Method and control device for controlling a computer tomography system

Description

[0001] The invention relates to a method and a control device for controlling a computed tomography system and a computed tomography system ("CT system").

[0002] In CT examinations of locally limited anatomy ("CT": computer tomography), eg For example, for the breast, conventional imaging techniques and image reconstruction capture an insufficient number of projection angles for the desired anatomy. In this specific case, projections through the spine would be used to depict the breast, axilla, and anterior thoracic wall, which have a high dose and may also be subject to artifacts. These may, for example, exhibit hardening artifacts.

[0003] Furthermore, the use of dedicated positioning aids (compression-free "hanging" imaging of the parenchyma) is particularly necessary for (female) breast imaging. However, these result in suboptimal patient positioning for conventional data acquisition and reconstruction (off-center positioning).

[0004] A reduction in image quality also occurs for a number of examinations without dedicated positioning aids, e.g. lateral positioning during liver intervention.

[0005] The cross-sectional imaging techniques used to monitor interventions and radiotherapy positioning (e.g., flat-panel CT) share the same basic problems and differ only in the pronounced cone beam projection compared to conventional CT technology. With regard to the CT-based breast imaging mentioned as an example, a dedicated breast CT exists. Due to the technical and physical constraints of the system, the technique used does not allow for visualization of the thoracic wall and axilla. Likewise, simultaneous visualization of both breasts is not possible, which has potentially negative implications for clinical use in dynamic examinations (e.g., contrast agent dynamics). Furthermore, simultaneous imaging and accessibility of the breast for interventions, as is achieved with MRI, is currently not possible with such a system.

[0006] Currently, only customized positioning aids are used to counteract this problem. In the field of CT-based breast imaging, analogous to MRI, there are individually manufactured positioning aids for imaging, or, in the case of dedicated breast scanners, corresponding structural measures for breast positioning.

[0007] It is an object of the present invention to provide an alternative, more convenient method and a corresponding device for controlling a computed tomography system, with which the disadvantages described above are avoided.

[0008] This object is achieved by a method according to patent claim 1, a control device according to patent claim 10 and a computed tomography system according to patent claim 12.

[0009] The method according to the invention is used to control a computed tomography system. It allows for improved image quality and also offers a dose reduction for the patient, particularly when using high-resolution CT techniques such as photon counting technology. Especially when imaging anatomical regions where high resolution combined with low contrast is advantageous for diagnostic results, the method offers the control of image artifacts while maintaining a comparatively low radiation dose.

[0010] The procedure includes the following steps: Defining an examination region of an examination object, defining a number of interfering structures, where an interfering structure is a structure that lies within the beam path of the computed tomography system and reflects or absorbs X-rays with an intensity outside a tolerance range, calculating the beam paths of the X-rays of a CT examination of the examination region and determining interfering angle regions of a gantry of the computed tomography system in which beam paths lead through an interfering structure and the examination region, performing a CT scan while the gantry is rotating and recording CT data, reconstructing an image dataset from the CT data while omitting determined interfering angle regions, outputting the image dataset.

[0011] Theoretically, the object under examination can be any body, and the examination area can be a part of that body or the entire body. Preferably, the object under examination is a human being, and the examination area is an organ or a body region. The examination area is typically determined prior to the examination.

[0012] A number of interfering structures are also identified prior to the examination. This can be a single one, or several. An interfering structure lies within the beam path of the computed tomography system, i.e. is hit by X-rays and reflects or absorbs them. However, not just any structures are considered interfering structures, but only those whose reflection or absorption is outside a tolerance range, e.g., above or below a predetermined limit. The tolerance range or corresponding materials and dimensions for structures are determined in advance. In a human, for example, bone material can be interfering, and larger bones, such as the spine in particular, can be viewed as interfering structures. However, parts of the patient bed or positioning aids could also be considered interfering structures.Essentially, a physician knows which structures have a disruptive influence on the images. These structures can then be defined as "interference structures" for the procedure. Preferred interfering structures have a known position in the body or in the area of ​​examination and are image regions with high Hounsfield units. However, air can also represent an interfering structure. In this case, image regions with the lowest Hounsfield units are preferred as interfering regions.

