DE102021211885A1 - Computer-implemented method for operating an X-ray device, X-ray device, computer program and electronically readable data carrier - Google Patents

Abstract

The invention relates to a computer-implemented method for operating an X-ray device (2) for recording a series of two-dimensional X-ray images along a recording trajectory of an X-ray tube (5) in one recording process, the X-ray images showing a recording area of the patient (7), the X-ray device (2) the X-ray tube (5), in which an electron beam (13) of a tube current is directed onto a focal point (14) of an anode (16) by means of an electric tube voltage, an X-ray detector (6), an actuator for converting the recording trajectory and a control device (8 ), wherein the focal spot (14) can be changed in terms of its size and/or shape and/or intensity distribution by means of an adjustment device (19, 20) of the X-ray tube (5), which can be controlled by the control device (8), the control device (8) as a function of at least one recording parameter that changes along the recording trajectory, at least one focal spot parameter that changes during the recording process and describes its size and/or shape and/or intensity distribution is determined and used to control the adjustment device (19, 20).

Description

The invention relates to a computer-implemented method for operating an X-ray device for recording a series of two-dimensional X-ray images along a recording trajectory of an X-ray tube in one recording process, the X-ray images showing a recording area of a patient, the X-ray device being the X-ray tube in which an electric tube voltage is used to generate an electron beam of a tube current is directed onto a focal spot of an anode, has an x-ray detector, an actuator for converting the recording trajectory and a control device, the focal spot being controlled in terms of its size and/or shape and/or intensity distribution by means of an adjustment device for the x-ray tube, which can be actuated by the control device , is changeable. In addition, the invention relates to an X-ray device, a computer program and an electronically readable data carrier.

X-ray imaging is widely used in medical diagnostics and also to monitor medical attacks. In this context, there are a large number of applications in which x-ray images of an imaging area of a patient are recorded by fluoroscopy with x-rays. To generate the required X-ray radiation, so-called X-ray tubes are usually used as X-ray emitters, in which an electron beam is shot from a cathode (electron emitter) under the influence of the so-called tube voltage onto an anode, in particular a rotary anode, where in a focal spot, which is also referred to as the focal point , the X-rays are produced. The x-ray radiation can then be emitted, for example through an exit window, in the direction of an x-ray detector of the x-ray device, with the recording area being arranged between the x-ray tube and the x-ray detector.

The size and/or intensity distribution of the focal spot are relevant for the image quality, for example the possible spatial resolution. It is therefore known, for example, to use adjustment devices in X-ray tubes, for example to provide an additional voltage between a grid or Wehnelt cylinder and the electrode emitter in order to focus the electron beam and keep the focal spot small. Such a voltage is often also referred to as a grid voltage. Other ways of influencing the focal spot include the use of focusing coils, quadrupole generating devices or the use of different focal spots that can be mixed in a multifocus device. It should also be noted at this point that the strength of the tube current can also have an influence on the size of the focal spot, which is caused by the repulsion among the electrons in the electron beam. Consequently, there are a large number of adjustment devices in order to influence the size, the shape and the intensity distribution of the focal spot.

In the field of radiography, fixed distances between the X-ray tube (“source”) and the X-ray detector, more precisely the image plane, are usually used. This distance is commonly referred to as the source-detector distance or "Source Image Distance" (SID). Fixed SIDs are, for example, 115 cm or 180 cm, mostly depending on the application using a focused antiscatter grid. In the meantime, x-ray devices have become known that allow freely selectable SIDs in the range of, for example, 100 cm to 200 cm, combined with the renunciation of the use of an anti-scatter grid. A larger SID, for example, has the advantage of reducing geometric distortions and allowing better access to the patient, while at the same time there is a higher power requirement on the x-ray tube.

DE 10 2006 032 607 A1 relates to an arrangement for generating electromagnetic radiation, in particular X-ray radiation. In this case, particles, in particular electrons, are directed onto a target by means of an adjustable focusing device, so that the particles in the target generate the electromagnetic radiation. There it is proposed to transmit the electromagnetic radiation through a calibration object and to record a transmission image of the object, which can be evaluated in order to adjust the focusing device as a function thereof. When setting the focusing device, other variables can also be taken into account, for example the focus-to-object distance, the focus-to-detector distance and the type of target. Once the setting has been made in this regard, the same focal spot settings are used during a computed tomography recording in which the focus-detector distance (corresponds to the SID) does not change.

The prior art also proposed new types of X-ray devices that allow relatively freely configurable positions of the X-ray tube in relation to the X-ray detector and thus also quite freely definable recording trajectories, in which, for example, both the X-ray tube and the X-ray detector are each on a robot arm as part of the recording trajectory realizing actuators can be attached. In this way, in particular, recording trajectories are also made possible, along which X-ray images of an X-ray image series are recorded, in which a different SID or other different recording parameters are present for each X-ray image.

