JP6494944B2 - X-ray CT system - Google Patents

Description

  Embodiments described herein relate generally to an X-ray CT (Computed Tomography) apparatus.

  2. Description of the Related Art Conventionally, there are X-ray CT apparatuses that can change the focus size of the focus of X-rays to be exposed. Such an X-ray CT apparatus controls, for example, an electric field or a magnetic field between a cathode and an anode in an X-ray tube on the basis of a control parameter for controlling a focal spot size, so that a cathode-side filament is connected to an anode-side filament. The focal spot size is changed by changing the thickness of the electron beam emitted toward the target.

  However, in the X-ray CT apparatus described above, even when the X-ray tube is controlled so as to emit X-rays based on a control parameter corresponding to a focal size having a predetermined size, the X-ray tube In some cases, the focal spot size does not become a predetermined size due to, for example, aging deterioration of the target or thermal expansion of the target due to irradiation with the electron beam. Therefore, in order to grasp the actual focal size in the X-ray tube, it is desired that a means for calculating the focal size in the X-ray tube is constructed in the X-ray CT apparatus.

JP 2011-24806 A

  The problem to be solved by the present invention is to provide an X-ray CT apparatus capable of calculating a focal spot size.

The X-ray CT apparatus of the embodiment includes an X-ray tube, a member, an X-ray detector, a calculation unit, an irradiation control unit, and a recording unit . The X-ray tube emits X-rays. A hole is formed in the member. The X-ray detector is provided on the opposite side of the member from the side where the X-ray tube is located, and generates X-ray detection data that has passed through the hole. The calculation unit calculates the size of the portion of the X-ray detector irradiated with the X-ray indicated by the X-ray detection data, the distance between the X-ray tube and the member, and the distance between the member and the X-ray detector. Based on the ratio, the focus size of the focus of the X-ray in the X-ray tube is calculated. The irradiation control unit emits X-rays with a control parameter corresponding to the focus size calculated by the calculation unit when the focus size calculated by the calculation unit is within the allowable range of the designated focus size. When the X-ray tube is controlled and the focus size calculated by the calculation unit is not within the specified focus size tolerance, the current control parameter is changed, and the X-ray is changed with the new control parameter after the change. The X-ray tube is controlled to irradiate. When the focus size based on the new control parameter after the change is within an allowable range of the designated focus size, the recording unit records the new control parameter after the change.

FIG. 1 is a diagram illustrating a configuration example of an X-ray CT apparatus according to the first embodiment. FIG. 2A is a diagram for explaining an example of a focus size and a method of controlling the focus size. FIG. 2B is a diagram for explaining an example of a focus size and a control method of the focus size. FIG. 3 is a diagram illustrating an example of a collimator according to the first embodiment. FIG. 4 is a diagram for explaining an example of a method for calculating the focus size. FIG. 5 is a diagram illustrating an example of a functional configuration of the X-ray irradiation control unit. FIG. 6 shows two types of focus, a focus size called a large focus size and a focus size called a small focus size, which can be specified in the X-ray CT apparatus according to the first embodiment. It is a figure which shows an example of the irradiation range of the X-ray which passed through the pinhole seen from the slice direction in each case of size. FIG. 7 is a flowchart for explaining an example of a focus size calculation process executed by the calculation unit according to the first embodiment. FIG. 8 is a diagram for explaining an example of a warning method according to the first embodiment. FIG. 9A is a flowchart for explaining the operation of the X-ray CT apparatus according to the first embodiment. FIG. 9B is a flowchart for explaining an example of a focus size control process executed by the calculation unit and the irradiation control unit according to the first embodiment. FIG. 10A is a diagram for explaining a collimator according to the second embodiment. FIG. 10B is a diagram illustrating a configuration example of the gantry device of the X-ray CT apparatus according to the second embodiment. FIG. 11 is a diagram illustrating a configuration example of a gantry device of an X-ray CT apparatus according to the third embodiment. FIG. 12A is a diagram for explaining a collimator according to the fourth embodiment. FIG. 12B is a diagram for describing an example of a method for calculating a focus size.

  Hereinafter, embodiments of the X-ray CT apparatus will be described in detail with reference to the accompanying drawings. The contents described in each embodiment can be applied in the same manner to other embodiments in principle.

(First embodiment)
First, the configuration of the X-ray CT apparatus according to the first embodiment will be described. FIG. 1 is a diagram illustrating a configuration example of an X-ray CT apparatus according to the first embodiment. As shown in FIG. 1, the X-ray CT apparatus according to the first embodiment includes a gantry device 10, a couch device 20, and a console device 30.

  The gantry device 10 is a device that irradiates the subject P with X-rays and generates projection data from X-ray detection data transmitted through the subject P. The gantry device 10 includes an X-ray irradiation control unit 11, an X-ray generation device 12, and the like. The X-ray detector 13, the collection unit 14, the rotating frame 15, the gantry driving unit 16, the optical member 17, and the focus size X-ray detector 18.

  The X-ray irradiation control unit 11 is a device that supplies a high voltage to the X-ray tube 12a as a high voltage generation unit. The X-ray irradiation control unit 11 adjusts the X-ray dose irradiated to the subject P by adjusting the tube voltage and tube current supplied to the X-ray tube 12a. In addition, the X-ray irradiation control unit 11 adjusts the X-ray irradiation range (fan angle and cone angle) irradiated to the subject P by adjusting the opening degree of the slit 12c_1 provided in the collimator 12c. Further, the X-ray irradiation control unit 11 controls the electric field or magnetic field between the cathode and the anode in the X-ray tube 12a based on the control parameter for controlling the focal spot size, and the cathode side filament to the anode The focal spot size is changed by changing the thickness of the electron beam emitted toward the target on the side. Here, the control parameter includes, for example, a value of a voltage applied to a grid provided between the filament in the X-ray tube 12a and the target.

  The X-ray generator 12 is an apparatus that generates X-rays and irradiates the subject P with the generated X-rays, and includes an X-ray tube 12a, a wedge 12b, and a collimator 12c.

