X-ray computed tomography device, x-ray high voltage device, and x-ray control method

Abstract

To improve accuracy of tube current modulation, responsiveness, and an accepted modulation width and the like at the time of kV switching.SOLUTION: A storage unit stores characteristics data showing a relation between a filament current value and a tube current output value upon switching between a first tube voltage and a second tube voltage lower than the first tube voltage. A setting unit is a unit that sets a tube current setting value for performing tube current modulation in parallel with switching between the first tube voltage and the second tube voltage. The setting unit sets the first tube current setting value at the time of application of either the first tube voltage or the second tube voltage as the reference tube voltage, and sets a second tube current setting value based on the characteristics data and the first tube current setting value at the time of application of the other tube voltage. In synchronization with the switching between the first tube voltage and the second tube voltage, a tube current control circuit switches between tube current feedback control based on the first tube current setting value at the time of application of the reference tube voltage, and tube current feedback control based on the second tube voltage setting value at the time of application of the other tune voltage.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The embodiments disclosed in the present specification and drawings relate to an X-ray computed tomography apparatus, an X-ray high voltage apparatus, and an X-ray control method. [Background technology]

[0002] Tube current modulation control is used as a method to reduce patient exposure in X-ray computed tomography. However, when tube current modulation control is performed in parallel with kV switching, which rapidly switches between high and low tube voltages, the tube current inevitably fluctuates with the tube voltage, making tube current modulation control difficult. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-192801 [Patent Document 2] Patent Publication No. 2021-126442 Summary of the Invention [Problem to be solved by the invention]

[0004] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to improve the accuracy, responsiveness, and allowable modulation width of tube current modulation during kV switching. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problem. Problems corresponding to the effects of each configuration shown in the embodiments described below can also be positioned as other problems. [Means for solving the problem]

[0005] An X-ray computed tomography apparatus according to an embodiment includes an X-ray tube, a memory unit, a tube voltage control circuit, a setting unit, and a tube current control circuit. The X-ray tube generates X-rays. The memory unit stores characteristic data representing a relationship between a filament current value and a tube current output value when a tube voltage applied to the X-ray tube is switched between a first tube voltage and a second tube voltage lower than the first tube voltage. The tube voltage control circuit switches the tube voltage applied to the X-ray tube between the first tube voltage and the second tube voltage. The setting unit sets a tube current setting value for performing tube current modulation in parallel with switching between the first tube voltage and the second tube voltage, and sets a first tube current setting value when a reference tube voltage of the first tube voltage and the second tube voltage is applied, and sets a second tube current setting value based on the characteristic data and the first tube current setting value when the other tube voltage of the first tube voltage and the second tube voltage is applied. The tube current control circuit switches, in synchronization with the switching between the first tube voltage and the second tube voltage, between tube current feedback control based on the first tube current setting value when the reference tube voltage is applied and tube current feedback control based on the second tube current setting value when the other tube voltage is applied. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a diagram showing an example of the arrangement of an X-ray computed tomography apparatus according to this embodiment. [Figure 2] FIG. 2 is a diagram showing an example of the configuration of an X-ray generation system including the X-ray tube and the X-ray high voltage device shown in FIG. [Figure 3] FIG. 3 is a diagram illustrating a processing procedure in the tube current variation measurement mode. [Figure 4] FIG. 4 is a graph showing the tube current output value [mA] and the tube current fluctuation amount for each of a plurality of filament current values ​​If [A]. [Figure 5] FIG. 5 is a graph illustrating the tube current characteristic data. [Figure 6] FIG. 6 is a diagram illustrating a processing procedure in a tube current modulation spectral scan. [Figure 7]FIG. 7 is a diagram illustrating tube current modulation information for applying a reference tube voltage (high tube voltage). [Figure 8] FIG. 8 is a diagram illustrating examples of tube current modulation information for applying a high tube voltage and tube current modulation information for applying a low tube voltage. [Figure 9] FIG. 9 is a diagram showing an example of a control sequence for tube current modulation spectral scanning. [Figure 10] FIG. 10 is a diagram illustrating an example of a display screen of the determination result as to whether or not it is necessary to reacquire the tube current characteristic data. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, an X-ray computed tomography apparatus, an X-ray high voltage apparatus, and an X-ray control method according to this embodiment will be described in detail with reference to the drawings.

[0008] There are various types of X-ray computed tomography apparatuses (CT apparatuses), such as third-generation CT and fourth-generation CT, and any of these types can be applied to this embodiment. Here, the third-generation CT is a rotate / rotate-type in which the X-ray tube and detector rotate together around the subject. The fourth-generation CT is a stationary / rotate-type in which a large number of X-ray detection elements arranged in a ring shape are fixed, and only the X-ray tube rotates around the subject.

[0009] FIG. 1 is a diagram showing an example of the configuration of an X-ray computed tomography apparatus 1 according to this embodiment. As shown in FIG. 1, the X-ray computed tomography apparatus 1 includes a gantry 10, a bed 30, and a console 40. Although FIG. 1 illustrates multiple gantry 10s for ease of explanation, the apparatus may actually include one or multiple gantry 10s. The gantry 10 is a scanning device configured to perform X-ray CT scans of a subject P. The bed 30 is a transport device on which the subject P to be scanned for X-ray CT scans is placed and which positions the subject P. The console 40 is a computer that controls the gantry 10. For example, the gantry 10 and the bed 30 are installed in a CT examination room, and the console 40 is installed in a control room adjacent to the CT examination room. The gantry 10, the bed 30, and the console 40 are connected to each other by wire or wirelessly so that they can communicate with each other. The console 40 does not necessarily have to be installed in the control room. For example, the console 40 may be installed in the same room as the gantry 10 and the bed 30. The console 40 may also be incorporated into the cradle 10 .

[0010] As shown in FIG. 1, the gantry 10 includes an X-ray tube 11, an X-ray detector 12, a rotating frame 13, an X-ray high voltage device 14, a control device 15, a wedge 16, a collimator 17, and a data acquisition system (DAS) 18.

[0011] The X-ray tube 11 irradiates the subject P with X-rays. Specifically, the X-ray tube 11 includes a cathode that generates thermoelectrons, an anode that generates X-rays upon receiving thermoelectrons flying from the cathode, and a vacuum tube that holds the cathode and anode. The X-ray tube 11 is connected to the X-ray high voltage device 14 via a high-voltage cable. A tube voltage is applied between the cathode and the anode by the X-ray high voltage device 14. The application of the tube voltage causes thermoelectrons to fly from the cathode toward the anode. A tube current flows as the thermoelectrons fly from the cathode toward the anode. X-rays are generated when the thermoelectrons collide with the anode.

[0012] The X-ray detector 12 detects X-rays emitted from the X-ray tube 11 and passing through the subject P, and outputs an electrical signal corresponding to the detected X-ray dose to the data acquisition circuitry 18. The X-ray detector 12 has a structure in which multiple X-ray detection element rows, each of which has multiple X-ray detection elements arranged in the channel direction, are arranged in the slice direction (row direction). The X-ray detector 12 is, for example, an indirect conversion type detector having a grid, a scintillator array, and a photosensor array. The scintillator array has multiple scintillators. The scintillator outputs light with an amount of light corresponding to the amount of incident X-rays. The grid is arranged on the X-ray incident surface side of the scintillator array and has an X-ray shielding plate that absorbs scattered X-rays. The grid is sometimes called a collimator (one-dimensional collimator or two-dimensional collimator). The photosensor array converts light from the scintillator into an electrical signal corresponding to the amount of light. A photodiode, for example, is used as the photosensor. The X-ray detector 12 may also be a direct conversion type detector.

