Multilayer x-ray detector and x-ray system

Abstract

To provide a multilayer X-ray detector which enables improved quantum efficiency of X-ray detection, in addition to sufficient spectrum separation of an X-ray image by means of a dual energy X-ray source.SOLUTION: There is provided a multilayer X-ray detector, in which sensor layers are arranged behind in an X-ray projection direction, a first sensor layer 10 is designed to convert an X-ray quantum of a first light-emission spectrum into a first signal, a second sensor layer 11 is designed to convert an X-ray quantum of a second light-emission spectrum into a second signal, and the multilayer X-ray detector incudes an intermediate space 14 arranged between the two sensor layers, at least one layer belt 15 which has at least two filter regions 16 having a plurality of material compositions and / or coatings and is designed to be bendable, and a transport mechanism for giving either the first filter region 16 or the second filter region 17 to the intermediate space 14.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The invention relates to a multi-layer X-ray detector according to claim 1 and to an X-ray system comprising a multi-layer X-ray detector according to claim 12. [Background technology]

[0002] In modern X-ray technology, dual energy X-ray tubes are used, i.e. X-ray tubes capable of emitting two different emission spectra. One of the emission spectra is generally high energy, the other somewhat lower energy. Among other things, the clear energy difference between the two sensor layers is important. For example, the percentage of soft tissue can be subtracted from the two multiple X-ray images that can be produced in this way, and thus bone density can be measured. The material composition of the whole body tissues can also be calculated.

[0003] In addition to a dual-energy X-ray tube, a dual-energy X-ray detector is also required to be able to read out the corresponding signal. Such known dual-energy X-ray detectors 9 (see FIG. 1) generally have two scintillator-based sensor layers, one behind the other in the X-ray projection direction 13. During recording, first the first sensor layer 10 and then the second sensor layer 11 are penetrated by the X-ray beam along the projection direction 13. To achieve sufficient spectral separation for dual-energy recording, a filter layer is typically present between the two sensor layers (e.g. a 1 mm thick copper filter layer 12). Such multi-layer X-ray detectors have: It is known, for example, from Stoer, Fredrik et al., "Performance Characterization of a Prototype Dual-Layer Cone-Beam Computed Tomography System," (Medical Physics Vol. 48, 11 (2021), pp. 6740-6754).

[0004] A disadvantage of multi-layer X-ray detectors is that the high absorption of the filter layers reduces the quantum efficiency of X-ray detection. Summary of the Invention [Problem to be solved by the invention]

[0005] It is an object of the present invention to provide a multi-layer X-ray detector that allows improved quantum efficiency of X-ray detection as well as sufficient spectral separation of X-ray images by means of a dual energy X-ray source. [Means for solving the problem]

[0006] This object is achieved according to the invention by a multi-layer X-ray detector as defined in claim 1 and by an X-ray system having a multi-layer X-ray detector as defined in claim 12. Advantageous embodiments of the invention are the subject matter of the respective associated dependent claims.

[0007] The multi-layer X-ray detector according to the invention comprises at least a first and a second sensor layer, which are arranged behind the other in the X-ray projection direction, the first sensor layer designed to convert X-ray quanta of a first spectrum (e.g. X-ray radiation spectrum) into a first signal and the second sensor layer designed to convert X-ray quanta of a second spectrum (e.g. X-ray radiation spectrum) into a second signal, an intermediate space arranged between the two sensor layers, at least one layer belt designed as bendable, which has at least two filter regions with multiple material compositions and / or coatings, and a transport mechanism capable of bringing either the first filter region or the second filter region into the intermediate space.

[0008] The layer belt is particularly flexible and can be bent, folded or rolled up without damaging the layer belt itself or the possible coating. The filter areas can be designed to have a large surface area, in particular a surface area that corresponds approximately to the surface area of ​​the second sensor layer, so that if necessary the entire intermediate space can be covered by one of the filter areas. The layer belt itself generally preferably has at least twice the area of ​​the second sensor layer (at least two filter areas) and may also be significantly larger (e.g. filter areas or neutral areas between three or more filter areas). The layer belt is preferably arranged in such a way that in the area of ​​the intermediate space the surface normal of the layer belt is parallel to the X-ray projection direction.

[0009] By means of the transport mechanism, either the first or the second filter region with the respective material composition and therefore the filter effect can be brought into the intermediate space between the two sensor layers as required. In this way, the user can select which filtering is required for the current application and can set it quickly and easily. Even during an ongoing procedure, a rapid switch between the two filter regions can be performed, for example within a few seconds. The X-ray detector offers a high degree of flexibility in terms of the spectral separation of at least two spectra for the X-ray recording. The filter regions have a composition or filter effect as homogeneous as possible.

