Image display in an angle-limited tomography procedure

Abstract

For image display in an angle-limited tomography procedure, a multitude of projection images representing an object (8) are obtained, and a three-dimensional image reconstruction is generated based on these. A first slice image (7) for a first section plane through the object (8) is generated based on the image reconstruction, and an area of ​​interest (9) of the object (8) is determined in the first slice image (7). In the first slice plane, a section line (10, 10a, 10b, 10c, 10d) of a second slice plane, which passes through the area of ​​interest (9), is determined. Depending on the position of the section line (10, 10a, 10b, 10c, 10d) and / or depending on the geometric extent of the area of ​​interest (9) in the first slice image (7), a computation area (11, 11a, 11b, 11c, 11d) around the second slice plane is determined.Based on the multitude of projection images, a second layer image is generated for the second section plane according to the calculation area (11, 11a, 11b, 11c, 11d).

Description

[0001] The present invention relates to a computer-implemented method for image display in an angle-limited tomography procedure, in which a plurality of projection images representing an object and corresponding to a plurality of different projection directions are obtained, and a three-dimensional image reconstruction is generated based on the plurality of projection images. The invention further relates to a data processing system for carrying out such a computer-implemented method, to an imaging system with such a data processing system, and to a corresponding computer program product.

[0002] Limited-angle tomography (LAT) is an X-ray imaging technique that generates a stack of tomographic images from a limited number of two-dimensional projection images. Here and in the following, limited-angle tomography is also referred to as tomosynthesis.

[0003] Tomosynthesis techniques enable three-dimensional visualization of anatomical structures with lower radiation exposure than, for example, computed tomography (CT) or cone-beam CT. By acquiring multiple projection images from different angles around the patient, i.e., with different projection directions, a series of thin slice images can be generated, which can then be reconstructed into a three-dimensional image, also known as a volumetric dataset. This allows for better visualization of complex structures such as the lungs and enables radiologists to identify and characterize lesions with a lower radiation dose.

[0004] With conventional tomosynthesis methods, the image quality obtained is generally insufficient for image-guided interventions, such as bronchoscopy. This limitation is due to the limited angular acquisition and the typically small number of projection directions, which can cause geometric distortions and fringe artifacts.

[0005] Approaches have been published to compensate for the missing projection components using deep learning algorithms, such as in Y. Huang et al.: “Data consistent artifact reduction for limited angle tomography with deep learning prior.”, International workshop on machine learning for medical image reconstruction. Cham: Springer International Publishing, 2019. One disadvantage is the requirement for large amounts of annotated training data, which can be problematic, especially in clinical settings, due to data protection regulations and the like.

[0006] Alternatively, F. Saad et al., in their article "Deformable 3D / 3D CT-to-digital-tomosynthesis image registration in image-guided bronchoscopy interventions" (Comput. Biol. Med. 171: 108-199), proposed a registration and reconstruction method to improve tomosynthesis image quality by utilizing diagnostic CT scans acquired prior to the tomosynthesis scan. In this approach, the previous CT image is compared to the intraoperative tomosynthesis image and used as an initial estimate for reconstruction. The additional CT scans increase the overall applied radiation dose.

[0007] It is an object of the present invention to provide a method for image display in angle-limited tomography, which increases the image quality and overcomes or reduces the aforementioned disadvantages.

[0008] The invention is based on the understanding that, due to the principle of angle-limited data acquisition, artifacts are not equally pronounced for all viewing directions or section planes through the imaged object. Therefore, it is proposed to define an area of ​​interest of the object in a first section plane through the object and to define a computational area for generating a layered image according to a second section plane that differs from the first, depending on the area of ​​interest thus determined.

[0009] According to one aspect of the invention, a computer-implemented method for image display in an angle-limited tomography procedure is described. In this method, a plurality of projection images representing an object and corresponding to a plurality of different projection directions are obtained, and a three-dimensional image reconstruction is generated based on the plurality of projection images. A first slice image for a first section plane, in particular a predetermined first section plane, through the object is generated based on the image reconstruction, and an area of ​​interest of the object is determined in the first slice image. In the first section plane, an intersection line of a second section plane, in particular a predetermined second section plane, which intersects the first section plane and, in particular, passes through the area of ​​interest in the first section plane, is determined.Depending on the position of the section line in the first section plane, in particular the position of the section line relative to the area of ​​interest, and / or depending on the geometric extent of the area of ​​interest in the first layer image, a computation area around the second plane is determined, wherein the computation area has a position and a layer thickness. Based on the multitude of projection images, a second layer image for the second section plane is generated according to the computation area and displayed, for example, in particular on a display device.

