EP4590075A1

EP4590075A1 - Adjustment of anode frequency based on requested scan mode

Info

Publication number: EP4590075A1
Application number: EP24152532.8A
Authority: EP
Inventors: Tobias REUSCH; Christian Herbert BLOME; Christoph Bathe; Paul VAN BEERS
Original assignee: Koninklijke Philips NV
Current assignee: Koninklijke Philips NV
Priority date: 2024-01-18
Filing date: 2024-01-18
Publication date: 2025-07-23
Also published as: WO2025153337A1

Abstract

A method (500) for controlling an anode rotation frequency of an x-ray source (50) of an x-ray system (100), wherein the method (500) comprises: selecting (S1) at least one scan operation of the x-ray system (100), determining (S2) at least one optimum rotation frequency of an anode (10) of the x-ray system (100) based on the selected scan operation, wherein the optimum rotation frequency is determined based on at least one scan operation parameter of the selected scan operation, and setting (S3) the anode rotation frequency to the determined optimum rotation frequency for each selected scan operation.

Description

FIELD OF THE INVENTION

The present invention relates to a method for controlling an anode rotation frequency of an x-ray source of an x-ray system, an x-ray source of an x-ray system, an x-ray system, a computer-program product and a computer-readable medium.

BACKGROUND OF THE INVENTION

In x-ray systems, the anode rotation frequency is one of the main design choices during x-ray source or tube development. Apart from basic mechanical considerations such as a burst frequency of an anode disk, the anode frequency is usually set to a fixed value based on a set of competing customer needs. However, common x-ray systems lack the possibility to properly address the different needs and requirements.

