Method for calibrating a measuring arrangement, and calibration arrangement in particular for carrying out the method

Abstract

The invention relates to a method for calibrating a CT measuring arrangement (6) which generates radiographs of measurement objects (1) by means of invasive radiation from a radiation source of a radiation generating device (11; 21; 31; 51), wherein - the invasive radiation penetrates a calibration object (41) and is detected by a radiation receiver (45, 46, 47) of a detection device, - radiographs of the calibration object (41) are generated from detection signals of the detection device that correspond to the radiation detected by the radiation receiver (45, 46, 47), and - by evaluation of the radiographs, geometry parameters of the measuring arrangement are determined, characterized in that the detection signals are generated while the position and orientation of the calibration object (41), of the radiation generating device (11; 21; 31; 51) and of the radiation receiver (45, 46, 47) within a sectional plane of the measuring arrangement (6), which plane intersects with a radiation source, the calibration object (41) and the radiation receiver (45, 46, 47), are kept constant, - invasive radiation is generated by each of a plurality of radiation sources of the radiation generating device (11; 21; 31; 51) and radiates from the particular radiation source through the calibration object (41), and - for the invasive radiation from each of the plurality of radiation sources, at least one of the radiographs is generated and evaluated to determine the geometry parameters.

Description

[0001] Method for calibrating a measuring arrangement and calibration arrangement, in particular for carrying out the method

[0002] The invention relates to a method for calibrating a measuring arrangement that generates transmission images of measurement objects using invasive radiation from a radiation source, in particular for calibrating a computed tomography (CT) measurement arrangement. The invention further relates to a calibration arrangement for calibrating such a measuring arrangement. In particular, the invention lies in the field of industrial metrology, where the measurement objects are products from industrial manufacturing, e.g., workpieces or complex components made up of a multitude of workpieces.

[0003] The use of invasive radiation for examining workpieces is well-established. In computed tomography (CT), for example, the workpiece is typically positioned on a rotary table and irradiated from different directions by rotating the table into various orientations. However, other geometries of the examination setup are also possible and known. The radiation, attenuated by extinction in the workpiece material, is detected with spatial and temporal resolution by a detection device. In practice, for example, between 800 and 1,200 projection images of the object are acquired, with the rotational orientation being changed by a constant angular amount between each projection. By applying one of several known tomographic reconstruction methods, such as filtered back projection, a three-dimensional image of the object (especially the workpiece) is calculated.The 3D image provides the local linear absorption coefficient for individual small volume regions (voxels). An example for CT is described in DE 3924 066 A1.

[0004] A key prerequisite for an accurate reconstruction of the measured object is knowledge of the geometry of the measurement setup. Information about the relative arrangement of the radiation source, the measured object, and the detection device must be available. In other words, the deviation between the geometry assumed for the reconstruction and the actual geometry must be as small as possible. A highly precise and permanently stable assembly, with regard to the positioning and orientation of the components, can form the basis for an accurate reconstruction. However, this requires considerable effort. Another or additional option is to perform a calibration.

[0005] Calibration can be performed by precisely measuring the radiation source, stage, and detection device during the initial setup of the measurement setup. The individual components are measured and precisely aligned using various external measuring instruments or aids (e.g., calipers, laser beam measuring device). The use of high-precision adjustment elements aims to ensure that even after controlled movement of elements within the measurement setup, the geometric relationships are known with sufficient accuracy for precise reconstruction. Methods exist for regularly recalibrating certain aspects of the overall geometry using X-ray images of suitable calibration objects.

[0006] Alternatively or additionally, parameters of the geometric relationships of the measuring arrangement can be determined by applying known X-ray image-based methods. In particular, a parameterized geometric model can be used as the basis, the parameters of which, and especially its geometric parameters, are determined by calibration. EP 1 760457 B1 describes such a method. It is based on the fact that for each radiograph of a calibration object, and for each calibration element (e.g., each sphere of the calibration object), two measured values ​​(in particular, an x- and a y-coordinate in the coordinate system of the detection device) are determined. If a calibration object has, for example, a plurality of n calibration elements, 2*n measured values ​​are obtained from one radiograph. The formulation of a system of equations therefore allows up to 2*n unknowns to be determined using known methods. Unknowns can, for example, be...the position and orientation of components of the CT measurement setup such as the X-ray tube, detection device, rotary table and positioning axes.

[0007] The method according to EP 1 760457 B1 makes it possible to determine the twelve parameters of a projection matrix (see Projection matrix (computer vision) - Wikipedia) from a single transmission image. These parameters can also be understood as a description of the source spot position, detector position, and detector orientation relative to the calibration target. To prevent the system of equations from being underdetermined, the three-dimensional (3D) coordinates of the calibration elements within the calibration target are determined beforehand and are therefore known. Otherwise, an additional 3*n unknowns would have to be determined.

[0008] A known solution for using calibration blocks even when the positions of the calibration elements are unknown is to use additional axes of motion to move the calibration block within the measurement setup. Assuming that the 3*n coordinates of the n calibration elements of a calibration block remain constant during a measurement, the parameters of a complete projection matrix can be determined by each additional radiograph taken with a change in the direction of transmission of the X-rays through the calibration object. This means that when using more than six calibration elements in the calibration block, each additional radiograph allows for the determination of additional measured values. Geometric parameters such as the relative positions of the X-ray source and the detection device can remain unchanged.As a result, an increasing number of unknowns (especially geometric parameters and other parameters) can be determined by evaluating the radiographs. With regard to the mathematical solution of a system of equations, each radiograph adds another equation. Thus, with a sufficiently large number m of radiographs, the system of equations is no longer underdetermined. In particular, in addition to the basic geometric parameters of the measuring setup, further parameters (unknowns) can also be determined, e.g., parameters that describe non-ideal geometric properties, such as wobble, runout, and axial runout of the rotary table on which the object being measured or the calibration object is located. In the case of linear axes of motion, corresponding parameters can be determined that account for the non-exactly (straight-line) linear motion (e.g.,...The movement of the object being measured (in the direction of or parallel to the direction of the rotary table's axis of rotation) can be described in a desired direction. Distortion errors in the detection device can also be determined.

[0009] However, calibration methods for CT measurement setups are also known that do not require an additional axis of movement (neither rotary nor linear). In this case, the calibration block can be pre-measured. With regard to the embodiment of a calibration block with multiple calibration elements, this means that the relative positions of the calibration elements are already known, as mentioned above, when the radiographic images acquired for calibration are evaluated to obtain the parameter values ​​to be determined by the calibration. To ensure that these known relative positions remain constant over time, a correspondingly complex manufacturing and / or design of the calibration block is required. Otherwise, the relative positions of the calibration elements must be repeatedly determined in a time-consuming manner.

[0010] An object of the present invention is to provide a calibration method and a corresponding calibration arrangement for CT measurement setups in which the calibration object (e.g., a calibration block) does not need to be moved about an axis of rotation for the purpose of acquiring the radiographic images, and in particular is not only stationary with respect to this axis of rotation (e.g., the axis of rotation perpendicular to a plane extending through the source spot, the calibration object, and the detection device), but is completely stationary. The calibration object can, for example, be the calibration block mentioned above. However, the calibration object can also comprise an arrangement of a plurality of calibration blocks.

