阅读说明：本技术 准直器元件的制造 (Manufacture of collimator elements ) 是由 T·厄格勒 V·克里斯蒂奇 于 2019-09-10 设计创作，主要内容包括：本发明涉及用于制造准直器元件(20)的方法。该方法至少具有以下步骤。在一个步骤中,涂覆光刻漆层(23)。使用栅格掩模(24)曝光光刻漆层(23),光刻漆层的曝光区域(25)与准直器元件的结构相对应。在此,准直器元件的结构被对准到共同的焦点。在另一个步骤中,通过形成准直器元件(20)的预结构(27)来显影光刻漆层(23’)。在另一个步骤中,借助于阴极溅射涂覆X射线吸收层(20’)。在另一个步骤中,至少除去预结构(27)的区域中的X射线吸收层(20’)。本发明还提供这样的准直器元件(20)、用于制造散射辐射准直器(37)的方法、这样的散射辐射准直器(37)、辐射检测器(31)以及CT设备(30)。(The invention relates to a method for producing a collimator element (20). The method has at least the following steps. In one step, a layer of photoresist (23) is applied. The layer of photoresist (23) is exposed using a grid mask (24), the exposed areas (25) of the layer of photoresist corresponding to the structure of the collimator elements. Here, the structure of the collimator elements is aligned to a common focal point. In a further step, the layer of photoresist (23') is developed by forming a pre-structure (27) of the collimator element (20). In a further step, an X-ray absorbing layer (20') is applied by means of cathode sputtering. In a further step, the X-ray absorbing layer (20') is removed at least in the region of the pre-structure (27). The invention further provides such a collimator element (20), a method for manufacturing a scatter radiation collimator (37), such a scatter radiation collimator (37), a radiation detector (31) and a CT apparatus (30).)

1. A method for manufacturing a collimator element (20) having at least the following steps:

I) applying a layer of a photo-resist (23),

II) exposing the photoresist layer (23) in a plurality of exposure regions (25) corresponding to a structure of the collimator elements, wherein the structures of the collimator elements are aligned to a common focus,

III) developing the photoresist layer (23') by forming a pre-structure (27) of the collimator element (20),

IV) applying an X-ray absorbing layer (20') by means of cathode sputtering, and

v) removing at least the X-ray absorbing layer (20') in a plurality of regions of the pre-structure (27).

2. The method of claim 1, wherein

The multiple exposure regions (25) are aligned to the focus by means of a grid device (24') having a plurality of grid masks (24), and/or

At least one grid mask (24) is exposed using a point light source (26).

3. The method according to any of the preceding claims, wherein the grid mask (24) has a plurality of shadow regions (28) having a shadow width (d') of less than 20 μm, preferably about 10 μm.

4. The method according to any one of the preceding claims, wherein the grid mask (24) has a plurality of shadow regions (28) which are spaced apart by an exposure width (b') of at most 400 μ ι η, preferably at most 300 μ ι η, particularly preferably at most 200 μ ι η, most particularly preferably at most 100 μ ι η.

5. The method according to any one of the preceding claims, wherein the X-ray absorbing layer (20') comprises tungsten as a constituent, preferably the X-ray absorbing layer is made of pure tungsten.

6. The method according to any one of the preceding claims, wherein steps I to VI are repeated.

7. The method according to claim 6, wherein in one iteration a plurality of exposure areas, which are offset with respect to the previous ones, are exposed such that a step structure of the collimator elements is formed, which step structure is aligned with a common focus.

8. A collimator element manufactured by the method according to any one of claims 1 to 7.

9. Collimator element, in particular according to claim 8, comprising several X-ray absorbing layers structured by means of lithography, the structure of which is aligned to a common focal point and which are preferably formed from pure tungsten.

10. Collimator element, in particular according to claim 8 or 9, having a plurality of grid walls (28') having a wall thickness (d) of less than or equal to 100 μm, preferably less than 50 μm, particularly preferably less than 20 μm, most preferably about 10 μm.

11. Collimator element, in particular according to any one of claims 8 to 10, having a plurality of grid walls (28') spaced apart by a well width (b) of at most 400 μ ι η, preferably at most 300 μ ι η, particularly preferably at most 200 μ ι η, most particularly preferably at most 100 μ ι η.

12. A method for manufacturing a scattered radiation collimator (37), having the steps of:

-providing several collimator elements (20) according to any one of claims 8 to 11, and

-joining a plurality of said collimator elements (20) into one scattered radiation collimator (37).

13. A scattered radiation collimator (37) comprising several collimator elements (20) according to any one of claims 8 to 11.

14. A radiation detector (31), in particular a photon counting X-ray detector, having a scatter radiation collimator (20) according to claim 13.

