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

Abstract

The invention relates to a method for controlling a C-arm (2) of a C-arm system (1). In the method for controlling a C-arm (2) of a C-arm system (1) a forward run of a rotation of the C-arm (2) is performed. The forward run of the rotation of the C-arm is started in a start position (SP v ) of the forward run with a lateral offset (lv) having a first offset value (-D) and the C-arm (2) is rotated in a forward direction until an end position (EP v ) of the forward run, wherein the lateral offset (lv) is reduced to a value 0. Furthermore a reverse run of the rotation of the C-arm (2) is performed. The reverse run is started in the end position (EP v ) of the forward run and the C-arm (2) is rotated in a reverse direction until an end position (EP r ) of the reverse run, wherein the lateral offset (lv) is increased in an opposite direction of the lateral offset (lv) of the forward run until the end position (EP r ) of the reverse run, wherein the lateral offset (lv) is increased to a second offset value (+D). Furthermore an imaging method for generating 3D image data (BD) of an examination object (O) is described. A control device (50) is also described. Furthermore a C-arm system (1) is given.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for controlling a C-arm of a C-arm system. In the method a forward run of a rotation of the C-arm and a reverse run of the rotation of the C-arm are performed. The invention further relates to an imaging method for generating 3D image data of an examination object. Furthermore, the invention also relates to a control device. Moreover, the invention also relates to a C-arm system. BACKGROUND

[0002] With modern imaging methods two-dimensional or three-dimensional image data are generated which can be used for the visual display of an examination object being imaged and which can also be used for other applications.

[0003] Imaging methods are usually based on the detection of X-rays. An X-ray system usually comprises an X-ray source and an X-ray detector opposite the X-ray source. In imaging, an examination object, in particular a patient, is positioned in a gap between the X-ray source and the X-ray detector, and an image is taken of the examination object. One type of X-ray system is the so-called C-arm system. In these X-ray systems, the X-ray source and the X-ray detector, which is usually a flat detector, are fixed on a C-shaped support element, also referred to as C-arm. Due to its shape, the C-arm and the corresponding diagnostic- or therapy device or X-ray detector can be moved in an orbit around the point of the patient to be examined or treated in order to thereby achieve different angular positions between the patient and the diagnostic- or therapy device or X-ray detector without the patient having to be moved.

[0004] If the local region to be examined or to be treated is to be imaged from different positions or if the imaging system or the X-ray detector is to be moved jointly in imaging a larger region of the examination object, the C-arm is rotated, for example, about a support axis which is centrally connected to the center of the C-arm.

[0005] In the field of interventional therapy, techniques for 3D imaging with C-arm angiography devices exist. However, a significant limitation compared to conventional CT systems is that the size of the flat detector limits the imaging region. The limited imaging region makes it impossible to detect many organs, such as the lungs, the liver, by a single shot. Furthermore, the projection data of almost all body regions are laterally cut off or truncated, which leads to image artifacts (truncation artifacts) in common reconstruction methods.

[0006] Current clinically used C-arm 3D imaging solutions with large imaging areas assume that the focal point (i.e., the point where electrons strike the anode of the X-ray source or the point where X-ray photons are emitted) is in the same relative position to the object being measured (the patient). In existing "large-volume" schemes of robotic systems, the focal point moves around the patient in a circular trajectory. Therefore, the distance to the patient remains constant. For angiography systems with rigid C-arms, this requires the isocenter of the C-arm to dynamically translate laterally in both directions in the plane of rotation during rotation around the patient, which is only achievable in complex robotic mechanical structures.

[0007] For classic isocentric vascular angiography systems, a trajectory of the isocentric point with lateral translation is used. This involves forward and reverse movement within the plane of rotation, along with an additional one-dimensional lateral motion. This is similar to... Figure 1 The trajectory shown places much lower demands on the mechanical design of the C-arm system, and even a simply constructed C-arm system can achieve a large 3D imaging range. However, Figure 1 The trajectory shown still has practical drawbacks:

[0008] - The endpoint of the forward run does not coincide with the starting point of the reverse run. Therefore, the system must move between runs. This may result in a time delay of a few seconds. Since the patient must hold their breath during the procedure, the time delay should be as short as possible.

