Imaging detector system for gamma radiation using unidirectional and bidirectional Compton scattering processes

Abstract

A device for generating one or more images of a source distribution of a gamma radiation field in the near and far field can include a detector system that includes several synchronized detectors for detecting radiation, system electronics that registers coincidence events, a data acquisition system that stores the measurement data of the coincidence events, and an analysis unit that performs an image reconstruction, which reconstructs one or more images of the source distribution of the radiation field.

Claims

1. A device for generating one or more images of a source distribution of a gamma radiation field in a near field and a far field, comprising: a detector system comprising a group of several synchronized detectors for detection of radiation, wherein at least one detector material has an atomic number of Z.sub.eff>30 and all detectors measure energies E and interaction points d, which occur in interactions of radiation with detector materials of the detectors, wherein the detector materials are segmented virtually and physically into voxels; a system electronics configured to register one or more coincidence events in response to interactions occurring in at least two detector voxels from a list of defined voxel pairs simultaneously; wherein a list of defined voxel pairs comprises all pairs which are formed in combination from all the detector voxels, and the defined voxel pairs comprise at least one detector voxel made from the detector material having the atomic number of Z.sub.eff>30; a data acquisition system configured to store the measurement data of the one or more coincidence events and determine a ranking for both detector voxels involved in each coincidence event, which defines a first detector voxel and a second detector voxel; wherein in each defined voxel pair, the voxel having the lower atomic number receives the number 1, and that one having the higher atomic number receives the number 2; wherein in case both detector voxels of a pair should have the same atomic number, the indication of 1 and 2, respectively, is made arbitrarily, the data acquisition system configured to sort the energies (E.sub.1, E.sub.2) measured in the coincidence events and the interaction points (d.sub.1, d.sub.2) corresponding to their indication 1, 2, and stores them in a chronological list together with the attributes y={d.sub.1, E.sub.1, d.sub.2, E.sub.2} and the detector time t; and an analysis unit connected to the data acquisition system, the analysis unit configured to generate projection data p(y) from the stored measurement data, which are defined as a function of the attributes y={d.sub.1, E.sub.1, d.sub.2, E.sub.2}, wherein a function σ(E.sub.1,E.sub.2) is applied, which is dependent on two energy values (E.sub.1, E.sub.2), and this function σ(E.sub.1,E.sub.2) when substituting E.sub.2 by C−E.sub.1 is traceable to a function σ(E.sub.1), which over an entire interval [0, C] is clearly defined, constant, and monotonous, wherein C is a constant, which represents a radiation energy C=E.sub.1+E.sub.2; and the analysis unit is configured to perform an image reconstruction that reconstructs one or more images ƒ (x) of the source distribution of the radiation field from the projection data p(y).

2. The device according to claim 1, wherein the detector system detects radiation fields, which have a discrete and/or a continuous distribution of radiation, wherein the detector system is located in a geometrical near field and/or far field of the radiation field; and/or that the radiation sources emit gamma, electron, positron, proton, ion and/or neutron radiation; and/or that the radiation originates from the radioactive decay of one or more radio nuclides; and/or that the radiation is the prompt gamma radiation, which is generated during the absorption of proton or ion radiation in target materials; and/or that the radiation is of low intensity, as for example, in astronomy.

3. The device of claim 2, characterized in that the detectors comprise: a scintillator with a photodetector and/or a semiconductor material; and/or that the scintillator comprises a pure or a doped material from the group of PVT, anthracene, stilbene, p-terphenyl, CaF.sub.2, BaF.sub.2, NaI, CeBr.sub.3, LaBr.sub.3, LaCl.sub.3, La(Br.sub.xCl.sub.1−x).sub.3, CsI, SrI.sub.2, CLYC, CLBC, CLCB, CLLB, BGO, LSO, LYSO, GAGG, YAP and/or YAG; and/or that the scintillator is present as a monolithic block or as pixelated scintillator module; and/or that the photodetector is a photomultiplier (PMT), a photomultiplier with location resolution (PSPMT), a silicon photomultiplier (SiPM), a silicon photomultiplier with location resolution (PS-SiPM) and/or a silicon photodiode; and/or that the semiconductor material comprises a material from the group of Si, Ge, GaAs, CdTe and/or CdZnTe; and/or that the semiconductor material has a planar or coaxial geometry and/or is available with segmented or unsegmented contacts; and/or that the scintillator and the semiconductor material, respectively, are subdivided virtually or physically into an arbitrary integer number of ≥1 voxels.

4. The device according to claim 3, wherein: the system electronics uses analog and/or digital electronic components; and/or that the analog electronic components comprise a combination of various modules, which comprise a high-voltage supply, a preamplifier, an amplifier, a pulse shaper, a charge integrator, a pulse height analyzer, a multichannel analyzer (MCA) and/or a coincidence circuit; and/or that the digital electronic components comprise a combination of various hardware and software components, which comprise a high-voltage supply, an A/D converter per detector voxel, a Field Programmable Gate Array (FPGA), a storage medium, a digital signal processor, and/or the analysis software.

5. The device of claim 4, wherein: the interaction points (d.sub.1, d.sub.2) are determined on the basis of the location resolving properties of the detectors, and/or on the basis of the available segmentation of the detectors; and/or that the interaction points (d.sub.1, d.sub.2) are defined as the spatial centers of a first and a second detector voxel of the detector voxels involved in a coincidence event; and/or that the functional value σ(E.sub.1,E.sub.2) is defined according to:
σ(E.sub.1,E.sub.2)=(E.sub.2−E.sub.1)/(E.sub.1+E.sub.2)

6. The device of claim 1, wherein: the analysis unit reconstructs the radiation field using projection data p(y) which is defined as a function of the attributes y={d.sub.1, E.sub.1, d.sub.2, E.sub.2}; and/or that for each element of p, a number of coincidence events is determined, which occur at a respective combination of a particular first detector voxel with a particular second detector voxel at a particular functional value σ(E.sub.1,E.sub.2); and/or that for each element of p, a number of coincidence events is determined, which occurs at a respective combination of a particular first detection location d.sub.1 with a particular second detection location d.sub.2 at a particular functional value σ(E.sub.1,E.sub.2).

