Imaging device, apparatus for imaging or characterizing materials comprising it and imaging method

Abstract

------ Imaging device, apparatus for imaging or characterizing materials comprising it and imaging method The present invention relates to an X-ray imaging device (1), comprising an X-ray source (2) generating a beam (F) of X-rays, a two-dimensional X-ray detector (3) comprising pixels (3a), a sample support (4) configured to support a sample (E), at least one modulator (5), the at least one modulator (5) being a membrane on which a spiral-shaped transmission modulation pattern is formed. Figure to be published with the abstract: Figure 1a

Description

Title of the invention: Imaging device, apparatus for imaging or characterizing materials comprising it and imaging method

[0001] The present invention relates to the field of X-ray imaging and more particularly relates to an X-ray imaging device, an apparatus for imaging or characterizing materials comprising it and an imaging method.

[0002] X-ray imaging is experiencing increasing growth for many applications, whether in the medical field, in the security field or in the field of materials characterization, in stand-alone mode or in coupling with other characterization techniques such as X-ray diffraction or scattering. An example of equipment for characterizing materials by X-ray scattering comprising an X-ray imaging device is for example described in the international patent application PCT / EP2020 / 087969.

[0003] Phase contrast imaging has made X-ray imaging of X-ray transparent materials possible by measuring the phase change of X-rays passing through these materials. New X-ray imaging methods, particularly in synchrotrons, now provide access to attenuation, phase shift and dark field (which refers to the visibility of structures smaller than the resolution of the X-ray detector). These new methods exploit the high coherence of synchrotron sources, whose properties cannot be easily reproduced in the laboratory. Transposing these techniques to conventional laboratory sources requires modifications, particularly in the method used to spatially modulate the intensity of the beam reaching or leaving the imaged sample.Conventional sources require the use of a modulator to introduce spatial variations in the intensity of the X-ray beam. Implementations of regular modulators such as gratings and meshes have been reported, as well as random modulators such as sandpaper. An example of such a sandpaper-based modulator is for example described in international patent application PCT / FR2020 / 051140.

[0004] The imaging method for obtaining, in addition to the attenuation obtained conventionally, the phase shift and the dark field requires generating sequences of images by moving the modulator. Regular modulations, also called periodic modulations, require complex optical setups and have limits in terms of exposure time, spatial resolution of the images obtained and intrinsic anisotropy. Thus, for a periodic modulator, the new positions of the modulator may not generate new information if the modulation pattern overlaps with itself (displacement corresponding to the modulation period). Performance is predictable (intensity gradients are controlled and known) but spatial sampling is limited (as shown by the Fourier transform of the modulator image).

[0005] Random modulations mitigate these problems, but require the combination of many exposures to achieve good image quality. Thus, for a random modulator, new modulator positions always generate new information (the pattern never repeats over successive modulator movements), but the overall performance is unpredictable. Some areas will not be sampled efficiently if the intensity gradients generated by the random modulator are too weak or too strong (which cannot be controlled).

[0006] There is therefore a need for the use of conventional X-ray sources with a modulator making it possible to obtain good X-ray phase contrast or dark field imaging with a few movements.

[0007] The invention provides a solution to the limitations of the prior art by proposing an aperiodic modulator which combines the best of the regular modulation and random modulation approaches. The invention can in particular be compatible with computer-assisted tomography installations for obtaining volumetric information from a series of two-dimensional (2D) images, and with time-resolved measurements such as elastography.

[0008] For an aperiodic modulator, new positions of the modulator always generate new information (the pattern never repeats during successive movements of the modulator). The performance is predictable and several spatial frequencies are sampled at once (as shown by the Fourier transform of the modulator image).

[0009] The present invention therefore relates to an X-ray imaging device, comprising an X-ray source generating an X-ray beam, a two-dimensional X-ray detector comprising pixels, a sample holder configured to support a sample, a modulator, the sample holder and the modulator being positioned consecutively in any order on the optical path between the X-ray source and the two-dimensional X-ray detector, and an electronic processing unit configured to generate imaging data from the X-rays detected by the two-dimensional X-ray detector, characterized in that the modulator comprises at least one membrane arranged transversely to the direction of propagation of the X-ray beam, the modulator having a minimum nominal transmission of the X-ray beam from the X-ray source of at least 5%, a transmission modulation pattern being formed in each membrane such that the X-ray transmission varies in the plane of the membrane, the transmission modulation pattern comprising local transmission extrema formed in the membrane, the positions of the local transmission extrema following, in the plane of the membrane, a two-dimensional spiral curve parameterized in polar coordinates calculated with a distance and an angle from a center of the spiral, a distance from the center of the spiral being defined by a monotonic function of the angle.

[0010] A modulator membrane is arranged transversely to the X-ray beam means that the X-ray beam passes through the thickness of the membrane. When the X-ray beam is parallel (collimated beam), the thickness direction of the membrane is parallel to the propagation direction of the X-ray beam, and when the beam is divergent, the thickness direction of the membrane is parallel to the generatrix of the cone formed by the X-ray beam.

[0011] The X-ray source may be monochromatic or polychromatic.

[0012] The spiral-shaped transmission modulation pattern creates an aperiodic pattern, which is never repeated in translation or rotation, which has the effect of optimizing the spatial distribution of the intensity modulations during successive shifts of the modulator necessary for the generation of the attenuation, phase shift and dark field images. The person skilled in the art will understand that other additional transmission modulation patterns can be superimposed on the spiral-shaped transmission modulation pattern, without departing from the scope of the present invention, since the mere presence of the spiral-shaped transmission modulation pattern will give the overall pattern the desired aperiodic character.

