X-ray computed tomography equipment

Abstract

To switch gains related to data collection in synchronization with switching of tube voltages.SOLUTION: An X-ray computed tomography apparatus according to an embodiment includes a tube voltage control part, a first signal generation part, a view switching part, a data collection part, a second signal generation part, and a gain switching part. The tube voltage control part switches tube voltages applied to an X-ray tube between a first tube voltage and a second tube voltage lower than the first tube voltage. The first signal generation part generates a first switch signal at a first time interval. The view switching part switches views on the basis of the first switch signal. The data collection part executes data collection by the view through an X-ray detector. The second signal generation part generates a second switch signal at a second time interval shorter than the first time interval. The gain switching part switches the gains of the data collection part on the basis of the second switch signal.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The embodiments disclosed in this specification and the drawings relate to an X-ray computed tomography apparatus. [Background technology]

[0002] One imaging technique using an X-ray computed tomography system is dual-energy scanning, in which imaging is performed while switching between two types of tube voltage to acquire two types of projection data corresponding to the two types of energy. The technique of alternating between tube voltages is called kV switching. During kV switching, the gain of the data acquisition circuit is not changed, and data acquisition is performed at the same gain (amplification factor). If kV switching is performed at the same gain, the signal-to-noise ratio (SNR) will deteriorate due to the small gain on the low tube voltage side, and the gain will be large on the high tube voltage side, causing overflow and the risk of artifacts and CT value deviations. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-74825 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 switch the gain related to data acquisition in synchronization with switching of the tube voltage. 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 a tube voltage controller, a first signal generator, a view switcher, a data acquisition unit, a second signal generator, and a gain switcher. The tube voltage controller switches 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. The first signal generator generates a first switching signal at a first time interval. The view switcher switches views based on the first switching signal. The data acquisition unit acquires data on a view-by-view basis via an X-ray detector. The second signal generator generates a second switching signal at a second time interval shorter than the first time interval. The gain switcher switches the gain of the data acquisition unit based on the second switching signal. [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 the first embodiment. [Figure 2] FIG. 2 is a diagram showing an example of a configuration of a main component related to kV switching according to the first embodiment. [Figure 3] FIG. 3 is a plan view showing an arrangement of X-ray detection elements. [Figure 4] FIG. 4 is a diagram showing the readout completion times of the electrical signals from each X-ray detection element array. [Figure 5] FIG. 5 is a diagram showing an example of a timing chart relating to switching between a high tube voltage gain and a low tube voltage gain according to the first embodiment. [Figure 6] FIG. 6 is a diagram showing an example of a timing chart relating to switching between a high tube voltage gain and a low tube voltage gain in a comparative example. [Figure 7] FIG. 7 is a timing chart for collecting drift correction data. [Figure 8] FIG. 8 is a timing chart for collecting offset correction data. [Figure 9] FIG. 9 is a diagram showing an example of a configuration of a main component related to kV switching according to the second embodiment. [Figure 10]FIG. 10 is a diagram showing an example of a timing chart relating to switching between a high tube voltage gain and a low tube voltage gain according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, an embodiment of an X-ray computed tomography apparatus will be described in detail with reference to the drawings. In the following description, components having the same or substantially the same functions as those described above with reference to the previous drawings will be assigned the same reference numerals and will be described only when necessary. Furthermore, even when the same parts are shown, the dimensions and proportions may differ depending on the drawing.

[0008] There are various types of X-ray computed tomography apparatuses (X-ray CT apparatuses) according to this embodiment, such as third-generation CT and fourth-generation CT, and any of these types can be applied to this embodiment. Here, a third-generation CT is a rotate / rotate-type in which an X-ray tube and a detector rotate together around the subject. A 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. Furthermore, the X-ray computed tomography apparatus according to this embodiment can be applied to a single-tube type in which one pair of an X-ray tube and a detector is mounted on a rotating ring, or a multi-tube type in which multiple pairs of X-ray tubes and detectors are mounted on a rotating ring, but the following description will be limited to the single-tube type.

[0009] (First embodiment) 1 is a diagram showing the configuration of an X-ray computed tomography apparatus 1 according to the first embodiment. The X-ray computed tomography apparatus 1 irradiates a subject P with X-rays from an X-ray tube 11 and detects the irradiated X-rays with an X-ray detector 12. The X-ray computed tomography apparatus 1 generates a CT image of the subject P based on the output from the X-ray detector 12.

[0010] 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 X-ray computed tomography apparatus 1 may include one or multiple gantry 10s. 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. The console 40 may also be incorporated into the cradle 10 .

[0011] 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.

[0012] 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 receives thermoelectrons flying from the cathode and generates X-rays, 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. The X-ray high voltage device 14 applies a tube voltage between the cathode and the anode. The application of the tube voltage causes thermoelectrons to fly from the cathode to the anode. The thermoelectrons flying from the cathode to the anode cause a tube current to flow. The application of a high voltage and the supply of a filament current from the X-ray high voltage device 14 causes thermoelectrons to fly from the cathode (filament) to the anode (target), and X-rays are generated when the thermoelectrons collide with the anode. For example, the X-ray tube 11 may be a rotating anode type X-ray tube that generates X-rays by irradiating a rotating anode with thermoelectrons.

[0013] It should be noted that the hardware for generating X-rays is not limited to the X-ray tube 11. For example, X-rays may be generated using a fifth-generation system instead of the X-ray tube 11. The fifth-generation system includes a focus coil that focuses the electron beam generated from the electron gun, a deflection coil that electromagnetically deflects the beam, and a target ring that surrounds half the circumference of the subject P and generates X-rays when the deflected electron beam collides with the target ring.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] The data acquisition circuitry 18 reads out from the X-ray detector 12 an electrical signal corresponding to the X-ray dose detected by the X-ray detector 12. The data acquisition circuitry 18 amplifies the read electrical signal and integrates the electrical signal over a view period to acquire projection data having digital values ​​corresponding to the X-ray dose over the view period. 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 digital data is transmitted to the console 40 via a non-contact data transmission device or the like.

[0021] In this embodiment, an integral X-ray detector 12 and an X-ray computed tomography apparatus 1 equipped with an integral X-ray detector 12 are described as examples, but the technology according to this embodiment can also be applied to a photon counting X-ray detector or an X-ray computed tomography apparatus equipped with a photon counting X-ray detector.

