X-RAY DETECTOR AND X-RAY IMAGING APPARATUS

Abstract

An X-ray detector (100) and an X-ray imaging apparatus (500) with such X-ray detector (100) are provided. The X-ray detector (100) comprises at least three scintillator layers (102a-e) for converting X-ray radiation into scintillator light (110), and at least two sensor arrays (104a, 104b), each comprising a plurality of photosensitive pixels (108a, 108b) aranged on a bendable substrate (106a, 106b) for receiving scintillator light (110) emitted by at least one of the scintillator layers (102a-e). Therein, a number of the scintillator layers (102a-e) is larger than a number of the sensor arrays (104a, 104b). The at least three scintillator layers (102a-e) and the at least two sensor arrays (104a, 104b) are arranged on top of each other, wherein at least one of the sensor arrays (104b) is arranged between at least two of the scintillator layers (102a-e), such that said at least two scintillator layers (102a-e) are optically coupled to said at least one sensor array (104b) at two opposite sides (103a, 103b) of said at least one sensor array (104b). Further, said at least one sensor (104b) array is configured to receive light emitted by said at least two scintillator layers (102a-e).

Claims

1. An X-ray detector, comprising: at least three scintillator layers for converting X-ray radiation into scintillator light; and at least two sensor arrays, each comprising a plurality of photosensitive pixels for receiving scintillator light emitted by at least one of the scintillator layers; wherein the photosensitive pixels of each of the sensor arrays are arranged on a bendable substrate; wherein a number of the scintillator layers is larger than a number of the sensor arrays; wherein the at least three scintillator layers and the at least two sensor arrays are arranged on top of each other; wherein at least one of the sensor arrays is arranged between at least two of the scintillator layers, such that said at least two scintillator layers are optically coupled to said at least one sensor array at two opposite sides of said at least one sensor array; and wherein said at least one sensor array is configured to receive light emitted by said at least two scintillator layers.

2. The X-ray detector according to claim 1, wherein each of the at least two sensor arrays is arranged between at least two of the scintillator layers; and wherein each of the sensor arrays is configured to receive light emitted by at least two of the scintillator layers arranged on two opposite sides of the respective sensor array.

3. The X-ray detector according to claim 1, further comprising: at least one switchable optical filter switchable between a first state in which the switchable optical filter is transparent for the scintillator light and a second state in which the switchable optical filter is blocking the scintillator light.

4. The X-ray detector according to claim 3, wherein the at least one switchable optical filter is an electrochromic optical filter.

5. The X-ray detector according to claim 3, wherein the at least one switchable optical filter is arranged between the at least two sensor arrays.

6. The X-ray detector according to claim 3, wherein the X-ray detector comprises at least one center scintillator layer arranged between the at least two sensor arrays; and wherein the at least one switchable optical filter is arranged between at least one of the sensor arrays and the at least one center scintillator layer.

7. The X-ray detector according to claim 3, further comprising: a first outer scintillator layer arranged on a first outer side of the X-ray detector; a second outer scintillator layer arranged on a second outer side of the X-ray detector opposite the first outer side; at least one center scintillator layer arranged between the at least two sensor arrays; wherein the at least one switchable optical filter is arranged between each of the at least two sensor arrays and the at least one center scintillator layer.

8. The X-ray detector according to claim 7, wherein a further center scintillator layer is arranged between the at least two sensor arrays; and wherein at least one further switchable optical filter is arranged between the two center scintillator layers.

9. The X-ray detector according to claim 1, further comprising at least one opaque layer for absorbing scintillator light.

10. The X-ray detector according to claim 1, wherein the substrate comprises at least one of glass and polymer material.

11. The X-ray detector according to claim 1, further comprising at least one metal layer for filtering the X-ray radiation.

12. An X-ray imaging apparatus, comprising: an X-ray source arrangement for emitting X-ray radiation; an X-ray detector comprising: at least three scintillator layers for converting the X-ray radiation into scintillator light; and at least two sensor arrays, each comprising a plurality of photosensitive pixels for receiving scintillator light emitted by at least one of the scintillator layers; wherein the photosensitive pixels of each of the sensor arrays are arranged on a bendable substrate; wherein a number of the scintillator layers is larger than a number of the sensor arrays; wherein the at least three scintillator layers and the at least two sensor arrays are arranged on top of each other; wherein at least one of the sensor arrays is arranged between at least two of the scintillator layers, such that said at least two scintillator layers are optically coupled to said at least one sensor array at two opposite sides of said at least one sensor array; and wherein said at least one sensor array is configured to receive light emitted by said at least two scintillator layers; and a controller for controlling at least one of the X-ray source arrangement and the X-ray detector.

13. The X-ray imaging apparatus according to claim 12, wherein the X-ray source arrangement and the X-ray detector are rotatable around a rotational axis of the X-ray imaging apparatus; wherein the X-ray source arrangement comprises at least a first X-ray source for emitting a first X-ray beam of a first energy range and a second X-ray source for emitting a second X-ray beam of a second energy range different from the first energy range; wherein the controller is configured to trigger the first X-ray source and acquire a first X-ray image, when the first X-ray source is located at an acquiring position around the rotational axis; and wherein the controller is configured to trigger the second X-ray source and acquire a second X-ray image when the second X-ray source is located at the acquiring position around the rotational axis.

14. The X-ray imaging apparatus according to claim 13, wherein the X-ray source arrangement comprises an X-ray tube with a first focal spot for emitting the first X-ray beam and a second focal spot for emitting the second X-ray beam.

15. A method for operating an X-ray imaging apparatus with an X-ray detector according to claim 1 and an X-ray source arrangement; wherein the X-ray source arrangement comprises a first X-ray source for emitting a first X-ray beam of a first energy range and a second X-ray source for emitting a second X-ray beam of a second energy range different from the first energy range; the method comprising the steps of: emitting the first X-ray beam with the first X-ray source, when the first X-ray source is located at an acquiring position around a rotational axis of the X-ray imaging apparatus; acquiring a first X-ray image with the X-ray detector, when the first X-ray source is located at the acquiring position; emitting the second X-ray beam with the second X-ray source, when the second X-ray source is located at the acquiring position; and acquiring a second X-ray image with the X-ray detector, when the second X-ray source is located at the acquiring position.

