Backscattered X-photon imaging device

Abstract

The invention relates to a backscattered X-photon imaging device comprising a plurality of X-ray sources (14, 16), all configured to illuminate an analysis area (12) in which an object to be imaged can be placed, and a pixelated X-ray detector (24) configured so as to detect X-photons that can be scattered by the object.

Description

The present disclosure relates to an imaging system employing x-ray photons. Most x-ray imaging systems operate in transmission, as is the case with conventional radiography. More precisely, some of the incident x-ray photons irradiating an object to be imaged are absorbed by the object. 5 The image is obtained using unabsorbed the x-ray photons having passed through the object, which is placed between the x-ray source and the detector. In certain situations, this type of radiology does not allow an image to be obtained. This is in particular the case in the context of inspection of a piece of luggage abandoned against a wall. It is then impossible to place the 10 object between the source and the detector. This is also the case in the presence of a substance that is opaque to x-rays, which appears as a uniform region in conventional radiography. Imaging using backscattered photons allows these situations to be addressed. This type of imaging takes advantage of the interaction between incident x-ray photons and the material 15 from which the objects to be imaged are formed. A number of effects cause photons to scatter in all directions and in particular in the direction of the source of incident radiation. Among the identified physical effects, Rayleigh and Compton scattering are principally of note. Nevertheless, the uptake of imaging using backscattered photons 20 has nevertheless been slow because image formation is difficult. The main reason is that, for photons the energy of which is comprised between 1 and 1000 keV, it is not possible to produce devices that operate in a similar way to optical focusing devices. The refractive index is too low to produce lenses, and the transparency of metals at these energies prevents the production of 25 mirrors. However, a plurality of techniques for producing an image from backscattered photons have been developed. A first technique consists in irradiating the object to be imaged by means of a fine beam of x-ray photons and in moving the beam to cover the entire object. This technique is known 30 as the flying-spot technique. At any given time, only a narrow region of the object is capable of emitting backscattered photons. It is then enough to collect all the emitted photons, irrespectively of their origin, using a detector with a single pixel. The image is reconstructed by scanning the entirety of 2021314651   10 Sep 2026 object by moving the beam of x-ray photons. The resolution of the obtained image is given by the geometry of the beam. A second technique consists in irradiating the object in its entirety with x-ray photons and in using a pixelated and collimated detector to collect 5 the backscattered photons. The collimator placed in front of each pixel of the detector is sufficiently anisotropic for each pixel to receive only photons from a region of the object located facing. The resolution of the image is then given by the detector and its collimator. A third technique also consists in irradiating the object in its 10 entirety and in using a pixelated detector. Unlike the second technique, this third technique does not use a collimator but rather an absorbing plate pierced with a hole, and hence this technique is called the pin-hole technique. The pin-hole technique has the advantage of simplicity. The size 15 of the hole is the most important parameter as regards the quality of the obtained image. To a first approximation, the hole diameter must be of the same order of magnitude, or even smaller, than the size of the pixels of the detector. A larger hole would result in a degradation of the resolution of the image. In contrast, the flux of photons passing through a hole remains of low 20 intensity, this leading to a signal-to-noise ratio that may be too low to obtain a usable image. In other words, to improve the signal-to-noise ratio, the dimensions of the hole must be increased, this degrading the spatial resolution of the image. The quality of the image is the result of a compromise between resolution and signal-to-noise ratio. 25              To increase the signal-to-noise ratio, one solution consists in increasing the amount of incident photons emitted by the source, this allowing the number of backscattered photons to be increased proportionally. However, certain objects are subject to maximum doses of radiation, particularly in medical imaging. In addition, x-ray sources are also limited in 30 the doses they are able to emit. These sources are essentially limited by thermal factors. The more radiation the source emits, the more it is heated. In the case of autonomously powered portable imaging systems, the emission of radiation is also limited by the batteries of the system. Another limitation of the pin-hole technique lies in the geometry of 35 the imaging system. In the object to be imaged, the regions closest to the 2021314651   10 Sep 2026 source receive more incident radiation than the regions furthest away. The amount of backscattered radiation is therefore a function of the distance to the source. In addition, the amount of backscattered radiation is also a function of an angle made between a direction passing through the source 5 and the point of the object struck by the incident radiation and a direction passing through this point and the hole in the absorbing plate. These two geometric characteristics lead to an intrinsic non-uniformity in the distribution of backscattered photons over the surface of the detector, independently of the object to be imaged. 10 Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the 15 present disclosure as it existed before the priority date of each of the appended claims. Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, 20 but not the exclusion of any other element, integer or step, or group of elements, integers or steps. Some embodiments of the present disclosure aim to overcome all or some of the aforementioned problems by providing an imaging device 25 employing backscattered x-ray photons that allows the quality of the obtained images to be improved by irradiating an object to be imaged by means of a plurality of distinct x-ray sources. Irradiation of the object with a plurality of distinct sources allows the uniformity of the flux of incident photons reaching the object to be 30 improved both in respect of intensity and in respect of angle of irradiation. According to one aspect of the present disclosure, there is provided an imaging device employing backscattered x-ray photons, comprising: • a plurality of x-ray sources, all configured to irradiate an analysis 35            region in which an object to be imaged may be placed, 2021314651   10 Sep 2026 • a pixelated x-ray detector configured to simultaneously collect a plurality of distinct data, an image delivered by the imaging device being formed by juxtaposing the distinct data, the pixelated detector being placed so as to detect x-ray photons potentially 5             scattered by the object, • an absorbing plate pierced with at least one orifice allowing x-ray photons potentially scattered by the object to pass through the orifice, the pixelated detector being placed so as to detect x-ray photons passing through the orifice. 10             According to another aspect of the present disclosure, there is provided an imaging device employing backscattered x-ray photons, comprising: a plurality of x-ray sources configured to simultaneously emit x-rays and all configured to irradiate an analysis region in which an object to be 15 imaged is placed, a pixelated x-ray detector configured to simultaneously collect a plurality of distinct data, an image delivered by the imaging device being formed by juxtaposing the distinct data, the pixelated detector being placed so as to detect backscattered x-ray photons potentially scattered by the 20 object from the plurality of x-ray sources, an absorbing plate pierced with at least one orifice allowing backscattered x-ray photons potentially scattered by the object to pass through the orifice, the pixelated detector being placed so as to detect backscattered x-ray photons passing through the orifice. 25 The one or more orifices may each form a diaphragm through which x-ray photons pass, between the object and the pixelated detector. Alternatively, the absorbing plate may be pierced with a plurality of orifices and form a collimator that is tailored to the pixelated detector, and that lets 30 only x-ray photons moving substantially in a predefined direction pass through. In this particular embodiment, the various x-ray sources are advantageously evenly distributed around the orifice. Each x-ray source advantageously comprises a cold cathode that 35 emits an electron beam via a field effect. 2021314651   10 Sep 2026 The imaging device may comprise one of the x-ray sources. The control module may be configured to make a plurality of sources emit simultaneously or to make one or more sources among the control module x-ray sources emit sequentially. 5             Each x-ray source is advantageously configured to irradiate, at a given time, the entirety of the analysis region. In this particular embodiment of the present disclosure, the absorbing plate may comprise a plurality of orifices. The imaging device then comprises a module for processing signals delivered by the detector, the 10 processing module being configured to extract the useful information representing the image of the object to be imaged. The present disclosure will be better understood and other advantages will become apparent on reading the detailed description of one 15 embodiment given by way of example, the description being illustrated by the attached drawing, in which: figure 1 schematically shows one example of an imaging device according to the present disclosure; figure 2 schematically shows one variant of the device of figure 1; 20            figure 3 schematically shows another variant of the device of figure 1. For the sake of clarity, the same elements have been designated by the same references in the various figures. 25            Figure 1 schematically shows one example of an imaging device 10 according to the present disclosure allowing backscattered x-ray photons to be detected. The imaging device 10 comprises a plurality of x-ray sources all configured to irradiate an analysis region 12 of the device 10. The objects to be imaged are placed in the analysis region 12. The shape of the beam 30 emitted by each source may be conical and cover the entire analysis region. Thus the sources do not need to be scanned to irradiate the analysis region 12 and all the points of the analysis region 12 are irradiated at the same time by all the x-ray sources. Alternatively, the various sources may be scanned to irradiate the analysis region 12. It is also possible to employ sources that are 35 unable to irradiate the entirety of the analysis region 12, with or without 2021314651   10 Sep 2026 scanning. The presence of a plurality of x-ray sources, even if each cannot irradiate the entirety of the analysis region, alone allows the uniformity of the irradiation of the analysis region 12 to be improved. In the illustrated example, two sources 14 and 16 have been shown. It is of course possible to 5 implement the present disclosure in a device comprising more than two x-ray sources. The sources 14 and 16 have been schematically shown in figure 1 by a dot forming the focal point from which the x-rays originate. In practice, in the context of the present disclosure, any type of x-ray source may be 10 employed, whether it possesses a focal point or not. By way of example, mention may be made of tubes employing a thermionic cathode. Among these tubes, tubes having a fixed anode or tubes having a rotating anode may be used. The latter type of tube has the advantage of better dissipation of the heat emitted when the electron beam emitted by the cathode reaches 15 the anode. It is also possible to employ cold-cathode tubes, in which an electron beam is emitted via a field effect. This type of tube is for example described in patent application WO 2019 / 011980 A1 filed in the name of the applicant. Cold-cathode x-ray sources have the advantage of compactness, allowing them to be employed, for example, in a portable imaging device 10. 