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

Abstract

The invention relates to a method for operating an X-ray device (14) with a carrier on which an X-ray source (19) and an X-ray detector (21) are arranged opposite each other, and an actuating device (17) for moving at least the carrier, in particular a C-arm (15), to set a projection geometry. The method comprises: - Providing a three-dimensional vascular model (1) of a vascular structure (3) of an examination object (22) describing the course of the vessel, in particular by means of midlines, from which projection images are to be taken with the X-ray device (14), wherein a target position (5) of an instrument (11) movable in the vascular structure (3) is marked in the vascular model (1), a starting position (2) of the instrument (11) in the vascular structure (3) of the vascular model (1) and a path (6) in the vascular structure (3) of the vascular model (1) from the starting position (2) of the instrument (11) to the target position (5), - Establishing control points (7) along the path (6), - Determination of an optimized progression (9) of projection geometries for the support points (7) in an optimization process of an objective function using the vessel model (1), wherein the objective function includes, in addition to at least one first term relating to the optimization of the image content for a viewer with the instrument (11) located at the respective support point (7), at least one second term which minimizes the number of changes of the projection geometry along the path (6) by movement of the support, and - Determination of positioning parameters for controlling the positioning device (17) for each projection geometry.

Description

[0001] The invention relates to a computer-implemented method for operating an X-ray device with a carrier on which an X-ray source and an X-ray detector are arranged opposite each other, and an actuating device for moving at least the carrier, in particular a C-arm, to adjust a projection geometry. The invention also relates to an X-ray device, a computer program, and an electronically readable data carrier.

[0002] For examinations and treatments of subjects where minimally invasive procedures are performed using an instrument within a vascular structure, the instrument is typically guided through the vascular structure to a target position for the examination and / or treatment. It is known to monitor the progress of this movement using an imaging X-ray system. For example, in a specific projection geometry, characterized in particular by the projection direction or the angulation angles of the C-arm in C-arm X-ray systems, low-dose projection images, especially fluoroscopy images, can be acquired. Numerous methods have already been described for processing such projection images for display on an output device of the X-ray system, for example, by enriching them with additional information.Processing can also include generating a new processing image based on information obtained from the projection image.

[0003] For example, in minimally invasive procedures, a catheter can be guided through the blood vessels of a section of a patient's circulatory system to a target location, such as a thrombus in stroke treatment or a feeding vessel in tumor embolization. Two-dimensional live projection images can be used to visualize the catheter's position and, particularly when contrast agents are administered, the blood vessels themselves.

[0004] Two-dimensional projection images are generally acquired using a specific projection geometry, which can be selected by the user. With a C-arm, the projection geometry is primarily described by its angulation, specifically its two angulation angles. The person performing the procedure typically wants to see both the instrument and the surrounding vessels, ideally all the way to the target position.

[0005] In the prior art, it is known to specify a fixed angulation or projection geometry, which usually provides a sufficiently suitable solution for performing the procedure as a whole. For example, the anterior-posterior direction of a patient can be chosen as the projection direction.

[0006] An improved approach has been proposed whereby a user, such as the person performing the procedure and / or a technical assistant, manually adjusts the projection geometry to provide an ideal overview of the current intervention situation. However, this requires time, which is limited during minimally invasive procedures. Furthermore, each adjustment interrupts the intervention workflow. Therefore, in interventions that allow for such manual adjustment, the projection geometry is often not modified, even though this would improve visibility and assessment of the intervention situation. Additionally, collimation, which could lead to dose reduction, and zoom factors are also frequently not chosen appropriately.In many cases, frequent communication between the person performing the procedure and a technical assistant is also required in order to adjust the projection geometry.

[0007] The invention is based on the objective of providing an aid for improved image support during minimally invasive procedures in vascular structures of examination subjects, which offers significantly improved image quality during the intervention while placing the least possible burden on users.

[0008] To solve this problem, the invention provides a computer-implemented method, an X-ray device, a computer program, and an electronically readable data carrier according to the dependent claims. Advantageous embodiments are described in the sub-claims.

[0009] A computer-implemented method according to the invention for operating an X-ray device with a carrier on which an X-ray source and an X-ray detector are arranged opposite each other, and an actuating device for moving at least the carrier, in particular a C-arm, to set a projection geometry, comprises the following steps: - Providing a three-dimensional vascular model of a vascular structure of an object under investigation, describing the course of the vessel, in particular by means of midlines, from which projection images are to be taken with the X-ray device, wherein a target position of an instrument movable in the vascular structure is marked in the vascular model, - Providing a starting position for the instrument in the vascular structure of the vascular model, - Providing a path in the vascular structure of the vascular model from the instrument's starting position to the target position, - Establishing control points along the path, - Determination of an optimized progression of projection geometries for the support points in an optimization process of an objective function using the vessel model, wherein the objective function includes, in addition to at least one first term relating to the optimization of the image content for a viewer with a medical instrument located at the respective support point, at least one second term that minimizes the number of changes in projection geometry along the path due to movement of the support, and - Determination of positioning parameters for controlling the positioning device for each projection geometry.

[0010] The support structure can advantageously be a C-arm. C-arm X-ray systems are frequently used in vascular examinations and as an adjunct to vascular treatments, for example in angiography systems or elsewhere in operating rooms. Although many of the following embodiments refer to such C-arm X-ray systems, the invention can also be applied to other types of supports, for example those with robotic arms that allow the X-ray detector and the X-ray tube to be moved separately.

[0011] The object of investigation could be, for example, a patient, and the vascular structure a section, particularly a vascular tree, of their circulatory system. However, the objects described here are also conceivable in the context of interventions on workpieces and the like, which may, for example, exhibit porous or other vascular structures.

