Multi-pixel Photon Counter Research Articles

Development of Gamma-Ray Detector Arrays Consisting of Diced Eu-Doped SrI2 Scintillator Arrays and TSV-MPPC Arrays

This article presents the development of diced SrI2:Eu arrays and their scintillation properties when coupled with a multipixel photon counter (MPPC) array. Using a dicing technique specific to halide scintillators, a high-energy resolution scintillator array is developed that is cost-effective and widely applicable. The developed SrI2:Eu arrays are of $3 \times 3 \times 3$ mm3/pixel $4 \times 4$ matrix (TYPE1) and $1 \times 1 \times 1$ mm3/pixel $9 \times 9$ matrix (TYPE2) structures. We fabricated test gamma-ray detector modules consisting of the TYPE1 and TYPE2 arrays coupled with an MPPC array. The mean peak to valleys ratio is 85.3 ± 14.9 for the TYPE1 array and 38.5 ± 16.6 for the TYPE2 array detector. The average energy resolutions obtained for the TYPE1 and TYPE2 gamma-ray detectors were 5.4 ± 0.4% full-width at half-maximum (FWHM) and 5.2 ± 0.6% FWHM, respectively, for 662-keV gamma-rays. The variation in the signal pulse height of the TYPE1 and TYPE2 detectors was only 10.6% and 10.4% in FWHM, respectively. These results demonstrated that the dicing technique proposed in this article could be applied to hygroscopic halide scintillators.

Study of Terrestrial and Cosmic UV Emissions from the International Space Station with the Mini-EUSO Telescope

Mini-EUSO is an imaging detector launched on the International Space Station on August 2019 with an unmanned Soyuz spacecraft. It is observing the Earth in a multispectral range comprising UV (300–400 nm), visible (400–780 nm) and NIR (1500–1600 nm). Mini-EUSO is accommodated on board the Russian Zvezda module, facing on a UV-transparent window in Nadir direction. The telescope main optics comprise two Fresnel lenses focusing light onto an array of 36 Hamamatsu multi-anode photomultiplier tubes, each of 64 channels for a total of 2304 pixels. In addition to the two ancillary cameras, Mini-EUSO contains an 8 × 8 array of Multi-Pixel Photon Counter SiPM. The Mini-EUSO main research objectives are the study of Ultra High Energy Cosmic Rays above 1021 eV and the search for Strange Quark Matter, even though, with its large field of view (44°), it will map an Earth ground area of 263 × 263 km2 every 2.5 µs, allowing to study several atmospheric event such as Transient Luminous Event (TLEs), meteoroids and marine bioluminescence.

Evaluation of the energy resolution of a prompt gamma-ray imaging detector using LaBr3(Ce) scintillator and 8 × 8 array MPPC for an animal study of BNCT

To develop boron neutron capture therapy (BNCT), it is desired to measure 10B concentration and obtain a two-dimensional 10B distribution in animal studies. In this research, we develop a prompt gamma-ray imaging detector to measure 10B distribution using a 50 mm × 50 mm x 10 mm LaBr3(Ce) scintillator and a multi-pixel photon counter (MPPC). To measure a two-dimensional 10B distribution, the 478 keV gamma-ray emitted from 10B(n,α)7Li reaction should be measured with the discrimination from 511 keV background gamma rays in each MPPC. Furthermore, as a characteristic of the detector, it is necessary to investigate whether the 478 keV events individually incident on the MPPC can be measured in two dimensions. In this study, we evaluated the energy resolution and performed a two-dimensional distribution measurement using a thermal neutron beam and prompt gamma rays from a boron sample.This system was able to obtain energy resolution as full width at half maximum at 511 keV of 5.0 ± 0.2% in all MPPC pixels, better than the 6.5% energy resolution required to discriminate between 478 and 511 keV gamma rays.When the region of interest (ROI) was set up from -3σ to – σ (first ROI) and -3σ to the median (second ROI) for the Gaussian distribution of a 478 keV gamma-ray peak using a 6.25 ppm sample, the detector count rate of the 478 keV gamma rays was 0.03 and 0.11 cps, respectively, without a collimator. Moreover, the effect due to the overlapping 511 keV gamma ray peak was approximately 2.0% in the first ROI and approximately 3.2% in the second ROI. In addition, the counts of 478 keV gamma rays were visualized in two-dimensional.

