X-ray high-voltage equipment, medical imaging diagnostic equipment, and X-ray CT scanner

Abstract

To achieve zero-voltage spectroscopy (ZVS) in an X-ray high-voltage device, regardless of the load. [Solution] The X-ray high-voltage device according to the embodiment comprises an inverter, a transformer, a capacitor, an inductance, a switching unit, an acquisition unit, and a control unit. The inverter converts a DC voltage to an AC voltage. The transformer supplies the tube voltage, which is obtained by boosting the AC voltage, to the X-ray tube. The capacitor is connected in parallel to the switching element of the inverter. The inductance is connected between the transformer and the capacitor, and a resonant current flows between the capacitor and the inductance. The switching unit changes the number of turns on the inverter side of the transformer. The acquisition unit acquires scan conditions, including the image quality after scanning. The control unit changes the on-time of the AC voltage input to the transformer by causing the switching unit to change the number of turns based on the scan conditions.

Description

Technical Field

[0001] The embodiments disclosed in this specification and the drawings relate to an X-ray high voltage device, a medical imaging diagnostic device, and an X-ray CT device.

Background Art

[0002] In an X-ray high voltage device, after converting an AC voltage to DC, it is made into a high frequency by an inverter and boosted through a transformer. Then, the boosted AC voltage is supplied to the X-ray tube. FIG. 9 is a diagram showing the circuit configuration of an X-ray high voltage device 14a according to the prior art.

[0003] In an X-ray high voltage device, by connecting a resonance capacitor in parallel to the switching element of the inverter, a ZVS (Zero Voltage Switching) control method using the resonance of the resonance capacitor and the leakage inductance is realized. ZVS is a technology for switching on and off the switching element after making the voltage of the resonance capacitor 0V. Thereby, it is possible to improve the efficiency and reduce the loss during switching.

[0004] However, in the conventional method, at low load where the on-time of the inverter is short, the energy stored in the leakage inductance becomes small, so the energy of the resonance capacitor may relatively become large. In that case, since the resonance current flows from the resonance capacitor to the leakage inductance, a negative charge accumulates in the resonance capacitor, so the following formula 1 cannot be satisfied, that is, there is a problem that ZVS cannot be realized. <U+

[0005] <U+ <U+

Equation

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] One of the problems to be solved by the embodiments disclosed in this specification and the drawings is to achieve zero-voltage switching (ZVS) in an X-ray high-voltage device regardless of the load. However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problems. The problems corresponding to the effects of each configuration shown in each of the following embodiments can also be regarded as other problems.

Means for Solving the Problems

[0008] The X-ray high-voltage device according to the embodiment includes an inverter, a transformer, a capacitor, an inductance, a switching unit, an acquisition unit, and a control unit. The inverter converts a DC voltage into an AC voltage. The transformer supplies a tube voltage obtained by boosting the AC voltage to an X-ray tube. The capacitor is connected in parallel to the switching element of the inverter. The inductance is connected between the transformer and the capacitor, and a resonant current flows between the inductance and the capacitor. The switching unit changes the number of turns on the inverter side of the transformer. The acquisition unit acquires scan conditions including the image quality of the image after scanning. The control unit changes the on-time of the AC voltage input to the transformer by causing the switching unit to change the number of turns based on the scan conditions.

Brief Description of the Drawings

[0009] [Figure 1] It is a block diagram showing a configuration example of an X-ray CT device according to the first embodiment. [Figure 2] It is a diagram showing the circuit configuration of an X-ray high-voltage device according to the first embodiment. [Figure 3] It is a diagram showing the temporal changes in the output voltage of the inverter and the waveform of the resonant current according to the second embodiment. [Figure 4] It is a table showing the relationship between the level of the load and the ripple pulse width of the tube voltage when the number of primary turns of the transformer is fixed. [Figure 5] This graph shows the relationship between time and the voltage of the charging capacitor, depending on the load level, when the number of primary windings of the transformer is fixed. [Figure 6] This graph shows the voltage waveform of the charging capacitor according to the third embodiment. [Figure 7] This is a flowchart showing the process for identifying the optimal contact point according to the fourth embodiment. [Figure 8] This diagram shows a table illustrating the relationship between the output power according to the fourth embodiment, the number of turns on the primary side of the transformer, and the ripple of the tube voltage. [Figure 9] This diagram shows the circuit configuration of a conventional X-ray high-voltage device. [Modes for carrying out the invention]

[0010] The embodiments of the X-ray high-voltage device, medical imaging diagnostic device, and X-ray CT device will be described in detail below with reference to the drawings.