16. The X-ray imaging apparatus according to claim 13, wherein the X-ray source arrangement comprises a first X-ray tube for emitting the first X-ray beam and a second X-ray tube for emitting the second X-ray beam.

17. A method of operating X-ray imaging apparatus, emitting X-ray radiation; converting X-ray radiation into scintillator light using at least three scintillator layers; and providing at least two sensor arrays, each comprising a plurality of photosensitive pixels for receiving scintillator light emitted by at least one of the scintillator layers; wherein the photosensitive pixels of each of the sensor arrays are arranged on a bendable substrate; wherein a number of the scintillator layers is larger than a number of the sensor arrays; wherein the at least three scintillator layers and the at least two sensor arrays are arranged on top of each other; wherein at least one of the sensor arrays is arranged between at least two of the scintillator layers, such that said at least two scintillator layers are optically coupled to said at least one sensor array at two opposite sides of said at least one sensor array; and wherein said at least one sensor array is configured to receive light emitted by said at least two scintillator layers.

18. The X-ray detector according to claim 1, further comprising at least one reflective layer for reflecting scintillator light.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The subject matter of the invention will be explained in more detail in the following with reference to exemplary embodiments which are illustrated in the attached figures, wherein:

[0052] FIGS. 1A to 1D each show schematically an X-ray detector according to an example;

[0053] FIG. 2 shows schematically an X-ray detector according to an embodiment;

[0054] FIG. 3A shows schematically an X-ray detector according to an embodiment;

[0055] FIGS. 3B, 3C, 3D each schematically illustrate an operation mode of the X-ray detector of FIG. 3A;

[0056] FIGS. 4A and 4B show schematically an X-ray detector according to an embodiment;

[0057] FIGS. 5A and 5B show schematically an X-ray detector according to an embodiment;

[0058] FIG. 6 shows schematically an X-ray detector according to an embodiment;

[0059] FIG. 7 shows schematically an X-ray detector according to an embodiment;

[0060] FIG. 8 shows schematically an X-ray imaging apparatus according to an embodiment;

[0061] FIG. 9 shows schematically an X-ray imaging apparatus according to an embodiment;

[0062] FIG. 10 shows a flow chart illustrating steps of a method for operating an X-ray imaging apparatus according to an embodiment.

[0063] In principle, identical, like and/or similar elements are provided with the same reference symbols in the figures. The figures are not to scale.

DETAILED DESCRIPTION OF EMBODIMENTS

[0064] FIG. 1A shows schematically an X-ray detector 100 according to an example.

[0065] The X-ray detector 100 of FIG. 1A comprises a scintillator layer 102 arranged on top of a sensor array 104. Therein, the scintillator layer 102 is stacked on top of the sensor array 104 along a stacking direction 101 of the X-ray detector 100.

[0066] The sensor array 104 comprises a glass substrate 106, on which a plurality of photosensitive pixels 108 are arranged.

[0067] X-ray radiation may impinge along an impinging direction 200 onto the X-ray detector 100, wherein the impinging direction 200 may be substantially antiparallel to the stacking direction 101. X-ray photons and/or X-ray quanta impinging onto the scintillator layer 102 are at least partly converted into scintillator light 110, which in turn is detected by at least a part of the photosensitive pixels 108 of the sensor array 104.

[0068] FIG. 1B shows schematically an X-ray detector 100 according to an example. If not stated otherwise, the X-ray detector 100 of FIG. 1B comprises the same features and/or elements as the X-ray detector 100 of FIG. 1A.

[0069] The X-ray detector 100 of FIG. 1B is a so-called dual energy X-ray detector 100 comprising a first scintillator layer 102a, a second scintillator layer 102b and a first sensor array 104a arranged between the first scintillator layer 102a and the second scintillator layer 102b. Underneath the second scintillator layer 102b a second sensor array 104b is arranged. Accordingly, along the stacking direction 101, the second sensor array 104b, the second scintillator layer 102b, the first sensor array 104a and the first scintillator layer 102a are stacked on top each other.

[0070] The first sensor array 104a comprises a first glass substrate 106a, on which a plurality of photosensitive pixels 108a is arranged. Similarly, the second sensor array 104b comprises a second glass substrate 106b, on which a plurality of photosensitive pixels 108b is arranged.

[0071] X-ray radiation impinging onto the X-ray detector 100 along impinging direction 200 usually comprises a certain energy range of X-ray photons. A low-energy portion of the X-ray radiation may be absorbed in the first scintillator layer 102a and generate scintillator light 110 in the first scintillator layer 102a. This scintillator light 110 generated in the first scintillator layer 102a is then detected by the first sensor array 104a. Thus, the first sensor array 104a may be configured for acquiring a low-energy X-ray image.

[0072] A high-energy portion of the X-ray radiation may, due to an increased mean free path length of high-energy X-ray photons, traverse the first scintillator layer 102a and the first sensor array 104a and generate scintillator light 110 in the second scintillator layer 102b. The scintillator light 110 generated in the second scintillator layer 102b by high-energetic X-ray photons is then detected by the second sensor array 104b. Thus, the second sensor array 104b may be configured for acquiring a high-energy X-ray image. Accordingly, by means of the X-ray detector 100 of FIG. 1B an image pair with a low-energy image and a high-energy image may be acquired in a single exposure of the X-ray detector 100 with X-ray radiation. In order to increase an energy separation between the first sensor array 104a and the second sensor array 104b, the second scintillator layer 102b may be thicker than the first scintillator layer 102a, wherein a thickness of the scintillator layers 102a,b may be measured along the stacking direction 101.

[0073] FIG. 1C shows schematically an X-ray detector 100 according to an example. If not stated otherwise, the X-ray detector 100 of FIG. 1C comprises the same features and/or elements as the X-ray detectors 100 of FIGS. 1A and 1B.

