Passive thermal control of x-ray tubes

A system for passive thermal control of an X-ray tube is provided. The system includes an X-ray tube having an electron beam target and including a rotary bearing assembly supporting the electron beam target in rotation. The rotary bearing assembly includes a stationary shaft and a bearing sleeve configured to rotate with respect to the stationary shaft during operation of the X-ray tube. The rotary bearing assembly also includes a first coolant flow path extending through a center of the stationary shaft and a second coolant flow path disposed through a radially inward portion of the stationary shaft disposed about the center of the stationary shaft. The rotary bearing assembly further includes a flow control valve configured to passively regulate flow of coolant through the second coolant flow path based on a pressure of the coolant.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of U.S. patent application Ser. No. 16/190,679, entitled “PASSIVE THERMAL CONTROL OF X-RAY TUBES”, filed Nov. 14, 2018, which is herein incorporated by reference in its entirety for all purposes.

BACKGROUND

The subject matter disclosed herein relates to X-ray tubes used in medical imaging and, in particular, to the thermal control of X-ray tubes.

In non-invasive imaging systems, X-ray tubes are used in fluoroscopy, projection X-ray, tomosynthesis, and computer tomography (CT) systems as a source of X-ray radiation. Typically, the X-ray tube includes a cathode and a target. A thermionic filament within the cathode emits a stream of electrons towards the target in response to heat resulting from an applied electrical current, with the electrons eventually impacting the target. Once the target is bombarded with the stream of electrons, it produces X-ray radiation and heat.

The X-ray radiation traverses a subject of interest, such as a human patient, and a portion of the radiation impacts a detector or photographic plate where the image data is collected. Generally, tissues that differentially absorb or attenuate the flow of X-ray photons through the subject of interest produce contrast in a resulting image. In some X-ray systems, the photographic plate is then developed to produce an image which may be used by a radiologist or attending physician for diagnostic purposes. In digital X-ray systems, a digital detector produces signals representative of the received X-ray radiation that impacts discrete pixel regions of a detector surface. The signals may then be processed to generate an image that may be displayed for review. In CT systems, a detector array, including a series of detector elements, produces similar signals through various positions as a gantry is displaced around a patient.

The X-ray tube has a useful life over a large number of examination sequences, and must generally be available for examination sequences upon demand in a medical care facility, as examination sequences may or may not be scheduled, for example due to emergency situations. When the X-ray tube is not in use, the X-ray tube may cool between imaging sequences, as no electrons are being emitted by the thermionic element (i.e., substantially no heat is being generated). This cooling may result in the target material dropping below its ductile to brittle transition temperature, which can result in fracture of the target or reduced operating life. Existing techniques to warm X-ray tubes are often unreliable and inefficient, as typical thermal transition processes may take up to one hour and can over or undershoot a desired target temperature, resulting in instability of the target material. In such cases, image sequences may be delayed or, in cases where imaging sequences are performed before the target is properly warmed, the target may rupture. Accordingly, a need exists for improved thermal control in X-ray tubes.

BRIEF DESCRIPTION

In one embodiment, a system for passive thermal control of an X-ray tube is provided. The system includes an X-ray tube having an electron beam target and including a rotary bearing assembly supporting the electron beam target in rotation. The rotary bearing assembly includes a stationary shaft and a bearing sleeve configured to rotate with respect to the stationary shaft during operation of the X-ray tube. The rotary bearing assembly also includes a first coolant flow path extending through a center of the stationary shaft and a second coolant flow path disposed through a radially inward portion of the stationary shaft disposed about the center of the stationary shaft. The rotary bearing assembly further includes a flow control valve configured to passively regulate flow of coolant through the second coolant flow path based on a pressure of the coolant.

