Calibrating and using a flexible X-ray imaging system

Abstract

A method for calibrated X-ray imaging is described, comprising an X-ray imaging system (10) with a variable-pose radiation source (1) (P1) and an X-ray detector (2) with a variable-pose position (P2) that can be controlled independently of the variable-pose position (P1) of the radiation source (1). In this method, an initial calibration (KAL0) is first performed by projecting an X-ray image of an X-ray phantom (PH) onto the X-ray detector (2) for a plurality of different positions (P1(n), P2(n)) of the radiation source (1) and the X-ray detector (2), thereby determining a plurality of initial projections (C(n, R0, t0)).The X-ray imaging system (10) is then used to acquire X-ray projection data (PD) of an object under investigation (OB). During the acquisition of the X-ray projection data (PD), optical image data (OBD1) representing relative poses (k(i)) of the X-ray detector (2) to the X-ray source (1) are determined for a plurality of different poses (P1(n), P2(n)) of the X-ray source (1) and the X-ray detector (2). Based on the relative poses (k(i)) of the X-ray detector (2) to the X-ray source (1) determined from the optical image data (OBD1) and based on the initial calibration (KAL0), corrected projections (C(n, R1, t1)) are determined. Finally, a reconstruction of X-ray image data (BD) is determined based on the acquired X-ray projection data (PD) and the corrected projections (C(n, R1, t1)). A calibration and control device (50) is also described. Furthermore, an X-ray imaging system (10) is described.

Description

[0001] The invention relates to a method for calibrated X-ray imaging with an X-ray imaging system comprising 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. The invention also relates to a calibration and control device. Furthermore, the invention relates to an X-ray imaging system.

[0002] Flexible robotic X-ray imaging systems, such as robot-assisted ceiling-mounted X-ray systems, can produce not only 2D images but also 3D images (cone-beam CT, CBCT). Especially when the X-ray tube (also called the radiation source) and the X-ray detector are not mechanically coupled, very precise mechanical calibration and adjustment of the system is necessary to ensure optimal positioning and orientation of the X-ray tube and detector in all spatial positions.

[0003] The calibration of a CBCT system is typically performed using X-ray images taken from a calibration phantom, also known as an X-ray phantom. The projection geometry can then be calculated based on these X-ray phantom images. However, the following conditions must be met for such calibration: The trajectory of the CBCT system must be reproducible around a mean value, except for statistical deviations. These statistical deviations can be corrected, for example, by jitter correction. The X-ray tube and the X-ray detector must move along paths that are reproducible relative to each other on average. This can be achieved through complete mechanical restraint, for example, via a C-arm or gantry, or partial restraint, for example, via ceiling-mounted stands on common supports, with simultaneous time-synchronized motion control.

[0004] However, it would also be attractive to use X-ray systems, especially CBCT systems, that are based on mechanically independent units for the X-ray tube and the X-ray detector. An example of this would be a rotating, motorized X-ray detector holder on a mobile stand, which could be used in combination with a ceiling-mounted X-ray stand for CBCT imaging.

[0005] The task is therefore to specify a method and a device for calibrating and applying an X-ray imaging system with mechanically independent units for the X-ray tubes and the X-ray detector.

[0006] This problem is solved by a method for calibrating and applying 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 calibration and control device according to claim 10 and an X-ray imaging system according to claim 11.

[0007] In the inventive method for calibrated X-ray imaging with an X-ray imaging system comprising 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, an initial calibration is first performed by projecting an X-ray image of an X-ray phantom onto the X-ray detector for a plurality of different poses of the radiation source and the X-ray detector, whereby a plurality of initial projections C(n, R0, t0) are determined. The radiation source is understood to be a device for the emission of X-rays, also referred to as an X-ray tube.

[0008] As explained later, initial optical image data can optionally be acquired from the X-ray source and / or the X-ray detector. Initial optical image data refers to image data generated not with X-rays, but with an additional image acquisition unit that can be used in parallel with an X-ray image or with a system consisting of an X-ray source and an X-ray detector. In this preferred variant, initial relative poses of the X-ray detector to the X-ray source are determined based on the initial optical image data. Since the optical image data includes information about the position and orientation of the X-ray source and / or the X-ray detector, it can be used to determine a relative pose between these components. "Optical" in this context means that no X-rays are used for image generation.The electromagnetic waves used to generate the optical image data are preferably in the visible range. However, imaging methods that operate with electromagnetic waves in the UV or IR range should also be included. An X-ray phantom is an object that exhibits certain imaging properties used to investigate and adapt the imaging behavior of an X-ray imaging system. In particular, the X-ray phantom can display patterns that are projected onto the X-ray detector by the X-rays and provide information about the relative position of the source to the X-ray detector.

[0009] An initial calibration is therefore performed by determining absolute calibrated poses of the X-ray source and the X-ray detector using an X-ray image projected onto the X-ray detector for a number of different poses. An "absolute pose" here refers to a pose within a stationary coordinate system of the X-ray imaging system. The X-ray phantom is preferably positioned precisely at the origin of the stationary coordinate system. The initial calibration is preferably performed in the world coordinate system of the X-ray phantom used for calibration. In contrast to the determination of relative poses, this step determines absolute poses of the X-ray source and the X-ray detector and compares them with values ​​used to control these components.The trajectories and absolute poses actually described by the radiation source and X-ray detector during calibration are generally not ideal. However, after calibration, the exact poses and deviations of the calibrated trajectories from the ideal trajectories are known. Therefore, after calibration, the exact path of the trajectories is known, as are the exact poses of the components when targeting predetermined poses or a predetermined trajectory. However, misalignments can cause the relative poses to deviate from the original relative poses. Recalibrating using an X-ray phantom would be time-consuming and would always carry the uncertainty that a misalignment could occur in the period between calibration and the actual X-ray image acquisition of an object or area under investigation.In particular, a deviation in the relative position of the radiation source and the X-ray detector may occur.