[0012] According to the invention, it is proposed to use certain determinable input information, namely a three-dimensional vessel model of the relevant vessel structure with a known target position therein, an initial position corresponding in particular to the current position at the time of determination, and a path from the initial position to the target position through the vessels of the vessel structure, in order to ultimately determine a course of projection geometries along the path in an optimization process. Here, optimization is not only aimed at ensuring optimal recognizability of the relevant information for guiding the instrument within the vessel structure, but also at reducing the number of changes in the projection geometry.This means that a suitable compromise is sought that, on the one hand, allows for good visibility of the aspects important for navigation, and on the other hand, permits a smooth procedure without too many interruptions. In other words, a reduced number of projection geometries is preferred to avoid constant repositioning of the user and frequent mental reorientation of the person performing the procedure. Since the determination of the projection geometries can be automated, no user interaction is necessary here either. By determining the positioning information, automatic adjustment when changing the projection geometry can also be enabled, thus relieving the user of this task as well.

[0013] This allows for high-quality, precise navigation of the instrument to the target position, as well as a fast, virtually interference-free procedure, and in particular, an acceleration of the minimally invasive intervention. Efficient execution also makes it possible to keep the X-ray dose low and, especially when patients are the subjects of the examination, to reduce the amount of contrast agent administered.

[0014] The at least one first term and the at least one second term in the objective function are preferably assigned a weighting factor. Such weighting factors allow the influence of the respective optimization goal to be appropriately selected. In exemplary embodiments, the weighting factors and / or their ratio can be chosen based on user input. This allows users to influence the optimization result according to their preferences. A user who places more value on perfect viewing angles can choose a higher weighting for the at least one first term, while a user who places more value on minimizing changes in projection geometries can assign a higher weighting to the at least one second term.

[0015] Optimization parameters can be geometric parameters describing the projection geometry at the respective support points. In particular, the optimization parameters can describe at least one angle of the C-arm, i.e., its angulation, for each support point. Preferably, two angles of the C-arm are used. Further optimization parameters can describe translational positions of the C-arm if these can be influenced by the positioning device and / or manual intervention. Beyond the mere position of the beam, zoom and collimation can also be optimized in the optimization process, as will be discussed in more detail below. Accordingly, optimization parameters can also be collimation parameters and / or zoom parameters.

[0016] Using the set of parameters for the positioning device, it can be directly controlled to adjust the appropriate projection geometry. Upon reaching a point where a change occurs, the projection geometry can be set directly, particularly after user confirmation. This method thus enables optimal preparation for the subsequent steps of the minimally invasive procedure.

[0017] In exemplary embodiments, the vessel model to be provided may be derived from a three-dimensional image dataset of the object under investigation, which is or will be registered with a coordinate system of the X-ray device. To determine the vessel model, trained analysis functions capable of identifying the centerlines and / or boundaries of the vessels can be used. Such analysis functions are already widely known in the art and can, for example, employ segmentation. The three-dimensional image dataset can be acquired directly with the device, for example, by rotating the imaging setup consisting of the X-ray tube and X-ray detector around the object under investigation (e.g., as a C-arm CT scan), or it can be acquired pre-interventionally, i.e., before the procedure with the instrument.The three-dimensional image dataset can be, for example, a magnetic resonance imaging (MRI) image dataset and / or a computed tomography (CT) image dataset. If the three-dimensional image dataset was not acquired with the X-ray unit or before a repositioning of the support and / or the object under examination that could not be detected by sensors, known 2D-3D or 3D-3D registration techniques can be used to register the three-dimensional image dataset, and thus also the vessel model, with the coordinate system of the X-ray unit.

[0018] In particular, the three-dimensional image dataset, possibly in conjunction with the vascular model, can also be used in a planning phase to manually and / or automatically select the target position there (and thus also in the vascular model), as is generally known. At least partially automatic determination of the target position is also conceivable, for example, by detecting a thrombus or tumor and / or, especially in the case of embolization, by flow simulation.

[0019] In a preferred further development, it may be provided that the initial position is determined as the current position of the instrument from two-dimensional projection images, in particular fluoroscopy images, at least one current projection geometry, in particular with the additional use of the vessel model and / or three-dimensional image dataset, and / or with the use of a tracking system of the X-ray unit. For example, the current position of the instrument can be tracked in real time in two-dimensional fluoroscopy images, as is generally known. If a registration does not already exist, this two-dimensional representation of the instrument and the vessel structure can be registered with the three-dimensional representation of the vessel structure, i.e., the vessel model.In such a case, but also with an already established registration, patient movements, particularly cyclical movements such as heartbeat and / or respiration, can be advantageously taken into account. Furthermore, the fact that the instrument is bound to the interior of the vascular structure can be advantageously considered during position determination. The result in any case is a current, three-dimensional position of the instrument, which represents the initial position in the initial situation to be evaluated for the optimization process. Alternatively or additionally, the invention may also provide for the X-ray device to have a tracking system to determine the current three-dimensional position of the instrument. Tracking techniques known in the prior art can be used for this purpose, for example, electromagnetic tracking, opto-acoustic tracking, and the like.Finally, it is also possible to start from a planned initial position, for example, a branch in a vascular tree leading to the target position, and so on. Such an initial position can be marked in the vascular model, just like the target position.

[0020] Various approaches can be used to determine the path, particularly suitable pathfinding functions that can find a route between two points in a vascular structure. For example, the path might be determined as the shortest connection through the vascular structure from the starting point to the target point. Boundary conditions can also be used, such as specific required vessel sizes, and the like. In non-malformed vascular trees in a patient's vascular system, it is often the case that the pathfinding function only needs to find a single possible path.