[0013] According to one embodiment, the modulator is positioned in the X-ray imaging device such that the local transmission extrema of the modulator form correspondingly on the two-dimensional X-ray detector local extrema of detected values, the X-ray detection value varying on the two-dimensional X-ray detector around each local extremum of detected values ​​between a local maximum value and a local minimum value, a modulation size being defined for each local extremum of detected values ​​as being the diameter around the local extremum of detected values ​​equivalent to the surface area of ​​the detector delimited by the contour of the isoline corresponding to an X-ray detection value equal to the average of the local maximum value and the local minimum value, the average of the modulation sizes, defined as the average modulation size,for the two-dimensional X-ray detector being between 2 and 50 pixels of the two-dimensional X-ray detector.

[0014] The isoline corresponds to the line connecting all pixels having the same value on the two-dimensional X-ray detector. It can be found either by analyzing the value of each pixel, either by binarization of the image detected on the two-dimensional X-ray detector.

[0015] The extrema on the same membrane, positioned on the spiral curve, can be of the same nature, that is to say only maxima or only minima, but can also be of different natures, that is to say maxima and minima mixed within the same membrane, irregularly or not.

[0016] The nominal transmission of the modulator is obtained, for a given X-ray imaging device and a given modulator comprising one or more membranes, by direct determination on an image of the modulator obtained under the nominal conditions of use of the X-ray imaging device. The nominal transmission of the modulator can thus be calculated, for each pixel of the two-dimensional X-ray detector, as the ratio of the detected value of the pixel on a first image obtained with the modulator and without the sample divided by the detected value of the same pixel on a second image obtained without the modulator and without the sample, the other elements of the X-ray imaging device (source and detector) being positioned and configured identically for the two images. The ratio of the two images makes it possible to generate a new image whose pixel value corresponds to the nominal transmission value calculated previously.On this transmission image, a global minimum, a global maximum, a global average transmission as well as local values ​​around the extrema can be determined. The nominal transmission is thus unitless.

[0017] The electronic processing unit may be integrated into the imaging device or remote, for example on a computer attached to the imaging device. When the electronic processing unit is integrated into the imaging device, it may in particular be an electronic device, for example a processor, a microprocessor, a microcontroller, a digital signal processor (DSP), a field programmable gate array (FPGA), an application-specific integrated circuit (ASIC), comprising or associated with memory which contains instructions for controlling the various elements of the imaging device. The electronic processing unit may also include inputs / outputs or even communication devices, wireless or wired.

[0018] The modulator according to the invention may have one or more membranes, arranged parallel to each other in any order with the sample on the optical path between the X-ray source and the two-dimensional X-ray detector. When there are several membranes, the membranes may be identical or different, have the same transmission modulation pattern or different transmission modulation patterns, without departing from the scope of the present invention, the person skilled in the art knowing how to adapt the number and structure of the membranes in function of the sample to be imaged and the characteristics of the imaging device. When there are several membranes for the modulator, the nominal transmission is calculated on the one hand with the membranes constituting the modulator and the sample, and on the other hand without the modulator and without the sample.

[0019] Advantageously, the sample holder can be rotatably mounted in the imaging device, being supported by an axis driven in rotation by a motor controlled by the electronic processing unit. Alternatively or additionally, the sample holder can be mounted so as to be movable in translation in any direction, by means of actuator(s) controlled by the electronic processing unit or even manually. Such actuators can, for example, be translation plates, pistons, rack devices, gears. The membrane(s) of the modulator can be movable in a similar manner by independent actuators.

[0020] Advantageously, each element of the imaging device according to the invention can be moved, manually or mechanically controlled.

[0021] It is understood that the sample support can take any form, for example a plate or a clamping device, a frame, an adhesive film partially transparent to X-rays, without the invention being limited to this effect, the person skilled in the art knowing how to adapt the sample support to the sample to be imaged and to the imaging device.

[0022] Similarly, any device is conceivable for introducing or moving the at least one membrane of the modulator into the imaging device.

[0023] The two-dimensional X-ray detector can take any form, and can in particular be a gas detector, a photo-transmissible film or screen, or a digital semiconductor sensor. The digital sensor can operate in indirect (scintillator) or direct (photodiode) detection.

[0024] The pixels of the two-dimensional X-ray detector can be square, rectangular or more generally polygonal.

[0025] According to one embodiment, the minimum nominal transmission of the modulator is between 10% and 50%.

[0026] According to one embodiment, the average modulation size is between 10 and 20 pixels of the two-dimensional X-ray detector.

[0027] According to one embodiment, the local transmission extrema of the modulator are generated by at least one of a local increase in the thickness of the membrane, a local decrease in the thickness of the membrane, a local change in the chemical composition of the membrane.

[0028] According to one embodiment, the average distance between two adjacent local modulator transmission extrema, defined as being the mo distance average modulation size, is between one and three times the average modulation size, preferably twice the average modulation size.

[0029] According to one embodiment, the center of the spiral is formed either on the membrane or outside the membrane.

