WO2008149292A2

WO2008149292A2 - Detection device for detecting radiation

Info

Publication number: WO2008149292A2
Application number: PCT/IB2008/052170
Authority: WO
Inventors: Roland Proksa; Jens-Peter Schlomka; Ewald RÖSSL
Original assignee: Koninklijke Philips Electronics N.V.; Philips Intellectual Property & Standards Gmbh
Priority date: 2007-06-08
Filing date: 2008-06-04
Publication date: 2008-12-11
Also published as: WO2008149292A3

Abstract

The present invention relates to a detection device for detecting radiation emitted from a radiation source, wherein the detection device (6) comprises a detection surface (19) and lamellae (18) protruding from the detection surface (19), wherein the lamellae (18) comprise a first end portion (20) close to the detection surface (19) and a second end portion (21) remote from the detection surface (19) and wherein the first end portion (20) has a larger width than the second end portion (21). The invention relates further to a computed tomography apparatus comprising this detection device.

Description

Detection device for detecting radiation

FIELD OF THE INVENTION

The present invention relates to a detection device, a detection method and a computer program for detecting radiation emitted from a radiation source. The invention relates further to a computed tomography apparatus comprising the detection device and a corresponding computed tomography method and computer program.

BACKGROUND OF THE INVENTION

WO 98/58389 discloses a detection device for detecting radiation emitted from a radiation source. The detection device comprises lamellae protruding from a detection surface of the detection device and generates detection values depending on the intensity of the radiation incident on the detection surface between the lamellae. The detection device is used in an X-ray imaging system having an X-ray radiation source. Ideally, the position of the X-ray radiation source is fixed relative to the position of the detection device. But, in real there are unwanted relative movements between the X-ray radiation source and the detection device.

The lamellae are used for diminishing the effect of scattering of X-ray photons in an examination zone between the X-ray radiation source and the detection device, but the lamellae also generate shadowing effects on the detection surface which depend on the position of the X-ray radiation source relative to the position of the detection device. If, as mentioned above, relative movements between the X-ray radiation source and the detection device are present, the shadowing effects caused by the lamellae vary. This results in variations of the detection values generated by the detection device caused by the relative movements only. Thus, these relative movements disturb the quality of the detection values.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a detection device, a detection method and a computer program for detecting radiation emitted from a radiation source, which generate detection values having an improved quality. It is a further object of the present invention to provide a corresponding computed tomography apparatus, computed tomography method and computer program for imaging a region of interest.

In a first aspect of the present invention a detection device for detecting radiation emitted from a radiation source is presented, wherein the detection device comprises a detection surface and lamellae protruding from the detection surface, wherein the lamellae comprise a first end portion close to the detection surface and a second end portion remote from the detection surface, wherein the first end portion has a larger width than the second end portion.

The invention is based on the idea that in the prior art relative movements between the radiation source and the detection device generate shadowing effects on the detection surface close to the lamellae. Therefore, if the lamellae have a larger width close to, in particular adjacent to, the detection surface, in particular yielding an enlarged cross- sectional area in a plane parallel to the detection surface, this enlarged width, in particular the enlarged cross-sectional area, covers a region on the detection surface, on which shadowing effects caused by relative movements between the radiation source and the detection device are present. The influence of these shadowing effects on the detection values generated by the detection device is therefore reduced, thereby improving the quality of the generated detection values.

Shadowing effects can, for example, occur, if the radiation source does not emit spatially homogenously, as it is generally the case in a focal spot of an X-ray tube, because, depending on the position of the radiation source relative to the detection device, different rays emitted from different parts of the radiation source are attenuated by the lamellae. This means, for example, that at a certain position of the radiation source relative to the detection device rays emitted from a certain location within the radiation source are attenuated by the lamellae and that at another position of the radiation source relative to the detection device rays emitted from another location within the radiation source are attenuated by the lamellae. Since in general the properties, in particular the intensity, of the rays depend on the emission location within the radiation source, for example within the focal spot, this causes shadowing effects in the prior art. It is preferred that the width of the lamellae decreases continuously from the first end portion to the second end portion. It is further preferred that the lamellae comprise a triangular cross-section extending from the first end portion to the second end portion. This improves a diminishing of the intensity of radiation, which causes the unwanted shadowing effects, by attenuation, for example, by absorption and/or reflection, at portions of the lamellae between the first end portion and the second end portion of the lamellae.

