Photomultiplier Array Research Articles

Submillimeter-Resolution PET for High-Sensitivity Mouse Brain Imaging.

PET is a powerful molecular imaging technique that can provide functional information on living objects. However, the spatial resolution of PET imaging has been limited to around 1 mm, which makes it difficult to visualize mouse brain function in detail. Here, we report an ultrahigh-resolution small-animal PET scanner we developed that can provide a resolution approaching 0.6 mm to visualize mouse brain function with unprecedented detail. Methods: The ultrahigh-resolution small-animal PET scanner has an inner diameter of 52.5 mm and axial coverage of 51.5 mm. The scanner consists of 4 rings, each of which has 16 depth-of-interaction detectors. Each depth-of-interaction detector consists of a 3-layer staggered lutetium yttrium orthosilicate crystal array with a pitch of 1 mm and a 4 × 4 silicon photomultiplier array. The physical performance was evaluated in accordance with the National Electrical Manufacturers Association NU4 protocol. Spatial resolution was evaluated with phantoms of various resolutions. In vivo glucose metabolism imaging of the mouse brain was performed. Results: Peak absolute sensitivity was 2.84% with an energy window of 400-600 keV. The 0.55-mm rod structure of a resolution phantom was resolved using an iterative algorithm. In vivo mouse brain imaging with 18F-FDG clearly identified the cortex, thalamus, and hypothalamus, which were barely distinguishable in a commercial preclinical PET scanner that we used for comparison. Conclusion: The ultrahigh-resolution small-animal PET scanner is a promising molecular imaging tool for neuroscience research using rodent models.

Handheld portable neutron gamma discrimination spectrometer for environmental detection

A compact and integrated neutron-gamma discrimination spectrometer that could be utilized for personal dosimetry and emergency response is urgently required. In this study, based on a CLYC scintillator coupled to silicon photomultiplier(SiPM) arrays, we designed a stand-alone, hand-held neutron-gamma discrimination spectrometer. After the analog-to-digital converter (ADC) digitizes the analog signal from the detector, the data is transmitted to a FPGA processor for online real-time processing, and then transmitted to a microcontroller through the serial peripheral interface(SPI) protocol, and the current detection result is displayed in real-time on the touch screen. By using the pulse signal discrimination(PSD) method, the spectrometer can simultaneously measure the spectrum of neutron and gamma events, with a resolution of 8.8% (at 1274.5 keV) and excellent linearity. The figure of merit (FOM) is 2.32 with optimized PSD parameters. The experimental results show that the spectrometer integrates the upper computer and detector, with real-time performance, portability and excellent neutron-gamma resolution. Online operation is realized through the touch screen, which greatly facilitates the real-time detection of radiation in the field environment.

Development of multichord ion Doppler spectroscopy system for toroidal flow measurement of field-reversed configuration.

A double-chord ion Doppler spectroscopy (IDS) system was developed to measure the ion temperature and flow velocity of field-reversed configuration (FRC) plasmas in the FRC amplification via a translation-collisional merging (FAT-CM) device. Adopting a Czerny-Turner mount monochromator and 16-channel photomultiplier tube array, the developed IDS system achieves high wavelength resolution and fast time response. In addition, two vertically aligned optical paths share the optical system up to the monochromator and then branch just before the detector, successfully reducing crosstalk to <1%. The Doppler broadening was measured at two measurement points in the FAT-CM device, simultaneously, and ion temperatures of ∼50eV were measured. Toroidal spin-up from 7 to 15 km/s and a steady flow velocity of ∼10 km/s were estimated from the Doppler shift obtained by the developed system. The observation of the toroidal flow velocity and the spatial profile of the ion temperature of the FRC plasma in the FAT-CM device were realized. These spectroscopic diagnostic's double chord capabilities will aid in understanding and improving the FRC plasmas.

Performance evaluation of VRAIN: a brain-dedicated PET with a hemispherical detector arrangement

