JP4759148B2 - Apparatus and method for increasing x-ray tube power per target thermal load - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates generally to x-ray tubes, and more particularly to x-ray tubes having a higher ratio of x-ray energy flux to power applied to a target.
[0002]
[Prior art]
X-ray devices used in the medical field are typically fixed by a cathode that is heated to emit a beam of electrons, an anode having a target (usually rotating) with one surface facing the cathode, and a window mount. And an X-ray tube including a glass and / or metal surrounding frame including an X-ray transmission window. Typically, the cathode is oriented so that electrons are incident on the focal point on the target surface at an angle of approximately 90 ° to the target surface. Part of the emitted electrons enter the target surface to generate X-rays, and part of the X-rays are emitted from the frame as an X-ray beam through the X-ray transmission window. Typically, the X-ray window is arranged to receive X-rays that are spaced from the target surface at an angle of approximately 7 ° with respect to the target surface. Some of the emitted electrons are backscattered without generating X-rays when they enter the target surface. Many of the backscattered electrons subsequently enter the frame including the X-ray transmission window and the window mounting portion, and heat the frame. The frame is also heated from the inside by other heat sources such as thermal radiation. The heated frame is typically cooled by a liquid refrigerant such as oil or water located between the frame and a surrounding casing having a dedicated X-ray transmission window.
[0003]
[Problems to be solved by the invention]
Less than approximately 1 percent of the power of electrons incident on the target surface is converted to x-ray power. Increasing the power of the electron beam will increase the x-ray power output of the tube. However, increasing the power of the electron beam results in an unacceptably high thermal load on the target, ultimately limiting the X-ray power output. What is needed is an x-ray tube assembly and method for generating x-rays to increase the ratio of x-ray tube power per target thermal load.
[0004]
[Means for Solving the Problems]
In the first embodiment of the present invention, the X-ray tube assembly includes an X-ray tube anode, an X-ray tube cathode and an X-ray tube window. The anode includes an X-ray generation target having a surface. The cathode has an electron beam axis. The electron beam axis intersects the target surface at the focal point and is directed at a first angle relative to the target surface. The first angle is in the range of 15 ° to 60 °. The window includes a surface having a center point, and a line connecting the focal point and the center point forms a second angle with respect to the target surface.
[0005]
In the second embodiment of the present invention, the X-ray tube assembly includes an X-ray tube anode, an X-ray tube cathode and an X-ray tube window. The anode includes an x-ray generating target having a surface. The cathode has an electron beam axis. The electron beam axis intersects the target surface at the focal point and is directed at a first angle relative to the target surface. The first angle is in the range of 15 ° to 60 °. The X-ray tube cathode generates electrons that produce X-rays having energy less than approximately 200 kV when incident on a target. The window includes a surface having a center point, and a line connecting the focal point and the center point forms a second angle with respect to the target surface. The second angle is smaller than the first angle. The electron beam axis and center point define a plane that is oriented substantially perpendicular to the target surface.
[0006]
The first method of the present invention is a method for generating X-rays and includes steps a) to c). Step a) includes generating an electron beam having an electron beam axis. Step b) directs the electron beam to be incident on the focal point on the surface of the X-ray generation target such that the electron beam axis makes a first angle in the range of 15 ° to 60 ° with the surface of the X-ray target. And generating X-rays. Step c) involves utilizing these X-rays that form a second angle with respect to the surface of the target.
[0007]
The second method of the present invention is a method for generating X-rays and includes steps a) to c). Step a) includes generating an electron beam having an electron beam axis. Step b) directs the electron beam to be incident on the focal point on the surface of the X-ray generation target such that the electron beam axis makes a first angle in the range of 15 ° to 60 ° with the surface of the X-ray target. And generating X-rays having energy less than approximately 200 kV. Step c) utilizes X-rays that form a second angle that is less than the first angle with respect to the target surface and that, together with the electron beam axis, define a plane that is oriented substantially perpendicular to the target surface. Including doing.
