Trajectory of a C-arm of a C-arm system

Abstract

A method for controlling a C-arm (2) of a C-arm system (1) is described. In this method, a forward rotation of the C-arm (2) is performed. The forward rotation is initiated at a starting position (SPv) of the forward movement of the C-arm (2) with a lateral offset (lv) of a first offset value (-D). The C-arm is then rotated forward to an end position (EPv) of the forward movement, at which point the lateral offset (lv) is reduced to a value of 0. A reverse rotation of the C-arm (2) is then performed.The reverse movement is started at the end position (EPv) of the forward movement, and the C-arm (2) is rotated in the reverse direction to an end position (EPr) of the reverse movement, whereby the lateral offset (lv) is increased in the opposite direction to the lateral offset (lv) of the forward movement up to a second offset value (+D) at the end position (EPr) of the reverse movement. Furthermore, an imaging method for generating 3D image data (BD) of an object under investigation (O) is described. A control device (50) is also described. Additionally, a C-arm system (1) is specified.

Description

The invention relates to a method for controlling a C-arm of a C-arm system. In the method, a forward travel of a rotation of the C-arm and a reverse travel of a rotation of the C-arm take place. The invention also relates to an imaging method for generating 3D image data from an examination object. The invention further relates to a control device. Moreover, the invention relates to a C-arm system.With the aid of modern imaging methods, two- or three-dimensional image data are generated, which can be used for visualizing an imaged examination object and, in addition, also for further applications.The imaging methods are often based on the detection of X-ray radiation. An X-ray system usually comprises an X-ray source and an X-ray detector opposite the X-ray source. During imaging, an examination object, in particular a patient, is positioned in the interspace between the X-ray source and the X-ray detector, from which an image recording is to be carried out. One type of X-ray system relates to so-called C-arm systems. In these X-ray systems, the X-ray source and the X-ray detector, usually a flat detector, are fastened to a c-shaped carrier element, also called a C-arm. Due to its shape, the C-arm and with it the associated diagnostic and treatment device or the X-ray detector can be moved orbitally around a point of a patient to be examined or treated, in order to achieve different angular positions between the patient and the diagnostic or treatment device or X-ray detector without having to rearrange the patient.If a subregion to be examined or treated is to be imaged from another position or if the imaging system or the X-ray detector is to be carried along during imaging of a larger region of the examination object, the C-arm is rotated, for example, about a support axis which is connected to the C-arm in the middle.3D imaging with the aid of C-arm angiography devices has meanwhile been established in the interventional environment. However, a significant limitation compared to the conventional CT system is the imaging range limited by the size of the flat detector. The limited imaging range has the consequence that many organs (e.g. lung, liver) cannot be detected with a single recording. In addition, the projection data for almost all body regions are laterally cut off or truncated, which leads to image artifacts (truncation artifacts) in conventional reconstruction methods.Solutions clinically used up to now for C-arm 3D imaging with a large imaging range assume that the relative position of the focal point (i.e. the point of impact of the electrons on the anode of the X-ray source or the point from which the X-ray photons of the X-ray radiation are emitted) to the measurement object (patient) is identical. In the existing large volume protocols on robotic systems, the focal point travels on a circular trajectory around the patient. Therefore, the distance from the patient remains the same. For angiography systems with a rigid C-arm, this requires that the isocentre point of the C-arm during rotation around the patient in the plane of rotation be laterally displaced dynamically in both directions, which is possible only by a complex robot mechanism.For classic isocentre angiography systems, a trajectory with a laterally displaced isocentre point is used. Forward and backward travel are carried out and additional one-dimensional lateral movements are simultaneously carried out in the plane of rotation. This trajectory, which is depicted in FIG. 2, makes far less demands on the mechanical construction of a C-arm system and enables large 3D mapping regions even in the case of C-arm systems of simple construction. However, the trajectory shown in FIG. 2 still has practical disadvantages:The end point of the forward run does not correspond to the start point of the backward run. Therefore, the system must be moved between runs. This may result in a time delay of several seconds. Since the patient must stop breathing during the acquisition, the time delay should be kept as