DE102006015355A1 - Focus-detector system on X-ray equipment for generating projective or tomographic X-ray phase-contrast exposures of an object under examination uses an anode with areas arranged in strips - Google Patents

Abstract

A bundled electron beam (BEB) (14) is controlled regarding its excursion in its direction by two pairs of plate electrodes (17.1,17.2;18.1,18.2) that operate vertically to each other. The BEB can use appropriate control of these plate electrodes to scan an anode (16) like scanning a TV picture line by line with a desirable gap and, as a result, can generate desired X-rays. Independent claims are also included for the following: (1) An X-ray system for generating projective phase-contrast exposures; (2) A method for generating projective or tomographic X-ray phase-contrast exposures of an object under examination with the help of a focus-detector system.

Description

The The invention relates to a focus / detector system of an X-ray apparatus for the generation of projective and tomographic phase-contrast images, consisting of a radiation source with a focus, a detector arrangement for the detection of X-radiation and a set of x-ray optics Grating, to determine the phase shift in the passage of X-rays through an examination object.

In Computed tomography generally becomes tomographic images an examination subject, in particular a patient, with the help absorption measurements of X-rays, which penetrate the object under investigation, made in usually a radiation source circular or spiral around the examination object is moved and on the, the radiation source opposite Page a detector, usually a multi-line detector with a Variety of detector elements, the absorption of radiation during Passage through the examination object measures. To tomographic Imaging will be from the measured absorbance data of all measured spatial Rays tomographic sectional images or volume data reconstructed. With these computed tomographic images, absorption differences can be very nicely defined in objects, however, areas become more similar chemical composition, which naturally also has a similar absorption behavior have, but insufficient shown in detail.

It Furthermore, it is known that the effect of the phase shift in Passage of a beam through an examination object essential stronger is the absorption effect of that penetrated by the radiation Matter. Such phase shifts are known manner the use of two interferometric gratings measured. Regarding this interferometric For example, measurement methods are based on X-ray phase imaging with a grating interferometer. T. Weitkamp at all, August 8, 2005 / Vol. 12, no. 16 / OPTICS EXPRESS " This method becomes an object under investigation of coherent X-radiation radiates through, then passed through a grid pair and immediately after the second grating the radiation intensity is measured. The first grid generates an interference pattern that is generated using the second grating on the underlying detector a moiré pattern maps. If the second grid is shifted slightly, the result is from this also a shift of the moiré pattern, ie a change of the local intensity in the underlying detector, which relative to the displacement of the second grid can be determined. If one carries for each detector element this Grid, that is for every ray, the intensity change dependent on from the displacement path of the second grid, so can determine the phase shift of the respective beam. Problematic, and therefore for the practice of computed tomography of larger objects not applicable, is that this method requires a very small radiation source, since for the formation of the interference pattern, a coherent radiation necessary is.

The The method shown in the above scripture requires either a radiation source with an extremely small focus, allowing a sufficient degree of spatial coherence is present in the radiation used. When using such a However, small focus is then used to examine one larger object adequate dose rate not given. But there is also the Possibility, a monochrome coherent radiation, for example, a synchrotron radiation to use as a radiation source, but this is the CT system In construction very expensive, so that a wide-ranging application is not possible.

This Problem leaves work around that within the focus / detector combination in the Beam path, immediately after the focus, a first Absorption grid is arranged. The orientation of the grid lines is in this case parallel to the grid lines of the following after the examination object Interference grating.

The Slots of the first grid produce a field of individually coherent beams a certain amount of energy, which is sufficient, with the help of in Beam direction behind the object arranged phase grating the to generate known interference patterns.

On this way it is possible Use radiation sources that have expansions, the normal ones X-ray tubes in CT systems respectively By light-ray systems correspond, so that, for example, in the field of general medical Diagnostics now with the help of X-ray devices too well differentiated soft tissue shots can be made.

It has been found in the realization of such an X-ray device for measuring the phase shift on large objects, such as a patient, that a fundamental problem is to produce sufficiently large phase and analysis grating, so that the necessary in such studies large detectors covered thereby can be. Another problem is that the required mechanisms for moving the analysis grid, especially when used in a computed tomography, in which the detector with high Rotates speed, is difficult to negotiate, so that too large X-ray optical grids alone from the instability of the grid itself can cause such large movements that they lead to large errors in recording the phase shift.

