NL2020607B1 - Scintillator array for limited light sharing for depth-of—interaction determination. - Google Patents

Abstract

The invention provides a scintillator array comprising an array of scintillator bars configured to absorb incoming gamma rays and scintillate, thereby emitting scintillation photons, wherein adjacent scintillator bars include interfaces, wherein a functional group of 11 adjacent scintillator bars include parallel configured interfaces, wherein each interface comprises an interface pattern of one or more reflective 10 sections and one or more transparent sections, wherein within the functional group Virtual linear paths along an axis perpendicular to the interfaces meet at least one reflective section of one of the interfaces within the functional group and at least one transparent section of one of the interfaces within the functional group, and wherein n23. 15

Description

FIELD OF THE INVENTION

The invention relates to a scintillator array with constrained light sharing between scintillator bars. The invention further relates to a gamma ray detector comprising such scintillator array. The invention further relates to a nuclear imaging system comprising such gamma ray detector.

BACKGROUND OF THE INVENTION

Scintillator arrays with light sharing between scintillator bars are known in the art. US2010270463, for instance, describes an apparatus for measuring a Depth-OfInteraction (DOI), comprising a crystal layer of a mono layer in which a plurality of crystals for absorbing gamma rays are consecutively arranged, scintillation light detectors 15 disposed at one end of the crystals and configured to detect scintillation light emitted from the crystal layer by the gamma rays, change means included in the crystals and configured to linearly change transmittance in a length direction of the crystals, and a control unit configured to calculate the DOI in the crystal layer on a basis of the first output signal and the second output signal. The scintillation light detector outputs the first 20 output signal in one direction and the second output signal in a direction at a right angle to the one direction. W02006064393, for instance, describes a radiation detector including scintillator pixels that each have a radiation-receiving end, a light-output end, and reflective sides extending there between. The reflective sides have a reflection characteristic varying between the radiation-receiving end and the light-output end such 25 that a lateral spread of light emanating from the light-output ends of the scintillator pixels responsive to a scintillation event generated in one of the scintillator pixels depends upon a depth of the scintillation event in the scintillator pixel. A plurality of light detectors optically communicate with the light-output ends of the scintillator pixels to receive light produced by scintillation events.

SUMMARY OF THE INVENTION

The present invention relates to nuclear imaging systems such as Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT). These systems are commonly used in clinical and research settings. In a typical application, a subject, e.g., an animal or patient, is administered a radionuclide marker that will accumulate in the body in a tissue-dependent manner. This marker (directly or indirectly) emits gamma rays (or X-rays) that are detected by the nuclear imaging system. The objective of these systems is to spatially resolve the location from which the gamma ray was emitted. Accurate spatial resolution relies on a variety of factors, one of which is the determination of the depth-of-interaction (DOI) in the scintillator crystal array.

The DOI is the depth (z-axis) in the scintillator crystal array (“scintillator array”, also “scintillation array”) where the gamma ray interacts with a scintillator crystal, especially a scintillator crystal bar (“scintillator bar”, also ’’scintillation bar”). This interaction results in the release of scintillation photons (or “optical photons”), which may then be detected by a photosensor unit downstream of the scintillator array. Per convention, the DOI is not the actual depth a gamma ray reaches in a scintillator bar, but rather the distance between the interaction location in a scintillator bar and the downstream photosensor unit. The ‘depth’ of the DOI is thus typically seen from the perspective of the photosensor unit. However, the photosensor unit can typically not determine the DOI, whereby valuable spatial information may be lost. Therefore, the invention provides another approach.

Current approaches to determine the DOI may rely on free light sharing across the scintillator array. The degree to which light is shared depends on the gamma ray DOI, i.e., the greater the gamma ray DOI - the greater the distance between the gamma ray interaction location and the downstream photosensor unit - the larger the area over which light spreads. Hence, the spread of light following a scintillation event provides information regarding the DOI, and thereby light sharing aids in resolving the DOI. However, light sharing also has drawbacks: there may be an increased chance of multiple gamma ray interactions being detected as one; and there may be an overall reduced performance. The reduction of performance may be a result of an increased impact of noise from each photosensor element (“photosensor”) in the photosensor unit that converts the scintillation photons to electrical signals. Each photosensor has its own background noise and sharing the total scintillation photons over a plurality of photosensors may reduce the overall signal-to-noise ratio, resulting in a worse energy resolution, i.e. a worse determination of the incident gamma ray energy, with potentially a larger impact at low energies (-100 keV).

Single-side readout scintillator-based gamma ray detection systems are typically unable to determine the depth in which the radiation interacted (z-axis), only the x-y planar position parallel to a back x-y spatially resolving photosensor unit. Those systems that can obtain DOI estimates may utilize high levels of light sharing across the full domain of the scintillator array to determine the gamma ray DOI, which may increase the chance of multiple radiation interaction events being detected as one, and in an overall reduced performance due to total signal sharing over multiple detection elements (Poisson statistics).

The present invention encompasses embodiments comprising a novel encoded partially reflective interface array design in which pixelated scintillator crystals are placed that may limit the extent of light sharing across the array to a desired range. In embodiments, these encoded interfaces may possess a step like structure spanning approximately half the interface height (z-axis), wherein each step may be separated into equally sized sub-regions. The number of sub-regions may be proportional to the desired light sharing range as a function of the number of pixels. Along each x-y axis the encoded interfaces may take turns of having all but one of the sub-regions either folly or partially non-reflective (transparent) in a periodic manner. These interfaces may be placed in a repeating pattern perpendicular to the desired direction of light sharing (i.e. x-axis) and then rotated, for example over 180 degrees, before being placed in the same manner along another desired direction of light sharing (y-axis). This interface structure may enable a unique light sharing distribution along the x- and y- axis dependent on the DOI, which can be retrieved with an appropriate analysis method, whilst limiting the extent of light sharing to minimize the probability of multiple events being detected as one.

Embodiments may have a major improvement with respect to the current state of the art single-side readout scintillator-based gamma ray detection systems in the use of a set of repeating encoded reflective interfaces. Current state of the art systems may use simple singular interface designs to enable light sharing and, as such, the extent of light sharing cannot be controlled without sub-crystal array segmentation using full reflective interfaces. The issue with using foil reflective interfaces is that when a gamma ray interacts in a nearby crystal its light sharing may be skewed resulting in degraded performance in determining interaction position and deposited energy. For these other systems either the pixelated scintillator array may be segmented into a number of limited light sharing regions, increasing the maximum count rate at the cost of position and energy performance, or no array segmentation may be used leading to an increased chance of multiple events being detected as one and to an overall reduced performance due to total signal sharing over multiple detection elements (Poisson statistics).

The use of a set of repeating encoded reflective interfaces according to this invention may create a virtual Rill reflective boundary (or “barrier”) at a desired distance from the site of interaction (i.e. say 3 scintillator bars away). The linear offset nature within encoded interfaces with removed sub-regions in each step means that for light travelling in a straight line these regions may effectively fill up, thereby closing the total open cross-section the light can pass through. The scintillation light (or “scintillation photons”) is (are) ultimately directed down to the sensor plane where they are detected by a photosensor unit.

The ability to control the light sharing range without the full reflective interface sub-crystal array segmentation may remove the degraded performance observed with having small local light sharing regions. In addition, the virtual boundary properties of the current invention may avoid the associate issues of increased chance of multiple events being detected as one when no segmentation is present.

In comparison to the other technologies discussed above, the present invention may both avoid their issues and provide a scintillator-based gamma ray detection system which has good 3D position and energy resolution whilst able to handle the count rate needed in clinical PET/SPECT imaging. With respect to currently used gamma ray detection arrays in clinical PET/SPECT systems the expected performance of the invention is on par with energy and x-y axis spatial resolution. It, however, may also yield DOI information, which current gamma ray detection arrays in clinical PET/SPECT systems do not measure, whilst still operating at the required event detection rates for clinical PET/SPECT. Finally, in terms of the raw material costs and construction complexity the present invention may be on par with currently implemented clinical PET/SPECT detectors.

This invention may allow an increase in imaging quality. The invention may also have applicability in radioactivity area monitors, gamma ray telescopes, proton therapy prompt gamma ray imaging cameras, and other imaging applications involving gamma rays and/or X-rays.

Hence, it is an aspect of the invention to provide an alternative scintillator array, and/or a gamma ray detector, and/or a nuclear imaging system, and/or a method to determine the DOI of a gamma ray, which preferably further at least partly obviate one or more of above-described drawbacks. The present invention may have as object to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

The current invention regards a scintillator array design with partially reflective interfaces that create unique light sharing distributions depending on the DOI of gamma rays. In particular, the light sharing may be restricted to a limited portion of the scintillator array, thereby reducing the above-mentioned drawbacks while enabling the determination of the DOI.

Therefore, in a first aspect the invention provides a scintillator array comprising an array of scintillator bars configured to absorb incoming gamma rays and scintillate, thereby emitting scintillation photons, wherein adjacent scintillator bars include interfaces, wherein a functional group of n adjacent scintillator bars include parallel configured interfaces, wherein each interface comprises an interface pattern of one or more reflective sections and one or more transparent sections, wherein within the functional group virtual linear paths along an axis perpendicular to the interfaces meet at least one reflective section of one of the interfaces within the functional group and at least one transparent section of one of the interfaces within the functional group, and wherein n>3.

