JP2014236848A - X-ray computer tomographic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray computer tomographic apparatus capable of reducing unnecessary exposure.SOLUTION: An X-ray computer tomographic apparatus includes: an X-ray tube for generating an X-ray; an X-ray detection part for detecting an X-ray that is generated by the X-ray tube and transmits an object to be examined; an X-ray diaphragm having a plurality of diaphragm blades for forming the X-ray generated by the X-ray tube according to an irradiation range and an irradiation position designated by a user; a temperature specification part for specifying the temperature in at least one place of the X-ray tube; a position determination part for determining the position of the plurality of diaphragm blades according to the specified temperature so as to maintain the irradiation range and the irradiation position designated by the user; and an X-ray diaphragm control part for moving the plurality of diaphragm blades to the determined plurality of positions respectively according to the specified temperature.

Description

  Embodiments described herein relate generally to an X-ray computed tomography apparatus.

  X-ray CT (Computed Tomography) devices and X-ray diagnostic devices and other radiological image diagnostic devices provide medical information of a subject as an image based on the X-ray intensity emitted from the X-ray tube and transmitted through the subject. It is a device to do. Therefore, the X-ray CT apparatus plays an important role in medical practice such as diagnosis and treatment by a doctor or the like. However, since the X-ray CT apparatus emits X-rays to the subject, unnecessary exposure to the subject becomes a problem. Unnecessary exposure occurs, for example, when X-rays that have passed through the subject are emitted outside the detection range of the X-ray detector. Therefore, an X-ray diaphragm for limiting the irradiation range of X-rays emitted from the X-ray tube is attached to the X-ray tube.

  The X-ray tube includes a cathode provided with a filament that emits thermoelectrons and an anode provided with a target that the electrons collide with. When a high voltage is applied between the anode and the cathode while the cathode filament is heated, electrons emitted from the cathode and accelerated by the high voltage collide with the target. Then, X-rays are emitted from the part (focal point) where a part of the kinetic energy of the electrons collides. However, since most of the kinetic energy of electrons is consumed as heat, the target becomes hot during shooting. The target that has become high temperature is deformed and moved due to thermal expansion or the like, and the focus position changes from the low temperature state shown in FIG. 10A to the high temperature state shown in FIG. 10B. In addition, as a factor that changes the position of the focal point, there are a change in the position of the X-ray and a change in the X-ray tube over time due to the application of a centrifugal force due to rotation during imaging. Then, as shown in FIG. 11, the irradiation range deviates from the irradiation range designated by the user during photographing. Therefore, the X-ray diaphragm is designed taking into consideration that the position of the focal point changes during imaging. Specifically, as shown in FIG. 12, the focus size when designing the X-ray diaphragm is estimated to be larger than the actual focus size. Then, as shown in FIG. 12, when the X-ray diaphragm is arranged to irradiate the same irradiation range, the penumbra when the focal spot size is designed large is designed to have a small focal spot size. It becomes wider than the penumbra of time and unnecessary exposure increases.

  An object is to provide an X-ray computed tomography apparatus capable of reducing unnecessary exposure.

  The X-ray computed tomography apparatus according to the present embodiment includes an X-ray tube that generates X-rays, an X-ray detection unit that detects X-rays generated from the X-ray tube and transmitted through the subject, and the X-ray tube. An X-ray diaphragm having a plurality of diaphragm blades for shaping the generated X-rays according to the irradiation range and irradiation position specified by the user, and a temperature specifying unit for specifying the temperature of at least one of the X-ray tubes, In order to maintain the irradiation range and irradiation position specified by the user, a position determination unit that determines the positions of the plurality of diaphragm blades according to the specified temperature, and according to the specified temperature, And an X-ray diaphragm controller that moves a plurality of diaphragm blades to the determined positions, respectively.

FIG. 1 is a block diagram showing the configuration of the X-ray computed tomography apparatus according to the first embodiment. FIG. 2 is a schematic diagram illustrating an example of an X-ray diaphragm of the X-ray computed tomography apparatus according to the first embodiment. FIG. 3 is an explanatory diagram for explaining an example of a focal position calculation method by the focal position calculation unit of the X-ray computed tomography apparatus according to the first embodiment. FIG. 4 is a diagram illustrating an example of a focal position table stored in the storage unit of the X-ray computed tomography apparatus according to the first embodiment. FIG. 5 is a flowchart showing an example of a focal position collection process of the X-ray computed tomography apparatus according to the first embodiment. FIG. 6 is a flowchart showing an example of automatic adjustment processing of the X-ray computed tomography apparatus according to the first embodiment. FIG. 7 is a block diagram showing a configuration of an X-ray computed tomography apparatus according to the second embodiment. FIG. 8 is a diagram illustrating an example of a blade position table stored in the storage unit of the X-ray computed tomography apparatus according to the second embodiment. FIG. 9 is a flowchart showing an example of automatic adjustment processing of the X-ray computed tomography apparatus according to the second embodiment. FIG. 10 is a diagram showing a change in the position of the focal point. FIG. 11 is a diagram illustrating a change in the irradiation range and the irradiation position according to the change in the focal position. FIG. 12 is a diagram showing an increase in unnecessary exposure due to the size of the focal spot size.

