Method and control device for controlling computed tomography system

Abstract

The invention relates to a 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, wherein the interfering structures are structures located within the beam path of the computed tomography system (1) and reflecting or absorbing X-ray radiation having an intensity beyond the tolerance range; calculating a beam path of the X-rays (R) of the CT examination of the examination region (U) and determining a disturbance angle range (W) of the beam path through the disturbance structure (S) and a gantry (2) of the computed tomography system on which the examination region (U) is located; cT recording is executed while the rack (2) rotates, and CT data (D) is recorded; reconstructing the image data set (B) from the CT data (D) without the determined disturbance angle range (W); and outputting the image data set (B). The invention also relates to a control device and a computed tomography system.

Description

Technical Field

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

[0002] In CT examinations ("CT": computed tomography) of locally restricted anatomy, such as the chest, the number of projection angles acquired using conventional recording techniques and image reconstruction is insufficient to display the desired anatomy. In this particular case, many projections through the spine are used to display the chest, axilla and anterior chest wall, which are high-dose and may also be affected by artifacts. For example, they may have hardening artifacts.

[0003] Furthermore, it is necessary to use special positioning aids (virtually non-compressive, "hanging" displays), especially when imaging the (female) breast. However, this results in a suboptimal positioning of the female patient for routine data acquisition and data reconstruction (off-center positioning).

[0004] Without dedicated positioning aids, a range of examinations also suffer from reduced image quality, such as lateral positioning in the case of liver interventions.

[0005] Cross-sectional techniques (eg, flat-panel CT) used to monitor interventional and radiation therapy placements exhibit the same basic problems as conventional CT techniques, differing only in the apparent problem of cone beam projections.

[0006] Taking CT-based chest imaging as an example, there are dedicated chest CTs. In this regard, due to the technical and physical conditions of the system, it is not possible to use the applied technology to display the chest wall and the axilla. Similarly, it is not possible to present both breasts at the same time, and for dynamic examinations (e.g. contrast agent dynamics), this may have an adverse effect on clinical use. In addition, such systems currently do not allow for simultaneous imaging of the chest and access to the chest for interventions (as is achieved in magnetic resonance imaging).

[0007] Currently, personalized positioning aids are only used to solve this problem. In the field of CT-based chest imaging, similar to magnetic resonance imaging, there are customized imaging positioning aids or, in the case of dedicated chest scanners, corresponding structural measures for positioning the chest. Summary of the invention

[0008] It is an object of the present invention to disclose an alternative, more convenient method and a corresponding device for controlling a computed tomography system, which avoids the above-mentioned disadvantages.

[0009] This object is achieved by a method according to claim 1 , a control device according to claim 10 and a computed tomography system according to claim 12 .

[0010] The method of the invention is used for controlling a computed tomography system. It allows to improve the image quality and also to reduce the dose for the patient, in particular when using high-resolution CT techniques (e.g. photon counting techniques). The method provides monitoring of image artifacts at a relatively low radiation dose, precisely when recording anatomical regions in which high resolution and low contrast behavior are advantageous for diagnostic statements.

[0011] The method comprises the following steps:

[0012] - define the inspection area of ​​the inspection object,

[0013] - defining a certain number of interfering structures, wherein interfering structures are structures which are located in the beam path of the computed tomography system and which reflect or absorb X-ray radiation with an intensity outside a tolerance range,

[0014] - calculating the X-ray beam path of a CT examination of the examination area and determining the interference angle range of the beam path through interfering structures and the gantry of the computed tomography system of the examination area,

[0015] - Perform CT recording while the gantry is rotating and record CT data,

[0016] - reconstructing the image data set from the CT data while omitting the determined interference angle range,

[0017] - Output image dataset.

[0018] The object of examination can be any body in theory, and the examination region can be a part of the body or the whole body. Preferably, the object of examination is a person, and the examination region is an organ or a body region. The examination region is usually defined before the examination.

