X-ray computed tomography apparatus

Abstract

The problem is to switch the gain involved in data acquisition in synchronization with the switching of the tube voltage. The solution is that, according to one embodiment, an X-ray computed tomography apparatus has a tube voltage control section, a first signal generation section, a view switching section, a data acquisition section, a second signal generation section, and a gain switching section. The tube voltage control section switches the 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 generation section generates a first switching signal at a first time interval. The view switching section switches a view based on the first switching signal. The data acquisition section performs data acquisition in units of views via an X-ray detector. The second signal generation section generates a second switching signal at a second time interval shorter than the first time interval. The gain switching section switches the gain of the data acquisition section based on the second switching signal.

Description

[0001] Related applications:

[0002] This application enjoys priority based on Japanese Patent Application 2022-009670, filed on January 25, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The embodiments described herein generally relate to X-ray computed tomography apparatus. Background Technology

[0004] As one of the imaging methods performed by X-ray computed tomography (CT) devices, dual-energy scanning involves switching between two types of tube voltages to capture two types of projection data corresponding to the two types of energy. The technique of alternately switching the tube voltage is called kV switching. In kV switching, the gain of the data acquisition circuit is not switched; data acquisition is performed with the same gain (amplification). When performing kV switching with the same gain, it is possible that the gain is low on the low tube voltage side, thus degrading the signal-to-noise ratio (SNR), while the gain is high on the high tube voltage side, causing overflow and producing artifacts or CT value deviations.

[0005] Existing technical documents:

[0006] Patent Document 1: Japanese Patent Application Publication No. 2020-74825 Summary of the Invention

[0007] The problem that the invention aims to solve:

[0008] One of the problems that the embodiments disclosed in this specification and accompanying drawings aim to solve is switching the gain involved in data acquisition in sync with the switching of the tube voltage. However, the problems to be solved by the embodiments disclosed in this specification and accompanying drawings are not limited to the above-mentioned problems. Problems corresponding to the effects of the various configurations shown in the embodiments described below can also be identified as other problems.

[0009] The X-ray computed tomography apparatus according to the embodiment includes a tube voltage control unit, a first signal generation unit, a view switching unit, a data acquisition unit, a second signal generation unit, and a gain switching unit. The tube voltage control unit switches the tube voltage applied to the X-ray tube between a first tube voltage and a second tube voltage that is lower than the first tube voltage. The first signal generation unit generates a first switching signal at a first time interval. The view switching unit switches the view based on the first switching signal. The data acquisition unit acquires data in units of the view via an X-ray detector. The second signal generation unit generates a second switching signal at a second time interval shorter than the first time interval. The gain switching unit switches the gain of the data acquisition unit based on the second switching signal.

[0010] Invention effects:

[0011] The purpose of the invention is to switch the gain involved in data acquisition in sync with the switching of tube voltage. Attached Figure Description

[0012] Figure 1 This is a diagram illustrating an example of the configuration of the X-ray computed tomography apparatus according to the first embodiment.

[0013] Figure 2 This is a diagram illustrating a configuration example of the main components related to the kV switch according to the first embodiment.

[0014] Figure 3 It is a plan view showing the arrangement of X-ray detection elements.

[0015] Figure 4 This is a graph showing the completion time of reading the electrical signals of each X-ray detection element array.

[0016] Figure 5 This is a diagram illustrating an example of a timing diagram related to the switching of high-voltage gain and low-voltage gain as described in the first embodiment.

[0017] Figure 6 This is a diagram illustrating an example of a timing diagram related to the switching of high-voltage gain and low-voltage gain in a comparative example.

[0018] Figure 7 It is a timing diagram related to the acquisition of drift correction data.

[0019] Figure 8 It is a timing diagram related to the acquisition of bias correction data.

[0020] Figure 9 This is a diagram illustrating a configuration example of the main components related to the kV switch as described in the second embodiment.

[0021] Figure 10 This is a diagram illustrating an example of a timing diagram related to the switching of high-voltage gain and low-voltage gain as described in the second embodiment.

[0022] Explanation of reference numerals in the attached figures:

[0023] 1X-ray computed tomography device

[0024] 10 racks

[0025] 11 X-ray tubes

[0026] 12 X-ray detectors

[0027] 13 Rotating Frame

[0028] 14 X-ray high-pressure device

[0029] 15. Control device

[0030] 16 wedge-shaped parts

[0031] 17 Collimator

[0032] 18 Data Acquisition Circuit

[0033] 19. Opening

[0034] 30 examination beds

[0035] 31 Abutment

[0036] 32 Support Frame

[0037] 33 Top Plate

[0038] 34. Examination bed drive device

[0039] 40 Console

[0040] 41 Memory

[0041] 42 monitors

[0042] 43 Input Interface

[0043] 44 Processing Circuit

[0044] 51, 54 Data Acquisition and Control Circuits

[0045] 52A / D conversion circuit

[0046] 53. Correction Circuit

[0047] 121 X-ray detection element

[0048] 122 Read switch

[0049] 123 Reading line

[0050] 124 X-ray detection element array

[0051] Voltage control circuit for transistors 141 and 142

[0052] 151 Drive unit

[0053] 152 VT signal generator

[0054] 441 Camera control function

[0055] 442 Refactoring Functionality

[0056] 443 Image processing functions

[0057] 444 Display control function

[0058] 445 Photography Plan Function

[0059] 511 Period Switching Control Circuit

[0060] 512 Read control circuit

[0061] 513 Gain Synchronization Signal Generation Circuit

[0062] 514 Gain Switching Control Circuit

[0063] 521 Gain Switch

[0064] 522 High Voltage A / D Converter

[0065] 523 Low-voltage A / D converter

[0066] 531 operational circuit

[0067] 532 Calibration Data Storage Device

[0068] 541 Period Switching Control Circuit

[0069] 542 Read control circuit

[0070] 543 Gain Synchronization Signal Generation Circuit

[0071] 544 gain switching control circuit

[0072] 545VT+ Signal Generator Detailed Implementation

[0073] The X-ray computed tomography apparatus according to the embodiment includes a tube voltage control unit, a first signal generation unit, a viewing period switching unit, a data acquisition unit, a second signal generation unit, and a gain switching unit. The tube voltage control unit switches the tube voltage applied to the X-ray tube between a first tube voltage and a second tube voltage lower than the first tube voltage. The first signal generation unit generates a first switching signal at a first time interval. The viewing period switching unit switches the viewing period based on the first switching signal. The data acquisition unit acquires data in units of the viewing period via an X-ray detector. The second signal generation unit generates a second switching signal at a second time interval shorter than the first time interval. The gain switching unit switches the gain of the data acquisition unit based on the second switching signal.

[0074] Hereinafter, embodiments of the X-ray computed tomography apparatus will be described in detail with reference to the accompanying drawings. Furthermore, in the following description, components that have the same or substantially the same function as those described in the previously illustrated drawings will be given the same reference numerals and will be repeated only where necessary. Additionally, even when depicting identical parts, their dimensions or ratios may sometimes differ depending on the accompanying drawings.

[0075] In the X-ray computed tomography apparatus (X-ray CT apparatus) involved in this embodiment, there are various types such as third-generation CT and fourth-generation CT, and any type can be applied to this embodiment. Here, the third-generation CT is a rotating / rotate-type in which the X-ray tube and detector are integrated and rotate around the subject. The fourth-generation CT is a stationary / rotate-type in which multiple X-ray detection elements are fixed in a ring array, and only the X-ray tube rotates around the subject. In addition, both the single-tube type, in which a single pair of X-ray tubes and detectors is mounted on a rotating ring, and the multi-tube type, in which multiple pairs of X-ray tubes and detectors are mounted on a rotating ring, can be applied to the X-ray computed tomography apparatus involved in this embodiment. In the following description, it will be referred to as the single-tube type.

