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  • 权利要求
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    • 专利摘要:
    A system and method for detecting gamma radiation, of the Compton camera type, comprising a gamma radiation source, at least one fast scintillator plate P1 whose rise time at the peak of light is less than 1ns, having a thickness greater than or equal to 10 mm, equipped with a network of segmented photodetectors (5) and a micro-electronic dedicated fast reading. The system is characterized in that it is capable of measuring spatio-temporal coordinates (X, Y, Z, T) and energy E in at least two successive positions of a gamma photon when said photon undergoes a Compton deviation at a first point A before being absorbed at a second point B, by recognizing non-scattered photon circles corresponding to each scintillation interaction. The system has a module estimating a valid Compton event. The detection system exists with two scintillator plates P1 and P2.
    公开号:FR3036500A1
    申请号:FR1554435
    申请日:2015-05-18
    公开日:2016-11-25
    发明作者:Hichem Snoussi；Alain Iltis
    申请人:Alain Iltis；
    IPC主号:
    专利说明:

    [0001] TECHNICAL FIELD OF THE INVENTION [0001] The invention relates to the imaging of gamma ray sources. More particularly, the invention relates to a Compton camera type gamma-ray detection system making it possible to reconstruct an image of the gamma sources, to precisely measure the spatio-temporal coordinates and their energies when said photons undergo a Compton deviation. The invention further relates to the use of the detection system in the fields including astronomy and medical. The invention also relates to the treatment of the Compton effect in time cameras. STATE OF THE PRIOR ART [0002] At present, the imaging of gamma ray sources (> 30 KeV) is carried out essentially for medical diagnostic purposes around two techniques: PET and SPECT. The SPECT is based on scintigraphy and allows images and three-dimensional reconstructions of organs and their metabolism by means of a set of gamma cameras rotating around a patient. The SPECT can use several gamma-ray energies, but the lead collimator that allows to know their direction of arrival absorbs more than 99%. PET uses a ring of segmented detectors. For PET, radiopharmaceuticals emitting positrons are used. These give rise to a pair of 511 KeV photons and it is possible to locate the emission by their simultaneous detection on the ring of detectors. [0003] A third technique, the Compton camera, is currently emerging. This technology allows as the SPECT to make an image whatever the gamma energy, but unlike the SPECT, all photons can contribute to the image. But, the applications of the Compton camera are today limited by its cost, the high level of noise and the difficulty of obtaining precise reconstructions. When using scintillating crystals to make an image of gamma radiation sources, the probabilistic nature of the gamma / material interaction is encountered. We notice essentially two effects: first, the gamma photon can be absorbed at any depth on its propagation path (Depth of Interaction Effect). The second effect is that all current imaging systems (pixel matrix or Anger camera) are based on the premise that the place where the maximum light emission takes place is the place where the gamma photon has been detected. Due to the Compton deviation, this postulate is just about the average of a large number of events. On the other hand, in the case of a PET scanner if the position of a single event is reconstructed, the error in the position may be several millimeters. The solution adopted is then to reject the events for which the deposited energy is not correct. This leads to rejecting a large number of events. The objective is to present a method for processing Compton scattering in a new type of detector the "time camera" described in French patent applications number: '1260596' and '1454417' of the same applicant, and to describe thus the operation of a Compton camera based on this type of "time camera" detector. [0008] The Compton scattering processing techniques have had a limited success so far as the Compton cameras to operate need a precise location of at least two events located on at least two plates (plate 1). & plate 2) and a precise measurement of the energy deposited on each plate. For this reason, to date all functional Compton cameras have been made with semiconductors. The Compton cameras made with semiconductors have the following problems: First, the stopping power of the semiconductor crystals is low. Large thicknesses are therefore required above 30 3036500 3 mm for 511 KeV. These crystals must be segmented, each pixel being read separately which increases the cost of the system. The second problem is that the cost of the system to cm3 is high (about $ 2000 / cm3) which limits the cameras of small systems. Another problem of Compton cameras thus realized is that the temporal response of the semiconductors is slow, greater than 10 ns. However, many spurious events are measured during the measurement of a Compton event which means that there is a lot of noise. The object of the invention is therefore to propose a technical solution 10 allowing an accurate determination of the coordinates (X, Y, Z, T, E) of each gamma event in the case where the incident photon has undergone a diffusion. Compton using the principles of the time camera. The invention thus proposes a Compton camera-type detector having the following advantages: It is a detector of the spectrometer and imager type. It thus makes it possible to measure both the energy of the gamma photons and their spatial distribution. - The detector works for any energy of the gamma photon, unlike the PET technique. Even if this concept works all the better because the energy is high because of the focusing of the energy deposit in the direction of propagation of the gamma ray. - The detector can use all the gamma photons incident due to the lack of collimator, unlike the SPECT. The main object of the invention is therefore to propose a new technique allowing: - to keep a good localization of each event in a time camera type detector in the case where the photon has undergone a Compton effect; to measure the energy of an event in a time camera type detector in the case where the photon has undergone a Compton effect; and - to realize an improved Compton camera by combining one or more detectors of the time camera type.
