Structured diffraction beamlet array

Abstract

The present disclosure relates to a beamlet diffraction fringe generation method for attenuation, differential phase-contrast and dark-field imaging. By generating a fringe through structured diffraction beamlet arrays (Fig. 10) from structured diffraction beamlet array optics (10), an intensity variation is induced by superposition. As this effect does not rely on Talbot-carpet orders, it provides a tool for arbitrary fringe geometry and size generation at any distance.

Description

[0001] Structured diffraction beamlet array

[0002] The present disclosure relates to an X-Ray imaging system and method for differential phase-contrast and dark-field imaging applications. Intensity modulated X-Ray imaging is an emergent technology providing new contrasts for security, building material and medical applications.

[0003] Phase sensitive X-Ray imaging provides a methodology to measure the refraction and diffusion properties with conventional hardware by detecting the change of the optics induced intensity fringe. The performance is directly dependent on the quality of the optics, which are often challenging to manufacture. Convenient design choices allow to optimize system requirements to the fabrication capabilities.

[0004] The present invention according to claim 1 provides a more simplistic way of generating intensity fringe patterns, which are measured and analyzed in order to retrieve the absorption, refraction and diffusion properties of the imaged sample / object. By inducing local diffraction beamlet arrays, which propagate at a diffraction structure periodicity related angle, arbitrary fringe patterns at any propagation distance can be achieved. Contrary to interferometers, the fringe is solely a result of the geometric structuring of the beamlets. This provides an interesting alternative to established interferometers or coded apertures. The invention can induce intensity fringes similar to Talbot carpets but with decoupled requirements for the otherwise overdefined phase grating parameters. Coded apertures can be optimized to higher intensities.

[0005] The present invention is addressed according to the claims of independent features, followed by advantageous embodiments from the dependent claims and the description.

[0006] According to the present disclosure, a diffraction beamlet fringe imaging device is specified with several advantages compared to other phase sensitive imaging techniques. By inducing beamlet arrays from a diffraction structure arrangement, the fringe is generated by superposition instead of interference, which can tune the optimum distance to the fringe independently from the fringe geometry. This fundamentally different approach to fringe generation opens the parameter space and relaxes the strict requirements of an interferometer. The method realized with the system according to the present invention is increasingly interesting for higher energy applications where grating fabrication limitations impact the design of conventional interferometry systems like Talbot-Lau interferometers as mostly high aspect ratio absorption gratings are difficult to manufacture.

[0007] Coded apertures block a significant amount of the incident radiation, increasing imaging time. Diffraction beam let arrays can provide a higher efficiency alternative to coded apertures by arranging the diffraction structures to yield desired fringe geometry. This approach utilizes more of the incident radiation compared to a blocking aperture, however higher order diffraction beam lets may induce additional features if the fringe is asymmetric.

[0008] Structured array diffraction systems can easily be extended to 2-dimensional structures which can be sensitive to 2 or more directions.

[0009] The Talbot-Lau interferometer is a state-of-the-art optical system, widely used in industrial and medical prototypes due to its well understood working principle and its adaptability to large source sizes as well as large detector pixel pitches. The interferometer in the most general case consists of a source grating, a phase grating which induces a fringe of a well-defined periodicity at a well-defined distance and an analyzer grating.

[0010] The absorption gratings are increasingly difficult to manufacture for higher photon energies while the phase grating inversely requires smaller phase grating pitches to enable compact systems. These competing interests can lead to impossible fabrication demands on pitch and structure height.

[0011] The disclosed invention instead utilizes geometric beam let superposition rather than interferometry which allows to decouple the fringe size and distance requirements to select both parameters independently. This enables fringe designs impossible with Talbot carpets and surprisingly solves an issue for the design of gratings in interferometers. High energy interferometers with high power sources are limited by the source grating pitch which in turn limits the phase grating pitch. This hinders a proper fringe formation on the detector or analyzer grating plane as it requires several meter long systems, reducing the flux immensely and negating the benefit of a high power tube altogether. Structured diffraction beam let arrays can solve this issue altogether and enables short high energy imaging systems as required for medical and industrial applications.