[0019] A certain number of interfering structures are also defined before the examination. It can be a single structure or multiple structures. The interfering structure is located in the beam path of the computed tomography system, that is, it is irradiated by the X-ray radiation and reflected or absorbed. However, not any structure is considered an interfering structure, but only the structure whose reflection or absorption intensity exceeds the tolerance range (for example, above or below a predetermined limit) is considered an interfering structure. The tolerance range of the structure or the corresponding material and size are predefined. In the case of humans, for example, bone material can be interfering, and larger bones, such as the spine in particular, can be considered as interfering structures. However, parts of the patient couch or placement aids can also be considered as interfering structures. Basically, the doctor knows which structures will interfere with the image. These structures can be defined as "interfering structures" in the method. Preferred interfering structures have a known position in the body or examination area and are image areas with high Hounsfield units. However, air may also constitute an interfering structure. In this case, the image area with the lowest Hounsfield unit is preferably used as the interfering area.

[0020] If the interfering structures are known, then their positions are also known in principle. For example, for humans, the skeletal structure is known, and even if it is not possible (at this time) to observe the inside of the human body, the position of the spine as an exemplary interfering structure can be easily specified.

[0021] With the known positions of the interfering structures and the defined position of the examination region, the beam path of the X-rays of the CT examination can now be calculated. Please note that the X-ray source is still switched off. Only the theoretical orientation is determined. Preferably, the patient (or the object under examination) is positioned so that the number of interfering structures is (obviously) located eccentrically of the isocenter.

[0022] Using the calculated beam orientations, it is then determined whether they pass through the interfering structure and the inspection region. The angle at which the X-rays emitted by the X-ray source pass through the interfering structure and the inspection region is called the "interference angle", and the range of the interference angle is called the "interference angle range". Therefore, the interference angle range is the angular range that the rotating gantry can occupy, within which the X-rays that pass through the interfering structure and the inspection region will be emitted. It is preferably tolerable if the X-rays only pass through the interfering structure after passing through the inspection region. Therefore, these angular ranges are preferably not considered as interference angle ranges.

[0023] Once the interference angle range is determined, CT recording can be performed using a rotating gantry, and CT data (ie, basic images) can be recorded in the process.

[0024] The image data set is then reconstructed based on the CT data. The determined interference angle ranges are omitted. Please note that not all interference angle ranges have to be omitted. For example, when there are two separate examination regions, the first interference angle range can be omitted for the reconstruction of the first image data set for the first examination region, while the second interference angle range can be omitted for the reconstruction of the second image data set for the second examination region.

[0025] A dose reduction can be achieved by switching off the X-ray source in the interference angle range during recording.

[0026] The reconstructed image data set is then outputted and can be displayed for immediate diagnosis or stored for subsequent diagnosis, for example.

[0027] The method thus essentially removes areas from the CT data that could impair the image. It should be noted in this regard that reconstruction generally requires recording angles slightly greater than 180°. It is therefore advantageous that, in the case of an opposite interfering angular range, the less interfering angular range is not considered an interfering angular range. Alternatively, the CT data for the interfering angular range can also be simulated or calculated (e.g. using a suitably trained artificial intelligence) and used for the reconstruction.

[0028] The interference angle range makes it possible to define the necessary projections for the examination area while avoiding projections with limited image quality and thus dose inefficiency. Specifically, for example, beam paths through the bony spine are avoided. This can occur in both sequential and helical recordings.

[0029] The control device for controlling a computed tomography system according to the invention is preferably designed to implement the method according to the invention. The control device comprises the following components:

[0030] an inspection unit, designed to define an inspection area of ​​the inspection object,

[0031] an interference structure unit, which is designed to define a number of interference structures, wherein an interference structure is a structure which is located in a beam path of the computed tomography system and which reflects or absorbs X-ray radiation with an intensity outside a tolerance range,

[0032] a computing unit, which is designed to calculate a beam path of X-rays for a CT examination of the examination area and to determine an interference angle range of a gantry of the computed tomography system, within which the beam path passes through interfering structures and the examination area,

[0033] a data interface, designed to output control commands for performing CT recording while the gantry is rotating, and to receive CT data,

[0034] - a reconstruction unit, designed to reconstruct an image data set from the CT data in a thin version omitting the determined interference angle range,

[0035] -Data interface, designed to output image datasets.

[0036] The functions of the components are described in detail above in the context of the method according to the invention.

[0037] The computer tomography system according to the invention is designed, either alternatively or additionally, to carry out the method according to the invention by including a control device according to the invention. Preferably, the CT system comprises a flat panel detector.

