WO2019219909A1 - X-ray tube having collimator, collimator apparatus for closed x-ray tube and use of such a collimator apparatus - Google Patents

Abstract

The invention relates to an X-ray tube (1) having a housing (2), a target (3) and an outlet window (4) for X-ray radiation (5) generated on the target (3), wherein: the outlet window (4) is fixed in an opening (14) in the housing (2) in an air-tight manner; the outlet window (4) is opposite the target (3) and is arranged inside the housing (2); a collimator disk (19) made of a highly X-ray-radiation-absorbent material and having a collimator opening (20) is arranged on the X-ray tube (1); and the collimator disk (19) is opposite the outlet window (4) on the side thereof facing away from the target and is located below the surface of the housing (2). The invention additionally relates to a collimator apparatus (18) for an X-ray tube (1), having a base frame (25), on which a fastening apparatus (24) for fastening the collimator apparatus (18) to a tube flange (9) of an X-ray tube (1) is arranged, and having a support wall (23), which is connected to the base frame (25) and is arranged on the same side of the base frame (25) as the fastening apparatus (24), and having a collimator disk (19) which is made of a highly X-ray-radiation-absorbent material, has a collimator opening (20) and is arranged on the end of the support wall (23) remote from the base frame (25). Finally, the problem is also solved by the use of a collimator apparatus (1) according to the invention on an X-ray tube (1), particularly on an X-ray tube (1) according to the invention, in order to reduce the penumbra on a detector (6) during imaging of an object (8) by means of the X-ray radiation (5) emitted by the X-ray tube (1).

Description

 X-ray tube with collimator, collimator device for closed X-ray tube and use of such a collimator device

The invention relates to an X-ray tube having a housing, a target, an exit window for X-ray radiation generated on the target, as well as to a collimator device for an X-ray tube and, moreover, to a use of such a collimator device for reducing the X-ray tube

Partial shadow when imaging an object. The invention generally relates to closed X-ray tubes, but it is particularly advantageous in bipolar X-ray tubes having an exit window for cone beams. These are X-ray tubes in which the target and the exit window lie at different potentials and whose exit windows allow the irradiation of a larger area. Although the X-ray tubes according to the invention also include those for medical applications, the invention can be replaced particularly advantageously in industrial X-ray tubes, for example in the context of nondestructive testing (NDT), which has a higher acceleration voltage for the electrons, in particular in one Range of at least 320 kV. The invention is particularly advantageous for use in X-ray tubes with a small focal spot, such as in mini-focus X-ray tubes - with a focus size in the range of 250 mpp to 1 mm. Closed X-ray tubes generally have an exit window made of beryllium. Beryllium is used because of its low atomic number and density in order to absorb as little of the generated radiation as possible. The size of the beryllium ester is matched to the nominal emission angle of the x-ray tube. Its thickness provides stability to ensure a firm separation between normal pressure outside and vacuum in the X-ray tube. The higher the kV class of the x-ray tube, the farther away, larger and thicker is the beryllium window used. To some extent, X-rays are absorbed and scattered by an element. If the energy of the photons is high, it is only scattered. For beryllium, this limit is about 50 keV. Already from an energy of about 15 keV, the proportion of scattering predominates. X-ray tubes were developed for the exposure of film. The objects are placed near the film without significant magnification. With the use of modern digital flat-panel detectors with a discrete pixel grid, magnification is usually used to bring the object closer to the source.

It turns out that the scattered radiation of the beryllium window creates a diffuse upstream luminous point (luminous surface) - this can also be called an apparent focal spot - whose spectrum in the cone used is only slightly lower than that of the primary focal spot of the X-ray tube. This radiation is able to penetrate the object as well as partially to back-beam it, so that a partial shade is created. In the projection this becomes visible in the form of the partial shadow, the extent of which depends on the magnification used. The additional radiation through the object, which comes from other angles than from the primary focal spot, also falsifies the counters of the detector behind the object.

The most common way to improve image quality is to attach collimators in the form of steel, tungsten, or lead plates to a tube flange located on the outer surface of the tube housing from two or four sides. These collimators can be stationary, changeable or motorized. However, this will only slightly diminish the above-described effect of creating a disturbing half-shadow, as much of the beryllium-scattered radiation can pass through the opening.

The object of the invention is to provide a simple possibility which reduces the size of the partial shadow when imaging an object by means of X-ray radiation originating from an X-ray tube.