[0013] If the abnormal structures are known, their location is also essentially known. For example, in a human, the bone structure is known, and the location of the spine can easily be identified as an example of an abnormal structure, even if one cannot (at this point) see inside the person.

[0014] With the known location of the interfering structure and the defined position of the examination area, the X-ray beam paths of a CT examination can now be calculated. Note that the X-ray source is still turned off. Only the theoretical paths are determined. It is preferable to position the patient (or the object under examination) so that the number of interfering structures is (significantly) eccentric to the isocenter.

[0015] The calculated beam paths are then used to determine whether they pass through an interfering structure and the examination area. The angles at which the X-ray source would emit X-rays passing through an interfering structure and the examination area are referred to as the "interference angle," and the range of the interfering angles is referred to as the "interference angle range." The interference angle ranges are therefore the angular ranges that the rotating gantry can assume, within which X-rays would be emitted that pass through an interfering structure and the examination area. It can be tolerated if an X-ray beam were to pass through the interfering structure only after passing through the examination area. These angular ranges can therefore preferably not be considered interference angle ranges.

[0016] Once the interference angle ranges have been determined, a CT scan can be performed using a rotating gantry, and CT data (basically images) can be acquired.

[0017] An image dataset is then reconstructed from this CT data. Identified areas of interference angle are omitted. Note that not all interference angles necessarily have to be omitted. For example, if two separate examination areas are present, a first interference angle area can be omitted for the reconstruction of a first image dataset of the first examination area, and a second interference angle area can be omitted for the reconstruction of a second image dataset of the second examination area.

[0018] A reduction in the dose can be achieved by switching off an X-ray source in the interference angle ranges during the image acquisition.

[0019] The reconstructed image dataset is then output. It can be displayed for immediate diagnosis or saved for later analysis.

[0020] The procedure essentially cuts out areas from the possible CT data that would degrade the image. It should be noted that reconstruction typically requires an acquisition angle of slightly more than 180°. Therefore, it is advantageous if, when there are opposing angle ranges of interference, the angle range where the interference is less severe is not considered an interference angle range. Alternatively or additionally, CT data for the interference angle ranges can be simulated or calculated (e.g., using a suitably trained AI) and used for reconstruction.

[0021] Using the interference angle ranges, the necessary projections for the examination area can be defined while avoiding projections that limit image quality and thus result in dose-inefficient projections. Specifically, for example, beam paths through the bony spine can be avoided. This can be done for both sequential and spiral images.

[0022] The control device according to the invention for controlling a computed tomography system is preferably designed to carry out the method according to the invention. It comprises the following components: an examination unit designed to define an examination region of an examination object, a disturbance structure unit designed to define a number of disturbance structures, wherein a disturbance structure is a structure that lies within the beam path of the computed tomography system and reflects or absorbs X-rays with an intensity outside a tolerance range, a calculation unit designed to calculate the beam paths of the X-rays of a CT examination of the examination region and to determine disturbance angle ranges of a gantry of the computed tomography system in which beam paths lead through a disturbance structure and the examination region, a data interface designed to output control commands for performing a CT scan while the gantry rotates and to receive CT data,a reconstruction unit designed to reconstruct an image data set from the CT data while omitting determined interference angle ranges, a data interface designed to output the image data set. ,

[0023] The function of the components has been described in detail above in the context of the method according to the invention.

[0024] A computed tomography system according to the invention comprises a control device according to the invention or is designed alternatively or additionally for implementing the method according to the invention. Preferably, the CT system comprises a flat-panel detector.

[0025] A large part of the aforementioned components of the control device can be implemented wholly or partially in the form of software modules in a processor of a corresponding computer system. A largely software-based implementation has the advantage that even previously used computer systems can be easily retrofitted by a software update in order to operate in the manner according to the invention. In this respect, the object is also achieved by a corresponding computer program product with a computer program that can be loaded directly into a computer system, with program sections in order to carry out the steps of the method according to the invention, at least the steps that can be carried out by a computer, when the program is executed in the computer system. Such a computer program product can, in addition to the computer program, optionally contain additional components such as documentation and / or additional components, also hardware components, such asHardware keys (dongles etc.) for using the software.