[0011] The invention is based on the idea that transmission images obtained for calibration, which are acquired from different directions when the calibration object is irradiated with invasive radiation, do not require rotation of the calibration object. Instead, it is possible, and proposed, that various locations are available for source spots (as radiation sources) of the invasive radiation, and that the calibration object is irradiated from these different locations to generate corresponding transmission images. Accordingly, the calibration object is irradiated from different directions with invasive radiation. In particular, at least one transmission image of the calibration object is generated for each source spot location and evaluated for calibration purposes.The term "source spot" refers to the local area of ​​a radiation-generating device (particularly at a target of the radiation-generating device) in which the invasive radiation originates and / or from which the invasive radiation is emitted. In conventional X-ray tubes, electrons are directed into this local area of ​​the target or onto the source spot, and the X-rays are generated by their deceleration within the source spot of the target. The term "focal spot" is also frequently used for X-ray tubes. However, the invention is not limited to X-rays. Rather, the invasive radiation can also lie in wavelength ranges outside the wavelength range of X-rays.In X-ray tubes and other radiation-generating devices where invasive radiation is produced by the deceleration of particles, the particles can be directed onto the target from the same side from which the invasive radiation is emitted. Such X-ray tubes are sometimes referred to as reflection tubes, although in fact no reflection of the same type of radiation occurs. Furthermore, the particles can be directed onto the target from the rear, if the front of the target is understood to be the side from which the invasive radiation is emitted. Both operating principles can be used to generate the invasive radiation according to the invention.

[0012] For example, a source control system allows for the relocation / selection of a radiation source and thus the irradiation of the calibration object with invasive radiation in different directions without having to move the calibration object. Preferably, the radiation generating device and the radiation receiver of the detection device for detecting the invasive radiation passing through the calibration object are also stationary, i.e., neither their position nor their orientation is changed. All these specifications refer in particular to a position and orientation with respect to a cross-sectional plane of the measuring arrangement that intersects a location of a specific (of several) radiation source of the radiation generating device, the calibration object, and the radiation receiver.If mobility is not required in a direction perpendicular to this cutting plane (as is the case in a specific embodiment described below), then both the calibration object and the radiation generating device and the radiation receiver can be stationary in 3-dimensional space throughout the entire acquisition of information for the radiographic images by generating detection signals from the radiation receiver.

[0013] In particular, a method for calibrating a measurement arrangement is proposed which generates transmission images of measurement objects by means of invasive radiation from a radiation source of a radiation generating device, especially for calibrating a computed tomography (CT) measurement arrangement, wherein the invasive radiation penetrates a calibration object and a resulting radiation is detected by a radiation receiver of a detection device of the measurement arrangement, wherein the calibration object has at least one calibration element, transmission images with an image of the at least one calibration element are generated from detection signals of the detection device corresponding to the radiation detected by the radiation receiver, and geometric parameters of a geometry of the measurement arrangement are determined by evaluation of the transmission images, the detection signals are generated while a position and an orientation of the calibration object,The radiation generating device and the radiation receiver of the detection device are kept constant within a cross-sectional plane of the measuring arrangement, which intersects a location of a specific radiation source of the radiation generating device, the calibration object and the radiation receiver, invasive radiation is generated by a plurality of radiation sources of the radiation generating device and the calibration object is irradiated from the respective radiation source and at least one of the transmission images is generated for the invasive radiation emanating from each of the plurality of radiation sources and is evaluated to determine the geometric parameters.

[0014] Furthermore, a calibration arrangement is proposed for calibrating a measuring arrangement that generates transmission images of measurement objects using invasive radiation from a radiation source, in particular for calibrating a computed tomography (CT) measurement arrangement, wherein the measurement arrangement to be calibrated is part of the calibration arrangement and comprises the following: a radiation generation device for generating the invasive radiation, a measurement chamber in which a measurement object can be arranged so that, during operation of the radiation generation device, invasive radiation penetrates the measurement object, wherein, in the case of calibration of the measuring arrangement, the measurement object is a calibration object, a detection device with a radiation receiver for detecting radiation that is a result of the transmission of the measurement object with the invasive radiation, wherein the detection device is configuredto generate at least one of a plurality of radiographic images of the measurement object from detection signals of the radiation receiver, wherein the calibration arrangement further comprises: an evaluation device configured to determine geometric parameters of a geometry of the measurement arrangement by evaluating the radiographic images, wherein the radiation generating device comprises a plurality of radiation sources, the calibration arrangement configured to generate invasive radiation from the plurality of radiation sources of the radiation generating device, which emanates from the radiation source and irradiates the calibration object, while determining the position and orientation of the calibration object, the radiation generating device and the radiation receiver of the detection device within a cross-sectional plane of the measurement arrangement, which defines a location of a specific radiation source of the radiation generating device,The calibration object and the radiation receiver are intersected, the detection device is designed to detect the invasive radiation emanating from each of the plurality of radiation sources through the radiation receiver and to generate at least one of the transmission images in each case, and the evaluation device is designed to evaluate the generated transmission images and to determine the geometric parameters.

[0015] The cutting plane can, in particular, be a plane that contains two of the three coordinate axes in a Cartesian coordinate system of the measuring setup, or that runs parallel to them. Alternatively or additionally, the cutting plane can be predefined.

[0016] As mentioned, the calibration object is irradiated with invasive radiation from various sources. These beams, each originating from one of the radiation sources, can pass through the calibration object simultaneously and / or sequentially. It is therefore possible, in particular, that the beams from all radiation sources used for calibration in the radiation generation device are generated simultaneously and pass through the calibration object over the same time interval. However, it is also possible that at least one of the radiation sources is activated to generate the corresponding beam if at least one of the radiation sources has already been activated. In particular, the first radiation source can also be deactivated before the second radiation source is activated. Therefore, it is also possible that at any given time during the irradiation of the calibration object, only one of the radiation sources is active.Combinations of these temporal sequences are possible. For example, a majority of the radiation sources can be active simultaneously, at least with some temporal overlap, whereas a majority of the radiation sources are only active sequentially. In particular, sequentially active radiation sources allow the location of a radiation source to be relocated or changed, especially by altering the control parameters of a particle optic that (approximately) focuses a particle beam onto a target of the radiation generation device. Focusing onto a single point is not usually performed when operating such invasive radiation sources, as this could damage or destroy the target material. The relocated radiation source can then be reactivated. The relocation or...Changing the location of a radiation source does not require moving any component of the radiation-generating device, such as the target of an X-ray tube. In particular, as will be explained in more detail below, an X-ray tube can have multiple emitters, so that a source spot can be generated at different locations on the target or an array of targets, each forming a radiation source.

[0017] In general, it is specifically provided that at least one of the plurality of radiation sources is activated to initiate operation of the respective radiation source, during which invasive radiation emanating from it and passing through the calibration object is detected by the radiation receiver. A radiation receiver of the calibration arrangement can, for this purpose, have a source control configured to activate at least one of the plurality of radiation sources to initiate operation of the respective radiation source, during which invasive radiation emanating from it and passing through the calibration object is detected by the radiation receiver. In this way, any number of the plurality of radiation sources can be activated, in particular all radiation sources of the plurality of radiation sources.Source control can, in particular, involve controlling a plurality of particle emitters (especially electrons) whose deceleration in a target material generates and emits invasive radiation, thus activating the radiation source. Source control can therefore, for example, be triggered by a higher-level control system and / or upon receiving a corresponding signal. It can activate a specific radiation source, as defined by the higher-level control system and / or the signal itself, by switching on the emitter (e.g., by initiating an electric current through the emitter). Furthermore, associated particle optics must be activated. For example, source control can also control the particle optics so that the particle beam strikes the target at a desired location (e.g., defined by the higher-level control system and / or a received signal), thus forming the source spot.

