JP5179748B2 - X-ray CT apparatus and computer program - Google Patents

Description

The present invention relates to X-ray CT apparatus and a computer program, and more particularly, to a technique for aligning the phantom for X-ray CT apparatus.

  The X-ray CT apparatus generates an X-ray beam from an X-ray source, detects an X-ray beam transmitted through a subject on a bed by an X-ray detector, and generates X-ray projection data. It is an apparatus that generates two-dimensional tomographic image data representing the internal form of a subject by performing reconstruction processing on the subject. In an X-ray CT apparatus capable of so-called helical scanning, an X-ray source and an X-ray detector in a rotating gantry (gantry) are rotated while moving the bed in the body axis direction (slice direction) of the subject. By performing the scan, a plurality of tomographic image data can be reconstructed by one scan.

  In order to acquire high-accuracy tomographic image data, it is necessary to calibrate the X-ray CT apparatus and maintain the apparatus performance. Therefore, it is necessary to adjust the apparatus by evaluating the performance of the apparatus at the time of shipment or delivery of the apparatus, and even after the operation of the apparatus is started, for example. Evaluation items include noise, contrast scale, spatial resolution, slice thickness, high contrast resolution, and low contrast resolution.

  The performance evaluation of the X-ray CT apparatus is performed using a pseudo object called a phantom that simulates a human body instead of an actual human body. FIG. 16 shows an example of a phantom. FIG. 16A shows the appearance of the phantom 100. The phantom 100 includes a cylindrical case 101. A cylindrical axis of the case 101 is represented by a symbol J. Here, the cylindrical axis means a rotationally symmetric axis of the cylindrical object (case 101).

  FIG. 16B shows a cross section 110 of the phantom 100 at an arbitrary slice position (excluding the vicinity of both ends). The case 101 of the phantom 100 is formed hollow. The hollow portion is filled with a filler 102 such as water.

  In order to ensure the accuracy of performance evaluation using such a cylindrical phantom 100, the phantom 100 must be arranged at a suitable installation position. For this purpose, it is necessary to make the cylindrical axis J of the phantom 100 coincide with the slice direction. Further, it is necessary to arrange the cylindrical axis J on the scan center (the rotation center of the X-ray source and the X-ray detector) and arrange the phantom 100 at the center of the inspection region.

  Conventionally, the installation of the phantom 100 has been performed as follows. First, the phantom 100 is placed on a bed to reconstruct tomographic image data. While observing the display image (tomographic image) of the tomographic image data, the operator adjusts the window width and the window level so that the outline of the phantom 100, that is, the case 101 is clearly displayed. Next, a cross scale (the crossing position at the center of the display screen indicates the scan center) is displayed over the tomographic image. The operator specifies by how much the center position of the case 101 shown in the tomographic image is displaced in which direction from the crossing position of the cross scale. Then, the installation position of the phantom 100 is moved, and the tomographic image is observed again to confirm the moved position. By repeating such a series of operations, the phantom 100 is installed at a target position.

  Patent Document 1 discloses a method for detecting the mounting posture in order to confirm whether or not the phantom is suitably installed. In the detection method described in this document, a phantom mounted on the rotation center (scan center) axis of the X-ray imaging system is scanned in the body axis direction at a horizontal view angle, and each projection data obtained thereby and predetermined The contour shape of the phantom in the two-dimensional projection image region is extracted by comparing with the threshold value, and the inclination of the phantom from the vertical direction is detected based on the extracted contour shape. That is, the attachment posture is detected by detecting the inclination of the side image (scano image) of the phantom.

JP 2001-31497 A

  In the conventional phantom installation method, since the movement amount of the phantom is specified by the operator's visual observation, it is difficult to install the phantom at the target position only by performing the above series of operations once. Usually, this series of work was repeated many times. Therefore, the phantom installation work took a long time and the burden on the worker was great.

  Moreover, since it is necessary to move the position of the phantom two-dimensionally in order to install the phantom at the target position, a skilled worker can grasp the moving direction and the moving amount relatively quickly. This work was difficult for non-workers. In addition, since such work also depends on the sense of the worker, there are some workers who do not easily improve even if they have gained experience.

  On the other hand, in the invention disclosed in Patent Document 1, posture detection is performed on the assumption that the phantom (its cylindrical axis) is arranged on the scan center. Therefore, when this method is used, the operation of matching the cylindrical axis of the phantom with the scan center must be performed manually in advance, which requires time and effort. In addition, this conventional invention also has a problem that it cannot be confirmed whether or not the phantom is arranged on the scan center.

  Furthermore, since only the result of scanning the phantom from the side is used in the invention of Patent Document 1, only the inclination with respect to the vertical direction can be detected. In actual installation work, the phantom may be inclined in the horizontal direction, but this conventional invention cannot cope with it.

  The present invention is intended to solve the above-described problems, and an object thereof is to provide a technique capable of easily and quickly aligning a phantom regardless of the skill level of an operator.

  Another object of the present invention is to provide a technique capable of performing phantom alignment with high accuracy and facilitating alignment operation. .

  In order to achieve the above object, the invention described in claim 1 includes a top plate on which a phantom having a cylindrical housing filled with a filling is installed, and an X-ray generation means for generating an X-ray beam. An X-ray detection means for detecting the X-ray beam transmitted through a phantom installed on the top plate, a rotation drive means for rotating the X-ray generation means and the X-ray detection means, and the X-ray detection means. Based on the detected X-ray beam, tomographic image data generating means for generating tomographic image data of the phantom, and based on the generated tomographic image data, the phantom with respect to the center of rotation by the rotation driving means Calculation means for calculating information relating to the displacement of the display, and display means for displaying information for positioning the phantom based on the information relating to the calculated displacement. It is an X-ray CT apparatus according to claim.

According to a sixth aspect of the present invention, there is provided a top plate on which a phantom having a cylindrical casing filled with a filling is installed, an X-ray generation means for generating an X-ray beam, and an installation on the top plate. X-ray detection means for detecting the X-ray beam transmitted through the phantom, rotation drive means for rotating the X-ray generation means and the X-ray detection means, and coordinates of the center of rotation by the rotation drive means. Based on the generated tomographic image data, storage means for storing in advance, tomographic image data generating means for generating tomographic image data of the phantom based on the X-ray beam detected by the X-ray detecting means, An extracting means for extracting partial tomographic image data corresponding to the housing of the phantom, and a circle for calculating the coordinates of the center of a circle passing through three different points in the extracted partial tomographic image data A first displacement for calculating a displacement of the cylindrical axis of the phantom with respect to the center of rotation based on the calculation means, the calculated coordinates of the center of the circle, and the stored coordinates of the center of rotation. a calculation unit, a plurality of different points in the extracted the partial tomographic image data, and the error calculating means for calculating an error for the circle, the calculated error determination means for determining whether more than a predetermined value An ellipse center calculating means for calculating coordinates of the center of an ellipse that passes through four different points in the extracted partial tomographic image data when it is determined that the error exceeds the predetermined value; Second displacement calculating means for calculating a displacement of the cylindrical axis of the phantom relative to the center of rotation based on the coordinates of the center of the ellipse and the stored coordinates of the center of rotation; When it is determined that the error exceeds the predetermined value, a radius calculating means for calculating a horizontal radius and a vertical radius of the ellipse, respectively, and based on the calculated horizontal and vertical radii An inclination angle calculating means for calculating an inclination angle of the cylindrical axis of the phantom with respect to a normal direction of the rotation surface of the rotation, and when the determination means determines that the error does not exceed the predetermined value, The displacement calculated by the first displacement calculation means is displayed, and when it is determined that the error exceeds the predetermined value, the displacement calculated by the second displacement calculation means and the inclination angle calculation An X-ray CT apparatus comprising: display means for displaying the tilt angle calculated by the means.

According to a ninth aspect of the present invention, there is provided a top plate on which a phantom having a cylindrical casing filled with a filling is installed, an X-ray generation means for generating an X-ray beam, and the top plate. An X-ray CT apparatus comprising: X-ray detection means for detecting the X-ray beam transmitted through the phantom, rotation drive means for rotating the X-ray generation means and the X-ray detection means, and display means; A function of generating tomographic image data of the phantom based on the X-ray beam detected by the X-ray detecting unit, and the rotation center of the rotation by the rotation driving unit based on the generated tomographic image data A function of calculating information on the displacement of the phantom, a function of causing the display means to display information for alignment of the phantom based on the information on the calculated displacement, Is a computer program to be executed.

  According to a twenty-seventh aspect of the present invention, data is collected while rotating an X-ray generation unit that generates an X-ray beam and an X-ray detection unit that detects the generated X-ray beam. A phantom holder for holding a phantom having a cylindrical casing filled with a filler on a top plate of a bed apparatus of an X-ray CT apparatus that generates tomographic image data based on data, the X-ray Phantom tilt that tilts the phantom controlled by the control means of the CT apparatus and held on the top plate in a tilt direction with reference to the normal direction of the rotation plane of the X-ray generation means and the X-ray detection means A phantom holder characterized by comprising driving means.

According to the invention described in claim 1 or claim 9 , when aligning the phantom installed on the top plate of the bed, based on the X-ray beam detected by the X-ray detection means, the phantom fault Image data is generated, and information on the displacement of the phantom relative to the rotation center (scan center) of the X-ray generation means and the X-ray detection means by the rotation driving means is calculated based on the generated tomographic image data. Since an X-ray CT apparatus that functions to display information for positioning the phantom on the display means based on the information about the displacement can be provided, the operator can change the displacement of the cylindrical axis of the phantom with respect to the scan center. Information for alignment based on this can be easily acquired. Therefore, regardless of the skill level of the operator, the cylindrical axis of the phantom can be easily aligned with the scan center.

According to the sixth aspect of the present invention, tomographic image data of the phantom is generated based on the X-ray beam detected by the X-ray detection means when aligning the phantom installed on the couch top. Then, partial tomographic image data corresponding to the phantom housing is extracted from the generated tomographic image data, and the coordinates of the center of a circle passing through two or more different points in the extracted partial tomographic image data are calculated. Based on the calculated coordinates of the center of the circle and the coordinates of the rotation center (scan center) of the X-ray generation means and X-ray detection means stored in advance in the storage means, the displacement of the cylindrical axis of the phantom with respect to the scan center It calculates the, for different points in the extracted partial tomographic image data, whether to calculate the error for the circle which is the calculated, the calculated error exceeds a predetermined value Disconnection, and when the error is determined to not exceed the predetermined value, it is possible to provide an X-ray CT apparatus which functions to display the displacement of the cylinder axis of the phantom relative to the scan center is the calculated. Furthermore, when it is determined that the error exceeds a predetermined value, the X-ray CT apparatus calculates the coordinates of the center of an ellipse that passes through two or more different points in the extracted partial tomographic image data. Based on the coordinates of the center of the ellipse and the stored coordinates of the scan center, the displacement of the cylindrical axis of the phantom relative to the scan center is calculated, and the horizontal radius and the vertical radius of the ellipse are respectively calculated. Based on the calculated horizontal and vertical radii, the inclination angle of the phantom cylinder axis with respect to the normal direction (slice direction) of the rotation plane of the rotation is calculated, and the displacement and inclination of the calculated phantom cylinder axis are calculated. It functions to display the angle on the display means. Accordingly, when it is determined that the error does not exceed the predetermined value, that is, when the inclination angle with respect to the phantom slice direction is small, the cylindrical axis of the phantom with respect to the scan center accurately obtained in the preceding process is determined. When the displacement is displayed and the phantom tilt angle is large, the subsequent processing is executed to calculate and display the phantom tilt angle and the displacement of the cylindrical axis. Therefore, in any case, since the worker can obtain the phantom arrangement state with high accuracy, it is possible to easily and quickly align the phantom regardless of the skill level of the worker. Become.

  An example of a preferred embodiment of an X-ray CT apparatus, a computer program, and a phantom holder according to the present invention will be described in detail with reference to the drawings as appropriate.

  Hereinafter, first to third embodiments of the X-ray CT apparatus according to the present invention will be described. In the first embodiment, an X-ray CT apparatus configured to calculate the installation state of the phantom and display the calculation result will be described. In the second embodiment, an X-ray CT apparatus configured to calculate the installation state of the phantom and automatically correct the installation state of the phantom by controlling the bed and the gantry based on the calculation result will be described. . In the third embodiment, an X-ray CT apparatus and a phantom holder configured to calculate the installation state of the phantom and move the phantom based on the calculation result will be described. Thereafter, a computer program for causing the X-ray CT apparatus to execute such processing will be described.