[0009] - During operation, the direction of motion along the lateral direction changes. Therefore, the sign of the velocity along the lateral direction changes in the AP direction (AP is an abbreviation for "anterior-posterior"). This change, especially in typical top-suspended systems, can lead to irreproducible geometric errors. Since 3D reconstruction requires very high shooting geometry accuracy, this can cause image artifacts.

[0010] Patent document DE 10 2020 209 703 A1 discloses a method for providing a three-dimensional image data set of an examination object, wherein the three-dimensional image data set can be reconstructed from first and second projection images. Patent document DE 10 2012 208 850 A1 discloses a method for recording radiation images with an X-ray apparatus, wherein a C-arm rotating around an isocenter during image recording is moved in a direction perpendicular to the longitudinal direction of a patient couch during image recording and this movement is taken into account when reconstructing radiation images from recorded image data. Patent document US 2020 / 0 054 297 A1 discloses a system comprising a gantry having an X-ray source and an X-ray detector opposite to each other, wherein the gantry is rotatable relative to a carrier, which is movable by a robot arm. Patent document DE 10 2011 086 754 A1 discloses a method for performing a rotational scan of an object with a C-arm system, wherein the C-arm rotates around the object during the scan, the rotational movement comprising a circumferential movement and a displacement movement. SUMMARY

[0011] Therefore, the technical problem to be solved by the present application is to provide a method and a control device for controlling a C-arm, by which imaging can be performed in a time-saving manner with reduced image artifacts.

[0012] The technical problem is solved by a method for controlling a C-arm of a C-arm system, an imaging method for generating a 3D image data of an examination object, a control device and a C-arm system.

[0013] In the method according to the application for controlling a C-arm of a C-arm system, preferably a top suspended C-arm system, a forward run of the rotation of the C-arm is carried out as described in the introduction. The forward run is initiated at a start position of the forward run of the C-arm with a lateral offset having a first offset value. Lateral offset is to be understood as a translation of the C-arm along a horizontal direction transverse to the patient couch. The focal spot of the X-ray source of the C-arm system is thereby also translated along the lateral direction. The C-arm is then rotated in a forward direction to an end position of the forward run, wherein the lateral offset is monotonously reduced to zero. In addition to the above-mentioned value of zero for the offset, the end point of the forward run also has a predetermined value of the orbit angle β. As will be explained in more detail later, the value of the orbit angle at the start point and the end point is chosen such that the imaging covers a sufficiently large angular range around the examination object. The value of the orbit angle β at the start point and the end point of the forward run is preferably at least 90° or -90°, respectively. The value of the orbit angle β at the start point and the end point of the forward run is preferably 100° or -100°, respectively. It is also preferred that the value of the orbit angle β at the start point and the end point of the forward run is preferably in the interval range [90°, 120°] or [-90°, -120°], respectively. Due to mechanical reasons, especially in top suspended systems, it is not possible to move at arbitrary angles. It is also possible to shift the start / end angle (from the ideal value = 100°) to 20°, a further shift would normally make the system mechanically unable to rotate.

[0014] As also described in the introduction, a reverse run of the rotation of the C-arm is then carried out, i.e. a rotation in a direction opposite to the direction of the forward run. The reverse run is initiated here first at the end position of the forward run and the C-arm is then rotated in the reverse direction to an end position of the reverse run. During the rotation, the lateral offset is monotonously increased in a direction opposite to the lateral offset of the forward run until a second offset value is reached at the end position of the reverse run. "Increased" is to be understood as an increase of the absolute value of the lateral offset. For example, if the lateral offset during the forward run is positive, the lateral offset during the reverse run is negative. If the lateral offset during the forward run is negative, the lateral offset during the reverse run is positive. It is advantageous that the trajectories of the forward run and the reverse run are different, so that additional image information of the patient can be acquired during the reverse run.

[0015] Unlike in conventional control methods, in the method according to the application, the end point of the forward run corresponds to the start point of the reverse run. It is advantageous that the C-arm does not have to be moved between the forward run and the reverse run. Since the patient has to hold his breath during the imaging, it is advantageous to avoid or keep the time delay between the forward run and the reverse run as short as possible.

[0016] It is furthermore advantageously achieved that the direction of the movement of the C-arm along the lateral direction is constant during the run, i.e. during the forward run and during the reverse run.