[0010] The use of such layered belts also ensures a high reliability of the filtering effect and there is a low risk of artifacts in the obtained X-ray images.

[0011] According to one embodiment of the present invention, the layer belt comprises a first spectral filter material having a first X-ray transmittance in a first filter region and a second spectral filter material having a second X-ray transmittance in a second filter region, the first X-ray transmittance being different from the second X-ray transmittance. Due to the multiple X-ray transmittances, multiple filter effects can also be selected as required.

[0012] In particular, the first X-ray transmission is less than 25% based on an X-ray photon energy of 50 keV, so that the first filter region has a particularly effective X-ray absorption spectrally. In this way, when the first filter region is arranged in the intermediate space, a particularly good spectral separation of the emission spectrum and therefore a particularly good dual-energy resolution can be achieved, and thus a precise analysis of the material composition of the examined object can be performed. For such purposes, the first filter material may contain or be made from at least one of the elements copper, tantalum, lead, aluminum, tin, brass or iron. For example, the first filter region can be designed to be sufficiently thick to absorb low-energy (e.g., 40-80 keV) photons sufficiently well and at the same time have the lowest possible absorption of high-energy photons (e.g., 100-120 keV), so that they reach the second sensor layer sufficiently well for reasons of detection and dose efficiency.

[0013] An advantageous method for a particularly large difference in the filter regions is that the second filter region has an X-ray transmission of more than 60%, in particular more than 90%, based on an X-ray photon energy of 50 keV, so that the second filter region has only a weak X-ray absorption effect or does not have any effect at all. If the second filter region is arranged in the intermediate space, a particularly good quantum efficiency can be achieved in this way in X-ray recording. This allows an X-ray detector with a first filter region with low X-ray transmission and a second filter region with high X-ray transmission to ensure good spectral separation in dual-energy operation and high quantum efficiency in normal operation depending on the setting of the conveyor belt, and can be used suitably for various applications with the same high quality.

[0014] According to a further embodiment of the invention, the layer belt is designed to be able to be wound up and / or unwound. For this purpose, the transport mechanism can have, for example, rollers around which the layer belt is wound up and unwound. In addition, there can also be one or more motors, which can, for example, rotate the rollers and thus move the layer belt. For example, rollers can be present on both sides of the sensor layer outside the intermediate space, and the rolling of the transport belt on one roller and the simultaneous rolling on the other roller can bring the respective filter area into the intermediate space.

[0015] According to a further embodiment of the invention, the conveying mechanism has rollers, through which the layer belt is designed to be movable, so that either the first filter area or the second filter area is conveyed into the intermediate space. In particular, the layer belt and the conveying mechanism are designed as a conveyor belt, in particular as a motorized conveyor belt. In this form, the layer belt can be designed, for example, as a continuous endless conveyor belt that is tensioned via two rollers and partially placed in the intermediate space, the two filter areas being placed on different sides of the rollers. The two rollers rotate by a motor drive, moving the conveyor belt so that, depending on the position, one of the filter areas can be placed in the intermediate space.

[0016] According to a further embodiment of the invention, the first sensor layer comprises a first scintillator material of a first thickness and a first readout circuit designed to detect photons generated by the first scintillator material from X-ray quanta of a first spectrum and generate a first signal therefrom, and the second sensor layer comprises a second scintillator material of a second thickness and a second readout circuit designed to detect photons generated by the second scintillator material from X-ray quanta of a second spectrum and generate a second signal therefrom. The operating principle of the sensor layers of the X-ray detector is known in principle.

[0017] According to a further embodiment of the invention, the multi-layer X-ray detector has a bendably designed second layer belt with at least two filter regions with multiple material compositions and / or coatings and a transport mechanism that can put either the first or the second filter region into the intermediate space. Multiple different filter effects can be produced by the two or more layer belts depending on which filter region is simultaneously placed in the intermediate space in each case. Such an X-ray detector offers multiple possibilities and variations between strong spectral separation and particularly high quantum efficiency.

[0018] According to a further embodiment of the present invention, the multi-layer X-ray detector is designed as either an X-ray flat detector or a fan detector. In an X-ray flat detector for a cone beam X-ray source, the sensor surface is generally flat and relatively large, for example [20x30cm or 30x40cm], and as a result, the conveyor belt and filter area are also large. A fan detector for CT applications is generally curved in the shape of a segment of a circle, for example long and narrow. The conveyor belt and filter area are also curved.