7. The device of claim 1, wherein a selection condition for coincidence events is applied with respect to the energy sum E.sub.1+E.sub.2 of the energies detected in both detector voxels of a pair; and/or that separate projection data p(y) is created for each detected radio nuclide; and/or that the analysis unit is configured to calculate a separate image ƒ(x) for each radio nuclide.

8. The device of claim 1, wherein: the images ƒ(x) represent an activity density, a flux density, and a dose rate density, respectively; and/or the images ƒ(x) are tomographic sectional images of an activity distribution of radio nuclides (for example, also radiopharmaceuticals).

9. The device of claim 1, wherein all the detectors have a same design, or that at least two of the detectors have a design different from each other.

10. The device according to claim 1, wherein: the detector system comprises at least four detector voxels in a substantially three-dimensional arrangement, and has a field of vision with a 4π spatial angle; or that the detector system comprises at least three detector voxels in a substantially two-dimensional arrangement, and has a hemispherical field of vision with a a 2π spatial angle; or that the detector system comprises at least three detector voxels in a substantially two-dimensional arrangement, and has a 360° field of vision in the plane of the radiation detectors; or that the detector system comprises at least two detector voxels in a one-dimensional detector row, and has a 180° field of vision from −90° to +90° perpendicular to the detector row.

11. The device of claim 1, wherein the detector system comprises a first group of detectors/voxels having an atomic number of Z.sub.eff>30, which have high probabilities for photoelectric absorption in the energy range from 100 keV to 3 MeV.

12. The device of claim 10, also comprising a second group of detectors/voxels having an atomic number of Z.sub.eff≤30, which have high probabilities for Compton radiation in the energy range from 100 keV to 3 MeV.

13. The device of claim 12, wherein: data is acquired from all detector pairs/voxel pairs, which may be formed in combination from the quantity of all detectors/voxels, wherein such detector pairs/voxel pairs are excluded, in which both detectors/voxels belong to the second group having an atomic number of Z.sub.eff≤30; and/or the mixed detector pairs/voxel pairs, which comprise the respectively one detector/voxel from the first group and one detector/voxel from the second group, are unidirectional, wherein the radiation predominantly is scattered in one direction; and/or the detector pairs/voxel pairs of the first group having an atomic number of Z.sub.eff>30 are bidirectional, wherein the radiation is scattered in both directions with a similar intensity.

14. The device of claim 1, wherein: an entirety of the detectors/voxels, which are comprised in the detector system, comprises a first homogeneous or heterogeneous annular, tubular, cylindrical, spherical, and/or polyhedral shape; and/or that the entirety of the detectors/voxels, which are comprised in the detector system, in addition to the first shape, comprise a second homogeneous or heterogeneous annular, tubular art, cylindrical, spherical, and/or polyhedral shape, and wherein the second shape is inscribed within the first shape, or wherein the second shape is arranged in an internal region, which is enclosed by the first shape as an outer shell; and/or wherein the first and/or the second shape are arranged around one or more central detectors.

15. The device of claim 1, wherein a part of the system or the entire system is configured as a locating device for radiation sources, as a Compton camera, as a Compton telescope, as a SPECT scanner, as a PET/SPECT hybrid scanner, as a SPECT sensor, and/or as a PET/SPECT hybrid sensor.

16. A method for the use of a device for generating one or more images of a source distribution of a gamma radiation field a, wherein the detector materials are segmented into voxels virtually and physically, wherein the method uses unidirectional and bidirectional Compton scattering processes and has a system matrix H, a defined functional value σ(E.sub.1,E.sub.2) and a list of defined voxel pairs, and is adapted for the acquisition of projection data p(y) of the measurement values and for the calculation of image data ƒ(x), the method comprising: creating a list with defined voxel pairs, wherein the defined voxel pairs comprise all pairs, which may be formed in combination from the quantity of the detector voxels, and wherein each pair comprises at least one detector voxel made from a material having an atomic number of Z.sub.eff>30; interconnecting all detectors/voxels in a coincidence circuit such that coincidence events are acquired in all defined voxel pairs; indicating the two detector voxels of each voxel pair with the numbers 1 and 2, respectively, wherein the detector voxel having the lower atomic number receives the number 1, and that one having the higher atomic number receives the number 2, wherein if both detectors voxels consist of the same material, the indication is made arbitrarily; defining a function σ(E.sub.1, E.sub.2) which is calculated from to energy values (E.sub.1, E.sub.2), wherein such functions σ(E.sub.1, E.sub.2) are allowable, which are traceable when substituting E.sub.2 by C−E.sub.1 to a function σ(E.sub.1), which for the entire interval [0, C] is clearly defined, constant, and monotonous; hereby, C is a constant, which represents the radiation energy C=E.sub.1+E.sub.2; acquiring measurement values y={d.sub.1, E.sub.1,d.sub.2, E.sub.2} of coincidence events, if interactions take place in respectively two detector voxels of all defined voxel pairs, wherein the measurement values originate from a radiation near field or far field, and the measurement values are the energies (E.sub.1, E.sub.2) measured in the detector voxels and the interaction points (d.sub.1, d.sub.2), associating coincidence events y={d.sub.1, E.sub.1, d.sub.2, E.sub.2} with a first detector voxel/detection location d.sub.1 and a second detector voxel/detection location d.sub.2; calculating the functional value σ(E.sub.1, E.sub.2) from two energy values (E.sub.1, E.sub.2) per coincidence event; acquiring the coincidence events corresponding to their first two detector voxel d.sub.1, their second detector voxel d.sub.2 and their σ(E.sub.1, E.sub.2) value in an element of the projection data p(y), wherein separate projection data p(y) is required for each radio nuclide; calculating one or more images ƒ(x) from the projection data p(y) by means of a statistical image reconstruction method of emission tomography using the system matrix H, wherein a separate image ƒ(x) is calculated for each radio nuclide; wherein the images ƒ(x) represent an activity distribution in a source volume or a flux density distribution over the directions of incidence.

