Collimator arrangement for an X-ray tube

Abstract

A collimator arrangement (4) for an X-ray tube (1) comprises a focus-adjacent aperture arrangement (5) with a plurality of focus-adjacent apertures (7) and a focus-distant aperture arrangement (6) with a plurality of focus-distant apertures (9). The focus-adjacent apertures (7) are adjustable between a maximally open position and a maximally closed position by means of a number of first actuators (8), such that the focus-adjacent apertures (7) form a large focus-adjacent aperture in the maximally open position and a small focus-adjacent aperture in the maximally closed position. The focus-distant apertures (9) are adjustable between a maximally open position and a maximally closed position by means of a number of second actuators (10), such that the focus-distant apertures (9) form a large focus-distant aperture in the maximally open position and a small focus-distant aperture in the maximally closed position.The first drives (8) and the second drives (10) are separate drives. By means of one of the first drives (8), a filter plate (11) can be moved across the large aperture near the focus when the focus-adjacent apertures (7) are in their fully open position.

Description

[0001] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identities are included.

[0002] The present invention relates to a collimator arrangement for an X-ray tube, - wherein the collimator arrangement comprises a focus-near aperture arrangement with a plurality of focus-near apertures and a focus-far aperture arrangement with a plurality of focus-far apertures, - wherein the focus-near apertures are adjustable between a maximally open position and a maximally closed position by means of a number of first drives, such that the focus-near apertures form a large focus-near aperture opening in the maximally open position and a small focus-near aperture opening in the maximally closed position, - wherein the apertures far from the focus are adjustable between a maximally open position and a maximally closed position by means of a number of second drives, so that the apertures far from the focus form a large aperture far from the focus in the maximally open position and a small aperture far from the focus in the maximally closed position.

[0003] Such a collimator arrangement is well known. In this arrangement, the secondary drives are identical to the primary drives. The primary drives typically act directly on the apertures furthest from the focus and, via an additional kinematic mechanism, on the apertures closest to the focus.

[0004] The collimator arrangement – ​​this applies equally to the prior art and to the present invention – is positioned more or less directly downstream of the X-ray source in the beam path from the X-ray source to the X-ray detector. In particular, the collimator arrangement is positioned between the X-ray source and a subject of investigation (often a human). The collimator arrangement's apertures limit the beam path from the X-ray source to the X-ray detector in order to expose the subject of investigation to the necessary amount – and no more – of ionizing X-rays.

[0005] Depending on the specific operating mode of the X-ray setup, various filter plates (usually made of copper) can be inserted into the beam path between the aperture assemblies near and far from the focus. These filter plates serve to harden the beam. They typically have relatively thin thicknesses, for example, 0.1 mm, 0.2 mm, and 0.3 mm. Similar to the various objectives of a microscope, the filter plates are mounted on a rotatable element, allowing one or neither of the filter plates to be inserted into the beam path as needed.

[0006] The publication DE 10 2016 204 870 A1 describes a collimation device for a beam of X-rays from an X-ray device intended for scanning an object under investigation, and an X-ray device with such a collimation device, wherein the collimation device has two slotted collimation devices arranged one behind the other in the direction of the beam and adjustable relative to each other, each with a fixed aperture for maximum collimation and a radiopaque area of ​​corresponding dimensions.

[0007] Utility model DE 20 2023 103 001 U1 discloses an X-ray collimator for the automated collimation of an X-ray field generated by an X-ray source, comprising a first collimation unit for symmetrical collimation of the radiation field relative to the central beam and a second collimation unit for asymmetrical further restriction of the previously symmetrically collimated radiation field.

[0008] The publication DE 42 42 835 A1 relates to a beam diaphragm with a modular filter and diaphragm arrangement and an adjustable housing cap, which encloses a frame laterally and at the front and over which actuable switching means are arranged to limit the adjustability of components of the X-ray diagnostic device.

[0009] It is necessary to calibrate the X-ray detector from time to time. For example, it may be necessary to calibrate the X-ray detector once a year. To calibrate the X-ray detector, a thicker filter plate is inserted into the beam path in the collimator assembly. This filter plate can be, for example, 0.6 mm or 2.1 mm thick.

