JP6169890B2 - X-ray tube control apparatus and X-ray CT apparatus - Google Patents

Description

  Embodiments described herein relate generally to an X-ray tube control device and an X-ray CT (Computed Tomography) device for controlling a triode X-ray tube.

  The triode X-ray tube includes, for example, an anode that is a rotating anode, a cathode that is a filament, and a grid as a focusing electrode. Generation of X-rays can be prevented by setting the grid voltage for the filament to a negative voltage exceeding the cut-off voltage, and X-rays can be irradiated by setting the grid voltage to zero.

  If the grid voltage is changed linearly between zero and the cut-off voltage, the tube current and the focal spot size also change linearly.

  As a method of realizing linear control of tube current or the like, for example, a method of controlling the grid voltage with a linear amplifier composed of a plurality of transistors is conceivable. However, since the grid voltage is high, the heat generation of the transistor is large. Therefore, a large heat dissipation mechanism for cooling the transistor is required. Furthermore, since the linear amplifier always consumes power when controlling the grid voltage, a large power source is also required.

JP 2002-33064 A

  An object of the embodiment is to realize highly efficient linear control of a grid voltage in a triode X-ray tube.

An X-ray tube control device according to an embodiment is an X-ray tube control device that controls an X-ray tube including an anode, a cathode, and a grid that blocks electrons emitted from the cathode toward the anode. Two switching elements, two diodes, a coil, a capacitor, and a control circuit are provided. The two switching elements are connected in series with power. And the connection point which connects two said switching elements and the said grid are connected. The two diodes are connected in antiparallel with each of the two switching elements. The coil is provided between the connection point and the grid. The capacitor is provided between the cathode and the grid. The control circuit opens one switching element of the two switching elements, and opens and closes the other switching element in accordance with a predetermined time ratio to control the voltage of the capacitor, thereby controlling the cathode. The grid voltage is changed.

The block diagram which shows the structure which shows the principal part of the X-ray CT apparatus which concerns on embodiment. The circuit diagram which shows the detailed structure of the high voltage apparatus and X-ray tube which concern on embodiment. The figure which shows the relationship between a grid voltage and a tube current. FIG. 3 is a circuit diagram in which a part of the configuration shown in FIG. 2 is extracted (switch Q2; ON). The circuit diagram which extracted a part of structure shown in FIG. 2 (switch Q2; OFF). The time chart explaining the effect | action by switching of the switching element Q2. The circuit diagram which extracted a part of structure shown in FIG. 2 (switch Q1; ON). The circuit diagram which extracted a part of structure shown in FIG. 2 (switch Q1; OFF). The time chart explaining the effect | action by switching of the switching element Q1. The figure for demonstrating the utilization example of the linear control of the tube current which concerns on embodiment. The figure for demonstrating the feedback circuit which concerns on a modification.

An embodiment will be described with reference to the drawings.
In the present embodiment, a high voltage apparatus mounted on an X-ray CT apparatus is disclosed as an example of an X-ray tube control apparatus.

  FIG. 1 is a block diagram showing a configuration showing a main part of an X-ray CT apparatus 1 in the present embodiment. As shown in the figure, the X-ray CT apparatus 1 includes a gantry device 2, a bed device 3, and a console device 4.

  The gantry device 2 includes an X-ray tube 5, an X-ray diaphragm unit 6, an X-ray detector 7, a rotating frame 8, a high voltage device 9, a gantry driving mechanism unit 10, a gantry / bed control unit 11, and a data collecting unit 12. Etc. The gantry device 2 has an opening 13 as an imaging space into which the subject P is sent.

  The X-ray tube 5, the X-ray diaphragm unit 6, and the X-ray detector 7 are attached to the rotating frame 8. The gantry driving mechanism unit 10 includes a structural mechanism that rotates the rotating frame 8 and a motor that operates the mechanism. By rotating the rotary frame 8, the X-ray tube 5 and the X-ray detector 7 face each other and rotate around the subject P conveyed into the opening 13.

  The high voltage device 9 controls the X-ray tube 5. Details of the high-voltage device 9 will be described later.

  The X-ray tube 5 is controlled by the high voltage device 10 to generate X-rays. The X-ray tube 5 in the present embodiment is a triode X-ray tube including an anode, a cathode, and a grid.