In another embodiment, an imaging system is provided. The imaging system includes an X-ray tube having an electron beam target and including a rotary bearing assembly supporting the electron beam target in rotation. The rotary bearing assembly includes a stationary shaft and a bearing sleeve configured to rotate with respect to the stationary shaft during operation of the X-ray tube. The rotary bearing assembly also includes a first coolant flow path extending through a center of the stationary shaft and a second coolant flow path disposed through a radially inward portion of the stationary shaft disposed about the center of the stationary shaft. The rotary bearing assembly further includes a flow control valve configured to passively regulate flow of coolant through the second coolant flow path based on a pressure of the coolant. The imaging system also includes a digital detector configured to receive radiation from the X-ray tube transmitted through a subject of interest. The imaging system further includes an image acquisition circuit configured to control acquisition of image data from the detector.

In a further embodiment, a system for passive thermal control of an X-ray tube is provided. The system includes an X-ray tube having an electron beam target and including a rotary bearing assembly supporting the electron beam target in rotation. The rotary bearing assembly includes a stationary shaft and a bearing sleeve configured to rotate with respect to the stationary shaft during operation of the X-ray tube. The rotary bearing assembly also includes a first coolant flow path extending through a center of the stationary shaft. The stationary shaft includes a first end having an inlet for the first coolant flow path and a second end disposed opposite the first end having an outlet for the first coolant flow path. The rotary bearing assembly further includes a second coolant flow path disposed through a radially inward portion of the stationary shaft disposed about the center of the stationary shaft. The rotary bearing assembly even further includes a flow control valve configured to passively regulate flow of coolant through the second coolant flow path based on a pressure of the coolant. The flow control valve includes a spring disposed adjacent the first end or the second end of the stationary shaft. The flow control valve is configured when closed to block the coolant from entering the second coolant flow path, and the flow control valve is configured when open to allow the coolant to flow into the second coolant flow path.

DETAILED DESCRIPTION

The present approaches are directed towards a system and a method for passively controlling the temperature of various components within an X-ray tube. For example, in embodiments of an X-ray tube wherein the target is rotatably connected to a rotary bearing (e.g., spiral groove bearing), it may be possible to control (e.g., increase and/or decrease) a rate of heat flux from the rotating anode assembly of the X-ray tube via a flow control valve (e.g., a poppet valve or spring loaded plunger housed in a bearing assembly). The flow control valve responds passively (in an open loop manner) to variation in a flow rate (i.e., pressure) of the coolant (e.g., oil). During standby mode, the flow control valve may minimize the rate of heat flux from the rotating anode assembly, when it is advantageous to keep the target assembly in a non-brittle regime to keep from having to undergo X-ray tube warm up. Prior to start of an X-ray exposure and shortly afterwards, the flow control valve may maximize the rate of heat flux from the rotating anode assembly in order to maximize patient throughput. The rotary bearing includes a stationary shaft and a sleeve disposed about and configured to rotate about the stationary shaft. A first coolant flow path is disposed through a center of the stationary shaft (e.g., through a valve stem of the flow control valve disposed within the stationary shaft) and a second coolant flow path is disposed through a radially inward portion of the stationary shaft disposed about the center of the stationary shaft. During operation, coolant flows through the first coolant path to regulate a temperature of a stator region of the X-ray tube whether the flow control valve is open or closed. When the flow control valve is closed, it keeps coolant from flowing into the second coolant flow path to regulate a temperature of the rotary bearing. However, when the flow control valve is open, it allows coolant to flow into the second coolant flow path to regulate a temperature of the rotary bearing. The disclosed embodiments will allow utilization of the full power capability of the X-ray tube without needing to precondition the X-ray tube or warm up the X-ray tube from a standby state. This enables maximum patient throughput while enabling the operation of the target assembly in a non-brittle regime, thus, reducing the probability of target rupture due to high strain rates in a brittle regime.

The thermal control system may be utilized in any X-ray tube, such as X-ray tubes utilized in fluoroscopy imaging systems, CT imaging systems, and so on.FIG. 1illustrates such an imaging system10for acquiring and processing image data, and is one embodiment in which thermal control according to the present approaches may be utilized. In the illustrated embodiment, system10is a computed tomography (CT) system designed to acquire X-ray image data, to reconstruct a tomographic image based upon the data, and to process the image data for display and analysis. Though the imaging system10is discussed in the context of medical imaging, the techniques and configurations discussed herein are applicable in other non-invasive imaging contexts, such as baggage or package screening or industrial nondestructive evaluation of manufactured parts.

