Device and method for taking a radiograph

Abstract

A device (1; 2; 3; 4; 5; 6; 7) for taking a radiograph comprises an x-ray source for providing x-rays (20) and an object receiver for accommodating an object (10) in the beam path of the x-rays (20). A propagation distance lengthening means (40) is disposed downstream of the object (10) in the beam path of the x-rays (20). A detector (50) is disposed downstream of the propagation distance lengthening means (40) in the beam path of the x-rays (20). In this case, the propagation distance lengthening means (40) is designed such that it increases a real propagation distance (z1), over which the x-rays (20) propagate between the propagation distance lengthening means (40) and the detector (50), to an effective propagation distance (zeff).

Description

[0001]Applicant: Karlsruhe Institute of Technology "Device and method for taking an X-ray image" Our reference: K 7567WO - hy / mu Device and method for taking an X-ray image The invention relates to devices and methods for taking an X-ray image. X-ray images are used, for example, in medicine to examine patients, but also in the examination of various samples. Various techniques are used for this purpose. The X-ray absorption of the object is normally used as the contrast mechanism for the X-ray images. For objects with low absorption, e.g. soft tissue in mammography, methods are being developed that make the phase shift that the X-rays experience when passing through the object visible. According to the current state of the art, phase contrast imaging can be carried out using coded aperture, grating-based, analyzer-based, interferometric or propagation-based techniques, among others (cf. e.g."Theoretical comparison of three X-ray phase-contrast imaging techniques: Propagation-based imaging, analyzer-based imaging and grating interferometry" by Diemoz, PC; Bravin, A.; Coan, P. (2012) in Optics Express 20 (3): 2789–2805. Doi:10.1364 / OE.20.002789 and https: / / iopscience.iop.org / article / 10.1088 / 0031-9155 / 58 / 1 / R1 / meta by Bravin 2012). The former methods are comparatively complicated, and in some cases, several individual images must be combined to generate the images. In these cases, only relatively slow dynamic measurements can be performed, and the total radiation dose is increased. With propagation-based phase contrast, the image contrast of the X-ray image generally increases the greater the distance between the imaged object and the detector. Both phase contrast and amplitude contrast contribute to the overall image contrast.Phase contrast is usually the dominant contribution. The term phase contrast is therefore used synonymously with image contrast below and includes the contribution of amplitude contrast. For example, very high contrasts can be achieved if the distance between the imaged object and the detector, also called the propagation distance, is several meters long, especially over 100m or even longer. A long propagation distance is particularly desirable for large samples (several mm, cm and larger) that are imaged with comparatively low spatial resolution. However, the realization of an X-ray imaging device with such a long propagation distance is only feasible in practice in extremely exceptional cases, see, for example, Cianciosi, F., Buisson, AL, Tafforeau, P., & Van Vaerenbergh, P. (2021, July). BM18, the New ESRF-EBS Beamline for Hierarchical Phase-Contrast Tomography. In 11. thMechanical Engineering Design of Synchrotron Radiation Equipment and Instrumentation (MEDSI'20), Chicago, IL, USA, 24-29 July 2021 (pp. 1-5). JACOW Publishing, Geneva, Switzerland. Against this background, the invention is based on the object of enabling improved X-ray images, in particular X-ray images with increased contrast and / or lower dose. Compared to grating- and coded-aperture-based methods, the object can be to improve image quality and resolution. Compared to propagation-based phase contrast with very long propagation distances, the object can be to improve image quality and enable a more compact design. Furthermore, it can be an object that the X-ray image is less influenced by the source size of the X-ray radiation. For example, requirements for the X-ray source can be relaxed, allowing compact light sources such asTable-top FELs and laboratory sources can be used as X-ray sources. This object is achieved by the subject matter of the independent claims. Preferred embodiments are the subject matter of the dependent claims. One aspect relates to a device for taking an X-ray image. The device comprises an X-ray source for providing X-rays, an object holder for holding an object in the beam path of the X-rays, and a propagation distance extension means arranged downstream of the object holder in the beam path of the X-rays. Furthermore, the device comprises a detector arranged downstream of the propagation distance extension means in the beam path of the X-rays.The propagation distance extension means is designed such that it extends at least a portion of a real propagation distance, along which the X-rays propagate between the propagation distance extension means and the detector, to an effective propagation distance. The X-ray source emits the X-rays, hereinafter also referred to as X-ray radiation. Of this X-ray radiation, essentially the rays of a single wavelength λ0 can be used for recording, or rays of different wavelengths. The X-ray source can emit the X-rays, in particular, in a first propagation direction, which forms the starting section of the beam path of the X-rays. The beam path of the X-rays can, for example, be deflected and / or shaped several times within the device. The X-ray source can either generate the X-rays itself, e.g.by means of electrical energy, or it can be designed to capture radiation and shape it so that it is emitted from the X-ray source along the first propagation direction of the X-rays. In this case, the X-ray source can only have an entrance area for irradiating X-rays. The object holder is designed to receive the object. The object holder is thus essentially designed as a free space that can receive the object. For this purpose, the object holder can, for example, have holders and / or a receiving surface that is or are designed to hold and / or fix the object in the beam path of the X-rays. In some embodiments, the object is also a component of the device. The object can be a sample, such as an object or a liquid, but also a living being such as a patient or an animal or body parts of the living being, e.g.a breast as in a cancer screening, a lung, a prostate, a beating heart or other organs. If a living being is to be imaged, the object image can be designed simply as a predefined free space, possibly with a marking, in which the living being is placed during the image capture. The X-rays are directed by the X-ray source either directly or indirectly onto the object, which can be at least partially penetrated by the X-rays. This interaction between the X-rays and the object occurs, which influences and / or changes the X-rays. Directly or indirectly after the interaction with the object, the X-rays propagate to the propagation distance extender, with which they interact. This interaction can also be made up of several individual interactions.Each individual interaction can comprise a reflection from and / or at least partial penetration or penetration of components of the propagation distance extension means. Within the scope of the invention, the term "reflection", "reflect", or similar, or the term "diffraction", "diffracted", or similar, is generally used to refer to this interaction with the propagation distance extension means, whereby both types of physical interaction can be meant. The propagation distance extension means can act on one or more image dimensions, so that the image contrasts are optionally enhanced in only one or more dimensions. During the interaction with the propagation distance extension means, the X-rays can be influenced in such a way that the wave field and / or cross-section of the X-rays and, if applicable, the image size of the X-ray image dependent thereon is reduced.Furthermore, the subsequent effective propagation distance can be increased by the interaction. The increase in the effective propagation distance can occur approximately with the square of the reduction in the wave field and / or the cross-section of the X-rays and thus, if applicable, the X-ray image. Through this interaction, at least a portion of the actual propagation distance, along which the X-rays propagate from the propagation distance extension means to the detector and / or an intermediate component of the device, is extended to an effective propagation distance. This extension of the actual propagation distance to a propagation distance effective for imaging is enabled by the propagation distance extension means. The effective propagation distance is longer than the actual propagation distance, e.g.at least 10 times longer, preferably at least 50 times longer, preferably at least 100 times longer, preferably at least 500 times or at least 1000 times longer. The section of the real propagation distance thus effectively extended can depend on the positioning of the detector or an intermediate component in the beam path after the propagation distance extension means. The further the detector and / or the intermediate component is from the propagation distance extension means, the greater this effectively extended section of the real propagation distance. After interacting with the propagation distance extension means, the X-rays are detected by the detector. One or more X-ray images can be created using the X-rays captured by the detector, which have interacted at least with the object and with the propagation distance extension means.The detector can be arranged either essentially perpendicular to the X-ray beam path or tilted to the vertical. With such a tilt of the detector, the extent of the X-ray image can be enlarged in one dimension depending on the tilt. The X-ray beam path can begin at the X-ray source and extend from there at least to the detector. In between, at least the object and then the propagation distance extension means are arranged in the beam path. However, other components, in particular beam shaping and / or magnification elements, can also be arranged in the beam path. The X-ray image created in this way can have a higher image contrast than images taken with conventional X-ray devices because the effective propagation distance of the X-ray radiation has been artificially increased after interaction with the object.The invention thus makes it possible to acquire X-ray images within a relatively small and thus easily realizable installation space, exhibiting an image contrast that conventionally requires propagation distances of several meters, e.g., several hundred meters. This means that