    [0002] SUMMARY OF THE INVENTION The invention relates to a gamma radiation detection system, of the Compton camera type, comprising a gamma radiation source, at least one fast scintillator plate P1 whose peak rise time 5 light is less than 1ns, having a thickness greater than or equal to 10 mm, equipped with a network of segmented photo-detectors and a micro-electronic dedicated fast reading system is characterized in that it is capable of measuring the spatio-temporal coordinates (X, Y, Z, T) and the energy E in at least two successive positions of a gamma photon when said photon 10 undergoes a Compton deviation at a first point A before being absorbed at a second point B, while recognizing non-scattered photon circles corresponding to each scintillation interaction. According to the invention, the gamma-ray detection system of the Compton camera type is characterized in that it comprises a single scintillator plate P1 of thickness greater than or equal to the mean free path of the gamma ray in the crystal. considered. Moreover, the gamma-ray detection system, Compton camera type includes two photodetector arrays respectively disposed on an input face and an output face of said scintillator plate P1. [0018] Advantageously, the input face and the output face of the scintillator plate are coupled to the photodetector array, they are polished and the coupling between said faces and the photodetector array is performed by a medium of index n less than 1.5, in order to provide a total angle of reflection. In particular, lateral faces and the input face of the scintillator plate P1 are not coupled to an array of photo-detectors, they are rough, and said faces are treated in such a way that the absorption of the photons incidents are maximum. Preferably, the input face of the plate P1 not coupled to a photodetector array is painted black to remove the reflection on said face. According to one embodiment of the invention, the detection system is characterized in that it further comprises a second scintillator plate P2, in that the plate P1 is thinner than the second plate P2. and in that the thickness of the scintillator plate P1 is such that the gamma photon undergoes a Compton deviation at a point A of said plate P1; the second scintillator plate P2 is of a thickness to absorb at least 50% of the gamma radiation energy, said second plate being separated from the plate P1 by a distance 'D' of at least 10 mm, preferably greater than the thickness of the thickest plate. The system further comprises a module 10 for estimating a valid event, said module being able to measure on said second plate P2 a coincidence trigger in a time window less than the maximum transfer time of the light between the plates P1 and P2 to identify valid Compton events. This coincidence time will in all cases be <1 ns. Preferably, the photodetector or photodetector array is of the SI-PM type, associated with an analog or digital ASIC, and the scintillator plates P1 and P2 are of the lutetium silicate and / or halide type. lanthanum. [0023] The invention furthermore relates to a method for determining the temporal space coordinates (X, Y, Z, T) and the energy E in at least two successive positions of a gamma photon having undergone Compton scattering. implemented in the above system. The method comprises the following steps: detecting the arrival time Ta of the non-scattered photons emitted by the Compton scattering at a first point A; Detecting the arrival time Tb of the non-scattered photons emitted at a second point B by the total absorption of the gamma photon; determining a circle CA corresponding to the non-scattered photons emitted by the Compton deviation of the gamma radiation at the point A, the diameter of the circle CA makes it possible to measure Xa, Ya and Za; - To determine a CB circle corresponding to the non-scattered photons emitted by the total absorption of the gamma photon at point B, the diameter of the circle CB makes it possible to measure Xb, Yb and Zb. the method comprises one of the following three cases: either; The photons emitted during the Compton scattering at A and the total absorption at B remain in the same light cone of the non-scattered photons emitted at A, the angle ac <Oc where ac is the deviation compron and Oc is the critical angle of total reflection and the circle CB is included in the circle CA in this case: counting the numbers of photons in said circles CA and CB; Defining the energy of a gamma photon, said energies Ea and Eb being proportional to the number of photons counted inside said circles CA and CB; either the Compton deviated photon leaves the cone of light, ac> Oc, the distance between points A and B is large and the circles CA and CB are distinct in this case: o determine a first event A corresponding to the most important energy; measuring the coordinates (Xa, Ya, Za, Ta) of said event at A and its energy Ea; determining a second event B corresponding to the lowest energy; measuring the coordinates of the event (Xb, Yb, Zb, Tb) and its energy Eb, calculating the initial energy of the gamma photon which is equivalent to the sum of the energies Ea + Eb; o Determine the Compton deviation angle by reconstructing the position of the two interactions; o Deduce the direction of