[0030] According to one embodiment, the X-ray source is one of a sealed tube, a microfocus tube, a rotating anode X-ray tube and a liquid anode X-ray tube. As indicated above, the X-ray source may be point-like or not, divergent or non-divergent, monochromatic or polychromatic, without the invention being limited in this respect.

[0031] According to one embodiment, the imaging device comprises at least one of an optic and a filter for modifying at least one of the energy spectrum and the geometry of the X-ray beam generated by the X-ray source.

[0032] The invention also relates to an apparatus operating with X-rays, being of a type among X-ray imaging apparatus, X-ray diffraction apparatus, X-ray scattering apparatus and X-ray fluorescence apparatus, characterized in that it comprises an X-ray imaging device as described above. An apparatus according to the invention may in particular be a tomography apparatus.

[0033] The invention also relates to an imaging method using an X-ray imaging device as described above or an apparatus as described above, characterized in that it comprises imaging the modulator without a sample on the optical path between the X-ray source and the two-dimensional X-ray detector and imaging the modulator with a sample on the optical path between the X-ray source and the two-dimensional X-ray detector to generate a pair of images.

[0034] According to one embodiment, the pair of images is generated for different positions of the modulator relative to a stationary position of the sample.

[0035] According to one embodiment, the image pair is generated for a stationary position of the modulator and a stationary position of the sample to image changes in the sample.

[0036] In order to better illustrate the object of the present invention, particular embodiments will now be described, in conjunction with the accompanying drawings.

[0037] In these drawings:

[0038] [Fig. 1a] is a schematic view of an X-ray imaging device according to an embodiment of the invention in a first imaging position, with modulator and without sample.

[0039] [Fig. 1b] is a schematic view of the X-ray imaging device of [Fig. 1a] in a second imaging position, with modulator and sample.

[0040] [Fig.2a] is a schematic view of an X-ray imaging device according to another embodiment of the invention in a first imaging position.

[0041] [Fig.2b] is a schematic view of the X-ray imaging device of [Fig.2a] in a second imaging position.

[0042] [Fig.3] represents different spirals which can be envisaged for the transmission modulation pattern of a modulator for an X-ray imaging device according to the invention.

[0043] [Fig.4] schematically represents two modulators for an X-ray imaging device according to the invention and their characteristics.

[0044] [Fig.5] represents the evolution of the RMSE criterion (mean square error criterion) as a function of the modulation size of a modulator for an X-ray imaging device according to the invention.

[0045] [Fig.6] represents the evolution of the SSIM (structural similarity index measure) as a function of the modulation size in pixels for different types of modulators.

[0046] [Fig.7] represents the evolution of the SSIM as a function of the type of transmission modulation pattern for different shapes of the sample.

[0047] [Fig.8] represents an image of a sample in dark field and directional dark field for a modulator according to the state of the art and a modulator according to the invention.

[0048] [Fig.9] represents the procedure for determining the modulation size for a non-spherical modulation.

[0049] If we now refer to Figures 1a and 1b, we can see that an X-ray imaging device 1 according to one embodiment of the invention is shown therein.

[0050] The X-ray imaging device 1 comprises an X-ray source 2, a two-dimensional X-ray detector 3 comprising pixels 3a facing the X-ray source 2, a sample support 4 consisting of a translation stage 4a supporting the sample E by means of a rod 4b, a modulator 5 and an electronic processing unit 6. The sample support 4 can be actuated manually or mechanically, in a motorized or non-motorized manner, to move the sample E within the imaging device 1. Although this is not shown so as not to complicate the drawing, the same arrangement can be envisaged for moving the modulator 5 within the imaging device 1.In the case where the imaging device 1 also allows additional measurements to be carried out such as X-ray diffraction or scattering measurements, the sample support 4 may be an integral part of a diffractometer goniometer or a motorized X, Y, Z stage of small and large angle scattering equipment (SAXS / WAXS equipment).

[0051] The X-ray source 2 may be one of a sealed tube, a microfocus tube, a rotating anode X-ray tube, or a liquid anode X-ray tube. The X-ray source 2 may be point-like or non-point-like, diverging or non-diverging, monochromatic or polychromatic, without the invention being limited in this respect. As by way of non-limiting example, the X-ray source 2 which can be used with the invention can be a microfocus tube equipped with a copper anode and supplied at 30 kV, emitting a polychromatic conical beam.

[0052] The two-dimensional X-ray detector 3 may be any type of known X-ray detector, the pixels 3a of the two-dimensional X-ray detector 3 being able to take any shape (square, rectangle, polygon and in particular hexagon or octagon). By way of non-limiting example, a two-dimensional X-ray detector 3 which may be used with the invention may be a hybrid pixel type detector made of silicon and operating in direct detection with square pixels of 75 μm having a surface area of ​​approximately 70 by 70 mm.

[0053] The sample holder 4 is configured to support a sample E to be imaged by the X-ray imaging device 1, and may take the schematic form shown in Figures 1a and 1b, but the person skilled in the art will understand that the sample holder 4 may take any form, in particular a plate or a clamping device, a frame, an adhesive film partially transparent to X-rays, a clamp, wires for holding the sample E, or even a flat surface on which all of the elements constituting the X-ray imaging device 1 are arranged.

[0054] Although this is not shown, the sample support 4 can be moved in translation and / or in rotation, by means of one or more actuators or manually, on guide rails or freely, these considerations being relative to the assembly chosen by the person skilled in the art who will be able to adapt the movable or non-movable nature of each element constituting the X-ray imaging device 1 according to the invention.