[0076] (First Embodiment)

[0077] Figure 1 This diagram illustrates the configuration of the 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 the irradiated X-rays are detected by an X-ray detector 12. Based on the output from the X-ray detector 12, the X-ray computed tomography apparatus 1 generates a CT image related to the subject P.

[0078] like Figure 1 As shown, the X-ray computed tomography apparatus 1 includes a stand 10, an examination table 30, and a control console 40. Furthermore, in Figure 1For ease of explanation, the stand 10 is shown in several illustrations, but the X-ray computed tomography apparatus 1 may have one or more stands 10. The stand 10 is a scanning device configured to perform X-ray CT imaging on a subject P. The examination table 30 is a transport device for placing and positioning the subject P, which is the object of X-ray CT imaging. The control console 40 is a computer that controls the stand 10. For example, the stand 10 and examination table 30 are located in the CT examination room, and the control console 40 is located in a control room adjacent to the CT examination room. The stand 10, examination table 30, and control console 40 are connected via wired or wireless means to communicate with each other. Furthermore, the control console 40 does not necessarily have to be located in the control room. For example, the control console 40 may be located in the same room as the stand 10 and examination table 30. Alternatively, the control console 40 may be assembled into the stand 10.

[0079] like Figure 1 As shown, the stand 10 has 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.

[0080] X-ray tube 11 irradiates the subject P with X-rays. Specifically, X-ray tube 11 includes: a cathode that generates thermionic electrons, an anode that receives thermionic electrons flying from the cathode and generates X-rays, and a vacuum tube that holds the cathode and anode together. X-ray tube 11 is connected to X-ray high-voltage device 14 via a high-voltage cable. A tube voltage is applied between the cathode and anode by X-ray high-voltage device 14. By applying tube voltage, thermionic electrons fly from the cathode toward the anode. A tube current flows as the thermionic electrons fly from the cathode toward the anode. By applying high voltage from X-ray high-voltage device 14 and supplying filament current, thermionic electrons fly from the cathode (filament) toward the anode (target), and X-rays are generated by collisions between the thermionic electrons and the anode. For example, X-ray tube 11 may be a rotating anode type X-ray tube that generates X-rays by irradiating thermionic electrons onto a rotating anode.

[0081] Furthermore, the hardware for generating X-rays is not limited to X-ray tube 11. For example, X-ray tube 11 can be replaced by a fifth-generation method to generate X-rays. The fifth-generation method includes: a focusing coil that converges the electron beam generated from the electron gun, a deflection coil that generates electromagnetic deflection, and a target ring that surrounds the subject P and generates X-rays by colliding with the deflected electron beam.

[0082] X-ray detector 12 detects X-rays irradiated from X-ray tube 11 and passing through the subject P, and outputs an electrical signal corresponding to the dose of the detected X-rays to data acquisition circuit 18. X-ray detector 12 has a structure in which multiple rows of X-ray detection elements arranged in the channel direction are arranged along the slice direction (column direction). X-ray detector 12 is, for example, an indirect conversion type detector having a grid, a scintillator array, and a photodetector array. The scintillator array has multiple scintillators. The scintillators output light in an amount corresponding to the incident X-ray dose. The grid is disposed on the X-ray incident surface side of the scintillator array and has an X-ray shielding plate that absorbs and scatters X-rays. Furthermore, the grid is sometimes referred to as a collimator (1D collimator or 2D collimator). The photodetector array converts the light into an electrical signal corresponding to the amount of light from the scintillators. For example, a photodiode is used as the photodetector. Alternatively, X-ray detector 12 can also be a direct conversion type detector.

[0083] The rotating frame 13 is an annular frame that supports the X-ray tube 11 and the X-ray detector 12, enabling them to rotate about a rotation axis (Z-axis). Specifically, the rotating frame 13 supports the X-ray tube 11 and the X-ray detector 12 opposite to each other. The rotating frame 13 is supported by a fixed frame (not shown) to allow it to rotate about the rotation axis. The rotating frame 13 is rotated about the rotation axis by a control device 15, thereby causing the X-ray tube 11 and the X-ray detector 12 to rotate about the rotation axis. The rotating frame 13 receives power from the drive mechanism of the control device 15 and rotates about the rotation axis at a certain angular velocity. The field of view (FOV) is set at the opening 19 of the rotating frame 13.

[0084] Furthermore, in this embodiment, the rotation axis of the rotating frame 13 in the non-tilted state or the length direction of the top plate 33 of the examination bed 30 is defined as the Z-axis direction, the axis orthogonal to the Z-axis direction and horizontal relative to the ground is defined as the X-axis direction, and the axis orthogonal to the Z-axis direction and perpendicular to the ground is defined as the Y-axis direction.

[0085] The X-ray high-voltage device 14 includes a high-voltage generating device and an X-ray control device. The high-voltage generating device includes electrical circuits such as a transformer and a rectifier, generating a high voltage applied to the X-ray tube 11 and supplying filament current to the X-ray tube 11. The X-ray control device controls the output voltage corresponding to the X-rays irradiated by the X-ray tube 11. The high-voltage generating device can be either a transformer or an inverter. The X-ray high-voltage device 14 can be installed in either a rotating frame 13 within the stage 10 or a fixed frame (not shown) within the stage 10.

[0086] 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 onto the subject P from the X-ray tube 11 is a predetermined distribution. For example, the wedge 16 may be a metal plate such as aluminum, such as a wedge filter or a bow-tie filter.

[0087] Collimator 17 defines the irradiation range of the X-rays transmitted through wedge 16. Collimator 17 supports multiple lead plates that shield the X-rays so that they can slide and adjust the shape of the slit formed by the multiple lead plates. In addition, collimator 17 is sometimes referred to as an X-ray aperture.

[0088] The data acquisition circuit 18 reads an electrical signal corresponding to the dose of X-rays detected by the X-ray detector 12. The data acquisition circuit 18 amplifies the read electrical signal and accumulates it during the viewing period, thereby acquiring projection data having a digital value corresponding to the dose of X-rays during that viewing period. The data acquisition circuit 18 is implemented, 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 control console 40 via a contactless data transmission device or the like.

[0089] Furthermore, in this embodiment, an accumulation-type X-ray detector 12 and an X-ray computed tomography apparatus 1 equipped with an accumulation-type X-ray detector 12 are used as examples for description. However, the technology involved in this embodiment can also be applied to photon-counting X-ray detectors or X-ray computed tomography apparatuses equipped with photon-counting X-ray detectors.

[0090] The control device 15 controls the X-ray high-voltage device 14 and the data acquisition circuit 18 for performing X-ray CT imaging according to the imaging control function 441 of the processing circuit 44 of the console 40. The control device 15 includes a processing circuit with a CPU (Central Processing Unit) or MPU (Micro Processing Unit), and drive mechanisms such as motors and actuators. The processing circuit includes a processor such as a CPU and a memory such as ROM (Read Only Memory) or RAM (Random Access Memory) as hardware resources. Alternatively, the control device 15 can be implemented using an ASIC or a Field Programmable Gate Array (FPGA). Furthermore, the control device 15 can also be implemented using other Complex Programmable Logic Devices (CPLDs) or Simple Programmable Logic Devices (SPLDs). The control device 15 has the function of receiving input signals from the input interface 43 (described later) mounted on the console 40 or the platform 10 and controlling the movement of the platform 10 and the examination bed 30. For example, the control device 15 receives input signals and controls the rotation of the rotating frame 13, the tilting of the platform 10, and the movement of the examination bed 30 and the top plate 33. Furthermore, the control device 15 controls the tilting of the platform 10 by rotating the rotating frame 13 around an axis parallel to the X-axis direction based on the tilt angle information input from the input interface mounted on the platform 10. The control device 15 can be installed on either the platform 10 or the console 40.

[0091] The examination table 30 includes a base 31, a support frame 32, a top plate 33, and an examination table drive device 34. The base 31 is disposed on the ground. The base 31 is a housing that supports the support frame 32 and is movable in a direction perpendicular to the ground (Y-axis direction). The support frame 32 is a frame disposed on the upper part of the base 31. The support frame 32 supports the top plate 33 and is movable along the rotation axis (Z-axis). The top plate 33 is a flexible plate for placing the subject P.