17. The method of claim 16, comprising at least one of: calibrating the signals of all detector voxels as absorbed radiation energy E; determining a suitable coordinate system; subdividing the measurement area for the functional value σ(E.sub.1,E.sub.2) into equidistant measurement value channels; creating one or more projection data sets p(y), which acquire the numbers of coincidence events, which are counted for a respective combination of a particular first detector voxel d.sub.1 with a particular second detector voxel d.sub.2 at a particular functional value σ(E.sub.1, E.sub.2), wherein a separate projection data set p(y) is created for each radio nuclide; creating one or more system matrixes H for each radio nuclide to be detected; creating and validating the system matrixes H by means of measurements using the detector system, or by means of Monte Carlo simulations or by means of a theoretical model; and transferring all system matrixes H to an algorithm of the image reconstruction, which processes the projection data p(y) and calculates the images ƒ(x).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention and exemplary embodiments thereof will be described below in further detail in connection with the drawings. It should be understood that like reference characters used in the drawings may identify like components. In the drawings:

(2) FIG. 1 shows an exemplary classification scheme for imaging detector systems into type A separated, type A mixed, and type B, according to three embodiments of the imaging detector system according to the invention;

(3) FIG. 2a is a schematic illustration that is not to scale of an exemplary annular detector system of type A separated according to an embodiment of the imaging detector system.

(4) FIG. 2b is a schematic illustration that is not to scale of an exemplary annular detection system of type A mixed according to an embodiment of the imaging detector system;

(5) FIG. 2c s a schematic illustration that is not to scale of an exemplary annular detection system of type B according to an embodiment of the imaging detector system according to the invention;

(6) FIG. 3 is a schematic illustration that is not to scale of an exemplary detector system of two detectors with components of the system electronics according to an embodiment of the imaging detector system according to the invention;

(7) FIG. 4a is a schematic illustration that is not to scale of an exemplary detector system of two detectors according to the invention;

(8) FIG. 4b is a schematic illustration that is not to scale of the data acquisition of an exemplary detector system of two detectors according to an embodiment of the imaging detector system according to the invention;

(9) FIG. 5a is a schematic illustration that is not to scale for the selection and identification of a first detector pair P1 in the detector system of FIG. 5d according to an embodiment of the imaging detector system according to the invention;

(10) FIG. 5b is a schematic illustration that is not to scale for the selection and identification of a second detector pair P2 in the detector system of FIG. 5d according to an embodiment of the imaging detector system according to the invention;

(11) FIG. 5c is a schematic illustration that is not to scale for the selection and identification of a third detector pair P3 in the detector system of FIG. 5d according to an embodiment of the imaging detector system according to the invention;

(12) FIG. 5d is a schematic illustration that is not to scale for the selection and identification of detector pairs using the example of a detector system of three detectors according to an embodiment of the imaging detector system according to the invention;

(13) FIG. 6a is a schematic illustration it is not to scale of an exemplary detector system of three detectors according to the invention;

(14) FIG. 6b is a schematic illustration that is not to scale of the data acquisition of an exemplary detector system of three detectors according to an embodiment of the imaging detector system according to the invention;

(15) FIG. 7a is a schematic illustration that is not to scale for the selection and identification of detector pairs in a first direction P1 in the detector system of FIG. 7e according to an embodiment of the imaging detector system according to the invention;

(16) FIG. 7b is a schematic illustration that is not to scale for the selection and identification of detector pairs of a second direction P2 in the detector system of FIG. 7e according to an embodiment of the imaging detector system according to the invention;

(17) FIG. 7c is a schematic illustration that is not to scale for the selection and identification of detector pairs in a third direction P3 in the detector system of FIG. 7e according to an embodiment of the imaging detector system according to the invention;

(18) FIG. 7d is a schematic illustration that is not to scale for the selection and identification of detector pairs in a fourth direction P4 in the detector system of FIG. 7e according to an embodiment of the imaging detector system according to the invention;

(19) FIG. 7e is a schematic illustration that is not to scale for the selection and identification of detector pairs using the example of a detector system of four detectors according to an embodiment of the imaging detector system according to the invention;

(20) FIG. 8a is a schematic illustration that is not to scale of an exemplary detector system of four detectors according to the invention;

(21) FIG. 8b is a schematic illustration that is not to scale of the data acquisition of an exemplary detector system of four detectors according to an embodiment of the imaging detector system according to the invention;

(22) FIG. 9a is a schematic illustration that is not to scale of a 2-plane Compton camera according to an embodiment of the prior art;

(23) FIG. 9b is a schematic illustration that is not to scale of a 2-plane Compton camera, which is configured as an imaging detector system of type A separated according to an embodiment of the imaging detector system according to the invention;

(24) FIG. 10a is a schematic illustration that is not to scale of a two-dimensional detector system with hemispherical field of vision according to an embodiment of the imaging detector system according to the invention;

(25) FIG. 10b is a schematic illustration that is not to scale of a two-dimensional detector system with a 360° field of vision in the detector plane according to an embodiment of the imaging detector system according to the invention;

(26) FIG. 11a is a schematic illustration that is not to scale of a fully spherical detector system of type A according to an embodiment of the imaging detector system according to the invention;