This invention enables specifically tailoring the degree of light sharing in a scintillator array, without the need for full reflective interfaces and corresponding degraded performance. The herein disclosed scintillator array may introduce virtual full reflective interfaces (also “virtual boundary” or “virtual barrier”) at a desired distance of each scintillator bar. For example, for n=4, a fraction of the scintillation photons originating in a terminal scintillation bar of a functional group and travelling along an axis perpendicular to the interfaces in the functional group may be reflected upon reaching the first interface, a (smaller) fraction may be reflected upon reaching the second interface, and essentially all remaining scintillation photons may be reflected upon reaching the third and last interface, wherein essentially all may indicate > 90%, such as >95%, especially >99%, including 100%. Hence, the invention enables light sharing between adjacent scintillator bars to aid in DOI-determination, while introducing a virtual full reflective interface to reduce the drawbacks known from light sharing scintillator arrays known from the prior art.

The term “virtual full reflective interface” refers to the feature that in embodiments a superposition of the interface patterns leads to a foil reflective configuration, i.e. all interface patterns together virtually lead to an interface that is fully reflective.

The invention is, however, not limited to embodiments wherein a virtual full reflective interface is introduced. For example, there may be a virtual linear path perpendicular to the interfaces that spans between two opposite ends of the scintillator array without encountering a single reflective interface. The invention enables the rational design of light sharing distributions in the scintillator array via the design of the interfaces included in adjacent scintillator bars. In general, however, the embodiments of the invention will comprise one or more virtual full reflective interfaces.

Here below, the invention is described in more detail.

A gamma ray is a type of photon. Gamma rays are defined according to two distinct definitions, both of which are used in the nuclear imaging field and herein. According to a first definition, gamma rays are the highest energy photons. Gamma rays have a partial overlap in the lower part of their energy spectrum with the highest energy (characteristic) X-rays, and gamma rays have no defined upper energy limit. This definition regards any photon with an energy above approximately 100 keV as a gamma ray. According to a second definition, a gamma ray is a photon emitted during the radioactive decay of an atomic nucleus from a high-energy state to a lower-energy state. This latter definition defines gamma rays by their origin irrespective of their energy. Following this definition, gamma rays do not have a defined energy range. Radionuclides used for SPECT emit gamma rays following the radioactive decay of an atomic nucleus. Such a gamma ray may have an energy below 100 keV, especially 70-90 keV, but also above 100 keV, especially 100-1000 keV, more especially gamma rays with an energy of 140 keV, 159 keV, 171 keV, 245 keV, 364 keV, 537 keV or 637 keV. Essentially all of the gamma rays emitted by major radiotracers, such as based on Tl-201, Tc-99m, 1-123,1131, In-111, F-18, C-l 1, etc., may be of interest. Hence, energies in the range of about 10 keV to 10 MeV may be of interest. Radionuclides used for PET can emit both gamma rays and positrons. When a positron encounters an electron an annihilation event, positron annihilation, takes place. In a positron annihilation event two 511 keV gamma rays are emitted in roughly opposite directions.

A characteristic X-ray is especially generated from the transition of an atomic bound electron to a lower, empty atomic state. The energies of these X-rays are dependent on the atom they come from and may be used in nuclear imaging systems, for example, in the case of iodine based radiotracers used in SPECT imaging.

The term ‘gamma ray’ herein relates to any photon that is used in nuclear imaging, irrespective of origin or energy and also includes (characteristic) X-rays.

The scintillator bars (“bars”) are especially configured to absorb gamma rays and emit a number of scintillation photons depending on the energy of each gamma ray. The scintillator bars may especially be scintillator crystal bars. Alternatively or additionally, the scintillator bars may especially be scintillator ceramic bars. Hence, the bars may be single crystals or ceramics. Combinations of a plurality of different bars, with e.g. bars being single crystals and bars being ceramic, may also be applied.

The scintillator bar comprises one or more scintillating materials, especially a single scintillation material. Especially, the scintillator bar may comprise one or more of thallium activated sodium iodide (NAFTI), bismuth germinate (BGO), cesium activated yttrium aluminum garnet (YAG:Ce), cesium activated lutetium aluminum garnet (LuAG:Ce), lanthanum bromide (LaBn), REiSiOvCe, wherein RE comprises especially one or more of Y, La, Lu, Gd and/or other rare earth elements, especially at least one or more of Y and Lu , etc., more especially wherein RE₂SiO<Ce comprises Lu2_xY_xSiO5:Ce (LYSO). Alternatively or additionally, the scintillator bar may comprise A4M3O12 material, wherein A comprise Bi and wherein M comprises one or more of Si and Ge, wherein at least part of M comprises Si. For instance, the single crystalline or ceramic A4M3O12 material comprises AtfGei-xSixjsOn, wherein 0.1<x<l, especially wherein x is at least 0.9. In specific embodiments, the single crystalline or ceramic A4M3O 12 material comprises (Bii.yREyLlVLOiz-, wherein y is selected from the range of 00.2, and wherein RE refers to one or more rare earth elements.

A gamma ray may interact with a scintillator bar and undergo a scintillation event. A scintillation event occurs when a scintillating material absorbs a gamma ray and ejects an electron that ionizes the surrounding material. The scintillating material then releases a plurality of scintillation photons, to return to a ground energy state, of energies corresponding to scintillation photons, wherein the scintillation photon energies may depend on the scintillating material, and wherein the sum of the scintillation photon energies of all released scintillation photons approximately equals the gamma ray energy. The scintillation photons (or “optical photons”) may be in the visible light spectaun. Especially, the scintillation photons may have a scintillation photon energy which can be detected by a photosensor unit configured downstream of the scintillator bars.

The scintillator bars may have dimensions like a length selected from a few millimeters to centimeters, such as 3-30 mm, especially 10-25 mm, such as 10-20 mm, and a width and depth selected from a few millimeters to centimeters, such as 1-20 mm, especially 1-10 mm. The width and depth may vary over the length, but will in general be constant. The scintillator bars may have a right regular prismatic shape, especially the scintillator bars may be right regular prisms, more especially right regular prisms with a square or a regular hexagonal base. The bars may also have a regular octagonal base. The bars may also have other polygonal bases, especially regular convex polygon bases. More especially, regular convex polygon bases with an even number of sides. The bars may also have different shapes, i.e. especially different cross-sectional shapes. Especially, however, essentially all bars may have essentially the same cross-sectional shapes and dimensions. The bars are especially elongated, with an axis of elongation. The bars may have a top (base) face, a bottom (base) face and a plurality of side faces. The top face and the bottom face may be perpendicular to the axis of elongation. The side faces may face the side faces of other scintillator bars, and the interfaces may be arranged along such facing side faces. The side faces may be polished, unpolished and/or roughened. Polishing of the side faces may result in better time-of-flight estimations, whereas roughening of the side faces may enable higher detector count rates before saturation.

The scintillator array comprises a plurality of scintillator bars, e.g. a single scintillator array may include in the range of 9-5,000,000, such as at least 9 bars, especially at least 49 scintillator bars, such as 256 bars. The scintillator array may comprise one or more layers of scintillator bars (along a z-axis). One or more scintillator bars may extend between layers, i.e., different scintillator bars may have different lengths. The number of scintillator bars in the different layers may differ. Especially, the number of scintillator bars in the different layers may be the same. More especially, the scintillator array has a single layer of scintillator bars, especially wherein all scintillator bars have the same length.

In embodiments, the scintillator bars in the scintillator array may be different. The scintillator bars may have different shapes. Alternatively or additionally, the scintillator bars may comprise different compositions of (one or more) scintillating materials (“composition”). The chemical composition of the scintillator bars may be position-dependent. For example, the composition of scintillator bars close to the edge of the array may be distinct to the composition of scintillator bars in the center. Especially, the composition may vary along an axis, especially along the z-axis. Such embodiments may have additionally beneficial features such as an improved resolution.

A cross-section (perpendicular to an axis of elongation of the scintillator bars and/or to the z-axis) of the scintillator array may resemble a pixelated grid, wherein the pixels comprise the scintillator bars, especially wherein each pixel is a scintillator bar, and wherein the grid lines comprise the interfaces. The grid lines may be thin, such as having a width of 0-100pm, especially 25-80 pm, such as 65 pm. Especially, the grid lines may be infinitesimally thin; i.e., the scintillator bars may essentially be touching. In general, the thickness of the grid lines depends on the type and thickness of the interface, especially the thickness of the grid lines equals the thickness of the interface. In embodiments, there may be an absence of holes between adjacent scintillator bars; the scintillator bars may be pressure-wrapped. The pixelated grid may be shaped by two sets of orthogonal parallel grid lines, especially two sets of equidistant parallel lines; more especially two sets of equidistant parallel lines may form a grid of squares. The pixelated grid may also be shaped by a plurality of connecting non-overlapping polygons, especially wherein the polygons are one or more of regular, convex and/or even-sided. For example, the pixelated grid may be a grid of squares; or a grid of convex pentagons; or a grid of squares and regular convex octagons. In embodiments, the pixelated grid may essentially be a tessellating grid.

In embodiments, the pixelated grid may be a grid of squares. Especially, the pixelated grid may comprise bixb2 pixels, wherein bi and bi are integer numbers, and wherein bi and Iv may be different numbers. Especially, bi and bi may be the same number. For example, the pixelated grid may comprise 3x3 pixels, or 16x16 pixels, or 24x24 pixels (i.e. scintillator bars).

The interfaces are configured at the common boundary of adjacent scintillator bars and are functionally coupled to the respective scintillator bars. Hence, adjacent scintillator bars share interfaces. In embodiments, the interface may cover the side surface of one of the adjacent scintillator bars, especially the interface may cover the side surface of two adjacent scintillator bars. The interface may also comprise (parts of) the adjacent scintillator bars. The interfaces comprise one or more reflective sections and one or more transparent sections, wherein the transparent sections are configured such that scintillation photons may travel between scintillator bars via the interfaces, and wherein the reflective sections are configured to limit how far the scintillation photons can travel. Hence, the term “interface” may refer to one or both side faces of two adjacent scintillator bars and/or may refer to the interspace between two adjacent bars that do not touch each other.

