JP7139185B2 - X-ray computed tomography device - Google Patents

Description

An embodiment of the present invention relates to an X-ray computed tomography apparatus.

There is an X-ray computed tomography apparatus equipped with an X-ray high voltage device capable of varying CT imaging parameters such as tube voltage. In this case, it is necessary to collect correction data for calibration or the like for each tube voltage value. Correction data is collected by rotating the X-ray tube and X-ray detector once for each tube voltage value. Therefore, as the types and number of stages of variable CT imaging parameters increase, the correction data collection time increases.

JP 2013-24784 A JP 2007-125129 A

The problem to be solved by the present invention is to collect correction data with high efficiency.

An X-ray computed tomography apparatus according to an embodiment includes an X-ray tube that generates X-rays, an X-ray detector that detects the X-rays generated from the X-ray tube, the X-ray tube and the X-ray detector. and a pedestal for rotatably supporting an apparatus around a rotation axis; and when the X-ray tube and the X-ray detector rotate, the X-ray tube generates X-rays, and a predetermined correction data collection target is generated. a control circuit for changing CT imaging parameters in one rotation; and correction data relating to the predetermined CT imaging parameters through the X-ray detector during rotation of the X-ray tube and the X-ray detector. a collection circuit for collecting the

FIG. 1 is a diagram showing the configuration of an X-ray computed tomography apparatus according to this embodiment. FIG. 2 is a diagram showing the concept of the correction data collection scan according to this embodiment. 3 is a diagram showing an example of a parameter table used by the processing circuit in the imaging planning function of FIG. 1. FIG. FIG. 4 is a diagram simply showing a CT imaging parameter acquisition sequence for a correction data acquisition scan according to the first embodiment. FIG. 5 is a diagram showing another acquisition sequence of CT imaging parameters related to the correction data acquisition scan according to the first embodiment. FIG. 6 is a diagram showing another acquisition sequence of CT imaging parameters related to the correction data acquisition scan according to the first embodiment. FIG. 7 is a diagram showing another acquisition sequence of CT imaging parameters related to the correction data acquisition scan according to the first embodiment. FIG. 8 is a diagram showing a CT imaging parameter acquisition sequence for a correction data acquisition scan according to the second embodiment. FIG. 9 is a diagram showing a CT imaging parameter acquisition sequence for a correction data acquisition scan according to the third embodiment. FIG. 10 is a diagram showing a CT imaging parameter acquisition sequence for another correction data acquisition scan according to the third embodiment. FIG. 11 is a diagram showing a CT imaging parameter acquisition sequence for a correction data acquisition scan according to the fourth embodiment. FIG. 12 is a diagram illustrating a correction data collection sequence according to the fifth embodiment. FIG. 13 is a diagram showing another acquisition sequence according to the fifth embodiment. FIG. 14 is a conceptual diagram of a standard method for collecting correction data.

An X-ray computed tomography apparatus according to this embodiment will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an X-ray computed tomography apparatus 1 according to this embodiment. As shown in FIG. 1, an X-ray computed tomography apparatus 1 according to this embodiment has a pedestal 10 and a console 100 . For example, the gantry 10 is installed in a CT examination room, and the console 100 is installed in a control room adjacent to the CT examination room. The gantry 10 and the console 100 are connected so as to be able to communicate with each other. The gantry 10 mounts an imaging mechanism for X-ray CT imaging. A console 100 is a computer that controls the gantry 10 .

As shown in FIG. 1, the gantry 10 has a substantially cylindrical rotating frame 11 with an opening. The rotating frame 11 is also called a rotating section. As shown in FIG. 1, an X-ray tube 13 and an X-ray detector 15 are attached to the rotating frame 11 so as to face each other across an opening. The rotating frame 11 is an annular metal frame made of metal such as aluminum. The mount 10 has a main frame made of metal such as aluminum. The mainframe is also called a fixed part. The rotating frame 11 is rotatably supported by the main frame.

The X-ray tube 13 generates X-rays. The X-ray tube 13 includes a vacuum tube holding a cathode that generates thermoelectrons, an anode that receives thermoelectrons flying from the cathode and generates X-rays, and a grid electrode provided between the cathode and the anode. . The X-ray tube 13 is connected to an X-ray high voltage device 17 via a high voltage cable. A tube voltage is applied between the cathode and the anode by the X-ray high voltage device 17 . Thermal electrons fly from the cathode to the anode by applying a tube voltage. A tube current flows due to thermal electrons flying from the cathode to the anode. The part of the anode that the thermoelectrons impinge on is called the focal point. A bias voltage is applied between the grid electrodes by an X-ray high voltage device 17 . Thermoelectrons flying from the cathode to the anode are deflected by applying a bias voltage. That is, by adjusting the bias voltage, the tube current, focal size and focal position are adjusted.

The X-ray high-voltage device 17 can be applied to any type of X-ray high-voltage device, such as a transformer type X-ray high-voltage device, a constant voltage type X-ray high-voltage device, a capacitor type X-ray high-voltage device, an inverter type X-ray high-voltage device, or the like. . The X-ray high voltage device 17 is attached to the rotating frame 11, for example. The X-ray high voltage device 17 adjusts X-ray parameters such as tube voltage, tube current, X-ray focal size and X-ray focal position under the control of the gantry control circuit 33 .

A collimator 21 is attached to the X-ray tube 13 . A collimator 21 shapes X-rays generated from the X-ray tube 13 . Specifically, the collimator 21 carries an X-ray shielding plate with a variable slit aperture. The collimator 21 adjusts the slit opening width by receiving power from the gantry driving device 23 and moving the X-ray shielding plate.

As shown in FIG. 1, the rotating frame 11 receives power from the gantry driving device 23 and rotates around the rotation axis Z at a constant angular velocity. In addition, the rotating frame 11 receives power from the gantry driving device 23 and tilts about a tilt axis that is horizontally perpendicular to the rotation axis Z. As shown in FIG. The gantry drive device 23 is housed in the gantry 10, for example.