[0010] Unless otherwise specified, all steps of the computer-implemented method can be performed by a data processing system comprising at least one data processing device. In particular, the at least one data processing device is configured or adapted to perform the steps of the computer-implemented method. For this purpose, the at least one data processing device may, for example, store a computer program containing instructions which, when executed by the at least one data processing device, cause the at least one data processing device to perform the computer-implemented method. The computer-implemented method may also be implemented wholly or partly in hardware. The terms "data processing system" and "at least one data processing device" may be used interchangeably here and in the following. This also applies to corresponding derivatives.

[0011] In the event that the at least one data processing device comprises two or more data processing devices, certain steps performed by the at least one data processing device can also be understood as different data processing devices performing different steps or different parts of a step. In particular, it is not necessary for each data processing device to perform the steps. In other words, the execution of the steps can be distributed among the two or more data processing devices.

[0012] Each embodiment of the computer-implemented method results in a corresponding embodiment of an image display method for an angle-limited tomography method that is not purely computer-implemented, by including corresponding steps for generating the multitude of projection images, in particular by means of an imaging device.

[0013] Receiving or receiving data or information can, for example, involve receiving or receiving the data, particularly by the data processing system, from a sending entity; reading the data from a data storage device; receiving or receiving a data stream containing the data; extracting the data from the data stream; and so on. This can be achieved, in particular, through wired or wireless data transmission. Specifically, data transmission can occur between a hardware and / or software interface of the sending entity and a hardware and / or software interface of the data processing system.

[0014] The multitude of projection images are, for example, a multitude of X-ray projection images. However, the method according to the invention is also applicable in principle to other imaging modalities that are based on the generation of projection images from different projection directions and a three-dimensional image reconstruction based thereon.

[0015] The numerous projection images are generated according to angle-limited data acquisition. In other words, the multitude of different projection directions does not cover the full angular range required for accurate three-dimensional reconstruction, but only a portion of it. For complete reconstruction, an angular range of at least 180°, or 180° plus the so-called fan angle of the X-ray system, is required. In angle-limited tomography, the swept-out angular range is smaller than 180°, for example, smaller than 120° or smaller than 60°. For example, the entire swept-out angular range lies within the range [30°, 150°], or within the range [30°, 90°], or within the range [30°, 60°].The swept angular range refers to a predefined pivot axis around which the corresponding X-ray source and, if applicable, the X-ray detector are rotated to achieve the different projection directions. Both circular trajectories, i.e., pure rotational movements, and spiral trajectories are possible, in which, in addition to the rotational movement, a translational movement occurs simultaneously or sequentially along the pivot axis.

[0016] The number of projection images is also usually significantly lower in angle-limited tomography procedures than in CT or CBCT procedures, and is, for example, in the range of 30 to 150 images or in the range of 30 to 80 images.

[0017] Three-dimensional image reconstruction can be generated according to a known reconstruction method for angle-limited tomography. The three-dimensional image reconstruction is achieved using a three-dimensional voxel grid, where the reconstruction method calculates a corresponding attenuation value for each voxel of the grid based on the multitude of projection images. The voxels of the voxel grid are typically cubes or cuboids, but in some embodiments they can also have other geometric shapes.

[0018] A projection direction can be understood here and in the following as the normal direction to a corresponding projection plane. A section plane, however, is to be understood as the section plane through the three-dimensional image reconstruction. Accordingly, the projection images for the first and second section planes do not necessarily have a projection direction perpendicular to the respective section plane.

[0019] A section plane is defined by its position and orientation, for example, by a corresponding normal direction to the section plane. The section line corresponds, in particular, to a straight line or a segment of a straight line. The position of the section line can therefore be understood as its position within the first layer image, perpendicular to the direction of extension of the line or line segment relative to the area of ​​interest. The position of the section line can also correspond to the perpendicular distance of a defined point on the contour of the area of ​​interest from the section line.

[0020] The first and second cutting planes can be perpendicular to each other, but this is not necessarily the case.

[0021] The pivot axis is also referred to as the z-axis of a Cartesian coordinate system. If the object is a human patient, the longitudinal axis of the body, i.e., the intersection of the sagittal plane with the patient's frontal plane, is typically oriented parallel to the z-axis. However, this is not strictly necessary.

[0022] The projection planes of the multitude of projection images are therefore all parallel to the z-axis, or rather, the z-axis lies within all projection planes. The projection directions of the multitude of projection directions thus lie within the xy-plane of the coordinate system.

