Centering an X-ray imaging system

Abstract

A method for centering an X-ray imaging system (20) with a variable-pose radiation source (S) and an X-ray detector (D) with a variable pose that can be controlled independently of the variable pose of the radiation source (S) is described. In this method, a predetermined pose (Pi_0_S) is set with the radiation source (S), and a pose (Pi_0_D) of the X-ray detector (R) corresponding to the predetermined pose (Pi_0_S) of the radiation source (S) is set. Subsequently, the actual pose (Pa_0_S) of the radiation source (S) and the actual pose (Pa_0_D) of the X-ray detector (D) are determined. Furthermore, an initial deviation (A) is determined. S ) the actual pose (Pa_0_S) of the emitter from the predetermined pose (Pi_0_S) of the emitter (S) and a second deviation (A D) the actual pose (Pa_0_D) of the X-ray detector is determined from the predetermined pose (Pi_0_D) of the X-ray detector (D). Finally, a corrected predetermined pose (Pi_1_S) for centering the emitter (S) is determined based on the first deviation (A). S ) and a corrected predetermined pose (Pi_1_D) for centering the X-ray detector (D) based on the second deviation (A D ) determined. A centering device (70) is also described. In addition, an X-ray imaging system (20) is described.

Description

[0001] The invention relates to a method for centering an X-ray imaging system comprising a variable-pose X-ray source and an X-ray detector with a variable pose that can be controlled independently of the variable pose of the X-ray source. The invention also relates to a centering device. Furthermore, the invention relates to an X-ray imaging system.

[0002] Flexible robotic X-ray imaging systems, such as C-arms or robot-assisted ceiling-mounted X-ray systems, can acquire not only 2D images but also 3D images (cone-beam CT, CBCT). Especially when the X-ray tube and detector are not mechanically coupled, as is the case with C-arms, very precise mechanical adjustment of the system is necessary to ensure optimal positioning and orientation of the X-ray tube and detector in all spatial positions. This requires considerable time and experienced service technicians. Furthermore, system components can deform during movement, leading to inaccuracies. Typically, the telescopic arms to which the X-ray tube and detector are attached flex slightly due to centrifugal forces, with the flexion increasing the further they are extended.

[0003] Through geometric calibration, the actual positions of the system are known, therefore the reconstruction can be performed correctly. Nevertheless, the problem remains that the central beam does not always hit the detector in the center. This has the following consequence for the image: - The position of the collimator on the projection cannot be correctly determined, as it is assumed that the detector is hit in the center. - The resulting image field is limited because the available detector area is not fully utilized. Furthermore, an area is irradiated that is not captured by the detector and therefore cannot be used. - If the collimator edges are located in the reconstructed area, this creates a bright edge at the edge of the image field.

[0004] Previously, in real-world 3D imaging, the projections were cropped by an additional 2 cm on each side to ensure that the collimator edge did not create artifacts in the reconstructed volume. If the deviations were very large, the system adjustment was repeated until the desired result was achieved. This meant that repeated system adjustments required significantly more effort.

[0005] From EP 3 692 918 A1, a machine learning method is known for learning artifacts generated by a scattering grid for a large number of X-ray images acquired using a C-arm in different positions.

[0006] From DE 10 2017 205 113 A1, a tomographic reconstruction depending on the attenuation of an X-ray beam during the transmission of an object is known.

[0007] From DE 10 2022 206 561 B3 a method for generating training data for training an algorithm for estimating position deviations of an imaging system is known.

[0008] The task is therefore to specify a method and a device for adjusting an X-ray imaging system, with which the aforementioned problems are at least mitigated.

[0009] This problem is solved by a method for centering an X-ray imaging system with a variable-pose emitter and an X-ray detector with a variable pose that can be controlled independently of the variable pose of the emitter according to claim 1, a centering device according to claim 11 and an X-ray imaging system according to claim 13.

