EP3987312A1

EP3987312A1 - Compton camera and method for campton 3d imaging

Info

Publication number: EP3987312A1
Application number: EP20800005.9A
Authority: EP
Inventors: Alain Iltis
Original assignee: ANDRA Agence Nationale Pour La Gestion Des Dechets Radioactifs; Damavan Imaging
Current assignee: ANDRA Agence Nationale Pour La Gestion Des Dechets Radioactifs; Damavan Imaging
Priority date: 2019-06-19
Filing date: 2020-06-19
Publication date: 2022-04-27
Also published as: EP3987314A1; WO2020254653A1; WO2020254673A1; FR3097655B1; FR3097655A1; US20200400593A1; US20220357291A1; FR3097656A1; FR3097656B1; WO2020254649A1; US11898972B2

Abstract

The invention relates to a device, a system and a method for using a multi-capture Compton camera, characterized by the use of at least two capturing centers from different positions.

Description

TITLE: COMPTON CAMERA AND COMPTON 3D IMAGING PROCESS

TECHNICAL FIELD OF THE INVENTION

The present application relates to the field of imaging and more particularly to the imaging of sources of gamma rays. In particular, the present application relates to a device, system and methods for imaging by detector of the Compton Camera type.

[0002] More specifically, the present application relates to a device, system and methods for imaging by Compton Camera called “multi-capture” (at least “bi-capture”), that is to say using at least two captures. Compton imaging performed from at least two different locations (either different locations of the same Compton Camera, or different locations of several separate Compton Cameras). The present application therefore details a new technology for detecting gamma rays combining several captures of Compton images and improvements made to cameras and / or image reconstruction methods using this type of multiple captures. The invention further relates to the use of such imaging and / or detection in the fields in particular of astronomy, the nuclear industry and the medical field.

STATE OF THE PRIOR ART

[0003] In the prior art relating to imaging from Compton cameras, it is known to measure the photons emitted by at least one scintillator (P1, P2) using a photodetector and a monitoring device. dedicated reading under the effect of gamma radiation. The scintillator, the photodetector and the dedicated reading device are here designated by the term “capture center” (CC in FIG. 1 or CC1 and CC2 in FIGS. 2 to 7) because they are the center of a capture of image, although they are in fact physically distributed in planes generally parallel to each other. Such a capture center (CC, CC1, CC2) makes it possible, thanks to the photons detected, to obtain Compton images following the interaction between an incident Gamma ray with the capture center, for example as shown in FIG. 1. However, the image reconstruction mode used by Compton cameras is fundamentally ambiguous. Indeed, we typically measure a vector corresponding to the characteristics of a first interaction (11) (or “diffusion”), which has a given energy (E1), then a vector corresponding to a second interaction (I2) (or “absorption "). The incident gamma radiation is then localized on a cone whose apex is 11 and the opening angle is given by the ratio between the measured energies of the two interactions (E1 / E2). Indeed, as shown in Figure 1, a first interaction (11) of a gamma ray with a scintillator will generate photons detectable by the capture center (CC) and deviate its trajectory, and a second interaction (I2) with a scintillator (identical or different from the first) will also generate photons detectable by the capture center (CC), which makes it possible to perform Compton imaging defining a Reconstruction Cone (CR) whose vertex is in the capture center ( CC) and whose base is a reconstruction ellipse (DR) formed by the intersection between the reconstruction cone (CR) and a reconstruction plane perpendicular to the imaging axis of the capture center (CC). The reconstruction plan can be defined using various means, such as for example telemetry, laser measurement or even by three-dimensional reconstruction of the Compton images. It will be noted that in the latter case, it is not necessary to make an assumption on the identification of the source with an optical object.

[0004] In the case of iterative algorithms, the idea is to consider a discretized model from the start. We then use algorithms to approach the solution. These methods allow greater flexibility with respect to the parameters that can be taken into account. However, convergence problems appear associated with the difficulty of choosing a criterion for stopping iterations. In addition, solving the problem can sometimes require significant memory resources and relatively long computation times. To represent the errors in the energy and position measurements, which impact the knowledge of the deflection angle, the cones used for reconstruction are given a wall thickness. This makes it possible to take into account the uncertainties in the calculation of the reconstruction.

[0005] Thus, as indicated in the example shown in FIG. 2, when a camera is used in the real case where the source / camera distance is great compared to the size of the detector and when we take into account the various errors, for each pair of photons detected we obtain two areas of intersection of cones which are two lines generating cones (CR) but one of them contains the source (S) real and the other contains an artifact (A1). The origin of the cones being identical, the two solutions (A1, S) are degenerated in depth: Whatever the reconstruction plane, the calculated angular direction is identical for the true source and for the artefact. This is why even for a Compton camera having a very low intrinsic noise, it is necessary to multiply the number (n) of detections of count photons (Compton images) and therefore of reconstructed cones in order to estimate the true position of the source. (S). Thus, as for example represented in FIG. 3, several Compton images (n to n + 3 in FIG. 3) obtained by the same capture center (CC1, FIG. 3) are used to estimate the position of the source despite the artefacts . In the real case, the errors result in a non-zero thickness of the wall of the cone. Therefore, it is often necessary to detect around 50 photons to have a realistic imaging of a point source. This ambiguity explains why Compton images often show artefacts in addition to real sources, which complicates the interpretation of the images. This solution known from the prior art has the drawback of limiting the accuracy of the imaging, while requiring a significant calculation time.

[0006] Current practice in the state of the art is to superimpose a gamma image on a visible image in order to identify the location of the source. This facilitates the interpretation of the images but does not make it possible to know, in particular in decontamination situations, whether the source is in front of a wall, behind the wall or in the wall. For this, it would be necessary to know the distance from the source by using gamma rays. In many situations, the energy of the radioactive source is attenuated by its presence in a stainless steel, concrete or lead container (often with thick walls). In such situations, the number of photons detected from the source is only a small fraction of the number of photons emitted: the activity of the source is underestimated. Having a way to estimate the real activity of the source would be valuable. [0007] In this context, it would therefore be advantageous to provide Compton imaging which has fewer drawbacks than the prior art, in terms of calculation time and energy of the source to be detected.

[0008] In current practice, it is customary to multiply the number of views to reconstruct an object in 3D. This generates a cost, either in exposure time if the camera has to be moved to obtain additional views, or in equipment cost if one uses equipment taking several views simultaneously and even more important in the case of a medical or veterinary application, requires large doses and does not optimize the radiation protection of patients, animals and personnel.

[0009] In this context, it would be interesting to propose Compton imaging which has fewer drawbacks than the prior art, in terms of acquisition time, speed of convergence of algorithms and quality of reconstructed images.

DISCLOSURE OF THE INVENTION

[0010] The object of the present invention is therefore to provide a Compton imaging device, system and method making it possible to overcome at least part of the drawbacks of the prior art. It will be noted that the terms "present invention" or "the invention" in fact designate, in the present application, simply possible embodiments and examples of implementation. These various embodiments, as well as their particular technical characteristics, could of course be isolated from each other or combined together by a person skilled in the art, in particular thanks to the functional considerations provided in the present application and according to the needs imposed by them. targeted applications according to the fields of application.

