A high power X-ray tube

Abstract

The present invention relates to an X-ray tube and a CT system using the X-ray tube. The X-ray tube has a vacuum chamber surrounded by a vacuum chamber wall, a cathode is arranged at one end of the vacuum chamber, and an anode target disk is arranged at the other end of the vacuum chamber. An electron beam is emitted from the cathode and hits the anode target disk at a high speed at a focal position, thereby exciting and generating X-rays. The X-ray tube has a control component, characterized in that: the anode target disk is a fixed anode target disk, and when the X-ray tube is working, the control component controls the focal position of the electron beam on the fixed anode target disk to change rapidly. The present invention adopts a fixed anode target disk, and by quickly changing the focal position of the electron beam on the fixed anode target disk, a peak power similar to that of a rotating target can be achieved. The scheme of the present invention can reduce the vacuum rotating component, and has the characteristics of a very simple structure. The scheme of the present invention can directly cool the target disk by oil, so that the effect of continuous operation can be achieved, and the stability of the system can be improved.

Description

Technical Field

[0001] The present invention relates to a high power X-ray tube for medical or industrial CT or two-dimensional imaging or quasi-three-dimensional imaging (such as limited-angle three-dimensional imaging). Background Art

[0002] X-ray tubes are mainly used in medical or industrial equipment such as X-ray machines and CT machines. When an external high voltage is applied, they generate X-rays for doctors to diagnose or treat patients or perform non-destructive testing on objects.

[0003] The power of an X-ray tube can range from a few kilowatts to 150 kilowatts. The X-ray tube has a fixed target, and a high-energy electron beam (60kV to 500kV) bombards the target to produce X-rays. In an X-ray tube, a high-energy electron beam is fired from the cathode to the anode target to produce X-rays, of which less than 1% of the energy is converted into X-ray radiation, and the other 99% of the energy is converted into heat energy at the anode, causing the temperature of the impacted part to rise rapidly.

[0004] In a fixed anode X-ray tube, electrons continuously hit the same position, causing the local temperature of the fixed anode X-ray tube to rise rapidly. Although it can be continuously loaded, the power is very low. In view of this, whether the heat energy generated by the X-ray tube when it is working can be conducted away in time has become a decisive factor restricting the continuous power of the X-ray tube (especially the fixed anode X-ray tube). In practical applications, the anode temperature of the X-ray tube is often too high, causing the target surface to crack or melt, and the anode temperature is too high, causing ignition inside the tube and cracking of the insulating oil, which seriously affects the working stability and service life of the product.

[0005] At present, the high-power target disks used in CT are all rotating anode targets. The rotating anode target adopts the method of driving the anode target disk to rotate at high speed in the vacuum tube shell by the anode bearing, thereby dispersing the heat to the entire target disk. The advantage of the rotating target is that the peak power can be very high, but the continuous power is not high, and this structure is very complicated, and the vacuum bearing is used, which is very easy to break. The heat conduction capacity of the bearing is very poor. After the CT scans the patient continuously, it may have to stop and cool down because the target disk is too hot. Under high vacuum conditions, the heat on the rotating anode X-ray tube target disk is mainly transferred to the vacuum tube shell through thermal radiation, and then the heat is taken away by the coolant flowing through the tube shell. At the same time, part of the heat is inevitably transferred to the anode bearing through heat conduction and heat radiation, causing the temperature of the metal ball to rise. If the heat transferred by heat conduction or heat radiation is too much, the metal ball will exceed the limit operating temperature, which will cause the bearing to get stuck, resulting in the failure of the entire X-ray tube. Summary of the invention

[0006] Based on the problems existing in the prior art, the technical problem to be solved by the present invention is to provide a high-power non-rotating target disk X-ray tube, which has a simple structure and good heat dissipation efficiency, can improve the heat dissipation efficiency of the X-ray tube, quickly dissipate the heat on the anode target, and extend the service life of the X-ray tube.