[0074] In contrast to the X-ray detector 100 of FIG. 1B, the X-ray detector 100 of FIG. 1C comprises a first sensor array 104a with a substrate 106a comprising polymer material. The substrate 106a may be a thin polymer foil, on which the photosensitive pixels 108a are arranged. Such sensor array 104a is also referred to as detector on foil.

[0075] Similarly, also the substrate 106b of the second sensor array 104b is a thin substrate foil comprising polymer material. This may allow to provide a cost-efficient, compact, flat, curved, bendable and/or flexible X-ray detector 100.

[0076] Analog to the X-ray detector 100 of FIG. 1B, the X-ray detector of FIG. 1C is a dual energy X-ray detector 100 configured for acquiring a low-energy image and a high energy image.

[0077] FIG. 1D shows schematically an X-ray detector 100 according to an example. If not stated otherwise, the X-ray detector 100 of FIG. 1D comprises the same features and/or elements as the X-ray detectors 100 shown in previous figures.

[0078] In contrast to the X-ray detector 100 of FIG. 1C, the first sensor array 104a and the second sensor array 104b of the X-ray detector 100 of FIG. 1D are arranged back-to-back. Accordingly, along the stacking direction 101, the X-ray detector 100 comprises the second scintillator layer 102b, the second sensor array 104b, the first sensor array 104a, and the first scintillator layer 102a.

[0079] Given the fact that scintillator light 110 is generated and/or emitted in each spatial direction, the second sensor array 104b of FIG. 4D is also configured to primarily detect the high energy portion of X-ray radiation.

[0080] FIG. 2 shows schematically an X-ray detector 100 according to an embodiment. If not stated otherwise, the X-ray detector 100 of FIG. 2 comprises the same features and/or elements as the X-ray detectors 100 shown in previous figures.

[0081] The X-ray detector 100 of FIG. 2 generally comprises a plurality of scintillator layers 102a, 102b, 102c and a plurality of sensor arrays 104a, 104b, wherein a number of scintillator layers 102a-c is larger than a number of sensor arrays 104a,b, i.e. the X-ray detector 100 comprises more scintillator layers 102a-c than sensor arrays 104a,b. In the example shown in FIG. 2, the X-ray detector 100 comprises in total three scintillator layers 102a-c and two sensor arrays 104a,b. Thus, the detector 100 of FIG. 2 may refer to a dual energy detector 100. However, the X-ray detector 100 may also comprise more than three scintillator layers 102a-c and/or more than two sensor arrays 104a,b.

[0082] More specifically, the X-ray detector 100 of FIG. 2 comprises a first outer scintillator layer 102a arranged on a first outer side 112 of the X-ray detector 100. The first outer side 112 may refer to a side of the X-ray detector 100, onto which X-ray radiation may impinge first along the impinging direction 200.

[0083] The X-ray detector 100 further comprises a second outer scintillator layer 102c arranged on a second outer side 114 of the X-ray detector 100. The first outer side 112 and the second outer side 114 of the X-ray detector 100 oppose each other and/or are arranged opposite to each other.

[0084] Further, the X-ray detector 100 comprises a center scintillator layer 102b arranged between the first outer scintillator layer 102a and the second outer scintillator layer 102c.

[0085] Moreover, the X-ray detector 100 comprises a first sensor array 104a arranged between the first outer scintillator layer 102a and the center scintillator layer 102b. A second sensor array 104b is arranged between the center scintillator layer 102b and the second outer scintillator layer 102c.

[0086] Accordingly, along the stacking direction 101 the X-ray detector 100 is composed of the second outer scintillator layer 102c, the second sensor array 104b, the center scintillator layer 102b, the first sensor array 104a, and the first outer scintillator layer 102a. Apart from that, the X-ray detector 100 is symmetric and/or symmetrically arranged with respect to a center plane 105 of the X-ray detector 100. Therein, the center plane 105 may be orthogonal to the stacking direction 101 and parallel to the first and/or second sides 112, 114 of the X-ray detector 100.

[0087] The first sensor array 104a comprises a first substrate 106a, on which a plurality of photosensitive pixels 108a is arranged. The first substrate 106a may be arranged on a side of the first sensor array 104a facing the center scintillator layer 102b or alternatively on a side of the first sensor array 104a facing the first outer scintillator layer 102a. Similarly, the second sensor array 104b comprises a second substrate 106b, on which a plurality of photosensitive pixels 108b is arranged. The second substrate 106b may be arranged on a side of the second sensor array 104b facing the center scintillator layer 102b or alternatively on a side of the second sensor array 104b facing the second outer scintillator layer 102c. The first and second substrates 106a,b may be thin and/or ultra-thin substrates. The first and second substrates 106a,b may comprise glass and/or polymer material. By way of example, the first and second substrates 106a,b may be substrate foils comprising Polylmide (PI), PolyTetraFluoroEthylene (PTFE), PolyEthylene Terephtalate (PET), PolyEthylen Naphtalate (PEN), and/or any combination thereof. A thickness of each of the first and second substrates 106a,b may range from several m to about 1 mm, and particularly from about 5 m to 500 m, more particularly from about 10 m to about 100 m. Each of (or at least one of) the first and second substrates 106a,b may be transparent for scintillator light 110.

[0088] The photosensitive pixels 108a,b may be arranged in an arbitrary pattern on the respective first or second substrate 106a,b. However, pixels 108a,b may be arranged in several columns and/or several rows in the respective substrate 106a,b. Apart from that, also read-out electronics for receiving electrical signals from the photosensitive pixels 108a,b and/or addressing electronics for addressing the photosensitive pixels 108a,b may be arranged on the respective first and/or second substrate 106a,b.

[0089] A first side 103a of the second sensor array 104b is optically coupled to the center scintillator 102b, such that the second sensor array 104b receives and/or collects scintillator light 110 emitted by the center scintillator layer 102b at the first side 103a. A second side 103b of the second sensor array 104b, which second side 113b opposes and/or is arranged opposite to the first side 103a, is optically coupled the second outer scintillator layer 102c, such that the second sensor array 104b receives and/or collects scintillator light 110 emitted by the second outer scintillator layer 102c at the second side 103b. Thus, the second sensor array 104b receives and/or collects scintillator light 110 from two scintillator layers 102b, 102c, which are arranged on two opposite sides 103a, 103b of the second sensor array 104b, as depicted in the encircled region in FIG. 2. Generally, this allows to design the center scintillator layer 102b thinner than e.g. the second scintillator layer 102b shown in the example of FIG. 1C, which in turn results in an increased DQE (detective quantum efficiency) and/or in an optimized MTF (modulation transfer function).