In the embodiment illustrated inFIG. 1, the CT imaging system10includes an X-ray source12, which may be thermally controlled in accordance with present embodiments, and is described in further detail below with respect toFIGS. 2 and 3. As discussed in detail below, the source12may include one or more X-ray tubes. For example, the source12may include an X-ray tube with a cathode assembly14and a target16as described in more detail with respect toFIG. 2below. The cathode assembly14accelerates a stream of electrons18(i.e., the electron beam) toward a target16. According to present embodiments, the target16is rotatably coupled to a bearing (e.g., spiral groove bearing). The spiral groove bearing is advantageously lubricated with liquid metal, as discussed in detail below.

During operation, the target16rotates, which allows the stream of electrons18to impact different portions of the target16to prevent deformation and overheating of the target16. The impact of the stream of electrons18on the target16causes the material of the target16to emit an X-ray beam20. In addition to the X-ray beam20, a large amount of thermal energy is generated during electron bombardment of the target16, which heats the surface of the target. The temperature of the target16, and by extension the source12, may be controlled by a thermal control system, as described in further detail below. In a general sense, the thermal control system regulates the flow of coolant through one or more parts of the source12. In combination with the liquid metal lubricated spiral groove bearing, which may generate heat when rotated, the thermal control system may allow thermal maintenance of the source12between uses (i.e., between imaging exposures).

The source12may be positioned proximate to a collimator22used to define the size and shape of the one or more X-ray beams20that pass into a region in which a subject24or object is positioned. Some portion of the X-ray beam is absorbed or attenuated by the subject24and the resulting X-rays26impact a detector array28formed by a plurality of detector elements. Each detector element produces an electrical signal that represents the intensity of the X-ray beam incident at the position of the detector element when the beam strikes the detector28. Electrical signals are acquired and processed to generate one or more scan datasets.

A system controller30commands operation of the imaging system10to execute examination and/or calibration protocols and to process the acquired data. With respect to the X-ray source12, the system controller30furnishes power, focal spot location, rotational speed of the target16, control signals and so forth, for the X-ray examination sequences. In some embodiments, the system controller30may include a thermal control system for controlling the temperature of one or more of the components within the X-ray source12, as discussed below. The detector28that receives the portion of the X-rays26from the source12is coupled to the system controller30, which commands acquisition of the signals generated by the detector28.

The system controller30may control the movement of a linear positioning subsystem32and a rotational subsystem34via a motor controller36. In an embodiment where the imaging system10includes rotation of the source12and/or the detector28, the rotational subsystem34may rotate the source12, the collimator22, and the detector28about the subject24. It should be noted that the rotational subsystem34might include a gantry having both stationary components (stator) and rotating components (rotor). The linear positioning subsystem32may enable the subject24, or more specifically a patient table that supports the subject24, to be displaced linearly. Thus, the patient table may be linearly moved within the gantry or within an imaging volume (e.g., the volume located between the source12and the detector28) and enable the acquisition of data from particular areas of the subject24and, thus the generation of images associated with those particular areas. Additionally, the linear positioning subsystem32may displace the one or more components of the collimator22, so as to adjust the shape and/or direction of the X-ray beam20. In embodiments in which the source12and the detector28are configured to provide extended or sufficient coverage along the z-axis (i.e., the axis associated with the main length of the subject24) and/or linear motion of the subject is not required, the linear positioning subsystem34may be absent.

The system controller30may include signal processing circuitry and associated memory circuitry. In such embodiments, the memory circuitry may store programs, routines, and encoded algorithms executed by the system controller30to operate the imaging system10, including the X-ray source12and associated thermal control system, and to process the data acquired by the detector28. In one embodiment, the system controller30may be implemented as all or part of a processor-based system such as a general purpose or application-specific computer system.