[0019] Furthermore, the invention comprises an X-ray system comprising a multi-layer X-ray detector according to one of the preceding claims, a dual-energy X-ray source designed to be switchable from emitting light of a first emission spectrum to emitting light of a second emission spectrum and vice versa, and a system controller for controlling the multi-layer X-ray detector and the dual-energy X-ray source.

[0020] The invention and further advantageous embodiments according to the features of the dependent claims are explained in more detail below with the help of exemplary embodiments shown diagrammatically in the drawings, but the invention is not consequently limited to these exemplary embodiments. [Brief description of the drawings]

[0021] [Figure 1] 1 shows a cross-sectional view of a multi-layer X-ray detector according to the prior art. [Diagram 2]1 shows a cross-sectional view of a multi-layer X-ray detector according to the invention having a layer belt with two filter regions in a first state. [Diagram 3] 3 shows a cross-sectional view of a multi-layer X-ray detector according to the invention having a layer belt with two filter regions in a second state. [Figure 4] 3 shows a cross-sectional view of a further multi-layer X-ray detector according to the invention having a layer belt with two filter regions in a first state. [Diagram 5] 1 shows a cross-sectional view of a multi-layer X-ray detector according to the invention having a two-layer belt. [Figure 6] 4 shows a cross-sectional view of a further multi-layer X-ray detector according to the invention having two layer belts. [Figure 7] 1 shows an X-ray system having a multi-layer X-ray detector and a dual-energy X-ray source. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] 1 shows a known dual energy X-ray detector 9 in which a fixed high X-ray absorption filter layer is present between a first scintillator based sensor layer 10 and a second scintillator based sensor layer 11 to achieve sufficient spectral separation for dual energy recording. However, such a dual energy X-ray detector 9 does not provide sufficient quantum efficiency for normal operation.

[0023] 2-6 show a multi-layer X-ray detector 19 with a layer belt 15, in which the filter region of the bendable layer belt 15 can be transported by various transport mechanisms into the intermediate space 14 between the first sensor layer 10 and the second sensor layer 11. Depending on the coating or composition of the filter region, various filters can be produced that achieve different effects, for example, these filters can ensure spectral separation in dual energy operation or provide sufficient quantum efficiency in normal operation.

[0024] 2 and 3 show a multi-layer X-ray detector 19 with a first scintillator-based sensor layer 10 and a second scintillator-based sensor layer 11, which are arranged behind each other in the X-ray projection direction 13. An intermediate space 14 is arranged between the two sensor layers 10, 11, for example over the entire length and width of the sensor layers. The multi-layer X-ray detector 19 also has a layer belt 15 designed as a bendable, rollable "endless" conveyor belt and tensioned, for example, via two rollers 18, which are arranged on both sides of the sensor layers 10, 11, in particular the second sensor layer 11. The rollers 18 are preferably arranged outside the angle of incidence of the X-ray radiation. The conveyor belt is arranged at least partially in the intermediate space 14 between the two sensor layers 10, 11 and extends at least partially, in particular completely, over the length and width of the sensor layers 10, 11. Rotation of the rollers 23 causes the conveyor belt to roll through the rollers 18, thereby changing its position.

[0025] The conveyor belt has at least two filter regions with different spectral filter materials (different compositions, thicknesses, densities, etc.) with, for example, different X-ray transmittances. In this case, for example, the first filter region 16 can have a first filter material with low X-ray transmittance and the second filter region 17 can have a second filter material with high X-ray transmittance. The filter material can be applied to the conveyor belt, for example, as a coating. The layer belt 15 is designed as a conveyor belt and can have the form of a film. The conveyor belt itself can also have multiple material compositions and / or multiple thicknesses and / or densities in the corresponding filter regions.

[0026] The first filter region 16 may have a coating that includes, or may be at least partially made of, one or more of the following materials: copper, tantalum, lead, aluminum, brass, tin, or iron. The coating may be, for example, thick enough to provide a significant filtering effect (e.g., 1 mm of copper). The second filter region 17 may have only a very thin coating of a material with high X-ray transmission, or no coating at all (e.g., only a layer belt / film), and thus have nearly 100% X-ray transmission. Alternatively, the first filter region may have a thick coating, and the second filter region may have a thin coating of the same material.

[0027] The sensor layers 10, 11 are constructed as in known multi-layer X-ray detectors. Thus, the first sensor layer 10 may comprise a first scintillator material of a first thickness and may comprise a first readout circuit, and the second sensor layer 11 may comprise a second scintillator material of a second thickness and may comprise a second readout circuit. Each readout circuit is designed to detect photons generated by the first scintillator material from X-ray quanta of a respective associated emission spectrum and generate a signal therefrom, which signal is used to generate an X-ray image.