  The X-ray diaphragm unit 6 has a plurality of slit plates, and adjusts the X-ray irradiation range irradiated to the subject P by moving the slit plates.

  The X-ray detector 7 is a two-dimensional array type detector (so-called multi-slice type detector) and has a plurality of X-ray detection elements arranged in a two-dimensional manner.

  The data acquisition unit (DAS) 12 takes in an electric signal output from each X-ray detection element of the X-ray detector 7, amplifies the taken electric signal, and converts the amplified electric signal into a digital signal. The converted digital signal is called projection data.

  The couch device 3 includes a couchtop 30 on which the subject P is placed, a couchtop support unit 31 that supports the couchtop 30, a couch drive mechanism unit 32, and the like. The bed driving mechanism 32 includes a structural mechanism that moves the top board 30 in the horizontal and vertical directions with respect to the placement surface, and a motor that operates the mechanism. During scanning, the couch driving mechanism 32 conveys the top 30 into the opening 13 under the control of the gantry / couch controller 12, thereby bringing the subject P into the imaging region (FOV) of the gantry device 2. Position.

  The gantry / bed controller 11 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. Each part of the bed apparatus 3 is controlled.

  The console device 4 includes a console control unit 40, a preprocessing unit 41, a reconstruction processing unit 42, an image storage unit 43, an image processing unit 44, a display unit 45, an input unit 46, and the like.

  The console control unit 40 includes a CPU, a ROM, a RAM, and the like, and controls each unit included in the console device 4. The preprocessing unit 41 receives projection data from the data collection unit 12 and performs preprocessing such as sensitivity correction and X-ray intensity correction.

  The reconstruction processing unit 42 reconstructs the projection data after the preprocessing is performed by the preprocessing unit 41 in accordance with parameters such as the reconstruction slice thickness, the reconstruction interval, the reconstruction function, and the reconstruction protocol. Then, reconstructed image data such as tomographic image data and volume data of the subject is generated.

  The image storage unit 43 includes projection data (raw data) sent from the data collection unit 12, projection data preprocessed by the preprocessing unit 41, and a reconstructed image generated by the reconstruction processing unit 42. Store data etc.

  The image processing unit 44 performs image processing for display such as window conversion and RGB processing on the reconstructed image data stored in the image storage unit 43, and outputs the processed data to the display unit 45. . The image processing unit 44 generates data such as a tomographic image of an arbitrary cross section, a projection image from an arbitrary direction, or a three-dimensional surface image using the reconstructed image data based on an instruction from the operator, and displays the data on the display unit 45 may be output. The display unit 45 displays an X-ray CT image based on the data output from the image processing unit 44.

  The input unit 46 includes devices such as a keyboard, various switches, a mouse, and a trackball. The input unit 46 is used for inputting various scan conditions such as a scan protocol and a reconstruction protocol.

The high voltage device 9 will be described.
FIG. 2 is a circuit diagram showing a detailed configuration of the high-voltage device 9 and the X-ray tube 5. The X-ray tube 5 includes, for example, an anode 51 that is a rotating anode, a cathode 52 that is a filament, and a grid 53 that serves as a focusing electrode. The tube current I of the X-ray tube 5 can be controlled by changing the voltage applied to the grid 53. In the following description, the potential of the grid 53 with respect to the cathode 52 is referred to as a grid voltage Vg. The relationship between the grid voltage Vg and the tube current I is shown in FIG. When the grid voltage Vg is increased in the negative direction while the tube voltage and the filament heating condition are kept constant, the tube current I decreases. A grid voltage at which the tube current I becomes zero is called a cut-off voltage.

  The high voltage device 9 includes a main inverter 100, a high voltage transformer 101, a high voltage rectifier 102, and a high voltage capacitor 103 as a circuit for applying a tube voltage to the X-ray tube 5. The main inverter 100 switches a direct current supplied from a commercial alternating current power supply via a rectifier (not shown) to generate an alternating voltage having a predetermined frequency. The high voltage transformer 101 is an insulating transformer including a primary winding 101 a connected to the main inverter 100 and two secondary windings 101 b connected to the high voltage rectifier 102. When AC is supplied from the main inverter 100 to the primary winding 101a, the AC voltage boosted from the secondary winding 101b to the high voltage rectifier 102 is output. The high voltage rectifier 102 and the high voltage capacitor 103 rectify and smooth the AC voltage input from the high voltage transformer 101 and apply the rectified and smoothed voltage between the anode 51 and the cathode 52 of the X-ray tube 5.