[0018] In principle, the various locations for the source spot can be activated and / or configured in different ways. In all cases, radiation sources are activated at different locations or positions within the measurement setup. The transmission images are generated, at least partially, for these different radiation sources. In particular, the radiation receiver can therefore detect invasive radiation emanating from the location of a first radiation source that has passed through the calibration object, and this applies accordingly to the other radiation sources that are activated during the execution of the calibration procedure. For example, a source control of the radiation generation device can activate a source spot area of ​​the radiation generation device, so that the invasive radiation now originates at a source spot within the activated source spot area and constitutes the radiation source.

[0019] As already mentioned, at least one of the radiation sources can be a source spot on a target where particles strike and are slowed down, thus generating the invasive radiation. In the case of an X-ray source, the particles are typically electrons. Therefore, with respect to at least one of the plurality of radiation sources, and preferably with respect to several or all of the plurality of radiation sources, a particle optics control can control the generation of at least one particle beam such that, upon striking a target of the radiation generation device, the particle beam forms a source spot of the invasive radiation as the radiation source.With regard to the calibration arrangement, at least one (and preferably all) of the plurality of radiation sources can be assigned a particle optics control system, which is designed to generate at least one particle beam which, upon striking a target of the radiation generation device, forms a source spot of the invasive radiation as a radiation source.

[0020] In principle, it is possible to change the location of a source spot area—that is, the position of a local area of ​​the radiation-generating device which, when operating accordingly, contains the source spot for the invasive radiation—by moving a component of the radiation-generating device that comprises the local area (in particular, the target or the area of ​​the target). The source spot can, in particular, be located within a source spot area. A source spot area is understood to be a local area in which a source spot can be located, whereby the exact position of the source spot can optionally be adjusted within the source spot area, as is common in some types of X-ray tubes, for example, by appropriately adjusting an electron optic to direct the electron beam onto the target of the X-ray tube.One well-known method is so-called wobbling, in which the exact position of the source spot is continuously changed in one direction and, upon reaching an end position, in the opposite direction, and so on. However, such measures do not achieve any significant change in the direction of the radiation passing through the object being measured or the calibration object.

[0021] However, within the scope of the invention claimed herein, it is preferred that no movement of components (such as targets) of the radiation generation device takes place to adjust the location of the source spot or, more generally, the radiation source. Therefore, no movement of components relative to the calibration object occurs to irradiate the calibration object with invasive radiation in a different direction. This refers to movements with respect to the aforementioned plane of section. In special embodiments, which, for example, serve to measure particularly large objects, it may optionally be provided to move the object of measurement or the radiation source in a direction transverse and, in particular, perpendicular to this plane of section and to obtain radiographic images in each case.Accordingly, in this case, a corresponding movement of the calibration object or at least a part of the radiation source transversely or perpendicularly to the cutting plane can be provided, and corresponding radiographic images can be obtained for calibration. However, there are also embodiments of the invention in which no such movement is provided in a direction transverse and, in particular, perpendicular to the aforementioned cutting plane. In this case, the position and orientation of the calibration object, the radiation generating device, and the radiation receiver of the detection device are constant with respect to all degrees of freedom of movement, while the detection signals are generated for all directions of irradiation of the calibration object with invasive radiation. In particular, these positions and orientations therefore remain constant when one radiation source is deactivated and another radiation source is activated.

[0022] In particular, a radiation source arrangement of the radiation generating device has a plurality of potential source spot areas, which can be activated individually and preferably independently of one another, such that a source spot is created within each activated source spot area. Activation creates a source spot in the respective source spot area, from which invasive radiation emanates.

[0023] In particular, a radiation-generating device unit with multiple source spot areas (e.g., an X-ray tube with a plurality of emitters) can be present, and within this unit, without moving it relative to the aforementioned sectional plane or without moving it at all, different source spot areas can be activated sequentially and / or simultaneously to generate invasive radiation, for example, by source control of the radiation-generating device. Furthermore, in this case, it is possible for several such units to be present, thus providing even more activatable source spot areas. For example, each unit has a plurality of emitters, each configured to emit particles (especially electrons) and direct them onto an associated source spot area of ​​a target, so that the invasive radiation is generated in a source spot of the source spot area.The term source spot therefore refers in particular to the state in which invasive radiation originates from the source spot.

[0024] Regarding a design for activating a radiation source, it is proposed that an electron optics control, which is, for example, part of the aforementioned source control, controls at least one electron beam in such a way that a source spot is created in a first source spot region, thus activating the radiation source. More generally, one can speak of particles or elementary particles instead of electrons, since not only electrons can generate invasive radiation by deceleration. Correspondingly, with respect to the calibration arrangement, a design exists in which the source control includes a particle optics control that is configured accordingly.

[0025] For each of the various locations, or more precisely, local areas, that are potentially available as source spot areas, a corresponding detector area of ​​the detection system is provided for the spatially resolved detection of the invasive radiation after it has penetrated the calibration object. In terms of the terminology used above for the detection system, which includes a radiation receiver, the various detector areas belong to the radiation receiver. The detector areas can, in particular, each be a sub-area or the entire area of ​​a detector panel. This means that the radiation receiver can, for example, have several detector panels arranged around the measurement space.Such detector panels can have sensor elements arranged in a plane, each sensor element configured to detect incident invasive radiation and convert it into a local measurement, particularly of the radiation flux density. However, sensor elements of a detector panel can also be arranged along a curved surface, such that the respective normal at different points on the curved surface points towards the measurement space. In particular, it is therefore also possible for the radiation receiver to have a single detector panel and yet extend over a substantial circumferential angle around the measurement space.For example, regardless of the design of the radiation receiver with respect to the detector panels, the radiation receiver can extend over a circumferential angle of at least 45 degrees, preferably at least 90 degrees, preferably more than 120 degrees, and particularly preferably at least 180 degrees around a center of the measuring space. The same preferably applies to an arrangement of potential source spot areas.

[0026] If no detector area were provided for invasive radiation emanating from a source spot and penetrating the calibration object, it would not be possible to detect this radiation and generate a corresponding transmission image. The invention therefore provides, in particular, that a potentially available source spot area is only used for generating invasive radiation if a suitable associated detector area is also available. This applies especially to the preferred case where the calibration object maintains its position and orientation within the aforementioned section plane of the measurement arrangement. In particular, the calibration object is therefore not moved within the section plane in this case to change the transmission direction.

[0027] Therefore, a configuration of the calibration procedure is proposed in which, for the majority of radiation sources, invasive radiation emanating from a source spot passes through the calibration object and is detected by a detector area of ​​the radiation receiver that is opposite the source spot (with respect to the measurement space or the calibration object). In particular, the calibration arrangement can be configured to activate a source spot area in each case, such that invasive radiation emanates from a source spot within the activated source spot area, passes through the calibration object in the measurement space, and is detected by the detector area of ​​the radiation receiver that is opposite the source spot.Therefore, the radiation receiver can have a plurality of detector areas, which are arranged in such a way and each is assigned to at least one of the source spot areas, such that the invasive radiation emanating from the respective source spot in the activated source spot area and passing through the calibration object hits the assigned detector area and is detected by it.

