Device for determining the control protocol for the C-arm system

Abstract

This invention relates to an apparatus for determining a control protocol for controlling a C-arm system including a radiation source. The control protocol includes a sequence of roll angles and a sequence of propeller angles. The apparatus includes: a tilt plane providing unit for providing a tilt plane tilted relative to a vertical plane; and a control protocol determining unit for determining the control protocol by determining the sequence of roll angles and the sequence of propeller angles, such that the radiation source follows a trajectory including a circular component in the tilt plane and allowing the C-arm system to acquire projection data for image reconstruction. The apparatus allows for the acquisition of computational images, such as tomographic images, with improved quality and reduces radiation in radiation-sensitive areas.

Description

Technical Field

[0001] This invention relates to apparatus, systems, methods, and computer programs for determining control protocols for controlling C-arm systems. Background Technology

[0002] Today, many interventional procedures are guided by medical imaging. Since it is often impossible to guide a patient into a closed CT system during medical procedures, C-arm systems are typically used to acquire computed tomography (CT) imaging data in applications where providing 3D X-ray tomographic images is advantageous. In this case, to acquire tomographic data, the radiation source and detector provided by the C-arm move along a circular trajectory in a vertical plane around the patient's region of interest. This can be easily achieved by simply rotating the C-arm around the propeller joint by a propeller angle exceeding 180 degrees (°).

[0003] While this method produces CT images of sufficient quality in many applications, particularly cone-beam CT images, image artifacts may occur in some applications, especially for the patient's head, due to the shadowing effect of high-attenuation objects, such as the patient's teeth. Furthermore, the region of interest can be vertically aligned with anatomical structures that are highly sensitive to X-ray radiation, allowing these highly sensitive areas to be subjected to high-intensity radiation during imaging using the aforementioned method. Summary of the Invention

[0004] One object of the present invention is to provide an apparatus, system, method, and computer program that allows the use of a C-arm system to acquire computed tomography images with improved quality. Furthermore, another object of the present invention is that the apparatus, system, method, and computer program also allow for the reduction of radiation in radiation-sensitive areas.

[0005] In a first aspect of the invention, an apparatus is provided for determining a control protocol for controlling a C-arm system including a radiation source, wherein the control protocol includes a sequence of roll angles and a sequence of propeller angles, wherein the apparatus includes a) a tilt plane providing unit for providing a tilt plane tilted relative to a vertical plane, and b) a control protocol determining unit for determining the control protocol by determining the sequence of roll angles and the sequence of propeller angles such that the radiation source follows a trajectory including a circular component in the tilt plane and allowing the C-arm system to acquire projection data for image reconstruction.

[0006] Because the control protocol determination unit determines the control protocol for controlling the C-arm system by determining the sequence of roll angles and the sequence of propeller angles, such that the radiation source follows a trajectory that includes a circular component in an inclined plane relative to the vertical plane and allows the C-arm system to acquire projection data for image reconstruction, preferably tomographic images, the inclined plane can be selected such that the region of interest is imaged during the acquisition of projection data for tomographic image reconstruction, while avoiding high-attenuation objects near the region of interest. Furthermore, radiation-sensitive areas near the region of interest can be avoided by correspondingly selecting the inclined plane. Therefore, the device allows for a control protocol for the C-arm system that allows for the acquisition of CT images with improved image quality while allowing for reduced radiation exposure to radiation-sensitive areas.

[0007] The apparatus is adapted to determine a control protocol for controlling a C-arm system. A C-arm system refers to an X-ray system comprising a radiation source and, for example, a detector mounted on a C-arm. In some embodiments, the C-arm system comprises two robotic arms, with the radiation source and detector provided on the two robotic arms, wherein the two robotic arms can operate independently. In other embodiments, only the radiation source moves, while the detector has a fixed position. Preferably, the C-arm system is a cone-beam C-arm CT system. Typically, the C-arm system is configured to rotate the radiation source and / or detector about at least two axes. The two axes of motion of the C-arm system are located in a horizontal plane and are perpendicular to each other. One of the two axes is called the propeller axis, and the other is called the roll axis. Therefore, the movement of the radiation source can be controlled by controlling the movement of the C-arm about the propeller axis and the roll axis. The apparatus is adapted to determine a control protocol for controlling the C-arm system, the control protocol comprising sequences of roll angles and sequences of propeller angles defined respectively based on the propeller axis and the roll axis. The sequences of roll angles and propeller angles define a sequence of specific positions of the radiation source in space, such that the sequence of positions forms the trajectory of the radiation source in space. Therefore, the trajectory of the radiation source provided on the C-arm of a C-arm system refers to the sequence of positions of the radiation source determined by the sequences of roll angles and propeller angles provided by the control protocol. Thus, the control protocol allows for control of the movement of the C-arm system, causing the radiation source to follow a specific trajectory during the acquisition of projection data for tomographic image reconstruction.

[0008] The tilt plane providing unit is adapted to provide a tilt plane that is tilted relative to a vertical plane. The tilt plane providing unit may be, for example, a storage unit for storing tilt planes, or the tilt plane providing unit may be connected to a storage unit for storing tilt planes. Furthermore, the tilt plane providing unit may be a receiving unit for receiving the tilt plane, for example, through an input unit where a user can input the tilt plane, wherein the tilt plane providing unit is then adapted to provide the tilt plane.

[0009] The tilted plane is tilted relative to the vertical plane. Specifically, a tilt angle can be defined between the normal to the tilted plane and the normal to the vertical plane, thus defining the amount of tilt of the tilted plane relative to the vertical plane. The tilted plane is tilted relative to the vertical plane such that the tilt angle, i.e., the amount of tilt, is always greater than zero and less than 90 degrees (°), where the tilt angle corresponds to an absolute value. In a preferred embodiment, the tilt angle is less than 20° and greater than zero. More preferably, if the object to be imaged is a human patient lying on a patient support, the vertical plane essentially refers to the axial plane of the patient. Alternatively, the vertical plane may essentially refer to the sagittal plane of the patient. Furthermore, the vertical plane can also be defined relative to other cross-sections passing through the patient, depending on the patient's position relative to the C-arm system. Preferably, the tilted plane is defined such that the intersection curve of the tilted plane and the vertical plane, i.e., the intersection line, lies within the horizontal plane. Even more preferably, the intersection curve of the tilted plane and the vertical plane corresponds to the roll axis or propeller axis of the C-arm system.