[0023] Due to the fundamental principle of angle-limited tomography, artifacts are least pronounced in slice planes that are parallel or approximately parallel to the central or mean projection direction of the swept-out angular range. For example, the angular range can be denoted by [α1, α2], where an angle of 0° corresponds to the y-axis of the coordinate system, and α1 < 0° and α2 > 0°. For example, α1 = -α2. Then, the least artifact impairment would be expected for a slice plane perpendicular to the y-axis, whereas comparatively strong artifacts would be expected for slice planes perpendicular to the z-axis or perpendicular to the x-axis.

[0024] The area of ​​interest corresponds to a region within the object that is of particular interest to the specific application or user. This could be a specific area within an organ, a lesion, a tumor, or the like.

[0025] To generate a layered image corresponding to a specific slice plane, which can then be displayed to a user and / or used for further processing, a computational region is defined around the slice plane. The data from the three-dimensional image reconstruction that lies within the computational region—that is, the data from the corresponding voxels—are then used to generate the layered image. For example, the data from the three-dimensional image reconstruction that lies within the computational region can be averaged. In certain implementations, the computational region can also be referred to as the averaging region. Alternatively, it is possible to use data from a multitude of projection images and perform a new reconstruction of the layered image based on the computational region. The computational region can then be considered a parameter of the reconstruction itself.The larger the computational area, the higher, for example, the signal-to-noise ratio of the layer image.

[0026] According to the invention, it is exploited that, due to the low artifact intensity in certain section planes, a particularly precise and reliable determination of the area of ​​interest is possible. Once this area is determined based on the first layer image, the computation area, in particular the layer thickness and / or the position of the computation area, can be precisely adapted to the area of ​​interest for generating the second layer image, in particular the position of the section line with respect to the area of ​​interest and / or the extent of the area of ​​interest, in order to improve the image quality of the second layer image.

[0027] The computational area corresponds, in particular, to an infinitely extended disk of constant thickness, which corresponds to the layer thickness of the computational area, or to an intersection of this disk with the spatial region in which data for the three-dimensional reconstruction are available. However, this is not mandatory. In particular, instead of a disk, a wedge-shaped figure can also be defined as the computational area, for example, a region defined by two non-parallel planes, or another geometric figure. It is also possible for the computational area to encompass the entire area of ​​interest. The position of the computational area corresponds, for example, to a position along the normal direction of the second section plane or to a position with respect to the section line.

[0028] It should be noted that a corresponding additional computational area may also be used to generate the first layer image. This can be predefined in a conventional manner, for example, by having a predetermined layer thickness and a predetermined position relative to the first section plane, such that the first section plane lies, for example, in the center of the additional computational area.

[0029] Determining the area of ​​interest involves, for example, determining its position and geometric extent within the first slice image. This can be achieved, for instance, by defining a contour of the area of ​​interest within the first slice image. Determining the area of ​​interest can be accomplished, for example, by applying a known segmentation algorithm, using CAD (computer-aided detection), or manually by a user who views the first slice image on a display device.

[0030] The geometric extent of the area of ​​interest corresponds, for example, to a geometric extent in the direction perpendicular to the line of intersection, i.e., a linear geometric extent in the direction perpendicular to the line of intersection.

[0031] The fact that the second cutting plane passes through the area of ​​interest can be understood to mean that the second cutting plane at least touches the area of ​​interest, i.e., that it shares at least one point with it.

[0032] According to at least one embodiment, the respective projection directions of the plurality of projection directions lie within the xy-plane of a Cartesian coordinate system. The plurality of projection directions sweeps an angular range around a pivot axis that corresponds to the z-axis of the coordinate system. For example, the angular range is symmetrical with respect to the y-axis of the coordinate system.

[0033] According to at least one embodiment, the plurality of projection directions includes a projection direction that is perpendicular to the first sectioning plane.

[0034] The perpendicular orientation also includes approximately perpendicular orientations, in particular with a tolerance range of ±δ, where δ = α / N, with the total number of the plurality of projection directions N and the swept angular range α, in particular α=|α1|+|α2|.

[0035] A particular advantage of such embodiments is that the image quality of the first slice image according to such a first slice plane is particularly high, or the severity of artifacts in such a first slice image is particularly low. For example, the first slice plane is parallel or approximately parallel to the xz-plane of the coordinate system, or, depending on the patient's position, to a frontal or coronal plane through the patient's body.

[0036] For example, the projection direction perpendicular to the first cutting plane corresponds to a central or mean projection direction of the swept angular range. In particular, the projection directions of the plurality of projection directions are symmetrically distributed around the central or mean projection direction and / or uniformly distributed within the swept angular range.

[0037] According to at least one embodiment, the second cutting plane is perpendicular to the first cutting plane.