  The high voltage device 9 includes a grid voltage inverter 200, a grid voltage transformer 201, a voltage doubler rectifier 202, a grid voltage circuit 203, a capacitor Cg, a resistor Rg, and a control circuit for controlling the grid voltage Vg. Circuit 204.

  The grid voltage inverter 200 switches a direct current supplied from a commercial alternating current power supply via a rectifier (not shown) to generate an alternating voltage having a predetermined frequency. The grid voltage transformer 201 is an insulating transformer including a primary winding 201 a connected to the grid voltage inverter 200 and a secondary winding 201 b connected to the voltage doubler rectifier 202. When alternating current is supplied from the grid voltage inverter 200 to the primary winding 201a, the boosted alternating voltage is output from the secondary winding 201b to the voltage doubler rectifier 202. For example, the output voltage of the secondary winding 201b is 1500V (AC), and the output voltage of the voltage doubler rectifier 202 is 3000V (DC).

  The grid voltage circuit 203 includes two switching elements Q1 and Q2, two diodes D1 and D2, two switch drive circuits A1 and A2, and a coil L. The switching elements Q1 and Q2 are connected in series to a voltage doubler rectifier 202 that is a power source of the grid voltage circuit 203 across a connection point with the grid 53. For example, MOSFETs can be used as the switching elements Q1, Q2. In the following description, the state where the switching elements Q1 and Q2 are closed is referred to as ON, and the state where the switching elements Q1 and Q2 are open is referred to as OFF.

  The diode D1 is connected in antiparallel with the switching element Q1. The diode D2 is connected in antiparallel with the switching element Q2. When a MOSFET is used as the switching element Q1, a diode built in the MOSFET may be used as the diode D1. Similarly, when a MOSFET is used as the switching element Q2, the diode D2 may be a diode built in the MOSFET.

  The switch drive circuit A1 turns on / off the switching element Q1. The switch drive circuit A2 turns on / off the switching element Q2.

  Coil L is arranged on a conducting wire connecting grid 53 to the connection point located between switching elements Q1 and Q2.

  The capacitor Cg is provided between the cathode 52 and the grid 53. The conducting wire connecting the grid 53 and the grid voltage circuit 203 and the conducting wire connecting the cathode 52 and the grid voltage circuit 203 are arranged in parallel in the high voltage cable connecting the high voltage device 9 and the X-ray tube 5. As the capacitor Cg, a distributed capacitance generated between these conductors and a stray capacitance generated between the cathode 52 and the grid 53 can be used. However, a capacitor as a circuit component may be used without using these distributed capacitance and stray capacitance. The resistance Rg indicates the presence of a leakage current generated between the cathode 52 and the grid 53 of the X-ray tube 5.

  The control circuit 204 drives the switch drive circuits A1 and A2 based on the grid voltage Vg and the target value of the grid voltage Vg.

The operation of the control circuit 204 will be described.
First, the operation when the tube voltage I of the X-ray tube 5 is lowered and the grid voltage Vg is controlled in the direction of reducing the focal spot size of the X-ray tube 5 will be described. In this case, charge is stored in the capacitor Cg so that the grid voltage Vg increases in the negative direction. During the operation, the switching element Q1 is turned off.

  4 and 5 are circuit diagrams showing the power supply E, the switching element Q2, the diode D1, the coil L, the capacitor Cg, and the resistor Rg of the grid voltage circuit 203 extracted from the configuration shown in FIG. The power source E is an output of the voltage doubler rectifier 202, and is, for example, 3000V. 4 shows a state where the switching element Q2 is turned on, and FIG. 5 shows a state where the switching element Q2 is turned off.

  When the switching element Q2 is turned on / off, the capacitor Cg can be charged according to the time ratio between the on state and the off state. When the switching element Q2 is turned on, a current passing through the power source E, the capacitor Cg, the coil L, and the switching element Q2 flows in the order shown by the arrows in FIG. As a result, the capacitor Cg is charged so that the grid 53 is negative with respect to the cathode 52. That is, the grid voltage Vg increases in the negative direction.