the propagation distance extension means can function and / or be designed as a contrast enhancement means. The propagation distance extension means can thus enhance the image contrast at the same actual propagation distance compared to conventional propagation-based phase contrast and / or it can reduce the required actual propagation distance required for a desired image contrast, thus enabling a more compact design. Both aspects can be realized simultaneously.The invention enables the source size of the X-rays to have a smaller impact on image quality and / or cause less source blur due to the shorter actual propagation distance, and / or to relax the requirements for the X-ray source. The device can be used in particular in medical and / or biological imaging, e.g. for mammography and / or cancer diagnosis, as well as in other low-dose applications and imaging of light materials, e.g. in materials research or in components. In contrast to, for example, grating-based methods, the phase contrast can be achieved without the wavefield of the X-ray radiation being structurally influenced by additional objects. The imprinting of an additional illumination structure, which may generate image artifacts, can therefore be avoided. Furthermore, the X-rays are not subject to any further significant losses.By additionally using a beam-shaping element in front of the object, the requirements for the source size of the X-rays can be relaxed and / or the distance between the X-ray source and the object can be reduced, as explained below. This can further improve the image quality and resolution compared to conventional propagation-based image contrast and / or increase the light yield of the X-ray source and / or reduce the distance of the object from the X-ray source. The additionally increased image contrast allows a reduction in the radiation dose, so that not only synchrotrons, FELs, etc., but also compact X-ray sources, such as those from PROCEEDINGS OF SPIE by Hornberger et al. (see https: / / www.spiedigitallibrary.org / proceedings / Download?urlId=10.1117%2F12.2591977) and / or Applied Sciences by Petrillo et al. (see https: / / www.mdpi.com / 2076-3417 / 13 / 2 / 752) and / or laboratory sources can be used. The invention can be combined with other X-ray methods. For example, the X-ray radiation can be structured with amplitude or phase gratings. In at least one of the embodiments, it is possible to record analyzer-based contrasts. In one embodiment, the propagation distance extension means comprises at least one demagnifier. The demagnifier is designed as a means for reducing the wave field and / or the beam cross-section of the X-ray image, thereby artificially shortening the propagation distance. In principle, the demagnifier can be based on various methods, e.g., an X-ray lens. A demagnifier works in the opposite and / or inverse manner to a magnifier.While a magnifier can enlarge the beam cross-section of an X-ray image and / or the cross-section of the X-ray wave field, the demagnifier reduces the beam cross-section of an X-ray image and / or the cross-section of the X-ray wave field. The demagnifier can be designed as a magnifier that is arranged upside down and / or inversely in the beam path of the X-rays, i.e., in such a way that it reduces the cross-section of the X-ray radiation. At least one of the demagnifiers of the propagation distance extension means can be designed as a Bragg demagnifier. The Bragg demagnifier can (analogously to the known Bragg magnifiers) have at least one asymmetrically cut crystal. The Bragg demagnifier can be designed with asymmetrically cut crystals in Bragg and / or Laue reflection.When reference is made to a Bragg demagnifier and / or a Bragg magnifier in the context of this invention, this includes not only the use of a crystal with Bragg reflection, but also the use of a crystal with Laue reflection. At least one of the demagnifiers of the propagation distance extender can be designed as an X-ray lens(es), such as a Fresnel lens(es), as a compound refractive lens(es) (see, for example, Snigireva, Irina, and Anatoly Snigirev, "X-ray microanalytical techniques based on synchrotron radiation," Journal of Environmental Monitoring 8.1 (2006): 33-42) and / or as a Kirkpatrick-Baetz mirror (hereinafter abbreviated as KB mirror, see, for example, P. Kirkpatrick and A. Baez, J. Opt. Soc. Am., 1948, 38, 766). By reducing the wave field in the spatial domain by a demagnifier, the diffraction angles, ieLateral spatial frequencies are magnified, allowing phase contrast to be detected even at shorter distances. Bragg magnifiers, which enlarge the cross-section of X-rays, are generally known to those skilled in the art; see, for example, "Bragg magnifier: A detector for submicrometer x-ray computer tomography" by M. Stampanoni et al., Journal of Applied Physics 92, 7630 (2002). Bragg demagnifiers, which reduce the cross-section of an X-ray beam, are also known to those skilled in the art, see for example Hirano, K. “Application of x-ray image magnifier and demagnifier to parallel beam x-ray computed tomography”, Journal of Physics D: Applied Physics 44.5 (2011): 055501. However, to date they have only been used to focus the X-rays and / or to reduce the size of the image, for example in order to be able to use a smaller detector, but not to generate increased contrast through virtual propagation extension.A Bragg demagnifier can extend the effective propagation distance to over one hundred meters in a small space, making it particularly suitable as a propagation distance extender. Bragg magnifiers and Bragg demagnifiers use one or more asymmetrically cut crystals. An asymmetrically cut crystal means that the crystal planes used for reflection and / or diffraction are not parallel to one of the crystal's surfaces, which is subsequently also referred to as the reflection surface. This can be achieved by asymmetrically cutting and / or grinding a crystal, or by using a reflection at a crystal plane that is not parallel to the reflection surface and / or cutting plane of the crystal. In the following, both cases will be referred to as an asymmetrically cut crystal.In these cases, when an essentially plane X-ray wave is irradiated, the beam cross-section changes upon reflection. This is because the X-rays are reflected by Bragg diffraction off the crystal planes, which are at an angle to the crystal surface. Thus, the angle of incidence is approximately equal to the angle of reflection with respect to the crystal planes and not with respect to the crystal surface. For a more detailed analysis, dynamic diffraction theory must be considered, see, for example, Authier, André. Dynamical theory of X-ray diffraction. Vol. 11. Oxford University Press on Demand, 2004. One speaks of a Bragg magnifier (which uses a cross-section angle, referred to below as positive) when the beam cross-section is increased, and of a Bragg demagnifier (negative cross-section angle) when the beam cross-section is reduced.In any case, the normal vector of the lattice planes used is not perpendicular to the section plane of the crystal used. A Bragg magnifier can be used as a beam expander to expand the cross-section of the X-rays in front of the object in one or two dimensions. In the following, this use is also referred to as a Bragg conditioner. If the cross-section of the X-rays is enlarged behind the object, this is also referred to as a Bragg magnifier. For monochromatic radiation from a spatially expanded source (not a pure point source), a Bragg conditioner effectively reduces the source size, e.g., linearly with the increase in the cross-section of the X-rays. According to the van Cittert-Zernike theorem, the object is therefore illuminated with greater spatial coherence.From a polychromatic perspective, however, the illumination angles on the object are not reduced and / or are even slightly increased. When using a Bragg conditioner without a Bragg demagnifier, the influence of the source size on the image quality is therefore similar to that without the use of a Bragg conditioner and / or even slightly worse. If there is no monochromator in front of the lens, the Bragg conditioner also acts as a broadband monochromator, i.e. the light output is reduced compared to white light. When using a Bragg conditioner and a Bragg demagnifier, ideally with the same crystal parameters, the Bragg demagnifier can compensate for the polychromatic spreading of the beam angles caused by the Bragg conditioner. This is especially true for non-dispersive arrangements. This makes it possible to utilize the property of the Bragg conditioner that effectively reduces the source size monochromatically (reduced source blur).In addition to the advantage of the propagation distance extension provided by the Bragg demagnifier, this combination also provides an improvement in image quality compared to an image taken without a Bragg conditioner and without a Bragg demagnifier, and at a real propagation distance that corresponds to the effective propagation distance when using a Bragg demagnifier. With this combination, longer effective propagation distances can be reasonably achieved than with conventional propagation-based image contrast, before the resolution is limited by the source size and thus the source blur. This can apply to all of the embodiments listed in which the combination of Bragg conditioner and Bragg demagnifier occurs. Asymmetrically cut crystals can also be used for divergent (curved wavefronts) and polychromatic X-rays. This means that if the source size is small enough, the X-ray source can, for example,be positioned close to the Bragg conditioner. The object may then be illuminated in different areas with different energies. For crystal combinations such as a Bragg conditioner and Bragg demagnifier, the angle acceptances should then be matched to one another, e.g. by choosing the same intersection angles. From the above considerations it follows that for a given light source (e.g. laboratory light source with a given source size and beam brilliance, compact source, e.g. table-top FEL), if necessary using a KB mirror, the beams can be conditioned in such a way that the optimum light output is achieved for the desired object size and resolution. This allows the overall setup to be ideally adapted to the source and constructed in a compact manner. By inserting a Bragg magnifier behind a Bragg demagnifier, the reduction effect caused by the Bragg demagnifier can be reduced or compensated for.This can lead to improved X-ray images. Furthermore, it enables the use of a highly efficient large-area detector, e.g., in low-dose applications. By using a Bragg magnifier behind a Bragg demagnifier, nonlinear effects of the propagation distance extender can also be compensated. This significantly simplifies the reconstruction of the object. An overall setup can therefore comprise an X-ray