Patent Publication Number: US-9414796-B2

Title: X-ray recording system for x-ray imaging at high image frequencies of an object under examination by way of direct measurement of the interference pattern

Description:
PRIORITY STATEMENT 
     The present application hereby claims priority under 35 U.S.C. §119 to German patent application number DE 102013205406.8 filed Mar. 27, 2013, the entire contents of which are hereby incorporated herein by reference. 
     FIELD 
     At least one embodiment of the invention generally relates to an x-ray recording system for x-ray imaging of an object under examination by way of direct measurement of an interference pattern, especially for differential real time-capable phase contrast imaging, with at least one x-ray emitter for generation of quasi-coherent x-ray radiation, an x-ray image detector, having a detector layer and detector pixels arranged in a matrix, a diffraction or phase grating which is disposed between the object under examination and the x-ray image detector and generates an interference pattern. 
     BACKGROUND 
     Differential phase-contrast imaging represents an imaging method which has attracted much attention for some time, especially in the Talbot-Lau interferometer arrangement. Thus for example the publication by F. Pfeiffer et al. [1], “Hard X-ray dark-field imaging using a grating interferometer”, Nature Materials 7, 2008, Pages 134 to 137, describes how, with the aid of an interferometric structure, which includes a conventional x-ray tube, three gratings and an x-ray detector, both absorption contrast, differential phase contrast and also dark-field contrast can be reconstructed from the same dataset. Similar information can be found in Joseph J. Zambelli, et al. [2], “Radiation dose efficiency comparison between differential phase contrast CT and conventional absorption CT”, Med. Phys. 37 (2010), Pages 2473 to 2479. 
     The wave nature of particles such as x-ray quanta allows the description of phenomena such as refraction and reflection with the aid of the complex refraction index
 
 n= 1−δ+ iβ.  
 