[0010] In other words, a plurality of initial projections, in particular projection matrices C(n,R0,t0), are initially calibrated using an X-ray phantom. Here, n is an index that uniquely describes a position on the X-ray detector trajectory and the radiation source trajectory. The radiation source and X-ray detector are also temporally synchronized. R0 is the initial rotation, and t0 is the initial displacement during calibration. R0 and t0 are preferably determined by the image acquisition unit.

[0011] Furthermore, the X-ray imaging system is used to acquire X-ray projection data from an object under investigation, whereby during the acquisition of the X-ray projection data, optical image data, which represent relative poses of the X-ray detector to the emitter, are determined for a plurality of different poses of the source and the X-ray detector.

[0012] The X-ray imaging system is used to acquire X-ray projection data of an object under investigation. During the acquisition of this data, new relative poses of the X-ray detector to the X-ray source are determined for a majority of the absolute calibrated poses of the X-ray source and the X-ray detector by repeatedly acquiring new optical image data. Thus, optical image data is acquired simultaneously with the actual X-ray exposure, allowing for the detection of deviations in the relative poses of the X-ray detector to the X-ray source.

[0013] Corrected projections C(n, R1, t1) are further determined based on the relative poses of the X-ray detector to the emitter determined on the basis of the (new) optical image data and on the basis of the initial calibration.

[0014] Finally, a reconstruction of X-ray image data is performed based on the recorded X-ray projection data and on the basis of the corrected projections C(n, R1, t1).

[0015] Based on the initial relative poses and the new relative poses, a transformation is determined that indicates the deviation of the poses of the radiation source and the X-ray detector during the acquisition of the X-ray projection data from the absolute calibrated poses of the initial calibration. The transformation is preferably determined by a regression, particularly preferably by a least squares method, which is preferably applied to the initial relative poses and the newly determined relative poses determined from the initial optical image data and the new optical image data.

[0016] In other words, during the actual X-ray imaging of an object, a different rotation R1 is determined by optical image acquisition, and a different translation t1 is determined, which differs from the initial rotation R0 already determined during calibration. This means that the coefficients of the initially calibrated projection matrices C(n,R0, t0) cannot be used. Therefore, a new rotation R1 and a new translation t1 must be determined simultaneously with the X-ray imaging by acquiring new optical image data. Based on the initial projection matrices C(n,R0,t0), the initial rotation R0 and translation t0, the new rotation R1 and the new translation t, a transformation F can now be determined with which the new projection matrices C(n, R_1,t_1) = TR(C(n, R0,t0), R0, t0, R1, t1) can be determined, which can be used for a subsequent image reconstruction.The transformation F is based on a decomposition of the projection matrix C(n,R0, t0) into vectors S, O, U, V, to which the difference between R0 and R1 as well as t0 and t1, which may be determined by regression, can be applied. The vector S indicates the position of the radiation source, the vector O indicates the position of the X-ray detector, and the vectors U and V define the X-ray detector area. The corrected vectors S, O, U, V can then be recombined to form the new projection matrices C(n,R1,t1) and used for image reconstruction to correct acquired X-ray projection data.

[0017] The described type of correction is also found in: „Kyriakou Y, Lapp RM, Hillebrand L, Ertel D, Kalender WA. Simultaneous misalignment correction for approximate circular cone-beam computed tomography. Phys Med Biol. 2008 Nov 21;53(22):6267-89. doi: 10.1088 / 0031-9155 / 53 / 22 / 001. Epub 2008 Oct 20. PMID: 18936522.“ erläutert.

[0018] Thus, X-ray image data is reconstructed based on the acquired X-ray projection data, the absolute calibrated poses of the radiation source and the X-ray detector, or the resulting initial projection matrices C(n,R0, t0), and the transformation TR. Advantageously, a variable proportion of the radiation source and X-ray detector poses can be calibrated virtually simultaneously during image acquisition based on optical image data, without requiring a separate second complete calibration. It suffices to capture the relative changes between the radiation source and X-ray detector poses, while the absolute poses only need to be calibrated once initially.

[0019] The calibration and control device according to the invention comprises a calibration unit for performing an initial calibration by means of an X-ray image of an X-ray phantom on the X-ray detector for a plurality of different poses of the emitter and the X-ray detector, wherein a plurality of initial projections C(n, R0, t0) are determined.

[0020] Part of the calibration and control device according to the invention is also a control unit for controlling an X-ray imaging system for acquiring X-ray projection data from an object under investigation, wherein during the acquisition of the X-ray projection data for a plurality of different poses of the radiation source and the X-ray detector, optical image data which represent relative poses of the X-ray detector to the radiation source are determined.

[0021] The calibration and control device according to the invention also includes a correction unit for determining corrected projections based on the relative poses of the X-ray detector to the emitter determined on the basis of the optical image data and on the basis of the initial calibration.

