JP2004139790A - X-ray tube device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the response of a tube current to a preset value in an X-ray tube device. <P>SOLUTION: The X-ray tube device is provided with a vessel 11 for maintaining a high vacuum, an anode 12 housed in the vessel, a cathode 13 housed in the vessel including a filament, a high-voltage power source 21 impressing a high voltage between the anode and the cathode, a filament heating power source 23 supplying the filament with heating current, a grid 14 arranged between the anode and the cathode, a grid-controlling power source 23 impressing a negative bias pressure on the grid against the cathode for blocking thermion emitted from the filament, and a control circuit 31 for controlling the filament heating power source in order to pass a higher current to the filament than the filament current corresponding to a preset tube current. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an X-ray tube device provided in an X-ray diagnostic device or the like.
[0002]
[Prior art]
In an X-ray tube apparatus, an electric current is applied to a cathode filament to heat it, and the emitted thermoelectrons collide with a target of an anode by a high voltage to generate an X-ray. The control of the tube current flowing by the electron beam from the cathode to the anode is generally performed by increasing or decreasing the current flowing through the cathode filament. By increasing or decreasing the filament current, the temperature of the filament changes, and the amount of thermoelectrons emitted from the filament changes. The tube current changes accordingly.
[0003]
In order to increase or decrease the filament temperature of the X-ray tube, the filament current is increased or decreased. However, since the filament has thermal inertia, a certain degree (about 1 second) is required for the temperature to follow the filament current fluctuation. Occurs. When the fluoroscopic trigger is pressed, the supply of the filament current is started together with the application of the tube voltage. Due to the thermal inertia, the actual tube current has not reached the set value for about 1 second until the filament temperature stabilizes at the set temperature.
[0004]
Therefore, the actual tube current does not reach the set value during a period of about one second from the fluoroscopic trigger until the filament temperature reaches the set temperature. As a result, the fluoroscopic image during this period is insufficient in density, and cannot be optimal for the operator performing the diagnosis.
[0005]
Also, when performing automatic brightness correction during the fluoroscopy period, that is, when dynamically changing the tube current during fluoroscopy so as to stabilize the brightness level, a delay occurs until the tube current actually changes to the set value. In other words, when the thickness of the subject changes suddenly, a certain amount of time is required until the luminance of the perspective image is stabilized.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to improve the responsiveness of a tube current to a set value in an X-ray tube device.
[0007]
[Means for Solving the Problems]
An X-ray tube device according to a first aspect of the present invention is a container holding a high vacuum, an anode housed in the container, a cathode containing a filament housed in the container, and the anode and the cathode. A high-voltage power supply for applying a high voltage between the filaments, a filament heating power supply for supplying a heating current to the filament, a grid disposed between the cathode and the anode, and blocking thermoelectrons emitted from the filament A grid control power supply for applying a negative bias voltage to the grid with respect to the cathode, and for a predetermined period from the start of X-ray irradiation, a current higher than a filament current corresponding to a predetermined tube current to the filament. And a control circuit for controlling the filament heating power supply for flowing.
An X-ray tube device according to a second aspect of the present invention is a container holding a high vacuum, an anode housed in the container, a cathode containing a filament housed in the container, and the anode and the cathode. A high-voltage power supply for applying a high voltage therebetween, a filament heating power supply for supplying a heating current to the filament, a grid disposed between the cathode and the anode, and a negative voltage applied to the grid with respect to the cathode. A potential in the active region between a potential of the cathode and the cutoff potential from a grid control power supply for applying a bias voltage of the above and a cutoff potential for blocking thermoelectrons emitted from the filament at the start of X-ray irradiation. In order to vary the bias voltage and to vary the bias voltage within the active region according to a controlled variation of the tube current during the X-ray irradiation period, And a control circuit for controlling the power supply lid control. An X-ray tube device according to a third aspect of the present invention is a container holding a high vacuum, an anode housed in the container, a cathode containing a filament housed in the container, and the anode and the cathode. A high-voltage power supply for applying a high voltage therebetween, a filament heating power supply for supplying a heating current to the filament, a grid disposed between the cathode and the anode, and a negative voltage applied to the grid with respect to the cathode. And a grid control power supply for applying a bias voltage, and for a predetermined period from the start of X-ray irradiation, controlling the filament heating power supply to flow a current higher than a filament current corresponding to a predetermined tube current to the filament, At the start of X-ray irradiation, the voltage in the active region between the potential of the cathode and the cut-off potential is changed from the cut-off potential for preventing thermions emitted from the filament. A control circuit that changes the bias voltage and controls the grid control power supply to change the bias voltage in the active region according to a controlled change in the tube current during the X-ray irradiation period. I do.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an X-ray tube device according to the present invention will be described with reference to the drawings according to a preferred embodiment. The X-ray tube device is applied in various fields such as a medical field and a nondestructive inspection field. Here, the medical field will be described as an example. Further, the X-ray tube device is equipped in various devices such as an X-ray diagnostic device and an X-ray CT in the medical field. An example of application to an X-ray diagnostic apparatus having a large number of tube current control opportunities will be described.