The invention is based on the object of specifying an improved x-ray device operation, particularly with regard to the image quality and/or the use of the performance potential of the x-ray tube, for exposure trajectories with exposure parameters that vary along these.

This object is achieved according to the invention by a computer-implemented method having the features of claim 1, an X-ray device having the features of claim 13, a computer program having the features of claim 14 and an electronically readable data carrier having the features of claim 15. Advantageous refinements result from the subclaims.

According to the invention, in a method of the type mentioned at the outset, the control device determines at least one focal spot parameter that changes during the acquisition process, which describes its size and/or shape and/or intensity distribution, as a function of at least one acquisition parameter that changes along the acquisition trajectory, and Activation of the setting device is used.

According to the invention, it is therefore proposed for the first time to vary properties of the focal spot, described by the focal spot parameter, at least essentially in real time from one x-ray image to the next during the recording process of an image series of x-ray images, i.e. within a diagnostic and/or monitoring x-ray application, in order to in this way an optimization of the image quality, in particular of the X-ray tube output, can be achieved. Within the scope of the present invention, which will be discussed in more detail below, this can involve different recording trajectories or series of X-ray images, so that the present invention can be used, for example, for tomosynthesis recording processes, 3D scanning processes, fluoroscopy processes and /or radiography recording processes in which a series of radiographs are recorded using different recording geometries along the recording trajectory. Here, an X-ray device is used that allows certain freedoms along the recording trajectory, for example varying source-detector distances (SIDs), different movement speeds of the X-ray tube during the recording of X-ray images and the like, whereby it is additionally or alternatively also conceivable to take better account of the Allow recording target.

Since anodes of X-ray tubes usually have certain load limits before damage to the material can occur, for example, these are expediently also taken into account within the scope of the present invention, as is known in principle. It can therefore be provided that at least one boundary condition describing the load capacity of the anode is additionally used when determining the focal spot parameter. Such boundary conditions can describe, for example, which power densities may be maintained over what time and the like. Nevertheless, as already indicated, an optimal utilization of the X-ray tube power that can be provided can be realized even with limitations due to the procedure of the present invention. In this regard, the control device can have a load unit, for example, which can also be referred to as a “tube load computer” and can monitor the generator power limit, for example.

According to the invention, the at least one focal spot parameter is ultimately varied according to the at least one varying recording parameter in order to be able to adapt, particularly in real time, to the current conditions with regard to optimal image quality and optimal utilization of the X-ray tube output. It can be generally and specifically provided that the at least one focal spot parameter is determined from the at least one recording parameter using a predetermined relationship, in particular a look-up table and/or a characteristic map and/or a functional relationship. For example, look-up tables and/or characteristics can be stored in the control device, the specific values of the at least one recording parameter that changes along the recording trajectory, and possibly additional input data, which will be discussed in more detail below, the at least one corresponding focal spot parameters assigned. Alternatively, a functional connection is also conceivable in principle.

In this context it is particularly advantageous if the relationship is determined from calibration data of a calibration measurement, in particular with a phantom for assessing a spatial resolution. As already explained, the properties of the focal spot, in particular its size, has a certain influence on the spatial resolution when recording an X-ray image and thus also on the image quality. Purely by way of example, in this regard, reference is made to that mentioned in the introduction DE 10 2006 032 607 A1 referenced calibration object described. This makes it possible, for example, to determine look-up tables, characteristic diagrams and/or functional relationships based on the calibration data for various desired spatial resolutions and recording parameters. Such procedures have already been described, for example, for fixed focal spot properties.

In a first, specific embodiment of the present invention, it can be provided with particular advantage that a source-detector distance (SID) and/or a source-object Distance ("Source Object Distance" - SOD) is used. This means that the focal spot characteristic, in particular the focal spot size, can be varied as a function of such a first acquisition parameter, particularly in the case of X-ray devices with an SID or SOD that can be flexibly changed during an acquisition process. It can be specifically provided that with a decreasing source-detector distance and/or source-object distance, a smaller focal spot and/or a centrally more elevated intensity distribution of the focal spot is selected. In a specific example, in the case of a tomosynthesis scan, the size of the focal spot can be adjusted in real time depending on the selected (free) SID and the image quality requirement, in such a way that the focal spot is reduced as the SID decreases.

Generally speaking, an acquisition trajectory with a changing SID and/or SOD can be implemented using suitable actuators, in particular including robotics, it being possible to react to the current SID and/or SOD in real time. For example, the size of the focal spot or the intensity distribution in the focal spot can be selected in such a way that a certain spatial resolution is maintained, even if the recording trajectory was freely defined, for example. This can also be understood as a kind of "on-the-fly adjustment", i.e. in real time along the trajectory. Thus, the image quality can be optimized for different SIDs/SODs, as well as the available X-ray tube power. Optimized focal spots can be set for freely approachable SIDs.