(27) FIG. 11b is a schematic illustration that is not to scale of a fully spherical detector system of type B according to an embodiment of the imaging detector system according to the invention;

(28) FIG. 12a is a schematic illustration that is not to scale of a two-dimensional detector system of type A according to an embodiment of the imaging detector system according to the invention;

(29) FIG. 12b is a schematic illustration that is not to scale of a cube-shaped detector system of type A according to an embodiment of the imaging detector system according to the invention;

(30) FIG. 12c is a schematic illustration that is not to scale of a tetrahedron-shaped detector system of type A according to an embodiment of the imaging detector system according to the invention;

(31) FIG. 13a is a schematic illustration that is not to scale of a tetrahedron-shaped detector system of type B according to an embodiment of the imaging detector system according to the invention;

(32) FIG. 13b is a schematic illustration that is not to scale of a cube-shaped detector system of type B according to an embodiment of the imaging detector system according to the invention;

(33) FIG. 14 is a diagram with simulation results for detector pairs of a cerbromide and a plastic detector according to an embodiment of the imaging detector system according to the invention;

(34) FIG. 15 is a diagram with simulation results for detector pairs of two cerbromide detectors according to an embodiment of the imaging detector system according to the invention;

(35) FIG. 16a-c are three diagrams with simulation results for cerbromide-plastic and cerbromide-cerbromide detector pairs according to an embodiment of the imaging detector system according to the invention;

(36) FIG. 16a is a graph comparing the simulation results for cerbromide-plastic and cerbromide-cerbromide detector pairs for a scintillator thicknesses of 25 mm;

(37) FIG. 16b is a graph comparing the simulation results for cerbromide-plastic and cerbromide-cerbromide detector pairs for a scintillator thicknesses of 50 mm;

(38) FIG. 16c is a graph comparing the simulation results for cerbromide-plastic and cerbromide-cerbromide detector pairs for a scintillator thicknesses of 75 mm;

(39) FIG. 17 is a schematic illustration that is not to scale of a measurement set up for the one-dimensional detector system from two radiation detectors according to an embodiment of the imaging detector system according to the invention;

(40) FIG. 18 is a diagram with measurement results for the two detector arrangement for direction measurement of a Co-60 source shown in FIG. 17 according to an embodiment of the imaging detector system according to the invention;

(41) FIG. 19 is a diagram with measurement results for the two-detector arrangement for direction measurement of a Cs-137 source shown in FIG. 17 according to an embodiment of the imaging detector system according to the invention.

DETAILED DESCRIPTION

(42) FIG. 1 shows an exemplary classification scheme for detector systems of type A and type B. Type A detector systems may be further differentiated according to the spatial arrangement of the detectors into type A separated and type A mixed.

(43) FIGS. 2a-c illustrate exemplary classification schemes of FIG. 1 using the example of annular detector systems. With respect to the arrangement type A separated, the detectors of lower atomic number form an outer ring around an inner central detector of medium to high atomic number. In the arrangement type A mixed, there is no central detector, each detector in the ring is surrounded by two detectors of the respectively other group. The arrangement of type B is a ring of similar detectors, in which all detectors consist of a material of medium to high atomic number.

(44) FIG. 3 shows a block diagram with an embodiment of the system electronics for the detector system made up by two detectors. The detector pairs shown consists of two detectors of medium to high atomic number. The radiation flux between the detectors is bidirectional.

(45) FIG. 4 schematically illustrates the exemplary data acquisition using the example of a detector system made up of two detectors of medium to high atomic number. FIG. 4a shows the detector system with the detector pair P1. FIG. 4b shows the data acquisition for the detector system of FIG. 4a. The number of coincidence events, which are registered at a particular value of a function σ(E.sub.1, E.sub.2) that is dependent on both energy values E.sub.1 and E.sub.2 is determined for the detector pair P1. The table shown in FIG. 4b is a tabular illustration of the projection data p(y) according to the invention.

(46) FIG. 5 schematically illustrates an exemplary embodiment of the selection and identification of detector pairs using the example of a detector system made up by three detectors of medium to high atomic number. The detector system illustrated in FIG. 5 comprises three bidirectional detector pairs P1, P2, and P3. FIG. 5a, 5b and Sc show examples for the identification of the detectors of a first pair P1 (FIG. 5a), a second pair P2 (FIG. 5b), and a third pair P3 (FIG. 5c) with the numbers 1 and 2, respectively.

(47) FIG. 6 schematically illustrates the exemplary process for data acquisition using the example of the detector system from FIG. 5. FIG. 6a shows the detector system with three detector pairs P1, P2, and P3. FIG. 6b shows the data acquisition for the detector system in FIG. 6a. For each detector pair P1, P2, and P3, the number of coincidence events is determined, which are registered at a particular value of a function σ(E.sub.1, E.sub.2) that is dependent on both energy values E.sub.1 and E.sub.2. The table shown in FIG. 6b is a tabular illustration of the projection data p(y) according to this invention.

(48) FIG. 7 schematically illustrates an exemplary selection and identification of detector pairs using the example of a detector system made up by four detectors of medium to high atomic number. The detector system illustrated in FIG. 7 comprises six bidirectional detector pairs. For embodiments of the invention in the far field, it is sufficient to select for directions P1, P2, P3 and P4. In the horizontal and in the vertical directions, there are two detector pairs respectively, which have the same direction. In the far field, both horizontal detector pairs may be detected together in the direction P1, as well as those vertical detector pairs may be detected together in the direction P2. FIGS. 7a, 7b, 7c and 7d show examples from the identification of the detectors of a first direction P1 (FIG. 7a), a second direction P2 (FIG. 7b), the third direction P3 (FIG. 7c), and a fourth direction P4 (FIG. 7d) having the numbers one and two, respectively.