Quantum Calibration of Multi-pixel Photon Counter and Its Application in High-Sensitivity Magnetometry With NV Center Ensemble

In recent years, quantum detector tomography (QDT) is widely used in many fields, such as non-Gaussian states preparation, quantum metrology, quantum communication and so forth. In this paper, we used QDT to completely characterize a photon-number-resolving detector (PNRD) based on a multi-pixel photon counter (MPPC) at 650 nm, which operated in continuous wave (CW) mode. Reconstructing the positive operator-valued measure (POVM) accurately by QDT could help us theoretically derived the operation performance of MPPC in quantum sensing with nitrogen-vacancy (NV) center ensemble. The reconstruction fidelity of MPPC is larger than 99.94%, which means that QDT is very reliable. Comparing with conventional silicon avalanche photodiode (Si-APD), the fluorescent contrast of optically detected magnetic resonance (ODMR) spectrum of NV center ensemble detected by MPPC could be significantly improved. Since its excellent linearity and outstanding photon-number-resolving capability, MPPC could be further used in the DC magnetometry of NV center ensemble. We can infer that the magnetic field sensitivity can be effectively improved by replacing Si-APD with MPPC. Reportedly, this is an extremely rare research on the application of MPPC in NV center magnetometry.

Development of Single-Ended Readout DOI Detector With Quadrisected Crystals

In this article, we developed the novel single-end readout depth-of-interaction (DOI) detector with quadrisected crystals comparable in size to a single photo sensor. The proposed DOI detector consists of 784 gadolinium aluminum gallium garnet (GAGG) crystals, which are arranged in four layers of $14\times14$ arrays coupled with an $8\times8$ multipixel photon counter (MPPC) array. The size of each GAGG crystal is $1.45\times 1.45\times4.5$ mm3. Also, each MPPC has a surface area of $3.0\times3.0$ mm2. One pair of four-layered crystals coupled with a partial optical window is arranged across two MPPCs. Boundaries without the partial optical window are covered with optical reflectors. Light sharing is done between a pair of four-layered crystals optically coupled at one end. Each pair is coupled with paired silicon photomultipliers of different patterns. Crystal identification from each pair is obtained from the output rate of two MPPCs. From 511-keV uniform irradiation, responses of all crystal elements in the four layers can be separated clearly on a 2-D position histogram after applying the Anger calculation. Also, DOI information can be mapped to each cluster on curved lines. The energy resolution for all crystals is 9.1% after event reduction of intercrystal scatter.

Four-dimensional calorimeter to discriminate gammas from neutrons for the KOTO experiment

We study the rare decay KL→π0νν̄ at the J-PARC KOTO experiment. This decay mode is highly suppressed in the Standard Model (SM). The signature of the decay is two gammas from a π0 decay and no other detectable particles. In the KOTO experiment, the two gammas are measured with a calorimeter which is composed of undoped cesium iodide (CsI) crystals. Each crystal is read out with a photomultiplier tube (PMT) attached on its rear side. One of the main backgrounds to KL→π0νν̄ is caused by neutrons in the beam halo. To reach the sensitivity predicted in the SM, we need to suppress the background further by a factor of ten. We developed a method to attach Multi Pixel Photon Counters (MPPCs) on the front end of the crystals. The depth of the interaction, measured with the timing difference between the MPPC signal from upstream and the PMT signal from downstream, is used to discriminate gammas from neutrons. We obtain four-dimensional information on the showers (timing and three-dimensional position) as well as their energies from the calorimeter. We installed MPPCs in the autumn of 2018 and took data during the beam time in 2019. Using the four-dimensional calorimeter, the background is suppressed by a factor of 45.