<First Embodiment>
[Overall configuration of the device]
With reference to FIG.1 and FIG.2, the whole structure of the X-ray CT apparatus which concerns on the 1st Embodiment of this invention is demonstrated. FIG. 1 shows an external configuration of an X-ray CT apparatus 1 according to this embodiment. FIG. 2 shows the internal configuration of the X-ray CT apparatus 1. The X-ray CT apparatus 1 according to the present embodiment includes a gantry 2, a bed 3, a computer apparatus 4, a monitor 5, and an input device 6 as in the prior art.

  The monitor 5 and the input device 6 are used as the console 7 of the X-ray CT apparatus 1 (see FIG. 2). The monitor 5 corresponds to an example of the “display unit” of the present invention, and is configured by an arbitrary display device such as an LCD or a CRT. The input device 6 includes an arbitrary input device such as a keyboard, a mouse, a trackball, a control panel, and a touch panel.

  The gantry 2 incorporates a rotatable support 21 as shown in FIG. The support 21 supports an X-ray tube 22 corresponding to an example of the “X-ray generation unit” of the present invention and an X-ray detector 23 corresponding to an example of the “X-ray detection unit” of the present invention. ing. The X-ray tube 22 generates X-rays based on a predetermined tube voltage and tube current applied by the high voltage generator 24, and this X-ray tube 22 is directed toward the subject P disposed in the opening 2A of the gantry 2. Irradiate a fan beam or cone beam. The X-ray detector 23 is supported at a position facing the X-ray tube 22 and has a configuration in which a plurality of X-ray detection elements for detecting the dose of the X-ray beam transmitted through the subject P are arranged in an array. ing.

  The support 21 is rotated around the opening 2 </ b> A by the support driving unit 25. The X-ray tube 22 and the X-ray detector 23 are rotated along with the rotation of the support 21 to scan the subject P, and thereby the X-ray dose of the X-ray beam transmitted through the subject P is measured from various directions. It comes to detect. The transmitted X-ray dose data (detection signal) detected by the X-ray detector 23 is sent to the data collection unit 26.

  The data collection unit 26 is a so-called DAS (Data Acquisition System), and has data collection elements arranged in an array like the X-ray detection elements of the X-ray detector 23, and detects X-rays. Data of the transmitted X-ray dose (detection signal) detected by the instrument 23 is collected. The data collection unit 26 performs amplification processing, A / D conversion processing, and the like on the collected data and transmits the collected data to the computer apparatus 4.

  The support driving unit 25 not only rotates the support 21 as described above, but also operates to tilt the support 21 with respect to the subject P. Thus, the support driving unit 25 corresponds to an example of each of the “rotation driving unit” and the “tilt driving unit” of the present invention. Note that the rotation driving means and the inclination driving means may be provided separately.

  As shown in FIG. 1, the bed 3 includes a top board 31 on which the subject P is placed, and a bed base 32 that supports the top board 31. The couch base portion 32 has a couchtop drive unit that moves the couchtop 31 in the front-rear direction (arrow direction in FIG. 1; horizontal direction), left-right direction (horizontal direction orthogonal to the front-rear direction), and up-down direction (vertical direction). 33 (see FIG. 2) is provided. The front-rear direction is the body axis direction of the subject P on the top 31.

  The computer device 4 is constituted by, for example, a general-purpose computer, and includes a microprocessor such as a CPU and an MPU, a memory such as a RAM and a ROM, a mass storage device such as a hard disk drive, and other devices (gantry 2, bed 3, console 7, It has a built-in interface for sending and receiving data and signals to and from other computer devices on a network (not shown).

  The computer apparatus 4 includes an apparatus control unit 41 that controls the operation of each unit of the X-ray CT apparatus 1 and an image processing unit 42 that performs image data generation processing based on data collected by the gantry 2 and various types of image processing. And are provided. The apparatus control unit 41 controls the rotation and tilt operations of the support 21 by the support drive unit 25, the operation control of the X-ray tube 22 by the high voltage generator 24, the operation control of the X-ray detector 23, and the data collection unit. 26, control of movement operation of the top plate 31 by the top plate drive unit 33, and the like are executed. The configuration and operation of the image processing unit 42 will be described in detail below.

[Control system configuration]
FIG. 3 shows an internal configuration of the X-ray CT apparatus 1 according to the present embodiment. Hereinafter, the configuration of the control system of the X-ray CT apparatus 1, particularly the configuration of the computer apparatus 4, will be described in detail with reference to FIG. In FIG. 3, drawing of blocks indicating the computer apparatus 4 is omitted in order to avoid complication of the drawing.

(Device control unit)
The device control unit 41 of the computer device 4 is configured by a microprocessor such as a CPU built in the computer device 4. This microprocessor performs the following control process by expanding and executing a computer program stored in a storage device such as a ROM or a hard disk drive built in the computer device 4 on the RAM.

  The apparatus control unit 41 includes a gantry control unit 51 that controls the gantry 2, a bed control unit 52 that controls the bed 3, and a console control unit 53 that controls the monitor 5 and the input device 6 (console 7). It has been.

(Gantry control unit)
The gantry control unit 51 controls each part of the gantry 2. For example, the gantry control unit 51 transmits a control signal to the support driving unit 25 to control the rotation operation and tilt operation of the support 21. In addition, the gantry control unit 51 transmits a control signal to the high voltage generation unit 24 to control the X-ray beam generation operation by the X-ray tube 22. The gantry control unit 51 also performs operation control of the X-ray detector 23, operation control of the data collection unit 26, and the like.

(Bed control section)
The couch controller 52 transmits a control signal to the couchtop drive unit 33 of the couch 3 to move the couchtop 31 in the front-rear direction, the left-right direction, and the up-down direction.

(Console control unit)
The console control unit 53 transmits an image signal (for example, R, G, and B video signals in the case of a color image) to the monitor 5 and causes the monitor 5 to display a target image.

  Further, the console control unit 53 receives an operation signal input from the input device 6 and executes an operation requested by the operation signal. For example, when an operation for tilting the gantry 2 is performed, an operation signal corresponding to the tilt requesting operation is input from the input device 6 to the console control unit 53. The console control unit 53 sends this operation signal to the gantry control unit 51, and the gantry control unit 51 tilts the gantry 2 by the required angle based on this operation signal. Further, when an operation for moving the top plate 31 of the bed 3 is performed, an operation signal corresponding to the top plate movement request operation is input from the input device 6 to the console control unit 53. The console control unit 53 sends this operation signal to the bed control unit 52, and the bed control unit 52 moves the top 31 based on this operation signal.

(Image processing unit)
Similar to the device control unit 41, the image processing unit 42 of the computer device 4 includes a microprocessor such as a CPU. The microprocessor executes a computer program stored in a storage device built in the computer device 4. Thus, the following processing is performed. In addition, the image processing unit 42 includes a storage device for storing various data related to processing, image data of a reconstructed image (tomographic image data), and the like.

  If the computer device 4 is connected to a network such as a LAN, the computer program is stored in a server on the network and the computer device 4 reads and executes the computer program via the network. (That is, it can be configured as a client server system).

  The image processing unit 42 includes a tomographic image data generation unit 60, an image storage unit 71, a data storage unit 72, a calculation processing unit 80, and an error processing unit 90. Each of these will be described below.

(Tomographic image data generator)
The tomographic image data generation unit 60 corresponds to an example of the “tomographic image data generation unit” of the present invention, and, similarly to the conventional X-ray CT apparatus, a circuit board (re-reader) on which a microprocessor such as a CPU is mounted. It is configured to include a pre-processing unit 61 and an image reconstruction unit 62, each of which is called a component board.

  The pre-processing unit 61 performs generation processing of projection data used for image reconstruction processing. Specifically, a series of processes called preprocessing such as logarithm calculation of data, reference correction, water correction, beam hardening correction, and body motion correction are performed on the data sent from the data collection unit 26 of the gantry 2. .

  The image reconstruction unit 62 performs processing by the image reconstruction method on the projection data generated by the preprocessing unit 61 to generate tomographic image data of the subject P. Examples of the image reconstruction method used include known methods such as a convolution / back projection method, a fan beam / convolution / back projection method, and a two-dimensional Fourier transform method.

(Image storage unit)
The image storage unit 71 stores the tomographic image data generated by the tomographic image data generation unit 60, and includes a large-capacity storage device such as a hard disk drive.

(Data storage unit)
The data storage unit 72 stores various data used in processing performed by the image processing unit 42, and includes a nonvolatile storage device such as a ROM or a hard disk drive. In particular, rotation center information 73 and error information 74 are stored in the data storage unit 72 in advance. The data storage unit 72 corresponds to an example of the “storage unit” of the present invention.

  The rotation center information 73 is information representing the coordinates of the scan center of the X-ray beam by the gantry 2, that is, the coordinates of the rotation center of the X-ray tube 22 and the X-ray detector 23 by the support driving unit 25. The rotation center information 73 is information including (255, 255) as the coordinates of the scan center when the display area of the reconstructed image on the monitor 5 is 512 × 512 pixels, for example. The coordinates of the scan center are set in advance. The reconstructed image is displayed on the monitor 5 so that the scan center (O) is arranged at the center position of the display area (see FIGS. 4 to 6).

  The error information 74 is information that is referred to in the processing by the error processing unit 90, and is information that represents an error threshold value that is a criterion for determination by the error determination unit 92 described later. The error information 74 will be described in detail in the description of the error processing unit 90.

  When the above-described client server system is employed, the storage contents of the data storage unit 72 may be stored on the server side, and may be appropriately read and referred to via the network.

(Calculation processing part)
The calculation processing unit 80 corresponds to an example of the “calculation unit” of the present invention, and includes a microprocessor such as a CPU that executes a program for evaluating the performance of the X-ray CT apparatus 1. For the performance evaluation of the X-ray CT apparatus 1, the phantom 100 (see FIG. 16) as described above is used. The phantom 100 is attached to the top plate 31 of the bed 3 with the posture adjusted so that the cylindrical axis J is along the slicing direction by using a predetermined attachment device.

  The calculation processing unit 80 includes a housing extraction unit 81, a circle center calculation unit 82, an ellipse center calculation unit 83, a displacement calculation unit 84, a radius calculation unit 85, and an inclination angle calculation unit 86.

(Case calculation unit)
The case extraction unit 81 corresponds to an example of the “extraction unit” of the present invention, and analyzes the image data (tomographic image data) of the reconstructed image of the phantom 100 generated by the tomographic image data generation unit 60 to obtain a phantom. A process of extracting tomographic image data (partial tomographic image data) corresponding to 100 cases 101 (housing) is performed. The case extraction unit 81 extracts a portion corresponding to the case 101 by analyzing the CT value of each pixel in the tomographic image data of the phantom 100, for example.

  FIG. 4 shows an example of partial tomographic image data extraction processing by the casing extraction unit 81. In FIG. 4 and FIG. 5 described later, it is assumed that the phantom 100 is arranged along the slice direction (Z direction), and the tomographic image is shown in a circle. Note that the case where the phantom 100 is arranged to be inclined with respect to the slice direction will be described later with reference to FIG.

  An image (tomographic image 100A) based on the tomographic image data of the phantom 100 corresponds to a tomographic image 101A corresponding to the case 101 of the phantom 100 and the filler 102 in the case 101, as shown in FIG. Part of the tomographic image 102A. The background area around the tomographic image 101A of the case 101 corresponds to the air (Air) around the phantom 100 installed on the top board 31.

  The phantom 100 (particularly the case 101) is made of a known material. The CT value corresponding to the case 101 in the tomographic image data of the phantom 100 can be acquired in advance by prior measurement or the like. Similarly, the CT value of the portion corresponding to the filling material 102 can be acquired in advance. Here, the CT value of the tomographic image 101A corresponding to the case 101, that is, the CT value of the partial tomographic image data corresponding to the case 101 in the tomographic image data is set to 500. Further, the CT value of the tomographic image 102A corresponding to the filler 102 is set to 300. Data of these CT values is stored in advance in the data storage unit 72, for example. Note that the CT value of the tomographic image 102A of the filler 102 may not be stored.

