Multi-layer X-ray detector and X-ray system

Abstract

For particularly flexible application with regard to dual energy, a multi-layer X-ray detector is provided, comprising at least a first and a second sensor layer, which sensor layers are arranged one behind the other in the X-ray projection direction, wherein the first sensor layer is configured to convert X-ray quanta of a first emission spectrum into first signals and the second sensor layer is configured to convert X-ray quanta of a second emission spectrum into second signals, an intermediate space arranged between the two sensor layers, and at least one bendable layer band which has at least two filter areas with different material composition and / or coating, as well as a transport mechanism by which either a first filter area or a second filter area can be brought into the intermediate space.

Description

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

[0002] Modern X-ray technology uses dual-energy X-ray tubes, which are capable of emitting two different emission spectra. One of these spectra is generally high-energy, while the other is lower-energy. A significant energy difference between the two sensor layers is crucial. From the two different X-ray images produced in this way, the proportion of soft tissue can be subtracted, allowing for the measurement of bone density. The material composition of all body tissue can also be calculated.

[0003] Dual-energy X-ray detectors are also necessary for dual-energy X-ray tubes in order to read out the corresponding signals. One such well-known dual-energy X-ray detector is shown in Figure 9. Fig. 1 - generally has two scintillator-based sensor layers arranged one behind the other in the X-ray projection direction 13. During acquisition, the first sensor layer 10 and then the second sensor layer 11 are penetrated by an X-ray beam along the projection direction 13. To achieve sufficient spectral separation for dual-energy imaging, a filter layer (e.g., a 1 mm thick copper filter layer 12) is typically present between the two sensor layers. Such multilayer X-ray detectors are known, for example, from Ståhl, Fredrik et al., “Performance characterization of a prototype dual-layer cone-beam computed tomography system”, Medical Physics Vol. 48, 11 (2021), pages 6740–6754.

[0004] One disadvantage of multilayer X-ray detectors is that the high absorption of the filter layer leads to a reduced quantum efficiency of X-ray detection.

[0005] The object of the present invention is to provide a multi-layer X-ray detector which, in addition to the sufficient spectral separation of X-ray images by means of a dual energy X-ray source, enables improved quantum efficiency of X-ray detection.

[0006] The problem is solved according to the invention by a multi-layer X-ray detector according to claim 1 and an X-ray system with a multi-layer X-ray detector according to claim 12. Advantageous embodiments of the invention are the subject of the respective dependent claims.

[0007] The multilayer X-ray detector according to the invention comprises at least a first and a second sensor layer, which sensor layers are arranged one behind the other in the X-ray projection direction, wherein the first sensor layer is configured to convert X-ray quanta of a first spectrum (e.g., X-ray emission spectrum) into first signals and the second sensor layer is configured to convert X-ray quanta of a second spectrum (e.g., X-ray emission spectrum) into second signals, an intermediate space arranged between the two sensor layers, and at least one bendable layer band which has at least two filter areas with different material composition and / or coating, as well as a transport mechanism by which either a first filter area or a second filter area can be brought into the intermediate space.

[0008] The layered strip is particularly flexible and can be bent, folded, or rolled without damaging the strip itself or any coatings. The filter areas can be large, in particular having an area approximately equal to the area of ​​the second sensor layer, so that the entire gap can be covered by one of the filter areas if required. The layered strip itself preferably has a total area at least twice that of the second sensor layer (at least two filter areas), but can also be significantly larger (e.g., neutral areas between the filter areas or even three or more filter areas). The layered strip is preferably arranged such that, in the area of ​​the gap, the surface normal of the layered strip is parallel to the X-ray projection direction.

[0009] The transport mechanism allows either the first or the second filter area, with its respective material composition and thus filtering effect, to be moved into the space between the two sensor layers as needed. This enables the user to select the required filtration for the current application and adjust it quickly and easily. Even during an ongoing procedure, a rapid switch between the two filter areas can be performed, for example, within a few seconds. The X-ray detector offers high flexibility in the spectral separation of at least two spectra from the X-ray images. The filter areas have a homogeneous composition and filtering effect.

[0010] The use of such layered tapes also ensures a high reliability of the filter effect; the risk of artifacts in resulting X-ray images is low.

[0011] According to one embodiment of the invention, the layered band comprises a first spectral filter material with a first X-ray transmittance in the first filter area and a second spectral filter material with a second X-ray transmittance in the second filter area, wherein the first and second X-ray transmittances differ. Depending on the requirements, a correspondingly different filter effect can be selected by means of the different X-ray transmittances.