Additionally or alternatively, in a particularly advantageous development of the present invention, it can be provided that an anatomy parameter relating to the recorded anatomy is used as at least a second of the at least one recording parameter that changes along the recording trajectory. This means that it is also possible to adapt the focal spot with regard to the anatomy visible in the current x-ray image or the viewing angle thereon. Specifically, it can be provided in particular that the anatomy parameter relates to a viewing direction of at least one anatomical feature and/or a visibility of at least one anatomical feature, with a higher one being used for at least one viewing direction and/or at least one viewing direction area and/or at least one visible anatomical feature focal spot parameter effecting spatial resolution in a corresponding X-ray image is selected. For example, if a standing patient is examined in order to obtain X-ray images of the spine under load, the recording trajectory can include recordings in (at least essentially) the anterior-posterior direction (AP direction) as well as in the lateral direction. According to the present invention, it can be provided in such an example that for the anterior-posterior directions, where there is a smaller patient thickness to be irradiated, an acquisition trajectory with a specifically smaller SID is selected in order to then also select a smaller focal spot and thus a improved examination, especially with regard to spatial resolution, of the vertebral bodies. In general, this means that the acquisition trajectory, in this case a varying acquisition parameter, for example the SID, can be selected in such a way that different focal spot settings are available for certain X-ray images of the series, so that these combined measures - variation of the acquisition parameter and appropriate variation of the focal spot parameter - a significant improvement in the image quality for certain anatomical features and/or viewing directions can be brought about in a targeted manner. In particular, for example, viewing directions with less patient thickness to be irradiated, and therefore lower demands on the power, lower SIDs and smaller sizes of the focal spot can be selected, which can also be better implemented due to the lower power required.

In other words, it can also be specifically provided in this context that the change in at least one of the at least one acquisition parameters along the acquisition trajectory, in particular the SID, is selected as a function of anatomy and/or patient information describing the anatomy in the acquisition area in such a way that certain viewing directions and/or for certain anatomical features a recording of at least one X-ray image with increased image quality compared to other X-ray images, in particular increased spatial resolution, by adjusting at least one of the at least one focal spot parameter according to the at least one of the at least one recording parameter and/or the viewing direction or the visible anatomical Feature takes place as the second recording parameter. In other words, a scan can be carried out along a free acquisition trajectory, for example, with variation of the focal spot (X-ray focus) depending on the respective field of view, the required level of detail of the resolution, the respective SID and preliminary information, in particular the anatomy and/or patient information, such that for the X-ray images, an optimal image quality is achieved, in particular with regard to a reconstruction taking place from the X-ray images. Anatomical and/or patient information can in particular also be derived from camera data of a 3D camera, as will be explained in more detail below, also with regard to the patient thickness to be irradiated for different viewing directions.

In an advantageous development of the present invention, a movement speed of the X-ray tube during the exposure time of one of the X-ray images can also be used as at least a third of the at least one recording parameter that changes along the recording trajectory, in particular for adapting the shape of the focal spot. In this context, it can also be expedient, in particular, to take into account the alignment of the x-ray tube with respect to the direction of movement, if this can also be different, which is the case with many x-ray devices with freely selectable recording trajectories. Furthermore, measures to compensate for such a movement during the exposure time of an x-ray image, such as a flying focal spot (FFS), can also be taken into account accordingly in this context. Generally speaking, the focal spot shape can therefore preferably be varied as a function of the movement speed of the x-ray tube, ie the scanning speed. In this case, the adaptation of the focus shape can, for example, be based not only on the movement speed per se but also on the direction of movement and/or the alignment of the x-ray tube with respect to the direction of movement. For example, due to the fact that the focal spot is "blurred" in the direction of movement anyway, a wider focal spot design can be selected without causing a visible deterioration in the image quality, whereby in compensation, for example, an optimization of the X-ray tube performance, particularly related to image quality, can take place.

A further development in this context can therefore provide that a focal spot parameter describing a wider focal spot in the direction of movement is selected with a higher movement speed. In interaction with the loading of the anode, it can also be said that the focal spot can be made smaller when there is a slower movement of the X-ray tube.

In another specific embodiment, however, it can also be provided that the shape of the instantaneous focal spot (i.e. not the “integrated” focal spot over the exposure time) is selected in such a way that, taking into account a smearing over the exposure time due to the movement speed, a certain ratio of the resulting spatial Resolution is adjusted perpendicular to the direction of movement and along the direction of movement. For example, a focal spot shape that appears round overall over the exposure time can be achieved with a correspondingly comparable spatial resolution.