  The casing extraction unit 81 refers to the CT value of each pixel of the tomographic image data of the tomographic image as shown in FIG. 4A, and extracts a pixel having a CT value (= 500) corresponding to the case 101. Accordingly, as shown in FIG. 4B, a tomographic image (partial tomographic image data) corresponding to the case 101 is extracted from the tomographic image 100A (tomographic image data) of the phantom 100.

  When displaying the processing result by the casing extraction unit 81 on the monitor 5, the CT value of pixels other than the pixel corresponding to the extracted partial tomographic image data is displayed as 0. At this time, for example, the CT value of pixels other than the portion corresponding to the outer peripheral surface of the case 101 in the partial tomographic image data may be set to zero. As a result, a tomographic image corresponding to the case 101 (the outer peripheral surface thereof) is displayed on a black background.

(Circle center calculator)
The circle center calculation unit 82 corresponds to an example of the “circle center calculation unit” of the present invention, and includes three different points in the partial tomographic image data (the portion corresponding to the case 101 of the phantom 100) extracted by the housing extraction unit 81. A process for calculating the coordinates of the center of the passing circle is performed.

The three points used for calculating the center coordinates of the circle are selected from the portion corresponding to the outer peripheral surface of the case 101, for example. In addition, you may select from the part etc. which are equivalent to the internal peripheral surface of case 101. FIG. An example of the selection of these three points is shown in FIG. In the figure, on the tomographic image 101a on the outer peripheral surface of the case 101, a point P1 (x ₁ , y ₁ ) having the smallest X coordinate, a point P2 (x ₂ , y ₂ ) having the largest X coordinate, The point P3 (x ₃ , y ₃ ) having the largest coordinate is selected. The X coordinate is a horizontal coordinate orthogonal to the slice direction (Z direction), and the Y coordinate is a vertical coordinate.

  The search process for the point P1 can be performed, for example, by searching for the coordinates of the pixel having the smallest X coordinate among the pixels having the CT value = 500 (the CT value corresponding to the case 101). Similarly, the search process for the point P2 can be performed by searching for the coordinate of the pixel having the maximum X coordinate among the pixels with the CT value = 500, and the search process for the point P3 is performed with the pixel having the CT value = 500. Can be performed by searching for the coordinate of the pixel having the maximum Y coordinate.

  For example, when there are a plurality of pixels having the maximum Y coordinate among the pixels having a CT value = 500, it is considered that the phantom 100 is arranged at a position greatly deviated in the + Y direction. Can be switched to search for the smallest pixel. In addition, when there are a plurality of pixels having the maximum (minimum) X coordinate, it is considered that the phantom 100 is greatly shifted in the X direction. Therefore, the pixel having the minimum (maximum) X direction and the pixel having the maximum Y coordinate. And to search for the smallest pixel.

  In order for the three points P1, P2, and P3 selected from the tomographic image 101A of the case 101 (that is, selected from the partial tomographic image data) to exist on the same circumference, the following conditions are satisfied. Need to be.

Further, when this circle equation is expressed as the following [Equation 2], the coordinates (x ₀ , y ₀ ) and the radius r of the center C are expressed as [Equation 3]. Also, the coefficients a, d, e, and f used in the formula of [Formula 2] used in the formula of [Formula 3] are given by the formulas of [Formula 4].

The circle center calculation unit 82 selects three points P1 (x ₁ , y ₁ ), P2 (x ₂ , y ₂ ), and P3 (x ₃ , y ₃ ) from the partial tomographic image data extracted by the casing extraction unit 81. To do. Then, the coordinate values of these three points P1 (x ₁ , y ₁ ), P2 (x ₂ , y ₂ ), and P3 (x ₃ , y ₃ ) are applied to each equation of [Equation 4] [Equation 2]. The values of the coefficients a, d, e, and f in the formula (1) are calculated, and the values of the coefficients are substituted into the first and second formulas of [Formula 3] to obtain the coordinates of the center C (x ₀ , y ₀ ) is calculated.

(Ellipse center calculation unit)
The ellipse center calculation unit 83 corresponds to an example of the “ellipse center calculation means” of the present invention, and the phantom 100 is inclined with respect to the slice direction (Z direction) as described in [Operation] described later. The coordinate of the center of an ellipse that passes through four different points in the partial tomographic image data extracted by the housing extraction unit 81 is calculated. Here, the center of the ellipse means the midpoint between the two focal points of the ellipse, in other words, the intersection of the major axis and the minor axis of the ellipse.

  When the phantom 100 is disposed so as to be inclined with respect to the slice direction, a cross-sectional image of a portion corresponding to the case 101 (partial tomographic image data) has an elliptical shape (see the cross-sectional image 101b in FIG. 6). Whether the phantom 100 is inclined is determined by an error processing unit 90 described later.

The four points used for calculating the center coordinates of the ellipse are selected from, for example, a portion corresponding to the outer peripheral surface of the case 101 (a portion corresponding to the inner peripheral surface may be used). An example of the selection of these four points is shown in FIG. The figure shows an elliptical tomographic image 101b of the outer peripheral surface of the case 101 in the tomographic image 100B of the phantom 100 arranged so as to be inclined in the vertical direction (Y direction) with respect to the slice direction (Z direction). Yes. In the present embodiment, the point Q1 (ξ ₁ , η ₁ ) having the smallest X coordinate, the point Q2 (ξ ₂ , η ₂ ) having the largest X coordinate, and the Y coordinate being the smallest on the tomographic image 101b of the outer peripheral surface. Point Q3 (ξ ₃ , η ₃ ) and point Q4 (ξ ₄ , η ₄ ) having the largest Y coordinate are selected.

  In order for these four points Q1, Q2, Q3, and Q4 to exist on the same ellipse, the following conditions must be satisfied.

Further, when this ellipse equation is expressed as the following [Equation 6], the coefficient of the equation is given by each equation of [Equation 7]. Further, the coordinates (ξ ₀ , η ₀ ) of the center K of the ellipse, the radius r _{x in} the X direction, and the radius r _{y in the} Y direction are expressed as [Equation 8], respectively.

The ellipse center calculation unit 83 has four points Q1 (ξ ₁ , η ₁ ), Q2 (ξ ₂ , η ₂ ), Q3 (ξ ₃ , η ₃ ), Q4 from the partial tomographic image data extracted by the casing extraction unit 81. (Ξ ₄ , η ₄ ) is selected. The coordinate values of these four points Q1 (ξ ₁ , η ₁ ), Q2 (ξ ₂ , η ₂ ), Q3 (ξ ₃ , η ₃ ), Q4 (ξ ₄ , η ₄ ) Applying to the formula, calculate the values of the coefficients A, C, D, E, and F of the formula [6], respectively, and assign the values of the coefficients to the second formula and the third formula of the formula 8 Then, the coordinates (ξ ₀ , η ₀ ) of the center K are calculated.

(Displacement calculation unit)
The displacement calculator 84 corresponds to an example of “displacement calculator”, “first displacement calculator”, and “second displacement calculator” of the present invention. The displacement calculation unit 84 is a cylinder of the phantom 100 with respect to the scan center O (the rotation center of the X-ray tube 22 and the X-ray detector 23) based on the calculation result by the circle center calculation unit 82 or the calculation result by the ellipse center calculation unit 83. A process for calculating the displacement of the axis J is performed.

  A displacement calculation process based on the calculation result by the circle center calculation unit 82 will be described. As described above, the circle calculation unit 82 selects the three points P1, P2, and P3 from the partial tomographic image data extracted by the casing extraction unit 81, and the center C of the circle that passes through these three points P1, P2, and P3. Are calculated (see FIGS. 4 and 5). Based on the calculated coordinates of the center C of the circle and the rotation center information 73 stored in the data storage unit 72, the displacement calculation unit 84 determines the displacement of the cylindrical axis J of the phantom 100 relative to the scan center O (Δx, Δy) is calculated.

Specifically, assuming that the calculated coordinates of the center C of the circle are (x ₀ , y ₀ ) and the coordinates of the scan center O shown in the rotation center information 73 are (255, 255), the displacement calculator 84 A displacement x ₀ -255 in the X direction and a displacement y ₀ -255 in the Y direction with respect to the scan center O are obtained. If the inclination of the cylindrical axis J of the phantom 100 with respect to the slicing direction (Z direction) is so small that it can be ignored, the tomographic image 101A of the case 101 is substantially circular, and therefore the displacement of the cylindrical axis J of the phantom 100 with respect to the scan center O (Δx, Δy) is substantially equal to the calculation result (x ₀ -255, y ₀ -255). Note that whether or not the inclination of the phantom 100 is negligible is synonymous with whether or not the inclination of the phantom 100 is negligible, and is determined by the error processing unit 90 described later.

  A displacement calculation process based on the calculation result by the ellipse center calculation unit 83 will be described. As described above, the ellipse calculation unit 83 selects four points Q1, Q2, Q3, and Q4 from the partial tomographic image data extracted by the casing extraction unit 81, and passes through these four points Q1, Q2, Q3, and Q4. The coordinates of the center K of the ellipse are calculated (see FIG. 6). The displacement calculator 84 calculates the displacement (Δξ, Δη) of the cylindrical axis J of the phantom 100 with respect to the scan center O based on the calculated coordinates of the center K of the ellipse and the rotation center information 73.

Specifically, assuming that the coordinates of the calculated center K of the ellipse are (ξ ₀ , η ₀ ) and the coordinates of the scan center O shown in the rotation center information 73 are (255, 255), the displacement calculation unit 84 Request X direction displacement xi] ₀ -255 of the center K relative to the scan center O and the Y-direction displacement xi] ₀ -255.

(Radius calculation part)
The radius calculation unit 85 corresponds to an example of the “radius calculation unit” of the present invention, and operates when the phantom 100 is arranged to be inclined with respect to the slice direction (Z direction), similarly to the ellipse center calculation unit 83. Thus, a process of calculating the radius in the horizontal direction (X direction) and the radius in the vertical direction (Y direction) of an ellipse passing through four different points in the partial tomographic image data extracted by the casing extraction unit 81 is performed. Note that whether or not the phantom 100 is inclined is determined by an error processing unit 90 described later.

The radius calculation unit 85 substitutes the coefficients A, C, D, E, and F obtained by the above equations [Equation 7] into the fourth equation of [Equation 8], thereby obtaining the X direction of the ellipse. The radius r _x is calculated. These coefficients A, C, D, E, by substituting the F in the fifth equation of [Equation 8], to calculate the radius r _y of the Y direction of the ellipse.

(Inclination angle calculation unit)
The inclination angle calculation unit 86 corresponds to an example of the “inclination angle calculation unit” of the present invention, and the ellipse horizontal direction (X direction) radius r _x and vertical direction (Y direction) calculated by the radius calculation unit 85 are used. Based on the radius r _y , a process of calculating an inclination angle of the cylindrical axis J of the phantom 100 with respect to the slice direction (Z direction) is performed.

  The slice direction (Z direction) coincides with the normal direction of the rotation plane (scanning plane) of the X-ray tube 22 and the X-ray detector 23 rotated together with the support 21 by the support driving unit 25. That is, the support 21 is driven by the support driving unit 25 so as to rotate within a predetermined plane (rotation plane), and the slice direction is the normal direction of the predetermined plane, that is, the rotation of the support 21. The direction is parallel to the axial direction.

  The inclination angle Δθ of the cylindrical axis J of the phantom 100 with respect to the slicing direction is obtained by the following equation.

Inclination angle calculating section 86, an ellipse with a radius r _x of radius calculation unit 85 has _calculated the r _y, by substituting this [equation 9] to determine the tilt angle Δθ of the cylinder axis J of the phantom 100 relative to the slice direction .

(Error processing part)
The error processing unit 90 performs processing related to an error with respect to the circle of the tomographic image 101A (the tomographic image 101a on the outer peripheral surface) of the case 101 considered by the circle center calculation unit 82 and the case 101 considered by the ellipse center calculation unit 83. Processing relating to an error with respect to the ellipse of the tomographic image (tomographic image 101b on the outer peripheral surface) is performed. The error processing unit 90 includes an error calculation unit 91 and an error determination unit 92 as described below.

(Error calculation part)
The error calculator 91 corresponds to an example of the “error calculator” of the present invention. As the first process, the error calculation unit 91 selects a plurality of points on the partial tomographic image data (the image data of the tomographic image 101A of the case 101 of the phantom 100) extracted by the casing extraction unit 81, and the circle A process of calculating errors of the plurality of points with respect to the circle (see [Equation 2]) considered in the process of the center calculation unit 82 is performed. As this error, for example, an error average represented by the following equation is used.

