JP2008167804A - X-ray ct apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simultaneously achieve image quality improvement, the reduction of the occurrence frequency of artifacts and the reduction of exposure of patients in an X-ray CT apparatus. <P>SOLUTION: The X-ray CT apparatus 10 comprises: a top plate 12 for placing a patient M; a rotation part 15 for holding an X-ray tube 21 and an X-ray detector 24 and integrally rotating the X-ray tube 21 and the X-ray detector 24 around the patient M; a rack apparatus 11 for holding the rotation part 15; and a scan control part for performing helical scan while controlling the top plate 12, the X-ray tube 21 and the rotation part 15. The scan control part moves a scan center in a horizontal direction, in a vertical direction or in the combined direction of the horizontal direction and the vertical direction within a series of helical scan to the patient M. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique of a medical image diagnostic apparatus that generates a slice image of a predetermined part, and more particularly to an X-ray CT apparatus that contributes to exposure reduction and image quality improvement.

  A known X-ray CT (Computerized Tomography) apparatus has an X-ray tube and a multi-channel X-ray detection element arranged in a plurality of rows facing each other with a subject such as a patient in between, While these are rotated through 360 ° around the patient, an X-ray beam is exposed from the X-ray tube to a predetermined part of the patient. Then, the X-ray dose transmitted through the predetermined part is measured as projection data by an X-ray detector, and image reconstruction processing is performed using a computer based on the projection data, thereby obtaining a slice image of the predetermined part.

  The progress of X-ray CT apparatus is remarkable, and a multi-slice X-ray CT apparatus has been developed in response to a strong demand from the medical field to take a higher resolution (high resolution) and a wider range of images. It has become quite popular. The multi-slice X-ray CT apparatus has an X-ray source that emits cone beam X-rays having a spread width in the z-axis direction (body axis direction) and a structure in which a plurality of detection element rows are arranged in the z-axis direction. And a dimension detector, so that a helical scan can be performed. With this configuration, volume data over a wide range inside the subject can be obtained with high accuracy and in a short time compared to a single slice X-ray CT apparatus.

  In imaging by the X-ray CT apparatus, setting is made so that the patient is inserted into the measurement space so that the body axis of the entire body of the patient matches the scan center of the measurement space. This is because the slice image is positioned at the center of the imaging region.

In view of this, an apparatus that positions the slice image at the center of the imaging region by calculating the distance between the sensor measured by a sensor rotating around the patient and the patient is disclosed (for example, see Patent Document 1).
Japanese Utility Model Publication No. 7-33304

  However, in reality, the patient's body thickness center is displaced vertically and horizontally along the body axis direction due to factors such as the patient's body shape, and does not coincide with the body axis of the entire patient's body. In the prior art, only the body thickness center in a certain part of the patient before the scan imaging is obtained. Therefore, if a helical scan is to be performed with the height of the top plate set before scan imaging, the body thickness center of the patient deviates from the scan center depending on the part. When the patient's body thickness center deviates from the scan center in this way, an overflow occurs near the scan center when a dose is applied in the direction of the patient's thickness near the scan center where the wedge is thinnest, and the slice image There is a problem that the area around the upper patient is blackened.

  In addition, when an overflow near the scan center is taken into account, there is a problem that the gain of the data acquisition system (DAS) cannot be increased so much that S / N (signal / noise) cannot be sufficiently improved. .

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide an X-ray CT apparatus capable of realizing improvement in image quality.

  It is another object of the present invention to provide an X-ray CT apparatus that can reduce the occurrence frequency of artifacts on an image.

  Another object of the present invention is to provide an X-ray CT apparatus that can reduce the exposure of a subject by a scanogram scan.

An object is to provide an X-ray CT apparatus.

  An X-ray CT apparatus according to the present invention provides a top plate on which a subject is placed and an X-ray that emits X-rays toward the subject, as described in claim 1 in order to solve the above-described problem. A rotating unit that holds the X-ray tube and an X-ray detector that detects X-rays transmitted through the subject, and rotates the X-ray tube and the X-ray detector as a unit around the subject; A gantry device that holds a rotating unit; and a scan control unit that executes a helical scan while controlling the top plate, the X-ray tube, and the rotating unit, and the scan control unit includes a series of steps for the subject. Within the helical scan, the scan center is moved in the horizontal direction, the vertical direction, or the combined direction of the horizontal direction and the vertical direction.

  The X-ray CT apparatus according to the present invention can improve the image quality of an image.

  Further, according to the X-ray CT apparatus according to the present invention, the occurrence frequency of artifacts on an image can be reduced.

  Furthermore, according to the X-ray CT apparatus according to the present invention, it is possible to reduce the exposure of the subject by the scanogram scan.

  An embodiment of an X-ray CT (computerized tomography) apparatus according to the present invention will be described with reference to the accompanying drawings.

  In the X-ray CT apparatus, a rotation / rotation (ROTATE / ROTATE) type in which an X-ray tube and an X-ray detector are rotated as one body, and a large number of detection elements are arrayed in a ring shape. There are various types such as a stationary / rotating type in which only the X-ray tube rotates around the subject, and the present invention can be applied to any type.

  FIG. 1 is a schematic diagram showing the apparatus configuration of a first embodiment of an X-ray CT apparatus according to the present invention.

  FIG. 1 shows an X-ray CT apparatus 10 according to the first embodiment. When the X-ray CT apparatus 10 moves from one imaging region (part) to the next imaging region within a series of helical scans, the X-ray CT apparatus 10 moves the top 12 in the left-right direction, the up-down direction, or the combined direction of the left-right direction and the up-down direction (x-axis). In the direction, the y-axis direction, or the combined direction of the x-axis direction and the y-axis direction) to bring the scan center closer to the body thickness center of the subject (patient). Hereinafter, in the X-ray CT apparatus 10, when moving from an imaging region in a series of helical scans to the next imaging region, the top 12 is moved in the y-axis direction, and the scan center is set to the body thickness center in the patient's y-axis direction. A case where the values are brought closer will be described as an example.

