Magnetic assist assembly having heat dissipation

In one example, a lift assembly may exert a force on a rotatable anode of an X-ray tube. The lift assembly may include a lift shaft and a lift electromagnet. The lift shaft may be coupled to the anode and may be configured to rotate around an axis of rotation of the anode. The lift electromagnet may be configured to apply a magnetic force to the lift shaft in a radial direction. The lift electromagnet may include a first pole and a second pole oriented towards the lift shaft. Windings may be positioned around the first pole. The lift assembly may include a heat dissipating structure.

BACKGROUND

The present disclosure generally relates to X-ray imaging systems, including embodiments relating to magnetic lift assemblies for X-ray sources used in X-ray imaging systems.

X-ray imaging systems typically include an X-ray source, a detector, and a support structure, such as a gantry, for the X-ray source and the detector. In operation, the X-ray source typically emits radiation, such as X-rays, toward an object. The radiation passes through the object and impinges on the detector. The detector receives the radiation and transmits data representative of the received radiation.

The X-ray source includes a cathode and an anode separated by a vacuum gap. X-rays are produced by applying an electrical current to an emitter of the cathode which emits electrons. The electrons accelerate towards and then impinge upon the anode. When the electrons impinge on the anode, some of the energy is converted to X-rays. The majority of the energy in the incident electron beam converts to heat in the anode. Because of high temperatures generated when the electron beam strikes the target, the anode can include features to distribute the heat generated, such as rotating a disc-shaped anode target. The disc-shaped anode target may be rotated by an induction motor via a bearing assembly.

The X-ray source and radiation detector can be components in an X-ray imaging system, such as a computed tomography (CT) system or scanner, which includes a gantry that rotates both the X-ray source and the detector to generate various images of the object at different angles. The gravitational (G) forces imposed by the rotation of the gantry and/or the rotation of the anode may result in stresses on components of the X-ray source. In particular, G forces resulting from the rotation of the gantry and/or the anode may result in stress on the bearing assembly of X-ray sources with rotating anodes. In addition, the stress on the bearing assembly may increase as rotation speeds increase, but increased rotation speeds may be desirable for high-performance X-ray sources and CT systems. The present disclosure includes solutions related to reducing the stresses on bearing assemblies in rotating X-ray imaging systems (e.g., CT scanners).

DETAILED DESCRIPTION

Reference will be made to the drawings and specific language will be used to describe various aspects of the disclosure. Using the drawings and description in this manner should not be construed as limiting its scope. Additional aspects may be apparent in light of the disclosure, including the claims, or may be learned by practice.

The invention relates to embodiments for dissipating heat generated by lift assemblies which may be used to reduce loads on rotating components of an X-ray tube. X-ray tubes generate heat during operation. Accordingly, X-ray tubes may include features such as rotating anodes to spread the heat generated. However, rotating components of a rotating anode may experience forces resulting from gantry rotation in CT systems. Thus, lift assemblies may be incorporated into X-ray tubes to counter balance the forces on rotating components. Such lift assemblies may also generate heat that may need to be dissipated. Accordingly, disclosed embodiments include example configurations to dissipate heat generated by the lift electromagnet.

Reference will now be made to the drawings to describe various aspects of example embodiments of the disclosure. It is to be understood that the drawings are diagrammatic and schematic representations of such example embodiments, and are not limiting of the disclosure, nor are they necessarily drawn to scale.

FIG. 1is a schematic diagram of an example rotary or rotating anode X-ray source100with a rotatable disc-shaped anode122. The X-ray source100includes a housing102and an X-ray insert110within the housing102. The housing102encloses the insert110. A fluid coolant such as a dielectric oil or air may fill the space or cavity between the housing102and the insert110to dissipate heat generated by the X-ray source100.

A cathode assembly114including a cathode112and an anode assembly120are positioned within an evacuated enclosure (or vacuum envelope) defined by the insert110. The anode assembly120includes the anode122, a bearing assembly130, and a rotor128mechanically coupled to the bearing assembly130. The anode122is spaced apart from and oppositely disposed to the cathode112. The anode122and cathode112are connected in an electrical circuit that allows for the application of a high voltage difference (or high electric potential) between the anode122and the cathode112. The cathode112includes an electron emitter116that is connected to a power source.

Prior to operation of the X-ray source100, the insert110may be evacuated to create a vacuum, which may be enclosed by the insert110. During operation, heat and electrical potential is applied to the electron emitter116of the cathode112to cause electrons, denoted as “e” inFIG. 1, to be emitted from the cathode112by thermionic emission. The application of a high voltage differential between the anode122and the cathode112then causes the electrons “e” to accelerate from the electron emitter116toward a focal spot on a focal track124that is positioned on the anode122. The focal track124may include, for example, a material having a high atomic (“high Z”) number such as tungsten (W), rhenium (Re) or other suitable material. As the electrons “e” accelerate, they gain a substantial amount of kinetic energy, and upon striking the rotating focal track124some of this kinetic energy is converted into X-rays, denoted as “x” inFIG. 1.

The focal track124is oriented so that emitted X-rays “x” may travel through an X-ray source window104. The window104includes an X-ray transmissive material, such as beryllium (Be), so the X-rays “x” emitted from the focal track124pass through the window104in order to strike an intended object and then a detector to produce an X-ray image.

As the electrons “e” strike the focal track124, a significant amount of the kinetic energy of the electrons “e” results in heat, a large portion of which is transferred to the focal track124, particularly in the region of the focal spot. To reduce the heat at a specific focal spot on the focal track124, a disc-shaped anode target is rotated at high speeds, typically using an induction motor that includes a rotor128and a stator106. The induction motor can be an alternating current (AC) electric motor in which the electric current in the rotor128needed to produce torque is obtained by electromagnetic coupling with the stator winding. The rotor128is mechanically coupled to the anode122through a hub of the bearing assembly130such that rotation of the rotor is transferred to the anode. In other configurations, the motor can be a direct current (DC) motor.