[0013] The rotating frame 13 is an annular frame that supports the X-ray tube 11 and the X-ray detector 12 rotatably around a rotation axis (Z-axis). Specifically, the rotating frame 13 supports the X-ray tube 11 and the X-ray detector 12 so that they face each other. The rotating frame 13 is supported on a fixed frame (not shown) so that it can rotate around the rotation axis. The rotating frame 13 is rotated around the rotation axis by the control device 15, thereby rotating the X-ray tube 11 and the X-ray detector 12 around the rotation axis. The rotating frame 13 receives power from a drive mechanism of the control device 15 and rotates around the rotation axis at a constant angular velocity. An image field of view (FOV) is set in an opening 19 of the rotating frame 13.

[0014] In this embodiment, the rotation axis of the rotating frame 13 in the non-tilted state or the longitudinal direction of the tabletop 33 of the bed 30 is defined as the Z-axis direction, the axis direction perpendicular to the Z-axis direction and horizontal to the floor surface is defined as the X-axis direction, and the axis direction perpendicular to the Z-axis direction and perpendicular to the floor surface is defined as the Y-axis direction.

[0015] The X-ray high voltage device 14 has a high voltage generator and an X-ray control device. The high voltage generator has electrical circuits such as a transformer and a rectifier, and generates a high voltage to be applied to the X-ray tube 11 and a filament current to be supplied to the X-ray tube 11. The X-ray control device controls the output voltage according to the X-rays emitted by the X-ray tube 11. The high voltage generator may be of a transformer type or an inverter type. The X-ray high voltage device 14 may be provided on the rotating frame 13 in the gantry 10, or on a fixed frame (not shown) in the gantry 10.

[0016] The wedge 16 adjusts the dose of X-rays irradiated onto the subject P. Specifically, the wedge 16 attenuates the X-rays so that the dose of X-rays irradiated from the X-ray tube 11 onto the subject P has a predetermined distribution. For example, the wedge 16 is made of a metal plate such as aluminum, such as a wedge filter or a bow-tie filter.

[0017] The collimator 17 limits the irradiation range of the X-rays that have passed through the wedge 16. The collimator 17 slidably supports multiple lead plates that shield the X-rays, and adjusts the shape of the slits formed by the multiple lead plates. The collimator 17 is sometimes called an X-ray aperture.

[0018] The data acquisition circuitry 18 reads out electrical signals from the X-ray detector 12 that correspond to the X-ray dose detected by the X-ray detector 12. The data acquisition circuitry 18 amplifies the read-out electrical signals and integrates the electrical signals over a view period to acquire detection data having digital values ​​that correspond to the X-ray dose over that view period. The detection data is called projection data. The data acquisition circuitry 18 is realized, for example, by an application specific integrated circuit (ASIC) equipped with circuit elements capable of generating projection data. The projection data is transmitted to the console 40 via a non-contact data transmission device or the like.

[0019] In this embodiment, an integral type X-ray detector 12 and an X-ray computed tomography apparatus 1 equipped with an integral type X-ray detector 12 are described as examples, but the technology according to this embodiment can also be applied to a photon counting type X-ray detector.

[0020] The control device 15 controls the X-ray high-voltage generator 14 and the data acquisition circuit 18 to perform X-ray CT imaging in accordance with the scan control function 52 of the processing circuit 45 of the console 40. The control device 15 includes a processing circuit having a central processing unit (CPU) or a microprocessing unit (MPU), etc., and a drive mechanism such as a motor and an actuator. The processing circuit includes, as hardware resources, a processor such as a CPU and memory such as a read-only memory (ROM) or a random-access memory (RAM). The control device 15 executes various functions using a processor that executes programs loaded in the memory. Note that various functions are not limited to being implemented by a single processing circuit. A processing circuit may be configured by combining multiple independent processors, and each processor may execute a program to implement each function. The control device 15 may also be implemented using an ASIC or a field programmable gate array (FPGA). The control device 15 may also be realized by another complex programmable logic device (CPLD) or simple programmable logic device (SPLD). The control device 15 has a function of receiving input signals from an input interface 43 (described later) attached to the console 40 or the gantry 10 and controlling the operation of the gantry 10 and the bed 30. For example, the control device 15 receives input signals and controls the rotation of the rotating frame 13, the tilt of the gantry 10, and the operation of the bed 30 and the tabletop 33. The control of tilting the gantry 10 is realized by the control device 15 rotating the rotating frame 13 around an axis parallel to the X-axis direction based on inclination angle (tilt angle) information input via an input interface attached to the gantry 10. The control device 15 may be provided in the gantry 10 or in the console 40.

[0021] The bed 30 includes a base 31, a support frame 32, a top plate 33, and a bed driving device 34. The base 31 is placed on the floor. The base 31 is a housing that supports the support frame 32 so that it can move vertically (in the Y-axis direction) relative to the floor. The support frame 32 is a frame provided on top of the base 31. The support frame 32 supports the top plate 33 so that it can slide along the rotation axis (Z-axis). The top plate 33 is a flexible plate on which the subject P is placed.

[0022] The bed driving device 34 is housed in the housing of the bed 30. The bed driving device 34 is a motor or actuator that generates power to move the support frame 32 on which the subject P is placed and the tabletop 33. The bed driving device 34 operates under the control of the console 40 or the like.

[0023] The console 40 has a memory 41, a display 42, an input interface 43, a communication interface 44, and a processing circuit 45. Data communication between the memory 41, the display 42, the input interface 43, the communication interface 44, and the processing circuit 45 is performed via a bus (BUS). Note that although the console 40 will be described as being separate from the gantry 10, the gantry 10 may include the console 40 or some of the components of the console 40.

[0024] The memory 41 is a storage device such as a hard disk drive (HDD), a solid state drive (SSD), or an integrated circuit storage device that stores various information. In addition to an HDD or SSD, the memory 41 may be a portable storage medium such as a compact disc (CD), a digital versatile disc (DVD), a Blu-ray (registered trademark) disc (BD), or a flash memory. The memory 41 may also be a drive device that reads and writes various information from and to a semiconductor memory element such as a flash memory or a RAM. The storage area of ​​the memory 41 may be located within the X-ray computed tomography apparatus 1 or in an external storage device connected via a network. The memory 41 stores, for example, projection data and reconstructed image data.

[0025] The display 42 displays various types of information. For example, the display 42 outputs CT images generated by the processing circuitry 45, a GUI (Graphical User Interface) for receiving various operations from the operator, and the like. Any of a variety of displays can be used as the display 42, as appropriate. For example, the display 42 can be a liquid crystal display (LCD), a cathode ray tube (CRT) display, an organic electroluminescence display (OLED), or a plasma display.

[0026] The display 42 may be installed anywhere in the control room. Alternatively, the display 42 may be installed on the pedestal 10. The display 42 may be a desktop type, or may be configured as a tablet terminal or the like capable of wireless communication with the main body of the console 40. Alternatively, one or more projectors may be used as the display 42.

[0027] The input interface 43 accepts various input operations from the operator, converts the accepted input operations into electrical signals, and outputs the electrical signals to the processing circuitry 45. For example, the input interface 43 accepts from the operator acquisition conditions for acquiring projection data, reconstruction conditions for reconstructing CT images, and image processing conditions for generating post-processed images from CT images. Examples of the input interface 43 that can be used include a mouse, keyboard, trackball, switch, button, joystick, touchpad, and touch panel display, as appropriate. Note that in this embodiment, the input interface 43 is not limited to a device equipped with physical operation components such as a mouse, keyboard, trackball, switch, button, joystick, touchpad, and touch panel display. For example, an electrical signal processing circuit that receives an electrical signal corresponding to an input operation from an external input device provided separately from the device and outputs the electrical signal to the processing circuitry 45 is also included as an example of the input interface 43. The input interface 43 may also be provided on the gantry 10. The input interface 43 may also be configured as a tablet terminal or the like capable of wireless communication with the console 40.

