X-ray detector for phase contrast and/or dark-field imaging

Abstract

The present invention relates to X-ray imaging. In order to reduce X-ray dose exposure during X-ray image acquisition, an X-ray detector is provided that is suitable for phase contrast and/or dark-field imaging. The X-ray detector comprises a scintillator layer (12) and a photodiode layer (14). The scintillator layer is configured to convert incident X-ray radiation (16) modulated by a phase grating structure (18) into light to be detected by the photodiode layer. The scintillator layer comprises an array of scintillator channels (20) periodically arranged with a pitch (22) forming an analyzer grating structure. The scintillator layer and the photodiode layer form a first detector layer (24) comprising a matrix of pixels (26). Each pixel comprises an array of photodiodes (28), each photodiode forming a sub-pixel (30). Adjacent sub-pixels during operation receive signals having mutually shifted phases. The sub-pixels that during operation receive signals having mutually identical phase form a phase group per pixel. The signals received by the sub-pixels within the same phase group per pixel during operation are combined to provide one phase group signal (32). The phase group signals of different phase groups during operation are obtained in one image acquisition. In an example, the pitch of the scintillator channels is detuned by applying a correcting factor c to a fringe period (P.sub.fringe) of a periodic interference pattern (35) created by the phase grating structure, wherein 0<c<2.

Claims

1. An X-ray detector for phase contrast imaging and/or dark-field imaging, comprising: a scintillator layer; and a photodiode layer; wherein the scintillator layer is configured to convert incident X-ray radiation modulated by a phase grating structure into light to be detected by the photodiode layer; wherein the scintillator layer comprises an array of scintillator channels periodically arranged with a pitch forming an analyzer grating structure; wherein the scintillator layer and the photodiode layer form a first detector layer comprising a matrix of pixels wherein each pixel comprises an array of photodiodes, each photodiode forming a sub-pixel; wherein adjacent sub-pixels during operation receive signals having mutually shifted phases; wherein the sub-pixels that during operation receive signals having mutually identical phase form a phase group per pixel; wherein the signals received by the sub-pixels within the same phase group per pixel during operation are combined to provide one phase group signal; wherein the phase group signals of different phase groups during operation are obtained in one image acquisition; wherein the pitch of the scintillator channels is detuned by applying a correcting factor c to a fringe period (p.sub.fringe) of a periodic interference pattern (35) created by the phase grating structure, wherein 0<c<2; wherein the X-ray detector comprises a second detector layer provided on one surface of the first detector layer, which one surface is perpendicular to an orientation of the scintillator channels of the first detector layer; where the second detector layer comprises a scintillator layer with an array of periodically arranged scintillator channels with the same pitch as the scintillator channels of the first detector layer and a photodiode layer; and wherein each scintillator channel of the second detector layer is arranged to be displaced in surface direction in relation to the adjacent scintillator channel of the first detector layer by half of the pitch.

2. Detector according to claim 1, wherein the sub-pixels within the same phase group per pixel are electrically connected with each other for combining the signals received by the sub-pixels within the same phase group into one phase group signal; and wherein each pixel further comprises readout electronics configured to receive the phase group signals of different phase groups in one image acquisition.

3. Detector according to claim 1, wherein the photodiodes form a continuous photosensitive layer of sub-pixels.

4. Detector according to claim 1, wherein the phase group signals of the different phase groups cover the complete phase of a wavefront of the X-ray radiation modulated by the phase grating structure.

5. Detector according to claim 1, wherein the phase group signals per pixel during operation are read out as readout signals.

6. Detector according to claim 4, wherein when there is an even number of phase group signals per pixel, a sum of all phase group signals per pixel and differences of pairs of phase group signals per pixel with a mutual phase shift of 7C during operation are read out as readout signals.

7. Detector according to claim 1, comprising light shield elements provided between two adjacent scintillator channels such that optical crosstalk between said two adjacent scintillator channels is reduced.

