Gadolinium Aluminum Gallium Garnet Research Articles

Comparative Validation of Scintillator Materials for X-Ray-Mediated Neuronal Control in the Deep Brain.

When exposed to X-rays, scintillators emit visible luminescence. X-ray-mediated optogenetics employs scintillators for remotely activating light-sensitive proteins in biological tissue through X-ray irradiation. This approach offers advantages over traditional optogenetics, allowing for deeper tissue penetration and wireless control. Here, we assessed the short-term safety and efficacy of candidate scintillator materials for neuronal control. Our analyses revealed that lead-free halide scintillators, such as Cs3Cu2I5, exhibited significant cytotoxicity within 24 h and induced neuroinflammatory effects when injected into the mouse brain. In contrast, cerium-doped gadolinium aluminum gallium garnet (Ce:GAGG) nanoparticles showed no detectable cytotoxicity within the same period, and injection into the mouse brain did not lead to observable neuroinflammation over four weeks. Electrophysiological recordings in the cerebral cortex of awake mice showed that X-ray-induced radioluminescence from Ce:GAGG nanoparticles reliably activated 45% of the neuronal population surrounding the implanted particles, a significantly higher activation rate than europium-doped GAGG (Eu:GAGG) microparticles, which activated only 10% of neurons. Furthermore, we established the cell-type specificity of this technique by using Ce:GAGG nanoparticles to selectively stimulate midbrain dopamine neurons. This technique was applied to freely behaving mice, allowing for wireless modulation of place preference behavior mediated by midbrain dopamine neurons. These findings highlight the unique suitability of Ce:GAGG nanoparticles for X-ray-mediated optogenetics. The deep tissue penetration, short-term safety, wireless neuronal control, and cell-type specificity of this system offer exciting possibilities for diverse neuroscience applications and therapeutic interventions.

Effect of Ga/Al ratio on the luminescent properties of inorganic scintillating GGAG:(4 mol%)Ce ceramic powder

Gadolinium gallium aluminum garnet doped with cerium (GGAG:Ce), a promising ceramic scintillator material, is being excessively explored for its high quality optical properties by the bandgap engineering with different Ga/Al ratio. In this study, GGAG:Ce powders were synthesized using a solvothermal method and sintered at 1300 °C to investigate the impact of the gallium-to-aluminum (Ga/Al) ratio on optical characteristics. The results revealed that a decrease in the Ga/Al ratio led to a decrease in particle size. This observation can be attributed to the different reactivity and growth kinetics of gallium and aluminum precursors during the solvothermal process. Perturbations from the optimized Ga/Al ratio of 1.5–1.77 and 1.27 resulted in substantially enhanced photoluminescence (PL) and radioluminescence (RL) spectra intensities. PL lifetime measurements of various Ga/Al ratio exhibit average PL lifetime between 48 and 57 ns. Specifically, the deviations to 1.77 and 1.27 ratios yielded approximately 125 % and 106 %, respectively, in observed luminescent measurements compared to other ratios. This enhancement in PL and RL intensity suggests that the Ga/Al ratio plays a critical role in modulating the optical properties of GGAG:Ce ceramic powders. The results of this study also highlight the importance of the Ga/Al ratio in tailoring the optical or luminescence characteristics of GGAG:Ce powders.

The Large Imaging Spectrometer for Solar Accelerated Nuclei (LISSAN): A next-generation solar gamma-ray spectroscopic imaging instrument concept