[0010] The control protocol determination unit is used to determine the control protocol. Determining the control protocol includes determining a sequence of roll angles and a sequence of propeller angles for the C-arm system, such that the radiation source follows a trajectory including a circular component in the inclined plane. Specifically, the control protocol determination unit is adapted to determine the roll angle based on the propeller angles used to determine the control protocol. Typically, the trajectory of an object in space can be described as a superposition of multiple motion components. For example, linear motion in any direction can be described as a superposition of motion along a horizontal axis and a suitably chosen vertical axis. The control protocol determination unit is adapted to determine the control protocol of the radiation source such that the trajectory of the radiation source includes at least a circular component in the inclined plane. If the radiation source follows a trajectory including only a circular component, the circular component corresponds to the movement of the radiation source along a circular path, i.e., a path forming a circle or a portion of a circle. The circular component of the trajectory lies in the inclined plane such that the radiation source does not leave the inclined plane while following a trajectory including only a circular component. Furthermore, the radiation provided by the radiation source is provided along the inclined plane such that at least a portion of the provided radiation is provided within the inclined plane and reaches the detector along a path within the inclined plane. For example, the control protocol determination unit can be adapted to determine the circular component as defined above by calculating the roll angle based on the propeller angle using a sine or cosine function, wherein the function can be selected such that the amplitude of the sine or cosine function corresponds to the tilt angle. Alternative methods, i.e., mathematical formulas, can be chosen for determining and calculating the corresponding circular component. In a further example, the control protocol determination unit can be adapted to determine the control protocol to first determine the desired trajectory of the radiation source in space, and then determine the sequence of roll angles and the sequence of propeller angles such that the radiation source C-arm system follows the determined trajectory.

[0011] The circular component in the tilted plane of the radiation source's trajectory allows for the acquisition of projection data from the region of interest, without having to acquire projection data from, for example, high-attenuation regions near the region of interest, which could lead to artifacts in the reconstruction of projection data in tomographic images.

[0012] The trajectory defined by the control protocol, determined by the control protocol determination unit, also allows the C-arm system to acquire projection data for tomographic image reconstruction. Specifically, the trajectory allows the acquisition of a complete projection dataset, for example, by providing projection data from multiple different views exceeding 180° plus a fan angle. However, depending on the radiation geometry provided by the radiation source, views less than 180° can also be used to construct a complete projection dataset. To ensure that the trajectory allows the acquisition of projection data usable for tomographic image reconstruction, the control protocol defining the radiation source trajectory can also be determined based on the principles used for acquiring cone-beam CT scans, for example, as disclosed in Chris C. Shaw's book, "Cone Beam Computed Tomography," 1st edition, CRC Press (2014).

[0013] In one embodiment, the trajectory further includes a non-circular component. Preferably, the control protocol determination unit is adapted to determine a control protocol such that the radiation source follows a trajectory including both circular and non-circular components; that is, such that the trajectory of the radiation source is a superposition of circular and non-circular components. The user can select the non-circular component, thereby enabling additional constraints on the trajectory motion. For example, the non-circular component can be selected such that the radiation source follows a trajectory that allows for the provision of projection data outside an inclined plane at a specific location. In another example, the non-circular component can be selected such that the radiation source follows a trajectory at a different distance from the object to be imaged, such as an elliptical trajectory in an inclined plane. In a preferred embodiment, when the C-arm system is controlled according to the determined control protocol, the non-circular component allows the C-arm system to acquire projection data along a trajectory that satisfies the Tuy condition. Typically, the trajectory of a radiation source outside the object satisfies the Tuy condition if any plane passing through the object intersects the trajectory. A more detailed explanation of the trajectory satisfying the Tuy condition can be found in the article “An inversion formula for cone-beam reconstruction” in HKTuy, SIAM J. Appl. Math., Vol. 43(3), pp. 546-552 (1983).

[0014] In a preferred embodiment, the non-circular component includes a forward and backward movement component of the radiation source perpendicular to the inclined plane. The superposition of this forward and backward movement component perpendicular to the inclined plane onto the circular component allows the radiation source to follow a trajectory that satisfies the Tuy condition regarding the region of interest to be imaged. Preferably, the non-circular component includes a forward and backward movement component that moves the radiation source forward and backward at least twice perpendicular to the inclined plane during the semi-circular motion of the radiation source.

[0015] To determine whether a possible trajectory satisfies the Tuy condition, for example, including the forward and backward motion components as non-circular components, the convex hull of the trajectory can be calculated and superimposed on the representation of the object to be imaged in a 3D viewer. In this case, if an object or region of interest of the object can be found within the convex hull of the trajectory, then the Tuy condition is satisfied for the possible trajectory. If it is necessary to determine a control protocol defining a trajectory that satisfies the Tuy condition, the control protocol determination unit can be adapted to adjust the characteristics of the trajectory such that the trajectory satisfies the Tuy condition, wherein the control protocol determination unit can then determine the control protocol such that the radiation source follows the desired trajectory. The characteristics of the trajectory may refer to, for example, the start and end points of the trajectory, the maximum and / or minimum values ​​of the roll angle, the positions of the maximum and / or minimum values ​​of the trajectory, etc., wherein adjusting these characteristics may also refer to adjusting the non-circular components of the trajectory, such as adjusting the forward and backward motion components, thereby adjusting the characteristics of the trajectory. Furthermore, preferably, the start and end portions of the trajectory are selected such that the X-ray system can easily follow the dynamics of the trajectory.

[0016] In one embodiment, the apparatus further includes a table position providing unit for providing the position and orientation of the table relative to the C-arm system, wherein an object to be imaged by the C-arm system is positioned on the table, wherein the control protocol determining unit is adapted to also determine a sequence of roll angles and a sequence of propeller angles based on the position and orientation of the table. The table position providing unit may be a storage unit storing the table position, or may be connected to a storage unit storing the table position. Furthermore, the table position providing unit may be a receiving unit receiving the table position and adapted to then provide the received table position. For example, the table position may be received from an input unit where a user inputs the table position or from a table position determining unit. For example, such a table position determining unit may determine the table position based on a measurement of the table position (e.g., optical measurement). An object to be imaged by the C-arm system is positioned on the table, wherein the object may be a living organism such as a human or animal, or an inanimate object such as a suitcase. Preferably, the object is a patient whose medical images are to be acquired using the C-arm system.

