Abstract:
The invention relates to the field of X-ray differential phase contrast imaging. For scanning large objects and for an improved contrast to noise ration, an X-ray device ( 10 ) for imaging an object ( 18 ) is provided. The X-ray device ( 10 ) comprises an X-ray emitter arrangement ( 12 ) and an X-ray detector arrangement ( 14 ), wherein the X-ray emitter arrangement ( 14 ) is adapted to emit an X-ray beam ( 16 ) through the object ( 18 ) onto the X-ray detector arrangement ( 14 ). The X-ray beam ( 16 ) is at least partial spatial coherent and fan-shaped. The X-ray detector arrangement ( 14 ) comprises a phase grating ( 50 ) and an absorber grating ( 52 ). The X-ray detector arrangement ( 14 ) comprises an area detector ( 54 ) for detecting X-rays, wherein the X-ray device is adapted to generate image data from the detected X-rays and to extract phase information from the X-ray image data, the phase information relating to a phase shift of X-rays caused by the object ( 18 ). The object ( 18 ) has a region of interest ( 32 ) which is larger than a detection area of the X-ray detector ( 18 ) and the X-ray device ( 10 ) is adapted to generate image data of the region of interest ( 32 ) by moving the object ( 18 ) and the X-ray detector arrangement ( 14 ) relative to each other.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to the field of X-ray imaging. In particular, the invention relates to an X-ray device for imaging an object, a method for controlling an X-ray device, a computer-readable medium and a program element. 
       BACKGROUND OF THE INVENTION 
       [0002]    X-ray differential phase-contrast imaging (DPCI) visualizes the phase information of coherent X-rays passing a scanned object. In addition to classical X-ray transmission imaging, DPCI may determine not only the absorption properties of the object along a projection line, but also the phase-shift of the transmitted X-rays, and thus may provide valuable additional information. After the object, a phase-shifting grating (also known as phase grating) is placed, working as a beam splitter. The resulting interference pattern contains the required information about the beam phase-shift in the relative position of its minima and maxima, typically in the order of several micrometers. Since a common X-ray detector, which may have a typical resolution in the order of 150 μm, may not be able to resolve such fine structures, the interference is sampled with a analyzer grating (also known as absorber grating), which features a periodic pattern of transmitting an absorbing strip with a periodicity similar to that of the interference pattern. The similar periodicity produces a Moiré pattern behind the grating with a much larger periodicity, which is detectable by a common X-ray detector. To obtain the differential phase-shift, the absorber grating and the phase grating are shifted laterally with respect to each other by fractions of the grating pitch, which is typically of the order of 1 μm. This movement is referred to as phase stepping or phase scanning. The phase-shift can be extracted from the particular Moiré pattern measured for each position of the absorber grating. 
         [0003]    For example, in EP 1 731 099 A1, an X-ray interferometer arrangement is shown that can be used to execute grating-based differential phase-contrast imaging. The X-ray interferometer comprises an incoherent X-ray source with a source grating and a detector arrangement with a phase grating and an absorber grating. 
       SUMMARY OF THE INVENTION 
       [0004]    In grating-based differential phase-contrast imaging, gratings with high aspect ratio are used. These gratings may need to be aligned well with the optical axis of the system. From a practical and of manufacturing point of view, the trenches or lamellae of the gratings may have to be preferable orthogonal to a flat substrate. If such a flat grating/detector arrangement is used, the visibility of structures of the object may drop quickly with the distance of the object to the optical axis. In particular, if the distance orthogonal to the grating orientation is considered, the visibility may drop quickly due to the misalignment between the trenches of the gratings and the X-rays. In the direction parallel to the orientation of the gratings, due to the increasing distance to the X-ray source, also the visibility may decrease. 
         [0005]    For an effective use, the grating lamellae may need to be aligned almost parallel to the incident X-ray wave vector. Otherwise, intended rectangular profiles for X-ray absorption or X-ray phase-shift become trapezoidal distant from the optical center, which may result in a strong decrease in the visibility of interference pattern and therefore in a degradation of the contrast to noise ratio. 
         [0006]    A further problem may arise from incoherently scattered X-ray radiation, which may be scattered by the object. The additionally scattered photons may create an unwished signal offset in the absorption image and may decrease the contrast to noise ratio not only in absorption image but also in the differential phase-contrast image. 
         [0007]    There may be a need for an X-ray device for differential phase contrast imaging provided to scan large objects and having an improved contrast to noise ratio. 
         [0008]    This need may be met by the subject-matter of the independent claims. Exemplary embodiments of the invention are evident from the dependent claims. 
         [0009]    A first aspect of the invention relates to an X-ray device for imaging an object. 
         [0010]    According to an embodiment of the invention, the X-ray device comprises an X-ray emitter arrangement and an X-ray detector arrangement, wherein the X-ray emitter arrangement is adapted to emit an X-ray beam through the object onto the X-ray detector arrangement. The X-ray emitter arrangement may be a device on one side of the object and the X-ray detector arrangement may be a further device on another side of the object, for example opposite to the X-ray emitter arrangement. For example for medical applications, the object may be a human or an animal lying on a table and the X-ray emitter arrangement is located over the object and the X-ray detector arrangement is located below the object on the table. 