It should also be noted at this point that it is of course fundamentally conceivable to use several acquisition parameters that change along the acquisition trajectory, for example at least one first, at least one second and at least one third acquisition parameter or subgroups thereof. For example, it is conceivable to bring about focal spot properties for free three-dimensional recording trajectories that are adapted, in particular optimized, to the movement speed of the X-ray tube, the SID and the image quality required in particular for different viewing directions and/or different anatomical features.

In a particularly expedient development of the present invention, it can be provided that at least one of the at least one acquisition parameter that changes along the acquisition trajectory and/or at least one of the at least one focal spot parameter using camera data from a 3D camera that moves with the X-ray tube is determined along a preliminary trajectory, which in particular corresponds at least essentially to the recording trajectory. For example, for this purpose a 3D camera can be motionally coupled to the X-ray tube, for example attached to it or to a housing surrounding it. No X-ray data is now recorded along the preliminary trajectory, only camera data that ultimately describes how the patient looks along the preliminary trajectory, which can essentially correspond to the recording trajectory, and what external shape, ie contour, he has. Out of The camera data can thus be used to determine the object contour, for example, but also the patient's object thickness to be irradiated. Such a patient contour and/or patient thickness can, for example, form an already mentioned piece of anatomy and/or patient information, whereby it is also conceivable, for example, to adapt anatomy models and the like based on the ascertained dimensions of the patient. Of course, further information can also be brought together here or alternatively used, for example the clinical question, a selected organ program, body regions to be recorded, recording modes and the like. From the camera data and/or other patient and/or anatomy information, which, as mentioned, can also include the clinical question and the like, the acquisition trajectory can be selected and/or acquisition parameters can be determined, in particular the at least one acquisition parameter that is along of the recording trajectory changed.

For example, it can be provided, starting from the preliminary trajectory, to adapt the recording trajectory, in particular with regard to the SID, in such a way that from certain viewing directions (possibly depending on the patient thickness to be irradiated) or for certain visible anatomical features, smaller SIDs and consequently smaller focal spots be chosen to provide particularly high spatial resolutions; In addition, of course, movement speeds of the X-ray tube can also be adjusted, for example with regard to a possible or occurring movement in the patient, in order to achieve a short overall recording time for the recording process, but at the same time to achieve recordings of higher resolution and to optimally utilize the performance potential of the X-ray tube. In other words, using such camera data, the recording trajectory and/or the required recording parameters, coupled to the focal spot properties, can be determined in advance or in an object-specific manner.

At this point, it should be noted again that recording parameters that can be appropriately determined from the camera data can also include the tube current, in particular as a function of the thickness to be irradiated and/or the materials to be irradiated, which certainly also have an influence on the focal spot, after, for example, the focal spot size also can increase with increasing tube current, but on the other hand the boundary conditions already mentioned with regard to the load capacity of the anode are also relevant. All of this is of course also taken into account accordingly with regard to the focal spot parameters. In particular, a tube current or another power-related recording parameter can also form one of the at least one recording parameter that changes during the recording trajectory, for example in order to compensate for the resulting different focal spot sizes "on the fly", i.e. during the recording process in real time, through other possibilities of the Adjust adjustment and the like.

Of course, it is also fundamentally conceivable in this context that the at least one focal spot parameter is additionally determined taking into account at least one other recording parameter that is constant over the recording trajectory. Such an acquisition parameter can, for example, also be a starting point, for example a selected organ program, an acquisition mode (tomosynthesis, 3D scan, radiography, . . . ) and the like. The desired resolving power can also be a constant and still have an influence on the determination of the focal spot parameter. For example, in specific exemplary embodiments it is therefore conceivable that, with a 3D scan as the recording mode, the focal spot properties along the recording trajectory depending on the recording area, i.e. the body area to be examined, the respective fields of view, the required level of detail of the resolution, the respective SID, the tube performance properties and/or or from advance information from camera data in real time. In another example, in a tomosynthesis scan, the focus size can be selected as a function of the selected, free SID and the image quality requirement, which can also be constant here. However, applications in radiography are also conceivable, where, for example, radiographic images are recorded as X-ray images from a number of recording geometries and different spatial resolutions are desired for these, which can be provided, for example, by varying SID and correspondingly varying focal spot sizes.

Within the scope of the present invention, however, it is also conceivable in an advantageous development that at least one of the at least one acquisition parameter, in particular the first acquisition parameter, is changed during the acquisition process, in particular a fluoroscopy. If, for example, a medical intervention and/or a physiological process is being monitored fluoroscopically within the patient, the operator may find it expedient, for example, to adjust the SID during the recording process by using appropriate operating elements. Then, in the context of the present invention, at for example in an image quality plus mode, can be reacted to immediately, for example by choosing a smaller focal spot in order to optimize the image quality. Of course, this can also be transferred to other recording parameters that can be adjusted during such processes.