The object is achieved by an X-ray tube having the features of patent claim 1. Due to the fact that the collimator disc tion below the surface of the tube housing closer to the exit window - and thus the beryllium disk - is than in the known devices in which the collimators on the tube flange - ie outside the tube housing - are arranged, it is possible to a large part of the beryllium window to cover (if detector size and detector distance are given). This means that so that the effective size of the diffused focal spot is significantly smaller than in the known from the prior art collimators, which are arranged on the tube flange, the case. Thus, the formation of penumbra is greatly reduced. The farther the detector is removed, or the smaller it is, the smaller the collimator aperture may be in beryllium writing, and the penumbra is reduced to a minimum, so that it is almost non-existent; Likewise, dark spots behind the object are not lightened by scattered radiation. As is conventional, a highly X-ray absorbing material is used for the collimator disc which is moreover preferably electrically conductive; for example tungsten, iron or lead. A disc in the sense of the invention is understood to mean a form in which the main extension is in one plane and has only a small thickness in the direction perpendicular thereto - in accordance with normal usage. The Kollimatorscheibe is preferably exchangeable with little effort connected to the housing. It is preferably a bipolar X-ray tube with an acceleration voltage of at least 320 kV, particularly preferably a 320 kV X-ray tube or a 450 kV X-ray tube or a 600 kV X-ray tube. The case of the

X-ray tube - that is, the vacuum-limiting body, the boundary between the interior of the X-ray tube, must prevail in the vacuum, and the atmospheric pressure outside space is preferably cylindrical and made of metal. The ends of the cylinder are sealed by the mostly ceramic high-voltage bushings. Preferably, the exit window is located in a recess of the housing. There is no hermetically sealed seal between the collimator disk and the exit window, but there is atmospheric pressure between them. The invention is not applicable to glass tubes, since in glass tubes no electrically conductive parts in direct contact or in may come close to a few millimeters with the glass vacuum body, as is the case according to the invention, when the collimator is arranged below the surface of the tubular housing. On the contrary, in the case of glass tubes, significantly thicker or more voluminous radiation absorbers made of nonconductive material are used, which absorb less radiation per material thickness than the tungsten or lead in the form of a thin disk used here.

An advantageous development of the invention provides that the collimator and the exit window are arranged parallel to each other and / or the distance between the collimator and exit window between 0 mm and 20 mm, preferably between 0.5 mm and 10 mm and more preferably between 1 mm and 5 mm. If the collimator disk and the exit window are aligned parallel to each other, the collimator disk may be closer to the exit window on average. The closer the collimator disc is to the focal spot, the smaller can be the collimator aperture, given the detector size and detector distance, which reduces the effective size of the diffuse focal spot and reduces the partial shadowing. The closer the collimator disk is to the exit window, the greater this effect. Preferably, however, the collimator disk should not rest against the exit window, since otherwise, when the collimator is jarred, a mechanical destruction of the exit window can occur, which in the case of closed x-ray tubes has the consequence that it must be replaced. A further advantageous embodiment of the invention provides that the Kollima- torscheibe is connected via a kcgclstumpfförmige support wall with a Befestigungsvorrich device on the target-facing side, which is connected to a tube flange which surrounds the opening of the housing on the outside thereof. As a result, the collimator disk can be brought close to the outlet window, which is located below the surface of the housing, by simple means, and can also be held securely there, without parts of the fastening / holder lying in the beam path. A further advantageous embodiment of the invention provides that the Kollima- torscheibe is round. The diameter is adapted to the diameter of the exit window of the respective tube and the thickness is determined by the energy of the X-ray tube and, depending on the material and kV class, should be so strong that more than 99% of the X-ray radiation is absorbed. A round design of the collimator disc has the advantage that it can be mounted without modification in the recess opposite the surface of the tube housing in which the exit window is located near the exit window of a common X-ray tube. Preferably, the collimator has a diameter of 63mm in a 450 kV and 600 kV X-ray tube from Comet AG.

A further advantageous development of the invention provides that the collimator disc consists of tungsten or a layer of lead and a layer of copper, wherein the thickness ratio of the layer of lead to that of copper is preferably 7: 3.

A further advantageous development of the invention provides that the collimator opening is arranged centrally in the collimator disk, in particular in the case of a round collimator disk, it is designed to be symmetrical with respect to two diametrically perpendicular diameters. As a result, in the case of a straight mounting position of the X-ray tube, the main beam direction of the usable X-ray radiation is located centrally in the collimator aperture, and the X-radiation optimally strikes the detector. Another advantageous development of the invention provides that the collimator opening is arranged displaced relative to the center of the collimator disk, in particular in the case of a round collimator disk symmetrical to a diameter and a secant, which is not diametrically perpendicular, and which is not a diameter. Such offset to the side training the collimator in the collimator has the advantage that the largest possible angle range for the usable X-ray radiation is given and the main beam direction of the usable X-ray radiation in a mounting position of the X-ray tube to twisted a few degrees, located centrally in the collimator and optimally hits the detector.