(49) FIG. 8 schematically illustrates an exemplary embodiment of data acquisition using the example of the detector system of FIG. 7. FIG. 8a shows the detector system with four detector pairs P1, P2, P3, and P4. FIG. 8b shows the data acquisition for the detector system in FIG. 8a. For each of the four directions P1, P2, P3, and P4, the number of coincidence events is determined, which are registered at a particular value of a function σ(E.sub.1, E.sub.2) that is dependent on both energy values E.sub.1 and E.sub.2. The table shown in FIG. 8b is a tabular illustration of the projection data p(y) according to this invention.

(50) FIG. 9a schematically illustrates the extension of a 2-plane Compton camera to an imaging detector system of type A separated according to exemplary embodiments of the invention. The 2-plane Compton camera shown in FIG. 9a with eight detectors comprises 16 unidirectional detector pairs.

(51) FIG. 9b schematically illustrates an exemplary embodiment in which four detectors of the rear detector plane may be combined into 6 bidirectional detector pairs, as illustrated in FIG. 9b. In a detector system of type A separated, the data of 16 unidirectional and 6 bidirectional detector pairs may be acquired and processed together. The image reconstruction methods of the 2-plane Compton camera may be extended correspondingly, in order to integrate the additional data sets of the rear type B detector plane into the image reconstruction. By the adjustment, the number of detector pairs increases from 16 to 22, whereby the efficiency and the image quality of the 2-plane Compton camera are increased.

(52) FIGS. 10a-10b schematically shows two use variants for detector systems with a two-dimensional arrangement of the detectors. In FIG. 10a, the exemplary two-dimensional detector system is illustrated as a hemispherical detector system, in FIG. 10b, the system is illustrated as an exemplary 360° panoramic system. The panoramic system of FIG. 10b, serves for measurement of two-dimensional direction distributions in the detector plane. The change of perspective may be effected by adjusting the image reconstruction method.

(53) FIG. 11a-11b shows a schematic illustration of two fully spherical detector systems.

(54) The fully spherical detector system of type A shown in FIG. 11a has the shape of a hexagon made up by six external detectors, which are grouped around two inner detectors. The detector system comprises twelve unidirectional detector pairs made up by respectively one inner and one outer detector. The two inner detectors additionally form a bidirectional detector pair. This thirteenth detector pair made up by the two inner detectors supplies additional information on the height angle of the radiation sources.

(55) FIG. 11b shows a schematic illustration of a fully spherical detector system of type B. The sixth detectors, which are arranged as an octahedron, may be combined into 15 bidirectional detector pairs.

(56) FIG. 12a-c shows a further detector variant of type A.

(57) The two-dimensional detector system illustrated in FIG. 12a schematically illustrates an embodiment that consists of three inner detectors of higher atomic number and six out of detectors of lower atomic number. They form a triangle in a hexagon. This yields 18 unidirectional and 3 bidirectional detector pairs (21 detector pairs in total).

(58) FIG. 12b schematically illustrates an embodiment that shows a cube shaped detector system. Four corners of the cube are occupied by detectors of high atomic number, these together form a tetrahedron. The tetrahedron made up by four detectors of high atomic number yields six bidirectional detector pairs. Additionally, incident radiation is also scattered from the four detectors of lower atomic number onto respectively four detectors of high atomic number, whereby 16 further unidirectional detector pairs are added. In total, 22 detector pairs are available.

(59) FIG. 12c schematically illustrates an exemplary embodiment that consists of a small tetrahedron, which is surrounded by a larger tetrahedron. The inner tetrahedron comprises four detectors of high atomic number, the outer tetrahedron comprises four detectors of low atomic number. The four detectors of high atomic number respectively are located at the face centers of the four lateral surfaces of the outer tetrahedron. The smaller tetrahedron made up by the detectors of high atomic number has a third of the lateral length of the enclosing outer tetrahedron. The “tetrahedron in tetrahedron” has 16 unidirectional and 6 bidirectional detector pairs (22 detector pairs in total).

(60) FIGS. 13a-b shows further variants for detector systems of type B. In FIG. 13a, an arrangement of four detectors in form of a tetrahedron with six bidirectional detector pairs is illustrated. The detector cube in FIG. 13b consists of eight detectors with 28 bidirectional detector pairs.

(61) FIG. 14 shows simulation results for unidirectional detector pairs with a cerbromide and a plastic detector. The diagram illustrates the influence of the scintillator thickness on the interaction probabilities for Compton single scattering P.sub.CSS in plastic scintillators and the photoelectric effect P.sub.PE in cerbromide crystals. The curves show the maximum probability P.sub.CSS.sup.max=Max(P.sub.CSS) and the maximum total probability P.sub.ges.sup.max=Max(P.sub.CSS.Math.P.sub.PE) as a function of the gamma energy assuming that both scintillators have the same dimension. In the energy range from 140 keV to 1400 keV, P.sub.CSS.sup.max always is above 20%, presumed that the scintillator thickness has been selected optimally. Moreover, it is illustrated at which scintillator thickness the maximum total probability P.sub.ges.sup.max is reached.

(62) FIG. 15 shows simulation results for bidirectional detector pairs of two cerbromide detectors. It is shown, which interaction probabilities for Compton single scattering P.sub.CSS.sup.max=Max(P.sub.CSS) and which total probabilities P.sub.ges.sup.max=Max(2.Math.P.sub.CSS.Math.P.sub.PE) may be achieved under optimum conditions. Below 300 keV, P.sub.CSS.sup.max decreases rapidly. In the energy range from 662 to 1332 keV, on the other hand, P.sub.CSS.sup.max is nearly constant at 18.5%. The curve for optimum scintillator thickness shows the thickness, at which—depending on the energy of the incident radiation—the maximum total probability P.sub.ges.sup.max is reached.