8. An interferometer for phase contrast X-ray imaging and/or dark-field X-ray imaging, comprising: a phase grating structure; and an X-ray detector according to one of the preceding claims; wherein the phase grating structure and the X-ray detector are arranged in an optical path such that the phase grating structure and the scintillator layer of the X-ray detector form an interferometer arrangement for correlating X-ray radiation.

9. An X-ray imaging system (100), comprising: an X-ray source (48); and an interferometer according to claim 8; wherein the X-ray source is configured to apply X-ray radiation to an object of interest (50) positionable in the optical path to be detected by the X-ray detector of the interferometer.

10. System according to claim 9, wherein the X-ray imaging system is: a medical imaging system; an inspection imaging system; or an industrial imaging system.

11. A method for phase contrast X-ray imaging and/or dark-field X-ray imaging, comprising the following steps: a) generating X-ray radiation modulated by a phase grating structure to examine an object of interest; and b) converting, by a scintillator layer of an X-ray detector, the modulated X-ray radiation into light and detecting the light by a photodiode layer of the X-ray detector; wherein the scintillator layer comprises an array of periodically arranged scintillator channels with a pitch forming an analyzer grating structure; wherein the scintillator layer and the photodiode layer form a first detector layer comprising a matrix of pixels; wherein each pixel comprises an array of photodiodes, each photodiode forming a sub-pixel; wherein adjacent sub-pixels during operation receive signals having mutually shifted phases; wherein the sub-pixels that during operation receive signals having mutually identical phase form a phase group per pixel; wherein the signals received by the sub-pixels within the same phase group per pixel are combined to provide one phase group signal; wherein the phase group signals of different phase groups are obtained in one image acquisition; wherein the pitch of the scintillator channels is detuned by applying a correcting factor c to a fringe period (p.sub.fringe) of a periodic interference pattern created by the phase grating structure, wherein 0<c<2; wherein the X-ray detector comprises a second detector layer provided on one surface of the first detector layer, which one surface is perpendicular to an orientation of the scintillator channels of the first detector layer; wherein the second detector layer comprises a scintillator layer with an array of periodically arranged scintillator channels with the same pitch as the scintillator channels of the first detector layer and a photodiode layer; and wherein each scintillator channel of the second detector layer is arranged to be displaced in surface direction in relation to the adjacent scintillator channel of the first detector layer by half of the pitch.

12. Computer program element for controlling an apparatus, which, when being executed by a processing unit, is adapted to perform the method steps of claim 11.

13. Computer readable medium having stored the program element of claim 12.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention will be described in the following with reference to the following drawings:

(2) FIG. 1 shows an example of an X-ray detector.

(3) FIG. 2 shows an example of an interferometer.

(4) FIGS. 3a and 3b show two further examples of an X-ray detector.

(5) FIG. 4a shows an example of a sampling pattern used in explaining the theory and operation of a conventional phase stepping method.

(6) FIG. 4b shows an example of a sampling pattern used in explaining the theory and operation of the X-ray detector according to an example of the invention.

(7) FIG. 5 shows an example of an X-ray imaging system.

(8) FIG. 6 shows an example of method steps of a method for phase contrast and/or dark-field X-ray imaging.

DETAILED DESCRIPTION OF EMBODIMENTS

(9) The present technique is generally directed towards an imaging technique, such as a mammography imaging technique, to generate useful images for medical and non-medical applications. As will be appreciated by those of ordinary skill in the art, the present techniques may be applied in various medical and non-medical applications, such as passenger and/or baggage screening, to provide useful two- or three-dimensional data and context. To facilitate explanation of the present techniques, however, a medical implementation will be generally discussed herein, though it is to be understood that non-medical implementations are also within the scope of the present techniques.

