X-ray source and X-ray imaging device

Abstract

An X-ray source (10) for emitting an X-ray beam (101) is proposed. The X-ray source (10) comprises an anode (12) and an emitter device (14), the emitter device comprising a cathode (16) for emitting an electron beam (15) towards the anode (12) and an electron optics (18) for focusing the electron beam (15) at a focal spot (20) on the anode (12). The X-ray source (10) further comprises a controller (22) configured to determine a switching action of the emitter device (14) and to actuate the emitter device (14) to perform the switching action, the switching action being associated with a change in at least one of a position of the focal spot (20) on the anode (12), a size of the focal spot (20) and a shape of the focal spot (20). The controller (22) is further configured to predict the size and shape of the focal spot (20) expected after the switching action based on the determined switching action before the switching action is performed. In addition, the controller (22) is configured to actuate the electron-optical device (18) to compensate for the change in the size and shape of the focal spot (20) caused by the switching action.

Description

Technical Field

[0001] The present invention relates to the field of X-ray imaging. In particular, the present invention relates to an X-ray source, to an X-ray imaging device, to a method for operating an X-ray source, to a program element, and to a computer-readable medium. Background Art

[0002] In certain X-ray imaging applications, an X-ray beam emitted by an X-ray source of an X-ray imaging device and / or at least one characteristic of the X-ray beam is modified during an imaging task. The X-ray beam may be changed, for example, in shape, size, direction of impact, intensity, frequency, energy and / or energy distribution of a pulsed X-ray beam. Typically, an X-ray beam is generated by emitting an electron beam from a cathode and focusing the electron beam at a focal spot on an anode, for example by means of electron optics, wherein X-ray photons are then generated and emitted to form the X-ray beam.

[0003] In order to steer the X-ray beam, for example, the electrical energy, electrical power, current and / or voltage supplied to the cathode can be changed. Moreover, the filter can be moved in and / or out of the X-ray beam during operation of the X-ray source. In addition, grid switching, spectral filtering and / or dynamic focal spot positioning techniques can be applied to steer the X-ray beam.

[0004] In order to ensure high quality of the X-ray images acquired in such imaging applications and / or to ensure that the characteristics of the X-ray beam for certain imaging are met, the focal spot of the electron beam at the anode should be accurately controlled. This can be a challenging task, especially if large variations of the X-ray beam are to be performed. Summary of the invention

[0005] It would therefore be desirable to provide an improved X-ray source and / or an improved X-ray imaging apparatus which allow acquisition of high quality X-ray images.

[0006] This is solved by the subject matter of the independent claims, wherein further embodiments are incorporated in the dependent claims and the following description.

[0007] Features and / or functions described hereinafter with reference to one aspect of the invention are equally applicable to any other aspect of the invention described hereinafter. In particular, features and / or functions described hereinafter with reference to an X-ray source are equally applicable to an X-ray imaging apparatus, a method for operating an X-ray source, a program element and a computer-readable medium, and vice versa.

[0008] According to a first aspect of the present invention, there is provided an X-ray source for emitting an X-ray beam. The X-ray source comprises an anode, an emitter device and a controller. The emitter device comprises a cathode and an electron optical device, the cathode being used to emit an electron beam toward the anode, and the electron optical device being used to focus the electron beam at a focal spot on the anode. The electron optical device may be configured to focus the electron beam, for example, based on generating an electric and / or magnetic field that deflects the electron beam. Therefore, the electron optical device may generally refer to a focuser and / or a deflector for the electron beam.

[0009] The controller is configured to determine, for example, a switching action of the emitter device for a given imaging task and to actuate the emitter device to perform the switching action, wherein the switching action is associated with a change in at least one of the position of the focal spot on the anode, the size of the focal spot and the shape of the focal spot. In addition, the controller is configured to predict the size and shape of the focal spot expected after the switching action, after the switching action is performed and / or after the switching action is performed based on the determined switching action before the switching action is performed and / or before the switching action is performed. Moreover, the controller can be configured to predict the position of the focal spot on the anode predicted after the switching action.

[0010] Furthermore, the controller may, for example, be configured to actuate the electron-optical device to compensate for a change in the size and shape of the focal spot induced by the switching action (e.g. expected to be induced based on the predicted size and shape of the focal spot). Therein, the controller may be configured to actuate the electron-optical device to compensate for the change in the size and shape of the focal spot before, during and / or after the switching action is performed (preferably before and / or during the switching action is performed). For this purpose, the controller may be configured to feed forward a control signal, for example, to the electron-optical device in order to actuate the electron-optical device to compensate for the change in the size and shape of the focal spot.

[0011] The controller may be configured to predict, estimate and / or determine the size and shape of the focal spot expected after the switching action is performed, ended and / or terminated before (i.e., before in time) the switching action is started, performed, ended and / or terminated. Thus, the term "before the switching action is performed" may refer to directly before the switching action is started, when the switching action is performed and / or before the switching action is terminated and / or ended. Similarly, the term "after the switching action" and / or "after the switching is performed" may refer to after the switching action ends and / or after the switching action is terminated.

[0012] The size of the focal spot may refer to the size of the focal spot along at least one spatial direction, preferably along two spatial directions. In general, the focal spot may refer to the area of ​​the outer surface of the anode where the electron beam impinges on the anode. Thus, the size of the focal spot may refer to the size of said area on the anode. Furthermore, the shape of the focal spot may refer to the geometric shape and / or geometry of the focal spot and / or said area.

[0013] In general, predicting the size and shape of the focal spot expected after the switching action allows for prospective and / or precise control of the focal spot, for example based on actuating the electron optics to correspond to the predicted size and shape of the focal spot. Therefore, the controller can be configured to control and / or prospectively control the size and shape of the focal spot based on the predicted size and shape of the focal spot expected after the switching action (for example based on actuating the electron optics according to the predicted shape and size of the focal spot). In other words, the controller can be configured to determine and / or compensate for any changes in the focal spot caused by the switching action before these changes actually occur. This can allow precise control of the X-ray beam emitted from the anode during the X-ray imaging task. For example, the shape, size, impact direction, intensity, frequency of the pulsed X-ray beam, the energy and / or energy distribution of the X-ray beam can be precisely controlled based on controlling the size and shape of the focal spot. In addition, by precisely controlling the X-ray beam, the image quality of the acquired X-ray images can be improved, in particular by reducing noise and / or increasing the resolution of the image. Moreover, for example, the dose delivered to the patient can be advantageously reduced.