  Hereinafter, X-ray computed tomography apparatuses according to first and second embodiments will be described with reference to the drawings. In the following description, components having substantially the same function and configuration are denoted by the same reference numerals, and redundant description will be given only when necessary.

(First embodiment)
FIG. 1 is a block diagram showing the configuration of the X-ray computed tomography apparatus according to the first embodiment. The X-ray computed tomography apparatus according to the first embodiment includes a CT gantry 10, a high voltage generation unit 11, a preprocessing unit 12, a reconstruction unit 13, an input unit 14, a focal position calculation unit 15, a storage unit 16, and a position determination. Unit 17, imaging control unit 18, mechanism control unit 19, X-ray diaphragm control unit 20, system control unit 21, and display unit 22.

  The CT gantry 10 includes a bed 101, a top plate 102, a rotation support mechanism 103, an X-ray tube 104, an X-ray detection unit 105, a slip ring 106, a temperature specifying unit 107, an X-ray diaphragm 108, a data collection unit 109, and a non-collection unit 109. A contact data transmission unit 110 is included.

  The bed 101 movably supports the top plate 102 on which the subject is placed. The couchtop driving unit (not shown) is driven according to the control of the mechanism control unit 19 described later, whereby the couchtop 102 moves in the direction along the Z axis, and the subject is moved as the couchtop 102 moves. It is moved into a diagnostic opening (not shown).

  The CT gantry 10 accommodates a rotation support mechanism 103. The rotation support mechanism 103 includes a rotation ring and a ring support mechanism that supports the rotation ring so as to be rotatable about the rotation axis Z. An X-ray tube 104, an X-ray detector 105, and a high voltage generator 11 are mounted on the rotating ring. The rotation ring is rotated about the rotation axis Z by driving a rotation drive unit (not shown) according to control of a mechanism control unit 19 described later.

  The X-ray tube 104 emits X-rays from the focal point upon receiving application of tube voltage and supply of tube current from the high voltage generator 11 via the slip ring 106. The high voltage generation unit 11 generates a high voltage for applying a tube voltage between the electrodes of the X-ray tube 104 and a tube current for supplying the X-ray tube 104 according to control by the imaging control unit 18 described later. To do. An X-ray restrictor 108 is attached to the X-ray emission window of the X-ray tube 104.

  The temperature specifying unit 107 specifies the temperature of the X-ray tube 104 according to the control of the system control unit 21 described later. As a method for specifying the temperature of the X-ray tube 104 by the temperature specifying unit 107, there are a method for specifying based on a scanning condition, a method for measuring indirectly, a method for measuring in a non-contact manner, and the like. In the method of specifying based on the scan condition, the temperature specifying unit 107 determines the tube current, the tube voltage, the number of exposures, the exposure time, and the like included in the scan conditions set by the user via the input unit 14 described later. Based on this, the temperature of the X-ray tube 104 is specified. In the method of indirectly measuring, the temperature specifying unit 107 detects the temperature of the cooling oil for cooling the X-ray tube 104, for example, at least one location of the X-ray tube 104 by a temperature sensor or the like. And the temperature of the X-ray tube 104 is specified based on the detected temperature. In the non-contact measurement method, the temperature specifying unit 107 detects light emitted from the X-ray tube 104 with a radiation thermometer or the like. Then, the temperature of the X-ray tube 104 is specified based on the output from a radiation thermometer or the like.

  The temperature specifying unit 107 outputs the specified temperature data to the X-ray diaphragm control unit 20 described later. The temperature data may be other parameters related to the temperature of the X-ray tube 104, for example, a heat capacity value of the X-ray tube 104, an OLP (Over Load Protection) value, or the like. The OLP value is a parameter calculated by dividing the heat capacity of the X-ray tube 104 by the limit heat capacity of the X-ray tube 104.

  The X-ray diaphragm 108 has a plurality of diaphragm blades for reducing unnecessary exposure to the subject. The plurality of diaphragm blades are moved according to the control of an X-ray diaphragm controller 20 described later. A cone having an X-ray divergence angle (fan angle) in the XY plane orthogonal to the rotation axis Z and an X-ray divergence angle (cone angle) in the rotation axis Z direction by moving a plurality of aperture blades. Shape beam-shaped X-rays.

