X-ray CT apparatus, controller and control method

Abstract

To stabilize a tube current of an X-ray tube during tube current modulation scanning in an X-ray CT apparatus.SOLUTION: An X-ray CT apparatus according to an embodiment is an X-ray CT apparatus capable of performing tube current modulation scanning and includes an X-ray tube, a storage unit, a tube voltage power supply unit, an update unit, and a specification unit. The X-ray tube irradiates a subject with X-rays. The storage unit stores characteristic data in which a filament current flowing through a filament inside the X-ray tube and a tube current flowing through the X-ray tube are associated with each other for each tube voltage applied to the X-ray tube. The tube voltage power supply unit periodically switches a tube voltage between a first tube voltage value and a second tube voltage value lower than the first tube voltage value to apply it to the X-ray tube. The update unit updates an instruction value of the tube current at a predetermined timing corresponding to the switching of the tube voltage. The specification unit specifies an instruction value of the filament current corresponding to the instruction value of the tube current on the basis of the characteristic data.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The embodiments disclosed in this specification and the drawings relate to an X-ray CT apparatus, a control device, and a control method. [Background technology]

[0002] In X-ray CT (Computed Tomography) devices, a spectral scan method is used to collect image data by alternately switching the tube voltage applied to the X-ray tube between high and low voltages while the X-ray tube is rotating within the gantry.

[0003] In the spectral scan method, the tube voltage is switched rapidly during the scan, so if feedback control of the tube current [mA] (hereinafter referred to as "tube current feedback control") is always performed, the "tube current / filament current" value will become unstable. Therefore, the tube current is stabilized by performing tube current feedback control only during periods when the tube voltage is high (hereinafter referred to as "high tube voltage periods"). Furthermore, during periods when the tube voltage is low (hereinafter referred to as "low tube voltage periods"), the filament current value specified at the end of the high tube voltage period is maintained.

[0004] The above-described tube current feedback control is effective when the tube current value is constant. However, in scans in which the tube current value is modulated, the filament current during the low tube voltage period follows the filament current value at the end of the high tube voltage period, so the tube current decreases by the amount that the tube voltage is lower. If the scan transitions to the high tube voltage period under this condition, the tube current becomes unstable.

[0005] Furthermore, because the tube current command signal is not synchronized with the spectral signal, depending on the timing of the switch, the tube current may not reach the command value during the high tube voltage period and may switch to a low tube voltage. After that, the tube current may not be stable, which may affect the image.

[0006] Fig. 9 is a time chart showing the time-dependent changes in each signal and detected value in tube current feedback control according to the conventional technology. As shown in Fig. 9, the detected tube voltage value and tube current feedback control are switched in response to the spectral signal S1. When the tube current instruction signal S2 is updated during a high tube voltage (High kV) period, the detected tube current value does not reach the indicated value during the high tube voltage period, and the filament current instruction signal S3 is at its maximum value, resulting in a transition to a low tube voltage (Low kV) period (period T1 in Fig. 9). On the other hand, when the tube current instruction signal S2 is updated during a low tube voltage period, the tube current feedback control is turned on during the next high tube voltage period. However, because the difference between the indicated and detected tube current values ​​becomes large, it takes time for the detected value to converge to the indicated value (period T2 in Fig. 9).

[0007] Furthermore, when the above-described tube current feedback control is performed, the detected tube current value falls below the indicated tube current value during the low tube voltage period, as shown in Fig. 10. This is because, due to the characteristics of the X-ray tube, when a filament current value IF1 corresponding to a tube current value I1 during the high tube voltage period is maintained, the tube current value I2 corresponding to the same filament current value IF1 during the low tube voltage period falls below the tube current value I1, as shown in Fig. 11.

[0008] Therefore, if tube current feedback control is always performed, as shown in FIG. 12, when a period transitions from a low tube voltage period to a high tube voltage period, the detected tube current value significantly exceeds the specified tube current value, resulting in unnecessary exposure to radiation from the patient or user. This will be explained with reference to FIG. 11. If the specified tube current value is set to I1 due to the characteristics of the X-ray tube, when the tube current value converges to I1 during the high tube voltage period, a filament current value IF1 flows. Next, after a transition from a high tube voltage period to a low tube voltage period, when the tube current value converges to I1, a filament current value IF2 flows. Then, when a transition from a low tube voltage period to a high tube voltage period occurs, a tube current value I3 flows corresponding to the filament current value IF2 at that time due to the characteristics of the X-ray tube at high tube voltage. In other words, the tube current value exceeds the actual specified tube current value I1 by (I3 - I1). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2022-15134 Summary of the Invention [Problem to be solved by the invention]

[0010] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to stabilize the tube current of an X-ray tube in a tube current modulation scan of an X-ray CT apparatus. 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 each embodiment described below can also be positioned as other problems. [Means for solving the problem]

[0011] An X-ray CT apparatus according to an embodiment is an X-ray CT apparatus capable of performing tube current modulation scanning, and includes an X-ray tube, a storage unit, a tube voltage power supply unit, an update unit, and an identification unit. The X-ray tube irradiates an object with X-rays. The storage unit stores characteristic data that associates, for each tube voltage applied to the X-ray tube, a filament current flowing through a filament in the X-ray tube with the tube current flowing through the X-ray tube. The tube voltage power supply unit periodically switches the tube voltage between a first tube voltage value and a second tube voltage value lower than the first tube voltage value and applies the tube voltage to the X-ray tube. The update unit updates the indicated value of the tube current at a predetermined timing corresponding to the switching of the tube voltage. The identification unit identifies an indicated value of the filament current corresponding to the indicated value of the tube current based on the characteristic data. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing an example of the arrangement of an X-ray CT apparatus according to first and second embodiments. [Figure 2] FIG. 1 is a block diagram showing an example of the configuration of an X-ray generation system according to the first embodiment. [Figure 3]5 is a graph showing the characteristics between a filament current and a tube current according to the first embodiment. [Figure 4] 4 is a time chart showing an example of changes over time in each signal and detected value according to the first embodiment. [Figure 5] 4 is a time chart showing an example of changes over time in each signal and detected value according to the first embodiment. [Figure 6] FIG. 10 is a block diagram showing an example of the configuration of an X-ray generation system according to a second embodiment. [Figure 7] 10 is a graph showing the characteristics between a filament current and a tube current according to the second embodiment. [Figure 8] 10 is a time chart showing an example of changes over time in each signal and detected value according to the second embodiment. [Figure 9] 10 is a time chart showing changes over time in each signal and detected value according to the prior art; [Figure 10] 10 is a time chart showing an example of changes over time in signals and detected values ​​according to the prior art; [Figure 11] 1 is a graph showing the characteristics between a filament current and a tube current according to the prior art. [Figure 12] 10 is a time chart showing changes over time in each signal and detected value according to the prior art; DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of an X-ray CT apparatus, a control apparatus, and a control method will be described in detail with reference to the drawings.