[0022] 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 CPU (Central Processing Unit) or an MPU (Micro Processing Unit), and a drive mechanism such as a motor and an actuator. The processing circuit includes a processor such as a CPU and memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory) as hardware resources. 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 implemented using 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 an input signal and performs control to rotate the rotating frame 13, control to tilt the gantry 10, and control to operate the bed 30 and the tabletop 33. The control to tilt 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 through an input interface attached to the gantry 10. The control device 15 may be provided in the gantry 10 or in the console 40.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] The memory 41 is a storage device such as an HDD (Hard Disk Drive), an SSD (Solid State Drive), or an integrated circuit storage device that stores various types of information. The memory 41 stores, for example, projection data and reconstructed image data. In addition to an HDD or SSD, the memory 41 may be a portable storage medium such as a CD (Compact Disc), a DVD (Digital Versatile Disc), or a flash memory. The memory 41 may also be a drive device that reads and writes various types of information from and to semiconductor memory elements such as flash memory and RAM (Random Access Memory). 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 a database, which will be described later.

[0027] The display 42 displays various types of information. For example, the display 42 outputs medical images (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, a liquid crystal display (LCD), a cathode ray tube (CRT) display, an organic electroluminescence display (OLED), or a plasma display can be used as the display 42. The display 42 may also be provided on the pedestal 10. The display 42 may also be a desktop type, or may be configured as a tablet terminal or the like capable of wireless communication with the console 40 main body.

[0028] 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. 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 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.

[0029] The processing circuitry 44 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 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 memory such as a ROM or RAM. The processing circuitry 44 executes an imaging control function 441, a reconstruction function 442, an image processing function 443, a display control function 444, an imaging planning function 445, and the like, by a processor that executes a program loaded in the memory. Each of the functions 441 to 445 is not limited to being realized by a single processing circuit. A processing circuit may be configured by combining multiple independent processors, and each processor may execute a program to realize each of the functions 441 to 445.

[0030] In the imaging control function 441, the processing circuitry 44 controls the X-ray high voltage generator 14, the control device 15, and the data acquisition circuitry 18 to perform a dual energy scan on the subject P.

[0031] In the reconstruction function 442, the processing circuitry 44 generates virtual monochromatic X-ray images, DECT (Dual Energy CT) images such as material decomposition images, etc. based on the projection data when a high tube voltage is applied and the projection data when a low tube voltage is applied output from the data acquisition circuitry 18.

[0032] In the image processing function 443, the processing circuitry 44 converts the DECT image 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 44 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 DECT image to generate rendering image data of an arbitrary viewpoint direction. Note that the generation of the rendering image of an arbitrary viewpoint direction may be performed by the reconstruction function 442.

[0033] In the display control function 444, the processing circuit 44 displays various images generated by the image processing function 443 on the display 42. The images displayed on the display 42 include DECT images, cross-sectional images of any cross section, rendering images of any viewpoint direction, etc. The images displayed on the display 42 include images for displaying an operation screen.

[0034] In the imaging plan function 445, the processing circuitry 44 sets an imaging plan for the dual energy scan.

[0035] The kV switching of the X-ray computed tomography apparatus 1 according to this embodiment will be described in detail below.

[0036] Fig. 2 is a diagram showing an example of the configuration of the main components related to kV switching according to the first embodiment. As shown in Fig. 2, the X-ray computed tomography apparatus 1 has an X-ray detector 12, an X-ray high voltage device 14, a control device 15, and a data acquisition circuit 18 as the main components related to kV switching.

[0037] 2, the X-ray detector 12 has a plurality of X-ray detection elements 121. Each X-ray detection element 121 has a scintillator that outputs light in an amount corresponding to the amount of incident X-rays, and a photosensor that converts the light from the scintillator into an electrical signal corresponding to the amount of light. The plurality of X-ray detection elements 121 are respectively connected to a plurality of readout switches 122, and are connected to the data acquisition circuit 18 via readout lines 123.

[0038] The read switch 122 is a switching element that is driven based on a read control signal from the read control circuit 512. For example, a MOS-type field effect transistor (Metal Oxide Semiconductor Field Effect Transistor: MOS-FET) can be used as the read switch 122. In response to an OFF signal, the read switch 122 opens, blocking the readout of electrical signals from the X-ray detection elements 121. When the read switch 122 is open, the X-ray detection elements 121 receive incident X-rays and store electrical signals. In response to an ON signal, the read switch 122 closes, and the electrical signals (charge signals) stored in the X-ray detection elements 121 are read out.

[0039] Fig. 3 is a plan view showing the arrangement of X-ray detection elements 121. As shown in Fig. 3, a plurality of X-ray detection elements 121 are arranged two-dimensionally in the row direction and channel direction on the X-ray incident surface of the X-ray detector 12. The row direction is defined as the Z-axis direction parallel to the central axis of the bore, and the channel direction is defined as the rotation direction of the rotating frame 13. A plurality of X-ray detection element rows 124 are arranged in the row direction.

[0040] In the X-ray detector 12 according to this embodiment, electrical signals are read out by a sequential readout method. In the sequential readout method, electrical signals are read out while shifting the time for each X-ray detection element row 124. As an example, electrical signals are read out in order from the first X-ray detection element row 124 to the last X-ray detection element row 124 while shifting the readout start timing in time.

[0041] 2, the control device 15 has a drive unit 151 and a VT signal generator 152. The drive unit 151 includes an actuator such as a motor and a power transmission mechanism such as a belt for transmitting the power generated by the motor. The drive unit 151 rotates the rotating frame 13 around the rotation axis (Z axis) at a predetermined angular velocity in accordance with a control signal from the console 40.

[0042] The VT signal generator 152 generates a first switching signal at a first time interval. Specifically, the VT signal generator 152 generates the first switching signal, which is an electrical pulse signal, at each first time interval corresponding to the time interval at which the rotating frame 13 rotates by a predetermined angle. The VT signal generator 152 is realized, for example, by a rotary encoder attached to the driving device 151. The first switching signal is a control signal used to switch views and is hereinafter referred to as a VT signal. The waveform of the VT signal is, although not particularly limited, assumed to be rectangular. The generated VT signal is output to the data acquisition circuit 18. The VT signal generator 152 is an example of a first signal generating unit.

[0043] 2, the X-ray high voltage device 14 has a tube voltage control circuit 141. The tube voltage control circuit 141 alternately switches the tube voltage applied to the X-ray tube 11 between a high tube voltage and a low tube voltage. The tube voltage control circuit 141 according to the first embodiment alternately switches the tube voltage between a high tube voltage and a low tube voltage based on a VT signal from a VT signal generator 152. The tube voltage control circuit 141 is an example of a tube voltage control unit.

[0044] As shown in FIG. 2, the data acquisition circuit 18 includes a data acquisition control circuit 51, an A / D conversion circuit 52, and a correction circuit 53.