Objective. For PET imaging systems, a smaller detector ring enables less intrinsic spatial resolution loss due to the photon non-collinearity effect as well as better balance between production cost and sensitivity, and a hemispherical detector arrangement is more appropriate for brain imaging than a conventional cylindrical arrangement. Therefore, we have developed a brain-dedicated PET system with a hemispherical detector arrangement, which has been commercialized in Japan under the product name of VRAINTM. In this study, we evaluated imaging performance of VRAIN. Approach. The VRAIN used 54 detectors to form the main hemispherical unit and an additional half-ring behind the neck. Each detector was composed of a 12 × 12 array of lutetium fine silicate crystals (4.1 × 4.1 × 10 mm3) and a 12 × 12 array of silicon photomultipliers (4 × 4 mm2 active area) with the one-to-one coupling. We evaluated the physical performance of VRAIN according to the NEMA NU 2–2018 standards. Some measurements were modified so as to fit the hemispherical geometry. In addition, we performed 18F-FDG imaging in a healthy volunteer. Main results. In the phantom study, the VRAIN showed high resolution for separating 2.2 mm rods, 229 ps TOF resolution and 19% scatter fraction. With the TOF gain for a 20 cm diameter object (an assumed head diameter), the peak noise-equivalent count rate was 144 kcps at 9.8 kBq ml−1 and the sensitivity was 25 kcps MBq−1. Overall, the VRAIN provided excellent image quality in phantom and human studies. In the human FDG images, small brain nuclei and gray matter structures were clearly visualized with high contrast and low noise. Significance. We demonstrated the excellent imaging performance of VRAIN, which supported the advantages of the hemispherical detector arrangement.

An automated QC station for the calibration of the Mu2e calorimeter readout units

The Mu2e calorimeter will employ Readout Units, each made of two Silicon Photomultipliers arrays and two Front End Electronics boards. To calibrate them, we have designed, assembled and put in operation an automated Quality Control (QC) station. Gain, collected charge and photon detection efficiency are evaluated for each unit. In this paper, the QC Station is presented, in its hardware and software aspects, summarizing also the tests performed on the ROUs and the first measurement results.

Test-beam demonstration of a TORCH prototype module

The TORCH time-of-flight detector is designed to provide a 15 ps timing resolution for charged particles, resulting in π/K particle identification up to 10 GeV/c momentum over a 10 m flight path. Cherenkov photons, produced in a quartz plate of 10 mm thickness, are focused onto an array of micro-channel plate photomultipliers (MCP-PMTs) which measure the photon arrival times and spatial positions. A half-scale (660 × 1250 × 10 mm3) TORCH demonstrator module has been tested in an 8 GeV/c mixed proton-pion beam at CERN. Customised square MCP-PMTs of active area 53 × 53 mm2 and granularity 64 × 64 pixels have been employed, which have been developed in collaboration with an industrial partner. The single-photon timing performance and photon yields have been measured as a function of beam position in the radiator, giving measurements which are consistent with expectations. The expected performance of TORCH for high luminosity running of the LHCb Upgrade II has been simulated.

Simulation of a Compton-pair imaging calorimeter and tracking system for the next generation of MeV gamma-ray telescopes

The astrophysical community is currently focusing its efforts in the development of a new generation of gamma-ray telescopes to detect low-energy photons in the MeV-GeV energy range, operating both in the Compton and pair conversion regimes. The reconstruction of the incident photons energy and direction is not straightforward, as the range of secondary particles produced by photon interactions is usually short. We propose a detector consisting of a tracker system based on scintillating fibers and of a Compton-pair imaging calorimeter made of CsI(Na) crystals coupled to wavelength shifting (WLS) fibers read out by Silicon Photomultiplier (SiPM) arrays. We have developed a dedicated simulation code to study the performance of this detector. The simulation takes into account the optical photon production and propagation inside the fibers and is used to optimize the fiber geometrical and optical properties and the design of the readout system.

Evaluation of a positron-emission-tomography-based SiPM readout for compact segmented neutron imagers

Gamma-ray emission from special nuclear material (SNM) is relatively easy to shield from detection using modest amounts of high-Z material. In contrast, fast-neutrons are much more penetrating and can escape relatively thick high-Z shielding without losing significant energy. Furthermore, fast neutrons provide a clear and unambiguous signature of the presence of SNM with few competing natural background sources. The challenge of detecting fast neutrons is twofold. First, the neutron flux from SNM are only a fraction of the corresponding gamma-ray flux. Second, fast neutrons can be difficult to differentiate from gamma rays. The ability to discriminate gamma rays from neutrons, combined with a neutron imaging capability, can in some situations enable the localization of SNM neutron sources distinct from background. With the developments of pulse-shape-sensitive plastic scintillators that offer excellent gamma-ray/neutron discrimination, and arrays of silicon photomultipliers combined with highly scalable and fast positron-emission-tomography (PET) multi-channel readout systems, field-deployable neutron imagers suitable for SNM detection might now be within reach. In this paper, we present a characterization of the performance of a recently available commercial PET-scanner readout, including its sensitivity to pulse-shape differences between fast neutrons and gamma rays, energy and timing resolution. We find that, while the pulse-shape discrimination is achievable with stilbene, further improvement of the readout is required to achieve it with the PSD-capable available plastic scintillators.