[0014] By way of example, the controller may be configured to provide a predictive control signal indicating and / or representing a predicted size and shape of the focal spot to the electron optical device before the switching action is performed, when the switching action is performed and / or when the switching action ends. With the aid of the predictive control signal, the electron beam may be adjusted, modified and / or regulated so that the focal spot has the predicted size and shape after the switching action is performed and / or ends. Furthermore, the controller may be configured to predict the size and shape of the focal spot in response to determining the switching action and / or in response to determining that the switching action is to be performed. Furthermore, the controller may be configured to actuate the electron optical device, for example by providing a predictive control signal, in response to predicting the size and shape of the focal spot predicted after the switching action. Furthermore, the controller may be configured to start the switching action, for example based on actuating the emitter device, in response to predicting the size and shape of the focal spot expected after the switching action and / or in response to actuating the electron optical device based on providing the predictive control signal. Specifically, the controller may be configured to actuate the electron optical device based on the predicted size and shape of the focal spot before, during or after the switching action is performed.

[0015] In general, a switching action may refer to any adjustment and / or actuation of an X-ray source that affects and / or modifies at least one of the size, shape and position of the focal spot on the anode. According to an embodiment, the switching action comprises at least one of changing the voltage supplied to the cathode, changing the current supplied to the cathode, changing the electrical power supplied to the cathode, changing the electric field between the anode and the cathode, changing the position of the focal spot on the anode by deflecting the electron beam using the electron optics, and / or turning on the X-ray beam. Furthermore, moving a filter for spectral filtering in and / or out of the X-ray beam in combination with another adjustment and / or actuation of the X-ray source (e.g., a change in the voltage and / or current supplied to the cathode) may also be referred to as a switching action. Those kinds of switching actions may be performed specifically when applying kV-peak switching (also referred to as kVp switching), grid switching, spectral filtering and / or dynamic focal spot positioning techniques.

[0016] Furthermore, the term "determining a switching action" may mean that the controller is configured to determine one or more parameters for operating the X-ray source. By way of example, the controller may be configured to determine a voltage supplied to the cathode, a current supplied to the cathode according to the switching action and / or the duty cycle. Furthermore, the controller may be configured for one or more time periods during which the X-ray beam is turned on and / or off. Moreover, the frequency of such time periods may be determined by the controller. Furthermore, the controller may be configured to determine a control signal provided to the electron optical device according to the determined switching action. Based on one or more of the parameters described above, the controller may predict the shape and size of the focal spot.

[0017] An X-ray source according to the present disclosure may be advantageously used in X-ray imaging applications, wherein the X-ray beam is modified during an imaging task and / or during image acquisition. Examples of such applications are dual energy X-ray and / or kV-peak switching applications, wherein the energy and / or energy distribution of the X-ray beam is changed during an imaging task, for example based on changing the voltage and / or current supplied to the cathode. Another example is grid switching, wherein the electron beam may be canceled for a certain time period during an imaging task, so that the X-ray beam is turned off during the time period, for example for dose modulation purposes. Another example is dynamic focal spot positioning, wherein the position of the focal spot on the anode may be altered and / or changed during an imaging task. In any one or a combination of the applications described above, spectral filtering may also be applied, for example based on changing a filter in the X-ray beam, moving a filter into the X-ray beam and / or moving a filter out of the X-ray beam. Such a filter may, for example, comprise a filter grating.

[0018] In at least some of the X-ray imaging described above, attempts have been made in the past to adjust the size and shape of the focal spot by means of a feedback control configured to compensate for changes in the size and shape of the focal spot caused by a specific switching action. However, such feedback control only allows compensation for changes caused by a specific switching action after the change has occurred and therefore after the change has been affected by the focal spot and / or the X-ray beam. In addition to this, such feedback control may not be able to compensate for changes caused by the switching action quickly enough, for example when large changes of the X-ray beam have to be performed within a short period of time and / or after a long period of time when the X-ray beam has been turned off.

[0019] In contrast, the prediction of the size and shape of the focal spot according to the present invention allows predictive or proactive control of the focal spot and / or the X-ray beam. Therefore, the controller can be configured to proactively determine a predictive control signal based on the predicted size and shape of the focal spot. In addition, the controller can be configured to determine and / or proactively determine a level of correction for the electron beam, for example in order to compensate for changes in the size and shape of the focal spot caused by the switching action. This allows for anticipated correction of any changes in size and shape that occur due to the switching action. For this purpose, the controller may include a predictive module, a predictive sub-controller, a predictive section and / or a predictive unit configured to predict the size and shape of the focal spot and / or configured to determine a predictive control signal. The controller may also be configured to feed forward the predictive control signal to other components of the X-ray source, such as feedback control and / or feedback control loops. If, in addition to the predictive control, feedback control is used in the X-ray source, for example, to fine-tune the shape and size of the focal spot, any potential errors in the predicted shape and size and / or the corresponding predictive control signal can be quickly and efficiently corrected by the feedback control, since the predicted shape and size of the focal spot should be close to the desired values, the feedback control can adjust the focal spot towards said desired values. Thus, by means of the predictive control according to the invention, a faster and more efficient overall control and / or adjustment of the shape and size of the focal spot can be provided.