It Object of the invention, a focus / detector system for an X-ray apparatus for the generation of projective or tomographic phase-contrast images to find which makes it possible with x-ray optics To get along lattices smaller size and at the same time lower demands on the mechanical stability of the grid provides.

These The object is solved by the features of the independent claims. Advantageous developments The invention are subject matter of the subordinate claims.

The inventors have recognized that it is possible to construct the focus / detector system in such a modular manner that in the beam path of the focus, on the one hand, a single source grating is used to generate the quasi-coherent radiation, wherein on the detector side a modularly constructed set of phase and detector systems is used. and analysis grating is used, each individual grating having a size that can be easily produced via a normal wafer production. As a rule, these are wafer sizes of about 5 × 5 cm ² or similarly formed wafers in the order of 15 × 2 cm ² . Using such compact grids, it is possible to construct individual modules consisting of a focus-side phase grating, a subsequent analysis grating, and a sub-detector directly behind the analysis grating, which in turn consists of a plurality of individual detector elements.

ever After construction of the grid / detector modules, it is then possible to Measurement of the phase shift of a subject passing through the examination object Strahls, to move the analysis grid of this module individually. However, there is also the possibility for one Series of detector modules a common drive for the there to provide arranged analysis grid. It is noted, however, that the drive not unconditional requirement for a grid / detector module according to the invention is, as with sufficiently local resolving detectors, the displacement of the analysis grid for measuring the phase shift not absolutely necessary.

• – einer Strahlenquelle mit einem Fokus und einem fokusseitigen Quellengitter, welches im Strahlengang angeordnet ist und ein Feld von strahlweise kohärenten Röntgenstrahlen erzeugt,
• – und einer Detektoranordnung mit einer Vielzahl von nebeneinander angeordneten Detektormodulen, welche jeweils in Strahlrichtung hintereinander angeordnet aufweisen:
• – mindestens ein Phasengitter, zur Erzeugung eines ersten Interferenzmusters,
• – ein Analysengitter, zur Erzeugung eines weiteren Interferenzmusters,
• – und flächig angeordnete Detektorelemente,
• – wobei die einzelnen Gitterlinien aller Gitter parallel zueinander ausgerichtet sind.

In accordance with the basic idea of the invention, the inventors propose a focus / detector system of an X-ray apparatus for producing projective or tomographic phase-contrast images, which consists of at least the following elements:

• A radiation source having a focus and a focus-side source grid which is arranged in the beam path and generates a field of beam-wise coherent X-rays,
• - And a detector array having a plurality of juxtaposed detector modules, which are arranged one behind the other in the beam direction:
• At least one phase grating, for producing a first interference pattern,
• An analysis grid, for producing a further interference pattern,
• And flat detector elements,
• - Wherein the individual grid lines of all grids are aligned parallel to each other.

As described above such a construction of a focus / detector system the use from relatively small X-ray optics Lattices that over easily a common one Wafer production can be produced.

Basically exists the possibility, To carry out the module variants differently, for example, by the grid lines formed grid surfaces of the phase and analysis grid the modules are aligned parallel to each other, or it exists the possibility, the grid surfaces each perpendicular to a beam to be aligned from the focus to Detector module runs and the grid surfaces cuts.

In the former variant is created in this way a common Grid area, as well as the phase grating as well for the following analysis grid, possibly also for the following Detector array. Advantageously, such an embodiment in particular when used with C-arm systems or when used in x-ray systems to create projective recordings. A problem can In this case, not all modules of a larger detector system may be identical. This means, it is possible using identical grating systems, however, it is necessary to to "package" the individual grids in differently designed housings.

The another, second-named variant creates the possibility that, for example in a CT detector, the individual lattice planes tangent to one Sphere or cylindrical surface be arranged around the focus. For example, the arrangement be done so that the beam intersects the grid surfaces each perpendicular, the respective center ray is that of the grid surfaces in their respective center cuts.

According to another variant of the Anord tion, the grating / detector modules can be arranged so that the centers of all phase grating surfaces have the same distance to the focus. That is, the grating / detector modules are thus arranged spherically around the focus over a certain segment. In this case, an embodiment may be advantageous in which the center points of all phase grating surfaces and / or the centers of all analysis grating surfaces and / or the centers of all detector surfaces of the individual modules have the same distance to the focus. In these variants, it is assumed in each case that the grid surfaces are planar in themselves. However, there is also the possibility that the phase grating surfaces and / or the analysis grating surfaces and / or the detector surfaces of the individual grating / detector modules are formed corresponding to a spherical surface segment with the focus as the center.