To avoid overheating the anode122from the heat generated by electrons “e”, the rotor128rotates the anode122at a high rate of speed (e.g., 80-300 Hz) about a centerline of a shaft so that the region of the anode exposed to the beam of electrons “e” varies along the focal track124. The X-ray source100can also include other cooling features to manage the heat generated by the anode122and the cathode112.

An X-ray source (such as the X-ray source100) and a radiation detector can be included in a rotational X-ray imaging system, such as a computed tomography (CT) scanner. CT involves the imaging of the internal structure of an object by collecting several projection images (“radiographic projections”) in a single scan operation (“scan”), and is widely used in the medical field to view the internal structure of selected portions of the human body. Typically, several two-dimensional projections are made of the object, and a three-dimensional representation of the object is constructed from the projections using various tomographic reconstruction methods. From the three-dimensional image, conventional CT slices through the object can be generated. The two-dimensional projections are typically created by transmitting radiation from an X-ray source through the object and collecting the radiation onto a two-dimensional imaging device (i.e., radiation detector), or imager, which may include an array of pixel detectors (simply called “pixels”). One example of such a CT system is shown inFIG. 2A.

FIG. 2Aillustrates an example of a gantry200of a rotating X-ray system. In some circumstances the gantry200may be referred to as a rotating assembly or a gantry assembly. The gantry200includes a stationary gantry frame204that supports a rotatable gantry frame202. The rotatable gantry frame202may support an X-ray source210and a radiation detector or imager (not shown). The gantry200also includes a gantry cover206to enclose the rotating components and/or the stationary gantry frame204as well as provide an aesthetic covering.

The rotatable gantry frame202may include an annular shape (i.e., ring shape) that rotates about a center of axis in a gantry aperture208of the rotatable gantry frame202. The centrifugal force (or gantry force), denoted via arrow260, on components disposed on the rotatable gantry frame202may exceed a unit of gravitational force (g-force, G's, g's, or G loads), and may be a multiple of the g-force (e.g., 20 times the g-force). For example, components on the X-ray source210, such as the bearing assembly, may experience a force of37g's if the X-ray source210is mounted on the rotatable gantry frame202at a radius of 0.7 meters from the center of axis and the rotatable gantry frame202is rotating at 0.275 seconds/rotation (sec/rot).

Generally, it is desirable for CT scanners to operate at higher rotational gantry speeds. However, operating CT scanners with gantries that rotate at higher speeds may adversely affect X-ray source bearing life because the bearing assemblies experience larger forces (e.g., g-forces from gantry rotation). In such circumstances, higher gantry speeds, and resultant centrifugal forces260, can decrease the life of the bearing assembly.

Some X-ray sources implement liquid metal bearings (LMB), which may be capable of effectively handling higher forces (e.g., g-forces). However, implementing LMB can significantly increase costs and may require significant changes to the system design (e.g., the design of the X-ray source).

Other X-ray sources may implement magnetic lift configurations to magnetically assist in supporting the rotating components of the X-ray source and to decrease the forces on the bearing assembly. In some circumstances, such configurations may be advantageous over LMB because they may be implemented in existing imaging systems and/or they may provide very cost effective backwardly compatible improvements. With attention toFIG. 2B, an example of a magnetic lift configuration will be described in further detail.

FIG. 2Billustrates a portion of the gantry200, and in particular, the X-ray source210attached to the rotatable gantry frame202. The X-ray source210includes a source housing211, an anode242that can receive electrons emitted by a cathode (112ofFIG. 1), a rotor234coupled to a shaft243of the anode242, a stator232surrounding the rotor234, a ferromagnetic lift shaft226coupled to the rotor234, and a lift electromagnet222(or lift multipole electromagnet or electromagnet) that can provide a magnetic lift force, denoted via arrow262, to the lift shaft226and thereby “lift” the rotor234and the shaft243of the anode242along the radial direction with respect to the axis of rotation of the gantry in opposition to the centrifugal force.

As used herein, lifting refers to an application of force along the radial direction of the lift shaft226. The lifting or lift force can be an attractive force that pulls two components together (e.g., the lift shaft226and the lift electromagnet222) or a repulsive or repelling force that pushes two components apart (e.g., the lift shaft226and the lift electromagnet222). In this disclosure, reference will be made to the lifting or the lift force as an attractive force, but the lifting or the lift force can be a force with any magnitude (positive or negative) along the radial direction.

For descriptive purposes,FIG. 2Bincludes a Cartesian coordinate system with the y-axis in the vertical direction, the x-axis in the horizontal direction, and the z-axis orthogonal to the x-y plane. The rotation of the gantry200occurs in the x-y plane and the centerline of the shaft243of the anode242or the axis of rotation of the anode242extends parallel to the z-axis. During gantry rotation, a centrifugal force260is applied to the X-ray source210orthogonal-axis213of the gantry200.

The lift electromagnet222may apply the magnetic lift force262(e.g., magnetic force, counter acting force, or balancing force) in substantially the opposite direction of the centrifugal force260so as to offset, dampen, reduce, or balance the forces (including the centrifugal force260of the gantry200) on the bearing assembly or anode assembly. The magnetic lift force262may result in one or more of the following: reduce vibration or noise, increase bearing life, increase the bearing load capability, control thermal contact, improve the centering and precision of the rotating assembly, and allow the use of smaller bearings (e.g., ball bearings or other rotating bearings). Additionally or alternatively, the assistance of the magnetic lift force262may permit the use of other bearing types in a rotating anode X-ray source. In the case of medical imaging, reducing vibration and noise may also improve the patient's and/or medical staff's experience.