  The X-ray CT apparatus 10 irradiates the patient M with X-rays while changing the X-ray exposure site of the patient M, and back-projects the inside of the patient M based on the transmitted X-rays. It is a device that reconstructs the inside as an image. The X-ray CT apparatus 10 finally generates a slice image and a three-dimensional image inside the patient M by performing a scan operation including each operation stage for executing a scanogram scan, a helical scan, and a scan plan. .

  The X-ray CT apparatus 10 includes a gantry 11 for scanning the patient M with X-rays, and the patient M placed inside the cavity of the gantry 11 in the left-right direction (x-axis direction), up and down The top plate 12 for moving in the direction (y-axis direction) and the body axis direction (z-axis direction), and the slice image (axial image) based on the data sent from the gantry device 11 while controlling the operation of the gantry device 11 ) Etc., and an operation console 13 for outputting (displaying).

  The gantry device 11 can operate in a tilt direction (not shown), and the gantry device 11 holds the rotating unit 15 and the fixed unit. The rotating unit 15 of the gantry device 11 holds an X-ray tube 21, a collimator 22, an opening control mechanism 23, an X-ray detector 24, and a data collection device 25. The X-ray tube 21 and the collimator 22 and the X-ray detector 24 are provided at positions facing each other across the cavity of the gantry device 11, that is, across the patient M. The rotating unit 15 is configured to rotate around the cavity while maintaining the positional relationship.

  The X-ray tube 21 emits X-rays from the tube (not shown) of the X-ray tube 21 toward the X-ray detector 24 by the power supplied from the high voltage generator 33.

  The collimator 22 has an opening for limiting the X-ray irradiation range irradiated from the X-ray tube 21.

  In addition, a wedge filter (not shown) is provided between the X-ray tube 21 and the patient M. The wedge filter is used for the purpose of reducing a low energy component that is absorbed by the patient M and cannot reach the X-ray detector 24 and for adjusting the dynamic range of the X-ray detector 24 at the center and the periphery.

  The opening control mechanism 23 adjusts the opening width of the collimator 22 according to a control signal from the main controller 31.

  The X-ray detector 24 has multi-row detection elements (a plurality of configurations (number of columns, number of channels, etc.) differing in the body axis direction for detecting X-rays from the X-ray tube 21 that has passed through the collimator 22 and the cavity. It may be a detection element). In the slice direction of the X-ray detector 24, 64 or more rows of X-ray detection elements, for example, 256 rows are arranged in parallel.

  The data collection device 25 is generally called a DAS (data acquisition system), amplifies a signal output from the X-ray detector 13 for each channel, and further converts it into a digital signal. The converted data (raw data) is supplied to the external operation console 13 via the IF 32 b of the gantry device 11. Note that an interface (not shown) using a slip ring, optical communication, or the like is interposed between the X-ray detector 24 and the data collection device 25. With this interface, the data collection device 25 can collect the output of the X-ray detector 24 while continuously rotating the gantry device 11.

  In addition, a main controller 31, IFs (interfaces) 32 a and 32 b, a high voltage generation device 33, a rotational movement mechanism 35, and a top plate movement mechanism 37 are provided in the fixed portion of the gantry device 11.

  The main controller 31 analyzes various commands received from the operation console 13 via the IF 32a, and based on the analysis, the high voltage generator 33, the opening control mechanism 23, the rotational movement mechanism 35, the top board movement mechanism 37, and the data collection apparatus. 25 outputs various control signals.

  The IFs 32a and 32b perform communication control according to each standard.

  The high voltage generator 33 is a device that supplies electric power necessary for X-ray exposure to the X-ray tube 21 and includes a high voltage transformer, a filament heating converter, a rectifier, a high voltage switch, and the like.

  The rotational movement mechanism 35 continuously rotates the rotating unit 15 by the drive signal from the main controller 31 so that the rotating unit 15 rotates around the cavity while maintaining the positional relationship.

  The top board moving mechanism 37 moves the top board 12 in the x-axis direction (left-right direction), the y-axis direction (up-down direction), and the z-axis direction (body axis direction) by a drive signal from the main controller 31.

  The operation console 13 is a so-called workstation configured based on a computer, and is capable of mutual communication with a network N such as a hospital basic LAN (local area network). The operation console 13 is mainly composed of basic hardware such as a CPU (central processing unit) 41, a memory 42, an HD (hard disc) 44, IFs 45a, 45b, and 45c, an input device 46, and a display device 47. . The CPU 41 is interconnected to each hardware component constituting the operation console 13 via a bus as a common signal transmission path. Note that the operation console 13 may include a recording medium drive 48.

  The CPU 41 executes a program stored in the memory 42 when a command is input by the operator operating the input device 46 or the like. Alternatively, the CPU 41 is read from a program stored in the HD 44, a program transferred from the network N, received by the IF 45c and installed in the HD 44, or read from a recording medium attached to the recording medium drive 48 and installed in the HD 44. The loaded program is loaded into the memory 42 and executed.

  The memory 42 combines elements such as a ROM (read only memory) and a RAM (random access memory), and stores an IPL (initial program loading), a BIOS (basic input / output system), and data. This is a storage device used for temporary storage of data.

  The HD 44 is configured by a nonvolatile semiconductor memory or the like. The HD 44 includes a program installed in the operation console 13 (including an OS (operating system) in addition to an application program for setting a scan plan described later), raw data, projection data, scanogram data, and slices. It is a storage device that stores data such as image data. In addition, the OS can be provided with a graphical user interface (GUI) that can use the graphics for displaying information to the operator and perform basic operations by the input device 46.