         [0011]    According to an embodiment of the invention, the X-ray emitter arrangement is adapted to generate an X-ray beam that is at least partial spatial coherent. It has to be understood, that an at least partial spatial coherent X-ray beam may comprise X-rays that are only locally spatial coherent. For example, only X-rays that are separated from each other less than 1 μm may have to be coherent. 
         [0012]    According to an embodiment of the invention, the X-ray emitter arrangement may comprise an X-ray source for generating spatial incoherent X-rays, for example an X-ray tube, and a source grating for creating an at least partial spatial coherent X-ray beam from the incoherent X-rays from the X-ray source. With such an arrangement, a beam of at least partial spatial coherent X-rays may be formed. 
         [0013]    According to an embodiment of the invention, the X-ray emitter arrangement is adapted to generate a fan-shaped X-ray beam. 
         [0014]    A fan-shaped X-ray beam may be a beam substantially in the form of a cone, i.e. the X-rays of the beam are coming from a region that is very small with respect to the object of interest, wherein the dimensions of the cone orthogonal to the axis of the cone substantially differ from each other. These two dimensions may be defined by a fan angle and a cone angle of the beam, wherein the fan angle is the small angle and the cone angle is the large angle, which may be as large that the fan-shaped beam covers the whole region of interest of the object. 
         [0015]    Also, a fan-shaped beam may be a beam in the form of a pie slice, wherein thickness or width of the pie slice is small compared to the length of the pie slice. In this case, the X-rays are parallel with respect to the thickness direction and spread with respect to another direction. 
         [0016]    A first dimension of the fan-shaped beam may be much larger than a second dimension, when the first dimension of the beam is at least 5 to 10 times longer than the second dimension of the beam. For example, the fan-shaped beam may have a rectangular cross-section orthogonal to the optical axis of the system wherein the one side of the rectangle is at least 5 to 10 times longer than the other side of the rectangle. 
         [0017]    According to an embodiment of the invention, the X-ray emitter arrangement comprises a collimator for limiting the X-ray beam to a fan-shaped X-ray beam. For example, the X-ray emitter arrangement may comprise an X-ray source that generates a coherent X-ray beam and the collimator generates a fan-shaped coherent X-ray beam from the X-rays emitted from the X-ray source. 
         [0018]    For example, the X-ray emitter arrangement may be equipped with a collimator generating a fan-beam and a source grating which generates a number of X-ray lines near the X-ray focal spot. The size of the detector along the axial direction may be limited to a range within which no significant degradation effects due to misaligned grating lamellae or slits may be expected. 
         [0019]    According to an embodiment of the invention, the X-ray detector arrangement comprises a phase grating and an absorber grating. A grating may be a plurality of parallel aligned slits or trenches, wherein the grating is more transparent to X-rays at the slits or trenches as between them. For example, the slits or trenches may be formed by lamellae that are formed on a substrate. 
         [0020]    According to an embodiment of the invention, the X-ray device is adapted to move the phase grating and the absorber grating relative to each other, in particular for executing a phase scanning step. For example, the X-ray device may comprise a step motor or piezo actuator for moving the phase grating with respect to the absorber grating or vice versa. By moving the two gratings relative to each other, behind the grating interference patterns are created that may be used to extract information, how the phase of spatial coherent X-rays has been shifted by the object. Generally, the X-ray device may be adapted to move the phase grating, the absorber grating and/or the source grating for executing a phase scanning step. 
         [0021]    According to an embodiment of the invention, the X-ray detector arrangement may comprise a detector for detecting X-rays. With such a detector, the interference patterns created by the phase grating and the absorber grating may be analyzed. For example, such a detector may comprise detector elements that are adapted to detect the intensity of X-rays falling on the respective detector element, i.e. the detector may be a detector for detecting intensities of X-rays. As a second example, the X-ray detector may be a detector adapted for counting photons, i.e. the detection of X-rays may be executed by counting X-ray photons falling onto the detector. 
         [0022]    According to an embodiment of the invention, the X-ray detector is an area detector. An area detector may be a detector that is adapted to detect a two-dimensional image. For example, an area detector may comprise detector elements or pixels that are arranged at a face of the detector in two dimensions for example in a rectangular pattern. It may be possible that the detection area of the detector does not have to be planar. 
         [0023]    According to an embodiment of the invention, the area detector, the phase grating and/or the absorber grating are adapted to the fan-shaped X-ray beam. This may mean that the area detector, the phase grating and the absorber grating may substantially have the same shape as the fan-shaped X-ray beam at the respective position of the respective component of the X-ray detector arrangement (i.e. the phase grating, the absorber grating and/or the area detector). For example, if the X-ray beam has a rectangular cross-section, the phase grating, the absorber grating and/or the X-ray detector may have a rectangular form. The phase grating, the absorber grating and the X-ray detector may have the same dimensions as the fan-shaped X-ray beam. For example, if the distance between the X-ray source or the X-ray emitter arrangement and the detector or the X-ray detector arrangement is about 1 m, the width of the detector in the direction orthogonal the fan-shaped beam may be about 6 cm. However, the (maximal) width of the detector may be smaller or larger. The width of the detector may be dependent on the aspect ratio, i.e. the relationship between height and pitch, of the used grating. 