The interfaces may comprise one or more reflective materials, especially one or more of a reflective foil, a reflective coating, a reflective tape, or an etching. Especially, the one or more reflective sections may comprise one or more of a reflective foil, a reflective coating, a reflective tape, or an etching. The reflective material reflects scintillation photons in a specular and/or a diffuse manner. Especially, the reflective material may be a material compatible with Magnetic Resonance Imaging (MRI) such that the scintillator array is compatible with MRI modalities.

The reflective foil may comprise polyethylene, such as a polyethylene terephthalate. Especially, the reflective foil may comprise Vikuiti™ Enhanced Specular Reflector (ESR) multilayer polymeric film.

The reflective coating may be obtained through sputter coating the scintillator bar with an optically reflective substance, especially with T1O2.

The reflective tape may comprise polytetrafluoroethylene (PTFE).

The reflective etching may be obtained by first scuffing the side face of the scintillator bar and then polishing the side face with laser etching to provide the one or more transparent sections. Alternatively, the side face may be polished with laser etching without prior scuffing of the side face. Typically, the surfaces of scintillator bars after they have been cut are sufficiently rough to have similar properties as the surfaces after scuffing. Yet alternatively, the surfaces of the scintillator bars may be non-rough and laser etching may be used to provide the one or more reflective sections.

The interface may comprise a first reflective material arranged on one of the two side faces of two adjacent non-touching scintillator bars, and a second reflective material arranged on the other of the two side faces of two adjacent non-touching scintillator bars. In embodiments, the first reflective material and the second reflective material may touch. In other embodiments, the first reflective material and the second reflective material may not touch. In the latter embodiments, the interface thus comprises the reflective material on the two side faces as well as the interspace between the two side faces and the reflective material arranged thereupon.

The interfaces may comprise one or more transparent materials. In general, the transparent material is a gas. Especially, the transparent material is air.

In embodiments wherein the reflective material is an etching, the transparent material may additionally comprise a scintillating material as in such embodiments the interface comprises part of the scintillator bars.

It will be clear to one skilled in the art that the interfaces are to be understood as the space comprising the arrangement (“sectioning”) of the one or more reflective and one or more transparent sections, wherein the space may comprise part of the scintillator bars and/or the interspace between the scintillator bars.

In embodiments, the scintillator array may comprise a structural framework. The structural framework may comprise a plurality of pockets (defined by the structural framework), and may further comprise the interfaces (i.e. the one or more reflective sections and one or more transparent sections). The structural framework is configured such that one or more scintillator bars may be inserted into a pocket. Especially, each pocket may be configured such that one or more scintillator bars may be inserted, especially one scintillator bar. After insertion of the scintillator bars into the structural framework, the structural framework, with the scintillator bars included, may be pressure-wrapped. The structural framework may especially comprise a reflective film or reflective sheet of material. The structural framework may be of a material such as selected from the group consisting of Vikuiti™ ESR and polytetrafluoroethylene sheeting. In yet a further aspect, the invention also provides the structural framework per se.

The functional group comprises n scintillator bars. The functional group comprises the interfaces included between the n scintillator bars. Especially, n>3. The n scintillator bars in a functional group lie on a straight line, wherein two scintillator bars at opposite ends are outer scintillator bars, and wherein the n scintillator bars include parallel interfaces. The functional group includes a plurality of virtual paths perpendicular to the interfaces. At least some of the virtual paths meet at least one reflective section and meet at least one transparent section of the interfaces, especially essentially all virtual paths meet at least one reflective section, such as >90% of the virtual paths, especially >95%, such as >99%, including 100%. At least some of the virtual paths may exclusively meet one of the reflective sections of the interface of any one of the outer bars, i.e., these virtual paths only meet the transparent sections of the other interfaces. In embodiments, some of the virtual paths may only meet reflective sections of the interfaces. Hence, a superposition of the reflective sections of successive interfaces in the functional group may cover the area of the scintillator bar side face, but a superposition of all but one of the reflective interfaces may not cover the area of the scintillator bar side face.

In embodiments wherein virtual full reflective interface are introduced, a functional group comprising n scintillator bars has an effective light sharing distance of z, wherein z=n-l, i.e., scintillation photons emitted during a scintillation event in an outer bar of the functional group and travelling perpendicular to the interfaces of the functional group can travel through z scintillator bars (including the outer bar) in the functional group prior to encountering a reflective interface. Hence, if z=2 and any one of the outer scintillator bars undergoes a scintillation event, the scintillation photons travelling perpendicular to the interfaces of the functional group may reach an adjacent scintillator bar, but essentially no scintillation photons will reach a next adjacent scintillator bar before encountering any one of the reflective sections of an interface.

In embodiments, the one or more reflective sections of each interface in a functional group may be exclusively met by one or more of the virtual linear paths perpendicular to the interfaces in the functional group. In such an embodiment, each of the interfaces forms one or more unique parts of the virtual full reflective interface that the functional group (as a whole) forms, i.e., a superposition of the one or more reflective sections of each of the interfaces in a functional group may comprise areas covered by the reflective sections of a plurality of interfaces, as well as areas exclusively covered by the reflective sections of any one of the interfaces, especially wherein the reflective sections of each interface exclusively cover one or more of the areas.

The scintillator array may comprise a plurality of functional groups. The functional groups may be scattered over the scintillator array. The scintillator array may comprise functional groups in a seemingly random arrangement. Especially, the scintillator array may comprise one or more (identical) patterns of functional groups across the array. More especially, the scintillator array comprises a plurality of regularly arranged functional groups.

The functional groups may overlap in scintillator bars and interfaces. Especially, a set of scintillator bars arranged in a straight line along an axis may be comprised in a plurality of functional groups. For example, if n=5 for all functional groups along the axis, a central functional group may share 4 bars with 2 other groups, 3 bars with yet 2 other groups, 2 bars with yet another 2 other groups, and 1 bar with still yet another 2 other groups along the same axis. A scintillator bar may also be comprised in a plurality of functional groups that do not lie along the same axis, for example orthogonally configured functional groups; especially a plurality of scintillator bars are each comprised in a plurality of functional groups that do not lie along the same axis, for example orthogonally configured functional groups. Especially, essentially all scintillator bars are comprised in one or more functional groups, more especially in a plurality of functional groups.

The functional groups in the scintillator array may have different numbers of scintillator bars: ni, n₂, ... n_n, wherein each n_x is an integer. The numbers ni-n_n may vary between functional groups not having parallel interfaces, i.e., for functional groups with different light sharing axes. Especially, the numbers n_x, may vary throughout the scintillator array. More especially, however, essentially all functional groups may comprise essentially the same number of scintillator bars. The number n of scintillator bars in a functional group is at least 3, and at most k, wherein k equals the largest number of scintillator bars arranged in a straight line. For example, for a 15x15 scintillator array k==l5. In general, n<k, such as k-1, or such as k. Especially, 3<n<10, such as 3<n<4.

As indicated above, n is the number of adjacent scintillator bars in the functional group. A functional group at least includes a linear array of (adjacent) scintillator bars).

In embodiments, the functional groups may be configured to introduce virtual full reflective interfaces. Alternatively, in other embodiments, the functional groups may be configured not to introduce virtual full reflective interfaces. For example, a 3x3 scintillator array may have functional groups - implying that the two interface patterns between the two sets of two adjacent bars are not identical - without introducing a virtual full reflective interface.

Hence, in embodiments within the functional group some virtual linear paths along an axis perpendicular to the interfaces meet at least one reflective section of one of the interfaces within the functional group and at least one transparent section of one of the interfaces within the functional group, and wherein n>3, and some, within the same functional group, may only meet transparent sections. In yet other embodiments, all virtual linear paths along an axis perpendicular to the interfaces meet at least one reflective section of one of the interfaces within the functional group and one or more meet at least one transparent section of one of the interfaces within the functional group (wherein n>3). In both type of embodiments, the amount of light travelling perpendicular to the interfaces is reduced each time it passes an interface. In the former embodiments, after n-1 passes there may in principle be intensity; in the later embodiments, after n-1 passes there may be no intensity anymore (i.e. for all virtual linear paths light is reflected at an earlier interface and the remaining light is reflected at the last interface).

The scintillator array may have one or more parallel virtual planes (“planes”). The virtual planes may be arranged along the z-axis of the scintillator array and may be perpendicular to the z-axis. The virtual planes may be arranged parallel to the top and/or bottom faces of the scintillator bars. Especially, at least one of the one or more virtual planes may be arranged equidistantly to the top and bottom faces of the scintillator bars, i.e., at least one of the one or more virtual planes may be arranged in the center of the scintillator array. The virtual planes may be arranged orthogonal to the interfaces. The virtual planes may divide the interfaces such that all one or more transparent sections or all one or more reflective sections of each interface are located at one side of each of the virtual planes, especially, the one or more transparent sections of an interface may be confined to one side of each of the virtual planes, such as confined between two virtual planes, more especially the one or more transparent sections of all interfaces in a functional group may be confined to one side of each of the virtual planes, most especially the one or more transparent sections of all interfaces in one or more of the functional groups are confined to one side of each of the virtual planes.

In embodiments, the transparent sections of non-parallel interfaces of any one of the scintillator bars may be confined between a different set of two virtual planes. Especially, the transparent sections of non-parallel interfaces of two functional groups may be confined between a different set of two virtual planes, wherein the two functional groups both comprise any one of the scintillator bars.