  The X-ray tube 12a emits X-rays. For example, the X-ray tube 12 a is a vacuum tube that generates an X-ray beam that is exposed to the subject P by a high voltage supplied by the X-ray irradiation control unit 11. The X-ray tube 12a generates an X-ray beam that spreads with a fan angle and a cone angle. The X-ray tube 12 a exposes the X-ray beam to the subject P as the rotating frame 15 rotates.

  The X-ray tube 12a is controlled by the X-ray irradiation control unit 11 to continuously expose X-rays around the subject P for full reconstruction, or exposure that can be half-reconfigured for half reconstruction. X-rays can be continuously exposed within a range (180 degrees + fan angle). Further, the X-ray tube 12 a modulates the intensity of X-rays to be exposed under the control of the X-ray irradiation control unit 11. For example, the X-ray tube 12a increases the intensity of X-rays to be exposed in a specific X-ray irradiation direction and is exposed in a range other than the specific X-ray irradiation direction under the control of the X-ray irradiation control unit 11. The intensity of the emitted X-ray can be reduced. The X-ray irradiation direction is also called a view.

  The wedge 12b is an X-ray filter for adjusting the X-ray dose of X-rays emitted from the X-ray tube 12a. The collimator 12 c is formed with a slit for narrowing the X-ray irradiation range in which the X-ray dose is adjusted by the wedge 12 b under the control of the X-ray irradiation control unit 11.

  The rotating frame 15 supports the X-ray generator 12 having the X-ray tube 12 a and the X-ray detector 13 so as to be rotatable around the subject P. The rotating frame 15 supports the X-ray generator 12 and the X-ray detector 13 so as to face each other with the subject P interposed therebetween. The rotating frame 15 is an annular frame that rotates at high speed on a circular orbit around the subject P by the gantry driving unit 16.

  The gantry driving unit 16 is a device that rotates the X-ray generator 12 and the X-ray detector 13 on a circular orbit around the subject P by rotating the rotary frame 15.

  The X-ray detector 13 detects X-rays that are exposed from the X-ray tube 12a and transmitted through the subject P. For example, the X-ray detector 13 detects X-rays that have been irradiated from the X-ray tube 12a and transmitted through the subject P by using two-dimensionally arranged X-ray detection elements. The X-ray detector 13 shown in FIG. 1 is a two-dimensional array type detector (surface detector) that outputs X-ray dose distribution data indicating a dose distribution of X-rays transmitted through the subject P. The X-ray detector 13 includes a plurality of X-ray detection elements (detection element arrays) arranged in the channel direction (Y-axis direction shown in FIG. 1), in the body axis direction of the subject P (Z-axis shown in FIG. 1). A plurality of rows along the direction and the slice direction). For example, the X-ray detector 13 has detection element rows arranged in 320 rows along the body axis direction of the subject P, and detects X-ray dose distribution data transmitted through the subject P over a wide range. The X-ray detector 13 is, for example, an integral type detector.

  The collection unit 14 is a DAS (data acquisition system), collects X-ray detection data (X-ray dose distribution data) detected by the X-ray detector 13, and generates projection data. For example, the collection unit 14 collects X-ray dose distribution data detected by the X-ray detector 13, performs amplification processing, A / D conversion processing, etc. on the collected X-ray dose distribution data, and performs projection data. And the generated projection data is transmitted to the pre-processing unit 34 of the console device 30 to be described later.

  The optical member 17 and the focus size X-ray detector 18 will be described later.

  The couch device 20 is a device on which the subject P is placed, and includes a couchtop 22 and a couch driving device 21 as shown in FIG. The top plate 22 is a plate on which the subject P is placed. The bed driving device 21 moves the subject P in the rotating frame 15 (in the imaging space) by moving the top plate 22 in the Z-axis direction under the control of a scan control unit 33 described later.

  For example, the gantry device 10 performs a helical scan that rotates the rotating frame 15 while moving the top plate 22 to scan the subject P in a spiral shape.

  The console device 30 is a device that accepts the operation of the X-ray CT apparatus by the operator and reconstructs CT image data from the projection data generated by the gantry device 10, and includes an input device 31, a display device 32, and a scan. It has a control unit 33, a preprocessing unit 34, a raw data storage unit 35, an image reconstruction unit 36, an image storage unit 37, and a control unit 38.

  The input device 31 has a mouse, a keyboard, buttons, pedals (foot switches), etc. used by an operator such as a doctor or engineer who operates the X-ray CT apparatus to input various instructions and various settings. Instruction and setting information is transferred to the control unit 38.

  The display device 32 is a monitor that is referred to by the operator, and displays CT image data under the control of the control unit 38 and receives various instructions and settings from the operator via the input device 31. GUI (Graphical User Interface) is displayed. For example, the operator uses the input device 31 to input examination information such as the body position at the time of imaging of the subject P placed on the top 22 into the examination information registration GUI.

  The scan control unit 33 controls the operations of the X-ray irradiation control unit 11, the gantry driving unit 16, the collection unit 14, and the bed driving device 21 under the control of the control unit 38. Thereby, the scan control unit 33 controls the X-ray scan processing of the subject P, the generation processing of the projection data group, and the data processing for the projection data group in the gantry device 10.

  The preprocessing unit 34 performs correction processing such as logarithmic conversion processing, offset correction, sensitivity correction, and beam hardening correction on the projection data transmitted from the collection unit 14 to generate corrected projection data. To do. For example, the preprocessing unit 34 performs sensitivity correction processing for correcting sensitivity between channels using the correction data, and generates corrected projection data. Hereinafter, the corrected projection data generated by the preprocessing unit 34 is referred to as raw data. The preprocessing unit 34 stores the raw data in the raw data storage unit 35.

  The raw data storage unit 35 stores the raw data generated by the preprocessing unit 34.

  The image reconstruction unit 36 generates various images from the raw data stored in the raw data storage unit 35, and stores the generated images in the image storage unit 37. For example, the image reconstruction unit 36 reconstructs a CT image by performing a back projection process (for example, a back projection process by an FBP (Filtered Back Projection) method) on the raw data, and the reconstructed CT image is an image storage unit 37. To store.