     In this case the imaginary part β describes the absorption on which current clinical x-ray imaging, such as computed tomography, angiography, radiography, fluoroscopy or mammography is based, and the real part δ describes the phase offset, which is observed in differential phase imaging. 
     An x-ray recording system is known from DE 10 2010 018 715 A1 in which an x-ray recording system for phase-contrast imaging of an object under examination is used for high-quality x-ray imaging, having at least one x-ray emitter with a plurality of field emission x-ray sources for emitting a coherent x-ray radiation, an x-ray image detector, a diffraction grating G 1  disposed between the object under examination and the x-ray image detector and a further grating G 2 , which is disposed between the diffraction grating G 1  and the x-ray image detector. 
     An x-ray recording system, which allows a differential phase-contrast imaging of the type stated at the start to be carried out, is known for example from U.S. Pat. No. 7,500,784 B2, which is explained with reference to  FIG. 1 . 
       FIG. 1  shows the typical main features of an x-ray recording system  1  for an interventional suite with a C-arm  2  held by a stand in the form of a six-axis industrial or articulated-arm robot, to the ends of which an x-ray radiation source, for example an x-ray emitter  3  with x-ray tube and collimator, and an x-ray image detector  4  as x-ray recording unit are attached. 
     By way of the articulated-arm robot known for example from U.S. Pat. No. 7,500,784 B2, which preferably has six axes of rotation and thereby six degrees of freedom, the C-arm  2  can be adjusted spatially in any given manner, for example by being rotated around a center of rotation between the x-ray emitter  3  and the x-ray image detector  4 . The inventive x-ray recording system  1  is especially able to be rotated around centers of rotation and axes of rotation in the C-arm plane of the x-ray image detector  4 , preferably around the center point of the x-ray image detector  4  and around the center point of axes of rotation intersecting with the x-ray image detector  4 . 
     The known articulated-arm robot has a base stand, which is rigidly mounted on a floor for example. A carousel, able to be rotated around an axis of rotation, is fastened thereto. A robot rocker is attached to the carousel, pivotable around a second axis of rotation, to which a robot arm pivotable around a third axis of rotation is fastened. Attached to the end of the robot arm, pivotable around a forth axis of rotation is a robot hand. The robot hand has a fastening element for the C-arm  2 , which is able to be pivoted around a fifth axis of rotation and able to be rotated around a sixth axis of rotation running at right angles thereto. 
     The realization of an x-ray recording system is not dependent on the industrial robots. Normal C-arm devices can also be used. 
     The x-ray image detector  4  can be a rectangular or square, flat x-ray detector, which preferably includes a scintillator (e.g. C s I) and an active matrix of photodiodes made of amorphous Silicon (a-Si). However CMOS-based integrating detectors or also counting detectors (e.g. CdTe or CZT and ASIC) can also be used. 
     Located on a table plate  5  of a patient support table, in the beam path of the x-ray emitter  3 , as the object under examination, is a patient  6  to be examined. Connected to the x-ray recording system  1  is a system control unit  7  with an imaging system  8 , which receives the image signals of the x-ray image detector  4  and processes them (operating elements are not shown for example). The x-ray images can then be viewed on displays of a monitor array  9 . The monitor array  9  can be held by way of a ceiling-mounted, longitudinally-movable, pivot, rotation and height-adjustable support system  10  with outriggers and a lowerable support arm. 
     Instead of the x-ray recording system  1  with the stand in the form of the six-axis industrial or articulated-arm robot as shown by way of example in  FIG. 1  the x-ray recording system  1  can, as shown in  FIG. 2  in simplified form also have a normal ceiling-mounted or floor-mounted holder for the C-arm  2 . 
     Instead of the C-arm  2  shown by way of example, the x-ray recording system  1  can also have separate ceiling-mounted and/or floor-mounted holders for the x-ray emitter  3  and the x-ray image detector  4 , which are electronically rigidly coupled for example. 
     In the current arrangements focused on for clinical phase-contrast imaging conventional x-ray tubes, currently available x-ray image detectors, such as are described for a example by Martin Spahn [3] in “Flat detectors and their clinical applications”, European Radiology, Volume 15 (2005), Pages 1934 to 1947, and three gratings G 0 , G 1  and G 2  are used, as is explained below with reference to  FIG. 2 , which shows a schematic structure of a Talbot-Lau interferometer for differential phase-contrast imaging with the extended tube focus, gratings G 0 , G 1  and G 2  and pixelated x-ray image detector. 
     The x-ray beams  12  emerging from a tube focus  11  of the non-coherent x-ray emitter  3 , for generation of coherent radiation, penetrate an absorption grating  13  (G 0 ), which brings about the local coherence of the x-ray emitter  3 , and also an object under examination  14 , for example the patient  6 . Through the object under examination  14  the wave front of the x-ray beams  12  is deflected by phase offsetting in such a way as illustrated by the normal  15  of the wave front without phase offsetting, i.e. without object, and the normal  16  of the wave front with phase offsetting. Subsequently the phase-offset wavefront passes through a diffraction or phase grating  17  (G 1 ) with a grating constant adapted to the typical energy of the x-ray spectrum for generation of interference lines or an interference pattern  18  and in its turn an absorbing analyzer grating  19  (G 2 ) for reading out the interference pattern  18  generated. Different interference patterns  18  arise with and without object. The grating constant of the absorbing analyzer grating  19  is adapted to that of the phase grating  17  and the remaining geometry of the arrangement. The absorbing analyzer grating  19  is disposed for example in the first or nth Talbot spacing (order). The absorbing analyzer grating  19  in this case converts the interference pattern  18  into an intensity pattern, which can be measured by the x-ray image detector  4 . Typical grating constants for clinical applications lie at a few μm, as can also be found in the cited literature references [1, 2]. 
     If the x-ray emitter  3  is sufficiently coherent, i.e. the tube focus  11  of the x-ray emitter  3  is sufficiently small and the generated radiation power is still sufficiently large, it is possible to dispense with the first grating G 0 , the absorption grating  13 . 
     The differential phase offsetting is now determined for each pixel of the x-ray image detector  4  according to the prior art by, through what is referred to as “phase stepping”  20 , which is indicated by an arrow, the absorbing analyzer grating  19  (G 2 ), being displaced in a number of steps (k=1, K, with e.g. K=4 to 8) by a corresponding fraction of the grating constant at right angles to the radiation direction of the x-ray beams  12  and lateral to the arrangement of the grating structure and by, for this configuration, the signal S k  arising during the imaging in the pixel of the x-ray image detector  4  being measured and the interference pattern  18  produced being sampled. For each pixel the parameters of a function describing the modulation (e.g. sine) are then determined by a suitable fit method, an adaptation or compensation method, to the signals S k  thus measured. These parameters are usually the amplitude A, the phase Φ and the average intensity I. 
     The comparison of specific derived variables from these fit parameters for each pixel, once with and once without object (or patient), then enables three different images to be created: 
     Absorption image, 
     Differential phase-contrast (DPC) image and 
     Dark-field image. 
     The visibility, i.e. the standardized difference between the maximum and minimum signal (or more precisely: amplitude standardized to the average signal) is in this case a measure for characterizing the quality of a Talbot-Lau interferometer. It is defined as the contrast of the sampled modulation 
     