[0021] Preferred embodiments of the present invention provide for the selection of support points that support points are defined at least at nodes in the vascular structure where several vessels meet, particularly at bifurcations, and / or are selected at least partially at a specific distance along at least one centerline of a vessel or vascular segment of the path. Advantageously, suitable projection geometries can be determined at least for locations where several possibilities for continuing the instrument exist due to branching, particularly at bifurcations. Especially at bifurcations, it is extremely important to obtain a good overview of the overall situation in order to be able to continue the instrument flawlessly, gently, and with precise accuracy, so that the method proposed here can provide specifically suitable information.Additional support points can also be defined between nodes. These can be placed at regular intervals between bifurcations, or based on features of the vessel structure, such as tight bends. For regular intervals, the spacing can be chosen, for example, in the range of 1 to 5 mm.

[0022] At least one of the first terms can be chosen from the group comprising: - for support points at and / or in a tolerance range around bifurcations of the vessel structure, a term to minimize the deviation of the projection direction of the projection geometry from the cross product of the course direction of the vessels of the bifurcation at the bifurcation according to the vessel model, - especially for support points that are not located at a bifurcation and / or outside the tolerance range, a term that minimizes the optical foreshortening of at least the vessel in which the support point is located and / or all vessels visible in the projection geometry along the path from the support point to the target position, particularly with increasing distance from the support point in the vessel structure, - a term that favors visibility of the instrument in the center of a projection image captured with the projection geometry, - a term maximizing the visible length of vessels along the path from the support point to the target position, - a term that minimizes the dose exposure for the subject of the investigation and / or at least one treatment and / or operating person, and - a term minimizing the shadowing of at least part of the vascular structure, in particular the instrument and / or the path from the support point to the target position, by other structures, in particular bones, of the object under investigation.

[0023] At bifurcations, it is therefore particularly advantageous to minimize the deviation of the projection direction of the projection geometry from the cross product of the course direction of the vessels or vessel segments at the bifurcation. In other words, at bifurcations, the cross product between lines fitted to the vessels can indicate the preferred viewing / projection direction, because the vessel segments then lie parallel to the image plane of the two-dimensional projection and can be well resolved and perceived. The deviation from this optimal projection direction can, for example, be evaluated using penalty costs in the objective function.

[0024] Particularly outside of anchor points, the optical foreshortening of vessels, especially those relevant for instrument guidance, can be minimized. This can refer to the vessel or vessel segment where the anchor point is located, but it can also affect multiple vessels along the path or even all vessel segments along the path to the target position. One approach is to reduce the weighting of optical foreshortening with increasing distance from the anchor point within the vessel structure. Alternatively, especially when contrast agent is administered, the entire path to the target position may be relevant, in which case the weighting can be set the same along the entire path.

[0025] Since users typically want the instrument in the center of the image, a first term can also facilitate the instrument's visibility in the center of a projection image captured with the projection geometry. For example, a central area within which the instrument is acceptable can be defined. This can also be implemented as a boundary condition.

[0026] The visible length of vessels along the path from the support point to the target position can also be maximized using a suitable first term. This can be used in addition to, or as an alternative to, minimizing optical foreshortening. Thus, a projection geometry can be sought that best shows the entire remaining path from the support position to the target position. This is particularly useful for contrast agent injections, where more than just the immediate vicinity of the instrument is relevant.

[0027] Further first terms can aim to minimize the dose exposure, both for the patient and for at least one treatment and / or operating person. Certain arrangements of the X-ray tube and the X-ray detector, for example, result in a higher dose exposure for the patient and especially for users, particularly the person performing the procedure (treatment person) and / or a technical assistant (operator). Such arrangements can be avoided by means of appropriate first terms. Dose models and similar methods, which specifically take scatter radiation into account, can be used for this purpose, as well as dose distributions specified or known for specific projection geometries, for example, in lookup tables or similar.Similar approaches are known, for example, from dose monitoring and can also be used in the optimization process.

[0028] It is also conceivable, additionally or alternatively, to use a term that minimizes the shadowing of at least part of the vascular structure, particularly the instrument and / or the path from the support point to the target position, by other structures, especially bones, of the subject. Thus, if the subject contains strongly shadowing structures, such as bones in the case of a patient, which could restrict image quality with regard to instrument guidance, the optimization process can also avoid such blockages via a suitable first term, for example, positioning the spine in the beam path to or from the instrument or the path. Information on the location of shadowing structures can be obtained, for example, from the aforementioned three-dimensional image dataset.

[0029] Preferably, for the second term, a change in projection geometry can be determined based on a change in at least one positioning parameter of the support, in particular its angulation angles, from one support point to the next. For example, if two angulation angles of a C-arm are used, a change can be detected, in particular, if at least one difference between the projection angles of the adjacent support points is non-zero. For example, the second term can include a corresponding mathematical expression for counting such changes.

[0030] The second term can be chosen proportionally to the number of changes in projection geometry along the path. This allows for a particularly simple algorithmic implementation that highlights the essential aspect—the number of changes in projection geometry along the path—and, for example, incorporates correspondingly increasing penalty costs into the objective function. However, suitable designs can also provide that each change in projection geometry is weighted according to its magnitude. In particular, changes that result in a longer and / or more complex adjustment process can incur higher penalty costs than those that represent only minor corrections. Ultimately, this can also favor smaller adjustment paths and thus further contribute to efficiency.The strength of the change can be described via a distance measure of the projection geometries, for example corresponding differences in angulation angles, or can also take into account the actually necessary adjustment paths of the carrier.

[0031] Advantageously, for each projection geometry, at least one collimation parameter, which describes the collimation of the projection images to be recorded, and / or one zoom parameter, which describes the zoom of the projection images to be recorded, can be determined. Further first and / or third terms of the objective function and / or boundary conditions yet to be discussed can also relate, at least partially, to the collimation and / or the zoom, for example, as penalty terms if at least one element of the group medical instrument at the support point, vessel segment of the path on the path from the support point to the target position, and target position is not imaged. In this context, more distant vessel segments can result in lower penalty values ​​than closer vessel segments.