Here, x ₀ represents the X-coordinate of the center C of the circle, Y coordinate of y ₀ is the center C, r is the radius of the circle (Formula 3 see). N is the number of samples (that is, the plurality of points) on the partial tomographic image data in calculating the average error, and is about 10 to 100, for example.

  The selection of the sample (a plurality of points) used for calculation of the error average is appropriately performed. For example, the average error may be calculated using all pixels (all points) forming partial tomographic image data. Alternatively, the pixels forming the partial tomographic image may be selected, for example, every 5 pixels, and the selected plurality of pixels may be used for error average calculation. In general, a large number of samples should be selected as much as possible when importance is placed on calculation accuracy of error averages, and a relatively small number of samples should be selected when importance is placed on processing time and CPU resources of calculation processing. To.

  The tomographic image 101A (the tomographic image 101a on the outer peripheral surface) of the case 101 shown in FIGS. 4 and 5 does not become a circle when the phantom 100 is inclined, for example. The error average of [Equation 10] is an index representing how much the tomographic image 101A (101a) deviates from the circle.

  On the other hand, the error calculation unit 91 selects a plurality of points on the partial tomographic image data extracted by the housing extraction unit 81 as the second processing, and the ellipse considered in the processing of the ellipse center calculation unit 83 (Refer to [Equation 8]) A process of calculating errors of the plurality of points is performed. As this error, for example, an error average represented by the following equation is used.

Here, xi] ₀ is the X coordinate of the center K of the ellipse, eta ₀ is the Y coordinate of the center K, r _x is an ellipse in the X direction of the radius, r _y denotes the radius of the ellipse in the Y direction ([Equation 8] see ). Further, N is the number of samples on the partial tomographic image data (that is, the plurality of points described above) in the calculation of the error average, as in the case of [Equation 10].

  The error average of [Equation 11] is an index representing how much the tomographic image 101b on the outer peripheral surface of the case 101 shown in FIG. 6 deviates from the ellipse considered in the processing of the ellipse center calculation unit 83.

(Error judgment part)
The error determination unit 92 corresponds to an example of the “determination unit” of the present invention, and performs a process of determining whether the error (error average) calculated by the error calculation unit 91 exceeds a predetermined value. The “predetermined value” in the present embodiment is an error average threshold value shown in [Equation 10] and [Equation 11], for example, “Threshold = 1.0”. This threshold value is data included in the error information 74 of the data storage unit 72. The error determination unit 92 compares the error average value calculated by the error calculation unit 91 with the threshold value (= 1.0) indicated in the error information 74 to determine the magnitude of the error average with respect to the threshold value.

[Operation]
The operation of the X-ray CT apparatus 1 according to this embodiment configured as described above will be described with reference to the flowchart of FIG. In addition, the operation | movement of each part of the X-ray CT apparatus 1 in the same figure is performed based on control of the apparatus control part 41. FIG.

  First, the worker attaches the phantom 100 to the top plate 31 of the bed 3 (S1). The phantom 100 is preferably attached in consideration of the cylindrical axis J of the phantom 100 being aligned with the scan center and the cylindrical axis J being aligned with the slice direction (Z direction).

  Next, the X-ray CT apparatus 1 is operated to generate tomographic image data of the phantom 100 (S2). Specifically, the gantry 2 collects X-ray dose data transmitted through the phantom 100 and sends it to the computer apparatus 4, and the tomographic image data generation unit 60 of the computer apparatus 4 generates the tomographic image data of the phantom 100 in a normal manner. Generate. The generated tomographic image data is stored in the image storage unit 71. Note that the image (reconstructed image) based on the tomographic image data is a tomographic image of the phantom 100 as shown in FIG.

  The processing shifts to processing by the calculation processing unit 80. First, the housing extraction unit 81 reads out the tomographic image data from the image storage unit 71 and analyzes it to extract the tomographic image data (partial tomographic image data) corresponding to the case 101 of the phantom 100 (S3). . An image based on the extracted partial tomographic image data is a tomographic image of the case of the phantom 100 as shown in FIG.

Next, the apparatus control unit 41 selectively operates the circle center calculation unit 82 to extract three points P1 (x ₁ , y ₁ ), P2 (x ₂ , y ₂ ), P3 (x ₃ , y ₃ ) is selected, and the coordinates (x ₀ , y ₀ ) of the center C of the circle passing through these three points P1, P2, P3 are calculated (S4).

Subsequently, the displacement calculation unit 84 calculates the coordinates (x ₀ , y ₀ ) of the calculated center C of the circle and the coordinates (255, 255) of the scan center O indicated in the rotation center information 73 stored in the data storage unit 72. ), The displacement (Δx, Δy) = (x ₀ -255, y ₀ -255) of the cylindrical axis J of the phantom 100 with respect to the scan center O is calculated (S5).

  Here, the apparatus control unit 41 operates the error processing unit 90. The error calculation unit 91 selects a plurality of points on the partial tomographic image data extracted in step S3 and applies to the circle considered in the process of step S4 (a circle passing through the three points P1, P2, and P3). Then, an error average of the plurality of points is calculated (S6).

  Further, the error determination unit 92 refers to the error information 74 stored in the data storage unit 72, and whether or not the error average value calculated in step S6 exceeds the threshold value (= 1.0) indicated in the error information 74. (S7).

(When the error average does not exceed the threshold)
When the error average value does not exceed the threshold (S7; N), the device control unit 41 displays the displacement (Δx, Δy) of the phantom 100 calculated in step S5 on the screen of the monitor 5 (S8). This display process is performed by the console control unit 53.

  Here, an example of the display mode of the displacement of the phantom 100 will be described. First, the displacement value can be displayed as it is, such as “vertical error: 10 mm, horizontal error: −5 mm” (see the coordinate axes in FIG. 5). Further, as shown in FIG. 5, the position of the center C with respect to the scan center O can be displayed graphically.

  Moreover, you may employ | adopt the display mode which specified the direction of displacement. That is, based on the definition of the direction of the X coordinate axis shown in FIG. 5, when the displacement Δx in the X direction is positive (+), the fact that the phantom 100 is displaced to the right is displayed, and when it is negative (−) Indicates that it is shifted to the left. Further, based on the definition of the direction of the Y coordinate axis shown in FIG. 5, when the displacement Δy in the Y direction is positive (+), it is displayed that the phantom 100 is displaced downward, and when it is negative (−). Indicates that it is displaced upward. As an example, a dialog box including the message “error in the vertical direction: 10 mm below, error in the horizontal direction: 5 mm left” can be displayed.

  Further, instead of displaying the displacement direction of the phantom 100 as described above, the direction in which the phantom 100 should be moved may be displayed. That is, when the displacement Δx in the X direction is positive (+), a message indicating that the phantom 100 should be moved leftward in FIG. 5 is displayed, and when it is negative (−), a message indicating that the phantom 100 should be moved rightward is displayed. In addition, when the displacement Δy in the Y direction is positive (+), the fact that the phantom 100 should be moved upward is displayed, and when it is negative (−), the fact that it should be moved downward is displayed. It may be. As an example, a dialog box including the message “Movement in the vertical direction: 10 mm upward, movement in the horizontal direction: 5 mm to the right” can be displayed. As described above, the display of the moving direction of the phantom 100 is also included in the “display of displacement”.

  Returning to the flowchart of FIG. The operator refers to the displacement of the phantom 100 displayed on the monitor 5 and operates the input device 6 to adjust the position of the top plate 31 of the bed 3 so that the cylindrical axis J of the phantom 100 is positioned on the scan center O. (S9).

  This completes the positioning operation of the phantom 100. The operator shifts to the performance evaluation work of the X-ray CT apparatus 1.

(When the error average exceeds the threshold)
When the error average value calculated in step S6 exceeds the threshold (S7; Y), the apparatus control unit 41 operates the ellipse center calculation unit 83 and the radius calculation unit 85, respectively. Note that the processes of the ellipse center calculation unit 83 and the radius calculation unit 85 described below (and the subsequent processes of the displacement calculation unit 84 and the inclination angle calculation unit 86) can be performed in an arbitrary order, and in parallel. Processing can also be performed.

The ellipse center calculation unit 83 has four points Q1 (ξ ₁ , η ₁ ), Q2 (ξ ₂ , η ₂ ), Q3 (ξ ₃ , η ₃ ), Q4 (ξ) from the partial tomographic image data extracted in step S3. ₄ and η ₄ ) are selected, and the coordinates (ξ ₀ , η ₀ ) of the center K of the ellipse passing through these four points Q1, Q2, Q3, and Q4 are calculated (S10).

Subsequently, based on the calculated coordinates (ξ ₀ , η ₀ ) of the ellipse center K and the coordinates (255, 255) of the scan center O shown in the rotation center information 73, the displacement calculation unit 84 scans the scan center. The displacement (Δξ, Δη) = (ξ ₀ -255, η ₀ -255) of the cylindrical axis J of the phantom 100 with respect to O is calculated (S11).

On the other hand, the radius calculation unit 85 calculates a radius r _{x in} the horizontal direction (X direction) and a radius r _y in the vertical direction (Y direction) of the ellipse passing through the four points Q1, Q2, Q3, and Q4 (S12). ).

Further, the tilt angle calculation unit 86 determines the cylinder of the phantom 100 in the slice direction (Z direction) based on the calculated radius r _{x in} the horizontal direction (X direction) and radius r _y in the vertical direction (Y direction). An inclination angle Δθ of the axis J is calculated (S13).

  Here, the device control unit 41 operates the error processing unit 90 again. The error calculation unit 91 selects a plurality of points on the partial tomographic image data extracted in step S3, and the ellipse (the ellipses passing through the four points Q1, Q2, Q3, and Q4) considered in the process of step S10. ) For the plurality of points is calculated (S14).

  Further, the error determination unit 92 refers to the error information 74 stored in the data storage unit 72, and whether or not the error average value calculated in step S14 exceeds the threshold value (= 1.0) indicated in the error information 74. Is determined (S15).

  When the error average value does not exceed the threshold value (S15; N), the apparatus control unit 41 uses the displacement (Δξ, Δη) of the phantom 100 calculated in step S11 and the inclination angle Δθ calculated in step S13. It is displayed on the screen of the monitor 5 (S16).

  The display mode of the displacement (Δξ, Δη) of the phantom 100 is the same as the displacement (Δx, Δy) in the description of step S8. For the tilt angle Δθ, a message such as “error in tilt direction: 3 degrees” is displayed.

  The operator refers to the displacement of the phantom 100 displayed on the monitor 5, operates the input device 6 to adjust the position of the top 31 of the bed 3 and the tilt angle of the gantry 2, so that the cylinder of the phantom 100 The axis J is arranged on the scan center O (S17).

  This completes the positioning operation of the phantom 100. The operator shifts to the performance evaluation work of the X-ray CT apparatus 1.

  On the other hand, when the error average value exceeds the threshold (S15; Y), the apparatus control unit 41 displays a warning message on the monitor 5 (S18). This warning message is a message including that the displacement and the inclination angle of the phantom 100 have not been obtained effectively and that the phantom needs to be mounted again. The worker performs work in response to the warning message.

  Thus, the phantom positioning operation by the X-ray CT apparatus 1 according to the present embodiment is completed. A modification of the phantom alignment operation will be described later.

[Action / Effect]
According to the X-ray CT apparatus 1 of the present embodiment as described above, the following operations and effects are exhibited.

  First, according to the X-ray CT apparatus 1, the phantom 100 attached to the top plate 31 of the bed 3 is automatically obtained from the displacement of the cylindrical axis J from the scan center O and is displayed. Therefore, the operator can easily grasp the displacement of the cylindrical axis J with respect to the scan center O. Therefore, the cylindrical axis J can be easily and quickly aligned with the scan center O regardless of the skill level of the operator. Here, instead of displaying the obtained displacement as it is, information for positioning the phantom 100 based on the displacement (for example, “Please move the phantom in the direction of ... centimeters”, etc. Message) may be displayed.

  In addition, since the tilt angle of the phantom 100 with respect to the slice direction is automatically obtained and displayed, the operator can easily grasp the tilt angle of the cylindrical axis J with respect to the slice direction. Therefore, regardless of the skill level of the operator, it is possible to easily and quickly align the cylindrical axis J along the slice direction. Here, instead of displaying the obtained tilt angle as it is, information for positioning the phantom 100 based on the tilt angle (for example, “tilt the phantom in the direction of ... centimeters”) Or the like) may be displayed.