[0028] The communication interface 44 includes a network interface card (NIC) for communicating various data via a network with external devices such as a workstation, PACS (Picture Archiving and Communication Systems), RIS (Radiology Information System), and HIS (Hospital Information System).

[0029] The processing circuitry 45 controls the overall operation of the X-ray computed tomography apparatus 1 in response to electrical signals of input operations output from the input interface 43. The processing circuitry 45 generates image data based on electrical signals output from the X-ray detector 12. For example, the processing circuitry 45 has, as hardware resources, a processor such as a CPU, MPU, or GPU, and memory such as a ROM or RAM. The processing circuitry 45 executes a scan condition setting function 51, a scan control function 52, a reconstruction function 53, an image processing function 54, a tube current variation amount measurement function 55, a tube current characteristics generation function 56, a reacquisition determination function 57, a display control function 58, and the like, by using a processor that executes programs loaded in the memory.

[0030] Note that each of the functions 51 to 58 does not necessarily have to be realized by a single processing circuit, but may be realized by combining a plurality of independent processors to form a processing circuit, and each processor may execute a program to realize each of the functions 51 to 58.

[0031] The processing circuitry 45 sets various scan conditions using the scan condition setting function 51. The scan according to this embodiment is a spectral scan (hereinafter referred to as a tube current modulation spectral scan) in which tube current modulation is performed in parallel with switching between a first tube voltage and a second tube voltage lower than the first tube voltage. The scan conditions set include the set value of the first tube voltage, the set value of the second tube voltage, the time change in the set value of the first tube current when the first tube voltage is applied (hereinafter referred to as first tube current modulation information), the time change in the set value of the second tube current when the second tube voltage is applied (hereinafter referred to as second tube current modulation information), and the rotation speed of the rotating frame 13. Here, the processing circuitry 45 generates first tube current modulation information, which is the time change in the first tube current set value for periodically modulating the tube current. Furthermore, the processing circuitry 45 generates second tube current modulation information, which is a time change of a second tube current setting value that changes in accordance with the periodic modulation of the tube current, based on the first tube current modulation information and the tube current characteristic data. The tube current characteristic data means data that represents the relationship between the filament current value and the tube current output value when the tube voltage applied to the X-ray tube 11 is switched between the first tube voltage and the second tube voltage.

[0032] The scan control function 52 causes the processing circuitry 45 to control the X-ray high voltage generator 14, the control device 15, and the data acquisition circuitry 18 to perform a tube current modulation spectral scan in accordance with the scan conditions set by the scan condition setting function 51. At this time, in synchronization with the switching between the first tube voltage and the second tube voltage, the X-ray high voltage generator 14 switches between tube current feedback control based on the first tube current setting value when a reference tube voltage of the first tube voltage and the second tube voltage is applied, and tube current feedback control based on the second tube current setting value when the other tube voltage is applied.

[0033] Using the reconstruction function 53, the processing circuitry 45 performs preprocessing on the projection data output from the data acquisition circuitry 18, such as logarithmic conversion, offset correction, inter-channel sensitivity correction, beam hardening correction, and interpolation for data loss due to tube voltage switching. The processing circuitry 45 performs material decomposition on the preprocessed projection data and performs reconstruction on the material-decomposed projection data to generate a CT image (hereinafter referred to as a reference material image). Reconstruction processing can use filtered back projection, iterative reconstruction, or reconstruction processing applying machine learning. The processing circuitry 45 may also perform reconstruction processing on projection data without material decomposition to generate a CT image (also called an integral image).

[0034] Using the image processing function 54, the processing circuitry 45 converts the CT image generated by the reconstruction function 53 into a cross-sectional image of an arbitrary cross section or a rendering image of an arbitrary viewpoint direction. The conversion is performed based on an input operation received from an operator via the input interface 43. For example, the processing circuitry 45 performs three-dimensional image processing such as volume rendering, surface volume rendering, image value projection processing, MPR (Multi-Planer Reconstruction) processing, and CPR (Curved MPR) processing on the CT image to generate a rendering image of an arbitrary viewpoint direction. Note that the generation of a rendering image of an arbitrary viewpoint direction may be performed directly by the reconstruction function 53.

[0035] Using the tube current variation measurement function 55, the processing circuitry 45 controls the X-ray high voltage device 14 and the control device 15 to execute a tube current variation measurement mode. The tube current variation measurement mode is a mode for measuring tube current variation, unlike an X-ray CT scan of the subject P. In the tube current variation measurement mode, the processing circuitry 45 measures, for each of a plurality of filament current values, the tube current output value of the X-ray tube 11 and the tube current variation, which is the amount of variation in the tube current output value, when the tube voltage is switched between a first tube voltage and a second tube voltage lower than the first tube voltage, with the filament current value fixed.

[0036] Using the tube current characteristics generation function 56, the processing circuitry 45 generates tube current characteristics data for a combination of the first tube voltage and the second tube voltage, based on the multiple filament current values, tube current output values, and tube current fluctuation amounts obtained by the tube current fluctuation amount measurement function 55. The tube current characteristics data is stored in the memory 41 or the like.

[0037] Using a reacquisition determination function 57, the processing circuitry 45 determines whether or not it is necessary to reacquire the tube current characteristic data, based on the amount of fluctuation in the filament current in response to switching between the first tube voltage and the second tube voltage. If it is determined that it is necessary to reacquire the tube current characteristic data, the tube current characteristic data is reacquired by a tube current fluctuation amount measurement function 55 and a tube current characteristic generation function 56. If it is determined that it is not necessary to reacquire the tube current characteristic data, the current tube current characteristic data continues to be used.

[0038] The display control function 58 causes the processing circuitry 45 to display various information on the display 42. As one example, the processing circuitry 45 displays various images generated by the image processing function 54 on the display 42. As another example, the processing circuitry 45 displays the determination result of the reacquisition determination function 57.

[0039] Although the console 40 has been described as a single console that executes multiple functions, multiple functions may be executed by separate consoles. The processing circuitry 45 is not limited to being included in the console 40, but may also be included in an integrated server that collectively processes projection data acquired by multiple medical image diagnostic devices. Post-processing may be performed by either the console 40 or an external workstation. Furthermore, processing may be performed simultaneously by both the console 40 and the workstation.

[0040] FIG. 2 is a diagram showing an example of the configuration of an X-ray generation system including the X-ray tube 11 and the X-ray high-voltage device 14 of FIG. 1. As shown in FIG. 2, the X-ray tube 11 houses a cathode 61 and an anode 63. The cathode 61 has a filament made of a metal such as tungsten. The cathode 61 is connected to the X-ray high-voltage device 14 via a cable or the like. The cathode 61 generates heat and emits thermoelectrons when a cathode voltage and a filament current are applied from the X-ray high-voltage device 14. The anode 63 is a disk-shaped electrode made of a heavy metal such as tungsten or molybdenum. The anode 63 rotates as the rotor (not shown) rotates around its axis. A high tube voltage is applied between the cathode 61 and the anode 63 by the X-ray high-voltage device 14. Thermoelectrons emitted from the cathode 61 collide with the anode 63 due to the action of the tube voltage. The anode 63 receives the thermoelectrons and generates X-rays.

[0041] 2, the X-ray high voltage device 14 includes a high voltage power supply 71, a tube voltage control circuit 72, a tube voltage detection circuit 73, a tube voltage comparison circuit 74, a tube voltage setting circuit 75, a filament power supply 76, a tube current control circuit 77, a filament current control circuit 78, a tube current detection circuit 79, a tube current comparison circuit 80, a tube current setting circuit 81, a memory 82, a filament current detection circuit 83, a filament current comparison circuit 84, and a filament current setting circuit 85. Each circuit of the X-ray high voltage device 14 is realized by, for example, an ASIC or an FPGA.