[0011] To this end, the invention relates to a device, a system and a method for using a Compton camera, characterized by the use of at least two centers for capturing distinct positions. [0012] Thus, the invention makes it possible to reduce the calculation time and / or to limit the number of photons necessary to obtain reliable imaging, unlike the prior art using only Compton images obtained from the same center. capture.

[0013] The invention is presented in two main parts

[0014] A first to focus on the use and benefits of a multi-capture Compton camera and also includes improvements to existing cameras which may or may not be coupled with the use of a multi-capture camera.

[0015] A second relates to a 3D imaging method using said Compton cameras and some of the various applications which result therefrom.

[0016] In general, as introduced in its preamble above, the present application proposes to use "Compton images" from different "Compton capture" positions. The term “Compton image” (or simply “image”) designates in the present application the imagery obtained from the vectors calculated on the basis of the data collected by a single determined “capture center” (of determined position, whatever the its technical specifications). On the other hand, the term “Compton capture” (or simply “capture”) designates in the present application the imagery obtained from the vectors calculated on the basis of the data collected by several determined “capture centers”, whether it is acts of the same capture center displaced in space between two successive images or of two distinct capture centers (CC1, CC2) producing independent images from different positions. The present application therefore provides various embodiments for its physical implementation in terms of device, system or method. Thus, the same camera will preferably be used in two successive positions or two identical cameras located in two different positions, but the present application also provides for the possibility of using two different cameras in two different positions.

According to one feature, the invention is characterized in that the distinct positions are separated by a distance less than or equal to twice the resolution. position (for example 1 ° or 2 °, even 3 °) (by preference to the angular resolution between two sources which is clearly superior: for example 6 ° to 8 °) of the capture center of the Compton camera in order to obtain a stereoscopic vision in a compact portable instrument.

[0018] According to one feature, the invention is characterized in that the distinct positions are separated by a distance less than but close to twice the angular resolution of the capture center of the Compton camera, in particular at the desired range for the camera.

[0019] According to a feature, the invention is characterized in that the separate positions are arranged in an arc centered on the position of the gamma ray source.

Many combinations can be considered without departing from the scope of the invention; those skilled in the art will choose one or the other depending on the economic, ergonomic, dimensional or other constraints that they will have to comply with.

Thus, in the prior art, as in the example shown in Figure 2, the position of a source (S) of gamma ray is estimated using this type of reconstruction discs (DR) of FIG. 1, by cumulating the successive Compton images obtained for the various photons detected by the capture center (CC). FIG. 2 illustrates the two possible reconstruction disks (DR) obtained by a single capture center (CC1) from two successive images (n and n + 1). These two reconstruction discs (DR) make it possible to estimate the real position of the source (S) by the intersection of the two reconstruction cones (CR), but the estimated position is ambiguous.

In general, as illustrated for example in a non-limiting manner in FIG. 4, the present application proposes to use Compton captures from at least two different capture centers (CC1, CC2). They can be several Compton images of the same camera or images of several separate cameras, or even cameras moving in space between different locations of capture centers. All that is said for a multi-capture camera can be reproduced with a monocular camera by moving the camera from a precisely known distance and by performing identical poses on condition of also knowing precisely the relative positions and the orientation of the optical axis of the camera.

However, in the case of mobile or time-varying sources as is the case for short-lived radiotracers used in the medical field ( ¹⁸ F), such a system operates in a less efficient and / or practical manner and / or specifies that the multi-capture camera which is therefore a preferred embodiment of the invention.

[0025] Constitution of a Compton multi-capture camera:

[0026] A multi-capture camera consists of two Compton C1 and C2 heads (each can be made up of a pair of diffuser + absorber plates). These two heads are ideally identical in terms of optical configuration / design, their optical axes are preferably parallel, the two heads being separated by a precisely known distance. These two cameras look at the same field of view.

[0027] The precision of the position of a point radioactive source obtained with a Compton camera is between 1 ° and 2 °. It is this parameter which is important for the design of a multi-capture camera. The distance between the two heads must under tend an angle greater than the angular accuracy of locating a source within the range of the camera. (For example a separation of 10 centimeters (cm) between the heads if the position accuracy is 1 ° and the target range is 10 meters)

If you want to make a portable camera, the distance between the two heads will be relatively small, for example 20 cm and this camera can operate in multi-capture mode up to at least 5 to 10 meters (m).

In this modality, it is important that the distance between the heads is not too great, for example less than 10 ° (<10 °) so that the observed field of view is not too different between the two images. Thus an angular distance between the heads greater than 30 ° (> 30 °) has a different utility, that of giving a three-dimensional image of an extended object.

[0031] Contributions of a multi-capture camera:

[0032] Gamma triangulation of the source.

The fact of measuring the angular position of a given source from two detectors C1 and C2 distant by a distance D, assuming an angular precision has on the position measurement (typically 1 to 2 ° depending on the configurations optics and the number of photons detected) makes it possible to estimate the distance of the gamma emission up to a distance Z = D / tangent (a)

[0034] Reduction of artefacts

[0035] We have seen previously that the Compton image reconstruction is by nature ambiguous, which causes multiple artifacts in the images, especially when the number of photons detected is low (less than 300 photons / source). Surprisingly, we found that with a small displacement of the shot (typically 20 cm for a distance of 300 cm), the position of the artifacts was completely different between the two images acquired by the cameras C1 and C2. This dual imaging therefore makes it possible to improve the signal / noise ratio of the reconstructed image. A conventional reconstruction is used here, the images acquired by the camera C1 are obtained by intersection of the cones coming from C1. The images acquired by the camera C2 are obtained by intersection of the cones coming from C2.

Certain detection of weak sources

The multi-capture camera is particularly suitable for the analysis of low contamination, or even of natural radioactivity. Indeed in this case the photon flux is low (a few photons / hour). It takes hours for the source to pass the detection threshold (50 photons / point source) and the natural background noise disturbs the measurement. On the other hand, if we have an estimate of the distance from the source, triangulation makes it possible to obtain detection with certainty.

[0039] Indeed, the relative position of a source on the two images is known and we have seen previously that the positioning of the noise was inadequate because it was random and / or different between the two images.

Furthermore, once the source has been located on the two images, it is possible to add the number of photons obtained on the two images, which increases the signal / noise ratio.

[0041] Exaltation of angular resolution

[0042] We have seen previously that when we bring two intense sources together, an image collapse occurs. This collapse occurs because a high density of intersections of Compton cones appears in an ellipse between the two sources. However, the position of the source is recognized by the density of intersections of Comptons cones.

This phenomenon is amplified by the fact that the dimension of the detector, in the case of a monocular camera, is small compared to the distance from the source, therefore the areas of intersection are extended objects (due to the uncertainties on the measurement of the various parameters) distributed around two lines by pair of cones.