A new charged particle detector for the KOTO experiment at J-PARC

We report the performance of a new scintillator array Downstream Charged Veto (DCV) for the J-PARC KOTO experiment to suppress the K L → π + π − π 0 decay background. Since the background originates from undetected charged pions passing through the beam hole of the electromagnetic calorimeter, the DCV detector was installed in vacuum downstream of the calorimeter. The DCV is composed of two plastic scintillator pipes read out by Multi Pixel Photon Counters through wavelength shifting fibers. The light yield was found to be 60 photoelectrons/0.8 MeV in a test bench when cosmic-rays pass through the center of the DCV. Energy calibration was performed using cosmic-rays after installation.

Performance Evaluation of Liquinert-Processed CeBr₃ Crystals Coupled With a Multipixel Photon Counter

Ce-doped scintillators are capable of shortening the time constant as the luminescence is caused by 5d $\to$ 4f transition of Ce3+. A scintillator with a short-time constant is suitable for time-of-flight (TOF)-positron emission tomography (PET). In this article, we conducted an evaluation of the energy resolution and coincidence resolving time (CRT) of Liquinert-processed cerium (III) bromide (CeBr3), which possesses a short-time constant and has a high light yield, using multipixel photon counter (MPPC) as a photon detector. The results indicate that an energy resolution of 5.02% (full width at half maximum (FWHM)) can be obtained from a 5-mm $\times \,\, 5$ -mm $\times \,\, 5$ -mm-CeBr3 cube coupled with a 6.0-mm $\times \,\, 6.0$ -mm-pitch MPPC. Furthermore, a CRT of 97.0 ps (FWHM) was achieved using a 3-mm $\times \,\, 3$ -mm $\times \,\, 1$ -mm-CeBr3 array coupled with a 3.0-mm $\times \,\, 3.0$ -mm-pitch through-silicon-via MPPC array, which has been proven effective for TOF-PET and Compton imaging. Moreover, a CRT of 198.7 ps (FWHM) was obtained using a current comparing type time-over-threshold circuit as a front-end readout application. We also determined that the energy resolution is independent of the shaping time but depends on the temperature. In addition, the CRT was found to be dependent on the frequency bandwidth of the signal measuring instrument.

2D microspatial distribution uniformity of photon detection efficiency and crosstalk probability of multi-pixel photon counters

Two-dimensional (2D) microspatial distribution uniformity of photon detection efficiency (PDE) and optical crosstalk probability Pct of multi-pixel photon counters (MPPCs) is studied. The experimental results show that the 2D spatial distribution of Pct is obviously uneven, i.e. Pct is larger at the corners and edges of a single pixel in MPPCs, which suggest a higher electrical field in the depletion region of the pixel at the corners and edges. The nonuniformity of the 2D spatial distribution of PDE also become evident when the size of the pixels of MPPCs is small, which signifies higher nonuniformity of the electric field distribution in MPPCs with small pixel size. A method is proposed for characterization of the 2D electrical field spatial distribution uniformity in a single pixel of MPPCs, which can be used for guiding the optimisation of the fabrication process of MPPCs and their properties. This promising method can naturally be extended to any Geiger avalanche photodiodes (G-APDs) and their arrays.