The source12may be controlled by an X-ray controller38contained within the system controller30. The X-ray controller38may be configured to provide power and timing signals to the source12. In addition, in some embodiments the X-ray controller38may be configured to selectively activate the source12such that tubes or emitters at different locations within the system10may be operated in synchrony with one another or independent of one another. According to the approaches described herein, the X-ray controller38may modulate activation or operation the thermionic emitter contained within the cathode assembly14and the rotational speed of the target16to thermally regulate the source12, as described below. Further, the X-ray controller38and/or system controller30may adjust coolant flow through portions of the source12to modulate the removal of thermal energy from the X-ray source12.

The system controller30may include a data acquisition system (DAS)40. The DAS40receives data collected by readout electronics of the detector28, such as sampled analog signals from the detector28. The DAS40may then convert the data to digital signals for subsequent processing by a processor-based system, such as a computer42. In other embodiments, the detector28may convert the sampled analog signals to digital signals prior to transmission to the data acquisition system40. The computer42may include or communicate with one or more suitable memory devices46that can store data processed by the computer42, data to be processed by the computer42, or routines and/or algorithms to be executed by the computer42. The computer42may be adapted to control features enabled by the system controller30(i.e., scanning operations, data acquisition, etc.), such as in response to commands and scanning parameters provided by an operator via an operator workstation48. From the workstation48, the operator may input various imaging routines.

The system10may also include a display50coupled to the operator workstation48that allows the operator to view relevant system data, imaging parameters, raw imaging data, reconstructed data, and so forth. Additionally, the system10may include a printer52coupled to the operator workstation48and configured to print any desired measurement results. The display50and the printer52may also be connected to the computer42directly or via the operator workstation48. Further, the operator workstation48may include or be coupled to a picture archiving and communications system (PACS)54. PACS54may be coupled to a remote system56, radiology department information system (RIS), hospital information system (HIS) or to an internal or external network, so that others at different locations can gain access to the image data.

As noted above, the present embodiments are directed towards passive thermal control of the X-ray source12. In accordance with one aspect of the embodiments disclosed herein, the passive thermal control may be performed using a flow control valve74that is connected to one or more components of the system10that may affect the temperature of the source12. Together, the control circuitry and associated components may form a thermal control system, an embodiment of which is depicted inFIG. 2. Specifically,FIG. 2illustrates a thermal control system60having a control circuit62connected to various components of the X-ray source12, which in the depicted embodiment is an X-ray tube64and is discussed below. The control circuit62is also connected to the rotational subsystem34, which may be a gantry as described above.

The control circuit62, in the illustrated embodiment, is connected to a coolant circulating system66configured to circulate coolant through and/or around the X-ray tube64. Components of the coolant circulating system66include a heat exchanger68having a coolant pump70(e.g., a variable speed or single speed pump) and a heat exchanging fan72, and a device for controlling the flow of coolant, such as a flow control valve74(e.g., a poppet valve or spring loaded plunger). The heat exchanger68utilizes the coolant pump70to motivate amounts (e.g., variable amounts or substantially continuous amounts) of coolant through one or more paths that may pass through and/or around the X-ray tube64. Additionally, the heat exchanger68uses the heat exchanging fan72to control the amount of heat rejection from the coolant (i.e., the temperature of the coolant). In this way, both the mass flow rate of the coolant and the coolant temperature may be controlled by the control circuit62. That is, the control circuit62may send control signals to the heat exchanging fan72and/or to the coolant pump70to control the amount of heat rejection from the coolant and the flow rate of the coolant, respectively. The flow control valve74may passively (e.g., in an open-looped manner) adjust the amount and/or location of coolant flowing through and/or around various components of the X-ray tube64, including through a central shaft of the tube and/or a radially inward portion of the stationary shaft disposed about the center of the stationary shaft of a stationary shaft of the bearing. For example, the flow control valve74may be preloaded to a set value. When the flow rate (i.e., pressure) of the coolant is below the set value, the flow control valve74is closed and keeps the coolant from flowing into a coolant flow path within a radially inward portion of the stationary shaft disposed about the center of the stationary shaft but allows coolant flow through the center of the shaft to cool the stator region of the X-ray tube64. When the flow rate of the coolant is at or above the set value, the flow control valve74is open and some of the coolant may be diverted to the radially inward portion of the stationary shaft disposed about the center of the stationary shaft while allowing coolant flow through the center of the shaft, thus, enabling the cooling of the bearing and the stator region of the X-ray tube64.