  FIG. 2 is a schematic diagram showing an example of the X-ray diaphragm 108 of the X-ray computed tomography apparatus according to the first embodiment. As shown in FIG. 2, for example, the X-ray diaphragm 108 includes a movable diaphragm blade L and a movable diaphragm blade R for shaping an X-ray cone angle, and a fixed diaphragm blade for shaping an X-ray fan angle. L and a fixed aperture blade R. The movable diaphragm blade L and the movable diaphragm blade R are independently moved under the control of the X-ray diaphragm controller 20 described later, thereby adjusting the cone angle. By adjusting the cone angle, the X-ray irradiation range and irradiation position on the detection surface of the X-ray detection unit 105 are changed. The X-ray diaphragm 108 outputs the position coordinate data of each of the plurality of diaphragm blades to the X-ray diaphragm controller 20 and a calculator described later. The position coordinates of the diaphragm blades are represented by a coordinate system having a predetermined position of the X-ray diaphragm 108 as an origin, for example. FIG. 2 is an example of a typical X-ray diaphragm 108 of the X-ray computed tomography apparatus. Therefore, the structure and operation of the X-ray diaphragm 108 are not limited to the example of FIG. For example, the fixed diaphragm blade for forming the X-ray fan angle may be a movable diaphragm blade. In addition, each of the plurality of diaphragm blades may be moved independently by the X-ray diaphragm controller 20 or may be moved in conjunction with each other.

  The X-ray detection unit 105 is attached at a position and an angle facing the X-ray tube 104 across the rotation axis Z. The X-ray detection unit 105 has a plurality of X-ray detection elements. The plurality of X-ray detection elements detect X-rays that have passed through the subject, and output a current signal corresponding to the intensity of the X-rays to the data collection unit 109. Here, a description will be given assuming that a single X-ray detection element constitutes a single channel. The plurality of channels are two-dimensional in two directions: a direction parallel to the rotation axis Z (slice direction) and an arc direction (channel direction) that is orthogonal to the rotation axis Z and gently curves around the X-ray focal point. Arranged. The X-ray detector having such a two-dimensional detection element arrangement may be configured by arranging a plurality of detection elements arranged in a line in the channel direction in a row in the slice direction. A plurality of modules arranged in an M × N matrix may be arranged.

  A data acquisition unit 109 (Data Acquisition System) converts a current signal into digital data (hereinafter referred to as pure raw data) by each channel of the X-ray detection unit 105. For this purpose, the data collection unit 109 includes, for example, an IV converter for converting a current signal into a voltage signal, an integrator for periodically integrating the voltage signal in synchronization with an X-ray irradiation cycle, An amplifier for amplifying the output signal of the integrator and an analog / digital converter for converting the output signal of the amplifier into a digital signal are provided for each channel. The pure raw data is transmitted to the preprocessing unit 12 via the non-contact data transmission unit 110 using magnetic transmission / reception or optical transmission / reception.

  The preprocessing unit 12 generates raw data by executing preprocessing on pure raw data according to preprocessing conditions designated by the user. Raw data is also called projection data. Preprocessing includes, for example, sensitivity non-uniformity correction processing between channels, X-ray strong absorber, processing for correcting an extremely low signal strength drop or signal drop mainly due to a metal part, and the like. The projection data is stored in the storage unit 16 in association with the channel number, the detection element row number, and the data representing the view angle when the data is collected.

  The reconstruction unit 13 generates CT image data by executing a reconstruction process on the projection data in accordance with a reconstruction condition designated by the user. The reconstruction condition includes a reconstruction method and a reconstruction parameter. The reconstruction method includes, for example, a Feldkamp reconstruction method. The reconstruction parameter includes, for example, a cross-sectional thickness. The pixel value assigned to each pixel constituting the CT image has a CT value corresponding to the X-ray attenuation coefficient related to the substance on the X-ray transmission path.

  The image processing unit generates display image data by performing image processing on CT image data in accordance with image processing conditions specified by the user. The image processing includes gradation conversion for manipulating the contrast of an image displayed on the display unit 22 described later based on the image data.

  The input unit 14 includes input devices such as a mouse and a keyboard, for example. Note that a trackball, a touch panel, a switch, or the like may be used as the input device. The input unit 14 functions as an interface for inputting instruction information from the user to the X-ray computed tomography apparatus according to the first embodiment. The instruction information is, for example, an imaging method and a scanning condition. Examples of the imaging method include scano imaging, helical imaging, and conventional scan imaging, and are selected from these imaging methods according to a user instruction via the input unit 14. The scan condition includes a condition related to photographing and a condition related to image reconstruction. For example, in the case of helical scan imaging, conditions related to imaging are tube voltage, tube current, scan speed, imaging time, number of exposures, helical pitch, imaging slice thickness, irradiation range, irradiation position, and the like. The irradiation position is a predetermined position in the irradiation range, for example, the midpoint of the irradiation range. On the other hand, the conditions related to image reconstruction are an image slice thickness, a reconstruction interval, the number of reconstructed images, and the like.