(10) FIG. 1 shows an X-ray detector 10 in accordance with an embodiment of the invention. The X-ray detector 10 comprises a scintillator layer 12 and a photodiode layer 14. The scintillator layer 12 is configured to convert incident X-ray radiation 16 modulated by a phase grating structure 18 (shown in FIG. 2) into light 19 to be detected by the photodiode layer 14. The scintillator layer 12 comprises an array of scintillator channels 20 (illustrated as a grid-like structure) periodically arranged with a pitch 22 forming an analyzer grating structure. The scintillator layer 12 and the photodiode layer 14 form a first detector layer 24 comprising a matrix of pixels 26. Each pixel 26 comprises an array of photodiodes 28, each photodiode forming a sub-pixel 30. For reasons of simplicity, only one pixel 26 is illustrated in FIG. 1 with a plurality of sub-pixels 30, indicated with an array of squares.

(11) Adjacent sub-pixels 30 during operation receive signals having mutually shifted phases. The sub-pixels 30 that during operation receive signals having mutually identical phases form a phase group per pixel. The signals received by the sub-pixels 30 within the same phase group per pixel during operation are combined to provide one phase group signal 32. The phase group signals 32 of different phase groups during operation are obtained in one image acquisition.

(12) The scintillator layer 12 converts X-rays into (visible) light. The scintillator layer 12 may also be referred to as micro-structured scintillator layer, since the scintillator layer 12 comprises an array of scintillator channels 20.

(13) The scintillator channels 20 may for example relate to the micro-columns in a structured scintillator material. The micro-columns are parallel, needle-like structures, which have a diameter from 250 nm (nanometer) to 10 m (micrometer). They number into the millions per square centimeter yielding very high resolution imaging performance. The structured scintillator material may be prepared for example by vacuum evaporation. Alternatively, micro-columns may be etched into silicon in order to manufacture a matrix that can be filled with a scintillator material like Thallium doped caesium iodide. When X-rays enter those channels, they are converted into light, which is reflected by the micro-columns' sidewalls and thus contained within the micro-columns.

(14) Now referring to FIG. 2, an interferometer 34 is illustrated for phase contrast and/or dark-field X-ray imaging. The interferometer 34 comprises the phase grating structure 18 and the X-ray detector 10 according to one of the embodiments described above and in the following. The phase grating structure 18 and the X-ray detector 10 are arranged in an optical path 36 indicated with a dashed line, such that the phase grating structure 18 and the scintillator layer 12 of the X-ray detector 10 form an interferometer arrangement for correlating X-ray radiation. The phase grating structure 18 may also be referred to as phase grating structure G1, and the scintillator layer 12 may also be referred to as analyzer grating structure G2. The phase grating structure 18 may have a period of p.sub.1 with phase shifting lines, which creates a line interference pattern 35 with a fringe period p.sub.fringe on a surface of the scintillator layer 12 with the Talbot self-imaging effect (when there is no object of interest positioned in the optical path 36). The fringe period p.sub.fringe of the interference pattern 35 is typically in the order or microns and much smaller than the detector spatial resolution.

(15) The scintillator layer 12 with the array of the scintillator channels 20 functions like an analyzer grating structure, which is used to determine the lateral position and amplitude of the interference pattern, which are related to the differential phase and scattering properties of an sample, for example, an part of an patient. Light converted by the scintillator layer 12 can be detected by the photodiode layer 14.

(16) It is also noted that in FIG. 2, the phase grating structure 18 is illustrated to have a periodicity in one dimension along the x-axis, which thus creates a line interference pattern 35 in the x direction. However, it is appreciated that the phase grating structure 18 may also have a periodicity in the other directions. For example, the phase grating structure 18 may have a periodicity in a direction perpendicular to the x-axis and the optical path 36, which may create a two-dimensional interference pattern. To facilitate explanation of the present techniques, however, a one-dimensional phase grating structure will be generally discussed herein, though it is to be understood that a two-dimensional phase grating structure is also within the scope of the present techniques.