[0020] According to an embodiment of the present invention, the controller is configured to predict the change in size and shape of the focal spot induced by the switching action and / or expected after the switching action is performed. The change in size and shape induced by the switching action can be predicted relative to the shape and size of the current focal spot before the switching action is performed, started, ended and / or terminated. Alternatively or additionally, the controller is configured to actuate the electron optical device to compensate for the change in size and shape of the focal spot caused by the switching action. For example, the controller can be configured to determine a predictive control signal based on the predicted change in size and shape of the focal spot. The predictive control signal can indicate the predicted change in size and shape, and / or indicate the size and shape of the focal spot after the switching action. Alternatively or additionally, the predictive control signal can indicate the correction and / or adjustment of the electron beam to compensate for the change in size and shape of the focal spot caused by the switching action. This allows any change in the size and shape of the focal spot to be corrected before such change actually occurs. In general, the controller can be configured to actuate the electron optical device before, during and / or after the switching action to compensate for the change. Thus, the controller may be configured to actuate the electron-optical device to compensate for the change before, during and / or after actuating the emitter device to perform the switching action. In other words, the controller may be configured to actuate the emitter device to perform the switching action in response to actuating the electron-optical device to compensate for the predicted change in the size and shape of the focal spot.

[0021] According to an embodiment of the invention, the controller is configured to predict the size and the shape of the focal spot based on predicting the width and height of the focal spot. This allows to accurately, quickly and / or precisely predict the size and shape of the focal spot.

[0022] According to an embodiment of the present invention, the controller is configured to predict the size and the shape of the focal spot based on a model that models the width and height of the focal spot as the current supplied to the cathode, the voltage supplied to the cathode and the thermal load of the anode. Therefore, the controller can be configured to determine the voltage, current and / or thermal load to determine the width and height of the focal spot after the switching action. Therein, the model can be an empirical model that can be determined, for example, based on calibration measurements and / or models. Predetermined values ​​for the width and height of the focal spot for one or more sets of voltage, current and / or thermal load can, for example, be stored in a list and / or a lookup table. The controller can be configured to determine the width and height of the focal spot based on the list and / or the lookup table. Moreover, the controller can be configured to interpolate and / or extrapolate one or more sets stored in the list and / or the lookup table.

[0023] According to an embodiment of the present invention, the controller is configured to predict the size and shape of the focal spot based on predicting the thermal load of the anode. In general, the thermal load of the anode may affect the size and / or shape of the focal spot, for example due to thermal expansion, and the thermal load of the anode may indicate the temperature of at least a part of the anode. Therefore, predicting the thermal load of the anode after the switching action may allow for accurate prediction of the shape and size of the focal spot. Therein, the thermal load may be calculated by the controller, for example, based on the current and / or voltage supplied to the cathode during and / or after the switching action. In addition, in order to calculate the thermal load, the time period (or its length) during which the X-ray beam is turned on and / or the time period (or its length) during which the X-ray beam is turned off can be considered. For example, if the X-ray beam is turned on for a certain period of time, the thermal load of the anode may reach a stable state. In this stable state, the thermal load of the anode may be derived from the current and / or voltage supplied to the cathode alone. If the X-ray beam is turned on for only a short period of time, so that the temperature or thermal load cannot yet reach a stable state, the time period and / or its length during which the X-ray beam is turned on may also be considered in order to calculate the thermal load of the anode.

[0024] According to an embodiment, the controller is configured to determine the thermal load of the anode expected after the switching action and / or after the switching action is performed based on a predetermined cooling rate of the anode. By way of example, a cooling rate and / or a cooling curve can be predetermined for the anode based on the voltage and / or current supplied to the cathode, wherein optionally the time period during which the X-ray beam is turned on and / or off can be taken into account. The cooling rate and / or the cooling curve can be stored in a data storage device of the X-ray source, and the controller can retrieve and / or the size and shape based on the predetermined cooling rate and / or cooling curve. In addition, the controller can be configured to determine the thermal load based on the past and / or previous thermal load of the anode before the switching action. Moreover, the time period during which the X-ray beam was turned off before the switching action can be taken into account by the controller to accurately predict the thermal load after the switching action and the shape and size of the focal spot.

[0025] According to an embodiment of the present invention, the emitter device further comprises a grid disposed between the cathode and the anode, wherein the grid is configured to cancel the electron beam in the on state of the grid and transmit the electron beam through the grid in the off state of the grid. The controller is configured to switch the grid between the on state and the off state by providing a grid switching signal to the grid. The grid switching signal may be, for example, a pulse width modulated signal. With the aid of the grid, the X-ray beam may be turned on when the grid is in the off state, and the X-ray beam may be turned off when the grid is in the on state. Thus, with the aid of the grid and / or the grid switching signal, the intensity of the X-ray beam emitted by the X-ray source may be changed during the imaging task. In general, the grid may be configured to accumulate repulsive negative charges to prevent electrons emitted by the cathode from reaching the anode. Alternatively, the grid may be configured to accumulate positive charges to withdraw and / or clear electrons from the cathode so that the electrons do not reach the anode.

[0026] According to an embodiment of the present invention, the controller is configured to determine the switching action based on a predetermined grid switching profile and / or based on analyzing a predetermined grid switching profile, wherein the grid switching profile defines and / or indicates the modulation of the intensity of the X-ray beam based on the sequence of at least one off state of the grid and at least one on state of the grid. The grid switching profile may, for example, include an entry with a current and / or voltage supplied to the cathode during the off state of the grid. The grid switching profile may also include an entry specifying the sequence of on states and off states of the grid. The controller may be configured to determine the voltage supplied to the cathode, the current supplied to the cathode and / or the duty cycle for one or more time periods when the X-ray beam is on and / or the grid is in the off state based on the grid switching profile. Moreover, the controller may be configured to determine one or more time periods when the X-ray beam is on and / or the grid is in the off state based on the grid switching profile. Therefore, the controller may derive one or more characteristics for one or more switching actions from the grid switching profile. The grid switching profile may be stored in a data storage device of the X-ray source, and / or the grid switching profile may be accessed by the controller to determine one or more switching actions.