  When the switching element Q2 is turned off, an electromotive force generated in the coil L causes a circulating current to return to the coil L through the diode D1 and the capacitor Cg as shown by an arrow in FIG.

  Here, if the resistance Rg is sufficiently small and power is appropriately consumed, when the switching element Q2 is repeatedly turned on / off in a predetermined cycle, the grid voltage Vg is obtained by the following equation.

Vg = −E · Ton / (Ton + Toff)
Here, Ton is a time for turning on the switching element Q2 in accordance with the cycle, and Toff is a time for turning off the switching element Q2 in accordance with the cycle. When the grid voltage Vg is determined according to this equation, the control circuit 204 can converge the grid voltage Vg to the target value by setting the on time Ton and the off time Toff to values corresponding to the target values.

  However, when the resistance Rg is large, the grid voltage Vg cannot be converged only by setting the on time Ton and the off time Toff, and the voltage of the capacitor Cg continues to rise. Therefore, the control circuit 204 in the present embodiment detects the grid voltage Vg, and stabilizes the grid voltage Vg at the target value by adjusting the time ratio between the on time Ton and the off time Toff according to the detection result.

  FIG. 6 is a time chart showing an example of the relationship between the voltage of the capacitor Cg, the current flowing through the coil L, and the on time Ton and the off time Toff. When lowering the tube current I of the X-ray tube 5, first, the control circuit 204 sets the on time to Ton1 and the off time to Toff1. The switch drive circuit A2 switches the switching element Q2 with an on time Ton1 and an off time Toff1. By this switching, the voltage of the capacitor Cg, that is, the grid voltage Vg increases in the negative direction. The current flowing through the coil L increases when the switching element Q2 is off and decreases when the switching element Q2 is on. In FIG. 6, the current change is shown with the direction from left to right in FIGS. 4 and 5 as positive.

  When it is detected that the grid voltage Vg has reached the target value, the control circuit 204 sets the on time to Ton2 (<Ton1) and the off time to Toff2 (> Toff1). The switch drive circuit A2 switches the switching element Q2 with an on time Ton2 and an off time Toff2. By this switching, the voltage of the capacitor Cg, that is, the grid voltage Vg is kept constant at the target value. The on-time Ton2 and the off-time Toff2 may be determined in advance so that the voltage drop due to the discharge of the capacitor Cg is compensated, for example, by switching at these time ratios. The current flowing through the coil L is almost zero, and slightly swings in the negative direction when the switching element Q2 is on.

  Next, an operation when the tube voltage I of the X-ray tube 5 is increased and the grid voltage Vg is controlled in the direction of increasing the focal spot size of the X-ray tube 5 will be described. In this case, the capacitor Cg is caused to discharge electric charges so that the grid voltage Vg goes to zero. During the operation, the switching element Q2 is turned off.

  7 and 8 are circuit diagrams showing the power supply E, the switching element Q1, the diode D2, the coil L, the capacitor Cg, and the resistor Rg of the grid voltage circuit 203 extracted from the configuration shown in FIG. In particular, FIG. 7 shows a state where the switching element Q1 is turned on, and FIG. 8 shows a state where the switching element Q1 is turned off.

  When the switching element Q1 is turned on, a current passing through the capacitor Cg, the coil L, and the switching element Q1 flows in the order shown by the arrows in FIG. At this time, a part of the energy stored in the capacitor Cg moves to the coil L, and the voltage of the capacitor Cg approaches zero. For this reason, the tube current I increases and the focal spot size changes.

  When the switching element Q1 is turned off, an electromotive force generated in the coil L causes a current passing through the diode D2, the coil L, the capacitor Cg, and the power source E in this order as shown by the arrows in FIG. With this current, the electric charge stored in the capacitor Cg is regenerated to the power source E, and the energy stored in the coil L is also regenerated to the power source E. Specifically, this electric charge is stored in a capacitor included in voltage doubler rectifier 202 shown in FIG.

  If such switching is continued, the electric charge of the capacitor Cg gradually moves to the power source E, so that the grid voltage Vg continues to approach zero.

