Cerium-doped Lutetium Yttrium Orthosilicate Research Articles

Monolithic scintillator PET detector by using light sharing between adjacent detector modules

A monolithic crystal-based positron emission tomography (PET) detector has a low cost and high sensitivity and allows determining 3D positions by scintillation light distribution. However, the edge effect inherent to scintillators deteriorates the position resolution of the detector toward the crystal borders due to the escape and reflection of the scintillation light. An increase in crystal thickness will improve the detection efficiency, but the edge effect becomes severe. To improve the position resolution and detection efficiency of scintillators, the light-sharing technique is developed. Two identical trapezoidal monolithic cerium-doped lutetium yttrium orthosilicate (LYSO) crystals with a bottom size of 25.80 × 25.80 mm2 and a thickness of 20 mm are optically coupled at one lateral face by an optical medium. The scintillation light near the optically coupled interface is jointly collected by two adjacent 8 × 8 SiPM arrays from the bottom faces. The SiPM signals are individually read out and processed by using the multichannel readout application-specific integrated circuits (ASICs) of TOFPET2 to provide a light distribution. The transverse positions and depth of interaction (DOI) are calculated from the measured light distribution. As expected, the optical glue with a refractive index of n = 1.68 shows better light sharing between two LYSO crystals than the coupling media of silicon grease (n = 1.40) and air. For the 20 mm thick monolithic LYSO-based PET detector, the transverse position resolution near the crystal edge is improved by nearly 30% by using the light-sharing method compared with the black-painted treatment. However, the DOI resolution near the edge of the crystal is not significantly improved, which may be attributed to the incomplete collection of scintillation light. The DOI resolution of the detector would be improved by using electronics with lower noise and SiPM arrays with smaller pixel.

Low energy X-ray dosimeter based on LYSO:Ce fluorescent powder.

Cerium-doped lutetium yttrium orthosilicate (LYSO:Ce) powder has been synthesized by the co-precipitation method. The influence of the Ce3+ doping concentration on the lattice structure and luminescence characteristics of LYSO:Ce powder was investigated by X-ray diffraction (XRD) and photoluminescence (PL). The XRD measurement indicates that the lattice structure of LYSO:Ce powder was not changed by doping ions. PL results show that LYSO:Ce powder has better luminescence performance when the Ce doping concentration is 0.3mol%. In addition, the fluorescence lifetime of the samples was measured, and the results show that LYSO:Ce has a short decay time. The radiation dosimeter was prepared by LYSO:Ce powder with a Ce doping concentration of 0.3mol%. Radioluminescence properties of the radiation dosimeter also were studied under X-ray irradiation at doses from 0.03 to 0.76Gy, with dose rate from 0.09 to 2.284Gy/min. The results show that the dosimeter has a certain linear relationship response and stability. The radiation responses of the dosimeter at different energies were obtained under X-ray irradiation with X-ray tube voltages ranging from 20 to 80kV. The results show that the dosimeter has a certain linear relationship response in the low energy range of radiotherapy. These results indicate the potential application of LYSO:Ce powder dosimeters in remote radiotherapy and online radiation monitoring.

Low intensity gamma-ray monitor for in-situ solids fraction measurements in liquids

A novel detection system has been designed to measure the settling of solids in tailing ponds in order to facilitate the reuse of water in oil sands extraction processing, tailings excavation, transportation and management. The system is based on a weak gamma ray source and an inexpensive scintillator-based detector. The system measures gamma ray photons which are transmitted through the material of interest which are detected by a combined scintillator and Multi Pixel Photon Counter (MPPC) detector. This non-destructive measurement allows the determination of the solids contents profile versus depth in a tailing pond. The attenuation of gamma radiation depends on the density of the solids within the fluid tailings and thus varies with the weight fraction of solids content of the tailings. Modelling of the system was carried out by Geant4 simulations. The system was deployed using a weak 133Ba gamma-ray source together with a simple microprocessor controller readout circuit to analyze the pulse height response of a Cerium doped Lutetium Yttrium Orthosilicate (LYSO (Ce)) scintillator crystal. The detection system is calibrated with the known samples and can measure solids content with a relative precision of within ∼2%.