If now we place the reconstruction plane at the distance from the source and that we only use to reconstruct the image the intersections between the cones from C1 and C2 ((C1 -C2) not C1 - C1 and not C2-C2)) the situation changes: due to the distance between the two optical centers, the intersection zones are reduced to conical arcs which are no longer degenerated into Z: the two reconstructed positions of the source change according to the chosen reconstruction plan: the solution is Z dependent.

We have seen above in the present application that it is relatively easy with a multi-capture camera to obtain the distance from the source and therefore the reconstruction plane. The true angular direction of the source being the same for all the photons emitted, we will have a zone of high intersection density for the true position of the source in X, Y, Z and a diffuse halo of false interactions around this position: the problem is no longer degenerated into Z. will thus be able to avoid image collapse.

Thus the images can be improved and we can hope for a gain of a factor of 2 to 3 on the angular resolution of our camera and find the angular resolution that is expected according to the diameter of an isolated spot as well that we would get it with an optical camera.

[0047] Furthermore, since the uncertainty factors on the reconstruction are greatly reduced, certain detection of the source will be obtained with this method with a lower number of photons, for example 15 to 20photons / camera.

This mode is therefore particularly advantageous for the detection of very low contamination.

[0049] Automatic management of extended object imagery:

We use a method of smoothing the reconstructed images: the LM / MLEM method. This method removes a large part of the artifacts and brings out the details as long as the statistics (number of photons / image voxel) are sufficient.

This method proceeds by successive iterations (between 10 and 30 in most situations). On the other hand, if we apply a large number of "smoothings" to the image of an extended object, the image is greatly degraded.

It is therefore important before choosing the number of smoothing performed to identify the point nature or extent of a source.

A factory calibration is carried out with a point source in different angular positions in the field of the camera. We thus obtain the "Point spread function (PSF)" (in English) of a point source as a function of the angle with respect to the optical axis:

We choose an area of the image to study In this area, the probable contour of the main source is determined.

The number of photons present in the source is estimated

We compare the profile of the source to PSF (Q) of a point source

The maximum number of smoothing to be applied in this case is determined as a function of the extent of the source and of the number of photons present.

[0059] Precise measurement of the flow of a naked source in a noisy context

The Compton camera repeatedly provides the number of photons which have contributed to building a given image. It is therefore possible to use it to estimate a flux of gamma rays.

[0061] It often happens that the source that we are looking for is located in the middle of other sources emitting at the same energy which can disturb the measurement.

In this case, the Compton image must be reconstructed over the entire space (4 Pi steradians). It is then necessary to identify the parasitic sources and exclude from the reconstruction the cones which pass through these parasitic sources. In this way, the disturbance of the counting rate is limited, which provides an electronic collimation of the signal collected by the device according to certain embodiments of the present application.

[0063] The present application also provides for the integration of at least one measurement of the flow of a screened source.

In fact, most often, the intense sources of radiation are located in a container which may be a metal barrel, a concrete enclosure, lead protection or any other type of material or radiation protection device.

In a dismantling context, it is necessary to know the intrinsic activity Fr of a source and not the apparent activity Fa of this source at the limits of its container. We will show that our multi-capture camera makes it possible to estimate the true activity. First of all, if we choose to make an image in the energy range corresponding to the peak of the source (for example 630-690 keV for a ¹³⁷ Cs source which emits at 662 keV) we only see the photons emitted by the source and which have not been diffused by the container, this makes it possible to measure the apparent flux Fa.

Next, we look at the energy spectrum. It must include scattered photons whose energy is lower than that of the source (typically for ¹³⁷ Cs 500-600 keV) if the source is significantly screened. Ideally, an energy range where there is no other apparent emission line is chosen for the analysis.

An image is then produced with these scattered photons (eg 500-600 keV): the source must attenuate or even disappear and we see the photons scattered by the container of the source.

Knowing the distance from the source and the solid angle undergone by the image of the scattered photons, we can measure the number of photons detected and therefore estimate the photon flux and the spatial distribution of scattered photons Fd.

To estimate the flux of photons absorbed by the container, we can cut the energy zone of the scattered photons in half and produce a 500-550 keV image and a 550-600 keV image. As the photoelectric effect drops rapidly with wavelength, comparing the number of photons detected in these two energy ranges allows an estimate of the absorption rate of the radiation. Fe

We then have Fr = Fa + Fd + Fe

Of course, this type of sophisticated processing is only possible if the images are statistically valid, that is to say if there is a number of photons "50 / voxel.

[0073] Precise measurement of the flow from a source in a disturbed context.

The image is reconstructed on 4 Pi and all the cones passing through sources or intense artefacts located outside the area of interest are removed from the reconstruction. In most cases, an initial estimate is available, even accurate to 10% of the distance from the source (visible multi-capture camera, physical measurement, laser range finder, etc.).

FIG. 2 represents an example of a conventional monocular Compton camera. In this classic example, the direction of incidence of each gamma photon performing a Compton effect in the detector is positioned on a cone. For each pair of gamma photons detected, there are one or two possible solutions which are two generating lines of the cone. In addition, for each reconstruction plan there are generally two solutions, only one of which represents the position of the source. Thus, in conventional cameras, the solution is degenerated into Z (i.e. uncertain as to the depth of the source, i.e. its distance from the camera) because whatever the position of the reconstruction plane, the two solutions appear angularly in the same place.

The second solution (that which does not contain the source) is that which generates artefacts (false concentrations) on reconstruction.

On the other hand from the moment when we change the observation point by a distance greater than the position error of the source (1 to 2 ° for our camera), the position of the artefacts which depends on statistical concentrations of more or less random points is changed (we no longer observe the artefacts in the same place) on the other hand the true source changes position in a predictable manner according to the displacement of the positions of the cameras.

[0079] Figure 4 shows the multi-capture camera (or the effect of a movement relative to the known trajectory of a monocular camera)

For each pair of gamma photons, if we consider only the intersections of the cones from camera A and those from camera B, the possible solutions are a conical arc (ellipse, parabola, etc.) . For each reconstruction plan there are generally two solutions, only one of which represents the position of the source. On the other hand, the solution is no longer degenerated into Z: beyond a certain distance there is no longer any solution. The angular position of the solutions is dependent on the reconstruction plan. However, the real source has a fixed angular direction, so the real source will emerge from the noise very quickly.

In the particular case where there are two close sources, there are many "false intersections" which appear in the area between the 2 sources. This leads to a collapse of the image in the central area with the reconstruction methods. For example, if we observe 2 sources of ¹³⁷ Cs of intensity 720 MBq and 230 MBq from a distance of 2.5 m with a Compton camera. The angular diameter of the spots is 2 °. So in conventional optics or could provide an angular resolution of 3 ° If the sources are separated by 8 ° they are perfectly resolved If the sources are separated by 6 ° we observe a collapse of the image in the central zone between the 2 sources.

[0082] In the case of a Multi-capture camera, for two close sources, the "false solutions" will be distributed in a diffuse halo in Z, while the real sources will be dense in the reconstruction plane. We should avoid collapse and recover a resolution of 3. This allows for a low cost camera.