Proton irradiation of SiPM arrays for POLAR-2

POLAR-2 is a space-borne polarimeter, built to investigate the polarization of Gamma-Ray Bursts and help elucidate their mechanisms. The instrument is targeted for launch in 2024 or 2025 aboard the China Space Station and is being developed by a collaboration between institutes from Switzerland, Germany, Poland and China. The instrument will orbit at altitudes between 340km and 450km with an inclination of {42}{^{circ }} and will be subjected to background radiation from cosmic rays and solar events. It is therefore pertinent to better understand the performance of sensitive devices under space-like conditions. In this paper we focus on the radiation damage of the silicon photomultiplier arrays S13361-6075NE-04 and S14161-6050HS-04 from Hamamatsu. The S13361 are irradiated with 58MeV protons at several doses up to 4.96Gy, whereas the newer series S14161 are irradiated at doses of 0.254Gy and 2.31Gy. Their respective performance degradation due to radiation damage are discussed. The equivalent exposure time in space for silicon photomultipliers inside POLAR-2 with a dose of 4.96Gy is 62.9years (or 1.78years when disregarding the shielding from the instrument). Primary characteristics of the I-V curves are an increase in the dark current and dark counts, mostly through cross-talk events. Annealing processes at {25}{^{circ }C} were observed but not studied in further detail. Biasing channels while being irradiated have not resulted in any significant impact. Activation analyses showed a dominant contribution of beta ^{+} particles around 511 keV. These resulted primarily from copper and carbon, mostly with decay times shorter than the orbital period.

Fiber-optical analysis of weak knock and pressure oscillations in a single cylinder research engine

The effect of characteristic cycle-to-cycle variations on knock in gasoline engines is not yet fully understood. The analysis requires the use of experimental techniques to characterize weak knock events on a cycle-individual basis. To this end, a novel processing method is presented that focuses on characterizing weak knock events using data from a fiber optic spark plug linked to a high-resolution (400 kHz) photo-multiplier array. The method was applied to a single cylinder research engine. By combining signal and image processing and reconstruction methods, it is shown that reliable automated detection of spatial knock origin is possible for Knock-Peak-Peak pressure values as low as 0.7 bar. Furthermore, the fiber optic spark plug data are used to accurately localize and characterize the pressure oscillations induced by auto-ignition which are shown to be closely related to the number, intensity, and relative location of individual knock events.

DH-Mammo PET: a dual-head positron emission mammography system for breast imaging

Objective. To develop a simultaneous positron emission tomography-Optical (OPET) breast imaging dual-head PET subsystem, called DH-Mammo PET, for accurate, early diagnosis and efficacy assessment of breast cancer with high resolution and sensitivity. Approach. We developed a breast-dedicated PET based on LYSO crystal, silicon photomultiplier array and multi-voltage threshold sampling technique. It consists of two detector heads, each with a detection area of 216 mm × 145.5 mm. The distance between the detector heads is fixed at 120 mm. In order to extract coincidences and correct data, GPU-based software coincidence processing, random, scatter, normalization, gap-filling and attenuation corrections were applied in turn. The images were reconstructed using maximum likelihood expectation maximization with depth of interaction (DOI) modeling. The performance of DH-Mammo PET was evaluated referring to NEMA NU 4–2008, NU 2–2007 and Chinese industry recommended standard YY/T 1835–2022. Besides, several clinical patient images of DH-Mammo PET were compared with those of a whole-body PET/CT. Main results. The energy resolution was 14.5%, and time resolution was < 1.31 ns. Indicated by the 22Na point source imaging, its spatial resolution was 2.60 mm (5.40 mm), 1.00 mm (1.04 mm), and 0.96 mm (0.93 mm) in the X, Y and Z directions, respectively, using the system response matrix with (without) DOI modeling. Indicated by the Derenzo phantom imaging, the spatial resolution was ∼3.0 mm, <1.2 mm, and <1.2 mm in the X, Y and Z directions. The system sensitivity was 6.87%, 4.89% and 3.37% with an energy window of 100–800, 250–750 and 350–650 keV, respectively. The scatter fraction was 26.43%, and the peak NECR was 162.6 kcps at 24.1 MBq for the modified rat-like phantom. As for the recovery coefficients, they ranged from 0.15 to 1.04 for rods between 1 and 5 mm obtained with a NEMA image quality phantom. The spill-over ratio for the air-filled and water-filled chamber was 0.05 and 0.11, respectively. DH-Mammo PET can provide more image details in clinical experiments and fulfil a fast scan with 60–120 s acquisition time. Significance. Good spatial resolution and high sensitivity of DH-Mammo PET would enable fast and accurate PET imaging of the breast. Besides, combining the DH-Mammo PET with the diffuse optical tomography would make full use of tumor metabolic imaging and tissue endogenous optical imaging, which would improve the accuracy of early clinical diagnosis of small lesions of breast cancers.