The setting device can preferably be a potential device for applying an electrical focusing potential between a cathode cover, in particular a Wehnelt cylinder, and an electrode emitter and/or a focusing coil and/or a quadrupole generating device and/or a multifocus device in which at least two different focal spots are weighted (or mixed) are used include. In other words, the expansion of the focal spot can be adjusted, for example, by magnetic compression of the electron beam using a focusing coil and/or by one or more quadrupoles and/or by applying an electrical potential between the electrode emitter and focus head, in particular Wehnelt cylinders, which apply analogously to the shape of the focal spot can. The electrical potential in this context is often also referred to as "grid voltage". It is also conceivable within the scope of the present invention, particularly if an intensity distribution in the focal spot is to be adjusted, to use an X-ray tube in which several focal spots, in particular of different sizes and/or differently shaped, can be used and mixed to produce a resulting focal spot. For example, it is conceivable to use a large focal spot and a smaller further focal spot located in the center of the large focal spot, in order to be able to set an increase in the intensity distribution in the center, for example, and the like. These procedures are known in principle in the prior art and can also be used accordingly within the scope of the present invention.

Conveniently, a rotating anode can be used as the anode. Rotating anodes (also known as anode plates) are rotated, as the name suggests, so that the focal spot ultimately runs along a focal path of the rotating anode, thus constantly changing its position in relation to the rotating anode, and significantly higher outputs are therefore conceivable.

At least one robot arm for holding the x-ray tube and/or the x-ray detector can be used as at least part of the actuator system. X-ray devices of this type offer a large number of degrees of freedom for moving the X-ray detector and the X-ray tube in particular, so that complex, freely selectable recording trajectories are conceivable, for example with changing SIDs, with regard to different viewing directions and the like.

In addition to the method, the present invention also relates to an X-ray device having an X-ray tube in which an electric tube voltage is used to direct an electron beam of a tube current onto a focal point of an anode, an X-ray detector, an actuator for converting the recording trajectory and a control device, the focal point in its size and/or shape and/or intensity distribution can be changed by means of an adjustment device of the x-ray tube, which can be controlled by the control device, which is characterized in that the control device is designed to carry out a method according to the invention. All statements regarding the method according to the invention can be transferred analogously to the X-ray device according to the invention, so that the advantages already mentioned can therefore also be obtained with this.

A computer program according to the invention can be loaded directly into the memory of a control device of an x-ray device and has program means to carry out the steps of a method according to the invention when the computer program is executed on the control device of the x-ray device. The computer program can be stored on an electronically readable data carrier according to the invention, which consequently has control information that includes at least one computer program according to the invention, so that when the data carrier is used in a control device of an X-ray device, this is configured to carry out a method according to the invention. The data carrier can in particular be a non-transient data carrier, for example a CD-ROM.

• 1 einen Ablaufplan eines Ausführungsbeispiels des erfindungsgemäßen Verfahrens,
• 2 eine mögliche Abhängigkeit der Brennfleckgröße vom Quelle-Detektor-Abstand (SID),
• 3 eine erfindungsgemäße Röntgeneinrichtung,
• 4 eine Prinzipdarstellung einer Röntgenröhre der Röntgeneinrichtung, und
• 5 die funktionale Struktur einer Steuereinrichtung der Röntgeneinrichtung.

Further advantages and details of the present invention result from the exemplary embodiments described below and from the drawing. show:

• 1 a flowchart of an embodiment of the method according to the invention,
• 2 a possible dependence of the focal spot size on the source-detector distance (SID),
• 3 an X-ray device according to the invention,
• 4 a schematic diagram of an x-ray tube of the x-ray device, and
• 5 the functional structure of a control device of the X-ray device.

1 shows a flowchart of an embodiment of the method according to the invention. In this case, an X-ray device is to be used to record a series of X-ray images, which has an X-ray tube as the X-ray emitter, in which, as is known, an X-ray beam is directed onto a focal point of an anode, here a rotating anode, in order to generate X-rays. Furthermore, the x-ray device has an x-ray detector and a control device for controlling its operation, which also implements the exemplary embodiment of the method according to the invention presented here. In the present case, different positions of the x-ray tube and the x-ray detector relative to one another can be selected using suitable actuators, for example robot arms, on which the x-ray tube and the x-ray detector are held, which results in the possibility of designing relatively free recording trajectories, so that in particular changing source-detector Distances (SIDs) can be realized, different viewing directions can be granted to a recording area of a patient, different movement speeds of the X-ray tube can be used and the like. The x-ray device also includes an adjustment device as part of the x-ray tube, via which the properties of the focal spot can be changed in a controlled manner by the control device, in this case the focal spot shape, the focal spot size and/or the intensity distribution of the focal spot.