       
         
           
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     References in this document to an image may possibly mean the triumvirate of absorption image, DPC image and dark field image. 
     The realization of the method presents many challenges, but in particular has two decisive disadvantages:
         The absorbing analyzer grating G 2  must be moved into different positions and then an x-ray acquisition carried out in each position. Such a method is thus conceivably unsuitable for moving objects (such as non-anaesthetized patients or patient organs, e.g. heart, lungs) if the object moves between the different measurements even by small distances. Likewise such an arrangement is unsuitable on account of the mechanical movement of the absorbing analyzer grating G 2 , in order to make possible real-time imaging or imaging at higher image frequencies of for example 15 images per second (I/s) or also 60 to 100 I/s. 3D imaging, in which x-ray tube and x-ray detector are rotated continuously around the patient, are also not possible in this way.   The fact that the absorbing analyzer grating G 2  is an analyzer grating with areas in which it is transparent for x-rays and in other areas is as non-transparent as possible means that dose (typically 50%) is lost behind the object or the patient, which is not effective in the image.       

     SUMMARY 
     At least one embodiment of the invention embodies an x-ray recording system in which a real time-capable phase-contrast imaging at high image frequencies is made possible, wherein the x-ray image detector has a structure which does not provide for any analyzer grating G 2  or for any mechanical movement of the x-ray image detector. 
     At least one embodiment of the invention is directed to an x-ray recording system. Advantageous embodiments are specified in the dependent claims. 
     At least one embodiment of the invention is directed to an x-ray recording system by the interference pattern in the nth Talbot order (with and without object) being detected directly by an x-ray image detector with a very high achievable local resolution, which amounts to at least half the wavelength of the interference pattern arising in the nth Talbot order in accordance with the Nyquist theory. 
     In accordance with at least one embodiment of the invention, the suitable function can be a fit function and/or a weighted averaging in accordance with the equation (X, Y)=Σ(x i , y i )·S i /ΣS i , wherein (X, Y) is the computed location, (x i , y i ) e.g. the center points of the detector pixels ( 22 ) involved in the averaging and S i  the measured pixel signals  26  in the corresponding pixels i. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in greater detail below with reference to the example embodiments shown in the drawing. In the figures: 
         FIG. 1  shows a known C-arm angiography system of an interventional suite with an industrial robot as support apparatus, 
         FIG. 2  shows a schematic layout of a known Talbot-Lau interferometer for differential phase-contrast imaging with extended tube focus, three gratings G 0 , G 1  and G 2  and pixelated detector, 
         FIG. 3  shows a schematic diagram of a detector structure in a side view with a detector layer and light-sensitive detector pixels, 
         FIG. 4  shows an example distribution of the output signals of the detector pixels according to  FIG. 3 , 
         FIG. 5  shows the detector arrangement according to  FIG. 3 , viewed from above with interaction of an x-ray quantum, 
         FIG. 6  shows the detector arrangement according to  FIG. 5  with local determination of the interaction as a result of the signal distribution, 
         FIGS. 7 to 12  show various examples of possibilities of pixel-to-pixel connections, 
         FIG. 13  shows a section of a resistance network for analog evaluation of a number of detector pixels, 
         FIG. 14  shows the circuit-technology structure of an embodiment of the inventive detector pixel, 
         FIG. 15  shows a circuit technology implementation of a central detector pixel with a number of neighboring detector pixels. 
     