Effect of Strong Azimuthal Swirl on Ignition and Light-Around in an Annular Combustor

Abstract In this paper, we investigate the effect of strong azimuthal swirl on ignition dynamics in a laboratory-scale annular combustor. Bulk azimuthal swirl was produced by a novel angled injector configuration, producing swirling jet flames oriented downwards toward the combustor backplane and in the azimuthal direction, replicating a simplified version of the SAFRAN spinning combustor concept. To provide more realistic flow conditions, the design included rich-quench-lean (RQL) staging via a circumferential distribution of dilution ports and an effusion cooled combustor backplane. High-speed imaging and an azimuthal array of photomultipliers to measure OH* chemiluminescence were used to characterize the ignition dynamics for different injector velocities and global equivalence ratios. The mass flows through the injectors, dilution ports, and effusion cooled backplane were independently metered so that the injector equivalence ratio and global equivalence ratio could be separately controlled. The light-around times were found to have no clear correlation with the injector velocity since the rich injector equivalence ratio meant the flame burned in a nonpremixed mode even though the global equivalence ratio was lean due to the RQL staging. However, it was found that lower injector velocities extended the lean ignition limit based on the global equivalence ratio. The ignition sequence during light-around (order in which the injectors are ignited) was found to be highly repeatable, igniting each consecutive injector in the anticlockwise direction (the direction of bulk swirl). In rare cases, the ignition sequence was observed to branch in both directions. Finally, in an effort to extend the lean ignition limit, the effect of azimuthal staging was investigated. Two configurations were tested. In the first configuration, the injectors on one half of the annulus were operated at a fixed equivalence ratio whereas the other half of the annulus was operated at a different equivalence ratio. In the second configuration, every second injector had the same equivalence ratio. Both configurations extended the lean extinction limit but the first configuration was the most effective.

Performance tests of the B-RAD radiation survey meter

This article discusses performance tests of the B-RAD by ELSE NUCLEAR. The B-RAD is a portable survey meter for γ-ray spectrometry and γ-ray dose rate measurements able to operate in the presence of a strong magnetic field. The detector uses a 15 mm right cylinder LaBr 3 crystal coupled with a 16-pixel Silicon Photomultiplier array. The crystal, the photodetector and the front-end electronics (the probe) are enclosed in a case connected with a cable to a control unit. The latter includes the main electronics, a customised battery pack, two displays and a Faraday cage.More in detail, this paper investigates the instrument performance inside magnetic field, including linearity of its response and its angular response. An operational test is also reported to demonstrate a practical application. The performed tests show that the B-RAD can operate inside magnetic fields up to 2.5 T. Two small shortcomings were observed: a pulling force is felt especially on the control unit, which becomes rather intense for values of the magnetic fields above 1 T, and a slight reduction of the signal gain with increasing magnetic field intensity when the control unit is inside the field. The latter causes a variation of the measured dose rate of less than 10% at 1.5 T. The response of the B-RAD with dose rate is linear up to 20 mSv/h with discrepancies between the reference and the measured dose rate within 10%. The response is isotropic from −120° to ＋120°; beyond this limit the measured dose rate drops by 66% probably because of the scattering of the source photons with the case and some shielding effects.

Measurement of angular correlations of Compton-scattered gamma quanta from positron annihilation using GAGG:Ce scintillator matrices with single-side readout

We measured azimuthal correlations of the Compton-scattered gamma quanta from positron annihilation with two 8 × 8 matrices of Gadolinium Aluminum Gallium Garnet doped with Cerium. Each detector matrix contains 64 crystals of size 3 mm × 3 mm × 20 mm and it is read-out by a single Silicon Photo-multiplier (SiPM) array, with one SiPM matching one pixel. The studied single-side readout concept keeps the modules compact and cost-efficient on a large scale. Coincidence events were recorded using a Na-22 source placed between the modules. We clearly identify and reconstruct the Compton scattering events and we observe the excess of orthogonally scattered gammas over the ones with the parallel azimuthal angles. We present the measured azimuthal modulation factors for several kinematic selection criteria and different inter-pixel distances.