[0010] Theoretically, it is conceivable to also arrange this filter plate on the rotating element. However, this would necessitate a very large volume for the rotating element and thus for the entire collimator assembly. This approach is therefore not used in practice. Instead, the prior art collimator assembly has mounting rails on the side of the aperture assembly furthest from the focus, into which this thicker filter plate can be manually inserted. Due to the widening of the radiation cross-section on the path from the X-ray source to the aperture assembly furthest from the focus, the thicker filter plate is relatively large and heavy.

[0011] The calibration of the X-ray detector is performed by a service technician according to current best practices. The service technician travels to the relevant X-ray system, inserts the thicker filter plate into the mounting rails, and then starts the calibration sequence.

[0012] The object of the present invention is to create possibilities by means of which a permanent arrangement of the thicker filter sheet in the collimator arrangement is made possible, whereby it should be possible to easily move the thicker filter sheet into and out of the beam path as required.

[0013] The problem is solved by a collimator arrangement having the features of claim 1. Advantageous embodiments of the collimator arrangement are the subject of dependent claims 2 to 9.

[0014] According to the invention, a collimator arrangement of the type mentioned above is designed by: - that the first drives and the second drives are different drives from each other and - that by means of one of the first drives, a filter plate can be moved across the large aperture near the focus in the maximum open position of the focus-adjacent apertures.

[0015] While using separate drives for adjusting the near-focus and far-focus apertures requires more drives than in the prior art, it allows for the use of smaller and less powerful drives. Most importantly, it eliminates the need for kinematic mechanisms required in the prior art to operate the same drives on both the near-focus and far-focus apertures. Coordinated adjustment of both the near-focus and far-focus apertures can be easily achieved by using position control for both the first and second drives. Furthermore, by using one of the first drives not only to adjust the near-focus apertures but also to move the filter plate, a separate drive for moving the filter plate is unnecessary.

[0016] The currently preferred method for adjusting the apertures near the focus point is: - that the focus-near apertures are arranged on a first side of a base plate that extends parallel to a plane defined by the large focus-near aperture opening, - that the first drive moves an intermediate element which is also located on the first side of the base plate, - that a cam guide is arranged on the intermediate element, into which a first drive pin arranged on one of the apertures near the focus engages, or conversely, that a first drive pin is arranged on the intermediate element, which engages in a cam guide arranged on one of the apertures near the focus, - that the scenery has a first section running parallel to the base plate and a second section adjoining the first section and running at an obtuse angle to the first section and - that this focus-adjusted aperture is always in the maximum open position when the first drive pin is in the first section of the cam track, and is always in the maximum closed position when the first drive pin is within the second section of the cam track and as far away as possible from the first section of the cam track.

[0017] This design allows for easy adjustment of the corresponding focus-adjusted aperture between its fully open and fully closed positions. This adjustment occurs while the first drive pin traverses the second section of the cam track.

[0018] In the simplest case, the single first drive adjusts only one of the apertures closest to the focus. However, it is also possible for the at least one first drive to adjust several of the apertures closest to the focus. For example, if—as is common practice—there are four apertures close to the focus that define a rectangular aperture opening close to the focus, then two first drives may be present, with each of the two first drives adjusting two opposite apertures simultaneously.

[0019] In the simplest case, there is only a single filter plate, which can be moved across the large aperture near the focus using a single first drive. If multiple first drives are present, each can move its own filter plate across the large aperture near the focus using its respective first drive. With two first drives, one or two filter plates (individually or together) can be moved across the large aperture near the focus as needed. With four first drives, up to four filter plates can be moved across the large aperture near the focus.

[0020] Preferably, the intermediate element is designed as a ring which can be rotated about an axis perpendicular to the base plate by means of a first drive. In this case, the axis contains the center of the large, near-focus aperture (and also the small, near-focus aperture). Particularly when the intermediate element is designed as a ring, it is also particularly easy to adjust two opposing apertures simultaneously using one and the same intermediate element.

[0021] Preferably, the first drive pin is positively guided by means of the cam guide. This eliminates the need for return springs or similar devices that exert a restoring force on the apertures near the focus. Consequently, it is also unnecessary to overcome such a restoring force using the single first drive. Therefore, the single first drive can be dimensioned relatively small.