  The X-ray CT apparatus 1 determines whether or not the cylindrical axis J of the phantom 100 is inclined to a degree that cannot be ignored with respect to the slice direction (see step S7 in the flowchart of FIG. 7), and according to the determination result. The processing content is changed.

  That is, when the inclination of the phantom 100 is negligible (S7; N), the cross-sectional image of the cylindrical phantom 100 is substantially circular, so that the center position of a circle passing through three points of the case 101 portion. Is considered to approximate the position of the cylindrical axis J of the phantom 100. The X-ray CT apparatus 1 obtains the displacement of the approximate position of the cylindrical axis J (the center position of the circle) with respect to the known scan center O. Therefore, when the inclination of the phantom 100 is negligible, the actual displacement of the cylindrical axis J with respect to the scan center O can be obtained with high accuracy.

  On the other hand, when the inclination of the phantom 100 is not negligible (S7; Y), since the cross-sectional image of the cylindrical phantom 100 is elliptical, the center position of the ellipse passing through the four points of the case 101 portion. However, it is considered that the position of the cylindrical axis J of the phantom 100 is approximated. The X-ray CT apparatus 1 obtains the displacement of the approximate position (ellipse center position) of the cylindrical axis J with respect to the known scan center O. Further, the approximate inclination angle of the cylindrical axis is obtained based on the radii of the ellipse in the X direction and the Y direction. Therefore, when the inclination of the phantom 100 is not negligible, both the actual displacement of the cylindrical axis J with respect to the scan center O and the inclination angle of the actual cylindrical axis J with respect to the slice direction are obtained with high accuracy. Can do.

  When the inclination of the phantom 100 is not negligible, an elliptical tomographic image may not be obtained for some reason. For example, when the cylindrical axis J of the phantom 100 has a large inclination angle with respect to the slicing direction, both ends of the phantom 100 are arranged so as to intersect the rotation plane of the X-ray tube 22 or the like, and therefore the fault The image has a rectangular shape (a rectangular tomographic image is obtained when the cylinder axis J and the slice direction are orthogonal to each other. If the angle between the cylinder axis J and the slice direction is close to a right angle, the center is obtained. In order to deal with such a case, the X-ray CT apparatus 1 determines whether or not the tomographic image can be regarded as an ellipse. (S15). When it can be regarded as an ellipse (S15; N), the displacement and the inclination angle calculated based on the ellipse passing through the four points are displayed. On the other hand, when it cannot be regarded as an ellipse (S15; Y), a warning message is displayed to prompt attention and rework. Thereby, it becomes possible to ensure the accuracy of the display content.

[Modification]
Various modifications related to the X-ray CT apparatus 1 according to the present embodiment will be described. It should be noted that the modified example related to the present embodiment can be appropriately adopted also in the second embodiment described later. Moreover, it is also possible to employ | adopt the structure which arbitrarily combined two or more of the following modifications.

[Modification 1]
When the inclination of the phantom 100 is not negligible (S7; Y), a warning message indicating that the phantom 100 is inclined or prompting to correct the inclination can be displayed on the monitor 5. By confirming this warning message, the operator can recognize that the phantom 100 is tilted to some extent, and can recognize the necessity of correcting it. As a result, it becomes possible to support the facilitation and speeding up of work.

  The warning message displayed when the inclination of the phantom 100 is not negligible (S7; Y) or when the tomographic image of the phantom 100 cannot be regarded as an ellipse (S15; Y) is the “notification” of the present invention. It corresponds to an example of “information”. This notification information is not limited to such a warning message. For example, visual information by lighting (flashing) of a warning lamp, auditory information such as a warning buzzer, tactile information by vibration of a device carried by an operator, etc. For example, the form is arbitrary as long as it is information capable of notifying the worker of the determination result.

  Such notification information is output under the control of the console control unit 53 of the device control unit 41. The console control unit 53 corresponds to an example of the “notification information output unit” of the present invention.

[Modification 2]
In the present embodiment, a configuration for calculating the tilt direction of the phantom 100 can be applied. The tomographic image of the phantom 100 has an elliptical shape with the tilt direction as the major axis. For example, in the tomographic image 100B shown in FIG. 6, the Y direction is the long axis, and therefore the phantom 100 is inclined in the vertical direction.

  Therefore, when an elliptical tomographic image is obtained, the direction of the major axis (for example, an angle with respect to the X coordinate or the Y coordinate) is obtained by analyzing the image. This direction is the inclination direction of the phantom 100. As for the inclination angle, based on the radius in the inclination direction (radius in the major axis direction) and the radius in the direction orthogonal to the inclination direction (radius in the short axis), the same as the formula [9] Can be sought. The obtained tilt direction is displayed on the monitor 5. As the display mode, character display in a tilt direction (for example, “direction of 10 degrees in the vertical direction”), graphic display, or the like is applied.

[Modification 3]
In this modification, the inclination direction of the phantom 100 is obtained by a method different from that of Modification 2. In this modification, the following processing is performed: (1) A plurality of tomographic image data at different slice positions of the phantom 100 is generated; (2) A cylindrical axis J of the phantom 100 based on the plurality of tomographic image data. (3) The specified inclination direction is displayed on the monitor 5. Hereinafter, a specific example of the processing contents of steps (1) to (3) will be described, and a specific example in the case of two slice positions will be described.

  (1) The phantom 100 is scanned with an X-ray beam by the gantry 2. At this time, the top 31 is moved to scan the phantom 100 at a plurality of different slice positions. The number of slice positions (Z coordinate values) to be scanned is arbitrary. As a scanning mode, a plurality of slice positions may be intermittently scanned by alternately repeating the movement of the top plate 31 and scanning, or a plurality of slice positions may be scanned continuously like a helical scan. Also good. The tomogram data generator 60 generates tomogram data corresponding to each slice position based on the scan result at each slice position.

  (2) The casing extraction unit 81 of the calculation processing unit 80 analyzes each of the generated tomographic image data, and extracts partial tomographic image data corresponding to the case 101 of the phantom 100, respectively. Next, the ellipse center calculation unit 83 calculates the coordinates of the center of the ellipse that passes through four different points for each of the extracted partial tomographic image data. Subsequently, the calculation processing unit 80 specifies the inclination direction of the phantom 100 based on the coordinates of the center of the ellipse at the plurality of slice positions and the coordinates of the plurality of slice positions. At this time, the inclination angle of the phantom 100 can also be calculated by considering the interval (distance) between a plurality of slice positions (described later).

  This step (2) may be executed by selecting at least two of the plurality of tomographic image data and using only the selected tomographic image data. That is, since the cylindrical axis J of the phantom 100 is a straight line, the center of the ellipse based on each tomographic image data is arranged on a substantially straight line. Therefore, if two of the plurality of tomographic image data are selected, the straight line connecting them will closely approximate the direction of the cylindrical axis J. When three or more tomographic image data are selected, an optimal straight line that minimizes the error with respect to the center of each ellipse is obtained by the least square method or the like, and the processing is executed by regarding it as the cylindrical axis J direction. it can.

  (3) The console control unit 53 causes the monitor 5 to display the specified tilt direction (and tilt angle). The tilt direction of the phantom 100 can be displayed as a message, for example, “the front end of the phantom (the end in the + Z direction) is upward” or a graphic display.

  (Specific Example) The case of generating tomographic image data at two slice positions will be described with reference to FIGS. The phantom 100 shown in FIG. 8 is arranged with the + Z direction end (front end) inclined upward (with the −Z direction end (rear end) inclined downward). The inclination angle of the cylindrical axis J with respect to the Z coordinate axis (slice direction) is Δθ. For simplicity of explanation, it is assumed that there is no inclination in the horizontal direction.

  Two slice positions for generating tomographic image data are Z = z1 and z2 (z1 <z2). The cross-sections 110 and 120 of the phantom 100 at each slice position Z = z1 and z2 are elliptical with the vertical direction (Y direction) as the major axis and the horizontal direction (X direction) as the minor axis.

  FIG. 9A shows a tomographic image 110B showing the cross section 110 at the slice position Z = z1, and FIG. 9B shows a tomographic image 120B showing the cross section 120 at the slice position Z = z2. 8 and 9 indicate the centers of the elliptical tomographic images 110B and 120B calculated by the elliptical center calculation unit 83, respectively.

  Furthermore, the symbol O in FIG. 9 indicates the scan center. As described above, the coordinates of the scan center O are (X, Y) = (255, 255). Further, the scan center O coincides with the Z coordinate axis as described above. The scan center O in FIG. 9A is identified with the intersection (z1 in FIG. 8) between the cross section 110B and the Z coordinate axis, and the scan center O in FIG. 9B is the intersection between the cross section 120B and the Z coordinate axis. (Z2 in FIG. 8).

  The coordinates of the center K1 of the tomographic image 110B at the first slice position Z = z1 are (X, Y) = (255, y1), and the coordinates of the center K2 of the tomographic image 120B at the second slice position Z = z2. Is (X, Y) = (255, y2), since the phantom 100 is inclined, y1 ≠ y2.

  Considering that the first and second slice positions Z = z1, z2 have a relationship of z2> z1, the inclination direction of the phantom 100 is specified as follows: (A) If y2> y1, the phantom The inclination direction of 100 is determined to be a state in which the front end portion is inclined upward and the rear end portion is inclined downward; (b) When y1> y2, the front end portion of the phantom 100 is downward. It is determined that the vehicle is inclined and the rear end portion is inclined upward.

  In the cases shown in FIGS. 8 and 9, the Y coordinate y1 of the center K1 of the tomographic image 110B is smaller than the Y coordinate y2 of the center K2 of the tomographic image 120B (y1 <y2). It corresponds to.

  In the above specific example, the case where the phantom 100 is inclined only in the vertical direction is considered. However, for example, when the phantom 100 is inclined only in the horizontal direction, the X coordinate of the center of the elliptical tomographic image at a plurality of slice positions. In consideration of the above, it is possible to specify an inclination direction in the horizontal direction with respect to the slice direction (Z coordinate) (for example, right direction / left direction toward the + Z direction). Further, when the inclination of the phantom 100 includes a vertical direction component (Y direction component) and a horizontal direction component (X direction component), the inclination direction of the phantom 100 is specified by considering each direction component. can do.

  (Calculation of Inclination Angle) Processing for calculating the inclination angle Δθ of the phantom 100 referred to in the above step (2) will be described. The information on which the tilt angle calculation process is based is the coordinates of the center of the ellipse of the tomographic image at the plurality of slice positions and the coordinates of the plurality of slice positions. Note that processing may be performed by selecting two of the plurality of slice positions.

  This will be specifically described with reference to FIGS. The calculation processing unit 80 calculates an interval (distance) δz = | z1−z2 | between two slice positions Z = z1 and z2. Further, an interval (distance) δ = | y1-y2 | between the ellipse centers K1 (255, y1) and K2 (255, y2) of the tomographic images 110B and 120B at the two slice positions Z = z1 and z2 is calculated. From the above, the inclination angle Δθ can be obtained from the following equation.

  In general, if the coordinates of the ellipse centers K1, K2 are (x1, y1), (x2, y2), the distance between K1 and K2 is δ = √ {(x1-x2) ^ 2 + (y1-y2) ^ 2 }.

  Instead of the calculation process using [Equation 9] in the above embodiment, the tilt angle calculation process described here can be performed.

[Modification 4]
In this embodiment, the center coordinates of a circle passing through three points corresponding to the case 101 of the phantom 100 are calculated (S4), the displacement of the phantom 100 based on the center coordinates is calculated (S5), and then the error average judgment (S7) is performed. However, the present invention is not limited to this.

  For example, based on the partial tomographic image data extracted in step S3, first, an error average is calculated and compared with a threshold. Only when the error average is equal to or less than the threshold, calculation of the center coordinates of the circle and displacement of the phantom 100 are performed. Can be configured to perform the calculation. As a result, when the error average exceeds the threshold value, processing such as calculation of the center coordinates of the circle can be omitted, and the processing can be speeded up.

[Modification 5]
In the present embodiment, the displacement and the inclination angle of the phantom 100 are displayed on a monitor so that an operator can recognize them. In view of this, it is possible to provide means for notifying which part of the input device 6 should be operated to the worker who has recognized the display content. Thereby, even when the operator is unfamiliar, it is possible to prevent a situation where an erroneous part is operated.