In a further embodiment, the transparent sections of all functional groups including interfaces perpendicular to a first axis may be confined between a first set of two virtual planes, whereas the transparent sections of all functional groups including interfaces perpendicular to a second axis may be confined between a second set of two virtual planes, wherein the first set and the second set share zero or one virtual planes. In such an embodiment, the DOI of a gamma ray in any one of the scintillator bars determines in which direction light is primarily shared.

In an exemplary embodiment, the scintillator array may comprise scintillator bars and include one or more virtual planes, wherein the scintillator bars have a shape selected from the group of right rectangular prisms, and wherein the scintillator bars have at least two orthogonally configured interfaces, wherein any one of the one or more virtual planes is configured at the center of the scintillator array and configured perpendicular to the at least two orthogonally configured interfaces. In a further development of the embodiment, the at least two orthogonally configured interfaces are confined to a different side of at least one of the virtual planes.

In another embodiment, the scintillator array may comprise scintillator bars and include one virtual plane, wherein the scintillator bars have a shape selected from the group of right rectangular prisms, and wherein the scintillator bars have at least two orthogonally configured interfaces, wherein the virtual plane is configured perpendicular to the at least two orthogonally configured interfaces, and wherein the virtual plane is configured at an offset from the center of the scintillator array. This offset may be selected to further optimize the scintillator array with regards to DOI detection or to any other parameter of the scintillator array. Specifically, there are at least two factors that cause a non-uniformity of spatial information depending on the DOI in the scintillator array: (i) gamma rays may interact with the scintillating material while travelling through the scintillator array, hence the probability density function of a gamma ray interaction in the scintillator array trails off with increased distance to the gamma ray source; and (ii) the closer a scintillation event occurs to a downstream photosensor unit, the larger the fraction of scintillation photons that is directed to the photosensor unit without encountering an interface. These factors may further inform the positioning of the virtual plane as well as the design of the interface patterns.

In yet another further embodiment, wherein the scintillator array has four virtual planes and right hexagonal prismatic scintillator bars, there may be three axes along which light can be shared in the x-y plane, wherein each of the three axes is perpendicular to a plurality of the light sharing interfaces, and wherein the interfaces may be configured such that the one or more transparent sections of the interfaces perpendicular to a first of the three axes are confined between a first and second virtual plane, and that the one or more transparent sections of the interfaces perpendicular to a second of the three axes are confined between a second and third virtual plane, and that the one or more transparent sections of the interfaces perpendicular to a third of the three axes are confined between a third and fourth virtual plane.

It is clear to a person skilled in the art that further embodiments may be possible, and that such spatially organized arrangements of interfaces and virtual planes may be beneficial for devising unique light sharing distributions depending on the DOI of an incident gamma ray.

The scintillator array may comprise one or more different interface patterns. Each interface pattern defines a unique sectioning of the one or more reflective sections and the one or more transparent sections of one or a plurality of the interfaces. The scintillator array may further include a plurality of sets of two or more interface patterns. Any one of the sets of interface patterns may be configured such that when successive parallel interfaces along an axis are shaped according to alternating interface patterns of the set, the scintillator bars sharing the respective interfaces form a functional group. For example, a set of three interface patterns A,B,C may successively shape parallel interfaces along an axis in an alternating manner ABCABCABC (or (ABC)_n) such that any four successive scintillator bars sharing three of the respective interfaces (ABC, BCA, or CAB) form a functional group. It is clear to a person skilled in the art that this concept can be generalized to tailor the light sharing distance in the scintillator array in a structured manner, wherein the light sharing distance may differ along different axes. Especially, the light sharing distance may be the same along different axes. Hence, a functional group may include a plurality of different interface patterns. Especially, a functional group of n scintillator bars may include n-1 different interface patterns.

A set of two or more interface patterns may comprise an area that is consistently allocated to the one or more reflective sections. Hence, whereas a superposition of the one or more reflective sections of all interface patterns in a set of interface patterns especially covers the full area of an interface, especially the full area of a scintillator bar side, a superposition of the one or more transparent sections of all interface patterns in a set of interface patterns does not cover the full area of an interface. The superposition of the one or more transparent sections may have a particular shape configured to provide unique light sharing distributions depending on a depth-ofinteraction, such as a V-shape, especially such as a step-wise V-shape. The consistent allocation of an area to the one or more reflective sections in a set of interface patterns may be especially relevant when the reflective material comprises a reflective film or a reflective tape. Especially, the outer edges of the interface patterns may be consistently sectioned to the one or more reflective sections to improve the adhesion of the reflective material, especially of the reflective film or of the reflective tape.

In embodiments, the interface patterns in a set of interface patterns may be regularly partitioned. For example, in an exemplary embodiment, the interface patterns of a set of 3 interface patterns are partitioned in n, r₂, ... r_x rectangular parts of equal width. The width may be in the range of 5-200 pm, especially 10-150 pm, more especially 15-40 pm. In this embodiment 2/3 parts are allocated to the one or more transparent sections in each interface pattern, and 1/3 of the parts are allocated to the one or more reflective sections in each interface pattern according to a regular scheme. For example, a first of the interface patterns allocates n, r₄, r₇, and each 3 part r_x hereafter to the reflective sections, and the remaining parts to the transparent sections. A second of the interface patterns then allocates r₂, r₅, r₈, and each 3 part r_x hereafter to the reflective sections, and the remaining parts to the transparent sections. The third of the interface patterns is constructed according to the same logic. In this way, if three successive interfaces include each of these interface patterns, the 4 respective scintillator bars including these three interfaces form a functional group having a virtual full reflective interface.

In a further development of the embodiment, each part r_x comprises an upper region r_xll, and a lower region r_xi, wherein the upper region and the lower region have a variable height, and wherein the combined heights of the upper region and the lower region equal the length of a scintillator bar along an axis of elongation. In such an embodiment, each lower region r_xi may be allocated to the one or more reflective sections in each interface pattern, whereas the upper regions may be allocated to the reflective sections of the interface patterns according to a regular scheme. For example, the reflective sections of a first of the interface patterns comprise regions ri_u, r_4u, r_7u, and each 3^rd region rxu hereafter. Similarly, the second and the third of the interface patterns comprise the regions r2u and r2u respectively, as well as each 3^ld region rxu thereafter. The heights of the upper and lower regions may also vary according to a regular scheme. For example, triplets of upper regions r_x._2u. γ_χ.]^ and r_xlJ. wherein x is a multiple of three, may have the same upper region height. The upper region height may then decrease or increase with each successive triplet in the interface pattern. For example, the upper region height exclusively increases for successive triplets until a turning point after which the height exclusively decreases. The turning point may be a central part r₍i/_2)n, and/or the part height may have reached a threshold such as half the length of the scintillator bar along an axis of elongation. Especially, the height of successive parts monotonically increases or decreases.

In embodiments, the partitioning may comprise a plurality of parts of regular width and/or height, but may also comprise a plurality of parts with varying part shapes. Especially, the partitioning may comprise a border part allocated to the reflective sections of each interface pattern, wherein the border part resembles a frame. It is clear to a person skilled in the art that many more sets of potentially advantageous interface patterns may be devised using such regular allocation of parts defined through a partitioning.

The invention further encompasses embodiments of a scintillator array having one or more virtual frill reflective interfaces, the scintillator array comprising a plurality of side-by-side right regular prismatic scintillator bars, wherein the scintillator bars have two opposite base faces and three or more side faces, wherein the side faces of adjacent scintillator bars share an interface, wherein the interface comprises an arrangement of a reflective material and a transparent material, wherein the arrangement is configured to vary between the two base faces of the scintillator bars such that a scintillation event in any one of the scintillator bars causes a spread of scintillation photons to other scintillator bars in the scintillator array, wherein the spread depends on the depth-of-interaction in the any one of the scintillator bars, and wherein the scintillation photons travelling on a path perpendicular to any one of the side faces of the any one of the scintillator bars meet the reflective material of any one of the interfaces before travelling through n bars, wherein n>3.

The invention further encompasses embodiments of a scintillator array having limited light dispersion and one or more virtual full reflective interfaces, the scintillator array comprising: an array of scintillator bars configured to absorb an incident gamma ray and undergo a scintillation event, thereby releasing scintillation photons; and interfaces configured between adjacent scintillator bars, wherein the interfaces comprise an arrangement of reflective material and transparent material wherein the arrangement is non-uniform along a length direction of the scintillator bars, and wherein the interfaces are configured such that the scintillation photons can travel from any one of the scintillator bars to an adjacent scintillator bar; and wherein the interfaces of a series of successive parallel interfaces in a light sharing direction are configured such that scintillation photons travelling perpendicular to the respective interfaces encounter the reflective material of any one of the respective interfaces before travelling through n scintillation bars, wherein n>3.

In a second aspect, the current invention also provides a gamma ray detector comprising the scintillator array according to any one of the preceding claims, wherein the gamma ray detector comprises one or more photosensor units, wherein the one or more photosensor units are configured to detect and measure scintillation photons from the scintillator bars.

A gamma ray detector is a device that detects gamma rays and resolves their position and/or energy. The gamma ray detector may comprise a position-resolving gamma ray detector, i.e., a gamma ray detector that is configured to determine the origin location of an incident gamma ray. The gamma ray detector may comprise a position-andenergy-resolving gamma ray detector, i.e., a gamma ray detector that is configured to determine the origin location and the energy of an incident gamma ray. The gamma ray detector may comprise one or more light guides, and may further comprise a collimator.

In embodiments of the current invention, the gamma ray detectors may measure one or more of the location, the time and the deposited energy of any gamma ray interaction, wherein measuring the location especially comprises estimating the depth-ofinteraction, and wherein measuring the time may serve for time-of-flight estimations.