It is further preferred that the detection surface is continuously sensitive for radiation between regions of the detection surface located on different sides of the lamellae. Since the width of the first end portion covers a part of the detection surface and, thus, reduces variations of the detection values caused by the shadowing effects, it is not necessary to have radiation insensitive regions on the detection surface in regions, on which the shadowing effects would be present, if the first end portion of the lamellae would not have a larger width than the second end portion. The detection surface can therefore be continuously radiation sensitive, which simplifies the production of the detection device and can therefore reduce production costs.

It is further preferred that the detection device is a photon-counting detection device. Photon-counting detection devices generally comprise a continuous radiation sensitive detection surface, which is preferentially the surface of a direct-conversion material, which directly converts incident radiation into electrical signals. Such a direct-conversion material is, for example, cadmium zinc telluride (CZT). The photon-counting detector is used for generating energy-dependent detection values. The first end portion of the lamellae cover a part of the radiation sensitive surface such that shadowing effects, which might be caused by a relative movement between the radiation source and the detection device, are reduced. Thus, a photon-counting detection device with the lamellae in accordance with the invention generates energy-dependent detection values, wherein shadowing effects on the detection values caused by relative movements between the radiation source and the detection device are reduced. Thus, the dependency of the energy-dependent detection values on the shadowing effects is reduced. It is further preferred that the width of the first end portion is dimensioned such that a predetermined movement of the radiation source and the detection device relative to each other does not change the intensity of the radiation between the lamellae, if an object is not present between the radiation source and the detection device. Depending on the dimensions of the radiation source and the detection device, the positions of the radiation source and the detection device and a predetermined, in particular maximal, relative movement between the radiation source and the detection device, the width of the first end portion of the lamellae can be determined such that the regions on the detection surface, on which the shadowing effects caused by the predetermined relative movements between the radiation source and the detection device occur, are covered by the first end position of the lamellae. The maximal relative movement between the radiation source and the detection device can be, for example, determined by calibration measurements. For instance, if a radiation source and a detection device of a computed tomography apparatus are used, the maximal relative movement between the radiation source, being, in this example, the focal spot of an X-ray tube, and the detection device can be determined during a rotational movement of the radiation source and the detection device relative to a region of interest located between the radiation source and the detection device. The maximal determined relative movement can be used for determining the required width of the first end portion of the lamellae. If the first end portion has been dimensioned such that movements of the radiation source and the detection device relative to each other do not change the intensity of the radiation between the lamellae, the shadowing effects caused by these relative movements do not or do substantially not influence the detection values anymore.

In the previously described preferred embodiment, the width of the first end portion is dimensioned such that a movement of the radiation source and the detection device relative to each other does not change the intensity of the radiation between lamellae, if an object is not present between the radiation source and the detection device. This definition does not mean that an object cannot be present between the radiation source and the detection device. If an object is present between the radiation source and the detection device and the radiation source and the detection device move relatively to each other, the radiation source and/or the detection device move also relatively to the object, wherein changes of the intensity can result, which are caused by a relative movement between the object and the radiation source and/or the detection device. These changes are still present. Only the changes generated by shadowing effects directly caused by a relative movement between the radiation source and the detection device are substantially eliminated by the detection device according to this preferred embodiment.

In a further aspect of the present invention a computed tomography apparatus for imaging a region of interest is presented, wherein the computed tomography apparatus comprises: a radiation source for emitting radiation, - a detection device for detecting projection data values depending on the radiation after having traversed the region of interest, a moving unit for moving the radiation source and the region of interest relatively to each other, a reconstruction unit for reconstructing an image of the region of interest using the detected projection data values, wherein the radiation source and the detection device are adapted for detecting the projection data values, while the moving unit moves the radiation source and the region of interest relatively to each other, wherein the detection device comprises a detection surface and lamellae protruding from the detection surface, wherein the lamellae comprise a first end portion close to the detection surface and a second end portion remote from the detection surface, wherein the first end portion has a larger width than the second end portion. In a further aspect of the present invention a detection method for detecting radiation emitted from a radiation source by a detection device is presented, wherein the detection device comprises a detection surface and lamellae protruding from the detection surface, wherein the lamellae comprise a first end portion close to the detection surface and a second end portion remote from the detection surface, wherein the first end portion has a larger width than the second end portion, wherein the detection method comprises the step of detecting the radiation on the detection surface on regions between the first end portions of the lamellae.