A further advantageous development of the invention provides that the collimator opening has a smaller area at its target-near end than at its intended end. Since the X-ray radiation from the small focal spot obliquely strikes the surface of the collimator disk, boundary surfaces which form the collimator opening are advantageous, which run along the oblique X-ray radiation so as not to generate any additional stray radiation at the remote target ends otherwise reaching into the marginal beams. This further reduces the formation of partial shade.

A further advantageous development of the invention provides that a pre-filter for beam hardening is arranged on the target-near or the target-distant surface of the collimator disk. The prefilter can be attached directly to the collimator disc or inserted into a dedicated device. As a result, no additional part is needed at a location other than that at which the collimator is arranged, and also the scattering surface of the prefilter is reduced to a minimum.

An alternative provides that the target is surrounded by a shell, in which at the point in the direction of the X-ray radiation reaches the exit window, an inner window made of beryllium is inserted and thereby a predominantly closed cavity is present around the target. The electrons pass from the filament through an opening in the envelope to the target.

The object is also achieved by a collimator device having the features of patent claim 11. By means of such a collimator, the collimator disc with the collimator opening in a simple manner in the position described above, the exit window opposite to be placed at a small distance. By replacing the entire collimator can on the geometric conditions in each case (distance and size of the detector and installation position of the x-ray tube) by means of a collimator disc matched thereto with collimator opening matching thereto. This is achieved, in particular, by virtue of the fact that the supporting wall together with the collimator disc fastened to it can be easily detached from the base frame and thus a simple replacement of the collimator disc is possible.

An advantageous development of the collimator device according to the invention provides that the support wall is frusto-conical. This shape of the supporting wall corresponds to the shape of the opening in the tube housing in which the outlet window is arranged and leads to the fact that the window carrier is not visible in the image.

A further advantageous development of the collimator device according to the invention provides that the support wall is releasably connected to the base frame, in particular via a support plate fixedly connected to it. As a result, it is not necessary to replace the entire collimator device when changing the collimator disc with matching collimator opening, which is tailored to the geometrical conditions, but only the carrier plate together with the supporting wall with a collimator disc mounted thereon. This leads to a reduction of the costs and the required resources.

A further advantageous development of the collimator device according to the invention provides that the fastening device has two adapters arranged on opposite ends of the base frame, which are formed in a circular arc at their ends facing away from the base frame and the radius of the circular arc is that of the housing of the x-ray tube in FIG Area of the opening corresponds. As a result, the collimator device can be very easily and securely attached to the housing of the x-ray tube, which is cylindrical in the region of the opening for the exit window.

A further advantageous development of the device according to the invention Kollimatorvorrich provides that the collimator is designed as they above to the Developments of the X-ray tube according to the invention is described. There are then the advantages listed there in detail.

The object is also achieved by the use according to claim 14. In this case, a collimator device according to the invention is used on an X-ray tube for reducing the partial shade when imaging an object on a detector by means of the X-ray radiation emitted by the X-ray tube. This results in the advantages given above in connection with the x-ray tube and the collimator device together with the respective developments. This applies in particular to the use of the collimator device on an x-ray tube according to the invention.

Further advantages and details of the invention will be explained with reference to the exemplary embodiments illustrated in the figures. The figures show:

1a is a schematic sectional view of a structure of an X-ray tube with a known collimator and a detector and an object to be imaged, FIG. 1b is a schematic sectional view as in FIG. 1b with an alternative target,

FIG. 2 a shows a schematic sectional view like that of FIG. 1 a but with a collimator device according to the invention,

FIG. 2b shows a schematic sectional view as in FIG. 2a with the alternative target of FIG. 1b,

FIG. 3 a shows a detailed enlargement of the area of the target and the exit window of the x-ray tube from FIG. 2 a, FIG. 3b shows a detailed enlargement of the area of the target and the exit window of the x-ray tube from FIG. 2b,

4 shows an oblique view of a collimator device according to the invention from the tube side with parts of the x-ray tube, FIG.

FIG. 5 shows a longitudinal section through FIG. 4,

FIG. 6 is a plan view of the collimator device of FIG. 4;

7a shows horizontal sections and views of two collimator discs according to the invention for a collimator device according to FIG. 3a, FIG.