  The image storage unit 37 stores various images generated by the image reconstruction unit 36. For example, the image storage unit 37 stores a CT image.

  The control unit 38 performs overall control of the X-ray CT apparatus by controlling operations of the gantry device 10, the couch device 20, and the console device 30. Specifically, the control unit 38 controls the scan (CT scan) performed by the gantry device 10 by controlling the scan control unit 33. Further, the control unit 38 controls the image reconstruction process in the console device 30 by controlling the preprocessing unit 34 and the image reconstruction unit 36. In addition, the control unit 38 controls the display device 32 to display various images stored in the image storage unit 37.

  The raw data storage unit 35 and the image storage unit 37 described above can be realized by a semiconductor memory element such as a RAM or a flash memory, a hard disk, an optical disk, or the like. In addition, the scan control unit 33, the preprocessing unit 34, the image reconstruction unit 36, and the control unit 38 described above include an integrated circuit such as an application specific integrated circuit (ASIC) and a field programmable gate array (FPGA), a central processing unit (CPU). It can be realized by an electronic circuit such as a processing unit (MPU) or a micro processing unit (MPU).

  The overall configuration of the X-ray CT apparatus according to the first embodiment has been described above. With this configuration, the X-ray CT apparatus according to the first embodiment calculates the focal size of the X-ray tube 12a by the X-ray irradiation control unit 11 performing the processing described below.

  Here, first, an example of the focus size and the control method of the focus size will be described. 2A and 2B are diagrams for explaining an example of a focus size and a control method of the focus size. FIG. 2A shows a configuration example of the X-ray tube 12a according to the present embodiment. As shown in FIG. 2A, the X-ray tube 12a includes a cathode filament 12a_1, an anode target 12a_2, a focusing tube 12a_3, and a grid 12a_4.

  The filament 12a_1 radiates thermal electrons toward the target 12a_2 when the filament current flows. Such a bundle of thermoelectrons is also referred to as an electron beam. The focusing cylinder 12a_3 is for suppressing the spread of generated thermoelectrons and is also referred to as a focusing cup.

  The target 12a_2 is set to a predetermined angle, for example, an angle of 12 ° or more and 20 ° or less with respect to the traveling direction of the thermoelectrons. The angle with respect to the traveling direction of the thermoelectrons is referred to as a target angle. The target 12a_2 generates X-rays when thermal electrons emitted from the filament 12a_1 collide. A bundle 12a_5 of X-rays generated on the target 12a_2 is irradiated in a direction corresponding to the target angle. At this time, as shown in the example of FIG. 2B, the X-ray focal point has two types of focal points: an actual focal point viewed from the filament 12a_1 side and an effective focal point viewed from the X-ray bundle 12a_5 side. In the present embodiment, the focus size refers to the size of the effective focus.

  Further, the grid 12a_4 generates a magnetic field having a magnitude corresponding to the magnitude of the voltage applied to the grid 12a_4 in a predetermined direction to control the thickness (beam diameter) of the electron beam. Thereby, the grid 12a_4 controls the focal spot size. The magnitude of the voltage applied to the grid 12a_4 is controlled by the X-ray irradiation control unit 11. The focal spot size in the X-ray tube 12a is controlled by the method as described above. The focus size can be changed by other methods. For example, the X-ray irradiation control unit 11 can also control the focal spot size by controlling the magnitude of the magnetic field generated by the focusing coil disposed around the electron beam.

  FIG. 3 is a diagram illustrating an example of the collimator 12c according to the first embodiment. As shown in the example of FIG. 3, the collimator 12c has a slit 12c_1 and a slit 12c_2. The slit 12c_1 and the slit 12c_2 are for narrowing the X-ray irradiation range in which the X-ray dose is adjusted by the wedge 12b. X-rays that have passed through the slit 12c_1 are applied to the X-ray detector 13. The size of the opening portion of the slit 12c_1 is controlled by the X-ray irradiation control unit 11. Further, the X-rays that have passed through the slit 12c_2 are applied to the optical member 17 as shown in FIGS. That is, the subject P is not irradiated with the X-rays that have passed through the slit 12c_2. Therefore, the scanning with the X-rays that have passed through the slit 12c_1 and the calculation of the focus size using the detection data of the X-rays that have passed through the slit 12c_2 can be performed simultaneously.

  The optical member 17 is provided outside the irradiation range of the X-rays that have passed through the slit 12c_1. For example, as shown in FIG. 1, the optical member 17 is provided outside the irradiation range of the X-rays that have passed through the slit 12c_1 in the channel direction. FIG. 4 is a diagram for explaining an example of a method for calculating the focus size. As shown in FIG. 4, the optical member 17 has a pinhole 17a. The diameter of the pinhole 17a is, for example, a minute size such that a main shadow hardly occurs on the focus size X-ray detector 18. For example, the diameter of the pinhole 17a is smaller than any focus size that can be set in the X-ray CT apparatus according to the present embodiment. For example, the diameter of the pinhole 17a is about the needle hole. The X-rays that have passed through the pinhole 17a are applied to the focus size X-ray detector 18. For example, as shown in the example of FIG. 4, the X-rays that have passed through the pinhole 17 a are irradiated onto the portion 18 a of the focus size X-ray detector 18. The pinhole 17a is an example of a hole. The optical member 17 is also simply referred to as a member.

  The focus size X-ray detector 18 is provided at a position where X-rays that have passed through the pinhole 17a are irradiated. Further, the focus size X-ray detector 18 is provided on the side opposite to the side where the X-ray tube 12 a is positioned with respect to the optical member 17. The focus size X-ray detector 18 detects X-rays that have passed through the pinhole 17a. For example, X-ray detection elements are two-dimensionally arranged in the focus size X-ray detector 18, and X-rays are detected by the X-ray detection elements. The focus size X-ray detector 18 shown in FIG. 4 is a two-dimensional array type detector that outputs X-ray dose distribution data (X-ray detection data) indicating the X-ray dose distribution that has passed through the pinhole 17a. . A plurality of X-ray detection elements (detection element arrays) arranged in the channel direction are arranged in the focus size X-ray detector 18 along the slice direction. The focus size X-ray detector 18 is, for example, an integral type detector. The output distribution of a plurality of X-ray detection elements, that is, the distribution of X-ray dose detected by the plurality of X-ray detection elements is referred to as an X-ray profile.

