JP2002033064A - Triode x-ray tube grid control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a triode X-ray tube grid control device miniaturized in a bias circuit of a grid, lowered in the manufacturing cost with number reduced of switch element. SOLUTION: An alternating current power source 19 is converted to the direct current output by a rectifier 20 and a smoothening capacitor 21. A high frequency inverter 22 is operated by the OFF signal of the X-ray radiating signal 41, at the same time, a switch element 17 is turned off through a switch element control circuit 30, the direct current output is converted to the high frequency output by the high frequency inverter 22, voltage is raised by a high frequency and high voltage transformer 23, the full wave rectification is performed by a full wave rectifying circuit 24, and smoothened by a cable floating capacitor 10, and the minus bias voltage is applied to a grid 31. The bias voltage rises less than 1 ms and the X-ray radiation is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray high voltage generator, and more particularly to a triode X-ray tube grid control device which controls the emission of X-rays using a triode X-ray tube device.

[0002]

2. Description of the Related Art Conventionally, in low-dose pulse fluoroscopy, if the X-ray waveform has a wave tail, the image quality decreases and the exposure dose that does not contribute to the image increases. To prevent this, a triode X-ray tube device is used to apply a focusing electrode (hereinafter, referred to as a grid) to a cathode (hereinafter, referred to as a filament) of the triode X-ray tube while a high voltage is applied. By changing the potential to a potential at which electrons can be emitted and a potential at which electrons cannot be emitted, emission of X-rays is controlled, and an X-ray waveform is pulsed. In a grid control device that controls the potential of the grid with respect to the filament of the triode X-ray tube, 4,000 V
It has a bias power supply of about the same degree, and is connected between the filament and the grid with the filament side being + and the grid side being-. A first switch element is connected between the grid and the bias power supply, and a second switch element is connected between the grid and the filament. The bias potential between the filament and the grid is controlled by turning these switches on and off. are doing. FIG. 3 shows a configuration diagram of a conventional grid control device. The triode X-ray tube device 8 includes a rotating anode 32.
, A cathode having a small focal filament 36 and a large focal filament 37 opposed thereto, and a grid 31 provided near the cathode. Then, between the rotating anode 32 and the cathode, a DC high voltage of + is applied from the high voltage generator 6 to the rotating anode 32 side and − is applied to the cathode side via the high voltage cable 7 from the high voltage generator 6. A heating current is supplied to the small focus filament 36 and the large focus filament 37 via 42. And
An AC output from a 50/60 Hz AC power supply 19 (commercial power supply) is sent to the primary side of the step-up transformer 25, and a high-voltage AC output appears on the secondary side. Then, the voltage is smoothed by a smoothing capacitor, converted into a high-voltage DC output, and used as a bias power supply. The smoothing capacitor of the full-wave voltage doubler rectifier circuit 26 has a withstand voltage of 2500 V, a resistance of 0.
A component of about 2 μF is used. This is because if the ripple of the bias power supply is large, the bias potential between the grid 31 and the cathode (small focal filament 36, large focal filament 37) drops to a potential at which electrons can be emitted, and X-rays are emitted. It is to prevent becoming. However, this smoothing capacitor is a large, high withstand voltage capacitor and is expensive. Further, the first switch element 18 for controlling the supply of the bias potential to the grid 31 is connected between the negative side of the bias power supply and the grid 31, and the grid 31 and the cathode (small focus, large focus filament 36,
37), the second switch element 17a is set to the same potential as the grid and the cathode (small focus, large focus filaments 36, 3).
7). Then, when X-ray emission is performed, the first switch element 18 is turned off and the second switch element 17a is turned on by the switch element control circuit 30 by the X-ray emission signal 41, so that the electron beam can be emitted without the bias voltage. I do. When the X-ray emission is stopped, the first switch element 18 is turned on, the second switch element 17a is turned off, the electron emission is disabled by applying the bias voltage, and the X-ray emission is turned off.