Design study of a brain-dedicated time-of-flight PET system with a hemispherical detector arrangement

Time-of-flight (TOF) is now a standard technology for positron emission tomography (PET), but its effective use for small diameter PET systems has not been studied well. In this paper, we simulated a brain-dedicated TOF-PET system with a hemispherical detector arrangement. We modeled a Hamamatsu TOF-PET module (C13500-4075LC-12) with 280 ps coincidence resolving time (CRT), in which a 12 × 12 array of multi pixel photon counters (MPPCs) is connected to a lutetium fine silicate (LFS) crystal array of 4.1 × 4.1 mm2 cross section each, based on one-to-one coupling. On the other hand, spatial resolution degradation due to the parallax error should be carefully addressed for the small diameter PET systems. The ideal PET detector would have both depth-of-interaction (DOI) and TOF capabilities, but typical DOI detectors that are based on light sharing tend to degrade TOF performance. Therefore, in this work, we investigated non-DOI detectors with an appropriate crystal length, which was a compromise between suppressed parallax error and decreased sensitivity. Using GEANT4, we compared two TOF detectors, a 20 mm long non-DOI and a 10 mm long non-DOI, with a non-TOF, 4-layer DOI detector with a total length of 20 mm (i.e. 5 × 4 mm). We simulated a contrast phantom and evaluated the relationship between the contrast recovery coefficient (CRC) and the noise level (the coefficient of variation, COV) for reconstructed images. The 10 mm long non-DOI, which reduces the parallax error at the cost of sensitivity loss, showed better imaging quality than the 20 mm long non-DOI. For example, the CRC value of a 10 mm hot sphere at COV = 20% was 72% for the 10 mm long non-DOI, which was 1.2 times higher than that of the 20 mm long non-DOI. The converged CRC values for the 10 mm long non-DOI were almost equivalent to those of the non-TOF 4-layer DOI, and the 10 mm long non-DOI converged faster than the non-TOF 4-layer DOI did. Based on the simulation results, we evaluated a one-pair prototype system of the TOF-PET detectors with 10 mm crystal length, which yielded the CRT of 250 ± 8 ps. In summary, we demonstrated support for feasibility of the brain-dedicated TOF-PET system with the hemispherical detector arrangement.

Characterisation of a new generation of VUV low-light sensors

Silicon Photo-Multipliers (SiPMs) have emerged as a compelling photo-sensor solution over the course of the last decade. In contrast to the widely used Photomultiplier Tubes (PMTs), SiPMs are low-voltage powered, optimal for operation at cryogenic temperatures, and have low radioactivity lev- els with high gain stability over the time in operational conditions. For these reasons, large-scale low-background cryogenic experiments, such as the next- generation Enriched Xenon Observatory experiment (nEXO), are migrating to a SiPM-based light detection system. In this paper we report on the charac- terization of the Hamamatsu VUV4 (S/N: S13370-6152) Vacuum Ultra-Violet (VUV) sensitive Multi-Pixel Photon Counters (MPPC)s as part of the develop- ment of a solution for the detection of liquid xenon scintillation light for the nEXO experiment.

Direct Measurement of Non-Classical Photon Statistics with a Multi-Pixel Photon Counter

Photon number resolving detectors with high accuracy bring broad applications in long-distance laser ranging, ultrafast spectroscopy, and quantum optics. In this paper, we observed the non-classical photon number distribution directly with a multi-pixel photon counter (MPPC) instead of a classic Hanbury-Brown and Twiss (HBT) system. The detector’s photon-number resolving ability was characterized by quantum detector tomography. To show the quantum feature of the detector, we further plotted the Wigner function, which was obtained corresponding to the positive operator value measure (POVM) elements. Finally, we declared the observation of non-classical photon statistics from a single color center in nanodiamond by using this detector.

