X-ray cathode shield

Abstract

To provide various methods and systems for a cathode of an X-ray imaging system.SOLUTION: In one example, a shield assembly for a cathode comprises a first shield part and a second shield part, the first shield part and the second shield part are spaced so that the first shield part and the second shield part are not in direct physical contact. In one embodiment, the first shield part comprises a disk shield (365) and a cathode mask (362), and the second shield part (304) surrounds a lower extender (420) of the cathode.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] FIELD OF THE INVENTION Embodiments of the subject matter disclosed herein relate to cathodes for imaging systems (eg, X-ray imaging systems). [Background technology]

[0002] In an X-ray tube, ionizing radiation is generated by accelerating electrons from a cathode to an anode in a vacuum using an electric field. The electrons are generated from a filament in the cathode through which an electric current flows. The filament can be heated by the current flow, releasing electrons from the cathode and accelerating them toward the anode. Additional filaments heated by currents of different voltages can be used to focus the electron beam toward the anode and affect the size and position of the X-ray emission spot. The cathode can be configured with an external shielding element (e.g., an electropolished shield) to maintain high voltage stability. Summary of the Invention

[0003] In one embodiment, a shield assembly for a cathode includes a first shield portion and a second shield portion, the first shield portion and the second shield portion being spaced apart from each other so as not to be in direct physical contact.

[0004] It should be understood that the foregoing summary is provided to introduce concepts in a simplified form that are further described in the detailed description. The foregoing summary is not intended to identify key features or essential features of the claimed subject matter, the scope of which is determined independently by the claims, separate from the detailed description. Moreover, the claimed subject matter is not limited to implementations that solve the above-noted shortcomings or any shortcomings noted in any part of this disclosure. [Brief explanation of the drawings]

[0005] The invention can be better understood from the following description of non-limiting embodiments, taken in conjunction with the accompanying drawings, in which: [Figure 1] FIG. 1 shows a block diagram of an example imaging system. [Figure 2] 2 shows a schematic cross-sectional view of an X-ray tube that may be included in the imaging system of FIG. 1; [Figure 3] 2 shows a first perspective view of a cathode that can be included in the imaging system of FIG. 1; [Figure 4] 4 shows a first cross-sectional view of the cathode of FIG. 3. [Figure 5] FIG. 4 shows a second perspective view of the cathode of FIG. 3. [Figure 6] 4 shows a third perspective view of the cathode of FIG. 3. [Figure 7] 4 shows a second cross-sectional view of the cathode of FIG. 3. [Figure 8] 4 shows a first example of a shielding component included in the cathode of FIG. 3. [Figure 9A] 4 shows a cross-sectional view of a first example of a shielding component included in the cathode of FIG. 3. [Figure 9B] 9B shows an enlarged view of a cross section of the shielding component shown in FIG. 9A. [Figure 10] 4 shows a second example of a shielding component included in the cathode of FIG. 3. DETAILED DESCRIPTION OF THE INVENTION

[0006] The following description relates to various embodiments of an X-ray tube cathode. The X-ray tube is included in an X-ray imaging system, an example block diagram of which is shown in FIG. 1. The X-ray imaging system can be an interventional X-ray imaging system, a fluoroscopic imaging system, a mammography imaging system, a fixed or mobile radiography (RAD) imaging system, a tomography imaging system, a computed tomography (CT) imaging system, or the like. The X-ray imaging system includes an X-ray source (e.g., an X-ray tube) that generates an irradiating X-ray beam. A cross-sectional schematic diagram of an X-ray tube is shown in FIG. 2. The X-ray tube of FIG. 2 includes an anode assembly and a cathode assembly housed within a vacuum frame. The cathode assembly includes a cathode cup that houses one or more cathode filaments, a lower extension that mechanically couples the cathode cup to a high-voltage power supply by an electrical lead, and a cathode shield, as shown in more detail in FIGS. 3-10.

[0007] FIG. 3 is a perspective view of a cathode, including a shield assembly. FIG. 4 shows a cross-section of the cathode, illustrating the location and shape of the shield sections that make up the shield assembly. The shield assembly includes a first shield section and a second shield section. The first and second shield sections are spaced apart so that the first and second shield sections are not in direct physical contact with each other. In one embodiment, the first shield section includes a cathode mask and a disk shield, and the second shield section surrounds the lower extension of the cathode. FIG. 5 is a rear perspective view of the shield assembly, illustrating the unshielded portion of the cathode. The rear view shows a rear gap in the cathode shield in areas of low field intensity, which increases the view factor and reduces the overall temperature of the cathode. FIG. 6 is a perspective view of a shield assembly including an exemplary focusing section of a cathode mask. FIG. 7 is a cross-sectional perspective view of an example of a disclosed cathode shield assembly. FIG. 8 is a perspective view of an example of a disclosed cathode shield. FIG. 9A shows a cross-section of an example of a disclosed cathode shield. Figure 9B shows a detail of the cross section shown in Figure 9A. Figure 10 shows an example of a second shield that can surround the lower extension of the cathode. Figures 3-10 are shown to scale, but other relative dimensions may be used.

[0008] Smart cathodes are used in imaging systems (such as X-ray imaging systems) to provide a focusing means for the coiled filament, allowing for a virtually infinite number of focal spot shapes and sizes depending on the electrode configuration. Smart cathodes can be configured to provide a variety of imaging services. For example, smart cathodes can be configured for diagnostic and interventional applications, where a current is passed through the coiled filament for a relatively long period of time. A smart cathode can include one or more coiled filaments, each with a different size to accommodate a range of currents appropriate for the application. Cathode shield elements are typically provided to maintain high voltage stability and to reduce electron emission field stresses in undesired locations. For example, a cathode assembly for a smart cathode can include an integrated cathode shield configured to prevent backscattered electrons from reaching electrical leads, the coiled filament, and focusing elements, as well as other components of the cathode assembly that are susceptible to field stresses.

[0009] However, conventional smart cathode systems present challenges. For example, operating the cathode generates a significant amount of heat. Cathode components, including ceramic insulators and electrical leads, are temperature-sensitive and may exceed a temperature threshold that can sufficiently degrade the cathode components. In some cases, a trade-off exists between cathode power density and maintaining an appropriate cathode temperature. Shielding that completely covers the cathode can exacerbate the problem by concentrating waste heat around temperature-sensitive components. Over time, thermal stress can lead to part replacement or equipment scrapping, increasing service time and operator costs. Another challenge is that smart cathodes may contain one or more coiled filaments. Failure to optimize the cathode shield for the respective sizes of the one or more coiled filaments can block the electric field of one or more of the multiple coiled filaments, resulting in a loss of focusing ability. Similarly, excessive field focusing can impair image quality.

[0010] Therefore, to at least partially address the above-mentioned problems, a cathode shield is disclosed herein. In one embodiment, the cathode shield assembly includes a first shield portion and a second shield portion, the first shield portion and the second shield portion being spaced apart from each other so that the first shield portion and the second shield portion are not in direct physical contact with each other. In one example, the first shield portion includes a cathode mask and a disk shield, and the second shield portion surrounds the lower extension. The disk shield's shape blocks heat and high voltage generated by the target from reaching sensitive components (e.g., ceramic insulators and electrical leads). The cathode mask shields components of the cathode cup (e.g., bolts and welds) or other fastening mechanisms for stabilizing the high voltage and focuses electrons emitted from one or more coiled filaments. The lower extension shield covers sensitive components (e.g., electrical functions and welds) and allows radiative heat transfer through a gap between the second shield portion and the first shield portion. Such a shield assembly ensures high voltage stability but allows much of the radiant heat to be transferred directly to the frame. Increased radiant heat transfer reduces the temperature of the cathode components and reduces the amount of conductive heat transferred to temperature-sensitive components (such as electrical leads and ceramic insulators). Heat reduction is particularly valuable in interventional applications, extending the reliability requirements of the HVC and allowing for longer "on" times for the filament.

[0011] In another embodiment, a cathode shield is disclosed that includes a cathode mask including a U-shaped central opening configured to receive a cathode cup, the outer periphery of the U-shaped central opening including a rounded edge. In one embodiment, the central opening of the disclosed cathode mask is U-shaped because a similar (e.g., substantially similar) difference is maintained between the rounded edge and one or more coiled filaments disposed in the cathode cup. In one embodiment, the rounded edge is an edge transition that is tailored to reduce local electron emission field stress at the edge of the cathode mask. Such a shield has the advantages of increased high voltage stability and increased field focus relative to the size and strength of the coiled filaments that may be included in a smart cathode.