arrival of the gamma photon at point A, from the position of the point A (Xa, Ya, Za), the position of the point B (Xb, Yb, Zb) and the energies Ea and Eb ; either 3036500 7 the Compton deviated photon leaves the light cone ac> Oc, the distance between the points A and B is small and the circles CA and CB are merged in this case: o adjust the light distribution by an ellipse of center A, the point B occupies one of the foci, the half minor axis corresponds to the radius RA of the circle CA and the half major axis corresponds to the distance AB + RB, where RB is the radius of the circle CB; o determine the position of the point A (Xa, Ya) given by the center of the ellipse; O determining the interaction depth Za in A which is given by the half-major axis of the ellipse (RA); o calculate the time Ta by correcting the times measured with Za; o determine the position of the point B (Xb, Yb) that is given by the focus of the ellipse; O determining the interaction depth Zb in B which is given by RB that is calculated with the half-major axis of the ellipse: by Distance (A - B) + RB; o calculate the time Tb by correcting the times measured with Zb; to measure the total energy Ea + Eb by integrating the photons over the whole of said ellipse; o measure the centroid of the photon distribution in the ellipse; o determining the initial point of interaction A or B, said initial point is the one which is closest to the center of gravity; O determining the deviation angle Compton ac by reconstructing the position of the two interactions at A and B. [0024] In another way, the invention relates to a method for determining temporal space coordinates (X, Y, Z , T) and energy E in the case where the circles CA and CB are merged and ac> Oc characterized by the following steps: 3036500 8 o adjust the overall light distribution by a composition of two circles CA and C, ; o determining the positions (Xa, Ya) and (Xb, Yb) of the respective interactions at A and B, said positions are given by the center of each circle CA and CB; o determining the depth of the Za and Zb interactions, by determining the diameter of the CA and CB circles; o measuring the total energy Ea + Eb by integrating the photons on the whole of said composition; O to determine the centroid of the global light distribution of photons in the composition of two circles; o determining the initial point of interaction A or B, said initial point is the one which is closest to the center of gravity of the global distribution of light; O determining the deviation angle Compton ac by reconstructing the position of the two interactions at A and B. [0025] The invention also comprises the use of the detection system in the field of astronomy and the medical field. industry to detect radioactive contaminations. BRIEF DESCRIPTION OF THE FIGURES [0026] Other features, details and advantages of the invention will become apparent on reading the description which follows, with reference to the appended figures, which illustrate: FIG. 1 shows the detection system according to FIG. invention in the case of a plate P1 and when the compton-scattered photon of angle ac remains in the same cone of light (ac less than ec); FIG. 2 shows the detection system according to the invention in the case of a plate P1 when the photon having undergone Compton diffusion of angle ac leaves the cone of light (deviation ac greater than Oc) existence of two distinct circles; Figure 3 shows the detection system according to the invention in the case where (deviation ac greater than 6c) existence of two circles coincide, the light distribution being adjusted by an ellipse; Figure 4 shows the principle of Figure 3, existence of two circles together, the light distribution being adjusted by a composition of two circles; FIG. 5 shows the detection system according to the invention with the plate P1 provided with two photodetector arrays respectively on an input face and an output face; Figure 6 shows an embodiment of the system with two scintillator plates P1 and P2. DETAILED DESCRIPTION [0027] The present invention utilizes a time camera capable of measuring both the position in space, time, and energy of each gamma photon. The principle of a time camera is taught in the patent applications No. 1260596 FR and No. 1454417 FRclu same applicant. In this type of time camera, for each scintillation event (photoelectric effect or Compton scattering) is identified a circle 20 corresponding to non-scattered photons which are the first detected. The non-scattered photons are distributed in a cone whose apex is the location of the interaction (X, Y, Z, T) and whose opening angle is the angle of total reflection on the face of the exit. When the gamma photon undergoes a photoelectric effect, there is only one circle. In what follows we seek to characterize the position and diameter of a circle and not the center of gravity of a light distribution. If the gamma photon undergoes Compton scattering and then a photoelectric effect, there are two circles that appear almost coincidentally in terms of detectors. In the case where the gamma photon undergoes a Compton deviation at point A (Xa, Ya, Za, Ta, Ea) before being absorbed at point B (Xb, Yb, Zb, Tb, Eb), The following three cases will be considered: FIG. 1 shows