High-resolution insert detectors used with positron emission tomography (PET) scanners can locally improve the spatial resolution of the system. PET detector performance depends on multiple factors, including the reflector material in the scintillator crystal arrays and the microcell size of the silicon photomul-tipliers (SiPMs). In this study, we compared dual-ended readout detectors comprising 24 × 24 LYSO arrays with 1.0-mm pitch and different reflectors—BaSO4 or Toray E60—read out by onsemi SiPMs with 35-μm microcells. We also evaluated detectors with 8 × 8 SiPM arrays from KETEK with 3.36-mm pitch and different microcell sizes—15, 25, or 50 μm—coupled to the LYSO array with BaSO4 reflector. Results showed that the BaSO4 reflector led to better detector performance than Toray, with flood quality of 2.55 ± 0.26, energy resolution of 11.9% (11.4%–13.1%), which im-proved to 9.6% (9.2% – 10.3%) after DOI-based calibration, depth-of-interaction (DOI) resolution of 2.04 ± 0.19 mm, and coin-cidence timing resolution (CTR) of 759 ± 109 ps. Among SiPMs with different microcell sizes, those with 25-μm microcells showed the best flood quality of 2.25 ± 0.32, with energy resolution of 12.7% (12.2%–13.7%) before and 10.6% (10.1% – 11.6%) after DOI-based calibration, DOI resolution of 2.03 ± 0.13 mm, and CTR of 855 ± 118 ps. Based on these results, an LYSO array with BaSO4 reflector read out by onsemi SiPM arrays with 35-μm microcells was selected as the candidate design for the high-resolution insert detectors being developed for the NeuroEXPLORER brain PET scanner.

Positron emission tomography (PET)/Compton hybrid imaging has the potential to become a transformative molecular imaging modality, leveraging the high sensitivity of PET systems and the multi-tracer capability of Compton imaging. Achieving high spatial resolution in a PET/Compton hybrid imaging system requires detectors capable of simultaneously resolving sub-millimeter crystals and maintaining high energy resolution - a critical challenge for preclinical PET/Compton systems. In this work, we developed an ultra-high-resolution detector that can be used as the scatter layer detector of a high spatial resolution PET/Compton hybrid system. This detector incorporates a 28 × 28 array of 0.26 × 0.26 × 2 mm3 gadolinium aluminum gallium garnet (GAGG) elements (0.32 mm pitch) and a position-sensitive silicon photomultiplier (PS-SiPM). The detector demonstrated good performance: (1) flood histograms with clear crystal element separation, (2) an average energy resolution of 12.1 ± 1.8% at 511 keV, and (3) a coincidence timing resolution (CTR) of 1006 ± 78 ps obtained using a 100 - 600 keV energy window for event selection.

Coincidence detection of cascade decay in single photon emission computed tomography (SPECT) can enhance image quality by detecting true events and rejecting uncorrelated scatter. This study presents the development of high-resolution detectors based on 24 × 24 gadolinium aluminum gallium garnet (GAGG) arrays with a 1.0 mm pitch and 8 × 8 silicon photomultiplier (SiPM) arrays with a 3.2 mm pitch, which were designed for preclinical coincidence SPECT applications. Compton scatter events from annihilation photons were employed to mimic cascade photons and to evaluate the timing performance of the detectors. Moreover, the performance of the detectors with and without using 1 mm thick clear acrylic sheets as light guides was compared. Flood histograms showed that all GAGG elements were clearly identified except a small number of edge crystals when events with energies in a 100 - 250 keV energy window were used, and the use of the light guide improved crystal identification. The detectors with light guides achieved coincidence timing resolutions of 678 ± 143 ps, 571 ± 118 ps, and 374 ± 74 ps with events in 100 - 250 keV, 100 - 450 keV, and 400 - 650 keV energy windows, respectively. The corresponding values provided by detectors without the light guide were 551 ± 135 ps, 458 ± 114 ps, and 314 ± 68 ps. Energy resolutions at 511 keV were 9.2 ± 0.7% and 11.0 ± 0.7% for detectors with and without the light guide, respectively. These results demonstrated that the developed GAGG-SiPM detector with the light guide was a suitable candidate for developing preclinical coincidence SPECT systems.