short as possible.The direction of movement in the lateral direction changes during a run. In the AP direction (AP is an acronym for "anterior-posterior"), the sign of the speed therefore changes in the lateral direction. This change can lead to unreproducible geometric inaccuracies, in particular in the case of typical ceiling-suspended systems. Since a very high geometrical accuracy of the recording is required for a 3D reconstruction, this can lead to image artifacts.The document DE 10 2020 209 703 A1 discloses a method for providing a 3D image data set of an examination object, wherein the 3D image data set can be reconstructed from first and second projection images. The document DE 10 2012 208 850 A1 discloses a method for recording radiation images using an X-ray apparatus, wherein a C-arm rotating about an isocenter during the image recording is moved in a direction perpendicular to a longitudinal direction of a patient bed during the image recording, and the movement is taken into account in a reconstruction of a radiation image from the recorded image data. US 2020 / 0 054 297 A1 discloses a system comprising a gantry with an X-ray source and an X-ray detector in opposition, wherein the gantry is rotatable relative to a carrier and the carrier is movable by means of a robot arm. The document DE 10 2011 086 754 A1 discloses a method for the rotational scanning of an object with a C-arm system, wherein the C-arm rotates around the object during the scanning and the rotational movement comprises a circular movement and a displacement movement.It is therefore an object of the present invention to specify a method and a control device for driving a C-arm, with which the imaging can be carried out in a time-saving manner and with reduced image artifacts.This object is achieved by a method for driving a C-arm of a C-arm system according to claim 1, by an imaging method for generating 3D image data from an object under examination according to claim 10, by a control device according to claim 11 and by a C-arm system according to claim 12.In the method according to the invention for controlling a C-arm of a C-arm system, preferably a ceiling-suspended C-arm system, a forward movement of a rotation of the C-arm is carried out, as already mentioned at the beginning. The forward travel is started at a start position of the forward travel of the C-arm with a lateral offset with a first offset value. A lateral offset is to be understood as a displacement of the C-arm in the horizontal direction transversely to the patient bed. The focal point of the X-ray source of the C-arm system is thus also shifted in the transverse direction. Then, the C-arm is rotated in the forward direction to a forward running end position, and the lateral offset is monotonously reduced to a value of 0. The end point of the forward travel has a predetermined value of an orbital angle β in addition to the value of 0 for the offset. As will be explained in more detail later, the value for the orbital angle of the starting point and the end point is selected such that a sufficiently extended angular range around the examination object can be covered by imaging. Values for orbital angles β of the starting points and ending points of the forward travel of at least 90° and -90° are preferred. Values for orbital angles β of the starting points and ending points of the forward travel of 100° and -100°, respectively, are particularly preferred. Likewise preferred are values for orbital angles β of the starting points and ending points of the forward travel, which lie in interval ranges of [90°, 120°] or [-90°, - 120°]. For mechanical reasons, in particular a ceiling suspended system cannot travel along any desired angulations. It would possibly be possible to shift the start / end angles up to 20° (from the ideal value=100°), and furthermore the system cannot usually rotate mechanically.As likewise mentioned at the beginning, a reverse rotation of a rotation of the C-arm is subsequently carried out, that is to say a rotation in the (rotational) direction opposite to the direction of the forward rotation. At this time, the backward travel is first started at the forward travel end position, and then the C-arm is rotated in the backward direction to a backward travel end position. In the rotation, the lateral offset in the opposite direction to the lateral offset of the forward travel is monotonically increased up to a second offset value at the end position of the rearward travel. "Increased" is intended to refer to an increase in an amount of the lateral offset. Thus, for example, if the lateral offset is positive during the forward travel, the lateral offset is negative during the rearward travel. If the lateral offset is negative in the forward run, the lateral offset is positive in the reverse run. The trajectory of the forward travel and of the backward travel advantageously differ, so that additional image information can be obtained from a patient during the backward travel.In contrast to conventional driving methods, in the method according to the invention, the end point of the forward travel corresponds to the start point of the backward travel. Advantageously, the