[0028] If necessary, either the first filter region 16 or the second filter region 17 can be moved into the intermediate space 14, for example in that a roller 18 driven by a motor rotates both in the same sense of rotation 23. For this purpose, the roller can have a drive (not shown). If the first filter region 16 with low X-ray transmission is located in the intermediate space 14 (shown in FIG. 2) and extends over the entire sensor surface of the second sensor layer 11, irradiation with a dual-energy X-ray source with different emission spectra results in spectral filtering, by means of which the tissue composition can be determined (for example by subtraction) from the obtained X-ray image. If the second filter region 17 with high X-ray transmission is located in the intermediate space 14 (shown in FIG. 3), a composite X-ray image with high quantum efficiency can be generated from the two X-ray images.

[0029] The transport mechanism can also be designed such that two rollers 18 are rotatably arranged on both sides of the second sensor layer 11 outside the intermediate space 14 (as shown in FIG. 4 ) and the layer belt 15 is wound by being wound from one roller 18 to the other roller 18, respectively. This is done, for example, by a motor-driven rotation of the two rollers 18 in the same direction of rotation 23. In this way, one filter area 16, 17 can also be arranged between the rollers 18, respectively, such that the filter area is located completely in the intermediate space 14 and extends, for example, on the second sensor surface 11. To ensure uniform filtration, the layer belt 15 has a (for example, predetermined) tension between the rollers 18. To maintain such tension, for example, a spring mechanism can be provided on one or both rollers 18.

[0030] 5 and 6 show a further exemplary embodiment of a multi-layer X-ray detector 19 with two transport mechanisms, each with a layer belt, whose filter regions can be arranged behind one another in the X-ray projection direction 13 in the intermediate space 14. In this way, further filter options can be created.

[0031] For example, in FIG. 5 there are two layer belts, namely a first layer belt 15.1 designed as an endless conveyor belt, tensioned via two rollers 18 and having a first filter area 16 and a second filter area 17, and a second layer belt 15.2 designed as an endless conveyor belt, tensioned via two rollers 18 as well and having a third filter area 16.2 and a fourth filter area 17.2. The first layer belt 15.1 is arranged, for example, within the second layer belt 15.2. In this case, the filter areas can be arranged overlapping as required in the intermediate space 14 in the X-ray projection direction 13 and can be combined as required. For example, the first filter area 16 of the first layer belt 15.1 can be combined with the third filter area 16.2 of the second layer belt 15.2 or with the fourth filter area 17.2 of the second conveyor belt 15.2. The overlapping provides a summed filter effect. Depending on the combination and on the individual filters, up to four different filter variants are possible here.

[0032] In this case, the conveyor belt may have filter areas with low X-ray transparency and filter areas with high X-ray transparency. The conveyor belt may be made, for example, from a film or belt, and the filter areas may be coated accordingly, or may be assembled from several parts. The materials of the filter areas may differ in composition, density, and thickness. The conveyor belts and their coatings should be flexible, bendable, and not subject to cracking or breakage due to rolling.

[0033] FIG. 6 shows two ply belts 15.1, 15.2 arranged behind each other in the X-ray projection direction 13, each ply belt having two rollers 18 with a transport mechanism as shown in FIG. 4. If both rollers 18 rotate motor-driven in the same direction of rotation 23, each of the two ply belts 15.1; 15.2 can be wound up by winding from one roller 18 to the other roller 18 depending on the position of each ply belt, so that one of the filter areas can be moved into the intermediate space 14. In this way, the two filter areas of the first ply belt 15.1 and the second ply belt 15.2 can always be arranged behind each other and can be superimposed in terms of the X-ray absorption effect. With two filter areas per ply belt, up to four different filter variants are also possible here.

[0034] Each layer belt can also have more than two filter regions, for example three or four. The motorized rollers 18 can be controlled by a controller with respect to their movement, for example to set specific positioning of the filter regions.

[0035] FIG. 7 shows an X-ray system with a multi-layer X-ray detector 19 and a dual-energy X-ray source 21 controlled by a system controller 24. The multi-layer X-ray detector 19 and the dual-energy X-ray source 21 can be arranged, for example, fixed on a C-arm 22, which is spatially adjustable (for example, in an orbital, rotational, or translational manner). In this case, the dual-energy X-ray source 21 can be designed to emit a cone beam, and the multi-layer X-ray detector 19 can be designed as a flat detector. In the case of a flat detector, the sensor layer is also designed as flat. The system controller can also be used to control the positioning of the filter area, for example, by moving the motorized rollers 18 according to the planned application.