[0011] [First Embodiment] Figure 1 is a block diagram showing an example configuration of an X-ray CT scanner 1 according to the first embodiment. As shown in Figure 1, the X-ray CT scanner 1 has a stand 10, a patient table 30, and a console 40. Although multiple stands 10 are shown in Figure 1 for illustrative purposes, in reality, there may be one or more stands. The X-ray CT scanner 1 is an example of a medical imaging diagnostic device.

[0012] The gantry 10 is a scanning device configured for X-ray CT imaging of a subject P. The patient table 30 is a transport device for placing and positioning the subject P to be X-ray CT imaging. The console 40 is a computer that controls the gantry 10. For example, the gantry 10 and patient table 30 are installed in the CT examination room, and the console 40 is installed in a control room adjacent to the CT examination room. The gantry 10, patient table 30, and console 40 are connected to each other by wired or wireless connections so that they can communicate with one another. Note that 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 patient table 30. Alternatively, the console 40 may be incorporated into the gantry 10.

[0013] As shown in Figure 1, the stand 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.

[0014] The X-ray tube 11 irradiates the subject P with X-rays. Specifically, the 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. The X-ray tube 11 is connected to the X-ray high-voltage device 14 via a high-voltage cable. A tube voltage is applied between the cathode and anode by the X-ray high-voltage device 14. The application of the tube voltage causes thermionic electrons to fly from the cathode to the anode. A tube current flows as thermionic electrons fly from the cathode to the anode. X-rays are generated when thermionic electrons collide with the anode.

[0015] The X-ray detector 12 detects X-rays irradiated from the X-ray tube 11 and passed through the subject P, and outputs an electrical signal corresponding to the detected X-ray dose to the data acquisition circuit 18. The X-ray detector 12 has a structure in which multiple rows of X-ray detection elements, each row of X-ray detection elements arranged in the channel direction, are arranged in the slice direction (column 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 scintillators output light with an amount of light corresponding to the incident X-ray dose. The grid is positioned 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 the amount of light from the scintillators into an electrical signal. For example, a photodiode is used as the photosensor. The X-ray detector 12 may also be a direct conversion type detector.

[0016] The rotating frame 13 is an annular frame that supports the X-ray tube 11 and the X-ray detector 12 so that they can rotate around a rotation axis (Z-axis). Specifically, the rotating frame 13 supports the X-ray tube 11 and the X-ray detector 12 facing each other. The rotating frame 13 is supported by a fixed frame (not shown) so that it can rotate around a rotation axis. The control device 15 rotates the rotating frame 13 around the rotation axis, thereby rotating the X-ray tube 11 and the X-ray detector 12 around the rotation axis. The rotating frame 13 rotates at a constant angular velocity around the rotation axis by receiving power from the drive mechanism of the control device 15. An image field of view (FOV) is set in the aperture 19 of the rotating frame 13.

[0017] As shown in Figure 1, in this embodiment, the rotation axis of the rotating frame 13 or the longitudinal direction of the top plate 33 of the bed 30 in the non-tilted state 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.

[0018] The X-ray high-voltage device 14 includes a high-voltage generator and an X-ray control device. The high-voltage generator has an electrical circuit including a transformer and a rectifier, and generates the high voltage applied to the X-ray tube 11 and the filament current supplied to the X-ray tube 11. The X-ray control device controls the output voltage according to the X-rays irradiated by the X-ray tube 11. The high-voltage generator may be of the transformer type or the inverter type. The X-ray high-voltage device 14 may be installed on the rotating frame 13 within the stand 10, or on the fixed frame (not shown) within the stand 10.

[0019] 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 to the subject P has a predetermined distribution. For example, the wedge 16 can be a metal plate such as aluminum, such as a wedge filter or a bow-tie filter.

[0020] The collimator 17 limits the irradiation range of 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 slit formed by the multiple lead plates. The collimator 17 is sometimes called an X-ray diaphragm.

[0021] The data acquisition circuit 18 reads an electrical signal from the X-ray detector 12 corresponding to the X-ray dose detected by the X-ray detector 12. The data acquisition circuit 18 amplifies the read-out electrical signal and integrates it over the viewing period to collect detection data having a digital value corresponding to the X-ray dose over the viewing period. The detection data is called projection data. 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 projection data is transmitted to the console 40 via a non-contact data transmission device or the like.