In a further aspect of the present invention a computed tomography method for imaging a region of interest is presented, wherein the computed tomography method comprises following steps: emitting radiation by a radiation source, detecting projection data values depending on the radiation after having traversed the region of interest by a detection device, which comprises a detection surface and lamellae protruding from the detection surface, wherein the lamellae comprise a first end portion close to the detection surface and a second end portion remote from the detection surface, wherein the first end portion has a larger width than the second end portion, moving the radiation source and the region of interest relatively to each other by a moving unit, reconstructing an image of the region of interest using the detected projection data values by a reconstruction unit, wherein the projection data values are detected on the detection surface on regions between the first end portions of the lamellae, while the radiation source and the region of interest move relatively to each other. In a further aspect of the present invention a computer program for detecting radiation from a radiation source is presented, wherein the computer program comprises program code means for causing a detection device as defined in claim 1 to carry out the steps of the detection method as defined in claim 8, when the computer program is run on a computer controlling the detection device.

In a further aspect of the present invention a computer program for imaging a region of interest is presented, wherein the computer program comprises program code means for causing a computed tomography apparatus as defined in claim 7 to carry out the steps of the computed tomography method as defined in claim 9, when the computer program is run on a computer controlling the computed tomography apparatus.

It shall be understood that the detection device of claim 1, the computed tomography apparatus of claim 7, the detection method of claim 8, the computed tomography method of claim 9 and the computer programs of claims 10 and 11 have similar and/or identical preferred embodiments as defined in the dependent claims. It shall be understood that a preferred embodiment of the invention can also be any combination of the dependent claims with the respective independent claim.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. In the following drawings

Fig. 1 shows schematically and exemplarily a computed tomography apparatus for imaging a region of interest,

Fig. 2 shows schematically and exemplarily a sectional view of a detection device for detecting radiation from a radiation source, Fig. 3 shows schematically and exemplarily a sectional view of a lamella of the detection device,

Fig. 4 shows schematically and exemplarily a sectional view of another lamella,

Fig. 5 shows schematically and exemplarily a sectional view of a further lamella,

Fig. 6 shows schematically and exemplarily a flow chart of a computed tomography method for imaging a region of interest,

Fig. 7 shows schematically and exemplarily a spectrum of a radiation source and Fig. 8 shows schematically and exemplarily spectra of a photo-electric effect, a Compton effect and of a substance within an object.

DETAILED DESCRIPTION OF EMBODIMENTS The computed tomography apparatus shown in Fig. 1 is a spectral computed tomography apparatus. The computed tomography apparatus includes a gantry 1 which is capable of rotation about a rotational axis R which extends parallel to the z direction. A polychromatic radiation source 2, which is, in this embodiment, an X-ray tube emitting polychromatic X-ray radiation, is mounted on the gantry 1. The radiation source 2 is provided with a collimator 3, which forms, in this embodiment, a conical radiation beam 4 from the radiation generated by the radiation source 2. The radiation traverses an object (not shown), such as a patient, in a region of interest in an examination zone 5 which is, in this embodiment, cylindrical. After having traversed the examination zone 5 the radiation 4 is incident on an energy-resolving detection device 6, which comprises a two-dimensional detection surface. The energy-resolving detection device 6 is mounted on the gantry 1.

The computed tomography apparatus comprises a moving unit having two motors 7, 8. The gantry 1 is driven at a preferably constant but adjustable angular speed by the motor 7. A motor 8 is provided for displacing the object, for example, a patient, who is arranged on a patient table in the examination zone 5, parallel to the direction of the rotational axis R or the z axis. These motors 7, 8 are controlled by a control unit 9, for instance, such that the radiation source 2 and the examination zone 5 and, thus, the region of interest within the examination zone 5 move relatively to each other along a helical trajectory. However, it is also possible that the object or the examination zone 5 is not moved, but that only the radiation source 2 is rotated, i.e. that the radiation source 2 moves along a circular trajectory relative to the object or the examination zone 5. Furthermore, in another embodiment, the collimator 3 can be adapted for forming another beam shape, in particular a fan beam, and the energy-resolving detection device 6 can comprise a detection surface, which is shaped corresponding to the other beam shape, in particular to the fan beam. The energy-resolving detection device 6 is, in this embodiment, a photon- counting detection device, which is schematically and exemplarily shown in Fig. 2.

