Patent Application
20250087439
The invention relates generally to X-ray tubes and, more particularly, to structures and methods of construction for the anode utilized in an X-ray tube.
X-ray systems, including computed tomography (CT) imaging systems, may include an X-ray tube, a detector, and a support structure for the X-ray tube and the detector. In operation, an imaging table, on which an object is positioned, may be located between the X-ray tube and the detector. The X-ray tube typically emits radiation, such as X-rays, toward the object. The radiation passes through the object on the imaging table and impinges on the detector. As radiation passes through the object, internal structures of the object cause spatial variances in the radiation received at the detector. The detector then generates data, and the system translates the data into an image, which may be used to evaluate the internal structures of the object. The object may include, but is not limited to, a patient in a medical imaging procedure or an inanimate object as in, for instance, a package.
X-ray tubes include a cathode and an anode having an anode target located within a high-vacuum environment. The anode is disposed in front of the cathode so that the focused electron beam from the cathode is accelerated across a cathode-to-anode vacuum gap and produces X-rays upon impact with the focal spot on the anode target. Electrons from the cathode hit successively different points of the anode target to reduce the maximum temperature reached locally by the anode target. In many configurations the anode is a circular material piece supported by a bearing structure to enable the anode to rotate in front of the cathode. Because of the high temperatures generated when the electron beam strikes the anode target, it is often necessary to rotate the anode assembly at a high rotational speed, causing the focal spot to be directed onto the rotating anode target along a focal spot track defined by the path of the focal spot along the rotating anode target, where the length L of the focal spot defines the width W of the focal spot track extending around the perimeter of the anode target.
As shown in
When a larger anode 1000 is desired to further increase the instant peak power on focal spot, due to weight considerations for a rotating anode 1000, the anode 1000 is made of two or more materials. In particular, the material forming the support member 1004 can be selected to be a lighter material than if the support member 1004 were designed to directly emit X-rays. In order to emit X-rays from the anode 1000, the support member 1004 is coated with a layer of an emission material 1008 having properties suitable for the emission of X-rays when struck by the beam of electrons from the cathode. The layer of electron emissive material 1008 has width between an outer diameter 1011 and an inner diameter 1013 of the support member 1004 of between 70 mm and 200 mm, such that the emissive material layer 1008 is disposed substantially over the entire surface 1010 of the support member 1004 that faces or positioned towards the cathode and the electron beam generated by the cathode. The electron beam is directed by the cathode onto a focal spot 1015 that is projected along a focal spot track 1012 on the layer of emissive material 1008 as the anode 1000 is rotated in order to direct the X-ray emitted from the emission material towards the desired area of the object being imaged and the detector. The size of the focal spot track 1012 can vary depending upon type or modality of imaging being performed by the X-ray tube including the anode 1000, as illustrated on the drum anode 1014 shown in
While many of the electrons 1020 in the electron beam striking the emissive material layer 1008 cause the emissive material to emit X-rays 1022 within the focal spot track 1012. other electrons 1024 striking the emissive material layer 1008 can bounce or rebound off of the emissive material layer 1008, as shown in
Therefore, it is desirable to develop an improved anode structure that significantly limits the generation of off focus radiation and that can significantly reduce the material costs associated with the construction of the anode.
In one exemplary embodiment of the invention, an anode for an X-ray tube has a rotating component, a body operably connected to the rotating component and adapted to rotate in conjunction with the rotating component, and at least one emissive material track defined on the body wherein the at least one emissive material track has a first width, and wherein the first width is less than or equal to twice a second width of a focal spot track on the body.
In another exemplary embodiment of the invention, an X-ray tube has a cathode assembly, and an anode assembly spaced from the cathode assembly, wherein the anode assembly includes a shaft, a sleeve disposed on the shaft, wherein one of the shaft and the sleeve is rotatable with regard to the other to form a rotating component and a stationary component, a body attached to the rotating component, and at least one emissive material track disposed on the body, wherein the at least one emissive material track has a first width, wherein the first width is less than or equal to twice a second width of a focal spot track on the body.