The gantry driving device 23 receives a drive signal from the gantry control circuit 33 and generates power for driving the collimator 21 for adjusting the slit opening width. Further, the gantry drive device 23 receives a drive signal from the gantry control circuit 33 and generates power for rotating or tilting the rotating frame 11 . Any motor such as a direct drive motor or a servo motor is used as the gantry drive device 23 .

A FOV is set in the opening of the rotating frame 11 . A top supported by a bed 25 is inserted into the opening of the rotating frame 11 . A subject is placed on the top plate. The bed 25 movably supports the top board. A bed driving device 27 is accommodated in the bed 25 . The bed driving device 27 receives a drive signal from the gantry control circuit 33 and generates power for moving the tabletop forward/backward, up/down, and left/right. The bed 25 positions the tabletop so that the imaging region of the subject is included in the FOV.

X-ray detector 15 detects X-rays generated from X-ray tube 13 . Specifically, the X-ray detector 15 has a plurality of detection elements arranged on a two-dimensional curved surface. Each sensing element has a scintillator and a photosensor. A scintillator is formed by a material that converts X-rays into photons. The scintillator converts incident X-rays into light with a photon amount corresponding to the amount of incident X-rays. A photosensor is a circuit element that amplifies light emitted from a scintillator and converts it into an electrical signal. As the optical sensor, for example, a photomultiplier tube, a photodiode, or the like is used. The detection element may be of an indirect conversion type that detects X-rays after converting them into photons as described above, or may be of a direct conversion type that directly converts X-rays into electrical signals.

A data acquisition circuit 19 is connected to the X-ray detector 15 . The data acquisition circuit 19 reads from the X-ray detector 15 an electric signal corresponding to the dose of X-rays detected by the X-ray detector 15, and the read electric signal has a variable amplification factor (hereinafter referred to as DAS gain). , and integrate the electrical signal over the view period to acquire raw data having a digital value corresponding to the x-ray dose over the view period. DAS gain is adjusted by the gantry control circuit 33 . The data collection circuit 19 is implemented by, for example, an ASIC (Application Specific Integrated Circuit) equipped with circuit elements capable of generating raw data. In this embodiment, raw data collected for calibration will be referred to as correction data. The data acquisition circuit 19 has a switch for changing the bundling unit of the readout channels of the detection elements. This bundling unit is called a DAS bundling unit. The switch is provided, for example, in front of an integration circuit that generates an integration signal or in front of an A/D converter that converts an integration signal into raw data. The data collection circuit 19 controls the switch according to the instruction from the gantry control circuit 33 to switch the DAS bundling unit.

As shown in FIG. 1, the gantry control circuit 33 controls the X-ray high-voltage device 17, the data acquisition circuit 19, and the gantry drive device 23 to perform X-ray CT imaging according to the imaging conditions from the processing circuit 101 of the console 100. and bed drive 27 synchronously. The gantry control circuit 33 according to the present embodiment executes X-ray CT imaging (hereinafter referred to as correction data acquisition scan) for collecting correction data. As hardware resources, the gantry control circuit 33 includes a processing unit (processor) such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit) and a storage device (such as a ROM (Read Only Memory) or a RAM (Random Access Memory)). memory). In addition, the gantry control circuit 33 is an ASIC, a field programmable gate array (FPGA), another complex programmable logic device (CPLD), a simple programmable logic device (Simple Programmable Logic Device). : SPLD).

As shown in FIG. 1, console 100 has processing circuitry 101 , display circuitry 103 , input circuitry 105 and memory circuitry 107 . Data communication between the processing circuit 101, the display circuit 103, the input circuit 105 and the memory circuit 107 is performed via a bus.

The processing circuit 101 has, as hardware resources, a processor such as a CPU, an MPU, or a GPU (Graphics Processing Unit), and a memory such as a ROM or a RAM. The processing circuit 101 implements a preprocessing function 111, a reconstruction function 113, an image processing function 115, an imaging planning function 117, and a system control function 119 by executing various programs. Note that the preprocessing function 111, the reconstruction function 113, the image processing function 115, the imaging planning function 117, and the system control function 119 may be implemented by the processing circuit 101 of one substrate, or may be implemented by the processing circuits 101 of a plurality of substrates. may be implemented in a distributed manner.

In the preprocessing function 111 , the processing circuit 101 performs preprocessing such as logarithmic conversion on the raw data transmitted from the gantry 10 . Raw data after preprocessing is also called projection data. Also, the processing circuit 101 performs calibration based on the correction data transmitted from the gantry 10 .

In the reconstruction function 113, the processing circuitry 101 generates a CT image representing the spatial distribution of CT values for the subject based on the preprocessed raw data. An existing image reconstruction algorithm such as the FBP (filtered back projection) method or the iterative reconstruction method may be used as the image reconstruction algorithm.

In the image processing function 115 , the processing circuit 101 performs various image processing on the CT image reconstructed by the reconstruction function 113 . For example, the processing circuit 101 performs three-dimensional image processing such as volume rendering, surface volume rendering, pixel value projection processing, MPR (Multi-Planer Reconstruction) processing, and CPR (Curved MPR) processing on the CT image to display the image. to generate

In the imaging planning function 117 , the processing circuit 101 draws up an imaging plan for the correction data acquisition scan automatically or in accordance with a user's instruction via the input circuit 105 .

In the system control function 119, the processing circuit 101 comprehensively controls the X-ray computed tomography apparatus 1 according to this embodiment. Specifically, the processing circuit 101 reads the control program stored in the storage circuit 107, develops it on the memory, and controls each part of the X-ray computed tomography apparatus 1 according to the developed control program.

A display circuit 103 displays various data such as a planning screen for a correction data acquisition scan and a CT image. As the display circuit 103, for example, a CRT display, a liquid crystal display, an organic EL display, an LED display, a plasma display, or any other display known in the art can be used as appropriate.

The input circuit 105 inputs various commands from the user. Specifically, the input circuit 105 has an input device and an input interface. The input device receives various commands from the user. A keyboard, a mouse, a trackball, a joystick, various switches, and the like can be used as input devices. The input interface supplies output signals from the input device to the processing circuit 101 via the bus.