The present application therefore aims to further protect:

On the one hand, at least one Compton multi-capture camera consisting of 2 neighboring detection sets observing the same field of view, characterized in that the two detection sets are separated by an angular distance greater than 1 ° at the maximum range of the camera in order to allow observation of a movement of a point source at the maximum range between two images taken simultaneously.

On the other hand, at least one camera with which the same effect is achieved by a precisely known relative movement of the camera between two shots, the position of the optical axis of the camera during these two shots of views being also known.

Furthermore, the present application also aims to protect, alternatively or in combination: - use of this type of camera to estimate the distance from a radioactive source by triangulation of gamma rays; - elimination of artefacts by keeping only the points which are preserved between the two images (coherent distance);

- use of such a camera to detect and produce an image from very weak sources <0.1 MicroRad / h while optimizing certainty;

A reconstruction method using a multi-capture camera which consists in considering for the reconstruction only the intersections of the cones coming from the camera C1 with those coming from the camera C2;

[0089] - an improvement in angular resolution linked to the use of the above reconstruction;

[0090] -A precise measurement of the flow of photons in a given area in a noisy context by eliminating all the cones which converge outside the area of interest;

[0091] - a use of a multi-capture camera to estimate the actual activity of a screened source using a measure of the direct photon flux and the scattered photon flux.

In the second part of the present application which follows, we present a 3D Compton reconstruction method which contains a combination of the advantages of the 1 D (one view), 2D (two views) and 3D (three views) mode of the Compton camera then, without limitation, a few applications.

The invention also relates to a method making it possible to create a three-dimensional and / or tomographic image of an object in Compton imaging gamma radiation, characterized in that it comprises one or more Compton cameras producing at least three views from of three known positions distributed each on one of the three axes (X, Y, Z) of a trihedron, the acquisition fields of said views having at least one overlap zone covering the object to be imaged.

[0094] According to one feature, the invention further relates to a Compton imaging method which comprises a reconstruction method using less than 10 photons / voxel per view to reconstruct the 3D image.

[0095] According to a particular feature, the invention relates to a Compton imaging method which comprises an electronic collimation step capable of excluding sources or photons originating from the areas that it is desired to exclude from the image.

[0096] According to a particular feature, said views can be acquired either simultaneously by three separate Compton cameras, or sequentially by moving at least one Compton camera on said 3 axes of the trihedron.

[0097] According to another feature, said trihedron is a trihedron with orthogonal X, Y and Z axes defining three directions of space, the source to be imaged being at the origin of the trihedron.

According to another feature, said Compton imaging method contains a method of tomographic reconstruction of said object to be imaged from at least two Compton views, the fields of view of which are distributed in three dimensions (X, Y, Z ) from space.

According to another feature, said Compton imaging method contains a Compton reconstruction method in which only the intersections of cones from different views are retained.

[00100] According to another feature, said Compton imaging method contains a Compton analysis process, used in the case where the intensity of the source is identical between several views, to filter the parasitic events for which said intensity of the source does not satisfy the law of the inverse of squared distances, not varying like 1 / d ² on each of the views, d being the distance from the source to the camera on each of the views. [00101] The invention further relates to a Compton imager comprising at least one Compton camera, producing at least three successive or simultaneous views by implementing the method according to at least one of the features described above.

[00102] According to another feature, one of said Compton cameras is mounted on a frame defining said trihedron.

[00103] According to another feature, at least one of said Compton cameras is mounted on at least one articulated arm capable of successively and simultaneously moving in all directions in space and being oriented along Euler angles, or in mode automatic, or in manual mode.

[00104] The invention also relates to the use of said Compton imager according to one of the features described above in various fields (medical, veterinary, industrial, security, etc.)

[00105] The invention further relates to a Compton imager comprising at least one CT-Scan head enabling a computed tomography image to be produced for attenuation correction in the images produced by Compton imaging.

[00106] The invention also relates to a Compton imager coupled to a medical accelerator.

[00107] The invention further relates to a Compton imager, all of the detection heads of which are facing each other around a bench, said bench being able to perform translational and rotational movements in a plane.

[00108] The invention further relates to the use of the Compton imager to improve the control of radiotherapy and hadron therapy treatments.

[00109] The invention further relates to the use of the Compton imager to improve the radiation protection of patients, staff, animals and the environment in the presence of one or more radioactive sources. The invention further relates to the use of the Compton imager for obtaining a tomographic image in gamma radiation of a living being with an injected dose of less than 20 MBq in less than 20 minutes for applications in the fields of medical, veterinary and preclinical imaging, to perform non-destructive testing.

BRIEF DESCRIPTION OF THE FIGURES

[00111] Other characteristics, details and advantages of the invention will emerge on reading the following description with reference to the appended figures, which illustrates:

- [Fig. 1] is a schematic representation of classic Compton imaging of the prior art,

- | Fig. 2] is a schematic representation of the reconstructions from two successive Compton images in the prior art,

- [Fig. 3] is a schematic representation of reconstructions from four successive Compton images in the prior art.

- [Fig. 4] is a schematic representation of the reconstructions from two Compton images obtained from two separate Compton captures, according to certain embodiments of the present application.

- [Fig. 5] is a schematic representation of reconstructions from three Compton images obtained by a first Compton capture and from two successive images obtained by a second Compton capture, according to certain embodiments of the present application.

- [Fig. 6] is a schematic representation of the reduction in the target volume of reconstructions from several Compton captures from a position close to angular resolution.

- [Fig. 7] is a schematic representation of the reduction in target volume of reconstructions from multiple Compton captures when the captures are moved in an arc centered on the source.

- [Fig. 8] is a schematic representation of the "classical" reconstruction of one of the directions of the trihedron (one view = X), from left to right

- A) Width of the cone corresponding to the measurement errors

- B) Intersection of 2 cones seen by the same camera presenting two extended intersection zones - C) Shape and volume of this intersection zone corresponding to the classic case: The solution is degenerated along the line of sight

[Fig. 9 a] is a schematic representation of two cones in two separate views.

[Fig. 9. b] is the schematic representation of the area of intersection of these two cones and of its volume.

- Fig. 9.c] and [Fig. 9.d] are the images of two sources ( ²² Na and ¹³⁷ Cs) detected by two separate views according to one embodiment of the invention (reconstructed image (MLM / MLEM) from said two views along the axis X [Fig. 9.c], along the Z axis [Fig. 9.d]:

- | Fig. 10] is a schematic representation of three Compton cameras distributed over the three axes (X, Y, Z) of a trihedron centered in O, [Fig. 11.a] is a schematic representation of three cones in three distinct views. [Fig. 11.b] is a schematic representation of the area of intersection of said three cones and of its volume. The [Fig. 12] represents an embodiment of the invention comprising two sources of 30 kBq, one of ¹³⁷ Cs, the other of ²² Na separated by 15 cm and observed from a distance of 50 cm. [Fig. 12. a] represents the XZ section obtained by “classical” 3D reconstruction by considering all the intersections between Compton cones. The position of the 2 sources is clearly visible but the image shows many artefacts. [Fig. 12. b] represents the same section XZ obtained by reconstruction according to certain embodiments of the invention using only the multi-view intersections and clearly showing the position of the two sources and the virtual disappearance of the artefacts. DETAILED DESCRIPTION

[00112] The object of the present invention is therefore to provide a Compton 3D reconstruction method, uses and a Compton imager making it possible to overcome at least part of the drawbacks of the prior art.