  FIG. 5 is a diagram illustrating an example of a functional configuration of the X-ray irradiation control unit 11. As shown in the example of FIG. 5, the X-ray irradiation control unit 11 includes a calculation unit 11a, an irradiation control unit 11b, a recording unit 11c, a warning unit 11d, and a memory 11e.

  The memory 11e stores a correspondence table 11f. In each record of the correspondence table 11f, a control parameter and a focus size are registered in association with each other. Further, the control parameter of each record may be updated by the recording unit 11c.

  The calculation unit 11a calculates a focus size by executing a focus size calculation process. Such a focus size calculation process is performed, for example, in a focus size control process described later. In the focus size control process described later, the calculation unit 11a executes the focus size calculation process at predetermined time intervals while the X-ray CT apparatus is scanning.

  Here, an example of the focus size calculation process executed by the calculation unit 11a will be described with reference to FIGS. FIG. 6 shows the case of two types of focus sizes, a focus size called a large focus size and a focus size called a small focus size, which can be set in the X-ray CT apparatus according to the first embodiment. It is a figure which shows an example of the irradiation range of the X-ray which passed through the pinhole 17a seen from the slice direction. FIG. 7 is a flowchart for explaining an example of a focus size calculation process executed by the calculation unit 11a according to the first embodiment. The small focus size is smaller than the large focus size.

  In the example of FIG. 6, the irradiation range indicated by the solid line is the irradiation range of X-rays that have passed through the pinhole 17a when the focus size is the small focus size. An irradiation range indicated by a broken line is an irradiation range of X-rays that have passed through the pinhole 17a when the focal spot size is a large focal spot size.

  The calculation unit 11a is the size of the portion 18a of the focus size X-ray detector 18 irradiated with the X-rays indicated by the X-ray dose distribution data (X-ray profile data) output by the focus size X-ray detector 18. Based on the ratio (A / B) of the distance A between the X-ray tube 12a and the optical member 17 and the distance B between the optical member 17 and the focus size X-ray detector 18, the X-ray tube 12a. The focal point size of the X-ray focal point at is calculated.

  For example, as illustrated in FIG. 7, the calculation unit 11 a first includes a plurality of X-rays arranged in the focus size X-ray detector 18 based on a two-dimensional X-ray dose distribution indicated by the X-ray profile data. An X-ray detection element that outputs an X-ray dose larger than a predetermined value (for example, 0) is specified from the detection elements (step S101). Here, the portion on the focus size X-ray detector 18 formed by the X-ray detection element specified in this way is a portion 18a irradiated with X-rays.

  Then, the calculation unit 11a identifies the center of the portion 18a in the channel direction and the center of the portion 18a in the slice direction (step S102).

  Then, the calculation unit 11a specifies an X-ray detection element to be processed from the specified center in the channel direction and the specified center in the slice direction (step S103). For example, in step S103, the calculation unit 11a moves back and forth in the channel direction from the X-ray detection element positioned in the center portion of the specified channel direction in addition to the X-ray detection element positioned in the center portion of the specified channel direction. A predetermined number α of X-ray detection elements are identified as first candidate X-ray detection elements to be processed. In addition to the X-ray detection element positioned at the center portion in the specified slice direction, the calculation unit 11a includes a predetermined number β of front and rear in the slice direction from the X-ray detection element positioned at the center portion in the specified slice direction. Are identified as second candidate X-ray detection elements to be processed. Then, the calculation unit 11a identifies the X-ray detection elements included in both the first candidate and the second candidate to be processed as the X-ray detection elements to be processed. The predetermined number α and the predetermined number β can be determined based on the size of the largest focus size among the focus sizes that can be specified in the X-ray CT apparatus according to the present embodiment, for example. .

  And the calculation part 11a calculates the average value of the X-ray dose which the some X-ray detection element arranged in the channel direction outputs with respect to a process target X-ray detection element for every slice direction. Thereby, the calculation unit 11a calculates an average X-ray dose distribution (X-ray dose distribution) in the channel direction (step S104). For example, as illustrated in FIG. 6, when the focus size is the small focus size, the calculation unit 11 a calculates an average X-ray dose distribution 40 a in the channel direction. Further, the calculation unit 11a calculates an average X-ray dose distribution 40b in the channel direction when the focus size is the large focus size. In addition, the magnitude | size of the vertical axis | shaft in the part of the X-ray dose distribution of the example of FIG. 6 shows the magnitude | size of the dose of X-rays. That is, the portion of the X-ray dose distribution in the example of FIG. 6 indicates the magnitude of the X-ray dose detected by each detection element.

  Then, the calculating unit 11a calculates the full width at half maximum (FWHM (Full Width at half maximum)) of the calculated X-ray dose distribution (step S105). For example, as illustrated in FIG. 6, when the calculation unit 11a calculates the X-ray dose distribution 40a in step S104, the calculation unit 11a calculates the full width at half maximum 41a of the X-ray dose distribution 40a. When the calculation unit 11a calculates the X-ray dose distribution 40b in step S104, the calculation unit 11a calculates the full width at half maximum 41b of the X-ray dose distribution 40b. In step S105, the full width at half maximum calculated by the calculation unit 11a is not an actual length corresponding to the full width at half maximum on the focus size X-ray detector 18, but a value indicating the number of X-ray detection elements. is there. Moreover, although the calculation part 11a illustrated about the case where the calculation part 11a calculates the irradiation range of the X-ray in a channel direction by the method as mentioned above in step S105, the calculation part 11a is the X-ray in a channel direction also by another method. The irradiation range can be calculated.