[0026] It should be noted that performing a CT scan corresponds to the transmission of corresponding control commands and the reception of CT data. The method can, in particular, be computer-implemented.

[0027] A computer-readable medium, e.g., a memory stick, a hard disk, or another portable or permanently installed data storage device, on which the program sections of the computer program that can be read and executed by a computer system are stored, can be used for transport to the computer system or control device and / or for storage on or in the computer system or control device. For this purpose, the computer system can, for example, have one or more cooperating microprocessors or the like.

[0028] Further, particularly advantageous embodiments and developments of the invention emerge from the dependent claims and the following description, wherein the claims of one claim category can also be developed analogously to the claims and description parts to form another claim category and, in particular, individual features of different embodiments or variants can be combined to form new embodiments or variants.

[0029] According to a preferred method, the CT data are acquired while omitting determined interference angle ranges. It is preferred that an X-ray source used for acquisition be switched off in interference angle ranges or at least its radiation output be reduced. This reduces the total dose. Dose modulation is preferably performed by changing beam parameters, e.g., kV setting or reference mAs.

[0030] If one wants to improve the images while maintaining the same total dose, then beam parameters, in particular the accelerating voltage and / or the current of the X-ray source, are preferably determined for the entire image based on a total angular range of 360° minus the interference angular ranges.

[0031] According to a preferred method, an interference angle range is considered to be an angle range in which rays from an X-ray source in the gantry first pass through an interference structure and then through the examination area. Since the beam is usually conical, these interference angle ranges have a more significant impact on the images than the opposite angle ranges in which the X-rays first pass through the examination area and only then hit the interference structure. The latter angle ranges can then be considered as angle ranges to be used for reconstruction (and recording).

[0032] According to a preferred method, the determination of a disturbance structure is based on a topogram of the object under investigation, a camera image of the object under investigation or a model of the object under investigation.

[0033] The object of investigation is preferably a human or animal body and a disturbing structure is a bone, a positioning aid or a part of the gantry.

[0034] According to a preferred method, the examination subject is positioned using a positioning aid. The determination of a perturbing structure is then preferably based on the position and shape of the positioning aid. In this case, the positioning aid is a perturbing structure. It is preferred that the isocenter of the examination area be determined after the examination subject has been positioned using the positioning aid. This determination is preferably performed automatically using image recognition or via communication between the positioning aid and the computed tomography system.

[0035] According to a preferred method, the examination object is fixed using a fixation device. The determination of an interfering structure is then preferably based on the position and shape of the fixation device. In this case, the fixation device, e.g., a screw, a plate, or another rigid body, is an interfering structure. This determination is preferably automated using image recognition or communication between the fixation device and the computed tomography system.

[0036] In practice, after inserting a dedicated positioning aid into the scanner, the new isocenter can be calibrated with respect to the anatomy of interest via manual input, image recognition, or direct communication between the positioning aid and the scanner. In the case of breast imaging, a predefined target region could be communicated to the CT scanner, e.g., the volume of the breast cup, or the position or extent of the breast. The same applies to fixation.

[0037] In this regard, a preferred control device comprises a positioning unit designed to determine the position of a positioning aid and / or fixation device. It is preferred that the positioning unit be designed to estimate the position based on images and / or to receive and evaluate information from the positioning aid.

[0038] According to a preferred method, when determining the interference angular ranges, it is checked whether, taking into account the entire angular range of 360° less the interference angular ranges, the remaining angular range superimposed with the remaining angular range rotated by 180° has a continuous angular range of 360°. Essentially, this check is carried out to determine whether at least 180° are available for reconstruction. It should be noted that this check does not necessarily have to be performed by rotating and superimposing a copy of the remaining angular range. However, if the remaining angular range has a complex structure, this checking method would be advantageous. If holes are present in such an overlay, then no 180° are available for reconstruction, meaning that information is missing in this case.

[0039] It is preferred that, in the event that the remaining angular range is smaller than 360°, simulated data is added to the CT data for a missing angular range before the image dataset is reconstructed, simulating images in the missing angular range. Alternatively or additionally, a missing angular range can be removed from the number of interfering angular ranges, since the interfering angular ranges are already known before an image is taken. For this purpose, it is preferred that a degree of interference is determined in the missing angular range and in an angular range rotated by 180° thereto, and that angular range with the lower degree of interference is removed from the interfering angular ranges. This is preferably the angular range in which the X-ray beam first passes through the examination area and only then strikes the interfering structure.