[0010] In the inventive method for centering an X-ray imaging system with a variable-pose X-ray source and an X-ray detector with a variable pose that can be controlled independently of the variable pose of the source, a predetermined pose Pi_0_S is first set with the source. In this context, "centering" means that the source and the X-ray detector are aligned with each other so that the X-rays generated by the source are centered on the X-ray detector. "Pose" means the position combined with the orientation of an object. "Variable pose" means that the pose of the source and the X-ray detector can be flexibly determined by control and that the source and the X-ray detector are not fixed to a potentially rotatable suspension.In particular, the X-ray tube and the X-ray detector, which can be controlled independently, are not mechanically coupled. The poses of the X-ray source and the X-ray detector are therefore designed to be variable relative to each other. In contrast to the fixed mounting of a source and an X-ray detector, as is typical with mechanical coupling, for example on a drum, the two elements of the X-ray imaging system can, in principle, be positioned and oriented independently of each other with respect to their pose, and are thus freely controllable. The "predetermined pose" represents a target pose specified by an imaging protocol. However, due to the aforementioned flexibility of the system, this target pose can easily differ from the actual pose, i.e., the current position of the source or the X-ray detector.

[0011] Furthermore, a position Pi_0_D of the X-ray detector corresponding to the predetermined position Pi_0_S of the radiation source is controlled. "Corresponding" in this context means that the X-ray detector is positioned exactly opposite the radiation source, such that the orientation of the detector surface matches the beam direction and the center of the X-ray beam intersects the center of the detector surface exactly.

[0012] After the initial control, the next step, a calibration step, determines the actual position Pa_0_S of the radiation source by measuring this position achieved through the control signal. The actual position Pa_0_D of the X-ray detector is also determined. These actual or calibrated position(s) may differ from the previously mentioned target position(s) Pi_0_S and Pi_0_D, particularly since the radiation source and the X-ray detector can be moved independently of each other.

[0013] Based on the measured values ​​thus obtained, a first deviation A is then determined. S the actual pose Pa_0_S of the emitter from the predetermined pose Pi_0_S of the emitter: AS=Pa_0_S−Pi_0_S.

[0014] A second deviation of the actual pose Pa_0_D of the X-ray detector from the predetermined pose Pi_0_D of the X-ray detector is also determined based on the measured values: AD=Pa_0_D−Pi_0_D.

[0015] Such a deviation A S , A D For example, the position can be determined by a vector representing the difference between the vector of the original predetermined pose and the vector of the actual pose of a component. Position and orientation can also be considered and evaluated separately, in which case norms of the difference between position vectors and orientation vectors are taken into account.

[0016] Based on the first deviation A S In one step to obtain adjustment data, a corrected predetermined pose Pi_1_S is determined for centering the emitter: Pi_1_S=Pi_0_S−AS.

[0017] Based on the second deviation A D A corrected predetermined pose Pi_1_D is determined for centering the X-ray detector: Pi_1_D=Pi_0_D−AD.

[0018] The target position Pi_0_S, Pi_0_D of the respective component is modified in such a way that the respective deviation determined by measurement is reduced or, in the optimal case, disappears completely.

[0019] Finally, preferably in an adjustment step, the emitter is controlled with the determined corrected predetermined pose Pi_1_S of the emitter and the X-ray detector is controlled with the determined corrected predetermined pose Pi_1_D of the X-ray detector, thereby achieving centering.

[0020] As will be explained in detail later, the inventive method can also be carried out repeatedly or even iteratively several times, with the deviation A S_n , A D_n the current position Pa_n_S, Pa_n_D AS_n=Pa_n_S−Pi_0_S, AD_n=Pa_n_D−Pi_0_D, from the original predetermined pose (n = 1, 2, 3, ...) it becomes progressively smaller until it reaches a predetermined threshold ASW falls below:

[0021] Preferably, the centering is carried out such that a central beam of the emitter hits the center of the X-ray detector and the central beam strikes the detector surface of the X-ray detector perpendicularly.

[0022] The actual positions of the radiation source and the X-ray detector can also be determined simultaneously, especially when calibration is performed with a spiral phantom.