[0090] In analogy to the second sensor array 104b, also the first sensor array 104a may be configured to receive and/or collect scintillator light 110 from two opposite sides of the first sensor array 104a. Accordingly, the first sensor array 104a may be optically coupled to the first outer scintillator layer 102a on a first side of the sensor array 104a, and optically coupled to the center scintillator layer 102b on a second side of the sensor array 104 opposite to the first side.

[0091] However, in the example shown in FIG. 2, a switchable optical filter 116 is arranged between the first sensor array 104a and the center scintillator layer 102b. It is to be noted that the switchable optical filter 116 is optional only. The switchable optical filter 116 is switchable between a first state, in which the switchable optical filter 116 is transparent for scintillator light 110, and a second state, in which the switchable optical filter 116 is blocking scintillator light 110. In the second state the scintillator light 110 may be absorbed by the switchable optical filter 116 and/or it may be reflected by the switchable optical filter 116. The switchable optical filter 116 may be configured to switch between the first state and the second state by receiving an electrical signal, e.g. from a controller of an X-ray imaging apparatus (see FIGS. 7 and 8) and/or from a controller of the X-ray detector 100. The switchable optical filter 116 may comprise e.g. viologen, transition metal oxide, such as e.g. tungsten trioxide, and/or any other suitable material. The switchable optical filter 116 may alternatively or additionally comprise one or more liquid crystals.

[0092] The first substrate 106a may be arranged on a side of the first sensor array 104a facing the center scintillator layer 102b or alternatively on a side of the first sensor array 104a facing the first outer scintillator layer 102a. In the embodiment shown in FIG. 2, the switchable optical filter 116 is in contact with the first substrate 106a. However, the first sensor array 104a may also be arranged, such that the switchable optical filter 116 may be in contact with the photosensitive pixels 108a and/or a protective layer covering at least a part of the photosensitive pixels 108a.

[0093] It is to be noted that a metal layer and/or metal filter may be arranged at the center plane 105. Such metal layer and/or metal filter may be a metal spectral-separation filter also acting as reflector. This may allow the X-ray detector 100 to be operated in at least two modes of operation, wherein applications requiring medium spectral separation the switchable optical filter 116 may be opaque in the second state, while for applications requiring high spectral separation the switchable optical filter 116 may be black in the second state, thus adding the scintillator layer 102b to the spectral separation filter and/or using scintillator layer 102b as spectral separation filter.

[0094] In the example shown in FIG. 2, the switchable optical filter 116 is switched to the second state, in which scintillator light 110 is reflected by the switchable optical filter 116, as indicated by the arrows depicting scintillator light 110 hitting the switchable optical filter 116. As a consequence, the first sensor array 104a is optically decoupled from the center scintillator layer 102b and only receives scintillator light 110 emitted by the first outer scintillator layer 102a. However, by switching the switchable optical filter 116 to the first state, the first sensor array 104a may be optically coupled to the center scintillator layer 102b, such that it receives scintillator light 110 from two opposite sides. Accordingly, by means of the switchable optical filter 116 a versatility of the X-ray detector 100 is increased, as the X-ray detector 100 may be operated in a plurality of operation modes by switching the switchable optical filter 116 to the first or second state. In an alternative embodiment the switchable filter may be replaced by a metal filter and/or a metal layer. Also, the X-ray detector 100 may comprise a metal filter and/or metal layer in addition to the switchable optical filter 116.

[0095] Further, it is to be noted that scintillator light 110 on the first side 112 of the X-ray detector 100 and on the second side 114 of the X-ray detector 100 may be reflected e.g. by arranging a reflective film 118 and/or a reflective layer 118 on the respective side 112, 114 and/or surface of the X-ray detector 100. However, the layers 118 may also be opaque layers 118 absorbing scintillator light 110.

[0096] When X-ray radiation with a certain energy distribution hits the X-ray detector 100 along the impinging direction 200, the low energy portion of the X-ray radiation is primarily converted to scintillator light 110 in the first outer scintillator layer 102. As the switchable optical filter 116 is in the second state, the first sensor array 104a only collects scintillator light 110 generated by the low-energy portion. Thus, the first sensor array 104a only detects low-energy X-ray radiation and acquires a low-energy X-ray image. In contrast, the high-energy portion of the X-ray radiation is mainly converted into scintillator light 110 in the center scintillator layer 102b and/or the second outer scintillator layer 102c. As the second sensor array 104b receives scintillator light 110 from both theses scintillator layers 102b, c, the second sensor array 104b detects the high-energy portion and acquires a high-energy X-ray image with high detection efficiency.

[0097] Moreover, it is to be noted, that each of the scintillator layers 102a-c may comprise any suitable scintillation material, such as e.g. CsI, GOS (Gadolinium Oxysulfide), garnet (e.g. LGGAG, Lutetium Gadolinium Gallium Aluminum Garnet), and/or NaL Further, the scintillator material may be a columnar grown scintillator material and/or a non-columnar grown scintillator material. The scintillator layers 102a-c of the X-ray detector 100 may comprise the same scintillator material or at least a part of the scintillator layers 102a-c may comprise different scintillator materials. By way of example, it may be favorable that the center scintillator layer 102b comprises scintillator material different from the scintillator material of the first and/or second outer scintillator layers 102a, c in order to optimize energy separation between the first sensor array 104a, and the second sensor array 104b.

[0098] Moreover, the scintillator layers 102a-2 may each have the same thickness, which is measured along the stacking direction 101, or at least a part of the scintillator layers 102a-c may have different thicknesses. Particularly, the first outer scintillator layer 102a may be thinner than the center scintillator layer 102b and/or the second outer scintillator layer 102c. Also, the center scintillator layer 102b and the second outer scintillator layer 102c may have the same thickness or different thicknesses. By way of example, the first outer scintillator layer 102a may have a thickness of about 0.1 mm to about 1.0 mm, typically about 0.3 mm, whereas the center scintillator layer 102b and the second outer scintillator layer 102c each may have a thickness of about 0.5 mm to about 1.5 mm, typically about 0.8 mm.