The gamma ray detector comprises one or more photosensor units, wherein the photosensor units comprise one or more photosensors, especially a plurality of photosensors, such as 1-5,000,000,000 photosensors, such as at least 4, like at least 16, such as at least 64. The photosensor units are configured to receive and count scintillation photons emitted by the scintillator bars, especially the photosensors are configured to receive and count scintillation photons emitted by the scintillator bars. The photosensors are functionally coupled to the scintillator bars, especially each scintillator bar may be coupled to one or more of the photosensors, more especially any one of the photosensors may be coupled to a plurality of scintillator bars, most especially each photosensor may be coupled to one scintillator bar. A photosensor coupled to a plurality of scintillator bars may, for example, be coupled to 2x2 scintillator bars or to 3x3 scintillator bars. The photosensor units may comprise a photosensor array.

The photosensors may comprise photomultiplier tubes. The photosensors may comprise digital photon counters. Also, the photosensors may comprise photodetectors, or hybrid photodetectors, or silicon-based Geiger-mode photodetectors. Especially, the photosensors may comprise silicon-based Photomultipliers (SiPMs), more especially the photosensors may comprise digital SiPMs. For instance, Philips Digital Photon Counting DPC3200 sensors may be applied. Hence, in embodiments the photosensor units comprise silicon photomultipliers (SiPM). SiPMs are a class of silicon single photon sensors based on single-photon avalanche diodes (SPAD). Especially, the SiPMs could be digital silicon photomultipliers (dSiPM) and/or digital photon counters (DPC). As known in the art, dSiPM and DPC, etc., may actually refer to the same class of devices, viz. SiPMs with integrated digital data acquisition, processing, and readout circuits.

The scintillator bars are configured to channel the scintillation photons to the one or more photosensor units. In specific embodiments, each scintillator bar may be configured to distribute the scintillation photons to one or more photosensors in the one or more photosensor units.

In specific embodiments, the gamma ray detector also comprises one or more light guides. The light guide is configured to channel scintillation photons from a scintillator bar towards individual photosensors in the photosensor unit. In addition, the light guide may especially be configured to reduce position-dependent differences in light collection efficiency. The gamma ray detector may also contain a plurality of light guides. The light guide is positioned in between the scintillator bars and any one of the one or more photosensor units. Each light guide is functionally coupled with one or more of the scintillator bars, especially with a plurality of scintillator bars, such as with 1-5,000 scintillator bars, such as at least 4, like at least 16, such as at least 64. The light guide is functionally coupled with the any one or more of the photosensor units. In this way, photons from the scintillator bars may propagate to the photosensor unit. The light guide may in embodiments have the shape of a plate and may be optically coupled, such as physically coupled to a side of the scintillator array. Hence, the (length and width) dimensions of the light guide(s) may essentially be the same as the of the (respective) scintillator array side(s).

The photosensor units are especially end-mounted to the (sides of the) scintillator bars, especially to the top and/or bottom sides (“ends”, “bases”) of the scintillator bars, more especially with light guides in between. Hence, the photosensors or photosensor units are configured at ends of the scintillator bars. Each bar may have (two) scintillator bar ends. These ends define the length of the scintillator bars. As indicated above, the bars may essentially have the same length or there may be bars with different length. Especially, at least one end of a plurality of bars, more especially essentially all bars, are directed to one or more of the photosensor units. In specific embodiments at least a part of the total number of bars have bar ends that are both directed to photosensor units. Hence, the gamma ray detector may be a single-side (“one-side”) readout detector, but may also be a double-side readout detector.

The fact that the photosensor units are end-mounted to the scintillator bars also includes embodiments wherein a light guide is configured between the bar(s) and the respective photosensor unit. Therefore, in specific embodiments the gamma ray detector further comprises one or more light guides configured downstream of the scintillator bars and upstream of the photosensor units, wherein one or more of the photosensor units comprise one or more photosensors, wherein the one or more of the photosensor units are functionally coupled to a respective light guide, wherein the respective light guide is configured to distribute the scintillation photons from the scintillator bars to the one or more photosensors in the respective photosensor unit. Note that the scintillator bar may thus have ends at which photosensor units may be arranged, which are both considered to be arranged downstream of the scintillator bar, as the photons are generated within the scintillator bar and may propagate to the scintillator bar end and be detected by the photosensor unit(s).

The scintillator array comprised in the gamma ray detector has a plurality of scintillator array side(s), wherein one or more of these sides, such as two or more, may be configured with a photosensor unit. The scintillator array sides not configured with a photosensor unit, may instead be configured with a reflective array interface (“cover”), such as a reflective foil, a reflective coating, a reflective tape, or an etching. The cover may comprise a different reflective material than the one or more reflective sections of the interfaces of the scintillator array. Especially, the cover may comprise the same reflective material as the one or more reflective sections. The cover is configured such that incident gamma rays are essentially not reflected, while essentially all incident scintillation photons are reflected. In embodiments, each scintillator array side may be configured with either one or more photosensor units, or with a cover.

The gamma ray detector may further comprise or be functionally coupled to a collimator. A collimator is a device configured to control one or more of beam (of rays) direction, beam (of rays) width, and beam (of rays) path. The collimator comprises one or more apertures through which a gamma ray can pass, and it comprises a collimator material configured to absorb gamma rays. The one or more apertures are configured to provide paths stretching between two opposite sides of the collimator along which a gamma ray can travel without encountering collimator material. A gamma ray travelling along a desired path may pass the aperture, such as a path coinciding with an optical axis of the collimator. A gamma ray not travelling along a desired path may not pass the collimator, and may be absorbed by the collimator material. The collimator is configured to filter gamma rays such that the outgoing beam of gamma rays is more focused or narrowed, especially such that only gamma rays with desired incident angles are accepted, more especially such that the directions of the outgoing gamma rays are more parallel than upstream of the collimator.

The gamma ray detector may comprise or be functionally coupled to a control system. The control system may be configured functionally coupled to the photosensor units such that the photosensor units provide one or more output signals upon measuring scintillation photons, and wherein the control system may process the output signals to estimate a scintillation event location, wherein the scintillation event location comprises a DOI, and/or wherein the control system may convert the output signal to an electronic output signal, especially to a digital output signal. The electronic and/or digital output signal may comprise an estimation of a scintillation event location, wherein the estimated scintillation event location comprises a DOI. The electronic output signal may be further processed by a device, especially a computer, functionally coupled to the gamma ray detector.

The term “controlling” and similar terms especially refer at least to determining the behavior or supervising the running of an element. Hence, herein “controlling” and similar terms may e.g. refer to imposing behavior to the element (determining the behavior or supendsing the running of an element), etc., such as e.g. measuring, displaying, actuating, opening, shifting, changing temperature, etc.. Beyond that, the term “controlling” and similar terms may additionally include monitoring. Hence, the term “controlling” and similar terms may include imposing behavior on an element and also imposing behavior on an element and monitoring the element. The controlling of the element can be done with a control system. The control system and the element may thus at least temporarily, or permanently, functionally be coupled. The element may comprise the control system. In embodiments, the control system and element may not be physically coupled. Control can be done via wired and/or wireless control. The term “control system” may also refer to a plurality of different control systems, which especially are functionally coupled, and of which e.g. one control system may be a master control system and one or more others may be slave control systems.

Hence, the current invention also provides a gamma ray detector comprising the aforementioned scintillator array, wherein the gamma ray detector comprises one or a plurality of photosensor units and a control system, wherein the scintillator bars are functionally coupled to one or more of the photosensor units, wherein the photosensor units are configured to detect and measure scintillation photons from coupled scintillator bars, and wherein the control system is configured to estimate a depth-of-interaction of a gamma ray in any one of the scintillator bars based on the detection of scintillation photons in the one or more photosensor units coupled to the scintillator bars comprised in the functional groups comprising the any one of the scintillator bars.

The invention further encompasses embodiments of a gamma ray detector having one or more virtual full reflective interfaces, wherein the gamma ray detector comprises a plurality of side-by-side right regular prismatic scintillator bars, one or more photosensor units and a control system, wherein the scintillator bars have two opposite base faces and three or more side faces, wherein one or more base faces of the scintillator bars are functionally coupled to any one of the one or more photosensor units, wherein the side faces of adjacent scintillator bars share an interface, wherein the interface comprises an arrangement of a reflective material and a transparent material, wherein the arrangement is configured to vary between the two base faces of the scintillator bars such that a scintillation event in any one of the scintillator bars causes a spread of scintillation photons to other scintillator bars in the scintillator array, wherein the spread depends on the depth-of-interaction in the any one of the scintillator bars, and wherein the scintillation photons travelling on a path perpendicular to any one of the side faces of the any one of the scintillator bars meet the reflective material of any one of the interfaces before travelling through n bars, wherein n>3, and wherein the one or more photosensor units are configured to detect the spread of scintillation photons and to provide an output signal, wherein the control system is configured to process the output signal to determine a depth-of-interaction of the scintillation event.

The invention further encompasses embodiments of a gamma ray detector having one or more virtual full reflective interfaces for depth-of-interaction determination using limited light dispersion, the gamma ray detector comprising: an array of scintillator bars configured to absorb an incident gamma ray and undergo a scintillation event, thereby releasing scintillation photons; and interfaces configured between adjacent scintillator bars, wherein the interfaces comprise an arrangement of reflective material and transparent material wherein the arrangement is non-uniform along a length direction of the scintillator bars, and wherein the interfaces are configured such that the scintillation photons can travel from any one of the scintillator bars to an adjacent scintillator bar; and wherein the interfaces of a series of successive parallel interfaces in a light sharing direction are configured such that scintillation photons travelling perpendicular to the respective interfaces encounter the reflective material of any one of the respective interfaces before travelling through n scintillation bars, wherein n >3; and one or more photosensor units functionally coupled to a plurality of scintillator bars, wherein the photosensor units are configured to detect the scintillation photons incident from functionally coupled scintillator bars and to provide output signals comprising a detection location; and a control system configured to process the output signals to determine a depth-of-interaction of the scintillation event.