[0017] Especially in a typical top-suspended system, such a change of the direction of motion during operation can lead to reproducibly geometric errors in conventional approaches. Since the 3D reconstruction requires a very high geometric accuracy of the shots, these errors can lead to image artifacts. Since the direction of motion when the C-arm is moved laterally is kept within the course of motion of the forward run and the course of motion of the reverse run, such image artifacts are now advantageously avoided.

[0018] In the imaging method for generating 3D image data of an examination object according to the application, projection data of the examination object are detected by using the method for controlling a C-arm of a C-arm system, and 3D image data are reconstructed on the basis of the detected projection data. Advantageously, 3D image data of an examination object, preferably a patient, with improved quality can be acquired by the imaging method according to the application.

[0019] The control device according to the application has a start unit for controlling a start position of the C-arm with a lateral offset having a first offset value in a forward run of a rotation of the C-arm and for starting the forward run in the start position of the forward run and for starting a reverse run of the rotation of the C-arm at a termination position of the forward run.

[0020] The control device according to the application further has a rotation unit for rotating the C-arm in the forward run along a forward direction to a termination position of the forward run, wherein the lateral offset is reduced to a 0 value, and for rotating the C-arm in the reverse run along a reverse direction to a termination position of the reverse run, wherein the lateral offset is increased along a direction opposite to the lateral offset of the forward run to a second offset value at the termination position of the reverse run. The control device according to the application has the same advantages as the method for controlling a C-arm of a C-arm system according to the application.

[0021] The C-arm system according to the application comprises a C-arm, preferably a C-arm-like support element, which is rotatable or pivotable about at least one rotation- or pivot axis. Furthermore, the C-arm system according to the application further comprises an X-ray source and an X-ray detector, said X-ray source being arranged at a first end of the C-arm, preferably of the C-arm-like support element, and said X-ray detector being arranged opposite the X-ray source at a second end of the C-arm. Furthermore, the C-arm system according to the application further comprises a control device according to the application. The C-arm system according to the application has the same advantages as the method for controlling a C-arm of a C-arm system according to the application.

[0022] Most of the above-mentioned components of the control device and the C-arm system can be implemented completely or partially in the form of software modules in the processor of the respective computing system. A largely software-based implementation has the advantage that a computing system that is already in use today can be retrofitted in a simple manner by means of a software update in order to work in the manner according to the application. In this respect, the technical problem is solved by a corresponding computer program product having a computer program which can be loaded directly into a computing system in program sections, which, when the program is executed in the computing system, can carry out the steps of the method according to the application for controlling a C-arm of a C-arm system. In addition to the computer program, such a computer program product can comprise additional components, such as documentation and / or additional components, and hardware components, such as hardware keys for the use of the software (dongles, etc.), if necessary.

[0023] A computer-readable medium, such as a memory stick, a hard disk or other removable or fixedly installed data carrier, on which program sections of a computer program that can be read and executed by a computing system are stored, can be used for transmission to the computing system or the control device and / or for storage in or at the computing system or the control device. The computing system may, for example, for this purpose have one or more microprocessors or similar devices that work together.

[0024] The following description contains, respectively, particularly advantageous design proposals and extensions of the application. Here, in particular, claims of one claim category can also be improved analogously to dependent claims of another claim category. Furthermore, different technical features of different embodiments and claims can also be combined within the scope of the application to form new embodiments.

[0025] In one design proposal of the method for controlling a C-arm of a C-arm system according to the application, the start position of the forward run of the C-arm has a first angular position. Furthermore, the end position of the forward run has a second angular position, and the end position of the reverse run has a third angular position. The first angular position, the second angular position and the third angular position here preferably have the same absolute value of the angle. It is advantageous if the angular range through which the C-arm and thus the X-ray detector and the X-ray source are moved in the forward run and the reverse run is symmetrical. A patient lying on a patient couch that is symmetrical with respect to the AP position (anterior-posterior position, the patient is irradiated along the vertical direction, the track angle is 0°) can advantageously be imaged from both sides from the same absolute value of the angle, respectively.