[0099] For scintillator layers that can be designed thin, such as the first outer scintillator layer 102a, it may be favorable to use a scintillator material different from CsI, which may be cheaper, but still may have a similar MTF compared with other, potentially thicker CsI scintillator layers 102b, c. Further, for the first outer scintillator layer 102a that is preferably used for capturing the low-energy portion of the emitted X-ray spectrum, a different composition, having a lower effective Z-value, than the scintillator layers 102b, c that are preferably used to capture the high-energy portion of the emitted X-ray spectrum may be beneficial. This may increase the difference in the energy spectrum captured between the first sensor array 104a and the second sensor array 104b of the X-ray detector 100.

[0100] FIG. 3A shows schematically an X-ray detector according to an embodiment. If not stated otherwise, the X-ray detector 100 of FIG. 3A comprises the same features and/or elements as the X-ray detectors 100 shown in previous figures. FIGS. 3B, 3C, 3D each schematically illustrate an operation mode of the X-ray detector 100 of FIG. 3A.

[0101] The X-ray detector 100 shown in FIG. 3A particularly comprises the same features and/or elements as the X-ray detector 100 shown FIG. 2. However, the switchable optical filter 116 of FIG. 2 is depicted as first switchable optical filter 116a in FIG. 3A. In addition to this first switchable optical filter 116a, the X-ray detector 100 of FIG. 3A comprises a second switchable optical filter 116b arranged between the second sensor array 104b and the center scintillator layer 102b. By arranging the first switchable optical filter 116a and the second switchable optical filter 116b between the first sensor array 104a and the second sensor array 104b, the X-ray detector 100 may be operated in a plurality of operation modes as indicated in FIGS. 3B, 3C and 3D.

[0102] It is to be noted that the first substrate 106a of the first sensor array 104a may be arranged on a side of the first sensor array 104a facing the center scintillator layer 102b or alternatively on a side of the first sensor array 104a facing the first outer scintillator layer 102a. Accordingly, the first switchable optical filter 116a may be in contact with the first substrate 106a or it may be in contact with the photosensitive pixels 108a and/or a protection layer covering the photosensitive pixels of the first sensor array 104a. Further, the second substrate 106b of the second sensor array 104b may be arranged on a side of the second sensor array 104b facing the center scintillator layer 102b or alternatively on a side of the second sensor array 104b facing the second outer scintillator layer 102c. Accordingly, the second switchable optical filter 116b may be in contact with the second substrate 106b or it may be in contact with the photosensitive pixels 108b and/or a protection layer covering the photosensitive pixels of the second sensor array 104b.

[0103] Referring to FIG. 3B, the first switchable optical filter 116a is switched to the second state, in which scintillator light 110 is reflected by the first switchable optical filter 116a. Thus, the first sensor array 104a only detects scintillator light 110 generated primarily by low-energy X-ray photons in the first outer scintillator layer 102a.

[0104] In contrast to the first switchable optical filter 116a, the second switchable optical filter 116b is switched to the first state, such that the second sensor array 104b is optically coupled to the center scintillator layer 102b and the second outer scintillator layer 102c. Accordingly, the second sensor array 104b receives scintillator light from both these scintillator layers 102b, c at two opposite sides 103a, 103b of the second sensor array 104b, as shown in the encircled region in FIG. 3B. In other words, the second sensor array 104b is illuminated with scintillator light 110 from two opposite sides 103a,b of the second sensor array 104b.

[0105] Referring to FIG. 3C, the first switchable optical filter 116a is switched to the first state and the second optical filter 116b is switched to the second state. Accordingly, scintillator light 110 is reflected by the second switchable optical filter 116b, and the first side 103a of the second sensor array 104b is optically decoupled from the center scintillator layer 102b, such that the second sensor array 104b only receives and/or detects scintillator light 110 from the second outer scintillator layer 102c. In contrast thereto, the first sensor array 104a is optically coupled on one side to the first outer scintillator layer 102a and on an opposite side to the center scintillator layer 102b. Thus, the first sensor array 104a receives and/or detects scintillator light 110 from both these layers 102a, 102b, as shown in the encircled region in FIG. 3C. In other words, the first sensor array 104a is illuminated from two opposite sides of the first sensor array 104a by scintillator light 110.

[0106] Referring to FIG. 3D, both the first switchable optical filter 116a and the second switchable optical filter 116b are switched to the second state, in which scintillator light 110 is reflected. Accordingly, the first sensor array 104a is optically coupled only to the first outer scintillator layer 102a, and the second sensor array 104b is optically coupled only to the second outer scintillator layer 102c. Thus, in this operation mode, the center scintillator layer 102b may be regarded as being switched off. Nonetheless, the center scintillator layer 102b contributes to the energy separation between the first sensor array 104a and the second sensor array 104b. In other words, scintillator light 110 from the center scintillator layer 102b neither contributes to the low-energy image captured with the first sensor array 104 nor to the high-energy image captured with the second sensor array 104b. Thus, the center scintillator layer 102b may be regarded as an extra filter increasing energy separation.

[0107] FIGS. 4A and 4B show schematically an X-ray detector 100 according to an embodiment. If not stated otherwise, the X-ray detector 100 of FIGS. 4A and 4B comprises the same features and/or elements as the X-ray detectors 100 shown in previous figures.

[0108] The X-ray detector 100 of FIGS. 4A and 4B comprises in total four scintillator layers 102a-d. A first outer scintillator layer 102a, a second outer scintillator layer 102d, a first center scintillator layer 102b, and a second center scintillator layer 102c, wherein the center scintillator layers 102b, 102c are arranged between the first sensor array 104a and the second sensor array 104b. The first outer scintillator layer 102a and the first center scintillator layer 102b may have the same thickness ranging from about 0.1 mm to about 1.0 mm, e.g. about 0.3 mm. Further, the second center scintillator layer 102b and the second outer scintillator layer 102d may have the same thickness ranging from about 0.5 mm to about 1.5 mm, e.g. about 0.8 mm.