In a third aspect, the current invention also provides a nuclear imaging system, the nuclear imaging system comprising one or more gamma ray detectors as defined herein, the nuclear imaging system further comprising a staging area and a control system functionally coupled to the gamma ray detectors, wherein the gamma ray detectors are configured to detect gamma rays emitted by a radioactive source in the staging area and to provide output signals, wherein the control system is configured to localize the radioactive source based on the output signals, and wherein an estimation of a depth-of-interaction of the gamma rays in the gamma ray detectors contributes to localizing the radioactive source.

The estimation of the depth-of-interaction may provide the nuclear imaging system with an increased spatial resolution in determining the spatial distribution of the radioactive source in the staging area. Hence, the nuclear imaging system disclosed in this invention may provide more accurate information, and thereby potentially more (medically) informative and valuable information, on the distribution of the radioactive source in a subject, for example in a human or small animal.

Nuclear imaging systems are specialized imaging systems for nuclear medicine. These systems are configured to locate a radioactive source within a subject by detecting the radiation that the radioactive source emits. The subject and the nuclear imaging system may move with respect to one another. The nuclear imaging system may comprise a moving gantry, especially wherein the moving gantry moves around the subject. The nuclear imaging system may comprise a moving staging area. The nuclear imaging system comprises one or more gamma ray detectors. These gamma ray detectors may be assembled in a partial or whole ring around the subject. Instead of the term “staging area” also the terms “subject area” or “sensing area” may be applied.

The radioactive source may be a radioactive source administered to a subject, especially to a human or a small animal. Especially, the radioactive source may be a radionuclide marker. Radionuclide markers will spread through the subject and concentrate in a tissue-dependent or process-dependent manner. For example, cancer cells may become enriched in the radionuclide marker. The radionuclide marker (or “radioactive source”) will directly or indirectly emit gamma rays, which can be detected through the nuclear imaging system, especially through the gamma ray detector, whereby the detection enables determining the origin location of the gamma ray. Hence, the gamma ray detection enables the determination of the spatial distribution of the locally accumulating radionuclide markers, and thereby the spatial distribution of a targeted tissue or process.

The nuclear imaging system may especially include a plurality of gamma ray detectors, each comprising one or more of the scintillator arrays. The plurality of gamma ray detectors may form a unit that may be configured at least partly rotatable around a staging area. The staging area may e.g. be configured to host a human.

Further, the nuclear imaging system may comprise or may be functionally coupled to a control system, configured to control the nuclear imaging system. Further, the control system may be configured to control the plurality of gamma ray detectors. Yet further, the control system may be configured to analyze the data generated by the gamma ray detector(s). Especially, the control system may be configured to estimate the location of the radioactive source in the staging area based on the output signals of the gamma ray detectors. More especially, the control system may be configured to estimate a scintillation event location in any one of the scintillator bars, based on the detected scintillation photons by the photosensor units in the gamma ray detector, wherein the scintillation event location comprises a DOI, and wherein the scintillation event location is used to estimate the location of the radioactive source.

In a fourth aspect, the current invention provides a method of measuring gamma rays escaping from an object with a gamma ray detector as defined herein, wherein the method comprises detecting scintillation photons from the gamma ray detector, wherein the gamma ray detector generates related detector signals and processes the detector signals. In embodiments, the method may be non-medical.

The invention further encompasses a method to measure a gamma ray in a gamma ray detection system comprising the aforementioned gamma ray detector and a control system, wherein the method comprises: any one of the scintillator bars interacting with a gamma ray at an interaction location and emitting scintillation photons; the interfaces controlling a spread of the scintillation photons through the scintillator array; the one or more photosensor units detecting the scintillation photons and recording the detection positions; the control system reconstaicting the spread of the scintillation photons through the scintillator array based on the detection positions of the scintillation photons; the control system estimating the interaction location based on the reconstructed spread, wherein the interaction location comprises a depth-of-interaction. In embodiments, the method may be non-medical.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

Fig. 1 schematically depicts exemplary interface patterns for interfaces. Fig. 1A-C schematically depict a set of interface patterns configured to provide functional groups comprising n=4 scintillator bars. Fig. ID schematically depicts a superposition of the reflective sub-sections of the interfaces of Fig. 1A-C. Fig. IE schematically depicts a superposition of the transparent sub-sections of the interfaces of Fig. 1A-C.

Fig. 2A-C schematically depict two adjacent scintillator bars and their interface, as well as a cross-section of two interfaces each bar shares with other adjacent bars. Fig. 2A schematically depicts an interface comprising a reflective coating. Fig. 2B schematically depicts an interface comprising a reflective foil and/or tape. Fig. 2C schematically depicts an interface comprising an etching.

Fig3A-B schematically depict a functional group comprising n=4 scintillator bars. Fig. 3 A schematically depicts an “exploded view” of the scintillator bars in a functional group, as well as several virtual paths perpendicular to the interfaces included between the scintillator bars. Fig. 3B schematically depicts a superposition of the reflective sections of the interfaces between the scintillator bars in Fig. 3 A.

Fig. 4 schematically depicts an exemplary embodiment of the scintillator array, wherein the scintillator array comprises 7x7 right prismatic scintillator bars having a square base, and wherein the scintillator array comprises a repeating set of interface patterns, and wherein the transparent sections of each interface are restricted to one side of a central virtual plane.

Fig. 5A-C schematically depict a cross-section of the scintillator array, wherein the cross-section resembles a pixelated grid, wherein the pixels are scintillator bars, and wherein the grid lines comprise the interfaces. Fig. 5A depicts a cross-section of the scintillator array depicted in Fig. 4, wherein four functional groups related to a center scintillator bar are drawn. Fig. 5B depicts a cross-section of the scintillator array depicted in Fig. 4. Fig. 5C depicts a cross-section of a scintillator array comprising right hexagonal prismatic scintillator bars.

Fig. 6 schematically depicts an exemplary embodiment of the gamma ray detector comprising the scintillator array depicted in Fig. 6, further comprising a photosensor unit. The scintillator array is bordered by the photosensor unit on one side and has a cover on the remaining sides. For visualization purposes part of the gamma ray detector is removed.

Fig. 7A-C schematically depict an exemplary spread of scintillation light in the gamma ray detector of Fig. 3, wherein the spread is determined by the detection of scintillation photons by the photosensors functionally coupled to each of the scintillator bars in a 1-on-l fashion. Fig. 7A schematically depicts the spread of scintillation photons emitted from a scintillation event near the ‘top’ of the scintillation array, i.e., near the side of the scintillation array opposite of the photosensor unit. Fig. 7B schematically depicts the spread of scintillation photons emitted from a scintillation event near the central plane of the array. Fig. 7C schematically depicts the spread of scintillation photons emitted from a scintillation event near the bottom of the scintillation array.

The schematic drawings are not necessarily to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Fig. 1 schematically depicts a non-limiting number of embodiments of interfaces 130 as well as interface patterns 180 for interfaces 130.

Fig. 1A-C schematically depict three interface patterns 180, 180A, 180B, 180C comprised in a set of interface patterns such that if three interfaces 130, 130A, 130B, 130C included in four successive adjacent scintillator bars 110 would include all three of the depicted interface patterns 130, 130A, 130B, 130C, the four respective scintillator bars 110 would be comprised in a functional group 150 having a virtual full reflective interface. The interface patterns 130, 130A, 130B, 130C cover the area of a side face 114 of a scintillator bar 110. Given the rectangular shape of the interface patterns 180, the ‘top’ of each pattern may align to either the top base face 112 or to the bottom base face 112 of the scintillator bar 110. Hence, these interface patterns 180 may be viewed as depicted as well as upside down (rotated over 180°along an axis perpendicular to the interface pattern 180). In the text and figures hereafter the ‘as-depicted’ orientation and the rotated orientation of each interface pattern 180 is referred to using the same reference numbers.

Fig. ID schematically depicts a superposition of the reflective sections 135, 135A, 135B, 135C of a top area of the interface patterns 180, 180A, 180B, 180C depicted in Fig. 1A-C. The superposition is formed by overlaying the reflective sections of the interfaces in Fig. 1A-C. This superposition conveys the regular allocation of reflective material 135 among the three interface patterns 180, 180A, 180B, 180C. Each of the interface patterns 180 includes two border areas which are consistently allocated to the reflective sections 135. The allocations in the remaining area follow a regular partitioning, wherein the interface patterns 180 are partitioned into 27 rectangular parts n, r₂, ... r₂7 of an equal width in the range of 15-40 pm, wherein each part r_x comprises an upper region r_xlt, and a lower region Γχΐ, wherein the upper region and the lower region have a variable height, wherein the combined heights of the upper region and the lower region are constant. Each of the lower regions r_x, is allocated to the reflective sections 135 in each interface pattern 180, whereas the upper regions are allocated to the reflective sections 135 of the interface patterns 180 according to a regular scheme: the reflective sections 135, 135A of a first of the interface patterns 180, 180A comprise regions ri_u, r_4u,

Γ7ι, and each 3^rd region thereafter. Similarly, the reflective sections 135, 135B, 135C of the second and the third of the interface patterns 180, 180B, 180C comprise r_2u and r_3u respectively, as well as each 3 region γ_χίι thereafter. The height of the upper regions also varies according to a regular scheme with respect to nine triplets of upper regions r_x.2_U. Γχ-iu. Fxu, wherein x is a multiple of three. The upper regions in any one of the triplets have the same upper region height. Specifically, the height of the i^th triplet of upper regions equals ^{5 5}'^)! * h, wherein h is the length of the interface pattern. The superposition also conveys the virtual full reflective interface 137 that a combination of each interface pattern 180A, 180B, 180C of a set of interface patterns 180, 180A, 180B, 180C provides.