[0009]
The X-ray diagnostic apparatus will be briefly described. In the X-ray diagnostic apparatus, the X-ray tube of the X-ray tube apparatus is provided with respect to an X-ray detector constituted by a combination of a flat panel or an image intensifier and a TV camera. It is held by an arm or a stand across the subject. Image data is generated and displayed based on the X-ray signal detected by the X-ray detector.
[0010]
FIG. 1 is a diagram showing a configuration of a main part of the X-ray tube device according to the present embodiment. The X-ray tube device includes a grid control X-ray tube 10, an X-ray high voltage device 20, and a control device 30. The X-ray tube 10 has a glass bulb 11 whose inside is kept in a high vacuum. The glass bulb 11 generally contains a rotating anode 12 and a cathode. The cathode is composed of a filament 13 and a focusing electrode (not shown). A grid 14 is arranged between the cathode and the anode 11.
[0011]
The X-ray high voltage device 20 includes a high voltage power supply 21 for applying a high voltage between the anode 12 and the cathode, a high voltage control circuit 22 for controlling the output of the high voltage power supply 21, and a filament control for the filament 13. A filament heating power supply 23 for supplying a current, a grid control power supply 24 for applying a negative bias voltage (grid control voltage) to the grid 14 with respect to the cathode 13, and a filament heating power supply 23 and a grid control power supply 24 are controlled. And a cathode control circuit 25.
[0012]
The control device 30 has an X-ray control circuit 31. The X-ray control circuit 31 supplies a tube voltage control signal to the high voltage control circuit 22. A voltage corresponding to the tube voltage control signal is applied between the anode 12 and the cathode. The X-ray control circuit 31 supplies a filament current control signal and a grid voltage control signal to the cathode control circuit 25. A filament control current corresponding to the filament current control signal is generated from the filament heating power supply 23. The current actually flowing through the filament 13 matches the filament control current when the tube current is not flowing, and matches the sum or difference between the filament control current and the tube current when the tube current is flowing. The grid control power supply 24 lowers the grid voltage from the cathode potential by a voltage corresponding to the grid voltage control signal. The emission of electrons can be controlled by adjusting the grid potential with respect to the cathode potential. Note that the potential for preventing emission of electrons from the cathode to the anode 12 is referred to as a cutoff potential. An area lower than the cutoff potential is called a cutoff area. In the voltage range from the cutoff potential to the cathode potential, emission of electrons from the cathode to the anode 12 is permitted, and the range is referred to as an active region.
[0013]
An operation unit 32 having a tube voltage setting unit, a tube current operation unit, and a see-through trigger button is connected to the X-ray control circuit 31. The X-ray control circuit 31 performs tube voltage control according to a tube voltage (tube voltage set value) set via the tube voltage setting unit and a tube current (tube current set value) set via the tube current setting unit. A signal, a filament current control signal, and a grid control signal are generated at the time of a fluoroscopic trigger. The X-ray control circuit 31 has an automatic brightness control circuit 33. The automatic brightness control function is a function for suppressing a change in the brightness level due to a change in the thickness or the like of the subject during the fluoroscopic period. The automatic brightness control circuit 33 outputs the output of the reference detector 34 or the X-ray image. The value of the tube current is dynamically determined so as to keep the reference value substantially constant. The X-ray control circuit 31 changes the filament current control signal and / or the grid control signal according to the tube current determined by the automatic brightness control circuit 33.
[0014]
FIG. 2 shows a time change of the filament current control signal and the grid voltage control signal controlled by the X-ray control circuit 31. When the operator presses the fluoroscopy trigger button, the fluoroscopy signal is displaced from the off level to the on level from the operation unit 32 to the X-ray control circuit 31, and this state continues until the fluoroscopy trigger button is pressed again. The fluoroscopy is performed while the fluoroscopy signal is maintained at the on level.
[0015]
Before the fluoroscopic trigger button is pressed, the filament current control signal is set by the X-ray control circuit 31 to a value corresponding to the relatively low preheating current _IPH . As a result, the preheating current _IPH flows through the filament 13, and the filament 13 is preliminarily heated.