Benchmarking novel optical fibre sensors for applications in radiation therapy

Detecting ionising radiation using scintillation light is a long-established technique, yet scintillator-based dosimetry in radiotherapy was not commercially available until recently. Scintillator materials can be organic or inorganic. Organic based scintillator detectors suffer from low light conversion efficiency and Cerenkov light ratio (CLR) coefficient energy dependence. The aim of this study was to characterise novel optical fiber sensors (OFS) based on an inorganic scintillating material for external beam radiotherapy due to the high sensitivity and high light conversion efficiency of inorganic scintillators. The sensor was constructed using a polymethyl methacrylate (PMMA) plastic optical fibre. The core of the PMMA was micro machined to make a cavity with a 700 μ m diameter and a 3 mm depth. The cavity was filled with the scintillating material terbium doped gadolinium oxysulphide (Gd2O2S:Tb) and then sealed with an epoxy. The scintillation material fluoresces on exposure to ionising radiation and the resultant emitted fluorescent light is detected using a multi-pixel photon counting module. Essential dosimetric properties were quantified, including the repeatability of the OFS system response, linearity of the output signal with radiation doses and dose rate and dose per pulse (DPP) dependency of the system. Percentage depth dose (PDD) and lateral dose profiles were measured for different field sizes and compared to the commercial W1 plastic scintillator and Monte Carlo simulations using BEAMnrc/DOSXYZnrc codes.

Demonstration of multiple contrast agent imaging for the next generation color X-ray CT

X-ray computed tomography (CT) is widely used for non-invasive diagnostic imaging of the inside of the human body. It should be noted that the approximate effective radiation dose in a patient is 10 mSv. Under such an environment, X-ray photons are severely piled-up. Therefore, conventional CT only reconstructs energy integrated image, which may consist of beam hardening artifacts that have proven to be a problem. In contrast, photon counting CT (PC-CT) offers a low-dose multicolor CT imaging. The PC-CT also enables K-edge imaging that can improve the blood–tissue contrast using specific contrast agents. Moreover, the PC-CT has great advantages in (1) the simultaneous imaging of multiple contrast agents, and (2) the absolute quantification of contrast agents. Owing to these advantages, the PC-CT system can provide more detailed tissue diagnosis than conventional CT systems. Recently, we proposed a novel PC-CT system (Morita et al., 2017; Arimoto et al., 2017, Maruhashi et al., 2018) consisting of multipixel photon counter (MPPC) coupled with a high-speed scintillator, which is a cost-effective and easy to assemble system, as compared to other PC-CT devices based on cadmium zinc telluride. In this paper, we operated the K-edge imaging of specific contrast agents using a 16-channel MPPC PC-CT system. Our PC-CT system established appropriate energy thresholds and operated the simultaneous imaging of multiple contrast agents such as iodine and gadolinium. In addition, we estimated the absolute concentration of these contrast agents. The results show that our PC-CT system can provide more accurate diagnostic medical imaging, as compared to the conventional CT system.

UV–Visible silicon detectors with zinc oxide nanoparticles acting as wavelength shifters