[0028] To generate a two-dimensional radiographic image, a two-dimensional detector area is required. The detection of the incident invasive radiation can be performed in two fundamentally different ways. Firstly, an array of sensor elements can be used; secondly, a sensor element or group of sensor elements can be moved to scan for incident radiation within the detector area and acquire the spatially resolved information required for a two-dimensional radiographic image. To avoid moving a sensor element or group of sensor elements, which in turn introduces motion errors that must be determined through calibration, the use of stationary arrays of sensor elements is preferred. Therefore, it is also preferred that the entire detector assembly be stationary with respect to the aforementioned plane of section.The use of different detector areas enables the detection of invasive radiation resulting from different directions of transmission through the calibration object. This requires that the source of the invasive radiation is not stationary with respect to the plane of the scan.

[0029] In particular, the calibration object can have known dimensions, which are then preferably taken into account when evaluating the radiographs and determining the geometric parameters. This can relate in particular to the positions of the calibration elements relative to each other, i.e., especially within a coordinate system of the calibration object. The advantage of such known positions of the calibration elements is that these positions do not need to be determined from the radiographs obtained during the calibration procedure. The number of parameters or unknowns to be determined by the calibration is therefore reduced. For example, only the position and orientation of the calibration object in the measurement setup need to be determined.However, there are circumstances, such as strong temperature fluctuations or when the calibration object has been subjected to significant mechanical forces, which may make it necessary to redetermine the positions of the calibration elements in advance (i.e., before performing a calibration procedure) or to obtain them again or for the first time from the radiographic images obtained during the calibration procedure.

[0030] As mentioned at the outset, a distinction must be made between a calibration object or calibration body on the one hand and calibration elements on the other. It is known, as stated, that at least one calibration element is determined whose position in the respective radiographic image is determined. In principle, it is also possible not only to determine a single position of a calibration element, but also, for example, its orientation. The calibration object preferably has a plurality of calibration elements. This makes it possible, in particular, as already known from the prior art, to determine the position of each calibration element in each of the radiographic images of the calibration object. However, the fact that such a position can be determined for all calibration elements in each of the radiographic images depends on the calibration elements being arranged in a suitable manner in the measurement setup.The calibration elements should therefore be arranged in such a way that they all produce individual images in the resulting radiographic image that can be evaluated at a sufficient distance from the images of all other calibration elements. The majority of the calibration elements have the advantage of providing additional information for calibration.

[0031] As mentioned, geometric parameters of the measurement setup are determined by evaluating the radiographs. In particular, these geometric parameters can refer to a geometric model that describes the geometry of the measurement setup. It is not impossible that, in addition to the geometric parameters, the evaluation of the radiographs will also reveal at least one other parameter of the measurement setup, and especially of the model. For example, another parameter might be determined that describes the conditions under which the detection signals from the radio frequency receiver are obtained from the measurement setup, such as the temperature prevailing during operation of the setup for calibration purposes. Such additional parameters can be not only physical parameters, but also, for example, purely mathematical parameters that describe changes in the values ​​of the geometric parameters over time.Parameters for the control of the radiation generation device, in particular parameters of the electron optics of an X-ray tube, are also among the other parameters.

[0032] Overall, it may be necessary to determine a value for a multitude of parameters through calibration. According to one embodiment of the invention, it is proposed that at least some of the multitude of parameters are not repeatedly determined by performing the calibration method according to the invention. Instead, an assignment can be determined for this portion of the multitude of parameters, which allows the determination of said portion of the multitude of parameters from at least one geometric parameter determined by the calibration method according to the invention (and / or at least one additional parameter), taking the assignment into account. Alternatively, the assignment can allow the determination of at least one parameter (e.g., a geometric parameter) that is relevant for the calibration, starting from parameters other than geometric parameters (e.g., at least one of the aforementioned additional parameters).As long as the assignment remains valid, the calibration method according to the invention can therefore be carried out repeatedly, although a reduced number of parameters need to be determined. A first such embodiment relates to the type of radiation source already mentioned several times, in which a target is irradiated with particles and the invasive radiation is generated by decelerating the particles. In this embodiment, a control parameter assignment is determined which, for at least one of the plurality of radiation sources, assigns a location of the source spot on the target to values ​​of control parameters of the particle optics control, so that the location of the source spot can be determined for the respective radiation source from the values ​​of at least one control parameter.For at least one (and preferably all) of the plurality of radiation sources, the location of the source spot on the target, determined from the actual values ​​of the control parameters of the particle optics control system using the control parameter assignment, is used as an input variable in the evaluation of the transmission images for determining the geometric parameters. The evaluation device can be configured to consider the location of the source spot on the target, determined from the actual values ​​of the control parameters of the particle optics control system using the control parameter assignment, as an input variable for at least one of the plurality of radiation sources when evaluating the transmission images for determining the geometric parameters.

[0033] Alternatively or additionally, a local assignment can be determined for at least one of the plurality of radiation sources, which assigns actual 3D locations on the surface of the target, defined in a three-dimensional coordinate system, to the 2D locations on the surface of the target defined in a two-dimensional coordinate system, whereby, when evaluating the transmission images to determine the geometric parameters for at least one of the plurality of radiation sources, a corresponding 2D location in the two-dimensional coordinate system is determined as one of the geometric parameters, and the 3D location of the radiation source is determined using the local assignment.The evaluation device of the calibration arrangement can be designed in such a way that, when evaluating the radiographic images to determine the geometric parameters for at least one of the majority of radiation sources, it identifies an associated 2D location in the two-dimensional coordinate system as one of the geometric parameters and, using the local assignment, determines the 3D location of the radiation source.Furthermore, a representation assignment can be determined which assigns relative positions to at least a subset of the plurality of radiation sources to a representative location of the radiation generating device, so that in a coordinate system related to the radiation generating device or to a component of the radiation generating device, each of the relative positions allows a location of the radiation source belonging to the respective relative position to be determined from the representative location, and wherein, in the evaluation of the transmission images for the determination of the geometric parameters, the representative location of the radiation generating device and an orientation of the radiation generating device are determined as geometric parameters, and the locations of the radiation sources belonging to the respective relative positions are determined using the representation assignment.The evaluation device of the calibration arrangement can be designed to determine the representative location of the radiation generating device and an orientation of the radiation generating device as geometric parameters when evaluating the radiographic images to determine the geometric parameters, and to determine the locations of the radiation sources belonging to the respective relative positions using the representation assignment.

[0034] Exemplary embodiments of the invention and circumstances relating to its implementation will now be described with reference to the accompanying drawing. The individual figures of the drawing schematically illustrate:

[0035] Fig. 1 shows a measuring arrangement with a radiation generating device, a measurement object and a two-dimensionally spatially resolved radiation receiver; Fig. 2 shows an embodiment of a radiation generating device that generates invasive radiation by means of particle radiation incident on a target.

[0036] Fig. 3 shows a radiation generation device with a plurality of particle detectors to illustrate the possibility of activating a plurality of source spot areas.

[0037] Fig. 4 shows an enlarged view of a section of the radiation generation device from Fig. 3 to illustrate the possibility of relocating at least one of the source spot areas by controlling the electron optics.

[0038] Fig. 5 is a top view of a calibration arrangement. Fig. 6 is a representation of a radiation generating device as in Fig. 2, except that the target is shown to have a non-planar surface. Fig. 7 is a representation illustrating that source spots distributed along a planar surface also generate invasive radiation which penetrates a calibration object in various directions.

