KR101092210B1 - The apparatus and method for X-ray generating - Google Patents

Abstract

The present invention relates to an X-ray generator and a method for preventing unnecessary X-rays from being irradiated and irradiated to a subject, comprising: a first step of applying electrons to a cold cathode to emit electrons; And a second step of applying a positive potential to a gate electrode to emit electrons from the cold cathode when the voltage applied to the cold cathode rises and a voltage higher than a predetermined ratio is applied to the cold cathode. Until the target voltage reaches a predetermined ratio or more, a reference potential or a negative potential is applied to the gate electrode to prevent electrons from being emitted from the cold cathode.

X-ray, cold cathode, CNT, electron emission, target

Description

The apparatus and method for X-ray generating

The present invention relates to an X-ray generator and a method for generating the same, and more particularly, to an X-ray generator and a method for generating a high-quality X-ray image with a low dose by increasing the electron emission efficiency.

In general, in the field of medical imaging and non-destructive testing, X-ray imaging with excellent permeability of materials is frequently used to observe the internal shape of a subject.

X-ray imaging is based on the principle that X-rays are irradiated to living subjects, and the degree of absorption of X-rays differs according to the difference in the density of substances inside the subject. Therefore, when X-rays are transmitted through biological tissues and observed on an X-ray photosensitive film or detector, the thicker tissues appear blacker than the lower-density tissues. Can be distinguished.

1 is a schematic view showing the configuration of a general X-ray imaging apparatus.

A general X-ray imaging apparatus, as shown in Figure 1, the X-ray tube (2) for directly generating X-rays, the high-voltage generator (1) for supplying the required voltage and current to the X-ray tube (2), And an X-ray detector (3) for detecting X-rays passing through the object, and a sequence control device (4) for controlling the operation of the X-ray tube (2) and the high voltage generator (1).

The X-ray tube 2 also includes a filament for emitting electrons, a focusing electrode for focusing the emitted electrons, and a target for generating X-rays when the focused electrons collide with each other.

Therefore, when a current flows through the filament of the X-ray tube 2 in the high voltage generator 1, the filament is heated, and electron emission is induced in the heated filament, and an electron cloud by the emitted electrons is formed around the filament. .

When a sufficient amount of electron clouds are formed and a high voltage of several tens to several hundred kV is applied across the X-ray tube 2, the electron clouds formed in the filament move toward the target by a strong electric field due to a large potential difference, and collide with the target. X-rays are generated.

In this process, the high voltage applied to both ends of the X-ray tube 2 does not maintain a constant value due to the time constant according to the load characteristic, and a transient excessive or low voltage is temporarily applied.

2 is a graph illustrating an output waveform of a general high voltage generator.

As shown in FIG. 2, the high voltage output value applied to the cathode and the anode of the X-ray tube in the general high voltage generator is applied to the filament or the focusing electrode due to the time constant according to the load characteristic of both ends of the X-ray tube as described above. The response is slower than the output value, and the transient state is temporarily excessive or degraded.

That is, the kinetic energy of electrons in the X-ray tube may vary according to the voltage applied to both ends of the filament and the target, and the amount of X-rays generated or the energy of X-rays may vary.

Therefore, in the case of overshoot, backswing, etc. as shown in FIG. 2, the voltage value applied to the X-ray tube is larger or lower than the high voltage value to be applied and is not kept constant. As this constantly changes, the impact energy of the electrons moving toward the target to the target is uneven or insufficient in quantity, and thus X-rays having uneven or low energy may occur.

In addition, the X-ray tube includes a window for radiating X-rays generated inside the tube to the outside to irradiate the subject, and the window is kept open even during the interval, so that unnecessary X generated in the X-ray tube The line is irradiated to the subject through the open window as it is, which may have a harmful effect on the human body or deteriorate the image quality of the X-ray detection image.

In order to emit electrons, a high voltage having a sufficient magnitude must be applied to the filament, and a preheating section that maintains the high voltage until a sufficient amount of electron clouds are formed around the filament is required. Some cause unnecessary X-rays to occur while first hitting the target, thereby reducing the X-ray emission efficiency for image diagnosis.

The present invention is to solve the problems according to the prior art described above, by using a CNT capable of emitting electrons even at room temperature as a cathode and controlling the potential applied to the gate electrode and the focusing electrode, unnecessary X-rays are generated and irradiated to the subject An object of the present invention is to provide an X-ray generator and a method of generating the same.