Fig. IE schematically depicts a superposition of the transparent sections 131 of the interface patterns 180, 180A, 180B, 180C depicted in Fig. 1A-C. This depiction conveys the stepwise V-shape 133 of the set of interface patterns 180 depicted in Fig. 1A-C, wherein the stepwise V-shape 133 spans half the height of the interface pattern 180. In other embodiments, the V-shape 133 may be smooth rather than stepwise. In yet further embodiments, the superposition of the transparent sections 131 of the interface patterns 180 in a set of interface patterns 180 may not resemble a V-shape 133 but have a different shape.

Fig. 2A-C schematically depict two adjacent scintillator bars 110 and their shared interface 130, as well as the interfaces 130 that the two scintillator bars 110 share with other non-depicted scintillator bars 110.

Fig. 2A schematically depicts the two scintillator bars 110, wherein the reflective sections 135 of the interfaces 130 comprise a reflective coating. This depiction includes two interface patterns 180 belonging to a set of two interface patterns 180. These reflective sections 131 and transparent sections 135 of these interface patterns 180 are arranged according to a regular partitioning having parts spanning the width of the scintillator bars 110 and part of the height. Specifically, in this partitioning the reflective sections 135 consistently have a larger height relative to the transparent sections 131. Hence, a superposition of the transparent sections 131 does not cover the area of a scintillator bar 110 side face 114, especially in the superposition the transparent sections 131 belonging to different interface patterns 180 do not directly border, thereby reducing the chance that a scintillation photon travelling along a virtual path 140 at an angle to an axis perpendicular to the interfaces 180 passes two consecutive interfaces 130.

Fig. 2B schematically depicts the two scintillator bars 110, wherein the reflective sections 135 of the interfaces 130 comprise a reflective film. In this embodiment the interface patterns 180 allocate the border of the interfaces 130 to the one or more reflective sections 135 such that the reflective film adheres better to the scintillator bars 110. In the depicted embodiment, the interfaces 130 comprise two sheets of reflective film and a thin layer of air in between the two sheets, wherein the facing side faces 114 of the scintillator bars 110 are both covered with one sheet of reflective film. In other embodiments, the reflective film may be replaced by a reflective tape.

Fig. 2C schematically depicts the two scintillator bars 110, wherein the reflective sections 135 of the interfaces 130 comprise an etching, wherein the etching causes the etched parts of the side face 114 of the scintillator bars 110 to become reflective. The etching may provide interface patterns 180 with a particularly detailed allocation of reflective sections 135 and/or transparent sections 131. In the depicted embodiment there is essentially no distance between the adjacent scintillator bars 110,

i.e., they are arranged side-to-side, especially wherein the scintillator bars 110 are pressure-wrapped.

Fig. 3 A schematically depicts a perspective of a functional group 150 with the scintillator bars 110 separated for visualization purposes. For visualization purposes, also the interfaces 130 included between adjacent scintillator bars 110 of the functional group 150 are solely depicted on one of the side faces 114 - the front face - of the scintillator bar 110 further to the back of the functional group 150. The virtual paths 140 perpendicular to the interfaces 130 are depicted as originating in the front scintillator bar 110 and extending towards the back scintillator bar 110. In this embodiment, there are no virtual paths 140 that solely encounter transparent sections 131 of the interfaces 130 of the functional group 150. Hence, this functional group 150 introduces a virtual full reflective interface 137.

Fig. 3B schematically depicts a superposition of the reflective sections 135 of the interfaces 130 depicted in Fig. 3A. The superposition clearly conveys the virtual full reflective interface 137 encountered by the virtual paths 140 travelling perpendicular to the interfaces 130 of the functional group 150 in Fig. 3A.

Fig. 4 schematically depicts a single-layered embodiment of the scintillator array 100, wherein the scintillator array 100 comprises 7x7 right prismatic scintillator bars 110 having a square base (top base face 112 and bottom base face 112) and four side faces 114, wherein the scintillator bars 110 are arranged along an x-axis and a y-axis, and wherein the interfaces 130, 130A, 13OB, 130C of the scintillator array 100 include the interface patterns 180, 180A, 180B, 180C of a first set of interface patterns 180 as depicted in Fig. 1A-C, wherein four adjacent scintillator bars 110 along an axis include three interfaces 130, 130A, 130B, 130C including each of the three interface patterns 180, 180A, 180B, 180C such that the respective four scintillator bars 110 form a functional group 150, and wherein the transparent sections 131 of each interface 130 are restricted to one side of a central virtual plane 170. The scintillator bars 110 have an axis of elongation parallel to the z-axis. The scintillator array 150 comprises (at least) a second set of interface patterns 180, wherein the interface patterns 180 of the second set are rotationally symmetrical to the interface patterns 180 of the first set, especially wherein a rotation of 180° of any of the interface patterns 180 of the first set yields any one of the interface patterns 180 of the second set. The interface patterns 180 of the first set are comprised in the interfaces 130 perpendicular to the y-axis, whereas the interface patterns 180 of the second set are comprised in the interfaces 130 perpendicular to the x-axis. In further embodiments, essentially all sets of four adjacent scintillator bars along an axis form a functional group. In such embodiment, the interfaces along an axis may follow a regular pattern of the interfaces 130A (A), 130B (B), and 130C (C) according to Fig. 1A-C, such as ABCABC.

Fig. 5A-C schematically depict a cross-section of embodiments of the scintillator array 100, wherein the cross-section resembles a pixelated grid 190, wherein the pixels are scintillator bars 110, and wherein the grid lines comprise the interfaces 130.

Fig. 5A depicts a cross-section of an embodiment of the scintillator array 100 as depicted in Fig. 4. In this depiction, four functional groups 150 comprising the central scintillator bar 110 are depicted. Hence, a gamma ray interaction in the central scintillator bar 110 results in a spread of scintillation photons to the other scintillator bars 110 in the depicted functional groups 150, wherein the spread of scintillation photons depends on the DOI of the gamma ray interaction. Specifically, each depicted functional group 150 includes a virtual full reflective interface 137 as seen from the central scintillator bar 110. Hence, any scintillation photons originating from a gamma ray interaction in the central scintillator bar 110 and travelling perpendicular to the interfaces 130 will not travel through more than three scintillator bars 110, including the central scintillator bar 110, prior to encountering a reflective section 135 of an interface 130.

Fig. 5B depicts a cross-section of an embodiment of the scintillator array 100 as depicted in Fig. 4. In this cross-section, the interfaces 130, 130A, 130B, 130C include interface patterns 180 according to a regular patterning. Specifically, each grid line comprises seven interfaces 130 wherein each of the seven interfaces 130, 130A, 130B, 130C includes the same interface pattern 180, wherein the interface patterns 180 are comprised in the set of interface patterns 180, 180A, 180B, 180C depicted in Fig. 1AC, wherein the interfaces 130, 130A, 130B, 130C in adjacent parallel grid lines include a different one of the interface patterns 180, 180A, 180B, 180C. Hence, in this embodiment, each set of four adjacent scintillator bars 110 along an axis is comprised in a functional group 150. Each scintillator bar 110 is thus comprised in a plurality (2-8) of functional groups 150, wherein at least one of the respective functional groups 150 lies along the x-axis, and at least one of the respective functional groups 150 lies along the yaxis. Each scintillator bar 110 is thus comprised in a plurality of functional groups 150, wherein at least some of the functional groups 150 are configured orthogonal.

Fig. 5C depicts a cross-section of another embodiment of the scintillator array 100, wherein the scintillator array 100 comprises right hexagonal prismatic scintillator bars 110. In this embodiment, the light sharing interfaces 130 are configured perpendicular to three axes Al, A2, and A3, wherein A2 is essentially equal to the X-axis, and wherein Al and A3 are a rotation of A2 over the z-axis over respectively 60 and 120 degrees. In this embodiment, the functional groups 150 vary in the number n of comprised scintillator bars 110. The depiction shows three functional groups 150, wherein the respective functional groups 150 comprise three, four, and five scintillator bars 110. In further embodiments, the scintillator array 100 may have an irregular arrangement of functional groups 150. For example, larger functional groups 150 may be present, and some scintillator bars 110 may not be comprised in any functional groups 150. In alternative further embodiments, the scintillator array 100 may have a regular arrangement of functional groups 150. For example, the functional groups 150 including interfaces 130 perpendicular to Al may comprise three scintillator bars 110, whereas the functional groups 150 including interfaces 130 perpendicular to A2 and A3 may respectively comprise four and five scintillator bars 110.

Fig. 6 schematically depicts an embodiment of the gamma ray detector 200 comprising an embodiment of the scintillator array 100 as depicted in Fig. 4, and further comprising a photosensor unit 210. For visualization purposes part of the scintillator array

100 has been removed to depict the internal structure of the gamma ray detector 200, highlighting the presence of different interface patterns 180, 180A, 180B, 180C. The scintillator array 100 is bordered by the photosensor unit 210 on one side and a reflective material (“cover”) 230 covers the other sides. The photosensor unit 210 comprises a plurality of photosensors 211. In this embodiment, the photosensors 211 are functionally coupled to the scintillator bars 110 in a 1-on-l fashion; in other embodiments, the photosensors 211 may be functionally coupled to a set of scintillator bars 110, such as with 2x2 scintillator bars 110 or 3x3 scintillator bars 110. The reflective material 230 reflects scintillation photons but does not appreciably reflect gamma rays, especially it does not reflect gamma rays. In further embodiments, the gamma ray detector 200 may comprise an additional photosensor unit 210 on the opposite side of the scintillator array 100 as the depicted photosensor unit 210. In such a further embodiment, the reflective material 230 does not cover the respective opposite side of the scintillator array 100. As shown in Fig. 6, at least two orthogonally configured interfaces are confined to a different side of the virtual plane 170, see the bars with some more detail at the front right edge.