[0023] Advantageously, the calibration and adjustment process according to the invention allows for precise control of the pose of an X-ray source and an X-ray detector in an X-ray imaging system. In this way, the occurrence of a disturbing image of a collimator on the imaging surface of the X-ray detector is avoided. Generally, the entire imaging surface of the X-ray detector can be used for imaging. In particular, it prevents the need to repeat an imaging procedure because the X-ray source and the collimator were not precisely aligned with each other.

[0024] The centering device according to the invention has a control unit for controlling a predetermined pose Pi_0_S with the emitter and for controlling a corresponding pose Pi_0_D of the X-ray detector which can be controlled independently of the predetermined pose Pi_0_S of the emitter.

[0025] The centering device according to the invention also includes a measuring unit for determining the actual pose Pa_0_S of the emitter and for determining the actual pose Pa_0_D of the X-ray detector.

[0026] Furthermore, the centering device according to the invention includes a deviation detection unit for determining a first deviation A S the actual pose Pa_0_S of the emitter from the predetermined pose Pi_0_S of the emitter and to determine a second deviation A D the actual pose Pa_0_D of the X-ray detector from the predetermined pose Pi_0_D of the X-ray detector.

[0027] Finally, the centering device according to the invention comprises a correction determination unit for determining a corrected predetermined pose Pi_1_S for centering the emitter based on the first deviation A Sand to determine a corrected predetermined pose Pi_1_D for centering the X-ray detector based on the second deviation A D The centering device according to the invention shares the advantages of the inventive method for centering an X-ray imaging system with a variable-pose emitter and an X-ray detector with a variable pose that can be controlled independently of the variable pose of the emitter.

[0028] The control unit of the centering device according to the invention is preferably configured to control the corrected predetermined pose Pi_1_S of the radiation source and the corrected predetermined pose Pi_1_D of the X-ray detector. Advantageously, not only is the target poses corrected, but this correction can also be implemented by control, so that the poses of the radiation source and the X-ray detector are adjusted or centered.

[0029] The X-ray imaging system according to the invention comprises an X-ray source whose position is variably controllable, an X-ray detector whose position is variably controllable independently of the variable position of the X-ray source, and a centering device according to the invention. The X-ray imaging system shares the advantages of the centering device and the method according to the invention for centering an X-ray imaging system with an X-ray source having a variable position and an X-ray detector with a variable position that can be controlled independently of the variable position of the X-ray source.

[0030] A large proportion of the aforementioned components of the centering device according to the invention can be implemented wholly or partially as software modules in a processor of a corresponding computing system, e.g., a control unit of an X-ray imaging system or a computer used to control such a system. A largely software-based implementation has the advantage that even previously used computing systems can be easily retrofitted by means of a software update to operate in the manner of the invention.

[0031] Therefore, the problem is also solved by a corresponding computer program product with a computer program that can be directly loaded into a computer system, containing program sections to execute the steps of the inventive method for centering an X-ray imaging system with a variable-pose radiation source and an X-ray detector with a variable pose that can be controlled independently of the variable pose of the radiation source when the program is executed in the computer system. In addition to the computer program, such a computer program product may optionally include additional components such as documentation and / or additional components, including hardware components such as hardware keys (dongles, etc.) for using the software.

[0032] For transport to the computer system or control unit and / or for storage on or in the computer system or control unit, a computer-readable medium, such as a memory stick, a hard drive, or other portable or permanently installed data carrier, can be used, on which the program sections of the computer program that can be read and executed by a computer system are stored. The computer system may, for example, have one or more cooperating microprocessors or similar components for this purpose.

[0033] The dependent claims and the subsequent description each contain particularly advantageous embodiments and further developments of the invention. In particular, the claims of one claim category may also be further developed analogously to the dependent claims of another claim category. Furthermore, within the scope of the invention, the various features of different embodiments and claims may also be combined to form new embodiments.

