Silicon Photomultiplier Technology Research Articles

Position-Sensitive Silicon Photomultiplier Arrays with Large-Area and Sub-Millimeter Resolution.

Silicon photomultipliers (SiPMs) are solid-state single-photon-sensitive detectors that show excellent performance in a wide range of applications. In FBK (Trento, Italy), we developed a position-sensitive SiPM technology, called "linearly graded" (LG-SiPM), which is based on an avalanche-current weighted-partitioning approach. It shows position reconstruction resolution below 250 μm on an 8 × 8 mm2 device area with four readout channels and minimal distortions. A recent development in terms of LG-SIPM is a larger chip version (10 × 10 mm2) based on FBK NUV-HD technology (near-ultraviolet sensitive), with a peak photon detection efficiency at 420 nm. Such a large-area detector with position sensitivity is very interesting in applications like MR-compatible PET, high-energy physics experiments, and readout of time-projection chambers, gamma and beta cameras, or scintillating fibers, with a reduced number of channels. These SiPMs were characterized in terms of noise, photon detection efficiency, and position resolution. We also developed tiles of 2 × 2 and 3 × 3 LG-SiPMs, reaching very large sensitive areas of 20 × 20 mm2 and 30 × 30 mm2. We implemented a "smart-channel" configuration, which allowed us to have just six output channels for the 2 × 2 elements and eight channels for the 3 × 3 element tiles, preserving a position resolution below 0.5 mm. These kinds of detectors provide a great advantage in compact and low-power applications by maintaining position sensitivity over large areas with a small number of channels.

Investigation of neutron/gamma-ray distribution in SiPM-based pulse shape discrimination using EJ-276 plastic scintillators

The distribution of neutrons and gamma-rays in mixed fields is a main interest in pulse shape discrimination (PSD) studies, and becomes more significant when it involves techniques such as machine learning which requires true data. One of the surest methods to label neutrons and gamma-rays is neutron Time-of-Flight. This can be applied to the identification of special nuclear materials and by extension to nuclear non-proliferation. Moreover, the integration of silicon photomultiplier (SiPM) technology can make the neutron Time-of-Flight system more compact. Two EJ-276 plastic scintillators, which are capable of PSD, were coupled to SiPMs. The actual portion of neutrons from a 252Cf source intruding the gamma-rays in PSD ratio distribution, labeled by neutron Time-of-Flight, was calculated and then compared with gamma-rejection ratio (GRR) for each threshold in SiPM-based pulse shape discrimination.

A compact and highly integrated 128-channel FPGA-based readout electronics for nuclear imaging application

As silicon photomultiplier (SiPM) technology develops, its possible applications are being growingly expanded. However, the current technical obstacle is the signal readout from large-scale, multi-pixel SiPMs, especially in a large nuclear imaging device. Although the application-specific integrated circuits (ASICs) provide ways to reach that goal, it needs a long period with iterative electronic process and a very high cost. We developed a high-integrated positron emission tomography (PET) electronics system with field programmable gate array based charge-to-digital converter (FPGA-QDC) technology instead of the ASICs. Unlike traditional FPGA-based charge readout method in which low-voltage differential signaling (LVDS) receivers serve as analog voltage comparators, in the proposed electronics system voltage-referenced receivers work as analog comparators.Theoretically, nearly all of input/output (I/O) ports in the FPGA can achieve the function of analog comparators using voltage-referenced I/O standard. The electronics system is constructed using off-the-shelf low-cost commercial components. Therefore, it is feasible to fast build a distributed readout system with multiple such electronics system. The flexibility and reconfigurability of the FPGA provide multi-channel grouping and diverse triggering for different kinds of detector configurations, such as row/column summation and resistor-based readout. These features are greatly sought after in readout electronics for the SiPM-based radiation detectors. Experimental results show that the proposed highly-integrated electronics system overcomes the bottleneck that has limited the development of advanced PET detectors and scanners.