  The input unit 14 includes an imaging start switch that triggers imaging of the subject and a warm-up start switch that triggers warm-up of the X-ray tube 104. The warm-up of the X-ray tube 104 is an advance preparation for imaging a subject for the purpose of warming the temperature of the X-ray tube 104 to a predetermined target temperature. If a high voltage at the time of imaging is applied to the X-ray tube 104 at a low temperature, the X-ray tube 104 may be broken or the life of the X-ray tube 104 may be shortened. Load is applied. Warming up the X-ray tube 104 has the effect of reducing the load on the X-ray tube 104. In the warm-up, for example, a voltage is applied to the X-ray tube 104 and X-rays are emitted from the X-ray tube 104 while rotating the rotating ring in a state where the subject is not inserted into the diagnostic aperture. Then, by gradually increasing the voltage applied to the X-ray tube 104, the temperature of the X-ray tube 104 is set to the target temperature. Detailed explanation of the warm-up will be described later.

  The focal position calculation unit 15 calculates the focal position of the X-ray tube 104 during the warm-up period. Specifically, the focal position calculation unit 15 determines the focal position of the X-ray tube 104 based on the X-ray detection range by the X-ray detection unit 105 and the positions of the plurality of diaphragm blades during the warm-up period. calculate.

  FIG. 3 is an explanatory diagram for explaining an example of a focal position calculation method by the focal position calculation unit 15 of the X-ray computed tomography apparatus according to the first embodiment. 3 is a cross-sectional view of FIG. 2 viewed from the X-axis direction in FIG. In the warm-up period, the movable diaphragm blades L and R are, for example, at positions where they become the narrowest slits according to the control of the X-ray diaphragm controller 20 in order to minimize the amount of X-ray scattering to the surroundings. It shall be fixed. Therefore, if the X-ray detection range changes during the warm-up period, it is caused by the movement of the focal position.

The focal position calculation unit 15 specifies the X-ray focal position P ₀ based on a plurality of parameters. The plurality of parameters, for example, the position P _L of the movable aperture blades _L, the position P _R0 and the position P _L0 in the irradiation range to a specific position P _R of the movable aperture blades _R, the irradiation range and an irradiation _position, and the movable This is the distance R from the diaphragm blade to the X-ray detection unit 105. Position P _R0 and the position P _L0 in the irradiation range, for example, correspond to the positions of both ends along the Z-axis of the irradiation range. Position P _R position P _L and the movable aperture blades R of the movable diaphragm blade L, as described above, on the basis of an output from the X-ray diaphragm 108 is identified in advance. Position _{P R0} and the position _{P L0} in the irradiation range is specified based on the detection range of the X-ray of the X-ray detection unit 105. The X-ray detection range is specified by the channel number of each of a plurality of X-ray detection elements that output current signals according to the detection of X-rays. The distance R is a known value at the time of designing the X-ray computed tomography apparatus according to the first embodiment, and is stored in the storage unit 16 in advance.

The focal position calculation unit 15 calculates the X-ray focal position P ₀ by substituting the plurality of parameters described above into a predetermined function. The calculated focal position data is stored in the storage unit 16 to be described later together with the corresponding temperature. The focal position calculation unit 15 sets the focal position corresponding to the temperature obtained during the warm-up period as the focal position corresponding to the temperature that was not obtained during the warm-up period, that is, the temperature higher than the target temperature of the warm-up period. Estimate based on Specifically, the focal position calculation unit 15 extrapolates data of a plurality of focal positions corresponding to a plurality of temperatures until the X-ray tube 104 reaches a target temperature from the temperature at the start of warm-up. By doing so, data of a plurality of focal positions corresponding to a plurality of temperatures from the target temperature to the limit temperature is estimated. As an extrapolation method, for example, linear extrapolation, polynomial extrapolation, or the like is used, and can be appropriately changed according to a user instruction.

  The focal position calculation unit 15 performs the above-described calculation of the focal position every time there is a change in the X-ray detection range by the X-ray detection unit 105. The focal position calculation unit 15 determines the above-described focal position every time the timing specified by the user in advance, for example, the temperature of the X-ray tube 104 becomes one of the plurality of temperatures specified by the user. Calculations may be performed. Whether the calculation of the focal position is triggered by a change in the X-ray detection range by the X-ray detection unit 105 or a timing designated in advance by the user is selected according to a user instruction. The calculated focal position data is stored in the storage unit 16 (to be described later) together with the temperature specified by the temperature specifying unit 107 under the control of the system control unit 21.