[0055] The modulator 5 according to the invention comprises in this first embodiment a membrane, that is to say a thin wall. Although the modulator 5 is shown in the figures with a rectangular shape, the person skilled in the art will understand that the modulator 5 can take any shape, and in particular a square, polygonal, round, oval shape, and more generally any shape, the invention not being limited in this respect, provided that the modulator 5 has at least part of its surface on the optical path of the X-rays between the X-ray source 2 and the two-dimensional X-ray detector 3. As indicated previously, the modulator 5 can be moved in a similar manner to the sample E, although this is not shown so as not to burden the figures.

[0056] As shown in the figures, the modulator 5 is arranged transversely to the X-ray beam F coming from the X-ray source 2, which means that the X-ray beam F passes through the thickness of the modulator 5. When the X-ray beam F is parallel, the thickness direction of the modulator 5 is parallel to the direction of propagation of the X-ray beam, and when the beam F is divergent, the thickness direction of the modulator 5 is parallel to the generator of the cone formed by the X-ray beam F.

[0057] As can be seen in [Fig. 1a], a transmission modulation pattern M, described in more detail below, is formed on the modulator 5.

[0058] The transmission modulation pattern M takes the form of a spiral portion as will be described below.

[0059] The square 5a formed on the modulator 5 in [Fig. 1a] represents the surface crossed by the beam F of X-rays coming from the source 2 on the modulator 5.

[0060] The square 3b formed on the two-dimensional X-ray detector 3 represents the image formed on the two-dimensional X-ray detector 3 by the beam F of X-rays coming from the X-ray source 2. The useful area of ​​the two-dimensional X-ray detector 3 is not necessarily square and may be smaller than the beam F. The two-dimensional X-ray detector 3 will then be moved to cover the entire area of ​​interest by successive exposures which will be reattached by the electronic processing unit 6.

[0061] The schematic square FE in [Fig. 1a] represents the spatial extent of the X-ray beam F in the plane of movement of the sample E.

[0062] The electronic processing unit 6 may be connected or integrated with the X-ray imaging device 1, and may be an electronic device, for example a processor, a microprocessor, a microcontroller, a digital signal processor (DSP), a field programmable gate array (FPGA), an application-specific integrated circuit (ASIC), comprising or associated with memory which contains instructions for controlling the various elements of the X-ray imaging device 1. The electronic processing unit 6 may also comprise inputs / outputs or even communication devices, wireless or wired.

[0063] Thus, for example, the processing of the data and the control of the X-ray imaging device 1 are carried out by separate computers. The control of the X-ray imaging device 1 and the digital processing of the images can be carried out indifferently by the same electronic device or separate electronic devices.

[0064] The X-ray imaging device 1 is used to image a sample E.

[0065] In a first step shown schematically in [Fig.1a], only the modulator 5 is placed in the optical path of the X-ray beam F between the X-ray source 2 and the two-dimensional X-ray detector 3, the image of the intersection of the X-ray beam F with the modulator 5, represented on the modulator 5 by the square 5a, being represented on the pixels 3a of the two-dimensional X-ray detector 3 by square 3b.

[0066] It is understood that the shape obtained on the two-dimensional X-ray detector 3 depends on the shape of the X-ray beam F.

[0067] In a second step, shown in [Fig.lb], the sample E is also placed with the modulator 5 in the optical path of the X-ray beam F between the X-ray source 2 and the two-dimensional X-ray detector 3, the intersection between the beam F and the median plane of the sample perpendicular to the direction of propagation of the beam being schematically represented by the square FE. The image of the sample E thus obtained on the two-dimensional X-ray detector is represented by the square 3c.

[0068] The person skilled in the art will understand that the order, on the optical path of the X-ray beam F between the X-ray source 2 and the two-dimensional X-ray detector 3, of the modulator 5 and the sample E is not important, since what is sought to be imaged on the two-dimensional X-ray detector 3 is the difference in image obtained in the presence and absence of the sample E on the optical path of the X-ray beam F. Thus, although the sample E is shown in Figures 1a and 1b downstream of the modulator 5 on the optical path of the X-ray beam F, the sample E could just as well be located upstream of the modulator 5 on the optical path of the X-ray beam F, without departing from the scope of the present invention.

[0069] The electronic processing unit 6 will use the two images, with and without sample E in the optical path of the X-ray beam F, to deduce the image of the sample E by using the spatial variations in the intensity of the X-ray beam F, generated by the modulator 5, with and without passing through the sample E.

[0070] Figures 2a and 2b show another embodiment of the X-ray imaging device 1, identical to the embodiment of Figures 1a and 1b, and in which the same elements carry the same reference numeral as for Figures 1a and 1b and will not be described in further detail.

[0071] The difference between the embodiment of Figures 2a and 2b and the embodiment of Figures 1a and 1b is that the modulator consists of two membranes 5, 5' in the optical path of the X-ray beam F.

[0072] The presence of two membranes 5 and 5' in this embodiment increases the spatial variations of the intensity of the X-ray beam F compared to the embodiment of Figures 1a and 1b.

[0073] The pattern formed on the two-dimensional X-ray detector 3 in the presence of the two membranes 5, 5', is shown schematically identical to that of Figures 1a and 1b so as not to complicate the drawing. The pattern actually formed on the two-dimensional X-ray detector 3 with two membranes 5, 5', as shown for this embodiment, would partly resemble the pattern formed in the 3rd row, 5th column of the [Fig.3]

[0074] The operation is otherwise identical to that described for the embodiment of Figures 1a and 1b and will not be described in more detail here.