    
    
     DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS 
     Various example embodiments will now be described more fully with reference to the accompanying drawings in which only some example embodiments are shown. Specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. The present invention, however, may be embodied in many alternate forms and should not be construed as limited to only the example embodiments set forth herein. 
     Accordingly, while example embodiments of the invention are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments of the present invention to the particular forms disclosed. On the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of the invention. Like numbers refer to like elements throughout the description of the figures. 
     Before discussing example embodiments in more detail, it is noted that some example embodiments are described as processes or methods depicted as flowcharts. Although the flowcharts describe the operations as sequential processes, many of the operations may be performed in parallel, concurrently or simultaneously. In addition, the order of operations may be re-arranged. The processes may be terminated when their operations are completed, but may also have additional steps not included in the figure. The processes may correspond to methods, functions, procedures, subroutines, subprograms, etc. 
     Methods discussed below, some of which are illustrated by the flow charts, may be implemented by hardware, software, firmware, middleware, microcode, hardware description languages, or any combination thereof. When implemented in software, firmware, middleware or microcode, the program code or code segments to perform the necessary tasks will be stored in a machine or computer readable medium such as a storage medium or non-transitory computer readable medium. A processor(s) will perform the necessary tasks. 
     Specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments of the present invention. This invention may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments of the present invention. As used herein, the term “and/or,” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that when an element is referred to as being “connected,” or “coupled,” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected,” or “directly coupled,” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between,” versus “directly between,” “adjacent,” versus “directly adjacent,” etc.). 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments of the invention. As used herein, the singular forms “a,” “an,” and “the,” are intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the terms “and/or” and “at least one of” include any and all combinations of one or more of the associated listed items. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper”, and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, term such as “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein are interpreted accordingly. 
     Although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, it should be understood that these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are used only to distinguish one element, component, region, layer, or section from another region, layer, or section. Thus, a first element, component, region, layer, or section discussed below could be termed a second element, component, region, layer, or section without departing from the teachings of the present invention. 
     At least one embodiment of the invention is directed to an x-ray recording system by the interference pattern in the nth Talbot order (with and without object) being detected directly by an x-ray image detector  4  with a very high achievable local resolution, which amounts to at least half the wavelength of the interference pattern arising in the nth Talbot order in accordance with the Nyquist theory. 
     This achieves the result that a real time-capable phase-contrast imaging is possible at a high image frequency. Neither an analyzer grating G 2  nor a mechanical movement of the x-ray image detector  4  is required for phase-contrast imaging. The local resolution can also be higher than that of the half wavelength of the interference pattern  18 . In precise terms the x-ray spectrum naturally also creates a spectrum of interference patterns of different wavelengths. What is meant here is the “design wavelength” of the structure which is optimized for the interference pattern of a specific x-ray energy, for example 50, 70 or 90 keV, arising. 
     In accordance with at least one embodiment of the invention the x-ray imaging can create an absorption image, a differential phase-contrast (DPC) image or a dark field image. 
     It has proved advantageous for the x-ray emitter  3  for generation of quasi-coherent x-ray radiation, to use an x-ray tube usually used in x-ray diagnostics or angiography with a relatively large tube focus  11  and for the coherence to be created by the use of an absorption grating G 0 . 
     In an advantageous manner, the x-ray emitter  3  for creation of quasi-coherent x-ray radiation can as an alternative have a plurality of field emission x-ray sources of sufficiently small focus sizes or a sufficiently powerful micro focus source. In this case no absorption grating G 0  is necessary. 