[0003]

The conventional triode X-ray tube grid control device is constructed as described above. However, the smoothing capacitor of the full-wave voltage doubler rectifier circuit 26 constituting the bias power supply is a triode X-ray tube. Since the bias voltage of the tube requires about 4000 V, the withstand voltage of the half-wave rectifier circuit of the full-wave voltage doubler rectifier circuit 26 requires a withstand voltage of 2500 V or more. The withstand voltage between the ground of the full-wave rectifier circuit 26 and the high voltage applied to the cathode of the triode X-ray tube device 8 is required. Therefore, a smoothing capacitor with a high withstand voltage is required, and there is a problem that the full-wave voltage doubler rectifier circuit 26 is expensive and large. The step-up transformer 25 also boosts the voltage at the commercial frequency, and the withstand voltage between the primary side, the secondary side, and the ground is
A high voltage or more applied to the cathode of the triode X-ray tube device 8 is required. Therefore, there is a problem that the size is large and the price is expensive. The first switch element 18 and the second switch element 17a also need to have a high withstand voltage. Therefore, when a vacuum tube or the like is used, it is expensive and large.
Further, when a semiconductor is used, there is a problem that a control circuit becomes complicated.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has a bias circuit of a triode X-ray tube device which is smaller and less expensive, and which has a reduced number of switch elements. An object is to provide an X-ray tube grid control device.

[0005]

In order to achieve the above object, a triode X-ray tube grid control device according to the present invention applies a negative bias voltage to a grid to a filament to generate thermoelectrons emitted from the filament. A grid control device for a triode X-ray tube device for blocking and controlling X-ray emission, wherein a switch element means for short-circuiting between a grid and a filament;
First rectifying means for converting an AC output from an AC power supply into a DC output, switching means for switching the DC output to convert it to an AC output at a predetermined frequency, and boosting means for boosting the voltage of the AC output; A second rectifier for converting the boosted AC output into a DC output and outputting the DC output as a bias voltage;
The short-circuit switch element of the switch element means is turned off when the X-ray emission signal is turned off, and simultaneously the switching of the switching means is started so that the bias is applied between the grid and the cathode. A voltage is applied to make it impossible to emit electrons, or when the X-ray emission signal is turned on, the switching of the switching means is stopped, and at the same time, the short-circuit switch element of the switch element means is turned on to eliminate the bias voltage and emit electrons. It is controlled to a possible state.

[0006] The triode X-ray tube grid control device of the present invention comprises:
When the X-ray radiation signal is turned off, a high-frequency inverter circuit and a high-frequency high-voltage transformer are used to raise the bias voltage in less than 1 ms when the X-ray radiation signal is turned off. The control circuit opens the switch element for short-circuiting between the grid and the cathode, applies a bias voltage between the grid and the cathode (filament), and sets a state in which electrons cannot be emitted. Also,
When the X-ray emission signal is turned on, the switching of the high-frequency inverter is stopped, and at the same time, the switch element is short-circuited so that the bias voltage is eliminated and electrons can be emitted.
Therefore, when the X-ray emission signal is off, the bias potential becomes 1
In less than 1 ms, it rises to a predetermined value, and in less than 1 ms, it becomes unable to emit electrons, and X-ray emission is stopped. As a result, the wave tail of the X-ray waveform is sharply cut, high image quality can be obtained, and the use of a high-frequency inverter circuit and a high-frequency high-voltage transformer reduces the size and cost of the bias circuit. Can be. Further, the number of switch elements can be reduced to one. Also, by rectifying the high-frequency high-voltage alternating current output from the secondary side of the high-frequency high-voltage transformer, the ripple of the bias power supply can be reduced even with the capacity of the stray capacitance between the low-voltage line core between the grid and the cathode (filament) in the high-voltage cable. In addition, it is possible to prevent the bias voltage from lowering to a potential at which electrons can be emitted. When the X-ray emission signal is turned on, the switching of the high-frequency inverter is stopped, and at the same time, the switch element is short-circuited to discharge the bias voltage charged in the stray capacitance between the grid and the cathode of the high-voltage cable in a short time. X-rays can be emitted in a state where they can be emitted. This eliminates the need for a smoothing high-voltage capacitor in the bias power supply circuit, so that the bias circuit can be reduced in size and cost.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the triode X-ray tube grid control device of the present invention will be described with reference to FIG. FIG. 1 shows a circuit diagram of a triode X-ray tube grid control device of the present invention.
The triode X-ray tube grid control device includes a first rectifier circuit for converting a commercial frequency AC power supply 19 into a DC output by a rectifier 20 and a smoothing capacitor 21, and switching this DC output to a predetermined high frequency. A high-frequency inverter 22 for converting to an AC output; a high-frequency high-voltage transformer 23 for boosting the voltage of the high-frequency output; and a bridge-structured full-wave rectifier circuit 24 for converting the boosted AC output to a DC output and outputting it as a bias voltage. The switch element control circuit 30 is operated by the second rectifier circuit and the X-ray emission signal 41 to short-circuit the grid 31 and the cathode (small focal filament 36, large focal filament 37).
And a suppression resistor 43 for protection of the bias voltage circuit and the diode 15. Then, the first rectifier circuit, the high-frequency inverter 22 and the high-frequency high-voltage transformer 2
3 and the second rectifier circuit (full-wave rectifier circuit 24) so that the bias voltage can reach the predetermined voltage at the predetermined frequency in less than 1 ms.