[0034] In a preferred embodiment of the inventive method for centering an X-ray imaging system with a variable-pose emitter and an X-ray detector with a variable pose that can be controlled independently of the variable pose of the emitter, the steps of the method are repeated in the case that the first deviation A S and / or the second deviation A D a predetermined threshold A SWThe corrected predetermined poses Pi_1_S and Pi_1_D are used as predetermined poses during the repetition. During the repetition, the corrected predetermined poses Pi_1_S and Pi_1_D are used for the control, but the values ​​of the original predetermined poses Pi_0_S and Pi_0_D are used to determine the first and second deviations, even during the repetition. This is necessary because the original target values ​​serve as a comparison with the current actual values ​​when determining the deviations. Advantageously, the threshold value A is used. SW A quality criterion is used for the accuracy of the centering, whereby the required accuracy is achieved, if necessary, by repeating the procedure.

[0035] In another preferred embodiment of the inventive method for centering an X-ray imaging system with a variable-pose emitter and a variable-pose X-ray detector, the steps of the method are repeated iteratively until the first deviation A S and / or the second deviation A D The centering must fall below a predetermined threshold. Advantageously, the centering is gradually approached to a predetermined accuracy value, with reaching the criterion for the desired accuracy constituting the termination condition.

[0036] In another embodiment of the method according to the invention, the deviations are determined using a phantom positioned within an examination area of ​​the X-ray imaging system. Advantageously, the determination of the deviations and the calibration can be performed by imaging the phantom, whereby the phantom is projected onto the detector surface of the X-ray detector. Thus, provided the phantom is correctly positioned, the position of the radiation source and the X-ray detector does not need to be measured externally, but can be determined by capturing a test image.

[0037] The phantom preferably comprises a spiral arrangement of spheres, which are imaged onto the detector surface of the X-ray detector. By imaging the spiral arrangement of spheres onto the detector surface of the X-ray detector, the position and orientation of the two components relative to the phantom can be measured particularly easily and precisely by imaging.

[0038] Alternatively, the position of the radiation source and the X-ray detector can also be determined by measuring their position from the outside. This method eliminates the need for a phantom.

[0039] The method according to the invention is particularly preferably applied to a plurality of predetermined poses of the radiation source and / or the X-ray detector, which form a trajectory. In particular, when a three-dimensional image of an area of ​​investigation is to be generated, the area of ​​investigation must be imaged from different angles, preferably from an angular range of at least 200 degrees. A trajectory can also be assigned to the radiation source and / or the X-ray detector, which they must each follow in order to image the area of ​​investigation from different directions. Advantageously, during adjustment, not only a single position of the radiation source and the X-ray detector is approached, but a plurality of positions or poses located on a trajectory that is used for this purpose.The system is designed to capture projection images of an area of ​​investigation from different directions and combine these projection images into a three-dimensional image. The 3D image is preferably generated by a filtered backprojection of the projection images. The projection images are captured from a plurality of predetermined positions.

[0040] It is highly advantageous to smooth the determined trajectory using a correction curve. This allows for more uniform imaging from different angles. The adjustment or centering described above refers to a systematic, reproducible deviation. However, the system can also exhibit non-reproducible deviations, caused, for example, by minor vibrations. For this reason, it is beneficial to further smooth such a trajectory with random deviations. Alternatively, multiple measurements of the deviations can be taken and averaging performed to suppress this non-reproducible component before the actual correction.

[0041] In a preferred embodiment of the method according to the invention, the trajectory is determined by repeatedly measuring the actual poses of the radiation source and / or the X-ray detector and by averaging the repeatedly measured values. Advantageously, the non-reproducible deviations described above are reduced.

[0042] In addition to adjustment prior to imaging, which is preferably performed once after the installation of an X-ray imaging system or at predetermined intervals, for example, once a year, a trajectory calibration can also be performed after image acquisition. Such calibration allows for the consideration of minimal deviations in the actual positions and orientations of the X-ray source and the X-ray detector during image reconstruction. Calibration is preferably performed before each imaging session or at a predetermined time or usage interval to ensure precise image reconstruction.

[0043] Calibrating the trajectory corresponds to the step of determining the actual pose. This determined pose can be used directly for image reconstruction, or for correcting the trajectory.