source, possibly one or more KB mirrors, possibly one or more beam expanders (such as Bragg conditioners), the free space for the object, a real propagation distance, the propagation distance extender (one or more Bragg demagnifiers), a real propagation distance z1, possibly one or more Bragg magnifiers followed by possibly another real propagation distance and a detector.In some embodiments, multiple Bragg magnifiers and / or Bragg conditioners and / or Bragg demagnifiers can be used to achieve the magnification and / or reduction of the cross-section of the X-ray radiation in one or two dimensions. The magnification and / or reduction can be carried out in multiple stages, e.g., by means of multiple Bragg demagnifiers connected in series. They can also be used to arrange the X-ray radiation in a suitable manner for the entire structure of the device, e.g., to easily enable the introduction of the object, e.g., a patient in a horizontal position, and / or a predetermined positioning of a rotation axis for a tomography image, e.g., vertically. The X-ray image can be created from a single image. This enables high temporal resolution, e.g., with living objects, and can enable dynamic measurements. The X-ray images can, e.g.,represent the dynamics of the object and / or be synchronized with it, e.g. to depict tissue mechanics by synchronizing with the heartbeat or respiration or other modulation of the object. X-ray images of tomograms are also possible. It is also possible to investigate the effects of medical treatment and / or to image a medical intervention. By exploiting the dose reduction, long-term studies can be conducted, e.g. recovery studies. In one embodiment, the propagation distance extension means comprises at least one asymmetrically cut crystal at which the X-rays are at least partially reflected and / or diffracted. Asymmetrically cut crystals are also used as Bragg magnifiers for enlarging an X-ray image. They are therefore equally suitable as Bragg demagnifiers for reducing the size of an X-ray image and simultaneously extending the propagation distance.Asymmetrically cut crystals are cut in such a way that the crystal planes at which the X-rays are to be reflected have a predetermined crystal plane angle to at least one crystal surface. The crystal planes at which the X-rays are reflected are not arranged symmetrically, for example parallel, to one of the surfaces of the crystal, but asymmetrically, for example at an angle. In a further development of this embodiment, the asymmetrically cut crystal(s) is(are) asymmetrically cut at a negative crystal plane angle between a crystal plane of the crystal structure of the crystal and a reflection surface of the crystal. In contrast to a Bragg magnifier, the crystal plane angle is negative and can be, for example, between -1° and -40°, in particular between -2° and -10°. This brings about a reduction in size as opposed to a magnification using a Bragg magnifier.The reflection surface of the crystal can be arranged facing the object in the X-ray beam path and / or be designed to reflect the X-rays from the object toward the detector and / or intermediate component. In a further development of this embodiment, the at least one asymmetrically cut crystal is cut taking into account the Bragg angle relevant for the crystal reflection used and / or is arranged in the X-ray beam path. The asymmetrically cut crystal is arranged in the X-ray beam path in such a way that it effects a predetermined extension of the effective propagation distance.Since the crystal is cut asymmetrically and the relevant reflection of the X-rays occurs only approximately at the Bragg angle of the crystal structure, the angle of incidence for the X-rays reflected at the reflection surface of the crystal is not, as is the case with a mirror surface, equal to the angle of reflection. This results in the desired image reduction, which has the effect of extending the effective propagation distance. In one embodiment, the propagation distance extension means is designed such that it causes an increase in the actual propagation distance after interaction of the X-rays with the object and the propagation distance extension means to an effective propagation distance of at least 10 m, preferably of at least 30 m, preferably of at least 50 m, preferably of at least 100 m, preferably of at least 200 m.At such an effective propagation distance, the phase contrast of the X-ray image is much more pronounced than at the propagation distances realized for conventional devices, ranging from a few centimeters up to possibly a few meters. In one embodiment, the effective propagation distance of the device is configured such that the absolute value of a phase contrast transfer function of the device for an imaging spatial frequency and / or an imaging spatial frequency range, in particular for the scanned Nyquist frequency of the detector, has approximately a maximum. Alternatively or additionally, the absolute value of this phase contrast transfer function for the imaging spatial frequency and / or the imaging spatial frequency range, in particular for the scanned Nyquist frequency of the detector, can be at least approximately 0.2, in particular at least approximately 0.5.This takes into account the phase contrast transfer function of the device as an imaging system, which depends on parameters of the device and / or image formation, in particular distances and / or crystal parameters and / or the energy of the X-rays. The phase contrast transfer function is usually abbreviated as PCFT (from the English "phase contrast transfer function") and applies to weak phase objects, but is independent of the object being imaged. Since the PCTF can also be negative, the absolute value of the PCTF is considered. In addition, the imaging spatial frequency and / or an imaging spatial frequency range is also taken into account. Thus, at least one imaging spatial frequency is taken into account. The imaging spatial frequency can also depend on the device, in particular on the detector used. The imaging spatial frequencies (or synonymously: spatial frequencies) can be and / or become predetermined depending on the object.For example, the Nyquist frequency can be considered as the imaging spatial frequency. The Nyquist frequency depends on the nature of the detector, in particular on the pixel size and / or pixel pitch of a radiation-detecting pixel array of the detector. For objects with weak phases, the relationship between the Fourier transform of the object phase and the Fourier transform of the image intensity is approximately linear. In this case, the image contrast can be approximately described by the contrast transfer function. A distinction is made between the amplitude contrast transfer function and the phase contrast transfer function. Since the amplitude is usually small compared to the phase, the amplitude contrast transfer function can often be neglected. The following descriptions therefore only concern the phase contrast transfer function.Furthermore, for the sake of simplicity, any influences of the crystal functions are not taken into account. Alternatively, in a more general approach, the contrast transfer function itself can be considered, which includes not only the PCFT but also the amplitude contrast transfer function. This can take into account both absorption and crystal effects, which are neglected in the following discussion. For objects that impose a strong rather than a weak phase on the wave field, image formation is not linear; rather, in addition to the first order, higher orders are decisive for image contrast. Therefore, for objects with strong phases, image formation cannot simply be described by a linear contrast transfer function. Nevertheless, the phase contrast transfer function can be used to estimate the contrast and adjust the parameters.The estimate used here can therefore also be used for objects with a strong phase. Furthermore, the calculations can also be performed taking into account the amplitude contrast transfer function and / or the influence of the complex reflection curves of the crystals. For objects with weak phases, the image contrast can be approximately described using the following phase contrast transfer function: Where z is the propagation distance between the object and the detector, k is the spatial frequency, also called the spatial frequency, k0=2π / λ0 is the X-ray wave vector, and λ0 is the X-ray wavelength. For weak phase objects, where the contrast generation can be described using the PCTF, the maximum phase contrast is achieved at a spatial frequency k=2π / λ if |PCTF| ≈ 1 applies at this spatial frequency. λ=2π / k is the wavelength corresponding to the spatial frequency k in the exit wave field behind the object. It should not be confused with the X-ray wavelength λ0. Since the PCTF is proportional to a sine function (see above), the condition for maximum phase contrast at a spatial frequency k can be described with the following equation: '( , . ( .3 4, 3 ) (* ≈ ) ∙ 0 → 2 ≈ * ( , = )4*This applies to n = 1, 3, 5, …, i.e., to all odd natural numbers. For example, n = 1 can apply here. An example of a useful propagation distance is given when the first maximum or minimum of the PCTF, i.e., for n = 1, lies at the sampled Nyquist frequency kmax = 2π / λmin = k: For example, if an object is imaged in a field of view of 5 cm at 30 keV, a detector with a resolution of 2000 x 2000 pixels, corresponding to a pixel size of Δx=25 μm, can be used. This results in the smallest resolvable spatial wavelength according to the Nyquist criterion being λ min=50μm and a propagation distance of approximately z≈30m would be necessary to reach the first maximum or minimum of the PCTF at the Nyquist frequency and thus generate sufficient contrast. At 60keV, z≈60m would be necessary. Alternatively, for n = 3, 5, ... the 2nd, 3rd, ... maximum or minimum can also be used or the contrast can be optimized for any k. In this case, the phase contrast for a spatial frequency k to be imaged and / or a spatial frequency range can already be sufficiently increased if the magnitude of the PCTF is not at a full maximum or minimum, i.e. |PCTF|≈1. Rather, it may be sufficient for some applications if the magnitude of the sinusoidal PCTF is at least approximately 0.2, preferably at least approximately 0.5. In the embodiment, the effective propagation distance of the device is configured and / or adjusted such that the magnitude of the PCTF at the spatial frequency to be imaged, e.g.at the Nyquist frequency or a lower spatial frequency, is a maximum and / or at least approximately 0.2 and / or at least approximately 0.5. This enables a controlled and effective improvement of the image with increased contrast. In one embodiment, the propagation distance extension means extends a real propagation distance z1, along which the X-rays propagate essentially