[0045] The data acquisition control circuit 51 is realized by a control circuit such as an FPGA, and controls the readout of electrical signals from the X-ray detector 12 and data acquisition by the A / D conversion circuit 52. Specifically, the data acquisition control circuit 51 has a view switching control circuit 511, a readout control circuit 512, a gain synchronization signal generation circuit 513, and a gain switching control circuit 514. The view switching control circuit 511, the readout control circuit 512, the gain synchronization signal generation circuit 513, and the gain switching control circuit 514 may be implemented on separate control boards in terms of hardware, or may be implemented on a single control board.

[0046] The view switching control circuit 511 switches views based on the VT signal. A view corresponds to a sampling period of digital data by the A / D conversion circuit 52. As an example, the time period during which the rotating frame 13 makes one rotation is divided into a plurality of views, such as 1000 or 2000 views. The view number is incremented by one each time a view is switched. The view switching control circuit 511 controls the readout control circuit 512 and the A / D conversion circuit 52 in accordance with the view switching. The view switching control circuit 511 is an example of a view switching unit.

[0047] The read control circuit 512 controls the opening and closing of a plurality of read switches 122 connected to the plurality of X-ray detection elements 121, respectively, using a sequential readout method. Specifically, the readout control circuit 512 controls the opening and closing of the plurality of read switches 122 so that readout from all X-ray detection element rows is completed, while shifting the timing at which the readout of electrical signals starts for each X-ray detection element row 124. When closing a readout switch 122, an ON signal is supplied, and when opening a readout switch 122, an OFF signal is supplied.

[0048] The gain synchronization signal generating circuit 513 generates a second switching signal at a second time interval (high frequency) shorter than the first time interval of the VT signal. The second switching signal is called a gain synchronization signal because it is used as a synchronization signal for switching the gain of the A / D conversion circuit 52 (hereinafter referred to as DAS gain). As an example, the gain synchronization signal is synchronized with the VT signal and has a pulse generation period that is an integer multiple of the pulse generation period of the VT signal. The method for generating the gain synchronization signal is not particularly limited, but as an example, it may be generated by upsampling the VT signal. The gain synchronization signal is supplied to the gain switching control circuit 514 and the A / D conversion circuit 52. The gain synchronization signal generating circuit 513 is an example of a second signal generating unit.

[0049] The gain switching control circuit 514 switches the DAS gain of the A / D conversion circuit 52 based on the gain synchronization signal. Specifically, the gain switching control circuit 514 switches the DAS gain between a DAS gain corresponding to a high tube voltage (hereinafter referred to as a high tube voltage gain) and a DAS gain corresponding to a low tube voltage (hereinafter referred to as a low tube voltage gain) based on the gain synchronization signal. The gain switching control circuit 514 switches between a high tube voltage gain and a low tube voltage gain so as to match the tube voltage corresponding to the digital data collected via the X-ray detector 12. Specifically, when switching to a high tube voltage gain, a high gain switching signal is supplied, and when switching to a low tube voltage gain, a low gain switching signal is supplied. The gain switching control circuit 514 is an example of a gain switching unit.

[0050] The A / D conversion circuit 52 collects data on a view-by-view basis via the X-ray detector 12. Specifically, under the control of the view switching control circuit 511 and the gain switching control circuit 514, the A / D conversion circuit 52 converts electrical signals read out from the X-ray detector 12 into digital data on a view-by-view basis at a high tube voltage gain or a low tube voltage gain. The A / D conversion circuit 52 performs A / D conversion at a high tube voltage gain on electrical signals generated in response to X-rays irradiated when a high tube voltage is applied, and performs A / D conversion at a low tube voltage gain on electrical signals generated in response to X-rays irradiated when a low tube voltage is applied. Specifically, the A / D conversion circuit 52 includes a gain switch 521, an A / D converter 522 for high tube voltage, and an A / D converter 523 for low tube voltage. The A / D conversion circuit 52 is an example of a data acquisition unit.

[0051] The gain switch 521 is provided in front of the A / D converter 522 for high tube voltage and the A / D converter 523 for low tube voltage, and switches the DAS gain between high tube voltage gain and low tube voltage gain in accordance with switching control by the gain switching control circuit 514. Specifically, the signal path after the gain switch 521 is branched into an A / D conversion system for high tube voltage gain and an A / D conversion system for low tube voltage gain. The gain switch 521 has a selector switch, such as a three-way switch. One output terminal is connected to an A / D converter 522 that amplifies an electrical signal at a high tube voltage gain and converts it into digital data, and the other output terminal is connected to an A / D converter 523 that amplifies an electrical signal at a low tube voltage gain and converts it into digital data. In response to a high gain switching signal, the three-way switch connects its input terminal to one output terminal, and the electrical signal read from the X-ray detector 12 is supplied to the A / D converter 522 for high tube voltage. In response to the low gain switching signal, the three-way switch connects the input terminal to the other output terminal, and the electrical signal read out from the X-ray detector 12 is supplied to the A / D converter 523 for low tube voltage.

[0052] The high tube voltage A / D converter 522 is an A / D converter that converts electrical signals into digital data at a high tube voltage gain. Specifically, the high tube voltage A / D converter 522 converts electrical signals supplied from the X-ray detection elements 121 into digital data by A / D conversion at a high tube voltage gain during a first view (hereinafter referred to as a high tube voltage view) corresponding to the application of a high tube voltage during a scan of the subject P, when the readout switch 122 is closed. This digital data is called high tube voltage projection data. The projection data is digital data used for image reconstruction.

[0053] The high tube voltage A / D converter 522 converts electrical signals generated when the readout switch 122 is open into digital data by A / D conversion at a high tube voltage gain during high tube voltage view. This digital data is called high tube voltage gain drift correction data. The drift correction data is digital data representing temporal fluctuations in digital values ​​due to changes in the characteristics of the A / D conversion circuit 52 during scanning. Correcting this temporal fluctuation in projection data is called drift correction. The drift correction data is used for drift correction of projection data. Furthermore, when a high tube voltage is being applied to the subject P outside of scanning, the A / D converter 522 converts electrical signals read out from the X-ray detection elements 121 when the readout switch 122 is closed into digital data by A / D conversion at a high tube voltage gain. This digital data is called high tube voltage gain offset correction data. The offset correction data is digital data representing temporal fluctuations in digital values ​​due to changes in the characteristics of the A / D conversion circuit 52 caused by individual differences, aging, etc. Correcting the temporal fluctuation occurring in the projection data is called offset correction. The offset correction data is used for offset correction of the projection data.

[0054] The low tube voltage A / D converter 523 is an A / D converter that converts electrical signals into digital data at a low / high tube voltage gain. Specifically, the low tube voltage A / D converter 523 converts electrical signals supplied from the X-ray detection elements 121 into digital data by A / D conversion at a low / high tube voltage gain during a second view (hereinafter referred to as a low tube voltage view) corresponding to the application of a low tube voltage during a scan of the subject P, when the readout switch 122 is closed. This digital data is referred to as low tube voltage projection data.