[0008]
In accordance with the present invention, a first angle (usually referred to as the electron beam incident angle, but here referred to as “α”) and a second angle (commonly referred to as the X-ray emission angle, here referred to as “β”). ) Provides several benefits and advantages. For example, computer benchmark simulations performed using experimental data show an increase in X-ray energy flux of approximately 1.5 when β is equal to 7 ° and α is equal to 15 ° to 20 °. This increase is calculated relative to the X-ray energy flux according to the prior art configuration where β is 7 ° and α is 9 °. In that comparison, the power applied to the target (ie, the thermal load measured by temperature) and the focus temperature of the target are the same in both the inventive configuration and the prior art configuration, and X of the inventive configuration. It will be apparent to those skilled in the art that the line spectra are filtered to obtain the same average photon (ie, x-ray) energy as prior art configurations for proper comparison. An increase of 1.5 means that the x-ray power output for the same heat load and the same focus temperature on the target of the present configuration increased by 50 percent compared to the prior art configuration. Also, the X-ray tube of the present configuration can be operated at the same X-ray power output and lower temperature (to extend the life of the tube) compared to the X-ray tube of the prior art configuration.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings, FIG. 1 schematically illustrates one embodiment of an X-ray tube assembly 10 of the present invention. In the first embodiment shown in FIG. 1, the X-ray tube assembly 10 includes an X-ray tube anode 12, an X-ray tube cathode 14 and an X-ray tube window 16. The anode 12 includes an X-ray generation target 18 having a surface 20. The cathode 14 includes an electron beam axis 22. The electron beam axis 22 intersects the surface 20 of the target 18 at the focal point 24 and is oriented at a first angle 26 with respect to the surface 20 of the target 18. The first angle 26 is in the range of 15 ° to 60 °. The window 16 is an x-ray transmissive window and includes a surface 28 having a center point 30 as is known to those skilled in the art. The center point 30 is a geometric center point. For example, when the surface of the window has a rectangular shape, the center point is a point where diagonal lines of the rectangle intersect. A line 32 connecting the focal point 24 and the center point 30 forms a second angle 34 with respect to the surface 20 of the target 18.
[0010]
In one design example, the first angle 26 is in the range of 15 ° to 30 °, and the second angle 34 is in the range of 5 ° to 15 °. In another design example, the first angle 26 is approximately 20 ° and the second angle 34 is approximately 7 °. In describing the present invention, the term “approximately x °” means “x ° ± 2 °”. In one configuration, the electron beam axis 22 and the center point 30 typically define a plane (ie, the plane of FIG. 1) that is oriented substantially perpendicular to the surface 20 of the target 18. In describing the present invention, the term “substantially vertical” means “vertical ± 2 °”. In one example, the cathode 14 generates electrons (arranged in a line around the electron beam axis 22) that are incident on a target 18 that generates X-rays having an energy less than approximately 200 kV. Some X-rays arranged in a line around the line 32 pass through the window 16 and are used for various purposes such as medical examinations. Usually, X-rays used for medical examination have an energy of less than approximately 200 kV. In describing the present invention, the term “less than about 200 kV” means “less than 205 kV”. The electron beam axis 22 is a directivity line indicating the traveling direction of these electrons whose orbit coincides with the electron beam axis 22. The line 32 is a directional line indicating the traveling direction of the X-ray whose orbit coincides with the line 32. In one embodiment, the second angle 34 is less than the first angle 26.
[0011]
In the second embodiment shown in FIG. 1, the X-ray tube assembly 10 includes an X-ray tube anode 12, an X-ray tube cathode 14 and an X-ray tube window 16. The anode 12 includes an X-ray generation target 18 having a surface 20. The cathode 14 includes an electron beam axis 22. The electron beam axis 22 intersects the surface 20 of the target 18 at the focal point 24 and is oriented at a first angle 26 with respect to the surface 20 of the target 18. The first angle 26 is in the range of 15 ° to 60 °. The cathode 14 generates electrons that produce X-rays having an energy less than approximately 200 kV when incident on the target 18. Window 16 is an x-ray transmissive window and includes a surface 28 having a center point 30 as is known to those skilled in the art. The center point 30 is a geometric center point. A line 32 connecting the focal point 24 and the center point 30 forms a second angle 34 with respect to the surface 20 of the target 18. The second angle 34 is smaller than the first angle 26. The electron beam axis 22 and the center point 30 define a plane (ie, the plane of FIG. 1) that is oriented substantially perpendicular to the surface 20 of the target 18. In one design example, the first angle 26 is in the range of 15 ° to 30 °, and the second angle 34 is in the range of 5 ° to 15 °. In another design example, the first angle 26 is approximately 20 ° and the second angle 34 is approximately 7 °.