[0027] According to an embodiment of the invention, the X-ray source further comprises a focal spot sensor for acquiring an image of the focal spot based on detecting X-ray radiation emitted from the anode, the acquired image indicating the shape, the size and the position of the focal spot on the anode. Therein, the controller is further configured to analyze the image acquired using the focal spot sensor in order to determine and / or thereby determine a change in at least one of the size, the shape and the position of the focal spot. Furthermore, the controller is configured to adjust at least one of the size, the shape and the position of the focal spot by actuating the electron optics if a change in at least one of the size, the shape and the position of the focal spot is determined after the switching action is performed. The focal spot sensor may be part of a feedback control of the X-ray source, wherein the feedback control may be configured to compensate for any change in size, shape and / or position after the switching action is performed, for example by fine tuning the electron optics. This may allow the size, shape and / or position of the focal spot to be adjusted, thereby making the focal spot largely unaffected, for example, by temperature changes and / or thermal loads of the anode. By predicting the shape and size before the switching action is performed and by actuating the emitter arrangement accordingly, it can be ensured that the feedback control of the X-ray source does not have to compensate for large changes in the size, shape and / or position of the focal spot after the switching action is performed. Based on the feedback control, only small changes, for example due to thermal expansion, can be corrected. This combination of predictive control and feedback control allows a more precise, faster, more efficient and more reliable control of the size and shape of the focal spot.

[0028] According to an embodiment of the present invention, the controller is configured to analyze the image acquired by the focal spot sensor when and / or only when the grid is in the closed state and the electron beam impinges on the anode. Alternatively or additionally, the controller is configured to discard the image acquired by the focal spot sensor when the grid is in the open state and the electron beam is cancelled by the grid. In this way, it can be ensured that the controller does not analyze dark images and / or images acquired by the focal spot sensor during the time period when the grid is in the open state and the electron beam is cancelled, but only analyzes images acquired by the focal spot sensor during the time period when the grid is in the closed state and the X-ray beam is on. Analyzing the image during the open state of the grid with the X-ray beam turned off may be misinterpreted by the controller as a loss of intensity, and the controller may try to compensate for this loss of intensity by actuating the electron optics. Therefore, by only analyzing the image of the focal spot sensor when the grid is in the closed state, erroneous actuation of the electron optics can be prevented.

[0029] According to an embodiment of the invention, the controller is configured to determine whether the image of the focal spot was acquired by the focal spot sensor during the off-state of the grid based on the grid switching signal provided to the grid. Thus, the grid switching signal may trigger the controller to analyze the image acquired by the focal spot sensor. Using the grid switching signal as an indicator for the on-state and / or off-state of the grid may allow accurately and reliably distinguishing between images of the focal spot sensor acquired during the on-state and the off-state of the grid.

[0030] According to a second aspect of the present invention, there is provided an X-ray imaging apparatus comprising an X-ray source as described above and hereinafter and an X-ray detector for detecting X-ray radiation emitted by the X-ray source.

[0031] According to a third aspect of the present invention, a method for operating an X-ray source is provided. The X-ray source may refer to an X-ray source as described above and below. Specifically, the X-ray source comprises an anode and an emitter device, the emitter device having a cathode for emitting an electron beam and having an electron optical device for focusing the electron beam at a focal spot on the anode. The X-ray source also includes a controller. The method comprises the following steps:

[0032] determining, with the controller, a switching action of the emitter arrangement, the switching action being associated with a change in at least one of a position of the focal spot on the anode, a size of the focal spot, and a shape of the focal spot;

[0033] predicting, with the controller, the size and the shape of the focal spot expected after the switching action based on the determined switching action; and

[0034] The transmitter device is actuated to perform the switching action.

[0035] Furthermore, the method may for example comprise the step of actuating the electron-optical device with the controller, thereby compensating for the change in the size and the shape of the focal spot induced (e.g. expected to be induced) by the switching action. Therein, the switching action may preferably be performed after and / or during actuation of the electron-optical device in order to compensate for the change in the size and shape of the focal spot. However, the switching action may alternatively or additionally be performed before actuation of the electron-optical device in order to compensate for the change in the size and shape of the focal spot.

[0036] According to a fourth aspect of the invention, there is provided a computer program element, which, when executed by a controller of an X-ray source, is configured to cause the X-ray source to perform a method as described above and in the following. The computer program element may comprise software instructions. The computer program element may, for example, be stored on a data storage device of the X-ray source, and the controller may be configured to access and execute the program element.

[0037] According to a fifth aspect of the invention, there is provided a computer-readable medium having stored thereon a program element as described above and in the following.

[0038] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The subject matter of the invention will be explained in detail hereinafter with reference to exemplary embodiments illustrated in the accompanying drawings, in which:

[0040] Figure 1 Schematically illustrates an X-ray imaging apparatus according to an exemplary embodiment of the present invention;

[0041] Figure 2 schematically illustrates an X-ray source according to an exemplary embodiment of the present invention;

[0042] Figure 3 schematically illustrates an X-ray source according to an exemplary embodiment of the present invention;

[0043] Figure 4 A flow chart illustrating the steps of a method for operating an X-ray source according to an exemplary embodiment of the invention is shown.

[0044] In principle, identical or similar components are provided with identical or similar reference symbols in the figures. DETAILED DESCRIPTION

[0045] Figure 1 An X-ray imaging device 100 according to an embodiment of the present invention is schematically shown. The X-ray imaging device may refer to any type of imaging system, such as a digital X-ray imaging system, a dual-energy or multi-energy X-ray imaging system, computed tomography (CT), spectral CT, interventional XR (IXR), digital XR (DXR), a C-arm system, and / or a multimodality system (like PET / CT).

[0046] The X-ray imaging device 100 includes an X-ray source 10 for generating and / or emitting an X-ray beam 101 toward an object 103 to be inspected, and an X-ray detector 102 for detecting at least a portion of the X-ray beam 101 that has passed through the object 103. The X-ray source 10 can refer to any X-ray source, such as an X-ray tube, a stereoscopic X-ray tube, or any other type. The X-ray source 10 will be described in more detail in subsequent drawings.

[0047] Likewise, the X-ray detector 102 can refer to any suitable X-ray detector 102. Specifically, the X-ray detector 102 can include a scintillator for converting X-ray photons into visible light. In addition, the X-ray detector 102 can include one or more detection elements for detecting light emitted from the scintillator. In addition, 102 can include a direct conversion detector for converting X-ray photons into electric charge, and can include detection elements for charge accumulation or single photon counting.