[00113] To this end, the invention relates to a Compton imaging method using one or more Compton cameras. Said Compton cameras produce at least three views [Fig. 10], [Fig. January 1 .c] (containing CCi capture _centers, _CC2, CC3 [Fig. 10]) from three known positions distributed over the three axes (X, Y, Z) each passing through a catch centers one of the Compton cameras. Advantageously, the implementation of said method allows the 3D reconstruction of the image of an object from a minimum of views, preferably three.

[00114] An advantage of using the method of the present invention is that it makes it possible to reduce the number of views necessary for the reconstruction of the image which imposes constraints (time, dose, cost, etc.). For example, multiplying the number of views has a cost, either in pause time if you have to move the camera to get enough views, or in equipment cost if you use equipment that takes multiple views simultaneously.

By reducing the position uncertainty by acquisition, the implementation of the method of the present invention makes it possible to combine the advantages of the detection mode of Compton cameras, of the original and novel method of selection of the photons required to reconstruct 3D image.

[00116] According to one particular feature, the method of the present invention comprises a 3D Compton reconstruction step requiring less than 10 photons / voxels to reconstruct the image. This is partly due to the finesse of our photon selection method which, by reducing the positional uncertainty by acquisition, improves the localization accuracy of the reconstruction gamma photons. [00117] According to another particularity, said method makes it possible, with very few photons compared to current conventional tomographic imagers, to reconstruct three-dimensional (3D) images of better or at least equivalent quality. Thus, by carrying out a simultaneous acquisition of the three views, one reduces significantly, for example in the medical field, the time, the dose and the cost generated only by the care, without taking into account the material.

Another not insignificant advantage which results from this improved precision of localization during the implementation of the method is that it induces a significant reduction in acquisition times.

[00119] In addition, avoiding the many constraints associated with mechanical collimators is advantageous and also allows to have large fields of view on the object to be imaged. This advantage used in the present invention makes it easy to cover in full the objects of large and small sizes that one wishes to image with a minimum of views.

[00120] The electronic collimation of Compton cameras improves sensitivity, compared for example with Anger cameras because it accepts photons regardless of their respective angles of incidence. It is also much more robust to disturbances from secondary and / or off-screen sources. Indeed, it is possible to exclude from the reconstruction cones which contain a source secondary to the one to be studied, for example a source outside the measurement field. By performing such processing we obtain an image and a count rate of the main source very similar to what we get in the absence of a secondary source. This electronic collimation is therefore able to exclude unwanted sources or photons and retain only those useful for reconstructing the image for a gain in quality and time.

[00121] According to one feature, the method of the present invention comprises a 3D Compton reconstruction step requiring less than 10 photons / voxels to reconstruct the image. This is in part due to the finesse of our photon selection method which improves the localization accuracy of reconstructing gamma photons for a better image with fewer hits compared to conventional imagers of the same type. In one embodiment, in a nonlimiting manner, it is possible to produce a 25D image from a single fixed position, that is to say a single acquisition (planar mode) and / or from the reconstruction of the depth (Z), if applicable.

[00123] In another embodiment, it can also be envisaged to perform one or more tomographic reconstruction (s) (axial or longitudinal) using the tomographic mode.

[00124] It may be difficult in certain cases, using only one or two views, to define all the contours of an object to be imaged, which contributes to inducing in the reconstructed images a certain number of artifacts. With fewer than three views sampling all three directions of space, information may be missing or poorly resolved for the 3D reconstruction of an object. Two simultaneous views, even close enough to the same object, however make it possible to remove the indeterminacy in depth in the Compton reconstruction and have many advantages (improvement of the signal / noise ratio, reduction of artefacts.).

[00125] According to one feature, a Compton 3D reconstruction is carried out from three views, each sampling one of the three directions of space. Acquisition times and number of moves according to each view defined at the user's discretion. As illustrated in [Fig.1.], H and are the two points of interaction and the direction of diffusion is given by the line d (l ₂ ) passing through h and I2. The point of absorption I2 apex of the Compton cone is the reference point locating the position of one of the views on one of the axes, the three axes forming a trihedron whose origin O [Fig. 10.] is the point of intersection of said axes.

[00126] The precise location of the site of emission of the detected photon is of crucial importance. For an ideal measurement according to a view, the origin of the absorbed photon is obtained on the surface of the Compton cone (apex cone I2, axis d (I ₁ l ₂ ), and opening half-angle teta [Fig . 1.]. Taking into account the measurement uncertainties, the origin of said photon no longer rests on the surface of the cone, but is located inside a volume surrounding this surface [Fig. 8. a.] . With two interactions ai and a2 of two photons detected from the same source (S) detected by the same Compton camera, on the same view (1 D mode), we obtain two intersection zones (z and Z2 ) extents of Compton cones [Fig. 8. b.], Showing the degeneration of the solution along the viewing axis of the Compton camera used. This degeneration induces many artefacts mainly the phantom source artefact in a reconstructed image. Another advantage of the process of the present invention is that it allows said degeneration to overcome.

[00128] The size of the intersection volumes of the cones in Compton imaging affects the speed of convergence of the reconstruction algorithms used.

[00129] The 1 D, 2D, 3D modes described below must be understood as being the number of spatial directions of view (s). 1-D mode for single-direction shooting (s); 2D mode for shooting (s) in 2 directions: and 3D mode for shooting (s) in three directions.

[00130] 1 D mode (shooting (s) in one direction)

[00131] According to one variant, two gamma photons coming from the same source are detected by a Compton camera along one of the axes of the trihedron (1 D mode). For a classic Compton reconstruction (in 1 D mode), the intersection volumes of the cones are quite large. For example, 2240 cm ³ for the intersection volume following a view [Fig. 8.c]

[00132] 2D mode (shooting (s) in 2 directions :).

[00133] According to another variant, the two gamma photons are detected either by two different Compton cameras, each along one of the three axes of the trihedron, or by a single Compton camera capable of successively producing two views, each along two different axes of the trihedron ([Fig. 9. a]; [Fig. 9. b]).

Such an arrangement of Compton cameras makes it possible to have two separate shots along two axes of a plane passing through the object to be imaged, the details of the object to be imaged are better circumscribed, better defined and better resolved than in 1 D mode. With two views along X and Y at 90 ° to each other, there is an interaction volume of the Compton cones of 1327 cm ³ [Fig. 9. b]. Lower than that obtained from the intersection of the Compton cones in acquisition 1 D. Moreover, many values of X and Y are excluded, the solution is no longer degenerate along the observation axes. An advantage of this embodiment is to accelerate the convergence of the reconstruction algorithm.

[00136] The [Fig. 9.c] and [Fig. 9.d] are the views and images obtained from the classical 2D reconstruction from views along X and along Y at 90 ° to each other. All intersections between cones are considered valid. The views are taken along the X and Y axes and the image shown along the Z axis where no observations are available.