[0040] According to a preferred method, two or more examination areas of the examination object are defined. Interference angle ranges are preferably determined separately for both examination areas. An interference angle range is assigned to an examination area if beam paths lead through an interference structure and the respective examination area. An image data set is then reconstructed separately for each examination area, omitting the determined interference angle ranges of the respective examination area. For example, ifIf an interference structure is defined and there is a first interference angle range for the first examination area and a second interference angle range for the second examination area, then the image data set for the first examination area is reconstructed by omitting the first interference angle range and the image data set for the second examination area is reconstructed by omitting the second interference angle range.

[0041] Preferably, it is determined which interference angle ranges assigned to the examination areas are identical. The CT data can then be acquired while omitting the identical interference angle ranges. If multiple examination areas are present, the respective interference angle ranges can be disjoint. The X-ray source should then not be switched off in an interference angle range, because then there might not be enough data available for reconstruction for one examination area. However, if there is a common interference angle range, the X-ray source can be switched off there to reduce the overall dose. Therefore, it is preferable to switch off an X-ray source used for the acquisition in the identical interference angle ranges, or at least reduce its radiation output.

[0042] This allows for optimization for multiple areas to be examined. For example, contrast-enhanced imaging of both breasts would require a different number of projections for image acquisition than for the individual imaging of a breast lesion to be biopsied. Regardless of this, reconstruction is preferably performed separately based on the optimal projections for the individual target volumes.

[0043] It is also preferred that an image dataset be reconstructed from two different projection sets. In the example of contrast agent dynamics, the acquisition could be optimized to meet the need for simultaneous acquisition of both breasts. Image reconstruction can preferably be based on individually optimized projections, which can then be combined into a single image. Two different interference angle ranges can exist for these different projection sets, so that the features for two examination areas can also be applied here.

[0044] According to a preferred method, a combination of a data sparsity reconstruction technique and an iterative solution approach is used to reconstruct an image data set. In this case, the admixture of projections to display structures is preferred, in particular biopsy needles, without the need for full data acquisition as required for the detailed imaging of breast tissue. Such methods are known in the art and are used, for example, in CT to calculate data outside the areas completely covered by the detectors (extend field of view). For the method according to the invention, these techniques are particularly advantageous when the X-ray source is switched off in interference angle ranges, i.e., no CT data is acquired from those areas.

[0045] According to a preferred method, the examination area is the chest or lungs. A preferred interfering structure is the spine.

[0046] It should be noted that a disturbing structure does not necessarily have to absorb or reflect a particularly large amount of radiation; depending on the type of examination, a disturbing structure can also reflect or absorb very little radiation (i.e., less than a predefined threshold). For example, in a biopsy of a bone process in the iliac crest, projections that contain a lot of information about the bone are preferred, while projections with high soft tissue information are excluded. Here, disturbing structures could be identified using a priori knowledge and / or topograms.

[0047] A combination of conventional dose modulation with selective projection selection (omission of interfering angle regions) for the dedicated reconstruction (e.g. zoomed spine) is also preferred. This can improve image quality while maintaining radiation efficiency. The method could also be used as a replacement or supplement to previous approaches to image quality improvement. For example, based on the information from a topogram, a foreign body in the examination object could be detected and defined as an interfering structure. Then, to avoid artifacts, e.g. metal artifacts, interfering angle regions can be defined for this foreign body. For example, in a lung image, the projections could be omitted based on a foreign body that has penetrated the lung.This represents a significant difference to iterative artifact reduction, since the proposed method already has precise knowledge of the introduced foreign body and can prospectively sort out projections.

[0048] The invention is explained in more detail below with reference to the accompanying figures using exemplary embodiments. In the various figures, identical components are provided with identical reference numerals. The figures are generally not to scale. They show: Figure 1 Roughly schematic representation of a CT system with an embodiment of a control device according to the invention for carrying out the method. Figure 2 a disturbance structure and a disturbance angle range, Figure 3 a flow chart for a possible sequence of a method according to the invention, Figure 4an example of a method according to the invention for recording two examination areas.