(63) FIG. 16a is a graph comparing the simulation results for cerbromide-plastic and cerbromide-cerbromide detector pairs for a scintillator thicknesses of 25 mm. For cerbromide-plastic detector pairs, the total probability is calculated by P.sub.ges=P.sub.CSS.Math.P.sub.PE, for cerbromide-cerbromide detector pairs by P.sub.ges=2.Math.P.sub.CSS.Math.P.sub.PE.

(64) FIG. 16b is a graph comparing the simulation results for cerbromide-plastic and cerbromide-cerbromide detector pairs for a scintillator thicknesses of 50 mm. For cerbromide-plastic detector pairs, the total probability is calculated by P.sub.ges=P.sub.CSS.Math.P.sub.PE, for cerbromide-cerbromide detector pairs by P.sub.ges=2.Math.P.sub.CSS.Math.P.sub.PE.

(65) FIG. 16c is a graph comparing the simulation results for cerbromide-plastic and cerbromide-cerbromide detector pairs for a scintillator thicknesses of 75 mm. For cerbromide-plastic detector pairs, the total probability is calculated by P.sub.ges=P.sub.CSS.Math.P.sub.PE, for cerbromide-cerbromide detector pairs by P.sub.ges=2.Math.P.sub.CSS.Math.P.sub.PE.

(66) FIG. 17 shows a schematic illustration for a measurement setup with a 1-dimensional detector system made up by two radiation detectors. The measurement setup may be realized as unidirectional or as bidirectional detector system. The field of vision of the detector system is limited to a semicircle.

(67) FIG. 18 shows measurement results for the two-detector-arrangement shown in FIG. 17 for direction measurement of a Co-60 source. The minimum measurement time for an accuracy of the angle of ±10° is illustrated as a function of the angle of incidence, measured in two detector variants with a cerbromide-cerbromide and a cerbromide-plastic detector pair. The local dose rate of the Co-60 source (10 μCi) was 0.11 μSv/h at the measurement point.

(68) FIG. 19 shows measurement results for the two-detector-arrangement shown in FIG. 17 for direction measurement of a Cs-137 source. The minimum measurement time for an accuracy of the angle of ±10° is illustrated as a function of the angle of incidence, measured in two detector variants with a cerbromide-cerbromide and a cerbromide-plastic detector pair. The local dose rate of the Cs-137 source (10 μCi) was 0.03 μSv/h at the measurement point.

(69) In the following, various imaging detector systems are described in detail in concrete embodiments. Examples of these are explained in the accompanying drawings. The detector systems presented here have been developed for the direction measurement of radiation sources in the far field. The detector systems use radiation detectors without local information concerning the interaction point. The image reconstruction methods are suitable for 2-dimensional and for the 3-dimensional direction measurement with stationary or almost stationary measurement conditions.

(70) At first, various embodiments for 3-dimensional detector topologies will be presented. The detectors of a detector system of type B may be arranged, e. g., at the corner points of a polyhedron (FIGS. 11b and 13). In most cases, the polyhedron preferably will be convex.

(71) With respect to a detector system of type A mixed, the detector shell may also be formed as a polyhedron. Detectors having a low and a high atomic number are distributed heterogeneously over the polyhedron.

(72) Selected corners of a type A mixed system in form of a polyhedron may be occupied with detectors of a high atomic number such that inscribed polyhedrons are created. For example, FIG. 12b shows a cube-shaped detector arrangement of type A mixed. Four cube corners are occupied by detectors of high atomic number. They together form a type B detector system having the shape of a tetrahedron.

(73) Detector systems of type A separated may be designed as polygons or polyhedrons of detectors having a low atomic number. In their interior, there is a group of detectors of high atomic number. The detector system shown in FIG. 11a comprises two inner detectors that are arranged one above the other, around which six ring detectors are grouped. It also is possible that the inner core of detectors having a high atomic number forms a small polyhedron within an outer polyhedron made up from detectors of low atomic number (FIGS. 12a and 12c).

(74) A detector material suitable for imaging detector systems for some embodiments of the system is the scintillator material cerbromide. Having an effective atomic number Z.sub.eff of 45.9, it is well suited as an absorbing detector material in unidirectional pairs as well as a scattering and absorbing material in bidirectional pairs, too. Cerbromide crystals have a density of 5.1 g/cm.sup.3. Typical values for the energy resolution are lying within the range from 3.8% to 4.2% at 662 keV. With a decay time (1/e) of approximately 20 ns, coincidences may be detected with a time resolution of a few nanoseconds.

(75) In the following, two embodiments for detector pairs will be presented by means of specific material combinations. Each one of the detector pairs shown here respectively comprises a cerbromide crystal. If the cerbromide crystal is combined with a plastic scintillator, a unidirectional detector pair is created. By forming pairs of respectively two cerbromide crystals, bidirectional detector pairs are created.

(76) For the dimensioning of the detectors, the interaction probabilities of the detector materials in the energy range, in which the device is to be used, has to be taken into consideration. For the gamma energies of Cs-137 and Co-60, the corresponding probabilities for cerbromide crystals and plastic scintillators are listed in Tab. 2 and 3. Detector planes with thicknesses of 1″, 2″, or 3″ and infinite lateral extension have been considered. The specifications for simple scattering are referred to events, in which the gamma radiation has been scattered one time, before leaving the scintillator through the front or rear side.

(77) TABLE-US-00002 TABLE 2 Cerbromide-plastic detector pair (respectively one plane) Probability P.sub.CSS for single scattering Probability P.sub.PE for (excluding multiple photoelectric Total probability nuclide scatterings) absorption P.sub.ges = P.sub.CSS .Math. P.sub.PE 1″ plastic 1″ CeBr.sub.3 Cs-137 17% 34%  6% Co-60 14% 18%  3% 2″ plastic 2″ CeBr.sub.3 Cs-137 23% 62% 14% Co-60 20% 42%  8% 3″ plastic 3″ CeBr.sub.3 Cs-137 24% 79% 19% Co-60 22% 60% 13%

(78) Table 2 interaction probabilities for single scattering in a detector plane of aplastic scintillator and for photoelectric absorption in a detector plane from crystalline CeBr.sub.3 depending on the nuclide energy and the scintillator thickness.