SUMMARY OF THE INVENTION

It is, inter alia, an object of the invention to provide an improved method and system, which addresses the above noted drawbacks. The invention is defined by the independent claims. Advantageous embodiments are defined in the dependent claims.
One aspect of the present invention relates to a method for controlling an anode rotation frequency of an x-ray source of an x-ray system. The method comprises selecting at least one scan operation of the x-ray system. The method further comprises determining at least one optimum rotation frequency of at least one anode of the x-ray system based on the selected scan operation, wherein the optimum rotation frequency is determined based on at least one scan operation parameter of the selected scan operation. The method further comprises setting the anode rotation frequency to the determined optimum rotation frequency for each selected scan operation.
Contrary to prior art methods and devices, the present invention may provide a dynamic adjustment of the anode rotation frequency with respect to each individual selected scan operation. By employing the present invention, an anode rotation frequency, which may correspond to as a rotational speed of the anode, may be accordingly tailored to the respective needs of each selected scan operation.
A scan operation may comprise one or more scans of a target of interest, wherein the scans are performed by the x-ray system. The scan operation may be a full scan or only a partial scan of the target of interest. For instance, the scan operation may comprise a first scan of a first part of the target of interest and a second scan of a second part of the target of interest. The method according to the present invention may accordingly allow to individually adapt the rotation frequency of the anode to each of the first scan and the second scan, or to perform the scans at another suitable frequency considering both scans, as will be explained further below. Of course, also more than two scans may be performed.
The x-ray system may be a suitable x-ray system for medical applications such as an x-ray imaging system, and may be, for instance, a computer tomography, CT, system or a cone beam CT system. The method of the present invention may be employable for any suitable x-ray source and x-ray system.
The x-ray source comprises a cathode and an anode. The cathode may emit an electron beam towards an angled surface of the anode, which is a rotating anode, from which surface upon impact of the electron beam an x-ray beam may be emitted towards the target of interest.
The anode may comprise a rotatable disc comprising a metal, for instance tungsten, that is suitable to emit x-ray radiation upon impact of an electron beam. However also different shapes and materials of the anode may be employed. Also more than one anode may be provided to generate x-ray radiation. The x-ray system, and in particular the anode may be accordingly controlled by a controller of the x-ray system.
The selection of the scan operation may be performed automatically by a computer or may be user selected. The x-ray system may accordingly allow a user to interact with the x-ray system such as via an interface, for instance a display, and for instance a keyboard or a computer mouse. However, further and/or different options for interacting with the x-ray system may be provided, such as via a touch screen, voice control, gesture control etc. The selection of the scan operation may be performed for instance based on the targets to be investigated by the x-ray system such as a full body of a patient or parts thereof, for instance a head, a leg etc. The selection of the scan operation may also be dependent for instance on a desired field of view, FOV, or a particular scanning pattern or a scanning method to be employed to perform a scan at the x-ray system.
An optimum rotation frequency may be a frequency that is determined from a number of distinct frequencies or may be a frequency determined from a continuous suitable range of frequencies. Said distinct frequencies or continuous suitable range of frequencies may be for instance predetermined or stored at a respective digital storage, such as a memory, and accordingly accessible by the x-ray system. A potential suitable anode frequency range may be pre-determined or may be dynamically generated. The determination of the optimum rotation frequency may consider respective advantages and disadvantages of higher and lower rotation frequencies. For instance, higher anode rotation frequencies may enable a higher power rating or an improved spiral groove bearing mechanical stiffness. At the same time, lower anode rotation frequencies may help to reduce for example spiral groove bearing friction losses, tube wear, system power consumption, etc. In case spiral groove bearings are provided to support the anode of the x-ray source, friction losses may increase quadratically with anode rotation frequency. The spiral groove bearings may be operated in continuous duty, i.e., they may be always rotated as soon as the x-ray system is switched on. The friction losses, which may be for instance in the order of approximately 1kW, may severely limit a maximum allowable power consumption of an x-ray system and/or its x-ray source. The anode rotation frequency may be accordingly chosen to meet an optimum regarding one or more of the above noted factors. The anode rotation frequency may be for instance optimized with respect to a desired performance of the x-ray system and/or may be optimized to achieve an increased lifetime of an x-ray source.
The optimum rotation frequency may be determined considering one or more scan operation parameters. The scan operation parameters may include any kind of parameters that may positively or negatively influence the scan operation. Examples of respective scan operation parameters are set forth further below. The optimum rotation frequency may be accordingly adapted to the most suitable rotation frequency with respect to one or more scan operation parameters. In other words, the optimum rotation frequency may be selected dependent on which of the one or more parameters is considered relevant for the selected scan operation and may reflect a respective desired optimum to these parameters. For instance, the optimum rotation frequency of the anode may be set to a value which is optimized for a power output. Or the optimum rotation frequency of the anode may be set to a value which is optimized for achieving a maximum longevity of the x-ray source. Or the optimum rotation frequency of the anode may be set to a value which is optimized considering both a power output and a longevity of the x-ray source.
The power rating P for short exposure times may be linked to the anode rotation frequency f, as expressed by the Osterkamp formula: $P \propto = \frac{\sqrt f}{l \cdot \sqrt{w}}$ . It may be accordingly desirable to maximize the anode rotation frequency to maximize the allowable power or minimize an x-ray radiation focal spot width w or length l.
In a first order approximation, the mechanical stiffness may be proportional to the anode rotation frequency, so it may be desirable to maximize the anode rotation frequency to provide the highest mechanical stiffness. In a second order approach the rotation frequency may be further increased to enforce a turbulent flow in a bearing lubricant, which results in even higher mechanical stiffness of the bearing. In bearings, liquid dynamics of the employed lubricant may exhibit laminar flows. However, turbulent flows may potentially be provided to allow for higher restoring forces.
If spiral groove bearings are provided to support the anode at the x-ray system, the wear of the bearing may be in first order related to integral number of anode revolutions. It may thus be desirable to minimize the anode frequency in order to minimize an incremental wear and maximize a lifetime of the x-ray source (e.g. an x-ray tube). If ball bearings are provided, the wear may be also influenced by the bearing clearance, which may be influenced by a bearing temperature. The bearing temperature may be influenced again from friction and external heat from other components.
Thus, the present invention may enable each scan to be performed with an individually optimized frequency. For instance, a minimum or maximum frequency to be set may be determined for each scan operation. For instance, the minimum frequency may be determined based on the power and/or rotation frequency requirements of a surview scan.
In an embodiment, the method may include:

determining an anode rotation frequency range,
receiving operation parameters for a scan with the x-ray system, and a temperature state of the x-ray source,
determining a minimum suitable anode rotation frequency within the frequency range, based on the scan parameters and x-ray source temperature state, and
adjusting the rotation frequency of the anode to the minimum suitable anode rotation frequency, prior to carrying out the scan.