First, a partial configuration of the inverter type X-ray high voltage device will be described. The triode X-ray tube device 8 has a small focal filament 36 and a large focal filament 37 on the cathode, has a rotating anode 32 rotating at high speed on the anode, and turns on the emission of thermoelectrons generated from the filament of the cathode. It is composed of a grid 31 that is turned off. The high-voltage generator 6 generates a high-voltage DC output and is applied via a high-voltage cable 7 between the rotating anode 32 and the cathode of the triode X-ray tube device 8. In the high voltage cable 7, there is a stray capacitance 9 between the high voltage wire core and the ground, and a stray capacitance 10 between the grid 31 and the filament wire core. Stray capacitance 10 between grid 31 and filament wire core
Is about 300 pF / m. The filament heating circuit 38 is connected to the triode X-ray tube device 8 via the heating transformer 42.
Is connected to the small focal filament 36 and the large focal filament 37, and heats the small focal filament 36 or the large focal filament 37 in accordance with the filament heating signal. The diode 15 and the resistor 16 are elements for stabilizing the potential between the grid 31 and the filament. The switch element 17 is a switch element for turning on and off the grid between the triode X-ray tube 31 and the filament. The switch element 17 is connected to the switch element control circuit 30 and is controlled on and off by an X-ray emission signal 41. The first rectifier circuit rectifies an AC output from an AC power supply 19 with a rectifier 20, smoothes it with a smoothing capacitor 21, and converts it into a DC output. The high-frequency inverter circuit 22 is configured by a semiconductor switching element, and switches the DC output of the first rectifier circuit at a high frequency to convert it into a high-frequency AC output. The high-frequency high-voltage transformer 23 is a transformer that insulates the primary circuit and the secondary circuit and the secondary circuit and the ground from each other with respect to a high voltage, and boosts a high-frequency AC input. The full-wave rectifier circuit 24 converts the boosted high-frequency AC input into a DC output by a bridge-structured rectifier, and the stray capacitance 10 between the grid 31 and the filament wire core exists. It is smoothed by the capacitor 10 to generate a DC bias voltage. Therefore, a large-sized smoothing capacitor unlike the related art is not required. The bias voltage is connected to the grid 31 of the triode X-ray tube on the negative side and to the common terminal (common) of the small focal filament 36 and the large focal filament 37 via the suppression resistor 43 on the positive side.