(17) Referring back to FIG. 1, the pixel 26, also referred to as super-pixel, which may for example have a dimension of 1 mm. It may be structured into e.g. 1000 sub-pixels of 1 m (in FIG. 1, only 16 sub-pixels are depicted).

(18) During operation, adjacent sub-pixels 30 receive signals having mutually shifted phases. The term mutually shifted phases relates to the phases that are shifted in relation to each other. It is noted that the mutually shifted phases as used herein refer to the signals being out of phases with each other. Signals with phase difference of n*2 (n is an integer) are considered to be in phase, and therefore do not have mutually shifted phases.

(19) In FIG. 1, the sub-pixels 30 that receive signals with different phases (i.e. mutually shifted phases of /2) are marked with different grey values or patterns, while the sub-pixels 30 that receive signals with identical phases (i.e. in phase) are marked with same grey value or pattern.

(20) Various methods may be appreciated for achieving a phase shift between adjacent sub-pixels 30.

(21) In an example, the photodiode pitch (i.e. the sub-pixel pitch 23) may be 1/n of the fringe period p.sub.fringe, where n in an integer larger than 1. The mutual phase shift between adjacent sub-pixels is 2/n. Every (n+1).sup.th sub-pixel 30 has identical mutually shifted phase and becomes member of the same phase group. FIG. 1 shows an example for n=4.

(22) In a further example, the pitch 22 of the scintillator channels 20 may be detuned by applying a correcting factor c to the fringe period p.sub.fringe of period interference patterns created by the phase grating structure 18, wherein 0<c<2; that is, pitch=c*p.sub.fringe. The detuned mode may be applicable to a scintillator layer that has X-ray insensitive gaps between adjacent scintillator channels. For example, FIGS. 3a and 3b show scintillator layers with a duty cycle (percentage of one pitch in which X-rays are detected) of 50%. In this manner, adjacent scintillator channels are configured to receive signals having mutually shifted phases. As indicated above, the scintillator channels 20 may be controllable in diameter from 250 nm to 10 m. Since the pitch 22 of the scintillator channels 20 is arranged to deviate from the fringe period (i.e. pitchp.sub.fringe) a phase shift is introduced between adjacent scintillator channels 20. Each sub-pixel 30, i.e. photodiode 28, may thus be assigned to a respective scintillator channel 20 such that the adjacent sub-pixels 30 during operation receive signals having mutually shifted phases determined by the scintillator channels 20. For example, the correcting factor c is 1.25. In other words, the scintillator layer 12 is designed to have a pitch 22 of 1.25*p.sub.fringe. Adjacent scintillator channels 20 have a phase offset of /2. Every fifth scintillator channels 20 will again have the same phase. Since each scintillator channel 20 is assigned with a photodiode 28, i.e. a sub-pixel 30. Every fifth sub-pixels 30 thus form a phase group of the pixel 26. Likewise, a correcting factor c of 0.75 can also introduce a phase offset of /2 between adjacent scintillator channels. Of course, the correcting factor c may also be 0.875, 1.1, 1.125, etc.

(23) It is also noted that the pitch 22 of the scintillator channels 20 as well as the sub-pixel pitch 23 of the sub-pixels 30 as shown in FIG. 1 are for illustrative purposes only. Although the scintillator channels 20 are illustrated to have the pitch 22 identical to the sub-pixel pitch 23 of the sub-pixels 30, it is to be understood that the pitch 22 and the sub-pixel pitch 23 may also be different. For example, the sub-pitch 23 is larger than the pitch 22.

(24) The sub-pixels 30 that during operation receive signals having mutually identical phases form a phase group per pixel.

(25) As indicated above, the term identical phase, also referred to as in-phase, relates to the situation where the signals have a phase difference of n*2, wherein n is an integer.