The storage circuit 107 is a storage device such as an HDD, an SSD, or an integrated circuit storage device that stores various information. Also, the storage circuit 107 may be a drive device or the like that reads and writes various information from/to a portable storage medium such as a CD-ROM drive, a DVD drive, and a flash memory. For example, the storage circuit 107 stores control programs and the like related to the correction data collection scan and the like according to this embodiment.

The operation of the X-ray computed tomography apparatus 1 according to this embodiment will be described in detail below.

As described above, the gantry control circuit 33 according to this embodiment executes a correction data collection scan to collect correction data. In a correction data acquisition scan, correction data is collected by CT scanning a phantom based on a reference material such as air (ie, no phantom and no subject) or water. The correction data is used for calibration of CT value conversion coefficients, calibration of positional deviations of the X-ray tube 13 and the X-ray detector 15, and the like. Correction data is collected for each possible value of the CT imaging parameter. There are many types of CT imaging parameters according to this embodiment, such as focus size, focus position, tube voltage, tube current, DAS gain, slit aperture width, and DAS bundling unit. The output or sensitivity of the X-ray detector 15 depends on the angle around the rotation axis Z (hereinafter referred to as the rotation angle). must be collected. Therefore, there is a need to collect correction data efficiently.

FIG. 14 is a conceptual diagram of a standard method for collecting correction data. Note that the CT imaging parameter in FIG. 14 is the focal size. As shown in FIG. 14, correction data for a small-sized focus (hereinafter referred to as a small focus), correction data for a medium-sized focus (hereinafter referred to as a medium focus), and large-sized focus (hereinafter referred to as a large focus) ) shall be collected. In a standard method, first, the focus size is set to a small focus, the X-ray tube 13 and the X-ray detector 15 are rotated once, and correction data are collected, and then the focus size is set to a medium focus. While rotating the X-ray tube 13 and the X-ray detector 15 once, correction data are collected. to collect. As described above, the X-ray tube 13 and the X-ray detector 15 need to be rotated for each focal size, so the X-ray tube 13 and the X-ray detector 15 must be rotated by the number of stages corresponding to the focal size. Therefore, as the types and number of stages of CT imaging parameters for which correction data are to be collected increase, the time and effort required to collect correction data increases.

FIG. 2 is a diagram showing the concept of the correction data collection scan according to this embodiment. In FIG. 2 as well, the CT imaging parameter is assumed to be the focal size for comparison with FIG. As shown in FIG. 2, in the correction data acquisition scan according to the present embodiment, correction data is acquired while the focus size is switched in order between small focus, medium focus, and large focus in each predetermined unit angle range. In this way, since the focal spot size is switched between the small focal point, the intermediate focal point and the large focal point in each predetermined unit angle range, the small focal point, the intermediate focal point and the large focal point are detected while the X-ray tube 13 and the X-ray detector 15 are rotated once. Correction data can be collected for The predetermined unit angle range is an angle range in which a change in the output or sensitivity of the X-ray detector 15 with respect to the rotation angle can be tolerated, in other words, an angle range in which the rotation angle dependency of the output or sensitivity of the X-ray detector 15 can be ignored. stipulated in Hereinafter, this predetermined angle range will be referred to as a unit allowable angle range.

The gantry control circuit 33 according to the present embodiment controls the X-ray high-voltage device 17 to rotate the X-ray tube 13 and the X-ray detector 15 (that is, when the rotating frame 11 rotates). X-rays are generated from 13, and at least one of the X-ray high voltage device 17 and the data acquisition circuit 19 is controlled to change predetermined CT imaging parameters for correction data acquisition within one rotation. More specifically, the gantry control circuit 33 according to the present embodiment controls the X-ray high voltage device 17 when the X-ray tube 13 and the X-ray detector 15 rotate (that is, when the rotating frame 11 rotates). X-rays are generated from the X-ray tube 13, and at least one of the X-ray high-voltage device 17 and the data acquisition circuit 19 is controlled to set the CT imaging parameters to be corrected data acquisition targets within each unit allowable angle range. Vary within the parameter value range.

First, construction of a CT imaging parameter acquisition sequence according to the present embodiment will be described. The CT scan parameter acquisition sequence is determined by the processing circuit 101 in the scan planning function 117 . The imaging planning function 117 is executed when planning a correction data collection scan. In the imaging planning function 117, the processing circuit 101 first determines the acquisition conditions in the correction data acquisition scan using the parameter table. A parameter table is implemented by a LUT (Look Up Table) or database.

FIG. 3 is a diagram showing an example of a parameter table. As shown in FIG. 3, the parameter table associates a set value with each of a plurality of CT imaging parameters. For example, as CT imaging parameters, focal size, focal position, tube voltage, tube current, DAS gain, slit aperture width, and DAS bundling unit are registered. As the setting values, values that can be taken by CT imaging parameters for which correction data is to be collected are registered. For example, when the CT imaging parameter is focus size, discrete values of small focus, medium focus, and large focus are associated as setting values related to focus size. Further, when the CT imaging parameter is the focal position, continuous values from -1 cm to +1 cm are associated as the setting values related to the focal position. In each unit allowable angle range, the parameter value of the CT imaging parameter is changed over the parameter value range from the lower limit value to the upper limit value of the setting value. Note that the set values shown in FIG. 3 are only examples, and the present invention is not limited to these. For example, the set value of the focus size may be four or more sizes instead of the three sizes of small focus, medium focus, and large focus, or may be continuous values from the lower limit size to the upper limit size. When the CT imaging parameter is a DAS bundling unit, discrete values of 0.5 mm, 1.0 mm, 2.0 mm, 4.0 mm, and 8.0 mm are associated as setting values related to the DAS bundling unit. The bundling mode assumes a square shape. In this case, for example, the set value “0.5 mm” means length×width=0.5 mm×0.5 mm. The bundling mode may be a rectangle.

Specifically, the processing circuit 101 selects CT imaging parameters for which correction data is to be collected from among a plurality of CT imaging parameters registered in the parameter table, either automatically or manually according to an instruction from the user via the input circuit 105. arbitrarily selected. When a CT imaging parameter is selected, the processing circuit 101 identifies a set value associated in the parameter table with the CT imaging parameter for which correction data is to be collected. Note that the number of CT imaging parameters for which correction data is to be collected is not limited to one type, and two or more types may be selected. Also, the set value can be modified to any value from the value registered in the parameter table through the input circuit 105 or the like.