[0042] The high-voltage power supply 71 generates a tube voltage to be applied to the X-ray tube 11 under control of a tube voltage control circuit 72. For example, in the case of an inverter-type X-ray high-voltage device, the high-voltage power supply 71 includes an AC / DC converter that converts AC voltage from a commercial power source into DC voltage, an inverter that converts the DC voltage of the AC / DC converter into AC voltage, a transformer that boosts the AC voltage from the inverter, and a high-voltage rectifying and smoothing circuit that rectifies and smoothes the AC voltage boosted by the transformer to generate a high DC voltage. The high DC voltage from the high-voltage rectifying and smoothing circuit is applied as a tube voltage between the cathode 61 and anode 63 of the X-ray tube 11.

[0043] The tube voltage detection circuit 73 detects, as a tube voltage value, the voltage applied between the cathode 61 and the anode 63. A signal (hereinafter referred to as a tube voltage output signal) of the detected tube voltage value (hereinafter referred to as a tube voltage output value) is supplied to a tube voltage comparison circuit 74.

[0044] The tube voltage setting circuit 75 switches the tube voltage setting value in synchronization with switching between the first tube voltage and the second tube voltage. The tube voltage setting circuit 75 sets the first tube voltage setting value for application of the first tube voltage, and sets the second tube voltage setting value for application of the second tube voltage. The first tube voltage setting value and the second tube voltage setting value are set by the scan condition setting function 51. A signal (hereinafter, tube voltage setting signal) indicating the tube voltage setting value (hereinafter, tube voltage setting value) is supplied to the tube voltage comparison circuit 74.

[0045] The tube voltage comparison circuit 74 receives the tube voltage setting signal from the tube voltage setting circuit 75 and the tube voltage output signal from the tube voltage detection circuit 73, and generates a signal indicating the difference between the tube voltage setting value and the tube voltage output value (hereinafter referred to as a differential voltage signal) by subtracting the tube voltage output signal from the tube voltage setting signal. The differential voltage signal is supplied to the tube voltage control circuit 72.

[0046] In a tube current modulation spectral scan, the tube voltage control circuit 72 switches the tube voltage applied to the X-ray tube 11 between a first tube voltage and a second tube voltage. The operation of switching between the first tube voltage and the second tube voltage is called kV switching. Specifically, the tube voltage control circuit 72 receives a synchronization signal from the control device 15 that indicates the timing of tube voltage switching, and controls the high-voltage power supply 71 based on a comparison between the tube voltage output value and the tube voltage set value, i.e., a differential voltage signal, at a timing in accordance with the synchronization signal. More specifically, the tube voltage control circuit 72 performs feedback control (hereinafter referred to as tube voltage feedback control) of the high-voltage power supply 71 so that the tube voltage output value converges to the tube voltage set value.

[0047] The filament power supply 76 generates a filament current for heating the filament of the cathode 61. Specifically, the filament power supply 76 has an inverter circuit that controls the current applied to the filament of the cathode 61. In the tube current modulation spectral scan, the filament power supply 76 performs feedback control using the tube current (hereinafter referred to as tube current feedback control) in accordance with control by a tube current control circuit 77, and in the tube current fluctuation measurement mode, performs feedback control using the filament current (hereinafter referred to as filament current feedback control) in accordance with control by a filament current control circuit 78.

[0048] The tube current detection circuit 79 is connected between the high-voltage power supply 71 and the X-ray tube 11. The tube current detection circuit 79 detects, as a tube current value, a current that flows due to the flow of thermoelectrons from the cathode 61 to the anode 63. A signal (hereinafter referred to as a tube current output signal) of the detected tube current value (hereinafter referred to as a tube current output value) is supplied to a tube current comparison circuit 80.

[0049] The tube current setting circuit 81 sets a tube current setting value for performing tube current modulation in parallel with switching between the first tube voltage and the second tube voltage. Specifically, the tube current setting circuit 81 sets a first tube current setting value when a reference tube voltage of the first tube voltage and the second tube voltage is applied, and sets a second tube current setting value based on tube current characteristic data and the first tube current setting value when the other of the first tube voltage and the second tube voltage is applied. Here, the tube current setting circuit 81 sets the first tube current setting value based on first tube current modulation information, and sets the second tube current setting value based on second tube current modulation information. More specifically, the tube current setting circuit 81 sets the current value of the first tube current modulation information to the first tube current setting value when the reference tube voltage is applied, and sets the current value of the second tube current modulation information to the second tube current setting value when the other tube voltage is applied. The first tube current modulation information, the second tube current modulation information, and the tube current characteristic data are stored in a memory 82. A signal indicating a tube current setting value (hereinafter, referred to as a tube current setting signal) is supplied to a tube current comparison circuit 80.

[0050] The tube current comparison circuit 80 receives as input the tube current setting signal from the tube current setting circuit 81 and the tube current output signal from the tube current detection circuit 79. The tube current comparison circuit 80 subtracts the tube current output signal from the tube current setting signal to generate a signal indicating the difference between the tube current setting value and the tube current output value (hereinafter referred to as the differential tube current signal). Specifically, when the reference tube voltage is applied, the tube current comparison circuit 80 generates a differential tube current signal indicating the difference obtained by subtracting the tube current output value from a first tube current setting value, and when another tube voltage is applied, generates a differential tube current signal indicating the difference obtained by subtracting the tube current output value from a second tube current setting value. The differential tube current signal is supplied to the tube current control circuit 77.

[0051] During tube current modulation spectral scanning, the tube current control circuit 77 performs tube current feedback control via the filament power supply 76. Specifically, in synchronization with switching between the first and second tube voltages, the tube current control circuit 77 switches between tube current feedback control based on a first tube current setting value when the reference tube voltage is applied and tube current feedback control based on a second tube current setting value when the other tube voltage is applied. More specifically, the tube current control circuit 77 controls the filament current generated by the filament power supply 76 in accordance with the differential tube current signal from the tube current comparison circuit 80, thereby controlling the tube current so that the differential tube current signal becomes zero, in other words, so that the tube current output value converges to the tube current setting value.

[0052] The filament current detection circuit 83 is connected between the filament power supply 76 and the X-ray tube 11. The filament current detection circuit 83 detects the output current of the filament power supply and outputs its effective value as a detected value. The effective value of the current for heating the filament of the cathode 61 is detected as a filament current value. A signal (hereinafter referred to as a filament current output signal) of the detected filament current value (hereinafter referred to as a filament current output value) is supplied to a filament current comparison circuit 84.

[0053] The filament current setting circuit 85 sets a plurality of filament setting values ​​to be used in the tube current fluctuation measurement mode. A signal indicating the filament current setting value (hereinafter, filament current setting signal) is supplied to the filament current comparison circuit 84.

[0054] The filament current comparison circuit 84 receives the filament current setting signal from the filament current setting circuit 85 and the filament current output signal from the filament current detection circuit 83. The filament current comparison circuit 84 subtracts the filament current output signal from the filament current setting signal to generate a signal indicating the difference between the filament current setting value and the filament current detection value (hereinafter referred to as the differential filament current signal). The differential filament current signal is supplied to the filament current control circuit 78.

[0055] In the tube current fluctuation measurement mode, the filament current control circuit 78 performs filament current feedback control via the filament power supply 76. Specifically, during kV switching, which alternates between the first tube voltage and the second tube voltage, the filament current control circuit 78 controls the filament current so that, for a target value among a plurality of filament current setting values, the filament current detection value converges to the target value, in other words, so that the differential filament current signal from the filament current comparison circuit 84 becomes zero.