[0022] The control device 15 controls the X-ray high-voltage device 14 and the data acquisition circuit 18 in order to perform X-ray CT imaging according to the imaging control function 451 of the processing circuit 45 of the console 40. The control device 15 has a processing circuit having a Central Processing Unit (CPU) or Micro Processing Unit (MPU), etc., and a drive mechanism such as a motor and actuator. The processing circuit 45 has a processor such as a CPU and memory such as Read Only Memory (ROM) or Random Access Memory (RAM) as hardware resources. The control device 15 performs various functions using the processor that executes the program loaded into memory. Note that the various functions are not limited to being realized by a single processing circuit. Multiple independent processors may be combined to form a processing circuit, and each processor may perform each function by executing a program. Furthermore, the control device 15 may be implemented by an ASIC or a Field Programmable Gate Array (FPGA).

[0023] Furthermore, the control device 15 may be implemented using other complex programmable logic devices (CPLDs) or simple programmable logic devices (SPLDs). The control device 15 has the function of controlling the operation of the frame 10 and the bed 30 by receiving input signals from an input interface 43, which will be described later, attached to the console 40 or the frame 10. For example, the control device 15 receives input signals and controls the rotation of the rotating frame 13, the tilt of the frame 10, and the operation of the bed 30 and the top plate 33. The control of tilting the frame 10 is implemented by the control device 15 rotating the rotating frame 13 around an axis parallel to the X-axis direction based on the tilt angle information input by the input interface attached to the frame 10. The control device 15 may be installed on the frame 10 or on the console 40.

[0024] The examination bed 30 comprises a base 31, a support frame 32, a top plate 33, and an examination bed drive device 34. The base 31 is installed on the floor. The base 31 is a housing that supports the support frame 32 so that it can move perpendicular to the floor (in the Y-axis direction). The support frame 32 is a frame provided on the upper part of the base 31. The support frame 32 supports the top plate 33 so that it can slide along the axis of rotation (Z-axis). The top plate 33 is a flexible plate on which the subject P is placed.

[0025] The bed drive unit 34 is housed within the casing of the bed 30. The bed drive unit 34 is a motor or actuator that generates power to move the support frame 32 on which the subject P is placed and the top plate 33. The bed drive unit 34 operates according to control from a console 40 or the like.

[0026] The console 40 includes a memory 41, a display 42, an input interface 43, a network interface 44, and a processing circuit 45. Data communication between the memory 41, the display 42, the input interface 43, the network interface 44, and the processing circuit 45 is performed via a bus (BUS). Although the console 40 is described separately from the mounting base 10, the mounting base 10 may include the console 40 or some of its components.

[0027] Memory 41 is a storage device such as a Hard Disk Drive (HDD), Solid State Drive (SSD), or integrated circuit memory device that stores various types of information. Memory 41 may also be a portable storage medium other than an HDD or SSD, such as a Compact Disc (CD), Digital Versatile Disc (DVD), Blu-ray® Disc (BD), or flash memory. Memory 41 may also be a drive device that reads and writes various types of information to and from semiconductor memory elements such as flash memory or RAM. Furthermore, the storage area of ​​Memory 41 may be located within the X-ray CT apparatus 1 or in an external storage device connected via a network. Memory 41 stores, for example, projection data and reconstructed image data. Memory 41 is an example of a storage unit.

[0028] The display 42 displays various types of information. For example, the display 42 outputs CT images generated by the processing circuit 45, a GUI (Graphical User Interface) for receiving various operations from the operator, etc. Various arbitrary 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 electroluminescent display (OLED), or a plasma display can be used as the display 42.

[0029] The display 42 may be installed anywhere in the control room. Alternatively, the display 42 may be installed on the stand 10. Furthermore, the display 42 may be a desktop type, or it may consist of a tablet terminal or the like that can communicate wirelessly with the console 40. Also, one or more projectors may be used as the display 42.

[0030] 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 45. For example, the input interface 43 receives from the operator the acquisition conditions when acquiring projection data, the reconstruction conditions when reconstructing CT images, and the image processing conditions when generating post-processed images from CT images. The input interface 43 can be, for example, a mouse, keyboard, trackball, switch, button, joystick, touchpad, and touch panel display, as appropriate. In this embodiment, the input interface 43 is not limited to those equipped with physical operating components such as a mouse, keyboard, trackball, switch, button, joystick, touchpad, and touch panel display. For example, an electrical signal processing circuit that receives electrical signals corresponding to input operations from an external input device separate from the device and outputs these electrical signals to the processing circuit 45 is also included as an example of the input interface 43. Furthermore, the input interface 43 may be provided on the stand 10. Also, the input interface 43 may consist of the console 40 main unit and a tablet terminal or the like that can communicate wirelessly.

[0031] The network interface 44 is composed of connectors that conform to parallel and serial connection specifications. When the X-ray CT device 1 is installed on a medical imaging system, the network interface 44 transmits and receives information with external devices on the network. For example, under the control of the processing circuit 45, the network interface 44 receives examination orders related to CT examinations from external devices and transmits detection data acquired by the X-ray CT device 1, as well as generated raw data or CT image data, to external devices.