FIG. 3Aillustrates a perspective view of the X-ray source210. As shown inFIG. 3A, the X-ray source210may include an envelope, also referred to as an insert,212that includes a wall (e.g., insert wall, vacuum wall or vacuum envelope wall) that encloses the cathode and anode in an evacuated enclosure (or vacuum envelope). The insert212may enclose an anode assembly240, a bearing assembly250, a motor assembly230and a lift assembly220. The lift electromagnet222may include a lift electromagnet core225with three poles formed in an “M” or “W” shape with windings (or coils or wires)224wrapped around the core225between the poles as shown, or around the poles.

FIG. 3Billustrates a perspective section view of the X-ray source210andFIG. 3Cillustrates a side cross section view of the X-ray source210. As shown inFIGS. 3B-3C, the anode assembly240, the bearing assembly250, the motor assembly230, and lift assembly220may facilitate rotation about an anode assembly centerline (or bearing centerline)248. The anode assembly240includes an anode242and an anode outer shaft244that supports the anode242. The anode assembly240also includes an anode inner shaft246that is coupled to the anode outer shaft244and rotatably coupled to the bearings252and254of the bearing assembly250.

The anode inner shaft246may include at least one bearing race (e.g., ball bearing race). For example, in the illustrated configuration the bearing assembly250includes the outer ball bearing252and a corresponding race on the anode inner shaft246, and an inner ball bearing254and a corresponding race. As used herein, outer refers to a relative position closer to an edge of the anode assembly240, closer to the anode242, or further away from the motor assembly230. Inner refers to a position closer to a middle of the anode assembly240, further away from the anode242, or closer to the motor assembly230.

Although the illustrated embodiment includes a roller element bearing (e.g., tool steel ball bearing or tool steel raceways), in other embodiments other bearing types may be implemented. For example, other configurations may include plain bearings (e.g., a sleeve bearing or a journal bearing), or hydrodynamic bearings, such as liquid metal bearings. U.S. patent application Ser. No. 14/968,078, filed Dec. 14, 2015, entitled, “Antiwetting Coating for Liquid Metal,” which is hereby incorporated by reference in its entirety, discloses an example of a liquid metal bearing.

The motor assembly230may include a stator232and a rotor234. The rotor234includes a rotor void236or opening on one end, which may be cylindrical. The rotor void236allows the rotor234to be attached to the anode shaft (e.g., the anode inner shaft246) and/or aligned with the bearing centerline248. The components (e.g., the anode shaft, the rotor234, or the rotor shaft) may be attached to each other using a permanent or semi-permanent fastening or attachment mechanisms. An insert wall215(or a portion of the insert wall) proximate the motor assembly230may be disposed between the rotor234and the stator232. The electromagnetic induction from the magnetic field of winding of the stator232may pass through the insert wall215to the rotor234. A small gap between the insert wall215and the rotor234allows the rotor234to rotate without mechanical resistance.

The lift assembly220includes the lift shaft226coupled to the rotor234and the lift electromagnet222that may apply a magnetic force on the lift shaft226. The lift shaft226may include a lift shaft void227or an opening, which may be cylindrical. A rotor-to-lift shaft adapter238may couple the rotor234to the lift shaft226. The rotor-to-lift shaft adapter238can include a non-ferromagnetic material to improve magnetic isolation between the motor assembly230and the lift assembly220which both use magnetic fields for operation. In non-illustrated configurations, the lift shaft226may be integrated with or permanently attached (e.g., welded or brazed) to the rotor234.

The lift electromagnet222may include at least two poles that are oriented towards the lift shaft226. In some configurations, the lift electromagnet222may include three poles (tri-pole) formed in an “M” or “W” shape with windings224wrapped around the core225(or a core web) between the poles.

Material choices may affect the performance of a magnetic device, such as the lift electromagnet222or the lift shaft226. Magnetic material needs to stay magnetized in vacuum (e.g., the vacuum envelope of an X-ray source) and after processing and be vacuum compatible, such as cold drawn carbon magnetic iron (CMI-C).

The lift electromagnet222or the lift shaft226may include ferromagnetic and/or ferrimagnetic materials. As used herein and for simplicity in describing the technology, a “ferromagnetic” material refers to a material that can exhibit spontaneous magnetization (i.e., either a ferromagnetic material or a ferrimagnetic material).

The windings224around the core225may include an electrical conductive material (e.g., copper or aluminum) with an electrically insulated sheath, such as enameled magnet wire (i.e., transformer wire or Litz wire).

Two factors that can reduce the lift force between the lift shaft226and the lift electromagnet222are the size of the lift gap and the presence of interstitial materials such as the insert wall with magnetic permeability greater than 1. As shown inFIG. 3C, a lift gap228may be the spacing between the lift shaft226and the lift electromagnet222. The lift gap228may include the insert wall214proximate the lift assembly220along with a vacuum between the insert wall214and the lift shaft226. In some examples, the lift gap228may include the space between the insert wall214and the lift electromagnet222when the lift electromagnet222does not touch the insert wall214, such as when the lift electromagnet222and the insert wall214have different electrical potentials. The lift gap228that includes the vacuum provides clearance for the lift shaft226to rotate without mechanical resistance (e.g., friction from touching the insert wall214or the lift electromagnet222).

Vacuum and air have a relative magnetic permeability (represented by μr), of1, thus minimizing the dampening of the electromagnetic coupling between the electromagnet shaft226and the lift electromagnet222. The insert wall214is typically made of a conductive material with a magnetic permeability >1 such that it increases the dampening of the electromagnetic coupling between the lift electromagnet222and the lift shaft226reducing the lift force.