The method may be at least partly computer-implemented, and may be implemented in software or in hardware, or in software and hardware.
Further, the method may be carried out by computer program instructions running on a data processor that provides data processing functions. The data processor may be a suitable computer, such as an electronic control module etc., which may also be a distributed computer system. The data processor or the computer, respectively, may comprise one or more of a processor, a memory, a data interface, or the like.
In a preferred embodiment of the present invention, the at least one scan parameter includes one or more of a power consumption of the x-ray source, a voltage applied to the x-ray source, a rotation frequency of a gantry of the x-ray system, a scan time of the selected scan operation and/or a temperature state of the x-ray source.
Thus, the anode rotation frequency may be suitably adapted to the needs and requirements or to boundary conditions of the respective x-ray system and the selected scan operation. The respective one or more scan parameters may be preset to distinct suitable values or ranges of the respective x-ray system and its components. Suitable scan parameters may be considered in the determination for each scan operation that may be performed with the x-ray system.
The power consumption may relate to the overall power consumption of the x-ray source or to the x-ray system or respective components thereof. This may include for instance a current or voltage supplied to the x-ray system or single components thereof.
The gantry may be a circular or a C-arm gantry and may be able to rotate around the target of interest, such as a patient, and may be adapted to hold the x-ray source and/or the corresponding x-ray detector, wherein the x-ray detector may be arranged at an opposite location with respect to the x-ray source at the gantry. If spiral groove bearings are provided at the x-ray system to support the anode, the mechanical stiffness of the bearings may relate to the capability of the bearing to suitably compensate centrifugal forces. A maximum gantry rotation frequency applicable in the x-ray system considering the mechanical stiffness may be defined.
The scan time may be the time that is needed to perform a partial or complete scan of a target of interest. The temperature state of the x-ray source may comprise a distinct temperature value or temperature range for one or more locations at the x-ray source. This may include for instance a currently detected temperature value or an (integrated) temperature value acquired over a certain time period. Also future predicted values, such as provided from an x-ray source temperature prediction computer model, of the temperature may be considered.
Each scan operation parameter may be considered individually or in combination with one or more further scan operation parameters. The present invention may of course also comprise considering other and different scan operation parameters. Each scan operation parameter may be detected via suitable sensors and/or detectors provided at the x-ray system or may be indirectly derived. For instance, an anode rotation frequency may be determined directly by measuring the anode frequency or may be derived indirectly by measuring the power drawn by a motor propelling the anode.
In a preferred embodiment of the present invention, the temperature state of the x-ray source, preferably of an anode bearing supporting the anode in the x-ray source, comprises a current temperature state for the current scan operation, and/or comprises a future predicted temperature state for the current scan operation and/or at least one subsequent scan operation.
Thus, an undesired overheating of the x-ray source, for instance of anode bearings supporting the anode at the x-ray source, may be prevented. Since the impact of excessive heat may shorten the lifetime of the respective components, the x-ray system may be accordingly protected from such excessive temperatures.
The current temperature may be the temperature that is currently present in the x-ray source and may relate to a distinct time point and or a time range at which said temperature occurs. The temperature state may be accordingly measured via respective temperature sensors. Accordingly, the system may be dynamically adjustable to currently measured temperatures of one or more parts of the x-ray system. Further, also predicted or simulated temperature states may be determined and considered for the whole scan or for partial scans. In other words, the occurrence of respective temperatures may be simulated for one or more parts of the x-ray system, such as the anode bearing. The bearing may be for instance in the form of a spiral groove bearing or in the form of a ball bearing.
The mechanical stiffness may be furthermore dependent on the temperature inside a bearing gap and a viscosity of a lubricant employed, for instance a liquid metal. Examples for suitable metals may include gallium, indium and/or tin. The bearing stiffness of sliding bearings may decrease with higher temperatures and reduced viscosity. Thus, a higher anode rotation frequency may be needed for higher bearing temperatures in order to retain a sufficient mechanical stiffness. As already noted above, the bearing temperature may likewise also concern the clearance of ball bearings.
In a preferred embodiment of the present invention, setting the anode frequency includes an acceleration and/or deceleration of the anode rotation.