[0092] The examination bed drive unit 34 is housed within the housing of the examination bed 30. The examination bed drive unit 34 is a motor or actuator that generates power to move the support frame 32 and the top plate 33 on which the subject P is placed. The examination bed drive unit 34 operates according to the control of the control console 40, etc.

[0093] The console 40 includes a memory 41, a display 42, an input interface 43, and processing circuitry 44. Data communication between the memory 41, display 42, input interface 43, and processing circuitry 44 is via a bus. Furthermore, while the console 40 and the platform 10 are described as separate units, the platform 10 may also include the console 40 or a portion of its components.

[0094] The memory 41 is a storage device that stores various types of information, such as an HDD (Hard Disk Drive), SSD (Solid State Drive), or integrated circuit storage device. For example, the memory 41 stores projection data or reconstructed image data. Besides HDDs and SSDs, the memory 41 can also be a portable storage medium such as a CD (Compact Disc), DVD (Digital Versatile Disc), or flash memory. The memory 41 can also be a drive device for reading and writing various types of information with semiconductor memory elements such as flash memory and RAM (Random Access Memory). Furthermore, the storage area of ​​the memory 41 can be located either within the X-ray computed tomography apparatus 1 or in an external storage device connected via a network. The database described later is stored in the memory 41.

[0095] The display 42 displays various information. For example, the display 42 outputs medical images (CT images) generated by the processing circuit 44, a GUI (Graphical User Interface) for handling various operations from the operator, etc. Various types of displays can be used as the display 42. For example, a liquid crystal display (LCD), a CRT (cathode ray tube) display, an organic EL (organic electroluminescent display) display, or a plasma display can be used as the display 42. Furthermore, the display 42 can also be mounted on the stand 10. Additionally, the display 42 can be a desktop type or a tablet computer terminal capable of wireless communication with the main unit of the control console 40.

[0096] The input interface 43 receives various input operations from the operator, converts the received input operations into electrical signals, and outputs them to the processing circuit 44. For example, the input interface 43 receives acquisition conditions when acquiring projection data, reconstruction conditions when reconstructing CT images, and image processing conditions when generating post-processed images from CT images. As the input interface 43, a mouse, keyboard, trackball, switch, button, joystick, touchpad, and touch panel display can be appropriately used, for example. Furthermore, in this embodiment, the input interface 43 is not limited to physical operating components such as a mouse, keyboard, trackball, switch, button, joystick, touchpad, and touch panel display. For example, a processing circuit that receives electrical signals corresponding to input operations from external input devices separate from the device and outputs these electrical signals to the processing circuit 44 is also included in the example of the input interface 43. Additionally, the input interface 43 can also be provided on the stand 10. Furthermore, the input interface 43 can also be configured as a tablet computer terminal or the like capable of wireless communication with the main body of the console 40.

[0097] The processing circuit 44 controls the overall operation of the X-ray computed tomography apparatus 1 in accordance with the electrical signals of the input operation output from the input interface 43. The processing circuit 44 generates image data based on the electrical signals output from the X-ray detector 12. For example, the processing circuit 44 has processors such as CPU, MPU, and GPU, as well as memories such as ROM and RAM as hardware resources. The processing circuit 44 executes imaging control functions 441, reconstruction functions 442, image processing functions 443, display control functions 444, imaging planning functions 445, etc., by the processor executing the program expanded in the memory. Each function 441 to 445 is not limited to being implemented by a single processing circuit. Multiple independent processors can also be combined to form a processing circuit, and each processor can execute the program to implement each function 441 to 445.

[0098] In the imaging control function 441, the processing circuit 44 controls the X-ray high-voltage device 14, the control device 15 and the data acquisition circuit 18 in order to perform dual-energy scanning on the subject P.

[0099] In the reconstruction function 442, the processing circuit 44 generates virtual monochrome X-ray images, material identification images, and other DECT (Dual Energy CT) images based on the projection data output from the data acquisition circuit 18 when the high tube voltage is applied and the projection data when the low tube voltage is applied.

[0100] In image processing function 443, processing circuit 44 converts the DECT image into a cross-sectional image of arbitrary cross-section or a drawn image from any viewpoint. This conversion is based on input received from the operator via input interface 43. For example, processing circuit 44 applies 3D image processing to the DECT image, such as volume rendering, surface rendering, image value projection processing, MPR (Multi-Planer Reconstruction) processing, and CPR (Curved MPR) processing, to generate drawn image data from any viewpoint. Alternatively, a drawn image from any viewpoint can also be generated by reconstruction function 442.

[0101] In the display control function 444, the processing circuit 44 causes the display 42 to display various images generated by the image processing function 443. The images displayed on the display 42 include DECT images, cross-sectional images of arbitrary sections, and images drawn from any viewpoint. The images displayed on the display 42 also include images used to display operation screens.

[0102] In the photography planning function 445, the processing circuit 44 sets the photography plan related to dual-energy scanning.

[0103] The kV switch of the X-ray computed tomography apparatus 1 according to this embodiment will be described in detail below.

[0104] Figure 2 This is a diagram illustrating a configuration example of the main components related to the kV switch according to the first embodiment. (See diagram for example.) Figure 2 As shown, the X-ray computed tomography apparatus 1 includes an X-ray detector 12, an X-ray high-voltage device 14, a control device 15, and a data acquisition circuit 18, which are the main components related to the kV switch.

[0105] like Figure 2 As shown, 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 a light quantity corresponding to the incident X-ray quantity, and a light sensor that converts the light quantity from the scintillator into an electrical signal corresponding to the light quantity. The plurality of X-ray detection elements 121 are respectively connected to a plurality of readout switches 122 and connected to a data acquisition circuit 18 via readout lines 123.

[0106] The readout switch 122 is a switching element driven by a readout control signal from the readout control circuit 512. For example, a MOS-type field-effect transistor (Metal Oxide Semiconductor Field Effect Transistor: MOS-FET) can be used as the readout switch 122. The readout switch 122 opens in response to an OFF (off) signal, disconnecting the electrical signal from the X-ray detection element 121. In the open state, the X-ray detection element 121 receives incident X-rays and accumulates an electrical signal. The readout switch 122 closes in response to an ON (on) signal, and the accumulated electrical signal (charge signal) in the X-ray detection element 121 is read.

[0107] Figure 3 This is a plan view showing the arrangement of the X-ray detection elements 121. For example... Figure 3 As shown, multiple X-ray detection elements 121 are arranged in a two-dimensional configuration along the column direction and the channel direction on the X-ray incident surface of the X-ray detector 12. The column direction is defined as the Z-axis direction parallel to the central axis of the cavity, and the channel direction is defined as the rotation direction of the rotating frame 13. Multiple columns 124 of X-ray detection elements are arranged along the column direction.

[0108] The X-ray detector 12 of this embodiment reads electrical signals using a successive readout method. In the successive readout method, electrical signals are read out in staggered time intervals, with each X-ray detection element column 124 as a unit. As an example, electrical signals are read out sequentially from the first X-ray detection element column 124 to the last X-ray detection element column 124, with the start timing of the reading staggered in time.

[0109] like Figure 2 As shown, the control device 15 includes 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 causes the rotating frame 13 to rotate around the rotation axis (Z-axis) at a predetermined angular velocity according to the control signal from the control console 40.

[0110] 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 as an electrical pulse signal according to a first time interval corresponding to the time interval of a predetermined angle of rotation of the rotating frame 13. The VT signal generator 152 is, for example, implemented by a rotary encoder installed in the drive device 151. The first switching signal is a control signal used for switching the viewing period, hereinafter referred to as the VT signal. The waveform of the VT signal is not particularly limited and is set to 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 generation unit.