Pushing the limit of BGO-based dual-ended Cherenkov PET detectors through photon transit time correction

Objective. The high production cost of commonly used lutetium-based fast scintillators and the development of silicon photomultipliers technology have made bismuth germanate (BGO) a promising candidate for time-of-flight positron emission tomography (TOF PET) detectors owing to its generation of prompt Cherenkov photons. However, using BGO as a hybrid scintillator is disadvantageous owing to its low photon statistics and distribution that does not conform well to a single Gaussian. To mitigate this, a proposal was made to increase the likelihood of detecting the first Cherenkov photons by positioning two photosensors in opposition at the entrance and exit faces of the scintillator and subsequently selectively picking an earlier timestamp. Nonetheless, the timing variation arising from the photon transit time remains affected by the entire length of the crystal, thereby presenting a possibility for further enhancement. Approach. In this study, we aimed to improve the timing performance of the dual-ended BGO Cherenkov TOF PET detector by capitalizing on the synergistic advantages of applying depth-of-interaction (DOI) information and crystal surface finishes or reflector properties. A dual-ended BGO detector was implemented using a 3 × 3 × 15 mm3 BGO crystal. Coincidence events were acquired against a 3 × 3 × 3 mm3 LYSO:Ce:Mg reference detector. The timing performance of the dual-ended BGO detectors was analyzed using conventionally proposed timestamp methods before and after DOI correction. Results. Through a DOI-based correction of photon transit time spread, we demonstrated a further improvement in the timing resolution of the BGO-based Cherenkov TOF PET detector utilizing a dual-ended detector configuration and adaptive arrival time pickoff. We achieved further improvements in timing resolution by correcting the offset spread induced by the fluctuation of timing signal rise time in the dual-ended detector. Significance. Although polishing the crystal surface was still favorable in terms of full-width-half-maximum value, incorporating DOI information from the unpolished crystal to compensate for photon travel time facilitated additional enhancement in the overall timing performance, thereby surpassing that achieved with the polished crystal.

Study experimental time resolution limits of recent ASICs at Weeroc with different SiPMs and scintillators

Medical applications, such as Positron Emission Tomography (PET), and space applications, such as Light Detection and Ranging (LIDAR), are in need of highly specialized ASICs. Weeroc, in collaboration with different partners, is highly involved in developing a new generation of front-end ASICs. In the context of a joined LIDAR project among Weeroc, CNES, and Airbus, Weeroc is working on the development of Liroc, an ASIC for space LIDAR application. Weeroc is also working on advancing ASICs for medical applications with Radioroc under development and intended to be used for PET applications. This study experimentally evaluates the time resolution limits of these ASICs in different configurations, with some of the most recent silicon photomultiplier (SiPM) technologies available on the market, coupled to different scintillation crystals. The best single-photon time resolution (SPTR) was achieved using FBK NUV-HD SiPMs with an FWHM of 90 ps with Liroc and 73 ps with Radioroc. Furthermore, the coincidence time resolution (CTR) of Radioroc was studied with different crystal sizes. Using a large LYSO:Ce,Ca crystal of (3 × 3 × 20 mm3) with Broadcom Near UltraViolet-Metal in Trench (NUV-MT) yields a CTR of 127 ps (FWHM). The best CTR of Radioroc was determined to 83 ps (FWHM) with Broadcom NUV-MT SiPMs coupled to LYSO:Ce,Ca (2 × 2 × 3 mm3)) from Taiwan Applied Crystal (TAC).

Comparison of the prognostic value of impaired stress myocardial blood flow, myocardial flow reserve, and myocardial flow capacity on low-dose Rubidium-82 SiPM PET/CT

BackgroundThe most reliable quantitative variable on Rubidium-82 (82Rb) cardiac PET/CT for predicting major adverse cardiovascular events (MACE) has not been characterized with low-dose silicon photomultipliers (SiPM) technology, which allows halving injected activity and radiation dose delivering less than 1.0 mSv in a 70-kg individual. Methods and ResultsWe prospectively enrolled 234 consecutive participants with suspected myocardial ischemia. Participants underwent 82Rb cardiac SiPM PET/CT (5 MBq/kg) and were followed up for MACE over 652 days (interquartile range 559-751 days). For each participant, global stress myocardial blood flow (stress MBF), global myocardial flow reserve (MFR), and regional severely reduced myocardial flow capacity (MFCsevere) were measured. The Youden index was used to select optimal thresholds.In multivariate analysis after adjustments for clinical risk factors, reduced global stress MBF < 1.94 ml/min/g, reduced global MFR < 1.98, and regional MFCsevere > 3.2% of left ventricle emerged all as independent predictors of MACE (HR 4.5, 3.1, and 3.67, respectively, p < 0.001). However, only reduced global stress MBF remained an independent prognostic factor for MACE after adjusting for clinical risk factors and the combined use of global stress MBF, global MFR, and regional MFCsevere impairments (HR 2.81, p = 0.027). ConclusionUsing the latest SiPM PET technology with low-dose 82Rb halving the standard activity to deliver < 1 mSv for a 70-kg patient, impaired global stress MBF, global MFR, and regional MFC were powerful predictors of cardiovascular events, outperforming traditional cardiovascular risk factors. However, only reduced global stress MBF independently predicted MACE, being superior to global MFR and regional MFC impairments. Graphical Abstract▪