[0038] Most of the above-mentioned components of the control device can be implemented in the processor of the corresponding computing system in full or in part in the form of software modules. The advantage of mainly implementing in software is that the computing system that has been used so far can also be transformed in a simple way by software updates so as to work in the manner according to the invention. In this regard, the task is also solved by a corresponding computer program product with a computer program, which can be directly loaded into the computing system and has program segments so that when the program is implemented in the computing system, the steps of the method according to the invention are implemented, at least the steps that can be implemented by the computer. In addition to the computer program, such a computer program product may also include additional components, such as documents and / or additional components, such as hardware components, such as hardware keys (dongles, etc.) for using the software.

[0039] It should be noted that performing a CT recording corresponds to transmitting corresponding control instructions and receiving CT data. The method can be implemented in particular by a computer.

[0040] Computer-readable media, such as memory sticks, hard disks or other removable or fixedly mounted data carriers, can be used for transport to a computing system or a control device and / or for storage at or in a computing system or a control device, in which program segments of a computer program that are readable and executable by a computing system are stored. For this purpose, a computing system can have, for example, one or more cooperating microprocessors or the like.

[0041] Further particularly advantageous designs and improvements of the invention result from the dependent claims and the following description, wherein the claims of one claim category may also be partially improved similarly to the claims and the description of another claim category, and individual features of different embodiments or variants may in particular also be combined to form new embodiments or variants.

[0042] According to a preferred method, the CT data are recorded with the determined interference angle range omitted. Preferably, the X-ray source used for recording is switched off within the interference angle range, or at least its radiation power is reduced. The total dose is thus reduced. Preferably, the dose modulation is performed as a function of the beam parameters (e.g. kilovolt setting or reference mAs).

[0043] If it is desired to improve the image while keeping the total dose constant, the beam parameters, in particular the acceleration voltage and / or the current intensity of the X-ray source, are preferably determined for the entire recording based on the entire angular range of 360° minus the interference angle range.

[0044] According to a preferred method, the angular ranges in which the beam of the X-ray source of the gantry first passes through the interfering structure and then through the examination region are considered as interference angular ranges. Since the beam is usually conical, these interference angular ranges have a more serious influence on the recording than the respectively opposite angular ranges in which the X-ray radiation first passes through the examination region and only then impinges on the interfering structure. The latter angular range can be considered as the angular range for reconstruction (and recording).

[0045] According to a preferred method, interfering structures are defined based on a topogram of the examination object, a camera recording of the examination object or a model of the examination object.

[0046] The examination object is preferably a human or animal body and the interfering structure is a bone, a positioning aid or a part of a scaffold.

[0047] According to a preferred method, the object to be examined is positioned with the aid of a positioning aid. Interfering structures are then preferably defined based on the position and form of the positioning aid. In this case, the positioning aid is therefore an interfering structure. Preferably, the isocenter of the examination region is defined after the object to be examined has been positioned with the aid of the positioning aid. The definition is preferably performed automatically with the aid of image recognition or with the aid of communication between the positioning aid and the computed tomography system.

[0048] According to a preferred method, the object under examination is fixed by means of a fixing device. Interfering structures are then preferably defined based on the position and form of the fixing device. Thus, in this case, the fixing device (e.g., a screw, a plate or another rigid body) is an interfering structure. The interfering structure is preferably also defined here automatically by means of image recognition or by means of communication between the fixing device and the computed tomography system.

[0049] In practice, after the introduction of a dedicated placement aid into the scanner by manual input, image recognition or by direct communication between the placement aid and the scanner, the calibration of the new isocenter can be performed according to the anatomical structure of interest. In the case of a chest display, a predefined target area can be transmitted to the CT scanner, such as the volume of the thorax or the position or extent of the thorax. The same applies to the fixation device.

[0050] In this respect, a preferred control device comprises a localization unit which is designed to determine the position of the positioning aid and / or the fixing means. Preferably, the localization unit is designed to estimate the position based on the image and / or to receive and evaluate information of the positioning aid.

[0051] According to a preferred method, in the context of determining the interfering angular range, a check is made as to whether the remaining angular range superimposed on the remaining angular range rotated by about 180° has a continuous angular range of 360° by taking into account the entire angular range of 360° minus the interfering angular range. Thus, it is essentially checked whether at least 180° is available for reconstruction. Please note that this check does not necessarily have to be carried out by rotating and superimposing copies of the remaining angular range. However, this checking procedure will be advantageous if the remaining angular range has a complex structure. If a gap should exist in the case of such a superposition, 180° is not available for reconstruction, i.e., information is missing in this case.