[0075] As for the previous embodiment, the person skilled in the art will understand that the order, in the optical path of the X-ray beam F, of the two membranes 5 and 5' constituting the modulator and of the sample E has no particular importance, and that any order can be envisaged. Thus, although the order shown in Figures 2a and 2b is, in the order on the optical path of the beam F from the X-ray source 2 to the two-dimensional X-ray detector 3, membrane 5, membrane 5' and sample E, any combination on the optical path is conceivable, the sample E being able to be located upstream of the two membranes 5 and 5' or between the membranes 5 and 5', without departing from the scope of the present invention.

[0076] Similarly, the invention is not limited by the number and relative positions of membranes arranged on the optical path of the X-ray beam F, and it is possible to envisage within the framework of the present invention more than two membranes for the modulator.

[0077] As indicated above, each membrane has a transmission modulation pattern formed therein such that the X-ray transmission varies in the plane of the membrane, the transmission modulation pattern comprising local transmission extrema formed in the membrane, the positions of the local transmission extrema following, in the plane of the membrane, a two-dimensional spiral curve parameterized in polar coordinates calculated with a distance and an angle from a center of the spiral, a distance from the center of the spiral being defined by a monotonic function of the angle.

[0078] Non-limiting examples of a spiral curve that the transmission modulation pattern on the membrane can take are shown in [Fig. 3], where each square represents a white background having a uniform X-ray transmission value, on which a spiral curve is formed, with each point of the spiral representing a point where the X-ray transmission is different from the X-ray transmission for the white background, hereinafter referred to as the local transmission extremum.

[0079] It is understood that other spiral shapes can be envisaged, and that other patterns can be added to the spiral pattern, without departing from the scope of the present invention, provided that the overall final pattern is aperiodic and never repeats itself either in translation or in rotation.

[0080] The spiral curve may occupy the entire membrane, with the center of the spiral curve at the center of the membrane and the spiral curve centered on the membrane, but the spiral curve may also not be centered on the membrane, with its center on the membrane, as for example in the second figure of the third line of [Fig.3] where the dotted square represents the membrane or the useful area of ​​the membrane crossed by the X-ray beam, or the spiral curve may also not be centered on the membrane, with its center outside the membrane, as for example in the third figure of the third line of [Fig.3], where the dotted square represents the membrane or the useful area of ​​the membrane crossed by the X-ray beam.

[0081] Any material, and in particular metals, oxides, polymers or composites, can be considered for the membrane constituting the modulator according to the invention.

[0082] The modulator has a minimum nominal transmission of at least 5% as measured on the imaging device in its nominal use configuration. This minimum nominal transmission value is controlled by the choice of material and thickness when designing the modulator.

[0083] Preferably, the minimum nominal transmission of the modulator is between 10% and 80%.

[0084] Preferably, the minimum nominal transmission should be between 10% and 50%.

[0085] The modulator has a maximum nominal transmission of up to 100% but not necessarily 100%.

[0086] The transmission modulation pattern formed in each membrane of the modulator is formed in the plane of the membrane traversed in use by the X-ray beam.

[0087] It can be formed in several ways, for example by at least one of a local increase in the thickness of the membrane, a local decrease in the thickness of the membrane, a local change in the chemical composition of the membrane.

[0088] [Fig.4] illustrates two examples of transmission modulation pattern formation, each row representing a modulator, the first column representing the modulator considered seen schematically in profile, the second column representing the transmission image obtained with the modulator considered and the third column representing an intensity profile following the arrow shown in the second column for the modulator considered.

[0089] In this non-limiting illustrative example, the modulator is constituted by a single round membrane, the person skilled in the art will however understand that the invention is not limited in this respect.

[0090] In the first line of [Fig.4], the transmission modulation pattern is formed by holes formed in the thickness of the membrane constituting the modulator.

[0091] In the second line of [Fig.4], the transmission modulation pattern is formed by conical projections formed on the membrane constituting the modulator.

[0092] The center of the holes or conical projections corresponds to a point on the spiral curve.

[0093] This difference in thickness of the membrane creates, when it is crossed by X-rays, a spatial variation in intensity of the X-rays due to the difference in thickness of the material crossed by the X-rays. The person skilled in the art will understand that a similar effect can be generated indifferently by a difference in thickness and / or chemical composition of the modulator inducing a local variation in transmission of the X-rays.

[0094] The third column of [Fig.4] illustrates the transmission extrema formed on the transmission image(s) of the membrane of the corresponding line, following the arrow shown in the second column. It follows from these figures that the change in transmission is not abrupt, because the holes or projections formed are not necessarily perfect and cylindrical and because the emission point of the X-ray source has a non-zero finite size, leading to a variation in transmission with local maxima and minima of transmission on the membrane.

[0095] For the membrane in the first line of [Fig.4], the transmission minima correspond to the average thickness of the membrane (excluding holes) (in gray in the second column) while the transmission maxima correspond to the holes (in white in the second column).

[0096] For the membrane in the second line of [Fig.4], the transmission maxima correspond to the average thickness of the membrane (excluding projections) (in white in the second column) while the transmission minima correspond to the projections (in black in the second column).