C-arm does not need to be moved between the forward travel and the reverse travel. Since the patient must stop his breath during the recording, a time delay between the forward run and the backward run is advantageously avoided or kept as short as possible.In addition, it is advantageously achieved that the direction of the movement of the C-arm in the lateral direction is not changed during a run, that is to say during the forward run and during the backward run.Such a change in the direction of movement during a run, in particular in the case of typical ceiling suspended systems, can lead to unreproducible geometric inaccuracies in the conventional procedure. Since a very high geometrical accuracy of the recording is required for a 3D reconstruction, these inaccuracies can lead to image artifacts. Advantageously, such image artifacts are now avoided, since the direction of movement during the lateral movement of the C-arm is retained within the movement sequence of the forward movement and within the movement sequence of the backward movement.In the imaging method according to the invention for generating 3D image data from an object under examination, projection data from the object under examination are acquired by using the method for driving a C-arm of a C-arm system, and 3D image data are reconstructed on the basis of the acquired projection data. Advantageously, 3D image data of an object under examination, preferably a patient, can be obtained with improved quality with the imaging method according to the invention.The control device according to the invention has a starting unit for controlling a starting position of a C-arm in a forward run of a rotation of the C-arm with a lateral offset with a first offset value and for starting the forward run at the starting position of the forward run and for starting a reverse run of a rotation of the C-arm at an end position of the forward run.The control device according to the invention also has a rotation unit for rotating the C-arm in forward travel in the forward direction up to the end position of forward travel, wherein the lateral offset is reduced to a value of 0, and for rotating the C-arm in backward travel in the backward direction up to an end position of backward travel, wherein the lateral offset in the opposite direction to the lateral offset of forward travel is increased up to a second offset value at the end position of backward travel. The control device according to the invention shares the advantages of the method according to the invention for controlling a C-arm of a C-arm system.The C-arm system according to the invention comprises a C-arm, preferably a C-arm support element, which is rotatable or pivotable about at least one rotational or pivot axis. In addition, the C-arm system according to the invention comprises an X-ray source which is arranged at a first end of the C-arm, preferably of the C-arm carrier element, and an X-ray detector which is arranged opposite the X-ray source at a second end of the C-arm. In addition, the C-arm system according to the invention comprises the control device according to the invention. The C-arm system according to the invention shares the advantages of the method according to the invention for controlling a C-arm of a C-arm system.A large part of the aforementioned components of the control device and of the C-arm system can be realized wholly or partly in the form of software modules in a processor of a corresponding computing system. A realization largely through software has the advantage that even previously used computing systems can be easily retrofitted with a software update in order to operate in the manner according to the invention. In this respect, the object is also achieved by a corresponding computer program product having a computer program which can be loaded directly into a computing system, having program sections in order to carry out the steps of the method according to the invention for controlling a C-arm of a C-arm system when the program is executed in the computing system. In addition to the computer program, such a computer program product can optionally comprise additional components, such as documentation and / or additional components, also hardware components, such as hardware keys (dongles, etc.) for using the software.For transport to the computing system or to the control device and / or for storage on or in the computing system or the control device, a computer-readable medium, e.g. a memory stick, a hard disk or another transportable or permanently installed data carrier, can be used, on which the program sections of the computer program that can be read in and executed by a computing system are stored. For this purpose, the computing system can have one or more cooperating microprocessors or the like, for example.The dependent claims and the following description each contain particularly advantageous embodiments and further developments of the invention. In this case, in particular, the claims of one claim category can also be developed analogously to the dependent claims of another claim category. In addition, within the scope of the invention, the various