[0014] [First embodiment] FIG. 1 is a diagram showing an example of the configuration of an X-ray CT apparatus 1 according to the first embodiment. As shown in FIG. 1, the X-ray CT apparatus 1 has a gantry 10, a bed 30, and a console 40. Although a plurality of gantry 10 are depicted in FIG. 1 for the sake of convenience, in reality, there may be one or more gantry 10. The X-ray CT apparatus 1 is capable of performing a spectral scan. A spectral scan is an example of a tube current modulation scan.

[0015] The gantry 10 is a scanning device configured to perform X-ray CT imaging of a subject P. The bed 30 is a transport device on which the subject P to be subjected to X-ray CT imaging 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. Alternatively, the console 40 may be incorporated into the gantry 10.

[0016] 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.

[0017] 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.

[0018] 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 a plurality of X-ray detection element rows, each of which has a plurality of 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 a plurality of 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.

[0019] 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.

[0020] In the first 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.

[0021] The X-ray high voltage device 14 has a high voltage generator and an X-ray control device. The high voltage generator has an electric circuit including a transformer, a rectifier, etc., 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] In the first embodiment, an integral type X-ray detector 12 and an X-ray CT device 1 equipped with an integral type X-ray detector 12 are described as examples, but the technology according to the first embodiment can also be applied to a photon counting type X-ray detector.

[0026] 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 imaging control function 441 of the processing circuit 44 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).

[0027] 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.

[0028] 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.

[0029] 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.

[0030] The console 40 has a memory 41, a display 42, an input interface 43, and a processing circuit 44. Data communication between the memory 41, the display 42, the input interface 43, and the processing circuit 44 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.

[0031] 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. 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, in addition to an HDD or SSD. The memory 41 may 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 CT apparatus 1 or in an external storage device connected via a network. The memory 41 stores, for example, projection data and reconstructed image data.

[0032] The display 42 displays various types of information. For example, the display 42 outputs CT images generated by the processing circuitry 44, 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.

[0033] The display 42 may be installed anywhere in the control room. Alternatively, the display 42 may be installed on the stand 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.

[0034] 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 44. 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. In the first 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 apparatus and outputs the electrical signal to the processing circuitry 44 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 main body.

[0035] The processing circuitry 44 controls the overall operation of the X-ray CT apparatus 1 in response to electrical signals of input operations output from the input interface 43. The processing circuitry 44 generates image data based on electrical signals output from the X-ray detector 12. For example, the processing circuitry 44 has, as hardware resources, a processor such as a CPU, MPU, or GPU, and memories such as ROM and RAM. The processing circuitry 44 executes an imaging control function 441, a reconstruction function 442, an image processing function 443, an imaging condition setting function 444, a tube current indication value update function 445, a display control function 446, etc., by a processor that executes programs loaded in the memory.

[0036] Note that each of the functions 441-446 is not limited to being 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 441-446.

[0037] The imaging control function 441 includes a function for controlling the X-ray high voltage generator 14, the control device 15, and the data acquisition circuitry 18 in accordance with the imaging conditions set by the imaging condition setting function 444, and for executing X-ray CT imaging. In the first embodiment, X-ray CT imaging is performed in which the tube voltage is alternately switched between a first tube voltage value and a second tube voltage value while modulating the tube current according to the X-ray tube angle (hereinafter referred to as the "spectral scan method"). The magnitude relationship between the first tube voltage value and the second tube voltage value is not particularly limited. For example, the first tube voltage value is a high tube voltage value, and the second tube voltage value is a low tube voltage value lower than the high tube voltage value.

[0038] The reconstruction function 442 includes a function for performing preprocessing such as logarithmic conversion processing, offset correction processing, inter-channel sensitivity correction processing, and beam hardening correction on the projection data output from the data acquisition circuitry 18. The reconstruction function 442 performs reconstruction processing using a filtered back projection method, an iterative reconstruction method, machine learning, or the like on the preprocessed projection data to generate a CT image.

[0039] The image processing function 443 includes a function for converting the CT image generated by the reconstruction function 442 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 image processing function 443 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 data 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 442.

[0040] The imaging condition setting function 444 includes a function for setting imaging conditions related to a spectral scan. Specifically, the imaging condition setting function 444 selects a first tube voltage value and a second tube voltage value to be used in a spectral scan. The selection of the tube voltage values ​​is performed either manually by a user via the input interface 43 or automatically in accordance with a predetermined algorithm. The imaging condition setting function 444 sets a tube current table indicating the time change of the tube current value under the first tube voltage value. The setting of the tube current table is performed either manually by a user via the input interface 43 or automatically in accordance with a predetermined algorithm.

[0041] The tube current instruction value update function 445 includes a function of updating the tube current instruction value in the table stored in the memory 148 of the X-ray high voltage device 14 at a predetermined timing corresponding to the switching of the tube voltage when the timing at which the tube voltage switches from a high voltage value to a low voltage value is detected. The predetermined timing is, for example, the timing at which the tube voltage switches. Alternatively, the predetermined timing may be a timing a predetermined time after the timing. The tube current instruction value update function 445 receives a spectral signal from the control device 15 and detects the timing at which the tube voltage switches. Alternatively, the tube current instruction value update function 445 may receive a tube voltage instruction signal or a tube voltage detection signal from the X-ray high voltage device 14 and detect the timing at which the tube voltage switches. The tube current instruction value update function 445 is an example of an update unit.