Fast growth of cerium-doped lutetium yttrium orthosilicate single crystals and their scintillation properties

The growth of high-quality and large-size cerium-doped lutetium yttrium orthosilicate (Ce:(LuY)2SiO5, Ce:LYSO) crystals with lower cost has great influence on their applications in various physical devices. According to the chemical bonding theory of single crystal growth, the fast thermodynamic growth direction of Ce:LYSO is [010] direction. In this work, the maximum pulling rate of 3.5 mm/h is obtained along [010] direction of Ce:LYSO via the Czochralski (Cz) method. Finally, Ce:LYSO bulk single crystals with diameter of 64 mm and length of 220 mm and mass of 4.2 kg are grown. The luminescence performance of low-doped Ce:LYSO for nuclear irradiation (22Na) detector device was studied. Light yield of 26193 ph/MeV and decay time of 38 ns are obtained. The present work provides a promising fast growth approach to achieving large size functional bulk crystal via both thermodynamic and kinetic controls.

Technical Note: Scintillation markers for real-time visual source tracking during skin high dose rate brachytherapy.

Treatment misadministration during high dose rate (HDR) brachytherapy is mainly caused due to gross errors in incorrect manual entry of catheter length and manual connection of hardware. The probability of these errors increases with increasing complexity of a surface applicator. A simple, real-time visual verification method was developed using a scintillator to enhance quality assurance (QA) measures for HDR surface brachytherapy and thus reduce manual errors and improve patient safety. Scintillation markers were fabricated from cerium-doped lutetium yttrium orthosilicate (LYSO) embedded in a polymer compound to form 5-mm diameter markers. To verify catheter-transfer tube connections, markers were attached to each channel of a Freiburg flap and irradiated with an 192 Ir source. To determine if the source reached the edge of a target, markers were placed along the periphery. The HDR source was visually tracked by following the illumination from the markers. The response of the markers was also verified in the presence of thermoplastic material overlaid on the Freiburg applicator. Scintillation markers emitted intense blue visible light upon irradiation when the HDR source was beneath the marker, verifying the source's presence in the correct catheter. The signal was clearly visible even when the marker was placed on top of the thermoplastic material covering the Freiburg Flap. Crosstalk from adjacent catheters was <50% of the maximum light intensity. Scintillation markers and paint were developed to successfully meet the challenge of visually tracking of HDR source during brachytherapy by surface applicators. This direct visualization of source allows real-time catheter verification during treatment, and correct superficial target coverage, thus preventing a medical event. It can easily be integrated into pre-existing QA program.

Performance evaluation of HiPET, a high sensitivity and high resolution preclinical PET tomograph

HiPET is a recently developed prototype preclinical PET scanner dedicated to high sensitivity and high resolution molecular imaging. The HiPET system employs a phoswich depth of interaction (DOI) detector design, which also allows identification of the large majority of the cross layer crystal scatter (CLCS) events. This work evaluates its performance characteristics following the National Electrical Manufacturers Association (NEMA) NU4-2008 protocol.The HiPET consists of twenty flat panel type detectors arranged in two rings. The inner diameter is 160 mm and the axial field of view (FOV) is 104 mm. Each detector is comprised of two layers of phoswich scintillator crystal arrays, a tapered, pixelated glass lightguide and a multi anode photomultiplier tube (MAPMT). The front (gamma ray entrance) layer is a 48 × 48 pixelated cerium doped lutetium yttrium orthosilicate (LYSO) scintillator array with individual crystals measuring 1.01 × 1.01 × 6.1 mm. The back (towards the PMT) layer is a 32 × 32 pixelated bismuth germanate (BGO) scintillator array with individual crystals measuring 1.55 × 1.55 × 8.9 mm.For energy windows of 250–650 keV and 350–650 keV, the peak absolute sensitivity at the center of the FOV was 13.5% and 10.4% including CLCS events, and 11.8% and 8.9% excluding CLCS events, respectively. The average detector energy resolution derived by averaging the individual crystal spectra was 11.7% ± 1.4% for LYSO and 17.0% ± 1.4% for BGO. The 3D ordered-subsets expectation maximization (OSEM) reconstructed image of a point source in air, ranged from 0.73 mm to 1.19 mm, with an average value of 0.93 ± 0.09 mm at all measured locations. The peak noise equivalent count rate (NECR) and scatter fraction were 179 kcps at 12.4 MBq and 6.9% for the mouse-sized phantom, and 63 kcps at 11.3 MBq and 18.3% for the rat-sized phantom. For the NEMA image quality phantom, the uniformity was 5.8%, and the spillover ratios measured in the water- and air-filled cold region chambers were 0.047 and 0.044, respectively. The recovery coefficients (RC) ranged from 0.31 to 0.92.These results and in vivo evaluation demonstrate that the HiPET can achieve high quality molecular imaging for biomedical applications.