[0049] Figure 1 shows an embodiment of a computed tomography (CT) system 1 with a radiation detector 4 and a radiation source 5. The radiation source 5 is configured to expose the radiation detector 4 with radiation. The CT system 1 shown comprises a gantry 2 with a rotor 3. The rotor 3 comprises an X-ray source 5 as the radiation source 5 and the radiation detector 4, which is configured to detect X-ray radiation.

[0050] The rotor 3 is rotatable about the rotation axis 8. The patient 6 is supported on the patient couch 7 and is movable along the rotation axis 8 by the gantry 2. The head of the patient 6 is supported on a positioning aid L. The computing unit 9 is provided for controlling the imaging system 1 and / or for generating an image data set based on signals detected by the radiation detector 4.

[0051] Typically, a (raw) X-ray image dataset of the examination subject 6 is acquired from a plurality of angular directions using the radiation detector 4, each with a different beam energy, i.e., two or more raw datasets. Subsequently, a (final) image dataset can be reconstructed based on the (raw) X-ray image dataset using a mathematical method, for example, comprising a filtered backprojection or an iterative reconstruction method.

[0052] The computing unit 9 serves here as a control device 9 for controlling the CT system 1. An input device 10 and an output device 11 are connected to this computing unit 9. The input device 10 and the output device 11 can, for example, enable interaction by a user or the display of a generated image data set B.

[0053] The control device 9 comprises a data interface 12 for receiving CT data, for outputting control commands and for outputting reconstructed image data sets (see also Figure 3 ).

[0054] In addition to the data interface 12, the control device also comprises an examination unit 13, a disturbance structure unit 14, a calculation unit 15, a reconstruction unit 16 and, in this example, also a position unit 17.

[0055] Examination unit 13 is used to define an examination area U of a patient 6. This area shows an area that could be suitable for an examination of the chest or lungs. In a simple case, the examination area can be defined by manual input. However, examination unit 13 can also provide tools for delimiting the examination area U in images or for defining the examination area U from examination specifications.

[0056] The interfering structure unit 14 defines a number of interfering structures S, where an interfering structure S is a structure that lies within the beam path of the computed tomography system 1 and reflects or absorbs X-ray radiation with an intensity outside a tolerance range. For example, it can be specified which structures in the human body are to be regarded as interfering structures S (e.g., the spine). Then, it can be determined which of these interfering structures S could interfere with a measurement of the examination area U. These are defined as the (relevant) interfering structures S.

[0057] The calculation unit 15 is used to calculate the beam paths of the X-rays R of a CT examination of the examination area U and to determine interference angle ranges W of a gantry 2 of the computed tomography system, in which beam paths lead through an interference structure S and the examination area U. With the known positions of the X-ray source 5, its known beam path and the known position of a specified interference structure, such a calculation can be carried out simply geometrically.

[0058] As stated above, the data interface 12 is used to output control commands for performing a CT scan while the rotator 3 of the gantry 2 is rotating, and to receive CT data D.

[0059] With the reconstruction unit 16, an image data set B can be reconstructed from the CT data D while omitting determined interference angle ranges W.

[0060] The data interface 12 then serves to output the reconstructed image data set B.

[0061] In this example, the control device 9 additionally comprises a positioning unit 17 designed to determine a position of a positioning aid L. The positioning unit 17 is designed in particular to estimate the position based on images and / or to receive and evaluate information of the positioning aid L.

[0062] Figure 2 shows a disturbing structure S, here the spine, and a disturbing angle range W. It can be assumed that an observer along the rotation axis of the Figure 1looking at the head of patient 6. Patient 6 is positioned somewhat eccentrically in gantry 2 so that the examination area U around his left breast is in the center. The (actually invisible) spine is indicated here as an interfering structure S. X-ray source 5 with its cone-shaped X-ray beam R is shown above patient 6. During an image acquisition, it rotates around patient 6. If it is located in the interfering angle area W, then X-ray beams R first pass through the spine and then through the examination area U. This is undesirable and therefore the interfering angle area W is excluded from the image acquisition (or at least from the reconstruction).