We present the Large Imaging Spectrometer for Solar Accelerated Nuclei (LISSAN), a new solar dedicated satellite instrument concept. LISSAN relies on an indirect Fourier imaging technique valid over an energy range from 40 keV up to 100 MeV. Spatial information is encoded into 15 moiré patterns by 15 pairs of slightly offset grids (bigrids) separated by a fixed distance enabling a predicted spatial resolution of 10”. The time, location, and energy of each incoming photon is recorded via a pixelated gadolinium aluminium gallium garnet (GAGG) crystal scintillator detector placed in alignment with each bigrid, therefore providing simultaneous imaging and spectroscopy from the same imaging system. X-ray and gamma-ray emission are key diagnostics of electron and ion acceleration, respectively. However, despite being a fundamental process that occurs throughout the Universe, particularly in the solar atmosphere, only one resolved gamma-ray image of ion acceleration in a solar flare has ever been achieved. LISSAN will shed new light on this process by providing spectral resolution better than 1.5% FWHM at 6.1 MeV, an imaging effective area at 2.2 MeV of 100 cm2 (more than 25 times greater than past missions such as RHESSI) and a 10 s cadence. Thanks to these significant advances over the previous satellite-based solar detectors, LISSAN will provide reliable imaging and the spectral characterization of both electron and ion acceleration in solar eruptive events simultaneously for the first time, enabling to it to answer several important open questions regarding solar particle acceleration and the initiation of space weather events.

Ga/Al ratio induced afterglow behavior of Ce3+:GAGG scintillation ceramics

This work investigated the optical and scintillation properties of cerium-doped gadolinium aluminum gallium garnet (Ce:GAGG) ceramics with different gallium-to-aluminum (Ga/Al) ratios. The optical transmittance, fluorescence spectra, fluorescence lifetime, light yield, scintillation decay, and afterglow characteristics of the ceramic samples were studied. The experimental results reveal that the decay time of Ce:GAGG ceramic is significantly decreased with the increase of Ga content. The mean decay time of 60 ns is achieved when the Ga/Al ratio is 3:2 in our experiment. The light yield of ceramics varies from 12,140 to 44,825 ph/MeV with the change of Ga content, and the highest light yield is achieved when the Ga/Al ratio is 2.4:2.6. Noteworthy fluctuation in the afterglow performance is affected by the Ga content significantly. The afterglow intensity of the sample with Ga/Al = 2:3 is approximately 0.5 % of its initial intensity after the X-ray excitation was turned off for 5 s. The formation mechanism of defects which is related with the afterglow behaviors were investigated and discussed.

Optimization of Yonsei Single-Photon Emission Computed Tomography (YSECT) Detector for Fast Inspection of Spent Nuclear Fuel in Water Storage

Background: The gamma emission tomography (GET) device has been reported a reliable technique to inspect partial defects within spent nuclear fuel (SNF) of pin-by-pin level. However, the existing GET devices have low accuracy owing to the high attenuation and scatter probability for SNF inspection condition. The purpose of this study is to design and optimize a Yonsei single-photon emission computed tomography version 2 (YSECT.v.2) for fast inspection of SNF in water storage by acquisition of high-quality tomographic images.Materials and Methods: Using Geant4 (Geant4 Collaboration) and DETECT-2000 (Glenn F. Knoll et al.) Monte Carlo simulation, the geometrical structure of the proposed device was determined and its performance was evaluated for the 137Cs source in water. In a Geant4-based assessment, proposed device was compared with the International Atomic Energy Agency (IAEA)-authenticated device for the quality of tomographic images obtained for 12 fuel sources in a 14 × 14 Westinghouse-type fuel assembly.Results and Discussion: According to the results, the length, slit width, and septal width of the collimator were determined to be 65, 2.1, and 1.5 mm, respectively, and the material and length of the trapezoidal-shaped scintillator were determined to be gadolinium aluminum gallium garnet and 45 mm, respectively. Based on the results of performance comparison between the YSECT.v.2 and IAEA’s device, the proposed device showed 200 times higher performance in gamma-detection sensitivity and similar source discrimination probability.Conclusion: In this study, we optimally designed the GET device for improving the SNF inspection accuracy and evaluated its performance. Our results show that the YSECT.v.2 device could be employed for SNF inspection.