[0039] The measuring arrangement 6, schematically depicted in Fig. 1, comprises a measurement object 1 located between a radiation generating device 2 (e.g., a radiation generating device that produces X-rays) and the radiation receiver 3 of a detection device. The radiation generating device 2 is not shown in detail and is identified only by the origin of a Cartesian coordinate system. The origin of the coordinate system (GKS) of the measuring arrangement, whose coordinate axes are labeled xc, yc, and ZG, corresponds to the position of the radiation source, which is ideally assumed to be a point. In the case of X-rays, the radiation source is a source spot on a target, which decelerates electrons upon impact and generates the X-rays. The point-like nature of the radiation source is an approximation.For example, depending on the design of a geometric model whose geometric parameters are determined, it can be taken into account that the radiation source is not point-like. However, as mentioned, it is not necessary for a geometric model to exist within the scope of the invention. The geometric parameters can, for example, also directly define the positions of components of the measuring arrangement.

[0040] In the depicted, highly simplified case compared to practical applications, the radiation receiver has a field of five by eight detector fields, each represented by squares (distorted due to perspective). Individual detector fields, each capable of providing independent detection signals, are designated with the reference symbol 4. In practice, detection devices with significantly more detector fields can be used. In particular, each detector field has at least one sensor element that detects the radiation incident on it.

[0041] As not shown in detail, the object 1 can be rotated about a vertical axis of rotation so that the radiation emitted by the radiation source 2, with respect to a coordinate system OKS (object coordinate system) of the object 1 (whose axes are labeled x0, yo, zo in Fig. 1), can incident from different directions and pass through the object 1. Geometrically, a rotation of the object 1 is equivalent to a rotation of the arrangement consisting of the radiation source and the detector array.

[0042] This can be utilized according to the invention. As already described, the radiation source can be relocated relative to the object being measured 1 to a different position, for example, to a different position in the xo-zo plane, whereby the invasive radiation emitted by the radiation source is directed towards the object being measured 1. It is also possible, as already mentioned, for multiple radiation sources to emit invasive radiation at least partially simultaneously, which penetrates and is detected in different directions for the various radiation sources. Therefore, changing the position of the radiation source preferably results in a corresponding change in the direction of radiation propagation, not only with respect to the embodiment described in Fig. 1, so that the object being measured or the calibration object is penetrated in every case.

[0043] The distance between the object being measured 1 and the detection device 3 may differ in practice from that shown, e.g., be significantly larger than shown, in order to avoid detecting the effects of secondary effects such as luminescence and Compton scattering, or to detect them only to a small extent, and / or so that the projection of the object being measured 1 fills the area of ​​the detection device to a greater degree.

[0044] In Fig. 1, the perpendicular distance of the X-ray source 2 to the plane of the detection device 3 is denoted by SD. A translation vector foG and an associated dotted arrow indicate that the coordinate system GKS of the radiation source 2 and the coordinate system OKS of the object being measured 1 can be transformed into each other for each direction of transmission.

[0045] After the detection device has acquired three X-ray images of the object 1 in numerous different rotational positions, a reconstructed three-dimensional image of the object 1 is calculated, for example, by filtered backprojection. The three-dimensional image is specified in the coordinates of the object 1. It has a value for each of the volume regions (voxels) of the image, which is a measure of the attenuation of the X-ray radiation in that volume region.

[0046] A key prerequisite for accurate reconstruction of the object being measured is knowledge of the geometry of the measurement setup. Specifically, precise information about the relative position and orientation of the object and the radiation source, as well as the distance between the radiation source and the detection device (or equivalent information), is required. More generally, information about the relative arrangement of the radiation source, the object being measured, and the detection device is necessary. Particularly when local measurement artifacts occur in CT scans (as is often the case due to the effect of so-called beam hardening), it is insufficient to determine individual external dimensions of the object being measured and to scale acquired image information or information derived from it.

[0047] A geometric model of the measuring arrangement shown in Fig. 1 is described in EP 1 760457 B1 according to the description of Figure 1 therein, which is identical to Fig. 1 of the present description. Reference is made to the geometric model described in EP 1 760457 B1 and to the method for determining the geometric parameters of this model. However, other geometric models with, for example, additional parameters can also be used. Such additional parameters have already been discussed in this description. In particular, as mentioned at the outset, the geometric model can also have the twelve parameters of a projection matrix, and at least these twelve parameters can be determined from the radiographic images obtained according to the invention.

[0048] Fig. 2 shows a side view of a conventional radiation generating device 11. An emitter 12 emits particles, in particular electrons, which strike a target 17 as particle radiation 16. By means of controlled optics 14 for influencing the direction of propagation of the particles, in particular the electrons, the particle radiation 16 is focused onto a source spot 15 of the target 17. The resulting invasive radiation, in particular X-rays, propagates from the source spot 15 in a cone shape, as it exits the radiation generating device 11 through an aperture 18. Such an aperture helps to comply with radiation protection regulations. It is not necessary for the function and use of the radiation generating device 11. In practice, such a cone is also referred to as a beam 19, in particular an X-ray beam.In particular, it is possible to use a plurality of such conventional X-ray tubes to realize the plurality of radiation sources in the calibration method according to the invention, which then together form the radiation generation device.

[0049] Fig. 3 shows a modification of the conventional radiation generation device 11 from Fig. 2. This illustrates the principle by which a suitable radiation generation device allows the location of the radiation source to be changed without moving the target or a corresponding component of another radiation generation device. The radiation generation device 21 shown in Fig. 3 is merely a schematic representation of the principle. The target 27 of the radiation generation device 21 extends in a straight line. In an alternative embodiment, the target extends around the measuring chamber of the measuring arrangement, for example along a curved circumferential line (as shown in Fig. 5).In a design similar to that of the radiation generation device 21, the target can further extend segmentally in a straight line, and the segments can be arranged along the curved circumferential line, or the target itself can have a curved surface extending along the circumferential line. The segments are therefore angled relative to each other in order to extend around the measuring chamber. The segments can also each be an instance of the radiation generation device 21 from Fig. 3.

[0050] Although Fig. 3 shows that the invasive radiation emanating from the various activatable source spot areas spreads parallel to each other in cone-shaped spatial coils, this is merely for the sake of clarity. Furthermore, the calibration object is not shown in Fig. 3. In this context, reference is made to Fig. 7, which shows a similar arrangement, but with only three radiation sources, generating invasive radiation that penetrates the calibration object in different directions.

[0051] The radiation generation device 21 has five emitters 22 for the emission of particles, in particular electrons. The resulting particle radiation 26 is designated by reference numeral 26 only for two of the emitters 22. In the specific embodiment shown here, the particle optics 24 extend continuously over the entire longitudinal extent of the target 27. In other embodiments, the particle optics may, for example, extend only along a section of the target. The representation of the arrangement of the particle optics 24 in Fig. 3 is also to be understood schematically. Specifically, an arrangement and configuration of the particle optics must be selected that enables the particle radiation to be focused onto a source spot within a source spot region of the target. For clarity, only one of the source spots is designated by reference numeral 25 in Fig. 3. A beam of invasive radiation propagates from each of these source spots 25.The conical rays are designated with the reference symbols 29a to 29e.

[0052] Figure 3 schematically indicates that the particle optics 24 is connected to an optical control unit 23 via a control connection represented by a dashed line. The optical control unit 23 is configured to control the particle optics 24 such that at least the source spot area of ​​one of the source spots can be shifted. Alternatively or additionally, an emitter control unit 30 can be provided, which can switch the individual emitters 22 on and off. For clarity, Figure 3 only shows that the emitter control unit 30 is connected to the emitter 22 located furthest to the left in the illustration. In particular, a higher-level source control unit (not shown) can be present, which controls the emitter control unit 30 and / or the optical control unit 23 to determine the location where a source spot area is activated.Preferably (not only in the embodiments described here) only one source spot area of ​​the measuring arrangement is active during an operating period.