[0038] This is particularly advantageous because, in this case, the first layer image allows for a very precise determination of whether the second section plane passes through the interior of the area of ​​interest or touches the area of ​​interest at its contour, or precisely where the second section plane passes through the area of ​​interest. Accordingly, the position of the section line can also be determined with great accuracy.

[0039] In some embodiments, the multitude of different projection directions includes the projection direction that is perpendicular to the first cutting plane, and additionally, the second cutting plane is perpendicular to the first cutting plane.

[0040] This is particularly advantageous because in this case the image quality of the first layer image is particularly high and artifacts perpendicular to the first section plane are particularly pronounced.

[0041] According to at least one embodiment, the second cutting plane is parallel to all projection directions of the multitude of different projection directions.

[0042] In such embodiments, the idea according to the invention is particularly advantageous, since artifacts are especially pronounced in such section planes. For example, the second section plane is parallel to all projection directions of the multitude of different projection directions and, in addition, the second section plane is perpendicular to the first section plane.

[0043] According to at least one embodiment, a first boundary position of maximum extent of the area of ​​interest in the direction perpendicular to the cutting line and / or a second boundary position of maximum extent of the area of ​​interest in the direction perpendicular to the cutting line are determined. The calculation area, in particular the position of the calculation area and / or the layer thickness of the calculation area, are determined depending on a distance, in particular a perpendicular distance, of the cutting line from the first boundary position and / or a distance, in particular a perpendicular distance, of the cutting line from the second boundary position.

[0044] In other words, if the first boundary position is determined, but not the second, then the calculation area is determined based on the distance of the cutting line from the first boundary position. If the second boundary position is determined, but not the first, then the calculation area is determined based on the distance of the cutting line from the second boundary position. If both the first and second boundary positions are determined, then the calculation area is determined based on the distance of the cutting line from the first boundary position and / or based on the distance of the cutting line from the second boundary position.

[0045] The boundary positions correspond, in particular, to points on the contour of the area of ​​interest in the first layer image, between which the area of ​​interest extends in a direction perpendicular to the section line. If the second section plane is perpendicular to the first section plane, the section line in the first layer image runs, in particular, horizontally. The first boundary position then corresponds, for example, to an upper boundary position in the vertical direction, and the second boundary position corresponds, for example, to a lower boundary position in the vertical direction.

[0046] By considering the first and / or second boundary position to define the calculation area, it can advantageously always be chosen so that the second layer image can represent the relevant structures in the area of ​​interest particularly well. In particular, this ensures that the calculation area lies entirely within the area of ​​interest, at least as far as this can be determined from the first layer image.

[0047] According to at least one embodiment, the position of the calculation area is determined depending on the position of the cutting line. For example, the second cutting plane is perpendicular to the first cutting plane.

[0048] Thus, the position of the computation area relative to the section line can be dynamically determined depending on the position of the section line within the area of ​​interest. In particular, the position of the computation area can be chosen such that the section line is not located in the center of the computation area if this is advantageous for generating the second layer image, for example, if it allows a larger portion or the entire computation area to lie within the area of ​​interest.

[0049] For example, the position of the calculation area can be determined depending on the distance of the cutting line from the first boundary position and / or the distance of the cutting line from the second boundary position.

[0050] According to at least one embodiment, the position of the cutting line corresponds to the first boundary position or the second boundary position. The position of the computational area and / or the layer thickness are determined such that a portion of the computational area lying outside the area of ​​interest is smaller than a portion of the computational area lying within the area of ​​interest, or such that the computational area lies entirely within the area of ​​interest. For example, the second cutting plane is perpendicular to the first cutting plane.

[0051] This ensures that a larger portion of the area of ​​interest is considered for calculating the second layer image, and / or a smaller portion of the object lying outside the area of ​​interest, than would be the case with a conventional definition of the calculation area, independent of the position of the section line. Furthermore, this preserves the boundary of the area of ​​interest. The image quality of the second layer image can thus be further improved.

[0052] According to at least one embodiment, the position and layer thickness of the computational area are determined such that the portion of the computational area lying outside the area of ​​interest is smaller than the portion of the computational area lying within the area of ​​interest, regardless of the position of the cutting line, or such that the computational area lies entirely within the area of ​​interest, regardless of the position of the cutting line. For example, the second cutting plane is perpendicular to the first cutting plane.

[0053] In other words, it is provided that for any position of the cutting line in the area of ​​interest, i.e., between the first boundary position and the second boundary position, where the first boundary position and the second boundary position are included as possible positions of the cutting line, the calculation area is always completely within the area of ​​interest, or at least the part of the calculation area that lies outside the area of ​​interest is always smaller than the remaining part of the calculation area.