[0036] A computed tomography X-ray system having a gantry on which the multi-layer X-ray detector 19 and the dual energy X-ray source 21 are arranged is also possible. In such a case, the X-ray detector is designed as a line detector and the sensor layer is designed to be curved.

[0037] The material of the coating of the filter region can also be mixed with other materials that increase its flexibility and / or elasticity to allow for damage-free rolling. The filter material can be applied to an elastic carrier material.

[0038] The term includes individuals of male, female, or any other gender identity, regardless of grammatical usage of the term.

[0039] The present invention can be briefly summarized as follows. For particularly flexible usability with respect to dual energies, a multi-layer X-ray detector is provided which comprises at least a first and a second sensor layer, which are arranged behind the other in the X-ray projection direction, the first sensor layer designed to convert X-ray quanta of a first emission spectrum into a first signal and the second sensor layer designed to convert X-ray quanta of a second emission spectrum into a second signal, an intermediate space arranged between the two sensor layers, at least one layer belt designed as bendable, which has at least two filter regions with a plurality of material compositions and / or coatings, and a transport mechanism capable of bringing either the first filter region or the second filter region into the intermediate space.

Claims

1. at least a first sensor layer (10) and a second sensor layer (11), one of said sensor layers (10, 11) being arranged behind the other in an X-ray projection direction (13), said first sensor layer (10) being designed to convert X-ray quanta of a first spectrum into a first signal and said second sensor layer (11) being designed to convert X-ray quanta of a second spectrum into a second signal; an intermediate space (14) arranged between the two sensor layers (10, 11); at least one layer belt (15) designed to be flexible, having at least two filter regions (16; 17) with a plurality of material compositions and / or coatings or a conveying mechanism capable of conveying either the first filter region (16) or the second filter region (17) into said intermediate space (14); A multi-layer X-ray detector (19).

2. said layer belt (15) comprising a first spectral filter material having a first X-ray transmittance in said first filter region (16) and a second spectral filter material having a second X-ray transmittance in said second filter region (17), the first and second X-ray absorption coefficients are different; The multi-layer x-ray detector of claim 1 .

3. The multi-layer x-ray detector of claim 2 , wherein the first x-ray transmission is less than 25% based on a photon energy of 50 keV.

4. 4. The multi-layer X-ray detector of claim 2 or 3, wherein the first filter material includes at least one element of copper, tantalum, lead, aluminum, tin, brass, or iron.

5. A multi-layer X-ray detector according to any one of claims 2 to 4, wherein the second X-ray transmission is more than 60%, in particular more than 90%, based on a photon energy of 50 keV.

6. 6. A multi-layer X-ray detector according to any one of the preceding claims, wherein the layer belt (15) is designed to be capable of being wound up and / or unwound.

7. 7. The multi-layer X-ray detector according to claim 1, wherein the transport mechanism has rollers (18) via which the layer belt (15) is designed to be movable such that either the first filter area (16) or the second filter area (17) is transported into the intermediate space.

8. 8. A multi-layer X-ray detector according to claim 1, wherein the layer belt (15) and the transport mechanism are designed as conveyor belts, in particular as motorized conveyor belts.

9. the first sensor layer (10) having a first scintillator material of a first thickness and a first readout circuit designed to detect photons generated by the first scintillator material from X-ray quanta of the first spectrum and generate a first signal therefrom; the second sensor layer (11) comprises a second scintillator material of a second thickness and a second readout circuit designed to detect photons generated by the second scintillator material from X-ray quanta of the second spectrum and to generate a second signal therefrom; A multi-layer X-ray detector according to any one of claims 1 to 8.

10. a bendable second layer belt (15.2) having at least two filter regions (16.2; 17.2) with multiple material compositions and / or coatings; a transport mechanism capable of moving one of the filter regions (16.2; 17.2) of the second layer belt (15.2) into the intermediate space (14); 10. A multi-layer X-ray detector according to claim 1, comprising:

11. The multi-layer X-ray detector according to any one of claims 1 to 10, designed either as an X-ray flat detector or as a fan detector.

12. a dual energy X-ray source (21) designed to be switchable from emitting radiation of the first spectrum to emitting radiation of the second spectrum and vice versa; a system controller (24) for controlling the multi-layer X-ray detector (19) and the dual-energy X-ray source (21); An X-ray system comprising a multi-layer X-ray detector (19) according to any one of claims 1 to 11.

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