[0017] The control protocol determination unit is also adapted to determine the sequence of roll angles and the sequence of propeller angles based on the position and orientation of the platform. For example, if the longitudinal axis of the platform is aligned with the propeller axis of the CT system, the control protocol determination unit is adapted to determine the sequence of roll angles and the sequence of propeller angles such that the sequence of propeller angles provides a circular motion of the radiation source around the platform and the sequence of roll angles provides an inclination of the trajectory relative to the vertical plane. In another example, if the platform is oriented such that the longitudinal axis of the platform is aligned with the roll axis of the C-arm system, the control protocol determination unit is adapted to determine the sequence of roll angles and the sequence of propeller angles such that the roll angles provide a circular motion of the radiation source around the platform, and the propeller angles provide an inclination of the trajectory relative to the vertical plane. Furthermore, the position and orientation of the platform can also be any position and orientation of the platform relative to the C-arm system, and the control protocol determination unit can be used to determine the sequence of roll angles and the sequence of propeller angles relative to these arbitrary positions and orientations of the platform such that the radiation source follows a trajectory with a circular component in the provided inclined plane. Preferably, the position and orientation of the tabletop also substantially define the position and orientation of the object (preferably, the patient) relative to the C-arm system. Therefore, when the control protocol determining unit is adapted to determine the control protocol based on the position and orientation of the tabletop, the control protocol determining unit is also adapted to determine the control protocol with respect to the position and orientation of the object provided on the tabletop. Furthermore, if the tabletop position and orientation are provided by the tabletop position providing unit, the tilt plane providing unit can be adapted to provide a tilt plane with respect to the position and orientation of the tabletop. For example, a vertical plane can be defined relative to the tabletop or the position and orientation of the object on the tabletop, such that a tilt plane can also be defined based on the tabletop and / or the position and orientation of the object on the tabletop.

[0018] In one embodiment, the control protocol determination unit is adapted to determine a sequence of roll angles and a sequence of propeller angles such that the risk of collision between a portion of the C-arm system and the table and / or object is minimized during the acquisition of projection data. For example, the control protocol determination unit may be adapted to determine a sequence of roll angles and a sequence of propeller angles such that the radiation source or another portion of the C-arm system (e.g., of the C-arm) is never in the same position as a portion of the table and / or object when the radiation source follows a predetermined trajectory. For example, the control protocol determination unit may be adapted to use the position of the table and / or object as a constraint for determining the trajectory. Alternatively or additionally, the control protocol determination unit may, for example, be adapted to determine a first trajectory and check whether the first determined trajectory includes a collision risk between a portion of the C-arm system and the table and / or patient. If such a collision risk is determined, the control protocol determination unit may be adapted to determine a new trajectory, for example, with a different starting position or a different non-circular component, wherein new trajectories are determined until a trajectory with no collision risk is found.

[0019] In one embodiment, the control protocol determination unit is adapted to determine the sequence of the roll angle and the sequence of the propeller angle such that the radiation source crosses the horizontal plane including the table and / or the object only once during the acquisition of projection data. If the radiation source crosses the horizontal plane including the table and / or the patient only once during the acquisition of projection data, there is only one collision hazard during the acquisition of CT images. Therefore, the risk of collision between the C-arm system and the table and / or the object can be reduced.

[0020] In one embodiment, the control protocol determining unit is adapted to determine a sequence of roll angles and a sequence of propeller angles such that, with the platform positioned such that its longitudinal axis is parallel to the propeller shaft of the C-arm system, the roll angle is substantially zero for all propeller angles through which the radiation source passes the horizontal plane including the platform and / or the object. With the platform positioned such that its longitudinal axis is substantially aligned with the propeller shaft of the C-arm system, a roll angle of substantially zero for all propeller angles through which the radiation source passes the horizontal plane including the platform and / or the patient reduces the risk of collision. Preferably, the control protocol determining unit is adapted to determine a non-circular component such that a superimposed trajectory including both circular and non-circular components can be achieved such that, for propeller angles through which the radiation source passes the horizontal plane including the platform and / or the patient, the roll angle is substantially zero. In a preferred embodiment, the circular component is combined with the non-circular component such that, for propeller angles through which the radiation source passes the horizontal plane including the platform and / or the object, positive or negative motion in the roll angle direction of one component cancels out positive or negative motion in the roll angle direction of the other component.

[0021] In one embodiment, the control protocol determining unit is adapted to determine the sequence of roll angles and the sequence of propeller angles such that, with the platform positioned such that its longitudinal axis is parallel to the propeller shaft of the C-arm system, the roll angle is less than 20 degrees for all propeller angles below the platform where the radiation source is located. Alternatively, the roll angle can be less than 10°. Maintaining a small roll angle, for example below 20°, for propeller angles where the radiation source is located below the platform significantly reduces the risk of collision between the C-arm and the platform, and thus increases the safety of the CT image acquisition process.

[0022] In one embodiment, the control protocol determination unit is adapted to determine a sequence of roll angles and a sequence of propeller angles such that the motion of the radiation source about more than one axis of rotation is minimized. Preferably, the control protocol determination unit is adapted to determine a sequence of roll angles and a sequence of propeller angles such that the roll angles are minimized to minimize the acceleration of the C-arms of the C-arm system. Large roll angles result in large acceleration of the C-arms of the C-arm system, which can cause vibration of the C-arms, thereby producing image artifacts when reconstructing the acquired projection data. Therefore, minimizing the roll angle during the acquisition of projection data allows for the reconstruction of tomographic images with higher image quality.

[0023] In one embodiment, the control protocol determination unit is adapted to determine a sequence of roll angles and a sequence of propeller angles such that acceleration in the direction parallel to the anode rotation axis of the radiation source is minimized. In conventional C-arm systems, the anode of the radiation source rotates about an anode rotation axis to provide radiation to the detector. If the control protocol is determined to minimize acceleration in the direction parallel to the anode rotation axis of the radiation source, the rotational load on the radiation tube can be minimized. This results in improved stability of the C-arm system during the acquisition of projection data for tomographic reconstruction, and thus improves the quality of the reconstructed images.

[0024] In another aspect of the invention, a system for controlling a C-arm system is provided, comprising a) means for determining a control protocol for controlling the C-arm system as described above, and b) a control unit for controlling the C-arm system according to the determined control protocol.

[0025] In another aspect of the invention, a method is provided for determining a control protocol for controlling a C-arm system including a radiation source, wherein the control protocol includes a sequence of roll angles and a sequence of propeller angles, wherein the method includes the steps of: a) providing an inclined plane tilted relative to a vertical plane; and b) determining a control protocol by determining the sequence of roll angles and the sequence of propeller angles such that the radiation source follows a trajectory including a circular component in the inclined plane and allowing the C-arm system to acquire projection data for image reconstruction.