         [0024]    For example, to scan the field of view of a region of interest of the object, a detector with a small fan angle, but a large cone angle that covers the entire object may be used. At each detector position, several projections may be taken with different relative grating positions, i.e. a phase scanning is performed, in order to allow phase retrieval. 
         [0025]    According to an embodiment of the invention, the X-ray device is adapted to generate image data from the detected X-rays and to extract phase information from the X-ray image data wherein the phase information relates to a phase-shift of X-rays caused by the object. As already said, by moving the phase grating and the absorber grating relative to each other, interference patterns from the X-rays transmitted through the object are created on the area detector. At a number of relative positions of the phase grating and the absorber gratings image data may be taken with the detector. From these image data, which contain interference patterns in the form of differing X-ray intensities, the phase-shift from one point to another point may be determined. 
         [0026]    According to a further embodiment of the invention, the object has a region of interest which is larger than a detection area of the X-ray detector. The X-ray device may be adapted to generate image data of the region of interest by moving the object and the X-ray detector arrangement relative to each other. 
         [0027]    In other words, the X-ray device may adapted to move the object and the X-ray detector arrangement relative to each other, such that a region of interest of the object may be scanned that is larger than the X-ray detector arrangement. 
         [0028]    This may have the advantage that the X-ray device has a high visibility in all parts of the scanned image and an improve contrast to noise ratio. 
         [0029]    For example, in a first step at a first relative position of the object and the X-ray detector, a phase scanning of a first part of the region of interest of the object may be done. I.e. at the first relative position, a series or plurality of raw data images with different relative positions of the phase grating and the absorber grating are recorded. With this series of raw data images, the X-ray device may create first image data, representing phase information of the first part of the region of interest. After that, in a second step, the X-ray device may move the object and the X-ray detector arrangement into a second relative position different from the first relative position. At this second relative position, the X-ray device scans a second part of the region of interest of the object. This is again done by taking a series of raw data images at different relative positions of the phase grating and the absorber grating. From these series or plurality of raw data images, the X-ray device may create second image data containing phase information of the second part of the region of interest. 
         [0030]    After that, the X-ray device may add the second image data to the first image data, to create aggregated image data containing phase information of the first part of the region of interest and of the second part of the region of interest. 
         [0031]    In other words, the X-ray device may be adapted to aggregate first image data containing phase information of a first part of the region of interest with second image data containing phase information of a second part of the region of interest to aggregated image data. The single image data may be put together to aggregated image data. 
         [0032]    It has to be understood that the above-mentioned steps may be repeated, i.e. a third part of the region of interest may be scanned and so on. The steps may be repeated until the whole region of interest is scanned. 
         [0033]    According to an embodiment of the invention, the X-ray emitter arrangement comprises an X-ray source with X-ray emitter lines adapted to generate the fan-shaped spatial at least partial coherent X-ray beam. In other words, the X-ray emitter arrangement may comprise a structured X-ray source comprising emitter lines, wherein the emitter lines fulfil substantially the same functions as the slits of the source grating. However, the emitter lines themselves may generate the X-rays. 
         [0034]    According to an embodiment of the invention, the X-ray emitter lines comprise a cathode with carbon nanotubes or other distributed X-ray sources for emitting electrons. Such an arrangement may have the advantage, that carbon nanotubes may be adapted to emit electrons at room temperature. 
         [0035]    According to an embodiment of the invention, the grating lines or grating slits of the source grating, the phase grating and/or the absorber grating are aligned parallel to the fan-shaped X-ray beam. The gratings may be aligned with the long edge of the detector. 
         [0036]    According to an embodiment of the invention, the X-ray device is adapted to move the object and the X-ray detector arrangement relative to each other in an axial direction orthogonal to the fan-shaped X-ray beam. Further, the X-ray device may be adapted to move the object and the X-ray detector arrangement together with the X-ray emitter arrangement relative to each other in the axial direction. In other words, the X-ray detector arrangement and the X-ray emitter arrangement may be rigidly mechanically connected with each other. 
         [0037]    The X-ray device may be adapted to conduct the movement in steps. Further each step may be adapted to the width or thickness of the detector, such that the image data taken at the different relative positions may be easily aggregated. It may also be possible, that the steps are such that the image data slightly overlap. 
         [0038]    According to an embodiment of the invention, the X-ray device comprises an actuator for moving the object with respect to the X-ray emitter arrangement and the X-ray detector arrangement. The X-ray emitter arrangement and the X-ray detector arrangement may be stationary with respect to the vicinity of the X-ray device or with respect to the ground and with respect to each other. 
         [0039]    The object may be attached to a component of the X-ray device movable by the X-ray device, for example the object is a human being lying on a movable table, wherein the X-ray device is able to move the component into the axial direction in defined steps, while differential phase contrast imaging snapshots or image data of object slices are performed at each scan position. This may have the advantage that the field of view is not limited in the axial direction except for the possible limits of the X-ray device, which can be extended very easily. A further advantage may be that no cone beam has to be used, i.e. a beam with a large fan angle and thus the incoherently scattered X-ray radiation may be limited to arise only in that volume of the object which is illuminated by the fan-beam, which may be quite smaller than the volume which would be illuminated for a large field of view detector. 