In a step S1, basic information required for planning the recording process is first provided and/or determined. The provision can be made, for example, by a user, for example by selecting a recording mode and/or an organ program and/or entering a clinical question and/or a body region to be examined, i.e. an examination area of the patient from which the series of X-ray images is to be recorded . Of course, a large number of other such pieces of anatomy and/or patient information are also conceivable. In a specific embodiment discussed here in more detail, basic information is also recorded in the form of camera data from a 3D camera that is motion-coupled to the x-ray tube while the x-ray tube travels a preliminary trajectory. The preliminary trajectory can include a trajectory that is especially suitable for detecting the patient geometry and/or already at least essentially correspond to or be similar to the recording trajectory to be used later, since the camera data are then obtained from projection geometries that are later to be used at least essentially in this way.

In a step S2, a specific recording trajectory to be used and recording parameters, of which at least one changes along the recording trajectory, are determined from the basic information of step S1, in particular the anatomy and/or patient information that includes the camera data. The camera data can also be used in the embodiment to specifically adapt the recording trajectory in such a way that specific recording conditions for specific viewing directions of the anatomy, for example essentially anterior-posterior and/or lateral viewing directions, and/or for specific viewing directions contained in the field of view anatomical features are given. For example, a smaller source-detector distance (SID) or source-object distance can be used for certain viewing directions where, based on the camera data, there is less patient thickness to be irradiated, or when certain anatomical features are visible in the field of view (SOD) are brought about. One of the changing recording parameters is then the SID or SOD (in addition to the viewing direction itself, which can also be considered a recording parameter). Furthermore, of course, adjustments can also be made that bring about specific viewing directions in a targeted manner or move specific anatomical features in a targeted manner into the field of view of the recording arrangement made up of x-ray tube and x-ray detector.

The camera data are particularly useful here, since they describe the external shape, and therefore the patient's contour. Anatomical information, at least roughly, can already be inferred by, for example, the adaptation/registration with anatomical atlases. The camera data are also used to a greater extent, as is known in principle, for example for a corresponding x-ray tube power adjustment depending on the thickness of the patient to be irradiated. The lower X-ray tube power required for a smaller thickness to be irradiated can be used for smaller focal spots, in particular, as explained above, in combination with a smaller SID.

As a result, recording parameters that change along the recording trajectory can include, for example, the SID and/or SOD as first recording parameters and/or recording parameters related to the viewing direction of the anatomy and/or the visibility of anatomical features as second recording parameters. Another recording parameter that is conceivable as an example and that can change along the recording trajectory is the movement speed of the x-ray tube, in particular during the exposure time of an x-ray image. Here, the X-ray tube are temporarily moved faster in sections of the recording trajectory in which X-ray images of lesser importance or lower requirements are recorded than in other sections of the recording trajectory in order to minimize the total recording time for the recording process of the series of X-ray images.

In step S3, at least some of the recording parameters that are variable along the recording trajectory are used to determine corresponding focal spot parameters that are then also variable along the recording trajectory. In the exemplary embodiments discussed in more detail here, focal spot parameters describe the focal spot size and/or the focal spot shape, but can also relate to the intensity distribution within the focal spot (e.g. in multi-focus X-ray tubes) and can be used to control the adjustment device of the X-ray tube to implement the corresponding focal spot properties . This means that the focal spot properties are adjusted in real time during the exposure process and, as it were, tracked changing exposure parameters in order to achieve optimal image quality and/or optimal utilization of the performance of the X-ray tube.

At least one predetermined relationship can be used to assign focal spot parameters to recording parameters and possibly other information, for example further, possibly also static recording parameters, which was determined, for example, on the basis of calibration data from a calibration measurement in which a phantom was used. Such a predetermined relationship is preferably available as a look-up table and/or as a characteristic diagram, but it can also be determined as a functional relationship.

This will now be explained in more detail on the basis of concrete embodiments. If the acquisition parameter that is variable along the acquisition trajectory is, for example, a first acquisition parameter, and therefore the SID and/or the SOD, the focal spot size in particular can be adjusted. This adjustment can be aimed at achieving a desired spatial resolution or even an optimized spatial resolution. For example, it is conceivable to use smaller focal spot sizes as the SID decreases in order to bring about a desired or even optimal resolution. A possible connection 1 between the focal spot size _AB and the SID is in 2 shown schematically.

In particular in combination with this, second acquisition parameters can also be used, provided they are not implicitly mapped via the SID, for example if, according to a specification for certain viewing directions and/or certain anatomical features, even higher requirements are to be placed on the spatial resolution or exactly the opposite the case is. Then, for example, smaller focal spot sizes can be used for certain visible anatomical features and/or certain viewing directions than for other viewing directions and/or visible anatomical features. This can, for example, be a connection 1 as shown in 2 is indicated schematically, modify in an additional dependency; However, it is also conceivable, for example, to consider only second recording parameters. Combined consideration of first and second acquisition parameters for the derivation of focal spot parameters and/or sole consideration of second acquisition parameters for the derivation of focal spot parameters can also be used, for example, to produce radiographic series of X-ray images that provide certain anatomical features and/or viewing directions with higher resolution and/or it 3D scans or tomosynthesis scans can be obtained in which, for example, certain important spatial directions also offer higher resolutions in reconstructed three-dimensional image datasets, and the like.