[0026] In order to obtain sufficient data for a 3D reconstruction, at least a circular arc segment of 200° has to be moved through. It is expedient here for the rotation to be carried out along a circular arc segment of 100° on the "left" and 100° on the "right" in the AP plane. For mechanical reasons, in particular in the case of top-suspended systems, it is not possible to move through arbitrary angles. It is also possible to shift the start / finish angle by a maximum of 20°, beyond which the system cannot be mechanically rotated.

[0027] The first angle position preferably has an angle of 100°, the second angle position preferably has an angle of -100° and the third angle position preferably has an angle of 100°. It can be advantageous to acquire image data from an angle range of 200°, so that the examination region or the examination object can be imaged from different directions. The image information detected from different directions can advantageously be combined into a 3D image of the examination region.

[0028] Therefore, an orbit angle of 100° is preferably used as a start position for the forward run and an orbit angle of -100° is preferably used as a finish position for the forward run. Furthermore, an orbit angle of -100° is used as a start position for the reverse run and an orbit angle of 100° is used as a finish position for the reverse run.

[0029] As described above, for the forward run and the reverse run, an angle range of at least 200° should preferably be moved through. The angle range moved through should likewise preferably be in the range of values between 180° and 240°, particularly preferably between 190° and 210°.

[0030] The first offset value and the second offset value particularly preferably have the same absolute value. Since the patient is usually approximately symmetrical to the sagittal plane, it is reasonable to use an offset which is equal in both directions.

[0031] In another particularly preferred variant of the method for controlling a C-arm of a C-arm system according to the application, in the forward run the rotation of the C-arm in the forward direction comprises the following steps:

[0032] - maintaining the first offset value of the lateral offset in the forward run between the start position and the AP position,

[0033] - gradually reducing the lateral offset to the value 0 between the AP position and the lateral position,

[0034] - maintaining the value 0 of the lateral offset in the range from the lateral position to the finish position of the forward run.

[0035] The first offset value for the lateral offset is advantageously continuously reduced at the start of the forward run until the lateral position, so that a uniform imaging is achieved.

[0036] Alternatively, in forward operation the offset is not reduced to zero at the lateral position, but only at the end position. Advantageously a continuous change of the offset up to the end position is achieved.

[0037] In the reverse operation, the rotation of the C-arm in the reverse direction preferably comprises:

[0038] - the value of the lateral offset is kept at zero in the range from the end position of the forward operation to the lateral position,

[0039] - during the rotation, the lateral offset is gradually increased between the lateral position and the AP position to an end value in the positive lateral direction, wherein the lateral offset is in the opposite direction relative to the lateral offset of the forward operation,

[0040] - the offset is kept between the AP position and the end position of the reverse operation.

[0041] It is advantageous if in the "right" quadrant, i.e. in the forward operation and in the reverse operation, no change of the offset occurs. This is because the change of the offset that occurs in the right quadrant has to be compensated by a movement in the left quadrant in the opposite direction. If a change of the offset occurs in both directions during the movement, the described disadvantage occurs, i.e. a change of the direction of movement in the lateral direction during the operation, as Figure 2 is shown for a conventional trajectory. It is therefore advantageous if the offset in one direction is determined before the start of the rotation, so that the offset does not change during the rotation in the right quadrant and remains unchanged until the end upon return.

[0042] In another preferred variant of the method for controlling a C-arm of a C-arm system according to the application, the maximum value of the lateral offset depends on the detector width. The maximum lateral offset should be chosen such that the images taken from the same angle in the forward operation and in the reverse operation can be connected. If the same value but with opposite signs is chosen as the maximum lateral offset in the forward operation and in the reverse operation, the offset maximum should be half the detector width. If the maximum lateral offset is smaller, an overlap region occurs between the image data taken at the same trajectory angle in the forward operation and in the reverse operation. The adjacent image taking can advantageously be combined more easily due to the overlap.

[0043] It is likewise preferred in the method for controlling a C-arm of a C-arm system according to the application that the maximum lateral offset is preferably dependent on the overlap of the X-ray detector in the forward run and in the reverse run. The overlap can have a value from 0 to 1. The value "0" here means that there is no overlap, and the value "1" means that the images taken in the C-arm positions with the same orbit angle in the forward run and in the reverse run overlap completely. The greater the overlap, the "smoother" the transition between the image data of the two image ensembles of the forward run and the reverse run. The redundant image data can be combined by interpolation methods with the two image ensembles.