The lift assembly220may apply a magnetic lift force on the rotating assembly (via the lift shaft226), which can, for example, improve the operating lifespan and/or increase the load bearing capability of the bearing assembly250and components thereof. The magnetic force of the lift electromagnet222may be used to counteract loads on the bearing assembly250, such as the centrifugal force of the gantry (e.g., the gantry200), as well as to dampen vibration and add stability to the anode assembly (e.g. anode assembly240) or other rotating components of the X-ray source. The forces generated by the lift assembly220may be applied anywhere on the rotating assembly including at the center of mass (or not at the center of mass) and may employ one or a combination of magnetic lift devices that provide the forces.

As mentioned, X-ray tubes generate heat during operation. For example, when electrons strike the focal track or target of an anode, the kinetic energy of the electrons create heat. Additionally or alternatively, bearing assemblies, electromagnet lift assemblies and/or motor assemblies may generate heat via friction and/or Joule heating, although the amount of heat may be less than the heat generated from electrons striking the anode. The heat generated may need to be dissipated to avoid thermally stressing X-ray tube components.

Accordingly, X-ray tubes may include features to dissipate heat. For example, rotating disc-shaped anodes may be implemented to spread the heat generated by the electron beam across a larger area. A fluid coolant such as a liquid or air may fill a space or cavity between the housing and the insert defining the evacuated envelope to dissipate heat generated by the X-ray tube. The coolant fluid may surround and cool various portions of the X-ray tube, such as the insert and motor stator. In some configurations, the coolant fluid may be a dielectric oil or other suitable coolant. Additionally or alternatively, X-ray tubes may include heat exchangers, to dissipate heat from the coolant fluid to an exterior of the X-ray tube.

When lift assemblies are incorporated into X-ray tubes to counter balance forces on rotating components resulting from gantry rotation in CT systems, the lift assemblies may also generate heat that may need to be dissipated. To generate the required lift force to counter balance gantry rotation forces, lift electromagnets may require relatively high current passing through its core or windings. In one example, a current of 5 amperes (A) or larger may be passed through the windings of a lift electromagnet. This current may heat up the windings, in some circumstances generating 500 watts (W) or more of heat. If the heat generated by the lift electromagnet is not suitably dissipated, it may compromise various components of the lift assembly and/or the X-ray tube. For example, electrical insulation (e.g., around the windings) or other electrical wiring may be damaged by excessive heat. In another example, the coolant (e.g., a dielectric oil) surrounding the insert of the X-ray tube may break down and fail when exposed to excessive heat. Accordingly, the heat generated by the lift assembly may need to be dissipated for the lift assembly and the X-ray tube to operate properly.

Accordingly, disclosed embodiments include example configurations to dissipate heat generated by the lift electromagnet. For example, in some embodiments the lift electromagnet may be cooled by a coolant, such as a dielectric oil, that surrounds the lift electromagnet. In some configurations the coolant that cools the lift electromagnet may be the same coolant that cools the other portions of the X-ray tube (e.g., the anode, bearing assembly and/or motor assembly) and may be positioned between the housing and the insert of the X-ray tube.

In addition, disclosed embodiments include example configurations to increase heat dissipation from the lift electromagnet to the coolant referred to herein as heat dissipating structures, thermal dissipating structures, cooling structures, or heat transfer structures. For example, materials with relatively high heat conductivity may be implemented at the interfaces of various components to increase heat dissipation. In another example, the surface area of certain components, such as the windings or the core of the lift electromagnet, may be increased to improve heat dissipation.

Furthermore, disclosed heat dissipating structures include configurations to direct the coolant around the lift electromagnet to improve the flow of coolant proximate the lift electromagnet, thereby improving cooling. Some example configurations implement free convention to direct the flow of coolant proximate the lift electromagnet. In such configurations, the force of the rotation of the gantry may direct the coolant to flow proximate the lift electromagnet. Fins or thin thermally conductive planar structures may be oriented in a manner to increase heat dissipation as the coolant is driven by coolant flow or the centrifugal force of the rotating gantry. In other configurations, forced convection may be implemented to direct the flow of coolant proximate the lift electromagnet. In such configurations, fins may be oriented in a manner to increase forced convection heat dissipation as the coolant is driven proximate the lift electromagnet.

FIG. 4Aillustrates a perspective view of an example of a lift electromagnet300. The lift electromagnet300may include suitable aspects described with respect to the lift electromagnet222ofFIG. 3C, such as a core302and with three poles304,306,308. Windings310,312, and314may be wrapped around the core302between the poles304,306,308. The windings310,312,314may include an electrical conductive material (e.g., copper, aluminum or another suitable conductive material) with an electrically insulated sheath, such as a polymer (e.g., polymide, or another suitable insulating material).

FIG. 4Billustrates a bottom section view of the lift electromagnet300. As illustrated, a thermal interface316may be positioned between the windings310,312,314and the poles304,306,308(or the core302proximate the poles304,306,308). The thermal interface316may include a material with a relatively high thermal conductivity, and may facilitate the transfer of heat away from the windings310,312,314during operation. Although not shown, the thermal interface316may also be positioned around the windings310,312,314or other portions of the lift electromagnet300. In some configurations, the thermal interface316may be positioned on an external surface of the lift electromagnet300or the windings310,312,314.