[0022] Preferably, the intermediate element further comprises a second drive pin that protrudes through a recess in the base plate. However, the second drive pin does not act on another aperture near the focus or on an aperture farther from the focus, but rather on the filter plate. The action on the filter plate is such that the filter plate is always out of the large aperture near the focus when the first drive pin is located in the second section of the cam track, and always across the large aperture near the focus when the first drive pin is located within the first section of the cam track at a predetermined position spaced apart from the second section of the cam track. Thus, the movement of the filter plate across or out of the large aperture near the focus occurs while the first drive pin is traversing the first section of the cam track.The predetermined location can, in particular, be the end of the first section of the scenery that is furthest away from the second section of the scenery.

[0023] Preferably, the filter plate has a curved or bent section so that the second drive pin can be moved under the filter plate while the first drive pin moves towards the second section of the cam guide in the first section. This makes it easier to synchronize the movement of the corresponding focus-near aperture and the movement of the filter plate.

[0024] Preferably, the collimator arrangement includes a return spring by means of which a restoring force is exerted on the filter plate when moving across the large aperture near the focus. This ensures, in particular, that no forced guidance of the filter plate by the second drive pin is required. The phrase "when moving across the large aperture near the focus" in conjunction with the phrase "a restoring force is exerted" is intended to clarify the direction in which the restoring force acts. Thus, when moving across the large aperture near the focus, the restoring force is directed against the movement of the filter plate; when moving out of the large aperture near the focus, it is directed with the movement of the filter plate.

[0025] Preferably, the collimator arrangement has a stop against which the filter plate is pressed by the return spring whenever it is not deflected too far in the direction of the large, focus-adjacent aperture by the second drive pin. This ensures that a defined rest position of the filter plate is reached once it has moved out of the large, focus-adjacent aperture.

[0026] Preferably, the movement of the filter plate is a pivoting movement about an axis that runs orthogonally to a plane defined by the large aperture near the focus. A pivoting movement about such an axis is more reliably achievable than a linear movement in a plane parallel to a plane defined by the large aperture near the focus. In particular, tilting of the filter plate is not possible.

[0027] The properties, features, and advantages of this invention described above, as well as the manner in which they are achieved, will become clearer and more readily understandable in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawings. These drawings show, in schematic representation: Fig. 1 an X-ray setup, Fig. 2 a focus-proximal aperture arrangement in a maximally open position, Fig. 3 the focus-near aperture arrangement of Fig. 2 in a maximally closed position, Fig. 4 a perspective view of a collimator arrangement from a slightly oblique angle above, Fig. 5 a perspective view of the collimator arrangement of Fig. 4 from the bottom diagonal, Fig. 6 an inner wall of an intermediate element in rolled-up representation and Fig. 7 a side view of a filter plate.

[0028] According to Fig. Apparatus 1 comprises an X-ray arrangement with an X-ray source 1. During operation, the X-ray source 1 emits X-rays, which are detected by an X-ray detector 2. The X-rays pass through a test object 3 (for example, a person). A collimator arrangement 4 is positioned between the X-ray source 1 and the test object 3. The collimator arrangement 4 has a focus aperture 5 and a focus aperture 6. The focus aperture 5 is positioned closer to the X-ray source 1 than the focus aperture 6.

[0029] The focus-near aperture arrangement 5 has several focus-near apertures 7, for example according to the illustration in the Fig. 2 and Fig. 3 four near-focus apertures 7. The near-focus apertures 7 are according to Fig. 1 by means of first drives 8 between a maximally open position ( Fig. 2) and a maximally closed position ( Fig. 3) Adjustable. In the fully open position, the focus-adjusted apertures 7 form a large focus-adjusted aperture opening ( Fig. 2) and in the fully closed position a small, focus-close aperture opening ( Fig. 3) Often, the adjustment of opposing, focus-close apertures 7 is effected in pairs by a single first drive 8. The focus-close aperture arrangement 5 is in Fig. 1 is shown in the fully closed position.

[0030] The aperture arrangement 6, located far from the focus, is generally constructed in a completely analogous manner to the aperture arrangement 5 located near the focus. It features several apertures 9 located far from the focus. The apertures 9 located far from the focus are configured according to Fig. 1 is adjusted by means of second drives 10. The second drives 10 are different from the first drives 8. The aperture arrangement 6, located away from the focus, is in Fig. 1 is shown in the fully open position.