[0012] In particular, the first X-ray transmittance is less than 25%, based on an X-ray photon energy of 50 keV, so that the first filter region exhibits particularly effective X-ray absorption. In this way, positioning the first filter region in the intermediate space allows for particularly good spectral separation of the emission spectra and thus particularly good dual-energy resolution, enabling a precise analysis of the material composition of the object under investigation. For such a purpose, the first filter material can contain or consist of at least one of the elements copper, tantalum, lead, aluminum, tin, brass, or iron. For example, the first filter region can be sufficiently thick so that it absorbs low-energy photons (e.g., 40–80 keV) adequately while simultaneously minimizing the absorption of high-energy photons (e.g., 50–80 keV).100-120keV), so that enough signal still arrives in the second sensor layer for reasons of detection and dose efficiency.

[0013] Advantageously, for a particularly large difference between the filter areas, the second X-ray transmittance is above 60%, especially above 90%, based on an X-ray photon energy of 50 keV, so that the second filter area has only a weak or no X-ray-absorbing effect. Positioning the second filter area in the gap between the two allows for particularly good quantum efficiency in X-ray imaging. An X-ray detector with a first filter area of ​​low X-ray transmittance and a second filter area of ​​high X-ray transmittance can therefore, depending on the conveyor belt setting, ensure good spectral separation in dual-energy operation and high quantum efficiency in normal operation, making it suitable and usable for various applications with equally high quality.

[0014] According to a further embodiment of the invention, the layered belt is designed to be wound and / or unwound. For this purpose, the transport mechanism can, for example, include rollers onto which the layered belt is wound and unwound. Additionally, one or more motors can be provided, which, for example, rotate the rollers and thereby move the layered belt. Thus, for example, a roller can be located on each side of the sensor layers outside the gap, and unwinding the transport belt on one roller while simultaneously winding it on the other roller brings the respective filter area into the gap.

[0015] According to a further embodiment of the invention, the transport mechanism has rollers over which the layered belt is movable such that either the first filter area or the second filter area is transported into the space between the rollers. In particular, the layered belt and the transport mechanism are designed as a conveyor belt, especially a motorized conveyor belt. In this form, the layered belt can be designed as a continuous, endless conveyor belt stretched over, for example, two rollers, which is partially arranged in the space between the rollers, with the two filter areas being located on opposite sides of the rollers. The motor drive rotates the two rollers and moves the conveyor belt, so that, depending on the position, one of the filter areas can be positioned in the space between the rollers.

[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, which first readout circuit is configured to detect photons generated by the first scintillator material from X-ray quanta of the first spectrum and to generate first signals from them. The second sensor layer comprises a second scintillator material of a second thickness and a second readout circuit, which second readout circuit is configured to detect photons generated by the second scintillator material from X-ray quanta of the second spectrum and to generate second signals from them. The operating principle of sensor layers in X-ray detectors is generally known.

[0017] According to a further embodiment of the invention, the multilayer X-ray detector has a second flexible layered band, which comprises at least two filter areas with different material compositions and / or coatings, as well as a transport mechanism by which either a first filter area or a second filter area can be moved into the space between the layers. A multitude of different filtering effects can be generated by using two or more layered bands, depending on which filter areas are positioned in the space simultaneously. Such an X-ray detector offers a wide range of possibilities and variations, from strong spectral separation to very high quantum efficiency.

[0018] According to a further embodiment of the invention, the multi-layer X-ray detector is configured either as a flat-panel X-ray detector or as a fan-shaped detector. In a flat-panel X-ray detector for cone-beam X-ray sources, the sensor surfaces are generally flat and relatively large, for example [20x30 cm or 30x40 cm], and consequently, the conveyor belt and filter areas are also correspondingly large. A fan-shaped detector for CT applications is generally curved in a circular segment shape, e.g., long but narrow. The conveyor belt and filter areas are also curved accordingly.