[0056] The memory 82 is a storage device such as an HDD, SSD, or integrated circuit storage device that stores various information. The memory 82 may also be a drive device that reads and writes various information from and to semiconductor memory elements such as CDs, DVDs, BDs, flash memories, and RAMs. The storage area of ​​the memory 82 may be located within the X-ray high voltage device 14, within the memory 41 of the console 40, or within an external storage device connected via a network.

[0057] Each circuit of the X-ray high voltage generator 14 is not limited to being realized by an ASIC or FPGA, but may also be realized by a CPLD or SPLD, or by a processor such as a CPU and a memory such as a ROM or RAM. Furthermore, the multiple circuits of the X-ray high voltage generator 14 may be configured by a single circuit, or may be configured by different circuits. Furthermore, each circuit of the X-ray high voltage generator 14 may be configured by a single circuit, or may be configured by combining multiple independent circuits.

[0058] An example of the operation of the X-ray computed tomography apparatus 1 according to this embodiment will be described below.

[0059] The X-ray computed tomography apparatus 1 according to this embodiment first executes a tube current variation measurement mode to measure tube current variations and generate tube current characteristic data, and then executes a tube current modulation spectral scan using the generated tube current characteristic data. First, the processing procedure in the tube current variation measurement mode will be described. In the following description, the first tube voltage will be referred to as the high tube voltage and the second tube voltage will be referred to as the low tube voltage. The high tube voltage value and the low tube voltage value may be set to any values, but as an example, they are arbitrarily selected from values ​​between 40 kV and 160 kV.

[0060] 3 is a diagram illustrating a processing procedure in the tube current variation measurement mode. As shown in FIG. 3, first, the processing circuitry 45 controls the X-ray high voltage generator 14 and the control device 15 using the tube current variation measurement function 55 to execute the tube current variation measurement mode (step SA1). In step SA1, the processing circuitry 45 measures the tube current output value of the X-ray tube 11 when the tube voltage is alternately switched between a high tube voltage and a low tube voltage, with each of a plurality of filament current values ​​fixed. In the tube current variation measurement mode, it is not necessary to place the subject P on the bed 30. After step SA1 is executed, the processing circuitry 45 uses the tube current variation measurement function 55 to measure the tube current variation for each of a plurality of filament current values ​​(step SA2).

[0061] Figure 4 is a graph showing the tube current output value mA and the tube current fluctuation amount for each of multiple filament current values ​​If [A]. In the graph shown in Figure 4, the vertical axis is defined as the tube current value mA, and the horizontal axis is defined as time. In the tube current fluctuation amount measurement mode, an arbitrary number n of filament current values ​​If is specified. The number n is set to a number that ensures an amount of data that can generate a tube current characteristic diagram. The filament current value If is set to an arbitrary value within the range of values ​​that can actually be taken in a tube current modulation spectral scan.

[0062] Here, as shown in the left diagram of FIG. 4, it is assumed that the filament current value If is set to f1. With the filament current value fixed at f1, the X-ray high voltage device 14 performs kV switching, which alternately switches the tube voltage between a high tube voltage and a low tube voltage, and measures and records the tube current output value when the high tube voltage is applied and the tube current output value when the low tube voltage is applied. The high voltage value and the low tube voltage value are set to values ​​that can actually be employed in a tube current modulation spectral scan. While the specific values ​​of the high tube voltage value and the low tube voltage value are not particularly limited, it is assumed that the high tube voltage value is 140 kV and the low tube voltage value is 80 kV.

[0063] In parallel with the kV switching, the filament current control circuit 78 performs filament current feedback control on the filament power supply 76 so that the filament current output value detected by the filament current detection circuit 83 is maintained at the filament current value f1. While the kV switching and filament current feedback are being performed, the tube current detection circuit 79 detects the tube current value. It is assumed that a tube current value Va1H is detected when a high tube voltage is applied, and a tube current value Va1L is detected when a low tube voltage is applied. The detected tube current values ​​are recorded in the memory 41, etc. When the tube current value is detected, the processing circuit 45 calculates a tube current fluctuation amount da1, which is the difference between the tube current value Va1H when a high tube voltage is applied and the tube current value Va1L when a low tube voltage is applied.

[0064] It is expected that the tube current values ​​Va1H and Va1L will actually fluctuate over time. In particular, the filament temperature is unstable and the tube current value tends to fluctuate immediately after the supply of filament current begins. Therefore, the processing circuit 45 may measure the tube current output value and the tube current fluctuation amount during a stable period of the filament temperature. More specifically, statistical values ​​such as the average or median of the tube current output value and the tube current fluctuation amount during the stable period may be measured. The stable period of the filament temperature may be set, for example, to a period after a predetermined time has elapsed since the start of the supply of filament current.

[0065] The above-mentioned measurement of the tube current value and the tube current fluctuation amount is performed for each of the n filament current values. Combinations of the tube current value and the tube current fluctuation amount are stored in memory 41 in association with the filament current value. Furthermore, combinations of the tube current value and the tube current fluctuation amount are measured and stored for each combination of the expected high tube voltage value and the expected low tube voltage value.

[0066] After step SA2 is performed, the processing circuitry 45 generates tube current characteristic data when kV switching is performed using the tube current characteristic generation function 56 (step SA3). In step SA3, the processing circuitry 45 generates tube current characteristic data for combinations of high and low tube voltage values ​​based on a plurality of filament current values ​​and the tube current output values ​​and tube current fluctuation amounts for each of the plurality of filament current values.

[0067] FIG. 5 is a graph illustrating an example of tube current characteristic data. The vertical axis of the graph shown in FIG. 5 is defined as the tube current value mA, and the horizontal axis is defined as the filament current value If. The processing circuit 45 plots the tube current values ​​when a high tube voltage is applied and the tube current values ​​when a low tube voltage is applied, which are stored in the memory 41, on a graph for each filament current value. Unmeasured filament current values ​​and their corresponding tube current values ​​can be interpolated or extrapolated from measured filament current values ​​and their corresponding tube current values. In this way, tube current characteristic data is generated. Note that a curve representing the relationship between the tube current value and the filament current value when the filament current value is constant will be referred to as a tube current characteristic curve.

[0068] The dominant factor affecting tube current is filament temperature. Therefore, supplying a filament current of a value (filament current setting value) corresponding to a tube current setting value to the filament does not necessarily result in a tube current output value that corresponds to the tube current setting value. As described above, the tube current characteristic data is generated based on the tube current values ​​obtained by actually performing kV switching at high and low tube voltages that can actually be employed for the X-ray tube 11 used in tube current modulation spectral scanning, thereby heating the filament. Therefore, the tube current characteristic data represents the variation in tube current value at the filament temperature when a filament current of each filament current value is supplied during kV switching at high and low tube voltages. By using such tube current characteristic data specific to the X-ray tube 11, it can be determined that, for example, the tube current when a low tube voltage (80 kV) is applied at a filament temperature where a tube current of Va1H flows when a high tube voltage (140 kV) is applied is Va1H - da1 = Va1L.

[0069] After step SA3 is performed, the processing circuitry 45 stores the tube current characteristic data generated in step SA3 (step SA4). The tube current characteristic data is stored in the memory 41 or the like for each combination of a high tube voltage value and a low tube voltage value.

[0070] This completes the process related to the tube current fluctuation measurement mode.

[0071] Next, the processing procedure in the tube current modulation spectral scan will be described.

[0072] 6 is a diagram illustrating a processing procedure in a tube current modulation spectral scan. Note that scan conditions such as high and low tube voltage values ​​used in the tube current modulation spectral scan are assumed to be set separately.