[0053] Fig. 4 shows parts of the arrangement depicted in Fig. 3, including the emitters 22, the particle optics 24, the optical control 23, and the beams 29. The rightmost beam 29e is further shown to be shifted to the left. The shifted beam is shown with a dashed line and is designated with the reference numeral 29e'. The optical control 23 is specifically designed to achieve this shift by appropriately controlling the particle optics. This shift results in a slightly altered direction of transmission through the calibration object (not shown in Fig. 4). However, this shift is particularly advantageous if wear or damage to the target material has occurred at the non-shifted source spot. The radiation generation device 21 shown with reference to Figs. 3 and 4 is merely one specific embodiment.In particular, a plurality of such radiation-generating devices can be part of the overall radiation-generating device present in a calibration arrangement. For example, the surfaces of the targets can be angled relative to each other, so that the surfaces as a whole extend over a circumferential angle around the measuring space of the calibration arrangement. As mentioned, however, the surfaces of the targets are preferably not flat but have a curved surface. Alternatively or additionally, the number of emitters in a radiation-generating device can be other than five, preferably with a plurality of emitters being present. However, it is also possible that at least some of the radiation-generating devices have only one emitter.In particular, a radiation generation device can also be built from a plurality of such parts, each with only one emitter, which has a plurality of activatable source spot areas or radiation sources.

[0054] Preferably, the particle radiation emanating from at least one of the emitters can be focused, as already described, by means of particle optics over a large area of ​​the surface of a target or several individual targets onto the desired source spot or source spot area.

[0055] Fig. 5 shows a calibration setup with a radiation generation device 31, which has a curved target 37 extending around the measuring chamber containing the calibration object 41 over a circumferential angle of more than 90 degrees. Active source spot areas, each with a single source spot 35, are shown for three operating states. In practice, however, only one of the source spot areas 35 is active at any given time. Furthermore, other source spot areas can be activated along the entire curved surface of the target 37. For all source spot areas combined, only one is active at any given time during operation of the radiation generation device 31. At least one transmission image of the calibration object 41 is acquired for each active source spot area.

[0056] The radiation receiver 44 is shown in the upper and right-hand section of Fig. 5. In this specific embodiment, it has three detector panels 45, 46, 47, each of which has a flat surface, but which are arranged around the measuring chamber containing the calibration object 41 along their surface area. Furthermore, the detector panels 45, 46, 47 are oriented such that they can detect the rays that may emanate from all possible source spot areas of the radiation generating device 31. Fig. 5 shows the rays 49a, 49b, 49c for the three source spot areas shown, or rather for their source spots 35. It should be noted that these rays generally cannot be completely detected by a single detector panel 45, 46, 47. For example, the ray 49a falls on both the detector panel 46 and the detector panel 47.However, the radiation-sensitive areas of the detector panels 45, 46, 47 are designed in such a way that they extend to their edges and can thus completely detect rays such as the illustrated ray 49a.

[0057] The previously mentioned calibration object 41 has a plurality of calibration elements 42, of which only two are designated with the reference numeral 42. A total of eight detector elements 42 are shown. These are not located in the same plane.

[0058] The top view in Fig. 5 has a viewing direction that is perpendicular to a possible cutting plane through the measuring arrangement. This cutting plane intersects, for example, the target 37 such that each of the possible source spot areas is intersected or at least touched by the cutting plane. This cutting plane also intersects the calibration object 41 and each of the detector panels 45, 46, 47, preferably along a center line.

[0059] Figure 5 shows that the radiation receiver extends around the measuring chamber containing the calibration object 41 at a circumferential angle of approximately 180 degrees. This is evident from the fact that an arrangement extending completely around the measuring chamber could be achieved with three additional detector panels. Instead of the radiation generation device 31, a different radiation generation device could be used that extends around the measuring chamber at a larger circumferential angle. For example, it could also extend around the chamber at a circumferential angle of 180 degrees. Instead of a radiation generation device with a curved target surface, target segments with flat surfaces could be used. Depending on the opening angle of the respective invasive radiation beam, the target segments with flat surfaces can be selected to be larger or smaller.For example, hexagonal or octagonal geometries are possible, taking into account the arrangement of the detector panels. Half of these geometries are formed by the radiation source and the other half by the radiation receiver, so that each activatable source spot area, as seen from the measurement room, corresponds to a radiation-sensitive area of ​​the radiation receiver. This allows, for example, transmission images with transmission directions varying over an angular range of slightly more than 180 degrees. Furthermore, with radiation source devices such as those described with reference to Figures 3 and 4, including their variations, it is possible to acquire linear transmission images, as if the calibration object were moving in a straight line.

[0060] Regarding the evaluation of the images of the calibration elements of a calibration object, such as the calibration object 41 from Fig. 5 with the calibration elements 42, reference is made to the description in EP 1 760457 B1 in the figure description under the subheading "D. Image processing evaluation of the X-ray images". Therein it is explained that the calibration elements can be formed by solid spheres of a material that attenuates the invasive radiation and generally appear in the transmission images as ellipses of low eccentricity. EP 1 760457 B1 describes a method for determining the centers of the ellipses, which is also applicable to the evaluation of the transmission images obtained according to the calibration method according to the invention.

[0061] If the positions of the calibration elements (for example, the spheres) within the calibration object are not precisely known, an initial estimate (e.g., a nominal position) can be used instead. The actual position of the calibration elements can then be optimized analogously to all other unknown parameters of the geometry of the measurement setup, i.e., determined by evaluating the acquired radiographic images.

[0062] For calibration by evaluating radiographic images, various parameters of the CT system relevant for CT reconstruction can be determined using compensation methods (e.g., the Levenberg-Marquardt algorithm or similar methods). These can include, for example, the following: - 3D positions of all calibration elements of the calibration object.

[0063] - 3D position of a source stain

[0064] - 6D Pose, i.e., 3D position and 3D orientation of the radiation receiver (if applicable, each)

[0065] 6D pose for different detector areas and / or panels of the radiation receiver)

[0066] - optionally also parametric description of a detector distortion

[0067] - optionally also time-dependent changes to individual parameters during calibration

[0068] Particularly for the source spot position, a calibration objective (e.g., of a pre-calibration) can be an assignment rule that depends on the parameters of the particle optics (e.g., electron optics) and yields the 3D source spot position as a result. This relates to the control parameter assignment mentioned above, which assigns a source spot location on the target to values ​​of control parameters of the particle optics control system for at least one of the majority of radiation sources, such that for the respective radiation source, the source spot location can be determined from the values ​​of at least one of these parameters.

[0069] The location of the source spot can be determined using control parameters. Parameters of particle optics can be, for example, the current flowing through an electromagnetic coil or electrical voltages applied to suitably positioned electrodes, thus influencing the electric field strength within the radiation generation device. Alternatively, a measured magnetic field strength, which depends on adjustable electrical voltages and currents, can also be considered a parameter of particle optics.

[0070] In general, the unknown parameters to be determined can be any parameters that may be used for subsequent processing of the radiographic images. In particular, these can be all parameters relevant for CT reconstruction, or parameters required for other algorithmic procedures, such as laminography analysis.