  The IFs 45a, 45b, and 45c perform communication control according to each standard. The IFs 45a and 45b communicate with the gantry device 11 and are connected to the IFs 32a and 32b of the gantry device 11, respectively. Further, the IF 45c has a function capable of being connected to the network N through a telephone line or the like, whereby the operation console 13 can be connected to the network N from the IF 45c.

  Examples of the input device 46 include a keyboard and a mouse that can be operated by an operator, and an input signal according to the operation is sent to the CPU 41. The operator can input the width of the X-ray exposure area in the slice direction to the operation console 13 via the input device 46. Further, the operator can set and input a scan range (to be described later) for obtaining a slice image via the input device 46.

  The display device 47 includes a D / A (digital / analog) converter, a monitor, and the like. By expanding the image data or the like in a memory such as a VRAM (video random access memory, not shown) that expands the image data to be displayed, a slice image, a three-dimensional image, or the like is displayed on the display device 47.

  The recording medium drive 48 is detachable from the recording medium, reads out data (including a program) recorded on the recording medium, outputs the data on the bus, and outputs data supplied through the bus. Write to a recording medium. Such a recording medium can be provided as so-called package software.

  FIG. 2 is a block diagram showing functions of the operation console 13 constituting the X-ray CT apparatus 10 of the first embodiment.

  When the CPU 41 of the operation console 13 shown in FIG. 1 executes a program, the operation console 13 includes a scan control unit 51, a preprocessing unit 52, a scanogram generation unit 53, a scan plan setting unit 54, an image reconstruction unit 55, and It functions as the image processing unit 56. In addition, although the component of the operation console 13 shall function when CPU41 runs a program, it is not limited to that case. The components of the operation console 13 may be provided in the operation console 13 as hardware such as a circuit.

  The scan control unit 51 has a function of performing overall control related to imaging processing. For example, at the time of scanogram scanning that is imaging for positioning, the scan control unit 51 scan conditions automatically selected according to patient information such as patient ID (identification) and patient name (or in manual mode, The aperture control mechanism 23, the high voltage generator 33, the rotary movement mechanism 35, and the top board movement mechanism 37 are controlled via the main controller 31 based on the scanning conditions set directly from the input device 46. That is, during the scanogram scan, the scan control unit 51 moves the top 12 in the z-axis direction while stopping the rotation of the rotating unit 15 that holds the X-ray tube 21 and the X-ray detector 24 ( An X-ray cone beam or an X-ray fan beam is exposed from one direction (moving the gantry device 11 in the z-axis direction), and scanogram imaging processing is performed.

  The pre-processing unit 52 performs logarithmic conversion processing and correction processing such as sensitivity correction on the raw data corresponding to one projection direction input from the data collection device 25 of the gantry device 11 via the IF 45b illustrated in FIG. Has the function to perform. The raw data for one direction subjected to various corrections is temporarily stored in a storage device such as the HD 44. The raw data for one direction preprocessed by the preprocessing unit 52 is referred to as “projection data”. Note that the scattered radiation may be removed from the projection data.

  The scanogram generation unit 53 has a function of generating a scanogram of the patient M based on the projection data for one direction generated by the preprocessing unit 52. As is well known, the scanogram scan is performed continuously with the patient M while moving the top 12 at a constant speed in the z-axis direction while stopping the rotation of the X-ray tube 21 and the X-ray detector 24. The transmitted X-rays are repeatedly detected by the X-ray detector 24. The scanogram is used when setting collection conditions and reconstruction conditions. In that case, the table 12 that holds the X-ray tube 21 and the X-ray detector 24 is fixed at a desired rotational position, and the top 12 is moved in the z-axis direction to collect data corresponding to a certain direction. . The scanogram generation unit 53 generates a scanogram based on the projection data of the data collected in this way. The scanogram is, for example, an image from the side direction, the front direction, or the back direction of the patient M. The generated scanogram is recorded in a storage device such as the HD 44 as necessary.

  The scan plan setting unit 54 has a function of setting a scan plan. The scan plan setting unit 54 generates, for example, a scan plan draft according to the input of patient information, examination purpose, examination site, and other items using the input device 46, and selects and corrects the scan plan draft. Build and display a screen that prompts On the screen of the scan plan, the patient information, the gantry device information, and the scanogram generated by the scanogram generation unit 53 are displayed, and the details of the scan condition are displayed. The scan conditions include a scan center (rotation center of the rotating unit 15), a tube current (mA), a tube voltage (kV), a helical scan start and end position, a scan mode, the number of scans, and an X-ray. A scanning speed representing the time required for one rotation of the tube 10 (shooting time in parentheses), reconstruction mode, field of view (FOV: field of view), and helical pitch representing the distance the top 12 moves at the scan speed. Etc. are included.

  The scan plan setting unit 54 removes the scan center and the tube current by inputting (selecting and correcting) from the input device 46 with respect to the initial setting of the scan condition excluding the scan center and the tube current displayed on the scan plan draft screen. The scan condition is set to a desired value.

  On the other hand, the scan plan setting unit 54 sets a required imaging area on the scanogram, and sets a tube current as a scanning condition for each imaging area. In addition, in order to describe the shooting area specifically, it is assumed here that the number of shooting areas is set to “2”. When the number of shooting areas is set to “2”, shooting areas corresponding to the number of shooting areas “2” are displayed on the scanogram.

  FIG. 3 is a diagram illustrating an example of an imaging region.

  The right side of FIG. 3 shows two imaging areas (a first imaging area and a second imaging area) on the scanogram in the front direction. The scanogram may be in the back direction or the side direction.