The thermal interface316may facilitate the transfer of heat to the core302which may act as a heat sink during operation of the lift electromagnet300(e.g., as the gantry is rotating). In some configurations, the relatively large thermal mass of the core302may store heat generated at the windings310,312,314during operation of the lift electromagnet300. The stored heat may transfer to the coolant (e.g., to the coolant surrounding the lift electromagnet300) after the lift electromagnet300is turned off. In particular, the heat may transfer to the coolant in between scans, when the gantry is not rotating and therefore the lift electromagnet300does not need to be operating. Additionally or alternatively, the thermal interface316may facilitate the transfer of heat from the windings310,312,314and the core302to the coolant. The thermal interface316may facilitate heat dissipation by increasing the thermal contact area between different components.

The thermal interface316may include a solid or liquid material that has a relatively high thermal conductivity. In some configurations the thermal conductivity of the thermal interface316may be higher than the thermal conductivity of the coolant (e.g., a dielectric oil). Additionally or alternatively, the thermal interface316may include a material that conforms to the surface of the windings310,312,314and the core302(i.e., a “conformable material”), thereby forming a good thermal contact with a sufficiently large surface area. Since the thermal interface316may at least partially contact the coolant in some areas, the material of the thermal interface316may be selected so it does not break down in the coolant and/or does not release material into the coolant that may contaminate the coolant.

In some configurations, the thermal interface316may be a thermal grease, epoxy, filler, or potting material with a relatively high thermal conductivity. In other configurations, the thermal interface316may be a foil with a relatively high thermal conductivity. For example, the thermal interface316may include a material with a thermal conductivity of at least 0.5 W/(m·K) between 50 W/(m·K) and 200 W/(m·K) between 50 W/(m·K) and 500 W/(m·K), or between 50 W/(m·K) and 2200 W/(m·K). The thermal interface316may include a material such as copper, gold, silver, diamond, boron nitride, aluminum or other suitable materials.

The thermal interface316may be positioned or formed using any suitable technique. For example, the thermal interface316may be positioned around the poles304,306,308before the windings310,312,314are wound around the core302. In another example, the thermal interface316may be injected as a liquid or viscoelastic solid in a position between the windings310,312,314and the core302. Gas or air pockets may be removed via evacuation or another suitable manner. The thermal interface316may then be cured or allowed to solidify.

FIGS. 5 and 6illustrate perspective views of another example of a lift electromagnet400. The lift electromagnet400may include suitable aspects described with respect to the lift electromagnet222ofFIG. 3Cand/or the lift electromagnet300ofFIG. 4A. In particular, the lift electromagnet400includes a core402and with three poles404,406,408. Windings410,412, and414may be wrapped around the core402between the poles404,406,408.

As shown inFIG. 5, the lift electromagnet400may include protrusions or fins416(e.g., thin thermally conductive planar structures) positioned on one or more of the windings410,412, and414. AlthoughFIG. 5shows the fins416positioned on the pole404, the other poles406,408may also include the fins416. Additionally or alternatively, as shown inFIG. 4B, the lift electromagnet400may include protrusions or fins418positioned on or between one or more of the windings410,412, and414.

In some configurations, the fins416or418may be inserted into the windings410,412, and414. For example, the fins416,418may be inserted in between adjacent windings410,412, and414or interwoven with the windings410,412, and414. In other configurations, the fins416,418may be coupled to the windings410,412, and414using any suitable adhesive or fastening mechanism. In configurations where the lift electromagnet400includes a thermal interface, such as a thermal grease, epoxy, potting material or filler, the fins416,418may be inserted into or coupled with the thermal interface. Additionally or alternatively, the fins416,418may be formed of the thermal interface material. In particular, the fins416,418may be molded or otherwise formed from potting material or filler.

The fins416,418may include a material that has a relatively high thermal conductivity. For example, the fins416,418may include a material with a thermal conductivity of at least 0.5 W/(m·K), between 50 W/(m·K) and 200 W/(m·K), between 50 W/(m·K) and 500 W/(m·K) or between 50 W/(m·K) and 2200 W/(m·K). In some configurations, the fins416,418may include a material such as copper, gold, silver, diamond, boron nitride, aluminum or other suitable materials. The fins416,418may increase the surface area through which heat may travel from the lift electromagnet400to the surrounding coolant.

In the configuration ofFIG. 5, a coolant flow, denoted by420, may be caused by the rotation of the gantry and may cause the coolant to flow in a direction parallel to the centrifugal force along the lift electromagnet400(or perpendicular to the lift shaft, or the axis of rotation of the anode or the lift shaft). The direction of the centrifugal force may be perpendicular to an axis of rotation of the gantry. Such configurations may be referred to as free convection configurations, because the coolant flows freely around the lift electromagnet400.

In such configurations, the fins416may be shaped and positioned to extend parallel to the centrifugal force (or perpendicular to the lift shaft, or the axis of rotation of the anode or the lift shaft), and therefore parallel to the coolant flow420. In particular, the largest or longest dimension of the fins416may be parallel to the centrifugal force420and/or the flow of coolant. In such configurations, the coolant may flow over the fins416to remove heat, and the surface area of the fins416exposed to the flowing coolant may be maximized to facilitate free convection cooling of the lift electromagnet400.

In some configurations, the coolant may flow freely as a result of the centrifugal force420. In other configurations, the coolant may be forced to flow in a certain direction around the lift electromagnet400, rather than flowing freely as a result of the centrifugal force420. Similarly, as illustrated inFIG. 6the coolant may be directed to flow in a direction422. Such configurations may be referred to as forced convection configurations, because the coolant is directed around the lift electromagnet400in a specific direction. However, in other configurations the coolant may flow freely as a result of the centrifugal force or other forces. In the illustrated configuration, the direction422is perpendicular to the centrifugal force caused by the rotation of the gantry. Additionally or alternatively, direction422may be parallel to an axis of rotation of an anode or a lift shaft. Furthermore, the direction422may be parallel to the channels defined in between the poles404,406,408. However, in other forced convection configurations, the coolant may be directed in any suitable direction around the lift electromagnet400.