[0022] Part of the calibration and control device according to the invention is also a reconstruction unit for performing a reconstruction of X-ray image data based on the acquired X-ray projection data and the corrected projections C(n, R1, t1).

[0023] The calibration and control device according to the invention shares the advantages of the inventive method for calibrated X-ray imaging with an X-ray imaging system with a beam source with variable pose and an X-ray detector with a variable pose that can be controlled independently of the variable pose of the beam source.

[0024] 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 calibration and control device according to the invention. The X-ray imaging system shares the advantages of the calibration and control device and the calibrated X-ray imaging method according to the invention with an X-ray imaging system having an X-ray source with 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.

[0025] A large proportion of the aforementioned components of the calibration and control 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.

[0026] 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 calibrated X-ray imaging with an X-ray imaging system having 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.

[0027] 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.

[0028] 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.

[0029] In one embodiment of the inventive method for calibrated X-ray imaging with an X-ray imaging system comprising 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, initial optical image data are acquired from the radiation source and / or the X-ray detector during the initial calibration step. Initial optical image data are defined as image data that are not generated with X-rays, but rather with an additional image acquisition unit that can be used in parallel with an X-ray image.

[0030] Furthermore, initial relative poses of the X-ray detector to the radiation source are determined based on the initial optical image data. Since the optical image data includes information about the position and orientation of the radiation source and / or the X-ray detector, it can be used to determine a relative pose between these components. The fact that only relative poses are recorded here is due to the optical image data being acquired from the perspective of the radiation source or the X-ray detector. Preferably, an image acquisition unit arranged on the radiation source captures an image of the X-ray detector or a marker arranged on the X-ray detector. The image is first captured in the coordinate system of the image acquisition unit and then converted to the coordinate system of the X-ray detector by a relative projection from a coordinate system of the image acquisition unit via a coordinate system of the radiation source.This is because the image acquisition unit is located in a different position than the X-ray focus. The initial relative poses determined in this way are later advantageously used as reference values ​​for determining the corrected projections.

[0031] In a preferred embodiment of the inventive method for calibrated X-ray imaging with an X-ray imaging system comprising 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, the initial optical image data are acquired for at least two poses of the radiation source and the X-ray detector rotated relative to each other by a predetermined angle. That is, the orientation of the radiation source and the X-ray detector differs for each image. A parameter curve can be fitted to the relative poses determined from these images as the trajectory of the radiation source and the X-ray detector and subsequently compared with such a trajectory determined during the actual X-ray imaging by acquiring new optical image data.Advantageously, the phase space of the possible poses is at least partially covered, so that deviations and changes from these poses can later be robustly determined during X-ray imaging.

[0032] In an alternative embodiment of the inventive method for calibrated X-ray imaging with an X-ray imaging system comprising 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, the predetermined angle is 90°. Advantageously, the phase space of the possible poses is broadly covered, so that deviations and changes from these poses can be determined more easily, reliably, and robustly.

[0033] In a preferred embodiment of the inventive method for calibrated X-ray imaging with an X-ray imaging system comprising 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, the initial optical image data are acquired by an image acquisition unit arranged on the radiation source, capturing an image of a marker arranged on the X-ray detector. If the intrinsic projection parameters, in particular the detector impact point and the focal length, are known, a relative pose of the radiation source to the X-ray detector can be determined based on these parameters and on the image of the marker.

[0034] Alternatively, the initial optical image data is acquired by capturing an image of a marker located on the radiation source using an image acquisition unit located on the X-ray detector. In this variant, the relative pose of the radiation source and the X-ray detector is acquired in the reverse direction.

[0035] During initial calibration, the absolute pose of the X-ray detector preferably comprises its position and two vectors that span the plane of the detector surface. Advantageously, not only the position of the X-ray detector but also its orientation is calibrated, since the orientation of the detector surface can also influence the X-ray projection data generated during X-ray imaging.

[0036] Preferably, the transformation incorporates a current rotation and / or a current translation of the X-ray detector. The deviation of the relative pose of the X-ray detector and the source from the initial relative pose that occurs during the actual X-ray generation can include both rotation and translation. Advantageously, both deviations are captured and can be incorporated into the correction of the acquired X-ray projection data. This increases the precision of the reconstruction of image data based on the corrected X-ray projection data.

[0037] The image acquisition unit used for recording the optical image data preferably comprises a camera. A camera can generate high-resolution image data that can be used for precise adjustment of the X-ray projection data used for image reconstruction.

[0038] Preferably, the relative poses of the radiation source and the X-ray detector are determined based on intrinsic projection parameters of the image acquisition unit and the X-ray detector. As already mentioned, this data can be used to precisely determine the relative pose of an object to an image acquisition unit.

[0039] The X-ray imaging system according to the invention is preferably configured to perform one of the following types of X-ray imaging: - a dynamic scanning method, in particular - a CBCT procedure, - a truncated CBCT procedure, - a slot scan method, - a True2Scale method, - a tomosynthesis method.

[0040] A dynamic scanning method involves changing and synchronized poses of the X-ray source and the X-ray detector. Therefore, the described method according to the invention can be advantageously applied to this type of method. The following special imaging methods are particular types of dynamic scanning methods.

[0041] CBCT is used to generate 3D image data through a rotating combination of a movable X-ray source and a relatively movable X-ray detector. Unlike a CT system, the X-ray beam is not fan-shaped, but cone-shaped.