[0048] In addition, the X-ray imaging apparatus 100 includes a controller 22 operatively coupled to the X-ray detector 102 and the X-ray source 10. However, the controller 22 may be a part of the X-ray source 10 (as described with reference to subsequent figures) and / or a part of the X-ray detector 102. Moreover, the controller 22 may refer to a controller arrangement 22 having one or more sub-controllers, modules and / or units.

[0049] Figure 2 An X-ray source 10 according to an exemplary embodiment of the invention is schematically shown.

[0050] The X-ray source 10 includes a housing 11 and an anode 12 arranged in the housing 11. The anode 12 may be any type of anode. For example, the anode 12 may be a rotatable and / or movable anode 12.

[0051] The X-ray source 10 further comprises an emitter arrangement 14 having a cathode 16 for emitting an electron beam 15 towards the anode 12. The emitter arrangement 14 further comprises an electron optic 18 for focusing the electron beam 15 on the anode 12 and / or on an outer surface thereof. The electron optic 18 may be configured to generate an electric field and / or a magnetic field to detect the electron beam 15 and to focus the electron beam 15 on the anode 12.

[0052] The electron beam 15 is focused at a focal spot 20 on the anode 12. The focal spot 20 may refer to a zone and / or region of the anode 12 where the electron beam 15 impinges on the anode 12. When impinging on the anode 12, the electron beam 15 generates X-ray radiation and / or X-ray photons emitted from the anode 12 and / or from the focal spot 20. At least a portion of the emitted X-ray photons are able to pass through an X-ray window 17 of the X-ray source 10 to form an X-ray beam 101.

[0053] The X-ray source 10 also includes a controller 22 operatively coupled to the emitter arrangement 14 , the electron optics 18 , and / or the cathode 16 .

[0054] Figure 2 The X-ray source 10 shown in FIG. 1 can be advantageously used in imaging applications, wherein the X-ray beam 101 and / or the characteristics of the X-ray beam 101 can be adjusted and / or modified during an imaging task and / or during the acquisition of an X-ray image. Specifically, Figure 1 The X-ray source 10 depicted in can be configured for kV-peak or kVp switching, wherein the energy and / or energy distribution of the X-ray beam 101 is modified and / or changed during an imaging task (such as, for example, for dual-energy X-ray imaging). During kV-peak switching applications, the electrical power supplied to the cathode 16 can be switched between at least two power levels in a corresponding switching action. For example, the voltage supplied to the cathode 16 can be changed from, for example, 80 kV to 140 kV during a single imaging task and / or during a switching action. Alternatively or additionally, the current supplied to the cathode 16 can be changed during the switching action. Therein, the actual switching action typically occurs within a fairly short time scale (e.g., in the range of microseconds to milliseconds).

[0055] However, any change in the voltage and / or current supplied to the cathode 16 may affect at least one of the shape, size and position of the focal spot 20 on the anode 12. This in turn may affect the X-ray beam 101 and / or the characteristics of the X-ray beam 101, for example due to a changed thermal load and / or temperature of the anode 12 and / or due to different properties of the electrons of the electron beam 15 impinging on the anode 12 with different energies. In order to ensure a high image quality of the X-ray images, it may be advantageous to precisely control the shape and size of the focal spot 20. This can be achieved by an X-ray source 10 according to the present invention, as described below.

[0056] The controller 22 is configured to determine a switching action of the emitter device 14. Determining the switching action may include determining one or more values ​​of parameters for operating the X-ray source 12, such as a voltage and / or current supplied to the cathode 16. The controller 22 may also determine other parameters of the switching action, such as a control signal provided to the electron-optical device 18, a time period during which the switching action is performed, and / or a time at which the switching action is performed. Such parameters of the switching action may be input to the X-ray source 10 by a user, and / or may be retrieved by the controller from the data storage device 24 and / or data stored therein. In addition, the controller 22 is configured to actuate the emitter device 14 to perform the switching action.

[0057] Prior to actuating the emitter arrangement 14 to perform the switching action, the controller 22 determines, calculates and / or predicts the shape and size of the focal spot 20 that is expected after the switching action. Based on the determined switching action, the controller 22 is able to predict and / or estimate the shape and size of the focal spot 20 that is expected to exist after the switching action is performed. Alternatively or additionally, the controller 22 is configured to determine a change in the size and shape of the focal spot 20 caused by the switching action. Thus, the controller 22 may be configured to determine a relative change in the size and shape of the focal spot, for example relative to the size and shape of the focal spot 20 before and / or previously and / or during the current operation of the X-ray source 12.

[0058] Furthermore, the controller 22 is configured to determine a predictive control signal based on the predicted size and shape of the focal spot 20 and / or based on a predicted change in the size and shape of the focal spot 20. The controller 22 may then provide a predictive control signal directly to the electron optics 18 before, during, at, and / or when the switching action is terminated, so as to adjust the electron beam 15, thereby taking into account the switching action and the resulting change in the size and shape of the focal spot. This allows predictive control of the shape and size of the focal spot 20 before any change in the focal spot 20 due to the performed switching action occurs or is evident. Thus, changes in the size and shape of the focal spot 20 caused by the switching action can be compensated before such changes actually occur. Thus, a more accurately controlled X-ray beam 101 and / or better image quality can be provided.

[0059] In general, the controller 22 can be configured to determine a switching action and predict the size and shape of the focal spot 20 in response to determining the switching action. Furthermore, the controller 22 can be configured to determine a predictive control signal in response to predicting the size and shape of the focal spot 20. Furthermore, the controller 22 can be configured to actuate the electron-optical device 18 based on the predictive control signal according to the predicted size and shape of the focal spot 20. In response thereto, the controller 22 can then initiate the switching action and / or actuate the emitter device 14 to perform the switching action.