  FIG. 9 is a time chart showing an example of the relationship between the voltage of the capacitor Cg, the current flowing through the coil L, and the on time Ton and the off time Toff of the switching element Q1. When increasing the tube current I of the X-ray tube 5, first, the control circuit 204 sets the on time of the switching element Q1 to Ton3 and the off time to Toff3. The switch drive circuit A1 switches the switching element Q1 with an on time Ton3 and an off time Toff3. By this switching, the voltage of the capacitor Cg, that is, the grid voltage Vg approaches zero. The current flowing through the coil L increases when the switching element Q1 is off and decreases when the switching element Q1 is on. In FIG. 9, the current change is shown with the direction from left to right in FIGS. 7 and 8 being positive.

  When it is detected that the grid voltage Vg has reached the target value, the control circuit 204 stops switching of the switching element Q1. When it is necessary to compensate for the voltage drop due to the discharge of the capacitor Cg, the control circuit 204 switches the switching element Q2 at the on time Ton2 and the off time Toff2 as shown in FIG. Is supplied to the capacitor Cg.

  As described above, the high voltage device 9 can set the grid voltage Vg to a desired value by switching the switching elements Q1 and Q2. That is, the high voltage device 9 can linearly change the grid voltage Vg. Therefore, linear control of the tube current I of the X-ray tube 5 and continuous control of the focal spot size can be realized.

An example of the use of such control will be described with reference to FIG.
The cross-sectional shape along the body axis of the subject P lying on the top 30 is an ellipse as shown in the upper part of FIG. The X-rays generated by the X-ray tube 5 are less likely to reach the X-ray detector 7 as the body thickness increases. If the X-ray energy is set so that good projection data can be collected at the thickest body thickness, the subject P is irradiated with X-rays of the energy even in a direction where the lower body thickness is sufficient. Become. That is, the subject P is unnecessarily exposed.

  Therefore, in this example, a method of linearly changing the tube current I according to the body thickness of the subject P while the X-ray tube 5 and the X-ray detector 7 are rotated once around the subject P is disclosed. .

  The rotation angle θ of the X-ray tube 5 and the X-ray detector 7 is defined with the position directly above the subject P as the rotation angle of 0 °. Usually, the body thickness of the subject P is minimum in the directions of the rotation angle 0 ° and the rotation angle 180 °, and is maximum in the directions of the rotation angle 90 ° and the rotation angle 270 °.

  Therefore, as shown in the lower part of FIG. 10, the high-voltage device 9 controls the tube current I so as to be minimum at the rotation angle 0 ° and the rotation angle 180 ° and maximum at the rotation angle 90 ° and the rotation angle 270 °. To do.

  Specifically, the relationship between the rotation angle θ and the target value of the grid voltage Vg for obtaining the tube current I as shown in the lower part of FIG. 10 is determined. Information representing such a relationship is stored in a memory included in the control circuit 204, for example. For example, the control circuit 204 receives a notification of the current rotation angle θ from the gantry / bed control unit 11 and reads a target value corresponding to the rotation angle θ from the memory. The control circuit 204 converges the grid voltage Vg to the target value by switching of the switching elements Q1 and Q2 described with reference to FIGS. If the rotational speed of the X-ray tube 5 is constant, the control circuit 204 refers to the above-mentioned memory as time passes without receiving a notification of the current rotational angle θ from the gantry / bed control section 11. What is necessary is just to change the target value of Vg.

  The tube current can be changed by the heating amount of the filament of the X-ray tube. However, the rotational speed of the X-ray tube in the X-ray CT apparatus is as high as about 0.3 seconds per rotation, for example, and the tube current cannot be followed by controlling the heating amount of the filament.

  According to the present embodiment described above, linear control of the tube current I of the X-ray tube 5 and continuous control of the focal spot size can be realized by switching the switching elements Q1 and Q2.

  In this system, a power element such as a transistor is not operated linearly like a conventional linear amplifier. Therefore, there is little loss in the switching elements Q1 and Q2, which are MOSFETs, for example, and a large heat dissipation mechanism is unnecessary.