[0063] Figure 3 shows a flow chart for a possible sequence of a method according to the invention for controlling a computer tomography system 1 as it is shown, for example, in Figure 1 is shown.

[0064] In step I, an examination area U of a patient 6 and a disturbing structure S are defined. In this example, this disturbing structure is the spine as shown in Figure 2 shown.

[0065] In step II, an interference angle range W of a gantry 2 of the computed tomography system 1 is determined by calculating the beam paths of the X-ray beams R that pass through an interference structure S and the examination area U.

[0066] In step III, a CT scan is performed while the gantry 2 rotates (i.e., its rotator 3 rotates). CT data D are acquired. It can be assumed that, to reduce the dose, the X-ray source 5 is switched off in the interference angle range W.

[0067] In step IV, an image data set B is reconstructed from the CT data D, omitting the determined interference angle ranges W, and then output.

[0068] Figure 4shows an example of a method for recording according to the invention. Two examination regions U 1 , U 2 are defined on a patient 6 and interference angle ranges W 1 , W 2 are determined separately for both examination regions U 1 , U 2 . An interference angle range W 1 , W 2 is assigned to an examination region U 1 , U 2 if beam paths lead through an interference structure S and the relevant examination region U 1 , U 2 . An image data set B is then reconstructed separately for each examination region U 1 , U 2 , omitting the determined interference angle ranges W 1 , W 2 of the relevant examination region U 1 , U 2 .

[0069] In this case, the interference angle ranges W 1 , W 2 do not overlap. This means that the X-ray source is not switched off when the CT data is acquired, since the 360° data can be used to reconstruct at least one of the examination areas U 1 , U 2 .

[0070] If there were an interference angle range W which was assigned to the two examination areas U 1 , U 2 (an identical interference angle range W), then the X-ray source 5 used for the recording could be switched off in this interference angle range W.

[0071] Finally, it should be noted once again that the figures described in detail above are merely exemplary embodiments that can be modified in a variety of ways by a person skilled in the art without departing from the scope of the invention. Furthermore, the use of the indefinite articles "a" or "an" does not exclude the possibility that the respective features may be present in multiple instances. Likewise, the terms "unit" and "device" do not exclude the possibility that the respective components may consist of several interacting subcomponents, which may also be spatially distributed. The expression "a number" is to be understood as "at least one." Regardless of the grammatical gender of a particular term, this includes persons of male, female, or other gender identities.

Claims

1. Method for controlling a computed tomography system (1), comprising the following steps: - defining an examination region (U) of an examination object (6), - defining a number of interfering structures (S), wherein an interfering structure (S) is a structure which is located within the beam path of the computed tomography system (1) and reflects or absorbs X-ray radiation with a strength outside of a tolerance range, - calculating the beam paths of the X-rays (R) of a CT examination of the examination region (U) and ascertaining interference angle ranges (W) of a gantry (2) of the computed tomography system at which beam paths run through an interfering structure (S) and the examination region (U), - carrying out a CT scan while the gantry (2) rotates, and recording CT data (D), - reconstructing an image dataset (B) from the CT data (D) with the omission of ascertained interference angle ranges (W), - outputting the image dataset (B).

2. Method according to claim 1, wherein the CT data (D) is recorded with the omission of ascertained interference angle ranges (W), preferably wherein an X-ray source (5) used for recording is switched off in interference angle ranges (W) or at least its radiation power is reduced, preferably wherein beam parameters, in particular the acceleration voltage and / or the current strength of the X-ray source (5), are determined for the entire recording on the basis of an entire angle range of 360° minus the interference angle ranges (W).

3. Method according to one of the preceding claims, wherein an angle range at which beams of an X-ray source (5) of the gantry (2) run firstly through an interfering structure (S) and then through the examination region (U) is regarded as an interference angle range (W).

4. Method according to one of the preceding claims, wherein defining an interfering structure (S) is based on a topogram of the examination object (6), a camera recording of the examination object (6) or a model of the examination object (6), preferably wherein the examination object (6) is a human or animal body and the interfering structure (S) is a bone, a positioning aid (L) or a part of the gantry (2).