[0032] Preferably, at least one boundary condition can be used as a boundary condition term of the objective function and / or as an additional condition to be checked. Such boundary conditions (constraints) are generally known for optimization problems and can, for example, relate to technical limitations of the X-ray equipment, unavoidable objectives of two-dimensional projection imaging, and the like. Specifically, it can be stipulated, for example, that at least one of the at least one boundary condition is chosen from the group comprising: - a predetermined arrangement of the X-ray detector above the object being examined, - a collision-free movement path between two projection geometries of a change, - visibility of the path to the target position for each projection geometry, and - at least one limitation imposed by the design of the X-ray equipment. By positioning the X-ray detector above the object being examined, it is ensured that the X-ray source is located below the object being examined, and thus, in particular, below any table, especially the patient table, of the X-ray equipment. This also reduces the radiation exposure of users. The absence of collisions in the movement path between two projection geometries can be checked, for example, by means of a collision protection system in the X-ray equipment. For instance, the collision protection system can query whether the path is free of collisions. In this way, it can be ensured that the changeover can be carried out.If a user, especially the person performing the procedure, wants to see certain aspects in each projection image, such as the entire path to the target position alongside the instrument, a suitable boundary condition can be defined. Finally, as already mentioned, boundary conditions can also be used to account for technical limitations of the X-ray equipment itself. It should be noted that boundary conditions can also be integrated into the objective function as a penalty term.

[0033] In summary, a high-dimensional, non-convex optimization problem with boundary conditions can be addressed, which can be solved using a suitable algorithm to find the optimal path of projection geometries over the support points. In an exemplary, advantageous embodiment, a Viterbi algorithm and / or a forward-backward algorithm can be used to perform the optimization process. Such algorithms have the advantage of finding a global optimum, but they operate with discrete values ​​for the optimization parameters. For example, support values ​​for the optimization parameters can be used at intervals of 1° to 10° with respect to the angulation angles. However, other solution algorithms, such as gradient-based methods, are also available.

[0034] In order to use the determined positioning information in a simple way for the implementation of image monitoring, it can be provided that a current position of the instrument in the vessel structure is tracked, whereby when a support point is reached at which a change of the projection geometry takes place according to the optimized course, in particular after confirmation by a user, the positioning device is controlled by means of the positioning parameter set of the projection geometry to be set.

[0035] It should be noted at this point that the method according to the invention relates solely to the operation of the X-ray device and its adjustment for taking projection images. It does not include the procedure itself, nor the administration of contrast agents, if applicable.

[0036] For example, as already explained, the current position of the instrument can be continuously tracked by evaluating two-dimensional projection images, particularly fluoroscopy images, and / or by using the tracking system. This allows the system to recognize when reference points are reached and, consequently, when a change in projection geometry is optimal. The system can then suggest the new projection geometry to the user. If the user approves it, i.e., accepts the new settings, the new projection geometry can be automatically set using the positioning information. This new projection geometry can then be used to capture two-dimensional projection images, ideally suited for monitoring the instrument's movement, as needed.

[0037] In particularly useful advanced training, it can be provided that user confirmation occurs simultaneously with the release of X-ray radiation and / or upon activation of a foot pedal. This way, the user does not need to use any additional control beyond the one already used to release the X-ray radiation and acquire projection images, and which, being foot-operated, causes minimal distraction from the examination object. It is also conceivable that a single action could both accept the new projection geometry and authorize the acquisition of at least one two-dimensional projection image within it. This also reduces the number of interactions with the X-ray equipment.

[0038] Appropriate further training can also provide for a recalculation based on the user's chosen projection geometry, starting from the modified projection geometry, if the user deviates from the optimized path's projection geometry. This means that if the user adjusts the support structure differently than recommended for the optimized path, a new optimized path can be calculated, particularly in real time, based on the user's chosen projection geometry. This allows for the consideration of differing user settings and preferences while still providing excellent support throughout the process.

[0039] In addition to the method, the present invention also relates to an X-ray device comprising a carrier on which an X-ray emitter and an X-ray detector are arranged opposite each other, an actuating device for moving at least the carrier to set a projection geometry and a control device, wherein the control device comprises: - a first interface for providing a three-dimensional vascular model of a vascular structure of an object under investigation, describing the course of the vessel, in particular by means of midlines, from which projection images are to be taken with the X-ray device, wherein a target position of an instrument movable in the vascular structure is marked in the vascular model, - a second interface for providing a starting position of the instrument in the vascular structure of the vascular model, - a third interface for providing a path in the vascular structure of the vascular model from the starting position of the instrument to the target position, - a defining unit for defining control points along the path, and - a determination unit for determining an optimized progression of projection geometries for the support points in an optimization process of an objective function using the vessel model, wherein the objective function includes at least a first term relating to the optimization of the image content for a viewer with a medical instrument located at the respective support point, and also at least a second term that minimizes the number of changes of the projection geometry along the path by movement of the carrier, and for determining control parameters for controlling the control device for each projection geometry.

[0040] All descriptions of the method according to the invention can be applied analogously to the X-ray device according to the invention and vice versa, so that the advantages already recognized can also be obtained with this device. The control unit can have at least one processor and at least one storage medium. Functional units of the control unit can be formed by hardware and / or software.

[0041] The interfaces can also be, at least partially, internal interfaces. For example, the control unit can also include a tracking unit for determining the current position of the instrument, particularly using two-dimensional projection images from the X-ray unit and / or a tracking system of the X-ray unit. The tracking unit can provide this current position via the second interface as the starting position for the determination unit, as well as for other functional units of the control unit. Additionally or alternatively, the control unit can also include a path determination unit, which can receive the starting position via the second interface and the vessel model via the first interface in order to determine the path from the instrument's starting position to the target position through the vessel structure and provide it via the third interface.As is generally known, the control unit can also include a recording unit that performs the recording operation of the X-ray device, for example, for recording individual two-dimensional projection images, in particular fluoroscopy images, and / or a set of projection images for a three-dimensional image data set. For this purpose, the control unit can also include a corresponding reconstruction unit for reconstructing the three-dimensional image data set from the set of projection images.