[0071] In one embodiment, the reconstruction of the source spot's position is simplified by first determining the shape of the 3D target surface (see Fig. 6). Fig. 6 shows a radiation generation device 51 as depicted in Fig. 2 and described with reference to Fig. 2. However, the surface of the target 17 is represented as a real 3D surface. This embodiment relates to the spatial mapping mentioned above, which maps 2D locations defined in a two-dimensional coordinate system at the target's surface to actual 3D locations defined in a three-dimensional coordinate system on the target's surface. "At" the surface means that the 2D location generally does not lie on the surface. For example, all 2D locations lie in a plane that extends along the actual surface of the target and is, for example, a plane of regression of the actual surface.

[0072] The underlying principle is that the target surface is not a plane and that its three-dimensional shape is crucial for determining the three-dimensional position of the source spot. The complex calibration required for this can be performed, for example, once during or after the production of the radiation generation device (such as the X-ray tube). At very small distances (i.e., with high spatial resolution), various positions on the target surface can be selected as the respective positions of a source spot by controlling the particle optics, and the corresponding 3D position of the source spot can be determined. From this multitude of measurements, parametric descriptions of the surface can be obtained, which assign the actual 3D position of the target surface to a 2D position in a plane along the target surface or to corresponding adjustment parameters of the particle optics.In the subsequent execution of the actual calibration procedure for calibrating the geometry of the measuring setup, the 3D source spot position can then be replaced by a 2D position on the target surface. As mentioned, the 2D position on the target depends in particular on the values ​​of the particle optics' setting parameters, especially parameters such as electric current, electric field strength, and the chosen emitter. The aim of the pre-calibration is therefore to map particle optics parameters and / or the two-dimensional position of the source spot on the target surface to the actual three-dimensional position of the source spot on the target surface.

[0073] This pre-calibration (which takes place before the evaluation of the radiographs according to the calibration method of the invention) reduces the number of parameters to be determined during the actual calibration. This means, for example, that fewer radiographs need to be taken from different radiation directions and / or that a smaller number of calibration elements of the calibration object need to be present and evaluated. This reduces the effort required for the actual calibration and / or speeds up the execution of the calibration procedure. In one embodiment, it is provided that knowledge of the arrangement of the individual radiation sources, i.e., the source spots or source spot areas, can be used to accelerate the actual calibration.This relates to the representation assignment mentioned above, which assigns relative positions to at least a subset of the plurality of radiation sources to a representative location of the radiation-generating device. This allows each relative position to be used in a coordinate system referenced to the radiation-generating device or a component thereof, enabling the determination of the location of the radiation source corresponding to that relative position from the representative location. For example, the fact that a plurality of particle optics for focusing the particle streams onto their respective assigned target areas behave in the same or at least a similar manner can be used to obtain knowledge about the positions of the individual radiation sources.Therefore, if the setting parameters, such as electric currents, electric voltages, or electric field strengths of a particle optics system, lead to a focusing of the particle beam at a specific relative position to the emitter, then it can be concluded that another, structurally identical particle optics system behaves in the same way. This can apply, for example, to a number of conventional radiation generation devices as shown in Fig. 2, or to the five parts of the system shown in Figs. 3 and 4.

[0074] Radiation generation device. Alternatively or additionally, the behavior of each of the particle optics used in the calibration setup can be determined by evaluating transmission images, which are obtained particularly when a calibration object is irradiated from different directions. Alternatively, this knowledge / assignment can be acquired during the production of the respective radiation generation devices.

[0075] During the actual calibration of the measuring setup, it is sufficient to determine the individual positions of source spots (e.g., the leftmost and rightmost source spots in Fig. 3) and use these to determine a representative position of the multi-emitter tube. The precise position of each active source spot can then be determined using the information obtained during pre-calibration. Pre-calibration therefore involves mapping the positions of the individual source spots or source spot areas to a representative position of the radiation-generating devices. This mapping is particularly advantageous when a multi-emitter radiation-generating device is movable within the calibration setup. In such cases, it is only necessary to determine the representative position and, if necessary, the actual orientation of the radiation-generating device during the actual calibration.

[0076] As mentioned previously, there may be reasons why a measurement object is movable in a direction transverse to, and especially perpendicular to, the aforementioned cutting plane through the measurement setup. In such a case, for example, a linear, rectilinear degree of freedom of movement perpendicular to the aforementioned cutting plane is provided. In other words, the measurement setup has, for example, a motor drive to generate movement according to this degree of freedom. Such movement is particularly necessary when large measurement objects cannot be fully captured by single radiographs during the actual measurement process because, for example, they are too tall. Accordingly, the measurement setup should also be calibrated with respect to this additional degree of freedom of movement, as such movements are generally not achievable exactly in a straight line along an assumed linear axis of motion.Corresponding movement errors are known, which are based, for example, on misalignments of the movement axis or a twisted movement pattern.

[0077] The calibration method according to the present invention can be extended in this case such that movements according to the additional degree of freedom are permitted and also performed to obtain radiographic images of the calibration object. The calibration object is therefore moved according to the additional degree of freedom, and radiographic images are obtained in various movement positions according to the calibration method of the invention. The evaluation of the radiographic images is then also carried out with regard to determining the parameters of the movement. For example, the calibration can be performed individually for different positions along the axis.Alternatively, all radiographs, including those for the various motion positions, can be evaluated together to determine all parameters, including the motion parameters of the additional degree of freedom. This can be achieved, for example, by jointly optimizing the adaptation of the parameters to the radiographs. A corresponding parameterized geometry model can be used, for instance, that describes all six degrees of freedom of movement or deviations from a target position and orientation of the object being measured or calibrated. These could be, for example, positional and / or angular deviations during movement along the linear axes of motion.

[0078] Fig. 7, similar to Figs. 3 and 4, shows a plurality of source spots 81a, 81b, 81c, arranged in pairs spaced apart from one another along a planar surface. At the top of Fig. 7, a calibration object 41 with a plurality of calibration elements 42 is shown. The calibration object 41 in Fig. 7 could, for example, be the calibration object 41 from Fig. 5. Furthermore, Fig. 7 shows the edges of solid angles in which the respective invasive radiation emanating from the source spots 81 propagates and penetrates the calibration object 41. Comparing the parallel cone-shaped areas shown in Figs. 3 and 4 with the edges shown in Fig. 7, it can be seen that the cone-shaped areas in Figs. 3 and 4 do not correspond to areas through which the same calibration object is penetrated.Optionally, if the source spots are fixed in position and therefore cannot be significantly altered, apertures can be provided that allow the radiation usable for illuminating the calibration object to pass through, but block radiation propagating in other directions. However, if the position of the source spots can be significantly altered, or if, for example, as shown in Fig. 5, any location along the surface of the target can be activated as a source spot, then apertures can be omitted. In this case, other measures must be taken to ensure radiation protection, such as radiation shields outside the measurement setup.

Claims

Patent claims 1. Method for calibrating a measuring arrangement (6) which uses invasive radiation from a radiation source of a radiation generating device (11; 21; 31 ;51) Transmittal images of measurement objects (1) are generated, in particular for calibrating a computed tomography (CT) measurement setup, wherein the invasive radiation penetrates a calibration object (41) and a resulting radiation is detected by a radiation receiver (45, 46, 47) of a detection device of the measurement setup (6), wherein the calibration object (41) has at least one calibration element (41), transmittal images of the at least one calibration element (42) are generated from detection signals of the detection device corresponding to the radiation detected by the radiation receiver (45, 46, 47), and geometric parameters of a geometry of the measurement setup are determined by evaluating the transmittal images, characterized in that the detection signals are generated while a position and an orientation of the calibration object (41), the radiation generating device (11; 21; 31;51) and the radiation receiver (45, 46, 47) of the detection device within a section plane of the measuring arrangement (6), which indicates a location of a specific radiation source of the radiation generating device (11; 21; 31; 51), the calibration object (41) and the radiation receiver (45, 46, 47), are kept constant, invasive radiation is generated from a plurality of radiation sources of the radiation generating device (11; 21; 31; 51) and the calibration object (41) is irradiated from the respective radiation source and at least one of the transmission images is generated for the invasive radiation emanating from each of the plurality of radiation sources and is evaluated to determine the geometric parameters.