5. Method according to one of the preceding claims, wherein the examination object (6) is positioned by means of a positioning aid (L) or fixed with a fixation and defining an interfering structure (S) is based on a position and a form of the positioning aid (L) or fixation, preferably wherein the isocentre of the examination region (U) is defined after positioning of the examination object (6) by means of the positioning aid (L), in particular automatically by means of an image recognition or by means of a communication between positioning aid (L) and computed tomography system (1).

6. Method according to one of the preceding claims, wherein in the course of ascertaining the interference angle ranges (W) it is checked whether considering the entire angle range of 360° minus the interference angle ranges (W), the remaining angle range overlaid with the remaining angle range rotated about 180° has a continuous angle range of 360°, preferably wherein in the case where the remaining angle range is less than 360°, a missing angle range, simulated data, which simulates recordings in the missing angle range, is added to the CT data (D) before reconstruction of the image dataset (B) and / or a missing angle range is removed from the number of interference angle ranges (W), wherein, in particular, a degree of interference in the missing angle range and an angle range rotated 180° thereto is ascertained and that angle range which has the smaller degree of interference is removed from the interference angle ranges (W) .

7. Method according to one of the preceding claims, wherein two or more examination regions (U1, U2) of the examination object (6) are defined, interference angle ranges (W1, W2) are separately ascertained for the two examination regions (U1, U2), wherein an interference angle range (W1, W2) is associated with an examination region (U1, U2) if beam paths run through an interfering structure (S) and the relevant examination region (U1, U2), and for each examination region (U1, U2) an image dataset (B) is separately reconstructed with the omission of ascertained interference angle ranges (W1, W2) of the relevant examination region (U1, U2), preferably wherein it is ascertained which interference angle ranges (W) associated with the examination regions (U1, U2) are identical, the CT data (D) is recorded with the omission of the identical interference angle ranges (W), preferably wherein an X-ray source (5) used for recording is switched off in the identical interference angle ranges (W) or at least its radiant power is reduced.

8. Method according to one of the preceding claims, wherein during reconstruction of an image dataset (B) a combination of a data sparsity reconstruction technique with an iterative solution approach is used, preferably an addition of projections in order to represent structures.

9. Method according to one of the preceding claims, wherein the examination region (U) is the chest or the lungs and wherein a preferred interfering structure (S) is the spinal column.

10. Control facility (9) for controlling a computed tomography system (1), comprising: - an examination unit (13) designed for defining an examination region (U) of an examination object (6), - an interfering structure unit (14) designed for defining a number of interfering structures (S), wherein an interfering structure (S) is a structure, which is located within the beam path of the computed tomography system (1) and reflects or absorbs X-ray radiation with a strength outside of a tolerance range, - a calculation unit (15) designed for calculating the beam paths of the X-rays (R) of a CT examination of the examination region (U) and ascertaining interference angle ranges (W) of a gantry (2) of the computed tomography system at which beam paths run through an interfering structure (S) and the examination region (U), - a data interface (12) designed for outputting control commands for carrying out a CT scan while the gantry (2) rotates, and for receiving CT data (D), - a reconstruction unit (16) designed for reconstructing an image dataset (B) from the CT data (D) with the omission of ascertained interference angle ranges (W), - a data interface (12) designed for outputting the image dataset (B).

11. Control facility according to claim 10, comprising a position unit (17) designed for ascertaining a position of a positioning aid (L) or a fixation, preferably wherein the position unit (17) is designed to estimate the position on the basis of images and / or receive and evaluate items of information of the positioning aid (L).

12. Computed tomography system (1), comprising a control facility (9) according to one of claims 10 to 11 and / or designed for carrying out a method according to one of claims 1 to 9.

13. Computer program product, comprising commands which on execution of the program by a computer prompt it to execute the steps of the method according to one of claims 1 to 9, wherein carrying out a CT recording corresponds to the transmission of corresponding control commands and the receiving of CT data (D).

14. Computer-readable storage medium, comprising commands which on execution by a computer prompt it to execute the steps of the method according to one of claims 1 to 9, wherein carrying out a CT recording corresponds to the transmission of corresponding control commands and the receiving of CT data (D) .