[0044] A phantom suitable for calibration, the “PDS-2” phantom, is described in “Improving 3D Image Quality of X-ray C-Arm Imaging Systems by using Properly Designed Pose Determination Systems for Calibrating the Projection Geometry” by Norbert Strobel et al., SPIE Medical Imaging 2003.

[0045] Depending on the manufacturer, there may also be differently looking phantoms for this step.

[0046] The invention is explained in more detail below with reference to the accompanying figures and exemplary embodiments. The figures show: Fig. 1 a schematic representation of a phantom with a number of opaque spheres arranged in a spiral, Fig. 2 a schematic top view of the trajectory of a radiation source and an X-ray detector of an X-ray imaging system, Fig. 3 A top view of an X-ray imaging system with a radiation source and an X-ray detector and the already in Fig. 2 shown trajectories and the path of the X-rays emitted by the source, Fig. 4 a top view of the in Fig. 3. X-ray imaging system already illustrated, in which the trajectory of the X-ray detector is slightly shifted and rotated compared to an ideal trajectory, Fig. 5 a top view of the in Fig. 3 and Fig. 4. X-ray imaging system already illustrated, with the trajectory of the X-ray detector corrected, Fig. 6 a flowchart illustrating the method for centering an X-ray imaging system with a variable-pose radiation source and a variable-pose X-ray detector according to an embodiment of the invention, Fig. 7 a schematic representation of a centering device according to an embodiment of the invention, Fig. 8 a schematic representation of an X-ray imaging system according to an embodiment of the invention.

[0047] In Fig. Figure 1 shows a schematic representation of a phantom 10a with a number of opaque spheres K arranged in a spiral. The pose of a radiation source and an X-ray detector can be determined from the pattern generated by the opaque spheres on the detector surface of an X-ray detector, or from the resulting projection image.

[0048] In Fig. Figure 2 shows a schematic top view of the trajectory SB of a radiation source and the trajectory DB of an X-ray detector of an X-ray imaging system 20. In the area between the two trajectories SB and DB, an imaging area 10 is shown, in which a patient can be positioned and imaged.

[0049] In Fig. Figure 3 is a top view of an X-ray imaging system 20 with a radiation source S and an X-ray detector D and the already in Fig. The trajectories SB and DB shown in Figure 2, as well as the beam path (shown as a dashed line between source S and X-ray detector D) of the X-rays emitted by source S, are illustrated. Fig. In equation 3, the radiation source S and the X-ray detector D have an ideal opposite position PS, PD and an ideal orientation rotated by 180° OS, OD. In this ideal arrangement, the X-ray beam is focused by the radiation source S onto the X-ray detector D.

[0050] In Fig. 4 is a top view of the in Fig. 3 already illustrated X-ray imaging system 20 shown, where the actual trajectory DB a of the X-ray detector D somewhat opposite an ideal trajectory DB ior is shifted and rotated from the predetermined trajectory of the X-ray detector D. As in Fig. As indicated in Figure 4, the X-ray beam from the source S no longer hits the X-ray detector D in the center, so that on one side (bottom left) of the detector surface of the X-ray detector D an edge is not irradiated and on the opposite side (top right) of the detector surface of the X-ray detector D the irradiation extends beyond the edge of the detector surface of the X-ray detector D.

[0051] In Fig. 5 is a top view of the in Fig. 3 and Fig. 4 already illustrated X-ray imaging system 20 shown, where the trajectory DB a The X-ray detector D was corrected. The corrected actual trajectory DB a The X-ray detector D now lies almost exactly on the original ideal trajectory DB. iof the X-ray detector D. A further adjustment would be possible, for example, by smoothing the corrected actual trajectory DB. a of the X-ray detector D, whereby, for example, a compensation curve is formed by the corrected actual trajectory DB. a the X-ray detector D is placed and a correction of the predetermined trajectory is carried out accordingly.