features of different exemplary embodiments and claims can also be combined to form new exemplary embodiments.In one embodiment of the method according to the invention for controlling a C-arm of a C-arm system, the start position of the forward movement of the C-arm has a first angular position. Furthermore, the end position of the forward travel has a second angular position and the end position of the rearward travel has a third angular position. In this case, the first angular position and the second angular position and the third angular position preferably have an angle with the same absolute value. Advantageously, a symmetrical angle range is traversed by the C-arm and thus also by the X-ray detector and the X-ray source during the forward travel and the backward travel. Advantageously, a patient lying on a patient couch symmetrically to the AP position (anterior-posterior position, the patient is irradiated from the vertical direction, the orbital angle is 0°) can be imaged from both sides from the respective angle of equal amount.In order to acquire sufficient data for a 3D reconstruction, at least one arc must be traversed at an angle of 200°. It is thus possible to rotate along an arc of 100° "left" and "right" of the AP plane. For mechanical reasons, in particular a ceiling suspended system cannot travel along any desired angulations. It may be possible to shift the start / end angles up to 20°, and the system may not rotate mechanically.Preferably, the first angular position has an angle of 100°, the second angular position has an angle of -100° and the third angular position has an angle of 100°. Advantageously, image data can be obtained from an angle range of 200°, so that an examination region or examination object can be imaged from different directions. Advantageously, the image information acquired from different directions can be combined to form a 3D image from the examination region.Thus, an orbital angle of 100° is preferably used as the starting position of the forward travel, and an orbital angle of -100° is preferably used as the ending position of the forward travel. Further, an orbital angle of -100° is used as the start position of the backward travel, and an orbital angle of 100° is used as the end position of the backward travel. As already mentioned above, at least an angular range of 200° should preferably be traversed for the forward running and the reverse running. Likewise preferably, the traversed angular range should lie in a value range from 180° to 240 degrees, particularly preferably in a value range from 190° to 210°.Particularly preferably, the first offset value and the second offset value have the same amount. Since patients are typically approximately symmetrical to the sagittal plane, it is reasonable to use an offset that is uniform in both directions.In a likewise particularly preferred variant of the method according to the invention for controlling a C-arm of a C-arm system, during the forward travel, the rotation of the C-arm in the forward direction comprises the following steps:maintaining the first offset value of the lateral offset in the forward travel between the start position and an AP position,gradually reducing the lateral offset between the AP position and a lateral position to the value 0,maintaining the lateral offset of 0 from the range of the lateral position to the end position of the forward run.Advantageously, the first offset value used for the lateral offset at the start of the forward travel is continuously reduced to the lateral position, so that uniform imaging is enabled.Alternatively, the offset in the forward travel can be reduced to the value 0 not already at the lateral position, but only until the end position. A continuous change of the offset up to the end position is advantageously achieved.Preferably, in the backward travel, rotating the C-arm in the backward direction comprises:maintaining the lateral offset of 0 in the range from the end position of the forward run to the lateral position,gradually increasing the lateral offset during rotation in the positive lateral direction between the lateral position and the AP position to a final value, wherein the lateral offset is formed in the opposite direction compared to the lateral offset of the forward travel,maintaining the offset between the AP position and the end position of the reverse travel.Advantageously, no offset change takes place in the "right" quadrant, i.e. in the forward run and in the reverse run. This is because a change in offset present in the right quadrant would have to be compensated for by a movement in the reverse direction in the left quadrant. When the displacement change passes in both directions during travel, there is a disadvantage described in that the direction of movement changes in the lateral direction during travel as in the conventional trajectory shown in FIG. 2. Therefore, it is preferable to set the displacement in a direction before the start of rotation, so that during the rotation in the right quadrant, the displacement is not changed, and when returning, the displacement is simply left the same to the end.In a likewise preferred variant of the