In still another exemplary embodiment of the disclosure, a method for minimizing off focus radiation generated in an imaging procedure using an X-ray tube includes the steps of providing an X-ray tube having a cathode assembly, and an anode assembly spaced from the cathode assembly, wherein the anode assembly includes a shaft, a sleeve disposed on the shaft, wherein one of the shaft and the sleeve is rotatable with regard to the other to form a rotating component and a stationary component, a body attached to the rotating component; and at least one emissive material track defined on the body, wherein the at least one emissive material track has a first width, and wherein the first width is less than or equal to twice a second width of a focal spot track on the body, directing the electron beam from the cathode assembly onto at least one the emissive material track along the focal spot track, and enabling electrons from the electron beam bouncing off of the emissive material track to contact the body on either side of the at least one emissive material track, wherein the emissive material track is formed of a material having a first atomic number and wherein the body is formed of a material having a second atomic number and wherein a ratio of the first atomic number to the second atomic number is at least 6.
It should be understood that the brief description above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.
As shown in
A processor 20 receives the signals from the detector 18 and generates an image corresponding to the object 16 being scanned. A computer 22 communicates with processor 20 to enable an operator, using operator console 24, to control the scanning parameters and to view the generated image. That is, operator console 24 includes some form of operator interface, such as a keyboard, mouse, voice activated controller, or any other suitable input apparatus that allows an operator to control the X-ray system 10 and view the reconstructed image or other data from computer 22 on a display unit 26. Additionally, console 24 allows an operator to store the generated image in a storage device 28 which may include hard drives, floppy discs, compact discs, cloud data storage, etc. The operator may also use console 24 to provide commands and instructions to computer 22 for controlling an X-ray source controller 30 that provides power and timing signals to X-ray source 12.
In operation, an electron beam 54 is produced by cathode assembly 44. In particular, cathode 52 receives one or more electrical signals via a plurality of electrical leads 56. The electrical signals may include power and timing/control signals that cause cathode 52 to emit electron beam 54 at one or more energies and at one or more frequencies. The electrical signals may also at least partially control the potential between cathode 52 and anode 48. Cathode 52 includes an insulator 58 from which an arm 60 extends. Arm 60 encloses electrical leads 56, which extend into a cathode cup 62 mounted at the end of arm 60. In some embodiments, cathode cup 62 includes focusing elements that focuses electrons emitted from a filament within cathode cup 62 to form electron beam 54.
X-rays 64 are produced when high-speed electrons of electron beam 54 from cathode 52 are suddenly decelerated upon impacting a focal spot/target surface 66 formed on anode target 48. The high-speed electrons forming electron beam 54 are accelerated toward the anode target 48 via a potential difference therebetween of, for example, twenty (20) to one hundred and sixty (160) kV for medical diagnostic imaging, including sixty (60) kV or more in the case of CT applications. The X-rays 64 are emitted through a radiation emission window 68 formed in frame 46 that is positioned toward a detector array, such as detector 18 of
Anode assembly 42 includes a rotor 72 and a stator (not shown) located outside X-ray source 40 and partially surrounding rotor 72 for causing rotation of anode/anode target 48 during operation. Anode target 48 is supported in rotation by a bearing assembly 50, which, when rotated, also causes anode target 48 to rotate about a centerline 70. As shown, anode target 48 has a generally annular shape, such as a disk, and an annular opening 74 in the center thereof for receiving bearing assembly 50.