[0052] The purpose of a smoothing operation is to remove the non-reproducible portion from the actual trajectory, i.e., the real trajectory DB. a to calculate and eliminate the errors. This requires measuring the entire trajectory. The 3-dimensional positions and orientations can be smoothed, for example, by convolution with a Gaussian kernel (comparable to a noise reduction operation). This means that the actual positions are transformed into smoothed actual positions, which are then used instead of the actual positions to calculate the correction values.

[0053] In Fig. Figure 6 shows a flowchart 600, which illustrates the procedure for centering an X-ray imaging system 20 (see Fig. 2 to Fig. 5) illustrated with a variable-pose emitter and an X-ray detector with a variable pose that can be controlled independently of the variable pose of the emitter according to an embodiment of the invention.

[0054] In step 6.I, the position values ​​of the radiation source S and the X-ray detector D are set for different "axes," which correspond to different orientation values. This means that the control of the radiation source S and the X-ray detector D is given predetermined ideal values ​​for different positions PS. i , PD i and orientations OS i , OD i hand over.

[0055] In step 6.II, a first position PS is set. i and a first axis or orientation OS iof the emitter S, although an actual position PS a and actual OS orientation a is achieved by the emitter S. The more or less pronounced deviation between the ideal position PS i and the actual position PS a and / or the ideal orientation OS i and the actual orientation OS a leads to a decentering of the X-ray beam on the detector surface of the X-ray detector D of the X-ray imaging system 20.

[0056] In step 6.III, a first position PD is established. i and a first axis or orientation OD i of the X-ray detector D, although an actual position PD a and an actual orientation OD a is achieved by the X-ray detector. The more or less pronounced deviation between the ideal position PD i and the actual position PDa leads to a decentering of the X-ray beam on the detector surface of the X-ray detector D of the X-ray imaging system 20.

[0057] In step 6.IV, a geometry calibration (GK) is performed, whereby a phantom 10 positioned in an examination area is imaged onto the detector surface of the X-ray detector D. During the geometry calibration, the actual positions (PS) are determined. a , PD a of the radiation source S and the X-ray detector D of the X-ray imaging system 20 are determined. The actual orientations OS are also determined. a , OD a of the radiation source S and the X-ray detector D were measured or determined.

[0058] In step 6.V, deviations A S , A Dbetween predetermined ideal poses of the emitter S and the X-ray detector D based on the known ideal values ​​and the actual values ​​of the positions and orientations of the emitter S and the X-ray detector D measured in step 6.IV.

[0059] In step 6.VI, a correction KR of the values ​​of the ideal position PD is performed. i and the ideal orientation OD i of the X-ray detector D and also a correction of the values ​​of the ideal position PS i of the emitter S and the ideal orientation OS i of the emitter S, where correction values ​​PS ik , OS ik , PD ik , OD ik be generated.

[0060] In step 6.VII, the adjustment made in step 6.VI is checked by means of a renewed geometry calibration, i.e., in particular, an image of the phantom 10 is taken and a check is carried out, whereby the actual poses of the emitter S and the X-ray detector D are compared with the values ​​PS set in step 6.I. i , OS i , PD i , OD i to be compared. If step 6.VII determines that a predetermined tolerance or deviation A exists, SW the determined deviation A is not exceeded, which is in Fig. If step 6 is marked with "n", then the process proceeds to step 6.VIII, in which the X-ray imaging system 20 is set up for operation with a corresponding correction KR by using the correction values ​​PS. ik , OS ik , PDi k , OD ikfor the control of the emitter S and the X-ray detector D. If, during step 6.VII, it is determined that the predetermined tolerance or deviation is still exceeded, the process proceeds to step 6.I and the adjustment is performed again, this time using the correction values ​​PS. ik , OS ik , PDi k , OD ik can be used for control in steps 6.II and 6.III.

[0061] In Fig. Figure 7 illustrates a schematic representation of a centering device 70 according to an embodiment of the invention.

[0062] The centering device 70 has a control unit 71 for controlling a predetermined pose Pi_0_S (which is a first position PS). i and a first axis or orientation OS ia radiation source S) with a radiation source S of an X-ray imaging system and for controlling a pose Pi_0_D corresponding to the predetermined pose Pi_0_S of the radiation source S (which is a first position PD) i and a first axis or orientation OD i (of an X-ray detector) of the X-ray detector D.