     With reference to  FIGS. 3-4 , the very high local resolution of the x-ray image detector ( 4 ) is achieved if 
     the detector pixel ( 22 ) of the x-ray image detector ( 4 ) has pixel sizes, of which the surfaces are significantly larger than the surfaces actually required for the resolution to be achieved, 
     the detector layer ( 21 ) includes the detector material, which creates many secondary quanta ( 25 ) for each absorbed x-ray quantum ( 23 ) and has such an inherently “bad” modulation transfer function (MTF) that the secondary quanta ( 25 ) occurred distributed over at least two detector pixels ( 22 ) and detected there as pixel signals ( 26 ), and 
     the location of the primary event ( 24 ) is reconstructed via measured pixel signals ( 26 ) in a number of pixels ( 32 ,  34 ). 
     Significantly more precisely than would be expected from the size of the detector pixels  22 , the location of the primary event  24  can be determined if it is determined with the aid of a suitable function via the pixel signals  26  measured in the neighboring pixels. 
     In accordance with at least one embodiment of the invention, the suitable function can be a fit function and/or a weighted averaging in accordance with the equation (X, Y)=Σ(x i , y i )·S i /ΣS i , wherein (X, Y) is the computed location, (x i , y i ) e.g. the center points of the detector pixels ( 22 ) involved in the averaging and S i  the measured pixel signals  26  in the corresponding pixels i. 
     In an advantageous manner the detector pixels  22  can be connected via pixel-to-pixel connections to at least the directly neighboring pixels and possibly the neighboring pixels after next. 
     It has proved advantageous for the reconstruction of the location of the primary event  24  to be undertaken directly in the pixel matrix and for each primary event  24  of the calculated location to be retained. 
     Processing can take place outside the x-ray image detector  4  if the signal levels of the pixel signals  26  of all pixels involved in these primary events  24  and a time stamp are retained and the reconstruction is undertaken later, wherein the detector pixels  22  involved are able to be allocated subsequently via the time stamp. 
     In an advantageous manner the detector layer  21  can include a scintillator material, in which the created secondary quanta  25 , the light photons, are distributed over a number of detector pixels  22 , wherein the speed of the scintillator material must be selected as a function of the level of the x-ray flow to be expected, so that no time constants are produced, wherein it is true to say that the higher the x-ray flow is, the “faster” the detector material must be. 
     It has proved to be advantageous for the x-ray image detector  4  to be an integrating detector with indirect conversion of the x-ray quanta by way of CsI as scintillator material and amorphous silicon or CMOS for the photodiode and readout structure or to be implemented as a photon counting detector with direct conversion of the x-ray quanta. 
     A section of the x-ray image detector  4  is shown schematically (cross-section) in  FIG. 3  with a detector layer  21  made of a conversion material and a layer lying therebelow with light-sensitive detector pixels  22 . An x-ray quantum  23  strikes the x-ray image detector  4  and creates a primary event  24  as a result of the absorption of the x-ray quantum  23  in the excited luminescent material of the detector layer  21 , through which secondary quanta  25  are emitted. These emitted secondary quanta  25  will be detected by the light-sensitive detector pixels  22 . 
       FIG. 4  now shows the possible distribution of the output signals according to  FIG. 3  as pixel signals  26 , which can be analog voltages or digital numerical values over which a fit function  27  has been laid as adaptation, which is a mathematical optimization method to determine or to estimate the unknown parameters of a model or of a predetermined function for a series of measurement data. The maximum  28  of the fit function  27  produces a virtual location or reconstructed location. In the ideal case the positions of the primary event  24  and the maximum  28  of the fit function  27  are identical. 
     The detector arrangement in accordance with  FIG. 3  is shown in  FIG. 5  in an overhead view with the x-ray quantum  23  striking the x-ray image detector  4 , which creates the primary event  24 . The emitted secondary quanta  25  (not shown) fall on differently strongly excited adjacent detector pixels  29 , wherein the different distribution of the pixel signals  26  is indicated schematically by squares of different sizes. 
     Now, from this distribution, as is illustrated with reference to  FIG. 6 , the virtual location  31  of the primary event  24  at which the x-ray quantum  23  has interacted with the detector material, is determined by way of suitable two-dimensional fit functions  30 , which are drawn-in here in the shape of circles. 
     It is now shown schematically, with reference to  FIGS. 7 to 12 , how the detector pixels  22  of the x-ray image detector  4 , shown viewed from above for determining the distribution of the pixel signals  26 , can be connected to one another. 