[0097] The average transmission around a transmission extremum can be calculated as the arithmetic mean of the local maximum transmission value and the local minimum transmission value around the local transmission extremum. For spherical-shaped modulation, the size can be determined as the full width at half maximum along a profile passing through the local extremum. For non-spherical-shaped modulation, the modulation size is determined as the diameter equivalent to the surface formed by the pixels whose measured value is greater than or equal to the average transmission around the extremum in the case of a local maximum, or less than or equal in the case of a local minimum. The contour of this surface is delimited by the isoline corresponding to the average value. Thus, for example on the [Fig.9], taking as an example a square-section hole formed on the modulator (9A), the modulation projected onto the two-dimensional X-ray detector is a rounded square (9B).

[0098] The modulation size can then be calculated from the contour defined by the isoline corresponding to the average of the minimum (black around the modulation) and of the local maximum (center of the square task) (9C). The modulation surface can be obtained on the obtained image (9D) and is defined by the pixels whose intensity is greater than or equal to the average in the case where the extremum is a local maximum, or less than or equal to the average in the case where the extremum is a local minimum, the modulation size then corresponding to the diameter of the equivalent circle of the same surface as the modulation surface (9E), whatever the shape of the pattern on the modulator.

[0099] The modulator can be manufactured by different methods, depending on the material and thickness.

[0100] As a non-limiting example, a modulator consisting of a PMMA membrane with cones (second row of [Fig.4]) can be produced by additive manufacturing (3D microprinting) using for example 2-photon polymerization. In this case, the PMMA cones are deposited on a SiO2 substrate, resulting in a composite membrane meeting the technical requirements (transmission contrast, modulation pattern and sizes). A pure silica membrane can also be produced by replication of an acrylate mask (mask fabricated by 3D microprinting). The feasibility with 125 pm thick silica has been verified. Modulators made of metals (Cu, Ni, Au) with holes can be produced by electroplating. A negative mask is made using a lithographic process and the metal is deposited in the voids of the mask. The mask material is then washed off to produce the patterned metal sheet.Finally, modulators with spherical holes can be produced by laser drilling (demonstration made on a 50 pm thick nickel sheet with 70 pm holes).

[0101] The points of the spiral curve therefore form an aperiodic transmission modulation pattern, not repeating by translation or rotation. In the embodiment shown, the extrema are of a single type on a membrane: maxima or minima. A membrane having both minima and maxima is also envisaged within the scope of the invention.

[0102] The transmission modulation pattern on the modulator created in correspondence on the two-dimensional X-ray detector of the local extrema of detected values, the X-ray detection value varying on the two-dimensional X-ray detector around each local extremum of detected values ​​between a local maximum value and a local minimum value, a modulation size being defined for each local extremum of detected values ​​as being the diameter around the local extremum of detected values ​​equivalent to the surface area of ​​the detector having an X-ray detection value greater than or equal to the average of the local maximum value and the local minimum value in the case where the local extremum is a maximum, or less than or equal to this average in the case where the local extremum is a minimum, the average of the modulation sizes, defined as average modulation size, for the detector being between 2 and 50 pixels projected onto the two-dimensional X-ray detector.

[0103] The average modulation size defined above depends on the geometry of the modulator and the spread function of the point of the X-ray imaging device. The average modulation size is between 2 and 50 pixels projected onto the two-dimensional X-ray detector. The modulation size is measured using the same geometric configurations and experimental parameters as for the measurements. Thus, the determined size corresponds to the geometry of the modulator convolved by the spread function of the X-ray imaging device.

[0104] Regarding the calculation of the modulation size of the modulator, the relationship between the average modulation size "dm" of the modulator in microns (pm) and the modulation size in pixels "dpix" on the two-dimensional X-ray detector can be estimated from:

[0105] [Math.l] , J ( M-1 ) ) 2- ( PSFdel )2 dm----—--M-------

[0106] with M the magnification of the assembly:

[0107] M=1 for a parallel beam

[0108] M= distance(source-detector) / distance(source-membrane) for a conical beam.

[0109] If an optical objective is placed in front of the two-dimensional X-ray detector, its magnification must be taken into account.

[0110] S is the size of the emission focus of the X-ray source (pm)

[0111] PSFdet is the detector point spread function (pm)

[0112] psize is the pixel size (pm).

[0113] Three examples for different applications of the X-ray imaging device of the invention are described below.

[0114] Example 1: Low resolution at low energy

[0115] Size of the target modulation on the detector dpix=14 (pixels)

[0116] Magnification M=7.2

[0117] Size of the source emission focus s=40 (pm)

[0118] PSF of the detector PSFdet=75 (pm)

[0119] Detector pixel size psize=75 (pm)

[0120] It is found that the modulation size on the modulator should be 142 pm. The relatively low energy (30 kVp Cu anode) allows the use of a 50 pm thin layer of nickel (minimum nominal transmission 10%).

[0121] Example 2: High-resolution, high-energy imaging

[0122] Target modulation size on the detector dpix=14 (pixels)

[0123] Magnification M=5

[0124] Size of the source emission focus s=6 (pm)

[0125] PSF of the detector PSFdet=85 (pm)

[0126] Detector pixel size psize=50 (pm)

[0127] It is found that the modulation size should be 138 pm. The relatively high energy (average energy = 100 keV) allows the use of a thin layer of 150 pm of gold.