[0054] This ensures that a larger proportion of the area of ​​interest is considered for calculating the second layer image, and / or a smaller portion of the object lying outside the area of ​​interest, than would be the case with conventional definition of the calculation area, independent of the position of the section line. This further improves the image quality of the second layer image.

[0055] According to at least one embodiment, the layer thickness of the calculation area is determined depending on the position of the cutting line. For example, the second cutting plane is perpendicular to the first cutting plane.

[0056] Thus, the layer thickness of the computation area can be dynamically determined depending on the position of the section line within the area of ​​interest. The greater the layer thickness, the better, for example, the image quality of the second layer image can be. By determining the layer thickness as described, the available area can be better utilized without requiring a large portion of the computation area to lie outside the area of ​​interest.

[0057] For example, the layer thickness of the calculation area can be determined depending on the distance of the cutting line from the first boundary position and / or the distance of the cutting line from the second boundary position.

[0058] According to at least one embodiment, the layer thickness of the calculation area is determined depending on the geometric extent of the area of ​​interest in the first cutting plane, for example depending on a distance of the first boundary position to the second boundary position in the direction perpendicular to the cutting line.

[0059] Thus, the layer thickness of the computation area can be dynamically determined depending on the geometric extent of the area of ​​interest. The greater the layer thickness, the better, for example, the image quality of the second layer image can be.

[0060] According to at least one embodiment, data from the multitude of projection images corresponding to the computation area are extracted, and the second layer image is generated based on the extracted data.

[0061] In other words, in such embodiments, the second layer image for the second section plane is generated according to the computation area based directly on the multitude of projection images.

[0062] Generating the second layer image can, for example, correspond to a renewed reconstruction, particularly a renewed three-dimensional image reconstruction, or to a partial reconstruction based only on the computational domain. This can also include averaging steps of the relevant data within the computational domain. In particular, dynamic averaging can be used, thereby preserving the boundaries of the area of ​​interest.

[0063] One advantage of generating the second layer image directly from the multitude of projection images is that these projection images have a higher spatial resolution than the three-dimensional image reconstruction. This allows for further improvement in the image quality of the second layer image.

[0064] According to at least one embodiment, image reconstruction data corresponding to the computation area are extracted and the second layer image is generated based on the extracted data.

[0065] In other words, in such embodiments, the second layer image is indirectly generated based on the multitude of projection images, since the three-dimensional image reconstruction was also generated depending on the multitude of projection images.

[0066] Generating the second slice image involves averaging the image reconstruction data within the computational domain. Specifically, dynamic averaging can be used, thus preserving the boundaries of the area of ​​interest. An advantage of generating the second slice image based on the image reconstruction data is that this data is already available, thereby reducing the computational effort required to generate the second slice image.

[0067] According to another aspect of the invention, a data processing system is provided which is configured to carry out a computer-implemented method according to the invention.

[0068] In the present disclosure, the terms "data processing system" and "at least one data processing device" can be used interchangeably. A data processing device can be understood to be, in particular, a data processing device that contains a processing circuit. The data processing device can thus, in particular, process data to perform arithmetic operations. This may also include operations to perform indexed accesses to a data structure, for example, a lookup table (LUT), as well as a data processing process implemented in hardware.

[0069] The data processing device may, in particular, contain one or more computers, one or more microcontrollers, and / or one or more integrated circuits, for example, one or more application-specific integrated circuits (ASICs), one or more field-programmable gate arrays (FPGAs), and / or one or more systems on a chip (SoCs). The data processing device may also contain one or more processors, for example, one or more microprocessors, one or more central processing units (CPUs), one or more graphics processing units (GPUs), and / or one or more signal processors, in particular one or more digital signal processors (DSPs).The data processing device may also include a physical or virtual network of computers or other units of the aforementioned type.

[0070] In various embodiments, the data processing device includes one or more hardware and / or software interfaces and / or one or more storage units.

[0071] A storage unit can be volatile data storage, for example as dynamic random access memory (DRAM) or static random access memory (SRAM), or as non-volatile data storage, for example as read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), flash memory or flash EEPROM, ferroelectric random access memory (FRAM), or magnetoresistive random access memory.It can be designed as MRAM (magnetoresistive random access memory) or as phase-change random access memory, PCRAM (phase-change random access memory).

[0072] According to a further aspect of the invention, an imaging system for angle-limited tomography is provided. The imaging system comprises a data processing system according to the invention, as well as an imaging device configured to generate the plurality of projection images.

