Device for the Detection of Gamma Rays with Active Partitions

Abstract

The invention relates to a device for the detection of gamma rays (1) coming from a source (2) without image truncation and without image overlapping, comprising, at least, two detection cells (3) and each of said cells comprising a detection space (7) adapted to receive the gamma rays (1) that penetrate through an opening (5), wherein said detection space (7) comprises one or more detection assemblies (8, 8′), with some of said assemblies (8′) being positioned such that they stand in the way of the gamma rays (1) coming into the overlap volume (11) thereof.

Claims

1. A device for the detection of gamma rays (1) coming from a source (2), comprising at least two contiguous detection cells (3), wherein each of said detection cells (3) comprises: a collimation element (4) comprising an opening (5) through which the gamma rays (1) coming from the source (2) can penetrate, defining a cone (6) of incidence; a detection space (7) adapted to receive the gamma rays (1) that penetrate through the opening (5), wherein said detection space (7) comprises one or more gamma ray detection assemblies (8, 8′); and wherein the theoretical projections of the cones (6) of incidence of the gamma rays (1) in two adjacent cells (3) have an overlap volume (11) within the detection space (7); the device being characterized in that at least one of the detection assemblies (8′) is arranged such that it stands in the way of the gamma rays (1) coming into the overlap volume (11).

2. The device according to the preceding claim, wherein one or more detection assemblies (8′) comprise at least one gamma ray blocking surface (12).

3. The device according to the preceding claim, wherein the blocking surface (12) is arranged as a separating partition between the detection cells (3), wherein said partition is in contact on both sides with detection assemblies (8′) of adjacent cells (3).

4. The device according to the preceding claim, wherein the separating partition and/or the detection assemblies (8, 8′) are arranged in a perpendicular or oblique manner with respect to a plane defined by the collimation element (4).

5. The device according to claims 1-2, wherein at least one of the detection cells (3) comprises at least two detection assemblies (8, 8′) arranged with their planes forming an angle with one another, such that the space subtended by said detection assemblies (8, 8′) encompasses the entire cone (6) of incidence of the gamma rays (1).

6. The device according to any of the preceding claims, wherein one or more detection assemblies (8, 8′) comprise one or more reflective elements (13) for guiding the paths of the gamma rays (1).

7. The device according to the preceding claim, wherein at least one of the reflective elements (13) comprises a rough or polished, retro-reflective or diffuse specular reflector or a combination thereof.

8. The device according to any of the preceding claims, wherein one or more detection assemblies (8, 8′) comprise an optically painted surface.

9. The device according to any of the preceding claims, wherein at least one of the detection assemblies (8, 8′) comprises a scintillating material as a gamma radiation-sensitive material (9) and at least one photodetector (10) connected to electronic signal readout and processing means of said photodetector.

10. The device according to the preceding claim, wherein the scintillating material comprises a pixelated solid, a monolithic solid, a liquid, gas or a combination thereof.

11. The device according to any of claims 9-10, wherein each detection cell (3) comprises different scintillating materials.

12. The device according to any of the preceding claims, wherein the photodetector (10) of at least one of the detection assemblies (8, 8′) comprises photomultipliers, avalanche diodes, photodiodes, phototransistors, photo-ICs or a combination thereof.

13. The device according to any of the preceding claims, wherein at least one of the detection assemblies (8, 8′) comprises a solid-state detector and/or a Cherenkov detector.

14. A system for generating images by means of the detection of gamma rays (1), such as in SPECT, characterized in that it comprises one or more devices according to any of the preceding claims, with the electronic signal readout and processing means thereof being connected to a device for reconstructing images from the processing of said signals.

15. The system according to the preceding claim, wherein said system is arranged on a mobile platform adapted to be oriented towards different regions of the source of gamma radiation.

Description

DESCRIPTION OF THE DRAWINGS

[0034] The preceding and other features and advantages will be better understood from the detailed description of the invention, as well as from the preferred embodiments referring to the attached drawings, in which:

[0035] FIG. 1 schematically shows the operation of the two typical gamma camera devices of the state of the art, with parallel hole collimators (left) and with a pinhole collimator (right).

[0036] FIG. 2 shows a known gamma ray detector module, formed by a sensitive material such as a scintillation block (which produces optical photons as a consequence of the interaction of a gamma ray with the material), a photodetector (sensitive to optical photons) and readout electronics (in charge of processing the electronic signals of the photodetector).