the detection system according to the invention in a first case where the photon undergoes Compton diffusion of angle α remaining in the same cone of light as non-diffused photons. The system comprises a plate P1, provided with a photodetector array 5 associated with microelectronic components 6. The plate P1 has a thickness greater than or equal to 10 mm. On this plate P1 is detected the arrival time Ta of non-scattered photons emitted by a Compton scattering at a first point A; then the arrival time Tb of photons which have undergone total absorption at a second point B is detected; and determining a circle CA corresponding to the photons emitted during a Compton deviation and a circle CB corresponding to the photons emitted during the complete absorption of the gamma photon. In this first case, the Compton deviation of angle ac is smaller than the angle Oc where Oc is the critical angle of total reflection. In this case, which is the most common, the non-scattered photons emitted by the interaction all remain in the same light cone, but their distribution may have an asymmetry ie the circle CB (corresponding to the point B) included in the circle CA corresponding to point A. However, in the same way as for a photoelectric event the diameter of the circle CA can measure Xa, Ya and Za. Thus, the diameter of the circle CB makes it possible to measure Xb, Yb and Zb. The reconstruction of the interaction makes it possible to measure Ta and Tb. Counting the number of photons in the CA and CB circles makes it possible to estimate the relative energy deposited at points A and B. In a simplified version of the treatment, only the widest circle (CA circle) is considered. . It should be noted that the Compton effect does not modify the accuracy of the measurement of the spatio-temporal coordinates of the point A. [0035] It is also considered, as illustrated in FIG. 2, the case where the photon having undergone Compton scattering. angle ac leaves the cone of light. In this case the deviation ac is greater than Oc. We obtain distinct events, that is to say existence of two simultaneous circles in time, contrary to the case of the pileup. Here again we have two cases: either the two circles coincide (Distance A-B 30 <Ra + Rb), or the two circles are distinct (Distance A-B> Ra + Rb). FIG. 2 represents the case where the two circles CA and CB are distinct. We recognize that this is a Compton scattering if Tb - Ta is close to Distance (AB) / c. In this case, each event is treated independently. The first detected event and / or that corresponding to the most important deposited energy is the initial event. The energy of the initial photon is equal to EA + EB. The position of the two points makes it possible to measure ac. In the case where the circles CA and CB are merged, it is recognized that it is a Compton scattering if Tb-Ta is close to A-B / c. In this case, as shown in FIG. 3, the light distribution can be adjusted by an ellipse 10 whose half small axis (b) corresponds to the radius of the first circle RA and of half major axis (a) corresponds to Distance A-B + RB. In this configuration, most of the precision is retained in the estimation of Xa, Ya and Za coordinates despite the Compton scattering. The position of point A (Xa, Ya) is given by the center of the ellipse. The depth of interaction at A is given by the half-axis of the ellipse, which makes it possible to calculate Za. We can then calculate Ta by correcting the times measured with Za. Thus the position of the point B is given by the focus of the ellipse (Xb, Yb). The interaction depth in B is given by the half-major axis of the ellipse (A-B + RB). Knowing A-B, one finds RB, which makes it possible to calculate Zb. Tb can then be calculated by correcting the measured times with Zb. The energy E is measured by integrating the photons on the whole of the said ellipse. EA + EB is the total energy. By calculating the centroid of the photon distribution in the ellipse we can find the initial point of interactions A or B which is closest to the centroid. [0038] Another method in the case where the two circles CA and CB are coincidental is to adjust the light distribution by a composition of two circles as shown in FIG. 4 in dashed lines. In this case, the center of each circle gives the position of the respective interactions Xa, Ya at A and Xb, Yb at B. The diameters of the circles CA and CA give the interaction depth Za and Zb. The energy is measured by integrating the photons on the whole of said composition. The initial point of interaction A or B is the one closest to the centroid of the global distribution of light. In addition, the reconstruction of the position of the two interactions makes it possible to estimate the deviation angle Compton ac. The EB / EA ratio must then check the laws of the Compton broadcast. Figure 5 shows the same case as Figure 1 except that the inlet face 5 1 and the outlet face 3 of the plate P1 are covered with segmented photodetectors with a maximum filling density. In this case, the photons which have undergone a Compton deviation of deviation angle ac are absorbed by the photodetector. We see the circle of non-scattered photons on each side of the plate and we carry out exactly the same treatments described above.