FIG. 7b alternative to the collimator disks shown in FIG. 7a,

Figure 8a is a sectional view as in Figure 3a but with tilted built-in

 X-ray tube and other collimator disc,

Figure 8b is a sectional view as in Figure 3b but with tilted built-in

 X-ray tube and other collimator disc,

Figure 9a horizontal section and view of a collimator disc according to the invention for a collimator according to Figure 8a; FIG. 9b alternative to the collimator disk shown in FIG. 9a and FIG

FIG. 10 Tomograms and line profiles of an object taken with a

 Collimator according to the prior art and with a collimator device according to the invention.

FIG. 1 a shows a schematic structure of an X-ray tube 1 according to the prior art. It is a closed mini-focus X-ray tube with a focal spot diameter in the range of 0.4 mm. In a housing 2 there is a target 3, which is bombarded with an electron beam 15 (see FIG. 3a) and emits X-radiation 5 at the location where it meets the target 3 -the focal spot 7. This exits through an exit window 4 of beryllium from the housing 2. The exit window is mounted in an opening 14 of the housing so as to come as close as possible to the focal spot 7. It is connected via a window support 13 and an associated tube flange 9 airtight to the housing 2. By a detector 6, which is arranged at a predetermined distance from the focal spot 7, a radiographic image of an object 8 is recorded by means of the X-ray radiation 5. The focal spot is so small that, because of its distance from the object 8 and the detector 6, it can be assumed to be approximately punctiform. If the exit window 4 were not present, only an image in the region of the primary shadow 11 originating from the primary radiation of the (quasi) punctiform focal spot 7 would be obtained at the detector 6 from the object 8. You would then get a sharp picture at the edges. However, there is a scattering of the X-ray radiation 5 at the exit window 4, so that the entire surface illuminated by the primary beam acts as a light spot for a secondary radiation. This means that due to simple geometric conditions in the edge region of the primary shadow 11, a partial shade 12 is formed. This also extends into the primary shadow 11; Thus the object 8 radiates in a certain way

Scope. To limit this effect is on the tube flange 9 a

Collimator 10 made of a strong X-ray absorbing material. The collimator 10 consists of four plates, which are made of steel, tungsten or lead and leave a rectangular passage open. These plates can be stationary, changeable or motorized. Despite the improvement by the collimator 10 over an arrangement without a collimator 10, a significant portion of a half shadow 12, as seen in Figure 1a, still remains. The already unsatisfactory result is further worsened if a prefilter (not shown) is used for the hardening of the X-radiation 5 near the tube flange 9, since this is irradiated over a large area and in turn serves as a source of stray radiation. Thus, depending on used filter material produces a similar disturbing effect, as through the exit window. 4

An alternative prior art is shown in FIG. 1b. This differs only with respect to the target 3 compared to Figure 1a. In FIG. 1 b, the target 3 is surrounded by a shell 30 into which an interior window 31 made of beryllium is inserted at the point in the direction in which the x-ray radiation 5 reaches the exit window 4, and thereby a closed cavity around the target 3 - with an opening in the shell 30, through which the electron beam 15 passes from the filament to the target 3 - is present. The electrons scattered at the target 3 can not leave this anode cavity and there emit their remaining energy mainly in the form of radiation and heat, which can be removed by an anode or target cooling. All other components are the same as in FIG. 1a. Identical or equivalent parts are the same in FIG. 1b as in FIG. 1a.

The invention reduces the effect of the formation of a partial shadow 12, as can be clearly seen from an X-ray tube 1 shown schematically in FIG. 2a. Identical or equivalent parts are denoted the same in FIG. 2a as in FIG. 1a. The difference from FIG. 1 a essentially consists in the fact that the collimator 10 is no longer arranged in the region of the tube flange 9 but as a collimator device 18 (see FIG. 3 a) in the region of the exit window 4 within the opening 14 in the housing 2. This results in a light spot for the secondary radiation due to scattered primary

X-radiation 5 from the focal spot 7, which is only as large as that of the

Collimator 10 freed area. This area can be significantly smaller than the area of the exit window 4, since only such primary radiation must come through the collimator 10 that the detector 6 is just completely illuminated. With otherwise the same geometric Verhäsnissen as in Figure 1a - ie the same distance of the detector 6 to the light spot 7 and the same surface of the detector 6 - this is directly. Due to the significantly smaller area from which secondary radiation can come, the penum shadow 12 becomes strong reduced and the image quality significantly increased. A comparison between a tomogram with a device according to FIG. 1a and one according to FIG. 2a is shown in FIG. 10 and will be explained in more detail below. FIG. 2b shows a further exemplary embodiment according to the invention. The only difference from the exemplary embodiment according to the invention shown in FIG. 2a is that the target 3 enclosed by the shell 30 and the inner window 31 according to FIG. 1b is formed instead of the target 3 shown in FIGS. 1a and 2a. All other

Ingredients are the same as in Figure 2a. Identical or equivalent parts are denoted identically in FIG. 2b as in FIG. 2a.