[0042] With particular advantage, the control unit also features a monitoring unit for checking whether the tracked, current position of the instrument along the path reaches a point where the optimized path indicates a change in projection geometry, and a control unit for actuating the positioning device upon reaching such a point, especially after confirmation by a user, using the set of parameters for the newly set projection geometry. The monitoring unit can use the current position of the tracking unit, which is provided via the second interface. It can also be configured to monitor whether there is a user-initiated deviation from the projection geometries along the optimized path and, if so, initiate a recalculation according to the optimization process, starting from the set, deviating projection geometry.

[0043] The X-ray unit may also include operating and output devices. For example, the operating devices may include a foot pedal with which the acquisition of a two-dimensional projection image, particularly a fluoroscopy image, can be triggered. Such a foot pedal proves particularly useful in minimally invasive procedures on the patient, where a user guides the instrument within the patient. The foot pedal can also be used to confirm the setting of a new projection geometry. Projection images acquired within the optimized projection geometries, particularly fluoroscopy images, can, generally speaking, be displayed on an output device, such as a monitor.The generally known processing methods are conceivable here, for example, overlays with a three-dimensional preoperative image dataset and / or the vascular model, in addition to annotations, highlighting, or replacements, particularly of the detected instrument, and the like. The control unit can advantageously include an output unit for processing and outputting projection images acquired in the projection geometries along the optimized course. The output unit can preferably be configured to highlight the (remaining) path to the target position. In this context, changes in the projection geometry along the path can also be indicated, for example, by a change in the highlight color, a marker along the path, and the like.

[0044] A computer program according to the invention can be directly loaded into a storage medium of a control unit of an X-ray device and comprises program elements which, when the computer program is executed on the control unit, cause it to perform the steps of a method according to the invention. The computer program can be stored on an electronically readable data carrier according to the invention, which therefore includes control information stored thereon, comprising at least one computer program according to the invention and designed such that, when the data carrier is used in a control unit of an X-ray device, the control unit is configured to carry out the method according to the invention. The electronically readable data carrier can be a non-transient data carrier, for example, a CD-ROM.

[0045] Further advantages and details of the present invention will become apparent from the exemplary embodiments described below and from the drawings.

[0046] The figures show: Fig. 1 a flowchart of an embodiment of the method according to the invention, Fig. 2. An example sketch of a vessel structure with support points. Fig. 3. Schematically, a prepared projection image. Fig. 4 a schematic diagram of an X-ray device according to the invention, and Fig. 5 the functional structure of a control unit of the X-ray equipment.

[0047] Fig. Figure 1 shows a flowchart of an embodiment of the method according to the invention. This method serves to plan image monitoring during a minimally invasive procedure with an instrument, in particular a catheter, in a vascular structure, especially a section of a patient's blood vessel system as the object of examination, and to adjust an X-ray device for acquiring two-dimensional projection images, in particular fluoroscopy images, for image monitoring. The X-ray device, as a support for an imaging arrangement consisting of an X-ray tube and an X-ray detector, has a C-arm which, in this case, can be rotated about two axes by means of an adjusting device in order to set different projection geometries, here angulations of the C-arm. Each angulation is characterized by two angulation angles.It is also conceivable that the positioning device provides further or different adjustment options for the support. The X-ray unit also includes a collimation device assigned to the X-ray tube and a zoom device assigned to the X-ray detector. These, too, are adjustable via the positioning device.

[0048] The following steps are performed using a control unit of the X-ray system. In step S1, basic input information is received via a first and a second interface. A vessel model 1, which may be a planning result, is received via the first, in this case external, interface. The vessel model 1 can be derived from a three-dimensional image dataset acquired before or at the beginning of the procedure using at least one trained analysis function. This can be done, for example, by detecting the midlines of the vessel structure, which can also describe the course of the vessels or vessel segments in the vessel model 1. The three-dimensional image dataset may have been acquired with a different imaging device, such as a magnetic resonance imaging (MRI) and / or computed tomography (CT) scan.However, it can also be acquired using the X-ray equipment itself, for example by rotating the C-arm around the object being examined (C-arm CT). In the latter case, a registration to the coordinate system of the X-ray equipment for the vessel model 1 is already given; otherwise, a 2D-3D registration or 3D-3D registration can be image-based in the case of a C-arm CT scan, so that the vessel model 1 is ideally known in the coordinate system of the X-ray equipment.

[0049] In vessel model 1, a target position for the instrument has already been marked. In a minimally invasive procedure on a patient, the target position could be, for example, a thrombus to be removed or a feeding vessel for embolization.

[0050] Furthermore, in step S1, the instrument's initial position within the vascular structure is received via a second interface, with several possibilities. Firstly, the instrument's current position can be tracked in step S2. Two variants are conceivable for this in the X-ray system, which can also be used in combination. In one variant, it is possible to track the instrument in real time in two-dimensional projection images, such as fluoroscopy images, by registering the two-dimensional representation of the instrument in the fluoroscopy images with the three-dimensional representation of the vascular structure, i.e., vessel model 1. This approach takes advantage of the fact that the instrument must move within the vascular structure. Respiratory and cardiac movements, as well as potential deformation of the vessels due to the instrument itself, can be taken into account accordingly.Thus, the three-dimensional position of the instrument, preferably its tip (e.g., the catheter tip), is known. In another variant, a tracking system of the X-ray unit is used to monitor the three-dimensional position of the instrument. For example, electromagnetic and / or opto-acoustic systems can be employed. In this first variant, the current position of the instrument can be used as the second starting position. In this case, the second interface is therefore internal.