[0037] FIG. 3a shows the problem of multiplexing in a multi-pinhole collimator. The incident gamma rays of the source of radiation pass through the openings before reaching the detector. Depending on the geometry, the aperture and inclination of the openings, overlaid regions can be produced in the detector, which prevent unambiguously identifying the opening through which an impacting gamma ray has previously passed.

[0038] FIG. 3b shows a two-dimensional cross section of the overlap problem shown in FIG. 3a.

[0039] FIG. 4 describes in two dimensions the concept of “active partition” of the invention. In said figure, it can be observed how said active partition comprises an additional detector element, which is advantageously placed in the detection space, to prevent the gamma rays from reaching the overlapping area of the contiguous cell. Since said element, in addition to blocking rays, is also a detector, all the necessary information (coordinates of the impact and corresponding opening) can be retrieved as a result of the use of photodetectors and corresponding signal readout electronics.

[0040] FIG. 5 shows a perspective view of a possible embodiment of the device of the invention equipped with four active partitions, a horizontal detector and a pinhole collimator. The main detector furthermore comprises a photodetector equipment and attached electronics. The active partitions may or may not have photodetectors and readout electronics. The cone of incidence schematically shows the area wherein the incident gamma rays can penetrate, due to the geometry and configuration of the pinhole collimator.

[0041] FIG. 6 describes in two dimensions a variation of the device with active partitions of the invention. In this case, the active partitions only have photodetectors and readout and electronics connected directly in the upper part of one of the sides, where said detector may be absent or replaced with a reflective surface. They are furthermore coupled to a horizontal main detector. For each active partition, all its faces (except the one coupled to the main detector and the one coupled to the lateral detector) must comprise reflective elements to prevent the optical photons from being able to escape from the detection cell. By analyzing the impact pattern of said optical photons, it is possible to distinguish whether the interaction has taken place in the main detector or in the active partition, without losing impact information with respect to any of the photons in the cone of incidence.

[0042] FIG. 7a-7b schematically describe a variation of the preceding figure. In this case, the active partitions have photodetectors and readout electronics attached directly on two of their (upper and lower) faces. Furthermore, said active partitions are separated from the main (horizontal) detector. The active partitions can also be inclined a certain angle with respect to the upper collimation element or with respect to the main detector.

[0043] FIG. 8 describes in two dimensions another possible configuration of the active partitions in the device of the invention. In this case, the active partitions are inclined, and the horizontal main detector is not necessary. The retrieved information and the operation of the device are equivalent to those of the preceding configurations.

[0044] FIG. 9 shows a possible second version of the device of the invention, made up of four active partitions and a pinhole collimator, wherein the active partitions are oriented at an angle. Like in the case of FIG. 8, the main detector in this configuration is not necessary, and the active partitions must have photodetectors and attached readout electronics. The cone of incidence in the figure schematically shows the area wherein the rays can penetrate in the detection space of the device, due to the geometry and configuration of the pinhole collimator.

[0045] FIG. 10 shows a possible outer gamma ray shielding casing in a detection system according to the invention, which can be made up of Pb, W or the like, for the purpose of preventing the background noise coming from areas outside the field of view of interest.

REFERENCES NUMBERS USED IN THE DRAWINGS

[0046]

TABLE-US-00001 (1) Gamma ray (2) Source of radiation (3) Detection cell (4) Collimation element (5) Opening (6) Cone of incidence of the gamma rays (7) Detection space (8) Assembly for the detection of gamma rays .sup. (8′) Assembly for the detection (active partition) of gamma rays (9) Gamma radiation-sensitive material (10)  Photodetectors (11)  Overlap volume (12)  Blocking surface (13)  Reflective element (14)  Covering or casing

DETAILED DESCRIPTION OF THE INVENTION

[0047] A detailed description of the invention in reference to different preferred embodiments thereof is described below based on FIGS. 4-10 herein. Said description is provided for the purposes of illustrating but not limiting the claimed invention.

[0048] As described in the preceding sections, the present invention relates to a device with a high-sensitivity and high-resolution multi-pinhole collimator for the detection of gamma rays, with an arbitrarily large FOV, characterized by the fact that it eliminates overlap, without losing information. By means of using active partitions, the detector of the device is capable of obtaining the gamma ray impact coordinates and unequivocally assigning the opening through which said gamma ray has previously passed. With this information, a correct LOR can be constructed for each event and, therefore, all the problems associated with the occurrence of artifacts associated with the overlap and the image truncation associated with the non-overlap are avoided. The gamma ray impact coordinates in the detector of the device can be obtained by means of standard methods such as, for example, by means of the distribution of the number of optical photons produced by a scintillation crystal, the distribution of the electrical charge produced in a semiconductor detector, Cherenkov radiation detection, etc. The depth of interaction (DOI) in the detector of the device can also be obtained with standard methods.