One of the advantages of this embodiment (conventional 2D reconstruction) is to highlight three problems, an artefact line along the axis of view, the image of the point source is not spherical and has a distortion along the same axes as the artifact, the image computation time is very long.

Smoothing can then be considered to reduce artifacts and better statistics, but they will remain problematic in the case of an extended source whose shape it is desired to reconstitute.

[00139] The [Fig. 9.c] and [Fig. 9.d] show that this defect is reduced if we observe along the X or Y axis where the observations (views) are made. These defects are of various origins, the poor definition of the contours of the object to be imaged induces naturally smaller defects along the view axis but more important if one is not in the view axis, the intersection of the wall of the cone (for example coming from Y) which does not contain the source with the viewing angle (X in this case). In fact, the angle of view is dense in cones along X, but poor in intersection of cones coming from Y.

[00140] In this embodiment, two interesting phenomena are demonstrated, the size of the task which contains the source is reduced compared to an observation along a single axis (the spatial resolution is greater). An advantage of this embodiment is that it makes it possible to correctly position the object with a very low number of photons (for example only ten per voxel in 3D versus about fifty per voxel for a 2D image, at from a simple view).

[00142] According to another particularity, only the intersections of cones originating from the X and Y views in the reconstruction are considered. All X-X and Y-Y intersections are eliminated, improving source location accuracy, speeding up algorithm convergence, and reducing artifacts from ghost sources.

[00143] According to another feature, an observation along the Z axis further reduces artifacts. Indeed, with this complete observation there is no longer a particular direction according to a view and the artifact is much less marked. Thus, one solution offered by the method is, to limit this problem, to observe the system along the Z axis.

[00144] 3D mode (shot (s) of view (s) in three directions).

[00145] According to another variant, three gamma photons from the same source are detected, either by three different Compton cameras, each along one of the three axes of the trihedron ([Fig. 10]; [Fig. 12]), or by a single Compton camera capable of producing three views, each along three different axes of the trihedron, or by two cameras, one producing a view along one of the axes of the trihedron and the other successively producing the other two views respectively on the other two axes of the trihedron. The purpose of these different Compton camera layout options is to cover all the possible configurations to ultimately make it possible to obtain three distinct shots along the three axes of a trihedron.

[00146] According to one embodiment, the views can be acquired, either simultaneously by three separate Compton cameras, or sequentially by a displacement of at least one Compton camera on said 3 axes X, Y and Z of the trihedron. According to one embodiment, the place of emission (S) of the detected photon coincides with the point of intersection (O) of the X, Y and Z origin axes of the trihedron [Fig. 10.].

[00148] According to another embodiment, said trihedron is a trihedron with orthogonal X, Y and Z axes defining three directions of space. Three views following the three directions of space constitute optimal observation conditions for a given source located at the origin of said trihedron, If the field of view is transparent to radiation, the views above and below are equivalent in information, and are those where the axes joining the source to the camera constitute an orthogonal trihedron.

In one embodiment, the source is simultaneously observed along the 3 axes of the trihedron and only the intersections which include the three viewing angles are considered, in the most general case there are only 8 possible point solutions for the source in space, 8 restricted zones if the cones have a certain thickness due to uncertainties [Fig. 9.a]

[00150] In the case where the 3 shots are taken such that the angle of the trihedron between the 3 cameras and the position of the source is 90 °, there are two possible position zones which are in a range distance to each of the relatively small views. The solutions are no longer degenerated in any direction. The volume of the solution zone is smaller than in 1 D and 2D modes. With three views, the interaction volume of the Compton cones [Fig. 1 1. b] is 360 cm3, approximately 20 times lower than that obtained from the intersection of the Compton cones in 1 D and 2D mode. This further accelerates the convergence of the classical reconstruction algorithm used. In addition, the spatial resolution of the reconstructed images is improved by switching from a 2D reconstruction to a 3D reconstruction.

[00151] According to another variant embodiment, the method contains a Compton reconstruction method in which only the intersections of cones from different views are retained. One of the advantages being by example, improving the source location accuracy which allows better reduction of ghost source artifacts in the reconstructed image.

If we compare 2 intersections of cones in 3D mode containing the same source but corresponding to two different groups of photons, the probability that the “phantom” solutions coincide is very low. The reconstruction technique will therefore converge with a very limited number of photons. (To a lesser extent this is also the case when considering all intersections).

We are moving from an imaging technique based on a probabilistic approach which requires a large number of photons (50 for a 1 D image) to a quasi-deterministic imaging technique which could provide a correct image with less than 10 photons / voxel. Another advantage which results from this is to make it possible to detect with certainty a low contamination with a reduced number of photons.

[00154] It will be noted that a voxel is generally defined as a unit of volume image the geometry of which is variable (cubic, cylindrical, spherical, etc.) and that this term should not be understood in a limiting manner.

Another advantage of imposing the presence of cones from the 3 views to consider an intersection zone as valid, is that this will considerably accelerate the convergence of the rear projection algorithm by removing the irrelevant zones to locate the source.

[00156] Another advantage is that this reduction in uncertainties leads to reducing the dimensions of the task which contains the image of the source. With three views we have a better angular resolution of the Compton camera.

[00157] According to another variant, said Compton imaging method further contains a Compton scanning process, used in the case where the intensity of the source is identical between several views, to filter the parasitic events for which said intensity of the source does not satisfy the law of the inverse of squared distances, not varying as 1 / d ² on each of the views, d being the distance from the source to the camera on each of the views. [00158] When a given source is observed simultaneously from several points or if the intensity of the radiation source is not significantly variable during the observation time and the relative positions of the shots in the space are precisely known, it is possible to exclude some of the solutions resulting from the intersections of cones by taking into account the law of variation of the number of photons detected with distance.

In particular, if the views of the source are simultaneous, it is possible in most cases to determine which of the two solutions is the correct one because the number of photons detected by each camera must vary as 1 / d ² depending on distance from the source, which is not generally verified for the "phantom" source.

[00160] The use of this 1 / d ² rule makes it possible to exclude a certain number of solutions, mainly those which are generated by the phantom sources.

Another variant of use of this rule in 1 / d ² allows in the present invention to refine the results of metrology of photon fluxes, activity measurement, precise localization and identification of various types of sources and hot spots.

[00162] In the event that the object to be imaged exhibits significant absorption of radiation, the views along the X axis and along the -X axis are not necessarily equivalent and must be observed. In this case, it may be necessary to take 6 views, or even more, depending on the extent of the absorption of the radiation.

[00163] On the other hand, the attenuation due to the scattered radiation (medical imaging) is not a problem since it is possible to obtain quantified images of the scattered radiation. It is therefore advantageous to use these images to correct the number of photons emitted.

The present invention further relates to a Compton imager comprising at least one Compton camera, capable of producing at least three successive or simultaneous views and implementing the Compton imaging method according to the particularities described above. [00165] According to one embodiment, said Compton imager comprises a Compton camera mounted on a frame defining the trihedron.