[0073] According to at least one embodiment of the imaging system, the imaging device is an X-ray imaging device, for example a C-arm device.

[0074] According to at least one embodiment, the imaging system has a display device, wherein the data processing system is configured to display the second layer image on the display device.

[0075] In some embodiments, the display device can also be considered part of the data processing system.

[0076] Further embodiments of the imaging system according to the invention follow directly from the various configurations of the computer-implemented method according to the invention, and vice versa. In particular, individual features and corresponding explanations as well as advantages relating to the various embodiments of the computer-implemented method according to the invention can be transferred analogously to corresponding embodiments of the imaging system according to the invention. In particular, the imaging system according to the invention is configured or programmed to carry out a computer-implemented method according to the invention. In particular, the imaging system according to the invention carries out the computer-implemented method according to the invention.

[0077] According to another aspect of the invention, a computer program with instructions is specified. When the instructions are executed by a data processing system, the instructions cause the data processing system to carry out a computer-implemented method according to the invention.

[0078] The instructions can be provided, for example, as program code. This program code can be provided, for example, as binary code or assembly language, and / or as source code in a programming language such as C, and / or as a program script, such as Python.

[0079] According to another aspect of the invention, a computer-readable storage medium is specified, in particular a physical and / or non-volatile computer-readable storage medium that stores a computer program according to the invention.

[0080] The computer program and the computer-readable storage medium are each computer program products containing the commands.

[0081] Further features and combinations of features of the invention will become apparent from the figures and their description, as well as from the claims. In particular, further embodiments of the invention need not necessarily include all features of any one of the claims. Further embodiments of the invention may have features or combinations of features not mentioned in the claims.

[0082] The invention is explained in more detail below with reference to specific embodiments and associated schematic drawings. In the figures, identical or functionally equivalent elements may be designated with the same reference numerals. The description of identical or functionally equivalent elements is not necessarily repeated with respect to different figures.

[0083] The figures show Fig. 1 a schematic representation of an exemplary embodiment of an imaging system according to the invention for angle-limited tomography; Fig. 2 a schematic block diagram of an exemplary embodiment of a computer-implemented method for image display according to the invention; Fig. 3 a schematic representation of first layer images and calculation areas for second layer images according to a further exemplary embodiment of a computer-implemented method for image display according to the invention; Fig. 4 a schematic representation of first layer images and calculation areas for second layer images according to a further exemplary embodiment of a computer-implemented method for image display according to the invention; and Fig. 5 a schematic representation of first layer images and calculation areas for second layer images according to a further exemplary embodiment of a computer-implemented method for image representation according to the invention.

[0084] In Fig. Figure 1 is an exemplary embodiment of an imaging system 1 according to the invention for angle-limited tomography, shown schematically.

[0085] The imaging system 1 includes an imaging device 3 which is configured to generate a multitude of projection images representing an object 8 and corresponding to a multitude of different projection directions.

[0086] Object 8 can be, for example, a patient or a part of the patient's body. The patient can be placed on a patient table 2 of the imaging system 1.

[0087] The imaging device 3 is shown as an example of a C-arm X-ray unit with an X-ray source 4 and an X-ray detector 5. However, the following explanations can be applied analogously to other imaging devices 3 that can generate projection images depicting an object 8 from a multitude of different projection directions. For example, the multitude of different projection directions is achieved by rotating the X-ray source 4 and the X-ray detector 5 along a trajectory, such as a circular or spiral trajectory, around a pivot axis, so that a predefined angular range is covered. The pivot axis is, in particular, parallel to or equal to the longitudinal axis of the patient's body.

[0088] The imaging system 1 comprises a data processing system 6 according to the invention, which is configured to perform a computer-implemented method for image display according to the invention in an angle-limited tomography method, based on the plurality of projection images.

[0089] Fig. Figure 2 schematically shows a block diagram of an exemplary embodiment of such a computer-implemented method according to the invention. Further aspects of various embodiments of the computer-implemented method are shown in the figures. Fig. 3 to Fig. 5 shown.

[0090] In step 200, the multitude of projection images is obtained, and a three-dimensional image reconstruction is generated based on these images. In step 220, a first layer image 7 is created for a first section plane through object 8 based on the image reconstruction, and an area of ​​interest 9 of object 8 is determined in this first layer image 7.

[0091] In the examples of Fig. 3 to Fig. 5 is the first section plane, for example, a coronal plane of the patient through object 8, namely the patient's lung. The area of ​​interest 9 can, for example, correspond to a tumor or other lesion.