In the following, the construction of a collimator device 18 according to the invention will be described in more detail with reference to FIG. 3 a - and subsequently also FIGS. 4 to 6 - according to the exemplary embodiment illustrated in FIG. 2 a. FIG. 3 a is an enlarged and detailed illustration of a section of FIG. 2 a in the area of the target 3 and the exit window 4.

The electron beam 15 strikes the target 3 in the focal spot 7 and generates there the primary X-radiation 5 whose edges are predetermined by the Kollimatorvorrichtung 18. However, due to the so-called target shadow only X-rays in the vertical direction of -10 ° to + 20 ° (the former is the angle below the main radiation direction 16 and the latter that above this) can be used. If, however, a symmetrical primary radiation direction 16 primary X-ray radiation 5 is to be used, it follows that only one X-ray beam 5 of ± 10 ° can be used. The X-ray radiation 5 has a vertical opening angle β of about 20 °.

In conjunction with Figure 3a, only the rough structure of the

Collimator device 18 described; Thereafter, the concrete embodiment of a slightly modified embodiment will be explained with reference to Figures 4 to 6. A carrier plate 26 is arranged on a base frame 25, which in turn is connected to a fastening device 24, which is used to connect the

 Collimator 18 with the tube flange 9 and thus the housing 2 of the X-ray tube 1 is used. In the formed within the limits of the tube flange 9 opening 4 in the housing 2 protrudes a support wall 23 which is fixedly connected to the support plate 26 into it. At the left end of the support wall 23, a collimator disk 19 fixedly connected to this with a collimator opening 20 is attached. The collimator disk 19 is - like that of the prior art - made of strong X-ray absorbing material, such as steel, tungsten or lead. The thickness of Kolliomatorscheibe 19 depends on which acceleration voltage has the X-ray tube used and what is used for a target 3. It is preferably designed so that 99% of

Bremsstrahlung spectrum of the resulting X-ray radiation in the collimator 19 are absorbed - at 450 kV and a tungsten target, for example, would use a tungsten or lead thickness of at least 7 mm. The boundary surfaces 22 of the collimator opening 20 are aligned obliquely to the main radiation direction 16. As a result, the collimator opening 20 has a smaller area at its target-near end than at its end remote from the target. Since the x-ray radiation 5 obliquely strikes the surface of the collimator disk 19 starting from the small focal spot 7, no additional scattered radiation can be produced at the boundary surfaces 22 which run along the oblique x-ray radiation 5. Unlike an embodiment with parallel to the main beam direction 16 extending boundary surfaces 22, where they would extend at the far end of the target in the marginal rays and would generate there Streustrah development. As a result, the formation of oil shadow 12 is further reduced.

A prefilter 17 for jet hardening is attached to the target-near surface of the collimator disk 19. Alternatively, the pre-filter 17 may be disposed on the remote side of the collimator disk 19; either directly at this or at a distance which is preferably in a range of 0 to 10 mm. The The scattered radiation resulting from the prefilter 17 can not increase the effect of the formation of partial shadows 12, since the collimator disk 19 located behind it in the propagation direction of the X-ray radiation 5 prevents this up to the area of the collimator opening 20. Alternatively, the prefilter 17 may be arranged in a pocket on the target remote surface of the collimator disk 19, so that the collimator disk 19 is even closer to the exit window 4. Essential to the invention is that the pre-filter 17 is illuminated only on a small area in order to have only the smallest possible scattering effect. Between the collimator 18 (here: between the disc 19 fixedly connected to the pre-filter 17) and the exit window 4 is still a small distance, so that the exit window 4 can not be accidentally mechanically damaged during insertion or shock of the collimator 8 , which would lead to the necessity of replacing the entire (closed) X-ray tube 1.

The exit window 4 is airtight soldered to a steel ring 21, which in turn is airtightly connected to a part of the housing 2. From the housing 2 extends in the vicinity of the steel ring 21, a truncated cone 29 which is fixedly connected to the outer part of the tube flange 9.