[0111] like Figure 2 As shown, the X-ray high-voltage device 14 includes 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-voltage tube and a low-voltage tube. The tube voltage control circuit 141 according to the first embodiment alternately switches the tube voltage between a high-voltage tube and a low-voltage tube 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.

[0112] like Figure 2 As shown, the data acquisition circuit 18 includes a data acquisition control circuit 51, an A / D conversion circuit 52, and a correction circuit 53.

[0113] The data acquisition control circuit 51 is implemented by control circuits such as FPGA, and controls the reading of electrical signals from the X-ray detector 12 and the data acquisition performed by the A / D conversion circuit 52. Specifically, the data acquisition control circuit 51 includes a period switching control circuit 511, a reading control circuit 512, a gain synchronization signal generation circuit 513, and a gain switching control circuit 514. The period switching control circuit 511, the reading control circuit 512, the gain synchronization signal generation circuit 513, and the gain switching control circuit 514 can be installed as hardware on individual control boards or on a single control board.

[0114] The view switching control circuit 511 switches the view period based on the VT signal. A view period corresponds to the sampling period of digital data by the A / D conversion circuit 52. For example, the time it takes for the rotating frame 13 to rotate one revolution is divided into multiple view periods, such as 1000 or 2000. By switching the view period, the view period number is incremented by 1. The view switching control circuit 511 controls the read control circuit 512 and the A / D conversion circuit 52 in accordance with the view period switching. The view switching control circuit 511 is an example of a view period switching unit.

[0115] The readout control circuit 512 controls the opening and closing of multiple readout switches 122, each connected to a plurality of X-ray detection elements 121, in a sequential readout manner. Specifically, the opening and closing of the multiple readout switches 122 is controlled to start reading at staggered electrical signal intervals for each X-ray detection element column 124, and to complete reading from all X-ray detection element columns. An ON (on) signal is supplied when the readout switch 122 is closed, and an OFF (off) signal is supplied when the readout switch 122 is open.

[0116] The gain synchronization signal generation circuit 513 generates a second switching signal at a second time interval (high frequency) shorter than the first time interval of the VT signal. This second switching signal is used in the synchronization signal for switching the gain (hereinafter referred to as DAS gain) of the A / D conversion circuit 52, and is therefore called the gain synchronization signal. As an example, the gain synchronization signal has a pulse generation period that is an integer multiple of the pulse generation period of the VT signal and is synchronized with it. The method for generating the gain synchronization signal is not particularly limited; as an example, it can 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 generation circuit 513 is an example of a second signal generation unit.

[0117] The gain switching control circuit 514 switches the DAS gain of the A / D conversion circuit 52 based on a gain synchronization signal. Specifically, the gain switching control circuit 514 switches the DAS gain between the DAS gain corresponding to the high tube voltage (hereinafter referred to as high tube voltage gain) and the DAS gain corresponding to the low tube voltage (hereinafter referred to as low tube voltage gain) based on the gain synchronization signal. The gain switching control circuit 514 switches between high tube voltage gain and low tube voltage gain in a manner that matches the tube voltage corresponding to the digital data acquired by the X-ray detector 12. Specifically, when switching to high tube voltage gain, a high-gain switching signal is supplied, and when switching to 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.

[0118] The A / D conversion circuit 52 acquires data in units of viewing period via the X-ray detector 12. Specifically, under the control of the viewing period switching control circuit 511 and the gain switching control circuit 514, the A / D conversion circuit 52 converts the electrical signal read from the X-ray detector 12 into digital data in units of viewing period using either high tube voltage gain or low tube voltage gain. The A / D conversion circuit 52 performs A / D conversion using high tube voltage gain for electrical signals generated by receiving X-rays irradiated when a high tube voltage is applied, and performs A / D conversion using low tube voltage gain for electrical signals generated by receiving X-rays irradiated when a low tube voltage is applied. Specifically, the A / D conversion circuit 52 includes a gain switcher 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.

[0119] Gain switch 521 is installed before the A / D converter 522 for high-voltage output and the A / D converter 523 for low-voltage output. According to the switching control of gain switching control circuit 514, it switches the DAS gain between high-voltage output gain and low-voltage output gain. Specifically, after gain switch 521, there are branches for an A / D conversion system for high-voltage output gain and an A / D conversion system for low-voltage output gain. Gain switch 521 may have, for example, a 3-way switch. An A / D converter 522, which amplifies the electrical signal and converts it into digital data at a high gain, is connected to one output terminal, and an A / D converter 523, which amplifies the electrical signal and converts it into digital data at a low gain, is connected to the other output terminal. A three-way switch, responding to a high-gain switching signal, connects the input terminal to one output terminal, supplying the electrical signal read from the X-ray detector 12 to the high-gain A / D converter 522. Similarly, a three-way switch, responding to a low-gain switching signal, connects the input terminal to the other output terminal, supplying the electrical signal read from the X-ray detector 12 to the low-gain A / D converter 523.

[0120] The A / D converter 522 for high-voltage applications converts electrical signals into digital data using high-voltage gain. Specifically, during the first viewing period (hereinafter referred to as the high-voltage viewing period) corresponding to scanning the subject P and applying high-voltage, the high-voltage A / D converter 522 performs A / D conversion on the electrical signal supplied from the X-ray detection element 121 when the readout switch 122 is closed, converting it into digital data using high-voltage gain. This digital data is referred to as high-voltage projection data. Projection data is digital data used for image reconstruction.

[0121] In the high-voltage A / D converter 522, during high-voltage viewing, the electrical signal generated when the read switch 122 is open is converted into digital data by applying A / D conversion with high-voltage gain. This digital data is called high-voltage gain drift correction data. Drift correction data is digital data that represents the time variation of the digital value associated with changes in the characteristics of the A / D conversion circuit 52 during scanning. The correction of this time variation generated in the projection data is called drift correction. Drift correction data is used for drift correction of the projection data. In addition, when high-voltage is applied, other than during scanning of the subject P, the A / D converter 522 converts the electrical signal read from the X-ray detection element 121 when the read switch 122 is closed into digital data by applying A / D conversion with high-voltage gain. This digital data is called high-voltage gain bias correction data. Bias correction data is digital data that represents the time variation of the digital value associated with changes in the characteristics of the A / D conversion circuit 52 associated with individual differences, aging, etc. The process of correcting for this temporal variation in the projected data is called offset correction. Offset correction data is used in offset correction of projected data.

[0122] The low-tube voltage A / D converter 523 is an A / D converter that converts electrical signals into digital data with low tube voltage gain. Specifically, during the second viewing period (hereinafter referred to as the low-tube voltage viewing period) corresponding to scanning the subject P and applying a low tube voltage, the low-tube voltage A / D converter 523 performs A / D conversion on the electrical signal supplied from the X-ray detection element 121 when the read switch 122 is closed, converting it into digital data with low tube voltage gain. This digital data is referred to as low-tube voltage projection data.

[0123] The low-tube voltage A / D converter 523, during the low-tube voltage period, performs A / D conversion on the electrical signal generated when the read switch 122 is closed, using the low-tube voltage gain to convert it into digital data. This digital data is referred to as low-tube voltage gain drift correction data. Furthermore, when the low-tube voltage is applied, excluding during scanning of the subject P, the low-tube voltage A / D converter 523 performs A / D conversion on the electrical signal read from the X-ray detection element 121 when the read switch 122 is closed, using the low-tube voltage gain to convert it into digital data. This digital data is referred to as low-tube voltage gain bias correction data.

[0124] The correction circuit 53 is a processor having an arithmetic circuit 531 and a correction data storage device 532. The arithmetic circuit 531 performs various data operations based on various digital data. As an example, the arithmetic circuit 531 performs drift correction on the projected data of the high-voltage period based on the drift correction data of the high-voltage gain, and performs drift correction on the projected data of the low-voltage period based on the drift correction data of the low-voltage gain. As another example, the arithmetic circuit 531 performs bias correction on the projected data of the high-voltage period based on the bias correction data of the high-voltage gain, and performs bias correction on the projected data of the low-voltage period based on the bias correction data of the low-voltage gain. The projected data of the high-voltage and low-voltage periods after various corrections are applied are supplied to the control console 40 via a data transmission device or the like. Furthermore, drift correction and bias correction may not be performed by the data acquisition circuit 18, for example, they may be performed by the processing circuit 44 of the control console 40.