Target 48 may be manufactured to include one or more metals or composites, such as tungsten, molybdenum, or any material that emit X-rays when bombarded with electrons. Target surface 66 of anode target 48 is selected to have a relatively high refractory value so as to withstand the heat generated by electrons impacting target surface 66, with the main properties for this selection being 1) melting temperature and 2) thermal conduction. In addition, to respect previous requirement of X-ray generation, the selected material must have an atomic number Z high enough with regards to the desired X-rays, for example, a Z as high as possible for Bremsstrahlung only, or with a specific Z if a specific or characteristic radiation to be generated is desired. Further, the space within insert or frame 46 and between cathode assembly 44 and anode assembly 42 is at vacuum pressure in order to avoid electron collisions with other atoms and to maximize an electric potential.
To avoid overheating of the target 48 when bombarded by the electrons, rotor 72 rotates target 48 at a high rate of speed (e.g., 50 to 250 Hz) about a centerline 70.
Bearing assembly 50 can be formed as necessary, such with a number of suitable ball bearings (not shown), but in the illustrated exemplary embodiment comprises a liquid lubricated or self-acting bearing, such as a liquid metal bearing, having adequate load-bearing capability and acceptable acoustic noise levels for operation within imaging system 10 of
In general, bearing assembly 50 includes a stationary component, such as shaft 76, and a rotating component, such as sleeve 78 that surrounds the shaft 76 and to which the anode/anode target 48 is attached. While shaft 76 is described with respect to
Referring now to
On a target surface 66 of the body 100 that is positioned to face the cathode 54 within the path of the electron beam 52 remitted from the cathode 54, the anode 48 includes an emissive material track 104 disposed thereon. The emissive material track 104 is formed of a suitably emissive material, including but not limited to tungsten and/or rhodium. In an exemplary embodiment of the disclosure, the difference between a first atomic number Z1 of the material forming the emissive material track 104 and a second atomic number Z2 of the relatively non-emissive material forming the body 100, or any other material 103 that is disposed on the surface 101 between the emissive material track 104 and the body 100 that is different than the material forming the body 100, should be at least 3% or more, or in another exemplary embodiment at least 7% or more, with the material forming the emissive material track 104 being higher in each case. In still a further exemplary embodiment, the ratio between the first atomic number Z1 of the material forming the emissive material track 104 and the second atomic number Z2 of the relatively non-emissive material forming the body 100, or any other material 103 that is disposed on the surface 101 between the emissive material track 104 and the body 100 that is different than the material forming the body 100, can be at least greater than 6, and in another exemplary embodiment is at least greater than 12, again with the material forming the emissive material track 104 being higher in each case. In one exemplary embodiment, the relatively non-emissive material forming the body 100 or material 103 is molybdenum, molybdenum alloy, or carbon, and the emissive material track 104 is formed from rhodium or tungsten alloy. In another exemplary embodiment, for medical imaging applications, highly emissive materials are molybdenum (Z=42) or rhodium (Z=45), in particular if their characteristic radiation spectrum is looked for, as in mammography, and in all applications, from mammography to CT etc., tungsten (Z=74) is preferred, alone or alloyed with rhenium (Z=75).
The emissive material track 104 is positioned on the body 100 to cover and/or encompass the focal spot track 106 followed by the focal spot 107 to be struck by the electron beam 52 as it moves due to rotation of the anode 48 during the operation of the X-ray source 40. The emissive material track 104 can be attached to the body 100 in any suitable manner, such as by welding or brazing the emissive material track 104 to the body 100, or by depositing material forming the emissive material track 104 directly onto the body 100 in a suitable manner to form the emissive material track 104.
In the illustrated exemplary embodiments, the emissive material track 104 has a planar, generally circular ring shape to extend round the body 100 along the entire path of the focal spot track 106, i.e., the track or path of the focal spot/target surface 66 along the anode 48 as the anode is rotated during operation of the X-ray tube 12, during rotation of the anode 48, with an inner diameter ring 108 and an outer diameter ring 110. The first width or width W1 of the emissive material track 104 between the inner ring 108 and the outer ring 110 is larger than the second width or width W2 of the focal spot track 106, as defined by the length L1 of the focal spot 107 defining the focal spot track 106, such that the entire focal spot track 106 can be encompassed within the width W1 emissive material track 104. Further, the width W1 of the emissive material track 104 is significantly less than the radius R of the body 100 from the shaft 76 or sleeve 78 secured to the body 100 to a peripheral edge 115 of the body.