The detection device 6 comprises a photon-counting element 14 for counting photons incident on the detection surface 19. The photon-counting element 14 comprises a cathode 15 forming the detection surface 19 and a corresponding anode 16. The cathode 15 and the anode 16 are located on opposite surfaces of a direct-conversion material CZT. In other embodiments, also other direct-conversion materials can be used. The cathode 15 is formed as a continuous conductive layer, in particular, a metallic conductive layer, and the anode 16 comprises several separate anode elements for providing a spatial resolution along the detection surface of the detection device. The photon-counting element 14 further comprises a read-out unit 17 for reading out the anode elements of the anode 16.

Radiation, which is incident on the detection surface 19, traverses the cathode 15 and is directly converted into electrons in CZT. The electrical field generated by the cathode 15 and the anode 16 forces the charge generated in the CZT to the anode elements of the anode 16, which are read out by the read-out unit 17. The read-out unit 17 comprises different energy thresholds, which can also be named as energy windows, and is adapted such that it counts the photons, which are incident on the detection surface 19, for each energy window, i.e. for energy window the read-out unit 17 provides the number of photons within the respective energy window. The read-out unit 17 generates for each energy window and for each anode element a detection value, which depends on the number of photons in the respective energy window.

A photon-counting element of a detection device, which can be used in accordance with the invention, is, for example, disclosed in "Multi-Energy X-ray Imaging with Linear CZT Pixel Arrays and Integrated Electronics", V. B. Cajipe et al., 14th Intl. Workshop on Room-Temperature Semiconductor X-Ray and Gamma-Ray Detectors, Rome, Italy, October 18 - 22, 2004.

Lamellae 18, which form, in this embodiment, an anti-scatter grid, are located on the detection unit 19. The lamellae 18 comprise a triangular cross-section, wherein a first end portion 20 adjacent to the detection surface 19 has a larger width than a second end portion 21 remote from the detection surface 19. The lamellae 18 are preferentially arranged in an anti-scatter grid such that the lamellae 18 form channels between them through which mainly primary radiation of the radiation source can pass. Secondary radiation, which is generated in the examination zone 5 between the radiation source 2 and the detection device 6 by scattering, should be absorbed by the lamellae 18. In this embodiment, the lamellae 18 are arranged such that secondary radiation, which has been scattered in the examination zone 5 in the fan direction, i.e. the scattered radiation, which has a component within a plane perpendicular to the rotational axis, is substantially absorbed by the lamellae 18. Thus, the lamellae 18 are preferentially arranged such that they are substantially parallel to direct rays located in a plane perpendicular to the rotational axis R. Fig. 2 shows a sectional view perpendicular to the rotational axis R. In this embodiment, the lamellae 18 extend parallel to the rotational axis R, wherein the dimensions of the lamellae 18 are not varied in the direction parallel to the rotational axis R. In Fig. 2, the rotational axis R is perpendicular to the drawing plane.

In Fig. 2, the lamellae 18, of which a single lamella 18 is schematically shown in Fig. 3, can be replaced by other lamellae, which also comprise a first end portion adjacent to the detection surface and a second end portion remote from the detection surface, wherein the first end portion has a larger width than the second end portion. For example, the lamella 19 schematically shown in Fig. 4, which has two concave opposite surfaces 24 and 25 such that the width of the first end portion 26 adjacent to a detection surface has a larger width than a second end portion 27 remote from the detection surface, can be used. A further example 30 of a lamella in accordance with the invention is schematically shown in Fig. 5. Also the lamella 30 comprises a first end portion 28 and a second end portion 29, wherein, if the lamella 30 is located on a detection surface, the first end portion 28 is adjacent to the detection surface and the second end portion 29 is remote from the detection surface and wherein the first end portion 28 has a larger width than the second end portion 29. In the sectional view shown in Fig. 5, the lamella 20 has the shape of a reversed T.