As shown inFIG. 6, the fins418may be shaped and positioned to extend substantially parallel to the direction422of coolant flow, and substantially perpendicular to the centrifugal force caused by the rotation of the gantry (or parallel to the lift shaft, or the axis of rotation of the anode or the lift shaft). In particular, the largest or longest dimension of the fins418may be generally parallel to the direction422and/or the flow of coolant. In such configurations, the coolant may flow over the fins418to remove heat, and the surface area of the fins418exposed to the flowing may be maximized to facilitate forced convection cooling of the lift electromagnet400.

As shown, the fins418may be substantially planar and may extend around each of the poles404,406,408. In some configurations, each of the poles404,406,408is surrounded by multiple dedicated fins418. For example, each of the fins418may be substantially planar with an opening defined to receive one of the poles404,406,408. In other configurations, each of the fins418surrounds all of three of the poles404,406,408. For example, each of the fins418may be substantially planar with three openings defined to receive each of the poles404,406,408.

In some circumstances, heat transfer for forced convection configurations may be greater than comparable free convection configurations because a larger amount of coolant flows over the fins418. In particular, the convective heat transfer coefficient for forced convection configurations may be multiple times larger than free convection configurations. In some circumstances, the convective heat transfer coefficient for forced convection configurations may be ten times larger than free convection configurations. Accordingly, forced convection configurations may be preferable in circumstances where large amounts of heat needs to be dissipated and removed. However, forced convection configurations may be more complicated and costly to implement, because components are required to force the coolant in specific directions and to specific areas of the lift electromagnet400.

FIG. 7Aillustrates a perspective view of another example of a lift electromagnet500andFIG. 7Billustrates a top view the lift electromagnet500. The lift electromagnet500may include suitable aspects described with respect to the lift electromagnets described above. In particular, the lift electromagnet500includes a core502and with three poles504,506,508. Windings510,512, and514may be wrapped around the core502between the poles504,506,508.

As shown, the lift electromagnet500may include openings516and518extending through the core502. The openings516may extend through the top of the core502to the spaces in between the poles504,506,508. The lift electromagnet500may also include slots or channels520positioned on the poles504,506,508(or extending the length of the poles504,506,508). In some configurations, the channels520may extend along the poles504,506,508and may be defined in the surface of the poles504,506,508. The openings518may extend through the top of the core502to the channels520to permit a coolant to travel in between the channels520and the openings518. AlthoughFIG. 7Ashows the channels520on the pole504, it should be appreciated that some or all of the poles504,506,508may include similar channels. The openings516,518and the channels520may be formed by any suitable process, for example, drilling or machining.

In some aspects,FIGS. 7A-7Bmay be free convention configurations where coolant flows freely around the lift electromagnet500. In other aspects, forced flow configurations may be implemented to direct coolant around the lift electromagnet500. A centrifugal force, denoted by522, caused by the rotation of the gantry may cause the coolant to flow in a direction parallel to the centrifugal force522along the lift electromagnet500. Additionally or alternatively, in some circumstances a coolant may include a thermal gradient, with hotter coolant positioned towards the bottom of the lift electromagnet500and cooler coolant positioned towards the top of the lift electromagnet500. In such circumstances, buoyancy may drive the hotter coolant upwards, parallel to the direction of the centrifugal force522.

The coolant may travel in between the poles504,506,508and through the openings516to transfer heat from the windings510,512,514and/or the poles504,506,508. Additionally or alternatively, the coolant may travel along the channels520and through the openings518to transfer heat from the windings510,514and/or the poles504,508. The channels520and the openings516,518may permit the coolant to flow parallel to centrifugal force522around and/or through the lift electromagnet500.

In other configurations, the coolant may be forced to flow in a certain direction around the lift electromagnet500, rather than flowing freely as a result of the centrifugal force522. In such configurations, a shroud may at least partially surround the lift electromagnet500and may include, inlets, outlets, channels and/or openings to direct coolant in specific directions (e.g., perpendicular to the centrifugal force522) around and/or through the lift electromagnet500.

The channels520and the openings516,518may be configured so as not to compromise the electromagnetic performance of the lift electromagnet500, and specifically the poles504,506,508and the windings510,512,514. Accordingly, the channels520and the openings516,518may be sized, shaped and positioned to avoid saturation in undesired places in the core502. For example, as shown inFIG. 7B, the openings516are substantially oval, with a longer dimension and a shorter dimension, and the longer dimension is positioned parallel to magnetic flux through the core502of the lift electromagnet500. Additionally or alternatively, the channels520may be configured so the cross-sectional area of the poles504,506,508is not decreased so as to negatively affect the electromagnetic performance of the lift electromagnet500.

In the free convection configurations described above, the rotation of the gantry may direct the flow of coolant around and through the lift electromagnets. When the gantry is at rest, the X-ray tube and therefore the lift electromagnets may be positioned at the top or the bottom of the gantry, and the force of gravity or buoyancy forces may drive the coolant around and through the lift electromagnets to transfer heat. Accordingly, the free convention configurations may operate to cool the lift electromagnets even in circumstances where the gantry is not rotating. Although in such circumstances the coolant may not flow through the lift electromagnets as rapidly as when the gantry is rotating, and therefore heat will not transfer as quickly.