An X-ray tube control volume80generally defines the area in which coolant may flow to affect the temperature of one or more components of the X-ray tube64. The X-ray tube control volume80may include the X-ray tube64and the components contained therein, as well as flow paths, conduits, cooling jackets, and so on that may experience varying levels of coolant flow and coolant temperature for thermal regulation. Components of the X-ray tube64that may be considered part of the X-ray tube control volume80, i.e., components that may affect the temperature of one or more components of the X-ray tube64, include a motor82that controls the rotation of a sleeve84to which the target16is attached for rotation, and a stationary shaft86about which the sleeve84rotates, and which also includes a coolant flow path88. In the illustrated embodiment, the coolant flow path88runs substantially along a longitudinal center opening of the stationary shaft86, and allows coolant to remove thermal energy from the stationary shaft86and, therefore, the components that may be in direct connection and/or thermal communication with the stationary shaft86. As described in greater detail below, another coolant flow path may run along and through the sleeve84. According to present embodiments, passively controlling the rate of heat flux from the rotating anode assembly of the X-ray tube64, may allow utilization of the full power capability of the X-ray tube64without needing to precondition the X-ray tube64or warm up the X-ray tube64from a standby state. This enables maximum patient throughput while enabling the operation of the target assembly in a non-brittle regime, thus, reducing the probability of target rupture due to high strain rates in a brittle regime.

According to certain embodiments, the bearing formed by the rotary sleeve84and the stationary shaft86may be a spiral groove bearing (SGB)90that is lubricated with a liquid metal material, i.e., materials that are liquid metal at room temperature, such as gallium (Ga) and/or Ga alloys. Indeed, some embodiments of the bearing90may conform to those described in U.S. patent application Ser. No. 12/410,518 entitled “INTERFACE FOR LIQUID METAL BEARING AND METHOD OF MAKING SAME,” filed on Mar. 25, 2009, the full disclosure of which is incorporated by reference herein in its entirety. For the purposes of the present discussion, the SGB90may also be referred to as the interface between the sleeve84and the stationary shaft86, which is the area containing the liquid metal material and the area where shear forces are applied to the liquid metal material.

Additionally, in some embodiments, the X-ray tube control volume80may include the thermionic emitter14of the X-ray tube64to which the control circuit62may be connected, either directly or indirectly. In such a configuration, the control circuit62may control the flux of the electron beam18generated by the thermionic emitter14, which allows the control circuit62to control the rate at which the target16is heated. However, it should be noted that the flux of the electron beam18may be determined based upon the parameters of a given imaging sequence in addition to or in lieu of the desired heating rate. In this way, there may be situations where the flux of the electron beam18suitable for a given imaging sequence may also correspond to a desired heating rate. This may allow the control circuit62to at least partially control the actual temperature of the target16and the X-ray tube components proximal thereto.

FIG. 3is a cross-sectional view of a portion of the X-ray tube64illustrating an embodiment of the flow control valve74for passively controlling the temperature of the X-ray tube64(e.g., having the flow control valve closed). In general, the X-ray tube64is as described inFIG. 2. The left and right sides ofFIG. 3may be referenced to as the cathode and motor/rotor sides, respectively. The components described herein may be described in this and subsequent figures by referencing an axial direction92, a radial direction94, and a circumferential direction96relative to a longitudinal axis98of the bearing90, the stationary shaft86, and/or the bearing sleeve84. In general, the shaft86and the bearing sleeve84are as described inFIG. 2.