[0031] According to Fig. A filter plate 11 is also present. The filter plate 11 is usually made of copper. It typically has a thickness of 0.6 mm or 2.1 mm. The filter plate 11 is movable across the large aperture near the focus. The phrase "movable across the large aperture near the focus" means that, in this case, the filter plate 11 completely covers the large aperture near the focus. Thus, only X-rays that have previously passed through the filter plate 11 reach the X-ray detector 2 from the X-ray source 1. This applies regardless of whether the filter plate 11 is located closer to the X-ray source 1 than the aperture assembly 5 near the focus or further away from the X-ray source 1 than the aperture assembly 5 near the focus (the latter being the case in Fig. 1 shown and is also preferred).

[0032] The filter plate 11 is moved by means of one of the first drives 8. The focus-near aperture 7, adjusted by this first drive 8, is in the maximum open position of the focus-near apertures 7 when the filter plate 11 is moved.

[0033] The Fig. 4 and Fig. Figure 5 shows a possible concrete design of the collimator arrangement 4. According to the Fig. 4 and Fig. In section 5, the collimator arrangement 4 has a base plate 12. The base plate 12 extends parallel to a plane defined by the large focus-adjacent aperture. The focus-adjacent apertures 7 are arranged on a first side of the base plate 12. Fig. 4 and Fig. Figure 5 shows only two of the focus-adjacent apertures 7, which are opposite each other. The side of the base plate 12 on which the focus-adjacent apertures 7 are arranged is referred to below, according to the usual arrangement (X-ray source 1 above - X-ray detector 2 below), as the top of the base plate 12.

[0034] The first drive 8, by means of which the filter plate 11 is also moved, is arranged on the base plate 12. The other first drives 8 are also generally arranged on the base plate 12. However, they are of subordinate importance for the further embodiments of the present invention and are therefore omitted in the Fig. 4 and Fig. 5 not shown. The following explanations always refer to the first drive 8, by means of which the filter plate 11 is also moved.

[0035] The first drive 8 proceeds according to Fig. 4 an intermediate element 13, which is also arranged on the top side of the base plate 12. For example, the first drive 8 can act on a toothed section 15 of the intermediate element 13 via a pinion 14. Currently, according to the illustration in the Fig. 4 and Fig. 5 preferably that the intermediate element 13 is designed as a ring. In this case, the ring is rotatable about an axis 16 by means of the first drive 8, which runs orthogonally to the base plate 12. The axis 16 contains according to Fig. 2 the center of the large, near-focus aperture and usually corresponding to the representation in Fig. 3 also the center of the small, near-focus aperture.

[0036] According to Fig. 4 A cam guide 17 is arranged on the intermediate element 13. A drive pin 18 engages in the cam guide 17 and is located on one of the apertures 7 near the focus. The drive pin 18 is referred to below as the first drive pin 18 to distinguish it linguistically from a second drive pin introduced later.

[0037] The inner wall of the intermediate element 13, including the track guide 17, is in Fig. 6 shown in an unrolled representation. According to Fig. 6 - also in terms of approach Fig. As can be seen in Figure 4, the track system 17 has a first section 19 and a second section 20. The first section 19 runs parallel to the base plate 12. The second section 20 adjoins the first section 19, but forms an obtuse angle α with the first section 19. The angle α is usually in the range between 150° and 170°.

[0038] If the intermediate element 13 is moved (in this case, rotated) by means of the first drive 8 while the first drive pin 18 is located in the second section 20, the height of the first drive pin 18 relative to the base plate 12 changes. As a result, the corresponding focus-near aperture 7 moves further towards its fully closed position the further the first drive pin 18 is raised relative to the base plate 12. Specifically, the corresponding focus-near aperture 7 is in its fully closed position when the first drive pin 18 is located within the second section 20 and as far away as possible from the first section 19. Conversely, if the first drive pin 18 is moved closer to the base plate 12, the corresponding focus-near aperture 7 moves further towards its fully open position the further the first drive pin 18 is moved towards the base plate 12.When the first drive pin 18 reaches the first section 19, the corresponding focus-near aperture 7 is in its fully open position. For moving the focus-near aperture 7, it can, for example, be pivoted about a pivot axis 21.

[0039] If the intermediate element 13 is moved (in this case rotated) by means of the first drive 8 while the first drive pin 18 is located in the first section 19, the height of the first drive pin 18 relative to the base plate 12 does not change due to the first section 19's parallel orientation to the base plate 12. Consequently, the corresponding focus-adjusted aperture 7 remains in its fully open position. This applies regardless of the current position of the first drive pin 18 within the first section 19.