  Further, when using a capacitance component such as a distributed capacitance between conductors in a high voltage cable connecting the high voltage device 9 and the X-ray tube 5 or a stray capacitance generated between the cathode 52 and the grid 53 as the capacitor Cg, Since there is no need to install a separate capacitor in the circuit, the number of parts can be reduced. Further, the number of components can be reduced by using diodes incorporated in the switching elements Q1 and Q2, which are MOSFETs, for example, as the diodes D1 and D2.

  Further, when the grid voltage Vg is brought close to zero, the electric charge of the capacitor Cg can be regenerated to the power source, so that power consumption can be suppressed. Furthermore, the power supply can be reduced in size.

  Thus, according to this embodiment, highly efficient linear control of the grid voltage Vg in the X-ray tube 5 is realizable.

  Furthermore, exposure of the subject P can be reduced by linearly controlling the tube current I as in the use example described with reference to FIG. In this case, since the projection data is collected by irradiating the subject P with X-rays having energy corresponding to the body thickness, a high-definition reconstructed image with few artifacts can be obtained.

  In addition to these, various suitable effects can be obtained from the configuration disclosed in the present embodiment.

(Modification)
Some variations are shown.

  In the above embodiment, the high voltage device 9 mounted on the X-ray CT apparatus 1 is disclosed as an example of the X-ray tube control apparatus. However, the configuration of the high voltage device 9 can be applied to other types of X-ray tube control devices. For example, a circuit configuration similar to that of the high voltage device 9 may be applied to an X-ray tube control device such as a high voltage device provided in the X-ray fluoroscopic apparatus.

  In the above-described embodiment, an example in which the tube current is linearly changed according to the body thickness while the X-ray tube 5 is rotated once around the subject P has been described. However, the configuration in the above embodiment can also be used in other situations. For example, when the X-ray tube 5 is rotated once, the tube current is limited only while a specific part such as an eye, which is likely to be adversely affected by X-rays, is located in front of the X-ray tube 5. The tube current I may be controlled linearly so that I becomes low.

  In the said embodiment, the case where the grid voltage inverter 200 and the grid voltage transformer 201 were used as a component for producing | generating the power supply for grid voltage Vg was shown. However, a secondary winding connected to the grid voltage circuit 203 is provided in the high voltage transformer 101 for supplying a high voltage to the X-ray tube 5, and the power supply for the grid voltage Vg is generated by the operation of the main inverter 100. Also good.

  In the above embodiment, when the tube current I of the X-ray tube 5 is lowered, after the grid voltage Vg reaches the target value, the control circuit 204 adjusts the time ratio between the on time Ton and the off time Toff of the switching element Q2. Thus, the grid voltage Vg is stabilized. However, when the grid voltage Vg reaches the target value, the control circuit 204 stabilizes the grid voltage Vg by adjusting the switching frequency of the switching element Q2 without changing the on time Ton and the off time Toff. Also good.

  Further, the control circuit 204 may adjust the ON time Ton and the OFF time Toff of the switching elements Q1 and Q2 by PWM (pulse width modulation) control so that the grid voltage Vg approaches the target value. An example of a feedback circuit for realizing such a configuration is shown in FIG.

  The feedback circuit 300 includes a polarity inverter 301, an error amplifier 302, and PWM circuits 303 and 304. The input to the minus terminal (−) of the polarity inverter 301 is the divided grid voltage Vg, and the input to the plus terminal (+) is a reference potential. The polarity inverter 301 inverts the polarity of the voltage input to the minus terminal (−) and outputs it to the minus terminal (−) of the error amplifier 302. For example, the polarity inverter 301 outputs a voltage of 3V to the minus terminal (−) of the error amplifier 302 when the grid voltage Vg is −1500V, and outputs a voltage of 2V of the error amplifier 302 when the grid voltage Vg is −1000V. Output to the minus terminal (-). The input to the plus terminal (+) of the error amplifier 302 is a voltage corresponding to the target value of the grid voltage Vg. This voltage is a value obtained by reducing the target value at the same ratio as the polarity inverter 301 and inverting the polarity. For example, the voltage is 3V when the target value is −1500V, and 2V when the target value is −1000V. is there.