20 Cold-cathode x-ray sources are also smaller in size than sources employing a thermionic cathode, this making it easier to increase the number of sources present in the imaging device 10. The imaging device 10 is based on the pin-hole principle. To this end, the device 10 comprises an absorbing plate 20. More precisely, the 25 plate is made of a material that absorbs x-rays. The absorbing plate 20 is pierced with at least one orifice 22 allowing x-ray photons scattered by the object to be imaged to pass through the orifice 22. In the variant shown in figure 1, the one or more orifices may each form a diaphragm through which x-ray photons pass. The diaphragm has a fixed aperture and may be likened 30 to a pin hole. In practice, the material of the absorbing plate 20 allows most of the radiation reaching it to be absorbed. Materials of high atomic number are used. In a portable device, i.e. in a device where it is sought to decrease overall mass, the inclination might be to decrease the mass of integrated components, and in particular the mass of the absorbing plate 20, in 35 particular by decreasing its thickness, this leading to a decrease in the 2021314651   10 Sep 2026 absorption of the plate 20. The material and thickness of the plate 20 are defined to allow the radiation absorbed by the plate and the radiation passing through the orifice 22 to be discriminated between. The imaging device 10 further comprises an x-ray detector 24 5 placed so as to detect x-ray photons passing through the orifice 22. The detector 24 is pixelated so as to identify the region of the object to be imaged by which the scattered photons were delivered. By pixelated detector, what is meant is any type of detector able to simultaneously collect various data in at least one direction. The image delivered by the device 10 is formed by 10 juxtaposing the various data. In other words, the number of distinct data collected by the detector defines the spatial resolution of the image delivered by the device 10. The image is formed via spatial juxtaposition of the various data collected by the detector 24. It may be a question of an analog detector, for example such as a photosensitive film, or of a digital detector possessing 15 a plurality of discrete pixels. In practice, digital detectors typically comprise several thousand to several million pixels. There are many families of digital detectors that may be employed in the context of the present disclosure. By way of example, mention may be made of flat-panel detectors employing indirect detection and possessing a scintillator that converts the x-ray 20 photons into photons at a wavelength suitable for the technology of the detectors. Mention may also be made of flat-panel detectors employing direct detection of x-ray photons. The flat panel extends in two dimensions. It is also possible to employ a strip detector extending in a single direction. It is also possible to employ an optical camera associated with a scintillator. 25 Screens employing photostimulated luminescence may also be used as detector in the context of the present disclosure. This type of screen is commonly used in a particular form of digital radiology often referred to by the acronym CR for Computed Radiography. The principle of this form of radiology consists in forming an image on the screen then in scanning the 30 screen with a dedicated device. The screen is then strongly irradiated so as to erase the image, before being used again. The present disclosure may also be implemented without an absorbing plate and with a collimated detector. More precisely, a collimated detector makes it possible to receive only photons coming from one direction 35 or having a small angular deviation from this one direction. Photons coming 2021314651   10 Sep 2026 from other directions are absorbed by a collimator placed between the detector and the region 12. This allows, for each pixel of the detector, the region of origin in the object to be determined. Irradiating the region 12 by means of a plurality of distinct x-ray 5 sources makes it possible to improve not only the uniformity of the irradiation of the region 12 but also the uniformity of the distribution of the backscattered photons over the detector 24. With a single source, two types of nonuniformities are observed. First of all, the distance to the source leads to a non-uniformity in the intensity of the irradiation as a result of the conical 10 spread of the incident beam. The closer a point of the object is to the source, the more incident photons it receives and, consequently, the more scattered photons it emits. It is thus possible to define, for each point of the object, an angle between a first direction passing through the point in question and the source and a second direction passing through the point in question and the 15 orifice 22. For a given flux of incident photons, the intensity of the scattered photons depends on the angle between the two directions. In figure 1, an angle 01 and an angle 02 have been shown for scattering from a point of the object receiving x-ray photons from the two sources 14 and 16, respectively. With a plurality of sources, the two types of non-uniformities due to the 20 distance to the source and due to angle tend to compensate for each other depending on the origin of the incident photons. In order to best decrease these two types of non-uniformities, the various x-ray sources are evenly distributed around the orifice 22. More precisely, the various sources are distributed around a circle the center of 