freely after interaction with the propagation distance extension means, to the following effective propagation distance z according to the following equation. eff : z eff = M 2z1+ c; where M is a magnification factor greater than 1 and c is a constant, e.g., c = 0. The magnification factor M can be the factor by which the X-ray image is reduced in size. The extension of the propagation distance thus occurs with the square of the image reduction, i.e., M². This is the case when using an asymmetrically cut crystal as a Bragg demagnifer. If the magnification occurs in two dimensions, different real propagation distances and magnifications, and thus different effective propagation distances for the respective dimensions, can be achieved. In one embodiment, a beam expander is arranged in the beam path of the X-rays upstream of the object image, which expands and / or enlarges the beam path of the X-rays. The beam expander can also be referred to as a conditioner.The beam expander can act similarly to an expansion lens in an optical device. The beam expander can cause a (e.g. small) X-ray beam to expand, thus creating a larger field of view, and / or improving the coherence properties of the X-rays. In one development, the beam expander is designed as at least one Bragg conditioner. Here, the beam expansion is achieved by means of at least one asymmetrically cut crystal (see explanations above). Thus, the X-rays are first expanded by means of the Bragg conditioner, then interact with the object, and only then again with the propagation distance extension means. This results in the advantages mentioned above. In one development, asymmetrically cut crystals of the same crystal type are used as the propagation distance extension means and as the beam expander.In one embodiment, the propagation distance extension means at least partially compensates for a polychromatic spreading of the X-ray beam angles caused by the Bragg conditioner. This can be particularly effective if asymmetrically cut crystals of the same crystal type are used for both components. In particular, a non-dispersive arrangement can be used here. This makes it possible to utilize the property that the Bragg conditioner effectively reduces the source size of the X-rays in a monochromatic manner. In one embodiment, at least one Bragg magnifier is arranged in the X-ray beam path downstream of the propagation distance extension means.The Bragg magnifier can enlarge the X-ray image reduced by the propagation distance extension means, thus reducing and / or compensating for the reduction effect caused by the propagation distance extension means and / or producing an overall enlargement of the X-ray image. Furthermore, this combination can reduce and / or compensate for nonlinear distortion effects of the X-rays. This can lead to improved X-ray imaging. Furthermore, it enables the use of a highly efficient large-area detector, e.g., in low-dose applications. In this embodiment, the propagation distance extension means specifically extends the portion of the actual propagation distance from the propagation distance extension means to the Bragg magnifier. The Bragg magnifier is thus incorporated into the X-ray beam path as an intermediate component.In a further development, asymmetrically cut crystals of the same crystal type are used as the propagation distance extender and the Bragg magnifier. This allows the magnification and reduction effects to be coordinated particularly easily. If a Bragg conditioner is also arranged as a beam expander in front of the object in the beam path, all of the asymmetrically cut crystals used can be crystals of the same crystal type. This also allows for particularly easy coordination of the components to match both the propagation distance and the X-ray image size. Nonlinear effects of the propagation distance extender can be compensated for by the Bragg magnifier.List of some preferred embodiments In one embodiment 1, a Bragg demagnifier is used as the propagation distance extension means, which reduces the cross-section of the X-rays in one dimension. In one embodiment 2, a Bragg demagnifier is used as the propagation distance extension means, which reduces the cross-section of the X-rays in one dimension, as well as a tilted detector. Thus, the X-ray image, which was reduced in one dimension by the Bragg demagnifier, can be recorded magnified in this dimension due to the tilt. In one embodiment 3, a Bragg demagnifier is used as the propagation distance extension means, which reduces the cross-section of the X-rays in one dimension, as well as a Bragg magnifier connected downstream of the propagation distance extension means in the beam path.In an embodiment 4, the device is designed as in embodiments 1, 2 or 3 and additionally has a Bragg conditioner arranged upstream of the object in the beam path, which Bragg conditioner enlarges the cross-section of the X-rays in one or two dimensions. In an embodiment 5, the device is designed as in one of embodiments 1 to 4 with the difference that the Bragg demagnifier reduces the cross-section of the X-rays in two dimensions. In an embodiment 6, the device is designed as in one of embodiments 1 to 5 with an upstream monochromator. In an embodiment 7, the device is designed as in one of embodiments 1 to 6 with an upstream X-ray lens, e.g. with at least one Kirkpatrick-Baetz mirror in one or two dimensions for parallelizing the X-ray radiation.In at least one embodiment, the propagation distance is increased in only one dimension. In this case, it can be advantageous for tomography to tilt a tomography axis into another dimension. In at least one embodiment, one or more monolithic crystals are used as a single component and / or in combination for multiple components. In at least one embodiment, at least one bent crystal is used as a Bragg conditioner and / or Bragg demagnifier and / or Bragg magnifier, which is adapted, for example, to the divergence of the incident X-rays. In at least one embodiment in which multiple crystals are used, the crystals can be arranged dispersively and / or non-dispersively in each dimension. A dispersive crystal arrangement here means that the X-rays are reflected by the crystals in the same direction and / or in the same sense of rotation (e.g. positively).A non-dispersive crystal arrangement here means that the X-rays are reflected by the crystals in different directions and / or in different senses of rotation (e.g., positive-negative). In at least one embodiment, the device has at least one monochromator. When using multiple crystals in the monochromator, these can be arranged dispersively or non-dispersively with respect to one another. The arrangement of the monochromator with respect to the subsequent crystals can also be dispersive or non-dispersive. In at least one embodiment, dark-field images are taken using analyzer-based contrasts by tilting one or more crystals. In at least one embodiment, the reduction in the size of the X-ray image and the increase in the propagation distance is achieved by a convergent beam. The convergence of the X-rays is achieved by a component in front of the object, e.g.,through an X-ray lens. One aspect relates to a method for taking an X-ray image, comprising the steps of: - providing X-rays; - arranging an object in the beam path of the X-rays; - arranging a propagation distance extension means in the beam path of the X-rays such that it is arranged downstream of the object in the beam path; and - detecting at least a portion of the X-rays after the X-rays have interacted with the propagation distance extension means. The propagation distance extension means is configured such that it extends at least a portion of a real propagation distance, along which the X-rays propagate between the propagation distance extension means and the detector, to an effective propagation distance. The method can be carried out using the device according to the aspect described above.Therefore, all statements regarding the device also relate to the method, and vice versa. The X-rays can be provided by an X-ray source. The object can be an object and / or a living being. The propagation distance extension means can be designed as a Bragg demagnifier that is correctly adjusted and arranged in the beam path. In one embodiment of the method, the effective propagation distance of the device is configured such that the magnitude of a phase contrast transfer function of the device has approximately a maximum for an imaging spatial frequency and / or an imaging spatial frequency range, in particular for the scanned Nyquist frequency of the detector.Alternatively or additionally, the magnitude of this phase contrast transfer function for the imaging spatial frequency and / or the imaging spatial frequency range, in particular for the scanned Nyquist frequency of the detector, can be at least approximately 0.2, in particular at least approximately 0.5. By taking this into account of the phase contrast transfer function of the device, in particular the Nyquist frequency of the detector and / or the spatial frequency to be imaged or the spatial frequency range to be imaged, a particularly controlled and effective increase in the phase contrast can be achieved. In the method, the phase contrast can thus be increased by a targeted amplification of the interference of the X-rays at the detector. In the method, fixed output parameters and adjustable control parameters can be used to improve and / or optimize the phase contrast of the X-ray image.In particular, the X-ray energy of the X-ray source and / or the actual propagation distance between the propagation distance extension means and the detector (or magnifier, depending on the embodiment, see below) can be used, since these are usually particularly easy to control and they have a significant influence on the phase contrast. One aspect relates to the use of a propagation distance extension means to increase the contrast of an X-ray image by means of a device according to the aspect described above. The propagation distance extension means brings about an extension of the effective propagation distance and thus an increase in the contrast of the X-ray image. One aspect relates to the use of a propagation distance extension means to improve the image quality of an X-ray image, in particular by reducing the source blur, by means of a device according to the aspect described above.In the context of this invention, the terms "substantially" and / or "approximately" can be used to include a deviation of up to 5% from a numerical value following the term, a deviation of up to 5° from a direction following the term and / or from an angle following the term. Terms such as above, below, above, below, lateral, etc. refer - unless otherwise specified - to the Earth's reference system in an operating position of the subject matter of the invention. The invention is described