[0032] The processing circuit 45 controls the operation of the entire X-ray CT apparatus 1 in accordance with the electrical signals of input operations output from the input interface 43. The processing circuit 45 generates image data based on the electrical signals output from the X-ray detector 12. For example, the processing circuit 45 has a processor such as a CPU, MPU, or GPU and memory such as ROM or RAM as hardware resources. The processor executes the program loaded into memory. The processing circuit 45 consists of an imaging control function 451, a reconstruction function 452, an image processing function 453, a condition acquisition function 454, a system control function 455, and the like.

[0033] Furthermore, each function 451-455 is not limited to being implemented by a single processing circuit. It is also acceptable to configure a processing circuit by combining multiple independent processors, and each function 451-455 is implemented by each processor executing a program.

[0034] The imaging control function 451 includes the function of controlling the X-ray high-voltage device 14, the control device 15, and the data acquisition circuit 18 according to the set imaging conditions, and performing X-ray CT imaging.

[0035] The reconstruction function 452 includes functions for performing preprocessing on the projection data output from the data acquisition circuit 18, such as logarithmic transformation, offset correction, inter-channel sensitivity correction, and beam hardening correction. The reconstruction function 452 then performs reconstruction processing on the preprocessed projection data using methods such as filtered back projection, iterative reconstruction, and machine learning to generate a CT image.

[0036] The image processing function 453 includes a function to convert the CT image generated by the reconstruction function 452 into a cross-sectional image of an arbitrary cross-section or a rendered image of an arbitrary viewpoint direction. The conversion is performed based on input operations received from the operator via the input interface 43. For example, the image processing function 453 applies 3D image processing such as volume rendering, surface volume rendering, image value projection processing, MPR (Multi-Planer Reconstruction) processing, and CPR (Curved MPR) processing to the CT image data to generate a rendered image of an arbitrary viewpoint direction.

[0037] The condition acquisition function 454 includes a function to acquire output conditions and scan conditions from the operator via the input interface 43. The output conditions are the power and tube voltage V output by the transformer T (see Figure 2). OUT (See Figure 2) Scan conditions include the equipment used (X-ray CT scanner, X-ray diagnostic equipment, or angiography equipment) and the image quality after scanning.

[0038] The system control function 455 includes a function to change the on-time of the AC voltage input to transformer T by changing the number of primary turns of transformer T to relay Ry (see Figure 2) based on scan conditions.

[0039] The condition acquisition function 454 and the system control function 455 may be executed by the processing circuit 45, or by the control board of the X-ray high-voltage device 14, or by the control device 15.

[0040] Figure 2 shows the circuit configuration of the X-ray high-voltage device 14 according to the first embodiment. Note that the X-ray high-voltage device 14 may be provided not only in the X-ray CT device, but also in the X-ray diagnostic device and the angiography device.

[0041] As shown in Figure 2, the X-ray high-voltage device 14 includes an AC power supply PS, an AC / DC conversion circuit ADC, an inverter INV, a relay Ry, a transformer T, and a Cockcroft-Walton circuit CW.

[0042] The AC power supply PS is either a three-phase AC power supply or a single-phase AC power supply. The AC / DC converter circuit ADC converts the AC current supplied from the AC power supply PS into DC current. The AC / DC converter circuit ADC functions as a DC power supply input to the inverter INV.

[0043] The inverter INV is a full-bridge circuit that functions as the inverter circuit for the X-ray high-voltage device 14. The inverter INV converts the DC voltage supplied from the AC / DC converter circuit ADC into a high-frequency AC voltage and outputs a voltage as an AC pulse power supply. Note that the inverter INV does not have to be a full-bridge circuit; for example, it may be a half-bridge circuit or a push-pull circuit.

[0044] Relay Ry switches the connection between inverter INV and the input contact (tap) of transformer T. The contact corresponds to the set value of the number of turns of the input (primary) coil of transformer T. In other words, relay Ry changes the number of turns on the inverter INV side of transformer T. Relay Ry is an example of a switching unit.

[0045] The transformer T boosts the AC voltage received from the inverter INV and supplies the boosted tube voltage to the X-ray tube 11 via the Cockcroft-Walton circuit CW. The Cockcroft-Walton circuit CW converts the AC voltage output from the transformer T into a high-voltage DC voltage and outputs it to the X-ray tube 11 as tube voltage.