(79) TABLE-US-00003 TABLE 3 Cerbromide-Cerbromide detector pair (respectively one plane) Probability P.sub.CSS for single scattering Probability P.sub.PE for (excluding multiple photoelectric Total probability Nuclide scatterings) absorption P.sub.ges = 2 .Math. P.sub.CSS .Math. P.sub.PE 1″ CeBr.sub.3 1″ CeBr.sub.3 Cs-137 18% 34% 12% Co-60 18% 18%  6% 2″ CeBr.sub.3 2″ CeBr.sub.3 Cs-137 13% 62% 16% Co-60 16% 42% 13% 3″ CeBr.sub.3 3″ CeBr.sub.3 Cs-137  8% 79% 13% Co-60 13% 60% 16%

(80) Table 3 interaction probabilities for single scattering and for photoelectric absorption in one detector plane of crystalline CeBr.sub.3 respectively depending on the nuclide energy and on the scintillator thickness.

(81) With a gamma energy of 662 keV, for cerbromide-cerbromide detector pairs the optimum scintillator thickness for single scattering lies within the range from 20 to 30 mm at 1332 keV, wherein the optimum is reached between 30 to 40 mm. For larger crystals, multiple scatterings increase, which do not contribute to usable direction information. The best values for the total probability P.sub.ges.sup.max in the energy range of Cs-137 and Co-60 are reached at 2″ to 3″ scintillator thicknesses.

(82) For energies below 300 keV, the cerbromide-plastic combination is—independent of the thickness—always superior to the cerbromide-cerbromide combination.

(83) Above of 300 keV, the situation is a little bit more complex. FIG. 16a illustrates that for a scintillator thickness of 1″, the total probability P.sub.ges for cerbromide-cerbromide pairs is higher than the one of cerbromide-plastic pairs above of 350 keV. A similar trend can also be observed at a 2″ scintillator thickness (FIG. 16b). At a scintillator thickness from 1″ to 2″, higher total probabilities can be achieved in a wide energy range for cerbromide-cerbromide pairs than for pairs of cerbromide and plastic. Detector systems, which exclusively consist of cerbromide detectors, therefore, are predestined for small compact handheld devices.

(84) For a good total probability in the energy range from 100 keV to 1500 keV, it is advantageous to combine the respective advantages of the uni- and bidirectional detections with each other. This may be achieved best with a type A system made up by cerbromide and plastic detectors, which has a high proportion of bidirectional detector pairs. For an optimum design for the energy range from 100 keV to 1500 keV, cerbromide and plastic detectors having a size from 2″ to 3″ are suitable.

(85) After various variants for the spatial detector arrangement and the detector materials have been dealt with, in the following, various measurements are presented, which may be performed by means of certain embodiments of the imaging detector system according to the invention.

(86) In its most simple design, embodiments of the imaging detector system according to the invention can consist of two radiation detectors. Such a detector system has been set up with two 3″×3″ cerbromide scintillation detectors in a distance of 18 cm (measured from center to center) (FIG. 17). Further, a second detector system has been used, which comprises a 3″×3″ cerbromide detector and a 3″×3″ plastic (EJ-200) detector. The second detector system has served as a basis for comparison, in order to be able to compare the bidirectional cerbromide-cerbromide detector pair to the unidirectional cerbromide-plastic detector pair.

(87) All scintillators have been cylindrically shaped and had a size of respectively 3″×3″. Each scintillation detector has been equipped with a photomultiplier and a high-voltage supply. Cerbromide and plastic scintillation detectors generate short fast pulses with large amplitudes, which may be connected to a digitizer directly without any preamplifier. The digitizer module comprised one A/D converter per detector respectively, with subsequent FPGA for digitalization of the signals, as well as a readout controller FPGA for fast analysis. The digitizer has had a sufficiently high sampling rate of 500 MS/s such that the signal path of the cerbromide and plastic detectors could be integrated digitally. The processed data have been read out from a PC by means of an USB, have been further processed by means of a measurement technology software, and have been displayed for the user.

(88) The field of vision of the two-detector-arrangement is delimited to a semicircle. It is to be noted that such a system is not able to determine on which side of the connection axis a radiation source is located.

(89) The data acquisition system has been configured according to the scheme of FIG. 3b. The projection data p(y) has been acquired as a histogram with the functional value σ(E.sub.1, E.sub.2) of eq. (4). The system matrixes H have been determined experimentally for both detector systems by setting up a radiation source under different angles of incidence with respect to the axis of the detector pair. System matrixes have been created for respectively two radio nuclides (Co-60 and Cs-137). The image reconstruction has been carried out by means of the Maximum Likelihood Expectation Maximization Method (MLEM). The result of the image reconstruction was a direction distribution ƒ(x) over the azimuth angle x in an angle range from 0° to 180°.

(90) The measurements have been carried out by means of a Co-60 (10 μCi) and a Cs-137 source (10 μCi) in one meter distance respectively. The measurements respectively have been run for one minute. At each point of time t, an estimated value for the direction of the source has been calculated at the maximum of the MLEM function ƒ(x). For data acquisition, 20 measurements have been carried out in total for each angle of incidence of the radiation source. For each angle of incidence from 0° to 180°, the minimum measurement time t.sub.90 has been determined in order to determine the angle of incidence with an accuracy of ±10° at 90% confidence level. t.sub.90 is defined as that time, from which on at least 18 of the total of 20 measurements are correct, i. e., are lying in an interval of ±10° around the true value. FIGS. 18 and 19 show the t.sub.90 measurement times for the cerbromide-cerbromide detector pair compared to the cerbromide-plastic detector pair over the angle range from 0° to 180°.