     Referring to  FIG. 7 , a central pixel  32  is connected via pixel-to-pixel connections  33  with the respective horizontal and vertical directly-neighboring pixels  34 . Thus five detector pixels  22  are grouped together in this arrangement. 
     A node  35  lying between the detector pixels  22  is connected according to  FIG. 8  via pixel-to-pixel connections  33  diagonally to directly-neighboring pixels  34 , so that four detector pixels  22  are grouped together. 
       FIG. 9  shows a version in which, radiating from the central pixel  32 , via pixel-to-pixel connections  33 , the respective horizontally and vertically and also diagonally directly-neighboring pixels  34  are connected. This allows the pixel signals  26  of nine detector pixels  22  to be grouped together. 
     The arrangement according to  FIG. 10  makes it possible for the pixel signals  26  of the diagonal directly-neighboring pixels  34  and their respective horizontal and vertical directly-neighboring pixels  34  to be detected by a node  35  lying between the detector pixels  22  via pixel-to-pixel connections  33 , so that a total of 12 detector pixels  22  will be evaluated. 
     In the example according to  FIG. 11 , starting from the arrangement of  FIG. 10 , the next diagonal neighboring pixels  34  will also be detected so that now a total of 16 detector pixels  22  contribute to the evaluation. 
       FIG. 12  shows a structure in which, starting from central pixel  32  with the primary event  24 , the respective horizontal and vertical direct and next neighboring pixels  34  as well is the diagonal directly-neighboring pixels  34  and their respective horizontal and vertical directly-neighboring pixels  34  are connected by way of pixel-to-pixel connections  33 . This allows the pixel signals  26  from twenty one detector pixels  22  to be grouped together. If the diagonal next neighboring pixels  34  are also included, twenty five detector pixels  22  can be evaluated. 
     A common analog evaluation of a number of detector pixels  22  can for example be achieved by a resistance network, which is shown in  FIG. 13  in cross-section only for the central pixel  32 . The resistance network has the resistor  36  (R(x + )), resistor  37  (R(y + )), resistor  38  (R(x − )), and resistor  39  (R(y − )), which are connected to connecting lines  40  (x + , x − , y + , y − ), via which the pixel signals  26  can be tapped off. With a suitable choice of resistors  36  to  39  and those of the neighboring pixels  34  a significantly higher local resolution than the pixel resolution can be achieved. 
       FIG. 14  now shows a schematic of the layout of a detector pixel  22 . The input signal of the light-sensitive element of the detector pixel  22  is supplied to an amplifier  41 , the output signal of which is digitized in an analog/digital converter (A/D converter)  42 , so that it is processed by a computation unit  43  and buffered in a memory  44  for further evaluation. The results are fed as an image signal via readout electronics  45  or readout logic to the imaging system  8 . Via connections  46  the detector pixels  22  are connected to one another for joint evaluation of their pixel signals  26 , as has been described with reference to the examples according to  FIGS. 7 to 12 . 
     By way of this memory  44  the signal levels of the pixel signals  26  of all pixels  32  and  34  involved in these primary events  24  and a time stamp can be maintained. The reconstruction can take place later for example outside the x-ray image detector  4 , by the pixel signals  26  of the detector pixels  22  involved being able to be allocated afterwards via the time stamp. 
     According to  FIG. 15  nine such detector pixels  22  are connected to one another. Starting from the connections  46  of the central pixel  32 , all pixel-to-pixel connections  33  go to the connections  46  of the eight neighboring pixels  34 . From these digital pixel signals  26 , by way of the computation unit  43  on the basis of a signal weighting (according to the equation (1)) or the two-dimensional fit functions  30  to the signal values, the maximum of the two dimensional fit function  30  is determined and thus a virtual location is established and a precise location signal calculated, which is stored, together with the level of the overall signal in memory  44 . The two location determinations described using the simple-to-implement signal weighting in accordance with equation (1) or a significantly more complex fit of a two dimensional fit function  30  are alternatives. 
     Advantages produced by at least one embodiment of the inventive structure of the x-ray image detector  4  for real time-capable phase-contrast imaging at high image frequencies through direct measurement of the interference pattern  18  include the following:
         with this structure no mechanical movements will be needed, since the intensity distribution in the nth Talbot order is measured directly with the x-ray image detector  4 , so that no absorbing analyzer grating G 2  and no phase stepping are needed,   it makes possible real-time imaging and   the dose loss through absorbing analyzer grating G 2  behind the patient—a significant disadvantage of the Talbot-Lau method with absorbing analyzer grating G 2  and phase stepping—does not arise here since with the realization described, this is not needed.       