[0042] Truncated CBCT procedures are described in the article Luckner C, Herbst M, Weber T, Beister M, Ritschl L, Kappler S, “High-speed slot-scanning radiography using small-angle tomosynthesis: Investigation of spatial resolution”, Medical Physics 46 (12), December 2019, pages 5454 - 5466 (see also https: / / aapm.onlinelibrary.wiley.com / doi / 10.1002 / mp. 13828).

[0043] Slot scan methods are described in DE 10 2016 221 205 B4. Slot scan methods are based on small-angle tomosynthesis.

[0044] In a tomosynthesis procedure, image data, for example for mammography or lung imaging, are acquired from different directions of a breast, and depth information is obtained on the basis of this image data to display a breast image.

[0045] In one variant of the calibration and control device according to the invention, the calibration and control device, preferably the calibration unit of the calibration and control device, has an initial unit for controlling an image acquisition unit for acquiring initial optical image data, which depicts a radiation source and / or an X-ray detector, and for receiving the initial optical image data.

[0046] In this variant, the calibration and control device according to the invention also includes a relative pose determination unit for determining initial relative poses of the X-ray detector to the emitter based on the initial optical image data.

[0047] Preferably, a transformation determination unit is provided as part of the correction unit of the calibration and control device according to the invention, or separately therefrom, for determining a transformation based on the initial relative poses and the new relative poses determined during the actual X-ray imaging. This transformation indicates a deviation of the poses of the radiation source and the X-ray detector from the absolute calibrated poses of the initial calibration. As already mentioned, the determined calibrations can be used for precise image reconstruction.

[0048] 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 an X-ray imaging system according to an embodiment of the invention, Fig. 2 a flowchart illustrating a method for calibrated X-ray imaging with an X-ray imaging system having a variable-pose emitter and an X-ray detector having a variable pose that can be controlled independently of the variable pose of the emitter according to a first embodiment of the invention, Fig. 3 a flowchart illustrating a method for calibrated X-ray imaging with an X-ray imaging system having a variable-pose emitter and an X-ray detector having a variable pose that can be controlled independently of the variable pose of the emitter according to a second embodiment of the invention, Fig. 4 a flowchart illustrating a method for calibrated X-ray imaging with an X-ray imaging system having a variable-pose emitter and an X-ray detector having a variable pose that can be controlled independently of the variable pose of the emitter according to a third embodiment of the invention, Fig. 5 a schematic representation of a calibration and control device according to an embodiment of the invention.

[0049] In Fig. Figure 1 shows a schematic representation of an X-ray imaging system 10 according to an embodiment of the invention. The X-ray imaging system 10 comprises a flexibly positionable X-ray source, referred to as source 1, visible in the center of the image, and a flexibly positionable X-ray detector 2 shown in the lower part of the image. An arrow points in the direction of the rotation axis of the flexibly positionable X-ray detector 2, indicating the z-direction of a world coordinate system, which in the simplest case is a cylindrical coordinate system with the z-axis as the axis of rotation or symmetry. The source 1 is attached to a ceiling 3 by means of a flexible support arm 1a. In addition to a beam aperture 1b for emitting the X-rays, a camera BAE, used as an optical image acquisition unit, is also arranged on the source 1. This camera is used to generate optical image data OBD0, OBD1 from the X-ray detector 2.The spotlight 1 can be moved into any desired pose P1(n) by automatically moving the flexible support arm 1a. Furthermore, in . Fig. 1. A patient bed 4 is visible, which is placed on a room floor 5. The X-ray detector 2 is arranged on a rotatable and movable support system 2a, with which the X-ray detector 2 can be moved into a desired position P2(n). A marker M is attached to the X-ray detector 2, which can be imaged by the camera BAE. In Fig. Figure 1 also shows vectors u and v that span the detector area of ​​the X-ray detector 2. An X-ray phantom PH is positioned on the patient table 4, which allows for an initial calibration KAL0 of the poses P1(n) of the radiation source 1 and the poses P2(n) of the X-ray detector for N different projections. The absolute calibrated poses P thus generated ABS 1(n), P ABS2(n), which are generated in the world coordinate system of the X-ray phantom PH, only need to be generated once and can be reused later for image reconstruction.

[0050] To compensate for deviations in the approach to the poses during imaging, initial relative poses k0(i) between the radiation source 1 and the X-ray detector 2 are first determined during the initial calibration KAL0 by generating initial optical image data OBD0 of the marker M using the camera BAE. If the X-ray imaging system 10 is later used to acquire X-ray projection data PD of an examination area UB of a patient (not shown), new optical image data OBD1 of the marker M are acquired during the acquisition of the X-ray projection data PD. Based on these new optical image data, new relative poses k(i) of the X-ray detector 2 to the radiation source 1 are determined. A transformation TR (see [reference missing]) can then be performed based on the initial relative poses k0(i) and the new relative poses k(i). Fig. 2) determine the deviation of the poses P1, P2 of the emitter 1 and the X-ray detector 2 from the absolute calibrated poses P ABS1 (n), P ABS 2(n). Finally, the transformation TR can be used for a kind of “virtual” calibration to generate current absolute poses P1(n), P2(n) of the source 1 and the X-ray detector 2, or pose data assigned to them, on the basis of which a reconstruction of X-ray image data BD (see Fig. 2) is carried out.

[0051] In Fig. Figure 1 also shows a calibration and control device 50 according to an embodiment of the invention, with which both calibration of the overall system and X-ray imaging can be carried out by sending control data SD and receiving optical image data OBD0, OBD1 and X-ray projection data PD.