in more detail below with reference to exemplary embodiments shown in the figures. The same or similar reference symbols can identify the same or similar features of the embodiments. Individual features shown in the figures can be implemented in other exemplary embodiments. They show: Fig. 1 a schematic representation of the X-ray phase contrast as a function of a propagation distance; Fig.2 shows a schematic representation of the effect of a propagation distance extension means in the beam path of X-rays; Fig. 3A shows a first device for taking an X-ray image according to a first embodiment; Fig. 3B shows a second device for taking an X-ray image according to a second embodiment; Fig. 3C shows a third device for taking an X-ray image according to a third embodiment; Fig. 3D shows a fourth device for taking an X-ray image according to a fourth embodiment; Fig. 3E shows a fifth device for taking an X-ray image according to a fifth embodiment; Fig. 4A shows an illustration of a wavefront incident on a detector; Fig. 4B shows two diagrams showing the reflectivity of the incident and outgoing reciprocal spatial frequencies at a Bragg demagnifier; Fig. 5A shows a sixth device for taking an X-ray image according to a sixth embodiment; Fig.5B shows a seventh device for taking an X-ray image according to a seventh embodiment; and Fig. 6 shows X-ray images of two objects, once taken with a device according to an embodiment and once taken with conventional propagation-based phase contrast at the same actual propagation distance. Fig. 1 shows a schematic representation of the X-ray phase contrast as a function of a propagation distance of the X-ray light. An incident wave of X-rays 20 falls on an object 10, which is schematically shown as a sphere. The X-rays 20 interact with the object 10; for example, a certain portion of the X-rays 20 can be absorbed, which is schematically shown as absorption at an absorption plane 30. Furthermore, Fig. 1 shows a first image plane 31 and a second image plane 32. The second image plane 32 is further away from the object 10 and the absorption plane 30 than the first image plane 31.Thus, the X-rays 20 have traveled a longer propagation distance in the second image plane 32 than in the first image plane 31. In an X-ray image taken at the level of the first image plane 31, the object 10 is shown with less contrast than in an X-ray image taken in the second image plane 32. This is shown schematically in the two image planes 31 and 32. The phase contrast of the X-rays 20 increases with increasing propagation distance due to the self-interference of the X-rays 20. Therefore, the X-ray image of the object 10 in the second image plane 32 can be seen with significantly higher contrast than in the first image plane 31. Fig. 2 shows a schematic representation of the prior art (upper diagram) and the effect of a propagation distance extension means 40 in the beam path of X-rays 20 (lower diagram). The X-rays 20 initially strike the object 10, with which they interact (cf.(also the absorption plane 30 shown schematically). In the upper diagram shown in Fig. 2, an X-ray image is taken in the first image plane 31, in which the X-rays 20 have traveled a real and effective propagation distance after interacting with the object 10. When taking an X-ray image in a second image plane 32, the contrast is increased due to the greater propagation distance. In the lower diagram shown in Fig. 2, a propagation distance extension means 40 is arranged in the beam path of the X-rays 20 after the object 10. The propagation distance extension means 40 effects an image reduction by a factor of M while simultaneously extending the propagation distance by the square of this factor M, i.e., by M. 2. An X-ray image is then taken in the third image plane 33. In this third image plane 33, the X-rays 20 are also actually propagated only by the same propagation distance up to the first image plane 31 as in the case shown in the upper diagram without the propagation distance extension means 40. However, in the lower diagram (caused by the propagation distance extension means 40) in the third image plane 33, the X-rays 20 are effectively propagated along an effective propagation distance zeff. The propagation extension means 40 extends a real propagation distance z1 (up to the third image plane 33) to an effective propagation distance z eff , for which: zeff = M 2z1 + c Here, c can be a constant, e.g., 0 m. In the third image plane 33 and after interaction with the propagation distance extension means 40, the X-ray beams 20 exhibit contrast properties as if they were propagated by the effective propagation distance zeff. With conventional propagation-based phase contrast (upper diagram), this contrast is only achieved after a real propagation distance z. 2, which corresponds, for example, to image plane 32. PROPAGATION-BASED PHASE-CONTRAST IMAGING Propagation-based phase-contrast imaging, also abbreviated as PB-PCI (propagation-based phase-contrast imaging), of large objects normally requires contrasts at low spatial frequencies, which are achieved at large propagation distances, thereby increasing the phase contrast. For the sake of simplicity, the description here is for monochromatic, coherent, and parallel illumination, but can also be extended to polychromatic illumination and / or partial coherence and / or divergent illumination. For the sake of simplicity, objects with weak phases are also considered here, but the concept can also be applied or extended to objects with absorption and / or strong phase.For objects with weak phases, the image contrast is approximately given by the following phase contrast transfer function, which is also abbreviated as PCTF (from the English “phase contrast transfer function”):. Where z is the propagation distance between the object and the detector, k is the spatial frequency, k0=2π / λ0 is the X-ray wave vector, and λ0 is the X-ray wavelength. A rough approximation of a useful propagation distance is given if, for example, the first maximum of the PCTF lies at the sampled Nyquist frequency kmax=2π / λmin: In one embodiment, an object is imaged in a field of view of 5 cm at 30 keV, where the field of view is also abbreviated as FoV (from the English "field of view"). For this purpose, a detector with a resolution of, for example, 2000 x 2000 pixels, corresponding to a pixel size of Δx=25 μm, can be used. This results in the smallest resolvable spatial wavelength according to the Nyquist criterion being λ. min=50μm and a propagation distance of approximately z≈30m would be necessary to reach the first maximum of the PCTF at the Nyquist frequency and thus generate sufficient contrast. At 60keV, z≈60m would be necessary. With even greater propagation distances, the contrast of the small spatial frequencies can be further enhanced. In practice, it is hardly possible to realize such large propagation distances. Therefore, the following exemplary embodiments are presented in which a Bragg demagnifier is used as a propagation distance extension means 40 in order to effectively extend the propagation distance of the X-rays 20. Such a Bragg demagnifier works according to the inverted operating principle of a Bragg magnifier. However, instead of enlarging an image of an X-ray using a Bragg magnifier and then recording it with a large-area detector, an image of the X-rays is reduced in size and, for example,recorded with a conventional indirect detector. This allows the effective propagation distance to be greatly increased. In general, the phase contrast can already be sufficiently increased if the PCTF magnitude is not at its full maximum, i.e. |PCTF|≈1. In fact, for some applications it may be sufficient if the PCTF magnitude is at least about 0.2, preferably at least about 0.5. Depending on the object to be examined, an improved and / or optimized phase contrast can be set. The setting can be made for a spatial frequency k. This can, for example, be selected depending on the object or be the Nyquist frequency of the camera, ie k max =2π / λ min=2π / 2Δx, where Δx is the effective pixel size of the detector in the object plane. When optimizing and / or adjusting the phase contrast, at least one of the following parameters can be set and / or optimized: · The X-ray energy of the X-ray source, which determines the X-ray wavelength λ0 and thus also the X-ray wavevector k0=2π / λ0 of the provided X-rays. The X-ray wavelength λ0 itself can therefore be used as a parameter. · A (real and physical) propagation distance z0 between the object holder and / or the object and the propagation distance extension means, e.g. the Bragg demagnifier. · The real propagation distance z1 between the propagation distance extension means and the detector (or magnifier, depending on the design, see below).At least one crystal parameter of the Bragg demagnifier: The crystal material of the Bragg demagnifier, the crystal reflection used by the Bragg demagnifier and the asymmetry angle of the Bragg demagnifier, together with the X-ray energy, determine the tilt angle of the crystals and the magnification factor M. The tilt angle of the crystals and / or the magnification factor M can therefore also be used as parameters. The magnification factor M, together with z0 (the propagation distance between the object holder and / or the object and the propagation distance extension means) and in particular z1 (actual propagation distance between the propagation distance extension means and the detector), determines the effective propagation distance z. eff fixed: z eff =z0+ M 2·z1. This is used in the above equation, i.e., z=zeff. In one embodiment, the task can be to improve and / or optimize the phase contrast of an X-ray image for at least one predetermined output parameter and by adjusting at least one control parameter. For example, the task can be to maximize the phase contrast of an X-ray image for the predetermined Nyquist frequency kmax of the detector. A crystal parameter of the Bragg demagnifier and the (real and physical) propagation distance z0 between the object image and / or the object and the propagation distance extension means, e.g., the Bragg demagnifier, can be used as the output parameter. The real propagation distance z1 between the propagation distance extension means and the detector (or magnifier, depending on the embodiment, see below) and / or the X-ray energy of the X-ray source can be used as the control parameter.The X-ray energy, with fixed crystal parameters, determines the Bragg angle and thus the tilt angle of the Bragg demagnifier crystal. By changing the actual propagation distance z1 and / or the X-ray energy and thus the Bragg angle, an initially barely present phase contrast can be improved to such an extent that an information-rich image of an object is enabled. In general, it can be advantageous to use the X-ray energy and / or the actual propagation