method according to the invention for controlling a C-arm of a C-arm system, the maximum value of the lateral offset depends on the detector width. The maximum lateral offset should be chosen so that the image recordings recorded from the same angle during the forward run and the backward run are connected. If the same value is selected as the maximum lateral offset in the forward run and in the reverse run, but with opposite signs, the offset should be at most half as large as the detector width. If the maximum lateral offset is smaller, an overlap region is produced between the image data of the forward run and the backward run, which were recorded with the same orbital angle. Advantageously, adjacent image recordings can be more easily combined due to the overlap.Likewise preferably, in the method according to the invention for controlling a C-arm of a C-arm system, the maximum value of the lateral offset depends on the overlap of the X-ray detector in the forward travel and in the reverse travel. The overlap can assume values from 0 to 1. Here, a value of "0" means that there is no overlap, and a value of "1" means that the images taken with a C-arm posture having the same orbital angle in the forward travel and the backward travel completely overlap. A larger overlap allows a "softer" transition between the image data of the two image volumes of the forward travel and the backward travel, which were acquired from the same orbital angle. The two image volumes can be merged by interpolation on the basis of the redundant image data.Particularly preferably, the value of the maximum lateral offset is determined from the product of the detector width and the difference between the value 1 and the value of the overlap of the X-ray detector in the forward travel and in the reverse travel at the same orbital angle.The value of the maximum lateral offset D is thereby obtained asIn this case, w is the width of the X-ray detector and ol is the overlap between the two image recordings in the two vertices-or generally formulated-in the case of an image recording with the same orbital angle. As already mentioned, the overlap between the values 1 and 0 can be selected.The maximum lateral offset D also corresponds to half the distance between the two vertices of the trajectories of the C-arm of the forward travel and of the backward travel.In a preferred embodiment of the method according to the invention for controlling a C-arm of a C-arm system, the C-arm is displaced from the usual 3D start position by the necessary maximum lateral offset lv=-D before the start of the acquisition. In the forward travel between the starting angle 100° and the AP position with an orbital angle β of 0°, the lateral offset lv remains at lv=-D."AP" is an abbreviation for "anterior-posterior" and describes a frontal image recording of a patient at a position or orientation or an orbital angle β=0°, wherein the patient is in a lying position and the connecting line between the X-ray source and the X-ray detector is oriented vertically. The AP position generally also corresponds to the apex of the respective trajectory in the forward travel and the backward travel. A starting angle or orbital angle of 100° means that the connecting line between the X-ray source and the X-ray detector is rotated beyond a lateral orientation at the start, in order to be able to travel over an increased angular range during the C-arm recording and thus to obtain additional spatial information about the examination region of the patient to be imaged. The examination region to be imaged is recorded at a starting angle of 100°, viewed obliquely from below.Between an orbital angle of 0°, i.e. the AP position, and an orbital angle of -90°, i.e. a lateral orientation of the connecting line between the X-ray source and the X-ray detector, the lateral offset of the C-arm during the rotation in the positive lateral direction is reduced to a lateral offset lv=0 and remains in the range of the orbital angle of -90° up to the final angle of -100° at a lateral offset lv=0. In the return, the lateral offset lv remains at the value 0 in the range of an orbital angle of -100° to -90°. Between an orbital angle of -90° and 0°, i.e. between a lateral orientation and an anterior-posterior orientation, the lateral offset lv is increased during the rotation in the positive lateral direction to a value lv=+D. Between an orbital angle β of 0° and 100°, the lateral offset lv remains at a value lv=+D.For the forward movement, the focal point of the X-ray source of the C-arm preferably describes the following trajectory a 1:for β>0°:for -90° < β < 0°:for β < - 90°:For the backward movement, the focal point of the X-ray source of the C-arm preferably describes the following trajectory a 2:for β>0°:for -90° < β < 0°:for β < - 90°:The orbital angle β describes the following curve:The value SCD specifies the distance between the X-ray source and the center of the C-arm system, i.e. the center in which the examination object or in particular the patient lies.A reconstruction of 3D image data can be carried out on the basis of the projection data recorded according to one of the variants of the method according