[0042] The display control function 446 includes a function to display various images generated by the image processing function 443 on the display 42. For example, a CT image, a cross-sectional image of an arbitrary cross section, a rendering image of an arbitrary viewpoint direction, a setting screen for imaging conditions, etc. are displayed on the display 42.

[0043] The X-ray generation system according to the first embodiment will now be described in more detail with reference to the drawings. Fig. 2 is a block diagram showing an example of the configuration of the X-ray generation system including the X-ray tube 11 and the X-ray high voltage device 14 shown in Fig. 1.

[0044] As shown in Fig. 2, the X-ray tube 11 houses a cathode 111 and an anode 113. The cathode 111 has a filament formed of a metal such as tungsten or nickel. The cathode 111 is connected to the X-ray high voltage device 14 via a cable or the like. The cathode 111 generates heat upon receiving the application of a cathode voltage and the supply of a filament current from the X-ray high voltage device 14, and emits thermoelectrons.

[0045] The anode 113 is a disk-shaped electrode made of a heavy metal such as tungsten or molybdenum. The anode 113 rotates as the rotor (not shown) rotates around its axis. A high tube voltage is applied between the cathode 111 and the anode 113 by the X-ray high voltage device 14. Thermoelectrons emitted from the cathode 111 collide with the anode 113 due to the action of the tube voltage. The anode 113 receives the thermoelectrons and generates X-rays.

[0046] 2, the X-ray high voltage device 14 includes a high voltage power supply 141, a tube voltage detection circuit 142, a tube voltage control circuit 143, a filament power supply 144, a tube current detection circuit 145, a tube current comparison circuit 146, a filament control circuit 147, and a memory 148. Each circuit of the X-ray high voltage device 14 is realized by, for example, an ASIC or an FPGA.

[0047] The high voltage power supply 141 generates a DC high voltage to be applied to the X-ray tube 11 under the control of the tube voltage control circuit 143. The DC high voltage is applied as a tube voltage between the cathode 111 and the anode 113 of the X-ray tube 11. The high voltage power supply 141 periodically switches the tube voltage between a high tube voltage value and a low tube voltage value lower than the high tube voltage value and applies the tube voltage to the X-ray tube 11. The high voltage power supply 141 is an example of a tube voltage power supply unit. The high tube voltage value is an example of a first tube voltage value. The low tube voltage value is an example of a second tube voltage value.

[0048] The tube voltage detection circuit 142 detects, as the tube voltage, the voltage applied between the cathode 111 and the anode 113. A signal (hereinafter referred to as a “tube voltage detection signal”) indicating the detected tube voltage value (hereinafter referred to as a “tube voltage detection value”) is transmitted to the filament control circuit 147.

[0049] In the spectral scan method, the tube voltage control circuit 143 switches the tube voltage applied to the X-ray tube 11 between a high tube voltage value (first tube voltage value) and a low tube voltage value (second tube voltage value). Specifically, the tube voltage control circuit 143 receives a spectral signal S1 (tube voltage modulation signal) that is a control signal that instructs the timing of tube voltage switching from the control device 15. The tube voltage control circuit 143 switches the tube voltage instruction value according to the timing at which the spectral signal S1 switches. The tube voltage control circuit 143 controls the tube voltage by transmitting a tube voltage instruction signal that indicates the tube voltage instruction value to the high-voltage power supply 141.

[0050] The filament power supply 144 generates a filament current for heating the filament of the cathode 111 under the control of the filament control circuit 147. More specifically, the filament power supply 144 has an inverter circuit that controls the voltage applied to the filament of the cathode 111. The filament power supply 144 generates the filament current by applying a voltage to the filament based on the indicated value of the filament current specified by the filament control circuit 147. The filament power supply 144 is an example of a filament power supply unit.

[0051] The tube current detection circuit 145 is connected between the high-voltage power supply 141 and the X-ray tube 11. The tube current detection circuit 145 detects, as a tube current, a current that flows due to the flow of thermoelectrons from the cathode 111 to the anode 113. A signal (hereinafter referred to as a "tube current detection signal") indicating the detected tube current value (hereinafter referred to as a "tube current detection value") is transmitted to the tube current comparison circuit 146. The tube current detection circuit 145 is an example of a detection unit.

[0052] The tube current comparison circuit 146 receives a tube current instruction signal indicating an instruction value of the tube current (hereinafter referred to as the "tube current instruction value") from the memory 148, and a tube current detection signal from the tube current detection circuit 145. The tube current comparison circuit 146 generates a differential current signal indicating a difference value (hereinafter referred to as the "tube current differential value") between the tube current instruction value indicated by the tube current instruction signal and the tube current detection value indicated by the tube current detection signal. The tube current comparison circuit 146 transmits the tube current instruction signal and the differential current signal to the filament control circuit 147. The tube current comparison circuit 146 may also transmit a tube current detection signal indicating the tube current detection value to the filament control circuit 147.

[0053] The filament control circuit 147 controls the tube current by controlling the filament current generated by the filament power supply 144. The filament control circuit 147 receives a tube voltage detection signal from the tube voltage detection circuit 142 during a scan. The filament control circuit 147 also receives a differential current signal and a tube current instruction signal from the tube current comparison circuit 146 during a scan. The filament control circuit 147 identifies an instruction value for the filament current that corresponds to an instruction value for the tube current at a predetermined tube voltage, based on the characteristic data. The characteristic data will be described later. The filament control circuit 147 is an example of an identification unit.

[0054] When the tube voltage detection value indicated by the tube voltage detection signal is a high tube voltage value, the filament control circuit 147 performs tube current feedback control. That is, the filament control circuit 147 determines a filament current command value so that the tube current detection value converges to the tube current command value as quickly as possible. In detail, the filament control circuit 147 receives a differential current signal from the tube current comparison circuit 146, and calculates a filament current command value from the tube current difference value indicated by the differential current signal in accordance with general feedback control (e.g., PID (Proportional Integral Derivative) control, etc.). Then, the filament control circuit 147 transmits a filament current command signal indicating the filament current command value to the filament power supply 144.