When the X-ray radiation signal 41 is turned on, the switching of the high-frequency inverter 22 is stopped, and at the same time,
The switching element 17 is turned on by the switching element control circuit 30 to short-circuit the grid 31 and the cathode to eliminate the bias voltage, and electrons are emitted from the cathode (small focal filament 36, large focal filament 37) toward the rotating anode 32. X-ray emission from the target. Further, when the X-ray emission signal 41 is turned off, the switch element 17 is turned off by the switch element control circuit 30, and at the same time, switching of the high-frequency inverter 22 is started. The X-ray emission is stopped in a state where electrons cannot be emitted in less than 1 ms.

Next, the operation will be described with reference to the timing chart of FIG. A, b, c, d, and e on the horizontal axis of the timing chart indicate time phases with a time axis,
The vertical items A, B, C, D, and E indicate signals and waveforms of each unit. First, it is assumed that an ON signal of the X-ray emission signal 41 is output from the operation circuit of the X-ray control device (not shown) (time A-a). The ON signal of the X-ray emission signal 41 is sent to the high-frequency inverter circuit 22. When the X-ray emission signal 41 is ON, the switching operation is stopped (at the time point Ba). At the same time, an ON signal of the X-ray emission signal 41 is sent to the switch element control circuit 30, and the switch element control circuit 30
7 is output, and the switch element 17 is turned on (at the time point C-a). When the switch element 17 is turned on, the grid 31 and the filament (small focal filament 36, large focal filament 37) are short-circuited to have the same potential, the bias voltage between the grid and the cathode becomes 0 V, and the electron emission is enabled ( D-a). On the other hand, the ON signal of the X-ray emission signal 41 is also sent to the high voltage generator 6, where a high voltage is applied and X-rays are emitted (at the point of Ea). X after predetermined time
When the line radiation signal 41 is turned off, the application of the high voltage from the high voltage generator 6 is stopped (at the point of Ab). Then, the off signal of the X-ray emission signal 41 is output to the high-frequency inverter circuit 22.
Sent to When turned off, the switching operation starts at a high frequency of about 10 kHz, and
The current starts to flow to the next side (Bb to c). The off signal of the X-ray emission signal 41 is sent to the switch element control circuit 30, and the on signal of the switch element 17 is turned off from the switch element control circuit 30, and the switch element 17 is turned off (C
-B time point). Since the switch element 17 is in the off state,
A bias voltage is applied between the filament and the grid 31 through the suppression resistor 43 from the bias power supply, and the stray capacitance 10 between the grid 31 and the filament wire core is charged.
The bias voltage rises (Db to c). The grid bias voltage is -370 with respect to the filament
When the voltage exceeds 0 V, electron emission is stopped (D-
(time point c) Then, the X-ray emission is stopped. (Time Ec) During the off period of the X-ray emission signal, the high-frequency inverter circuit 2
2 is continuously performed (Bd to e)
Time).

The voltage pulsation rate (= K) of the bias power supply is as follows: resistance 16 (about 1 cmΩ) (= R), stray capacitance 10 between grid 31 and filament core (300 pF / 22 m).
m × 22m = 6600 pF) (= C) and switching frequency (about 10 kHz) (= f), K = [1−
exp {-1 / (2f.CR)}]. times.100%, which is 1% or less. Therefore, the bias voltage of the grid 31 is kept at -3700 V or more, and the electron emission is continuously prevented (at the time point Dd). At this time, the output from the high voltage generator 6 is stopped, but the high voltage charged in the stray capacitance 9 between the high voltage wire core in the high voltage cable 7 and the ground remains and continues (at the point of Ed). . When the X-ray emission signal 41 is turned on again, the X-ray emission signal 41 is sent to the high-frequency inverter circuit 22, and the switching operation is stopped by turning on the X-ray emission signal 41, and the output of the bias voltage is stopped (at the point of De).
Further, an ON signal of the X-ray emission signal 41 is sent to the switch element control circuit 30, and the switch element 17 is turned on. When the switch element 17 is turned on, the electric charge charged in the stray capacitance 10 between the grid 31 and the filament wire core flows through a closed loop formed by the switch element 17, so that the grid 31 and the filament have the same potential and can emit electrons. State (at the point of Ce). Further, the X-ray emission signal 41 ON is also sent to the high voltage generator 6 and a high voltage is output, and X
A line is emitted (at Ee)