A Another variant of the focus / detector system according to the invention can provide that at least one device for relative displacement at least an analysis grid against the Phase gratings perpendicular to the beam direction and perpendicular to the longitudinal direction the grid lines is provided on at least two analysis grid at least two grating / detector modules acts. So that means that in the Focus / detector system a drive device or adjustment device present, the at least two analysis grid of different detector modules drives. For example, such an embodiment may be used if multiple analysis grids are on the same radius respectively are arranged at the same level, so that moving one analysis grid simultaneously with the offset of the other this level or sphere arranged analyzer grid goes on.

A another variant may provide that each grid / detector module has its own Drive device for the analysis grid is provided so that this drive device even just moved this analyzer grid. With respect to the drive device can in addition to electric motor drive devices, for example a piezoelectric element can be used, which on the one hand very accurate Moving paths allowed and on the other hand, only a little susceptible against the high centrifugal forces, the acting in a CT detector is.

considered one the arrangement of the individual grid / detector modules in the focus / detector system, so can These are arranged, for example, checkerboard. this will a preferred variant for Focus / detector systems used for a C-arm system would or for the use in x-ray systems for generating projective recordings.

Especially preferred for CT systems with detectors installed in a gantry is an arrangement where the individual grid / detector modules form a single line in the projection from the focus. Such detector modules then have no square or approximately square Training, but are more aligned in the z direction of the CT system so that the detector, because of the many lines next to each other arranged detector elements as a multi-line or multi-line detector is formed, but has only a single row of detector modules. It is noted, however, that other design options within the scope of the invention.

According to the invention, the grating / detector modules should be designed and arranged such that each grating / detector module and its grating arrangement - in particular also in conjunction with the source grating on the side of the focus - satisfy the following geometric conditions:

p_o

= Gitterperiode des Quellengitters G₀,

p₁

= Gitterperiode des Phasengitters G₁,

p₂

= Gitterperiode des Analysengitters G₂,

d

= Abstand des Phasengitters G₁ zum Analysengitter G₂ in Fächerstrahlgeometrie,

d^≡

= Abstand des Phasengitters G₁ zum Analysengitter G₂ unter Parallelgeometrie,

l

= Abstand des Quellengitters G₀ zum Phasengitter G₁,

λ

= ausgewählte Wellenlänge der Strahlung,

h₁

= Steghöhe des Phasengitters G₁ in Strahlrichtung,

n

= Brechungsindex des Gittermaterials des Phasengitters.

Where:

p _o

= Grating period of the source grating G ₀ ,

p ₁

= Grating period of the phase grating G ₁ ,

p ₂

= Grating period of the analysis grid G ₂ ,

d

= Distance of the phase grating G ₁ to the analysis grating G ₂ in fan beam geometry,

d ^≡

= Distance of the phase grating G ₁ to the analysis grating G ₂ under parallel geometry,

l

= Distance of the source grating G ₀ to the phase grating G ₁ ,

λ

= selected wavelength of radiation,

h ₁

= Web height of the phase grating G ₁ in the beam direction,

n

= Refractive index of the grating material of the phase grating.

Corresponding In accordance with the principles of the invention, the inventors propose that the focus / detector systems described above, for example in an X-ray system for producing projective phase contrast images with at least a focus / detector system can be used.

In addition, such focus / Detek tor systems in C-arm systems that can be used to produce projective and tomographic phase contrast acquisitions.

Of Further, and more preferably, the inventors propose that described focus / detector systems in X-ray CT systems for generating tomographic Phase contrast recordings use, these X-ray CT systems at least a focus / detector system, in the manner previously described, or can also have multiple focus / detector systems, each on a rotatable Gantry are arranged. If several focus / detector systems are used, so can these both angularly offset and in the direction of the system axis of the CT system staggered. Combinations for this are also within the scope of the invention.

• – das Untersuchungsobjekt wird mit mindestens einem modular aufgebauten Fokus/Detektor-System der zuvor beschriebenen Art kreis- oder spiralförmig abgetastet, wobei durch mindestens drei Intensitätsmessungen mit jeweils versetzt angeordneten Analysengittern die Phasenverschiebung der Strahlen beim Durchtritt durch das Objekt ermittelt werden,
• – für Strahlen, die aufgrund des modularen Aufbaus des Detektors nicht oder nicht genau gemessen werden können, wird die Phasenverschiebung durch benachbarte Werte interpoliert,
• – aus den gemessenen und den durch Interpolation ermittelten Phasenverschiebungen der Strahlen werden tomographische Phasenkontrastaufnahmen rekonstruiert.