[0019] The invention further comprises an X-ray system comprising a multilayer X-ray detector according to one of the preceding claims, comprising a dual energy X-ray source which is switchable from emission of the first emission spectrum to emission of the second emission spectrum and vice versa, and comprising a system control for controlling the multilayer 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 reference to schematically illustrated exemplary embodiments in the drawing, without thereby limiting the invention to these exemplary embodiments. The drawing shows: Fig. 1 a sectional view of a state-of-the-art multi-layer X-ray detector; Fig. 2 a sectional view of a multilayer X-ray detector according to the invention with a layered band having two filter areas in a first state; Fig. 3 a sectional view of a multilayer X-ray detector according to the invention with a layered band having two filter areas in a second state; Fig. 4 a sectional view of another multilayer X-ray detector according to the invention with a layered band having two filter areas in a first state; Fig. 5 a sectional view of a multilayer X-ray detector according to the invention with two layer bands; Fig. 6 a sectional view of another multilayer X-ray detector according to the invention with two layer bands; and Fig. 7 an X-ray system with a multi-layer X-ray detector and a dual energy X-ray source.

[0021] In the Fig. Figure 1 shows a known dual-energy X-ray detector 9, as already described, in which a permanently installed, strongly X-ray-absorbing filter layer is present between a first scintillator-based sensor layer 10 and a second scintillator-based sensor layer 11 in order to achieve sufficient spectral separation for dual-energy imaging. However, sufficient quantum efficiency is not possible with such a dual-energy X-ray detector 9 during normal operation.

[0022] In the Fig. Figures 2 to 6 show multilayer X-ray detectors 19 with layered bands 15, in which filter regions of a flexible layered band 15 can be transported by various transport mechanisms into a space 14 between the first sensor layer 10 and the second sensor layer 11. Depending on the coating or composition of the filter regions, different filters can be created, which achieve different effects, e.g., by either providing spectral separation in dual-energy operation or ensuring sufficient quantum efficiency in normal operation.

[0023] In the Fig. 2 and Fig. Figure 3 shows a multilayer X-ray detector 19 with a first scintillator-based sensor layer 10 and a second scintillator-based sensor layer 11, which sensor layers 10 and 11 are arranged one behind the other in the X-ray projection direction 13. A gap 14 is located between the two sensor layers 10 and 11, for example, extending over the entire length and width of the sensor layers. The multilayer X-ray detector 19 also has a layer belt 15 designed as a flexible, rollable, "endless" conveyor belt, which is stretched over, for example, two rollers 18, wherein the rollers 18 are arranged on both sides of the sensor layers 10 and 11, in particular the second sensor layer 11. Preferably, the rollers 18 are arranged outside the angle of incidence of the X-ray radiation.The conveyor belt is located at least partially in the space 14 between the two sensor layers 10; 11 and extends at least partially, and in particular completely, over the length and width of the sensor layers 10; 11. By rotating 23 the rollers, the conveyor belt is rolled over the rollers 18 and thereby changed in its position.

[0024] The conveyor belt has at least two filter sections, which, for example, contain different spectral filter materials (different composition, thickness, density, etc.) with different X-ray transmittance. For example, a first filter section 16 can contain a first filter material with low X-ray transmittance, and a second filter section 17 can contain a second filter material with high X-ray transmittance. The filter materials can, for example, be applied to the conveyor belt as a coating. The conveyor belt 15 can be in the form of a film. The conveyor belt itself can also have different material compositions and / or different thicknesses and / or densities in the respective filter sections.

[0025] The first filter area 16 can, for example, have a coating containing one or more of the materials copper, tantalum, lead, aluminum, brass, tin, or iron, or be at least partially composed of these materials. The coating is thick enough to exert a significant filtering effect (e.g., 1 mm copper). The second filter area 17 can have only a very thin coating of a material with high X-ray transmittance, or no coating at all (e.g., just the layered strip / foil), thus exhibiting an X-ray transmittance close to 100%. Alternatively, the first filter area can have a thick coating and the second filter area a thin coating of the same material.

[0026] The sensor layers 10 and 11 are structured similarly to those in known multilayer X-ray detectors. The first sensor layer 10 can comprise a first scintillator material of a first thickness and a first readout circuit, while the second sensor layer 11 can comprise a second scintillator material of a second thickness and a second readout circuit. The respective readout circuits are designed to detect photons generated by the first scintillator material from X-ray quanta of the corresponding emission spectrum and to generate signals from these photons, which are then used to create X-ray images.