In some embodiments, the resistance through the windings may be configured to facilitate cooling of the lift electromagnets. Referring toFIGS. 7A-7Bas an example, the outer poles504,508and the corresponding windings510,514may be relatively easier to cool than the inner pole506and the windings512. In particular, the outer windings510,514may be exposed to a larger amount of coolant and it may be easier to direct more coolant around the outer windings510,514. Accordingly, the outer windings510,514may be configured to have a higher resistance than the inner windings512. In such configurations, the outer windings510,514may heat up more than the inner windings512because of the increased resistance. Additionally or alternatively, a higher gauge wire may be used for the outer windings510,514than the inner windings512. In such configurations, a diameter of the outer windings510,514may be greater than a corresponding diameter of the inner windings512. Higher gauge wire may be used for the outer windings510,514because the outer windings510,514are relatively easier to cool when compared to the inner windings512because they are positioned at the periphery of the lift electromagnet300.

In further embodiments a lift electromagnet and its windings may be at least partially surrounded by an electrically non-conductive potting material such as epoxy. Such configurations may eliminate any space in between the windings, and may provide a better heat interface between the windings and a core of the lift electromagnet because the epoxy increases thermal conduction and heat transfer. Additionally or alternatively, such configurations may decrease the likelihood of gas bubbles or other contaminants forming in the coolant due to excessive heat. This in turn may decrease the likelihood of arcing or artifacts caused by gas bubbles. In some aspects, cooling fins or channels may be molded into the potting material to increase heat transfer via convection.

In further configurations, a duct, shroud, or jet could be directed at a lift electromagnet. An example of such configurations is illustrated inFIGS. 8A-8D.FIG. 8Ais a top schematic view andFIG. 8Bis a bottom schematic view of an example shroud602(or duct or jet) that directs flow around a lift electromagnet600.FIG. 8Cis a top schematic view andFIG. 8Dis a bottom schematic view of another example of a shroud612(or duct or jet) that directs flow around the lift electromagnet600.

As illustrated inFIGS. 8A-8B, in some aspects the shroud602may include an inlet604and outlet606, or any suitable number of inlets and outlets. The inlet604may permit coolant to enter a cavity608defined by the shroud and the outlet606may permit coolant to exit the cavity608. The lift electromagnet600may be positioned at least partially or entirely in the cavity608. The inlet604of the shroud may be fluidly coupled to an outlet of an aperture cooling duct, a duct run in parallel, or a separate duct.

As indicated by the arrows, the coolant may be forced around or through the lift electromagnet600at higher velocities in desired areas, for example, in between adjacent sets of windings. In one example, the shroud602may direct coolant proximate the windings and/or in between the poles of the lift electromagnet600. Accordingly, in some embodiments at least some of the inlets may be aligned with the spaces in between the poles of the lift electromagnet600. Although the shroud602is illustrated to be substantially surround the lift electromagnet600, other configurations may be implemented.

For example, as illustrated inFIGS. 8C-8D, the shroud612partially surrounds the lift electromagnet600. In such configurations, the shroud612defines a cavity618that receive and partially surrounds the lift electromagnet600. In such configurations, the coolant may be forced around or through the lift electromagnet600at higher velocities in desired areas, as indicated by the arrows. The shroud612may include an inlet614and outlet616, or any suitable number of inlets and outlets. The inlet614may permit coolant to enter a cavity618defined by the shroud612and the outlet606may permit coolant to exit the cavity618.

As mentioned, the shrouds, ducts or jets may include any suitable number of inlets and/or outlets. In some configurations, a shroud may include at least two inlets, or may include four inlets, or any suitable number of inlets. The size of the inlets of the shroud may be selected to direct coolant in desired volumes or desired velocity around or through the lift electromagnet. For example, the inlets directing coolant in the spaces between the poles may be larger in size (e.g., diameter or at least one dimension) than the inlets directing coolant around the sides of the lift electromagnet. In such configurations, the different inlets will direct coolant at different volumes and velocities.

In some circumstances, the duct, shroud, or jet may be molded or 3D printed. In some aspects, the duct, shroud, or jet may include or may be formed of material that is resistant to degradation, contamination or damage from the coolant fluid. For example, the duct, shroud, or jet may be formed of a polymer.

In some embodiments, the duct, shroud, or jet could be included with the other heat dissipating structures described herein. For example, the duct, shroud, or jet could be included with fins, openings, or a thermal interface. In some aspects, the duct, shroud, or jet may align with the heat dissipating structures such as the fins or the openings. The duct, shroud, or jet may be configured to ensure that the forced flow cools the lift electromagnet with minimal leakage to the ambient volume of fluid in a housing surrounding the lift electromagnet without passing by the lift electromagnet.

As mentioned, in some embodiments the coolant that removes heat from areas of the lift electromagnet may be the same coolant that cools the other portions of the X-ray tube (e.g., the insert and/or stator assembly). In other embodiments, the lift electromagnet may use a separate coolant and/or cooling configurations than other portions of the X-ray tube. In such configurations, the coolant may be selected to improve cooling of the lift electromagnet, for example, by using a coolant with better thermal properties. For example, a coolant fluid may have a thermal conductivity of up to 0.2 W/(m·K). Although coolants with better thermal properties may be relatively more expensive, since the volume of coolant necessary to cool the lift electromagnet may be less than the volume of coolant required to cool the rest of the X-ray assembly, it may be cost effective to use a more expensive coolant to cool just the lift electromagnet.

In other embodiments, cooling fins may be included directly on the lift electromagnet (e.g., the core of the lift electromagnet) rather than on windings. Such configurations may be implemented if there is a relatively good thermal link between the core and the windings of the lift electromagnet. An example of such a configuration is illustrated inFIG. 9.

FIG. 9is a schematic cross section of another example of a lift electromagnet624. As illustrated, in some configurations, fins624may be positioned on the top of the lift electromagnet624. In particular, the fins624may be positioned on a curved surface of a core622of the lift electromagnet624. In some circumstances, the fins624may be machined into a surface of the electromagnet624. In such configurations, the fins624may be include depths that correspond to the depth or radius of the curved surface.