The above explanations also apply to a modified target 3 according to FIG. 3b, since it does not depend on the configuration of the target 3 according to the above explanations regarding FIG. FIG. 3b shows an enlarged and detailed illustration of a section of FIG. 2b in the region of the target 3 and the exit window 4. Identical or equivalent parts are identified in the same way in FIG. 3b as in FIG. 3a.

In FIGS. 4 to 6, a slightly modified form is shown in FIG. 3a

Collimator 18 shown. The oblique view of Figure 4 shows the collimator 18 from the tube side; Figure 5 is a longitudinal section through the collimator device 18 of Figure 4; Figure 6 is a plan view - that is, from the side facing away from the housing 2 of the x-ray tube 1 -to the collimator device 18. In the following, the collimator device 18 will be described in more detail with reference to the three figures mentioned. She is together with the

 Tube flange 9 shown.

The tube flange 9 has on its underside in the form of a cylinder jacket (to be able to set it well on the housing 2 of the X-ray tube 1) and has an opening centrally. By penetrating this opening, a truncated cone 29 is present as part of the tube flange 9.

At the targetnahnen end of the support wall 23 is the collimator 19 with the collimator 20 - the oblique boundary surfaces 22 - arranged. The carrier wall 23 is fixedly connected to the carrier plate 26 at its remote end.

The base frame 25 is fixed to the tube flange 9 on its outer side via fastening devices 24 - here in the form of four screws - connected. The carrier plate 26, however, is very easily detachable via two closure elements 28 which are deflectable against spring force to the outside of the base frame 25 and the carrier plate 26 against corresponding, formed on the base frame 25 stops 27, connected to the base frame 25. Due to the interchangeability of the support plate 26 together with the support wall 23 and

Collimator 19, this component can easily on the geometric

Be tuned conditions by the required for the particular structure collimator 19 with the appropriate for the application

Collimator opening 20 is used.

In Figure 7a are two collimator 19 with different

Collimator openings 20 are shown, each having inclined boundary surfaces 22. These collimators are in installation positions of the X-ray tube. 1 is used, in which the electron beam 15 is perpendicular to the main radiation direction 16, as is the case in Figure 3a.

The upper collimator disk 19 has a square collimator opening 20; the lower collimator disk 19 has a rectangular collimator opening 20. In the respective right-hand representations, plan views of the collimator disks 19 are shown and in the respective left-hand representations longitudinal sections in the horizontal direction in the right-hand representations. The specific sizes for the embodiments shown here are only exemplary. The diameter of the two Kollimatorscheiben 19 is the

Exit window 4, as well as the fit adjusted - he is at a 450 kV X-ray tube Comet AG 63 mm - and their distance A to the focal spot 7 is 63 mm; the collimator opening 20 in the upper example has on its side facing the focal spot 7 a size of 18.45 mm and at its side facing away from the focal spot 7 21, 38 mm. This results in a horizontal opening angle g for the X-ray beam of ± 8.33 °. With the lower Ausfüh approximately example, a twice as wide beam cone 5 is illuminated as in the upper embodiment - with otherwise the same geometry as is required in Meßkreiserweiterungen with composite detector images.

In the example below are the corresponding sizes for the

Collimator opening 20 thus 36.9 mm and 42.76 mm, resulting in a horizontal opening angle g of ± 16.32 °. As described above, the collimator disk 19 is made of tungsten or similar material whose thickness is adapted to the desired absorption. For example, it may be a 10 mm thick layer of pure tungsten or a 7 mm thick layer of lead with an additional 3 mm thick copper layer. For X-ray tubes 1 with other voltages or other manufacturers, a corresponding adaptation of the above-mentioned dimensions is necessary, which the person skilled in the art can make on the basis of the embodiments of the above 450 kV X-ray tube from Comet AG. FIG. 7b shows alternative embodiments of the collimator disks 19 shown in FIG. 7a. Their only difference is that the respective boundary surfaces 22 are not oblique, but run perpendicular to the surface. Such embodiments have the advantage that they are easier to manufacture than the embodiments with obliquely extending boundary surfaces 22. A disadvantage of the exemplary embodiments according to FIG. 7b compared to that of FIG. 7a is that the obliquely extending marginal rays of the x-radiation 5 form part of the collimator disk 19 penetrate and produce there to a small extent scattered radiation. In the case of a 450 kV X-ray tube, however, this effect is so small when using tungsten as material for the collimator disk 19 that it does not significantly affect weight.

Figure 8a is a section similar to that of Figure 3a, wherein the

X-ray tube 1 is installed in a different mounting position and another

Collimator 19 is used. In the following, only the differences from FIG. 3a will be discussed.