[0052] In Fig. Figure 2 is a flowchart 200 illustrating a method for calibrated X-ray imaging with an X-ray imaging system 10 with a radiation source 1 with variable pose P1 and an X-ray detector 2 with a variable pose 2 that can be controlled independently of the variable pose P1 of the radiation source 1 according to a first embodiment of the invention.

[0053] In step 2.I, initial optical image data OBD0 is first acquired by a camera BAE mounted on the radiation source 1 from a marker M attached to the X-ray detector 2 for a plurality i = 2 of different initial relative poses k0(i) of the X-ray detector 2 to the radiation source 1. The targeted poses of the radiation source and the X-ray detector are selected such that the orientation of the radiation source 1 differs by an angle of 90° between the different poses. In other words, different orientations of the radiation source 1 and the X-ray detector 2 are set, each differing by 90°, so that the phase space of the possible poses is covered reasonably evenly.

[0054] In step 2.II, initial relative poses k0(i) of the X-ray detector 2 to the emitter 1 are determined based on the initial optical image data OBD0.

[0055] In step 2.III, an initial calibration KAL0 is performed by determining absolute calibrated poses P. ABS 1 (n), P ABS 2(n) of the emitter 1 and the X-ray detector 2 by means of an X-ray image of an X-ray phantom PH on the X-ray detector 2 for a plurality of different poses P1(n), P2(n) of the emitter 1 and the X-ray detector 2.

[0056] In step 2.IV, the X-ray imaging system 10 is used to acquire X-ray projection data PD of an examination object OB. During the acquisition of the X-ray projection data PD, a majority of the absolute calibrated poses P are recorded. ABS 1(n), P ABS 2(n) of the emitter 1 and the X-ray detector 2 each acquire new optical image data OBD1 from the camera BAE of the marker M.

[0057] Based on the new optical image data OBD1 acquired in step 2.IV, new relative poses k(i) of the X-ray detector 2 to the emitter 1 are determined in step 2.V.

[0058] In step 2.VI, a transformation TR is determined based on the initial relative poses k0(i) and the new relative poses k(i). The transformation TR yields a deviation of the poses P1, P2 of the radiation source 1 and the X-ray detector 2 during the acquisition of the X-ray projection data PD from the absolute calibrated poses P ABS 1(n), P ABS 2(n) of the initial calibration KAL0.

[0059] In step 2.VII, X-ray image data BD are based on the acquired X-ray projection data PD, the absolute calibrated poses P. ABS 1(n), (P ABS The absolute calibrated poses P of emitter 1, X-ray detector 2, and transformation TR are reconstructed. ABS 1(n), (P ABS2(n) is corrected using the TR transformation and the corrected poses are used to reconstruct the image data BD.

[0060] In Fig. Figure 3 shows a flowchart 300 illustrating a method for calibrated X-ray imaging with an X-ray imaging system 10 having a variable-pose radiation source 1 and an X-ray detector 2 with a variable pose that can be controlled independently of the variable pose of the radiation source 1, according to a second embodiment of the invention. The flowchart is shown in Figure 3. Fig. 3. The illustrated flowchart 300 and the accompanying text are intended to clarify the procedure of the method according to the invention in detail using a simple numerical example.

[0061] In step 3.I, the following steps are initially performed similarly to the one described in Fig. Figure 2 illustrates initial optical image data OBD0 acquired by a camera BAE from a marker M attached to the X-ray detector 2 for a plurality of three different initial relative poses k0(i) of the X-ray detector 2 to the radiation source 1. These poses are chosen such that the orientation of the radiation source 1 differs by an angle of 90° between the different poses.

[0062] In step 3.II, initial relative poses k0(i) of the X-ray detector 2 to the emitter 1 are determined based on the initial optical image data OBD0.

[0063] In the particularly simple case explained here, the radiation source 1 and the X-ray detector 2 are aligned in the z-direction (see Fig. 1) Shifted relative to each other by one centimeter. For simplicity, only relative positions are considered in this example. The relative positions would then be simple: k0(1)=(Δφ=90°−270°,R1−R2[cm],Δz=1[cm]), k0(2)=(Δφ=180°−0°,R1−R2[cm],Δz=1[cm]), k0(3)=(Δφ=270°−90°,R1−R2[cm],Δz=1[cm]).

[0064] Here, R1 denotes the radial distance of the emitter 1 to the z-axis, R2 denotes the radial distance of the X-ray detector 2 to the z-axis, the angular differences Δφ denote the differences of the respective angular positions φ1, φ2 of the emitter 1 and the X-ray detector 2 during the acquisition of the initial optical image data OBD0, and Δz =1 [cm] denotes a displacement between the emitter 1 and the X-ray detector 2 in the z-direction, which occurs in each of the three different orientations of the emitter 1 and the X-ray detector 2 in space.

[0065] In step 3.III, an initial calibration KAL0 is performed by determining absolute calibrated poses P. ABS 1(n), P ABSThe radiation pattern of radiation source 1 and X-ray detector 2 is determined by an X-ray image of an X-ray phantom PH on the X-ray detector 2 for a plurality of different poses P1(n), P2(n) of radiation source 1 and X-ray detector 2. The number of calibrated projections in this case is N = 13.