Broad spectral response of photon detectors without cryogenic cooling is of great interest in many fields of application like spectroscopy and high-energy particle physics. In order to achieve broad spectral range, different approaches can be found in literature. One approach is the multijunction detector incorporating different kind of absorbers. The drawback here is the fabrication cost as well as complicated fabrication technique [1]. Another approach is the application of wavelength shifters which absorb the UV light and re-emit it in the lower energy range which preferably matches the peak sensitivity of the detector. The application of chemical wavelength shifters like e.g. Tetraphenyl Butadiene (TPB) has been reported, but they posses some drawbacks like instability in contact with some substances and photo-degradation behavior [2]. There is also a concept of the application of luminescent nanoparticles on top of the detector, which act as wavelength shifters [3]. This approach has several advantages such as little interference in the detector structure (even the UV-blocking window of the detector does not pose a problem), straightforward deposition technique and large possibility of adjustment of the spectral regions depending on the kind of the nanoparticles. Thanks to the quantum confinement related to small size of the particles, the bandgap of the material can be engineered, therefore the absorption and emission properties of the material can be tuned. Other feature which has an impact on the emission and excitation properties are the defects, which can act as luminescent centers. The wavelength shifters considered for this application are two kinds of commercially available zinc oxide (ZnO) nanoparticles. The differences between them lay in the size and the structural quality, which influence their optical properties like emission and excitation spectra as well as photoluminescence quantum yield. For the application they are distributed in the poly (methyl methacrylate) – PMMA - matrix and spin-coated on the detector window. The work consists of the analysis of the parameters of the zinc oxide nanopowders only as well as the nanopowders dispersed in the PMMA matrix. The problem has been investigated both theoretically and experimentally. The experimental part involved examination of the samples deposited on the laboratory glass and finally on the photodetector. Apart from the kind of zinc oxide nanoparticles, the technological parameters which were optimised was the concentration of ZnO in PMMA as well as thickness of the layer. Two types of photodetectors have been considered for modification: silicon photodiodes with broad spectral response from 190 nm to 1000 nm and Multi Pixel Photon Counters (MPPC) sensitive in the range 270 – 900 nm. These latter ones are used for sophisticated applications as well as single-photon detection. The comparison of parameters of the detectors before and after modification is shown. 1.Gessert, T.A., Colegrove, E., Stafford, B., Kodama, R., Gao, W., Moutinho, H.R., Kuciauskas, D., Reedy, R.C., Barnes, T.M., Sivananthan, S. MRS Advances, 1 (50), pp. 3391-3402 (2016) 2.Alvarez, V. et al., Journal of Instrumentation 7, P02010 (2012) 3.Sahi, S., Magill, S., & Ma, L., Xie, J., Chen, W., Jones, B., Nygren, D., Scientific Reports. 8:10515, (2018)

Estimation of the detected background by the future gamma ray transient mission CAMELOT

AbstractThis study presents a background estimation for the CubeSats Applied for MEasuring and LOcalising Transients (CAMELOT), which is a proposed fleet of nanosatellites for the all‐sky monitoring and timing‐based localization of gamma ray transients with precise localization capability at low Earth orbits. CAMELOT will allow us to observe and precisely localize short gamma ray bursts (GRBs) associated with kilonovae, long GRBs associated with core‐collapse massive stars, magnetar outbursts, terrestrial gamma ray flashes, and gamma ray counterparts to gravitational wave sources. A fleet of at least nine 3U CubeSats is proposed to be equipped with large and thin CsI(Tl) scintillators read out by multipixel photon counters (MPPC). A careful study of the radiation environment in space is necessary to optimize the detector casing, estimate the duty cycle due to the crossing of the South Atlantic Anomaly and polar regions, and minimize the effect of the radiation damage of MPPCs.

A compact MPPC-based camera for omnidirectional (4π) fast-neutron imaging based on double neutron–proton elastic scattering

Abstract Neutron localization, which finds (localizes) neutron sources , is a non-destructive method used in the application of nuclear emergency response and special nuclear material (SNM) localization. Fast neutrons from SNM fission can be detected using a hydrogen-rich scintillation detector system with relatively high efficiency. In this study, we proposed a compact multi-pixel photon counter (MPPC)-based neutron scattering camera prototype consisting of sixteen plastic scintillator pillars. This camera is capable of detecting fast neutrons produced by neutron sources in the far-field. It provides a three-dimensional structure to detect incident neutrons with omnidirectional (4 π ) field-of-view. Based on double neutron–proton elastic scattering, a reconstructed image can be achieved by using an Am–Be source. Besides, time-of-flight technology was adopted for separating neutron signals from the gamma-ray background radiation. The results of the imaging efficiency and the average imaging resolution are reported in this article. This camera offers good prospects to expand the application field of SNM localization for nuclear security and proliferation deterrence.