[0128] Example 3: High-energy medical imaging

[0129] Target modulation size on the detector dpix=12 (pixels)

[0130] Magnification M=2.5

[0131] Size of the source emission focus s=50 (pm)

[0132] PSF of the detector PSFdet=100 (pm)

[0133] Detector pixel size psize=50 (pm)

[0134] It is found that the modulation size should be 235 pm. The relatively high energy (anode W 120 kVp) allows the use of a thin layer of 50 pm of gold.

[0135] The minimum nominal transmission is controlled by the combination of the material of the membrane constituting the modulator and its thickness. It is chosen according to the energy spectrum of the X-ray source and the efficiency of the X-ray detector, by applying the Beer-Lambert law which links the transmission, the attenuation of the X-rays (dependent on the material and the energy) and the thickness:

[0136] tr=exp(-p*x)

[0137] with tr the transmission, p the linear attenuation coefficient of the material and x the thickness.

[0138] The table below gives the membrane thickness, for a modulator consisting of a single membrane, to obtain 30% minimum nominal transmission (i.e. the maximum thickness) as a function of the average energy of the source and the membrane material, assuming a detection efficiency of 100% at the energy considered.

[0139] [Tables 1] Average source energy Material Gold Aluminum Nickel Copper Silica PMMA 8 keV 3 pm 88 pm 27 pm 25 pm 100 pm 1.5 mm 100 keV 120 pm 26 mm 3.0 mm 2.9 mm 28 mm 61 mm

[0140] Figures 5, 6 and 7 represent the result of numerical simulations allowing to evaluate the performance of the aperiodic transmission modulation pattern as described in the invention. The characteristics of the simulated imaging device are as follows, representative of a device that can be integrated into a small angle X-ray scattering (SAXS) equipment: the X-ray source is polychromatic with a copper anode with an emission focus size of 50 pm, an average energy of 8.6 keV. The two-dimensional X-ray detector is 1030x514 pixels with a pixel size of 75 pm. The source-sample distance is 550 mm with a source-membrane distance of 330 mm and a membrane-sample distance of 220 mm. The sample-detector distance is 1825 mm (the same performance trends having been observed over a distance between 50 mm and 4500 mm). Referring to [Fig.5], we can see that the RMSE criterion (Root Mean Square Error) is represented as a function of the modulation size in pixels. This RMSE criterion quantifies the difference between the digitally obtained image and the exact theoretical image, a low value indicating better image quality.

[0141] It follows from this figure that there is an average modulation size of 14 pixels for which the squared error is minimal, with an increase in the RMSE around this minimal value.

[0142] [Fig.6] shows the values ​​of the SSIM criterion (Structural Similarity Index Measure) for different modulation patterns formed on the modulator as a function of the modulation size in pixels. This SSIM criterion quantifies the similarity between the digitally obtained image and the exact theoretical image, a high value indicating better image quality. It follows from this figure that the aperiodic spiral transmission modulation pattern according to the invention gives the best SSIM values ​​compared to a random pattern or to square or hexagonal periodic patterns.

[0143] [Fig.7] represents the values ​​of the SSIM criterion as a function of the sample shape, for different transmission modulation patterns.

[0144] The aperiodic pattern according to the invention gives the best SSIMs, whatever the shape of the sample.

[0145] Experimental measurements show that the use of spiral modulation improves image quality, notably thanks to a better signal / noise ratio.

[0146] [Fig.8] shows the improvement in image quality, by experimental verification on dark field (first line) and directional dark field (second line) images of a nylon thread (on the left in each image) and two strands of carbon fibers (on the right in each image), with a state-of-the-art sandpaper-type modulator (first column) with a random transmission modulation pattern and a modulator according to the invention with a random transmission modulation pattern. spiral aperiodic transmission modulation (second column).

[0147] To calculate the signal-to-noise ratio, two equal-sized regions of interest (ROIs) are defined: one within the fiber, where the average signal intensity is calculated, and the other around the fibers, where the noise is estimated by measuring the standard deviation of the data.

[0148] The ratio of the two values ​​constitutes the signal-to-noise ratio designated SNR. The ROIs are defined with the same parameters on each of the four images, as represented by the rectangles in the figures.

[0149] The dark field signal-to-noise ratio (first row) is 6 for the state-of-the-art modulator (first column) versus 11 for the modulator according to the invention (second column).

[0150] The signal-to-noise ratio in directional dark field (second row) is 8 for the modulator of the state of the art (first column) against 23 for the modulator according to the invention (second column).

[0151] The spiral aperiodic modulation pattern modulator therefore gives better results than the modulators of the state of the art.

[0152] The imaging device according to the invention can be used for one or more exposures by positioning the modulator and the sample in the path of the X-ray beam.

[0153] The imaging device according to the invention can also be used to generate one or more pairs of images of the modulated beam alone and of the modulated beam with the sample inserted along the trajectory.

[0154] In one embodiment of the invention, one or more pairs of images are generated with different positions of the modulator relative to a stationary sample. Numerical methods are applied to one or more pairs of images to extract additional imaging modalities such as attenuation, displacement and dark field. This analysis is based on the use of algorithms of two types called explicit or implicit. The explicit methods consist of comparing the local distortions of the reference pattern by the presence of the sample, it is an iterative comparison, pixel by pixel. A non-exhaustive list of these algorithms can be cited: XSVT, UMPA, XSS.Implicit methods are based on solving a system of equations whose unknowns are the image modalities to be reconstructed (absorption, phase, dark field) and whose input data are the pairs of images of the modulator alone and of the modulator with the sample. Several implicit algorithms exist such as Optical Flow (OF) or the Low Coherence System (LCS).