[0049] Preferably and as shown in FIGS. 4-10, the device of the invention allows gamma rays (1) coming from a source (2) of radiation to be detected, wherein said device comprises at least two contiguous detection cells (3), and wherein each of said detection cells (3) comprises: [0050] a collimation element (4) comprising an opening (5) through which the gamma rays (1) coming from the source (2) can penetrate, defining a cone (6) of incidence; [0051] a detection space (7) adapted to receive the gamma rays (1) that penetrate through the opening (5), wherein said detection space (7) comprises one or more detection assemblies (8, 8′), equipped with at least one gamma radiation-sensitive material (9) and at least one photodetector (10) connected to electronic signal readout and processing means of said photodetector (10).

[0052] As seen in FIGS. 4 and 8 herein, the theoretical projections of the cones (6) of incidence of the gamma rays (1) in the two cells (3) have an overlap volume (11) within the detection space (7). Nevertheless, to prevent said overlap of the gamma rays (1) from effectively occurring in said volume (11), the detection assemblies (8′) of the device of the invention are advantageously arranged within the detection space (7), such that they stand in the way of the paths of the gamma rays (1) the projection of which comes into the overlap volume (11) within said detection space. The device could furthermore optionally contain an additional blocking surface (12), made of Pb, W or the like, which prevents the passage of gamma rays (1) into the overlap volume (11). Any overlapping path of the gamma rays (1) is thereby blocked, but at the same time the device is capable of measuring the contribution of all of such rays in the absence of image truncation.

[0053] In a preferred embodiment of the invention shown in FIGS. 4 and 5, the photodetectors are arranged on the separating surface of the detection cells (3) which are in contact with the detection assemblies (8) of adjacent cells (3).

[0054] Preferably, the walls of the detection cells (3) and/or the detection assemblies (8, 8′) comprise one or more reflective elements (13) for guiding the paths of the gamma rays (1). This embodiment is shown schematically in FIG. 6, wherein it can be seen how said reflective elements (13) allow the paths to be guided to the photodetectors (10) of the device, thus complying with the dual function thereof of eliminating any overlapping scenario of the gamma rays (1), but without causing any truncation of the obtained images.

[0055] In another preferred embodiment of the invention, the separating partition and/or the detection assemblies (8, 8′) are arranged in a perpendicular or oblique manner with respect to the plane defined by the collimation element (4), wherein said partition can furthermore be positioned at different distances (d, d′) and at arbitrary angles (θ) with respect to the mentioned element (4). This situation is schematically illustrated in FIGS. 7a-7b herein.

[0056] In another preferred embodiment of the invention, illustrated by FIGS. 8-9, at least one of the detection cells (3) comprises at least two detection assemblies (8, 8′) arranged with their planes forming an angle with one another, such that the space subtended by said detection assemblies (8, 8′) encompasses the entire cone (6) of incidence of the gamma rays (1).

[0057] In different preferred embodiments of the invention, the gamma ray absorption surfaces of the collimators having one or more openings (5) comprise dense materials having suitable thickness such that they are capable of stopping said gamma rays in the energy range of interest, such as Pb or W. Likewise, the geometry and the configuration of the aperture of each opening (5) can have any shape, inclination and radius.

[0058] The sensitive material (9) of the device for detection can be any material producing a measurable physical magnitude when the radiation interacts with said material. Some examples are scintillating, monolithic or pixelated crystals, semiconductors such as Si, Ge, CdTe, GaAs, Pbl2, Hgl2, CZT, etc. for solid-state detectors, xenon for scintillation and Cherenkov radiation detectors, etc. Furthermore, the sensitive materials (9) can be encapsulated or exposed, coupled to an optical reflective surface and/or using any known technique to improve the quality of the collected data. The optical reflective surfaces (13) can be polished or rough, specular, diffuse, retro-reflective or a combination thereof. Likewise, one or more detection assemblies (8, 8)′ can comprise an optically painted surface.