    [0003] However, the propagation of the gamma ray from the input face 1 to the output face 3 introduces an asymmetry between the two faces. In a certain way, the image on the input face 1 is the inverse of the image on the output face 3. The advantage of covering each side of the plate P1 with photodetectors 5 is two independent estimates of the coordinates of each event (X, Y, Z, T, E) are obtained. In addition, the comparison of the light distributions on each side of the plate makes it possible to remove any ambiguities in the reconstruction if the photon has undergone at least one Compton scattering. Moreover, the number of photons used for the reconstruction is doubled and thus the energy resolution for each photon is improved since the energy resolution depends on the number of photons collected. The disadvantage of the above configuration is in the cost of micro-electronic components used on each plane of photo-detectors. Indeed, in this case we double the price of electronics. This configuration is interesting mainly on a thick plate and especially in the case of a single-plate Compton camera where one seeks to reconstruct the path of the gamma photon in the crystal. For photons of known energy (PET) or known direction of arrival (SPECT), it is possible to simplify the analysis of events. In this case, in fact, the sole aim is to determine the initial point of impact of the photon (XA, YA, ZA), its arrival time TA and the overall energy of the EA + EB interaction. We have seen that in all cases it is possible to correctly measure the position of the initial interaction despite Compton scattering. In addition, it is possible to have an estimate of the vector AB between the two successive interactions and the EA and EB energy deposited at each interaction. It is therefore possible with such a system to make a Compton camera with a single scintillator plate. A single-plate system will not be optimum in terms of performance, but it will be very advantageous in terms of cost and efficiency in terms of detection (high percentage of gamma rays totally absorbed by the detector). In another embodiment of the system to suppress the reflection of gamma rays on the unused faces for detection (side faces and input face if we have only one detector array), those These are treated in such a way that the absorption of the incident photons is maximum.
    [0004] Indeed, if the photons are reflected on these faces, they come noisy the detection of the circle of non-broadcast. The fact of treating all the faces not used for the detection, called "sterile" faces, makes it possible to increase from 50 to 100% the integration time of the temporal images (ie to go from 750 ps to 1500 ps) for a given detected non-scattered photon rate (ie 90% of the detected photons are not diffused). The non-coupled faces of a detector array are rough and treated so as to absorb as much as possible the incident radiation to avoid unwanted reflections to the detectors. This treatment must avoid reflections on the so-called "sterile" faces, in particular by index jump. The treatment may be composed of an anti-reflection deposit of any known type, followed by the deposition of a layer of absorbent material. It may also consist of a deposit of a high-index resin (n> 1.5) loaded with absorbent material. [0049] If the "sterile" faces are simply painted black, in a conventional manner because of the significant index contrast between the crystal (n = 1.9) and the paint 3036500 (n <1.5) a most of the photons are reflected towards the inside of the crystal. The faces coupled to detector arrays are preferably polished. The coupling between these faces and the detectors is performed by a medium 5 of low index (n <1.5) in order to provide a total reflection angle. Simulation of the three cases of Compton effect The conditions of the simulation are as follows: Crystal LaBr3: Ce of thickness 30 mm of index n = 1.9 coupling with the photodetector with grease (n = 1.4 ). For each image the position of the photons detected at a given time is indicated: 200 ps - 700 ps - 16000 ps (16ns) Each image also shows a simulation of what is seen on each segmented photodetector. Point A of the Compton scattering positioned at Z = 5 mm for the three cases: Case n ° 1 (alpha <theta) point B total absorption at Z = 15 mm. Case 2 (alpha> theta) Adjacent compton: point B total absorption at Z = 15 MM.