15. A CT apparatus (30) with a radiation detector (31) according to claim 14.

Technical Field

The invention relates to a method for producing a collimator element and to such a collimator element, to a method for producing a scattered radiation collimator, to such a scattered radiation collimator and to the use thereof, to a radiation detector and to a CT device.

Background

During the transmission of X-ray or gamma radiation (also referred to as "radiation" for short), known scattered radiation is generated by the interaction of the radiation with the object, by the object to be examined by means of the radiation. In the case of examinations by means of, for example, X-ray computed tomography, scattered radiation is undesirable, because it leads to artifacts in the image reconstructed from the recorded attenuation values.

In order to suppress such unwanted scattered radiation, for radiation detectors in transmission tomography apparatuses, such as X-ray computed tomography apparatuses, so-called scattered radiation collimators or scattering grids (ASG-anti scatter grids) are used which are connected upstream of the radiation detectors in the direction of incidence of the radiation. In the case of an X-ray computed tomography apparatus having an X-ray source and a radiation detector for detecting X-rays generated by the X-ray source, such a scattered radiation collimator usually comprises a plurality of collimator elements which are preferably aligned with the focal spot of the X-ray source.

Currently, radiation detectors can in principle be divided into two types: direct conversion detectors and indirect conversion detectors, also referred to below as optical conversion detectors. In the case of a direct conversion detector, incident radiation (e.g., X-ray or gamma radiation) is directly converted into a voltage signal. In contrast, in the case of optically converted radiation detectors, so-called scintillators are used to convert the radiation to be detected first into radiation in the frequency range of the (usually visible) light. A downstream photo detector arrangement detects these photons and in turn generates a voltage signal from these photons.

The individual radiation detector modules (whether of the direct conversion type or the indirect conversion type) are formed by being separated from each other from the overall detector material. In practice, the relevant collimator elements are nowadays usually formed by plates, so-called collimator plates, which project perpendicularly between the pixels from the radiation entrance face of the radiation detector module.

The collimator element serves to efficiently intercept obliquely incident scattered radiation and substantially only allows radiation incident as far as possible in the main direction of radiation to enter the radiation detector module. In the following, the main direction of the radiation to be detected can be considered to be the following radiation propagation direction: in this radiation propagation direction, a substantial part of the radiation to be detected falls on the radiation detector, and this radiation propagation direction may be defined, for example, by a collimator element. In this context, it is generally ensured that the radiation to be detected falls substantially perpendicularly from the radiation source onto the radiation entry face, that is to say the main direction is perpendicular to the radiation entry face. Herein, the term "substantially perpendicular" should be understood as: the respective directions are perpendicular to each other within a certain tolerance, i.e. for example a deviation of the wall position or a deviation of the in-focus.

From the radiation direction behind the patient, the scattered radiation is suppressed by means of a collimator. That is, in addition to scattered radiation, the collimator also suppresses radiation that is directly/perpendicularly incident on the detector. This fraction of radiation corresponds to a loss of dose. In other words, the collimator element reduces the effective detector area (geometric DQE). The object should therefore be to make the collimator wall as thin as possible, but still thick enough to effectively suppress scattered radiation incident "off-normal". Because radiation absorption in a material is exponential (beer-lambert law) with respect to the thickness of the material, there is a lower limit to the thickness of the wall before it becomes almost transparent.

Current manufacturing methods for 3D ASG are limited in terms of minimum wall thickness (e.g., plate construction, Selective Laser Melting (SLM)). In addition, in practicing the known methods, the proportion of tungsten is in some cases only about 50% by volume. Therefore, the goal should be to make thinner walls with better X-ray absorption properties.

Today, the requirements on the accuracy of the manufacturing and positioning of the collimator elements on the radiation detector are rather high. At the same time, it is expected that these requirements will increase even further in the future, so that the tolerances can no longer or only marginally (i.e. costly to produce and to malfunction) be met with the prior art.

Medical imaging is constantly improving. Here, for exampleIn the field of UHR-CT (ultra high resolution computed tomography), as the pixel size becomes smaller, the requirements on the focus quality and/or size in general and in particular with regard to screening of scattered radiation and manufacturing tolerances also increase. The tolerance reduction in the manufacture, positioning and alignment of the collimator elements is mainly the sum of the z-direction

The overall trend of the smaller pixels in the direction is relevant. These directions refer to directions which substantially form a plane aligned substantially perpendicular to the main direction of the radiation to be detected. In imaging systems such as CT, PET or SPECT detectors, the sum of the z-directions is obtained by a circular or part-circular detector which rotates about an axis of rotational symmetry and in some cases on an orbital path

The direction is defined as the insertion direction (z direction) parallel to the axis of rotational symmetry and the axis of rotation: (

Direction). Higher resolution radiation detectors can be realized both temporally and spatially, as the pixels are made smaller in one or both of these directions. However, the smaller the pixels, the more precisely they and the collimator elements have to be manufactured and arranged, both in terms of between pixels and between collimator elements and relative to each other.