Thus, a desired optimum rotation frequency may be easily achieved by suitably adjusting the rotation frequency or speed of the anode. Hence, a respective propelling and/or braking of the rotation of the anode, such as for instance with a motor responsible for propelling the anode rotation, may be accordingly controlled in accordance with the determined optimum rotation frequency. When determining an optimum rotation frequency, the time necessary to accelerate or decelerate an anode to the distinct optimum rotation may be taken into account. After the scan, the anode may be decelerated to a standby frequency, as will be set forth further below, or to a standstill. Acceleration and deceleration may be determined with respect to one or more scan operation parameters of the selected scan operation.
In a preferred embodiment of the present invention, when two or more scan operations are selected, the invention further comprises determining an anode rotation frequency adjustment time necessary to accelerate or decelerate the anode rotation from a first optimum rotation frequency of a first scan operation to a second optimum rotation frequency of a subsequent second scan operation.
Hence, for the determination of the optimum rotation frequency system requirements may be considered, such as the ability of the system to accelerate or decelerate the anode in a certain amount of time. This may be taken into account when a scan operation is planned and executed. Different optimum rotation frequencies may be accordingly set for different scan operations or different x-ray systems. However, dependent on the determination of the respective optimum rotation frequency, the system may also comprise configurations, at which for different scan operations the same optimum rotation frequency is determined and accordingly set.
In a preferred embodiment of the present invention, when the anode rotation frequency adjustment time is determined being sufficient for an acceleration or deceleration of the anode rotation from the first optimum rotation frequency to the second optimum rotation frequency, the anode rotation frequency is set to the first optimum rotation frequency for performing the first scan operation and subsequently set to the second optimum rotation frequency for performing the second scan operation.
Thus, the system may consider a sequence of scan operations to be executed when determining first and second optimum rotation frequencies and the respective times necessary to accelerate or decelerate the anode rotation. This may facilitate planning and execution of a sequence of scans. If the time may be determined to be sufficient to switch between the anode rotation frequencies of the respective measurements, each scan operation may be performed at an individual optimum rotation frequency determined for the respective scan operation. The method may of course also comprise configurations with more than two scan operations, such as three, four, five and more scan operations, and for each scan operation an individual optimum rotation frequency may be determined and set.
In a preferred embodiment of the present invention, when the anode rotation frequency adjustment time is determined to be insufficient for an acceleration or deceleration of the anode rotation from the first optimum rotation frequency to the second optimum rotation frequency, the anode rotation frequency is set to a third optimum rotation frequency for performing the first scan operation and the second scan operation.
This may allow to further enhance planning and execution of a sequence of scans. Thus, if it is determined that there is no sufficient time between the respective scans to switch from a first to a second optimum rotation frequency, a different optimum frequency may be determined and set to perform both scan operations at this different third optimum frequency. The determination of the third optimum rotation frequency may accordingly consider one or more of the scan operation parameters of the first, the second or both scan operations. The third optimum rotation frequency may be accordingly a compromise between the different requirements and parameters of both scans. The third optimum rotation frequency may also correspond to one of the first anode rotation frequency or the second anode rotation frequency and may be determined and set suitable for both scan operations. The method may of course also comprise configurations with more than two scan operations, such as three, four, five and more scan operations, and for each scan operation an individual optimum rotation frequency may be determined and set. Furthermore, also one or more different rotation frequencies may be determined for an arbitrary subset of the two or more scan operations.
The present invention may not be delimited in this respect but may also include any combinations of the above-described determination of the respective optimum rotation frequencies. For instance, four scan operations may be selected and the system may determine that there is sufficient time for acceleration or deceleration from the first scan operation to the second scan operation. Accordingly, individual optimum rotation frequencies may be determined and set for each of the first and the second scan operations. Further, the system may determine that there is insufficient time to switch an acceleration or deceleration from the third scan operation to the fourth scan operation. Accordingly, a combined optimum rotation frequency may be determined and set for the third and the fourth scan operation. The present invention is of course not limited thereto.