The scope of the invention also includes a method for generating tomographic images of an examination subject, preferably a patient, wherein at least the following method steps are performed:

• The object to be examined is scanned in a circle or in a spiral shape with at least one modular focus / detector system of the type described above, wherein the phase shift of the beams as they pass through the object are determined by at least three intensity measurements with staggered analysis gratings each,
• For beams which can not or can not be measured accurately due to the modular design of the detector, the phase shift is interpolated by adjacent values,
• - From the measured and determined by interpolation phase shifts of the beams tomographic phase contrast images are reconstructed.

On this way, the problem of the modular design of such focus / detector systems is compensated, according to which not any packing density in the range of Abutting surfaces of the Detector modules a somewhat uneven sampling takes place. By a corresponding interpolation of these unmeasured values appropriate compensation can be created.

In the following the invention with reference to preferred embodiments with reference to the figures will be described in more detail, with only the features necessary for understanding the invention features are shown. The following reference numbers are used here: 1 : CT system; 2 : first X-ray tube; 3 : first detector; 4 : second x-ray tube; 5 : second detector; 6 : Gantry housing; 7 : Patient; 8th : Patient couch; 9 : System axis; 10 : Control and computing unit; 11 : Storage; 12 : Piezoelectric element; 13 : Spring element; 14 : Wall of the grid / detector module; D: entire detector; D _i : detector of a grating / detector module; D _x : detector module; d: distance of the phase grating G ₁ to the analysis grating G ₂ in fan beam geometry; d ^≡ : distance of the phase grating G ₁ to the analysis grating G ₂ under parallel geometry; F ₁ : focus; G ₀ : source grid; G ₁ , G _1i : phase grating; G ₂ , G _2i : analysis grid; G _Dx : grid / detector module; h ₀ : ridge height of the source lattice; h ₁ : web height of the phase grating; h ₂ : web height of the analysis grid; l: distance of the source grating G ₀ to the phase grating G ₁ ; n: refractive index of the grating material of the phase grating; P: patient; p _o : grating period of the source lattice; p ₁ : grating period of the phase grating; p ₂ : grating period of the analysis grid; Prg _x : programs; S: system axis; x _G : offset of the analysis grid; λ: wavelength of the X-rays.

The Figures show in detail:

1 : Schematic 3D representation of a focus / detector system with grating set for determining phase shifts;

2 : Schematic 3D representation of a focus / detector system with three grid / detector modules;

3 : Top view of a CT detector consisting of eight grid / detector modules;

4 : Cross section perpendicular to the system axis on the grating / detector modules of the CT detector 3 ;

5 : View of a detector for recording projective phase-contrast images consisting of 8 × 6 checkerboard-like composite grid / detector modules;

6 : 3D representation of a focus / detector system of a C-arm system with even gratings and level detector;

7 : Section through an analysis grid with displacement device;

8th : X-ray CT system with focus / detector systems according to the invention in 3D view.

The 1 shows a schematic 3D representation of a focus / detector system of an X-ray CT with a lying in the beam path patient P as the examination object. The focus F ₁ and the detector D are arranged on a gantry not shown here and move in a circle around the system axis S. In addition, during the rotation of the focus / detector system, a linear movement of the patient P in system axes In the beam path of the focus / detector system, three X-ray optical grids G ₀ , G ₁ and G ₂ are arranged, the first grating G ₀ , which is also called source grating, is mounted in the immediate vicinity of the focus F ₁ and is irradiated by the X-ray radiation. The actual examination object or the patient P then follows in the propagation direction of the X-ray radiation. Before the detector D lying on the other side of the system axis S, the second grating G ₁ , called a phase grating, first follows. This is followed in the direction of radiation by the third grating G ₂ , called the analysis grating, which is advantageously arranged directly in front of the detector D. The detector D has at least one line with a plurality of detector elements, preferably, the detector D is constructed as a multi-line or multi-line detector, which is equipped with a plurality of detector rows arranged in parallel with each egg ner plurality of detector elements. During the scanning, the connecting lines between the focus F ₁ and the individual detector elements each represent an X-ray beam arranged in space whose intensity change is measured by the respective detector element.