[0026] In another aspect of the invention, a computer program is provided for providing a control protocol for a C-arm system, wherein the computer program includes program code units that, when the computer program is run on the system, cause the device to perform the steps of the method described above.

[0027] It should be understood that the apparatus, system, and computer program described in the embodiments of the present invention have similar and / or identical preferred embodiments, particularly as defined in the dependent claims.

[0028] It should be understood that the preferred embodiments of the present invention may also be any combination of the dependent claims or the above embodiments with their respective independent claims.

[0029] These and other aspects of the invention will become apparent and will be explained with reference to the embodiments described herein. Attached Figure Description

[0030] These and other aspects of the applicator device, system, and method according to the present invention will be further illustrated and described with reference to the accompanying drawings, wherein,

[0031] Figure 1 An embodiment of a system including means for providing a control protocol for a C-arm system is illustrated schematically and exemplary.

[0032] Figure 2 A schematic diagram illustrating the principles of the invention in more detail is shown.

[0033] Figure 3 An exemplary sequence of roll angle and propeller angle is shown in one embodiment of the device.

[0034] Figure 4 Exemplary sequences of roll angle and propeller angle for known control protocols and control protocols according to embodiments of the present invention are shown, and

[0035] Figure 5 A flowchart illustrating an exemplary embodiment of a method for providing a control protocol for controlling a C-arm system is shown. Detailed Implementation

[0036] Specific embodiments will now be described in more detail with reference to the accompanying drawings. In the following description, the same reference numerals are used for the same elements, even in different drawings. Contents defined in the description, such as detailed constructions and elements, are provided to aid in a comprehensive understanding of the exemplary embodiments. Furthermore, well-known functions or structures are not described in detail, as this would obscure the embodiments with unnecessary detail.

[0037] Figure 1 An embodiment of a system for controlling a C-arm system is illustrated schematically and exemplary, the system including means for determining a control protocol for controlling the C-arm system. System 100 includes a control unit 110 for controlling the movement of the C-arm 144 of the C-arm system 140 according to the control protocol determined by means 120.

[0038] The exemplary C-arm system 140 of this embodiment includes an attachment device 141, which can be movably and / or rotatably attached to a ceiling, or a wall or floor of a room including the C-arm system 140. Furthermore, the C-arm system 140 includes a C-arm 144 attached to the attachment device 141 via a roll device 143 and a propeller device 142. The propeller device 142 allows rotational movement 148 about a propeller axis defined by the propeller device 142. In the preferred embodiment shown herein, the propeller device 142 provides a propeller shaft located in a horizontal plane. The roll device 143 allows roll movement 147 of the C-arm 144 about a roll axis. In the preferred embodiment shown, the roll axis is also located in a horizontal plane and perpendicular to the propeller shaft. The C-arm 144 also includes a radiation source 145 and a radiation detector 146 for detecting radiation from the radiation source 145 that has passed through an object lying on a table 131, such as a patient 130.

[0039] Control unit 110 is adapted to control the movement of C-arm 144. Specifically, control unit 110 controls the movement of C-arm 144 relative to propeller movement 148 and tilt movement 147. Furthermore, control unit 110 is adapted to control C-arm system 140 such that radiation source 145 follows a sequence of positions determined by specific roll angles and propeller angles defined in the control protocol provided by device 120. At each position provided by the control protocol, images of patient 130 can be acquired. When C-arm system 140 is initiated from a non-moving position of C-arm 144, control unit 110 may also be adapted to control the movement of C-arm 144 such that C-arm 144 is slowly accelerated and, if a desired speed is reached, begins to follow the sequence of positions provided by the control protocol. For example, control unit 110 may be adapted to control C-arm 144 according to a predetermined acceleration trajectory of radiation source 145 at the start of movement of C-arm 144, and control unit 110 may then be adapted to control C-arm 144 such that the acceleration trajectory is connected to the trajectory of radiation source 145 provided by the control protocol without interruption, such that the acceleration trajectory and the trajectory provided by the control protocol result in continuous movement of C-arm 144. Preferably, control unit 110 controls C-arm system 140 such that projection data, i.e., images of patient 130, begins to be acquired after the acceleration trajectory has been followed.

[0040] Apparatus 120 is adapted to determine a control protocol for C-arm system 140. Apparatus 120 includes a tilt plane providing unit 121 and a control protocol determining unit 122. Tilt plane providing unit 121 is adapted to provide a tilt plane 133 tilted relative to vertical plane 132. For example, the tilt plane providing unit may be configured to receive a desired tilt plane 133 from a user and provide the received tilt plane 133. Preferably, the tilt plane providing unit receives a desired tilt angle between the tilt plane 133 and vertical plane 132 and a desired tilt direction, and provides the tilt plane 133 based on the tilt angle and tilt direction. Alternatively, the tilt angle may be provided along with a positive or negative sign to indicate the tilt direction of the tilt plane, wherein the relationship between the positive / negative sign and the tilt direction may be based on a predetermined agreement. Furthermore, tilt plane providing unit 121 may be configured to provide the user with multiple possible trajectories, multiple fixed tilt angles, and / or multiple fixed tilt planes, wherein tilt plane providing unit 121 is then adapted to provide the tilt plane based on the user's selection.

[0041] The control protocol determination unit 122 is adapted to determine a control protocol by determining a sequence of roll angles and a sequence of propeller angles, such that the radiation source 145 follows a trajectory that includes a circular component in the tilted plane 133 and also allows the C-arm system 140 to acquire projection data for tomographic image reconstruction. For example, if the trajectory of the radiation source 145 includes only a circular component in the tilted plane, the control protocol determination unit 122 is adapted to determine a roll angle provided by the roll device 143 for each propeller angle provided by the propeller device 142, such that the radiation source 145 is located within the tilted plane 133. In the embodiment shown here, this corresponds to a radiation source 145 providing radiation to the detector 146 within the tilted plane 133. The advantages of such a trajectory are as follows: Figure 2 As shown.