In the imaging planning function 117, the processing circuit 101 sets the unit allowable angle range to one of a plurality of predetermined values. In addition, the processing circuit 101 may set the unit allowable angular range according to the type of CT imaging parameter for which correction data is to be collected. For example, the unit allowable angular range is determined according to the angular range necessary for switching to all set values of CT imaging parameters. When the CT imaging parameter is focus size and the set values are small focus, medium focus and large focus, the unit allowable angle range is the angle required to switch the focus size to all of small focus, medium focus and large focus. set above the range. In this case, the processing circuit 101 has a table or database that associates the types of CT imaging parameters with the unit allowable angle range, and uses the table or database to obtain the unit allowable angle from the CT imaging parameters for which correction data is to be collected. Determine the range automatically.

Also, in the imaging planning function 117, the processing circuit 101 may determine the unit allowable angle range according to the acquisition conditions regarding the correction data acquisition scan. Acquisition conditions used to determine the unit allowable angular range include, for example, CT imaging parameters, slice thickness, and rotational speed of the rotating frame 11 . For example, when the rotation speed is high, the centrifugal force acting on the X-ray tube 13 and the X-ray detector 15 increases, and the X-ray tube 13 and the X-ray detector 15 shake greatly. When the rotation speed is set to a small value and the rotation speed is low, the centrifugal force acting on the X-ray tube 13 and the X-ray detector 15 is small and the shake of the X-ray tube 13 and the X-ray detector 15 is small. The angular range is set to relatively large values. In addition, when the focus size, which is a CT imaging parameter, is a large focus, the unit allowable angle range is set to a relatively large value, and when the focus size is a small focus, the unit allowable angle range is set to a relatively small value. be.

When the type of CT imaging parameter, the set value of the CT imaging parameter, and the unit allowable angle range are determined, the processing circuit 101 performs CT imaging based on the type of CT imaging parameter, the set value of the CT imaging parameter, and the allowable unit angle range. Construct an acquisition sequence of imaging parameters. Image quality is not required in the correction data acquisition scan because the subject is not imaged. Therefore, even if the number of stages of CT imaging parameters to be switched during one rotation of the rotating frame 11 is larger than the number of stages of normal scanning requiring high image quality, the processing circuit 101 can Construct the acquisition sequence to switch to the setting value of Specifically, if the focus size is switched from a small focus to a medium focus to a large focus while the rotating frame 11 makes one revolution, the image quality is significantly degraded. There is no practical benefit to switching the focus size in multiple steps during one cycle. Since image quality is not required in the correction data acquisition scan, restrictions on the number of stages for ensuring image quality can be ignored. That is, in the correction data acquisition scan according to the present embodiment, it is possible to switch between all sizes of small focus, medium focus, and large focus in each unit allowable angle range. Data can be collected quickly. That is, the processing circuit 101 can construct an acquisition sequence that emphasizes correction data acquisition efficiency and that changes the parameter values of the CT imaging parameters with the number of steps, the mode of change, and the degree of change that are not permitted in normal scans that require image quality. . Information about the constructed acquisition sequence (hereinafter referred to as acquisition sequence information) is stored in the storage circuit 107 .

Various embodiments of correction data collection scans are described below.

(Example 1)
The gantry control circuit 33 according to the first embodiment causes the X-ray tube 13 to generate X-rays when the rotating frame 11 rotates, and sets one type of CT imaging parameter for correction data acquisition discretely in each unit allowable angle range. change in a meaningful way.

FIG. 4 is a diagram simply showing a CT imaging parameter acquisition sequence for a correction data acquisition scan according to the first embodiment. Acquisition sequences show changes in parameter values of CT imaging parameters over the course of the tube position or view. The vertical axis in FIG. 4 is defined by the parameter values of the CT imaging parameters, and the horizontal axis is defined by the rotation angle (hereinafter referred to as tube position) [°] of the X-ray tube 13 about the rotation axis Z. As shown in FIG. In FIG. 4, the focus size is given as a specific example of the CT imaging parameter. The focus sizes are called first size, second size, third size and fourth size in ascending order. The unit allowable angular range RA is set to 30°, for example.

When the gantry control circuit 33 according to the first embodiment receives the instruction to start the correction data acquisition scan, the gantry control circuit 33 operates the X-ray high-voltage device 17, the data acquisition circuit 19, and the gantry drive device 23 according to the acquisition sequence information stored in the storage circuit 107. Synchronously controlled to perform correction data acquisition scans. Specifically, the gantry control circuit 33 controls the gantry drive device 23 to rotate the rotating frame 11 around the rotation axis Z. As shown in FIG. When the rotation speed of the rotating frame 11 reaches a constant speed and the tube position of the X-ray tube 13 reaches the start tube position of the correction data acquisition scan, the gantry control circuit 33 controls the X-ray high voltage device 17. X-rays are emitted from the X-ray tube 13 . A data acquisition circuit 19 acquires correction data for each view via the X-ray detector 15 . The correction data for each view is stored in the storage circuit 107 in association with the number of views, the types of CT imaging parameters, and the set values.

Along with X-ray irradiation, the gantry control circuit 33 controls at least one of the X-ray high-voltage device 17 and the data acquisition circuit 19 to set the parameter values of the CT imaging parameters to a plurality of set values in each unit allowable angle range RA. switch in order. For example, in the case of FIG. 4, the gantry control circuit 33 controls the X-ray high voltage device 17 to set the focal spot size to the first size, second size, third size and fourth size in each unit allowable angular range RA. switch in order. Each focal spot size is maintained for a constant angular interval (hereafter referred to as the plateau period). The stable period is determined by the imaging planning function 117 of the processing circuit 101 based on the unit allowable angle range RA and the number of stages of setting values to be switched in the unit allowable angle range RA. For example, the processing circuit 101 determines a value obtained by dividing the unit allowable angular range RA by the number of steps in the stable period. In the case of FIG. 4, the unit allowable angle range RA is 30° and the number of steps is 4, so the stable period is determined to be less than 30°/4. In the first embodiment, the switching order of the focal size in each unit allowable angle range RA is the same in ascending order.