It should be noted that in the case of so-called C-arm devices, which also fall under the class of the CT systems mentioned here, the detector D is not formed as a cylinder segment about the focus F ₁ , as shown, but a plane Form has. In the case of projective X-ray systems, which do not move around the examination object during the scans, the detector D is also generally planar.

The line orientation of the grids G ₀ to G ₂ is designed such that the grating lines of all three grids run parallel to one another. It is advantageous but not necessary if these grid lines are also oriented parallel or perpendicular to the system axis S. In the variants shown, the grids G ₀ to G ₂ are flat and aligned perpendicular to the center line between the focus and detector center.

The first grid G ₀ has a period p _{0 of} the grid line and a height h _{0 of} the grid bars. Correspondingly, the grids G ₁ and G _{2 are also} equipped with a height h ₁ or h ₂ and a period p ₁ or p ₂ . For the function of the method according to the invention, it is necessary for the distance l between the grid G ₀ and the G ₁ and the distance d between the grid G ₁ and the G _{2 to be} in a specific relationship to one another. It applies here P 0 = p 2 × l d

The distance of the detector D ₁ with its detector elements from the last grid G ₂ is irrelevant. The height h _{1 of} the webs of the phase grating should be selected such that the following formula applies in accordance with the considered wavelengths, that is to say the considered energy of the X-radiation and with reference to the respective grating material:

in this connection n denotes the refractive index of the grating material and λ the wavelengths of the X-rays, in which the phase shift is to be measured. Advantageous this grid is set to an energy that is a characteristic line in the X-ray spectrum the anode used corresponds.

The height h _{2 of} the analysis grid must be sufficient to produce effective absorption differences between the X-ray irradiated webs and the largely vacant areas of the grid in order to create a corresponding moiré pattern on the back.

mit d^≡ dem Abstand des Phasengitters G₁ zum Analysengitter G₂ unter Annahme einer Parallelgeometrie, und dem Abstand d des Phasengitters G₁ zum Analysengitter G₂ in Fächerstrahlgeometrie.Furthermore, the following geometric relationships in the grid set also apply:

with d ^≡ the distance of the phase grating G ₁ to the analysis grid G ₂ assuming a parallel geometry, and the distance d of the phase grating G ₁ to the analysis grid G ₂ in fan beam geometry.

As can be seen from this illustration, take the dimensions of the phase grating G ₁ and the analysis grid G ₂ sizes that are barely displayed on the normal production of wafers or at least not cost feasible. For the purposes of the invention it is therefore proposed to divide the grids G ₁ and G ₂ modular. For example, this can happen as it is in the 1 is indicated, namely, the grids G ₁ and G ₂ can be subdivided in the direction of the system axis, so that elongated grid elements arise, which then have to be fixed in modules in the focus / detector element. In this schematic representation of 1 For example, the individual phase and analysis grids are arranged such that the sum of all the phase gratings together lie on a common plane, while the analysis grids of the modules also form a common grid plane.

In the 2 another variant is shown. Here is in the focus / detector system shown - similar to the 1 Also shows a single source grid G ₀ , but the focus / detector system on the detector side consists of three grating / detector modules, the phase and analysis grids and the areas of the detector elements of each module being aligned parallel to each other and all three grids / Detector modules are fan-like to the focus F ₁ are arranged. Each individual module consists of a phase grating G _1x , an analysis grating G _2x following in the beam _direction , with the immediately following detector module D _x , wherein each individual detector module consists of a multiplicity of detector elements arranged in a checkerboard pattern, which are not shown here.

If such a structure of the focus / detector system is refined, so that more detector modules are used, the result is in the projection of the focus, an arrangement of the grid / detector modules, as shown in the 3 is shown. Here, eight fan-like arranged grid / detector modules are shown, wherein the alignment of the grid lines in this grid / detector modules is present perpendicular to the system axis.

If this arrangement is cut perpendicular to the system axis, the result is a representation as in FIG 4 , These 4 shows the fan-like arrangement of eight grating / detector modules G _D1 to G _D8 , which are rectangular in this section and each having a phase grating G _1x with a subsequent analysis grid G _2x and a detector module D _x . As can be seen from this figure, in this construction, a gap is formed on the side facing away from the focus in the area of the detector modules D _x . Similar gaps can arise, for example, solely by the finite thickness of module housings. Such gaps also lead to gaps in the scan or at least scan errors and artifacts. For this purpose, it is advantageous to bridge such areas by interpolations or to match them to one another in such a way that artifacts in the imaging are avoided. This can preferably already be done when creating complete projection data records or it can also be the finished volume records processed accordingly.