[0060] In order to determine the shape and size of the focal spot 20 expected after the switching action, the controller 22 may determine the width and height of the focal spot 20 expected after the switching action. For example, the controller 22 may determine the voltage and / or current supplied to the cathode 16 after the switching action based on the determined switching action, and the controller can estimate and / or calculate the width and height of the focal spot 20. Moreover, the time period (or its length) during which the X-ray beam is turned on and / or off can be taken into account to calculate the width and height of the focal spot 20, which time period (or its length) during which the X-ray beam is turned on and / or off can be determined, for example, based on a switching profile describing one or more switching actions performed during image acquisition. Therefore, the width and height of the focal spot 20 may be a function of the voltage and / or current supplied to the cathode 16. Such a function may be predetermined, for example, based on measurements, and the functional relationship may be stored in the data storage device 24. Moreover, the width and height of the focal spot 20 may be determined by the controller 22 based on a model that models the height and width of the focal spot 20 as a function of the voltage and / or current supplied to the cathode. Alternatively or additionally, a lookup table may be stored in the data storage device 24 and the controller may determine the width and height of the focal spot 20 based on the lookup table.

[0061] Alternatively or additionally, the controller 22 can be configured to determine the expected thermal load and / or temperature of at least a portion of the anode 12 after the switching action. Based on the determined thermal load and / or temperature, the controller 22 can then predict the shape and size of the focal spot 20 after the switching action.

[0062] The controller 22 may determine the heat load and / or the temperature, for example, based on a predetermined cooling rate and / or cooling curve of the anode, based on which the temperature of the anode may be calculated as a function of the current and / or voltage supplied to the cathode 16. In this, the previous operation of the X-ray source may be taken into account, for example a period of time before the switching action, during which the X-ray beam was turned off. The cooling rate and / or cooling curve may be stored in the data storage device 24. Thus, the controller 22 may be configured to predict the size and shape of the focal spot 20 based on the voltage supplied to the cathode 16 after the switching action, based on the current supplied to the cathode 16 after the switching action and / or based on the heat load expected after the switching action. For this purpose, the controller 22 may be configured to predict the shape and size of the focal spot 20 based on a model that models the width and height of the focal spot 20 as the supplied voltage, current and / or heat load of the anode. Alternatively or additionally, a lookup table may be stored in the data storage device 24, and the controller 22 may determine the width and height of the focal spot 20 expected after the switching action based on the lookup table. It should be noted that in addition to changing the voltage and / or current supplied to the cathode 16 during the switching action, the filter and / or filter grating may also be moved into and / or out of the X-ray beam 101 during the switching action.

[0063] Furthermore, instead of or in addition to the kV-peak switching described above, dynamic focal spot positioning may also be applied, wherein the position of the focal spot 20 on the anode may be changed in a separate switching action or simultaneously with changing the voltage and / or current supplied to the cathode 16 by deflecting the electron beam 15 using the electron optics 18. Similar to the description above, the controller 22 is configured to infer the size and shape of the focal spot 20 by changing the position of the focal spot 20 on the anode 12, and actuate the electron optics 18 to compensate for this change in position.

[0064] Alternatively or additionally, grid switching may be applied, wherein the X-ray beam 101 is turned on and / or off during an imaging task, such as in Figure 3 Described in detail in .

[0065] It should be noted that Figure 2 The exemplary embodiment of the X-ray source 10 illustrated in FIG. 1 can also include, for example, Figure 3 Specifically, Figure 2 The X-ray source 10 can also include as hereinafter referred to Figure 3 A focal spot sensor 28 and / or feedback control 30 are depicted.

[0066] Figure 3 An X-ray source 10 according to an exemplary embodiment of the present invention is schematically shown. If not otherwise stated, Figure 3 The X-ray source 10 includes a reference Figure 1 and 2 The X-ray source 10 described above may have the same features, functions and / or elements.

[0067] exist Figure 3 , the emitter arrangement 14 includes a grid 26 disposed between the cathode 16 and the anode 12. In an on state of the grid 26, the grid 26 cancels the electron beam 15 and thus turns off the X-ray beam 101. In an off state of the grid 26, the electron beam 15 is able to pass through the grid 26 and impinge on the anode 12, causing the X-ray beam 101 to turn on. The controller 22 is operatively coupled to the grid 26 and is configured to switch the grid 26 between an on state and an off state based on providing a grid switching signal to the grid 26. The grid switching signal may refer to a pulse width modulated signal for actuating the grid 26. Such grid switching may be particularly advantageous for generating a pulsed X-ray beam and / or for dose modulation techniques, wherein the intensity of the X-ray beam 101 is changed based on switching the grid 26 between an on state and an off state. The sequence of on states and off states of the grid 26 may be defined, for example, in a grid switching profile, which may be stored in the data storage device 24 and / or provided to the controller 22. The controller 22 may then determine a grid switching signal based on the grid switching profile and actuate the grid 16 accordingly.

[0068] Figure 3 The X-ray source 10 depicted in FIG. 1 further comprises a focal spot sensor 28 for acquiring an image of the focal spot 20 based on detecting X-ray radiation emitted from the focal spot 20 and transmitted, for example, through a window 29 in the housing 11. During operation of the X-ray source 10, the controller 22 analyzes the images acquired with the focal spot sensor 28 to monitor the shape, size and position of the focal spot 20. Furthermore, the controller 22 determines changes in the size, shape and / or position of the focal spot 20 based on analyzing the images acquired with the focal spot sensor 28. Furthermore, the controller 22 actuates the electron-optical device 18 to compensate for changes in the size, shape and / or position of the focal spot 20. Thus, the focal spot sensor 28 and the controller 22 or a dedicated module, part, section, sub-controller or unit of the controller 22 form a feedback control 30 of the X-ray source 10 for stabilizing the focal spot 20 according to its shape and size based on actuating the electron-optical device 18. The feedback control 30 may be particularly advantageous for compensating for thermal expansion of the anode 12 during operation.

[0069] However, the actuation of the electron-optical device 18 based on the image of the focal spot sensor 28 is not to be confused with the prediction of the shape and size of the focal spot before the switching action is performed and the corresponding actuation of the electron-optical device 18 based on the predicted shape and size. For predictive control, the controller 22 may determine the switching action based on the grid switching signal and / or based on the grid switching profile, and predict the shape and size of the focal spot 20 for the determined switching action. Determining the switching action may include determining a time period of an on state and / or an off state of the grid 26, a voltage supplied to the cathode, a current supplied to the cathode, and / or a control signal supplied to the electron-optical device 18. Based on the predicted shape and size of the focal spot 20, the controller 22 may actuate the electron-optical device 18 to compensate for the switching action, as referenced Figure 2 Described.