Development of a compact and cost-effective PET detector module for a small-animal PET system with FESA ASIC

Due to the high cost and large channel number in positron emission tomography (PET) systems, the integration level and cost performance must be considered in the construction of commercial PET systems. In this paper, a highly integrated readout electronic system was designed and implemented based on a self-developed FESA (Front End for SiPM Arrays) readout ASIC; a compact cost-effective detector module with four lined up detector heads was built, and its performance was evaluated. Each detector head consisted of a 24× 24 LYSO crystal array (each crystal element had dimensions of 0.99 × 0.99 × 15 mm3), one end coupling to an 8 × 8 silicon photomultiplier array (SiPM array with dimensions of 3.2 × 3.2 mm2 each), and the other end covered with a 1 mm thick light guide layer. Since the front-end FESA readout chip employed a row-column summing circuit to reduce the readout channels from 64 to 16, we tried a new depth encoding method based on a single-end readout with the structure. The test results showed that the average coincidence time resolution (CTR), energy resolution, and depth of interaction (DOI) resolution of the detector are 413 ps, 15.7%, and 5.2 mm, respectively, while the crystal array in the detector head with 9-to-1 coupling can be clearly separated in the flood image. Compared with the detector head without the depth encoding ability, the clearness of the flood image was slightly decreased, but the energy resolution and time performance remained the same. We also implemented a central control board that connected all detector modules via fiber connections. The data from the detector modules could be collected over the connections, and the system central clock could be precisely distributed; therefore, the compactness of the electronics system was further enhanced.

A Compact Dual Gamma Neutron Detector Based on NaI(Tl+Li) Scintillator Readout with SiPM

Sodium iodide crystal co-doped with thallium and lithium is a promising scintillator with wide application prospects for dual gamma neutron detection. In this study, a compact gamma/neutron detector was developed based on 2-inch NaI(Tl+Li) (NaIL) scintillator readout with 8 × 8 silicon photomultiplier (SiPM) array. Dedicated transimpedance amplifier circuit was developed for the SiPM array. The energy resolution and response linearity with the SiPM array were evaluated and compared to those obtained with photomultiplier tube (PMT) readout. The energy resolution for 661.6 keV gamma rays was measured as 7.0% and 6.5% with SiPM array and PMT, respectively. The linear response of the SiPM array is almost the same as that of the PMT in the energy range up to ~4 MeV. Neutron and gamma pulse shape discrimination was evaluated by acquiring the pulse waveforms with a digitizer (12 bit/250 MSPS) and off-line analysis. The best figure of merit (FOM) was measured as 3.75 for the SiPM array with optimized parameters, close to the performance measured with PMT (FOM = 4.07). The experimental results show that the NaIL scintillator readout with SiPM array exhibit energy resolution equivalent to NaI(Tl) gamma detectors and excellent neutron/gamma discrimination, making it especially suitable for compact devices requiring gamma and neutron dual detection capabilities.

Demonstration of fast multiplicity counting of 252Cf using plastic scintillators and silicon photomultipliers

We present a first prototype for a multiplicity counter of fast neutrons and γ rays, based on plastic scintillators coupled to silicon photomultiplier arrays, where the SiPMs are read out individually by the TOFPET2 ASIC providing time-stamps and charge information. We demonstrate the capabilities of our counter by measuring the Singles-, Doubles- and Triples-event rates of neutrons and γ rays (without pulse shape discrimination), for a 252Cf source with a nominal activity of 4.9 μCi, and comparing them with a GEANT4 simulation of the process.

Data Compression in the NEXT-100 Data Acquisition System.

NEXT collaboration detectors are based on energy measured by an array of photomultipliers (PMT) and topological event filtering based on an array of silicon photomultipliers (SiPMs). The readout of the PMT sensors for low-frequency noise effects and detector safety issues requires a grounded cathode connection that makes the readout AC-couple with variations in the signal baseline. Strict detector requirements of energy resolution better than 1% FWHM require a precise baseline reconstruction that is performed offline for data analysis and detector performance characterization. Baseline variations make it inefficient to apply traditional lossy data compression techniques, such as zero-suppression, that help to minimize data throughput and, therefore, the dead time of the system. However, for the readout of the SiPM sensors with less demanding requirements in terms of accuracy, a traditional zero-suppression is currently applied with a configuration that allows for a compression ratio of around 71%. The third stage in the NEXT detectors program, the NEXT-100 detector, is a 100 kg detector that instruments approximately five times more PMT sensors and twice the number of SiPM sensors than its predecessor, the NEXT-White detector, putting more pressure in the DAQ throughput, expected to be over 900 MB/s with the current configuration, which will worsen the dead time of the acquisition data system. This paper describes the data compression techniques applied to the sensor data in the NEXT-100 detector, which reduces data throughput and minimizes dead time while maintaining the event rate to the level of its predecessor, around 50 Hz.