[00166] According to another embodiment, at least one of the Compton cameras of said Compton imager is mounted on at least one articulated arm which can successively and simultaneously move in all directions in space and be oriented along the angles of Euler, either in automatic mode or in manual mode. This facilitates the deployment of the cameras around the object to be imaged and also makes it possible to consider and achieve all types of possible and desired orientations for different arrangements of the view heads of each of the cameras. Another advantage is to make it possible to bring the detection heads closer to the area to be imaged and thus reduce the acquisition time and at the same time the dose and, to improve the spatial resolution of the image, to be able to achieve the various view positions desired regardless of the geometric constraints.

[00167] According to another embodiment, the automatic mode is controlled remotely. So for some use it is not necessary to have an operator near the object to be imaged.

[00168] According to another embodiment, said Compton camera are mounted on aircraft (for example a drone, etc.) or on a land drone thus making it possible to produce views of an object to be imaged located in a zone of particularly restrictive access (at sea, space, contaminated area, ...).

[00169] In a nonlimiting manner, the present invention relates to the use of the Compton imager according to the particularities described above in many fields (health, industry, environment, safety).

In the field of health for example, one of the main interests of Compton 3D imaging compared to other imaging modalities, PET imaging for example, it makes it possible to obtain tomographic images, which are certainly less resolved. , but on the one hand with a dose injected by a factor of 10 to 20 lower, and contributes significantly to improving the radiation protection of patients, staff, animals and the environment.

[00171] On the other hand, the low cost of the device of the present invention compared to a PET scan (5% of the cost of a PET scan) makes it more accessible.

[00172] In addition, the small footprint of the detectors, therefore easy access to the patient, favors the establishment of new applications such as image-guided surgery, etc.

[00173] In a non-limiting manner, the present invention relates to the use of the Compton imager for medical imaging, for veterinary imaging, for preclinical checks.

[00174] One of the advantages of the Compton imager of the present invention is that it is particularly suitable for imaging large animals (horses, cows, elephant, giraffe ...).

[00175] According to another particularity of use, the Compton method and imager of the present application also relates to the field of pharmacokinetic studies (diffusion of the tracer in the body). Scanning of potentially cancerous patients to locate hot spots, the injected dose being so low (and therefore cheap) that it does not pose a risk to the patient. It also makes it possible to increase the number of frequent post-treatment images for better patient follow-up with a severely restricted dose.

[00176] Thus, the use of the Compton imager of the present invention allows a patient to accumulate advantages in terms of quality of care, cost and treatment time, better post-treatment follow-up.

[00177] In a non-limiting manner, the present invention relates to the use of the Compton imager in industry, for example for the detection of faults in various types of structures, for performing non-destructive testing, etc.

[00178] In a non-limiting manner, the present invention relates to the use of the Compton imager to obtain the image of radioactivity distributions, in deduce the activity of one or more sources in industry, locate (place of emission of the photon) the sources in the containers. Indeed, with a precise measurement of the broadcast, we have a good estimate of the real activity of a source.

[00179] For example, the implementation of the method on a storage drum of dimensions 600 x 925 mm (which can be a good approximation of the size of the human torso) leads to an image (MLM / MLEM) in 20 minutes at 1.3 meters from the center with a dose of only 4.5 MBq of ⁶⁰ Co using the Compton 3D reconstruction method described in the present invention. In a comparative manner, for a PET scanner with an equivalent exposure time (20 minutes), 250 MBq is injected, with the PET detectors placed less than 40 cm from the center of the object to be imaged.

Another example illustrated by [fig.12] shows an embodiment of the invention where two sources ( ¹³⁷ Cs and ²² Na) of 30 kBq each, separated by 15 cm are observed (3 views in three directions distinct) at a distance of 50 cm from the origin of the trihedron. By comparing our images reconstructed by a classical method (all intersections) (MLM / MLEM) [Fig.12 b] with those obtained using the same reconstruction and acquisition parameters [Fig.12. a] on a Compton imager by the method according to certain embodiments of the invention (only the multi-view intersections), a clear improvement is observed without any ambiguity.

[00181] According to a non-limiting feature, the Compton imager described is applied to humans, with the same field of view, three Compton cameras being 40 cm from the center of the area of interest. The number of photons detected increases by a factor of 10. A tomographic image is obtained in 2 minutes, either by injecting only 0.5 MBq, or a better resolved image by posing longer. The three parameters (time, dose, image quality) can be adjusted depending on the relevance, the analysis, generally depending on the information sought.

[00182] According to a particular feature of use, the invention relates to the use of the Compton imager to produce tomographic images in gamma radiation (of a living being, of an animal, etc.) with an injected dose. less than 20 MBq for a time t less than 20 minutes. The many advantages (in quality of care, cost, treatment time, ALARA, etc.) made available by the device are thus combined for a patient.

[00183] Another advantage of Compton cameras is the possibility that they offer to take views with large field sizes. Compared to PET cameras the difference in field of view is significant (8100 square degrees versus 25 square degrees if PET modules of the same size as Compton modules were used).

[00184] Another advantage for using Compton cameras is that in Compton imagery, a probability density is imaged. The image is sensitive to the neighborhood, which speeds up the convergence of the reconstruction. Unlike the pointillist PET image, each LOR is independent.

[00185] According to another particularity of use, the Compton method and imager of the present application is suitable and just as effective in the case of sources whose intensity is constant or weakly variable over time.

[00186] According to one feature, it is possible by moving the camera and by performing at least 3 poses (views) of the same object so that the vector joining the source and the camera has projections of at least 50% (in total or 50% along each axis) according to the 3 axes of an orthogonal trihedron. The case where the 3 observations take place according to a trihedron (X, Y, Z) with respect to the source is optimal. This can be done for example by installing a camera according to the invention on a robotic arm or a land or air drone. The goal is to have all the necessary configurations to avoid having missing views.

[00187] In the case where the source is variable (medical applications) or if it is desired to have an image acquisition period as short as possible, it is advantageous to simultaneously acquire the 3 views along X, Y, Z during one and the same pose.

[00188] According to another particularity, the invention relates to the application of the method and of the Compton imager described in the field of the nuclear industry. to perform a 3D tomography of containers of radioactive substances (for example waste drums) by observing them for less than 20 minutes in a dedicated facility. This gives a tomographic visualization of the distribution of radioactivity isotope by isotope (the detector is initially calibrated to the different energies of the various isotopes) in the waste drum. This makes it possible to precisely know the content of a barrel and to foresee possible problems during its pressing (radiation protection). Since we have the distance and the activity of the isotope point by point, it is possible to precisely calculate the source term isotope by isotope and then calculate the activity at the walls of the container without the need for expose an operator to radioactivity. It also makes it possible to observe inaccessible areas such as the bottom of a barrel.

[00189] According to one embodiment, the Compton imager of the present invention comprises at least one CT-Scan head enabling a tomodensitometric image to be produced. An advantage of this embodiment is that it allows the user to make attenuation corrections. The CT-scan head provides an image of the skeleton and further improves the localization of an organ in the body relative to the bone landmark.