In this manner, the gantry control circuit 33 sequentially switches the focus size to the first size, second size, third size, and fourth size in each unit allowable angle range RA while the rotating frame 11 makes one revolution, and data Correction data is collected by controlling the collection circuit 19 . Thereby, the correction data regarding the first size, the second size, the third size and the fourth size can be collected while the rotating frame 11 completes one revolution.

Although the CT imaging parameter is the focus size in FIG. 4, it may be the focus position, tube voltage, tube current, DAS gain, or slit aperture width. When the CT imaging parameter is the focal position, tube voltage, tube current, or slit opening width, the gantry control circuit 33 controls the gantry driving device 23 to change the parameter value of the CT imaging parameter. When the CT imaging parameter is the DAS gain, the gantry control circuit 33 controls the data acquisition circuit 19 to change the parameter value of the CT imaging parameter.

The values of the CT imaging parameters are not stable between stages (transitional period) of the CT imaging parameters. Therefore, the gantry control circuit 33 may control the X-ray high-voltage device 17 to stop X-ray irradiation from the X-ray tube 13 during the transition period. Further, the gantry control circuit 33 may control the data collection circuit 19 to stop collection of correction data in the transitional period. Alternatively, the memory circuit 107 may discard the correction data collected by the data collection circuit 19 during the transitional period.

As shown in FIG. 4, it is assumed that the parameter values of the CT imaging parameters increase from the lower limit to the upper limit in each unit allowable angle range RA. However, the manner in which the parameter values are changed is not limited to this.

5, 6, and 7 are diagrams showing other acquisition sequences of CT imaging parameters related to the correction data acquisition scan according to the first embodiment. 5, 6 and 7 also illustrate the transition between stages. Assume that the CT imaging parameter in FIGS. 5, 6 and 7 is the tube voltage [kV]. It is assumed that the set values of the tube voltage are the first tube voltage value, the second tube voltage value, the third tube voltage value, which are the lower limit values, and the fourth tube voltage value, which is the upper limit value.

In the case of FIG. 5, the X-ray high voltage device 17 discretely increases the tube voltage from the lower limit value to the upper limit value in each unit allowable angle range RA, and then discretely decreases the tube voltage from the upper limit value to the lower limit value. The upward change from the lower limit value to the upper limit value and the downward change from the upper limit value to the lower limit value are alternately repeated for each unit allowable angle range RA. The X-ray high-voltage device 17 keeps the tube voltage at a constant value over three views (stable period) in each unit allowable angular range RA, and switches the tube voltage value during one view (transitional period).

In the case of FIG. 6, the X-ray high voltage device 17 alternately repeats the lower limit value of the tube voltage and the other set value while increasing the other set value in each unit allowable angle range RA, and then repeats the upper limit value. A value and another set value are alternately repeated while the other set value is decreased. The zigzag change described above is repeated for each unit allowable angular range RA. The X-ray high-voltage device 17 keeps the tube voltage at a constant value over three views (stable period) in each unit allowable angular range RA, and switches the tube voltage value during one view (transitional period).

In the case of FIG. 7, correction data on the tube voltage for dual energy (DE: Dual Energy) and correction data on the tube voltage for single energy (SE: Single Energy) are collected in order in each unit allowable angle range RA. be. In this case, the X-ray high voltage device 17 sequentially switches the tube voltage between the dual energy tube voltage value and the single energy tube voltage value in each unit allowable angle range RA. There are two types of tube voltage values for dual energy, for example, a low voltage value (first tube voltage value) and a high voltage value (fourth tube voltage value). There are four types of tube voltage values for single energy, for example, a first tube voltage value, a second tube voltage value, a third tube voltage value, and a fourth tube voltage value. In each unit allowable angle range RA, the X-ray high voltage device 17 first sets the tube voltage to a low voltage value (first tube voltage value) and a high voltage value (fourth tube voltage value) to collect correction data for dual energy. ), and then switch the tube voltage to the first tube voltage value, the second tube voltage value, the third tube voltage value, and the fourth tube voltage value in order to collect correction data for single energy. . The X-ray high-voltage device 17 keeps the tube voltage at a constant value over three views (stable period) in each unit allowable angular range RA, and switches the tube voltage value during one view (transitional period).

As described above, the gantry control circuit 33 according to the first embodiment generates X-rays from the X-ray tube 13 when the rotating frame 11 rotates, and sets one type of CT imaging parameter for correction data collection to the unit allowable angle Change discretely for each range. Since the gantry control circuit 33 according to the first embodiment can collect all the correction data regarding a plurality of setting values related to one type of CT imaging parameter during one rotation of the rotating frame 11, the correction data can be quickly collected. can do.

(Example 2)
In Example 1, the CT imaging parameters are assumed to change discretely. However, this embodiment is not limited to this. The gantry control circuit 33 according to the second embodiment continuously changes one type of CT imaging parameter for correction data acquisition.

FIG. 8 is a diagram showing a CT imaging parameter acquisition sequence for a correction data acquisition scan according to the second embodiment. Note that, in FIG. 8, as in FIG. 4, the focus size is given as a specific example of the CT imaging parameter. The vertical axis in the upper, middle and lower stages of FIG. 8 is defined as the focus size, and the horizontal axis is defined as the tube position [°]. The setting value of the focus size according to the second embodiment takes continuous values from the lower limit to the upper limit.

As shown in FIG. 8, the gantry control circuit 33 according to the second embodiment controls the X-ray high-voltage device 17 to set the focal spot size between the lower limit value and the upper limit value for each unit allowable angle range RA. is changed continuously. Specifically, various modes are possible as a method of continuous change. For example, as shown in the upper part of FIG. 8, the X-ray high-voltage device 17 linearly changes the focus size from the lower limit to the upper limit in each unit allowable angle range RA. In this case, the focus size changes in a triangular wave. As shown in the middle of FIG. 8, the X-ray high-voltage device 17 linearly changes the focus size from the lower limit to the upper limit in each unit allowable angle range RA, and then linearly changes from the upper limit to the lower limit. change in a meaningful way. In this case, the focal spot size will change in a sawtooth pattern. By alternately repeating the ascending order change and the descending order change of the focal spot size, it is possible to suppress abrupt changes in the focal spot size. As shown in the lower part of FIG. 8, the X-ray high-voltage device 17 nonlinearly changes the focus size from the lower limit to the upper limit in each unit allowable angle range RA, and then nonlinearly from the upper limit to the lower limit. change in a meaningful way. More specifically, the rate of change with time of the focus size is small in the vicinity of the lower limit and the upper limit, and the rate of change with time of the focus size is increased in the middle. In this case, the focal spot size changes in a sine wave. In this way, by reducing the temporal change rate near the lower limit and the upper limit, it is possible to suppress a rapid change in the focal size when switching between the ascending order change and the descending order change.