[0063] Part of the centering device 70 is also a measuring unit 72 for determining the actual pose Pa_0_S (which is an actual position PS). a of the radiation source S of the X-ray imaging system 20 and an actual orientation OS a of the radiation source S of the X-ray imaging system 20) of the radiation source S and to determine the actual pose Pa_0_D (which is an actual position PD) a of the X-ray detector D of the X-ray imaging system 20 and an actual orientation OD a of the X-ray detector D includes) of the X-ray detector D.

[0064] The centering device 70 also includes a deviation determination unit 73 for determining a first deviation A S the actual pose Pa_0_S of the emitter from the predetermined pose Pi_0_S of the emitter S and to determine a second deviation A D the actual pose Pa_0_D of the X-ray detector from the predetermined pose Pi_0_D of the X-ray detector D.

[0065] Furthermore, the centering device 70 has a correction determination unit 74 for determining a corrected predetermined pose Pi_1_S of the emitter S based on the first deviation A S and to determine a corrected predetermined pose Pi_1_D of the X-ray detector D based on the second deviation A D The correction values ​​can also be transmitted to the control unit 71 to control the radiation source S and the X-ray detector D with the corrected values ​​and to adjust the poses of the radiation source S and the X-ray detector D.

[0066] In Fig. Figure 8 illustrates a schematic representation of an X-ray imaging system 20 according to an embodiment of the invention. The X-ray imaging system 20 comprises the components shown in Figure 8. Fig. Figure 7 illustrates a centering device 70 and a scan unit 21 with an X-ray source S and an X-ray detector D. The centering device 70 is part of a control unit 22, which is configured to control the scan unit 21 during imaging. Modified control data SDM is transmitted from the control unit 22 to the scan unit 21. The control data SDM is applied by the centering device 70 to the... Fig. 1 to Fig. Figure 7 illustrates a modified method to position and orient the X-ray detector D and the emitter S of the scan unit 21 correctly during imaging. Furthermore, projection data from a phantom (not shown) is received by the control unit 22 from the X-ray detector D to generate the image shown in Figure 7. Fig. The input data of the centering device 70 shown in Figure 7, i.e., the actual pose Pa_0_S of the emitter S and the actual pose Pa_0_D of the X-ray detector D, are to be determined and these are to be sent to the centering device 70 (see also Figure 7). Fig. 7) to transmit.

[0067] Finally, it should be noted once again that the methods and devices described above are merely preferred embodiments of the invention and that the invention can be varied by a person skilled in the art without departing from the scope of the invention, insofar as it is defined by the claims. For the sake of completeness, it should also be noted that the use of the indefinite articles "a" or "an" does not preclude the possibility that the features in question may be present multiple times. Likewise, the term "unit" does not preclude the possibility that it consists of several components, which may also be spatially distributed. Regardless of the grammatical gender of a particular term, persons of male, female, or other gender identities are included.