[0012]
The first method of the present invention is a method for generating X-rays and includes steps a) to c). Step a) includes generating an electron beam having an electron beam axis 22. In step b), the surface of the X-ray generation target 18 is directed by directing the electron beam so that the electron beam axis 22 forms a first angle 26 in the range of 15 ° to 60 ° with respect to the surface 20 of the X-ray target 18. Including incident at a focal point on 20 (having a geometric center called focal point 24) and generating X-rays. Step c) involves utilizing these X-rays that form a second angle 34 with respect to the surface 20 of the target 18.
[0013]
In one application of the first method of the present invention, the first angle 26 is in the range of 15 ° to 30 °, and the second angle is in the range of 5 ° to 15 °. In another application of the first method, the first angle 26 is approximately 20 ° and the second angle is approximately 7 °. In one example of the first method of the present invention, step c) involves using, together with the electron beam axis 22, x-rays that define a plane that is oriented substantially perpendicular to the surface 20 of the target 18. In another example of the first method, step b) includes generating X-rays having an energy less than approximately 200 kV. In one example of use, the second angle 34 is less than the first angle 26.
[0014]
The second method of the present invention is a method for generating X-rays and includes steps a) to c). Step a) includes generating an electron beam having an electron beam axis 22. In step b), the surface of the X-ray generation target 18 is directed by directing the electron beam so that the electron beam axis 22 forms a first angle 26 in the range of 15 ° to 60 ° with respect to the surface 20 of the X-ray target 18. 20 incident on a focal point on 20 (having a geometric center point called focal point 24) and generating X-rays. Step c) is a plane that forms a second angle 34 that is less than the first angle 26 with respect to the surface 20 of the target 18 and that is oriented with the electron beam axis 22 substantially perpendicular to the surface 20 of the target 18. Using X-rays that define In one application of the second method of the present invention, the first angle 26 is in the range of 15 ° to 30 ° and the second angle is in the range of 5 ° to 15 °. In another application of the second method, the first angle 26 is approximately 20 ° and the second angle is approximately 7 °.
[0015]
Applicants have identified a first angle 26 (usually referred to as the electron beam incident angle, referred to herein as “α”) and a second angle 34 (usually referred to as the X-ray emission angle, where “ Several experiments were conducted to obtain data on the increase in X-ray energy flux for various values of [beta]. “Increase” refers to the X-ray energy flux for various values of the first angle and the second angle, where the first angle 26 is 90 ° (ie, α is equal to 90 °) and the second angle 34 is Meaning divided by the X-ray energy flux obtained using a prior art configuration of 7 ° (ie β equals 7 °). Here, the power applied to the target 18 (ie, the thermal load measured at temperature) is the same for both the configuration of the present invention and the configuration of the prior art, and the X-ray spectrum of the configuration of the present invention is proper. It will be apparent to those skilled in the art that the average photon (ie, x-ray) energy is filtered to obtain the same average photon (ie, x-ray) energy as prior art configurations. An increase of 1.5 means that the x-ray power output for the same heat load and the same focal temperature at the target 18 of the present configuration is increased by 50 percent compared to the prior art configuration. Also, the X-ray tube assembly 10 of the present configuration is operated at the same X-ray power output and at a lower temperature (to extend the life of the tube) compared to the X-ray tube assembly of the prior art configuration. be able to.
[0016]
Applicants have used Monte-Carlo computer program simulation based on electron microscopy computer code optimized for 100-150 kV using experimental data for benchmarking computer programs. I did it. The results of a Monte Carlo simulation with a benchmark test show an x-ray energy flux increase where the y axis represents α (ie, the first angle 26) and the x axis represents β (ie, the second angle 34). As a -y contour map, it is presented in FIG. Surprisingly, Applicants have discovered a “sweet spot” that has an increase of at least 1.5 (ie, on and within the enclosed 1.50 contour line of FIG. 2). It is difficult to manufacture an X-ray tube with an α of less than 15 ° (ie, the first angle 26) and / or a β of less than 5 ° (ie, the second angle 34) due to mechanical and design reasons. It will be apparent to those skilled in the art. Also, mechanically and designally, a prior art X-ray tube configuration having 9 ° α and 7 ° β is modified to have an α of approximately 20 ° while maintaining β at approximately 7 °. It should also be noted that an increase in X-ray energy flux can result in close to 1.50, as is apparent from FIGS. A more extensively designed envelope that provides an improvement in x-ray energy flux increases, as is apparent from FIG. 2, with moderate mechanical redesign, α (first angle) in the range of 15 ° -30 °. 26) and β (second angle) smaller than α and in the range of 5 ° to 15 °. Although not on the scale of FIG. 2, the present applicants have found that when α is in the range of 15 ° to 60 ° and β is smaller than α, an improvement in X-ray energy flux is observed.