[00190] The CT-Scan head of the present invention includes any type of detector X-ray tube combination making it possible to determine the attenuation maps or to produce X-ray images.

[00191] According to one feature, the Compton imager is coupled to a medical accelerator to perform dosimetry-in vivo measurements and thus makes it possible to check that the treatment actually delivered is indeed that which has been planned.

[00192] The term medical accelerator here designates any type of medical treatment device that generates gamma or X photons in any way, with energies within the range of said Compton cameras greater than 200 keV.

[00193] According to one embodiment, the coupling is carried out using articulated arms facilitating the optimum positioning desired for the measurement to be carried out. [00194] According to one embodiment, the detection heads are each facing one another around a bench, said bench capable of performing translational and rotational movements in a plane.

[00195] The bench described above can be a bed, a table or any other device of the same type allowing the correct positioning of the area to be imaged in the field (s) of view of the Compton cameras.

[00196] The translation and rotation movements not only facilitate the positioning but more importantly make it possible to perform an acquisition in scanning mode (step by step or continuously).

[00197] The scanning mode described above comprises a displacement of the bench in the desired direction to make it possible to image areas beyond the range of the fields of view of the Compton cameras (for example in medicine a whole body acquisition to see the distribution of 'a radionuclide throughout the body).

[00198] The invention further relates to the use of the Compton imager of the present invention for improving the control of hadron therapy treatments. Indeed, the correlation between the position of emission of the prompt gamma rays and the position of the Bragg peak makes it possible to control the quality of hadron therapy treatments. The energy of the prompt gammas varies from some hundred keV to several MeV favoring Compton scattering. In this embodiment, the Compton imager of the present invention allows with unequaled localization precision the place of emission of each prompt gamma photons. Thus the correlation can be made and facilitates the monitoring of treatments. Another advantage of using said Compton imager is its very good energy resolution enabling it to detect and discriminate the entire spectrum of said prompt gammas. An additional advantage of the invention is the temporal resolution of the detectors employed (less than 200 picoseconds / ps) making it possible to attribute the photons detected to a particular phase of the pulsed flux of photons detected (for example rising edge of the pulse of photons emitted by the device) [00199] In a non-limiting manner, the present invention relates to the use of the Compton imager to improve the radiation protection of patients, staff, animals and the environment in the presence of one or more radioactive sources.

In a nonlimiting manner, in the field of security, it can be envisaged an implementation of the method of the present application by the customs services, for example for the detection and localization of sources (even very weak ones) in the containers for example or any other type of target of interest.

It is easily understood from reading the present application that the features of the present invention, as generally described and illustrated in the figures, can be arranged and designed according to a wide variety of different configurations. Thus, the description of the present invention and the accompanying figures are not intended to limit the scope of the invention, but simply represent selected embodiments.

[00202] Those skilled in the art will understand that the technical characteristics of a given embodiment can in fact be combined with characteristics of another embodiment, unless the reverse is explicitly mentioned or it is not be obvious that these characteristics are incompatible. In addition, the technical characteristics described in a given embodiment can be isolated from the other characteristics of this mode unless the reverse is explicitly mentioned.

Finally, those skilled in the art will understand that the information contained in the figures, in particular that of Figures 1 to 11, will be technical information that can be incorporated into this text as an appendix.

[00204] It should be obvious to those skilled in the art that the present invention allows embodiments in many other specific forms without departing from the field defined by the requested protection, they should be considered as illustration and the invention should not be limited to the details given above. LIST OF REFERENCE SIGNS

[00205]

CC. Capture center

PRC, PC1, PC2. Compton DR Imaging Reconstruction Plans. Compton Imaging Reconstruction Discs

A, A1, A2. Artifacts obtained by classical imagery

S. Source

DIC. Distance between capture centers

AIC. Inter-center capture angle

Claims

1. Process for creating a three-dimensional and / or tomographic image of an object in Compton imaging gamma radiation, characterized in that it comprises one or more Compton cameras producing at least three views from three known positions each distributed over one of the three axes (X, Y, Z) of a trihedron, the acquisition fields of said views having at least one overlap area covering the object to be imaged

2. Compton imaging method according to claim 1, characterized in that it comprises a reconstruction method using less than 10 photons / voxel per view to reconstruct the 3D image,

3. Compton imaging method according to claim 1 to 2, characterized in that it comprises an electronic collimation step capable of excluding sources or photons originating from areas that it is desired to exclude from the image.

4. Compton imaging method according to claim 1 to 3, characterized in that the views can be acquired either simultaneously by three separate Compton cameras, or sequentially by moving at least one Compton camera on said 3 axes of the trihedron.

5. Compton imaging method according to claim 1 to 4, characterized in that said trihedron is a trihedron with orthogonal X, Y and Z axes defining three directions in space, the source to be imaged being at the origin of the trihedron. .

6. Compton imaging method according to claim 1 to 5, characterized in that it contains a method of tomographic reconstruction of said object to be imaged from at least two Compton views, the fields of view of which are distributed in three dimensions. (X, Y, Z) of space.

7. Compton imaging method according to claims 1 to 6, characterized in that it contains a Compton reconstruction method in which only the intersections of cones from different views are retained.

8. Compton imaging method according to claims 1 to 7, characterized in that it contains a Compton scanning process, used in the case where the intensity of the source is identical between several views, to filter the parasitic events for which said source intensity does not satisfy the law of the inverse of the squared distances, not varying as 1 / d ² on each of the views, d being the distance from the source to the camera on each of the views.

9. Compton imager comprising at least one Compton camera, producing at least three successive or simultaneous views by implementing the method according to the preceding claims.

10. Compton imager according to claim 8, characterized in that it comprises one of said Compton cameras mounted on a frame defining said trihedron.

1 1. Compton imager according to claim 8 to 9 characterized that at least one of said Compton cameras is mounted on at least one articulated arm capable of successively and simultaneously moving in all directions of space and being oriented along Euler angles, either in automatic mode or in manual mode.

12. Compton imager according to at least one of claims 8 to 10, characterized in that it comprises at least one CT-Scan head making it possible to produce a tomodensitometric image

13. Compton imager according to at least one of claims 8-1 1, characterized in that it is coupled to a medical accelerator

14. Compton imager according to at least one of claims 8 to 12, characterized in that the detection heads are each facing around a bench, said bench being able to perform translational and rotational movements in a plane.

15. Use of the Compton imager according to at least one of claims 8 to 13, in the fields of medical, veterinary and preclinical imaging.

16. Use of the Compton imager according to at least one of claims 8 to 13 for non-destructive testing.

17. Use of the Compton imager according to at least one of claims 8 to 13 to obtain the image of radioactivity distributions in industry.

18. Use of the Compton imager according to at least one of claims 8 to 13 for obtaining a tomographic image in gamma radiation of a living being with an injected dose of less than 20 MBq in less than 20 minutes.

19. Use of the Compton imager according to at least one of claims 8 to 13 to improve the radiation protection of patients, staff, animals, the environment in the presence of one or more radioactive sources.

20. Use of a Compton imager according to at least one of claims 8 to 13 for improving the control of hadron therapy treatments.