[0055] In other words, the filament control circuit 147 specifies a filament current command value for the high tube voltage period based on the characteristic data, from the tube current command value updated by the tube current command value update function 445 and the tube current detection value detected by the tube current detection circuit 145. The filament power supply 144 applies a voltage to the filament based on the specified filament current command value for the high tube voltage period.

[0056] When the tube voltage detection value indicated by the tube voltage detection signal is a low tube voltage, the filament control circuit 147 performs filament current feedback control. That is, the filament control circuit 147 determines the filament current setting value so that the filament current detection value converges to the filament current instruction value as quickly as possible. In detail, the filament control circuit 147 receives a tube current instruction signal from the tube current comparison circuit 146 and calculates a filament current instruction value for the high tube voltage period from the tube current instruction value indicated by the tube current instruction signal. This will be described in detail later. Then, the filament control circuit 147 transmits a filament current instruction signal indicating the filament current instruction value to the filament power supply 144. Note that the filament control circuit 147 may read the tube current instruction value from a table in the memory 148.

[0057] The memory 148 stores various control parameters, such as tube current command values ​​and predetermined thresholds (convergence criteria) used in various feedback controls. Specifically, the memory 148 stores, for each tube voltage applied to the X-ray tube 11, characteristic data associating the filament current flowing through the filament in the X-ray tube 11 with the tube current flowing through the X-ray tube 11, and the command value of the tube current. The memory 148 is a storage device such as an HDD, SSD, or integrated circuit storage device that stores various information. The memory 148 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 148 may be located within the X-ray high voltage generator 14 or within an external storage device connected via a network.

[0058] 3 is a graph showing the characteristics between the filament current and the tube current according to the first embodiment. Of the two graphs, one shows the characteristics at a high tube voltage, and the other shows the characteristics at a low tube voltage. The data for the graph is stored, for example, in the memory 148 of the X-ray high voltage device 14. The filament control circuit 147 then references the graph data in the memory 148 when calculating the filament current instruction value for the high tube voltage period from the tube current instruction value. That is, the filament control circuit 147 identifies the filament current instruction value corresponding to the tube current instruction value from the graph at the high tube voltage. Note that the filament control circuit 147 may reference a lookup table with discrete values ​​instead of a graph with continuous values.

[0059] Fig. 4 is a time chart showing an example of changes over time in each signal and detection value according to the first embodiment. Fig. 4 is a time chart showing a case where the tube current command signal S2 is updated when the spectral signal S1 switches from a high tube voltage (High kV) to a low tube voltage (Low kV). This will be explained in detail below.

[0060] The spectral signal S1 is a control signal that indicates the timing of tube voltage switching. The spectral signal S1 is transmitted from the control device 15 to the tube voltage control circuit 143 of the X-ray high voltage device 14. As shown in Fig. 4, the spectral signal S1 periodically alternates between a high tube voltage and a low tube voltage.

[0061] The tube voltage is a voltage applied to the X-ray tube 11 from the high-voltage power supply 141 by the tube voltage control circuit 143 controlling the high-voltage power supply 141 in accordance with the spectral signal S1. The detected tube voltage value is the value of the tube voltage detected by the tube voltage detection circuit 142. Similar to the spectral signal S1, the detected tube voltage value alternates between a high tube voltage and a low tube voltage. Note that the detected tube voltage value does not rise immediately upon startup from 0 kV, but gradually increases toward the high tube voltage value.

[0062] Tube current feedback control is turned on (i.e., executed) during a high tube voltage period. Tube current feedback control is turned off (i.e., not executed) during a low tube voltage period. During a low tube voltage period, filament current feedback control is executed instead of tube current feedback control.

[0063] The tube current instruction signal S2 is a signal indicating the instruction value of the tube current. The tube current instruction signal S2 is set to the tube current instruction value read by the tube current comparison circuit 146 from the memory 148, and is transmitted to the filament control circuit 147. The tube current instruction value update function 445 updates the tube current instruction value in the memory 148 at the timing when the tube voltage switches from a high tube voltage value to a low tube voltage value. As a result, the tube current instruction signal S2 is updated at the timing when the tube voltage switches from a high tube voltage value to a low tube voltage value.

[0064] The detected tube current value is the value of the tube current detected by the tube current detection circuit 145. The tube current of the X-ray tube 11 has characteristics that depend on the filament current and the tube voltage. During a high tube voltage period, the detected tube current value is initially significantly lower than the indicated tube current value, so it takes time for it to converge to the indicated tube current value. On the other hand, during a low tube voltage period, even if the detected filament current value does not change, the detected tube voltage value is low, so the detected tube current value initially decreases and then stabilizes.

[0065] The filament current instruction signal S3 is a signal that indicates the filament current instruction value. The filament current instruction value is determined according to the tube current difference value and the optimum filament current value. The filament current instruction signal S3 is transmitted from the filament control circuit 147 to the filament power supply 144. As shown in FIG. 4 , during the high tube voltage period, the tube current feedback control is turned on, and therefore the graph of the filament current instruction signal S3 has a high, projecting shape in order to reduce the initially large tube current difference value. Once the tube current difference value decreases and the detected tube current value converges to the tube current instruction value, the filament current instruction signal S3 stabilizes. During the low tube voltage period, the tube current feedback control is turned off and the filament current feedback control is turned on, so the filament current instruction signal S3 remains stable.

[0066] The filament current detection value is the value of the filament current detected by the filament power supply 144. In response to the filament current instruction signal S3, the filament current detection value rises at the beginning of the high tube voltage period, but remains stable during other periods.

[0067] According to the above, the tube current instruction signal is updated when the spectral signal S1, the tube voltage instruction value, or the detected tube voltage value switches from a high tube voltage to a low tube voltage. As a result, the tube current instruction signal is not updated during the high tube voltage period, and the filament current remains stable even when the high tube voltage period is transitioned to the low tube voltage period.