The current grid structure is of the order of about 1mm²Wherein the wall thickness is slightly larger than 100 μm.

Although the alignment of the grid walls in the collimating element is known in practice, further improvements are still needed with regard to the tolerance aspects of the grid walls (e.g. obliquely standing grid walls as far as possible) and the manufacturing costs.

Disclosure of Invention

It is an object of the invention to achieve a scattered radiation collimator with improved dose efficiency.

According to the invention, this object is achieved by a method for manufacturing a collimator element and a collimator element, a method for manufacturing a scattered radiation collimator, a radiation detector, and a CT apparatus according to the invention.

The above mentioned method for manufacturing a collimator element comprises at least the following steps: in one step, a layer of a photoresist is applied with a thickness of at least 0.5 mm. In a further step, the photoresist layer is exposed in an exposure region, which corresponds to the structure of the collimator element. Herein, the structure of collimator elements is aligned to a common focal point. The layer of photoresist is then developed by forming a pre-structure of the collimator element. In a further step, the X-ray absorbing layer is applied by means of cathode sputtering. In a further step, the X-ray absorbing layer is removed at least in the region of the pre-structure.

The term "collimator element" should be understood as an integral part or component of the scattered radiation collimator. The collimator elements form at least part of a scattered radiation collimator and have taken the form of a grid shape, as will be explained in more detail below. In the context of the present invention, the term "grid" should be understood to include an arrangement of a first plurality of substantially mutually parallel grid walls intersecting a second plurality of also substantially mutually parallel grid walls transverse (preferably perpendicular) to the first plurality of substantially mutually parallel grid walls in a common plane. In this arrangement, grid wells (simply "wells") are formed between the grid walls. Herein, the term "substantially" means that the walls are only nearly parallel. However, when viewed in more detail, the walls are all slightly inclined towards each other so that the walls are in focus. In other words, the walls all converge radially towards the focal point. In this case, the nearly parallel walls are inclined, for example, by less than 1 ° or less than 1 °.

The substrate may in principle comprise any desired material, the substrate surface being particularly smooth and flat. That is, the height difference of the surface of the substrate as a whole is at most several micrometers. The substrate may be made of, for example, aluminum, glass, silicon dioxide, or the like.

Preferably, in a preliminary step, a layer of sacrificial lacquer, for example several tens of nanometers thick, is applied to the substrate, for example by spin coating. The term "spin coating" is generally understood to mean a process of coating a thin uniform layer by rotation. Herein, first, a desired amount of a solution (that is, a layer material dissolved in a solvent) is applied to the center of a substrate. Depending on the desired layer thickness and the solution used, the acceleration, the rotational speed and the duration are set on the spin coating device and a corresponding spin process is carried out. During this time, the solution is uniformly distributed over the substrate surface. Typically, the solution used is a polymer solution, wherein the molar mass and distribution of the solution also influences the layer thickness.

In order to obtain a solid layer, the solvent must be removed. Some of the solvent had evaporated during the spinning process. This may be facilitated by, for example, simultaneous or subsequent heating (tempering, soft and/or hard baking, and combinations thereof) at 200 ℃ for 60 seconds. As sacrificial lacquer layer, use may be made, for example, of Omnicoat^TM。

The layer of photoresist is applied to the layer of sacrificial lacquer, for example by means of spin coating as described above, by means of metering methods or the like (for example by means of spraying, nozzles or the like). The layer of photoresist is preferably a negative photoresist layer or a negative photoresist. SU-8 or NLOF are suitable as a photoresist layer, for example.

The applied lacquer layer, that is to say the photoresist layer and the sacrificial lacquer layer (hereinafter also referred to as coating system), is exposed to intense UV light through a grid mask or exposure mask. That is to say, the lacquer system is subjected to electromagnetic radiation in the wavelength range from 300nm to 400nm, preferably hard UV light with a wavelength of less than 350 nm. In this context, the dimensions of the grid mask have substantially corresponded to the grid structure of the collimator element to be manufactured. Herein, the term "substantially" means that the influence of diffraction can be considered in the size of the grid mask. Due to the high thickness level of the photoresist layer according to the invention, the exposure time of the layer to UV light (that is to say the duration of the exposure) is more than 40 seconds, preferably about 60 seconds.