[0051] However, it is also possible to define the starting position 2 differently, for example, if the instrument has not yet been inserted into the object under investigation. In this case, a planned starting point within the object under investigation, which is easily accessible, can be used as starting position 2. Such a starting position can also be specified by the user during a planning phase.

[0052] In step S3, the vessel model 1 with the target position and the starting position 2 are used to determine a path through the vessel structure from the starting position 2 to the target position, for example, using a pathfinding algorithm. This can be the shortest possible path. The path is provided via a third interface, which in this example is internal.

[0053] Fig. Figure 2 schematically depicts a vascular structure 3, in this case a vascular tree as a section of a patient's vascular system. The vascular structure 3 comprises a multitude of vessels or vessel segments connected at bifurcations 4 (i.e., branching points / nodes) and represented by their midlines. Also shown are the starting position 2 and the target position 5, here exemplified as the supply vessel to a tumor that is to be treated with embolization. The path 6 from the starting position 2 to the target position 5 is shown in bold.

[0054] In step S4, 6 control points 7 are established along the path (compare Fig. 2) determined, preferably also using the starting position 2 and the target position 5 as support points 7. In any case, support points 7 are chosen at bifurcations 4, as Fig. 2 can be seen. Further support points 7 can also be used, for example at regular intervals between bifurcations 4, as shown here by way of example only between the last bifurcation 4 and the target position 5.

[0055] In step S5, compare again Fig. 1. An optimization process then takes place to determine an optimized path 9 of projection geometries along the support points 7 and thus along path 6. This can be based on a specific, predefined, projection geometry, or, particularly in the case of advance planning, a completely free choice can be made. The objective function for the optimization process, which here uses the Viterbi algorithm, contains not only initial terms that address the best possible recognizability of relevant features in two-dimensional projection images of the projection geometry, but also at least one second term that favors the fewest possible changes in projection geometry along path 6. The initial and second terms can be weighted to emphasize respective aspects, and this weighting can optionally be selected by the user.In this specific example, the previously mentioned angulation angles are used as optimization parameters, although other or different positioning parameters of the support, here the C-arm, can also be used. Furthermore, collimation parameters and a zoom parameter are expediently included; their optimization aspects can be contained in the first terms or represented by third terms. Finally, boundary conditions are also used, resulting in a high-dimensional, non-convex optimization problem with boundary conditions. Schematically, the optimization problem can be written such that the desired solution L, i.e., the optimized path (described by optimization parameters for each support point 7), is obtained as follows. L = argmin (first terms + second term) st boundary conditions.

[0056] The objective function (first terms + second term) can also contain third terms as well as boundary conditions formulated as boundary condition terms.

[0057] The first terms are chosen from the group encompassing - for support points 7 at and / or in a tolerance range around bifurcations 4 of the vessel structure 3, a term to minimize the deviation of the projection direction of the projection geometry from the cross product of the course direction of the vessels of the bifurcation 4 at the bifurcation according to the vessel model 1, - especially for support points 6 that are not located at a bifurcation 4 and / or outside the tolerance range, a term that minimizes the optical foreshortening of at least the vessel in which the support point 7 is located and / or all vessels of the path 6 from the support point 7 to the target position 5 visible in the projection geometry, particularly with increasing distance from the support point 7 in the vessel structure 3, - a term that favors visibility of the instrument in the center of a projection image captured with the projection geometry, - a term maximizing the visible length of vessels along path 6 from support point 7 to target position 5, - a term that minimizes the dose exposure for the subject of the investigation and / or at least one treatment and / or operating person, and - a term minimizing the shadowing of at least part of the vascular structure 3, in particular the instrument and / or the path 6 from the support point 7 to the target position 5, by other structures, in particular bones, of the object under investigation.

[0058] It should be noted at this point that, particularly when a contrast agent is to be administered, the terms relating to optical foreshortening or visible length are preferably chosen in such a way that the entire remaining path 6 to the target position 5 is best represented.

[0059] The second term can be chosen proportionally to the number of changes in projection geometry along path 6 caused by movement of the support, i.e., the C-arm. In exemplary embodiments, each change in projection geometry can be weighted with a change magnitude. Changes in projection geometry can be identified by the fact that the difference between identical optimization parameters, here angulation angles, at adjacent support points 7 is not equal to zero.

[0060] Regarding the collimation parameters and / or the zoom parameter, a choice can be made, for example, to remove as many features or image components as possible that are not relevant for guiding the instrument, such as everything except the instrument (which is assumed to be at the respective support point 7), the target position 5 and the vessels between the two.

[0061] Boundary conditions may, for example, include a predetermined arrangement of the X-ray detector above the object under investigation, a required collision-free movement path between two projection geometries of a change, visibility of the path 6 to the target position 5 for each projection geometry and / or at least a limitation given by the technical design of the X-ray device.

[0062] In the situation of Fig. 2. For example, up to bifurcation area 8, where a vessel branches downwards, all vessel courses and bifurcations 4 can be depicted with sufficiently high quality using a specific, fixed projection geometry. However, this geometry must be changed at bifurcation area 8 in order to represent this bifurcation 4, if possible, in such a way that the vessels run at least approximately parallel to the image plane of a recorded two-dimensional projection image. This necessary change in projection geometry can be represented accordingly in the optimized path 9 (see Figure 1). Fig. 1), which is the result of the optimization process in step S5. For each of the projection geometries to be used, corresponding positioning information for the actuator is also provided in step S5 so that it can then be controlled directly.

[0063] In the present example, a global optimum can be found using the Viterbi algorithm, although discrete values ​​are used for the optimization parameters, for example, angles at intervals of 1° to 10°. Other solution methods can also be used.