  The storage unit 16 is a semiconductor storage device such as a flash SSD (Solid State Disk) that is a semiconductor storage element, an HDD (Hard Disk Drive), or the like. The storage unit 16 stores the raw data associated with the channel number, the detection element row number, and the data indicating the view angle when the data is collected. The storage unit 16 may store projection data, CT image data, and display image data. Further, the storage unit 16 stores a plurality of focal position data together with a plurality of corresponding temperature data. The storage unit 16 may store a correspondence table in which a plurality of focal positions correspond to a plurality of temperatures (hereinafter referred to as a focal position table). The focal position table is generated by a focal position collection process described later. However, the focal position table may be stored in advance in the storage unit 16 based on the design value when the X-ray computed tomography apparatus according to the first embodiment is designed. The storage unit 16 may accumulate and store a plurality of focal position data, a focal position table, and the like stored together with a plurality of temperature data stored in the past.

  FIG. 4 is a diagram illustrating an example of a focal position table stored in the storage unit 16 of the X-ray computed tomography apparatus according to the first embodiment. As shown in FIG. 4, the focal position table is a correspondence table in which a plurality of focal positions are associated with a plurality of temperatures. According to the focal position table shown in FIG. 4, for example, the focal position when the temperature of the X-ray tube 104 is 20 degrees is specified as (x, y, z) = (x1, y1, z1).

  The position determining unit 17 determines the positions of the plurality of diaphragm blades in accordance with the temperature specified by the temperature specifying unit 107 during the imaging period of the subject. Then, the position determination unit 17 outputs the determined position data of the plurality of aperture blades to the X-ray aperture controller control unit 20. The position determining unit 17 includes a focal position specifying unit 171 and a blade position calculating unit 172.

  The focal position specifying unit 171 specifies the focal position of the X-ray tube 104 according to the temperature of the X-ray tube 104. Specifically, the focal position specifying unit 171 specifies the focal position according to the temperature specified by the temperature specifying unit 107 by referring to the storage unit 16. The focal position specifying unit 171 outputs the specified focal position data to the blade position calculating unit 172.

  The blade position calculation unit 172 calculates the position of each of the plurality of diaphragm blades according to the temperature of the X-ray tube 104. Specifically, the blade position calculation unit 172 calculates the position of each of the plurality of aperture blades based on the focus position data from the focus position specifying unit 171 and the irradiation range and irradiation position specified by the user. .

  The imaging control unit 18 sends a control signal corresponding to a scanning condition input by the user via the input unit 14, such as a tube voltage, a tube current, a scanning speed, and an imaging time, to the high voltage generation unit 11 and the X-ray detection unit. And 105.

  The mechanism control unit 19 sends a control signal corresponding to the scan condition input by the user via the input unit 14, for example, the scan speed, the imaging time, the helical pitch, and the imaging slice thickness to the rotation driving unit and the bed 101 driving unit. Output.

  The X-ray diaphragm control unit 20 controls the X-ray diaphragm 108 based on the scanning conditions input by the user via the input unit 14, for example, the irradiation range and irradiation position. Specifically, the X-ray diaphragm controller 20 moves each of the plurality of diaphragm blades so that the X-rays emitted from the X-ray tube 104 are irradiated to the irradiation range and irradiation position input by the user. The control signal for making it output is output to the X-ray restrictor 108. In addition, the X-ray diaphragm controller 20 controls the X-ray diaphragm 108 based on the data of the positions of the plurality of diaphragm blades determined by the position determination unit 17. Specifically, the X-ray diaphragm control unit 20 outputs a control signal for moving each of the plurality of diaphragm blades to the X-ray diaphragm 108 in order to maintain the irradiation range and irradiation position input by the user. To do.

  The system control unit 21 includes a CPU (Central Processing Unit), a memory circuit, and the like. The system control unit 21 temporarily stores information input to the X-ray computed tomography apparatus according to the first embodiment via the input unit 14 in a memory circuit. The system control unit 21 controls each unit of the X-ray computed tomography apparatus according to the first embodiment based on the input information.

  The display unit 22 displays the CT image reconstructed by the reconstruction unit 13 according to the user instruction.

  The X-ray computed tomography apparatus according to the first embodiment has a focus position collection function and an automatic adjustment function. Processing related to the focal position collection function (hereinafter referred to as focal position collection processing) is executed during the warm-up period of the X-ray tube 104 in accordance with a user instruction. On the other hand, the automatic adjustment function is executed during the imaging period of the subject. Hereinafter, the warm-up period and the imaging period of the subject will be described separately.

(Focus position collection function)
The focal position collection function is a function in which the X-ray computed tomography apparatus according to the first embodiment collects focal position data corresponding to the X-ray tube 104 during the warm-up period of the conventional X-ray tube 104 described above. is there. The focal position collection process will be described with reference to FIG. Note that the user can also select whether or not to execute the focus position collection process via the input unit 14.