Feasibility study of spent fuel internal tomography (SFIT) for partial defect detection within PWR spent nuclear fuel

The International Atomic Energy Agency (IAEA) mandates safeguards to ensure non-proliferation of nuclear materials. Among inspection techniques used to detect partial defects within spent nuclear fuel (SNF), gamma emission tomography (GET) has been reported to be reliable for detection of partial defects on a pin-by-pin level. Conventional GET, however, is limited by low detection efficiency due to the high density of nuclear fuel rods and self-absorption. This paper proposes a new type of GET named Spent Fuel Internal Tomography (SFIT), which can acquire sinograms at the guide tube. The proposed device consists of the housing, shielding, C-shaped collimator, reflector, and gadolinium aluminum gallium garnet (GAGG) scintillator. For accurate attenuation correction, the source-distinguishable range of the SFIT device was determined using MC simulation to the region away from the proposed device to the second layer. For enhanced inspection accuracy, a proposed specific source-discrimination algorithm was applied. With this, the SFIT device successfully distinguished all source locations. The comparison of images of the existing and proposed inspection methods showed that the proposed method, having successfully distinguished all sources, afforded a 150 % inspection accuracy improvement.

Extra long phosphorescence in organic materials at cryogenic temperatures investigation

In this paper, investigations of extra-long phosphorescence in organic materials and optical crystals at cryogenic temperatures are presented. This study continues the cycle of our previous works devoted to the physical mechanism understanding of the long-run phosphorescence excitation. We wish to create an advanced and efficient laser for the media based on the Shpolsky matrix analogue. Another goal is to consider the possibility of building an optical processor with an extra-long phosphorescence effect. For this purpose we were examining the experimental setup of complicated organic materials: cocamidopropyl betadine C19H38N2O3, polyethylene terephthalate (C10H8O4) n , perfluoro (2-methyl-3-pentanone, Novec 649) CF3CF2C(O)CF(CF3)2, Kalosha benzine (benzine BR-2, Nefras С2 80/120). Different optic and piezo crystals were also investigated: gadolinium aluminum gallium garnet Gd3Ga3Al2O12:Ce, lanthanum gallium silicate La3Ga5SiO14, terbium gallium garnet Tb3Ga5O12 , La3Ga5,5Ta0,5O14.

Measurement of the non-linearity in the [formula omitted]-ray response of the GAGG:Ce inorganic scintillator

A characteristic of every inorganic scintillator crystal is its light yield, i.e., the amount of emitted scintillation photons per unit of energy deposited in the crystal. Light yield is known to be usually non-linear with energy, which impacts the spectroscopic properties of the scintillator.Cerium-doped gadolinium–aluminium–gallium garnet (GAGG:Ce) is a recently developed scintillator with several interesting properties, which make it very promising for space-based γ-ray detectors, such as in the HERMES nanosatellite mission. In this paper we report an accurate measurement of the GAGG:Ce non-linearity in the 20–662 keV γ-ray energy interval, using a setup composed of three samples of GAGG:Ce crystals read out by Silicon Drift Detectors (SDDs).

Development and evaluation of a compact gamma camera for radiation monitoring

The purpose of this study is to perform radiation monitoring by acquiring gamma images and real-time optical images for 99mTc vial source using charge couple device (CCD) cameras equipped with the proposed compact gamma camera. The compact gamma camera measures 86 × 65 × 78.5 mm3 and weighs 934 g. It is equipped with a metal 3D printed diverging collimator manufactured in a 45° field of view (FOV) to detect the location of the source. The circuit's system uses system-on-chip (SoC) and field-programmable-gate-array (FPGA) to establish a good connection between hardware and software. In detection modules, the photodetector (multi-pixel photon counters) is tiled at 8 × 8 to expand the activation area and improve sensitivity. The gadolinium aluminium gallium garnet (GAGG) measuring 0.5 × 0.5 × 3.5 mm3 was arranged in 38 × 38 arrays. Intrinsic and extrinsic performance tests such as energy spectrum, uniformity, and system sensitivity for other radioisotopes, and sensitivity evaluation at edges within FOV were conducted. The compact gamma camera can be mounted on unmanned equipment such as drones and robots that require miniaturization and light weight, so a wide range of applications in various fields are possible.