Fig. 7A-C schematically depict an exemplary spread 161 of scintillation light (“scintillation photons”) 160 in an embodiment of the gamma ray detector 200, wherein the spread 161 is measured by the detection of scintillation photons 160 by the photosensors 211 functionally coupled to each of the scintillator bars 110. In this pixelated grid 190 depiction, the hatching of each pixel (scintillator bar 110) indicates a relative amount of scintillation light 160 detected by the photosensors 211 functionally coupled to the respective scintillator bar 110, wherein the quantity of detected scintillation light 160 is indicated via hatching, wherein the most dense hatching indicates no detected scintillation light 160 and white indicates a relatively large amount of detected scintillation light 160. The scintillator array 100 in this embodiment of the gamma ray detector 200 resembles the scintillator array of Fig. 4. Especially, the top half of the scintillator array 100 - above the central plane 170 - has interfaces 130 perpendicular to the y-axis, whereas the bottom half of the scintillator array 100 has interfaces 130 perpendicular to the x-axis. In the depicted examples, scintillation events take place at different DOI in the central scintillator bar 110 of the 7x7 scintillator array. The central scintillator bar 110 is part of a plurality of functional groups 150, wherein at least some of the functional groups 150 each comprise four scintillator bars 110 (n=4), wherein four of the functional groups 150 are particularly relevant for the depicted examples. In these four functional groups 150 the central scintillator bar 110 of the scintillator array 100 is an outer scintillator bar 110 for the respective functional group 150. Hence, the spread 160 of scintillation light 161 from the central bar 110 essentially reaches two scintillator bars 110 in a given direction prior to encountering the last interface 130 of a virtual full reflective boundary 137. Fig. 7A schematically depicts the spread 161 of scintillation photons 160 emitted from a scintillation event near the ‘top’ of the scintillator array 100, i.e., near the side of the scintillation array 100 opposite of the photosensor unit 210, wherein the spread 161 of scintillation light 160 primarily lies along the y-axis. Fig. 7B schematically depicts the spread 161 of scintillation photons 160 emitted from a scintillation event near the central plane 170 of the scintillator array 100, wherein the spread 160 of scintillation light 161 is roughly identical along the x-axis and the y-axis.

Fig. 7C schematically depicts the spread 160 of scintillation photons 161 emitted from a scintillation event near the bottom of the scintillation array 100, wherein the spread 160 of scintillation light 161 primarily lies along the x-axis. The unique patterns of the spread 160 of scintillation light 161 depending on the DOI in the scintillator array 110 enables the estimation of the DOI, i.e., the larger the DOI the higher in the scintillator array 110 the scintillation event takes place, thus the larger the proportion is of the spread 160 of the scintillation light 161 that lies along the y-axis.

The terms “upstream” and “downstream” relate to an arrangement of items or features relative to the propagation of rays from a ray generating means wherein relative to a first position within a ray from the ray generating means, a second position in the ray closer to the ray generating means is “upstream”, and a third position within the ray further away from the ray generating means is “downstream”.

The terms “substantially” and “essentially” herein, such as in “substantially all light” or in “substantially consists”, will be understood by the person skilled in the art. The terms “substantially” and “essentially may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjectives substantially and essentially may also be removed. Where applicable, the terms “substantially” and “essentially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%. The term “comprise” includes also embodiments wherein the term “comprises” means “consists of’. The term “and/or” especially relates to one or more of the items mentioned before and after “and/or”. For instance, a phrase “item 1 and/or item 2” and similar phrases may relate to one or more of item 1 and item 2. The term comprising may in an embodiment refer to consisting of' but may in another embodiment also refer to containing at least the defined species and optionally one or more other species.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

The devices herein are amongst others described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation or devices in operation.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb to comprise and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article a or an preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The invention further applies to a device comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterizing features described in the description and/or shown in the attached drawings.

The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.

The project leading to this application has received funding from the European

Union’s Horizon 2020 research and innovation program under grant agreement No 667211.

Claims (18)

Conclusions A scintillator arrangement (100) comprising an arrangement of scintillator bars (110) configured to absorb and scintillate incoming gamma rays, thereby emitting scintillation photons (160), wherein neighboring scintillator bars (110) comprise interfaces (130), wherein a functional group (150) of n neighboring scintillator bars (110) comprises interfaces (130) configured in parallel, each interface (130) comprising an interface pattern (180) of one or more reflective sections (135) and one or more transparent sections (131), wherein within the functional group (150) virtual linear paths (140) along an axis perpendicular to the interfaces (130) at least one reflective section (135) of one of the interfaces (130) within the functional group (150) and at least one transparent section (131) of one of the interfaces (130) within the functional group (150), and where n> 3. The scintillator arrangement (100) according to claim 1, wherein all virtual linear paths (140) along an axis perpendicular to the interfaces (130) have at least one reflective section (135) of one of the interfaces (130) within the functional group ( 150). The scintillator arrangement (100) according to any of the preceding claims, wherein the scintillator bars (110) have one or more shapes selected from the group of straight regular prisms, and wherein the scintillator bars have an upper base plane (112), a lower base plane and a have an even number of side faces (114). The scintillator arrangement (100) according to any of the preceding claims, wherein the reflective sections (135) of each interface (130) included in the functional group (150) are configured such that for each of the interfaces (130) one or more of the virtual linear paths (140) only meet the reflective sections (135) of the respective interface (130). The scintillator arrangement (100) according to any of the preceding claims, comprising a plurality of functional groups (150). The scintillator arrangement (100) according to claim 5, comprising a plurality of regularly arranged functional groups (150). The scintillator arrangement (100) according to any of the preceding claims 5-6, wherein each scintillator rod (110) is included in one or more functional groups (150). The scintillator arrangement (100) according to any of the preceding claims 5-7, wherein each scintillator rod (110) is included in a plurality of functional groups (150), wherein at least two of the functional groups (150) of the plurality of functional groups (150) have non-parallel interfaces (130). The scintillator arrangement (100) according to any of the preceding claims, wherein the scintillator arrangement (100) comprises one or more parallel virtual planes (170) perpendicular to the interfaces (130), and wherein the transparent sections (131) of all interfaces (131) 130) within one or more of the functional groups (150) to one side of each of the virtual planes (170). The scintillator arrangement (100) according to claim 9 and one of the preceding claims 5-8, wherein the scintillator bars (110) have a shape selected from the group of straight rectangular prisms, the scintillator bars (110) having at least two orthogonally configured interfaces (130), wherein one of the one or more virtual planes (170) is configured in the center of the scintillator arrangement (100) and configured perpendicular to the at least two orthogonally configured interfaces (130), and wherein the at least two Orthogonally configured interfaces to another side of at least one of the virtual planes (170) are limited. The scintillator arrangement (100) according to any of the preceding claims, wherein the scintillator arrangement (100) comprises a predetermined number of different interface patterns (180) wherein each interface pattern (180) has a unique sectional distribution of the one or more reflective sections (135) and defines one or more transparent sections (131). The scintillator arrangement (100) according to any of the preceding claims, wherein the scintillator arrangement (100) comprises a plurality of sets of different interface patterns (180), the interfaces (130) included in the functional group (150) each of the interface patterns (180) of one of the one or more sets of interface patterns (180) comprise a single time. The scintillator arrangement (100) according to any of the preceding claims, wherein a superposition of the one or more transparent sections (131) of the interfaces (130) in one or more of the functional groups (150) has a symmetrical stepwise V-shape (133). The scintillator arrangement (100) according to any of the preceding claims, wherein the interfaces (130) include one or more of a reflective film on a side face (114) of a scintillator rod (110), a reflective coating on a side face (114) of a scintillator rod (110), a reflective tape on a side surface (114) of a scintillator rod (110), or an etching of a side surface (114) of a scintillator rod (110). A gamma ray detector (200) comprising the scintillator arrangement (100) according to any one of the preceding claims, wherein the gamma ray detector (200) comprises one or more photosensor units (210), the one or more photosensor units (210) being configured to detect and measuring scintillation photons (160) from the scintillator bars (HO). The gamma ray detector (200) according to claim 15, wherein the gamma ray detector (200) further comprises a collimator configured upstream of the scintillator arrangement (100), the collimator configured to collimate incoming gamma rays. The gamma ray detector (200) according to any of claims 15-16, wherein the gamma ray detector (200) further comprises one or more light guides, the light guides being configured downstream of the scintillator rods (110) and upstream of the photo sensor units (210), wherein the one or more photosensor units (210) comprise a plurality of photosensors (211), and wherein the light guides are configured to guide the scintillation photons (160) from the scintillator bars (110) to the photosensors (211). A nuclear imaging system comprising one or more gamma ray detectors (200) according to any of claims 15-17, wherein the nuclear imaging system further comprises a deployment area and a control system functionally coupled to the gamma ray detectors (200), wherein the gamma ray detectors (200) are configured to detect gamma rays emitted from a radioactive source in the deployment area and to provide output signals, the operating system configured to locate the radioactive source based on the output signals, and an estimate of a depth of interaction of the gamma rays in the gamma ray detectors (200) contributes to locating the radioactive source. 131 135B FIG. 1D FIG. 1E FIG. 2A 180 110 180 FIG. 2B FIG. 2C FIG. 3B