  Then, the calculation unit 11a converts the calculated full width at half maximum into an actual length corresponding to the full width at half maximum on the focus size X-ray detector 18 (step S106). For example, the calculation unit 11a calculates, as an actual length, a value obtained by multiplying the calculated full width at half maximum by a pixel pitch that is a distance between adjacent X-ray detection elements (full width at half maximum × pixel pitch).

  Then, the calculation unit 11a uses a value (actual length × (A / B)) obtained by multiplying the actual length calculated in step S106 by the ratio (A / B) of the distance A and the distance B as the focus. Is calculated as the length of one side (step S107). Note that the length of one side calculated in step S107 is the length of one side in the channel direction when the focal point is regarded as a square shape. By the method as described above, the calculation unit 11a calculates the focus size in the channel direction.

  Then, the calculation unit 11a calculates the length of one side in the slice direction of the focus by the same method. For example, as illustrated in FIG. 7, the calculation unit 11 a calculates an average value of X-ray doses output from a plurality of X-ray detection elements arranged in the slice direction with respect to the X-ray detection element to be processed, as a channel. Calculate for each direction. Thereby, the calculation unit 11a calculates an average X-ray dose distribution in the slice direction (step S108).

  Then, the calculation unit 11a calculates the full width at half maximum of the X-ray dose distribution calculated in step S108 (step S109).

  The calculating unit 11a converts the calculated full width at half maximum into an actual length corresponding to the full width at half maximum on the focus size X-ray detector 18 (step S110).

  Then, the calculation unit 11a uses a value (actual length × (A / B)) obtained by multiplying the actual length calculated in step S110 by the ratio (A / B) of the distance A and the distance B as the focus. Is calculated as the length of one side (step S111), and the focus size calculation process is terminated. Note that the length of one side calculated in step S111 is the length of one side in the slice direction when the focal point is regarded as a square shape.

  The calculation unit 11a calculates the length of one side in the channel direction and the length of one side in the slice direction as the focus size by executing the focus size calculation process described above. Note that the calculation unit 11a can also perform the processes in steps S104 to S107 after performing the processes in steps S108 to S111 in the focus size calculation process. Thereby, the calculation unit 11a can also calculate the length of one side in the channel direction after calculating the length of one side in the slice direction.

  Returning to the description of FIG. 5, each time the focus size is calculated by the calculation unit 11 a, the irradiation control unit 11 b sets the current control parameter when the calculated focus size is not within the specified focus size tolerance. The X-ray tube 12a is controlled so as to emit X-rays with the new control parameters after the change.

  For example, when the focus size is designated by the scan control unit 33, the irradiation control unit 11b refers to the correspondence table 11f and acquires a control parameter corresponding to the designated focus size. Then, the irradiation control unit 11b controls the electric field and magnetic field between the cathode and the anode in the X-ray tube 12a using the acquired control parameter, and moves from the cathode-side filament 12a_1 to the anode-side target 12a_2. The thickness of the emitted electron beam is controlled. Thereby, the irradiation controller 11b controls the focal spot size to be the designated focal spot size.

  However, the focus size in the X-ray tube 12a may not be the specified focus size due to the aging of the X-ray tube 12a, the thermal expansion of the target 12a_2 due to the electron beam irradiation, or the like. Therefore, each time the focus size is calculated by the calculation unit 11a, the irradiation control unit 11b determines whether or not the calculated focus size is within the specified focus size tolerance.

  Then, when the calculated focus size is not within the specified focus size tolerance, the irradiation control unit 11b changes the control parameter at the present time. For example, the irradiation control unit 11b changes the control parameter at the current time according to the amount of deviation between the calculated focus size and the designated focus size. Then, the irradiation control unit 11b controls the electric field and magnetic field between the cathode and the anode in the X-ray tube 12a using the new control parameter after the change, and the cathode-side filament 12a_1 to the anode-side target. The thickness of the electron beam emitted toward 12a_2 is controlled. Thereby, the focus size in the X-ray tube 12a is based on the new control parameter. In this way, the irradiation control unit 11b performs feedback control so as to bring the focus size in the X-ray tube 12a closer to the designated focus size.

  When the focus size calculated by the calculation unit 11a is within an allowable range of the designated focus size, the recording unit 11c records the current control parameter.

  For example, when the irradiation control unit 11b determines that the calculated focus size is within an allowable range of the designated focus size, the recording unit 11c specifies the designated focus size from all the records in the correspondence table 11f. Specify the record in which is registered. Then, the recording unit 11c updates the control parameter registered in the identified record to the control parameter at the current time, and records the control parameter at the current time in association with the designated focus size. Thereby, the recording unit 11c can record the control parameter capable of setting the focus size in the X-ray tube 12a to the designated focus size in the correspondence table 11f.

  The warning unit 11d issues a warning to the user when the focus size calculated by the calculation unit 11a is not within an allowable range of the designated focus size.

  For example, when the irradiation control unit 11b determines that the calculated focus size is not within the specified focus size allowable range, the warning unit 11d reads “X-ray irradiation with a control parameter corresponding to the specified focus size. An instruction to display the warning message on the display device 32 is transmitted to the control unit 38 as a result that the designated focus size and the actual focus size are significantly different. Thereby, the control part 38 controls the display apparatus 32 so that the above-mentioned warning message is displayed. As a result, as shown in FIG. 8, the display device 32 indicates that “when the X-ray irradiation is performed with the control parameter corresponding to the designated focus size, the designated focus size and the actual focus size are significantly different. Warning message is displayed.

  Next, the operation of the X-ray CT apparatus according to the first embodiment will be described using the flowchart of FIG. 9A.

  In step S201, when the inspection is started, the control unit 38 controls the display device 32 to display an input screen for generating a scan plan.

  In step S <b> 202, the operator refers to the scan plan generation input screen displayed on the display device 32, and inputs an instruction for generating a scan plan on the input screen via the input device 31. The control unit 38 generates a scan plan in accordance with an operator instruction input via the input device 31. The control unit 38 notifies the scan control unit 33 of the generated scan plan.