While in the 3 and 4 the training of a detector for a CT system with a revolving gantry is shown in the 5 the construction of a focus / detector system for a C-arm system or for a simple projective X-ray system shown. Here, the individual grid / detector modules are arranged like a checkerboard, the orientation of the grid lines of all grids used being the same and corresponding to the orientation of the source grid.

The arrangement of such grating / detector modules in the entire focus / detector system is in the 6 shown. This shows the focus / detector module according to the invention with a flat and almost square aligned detector D, which consists of a plurality of grid / detector modules, which form the sum of the area of the phase grating G ₁ and the subsequent analysis grating G ₂ .

The 7 shows a detail of a grid / detector module in the region of the analysis grid in section perpendicular to the grid lines. The analysis grid G ₂ is on both sides in the walls 14 of the grid / detector module clamped, wherein on one side between the analysis grid G _2i and the wall 14 a piezo element 12 is arranged and on the opposite side a spring element 13 is present. becomes the piezo element 12 subjected to a corresponding voltage, there is a longitudinal displacement x _{G of} the analysis _grid G _2i , which is required to determine the phase shift of the beam at this location with the aid of at least three measurements at different deflected analysis grid.

A complete computer CT system for carrying out the method according to the invention is in 8th shown. This shows the CT system 1 which has a first focus / detector system with an x-ray tube 2 and an opposite detector 3 has, on a gantry, not shown in a gantry housing 6 are arranged. In the beam path of the first focus / detector system 2 . 3 is a grid system according to the 1 to 3 arranged so that the patient 7 that is on one of the system axis 9 movable patient bed 8th can be pushed into the beam path of the first focus / detector system and is scanned there. The control of the CT system is provided by a computing and control unit 10 performed in a store 11 Programs Prg ₁ to Prg _n are stored, which carry out the inventive method described above and reconstruct from the measured radiation-dependent phase shifts and absorptions corresponding tomographic images.

Optionally, instead of the single focus / detector system, a second focus / detector system can be arranged in the gantry housing. This is in the 8th through the X-ray tube shown in dashed lines 4 and the dashed detector shown 5 indicated.

It is understood that the abovementioned features of the invention can be used not only in the respectively specified combination but also in other combinations or alone, without the scope of the invention leave.

Claims (22)