In a preferred embodiment of the present invention, the invention further comprises determining a standby frequency of the anode at which no scan operation is performed, wherein, when only one scan operation is selected, the anode is accelerated from the standby frequency to the determined optimum rotation frequency of the scan operation to perform the selected scan operation and decelerated back to the standby frequency after performing the selected scan operation, and, when more than one scan operation is selected, the anode is accelerated from the standby frequency to the determined optimum rotation of the selected first scan operation frequency to perform the selected first scan operation and subsequently accelerated or decelerated to the determined optimum rotation of at least one selected second scan operation frequency to perform the selected second scan operation and decelerated back to the standby frequency after performing the selected second scan operation.
Thus, the system may also be suitable when a standby frequency of the anode may be provided. In other words, an acceleration may be performed starting from the certain standby frequency and not from a standstill and likewise the deceleration may be performed down to the standby frequency and may be accordingly not completely stopped. As noted above, e.g. for spiral groove bearings, the x-ray system may be operated in a continuous manner such that the anode is always rotating as soon as the x-ray system is switched on. The standby frequency may be accordingly not bound or related to a particular scan operation. The standby frequency may be selected for instance being low enough to prevent undesired wear and friction but may be selected being high enough to keep the metal lubricant of the bearing in a liquid state. Thus, the present invention may consider respective distinct configurations of the x-ray system, such as a distinct metal used as lubricant and or a temperature level provided at the spiral groove bearings. Also more than one second scan operation may be selected and performed after the first selected scan operation, for instance three, four, five and more scan operations.
In a preferred embodiment of the present invention, the optimum rotation frequency is a lowest possible anode rotation frequency at which the selected scan operation can be performed.
Thus, the invention may allow for a particular reduced wear and friction losses of the respective parts of the x-ray system, in particular regarding parts of the anode, such as an anode bearing. At the same time, the method of the present invention may likewise ensure a reliable operation during the envisioned scan operation(s). The lowest possible frequency may be accordingly dependent on respective scan operation parameters of the selected scan operation, such as for instance a scanning length, a field of view and/or an image contrast to be achieved.
In a preferred embodiment of the present invention, the invention comprises a continuous monitoring of the scan operation parameter, wherein the optimum rotation frequency is dynamically set based on the result of the continuously monitored scan operation parameter.
Thus, a particularly optimized scan operation may be achieved, since the invention may not only take into account a predicted scan operation parameter, such as a temperature of a bearing, but may also consider currently measured values. Thus, in case of malfunction or if certain operation parameters exceed predefined limits, the optimum rotation frequency may be dynamically adjusted. In case it may be determined that an operation scan parameter exceeds a limit or threshold, the adjustment of the optimum anode rotation frequency may be performed for instance during the scan operation. In another embodiment, the present scan may be maintained unchanged, but a subsequent scan may be modified to take into account the new scan operation parameters. For instance, if the bearings may comprise an unexpectedly high temperature during the first scan, a subsequent second scan may accordingly take into account the increased temperature and may accordingly adapt the anode rotation frequency appropriately. The monitoring may be performed continuously or may be performed at certain time instances, for instance at the beginning and at the end of a respective scan operation.
The present invention also relates to an x-ray source of an x-ray system. The x-ray source comprises a rotatable anode, wherein the rotatable anode is adapted to be controlled according to any method of the present invention.
Thus, an improved anode comprising an individually controlled rotation may be provided, which may allow for a particularly reduced wear and an increased longevity while ensuring a proper irradiation of a target of interest to be measured for each individual scan. At the x-ray source, an electron beam may be emitted from a cathode towards a surface of a rotating anode, which may be a metal anode comprising for instance tungsten. The electron beam may impact an angled surface of the anode and x-ray radiation may be emitted in an angled manner towards a target of interest. The anode may comprise anode bearings, which rotatably support the anode in the x-ray source. The anode bearings may be for instance provided in form of ball bearings or in form of spiral groove bearings. The features and advantages outlined with respect to the system and the method of the present invention similarly apply to the x-ray source described herein.