[0007] The present invention provides an X-ray tube, which has a vacuum chamber surrounded by a vacuum chamber wall, a cathode is arranged at one end of the vacuum chamber, and an anode target plate is arranged at the other end of the vacuum chamber. An electron beam is emitted from the cathode and strikes the anode target plate at a high speed at a focal position, thereby exciting and generating X-rays. The X-ray tube has a control component, which is characterized in that: the anode target plate is a fixed anode target plate, and when the X-ray tube is working, the control component controls the electron beam to rapidly change the focal position on the fixed anode target plate.

[0008] Furthermore, in the X-ray tube of the present invention, the control assembly includes a deflection and focusing magnetic pole assembly, and the focus position of the electron beam on the fixed anode target disk is changed by the deflection and focusing magnetic pole assembly.

[0009] Furthermore, two pairs of dipole electromagnets are located downstream of the cathode. The magnetic field range generated by the two pairs of dipole electromagnets can make the deflection range of the electron beam cover the entire area of ​​the fixed anode target disk.

[0010] Furthermore, one or more quadrupole electromagnets are superimposed at the same position or at different positions before and after the dipole electromagnet, which can achieve a better focusing effect on the electron beam and keep the size of the target spot optimized.

[0011] Furthermore, the X-ray tube has a plurality of cathodes, and the control component includes cathode switches corresponding to the plurality of cathodes one by one, and the focus position of the electron beam on the fixed anode target plate is rapidly changed by controlling the on or off of each cathode switch.

[0012] Furthermore, the cathode is a cold cathode or a hot cathode. A cold cathode is a cathode that emits electrons through the field emission effect by applying a strong electric field to the cathode surface. A hot cathode is a filament that is heated by current to increase the energy of electrons in the filament. Under an external electric field, electrons are emitted by crossing the potential barrier of the filament material.

[0013] Furthermore, a pair of electrodes or two pairs of electrodes or a pair of dipole electromagnets or two pairs of dipole electromagnets or one or two quadrupole electromagnets are provided downstream of each cathode to generate a strong electrostatic field or magnetic field, thereby achieving a deviation of the electron beam by half a pixel distance in one or two directions of the fixed anode target plate.

[0014] Furthermore, the jumping positions of the electron beam of the present invention between different points on the fixed anode target disk can be each time separated by a fixed distance or generated according to a specific algorithm or the next target point jumped to can be the farthest from a weighted average position of several previous target points.

[0015] Furthermore, the surface of the fixed anode target plate bombarded by the electron beam is a layer of tungsten material with a thickness of several microns to several hundred microns, and a layer of transition material in the middle. The requirements for the transition material are that the melting point is relatively high, the thermal conductivity coefficient is high, and the thermal expansion coefficient is between tungsten and the high thermal conductivity material on the outside. This material can be but is not limited to aluminum nitride (AlN), silicon carbide (SiC) or other high-temperature materials with a thickness of several microns to tens of microns. Another function of this material is to act as a transition layer to reduce the stress caused by thermal expansion between the tungsten material and the outermost thermal conductive material. The outermost material is a material with high thermal conductivity. These materials may include but are not limited to diamond, copper, silver, gold and other materials.

[0016] Under certain conditions, the tungsten coating can be directly plated on the outermost material with the highest thermal conductivity without using an intermediate transition material.

[0017] The present invention also provides a CT system, which has the aforementioned X-ray tube, an X-ray detector, a CT frame, and a computer system; wherein the computer system can control the cathode and the deflection and focusing magnetic pole components in the X-ray tube in real time to realize the formation of target points of the electron beam at different positions on the fixed anode target surface; the computer system also has an image processing module, which can reconstruct multiple two-dimensional images collected by the detector into three-dimensional images or other suitable expressions.

[0018] Furthermore, during the CT scanning process, the electron beam is moved in the direction opposite to the rotation of the CT during each two-dimensional imaging process to reduce the change in the spatial position of the electron beam target during each two-dimensional imaging process or to keep the spatial position of the electron beam target unchanged. The controller records the position of the focus of each X-ray, and the position information is used to create a three-dimensional image during the reconstruction process.