to the invention using the trajectories a 1, a 2 according to the invention, as described in DE 10 2020 209 703 A1.The invention is explained in more detail below with reference to the attached figures on the basis of exemplary embodiments. The following are shown: FIG. 1 is a schematic illustration of a conventional C-arm system, FIG. 2 shows a schematic illustration of a conventional trajectory of a C-arm of a C-arm system, FIG. 3 shows a schematic illustration of a trajectory of a C-arm of a C-arm system according to an exemplary embodiment of the invention, FIG. 4 is a flow chart illustrating a method for driving a C-arm of a C-arm system, FIG. 5 shows a schematic illustration of a control device according to an exemplary embodiment of the invention, FIG. 6 is a flow chart illustrating an imaging method for generating 3D image data from an object under examination according to an embodiment of the invention.In FIG. 1, a C-arm system 1 according to a first exemplary embodiment of the invention is illustrated. The C-arm system 1 comprises a c-arm support element 2, also referred to for short as C-arm 2, on which an X-ray source 3 is arranged at one end of the C-arm 2, which is drawn as the lower end in FIG. 1, i.e. the end facing away from the ceiling DE of a room on which the C-arm system 1 is suspended, and an X-ray detector 4 is arranged at the other end of the C-arm 2, which is drawn as the upper end in FIG. 1, i.e. the end facing the ceiling DE.Between the X-ray source 3 and the X-ray detector 4 a patient couch L is arranged on which a patient O to be examined is arranged. The C-arm 2 is connected by a C-arm suspension 5 to a base 6, which is fastened to the ceiling DE. During an image recording of the patient O, X-rays are emitted by the X-ray source 3 and captured by the X-ray detector 4 of the C-arm system 1.The captured measurement signals or measurement data obtained therefrom are used for image reconstruction.FIG. 2 shows a schematic representation 20 of a conventional trajectory of a C-arm of a C-arm system. Forward and backward travel are carried out and additional one-dimensional lateral movements are carried out in the plane of rotation. The forward travel starts at the starting point SP v of the forward travel shown on the right side of the graph in FIG. 2 at an orbital angle β=100° with a lateral offset lv of -D*cos (100°), where D is the maximum lateral offset. At orbital angle β= 90°, the lateral offset is lv=0. Up to an orbital angle β of 0°, a lateral offset lv=-D is continuously built up. Then, the focus of the AP position AP reaches v of the forward run, i.e., the point having the highest y value, i.e., the apex of the forward run. Subsequently, the lateral offset lv up to the orbital angle β=-90° is reduced to a value of 0. At the forward travel end point EP v the lateral offset lv is again at a value of -D*cos (-100°).Then, the focal point of the C-arm is shifted to the start point SP r of the backward travel. This focal point is at an orbital angle β=-100°. The lateral offset lv is at a value of +D cos (-100°). At orbital angle β=-90°, lateral offset lvis the value 0. Subsequently, the lateral offset lv up to the orbital angle increases from 0° to the value +D. Subsequently, the AP position AP r, i.e., the peak of the backward travel, is reached. Thereafter, the value of the lateral offset lv up to the orbital angle is reduced from 0° to 0 and is D*cos(100°) at the backward travel end point EP r.The trajectories shown in FIG. 2 place relatively low demands on the mechanical construction of a C-arm system 1 and enable large 3D imaging regions even in the case of significantly more cost-effective systems. The forward running end point EP v does not correspond to the backward running start point SP r. Therefore, the system must be moved between runs. This may result in a time delay of several seconds. Since the patient O must stop his breath during the recording, the time delay should be kept as short as possible. The direction of movement in the lateral direction changes during a run. Therefore, at the AP direction (β=0°), the sign of the speed of the offset of the focal point in the lateral direction changes. This change can lead to unreproducible geometric inaccuracies, in particular in the case of typical ceiling-suspended systems. Since a very high geometrical accuracy is required for a 3D reconstruction when acquiring the X-ray projection data on which the 3D reconstruction is based, this can lead to image artifacts.For the forward movement, the focal point of the X-ray source of the C-arm describes the following trajectory:For the backward movement, the focal point of the X-ray source of the C-arm describes the following trajectory:The orbital angle describes the following curve:Half the distance D between the two vertices or AP positions AP v, AP r or the maximum offset D results inIn this case, w is the width of the X-ray detector and ol is the overlap between the two image recordings in the two vertices or AP positions AP v, AP r.FIG. 3 shows a schematic representation 30 of a trajectory of a C-arm of a C-arm system 1 according to an exemplary embodiment of the invention.In this