The present invention also relates to an x-ray system comprising an x-ray source. The x-ray source comprises a rotatable anode. The x-ray system further comprises a controller, wherein the controller is configured to carry out and/or control any method of the present invention.
An x-ray system may be a medical x-ray imaging system that allows to detect x-ray radiation in a medical context and may accordingly allow to detect medical targets of interest, such as, for instance portions of a body of a patient or a full body. The x-ray radiation may be detected by a respective x-ray radiation detector which may be any suitable detector for receiving and detecting x-ray radiation.
Further components may be provided at the x-ray system such as one or more shutters and/or a support structure. The support structure may be a structure to which the radiation source and/or the radiation detector and/or further components of the imaging system may be mounted and/or in which the radiation source, the radiation detector and/or further components may be incorporated, such as an x-ray tube head, a gantry or a C-arm.
Also more than one x-ray radiation source may be provided. The x-ray radiation source may be configured to emit an x-ray radiation beam of a defined shape towards a target of interest such that a distinct area of the target of interest could be irradiated. The x-ray radiation may be emitted for instance in the form of a cone. Also more than one x-ray radiation detector may be provided.
The controller may be a single device or an arrangement of a plurality of devices that may allow to control the x-ray system to investigate a target of interest. This may include but is not limited to one or more motors and respective controls that may enable to move a patient, the gantry, the x-ray source and/or the x-ray detector in a suitable manner. In particular, the controller may be configured to control an anode rotation frequency of the x-ray source. The components of the x-ray system, such as for instance the x-ray radiation source or the x-ray radiation detector, may be configured to be moved along predetermined paths and/or along paths that may be tracked. Moreover, the components of the x-ray system, such as, for instance, the x-ray radiation source or the x-ray radiation detector, may be moved prior to imaging, for example for adjusting the settings of the imaging system to the target of interest to be acquired and/or to set a desired FOV. The controller may comprise or otherwise interact with a processor, such as but not limited to a computer, a computer network, and/or another programmable apparatus, such as a single and/or multi core processing unit, a graphics processing unit, an accelerated processing unit, a digital signal processor, a field programmable gate array, an application-specific integrated circuit, etc.
In a preferred embodiment, the x-ray system is a medical x-ray imaging system, for instance a computer tomography, CT, system or a cone beam CT system. Accordingly, an improved medical x-ray imaging system with a reduced overall wear and an increased longevity may be provided, which may be individually adapted to the needs and requirements of the system and/or a user.
The present invention further relates to a computer program product comprising computer-readable instructions which, when executed by a computer, cause the computer to carry out and/or control any of the methods of the present invention.
The features of the system and the method according to the present invention may be implemented by respective suitable digital or computational circuitry, which can include, for instance, one or more computers, apps and/or networks. The method may be at least partly computer-implemented, and may be implemented in software or in hardware, or in software and hardware. Further, the method may be carried out by computer program instructions running on a data processor that provide data processing functions. The data processor may be a suitable computer, such as an electronic control module etc., which may also be a distributed computer system. The data processor or the computer, respectively, may comprise one or more of a processor, a memory, a data interface, or the like.
The present invention further relates to a computer readable medium having stored thereon computer-readable instructions which, when executed by a computer, cause the computer to carry out and/or control any of the methods of the present invention.
The features and advantages outlined above in the context of the system and the method similarly apply to the computer program product and the computer-readable medium described herein. Likewise, any features and advantages noted with regard to the method of the present invention apply accordingly to the system of the present invention and vice versa. A computer program (product) may be stored and/or distributed on a suitable medium such as an optical storage medium or a solid-state medium, supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.
Further features, examples, and advantages will become apparent from the following detailed description of preferred embodiments and the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to illustrate its practicality, figures are provided in the following and reference is made thereto. It should be understood that the figures represent only exemplary embodiments and thus in no way limit the scope of the claimed invention. Identical or like-acting elements are indicated throughout by the same reference signs. Any reference signs in the claims should not be construed as limiting the scope of the claims.
In the accompanying drawings:

Fig. 1 illustrates a schematic, not to scale view of an x-ray system according to an embodiment of the present invention;
Fig. 2 schematically illustrates an x-ray source according to an embodiment of the present invention;
Fig. 3 is a flowchart schematically illustrating a method according to an embodiment of the present invention; and
Fig. 4 schematically illustrates the impact of different rotation frequencies to the power consumption of an x-ray system.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 illustrates an x-ray system 100 according to an embodiment of the present invention. In the depicted embodiment, the x-ray system 100 is a medical x-ray imaging system comprising an x-ray radiation source 50 and an x-ray radiation detector 60. The x-ray radiation source 50 is configured to emit a beam of radiation 52 towards a target of interest 70, for instance a patient. In the depicted embodiment, the patient lies on a bed 72, which can be laterally moved with respect to the x-ray radiation beam 52 as indicated by the double arrow. The radiation source 50 is arranged at a gantry 80, which is in the depicted embodiment a circular gantry that rotates around the patient as indicated by the arrow 82. As is indicated in the figure, the x-ray radiation beam 52 is generated at the x-ray source 50 and the radiation passes at least partially through the target of interest 70. By passing through the target of interest 70, at least part of the radiation is absorbed or deflected. The x-ray radiation detector 60 is arranged at a side of the gantry 80 opposite to the x-ray source 50. The x-ray detector 60 is accordingly configured to detect x-ray radiation 52, which may be emitted in form of a cone passing by and/or through the target of interest 70.
The x-ray system 100 comprises a controller 150, for suitably controlling one or more of the elements of the x-ray system 100 to perform the method according to the present invention, for instance the method of the embodiment 500 described with respect to figure 3. The controller 150 may be a single device or an arrangement of a plurality of devices that may allow to control the x-ray system 100 to investigate a target of interest. In further embodiments, the controller 150 is not integrated, at least partly, in the x-ray system 100.
In the illustrated embodiment, the x-ray system 100 comprises a computer 200. In further embodiments, the computer 200 is not integrated, at least partly, in the x-ray system 100.
Further, the x-ray system 100 comprises a computer program product 400. In further embodiments, the computer program product 400 is not integrated, at least partly, in x-ray system 100.
The computer program product 400 comprises computer-readable instructions which, when executed by the computer 200, cause the computer 200 to carry out and/or control a method for controlling an anode rotation frequency of an x-ray source 50 of an x-ray system 100, as described herein, for instance the method 500 described with respect to figure 3.
In the illustrated embodiment, the x-ray system 100 comprises a computer readable medium 300. In further embodiments, the computer readable medium 300 is not integrated, at least partly, in the x-ray system 100.
The computer readable medium 300 has stored thereon computer-readable instructions which, when executed by the computer 200, cause the computer 200 to carry out and/or control a method for acquiring images by an x-ray system 100, as described herein, for instance the method 500 described with respect to Fig. 3.
Fig. 2 illustrates an x-ray radiation source 50 controlled according to an embodiment of the present invention. In the x-ray source 50 an electron beam 16 is emitted from a cathode 40 towards a surface of a rotating anode 10, which may be a metal anode comprising for instance tungsten. The electron beam 16 impacts the angled surface of the anode 10 and x-ray radiation 52 is emitted in an angled manner towards the target of interest 70, e.g. in a 90° angle, as depicted in Fig. 1. Of course, also different angles may be employed dependent on the surface angle and the irradiation direction. The anode 10 comprises anode bearings 12, which rotatably support the anode in the x-ray source 50. The anode bearings 12 could be for instance provided in form of ball bearings or in form of spiral groove bearings.
Fig. 3 illustrates a flowchart of a method 500 for controlling an anode rotation frequency of an x-ray source 50 of an x-ray system 100 as described herein, for instance with respect to Figs. 1 and 2. In the depicted embodiment, the method 500 comprises selecting S1 at least one scan operation of the x-ray system 100. Further, the depicted embodiment of the method 500 comprises determining S2 at least one optimum rotation frequency of an anode 10 of the x-ray system 100 based on the selected scan operation, wherein the optimum rotation frequency is determined based on at least one scan operation parameter of the selected scan operation. Further, the depicted embodiment of the method 500 comprises setting S3 the anode rotation frequency to the determined optimum rotation frequency for each selected scan operation. Further, the depicted embodiment of the method 500 comprises performing S4 the selected scan operation. Further, the depicted embodiment of the method 500 comprises continuously monitoring S5 the scan operation parameter, wherein the optimum rotation frequency is dynamically set based on the result of the continuously monitored scan operation parameter.
Fig. 4 illustrates an exemplary power consumption of an x-ray system 100 as described herein, for instance with respect to Fig. 1. On the horizontal axis the scan time in seconds is illustrated and on the vertical axis the supplied or consumed power in kilowatts is illustrated. The maximum permittable power consumption is shown for a large focal spot and an operation frequency of the x-ray source 50 at 180 Hz and an operation frequency of the x-ray source 50 at 90 Hz. As will be appreciated, the higher the maximum allowable power consumption is, the higher is usually also the achievable output of the radiation source 50. The maximum allowable power consumption is for instance delimited by the heat that is internally created in the x-ray system 10, such as for instance heat occurring due to friction in the bearings 12 of the anode. As is apparent from the figure, at the beginning of the scan (up to ~12 s), the illustrated system is allowed to draw a higher power for the higher operating frequency of 180 Hz (cf. max. power consumption of 80 kW) compared to the lower operating frequency (cf. max power consumption of 75 kW). That is, for shorter scanning times, the system running at a higher operating frequency has lower frictional losses and thus less heat is generated. Consequently, more power can be consumed by the x-ray system 100 and a higher output can be achieved at the higher operating frequency. Accordingly, for shorter scan times and when a high output of the x-ray radiation source 50 is desired, the system may preferably be operated at the higher operating frequency.
However, beyond ~12s scan time, the maximum permittable power consumption for the higher operating frequency of 180 Hz drops below the maximum permittable power consumption for the lower operating frequency of 90Hz. That is, for longer scanning times, the system running at a lower operating frequency of 90 Hz has lower frictional losses and thus less heat is generated compared to the higher operating frequency of 180 Hz. Consequently, more power can be consumed by the x-ray system and a higher output can be achieved at the lower operating frequency. Accordingly, for longer scan times and when a high output of the x-ray radiation source 50 is desired, the system may be preferably operated at the lower operating frequency.
It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. The word "comprising" does not exclude the presence of elements or acts other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. Measures recited in mutually different dependent claims may advantageously be used in combination.