         [0040]    According to an embodiment of the invention, the X-ray device may comprise an actuator for moving the X-ray emitter arrangement and/or the X-ray detector arrangement with respect to the object. In this case, the object may be stationary with respect to the vicinity of the X-ray device. 
         [0041]    For example, the object may be fixed stationary, while the X-ray emitter arrangement and the X-ray detector arrangement which may be connected with each other may be moved in defined steps or continuously with respect to the object. 
         [0042]    According to an embodiment of the invention, the X-ray device comprises an actuator for moving the X-ray emitter arrangement and/or the X-ray detector arrangement around the object, for example in a rotational movement. In this case, the X-ray detector arrangement may be moved around the object to different positions, for example with the help of a rail the detector arrangement is sliding on, and the X-ray emitter arrangement may be rotated around an axis, such that the emitted fan-shaped X-ray beam falls onto the detector. However, it is possible, that the X-ray emitter arrangement and the X-ray detector arrangement are rigidly mechanically connected, for example by a arm, and are rotated around a common rotation axis. 
         [0043]    A large field of view may be covered by rotating the detector arrangement around an axis through the focal spot. 
         [0044]    The X-ray device performing a rotational motion of the detector and/or the X-ray emitter arrangement may be used for mammography. 
         [0045]    The relative movement of the object and the X-ray detector arrangement (may be together with the X-ray emitter arrangement) either linear or rotational may comprise a plurality of steps. In each step, image data, which has a small dimension with respect to the moving direction due to the fan-shaped beam, but which may comprise the whole region of interest in the direction orthogonal to the movement, may be recorded. After that, the image data may be joined to a complete image of this complete region of interest of the object. 
         [0046]    According to an embodiment of the invention, the X-ray device is adapted to move at least one grating, for example the phase grating, the absorber grating or the source grating (for example in the axial direction) such that the one grating remains fixed with respect to the object, when the object moves relative to the X-ray emitter arrangement or the X-ray detector arrangement. In other words, at least one of the gratings is moved such that in the moving reference system of the object a phase scanning of the object may be executed. 
         [0047]    In this case, the grating lines may be aligned orthogonal to the scan axis or axial direction. Therefore, the phase stepping direction may be parallel to the axial direction (linear relative movement) or substantially parallel to the rotation direction (rotational movement of the object). 
         [0048]    In this case, the movement of at least one grating may be performed in large steps, wherein the relative movement of the object and the detector arrangement may be performed in small steps or continuously. The movement of the at least one grating in a large step may be executed between two phase stepping sequences. 
         [0049]    For example, the phase stepping may be performed in large steps for the source grating (for example by a scanning actuator means) and in smaller steps (or continuously) for either the object or the detector arrangement. Generally, it is also possible that the large steps may be also performed for the phase grating and/or the absorber grating. 
         [0050]    For example, a large step may be identical to n small steps with n being the number of total phase steps per view or per phase scanning. 
         [0051]    This arrangement may have the advantage, that larger masses (for example the object or the whole X-ray device except the source grating) have not to be accelerated during single steps, but can be instead moved in a constant speed. 
         [0052]    An efficient way to combine the scanning direction with the direct direction of phase stepping may be possible if the grating lines are aligned orthogonal to the axial direction. In this case, one of the gratings may be kept at a fixed position during a phase stepping cycle or phase stepping step, while the other gratings (in general combined with the X-ray emitter and/or detector arrangement as an inertial mass) may be moved with constant speed. After a phase scanning cycle or a phase scanning step, the fixed grating (with low mass) can be moved in a large step by a slice width. 
         [0053]    According to an embodiment of the invention, the X-ray emitter arrangement comprises an X-ray source with switchable emitter lines. This means, that not all the emitter lines may be activated together but that some or all of the emitter lines may be switched on and off independently from each other. For example, this may be done with an anode above a cathode with carbon nanotubes, wherein the anode comprises different strips they may be independently from each other connected with a voltage source. 
         [0054]    According to an embodiment of the invention, the X-ray emitter arrangement is larger in the direction of movement than the X-ray detector arrangement, wherein the X-ray device is adapted to switch the emitter lines such that solely the emitter lines opposite to the X-ray detector arrangement are switched on for a phase scan. For example, the X-ray source may be spatially fixed but may provide individually switchable emitter lines over the whole scanning range. While the detector may be moved continuously or in steps, the emitter lines currently opposite of the detector arrangement may be individually switched on and off. 
         [0055]    If the extension of an X-ray emitter arrangement is made large enough with individually switchable emitter lines, it may be possible that the stepping of the X-ray emitter arrangement becomes obsolete, as single emitter lines may be switched on or off directly opposite to the moving X-ray detector arrangement. 
         [0056]    According to an embodiment of the invention, the X-ray device is adapted to analyze an X-ray intensity of the X-rays at the X-ray detector arrangement during a first scan step. For example, the detected X-ray intensity is analyzed by the X-ray device during the scan for each position in order to evaluate the dose efficiency. 