[0055] The low tube voltage A / D converter 523 converts the electrical signals generated when the readout switch 122 is closed into digital data at a low / high tube voltage gain during a low tube voltage view. This digital data is called low tube voltage gain drift correction data. The low tube voltage A / D converter 523 also converts the electrical signals read out from the X-ray detection elements 121 when the readout switch 122 is closed during a low tube voltage application outside of a scan of the subject P at a low / high tube voltage gain, and converts the electrical signals into digital data. This digital data is called low tube voltage gain offset correction data.

[0056] The correction circuitry 53 is a processor having an arithmetic circuitry 531 and a correction data storage device 532. The arithmetic circuitry 531 performs various data calculations based on various digital data. As an example, the arithmetic circuitry 531 performs drift correction on projection data of a high tube voltage view based on drift correction data for a high tube voltage gain, and performs drift correction on projection data of a low tube voltage view based on drift correction data for a low tube voltage gain. As another example, the arithmetic circuitry 531 performs offset correction on projection data of a high tube voltage view based on offset correction data for a high tube voltage gain, and performs offset correction on projection data of a low tube voltage view based on offset correction data for a low tube voltage gain. The projection data for high tube voltage and low tube voltage that have undergone various corrections are supplied to the console 40 via a data transmission device or the like. Note that the drift correction and offset correction do not have to be performed by the data acquisition circuitry 18, but may be performed by, for example, the processing circuitry 44 of the console 40.

[0057] The correction data storage device 532 stores high tube voltage gain drift correction data, high tube voltage gain offset correction data, low tube voltage gain drift correction data, and low tube voltage gain offset correction data.

[0058] Next, an example of the operation of the main components relating to kV switching in the X-ray computed tomography apparatus 1 of Fig. 1 will be described. For the sake of illustration, the number of X-ray detection element rows is assumed to be 320.

[0059] FIG. 4 is a diagram showing the readout completion time of electrical signals from each X-ray detecting element array. The vertical axis of FIG. 4 represents the X-ray detecting element array number (acquisition row number), and the horizontal axis represents the view. The diagonal solid lines in FIG. 4 represent lines connecting the times when the readout of electrical signals from each X-ray detecting element array was performed. Note that the readout of electrical signals from each X-ray detecting element array is assumed to be instantaneous. That is, the diagonal solid lines represent the readout completion time of electrical signals from each X-ray detecting element array. In FIG. 4, it is assumed that the readout of electrical signals is performed sequentially from the X-ray detecting element array with row number "1" to the X-ray detecting element array with row number "320." For example, in the X-ray detecting element 121 belonging to the starting row "1," electrical signals are accumulated (integrated) from the start time of each view, instantaneous readout is performed at the end time of that view, and electrical signals are accumulated again from the start time of the next view. As shown in FIG. 4, in the sequential readout method, the readout start timing is shifted for each X-ray detecting element array. Therefore, in the X-ray detection element rows other than the start row "1", the start time of each view does not match the readout time, resulting in a delay in the readout of the electrical signals. The farther the X-ray detection element row is from the start row "1", the more delayed (deviation) the electrical signal readout time is from the readout time at the start row "1" (i.e., the start time of the view). In the final row "320", the electrical signal readout time is delayed by a period T41 from the readout time at the start row "1".

[0060] In each view, switching of the tube voltage is prohibited until readout of the X-ray detection element row of the final row "320" is completed. Therefore, switching of the tube voltage is permitted during a period T42 from the time when readout of the X-ray detection element row of the final row "320" is performed until the start time of the next view.

[0061] Next, switching between high tube voltage gain and low tube voltage gain according to the first embodiment will be described. Fig. 5 is a diagram showing an example of a timing chart relating to switching between high tube voltage gain and low tube voltage gain according to the first embodiment. It is assumed that there are N rows of X-ray detection elements.

[0062] As shown in Fig. 5, the VT signal generator 152 repeatedly outputs a VT signal at a fixed first time interval, and the view switching control circuit 511 switches views in response to the output of the VT signal. The X-ray high voltage generator 14 alternately switches the tube voltage (kV) between a high tube voltage and a low tube voltage for each view. In reality, the high tube voltage and the low tube voltage do not switch instantaneously, but rather there is a transition period of several views. In Fig. 5, the stable period in which the voltage value is stable is set to 1.5 views, and the transition period of the tube voltage is also set to 1.5 views.

[0063] As shown in Fig. 5, a gain synchronization signal generating circuit 513 repeatedly outputs a gain synchronization signal at a second time interval shorter than the first time interval in synchronization with the VT signal. The gain synchronization signal is supplied to a gain switching control circuit 514 and an A / D conversion circuit 52. The gain switching control circuit 514 alternately switches the DAS gain between a high tube voltage gain and a low tube voltage gain based on the gain synchronization signal. More specifically, the gain switching control circuit 514 notifies the A / D conversion circuit 52 of a gain switching instruction in synchronization with a first pulse of the gain synchronization signal in the stable period. As the gain switching instruction, when switching to a high tube voltage gain, a high gain switching signal is supplied to the A / D conversion circuit 52, and when switching to a low tube voltage gain, a low gain switching signal is supplied to the A / D conversion circuit 52.

[0064] Various embodiments of the gain change plan for switching to a high tube voltage gain or a low tube voltage gain are possible. As an example, by implementing the imaging planning function 445, the processing circuitry 44 creates a list (hereinafter referred to as a gain switching plan) in which the type of DAS gain is pre-assigned to a view number, such as a low tube voltage gain for the first view and a high tube voltage gain for the fourth view, when planning a scan. The gain switching plan is supplied to the gain switching control circuit 514 before scanning. During scanning, the gain switching control circuit 514 applies the current view number to the gain switching plan to identify the type of DAS gain corresponding to the current view number, and notifies the A / D conversion circuitry 52 of a gain switching instruction to the identified type. The current view number may be notified from the view switching control circuit 511.

[0065] As another example, a gain switching instruction may be transmitted from the processing circuitry 44 of the console 40 to the gain switching control circuit 514 in real time during scanning. More specifically, the processing circuitry 44 applies the current view number to the gain switching plan to identify the type of DAS gain corresponding to the current view number, and transmits a gain switching instruction for the identified type to the gain switching control circuit 514. At this time, the processing circuitry 44 may transmit the gain switching instruction in synchronization with the VT signal. The gain switching control circuit 514 may notify the A / D conversion circuit 52 of the same gain switching instruction as the gain switching instruction from the processing circuitry 44 in the switching instruction view of the current view.

