Imaging device, imaging apparatus or material characterization device comprising it, and imaging method

Abstract

------ Imaging device, imaging apparatus or material characterization apparatus comprising thereon and imaging method. The present invention relates to an X-ray imaging device (1), comprising an X-ray source (2) generating an X-ray beam (F), a two-dimensional X-ray detector (3) comprising pixels (3a), a sample holder (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 abbreviation: Figure 1a

Description

Title of the invention: Imaging device, imaging apparatus or material characterization apparatus comprising it and imaging method

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

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

[0003] Phase-contrast imaging has made it possible to X-ray image materials transparent to X-rays 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 entering 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 described in international patent application PCT / FR2020 / 051140.

[0004] The imaging method for obtaining, in addition to the conventionally obtained attenuation, the phase shift and the dark field requires generating image sequences by moving the modulator. Regular modulations, also called periodic modulations, require complex optical setups and have limitations in terms of exposure time, spatial resolution of the obtained images, and intrinsic anisotropy. Thus, for a periodic modulator, the new positions The modulator may not generate new information if the modulation pattern overlaps with itself (the shift 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 combining numerous exposures to obtain good image quality. Thus, for a random modulator, new positions of the modulator always generate new information (the pattern never repeats during successive movements of the modulator), 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 enabling good X-ray phase contrast or dark-field imaging to be obtained in small movements.

[0007] The invention provides a solution to the limitations of the prior art by proposing an aperiodic modulator that combines the best of both regular and random modulation approaches. In particular, the invention can be compatible with computed tomography (CT) systems 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 the same time (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 along 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 disposed 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 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, meaning that the X-ray beam passes through the thickness of the membrane. When the X-ray beam is parallel (collimated beam), the direction of the membrane thickness is parallel to the direction of propagation of the X-ray beam, and when the beam is divergent, the direction of the membrane thickness is parallel to the generatrix of the cone formed by the X-ray beam.

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

[0012] The spiral-shaped transmission modulation pattern creates an aperiodic pattern that never repeats in either translation or rotation. This optimizes the spatial distribution of intensity modulations during successive modulator shifts necessary for generating attenuation, phase shift, and dark-field images. Those 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 gives 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 correspond on the two-dimensional X-ray detector to 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 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, the value 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 analysis of 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, i.e. only maxima or only minima, but can also be of different natures, i.e. 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 operating conditions 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 both images. The ratio of the two images makes it possible to generate a new image whose pixel values ​​correspond to the nominal transmission value calculated previously.We can determine from this transmission image a global minimum, a global maximum, a global average transmission, as well as local values ​​around the extrema. The nominal transmission is therefore dimensionless.

[0017] The electronic processing unit may be integrated into the imaging device or located remotely, for example on a computer connected 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), or an application-specific integrated circuit (ASIC), comprising or associated with memory containing instructions for controlling the various elements of the imaging device. The electronic processing unit may also include inputs / outputs or even wireless or wired communication devices.

[0018] The modulator according to the invention may have one or more membranes, arranged parallel to each other in any order with the sample in 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, a person skilled in the art knowing how to adapt the number and structure of the membranes in depending on 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, supported by a shaft driven in rotation by a motor controlled by the electronic processing unit. Alternatively or in addition, the sample holder can be mounted to move 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 stages, pistons, rack and pinion mechanisms, or gears. The modulator membrane(s) can be moved in a similar manner by independent actuators.

[0020] Advantageously, each element of the imaging device according to the invention is movable, either manually or in a mechanically controlled manner.

[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 purpose, 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 at least one membrane of the modulator in the imaging device.

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

[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 membrane thickness, a local decrease in membrane thickness, 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 the mo distance average modulation, 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 non-point-like, diverging or non-diverging, monochromatic or polychromatic, without limiting the invention in this respect.

[0031] According to one embodiment, the imaging device includes at least one of an optic and a filter for modifying at least one of the energy spectrum and 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 over the optical path between the X-ray source and the two-dimensional X-ray detector and imaging the modulator with a sample over 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 image pair 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 attached drawings.

[0037] On these drawings:

[0038] [Fig. la] 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. la] 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 possible spirals 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 squared 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 forms 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 prior 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 is represented there according to an embodiment of the invention.