     The inventive method of at least one embodiment described here is based on the interference pattern  18  in the nth Talbot order (with and without object) being measured directly by a suitable x-ray image detector  4 . For this purpose however a very high local resolution is needed. An x-ray image detector  4  having a resolution of at least half the wavelength of the interference pattern  18  in accordance with the Nyquist Theorem arising in the nth Talbot order, is realized as follows:
         pixel sizes can be used in the x-ray image detector  4 , the surfaces of which are significantly larger than the surfaces actually required for the resolution to be achieved.   a detector material is used which for each absorbed x-ray photon creates many secondary quanta  25  and has an inherently “bad” MTF (Modulation transfer function), so that the secondary quanta  25  are distributed over at least two—as a rule significantly more—detector pixels  22  and are detected there has pixel signals  26  (e.g. scintillator material would be suitable here in which the created light photons are distributed over a number of detector pixels  22 . It is true to say here that the higher the x-ray flow to be expected is, the “faster” the detector material must be—small time constants).   the location of the x-ray absorption event, of the primary event  24  is reconstructed by the measured pixel signals  26  in the adjacent pixels, the neighboring pixels  34 . The absorption location of the x-ray quantum  23  can be determined significantly more precisely via the pixel signals  26  measured in the neighboring pixels  34  with the aid of a suitable function, for example the fit function  27 , than would be expected from the size of the detector pixels  22 .   a connection of the pixels is necessary, at least of the directly-neighboring pixels  34  possibly the neighboring pixels  34  after next, etc. The reconstruction can for example be undertaken directly in the pixel matrix and for each event the computed location (x, y) can be recorded or the signal levels of all pixels involved in this primary event  24  and a time stamp can be recorded and the reconstruction can take place later, e.g. outside the x-ray image detector  4 , by the detector pixels  22  involved being able to be allocated subsequently via the time stamp. Further options are conceivable so that these cited examples are not restrictive.       