[0073] As shown in Fig. 6, the processing circuitry 45 generates tube current modulation information for applying a reference tube voltage using the scan condition setting function 51 (step SB1). The reference tube voltage refers to the tube voltage that serves as the reference for tube current modulation, either the high tube voltage or the low tube voltage. Specifically, it refers to the tube voltage at which tube current modulation information is generated based on the subject's body thickness. In the following description, the reference tube voltage is assumed to be the high tube voltage, and the other tube voltage is assumed to be the low tube voltage.

[0074] FIG. 7 is a diagram illustrating an example of tube current modulation information for applying a reference tube voltage (high tube voltage). The vertical axis of FIG. 7 is defined as the tube current value (mA), and the horizontal axis is defined as time. Time represents the elapsed time from the start of X-ray exposure and corresponds to the X-ray tube angle. FIG. 7 shows tube current modulation information for one revolution of the X-ray tube. The tube current modulation information for applying the reference tube voltage represents the change in the tube current setting value over time when a high tube voltage is applied. The tube current value at each time point is determined, for example, based on the X-ray tube angle corresponding to that time point and the object thickness (more specifically, the water equivalent thickness) of the X-ray path at that X-ray tube angle. The object thickness may be measured by performing image processing on a positioning image, by an optical camera or laser, or by a user input via the input interface 43. The processing circuitry 45 determines the object thickness for each time point and determines the set tube current value using an existing algorithm based on the determined object thickness and the image quality evaluation value. The image quality evaluation value may be SNR (Signal-to-Noise Ratio), CNR (Contrast-to-Noise Ratio), etc. The set tube current value may be set to the minimum radiation dose that provides uniform image quality regardless of the X-ray tube angle.

[0075] After step SB1 is performed, the processing circuitry 45 reads out tube current characteristic data (step SB2). The tube current characteristic data associated with the combination of the high tube voltage value and the low tube voltage value to be used in the tube current modulation spectral scan to be performed is read out from the memory 41.

[0076] When step SB2 is performed, the processing circuitry 45 uses the tube current characteristic data read out in step SB2 to generate tube current modulation information for applying a low tube voltage from tube current modulation information for applying a high tube voltage using the scan condition setting function 51 (step SB3).

[0077] 8 is a diagram illustrating tube current modulation information for high tube voltage application (High kV) and tube current modulation information for low tube voltage application (Low kV). The vertical axis of FIG. 8 is defined as the tube current value (mA), and the horizontal axis is defined as time. Time represents the elapsed time from the start of X-ray exposure and corresponds to the X-ray tube angle. For each point of the tube current modulation information for high tube voltage application, the processing circuitry 45 identifies the tube current fluctuation amount, which is the amount of fluctuation in the tube current output value under the same filament current value, based on the tube current characteristic data, and calculates the tube current setting value for low tube voltage application based on the tube current setting value for high tube voltage application and the tube current fluctuation amount, thereby generating tube current modulation information for low tube voltage application.

[0078] First, a time point to be processed is set. The time points to be processed are set sequentially for all time points constituting the tube current modulation information. As an example, assume that time Tp1 is set. First, a tube current setting value V1H at time Tp1 is identified from the tube current modulation information for high tube voltage application. Next, the same tube current value V1H is identified from the tube current characteristic curve for high tube voltage in the tube current characteristic data for the same combination of high tube voltage and low tube voltage, and a tube current fluctuation amount DA at the identified tube current value V1H is identified. Then, a tube current setting value V1L for low tube voltage application is determined by subtracting the identified tube current fluctuation amount DA from the tube current value V1H. For example, if the tube current value at time Tp1 is Va1H, a tube current fluctuation amount da1 is identified from the tube current characteristic curve for high tube voltage in the tube current characteristic data of FIG. 5, and a tube current setting value Va1L for low tube voltage application is determined by subtracting the tube current fluctuation amount da1 from the tube current setting value Va1H. By performing the above process at each point in time, it is possible to generate tube current modulation information for applying a low tube voltage.

[0079] As described above, the tube current characteristic data is generated based on the tube current values ​​obtained by heating the filament of the X-ray tube 11 used for tube current modulation spectral scanning and performing kV switching at the combinations of high and low tube voltages actually used. Therefore, by generating a tube current characteristic curve for low tube voltage from a tube current characteristic curve for high tube voltage using the tube current characteristic data, it is possible to obtain tube current setting values ​​for high and low tube voltages at the same filament temperature at each point in time. Alternating between setting the tube current from the high and low tube voltage tube current characteristic curves thus obtained allows continuity of filament temperature to be maintained across kV switching, which is expected to enable accurate tube current feedback control at both high and low tube voltages.

[0080] After step SB3 is performed, the processing circuitry 45 performs a tube current modulation spectral scan (step SB4) using the scan control function 52. In step SB4, the processing circuitry 45 switches the tube current setting value based on the tube current modulation information for high tube voltage application generated in step SB1 and the tube current modulation information for low tube voltage application generated in step SB3, in synchronization with the switching between high tube voltage and low tube voltage, thereby performing tube current feedback control both when a high tube voltage is applied and when a low tube voltage is applied.

[0081] FIG. 9 is a diagram showing an example of the control sequence for tube current modulation spectral scanning. As shown in the first row of FIG. 9, tube current modulation information for applying a high tube voltage is acquired in step SB1, and tube current modulation information for applying a low tube voltage is acquired in step SB3. Note that because kV switching is rapid relative to such changes, the second row of FIG. 9 shows a diagram with a partially expanded time axis. As shown in the second row of FIG. 9, the set tube current value is actually set discretely. It is also possible for the tube current value to be switched multiple times during a single application period of a high or low tube voltage.

[0082] The third row of Figure 9 shows the transition of the final tube current setting value, and the fourth row of Figure 9 shows the transition of the tube voltage setting value. As shown in the fourth row of Figure 9, in a tube current modulation spectral scan, the tube voltage control circuit 72 performs kV switching by alternately switching between a high tube voltage setting value and a low tube voltage setting value in accordance with a synchronization signal, thereby performing tube voltage feedback control. The synchronization signal is a signal that alternates between a high level and a low level every time the X-ray tube angle rotates a certain angle. The high level corresponds to the application period of a high tube voltage, and the low level corresponds to the application period of a low tube voltage. The synchronization signal is supplied from the control device 15 or the like.

[0083] In parallel with the kV switching, the tube current control circuit 77 alternately switches the tube current setting value based on the tube current modulation information for high tube voltage application and the tube current modulation information for low tube voltage application in accordance with the synchronization signal, thereby performing tube current feedback control at both high and low tube voltage application. Specifically, the tube current setting circuit 81 tracks the current time based on the tube current modulation information for high tube voltage application and the tube current modulation information for low tube voltage application. When the synchronization signal switches from LOW to HIGH, the tube current setting circuit 81 identifies the tube current setting value at the current time based on the tube current modulation information for high tube voltage application and sets the identified tube current setting value as the final tube current setting value. The tube current setting signal corresponding to the final tube current setting value is supplied to the tube current comparison circuit 80. The tube current comparison circuit 80 outputs a differential tube current signal between the tube current setting signal and the tube current output signal.

[0084] The tube current control circuit 77 controls the tube current so that the differential tube current signal converges to zero, in other words, so that the tube current output value converges to the final tube current setting value, thereby performing tube current feedback control when a high tube voltage is applied.