Evaluation of SiPM-based readout system with gain stabilization for TL dosimetry

As the silicon photomultiplier (SiPM) technology has developed and matured, it has opened up avenues for its use in various luminescence dosimetry applications. However, the temperature sensitivity of SiPMs needs to be considered in settings where a SiPM-driven system may be affected by heat, such as during thermoluminescence (TL) measurements. This study investigated the TL signal reproducibility and temperature dependence of SiPMs (3×3mm2,50μm) using a Risoe TL/OSL-DA-20 reader, a gain stabilizing driver circuit, and a data acquisition (DAQ) module. The signal variation was insignificant when the temperature varied by less than 2 °C. However, when there was no temperature control, the signal loss occurred due to increased dark counts. We assessed four commercial dosimeters and compared them to conventional TL detection via a photomultiplier tube (PMT) in terms of dose-response, detection limits, and TL glow-curve characteristics. The slope in the dose-response (i.e., sensitivity) of the SiPM-based system was 1.5 to 3 times lower compared to PMT depending on the dosimeter. We explored the viability of TL readings by examining the potential reduction in sensitivity and dark counts due to the SiPM's photon-resolving feature. While the evaluation results of the suggested system demonstrate its practical usefulness, there are still unexplored areas that warrant further investigation. These are discussed in relation to the dark count rate, which is a major parameter that can impede the overall performance.

Photon-Counting Computed Tomography and Scintillator-Based Detectors: A Simulation Analysis With Scintillating and Reflecting Materials Currently on the Market

During the last decade, Photon-Counting Computed Tomography (PCCT) has been quickly developing and it is expected to revolutionize the X-ray imaging field. Rapid development has also been ongoing in the scintillator and photosensor fields: fast inorganic scintillators have become available on the market and the silicon photomultiplier (SiPM) technology has made substantial progress. Therefore, SiPM-based scintillator detectors may soon be successfully applied in challenging applications like PCCT. In this work, a simulation framework is developed to evaluate detectors composed of scintillators coupled to SiPMs. The idea is to combine Monte Carlo simulations and a library to generate SiPM signals. Focus is given to six fast inorganic scintillators currently on the market (Ce:LYSO, Ce:LuAP, Pr:LuAG, Ce:LuAG, Ce:GGAG (ceramic), Ce:GAGG (single crystal)) and different TiO2-epoxy mixtures. The main properties of scintillating and reflecting materials to be defined in the simulation database are characterised experimentally. Using a virtual model created within this framework, an analysis of the performance in PCCT of a SiPM-based scintillator detector composed of the considered materials is performed. Simulated pulses are processed to report on the count-rate capability. Among the studied crystals, Ce:LYSO would enable sustaining the highest rate of interacting X-ray (2.5 Mcps/pixel with 30% of pile-up). Ce:GAGG could also handle a rate ~ 1 Mcps/pixel with identical pile-up conditions. Other materials show a slow decay time in their scintillation kinetics, implicating a < 1 Mcps/pixel count rate. A qualitative evaluation of the energy binning efficiency is also accomplished, by defining this parameter as a quality metric for multiclass classification. Scintillators with high light yield and good energy resolution (Ce:LYSO, Ce:GAGG and Ce:GGAG) present the best energy binning performance, as expected. The dependence of this aspect is explored as a function of the pulse processing method used, the crystals size and the pile-up probability. Resulting trends respect predictions, even though for a more quantitative analysis a more in-depth study is required.

High-sensitivity low-noise photodetector using a large-area silicon photomultiplier.