Testing the gallium anomaly

We study the online detection by gallium capture of mono-energetic neutrinos produced by a $^{51}$Cr radioactive source in a scintillation experiment. We find that cerium-doped gadolinium aluminum gallium garnet (GAGG) is a suitable scintillator which contains about 21% of gallium per weight and has a high mass density and light yield. Combined with a highly efficient light detection system this allows tagging of the subsequent germanium decay and thus a clean distinction of gallium capture and elastic neutrino electron scattering events. With 1.5 tons of scintillator and 10 source runs of 3.4MCi, each, we obtain about 760 gallium capture events with a purity of 85% and 680,000 neutrino electron scattering events, where the latter provide a precise normalization independent of any nuclear physics. This configuration would allow to test the gallium anomaly at more than $5\sigma$ in an independent way.

Structural and Scintillation Properties of Ce3+:Gd3Al3Ga2O12 Translucent Ceramics Prepared by One-Step Sintering.

Cerium-doped gadolinium aluminum gallium garnet (Ce3+:Gd3Al3Ga2O12, Ce3+:GAGG) ceramic is a promising scintillation material. In this study, Ce3+:Gd3Al3Ga2O12 scintillation ceramics were prepared by the one-step sintering of commercially available Gd2O3, Al2O3, Ga2O3, and CeO2 powders in a flowing oxygen atmosphere at 1600 °C by solid-phase reaction sintering. For all the Ce3+:Gd3Al3Ga2O12 ceramic samples doped with different amounts of Ce3+ doping, dense ceramics were obtained. The structure, photoluminescence, and scintillation properties of the Ce3+:Gd3Al3Ga2O12 ceramics have been investigated. The average grain size of samples sintered at 1600 °C is about 2 μm. The X-ray excitation luminescence peak is around 560 nm, which is consistent with that of Ce3+:Gd3Al3Ga2O12 single crystals, matching well with the computed tomography X-ray detector's response sensitivity. The light yield is higher compared to the standard reference sample-lutetium yttrium orthosilicate single crystal.

The co-optimization of efficiency and emission bandwidth in GSAGG:Cr3+ NIR ceramic phosphors

The NIR phosphor-converted light-emitting diode (NIR pc-LED) is a new near-infrared light source that has been widely studied. Among various NIR phosphors, Cr3+ doped gadolinium aluminum gallium garnet (GAGG:Cr3+) ceramic phosphor has shown great potential due to its ultra-high efficiency and thermal stability. Despite its capabilities, its detection range may be limited due to a relatively narrow emission bandwidth. To make the GAGG:Cr3+ ceramic phosphors achieve both high efficiency and broadband emission, a series of Gd3Al2-x-yScxGa3O12:yCr3+ (GASGG:Cr3+) ceramic phosphors were prepared. Thanks to the decrease of crystal field strength with the doping of Sc3+, the full width at half maximum (FWHM) of GASGG:Cr3+ ceramic phosphors were extended from 84 nm to 117 nm, and the emission peak exhibited a red-shift of 46 nm. Meanwhile, it still retained extremely high external quantum efficiency (EQE = 47%) and excellent thermal stability (90.7%@150 °C). Then, a NIR pc-LED prototype device was fabricated by combining GASGG:Cr3+ ceramic phosphor with a blue LED chip. The NIR light output power and the photoelectric conversion efficiency of this device achieved 646 mW and 19.2%, respectively. Finally, the application effect in night vision and venography of this prototype device was demonstrated.