[0092] In step 240, a section line 10, 10a, 10b, 10c, 10d of a second section plane, which passes through the area of ​​interest 9, is determined in the first section plane. The second section plane can, for example, be perpendicular to the first section plane xz. In the examples of Fig. 3 to Fig. 5 corresponds, for example, to the second section plane xy, a transverse plane or axial plane through the patient's body.

[0093] In step 260, depending on the position of the section line 10, 10a, 10b, 10c, 10d and / or depending on the geometric extent of the area of ​​interest 9 in the first layer image 7, a calculation area 11, 11a, 11b, 11c, 11d around the second section plane is determined. For this purpose, in particular, a layer thickness of the calculation area 11, 11a, 11b, 11c, 11d and a position of the calculation area 11, 11a, 11b, 11c, 11d with respect to the section line 10, 10a, 10b, 10c, 10d are determined.

[0094] In step 280, a second layer image for the second section plane is generated based on the multitude of projection images, according to the calculation area 11, 11a, 11b, 11c, 11d. This can be done, for example, directly based on the multitude of projection images or indirectly based on the three-dimensional image reconstruction.

[0095] In the example of the Fig. Figure 3 shows, from left to right, the first cross-sectional images 7 with four different positions of the section line 10a, 10b, 10c, 10d. The layer thickness of the computation area 11a, 11b, 11c, 11d is the same for all four cases, and the position of the computation area 11a, 11b, 11c, 11d is determined depending on the position of the section line 10a, 10b, 10c, 10d, in particular such that the computation area 11a, 11b, 11c, 11d lies completely within the area of ​​interest 9 in all four cases, whereby the contour of the area of ​​interest 9 also lies within the area of ​​interest 9.

[0096] In the first section 7, on the far left, the position of section line 10a corresponds to an upper boundary position of the area of ​​interest 9. The calculation area 11a extends from section line 10a exclusively downwards into the area of ​​interest 9. "Upper" and "downwards" here refer to the positive and negative z-directions, respectively. In the first section 7, in the second position from the left, section line 10b is located below the upper boundary position of the area of ​​interest 9. The calculation area 11b extends symmetrically upwards and downwards from section line 10b. The same applies analogously to the first section 7, in the third position from the left, section line 10c, and calculation area 11c. In the first section 7, on the far right, the position of section line 10d corresponds to a lower boundary position of the area of ​​interest 9. The calculation area 11d extends from section line 10a exclusively upwards into the area of ​​interest 9.

[0097] As in Fig. 3 are in the example of the Fig. Four cross-sectional images from left to right show four different positions of the section line 10a, 10b, 10c, 10d. The positions of the section line 10a, 10b, 10c, 10d correspond to those in Fig. 3 shown. However, the layer thickness of the calculation area 11a, 11b, 11c, 11d also depends on the positions of the section lines 10a, 10b, 10c, 10d. Thus, different parts of the area of ​​interest 9 can be used according to the specific requirements of the second layer image.

[0098] In Fig.Figure 5 shows two initial cross-sectional views 7 with different geometric extents of the area of ​​interest 9. In particular, the extent H differs between the upper and lower boundary positions in the z-direction. In the case shown above, H is smaller than in the case shown below. Here, the layer thickness of the computational area 11 is determined depending on the geometric extent of the area of ​​interest 9. Specifically, in the case with the larger extent H, the layer thickness of the computational area 11 is also greater.

[0099] As described, the invention enables image display in angle-limited tomography with increased image quality.

[0100] In some embodiments, automatic adjustment of the slice thickness of the computational area 11a, 11b, 11c, 11d for an axial slice image is proposed, based on the area of ​​interest 9, which is visible on a coronal slice image. The area of ​​interest 9 corresponds, for example, to a lesion. This allows the difference in the detectability of the lesion in different anatomical planes to be exploited. Due to the lesion's good detectability in the sagittal plane, it can, for example, be detected using a CAD algorithm. The CAD algorithm provides the location of the lesion in the sagittal plane, from which the slice thickness for the axial plane can be calculated. Alternatively, the lesion can also be marked manually.Assuming that the cranial-caudal axis is designated as the z-axis, i.e. the axis perpendicular to the axial layer, the layer thickness can be adapted based on the z-position of the section line 10a, 10b, 10c, 10d within the area of ​​interest 9.

[0101] Further advantages of various implementation examples include easy integration into existing reconstruction and visualization methods without altering the image data, which would increase the risk of information loss or artifacts not present in the raw data. Furthermore, no additional imaging data, such as a prior CT scan, is required.

[0102] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identities are included.