  On the other hand, the left side of FIG. 3 shows a seating system with the slice plane (tomographic plane) along the body axis direction as the horizontal axis and the tube current value as the vertical axis. With respect to the initial setting of the size of the two shooting areas on the scanogram, the boundary line between the shooting areas or the outer frame of the shooting area is arbitrarily moved by using the input device 46 so that each shooting area can be set in a desired manner. Set to size. Then, the scan plan setting unit 54 sets a value of an image SD (standard deviation) for each imaging region as a scan plan. Image noise is inevitable in the reconstructed slice image. The image noise typically defines a variation in CT value of a homogeneous phantom image as a standard deviation, and is usually referred to as an image SD. In order to make a diagnosis by observing the reconstructed slice image, for example, in order to distinguish whether the shadow on the slice image is noise or a tumor, it is necessary to consider the image SD in which the slice image is unique. The scan plan setting unit 54 uses the real EC technique to automatically calculate the tube current for each designated imaging area for the designated image SD from the CT value of the scanogram at the corresponding position. That is, the scan plan setting unit 54 calculates the tube current necessary for realizing each set image SD for each imaging region based on the CT value of the scanogram in each imaging region. According to the real EC technique, it is possible to obtain a slice image having a uniform image quality regardless of the patient's body shape, and to reduce the exposure of the patient M as compared with the case of collecting with a constant tube current. it can.

  In addition, the scan plan setting unit 54 sets a scan center as a scan condition for each required imaging region (here, the above-described imaging region). When the number of imaging regions is set to “2”, a scan center line corresponding to the number of imaging regions “2” is displayed on the scanogram in the side direction.

  FIG. 4 is a diagram illustrating an example of the scan center for each imaging region.

  FIG. 4 shows the scan center line for each of the two imaging regions on the scanogram in the lateral direction. With respect to the initial setting at the scan center for each of the two imaging regions on the scanogram, the operator can arbitrarily move the scan center line for each imaging region using the input device 46, so that each scan center for each imaging region is desired. The position is set. With this setting, the y-axis direction component of each scan center for each imaging region is set. It is also possible to set the x-axis direction component of each scan center for each imaging region by setting the scan center line of the two imaging regions on the front or back scanogram.

  2 performs the aperture control mechanism 23, the high voltage generator 33, the rotary movement mechanism 35, and the top board movement mechanism 37 in accordance with the scan plan set by the scan plan setting section 54 during the helical scan. To control. That is, during the helical scan, the scan control unit 51 continuously rotates the rotating unit 15 that holds the X-ray tube 21 and the X-ray detector 24 and moves the top 12 in the z-axis direction (the gantry device). The X-ray cone beam or the X-ray fan beam is exposed from the 360 degree direction (moving 11 in the z-axis direction), and the slice image of the first imaging region is imaged. In addition, the scan control unit 51 raises the top plate 12 via the top plate moving mechanism 37 and then continuously rotates the rotating unit 15 that holds the X-ray tube 21 and the X-ray detector 24. While moving the plate 12 in the z-axis direction, an X-ray cone beam or an X-ray fan beam is exposed from a 360-degree direction, and a slice image in the second imaging region is imaged.

  FIG. 5 is a schematic diagram for explaining each scan center for each imaging region in a series of helical scans.

  FIG. 5 is a diagram illustrating a relative positional relationship between the gantry device 11 and the top plate 12 in the X-ray CT apparatus 10 according to the first embodiment. As shown in FIG. 5, when moving from the first imaging area to the second imaging area in a series of helical scans, the top 12 is moved in the y-axis direction.

  Also, the preprocessing unit 52 shown in FIG. 2 performs logarithmic conversion processing on the raw data corresponding to the projection direction of 360 degrees input from the data collection device 25 of the gantry device 11 via the IF 45b shown in FIG. It has a function of performing correction processing such as correction. The raw data for the 360 degrees direction subjected to various corrections is temporarily stored in a storage device such as the HD 44. Note that the raw data for the 360 degree direction preprocessed by the preprocessing unit 52 is referred to as “projection data”. Note that the scattered radiation may be removed from the projection data.

  The image reconstruction unit 55 has a function of reconstructing slice image data as biological information inside the patient M based on the projection data for 360 degrees directions generated by the control of the scan control unit 51. The image reconstruction unit 55 performs reconstruction methods such as fan beam reconstruction assuming that the backprojection paths in the slice direction are parallel and cone beam reconstruction in consideration of the X-ray exposure angle (cone angle) in the slice direction. Use to reconstruct slice image data.

  The image processing unit 56 has a function of performing image processing for display, such as window conversion and RGB (red green blue) processing, on the slice image data generated by the image reconstruction unit 55. In addition, the image processing unit 56 generates a so-called pseudo three-dimensional image such as a slice image of an arbitrary cross section, a projection image from an arbitrary direction, a three-dimensional surface image, and the like based on an instruction from the operator.

  Next, the operation of the X-ray CT apparatus 10 of the first embodiment will be described using the flowchart shown in FIG.

  First, the operator uses the input device 46 of the X-ray CT apparatus 10 to input patient information such as a patient ID and a patient name. Next, the operator uses the input device 46 of the X-ray CT apparatus 10 to specify the scanogram direction (front surface direction, back surface direction, side surface direction, etc.), etc. A scanogram scan is performed (step S1). The raw data for one direction transferred from the X-ray detector 24 to the operation console 13 via the data collection device 25, IF 32 b and IF 45 b is preprocessed by the operation console 13.

  When the scanogram scan is completed, a scan plan is set (step S2). For example, when the operator inputs items such as patient information, examination purpose, and examination site, a scan plan is generated and displayed accordingly. On the screen of the scan plan, the patient information, the gantry device information, and the scanogram generated in step S1 are displayed, and the details of the scan condition are displayed.

  In the setting of the scan plan in step S2, first, the scan center and the scan center displayed on the screen of the scan plan and the input from the input device 46 (selection or correction) for the initial setting of the scan condition excluding the tube current are selected. The scan condition excluding the tube current is set to a desired value (step S2a).