[0046] The X-ray high-voltage apparatus 14 further includes a resonant capacitor Cs and a leakage inductance Ll. The resonant capacitor Cs is connected in parallel to the switching element of the inverter INV. The leakage inductance Ll is connected between the transformer T and the resonant capacitor Cs, and a resonant current flows between the resonant capacitor Cs and the Ll.

[0047] System control function 455 controls the tube voltage V OUTWhen it is constant and the switching loss reduction mode is selected according to the scanning conditions, the relay Ry is switched to decrease the number of primary turns N1 of the transformer T. The details will be described below.

[0048] The relationship between the primary and secondary powers of the transformer T shown in FIG. 2 is expressed by the following equation (2). Here, let the current on the primary side of the transformer T be i1, the current on the secondary side of the transformer T be i2, the voltage on the primary side be v1, the voltage on the secondary side be v2, and the on-time of the inverter INV be T ON shall be.

[0049]

Equation

[0050]

Equation

[0051] When outputting the same tube voltage V OUT , when switching the number of primary turns N1, since v1, N2, and α are constant, the secondary voltage v2 and the on-time T ON change as follows. That is, when increasing the number of primary turns N1, the secondary voltage v2 decreases and the on-time T ON increases. On the other hand, when decreasing the number of primary turns N1, the secondary voltage v2 increases and the on-time T ON decreases.

[0052] Specifically, according to Equation (3), if the tube voltage V OUT is constant, when decreasing the number of primary turns N1 of the transformer T, the secondary voltage v2 increases accordingly, and the on-time T ONThis becomes smaller. And, according to Equation 2, since the primary voltage v1 is constant, the current i1 becomes larger under the output condition of constant power. Consequently, even at low load, the energy stored in the leakage inductance Ll becomes larger. As a result, the resonant current flows from the leakage inductance Ll to the resonant capacitor Cs, making it easier to realize ZVS.

[0053] [Second Embodiment] The second embodiment relates to a process for selecting the optimal ZVS operation in an X-ray high-voltage device 14 by changing the number of primary turns N1 of the transformer T. The system control function 455 controls the tube voltage V OUT If the value is constant and the switching loss reduction mode is selected according to the scan conditions, the number of turns N1 on the primary side (inverter side) of the transformer T is changed to the relay Ry, and the setting value of the number of turns N1 is determined based on the result of comparing the flow of the resonant current and the timing at which the switching element turns on for each changed number of turns N1. The details are explained below.

[0054] As shown in Equation 3, the tube voltage V OUT Under the output condition that the voltage is constant, by switching the contacts of relay Ry, the number of turns N1 on the primary side of transformer T is changed, thereby changing the secondary side voltage v2 of transformer T and the on-time T of inverter INV. ON It changes.

[0055] As described above, even if the output conditions are the same, the on-time T of the inverter INV will vary depending on the selected contact. ON The energy stored in the leakage inductance Ll changes. Also, the on-time T of the inverter INV ON The energy stored in the capacitor flows as a resonant current into the resonant capacitor Cs during the off-time. When the resonant current flows into the resonant capacitor Cs, negative charge is released from the capacitor Cs, making ZVS operation easier. Therefore, by checking the resonant current at each contact, it is possible to select the contact that enables optimal ZVS operation.

[0056] Figure 3 shows the temporal changes between the output voltage of the inverter INV according to the second embodiment and the waveform of the resonant current. In Figure 3(a), the ON time T of the inverter INV ON The period is one-quarter of the original period. When the inverter INV is turned off, a resonant current begins to flow, causing damped oscillations. Then, at the timing when the inverter INV is turned on again, the direction of the resonant current is positive. That is, the resonant current flows from the leakage inductance Ll to the resonant capacitor C. S As the current flows through it, the negative charge is removed from the resonant capacitor Cs, thus satisfying equation 1 above. This makes it possible to realize ZVS.

[0057] Therefore, the system control function 455 determines that when the switching element of inverter INV turns on, the resonant current is transmitted from the leakage inductance Ll to the resonant capacitor C. S Determine the set value for the number of primary turns N1 when the current flows through the circuit.

[0058] On the other hand, in Figure 3(b), the ON time T of the inverter INV is ON The period is half of the original period. When the inverter INV is turned off, a resonant current begins to flow, causing damped oscillations. Then, at the timing when the inverter INV is turned on again, the direction of the resonant current is negative. That is, because the resonant current flows from the resonant capacitor Cs to the leakage inductance Ll, a negative charge accumulates in the resonant capacitor Cs, so equation 1 above can no longer be satisfied. As a result, ZVS cannot be realized.