Claims

[1] Computer-implemented method for image display in an angle-limited tomography procedure, wherein - a multitude of projection images representing an object (8) and corresponding to a multitude of different projection directions are obtained, and a three-dimensional image reconstruction is generated based on the multitude of projection images; - a first layer image (7) for a first section plane through the object (8) is generated based on the image reconstruction and an area of ​​interest (9) of the object (8) is determined in the first layer image (7); - in the first section plane a section line (10, 10a, 10b, 10c, 10d) of a second section plane, which passes through the area of ​​interest (9), is determined; - depending on a position of the section line (10, 10a, 10b, 10c, 10d) and / or depending on a geometric extent of the area of ​​interest (9) in the first layer image (7), a computation area (11, 11a, 11b, 11c, 11d) around the second section plane is determined, wherein the computation area (11, 11a, 11b, 11c, 11d) has a position and a layer thickness; and - based on the multitude of projection images, a second layer image for the second section plane is generated according to the calculation area (11, 11a, 11b, 11c, 11d). [2] Computer-implemented method according to claim 1, wherein the second cutting plane is perpendicular to the first cutting plane. [3] Computer-implemented method according to claim 2, wherein - a first boundary position of maximum extent of the area of ​​interest (9) in the direction perpendicular to the line of intersection (10, 10a, 10b, 10c, 10d) and / or a second boundary position of maximum extent of the area of ​​interest (9) in the direction perpendicular to the line of intersection (10, 10a, 10b, 10c, 10d) are determined; and - the calculation area (11, 11a, 11b, 11c, 11d) is determined depending on a distance of the section line (10, 10a, 10b, 10c, 10d) from the first boundary position and / or a distance of the section line (10, 10a, 10b, 10c, 10d) from the second boundary position. [4] Computer-implemented method according to one of the preceding claims, wherein the position of the computation area (11, 11a, 11b, 11c, 11d) is determined depending on the position of the section line (10, 10a, 10b, 10c, 10d). [5] Computer-implemented method according to claim 4 and claim 3, wherein the position of the cutting line (10, 10a, 10b, 10c, 10d) corresponds to the first boundary position or the second boundary position and the position of the computation area (11, 11a, 11b, 11c, 11d) is determined such that a part of the computation area (11, 11a, 11b, 11c, 11d) that lies outside the area of ​​interest (9) is smaller than a part of the computation area (11, 11a, 11b, 11c, 11d) that lies within the area of ​​interest (9), or such that the computation area (11, 11a, 11b, 11c, 11d) lies completely within the area of ​​interest (9). [6] Computer-implemented method according to any one of claims 1 to 4, wherein the position and layer thickness of the computation area (11, 11a, 11b, 11c, 11d) are determined such that a part of the computation area (11, 11a, 11b, 11c, 11d) that lies outside the area of ​​interest (9) is smaller than a part of the computation area (11, 11a, 11b, 11c, 11d) that lies inside the area of ​​interest (9), regardless of the position of the section line (10, 10a, 10b, 10c, 10d), or such that the computation area (11, 11a, 11b, 11c, 11d) is completely within the area of ​​interest, regardless of the position of the section line (10, 10a, 10b, 10c, 10d). (9) is located. [7] Computer-implemented method according to one of the preceding claims, wherein the layer thickness of the computation area (11, 11a, 11b, 11c, 11d) is determined depending on the position of the section line (10, 10a, 10b, 10c, 10d). [8] Computer-implemented method according to one of the preceding claims, wherein the layer thickness of the computation area (11, 11a, 11b, 11c, 11d) is determined depending on the geometric extent of the area of ​​interest (9) in the first section plane. [9] Computer-implemented method according to one of the preceding claims, wherein data from the plurality of projection images corresponding to the computation area (11, 11a, 11b, 11c, 11d) are extracted and the second layer image is generated based on the extracted data. [10] Computer-implemented method according to any one of claims 1 to 8, wherein image reconstruction data corresponding to the computation area (11, 11a, 11b, 11c, 11d) are extracted and the second layer image is generated based on the extracted data. [11] Computer-implemented method according to one of the preceding claims, wherein the plurality of different projection directions includes a projection direction that is perpendicular to the first cutting plane and / or the second cutting plane is parallel to all projection directions of the plurality of different projection directions. [12] Data processing system (6) configured to carry out a computer-implemented method according to any of the preceding claims. [13] Imaging system (1) for angle-limited tomography comprising a data processing system (6) according to claim 12 and an imaging device (3) configured to generate the plurality of projection images. [14] Imaging system (1) according to claim 13, wherein the imaging device (3) is designed as an X-ray C-arm device. [15] Computer program product comprising instructions which, when executed by a data processing system (6), cause the data processing system (6) to carry out a computer-implemented method according to any one of claims 1 to 11.

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