[0019] Beneficial effects of the present invention:

[0020] 1. The present invention adopts a fixed anode target disk. By quickly changing the focus position of the electron beam on the fixed anode target disk, the peak power similar to that of a rotating target can be achieved. The scheme of the present invention can reduce the vacuum rotating components and has the characteristics of a very simple structure. The scheme of the present invention can directly cool the target disk by oil, thereby achieving a continuous working effect and improving the stability of the system;

[0021] 2. The solution of the present invention can further optimize the algorithm of focus jump to maximize the heat dissipation efficiency of the fixed anode target plate;

[0022] 3. The present invention can increase the number of focal points on the fixed anode target plate by the half pixel distance of the electron beam deflection, and can significantly improve the spatial resolution;

[0023] 4. The present invention allows the electron beam to move in the direction opposite to the rotation of the CT during each two-dimensional imaging, thereby reducing the change in the spatial position of the electron beam target during each two-dimensional imaging process or keeping the spatial position of the electron beam target unchanged, which can further improve the spatial resolution.

[0024] The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0026] Figure 1 is a schematic diagram of an X-ray tube according to an embodiment of the present invention;

[0027] Figure 2 is a schematic diagram of an electromagnet in one embodiment of the present invention;

[0028] Figure 3 is a schematic diagram of a fixed anode target plate according to an embodiment of the present invention;

[0029] Figure 4 is a schematic diagram of a CT system equipped with an X-ray tube of the present invention;

[0030] Figure 5 FIG. 1 is a schematic diagram of the focus of a fixed anode target according to an embodiment of the present invention.

[0031] The following are the descriptions of the reference numerals:

[0032] 1- cathode; 2- fixed anode target; 3- vacuum chamber wall; 4- electron beam; 5- deflection and focusing magnetic pole assembly. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0034] Embodiment 1

[0035] The present invention provides an X-ray tube, which has a vacuum chamber surrounded by a vacuum chamber wall, a cathode is arranged at one end of the vacuum chamber, and an anode target plate is arranged at the other end of the vacuum chamber. An electron beam is emitted from the cathode and strikes the anode target plate at a high speed at a focal position, thereby exciting and generating X-rays. The X-ray tube has a control component, which is characterized in that: the anode target plate is a fixed anode target plate, and when the X-ray tube is working, the control component controls the focal position of the electron beam on the fixed anode target plate to change rapidly, thereby generating an effect of rapid scanning of the electron beam on the fixed anode target plate.

[0036] The present invention produces an effect of rapid scanning of the electron beam on the fixed anode target disk by changing the focal position of the electron beam on the fixed anode target disk, thereby forming the effect of a virtual rotating target; the focal position of the electron beam changes rapidly, so that the residence time of the electron beam at a single position on the anode target disk is very short, and the rapid change of the focal position of the electron beam can disperse the heat to the entire area of ​​the anode target disk, thereby ensuring that the anode target disk has a better cooling effect.

[0037] For further information, see Figure 1 The control assembly of the X-ray tube of the present invention includes a deflection and focusing magnetic pole assembly 5, which can change the focal position of the electron beam 4 on the fixed anode target plate 2 to achieve rapid scanning of the electron beam;

[0038] More specific:

[0039] The cathode is a hot cathode, which is made of tungsten, molybdenum, tantalum or other materials with low work function. The cathode material is heated to a temperature of thousands of degrees. The electron beam escapes from the cathode material and hits the fixed anode target disk under the drive of a strong electric field. There can be one or more hot cathodes, such as two, three or five. Downstream of the hot cathode are two pairs of dipole electromagnets, which can deflect the electron beam in a larger range. The magnetic force range of the two pairs of dipole electromagnets can make the deflection range of the electron beam cover the entire area of ​​the fixed anode target disk, thereby forming a very tightly arranged electron beam focus position on the fixed anode target disk.