[0066] Although the gain switching plan is described as a list in which a DAS gain type is set for each view number, this is not limiting. For example, if the DAS gain types are different for odd-numbered and even-numbered view numbers, the gain switching plan may be a list in which a DAS gain type is set for each odd number and even number. Furthermore, the gain switching plan may be expressed by a relational expression between the view number and the DAS gain type.

[0067] As described above, when a gain switching instruction is given at the first pulse of the gain synchronization signal, the gain switcher 521 of the A / D conversion circuit 52 switches the DAS gain in synchronization with the second pulse that follows the first pulse.

[0068] Specifically, during a stable period of low tube voltage (such as the fourth view in FIG. 5 ), the gain switching control circuit 514 issues a gain switching instruction to the A / D conversion circuit 52 to switch the gain to a low tube voltage gain in synchronization with the first pulse of the gain synchronization signal. Then, in synchronization with the second pulse following the first pulse, the gain switcher 521 switches from the high tube voltage gain to the low tube voltage gain. Immediately after switching the DAS gain, the operation of the low tube voltage A / D converter 523 is unstable, and therefore the period from when the DAS gain is switched to the start time of the next view is used for stabilizing the low tube voltage A / D converter 523.

[0069] Similarly, during a stable period of high tube voltage (such as the first or seventh view in FIG. 5), a gain switching instruction to high tube voltage gain is sent to the A / D conversion circuit 52 in synchronization with the first pulse of the gain synchronization signal. Then, in synchronization with the second pulse following the first pulse, the gain switcher 521 switches from the low tube voltage gain to the high tube voltage gain. The period from when the DAS gain is switched to the start time of the next view is used for stabilization of the high tube voltage A / D converter 522.

[0070] The second pulse may be the pulse immediately following the first pulse, or may be a pulse several pulses later as long as it is output to the same view.

[0071] As shown in FIG. 5, the readout control circuit 512 sequentially stores (integrates) and reads out electricity from the X-ray detector 12 in synchronization with the VT signal. More specifically, during a stable period of high tube voltage or low tube voltage, the readout switch 122 is closed to store electricity in the X-ray detection elements 121. The start time of the charge storage is shifted for each X-ray detection element row or for each predetermined number of rows, and the charge storage is performed for a time length equivalent to approximately one view period. Electrical signals are read out from the X-ray detection elements 121 in order from the X-ray detection element row in which charge storage has been completed. During a period T51 from the end of charge storage until a predetermined time has elapsed, the readout switch 122 is opened to read out electrical signals from the X-ray detection elements 121. During a period T52 from the end of the period T51 until the predetermined time has elapsed, reading out is performed for drift correction data. It is assumed that no electrical signals are stored in the X-ray detection elements 121 during the period T52. Drift correction data is read out from the X-ray detection element 121 in a state where no power is stored.

[0072] As described above, readout starts at different times within the same view for each X-ray detection element row 124. Electrical signals stored by X-ray irradiation in the first view are read out in the following second view. As shown in Fig. 5, as the readout delay of electrical signals increases from the first row to the Nth row, readout is performed across the second and third views in the X-ray detection element rows from the second row onwards.

[0073] After the readout of the electrical signals is completed, the electrical signals are converted into digital data at the set DAS gain by the high tube voltage A / D converter 522 or the low tube voltage A / D converter 523. Specifically, since the DAS gain is set to the high tube voltage gain during the application period of the high tube voltage, the electrical signals are supplied from the X-ray detection elements 121 to the high tube voltage A / D converter 522 and converted into projection data at the high tube voltage gain. Since the DAS gain is set to the low tube voltage gain during the application period of the low tube voltage, the electrical signals are supplied from the X-ray detection elements 121 to the low tube voltage A / D converter 523 and converted into projection data at the low tube voltage gain.

[0074] Here, the difference between this embodiment and the comparative example will be described. The comparative example is a method in which gain switching instructions and data collection by an A / D conversion circuit are performed in synchronization with the VT signal.

[0075] 6 is a diagram showing an example of a timing chart relating to switching between high and low tube voltage gains in a comparative example. Note that, in the comparative example, similarly to FIG. 5, the stable period and the transition period are set to 1.5 views.

[0076] As shown in FIG. 6 , in the comparative example, a gain switching instruction and data acquisition by the A / D conversion circuit are performed in synchronization with the VT signal. For example, even if a gain switching instruction is performed in synchronization with the VT signal in the fourth view, no further VT signal is output for that view, so data acquisition by the A / D conversion circuit cannot be performed. Data acquisition finally begins in synchronization with the VT signal output in the next, fifth view. In the first row, all of the charges accumulated when a low tube voltage was applied in the fourth view are read out at a low tube voltage gain in the fifth view. However, in the second and subsequent rows of X-ray detection elements, such as the Nth row, electrical signal readout is performed across the fifth and sixth views. However, in the sixth view, the DAS gain is switched to a high tube voltage gain, so the charges accumulated when a low tube voltage was applied are read out at a high tube voltage gain. That is, in the comparative example, the tube voltage related to charge accumulation and the tube voltage related to the DAS gain do not match in the X-ray detection element rows where readout is performed across views. This mismatch results in data acquisition at a high tube voltage gain for electrical signals stored when a low tube voltage is applied, and at a low tube voltage gain for electrical signals stored when a high tube voltage is applied, making it impossible to acquire data at an appropriate gain. Furthermore, if there are two or more stable views, data acquisition will be performed at both high and low tube voltage gains for the same tube voltage, degrading the quality of the projection data.

[0077] According to this embodiment, as shown in Fig. 5, even in an X-ray detection element array in which readout is performed across views, the tube voltage during charging and the tube voltage related to the DAS gain are matched. This enables DAS gain switching synchronized with kV switching. As a result, data acquisition can be performed with a high tube voltage gain in high tube voltage views and with a low tube voltage gain in low tube voltage views, making it possible to acquire data with an appropriate DAS gain for both high and low tube voltages.

[0078] Next, the collection of drift correction data will be described. The data collection circuitry 18 collects drift correction data for a high tube voltage gain and second drift correction data for a low tube voltage gain during a scan of the subject.

[0079] 7 is a timing chart related to the collection of drift correction data. As shown in FIG. 7, the tube voltage control circuit 141 alternately switches the tube voltage between a high tube voltage (High) and a low tube voltage (Low). As described above, the gain switching control circuit 514 alternately switches the DAS gain between a gain for a high tube voltage (High) and a gain for a low tube voltage (Low) in synchronization with the switching of the tube voltage. It is assumed that no DAS gain is set during the transition period of the tube voltage.

