantry 40 X-ray tube 50 Collimator 60 Reference phantom 90 X-ray detector (multi-detector)
91 Data Collection Unit (DAS)
100 subjects

Claims (9)

Correction of X-ray scattering components in an X-ray CT apparatus that includes an X-ray tube and an X-ray detector facing each other across the subject and reconstructs a CT tomogram of the subject based on the detection signal of the X-ray detector A method,
A correction table that defines the relationship between the X-ray projection length and the X-ray scattering component correction amount;
Extracting a plurality of projection data below a predetermined threshold based on projection data of each channel obtained by scout scanning the subject from at least one direction;
Based on the extracted projection data and the reference data representing the X-ray beam intensity, each X channel corresponding to each detection channel of the subject cross section is determined using a predetermined X-ray attenuation coefficient defined in advance for the subject cross section. Obtaining an X-ray projection length;
Creating graphic data representing the cross-sectional shape of the subject based on the obtained X-ray projection length data, which can be generated and processed by a computer;
Estimating an X-ray projection length corresponding to each detection channel of the cross section of the subject at each view angle based on the intersection relationship between the created graphic data and the virtual X-ray beam corresponding to each view angle;
A method for correcting an X-ray scattering component, comprising: referring to the correction table based on the estimated X-ray projection length and correcting X-ray scattering components for projection data obtained by scanning the subject. Correction of X-ray scattering components in an X-ray CT apparatus that includes an X-ray tube and an X-ray detector facing each other across the subject and reconstructs a CT tomogram of the subject based on the detection signal of the X-ray detector A method,
A correction table that defines the relationship between the X-ray projection length and the X-ray scattering component correction amount;
Extracting a plurality of projection data below a predetermined threshold based on projection data of each channel at each view angle obtained by scanning the subject;
Based on each of the extracted projection data and reference data representing the X-ray beam intensity, each detection channel of the subject cross section at each view angle using a predetermined X-ray attenuation coefficient defined in advance for the subject cross section Estimating an X-ray projection length corresponding to
A method for correcting an X-ray scattering component, comprising: referring to the correction table based on the estimated X-ray projection length and correcting X-ray scattering components for projection data obtained by scanning the subject. After the step of extracting a plurality of projection data less than the predetermined threshold value, a step of obtaining a plurality of average data by averaging each predetermined number of adjacent projection data in the extracted, and the plurality of average data obtained The step of interpolating and approximating a smooth curve between them and the step of extracting a plurality of projection data based on the interpolated and approximated curve are provided. Correction method. A computer-executable program for causing a computer to execute the X-ray scattering component correction method according to claim 1. In an X-ray CT apparatus comprising an X-ray tube and an X-ray detector facing each other with a subject interposed therebetween, and reconstructing a CT tomogram of the subject based on a detection signal of the X-ray detector,
A correction table that defines the relationship between the X-ray projection length and the X-ray scattering component correction amount;
Extraction means for extracting a plurality of projection data below a predetermined threshold based on projection data of each channel obtained by scout scanning the subject from at least one direction;
Based on the extracted projection data and the reference data representing the X-ray beam intensity, each X channel corresponding to each detection channel of the subject cross section is determined using a predetermined X-ray attenuation coefficient defined in advance for the subject cross section. A calculation means for obtaining an X-ray projection length;
Creating means for creating graphic data representing a cross-sectional shape of the subject based on the obtained data of each X-ray projection length, which can be generated and processed by a computer;
Estimating means for estimating an X-ray projection length corresponding to each detection channel of the cross section of the subject at each view angle based on the intersection relationship between the created graphic data and the virtual X-ray beam corresponding to each view angle;
An X-ray CT apparatus comprising: correction means for correcting an X-ray scattering component with respect to projection data obtained by scanning the subject with reference to the correction table based on the estimated X-ray projection length. In an X-ray CT apparatus comprising an X-ray tube and an X-ray detector facing each other with a subject interposed therebetween, and reconstructing a CT tomogram of the subject based on a detection signal of the X-ray detector,
A correction table that defines the relationship between the X-ray projection length and the X-ray scattering component correction amount;
Extraction means for extracting a plurality of projection data below a predetermined threshold based on the projection data of each channel at each view angle obtained by scanning the subject;
Based on each of the extracted projection data and reference data representing the X-ray beam intensity, each detection channel of the subject cross section at each view angle using a predetermined X-ray attenuation coefficient defined in advance for the subject cross section Estimating means for estimating the X-ray projection length corresponding to
An X-ray CT apparatus comprising: correction means for correcting an X-ray scattering component with respect to projection data obtained by scanning the subject with reference to the correction table based on the estimated X-ray projection length. A plurality of average data obtained by averaging each predetermined number of adjacent projection data extracted by the extraction means is interpolated / approximate with a smooth curve, and a plurality of projection data is based on the interpolated / approximate curve. The X-ray CT apparatus according to claim 5, further comprising second extracting means for extracting. 7. The X-ray CT apparatus according to claim 5, wherein the correction table is previously detected and created for each detection channel with respect to a reference phantom having a uniform and different size. The X-ray CT apparatus according to claim 5 or 6, wherein the reference phantom is made of an acrylic resin.

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