[0027] Depending on requirements, either the first filter area 16 or the second filter area 17 can now be moved into the space 14 by rotating the rollers 18, e.g., by means of a motor, in the same direction 23. The rollers can have drives (not shown) for this purpose. If the first filter area 16 with the low X-ray transmittance is located in the space 14 – shown in Fig. 2 - and extends over the entire sensor area of ​​the second sensor layer 11, spectral filtering occurs when irradiated by a dual-energy X-ray source with different emission spectra, allowing tissue compositions to be determined from the resulting X-ray images (e.g., by subtraction). If the second filter area 17 with high X-ray transmittance is located in the space 14 - shown in Fig. 3 - thus, a composite X-ray image with high quantum efficiency can be generated from the two X-ray images.

[0028] The transport mechanism can also be used - as in Fig. As shown in Figure 4, the sensor layer 15 is designed such that two rollers 18 are rotatably arranged on both sides of the second sensor layer 11 outside the space 14, and the layer strip 15 is wound from one roller 18 onto the other. This is achieved, for example, by motor-driven rotation of both rollers 18 in the same direction of rotation 23. In this way, a filter area 16; 17 can also be positioned between the rollers 18 so that it is completely located in the space 14 and extends, for example, over the second sensor surface 11. To ensure uniform filtration, the layer strip 15 has a (for example, predefined) tension between the rollers 18. To maintain such tension, a spring mechanism can, for example, be provided in one or both of the rollers 18.

[0029] In the Fig. 5 and Fig. Figure 6 shows further embodiments of multilayer X-ray detectors 19, each of which has two transport mechanisms with layered bands, the filter areas of which can be arranged one behind the other in the space 14 in the X-ray projection direction 13. This allows for the creation of further filtering options.

[0030] In the Fig. In Figure 5, for example, two conveyor belts are present: a first conveyor belt 15.1, designed as an endless conveyor belt, which is stretched over two rollers 18 and has a first filter area 16 and a second filter area 17; and a second conveyor belt 15.2, also designed as an endless conveyor belt, which is stretched over two rollers 18 and has a third filter area 16.2 and a fourth filter area 17.2. The first conveyor belt 15.1 is, for example, arranged within the second conveyor belt 15.2. The filter areas can be superimposed within the space 14 in the X-ray projection direction 13 and combined as required. For example, the first filter area 16 of the first conveyor belt 15.1 can be combined with the third filter area 16.2 of the second conveyor belt 15.2 or, alternatively, with the fourth filter area 17.2 of the second conveyor belt 15.2. The superimposition results in a cumulative filtering effect.By combining and depending on the individual filters, up to four different filter variants are possible here.

[0031] Each conveyor belt can have a filter area with low X-ray transmittance and a filter area with high X-ray transmittance. The conveyor belts can consist of, for example, a film or a strip, and be coated accordingly in the filter areas or assembled from different sections. The materials of the filter areas can vary in composition, density, and thickness. The conveyor belts and their coatings are flexible and bendable and should not develop cracks or breaks during unwinding.

[0032] In the Fig. Figure 6 shows two layered belts 15.1 and 15.2 arranged one behind the other in the direction of X-ray projection 13, each with two rollers 18, each of which has a transport mechanism as in Fig. Figure 4 shows that each of the two layered belts 15.1 and 15.2 can be wound from one roller 18 to the other by unwinding it in the same direction of rotation 23 when both rollers 18 are rotated by motor. This allows one of the filter areas for each layered belt to be moved into the space 14, depending on its position. In this way, two filter areas—one from the first layered belt 15.1 and one from the second layered belt 15.2—can always be arranged one behind the other and thus superimposed in their X-ray absorption effects. With two filter areas per layered belt, up to four different filter variants are possible.

[0033] Each conveyor belt can also have more than two, e.g., three or four filter areas. The motor-driven rollers 18 can, for example, be controlled by a controller with regard to their movement in order to set a specific positioning of the filter areas.

[0034] In the Fig.Figure 7 shows an X-ray system with a multi-layer X-ray detector 19 and a dual-energy X-ray source 21, which is controlled by a system controller 24. The multi-layer X-ray detector 19 and the dual-energy X-ray source 21 can, for example, be fixedly mounted on a C-arm 22, which is spatially adjustable (e.g., orbitally, rotationally, or translationally). In this case, the dual-energy X-ray source 21 can be configured to emit a cone beam, and the multi-layer X-ray detector 19 can be configured as an area detector. In an area detector, the sensor layers are also planar. The system controller can also be used to control the positioning of the filter areas by moving the motorized rollers 18, depending, for example, on the intended application.

[0035] A computed tomography X-ray system is also possible, which has a gantry in which the multi-layer X-ray detector 19 and the dual-energy X-ray source 21 are arranged. In such a case, the X-ray detector is designed as a line detector and the sensor layers are curved.