[0059] According to the above, tube voltage V OUT Even under the output condition of constant voltage, the behavior of the resonant current differs depending on the contacts of the selected relay Ry. By checking the resonant current for each contact, the optimal contact for achieving ZVS can be selected. In other words, by adding a relay Ry that can change the number of primary turns N1 of the transformer T in the X-ray high-voltage device 14, ZVS operation becomes possible even at low loads.

[0060] [Third Embodiment] The third embodiment relates to a process for reducing tube voltage ripple in an X-ray high-voltage device 14 by changing the number of primary turns N1 of the transformer T. Tube voltage ripple refers to the tube voltage V OUT In this context, a smoothing circuit (in this case, a Cockcroft-Walton circuit CW) cannot produce a perfectly constant voltage, and this refers to the slight voltage fluctuations that inevitably occur.

[0061] The tube voltage ripple is due to the charging capacitor C in the Cockcroft-Walton circuit CW. C The voltage V used for charging and discharging C Corresponds to the charging capacitor C. C The discharge time varies depending on the discharge resistance, i.e., the load condition of the X-ray tube 11. On the other hand, the charging capacitor C C The charging time is determined by the characteristic value and adjustment. The characteristic value here refers to the charging capacitor C C The capacitance C and the charging capacitor C C This refers to the resistance component R in the circuit, such as ESR (Equivalent Series Resistance). Furthermore, adjustment refers to the on-time T of the inverter INV. ON and off time T OFF Given that the total time is fixed, the on-time T ON And, off time T OFF The goal is to adjust the distribution of these factors.

[0062] Figure 4 is a table showing the relationship between load level and tube voltage ripple amplitude when the primary windings of transformer T are fixed. Figure 5 shows the relationship between charging capacitor C and load level when the primary windings of transformer T are fixed. C Voltage V C This is a graph showing the change over time.

[0063] When the output conditions of the X-ray high-voltage device 14 are low load, the charging capacitor C is as shown in Figure 5(a). C During discharge, i.e., the off-time T of the inverter INV. OFF The slope of the graph (voltage V over time) CSince the rate of change is small, the pulsation width of the tube voltage ripple becomes small. Also, when the output conditions of the X-ray high-voltage device 14 are high load, as shown in Figure 5(c), the charging capacitor C C During discharge, i.e., the off-time T of the inverter INV. OFF The slope of the graph is steep at this point. However, the charging capacitor C C The charging time, i.e., the on-time T of the inverter INV. ON Because the interval is long, the pulsation width of the tube voltage ripple becomes smaller.

[0064] On the other hand, when the output conditions of the X-ray high-voltage device 14 are at a medium load, the charging capacitor C is as shown in Figure 5(b). C The absolute values ​​of the slopes of the graphs for charging time and discharging time become approximately equal. Consequently, under medium load, charging time and discharging time are almost equal. Therefore, the pulsation width of the tube voltage ripple is determined without being able to adjust the distribution between charging time and discharging time, and the pulsation width cannot be reduced except by increasing the resolution of this distribution adjustment.

[0065] Therefore, the system control function 455 controls the tube voltage V OUT If the voltage remains constant and the tube voltage ripple reduction mode is selected according to the scan conditions, the relay Ry is instructed to switch its contacts to increase the primary turn count N1. Then, the system control function 455 decreases the output voltage of the transformer T by increasing the primary turn count N1, thereby reducing the charge capacitor C connected to the output side of the transformer T. C Reduce the charging speed.

[0066] The following explains in detail how using a transformer T with a relay Ry connected to its primary side can make the medium-load region appear as the high-load region.

[0067] Figure 6 shows the charging capacitor C according to the third embodiment. C These are graphs showing the voltage waveforms. Figure 6(a) is the graph before increasing the number of primary turns N1 of transformer T. Figure 6(b) is the graph after increasing the number of primary turns N1 of transformer T.

[0068] Tube voltage V OUT This is as shown in Equation 3 above. Tube voltage V OUT Regarding the ripple, the charging capacitor C of the Cockcroft-Walton circuit CW C The pulsation amplitude of the ripple is determined by the charging and discharging of the X-ray tube 11. The discharge time is constant due to the load condition of the resistance of the X-ray tube 11. Regarding the charging time, the on time T of the inverter INV is determined by equation 4 below. ON It is possible to find V. C is the charging capacitor C C The voltage is C, where C is the charging capacitor C. C The capacitance is R, and R is the charging capacitor C. C This shows the resistance component in the circuit.

[0069]

number

[0070] This means that even if the output conditions are the same, the tube voltage V OUT This allows for a reduction in the ripple pulsation amplitude. In other words, in the medium-load region where tube voltage ripple is conventionally large, it is possible to reduce tube voltage ripple to the same extent as in the high-load region.