[0012] A technical advantage of the shield for smart cathodes disclosed herein is that it can increase the power output capability of cathode tubes by increasing heat transfer. Another technical advantage of the shield disclosed herein is that it improves electron focusing by adjusting the outer edge of the cathode mask to the size of the coiled filament. The geometry of the disclosed shield components also contributes to improved high voltage reliability. Commercial advantages include the potential for lower cost cathode tubes due to increased power density and the potential for smaller packaging. Other advantages include reduced inspection time and associated labor costs.

[0013] Before further describing the smart cathode system with a shield assembly having a focusing section and increased radiative heat transfer between the cathode and the frame, an exemplary imaging system in which the cathode may be implemented is shown. Referring to FIG. 1 , a block diagram of one embodiment of an imaging system 10 is shown, configured to both acquire raw image data and process the image data so that it can be displayed and / or analyzed, according to an exemplary embodiment. It will be appreciated that various embodiments are applicable to numerous x-ray imaging systems that implement x-ray tubes, such as x-ray radiography (RAD) imaging systems, x-ray mammography imaging systems, fluoroscopic imaging systems, tomographic imaging systems, or CT imaging systems. The following description of the imaging system 10 is merely one example of such an implementation and is not intended to be limiting with respect to modality.

[0014] As shown in FIG. 1, imaging system 10 includes an x-ray device or x-ray source 12 configured to project an x-ray beam 14 that passes through an object 16. The object 16 may include a subject, baggage, or other object being scanned. X-ray source 12 may be a conventional x-ray tube that generates x-rays 14 having an energy spectrum typically ranging from 30 keV to 200 keV. After passing through object 16 and being attenuated, x-rays 14 impinge on a detector assembly 18. Each detector module of detector assembly 18 generates an analog electrical signal that represents the intensity of the impinging x-ray beam and, therefore, the attenuated beam as it passes through object 16. In one embodiment, detector assembly 18 is a scintillator-based detector assembly, although direct conversion detectors (e.g., CdTe, CZT, Si detectors, etc.) may also be implemented.

[0015] The processor 20 receives signals from the detector assembly 18 and generates an image corresponding to the object 16 being scanned. The computer 22 communicates with the processor 20 so that an operator can control scanning parameters and view the generated images using an operator console 24. That is, the operator console 24 includes some form of operator interface (such as a keyboard, mouse, voice-activated controller, or any other suitable input device that enables the operator to control the imaging system 10 and view reconstructed images or other data from the computer 22 on a display device 26). The operator console 24 also enables the operator to store the generated images on a storage device 28, which may include a hard drive, floppy disk, compact disk, etc. The operator can also use the operator console 24 to provide commands and instructions to the computer 22 for controlling a source controller 30, which provides power and timing signals to the x-ray source 12.

[0016] FIG. 2 shows a schematic cross-sectional view of an X-ray device or X-ray source 200 included in the imaging system of FIG. 1. For example, the X-ray source 200 is an exemplary embodiment of the X-ray source 12 of FIG. 1 and can be formed by an X-ray tube 40 including an anode assembly 42, a cathode assembly 44, and a collector assembly 82. To facilitate comparison between the various views shown, a set of reference axes 201 is illustrated, showing the x-axis, y-axis, and z-axis. The X-ray tube 40 is comprised of the anode assembly 42, the cathode assembly 44, and the collector assembly 82 and is supported within a housing or frame 46. The frame houses at least a portion of the anode assembly 42, the cathode assembly 44, and the collector assembly 82. The frame 46 houses the anode 48 having the target 66, the bearing assembly 50, and the cathode 52. The frame 46 defines a region of relatively low pressure (e.g., vacuum) relative to the surroundings, in which high voltages are generated. Additionally, the frame 46 may be placed within a casing (not shown) filled with a cooling medium (such as oil) and which also includes high voltage insulation. Although the above description has referred to the anode 48 comprising the target 66 as a common component of the x-ray tube 40, the anode 48 and target 66 may be separate components in alternative embodiments of the x-ray tube.

[0017] In operation, an electron beam is generated by the cathode assembly 44. In particular, the cathode 52 receives one or more electrical signals through a series of electrical leads 56. The electron beam travels through a space 54 between the cathode 52 and a target 66 on the anode 48. The electrical signals may be timing / control signals that cause the cathode 52 to emit an electron beam of one or more energies and one or more frequencies. The electrical signals may also at least partially control the electrical potential between the cathode 52 and the anode 48. The cathode 52 includes a central insulating shell 58 from which extends a mask 60. The mask 60 encloses electrical leads 56 that extend to a cathode cup 62 attached to the end of the mask 60. In some examples, the cathode cup 62 acts as an electrostatic lens that focuses electrons emitted from a filament within the cathode cup 62 to form the electron beam.

[0018] The exterior surfaces of the cathode 52 (e.g., the surfaces of the mask 60 and the cathode cup 62) are covered with a shield capable of withstanding the high electric field stress between the high potential of the cathode 52 and the ground plane of the frame 46. In one embodiment, the shield includes a first shield portion 202 and a second shield portion 204. In this embodiment, the first shield portion 202 and the second shield portion 204 are spaced apart and do not directly contact each other physically. In one embodiment, the first shield portion 202 can include a disk shield and a cathode mask, and the second shield portion 204 can surround the mask 60. Examples of the first shield portion 202 and the second shield portion 204 are shown in more detail in FIGS. 3-10. In one embodiment, as shown in the schematic diagram of the x-ray source 200, the first shield portion 202 is a single, continuous member that is integrally formed. For example, there can be no welds or seams joining the disk shield and the cathode mask that make up the first shield portion 202. The first shield portion 202 can be a monolithic structure. Alternatively, the disk shield and cathode mask that make up the first shield portion 202 can be formed separately and welded to the cathode assembly.

[0019] X-rays 64 are generated when high-speed electrons of the electron beam travel from the cathode 52 toward the target 66 formed on the anode 48 and are rapidly decelerated by the potential difference between the cathode 52 and the target 66 (e.g., a potential difference of sixty thousand (60,000) volts or more for CT applications). The focusing electrode assembly 82 may include an electron collector 84 and a window 68, through which the x-rays 64 generated by the anode assembly 42 are emitted. The electron collector 84 holds the window 68 in place in the frame 46 and may also absorb backscattered electrons. The x-rays 64 are emitted through the window 68 formed in the frame 46 toward a detector array (such as the detector assembly 18 in FIG. 1).

[0020] The anode assembly 42 includes a rotor 72 and a stator (not shown) disposed outside the x-ray tube 40 and surrounding the rotor 72 to cause rotation of the anode 48 during operation. The anode 48 is rotatably supported by a bearing arm or assembly 50, which rotates to rotate the anode 48 about its centerline 70. The centerline 70 thus defines an axis of rotation for the anode 48 and bearing assembly 50. As shown, the anode 48 has an annular shape, with a circular opening 74 at its center for receiving the bearing assembly 50.

[0021] The anode 48 can be fabricated to include multiple metals or alloys, such as tungsten, molybdenum, copper, or any material that contributes to bremsstrahlung (e.g., slowing radiation) when struck by electrons. The target 66 of the anode 48 can be selected to have a relatively high refractory coefficient to withstand the heat generated by electrons striking the anode 48. Additionally, the space between the cathode assembly 44 and the anode 48 can be a vacuum to minimize electron collisions with other atoms and maximize the electrical potential.

[0022] To avoid overheating of the anode 48 when struck by electrons, the rotor 72 rotates the anode 48 at high speeds (e.g., 90-250 Hz) about the centerline 70. In addition to rotating the anode 48 within the frame 46, in CT applications, the entire x-ray tube 40 rotates around the object (such as the object 16 of the imaging system 10 of FIG. 1 ), typically at a rate of 1 Hz or faster.

[0023] Although different embodiments of bearing assembly 50 can be formed from a number of suitable ball bearings or the like, in the exemplary embodiment shown, bearing assembly 50 includes a liquid metal hydrodynamic bearing having suitable load capacity and acceptable acoustic noise levels for operation within imaging system 10 of FIG. 1 .

[0024] Generally, bearing assembly 50 includes a stationary component (such as central shaft 76) and a rotating portion (such as sleeve 78 to which anode 48 is attached). While central shaft 76 is illustrated in FIG. 2 as the stationary part of bearing assembly 50 and sleeve 78 is illustrated as the rotating part of bearing assembly 50, embodiments of the present disclosure are also applicable to embodiments in which central shaft 76 is the rotating shaft and sleeve 78 is the stationary part. In such a configuration, rotation of central shaft 76 would result in rotation of anode 48.

[0025] The central shaft 76 may optionally include a cavity or coolant passage 80 through which a coolant (not shown), such as oil, may flow to cool the bearing assembly 50. In this manner, the coolant may transfer heat generated at the anode 48 of the X-ray tube 40 away from the anode 48 and out of the X-ray tube 40. Additionally, in straddle-mounted X-ray tube configurations, the coolant passage 80 extends along the longitudinal length of the X-ray tube 40 (e.g., along the centerline 70). In alternative embodiments, the coolant passage 80 may be formed in only a portion of the X-ray tube 40, such as in a configuration in which the X-ray tube 40 is cantilevered when placed in an imaging system.