Developing high-performance detectors with compact readout electronics is essential for enhancing the capabilities of small animal PET systems. In this study, we present a prototype PET detector with dual-ended readout, utilizing our recently developed electronics based on multicycle-encoding FPGA-ADC technology. The prototype includes two detector modules, each comprising a 20 x 20 array of 0.73 x 0.73 x 20 mm3 polished Lutetium-yttrium oxyorthosilicate (LYSO) crystals with Toray reflector and a pitch size of 0.8 mm. Each crystal array is coupled with two silicon photomultiplier (SiPM) arrays (8 x 8 channels with unit effective photosensitive area of 2 x 2 mm2) and two light guides. The detector's performance was evaluated in terms of flood histograms, energy resolution, timing resolution, and depth-of-interaction (DOI) resolution under various conditions. To find out the condition for best performance, measurements were taken at bias voltages ranging from 52.25 V to 53.75 V with an increment of 0.25 V, and at three different temperatures (5 degrees C, 15 degrees C and 20 degrees C). Additionally, performances under two energy windows, 250-650 keV and 350-650 keV, were analyzed. The optimal operating condition is figured out to be using an energy window of 350-650 keV and a bias voltage of 53.00 V under a temperature of 5 degrees C. Under these conditions, the average energy resolution, timing resolution, and DOI resolution across all crystals were 23.2 +/- 7.62%, 4.54 +/- 1.21 ns, and 2.98 +/- 0.51 mm, respectively. These results demonstrate that the developed PET detector is suitable for high-performance small animal PET systems, which can offer good spatial resolution, timing accuracy, and DOI capability.

OBJECTIVE:Continuous resistive layer position-sensitive silicon photomultiplier (CRL PS-SiPM) is a class of position-sensitive SiPMs developed for the readout of fine-pitch scintillator crystal arrays. This study aimed to evaluate the performance of dual-ended readout positron emission tomography (PET) detectors based on CRL PS-SiPMs and 0.5 mm pitch LYSO arrays. APPROACH:A dual-ended readout detector was constructed by coupling two CRL PS-SiPMs to both ends of a 10 × 10 array of polished LYSO elements, each measuring 0.44 × 0.44 × 20 mm³. Each CRL PS-SiPM had an active area of 6.24 × 6.24 mm² and was fabricated using 20 µm microcells. Detector performance, including flood histogram quality, energy resolution, and coincidence timing resolution, was characterized at bias voltages ranging from 30.0 to 33.0 V in 0.5 V increments, and at 3 °C, 14 °C, and 24 °C. Depth-of-interaction (DOI) resolution was evaluated at the optimal bias voltage determined from the flood histogram and at all three temperatures. MAIN RESULTS:Temperature had a negligible effect on detector performance, indicating that CRL PS-SiPMs are practical photodetector candidates for high spatial resolution PET scanners. All LYSO crystals were clearly resolved in the flood histograms. At 24 °C and a bias voltage of 32.5 V, which provided the best flood histogram, the average energy resolution, coincidence timing resolution, and DOI resolution across all crystals were 22.7 ± 3.4%, 1152 ± 43 ps, and 1.78 ± 0.20 mm, respectively. SIGNIFICANCE:These results demonstrate that CRL PS-SiPMs are promising photodetectors for high spatial resolution PET applications, particularly for systems requiring detectors with sub-millimeter pitch scintillator crystal arrays and DOI capability.