case, before the start of the acquisition, the C-arm is displaced from the usual 3D start position by the necessary lateral offset lv=-D. In the forward travel between the starting angle 100° and an orbital angle of 0°, the lateral offset lv remains at lv=-D. Between an orbital angle β=0° and β=-90° during the rotation in the forward direction, the offset lv is changed from the value -D to the value lv=0 and remains there in the range of the orbital angle β from -90° up to the final angle of -100°.In the backward travel, the lateral offset lv=0 is maintained in the range of an orbital angle β of -100° to -90°. Subsequently, the lateral offset lv between the orbital angle β of -90° and 0° or the AP position AP r of the backward travel increases to a value of +D. Thereafter, the lateral offset lv until the end point EP r of the backward travel is kept constant at its maximum value lv=+D.The trajectories a 1, a 2 of the forward travel and the backward travel are obtained from the formulae (2) to (7) which have been described in detail in the general part of the present patent application.FIG. 4 shows a flow chart which illustrates a method for driving a C-arm of a C-arm system 1 according to an exemplary embodiment of the invention.In step 4.I, the C-arm is displaced from the usual centered 3D start position by a lateral offset lv=-D before the start of the acquisition.In step 4.II, the lateral offset lv=-D in the forward travel between the starting angle 100° and the AP position of 0° is maintained.In step 4.III, the lateral offset lv between the orbital angles β is gradually reduced from 0° and -90° during the rotation in the positive lateral direction to a value of 0.In step 4.IV, the lateral offset lv=0 is maintained in the range of an orbital angle β from -90° to the final angle -100°.In step 4.V, the lateral offset of 0 in the backward movement is likewise maintained in the range of an orbital angle β of -100° to -90°.In step 4.VI, the lateral offset lv is gradually increased between an orbital angle β of between -90° and 0° during the rotation in the positive lateral direction to a value of +D.In step 4.VII, the lateral offset lv up to the orbital angle β=30°, i.e. up to the end point EP r of the backward travel, is maintained at the maximum offset lv=+D.FIG. 5 illustrates a schematic illustration of a C-arm system 1 with a control device 50 (marked with dashed lines) according to an exemplary embodiment of the invention. In addition to the control device, the C-arm system 1 also comprises a C-arm with an X-ray source and an X-ray detector (not shown).The control device 50 has a starting unit 51 for controlling a starting position SP v a C-arm 2 in a forward run of a rotation of the C-arm 2 with a lateral offset lv with a first offset value -D and for starting the forward run at the starting position SP v of the forward run. The starting unit 51 is also configured to start a reverse run of a rotation of the C-arm 2 at a forward run end position EP v which simultaneously represents the reverse run start position SP r.The controller 50 also includes a rotation unit 52 for rotating the C-arm 2 in the forward travel in the forward direction to the end position EP v of the forward travel, wherein the lateral offset lv is reduced to a value of 0.The rotation unit 52 is also configured to rotate the C-arm 2 in the backward direction in the backward direction up to an end position EP r of the backward movement, wherein the lateral offset lv in the opposite direction to the lateral offset lv of the forward movement is increased up to a second offset value +D at the end position EP r of the backward movement.During a forward travel and a backward travel, projection data PD are recorded from an examination object (not shown) by an X-ray detector (not shown) arranged on the C-arm 2.Part of the C-arm system 1 is also a reconstruction unit 53 which is configured to reconstruct projection data PD 3D image data BD acquired from an object under examination by the X-ray detector of the C-arm 2.FIG. 6 shows a flow chart 600 which illustrates an imaging method for generating 3D image data BD from an examination object O according to an exemplary embodiment of the invention.In step 6.I, projection data PD of the examination object O are acquired by applying the method for driving a C-arm 2 of a C-arm system 1.In step 6.II, 3D image data BD are reconstructed on the basis of the acquired projection data PD.Finally, it is pointed out once again that the described C-arm systems are merely preferred exemplary embodiments of the invention and that the invention can be varied by the person skilled in the art without departing from the scope of the invention, insofar as it is specified by the claims. For example, for the sake of completeness, it is also pointed out that the use of the indefinite article "a" or "an" does not exclude that the features in question can also be present multiple times. Likewise, the term "unit" does not exclude it being composed of a plurality of components which may optionally also be spatially distributed.Regardless of the grammatical sex of a certain term, individuals with male, female or other sex identity are included.