  The output of the error amplifier 302 is connected to each of the PWM circuits 303 and 304. The PWM circuit 303 outputs a drive waveform to the switch drive circuit A1. This drive waveform includes a pulse representing the on time Ton or the off time Toff of the switching element Q1. The switch drive circuit A1 turns on / off the switching element Q1 according to the drive waveform. When the voltage output from the error amplifier 302 has a negative polarity, the PWM circuit 303 sets the pulse width of the drive waveform so that the ON time Ton of the switching element Q1 is longer and the OFF time Toff is shorter as the voltage is larger. adjust.

  The PWM circuit 304 outputs a drive waveform to the switch drive circuit A2. This drive waveform includes a pulse representing the on time Ton or the off time Toff of the switching element Q2. The switch drive circuit A2 turns on / off the switching element Q2 according to the drive waveform. When the voltage output from the error amplifier 302 has a positive polarity, the PWM circuit 304 has a drive waveform so that the ON time Ton of the switching element Q2 is longer and the OFF time Toff is shorter as the absolute value of the voltage is larger. Adjust the pulse width.

  In the feedback circuit 300 having such a configuration, when the grid voltage Vg is lower than the target value, the output of the error amplifier 302 has a positive polarity, the PWM circuit 304 operates, and the switching element Q2 is turned on / off. As the grid voltage Vg approaches the target value, the ON time Ton of the switch Q2 is shortened, and the grid voltage Vg is stabilized at the target value.

  On the other hand, when the grid voltage Vg is higher than the target value, the output of the error amplifier 302 has a negative polarity, the PWM circuit 303 operates, and the switching element Q1 is turned on / off. As the grid voltage Vg approaches the target value, the ON time Ton of the switch Q1 is shortened, and the grid voltage Vg is stabilized at the target value.

  Even when such PWM control is used, the grid voltage Vg or the tube current I can be controlled linearly.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... X-ray CT apparatus, 5 ... X-ray tube, 9 ... High voltage apparatus, Cg ... Capacitor, Rg ... Resistance, Q1, Q2 ... Switching element, D1, D2 ... Diode, A1, A2 ... Switch drive circuit, L ... Coil, 51 ... Anode, 52 ... Cathode, 53 ... Grid, 100 ... Main inverter, 101 ... High voltage transformer, 102 ... High voltage rectifier, 103 ... High voltage capacitor, 200 ... Grid voltage inverter, 201 ... Grid voltage transformer, 202 ... voltage doubler rectifier, 203 ... grid voltage circuit, 204 ... control circuit.

Claims (5)

An X-ray tube control device for controlling an X-ray tube comprising an anode, a cathode, and a grid that blocks electrons emitted from the cathode toward the anode,
And two switching elements connected in series, the two connection point for connecting the switching elements to each other and the grid is connected to the power supply,
Two diodes connected in anti-parallel with each of the two switching elements;
A coil provided between the connection point and the grid;
A capacitor provided between the cathode and the grid;
One of the two switching elements is opened, and the other switching element is opened / closed according to a predetermined time ratio to control the voltage of the capacitor, thereby controlling the voltage of the grid with respect to the cathode. A control circuit to change,
An X-ray tube control device.   The capacitance component between the cathode and the grid, and a capacitance component between conductors included in a cable connecting the X-ray tube control device and the X-ray tube are used as the capacitor. X-ray tube control device.   The X-ray tube control device according to claim 1, wherein the two switching elements are MOSFETs, and the two diodes are diodes built in the MOSFET. The X-ray tube is mounted on an X-ray CT apparatus, rotates around the subject,
The X-ray tube control apparatus according to claim 1, wherein the control circuit changes the predetermined time ratio according to a rotation angle of the X-ray tube. An X-ray tube comprising an anode, a cathode, and a grid that blocks electrons emitted from the cathode toward the anode;
And two switching elements connected in series, the two connection point for connecting the switching elements to each other and the grid is connected to the power supply,
Two diodes connected in anti-parallel with each of the two switching elements;
A coil provided between the connection point and the grid;
A capacitor provided between the cathode and the grid;
One of the two switching elements is opened, and the other switching element is opened / closed according to a predetermined time ratio to control the voltage of the capacitor, thereby controlling the voltage of the grid with respect to the cathode. A control circuit to change,
An X-ray CT apparatus comprising:

Images