Depth-of-interaction (DOI) encoding is an effective strategy for reducing parallax error and preserving spatial resolution in positron emission tomography (PET), particularly in compact small-animal scanners. To enable efficient simulation-driven design of DOI-capable systems, we extend the GPU-accelerated Monte Carlo toolkit gPET to support flexible multi-layer detector geometries. The original three-level hierarchical detector model in gPET (panel-module-crystal) was expanded by introducing an intermediate "layer" level, enabling parameterized modeling of stacked scintillator architectures. The photon transport algorithm was correspondingly updated to sample interactions across multiple layers and detector panels while preserving GPU-efficient memory usage. The framework was validated using three scanner configurations: a conventional single-layer ring (H2RSPET-1CL), an aligned split-layer design (H2RSPET-1CL-split), and an offset dual-layer design (H2RSPET-2CL). System performance was evaluated following NEMA NU4-2008 protocols using sensitivity, spatial resolution, and Derenzo phantom simulations with CASToR-based maximum likelihood expectation maximization reconstruction. The H2RSPET-1CL and H2RSPET-1CL-split configurations produced statistically identical hit distributions, while H2RSPET-2CL exhibited the expected offset interaction patterns. Sensitivity of H2RSPET-2CL remained comparable to H2RSPET-1CL, generally within about 2-5 percent, while radial spatial resolution improved substantially (0.8-1.6 mm vs. 1.0-4.2 mm from the center to a 50 mm radial offset). Runtime performance remained essentially unchanged between configurations. The extended gPET framework therefore enables fast and flexible simulation of multi-layer PET detectors and supports efficient optimization of DOI-enabled PET system designs.

Positron emission tomography (PET) is the most sensitive in vivo molecular instrumentation. The image quality of PET can be significantly enhanced by incorporating time-of-flight (TOF) and depth-of-interaction (DOI) information. In this study, whole-body TOF-DOI PET detectors based on the dual-ended readout method were developed to simultaneously provide good TOF and DOI information. Each detector consisted of two 8 × 8 Hamamatsu S14161-3050-08 silicon photomultiplier (SiPM) arrays coupled to both ends of an 8 × 8 lutetium-yttrium oxyorthosilicate (LYSO) array with a thickness of 20 mm. Both the LYSO and SiPM arrays had a pitch of 3.2 mm, allowing each LYSO element to be coupled to two SiPM elements, one at each end of the crystal, to achieve the optimal timing resolution. Experimental results demonstrated that the detectors achieved a coincidence timing resolution of 234 ± 7 ps, an energy resolution of 13.7 ± 2.0%, and a DOI resolution of 2.6 ± 0.2 mm. These results suggest that the developed detectors are suitable for constructing whole-body TOF-DOI PET scanners with uniform spatial resolution across the entire field-of-view.

Positron emission tomography (PET) detectors suffer from time-walk when the leading edge discriminator is employed for timing pick-off as well as a timing-shift when thick crystals are utilized due to the depth-of-interaction (DOI) effect. In this study, a combined time-walk and timing-shift correction method was proposed for dual-ended readout PET detectors. To evaluate the proposed method, a pair of dual-ended readout PET detectors was constructed. Each detector was based on two Hamamatsu S14161-3050-08 silicon photomultiplier (SiPM) arrays coupled to both ends of an 8 × 8 arrays of 3.1 × 3.1 × 20 mm3 LYSO crystals with a 3.2 mm pitch. By employing the relationship between the energies and detected time differences of events, the time-walk and timing-shift were effectively corrected. The coincidence time resolution of the two detectors improved from 260.7 ± 1.0 ps to 229.4 ± 1.0 ps when a 400-650 keV energy window was used to select events. These results demonstrate the effectiveness of the proposed time-walk and timing-shift correction method.