[0125] The calibration data storage device 532 stores the drift correction data of the high-voltage gain, the bias correction data of the high-voltage gain, the drift correction data of the low-voltage gain, and the bias correction data of the low-voltage gain.

[0126] Next, an explanation Figure 1 An example of the operation of the main components involved in the kV switch in the X-ray computed tomography apparatus 1. Furthermore, the number of X-ray detection element rows is set to 320 for illustration.

[0127] Figure 4 This is a graph showing the time when the electrical signal is read from each X-ray detection element column. Figure 4 The vertical axis represents the X-ray detection element column number (acquisition column number), and the horizontal axis represents the viewing period. Figure 4 The slanted solid line shown represents the line connecting the moments when electrical signals are read from each X-ray detection element array. Furthermore, the reading of electrical signals from each X-ray detection element array is assumed to occur instantaneously. That is, the slanted solid line represents the moment when the reading of electrical signals from each X-ray detection element array is completed. Figure 4 In this configuration, the electrical signals are read sequentially from column number "1" of the X-ray detection element to column number "320". For example, in the X-ray detection element 121 belonging to column "1", electrical signal charging (accumulation) is performed at the beginning of each viewing period, and a reading is performed instantaneously at the end of that viewing period. Charging is then performed again at the beginning of the next viewing period. Figure 4As shown, in the successive reading method, the reading start timing is staggered for each X-ray detection element column. Therefore, in X-ray detection element columns other than the starting column "1", the start time of each viewing period is inconsistent with the reading implementation time, resulting in a reading delay of the electrical signal. The further the X-ray detection element column is from the starting column "1", the more delayed (deviation) the electrical signal reading time is relative to the reading implementation time in the starting column "1" (i.e., the start time of the viewing period). In the final column "320", a delay equivalent to the electrical signal reading time of period T41 is generated relative to the reading time in the starting column "1".

[0128] During each viewing period, switching of the tube voltage is prohibited until the reading of the X-ray detection element column of the final column "320" is completed. Therefore, during the period T42 from the time the reading of the X-ray detection element column of the final column "320" is implemented until the start time of the next viewing period, switching of the tube voltage is permitted.

[0129] Next, the switching between high-voltage gain and low-voltage gain involved in the first embodiment will be explained. Figure 5 This is a diagram illustrating an example of a timing diagram related to the switching of high-voltage gain and low-voltage gain according to the first embodiment. The X-ray detection element column is arranged in N columns (rows).

[0130] like Figure 5 As shown, the VT signal generator 152 repeatedly outputs the VT signal at certain first time intervals, and the viewing period switching control circuit 511 switches the viewing period based on the output of the VT signal. Through the X-ray high-voltage device 14, the tube voltage (kV) is alternately switched between high-voltage and low-voltage tubes for each viewing period. In reality, the high-voltage tubes and low-voltage tubes cannot switch instantaneously; there is a transition period of approximately several viewing periods. Figure 5 In this context, the stabilization period of the voltage value is set to 1.5 hours, and the transition period of the tube voltage is also set to 1.5 hours.

[0131] like Figure 5As shown, in sync with the VT signal, the gain synchronization signal generation circuit 513 repeatedly outputs a gain synchronization signal at a second time interval shorter than the first time interval. The gain synchronization signal is supplied to the gain switching control circuit 514 and the A / D conversion circuit 52. Based on the gain synchronization signal, the gain switching control circuit 514 alternately switches the DAS gain between high-voltage gain and low-voltage gain. More specifically, the gain switching control circuit 514 synchronously notifies the A / D conversion circuit 52 of a gain switching instruction with the first pulse of the gain synchronization signal during the stabilization period. As a gain switching instruction, a high-gain switching signal is supplied to the A / D conversion circuit 52 when switching to high-voltage gain, and a low-gain switching signal is supplied to the A / D conversion circuit 52 when switching to low-voltage gain.

[0132] Various embodiments are possible regarding the gain change plan for switching between high-voltage gain and low-voltage gain. As an example, by implementing the photography planning function 445, the processing circuit 44, during scan planning, creates a list (hereinafter referred to as the gain switching plan) that pre-sets the DAS gain category for each viewing period number, with the first viewing period being low-voltage gain and the fourth viewing period being high-voltage gain. The gain switching plan is supplied to the gain switching control circuit 514 before scanning. During scanning, the gain switching control circuit 514 substitutes the current viewing period number into the gain switching plan to determine the DAS gain category corresponding to the current viewing period number and notifies the A / D conversion circuit 52 of a gain switching instruction to the determined category. The current viewing period number is then notified from the viewing period switching control circuit 511.

[0133] As another example, a gain switching instruction can also be sent in real time from the processing circuit 44 of the console 40 to the gain switching control circuit 514 during scanning. More specifically, the processing circuit 44 substitutes the current viewing period number into the gain switching plan to determine the category of DAS gain corresponding to the current viewing period number, and sends a gain switching instruction to the determined category to the gain switching control circuit 514. In this case, the processing circuit 44 can also send the gain switching instruction synchronously with the VT signal. The gain switching control circuit 514, within the switching indication period of the current viewing period, notifies the A / D conversion circuit 52 of the same gain switching instruction as that from the processing circuit 44.

[0134] Furthermore, the gain switching plan is set as a list of DAS gain categories assigned for each viewing period number, but it is not limited to this. For example, if the DAS gain category for the odd-numbered viewing period number is distinguished from the DAS gain category for the even-numbered viewing period number, the gain switching plan can also be a list of DAS gain categories assigned separately for odd and even periods. Alternatively, the gain switching plan can also be expressed by a formula relating the viewing period number to the DAS gain category.

[0135] As described above, when a gain switching indication is given in the first pulse of the gain synchronization signal, the gain switcher 521 of the A / D conversion circuit 52 performs DAS gain switching synchronously with the second pulse that follows the first pulse.

[0136] Specifically, during the stabilization period of the low tube voltage ( Figure 5 In the fourth viewing period (e.g.), the gain switching control circuit 514 synchronously notifies the A / D conversion circuit 52 of a gain switching instruction to low-transistor voltage gain, in sync with the first pulse of the gain synchronization signal. Then, the gain switcher 521 synchronously switches from high-transistor voltage gain to low-transistor voltage gain with the second pulse following the first pulse. Immediately after the DAS gain switch, the operation of the low-transistor voltage A / D converter 523 is unstable; therefore, the period from the implementation of the DAS gain switch until the start of the next viewing period is used for stabilization of the low-transistor voltage A / D converter 523.

[0137] Similarly, during the steady-state period of the high-voltage ( Figure 5 During the first or seventh viewing period (or similar), the A / D conversion circuit 52 is notified of a gain switching instruction to the high-voltage gain in sync with the first pulse of the gain synchronization signal. Then, the gain switch 521 switches from low-voltage gain to high-voltage gain in sync with the second pulse following the first pulse. The period from the implementation of the DAS gain switching until the start of the next viewing period is used for stabilization of the high-voltage A / D converter 522.

[0138] Furthermore, the second pulse can be the pulse following the first pulse, as long as it is a pulse output within the same visual period, or it can be several subsequent pulses.

[0139] like Figure 5As shown, synchronously with the VT signal, the readout control circuit 512 sequentially charges (accumulates) and reads from the X-ray detector 12. More specifically, during the stabilization period of the high-voltage or low-voltage tube, the readout switch 122 is closed, and the X-ray detection element 121 charges. The charging start time is staggered for each column or a predetermined number of columns of X-ray detection elements, and the charging is carried out for a time length equivalent to approximately one viewing period. Starting from the column of X-ray detection elements where charging has ended, electrical signals are read sequentially from the X-ray detection elements 121. During the period T51 from the end of charging until the predetermined time has elapsed, the readout switch 122 is opened, and electrical signals are read from the X-ray detection elements 121. During the period T52 from the end of period T51 until the predetermined time has elapsed, data for drift correction is read. It is assumed that the X-ray detection element 121 has not accumulated an electrical signal during period T52. In the uncharged state, drift correction data is read from the X-ray detection element 121.