    [0005] Case No. 3 (alpha = pi / 2) Compton disjoint: total absorption point at Z = 5 mm. In current photodetectors, the detection of photons is subject to threshold effects. If we want to get out of the background noise of the detectors (dark counts) it is necessary to detect 1.5 to 2 photo-electrons. Since the integration time Ti is short, typically less than 2 ns, the number of photons to be detected during Ti may be less than the threshold for the peripheral pixels. The integration time is given by the time at which the number of photons detected outside the circle of non-scattered photons passes a certain threshold. The number of photons emitted by interaction in the angular sector of non-scattered photons is constant. The photon / pixel density depends on the diameter of the circle. The maximum diameter of the circle depends on the thickness of the crystal. We can therefore play on the density of 3036500 photons / pixels by varying the thickness of the crystal scintillator. Thus, the more the detector is finely segmented, the more it may be advantageous to use thin crystals. Moreover, the integration time Ti (less than 2 ns) being short with respect to the possibilities of the best current electronics, it is advantageous to look for ways to count the photons longer. The integration time given by the time at which the number of photons detected off the disk of the non-scattered photons passes a certain threshold (for example 90%), the passage of this threshold depends essentially on the number of 10 photons scattered on the the crystal's input face 1, or on the lateral faces for the pixels located within a crystal thickness of the edges. Since for a Compton imager, it can be used to measure X, Y, Z, T, E only the non-scattered photons, it may be advantageous to remove all other photons. A known way of doing this may be to paint the side faces and the input face 1 (the faces not used for detection) in black in order to absorb all the photons coming out of the crystal. However, since the paint index (typically 1.5) is less than the crystal index 1.8 to 1.9, a majority of the photons are reflected by the index jump and return to disturb the signal. . A more advantageous way of carrying out the invention is therefore either to find a black product of index close to that of the scintillator, or to carry out an antireflection treatment by any known means on the lateral faces and the inlet face 1 of the crystal, then apply a black absorbent deposit on this anti-reflective treatment. [0054] Another way of achieving this result may be to deposit on these crystal faces a resin of high index 'n' (n> 1.5), preferably n greater than 1.7, loaded with absorbent particles. This treatment has the following advantages: By greatly reducing the number of photons detected outside the light cone of the non-scattered photons, the time during which the first photons can be counted to define the position of the circle is increased 3036500 16 [ 0056] This system also makes it possible to strongly limit the edge effects and thus to exploit the entire detector for imaging. This antireflection treatment can be carried out by interfering layers, photonic crystals or gradual index adaptation obtained by nanostructuring as disclosed in European Patent Application No. 4305365.0 filed March 13, 2014 "Structuring for the first time". optimization of the photon collection in scintillating crystals and associated technological solutions ". FIG. 6 shows a second embodiment of the system according to the invention comprising two scintillator plates P1 and P2, photodetector networks 5 and the associated electronics not shown, the networks being bonded to each plate. P1 and P2. The plate P1 is thinner than the plate P2. . On this plate P1 one seeks to obtain a Compton scattering in a first coordinate point A (Xa, Ya, Za, Ta, Ea). The second plate P2 is thicker than the plate P1. The thickness of said second plate P2 makes it possible to absorb at least 50% of the energy of the gamma ray at a coordinate point B (Xb, Yb, Zb, Tb, Eb). The second plate P2 is separated from the plate P1 by a distance 'D' of at least 10 mm, preferably 30 mm. The system includes a module for estimating a valid Compton event. Said module is able to measure on the second plate P2 a coincidence trigger Tb in a time window less than 1 ns to identify valid Compton events. Let D 'be the distance between the two plates of the Compton camera, EP1 the thickness of the first plate, EP2 the thickness of the second plate. The maximum transfer time of a photon perpendicular to the detector is: [0060] The time Tmax = EP1 * (n / c) + D '/ c + EP2 * (n / c). For simplicity, in the case of oblique propagation, T <1.5 Tmax is considered. The detection time of a Compton event detected on the two plates will therefore check: D '/ c <TB-TA <1.5 Tmax. In the case of a 3036500 system 17 LaBr3 optimized for 511 KeV (EP1 = 10 mm, D = 30 mm, EP2 = 30 mm) this would give: 100 ps <TB -TA <380 ps. This very strict time condition makes it possible to reject all events that are not strict Compton broadcasts. Such precise temporal windowing is possible with the electronics developed for time cameras and for digital Si-PM type detectors. The probability of two coincident events in such a short time (excluding Compton) is very low. This windowing therefore allows a strong reduction of the noise of the detectors. Thus, it can be seen that the invention makes it possible to make two types of Compton camera: 1) A single-plate camera with a precision and a moderate but compact sensitivity and a moderate cost. 2) A very sensitive multi-plate camera due to noise rejection by temporal windowing, more accurate because of the better angular definition of the path of the gamma photon, but more cumbersome and expensive. Note that in the detection system according to the invention consists of a single plate P1 or two plates P1 and P2, we keep a good localization of each event in a detector in the case where the photon has undergone a Compton effect and more precisely the energy of an event 20 is measured in a time camera type detector in the case where the photon has undergone a Compton effect. Furthermore, an improved Compton camera can be made by combining one or more time camera type detectors. Another advantage of the system according to the invention is its use in fields including medical and astronomy. The detection system according to the invention can also be used in industry for detecting radioactive contaminations. Many combinations can be envisaged without departing from the scope of the invention; the person skilled in the art will choose one or the other depending on the economic, ergonomic, dimensional or other constraints to be respected.