[0016]
Also, before the fluoroscopy trigger button is pressed, the grid control signal is set to a value corresponding to a potential in the cutoff region lower than the cathode potential and lower than the active region. The cutoff potential is set to a potential low enough to completely prevent electron emission from the cathode to the anode 12.
[0017]
When fluoroscopy trigger button is pressed, the filament current control signal, the X-ray control circuit 31, a value corresponding to the pre-heating current I _PH, than the filament current I ₂₁ corresponding to the set value I ₁₁ of the tube current is rapidly increased to a value corresponding to the predetermined value ΔI is higher by filament current values (preflash current value) I _P1. Filament current control signal during a very short predetermined time, is maintained at a value corresponding to the pre-flash current value I _P1, then, it is changed to a value corresponding to the filament current value I _21.
[0018]
Thus extremely short time period from the perspective trigger, filament current, by being flowed at a value higher than the filament current value I ₂₁ corresponding to the set value I ₁₁ of the tube current, a filament current from the initial perspective trigger, than flows in filament current value I ₂₁ corresponding to the set value I ₁₁ of the tube current, filament, the preheat temperature, the time required to rise to a temperature corresponding to the set value I ₁₁ of the tube current is reduced You.
[0019]
When the fluoroscopy trigger button is pressed, the grid voltage control signal is sharply displaced by the X-ray control circuit 31 from a value corresponding to the potential in the cutoff region to a value corresponding to the potential in the active region. You. As a result, the grid voltage rises sharply from the potential in the cutoff region to the potential in the active region, and emission of electrons from the cathode to the anode 12 is permitted.
[0020]
In this way, by applying the preflash control and the grid voltage control at the time of the fluoroscopic trigger, the tube current is set to a set value more rapidly than the case where neither the preflash control nor the grid voltage control is performed as shown in FIG. Stand up until. As a result, it is possible to shorten the period in which the concentration is insufficient, which has been a conventional problem.
[0021]
As shown in FIG. 3, the pre-flash control is performed at the time of triggering, but even when grid voltage control is not performed, the rise time to the set value of the tube current is shorter than when both are not performed. Is done. Therefore, the X-ray control circuit 31 is equipped with not only a mode in which both preflash control and grid voltage control are performed, but also a mode in which preflash control is performed and grid voltage control is not performed. You may do it.
[0022]
Next, during the fluoroscopy period, the value of the tube current is changed by the automatic brightness control function. For variation of the tube current, a filament current control signal, the X-ray control circuit 31, a value corresponding to the filament current value I ₂₁ corresponding to the initial setting value I ₁₁ of the tube current, the variation tube current It is displaced to the value corresponding to the filament current value I ₂₂ corresponding to the value I _12. Whereby the filament current, the filament current value I ₂₁ corresponding to the initial setting value I _11, changes the filament current value I ₂₂ corresponding to the value I ₁₂ variations tube current. However, due to the thermal inertia of the filament 13, the filament temperature does not change instantaneously with the displacement of the filament current. Therefore, the tube current is displaced with a delay with respect to the displacement of the filament current.
[0023]
In order to shorten the delay time, the displacement of the grid voltage is used together with the displacement of the filament current together with the filament current control. That is, for example, when the tube current is reduced from I ₁₁ to I ₁₂ , the grid voltage control signal is changed by the X-ray control circuit 31 from the value V ₁₁ close to the cathode potential to V ₁₂ having a low electron emission rate in the active region. When the tube current is increased from I ₁₂ to I ₁₃ , the grid voltage control signal is raised by the X-ray control circuit 31 from the value V ₁₂ to V ₁₃ having a high electron emission rate in the active region. Is changed to
[0024]
When the tube current is increased during the fluoroscopy period, the pre-flash control is performed as in the case of the trigger. In other words, the filament current control signal, the X-ray control circuit 31, during the extremely short predetermined time from the time of tube current increases, higher by a predetermined value ΔI than the filament current value I ₂₃ corresponding to the luminance control value I ₁₃ of the tube current The value is sharply increased to a value corresponding to the _preflash current value _IP2 . Thus at the time the tube current increases, then a very short time period, by filament current is flowed at high values I _P2 than the filament current value I ₂₃ corresponding to the luminance control value I ₁₃ of the tube current, the filament temperature rises in a short time to a temperature corresponding to the luminance control value I ₁₃ of the tube current.
[0025]
As described above, by using both the preflash control and the grid voltage control at the time of triggering and during the fluoroscopic period, the responsiveness of the tube current can be improved.
[0026]
As shown in FIG. 4, during the fluoroscopy period, the tube current control for brightness control is realized by grid voltage control alone while maintaining the filament current at a constant value corresponding to the maximum tube current during fluoroscopy. You may do it.