[0080] The A / D conversion circuit 52 acquires, as projection data, digital data output from the A / D converter 522 when the readout switch 122 is closed at a first DAS gain (high tube voltage gain) in a first view (high tube voltage view) corresponding to the application of a high tube voltage, and acquires, as first drift correction data (drift correction data for high tube voltage) at a high tube voltage gain, digital data output from the A / D converter 522 when the readout switch 122 is open after the acquisition of the projection data. Furthermore, the A / D conversion circuit 52 acquires, as projection data, digital data output from the A / D converter 523 when the readout switch 122 is closed at a low tube voltage gain in a second view (low tube voltage view) corresponding to the application of a low tube voltage, and acquires, as second drift correction data (drift correction data for low tube voltage) at a low tube voltage gain, digital data output from the A / D converter 523 when the readout switch 122 is closed after the acquisition of the projection data, and acquires, as second drift correction data (drift correction data for low tube voltage) at a low tube voltage gain. Therefore, the drift correction data for high tube voltages is missing when low tube voltages are applied and during the transition period, and the drift correction data for low tube voltages is missing when high tube voltages are applied and during the transition period.

[0081] As shown in FIG. 7 , the arithmetic circuit 531 generates drift correction data D70 for high tube voltage gains missing in a low tube voltage view based on drift correction data D71 for high tube voltage gains collected in a high tube voltage view prior to the low tube voltage view and / or drift correction data D72 for low tube voltage gains collected in the same low tube voltage view. Similarly, the arithmetic circuit 531 generates drift correction data D73 for low tube voltage gains missing in a high tube voltage view based on drift correction data D74 for low tube voltage gains collected in a low tube voltage view prior to the high tube voltage view and / or drift correction data D71 for high tube voltage gains collected in the same high tube voltage view. Drift correction data generated based on previously collected drift correction data will be referred to as calculated drift correction data. Calculated drift correction data can be generated by various methods. Several generation methods are described below.

[0082] (Method 1) The arithmetic circuitry 531 calculates calculated drift correction data D70 for high tube voltage gain for multiple views during the period from one high tube voltage view to the next, based on actually measured drift correction data D71 for high tube voltage acquired at the immediately preceding high tube voltage gain. Specifically, the drift correction data for high tube voltage in a low tube voltage view (stable period) is considered to be a repetition of the actually measured drift correction data for high tube voltage in the immediately preceding high tube voltage view (stable period), and the moving average of the actually measured drift correction data for high tube voltage is set as the drift correction data for high tube voltage in the low tube voltage view (stable period). Note that the drift correction data for high tube voltage in the transition periods immediately before and after a low tube voltage view (stable period) may be set as the moving average of the actually measured drift correction data for high tube voltage in the immediately preceding high tube voltage view (stable period), or may be calculated by applying appropriate correction to the moving average. Missing portions of the drift correction data for low tube voltage gain can also be generated in a similar manner.

[0083] (Method 2) The arithmetic circuit 531 calculates high tube voltage gain drift correction data D70 for multiple views during the period from one high tube voltage view to the next high tube voltage view, based on the actually measured low tube voltage drift correction data D72 for those multiple views. Specifically, the arithmetic circuit 531 analyzes the behavioral tendency of the actually measured low tube voltage drift correction data D72 for those multiple views to calculate a correction value, and applies that correction value to the drift correction data D71 for the immediately preceding high tube voltage view to calculate the calculated high tube voltage drift correction data D70. Missing portions of low tube voltage gain drift correction data can also be generated in a similar manner.

[0084] (Method 3) The arithmetic circuitry 531 calculates high tube voltage gain drift correction data D70 for multiple views during the period from one high tube voltage view to the next high tube voltage view, based on the actually measured low tube voltage drift correction data D72 for those multiple views. Specifically, the arithmetic circuitry 531 calculates calculated high tube voltage drift correction data D70 by biasing the actually measured low tube voltage drift correction data D70 for those multiple views so that it matches the average value of the immediately preceding high tube voltage gain drift correction data D71. Missing low tube voltage gain drift correction data can also be generated in a similar manner.

[0085] (Method 4) The arithmetic circuitry 531 generates missing portions of drift correction data using a machine learning model. As an example, a machine learning model trained to input high tube voltage gain drift correction data for a first view and output high tube voltage gain drift correction data for a second view that follows the first view can be used. In this case, the arithmetic circuitry 531 can apply measured high tube voltage gain drift correction data for the high tube voltage view to the machine learning model to generate calculated high tube voltage gain drift correction data for the low tube voltage view that follows the high tube voltage view. Missing portions of low tube voltage gain drift correction data can be generated in a similar manner. As another example, a machine learning model trained to input low tube voltage gain drift correction data for a first view and output high tube voltage gain drift correction data for the first view can be used. In this case, the arithmetic circuitry 531 can apply measured low tube voltage gain drift correction data for the low tube voltage view to the machine learning model to generate calculated high tube voltage gain drift correction data for the low tube voltage view. The missing portion of the drift correction data for low tube voltage gain can also be generated in a similar manner.

[0086] (Method 5) The arithmetic circuitry 531 may generate missing portions of drift correction data for high tube voltage gain by correcting the immediately preceding actually measured drift correction data for high tube voltage gain based on temperature data of devices in the X-ray detector 12 and / or the data acquisition circuitry 18. Temperature data is measured by a temperature measuring device for devices in the X-ray detector 12 and / or the data acquisition circuitry 18. It is possible to analyze temperature fluctuations of the devices in the view preceding the view corresponding to the missing portions, and generate calculated drift correction data for high tube voltage based on the temperature fluctuations. Drift correction data for missing portions of low tube voltage gain can also be generated in a similar manner.

[0087] The measured or calculated drift correction data generated by the above method is stored in the correction data storage device 532 in association with the corresponding DAS gain type and view number. According to this embodiment, it is possible to collect drift correction data for high tube voltage gains and drift correction data for low tube voltage gains. Furthermore, by interpolating missing portions using the above method, it is possible to collect drift correction data for high tube voltage gains and drift correction data for low tube voltage gains across all views.

[0088] Next, the collection of offset correction data will be described. The data collection circuitry 18 collects first offset correction data corresponding to a high tube voltage gain and second offset correction data corresponding to a low tube voltage gain.

[0089] FIG. 8 is a timing chart for collecting offset correction data. As shown in FIG. 8, a CT examination has pre-scan, scan, and post-scan phases. During the scan phase, dual-energy scanning is performed using kV switching, as described above. Before and / or after the scan, the data acquisition circuitry 18 collects offset correction data for a high tube voltage gain and offset correction data for a low tube voltage gain. When a high tube voltage is applied, the data acquisition circuitry 18 collects digital data output from the A / D converter 522 when the readout switch 122 is closed or open as offset correction data for a high tube voltage gain, and when a low tube voltage is applied, the data acquisition circuitry 18 collects digital data output from the A / D converter 523 when the readout switch 122 is closed or open as offset correction data for a low tube voltage gain. The offset correction data for each DAS gain does not need to be collected for all 360-degree views, but may be collected for any view. The collected offset correction data for each DAS gain can be used for both acquired and non-acquired views.