BACKGROUND:High-resolution and high-sensitivity small-animal positron emission tomography (PET) scanners are essential non-invasive functional imaging tools in preclinical research. To develop small-animal PET scanners with uniform and high spatial resolution across the field-of-view, PET detectors capable of providing good depth-of-interaction (DOI) information are critical. Dual-ended readout detectors based on lutetium-yttrium oxyorthosilicate (LYSO) arrays with fine pitch represent a promising approach, wherein the choice of inter-crystal reflector significantly impacts the detector performance. Toray E60, with a 50 µm thickness, has been used for over two decades as an inter-crystal reflector for fabricating LYSO arrays used in dual-ended readout detectors. However, the Toray E60 has recently been discontinued. PURPOSE:This study aims to identify an optimal alternative to the Toray E60 reflector, facilitating the continued development of dual-ended readout detectors for high-resolution and high-sensitivity small-animal PET scanners. METHODS:Five dual-ended readout detectors based on 10 × 10 LYSO arrays were constructed and evaluated. These LYSO arrays employed different reflectors: Toray E60 with 50 µm thickness, Barium sulfate (BaSO4) with 80 µm thickness, and Toray E20 with thicknesses of 40, 52, and 76 µm. All LYSO arrays featured the same pitch of 0.5 mm and thickness of 20 mm. Two linearly-graded silicon photomultipliers (LG-SiPMs) served as photodetectors. The performance of the five detectors in terms of crystal identification ability, energy resolution, coincidence timing resolution (CTR), and DOI resolution was comprehensively compared. RESULTS:Among the five reflectors, the detector based on the LYSO array with the 52 µm thick Toray E20 reflector exhibited the best crystal identification ability and achieved an energy resolution of 20.2 ± 3.8%, a DOI resolution of 2.07 ± 0.48 mm, and a CTR of 882 ± 38 ps. Conversely, the detector based on the LYSO array with the 50 µm thick Toray E60 reflector showed an energy resolution of 22.0 ± 3.3%, a DOI resolution of 1.88 ± 0.25 mm, and a CTR of 833 ± 32 ps. CONCLUSIONS:The Toray E20 reflector with a thickness of 52 µm represents a viable alternative to the discontinued Toray E60 with a 50 µm thickness. It is suitable for fabricating finely pitched and thick LYSO arrays used in dual-ended readout detectors to develop high-resolution and high-sensitivity small-animal PET scanners.

Objective. Position-sensitive silicon photomultipliers (PS-SiPMs) are promising photodetectors for ultra-high spatial resolution small-animal positron emission tomography (PET) scanners. This paper evaluated the performance of the latest generation of linearly-graded SiPMs (LG-SiPMs), a type of PS-SiPM, for ultra-high spatial resolution PET applications using LYSO arrays from two vendors.Approach. Two dual-ended readout detectors were developed by coupling LG-SiPMs to both ends of the two LYSO arrays. Each LG-SiPM has an active area of 9.8 × 9.8 mm2. Both LYSO arrays consist of 20 × 20 arrays of 0.44 × 0.44 × 20 mm3polished LYSOs with a pitch of 0.5 mm. The performance of the two detectors was compared in terms of flood histogram, energy resolution, timing resolution, and depth-of-interaction (DOI) resolutions.Main results. Flood histograms showed clear identification of all LYSO elements except for some edge crystals due to the larger size of the LYSO arrays compared to the active area of the LG-SiPMs and the misalignment between LG-SiPMs and LYSO arrays in the assembled detectors. At a bias voltage of 37.0 V, the detectors utilizing the Tianle LYSO array and EBO LYSO array provided energy resolutions of 17.5 ± 2.2 and 18.6 ± 2.0%, timing resolutions of 0.75 ± 0.03 and 0.78 ± 0.03 ns, and DOI resolutions of 2.16 ± 0.15 and 2.31 ± 0.12 mm, respectively.Significance. The results presented in this paper demonstrate that the new generation LG-SiPMs are promising photodetectors for ultra-high spatial resolution small-animal PET scanner applications.