distance z1 between the propagation distance extension means and the detector (or magnifier, depending on the design, see below) as control parameters, as these are usually easy to adjust and have a significant influence on the phase contrast. Thus, the X-ray energy can be easily controlled using a control element on the X-ray source. Similarly, the actual propagation distance z1 can also be controlled using an actuator.Alternatively, the X-ray energy of the X-ray source and the arrangement geometry can be used as input parameters, i.e. the actual propagation distances z0 and z1. The crystal parameters can then be set as adjustment parameters to improve and / or optimize the phase contrast. For example, a separate set of crystals can be used for each setting. WORKING PRINCIPLE OF A BRAGG DEMAGNIFIER The following presents the general working principle of a Bragg demagnifier based on asymmetrically cut crystals. The Bragg demagnifier increases the effective propagation distance, while keeping the actual propagated distance reasonably dimensioned. The X-ray image is reduced in size approximately linearly by a factor of M, which is accompanied by an enlargement of the reciprocal position space k → M k. Fresnel propagation is taken into account. it follows that the propagation distance is increased by the square of the factor M, i.e. by M 2. In addition, the quality of the X-ray image with the actually smaller propagation distance can benefit from the source blur being reduced by a factor of M. For the sake of simplicity, this working principle will be considered only in one dimension below, but this can also be transferred to a second dimension. Similar to a Bragg magnifier, crystals can also be used as Bragg demagnifiers in which the crystal surface does not coincide with the crystal planes at which the X-ray beam is reflected in Bragg reflection, but in which the crystal surface is cut at a predetermined angle to these crystal planes of the crystal lattice. Fig. 3A shows an embodiment of a first device 1 for taking an X-ray image in a schematic view.The X-rays 20, which are present as a wave field, fall after interaction with the object 10 to be recorded (which is shown only symbolically as a rodent) with the spatial frequencies k. inonto the crystal of a Bragg demagnifier 41. Instead of the object 10, the first device 1 could also initially have only an object receptacle, onto or into which the object 10 is placed prior to the receptacle being taken. This crystal is cut such that a crystal plane 43 of the crystal lattice is at a crystal plane angle α to a reflection surface 42 of the Bragg demagnifier 41. This reflection surface 42 is positioned in the beam path of the X-rays 20 after the object 10 such that the X-rays, after interacting with the object 10, strike the reflection surface 42 and interact with it there, e.g., being at least partially reflected by it. The crystal planes 43 are shown in Figures 3A to 3C as hatching of the crystal components 41, 60, and 62, e.g., as hatching of the Bragg demagnifier 41 shown in Fig. 3A.The Bragg demagnifier 41 can be arranged in the beam path of the X-rays 20 such that the X-rays 20 strike the crystal planes 43 at approximately the Bragg angle. This results in an approximately symmetrical reflection at the crystal planes 43, in which the angle of incidence of the X-rays 20 with respect to the crystal planes 43 is approximately the angle of reflection of the X-rays 20. However, an asymmetrical reflection occurs with respect to the reflection surface 42 of the Bragg demagnifier 41. This is also referred to as asymmetrical Bragg reflection. In the case shown in Fig.In the device shown in Figure 3A, the X-rays 20, after interaction with the object 10, first propagate by the (real and physical) propagation distance z0 between the object 10 and the Bragg demagnifier 41 and / or the reflection surface 42, and then by the (real and physical) propagation distance z1 between the Bragg demagnifier 41 and / or the reflection surface 42 and a detector 50, which detects the X-rays 20. This results in an effective propagation distance zeff after interaction with the Bragg demagnifier 41 as: zeff = z0 + M. 2 · z1; where M is the factor of image reduction. Fig. 4B shows schematically in two reflectivity diagrams that the reduction of the cross-section of the X-rays by the Bragg demagnifier 41 in real space is accompanied by an increase in the reciprocal spatial frequencies k in to k outafter interaction with the crystal of the Bragg demagnifier 41. Intuitively simplified, a linearized monochromatic image propagation can be considered. Here, the reciprocal spatial frequencies k out after interaction with the Bragg Demagnifier 41 approximately proportional to the reciprocal spatial frequencies kin before interaction with the Bragg Demagnifier 41: Here m << 1 is the reduction factor and M = 1 / m >> 1 is the inverse magnification, which is given by: Here, α<0 is the asymmetric crystal plane angle of the Bragg demagnifier 41 (see also Fig.3A); θ B the Bragg angle for the crystal used, and Δθ oc and Δθ hc are the Bragg shifts of the incident and reflected X-ray beams 20, respectively. In a one-dimensional view and neglecting the reflection curve of the crystal, the propagated image g BDafter interaction with the Bragg Demagnifier 41: As above, the real propagation distance z0 is the distance between the object 10 and the Bragg demagnifier 41 and / or the reflection surface 42, and the real propagation distance z1 is the distance between the Bragg demagnifier 41 and / or the reflection surface 42 and the detector 50. F is the Fourier transform of the object wave f. In contrast, for the propagated image g free in free space after propagation over the distance z=z0 + z1: Using the paraxial Fresnel approximation, In contrast, the propagated image g free in free space: Therefore, taking the above equations into account, it can be seen that the X-ray image is actually reduced by M and the effective propagation distance is increased as follows: In practice, for example, a Si(220) crystal with a crystal plane angle of -5.92° can be used as a Bragg demagnifier 41 and irradiated with X-rays with an energy of 27 keV. This results in a gain factor M 2 =178 as the magnification factor of the propagation distance. This means that only a real propagation distance z1= z eff / M 2 = 0.17m is necessary to achieve an effective propagation distance z eff of 30m (plus z0). The above derivation is calculated under the assumption of linear image propagation, for which kout = M · kin applies. In reality, however, a Bragg demagnifier, similar to the Bragg magnifier, is a shift-variant system with a non-linear dependence kout(kin), which is given by: Here, βin and βout are the angles between the reflection surface 42 of the crystal of the Bragg demagnifier 41 and the incident and reflected principal rays, respectively, which define the optical axis, see Fig. 4A. For nonlinear and shift-variant systems, phase reconstruction is not so easy. Fig. 4A shows an illustration of the derivation of the above formula for kout(kin). The X-rays 20 with wavelength λ0 fall from the object plane, i.e., after interaction with the object 10, onto the reflection surface 42 of the Bragg demagnifier 41 and are reflected there to the detection plane of the detector 50. The diffraction at the Bragg demagnifier 41 is given by: where ℎ = |y|lm0 ∝ is a component of the reciprocal lattice vector |y| = 2C c lm0{ Uparallel to the reflection surface 42. The angles of incidence and reflection to the reflection surface 42 of the crystal are each given by p <3 = { U + ∆{ Dw −∝ and p DEF = { U + ∆{ }w +∝. ~ <3 = 0 corresponds to the center of the diffraction curve. The relationship between ~ <3,DEF and C <3,DEF is given by C <3,DEF = C c lm0~ <3,DEF. Fig. 3B shows an embodiment of a second device 2 for taking an X-ray image in a schematic view. The second device 2 largely corresponds to the first device 1 shown in Fig. 3A. In addition to the components of the first device 1, the second device 2 has a beam expander 60 with which the X-rays 20 interact in the beam path in front of the object 10. The beam expander 60 can be designed as a Bragg magnifier and / or Bragg conditioner, which expands the X-rays 20 before they impinge on the object 10. The beam expander 60 can thus also be designed as at least one asymmetrically cut crystal and / or as a conditioner in order to expand the X-rays 20. Fig. 3C shows an embodiment of a third device 3 for taking an X-ray image in a schematic view.The third device 3 has all the components of the first device 1 and the second device 2. In addition, the third device 3 has a Bragg magnifier 62, by means of which the X-rays 20 are expanded and magnified again after the Bragg demagnifier 41 in the beam path before they hit the detector 50. Thus, the Bragg magnifier 62 can also be designed as at least one asymmetrically cut crystal in order to expand the X-rays 20. The Bragg magnifier 62 can have the same cut (in the negative) as the Bragg demagnifier 41. The wave of the X-rays 20 emanating from the Bragg demagnifier 41 is the wave incident on the Bragg magnifier 62, which is why kin,BM = kout applies. If oppositely directed but equally cut crystals are used, then α applies. BM = β and β BM = α, whereby the X-rays 20 emitted by the Bragg Magnifier 62 are transferred to: k out,BM (kin,BM ) = k out,BM (k out ) = k in In other words, the X-rays kout,BM emitted by the Bragg Magnifier 62 are approximately parallel and similarly expanded as the X-rays k incident on the Bragg Demagnifier 41 after interaction with the object. in, however, have covered a greater effective propagation distance. Thus, by using the non-dispersively directed Bragg magnifier 62, the non-linear shift-variant effects caused by the Bragg demagnifier 41 can be compensated. This can improve the image quality of the X-ray image and simplify reconstruction of the object wave. The combination of the Bragg magnifier 62 with the Bragg demagnifier 41 also makes it possible to acquire X-ray images with a low radiation dose, e.g. by capturing the image magnified again by means of the Bragg magnifier 62 using a highly efficient large-area detector as detector 50. Therefore, the detector 50 can be designed as such a large-area detector, in particular in embodiments in which a Bragg magnifier 62 is connected downstream of the Bragg demagnifier 41.Similar to a Bragg Magnifier, the Bragg Demagnifier 41's reduction factor m is given by: ^ =J<3(LMN∆LSQN∝)J. <3(LMN∆LPQ;∝) . Here, α<0 is again the asymmetric crystal plane angle of the Bragg demagnifier 41 (see also Fig. 3A); θB is the Bragg angle, and Δθoc and Δθhc are the Bragg shifts of the incident and reflected beam of X-rays 20, respectively. The reduction factor ^ depends on the energy and can be varied with it, since the Bragg angle θ B depends on the energy. The smallest