The photoresist layer is then developed. That is, in the case of a negative photoresist layer, the unexposed regions are dissolved away using a solvent such as MR-Dev 600 (under agitation)Coating with stirring for 30 minutes). That is, in the case of a negative photoresist layer, the exposed regions become insoluble by photopolymerization and remain on the substrate (in the case of a positive photoresist layer, this is the opposite, that is, the exposed regions become readily soluble). Thus, an exposure area "corresponding to" the structure of the collimator element means that the exposure area takes a form which is substantially identical or complementary to the structure of the collimator element. Then, passing through O²The sacrificial lacquer layer was removed by plasma (for 30 seconds). This results in a kind of pre-structure which takes a negative or complementary form to the collimator element to be produced. In the following, therefore, the pre-structure may be used as a template or "mould" for the grid to be produced, and already with the dimensions of the grid.

By means of cathode sputtering, an X-ray absorbing layer is applied to the pre-structures or introduced between the pre-structures. In general, the term is used to describe a process in which atoms from a solid (target) are isolated by bombardment with energy-rich ions, such as inert gas ions, and enter the gas phase. Known sputtering methods are, for example, ion beam sputtering, RF sputtering, DC sputtering, magnetron sputtering, reactive sputtering, and the like. For this purpose, the substrate with the pre-structure is brought close to the target so that atoms ejected from the target can condense onto the pre-structure. The target atoms arrive at the substrate together with the pre-structure and the cathode sputtering is performed in vacuum. In this arrangement, the target and the X-ray absorbing layer to be produced may in principle comprise any material which absorbs X-rays to a significant extent, for example tantalum, tungsten or the like.

The focal point at which the collimator element to be manufactured is aimed is in particular the focal point. Therefore, the size of the focal spot is negligible. The focal point in this context corresponds to an imaginary focal point of the radiation source, from which the collimator element is manufactured, and the alignment corresponds to the radiation geometry, in which the collimator element is to be used. In operation, due to the alignment of the structures or grid walls, the direct radiation generated thereby passes unhindered through the collimator element while scattered radiation is suppressed.

Finally, the photoresist layer and the appropriate sacrificial lacquer layer are removed by wet-chemical means. For this purpose, the photolithographic coating material may be dissolved in a suitable aggressive solvent, such as TMAH (tetramethylammonium hydroxide), NMP (N-methyl-2-pyrrolidone) or acetone, for example. In order to dissolve the sacrificial lacquer layer, so-called strippers, such as MF 319 or MFCD 26, are used. The photoresist layer and/or the sacrificial lacquer layer are dissolved, where appropriate, with stirring or with the aid of ultrasound. The paint layer is lifted from the side walls (edges). Thereafter, the X-ray absorbing layer remains only in the region in direct contact with the substrate.

In this context, it is preferred to use a layer of a photoresist which enables the production of large layer heights in one lithography step. This aspect avoids performing multiple photolithography steps. On the other hand, it is no longer necessary to stack and bond multiple grid layers to each other. By contrast, by means of the method according to the invention, the collimator or grid element is applied to the substrate in one piece or in several repetitions of the method, by cathode sputtering. This advantageously provides a more advantageous and efficient manufacturing process in terms of time and smaller tolerances. As already mentioned above, the basic criteria for the tolerances of the grid walls are: collimator elements suitable for relatively small pixels are manufactured. This is achieved by the present invention.

In principle, the above-mentioned method can also be carried out with a positive photoresist layer without major changes. In order to place the wells in shadow, the elements required for this may be connected to one another, for example by thin support struts. On the one hand, these elements partially obscure the region of the grid wall to be exposed and, on the other hand, disadvantageously make the exposure mask more fragile. In contrast, a grid mask for a negative photoresist layer, by means of which the wells are exposed and the grid walls are placed in shadow, is substantially easier to manufacture.

The above mentioned collimator element is manufactured by the method according to the invention.

The above mentioned method for manufacturing a scattered radiation collimator comprises at least the following steps. In one step, several collimator elements according to the invention are provided. In a further step, the collimator elements are joined to form a scattered radiation collimator. Herein, "a number" means one or more. In principle, it is possible within the context of the present invention to manufacture a scattered radiation collimator having only one collimator element. However, due to the shape of the radiation detector (in the form of a circular chord) in a CT apparatus, it is often more advantageous and simpler to manufacture a scatter radiation collimator from a plurality of collimator elements. When engaged, each collimator element is preferably aligned to a focal point. The joining can be achieved, for example, by form-fitting and/or force-fitting and/or by means of gluing, welding, soldering or the like. The above-mentioned scattered radiation collimator therefore comprises several collimator elements according to the invention and is in particular manufactured according to the above-described method according to the invention.

Accordingly, the radiation detector mentioned at the outset comprises a scattered radiation collimator according to the invention. The radiation detector may take the form of a CT, PET or SPECT detector. The radiation detector is in particular a photon counting X-ray detector, and where appropriate also an energy resolving X-ray detector. Here, a grid well is associated with each pixel of the radiation detector. That is, the grid well is positioned relative to the pixel such that direct (non-scattered) radiation falls on the pixel through the grid well.