[0040] The arrangement of the cam guide 17 and the first drive pin 18 can also be inverted. It is therefore a reversal of the arrangement shown in the Fig. 4 and Fig. In the embodiment shown in Figure 5, it is also possible that the first drive pin 18 is arranged on the intermediate element 13 and that the drive pin 18 engages in a cam guide 17 arranged on the corresponding focus-adjacent aperture 7. The operating principle remains unchanged.

[0041] According to Fig. 6. At every point along the cam track 17 where the first drive pin 18 is located at that moment, the movement of the first drive pin 18 is limited by the cam track 17 both upwards (away from the base plate 12) and downwards (towards the base plate 12). The first drive pin 18 is thus positively guided by the cam track 17. Alternatively, it would be possible to guide the first drive pin 18 only on one side by means of an edge of the cam track 17 and to apply a spring force to the corresponding focus-adjacent aperture 7 in the direction of this edge. However, this design is not preferred.

[0042] As already mentioned, the intermediate element 13 has, in addition to the first drive pin 18, a further drive pin 22, hereinafter referred to as the second drive pin 22. The second drive pin 22 projects according to Fig. 5 through a recess 23 in the base plate 12 through the base plate 12. The second drive pin 22 acts on the filter plate 11, which according to Fig. 5 is arranged on the underside of the base plate 12. Specifically, in the illustration of Fig. 5. The filter plate 11 can be pivoted about an axis 24 by the second drive pin 22. The movement of the filter plate 11 is therefore a pivoting movement about the axis 24. The axis 24 runs orthogonally to a plane defined by the large aperture near the focus. In the case of the given arrangement of the filter plate 11 on the base plate 12, the axis 24 also runs orthogonally to the base plate 12.

[0043] Fig. Figure 5 shows a position (rotational position) in which the second drive pin 22 just begins to act on the filter plate 11, provided that the intermediate element 13 is in the representation of Fig. 5 is rotated clockwise, or just ceases to act on the filter plate 11 if the intermediate element 13 is rotated counterclockwise. The filter plate 11 is located in Fig. 5 is therefore in a resting position in which it has not moved – not even partially – across the large, near-focus aperture. However, the further the intermediate element 13 moves, starting from the in Fig. The position shown in point 5, the further clockwise the filter plate 11 is turned from the one in Fig. The position shown in section 5 is pivoted around axis 24. This happens at the latest when the second drive pin 22 engages the axis shown in section 5. Fig. Once the lower end of the recess 23 is reached, the filter plate 11 has moved across the (add: entire) large focus-adjacent aperture opening.

[0044] During the entire movement of the filter plate 11 (and the corresponding positions or rotations of the intermediate element 13), the first drive pin 18 is located in the first section 19 of the cam track 17. Conversely, it follows that the filter plate 11 has always (completely) moved out of the large, focus-near aperture when the first drive pin 18 is located in the second section 20 of the cam track 17. Furthermore, for the same reason, the filter plate 11 has (completely) moved beyond the large, focus-near aperture when the first drive pin 18 is located within the first section 19 at a predetermined position that is spaced apart from the second section 20. Typically, this predetermined position will be the end of the first section 19 that is spaced apart from the second section 20. However, the latter is of secondary importance.

[0045] According to the representation in Fig. 5 preferably includes a return spring 25. By means of the return spring 25, a restoring force is exerted on the filter plate 11 when moving through the large aperture near the focus. The in Fig. The return spring 25 shown in Figure 5 is therefore a tension spring. However, with a different arrangement of the return spring 25, a design as a compression spring or a coil spring is also possible. The return spring 25 presses the filter plate 11 against a stop 26, unless it is deflected towards the large, near-focus aperture by the second drive pin 22.

[0046] The filter plate 11 has according to Fig. Figure 7 shows an initial section 27, an end section 28, and an intermediate section 29 between the initial section 27 and the end section 28. The end section 28 is the section of the filter plate 11 that is moved across the large aperture near the focus. The initial section 27 is the section of the filter plate 11 in which the axis 24 is located. The intermediate section 29 is curved or—as in Fig. Figure 7 is shown – bent. Due to the intermediate section 29, the end section 28 is spaced away from the base plate 12. This allows the second drive pin 22 to move under the filter plate 11, while the first drive pin 18 moves in the first section 19 of the cam guide 17 towards the second section 20 of the cam guide 17. This design facilitates the necessary decoupling of the travel curve of the focus-adjacent apertures 7 on the one hand and the travel curve of the filter plate 11 on the other.