[0026] As described above, a cathode shield is desired that maintains high voltage stability, increases heat transfer to the frame, and optimizes electron field focusing for one or more coiled filaments of varying strength. The shields described herein can provide improved high voltage stability and a longer usable life compared to conventional smart cathodes. In one example, a cathode shield assembly includes a first shield portion and a second shield portion, the first shield portion and the second shield portion spaced apart so that the first shield portion and the second shield portion are not in direct physical contact. Such a cathode shield shields areas of high electric field stress while increasing radiative heat transfer from areas of the cathode susceptible to low electric field stress and high heat. In one embodiment, the first shield portion includes a cathode mask and a disk shield, and the second shield portion surrounds a lower extension of the cathode. In one embodiment, the disk shield is a substantially concave disk having a curved lip and a cutout, through which a portion of the cathode (e.g., the cathode cup) protrudes. The cutout can be a substantially rectangular cutout offset from the center of the disk shield. The cathode mask includes a U-shaped central opening configured to receive a cathode cup. In one embodiment, the outer periphery of the U-shaped central opening includes a rounded edge. The U-shaped central opening can include multiple radius bends formed to focus one or more coiled filaments of the cathode. The rounded edge can have a bend angle formed to reduce electric field stress at the outer periphery of the central opening.

[0027] The location and shape of the shielding sections balance optical and electrostatic considerations by increasing the view factor in areas of low electron emission field stress while contributing to high voltage stability. For example, the shape of the first shielding section concentrates the field stress at the outer periphery of the shield, while the gap spacing between the first and second shielding sections exposes the low field stress areas of the cathode. Therefore, compared to conventional cathodes with fully enclosed shields, the system described herein provides a cathode with reduced component temperatures, improved high voltage stability, and improved image quality due to the tailored field focusing. This, in turn, increases the usable life of the cathode and reduces part replacement and inspection times.

[0028] FIG. 3 shows a perspective view of a cathode assembly 300, which may be one embodiment of the cathode assembly 44 of FIG. 2. Components in the cathode assembly 300 that are equivalent to components in the x-ray tube 40 of FIG. 2 are similarly numbered. A set of reference axes 301 is shown to allow for comparison between the depicted views, and includes an x-axis, a y-axis, and a z-axis. The x-axis may be referred to as the lateral axis, the z-axis may be referred to as the vertical axis, and the y-axis may be referred to as the longitudinal axis.

[0029] As described above, the cathode assembly 300 emits electrons from the cathode, which are received by an anode assembly (e.g., anode assembly 42 of FIG. 2) to generate x-rays. The cathode assembly 300 may include a large insulator 358, a lower extension 405 (see FIG. 4), and a cathode 52 including a cathode cup 62. The large insulator 358 may be equivalent to the central insulating shell 58, and the lower extension 405 may be equivalent to the mask 60 as described with reference to FIG. 3.

[0030] The cathode cup 62 can include a focusing element and one or more coiled filaments. In one embodiment, the focusing element can be a single, continuous structure having at least one channel sized to accommodate a thermionic filament disposed therein and at least one focusing portion located laterally of the at least one channel. In one embodiment, the focusing portion and channels of the focusing element can have rounded corners and edges and a smooth geometry, as opposed to corners that meet at a linear angle. In one embodiment, the focusing element can include multiple coiled filaments. In the illustrated example, the focusing element 375 is shown in simplified form in FIGS. 3-4 and in detail in FIGS. 6-7 and can be configured as a continuous, single (e.g., monolithic) grid electrode with an electron-emitting filament disposed in each of at least three channels shaped to focus emitted electrons into a single electron beam. The focusing element 375 incorporates a first filament 376, a second filament 378, and a third filament 380. The spacing between the three filaments can be adjusted based on the size and strength of each of the filaments. In one example, the focusing element 375 has a substantially rectangular shape (e.g., when viewed down the y-axis) to account for the spacing between the three filaments. The focusing element 375 may also have a U-shape or bowl-shape (e.g., when viewed down the z-axis) such that the sides of the focusing element are higher than the center of the focusing element. As previously described with reference to FIG. 2, the cathode assembly 300 can provide electrons at various energy levels from each of one or more coiled filaments to a target (e.g., target 66 in FIG. 2). The cathode cup 62 is partially surrounded by a cathode shield assembly.

[0031] In one embodiment, the cathode shield assembly includes a first shield portion 302 and a second shield portion 304, where the first shield portion 302 is spaced apart from the second shield portion 304 and the first and second shield portions 302 and 304 are not in contact. The first shield portion 302 can be the same as or similar to the first shield portion 202, and the second shield portion 304 can be the same as or similar to the second shield portion 204 (described with reference to FIG. 2). The first and second shield portions 302 and 304 can be separated by a gap spacing between the first and second shield portions 302 and 304, which will be described with reference to FIG. 4 below. As described in more detail below, the first shield portion 302 includes a disk shield 365 and a cathode mask 362. The second shield portion 304 surrounds a lower extension 405. The second shield portion 304 can be ring-shaped. In one embodiment, the disk shield 365 includes a cutout or opening for receiving the cathode cup 62, and a portion of the disk shield 365 is securely mechanically coupled to the lower extension 405. The cathode cup 62 is partially surrounded by the cathode mask 362. The first shield portion 302 and the second shield portion 304 cooperate to protect the components of the cathode 52 (such as the filament, focusing element, and electrical leads) from high temperatures and backscattered electrons, provide high voltage stability, and simultaneously increase radiative heat transfer to the frame 46.

[0032] The disc shield 365 may be substantially concave and substantially disc-shaped. The disc shield 365 may have a first outer surface 322. The first outer surface 322 may include a curved lip 310, a flat region 312, and an angled transition 314 between the curved lip 310 and the flat region 312. In one example, the curved lip 310 and the angled transition 314 are angled downward relative to the z-axis toward the flat region 312. The curved lip 310 may also extend downward relative to the z-axis to form a surface 316. The surface 316 is part of the curved lip 310 and extends radially about a central axis 317. The first outer surface 322 may be a surface centered on the central axis 317. In one embodiment, the disk shield 365 can include a first cutout, which can be defined by an opening in the first outer surface 322, an opening in the first inner surface 404 (see FIG. 4), and the first cutout surface 324. In one embodiment, the first cutout can be a substantially rectangular cutout that is offset from the center of the disk shield 365. For example, the first cutout can be located above a first centerline 315 that longitudinally bisects the cathode assembly 300. The shape of the disk shield 365 is described in further detail below with reference to FIGS. 4-7.

[0033] In one embodiment, the cathode cup 62 can protrude through the first cutout, and the cathode mask 362 can receive the cathode cup 62. The cathode mask 362 can have a substantially cylindrical shape with a rectangular extension 326. The cathode mask 362 includes a second outer surface 330 and a second inner surface 434 (see FIG. 4 ). In one embodiment, the second outer surface 330 and the first outer surface 322 form a continuous, integral surface of the first shield portion 302. In one embodiment, the substantially cylindrical, rectangular extension 326 includes a plurality of sidewalls 328 disposed perpendicular to the front panel 332, where the sidewalls 328 and the front panel 332 meet without sharp edges. In other words, the shape of the cathode mask has rounded edges at the transitions between the sidewalls, the front panel, and the rectangular extension. The cathode mask 362 has a central opening 340 that may be defined by an opening in the second outer surface 330 , an opening in the second inner surface 434 (see FIG. 4 ), and a lip or outer periphery 338 .

[0034] In one embodiment, the cathode mask 362 is shaped to accommodate the focusing element 375 and coiled filaments of the cathode cup 62. For example, the rectangular extension 326 surrounds the focusing element 375. The cathode mask 362 can be shaped to maintain an equal distance between each of the multiple coiled filaments (e.g., first filament 376, second filament 378, and third filament 380) disposed in the focusing element 375 and the outer periphery 338 of the central opening 340. In one embodiment, the central opening 340 can be configured as a U-shape (e.g., when viewed down the z-axis), and the outer periphery 338 can have rounded edges. The U-shape and rounded edges are examples of focusing features of the cathode mask 362 that can be adjusted to achieve optical and electrostatic balance. The shape and focusing features of the cathode mask 362 are described in more detail below with reference to FIGS. 4-9B.

[0035] Figure 4 shows a cross-sectional view 400 of the cathode assembly 300 of Figure 3, as shown by a lateral cut along dashed line 4-4 in Figure 3. Like components are numbered like in Figure 3. A set of reference axes 401 is shown to allow comparison between the views shown, indicating the x-axis, y-axis, and z-axis.