[0070] Before the X-ray beam 101 is switched on and / or off by means of the grid 26, i.e. during a grid switching operation of the X-ray source 10, the controller 22 can predetermine the duty cycle, the on state and / or the off state of the grid 26 based on the switching signal and / or based on the grid switching profile. This information can then be used to predict the shape and size of the focal spot 20, to proactively determine predictive control signals and / or corrections for changes in the size and shape of the focal spot 20, as referenced Figure 2 In contrast to such forward-looking and / or predictive control, adjustment of the electron beam 15 by means of the feedback control 30 and / or the focal spot sensor 28 can be used to fine-tune the electron beam 15 and / or the electron optics 18, for example to compensate for thermal expansion during the off state of the grid 26, as will be described in more detail below.

[0071] Figure 3The feedback control 30 depicted in FIG. 1 can be considered to be based on the following insights and discoveries. When using the grid 26 in combination with focal spot sensing by means of a focal spot sensor 28 and a corresponding feedback control 30, for example in a grid switching X-ray source 10 or a grid switching tube, it may be desirable to take certain precautions in order to ensure that time periods during which the electron beam 15 is cancelled are not interpreted by the controller 22 as a loss of intensity when analyzing the images of the focal spot sensor 28. Therefore, when using the grid 26 for grid switching, the sampling rate of the feedback control 30 may be irregular. In addition to this, the time period between consecutive X-ray images may vary, and therefore, the temperature of the anode 12 may also vary between two consecutive X-ray images. Such temperature differences may in turn affect the size and shape of the focal spot 20, which will cause the feedback control 30 to strive to correct large deviations or changes, for example when compared to a continuously operated X-ray source 10. This may be the case in particular if the grid 26 is used for dose modulation, where, for example, certain gantry rotation angles may cause significantly greater thermal loads on the anode 12 than other rotation angles. Furthermore, when dynamic focal spot positioning is used, e.g. for filter modulation to filter via filter tuning spectrum filtering, it is also possible to switch between two positions of the focal spot 20 with two different intensities. Furthermore, dose control can be directly influenced by the measured beam intensity, e.g. in a C-arm system. For example in case of frame-to-frame modulation, the feedback control 30 will typically adjust the voltage and / or current according to a given dose change and time constant. All these aspects should preferably be taken into account in the feedback control 30 to control the shape and size of the focal spot 20 in order to ensure high image quality.

[0072] As described above, the focal spot sensor 28 is configured to dynamically monitor the shape and size of the focal spot 20. In order to avoid any correction of the shape and size of the focal spot 20 based on images of the focal spot sensor acquired when the X-ray beam is off and / or when the grid is in the on state, the controller 22 is configured to analyze images of the focal spot sensor 28 only when the grid is in the off state, and discard images of the focal spot sensor 28 acquired when the grid is in the on state. The controller 22 may determine whether a given image of the focal spot sensor 28 is acquired during the off state of the grid 26 based on the grid switching signal and / or based on the grid switching profile. For example, the grid switching signal may be used to trigger the analysis of images acquired by the focal spot sensor 28, so that the controller 22 only analyzes images of the focal spot sensor acquired when the grid 26 is in the off state. By way of example, the grid switching signal may be used by the controller 26 to sample and hold images of the focal spot sensor 28, thereby preventing the feedback control 30 from being misled by analyzing dark images when the X-ray beam 101 is off.

[0073] Thus, by only acquiring images of the focal spot sensor 28 acquired during an off state of the grid 26 and / or when the X-ray beam 101 starts, the control and / or regulation of the shape and size of the focal spot 20 by means of the feedback control 30 can be significantly improved.

[0074] In addition to this feedback control 30, during a period of predictive control, the controller 22 can determine and / or predict the expected thermal load of the anode 12, as shown in FIG. Figure 2 as described. The thermal load of the anode 12 may be determined, for example, based on a grid switching profile defined therein for at least a subset of the switching actions. Thus, the controller 22 may have access to previous knowledge about the immediate requirements in terms of the X-ray on phase and may therefore be able to predict predictive control signals that compensate for any changes in the size and shape of the focal spot, for example based on a model that models the thermal load of the anode 12 as a function of the current and / or voltage supplied to the cathode, in particular before any changes in the focal spot are evident. This may also be advantageous for reducing control transients that may occur after relatively extended X-ray off phases, wherein the feedback control 30 may still otherwise apply sufficient corrections at higher anode temperatures. Previous knowledge allows the controller 22 to predict the anode temperature when the X-ray beam 101 is switched on again, thereby reducing the reaction time of the feedback control 30.

[0075] Emphasis is on reference Figures 1 to 3 Any features, functions and / or functionalities described in any of the above may be combined.

[0076] Figure 4 A flow chart illustrating the steps of a method for operating an X-ray source 10 according to an exemplary embodiment of the present invention is shown. If not otherwise stated, the X-ray source 10 comprises the same Figures 1 to 3 The X-ray source 10 may include the same features, functions and / or elements as any of the X-ray sources 10 described in any of the above. Specifically, the X-ray source 10 includes an anode 12 and an emitter device 14, the emitter device 14 having a cathode 16 for emitting an electron beam 15, and having an electron optical device 18 for focusing the electron beam 15 at a focal spot 20 on the anode 12. The X-ray source 10 also includes a controller 22.

[0077] In step S1 of the method, a switching action of the emitter arrangement 14 is determined by the controller 22 , wherein the switching action is associated with a change in at least one of a position of the focal spot 20 on the anode 12 , a size of the focal spot 20 , and a shape of the focal spot 20 .

[0078] In a further step S2, based on the determined switching action, the size and shape of the focal spot 20 expected after performing the switching action is predicted by the controller 22 based on the determined switching action. Optionally, in step S2, the controller 22 may predict the change in size and shape of the focal spot 20 caused by the switching action.