[0050] The X-ray imaging device 1 comprises an X-ray source 2, a two-dimensional X-ray detector 3 comprising pixels 3a opposite the X-ray source 2, a sample holder 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 holder 4 is actuated manually or mechanically, motorized or not, to move the sample E within the imaging device 1. Although not shown to avoid complicating the drawing, the same arrangement can be considered for moving the modulator 5 within the imaging device 1.In the case where the imaging device 1 also allows for complementary measurements 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 limiting the invention in this respect. As By way of non-limiting example, the X-ray source 2 that can be used with the invention can be a microfocus tube equipped with a copper anode and powered at 30 kV, emitting a polychromatic conical beam.

[0052] The two-dimensional X-ray detector 3 can be any known type of 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 that can be used with the invention can be a hybrid pixel-type detector made of silicon and operating in direct detection with square pixels of 75 pm having a surface area of ​​approximately 70 by 70 mm.

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

[0054] Although not shown, the sample support 4 can be moved in translation and / or 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 know how 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, i.e., a thin wall. Although the modulator 5 is shown in the figures with a rectangular shape, those skilled in the art will understand that the modulator 5 can take any shape, and in particular a square, polygonal, round, oval, and more generally any shape, the invention not being limited in this respect, provided that the modulator 5 has at least a portion of its surface in the optical path of the X-rays between the X-ray source 2 and the two-dimensional X-ray detector 3. As previously indicated, the modulator 5 can be moved in a similar manner to the sample E, although this is not shown to avoid making the figures too cumbersome.

[0056] As shown in the figures, the modulator 5 is arranged transversely to the X-ray beam F 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 generatrix 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 part as will be described below.

[0059] The square 5a formed on the modulator 5 in [Fig. 1a] represents the surface crossed by the X-ray beam F 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 X-ray beam F 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 stitched together by the electronic processing unit 6.

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

[0062] The electronic processing unit 6 can be connected to or integrated into the X-ray imaging device 1, and can be an electronic device, for example a processor, a microprocessor, a microcontroller, a digital signal processor (DSP), a field-programmable pre-diffused 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 can also include inputs / outputs or even communication devices, wireless or wired.

[0063] Thus, for example, data processing and control of the X-ray imaging device 1 are performed by separate computers. Control of the X-ray imaging device 1 and digital image processing can be performed interchangeably by the same electronic device or by separate electronic devices.

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

[0065] In a first step schematically represented 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. 1b], 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] A person skilled in the art will understand that the order of the modulator 5 and the sample E in the optical path of the X-ray beam F between the X-ray source 2 and the two-dimensional X-ray detector 3 is irrelevant, since what is 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 in 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 in the optical path of the X-ray beam F, the sample E could just as easily be located upstream of the modulator 5 in 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 exploit 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 exploiting the spatial variations of 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 represent another embodiment of the X-ray imaging device 1, identical to the embodiment of Figures 1a and 1b, and in which the same elements bear the same reference number 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 schematically represented identically to that in Figures 1a and 1b so as not to overburden the drawing. The pattern actually formed on the two-dimensional X-ray detector 3 with two membranes 5, 5', as represented 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 with the previous embodiment, those 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 is not of particular importance, and that any order can be considered. Thus, although the order shown in Figures 2a and 2b is, in the order along the optical path of the X-ray 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 along 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 consider 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 in it, 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 the 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, referred to above as the local transmission extremum.

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

[0080] The spiral curve can 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 can 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 operating configuration. This minimum nominal transmission value is controlled by the choice of material and thickness during the design of 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 through which the X-ray beam passes during use.

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

[0088] Fig. 4 illustrates two examples of transmission modulation pattern formation, each line 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 along the arrow shown on the second column for the modulator considered.

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

[0090] On 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] On 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 membrane thickness creates, when X-rays pass through it, a spatial variation in X-ray intensity due to the difference in thickness of the material through which the X-rays pass. Those skilled in the art will understand that a similar effect can be generated by a difference in thickness and / or chemical composition of the modulator, inducing a local variation in X-ray transmission.

[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 protrusions formed are not necessarily perfect and cylindrical and because the emission point of the X-ray source has a finite non-zero size, leading to a variation in transmission with local maxima and minima of transmission on the membrane.

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

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

[0097] The average transmission around a transmission extremum can be calculated as the arithmetic mean of the maximum local transmission value and the minimum local transmission value around the local transmission extremum. For a spherical modulation, the size can be determined as the full width at half maximum along a profile passing through the local extremum. For a non-spherical 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 to it 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, in [Fig.[9], taking as an example a hole with a square cross-section 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 image obtained (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 area as the modulation surface (9E), regardless of the shape of the pattern on the modulator.