[0052] Preferably, in the case of a remaining angular range of less than 360°, before the reconstruction of the image data set, for the missing angular ranges, simulated data simulating the recording in the missing angular range are added to the CT data. Alternatively or additionally, since the interfering angular range is actually known before the recording, the missing angular range can be removed from the certain number of interfering angular ranges. For this purpose, it is preferred to determine the degree of interference in the missing angular range and in an angular range rotated 180° relative thereto, and to remove the angular range with a lower degree of interference from the interfering angular range. This is preferably an angular range in which the X-rays first pass through the examination region and only then impinge on the interfering structures.

[0053] According to a preferred method, two or more inspection areas of the inspection object are defined. The interference angle ranges of the two inspection areas are preferably measured separately. If the light beam path passes through an interference structure and a relevant inspection area, the interference angle range is associated with the inspection area. Then, an image data set is reconstructed separately for each inspection area, omitting the determined interference angle range of the relevant inspection area. Therefore, if, for example, an interference structure is defined and there is a first interference angle range for the first inspection area and a second interference angle range for the second inspection area, the image data set is reconstructed for the first inspection area when the first interference angle range is omitted, and the image data set is reconstructed for the second inspection area when the second interference angle range is omitted.

[0054] Preferably, it is determined which interference angle ranges associated with the examination regions are identical. The CT data can then be recorded while omitting the identical interference angle ranges. If there may be multiple examination regions, the individual interference angle ranges can be separated. Therefore, within the interference angle ranges, the X-ray source should not be switched off, since then there may not be enough data for reconstructing the examination region. However, if there are shared interference angle ranges, the X-ray source can be switched off to reduce the total dose. Therefore, it is best to switch off the X-ray source used for recording within the same interference angle range, or at least reduce its radiation power.

[0055] Thus, multiple areas to be examined can be optimized. For example, the contrast agent dynamics of both breasts will require a different number of projections for image acquisition than the number of projections required for the individual representation of a breast lesion to be biopsied. In any case, the reconstruction is performed individually, preferably based on the best projection of a single target volume.

[0056] It is also preferred that the image data set is reconstructed from two different projection sets. In the example of contrast agent dynamics, the acquisition can be optimized to meet the need to acquire both breasts simultaneously. The image reconstruction can preferably be based on a single optimized projection, which can then be combined again into one image. For these different projection sets, there can be two different interference angle ranges, so that the characteristics of the two examination regions can also be applied here.

[0057] According to a preferred method, a combination of data sparsity reconstruction techniques and iterative solution methods is used when reconstructing the image data set. In order to represent structures, in particular the structure of the biopsy needle, projections are preferably added without a complete data acquisition, which is necessary for a detailed representation of the breast tissue. Such methods are known in the prior art and are used, for example, in CT to calculate data outside the area that is completely captured by the detector (extended field of view). These techniques are particularly advantageous for the method according to the invention if the X-ray source is switched off in the interference angle range, i.e. no CT data are recorded therefrom.

[0058] According to a preferred method, the examination region is the chest or the lungs. A preferred interfering structure is the spine.

[0059] It should be noted that interfering structures do not necessarily have to absorb or reflect a large amount of radiation, but rather, depending on the type of examination, they can also reflect or absorb a particularly small amount of radiation (i.e., less than a predetermined limit value). For example, in the case of a biopsy of the iliac crest bony prominence, projections containing a large amount of bone information are preferred, while projections containing a large amount of soft tissue information are omitted. Interfering structures can be defined here using prior knowledge and / or scout images.