[0155] In another embodiment, images of the modulator and the sample are acquired to track changes in the sample. One or more images of the modulator without the sample may be acquired before, during, or after the series. temporal sequences representing stages of sample evolution. Numerical methods are applied to the image sequence to extract additional imaging modalities reflecting the sample's evolution throughout the experiment. An example is elastography, the objective of which is to analyze the speed of movement of a mechanical wave. The distortions of the pattern caused by the mechanical wave are then analyzed from one image to the next by implicit or explicit algorithms, such as those mentioned above.

[0156] In another embodiment, the two acquisition methods are combined to acquire a time sequence of one or more pairs of images.

[0157] The electronic processing unit makes it possible to obtain the desired image from the captured image pairs.

Claims

Claims

1. - X-ray imaging device (1), comprising an X-ray source X-ray source (2) generating a beam (F) of X-rays, a two-dimensional X-ray detector (3) comprising pixels (3a), a sample holder (4) configured to support a sample (E), a modulator (5, 5'), the sample holder (4) and the modulator (5, 5') being positioned consecutively in any order on the optical path between the X-ray source (2) and the two-dimensional X-ray detector (3), and an electronic processing unit (6) configured to generate imaging data from the X-rays detected by the two-dimensional X-ray detector (3), characterized in that the modulator (5, 5') comprises at least one membrane arranged transversely to the direction of propagation of the beam (F) of X-rays, the modulator having a minimum nominal transmission of the beam (F) of X-rays from the X-ray source (2) of at least 5%,a transmission modulation pattern being formed in each membrane such that the X-ray transmission varies in the plane of the membrane, the transmission modulation pattern comprising local transmission extrema formed in the membrane, the positions of the local transmission extrema following, in the plane of the membrane, a two-dimensional spiral curve parameterized in polar coordinates calculated with a distance and an angle from a center of the spiral, a distance from the center of the spiral being defined by a monotonic function of the angle.,

2. - X-ray imaging device (1) according to claim 1, ca characterized by the fact that the modulator (5, 5') is positioned in the X-ray imaging device (1) such that the local transmission extrema of the modulator (5, 5') form correspondingly on the two-dimensional X-ray detector (3) local extrema of detected values, the X-ray detection value varying on the two-dimensional X-ray detector (3) around each local extremum of detected values ​​between a local maximum value and a local minimum value, a modulation size being defined for each local extremum of detected values ​​as being the diameter around the local extremum of detected values ​​equivalent to the surface area of ​​the detector delimited by the contour of the isoline corresponding to an X-ray detection value equal to the average of the value the maximum local value and the minimum local value, the average modulation size, defined as average modulation size, for the two-dimensional X-ray detector (3) being between 2 and 50 pixels of the two-dimensional X-ray detector (3).

3. - X-ray imaging device (1) according to claim 2, characterized in that the minimum nominal transmission of the modulator is between 10% and 50%.

4. - X-ray imaging device (1) according to any one of claims 2 and 3, characterized in that the average modulation size is between 10 and 20 pixels of the two-dimensional X-ray detector (3).

5. - X-ray imaging device (1) according to any one of claims 2 to 4, characterized in that the local transmission extrema of the modulator (5, 5') are generated by at least one of a local increase in the thickness of the membrane, a local decrease in the thickness of the membrane, a local change in the chemical composition of the membrane.

6. - X-ray imaging device (1) according to any one of claims 2 to 5, characterized in that the average distance between two adjacent modulator local transmission extrema, defined as the average modulation distance, is between one and three times the average modulation size, preferably twice the average modulation size.

7. - An X-ray imaging device (1) according to any one of claims 1 to 6, characterized in that the center of the spiral is formed either on the membrane or outside the membrane.

8. - An X-ray imaging device (1) according to any one of claims 1 to 7, characterized in that the X-ray source (2) is one of a sealed tube, a microfocus tube, a rotating anode X-ray tube, and a liquid anode X-ray tube.

9. - An X-ray imaging device (1) according to any one of claims 1 to 8, characterized in that it comprises at least one of an optic and a filter for modifying at least one of the energy spectrum and the beam geometry of the X-ray beam (F) generated by the X-ray source.

10. - An X-ray operating apparatus, being one of an X-ray imaging apparatus, an X-ray diffraction apparatus, an X-ray scattering apparatus and an X-ray fluorescence apparatus. X, characterized in that it comprises an X-ray imaging device (1) according to any one of claims 1 to 9.

11. - An imaging method using an X-ray imaging device (1) according to any one of claims 1 to 9, characterized in that it comprises imaging the modulator (5, 5') without a sample (E) on the optical path between the X-ray source (2) and the two-dimensional X-ray detector (3) and imaging the modulator (5, 5') with a sample (E) on the optical path between the X-ray source (2) and the two-dimensional X-ray detector (3) to generate a pair of images.

12. - Imaging method according to claim 11, characterized in that the pair of images is generated for different positions of the modulator (5, 5') relative to a stationary position of the sample (E).

13. - Imaging method according to claim 11, characterized in that the image pair is generated for a stationary position of the modulator (5, 5') and a stationary position of the sample (E) to image changes of the sample (E).

Images