         [0057]    According to an embodiment of the invention, the X-ray device is adapted to set an intensity of the X-rays emitted by the X-ray emitter arrangement for a second scan step based on the analyzed X-ray intensity of the first scan step. For example, the X-ray intensity for each line or for each scan position is adapted for dose efficiency using the dose efficiency analysis results of prior scanned lines or positions. 
         [0058]    According to an embodiment of the invention, the X-ray device is adapted to set the scan speed of a second scan step based on the analyzed X-ray intensity of the first scan step. The scan speed during a scan step may be the speed of the movement of the object or the X-ray emitter arrangement or the X-ray detector arrangement. The scan speed may also be the speed of the grating during one phase scanning step. For example, the scan speed and thus the X-ray exposure per line or per scan step is adapted for dose efficiency using the dose efficiency analysis results of prior scanned lines or prior scan steps. 
         [0059]    The first scan step and the second scan step may be individually phase scanning steps at different relative positions of the components of the X-ray device, when the X-ray device is moving the object and the X-ray detector arrangement relative to each other continuously or in small steps. 
         [0060]    For example, the image data of a line or the image data generated during one phase scanning step may be real-time analyzed for dose efficiency, in order to maintain a homogeneous contrast to noise ratio. As a result of the dose efficiency analysis, either the X-ray intensity or the scan speed may be adjusted or set. Also a combination thereof may be adjusted or set. For example, in a medical imaging application only a thin object slice may be scanned for a phase scanning step and the dose spent for the next step and therefore the total harmfulness to the patient due to X-ray exposure may be reduced. 
         [0061]    This may have the advantage that the X-ray dose a patient is exposed may be decreased. If a large detector is used, a local illuminating X-ray intensity is directly coupled to the tube load, which means that the dose which may be optimally adapted to a first part of the image area might not be optimally adapted to another area of the image area, which, for example, may be caused by different object thicknesses at the two areas. The applied X-ray intensity is adapted to the local object properties during the overall scan, in order to optimize the deposited dose for a more homogeneous contrast to noise ratio in the image. 
         [0062]    A further aspect of the invention is a method for controlling an X-ray device. 
         [0063]    According to an embodiment of the invention, the method comprises the steps of: generating a fan-shaped at least partial spatial coherent X-ray beam; transmitting the X-ray beam through an object, a phase grating and an absorber grating onto an X-ray area detector; generating image data from X-rays detected by the X-ray area detector; extracting phase information from the image data, the phase information relating to a phase-shift of X-ray caused by the object. 
         [0064]    According to an embodiment of the invention, the method comprises the steps of: moving the object and the X-ray detector arrangement relative to each other; generating image data of a region of interest of the object, wherein the region of interest is larger than a detection area of the X-ray area detector. 
         [0065]    According to an embodiment of the invention, the method comprises the step of: Generating the fan-shaped at least partial spatial coherent X-ray beam with an X-ray source having X-ray emitter lines, in particular X-ray emitter lines comprising a cathode with carbon nanotubes. 
         [0066]    According to an embodiment of the invention, the method comprises the step of: Moving at least one grating, for example the phase grating, the absorber grating or the source grating such that the at least one grating remains fixed with respect to the object, when the object, the X-ray emitter arrangement and/or the X-ray detector arrangement move relative to each other. 
         [0067]    According to an embodiment of the invention, the method comprises the steps of: 
         [0068]    Moving the object, the X-ray emitter arrangement and/or the X-ray detector continuously or in small steps relative to each other; Moving at least one of the gratings in large steps. 
         [0069]    According to an embodiment of the invention, the method comprises the step of: 
         [0070]    Analysing an X-ray intensity of the X-rays at the X-ray detector arrangement during a first scan step. 
         [0071]    According to an embodiment of the invention, the method comprises the step of: 
         [0072]    Setting an intensity of the X-rays emitted by the X-ray emitter arrangement for a second scan step based on the analysed X-ray intensity of the first scan step. 
         [0073]    According to an embodiment of the invention, the method comprises the step of: 
         [0074]    Setting a scan speed of a second scan step based on the analysed X-ray intensity of the first scan step. 
         [0075]    It has to be understood that method steps described with respect to the device may also be embodiments of the method and vice versa. 
         [0076]    The X-ray device and the method for controlling an X-ray device may be used in stationary transmission geometries (i.e. mammography, fluoroscopy) but also for computed tomography (CT) or related rotational X-ray imaging technologies. 
         [0077]    A further aspect of the invention relates to a computer-readable medium, in which a computer program for controlling an X-ray device is stored, which, when being executed by a processor (for example a processor of the X-ray device), is adapted to carry out the steps of the method as described in the above and in the following. 
         [0078]    A computer-readable medium may be a floppy disk, a hard disk, an USB (Universal Serial Bus) storage device, a RAM (Random Access Memory), a ROM (Read Only memory) and an EPROM (Erasable Programmable Read Only Memory). A computer readable medium may also be a data communication network, e.g. the Internet, which allows downloading a program code. 
         [0079]    A further aspect of the invention relates to a program element (for example a computer program) for controlling an X-ray device, which, when being executed by a processor (for example a processor of the X-ray device), is adapted to carry out the steps of the method as described in the above and in the following. 