The application of silicon photomultiplier (SiPM) technology for weak-light detection at a single photon level has expanded thanks to its better photon detection efficiency in comparison to a conventional photomultiplier tube (PMT). SiPMs with large detection area have recently become commercially available, enabling applications where the photon flux is low both temporarily and spatially. On the other hand, several drawbacks exist in the usage of SiPMs such as a higher dark count rate, many readout channels, slow response time, and optical crosstalk; therefore, users need to carefully consider the trade-offs. This work presents a SiPM-embedded compact large-area photon detection module. Various techniques are adopted to overcome the disadvantages of SiPMs so that it can be generally utilized as an upgrade from a PMT. A simple cooling component and recently developed optical crosstalk suppression method are adopted to reduce the noise which is more serious for larger-area SiPMs. A dedicated readout circuit increases the response frequency and reduces the number of readout channels. We favorably compare this design with a conventional PMT and obtain both higher photon detection efficiency and larger-area acceptance.

Low-energy X-ray spectroscopy with RGB-HD SiPMs coupled to CsI(Tl) scintillator

The continuous improvement of Silicon Photomultiplier (SiPM) characteristics opens new perspectives for the application of these detectors in middle to low energy X-ray scintillation light readout. Compared to traditional PET detectors this application poses an additional challenge because of the much lower number of photons generated in the scintillator. Many SiPM characteristics influence the energy resolution of the detected radiation, including Photon Detection Efficiency (PDE), primary noise and Excess Noise Factor (ENF). The most recent development of the RGB-HD SiPM technology at Fondazione Bruno Kessler (FBK, Italy) provides a PDE up to 40% at 550 nm while keeping the Dark Count Rate (DCR) below 500 kc.p.s./mm2. A low DCR value is fundamental in improving the energy resolution for soft X-rays. In this work we coupled a 1×1 mm2 RGB-HD SiPM to a 0.9×0.9×2 mm3 CsI(Tl) crystal allowing the detection of 55Fe 5.9 keV photons with an energy resolution of 39% FWHM. A 4×4 mm2 RGB-HD SiPM with a 3×3×5 mm3 CsI(Tl) was used for the readout of a 57Co source (6.4 keV, 14.4 keV and 122 keV) in order to prove the dynamic range of the system. The energy resolution of these three peaks shows different trends with respect to the SiPM bias and to the signal integration time. This is related to the fact that SiPM parameters such as PDE, DCR and ENF, and readout parameters such as integration time, become more or less relevant depending on the energy of the primary photon.

Phantom study of an in-house amplitude-gating respiratory method with silicon photomultiplier technology positron emission tomography/computed tomography

PurposeThe objective of this phantom study was to determine whether breathing-synchronized, silicon photomultiplier (SiPM)-based PET/CT has a suitable acquisition time for routine clinical use. MethodsAcquisitions were performed in list mode on a 4-ring SiPM-based PET/CT system. The experimental setup consisted of an external respiratory tracking device placed on a commercial dynamic thorax phantom containing a sphere filled with [F-18]-fluorodeoxyglucose. Three-dimensional sinusoidal motion was imposed on the sphere. Data were processed using frequency binning and amplitude binning (the "DMI” and “OFFLINE” methods, respectively). PET sinograms were reconstructed with a Bayesian penalized likelihood algorithm. ResultsRespiratory gating from a 150‑sec acquisition was successful. The DMI and OFFLINE methods gave similar activity profiles but both were slightly shifted in space; the latter profile was closest to the reference acquisition. ConclusionWith SiPM PET/CT systems, the amplitude-based processing of breathing-synchronized data is likely to be feasible in routine clinical practice.