  Next, an imaging region is set on the scanogram, and a tube current as a scanning condition is calculated and set for each imaging region (step S2b).

  Next, a scan center as a scan condition is set for each required imaging region (here, the above-described imaging region) (step S2c).

  A helical scan is performed according to the scan plan set in step S2 (step S3). In step S3, the rotating unit 15 holding the X-ray tube 21 and the X-ray detector 24 is continuously rotated, and the X-ray cone beam or the X-ray fan is viewed from 360 degrees while moving the top 12 in the z-axis direction. The beam is exposed, and a slice image of the first imaging region is captured. Next, in step S3, after the top plate 12 is raised through the top plate moving mechanism 37, the rotating unit 15 holding the X-ray tube 21 and the X-ray detector 24 is continuously rotated, and the top plate 12 is moved. While moving in the z-axis direction, an X-ray cone beam or an X-ray fan beam is exposed from a 360-degree direction, and a slice image in the second imaging region is imaged. The raw data for the 360 degree direction transferred from the X-ray detector 24 to the operation console 13 via the data collection device 25, IF 32b, and IF 45b is preprocessed by the operation console 13.

  Next, based on the projection data for 360 degrees direction generated in step S3, slice image data as biological information inside the patient M is reconstructed (step S4).

  Image processing for display such as window conversion and RGB processing is performed on the slice image data generated in step S4 (step S5), and the slice image is displayed on the display device 47 (step S6). In addition, the image processing unit 56 generates a so-called pseudo three-dimensional image such as a slice image of an arbitrary cross section, a projection image from an arbitrary direction, a three-dimensional surface image, and the like based on an instruction from the operator.

  FIG. 7 is a conceptual diagram illustrating a display example of a slice image.

  FIG. 7 shows a slice image I1 of the slice plane included in the first imaging area and a slice image I2 of the slice plane included in the second imaging area. As shown in FIG. 7, when the slice images I1 and I2 are displayed, the display is performed by performing processing such as enlargement to the most suitable size so that the body thickness center of the patient M is always the display center. May be.

  According to the X-ray CT apparatus 10 of the first embodiment, the top plate 12 is moved in the left-right direction, the up-down direction, or a combination of the left-right direction and the up-down direction, and the scan center is brought close to the body thickness center of the patient M to perform the helical scan. By implementing the above, it is possible to arrange the portion where the patient M is the thickest and needs the dose at the center of the scan where the wedge thickness is the thinnest and the dose is the largest, and the image quality can be improved.

  Further, according to the X-ray CT apparatus 10 of the first embodiment, the top 12 is moved in the left-right direction, the up-down direction, or the direction in which the left-right direction and the up-and-down direction are combined, and the scan center is brought close to the body thickness center of the patient M. By performing the helical scan, it is possible to reduce the occurrence frequency of an artifact in which the periphery of the center of the image of the patient M falls black due to the overflow caused by the deviation between the body thickness center of the patient M and the scan center.

  In the first embodiment, the case where the body thickness center of the patient M is brought close to the scan center has been described. However, the present invention is not limited to this case. For example, the region of interest may be brought closer to the scan center.

  FIG. 8 is a schematic view showing the apparatus configuration of the second embodiment of the X-ray CT apparatus according to the present invention.

  FIG. 8 shows an X-ray CT apparatus 10A of the second embodiment. The X-ray CT apparatus 10A performs X-ray irradiation in a series of helical scans and collects projection data by the helical scan, and at the same time, moves the top 12 in the x-axis direction, the y-axis direction, or the x-axis direction. The movement in the combination direction in the y-axis direction is interlocked. That is, the X-ray CT apparatus 10 </ b> A moves the top 12 in the x-axis direction, the y-axis direction, or the combined direction of the x-axis direction and the y-axis direction within a series of helical scans. Helical scanning is performed while matching the center. Hereinafter, in the X-ray CT apparatus 10B, an example in which the scan center is aligned with the body thickness center in the y-axis direction of the patient by moving the top 12 in the y-axis direction during the series of helical scans or during the series of helical scans. I will explain to you.

  The X-ray CT apparatus 10A includes a gantry device 11A, a top plate 12, and an operation console 13A. In the X-ray CT apparatus 10A shown in FIG. 8, the same components as those in the X-ray CT apparatus 10 shown in FIG.

  An IF 32c and an appearance information acquisition device 61 are provided in the fixed portion of the gantry device 11A.

  The IF 32c performs communication control according to each standard.

  Examples of the appearance information acquisition device 61 include a laser transmission / reception device and a camera. The laser transmission / reception apparatus automatically (or manually) measures the body thickness center of the patient M for each slice surface by using a laser in advance or simultaneously with the helical scan for the vertical movement amount of the top 12.

  FIG. 9 is a diagram illustrating an installation example of the laser transmitting / receiving apparatus.

  As shown in FIG. 9, the transmitting side and the receiving side of the laser transmitting / receiving apparatus are installed on the gantry 11 </ b> A with a patient (phantom in this figure) M interposed therebetween. The laser transmission / reception device provided in the fixed part of the gantry device 11 </ b> A can measure the position of the patient M by performing transmission / reception of the laser to / from the patient M placed on the top 12.

  The operation console 13A shown in FIG. 8 is provided with an IF 45c. The IF 45c performs communication control according to each standard with the IF 32c.

  FIG. 10 is a block diagram illustrating functions of the operation console 13A in the second embodiment.

  When the CPU 41 of the operation console 13A illustrated in FIG. 8 executes the program, the operation console 13A includes a scan control unit 71, a preprocessing unit 72, a scanogram generation unit 73, a scan plan setting unit 74, an image reconstruction unit 75, and It functions as the image processing unit 76. Note that the components of the operation console 13A function when the CPU 41 executes a program, but are not limited to this case. The components of the operation console 13A may be provided in the operation console 13A as hardware such as a circuit.