Synthesis of the cerium doped Gd3Al3Ga2O12-based glass nanoceramics: Luminescence and optical absorption properties

Cerium doped gadolinium gallium aluminum garnet (Gd3Al3Ga2O12, GAGG) was synthesized in the glass ceramics form by the crystallization from Gd2O3–Al2O3–Ga2O3–SiO2–CeO2 glass in the following weight proportion: 101 : 26: 47 : 25: 1. The spatial distribution and incorporation of Ce into the GAGG ceramic grains as well as the luminescence and scintillation performance are studied carrying out correlated experiments of photo-, radio- and cathodoluminescence including decay kinetics as well as energy dispersive X-ray spectroscopy combined with scanning electron microscopy. Optical absorption features were investigated using photothermal deflection spectroscopy. Cerium stays within the material mostly in the Ce3+ charge state. Its distribution in the bulk of the sample exhibits irregular trend indicating the tendency to coalesce in the middle.

Edge effect reduction of high-resolution PET detectors using LYSO and GAGG phoswich crystals

Objective. Small-animal positron emission tomography (PET) is a powerful preclinical imaging tool in animal model studies. The spatial resolution and sensitivity of current PET scanners developed for small-animal imaging need to be improved to increase the quantitative accuracy of preclinical animal studies. This study aimed to improve the identification capability of edge scintillator crystals of a PET detector which will enable to apply a crystal array with the same cross-section area as the active area of a photodetector for improving the detection area and thus reducing or eliminating the inter-detector gaps. Approach. PET detectors using crystal arrays with mixed lutetium yttrium orthosilicate (LYSO) and gadolinium aluminum gallium garnet (GAGG) crystals were developed and evaluated. The crystal arrays consisted of 31 × 31 array of 0.49 × 0.49 × 20 mm3 crystals; they were read out by two silicon photomultiplier arrays with pixel sizes of 2 × 2 mm2 that were placed at both ends of the crystal arrays. The second or first outermost layer of the LYSO crystals was replaced by GAGG crystals in the two crystal arrays. The two crystal types were identified using a pulse-shape discrimination technique to provide better edge crystal identification. Main results. Using the pulse shape discrimination technique, almost all (except for a few edge) crystals were resolved in the two detectors; high sensitivity was achieved by using the scintillator array and the photodetector with the same areas and achieved high resolution by using crystals with sizes equal to 0.49 × 0.49 × 20 mm3. Energy resolutions of 19.3 ± 1.8% and 18.9 ± 1.5%, depth-of-interaction resolutions of 2.02 ± 0.17 mm and 2.04 ± 0.18 mm, and timing resolutions of 1.6 ± 0.2 ns and 1.5 ± 0.2 ns were achieved by the two detectors, respectively. Significance. In summary, novel three-dimensional high-resolution PET detectors consisting of a mixture of LYSO and GAGG crystals were developed. The detectors significantly improve the detection area with the same photodetectors and thus improve the detection efficiency.

Development of 64-channel LSI with ultrafast analog and digital signal processing dedicated for photon-counting computed tomography with multi-pixel photon counter

X-ray computed tomography (CT) is non destructive visualization inside the human body. Recently, X-ray photon-counting CT (PC-CT) has drawn attention for reducing the high doses used for patients and acquiring spectral information to identify materials. To enable photon-counting imaging with a wide region (∼60 mm long) of a small animal, we developed a photon-counting system using a 64-channel multi-pixel photon counter (MPPC) array with a fast temporal response (a few nanoseconds) and a very large signal gain (∼106), combined with a 64-channel yttrium–gadolinium–aluminum–gallium garnet scintillator array. In particular, to realize ultra-fast analog and digital signal processing (>10 MHz/channel), we developed a 64-channel large-scale integrated circuit (LSI) named MPPC-CT64. We had previously developed a 16-channel PC-CT system with a 16-channel LSI (MPPC-CT16). Although the MPPC-CT16 realized photon-counting imaging for a ∼16-mm-long phantom, there were some energy uncertainties in the LSI, which degraded the obtained CT image quality. The MPPC-CT64 implements a function for correcting the threshold energies and also increases the number of energy thresholds from four to six, which provides more precise measurements of CT values dependent on X-ray energy. In this paper, we briefly present the electric architecture and performance evaluation of the LSI combined with MPPCs.