25 which lies on an axis passing through the orifice 22. In the example shown, the two sources 14 and 16 are radially opposite on the circle defined above. In figure 1, the circle is seen from the side. The imaging device 10 comprises a module 26 for controlling the x-ray sources (14, 16). The control module 26 may be configured so that the 30 various sources can emit simultaneously. Simultaneous emission allows the signal-to-noise ratio of the image of the object obtained by the detector 24 to be improved. Specifically, for a source taken in isolation, the maximum x-ray flux that it may emit is mainly related to its ability to dissipate heat. By multiplying the number of sources, the flux of x-ray photons reaching the 35 object to be imaged is increased accordingly. If, on the contrary, the signal- 2021314651   10 Sep 2026 to-noise ratio of a single source is considered sufficient, by multiplying the number of sources, to reach the same flux of incident x-ray photons, the time for which the various sources emit may be decreased. This allows the integration time of each pixel of the detector 24 to be decreased. In a digital 5 detector, the decrease in integration time allows the impact of the leakage current of each pixel to be decreased and therefore allows the quality of the signals collected and consequently the quality of the image of the object to be improved. Alternatively or even in addition, it is possible to configure the 10 control module 26 so that the various sources are able to emit sequentially. Sequential emission may be advantageous, in particular to limit the instantaneous power consumption of the device by distributing over time the turn-on of the various x-ray sources. In the device 10, the control module 26 may be configured to allow a user to choose between simultaneous emission 15 and sequential emission. These two types of emission may even be combined by allowing P sources among N to emit simultaneously, N being the total number of sources and P being a natural integer strictly lower than N. The P selected sources rotate sequentially among the N sources. 20             Figure 2 shows a variant imaging device 10 in which the sources 14 and 16 and the detector 24 are found. Unlike the device 10 of figure 1, the absorbing plate forms a collimator 28 tailored to the detector 24. In other words, the collimator 28 is pierced with a plurality of orifices that let pass through only x-ray photons moving substantially in a predefined direction 29. 25 The collimator 28 has the same area as the detector 24. The pitch of the orifices of the collimator 28 is equal to or a multiple of the pitch of the pixels of the detector 24. In the example shown, the direction 29 is perpendicular to the plane of the detector 24. X-ray photons diverging from the direction 29 are absorbed by the 30 collimator 28. In figure 2, pixels of the detector 24 receiving x-ray photons having passed through the collimator 28 have been shaded a darker gray than the other pixels. In the variant of figure 1 the image formed on the detector 24 is inverted, whereas in the variant of figure 2 it is not. 2021314651   10 Sep 2026 Figure 3 shows a variant imaging device 30 in which the sources 14 and 16 and the detector 24 are found. Unlike the device 10, the device 30 comprises a plate 32 pierced with a plurality of orifices 34, 36, 38, 40, 42, 44 and 46. In the example shown, the various orifices are distributed along a 5 given axis of the plate 32, the vertical axis in figure 3. In practice, in the case of a planar detector 24, the various orifices are distributed over an area of the plate 32, for example one with a circular outline. The orifices may be discrete. More generally, the absorption of the plate 32 varies according to a two-variable function in a spatial coordinate system of the plate. The function may 10 for example be written: f(x, y), x and y being two Cartesian coordinates of the area of the plate 32. The image I(x, y) delivered by the detector depends both on the object, useful data on which it is sought to obtain in an x, y coordinate system: O(x, y), and on the function f(x, y). The imaging device 30 comprises a module 50 for processing signals delivered by the detector 24 and 15 configured to extract the useful information O(x, y) representing the image of the object. The signals delivered by the detector 24 form a convolution of elementary signals resulting from photons having passed through each of the orifices 34 to 46. The processing module 50 advantageously implements a deconvolution-based algorithm to find the image of the object O(x, y). It will 20 be noted that if the images projected onto the detector via the various orifices do not overlap, the deconvolution algorithm approaches a simple superposition of the images, possibly with processing allowing the impact of parallax effects to be decreased. With respect to the device 10, the device 30 allows the flux of 25 photons reaching the detector 24 and therefore the signal-to-noise ratio of the image to be substantially increased. This improvement is however obtained at the expense of a slight loss of spatial resolution, which may remain acceptable given the increase in image quality due to the improvement in signal-to-noise ratio. 30 In the various variants, the processing module 50 is configured to deliver the image delivered by the device 10 or 30. More precisely, the processing module 50 collects the data delivered by the detector 24 and juxtaposes them to form an image of the object located in the analysis region 35  12. When the detector 24 is digital, the processing module 50 receives the 2021314651   10 Sep 2026 data from the various pixels, for example in the form of a charge or a voltage. The processing module 50 may comprise one or more analog-to-digital converters and a multiplexer allowing the image to be delivered in the form of a digital frame. In the case of the detector 30 equipped with the plate 32, the 5 deconvolution processing may be carried out on the digital data downstream of the analog-to-digital converter.