(26) The phase group is dependent on the sub-pixel pitch of an array of sub-pixels. For example, if adjacent sub-pixels have a phase offset of /m, every (m+1).sup.th sub-pixels form a phase group. The minimum number of phase groups in one interferometer period that allows extracting the phase is three in the case of a sinusoidal intensity oscillation. Of course, the adjacent sub-pixels may have smaller phase offset to obtain a better result.

(27) In order to obtain the phase group signals of the same phase group, the sub-pixels within the same phase group per pixel may be electrically connected with each other for combining the signals received by the sub-pixels within the same phase group into one phase group signals 32. Each pixel 26 may further comprise readout electronics 38 configured to receive the phase group signals 32 of different phase groups in one image acquisition.

(28) For example, in FIG. 1, every fifth sub-pixels 30 are configured to receive signals with identical phase. In other words, every fifth sub-pixels 30 form a phase group in the pixel 26. The sub-pixels 30 within the same phase group may be electrically connected (indicated with connected lines) and the received signals may be combined, for example, by sub-unit of the readout electronics 38 that performs addition of signals. The electrical connection may be either permanent (fixed by a permanent electrical connection scheme) or switchable.

(29) The phase group signals 32 of different phase groups are able to be obtained in one image acquisition, or in one imaging step. The phase group signals 32 of the different phase groups may cover the complete phase of a wavefront of the X-ray radiation 16 modulated by the phase grating structure 18.

(30) The phase group signals 32 may be further processed in the readout electronics 38 and read out.

(31) In an example, the phase group signals 32 per pixel during operation are read out as readout signals. In other words, all phase group signals 32 per pixel are read out. For example, in FIG. 1, four phase group signals 32 are read out as four readout signals.

(32) In a further example (not further shown), when there is an even number of phase group signals 32 per pixel, a sum of all phase group signals 32 per pixel and differences of pairs of phase group signals 32 per pixel with a mutual phase shift of it during operation are read out as readout signals.

(33) In other words, if there is an even number of phase group signals 32, there exist pairs of phase group signals 32 with a mutual phase shift of . The readout of all phase group signals may be replaced by reading out the sum of all phase group signals 32 and the difference of the signals of all pairs of phase group signals 32 with a mutual phase shift of .

(34) For example, when there are N (N is an even number) phase group signals, if the phase group signals are g.sub.i (i=1, 2, . . . , N) and the mutual phase shift of any pair g.sub.i and g.sub.i+N/2 is , the following signals are generated and read out: g.sub.1+g.sub.2+ . . . g.sub.N, g.sub.1g.sub.1+N/2, g.sub.2g.sub.2+N/2, . . . , g.sub.N/2g.sub.N. In this manner, the number of readout signals per pixel is reduced from N to (N/2+1). The required operation to transform the phase group signals to the readout signals may be implemented in the readout electronics, which may be either analogue or digital. In the example of FIG. 1, the number of readout signals per pixel may be further reduced to 3. In a further example, if N is 16, the number of readout signals per pixel may be further reduced to 9.

(35) The number of readout signals may further by reduced if the extraction of the mean intensity, the differential phase and the modulation depth from the acquired phase group signals is generated per super-pixel and read out.

(36) Advantageously, the use of micro-structured scintillator layer as an analyzer grating structure may improve the visibility (a measure for the acquisition quality of the interferometer) of the received signals compared to the conventional absorber grating. In addition, the combination of signals received by the sub-pixels into a limited number of phase groups (e.g. four phase groups in FIG. 1) may reduce the number of photodiode channels and read-outs, thus simplifying the design and layout of the X-ray detector. Since a phase-contrast signal that covers a complete phase of a wavefront of the X-ray radiation is extracted without the need of actual phase stepping (which may imply multiple exposures and low speed), a fast, low-dose, and high sensitive (phase-contrast) X-ray imaging may be achieved.

(37) Further, although only one pixel 26 and 16 sub-pixels 30 are illustrated in FIG. 1, the photodiodes 28 may form a continuous photosensitive layer of sub-pixels 30.