[0090] There are three main methods for collecting offset correction data.

[0091] 8, in Pattern 1, both offset correction data for a high tube voltage gain and offset correction data for a low tube voltage gain are collected before scanning. The offset correction data for a high tube voltage gain may be collected first, and the offset correction data for a low tube voltage gain may be collected later, or the offset correction data for a low tube voltage gain may be collected first, and the offset correction data for a high tube voltage gain may be collected later.

[0092] 8, in Pattern 2, offset correction data with a high tube voltage gain is collected before the scan, and offset correction data with a low tube voltage gain is collected after the scan. Conversely, offset correction data with a low tube voltage gain may be collected before the scan, and offset correction data with a high tube voltage gain may be collected after the scan.

[0093] 8, in pattern 3, both high tube voltage gain offset correction data and low tube voltage gain offset correction data are collected both before and after scanning. For example, before scanning, the high tube voltage gain offset correction data is collected prior to the low tube voltage gain offset correction data, and after scanning, the low tube voltage gain offset correction data is collected prior to the high tube voltage gain offset correction data. Note that there are no particular limitations on the order in which the high tube voltage gain offset correction data and the low tube voltage gain offset correction data are collected before and after scanning.

[0094] The measured or calculated offset correction data generated by the above method is stored in the correction data storage device 532. According to this embodiment, it is possible to collect offset correction data for high tube voltage gains and offset correction data for low tube voltage gains.

[0095] (Second embodiment) 9 is a diagram showing an example of the configuration of the main components related to kV switching according to the second embodiment. In the following description, components having substantially the same functions as those in the first embodiment are given the same reference numerals, and will be described repeatedly only when necessary.

[0096] 9, the X-ray computed tomography apparatus 1 according to the second embodiment has, as main components related to kV switching, an X-ray detector 12, an X-ray high-voltage device 14, a control device 15, and a data acquisition circuit 18. The data acquisition control circuit 54 of the data acquisition circuit 18 has a view switching control circuit 541, a readout control circuit 542, a gain synchronization signal generation circuit 543, a gain switching control circuit 544, and a VT+ signal generator 545.

[0097] The view switching control circuit 541 switches views based on the VT signal from the VT signal generator 152, similar to the view switching control circuit 511 of the first embodiment.

[0098] The read control circuit 542, like the read control circuit 512 of the first embodiment, controls the opening and closing of a plurality of read switches 122 connected to a plurality of X-ray detection elements 121, respectively, in a sequential readout manner.

[0099] The gain synchronization signal generating circuit 543 generates a gain synchronization signal, similar to the gain switching control circuit 514 of the first embodiment.

[0100] The VT+ signal generator 545 generates a VT+ signal which is a signal notifying that readout of electrical signals from all the X-ray detection element arrays 124 has been completed. As described above, the readout control circuit 542 supplies an ON signal to the readout switch 122 in the storage view and an OFF signal in the readout view for each X-ray detection element array 124. The VT+ signal generator 545 monitors the supply of an OFF signal from the readout control circuit 542, and generates the VT+ signal when an OFF signal is supplied to the readout switch 122 for the last X-ray detection element array 124. The VT+ signal generator 545 may generate the VT+ signal with an arbitrary delay time from the time when the OFF signal is supplied. The VT+ signal is supplied to the tube voltage control circuit 142 and the gain switching control circuit 544.

[0101] The gain switching control circuit 544 switches the DAS gain based on the gain synchronization signal and the VT+ signal. Specifically, the gain switching control circuit 544 switches the DAS gain between a high tube voltage gain and a low tube voltage gain at the timing when both the gain synchronization signal and the VT+ signal are output (i.e., at the timing of AND of the gain synchronization signal and the VT+ signal). The gain change plan for switching to a high tube voltage gain or a low tube voltage gain is the same as in the first embodiment. Note that when the processing circuitry 44 transmits a gain switching instruction to the gain switching control circuit 514, it is preferable to transmit the gain switching instruction in synchronization with the VT+ signal. This allows the gain switching control circuit 514 to notify the A / D conversion circuit 52 of the gain switching instruction at the next view after receiving the VT+ signal.

[0102] The tube voltage control circuit 142 according to the second embodiment switches the tube voltage between a high tube voltage and a low tube voltage based on a VT+ signal, not a VT signal. By switching the tube voltage based on the VT+ signal, it becomes possible to start switching the tube voltage immediately after readout of all the X-ray detection element rows 124 is completed.

[0103] Next, a description will be given of switching between a high tube voltage gain and a low tube voltage gain according to the second embodiment. Fig. 10 is a diagram showing an example of a timing chart relating to switching between a high tube voltage gain and a low tube voltage gain according to the second embodiment.

[0104] As shown in FIG. 10 , the VT signal generator 152 repeatedly outputs a VT signal at a fixed first time interval, and the view switching control circuit 511 switches views in response to the output of the VT signal. The VT+ signal generator 545 outputs a VT+ signal when signal readout of the final column is completed. The gain switching control circuit 544 notifies the A / D conversion circuit 52 of a gain switching instruction in synchronization with the output of a first pulse of the gain synchronization signal for the view following the output of the VT+ signal. The gain switcher 521 of the A / D conversion circuit 52 switches the DAS gain in synchronization with the output of a second pulse following the first pulse. The second pulse may be the pulse output immediately following the first pulse, or may be the pulse output several pulses later. As a result, similar to the first embodiment, the tube voltage during charging and the tube voltage related to the DAS gain are matched.

[0105] 5, in the second embodiment, the readout control circuit 512 sequentially stores (integrates) and reads out electricity from the X-ray detector 12 in synchronization with the VT signal. More specifically, in a view in a stable period of high tube voltage or low tube voltage, the readout switch 122 is closed to store electricity in the X-ray detection elements 121. The start time of the storage is shifted for each X-ray detection element row or for each predetermined number of rows, and the storage is performed for a time length equivalent to approximately one view period. Electrical signals are read out from the X-ray detection elements 121 in order from the X-ray detection element row in which storage is completed. In a period T101 from the end of storage until a predetermined time has elapsed, the readout switch 122 is opened to read out electrical signals from the X-ray detection elements 121. In a period T102 from the end of the period T101 until the predetermined time has elapsed, readout for drift correction data is performed.