resolvable spatial wavelength λ min is approximately given by the angle assumption of the crystal used, i.e., the Darwin width used. According to the Abbe criterion, the following applies: where δ is half the aperture angle, in this case given by the Darwin width δoc. From the resolution thus calculated, a reasonable and / or required pixel size and / or resolution of the detector 50 can be calculated. The resolution λ min depends on the energy, since the Darwin width δ oc depends on the energy. It is therefore possible to change the reduction factor ^ and thus the resolution λ by changing the energy of the X-rays. minto vary. The incidence area for the incoming X-rays 20 is limited by the length of the crystal. A Bragg magnifier as beam expander 60, such as is used in the second and third devices 2 and 3, can enlarge the illuminated field of view FoV (from the English "field of view"). In one tested embodiment, an asymmetrically cut Si(220) crystal is used as the Bragg demagnifer 41. The following Table 1 shows the parameters resulting for this Si 220 crystal at different output energies, such as the input FoV, the input FWHM (from the English "full width at half maximum") of the Darwin curve, the spatial intrinsic resolution λmin, which is given by the above equation, the inverse magnification factor M and the magnification factor of the effective propagation distance.Table 1: Parameters for an X-ray image acquisition using a Si(220) crystal with a crystal length of 21 cm and a crystal plane angle α=-5.92° as Bragg demagnifier: E[keV] Input FoV[mm] Input FWHM[µrad] λmin. [µm] I = 1 Gain factor M 2 ^ 27.0 46.48 1.88 48.7 13.15 178 28.0 45.60 1.58 56.1 17.67 312 29.0 44.78 1.26 67.8 25.67 659 30.0 44.01 0.91 91.0 45.35 2057 30.5 43.65 0.70 116.4 71.34 5090 31.0 43.30 0.42 190.4 144.73 20947 In general, the wavelength of X-rays 20 depends on the specified energy of the X-rays. For example, if an energy E of 29.0 keV is used, the spatial resolution λmin is 67.8µm and the gain factor M is used to extend the effective propagation distance. 2of 660. This results in a significant improvement in the image contrast in the X-ray image recorded by the detector 50. Fig. 3D shows an embodiment of a fourth device 4 for recording an X-ray image in a schematic view. This fourth device 4 is largely similar to the first device 1 shown in Fig. 3A. In contrast to this first device 1, the detector 50 of the fourth device 4 is not arranged perpendicularly, but rather tilted at an angle to the beam path of the X-rays 20 striking the detector 50. This allows the X-ray image to be "magnified" in the dimension of the tilt direction. The tilt angle to the perpendicular to the beam path can be from approximately 5° to approximately 85°, preferably from approximately 60° to approximately 85°, in order to achieve the greatest possible magnification with sufficient image quality.To completely compensate for the reduction effect of the Bragg demagnifier 41, a tilt of 90°-arcsin(1 / M) can be performed, for example by approximately 78° (at M=5), by approximately 84° (at M=10), or by approximately 89.5° (at M=100). The tilt can be performed about a tilt axis that is approximately perpendicular to the beam path and is also arranged approximately parallel to a recording surface of the detector. The tilt axis can be approximately perpendicular to the plane of the drawing in Fig. 3D. The detector 50 tilted in this way can be used, in particular, in an embodiment with a Bragg demagnifier 41, which reduces the beam path of the X-rays 20 in cross-section in only one dimension, for example in the dimension of the plane of the drawing in Fig. 3D. Fig. 3E shows an embodiment of a fifth device 5 for recording an X-ray image in a schematic view. This fifth device 5 is largely similar to the third device 3 shown in Fig.3C.In addition to the components of the third device 3, the fifth device 5 has a mirror 64, which is positioned between an X-ray source 25 of the X-rays 20 and the beam expander 60. The mirror 64 is designed as a beam-shaping element, e.g., as a KB mirror. The mirror 64 shapes the X-rays 20 so that they fall parallel to one another in one direction onto the beam expander 60. Fig. 5A shows an embodiment of a sixth device 6 for taking an X-ray image in a schematic view. The sixth device 6 is constructed similarly to the second device 2 shown in Fig. 3B, but with two-dimensional components. It also has a beam expander in the beam path of the X-rays 20, which here, however, is constructed in two parts and has a first beam expander 60a and a second beam expander 60b.The first beam expander 60a enlarges the cross-section of the X-rays 20 in a first dimension, and the second beam expander 60b enlarges the cross-section of the X-rays 20 in a second dimension, which is different from the first dimension. Thus, after interaction with the two beam expanders 60a, 60b, the cross-section of the X-rays 20 is enlarged in two dimensions. The first beam expander 60a can be configured as a first Bragg conditioner and / or the second beam expander 60b can be configured as a second Bragg conditioner. The X-rays 20 initially interact with the first Bragg conditioner, i.e., the first beam expander 60a, and are reflected from there onto the second Bragg conditioner, i.e., the second beam expander 60b, and from there toward the object 10.The X-ray beams 20 thus expanded in two dimensions then strike the object 10, which is arranged on an object holder 12. There, they interact with the object 10. Next, a two-part Bragg demagnifier is arranged in the beam path of the X-rays as a propagation distance extension means, which has a first Bragg demagnifier 41a and a second Bragg demagnifier 41b. Both Bragg demagnifiers 41a, 41b reduce the cross-section of the X-ray radiation 20 in a different dimension. For example, the first Bragg demagnifier 41a can reduce the cross-section of the X-ray radiation 20 in the second dimension in which the second beam expansion means 60b previously enlarged it, and the second Bragg demagnifier 41b can reduce the cross-section of the X-ray radiation 20 in the first dimension in which the first beam expansion means 60a previously enlarged it.After interaction with this two-part Bragg demagnifier 41a, 41b, the cross-section of the X-ray beams 20 is reduced in two dimensions, and the effective propagation distance is correspondingly also extended in two dimensions. Therefore, the X-ray beams 20 strike the detector 50 with a two-dimensionally extended effective propagation distance. Fig. 5B shows a schematic view of an embodiment of a seventh device 7 for taking an X-ray image. The seventh device 7 is constructed similarly to the third device 3 shown in Fig. 3C, but with two-dimensional components. Thus, the seventh device 7 initially has all the components that the sixth device 6 shown in Fig. 5A also has. In addition, it also has a two-part Bragg magnifier, which is arranged in the beam path of the X-ray beams 20 between the two-part Bragg demagnifier 41a, 41b and the detector 50.The two-part Bragg magnifier has a first Bragg magnifier 62a and a second Bragg magnifier 62b. Both Bragg magnifiers 62a, 62b enlarge the cross-section of the X-ray radiation 20 in a different dimension. For example, the first Bragg magnifier 41a can enlarge the cross-section of the X-ray radiation 20 in the first dimension, in which the first beam expander 60a also previously enlarged it, and the second Bragg magnifier 62b can reduce the cross-section of the X-ray radiation 20 in the second dimension, in which the first beam expander 60a previously enlarged it. Thus, after interaction with the two Bragg magnifiers 62a, 62b, the cross-section of the X-rays 20 is enlarged in two dimensions before the X-rays 20 are detected by the detector 50.The order of the individual crystal arrangements within the two- or multi-part Bragg conditioner, Bragg demagnifier, and Bragg magnifier can be varied. For example, with a demagnifier, the reduction can occur first in the first dimension and then in the second dimension, or first in the second dimension and then in the first dimension. Fig. 6 shows X-ray images of two different objects: a blackberry leaf in the two left-hand X-ray images and a mouse liver in ethanol in the two right-hand X-ray images. The X-ray images shown were taken using a Bragg conditioner to expand the mm-sized synchrotron beam cross-section to 5 cm x 5 cm. The two upper X-ray images were taken with a Bragg demagnifier, similar to the second device 2 shown in Fig. 3B.The two lower X-ray images were taken in the conventional manner without the use of a Bragg demagnifier. The detector 50 used in each case was positioned at a real propagation distance z1 of one meter from the Bragg demagnifier 41, or in the lower images (without demagnifier) ​​at a distance of 1 m from the object. The inverse magnification factor M of the Si(220) crystal used as the Bragg demagnifier 41 was 25.7 (cf. third row of Table 1 at 29.0 keV), and the gain factor M. 2= 660 and thus the effective propagation distance zeff = 660m. All crystals were asymmetrically cut to a crystal plane angle of α = ±5.92° and had dimensions of 21cm x 8cm x 2cm. The crystal plane angle α of the Bragg Demagnifier 41 was cut to -5.92°, while the crystal plane angle α of the crystal used as Bragg Magnifier 60 was cut to +5.92°. The crystal plane angle of -5.92° can also be achieved by installing a crystal with a crystal plane angle of +5.92° rotated by 180° and vice versa. An indirect detector (from Optique Peter, 69210 Lentilly, France with a 5x objective lens) and a pco.edge 5.5 CMOS camera (from PCO AG, 93309 Kelheim, Germany) were used as the detector for the images in the top row.For the images in the bottom row, a large-area detector (Shad-o-box HS from Deledyne DALSA, N2V 2E9 Waterloo, Canada) was used, with a spatial resolution similar to the effective resolution in the Bragg demagnifier images. While virtually no structures are visible in the bottom two conventionally acquired X-ray images, clear structures are visible in the two Bragg demagnifier X-ray images. This demonstrates how contrast and thus image quality can be improved using a Bragg demagnifier.List of reference symbols 1 first device 2 second device 3 third device 10 object 12 object holder 20 x-rays 25 x-ray source 30 absorption plane 31 first image plane 32 second image plane 33 third image plane 40 propagation distance extension means 41 Bragg demagnifier 41a first Bragg demagnifier 41b second Bragg demagnifier 42 reflection surface 43 crystal plane 50 detector 60 beam expansion means 60a first beam expansion means 60b second beam expansion means 62 Bragg magnifier 62a first Bragg magnifier 62b second Bragg magnifier 64 mirror α crystal plane angle M factor z0 propagation distance between object and propagation distance extension means z. 1 first propagation distance zeff effective propagation distance