An X-ray generator according to an embodiment of the present invention for this purpose, the cold cathode X-ray tube for generating X-rays by emitting electrons at room temperature; And a high voltage generator for applying a voltage and a current for generating X-rays to the cold cathode X-ray tube, wherein the high voltage generator has a high voltage output value applied to both ends of the cold cathode X-ray tube. Until the ratio is greater than or equal to the gate electrode of the cold cathode X-ray tube by applying a reference potential or a negative potential to suppress the emission of electrons to improve the efficiency.

In addition, the X-ray generating method according to an embodiment of the present invention, the first step to emit electrons by applying a voltage to the cold cathode; And a second step of applying a positive potential to a gate electrode to emit electrons from the cold cathode when the voltage applied to the cold cathode rises and a voltage higher than a predetermined ratio is applied to the cold cathode. Until the target voltage reaches a predetermined ratio or more, a reference potential or a negative potential is applied to the gate electrode to prevent electrons from being emitted from the cold cathode.

In addition, in the first step, by applying a positive potential to the focusing electrode while applying the reference potential or the negative potential to the gate electrode, even if electrons are emitted from the cold cathode, it is possible to prevent collision with a target to generate unnecessary X-rays. Suppress

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

In the present specification, an X-ray generator according to the present invention will be described as an example of being applied to an X-ray imaging apparatus, but the present invention is not limited thereto and may be applied to various applications using X-rays.

In addition, when the X-ray generator according to the present invention is applied to the X-ray imaging apparatus, the sequence control device for controlling the operation of the X-ray detector and the X-ray tube and high voltage generator to detect the X-rays passing through the subject The general description of the specific configuration and operation of the module will be omitted.

3 is a diagram showing the configuration of an X-ray generator according to a preferred embodiment of the present invention.

X-ray generator according to a preferred embodiment of the present invention, as shown in Figure 3, comprises an X-ray tube and a high voltage generator (1 '), the X-ray tube is a vacuum tube, cold cathode 10, The gate electrode 15, the focusing electrode 20, and the target 30 are configured to be included. In addition, X-rays are generated as various voltages controlled by the high voltage generator 1 ′ are applied to the cold cathode 10, the gate electrode 15, the focusing electrode 20, and the target 30, respectively.

 The high voltage generator 1 ′ is a device for applying a high voltage output value to the target 30 and the cold cathode 10 or applying a voltage of negative or positive potential to the gate electrode 15 and the focusing electrode 20.

The cold cathode 10 is a cathode having a concept opposite to a hot cathode that emits electrons by heating, and supplies electrons by secondary electron emission, photoelectron emission, or electric field emission by ion bombardment without heating.

In the embodiment of the present invention, carbon nanotubes (CNTs) are applied to the cold cathode 10, and the carbon nanotubes 10 are electrons emitted by tunneling when a voltage of a predetermined size or more is applied to the gate electrode. Also, the electron emission is easy, and the electron emission response characteristic is very good, so that the time taken for the electron to be emitted from the CNT after applying the voltage to the gate electrode is very short. Therefore, it is possible to save the amount of power consumed during the preheating section, which has been required to heat the filament and form a sufficient amount of electron clouds, and the efficiency can be improved accordingly.

The CNT 10 may be disposed at one end facing the target 30 of the X-ray tube, and may be provided as a direct growth or paste type, but is not limited thereto. In addition, the W-type gate electrode 15 is disposed on the upper surface of the CNT 10.

Therefore, when a constant voltage sufficient for electron emission is applied to the gate electrode 15, electrons are emitted from the CNT 10 to form electron clouds around the CNT 10, and at both ends (cathode and anode) of the X-ray tube. When the high voltage output value is applied, the electron cloud formed by the strong electric field according to the potential difference moves quickly to the focal point of the target 30 of the anode.

Here, the cathode of the X-ray tube represents one end where the CNT 10 is disposed, and the anode of the X-ray tube represents the target 30 or one end to which the target 30 is connected.

Meanwhile, a plurality of electrons moving toward the target 30 collide with the target 30 to generate X-rays, and the focusing electrode 20 has a coin or negative potential in contrast to the gate electrode 15 of the CNT. Is applied to enable the electron cloud to focus on the target 30 focus.