[0036] The cross-sectional view 400 shows the cathode cup 62, the large insulator 358, the lower extension 405, and the cathode shield that partially surrounds the cathode 52 and includes the first shield portion 302 and the second shield portion 304. The cathode cup 62 includes multiple electrical leads (not shown). The lower extension 405 couples the cathode cup 62 to the large insulator 358 and surrounds multiple high-voltage cables 56 (shown schematically). The multiple high-voltage cables 56 couple the multiple electrical leads to a high-voltage power supply. A disk shield 365 can be coupled to a surface 462 of the lower extension 405, a cathode mask 362 can be coupled to the cathode cup 62 and can partially shield the cathode cup 62, and the second shield portion 304 can form a sleeve or ring around the lower extension 405.

[0037] The cathode cup 62 may further include a base 444, an insulator 446, and a weld pad 448. The cathode cup 62 may include one or more brazing foils that may be used to couple the insulator 446 to the base 444 and the weld pad 448 (e.g., by brazing), respectively. In one embodiment, the insulator 446 may be a ceramic insulator (e.g., an insulator formed of ceramic). In another example, the insulator 446 may be formed of a material that sufficiently insulates the base 444 from the weld pad 448. The insulator 446 may have a rectangular ring shape with a hollow center. For example, the insulator 446 may have a rectangular shape with curved edges and a rectangular cutout with curved edges in the center of the insulator 446. The base 444 may be formed of a metal (e.g., nickel, steel, Kovar, niobium, etc.) and may have a continuous stepped structure including a first level 444a and a second level 444b. A plurality of electrical leads are coupled to the rear surface 426 of the base 444. The weld pad 448 may be ring-shaped with rounded corners connecting straight edges and a hollow portion. The weld pad 448 may also be formed of a metal (e.g., nickel, steel, kovar, niobium, etc.). The ring-shaped structure of the insulator 446 and the weld pad 448 allows the second level 444b of the base 444 to pass through a central portion of the insulator 446 and the weld pad 448. The insulator 446 may circumferentially surround the second level 444b of the base 444.

[0038] The weld pad 448, base 444, brazing foil, and insulator 446 can be brazed together using torch brazing, induction brazing, resistance brazing, or another brazing method in which the weld pad 448, base 444, and insulator are joined by a filler material (e.g., brazing foil). For example, the filler material can be used to bond the insulator to the base 444 and weld pad 448 by brazing.

[0039] In one embodiment, the base 444 of the cathode cup 62 can be coupled to the mounting wall 460 of the lower extension 405 in an angled manner. For example, the mounting wall 460 of the lower extension 405 can be disposed substantially perpendicular to a second centerline 458. The second centerline 458 can be substantially collinear with or formed from the central axis 317. The second centerline 458 bisects the cathode assembly 300 longitudinally. A second dashed line 464 indicates that the mounting wall 460 is substantially vertical. The rear surface 426 of the cathode cup 62 can be tilted at a tilt angle 466 relative to the second dashed line 464. In one embodiment, the cathode cup 62 and the lower extension 405 have tolerances that control the tilt angle to + / - 0.25°.

[0040] In one example, the lower extension 405 can include one or more windows 450 defined by an opening in the lower extension's outer surface 452, an opening in the lower extension's inner surface 454, and the lower extension's window surface 456. The windows 450 can contribute to cooling of cathode components, such as multiple electrical leads (e.g., ribbons, wires, cables, pins, or other electrical connections) located on the cathode cup's rear surface 426 that couple one or more of the multiple coiled filaments housed in the cathode cup 62 (e.g., the third filament 380) to the high-voltage cable 56. A sleeve element 468 can be interposed between the lower extension 405 and the small insulator 428.

[0041] In the illustrated example, the disc shield 365 has an outer portion 406 and an inner portion 408. The distance between the outer portion 406 and the inner portion 408 can define a disc shield width 412 relative to the y-axis. The curved lip 310 can define an arcuate surface integral with the disc shield 365. The curved lip 310 extends between the outer portion 406 and an outer peripheral edge 416 of the disc shield 365. The curved lip 310 can have multiple points of curvature change on the cross-sectional view 400 taken along line 4-4. One point of curvature change can be located on the surface 316, where the curved lip 310 can curve toward the outer portion 406 or the outer peripheral edge. Another point of curvature change can be located near the outer portion 406, where the curved lip 310 can bend toward the outer peripheral edge 416 and form the angled transition 314. Another curvature transition point may be located near the outer peripheral edge 416, causing the curved lip 310 to curve toward the outer portion 406. After bending at the curvature transition point, the curved lip 310 may terminate in an axial region between the outer portion 406 and the outer peripheral edge 416 and expand radially about the second centerline 458. The multiple curvature transition points may be reflected on portions of the curved lip 310 opposite the second centerline 458. The multiple curvature transition points may be part of a ring or other function that is radially disposed relative to the second centerline 458 when the curved lip 310 is projected into three-dimensional space.

[0042] An angled transition 314 extends between the outer portion 406 and the flat region 312. The angled transition 314 is angled at an angle 418 relative to an axial length 420 over a radius change section 422. The flat region 312 is offset from the inner portion 408 by a first offset 424. In one embodiment, the disk shield 365 can be welded to the lower extension 405. For example, the flat region 312 can be laser welded to a surface 462 of the mounting wall 460.

[0043] In one embodiment, the cathode cup 62 protrudes through the first cutout portion of the disk shield 365. The cathode mask 362 is configured to receive the cathode cup 62. The central opening 340 is located opposite an opening face 480 of the cathode mask 362. The cathode cup 62 can be received at the opening face 480. In one embodiment, the second inner surface 434 can be in flush contact with a base 444 of the cathode cup 62, and an air gap 440 can be formed between the second inner surface 434 and the focusing element 375, insulator 446, and weld pad 448 of the cathode cup 62. In one embodiment, the cathode mask 362 can be welded to the cathode cup 62. For example, the cathode mask 362 can be laser welded to the base 444. The focusing element 375 of the cathode cup 62 can be partially exposed by a central opening 340 in the cathode mask 362, and the multiple sidewalls 328 and outer periphery 338 surround the focusing element 375 and a filament (e.g., a third filament 380) disposed in the cathode cup 62. The rear surface 426 of the cathode cup 62 can be exposed (or partially exposed) by an opening 480 in the cathode mask 362. The curved lip 310 of the disk shield 365 can partially shield the rear surface 426 of the cathode cup 62. For example, the curved lip 310 can shield a portion of the rear surface 426 having a high electric field intensity (e.g., near the contact between the cathode mask 362 and the first level 444a).

[0044] The shape of the first shield portion 302 concentrates electric field stresses at the first outer surface 322 and the second outer surface 330, preventing heat generated at the anode target (e.g., target 66 of the anode 48 in FIG. 2 ) from reaching temperature-sensitive components, including, for example, the large insulator 358, the small insulator 428, and the electrical leads. The first shield portion 302 also improves high-voltage stability. For example, the cathode mask 362 contributes to high-voltage stability by shielding welds (e.g., weld pad 448), brazes, fasteners, or other types of fastening mechanisms that make up the cathode cup 62. In addition, the shape of the cathode mask 362, which provides a smooth, rounded transition between the side walls 328 and the front panel 332, contributes to high-voltage stability. Additionally, the shape of the central opening 340 reduces electric field stresses at the ends of the cathode mask 362 and increases the focusing field of the coiled filament, as described in more detail below. As another example, the shape of the disk shield 365 contributes to high-voltage stability. For example, the angled transition 314 provides a smooth transition, without sharp corners, to the curved lip 310, reducing electric field stress at the outer periphery 416. For example, by shielding temperature-sensitive components with the first shield portion 302, the rear surface 426 of the cathode cup 62 can be exposed (e.g., unshielded). The open surface 480 of the cathode mask 362 allows more radiant heat to be transferred from the cathode cup 62 to the frame 46 without compromising high-voltage stability.

[0045] By concentrating electric field stresses on the first outer surface 322 and the second outer surface 330 of the first shield portion 302 and preventing temperature-sensitive components from being exposed to the high temperatures generated at the anode, the disclosed cathode shield simultaneously exposes portions of the cathode 52 that were previously enclosed. For example, the disclosed cathode shield exposes portions of the cathode 52 that have lower electric field strength, higher temperatures, and a view factor relative to the frame 46. This selective shielding sufficiently reduces the temperature of the cathode components, reducing the amount of heat transferred to the plurality of high-voltage cables 56. The first shield portion 302 is described in further detail below.