[0068] 4, the filament control circuit 147 determines the filament current instruction value for the high tube voltage period from the tube current instruction value during the low tube voltage period, and transmits a filament current instruction signal indicating this instruction value to the filament power supply 144. For example, according to FIG. 3, when the tube current instruction value is I1, the characteristics during low tube voltage are such that the filament current is controlled to flow at 4.5 A. When the low tube voltage period transitions to the high tube voltage period in this state, the filament current is greater than 4 A during high tube voltage, and so the tube current temporarily exceeds the instruction value I1.

[0069] Therefore, in the control of FIG. 5 , the filament control circuit 147 determines, during the low tube voltage period, 4 A, which is the filament current for the high tube voltage period, as the designated value from the tube current designated value I1. FIG. 5 is a time chart showing an example of temporal changes in each signal and detection value according to the first embodiment. In addition to the control of FIG. 4 , FIG. 5 is a time chart showing a case in which, during the low tube voltage period, a filament current designated value for the high tube voltage period is determined from the tube current designated value, and filament current feedback control is performed. Here, the filament control circuit 147 determines, based on the characteristic data, the filament current designated value for the high tube voltage period from the tube current designated value updated by the tube current designated value update function 445. Then, during the low tube voltage period, the filament power supply 144 applies a voltage to the filament based on the filament current designated value determined by the filament control circuit 147. Below, differences from FIG. 4 will be mainly described.

[0070] The spectral signal S1 and the detected tube voltage value are the same as those in Figure 4. Tube current feedback control is turned on during high tube voltage periods and turned off during low tube voltage periods. During low tube voltage periods, filament current feedback control is executed instead of tube current feedback control. As in Figure 4, the tube current command signal S2 is updated when the tube voltage switches from a high voltage value to a low voltage value.

[0071] During the first high tube voltage period, the detected tube current value is initially 0 mA, which is significantly lower than the indicated tube current value, and so it takes time for the detected tube current value to converge to the indicated tube current value. Meanwhile, at the timing of switching from the high tube voltage period to the low tube voltage period, the tube current indication signal S2 is updated, and filament current feedback control is executed using the filament current indication value for high tube voltage calculated from the indicated tube current value as the appropriate value. During the low tube voltage period, the detected tube current value initially drops, as in Figure 4, but then stabilizes, approaching the indicated tube current value. Therefore, from the second high tube voltage period onwards, the detected tube current value quickly converges to the indicated tube current value.

[0072] As shown in Figure 5, during the high tube voltage period, tube current feedback control is turned on, and the graph of the filament current instruction signal S3 has a high, projecting shape in order to reduce the initially large tube current difference value. Once the tube current difference value decreases and the detected tube current value converges to the tube current instruction value, the filament current instruction signal S3 stabilizes. During the low tube voltage period, filament current feedback control is executed, and the filament current instruction signal S3 indicates the filament current instruction value at the high tube voltage as the appropriate value.

[0073] In response to the filament current instruction signal S3, the filament current detection value initially rises slightly during the high tube voltage period but then stabilizes.In the low tube voltage period, the filament current detection value initially rises gradually to an appropriate value but then stabilizes.

[0074] According to the above, during a low tube voltage period, the filament control circuit 147 identifies a filament current instruction value for a high tube voltage from the updated tube current instruction value and performs feedback control to that filament current instruction value, thereby stabilizing the filament current. As a result, when the next high tube voltage period begins, the necessary filament current is already flowing, so the detected tube current value quickly converges to the tube current instruction value. Therefore, during a high tube voltage period, the actual tube current quickly converges to the instruction value, enabling stable tube current control, which ultimately contributes to improving the image quality of X-ray images.

[0075] 5, as shown in FIG. 3, the filament current during the high tube voltage period for the tube current command value I1 is 4 A, and therefore the tube current during the low tube voltage period is I2, which is smaller than the tube current command value I1. Therefore, as a modification of the first embodiment, the filament control circuit 147 may control the filament current during the low tube voltage period so that the detected tube current value approaches the tube current command value I1 as closely as possible. For example, the filament control circuit 147 may set the filament current value during the low tube voltage period for a tube current value between I1 and I2 as the filament current command value.

[0076] The following description will be given with reference to Fig. 3. The filament control circuit 147 specifies a filament current value of 4A for the high tube voltage period from the tube current instruction value I1 updated by the tube current instruction value update function 445 based on the characteristic data. Next, the filament control circuit 147 specifies a tube current value I2 for the low tube voltage period from the filament current value 4A. Then, the filament control circuit 147 specifies a filament current instruction value for the low tube voltage period (an intermediate value between 4A and 4.5A) from the intermediate value between the tube current instruction value I1 and the tube current value I2. The filament power supply 144 applies a voltage to the filament based on the specified filament current instruction value during the low tube voltage period.

[0077] Second Embodiment The X-ray generation system according to the second embodiment will be described in more detail with reference to the drawings. The configuration example of the X-ray CT device 1 shown in Fig. 1 is also applicable to the second embodiment. Fig. 6 is a block diagram showing a configuration example of the X-ray generation system including the X-ray tube 11 and the X-ray high voltage device 14 of Fig. 1. Below, differences from the description of Fig. 2 of the first embodiment will be described.

[0078] 6, the X-ray high voltage device 14 includes a high voltage power supply 141, a tube voltage detection circuit 142, a tube voltage control circuit 143, a filament power supply 144, a tube current detection circuit 145, a tube current comparison circuit 146, a filament control circuit 147, a memory 148, and a tube current control circuit 149. Each circuit of the X-ray high voltage device 14 is realized by, for example, an ASIC or an FPGA.

[0079] The high voltage power supply 141, the tube voltage detection circuit 142, the tube voltage control circuit 143, the filament power supply 144, and the tube current detection circuit 145 are the same as those described with reference to FIG.

[0080] The tube current comparison circuit 146 receives a tube current instruction signal indicating a tube current instruction value from the tube current control circuit 149 and a tube current detection signal from the tube current detection circuit 145. The tube current comparison circuit 146 generates a differential current signal indicating a tube current difference value between the tube current instruction value indicated by the tube current instruction signal and the tube current detection value indicated by the tube current detection signal. The tube current comparison circuit 146 transmits the differential current signal to the filament control circuit 147.