[0060] For dedicated reconstructions (e.g. a scaled spine), a combination of conventional dose modulation with selective projection selection (omitting interference angle ranges) is also preferred. Thus, the image quality can be improved while maintaining beam efficiency. The method can also be used to replace or supplement previous methods for improving image quality. For example, based on the information of the scout image, a foreign body can be identified in the object under examination and defined as an interfering structure. Then, an interference angle range can be defined for the foreign body, for example to avoid artifacts, such as metal artifacts. For example, when displaying the lungs, projections can be omitted based on foreign bodies that have already penetrated into the lungs. This is very different from iterative artifact reduction, because in the proposed method, there is already a precise knowledge of the introduced foreign body and the expected projections can be screened out. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The present invention will be described in more detail again with reference to the drawings, using exemplary embodiments and will be explained by way of example. In this case, identical components are provided with the same reference numerals in the different drawings. These drawings are generally not to scale. Here:

[0062] Figure 1 The schematic diagram of a CT system is shown, which has an exemplary embodiment of a control device according to the invention for carrying out the method.

[0063] Figure 2 The interference structure and the interference angle range are shown.

[0064] Figure 3 A sequence diagram showing one possible sequence of the method of the invention,

[0065] Figure 4 An example of the method according to the invention for recording two examination regions is shown. DETAILED DESCRIPTION

[0066] Figure 1 An embodiment of a computed tomography system (CT system) 1 is shown having a radiation detector 4 and a radiation source 5. The radiation source 5 is embodied to irradiate the radiation detector 4 with radiation. The CT system 1 shown comprises a gantry 2 having a rotating body 3. The rotating body 3 comprises an X-ray source 5 as the radiation source 5 and a radiation detector 4, which is embodied to detect X-ray radiation.

[0067] The rotating body 3 can rotate around the rotation axis 8. The patient 6 is located on the treatment couch 7 and can be moved along the rotation axis 8 by the gantry 2. The head of the patient 6 is placed on the positioning aid 1. The processing unit 9 is configured to control the imaging system 1 and / or to generate an image data set based on the signals detected by the radiation detector 4.

[0068] The (raw) X-ray image data sets of the examination object 6 are usually recorded from a plurality of angular directions with one beam energy each, i.e. two or more raw data sets, by means of the radiation detector 4. Then, the (final) image data set can be reconstructed based on the (raw) X-ray image data sets by mathematical methods (for example including filtered back projection or iterative reconstruction methods).

[0069] 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 the computing unit 9. The input device 10 and the output device 11 can enable interaction by a user, for example, or enable presentation of a generated image data set B.

[0070] The control device 9 comprises a data interface 12 for receiving CT data, outputting control commands and outputting reconstructed image data sets (see also Figure 3 ).

[0071] In addition to the data interface 12 , the control device also comprises a checking unit 13 , a disturbance structure unit 14 , a computing unit 15 , a reconstruction unit 16 and, in the present example, a localization unit 17 .

[0072] The examination unit 13 is used to define an examination region U of the patient 6. Here, an area that may be suitable for examining the chest or lungs is represented. In a simple case, the examination region can be defined by manual input. However, the examination unit 13 can also define a tool for defining the examination region U in the image, or define a tool for defining the examination region U according to regulations for examination.

[0073] The interfering structure unit 14 defines a certain number of interfering structures S, wherein the interfering structures S are structures which are located in the beam path of the computed tomography system 1 and which reflect or absorb X-ray radiation with an intensity outside a tolerance range. It can be predetermined, for example, which structures in the human body are to be regarded as interfering structures S (e.g., the spine), and then it can be determined which interfering structures S may interfere with the measurement of the examination region U. These interfering structures are defined as (relevant) interfering structures S.

[0074] The computing unit 15 is used to calculate the beam path of the X-rays R of the CT examination of the examination region U and to determine the interference angle range W of the gantry 2 of the computed tomography system, within which the beam path passes through the interfering structure S and the examination region U. With the known positions of the X-ray sources 5, their known beam paths and the known positions of the defined interfering structures, geometric calculations can be easily performed.

[0075] As described above, the data interface 12 is used to output a control command for performing CT recording while the rotating body 3 of the gantry 2 rotates, and to receive the CT data D.

[0076] The reconstruction unit 16 can be used to reconstruct an image data set B from the CT data D while omitting the determined interference angle range W.

[0077] Thereafter, the data interface 12 is used to output the reconstructed image data set B.

[0078] In this example, the control device 9 further comprises a localization unit 17 which is designed to determine the position of the positioning aid 1. The localization unit 17 is designed in particular to estimate the position based on the image and / or to receive and evaluate information of the positioning aid 1.