(38) FIG. 3a and FIG. 3b show two further examples of the X-ray detector 10, which comprises X-ray insensitive gaps between adjacent scintillator channels. In FIGS. 3a and 3b, these gaps are illustrated as intervals between adjacent scintillator channels. The X-ray insensitive gaps (or areas) may be formed for example by etching process. X-rays that pass through these gaps cannot be converted into light.

(39) In both examples, a second detector layer 40 is provided on one surface of the first detector layer 24. The surface is perpendicular to an orientation of the scintillator channels 20 of the first detector layer 24. The second detector layer 40 comprises a scintillator layer 42 with an array of periodically arranged scintillator channels 44 with the same pitch as the scintillator channels 20 of the first detector layer 24. The scintillator layer also comprises a photodiode layer 46. Each scintillator channel 44 of the second detector layer 40 is arranged to be displaced in surface direction in relation to the adjacent scintillator channel 20 of the first detector layer 24 by half of the pitch 47.

(40) The term perpendicular refers to an angle of approximately 90, comprising a deviation of +/15 for example.

(41) In an example, shown in FIG. 3a, the first 24 and the second 40 detector layers are arranged with their photodiode layer 14, 46 and scintillator layers 12, 42 in a stacked order, each detector layer 24, 40 having the same orientation with respect to incoming X-ray radiation 16.

(42) In a further example, shown in FIG. 3b, the first 24 and the second 40 detector layers are arranged in a stacked arrangement with their photodiode layers 14, 46 back to back, the first 24 and second 40 detector layers having an opposite orientation with respect to incoming X-ray radiation 16.

(43) In this manner, X-rays, which pass through the X-ray insensitive gaps between adjacent scintillator channels of the first detector layer, can be detected or captured by the scintillator channels of the second detector layer, or vice versa. X-ray dose utility may thus be improved.

(44) As a further option to the above-mentioned embodiments, light shield elements (not further shown), may be provided between two adjacent scintillator channels 20, 44 such that optical crosstalk between said two adjacent scintillator channels is reduced.

(45) The light shield elements may be either optical filters for selectively transmitting light of different wavelengths, or optical reflectors for selectively reflecting light of different wavelengths. The light shield may be selected to block completely all the light. The light shield elements may be provided as a grid-like or grating-like structure. The light shield elements may be provided with a width of maximum half the pitch width. In case of the light shield elements being transparent to X-ray, by a displacement of the second detector layer of half the pitch, or period, the part of X-ray radiation that has not been affected by the scintillator elements of the first detector layer is also used for image data detection.

(46) FIG. 4a demonstrates an example of a sampling pattern used in explaining the theory and operation of a conventional phase stepping method, whilst FIG. 4b shows an example of a sampling pattern used in explaining the theory and operation of the X-ray detector 10 according to an embodiment of the invention.

(47) In FIGS. 4a and 4b, the horizontal axis represents the x-axis (arbitrary unit), and the vertical axis represents intensity (arbitrary unit).

(48) A conventional interferometer generates an X-ray wave pattern at the analyzer grating structure G.sub.2 with intensity along x of:
I(x)=a(1+v cos(2x/p.sub.fringe+))

(49) The following three imaging parameters are needed to be extracted:

(50) a is the mean intensity used to estimate the absorption;

(51) v is the modulation depth of the interferometer coding to estimate dark field signal; and

(52) is the differential phase.

(53) Now looking to just one detector pixel, since the system is not able to provide a higher spatial resolution as the detector resolution, the three parameters are considered to be constant over the pixel under consideration.