  In step S <b> 203, the operator prompts the subject P to be placed on the top plate 22 of the bed apparatus 20. The operator inputs an instruction to the input device 31 so as to move the subject P to the scan start position. The control unit 38 controls the operation of the bed apparatus 20 in accordance with an operator instruction input via the input device 31. The couch device 20 moves the position of the subject P to the scan start position under the control of the control unit 38. When the subject P moves to the scan start position by the operation of the bed apparatus 20, the operator inputs a scan start instruction to the input device 31.

  In step S204, scanning based on the scan plan is started. In step S <b> 204, when an operator's scan start instruction is input via the input device 31, the control unit 38 notifies the scan control unit 33 that scanning is started. When notified of the start of scanning from the control unit 38, the scan control unit 33 gives various instructions to the X-ray irradiation control unit 11, the collection unit 14, the gantry driving unit 16, and the bed driving device 21. For example, the scan control unit 33 starts the X-ray irradiation at the timing and intensity based on the scan plan notified from the control unit 38, and stops the X-ray irradiation at the timing based on the scan plan. The controller 11 is instructed. Here, the scan control unit 33 designates the focus size based on the scan plan so that the focus size in the X-ray tube 12a becomes the focus size based on the scan plan, and the designated focus size is designated as the X-ray irradiation control unit 11. Notify In addition, the scan control unit 33 instructs the collection unit 14 to transmit the projection data to the preprocessing unit 34 at a timing based on the scan plan. Further, the scan control unit 33 instructs the gantry driving unit 16 to start the rotation of the rotary frame 15 at a timing based on the scan plan and to stop the rotation of the rotary frame 15 at a timing based on the scan plan. The scan control unit 33 starts the movement of the subject P placed on the bed apparatus 20 in the Z-axis direction at the timing and speed based on the scan plan, and at the timing based on the scan plan. The couch device 20 instructs the couch driving device 21 to stop moving in the Z-axis direction.

  When an instruction is given by the scan control unit 33, each of the X-ray irradiation control unit 11, the collection unit 14, the gantry driving unit 16, and the bed driving device 21 performs an operation based on the instruction of the scan control unit 33.

  Based on the instruction of the scan control unit 33, the X-ray irradiation control unit 11 starts X-ray irradiation at the timing and intensity based on the scan plan, and stops the X-ray irradiation at the timing based on the scan plan. The X-ray tube 12a is controlled. As a result, the X-ray tube 12a starts X-ray irradiation at the timing and intensity based on the scan plan, and stops X-ray irradiation at the timing based on the scan plan.

  Further, the irradiation control unit 11b of the X-ray irradiation control unit 11 uses an electric field or magnetic field between the cathode and the anode in the X-ray tube 12a using a control parameter corresponding to the focal spot size designated by the scan control unit 33. To control the thickness of the electron beam emitted from the cathode-side filament 12a_1 toward the anode-side target 12a_2. Thereby, the irradiation controller 11b controls the focal spot size to be the designated focal spot size.

  The gantry driving unit 16 controls the rotation frame 15 to start rotation at a timing based on the scan plan and controls the rotation frame 15 to stop at a timing based on the scan plan based on an instruction from the scan control unit 33. To do. Thereby, the rotation frame 15 starts to rotate at a timing based on the scan plan and stops at a timing based on the scan plan.

  The couch driving device 21 starts moving in the Z-axis direction at a timing and speed based on the scan plan based on an instruction from the scan control unit 33, and stops moving in the Z-axis direction at a timing based on the scan plan. Thus, the bed apparatus 20 is controlled. Thereby, the bed apparatus 20 starts moving in the Z-axis direction at the timing and speed based on the scan plan, and stops moving in the Z-axis direction at the timing based on the scan plan.

  The collection unit 14 transmits projection data to the preprocessing unit 34 at a timing based on the scan plan based on an instruction from the scan control unit 33. Here, the preprocessing unit 34 performs correction processing such as logarithmic conversion processing, offset correction, sensitivity correction, and beam hardening correction on the projection data transmitted from the collection unit 14 under the control of the control unit 38. To generate raw data. The preprocessing unit 34 stores the raw data in the raw data storage unit 35 under the control of the control unit 38. Under the control of the control unit 38, the image reconstruction unit 36 reconstructs a CT image by performing a back projection process on the raw data, and stores the reconstructed CT image in the image storage unit 37.

  When the CT scan is started in step S204, in step S205, the calculation unit 11a determines whether it is the timing at which the focus size control process is performed. For example, since the focus size control process is executed at a predetermined time interval (for example, every 10 seconds), the calculation unit 11a determines whether or not the current time is the timing for executing this focus size control process. To do. If the calculation unit 11a determines that it is not time to perform the focus size control process (step S205; No), the calculation unit 11a proceeds to step S207.

  When the calculation unit 11a determines that it is time to perform the focus size control process (step S205; Yes), in step S206, the calculation unit 11a and the irradiation control unit 11b execute the focus size control process.

  FIG. 9B is a flowchart for explaining an example of a focus size control process executed by the calculation unit 11a and the irradiation control unit 11b according to the first embodiment. As shown in FIG. 9B, in step S301, the calculation unit 11a executes the focus size calculation process shown in the flowchart of FIG. 7 to calculate the focus size in the X-ray tube 12a.

  In step S302, the irradiation control unit 11b determines whether or not the calculated focus size is within an allowable range of the specified focus size. If the irradiation control unit 11b determines that the calculated focus size is within the specified focus size tolerance (step S302; Yes), the processing result is stored in the internal memory, and the process returns.

  On the other hand, when the irradiation control unit 11b determines that the calculated focus size is not within the specified focus size tolerance (step S302; No), as described above, the focus size in the X-ray tube 12a. The feedback control is performed so as to bring the focal point closer to the designated focus size (step S303). Then, the irradiation control unit 11b stores the processing result in the internal memory and returns.

  Returning to FIG. 9A, the scan control unit 33 determines whether or not the scan based on the scan plan generated in step S202 is completed (step S207). If the scan control unit 33 determines that the scan based on the scan plan has not ended (step S207; No), the scan control unit 33 returns to step S205.