A Compton polarimeter using scintillators read out with MPPCs through Citiroc ASIC

In recent years, a number of purpose-built scintillator-based polarimeters have studied bright astronomical sources for the first time in the hard X-ray band (tens to hundreds of keV). The addition of polarimetry can help data interpretation by resolving model-dependent degeneracies. The typical instrument approach is that incident X-rays scatter off a plastic scintillator into an adjacent scintillator cell. In all missions to date, the scintillators are read out using traditional vacuum tube photo-multipliers (PMTs). The advent of solid-state PMTs ("silicon PM" or "MPPC") is attractive for space-based instruments since the devices are compact, robust and require a low bias voltage. We have characterised the plastic scintillator, EJ-248M, optically coupled to a multi-pixel photon counter (MPPC) and read out with the Citiroc ASIC. A light-yield of 1.6 photoelectrons/keV has been obtained, with a low energy detection threshold of $\lesssim$5 keV at room temperature. We have also constructed an MPPC-based polarimeter-demonstrator in order to investigate the feasibility of such an approach for future instruments. Incident X-rays scatter from a plastic-scintillator bar to surrounding cerium-doped GAGG (Gadolinium Aluminium Gallium Garnet) scintillators yielding time-coincident signals in the scintillators. We have determined the polarimetric response of this set-up using both unpolarised and polarised $\sim$50 keV X-rays. We observe a clear asymmetry in the GAGG counting rates for the polarised beam. The low-energy detection threshold in the plastic scintillator can be further reduced using a coincidence technique. The demonstrated polarimeter design shows promise as a space-based Compton polarimeter and we discuss ways in which our polarimeter can be adapted for such a mission.

An LED PLD based controller for experimental characterization of an optical fibre sensor system for measurement of x-ray radiation in clinical linacs

A novel robust compact light emitting diode (LED) based laboratory simulator system for mimicking the output from an optical fibre sensor used to detect therapeutic X-ray pulses from a clinical linear accelerator (linac) is described and performance characterised with reference to real clinical data. The purpose of configuring the LED system is to facilitate accurate assessment of the operating characteristics of the optical fibre based measurement system without having to deploy it in the clinic, thus minimising the need for expensive repeated clinical testing. The output signal from the scintillation material based optical fibre sensor is known to be pulsatile in response to the pulsed X-ray output of the linac. An in-depth knowledge of the characteristics of the X-ray pulsed waveform arising from a series of previous clinical based measurements has facilitated the design and construction of the dedicated LED source described in this article. Results are presented using a field programmable gate array (FPGA) LED simulator source system that replicates a wide range of the linac’s pulsed output waveforms including being able to vary the amplitude, pulse width and frequency (repetition rate) of the source. These results are compared to recent results captured using a multi-pixel photon counting (MPPC) detector in the clinic for proving efficacy.

Performance Characterization of MPPC Modules for TOF-PET Applications

PET detectors commonly feature large numbers of multipixel photon counters (MPPCs), requiring data acquisition systems with significant signal multiplexing or using application specific integrated circuits (ASICs) for independent MPPC readout. We evaluate here two Hamamatsu C13500-4075LC-12 detector modules designed for time-of-flight (TOF) PET. Each module has a 12 $ {\times }$ 12 lutetium fine silicate crystal array (4.2 $ {\times }$ 4.2 $ {\times }$ 20 mm3) one-to-one coupled to a 12 $ {\times }$ 12 array of 4 mm MPPCs. Each detector has 8 18-channel ASICs utilizing time-over-threshold (ToT) readout. At low event rates, the detectors have full-width at half-maximum (FWHM) energy resolution of 11.8%±0.4%, measured in linearized energy spectra, and 275 ps FWHM coincidence timing resolution (CTR) using energy window of ±1 photopeak FWHM. The 511 keV photopeak amplitude in the ToT spectrum changed 0.24%/°C. There was <10% event loss up to 1450 kcps/detector. From count rates of 35–1450 kcps the 511 keV photopeak position varied by 1.2%, while photopeak FWHM in the ToT spectra increased by 54%, from 5.8% to 9.0%, corresponding to energy resolution changing from 11.8% to approximately 18.0%. Over this count rate range the CTR varied from 285 to 435 ps FWHM. The TOF-PET module performance suggests they are well suited to use in whole-body PET applications.