Novel Detector Assembly for Neutron/Gamma-Ray Discrimination Applications Based on Large-Sized Scintillators Coupled to Large Area SiPM Arrays

In this work, we propose a prototype of a compact detector assembly capable of discriminating between neutrons and gamma rays, by performing pulse shape analysis. The device takes advantage of recent improvements in silicon photomultiplier (SiPM) technology and the excellent neutron/gamma-ray discrimination capabilities of new plastics and standard liquid scintillators. Our work is focused on the read-out of small-, medium-, and large-sized organic scintillators with large-area SiPM arrays ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4 \times 4$ </tex-math></inline-formula> NUV and RGB-SiPM arrays, 17 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$ </tex-math></inline-formula> 17 mm). In particular, we used EJ-276 (and its old version EJ-299) and EJ-276G plastic scintillators of several sizes (ranging from 20- to 50-mm diameter) and two large liquid scintillator cells (EJ-301 and EJ-309, 50 mm diameter <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 50$ </tex-math></inline-formula> mm thickness). Moreover, we show the comparison of neutron/gamma-ray discrimination performance between SiPM and standard photomultiplier read-out configurations. The presented innovative device could be used in different fields, first in fundamental nuclear physics experiments, as an ancillary neutron detector for the active target at the selective production of exotic species (SPES) facility at the Legnaro National Laboratories in Italy. Additionally, it could be used in radiation monitoring applications, as a fast neutron/gamma-ray counter to be embedded in unmanned vehicles for radiation monitoring.

Cherenkov Radiation–Based Coincidence Time Resolution Measurements in BGO Scintillators

Bismuth germanate oxide (BGO) scintillators can be re-introduced in time-of-flight positron emission tomography (TOF-PET) by exploiting the Cherenkov luminescence emitted as a result from 511 keV interactions. Accessing the timing information from the relatively few emitted Cherenkov photons is now possible due to the recent improvements in enhanced near-ultraviolet high-density (NUV-HD) silicon photomultiplier (SiPM) technology, fast and low noise readout electronics, and the development of efficient data post-processing methods. In this work, we aim to develop a scalable detector element able to achieve excellent coincidence time resolution (CTR) required for TOF-PET using BGO scintillator elements of various lengths. The proposed detector element is optically coupled to 3.14 × 3.14 mm2 NUV-sensitive SiPMs mounted on a custom design circuit board. In particular, we have evaluated the CTR performance of BGO crystal elements of dimensions 3 × 3 × 3 mm3, 3 × 3 × 5 mm3, 3 × 3 × 10 mm3, and 3 × 3 × 15 mm3, with chemically etched surfaces and wrapped in Teflon tape. To achieve excellent CTR performance, we apply state-of-the-art post-processing methods during data analysis. Best values of 156 ± 6 ps, 188 ± 5 ps, 228 ± 8 ps, and 297 ± 8 ps CTR FWHM have been achieved for the 3, 5, 10, and 15 mm length BGO crystals, respectively. These values improve to 105 ± 6 ps, 127 ± 8 ps, 133 ± 4 ps, and 189 ± 8 ps CTR FWHM, when only considering the Cherenkov component of the timing signal, which is extracted by considering the events with the fastest rise time (20% of the total data). The accurate classification of the events based on their rise time is possible; thanks to the implementation of a dual threshold approach that sets the lower threshold below one light photon equivalent level and the upper one above the signal amplitude of a single photon avalanche diode (SPAD).

Balloon flight test of a CeBr3 detector with silicon photomultiplier readout

Recent advances in silicon photomultiplier (SiPM) technology and new scintillator materials allow for the creation of compact high-performance gamma-ray detectors which can be deployed on small low-cost satellites. A small number of such satellites can provide full sky coverage and complement, or in some cases replace the existing gamma-ray missions in detection of transient gamma-ray events. The aim of this study is to test gamma-ray detection using a novel commercially available CeBr3 scintillator combined with SiPM readout in a near-space environment and inform further technology development for a future space mission. A prototype gamma-ray detector was built using a CeBr3 scintillator and an array of 16 J-Series SiPMs by ON Semiconductor. SiPM readout was performed using SIPHRA, a radiation-tolerant low-power integrated circuit developed by IDEAS. The detector was flown as a piggyback payload on the Advanced Scintillator Compton Telescope balloon flight from Columbia Scientific Balloon Facility. The payload included the detector, a Raspberry Pi on-board computer, a custom power supply board, temperature and pressure sensors, a Global Navigation Satellite System receiver and a satellite modem. The balloon delivered the detector to 37 km altitude where its detection capabilities and readout were tested in the radiation-intense near-space environment. The detector demonstrated continuous operation during the 8-hour flight and after the landing. It performed spectral measurements in an energy range of 100 keV to 8 MeV and observed the 511 keV gamma-ray line arising from positron annihilation in the atmosphere with full width half maximum of 6.8%. During ascent and descent, the detector count rate peaked at an altitude of 16 km corresponding to the point of maximum radiation intensity in the atmosphere. Despite several engineering issues discovered after the flight test, the results of this study confirm the feasibility of using CeBr3 scintillator, SiPMs, and SIPHRA in future space missions.