[0027]
Instead of the pre-flash control at the time of the fluoroscopic trigger, as shown in FIG. 5, after the system is turned on and before the fluoroscopic trigger, at the stage when the operation of the X-ray diagnostic apparatus becomes possible, the filament current is reduced. Maintain a constant value corresponding to the maximum tube current of the fluoroscopy, maintain the grid voltage at the voltage in the cutoff region, prevent electron emission, and, together with the fluoroscopy trigger, activate the grid voltage from the voltage in the cutoff region. The voltage in the region may be sharply increased. At the time of the fluoroscopic trigger, the temperature of the filament 13 is already at a temperature at which the maximum fluoroscopic tube current can be output, so the time delay until the tube current is stabilized depends only on the grid control. Therefore, the time required for the fluoroscopic image to stabilize at the fluoroscopic trigger can be reduced.
[0028]
According to the present embodiment, the time from a trigger instruction for fluoroscopy to obtaining a stable fluoroscopic image is reduced. In addition, when luminance changes due to a change in the thickness of the subject during fluoroscopy, the tube current can be quickly displaced.
[0029]
(Modification)
The present invention is not limited to the above-described embodiment, and can be implemented in various forms without departing from the spirit of the invention at the stage of implementation. Furthermore, the above-described embodiment includes various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, some components may be deleted from all the components shown in the embodiment.
[0030]
【The invention's effect】
According to the present invention, the responsiveness of the tube current is improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an X-ray tube device according to an embodiment of the present invention.
FIG. 2 is a diagram showing a time change of a filament current and a grid voltage controlled by the X-ray control circuit of FIG. 1;
FIG. 3 is a diagram showing a time change of a tube current by the control of FIG. 2;
FIG. 4 is a diagram showing a temporal change of a filament current and a grid voltage by another control of the X-ray control circuit of FIG. 1;
FIG. 5 is a diagram showing a time change of a filament current and a grid voltage under still another control of the X-ray control circuit of FIG. 1;
[Explanation of symbols]
10. Grid control X-ray tube,
11 ... Glass bulb,
12… Anode,
13 ... filament,
14 ... grid,
20 X-ray high voltage device,
21 ... High voltage power supply,
22 high voltage control circuit,
23 ... filament heating power supply,
24 ... grid control power supply
25 ... Cathode control circuit,
30 ... Control device,
31 ... X-ray control circuit,
32 ... operation unit,
33 ... Automatic brightness control circuit
34 ... Reference detector.

Claims (3)

A container for holding a high vacuum,
An anode housed in the container,
A cathode including a filament housed in the container;
A high-voltage power supply that applies a high voltage between the anode and the cathode,
A filament heating power supply for supplying a heating current to the filament,
A grid disposed between the cathode and the anode,
A grid control power supply that applies a negative bias voltage to the grid with respect to the cathode to block thermoelectrons emitted from the filament;
A control circuit for controlling the filament heating power supply for flowing a current higher than a filament current corresponding to a predetermined tube current to the filament for a predetermined period from the start of X-ray irradiation. Tube equipment. A container for holding a high vacuum,
An anode housed in the container,
A cathode including a filament housed in the container;
A high-voltage power supply that applies a high voltage between the anode and the cathode,
A filament heating power supply for supplying a heating current to the filament,
A grid disposed between the cathode and the anode,
A grid control power supply for applying a negative bias voltage to the grid with respect to the cathode,
Changing the bias voltage from a cut-off potential that blocks thermoelectrons emitted from the filament at the start of X-ray irradiation to a potential in the active region between the potential of the cathode and the cut-off potential; An X-ray tube comprising: a control circuit for controlling the grid control power supply to change the bias voltage in the active region according to a controlled change in tube current during an irradiation period. apparatus. A container for holding a high vacuum,
An anode housed in the container,
A cathode including a filament housed in the container;
A high-voltage power supply that applies a high voltage between the anode and the cathode,
A filament heating power supply for supplying a heating current to the filament,
A grid disposed between the cathode and the anode,
A grid control power supply for applying a negative bias voltage to the grid with respect to the cathode,
For a predetermined period from the start of X-ray irradiation, the filament heating power supply is controlled so that a current higher than a filament current corresponding to a predetermined tube current flows through the filament, and thermoelectrons emitted from the filament at the start of X-ray irradiation The bias voltage is changed from a cut-off potential to prevent the potential in the active region between the potential of the cathode and the cut-off potential, and the X-ray irradiation is controlled according to a controlled variation of the tube current during the X-ray irradiation period. An X-ray tube apparatus comprising: a control circuit that controls the grid control power supply to change the bias voltage in an active region.

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