[0040] Furthermore, one or more quadrupole electromagnets may be arranged at the overlapped position of the two pairs of dipole electromagnets, for example, Figure 2 As shown, a quadrupole electromagnet is also arranged at the overlap of two pairs of dipole electromagnets, and the quadrupole electromagnet can control the size of the focus in the width and length directions. The above-mentioned dipole and quadrupole electromagnets can be wound on an iron core and can share windings to form a combined magnet. Two such combined magnets can be used to accurately control the length and width of the X target point.

[0041] In this manner, the cathode may also be a cold cathode, in which a strong electric field is applied to the cathode surface, and electrons are emitted from the cathode through the effect of field emission.

[0042] Furthermore, the fixed anode target disk is a material that can withstand high power and has a very fast heat dissipation function. It is composed of one or several different materials. One composition is as follows: the surface of the fixed anode target disk bombarded by the electron beam is a layer of tungsten material, the thickness of which can range from several microns to several hundred microns, and a layer of transition material in the middle. The requirements for the transition material are that the melting point is relatively high, the thermal conductivity coefficient is high, and the thermal expansion coefficient is between tungsten and the high thermal conductivity material outside. This material can be but is not limited to aluminum nitride (AlN), silicon carbide (SiC) or other high-temperature materials, with a thickness of several microns to tens of microns. Another function of this material is to act as a transition layer to reduce the stress caused by thermal expansion between the tungsten material and the outermost thermal conductive material. The outermost is a material with high thermal conductivity. These materials can include but are not limited to diamond, copper, silver, gold and other materials.

[0043] The size of the fixed anode target plate can range from a few centimeters to more than ten centimeters square, and can be rectangular or circular.

[0044] Figure 3 A possible focus distribution form of a fixed anode target disk is shown. The focus of the X-rays emitted by the fixed anode target disk is very densely and evenly or non-uniformly distributed on the target, such as Figure 3 As shown in (a) in the figure, the X-ray focal points are located very closely together, and adjacent focal points can be completely adjacent to each other or even partially overlap. The number of focal points ranges from a few to hundreds. Partially overlapping focal points can be controlled very precisely, with a difference of only half a pixel, such as Figure 3 As shown in (b), this can improve the imaging resolution of CT. The distribution range of the focus can reach more than ten centimeters to the left and right (X direction) and several centimeters up and down (Z direction). The size of the X-ray tube is very small. A CT is equipped with one or more X-ray tubes, which can provide multiple cathode emission high-voltage power supplies and detectors.

[0045] like Figure 4 As shown in the figure, during the CT operation, the CT bracket, X-ray tube and detector can rotate at a speed of 0.5 to 4 turns per second. During the rotation, the focus of the electron beam keeps jumping at these possible positions. The time at each focus position is very short, such as tens of microseconds, and then it jumps to the next position, so that the temperature of the focus on the fixed anode target plate will not rise too quickly. The CT scanning process obtains hundreds to thousands of projections, and the reconstruction algorithm automatically creates a three-dimensional image based on the projections and angle position information.

[0046] The schematic diagram of X-ray jumping between different points on the fixed anode target is as follows Figure 3 As shown in (c), it can be a sequential jump, or by controlling random jumps, for example, Figure 3The numbers indicated in (c) can be jumped in sequence, or optimized according to a certain algorithm.