  FIG. 5 is a flowchart showing an example of a focal position collection process of the X-ray computed tomography apparatus according to the first embodiment.

(Step S11)
Warming up is started in accordance with a user instruction via the input unit 14. In accordance with the control of the X-ray diaphragm control unit 20, the plurality of diaphragm blades are moved so that the slit becomes the narrowest.

(Step S12)
The rotating ring is rotated at a predetermined speed by the mechanism control unit 19. Under the control of the imaging control unit 18, the high voltage generation unit 11 starts applying a voltage and supplying a current to the X-ray tube 104. The temperature specifying unit 107 starts specifying the temperature of the X-ray tube 104.

(Step S13)
X-rays emitted from the X-ray tube 104 are detected by the X-ray detection unit 105. Immediately after the start of warm-up or when the X-ray detection range of the X-ray detection unit 105 changes, the process proceeds to step S14.

(Step S14)
The focal position calculation unit 15 calculates the focal position of the X-ray tube 104.

(Step S15)
Under the control of the system control unit 21, the focus position data calculated by the focus position calculation unit 15 is stored in the storage unit 16 together with the temperature data specified by the temperature specifying unit 107.

(Step S16)
Until the temperature of the X-ray tube 104 reaches the target temperature, the processing from step S13 to step S15 is repeatedly executed. When the temperature of the X-ray tube 104 reaches the target temperature, the process proceeds to step S18.

(Step S17)
Warm-up is completed, and each part of the X-ray computed tomography apparatus according to the first embodiment enters a standby state.

(Automatic adjustment function)
The automatic adjustment function allows the X-ray computed tomography apparatus according to the first embodiment to maintain the irradiation range and irradiation position designated by the user according to the temperature of the X-ray tube 104 during the imaging period of the subject. The function of automatically moving the movable diaphragm blades. Processing related to the automatic adjustment function (hereinafter, automatic adjustment processing) will be described with reference to FIG.

  FIG. 6 is a flowchart showing an example of automatic adjustment processing of the X-ray computed tomography apparatus according to the first embodiment. Note that the temperature specifying unit 107 specifies the temperature of the X-ray tube 104 continuously from the warm-up period to the start of imaging of the subject.

(Step S21)
Scan conditions are set according to a user instruction via the input unit 14.

(Step S22)
Imaging of the subject is started in accordance with a user instruction via the input unit 14. Under the control of the imaging control unit 18, the high voltage generation unit 11 starts applying a high voltage and supplying a current to the X-ray tube 104 according to the scan condition. Further, the mechanism control unit 19 rotates the rotating ring at a speed according to the scanning conditions, and the top plate 102 is moved to the diagnosis opening at a speed according to the scanning conditions.

(Step S23)
The focus position specifying unit 171 specifies the focus position corresponding to the temperature specified by the temperature specifying unit 107. Based on the focal position and the irradiation range and irradiation position designated by the user, the blade position calculation unit 172 determines the position of each of the plurality of aperture blades. Then, in order to irradiate the irradiation range and irradiation position specified by the user with X-rays or to maintain the irradiation range and irradiation position specified by the user, the X-ray diaphragm controller 20 determines The plurality of aperture blades are respectively moved to the positions.

(Step S24)
Projection data regarding the subject is collected by each unit of the X-ray computed tomography apparatus according to the first embodiment.

(Step S25)
The temperature of the X-ray tube 104 specified by the temperature specifying unit 107 is referred to by the storage unit 16 by the X-ray diaphragm control unit 20. If the identified temperature of the X-ray tube 104 is stored in the storage unit 16, the process proceeds to step S23. If the identified temperature of the X-ray tube 104 is not stored in the storage unit 16, the process proceeds to step S26.

(Step S26)
Steps S24 to S26 are repeatedly executed until imaging of the subject is completed.

(Second Embodiment)
In 1st Embodiment, the memory | storage part 16 memorize | stores the data of several focus positions with the data of several temperature corresponding respectively. During the imaging period of the subject, the position determining unit 17 determines the positions of the plurality of aperture blades based on the focal position corresponding to the temperature specified by the temperature specifying unit 107 and the irradiation range and irradiation position specified by the user. It is determined. On the other hand, in 2nd Embodiment, the memory | storage part 16 memorize | stores the correspondence table | surface (henceforth a blade position table | surface) provided with two or more correspondence of the position of each of several aperture blades with respect to the temperature of the X-ray tube 104. FIG. During the imaging period of the subject, the position determination unit 17 refers to the blade position table stored in the storage unit 16 to determine the positions of the plurality of diaphragm blades according to the temperature specified by the temperature specifying unit 107. can do. Hereinafter, differences from the first embodiment will be described.