A change mode of the set values of the CT imaging parameters such as the focus size can be designated by the user via the input circuit 105 . In the imaging planning function 117, the processing circuit 101 constructs an acquisition sequence so that the set values of the CT imaging parameters are changed in each permissible angle unit according to the designated change mode.

As described above, the gantry control circuit 33 according to the second embodiment causes the X-ray tube 13 to generate X-rays when the rotating frame 11 rotates, and sets one type of CT imaging parameter for correction data collection to the unit allowable angle Change continuously for each range. Since the gantry control circuit 33 according to the second embodiment can collect all correction data regarding a plurality of setting values related to one type of CT imaging parameter during one rotation of the rotating frame 11, the correction data can be quickly collected. can do.

(Example 3)
It is assumed that the CT imaging parameters according to Examples 1 and 2 are of one type. However, this embodiment is not limited to this. Assume that there are two types of CT imaging parameters according to the third embodiment.

FIG. 9 is a diagram showing a CT imaging parameter acquisition sequence for a correction data acquisition scan according to the third embodiment. Note that in FIG. 9, the focus position and the focus size are given as specific examples of CT imaging parameters. The vertical axis in FIG. 9 defines the focus position and focus size, and the horizontal axis defines the tube position [°]. The set value of the focus position according to the third embodiment changes continuously from the lower limit to the upper limit, and the set value of the focus size changes stepwise from the lower limit to the upper limit.

First, determination of acquisition conditions for correction data acquisition scans for two types of CT imaging parameters will be described. In the imaging planning function 117, the processing circuit 101 first selects two types of CT imaging parameters automatically or manually according to an instruction from the user via the input circuit 105, and each of the selected two types of CT imaging parameters Set values are determined using the parameter table. For example, in the case of FIG. 9, focus size and focus position are selected as CT imaging parameters. The focus size setting values are discrete values of the first size, second size, third size and fourth size, and the focus position setting values are continuous values from the lower limit to the upper limit.

Next, the processing circuit 101 sets one of the selected two types of CT imaging parameters as a CT imaging parameter for switching setting values at a low speed (hereinafter referred to as a low speed switching parameter), and sets the other as a low speed switching parameter. A CT imaging parameter (hereinafter referred to as a high-speed switching parameter) that switches the setting value at a high speed is set. For example, the processing circuit 101 sets a CT imaging parameter whose set value is a discrete value among the selected two types of CT imaging parameters as a low-speed switching parameter, and sets a CT imaging parameter whose set value is a continuous value as a high-speed switching parameter. Set to parameter. When the setting values of both of the selected two types of CT imaging parameters are discrete values, the processing circuit 101 compares the switching speeds of the two types of CT imaging parameters, and selects the CT imaging with the faster switching speed. A parameter is set as a high-speed switching parameter, and a CT imaging parameter with a lower switching speed is set as a low-speed switching parameter. For example, in the case of FIG. 9, the setting value of the focus size is a discrete value and the setting value of the focus position is a continuous value, so the focus size is set as the slow switching parameter and the focus position is set as the fast switching parameter. .

Then, the processing circuit 101 is configured so that the setting value of the low-speed switching parameter discretely changes in a predetermined manner in each unit allowable angle range RA, and the high-speed switching parameter changes in a predetermined manner in each setting value of the low-speed switching parameter. , to construct the acquisition sequence. The length of time of the stable period for each set value of the low-speed switching parameter is set to be longer than the time required to change the high-speed switching parameter to all set values. For example, in the case of FIG. 9, in each unit allowable angle range RA, the focal size sequentially changes from the first size to the fourth size at regular intervals, and the focal position linearly changes from the lower limit to the upper limit in each focal size. Acquisition sequences are constructed to vary. It is assumed that the unit allowable angular range RA has an angular range necessary to change the low-speed switching parameter to all set values. Acquisition sequence information is stored in the storage circuit 107 .

When the gantry control circuit 33 according to the third embodiment receives the instruction to start the correction data acquisition scan, the gantry control circuit 33 operates the X-ray high-voltage device 17, the data acquisition circuit 19, and the gantry drive device 23 according to the acquisition sequence information stored in the storage circuit 107. Synchronously controlled to perform correction data acquisition scans. Specifically, the gantry control circuit 33 controls the gantry drive device 23 to rotate the rotating frame 11 around the rotation axis Z. As shown in FIG. When the rotation speed of the rotating frame 11 reaches a constant speed and the tube position of the X-ray tube 13 reaches the start tube position of the correction data acquisition scan, the gantry control circuit 33 controls the X-ray high voltage device 17. X-rays are emitted from the X-ray tube 13 . A data acquisition circuit 19 acquires correction data for each view via the X-ray detector 15 . The correction data for each view is stored in the storage circuit 107 in association with the number of views, the types of CT imaging parameters, and the set values.

Along with X-ray irradiation, the gantry control circuit 33 controls at least one of the X-ray high-voltage device 17 and the data acquisition circuit 19 to set the parameter value of the low-speed switching parameter to a plurality of set values in each unit allowable angle range RA. while sequentially changing the parameter value of the high-speed switching parameter to a plurality of setting values in a period in which the parameter value of the low-speed switching parameter maintains each set value. For example, in the case of FIG. 9, the gantry control circuit 33 discretely changes the focus size from the lower limit value to the upper limit value in each unit allowable angle range RA, while the focus size maintains one set value. , the focal position is continuously changed from the lower limit to the upper limit. The gantry control circuit 33 controls and corrects the data collection circuit 19 while changing the low-speed switching parameter and the high-speed switching parameter over all set values for each unit allowable angular range RA while the rotating frame 11 makes one revolution. Collect data. As a result, correction data relating to all combinations of low-speed switching parameter setting values and high-speed switching parameter setting values can be collected while the rotating frame 11 makes one revolution, so that these correction data can be collected quickly. can be done.