[0140] As described above, readings are initiated at staggered times within the same viewing period for each X-ray detection element column 124. The electrical signal accumulated by X-ray irradiation in the first viewing period is read in the next viewing period, i.e., the second viewing period. Figure 5 As shown, as the reading delay of the electrical signal increases from column 1 to column N, readings are performed across the second and third viewing periods in the X-ray detection element columns after column 2.

[0141] After the electrical signal is read, it is converted into digital data by either the high-voltage A / D converter 522 or the low-voltage A / D converter 523 with the set DAS gain. Specifically, during the application of the high-voltage, the DAS gain is set to the high-voltage gain, so the electrical signal is supplied from the X-ray detection element 121 to the high-voltage A / D converter 522 and converted into projection data with the high-voltage gain. During the application of the low-voltage, the DAS gain is set to the low-voltage gain, so the electrical signal is supplied from the X-ray detection element 121 to the low-voltage A / D converter 523 and converted into projection data with the low-voltage gain.

[0142] Here, the differences between this embodiment and the comparative example will be explained. The comparative example is a method of gain switching indication synchronized with the VT signal and data acquisition performed by the A / D conversion circuit.

[0143] Figure 6 This is a diagram illustrating an example of the timing diagram related to the switching of the high-voltage gain and low-voltage gain in a comparative example. Furthermore, the comparative example also... Figure 5 Similarly, the stabilization period and the transition period are set at 1.5 periods.

[0144] like Figure 6 As shown, according to the comparative example, gain switching indication and data acquisition by the A / D conversion circuit are performed synchronously with the VT signal. For example, even if gain switching indication is performed synchronously with the VT signal in the fourth viewing period, the VT signal will not be output in that viewing period, so data acquisition by the A / D conversion circuit is not possible. Data acquisition is then performed gradually in sync with the output VT signal in the subsequent fifth viewing period. In column 1, the charge accumulated when a low tube voltage is applied in the fourth viewing period is read out in the fifth viewing period with a low tube voltage gain. However, in the X-ray detection element columns after column 2 (column N), electrical signals are read out across the fifth and sixth viewing periods. However, in the sixth viewing period, the DAS gain is switched to a high tube voltage gain, so the charge accumulated when a low tube voltage is applied is read out with a high tube voltage gain. That is, in the comparative example, the tube voltage associated with charge accumulation and the tube voltage associated with DAS gain become inconsistent in the X-ray detection element columns that are read out across viewing periods. Due to this inconsistency, data is acquired using the high-voltage gain for electrical signals accumulated when a low-voltage tube is applied, but using the low-voltage gain for the same electrical signal, resulting in an inability to acquire data with an appropriate gain. Furthermore, when the settling period is more than two viewing periods, acquiring data using both high-voltage and low-voltage gains for the same tube voltage degrades the quality of the projected data.

[0145] According to this embodiment, such as Figure 5 As shown, even for X-ray detector arrays that read across viewing periods, the tube voltage associated with energy storage and the tube voltage associated with DAS gain become consistent. Therefore, DAS gain can be switched synchronously with the kV switch. Furthermore, as a result, data acquisition can be performed with high tube voltage gain during high tube voltage viewing periods and with low tube voltage gain during low tube voltage viewing periods, thus enabling data acquisition with appropriate DAS gain for both high and low tube voltages.

[0146] Next, the acquisition of drift correction data will be explained. When scanning the subject, the data acquisition circuit 18 acquires drift correction data of the high-voltage gain and second drift correction data of the low-voltage gain.

[0147] Figure 7 This is a timing diagram related to the acquisition of drift correction data. For example... Figure 7As shown, the tube voltage control circuit 141 alternately switches the tube voltage between high tube voltage (high) and low tube voltage (low). Additionally, as described above, the DAS gain is switched alternately between high tube voltage (high) gain and low tube voltage (low) gain in sync with the tube voltage switching by the gain switching control circuit 514. Regarding the tube voltage transition period, it is assumed that no DAS gain is set.

[0148] In the first viewing period (high-voltage viewing period) corresponding to the application of high-voltage, the A / D conversion circuit 52 acquires the digital data output from the A / D converter 522 when the read switch 122 is closed as projection data using the first DAS gain (high-voltage gain). After acquiring this projection data, it acquires the digital data output from the A / D converter 522 when the read switch 122 is open using the high-voltage gain as the first drift correction data (drift correction data for high-voltage). Furthermore, in the second viewing period (low-voltage viewing period) corresponding to the application of low-voltage, the A / D conversion circuit 52 acquires the digital data output from the A / D converter 523 when the read switch 122 is closed as projection data using the low-voltage gain. After acquiring this projection data, it acquires the digital data output from the A / D converter 523 when the read switch 122 is open using the low-voltage gain as the second drift correction data (drift correction data for low-voltage). Therefore, drift correction data for high-voltage tubes is missing when low-voltage tubes are applied and during the transition period.

[0149] like Figure 7 As shown, the arithmetic circuit 531 generates drift correction data D70 for the high-voltage gain that is missing in the low-voltage period, based on high-voltage gain drift correction data D71 acquired during the high-voltage period prior to the low-voltage period and / or low-voltage gain drift correction data D72 acquired during the same low-voltage period. Similarly, the arithmetic circuit 531 generates drift correction data D73 for the low-voltage gain that is missing in the high-voltage period, based on low-voltage gain drift correction data D74 acquired during the low-voltage period prior to the high-voltage period and / or high-voltage gain drift correction data D71 acquired during the same high-voltage period. The drift correction data generated based on the acquired drift correction data is called the drift correction data obtained through calculation. The drift correction data obtained through calculation can be generated using various methods. Several generation methods are described below.

[0150] (Method 1) The arithmetic circuit 531 calculates drift correction data D70 for the high-voltage gain of multiple periods from a certain high-voltage period until the next high-voltage period, based on the measured high-voltage drift correction data D71 acquired with the high-voltage gain of the preceding period. Specifically, the drift correction data for the high-voltage gain in the low-voltage period (stable period) is regarded as a repetition of the measured drift correction data for the high-voltage gain in the preceding high-voltage period (stable period), and the moving average of the measured drift correction data for the high-voltage gain is set as the drift correction data for the high-voltage gain in the low-voltage period (stable period). Furthermore, the drift correction data for the high-voltage gain in the transition periods immediately before and immediately after the low-voltage period (stable period) can be either set as a moving average of the measured drift correction data for the high-voltage gain in the preceding high-voltage period (stable period), or the moving average can be appropriately corrected for calculation. Missing portions of the drift correction data for the low-voltage gain can also be generated in the same way.

[0151] (Method 2) The operational circuit 531 calculates the drift correction data D70 of the high-voltage gain for multiple periods based on the measured low-voltage drift correction data D72 for the low-voltage period from a certain high-voltage period until the next high-voltage period. Specifically, a correction value is calculated by analyzing the tendency of the measured low-voltage drift correction data D72 for the multiple periods, and this correction value is applied to the drift correction data D71 of the immediate high-voltage period to calculate the drift correction data D70 for the high-voltage. Missing portions of the low-voltage gain drift correction data can also be generated in the same way.

[0152] (Method 3) The arithmetic circuit 531 calculates the drift correction data D70 of the high-voltage gain for multiple periods based on the measured low-voltage drift correction data D72 for the low-voltage gain during a period from a certain high-voltage period until the next high-voltage period. Specifically, a bias is applied to match the average value of the measured low-voltage drift correction data D70 for the low-voltage gain during the multiple periods with the average value of the preceding high-voltage gain drift correction data D71, thereby calculating the calculated high-voltage drift correction data D70. Missing portions of the low-voltage gain drift correction data can also be generated in the same way.