The flow control valve74includes a valve stem100, a spring102, and a spring loaded piston or plunger104. The valve stem100is disposed within and extends axially92through a central portion105of the shaft86. In particular, the shaft86includes an outer portion106and an inner portion108(radially94inward of the outer portion106and radially94outward of the center portion105of the shaft86) and the valve stem100extends axially92completely through the inner portion108. The valve stem100includes a first end110and a second end112disposed adjacent the cathode and motor/rotor sides, respectively. The second end112includes a fastener114(e.g., nut) that secures the valve stem100in place within the shaft86. The first end110includes a flange116. The flange116abuts a seat118to keep a coolant (e.g., oil) from flowing around a periphery of the flange116. The flange116includes centrally located inlet120for receiving the coolant. The valve stem100includes a cavity122downstream of the flange116that extends to an outlet124at the second end112. Together, the inlet120and the cavity122define a first coolant flow path126. Coolant flows axially92from the cathode side towards the motor/rotor side through the first coolant flow path126(as indicated by arrows127) into a shaft adapter128where eventually the coolant exits radially94via holes130(as indicated by arrows131) to cool a stator region132(e.g., between the stator and the motor can) of the X-ray tube64. Coolant flows through the first coolant path126whether the flow control valve74is open or closed.

As depicted, the flow control valve74is closed. The flow control valve74is spring loaded to a set value. As depicted, the spring102contacts the inner portion108of the shaft86and the plunger104. The spring102exerts the preload force against the plunger104causing the plunger104to abut against the flange116. The flange116includes multiple openings117(seeFIG. 4) circumferentially96spaced apart from each other and disposed radially94outward of the inlet120. The openings117extend both circumferentially96and radially94. The number of openings117may vary (as depicted the flange116includes four openings117). When the plunger104abuts the flange116it blocks flow of the coolant through the openings117and into a second coolant flow path134. The inner portion108of the shaft86includes multiple fins circumferentially96spaced apart from each other (seeFIG. 7) that extend axially92along an entire length of the inner portion108from a first end136to a second end138. The first end136and the second end138may serve as either inlets or outlets for the second coolant flow path134. As depicted, the first end136and the second end138function as an inlet140and an outlet142, respectively. The fins define flow channels for the coolant to cool the shaft86(and the bearing90) in both axial92and circumferential directions96. When the flow rate (i.e., pressure) of the coolant is below the set value (i.e., less than the preloaded force), then the valve74is closed (i.e., the plunger104abuts the flange116) and coolant does not flow into the second coolant flow path134. In this closed position (e.g., during standby mode), the flow control valve74may minimize the rate of heat flux from the rotating anode assembly, when it is advantageous to keep the target assembly in a non-brittle regime to keep from having to undergo X-ray tube64warm up. However, as depicted inFIG. 5, when the flow rate (i.e., pressure) of the coolant is equal to or greater than the set value (e.g., prior to start of an X-ray exposure and shortly afterwards), the coolant flow through the openings in the flange116axially92displaces the plunger104towards the first end136of the inner portion108of the shaft86opening the valve74and enabling coolant to flow around the plunger104and into the second coolant flow path134via inlet140(as depicted by arrows144). This results in the split of the coolant flow between the stator region132and the bearing90. Prior to start of an X-ray exposure and shortly afterwards, the flow control valve74may maximize the rate of heat flux from the rotating anode assembly in order to maximize patient throughput.

In certain embodiments, the shape of the flange116and/or the plunger104may vary. For example, as depicted inFIGS. 6 and 7, the flange116includes an L-shaped cross-sectional shape extending radially94from adjacent the inlet120. An axial portion146of the flange116abuts the seat118. The plunger104include a tapered profile. In particular, the plunger104tapers from a first end148(e.g., adjacent the flange116) to a second end150in the axial direction92. In certain embodiments, a plate152is coupled to the flange116. The plate152is coupled to multiple pins or protrusions154. Each pin154extends into and through a portion of a respective opening117of the flange116. Each pin154includes a first end156and a second end158. The first end156engages the plate152. The second end158engages recesses or cavities160within the plunger104when the valve74is in the closed position. The plunger104includes multiple cavities160to engage respective pins154.