The radiation detector described above can in principle be a component of any desired X-ray apparatus, such as a radiography apparatus, an angiography apparatus or in particular a CT apparatus. The above mentioned CT device comprises a radiation detector according to the invention. The basic functions of the radiation detector and the CT apparatus are known to the person skilled in the art and therefore no further explanation will be given here.

Hence, new radiation detectors and/or CT devices may be made which already have collimator elements and/or scatter radiation collimators according to the invention. However, advantageously, already existing radiation detectors or CT devices can be retrofitted with the collimator element according to the invention and/or the scatter radiation collimator according to the invention.

According to the invention, the scattered radiation collimator according to the invention is used to absorb scattered radiation before it falls on the radiation detector.

Further particularly advantageous embodiments and developments of the invention become apparent from the following description. In particular, individual features of different exemplary embodiments or variants can also be combined to form new exemplary embodiments or variants.

Preferably, the exposure area is aligned to the focus by means of a grid arrangement with several grid masks. Herein, the grid masks together form apertures for light aligned in focus. That is, it is preferable that the grid masks have different structures, wherein the structures of the grid masks closer to the light source preferably take a finer form, and the structures of the grid masks closer to the substrate preferably take a coarser form with respect to each other. Since the light used for polymerizing the layer of photoresist can only penetrate the holes formed by the two grid masks, only the regions of the layer of photoresist that lie in lines that continue beyond these holes are polymerized. Thus, the exposure may be performed, for example, using a surface light source preferably composed of uniform radiation. Also, by using the grid arrangement described above, exposure can be performed using a point light source, as described below.

Alternatively or additionally, the at least one grid mask is preferably exposed using a point light source. In this case, the point light sources are preferably arranged at the location of the focal point, or the grid mask is modified accordingly (for example by a suitable thickness, spacers from a lacquer layer system, etc.). This replicates the geometry of the radiation with which the collimator element is to be subsequently utilized. It is thus already ensured that the regions of the photoresist layer to be polymerized are in focus by means of the point light sources and the exposure through the at least one grid mask. The exposure using a point light source may be combined with the above-described grid arrangement, for example, in order to obtain sharper edges.

In this case, the point light source may take the form of, for example, a UV laser. Additionally or alternatively, in the case of a conventional light source (not a laser), suitable optical elements may be used to improve or create the point characteristics of the light source. In this context, the optical element preferably uses a pinhole diaphragm, a grating or a combination thereof.

Preferably, a layer of a photoresist is used, by means of which a relatively thick layer can be obtained. This advantageously makes it possible to obtain the desired grid height in one or several lithography steps, as described in more detail below.

SU-8 is obtained, for example, with different viscosities, which are controlled by the proportion of solvent in the photoresist layer.

Negative lacquer layers with a larger layer thickness of at least 1mm are available, for example SU-81000, SU-83050. They are therefore preferably used in the context of the method according to the invention.

Sealing of the photoresist layer or sacrificial lacquer layer by the X-ray absorbing layer is to be avoided, since as a result the solvent no longer acts on the lacquer layer and thus lift-off can be prevented. For protection against sealing, the thickness of the lacquer layer is preferably chosen to be greater than the thickness of the X-ray absorbing layer. The thickness ratio between the lacquer layer and the X-ray absorbing layer is at least 1: 1. For this purpose, the photoresist layer is coated with a layer of preferably at least 0.5mm, particularly preferably at least 1mm, very particularly preferably 2mm, even more preferably 3 mm.

In principle, the thinner the wall of the collimator element, the more the DQE (detected quantum efficiency) will increase, since this shields the smaller detection surface area of the radiation detector. The grid mask therefore preferably has shadow regions whose shadow width is less than or equal to 100 μm, particularly preferably less than 50 μm, very particularly preferably less than 20 μm, most preferably about 10 μm. The collimator element according to the invention, in particular a collimator element produced according to the method of the invention, thus preferably has grid walls with a wall thickness of less than or equal to 100 μm, particularly preferably less than 50 μm, very particularly preferably less than 20 μm, most preferably about 10 μm.

In summary, previously customary tolerances for the thickness and alignment of the grid walls of about 20 μm can advantageously be significantly reduced using the method according to the invention.

In order to accommodate the currently conventional or actual future generations of pixels of the radiation detector, the grid mask preferably has shadow areas which are spaced apart by an exposure width of at most 400 μm, particularly preferably at most 300 μm, very particularly preferably at most 200 μm, even more preferably at most 100 μm. Thus, according to the collimator element of the invention, the collimator element according to the invention (in particular, the collimator element produced according to the method of the invention) has grid walls spaced apart by a well width, which is preferably at most 400 μm, particularly preferably at most 300 μm, very particularly preferably at most 200 μm, even more preferably at most 100 μm.