Ultrasensitive On-Field Luminescence Detection Using a Low-Cost Silicon Photomultiplier Device.

The availability of portable analytical devices for on-site monitoring and rapid detection of analytes of forensic, environmental, and clinical interest is vital. We report the development of a portable device for the detection of biochemiluminescence relying on silicon photomultiplier (SiPM) technology, called LuminoSiPM, which includes a 3D printed sample holder that can be adapted for both liquid samples and paper-based biosensing. We performed a comparison of analytical performance in terms of detectability with a benchtop luminometer, a portable cooled charge-coupled device (CCD sensor), and smartphone-integrated complementary metal oxide semiconductor (CMOS) sensors. As model systems, we used two luciferase/luciferin systems emitting at different wavelengths using purified protein solutions: the green-emitting P. pyralis mutant Ppy-GR-TS (λmax 550 nm) and the blue-emitting NanoLuc (λmax 460 nm). A limit of detection of 9 femtomoles was obtained for NanoLuc luciferase, about 2 and 3 orders of magnitude lower than that obtained with the portable CCD camera and with the smartphone, respectively. A proof-of-principle forensic application of LuminoSiPM is provided, exploiting an origami chemiluminescent paper-based sensor for acetylcholinesterase inhibitors, showing high potential for this portable low-cost device for on-site applications with adequate sensitivity for detecting low light intensities in critical fields.

Novel neutron detector assembly based on SiPM readout to be coupled with the Active Target for SPES

The Active Target ATS (Active Target for SPES) is a new time-projection chamber designed for reaction and decay studies with nuclei far from stability. The physics cases for the new-generation active target are related to the ongoing developments of facilities for radioactive ion beams. Thanks to its flexibility, this instrument will be capable of taking advantage of the most exotic beams which will become available at the SPES facility under construction at the Legnaro National Laboratories in Italy. Particular attention will be also paid to couple it with ancillary detectors, for both charged and neutral (gamma and neutrons) particles. In particular, in this work, we will focus the attention on the neutron ancillary detectors. The proposed prototype is a compact device able to discriminate, by performing pulse shape analysis, between neutrons and gamma. The device take advantage of recent improvements in silicon photomultiplier (SiPM) technology and the development of new plastic scintillators exhibiting neutron/gamma discrimination capability. Our work is focused on the read-out with silicon photomultipliers arrays of EJ-276 (and its old version EJ-299) and EJ-276G scintillators of several sizes (ranging from 20 mm to 50 mm diameter). Moreover, we will show the comparison of discrimination performances between SiPM and standard photomultiplier read-out configurations.

Hand-foot monitors for nuclear plants based on scintillator–WLS–SiPM technology

The technology of charged particles detection by a plastic scintillator light from which is collected by wavelength shifting fiber (WLS) on Silicon Photomultiplier (SiPM) is widely used in high energy physics. We present in this article the new personnel surface contamination monitoring assembly based on that technology as a result of about two years R&D research. This assembly is used for contamination control of hands, feet and clothes at nuclear power plants, nuclear facilities and other objects that work with radioactive materials. Setup design, main parameters and its measurement procedures are presented. It has high efficiency to α and β particles in wide energy range, large dynamic range, very good area uniformity and excellent temperature stability. Dynamic range of measured particle fluence rate equals: 1 – 106 Hz·cm2·min for β-module and 0.1 – 2·104 Hz·cm2·min for α-module. Variations of the module response in temperature range from –20 C up to +50 C doesn`t exceed 3%.