[0085] Similarly, when the synchronization signal switches from HIGH to LOW, the tube current setting circuit 81 identifies the tube current setting value at the current time from the tube current modulation information for applying a low tube voltage, and sets the identified tube current setting value as the final tube current setting value. The tube current setting signal corresponding to the final tube current setting value is supplied to the tube current comparison circuit 80. The tube current comparison circuit 80 outputs a differential tube current signal between the tube current setting signal and the tube current output signal, and the tube current control circuit 77 controls the tube current so that the differential tube current signal converges to zero, in other words, so that the tube current output value converges to the final tube current setting value. In this way, tube current feedback control is performed when applying a low tube voltage.

[0086] For example, at time Tp2 when the synchronization signal switches from LOW to HIGH, a tube current setting value V2H is set as the final tube current setting value from the tube current modulation information for applying a high tube voltage, and tube current feedback control is performed based on the tube current setting value V2H when the high tube voltage is applied. At time Tp3 when the synchronization signal switches from HIGH to LOW, a tube current setting value V2L is set as the final tube current setting value from the tube current modulation information for applying a low tube voltage, and tube current feedback control is performed based on the tube current setting value V2L when the low tube voltage is applied.

[0087] As described above, according to this embodiment, it is possible to maintain continuity of filament temperature across kV switching, making it possible to accurately perform tube current feedback control both when a high tube voltage is applied and when a low tube voltage is applied.

[0088] This completes the process for the tube current modulation spectral scan.

[0089] The above embodiment is merely an example, and the present embodiment is not limited to this embodiment. Various elements can be deleted, added, and / or modified without departing from the gist of the invention.

[0090] 6 , for example, tube current modulation information for low tube voltage application is generated in advance before performing a tube current modulation spectral scan, and during the scan, a tube current setting value is set from the tube current modulation information for low tube voltage application. However, this embodiment is not limited to this. Instead of generating tube current modulation information for low tube voltage application, a tube current setting value for low tube voltage application may be determined and set in real time during the scan from tube current modulation information for high tube voltage application and tube current characteristic data. Specifically, the tube current setting circuit 81 tracks the current time in the tube current modulation information for high tube voltage application and the tube current modulation information for low tube voltage application, and, upon the synchronization signal switching from HIGH to LOW, identifies the tube current value at the current time from the tube current modulation information for high tube voltage application, identifies the tube current fluctuation amount corresponding to the identified tube current value from the tube current characteristic data, and sets the value obtained by subtracting the identified tube current fluctuation amount from the tube current value as the tube current setting value.

[0091] It is expected that the characteristics of the X-ray tube 11 will change over time. If the filament deteriorates due to long-term use, the fluctuation in filament current will change significantly during kV switching. Therefore, the processing circuitry 45 uses the reacquisition determination function 57 to determine whether or not it is necessary to reacquire the tube current characteristic data based on the amount of fluctuation in the filament current in response to switching between high and low tube voltages. The processing circuitry 45 then uses the display control function 58 to display the result of the determination as to whether or not reacquisition is necessary.

[0092] For example, the filament current detection circuit 83 records the amount of fluctuation in the filament current each time kV switching is performed. Specifically, the amount of fluctuation in the filament current that accompanies switching from a high tube voltage application to a low tube voltage application or from a low tube voltage application to a high tube voltage application is recorded in memory 41, memory 82, etc. Note that kV switching may be performed during a tube current modulation spectral scan or during a tube current fluctuation measurement mode.

[0093] The processing circuit 45 compares the amount of fluctuation in the filament current to be determined with the allowable value. The amount of fluctuation in the filament current to be determined is arbitrarily set from the amounts of fluctuation recorded in the memory 41, memory 82, etc. The allowable value may be set to a value that divides the amount of fluctuation measured with a deteriorated filament into the amount of fluctuation measured with a non-deteriorated filament, or may be set to a value that represents the amount of fluctuation measured with a deteriorated filament. The allowable value may be set to a value obtained by statistical analysis, etc., or may be set to a value arbitrarily determined by a user, etc. If the amount of fluctuation in the filament current to be determined is larger than the allowable value, the processing circuit 45 determines that reacquisition of the tube current characteristic data is necessary. On the other hand, if the amount of fluctuation in the filament current to be determined is smaller than the allowable value, the processing circuit 45 determines that reacquisition of the tube current characteristic data is not necessary. The result of the determination as to whether reacquisition is necessary is displayed on the display 42 in a predetermined layout.

[0094] 10 is a diagram illustrating a display screen I1 showing the result of the determination of whether or not reacquisition of tube current characteristic data is necessary. As shown in FIG. 10, the display screen I1 has a display field I11 and a display field I12. The display field I11 displays a comparison between the amount of fluctuation in the filament current "XXX" and the allowable value "XXX", such as "XXX > XXX". The display field I12 displays a message regarding the need for reacquisition. For example, if the amount of fluctuation in the filament current being determined is greater than the allowable value and it is determined that reacquisition of the tube current characteristic data is necessary, a message such as "The amount of fluctuation in the filament current exceeds the allowable value" or "Please reacquire the tube current characteristic data" is displayed.

[0095] If it is determined that the tube current characteristic data needs to be reacquired, the tube current fluctuation measurement mode illustrated in FIG. 3 is executed, and the tube current characteristic data is reacquired. By monitoring the amount of fluctuation in the filament current in this manner, it is possible to determine whether or not the tube current characteristic data needs to be reacquired. By reacquiring the tube current characteristic data in accordance with filament deterioration, it is possible to perform tube current feedback control based on tube current characteristic data that matches the behavior of the actual filament temperature or filament current, thereby improving the accuracy of tube current modulation.

[0096] According to some of the above-described embodiments, the X-ray computed tomography apparatus 1 includes an X-ray tube 11, a memory 82, a tube voltage control circuit 72, a tube current setting circuit 81, and a tube current control circuit 77. The X-ray tube 11 generates X-rays. The memory 82 stores tube current characteristic data representing the relationship between a filament current value and a tube current output value when the tube voltage applied to the X-ray tube 11 is switched between a first tube voltage and a second tube voltage lower than the first tube voltage. The tube voltage control circuit 72 switches the tube voltage applied to the X-ray tube 11 between the first tube voltage and the second tube voltage. The tube current setting circuit 81 is a unit that sets a tube current set value for performing tube current modulation in parallel with switching between the first and second tube voltages, and sets a first tube current set value when a reference tube voltage of the first and second tube voltages is applied, and sets a second tube current set value based on the tube current characteristic data and the first tube current set value when the other of the first and second tube voltages is applied. The tube current control circuit 77 performs tube current feedback control based on the first tube current set value when the reference tube voltage is applied, and performs second tube current feedback control based on the second tube current set value when the other tube voltage is applied, in synchronization with switching between the first and second tube voltages.

[0097] According to the above configuration, the tube current characteristic data is generated based on the tube current value obtained under the heated filament, which is heated by actually performing kV switching at high and low tube voltage values ​​that can actually be employed for the X-ray tube 11 used in tube current modulation spectral scanning. Based on the tube current characteristic data and the first tube current setting value when the reference tube voltage is applied, it is possible to ensure continuity of the filament temperature between when the first tube voltage and when the second tube voltage are applied. This makes it possible to suppress fluctuations in the filament current across kV switching, and is expected to enable accurate implementation of tube current feedback control based on the first tube current setting value and tube current feedback control based on the second tube current setting value.

[0098] There is a control method (hereinafter referred to as the comparative method) in which tube current feedback control is performed when a reference tube voltage is applied, but not when the other tube voltage is applied. In the comparative method, tube current feedback control is alternately switched on and off, causing large fluctuations in filament current when switching. In order to suppress fluctuations in filament current, it is necessary to reduce the difference between the maximum and minimum tube current values ​​of tube current modulation (tube current fluctuation amount), which makes it impossible to reduce radiation exposure as desired.