In some configurations, the top of the lift electromagnet may be in contact with the housing of the X-ray tube for direct exposure to the exterior of the X-ray tube (e.g., when the lift electromagnet is at the same voltage potential as the X-ray tube housing). The X-ray tube may be surrounded by air or other fluid acting as a coolant, and fans or other cooling devices may be used to cool the housing. In such configurations, fins may be added to the exterior of the housing proximate the lift electromagnet to facilitate heat dissipation from the lift electromagnet to the air exterior of the housing of the X-ray tube. Such configurations may include free convection cooling or forced convection cooling via air flow as the gantry is rotating. In other configurations, the lift electromagnet may be positioned outside the housing of the X-ray tube, such configurations may permit the lift electromagnet to be cooled in other manners similar to those described herein.

In some embodiments, spacers may be positioned in between the turns of the windings to increase heat dissipation from the windings. An example of such a configuration is illustrated inFIG. 10.FIG. 10is a perspective view of another example of a lift electromagnet630. As illustrated, spacers632may be positioned in between the turns of the windings634. Such configurations may increase heat dissipation from the windings634. The spacers632may be formed of a material with relatively high heat conductivity. For example, the spacers632may include copper, gold, silver, diamond, boron nitride, aluminum, highly ordered pyrolytic graphite (HOPG) or other suitable materials. The spacers632may be a solid material or may be hollow on the inside. Configurations that include the spacers632may permit coolant fluid to flow in between adjacent turns of the windings, thereby facilitating cooling. Additionally or alternatively, the spacers632may include a void or multiple voids or openings to allow cooling fluid to penetrate the spacers632to facilitate cooling.

In one example, a lift assembly (220) may exert a force on a rotatable anode (242) of an X-ray tube. The lift assembly (220) may include a lift shaft (226) and a lift electromagnet (300,400,500,600,630). The lift shaft (226) may be coupled to the anode (242) and may be configured to rotate around an axis of rotation of the anode (242). The lift electromagnet (300,400,500,600,630) may be configured to apply a magnetic force to the lift shaft (226) in a radial direction. The lift electromagnet (300,400,500,600,630) may include a first pole and a second pole oriented towards the lift shaft (226). Windings (224) may be positioned around the first pole. The lift assembly (220) may include a heat dissipating structure.

The heat dissipating structure may include a duct, shroud, or jet (602,612) configured to direct coolant around the lift electromagnet (300,400,500,600,630). The heat dissipating structure may include a shroud (602,612) that at least partially surrounds the lift electromagnet (300,400,500,600,630) to force coolant around the lift electromagnet (300,400,500,600,630).

The heat dissipating structure may include one or more fins (416,418) coupled to the windings (224), extending out of the windings (224), or embedded in the windings (224). The fins (416,418) may be oriented parallel or perpendicular to the lift shaft (226). A largest dimension of the heat dissipating structure may be substantially parallel or perpendicular to the lift shaft (226).

The heat dissipating structure may be a thermal interface material (316) positioned on an external surface of the lift electromagnet (300,400,500,600,630), the windings (224), or between the lift electromagnet (300,400,500,600,630) and the windings (224). The thermal interface material (316) may have a higher thermal conductivity than a thermal conductivity of a coolant at least partially surrounding the lift electromagnet (300,400,500,600,630). The thermal interface material (316) may at least partially conforms to the windings (224). The thermal interface material (316) may include a thermal grease, epoxy, filler, or potting material.

The heat dissipating structure may include one or more openings (516,518) extending through the lift electromagnet (300,400,500,600,630) in a direction of fluid flow. The openings (516,518) may extend to a space between the first pole and the second pole. The heat dissipating structure may include one or more channels (520) positioned on the first pole and one or more openings (518) extending through the lift electromagnet (300,400,500,600,630) to the channels (520). A coolant may be positioned at least partially around the lift electromagnet (300,400,500,600,630).

In another example embodiment, a method may include rotating an anode assembly (240) of an X-ray source, applying a magnetic force by a lift electromagnet (300,400,500,600,630) to a lift shaft (226) coupled to the anode assembly (240), and cooling the lift electromagnet (300,400,500,600,630) using a heat dissipating structure. Cooling the lift electromagnet (300,400,500,600,630) may include directing a coolant at least partially around the lift electromagnet (300,400,500,600,630). Cooling the lift electromagnet (300,400,500,600,630) may include forcing a coolant at least partially around the lift electromagnet (300,400,500,600,630) using a duct, shroud, or jet that directs coolant around the lift electromagnet (300,400,500,600,630). Cooling the lift electromagnet (300,400,500,600,630) may include directing coolant through fins coupled to the lift electromagnet (300,400,500,600,630) or through openings or channels defined in the lift electromagnet (300,400,500,600,630).

In another example embodiment, a lift assembly (220) may be configured to exert a force on a rotatable anode (242) of an X-ray source. The lift assembly (220) may include a lift shaft means coupled to the anode (242) for rotating around an axis of rotation of the anode (242), a lift electromagnet (300,400,500,600,630) means for applying a magnetic force to the lift shaft in a radial direction, and heat dissipating means for cooling the lift electromagnet (300,400,500,600,630).

The terms and words used in this description and claims are not limited to the bibliographical meanings, but, are merely used to enable a clear and consistent understanding of the disclosure. It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces.

Aspects of the present disclosure may be embodied in other forms without departing from its spirit or essential characteristics. The described aspects are to be considered in all respects illustrative and not restrictive. The claimed subject matter is indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.