LIST OF REFERENCE SIGNS

10: anode
12: anode bearing
14: anode impact surface
16: electron beam
18: anode rotation
40: cathode
50: x-ray source
52: x-ray radiation
60: x-ray detector
70: target of interest
72: patient bed
80: gantry
82: gantry rotation
100: x-ray system
150: controller
200: computer
300: computer-readable medium
400: computer-program product
500: embodiment of the method
S 1 to S5 method acts
S 1: selecting at least one scan operation
S2: determining at least one optimum rotation frequency
S3: setting the anode rotation frequency
S4: perform the selected scan operation
S5: continuous monitoring of the scan operation parameter

Claims

A method (500) for controlling an anode rotation frequency of an x-ray source (50) of an x-ray system (100), wherein the method (500) comprises:
selecting (S 1) at least one scan operation of the x-ray system (100),

determining (S2) at least one optimum rotation frequency of at least one anode (10) of the x-ray system (100) based on the selected scan operation, wherein the optimum rotation frequency is determined based on at least one scan operation parameter of the selected scan operation, and

setting (S3) the anode rotation frequency to the determined optimum rotation frequency for each selected scan operation.
The method according to the preceding claim,
wherein the at least one scan parameter includes one or more of a power consumption of the x-ray source (50), a voltage applied to the x-ray source (50), a rotation frequency of a gantry (80) of the x-ray system (100), a scan time of the selected scan operation and/or a temperature state of the x-ray source (50).
The method according to the preceding claim,
wherein the temperature state of the x-ray source (50), preferably of an anode bearing (12) supporting the anode (10) in the x-ray source (50), comprises a current temperature state for the current scan operation, and/or comprises a future predicted temperature state for the current scan operation and/or at least one subsequent scan operation.
The method according to any of the preceding claims,
wherein setting the anode frequency includes an acceleration and/or deceleration of the anode rotation (18).
The method according to the preceding claim,
wherein, when two or more scan operations are selected, the method (500) further comprises determining an anode rotation frequency adjustment time necessary to accelerate or decelerate the anode rotation (18) from a first optimum rotation frequency of a first scan operation to a second optimum rotation frequency of a subsequent second scan operation.
The method according to the preceding claim,
wherein, when the anode rotation frequency adjustment time is determined to be sufficient for an acceleration or deceleration of the anode rotation from the first optimum rotation frequency to the second optimum rotation frequency, the anode rotation frequency is set to the first optimum rotation frequency for performing the first scan operation and subsequently set to the second optimum rotation frequency for performing the second scan operation.
The method according to any of the preceding claims 5 or 6,
wherein, when the anode rotation frequency adjustment time is determined to be insufficient for an acceleration or deceleration of the anode rotation from the first optimum rotation frequency to the second optimum rotation frequency, the anode rotation frequency is set to a third optimum rotation frequency for performing the first scan operation and the second scan operation.
The method according to any of the preceding claims 4 to 7,
wherein the method further comprises determining a standby frequency of the anode (10) at which no scan operation is performed,

wherein, when only one scan operation is selected, the anode (10) is accelerated from the standby frequency to the determined optimum rotation frequency of the scan operation to perform the selected scan operation (S4) and decelerated back to the standby frequency after performing the selected scan operation, and,

when more than one scan operation is selected, the anode (10) is accelerated from the standby frequency to the determined optimum rotation of the selected first scan operation frequency to perform the selected first scan operation (S4) and subsequently accelerated or decelerated to the determined optimum rotation of at least one selected second scan operation frequency to perform the selected second scan operation (S4) and decelerated back to the standby frequency after performing the selected second scan operation.
The method according to any of the preceding claims,
wherein the optimum rotation frequency is a lowest possible anode rotation frequency at which the selected scan operation can be performed.
The method according to any of the preceding claims,
wherein the method comprises a continuous monitoring of the scan operation parameter (S5), and wherein the optimum rotation frequency is dynamically set based on the result of the continuously monitored scan operation parameter.
An x-ray source (50) of an x-ray system (100),
wherein the x-ray source (50) comprises a rotatable anode (10), and wherein the rotatable anode (10) is adapted to be controlled according to a method of any of the preceding claims 1 to 10.
An x-ray system (100) comprising an x-ray source (50), wherein the x-ray source (50) comprises a rotatable anode (10), wherein the x-ray system (100) further comprises a controller (150) configured to carry out and/or control a method according to any of the preceding claims 1 to 10.
The x-ray system (100) according to the preceding claim, wherein the x-ray system (100) is a medical x-ray imaging system.
A computer-program product (400) comprising computer readable instructions, which, when executed by a computer (200), cause the computer (200) to carry out and/or control the method of any of claims 1 to 10.
A computer-readable medium (300) having stored thereon computer readable instructions which, when executed by a computer (200), cause the computer (200) to carry out and/or control the method of any of claims 1 to 10.