The image quality of positron emission tomography (PET) can be significantly enhanced by using time-of-flight (TOF) and depth-of-interaction (DOI) information. PET detectors are pivotal in determining the TOF and DOI capabilities of PET scanners. This study developed and evaluated TOF-DOI PET detectors based on the dual-ended readout method and lutetium-yttrium oxyorthosilicate (LYSO) arrays with two different pitches and reflector configurations. Specifically, the performance of detectors based on three types of LYSO arrays with 20 mm thickness, 8 × 8 arrays with a 3.2 mm pitch, 16 × 16 arrays with a 1.6 mm pitch and normal reflectors, and 16 × 16 arrays with a 1.6 mm pitch and partial short reflectors, were assessed. Hamamatsu S14161-3050-08 silicon photomultiplier arrays were used as the photodetectors, and PETsys TOFPET2 was used as the readout electronics. The flood histograms showed that all crystals in the three types of LYSO arrays were clearly resolved. The detectors based on the 8 × 8 LYSO arrays provided a coincidence timing resolution (CTR) of 207 ± 5 ps and a DOI resolution of 3.9 ± 0.6 mm. The detectors based on the 16 × 16 LYSO arrays with normal reflectors provided a CTR of 218 ± 7 ps and a DOI resolution of 2.6 ± 0.2 mm. In comparison, the detector based on the 16 × 16 LYSO arrays with partial short reflectors provided a CTR of 228 ± 11 ps and a DOI resolution of 2.9 ± 0.3 mm, and superior crystal resolvability compared to the detectors based on the 16 × 16 LYSO arrays with normal reflectors. These detectors are promising candidates for developing whole-body and brain PET scanners, offering effective sensitivity and uniform spatial resolution improvements across the field-of-view.

Simultaneous PET/SPECT imaging instruments could enable comprehensive molecular characterization by combining the very high sensitivity and spatial resolution of PET with the ability to image a broad range of radionuclides, including therapeutic isotopes with SPECT. While PET and SPECT hardware can be integrated into a single hardware system, one of the major challenges in simultaneous PET/SPECT imaging is the down-scatter contamination from PET tracers, which can significantly degrade SPECT image quality and quantitative accuracy. In this study, we evaluated the efficacy of using anti-coincidence and active shielding techniques to reject the down-scatter contamination in SPECT data. Using GEANT4 simulations, we analyzed the performance tradeoffs resulting from different choices of active shielding component design, coincidence time windows, and SPECT detector materials (CZT versus GAGG). The anti-coincidence technique effectively rejected contamination events, achieving a signal-to-noise (SNR) enhancement from 0.29 to 1.48 and noise equivalent count rate (NECR) improvement from 41.3 to 89.1 cps with moderate active shielding. Even without active shielding, anti-coincidence alone significantly improved SPECT image quality (SNR: 1.38; NECR: 87.0 cps), making it practical for systems where shielding is constrained. In reconstructed images, anti-coincidence improved contrast from 0.78 (raw) to 0.96 and reduced noise from 1508 to 257 counts, outperforming traditional triple-energy-window (TEW) correction (contrast: 0.84; noise: 855). The anti-coincidence technique is also compatible with post-processing scatter corrections, offering a promising strategy for future hybrid PET/SPECT systems in both preclinical and clinical settings.

We present a novel anti-coincidence technique combined with active shielding to reduce crosstalk from PET tracers to SPECT data acquisition in a proposed simultaneous PET/SPECT scanner. By detecting coincidence events between PET and SPECT detectors, the method identifies and rejects scattered photons during event acquisition. It is compatible with conventional scatter correction algorithms and remains effective in lowactivity scenarios. To evaluate the effectiveness of this technique, we implemented the technique in a simulated simultaneous PET/SPECT system using GEANT4. Simulation results demonstrate a $\boldsymbol{\sim} \mathbf{85\%}$ reduction in down-scattered events, leading to substantial improvements in projection-domain image quality: SNR increased from 0.29 to 1.48, and NECR improved from 41 cps to 89.3 cps, compared to the results without using anticoincidence and active shielding. In the reconstructed phantom images, CNR improved from 7.25 to $\mathbf{28.23}$. These results highlight the technique's potential to significantly enhance image quality in hybrid PET/SPECT systems and therefore allow imaging of lowactivity single photon emitters (such as therapeutic alpha-emitters) with simultaneous PET acquisition.