[0046] The second shield portion 304 is an open, cylindrical or ring-shaped member that surrounds the lower extension 405. The second shield portion 304 has an annular inner surface 430 and an annular outer surface 432. In one embodiment, the annular inner surface 430 is in face-to-face contact with the outer surface 452 of the lower extension. In one embodiment, the second shield portion 304 can be welded to the outer surface 452 of the lower extension. In one embodiment, the second shield portion 304 can have a flared lip 472 on one side of the first circular opening and a flat rim 474 on the opposite side of the second circular opening. The flared lip 472 can abut a small insulator 428. In one embodiment, the second shield portion 304 can have a third length 476 relative to the y-axis. In one embodiment, the second shield portion 304 can be spaced apart from the first shield portion 302 by a gap distance 478 relative to the y-axis. The third length 476 and the gap spacing 478 may be axial relative to the second centerline 458 .

[0047] In one embodiment, second shield portion 304 is configured to shield components contained within lower extension 405 that would otherwise increase high voltage instability while allowing as much radiative heat transfer as possible. For example, third length 476 and gap spacing 478 of second shield portion 304 can be optimized to balance weld coverage, proximity to ground, cathode component temperature, and view factor relative to frame 46. In one embodiment, gap spacing 478 can be 25 mm to 30 mm. Second shield portion 304 is described in further detail below.

[0048] In one embodiment, the disk shield 365 and cathode mask 362 of the first shield portion 302 are a single, continuous, integrally formed member, as described with reference to FIG. 2 . In another embodiment, the disk shield 365 and cathode mask 362 are formed as separate elements. The first shield portion 302 and the second shield portion 304 can be formed of a metal (e.g., nickel, steel, Kovar, or niobium). The shield surfaces may have an electropolished finish. In one example, the first shield portion 302 and the second shield portion 304 can be nickel, and the first outer surface 322, the second outer surface 330, and the annular inner surface 430 can be electropolished nickel.

[0049] Figure 5 shows a rear view 500 of the cathode assembly 300 of Figure 3. Like components to Figure 3 are like numbered, including the first shield portion 302, the second shield portion 304, the cathode cup 62, and the frame 46. A set of reference axes 501 is shown, indicating the x-axis, y-axis, and z-axis, to allow comparison between the views shown.

[0050] The position and shape of the first shield portion 302 and the second shield portion 304 result in low electric field stress in the open view factor area. For example, dotted line 502 shows the curvature of the first shield portion 302 which shields the high electric field stress area of the cathode cup 62. In one example, the curvature and highly polished nickel surface provide a 1*10 per meter 7 The field strength in the unshielded areas of the gap distance 478 and rear surface 426 can be made sufficiently low (e.g., 0 to 2.5*10 6 In one embodiment, the view factor for the frame 46 of the gap spacing 478 and the unshielded area of the rear surface 426 can have an emissivity in the range of 0.4 to 0.7. In one embodiment, the first shield portion 302 and the second shield portion 304 are configured to shield the cathode cup 62 from the electric field stress intensity that is less than a threshold intensity (e.g., 2.5*10 6 V / m) and expose portions where the view factor for the frame is greater than the emissivity threshold (e.g., greater than an emissivity of 0.4).

[0051] The open shield section increases the view factor and corresponding radiative heat transfer from the cathode 52 to the frame 46. Additionally, the gap spacing 478 between the second shield section 304 and the first shield section 302 allows for enhanced component cooling while leaving the window 450 in the lower extension 405 unshielded. As a result, the overall temperature of the cathode is reduced. For example, components sensitive to high temperatures, such as the multiple electrical leads (not shown) that carry current to the coiled filament and the cathode cup insulator (e.g., insulator 446 in FIG. 4), can be cooled sufficiently to improve component reliability.

[0052] Figure 6 shows a front view 600 of the cathode assembly 300 of Figure 3. Like components are numbered as in Figure 3, including the cathode mask 362 and disk shield 365 that make up the first shield section 302, the cathode cup 62, and the second shield section 304. A set of reference axes 601 is shown, indicating the x-axis, y-axis, and z-axis, to allow for comparison between the views shown.

[0053] In one example, the cathode cup 62 may include a medium filament disposed in the first channel 602, a small filament disposed in the second channel 604, and a large filament disposed in the third channel 606. The filaments may be the first filament 376, the second filament 378, and the third filament 380 described with reference to FIG. 3. In other examples, the filaments may be the same size or different sizes. The filaments may be disposed at different heights within their respective channels relative to the rear surface of the base 444 (see FIG. 4). Each of the filaments in the first channel 602, the second channel 604, and the third channel 606 may have a lateral spacing relative to adjacent filaments, where the lateral spacing is defined as the lateral distance, relative to a horizontal axis (e.g., the x-axis), between the center point of the diameter of the first filament and the center point of the diameter of the second filament.

[0054] To accommodate the lateral spacing, size, and relative height of each filament, the cathode mask 362 can be configured with a shape that focuses the electrons emitted from the filaments into a single electron beam. In one embodiment, the central opening 340 and the outer periphery 338 of the central opening 340 can include various bends. For example, the central opening 340 has a U-shape, and the outer periphery 338 can include a rounded edge. Such bends can maintain a similar distance between the outer periphery and each filament, thereby increasing the electric field strength. For example, the bends can include multiple bends, multiple bends with various bend radii, and multiple bends of various dimensions.

[0055] As a first example of a curved portion, a first curved portion 680 includes a first axis 608 and a second axis 610 aligned parallel to the x-axis, and a second curved portion 682 includes a third axis 612 and a fourth axis 614 aligned parallel to the y-axis. The outer periphery 338 converges to the first axis 608 until it reaches the first curved portion 680. In one example, the first curved portion 680 can have a first bend radius ranging from 2 millimeters (mm) to 6 mm and a first bend dimension 676 ranging from 4.1 mm to 4.7 mm. The first curved portion 680 can be a longitudinal bend along the y-axis. The outer periphery 338 converges to the second axis 610 at the second curved portion 682. The second curved portion 682 can have a second bend radius. In one example, the first bend radius of the first bent portion 680 and the second bend radius of the second bent portion 682 can be different dimensions. For example, the second bend portion 682 can have a second bend radius ranging from 12 mm to 14 mm and a second bend dimension 674 ranging from 3 mm to 5 mm. The second bend portion can be a lateral bend along the x-axis. In the illustrated example, the outer periphery 338 includes a third bend portion 684 that mirrors the second bend portion 682 and a fourth bend portion 686 that mirrors the first bend portion 680. The first bend portion 680, the second bend portion 682, the third bend portion 684, and the fourth bend portion 686 form a U-shape when viewed along the z-axis. In one embodiment, first curved portion 680, second curved portion 682, third curved portion 684, and fourth curved portion 686 have a profile tolerance based on dimensions and radii. In one example, the profile tolerance is ±1 mm.

[0056] As disclosed herein, incorporating a curved portion into the central opening of the cathode mask improves x-ray image quality by tailoring the focused field to the size, strength, and position of each filament of one or more filaments. Another benefit is that the curved portion reduces the electric field stress at the end of the cathode cup, thus correspondingly improving high voltage stability. Further examples of curved portions are described in more detail below.

[0057] Figure 7 shows a cross-sectional view 700 of the cathode assembly 300 of Figure 3, taken along lateral cut line 7-7 in Figure 6. Like components are numbered similarly to Figure 3. To allow for comparison between the views shown, a set of reference axes 701 is shown, indicating the x-axis, y-axis, and z-axis.

[0058] Cross-sectional view 700 shows the height of the first filament 376 in the first channel 602 and the second filament 378 in the second channel 604 relative to the rear surface 426 of the cathode cup 62. The U-shaped bend as described with reference to FIG. 6 can maintain the same distance between the outer periphery and the filament. Conversely, if a conventional circular cathode cup shield (or cathode mask) or a uniform rectangular shield were used, the electric field strength around the filaments would be minimized (especially around the smallest filaments and / or furthest from the uniform outer periphery).

[0059] In the illustrated example, the first surface 702 represents a yz plane cutting the outer periphery 338 of the central opening 340 and the second filament 378 of the second channel 604. Relative to the rear surface 426, the height of the second filament 378, indicated by dashed arrow 710, and the height of the outer periphery 338, indicated by dashed arrow 708, have a first difference, indicated by dashed arrow 712. The first difference may be a depth measured at the first surface 702 between the xz plane corresponding to the second filament 378 and the xz plane corresponding to the outer periphery 338. The second surface 704 represents a yz plane cutting the outer periphery 338 and the first filament 376 of the first channel 602. Relative to the rear surface 426, the height of the first filament 376, indicated by dashed arrow 706, and the height of the outer periphery 338, indicated by dashed arrow 714, have a second difference, indicated by dashed arrow 716. Similarly, the second difference can be a depth measured at the second surface 704 between an x-z plane parallel to the first filament 376 and an x-z plane parallel to the outer periphery 338. Note that the dashed arrows 714 and 706 extend to the rear surface 426, but are only partially illustrated. In one embodiment, the first difference and the second difference can be the same. In one embodiment, the first difference and the second difference can differ by a threshold value. In other words, each coiled filament can be positioned within a threshold depth from the rounded edge of the cathode mask. In one embodiment, a defining factor for the geometry of the disclosed cathode mask is maintaining a substantially similar difference between the outer periphery of the central opening and each of the one or more coiled filaments.