[0047] Furthermore, the jumping positions of X-rays between different points on the fixed anode target plate are optimized using a certain algorithm, so that the target can withstand the maximum power or the temperature of the target surface is kept at the lowest. For example, there is an algorithm that makes the next target point to jump to be the farthest from the weighted average position of several previous target points. For example, if N target points are selected last time, the weighted average position of N target points is calculated first. Then the position of the N+1th target point is P N+1 =Pi, the choice of i is to maximize the distance in the following formula:

[0048]

[0049] Furthermore, the focus jump changes are divided into two levels:

[0050] The first level is to use 4 relatively close points as a group of focal points, two in the Z and X directions, and the spacing of a group of 4 focal points is half of the CT detector pixel or (the specific value is adjusted with the position of the imaging center). In a two-dimensional imaging process, the focus position jumps at these 4 focus positions, which can increase the spatial resolution. This setting of deviating the focus by half a pixel distance can increase the spatial resolution of CT. Since under the condition that other conditions remain unchanged (same X-ray focus size, same detector pixel size, etc.), this setting of deviating the focus by half a focus distance is equivalent to doubling the number of X-ray focus positions, and the added X-ray focus position is in the middle of the original X-ray focus position, so that the number of X-ray focus is doubled, and the spacing between each focus is half of the original, which can increase the spatial resolution.

[0051] The second level is large-scale jumps, that is, in the process of imaging different two-dimensional images, the spatial position of the focus changes greatly, the focus jumps far, and the longer the interval, the more conducive to heat dissipation.

[0052] As a specific embodiment, please refer to the attached Figure 5 To illustrate the two-level beating mode of the present invention, for example, the beating can be performed in the four focal points of each small area and then transferred to other distant areas for the next group of four beatings, corresponding to the attached Figure 5 The beats are arranged according to 11-12-13-14-21-22-23-24.

[0053] As other optional embodiments, the change of the electron beam focus of the present invention can be any combination of the jump of the second layer in a large range and the jump of the first layer in a small range. For example, it can also be according to the attached Figure 5The beating sequence shown is 11-21-31-41-12-22-32-42-13-23-33-43-14-24-34-44.

[0054] Embodiment 2

[0055] According to another embodiment of the present invention, a plurality of cathodes are provided, and the control assembly includes cathode switches corresponding to the plurality of cathodes one by one, and the focus position of the electron beam on the fixed anode target disk is rapidly changed by controlling the on or off of each cathode switch, thereby realizing rapid scanning of the electron beam; more specifically:

[0056] The cathode is a cold cathode. A strong electric field is applied to the cathode surface, and electrons are emitted from the cathode through the effect of field emission. Multiple cathodes are set up, corresponding to the number of focal points. Each focal position has a corresponding cathode. In this way, there is no need for a deflection system, but only a cathode switch is used to control the cathode on or off, so that the electron beam can generate targets in different places.

[0057] Furthermore, for multiple cathodes in this manner, a pair of electrodes or two pairs of electrodes or a pair of dipole electromagnets or two pairs of dipole electromagnets or one or two quadrupole electromagnets are also provided downstream of each cathode, which can generate a strong electrostatic field or magnetic field, thereby achieving the electron beam deviating by half a pixel distance in one or two directions of the fixed anode target plate.

[0058] The setting of making the focus deviate by half a pixel distance can increase the spatial resolution of CT. Under the condition that other conditions remain unchanged (same X-ray focus size, same detector pixel size, etc.), the setting of making the focus deviate by half a focus distance is equivalent to doubling the number of X-ray focus positions, and the additional X-ray focus position is in the middle of the original X-ray focus position. In this way, the number of X-ray focus is doubled, and the spacing between each focus is half of the original, which can increase the spatial resolution.

[0059] Embodiment 3

[0060] The present invention also provides a CT system, comprising the aforementioned X-ray tube, an X-ray detector, a CT frame, and a computer system; wherein the computer system can control the control components in the X-ray tube in real time to enable the electron beam to form target points at different positions on the fixed anode target surface; the computer system also has an image processing module that can reconstruct multiple two-dimensional images collected by the detector into three-dimensional images or other suitable expressions.

[0061] Furthermore, during the CT scanning process, the electron beam is moved in the opposite direction of the CT rotation during each two-dimensional imaging, thereby reducing the spatial position change of the electron beam target during each two-dimensional imaging process.