[0153] (Method 4) The arithmetic circuit 531 uses a machine learning model to generate the missing portions of the drift correction data. As an example, a machine learning model can be used, trained to input drift correction data of the high-voltage gain in the first period and output drift correction data of the high-voltage gain in the second period, which is later than the first period. In this case, the arithmetic circuit 531 can apply the measured drift correction data of the high-voltage gain in the high-voltage period to the machine learning model and generate the calculated drift correction data of the high-voltage gain in the low-voltage period, which is later than the high-voltage period. The missing portions of the low-voltage gain drift correction data can also be generated in the same way. As another example, a machine learning model can be used, trained to input drift correction data of the low-voltage gain in the first period and output drift correction data of the high-voltage gain in the first period. In this case, the arithmetic circuit 531 can apply the measured drift correction data of the low-voltage gain in the low-voltage period to the machine learning model and generate the calculated drift correction data of the high-voltage gain in the low-voltage period. The missing data regarding the drift correction of the low-voltage gain can also be generated in the same way.

[0154] (Method 5) The arithmetic circuit 531 can also generate the missing portion of the high-voltage gain drift correction data by correcting the immediately preceding measured high-voltage gain drift correction data based on the temperature data of the devices within the X-ray detector 12 and / or data acquisition circuit 18. Regarding the devices within the X-ray detector 12 and / or data acquisition circuit 18, temperature data is measured by a temperature measuring device. The temperature variation of this device in the period preceding the period corresponding to the missing portion can be analyzed, and the calculated high-voltage drift correction data can be generated based on this temperature variation. The missing portion of the low-voltage gain drift correction data can also be generated in the same way.

[0155] 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 category and viewing period number. According to this embodiment, drift correction data of high-voltage gain and low-voltage gain can be collected. In addition, by interpolating the missing parts using the above method, drift correction data of high-voltage gain and low-voltage gain can be collected throughout the entire viewing period.

[0156] Next, the acquisition of bias correction data will be explained. The data acquisition circuit 18 acquires the first bias correction data corresponding to the high-voltage gain and the second bias correction data corresponding to the low-voltage gain.

[0157] Figure 8 This is a timing diagram related to the acquisition of bias correction data. For example... Figure 8 As shown, CT examinations can be performed before, during, and after scanning. In the scanning mode, as described above, dual-energy scanning is performed based on a kV switch. Before and / or after scanning, the data acquisition circuit 18 acquires bias correction data for the high-voltage gain and bias correction data for the low-voltage gain. When the high-voltage is applied, the data acquisition circuit 18 acquires the digital data output from the A / D converter 522 when the read switch 122 is closed or open, as bias correction data for the high-voltage gain. When the low-voltage is applied, the data acquisition circuit 18 acquires the digital data output from the A / D converter 523 when the read switch 122 is closed or open, as bias correction data for the low-voltage gain. It is not necessary to acquire bias correction data for each DAS gain throughout the entire 360-degree viewing period; acquisition is possible at any viewing period. The acquired bias correction data for each DAS gain can be used for both the acquired and unacquired viewing periods.

[0158] The methods for acquiring bias correction data can be roughly divided into three modes.

[0159] like Figure 8 As shown, in mode 1, bias correction data for both the high-voltage gain and the low-voltage gain are acquired before scanning. The high-voltage gain bias correction data can be acquired first, followed by the low-voltage gain bias correction data, or vice versa.

[0160] like Figure 8 As shown, in Mode 2, bias correction data for the high-voltage gain is acquired before scanning, and bias correction data for the low-voltage gain is acquired after scanning. Conversely, bias correction data for the low-voltage gain can also be acquired before scanning, and bias correction data for the high-voltage gain can be acquired after scanning.

[0161] like Figure 8 As shown, in Mode 3, bias correction data for both the high-voltage gain and the low-voltage gain are acquired before and after scanning. For example, before scanning, the high-voltage gain bias correction data is acquired before the low-voltage gain bias correction data, and after scanning, the low-voltage gain bias correction data is acquired before the high-voltage gain bias correction data. Furthermore, the acquisition order of the high-voltage gain bias correction data and the low-voltage gain bias correction data before and after scanning is not particularly limited.

[0162] The measured or calculated bias correction data generated by the above method is stored in the correction data storage device 532. According to this embodiment, bias correction data of high tube voltage gain and bias correction data of low tube voltage gain can be acquired.

[0163] (Second Implementation)

[0164] Figure 9 This is a diagram illustrating a configuration example of the main components related to the kV switch according to the second embodiment. Furthermore, in the following description, components having substantially the same function as those in the first embodiment will be labeled with the same reference numerals and will be described repeatedly only where necessary.

[0165] like Figure 9 As shown, the X-ray computed tomography apparatus 1 according to the second embodiment 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 involved in the kV switch. In addition to a period switching control circuit 541, a readout control circuit 542, a gain synchronization signal generation circuit 543, and a gain switching control circuit 544, the data acquisition control circuit 544 of the data acquisition circuit 18 also includes a VT+ signal generator 545.

[0166] The period switching control circuit 541 is similar to the period switching control circuit 511 in the first embodiment, and switches the period based on the VT signal from the VT signal generator 152.

[0167] The readout control circuit 542 is similar to the readout control circuit 512 in the first embodiment, and controls the opening and closing of the plurality of readout switches 122 that are respectively connected to the plurality of X-ray detection elements 121 in a sequential readout manner.

[0168] The gain synchronization signal generation circuit 543 generates a gain synchronization signal in the same way as the gain switching control circuit 514 in the first embodiment.

[0169] The VT+ signal generator 545 generates a VT+ signal, which is a signal notifying that the reading of the electrical signal from all X-ray detection element rows 124 has ended. As described above, the readout control circuit 542 supplies an ON (on) signal to the readout switch 122 in units of X-ray detection element rows 124 during the storage period and an OFF (off) signal during the reading period. The VT+ signal generator 545 monitors the supply of the OFF (off) signal of the readout control circuit 542 and generates the VT+ signal as a trigger when an OFF (off) signal is supplied to the readout switch 122 corresponding to the last X-ray detection element row 124. Furthermore, the VT+ signal generator 545 can also generate the VT+ signal by delaying any amount of time from the moment the OFF (off) signal is supplied. The VT+ signal is supplied to the tube voltage control circuit 142 and the gain switching control circuit 544.

[0170] The gain switching control circuit 544 switches the DAS gain based on the gain synchronization signal and the VT+ signal. Specifically, when the timing of both the gain synchronization signal and the VT+ signal is output (i.e., the timing of the AND operation of the gain synchronization signal and the VT+ signal), the gain switching control circuit 544 switches the DAS gain between high-voltage gain and low-voltage gain. The gain change plan regarding switching to high-voltage gain or low-voltage gain is the same as in the first embodiment. Furthermore, when the processing circuit 44 sends a gain switching instruction to the gain switching control circuit 514, the gain switching instruction can be sent synchronously with the VT+ signal. Thus, the gain switching control circuit 514 can notify the A / D conversion circuit 52 of the gain switching instruction in the next period after receiving the VT+ signal.

[0171] The tube voltage control circuit 142 in the second embodiment switches the tube voltage between high tube voltage and low tube voltage based on the VT signal, rather than the VT signal. By switching the tube voltage based on the VT+ signal, the tube voltage switching operation can be performed immediately after the reading of all X-ray detection element arrays 124 is completed.

[0172] Next, the switching between high-voltage gain and low-voltage gain involved in the second embodiment will be explained. Figure 10 This is a diagram illustrating an example of a timing diagram related to the switching of high-voltage gain and low-voltage gain as described in the second embodiment.