[0060] The cross-sectional view 700 shows rounded edges 718. The rounded edges 718 can be tailored to reduce local electron emission field stress at the edges of the cathode mask (e.g., the outer periphery 338 of the central opening 340). In one example, the rounded edges can be curved perpendicular to the z-axis. An example of a cathode mask including a rounded edge shape is described in more detail with reference to FIGS. 8 and 9A-9B.

[0061] 8 shows a perspective view of an example cathode mask 800 that is part of a cathode shield assembly for a cathode. The cathode mask 800 can be the same as or similar to the cathode mask 362 described with reference to FIGS. 3-7. A set of reference axes 801 is shown, indicating the x-axis, y-axis, and z-axis, to allow comparison between the views shown.

[0062] In one embodiment of the disclosed cathode shield assembly, the cathode mask 800 is pillar-shaped with a rectangular extension 811. The cathode mask 800 is mirror-symmetrical about a lateral symmetry line 802. In other embodiments of the disclosed cathode shield assembly, the cathode mask may not be laterally symmetrical. The cathode mask 800 has a first sidewall 804, a second sidewall 806, and a third sidewall 808. The first sidewall 804 faces the second sidewall 806, and the third sidewall 808 is disposed perpendicular to and between the first sidewall 804 and the second sidewall 806. The cathode mask 800 has a front panel 812 disposed perpendicular to the first sidewall 804, the second sidewall 806, and the third sidewall 808. The cathode mask 800 has a short extension 810 extending from a front panel 812 that is parallel to a third sidewall 808. The first sidewall 804, second sidewall 806, third sidewall 808, and front panel 812 meet without forming a sharp angle. For example, the transition surface 814 from the first sidewall 804 to the front panel 812 may be gently rounded or chamfered from the xz extent of the front panel 812 to the yz extent of the first sidewall 804.

[0063] In the illustrated example, excluding the rectangular extension 811, the overall dimensions of the cathode mask 800 are a first height 822, a first depth 826, and a first width 838. The front panel 812 extends to a second depth 840 that is shorter than the first depth 826, and may be approximately half the first depth 826. The short extension 810 has a second height 846 that is shorter than the first height 822.

[0064] The rectangular extension 811 is disposed in the upper half of the cathode mask 800 relative to the horizontal centerline 803. The rectangular extension 811 may have a first segment 816, a second segment 818, a third segment 832, and a fourth segment 834. The first segment 816 is an extension of the first sidewall 804, the second segment 818 is an extension of the second sidewall 806, and the third segment 832 is an extension of the third sidewall 808. The fourth segment 834 intersects the front panel 812 approximately perpendicularly, thus forming a short wall. The first segment 816 and the second segment 818 may have a third length 830 that is shorter than the first depth 826. The third segment 832 and the fourth segment 834 may have a length that is approximately the same as a first width 838 of the overall dimension of the cathode mask 800.

[0065] The rectangular extension 811 can be substantially U-shaped with respect to the lateral line of symmetry 802. For example, the rectangular extension 811 can have tall sides with a second height 842 and a shorter central portion with a third height 844. The first segment 816 and the second segment 818 can be approximately the second height 842. The third segment 832 and the fourth segment 834 can be approximately the second height 842 near the ends of the first segment 816 and the second segment 818, tapering to the third height 844 toward the lateral line of symmetry 802. The shape of the rectangular extension is influenced by the dimensions of the focusing element and the arrangement of the coiled filaments of the focusing element.

[0066] The first segment 816, the second segment 818, the third segment 832, and the fourth segment 834 can have an extended surface 848. The extended surface 848 can be part of an outer shield surface 850. The first sidewall 804, the second sidewall 806, the third sidewall 808, and the short extension 810 can have a columnar outer periphery 825. A central opening of the cathode mask 800 can be defined by the openings in the extended surfaces 848, the openings in the inner shield surface 852, and the outer periphery 824. In this manner, the extended surface 848 can form an outer periphery or frame of the central opening.

[0067] In one embodiment, the extended surface 848 has rounded edges. For example, the extended surface 848 curves or rolls inward toward the inner shield surface 852 to form a curved edge transition around the opening. For example, the extended surface 848 can curve from a plane generally perpendicular to the xy plane of the cathode mask 800 to a plane generally parallel to the xy plane in some embodiments. When the cathode assembly is assembled, the central opening can receive a cathode cup, the cylindrical outer surface 825 can be generally flush with the rear surface of the cathode cup, and the extended surface 848 can surround a focusing element (such as the rear surface 426 and focusing element 375 of the cathode cup 62 described with reference to FIGS. 2-7 ).

[0068] FIG. 9A shows a cross-section 900 of the cathode mask 800 of FIG. 8, taken along dashed line 9-9 in FIG. 8. The cross-section 900 illustrates an example of a convergence portion of the cathode mask 800. The convergence portion is an edge transition portion of the central opening of the cathode mask. In this example, the edge transition portion may be a peripheral edge that includes rounded edges. FIG. 9B is a detailed view 950 of the cross-section shown in FIG. 9A. Similar components are numbered similarly to FIG. 8. A set of reference axes 901 is illustrated to allow comparison between FIGS. 9A and 9B, showing the x-axis, y-axis, and z-axis.

[0069] The cross-sectional view 900 is taken through the third segment 832 of the third side wall 808 and the fourth segment 834 of the front panel 812 and shows the rounded edge 902. The walls 904 of the cathode mask 800 can be bent to form the rounded edge 902. For example, the walls 904 in the region of the rectangular extension 811 can be formed to be bent perpendicular to the z-axis, with the inner portion facing toward the centerline 911 of the central opening. The curved portion of the wall 904 can be fully rounded along the longitudinal axis. The rounded edge 902 can include a substantially rounded extension surface 848 and a peripheral edge 906 facing the centerline 911.

[0070] The curved portion of the rounded edge 902 can be the same at each end of the rectangular extension 811, and the first segment 816, the second segment 818 (see FIG. 8), the third segment 832, and the fourth segment 834 can be curved to the same dimensions. The rounded edge 902 protects the outer periphery 906 from electric field stresses and allows the coiled filament or filaments to achieve a sufficient focusing field.

[0071] 9B details example dimensions of the rounded edge 902. The rounded edge 902 is electrostatically advantageous and limits the kV / mm of the shielded area. The rounded feature provides the same kV / mm as a larger radius without extending "further down" toward the grid electrode (e.g., focusing element 375). By not extending "further down," a larger opening can be created, which increases the focusing field and increases electron emission.

[0072] In the illustrated example, the rounded edge 902 can be generally parallel to a first axis 908 along a first length 910. An intersecting second axis 914 and the first axis 908 are at a right angle. A third axis 916 intersects the perimeter edge 906, the first axis 908, and the second axis 914. The intersecting third axis 916 and the second axis 914 form a bend angle 912. In one example, the bend angle 912 can have a lower threshold angle of 69° and an upper threshold angle of 75°.

[0073] The first bend portion 918 has a first bend radius 920. In one example, the first bend radius 920 can have a lower radius threshold of 1.5 mm and an upper radius threshold of 2.5 mm. The second bend portion 922 has a second bend radius 924. In one example, the second bend radius 924 can have a lower radius threshold of 1.9 mm and an upper radius threshold of 2.5 mm. In one example, the first bend radius 920 and the second bend radius 924 can be different dimensions. The rounded edge 902 includes a first bend length 928 between the second axis 914 and the fourth axis 926, the first bend length 928 being the length of the first bend portion 918 and the second bend portion 922 relative to the y-axis. The rounded edge 902 includes a second bend length 930 that is the length of the first bend portion 918 and the second bend portion 922 relative to the z-axis. In one embodiment, the first bend length 928 can be longer than the second bend length 930.

[0074] Thus, in at least some embodiments, the cathode masks disclosed herein can include various curved portions, i.e., curved portions at edge transitions (e.g., rounded edges 902) and U-shaped curved portions at central openings (e.g., central opening 340). These converging portions of a cathode mask (e.g., cathode mask 800) can cooperate to increase the converging field of one or more coiled filaments of different strengths and / or dimensions, thereby reducing high voltage instabilities.