[0044] The value of the maximum lateral offset is preferably determined by the product of the width of the detector and the difference between the value of the overlap of the X-ray detector in the forward run and in the reverse run with the same orbit angle and the value 1.

[0045] The value of the maximum lateral offset D here is

[0046]

[0047] Here, w is the width of the X-ray detector, and ol is the overlap of the two image takings in the two vertices, or in general the overlap of the image takings with the same orbit angle. As mentioned previously, the overlap can be chosen between 1 and 0.

[0048] The maximum lateral offset D also corresponds to half the distance between the two vertices of the C-arm trajectories of the forward run and the reverse run.

[0049] In a preferred design of the method for controlling a C-arm of a C-arm system according to the application, the C-arm is offset with the necessary maximum lateral offset lv=-D from the usual 3D start position before the acquisition is started. In the forward run between the start angle 100° and the AP position with the orbit angle β = 0°, the lateral offset lv remains lv=-D.

[0050] "AP" is an abbreviation for "anterior-posterior" and describes an image taking of the front of the patient at a position or orientation or orbit angle β = 0°, in which the patient is in a lying position, and the line between the X-ray source and the X-ray detector is oriented perpendicularly. The AP position usually also corresponds to the vertex of the respective trajectory in the forward run and in the reverse run. The start angle or orbit angle of 100° means that the line between the X-ray source and the X-ray detector is rotated beyond the lateral orientation at the start, in order to be able to move through a greater angular range in the C-arm taking and thus to obtain additional spatial information about the examination region of the patient to be imaged. With a start angle of 100°, the examination region to be imaged is figuratively taken from below.

[0051] Between the orientation of the orbit angle of 0°, i.e. the AP position, and the orientation of the orbit angle of -90°, i.e. the lateral of the line between the X-ray source and the X-ray detector, the lateral offset of the C-arm decreases during the rotation along the positive lateral direction to the lateral offset lv=0 and remains the lateral offset lv=0 in the range from the orbit angle of -90° to the end angle of -100°. In return, the lateral offset lv remains 0 in the range of the orbit angle of -100° to -90°. Between the orbit angle of -90° and 0°, i.e. between the lateral and the cranial-caudal orientation, the lateral offset lv increases during the rotation along the positive lateral direction to the value lv=+D. Between the orbit angle of 0° and 100°, the lateral offset lv remains the value lv=+D.

[0052] For the forward run, the focus of the X-ray source of the C-arm preferably describes the following trajectory a1 :

[0053] For β > 0°:

[0054]

[0055] For -90° < β < 0°:

[0056]

[0057] For β < -90°:

[0058]

[0059] For the reverse run, the focus of the X-ray source of the C-arm preferably describes the following trajectory a2:

[0060] For β > 0°:

[0061]

[0062] For -90° < β < 0°:

[0063]

[0064] For β < -90°:

[0065]

[0066] The orbit angle β describes the following curve:

[0067]

[0068] The value SCD represents 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 is located.

[0069] As described in DE 10 2020 209 703 A1, 3D image data can be reconstructed from the projection data taken along the trajectories a1, a2 according to the application, depending on one of the variants of the method according to the application. BRIEF DESCRIPTION OF DRAWINGS

[0070] The application is explained in more detail below by means of embodiments with reference to the drawings. In the drawings:

[0071] Figure 1 A schematic diagram of a conventional C-arm system is shown,

[0072] Figure 2 A schematic diagram of conventional trajectories of a C-arm of a C-arm system is shown,

[0073] Figure 3 A schematic diagram of trajectories of a C-arm of a C-arm system according to one embodiment of the application is shown,

[0074] Figure 4 A flowchart is shown, which illustrates a flowchart of a method for controlling a C-arm of a C-arm system,

[0075] Figure 5 A schematic diagram of a control device according to one embodiment of the application is shown,

[0076] Figure 6 A flowchart is shown, which illustrates an imaging method for generating 3D image data of an examination object according to one embodiment of the application. DETAILED DESCRIPTION

[0077] Figure 1 A C-arm system 1 according to a first embodiment of the application is shown. The C-arm system 1 comprises a C-arm-like support element 2, also referred to simply as C-arm 2, wherein an X-ray source 3 is arranged at one end of the C-arm 2, which end is shown in Figure 1 as the lower end, i.e. the end facing away from the top DE of the space in 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 end is shown in Figure 1 as the upper end, i.e. the end facing towards the top DE.