[0081] The filament control circuit 147 controls the tube current by controlling the filament current generated by the filament power supply 144. The filament control circuit 147 receives a tube voltage detection signal from the tube voltage detection circuit 142 during a scan. The filament control circuit 147 also receives a tube current instruction signal from the tube current control circuit 149 during a scan, and receives a differential current signal from the tube current comparison circuit 146. The filament control circuit 147 identifies a filament current instruction value corresponding to a tube current instruction value at a predetermined tube voltage based on the characteristic data. The characteristic data indicates the characteristics between the filament current and the tube current for each tube voltage. The filament control circuit 147 is an example of an identification unit.

[0082] When the detected tube voltage value indicated by the tube voltage detection signal is a high tube voltage value, the filament control circuit 147 identifies a filament current instruction value for the high tube voltage period from the tube current instruction value based on the characteristic data. The filament power supply 144 applies a voltage to the filament based on the identified filament current instruction value during the high tube voltage period.

[0083] When the tube voltage detection value indicated by the tube voltage detection signal is a low tube voltage value, the filament control circuit 147 specifies a filament current instruction value for the low tube voltage period from the tube current instruction value based on the characteristic data. The filament power supply 144 applies a voltage to the filament based on the specified filament current instruction value during the low tube voltage period.

[0084] The filament control circuit 147 also performs tube current feedback control. That is, the filament control circuit 147 determines the filament current command value so that the tube current detection value converges to the tube current command value as quickly as possible. In particular, the filament control circuit 147 receives a differential current signal from the tube current comparison circuit 146, and calculates the filament current command value from the tube current difference value indicated by the differential current signal in accordance with general feedback control (e.g., PID (Proportional Integral Derivative) control, etc.). The filament control circuit 147 then transmits a filament current command signal indicating the filament current command value to the filament power supply 144. The filament power supply 144 applies a voltage to the filament based on the filament current command signal received from the filament control circuit 147.

[0085] The memory 148 stores various control parameters, such as tube current command values ​​and predetermined thresholds (convergence criteria) used in various feedback controls. Specifically, the memory 148 stores characteristic data associating the filament current flowing through the filament in the X-ray tube 11 with the tube current flowing through the X-ray tube 11 for each tube voltage applied to the X-ray tube 11. The memory 148 is a storage device, such as an HDD, SSD, or integrated circuit storage device, that stores various pieces of information. The memory 148 may also be a drive device that reads and writes various pieces of information from and to semiconductor memory elements, such as CDs, DVDs, BDs, flash memories, and RAMs. The storage area of ​​the memory 148 may be located within the X-ray high voltage generator 14 or within an external storage device connected via a network. The memory 148 is an example of a storage unit.

[0086] The tube current control circuit 149 determines the tube current command value. Specifically, during periods of high tube voltage values, the tube current control circuit 149 acquires a predetermined tube current value from the control device 15 and determines it as the tube current command value. On the other hand, during periods of low tube voltage values, the tube current control circuit 149 identifies a filament current value associated with a predetermined tube current value corresponding to a high tube voltage value based on the characteristic data stored in the memory 148, and determines the tube current value associated with the identified filament current value corresponding to the low tube voltage value as the tube current command value. The tube current control circuit 149 then transmits a tube current command signal indicating the determined tube current command value to the tube current comparison circuit 146 and the filament control circuit 147. The timing of transmitting the tube current command signal will be described later. The tube current control circuit 149 is an example of an update unit.

[0087] 7 is a graph showing the characteristics between the filament current and the tube current according to the second embodiment. This graph is an example of characteristic data. Of the two graphs, the solid line shows the characteristics at high tube voltage, and the dashed line shows the characteristics at low tube voltage. The data of the graphs is stored, for example, in the memory 148 of the X-ray high voltage device 14.

[0088] Referring to FIG. 7 , an example of operation will be described in which the tube current control circuit 149 determines the tube current command value for a high tube voltage to be I1. When the tube current value converges to I1 during a high tube voltage period, a filament current value IF1 flows. After transitioning from a high tube voltage period to a low tube voltage period, the tube current control circuit 149 maintains the tube current command value at I1 during the high tube voltage period during the first half of the view. When the tube current value converges to I1 during the low tube voltage period, a filament current value IF2 flows. During the second half of the low tube voltage period, the tube current control circuit 149 switches the tube current command value to I2. When the tube current value converges to I2 during the low tube voltage period, a filament current value IF1 flows. After transitioning from a low tube voltage period to a high tube voltage period, the tube current control circuit 149 returns the tube current command value to I1. In this way, even if the tube current command value is increased from I2 to I1, IF1 is already flowing as the filament current, and the tube current value converges without exceeding I1.

[0089] Then, when calculating the filament current instruction value from the tube current instruction value determined by the tube current control circuit 149, the filament control circuit 147 refers to the graph data in the memory 148. That is, the filament control circuit 147 identifies the filament current instruction value corresponding to the tube current instruction value from the graph at the time of high tube voltage or low tube voltage. Note that the filament control circuit 147 may refer to a lookup table with discrete values ​​instead of a graph with continuous values.

[0090] 7, control may be performed so that the difference between the tube currents I1 and I2 becomes smaller. For example, the filament control circuit 147 identifies a filament current value IF1 associated with the tube current value I1 corresponding to a high tube voltage value based on the characteristic data. Next, the filament control circuit 147 identifies a tube current value I2 associated with the identified filament current value IF1 corresponding to a low tube voltage value. Then, the filament control circuit 147 identifies a filament current value (an intermediate value between IF1 and IF2) associated with an intermediate value between the tube current value I1 and the identified tube current value I2, which corresponds to the low tube voltage value.

[0091] Fig. 8 is a time chart showing an example of time-dependent changes in each signal and detection value according to the second embodiment. Fig. 8 is a time chart showing a case where the tube current instruction signal S2 is updated at the timing when the view is switched. This will be explained in detail below.