  Similar to the scan control unit 51 shown in FIG. 2, the scan control unit 71 has a function of performing overall control related to imaging processing. For example, at the time of scanogram scanning, which is image capturing for positioning, the scan control unit 71 uses the opening control mechanism 23, the high-level control based on the scanning conditions automatically selected based on patient information such as patient ID and patient name. The voltage generator 33, the rotational movement mechanism 35, and the top board movement mechanism 37 are controlled. That is, during the scanogram scan, the scan control unit 51 moves the top plate 12 in the z-axis direction while stopping the rotation of the rotating unit 15 that holds the X-ray tube 21 and the X-ray detector 24. An X-ray cone beam or an X-ray fan beam is exposed from the direction, and scanogram imaging processing is performed.

  Similar to the preprocessing unit 52 shown in FIG. 2, the preprocessing unit 72 performs logarithmic conversion processing, sensitivity correction, and the like on raw data for one direction input from the data collection device 25 of the gantry device 11 via the IF 45b. Has a function of performing the correction process.

  The scanogram generation unit 73 has a function of generating a scanogram of the patient M based on the projection data for one direction generated by the preprocessing unit 72, similarly to the scanogram generation unit 53 shown in FIG.

  The scan plan setting unit 74 has a function of setting a scan plan, similar to the scan plan setting unit 54 shown in FIG. In addition, the scan plan setting unit 74 calculates the body thickness center of the patient M for each slice plane based on the appearance information of the patient M acquired by the appearance information acquisition device 61. Then, the scan plan setting unit 74 adds a body thickness center line of the patient M on the scanogram in the lateral direction generated by the scanogram generation unit 73, and creates a scan plan that matches the body thickness center of the patient M with the scan center. Has the function to set. FIG. 11 is a conceptual diagram showing the body thickness center line on the scanogram.

  The scan control unit 71 controls the aperture control mechanism 23, the high voltage generator 33, the rotary movement mechanism 35, and the top board movement mechanism 37 according to the scan plan set by the scan plan setting unit 74 during the helical scan. That is, during the helical scan, the scan control unit 71 continuously rotates the rotating unit 15 that holds the X-ray tube 21 and the X-ray detector 24, and moves the top 12 in the z-axis direction and the y-axis direction. Then, the X-ray cone beam or the X-ray fan beam is irradiated from the 360 degree direction while the body thickness center of the patient M is matched with the scan center, and the slice image photographing process is performed. Note that, when the scan center is moved during the helical scan, the scan control unit 71 may synchronize the movement amount of the scan center with the movement amount in the slice direction.

  Similar to the preprocessing unit 52 shown in FIG. 2, the preprocessing unit 72 performs logarithmic conversion processing and sensitivity correction on the raw data for 360 degrees direction input from the data collection device 25 of the gantry device 11 via the IF 45 b. And the like.

  The image reconstruction unit 75 has a function of reconstructing slice image data as biological information inside the patient M based on the projection data for 360 degrees direction generated by the control of the scan control unit 71.

  Here, the image reconstruction unit 75 reconstructs the slice image of the reference slice plane based on the projection data P (r, θ) output by the preprocessing unit 72. Further, the image reconstruction unit 75 re-projects the slice image of the non-reference slice plane other than the reference slice plane by rearranging the projection data P (r, θ) output by the preprocessing unit 72 according to a predetermined formula. Reconfiguration is performed based on the data P ′ (r ′, θ).

  FIG. 12 is a diagram for explaining an expression for rearranging projection data.

は、天板１２のｘ軸方向及びｙ軸方向の移動ベクトルである。

FIG. 12 shows a coordinate system (x, y) on the reference slice plane and a coordinate system (x ′, y ′) on the non-reference slice plane. The projection data P (r, θ) for 360 degrees generated by photographing on the non-reference slice plane is rearranged by the following equation (1) with reference to the coordinate system (x, y) on the reference slice plane. Is done. In addition,

Are movement vectors of the top plate 12 in the x-axis direction and the y-axis direction.

  Also, the image processing unit 76 shown in FIG. 10 performs display such as window conversion and RGB processing on the slice image data generated by the image reconstruction unit 75, as in the case of the image processing unit 56 shown in FIG. A function of performing image processing.

  Next, the operation of the X-ray CT apparatus 10A of the second embodiment will be described using the flowchart shown in FIG.

  First, the operator uses the input device 46 of the X-ray CT apparatus 10 to input patient information such as a patient ID and a patient name. Next, the operator uses the input device 46 of the X-ray CT apparatus 10 to perform an input for designating the scanogram direction and the like to execute the scanogram scan, thereby performing the scanogram scan (step S11). . The raw data for one direction transferred from the X-ray detector 24 to the operation console 13 via the data collection device 25, IF 32 b and IF 45 b is preprocessed by the operation console 13.

  When the scanogram scan is completed, a scan plan is set (step S12). For example, when the operator inputs items such as patient information, examination purpose, and examination site, a scan plan is generated and displayed accordingly. On the screen of the scan plan, the patient information and the gantry device information and the scanogram generated in step S11 are displayed, and the details of the scan conditions are displayed.

  In the setting of the scan plan in step S12, first, the scan condition excluding the tube current by the input (selection or correction) from the input device 46 with respect to the initial setting of the scan condition excluding the tube current displayed on the screen of the scan plan draft. Is set to a desired value (step S12a).

  Next, an imaging region is set on the scanogram, and a tube current as a scanning condition is calculated and set for each imaging region (step S12b).

  On the other hand, based on the appearance information of the patient M acquired by the appearance information acquisition device 61, the body thickness center of the patient M for each slice plane is calculated (step S12c), and the body thickness center of the patient M is matched with the scan center. Generate a scan plan.