[0064] In the further course of the procedure, the first projection geometry is automatically set in step S6, if necessary. In this projection geometry, two-dimensional projection images, such as fluoroscopy images, can then be acquired in step S7, possibly upon request from a user via a foot pedal on the X-ray unit. In this process, step S8 continuously checks, using the current position of the instrument provided by tracking step S2, whether a reference point 7 is reached at which the optimized path 9 indicates a change in the projection geometry.If this is the case, the new projection geometry to be set is suggested to the user, who can then accept it, again using the aforementioned foot pedal or another control device, and thus enable the automatic setting according to the corresponding setting information in step S9. Preferably, the foot pedal can be used to enable both the automatic setting of the new projection geometry and the acquisition of further two-dimensional projection images, in particular fluoroscopy.

[0065] However, since it is also possible that a user deliberately deviates from the suggested projection geometry, this can be checked in step S10. If a deviation is detected, a new optimization process is started in step S5, where the starting position 2 is now the current position of the instrument and the user-defined projection geometry is used as the basis.

[0066] If step S8 determines that no change in projection geometry is necessary, or if step S10 determines that there is no user-initiated change to the projection geometry, the process returns to step S7, i.e., the acquisition of two-dimensional projection images, if necessary upon request.

[0067] The projection images acquired in step S7 are displayed on an output device, such as a monitor of the X-ray unit, in a step not shown for clarity. At this stage, the two-dimensional projection images can be further processed, for example, by highlighting the instrument and / or the (remaining) path 6. This processing can also alert the user to upcoming changes in projection geometry along path 6.

[0068] Fig. Figure 3 shows an example of a processed projection image 10. The instrument 11, specifically its tip, is highlighted. The instrument 11 is located at a bifurcation 4, which, due to the optimized course 9 of the projection geometries, is conveniently viewed from such a position that the corresponding vessels deviate only slightly from parallel to the image plane. The further path 6 to the target position 5 is also highlighted. A symbol 12 indicates that a change in projection geometry is imminent in a bifurcation area 8. The tumor 13 to be treated in this example is also visible.

[0069] Instrument 11 is positioned as centrally as possible, as requested by many users and facilitated by a suitable first term and / or boundary condition.

[0070] The process ends when target position 5 is reached.

[0071] Fig. Figure 4 shows a schematic diagram of an X-ray device 14 according to the invention. This device has a C-arm 15 as its support, which is held on a stand 16 and can be moved into various angulations via an adjusting device 17, as schematically indicated by the arrow 18. Opposite each other on the C-arm 15 are an X-ray source 19 with a collimator 20, which is also adjustable via the adjusting device 17, and an X-ray detector 21. An object 22, here a patient 23, can be positioned on a patient table 24.

[0072] In addition to a control unit 25 for controlling the operation of the X-ray device 14, this also includes a collision protection system 26 for preventing collisions between components of the X-ray device 14 and other components, persons, and / or other objects, as is generally known in the prior art. The collision protection system 26 can, for example, provide information on whether a change between projection geometries is possible without collision. Furthermore, a tracking system 27 is provided for the instrument 11 (only indicated here), which serves to determine its position and can operate, for example, electromagnetically or opto-acoustically.

[0073] A monitor 28, serving as an output device 29, can be used to display clearly visible projection images 10, particularly fluoroscopy images, from a surgical position on the patient 23. Simple user inputs can be made using a foot pedal 30, serving as an operating device 31, for example, to release radiation for the acquisition of projection images and / or to confirm a proposed projection geometry.

[0074] Of course, the X-ray device 14 can also have other components, such as sensors for dose monitoring as well as other operating devices and / or output devices.

[0075] Fig.Figure 5 shows the functional structure of the control unit 25 in more detail with regard to some functional units. In addition to a storage medium 32, the control unit 25 initially comprises a first interface 33, which in this case is an external interface. The vessel model 1 can be received via the first interface during step S1. A tracking unit 34 uses two-dimensional projection images acquired according to step S2 and / or the tracking system 27 to provide a current position of the instrument 11, in particular of its instrument tip, via a second, here internal, interface 35 (again, in particular during step S1).

[0076] A path determination unit 36 ​​uses the current position as starting position 2 and the vessel model 1 with the target position 5 to determine the path 6 from the starting position 2 to the target position 5 according to step S3. This path is provided by a third, again internal, interface 44. In a setting unit 37, the support points 7 are then defined according to step S4. In a determination unit 38, the optimization process can then take place according to step S5, in particular together with the determination of corresponding positioning information.

[0077] A control unit 39 uses the positioning information to adjust the projection geometries of the optimized path 9 according to steps S6 and S9. As is generally known, projection images can be acquired using a recording unit 40, particularly also in step S7. In the case of three-dimensional acquisitions (C-arm CT), a reconstruction unit 41 can be used to reconstruct three-dimensional image datasets from projection images.

[0078] If instrument 11 is located at a different current position along path 6, as provided by tracking unit 34, a monitoring unit 42 can, according to step S8, monitor whether a change in projection geometry is pending according to the optimized path 9 and trigger the corresponding actions. Monitoring unit 42 can also, according to step S10, monitor whether the user deviates from the projection geometries of path 9.

[0079] Finally, the control unit 25 can also have an output unit 43 in which processed projection images 10 can be determined, in particular with additional marking of positions for changing projection geometries.

[0080] The control unit 25 can of course also have further functional units, which are not shown in detail here for the sake of clarity, for example a user interaction unit with regard to the foot pedal 30 or other operating means 31, a dose monitoring unit to provide information regarding corresponding first terms of the target function and the like.

[0081] This patent application aims to include persons of male, female or other gender identities, regardless of the grammatical gender of a given term.