[0106] As described above, according to the second embodiment, the tube voltage and the DAS gain are switched in synchronization with the VT+ signal, so that the DAS gain can be switched in synchronization with the KV switching.

[0107] According to at least one of the embodiments described above, the gain related to data acquisition can be switched in synchronization with the switching of the tube voltage.

[0108] 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 functions by reading and executing a program stored in a memory circuit. Note that instead of storing a program in a memory circuit, a program may be directly embedded in the processor circuit. In this case, the processor realizes its functions by reading and executing the program embedded in the circuit. Alternatively, instead of executing a program, a function corresponding to the program may be realized by combining logic circuits. Note that each processor in this embodiment is not limited to being configured as a single circuit, but may be configured as a single processor by combining multiple independent circuits to realize its function. Furthermore, multiple components in FIGS. 1, 2, and 9 may be integrated into a single processor to realize its function.

[0109] 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]

[0110] 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 Collection Circuit 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 Processing circuit 51,54 Data collection control circuit 52 A / D conversion circuit 53 Correction circuit 121 X-ray detector 122 Readout switch 123 Readout line 124 X-ray detector array 141,142 Tube voltage control circuit 151 Drive unit 152 VT signal generator 441 Shooting control function 442 Reconfiguration function 443 Image Processing Function 444 Display Control Function 445 Shooting planning function 511 View switching control circuit 512 read control circuit 513 Gain Sync Signal Generator 514 Gain switching control circuit 521 Gain switch 522 High-Voltage A / D Converter 523 A / D Converter for Low Tube Voltage 531 Arithmetic circuit 532 Correction data storage device 541 View switching control circuit 542 read control circuit 543 Gain Sync Signal Generator 544 Gain switching control circuit 545 VT+ Signal Generator

Claims

1. A first signal generating unit that generates a first switching signal at a first time interval corresponding to a time interval during which a rotating frame supporting an X-ray tube and an X-ray detector rotates by a predetermined angle; a tube voltage control unit that switches a tube voltage applied to the X-ray tube between a first tube voltage and a second tube voltage lower than the first tube voltage based on the first switching signal; a view switching unit that switches views based on the first switching signal; a data acquisition unit that acquires data in units of views via an X-ray detector; a second signal generating unit that generates a second switching signal synchronized with the first switching signal at a second time interval that is shorter than the first time interval; a gain switching unit that switches the gain of the data collecting unit based on the second switching signal; An X-ray computed tomography apparatus comprising:

2. 2. The X-ray computed tomography apparatus according to claim 1, wherein the gain switching unit switches the gain between a first gain corresponding to the first tube voltage and a second gain corresponding to the second tube voltage based on the second switching signal.

3. The X-ray computed tomography apparatus according to claim 2 , wherein the gain switching unit switches between the first gain and the second gain so as to match a tube voltage corresponding to data acquired via the X-ray detector.

4. 4. The X-ray computed tomography apparatus according to claim 3, wherein the data acquisition unit acquires first drift correction data corresponding to the first gain and second drift correction data corresponding to the second gain during a scan of the subject.

5. the X-ray detector includes an X-ray detection element and a read switch for the X-ray detection element; the data acquisition unit is connected to the X-ray detection elements via the readout switches and has an A / D converter that converts electrical signals into digital data; The data collection unit In a first view corresponding to application of the first tube voltage, the digital data output from the A / D converter when the readout switch is closed is collected as projection data, and the digital data output from the A / D converter when the readout switch is open after collection of the projection data is collected as the first drift correction data; In a second view corresponding to application of the second tube voltage, the digital data output from the A / D converter when the readout switch is closed is collected as the projection data, and the digital data output from the A / D converter when the readout switch is open after collection of the projection data is collected as the second drift correction data.

5. An X-ray computed tomography apparatus according to claim 4.

6. Further comprising a memory unit, The data collection unit generating calculated second drift correction data in the first view based on the first drift correction data collected in the first view and / or the second drift correction data collected in the second view, for the second drift correction data missing in the first view; generating calculated first drift correction data in the second view based on the second drift correction data collected in the second view and / or the first drift correction data collected in the first view for the first drift correction data missing in the second view; the storage unit stores the calculated second drift correction data in the first view, the first drift correction data collected in the first view, the calculated first drift correction data in the second view, and the second drift correction data collected in the second view in association with a gain type and a view number.

6. An X-ray computed tomography apparatus according to claim 5.

7. 6. The X-ray computed tomography apparatus according to claim 5, wherein the data acquisition unit corrects the first drift correction data acquired in the first view and / or the second drift correction data acquired in the second view with temperature data of the data acquisition unit measured in the first view, for the second drift correction data missing in the first view, to generate calculated second drift correction data in the first view.

8. 4. The X-ray computed tomography apparatus according to claim 3, wherein the data acquisition unit acquires first offset correction data corresponding to the first gain and second offset correction data corresponding to the second gain outside of a scan of the subject.

9. the X-ray detector includes an X-ray detection element and a read switch for the X-ray detection element; the data acquisition unit is connected to the X-ray detection elements via the readout switches and has an A / D converter that converts electrical signals into digital data; the data collection unit collects, as the first offset correction data, the digital data output from the A / D converter when the readout switch is closed during application of the first tube voltage, and collects, as the second offset correction data, the digital data output from the A / D converter when the readout switch is closed during application of the second tube voltage.

9. An X-ray computed tomography apparatus according to claim 8.

10. The data collection unit collecting the first offset-corrected data and the second offset-corrected data before scanning; collecting the first offset-corrected data before a scan and collecting the second offset-corrected data after a scan; collecting the second offset correction data before a scan and collecting the first offset correction data after a scan; or collecting the digital data at the first gain and the digital data at the second gain before and after a scan, respectively; generating the first offset correction data based on the digital data at the first gain before and after the scan; and generating the second offset correction data based on the digital data at the second gain before and after the scan.

10. An X-ray computed tomography apparatus according to claim 9.

11. 2. The X-ray computed tomography apparatus according to claim 1, wherein the second signal generating section upsamples the first switching signal to generate the second switching signal synchronized with the first switching signal.

12. the second signal generating unit generates, as the second switching signal, a first pulse and a second pulse following the first pulse during the first time interval; the gain switching unit supplies a switching instruction to the data collecting unit in synchronization with the first pulse; the data collecting unit switches to a gain corresponding to the switching instruction in synchronization with the second pulse; 2. An X-ray computed tomography apparatus according to claim 1.

13. 2. The X-ray computed tomography apparatus according to claim 1, wherein the gain switching unit switches the gain of the data acquisition unit based on the second switching signal and a third switching signal that is generated at a timing when charge readout from all detection element rows of the X-ray detector is completed.

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