         [0080]    These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment described hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0081]    Below, embodiments of the present invention are described in more detail with reference to the attached drawings. 
           [0082]      FIG. 1  shows an X-ray device according to an exemplary embodiment of the invention. 
           [0083]      FIG. 2  shows an X-ray device according to an exemplary embodiment of the invention in a different direction. 
           [0084]      FIG. 3  shows an X-ray emitter arrangement according to an exemplary embodiment of the invention. 
           [0085]      FIG. 4  shows an X-ray emitter arrangement according to an exemplary embodiment of the invention. 
           [0086]      FIG. 5  shows an X-ray detector arrangement according to an exemplary embodiment of the invention. 
           [0087]      FIG. 6  shows a three-dimensional view of an X-ray beam and a detector according to an exemplary embodiment of the invention. 
           [0088]      FIG. 7  shows an X-ray device according to an exemplary embodiment of the invention. 
           [0089]      FIG. 8  shows an X-ray device according to a further exemplary embodiment of the invention. 
           [0090]      FIG. 9  shows an X-ray device according to a further exemplary embodiment of the invention. 
           [0091]      FIG. 10  shows a flow diagram for a method for controlling an X-ray device according to an exemplary embodiment of the invention. 
       
    
    
       [0092]    The reference symbols used in the drawings, and their meanings, are listed in summary form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures. 
       DETAILED DESCRIPTION OF EMBODIMENTS 
       [0093]      FIG. 1  shows schematically an X-ray device  10  with an X-ray emitter arrangement  12  and an X-ray detector arrangement  14 . The X-ray emitter arrangement  12  is adapted to emit a fan-shaped and at least partial coherent X-ray beam  16 . The X-ray beam  16  is transmitted through an object  18  for example a human being, on a table  19 . 
         [0094]    In the embodiment shown in  FIG. 1 , the X-ray emitter arrangement  12  and the X-ray detector arrangement  14  are stationary with respect to the environment of the X-ray device  10  and the object  18  may be moved in an axial direction A orthogonal to the optical axis O of the X-ray device  10 . For moving the table  19  in the axial direction A, the X-ray device  10  comprises an actuator  20 , for example step motor  20 , that is adapted to move the table  19  with the object  18  in small steps in the axial direction A. 
         [0095]    The X-ray device  10  further has a controller  22  with a processor  24 . The controller  22  is connected to the X-ray emitter arrangement  12  over a signal line  26 , to the X-ray detector arrangement  14  over a signal line  28  and to the actuator  20  over a signal line  30 . Over these signal lines  26 ,  28 ,  30 , the controller  22  controls the X-ray emitter arrangement  12 , the X-ray detector arrangement  14  and the actuator  20 . Further, the controller  22  is adapted to receive image data taken by the X-ray detector arrangement  14  over the signal line  28 . 
         [0096]    As shown in  FIG. 1 , the fan-shaped beam  16  has a small fan angle f and the detector  14  has a width w that is adapted to this small fan angle f. For example, if the distance d between the X-ray emitter arrangement  12  and the X-ray detector arrangement  14  is about 1 m, the width w of the detector arrangement  14  may be 6 cm, or even smaller. This may guarantee a good visibility even at the ends of the detector arrangement  14  in the direction A. 
         [0097]    Since the fan angle f of the beam  16  is small, not the entire region of interest  32  of the object  18  is covered by the X-ray beam  16 . 
         [0098]      FIG. 2  shows an X-ray emitter arrangement  12  and an X-ray detector arrangement  14  that may be used together with all the embodiments of X-ray devices shown in the figures. 
         [0099]      FIG. 2  shows a view of the X-ray beam  16  in the direction A of  FIG. 1 . The X-ray beam  16  has a cone angle c that is much larger than the fan angle f. Also, the detector arrangement  14  has a length l that is much larger than the width w of the X-ray detector arrangement  14 . For example, the length l may be about 50 cm. Due to the large cone angle c of the beam  16 , the entire object  18  or the entire region of interest  32  is covered by the fan-shaped beam  16  in a plane orthogonal to the axial direction A. 
         [0100]      FIG. 3  shows an embodiment of an X-ray emitter arrangement  12 . The X-ray emitter arrangement  12  comprises an incoherent X-ray source  34 , for example an X-ray tube  34 , a source grating  36  and a collimator  38 . All these components  34 ,  36 ,  38  may be situated inside a housing  40  of the X-ray detector arrangement  12 . The X-ray source  34  may be activated and deactivated by the controller  22  over the signal line  26 . When the X-ray source  34  is working, it emits incoherent X-ray beams, which fall on the source grating  36 . After leaving the source grating  36 , the X-ray beam  16  is locally coherent. With the collimator  38  the X-ray beam  16  is limited to a small fan angle f and to the cone angle c. 
         [0101]    The X-ray emitter arrangement  12  may further comprise an actuator  37  for moving the source grating  36  (for example a piezo drive or step motor  37 ). 