[0079] Figure 2 The interfering structure S (here the spine) and the interfering angle range W are shown. It can be assumed that the observer is moving along Figure 1 The rotation axis of is observing the head of the patient 6. Here, the patient 6 is positioned slightly eccentrically in the gantry 2, so that the examination region U is centered around his left chest. The (practically invisible) spine is represented here as an interfering structure S. The X-ray source 5 and its cone of X-rays R are shown above the patient 6. During the recording, the X-ray source rotates around the patient 6. When it is within the interference angle range W, the X-rays R first pass through the spine and then through the examination region U. This is undesirable, so the interference angle range W is omitted from the recording (or at least from the reconstruction).

[0080] Figure 3 A sequence diagram showing a possible sequence of the method according to the invention for controlling a computed tomography system 1 is shown, for example Figure 1 shown.

[0081] In step I, the examination region U of the patient 6 and the interfering structure S are defined. In this example, the interfering structure is the spine. Figure 2 shown.

[0082] In step II, the interference angle range W of the gantry 2 of the computed tomography system 1 is determined by calculating the beam path of the X-rays R which pass through the interfering structure S and the examination region U.

[0083] In step III, CT recording is performed while the gantry 2 rotates (ie, its rotating body 3 rotates). In this process, CT data D are recorded. It can be assumed that the X-ray source 5 is turned off within the interference angle range W in order to reduce the dose.

[0084] In step IV, an image data set B is reconstructed from the CT data D, omitting the determined interference angle range W, and is then output.

[0085] Figure 4An example of the recording method according to the invention is shown. Two examination regions U1, U2 are defined on a patient 6 and interference angle ranges W1, W2 are determined for the two examination regions U1, U2, respectively. If the beam path passes through an interfering structure S and the relevant examination region U1, U2, the interference angle ranges W1, W2 are associated with the examination region U1, U2. Then, an image data set B is reconstructed separately for each examination region U1, U2, omitting the determined interference angle ranges W1, W2 of the relevant examination region U1, U2.

[0086] In this case, the interference angle ranges W1 , W2 do not overlap. This means that the X-ray source is not switched off when recording CT data, since the reconstructed 360° data can be used for at least one examination region U1 , U2 .

[0087] If there is an interference angle range W associated with both examination regions U1 , U2 (same interference angle range W), the X-ray source 5 for recording can be switched off within this interference angle range W.

[0088] Finally, it is pointed out again that the drawings described in detail above are only embodiments, and those skilled in the art may modify the embodiments in different ways without departing from the scope of the present invention. In addition, the use of the indefinite article "a" or "an" does not exclude that the relevant features may appear multiple times. The terms "unit" and "device" do not exclude that the relevant components may be composed of multiple interacting subcomponents, which may also be distributed in space if necessary. The expression "a certain number" should be understood as "at least one". Regardless of the grammatical gender of a particular term, individuals with male or female gender identity are also included in the term.

Claims

1. A method for controlling a computer tomography system (1), comprising the following steps: - defining an inspection area (U) of the inspection object (6), - defining a certain number of interfering structures (S), wherein interfering structures (S) are structures which are located in the beam path of the computed tomography system (1) and which reflect or absorb X-ray radiation with an intensity outside a tolerance range, - calculating the beam path of the X-rays (R) of the CT examination of the examination region (U) and determining the interference angle range (W) of the gantry (2) of the computed tomography system, in which the beam path passes through the interfering structure (S) and the examination region (U), - performing CT recording while the gantry (2) is rotating and recording CT data (D), - reconstructing an image data set (B) from the CT data (D) while omitting the determined interference angle range (W), - outputting said image dataset (B).

2. A method according to claim 1, wherein the CT data (D) are recorded while omitting a determined interference angle range (w), preferably wherein an X-ray source (5) used for recording is switched off within the interference angle range (W), or at least the radiation power of the X-ray source is reduced, preferably wherein beam parameters, in particular the acceleration voltage and / or current intensity of the X-ray source (5), are determined for the entire recording based on the entire angular range of 360° minus the interference angle range (W).

3. The method according to claim 1 , wherein the interference angle range (W) is regarded as an angular range in which the beam of the X-ray source (5) of the gantry (2) first passes through the interfering structure (S) and then through the examination region (U).