  A helical scan is performed according to the scan plan (step S13). In step S13, the rotation unit 15 holding the X-ray tube 21 and the X-ray detector 24 is continuously rotated, and the top plate 12 is moved in the z-axis direction and the y-axis direction to scan the body thickness center of the patient M. An X-ray cone beam or an X-ray fan beam is exposed from a 360 degree direction while being matched with the center, and a slice image photographing process is performed. The raw data for the 360 degree direction transferred from the X-ray detector 24 to the operation console 13 via the data collection device 25, IF 32b, and IF 45b is preprocessed by the operation console 13.

  Next, as described with reference to FIG. 12, based on the projection data for the 360-degree direction generated in step S13, slice image data as biometric information inside the patient M is reconstructed (step S14). .

  Image processing for display such as window conversion and RGB processing is performed on the slice image data generated in step S14 (step S15), and the slice image is displayed on the display device 47 (step S16). In step S15, a so-called pseudo three-dimensional image such as a slice image of an arbitrary cross section, a projection image from an arbitrary direction, or a three-dimensional surface image is generated based on an instruction from the operator.

  FIG. 14 is a block diagram showing a modification of the function of the operation console 13A in the second embodiment.

  When the CPU 41 of the operation console 13A illustrated in FIG. 8 executes the program, the operation console 13A serves as a scan control unit 81, a preprocessing unit 82, a scan plan setting unit 84, an image reconstruction unit 85, and an image processing unit 86. Function. Note that the components of the operation console 13A function when the CPU 41 executes a program, but are not limited to this case. The components of the operation console 13A may be provided in the operation console 13A as hardware such as a circuit.

  The scan plan setting unit 84 has a function of setting a scan plan, similarly to the scan plan setting unit 74 shown in FIG. The scan plan setting unit 84 has a function of generating a scanogram substitute image based on the appearance information in the lateral direction of the patient M acquired by the appearance information acquisition device 61. FIG. 15 shows an example of a scanogram substitute image generated based on the appearance information in the lateral direction of the patient (model) M acquired by the camera as the appearance information acquisition device 61. By displaying the substitute image on the display device 47 by the scan plan setting unit 84, the operator automatically or manually sets the position of the patient M. The scan plan setting unit 84 automatically or manually sets the tube current in the Real EC technique based on the substitute image.

  The scan control unit 81 is similar to the scan control unit 71 shown in FIG. 10 according to the scan plan set by the scan plan setting unit 74, the opening control mechanism 23, the high voltage generator 33, the rotational movement mechanism 35, and the top board movement mechanism. 37 is controlled.

  Similarly to the preprocessing unit 72 shown in FIG. 10, the preprocessing unit 82 performs logarithmic conversion processing and sensitivity correction on raw data for 360 degrees direction input from the data collection device 25 of the gantry device 11 via the IF 45 b. And the like.

  Similar to the image reconstruction unit 75 shown in FIG. 10, the image reconstruction unit 85 uses the projection data for the 360 degree direction generated by the control of the scan control unit 81 as biometric information inside the patient M. It has a function of reconstructing slice image data.

  Similar to the image processing unit 76 shown in FIG. 10, the image processing unit 86 performs image processing for display such as window conversion and RGB processing on the slice image data generated by the image reconstruction unit 85. It has a function.

  In addition, when calculating | requiring the body thickness center of the patient M, the body thickness center of the patient M for every slice surface was calculated based on the external appearance information of the patient M acquired by the external appearance information acquisition apparatus 61, However, It is limited to that case. It is not a thing. For example, when obtaining the body thickness center of the patient M, the body thickness center in a certain slice plane may be calculated using projection data in a slice plane immediately before a certain slice plane or a real-time reconstructed image.

  Next, the operation of the modified example of the X-ray CT apparatus 10A of the second embodiment will be described using the flowchart shown in FIG.

  The appearance information of the patient M placed on the top board 12 is obtained using the appearance information acquisition device 61 while moving the top board 12 in the z-axis direction, and a scanogram substitute image for the patient M is obtained based on the appearance information. Is generated (step S21).

  When the generation of the substitute image is completed, a scan plan is set (step S22). For example, when the operator inputs items such as patient information, examination purpose, and examination site, a scan plan is generated and displayed accordingly. On the screen of the scan plan, the patient information and the gantry device information and the substitute image generated in step S21 are displayed, and the details of the scan condition are displayed.

  In the setting of the scan plan in step S22, first, the scan condition excluding the tube current by the input (selection or correction) from the input device 46 for the initial setting of the scan condition excluding the tube current displayed on the screen of the scan plan draft. Is set to a desired value (step S22a).

  Next, an imaging region is set on the scanogram, and a tube current as a scanning condition is calculated and set for each imaging region (step S22b).

  On the other hand, based on the appearance information of the patient M acquired by the appearance information acquisition device 61, the body thickness center of the patient M for each slice plane is calculated (step S22c), and the body thickness center of the patient M is matched with the scan center. Generate a scan plan.

  A helical scan is performed according to the scan plan (step S23). In step S23, the rotating unit 15 holding the X-ray tube 21 and the X-ray detector 24 is continuously rotated, and the top plate 12 is moved in the z-axis direction and the y-axis direction to scan the body thickness center of the patient M. An X-ray cone beam or an X-ray fan beam is exposed from a 360 degree direction while being matched with the center, and a slice image photographing process is performed. The raw data for the 360 degree direction transferred from the X-ray detector 24 to the operation console 13 via the data collection device 25, IF 32b, and IF 45b is preprocessed by the operation console 13.

  Next, as described with reference to FIG. 12, based on the projection data for the 360-degree direction generated in step S23, slice image data as biometric information inside the patient M is reconstructed (step S24). .