4 is a graph illustrating a voltage waveform applied to an X-ray tube according to a preferred embodiment of the present invention, and FIG. 5 is a diagram illustrating an X-ray generation operation in the X-ray tube according to FIG. 4.

Even in the embodiment of the present invention in which CNTs having good electron emission response characteristics are applied to the cathode, the high voltage output value V _H applied across the CNT 10 and the target 30 is gated due to the response characteristics of the internal circuit of the high voltage generator. It has a longer response characteristic than the response characteristic of other control voltages applied to the electrode 15 or the focusing electrode 20. Therefore, as shown in FIG. 4, the voltage rise period from the time point A at which the voltage starts to be applied to the time point at which the target voltage is reached, and the time point at which the voltage of 0 V is applied from the time when the applied voltage starts to fall from the target voltage ( There is a voltage drop section up to D).

Therefore, in the high voltage generator according to the preferred embodiment of the present invention, as shown in FIG. 4, the time point at which the high voltage output value V _H applied to both ends of the cathode and the anode of the X-ray tube becomes a predetermined ratio or more than a target voltage. By controlling the voltage applied to the gate electrode 15 and the focusing electrode 20 during the period from (B) to the time (C) to be less than the predetermined ratio to improve the generation efficiency of X-rays and unnecessary X-rays to the subject Do not investigate.

In addition, the window 40 positioned near the target 30 to emit X-rays generated when the electrons collide with the target 30 to the outside is maintained in the open state only in the section BC of the predetermined ratio or more (S). In the previous section AB or the subsequent section CD, the control may be performed in a closed state to prevent X-rays not having sufficient energy from being emitted to the outside.

In particular, the high voltage generator according to the embodiment of the present invention applies a negative potential to the focusing electrode 20 in the section BC in which the window 40 is open, but in other sections, the potential V _F of the focusing electrode is increased. Voltage is applied to have a reference potential or a positive potential to cause electrons around the CNT 10 to diverge or focus towards the focusing electrode 20.

The predetermined ratio is set so that X-rays with sufficient energy are generated when the electrons emitted from the CNT 10 collide with the target 30 to be irradiated to the subject, and the electric field size formed at both ends of the X-ray tube The kinetic energy / collision energy value of the electrons varies, and the potential of the focusing electrode 20 or the open / closed state of the window 40 is determined based on the voltage value corresponding to the ratio.

Therefore, in the present specification, the predetermined ratio is 75% of the target voltage as an example, but is not limited thereto. The window 40 may be opened or the focusing electrode 20 and the gate electrode may be opened only in a section where the target voltage value is applied. When the potential of (15) is to be controlled, the ratio may be set to 100%.

Meanwhile, in the previous section AB, the reference potential is applied to the gate electrode 15 so that electrons are not emitted even when the high voltage output value V _H is applied across the X-ray tube in the previous section AB with respect to the section BC in which the window 40 is opened. Or apply a negative potential (V _G ). Since the gate electrode 15 functions to induce electron emission with respect to the CNT 10 operating as an emitter, electrons may be emitted from the CNT 10 only when a voltage having a predetermined magnitude is applied to the gate electrode 15. . Accordingly, by applying the reference potential or the negative potential (V _G ) to the gate electrode 15, it is possible to prevent electrons from being emitted from the CNT 10.

In addition, when electrons are present in the X-ray tube during the previous section AB, a reference potential or a positive potential is applied to the focusing electrode 20 to prevent these electrons from colliding with the target 30 (V _F ). Induces electrons to collect toward the focusing electrode 20.

Accordingly, the electrons can be prevented from moving toward the target 30 even when the high voltage output value V _H is not applied.

The high voltage output value V _H applied to both ends of the target 30 operating as the cathode and the anode of the CNT 10 side increases until the target voltage value is reached. When a value of 75% or more is applied (BC section), a voltage V _G of a predetermined magnitude is applied to the gate electrode 15 to emit electrons. At the same time, when the voltage V _F for the negative potential is applied to the focusing electrode 20, a plurality of electrons emitted from the CNT 10 move toward the target 30 through the focusing electrode 20, and the target 30 is moved to the target 30. X-rays are generated when colliding with the focal point.