Finally, in a specific example, it is also conceivable to adjust the focal spot shape as a function of the movement speed of the X-ray tube during the exposure time (third acquisition parameter), in particular in such a way that a faster movement speed can be used to select a wider focus to optimize the X-ray tube performance.

In this context, it should also be noted in general that, of course, the boundary conditions resulting from the properties and the load capacity of the x-ray tube are taken into account in all of these variants/determination processes for focal spot parameters, so that overloading of the anode is avoided.

In a step S4, the X-ray images are then recorded along the recording trajectory, with the setting device being used by means of the focal spot parameters for “on the fly” adaptation of the focal spot properties and, of course, the recording being carried out overall using the recording parameters. In an optional step S5, derived image datasets can also be reconstructed from the x-ray images in a corresponding mode, for example in the case of a tomosynthesis scan or a 3D scan of a three-dimensional image dataset.

It should be noted at this point that the present invention can of course be used for various operating modes, for example the 3D scans or tomography scans already mentioned, but also radiography exposure sequences and the like. In particular, the procedure described can also be used if a recording parameter changes while the recording process is already in progress, for example as a result of an operator action on a control element. If, for example, the SID is changed during fluoroscopic monitoring, the focal spot size can be adjusted in real time. Specific adjustment devices are already known in the prior art, for example using electromagnetic fields, specifically so-called “grid voltages” on the Wehnelt cylinder, quadrupole generating devices and similar focusing devices.

3 shows schematically an exemplary embodiment of an X-ray device 2 according to the invention, which in the present case is embodied as a ceiling-mounted, robotic imaging system. In this case, for example, robotic arms 3 , here designed to be telescopic, can be guided in a rail system 4 and carry an X-ray tube 5 and an X-ray detector 6 as part of the recording arrangement. A patient 7 can be positioned between the X-ray tube 5 and the X-ray detector 6, for example standing in the context of a spinal column exposure, whereby a wide variety of exposure trajectories, in particular so-called “free” exposure trajectories, can be implemented due to the mobility of both the X-ray tube 5 and the X-ray detector 6. In addition to the robot arms 3, the actuator system can also include other components, for example adjustment devices on the X-ray tube 5 and the X-ray detector 6 itself.

In the present case, a 3D camera 29 is also attached to the x-ray tube 5 so that, as described above, the camera data can be recorded along the preliminary trajectory.

The operation of the X-ray device 2 is controlled by a control device 8 which is designed to carry out the method according to the invention. As is known in principle, the control device 8 can also be assigned an operating device with a display device and an input device, which for the sake of simplicity is shown in 3 is not shown in detail.

4 shows the structure of the X-ray tube 5 in more detail in the form of a schematic diagram. In an evacuated container 9, in which there is therefore a vacuum, this has a cathode 10 as an electron emitter 11, a filament 12 being used specifically to emit the electrons. The resulting electron beam 13 strikes a focal spot 14 on the focal path 15 of a rotary anode 16 so that X-ray radiation 17 is generated in the anode material of the rotary anode 16 and exits through a corresponding radiation window 18 .

As already discussed, the x-ray tube 5 also has at least one adjusting device 19, 20 in order to influence, in particular to focus and/or shape, the electron beam 18, so that the properties of the focal spot 14 are also adjusted accordingly. Since there are a number of design options for such adjusting devices 19, 20 in the prior art, these are only indicated schematically and can, for example, provide a variable grid voltage just like electromagnetic fields, in particular quadrupole fields by a corresponding quadrupole generating device. In summary, the electron beam 13 is preferably influenced electromagnetically in order to bring about defined properties of the focal spot 14 by means of the focal spot parameters used to control the setting device 19 , 20 .

5 shows the functional structure of the control device 8 in more detail. This initially has a storage means 21 in which X-ray images, predetermined relationships, in particular look-up tables and/or characteristic diagrams, and other data can be stored. Also known in principle is a recording unit 22 that uses recording parameters to control the components of the x-ray device 2 in such a way that the desired x-ray images are recorded. A load unit 23 monitors the status of the x-ray tube, in particular with regard to its current load limits, so that it can provide appropriate boundary conditions, for example, and also enable exposure parameters or focal spot parameters to be adjusted instantaneously, for example when operating limits are reached.

For example, acquisition parameters and basic information, for example basic information relating to the patient, the anatomy and the like, can be received via an interface 24, which can be processed in a preparation unit 25 to carry out step S1. The preparation unit 25 can also be designed to record camera data along a preliminary trajectory, which in particular can describe the patient's contour and/or patient's thickness for different viewing directions.