[0066] The absolute poses can have, for example, the following coordinates: PABS1(n=1)=(30°,R1[cm],z=0[cm]), PABS1(n=2)=(40°,R1[cm],z=0[cm]), PABS1(n=13)=(150°,R1[cm],z=0[cm]); PABS2(n=1)=(210°,R2[cm],z=1[cm]), PABS2(n=2)=(220°,R2[cm],z=1[cm]), PABS2(n=13)=(350°,R2[cm],z=1[cm]).

[0067] The actual calibration is now complete.

[0068] When using the X-ray imaging system 10 in step 3.IV to acquire X-ray projection data PD of an examination object OB, during the acquisition of the X-ray projection data PD for a majority of the absolute calibrated poses P ABS 1(n), P ABS 2(n) of the emitter 1 and the X-ray detector 2 each acquire new optical image data OBD1 from the camera BAE of the marker M.

[0069] In step 3.V, new relative poses k(i) of the X-ray detector 2 to the emitter 1 are then determined based on this new optical image data OBD1: k(1)=(Δφ=30°−210°,R1−R2[cm],Δz=2[cm]), k(2)=(Δφ=90°−270°,R1−R2[cm],Δz=2[cm]), k(3)=(Δφ=150°−350°,R1−R2[cm],Δz=2[cm]).

[0070] While the relative angles φ1 - φ2 of the emitter 1 and the X-ray detector 2, as well as the relative axial distances R1 - R2 to the z-axis, have not changed, the X-ray detector 2 has shifted by another centimeter in the z-direction relative to the emitter 1 compared to the initial calibration KAL0.

[0071] Based on the initial relative poses k0(i) and the new relative poses k(i), a transformation R is now calculated in step 3.VI, which in this simple case only includes a translation t: TR=t=(0,0,Δz=1[cm]).

[0072] The true coordinates P1, P2 of the radiation source 1 and the X-ray detector 2 are therefore: P1 / 2(n)=t+PABS1 / 2(n).

[0073] Specifically, the projections yield the following results: P1(n=1)=(30°,R1[cm],z=0[cm]), P1(n=2)=(40°,R1[cm],z=0[cm]), P1(n=13)=(150°,R1[cm],z=0[cm]); P2(n=1)=(210°,R2[cm],z=2[cm]), P2(n=2)=(220°,R2[cm],z=2[cm]), P2(n=13)=(350°,R2[cm],z=2[cm]).

[0074] In step 3.VII, a reconstruction is now carried out based on the projection data PD corrected in this way, whereby the positions P1 / 2(n) of the emitter 1 and the X-ray detector 2 are given as P1 / 2(n) = t + P ABS 1 / 2(n) of the image reconstruction will be used as the basis.

[0075] In Fig. Figure 4 is a flowchart 400 illustrating a method for calibrated X-ray imaging with an X-ray imaging system 10 having a variable-pose radiation source 1 and an X-ray detector 2 having a variable pose that can be controlled independently of the variable pose of the radiation source 1, according to a third embodiment of the invention. In the Fig. In the third embodiment illustrated in Figure 4, not only is there a misaligned displacement Δz between the emitter 1 and the X-ray detector 2 in the direction of the z-axis, but also a rotation Δφ. Therefore, the transformation TR calculated in step 4.VI includes not only a translation t but also a rotation R.

[0076] In step 4.I, as in the previous examples, initial optical image data OBD0 are again acquired by a camera BAE from a marker M attached to the X-ray detector 2 for a plurality of three different initial relative poses k0(i) of the X-ray detector 2 to the radiation source 1. These poses are chosen such that the orientation of the radiation source 1 differs by an angle of 90° between the different poses.

[0077] In step 4.II, initial relative poses k0(i) of the X-ray detector 2 to the emitter 1 are determined based on the initial optical image data OBD0.

[0078] In the specific case described here, the radiation source 1 and the X-ray detector 2 are shifted relative to each other by one centimeter in the z-direction and rotated relative to each other by one degree in the φ-direction. For the sake of simplicity, only relative positions are considered in this example. The relative positions would then be: k0(1)=(Δ(91°,270°)=181°,R1−R2[cm],Δz=1[cm]), k0(2)=(Δ(181°,0°)=181°,R1−R2[cm],Δz=1[cm]), k0(3)=(Δ(271°,90°)=181°,R1−R2[cm],Δz=1[cm]).

[0079] Here, R1 denotes the radial distance of the emitter 1 to the z-axis, R2 denotes the radial distance of the X-ray detector 2 to the z-axis, the angles denote the respective angular positions φ1, φ2 of the emitter 1 and the X-ray detector 2 during the acquisition of the initial optical image data OBD0, and Δz =1 [cm] denotes a displacement between the emitter 1 and the X-ray detector 2 in the z-direction, which occurs in each of the three different orientations of the emitter 1 and the X-ray detector 2 in space.

[0080] In step 4.III, an initial calibration KAL0 is performed by determining absolute calibrated poses P. ABS 1 (n), P ABSThe projections of the radiation source 1 and the X-ray detector 2 are performed by means of an X-ray image of an X-ray phantom PH on the X-ray detector 2 for a plurality of different poses P1(n), P2(n) or projections of the radiation source 1 and the X-ray detector 2. The number of calibrated projections in this case is N = 13.

[0081] The absolute poses can have, for example, the following coordinates: PABS1(n=1)=(31°,R1[cm],z=0[cm]), PABS1(n=2)=(41°,R1[cm],z=0[cm]), PABS1(n=13)=(151°,R1[cm],z=0[cm]); PABS2(n=1)=(210°,R2[cm],z=1[cm]), PABS2(n=2)=(220°,R2[cm],z=1[cm]), PABS2(n=13)=(350°,R2[cm],z=1[cm]).