[0078] A patient couch L is located between the X-ray source 3 and the X-ray detector 4, on which patient couch a patient O to be examined is arranged. The C-arm 2 is connected by a C-arm suspension device 5 to a base 6, which is fixed at the top DE. When an image is taken of the patient O, X-rays are emitted from the X-ray source 3 and detected by the X-ray detector 4 of the C-arm system 1. The detected measurement signals or measurement data obtained therefrom are used for image reconstruction.

[0079] Figure 2A schematic diagram 20 shows the conventional trajectory of the C-arm in a C-arm system. Here, forward and reverse movements occur in the plane of rotation, with an additional one-dimensional lateral motion. Forward movement begins at the starting point SP. v Starting from, the starting point is as follows: Figure 2 As shown on the right, the orbital angle β = 100°, and the lateral offset lv is -D*cos(100°), where D is the maximum lateral offset. When the orbital angle β = 90°, the lateral offset lv = 0. The lateral offset lv = -D is continuously formed until the orbital angle β is 0°. The focus then reaches the forward-moving AP position. v This is the point with the largest y-value, which is also the vertex of the forward movement. The lateral offset lv then decreases until it decreases to 0 when the orbital angle β = -90°. The point at the end of the forward movement is EP. v At that point, the value of the lateral offset lv is again -D*cos(-100°).

[0080] The focus of the C-arm then moves to the starting point SP of the reverse movement. r The focus is located at an orbital angle β = -100°. The lateral offset lv has a value of +Dcos(-100°). At an orbital angle β = -90°, the lateral offset lv has a value of 0. The lateral offset lv then increases until it reaches a value of +D at an orbital angle of 0°. Afterwards, it reaches position AP. r This is the vertex of the reverse run. Afterward, the lateral offset lv value decreases until it reaches 0 when the orbital angle is 0°, and terminates at the reverse run's endpoint EP. r The value at point is D*cos(100°).

[0081] Figure 2 The trajectory shown places relatively low demands on the mechanical design of the C-arm system 1, and achieves a large 3D imaging range even at a significantly lower cost. The endpoint EP of the forward movement. v Starting point SP in reverse order r Inconsistency. Therefore, the system must move between runs. This can result in a time delay of several seconds. Since the patient O must hold their breath during imaging, the time delay should be as short as possible. During a run, the direction of movement along the lateral direction changes. Therefore, for the AP direction (β = 0°), the sign of the velocity of the focus's lateral shift changes. This change, especially in typical top-suspended systems, can lead to non-reproducible geometric errors. Since 3D reconstruction requires very high geometric accuracy when examining the X-ray projection data upon which it is based, this can cause image artifacts.

[0082] For forward motion, the focal point of the X-ray source in the C-arm describes the following trajectory:

[0083]

[0084] For the reverse run, the focus of the X-ray source of the C-arm describes the following trajectory:

[0085] The orbit angle describes the following curve:

[0086]

[0087] The half of the distance D between the two vertex or AP positions AP v , AP r or the maximum deviation D is

[0088]

[0089] Here, w is the width of the X-ray detector and ol is the overlap between two image takings in the two vertex or AP positions AP v , AP r .

[0090]

[0091] A trajectory diagram 30 of a C-arm of a C-arm system 1 according to an embodiment of the application is shown. Figure 3 Here, before starting the acquisition, the C-arm is translated with the necessary lateral deviation lv=-D from the usual 3D start position. In the forward run between the start angle of 100° and the orbit angle of 0°, the lateral deviation lvremains at lv=-D. During the rotation in the forward direction between the orbit angle of β=0° and β=-90°, the deviation lvchanges from the value -D to the value lv=0 and remains constant in the range from the orbit angle of -90° to the end angle of -100°.

[0092] In the reverse run, the lateral deviation lv=0 is maintained in the range of the orbit angle β from -100° to -90°. Then between -90° and 0° of the orbit angle β or between the orbit angle of -90° and the AP position AP r of the reverse run, the lateral deviation lvincreases to the value +D. Thereafter, the lateral deviation lvremains constant at its maximum value lv=+D until the end point EP r of the reverse run.