Focus / detector system (F ₁ , D) of an X-ray apparatus ( 1 ) for producing projective or tomographic phase contrast images, at least consisting of: 1.1. a radiation source ( 2 ) with a focus (F ₁ ) and a focus-side source grating (G ₀ ), which is arranged in the beam path and generates a field of beam-wise coherent X-rays, 1.2. and a detector arrangement with a multiplicity of juxtaposed grid / detector modules (GD _x ), which are arranged one after the other in the beam direction in each case: 1.2.1. at least one phase grating (G _1x ), for producing a first interference pattern, 1.2.2. an analysis grid (G _2x ), to generate another interference pattern, 1.2.3. and flat detector elements (D _x ), 1.2.4. wherein the individual grid lines of all grids (G ₀ , G _1x , G _2x ) are aligned parallel to each other. Focus / detector system according to the preceding claim 1, characterized in that the grid surfaces formed by the grid lines of the phase and analysis _{grids of} the modules (G _Dx ) are aligned parallel to each other. Focus / detector system according to the preceding claim 1, characterized in that the grid surfaces each perpendicular to a beam which extends from the focus to the grating / detector module and the grid surfaces intersect. Focus / detector system according to the preceding claim 3, characterized in that the beam, the grid surfaces respectively perpendicularly intersects, which is the center ray, which the grid faces in whose respective center cuts. Focus / detector system according to the preceding claim 4, characterized in that the grating / detector modules (G _Dx ) are arranged so that the centers of all phase grating surfaces have the same distance to the focus (F ₁ ). Focus / detector system according to one of the preceding claims 4 to 5, characterized in that the grating / detector modules (GD _x ) are arranged so that the centers of all analysis grating surfaces have the same distance from the focus (F ₁ ). Focus / detector system according to one of the preceding claims 4 to 6, characterized in that the grating / detector modules (G _Dx ) are arranged so that the centers of all detector _surfaces , consisting of the sum of areally arranged detector elements, the same distance to the focus (F ₁ ). Focus / detector system according to the preceding claim 4, characterized in that the phase grating surfaces are each formed on a spherical surface segment with the focus (F ₁ ) as the center. Focus / detector system according to one of the preceding claims 4 or 8, characterized in that the analysis grid surfaces are each formed on a spherical surface segment with the focus (F ₁ ) as the center. Focus / detector system according to one of the preceding claims 4 or 8-9, characterized in that the detector surfaces of a grating / detector module (G _Dx ), consisting of the sum of areally arranged detector _elements , each on a spherical surface segment with the focus ( F ₁ ) as the center. Focus / detector system according to one of the preceding claims 1 to 10, characterized in that at least one device ( 12 . 13 ) is provided for relative displacement of at least one analysis grid (G _2x ) relative to the phase gratings (G _1x ) perpendicular to the beam direction and perpendicular to the longitudinal direction of the grid lines, which acts on at least two analysis grid (G _1x ) at least two grating / detector modules (G _Dx ) , Focus / detector system according to one of the preceding claims 1 to 10, characterized in that per grating / detector module (G _Dx ) a device for relative displacement of the analysis grid of this grating / detector module (G _Dx ) relative to the phase grating of this grid / Detector module (G _Dx ) is provided perpendicular to the beam direction and perpendicular to the longitudinal direction of the grid lines. Focus / detector system according to one of the preceding claims 1 to 12, characterized in that the grid / detector modules (G _Dx ) in the projection from the focus (F ₁ ) are arranged like a checkerboard. Focus / detector system according to one of the preceding claims 1 to 12, characterized in that the grid / detector modules (G _Dx ) in the projection from the focus (F ₁ ) from a single line form. Focus / detector system according to one of the preceding claims 1 to 12, characterized in that the grating / detector modules (G _Dx ) are designed and arranged such that each grating / detector module (G _Dx ) and its grating arrangement (G _1x , G _2x ) satisfies the following geometric conditions:

where: p _o = grating period of the source grating G ₀ , p ₁ = grating period of the phase grating G ₁ , p ₂ = grating period of the analysis grating G ₂ , d = distance of the phase grating G ₁ to the analysis grating G ₂ in fan beam geometry, d ^≡ = distance of the phase grating G ₁ to the analysis grating G ₂ under parallel geometry, l = distance of the source grating G ₀ to the phase grating G ₁ , λ = selected wavelength of the radiation, h ₁ = web height of the phase grating G ₁ in the beam direction, n = refractive index of the grating material of the phase grating. X-ray system for producing projective phase-contrast images with at least one focus / detector system (F ₁ , D) according to one of the preceding claims 1 to 15. X-ray C-arm system for the generation of projective and tomographic phase-contrast images with a focus / detector system according to any one of the preceding claims 1 to 15, which rotates on an object to be examined C-bow is arranged. X-ray CT system ( 1 ) for generating tomographic phase-contrast images with at least one focus / detector system according to one of the preceding claims 1 to 15, which is mounted on an object to be examined ( 7 ) rotatable gantry is arranged. X-ray system ( 1 ) according to one of the preceding claims 16 to 18, characterized in that a computing unit ( 10 ) for controlling the analysis grid (G _2x ) and calculating the phase shift (φ) from a plurality of intensity measurements of the same beam with differently offset analysis grids (G _2x ) is provided. X-ray system according to one of the preceding claims 16 to 19, characterized in that it has a computing and control unit ( 10 ), which contains program code (Prg _x ), which executes the method according to the following method claim 22 in operation. Storage medium of an X-ray system or for an X-ray system, characterized in that the storage medium ( 11 ) Program code (Prg _x ), which in the operation of the X-ray system according to the following method claim 22 performs. Method for generating tomographic images of an examination object, preferably a patient ( 7 ), wherein at least the following method steps are carried out: 22.1. the examination object ( 7 ) is scanned with at least one modular focus / detector system (F ₁ , D) according to any one of claims 1 to 15 circular or spiral, wherein by at least three intensity measurements with each staggered analysis grids (G _2x ) the phase shift (φ) of the rays passing through the examination subject ( 7 ), 22.2. for beams which can not be measured accurately due to the modular structure of the detector (D), the phase shift (φ) is interpolated by adjacent values, 22.3. From the measured and determined by interpolation phase shifts (φ) of the beams tomographic phase contrast images are reconstructed.