    权利要求:
    Claims (11)
    [0001]
    REVENDICATIONS1. Compton camera-type gamma ray detection system comprising a gamma radiation source, at least one fast scintillator plate P1 whose peak light rise time is less than 1ns, having a thickness greater than or equal to 10 mm , equipped with a network of segmented photodetectors (5) and a micro-electronic dedicated fast reading characterized in that it is capable of measuring the spatio-temporal coordinates (X, Y, Z, T) and the energy E in at least two successive positions of a gamma photon when said photon undergoes a Compton deviation at a first point A before being absorbed at a second point B, while recognizing non-scattered photon circles corresponding to each scintillation interaction.
    [0002]
    2. Compton camera type gamma radiation detection system according to claim 1 characterized in that it comprises a single scintillator plate P1 of greater than or equal to the mean free path of the gamma ray in the crystal considered.
    [0003]
    3. Compton camera-type gamma-ray detection system according to claim 2, characterized in that it comprises two photodetector arrays arranged respectively on an input face (1) and an output face (3) of said scintillator plate P1.
    [0004]
    A Compton camera type gamma ray detection system according to claim 3, wherein the input face (1) and the output face (3) of the scintillator plate (P1) are coupled to the photodetector array. (5), are polished so that the coupling between said faces and the photodetector array is made by a medium of index n less than 1.5, in order to provide a total reflection angle.
    [0005]
    5. Detection system according to claim 1 wherein side faces and an entrance face (1) upland plate (P1) are not coupled to a network of photodetectors (5) and are rough, said faces are processed so that the absorption of the incident photons is maximum. 3036500 19
    [0006]
    6. Detection system according to claim 5 wherein, the input face (1) of the plate P1 not coupled to a photodetector array is painted black in order to suppress the reflection on said face.
    [0007]
    7. Detection system according to claim 1, characterized in that it furthermore comprises a second scintillator plate P2, in that the plate P1 is thinner than the second plate P2 and in that the thickness of the plate the scintillator P1 is such that the gamma photon undergoes a Compton deviation at a point A of said plate P1, in that the second scintillator plate P2 is of a thickness making it possible to absorb at least 50% of the energy of the gamma radiation, said second plate P2 being separated from the plate P1 by a distance 'D' of at least 10 mm, preferably greater than the thickness of the thickest plate, and in that it further comprises a module for estimating a valid event, said module being able to measure on said second plate P2 a coincidence trigger in a time window less than the maximum transfer time of the light between the plates P1 and P2 to identify Compton events val ideas.
    [0008]
    8. Detection system according to one of claims 1 to 7 wherein the fragmented photodetector array (5) is of SI-PM type, and is associated with an analog or digital ASIC.
    [0009]
    9. Detection system according to claims 7 or 8 characterized in that the scintillator plates P1 and P2 are Lutetium silicate type and / or lanthanum halide.