As described above, in pulse fluoroscopy in which X-rays are repeatedly turned on and off by grid control using a triode X-ray tube, the circuit of the high-frequency inverter 22 is switched at high speed when X-rays are cut off, and the grid 31 and the cathode are switched. A bias voltage is applied in between, and a rise to the bias voltage is started in less than 1 ms.
Electron emission is disabled, and X-ray emission is stopped. At the start of X-ray emission, the inverter operation is stopped, the supply of bias power is stopped, and the electric charge charged in the floating capacitance 10 between the grid 31 and the filament core is discharged by closing the switch element 17 to discharge the same potential. Then, X-ray emission is started in an electron emission enabled state. By performing an inverter operation of about 10 kHz, the high-voltage cable 7
Stray capacitance 10 (2
A bias potential with little pulsation can be obtained at about 6600 pF at 2 m. Therefore, an expensive and large high-voltage capacitor can be eliminated. Further, since the high-voltage capacitor is eliminated, the bias voltage is only charged to the floating capacitance 10, and the switch element 17 for opening and closing the bias power supply is provided.
Can be omitted, and the control circuit of the switch element 17 can be halved.

[0013]

The triode X-ray tube grid control device of the present invention is constructed as described above, and uses a high-frequency inverter circuit and a high-frequency high-voltage transformer as a power supply circuit constituting a bias power supply to reduce the bias voltage to 1 ms. At the same time, the switch element for short-circuiting between the grid and the cathode is opened, and a bias voltage is applied to make it impossible to emit electrons.
X-ray emission is stopped in less than ms. As a result, the wave tail of the X-ray waveform is sharply cut, high image quality can be obtained, and the use of a high-frequency inverter circuit and a high-frequency high-voltage transformer reduces the size and cost of the bias circuit. Can be. In addition, the number of switch elements is set to 1
It can be reduced to individual. Also, even with a capacitance of about the stray capacitance between the low voltage line core between the grid and the cathode (filament) in the high voltage cable, the ripple of the bias power supply can be reduced. Need not be provided, the circuit can be simplified, the reliability of the device can be increased, and the size and cost of the bias circuit can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a triode X-ray tube grid control device of the present invention.

FIG. 2 is a diagram showing a timing chart of the triode X-ray tube grid control device of the present invention.

FIG. 3 is a diagram showing a configuration diagram of a conventional triode X-ray tube grid control device.

[Explanation of symbols]

 6 High voltage generator 7 High voltage cable 8 Triode X-ray tube device 9 Floating capacitance 10 Floating capacitance 17 Switch element 22 High frequency inverter 23 High frequency high voltage transformer 24 Full wave rectifier circuit 25 Boost transformer 26 ... Full-wave voltage rectifier circuit 30 ... Switch element control circuit 31 ... Grid 32 ... Rotating anode 36 ... Small focal filament 37 ... Large focal filament 41 ... X-ray emission signal

Claims (1)

[Claims] In a grid control device of a triode X-ray tube device for controlling a X-ray emission by applying a negative bias voltage to a filament to a grid to block a thermal electron emitted from the filament, a grid between the grid and the filament is provided. Switch element means for short-circuiting, a first rectifying means for converting an AC output from the AC power supply to a DC output, a switching means for switching the DC output to convert it to an AC output of a predetermined frequency, and Boosting means for boosting the voltage;
A second rectifier for converting the boosted AC output into a DC output and outputting the DC output as a bias voltage, wherein the bias voltage can reach the predetermined voltage in less than 1 ms at the predetermined frequency, When the radiation signal is turned off, the short-circuit switch element of the switch element means is turned off, and at the same time, the switching of the switching means is started to apply a bias voltage between the grid and the cathode to make it impossible to emit electrons. A triode X-ray tube grid wherein the switching of the switching means is stopped when a signal is turned on, and at the same time, the short-circuit switch element of the switch element means is turned on to eliminate a bias voltage and control the electron emission to be possible. Control device.