[0075] 10 shows a perspective view of an example of a second shield portion 1000 that is part of a cathode shield assembly for a cathode. The second shield portion 1000 can be the same as or similar to the second shield portion 304 described with reference to FIGS. 3-7. A set of reference axes 1001 is shown, indicating the x-axis, y-axis, and z-axis, to allow comparison between the views shown.

[0076] In one embodiment of the disclosed cathode shield assembly, the second shield portion 1000 can be substantially ring-shaped. The second shield portion 1000 is radially symmetrical about a radial symmetry line 1002. The second shield portion 1000 has an annular wall 1004. The annular wall 1004 has an annular outer surface 1006 and an annular inner surface 1008. The second shield portion 1000 has a central hollow portion defined by a first circular opening in the inner surface 1014, a second circular opening in the outer surface 1016, and the annular inner surface 1008. In one example, the second shield portion 1000 can have a flat rim 1012 on the inner surface 1014 and a flared lip 1010 on the outer surface 1016. When assembled into the cathode assembly, the central hollow portion can surround a lower extension (such as lower extension 405 in FIG. 4 ). The flared lip 1010 can contact a ceramic insulator (such as small insulator 428 in FIG. 4). A flat rim 1012 can be provided on the mating portion of the lower extension. In one example, the annular inner surface 1008 of the flat rim 1012 can be in surface contact with one or more window surfaces of the lower extension (such as lower extension window surface 456 of window 450 in FIG. 4).

[0077] The second shield portion 1000 can have a ring length 1018 relative to the y-axis. The second shield portion can have a first inner diameter 1020 and a second inner diameter 1022 relative to the radial symmetry line 1002. The first inner diameter 1020 can be determined, for example, based on the dimensions of the lower extension (e.g., lower extension 405). The second inner diameter 1022 can be determined based on the shape (e.g., the outward angle) of the flared lip 1010. The ring length 1018 can be determined based on several factors. For example, by keeping the gap space (e.g., gap spacing 478 shown in FIG. 4 ) between the first shield portion (e.g., first shield portion 302) and the second shield portion 1000 as wide as possible, radiative heat transfer can be increased. However, if the length of the second shield is made too short, the shielding effectiveness of the grounded cathode components can be reduced. In addition, reduced shielding effectiveness for cold components can result in insufficient cooling. Determining the appropriate length can involve a trade-off between covering the weld, which can interfere with high voltage stability, and allowing as much radiative heat transfer as possible.

[0078] By separating the shield into a first shield section and a second shield section, as opposed to the one-piece cathode shielding common in x-ray systems, the disclosed shield promotes radiative heat transfer to the frame and reduces overall cathode temperature. The disclosed curved section of the cathode mask has the additional benefit of increasing the focusing power of one or more coiled filaments (e.g., the exemplary three-filament configuration shown in Figures 3-7) and reducing electric field stress at the cathode mask terminations. When used in smart cathode systems, the cathode shield assembly can improve high voltage stability, extend x-ray tube life, and improve resolution and accuracy for a variety of x-ray applications.

[0079] In some examples, the disclosed cathode shield can include a cathode mask having a central opening and outer peripheral edge of a different shape. As one example, the cathode assembly can include a cathode cup having only a single coiled filament. For such a cathode assembly, as one example, the cathode mask can have a square extension rather than a rectangular extension, and the outer peripheral edge of the central opening can include a rounded edge. Alternatively, the extension can be oval or circular, and the outer peripheral edge can have a curved end transition. As another example, the cathode assembly can include a coiled filament positioned within the cathode cup such that the straight sides are better suited for electric field focusing, rather than the exemplary U-shape. In such examples, a cathode shield including an opening (e.g., by virtue of gap spacing and a large view factor) can support various configurations of cathode cups and coiled filaments while still providing the advantage of promoting radiant heat transfer.

[0080] In other embodiments, the disclosed cathode shields can include cathode masks (e.g., cathode mask 800) having a central opening and a peripheral edge formed with one or more curved portions, used in combination with complementary shield portions of different configurations. As an example, a cathode mask having a U-shaped central opening and rounded edges can be used with a disk shield of a different shape. For example, the disk shield can be shaped differently to increase the view factor for frames of a different shape and / or to shield larger or differently aligned insulators. In such examples, a cathode mask incorporating the disclosed curved portions at the central opening and peripheral edge can increase the focal field of a smart cathode having one or more coiled filaments while supporting various x-ray tube designs.

[0081] In this way, selective shielding can be used in areas of high electric field stress while leaving other areas open, reducing heat conduction and concentration in and around temperature-sensitive cathode components. By configuring the cathode mask shield to tailor the focusing by one or more coiled filaments, smart cathodes can achieve a range of currents suitable for diagnostic and interventional applications without losing focusing power. The technical effect is increased x-ray tube life, improved x-ray tube reliability, and improved x-ray beam delivery performance.

[0082] The present disclosure also provides a support for a shield assembly for a cathode. The shield assembly for a cathode includes a first shield portion and a second shield portion, the first shield portion and the second shield portion being spaced apart from each other so as not to be in direct physical contact. In a first embodiment of the system, the first shield portion includes a disk shield and a cathode mask, and the second shield portion surrounds a lower extension of the cathode. In a second embodiment of the system, optionally including the first embodiment, the disk shield includes a substantially concave disk having a curved lip, and the cathode mask includes a central opening configured to receive a cathode cup. In a third embodiment of the system, optionally including one or both of the first and second embodiments, the disk shield includes a first cutout portion, a cathode cup protruding from the first cutout portion, the first cutout portion being substantially rectangular and offset from the center of the disk shield. In a fourth system embodiment, optionally including one or more of the first through third systems, the second shield portion is substantially ring-shaped. In a fifth system embodiment, optionally including one or more of the first through fourth systems, the cathode mask is post-shaped with a rectangular extension. In a sixth system embodiment, optionally including one or more of the first through fifth systems, the second shield portion is a ring-shaped member having a flared lip on a first circular opening side and a flat rim on an opposing second circular opening side. In a seventh system embodiment, optionally including one or more of the first through sixth systems, the disk shield and the cathode mask are a single, integrally formed, continuous member.

[0083] The present disclosure also provides a support for a cathode assembly for an X-ray device. The cathode assembly for an X-ray device includes a cathode cup that houses a focusing element, a lower extension that couples the cathode cup to an insulator, the lower extension surrounding an electrical lead, and a cathode shield assembly including a first shield portion and a second shield portion, the first shield portion and the second shield portion being spaced apart from each other so as not to be in direct physical contact with each other. In a first embodiment of the system, the first shield portion includes a disk shield and a cathode mask, and the second shield portion surrounds the lower extension. In a second embodiment of the system, optionally including the first embodiment, the system includes a gap between the first shield portion and the second shield portion, the gap exposing a rear surface of the cathode cup and a portion of the lower extension. In a third embodiment of the system, optionally including one or both of the first and second embodiments, the first shield portion and the second shield portion are formed from electropolished nickel. In a fourth embodiment of the system, optionally including one or more of the first through third embodiments, the cathode cup is mounted to the lower extension at an angle. In a fifth embodiment of the system, optionally including one or more of the first through fourth embodiments, the focusing element includes two or more coiled filaments. In a sixth embodiment of the system, optionally including one or more of the first through fifth embodiments, the disk shield includes a substantially concave disk with a curved lip, the cathode mask has a central opening configured to receive the cathode cup, and the second shield portion is substantially ring-shaped.

[0084] The present disclosure also provides support for an imaging system. The imaging system includes a collector electrode assembly, an anode assembly, a cathode assembly configured to focus an electron beam onto the anode assembly, and a frame that houses at least a portion of the collector electrode assembly, the anode assembly, and the cathode assembly. The cathode assembly includes a cathode cup attached to a lower extension and a cathode shield assembly, the cathode shield assembly including a first shield portion and a second shield portion, the first shield portion and the second shield portion being spaced apart so as not to contact each other. In a first embodiment of the system, the first shield portion includes a disk shield and a cathode mask, and the second shield portion surrounds the lower extension. In a second embodiment of the system, optionally including the first embodiment, the cathode shield assembly exposes a portion of the cathode cup where an electric field stress intensity is less than an intensity threshold and where a view factor relative to the frame is greater than an emissivity threshold. In a third embodiment of the system, optionally including one or both of the first and second embodiments, the collector assembly includes a window through which x-rays generated by the anode assembly are emitted and an electron collector for absorbing backscattered electrons within the imaging system. In a fourth embodiment of the system, optionally including one or more of the first through third embodiments, the anode assembly includes a target onto which the electron beam is focused, a rotor, and a bearing arm.