(54) The detector resolution is not sufficient to sample the high spatial signal frequency (e.g. p.sub.fringe10 m). The conventional phase stepping method applies the trick to sample the wave with a well-defined spatial frequency of 2/p.sub.fringe using the analyzer grating structure G.sub.2. Behind the analyzer grating structure G.sub.2, the comb-filtered wave is measured by using a larger detector pixel (e.g. 1 mm). The pixel sums the comb-filtered wave over the entire detector pixel. Because the spatial wave frequency matches p.sub.fringe, the sum of several points of the wave at the same relative phase is obtained. If there is no variation of the three wave parameters, the individual signal contribution should be identical and the detector averaging has no negative impact. The signal wave is obtained by measuring at a well-defined phase. In order to obtain the three imaging parameters, these measurements at different comb-filter positions are repeated by shifting the analyzer grating structure G.sub.2 (mechanically or digitally). The large detector pixel integrates these signals in multiple acquisitions.

(55) The principle of the conventional phase stepping method is demonstrated in FIG. 4a. The left column shows (four times) the wave pattern before the analyzer grating structure G.sub.2. The right column shows the comb-filtered signals for four different x offsets (i.e. signals of different phase group). The large detector pixel integrates these signals in four acquisitions.

(56) The principle of the X-ray detector 10 according to an embodiment of the invention is illustrated in FIG. 4b. If a high resolution scintillator and a fine structured photodiode array are used, the wave pattern is sampled using the effective comb structure of the photodiode array. For example, if the pitch of the photodiode array is p.sub.fringe/4, a situation as shown in FIG. 4b is obtained. In FIG. 4b, each photodiode sub-pixel samples one quarter of one fringe period. For data reduction, the signals from all sub-pixel of each pixel with mutually the same phase, i.e. signals from the sub-pixels within the same phase groups in a pixel are combined, e.g. summed. Signals from the same phase groups are indicated with the same gray level in FIG. 4b.

(57) Compared to a conventional phase stepping method as demonstrated in FIG. 4a, phase stepping may not be required anymore because the required phase offsets are measured in one acquisition. Furthermore, the functionality of the analyzer grating structure G2 is replaced with the microstructured scintillator layer 12, which is combined with the X-ray detector into one unit. Since X-rays are neither blocked nor not detected in the structured scintillator design, the dose efficiency may be improved. The visibility may also be improved, because the phase interval integrated by the detector is reduced. In the two examples demonstrated in FIGS. 4a and 4b, a conventional design samples the wave by integration of an interval of p.sub.fringe/2. This is reduced to an interval of p.sub.fringe/4 in the example given in FIG. 4b. If we model the effective comb-filtration with a convolution with a rectangle, the frequency response for the interesting spatial frequency is improved from (sin(/2))/(/2)0.64 to (sin(/4))/(/4)0.9 giving about 40% better visibility.

(58) FIG. 5 shows an X-ray imaging system 100, comprising an X-ray source 48 and an interferometer according to one of the embodiments described above. The X-ray source 48 is configured to apply X-ray radiation 16 to an object of interest 50 positionable in the optical path 36 to be detected by the X-ray detector 10 of the interferometer 34.

(59) The X-ray source 48 may be a conventional X-ray tube. A source grating structure G.sub.0 (not further shown) may be introduced to ensure sufficient spatial coherence. The source grating structure G.sub.0 divides the X-ray source 48 into many mutually incoherent line sources, each of which adds constructively (but incoherently) to the interference pattern. Alternatively, the X-ray source 48 may be a source with a spatial coherence, e.g. high brilliant synchrotron radiation sources with monochromatic and almost parallel beam.

(60) Unlike conventional phase stepping method, the phase information can be acquired in one image acquisition. In other words, two major disadvantages (low-speed and multiple exposures) associated with the conventional phase-stepping techniques may be removed (or at least reduced).

(61) The X-ray imaging system 100 may be a medical imaging system, an inspection imaging system, or an industrial imaging system.

(62) The term medical imaging relates to irradiating an object with radiation, e.g. X-ray radiation, produced by an X-ray source and to detect the respective attenuation and/or phase information by an X-ray detector. Parts of the energy of the X-ray beam are absorbed when passing the object. On the opposite side of the object of interest, i.e. a portion of patient, a detector or a film captures attenuation and/or phase information, resulting in a medical or clinical image.