(91) The bidirectional measurement by means of the cerbromide-cerbromide detector pair is characterized by its large field of vision, which covers the entire angle range from 0° to 180°. For Co-60, all t.sub.90 measurement times of the cerbromide-cerbromide detector pair were below 8 s and for Cs-137 below 12 s.

(92) On the other hand, the field of vision of the unidirectional cerbromide-plastic detector pair is actually delimited to about 100°. The direction measurement is achieved fast and reliably on the side of the plastic detector, on the other side of the cerbromide detector, in contrast, the direction measurement is only possible at the very late point of time or even is not possible at all.

(93) Within the field of vision, which is delimited to about 100° for the cerbromide-plastic detector pair, the t.sub.90 measurement times of both detector pairs have a similar magnitude. Only slight differences have been determined between the bidirectional cerbormide-cerbromide and the unidirectional cerbromide-plastic detector pairs.

(94) The measurements reveal that bidirectional cerbromide-cerbromide detector pairs are very well suited for direction measurement. With respect to a quantitative evaluation, cerbromide-cerbromide detector pairs yield similarly good results as cerbromide-plastic detector pairs, their measurement range is even larger because the entire angle range from 0° to 180° can be measured.

(95) Statements for 1-dimensional detector systems may be deduced from the measurement results. Here, an embodiment for a type A mixed system will be considered, in which a cerbromide and a plastic detector are respectively arranged in a row, one behind the other. The detector row is able to measure the entire angle range from 0° to 180°, because in the row, there are unidirectional detector pairs formed from respectively one cerbormide and one plastic detector, which have the plastic detector arranged on the left side as well as on the right side. In another embodiment for a type B system, the entire row consists of cerbromide detectors. Each pair in a cerbromide detector row covers the entire angle range from 0° to 180°.

(96) Besides the detector materials cerbromide and plastic from the system variants presented here, a plurality of further detector materials is known, which may be used for embodiments of the invention. In particular, semiconductor and scintillator materials may also be combined with each other. A frequently used construction principle in detector systems of type A is the combination of a silicon pad or strip detector with a scintillation detector, as NaI, CsI, CeBr.sub.3 or LaBr.sub.3.

(97) Various designs for the construction of radiation detectors are known in the field of detector engineering. For each detector design, there are, in turn, electronics components available that are adjusted to the respective design. Specialists in this technical field are able to optimize the experimental setup for certain detector requirements without any difficulties.

(98) For the image reconstruction, there are a plurality of methods available. Basically, all statistical image reconstruction methods of emission tomography are suitable within the meaning of the invention for the imaging detector system according to the invention. The embodiments described above use the Maximum Likelihood Expectation Maximization Method (MLEM), which belongs to the group of the EM image reconstruction methods. Other known methods from the group of EM methods are, for example Ordered Subset Expectation Maximization (OSEM) List Mode—Maximum Likelihood Expectation Maximization (LM-MLEM) List Mode—Ordered Subset Expectation Maximization (LM-OSEM) algorithm EM methods with penalty functions, e.g. for sparse solutions Generalized Expectation Maximization (GEM) Space-Alternating Generalized EM (SAGE)

(99) Moreover, further statistical methods are known in the field of emission tomography, which represent method embodiments suitable for the imaging detector system. These comprise: Algebraic reconstruction technique (ART) Maximum A Posterior algorithm (MAP) Maximum Entropy algorithm (ME) Origin Ensemble algorithm (OE)

(100) Embodiments of the imaging detector system together with embodiments of the method described here meets the requirements, which are posed to the direction measurement, detection and mapping of radiation sources in ABC and radiation protection. Embodiments of invention can enrich the field of radiation detection with directional resolution by various aspects, amongst others, by the following contributions: field of vision over the entire 4π spatial angle fast direction determination typical angular resolution at a dose rate of the source of 0.5 μSv/h after 2 s: better than 10° after 3 s: better than 5° recognition of multiple sources of similar and different nuclides with separate direction and intensity measurement compact device shapes with few detectors: ≥2 detectors for two-dimensional detection in the plane ≥3 detectors for three-dimensional detection in a half space ≥4 detectors for three-dimensional detection with 4π spatial angle setups, which use only one detector material or several materials in geometrical arrangements that can be flexibly designed simple and fast algorithms, which yield results in real-time device supports detection and mapping of radiation sources various usage options: stationary and mobile, with one or more devices motion tracking and tracking of moving radiation sources possible

(101) Moreover, the imaging detector system can also be suitable for applications in nuclear medicine. Embodiments of the invention can open various new possibilities in medical imaging by means of gamma radiation, amongst others, by the following contributions: highly efficient SPECT scanners without collimators on the basis of the Compton effect SPECT scanners for gamma radiation in the energy range >200 keV reduction of exposure to radiation for the patients setups, which use only one detector material for several materials in geometrical arrangements that can be flexibly designed use of PET scanners as SPECT and PET/SPECT hybrid scanners algorithms from emission tomography can be used new imaging techniques for radiopharmaceuticals, which are single photon and positron emitters compact designs for SPECT and PET/SPECT hybrid sensors in decentral diagnostics

(102) A further use option for embodiments of the imaging detector system is in astronomy using gamma radiation. The invention supports the construction of new Compton telescopes as imaging detector systems according to the invention with improved sensitivity at the same material input.

(103) The present invention has been described by means of some specific embodiments of the devices and methods. Persons skilled in the art in the field of radiation detection, of course, are able to modify these embodiments without departing from the principles and the spirit of the invention, the scope of protection of which is defined in the claims and its equivalents.