  Image processing for display such as window conversion and RGB processing is performed on the slice image data generated in step S24 (step S25), and the slice image is displayed on the display device 47 (step S26). In step S25, a so-called pseudo three-dimensional image such as a slice image of an arbitrary cross section, a projection image from an arbitrary direction, or a three-dimensional surface image is generated based on an instruction from the operator.

  According to the X-ray CT apparatus 10A of the second embodiment, the top plate 12 is moved in the left-right direction, the up-down direction, or the combined direction of the left-right direction and the up-down direction, and the scan center is aligned with the body thickness center of the patient M. By performing the scan, it is possible to arrange the portion where the patient M is the thickest and needs the dose at the center of the scan where the wedge thickness is the thinnest and the dose is the largest, and the image quality can be improved.

  In addition, according to the X-ray CT apparatus 10A of the second embodiment, the top 12 is moved in the left-right direction, the up-down direction, or the combined direction of the left-right direction and the up-down direction, and the scan center is matched with the body thickness center of the patient M. However, by performing the helical scan, it is possible to reduce the occurrence frequency of an artifact in which the periphery of the center of the image of the patient M falls black due to the overflow caused by the deviation between the body thickness center of the patient M and the scan center.

  Furthermore, according to the X-ray CT apparatus 10 </ b> A of the second embodiment, a scanogram scan is not required by generating a substitute image of a scanogram based on the appearance information of the patient M acquired using the appearance information acquisition device 61. The exposure of the patient M due to the scanogram scan can be reduced.

  In the second embodiment, the case where the body thickness center of the patient M is brought close to the scan center has been described. However, the present invention is not limited to this case. For example, the region of interest may be brought closer to the scan center.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the apparatus structure of 1st Embodiment of the X-ray CT apparatus concerning this invention. The block diagram which shows the function of the operation console which comprises the X-ray CT apparatus of 1st Embodiment. The figure which shows an example of an imaging | photography region. The figure which shows an example of the scan center for every imaging | photography area | region. Schematic for demonstrating each scan center for every imaging | photography area | region in a series of helical scans. The flowchart which shows operation | movement of the X-ray CT apparatus of 1st Embodiment. The conceptual diagram which shows the example of a display of a slice image. Schematic which shows the apparatus structure of 2nd Embodiment of the X-ray CT apparatus concerning this invention. The figure which shows the example of installation of a laser transmitter / receiver. The block diagram which shows the function of the operation console in 2nd Embodiment. The conceptual diagram which shows the body thickness centerline on a scanogram. The figure for demonstrating the type | formula which rearranges projection data. The flowchart which shows operation | movement of the X-ray CT apparatus of 2nd Embodiment. The block diagram which shows the modification of the function of the operation console in 2nd Embodiment. The figure which shows an example of the alternative image of a scanogram. The flowchart which shows the operation | movement in the modification of the X-ray CT apparatus of 2nd Embodiment.

Explanation of symbols

10, 10A X-ray CT apparatus 11 Mounting device 12 Top panel 13 Operation console 21 X-ray tube 24 X-ray detector 46 Input device 47 Display devices 51, 71, 81 Scan control units 52, 72, 82 Pre-processing units 53, 73 Scanogram generation units 54, 74, 84 Scan plan setting units 55, 75, 85 Image reconstruction units 56, 76, 86 Image processing units

Claims (13)

A top plate on which the subject is placed;
An X-ray tube that emits X-rays toward the subject and an X-ray detector that detects X-rays transmitted through the subject are held, and the X-ray tube and the X-ray detector are integrated. A rotating unit that rotates around the subject;
A gantry device for holding the rotating unit;
A scanning control unit that executes a helical scan while controlling the top plate, the X-ray tube, and the rotating unit;
The X-ray CT apparatus, wherein the scan control unit moves a scan center in a horizontal direction, a vertical direction, or a combination direction of the horizontal direction and the vertical direction in a series of helical scans on the subject. The X-ray CT apparatus according to claim 1, wherein the scan control unit moves the scan center during the series of helical scans. The X-ray CT apparatus according to claim 1, wherein the scan control unit moves the top plate in a vertical direction when moving the scan center in the series of helical scans. The X-ray according to claim 1, wherein the scan control unit synchronizes a movement amount of the scan center and a movement amount in a slice direction when moving the scan center in the series of helical scans. CT device. The X-ray CT apparatus according to claim 1, wherein the top plate is moved so that a body thickness center or a region of interest of the subject always matches the scan center. The X-ray CT apparatus according to claim 5, wherein when obtaining the body thickness center or the region of interest, a scanogram in at least one of a front direction, a back direction, and a side direction is used. 7. The body thickness center is obtained based on appearance information acquired using a laser transmitting / receiving apparatus in which the subject is sandwiched between the transmission side and the reception side with the subject interposed therebetween. X-ray CT system. The X-ray CT apparatus according to claim 5, wherein the body thickness center is obtained based on appearance information acquired using a camera installed on the gantry device. A scanogram substitute image is generated based on appearance information acquired by the laser transmitting / receiving apparatus or the camera, and the position of the subject is automatically or manually set based on the substitute image. The X-ray CT apparatus according to any one of 7 and 8. An alternative image of a scanogram is generated based on appearance information acquired by the laser transmitting / receiving apparatus or the camera, and real EC tube current is automatically or manually set based on the alternative image. Item 9. The X-ray CT apparatus according to any one of Items 7 and 8. The X-ray CT apparatus according to claim 5, wherein the body thickness center is obtained using projection data or a real-time reconstructed image on the immediately preceding slice plane. The X-ray CT apparatus according to claim 1, wherein when displaying a reconstructed image, the body thickness center of the subject is a display center. The X-ray CT apparatus according to any one of claims 1 to 12, wherein when displaying the reconstructed image, enlargement reconstruction or image enlargement is performed so as to be optimal for the image size.

Images