Claims

1. An imaging device employing backscattered x-ray photons, comprising:a plurality of x-ray sources configured to simultaneously emit x-rays and all configured to irradiate an analysis region in which an object to be5 imaged is placed,a pixelated x-ray detector configured to simultaneously collect a plurality of distinct data, an image delivered by the imaging device being formed by juxtaposing the distinct data, the pixelated detector being placed so as to detect backscattered x-ray photons potentially scattered by the10 object from the plurality of x-ray sources,an absorbing plate pierced with at least one orifice allowing backscattered x-ray photons potentially scattered by the object to pass through the orifice, the pixelated detector being placed so as to detect backscattered x-ray photons passing through the orifice.

152. The imaging device as claimed in claim 1, wherein the one or more orifices each form a diaphragm through which backscattered x-ray photons pass, between the object and the pixelated detector.20            3. The imaging device as claimed in claim 1, wherein theabsorbing plate is pierced with a plurality of orifices and forms a collimator that is tailored to the pixelated detector, and that lets only backscattered x-ray photons moving substantially in a predefined direction pass through.25            4. The imaging device as claimed in one of the preceding claims,wherein the various x-ray sources are evenly distributed around the orifice.

5. The imaging device as claimed in claim 4, wherein the various sources are distributed around the orifice in a circle where the center of the30 circle lies on an axis passing through the orifice.

6. The imaging device as claimed in any one of the preceding claims, wherein each x-ray source comprises a cold cathode that emits an electron beam via a field effect.2021314651   10 Sep 20267. The imaging device as claimed in any one of the preceding claims, comprising a module for controlling the x-ray sources, which module is configured to make one or more sources among the x-ray sources emit sequentially.

58. The imaging device as claimed in any one of the preceding claims, wherein each x-ray source is configured to irradiate, at a given time, the entirety of the analysis region.10            9. The device as claimed in any one of the preceding claims,wherein the absorbing plate comprises a plurality of orifices, the imaging device comprising a module for processing signals delivered by the detector, the processing module being configured to extract information representing the image of the object to be imaged.15

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