[0093] The trajectories al, a2 of the forward run and the reverse run are derived from the equations (2) to (7) which are described in detail in the general part of the patent application.

[0094]

[0095] Figure 4A flow chart is shown which illustrates a method for controlling a C-arm of a C-arm system 1 according to an embodiment of the application.

[0096] In step 4.I, the C-arm is translated from the usual centrally located 3D start position with a lateral offset lv=-D before acquisition start.

[0097] In step 4.II, the lateral offset lv=-D is maintained during the forward run between the start angle of 100° and the AP position of 0°.

[0098] In step 4.III, the lateral offset lv is gradually decreased to the value 0 along the positive lateral direction during rotation between the orbit angle β of 0° and -90°.

[0099] In step 4.IV, the lateral offset lv=0 is maintained in the range from the orbit angle β of -90° to the end angle of -100°.

[0100] In step 4.V, the lateral offset of 0 is likewise maintained during the backward run in the range of the orbit angle β of -100° to -90°.

[0101] In step 4.VI, the lateral offset lv is gradually increased to the value +D along the positive lateral direction during rotation between the orbit angle β of 0° and -90°.

[0102] In step 4.VII, the lateral offset lv is maintained until the orbit angle β=100°, i.e. the end point EP of the backward run at the maximum offset lv=+D r .

[0103] Figure 5 A schematic diagram of a C-arm system 1 with a control device 50 (indicated by dashed lines) according to an embodiment of the application is shown. In addition to the control device, the C-arm system 1 comprises a C-arm with an X-ray source and an X-ray detector (not shown).

[0104] The control device 50 has a start unit 51 for controlling a start position SP of a C-arm 2 in a forward run of a rotation of the C-arm 2 with a lateral offset lv having a first offset value -D v and for starting the forward run in the start position SP v of the forward run. The start unit 51 is further provided for starting a backward run of the rotation of the C-arm 2 in an end position EP v of the forward run, which is at the same time a start position SP r of the backward run.

[0105] The control device 50 also includes a rotating unit 52, which is used to rotate the C-arm 2 in the forward direction during forward operation until the end position EP of the forward operation. v , where the lateral offset lv is reduced to a value of 0.

[0106] The rotating unit 52 is also configured to rotate the C-arm 2 in the reverse direction during reverse operation until the end position EP of the reverse operation. r The lateral offset lv increases in the opposite direction to the lateral offset lv during forward movement until it reaches the termination position EP during reverse movement. r The value is increased to the second offset value +D.

[0107] During forward and reverse operation, projection data PD from the object being inspected (not shown) is detected by an X-ray detector (not shown) arranged at C-arm 2.

[0108] Reconstruction unit 53 is also part of C-arm system 1. This reconstruction unit is configured to reconstruct 3D image data BD based on projection data PD of the object being examined, detected by the X-ray detector of C-arm 2.

[0109] Figure 6 A flowchart 600 is shown, illustrating an imaging method for generating 3D image data BD of an object to be examined, according to an embodiment of the present invention.

[0110] In step 6.I, the projection data PD of the object to be inspected is detected by using the C-arm 2 used to control the C-arm system 1.

[0111] In step 6.II, 3D image data BD is reconstructed based on the detected projection data PD.

[0112] Finally, it should be clarified that the aforementioned C-arm is merely a preferred embodiment of the present invention, and the present invention can be modified by those skilled in the art as long as it does not depart from the scope of protection of the present invention as given by the claims. For completeness, it should also be noted, for example, that the use of the indefinite article "a" does not preclude the existence of multiple related features. Similarly, the term "unit" does not preclude it from being composed of multiple parts, which may, if necessary, be spatially distributed.

[0113] Regardless of the grammatical gender of a particular term, people with male or female gender identities are included.

Claims

1. A method for controlling a C-arm (2) of a C-arm system (1), the method having the following steps: - performing a forward run of a rotation of the C-arm (2), the forward run having the following sub-steps: - starting a forward run with a lateral offset (lv) having a first offset value (-D) in a start position (SP v ) of the forward run of the C-arm (2) - rotating the C-arm (2) along the forward direction until an end position of forward travel (EP v ), wherein, - decreasing a lateral offset (lv) to a value 0, - performing a reverse run of a rotation of the C-arm (2), the reverse run having the following sub-steps: - at the end position (EP v ) of the forward run, starting a reverse run, - rotating the C-arm (2) along the reverse direction until an end position of the reverse run (EP r ), wherein the lateral offset (lv) increases along the reverse direction of the lateral offset (lv) of the forward run until the increase at the end position of the reverse run (EP r ) is the second offset value (+D).