         [0102]      FIG. 4  shows a further embodiment of an X-ray emitter arrangement  112 . The X-ray emitter arrangement  112  comprises a cathode  42  with carbon nanotube based emitters (or other cold cathode emitters)  44  and an anode  46 . The anode  46  comprises several elements they may be connected to a voltage source or high voltage generator independently from each other by the controller  22  Alternatively, the single carbon nanotube emitters  44  may be switched independently from each other and the anode  46  has a connection to a high voltage generator. As indicated in  FIG. 4 , only certain anode elements are radiating and X-rays are produced only at the (activated) anode elements. 
         [0103]    The X-ray emitter arrangement  112  has therefore several emitter lines  48  that may be activated independent from each other by the controller  22 . 
         [0104]    It has to be noted, that the X-ray beam  16  produced by the X-ray emitter arrangement  112  has parallel X-rays. However, by using a bent anode  42 , a X-ray beam  16  as shown in  FIG. 6 , which has X-rays that are spreading in two directions or an X-ray beam with X-rays that are only spreading in one direction, for example as for the X-ray device of  FIG. 9 , may be produced. 
         [0105]      FIG. 5  shows a X-ray detector arrangement  14  with phase grating  50 , absorber grating  52  and an area detector  54 . The components  50 ,  52 ,  54  of the X-ray detector arrangement  14  all may be situated in a housing  56 . The X-ray detector arrangement  14  comprises an actuator  53  for moving the phase grating  50  and absorber grating  52  relative to each other in the direction P. 
         [0106]    For conducting a complete phase scan, the controller  22  may move the phase grating  50  and the absorber grating  52  relative to each other in the direction P (which may be parallel to the direction A) in small steps. Due to the X-rays  16  which have passed the object  18  and are falling onto the phase grating  50  and the absorber grating  52 , patterns of different intensity of X-rays are formed on the area detector  54 . At each of the plurality of relative positions of the phase grating  50  and the absorber grating  52 , the detector  54  takes an image of the respective intensities and sends this raw image data to the controller  22 . From the plurality of different raw image data taken during one phase scan, the controller  22  calculates image data containing phase information of the X-rays passed through the object  18 . 
         [0107]      FIG. 6  shows a three-dimensional view of the cone-beam  16  and the X-ray detector arrangement  14 . As may be seen from  FIG. 6 , the grating lines  58  of the phase grating  50  and the absorber grating  52  are parallel to the longer sides of the X-ray detector arrangement  14 . In other words, the grating lines  58  may be orthogonal to the axial direction A. 
         [0108]    The X-ray device shown in  FIG. 1  may be controlled by the controller  22  in the following way: 
         [0109]    The object  18  is moved by the table  19  (and the actuator  20 ) to a position wherein a first slice of the region of interest  32  may be imaged. At this position a first phase stepping, i.e. scanning of the part of the region of interest  32  is conducted and the respective image data is produced. After that, the object  18  is moved to the next position wherein the next slice of the region of interest  32  is scanned. Also, image data of this second slice is produced by the controller  22 . 
         [0110]    The distance between the two positions is such that the image data obtained at the two positions slightly overlap, such that aggregated image data may be obtained. 
         [0111]    In this way, the X-ray device  10  takes image data from further slices of the region of interest  32  until the whole region of interest  32  is scanned. The entire image data taken at the different positions of the object containing phase information of the different slices of the region of interest  32  may at the end be aggregated to one image containing information on the whole region of interest  32 . 
         [0112]    Besides the movement of the object  18  in large steps, it is also possible in an alternative embodiment to move the object  18  in very small steps or continuously. 
         [0113]    During the continuous movement of the object  18 , the whole region of interest  32  is scanned and the phase scanning is combined with the movement of the object  18 . To this end, at least one of the gratings  36 ,  50 ,  52  has to be kept at a fixed position with respect to the object  18  during a phase stepping cycle. After a phase scanning cycle, the fixed grating(s)  36 ,  50 ,  52  has to be moved in a large step by a slice. At each phase scanning cycle, image data from the respective slices of the region of interest  32  are taken, which at the end can be put together or aggregated to aggregated image data showing the whole region of interest  32 . 
         [0114]      FIG. 7  shows a further embodiment of an X-ray device  110 . Contrary to the X-ray device  10  of  FIG. 1 , the X-ray device  110  has a stationary table  19 . Thus the object  18  remains stationary with respect to environment of the X-ray device  110 . The X-ray emitter arrangement  12  and the X-ray detector arrangement  14  of the X-ray device  110  are rigidly connected with each other, for example by an arm  60 , with which both the arrangements  12  and  14  may be moved in the axial direction A with the aid of an actuator  62 . 
         [0115]    Similar to the embodiment of  FIG. 1 , the movement of the combination of the X-ray emitter  12  and the X-ray detector  14  can be executed either in steps or continuously. If the movement is conducted in steps, at each step, the X-ray device  110  may take image data of the region of interest  32  and at the end may aggregate an overall image of the region of interest  32 . If the movement is done continuously or in small steps, the phase scanning and the movement have to be combined as described above with respect to the embodiment of  FIG. 1 . 
         [0116]      FIG. 8  shows a further embodiment of an X-ray device  210 . In the embodiment shown in  FIG. 8 , the X-ray device  210  is adapted to rotate the X-ray detector arrangement  14  about the focal spot  64  of the X-ray device  210 .  FIG. 8  shows the detector arrangement  14  in three different positions, in which the X-ray beams  16  directed to the X-ray detector arrangement  14  covers the whole region of interest  32 . 