[0109] Moreover, a reflective and non-switchable layer 118 is arranged between the first and second center scintillator layers 102b, 102c. By means of the reflective layer 118, scintillator light 110 from both, the first and the second center scintillator layers 102b, 102c is reflected. This may increase an overall detection efficiency. However, the reflective layer may alternatively be an opaque layer 118. Layer 118 may be reflective and/or opaque on both sides, which are in contact with the scintillator layers 102b, 102c. Also, one side of the layer 118 may be opaque and an opposite side may be reflective.

[0110] Further, a switchable optical filter 116 is arranged between the first sensor array 104a and the first center scintillator layer 102b.

[0111] It is to be noted that the first substrate 106a of the first sensor array 104a may be arranged on a side of the first sensor array 104a facing the first center scintillator layer 102b or alternatively on a side of the first sensor array 104a facing the first outer scintillator layer 102a. Accordingly, the switchable optical filter 116a may be in contact with the first substrate 106a or it may be in contact with the photosensitive pixels 108a and/or a protection layer covering the photosensitive pixels of the first sensor array 104a.

[0112] In FIG. 4A the switchable optical filter 116 is in the first state and in FIG. 4B the switchable optical filter 116 is in the second state. Accordingly, in FIG. 4A the first and the second sensor arrays 104a, 104b are illuminated from two opposite sides, whereas in FIG. 4B only the second sensor array 104b is illuminated from two opposite sides.

[0113] The switchable optical filter 116 in the first state as shown in FIG. 4A may advantageously increase an overall absorption of X-ray radiation, which may be favorable in a non-spectral imaging mode of the detector 100. In contrast, the switchable optical filter 116 in the second state as shown in FIG. 4B may advantageously increase energy separation, which may be favorable in spectral X-ray imaging.

[0114] Optionally, a metal filter 119 may be arranged in any of the scintillator layers 102a-d, which may increase an energy separation between the first and second sensor array 104a, 104b. Such metal filter 119 may be arranged additionally or alternatively to the reflective and/or opaque layer 118.

[0115] Moreover, the embodiment shown in FIGS. 4A and 4B may advantageously be used in dual beam applications. By way of example, when a high-energy beam is used for imaging, the switchable optical filter 116 may be switched to the second state as shown in FIG. 4B. This way, a high-energy image may be captured with the second sensor array 104b, while the first sensor array 104a may capture a low-energy image at this beam energy. Further, when a low-energy beam is used, the switchable optical filter may be switched to the first state as shown in FIG. 4A, thus both the first sensor array 104a and the second sensor array 104b may capture a low-energy image. The low-energy images of all exposures may then be added, allowing to increase dose efficiency. The low-energy image of the low energy beam could be used to generate more than two images of different mean absorbed X-ray energy.

[0116] FIGS. 5A and 5B show schematically an X-ray detector 100 according to an embodiment. If not stated otherwise, the X-ray detector 100 of FIGS. 5A and 5B comprises the same features and/or elements as the X-ray detectors 100 shown in previous figures.

[0117] The X-ray detector comprises in total five scintillator layers 102a-102e, each having the same thickness ranging from 0.1 mm to about 1.0 mm, e.g. about 0.3 mm. In contrast to the embodiment shown in FIGS. 4A and 4B, the X-ray detector 100 of FIGS. 5A and 5B comprises a further scintillator layer 102d arranged between the second sensor array 104b and the second outer scintillator layer 102e. Between the further scintillator layer 102d and the second outer scintillator layer 102e, a second switchable optical filter 116b is arranged in addition to the first switchable optical filter 116a, which is arranged between the first sensor array 104a and the first center scintillator layer 102b.

[0118] It is to be noted that the first substrate 106a of the first sensor array 104a may be arranged on a side of the first sensor array 104a facing the first center scintillator layer 102b or alternatively on a side of the first sensor array 104a facing the first outer scintillator layer 102a. Accordingly, the first switchable optical filter 116a may be in contact with the first substrate 106a or it may be in contact with the photosensitive pixels 108a and/or a protection layer covering the photosensitive pixels of the first sensor array 104a. Further, the second sensor array 104b may be arranged such that the second substrate 106b may be in contact with the further scintillator layer 102d or such that it may be in contact with the second center scintillator layer 102c.

[0119] In FIG. 5A both the first and the second switchable optical filters 116a, 116b are in the first state, whereas in FIG. 5B, the second switchable optical filter 116b is switched to the second state. When both switchable optical filters 116a, 116b are in the first state as shown in FIG. 5A, an overall absorption of X-ray radiation may be increased. This operation mode may e.g. be used when imaging thick objects, e.g. obese patients. In contrast, when the second optical filter 116b is switched to the second state as shown in FIG. 5B, a resolution may be increased, which may e.g. be used for imaging thin objects, such as e.g. vessels.

[0120] FIG. 6 shows schematically an X-ray detector 100 according to an embodiment. If not stated otherwise, the X-ray detector 100 of FIG. 6 comprises the same features and/or elements as the X-ray detectors 100 shown in previous figures.

[0121] The X-ray detector 100 of FIG. 6 comprises in total four scintillator layers 102a-102d. More specifically, the detector 100 comprises a first outer scintillator layer 102a, a second outer scintillator layer 102d, a first center scintillator layer 102b and a second center scintillator layer 102c, wherein the two center scintillator layers 102b, 102c are arranged between the first sensor array 104a and the second sensor array 104b.

[0122] Between the first sensor array 104a and the first center scintillator layer 102b a first switchable optical filter 116a is arranged.

[0123] Further, between the first center scintillator layer 102b and the second scintillator layer 102b, a second switchable optical filter 116b is arranged.

[0124] Moreover, a third switchable optical filter 116c is arranged between the second sensor array 104b and the second center scintillator layer 102c.

[0125] By arranging three switchable optical filters 116a-116c in the X-ray detector 100, a number of operation modes of the X-ray detector 100 may be further increased.