A Square-Bordered Position-Sensitive Silicon Photomultiplier Toward Distortion-Free Performance With High Spatial Resolution

A two-dimensional (2D) square-bordered position-sensitive (PS) silicon photomultiplier (SiPM) toward distortion-free performance with high spatial resolution is reported in this letter. The device, based on SiPM technology of an epitaxial quenching resistor, contains a central cap resistive region enclosed by a narrow square-shaped metal ring contact located at the surface periphery. Four small output metal pads are connected to the metal ring at each corner to read out signal charges. With an active area of 6.14 mm x 6.14 mm, the PS-SiPM demonstrated an average position measurement error (PME) of 86.9 μm without correction, which accounted for 1.4% of the side length of the active area. The average position resolutions were demonstrated to be ~130.7 μm and ~135.6 μm in the X and Y directions, respectively, for incident light with a spot diameter of 80 μm and a mean photoelectron number (MPEN) of ~600. In addition, an intrinsic radioactive-light image of a pixelated 12 × 12 lutetium-yttrium oxyorthosilicate (LYSO) array with each element volume of 0.475 × 0.475 × 6 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> was clearly resolved by the 2D square-bordered PS-SiPM.

Design and measurement of Trans-PET basic detector module II using 6× 6 SiPM array for small-animal PET

Silicon photomultiplier (SiPM) coupled scintillation detectors, are considered as promising tools for basic design of imaging instrumentation for the next generation PET, PET/MRI, SPECT and autoradiography scanners. The precise technical knowledge is inadequate, and still some challenges need to be addressed in order to successfully implement the SiPM technology in high resolution PET systems. Firstly, the advantages of SiPM pixel array 1:1 coupled crystal detector were obvious, and has minimized the position resolution errors of charge sharing in multiplexing circuits. However, in the system level, too many electronic channels have perplexed with complications, such as complex, messy electronics or dedicated ASIC chips. Multiplexing circuits were usually used to lower the complexity and cost of electronics, which has resulted in gradual deterioration of the performances of the detectors. Secondly, the light guide has become a necessity in high-resolution preclinical PET detectors. For a complete SiPM detector block, the light yield of outermost two rows/columns crystals were blurred due to the edge effects. In order to avoid this edge deterioration effect, crystal array size was reduced than that of the SiPM array in many PET detectors. The PET system built by these detectors had big gaps between the detector modules, which has largely affected the quality of reconstructed images. In order to solve these key problems, the Trans-PET basic detection module (BDM) II was designed and implemented in this study. This module was a flexible, easy to upgrade, simple, box geometry, small animal PET scanner. A better balance could be achieved by this detector, while reducing the electronic channels, and could simultaneously enhance the position resolution and time performance. A specially customized semi-cutting light guide had been designed, which could be optically multiplexed and diffused to optimize the effect of edge deterioration, so that both the outermost and inner crystals could be clearly distinguished. Specifically, in this PET module, two type crystal arrays with different crystal size had been designed, 13× 13 crystal array with 1.89 mm width and 18× 18 crystal array with 1.2 mm width, based on the same 6× 6 SiPM array and frond-end electronics. The total area of 6× 6 SiPM was 25.0× 25.0 mm2, which was similar to Hamamatsu PSPMT R8900. The area of the SiPM array was slightly smaller than the size of the crystal array, in order to reduce the gap of the PET system built by this detector. The purpose of this study was to evaluate the performance of this detector module, including position profile quality, energy resolution, timing resolution in different operating environment. Based on this detector module, PET scanners can easily be designed with different shapes such as, quadrilaterals, hexagonals, octagonals, dodecagonals, twenty-four-sides, and other shapes.

Selection of PET Camera and Implications on the Reliability and Accuracy of Absolute Myocardial Blood Flow Quantification.

PET scanner design and performance evaluation has been driven historically by the imaging requirements for whole-body imaging in oncology. Cardiac PET imaging for accurate quantification of myocardial blood flow (MBF) using short-lived tracers such as rubidium-82 imposes additional requirements for wide dynamic range and high count-rate accuracy. This paper examines the technical challenges encountered in cardiac imaging of myocardial perfusion and blood flow quantification. The newest PET-CT scanners using digital silicon photomultiplier technology have high absolute sensitivity (4-20%) and time-of-flight resolution (3-7cm) which further improves image quality. The concept of "integral" noise equivalent counts (iNEC) is introduced to compare scanner count-rate performance over the wide dynamic range encountered in MBF imaging with rubidium-82. The latest-generation digital PET scanners with wide axial field-of-view and enhanced time-of-flight resolution should enable accurate quantification of MBF, without any compromise in the quality of conventional ECG-gated myocardial perfusion images.