The two types of CT imaging parameters are not limited to the above examples. For example, as shown in FIG. 10, the CT imaging parameters are set to the focal position and the DAS bundling unit. The vertical axis in FIG. 10 is defined by the focus position and the DAS bundle unit, and the horizontal axis is defined by the tube position [°]. The set value of the focal position according to the third embodiment continuously changes from the lower limit to the upper limit, and the set value for each DAS bundle varies from the lower limit (0.5 mm in FIG. 3) to the upper limit (0.5 mm in FIG. 3). In the case of , it is changed stepwise up to 8.0 mm). In this case also, the focus position and the DAS bundling unit can be sequentially changed in a nested manner while the rotating frame 11 makes one revolution by the above method. As a result, it is possible to quickly collect correction data relating to the focal position and the DAS bundling unit.

(Example 4)
In Examples 1, 2 and 3, it was assumed that all correction data could be collected in one round. However, it may not be possible to collect all the correction data in one round because, for example, the CT imaging parameters cannot be changed over all set values within the unit allowable angle range. The X-ray computed tomography apparatus according to the fourth embodiment determines the number of laps.

In the imaging planning function 117, the processing circuit 101 determines the ratio between the unit allowable angle range and the minimum angle range (hereinafter referred to as the minimum required angle range) necessary to change the CT imaging parameters over all setting values. Based on this, the number of revolutions of the rotating frame 11 in the correction data acquisition scan is determined. If the minimum necessary angle range is equal to or less than the unit allowable angle range, the processing circuit 101 sets the number of turns to one. If the minimum required angle range is larger than the unit allowable angle range and is less than or equal to twice the unit allowable angle range, the processing circuit 101 sets the number of rounds to two rounds. Similarly, when the minimum required angle range is greater than twice the unit allowable angle range and less than or equal to three times the unit allowable angle range, the processing circuitry 101 sets the number of turns to three. The minimum necessary angle range is determined based on, for example, the number of stages (the number of set values) of CT imaging parameters for which correction data is to be collected and the rate of change of the parameter values.

FIG. 11 is a diagram showing a collection sequence when the number of laps is two. In FIG. 11, the tube position in the first round is from 0° to 360°, and the tube position in the second round is from 360° to 720°. Let the fast switching parameter be the tube voltage [kV] and the slow switching parameter be the focal spot size. As shown in FIG. 11, since the change speed of the tube voltage [kV] and the focus size is relatively slow, it is possible to realize all combinations of the tube voltage [kV] and the focus size in one unit allowable angle range RA. shall not be possible. In this case, the number of laps is determined to be two laps according to the method of determining the number of laps described above.

When the number of rounds is two, the gantry control circuit 33 reverses the change order of the low-speed switching parameter between the first round and the second round. This makes it possible to collect correction data for all combinations of set values of the low-speed switching parameter and the high-speed switching parameter in each angular range. For example, as shown in FIG. 11, the focus size is changed in ascending order from the first size to the fourth size in the first round, and the focus size is changed in descending order from the fourth size to the first size in the second round. . Therefore, for example, in the unit allowable angle range RA from 0° to 30° in the first round, the correction data related to the first size and the second size are collected, and the unit allowable angle range RA in the same range (360° to 390°) in the second round is collected. Correction data for the third size and the fourth size are collected in the angular range RA. Therefore, it is possible to collect correction data for all combinations of set values of the focal spot size and the tube voltage in the angular range.

It should be noted that the target for which the change order of the set values is reversed between the first round and the second round is not limited to only the low speed switching parameter. That is, the change order of the setting values of the high-speed switching parameter may be reversed together with the low-speed switching parameter. Also, even when there is one type of CT imaging parameter, the change order of the setting values may be reversed between the first round and the second round.

(Example 5)
The X-ray computed tomography apparatus 1 according to the fifth embodiment measures the afterglow characteristics (afterglow) of the X-ray detector 15 together with correction data.

FIG. 12 is a diagram illustrating a correction data collection sequence according to the fifth embodiment. Assume that the CT imaging parameter in FIG. 12 is tube current [mA] as an example. As shown in FIG. 12, the gantry control circuit 33 discretely changes the parameter value of the tube current from the lower limit value to the upper limit value in each unit allowable angle range RA. The gantry control circuit 33 controls the X-ray high-voltage device 17 in synchronization with the change timing of the tube current to repeatedly irradiate pulsed X-rays. The peak value of the electric signal output by the X-ray detector 15 in the X-ray irradiation stop period RO exhibits nonlinear changes that depend on the tube voltage and the tube current. The gantry control circuit 33 controls the data acquisition circuit 19 to acquire correction data via the X-ray detector 15 not only during the pulse X-ray irradiation period, ie, the tube current stabilization period, but also during the X-ray irradiation stop period RO. do. The afterglow of the X-ray detector 15 greatly affects the correction data collected during the X-ray irradiation stop period RO. Correction data collected during the X-ray irradiation stop period RO will be referred to as afterglow data. The afterglow data is stored in the storage circuit 107 in association with the tube position, the type of CT imaging parameter, and the previous set value.

As described above, in the fifth embodiment, the gantry control circuit 33 stops X-ray irradiation between stages of CT imaging parameters and collects afterglow data during the X-ray irradiation stop period. As a result, the efficiency of collecting afterglow data can also be improved.

In the above embodiment, the afterglow characteristic data is collected between stages of CT imaging parameters. However, this embodiment is not limited to this. The afterglow data may be collected at any timing as long as the X-ray irradiation is stopped.