[0042] exist Figure 2 The image slice 200 of a tomographic reconstruction of patient 130 is shown. In this case, the tomographic image of patient 130 was acquired using conventional tomographic image acquisition with a C-arm system (such as C-arm system 140), where the tilt plane 133 is not defined and the trajectory of the radiation source 145 includes the principal circular component within the vertical plane 132. This is schematically indicated by the orientation of box 210. In this case, the projection of the patient's teeth, which can be considered highly attenuated objects, shown in region 211, results in image artifacts that are very prominent during image reconstruction, for example, in region 212. In particular, the image artifacts are very prominent in region 212, located within a portion of the image reconstruction of interest for the patient's diagnosis, such as the patient's head in cases of brain injury frequently assessed using tomographic imaging. Figure 2The image is also schematically illustrated as being acquired by radiation source 145 along a circular component located within a tilted plane 133. In this case, as schematically indicated by box 220, the radiation provided by radiation source 145 to detector 146 follows a path that does not cause image artifacts of the patient's teeth within the region of interest (like the brain) of the patient's head. Therefore, providing tilted plane 133 allows for the selection of a path for the radiation provided by radiation source 145, a path that allows for the avoidance of image artifacts caused, for example, by high-attenuation objects in the region of interest.

[0043] In the following sections, some exemplary trajectories will be discussed, in which it is assumed that the platform 131 and the object are in the head position, i.e., the longitudinal axis of the platform 131 is oriented parallel to the propeller shaft, such that the propeller shaft corresponds substantially to the line 131 passing through the middle of the platform. Figure 3 An exemplary representation of the sequence of propeller angles with respect to propeller axis 320 and roll angles with respect to propeller axis 310 is shown, where the tilt plane 133 is defined by a tilt angle of 15°, which defines the trajectory of the radiation source 145 within the tilt plane 133. To define the orientation of the tilt plane, in this case, it is further defined that the C-arm should tilt -15° when the radiation source 145 is below the platform 131. In this exemplary case, the radiation source 145 follows a trajectory that includes only a circular component within the tilt plane 133. To ensure that the trajectory lies within the tilt plane 133 with a tilt angle of 15° tilted in the direction toward the C-arm system 140, the roll angle must be -15° when the propeller angle is 0°, the roll angle must be 0° when the propeller angle is -90° or +90°, and the roll angle must be +15° when the propeller angle is -180° or +180°. This is illustrated by graph 330.

[0044] For example, the trajectory shown in Figure 330 can be determined using the following formula:

[0045] (1)

[0046] in, Indicates the roll angle. Within the range of 0 to 1 and indicating the propeller angle, Corresponding to the provided tilt angle, It is the selected frequency of the trajectory, and Corresponding to the selected phase shift. Parameter This can be determined by varying the range of the propeller angle. For example, if the propeller angle range is from 0° to 360°, then for This range can be linearly transformed to the range of 0 to 1. Frequency It refers to the spatial frequency and indicates the number of oscillations of the C-arm around the roll axis during a complete rotation of the C-arm around the propeller shaft.

[0047] For example, if the trajectory should only include the circular component in the inclined plane, It can be selected as 1 and It can be selected as 0. In other embodiments, the parameter and Other requirements for achieving a trajectory can be met, such as for selecting... A value greater than 1 is used to introduce non-circular components or to be used by selecting accordingly. This is to determine the start and end points of the trajectory. Additionally, This can also be used to determine where, in the trajectory of radiation source 145, the maximum roll angle relative to the platform 131 is provided. Furthermore, other conditions can be introduced into the above formula. For example, providing a symmetrical trajectory is often advantageous, on which conditions are applied.

[0048] (2)

[0049] This condition makes the above formula (1) as follows:

[0050] (3)

[0051] Using this relationship to replace the first formula Thus, the roll angle formula that satisfies the symmetry condition of a symmetric trajectory is obtained.

[0052] In order for the C-arm system 140 to acquire projection data for tomographic image reconstruction, a complete set of views of the patient 130 must be acquired. This can be achieved, for example, by acquiring projection data from multiple views exceeding 180° around the propeller axis. Therefore, the control protocol determination unit 122 can be adapted to... Figure 3 The curve 330 shown identifies any range slightly greater than 180° as the position sequence of the radiation source 145 and the corresponding roll angle sequence and propeller angle sequence as the control protocol. For example, in one embodiment, the control protocol determination unit 122 may determine the roll angle sequence and propeller angle sequence between -100° and +100° propeller angles in the curve 330 as part of the control protocol.

[0053] In more advanced embodiments, the trajectory followed by the radiation source 145 may include additional non-circular components. In these cases, the control protocol determination unit 122 may be adapted, for example, to determine the non-circular components such that the C-arm system 140 can obtain projection data that satisfies the Tuy condition. In particular, non-circular components may be introduced, which include the forward and backward movement component of the radiation source 145 perpendicular to the inclined plane 133. Furthermore, the trajectory may be chirped by introducing more trajectory components, wherein chirping corresponds to providing additional trajectory components such that the resulting components include frequencies that vary with the propeller angle, for example, as in Figure 4 The curve is shown in graph 420. Regarding... Figure 4 To explain such a trajectory in more detail, graph 410 illustrates the chirp in the known case where the tilt plane 133 is not provided and the radiation source 145 follows a trajectory that satisfies the Tuy condition, including a circular component located within the vertical plane 132. Axis 440 shows the roll angle and axis 430 shows the propeller angle for such a trajectory when it is chirped. The chirp causes the trajectory in graph 410 to have a frequency shift from a lower frequency at a lower propeller angle to a higher frequency at a higher propeller angle.

[0054] Figure 420 illustrates the sequence of roll and propeller angles for the case of an inclined plane 133 with a tilt angle of 15° according to the present invention. To satisfy the Tuy condition, the trajectory of the radiation source 145 includes an additional non-circular component, which includes back-and-forth motion about a roll axis between -17° and +17°. In this case, the addition of the back-and-forth motion component is chosen such that for propeller angles between -160° and -90°, the back-and-forth motion and roll motion of the circular component in the inclined plane 133 almost cancel each other out, resulting in only small roll angles for these propeller angles. This leads to a chirped trajectory and has the further advantage of avoiding partial collisions with the table 131 or the patient 130.

[0055] Accordingly, graph 420 is also an example of another embodiment of the present invention, wherein device 120 further includes Figure 1 A table position providing unit, not shown, is adapted to provide the position and orientation of the table 131. In such an embodiment, the control protocol determining unit 122 is adapted to further determine a control protocol including a sequence of roll angles and a sequence of propeller angles based on the position and orientation of the table 131. For example, when the control protocol determining unit 122 is adapted to take into account the position and orientation of the table 131, a sequence of roll angles and a sequence of propeller angles of the control protocol can be determined such that the risk of collision between a portion of the C-arm 144 and a portion of the table 131 or the patient 130 can be minimized. For example, if the trajectory of the radiation source 145 includes only a circular component in the inclined plane 133, the control protocol determining unit 122 can be adapted to determine based on Figure 3The curve 330 shown selects a sequence of propeller angles such that the propeller angle of the radiation source 145 or detector 146, located within a horizontal plane passing through the patient 130 or the table 131, is provided only once in the trajectory of the radiation source 145. In the exemplary embodiment shown here, this would correspond to selecting a sequence of propeller angles including approximately 90° only once, wherein such a sequence could be a sequence of propeller angles between -60° and 120° respectively.