Claims

[1] Computer-implemented method for operating an X-ray device (14) with a carrier on which an X-ray source (19) and an X-ray detector (21) are arranged opposite each other, and an actuating device (17) for moving at least the carrier, in particular a C-arm (15), to set a projection geometry, comprising the following steps: - Providing a three-dimensional vascular model (1) of a vascular structure (3) of an examination object (22) describing the course of the vessel, in particular by means of midlines, from which projection images are to be taken with the X-ray device (14), wherein a target position (5) of an instrument (11) movable in the vascular structure (3) is marked in the vascular model (1), - Providing a starting position (2) of the instrument (11) in the vascular structure (3) of the vascular model (1), - Providing a path (6) in the vascular structure (3) of the vascular model (1) from the starting position (2) of the instrument (11) to the target position (5), - Establishing control points (7) along the path (6), - Determination of an optimized progression (9) of projection geometries for the support points (7) in an optimization process of an objective function using the vessel model (1), wherein the objective function, in addition to at least a first term relating to the optimization of the image content for a viewer with the instrument (11) located at the respective support point (7), also includes at least a second term that minimizes the number of changes of the projection geometry along the path (6) by movement of the support, and - Determination of positioning parameters for controlling the positioning device (17) for each projection geometry. [2] Method according to claim 1, characterized by, that the vessel model (1) to be provided is determined from a three-dimensional image data set of the object under investigation (22), which is or will be registered with a coordinate system of the X-ray device (14). [3] Method according to claim 1 or 2, characterized by , that the starting position (2) is determined as the current position of the instrument (11) from two-dimensional projection images, in particular fluoroscopy images, at least one current projection geometry, in particular using the vessel model (1) and / or three-dimensional image data set, and / or using a tracking system (27) of the X-ray device (14). [4] Method according to any of the preceding claims, characterized by, that support points (7) are determined at least at nodes of the vascular structure (3) where several vessels meet, in particular at bifurcations (4) and / or are chosen at least partially at a certain distance along at least one midline of a vessel of the path (6). [5] Method according to any of the preceding claims, characterized by , that at least one of the at least one first term is chosen from the group comprising: - for support points (7) at and / or in a tolerance range around bifurcations (4) of the vessel structure (3) a term to minimize the deviation of the projection direction of the projection geometry from the cross product of the course direction of the vessels of the bifurcation (4) at the bifurcation according to the vessel model (1), - especially for support points (7) that are not located at a bifurcation (4) and / or outside the tolerance range, a term that gives less weight to, minimizes, the optical foreshortening of at least the vessel in which the support point (7) is located and / or of all vessels visible in the projection geometry of the path (6) from the support point (7) to the target position (5), especially with increasing distance from the support point (7) in the vessel structure (3), - a term that favors the visibility of the instrument (11) in the center of a projection image taken with the projection geometry, - a term maximizing the visible length of vessels along the path (6) from the support point (7) to the target position (5), - a term minimizing the dose exposure for the subject of the investigation (22) and / or at least one treatment and / or operating person, and - a term minimizing the shadowing of at least part of the vascular structure (3), in particular the instrument (11) and / or the path (6) from the support point (7) to the target position (5), by other structures, in particular bones, of the object under investigation (22). [6] Method according to any of the preceding claims, characterized by , that the second term is chosen proportionally to the number of changes in projection geometry along the path (6) and / or each change in projection geometry is weighted with a strength of change. [7] Method according to any of the preceding claims, characterized by , that for the second term a change in the projection geometry is determined by means of a change in at least one positioning parameter of the support, in particular its angulation angles, from one support point (7) to the next. [8] Method according to any of the preceding claims, characterized by, that for each projection geometry at least one collimation parameter, which describes the collimation of the projection images to be recorded, and / or one zoom parameter, which describes the zoom of the projection images to be recorded, is determined. [9] Method according to any of the preceding claims, characterized by , that at least one boundary condition is used as a boundary condition term of the objective function and / or as an additional condition to be checked. [10] Method according to any of the preceding claims, characterized by , that a current position of the instrument (11) in the vascular structure (3) is tracked, wherein, upon reaching a support point (7) at which a change of the projection geometry according to the optimized course (9) takes place, in particular after confirmation by a user, the positioning device (17) is controlled by means of the positioning parameter set of the projection geometry to be set. [11] Method according to claim 10, characterized by , that the user confirmation occurs together with the release of X-rays and / or upon activation of a foot pedal (30). [12] Method according to any of the preceding claims, characterized by , that in the event of a user-initiated deviation from the projection geometries of the optimized route (9), a recalculation is carried out according to the optimization process starting from the set deviating projection geometry. [13] X-ray device (14) comprising a carrier on which an X-ray emitter (19) and an X-ray detector (21) are arranged opposite each other, an actuating device (17) for moving at least the carrier to set a projection geometry and a control device (25), wherein the control device (25) comprises: - a first interface (33) for providing a vessel model (1) of a vessel structure (3) of an examination object (22) that describes the course of the vessel, in particular by means of midlines, in three dimensions, from which projection images are to be taken with the X-ray device (14), wherein a target position (5) of an instrument (11) movable in the vessel structure (3) is marked in the vessel model (1), - a second interface (35) for providing a starting position (2) of the instrument (11) in the vascular structure (3) of the vascular model (1), - a third interface (44) for providing a path (6) in the vascular structure (3) of the vascular model (1) from the starting position (2) of the instrument (11) to the target position (5), - a defining unit (37) for defining support points (7) along the path (6), and - a determination unit (38) for determining an optimized progression (9) of projection geometries for the support points (7) in an optimization process of an objective function using the vessel model (1), wherein the objective function, in addition to at least one first term relating to the optimization of the image content for a viewer with the instrument (11) located at the respective support point (7), also includes at least one second term that minimizes the number of changes of the projection geometry along the path (6) by moving the carrier, and for determining control parameters for controlling the control device (17) for each projection geometry. [14] Computer program comprising programming means which, when the computer program is executed on a control device (25) of an X-ray device (14), causes the latter to execute a method according to any one of claims 1 to 12. [15] Electronically readable data carrier on which a computer program according to claim 14 is stored.

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