In order to achieve the best possible absorption, the X-ray absorbing layer preferably comprises tungsten as a constituent. It is particularly preferred that the X-ray absorbing layer is made of pure tungsten (that is to say as much as 100% of tungsten) since this absorbs radiation even better. The collimator element according to the invention is thus particularly preferably made of pure tungsten.

In order to obtain a sufficient height of the collimator element, in the method according to the invention, steps I to VI are preferably repeated, wherein the exposure area and the grid mask used are adjusted accordingly if necessary. Advantageously, the height of the grid may be adjusted within the scope of the invention according to the size of the grid structure or grid well.

Preferably, in one repetition, an exposure area which is offset from the previous exposure area is exposed such that a stepped structure of collimator elements is formed which is aligned to a common focus. This can be achieved relatively simply, for example by means of a corresponding set of grid mask or multiple grid masks and area exposure (preferably area uniform exposure). Here, the previously generated stepped grid mask is replaced by a grid mask for the next step following the arrangement to be manufactured according to the structure, before the next repetition of the method steps.

Herein, the scattered radiation collimation depends in particular on the so-called well ratio, or on the well size in contrast thereto. The well size specifies the ratio of the spacing between two mutually opposite well walls to the well height or the height of the collimator element. Thus, the smaller the spacing between the opposing well walls, the smaller the height of the collimator element can be with the same well ratio.

In the case of dual-energy CT applications and multi-energy CT applications, the requirements on the collimation of the scattered radiation are particularly high. Herein, for example, a well ratio of 1:20 is required. The height of the collimator element to be manufactured can thus be determined by the defined pixel size.

The small tolerances achievable according to the invention, which have been described above, enable good collimation of small pixels, while having a negligible effect on the detected quantum efficiency. The relatively large height of the collimator element, which can be achieved according to the invention and as described above, enables sufficient collimation of the incident radiation even for relatively large pixels. Thus, using the method according to the invention, collimator elements for a wide range of applications can be manufactured.

Preferably, the substrate is removed from the collimator element. This can be performed, for example, by means of suitable dry and/or wet chemical methods. In dry chemical terms, the substrate may be removed from the collimator element, for example by grinding. More effectively, however, the substrate is particularly preferably separated or removed from the collimator element by wet-chemical means with the aid of a solvent suitable for the substrate, such as hydrofluoric acid (HF).

Drawings

The invention is explained in more detail below with reference to exemplary embodiments and by means of the figures. Herein, the same components have the same reference numerals in different drawings. The figures are generally not drawn to scale. Wherein:

fig. 1 shows a schematic block diagram of an exemplary embodiment of a method of manufacturing a collimator element according to the present invention;

fig. 2 shows a schematic cross-sectional view of the product after manufacturing steps I) and II) of the method illustrated by fig. 1;

FIG. 3 shows a plan view of the product of FIG. 2;

fig. 4 shows a schematic cross-sectional view during the manufacturing step III) and a schematic cross-sectional view after the manufacturing step IV) of the method illustrated by fig. 1;

FIG. 5 shows a plan view of the product of FIG. 4;

fig. 6 shows a schematic cross-sectional view during the manufacturing step V) and a schematic cross-sectional view after the manufacturing step VI) of the method illustrated by fig. 1;

fig. 7 shows a plan view of the product of fig. 6, i.e. an exemplary embodiment of a collimator element according to the present invention;

fig. 8 shows a rough schematic cross-sectional view of another exemplary embodiment of a collimator element according to the present invention; and

fig. 9 shows a perspective view of an exemplary embodiment of a CT apparatus according to the present invention.

Detailed Description

Fig. 1 shows, by way of example, a schematic block diagram of a process of a manufacturing method according to the invention of a collimator element 20 according to the invention. Fig. 1 is explained in more detail below with reference to fig. 2 to 7.

In a preliminary step I', the Omnicoat is applied by means of spin coating^TMThe sacrificial lacquer layer 21. For this purpose, the amount was 50. mu.l/2.25 cm²Omnicoat^TMIs metered onto a planar substrate 22 made of, for example, silicon oxide. Then, first, the coating was spin coated with Omnicoat 500rpm^TMThen rotated at 300rpm for 50 seconds. Thereafter, the coated Omnicoat^TMHeating to 160 ℃ for 30 seconds for curing purposes. The above process is repeated once. Finally, 50. mu.l/2.25 cm were metered in again²Omnicoat^TMAnd the system was rotated at 500rpm for 10 seconds and then at 300rpm for 50 seconds. Then, heat to 200 ℃ for 60 seconds to cure the entire sacrificial lacquer layer.