The lamellae 18, 19 and 30 are not drawn to scale in Figures 3, 4 and 5, respectively. In real, the ratio of the height of the lamellae to the width of the lamellae is larger than the ratio shown in Figures 3, 4 and 5. The small ratio of the height of the lamellae to the width of the lamellae has been chosen in Figures 3, 4 and 5 in order to clearly illustrate the differences of the cross-sections of the lamellae extending from the first end point to the second end point.

The detection values, which are projection data values, are provided to an image generation device 10 for generating an image of the region of interest, which is located in the examination zone 5. The region of interest preferentially contains a object or a part of an object. The image generation device 10 comprises a calculation unit 12 for determining at least one attenuation component, which is, for example, a Compton effect component, a photo-electric effect component or a K-edge component of a material within the region of interest, and a reconstruction unit 13 for reconstructing an image of the region of interest using at least one of the determined one or more attenuation components. The reconstructed image can finally be provided to a display unit 11 for displaying the image. Also the image generation device 10 is preferably controlled by the control unit 9.

The detection values, which have been transmitted to the image generation device 10, are energy-resolved detection values, for the reconstruction the calculation unit 12 determines from these detection values different attenuation components, which represent, for example, the absorption properties of different materials within the region of interest and/or a Component effect component and/or a photo-electric effect component and/or a K- edge component. At least one of these attenuation components is transmitted to the reconstruction unit 13, which reconstructs an image of the region of interest, using at least one of the determined attenuation components. Preferentially, the reconstruction unit 13 uses only one attenuation component for reconstruction an image of the region of interest. Such an image is not disturbed by the influence of other effects, which correspond to the other determined attenuation components. In addition, variations of the intensity of the radiation incident on the detection surface generated by shadowing effects caused by a relative movement between the detection device 6 and the radiation source 2 are reduced by covering the region of the detection surface 19, on which shadowing effects would be present, by the first end portion 20. This results in detection values having an improved quality and an image of the region of interest with reduced artifacts. A determination of the attenuation components by the calculation unit 12 is, for example, known from "Energy-selective reconstructions in X-ray Computerized Tomography", R.E. Alvarez, A. Macovski, Phys. Med. Biol, 1976, Vol. 21, No. 5, 733-744.

Since the region of interest has been illuminated by the radiation 4 from different directions and since for each of these directions at least one attenuation component has been determined by the calculation unit 12, the reconstruction unit 13 can use standard computed tomography reconstruction techniques, like a filtered backprojection, for reconstructing an image of the region of interest.

In the following a computed tomography method for imaging a region of interest will be described with reference to a flow chart shown in Fig. 6. In step 101, the radiation source 2 rotates around the rotational axis R and the object or the examination zone 5 is not moved, i.e. the radiation source 2 travels along a circular trajectory around the object or the examination zone 5. In another embodiment, the radiation source 2 can move along another trajectory, for example, a helical trajectory, relative to the object. The radiation source 2 emits polychromatic radiation traversing the object at least in a region of interest. The object is, for example, a human heart of a patient, wherein a contrast agent, like an iodine or gadolinium based contrast agent, which has K- edges within the range of the primary radiation energies, has preferentially been injected in advance. The radiation, which has passed the object and preferentially the substance within the object, is detected by the detection device 6 between the first end portions 20 of the lamellae 18 on the detection surface 19. The detection device 16 generates energy-resolved detection values being energy-resolved projection data values.

In step 102, the calculation unit 12 determines at least one attenuation component, which is, in this embodiment, preferentially the K-edge component of the contrast agent present within the object. In other embodiments, alternatively or in addition, other attenuation components can be determined by the calculation unit 12, like a Compton effect component, a photo-electric effect component or K-edge components of different materials within the region of interest.

In the following, exemplarily, the determination of the K-edge component of a contrast agent present within the object will be described.