4. A method according to any of the preceding claims, wherein an interfering structure (S) is defined based on a positioning image of the inspection object (6), a camera recording of the inspection object (6) or a model of the inspection object (6), preferably, wherein the inspection object (6) is a human or animal body and the interfering structure (S) is a bone, a placement aid (L), or a part of the frame (2).

5. The method according to claim 1 , wherein the object to be examined ( 6 ) is positioned with the aid of a positioning aid (L) or is fixed using a fixing device, and the interfering structure (S) is defined based on the position and form of the positioning aid (L) or the fixing device, Preferably, the isocenter of the examination region (U) is defined after the examination object (6) has been positioned with the aid of the positioning aid (L), in particular automatically with the aid of image recognition or with the aid of communication between the positioning aid (L) and the computed tomography system (1).

6. A method according to any one of the preceding claims, wherein: In the context of determining the interfering angular range (W), a check is made as to whether the remaining angular range superimposed on the remaining angular range rotated by 180° has a continuous angular range of 360° by taking into account the entire angular range of 360° minus the interfering angular range (W), Preferably, in the case where the remaining angular range is less than 360°, before reconstructing the image data set (B), for the missing angular range, simulated data are added to the CT data (D), the simulated data simulating the recording in the missing angular range, and / or the missing angular range is removed from a certain number of the interfering angular ranges (W), wherein in particular the degree of interference in the missing angular range and the degree of interference in the angular range rotated 180° relative to the missing angular range are determined, and the angular range with a lower degree of interference is removed from the interfering angular range (W).

7. The method according to claim 1 , wherein two or more examination regions (U1, U2) of the examination object (6) are defined, an interference angle range (W1, W2) is determined for each of the two examination regions (U1, U2), wherein if the beam path passes through an interfering structure (S) and an examination region (U1, U2), the interference angle range (W1, W2) is associated with the relevant examination region (U1, U2), and an image data set (B) is reconstructed separately for each examination region (U1, U2) by omitting the determined interference angle range (W1, W2) of the relevant examination region (U1, U2), Preferably, it is determined which interference angle ranges (W) associated with the examination areas (U1, U2) are the same, and the CT data (D) are recorded while omitting the same interference angle ranges (W), preferably, wherein the X-ray source (5) used for recording is turned off within the same interference angle range (W), or at least the radiation power of the X-ray source is reduced.

8. A method according to any one of the preceding claims, wherein: When reconstructing the image dataset (B), a combination of data sparsity reconstruction techniques and iterative solution methods are used, preferably mixing in projections to represent structure.

9. The method according to any of the preceding claims, wherein the examination region (U) is the chest or the lungs and wherein the preferred interfering structure (S) is the spine.

10. A control device (9) for controlling a computer tomography system (1), comprising: - an inspection unit (13) designed to define an inspection area (U) of the inspection object (6), - an interfering structure unit (14) designed to define a number of interfering structures (S), wherein the interfering structures (S) are structures which are located in the beam path of the computed tomography system (1) and which reflect or absorb X-ray radiation with an intensity outside a tolerance range, - a computing unit (15) designed to calculate the beam path of the X-rays (R) of the CT examination of the examination region (U) and to determine an interference angle range (W) of the gantry (2) of the computed tomography system, in which the beam path passes through the interfering structure (S) and the examination region (U), - a data interface (12) designed to: output control commands for performing CT recording while the gantry (2) is rotating, and to receive CT data (D), - a reconstruction unit (16) designed to reconstruct the image data set (B) from the CT data (D) while omitting the determined interference angle range (W), - a data interface (12) designed to output the image data set (B).

11. The control device according to claim 10, comprising a positioning unit (17) which is designed to determine the position of a positioning aid (L) or a fixing device, Preferably, the positioning unit (17) is designed to estimate the position based on an image and / or to receive and evaluate information from the positioning aid (L).

12. A computed tomography system (1) comprising a control device (9) according to any one of claims 10 to 11 and / or designed to carry out a method according to any one of claims 1 to 9.

13. A computer program product comprising instructions which, when the program is executed by a computer, cause the computer to perform the steps of the method as claimed in any one of claims 1 to 9, wherein performing a CT recording corresponds to transmitting corresponding control instructions and receiving CT data (D).

14. A computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to perform the steps of the method of any one of claims 1 to 9, wherein performing CT recording corresponds to transmitting corresponding control instructions and receiving CT data (D).

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