[0079] In a further step S3, the emitter arrangement 14 is actuated by the controller 22 to perform the switching action. Before, during or after the switching action, the controller 22 may further actuate the electron optics 18 based on the predicted size and shape of the focal spot 20, so that any changes and / or variations in the size and shape of the focal spot 20 caused by the switching action are compensated.

[0080] Although the present invention has been illustrated and described in detail in the drawings and the foregoing description, these illustrations and descriptions should be considered illustrative or exemplary rather than restrictive; the present invention is not limited to the disclosed embodiments. Other variations of the disclosed embodiments can be understood and implemented by those skilled in the art in practicing the claimed invention by studying the drawings, the disclosure, and the appended claims.

[0081] In the claims, the word "comprising" does not exclude other elements or steps, and the word "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. An X-ray source (10) for emitting an X-ray beam (101), the X-ray source (10) comprising: Anode (12); an emitter device (14) comprising a cathode (16) for emitting an electron beam (15) towards the anode (12) and an electron optics (18) for focusing the electron beam (15) at a focal spot (20) on the anode (12); as well as a controller (22) configured to determine a switching action of the emitter device (14) and configured to actuate the emitter device (14) to perform the switching action, the switching action being associated with a change in at least one of a position of the focal spot (20) on the anode (12), a size of the focal spot (20) on the anode (12), and a shape of the focal spot (20) on the anode (12); wherein the controller (22) is configured to predict the size and the shape of the focal spot (20) expected after the switching action based on the determined switching action before the switching action is performed; and Wherein the controller (22) is configured to actuate the electron-optical device (18) to compensate for the change in the size and the shape of the focal spot (20) caused by the switching action.

2. The X-ray source (10) according to claim 1, in, The controller (22) is configured to predict changes in the size and the shape of the focal spot (20) caused by the switching action.

3. The X-ray source (10) according to claim 1 or 2, in, The switching action comprises changing at least one of: a voltage supplied to the cathode (16), a current supplied to the cathode (16), a position of the focal spot (20) on the anode (12) by deflecting the electron beam (15) using the electron optics (18), and switching on the X-ray beam (101).

4. The X-ray source (10) according to claim 1 or 2, in, The controller (22) is configured to predict the size and the shape of the focal spot (20) based on predicting a width and a height of the focal spot (20).

5. The X-ray source (10) according to claim 1 or 2, in, The controller (22) is configured to predict the size and the shape of the focal spot (20) based on a model that models the width and height of the focal spot (20) as a function of the current supplied to the cathode (16), the voltage supplied to the cathode (16), and the thermal load of the anode (12).

6. The X-ray source (10) according to claim 1 or 2, in, The controller (22) is configured to predict the size and the shape of the focal spot (20) based on a predicted thermal load of the anode (12); and / or The controller (10) is configured to determine a thermal load of the anode (12) expected after the switching action based on a predetermined cooling rate of the anode (12).

7. The X-ray source (10) according to claim 1 or 2, in, The emitter device (14) further comprises a mesh (26) interposed between the cathode (16) and the anode (12), wherein the grid (26) is configured to cancel the electron beam (15) when the grid (26) is in an open state, and to transmit the electron beam (15) when the grid (26) is in a closed state; and The controller (22) is configured to switch the grid (26) between the on state and the off state by providing a grid switching signal to the grid (26).

8. The X-ray source according to claim 7, in, The controller (22) is configured to determine the switching action based on a predetermined grid switching profile, the grid switching profile defining a modulation of the intensity of the X-ray beam (101) based on a sequence of at least one closed state of the grid (26) and at least one open state of the grid (26).

9. The X-ray source (10) according to claim 7, further comprising: a feedback control (30) having a focal spot sensor (28) for acquiring an image of the focal spot (20) based on detecting X-ray radiation emitted from the anode (12), the acquired image indicating the shape, the size and the position of the focal spot (20) on the anode (12); and wherein the controller (22) is further configured to analyze the image acquired by the focal spot sensor (28) to determine a change in at least one of the size, shape, and position of the focal spot (20); and The controller (22) is configured to adjust at least one of the size, shape and position of the focal spot (20) by actuating the electronic optical device (18) if a change in at least one of the size, shape and position of the focal spot (20) is determined after the switching action is performed.

10. The X-ray source (10) according to claim 9, in, The controller (22) is configured to analyze the image acquired by the focal spot sensor (28) when the grid (26) is in the closed state and the electron beam (15) impinges on the anode (12); and / or Wherein the controller (22) is configured to discard the image acquired by the focal spot sensor (28) when the grid (26) is in the on state and the electron beam (15) is cancelled by the grid (26).

11. The X-ray source (10) according to claim 9, in, The controller (22) is configured to determine, based on the grid switching signal, whether the image of the focal spot (20) is acquired by the focal spot sensor (28) during the closed state of the grid (26).

12. An X-ray imaging device (100), comprising: An X-ray source (10) according to any one of the preceding claims; as well as An X-ray detector (102) is used to detect X-ray radiation emitted by the X-ray source (10).

13. A method for operating an X-ray source (10), in, The X-ray source (10) comprises an anode (12), an emitter device (14) having a cathode (16) for emitting an electron beam (15), and having electron optics (18) for focusing the electron beam (15) at a focal spot (20) on the anode (12), and a controller (22). Wherein, the method comprises the following steps: determining, with the controller (22), a switching action of the emitter device (14), the switching action being associated with a change in at least one of a position of the focal spot (20) on the anode (12), a size of the focal spot (20), and a shape of the focal spot (20); predicting, using the controller (22), the size and the shape of the focal spot (20) expected after performing the switching action based on the determined switching action; actuating the electron optics (18) using the controller (22) to compensate for changes in the size and shape of the focal spot (20) caused by the switching action; and The transmitter device (14) is actuated to perform the switching action.

14. A computer program element which, when run by a controller (22) of an X-ray source (10), is configured to cause the X-ray source (10) to perform the method according to claim 13.

15. A computer-readable medium having stored thereon a program element according to claim 14.

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