[0071] [Fourth Embodiment] The fourth embodiment relates to a process for identifying the optimal contact among the contacts of the relay Ry in the X-ray high-voltage device 14. Figure 7 is a flowchart of the process for identifying the optimal contact according to the fourth embodiment. Figure 8 shows the output power, the number of turns N1 on the primary side of the transformer T, and the tube voltage V according to the fourth embodiment. OUTThis is a diagram of a table showing the relationship with ripple. Below, referring to Figure 8, we will explain the process of identifying the optimal contact point in accordance with Figure 7.

[0072] In step S1, the processing circuit 45 of the console 40, the condition acquisition function 454 acquires an output condition, which is a predetermined value of the power that transformer T outputs to the X-ray tube 11. Then, the system control function 455 extracts one or more contacts of relay Ry that are included in the region where ZVS is feasible, based on the output condition of transformer T, as selection candidates. This process is carried out with reference to the table shown in Figure 8.

[0073] As shown in Figure 8, for example, when the output power is P1, contacts E1 and E2 are extracted. Next, when the output power is P2, contacts E2 to E4 are extracted. Then, when the output power is P3, contacts E4 and E5 are extracted. Note that for each output condition (for example, the output power), the processes in steps S1 to S7 are executed in advance.

[0074] In step S2, the condition acquisition function 454 acquires scan conditions, including the image quality after scanning. Then, the system control function 455 selects either the switching loss reduction mode or the tube voltage ripple reduction mode according to the scan conditions. The switching loss reduction mode and the tube voltage ripple reduction mode will be described later.

[0075] In step S3, the system control function 455 determines whether or not the switching loss reduction mode has been selected. If the switching loss reduction mode has been selected (YES in step S3), the system control function 455 proceeds to the process in step S4. If the switching loss reduction mode has not been selected (i.e., the tube voltage ripple reduction mode has been selected) (NO in step S3), the system control function 455 proceeds to the process in step S5.

[0076] In step S4, if the system control function 455 selects the switching loss reduction mode, it identifies a contact that can achieve a suitable ZVS. As described in the second embodiment, the system control function 455 searches for the contact that can achieve the optimal ZVS from among the one or more contacts extracted in step S1, while observing the waveform of the resonant current and the voltage of the switching element.

[0077] In step S5, if the system control function 455 selects the tube voltage ripple reduction mode, it identifies the contact with the smallest tube voltage ripple. As described in the third embodiment, the system control function 455 searches for the contact with the smallest tube voltage ripple from among the one or more contacts extracted in step S1. In practice, as shown in Figure 8, the contact with the maximum number of primary turns N1 of the transformer T is identified.

[0078] In step S6, the condition acquisition function 454 determines whether there are any other different scan conditions. If there are other scan conditions (YES in step S6), the condition acquisition function 454 returns to the process in step S2. If there are no other scan conditions (NO in step S6), the condition acquisition function 454 proceeds to the determination in step S7.

[0079] In step S7, the condition acquisition function 454 determines whether there are other output conditions with different power values. If there are other output conditions (YES in step S7), the condition acquisition function 454 returns to the process in step S1. If there are no other output conditions (NO in step S7), the condition acquisition function 454 proceeds to the process in step S8.

[0080] In step S8, the system control function 455 stores a table in memory 41 that associates the output conditions, scan conditions, and the contact numbers of relay Ry. The table is an example of data. The contact numbers correspond to the set value of the primary side turns N1 of transformer T.

[0081] In step S9, when the condition acquisition function 454 acquires the output conditions and scan conditions during the actual scan, the system control function 455 refers to the table stored in memory 41 to identify the contact number from the output conditions and scan conditions, and causes the relay Ry to switch the contact to the position of that number.

[0082] According to the above, by switching the contacts of relay Ry within the ZVS feasible region, optimal ZVS operation can be achieved, or the tube voltage ripple can be reduced.

[0083] In addition, the X-ray CT apparatus 1 may be configured to select a switching loss reduction mode and a tube voltage ripple reduction mode. For example, in photon counting CT, it is necessary to keep the X-ray high-voltage device 14 at a low temperature in order to bring out the performance of the semiconductor used in the X-ray detector 12. In this case, the switching loss reduction mode is selected to suppress heat generation due to switching losses.

[0084] On the other hand, even with X-ray CT scanner 1, if noise suppression is desired, the tube voltage ripple reduction mode is selected. For example, when examining myocardial fibrosis using ECV (extracellular volume fraction), when performing examinations to find diseases embedded in normal organs, or when diagnosing the head using FBP (Filtered Back Projection), accuracy of the X-ray image is required, so the tube voltage ripple reduction mode is selected.