Study on the Possibility of Neutron Gamma Discrimination in GAGG Crystal

The scintillators capable of neutron detection are being the research hotspot recently. In this manuscript, we investigated the possibility of cerium-doped gadolinium aluminium gallium garnet (GAGG: Ce) crystal to achieve neutron gamma discrimination through pulse shape discrimination (PSD) method. PSD is a method based on the principle that the waveforms of scintillation light differ for different particles. The experiments show that it’s hard for single GAGG crystal to distinguish the neutron from the gamma-ray. Therefore, a composite crystal made of gamma-sensitive crystal and GAGG crystal was furtherly developed. Using the 252Cf neutron source, the composite is proven to be capable of discriminating the neutrons from the gamma-ray and the corresponding FOM is 3.33.

Development of modified scintillator-based single-crystal position-sensitive 4[formula omitted] Compton camera for a portable radiation imaging device

After the nuclear accident at the Fukushima Daiichi Nuclear Power Plant, researchers focused on the accident and studied the effects of leaked radiation based on radiation detection and measurement. Many methods can be used for monitoring and mapping natural and leaked radionuclides; however, portable detectors installed in unmanned ground or aerial vehicles (UAVs) can measure radioactivity near the target point, preventing damage to the human body from radiation in highly contaminated areas. Compton cameras have a wider field-of-view (FOV) and less weight than a detector system that uses a mechanical collimator. In a previous study, a position-sensitive 4π Compton camera based on a lutetium–yttrium oxyorthosilicate (LYSO) scintillator attached to silicon photomultipliers (SiPMs) was developed. Compared with a semiconductor-based Compton camera operating with a power device supplying more than a thousand volts, our system requires a maximum of approximately several tens of volts. In addition, our Compton camera has a single-crystal structure; hence, it has advantages in terms of FOV and efficiency over a Compton camera that utilizes separate detectors. In this study, a modified scintillator-based Compton camera was created using an advanced SiPM model and a gadolinium aluminum gallium garnet (GAGG) scintillator. In the experiment, 133Ba, 22Na, and 137Cs radionuclides were used for data acquisition, and simple back-projection and list-mode maximum likelihood expectation maximization algorithms were used to reconstruct the Compton images. The 4π FOV coverage was evaluated using Compton imaging and angular resolution measure (ARM), and the results indicated that FOV coverage was degraded when the angle between the radiation source and the perpendicular axis of the detector was near 45°. The degradation of the ARM reflected as the bimodal distribution became more severe for the Compton camera based on the LYSO scintillator than that based on the GAGG scintillator, which was attributed to the intrinsic radiation of LYSO from 176Lu considered as background noise. In the evaluation of intrinsic efficiency, the influence of intrinsic radiation was significantly large. Without background noise rejection, the intrinsic efficiencies for 356, 511, and 662 keV radiation were 0.66%–1.28%, and 1.50%–3.05% for the detection system based on the GAGG and LYSO scintillators, respectively. After background noise rejection, the intrinsic efficiencies were re-calculated as 0.64%–1.27% and 1.39%–1.72% for the detection system based on the GAGG and LYSO scintillator, respectively.

Spectral Regulation and Efficiency Optimization in Cr3+‐Doped Gadolinium Aluminum Gallium Garnet Near‐Infrared Ceramic Phosphors via Crystal‐Field Engineering

AbstractThe near‐infrared (NIR) phosphor‐converted light‐emitting diode (pc‐LED) is a new NIR light source with both compact structure and high efficiency, and its performances is greatly depended on the NIR phosphors. Herein, this work presents a Cr3+‐doped gadolinium aluminum gallium garnet (GAGG:Cr3+) NIR ceramic phosphor with a broadband emission in the range of 650–850 nm, and optical performances that can be regulated via crystal‐field engineering. By optimizing the Al/Ga ratio, an external quantum efficiency as high as 65% is observed. The thermal stability is enhanced with the increase of Al content, which is attributed to the broadening of bandgap and the weakening of electron–phonon coupling effect. The NIR light output powers of the fabricated device based on the GAGG:Cr3+ ceramic are up to 88.9 mW @ 10 mA and 1247.7 mW @ 200 mA, while the electro‐optical conversion efficiencies were 28.5% @ 10 mA and 17.7% @ 200 mA, respectively. In addition, the NIR pc‐LED exhibited a strong penetrability such that the veins in a palm could be clearly identified, allowing for its potential use in biosecurity applications.