[0082] The actual calibration is now complete.

[0083] When using the X-ray imaging system 10 in step 4.IV to acquire X-ray projection data PD of an examination object OB, during the acquisition of the X-ray projection data PD for a majority of the absolute calibrated poses P ABS 1(n), P ABS 2(n) of the emitter 1 and the X-ray detector 2 each acquire new optical image data OBD1 from the camera BAE of the marker M.

[0084] In step 4.V, new relative poses k(i) of the X-ray detector 2 to the emitter 1 are then determined based on this new optical image data OBD1: k(1)=(Δ(32°,210°)=182°,R1−R2[cm],Δz=2[cm]), k(2)=(Δ(92°,270°)=182°,R1−R2[cm],Δz=2[cm]), k(3)=(Δ(152°,350°)=182°,R1−R2[cm],Δz=2[cm]).

[0085] Here, in contrast to the situation in Fig. In the illustrated embodiment 3, the relative angles φ1 - φ2 of the emitter 1 and the X-ray detector 2 also changed after the initial calibration KAL0, while the relative axial distances R1 - R2 to the z-axis did not change, and the X-ray detector 2 shifted by one centimeter in the z-direction relative to the emitter 1 compared to the initial calibration KAL0.

[0086] Based on the initial relative poses k0(i) and the new relative poses k(i), a transformation R is again calculated in step 4. VI, which in this simple case only includes a translation t: TR=R+t=(Δφ=1°,0,Δz=1[cm]).

[0087] The true coordinates P1, P2 of the radiation source 1 and the X-ray detector 2 are therefore: P1 / 2(n)=R+t+PABS1 / 2(n).

[0088] Specifically, the projections yield the following results: P1(n=1)=(32°,R1[cm],z=0[cm]), P1(n=2)=(42°,R1[cm],z=0[cm]), P1(n=13)=(152°,R1[cm],z=0[cm]); P2(n=1)=(210°,R2[cm],z=2[cm]), P2(n=2)=(220°,R2[cm],z=2[cm]), P2(n=13)=(350°,R2[cm],z=2[cm]).

[0089] In step 4.VII, a reconstruction is now carried out based on the projection data PD corrected by the pose correction, whereby the positions of the emitter 1 and the X-ray detector 2 are given by P1 / 2(n) = R + t + P ABS 1 / 2(n) of the image reconstruction will be used as the basis.

[0090] In Fig. Figure 5 shows a schematic representation of a calibration and control device 50 according to an embodiment of the invention.

[0091] The calibration and control unit 50 comprises an initialization unit 51 for controlling a camera BAE of an emitter 1 of an X-ray imaging system 10 with control data SD for generating initial optical image data OBD0, which image an X-ray detector 2 from an emitter 1, and for receiving this initial optical image data OBD0. Also part of the calibration and control unit 50 is a relative pose determination unit 52 for determining initial relative poses k0(i) of the X-ray detector (2) to the emitter (1) based on the initial optical image data OBD0.

[0092] The calibration and control device 50 further comprises a calibration unit 53 for performing an initial calibration KAL0 by determining absolute calibrated poses P ABS 1(n), P ABSThe X-ray image of an X-ray phantom PH is projected onto the X-ray detector 2 for a plurality of different poses P1(n), P2(n) of the X-ray source 1 and the X-ray detector 2. For this purpose, control data SD is transmitted to the X-ray source 1 and the X-ray detector 2, and X-ray projection data PD is received from the X-ray detector 2.

[0093] Furthermore, the calibration and control device 50 includes a control unit 54. The control unit serves to control an X-ray imaging system 10 for X-ray imaging of an examination object OB. During the acquisition of the X-ray projection data PD for a majority of the absolute calibrated poses P ABS 1(n), P ABS New optical image data OBD1 are acquired by the emitter 1 and the X-ray detector 2, and new relative poses k(i) of the X-ray detector 2 to the emitter 1 are determined on the basis of these.

[0094] Furthermore, the calibration and control unit 50 includes a transformation determination unit 55 for determining a transformation TR based on the initial relative poses k0(i) and the new relative poses k(i). The transformation TR indicates a deviation of the poses P1, P2 of the radiation source 1 and the X-ray detector 2 from the absolute calibrated poses P ABS 1(n), P ABS 2(n) of the initial calibration KAL0.

[0095] Part of the calibration and control unit 50 is also a reconstruction unit 56 for performing a reconstruction of X-ray image data BD based on the acquired X-ray projection data PD, the absolute calibrated poses P ABS 1(n), P ABS 2(n) of the emitter 1 and the X-ray detector 2 and the transformation TR.