[0036] The coating material for the filter areas can also be mixed with other materials that increase flexibility and / or elasticity to allow for damage-free unwinding. The filter material can be applied to an elastic backing material.

[0037] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identities are included.

[0038] The invention can be summarized as follows: For particularly flexible application with regard to dual energy, a multi-layer X-ray detector is provided, comprising at least a first and a second sensor layer, which sensor layers are arranged one behind the other in the X-ray projection direction, wherein the first sensor layer is configured to convert X-ray quanta of a first emission spectrum into first signals and the second sensor layer is configured to convert X-ray quanta of a second emission spectrum into second signals, an intermediate space arranged between the two sensor layers, and at least one bendable layer band, which has at least two filter areas with different material composition and / or coating, as well as a transport mechanism by which either a first filter area or a second filter area can be brought into the intermediate space. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited non-patent literature

[0000] Ståhl, Fredrik et al., “Performance characterization of a prototype dual-layer cone-beam computed tomography system”, Medical Physics Vol. 48, 11 (2021), pages 6740-6754

[0003]

Claims

[1] Multi-layer X-ray detector (19), comprising • at least one first sensor layer (10) and one second sensor layer (11), which sensor layers (10: 11) are arranged one behind the other in the X-ray projection direction (13), wherein the first sensor layer (10) is designed to convert X-ray quanta of a first spectrum into first signals and the second sensor layer (11) is designed to convert X-ray quanta of a second spectrum into second signals, • a gap (14) arranged between the two sensor layers (10; 11), and • at least one flexible layered band (15) which has at least two filter regions (16; 17) with different material compositions and / or coatings, and a transport mechanism by which either a first filter region (16) or a second filter region (17) can be brought into the intermediate space (14). [2] Multi-layer X-ray detector according to claim 1, wherein the layer band (15) has a first spectral filter material with a first X-ray transmittance in the first filter region (16) and a second spectral filter material with a second X-ray transmittance in the second filter region (17), wherein the first and the second X-ray absorption coefficients differ. [3] A multilayer X-ray detector according to claim 2, wherein the first X-ray transmittance is less than 25% based on a photon energy of 50 keV. [4] A multilayer X-ray detector according to claim 2 or 3, wherein the first filter material contains at least one of the elements copper, tantalum, lead, aluminum, tin, brass or iron. [5] Multilayer X-ray detector according to one of claims 2 to 4, wherein the second X-ray transmittance is greater than 60%, in particular greater than 90%, based on a photon energy of 50 keV. [6] Multi-layer X-ray detector according to one of the preceding claims, wherein the layered strip (15) is designed to be rollable and / or unrollable. [7] Multi-layer X-ray detector according to one of the preceding claims, wherein the transport mechanism comprises rollers (18) over which the layered belt (15) is designed to be movable in such a way that either the first filter region (16) or the second filter region (17) is transported into the intermediate space. [8] Multi-layer X-ray detector according to one of the preceding claims, wherein the layer belt (15) and the transport mechanism are designed as a conveyor belt, in particular as a motorized conveyor belt. [9] Multi-layer X-ray detector according to one of the preceding claims, wherein the first sensor layer (10) comprises a first scintillator material of a first thickness and a first readout circuit, which first readout circuit is designed to detect photons generated from X-ray quanta of the first spectrum by the first scintillator material and to generate first signals therefrom, and wherein the second sensor layer (11) comprises a second scintillator material of a second thickness and a second readout circuit, which second readout circuit is designed to detect photons generated from X-ray quanta of the second spectrum by the second scintillator material and to generate second signals therefrom. [10] Multi-layer X-ray detector according to one of the preceding claims, comprising a second flexible layered band (15.2) which has at least two filter regions (16.2; 17.2) with different material composition and / or coating, and a transport mechanism by which one of the filter regions (16.2; 17.2) of the second layered band (15.2) can be brought into the intermediate space (14). [11] Multi-layer X-ray detector according to one of the preceding claims, which is designed either as a flat X-ray detector or as a fan detector. [12] X-ray system, comprising a multi-layer X-ray detector (19) according to one of the preceding claims, comprising a dual energy X-ray source (21) which is designed to be switchable from emitting the first spectrum to emitting the second spectrum and vice versa, and comprising a system controller (24) for controlling the multi-layer X-ray detector (19) and the dual energy X-ray source (21).

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