[0085] Furthermore, in X-ray diagnostic equipment and angiography equipment, when transcatheter intervention (stent placement in cerebral or coronary arteries, or heart valve implantation) is performed, high accuracy of the X-ray image is required, so the tube voltage ripple reduction mode is selected.

[0086] According to at least one embodiment described above, ZVS can be achieved in an X-ray high-voltage device regardless of the load.

[0087] Note that the condition acquisition function 454 is an example of an acquisition unit. The system control function 455 is an example of a control unit.

[0088] While several embodiments have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be implemented in a variety of other forms, 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 and spirit of the invention, as well as in the claims and their equivalents. [Explanation of symbols]

[0089] 1...X-ray CT device 11...X-ray tube 14…X-ray high-voltage equipment 41…Memory C S ...resonant capacitor INV…Inverter Ll... Leakage Inductance N1...Number of turns on the primary side Ry…Relay T... Transformer V OUT ...tube voltage 454…Condition acquisition function 455... System control function

Claims

1. An inverter that converts DC voltage to AC voltage, A transformer that supplies the tube voltage obtained by boosting the aforementioned AC voltage to the X-ray tube, A capacitor connected in parallel to the switching element of the inverter, An inductance connected between the transformer and the capacitor, through which a resonant current flows, A switching unit for changing the number of turns on the inverter side of the transformer, An acquisition unit that acquires scan conditions, including the image quality after scanning, A control unit that changes the on-time of the AC voltage input to the transformer by changing the number of turns in the switching unit based on the scan conditions, An X-ray high-voltage device equipped with the following features.

2. When the control unit has selected a switching loss reduction mode according to the scan conditions, the tube voltage is constant. The number of turns is reduced in the switching section. The X-ray high-voltage apparatus according to claim 1.

3. When the control unit has selected a switching loss reduction mode according to the scan conditions, the tube voltage is constant. While changing the number of turns in the switching unit, Based on the results of comparing the flow of the resonant current and the timing at which the switching element turns on for each changed number of turns, the set value for the number of turns is determined. The X-ray high-voltage apparatus according to claim 1.

4. The control unit, The set value of the number of turns is determined when the resonant current flows from the inductance to the capacitor at the aforementioned timing. The X-ray high-voltage apparatus according to claim 3.

5. When the control unit has selected a tube voltage ripple reduction mode according to the scan conditions, the tube voltage is constant. The number of turns is increased in the switching section. The X-ray high-voltage apparatus according to claim 1.

6. The control unit, By increasing the number of turns, the output voltage of the transformer is reduced, thereby lowering the charging speed of the capacitor connected to the output side of the transformer. The X-ray high-voltage apparatus according to claim 5.

7. The control unit, Prior to the output conditions of the transformer, one or more setting values ​​for the number of turns that are in the range where ZVS can be realized are extracted, and a switching loss reduction mode or a tube voltage ripple reduction mode is selected according to the scan conditions. When the aforementioned switching loss reduction mode is selected, a suitable ZVS setting value is identified from the extracted setting values, When the tube voltage ripple reduction mode is selected, the setting value with the smallest tube voltage ripple is identified from the extracted setting values. The data relating the output conditions and scan conditions to the identified setting value is stored in the storage unit. When the acquisition unit acquires the output conditions and scan conditions during an actual scan, it refers to the data stored in the storage unit to identify the set value from the output conditions and scan conditions, and instructs the switching unit to change the number of turns to that set value. The X-ray high-voltage apparatus according to claim 1.

8. An inverter that converts DC voltage to AC voltage, A transformer that supplies the tube voltage obtained by boosting the aforementioned AC voltage to the X-ray tube, A capacitor connected in parallel to the switching element of the inverter, An inductance connected between the transformer and the capacitor, through which a resonant current flows, A switching unit for changing the number of turns on the inverter side of the transformer, An acquisition unit that acquires scan conditions, including the image quality after scanning, A control unit that changes the on-time of the AC voltage input to the transformer by changing the number of turns in the switching unit based on the scan conditions, and A medical imaging diagnostic device equipped with [a specific feature].

9. An inverter that converts DC voltage to AC voltage, A transformer that supplies the tube voltage obtained by boosting the aforementioned AC voltage to the X-ray tube, A capacitor connected in parallel to the switching element of the inverter, An inductance connected between the transformer and the capacitor, through which a resonant current flows, A switching unit for changing the number of turns on the inverter side of the transformer, An acquisition unit that acquires scan conditions, including the image quality after scanning, A control unit that changes the on-time of the AC voltage input to the transformer by changing the number of turns in the switching unit based on the scan conditions, and An X-ray CT scanner equipped with [a specific feature].

Images