The input to the calculation unit 12 are energy-resolved detection values d_t for a plurality, at minimum three, energy windows. These detection values d_t show a spectral sensitivity D₁ (E) of the i-th energy window b_t . The spectral sensitivity D₁ (E) is known or can be determined by calibration. Furthermore, an emission spectrum T (E) of the radiation source 2, which is, in this embodiment, a polychromatic X-ray tube, is also known or can be measured prior to step 101. An example for such an emission spectrum T (E) of a polychromatic X-ray tube is schematically shown in Fig. 7. In the calculation unit 12 the generation of the detection values d_t is modelled as linear combination of the photo-electric effect with spectrum P (E) , the Compton effect with spectrum C(E) and the contrast agent with a K-edge with spectrum K (E) .

Spectra P (E) , C(E) and K (E) are exemplarily and schematically shown in

Fig. 8.

The generation of the detection signals can be modelled by following system:

d, = {dE T(E)D₁

_{+ Pcomptm}C(E) + p_K__edgeK(E))] , (1)

wherein _/ø_photo,_/øc_ompton'_/°κ-_edge ^{are me} density length products of the photo-electric component, the Compton component and the K-edge component, respectively.

Since at least three detection signals d_l,d₂,d₃ are available for the at least three energy windows b_ub₂,b₃ a system of at least three equations is formed having three unknowns, which are the three density length products, which can thus be solved with known numerical methods in the calculation unit 12. If more than three energy windows are available, it is preferred to use a maximum likelihood approach that takes the noise statistics of the measurements into account. Generally, three energy windows are sufficient. In order to increase the sensitivity and noise robustness, however, it is preferred to have more detection values for more energy windows.

In step 103, the determined K-edge component, i.e. the density length product Pκ-_edge ' is transmitted to the reconstruction unit 13. Since the radiation source 2 moves relative to the object or the examination zone 5, the detection values, and, therefore, the determined density products p_κ__edge , correspond to radiation having traversed the object and the examination zone 5 and the contrast agent within the object in different angular directions. Thus, a K-edge image can be reconstructed by using conventional computed tomography reconstruction methods, like a filtered backprojection of the density length product p_κ__edge . Although, in the above described embodiment, the detection device is a photon-counting detection device comprising CZT as direct-conversion material, the detection device can also be another kind of detection device, which has lamellae protruding from a detection surface, wherein the lamellae comprise a first end portion adjacent to the detection surface and a second end portion remote from the detection surface, wherein the first end portion has a larger width than the second end portion. For example, the photon- counting detection device can comprise another direct-conversion material like another CdTe-type material, wherein a CdTe-type material comprises cadmium, tellure and preferentially a further element. A CdTe-type material is, for example, CdTe or CdMnTe. Also other II-VI semiconductors and III-V semiconductors can be used as conversion material. The detection device can also be a conventional detection device, which is not photon-counting.

Although in the above described embodiment, the lamellae form an anti- scatter grid, the lamellae can also form other kind of grids. Furthermore, in the above described embodiment, the lamellae have been illustrated as being an anti-scatter grid in the fan direction of the radiation. But, in addition or alternatively, the lamellae can form an anti- scatter grid in the cone direction of the radiation.

Furthermore, the lamellae do not have to be distributed over the whole detection surface. The detection surface can comprise regions, on which the lamellae are arranged, i.e. e.g. on which an anti-scatter grid is present, and regions, on which lamellae are not located, i.e. e.g. on which an anti-scatter grid is not present. In particular, Fig. 2 shows on the left and the right side of each anode element a lamella 18. In other embodiments, anode elements can be present, which do not have lamellae 18 at opposite sides. In the above described embodiment, a computed tomography apparatus has been described, which is a spectral computed tomography apparatus. In other embodiments, the computed tomography apparatus can be a conventional computed tomography apparatus or another apparatus comprising a radiation source and a detection device. If a conventional computed tomography apparatus is used, a calculation unit for determining attenuation components is not needed.

A lamella can be integrally formed, but a lamella can also be composed of several elements.

In the above described embodiment, a K-edge component of a contrast agent within an object is calculated by the calculation unit 12 and an K-edge image is reconstructed by the reconstruction unit 13. In other embodiments, other attenuation components can be determined and an image of one or several of these attenuation components can be reconstructed. In particular, a contrast agent does not have to be present within an object and a K-edge component from the object can be determined.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

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.

A single unit or device may fulfill the functions of several items recited in the claims. 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.