    [0010]
    10. A method for determining the space-time coordinates (X, Y, Z, T) and energy E in at least two successive positions of a Compton-scattered gamma photon implemented in a system according to the invention. one of claims 1 to 9 comprising the steps of: detecting the arrival time Ta of the non-scattered photons emitted by the Compton scattering at a first point A; Detecting the arrival time Tb of the non-scattered photons emitted at a second point B by the total absorption of the gamma photon; 3036500 20 - To determine a circle CA corresponding to the non-scattered photons emitted by the Compton deviation of the gamma radiation at the point A, the diameter of the circle CA makes it possible to measure Xa, Ya and Za; To determine a circle CB corresponding to the non-scattered photons emitted by the total absorption of the gamma photon at point B, the diameter of the circle CB makes it possible to measure Xb, Yb and Zb. the method comprises one of the following three cases: either the photons emitted during the Compton scattering at A and the total absorption at B remain in the same light cone of the non-scattered photons emitted at A, the angle ac <Oc where ac is the Compton deviation and Oc is the critical angle of total reflection and the circle CB is included in the circle CA in this case: - calculate the diameters of the circles CA and CB to measure (Xa, Ya, Za ) and (Xb, Yb, Zb); counting the photon numbers in said circles CA and CB; Defining the energy of a gamma photon, said energies Ea and Eb being proportional to the number of photons counted within said CA and CB circles; either the Compton deflected photon leaves the light cone, ac> Oc, the distance between the points A and B is large and the circles CA and CB are distinct in this case: o determine a first event A corresponding to the most important energy; measuring the coordinates (Xa, Ya, Za, Ta) of said event at A and its energy Ea; determining a second event B corresponding to the lowest energy; measuring the coordinates of the event (Xb, Yb, Zb, Tb) and its energy Eb o The initial energy of the gamma photon is equivalent to the sum of the energies Ea + Eb; o Determine the Compton deviation angle by reconstructing the position of the two interactions 3036500 21 o Deduce the direction of arrival of the gamma photon at the point, from the position of the point A (Xa, Ya, Za), the position of the point B (Xb, Yb, Zb) and energies Ea and Eb; either the Compton deviated photon leaves the cone of light ac> Oc, the distance between points A and B is small and the circles CA and CB are merged o adjust the light distribution by an ellipse of center A, the point B occupies one of the foci, the half minor axis corresponds to the radius RA of the circle CA and the half major axis corresponds to the distance AB + RB, where RB is the radius of the circle CB; o determine the position of the point A (Xa, Ya) given by the center of the ellipse; o determining the interaction depth Za in A which is given by the half-major axis of the ellipse RA; O calculating the time Ta by correcting the times measured with Za; o determine the position of the point B (Xb, Yb) that is given by the focus of the ellipse; o determine the interaction depth Zb in B which is given by RB calculated from the half-major axis of the ellipse: by Distance 20 (A - B) + RB; o calculate the time Tb by correcting the times measured with Zb; o measure the total energy Ea + Eb by integrating the photons on the whole of said ellipse; measuring the centroid of the photon distribution in the ellipse; o determining the initial point of interaction A or B, said initial point is the one which is closest to the center of gravity; o determine the Compton ac deviation angle by reconstituting the position of the two interactions at A and B.
    [0011]
    11. A method for determining the time-space coordinates (X, Y, Z, T) and energy E according to claim 10 further in the case where the circles CA and CB are merged and ac> Oc characterized by the following steps : 3036500 22 o adjust the overall light distribution by a composition of two circles CA and C,; o determining the positions (Xa, Ya) and (Xb, Yb) of the respective interactions at A and B, said positions are given by the center of each circle CA and CB; o determining the depth of the Za and Zb interactions, by determining the diameter of the CA and CB circles; o measuring the total energy Ea + Eb by integrating the photons on the whole of said composition; O to determine the centroid of the global light distribution of photons in the composition of two circles; o determining the initial point of interaction A or B, said initial point is the one which is closest to the center of gravity of the global distribution of light; O determine the Compton ac deviation angle by reconstructing the position of the two interactions at A and B.
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    同族专利:
    公开号 | 公开日
    JP6678687B2|2020-04-08|
    WO2016185123A1|2016-11-24|
    EP3298435A1|2018-03-28|
    FR3036500B1|2017-06-23|
    CN107850677B|2021-08-27|
    US20180217276A1|2018-08-02|
    CN107850677A|2018-03-27|
    US10509134B2|2019-12-17|
    JP2018522216A|2018-08-09|
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    优先权:
    申请号 | 申请日 | 专利标题
    FR1554435A|FR3036500B1|2015-05-18|2015-05-18|SYSTEM AND METHOD FOR DETECTING GAMMA RADIATION OF COMPON CAMERA TYPE.|FR1554435A| FR3036500B1|2015-05-18|2015-05-18|SYSTEM AND METHOD FOR DETECTING GAMMA RADIATION OF COMPON CAMERA TYPE.|
    PCT/FR2016/051150| WO2016185123A1|2015-05-18|2016-05-13|Compton camera system and method for detecting gamma radiation|
    US15/574,721| US10509134B2|2015-05-18|2016-05-13|Compton camera system and method for detecting gamma radiation|
    JP2017560593A| JP6678687B2|2015-05-18|2016-05-13|Compton camera system and method for detecting gamma radiation|
    EP16726366.4A| EP3298435A1|2015-05-18|2016-05-13|Compton camera system and method for detecting gamma radiation|
    CN201680039840.6A| CN107850677B|2015-05-18|2016-05-13|Compton camera system and method for detecting gamma radiation|
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