Claims

Applicant: Karlsruhe Institute of Technology “Device and method for taking an X-ray image” Our reference: K 7567WO – hy / mu Patent claims 1.Device (1; 2; 3; 4; 5; 6; 7) for taking an X-ray image, comprising: - an X-ray source for providing X-rays (20); - an object holder (12) for holding an object (10) in the beam path of the X-rays (20); - a propagation distance extension means (40) arranged downstream of the object holder (12) in the beam path of the X-rays (20); and - a detector (50) arranged downstream of the propagation distance extension means (40) in the beam path of the X-rays (20); wherein the propagation distance extension means (40) is designed such that it extends at least a portion of a real propagation distance (z1), along which the X-rays (20) propagate between the propagation distance extension means (40) and the detector (50), to an effective propagation distance (zeff).

2. The device according to claim 1, wherein the propagation distance extension means (40) comprises at least one demagnifier (41; 41a, 41b). 3.Device according to claim 1 or 2, wherein the propagation distance extension means (40) comprises at least one asymmetrically cut crystal at which the X-rays (20) are at least partially reflected and / or diffracted.

4. Device according to claim 3, wherein the asymmetrically cut crystal is asymmetrically cut at a negative crystal plane angle (α) between a crystal plane (43) of the crystal structure of the crystal and a reflection surface (42) of the crystal.

5. Device according to claim 3 or 4, wherein the at least one asymmetrically cut crystal is cut taking into account the crystal reflection used for the crystal. 2 relevant Bragg angle (θB) and / or arranged in the beam path of the X-rays (20).

6. Device according to one of the preceding claims, wherein the propagation distance extension means (40) is designed such that it causes an increase in the actual propagation distance (z1) after interaction of the X-rays (20) with the object and the propagation distance extension means (40) to an effective propagation distance (zeff) of at least 30 m. 7.Device according to one of the preceding claims, wherein the effective propagation distance (zeff) of the device is configured such that - the magnitude of a phase contrast transfer function (PCTF) for an imaging spatial frequency and / or an imaging spatial frequency range, in particular for the sampled Nyquist frequency of the detector, has approximately a maximum; and / or - the magnitude of the phase contrast transfer function (PCTF) of the device for the imaging spatial frequency and / or the imaging spatial frequency range, in particular for the sampled Nyquist frequency of the detector (50), is at least approximately 0.2, in particular at least approximately 0.

5. 8.Device according to one of the preceding claims, wherein the propagation distance extension means (40) extends a real propagation distance z1, along which the X-rays propagate substantially freely after interaction with the propagation distance extension means (40), to the following effective propagation distance zeff according to the following equation: zeff = M. 2 ·z1 + c; where M is a magnification factor greater than 1 and c is a constant.

9. Device according to one of the preceding claims, wherein a beam expander (60; 60a, 60b) is arranged in the beam path of the X-rays (20) in front of the object holder (12), which expands and / or enlarges the beam path of the X-rays (20), and which is designed in particular as at least one Bragg conditioner. 3 10. The device according to claim 9, wherein asymmetrically cut crystals of the same crystal type are used as the propagation distance extension means (40) and as the beam expansion means; and / or wherein the propagation distance extension means (40) at least partially compensates for a polychromatic spreading of the beam angles of the X-rays (20) caused by the Bragg conditioner.

11. The device according to one of the preceding claims, wherein at least one Bragg magnifier (62; 62a, 62b) is arranged in the beam path of the X-rays (20) downstream of the propagation distance extension means (40); wherein, in particular, asymmetrically cut crystals of the same crystal type are used as the propagation distance extension means (40) and as the Bragg magnifier (62; 62a, 62b).A method for taking an X-ray image, comprising the steps of: - providing X-rays (20); - arranging an object (10) in the beam path of the X-rays (20); - arranging a propagation distance extension means (40) in the beam path of the X-rays (20) such that it is arranged downstream of the object (10) in the beam path; and - detecting at least a portion of the X-rays (20) after the X-rays (20) have interacted with the propagation distance extension means (40); wherein the propagation distance extension means (40) is configured such that it extends at least a portion of a real propagation distance (z1), along which the X-rays (20) propagate between the propagation distance extension means (40) and the detector (50), to an effective propagation distance (zeff). 13.Method according to claim 12, wherein the effective propagation distance (zeff) of the device is configured such that - the magnitude of a phase contrast transfer function (PCTF) for an imaging spatial frequency and / or an imaging spatial frequency range,. 4, in particular for the sampled Nyquist frequency of the detector, has approximately a maximum; and / or - the magnitude of the phase contrast transfer function (PCTF) of the device for the imaging spatial frequency and / or the imaging spatial frequency range, in particular for the sampled Nyquist frequency of the detector (50), is at least approximately 0.2, in particular at least approximately 0.

5.

14. Using a propagation distance extension means (40) to increase the contrast of an X-ray image by means of a device (1; 2; 3; 4; 5; 6; 7) according to one of claims 1 to 11.

15. Using a propagation distance extension means (40) to improve the image quality of an X-ray image, in particular by reducing the source blur, by means of a device (1; 2; 3; 4; 5; 6; 7) according to one of claims 1 to 11.

Images