In a further step I, a photo-resist layer 23 of SU-83050 is applied to the cured sacrificial lacquer layer 21 by means of spin coating. For this, in the first subprocess, 0.2ml/2.25cm²SU-83050 is metered onto the sacrificial lacquer layer 21. The substrate was then rotated at 500rpm for 20 seconds followed by 1000rpm for 20 seconds to evenly distribute the applied layer of photoresist. The first sub-process is repeated twice. Then, in a second subprocess, a further 0.2ml/2.25cm is metered in²Then the substrate coated with the layer was rotated at 500rpm for 30 seconds. The second sub-process is repeated once. For curing, the substrate coated with the layer is first baked at 65 ℃ for 60 seconds and then added over a period of 60 secondsHeated to 95 ℃ and baked for 6 hours.

The results or products of steps I' and I are illustrated in cross-section in fig. 2 and in plan view in fig. 3. Fig. 2 shows the structure of the layers. The substrate 22 made of silicon may in principle have any desired thickness. In this case, for example, its thickness is 0.525 mm. Followed by a sacrificial lacquer layer 21, for example of thickness 0.06 μm, and finally a photoresist layer 23, for example of thickness 500 μm. The plan view in fig. 3 shows only the smooth layer 23 of the photoresist.

In a further step II (see fig. 4), the photoresist layer 23 and the sacrificial lacquer layer 21 are irradiated by an ultraviolet point light source 26 through a grid mask arrangement 24'. Grid mask arrangement 24' includes two grid masks 24. In this case, the grid masks 24 are constructed and arranged such that they form an exposure area 25 having an exposure width b', through which exposure area 25 UV radiation (schematically indicated herein by arrows) passes. Further, the grid mask arrangement 24' has a shadow region 28, which shadow region 28 has a shadow width d ', which shadow width d ' shields the lacquer layer 21, 23 from UV radiation. The exposure area 25 and the shadow area 28, which represent a continuation of the grid mask arrangement 24', correspond here substantially (that is to say without taking into account the influence of diffraction effects) in their shape and size to the collimator element 20 to be produced. During irradiation, the photoresist layer 23 is polymerized and cured in the exposed areas 25.

Although a UV light source is illustrated and described herein as a point light source 26, the method according to the invention using a grid arrangement 24' may also be performed with a surface light source, for example, in order to achieve a more uniform polymerization. Thus, instead of a point light source 26, another point light source, a flat lamp or another suitable UV light source may be used, for example.

To further cure the polymerized area of the photoresist layer 23, it was heated at 95 ℃ for 6 minutes in a post exposure bake.

In a further method step III, the photoresist layer 23 is developed by placing the substrate 22 with the lacquer layer in a developer bath, for example in MR-Dev 600 for 30 minutes, by stirring and then heating at 130 ℃ for 60 minutes. During this time, the unexposed and therefore unpolymerized regions of the photoresist layer 23 are dissolved away. The sacrificial lacquer layer 21 underneath it is then removed by the action of the O2 plasma thereon for 30 seconds. The developed photoresist layer 23 'and the sacrificial paint layer 21' now together have a pre-structure 27, which pre-structure 27 is complementary to the collimator element 20 to be manufactured. Then, the baking of the substrate with the pre-structure 27 is completed at 130 ℃ for 60 minutes.

Fig. 5 shows a grid-like pre-structure 27 in a plan view. The pre-structure 27 is surrounded by a planar surface of the developed photo-resist layer 23'. The pre-structure 27 has a first number of mutually substantially parallel channels 29 'and perpendicular thereto a second number of also mutually substantially parallel channels 29'.

In a further step IV (see fig. 6), a pure tungsten layer 20' of, for example, 370 μm thickness is deposited uniformly on the substrate 22 and the developed lacquer layers 21', 23' by means of cathode sputtering. The tungsten layer 20' condenses or deposits in the channels 29' of the pre-structure 27 and on the developed photoresist layer 23 '. The developed photoresist layer 23 'and the sacrificial paint layer 21' are not sealed due to the height difference between the channel 29 'and the upper side of the developed photoresist layer 23'.

In the next step V, the substrate 22 with the developed lacquer layers 21', 23' and tungsten layer 20' is treated, if appropriate, with stirring or ultrasound, using a strong solvent such as NMP. As a result, the photoresist layer 23' is removed. The sacrificial lacquer layer 21' is removed, where appropriate, by stirring or ultrasonic treatment with a so-called stripper, such as MFCD 26 or MF 319. The tungsten layer 20' remains only in the areas within the pre-structure 27 where it has been deposited directly on the substrate 22, thus forming the collimator element 20.