In contrast to the installation position of the X-ray tube 1 in Figure 3a, in which the electron beam 15 perpendicular to the main radiation direction 16 of the primary

X-ray radiation is 5, the X-ray tube 1 is installed in Figure 8 by a mounting angle a of 5 °. This means that the electron beam 15 is not perpendicular to the main beam direction 16 - which is perpendicular to the detector 6, not shown - is, but the angle between these two is only 85.

As a result, the surface of the target 3 is inclined further to the right - which also turns the target shadow to the bottom right - and thus a larger symmetrical angle arc around the main beam axis 16 can be used since the target does not hide the angle range below the main beam axis 16 so much. This achieves a vertical opening angle β of the X-ray beam 5 of ± 15 ° (instead of the ± 10 ° in FIG. 3). In order to be able to use the entire enlarged vertical opening angle β, however, the collimator opening 20 in the collimator disk 19 has to move away from its center be moved up; otherwise of the same dimensions for the collimator opening 20

The only difference of the invention shown in Figure 8b

 Embodiment with respect to the embodiment of the invention shown in Figure 8a is that the target 3 of the shell 30 and the inner window 31 is enclosed - with the above-described opening in the sleeve 30, through which the electron beam 15 from the filament to the target 3 passes instead of the target 3 shown in Figure 8a. All other components are the same as in Figure 8a. The same or equivalent parts are denoted the same in FIG. 8b as in FIG. 8a. The above explanations regarding FIG. 8a also apply to the modified target 3 according to FIG. 8b, since, according to the above explanations regarding FIG. 8a, it does not depend on the design of the target 3, but solely on its installation angle a of 5 °

Main beam direction 16.

In FIG. 9a, comparable to FIG. 7a, a plan view of the collimator disk 19 installed in the embodiment of FIG. 8a and a cross section through it are shown. The dimensions of the Kolimatoröffnung 20 are the same as those in the upper part of Figure 7a, it is relative to this only from the center out to the right. The material of the collimator disk 19 is also the same as in FIG. 7a, and the same horizontal opening angle g is present as in FIG. 7a, except that it is inclined on the surface of the collimator disk 19. The boundary surfaces 22 have different angles to the surface of the collimator disk 19, since the main beam direction 16 is not perpendicular to this surface in the rotated installation position to ensure that the marginal rays X-radiation 5 run parallel to these boundary surfaces 22 and thus no stray radiation is generated at it.

In accordance with FIG. 7b, FIG. 9b shows an exemplary embodiment of a collimator disk 19 with a surface perpendicular to the surface of the collimator disk 19 Boundary surfaces 22 shown. With regard to the advantages and disadvantages compared with the exemplary embodiment shown in FIG. 9a, the embodiment explained above for FIG. 7b applies analogously. In general, it can be said that the farther the detector 6 from the

 X-ray tube 1 and thus the focal spot 7 is removed or the smaller the detector 6, the smaller the collimator opening 20 can be and the half shadow 12 is reduced to a minimum, so that the situation of a punctiform focal spot 7 is almost reached. With the solution according to the invention, the half shadow 12 at the edge of the projected object 8 is greatly reduced and dark spots behind the object 8 are not additionally reduced

Object scattered radiation brightened.

A simple example is the CT scan of FIG

Aluminum cylinder. In the illustrated example it has a diameter of 75 mm with a tube voltage of 450 kV, as used for example in an test according to ASTM E 1695.

FIGS. 10 (a) and (b) respectively show a tomogram at the top and a tomogram at the bottom

Line profile of the aluminum cylinder. The recording parameters are identical in both cases: X-ray tube MXR-451 HP / 11 I Y.TU450-D11, 1.5mA, 1, 5 mm Sn + 0.5 mm Cu pre-filter, Perkin bucket XRD1621 AN18 with detector distance 1.700 mm, magnification 3, 8th. In the left-hand example (FIG. 10 (a)), the collimator solution according to the prior art from FIG. 1 was used on the tube flange 9 and in the right-hand example (FIG. 10 (b)) a collimator device 18 according to the invention was used - in which the collimator disk 19 is arranged directly on the exit window 4. The ideal result would be a constant plateau in the material, ie a horizontal line in the middle region of the respective line profile in the lower part of FIG. 10. By effects such as jet hardening, a slight valley is normally to be observed centrally downwards. Figure 10 (a), however, shows in the middle an unusual maximum. This is often explained with scattered radiation from object 8, which is not true. By using the collimator device 18 according to the invention, the maximum is greatly reduced and the line profile (lower part of FIG. 10 (b)) almost equals the expected image.