[0092] The spectral signal S1 is a control signal that indicates the timing of switching the tube voltage. The spectral signal S1 is transmitted from the control device 15 to the tube voltage control circuit 143 and the tube current control circuit 149 of the X-ray high voltage device 14. As shown in Fig. 8, the spectral signal S1 periodically switches between a high tube voltage and a low tube voltage.

[0093] The view period per one time is determined by the number of data acquisitions per rotation of the rotating frame 13. In the example shown in FIG. 8, the spectral signal S1 switches every 10 views. The control device 15 notifies the tube current control circuit 149 of the timing at which the view switches. The tube current control circuit 149 acquires the timing at which the view switches from the control device 15, and switches the tube current instruction value at a predetermined timing corresponding to the acquired timing. The predetermined timing includes the timing at which the view switches. The control device 15 and the tube current control circuit 149 are examples of an update unit. The tube current feedback control is always on and is continuously performed by the tube current comparison circuit 146 and the filament control circuit 147 .

[0094] The tube voltage is a voltage applied to the X-ray tube 11 from the high-voltage power supply 141 by the tube voltage control circuit 143 controlling the high-voltage power supply 141 in accordance with the spectral signal S1. The detected tube voltage value is the value of the tube voltage detected by the tube voltage detection circuit 142. Similar to the spectral signal S1, the detected tube voltage value alternates between a high tube voltage and a low tube voltage. Note that the detected tube voltage value does not rise immediately when started from 0 V, but gradually increases toward the high tube voltage value.

[0095] The tube current command signal S2 is a signal indicating a tube current command value. A tube current command value determined by the tube current control circuit 149 is set in the tube current command signal S2, and the signal is transmitted to the tube current comparison circuit 146 and the filament control circuit 147. The tube current detection value is the value of the tube current detected by the tube current detection circuit 145. The tube current of the X-ray tube 11 has characteristics that depend on the filament current and the tube voltage. Switching of the tube current command value and changes in the tube current detection value will be described below.

[0096] 8, the tube current control circuit 149 sets the tube current command value to I1 during the high tube voltage period and the first half of the low tube voltage period (e.g., 7 views) after the start of a spectral scan. At the start of the high tube voltage period, the detected tube current value rises slightly late, but quickly converges to I1. At the start of the low tube voltage period, the detected tube current value fluctuates downward, but soon converges to I1.

[0097] The control device 15 determines the timing of view switching at which the tube current instruction value should be switched from the tube current value I1 based on the difference between the filament current value IF1 associated with the tube current value I1 corresponding to the high tube voltage value and the filament current value IF2 associated with the tube current value I1 corresponding to the low tube voltage value, and notifies the tube current control circuit 149 of the timing.

[0098] During the low tube voltage period, the tube current control circuit 149 switches the tube current instruction value from the tube current value I1 to the tube current value I2 associated with the filament current value IF1 corresponding to the low tube voltage value at the timing of view switching specified and notified by the control device 15. Then, the tube current control circuit 149 transmits a tube current instruction signal S2 indicating the switched tube current instruction value I2 to the tube current comparison circuit 146 and the filament control circuit 147.

[0099] This suppresses the tube current from the timing mentioned above in the latter half of the low tube voltage period (for example, for three views), thereby preventing tube current overshoot when the tube voltage switches from a low tube voltage value to a high tube voltage value, thereby preventing unnecessary exposure of patients and users. In addition, it stabilizes the tube current of the X-ray tube 11, contributing to improved image quality of CT images.

[0100] Furthermore, the control device 15 notifies the tube current control circuit 149 of the timing at which the tube voltage switches from the low tube voltage value to the high tube voltage value. The tube current control circuit 149 returns the tube current instruction value to the tube current value I1 at the timing notified by the control device 15, i.e., when the tube voltage switches from the low tube voltage value to the high tube voltage value. The tube current control circuit 149 then transmits a tube current instruction signal S2 indicating the tube current instruction value I1 to the tube current comparison circuit 146 and the filament control circuit 147.

[0101] According to this, the tube current instruction value I2, which was temporarily suppressed during the low tube voltage period, is raised to the original tube current instruction value I1 when switching to the high tube voltage period, which slows down the rise of the tube current detection value. Therefore, although there is a possibility that at least the first view after the tube voltage is switched to the high tube voltage value will be invalid, the effect of preventing unnecessary exposure of the patient or user and stabilizing the tube current of the X-ray tube 11 takes priority.

[0102] The filament current instruction signal S3 is a signal indicating a filament current instruction value. The filament current instruction value is determined according to the tube current instruction value and the tube current difference value. The filament current instruction signal S3 is transmitted from the filament control circuit 147 to the filament power supply 144. The filament power supply 144 applies a voltage to the filament based on the filament current instruction signal S3 received from the filament control circuit 147. The filament current detection value is the value of the filament current detected by the filament power supply 144.

[0103] In the second embodiment, a configuration has been described in which the X-ray CT apparatus 1 includes the X-ray high voltage device 14 and the control device 15. However, the X-ray high voltage device 14 and the control device 15 may be installed as hardware separate from the X-ray CT apparatus 1, and may externally control the voltage and current related to the X-ray tube 11 of the X-ray CT apparatus 1. In other words, a system configuration may be provided that includes the X-ray CT apparatus 1 and a control device for the X-ray CT apparatus 1.

[0104] According to at least one of the embodiments described above, the tube current of the X-ray tube can be stabilized in a tube current modulation scan of an X-ray CT apparatus.

[0105] 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]

[0106] 1...X-ray CT device 11...X-ray tube 14...X-ray high voltage device 30...bed 141...high voltage power supply 144...filament power supply 145...tube current detection circuit 147...filament control circuit 148...memory 149...tube current control circuit 15...control device 445...tube current indication value update function P...subject

Claims

1. An X-ray CT apparatus capable of performing tube current modulation scanning, an X-ray tube that irradiates an object with X-rays; a storage unit that stores characteristic data that associates, for each tube voltage applied to the X-ray tube, a filament current flowing through a filament in the X-ray tube with a tube current flowing through the X-ray tube; a tube voltage power supply unit that periodically switches the tube voltage between a first tube voltage value and a second tube voltage value lower than the first tube voltage value and applies the tube voltage to the X-ray tube; an updating unit that updates the indicated value of the tube current at a predetermined timing according to the switching of the tube voltage; an identification unit that identifies an instruction value of a filament current corresponding to the instruction value of the tube current based on the characteristic data; An X-ray CT device equipped with the above.