In this case, when electrons and coin positions are applied to the focusing electrode 20 or a higher negative potential voltage is applied to induce a repulsive force, a plurality of electrons forming the electron clouds are focused and moved more precisely to the target 30 focal point. In addition, while colliding strongly with the target focus, X-rays of energy required for high-quality X-ray imaging are generated.

In addition, when the window 40 of the X-ray tube is opened in the section BC, the X-rays generated at the focus of the target 30 are emitted to the outside through the window 40 and irradiated to the external subject and penetrate the subject. As one X-ray reaches the X-ray detector, an image of the internal structure of the subject may be acquired.

After that, when the high voltage output value (V _H ) applied as the target voltage falls and is applied at a value less than 75% of the target voltage, the window in the open state is closed to prevent the X-rays from being generated and exposed to the outside. S), and the potential V _G of the gate electrode 15 is equal to or less than the reference potential. In this case, when the reference potential or the positive potential is applied to the focusing electrode 20 (V _F ), electrons existing in the X-ray tube may be emitted to the target 30.

Accordingly, in the high voltage waveform (V _H ) applied to the X-ray tube, electrons that collide with the target 30 in the X-ray tube during the rise time, overshoot, and backswing period are minimized, thereby generating harmful low-energy X-rays. By suppressing and preventing the deterioration of the image quality of the X-ray detection image, a high quality X-ray image can be obtained.

As described above, the X-ray generator and the method according to the present invention have been described with reference to the illustrated drawings, but are not limited by the embodiments and drawings disclosed herein, in the X-ray tube having a CNT as a cathode The technical idea of the present invention to appropriately adjust the potential applied to the gate electrode and the focusing electrode to prevent unnecessary X-rays from being irradiated or irradiated to an external subject and to improve the generation efficiency of X-rays is within a protected range. It will be apparent to those skilled in the art that the present invention can be easily modified.

1 is a schematic view showing the configuration of a general X-ray generator,

2 is a graph illustrating an output waveform of a general high voltage generator;

3 is a view showing the configuration of an X-ray generator according to a preferred embodiment of the present invention;

4 is a graph showing a voltage waveform applied to an X-ray tube according to a preferred embodiment of the present invention, and

5 is a diagram illustrating an X-ray generation operation in the X-ray tube according to FIG. 4.

<Explanation of symbols for the main parts of the drawings>

1: high voltage generator 10: carbon nanotube

15: gate 20: focusing electrode

30: Target 40: Windows

Claims (8)

A cold cathode X-ray tube emitting electrons at room temperature to generate X-rays; And It includes a high voltage generator for applying a voltage and current to the X-ray tube to generate a cold cathode X-ray tube, The high voltage generator is configured to prevent electron emission by applying a reference potential or a negative potential to a gate electrode of the cold cathode X-ray tube until a high voltage output value applied to both ends of the cold cathode X-ray tube becomes a predetermined ratio or more than a target voltage. X-ray generator, characterized in that. The method of claim 1, The cold cathode X-ray tube is an X-ray generator using a carbon nanotube (CNT) as a cathode. The method of claim 2, The cold cathode X-ray tube of the X-ray generator is a gate electrode is a W-type electrode disposed on the upper surface of the carbon nanotubes. The method of claim 2, The cold cathode X-ray tube includes a focusing electrode that focuses electrons emitted from the carbon nanotubes, The high voltage generator is configured to apply a positive potential to the focusing electrode while the reference potential or the negative potential is applied to the gate electrode to move the emitted electrons toward the focusing electrode when electrons are emitted. Applying a voltage to the cold cathode to emit electrons; A second step of applying a positive potential to a gate electrode when electrons are emitted from the cold cathode when the voltage applied to the cold cathode rises and a voltage higher than a predetermined ratio is applied to the cold cathode; Wherein the first step includes applying a reference potential or a negative potential to the gate electrode until the voltage reaches a predetermined ratio or more with respect to the target voltage to prevent electrons from being emitted from the cold cathode. The method of claim 5, In the first step, the positive potential is applied to the focusing electrode while applying the reference potential or the negative potential to the gate electrode. The method of claim 5, In the second step, the reference potential or the negative potential is applied to the focusing electrode while the positive potential is applied to the gate electrode. The method of claim 5, In the second step, while the positive potential is applied to the gate electrode, the window is opened so that the X-ray generated by the collision with the target is irradiated to the external subject.

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