Claims

Method for controlling a C-arm (2) of a C-arm system (1), having the steps of: - carrying out a forward run of a rotation of the C-arm (2), comprising the substeps of: - starting the forward run at a start position (SP v) of the forward run of the C-arm (2) with a lateral offset (lv) with a first offset value (-D), - rotating the C-arm (2) in the forward direction up to an end position (EP v) of the forward run, wherein the lateral offset (lv) is reduced to a value of 0, - carrying out a backward run of a rotation of the C-arm (2), comprising the substeps of: - starting the backward movement at the end position (EP v) of the forward movement, - rotating the C-arm (2) in the backward direction up to an end position (EP r) of the backward movement, wherein the lateral offset (lv) in the opposite direction to the lateral offset (lv) of the forward movement is increased up to a second offset value (+D) at the end position (EP r) of the backward movement.Method according to claim 1, wherein - the starting position (SP v) of the forward travel of the C-arm (2) has a first angular position, - the ending position (EP v) of the forward travel has a second angular position, and - the ending position (EP r) of the backward travel has a third angular position, wherein the first angular position and the second angular position and the third angular position have an angle with the same absolute value.Method according to claim 2, wherein - the first angular position has an angle of 100°, - the second angular position has an angle of -100°, - the third angular position has an angle of 100°.Method according to one of the preceding claims, wherein the first offset value (-D) and the second offset value (+D) have the same amount (D).Method according to any of the preceding claims, wherein in the forward travel rotating the C-arm (2) in the forward direction comprises the following substeps: - maintaining the first offset value (-D) of the lateral offset (lv) in the forward travel between the starting position (SP v) and an AP position (AP v) of the forward travel, - gradually reducing the lateral offset (lv) between the AP position (AP v) of the forward travel and a lateral position to the value 0, - maintaining the lateral offset (lv) with the value 0 from the range of the lateral position to the end position (EP v) of the forward travel.Method according to any one of the preceding claims, wherein in the backward travel, rotating the C-arm (2) in the backward direction comprises the following substeps: - maintaining the lateral offset (lv) with the value 0 in the range from the end position (EP v) of the forward travel to the lateral position, - gradually increasing the lateral offset (lv) during the rotation in the positive lateral direction between the lateral position and the AP position (AP r) of the backward travel to an end value (+D), - maintaining the offset (lv) between the AP position (AP r) of the backward travel and the end position (EP r) of the backward travel.Method according to one of the preceding claims, wherein a maximum value (D) of the lateral offset (lv) depends on a detector width (w).Method according to one of the preceding claims, wherein a maximum value (D) of the lateral offset (lv) depends on an overlap (ol) of the X-ray detector (4) in the forward run and in the reverse run at the same orbital angles (β) in each case.Method according to one of the preceding claims, wherein the maximum value (D) of the lateral offset (lv) is determined on the basis of the product of the detector width (w) and the difference between the value 1 and the value of the overlap (ol) of the X-ray detector (4) in the forward travel and in the backward travel at the same orbital angle (β).Imaging method for generating 3D image data (BD) of an object under examination (O), comprising the steps of: - acquiring projection data (PD) of the object under examination (O) by applying the method for driving a C-arm (2) of a C-arm system (1) according to one of the preceding claims, - reconstructing 3D image data (BD) on the basis of the acquired projection data (PD).Control device (50), comprising: - a starting unit (51) for - driving a starting position (SP v) of a C-arm (2) in a forward run of a rotation of the C-arm (2) with a lateral offset (lv) with a first offset value (-D) and for starting the forward run at the starting position (SP v) of the forward run and - for starting a backward run of a rotation of the C-arm (2) at an end position (EP v) of the forward run, - a rotation unit (52) for - rotating the C-arm (2) in the forward run in the forward direction up to the end position (EP v) of the forward run, wherein the lateral offset (lv) is reduced to a value of 0, and - rotating the C-arm (2) in the reverse direction in the reverse direction up to an end position (EP r) of the reverse direction, wherein the lateral offset (lv) in the opposite direction of the lateral offset (lv) of the forward direction is increased up to a second offset value (+D) at the end position (EP r) of the reverse direction.C-arm system (1) comprising: - a C-arm (2) which is rotatable or pivotable about at least one rotational or pivot axis, - an X-ray source (3) which is arranged at a first end of the C-arm (2), - an X-ray detector (4) which is arranged opposite the X-ray source (3) at a second end of the C-arm (2) for capturing projection data (PD) from an examination object (O), - a control device (50) according to claim 11, - a reconstruction unit for reconstructing image data on the basis of the captured projection data (PD).A computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the steps of the method of any one of claims 1 to 10.A computer readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method of any one of claims 1 to 10.

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