A neural network-based algorithm for simultaneous event positioning and timestamping in monolithic scintillators

Objective. Monolithic scintillator crystals coupled to silicon photomultiplier (SiPM) arrays are promising detectors for PET applications, offering spatial resolution around 1 mm and depth-of-interaction information. However, their timing resolution has always been inferior to that of pixellated crystals, while the best results on spatial resolution have been obtained with algorithms that cannot operate in real-time in a PET detector. In this study, we explore the capabilities of monolithic crystals with respect to spatial and timing resolution, presenting new algorithms that overcome the mentioned problems. Approach. Our algorithms were tested first using a simulation framework, then on experimentally acquired data. We tested an event timestamping algorithm based on neural networks which was then integrated into a second neural network for simultaneous estimation of the event position and timestamp. Both algorithms are implemented in a low-cost field-programmable gate array that can be integrated in the detector and can process more than 1 million events per second in real-time. Results. Testing the neural network for the simultaneous estimation of the event position and timestamp on experimental data we obtain 0.78 2D FWHM on the (x, y) plane, 1.2 depth-of-interaction FWHM and 156 coincidence time resolution on a LYSO monolith read-out by 64 Hamamatsu SiPMs. Significance. Our results show that monolithic crystals combined with artificial intelligence can rival pixellated crystals performance for time-of-flight PET applications, while having better spatial resolution and DOI resolution. Thanks to the use of very light neural networks, event characterization can be done on-line directly in the detector, solving the issues of scalability and computational complexity that up to now were preventing the use of monolithic crystals in clinical PET scanners.

Performance evaluation of side-by-side optically coupled monolithic LYSO crystals.

BackgroundSignificant interest has been recently shown for using monolithic scintillation crystals in molecular imaging systems, such as positron emission tomography (PET) scanners. Monolithic‐based PET scanners result in a lower cost and higher sensitivity, in contrast to systems based on the more conventional pixellated configuration. The monolithic design allows one to retrieve depth‐of‐interaction information of the impinging 511 keV photons without the need for additional hardware materials or complex positioning algorithms. However, the so‐called edge‐effect inherent to monolithic‐based approaches worsens the detector performance toward the crystal borders due to the truncation of the light distribution, thus decreasing positioning accuracy.PurposeThe main goal of this work is to experimentally demonstrate the detector performance improvement when machine‐learning artificial neural‐network (NN) techniques are applied for positioning estimation in multiple monolithic scintillators optically coupled side‐by‐side.MethodsIn this work, we show the performance evaluation of two LYSO crystals of 33 × 25.4 × 10 mm3 optically coupled by means of a high refractive index adhesive compound (Meltmount, refractive index n = 1.70). A 12 × 12 silicon photomultiplier array has been used as photosensor. For comparison, the same detector configuration was tested for two additional coupling cases: (1) optical grease (n = 1.46) in between crystals, and (2) isolated crystals using black paint with an air gap at the interface (named standard configuration). Regarding 2D photon positioning (XY plane), we have tested two different methods: (1) a machine‐learning artificial NN algorithm and (2) a squared‐charge (SC) centroid technique.ResultsAt the interface region of the detector, the SC method achieved spatial resolutions of 1.7 ± 0.3, 2.4 ± 0.3, and 2.6 ± 0.4 mm full‐width at half‐maximum (FWHM) for the Meltmount, grease, and standard configurations, respectively. These values improve to 1.0 ± 0.2, 1.2 ± 0.2, and 1.2 ± 0.3 mm FWHM when the NN algorithm was employed. Regarding energy performance, resolutions of 18 ± 2%, 20 ± 2%, and 23 ± 3% were obtained at the interface region of the detector for Meltmount, grease, and standard configurations, respectively.ConclusionsThe results suggest that optically coupling together scintillators with a high refractive index adhesive, in combination with an NN algorithm, reduces edge‐effects and makes it possible to build scanners with almost no gaps in between detectors.