FIG. 13 is a diagram showing another acquisition sequence according to the fifth embodiment. As shown in FIG. 13, the gantry control circuit 33 controls the X-ray high-voltage device 17 to repeat X-ray irradiation and stop. The gantry control circuit 33 controls the X-ray high-voltage device 17 to emit X-rays during the X-ray irradiation period ON. The X-ray irradiation period ON and the X-ray irradiation stop period OFF may be set in any tube position range. During the X-ray irradiation period ON, the gantry control circuit 33 may simply irradiate the X-rays without changing the parameter values of the CT imaging parameters. At least one of the acquisition circuit 19 may be controlled to change the parameter values of the CT imaging parameters. During the X-ray irradiation stop period OFF, the gantry control circuit 33 controls the data acquisition circuit 19 to acquire afterglow data.

Since image quality is not required even in the acquisition of afterglow data, X-ray irradiation stop periods can be set at a higher frequency or for a longer period of time than in scanning for the purpose of imaging, as described above. Therefore, the gantry control circuit 33 according to the fifth embodiment can efficiently collect afterglow data.

As described in Examples 1-5 above, the X-ray computed tomography apparatus 1 according to this embodiment includes the X-ray tube 13, the X-ray detector 15, the rotating frame 11, the gantry control circuit 33, and the data acquisition circuit. 19. The X-ray tube 13 generates X-rays. X-ray detector 15 detects X-rays generated from X-ray tube 13 . The rotating frame 11 supports the X-ray tube 13 and the X-ray detector 15 so as to be rotatable around the rotation axis Z. As shown in FIG. When the X-ray tube 13 and the X-ray detector 15 rotate, the gantry control circuit 33 causes the X-ray tube 13 to generate X-rays and sets predetermined CT imaging parameters for correction data collection to the X-ray detector. 15 output or sensitivity changes within a predetermined parameter value range for each unit allowable angular range. The data collection circuit 19 collects correction data regarding a predetermined parameter value range of predetermined CT imaging parameters via the X-ray detector 15 while the X-ray tube 13 and the X-ray detector 15 are rotating.

With the above configuration, the X-ray computed tomography apparatus 1 according to the present embodiment sets the CT imaging parameter to a predetermined parameter value range for each unit allowable angle range based on the dependence of the output or sensitivity of the X-ray detector on the tube position. to change. The purpose of the correction data collection scan is to collect correction data, so unlike the normal scan for imaging the subject, image quality is not required. That is, in the correction data acquisition scan, the parameter values of the CT imaging parameters can be changed with the number of steps, the mode of change, and the degree of change that are not permitted in the normal scan, which requires high image quality. You can build sequences. Therefore, even when the set values of the CT imaging parameters are multistage, the correction data for all the set values can be collected with a smaller number of turns than in the conventional art.

According to at least one or more embodiments described above, it is possible to collect correction data with high efficiency.

While several embodiments of the invention have been described, these embodiments have been 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 modifications can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, as well as the scope of the invention described in the claims and equivalents thereof.

DESCRIPTION OF SYMBOLS 1... X-ray computed tomography apparatus, 10... Mounting frame, 11... Rotating frame, 13... X-ray tube, 15... X-ray detector, 17... X-ray high-voltage apparatus, 19... Data acquisition circuit, 21... Collimator, 23 Table driving device 25 Bed 27 Bed driving device 33 Frame control circuit 100 Console 101 Processing circuit 103 Display circuit 105 Input circuit 107 Storage circuit 111 Preprocessing function , 113 ... reconstruction function, 115 ... image processing function, 117 ... imaging planning function, 119 ... system control function.

Claims (9)

an X-ray tube for generating X-rays;
an X-ray detector that detects X-rays generated from the X-ray tube;
a pedestal supporting the X-ray tube and the X-ray detector rotatably around a rotation axis;
a control circuit for generating X-rays from the X-ray tube and changing predetermined CT imaging parameters for correction data acquisition during one rotation when the X-ray tube and the X-ray detector are rotated; ,
an acquisition circuit for acquiring correction data relating to the predetermined CT imaging parameters via the X-ray detector when the X-ray tube and the X-ray detector are rotated;
An X-ray computed tomography apparatus comprising
The control circuit sequentially changes a first parameter out of the predetermined CT imaging parameters in multiple stages, and changes a second parameter out of the predetermined CT imaging parameters to each stage of the first parameter. sequentially change in multiple stages in
X-ray computed tomography equipment . The control circuit changes the predetermined CT imaging parameter within a predetermined parameter value range for each unit angle range that allows a change in the output or sensitivity of the X-ray detector with respect to the rotation angle about the rotation axis. 2. An X-ray computed tomography apparatus according to claim 1. A process of determining the number of turns of the X-ray tube and the X-ray detector based on the ratio of the unit angle range and the angle range required to change the first parameter over all set values. 3. The x-ray computed tomography system of claim 2 , further comprising circuitry. The control circuit causes the X-ray tube and the X-ray detector to make a full cycle to collect the correction data when the first parameter can be varied over all set values within the unit angular range. 3. An X-ray computed tomography apparatus according to claim 2 . The control circuit controls the X-ray tube and the X-ray detector to collect the correction data when the first parameter cannot be varied over all set values within the unit angular range. 3. The X-ray computed tomography apparatus according to claim 2 , wherein the rotation is performed by a number of revolutions based on a ratio between the angular range and the angular range required to vary the first parameter over all set values. 6. The X-ray computed tomography according to claim 5 , wherein said control circuit reverses the order of change of said first parameter in a first cycle and a second cycle of said X-ray tube and said X-ray detector. photographic equipment. The control circuit stops X-ray irradiation from the X-ray tube between steps of the first parameter when changing the first parameter in multiple steps ,
The collection circuit collects the correction data for measuring afterglow characteristics of the X-ray detector during a period in which X-ray irradiation from the X-ray tube is stopped.
The X-ray computed tomography apparatus according to claim 1 . 3. The X-ray computed tomography apparatus according to claim 2, further comprising a processing circuit that determines said unit angular range according to at least one of said predetermined CT imaging parameter type, slice thickness, and rotation speed around said rotation axis. . A processing circuit for setting at least two of X-ray focal size, X-ray focal position, tube voltage, tube current, DAS gain, slit opening width, and DAS bundling unit to the predetermined CT imaging parameters. 2. The X-ray computed tomography apparatus according to 1.

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