  FIG. 7 is a block diagram showing a configuration of an X-ray computed tomography apparatus according to the second embodiment.

  The blade position calculation unit 172 calculates the position of each of the plurality of diaphragm blades according to the temperature of the X-ray tube 104. Specifically, the blade position calculation unit 172 calculates the position of each of the plurality of diaphragm blades based on the focal position data stored in the storage unit 16 and the irradiation range and irradiation position specified by the user. To do. The blade position calculation unit 172 outputs the position data of each of the plurality of aperture blades to the correspondence table generation unit 23.

  The correspondence table generator 23 generates a blade position table having a plurality of correspondences of the positions of the plurality of diaphragm blades calculated by the blade position calculator 172 with respect to the temperature of the X-ray tube 104. The correspondence table generator 23 generates a blade position table before imaging the subject.

  The storage unit 16 stores the blade position table data generated by the correspondence table generation unit 23. Note that the storage unit 16 may accumulate and store data of the blade position table generated in the past.

  FIG. 8 is a diagram illustrating an example of a blade position table stored in the storage unit 16 of the X-ray computed tomography apparatus according to the second embodiment. The blade position table shown in FIG. 8 is generated based on the data of the focal position table shown in FIG. 4 and the irradiation range and irradiation position designated by the user. According to the blade position table shown in FIG. 8, for example, the position of the movable diaphragm blade L when the temperature of the X-ray tube 104 is 20 degrees is (x, y, z) = (xL1, yL1, zL1) and movable. The position of the diaphragm blade R is specified as (x, y, z) = (xR1, yR1, zR1).

  The position determination unit 17 determines the positions of the plurality of diaphragm blades according to the temperature specified by the temperature specifying unit 107 by referring to the blade position table during the imaging period of the subject.

  FIG. 9 is a flowchart showing an example of automatic adjustment processing of the X-ray computed tomography apparatus according to the second embodiment. Note that the temperature specifying unit 107 specifies the temperature of the X-ray tube 104 continuously from the warm-up period to the start of imaging of the subject.

(Step S31)
Scan conditions are set according to a user instruction via the input unit 14.

(Step S32)
The correspondence table generator 23 generates a blade position table.

(Step S33)
Imaging of the subject is started in accordance with a user instruction via the input unit 14. Under the control of the imaging control unit 18, the high voltage generation unit 11 starts applying a high voltage and supplying a current to the X-ray tube 104 according to the scan condition. Further, the mechanism control unit 19 rotates the rotating ring at a speed according to the scanning conditions, and the top plate 102 is moved to the diagnosis opening at a speed according to the scanning conditions.

(Step S34)
The position determination unit 17 refers to the blade position table and determines the positions of a plurality of diaphragm blades corresponding to the temperature specified by the temperature specifying unit 107. Then, in order to irradiate the irradiation range and irradiation position specified by the user with X-rays or to maintain the irradiation range and irradiation position specified by the user, the X-ray diaphragm controller 20 determines The plurality of aperture blades are respectively moved to the positions.

(Step S35)
Projection data relating to the subject is collected by each unit of the X-ray computed tomography apparatus according to the second embodiment.

(Step S36)
The temperature of the X-ray tube 104 specified by the temperature specifying unit 107 is referred to by the X-ray diaphragm control unit 20 in the blade position table. If the identified temperature of the X-ray tube 104 is registered in the blade position table, the process proceeds to step S34. If the identified temperature of the X-ray tube 104 is not registered in the blade position table, the process proceeds to step S37.

(Step S37)
Steps S35 to S36 are repeatedly executed until imaging of the subject is completed.

  According to the X-ray computed tomography apparatus according to the first and second embodiments described above, the following effects can be obtained.

  The X-ray computed tomography apparatus according to the first and second embodiments can collect data on the focal position of the X-ray tube 104 corresponding to the temperature of the X-ray tube 104. The collected data of the plurality of focal positions are stored together with the corresponding temperatures. In the imaging period of the subject, each of the plurality of aperture blades for maintaining the irradiation range and irradiation position specified by the user according to the temperature of the X-ray tube 104 by referring to the storage unit 16. The position can be determined. In other words, even when the focal position changes as the temperature of the X-ray tube 104 changes, each of the plurality of diaphragm blades can be moved in accordance with the change in the focal position. It is not necessary to estimate the focal spot size when designing the line restrictor 108 to be larger than the actual focal spot size in order to consider the temperature change in advance.

  In addition, the X-ray computed tomography apparatuses according to the first and second embodiments respectively correspond to a plurality of collected focal position data during the warm-up period of the X-ray tube 104 before imaging the subject. It can be stored with multiple temperature data. Therefore, the X-ray computed tomography apparatus according to the first and second embodiments is not limited to the change in the focal position due to the temperature change of the X-ray tube 104 during the imaging period of the subject, but the change in the focal position due to other factors. For example, in consideration of the focal position that changes every time photographing is performed due to the centrifugal force caused by the rotation during photographing being applied to the X-ray tube 104 or the time-dependent change of the X-ray tube 104, each of the plurality of diaphragm blades. The position can be determined. Therefore, the X-ray computed tomography apparatus according to the first and second embodiments can reduce unnecessary exposure.