As described above and depicted inFIG. 7, the inner portion108of the shaft86includes multiple fins162circumferentially96spaced apart from each other (seeFIG. 7) that extend axially92along an entire length of the inner portion108from a first end136to the second end. In this embodiment, the first end136serves as the inlet140for the second coolant flow path134. The fins162define flow channels164for the coolant to cool the shaft86(and the bearing90) in both axial92and circumferential directions96.

In certain embodiments, portions of the flow control valve74may be disposed on the motor/rotor side of the X-ray tube64.FIGS. 8 and 9are cross-sectional views of a portion of the X-ray tube64illustrating an embodiment of the flow control valve74for passively controlling the temperature of an X-ray tube having the flow control valve74closed and open, respectively.

The flow control valve74includes the valve stem100and the spring102. The valve stem100is disposed within and extends axially92through the central portion105of the shaft86. In particular, the shaft86includes an outer portion106and an inner portion108as described above and the valve stem100extends axially92completely through the inner portion108. The valve stem100includes the first end (seeFIG. 3) and a second end112disposed adjacent the cathode and motor/rotor sides, respectively. The second end112includes a flange166. The flange166(when the valve74is closed) abuts the end138of the inner portion108of the shaft86to keep a coolant (e.g., oil) from flowing into the second coolant flow path134described above. The flange116includes the centrally located outlet124for discharging the coolant from the first coolant flow path126. In certain embodiments (seeFIG. 9), an insert168disposed within the second end112may define the outlet124. As described above, coolant flows axially92from the cathode side towards the motor/rotor side through the first coolant flow path126into the shaft adapter128where eventually the coolant exits radially94via holes (seeFIG. 3) to cool a stator region of the X-ray tube64. Coolant flows through the first coolant path126whether the flow control valve74is open or closed.

The flow control valve74is spring loaded to a set value. As depicted, the spring102contacts both the shaft adapter128and the flange166. In particular, a portion170of the spring102may extend axially92into the shaft adapter128. The spring102exerts the preload force against the flange166causing the flange166to abut against the end138of the second coolant flow path134(when the valve74is closed). When the flange166abuts the end138it blocks flow of the coolant into the second coolant flow path134. As depicted, the second end138functions as an inlet172. When the flow rate (i.e., pressure) of the coolant is below the set value (i.e., less than the preloaded force), then the valve74is closed (i.e., the flange166abuts the end138) and coolant does not flow into the second coolant flow path134. In this closed position (e.g., during standby mode), the flow control valve74may minimize the rate of heat flux from the rotating anode assembly, when is advantageous to keep the target assembly in a non-brittle regime to keep from having to undergo X-ray tube64warm up. However, as depicted inFIG. 9, when the flow rate (i.e., pressure) of the coolant is equal to or greater than the set value (e.g., prior to start of an X-ray exposure and shortly afterwards), the coolant flow axially92displaces the flange166towards the shaft adapter128opening the valve74and enabling coolant to inlet172and into the second coolant flow path134(as depicted by arrows174). This results in the split of the coolant flow between the stator region and the bearing90. Prior to start of an X-ray exposure and shortly afterwards, the flow control valve74may maximize the rate of heat flux from the rotating anode assembly in order to maximize patient throughput.

Technical effects of the disclosed embodiments include providing the flow control valve that enables passive (e.g., in an open-looped manner) control of cooling portions of the X-ray tube. In particular, when the flow control valve is closed, it enables coolant flow to cooling the stator region of the X-ray tube. When the flow control valve is open, it splits the coolant flow between the stator region and the bearing. The disclosed embodiments enables the rotating anode assembly of the X-ray tube to operate without operating in a brittle regime. In addition, the disclosed embodiments, reduce the probability of a target rupture and X-ray tube failure. Future, the disclosed embodiments enable utilization of the X-ray tube without warm up to provide on demand power capability and to increase patient throughput.