[0012] The disclosure described herein will be more fully understood from the accompanying drawings and the description given below. They should not be considered limiting to the invention described in the appended claims. The drawings in which:

[0013] Figure 1 shows a structured diffraction structure arrangement from top-view;

[0014] Figure 2 shows a rough intensity distribution as generated by the arrangement from Figure 1 ;

[0015] Figure 3 shows a different arrangement of the diffraction structures compared to Figure 1 from top-view;

[0016] Figure 4 shows a rough intensity distribution as generated by the arrangement from Figure 3;

[0017] Figure 5 shows a 2 directional diffraction structure arrangement from top-view

[0018] Figure 6 shows a rough intensity distribution as generated by the arrangement from Figure 5;

[0019] Figure 7 shows an alternative example of a 2 directional diffraction structure arrangement from top-view;

[0020] Figure 8 shows a rough intensity distribution as generated by the arrangement from Figure 7;

[0021] Figure 9 shows a structured diffraction beam let array system with coherence inducing optics like a source grating and an analyser;

[0022] Figure 10 shows the diffraction beam let array as generated by a diffraction structure arrangement at different fringe orders. Reference will now be made in detail to certain embodiments, examples of which are illustrated in the accompanying drawings, where some, but not all features are shown. Indeed, the embodiments disclosed herein may include many different forms and should not be construed as limited to the herein set embodiments. Where possible, reference numbers will be used to refer to like components or parts.

[0023] Figure 1 shows a diffraction structure arrangement as seen from the top, illustrating a possible design of a 1 -dimensional fringe system. The diffraction structure arrangement consists of transmission regions and diffraction structures which induce diffraction orders under pitch (1 ) related angles. Depending on the fringe requirements the pitch (1 ) and arrangement distance (2) can be chosen accordingly.

[0024] Figure 2 shows an exemplar illustration of a fringe pattern of 50 % duty cycle as the diffraction structure arrangement shown in Figure 1 would generate, where the regions behind the diffraction structures become darker (3) as radiation scatters away from the region, while the non-diffracting region becomes superimposed by the diffraction induced beamlets and obtains increased intensity

[0025] (4).

[0026] Figure 3 shows a structured diffraction arrangement with a different duty cycle compared to Figure 1 .

[0027] Figure 4 shows the intensity distribution generated by a structured diffraction arrangement as shown in Figure 3 where also unaffected transmission regions

[0028] (5) appear.

[0029] Figure 5 shows a 2-dimensional structured diffraction arrangement with a periodicity (1 ) and arrangement distance (2) in horizontal direction as well as a periodicity (6) and arrangement distance (7) in vertical.

[0030] Figure 6 shows the checkboard fringe pattern such a structured diffraction arrangement can induce. There are regions with increased intensity (8) from the superimposed diffraction beamlets generated by the surrounding diffraction structures, low intensity (3) from the diffraction structure regions as well as uninfluenced transmission regions (4). Figure 7 shows an adaption where each diffraction region is the superposition of a diffraction structure in two directions, effectively resulting in a pillar structure with a vertical diffraction structure period (1 ), arrangement distance (2) as well as a horizontal diffraction structure period (6) and arrangement distance (7).

[0031] Figure 8 shows a uniform checkboard pattern the configuration in Figure 7 can induce.

[0032] Figure 9 shows a structured diffraction beamlet array system comprising a source (12), an optics arrangement, a detector (13) and a control system (17), where structured diffraction beamlet array optics (10) induce the fringe. The decoupled structure and arrangement optics parameters allow solutions for any choice of system length, pitch of the source (9) and analyzer optics (11 ) and photon energy used. Therefore, the optics can induce the required fringe size at any position between the source (9) and analyzer (11 ) optics. The structured diffraction beamlet array optics shows a zoom-in on a triangular (14) and a rectangular (15) diffraction structures arrangement. The optics can be made from gratings.

[0033] Figure 10 shows simulated diffraction beamlet arrays as optics shown in Figures 1 and 9 would generate in a cone beam geometry for a first (18) and third (19) order fringe.