With this configuration for the emissive material track 104, referring to the schematic cross-sectional view of the anode 48 in
In an exemplary embodiment for the emissive material track 104, the width W1 of the emissive material track 104 is determined to be between less than or equal to about two (2) times or less than or equal to about one and a half (1.5) times the width W2 of the focal spot track 106. Further, in another exemplary embodiment, the emissive material track 104 extends outwardly to each side of the width W2 of the focal spot track a specified distance, such that the edges of the focal spot track 106 are spaced inwardly from each of the inner ring 108 and the outer ring 110 of the emissive material track 104.
In one exemplary embodiment, as the width W2 of the focal spot track 106 can be between about 0.10 mm to about 10.0 mm, the corresponding width W1 of the emissive material track 104 between the inner ring 108 and the outer ring 110 can be between about 0.15 mm and 15.0 mm. In another alternative exemplary embodiment, the width W1 of the emissive material track 104 between the inner ring 108 and the outer ring 110 can be between about 0.20 mm and 20.0 mm for the same width W2 of the focal spot track 106. In one particular exemplary embodiment, the emissive material track 104 has a width W1 of up to about 25 mm for the same width W2 of the focal spot track 106. In another particular exemplary embodiment, the emissive material track 104 can have an outer ring 110 that conforms to a peripheral edge 115 of the body 100, such that the emissive material track 104 can wrap around outer edge 115 of the body 100.
In still another alternative exemplary embodiment, regardless of the actual width of the emissive material track 104, the focal spot track 106 is centered within the emissive material track 104. In still a further alternative exemplary embodiment, the emissive material track 104 extends outwardly to each side of the focal spot track 106 a distance of approximately one quarter of the width W2 of the focal spot track 106.
Referring now to
The emissive material tracks 154,156 can be spaced from one another, exposing one or more portions of the body 150, or any other material 153 that is disposed on the surface 151 between the emissive material tracks 154,156 and the body 150 that is different than the material forming the body 150, between the pair of emissive material tracks 154,156. The emissive material tracks 154,156 can be formed of the same type of emissive material, or can be formed from different types of emissive materials, such as chromium, aluminum, yttrium, zirconium, magnesium, silicon, silver, titanium, molybdenum, rhodium and tungsten. Alternatively, as shown in
The emissive material tracks 154,156 each have a different width, W3 for track 154 and W4 for track 156, such that the tracks 154 and 156 accommodate focal spot tracks 158,160 having different widths, i.e., W5 for focal spot track 158 and W6 for focal spot track 160 corresponding to the lengths L2 and L3 of the focal spots 107 defining each focal spot track 158,160, and that are each less than the width W7 of the surface 151 of the body 150. The widths W3 and W4 of the emissive material tracks 154,156 each conform to the widths W5 and W6 for the focal spot tracks 158,160 according to the parameters of one or more of the embodiments discussed previously with regard to the anode 48 and the emissive material track 104 and focal spot track 106 disposed thereon. Further, with this configuration for the anode 148, the single anode 148 can be employed for use in imaging procedures requiring different focal lengths, as the electron beam 54 can be directed onto the desired focal spot 107 and associated focal spot track(s) 158,160 and emissive material track(s) 154,156 to provide the improvements to the operation of the anode 148 provided by the emissive material tracks 154,156 as discussed previously.
In still another exemplary embodiment of the disclosure, referring now to
The cover 162 can be deposited in any suitable manner on the areas of the body 100 outside of the focal spot track(s) 106,158, 160, with the material forming the cover 162 having suitable non-emission properties and a thickness of between 10 μm-100 μm, in one exemplary embodiment.
In still another exemplary embodiment of the disclosure, referring now to
The written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims. or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