2. The method of claim 1, wherein at least one first of the plurality of Radiation sources are activated to enable the operation of the respective radiation source. to start, in which invasive radiation emanating from it, which passes through the calibration object, is detected by means of the radiation receiver (45, 46, 47).

3. Method according to claim 1 or 2, wherein, with respect to at least one of the plurality of radiation sources, a particle optics control controls the generation of at least one particle beam such that, upon striking a target of the radiation generation device, the particle beam forms a source spot of the invasive radiation as a radiation source.

4. Method according to claim 3, wherein a control parameter assignment is determined which assigns a location of the source spot on the target to values ​​of control parameters of the particle optics control for at least one of the plurality of radiation sources, such that the location of the source spot can be determined for the respective radiation source from the values ​​of at least one control parameter, and wherein, for at least one of the plurality of radiation sources, the location of the source spot on the target determined from the actual values ​​of the control parameters of the particle optics control using the control parameter assignment is used as an input variable in the evaluation of the transmission images for determining the geometry parameters.

5. Method according to one of claims 1 to 4, wherein for at least one of the plurality of radiation sources a local assignment is determined which assigns to the 2D locations defined in a two-dimensional coordinate system on the surface of the target actual 3D locations defined in a three-dimensional coordinate system on the surface of the target, and wherein, in the evaluation of the transmission images for the determination of the geometric parameters for at least one of the plurality of radiation sources, an associated 2D location in the two-dimensional coordinate system is determined as one of the geometric parameters and, using the local assignment, the 3D location of the radiation source is determined.

6. A method according to any of the preceding claims, wherein a representation assignment is determined which assigns relative positions to at least a subset of the plurality of radiation sources to a representative location of the radiation generating device, such that it is in a manner that is based on the A coordinate system relating to a radiation generating device or to a component of the radiation generating device allows each of the relative positions to be determined from the representative location a location of the radiation source belonging to the respective relative position, and wherein, in the evaluation of the transmission images for the determination of the geometric parameters, the representative location of the radiation generating device and an orientation of the radiation generating device are determined as geometric parameters and, using the representation assignment, the locations of the radiation sources belonging to the respective relative positions are determined.

7. Method according to one of the preceding claims, wherein each plurality of radiation sources is assigned one of a plurality of detector areas of the radiation receiver (45, 46, 47), wherein the detector areas are arranged such that the invasive radiation emanating from the respective radiation source and passing through the calibration object (41) strikes the assigned detector area and is detected by it.

8. Calibration arrangement for calibrating a measuring arrangement (6) which generates transmission images of measurement objects (1) by means of invasive radiation from a radiation source, in particular for calibrating a computed tomography (CT) measuring arrangement, wherein the measurement arrangement (6) to be calibrated is part of the calibration arrangement and comprises: a radiation generating device (11; 21; 31; 51) for generating the invasive radiation, a measuring room in which a measurement object (1) can be arranged, such that during operation of the radiation generating device (11; 21; 31;51) invasive radiation penetrates the object being measured (1), wherein the object being measured (1) is a calibration object (41) in the case of calibration of the measuring arrangement, a detection device with a radiation receiver (45, 46, 47) for detecting radiation which is a result of irradiating the object being measured (1) with the invasive radiation, wherein the detection device is configured to generate at least one of a plurality of radiographic images of the object being measured (1) from detection signals of the radiation receiver (45, 46, 47); wherein the calibration arrangement further comprises: an evaluation device configured to determine geometric parameters of a geometry of the measuring arrangement (6) by evaluating the transmission images, characterized in that the radiation generating device has a plurality of radiation sources, the calibration arrangement is configured to generate invasive radiation from each of the plurality of radiation sources of the radiation generating device (11; 21; 31; 51), which emanates from the radiation source and irradiates the calibration object (41), while a position and an orientation of the calibration object (41), the radiation generating device (11; 21; 31; 51) and the radiation receiver (45, 46, 47) of the detection device within a section plane of the measuring arrangement (6), which defines a location of a specific radiation source of the radiation generating device (11; 21; 31; 51), the calibration object (41) and the radiation receiver (45, 46, 47), are kept constant, the detection device is designed to detect the invasive radiation emanating from each of the plurality of radiation sources through the radiation receiver and to generate at least one of the transmission images, and the evaluation device is designed to evaluate the generated transmission images and to determine the geometric parameters.

9. Calibration arrangement according to the preceding claim, wherein the radiation generating device (11; 21; 31; 51) has a source control configured to activate at least one of the plurality of radiation sources in order to start operation of the respective radiation source in which invasive radiation emanating from it, passing through the calibration object, is detected by means of the radiation receiver (45, 46, 47).

10. Calibration arrangement according to claim 8 or 9, wherein at least one of the plurality of radiation sources is assigned a particle optics control system configured is to generate at least a particle beam which, upon striking a target of the radiation generation device, forms a source spot of invasive radiation as a radiation source.

11. Calibration arrangement according to claim 10, wherein the evaluation device is configured using a control parameter assignment which assigns a location of the source spot on the target to values ​​of control parameters of the particle optics control for at least one of the plurality of radiation sources, such that the location of the source spot can be determined for the respective radiation source from the values ​​of at least one control parameter, and in the evaluation of the transmission images for determining the geometry parameters, the location of the source spot on the target determined from the actual values ​​of the control parameters of the particle optics control using the control parameter assignment is taken into account as an input variable for at least one of the plurality of radiation sources.

12. Calibration arrangement according to one of claims 8 to 11, wherein the evaluation device is configured to assign, for at least one of the plurality of radiation sources, a local assignment that assigns actual 3D locations on the surface of the target, defined in a three-dimensional coordinate system, to the 2D locations on the surface of the target defined in a two-dimensional coordinate system, to determine an associated 2D location in the two-dimensional coordinate system as one of the geometric parameters for at least one of the plurality of radiation sources when evaluating the transmission images to determine the geometric parameters, and to determine the 3D location of the radiation source using the local assignment.

13. Calibration arrangement according to one of the preceding claims directed to a calibration arrangement, wherein the evaluation device is configured using a representation assignment that assigns relative positions to at least a subset of the plurality of radiation sources to a representative location of the radiation generating device, such that it is configured in a manner directed to the The coordinate system relating to the radiation generating device or to a component of the radiation generating device allows each of the relative positions to be determined from the representative location a location of the radiation source belonging to the respective relative position, to determine the representative location of the radiation generating device and an orientation of the radiation generating device as geometric parameters when evaluating the transmission images to determine the geometric parameters, and to determine the locations of the radiation sources belonging to the respective relative positions using the representation assignment.

14. Calibration arrangement according to one of claims 8 to 13, wherein each plurality of radiation sources is assigned one of a plurality of detector areas of the radiation receiver (45, 46, 47), wherein the detector areas are arranged such that the invasive radiation emanating from the respective radiation source and passing through the calibration object (41) strikes the assigned detector area and is detected by it.

Images