[0173] like Figure 10 As shown, the VT signal generator 152 repeatedly outputs the VT signal at a certain first time interval, and the viewing period is switched by the viewing period switching control circuit 511 based on the output of the VT signal. Additionally, the VT+ signal generator 545 outputs the VT+ signal at the timing when the signal reading of the final column ends. The gain switching control circuit 544 synchronously notifies the A / D conversion circuit 52 of the gain switching instruction in the next viewing period after the VT+ signal is output, using the output of the first pulse of the synchronization signal. Then, the gain switcher 521 of the A / D conversion circuit 52 switches the DAS gain synchronously with the output of the second pulse, which follows the first pulse. The second pulse can be either the pulse following the first pulse or several subsequent pulses. Thus, similar to the first embodiment, the tube voltage associated with energy storage and the tube voltage associated with the DAS gain become consistent.

[0174] Furthermore, in the second embodiment, it is also related to Figure 5Similarly, in the first embodiment shown, the X-ray detector 12 is sequentially charged (accumulated) and read out in sync with the VT signal by the readout control circuit 512. More specifically, during the observation period of the stable high tube voltage or low tube voltage, the readout switch 122 is closed, and the X-ray detection element 121 is charged. The charging start time is staggered for each column or a predetermined number of columns of X-ray detection elements, and the charging is carried out for a time length equivalent to approximately one observation period. Starting from the column of X-ray detection elements where charging has ended, the electrical signal is read out sequentially from the X-ray detection element 121. During the period T101 from the end of charging until the predetermined time has elapsed, the readout switch 122 is opened, and the electrical signal is read out from the X-ray detection element 121. During the period T102 from the end of period T101 until the predetermined time has elapsed, data for drift correction is read out.

[0175] As described above, according to the second embodiment, the switching of the tube voltage and the switching of the DAS gain are performed synchronously with the VT+ signal, thus enabling the switching of the DAS gain synchronously with the KV switch.

[0176] According to at least one of the embodiments described above, the gain involved in data acquisition can be switched synchronously with the switching of tube voltage.

[0177] The term "processor" used in the above description refers to circuits such as CPU, GPU, or Application Specific Integrated Circuit (ASIC), programmable logic device (e.g., Simple Programmable Logic Device (SPLD), Complex Programmable Logic Device (CPLD), and Field Programmable Gate Array (FPGA)). The processor implements its function by reading and executing a program stored in a memory circuit. Alternatively, instead of storing the program in a memory circuit, the program can be directly loaded into the processor's circuitry. In this case, the processor implements its function by reading and executing the program loaded into the circuitry. Alternatively, the function corresponding to the program can be implemented through a combination of logic circuits, rather than by executing the program. Furthermore, the processors in this embodiment are not limited to being configured as a single circuit; multiple independent circuits can be combined to form one processor and implement its function. Furthermore, it is also possible to... Figure 1 , Figure 2 and Figure 9Multiple components are integrated into a single processor to achieve their functions.

[0178] Several embodiments have been described above, but these embodiments are provided as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other ways, and various omissions, substitutions, modifications, and combinations of embodiments are possible without departing from the spirit of the invention. These embodiments and their variations are included in the scope or spirit of the invention and in the scope of the invention as described in the patent claims and its equivalents.

[0179] The foregoing has described several embodiments of the present invention, but these embodiments are provided as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope or spirit of the invention, and are included in the scope of the invention and its equivalents as set forth in the patent claims.

Claims

1. An X-ray computed tomography (CT) device, wherein, have: The tube voltage control unit switches the tube voltage applied to the X-ray tube between a first tube voltage and a second tube voltage that is lower than the first tube voltage; The first signal generation unit generates a first switching signal at a first time interval; The viewing period switching unit switches the viewing period based on the first switching signal; The data acquisition unit acquires data in units of the stated viewing period via an X-ray detector. The second signal generation unit generates a second switching signal that is synchronized with the first switching signal at a second time interval that is shorter than the first time interval; as well as The gain switching unit switches the gain of the data acquisition unit based on the second switching signal. The gain switching unit switches the gain between a first gain corresponding to the voltage of the first transistor and a second gain corresponding to the voltage of the second transistor based on the second switching signal.

2. The X-ray computed tomography apparatus as described in claim 1, wherein, The gain switching unit switches between the first gain and the second gain in a manner that matches the tube voltage corresponding to the data acquired via the X-ray detector.

3. The X-ray computed tomography apparatus as described in claim 2, wherein, When scanning the subject, the data acquisition unit acquires first drift correction data corresponding to the first gain and second drift correction data corresponding to the second gain.

4. The X-ray computed tomography apparatus as described in claim 3, wherein, The X-ray detector has an X-ray detection element and a readout switch for the X-ray detection element. The data acquisition unit includes an A / D converter, which is connected to the X-ray detection element via the readout switch to convert electrical signals into digital data. The data acquisition unit, During the first viewing period corresponding to the application of the first tube voltage, the digital data output from the A / D converter when the read switch is closed is acquired as projection data. After the projection data is acquired, the digital data output from the A / D converter when the read switch is open is acquired as the first drift correction data. During the second viewing period corresponding to the application of the second tube voltage, the digital data output from the A / D converter when the read switch is closed is acquired as the projection data. After the projection data is acquired, the digital data output from the A / D converter when the read switch is open is acquired as the second drift correction data.

5. The X-ray computed tomography apparatus as described in claim 4, wherein, The data acquisition unit, Based on the first drift correction data acquired in the first viewing period and / or the second drift correction data acquired in the second viewing period, the second drift correction data missing in the first viewing period is generated. Based on the second drift correction data acquired in the second viewing period and / or the first drift correction data acquired in the first viewing period, the first drift correction data missing in the second viewing period is generated.

6. The X-ray computed tomography apparatus as described in claim 4, wherein, The data acquisition unit uses the temperature data measured in the first viewing period to correct the first drift correction data acquired in the first viewing period and / or the second drift correction data acquired in the second viewing period, so as to generate the second drift correction data that was missing in the first viewing period.

7. The X-ray computed tomography apparatus as described in claim 2, wherein, In addition to scanning the subject, the data acquisition unit acquires first bias correction data corresponding to the first gain and second bias correction data corresponding to the second gain.

8. The X-ray computed tomography apparatus as described in claim 7, wherein, The X-ray detector has an X-ray detection element and a readout switch for the X-ray detection element. The data acquisition unit includes an A / D converter, which is connected to the X-ray detection element via the readout switch to convert electrical signals into digital data. When the voltage of the first transistor is applied, the data acquisition unit acquires the digital data output from the A / D converter when the read switch is closed as the first bias correction data. When the voltage of the second transistor is applied, the data acquisition unit acquires the digital data output from the A / D converter when the read switch is closed as the second bias correction data.

9. The X-ray computed tomography apparatus as described in claim 8, wherein, The data acquisition unit, The first bias correction data and the second bias correction data were acquired before scanning. Alternatively, the first offset correction data can be acquired before scanning, and the second offset correction data can be acquired after scanning. Alternatively, the second offset correction data can be acquired before scanning, and the first offset correction data can be acquired after scanning. Alternatively, the digital data under the first gain and the digital data under the second gain are acquired before and after scanning, respectively. The first bias correction data is generated based on the digital data under the first gain before and after scanning, and the second bias correction data is generated based on the digital data under the second gain before and after scanning.

10. The X-ray computed tomography apparatus as claimed in claim 1, wherein, The second signal generating unit upsamples the first switching signal to generate the second switching signal that is synchronized with the first switching signal.

11. The X-ray computed tomography apparatus as claimed in claim 1, wherein, The second signal generating unit generates a first pulse and a second pulse that follows the first pulse during the first time interval, as the second switching signal. The gain switching unit supplies a switching instruction to the data acquisition unit synchronously with the first pulse. The data acquisition unit switches to the gain corresponding to the switching indication synchronously with the second pulse.

12. The X-ray computed tomography apparatus as claimed in 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 generated at a timing point when the reading of charge from all detection element columns of the X-ray detector ends.

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