  As described above, the input device 6 is used for an operation for moving the top 31 of the bed 3 and an operation for tilting (tilting) the gantry 2. It corresponds to “means” and “inclination operation means”. The input device 6 is provided with a top panel operation button for moving the top panel 31 and a tilt operation button for tilting the gantry 2 (both not shown).

  In this modification, a light source such as an LED is provided inside and below the top panel operation button and the tilt operation button. When the console controller 53 displays only the displacement of the phantom 100 on the monitor 5, the console controller 53 supplies power to the input device 6 to light the LED in the top panel button. Further, when displaying the displacement and tilt angle of the phantom 100, power is supplied to the input device 6 to light the LEDs inside the top panel button and the tilt operation button. This makes it clear at a glance which part of the input device 6 should be operated. The notification of the position of the operation button may be performed by a method such as blinking the light source.

  When the top panel operating means and the tilt operating means are soft keys displayed on the monitor 5, the position is notified by turning on (flashing) the soft keys or changing the display color. be able to. Further, the position of the operation button or soft key may be notified by voice.

[Modification 6]
As shown in the flowchart of FIG. 7, in this embodiment, the displacement of the phantom 100 with respect to the scan center is obtained based on a circle passing through three points of the partial tomographic image data, and the error relative to the circle of the partial tomographic image data sets the threshold value. In the case of exceeding, the displacement of the phantom 100 with respect to the scan center and the inclination angle with respect to the slice direction are obtained based on the ellipse passing through the four points of the partial tomographic image data. The processing by the X-ray CT apparatus according to the present invention is not limited to this, and for example, the following processing may be performed.

  A calculation process based on a circle passing through three points of partial tomographic image data is not performed, and only a calculation process based on an ellipse passing through four points of partial tomographic image data can be performed. That is, it can comprise so that the process after step S10 (it should just include step S10-S13, S16 at least) should be performed following step S1-S3 of FIG. This is because the calculation result by the calculation process based on the circle can be obtained by the calculation process based on the ellipse, considering that “circle” is a kind of “ellipse”.

[Modification 7]
In the present embodiment, when performing calculation processing based on a circle (steps S4 to S6 in FIG. 7), a circle that passes through three points of the partial tomographic image data is used as the circle. It is possible to perform the same processing using a circle.

  An example of using a circle passing through two points of partial tomographic image data will be described. Among the three points P1 to P3 shown in FIG. 5, two points are used: a point P1 having the smallest X coordinate and a point P2 having the largest X coordinate (the point P3 having the largest Y coordinate and the point having the smallest Y coordinate may be used. ). The circle center calculation unit 82 calculates the coordinates of the midpoint between the points P1 and P2. The displacement calculator 84 calculates the displacement of the midpoint with respect to the scan center O. The midpoint displacement is equal to the displacement of the center C of the circle calculated in the above embodiment with respect to the scan center O.

  Similarly, for the calculation process based on the ellipse (steps S10 to S14 in FIG. 7), it is sufficient to consider only two points in the partial tomographic image data in order to calculate the center K of the ellipse. For example, out of the four points Q1 to Q4 shown in FIG. 6, the point Q1 having the smallest X coordinate and the point Q2 having the largest X coordinate are selected, and the coordinates of the center point thereof are calculated, so that Coordinates can be acquired.

  When the tilt direction of the phantom 100 is the horizontal direction or the vertical direction, the horizontal radius and the vertical radius are calculated by considering three points (for example, points Q1 to Q3) of the partial tomographic image data. Thus, the tilt angle can be calculated.

[Modification 8]
The X-ray CT apparatus 1 of the present embodiment calculates both the displacement of the cylindrical axis J of the phantom 100 with respect to the scan center O and the inclination angle (inclination direction) of the cylindrical axis J with respect to the slice direction, and displays them. However, only one of them may be calculated and displayed. Further, only the center coordinates of a circle based on tomographic image data may be calculated, or only the center coordinates of an ellipse may be calculated.

<Second Embodiment>
In the first embodiment described above, the X-ray CT apparatus having a configuration for displaying the displacement of the phantom and the calculation result of the tilt angle on the monitor has been described. On the other hand, in the second embodiment described below, an X-ray CT apparatus having a configuration for automatically correcting the installation state of the phantom based on the calculation results of the phantom displacement and the inclination angle will be described.

  The X-ray CT apparatus of this embodiment has the same external configuration (see FIG. 1), internal configuration (see FIG. 2), and control system configuration (see FIG. 3) as in the first embodiment. Hereinafter, these figures will be referred to. Note that the X-ray CT apparatus of the present embodiment is represented by the same reference numeral 1 as in the first embodiment.

  Here, a system for carrying out maintenance of X-ray CT apparatuses installed in a plurality of medical institutions will be described. A schematic configuration of this maintenance system is shown in FIG. Each medical institution or the like is provided with one or more X-ray CT apparatuses (three are installed in FIG. 10).

  Reference numerals 4A, 4B, and 4C denote computer apparatuses 4 of the respective X-ray CT apparatuses. Reference numerals 5A, 5B, and 5C represent the monitors 5 of the respective X-ray CT apparatuses. Reference numerals 6A, 6B, and 6C represent the input devices 6 of the respective X-ray CT apparatuses.

  Each computer apparatus 4A, 4B, 4C is connected to the server apparatus (hospital server) 1000 via LAN in a medical institution. The in-hospital server 1000 analyzes the image data of the captured image of the phantom 100 and calculates the average value and standard deviation of CT values. Further, the in-hospital server 1000 performs performance evaluation of the X-ray CT apparatus 1 by comparing the calculation result with an appropriate value, and creates a report including the evaluation result. It should be noted that a part or all of these operations may be configured to be performed by the computer devices 4A to 4C and the service server 2000.

  The hospital server 1000 of each medical institution or the like is connected to the service server 2000 via a WAN (Wide Area Network). The service server 2000 is installed in a service center or the like that provides a maintenance service for the X-ray CT apparatus 1.

  Each in-hospital server 1000 transmits information related to the event, identification information of the X-ray CT apparatus 1, and the like to the service server 2000 when a predetermined event such as a device failure, an error, or a decrease in device performance occurs. . The service server 2000 receives information from the in-hospital server 1000 and notifies the service provider and the like. The service server 2000 accumulates information transmitted from the hospital server 1000 and performs analysis. This analysis result is used, for example, for bug correction and research and development of an X-ray CT apparatus.

  An example of the operation of the X-ray CT apparatus 1 and the service system is shown in FIG. Note that the same steps as those in the first embodiment are denoted by the same reference numerals as those in the flowchart of FIG.

  Steps S1 to S7 are the same as those in the first embodiment. When it is determined in step S7 that the average error is equal to or less than the threshold value (S7; N), the couch controller 52 controls the top board drive unit 33 based on the displacement calculated in step S5, and the displacement is determined. The position of the top 31 is moved so as to cancel, that is, the cylindrical axis J is arranged on the slice center O (Z coordinate axis) (S21). Specifically, the top plate 31 is moved by (−Δx, −Δy) with respect to the displacement (Δx, Δy) of the cylindrical axis J of the phantom 100 with respect to the scan center O.

  At this time, the top plate 31 may be manually moved to move in the vertical direction or the horizontal direction. In this case, it is desirable to display the calculation result (and displacement direction) of the displacement amount in the moving direction operated by manual input on the monitor 5 as in step S8 of FIG. Moreover, it is desirable to notify the position of the operation button for manual input as in Modification 5 of the first embodiment.

  When the adjustment of the top position is completed, the X-ray CT apparatus 1 collects projection data by irradiating the phantom 100 with X-rays and reconstructs an image of the phantom 100 (S26). The reconstructed image data is transmitted to the hospital server 1000 via the LAN.

  The in-hospital server 1000 analyzes the image data of the reconstructed image of the phantom 100, evaluates the performance of the X-ray CT apparatus 1, and creates a report (S27). The in-hospital server 1000 transmits the created report to the X-ray CT apparatus 1 via the LAN. Here, when the evaluation result is bad, the hospital server 1000 transmits the evaluation result or the like to the service server 2000 via the WAN.

  The X-ray CT apparatus 1 outputs the report received from the hospital server 1000 (S28). Report output modes include display output on the monitor 5 and print output by a printer (not shown). With the above, the performance evaluation of the X-ray CT apparatus 1 using the phantom 100 is completed. The operator of the X-ray CT apparatus 1 can change various settings of the X-ray CT apparatus 1 with reference to the output report.

  When it is determined in step S7 that the average error is equal to or less than the threshold (S7; Y), the coordinates of the center K of the ellipse that passes through four points on the partial tomographic image data are calculated as in the first embodiment. (S10) Based on the coordinates of the center K of the ellipse and the coordinates of the scan center O, the displacement of the cylindrical axis J of the phantom 100 relative to the scan center O is calculated (S11).

  Further, for example, the process described in the first embodiment and the process described in the modification 3 thereof are performed to specify the tilt direction of the phantom 100 (S22), and the tilt angle is calculated (S23).

  Next, an error average of partial tomographic image data for the ellipse is calculated (S14), and it is determined whether or not the value exceeds a threshold value indicated in the error information 74 (S15).

  When the error average value exceeds the threshold value (S15; Y), a warning message is displayed as in the first embodiment (S18).

  On the other hand, when the error average value does not exceed the threshold value (S15; N), the bed control unit 52 controls the top plate driving unit 33 based on the displacement calculated in step S11, similarly to step S21. Then, the position of the top plate 31 is moved so as to cancel the displacement (S24).

  Further, the gantry control unit 51 controls the support driving unit 25 based on the tilt direction specified in step S22 and the tilt angle calculated in step S23, and cancels the tilt direction and tilt angle. That is, the support 21 is tilted (tilted) so that the normal direction of the rotation plane (scanning plane) of the X-ray tube 22 and the X-ray detector 23 is aligned with the cylindrical axis J of the phantom 100 (S25). Specifically, when the tilt angle is Δθ, the support 21 is tilted by an angle Δθ in the direction opposite to the specified tilt direction. Thereby, the scan surface is arranged in a state orthogonal to the cylindrical axis J.

  When the adjustment of the top position and the tilt angle is completed, the X-ray CT apparatus 1 collects projection data by irradiating the phantom 100 with X-rays and reconstructs an image of the phantom 100 (S26). The in-hospital server 1000 analyzes the image data of the reconstructed image of the phantom 100, evaluates the performance of the X-ray CT apparatus 1, and creates a report (S27). The X-ray CT apparatus 1 outputs a report created by the hospital server 1000 (S28). With the above, the performance evaluation of the X-ray CT apparatus 1 using the phantom 100 is completed.

  According to the present embodiment as described above, with respect to the phantom 100 attached to the top plate 31 of the bed 3, the displacement of the cylindrical axis J from the scan center O is automatically calculated and based on the calculated displacement. Since the top plate 31 is automatically moved so as to place the cylindrical axis J on the scan center O, the operator performs an alignment operation of the cylindrical axis J of the phantom 100 with respect to the scan center O. There is no need to do it. Therefore, the phantom 100 can be easily and quickly positioned regardless of the skill level of the operator.

  Further, the tilt angle of the phantom 100 with respect to the slice direction is automatically calculated, and the X-ray tube 22 and the X-ray tube 22 and the X-ray tube 22 are arranged so that the scan plane of the X-ray beam by the gantry 2 is orthogonal to the slice direction according to the tilt angle. Since the rotation surface of the line detector 23 is configured to be automatically tilted, the operator does not need to adjust the tilt angle of the phantom 100. Therefore, the phantom 100 can be easily and quickly aligned regardless of the skill level of the operator.

  Further, similarly to the first embodiment, it is determined whether or not the inclination angle of the phantom 100 can be ignored, and the processing content is changed according to the determination result, so that the cylindrical axis J with respect to the scan center O is determined. And the inclination angle of the cylindrical axis J with respect to the slicing direction can be obtained with high accuracy. Thereby, automatic adjustment of the position and tilt angle of the top plate 31 can be performed with good accuracy.

  Further, it is possible to output a warning message similar to that in the first embodiment.

<Third Embodiment>
In the second embodiment described above, the X-ray CT apparatus that controls the bed and the gantry based on the calculation results of the phantom displacement and the tilt angle to adjust the installation state of the phantom has been described. In the third embodiment described below, an X-ray CT apparatus that adjusts the installation state of the phantom by moving the phantom based on the calculation result of the displacement and the inclination angle of the phantom will be described.