[0059] In a detection system according to the invention, each detector device can be adjacent to another one forming a given assembly, and said assembly can be organized with respect to the other one, for example forming a closed or open structure. The components of a detector system can be identical or different, depending on their specific design conditions.

[0060] A detection assembly (8, 8′) of the device can have an arbitrary shape, and can measure any physical magnitude which provides spatial and/or temporal information of at least one interaction cloud of one or more sensitive materials. Examples of such detection elements are solid-state detectors, scintillation detectors, etc.

[0061] Examples of solid-state detectors are semiconductors such as Si, Ge, CdTe, GaAs, Pbl.sub.2, Hgl.sub.2, CZT or HgCdTe (also known as CTM), Cherenkov radiators such as PbF.sub.2, NaBi (WO.sub.4).sub.2, PbWO4, MgF.sub.2, C.sub.6F.sub.14, C.sub.4F.sub.10 or silica aerogel. Scintillator elements, such as organic or inorganic crystal scintillators, liquid scintillators or gas scintillators can also be used. Scintillators can produce a detection signal which is due both to scintillation processes and to Cherenkov radiation processes.

[0062] Organic crystal scintillators can be, for example, anthracene, stilbene, naphthalene, liquid scintillators (for example, organic liquids such as p-terphenyl (C.sub.18H.sub.14), 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole PBD (C.sub.20H.sub.14N.sub.20), butyl PBD (C.sub.24H.sub.22N.sub.20), PPO (C.sub.15H.sub.11NO), dissolved in solvents such as toluene, xylene, benzene, phenylcyclohexane, triethylbenzene or decalin), gas scintillators (such as nitrogen, helium, argon, krypton, xenon), inorganic crystal scintillators, or combinations of any of the foregoing.

[0063] The commonly known inorganic scintillation crystals can be, for example, cesium iodide (CsI), thallium doped cesium iodide (CsI (Tl)), bismuth germanate (BGO), thallium doped sodium iodide (NaI (Tl)), barium fluoride (BaF.sub.2), europium doped calcium fluoride (CaF.sub.2(Eu)), cadmium tungstate (CdWO.sub.4), cerium doped lanthanum chloride (LaCb(Ce)), cerium doped lutetium-yttrium silicates (LuYSiOs(Ce)(YAG (Ce)), silver doped zinc sulfide (ZnS(Ag)) or cerium (III) doped yttrium-aluminum granite Y.sub.3Al.sub.5O.sub.12 (Ce) or LYSO. Additional examples are CsF, KI(TI), CaF.sub.2(Eu), Gd.sub.2SiO.sub.5[Ce] (GSO), LSO.

[0064] As mentioned above, the scintillators according to the present invention can be monolithic crystals or pixelated crystals, or any combination thereof. Preferably, the scintillator, however, will be a single-crystal (monolithic block), given that pixelated crystals introduce more dead areas into the gamma ray detector, therefore providing less sensitivity to the detector device compared with single-crystals.

[0065] The device for detection (of scintillating photons) can be formed, for example, by photosensors. The photosensors can be matrices of silicon photomultipliers (SiPM), single-photon avalanche diodes (SPAD), digital SiPMs, avalanche photodiodes, position-sensitive photomultipliers, photomultipliers, phototransistors, photodiodes, photo-ICs or combinations thereof. This means that a detector device can be coupled, for example, to a SiPM matrix and another detector device can be coupled to a matrix of phototransistors in a detection system according to the preceding definitions.

[0066] In other embodiments of the invention, it is also possible to use multiple photodetectors (10) to provide a single data matrix. If a detector element is not large enough to cover a desired surface, it is possible to arrange two or more detectors in a matrix and combine their readouts to obtain a larger data matrix. The data matrix can be expressed using any desired coordinate system (Cartesian, cylindrical, spherical, etc.).

[0067] Another object of the present invention relates to a system for generating images by means of the detection of gamma rays, comprising one or more devices according to any of the embodiments described herein. In said system, the electronic signal readout and processing means of the photodetectors (10) are preferably connected to a device for reconstructing images from the processing of said signals. An example of said system is schematically depicted in FIG. 10, wherein it can be seen how the system is configured with five collimation openings (5), associated with their respective collimation cells (3) (not shown in the figure), said cells being protected by a covering or casing (14) which preferably absorbs gamma radiation.

[0068] In a preferred embodiment of the system of the invention, the system can be arranged on a mobile platform adapted to be oriented towards different regions of the source (2) of gamma radiation.