  On the other hand, if the scan control unit 33 determines that the scan based on the scan plan has ended (step S207; Yes), the scan based on the scan plan is ended in step S208. In step S208, each of the X-ray irradiation control unit 11, the gantry driving unit 16, and the bed driving device 21 performs an operation based on an instruction from the scan control unit 33 in step S204.

  Based on an instruction from the scan control unit 33, the X-ray irradiation control unit 11 controls the X-ray tube 12a so as to stop the X-ray irradiation at a timing based on the scan plan. Thereby, the X-ray tube 12a stops X-ray irradiation at the timing based on the scan plan.

  The gantry driving unit 16 controls the rotating frame 15 to stop at a timing based on the scan plan based on an instruction from the scan control unit 33. Thereby, the rotation frame 15 stops at the timing based on the scan plan.

  The couch driving device 21 controls the couch device 20 to stop the movement in the Z-axis direction at the timing based on the scan plan based on the instruction of the scan control unit 33. Thereby, the bed apparatus 20 stops moving in the Z-axis direction at a timing based on the scan plan.

  In step S209, the control unit 38 controls the display device 32 to display a selection screen for determining whether or not to perform another CT scan. When performing another CT scan, the operator selects an option for performing another CT scan via the input device 31. In this case (step S209; Yes), the control unit 38 controls the display device 32 so as to display the input screen for generating the scan plan, and proceeds to step S202.

  On the other hand, when another CT scan is not performed, the operator selects an option indicating that another scan is not performed via the input device 31. In this case (step S209; No), the inspection ends.

  The X-ray CT apparatus according to the first embodiment has been described above. As described above, the X-ray CT apparatus according to the first embodiment can calculate the focal spot size.

  In addition, the X-ray CT apparatus according to the first embodiment performs feedback control such that the focal spot size in the X-ray tube 12a approaches the designated focal spot size. Therefore, the X-ray CT apparatus according to the first embodiment can automatically bring the focus size close to the designated focus size.

  Further, the X-ray CT apparatus according to the first embodiment records the current control parameter when the focus size calculated by the calculation unit 11a is within an allowable range of the designated focus size. Therefore, the X-ray CT apparatus according to the first embodiment records a control parameter capable of setting the focus size in the X-ray tube 12a to the designated focus size. Therefore, according to the X-ray CT apparatus according to the first embodiment, when the focus size is designated and the control parameter corresponding to the designated focus size is recorded, the recorded control is performed. Using the parameters, the focus size in the X-ray tube 12a can be quickly set to the designated focus size.

  In addition, the X-ray CT apparatus according to the first embodiment warns the operator when the focus size calculated by the calculation unit 11a is not within an allowable range of the designated focus size. Therefore, according to the X-ray CT apparatus according to the first embodiment, the X-ray tube 12a has deteriorated over time, or an abnormality such as thermal expansion of the target 12a_2 due to irradiation with the electron beam occurs. Can grasp what is being done.

  In the first embodiment, the focus size X-ray detector 18 included in the X-ray CT apparatus is illustrated as an integral type. However, the focus size X-ray detector 18 may be another type of X-ray. A detector can also be employed. For example, the focus size X-ray detector 18 may be a photon counting type detector.

  The X-ray CT apparatus according to the first embodiment can also execute the above-described focus size control process according to an instruction from the operator. For example, the operator inputs an instruction to execute the focus size control process to the input device 31 when performing periodic inspection of the X-ray CT apparatus. When an instruction to execute the focus size control process is transferred from the input device 31 to the control unit 38, the calculation unit 11a and the irradiation control unit 11b are controlled by the scan control unit 33 under the control of the control unit 38. The focus size control process is executed. Note that, when the focus size control process is executed by an operator's instruction, the X-ray CT apparatus determines each of a plurality of focus sizes (for example, a large focus size and a small focus size) that can be set in the X-ray CT apparatus. Designate and record corresponding control parameters for each designated focus size.

  The X-ray CT apparatus according to the first embodiment can also execute the above-described focus size control process during warm-up. In the focus size control process executed at the time of warm-up, the X-ray CT apparatus designates only a specific focus size designated by the user from among a plurality of settable focus sizes, and the focus size in the X-ray tube 12a. Records the control parameters for the specified focal point size. Therefore, the X-ray CT apparatus records the corresponding control parameters only for the necessary focus size specified by the user during warm-up. As a result, the time required for the focus size control process during warm-up can be reduced.

(Second Embodiment)
In the above-described first embodiment, the case where the optical member 17 is provided outside the irradiation range of the X-rays that have passed through the slit 12c_1 in the channel direction has been described. However, the optical member 17 may be provided outside the irradiation range of the X-rays that have passed through the slit 12c_1 in the slicing direction. Such an embodiment will be described as a second embodiment with reference to FIGS. 10A and 10B. In addition, about the structure similar to 1st Embodiment, the same code | symbol may be attached | subjected and description may be abbreviate | omitted.

  FIG. 10A is a diagram for explaining a collimator 12c according to the second embodiment. As shown in FIG. 10A, the collimator 12c according to the second embodiment is different from the collimator 12c according to the first embodiment in that a slit 12c_3 is formed in the slice direction instead of the slit 12c_2. .

  FIG. 10B is a diagram illustrating a configuration example of the gantry device 10 of the X-ray CT apparatus according to the second embodiment. As illustrated in FIG. 10B, the optical member 17 according to the second embodiment is provided outside the irradiation range of the X-rays that have passed through the slit 12c_1 in the slicing direction. Then, the X-rays that have passed through the slit 12c_3 are irradiated to the optical member 17 according to the second embodiment, as shown in FIG. 10B. That is, the subject P is not irradiated with the X-rays that have passed through the slit 12c_3. Therefore, the scan using the X-ray detection data passing through the subject P through the slit 12c_1 and the calculation of the focus size using the X-ray detection data passing through the slit 12c_3 can be performed simultaneously. It becomes.

  Further, the focus size X-ray detector 18 according to the second embodiment is provided closer to the X-ray tube 12 a than the subject P. Thereby, it can suppress that the subject P and the X-ray detector 18 for focus sizes contact during a scan.