2. The method according to claim 1, wherein - The starting position of the forward movement of the C-arm (2) (SP) v It has a first angular position. - the end position (EP v ) of the forward run has a second angular position, and - the end position (EP r ) of the reverse run has a third angular position, wherein the first, second and third angular positions have the same absolute value of an angle.

3. The method according to claim 2, - 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°.

4. The method according to any of the preceding claims, wherein, the first offset value (-D) and the second offset value (+D) have the same absolute value (D).

5. The method according to any one of the preceding claims, wherein, In the forward run, the rotation of the C-arm (2) along a forward direction comprises the following sub-steps: - in forward operation a first offset value (-D) of the lateral offset (lv) between the start position (SP v ) and the AP position (AP v ) of forward operation is maintained, - said lateral offset (lv) gradually decreases to 0 between the AP position (AP v ) and the lateral position for a forward running AP, - the value of said lateral offset (lv) is kept equal to 0 in the range from the lateral position to the end position of forward travel (EP v ).

6. The method according to any one of the preceding claims, wherein, In the reverse run, the rotation of the C-arm (2) along a reverse direction comprises the following sub-steps: - keeping the value of the lateral deviation (lv) equal to 0 in the range from the end position of forward running (EP v ) to the lateral position, - keeping the value of the lateral deviation (lv) equal to 0 in the range from the end position of forward running (EP v ) to the lateral position, - during rotation, said lateral offset (lv) gradually increases along a positive lateral direction between a lateral position and a counter- running AP position (AP r ) to an end value (+D), - maintaining the offset (lv) between the AP position in reverse run (AP r ) and the end position in reverse run (EP r ).

7. The method according to any one of the preceding claims, wherein, A maximum value (D) of the lateral offset (lv) depends on a detector width (w).

8. The method of any 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 the reverse run with the same value of a track angle (β).

9. The method of any of the preceding claims, wherein, A maximum value (D) of the lateral offset (lv) is determined based on a product of a detector width (w) and a difference between a value of an overlap (ol) of the X-ray detector (4) in the forward run and the reverse run with the same value of a track angle (β) and a value of 1.

10. An imaging method for generating 3D image data (BD) of an examination object (O), the method having the following steps: - detecting projection data (PD) of an examination object (O) by using a method for controlling a C-arm (2) of a C-arm system (1) according to any one of the preceding claims, - reconstructing 3D image data (BD) based on the detected projection data (PD).

11. A control device (50) having: - a start unit (51) for - controlling the start position (SP v ) of the C-arm (2) in the forward run of the rotation of the C-arm (2) with a lateral offset (lv) having a first offset value (-D) and for starting the forward run in the start position (SP v ) of the forward run, and - at the end position (EP v ) of the forward run, a reverse run of the rotation of the C-arm (2) is initiated, - a rotation unit (52) for - rotating the C-arm (2) in a forward direction along the forward direction in a forward run until an end position (EP v ) of the forward run, wherein decreasing a lateral offset (lv) to a value 0, and - rotating the C-arm (2) in a reverse run along a reverse direction until an end position (EP r ) of the reverse run, wherein the lateral offset (lv) increases along the reverse direction of the lateral offset (lv) of the forward run until the increase at the end position (EP r ) of the reverse run is the second offset value (+D).

12. A C-arm system (1) having: - a C-arm (2) rotatable or pivotable about at least one rotation- or pivot axis, - an X-ray source (3) arranged at a first end portion of the C-arm (2), - an X-ray detector (4) arranged opposite to the X-ray source (3) at a second end portion of the C-arm (2) for detecting projection data (PD) of an examination object (O), - a control device (50) according to claim 11, - a reconstruction unit for reconstructing image data based on the detected projection data (PD).

13. 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 according to any one of claims 1 to 10.

14. A computer readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method according to any one of claims 1 to 10.

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