[0062] During the CT rotation process, during each two-dimensional imaging process, the focus on the fixed anode target disk is moving, following the rotation of the CT bracket. For example, during a two-dimensional imaging process, it moves about 2 mm. This follow-up movement of the focus will lead to a reduction in the resolution of the CT image. The X-ray tube of the present invention has the function of deflecting the electron beam, which can make the electron beam move in the opposite direction of the CT rotation during each two-dimensional imaging, so that the position of the target in space can remain unchanged or reduce changes during each two-dimensional imaging process. This will help improve the spatial resolution of the CT image.

[0063] The speed of the focus can be adjusted using the following formula:

[0064] V F =-α×ω CT ×R CT

[0065] ω CT : Angular frequency speed of CT gantry rotation

[0066] R CT : Radius from focus to CT center

[0067] V F :Focus moving speed

[0068] α: optimization factor, ranging from 0 to 2

[0069] It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or apparatus.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations, and the scheme of replacing and combining some features between multiple embodiments of the present invention is also within the scope of the disclosure of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An X-ray tube, comprising a vacuum chamber surrounded by a vacuum chamber wall, a cathode disposed at one end of the vacuum chamber, and an anode target disposed at the other end of the vacuum chamber, wherein an electron beam is emitted from the cathode and strikes the anode target at a high speed at a focal position, thereby exciting and generating X-rays, the X-ray tube comprising a control assembly, characterized in that: The anode target disk is a fixed anode target disk. When the X-ray tube is working, the control component controls the focus position of the electron beam on the fixed anode target disk to change rapidly. The position change algorithm of the electron beam between different points on the fixed anode target disk includes making the next target point to be jumped to be the farthest from a weighted average position of several target points last time. The method of making the next target point to be jumped to be the farthest from a weighted average position of several target points last time includes selecting N target points last time, first calculating the weighted average position of the N target points, and then the position of the N+1th target point is P N+1 =Pi, the choice of i is to maximize the distance in the following formula:

2. The X-ray tube according to claim 1, characterized in that: The control component comprises a deflection and focusing magnetic pole component, and the focus position of the electron beam on the fixed anode target disk is changed by the deflection and focusing magnetic pole component.

3. The X-ray tube according to claim 2, characterized in that: Downstream of the cathode are two pairs of dipole electromagnets. The magnetic field range generated by the two pairs of dipole electromagnets can make the deflection range of the electron beam cover the entire area of ​​the fixed anode target disk.

4. The X-ray tube according to claim 3, characterized in that: One or more quadrupole electromagnets are superimposed at the same position or at different positions before and after the dipole electromagnet.

5. The X-ray tube according to claim 1, characterized in that: The invention has a plurality of cathodes, and the control component comprises cathode switches corresponding to the plurality of cathodes one by one, and the focus position of the electron beam on the fixed anode target plate is rapidly changed by controlling the on or off of each cathode switch.

6. The X-ray tube according to claim 5, characterized in that: A pair of electrodes or two pairs of electrodes or a pair of dipole electromagnets or two pairs of dipole electromagnets or a quadrupole electromagnet or two quadrupole electromagnets are also arranged downstream of each cathode to generate a strong electrostatic field or magnetic field, thereby achieving the electron beam deviating by a distance of half a pixel in one or two directions of the fixed anode target disk.

7. A CT system, characterized in that: An X-ray tube as claimed in any one of claims 1 to 6, further comprising a detector, a CT rack and a computer system; wherein the computer system controls the control components in the X-ray tube in real time to realize that the electron beam forms target points at different positions on the fixed anode target surface; the computer system also has an image processing module, which can reconstruct multiple two-dimensional images collected by the detector into a three-dimensional image.

8. The CT system according to claim 7, characterized in that: During the CT scanning process, the electron beam is moved in the opposite direction of the CT rotation during each two-dimensional imaging process to reduce the change in the spatial position of the electron beam target or keep the spatial position of the electron beam target unchanged during each two-dimensional imaging process.

Images