[0034] LIST OF REFERENCE SYMBOLS

[0035] 1 diffraction structure period

[0036] 2 diffraction structure arrangement distance

[0037] 3 low intensities at diffraction region

[0038] 4 high intensities at transmission region

[0039] 5 unaltered intensity transmission region

[0040] 6 diffraction structure period in second direction perpendicular to beam axis

[0041] 7 diffraction structure arrangement distance in second direction perpendicular to beam axis

[0042] 8 very high intensity at transmission region for first fringe order and 2 dimensional beamlet superposition

[0043] 9 spatial coherence generating optiks like a source grating

[0044] 10 1 dimensional structured diffraction beamlet array optics

[0045] 11 analyser optics like an analyser grating

[0046] 12 photon source

[0047] 13 detector with pixels

[0048] 14 zoom-in on structured diffraction beamlet array optics with triangular diffraction structures

[0049] 15 zoom-in on structured diffraction beamlet array optics with rectangular diffraction structures

[0050] 16 positioning options for structured diffraction beamlet array optics

[0051] 17 system controls, image acquisition and image analysis device

[0052] 18 structured diffraction beamlet array fringe generation simulation in first order

[0053] 19 structured diffraction beamlet array fringe generation simulation in third order

Claims

CLAIMS1. A non-interferometric X-Ray or particle beam imaging system for attenuation, differential phase contrast and / or dark-field imaging, comprising; a. an X-Ray source or a particle beam source, providing a mono- or polychromatic X-ray photon field or particle beam resp. at any energy, b. structured diffraction beamlet array optics, which can be a single or multiple gratings, comprising diffraction structures and transmission regions, wherein the arranged diffraction structures induce diffraction order beam lets at design specific angles and superimpose with the transmission beamlets downstream to form an intensity fringe at a design specific distance, not generated by interference but the geometric superposition of the induced structured diffraction beamlet array, c. an X-Ray detector, which is preferably energy resolving, to measure the intensity fringe generated by the structured diffraction beamlet array optics, d. hardware and software to control the system, record the images and retrieve the data from the phase stepping curve for each pixel or fringe scanning.

2. The system according to claim 1 , wherein the diffraction structure comprises a rectangular structure of any relative phase shift (including 7t-shifting) or various other diffraction structures such as triangular structures or any combination of diffraction inducing structures of any phase shift.

3. The system according to any of the claims, wherein the diffraction structures are arranged in one or multiple directional patterns, wherein the different directions preferably each have varying diffraction structure pitches and / or structure arrangement distances.

4. The system according to any of the preceding claims, where the system is sensitive to fringe pattern changes in multiple directions.

5. The system according to any of the preceding claims, wherein the structured diffraction beamlet array optics is made up of an arrangement of singleoptics elements or multiple structured diffraction beamlet array optics elements.

6. The system according to any of the preceding claims, wherein an analyzer optics element is utilized to measure the intensity fringe for pixel sizes exceeding the fringe Nyquist limit.

7. The system according to any of the preceding claims, wherein a source grating, a pinhole, a blind, a coded aperture or similar coherence inducing optical devices are used to induce spatial coherence as commonly done for large focal spot radiation sources.

8. The system according to any of the previous claims, where the optics are preferably aligned in most or all spatial directions to each other in order to tune and optimize the signal.

9. The system according to any of the proceeding claims, where one of the optics elements (9, 10, 11 ) is shifted by a fraction of its pitch (of any of the present directions) through added mechanics or scanned in any other way (like fringe scanning), in order to retrieve an image series providing a phase stepping curve with an analysis protocol to retrieve the attenuation, differential phase contrast and dark-field information for each pixel or binned clusters of pixels of the detector by means of Fourier decomposition or curve fitting.

10. The system according to any of the preceding claims where a sample is placed in the system.11 . The system according to any of the preceding claims, where a fan or cone beam is utilized with straight or bent optics.

12. The system according to any of the preceding claims, comprising of multiple structured diffraction beamlet array optics.

13. The system according to any of the preceding claims, where a coded aperture is optimized by adding diffraction beamlet array structures to the coded aperture.

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