[0126] It is to be noted that the first substrate 106a of the first sensor array 104a may be arranged on a side of the first sensor array 104a facing the first center scintillator layer 102b or alternatively on a side of the first sensor array 104a facing the first outer scintillator layer 102a. Accordingly, the first switchable optical filter 116a may be in contact with the first substrate 106a or it may be in contact with the photosensitive pixels 108a and/or a protection layer covering the photosensitive pixels 108a of the first sensor array 104a. Further, the second substrate 106b of the second sensor array 104b may be arranged on a side of the second sensor array 104b facing the second center scintillator layer 102c or alternatively on a side of the second sensor array 104b facing the second outer scintillator layer 102d. Accordingly, the third switchable optical filter 116c may be in contact with the second substrate 106b or it may be in contact with the photosensitive pixels 108b and/or a protection layer covering the photosensitive pixels 108b of the second sensor array 104b.

[0127] FIG. 7 shows schematically an X-ray detector 100 according to an embodiment. If not stated otherwise, the X-ray detector 100 of FIG. 7 comprises the same features and/or elements as the X-ray detectors 100 shown in previous figures.

[0128] The X-ray detector 100 of FIG. 7 comprises in total three scintillator layers 102a, 102b, 102c. More specifically, the X-ray detector 100 comprises an outer scintillator layer 102a arranged on a first outer side of the X-ray detector 100. The two further scintillator layers 102b, 102c are arranged between the first sensor array 104a and the second sensor array 104b, such that the first and second sensor arrays 104a, 104b are separated by the two scintillator layers 102b, 102c along the stacking direction 101.

[0129] Further, a switchable optical filter 116 is arranged between scintillator layer 102b and scintillator layer 102c, such that the two scintillator layers 102b, 102c are separated by the switchable optical filter 116 along the stacking direction 101.

[0130] In the embodiment shown in FIG. 7 the second sensor array 104b is arranged on a second outer side of the X-ray detector 100 opposite to the side, on which the first outer scintillator layer 102a is arranged. Accordingly, the first sensor array 104a is arranged to collect and/or receive scintillator light 110 from two opposite sides, i.e. at least from the scintillator layers 102a, 102b, whereas the second sensor array 104b is arranged to receive and/or collect scintillator light 110 from one side only, i.e. at least from scintillator layer 102c.

[0131] In the embodiment shown in FIG. 7 X-ray radiation impinges along impinging direction 200 onto the X-ray detector 100, wherein the outer scintillator layer 102 is hit first by the X-ray radiation. In other words, the outer scintillator layer 102a may be arranged towards to, in direction of and/or facing an X-ray source. However, it is to be noted, that the X-ray detector 100 may also be arranged such that X-ray radiation first impinges onto the second senor array 104b and/or the second substrate 106b. In other words, the second sensor array 104b may be arranged towards to, in direction of and/or facing to an X-ray source.

[0132] The first substrate 106a of the first sensor array 104a may be arranged such that the first substrate 106a is in contact with the outer scintillator layer 102a or such that it is in contact with scintillator layer 102b. Similarly, the second substrate 106b of the second sensor array may be arranged such that it is in contact with scintillator layer 102c or such that the photosensitive pixels 108b of the second sensor array 104b or a protection layer covering the photosensitive pixels 108b is in contact with scintillator layer 102c.

[0133] Further, it is to be noted that in any of the embodiments shown in FIGS. 2 to 7, the switchable optical filter 116, 116a, 116b, 116c may have a pixel structure and/or the switchable optical filter 116, 116a, 116b, 116c may be a pixelated switchable optical filter. In other words, the switchable optical filter 116, 116a, 116b, 116c may comprise an array of switchable optical filter elements. The pixel structure of the switchable optical filter 116, 116a, 116b, 116c may correlate with a geometrical arrangement of the photosensitive pixels 108a, 108b of at least one of the sensor arrays 104a, 104b. Accordingly, the pixel structure of the switchable optical filter 116, 116a, 116b, 116c may be matched with at least one of the sensor arrays 104a, 104b and/or with a geometrical arrangement of the photosensitive pixels 108a, 108b of at least one of the sensor arrays 104a, 104b. The state of the switchable optical filter 116, 116a, 116b, 116c may be the same for all switchable optical filter elements or the state may be controlled pixel-wise, such that a part of the switchable optical filter elements may be in the first state and another part of the switchable optical filter elements may be in the second state. Therein, each switchable optical filter element may be controlled and/or switched independently. Also, the X-ray detector 100 may comprise any combination of at least one pixelated switchable optical filter 116, 116a, 116b, 116c with a plurality of switchable optical filter elements and at least one un-pixelated switchable optical filter 116, 116a, 116b, 116c.

[0134] FIG. 8 shows schematically an X-ray imaging apparatus 500 according to an embodiment.

[0135] The X-ray imaging apparatus 500 comprises an X-ray source arrangement 502. The X-ray source arrangement may be a single X-ray source or a multi X-ray source comprising two or more X-ray sources.

[0136] The X-ray imaging apparatus 500 further comprises an X-ray detector 100 as described above and in the following. Particularly, the X-ray detector 100 may be an X-ray detector 100 as described in more detail with reference to FIGS. 2 to 7. However, it is to be noted that the X-ray imaging apparatus 500 is not restricted to an X-ray detector 100 as shown in previous figures, but rather can comprise any type of X-ray detector.

[0137] Further, the X-ray imaging apparatus 500 comprises a controller 504 for controlling the X-ray source arrangement 502 and/or the X-ray detector 100. The controller 504 may refer to a control circuitry 504, a control module 504 and/or a control unit 504. The controller 504 may particularly be configured to trigger an emission of an X-ray beam 506, which X-ray beam 506, after passing through an object 508 to be examined, is detected by means of the X-ray detector 100. Moreover, the controller 504 may be configured to switch a switchable optical filter 116, which may be present in the X-ray detector 100 as described with reference to FIGS. 2 to 7. Further, the controller 504 may be configured for image processing and/or for data processing of X-ray images acquired and/or captured with the X-ray detector 100.