[0056] If an additional non-circular component is introduced into the trajectory of the radiation source 145, for example, to satisfy the Tuy condition, this additional non-circular component can be selected to manipulate the trajectory of the radiation source 145, thereby minimizing the collision risk between the C-arm 144 and the table 131 or the patient 130. As described above, an example of this embodiment is... Figure 4 The curve is given in graph 420.

[0057] For example, the chirping trajectory shown in Figure 420 and discussed above can be determined by using the following formula, which corresponds to the extension of formula (1):

[0058] (4)

[0059] In this formula, the parameters corresponding to those in formula (1) are represented by the same characters, and and These are the parameters for controlling the chirp of the control trajectory. and Can be related to frequency They are used together to introduce non-circular components, for example, to satisfy the Tuy condition. However, other conditions can also be introduced into the trajectory using the above formula (4). For example, in some embodiments, in Provides the maximum value of the trajectory. Specifically, this condition can be used to acquire trajectories that satisfy the Tuy condition, as such boundary conditions make it more difficult to find the plane through which the trajectory passes the radiation source 145. If m is chosen as 0 in this case, this condition results in the following phase shift:

[0060] (5)

[0061] In formula (4) Using this relationship substitution, the roll angle formula satisfies the following condition: the maximum value of the trajectory is always within... Provided here, as described above, it makes it easier to find trajectories that satisfy the Tuy condition. Depending on the given example, other conditions for the trajectory can also be selected and incorporated into formula (4). It should be noted that formulas (1) and (4) above are only used to describe the trajectories defined in the above embodiments and to determine the corresponding roll angle and propeller angle. Alternatively, these formulas can be used in modified forms or other mathematical descriptions, such as series expansions like Fourier series, which can be used to describe the trajectory and determine the corresponding roll angle and propeller angle under specific conditions.

[0062] In the following text, see references Figure 5 The flowchart shown illustrates an embodiment of a method 500 for determining a control protocol for controlling a C-arm system 140. In step 510, an inclined plane 133 is provided relative to a vertical plane 132. For example, the inclined plane 133 may be provided with reference to user input. In the next step 520, a control protocol is determined by determining a sequence of roll angles and a sequence of propeller angles of the C-arm 144 of the C-arm CT system 140, such that the radiation source 145 follows a trajectory that includes a circular component in the inclined plane 133 and allows the C-arm system 140 to acquire projection data for tomographic image reconstruction.

[0063] In many applications, cone-beam C-arm systems use cone-beam CT scans to visualize a patient's soft tissue in three dimensions, such as visualizing a stroke in the head or a tumor in the liver. Currently, this type of cone-beam CT is achieved using a circular trajectory of the radiation source, i.e., a circular trajectory in the vertical plane. With such a trajectory, accurate reconstruction can only be obtained within the plane of rotation. Outside the plane of rotation, i.e., in the vertical plane, cone-beam CT exhibits more pronounced artifacts than when far from this plane. This is due to the failure to meet the Tuy condition.

[0064] Artifact-free tomographic images can be obtained through the additional non-circular component of the trajectory. For such a trajectory, the closed region of the trajectory, i.e., the convex hull, must enclose the region of interest to satisfy the Tuy condition. Such a trajectory can be achieved using a C-arm system, for example, through biaxial scanning, i.e., by providing a sequence of propeller angles and roll angles during the acquisition of projection data. In such biaxial scanning, i.e., during the acquisition of projection data, the C-arm of the C-arm CT system moves according to a predetermined control protocol including the sequence of propeller angles and the sequence of roll angles, moving simultaneously on the primary rotation axis (e.g., the propeller rotation axis) and the secondary rotation axis (e.g., the roll rotation axis). In this case, the system must move more than 180° around the primary axis in the same manner as in circular scanning, while simultaneously moving back and forth on the secondary rotation axis. In one example of neuroimaging, the C-arm is positioned to scan the patient's head, with the primary rotation axis realized by the propeller axis and the secondary rotation axis realized by the roll axis.

[0065] According to the invention, instead of a circular scan in the vertical plane 132, an angled scan in the inclined plane is provided by using an inclined C-arm. For example, in an angled head CT scan, fewer artifacts of teeth in the cerebellum can be expected. Furthermore, in this example, the X-ray dose on the thyroid gland (which is the most sensitive organ in this region) can be significantly reduced.

[0066] Therefore, this invention proposes, for example, angled cone-beam CT scanning. Cone-beam CT scanning including a circular component in an inclined plane tilted relative to the vertical plane is advantageous for, for example, neuroimaging. For most applications, a slight angle of the inclined plane, with an absolute angle of 10° to 25°, is expected to be sufficient. The angle, i.e., motion in the inclined plane, can be provided by roll motion, for example, in neuroimaging, where the stage is in a head position, i.e., the stage is positioned such that the longitudinal axis of the stage is parallel to the propeller axis. In this case, since the roll sleeve, i.e., the roll device, is physically connected to the propeller device, and during the scan, the propeller device moves the C-arm more than 180°, the roll angle should not remain constant to achieve motion in the inclined plane. Instead, the roll angle should be continuously adjusted to provide motion in the inclined plane. In addition to the circular component in the inclined plane, the trajectory may also include other components, such as motion components for satisfying the Tuy condition.

[0067] For purely circular scans, i.e., scans containing only the circular component in the tilted plane, in the case of head scans, i.e., when the propeller position is below -90° and above +90°, the angle (i.e., tilt) results in a positive roll angle below the table. In such applications, the angle may lead to collisions with the table and / or the patient. This risk is further increased for obese patients or when the patient is off-center. In one embodiment of the invention, additional measures are proposed to avoid or reduce the risk of collision when determining the trajectory of the radiation source.