The basic information is then used in a parameterization unit 26 in order to define the recording parameters and the recording trajectory in accordance with step S2, whereupon the corresponding focal spot parameters can be determined in a determination unit 27 in accordance with step S3. The recording according to step S4 can then be performed by the recording unit 22; optionally there can be a reconstruction unit 28 for carrying out the optional step S5.

Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited by the disclosed examples and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102006032607 A1 [0005, 0013]

Claims (15)

Computer-implemented method for operating an X-ray device (2) for recording a series of two-dimensional X-ray images along a recording trajectory of an X-ray tube (5) in one recording process, the X-ray images showing a recording area of the patient (7), the X-ray device (2) containing the X-ray tube (5 ), in which an electron beam (13) of a tube current is directed onto a focal spot (14) of an anode (16) by means of an electric tube voltage, has an X-ray detector (6), an actuator for converting the recording trajectory and a control device (8), wherein the focal spot (14) can be changed in its size and/or shape and/or intensity distribution by means of an adjustment device (19, 20) of the X-ray tube (5), which can be controlled by the control device (8), characterized in that by the control device (8) as a function of at least one recording parameter that changes along the recording trajectory, at least one focal spot parameter that changes during the recording process and describes its size and/or shape and/or intensity distribution is determined and used to control the adjustment device (19, 20). procedure after claim 1 , characterized in that at least one boundary condition describing the load capacity of the anode (16) is additionally used when determining the focal spot parameter. procedure after claim 1 or 2 , characterized in that a source-detector distance and/or a source-object distance is used as at least a first of the at least one recording parameter that changes along the recording trajectory. procedure after claim 3 , characterized in that as the source-detector distance and/or source-object distance decreases, a smaller focal spot (14) and/or a centrally more elevated intensity distribution of the focal spot (14) is selected. procedure after claim 3 or 4 , characterized in that depending on additional information describing the recording process, in particular additional information describing a clinical question for the recording process and/or an additional recording parameter, a, in particular predetermined, connection to the at least one first recording parameter used to determine the focal point parameter is modified and/or or is selected. Method according to one of the preceding claims, characterized in that an anatomy parameter relating to the recorded anatomy is used as at least a second of the at least one recording parameter which changes along the recording trajectory. procedure after claim 6 , characterized in that the anatomy parameter relates to a viewing direction of at least one anatomical feature and/or a visibility of at least one anatomical feature, wherein for at least one viewing direction and/or at least one viewing direction area and/or at least one visible anatomical feature a higher spatial resolution in a corresponding X-ray image effecting focal spot parameter is selected. Method according to one of the preceding claims, characterized in that a movement speed of the X-ray tube (5) during the exposure time of one of the X-ray images is used as at least a third of the at least one recording parameter that changes along the recording trajectory, in particular for adapting the shape of the focal spot (14 ). procedure after claim 8 , characterized in that a focal spot parameter describing a wider focal spot (14) in the direction of movement is selected with a higher movement speed and/or the shape of the instantaneous focal spot (14) is selected such that, taking into account a smearing over the exposure time due to the movement speed, a specific Ratio of the resulting spatial resolution perpendicular to the direction of movement and along the direction of movement is adjusted. Method according to one of the preceding claims, characterized in that at least one of the at least one recording parameter, which changes along the recording trajectory, and/or at least one of the at least one focal spot parameter using camera data from a 3D camera (29) connected to the X-ray tube (5) is moved, is determined along a preliminary trajectory, in particular at least substantially corresponding to the recording trajectory. Method according to one of the preceding claims, characterized in that the at least one focal spot parameter is additionally determined taking into account at least one further recording parameter which is constant over the recording trajectory. Method according to one of the preceding claims, characterized in that the setting device (19, 20) comprises a potential device for applying an electrical focusing potential between a cathode cover, in particular a Wehnelt cylinder, and an electron emitter and/or a focusing coil and/or a quadrupole generating device and/or a Multi-focus device, in which at least two different focal spots (14) are used in a weighted manner. X-ray device (2), having an X-ray tube (5) in which an electric tube voltage is used to direct an electron beam (13) of a tube current onto a focal point (14) of an anode (16), an X-ray detector (6), actuators for converting the Recording trajectory and a control device (8), the size and/or shape and/or intensity distribution of the focal spot (14) being changeable by means of an adjustment device (19, 20) of the X-ray tube (5), which can be controlled by the control device (8). is characterized in that the control device (8) is designed to carry out a method according to one of the preceding claims. Computer program which comprises the steps of a method according to one of Claims 1 until 12 carries out when it is executed on a control device (8) of an X-ray device (2). Electronically readable data carrier on which a computer program according to the preceding claim is embodied.

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