[0085] 2-10 illustrate exemplary configurations of the relative positions of various elements. When elements are shown as being in direct contact with or directly connected to one another, these elements can, in at least one embodiment, be referred to as directly contacting elements or directly connected elements, respectively. Similarly, elements shown as being contiguous or adjacent to one another can, in at least one embodiment, be referred to as contiguous elements or adjacent elements, respectively. As an example, elements in surface contact with one another can be referred to as surface contacting elements. As another example, elements spaced apart from one another can, in at least one embodiment, be referred to as separated elements if there is space between the elements but not other elements. As another example, elements shown above and below one another, opposite one another, or left and right from one another can be referred to as above and below, opposite one another, or left and right. Furthermore, as shown in the figures, in at least one embodiment, the topmost element or the uppermost point of an element can be referred to as the "top" of the element, and the bottommost element or the lowermost point of an element can be referred to as the "bottom" of the element. As used herein, top / bottom, upper / lower, and above / below represent relative to the vertical axis of the figure and are used to describe the relative positions of elements of the figure with respect to one another. Thus, elements shown on top of other elements, in one example, are vertically positioned above the other elements. As yet another example, the shapes of elements shown in the figures can be said to have those shapes (e.g., circular, rectilinear, flat, curved, rounded, chamfered, angled, etc.). Furthermore, elements shown to intersect with one another, in at least one example, can be referred to as intersecting elements or intersecting elements. Furthermore, elements shown within or outside of other elements can, in one example, be referred to as elements shown within or outside of other elements.

[0086] As used herein, elements or steps described in the singular and preceded by the words "a" or "an" should be understood as not excluding a plurality of such elements or steps, unless the exclusion is explicitly stated. Furthermore, references to "one embodiment" of the invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Furthermore, unless expressly stated to the contrary, embodiments that "comprising," "including," or "having" an element or elements having a particular characteristic may include additional elements that do not possess that characteristic. The terms "including" and "in which" are used as the plain-language equivalents of the terms "comprising" and "wherein," respectively. Furthermore, terms such as "first," "second," and "third" are used merely as labels, and are not intended to impose numerical requirements or a specific positional order on their objects.

[0087] As used herein, the term "about" is interpreted to mean ±5% of the range unless otherwise specified, and the term "substantially concave" means that an element does not have to be perfectly concave, but has a shape sufficient enough for one of ordinary skill in the art to consider it concave. As used herein, the term "substantially rectangular" means that an element does not have to be perfectly rectangular, but has a shape sufficient enough for one of ordinary skill in the art to consider it rectangular. As used herein, the term "substantially cylindrical" means that an element does not have to be perfectly cylindrical, but has a shape sufficient enough for one of ordinary skill in the art to consider it cylindrical.

[0088] This written description uses examples to disclose the invention, including the best mode, and also enables any person skilled in the art to practice the invention, including making and using any devices or systems, and performing any methods incorporated therein. 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 contain structural elements that do not differ from the literal language of the claims, or equivalent structural elements that do not differ substantially from the literal language of the claims. [Explanation of symbols]

[0089] 10 Imaging System 12 X-ray source 14 X-ray beam 16 Object 18 Detector Assembly 20 processors 22 Computer 24 Operator Console 26 Display device 28 Storage device 30 Source Controller 40 x-ray tube 42 Anode Assembly 44 Cathode Assembly 46 frames 48 Anode 50 Bearing Assembly 52 Cathode 54 Space 58 Central insulating shell 60 Mask 62 Cathode cup 64 X-ray 66 Target 68 Windows 70 center line 72 rotor 74 Opening 76 Central Shaft 78 Sleeve 80 refrigerant flow path 82 Focusing electrode assembly 84 Electronic Collector 200 X-ray source 202 First Shield Section 204 Second Shield Section 300 Cathode Assembly 302 First Shield Section 304 Second Shield Section 310 Lip 312 flat area 314 Inclined Transition 315 First Center Line 316 Surface 317 Center axis 322 First Outer Surface 324 sides 326 Extension 328 Side wall 330 Second Outer Surface 332 Front Panel 338 outer edge 340 central opening 358 Large Insulator 362 Cathode Mask 365 Disc Shield 375 Focusing Element 376 First Filament 378 Second Filament 380 Third Filament 404 First Interior 405 Lower extension 406 Outer part 408 Inner part 412 Disc Shield Width 416 Outer edge 418 Inclination Angle 420 length 424 First Offset 426 Rear 428 Small Insulator 440 Air Gap 444 Base 446 Insulator 448 Welding Pad 460 Mounting wall 462 sides 464 Second dashed line 466 Tilt Angle 468 Sleeve parts 472 Flared Lip 474 rims 476 Third Length 478 Gap Spacing 480 opening area 502 dotted line 602 First Channel 604 Second Channel 606 Third Channel 608 First Axis 610 Second Axis 612 Third Axis 614 Fourth Axis 674 Second bending dimension 676 First bending dimension 680 First bend 682 Second bend 684 Third Bend 686 Fourth Bend 702 First Side 704 Second Side 718 Edge 800 Cathode Mask 802 Line of symmetry 803 Horizontal centerline 804 First side wall 806 Second side wall 808 Third Sidewall 810 Extension 811 Rectangular extension 812 Front Panel 814 Transition Surface 816 First Segment 818 Second Segment 822 First Height 824 Peripheral Surface 825 Outer surface 826 First Depth 830 Third Length 832 Third Segment 834 Fourth Segment 838 First Width 840 Second Depth 842 Second Height 844 Third Height 846 Second Height 848 Extension surface 850 outer shield surface 852 Inner shield surface 852 Internal shield surface 904 Wall 906 outer edge 908 First Axis 910 First Length 911 Center line 912 bending angle 914 Second Axis 916 Third Axis 918 First bend 920 First bending radius 922 Second bending section 924 Second bending radius 926 Fourth Axis 928 First bending length 930 Second bending length 1000 Second shield part 1002 Radial symmetry line 1004 Circular Wall 1006 Circular outer surface 1008 Annular inner surface 1010 Flared Lip 1012 Edge 1014 Inside 1016 External surface 1018 Circular Length 1020 First inner diameter 1022 Second inner diameter

Claims

1. A shield assembly for a cathode assembly including a cathode cup and a lower extension (405) connecting the cathode cup to an insulator (58), a first shield portion (202) and a second shield portion (204); the first shield portion includes a disk shield (365) and a cathode mask (362) that partially surrounds the cathode cup, and the second shield portion surrounds the lower extension (405); A shield assembly, wherein the first shield portion and the second shield portion are spaced apart from each other so as not to be in direct physical contact with each other.

2. 2. The shield assembly of claim 1, wherein the disk shield (365) comprises a substantially concave disk having a curved lip (310), and the cathode mask includes a central opening (340) configured to receive a cathode cup (62).

3. 2. The shield assembly of claim 1, wherein the disk shield (365) includes a first cutout portion, a cathode cup (62) protruding from the first cutout portion, the first cutout portion being generally rectangular and offset from the center of the disk shield.

4. The shield assembly of claim 1 , wherein the second shield portion (304) is generally ring-shaped.

5. The shield assembly of claim 1 , wherein the cathode mask (362) is post-shaped with rectangular extensions.

6. 2. The shield assembly of claim 1, wherein the second shield portion (304) is a ring-shaped member having a flared lip (472) on a first circular opening side and a flat rim (474) on an opposing second circular opening side.

7. The shield assembly of claim 1 , wherein the disk shield and the cathode mask are integrally formed as a single continuous member (202).

8. 1. A cathode assembly for an x-ray device, comprising: a cathode cup (62) containing a focusing element (375); a lower extension (405) connecting the cathode cup to the insulator (58), the lower extension surrounding the electrical lead (56); and A cathode shield assembly including a first shield portion (202) and a second shield portion (204), the first shield portion and the second shield portion being spaced apart from each other so as not to be in direct physical contact with each other. Including, The cathode assembly, wherein the first shield portion includes a disk shield (365) and a cathode mask (362) that partially surrounds the cathode cup, and the second shield portion surrounds the lower extension.

9. 10. The cathode assembly of claim 8, including a gap spacing (478) between the first shield portion and the second shield portion, the gap spacing exposing a rear surface (426) of the cathode cup and a portion of the lower extension.

10. The cathode assembly of claim 8, wherein the first shield portion (302) and the second shield portion (304) are formed from electropolished nickel.

11. The cathode assembly of claim 8, wherein the cathode cup (62) is mounted (466) to the lower extension (405) in an inclined manner.

12. The cathode assembly of claim 8, wherein the focusing element (375) comprises two or more coiled filaments.

13. 9. The cathode assembly of claim 8, wherein the disk shield (365) comprises a generally concave disk having a curved lip (310), the cathode mask (362) has a central opening (340) configured to receive the cathode cup (62), and the second shield portion (304) is generally ring-shaped.

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