Almost all high spatial resolution positron emission tomography (PET) detectors based on pixelated scintillator arrays utilize crystal arrays with smaller pitches than photodetector arrays, leading to challenges in resolving edge crystals. To address this issue, this paper introduces a novel multi-resolution silicon photomultiplier (SiPM) array design aimed at decreasing the number of readout channels required while maintaining the crystal resolvability of the detector, especially for edge crystals. The performance of a pseudo 9 × 9 multi-resolution SiPM array, consisting of 6.47 × 6.47 mm, 6.47 × 3.07 mm, and 3.07 × 3.07 mm SiPMs, was compared to those of a pseudo 8 × 8 SiPM array with a 6.8 mm pitch, and a 16 × 16 SiPM array with a 3.4 mm pitch using a 36 × 36 LYSO array with a pitch of 1.5 mm. The large-size pseudo SiPMs were implemented by digitally grouping multiple 3.07 × 3.07 mm SiPMs. The flood histograms show that the edge crystal resolvability of the pseudo 9 × 9 multi-resolution SiPM array is comparable to that of the 16 × 16 SiPM array and is significantly better than that of the 8 × 8 SiPM array.

Bismuth germanate (BGO)-based positron emission tomography (PET) detectors are potential candidates for low-dose imaging PET scanners, owing to the high stopping power and low background radiation of BGO. In this paper, we compared the performance of two dual-ended readout PET detectors based on 15 × 15 BGO arrays. Both arrays had the same 1.1 mm pitch but utilized different reflectors -barium sulfate (BaSO4) and enhanced specular reflector film (ESR) -for high-resolution PET applications. The detectors were constructed with Hamamatsu 13361-2050-08 SiPM arrays. Each BGO element had dimensions of 1.02 × 1.02 × 20 mm3. The lateral surfaces of the BGO elements were unpolished (saw-cut), while the two ends were polished. Flood histograms showed that the detector based on the BGO array with BaSO4 reflector had much better crystal identification and depth-of-interaction (DOI) resolution. Specifically, the energy, DOI, and timing resolutions for the detector using the BGO array with BaSO4 reflector were 19.8 1.5%, 4.13 0.48 mm, and 2.80 0.23 ns, respectively. In contrast, the values obtained using the BGO array with ESR reflector were 20.9 2.1%, 7.69 1.92 mm, and 2.93 0.20 ns, respectively.

Positron emission tomography (PET) is the most sensitive in vivo molecular imaging technique available. Small animal PET has been widely used in studying pharmaceutical biodistribution and disease progression over time by imaging a wide range of biological processes. However, it remains true that almost all small animal PET studies using mouse or rat as preclinical models are either limited by the spatial resolution or the sensitivity (especially for dynamic studies), or both, reducing the quantitative accuracy and quantitative precision of the results. Total-body small animal PET scanners, which have axial lengths longer than the nose-to-anus length of the mouse/rat and can provide high sensitivity across the entire body of mouse/rat, can realize new opportunities for small animal PET. This article aims to discuss the technical opportunities and challenges in developing total-body small animal PET scanners for mice and rats.