[0017]
The foregoing has been a description of methods and representations of embodiments of the present invention for purposes of illustration. The above description is not exhaustive and does not limit the invention to the forms disclosed. Obviously, many modifications and variations are possible in view of the above teachings. The scope of the present invention should be defined by the appended claims.
[Brief description of the drawings]
FIG. 1 is a schematic view of an embodiment of an X-ray tube assembly of the present invention.
FIG. 2 is a contour line showing an increase in X-ray energy flux for various values of α and β (denoted in °), with an azimuth angle of 0 °, with some contour lines omitted for purposes of clarity of the drawing. Figure.
FIG. 3 is a diagram illustrating the increase in X-ray energy flux for various values of α (indicated in °) when β is 7 °.
[Explanation of symbols]
10 X-ray tube structure 12 X-ray tube anode 14 X-ray tube cathode 16 X-ray tube window 18 X-ray generation target 20, 28 Surface 22 Electron beam axis 24 Focus 26 First angle 30 Center point 32 Line 34 Second angle

Claims (8)

a) an X-ray tube anode comprising an X-ray generating target having a surface;
b) an X-ray tube cathode having an electron beam axis, wherein the electron beam axis intersects the surface of the target at a focal point, and the electron beam axis is at a first angle with respect to the surface of the target. An X-ray tube cathode that is oriented and wherein the first angle is approximately 20 ° ;
c) an X-ray tube window including a surface having a center point, wherein a line connecting the focal point and the center point forms a second angle with respect to the surface of the target ; An X-ray tube structure comprising: an X-ray tube window having an angle of approximately 7 ° . The x-ray tube assembly according to claim 1, wherein the electron beam axis and the center point define a plane oriented substantially perpendicular to the surface of the target. The X-ray tube structure according to claim 1, wherein the X-ray tube structure generates X-rays having an energy of less than about 200 kV. a) an X-ray tube anode comprising an X-ray generating target having a surface;
b) an X-ray tube cathode that has an electron beam axis and generates electrons that produce X-rays having an energy of less than 200 kV when incident on the target, the electron beam axis at the focal point; An x-ray tube cathode that intersects the surface of the target and the electron beam axis is oriented at a first angle with respect to the surface of the target, the first angle being approximately 20 ° ;
An X-ray tube window including a surface having c) a center point, a line connecting the said center point and the focal point, without a second angle of approximately 7 ° relative to the surface of the target, the electronic An X-ray tube assembly comprising: a beam axis; and an X-ray tube window defining a plane in which the center point is oriented substantially perpendicular to the surface of the target. In a method for generating X-rays,
a) generating an electron beam having an electron beam axis;
b) A process of directing the electron beam and causing it to enter a focal point on the surface of the X-ray generation target to generate X-rays, wherein the electron beam axis is a first angle approximately 20 ° with respect to the surface of the target. A process of generating the X-ray, which is configured to make an angle of
c) utilizing X-rays that form a second angle of approximately 7 ° with respect to the surface of the target. The method of claim 5, wherein the electron beam axis and the center point define a plane that is oriented substantially perpendicular to the surface of the target. 7. A method according to claim 5 or 6, wherein step b) generates X-rays having an energy less than approximately 200 kV. In a method for generating X-rays,
a) generating an electron beam having an electron beam axis;
b) directing the electron beam into a focal point on the surface of the X-ray generation target to generate X-rays having an energy of less than about 200 kV, wherein the electron beam axis is incident on the surface of the target Generating X-rays at a first angle of about 20 ° with respect to the X-rays;
c) These X-rays defining a plane that forms a second angle of approximately 7 ° with respect to the surface of the target and that, together with the electron beam axis, is oriented substantially perpendicular to the surface of the target. And a process comprising:

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