Calculations, determinations and backprojections or other kinds of calculations performed by one or several units or devices can be performed by any other number of units or devices. For example, the steps 102 and 103 can be performed by a single unit or by any other number of different units. The calculations, determinations, backprojections and/or the control of the computed tomography apparatus in accordance with the above described computed tomography method can be implemented as program code means of a computer program and/or as dedicated hardware. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A detection device for detecting radiation (4) emitted from a radiation source (2), wherein the detection device (6) comprises a detection surface (19) and lamellae (18) protruding from the detection surface (19), wherein the lamellae (18) comprise a first end portion (20) close to the detection surface (19) and a second end portion (21) remote from the detection surface (19), wherein the first end portion (20) has a larger width than the second end portion (21).

2. The detection device as defined in claim 1, wherein the width of the lamellae (18) decreases continuously from the first end portion (20) to the second end portion (21).

3. The detection device as defined in claim 1, wherein the lamellae (18) comprise a triangular cross-section extending from the first end portion (20) to the second end portion (21).

4. The detection device as defined in claim 1, wherein the detection surface (19) is continuously sensitive for radiation (4) between regions of the detection surface (19) located on different sides of the lamellae (18).

5. The detection device as defined in claim 1, wherein the detection device (6) is a photon-counting detection device.

6. The detection device as defined in claim 1, wherein the width of the first end portion (20) is dimensioned such that a predetermined movement of the radiation source (2) and the detection device (6) relative to each other does not change the intensity of the radiation (4) between the lamellae (18), if an object is not present between the radiation source (2) and the detection device (6).

7. A computed tomography apparatus for imaging a region of interest, wherein the computed tomography apparatus comprises: a radiation source (2) for emitting radiation (4), a detection device (6) for detecting projection data values depending on the radiation (4) after having traversed the region of interest, a moving unit for moving the radiation source (2) and the region of interest relatively to each other, a reconstruction unit (13) for reconstructing an image of the region of interest using the detected projection data values, wherein the radiation source (2) and the detection device (6) are adapted for detecting the projection data values, while the moving unit moves the radiation source (2) and the region of interest relatively to each other, wherein the detection device (6) comprises a detection surface (19) and lamellae (18) protruding from the detection surface (19), wherein the lamellae (18) comprise a first end portion (20) close to the detection surface (19) and a second end portion (21) remote from the detection surface (19), wherein the first end portion (20) has a larger width than the second end portion (21).

8. A detection method for detecting radiation (4) emitted from a radiation source (2) by a detection device (6), the detection device (6) comprising a detection surface (19) and lamellae (18) protruding from the detection surface (19), wherein the lamellae (18) comprise a first end portion (20) close to the detection surface (19) and a second end portion (21) remote from the detection surface (19), wherein the first end portion (20) has a larger width than the second end portion (21), wherein the detection method comprises the step of detecting the radiation (4) on the detection surface (19) on regions between the first end portions (20) of the lamellae (18).

9. A computed tomography method for imaging a region of interest, wherein the computed tomography method comprises following steps: emitting radiation (4) by a radiation source (2), detecting projection data values depending on the radiation (4) after having traversed the region of interest by a detection device (6), which comprises a detection surface (19) and lamellae (18) protruding from the detection surface (19), wherein the lamellae (18) comprise a first end portion (20) close to the detection surface (19) and a second end portion (21) remote from the detection surface (19), wherein the first end portion (20) has a larger width than the second end portion (21), moving the radiation source (2) and the region of interest relatively to each other by a moving unit, reconstructing an image of the region of interest using the detected projection data values by a reconstruction unit (13), wherein the projection data values are detected on the detection surface (19) on regions between the first end portions (20) of the lamellae (18), while the radiation source (2) and the region of interest move relatively to each other.

10. A computer program for detecting radiation (4) from a radiation source (2), the computer program comprising program code means for causing a detection device (6) as defined in claim 1 to carry out the steps of the detection method as defined in claim 8, when the computer program is run on a computer controlling the detection device (6).

11. A computer program for imaging a region of interest, the computer program comprising program code means for causing a computed tomography apparatus as defined in claim 7 to carry out the steps of the computed tomography method as defined in claim 9, when the computer program is run on a computer controlling the computed tomography apparatus.