[0047] The present invention has many advantages. In particular, it provides a simple way to integrate the filter plate 11 into the collimator arrangement 4 and to automatically move the filter plate 11 into the beam path from the X-ray source 1 to the X-ray detector 2. The collimator arrangement 4 according to the invention can be built compactly. Due to the automated movement of the filter plate 11, even the calibration process itself can be automated.

Claims

[1] Collimator arrangement for an X-ray tube (1), - wherein the collimator arrangement comprises a focus-near aperture arrangement (5) with a plurality of focus-near apertures (7) and a focus-far aperture arrangement (6) with a plurality of focus-far apertures (9), - wherein the focus-near apertures (7) are adjustable between a maximally open position and a maximally closed position by means of a number of first drives (8), such that the focus-near apertures (7) form a large focus-near aperture opening in the maximally open position and a small focus-near aperture opening in the maximally closed position, - wherein the focus-distant apertures (9) are adjustable between a maximally open position and a maximally closed position by means of a number of second drives (10), such that the focus-distant apertures (9) form a large focus-distant aperture opening in the maximally open position and a small focus-distant aperture opening in the maximally closed position, characterized by , - that the first drives (8) and the second drives (10) are different drives from each other and - that by means of one of the first drives (8) in the maximum open position of the focus-near apertures (7) a filter plate (11) can be moved over the large focus-near aperture opening. [2] Collimator arrangement according to claim 1, characterized by , - that the focus-near apertures (7) are arranged on a first side of a base plate (12) which extends parallel to a plane defined by the large focus-near aperture opening, - that the first drive (8) moves an intermediate element (13) which is also arranged on the first side of the base plate (12), - that a cam guide (17) is arranged on the intermediate element (13), into which a first drive pin (18) arranged on one of the focus-adjacent apertures (7) engages, or conversely, that a first drive pin (18) is arranged on the intermediate element (13), which engages in a cam guide (17) arranged on one of the focus-adjacent apertures (7), - that the cam track (17) has a first section (19) running parallel to the base plate (12) and a second section (20) adjoining the first section (19) and running at an obtuse angle (α) to the first section (19) and - that this focus-near aperture (7) is always in the maximum open position when the first drive pin (18) is in the first section (19) of the cam guide (17), and is always in the maximum closed position when the first drive pin (18) is within the second section (20) of the cam guide (17) and is as far away as possible from the first section (19) of the cam guide (17). [3] Collimator arrangement according to claim 2, characterized by , that the intermediate element (13) is designed as a ring which can be rotated by means of a first drive (8) about an axis (16) running orthogonally to the base plate (12), and that the axis (16) contains the center of the large focus-near aperture opening. [4] Collimator arrangement according to claim 2 or 3, characterized by , that the first drive pin (18) is guided by means of the cam guide (17). [5] Collimator arrangement according to claim 2, 3 or 4, characterized by , that the intermediate element (13) has a second drive pin (22) which protrudes through a recess (23) in the base plate (12) and acts on the filter plate (11) in such a way that the filter plate (11) is always moved out of the large focus-near aperture when the first drive pin (18) is located in the second section (20) of the cam guide (17), and is always moved across the large focus-near aperture when the first drive pin (18) is located within the first section (19) of the cam guide (17) at a predetermined position spaced apart from the second section (20) of the cam guide (17). [6] Collimator arrangement according to claim 5, characterized by, that the filter plate (11) has a bent or kinked section (29) so that the second drive pin (22) can be moved under the filter plate (11) while the first drive pin (18) moves in the first section (19) of the cam guide (17) towards the second section (20) of the cam guide (17). [7] Collimator arrangement according to one of the above claims, characterized by , that the collimator arrangement has a return spring (25) by means of which a restoring force is exerted on the filter plate (11) when moving through the large focus-near aperture. [8] Collimator arrangement according to claim 7, characterized by , that the collimator arrangement has a stop (26) against which the filter plate (11) is pressed by the return spring (25) whenever it is not deflected towards the large focus-near aperture by the second drive pin (22). [9] Collimator arrangement according to any one of the above claims, characterized by , that the movement of the filter plate (11) is a pivoting movement about an axis (24) which is orthogonal to a plane defined by the large focus-near aperture.

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