In fig. 7 a collimator element 20 according to the invention is illustrated in plan view. In this illustration, a first number of mutually substantially parallel grid walls 29 and a second number of mutually substantially parallel grid walls 29 perpendicular thereto are shown, which are still arranged on the substrate 22 and correspond to the pre-structures 27. The wall thickness d of the grid cell walls 29 is e.g. 10 μm and each grid cell wall is arranged spaced apart by a well width b of e.g. 200 μm. This therefore yields a well ratio of 1:20, which is also suitable for dual and multi-energy applications.

Fig. 8 illustrates in a rough schematic cross-sectional view a further exemplary embodiment of a collimator element according to the present invention on a substrate 22. In the repetition of the above described method steps I to V, three tungsten layers 20' are coated onto the substrate 22. In each of these repetitions, a different grid mask 24 is used in order to generate a corresponding structure of the respective tungsten layer 20'. In this case and according to the invention, the overall structure of the collimator element 20 formed by the tungsten layer 20' is in focus.

As mentioned above, the drawings are schematic and not drawn to scale. In particular, the angles shown in fig. 6 and 8 are exaggerated in fig. 4, between the light beam and the angle created between the exposure area 25 and the grid walls 29 for illustrative purposes. In a practical arrangement in an X-ray system, they are essentially created by the spacing between opposing grid walls 29, which constitute the detector pixels, and the spacing between the detector surfaces is used to focus the X-ray source. In each case, the angle between two opposite grid cell walls 29 is preferably less than 1 °.

In a final method step VI, the substrate 22 is removed from the collimator element 20. This is preferably done by wet-chemical methods, for example, with the aid of hydrofluoric acid (HF). The hydrofluoric acid dissolves the substrate 22 made of silicon dioxide but does not attack the collimator element 20 made of tungsten. The collimator element 20 according to the invention has been generally described with reference to fig. 7.

In order to manufacture a scattered radiation collimator according to the invention, several collimator elements according to the invention manufactured in the above-described manner are provided and joined together, for example by gluing, such that they are arranged, for example, in sections of a part of a circle.

Fig. 9 shows by way of example and in a rough schematic form a computer tomography apparatus or CT apparatus 30 according to the invention. The computer tomography apparatus 30 comprises a patient table 35 for supporting a patient 34 as an object under investigation. The patient table 35 can be moved along the system axis 36 into the measurement region and by doing so the patient 34 can be positioned in the measurement region. The computer tomography apparatus 30 further comprises a gantry 32, which gantry 32 has a source radiation detector arrangement 33, 31 which is mounted such that it can be rotated about a system axis 36. The source radiation detector arrangement 33, 31 has an X-ray source 33 and an exemplary embodiment of a radiation detector 31 according to the present invention, which are aligned relative to each other such that, during operation, X-rays emitted from a focal spot of the X-ray source 33 fall on the radiation detector 31. An exemplary embodiment of a scattered radiation collimator 37 according to the present invention is arranged on the side of the radiation detector 31 directed towards the X-ray source 33. The scatter radiation collimator 37 has several collimator elements 20 according to the invention, which are arranged on an inner section of a portion of a circle of the radiation detector 31, i.e. on the side pointing towards the system axis 36.

A scatter radiation collimator 37 collimates the X-rays once they have passed through the patient. As a result, the influence of scattered radiation during acquisition is largely avoided. For each projection, the radiation detector 31 generates a set of projection data. The projection data is then further processed to produce a resultant image.

The use of such a computer tomography apparatus 30 for 3D image reconstruction is known. In order to capture an image of the object (region of interest) under investigation, projection data are detected from a plurality of different projection directions as the source radiation detector arrangement 33, 31 is rotated. In the case of helical scanning, during the rotation of the source radiation detector arrangement 33, 31, for example, while the patient table 35 is continuously moved in the direction of the system axis 36. Thus, with this type of scan, the X-ray source 33 and the radiation detector 31 move around the patient 34 in a helical path. The precise construction and specific mode of operation of such a CT apparatus 30 is known to those skilled in the art and will not be described in detail herein.

The photolithographic method and the cathode sputtering method are truly established processes that allow high manufacturing accuracy and at the same time low manufacturing costs. Thus, with the method according to the invention, a collimator element and a scattered radiation collimator can be manufactured at lower costs, which also meets higher requirements for manufacturing tolerances. As a result, post-processing is also largely avoided.

Finally, it should also be pointed out again that the device described in detail above is merely an exemplary embodiment, which can be modified in various ways by a person skilled in the art without departing from the scope of the invention. Further, the use of the indefinite articles "a" and "an" does not exclude the possibility that a feature referred to may also occur more than once. Likewise, the terms "device" and "element" do not exclude the possibility that the component in question comprises a plurality of cooperating partial components, which may also be spatially separated from one another if desired.