[0068] For example, when determining the sequence of roll angles and the sequence of propeller angles, important aspects of the trajectory that the control protocol determination unit can consider could be the integrity of the trajectory relative to the Tuy conditions, the minimum use of different rotation axes to improve stability and repeatability, moderate or minimum acceleration of the radiation source (i.e., the X-ray tube) parallel to the anode rotation axis to minimize rotational load on the tube, minimizing image acquisition time to avoid motion artifacts and achieving higher spatial resolution by reducing the angular range in the propeller rotation direction, or increasing rotation and acceleration, and / or minimizing collision risk.

[0069] Specifically, in the proposed embodiments, the control protocol determination unit can be adapted to minimize collision risk, for example, by selecting a starting position relative to the table or the patient's position. For example, a symmetrical scan with a propeller angle from -100° to +100° creates two channels for the table and the patient's shoulder in a head scan, while if an open trajectory is selected, i.e., a trajectory with a propeller angle from -80° to +120°, only one channel for the table and the patient's shoulder is provided in a head scan, thus providing sufficient space to position the patient and avoid collisions. Furthermore, if a non-circular component (e.g., forward and backward motion satisfying the Tuy condition) is added to the circular component in the inclined plane, this non-circular component can be defined such that the overall trajectory of the radiation source is substantially 0° when the C-arm passes over the patient's table and / or shoulder to avoid collisions. For conventional head scans, this condition applies to approximately -90° or +90°. Additionally, if a non-circular component, such as forward and backward motion, is provided to satisfy the Tuy condition, the non-circular component can be selected such that the total roll angle of the radiation source trajectory is negative below the table. Below the table, negative roll angle moves the C-arm in a conventional head scan into free space, while positive roll angle moves it toward the table and / or the patient. For example, a non-circular component can be selected such that the negative roll angle of the non-circular component below the table cancels out or reduces the positive roll angle that might be needed to provide the circular component in an inclined plane. Thus, collision risk can be avoided or reduced.

[0070] It was also suggested that, for specific applications, relaxing the criteria used to determine the control protocol might be acceptable to support other recommendations, such as providing an aspect of moderate / minimum acceleration of the X-ray tube parallel to the axis of anode rotation. This could be achieved, for example, by allowing a chirp at a sinusoidal frequency while satisfying all other constraints and providing only a lateral crossover. Furthermore, minimizing the propeller angle to minimize scan time may violate the Tuy condition. However, in moderate cases, this is acceptable, where voxels causing artifacts can be masked in the reconstructed volume rather than displayed to the user. Additionally, depending on the patient's size, a trajectory with a lower angle, i.e., the tilt of the tilt plane, can be selected. For example, in some applications where the trajectory includes a 60° propeller angle and approximately 10° roll angle during head scans of very obese patients, this could lead to collisions. In such cases, the tilt of the tilt plane could be reduced to prevent such collisions.

[0071] Such trajectories can be achieved using a classic C-arm system or a C-arm system that allows two robotic arms to move the source and detector independently. The latter also allows for variations in the source-detector distance during acquisition. For a larger field of view, an eccentric detector can also be used to perform the trajectory twice at two different offset locations.

[0072] While the C-arm system described in the above embodiments is a conventional C-arm system, in other embodiments, the C-arm system may also be a C-arm system in which the detector and the source can be moved independently of each other using two robotic arms. In this case, the propeller and roll angles can be defined according to conventional C-arm systems, for example, relative to the line of sight between the radiation source and the detector.

[0073] Although in the above embodiments the platform is provided at the head position, i.e., in the typical position for providing tomographic images of the patient's head, in other embodiments the platform can be positioned and oriented in different ways. For example, the platform orientation can be perpendicular to the direction shown in the example above. In this case, the control protocol determination unit is adapted to determine a sequence of roll angles and a sequence of propeller angles, such that the propeller angles provide the tilt of the C-arm required to move the radiation source in the corresponding tilt plane and the roll angles provide the movement required to acquire projection data for tomographic image reconstruction. Furthermore, in other embodiments, the platform can be arbitrarily oriented and positioned relative to the C-arm system, and the control protocol determination unit is adapted to take into account the position and orientation of the platform to provide a corresponding trajectory of the radiation source.

[0074] Although the object in the above embodiments is a patient, in other embodiments the object can be an animal or even an inanimate object, such as a suitcase. Therefore, while the invention has been described in the above embodiments within the context of a medical application, it can also be applied to other contexts, such as border control.

[0075] Although the region of interest imaged in the above embodiments is the patient's head, in other embodiments, other regions of interest, such as the heart, liver, or any other organ of the patient, can be imaged. The principles described regarding the patient's head can be applied accordingly to these other regions of interest.

[0076] Those skilled in the art, through studying the accompanying drawings, the disclosure, and the claims, will be able to understand and implement other variations of the disclosed embodiments when practicing the claimed invention.

[0077] In the claims, the word "comprising" does not exclude other elements or steps, and the words "a" or "an" do not exclude a plurality.

[0078] A single unit or device can perform the functions of several items listed in the claims. Although specific measures are recited in different dependent claims, this does not imply that combinations of these measures cannot be used advantageously.

[0079] Processes such as generating a tilt plane or determining a control protocol, which are performed by one or more units or devices, can be performed by any other number of units or devices. For example, these processes can be performed by a single device. The processes and / or controls of these devices for determining the control protocol can be implemented as program code units of a computer program and / or as dedicated hardware.

[0080] Computer programs can be stored / distributed on suitable media, such as optical storage media or solid-state media that are provided together with or as part of other hardware, but computer programs can also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems.

[0081] Various aspects of the present invention can be implemented in a computer program product, which may be a collection of computer program instructions stored on a computer-readable storage device that can be executed by a computer. The instructions of the present invention can be any interpretable or executable code mechanism, including but not limited to scripts, interpretable programs, dynamic link libraries (DLLs), or Java classes. The instructions can be provided as a complete executable program, a partial executable program, as a modification (e.g., an update) to an existing program, or as an extension (e.g., a plugin) to an existing program. Furthermore, portions of the processing of the present invention can be distributed across multiple computers or processors.

[0082] As described above, a computer program can enable a processor or controller to implement control methods according to a control protocol. A processor or controller can be implemented in various ways, using software and / or hardware, to perform a variety of desired functions. A processor is one example of a controller, employing one or more microprocessors that can be programmed using software (e.g., microcode) to perform the desired functions. However, a controller can be implemented with or without a processor, and can also be implemented as a combination of dedicated hardware for performing some functions and a processor (e.g., one or more programmed microprocessors and associated circuitry) for performing other functions.

[0083] Examples of controller components that may be used in various embodiments of this disclosure include, but are not limited to, conventional microprocessors, application-specific integrated circuits (ASICs), and field-programmable gate arrays (FPGAs).