Claims

[1] Method for centering an X-ray imaging system (20) with a variable pose source (S) and an X-ray detector (D) with a variable pose that can be controlled independently of the variable pose of the source (S), comprising the steps: i) Controlling a predetermined pose (Pi_0_S) with the spotlight (S), ii) Controlling a predetermined pose (Pi_0_D) of the X-ray detector (R) corresponding to the predetermined pose (Pi_0_S) of the radiation source (S), iii) Determining the actual pose (Pa_0_S) of the emitter (S), iv) Determining the actual pose (Pa_0_D) of the X-ray detector (D), v) Determining a first deviation (A S ) the actual pose (Pa_0_S) of the emitter (S) from the predetermined pose (Pi_0_S) of the emitter (S), vi) Determining a second deviation (A D) the actual pose (Pa_0_D) of the X-ray detector (D) from the predetermined pose (Pi_0_D) of the X-ray detector (D), vii) Determining a corrected predetermined pose (Pi_1_S) for centering the emitter (S) based on the first deviation (A S ), viii) Determining a corrected predetermined pose (Pi_1_D) for centering the X-ray detector (D) based on the second deviation (A D ). [2] The method of claim 1, wherein steps i) to viii) are repeated in the event that the first deviation (A S ) and / or the second deviation (A D ) exceed a predetermined threshold, whereby the corrected predetermined poses (Pi_1_S, Pi_1_D) are used as predetermined poses (Pi_0_S, Pi_0_D) for control in steps i) and ii), but in steps vi) and vii) to determine the first and second deviation (A S , A D) the values ​​of the original predetermined poses (Pi_0_S, Pi_0_D) are used. [3] Method according to claim 1 or 2, wherein steps i) to viii) are iteratively repeated until the first deviation (A S ) and / or the second deviation (A D ) fall below a predetermined threshold. [4] Method according to one of the preceding claims, wherein the determination of the actual positions (Pa_0_S, Pa_0_D) and the deviations (A S , A D ) is based on a phantom (10) which is positioned in an examination area of ​​the X-ray imaging system (20). [5] Method according to claim 4, wherein the phantom (10) comprises a spiral arrangement of spheres (K) which are imaged onto the X-ray detector (D). [6] Method according to claim 5, wherein steps i) to viii) are applied to a plurality of predetermined poses (Pi_0_S, Pi_0_D) of the emitter (S) and / or the X-ray detector (R) which form a trajectory. [7] Method according to claim 6, wherein the determined trajectory is smoothed by a compensating curve. [8] Method according to one of the preceding claims, wherein the trajectory is determined by repeatedly measuring the actual poses (Pa_0_S, Pa_0_D) of the emitter (S) and / or the X-ray detector (R) and by averaging the repeatedly measured values. [9] Method according to one of the preceding claims, wherein the centering is carried out by controlling the emitter (S) with the corrected predetermined pose (Pi_1_S) of the emitter (S) and the X-ray detector (D) with the corrected predetermined pose (Pi_1_D) of the X-ray detector (D). [10] Method according to claim 9, wherein the centering is carried out such that a central beam of the emitter (S) hits the center of the X-ray detector (D) and the central beam strikes a detector surface of the X-ray detector (D) perpendicularly. [11] Centering device (70), comprising: - a control unit (71) for controlling a predetermined pose (Pi_0_S) with the emitter (S) and for controlling a corresponding pose (Pi_0_D) of the X-ray detector (R) that can be controlled independently of the predetermined pose (Pi_0_S) of the emitter (S), - a measuring unit (72) for determining the actual pose (Pa_0_S) of the emitter (S) and for determining the actual pose (Pa_0_D) of the X-ray detector (D), - a deviation detection unit (73) for determining a first deviation (A S) the actual pose (Pa_0_S) of the emitter from the predetermined pose (Pi_0_S) of the emitter (S) and to determine a second deviation (A D ) the actual pose (Pa_0_D) of the X-ray detector from the predetermined pose (Pi_0_D) of the X-ray detector (D), - a correction determination unit (74) for determining a corrected predetermined pose (Pi_1_S) for centering the emitter (S) based on the first deviation (A S ) and to determine a corrected predetermined pose (Pi_1_D) for centering the X-ray detector (D) based on the second deviation (A D ). [12] Centering device (70) according to claim 11, wherein the control unit (71) is configured to control the emitter (S) with the corrected predetermined pose (Pi_1_S) of the emitter (S) and to control the X-ray detector (D) with the corrected predetermined pose (Pi_1_D) of the X-ray detector (D). [13] X-ray imaging system (20), comprising: - a spotlight (S) whose pose can be variably controlled, - an X-ray detector (D) whose pose can be controlled independently of the pose of the radiation source (S), - a centering device (70) according to claim 11 or 12. [14] Computer program product comprising instructions which, when the program is executed by a computer, cause it to perform the steps of the method according to any one of claims 1 to 10. [15] Computer-readable storage medium comprising instructions which, when executed by a computer, cause it to perform the steps of the method according to claims 1 to 10.

Images