Especially in 3D reconstructions of a CT scan, there are clear

Improvements in the form of reduced fake density in internal cavities, which are never seen without occluding material in a CT scan.

LIST OF REFERENCE NUMBERS

1 x-ray tube

 2 housings

3 target

 4 exit window

 5 x-ray radiation

 6 detector

 7 focal spot

8 object

 8 'illustration of the object

 9 tube flange

 10 collimator

 1 1 primary shade

12 partial shade

 13 window carrier

 14 opening

 15 electron beam

 16 main beam direction

17 pre-filters

 18 collimator device

 19 collimator disc

 20 collimator opening

 21 steel ring

22 boundary surface

 23 supporting wall

 24 fastening device, screw

 25 basic frames

 26 carrier plate

27 stop

 28 closure element

29 truncated cone A distance focal spot - collimator disc a installation angle

ß vertical opening angle of the x-ray beam g horizontal opening angle of the x-ray beam

Claims

claims 1, X-ray tube (1) having a housing (2), a target (3) and an outlet window (4) for X-radiation (5) generated at the target (3), wherein the exit window (4) is airtight in an opening (14 ) of the housing (2) is fixed, wherein the exit window (4) the target (3) opposite and within the housing (2) is arranged, wherein at the x-ray tube (1) a Kollimatorscheibe (19) of a strong X-rays absorbent material is arranged with a collimator opening (20),  characterized in that  the collimator disk (19) lies opposite the exit window (4) on its target-facing side and is located below the surface of the housing (2). 2. X-ray tube (1) according to claim 1, wherein the Kollimatorscheibe (19) consists of an electrically conductive material, such as tungsten, iron or lead. 3. X-ray tube (1) according to one of the preceding claims, wherein the Kollimatorscheibe (19) has a thickness which causes at least a weakening of the emitted and going through them X-rays of 99%, in particular between 5 mm and 25 mm, especially preferably between 7 mm and 20 mm. 4. X-ray tube (1) according to one of the preceding claims, wherein the Collimator (19) and the exit window (4) are arranged parallel to each other and / or the distance between the collimator (19) and exit window (4) between 0 mm and 20 mm, preferably between 0.5 mm and 10 mm and more preferably between 1 mm and 5 mm. 5. X-ray tube (1) according to one of the preceding claims, wherein the collimator disc (19) via a frustoconical support wall (23) with a a fastening device (24) is connected to the target-facing side, which is connected to a tube flange (9) which surrounds the opening (14) of the housing (2) on the outside thereof. 6. X-ray tube (1) according to any one of the preceding claims, wherein the collimator (20) is arranged centrally in the collimator (19), in particular in a round collimator (19) is formed symmetrically to two mutually perpendicular diameters. 7. X-ray tube (1) according to one of the claims 1 to 5, wherein the Kolli matoröffnung (20) is arranged to the center of the collimator (19) arranged on, in particular in a round collimator (19) symmet rally to a diameter and perpendicular thereto standing secant, which is not a diameter is formed. 8. X-ray tube (1) according to one of the preceding claims, wherein the collimator opening (20) has a smaller area at its target-near end than at its farther end. 9. X-ray tube (1) according to one of the preceding claims, wherein at the target-near or the targetfernen surface of the collimator (19), a pre-filter (17) is arranged for Strahlaufhärtung. 10. X-ray tube (1) according to one of the preceding claims, wherein the target (3) by a sheath (30) is in the at the point in the direction of the X-radiation (5) to the exit window (4), an inner window (31) is inserted from beryllium and thereby a predominantly closed cavity around the target (3) is present. 11. Collimator device (18) for an X-ray tube (1) with a base frame (25) to which a fastening device (24) for fastening the collimator device (18) to a tube flange (9) of an X-ray tube (1) is attached. is arranged, and with a support wall (23), which is releasably connected to the base frame (25) and arranged on the same side of the base frame (25) as the fastening device (24), and with a Kollimatorscheibe (19) of highly X-ray absorbing material having a collimator opening (20) and disposed on the end of the support wall (23) facing away from the base frame (25). 12. collimator device (18) according to claim 11, wherein the T ragwand (23) is frusto-conical. A collimator device (18) according to any one of claims 11 or 12, wherein the collimator disc (19) is formed as indicated in any one of claims 4 to 7. 14. Use of a collimator device (18) according to one of the claims 11 to 13 on an x-ray tube (1), in particular an x-ray tube (1) according to one of the claims 1 to 10, for reducing the partial shadow when imaging an object (8 ) by means of the X-ray (5) emitted by the X-ray tube (1) on a detector (6).