[0084] In various implementations, the processor or controller may be associated with one or more storage media, such as volatile and non-volatile computer memories, such as RAM, PROM, EPROM, and EEPROM. The storage media may be encoded with one or more programs that perform desired functions when executed on one or more processors and / or controllers. The various storage media may be fixed within the processor or controller, or they may be portable, allowing one or more programs stored thereon to be loaded into the processor or controller.

[0085] Any reference numerals in the claims should not be construed as limiting the scope.

[0086] This invention relates to an apparatus for determining a control protocol for controlling a C-arm system including a radiation source. The control protocol includes a sequence of roll angles and a sequence of propeller angles. The apparatus includes: a tilt plane providing unit for providing a tilt plane tilted relative to a vertical plane; and a control protocol determining unit for determining the control protocol by determining the sequence of roll angles and the sequence of propeller angles, such that the radiation source follows a trajectory including a circular component in the tilt plane and allowing the C-arm system to acquire projection data for tomographic image reconstruction. The apparatus allows for the acquisition of computed tomographic images with improved quality and reduces radiation in radiation-sensitive areas.

[0087] Although the invention has been illustrated and described in detail in the accompanying drawings and the foregoing description, such illustrations and descriptions should be considered illustrative or exemplary, and not restrictive. The invention is not limited to the disclosed embodiments.

[0088] Those skilled in the art, through studying the accompanying drawings, disclosure, and claims, will understand and implement other variations of the disclosed embodiments when practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the words "a" or "an" do not exclude a plurality. Although specific measures are recited in dissimilar dependent claims, this does not imply that combinations of these measures cannot be advantageously used. Computer programs may be stored / distributed on suitable media such as optical storage media or solid-state media provided with or as part of other hardware, but may also be distributed in other forms such as via the Internet or other wired or wireless telecommunications systems. No reference numerals in the claims should be construed as limiting the scope.

Claims

1. An apparatus for determining a control protocol for controlling a C-arm system (140) including a radiation source (145), wherein, The control protocol includes a sequence of roll angles of the C-arm and a sequence of propeller angles of the C-arm system, wherein the device (120) includes: An inclined plane providing unit (121) is used to provide an inclined plane (133) inclined relative to a vertical plane (132), and A control protocol determination unit (122) is configured to determine the trajectory of the radiation source by determining a sequence of roll angles and a sequence of propeller angles, the trajectory including a non-circular component and a circular component in the tilted plane, and to determine a control protocol such that the radiation source (145) follows the trajectory, thereby allowing the C-arm system (140) to acquire projection data for image reconstruction of the region of interest, wherein, when the C-arm system (140) is controlled according to the determined control protocol, the non-circular component allows the C-arm system (140) to acquire projection data along a trajectory that satisfies the Tuy condition.

2. The apparatus according to claim 1, wherein, The non-circular component includes the forward and backward movement component of the radiation source (145) perpendicular to the inclined plane.

3. The apparatus according to any one of claims 1-2, wherein, The device (120) further includes a table position providing unit for providing the position and orientation of the table (131) with respect to the C-arm system (140), wherein the object (130) to be imaged by the C-arm system (140) is positioned on the table (131), wherein the control protocol determining unit (122) is adapted to also determine the sequence of roll angles and the sequence of propeller angles based on the position and orientation of the table (131).

4. The apparatus according to claim 3, wherein, The control protocol determination unit (122) is adapted to determine the sequence of the roll angle and the sequence of the propeller angle such that the risk of collision between a portion of the C-arm system (140) and the platform (131) and / or the object (130) is minimized during the acquisition of the projection data.

5. The apparatus according to any one of claims 3 and 4, wherein, The control protocol determination unit (122) is adapted to determine the sequence of the roll angle and the sequence of the propeller angle such that during the acquisition of projection data, the radiation source (145) crosses the horizontal plane including the platform (131) and / or the object (130) only once.

6. The apparatus according to any one of claims 3 to 5, wherein, The control protocol determination unit (122) is adapted to determine the sequence of roll angles and the sequence of propeller angles such that, when the platform (131) is positioned such that the longitudinal axis of the platform (131) is parallel to the propeller shaft of the C-arm system (140), the roll angle is substantially zero for all propeller angles through which the radiation source (145) passes the horizontal plane including the platform (131) and / or the object (130).

7. The apparatus according to any one of claims 3 to 6, wherein, The control protocol determination unit (122) is adapted to determine the sequence of roll angles and the sequence of propeller angles such that, when the platform (131) is positioned such that the longitudinal axis of the platform (131) is parallel to the propeller shaft of the C-arm system (140), the roll angle is less than 20° for each propeller angle of the radiation source (145) above the platform (131).

8. The apparatus according to any one of claims 1-2, wherein, The control protocol determination unit (122) is adapted to determine the sequence of the roll angle and the sequence of the propeller angle such that the motion of the radiation source (145) around more than one rotation axis is minimized.

9. The apparatus according to any one of claims 1-2, wherein, The control protocol determination unit (122) is adapted to determine the sequence of the roll angle and the sequence of the propeller angle such that the acceleration in the direction parallel to the anode rotation axis of the radiation source (145) is minimized.

10. A system for controlling a C-arm system (140), comprising: The apparatus (120) for determining a control protocol for controlling a C-arm system (140) including a radiation source (145) as described in claim 1, and Control unit (110) for controlling the movement of the C-arm (144) of the C-arm system (140) according to a determined control protocol.

11. A method for determining a control protocol for controlling a C-arm system (140) including a radiation source (145), wherein, The control protocol includes a sequence of roll angles of the C-arm and a sequence of propeller angles of the C-arm system, wherein the method (500) includes the following steps: Provide (510) an inclined plane (133) that is tilted relative to the vertical plane (132), and The trajectory of the radiation source (122) is determined by determining the sequence of the roll angle and the sequence of the propeller angle, the trajectory including a non-circular component and a circular component in the tilted plane, and a control protocol is determined such that the radiation source (145) follows the trajectory, thereby allowing the C-arm system (140) to acquire projection data for image reconstruction of the region of interest, wherein, when the C-arm system (140) is controlled according to the determined control protocol, the non-circular component allows the C-arm system (140) to acquire projection data along a trajectory that satisfies the Tuy condition.

12. A computer program product comprising a computer program for providing a control protocol for a C-arm system (140), wherein, The computer program includes program code units configured to cause the device to perform the steps of the method according to claim 11 when the computer program is running on the device according to claim 1.

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