         [0117]    For the movement of the X-ray detector arrangement  14 , the X-ray device  210  comprises an actuator  66 . Further, the X-ray emitter arrangement  12  is rotatable about the focal spot  64 . For example, the X-ray emitter arrangement  12  and the X-ray detector arrangement  14  are connected with each other by an arm, which may be rotated around an axis. Contrary as indicated in  FIG. 8 , this rotation also may be around an axis that is different from an axis through the focal spot  64 . 
         [0118]    As already explained with respect to the X-ray devices  10  and  110  of  FIG. 1  and  FIG. 7 , respectively, the rotational movement of the X-ray detector arrangement  14  may either be conducted in large steps or continuously (or in small steps), wherein in the first case, phase scanning is executed at each position and in the second case the phase scanning is combined with the continuous movement of the detector arrangement  14  with respect to the object  18 . 
         [0119]      FIG. 9  shows a further embodiment of an X-ray device  310 . The X-ray device  310  comprises an X-ray emitter arrangement  312  wherein the X-ray emitter arrangement  312  comprises an X-ray emitter that is adapted to generate an emitter beam  16  within the whole scanning region. For example, the X-ray emitter arrangement  312  may be designed like the X-ray emitter arrangement  112  shown in  FIG. 4  with a plurality of emitter lines distributed over the extension of the X-ray emitter arrangement  312  in the direction A. 
         [0120]    The X-ray emitter device  310  comprises an X-ray detector arrangement  14  that is movable along the direction A, for example by an actuator  66  like a step motor or piezo drive  66 . When the X-ray detector arrangement  14  is moved to a certain position, only the emitter lines  48  opposite to the X-ray emitter arrangement  14  may be activated to generate the X-ray beam  16 . 
         [0121]    Again the movement of the X-ray detector arrangement may be conducted in large steps or continuously, wherein either at each position a phase scan is conducted or the phase scanning is combined with the continuous movement. 
         [0122]      FIG. 10  shows a flow diagram of a method of controlling an X-ray device  10 ,  110 ,  210 ,  310  that may be executed by the processor  24  of the controller  22 . 
         [0123]    In a step S 10 , the scanning of the region of interest  32  is initiated by moving either the object  18  or the detector arrangement  14  to the start position, where the scanning has to be started. 
         [0124]    In a step S 12 , image data of a first slice of the region of interest  32  is recorded. After that, in step S 14 , either the object  18  or the X-ray detector arrangement  14  are moved in a large step to the next relative position were the next phase scanning has to be made. 
         [0125]    Alternatively, the phase scanning of a slice of the region of interest  32  may be done while the object  18  or the X-ray detector arrangement  14  is moving continuously or in small steps. To this end, in step S 16 , a continuous movement or a movement in small steps of the object  18  and the X-ray detector arrangement  14  relative to each other is started during which the phase scanning is performed. After that, in a step S 18 , the fixed grating,  36 ,  50 ,  52  has to be moved in a large step by a slice width. 
         [0126]    In both cases, in a step S 20 , the X-ray intensity is analyzed by analysing the recorded image data to evaluate the dose efficiency of the actual scan. 
         [0127]    In a step S 22 , the X-ray intensity of the X-ray emitter arrangement  12 ,  112 ,  312  may be adapted or set, using the dose efficiency analysis results of step S 20 . Alternatively or additionally, the scan speed, i.e. the speed of the movement of the gratings  36 ,  50 ,  52  and/or the speed of the movement of the object  18  relative to the arrangements  12 ,  14 , is adapted or set, using the dose efficiency analysis results of step S 20 . 
         [0128]    After that, if not the end of the region of interest  32  has been reached, the method continues either at step S 12  or at step S 16  for executing a phase scan for the next slice. 
         [0129]    If the whole region of interest  32  has been scanned, in step S 24 , the image data scanned for the different slices covering the region of interest  32  are aggregated or put together to form an overall image data containing a scan of the whole region of interest  32 . 
         [0130]    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. 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 controller or other unit may fulfil 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. Any reference signs in the claims should not be construed as limiting the scope. 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
           10 ,  110 ,  210 ,  310  X-ray device 
           12 ,  112  X-ray emitter arrangement 
           14  X-ray detector arrangement 
           16  X-ray beam 
           18  object 
         O optical axis 
         A axial direction 
           19  table 
           20  actuator 
           22  controller 
           24  processor 
           26 ,  28 ,  30  signal line 
           32  region of interest 
         f fan angle of beam 
         c cone angle of beam 
         w width of detector 
         d distance of emitter arrangement to detector arrangement 
         l length of detector 
           34  X-ray source 
           36  source grating 
           37  actuator 
           38  collimator 
           40  housing 
           42  cathode 
           44  carbon nanotube emitters 
           46  anode 
           48  emitter lines 
           50  phase grating 
           52  absorber grating 
           53  actuator 
           54  area detector 
           56  housing 
         P direction of movement of gratings 
           58  grating lines 
           60  arm 
           62  actuator 
           64  focal spot 
           66  actuator