  In addition, the X-ray computed tomography apparatus according to the first and second embodiments can accumulate the data of the focal position table and the blade position table generated in the past. Therefore, even when the X-ray computed tomography apparatus according to the first and second embodiments is used in an emergency, an effect of reducing unnecessary exposure can be obtained.

  Although the embodiment of the present invention has been described, this embodiment is presented as an example and is not intended to limit the scope of the invention. This embodiment 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 modifications thereof are included in the scope and spirit of the invention, and are also included in the invention described in the claims and equivalents thereof.

DESCRIPTION OF SYMBOLS 10 ... CT gantry, 11 ... High voltage generation part, 12 ... Pre-processing part, 13 ... Reconstruction part, 14 ... Input part, 15 ... Focus position calculation part, 16 ... Memory | storage part, 17 ... Position determination part, 18 ... Imaging | photography Control unit, 19 ... Mechanism control unit, 20 ... X-ray diaphragm control unit, 21 ... System control unit, 22 ... Display unit, 23 ... Correspondence table generation unit, 101 ... Bed, 102 ... Top plate, 103 ... Rotation support mechanism , 104 ... X-ray tube, 105 ... X-ray detection unit, 106 ... slip ring, 107 ... temperature specifying unit, 108 ... X-ray restrictor, 109 ... data collection unit, 110 ... non-contact data transmission unit

Claims (8)

An X-ray tube that generates X-rays;
An X-ray detector that detects X-rays generated from the X-ray tube and transmitted through the subject;
An X-ray diaphragm having a plurality of diaphragm blades for shaping the X-rays generated by the X-ray tube according to the irradiation range and irradiation position specified by the user;
A temperature specifying unit for specifying the temperature of at least one location of the X-ray tube;
In order to maintain the irradiation range and irradiation position designated by the user, a position determination unit that determines the positions of the plurality of diaphragm blades according to the specified temperature;
An X-ray diaphragm controller that moves the plurality of diaphragm blades to the determined plurality of positions according to the specified temperature;
An X-ray computed tomography apparatus comprising: The position determination unit
A focal position identifying unit that identifies the focal position of the X-ray tube corresponding to the identified temperature;
A blade position calculator that calculates the positions of the plurality of diaphragm blades corresponding to the specified temperature based on the specified focal position and the irradiation range and irradiation position specified by the user; ,
The X-ray diaphragm control unit moves the plurality of diaphragm blades to the calculated positions of the plurality of diaphragm blades according to the specified temperature,
The X-ray computed tomography apparatus according to claim 1. In the warm-up period for warming the X-ray tube to a predetermined target temperature, a plurality of points specified based on the X-ray detection range of the X-ray detection unit and the positions of the plurality of diaphragm blades in the warm-up period A storage unit that stores the focal position of each together with a plurality of corresponding temperatures,
The focal position specifying unit specifies the focal position of the X-ray tube corresponding to the specified temperature by referring to the storage unit;
The X-ray computed tomography apparatus according to claim 2. The X-ray tube further includes a storage unit that stores data of a correspondence table in which a plurality of focal positions correspond to a plurality of temperatures,
The focal position identifying unit identifies the focal position of the X-ray tube corresponding to the identified temperature by referring to the identified temperature in the correspondence table;
The X-ray computed tomography apparatus according to claim 2. A storage unit for storing data of another correspondence table including a plurality of correspondences of the positions of the plurality of diaphragm blades with respect to the temperature of the X-ray tube;
The position determination unit determines the position of each of the plurality of diaphragm blades corresponding to the specified temperature by referring to the other correspondence table according to the specified temperature;
The X-ray computed tomography apparatus according to claim 1. A correspondence table generating unit for generating the other correspondence table based on the focal position of the X-ray tube corresponding to the temperature of the X-ray tube and the irradiation range and irradiation position designated by the user; ,
The X-ray computed tomography apparatus according to claim 5. The focal position of the X-ray tube corresponding to the temperature of the X-ray tube is determined based on the X-ray detection range of the X-ray detection unit and the warm in the warm-up period for warming the X-ray tube to a predetermined target temperature. Being specified based on the position of the plurality of diaphragm blades in the up period,
The X-ray computed tomography apparatus according to claim 6. The X-ray diaphragm control unit individually moves a plurality of diaphragm blades of the X-ray diaphragm according to the specified temperature;
The X-ray computed tomography apparatus according to claim 1.

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