     A simple signal-weighted averaging over the locations at which the primary events  24 , the absorption of the x-ray quantum  23 , has been verified is suitable for example as a function for improving the local resolution:
 
( X,Y )=Σ( x   i   ,y   i )· S   i   /ΣS   i   (1)
 
     (X, Y) is the calculated (average) location, (x i , y i ) e.g. the center points of the detector pixels  22  involved in the averaging and S i  the measured pixel signals  26  in the corresponding pixels i. The sum is formed over all pixels i of the neighborhood (as shown for example in  FIGS. 7 to 12 ). 
     In such cases the detector pixels  22  are either placed around a central pixel  32  (examples in  FIGS. 7, 9 and 12 ) or also around a node  35  lying between detector pixels  22  (examples in  FIGS. 8, 10 and 11 ). 
     In principle such an averaging method can be carried out in the analog or in the digital “space”. 
     In the analog space the analog pixel signals  26  are present in accordance with the energy deposited in the corresponding detector pixels  22 . The location can be determined by a network of resistors  36  to  39 , which are arranged connected between the detector pixels  22 :
 
 X=c ·Σ( x   +   −x   − ), Y=c ·Σ( y   +   −y   − )  (2)
 
wherein
 
c is a suitable constant.
 
     The values x + , x − , y + , y −  are formed from those detector pixels  22  which are formed in the resistance network  36  to  39  in the area of a central pixel  32  or of a node  35  lying between detector pixels  22  (see also  FIG. 13 ). 
     If the pixel signals  26  are available digitally, i.e. after amplification and conversion of the analog signal in the corresponding detector pixels  22  with a sufficiently resolving analog-to-digital converter (ADC)  42  for example, the location can be computed by way of the equation (1) for a digital networking between the corresponding detector pixels  22  (as indicated in the  FIGS. 7 to 12 ). 
     The architecture of such detector pixels  22  and the connection with the neighboring pixels  34  is shown by way of example in  FIG. 15 , where each detector pixel  22  is linked to its eight directly-neighboring pixels  34  (this corresponds to the case depicted in  FIG. 9 ). A section from a pixel matrix is shown in  FIG. 15 , with connection of a central pixel  32  to its eight neighboring pixels  34 . A precise location signal is computed by signal weighting from the digital pixel signal  26  of the central pixel  32  and its eight neighboring pixels  34 , which is stored, together with the level of the overall signal, in memory  44  and later, after a readout process is made available to the detector matrix of the periphery. 
     More complex variants of the location determination are for example two-dimensional fit function  30  to the local distribution of the pixel signals  26 , as is indicated graphically in  FIGS. 4 and 6 . 
       FIGS. 3 and 4  reflect a schematic representation of how secondary quanta  25  of the primary event  24  (absorption of the x-ray quantum  23 ) are distributed over different detector pixels  22  and accordingly generate pixel signals  26  of different levels. From the location, e.g. a central pixel  32  or a node  35 , the pixel signals  26  and their signal level, with the aid of a suitable function, e.g. the fit function  27 , the maximum of the fit function  27  can be determined as virtual location  31 , the accuracy of which is significantly higher than the rastering of the detector pixels  22 . This virtual location  31  is the reconstructed location of the primary event  24 , of the absorption of the x-ray quantum  23 . 
     A two-dimensional representation of this state of affairs can be found in  FIGS. 5 and 6 , in which an x-ray quantum  23  strikes the conversion material of the detector layer  21 , interacts and creates a number of pixel signals  26  in a number of neighboring detector pixels  29 . In  FIG. 6 , on the basis of the signal distribution the location is determined by way of a suitable two-dimensional fit function  30  at which the x-ray quantum  23  has interacted with the conversion material. 
     A few examples of pixel-to-pixel connections  33  can be found in  FIGS. 7 to 12 . A central pixel  32  or a node  35  between the detector pixels  22  are connected to the direct horizontal and vertical and/or diagonal neighboring pixel  34 . In the examples according to  FIGS. 9 to 12 , as well as the directly-neighboring pixels  34 , there are additionally the next neighboring pixels  34 . 
       FIG. 13  depicts a section from a resistance network only for the central pixel  32 , from which, with a suitable choice of resistors  36  to  39  and those of the neighboring pixels  34 , a significantly higher local resolution than the pixel resolution can be achieved. 
       FIGS. 14-15  illustrate a section from a pixel matrix, with connection of a central pixel  32  to its eight neighboring pixels  34 . A precise location signal is computed by signal weighting from the digital pixel signals  26  of the central pixel  32  and its neighboring pixels  34 , which is stored, together with the level of the overall signal, in memory  44 . 
     The patent claims filed with the application are formulation proposals without prejudice for obtaining more extensive patent protection. The applicant reserves the right to claim even further combinations of features previously disclosed only in the description and/or drawings. 
     The example embodiment or each example embodiment should not be understood as a restriction of the invention. Rather, numerous variations and modifications are possible in the context of the present disclosure, in particular those variants and combinations which can be inferred by the person skilled in the art with regard to achieving the object for example by combination or modification of individual features or elements or method steps that are described in connection with the general or specific part of the description and are contained in the claims and/or the drawings, and, by way of combinable features, lead to a new subject matter or to new method steps or sequences of method steps, including insofar as they concern production, testing and operating methods. 
     References back that are used in dependent claims indicate the further embodiment of the subject matter of the main claim by way of the features of the respective dependent claim; they should not be understood as dispensing with obtaining independent protection of the subject matter for the combinations of features in the referred-back dependent claims. Furthermore, with regard to interpreting the claims, where a feature is concretized in more specific detail in a subordinate claim, it should be assumed that such a restriction is not present in the respective preceding claims. 
     Since the subject matter of the dependent claims in relation to the prior art on the priority date may form separate and independent inventions, the applicant reserves the right to make them the subject matter of independent claims or divisional declarations. They may furthermore also contain independent inventions which have a configuration that is independent of the subject matters of the preceding dependent claims. 
     Further, elements and/or features of different example embodiments may be combined with each other and/or substituted for each other within the scope of this disclosure and appended claims. 
     Although the invention has been illustrated and described in detail on the basis of the preferred example embodiment, the invention is not limited by the disclosed examples and other variations can be derived herefrom by the person skilled in the art, without departing from the scope of protection of the invention.