Ultrafast GGAG:Ce X-ray scintillation ceramics with Ca2+ and Mg2+ co-dopants

Among the aluminate garnet materials, cerium-doped gadolinium gallium aluminum garnet ceramics (GGAG:Ce) show fast scintillation properties, which suggests that they have promising applications in medical imaging, high-energy ray detection and high-power LED lighting. In this study, Gd3Ga3Al2O12:Ce scintillation ceramics co-doped with Me2+ (Me = Mg, Ca) are fabricated using a two-steps route: a solid-state reaction followed by annealing in air. The optical and scintillation properties, including the absorption, radio luminescence (RL), light yield, and decay time, of these co-doped ceramics are studied in detail. Doping with Mg2+ and Ca2+ leads to the oxidation of Ce3+ to Ce4+, which accelerates the scintillation process and decreases the light yield. Co-doping with Ca2+ and Mg2+ shows a synergistic effect on this phenomenon. Compared with 0.2 at% Ca2+ or 0.2 at% Mg2+ single-doped GGAG:Ce, the GGAG:Ce co-doped with 0.1 at% Ca2+ and 0.1 at% Mg2+ has the fastest decay time (∼31 ns) and maintains a relatively high light yield (∼27400 ± 1600 ph/MeV, 77% of undoped GGAG:Ce). These findings shed new light on designing Ce-activated garnet scintillator materials with ultra-fast decay time for applications in time-of-flight (TOF) PET technology.

Ultra-high-resolution depth-encoding small animal PET detectors: Using GAGG and LYSO crystal arrays.

Small animal positron emission tomography (PET) scanners are widely used in current biomedical research. The study aimed to develop high-efficiency and ultra-high-resolution detectors that could be used to develop a small animal PET scanner with high sensitivity and spatial resolution approaching to its physical limit. Four crystal arrays were fabricated and measured in this study. Crystal arrays 1 and 2 consisted of 38×38 gadolinium aluminum gallium garnet (GAGG) and lutetium-yttrium oxyorthosilicate (LYSO) crystals of 0.4×0.4×20mm3 size. Crystal array 3 consisted of 16×16 GAGG crystals of 0.3×0.3×20mm3 size, and crystal array 4 consisted of 24×24 LYSO crystals 0.3×0.3×20mm3 in size. The crystal arrays were dual-ended readouts using 8×8 silicon photomultiplier (SiPM) arrays of 2×2mm2 pixel area. The SiPM array was readout using a signal multiplexing circuit to convert the 64 output signals into four position-encoding signals. The performances of the four detectors in terms of flood histogram, energy resolution, depth of interaction (DOI) resolution, and timing resolution were measured. The GAGG detectors provided better flood histograms, ∼30% higher photopeak amplitude, ∼20% higher energy resolution, ∼12% worse DOI resolution, and ∼15% worse timing resolution compared with LYSO detectors of the same crystal size. These four detectors provided DOI resolutions of <2mm, energy resolutions of <22%, and timing resolutions of <1.6ns. All crystals of 0.4×0.4×20mm3 and 0.3×0.3×20 mm3 could be clearly resolved if the crystal array was 1mm smaller in the four sides than that in the SiPM array. High DOI resolution PET detectors were developed using both GAGG and LYSO arrays with crystal sizes of 0.3 and 0.4mm, respectively, and a length of 20mm. The detectors can be used in the future to develop small animal PET scanners, especially dedicated mouse imaging PET scanners, which can simultaneously achieve high sensitivity and ultra-high spatial resolution.