[0096] 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. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2016 221 205 B4

[0043] Cited non-patent literature

[0000] Kyriakou Y, Lapp RM, Hillebrand L, Ertel D, Calendar WA. Simultaneous misalignment correction for approximate circular cone-beam computed tomography. Phys Med Biol. 2008 Nov 21;53(22):6267-89. doi: 10.1088 / 0031-9155 / 53 / 22 / 001. Epub 2008 Oct 20. PMID: 18936522

[0017] Luckner C, Herbst M, Weber T, Beister M, Ritschl L, Kappler S, “High-speed slot-scanning radiography using small-angle tomosynthesis: Investigation of spatial resolution”, Medical Physics 46 (12), December 2019, pages 5454–5466 (see also https: / / aapm.onlinelibrary.wiley.com / doi / 10.1002 / mp.13828

[0042]

Claims

[1] Method for calibrated X-ray imaging with an X-ray imaging system (10) having a variable pose (P1) emitter (1) and an X-ray detector (2) having a variable pose (P2) that can be controlled independently of the variable pose (P1) of the emitter (1), comprising the steps: - Performing an initial calibration (KAL0) by X-ray imaging of an X-ray phantom (PH) on the X-ray detector (2) for a plurality of different poses (P1(n), P2(n)) of the source (1) and the X-ray detector (2), whereby a plurality of initial projections (C(n, R0, t0)) are determined, - Applying the X-ray imaging system (10) to acquire X-ray projection data (PD) of an object under investigation (OB), wherein, during the acquisition of the X-ray projection data (PD), optical image data (OBD1) representing relative poses (k(i)) of the X-ray detector (2) to the X-ray source (1) are determined for a plurality of different poses (P1(n), P2(n)) of the source (1) and the X-ray detector (2), - Determining corrected projections (C(n, R1, t1)) based on the relative poses (k(i)) of the X-ray detector (2) to the emitter (1) determined on the basis of the optical image data (OBD1) and on the basis of the initial calibration (KAL0), - Performing a reconstruction of X-ray image data (BD) based on the acquired X-ray projection data (PD) and the corrected projections (C(n, R1, t1)). [2] Method according to claim 1, wherein the step of performing an initial calibration (KAL0) comprises the sub-steps: - Acquisition of initial optical image data (OBD0) from the radiation source (1) and / or the X-ray detector (2), - Determining initial relative poses (k0(i)) of the X-ray detector (2) to the source (1) based on the initial optical image data (OBD0), - Determining absolute calibrated poses (P ABS 1(n), P ABS 2(n)) of the source (1) and the X-ray detector (2), on the basis of which the majority of initial projections (C(n, R0, t0)) are determined, by the X-ray imaging of an X-ray phantom (PH) on the X-ray detector (2) for a majority of different poses (P1(n), P2(n)) of the source (1) and the X-ray detector (2). [3] Method according to claim 2, wherein the initial optical image data (OBD0) are acquired for at least two poses (P1(i), P2(i)) of the emitter (1) and the X-ray detector (2) rotated relative to each other by a predetermined angle. [4] Method according to claim 3, wherein the predetermined angle is 90°. [5] Method according to any one of claims 2 to 4, wherein the initial optical image data (OBD0) and the optical image data (OBD1) are acquired by image acquisition of a marker (M) arranged on the X-ray detector (2) by an image acquisition unit (BAE) arranged on the emitter (1). [6] Method according to any one of claims 2 to 5, wherein the initial optical image data (OBD0) and the optical image data (OBD1) are acquired by an image acquisition unit (BAE) of a marker (M) arranged on the emitter (1) arranged on the X-ray detector (2). [7] Method according to any of the preceding claims, wherein the step of determining corrected projections (C(n, R1, t1)) comprises determining a transformation (TR) based on the initial relative poses (k0(i)) and the new relative poses (k(i)) and applying the transformation (TR) to the initial projections (C(n, R0, t0)). [8] Method according to one of the preceding claims, wherein the initial projections (C(n, R0, t0)) and the corrected projections (C(n, R1, t1)) comprise the positions (S,O) of the emitter (1) and the X-ray detector and two vectors (u, v) spanning the plane of the detector surface of the X-ray detector (2). [9] Method according to one of the preceding claims, wherein the relative poses (k0(i), k(i)) are determined on the basis of intrinsic projection parameters of the image acquisition unit (AAU) and the X-ray detector (2). [10] Calibration and control device (50), comprising: - a calibration unit (53) for performing an initial calibration (KAL0) by means of an X-ray image of an X-ray phantom (PH) on an X-ray detector (2) for a plurality of different poses (P1(n), P2(n)) of a source (1) and the X-ray detector (2), wherein a plurality of initial projections (C(n, R0, t0)) are determined, - a control unit (54) for controlling an X-ray imaging system (10) for acquiring X-ray projection data (PD) from an object under investigation (OB), wherein, during the acquisition of the X-ray projection data (PD), optical image data (OBD1) which represent relative poses (k(i)) of the X-ray detector (2) to the X-ray source (1) are determined for a plurality of different poses (P1(n), P2(n)) of the source (1) and the X-ray detector (2), - a correction unit (55) for determining corrected projections (C(n, R1, t1)) based on the relative poses (k(i)) of the X-ray detector (2) to the emitter (1) determined on the basis of the optical image data (OBD1) and on the basis of the initial calibration (KAL0), - a reconstruction unit (56) for performing a reconstruction of X-ray image data (BD) based on the acquired X-ray projection data (PD) and the corrected projections (C(n, R1, t1)). [11] X-ray imaging system (10) comprising: - a spotlight (1) that can be variably controlled with respect to its pose (P1), - an X-ray detector (D) whose pose (P2) can be controlled independently of the pose (P1) of the radiation source (1), - a calibration and control device (50) according to claim 10. [12] X-ray imaging system according to claim 11, which is configured to perform one of the following types of X-ray imaging: - a dynamic scanning method, - a CBCT procedure, - a truncated CBCT procedure, - a slot scan method, - a True2Scale method, - a tomosynthesis method. [13] 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 9. [14] 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 9.

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