(Third embodiment)
In the first and second embodiments described above, the case where the optical member 17 is provided outside the irradiation range of the X-rays that have passed through the slit 12c_1 has been described. However, the optical member 17 may be provided inside the irradiation range of the X-rays that have passed through the slit 12c_1. Thus, such an embodiment will be described as a third embodiment with reference to FIG. In addition, about the structure similar to 1st Embodiment and 2nd Embodiment, the same code | symbol may be attached | subjected and description may be abbreviate | omitted.

  FIG. 11 is a diagram illustrating a configuration example of the gantry device 10 of the X-ray CT apparatus according to the third embodiment. As shown in FIG. 11, in the gantry device 10 according to the third embodiment, the optical member 17 is provided inside the irradiation range of the X-rays that have passed through the slit 12c_1. That is, the optical member 17 is irradiated with X-rays that have passed through the slit 12c_1. Moreover, the gantry device 10 according to the third embodiment includes a pinhole driving unit 17b. The pinhole driving unit 17 b controls the position of the optical member 17 under the control of the scan control unit 33. For example, when the X-ray CT apparatus is regularly inspected or when the X-ray CT apparatus is warmed up, the control unit 38 causes the scan control unit 33 to position the optical member 17 directly below the X-ray tube 12a. Instruct. The scan control unit 33 given such an instruction instructs the pinhole driving unit 17b to position the optical member 17 directly below the X-ray tube 12a. The pinhole driving unit 17b to which such an instruction is given positions the optical member 17 directly below the X-ray tube 12a.

  In the third embodiment, the X-ray detector 13 is irradiated with X-rays that have passed through the pinhole 17a formed in the optical member 17 positioned directly below the X-ray tube 12a. In the third embodiment, the X-ray irradiation control unit 11 uses the X-ray detection data output from the X-ray detector 13 so that the focus size is the same as that in the first embodiment and the second embodiment. Calculation processing and focus size control processing are performed.

  In the third embodiment, X-rays are irradiated to the X-ray detection element disposed immediately below the X-ray tube 12a. Here, the shape formed by the X-ray irradiation region on the X-ray detector 13 when the X-ray detection element arranged immediately below the X-ray tube 12a is irradiated with X-rays is shaped 1 And Further, the shape formed by the X-ray irradiation region on the X-ray detector 13 is formed when X-rays are irradiated to the X-ray detection element arranged at a position not directly below the X-ray tube 12a. 2. Shape 1 is more similar to the shape of the effective focus than shape 2. Therefore, in the third embodiment, the focus size can be calculated with high accuracy.

(Fourth embodiment)
In the first to third embodiments described above, the focus size is calculated using the detection data of the X-rays that have passed through the pinhole 17a. However, the slit size formed in the collimator 12c can have the same function as a pinhole, and the focus size can be calculated using the detection data of the X-rays that have passed through the slit. Therefore, such an embodiment will be described as a fourth embodiment with reference to FIGS. 12A and 12B. In addition, about the structure similar to 1st Embodiment-3rd Embodiment, the same code | symbol may be attached | subjected and description may be abbreviate | omitted.

  FIG. 12A is a diagram for explaining a collimator 12c according to the fourth embodiment. As shown in FIG. 12A, the collimator 12c according to the fourth embodiment is formed with slits 12c_4 and slits 12c_5. The slit 12c_4 and the slit 12c_5 are examples of holes.

  And the calculation part 11a which concerns on 4th Embodiment uses the detection data of the X-ray which passed slit 12c_4, as shown to FIG. 12B, Like 1st Embodiment-3rd Embodiment, The length of one side when the focal point is viewed from the slice direction is calculated. In addition, the calculation unit 11a according to the fourth embodiment uses the X-ray detection data that has passed through the slit 12c_5 to view the focal point from the channel direction as in the first to third embodiments. Calculate the length of one side. In this way, the calculation unit 11a according to the fourth embodiment calculates the focus size.

  According to the X-ray CT apparatus of at least one embodiment described above, the focal spot size can be calculated.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

12a X-ray tube 17 Optical member 18 X-ray detector 11a Calculation unit

Claims (4)

An X-ray tube that emits X-rays;
A member formed with a hole;
An X-ray detector provided on the side opposite to the side where the X-ray tube is positioned with respect to the member, and generating detection data of the X-rays that have passed through the hole;
The size of the portion of the X-ray detector irradiated with the X-ray indicated by the X-ray detection data, the distance between the X-ray tube and the member, and the member and the X-ray detector A calculation unit for calculating a focal spot size of the focal point of the X-ray in the X-ray tube based on a ratio to a distance;
When the focal point size calculated by the calculating unit is within an allowable range of the designated focal point size, the X-ray is irradiated with a control parameter corresponding to the focal point size calculated by the calculating unit. When the tube size is controlled and the focus size calculated by the calculation unit is not within the specified focus size tolerance, the current control parameter is changed, and the X-ray is changed with the new control parameter after the change. An irradiation control unit for controlling the X-ray tube so as to irradiate
When the focus size based on the new control parameter after the change is within an allowable range of the designated focus size, a recording unit that records the new control parameter after the change;
An X-ray CT apparatus comprising: The calculation unit repeatedly calculates the focus size during a CT scan,
Each time the focus size is calculated by the calculation unit , the irradiation control unit, when the calculated focus size is within the specified focus size tolerance range, is controlled with a control parameter corresponding to the calculated focus size. It controls the X-ray tube so as to irradiate the line, X-rays CT apparatus according to 請 Motomeko 1.   Whenever the focus size is calculated by the calculation unit, the irradiation control unit changes the current control parameter when the calculated focus size is not within the specified focus size tolerance range, The X-ray CT apparatus according to claim 2, wherein the X-ray tube is controlled to irradiate X-rays with various control parameters. The focal spot size calculated by the calculation unit, and if not within the allowable range of the designated focal spot size, claims 1 to 3, further comprising a warning unit that performs a warning to the steering author X-ray CT apparatus as described in any one of these .

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