[Constitution]
The configuration of the X-ray CT apparatus 1 ′ of this embodiment will be described with reference to FIGS. The X-ray CT apparatus 1 ′ has substantially the same configuration as that of the first embodiment.

  The phantom holder 200 is an instrument for holding the phantom 100 on the top plate 31, and can be attached on the top plate 31 of the X-ray CT apparatus 1 'as shown in FIG. The attachment form of the phantom holder 200 with respect to the top plate 31 is the same as the conventional one. The phantom holder 200 is attached to, for example, the end of the top plate 31 on the gantry 2 side, that is, one end of the top plate 31 in the longitudinal direction. The phantom holder 200 corresponds to an example of “phantom holding means” of the present invention.

  One end of a connection line 200a is connected to the surface of the housing of the phantom holder 200 opposite to the gantry 2. The other end of the connection line 200 a is connected to a connector portion 32 a provided on the side surface of the bed base portion 32. In addition, when removing the phantom holder 200 from the top plate 31, the connection line 200a is removed from the connector part 32a.

  The connection line 200a is used to input an electrical signal transmitted from the computer apparatus 4 to the phantom holder 200, and supplies current from a power source (not shown) to the phantom holder 200. In the present embodiment, the electrical signal transmitted from the computer apparatus 4 is input to the phantom holder 200 through the connection line 200a via the gantry 2 and the bed base 32.

  The configuration of the phantom holder 200 will be described with reference to FIG. The phantom 100 is mounted on a plate-like phantom mounting portion 223. The cylindrical phantom 100 is mounted such that one end thereof (that is, one of the two circular surfaces) is in contact with one surface of the phantom mounting portion 223.

  One surface side of the plate-like support portion 222 is connected to the other surface side of the phantom mounting portion 223. The upper surfaces of the phantom mounting part 223 and the support part 222 are connected by a connecting member 224. The surface of the support portion 222 on the phantom mounting portion 223 side is inclined with respect to the Y direction (vertical direction). The lower end sides of the phantom mounting portion 223 and the support portion 222 are connected by a drive shaft 203 of an actuator 203 described later.

  One end of a support shaft 221 is connected to the other surface side of the support portion 222. The other end side of the support shaft 221 is disposed in the housing of the phantom holder 200.

  The phantom holder 200 is provided with actuators 201, 202, 203 such as a stepping motor. The actuators 201, 202, and 203 are configured to operate independently based on electrical signals from the computer device 4. Note that connection lines for sending electric signals to the actuators 201, 202, and 203 are not shown.

  A moving member 211 having a longitudinal direction in the Y direction (vertical direction) is in contact with a drive shaft of the actuator 201 (for example, a rotation shaft of a stepping motor). Helical grooves are formed on the drive shaft of the actuator 201 and the surface of the moving member 211, respectively. The drive shaft of the actuator 201 and the moving member 211 are arranged so that the concaves and convexes of the grooves fit each other. One end side (the upper end side in FIG. 13) of the moving member 211 is connected to the support shaft 221. With such a configuration, the moving member 211 and the support shaft 221 integrally move in the Y direction according to the rotation direction and rotation angle of the drive shaft of the actuator 201. Thereby, the phantom 100 mounted on the phantom mounting part 223 moves in the Y direction.

  Similarly, the driving shaft 202a of the actuator 202 (for example, the rotation shaft of the stepping motor) is brought into contact with a moving member 212 having a longitudinal direction in the X direction (the direction perpendicular to the Y direction and the Z direction; the horizontal direction). Yes. Helical grooves are formed on the surfaces of the drive shaft 202a of the actuator 202 and the moving member 212, respectively. Accordingly, the moving member 212 and the support shaft 221 integrally move in the X direction according to the rotation direction and rotation angle of the drive shaft 202a, and the phantom 100 mounted on the phantom mounting portion 223 moves in the X direction. It is like that.

  The actuator 203 is fixed to the support portion 222. A drive shaft 203 a of the actuator 203 (for example, a rotation shaft of a stepping motor) passes through the vicinity of the lower end of the support portion 222. Furthermore, the tip of the drive shaft 203a is inserted into a hole (not shown) of the phantom mounting portion 223. A spiral groove is formed on the surface of the drive shaft 203a. A spiral groove is also formed on the inner wall of the hole of the phantom mounting portion 223. The groove of the drive shaft 203a and the groove of the hole portion are fitted with the recesses and protrusions of each other.

  As described above, the upper surfaces of the phantom mounting portion 223 and the support portion 222 are connected by the connecting member 224. When the drive shaft 203a of the actuator 203 rotates, the phantom mounting portion 223 moves around the connection position of the connection member 224 with respect to the drive shaft 203a due to the fitting of the grooves described above. Thereby, the cylindrical axis J of the phantom 100 is inclined in the vertical direction (Y direction) with respect to the Z direction. This inclination corresponds to the tilt of the gantry 2.

  Here, the surface of the support portion 222 on the phantom mounting portion 223 side is inclined as described above. Thereby, by rotating the drive shaft 203a of the actuator 203 in a certain direction, the front side of the phantom 100 (the side not mounted on the phantom mounting portion 223; the left side in FIG. 13) is tilted upward. If the drive shaft 203a is rotated in the reverse direction, the front side can be inclined downward. The phantom 100 is inclined by an angle corresponding to the rotation angle of the drive shaft 203a.

  Note that the rotation direction of the drive shaft 203 a of the actuator 203 can be switched by the control of the computer device 4. Similarly, the rotation direction of the drive shaft of the actuator 201 and the drive shaft 202a of the actuator 202 can also be switched by the control of the computer device 4.

  Further, when each of the actuators 201, 202, and 203 is a stepping motor, the computer device 4 transmits an electrical signal having a pulse number corresponding to a target rotation angle to the actuators 201 to 203. Here, the rotation angle of the drive shaft corresponding to one pulse is set in advance. The actuators 201 to 203 rotate the drive shaft by a rotation angle corresponding to the number of pulses of the signal transmitted from the computer apparatus 4. Accordingly, the phantom 100 can be moved in the X direction and the Y direction by a target movement amount, and the phantom 100 can be tilted by a target tilt angle.

  When the actuators 201 to 203 other than the stepping motor are applied, the phantom 100 is moved by a target movement amount and tilted by a target tilt angle by performing control according to the configuration of the actuators 201 to 203. Configure.

  Next, the configuration of the control system of the X-ray CT apparatus 1 ′ of this embodiment will be described with reference to FIG. The control system of the X-ray CT apparatus 1 ′ is configured in substantially the same manner as in the first embodiment (see FIGS. 2 and 3).

  The device control unit 41 of the computer device 4 of the X-ray CT apparatus 1 ′ is provided with a holder control unit 54. The holder control unit 54 controls the operation of the phantom holder 200. More specifically, the holder control unit 54 moves or tilts the phantom 100 by transmitting the aforementioned signal to each of the actuators 201 to 203 and rotating the drive shaft.

  In FIG. 14, it is described that the signal from the holder control unit 54 is directly input to the phantom holder 200, but actually, as shown in FIG. 12, the signal is The information is input to the phantom holder 200 via the gantry 2 and the bed 3.

[Operation]
The operation of the X-ray CT apparatus 1 ′ of this embodiment will be described with reference to the flowchart of FIG. In the following, details of the displacement and inclination angle calculation processing of the phantom 100 described in the first and second embodiments will be omitted.

  First, the phantom holder 200 is attached to the top plate 31, and the phantom 100 is mounted on the phantom mounting portion 223 (S31). Next, collection of projection data for the phantom 100 and image reconstruction are performed to generate tomographic image data of the phantom 100 (S32). The casing extraction unit 81 extracts partial tomographic image data corresponding to the case 101 from the tomographic image data (S33). The calculation processing unit 80 and the error processing unit 90 analyze the partial tomographic image data, and calculate the displacement in the X direction, the displacement in the Y direction, and the tilt angle of the phantom 100 (S34). These calculation results are sent to the holder control unit 54 of the apparatus control unit 41.

  The holder control unit 54 generates a signal based on the calculation results of the displacement in the X direction, the displacement in the Y direction, and the tilt angle, and transmits the signal to the phantom holder 200 (S35).

  A specific example of this process will be described. First, the holder control unit 54 determines the rotation direction of the drive shaft 202a (movement direction in the X direction) based on the calculation result of the displacement in the X direction and the rotation angle of the drive shaft 202a of the actuator 202 with respect to one pulse. The number of pulses (movement amount) is obtained, and a signal corresponding to the result is generated. And the holder control part 54 transmits this signal with the identification information which identifies the actuator 202. FIG. Thereby, this signal is transmitted toward the actuator 202.

  The signal generation process based on the calculation result of the displacement in the Y direction and the signal transmission process toward the actuator 201 can be similarly performed.

  A signal generation process and a transmission process for controlling the actuator 203 will be described. Based on the calculation result of the tilt direction and the rotation angle of the drive shaft 203a of the actuator 203 with respect to one pulse, that is, the tilt angle of the phantom 100 with respect to one pulse, the holder control unit 54 determines the rotation direction of the drive shaft 203a. The number of pulses is obtained, and a signal corresponding to the result is generated. And the holder control part 54 transmits this signal with the identification information of the actuator 203. FIG.

  Each actuator 201-203 operates based on the signal from the holder control unit 54, and rotates each drive shaft (S36). Thereby, the positional deviation of the phantom 100 in the X direction and the Y direction, and the inclination of the phantom 100 are adjusted.

  Next, the X-ray CT apparatus 1 ′ collects projection data by irradiating the phantom 100 with X-rays and reconstructs an image of the phantom 100 (S37). The reconstructed image data is transmitted to the hospital server 1000 via the LAN (see FIG. 10).

  The in-hospital server 1000 analyzes the image data of the reconstructed image of the phantom 100, evaluates the performance of the X-ray CT apparatus 1 ', and creates a report (S38). The in-hospital server 1000 transmits the created report to the X-ray CT apparatus 1 ′ via the LAN. Here, when the evaluation result is bad, the hospital server 1000 transmits the evaluation result or the like to the service server 2000 via the WAN.

  The X-ray CT apparatus 1 ′ outputs the report received from the hospital server 1000 (S39). This is the end of the operation according to the present embodiment. The operator of the X-ray CT apparatus 1 ′ can change various settings of the X-ray CT apparatus 1 ′ as necessary by referring to the output report.

[Action / Effect]
The operation and effect of the X-ray CT apparatus 1 'of this embodiment will be described.

  According to the X-ray CT apparatus 1 ′, the displacement in the X direction and the displacement in the Y direction of the phantom 100 arranged on the top plate 31 and the inclination angle are calculated, and the phantom 100 is determined based on the calculation result. Since it is configured to move or tilt in the X direction or the Y direction, the operator does not need to manually perform the positioning operation of the phantom 100. Therefore, it is possible to easily and quickly align the phantom 100 regardless of the skill level of the operator.

  In addition, according to the X-ray CT apparatus 1 ′, it is possible to improve the accuracy of alignment of the phantom 100. That is, in the second embodiment described above, the top plate 31 and the gantry 2 are driven to adjust the position of the phantom 100, so that the gantry 2 is only accurate with a unit moving distance of the top plate 31 or more. It is possible to adjust the position of the phantom 100 only with an accuracy equal to or greater than the unit inclination angle. On the other hand, in this embodiment, it is possible to improve the position adjustment of the phantom 100 by setting the unit rotation angle of the drive shaft of the actuators 201 to 203 small. As a specific example, stepping motors having a small rotation angle of the drive shaft corresponding to one pulse can be used as the actuators 201 to 203.

[Modification]
Various modifications relating to the X-ray CT apparatus 1 'according to the present embodiment will be described.

  The X-ray CT apparatus 1 'is configured to automatically adjust all of the displacement in the X direction, the displacement in the Y direction, and the tilt angle, but automatically adjusts at least one of these three. It is sufficient if it is configured to do so.

  The X-ray CT apparatus 1 ′ adjusts the inclination of the phantom 100 in the vertical direction with respect to the normal direction of the rotation surface of the gantry 2 (by the operation of the actuator 203). In the present invention, it is possible to adjust the inclination in an arbitrary direction, such as adjusting the inclination of the phantom 100 in the horizontal direction with respect to the normal direction of the rotation surface of the gantry 2. At this time, it is necessary to provide an actuator corresponding to the adjustment direction of the inclination of the phantom 100.