2. a filament power supply unit that applies a voltage to the filament based on the specified indication value of the filament current; Furthermore, The update unit updating the indicated value of the tube current at the predetermined timing when the tube voltage is switched from the first tube voltage value to the second tube voltage value; The identification unit determining an indicated value of a filament current corresponding to an indicated value of the tube current at a predetermined tube voltage based on the characteristic data; The X-ray CT apparatus according to claim 1 .

3. the specifying unit specifies, based on the characteristic data, an indicated value of the filament current during a period in which the tube voltage is the first tube voltage value from the indicated value of the updated tube current; the filament power supply unit applies a voltage to the filament based on the specified instruction value of the filament current during a period in which the tube voltage is the second tube voltage value. The X-ray CT apparatus according to claim 2.

4. a detector for detecting the tube current; the specifying unit specifies an indicated value of the filament current during a period in which the tube voltage is the first tube voltage value, from the updated indicated value of the tube current and the detected value of the tube current, based on the characteristic data; the filament power supply unit applies a voltage to the filament during the period based on the specified instruction value of the filament current; The X-ray CT apparatus according to claim 2.

5. The specifying unit, based on the characteristic data, Identifying the value of the filament current during a period in which the tube voltage is at the first tube voltage value from the updated indicated value of the tube current; identifying a value of the tube current during a period in which the tube voltage is at the second tube voltage value from the value of the filament current; specifying an instruction value of the filament current during a period in which the tube voltage is the second tube voltage value from an intermediate value between the instruction value of the tube current and the value of the tube current; the filament power supply unit applies a voltage to the filament based on the specified instruction value of the filament current during a period in which the tube voltage is the second tube voltage value. The X-ray CT apparatus according to claim 2.

6. The update unit updating the indicated value of the tube current with a timing at which a view is switched, the timing being determined by the number of data acquisitions per rotation of a rotating frame, as the predetermined timing; The X-ray CT apparatus according to claim 1 .

7. The update unit During the period of the first tube voltage value, a predetermined tube current value is determined as the indicated value of the tube current, During the period of the second tube voltage value, a filament current value associated with the predetermined tube current value corresponding to the first tube voltage value is identified based on the characteristic data, and the tube current value associated with the identified filament current value corresponding to the second tube voltage value is determined as the indicated value of the tube current. The X-ray CT apparatus according to claim 6.

8. The update unit when the tube voltage is switched from the second tube voltage value to the first tube voltage value, the indicated value of the tube current is set to the predetermined tube current value. The X-ray CT apparatus according to claim 7.

9. The update unit determining a timing of switching the view at which the indicated value of the tube current should be switched from the predetermined tube current value based on a difference between a filament current value associated with the predetermined tube current value corresponding to the first tube voltage value and a filament current value associated with the predetermined tube current value corresponding to the second tube voltage value; switching the indicated value of the tube current from the predetermined tube current value to a tube current value associated with the specified filament current value corresponding to the second tube voltage value at a timing of switching the specified view during the period of the second tube voltage value; The X-ray CT apparatus according to claim 7.

10. The specifying unit, based on the characteristic data, identifying a filament current value associated with the predetermined tube current value corresponding to the first tube voltage value; Identifying a tube current value associated with the identified filament current value corresponding to the second tube voltage value; identifying a filament current value associated with an intermediate value between the predetermined tube current value and the identified tube current value, the filament current value corresponding to the second tube voltage value; The X-ray CT apparatus according to claim 7.

11. A control device for an X-ray CT apparatus capable of performing tube current modulation scanning, comprising: a storage unit that stores characteristic data that associates, for each tube voltage applied to an X-ray tube that irradiates an object with a filament current flowing through the X-ray tube, with a tube current flowing through the X-ray tube; a tube voltage power supply unit that periodically switches the tube voltage between a first tube voltage value and a second tube voltage value lower than the first tube voltage value and applies the tube voltage to the X-ray tube; an updating unit that updates the indicated value of the tube current at a predetermined timing according to the switching of the tube voltage; an identification unit that identifies an instruction value of a filament current corresponding to the instruction value of the tube current based on the characteristic data; A control device comprising:

12. a filament power supply unit that applies a voltage to the filament based on the specified indication value of the filament current; Furthermore, The update unit updating the indicated value of the tube current at the predetermined timing when the tube voltage is switched from the first tube voltage value to the second tube voltage value; The identification unit determining an indicated value of a filament current corresponding to an indicated value of the tube current at a predetermined tube voltage based on the characteristic data; The control device according to claim 11.

13. The update unit updating the indicated value of the tube current with a timing at which a view is switched, the timing being determined by the number of data acquisitions per rotation of a rotating frame, as the predetermined timing; The control device according to claim 11.

14. A control method for an X-ray CT apparatus capable of performing tube current modulation scanning, comprising: storing characteristic data that associates, for each tube voltage applied to an X-ray tube that irradiates an object with a filament current flowing through the X-ray tube, with a tube current flowing through the X-ray tube; applying the tube voltage to the X-ray tube by periodically switching between a first tube voltage value and a second tube voltage value lower than the first tube voltage value; updating the indicated value of the tube current at a predetermined timing according to the switching of the tube voltage; determining an indicated value of a filament current corresponding to the indicated value of the tube current based on the characteristic data; Control method.

15. applying a voltage to the filament based on the identified indicated value of the filament current; updating the indicated value of the tube current at the predetermined timing when the tube voltage is switched from the first tube voltage value to the second tube voltage value; determining an indicated value of a filament current corresponding to an indicated value of the tube current at a predetermined tube voltage based on the characteristic data; The control method according to claim 14.

16. updating the indicated value of the tube current with a timing at which a view is switched, the timing being determined by the number of data acquisitions per rotation of a rotating frame, as the predetermined timing; The control method according to claim 14.

Images