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

[0100] By way of non-limiting example, a modulator consisting of a PMMA membrane with cones (second row of [Fig. 4]) can be produced by additive manufacturing (3D micro-printing) using, for example, two-photon polymerization. In this case, the PMMA cones are deposited on a SiO2 substrate, resulting in a composite membrane that meets the technical requirements (transmission contrast, modulation pattern, and sizes). A pure silica membrane can also be produced by replicating an acrylate mask (a mask manufactured by 3D micro-printing). Feasibility with 125 µm thick silica has been verified. Metal (Cu, Ni, Au) modulators with holes can be produced by electroplating. A negative mask is created using a lithographic process, and the metal is deposited in the mask voids. The mask material is then removed by washing to produce the patterned metal sheet.Finally, modulators with spherical holes can be produced by laser drilling (demonstration done on a 50 µm thick nickel sheet with 70 µm holes).

[0101] The points of the spiral curve thus form an aperiodic transmission modulation pattern, which does not repeat under translation or rotation. In the embodiment shown, the extrema are of only one 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 is created correspondingly on the two-dimensional X-ray detector to 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 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 with the spread function of the X-ray imaging device.

[0104] Regarding the calculation of the modulator modulation size, 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 spread function of the detector point (pm)

[0112] psize is the size of the pixel (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] Target modulation size on detector dpix=14 (pixels)

[0116] Magnification M=7.2

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

[0118] Detector PSF=75 (pm)

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

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

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

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

[0123] Magnification M=5

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

[0125] PSF of 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 150 pm gold thin film.

[0128] Example 3: High-energy medical imaging

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

[0130] Magnification M=2.5

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

[0132] Detector PSF=100 (pm)

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

[0134] It is noted that the modulation size should be 235 pm. The relatively high energy (anode W 120 kVp) allows the use of a 50 pm thin film 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 Beer-Lambert's law which relates transmission, X-ray attenuation (dependent on the material and energy) and 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 thickness of the membrane, for a modulator consisting of a single membrane, to obtain 30% of minimum nominal transmission (i.e. the maximum thickness) as a function of the average energy of the source and the material of the membrane, 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) system: the X-ray source is polychromatic with a copper anode with a focal spot size of 50 pm and 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 distances between 50 mm and 4500 mm). Referring to [Fig.[5], we can see that the RMSE (Root Mean Square Error) criterion 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 RMSE around this minimum value.

[0142] Figure 6 shows the values ​​of the SSIM (Structural Similarity Index Measure) for different modulation patterns formed on the modulator as a function of the modulation size in pixels. This SSIM 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 periodic square or hexagonal patterns.

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

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

[0145] Experimental measurements show that the use of spiral modulation improves image quality, in particular through a better signal / noise ratio.

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

[0147] To calculate the signal-to-noise ratio, two areas of interest (ROIs) of equal size are defined: one in 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 signal-to-noise ratio in dark field (first row) is 6 for the prior art modulator (first column) versus 11 for the modulator according to the invention (second column).

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

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

[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 two types of algorithms, known as explicit or implicit. Explicit methods consist of comparing the local distortions of the reference pattern with the presence of the sample; this is an iterative, pixel-by-pixel comparison. A non-exhaustive list of these algorithms includes: XSVT, UMPA, and XSS.Implicit methods rely on solving a system of equations where the unknowns are the image modalities to be reconstructed (absorption, phase, dark field) and the input data are the image pairs 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 the evolution of the sample. One or more images of the modulator without the sample may be acquired before, during, or after the series temporal representations depict 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. One example is elastography, which aims to analyze the speed of a mechanical wave. The distortions in the pattern caused by the mechanical wave are then analyzed from one image to the next using 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 pairs of captured images.

Claims

Demands

1. - X-ray imaging device (1), comprising a source of X-rays (2) generating an X-ray beam (F), 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 disposed transversely to the propagation direction of the X-ray beam (F), the modulator having a minimum nominal transmission of the X-ray beam (F) 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') correspond on the two-dimensional X-ray detector (3) to 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 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 value local maximum and local minimum value, the average of the modulation sizes, 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 membrane thickness, a local decrease in membrane thickness, 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 local modulator 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. - 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. - 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. - X-ray imaging device (1) according to any one of claims 1 to 8, characterized in that it comprises at least one of optics and a filter for modifying at least one of the energy spectrum and beam geometry of the X-ray beam (F) generated by the X-ray source.

10. - 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 X, characterized in that it comprises an X-ray imaging device (1) according to any one of claims 1 to 9.

11. - 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) over 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) over 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 image pair 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 in the sample (E).

Images