  In addition, the X-ray CT apparatus 1 ′ is configured to automatically operate the phantom holder 200, but displays the displacement and inclination of the phantom 100 on the monitor 5 as in the first embodiment. The phantom holder 200 can be configured to operate by operating the input device 6 by the operator.

  Although omitted in the description of the operation of the X-ray CT apparatus 1 ′, a warning message is output when the position error of the phantom 100 is large, as in the first and second embodiments. It is also possible to configure.

[Phantom holder]
The phantom holder 200 of the X-ray CT apparatus 1 ′ corresponds to an example of the “phantom holder” of the present invention. The phantom holder 200 operates under the control of the device control unit 41 of the X-ray CT apparatus 1 ′, and the actuators 201 to 203 move the phantom 100 held on the top plate 31 in the vertical direction or the horizontal direction. It has.

  Here, the device control unit 41 corresponds to an example of the “control unit” of the present invention. The actuators 201 and 202 correspond to an example of “phantom driving means” that moves the phantom 100 in the vertical direction (Y direction) and the horizontal direction (X direction), respectively. Further, the actuator 203 functions as “phantom tilt driving means” for tilting the phantom 100 in the tilt direction with the normal direction of the rotation surface of the gantry 2 as a reference.

  The normal direction of the rotating surface of the gantry 2 coincides with the Z direction when the X-ray tube 22 and the X-ray detector 23 are arranged in the vertical plane. When the X-ray tube 22 and the X-ray detector 23 are not arranged in the vertical plane, the normal direction of the rotation surface of the gantry 2 includes a plane including a straight line connecting the X-ray tube 22 and the X-ray detector 23. The direction is orthogonal to the (rotation plane). Further, “an inclination direction with respect to the normal direction” means an inclination direction in a direction in which the inclination angle with respect to the normal direction is increased or decreased.

  By using such a phantom holder 200, it is possible to increase the accuracy of positioning of the phantom 100. Moreover, since the input device 6 can be operated and the position of the phantom 100 can be adjusted instead of operating the operation unit such as the knob of the phantom holder as in the prior art, the position of the phantom can be easily and quickly adjusted. It becomes possible.

[Computer program]
The processing according to the first, second, and third embodiments described above is executed by the microprocessor of the computer device 4 based on the computer program stored in the hard disk drive or the like. In particular, the device control unit 41 and the image processing unit 42 operate according to this computer program.

  Such a computer program can be stored in an arbitrary storage medium so that it can be read by a computer. As the storage medium, floppy (registered trademark) disk, CD-ROM, CD-R (W), DVD-ROM, DVD-R (W), DVD-RAM, MO, various memory cards, and other electrical methods, Any structure that can store data by any physical method such as a magnetic method or an optical method can be used.

  It is also possible to store the computer program in a server or storage device on a network such as the Internet or a LAN, and to access and use the computer program 4 via the network.

  The configuration described in detail above is merely a specific example for suitably carrying out the present invention. Therefore, arbitrary modifications within the scope of the gist of the present invention can be made as appropriate.

1 is a schematic perspective view illustrating an example of an external configuration of a first embodiment of an X-ray CT apparatus according to the present invention. 1 is a schematic block diagram showing an example of an internal configuration of a first embodiment of an X-ray CT apparatus according to the present invention. It is a schematic block diagram showing an example of the structure of the control system of 1st Embodiment of the X-ray CT apparatus which concerns on this invention. It is the schematic for demonstrating the partial tomographic image data extraction process by the housing | casing extraction part of 1st Embodiment of the X-ray CT apparatus which concerns on this invention. FIG. 4A shows an outline of a tomographic image based on the phantom tomographic image data generated by the tomographic image generation unit. FIG. 4B shows an outline of a tomographic image based on partial tomographic image data corresponding to the phantom case extracted by the housing extraction unit. It is the schematic for demonstrating an example of the selection aspect of three different points on the partial tomogram data by the circle center calculation part of 1st Embodiment of the X-ray CT apparatus which concerns on this invention. It is the schematic for demonstrating an example of the selection aspect of four different points on the partial tomogram data by the ellipse center calculation part of 1st Embodiment of the X-ray CT apparatus which concerns on this invention. It is a flowchart showing an example of operation | movement of 1st Embodiment of the X-ray CT apparatus which concerns on this invention. It is a schematic perspective view showing the state of the phantom arrange | positioned in inclination in the modification 3 of 1st Embodiment of the X-ray CT apparatus which concerns on this invention. It is the schematic showing an example of the tomogram of a phantom in the modification 3 of 1st Embodiment of the X-ray CT apparatus which concerns on this invention. FIG. 9A shows a tomographic image of the phantom at the first slice position, and FIG. 9B shows a tomographic image at the second slice position. It is the schematic showing an example of the structure of the maintenance system which implements the maintenance of the X-ray CT apparatus which concerns on this invention. It is a flowchart showing an example of operation | movement of 2nd Embodiment of the X-ray CT apparatus which concerns on this invention. It is a schematic perspective view showing an example of the external appearance structure of 3rd Embodiment of the X-ray CT apparatus concerning this invention. It is a schematic side view showing an example of the structure of the phantom holder of 3rd Embodiment of the X-ray CT apparatus which concerns on this invention. It is a schematic block diagram showing an example of the structure of the control system of 3rd Embodiment of the X-ray CT apparatus which concerns on this invention. It is a flowchart showing an example of operation | movement of 3rd Embodiment of the X-ray CT apparatus which concerns on this invention. It is the schematic showing the structure of the cylindrical phantom for the performance evaluation of a X-ray CT apparatus. FIG. 16A is a schematic perspective view illustrating an external configuration of a phantom. FIG. 16B is a schematic cross-sectional view illustrating a cross-sectional form of the phantom.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1 'X-ray CT apparatus 2 Gantry 21 Support body 22 X-ray tube 23 X-ray detector 25 Support body drive part 3 Bed 31 Top plate 33 Top plate drive part 4 Computer apparatus 41 Apparatus control part 51 Gantry control part 52 Sleeper Control unit 53 Console control unit 54 Holder control unit 42 Image processing unit 60 Tomographic image data generation unit 72 Data storage unit 80 Calculation processing unit 81 Case extraction unit 82 Circle center calculation unit 83 Ellipse center calculation unit 84 Displacement calculation unit 85 Radius Calculation unit 86 Inclination angle calculation unit 90 Error processing unit 91 Error calculation unit 92 Error determination unit 5 Monitor 6 Input device 100 Phantom 101 Case J Cylindrical shaft 200 Phantom holder 201, 202, 203 Actuator 1000 Hospital server 2000 Service server O Scan center P1 to P3 3 points on the partial tomographic image data Hearts Q1-Q4 4 points on the partial tomographic image data Center of ellipse

Claims (9)

A top plate on which a phantom having a cylindrical casing filled with a filler is installed;
X-ray generation means for generating an X-ray beam;
X-ray detection means for detecting the X-ray beam transmitted through the phantom installed on the top plate;
Rotation drive means for rotating the X-ray generation means and the X-ray detection means;
Based on the X-ray beam detected by the X-ray detection means, tomographic image data generating means for generating tomographic image data of the phantom;
Calculation means for calculating information on displacement of the phantom with respect to the center of rotation by the rotation driving means based on the generated tomographic image data;
Display means for displaying information for positioning the phantom based on the calculated information on the displacement;
An X-ray CT apparatus comprising: Storage means for storing in advance the coordinates of the center of rotation by the rotation drive means;
The calculating means includes
Extracting means for extracting partial tomographic image data corresponding to the housing of the phantom from the tomographic image data generated by the tomographic image data generating means;
A circle center calculating means for calculating coordinates of a center of a circle passing through three different points in the extracted partial tomographic image data;
Displacement calculating means for calculating a displacement of the cylindrical axis of the phantom with respect to the center of rotation based on the calculated coordinates of the center of the circle and the stored coordinates of the center of rotation;
The X-ray CT apparatus according to claim 1 , comprising: Storage means for storing in advance the coordinates of the center of rotation by the rotation drive means;
The calculating means includes
Extracting means for extracting partial tomographic image data corresponding to the housing of the phantom from the tomographic image data generated by the tomographic image data generating means;
Ellipse center calculating means for calculating coordinates of the center of an ellipse that passes through four different points in the extracted partial tomographic image data;
Displacement calculating means for calculating the displacement of the cylindrical axis of the phantom with respect to the center of rotation based on the calculated coordinates of the center of the ellipse and the stored coordinates of the center of rotation;
The X-ray CT apparatus according to claim 1 . Error calculating means for calculating an error with respect to the circle at a plurality of different points in the partial tomographic image data extracted by the extracting means;
Determining means for determining whether the calculated error exceeds a predetermined value;
Notification information output means for outputting notification information when it is determined that the error exceeds a predetermined value;
The X-ray CT apparatus according to claim 2 , comprising: Error calculating means for calculating an error with respect to the ellipse at a plurality of different points in the partial tomographic image data extracted by the extracting means;
Determining means for determining whether the calculated error exceeds a predetermined value;
Notification information output means for outputting notification information when it is determined that the error exceeds a predetermined value;
The X-ray CT apparatus according to claim 3 , further comprising: A top plate on which a phantom having a cylindrical casing filled with a filler is installed;
X-ray generation means for generating an X-ray beam;
X-ray detection means for detecting the X-ray beam transmitted through the phantom installed on the top plate;
Rotation drive means for rotating the X-ray generation means and the X-ray detection means;
Storage means for storing in advance the coordinates of the center of rotation by the rotation driving means;
Based on the X-ray beam detected by the X-ray detection means, tomographic image data generating means for generating tomographic image data of the phantom;
Extraction means for extracting partial tomographic image data corresponding to the housing of the phantom from the generated tomographic image data;
A circle center calculating means for calculating coordinates of a center of a circle passing through three different points in the extracted partial tomographic image data;
First displacement calculating means for calculating a displacement of the cylindrical axis of the phantom with respect to the center of rotation based on the calculated coordinates of the center of the circle and the stored coordinates of the center of rotation;
Error calculating means for calculating an error with respect to the circle at a plurality of different points in the extracted partial tomographic image data;
Determining means for determining whether the calculated error exceeds a predetermined value;
An ellipse center calculating means for calculating the coordinates of the center of an ellipse passing through four different points in the extracted partial tomographic image data when it is determined that the error exceeds the predetermined value;
Second displacement calculating means for calculating a displacement of the cylindrical axis of the phantom with respect to the center of rotation based on the calculated coordinates of the center of the ellipse and the stored coordinates of the center of rotation;
A radius calculating means for calculating a horizontal radius and a vertical radius of the ellipse, respectively, when it is determined that the error exceeds the predetermined value;
An inclination angle calculating means for calculating an inclination angle of the cylindrical axis of the phantom with respect to a normal direction of the rotation surface of the rotation based on the calculated radii in the horizontal direction and the vertical direction;
When the determination means determines that the error does not exceed the predetermined value, the displacement calculated by the first displacement calculation means is displayed, and when the error is determined to exceed the predetermined value Display means for displaying the displacement calculated by the second displacement calculating means and the inclination angle calculated by the inclination angle calculating means;
An X-ray CT apparatus comprising: A top plate operating means for moving the top plate;
Means for notifying the position of the top panel operating means in accordance with the display by the display means;
X-ray CT apparatus according to claim 1 or claim 6, further comprising a. A tilt operation means for tilting the X-ray generation means and the X-ray detection means integrally;
Means for informing the position of the tilt operation means in accordance with the display of the tilt angle by the display means;
The X-ray CT apparatus according to claim 6 , further comprising: A top plate on which a phantom having a cylindrical casing filled with a filler is installed, X-ray generation means for generating an X-ray beam, and the X-ray beam transmitted through the phantom installed on the top plate An X-ray CT apparatus comprising an X-ray detection means for detecting, a rotation driving means for rotating the X-ray generation means and the X-ray detection means, and a display means,
A function of generating tomographic image data of the phantom based on the X-ray beam detected by the X-ray detection means;
A function for calculating information on the displacement of the phantom relative to the center of rotation by the rotation driving means based on the generated tomographic image data;
A function for causing the display means to display information for positioning the phantom based on the calculated information on the displacement;
A computer program that executes

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