[0099] According to this embodiment, it is possible to perform tube current feedback at both the reference tube voltage and the other tube voltage while suppressing fluctuations in the filament current, and therefore it is possible to increase the amount of tube current fluctuation compared to the comparative example method, and ultimately to reduce the amount of radiation exposure compared to the comparative example method.

[0100] According to at least one of the embodiments described above, it is possible to improve the precision, responsiveness, allowable modulation width, etc. of tube current modulation during kV switching.

[0101] The term "processor" used in the above description refers to a circuit such as a CPU, a GPU, an application specific integrated circuit (ASIC), a programmable logic device (e.g., a simple programmable logic device (SPLD), a complex programmable logic device (CPLD), and a field programmable gate array (FPGA)). A processor realizes its function by reading and executing a program stored in a memory circuit. Note that instead of storing a program in a memory circuit, the program may be directly embedded in the processor circuit. In this case, the processor realizes its function by reading and executing the program embedded in the circuit. On the other hand, if the processor is, for example, an ASIC, the function is directly embedded in the processor circuit as a logic circuit instead of storing the program in a memory circuit. Note that each processor in this embodiment is not limited to being configured as a single circuit for each processor, but may be configured as a single processor by combining multiple independent circuits to realize its function. Furthermore, multiple components in FIGS. 1 and 2 may be integrated into a single processor to realize its function.

[0102] Although several embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations of embodiments can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0103] 1 X-ray computed tomography equipment 10 Mounting stand 11 X-ray tube 12 X-ray detector 13 Rotating Frame 14 X-ray high voltage device 15 Control device 16 Wedge 17 Collimator 18 Data Acquisition System (DAS) 19 Opening 30 berths 31 Foundation 32 Support frame 33 Top plate 34 Bed drive unit 40 Console 41 memory 42 Display 43 Input Interface 44 Communication Interface 45 Processing circuit 51 Scan condition setting function 52 Scan control function 53 Reconfiguration function 54 Image processing functions 55 Tube current fluctuation measurement function 56 Tube current characteristics generation function 57 Reacquisition judgment function 58 Display control function 61 Cathode 63 Anode 71 High voltage power supply 72 Tube voltage control circuit 73 Tube voltage detection circuit 74 Tube voltage comparison circuit 75 Tube voltage setting circuit 76 Filament power supply 77 Tube current control circuit 78 Filament current control circuit 79 Tube current detection circuit 80 Tube current comparison circuit 81 Tube current setting circuit 82 memory 83 Filament current detection circuit 84 Filament current comparison circuit 85 Filament current setting circuit

Claims

1. an X-ray tube that generates X-rays; a storage unit that stores characteristic data representing a relationship between a filament current value and a tube current output value when a tube voltage applied to the X-ray tube is switched between a first tube voltage and a second tube voltage that is lower than the first tube voltage; a tube voltage control circuit that switches a tube voltage applied to the X-ray tube between the first tube voltage and the second tube voltage; a setting unit that sets a tube current setting value for performing tube current modulation in parallel with switching between the first tube voltage and the second tube voltage, the setting unit setting a first tube current setting value when a reference tube voltage of the first tube voltage and the second tube voltage is applied, and setting a second tube current setting value based on the characteristic data and the first tube current setting value when the other tube voltage of the first tube voltage and the second tube voltage is applied; a tube current control circuit that performs tube current feedback control based on the first tube current setting value when the reference tube voltage is applied, and tube current feedback control based on the second tube current setting value when the other tube voltage is applied, in synchronization with switching between the first tube voltage and the second tube voltage; An X-ray computed tomography apparatus comprising:

2. a modulation information generating unit that generates first tube current modulation information, which is a time change of the first tube current setting value for periodically modulating a tube current, and generates second tube current modulation information, which is a time change of the second tube current setting value, based on the first tube current modulation information and the characteristic data; the setting unit sets a current value of the first tube current modulation information to the first tube current setting value when the reference tube voltage is applied, and sets a current value of the second tube current modulation information to the second tube current setting value when the other tube voltage is applied.

2. An X-ray computed tomography apparatus according to claim 1.

3. 3. The X-ray computed tomography apparatus according to claim 2, wherein the modulation information generating unit generates the second tube current modulation information by specifying, for each point of the first tube current modulation information, a tube current fluctuation amount, which is a fluctuation amount of a tube current output value under the same filament current value, based on the characteristic data, and calculating the second tube current setting value based on the first tube current setting value and the tube current fluctuation amount.

4. 3. The X-ray computed tomography apparatus according to claim 2, wherein the modulation information generating unit calculates the first tube current modulation information based on a body thickness of the subject and an image quality evaluation value.

5. a tube current measuring unit that measures, for each of a plurality of filament current values, a tube current output value of the X-ray tube and a tube current fluctuation amount that is a fluctuation amount of the tube current output value when a tube voltage is switched between the first tube voltage and the second tube voltage with the filament current value fixed; a characteristic generating unit that generates the characteristic data for a combination of the first tube voltage and the second tube voltage based on the plurality of filament current values ​​and the tube current output value and the tube current fluctuation amount for each of the plurality of filament current values.

2. An X-ray computed tomography apparatus according to claim 1.

6. 6. The X-ray computed tomography apparatus according to claim 5, wherein the tube current measuring unit measures the tube current output value and the tube current fluctuation amount when the temperature of a filament included in the X-ray tube is stable.

7. a filament current measuring unit that measures a filament current flowing through a filament included in the X-ray tube; a determination unit that determines whether or not the characteristic data needs to be reacquired based on a fluctuation amount of the filament current in response to switching between the first tube voltage and the second tube voltage; a display control unit that displays the determination result of whether or not re-acquisition is necessary, 2. An X-ray computed tomography apparatus according to claim 1.

8. 2. The X-ray computed tomography apparatus according to claim 1, wherein the reference tube voltage is the first tube voltage.

9. a storage unit that stores characteristic data representing a relationship between a filament current value and a tube current output value when a tube voltage applied to an X-ray tube is switched between a first tube voltage and a second tube voltage that is lower than the first tube voltage; a tube voltage control circuit that switches a tube voltage applied to the X-ray tube between the first tube voltage and the second tube voltage; a setting unit for setting a tube current setting value for periodically modulating a tube current of the X-ray tube in parallel with switching between the first tube voltage and the second tube voltage, the setting unit setting a first tube current setting value when a reference tube voltage of the first tube voltage and the second tube voltage is applied, and setting a second tube current setting value based on the characteristic data and the first tube current setting value when the other of the first tube voltage and the second tube voltage is applied; a tube current control circuit that switches, in synchronization with switching between the first tube voltage and the second tube voltage, between tube current feedback control based on the first tube current setting value when the reference tube voltage is applied and tube current feedback control based on the second tube current setting value when the other tube voltage is applied; An X-ray high voltage device comprising:

10. switching a tube voltage applied to an X-ray tube between a first tube voltage and a second tube voltage lower than the first tube voltage; a step of setting a tube current setting value for periodically modulating a tube current of the X-ray tube in parallel with switching between the first tube voltage and the second tube voltage, wherein a first tube current setting value is set when a reference tube voltage of the first tube voltage and the second tube voltage is applied, and a second tube current setting value based on characteristic data and the first tube current setting value is set when the other of the first tube voltage and the second tube voltage is applied, the characteristic data representing a relationship between a filament current value and a tube current output value when the tube voltage applied to the X-ray tube is switched between the first tube voltage and the second tube voltage; switching, in synchronization with the switching between the first tube voltage and the second tube voltage, between tube current feedback control based on the first tube current setting value when the reference tube voltage is applied and tube current feedback control based on the second tube current setting value when the other tube voltage is applied; An X-ray control method comprising:

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