(63) The term inspection imaging system may also be referred to as security imaging system. For example, airport security luggage scanners use X-rays for inspecting the interior of luggage for security threats before loading on aircraft. Border control truck scanners use X-rays for inspecting the interior of trucks.

(64) An industrial imaging system may be used for inspecting materials for hidden flaws by using the ability of short X-rays to penetrate various materials.

(65) FIG. 6 shows a method 200 for phase contrast and/or dark-field X-ray imaging. The method comprises the following steps:

(66) In a first step 202, also referred to as step a), X-ray radiation is generated to examine an object of interest, the X-ray radiation being modulated by a phase grating structure.

(67) In a second step 204, also referred to as step b), the modulated X-ray radiation is converted into light by a scintillator layer of an X-ray detector, and the light is detected by a photodiode layer of the X-ray detector.

(68) In the second step 204, i.e. in step b), the scintillator layer comprises an array of periodically arranged scintillator channels with a pitch forming an analyzer grating structure. The scintillator layer and the photodiode layer form a first detector layer comprising a matrix of pixels. Each pixel comprises an array of photodiodes, each photodiode forming a sub-pixel. Adjacent sub-pixels during operation receive signals having mutually shifted phases. The sub-pixels that during operation receive signals having mutually identical phase form a phase group per pixel. The signals received by the sub-pixels within the same phase group per pixel are combined to provide one phase group signal. The phase group signals of different phase groups are obtained in one image acquisition.

(69) In an example, the phase group signals per pixel during operation are read out as readout signals.

(70) In a further example, when there is an even number of phase group signals per pixel, a sum of all phase group signals per pixel and differences of pairs of phase group signals per pixel with a mutual phase shift of it during operation are read out as readout signals.

(71) In another exemplary embodiment of the present invention, a computer program or a computer program element is provided that is characterized by being adapted to execute the method steps of the method according to one of the preceding embodiments, on an appropriate system.

(72) The computer program element might therefore be stored on a computer unit, which might also be part of an embodiment of the present invention. This computing unit may be adapted to perform or induce a performing of the steps of the method described above. Moreover, it may be adapted to operate the components of the above described apparatus. The computing unit can be adapted to operate automatically and/or to execute the orders of a user. A computer program may be loaded into a working memory of a data processor. The data processor may thus be equipped to carry out the method of the invention.

(73) This exemplary embodiment of the invention covers both, a computer program that right from the beginning uses the invention and a computer program that by means of an up-date turns an existing program into a program that uses the invention.

(74) Further on, the computer program element might be able to provide all necessary steps to fulfil the procedure of an exemplary embodiment of the method as described above.

(75) According to a further exemplary embodiment of the present invention, a computer readable medium, such as a CD-ROM, is presented wherein the computer readable medium has a computer program element stored on it which computer program element is described by the preceding section.

(76) A computer program may be stored and/or 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.

(77) However, the computer program may also be presented over a network like the World Wide Web and can be downloaded into the working memory of a data processor from such a network. According to a further exemplary embodiment of the present invention, a medium for making a computer program element available for downloading is provided, which computer program element is arranged to perform a method according to one of the previously described embodiments of the invention.

(78) It has to be noted that embodiments of the invention are described with reference to different subject matters. In particular, some embodiments are described with reference to method type claims whereas other embodiments are described with reference to the device type claims. However, a person skilled in the art will gather from the above and the following description that, unless otherwise notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters is considered to be disclosed with this application. However, all features can be combined providing synergetic effects that are more than the simple summation of the features.

(79) 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 in practicing a claimed invention, from a study of the drawings, the disclosure, and the dependent claims.

(80) The figures are only schematically illustrated and not to scale. Same reference signs refer to same or similar features throughout the figures.

(81) 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 processor or other unit may fulfil the functions of several items re-cited in the claims. The mere fact that certain measures are re-cited 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.