Positron emission tomography/magnetic resonance imaging (PET/MRI) is a powerful tool for brain imaging, but the spatial resolution of the PET scanners currently used for brain imaging can be further improved to enhance the quantitative accuracy of brain PET imaging. The purpose of this study is to develop an MR-compatible brain PET scanner that can simultaneously achieve a uniform high spatial resolution and high sensitivity by using dual-ended readout depth encoding detectors. The MR-compatible brain PET scanner, named SIAT bPET, consists of 224 dual-ended readout detectors. Each detector contains a 26 × 26 lutetium yttrium oxyorthosilicate (LYSO) crystal array of 1.4 × 1.4 × 20 mm3 crystal size read out by two 10 × 10 silicon photomultiplier (SiPM) arrays from both ends. The scanner has a detector ring diameter of 376.8 mm and an axial field of view (FOV) of 329 mm. The performance of the scanner including spatial resolution, sensitivity, count rate, scatter fraction, and image quality was measured. Imaging studies of phantoms and the brain of a volunteer were performed. The mutual interferences of the PET insert and the uMR790 3 T MRI scanner were measured, and simultaneous PET/MRI imaging of the brain of a volunteer was performed. A spatial resolution of better than 1.5 mm with an average of 1.2 mm within the whole FOV was obtained. A sensitivity of 11.0

In this paper, the performance of two dual-ended readout PET detectors based on 15 × 15 BGO arrays were compared. The crystal elements of one BGO array have polished lateral surfaces, while the crystal elements of the other BGO array have unpolished lateral surfaces. The two ends of the BGO elements are polished. The two BGO arrays both have a pitch size of 1.6 mm and thickness of 20 mm, and BaSO4 with a thickness of 80 μm was used as the reflector. Hamamatsu S14161-0305-08 SiPM arrays were used as photodetectors. All the measurements were performed at a bias voltage of 41.0 V and a temperature of 23.5 °C. The flood histograms show that all the crystal elements in the two BGO arrays were clearly resolved. The detector based on the BGO array with polished lateral surfaces provides an energy resolution of 16.9 ± 1.3%, timing resolution of 3.2 ± 0.2 ns, and DOI resolution of 18.4 ± 2.2 mm. In comparison, the detector based on the BGO array with unpolished lateral surfaces provides an energy resolution of 17.7 ± 2.0%, timing resolution of 3.5 ± 0.3 ns, and DOI resolution of 3.2 ± 0.2 mm.

Objective: Dual-ended readout depth-encoding detectors based on bismuth germanate (BGO) scintillation crystal arrays are good candidates for high-sensitivity small animal positron emission tomography used for very-low-dose imaging. In this paper, the performance of three dual-ended readout detectors based on 15 x 15 BGO arrays with three different reflector arrangements and 8 x 8 silicon photomultiplier arrays were evaluated and compared. Approach: The three BGO arrays, denoted wo-ILG (without internal light guide), wp-ILG (with partial internal light guide), and wf-ILG (with full internal light guide), share a pitch size of 1.6 mm and thickness of 20 mm. Toray E60 with a thickness of 50 mu m was used as inter-crystal reflector. All reflector lengths in the wo-ILG and wf-ILG BGO arrays were 20 and 18 mm, respectively; the reflectors in the wp-ILG BGO array were 18 mm at the central region of the array and 20 mm at the edge. By using 18 mm reflectors, part of the crystals in the wp-ILG and wf-ILG BGO arrays worked as internal light guides. Main results: The results showed that the detector based on the wo-ILG BGO array provided the best flood histogram. The energy, timing and DOI resolutions of the three detectors were similar. The energy resolutions full width at half maximum (FWHM value) based on the wo-ILG, wp-ILG and wf-ILG BGO arrays were 27.2 +/- 3.9%, 28.7 +/- 4.6%, and 29.5 +/- 4.7%, respectively. The timing resolutions (FWHM value) were 4.7 +/- 0.5 ns, 4.9 +/- 0.5 ns, and 5.0 +/- 0.6 ns, respectively. The DOI resolution (FWHM value) were 3.0 +/- 0.2 mm, 2.9 +/- 0.2 mm, and 3.0 +/- 0.2 mm, respectively. Over all, the wo-ILG detector provided the best performance.