[0138] The X-ray imaging apparatus 500 may be any type of X-ray imaging apparatus, such as, e.g. a CT imaging apparatus, a CBCT imaging apparatus, a cone beam imaging apparatus or a C-arm system.

[0139] FIG. 9 shows schematically an X-ray imaging apparatus 500 according to an embodiment. Particularly, FIG. 9 illustrates an operation of the imaging apparatus 500. If not stated otherwise, the X-ray imaging apparatus 500 of FIG. 9 comprises the features and/or elements as the X-ray imaging apparatus 500 of FIG. 8. For simplicity, the controller 504 is not shown in FIG. 9.

[0140] In the X-ray imaging apparatus 500 the X-ray detector 100 and the X-ray source arrangement 502 are rotatable around a rotational axis 510 of the X-ray imaging apparatus 500. As indicated in FIG. 9, the rotational axis 510 may be parallel to a z-axis. The rotational movement of the X-ray detector 100 and the X-ray source arrangement 502 is illustrated by the arrows 512 in FIG. 9. It is to be noted that a rotation radius of the X-ray detector 100 and the X-ray source arrangement 502 may differ from each other.

[0141] The X-ray source arrangement 502 comprises a first X-ray source 502a for emitting a first X-ray beam 506a of a first energy range and a second X-ray source 502b for emitting a second X-ray beam 506b of a second energy range different from the first energy range.

[0142] The controller 504 is configured for triggering the first X-ray source 502a and for acquiring a first X-ray image, when the first X-ray source 502a is located at an acquiring position 514 around the rotational axis 510. Further, the controller 504 is configured for triggering the second X-ray source 502b and for acquiring a second X-ray image, when the second X-ray source 502b is located at the acquiring position 514 around the rotational axis 510.

[0143] Accordingly, when an X-ray source arrangement 502 comprising the first X-ray source 502a and the second X-ray source 502b is used, a first X-ray image is captured by activating the first X-ray source 502a at the acquiring position 514. After a certain period of time, the second X-ray source 502b may, due to the rotational movement, arrive at the acquiring position 514. When the second X-ray source 502b arrives at the acquiring position, the second X-ray image is captured. This way, the rotation speed and the exposures, e.g. taking into account a distance between the first and second X-ray sources 502a, 502b, may be synchronized. In other words, an acquisition frequency may be synchronized with a rotation frequency of the X-ray imaging apparatus 500. This allows the first X-ray image to be coincident in space with the second X-ray image.

[0144] It is to be noted, that also by using a single X-ray source 502, 502b this synchronization can be achieved by rotating the X-ray source 502a, 502b completely by 360 around the rotational axis 510.

[0145] Further it is to be noted that this synchronization is applicable in kVp-switching approaches, in which the first X-ray beam 506a and the second X-ray beam 506b are generated by means of a pre-filter.

[0146] Moreover, this synchronization is applicable for a stereo X-ray tube and/or for a dual focal spot X-ray source arrangement 502. In other words, the X-ray source arrangement 502 may comprise an X-ray tube with a first focal spot 503a for emitting the first X-ray beam 506a and a second focal spot 503b for emitting the second X-ray beam 506b. Alternatively or additionally the X-ray source arrangement 502 may comprise a first X-ray tube 503a for emitting the first X-ray beam 506a and a second X-ray tube 503b for emitting the second X-ray beam 506b.

[0147] Moreover, it is to be noted that using the X-ray detector 100 as described with reference to at least one of FIGS. 2 to 7 during each exposure, i.e. when the first beam 506a or the second beam 506b is emitted, the first sensor array 104a as well as the second sensor array 104b captures a separate X-ray image. Accordingly, the first X-ray image acquired during exposure with the first beam 506a refers to a first image pair. Similarly, the second X-ray image acquired during exposure with the second beam 506b refers to a second image pair, wherein the image pairs may be coincident in time and space. Acquiring the first and the second X-ray images thus results in total in four images, which can be advantageously combined in order to increase dose efficiency of the X-ray imaging apparatus 500.

[0148] By way of example, the first beam 506a may be a low kV beam 506a and the second beam 506b may be a high kV beam 506b. When exposing the X-ray detector 100 with the low kV beam 506a, both the first sensor array 104a and the second sensor array 104b capture and/or acquire a low-energy image. In contrast, when exposing the X-ray detector 100 with the high kV beam 506b, the first sensor array 104a acquires and/or captures a low-energy image, whereas the second sensor array 104b captures and/or acquires a high-energy image. The three low-energy images acquired during both exposures, i.e. during exposure with the low kV beam 506a and the high kV beam 506b, may advantageously be added and/or combined. This results in a dose efficient low-energy total image.

[0149] Moreover, adding and/or combining all four images gives a dose efficient non-spectral image.

[0150] FIG. 10 shows a flow chart illustrating steps of a method for operating an X-ray imaging apparatus 500 according to an embodiment. If not stated otherwise, the X-ray imaging apparatus 500 comprises the same features and/or elements as the X-ray imaging apparatus 500 of FIGS. 8 and 9. Particularly, the X-ray imaging apparatus 500 comprises an X-ray detector 100 as described with reference to FIGS. 2 to 7.

[0151] The X-ray imaging apparatus 500 comprises an X-ray source arrangement 502 with a first X-ray source 502a for emitting a first X-ray beam 506a of a first energy range and a second X-ray source 502b for emitting a second X-ray beam 506b of a second energy range different from the first energy range.

[0152] The method comprises a step Si of emitting the first X-ray beam 506a with the first X-ray source 502a, when the first X-ray source 502a is located at an acquiring position 514 around a rotational axis 510 of the X-ray imaging apparatus 500.

[0153] In a step S2 a first X-ray image is acquired and/or captured with the X-ray detector 100, when the first X-ray source 502a is located at the acquiring position 514.

[0154] In a further step S3 the second X-ray beam 506b is emitted with the second X-ray source 502b, when the second X-ray source 502b is located at the acquiring position 514. Further, in a step S4 a second X-ray image is acquired and/or captured with the X-ray detector 100, when the second X-ray source 502b is located at the acquiring position 514.

[0155] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art and practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0156] In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.