Characterization of CsI(Tl) and LYSO(Ce) scintillator detectors by measurements and Monte Carlo simulations

In this study, we investigated the performance of two cuboid scintillation detectors: thallium-activated cesium iodide [CsI(Tl)] and cerium-doped lutetium yttrium orthosilicate [LYSO(Ce)]. The CsI and LYSO crystals were 5 mm thick with an active area of 10 mm × 10 mm. The LYSO scintillator is characterized by its high stopping power and non-hygroscopicity (neither packaging nor light guide are required). Nevertheless, the main disadvantages of LYSO detectors are a lower light output (32 photons/keV) and an intrinsic radioactivity caused by the β− decay of 176Lu (half-life 3.78 × 1010 years). In contrast, CsI crystals present a relatively high light output (54 photons/keV) allowing better energy resolution; however, the drawback of a CsI detector is low detection efficiency.First, we measured the photon detection efficiency of each scintillator in the photon energy range of 60–1332 keV using radioactive sources. Second, we computed detector efficiencies using the Monte Carlo codes MCNP and Geant4. A comparison between simulated and measured efficiencies showed a good agreement. This comparison confirmed the validity of the mathematical models developed for the two scintillation detectors CsI(Tl) and LYSO(Ce) under investigation.

NEMA NU-4 performance evaluation of a non-human primate animal PET

The Eplus-260 primate PET is an animal PET imaging system developed by the Institute of High Energy Physics, Chinese Academy of Sciences, which is designed to image non-human primates, especially the brain of large non-human primates. The system consists of 48 block detectors arranged in two 24-sided rings with a ring diameter of 263 mm and an axial extent of 64 mm. Each block detector is composed of a 16 × 16 cerium-doped lutetium–yttrium orthosilicate crystal array with a pixel size of 1.9 × 1.9 × 10 mm3. This article presents a performance evaluation of the PET scanner according to the National Electrical Manufacturers Association NU-4 2008 standards. All measurements were made for an energy window of 360–660 keV and a coincidence timing window of 2 ns. In terms of the FWHM, the FBP reconstructed spatial resolution results in all three directions at the radial position of 5 mm were better than or approached to 2 mm, and remained below 3.0 mm within the central 5 cm diameter of the FOV. The peak absolute sensitivity of the scanner was measured 1.80%. For a monkey-sized phantom, the scatter fraction was 34.2% and the peak noise equivalent count rate (NECR) was 26.5 kcps at 64.3 kBq/cc. The overall imaging capabilities of the scanner were also assessed using in vivo imaging study of a rhesus macaque. The performance measurements demonstrate that the Eplus-260 primate PET scanner has the potential ability to obtain good quality and high-contrast images for non-human primates, especially the brain of large non-human primates and could be considered as one technologically advanced dedicated non-human primate PET scanner available today.

A compact scintillator based position sensitive detector system for gamma ray tracking applications

Abstract A Cerium doped Lutetium Yttrium Orthosilicate (LYSO) crystal based precision gamma detection system has been developed using a position sensitive photomultiplier tube, with minimal pulse processing requirements. The assembly’s detailed characterization has been reported in this work. This kind of a setup with a precise spatial resolution can be very useful for scanning high purity germanium detectors that use pulse shape analysis algorithms for signal processing in gamma ray spectroscopy experiments. The highly pure LYSO crystal used here is custom-made and the overall setup including the multi anode readout photomultiplier tube is compact. The system has been tested for energy, timing and position information regarding gamma photons interacting within the crystal using a coincidence mechanism. Position sensitivity has been found to be in the anticipated range of a few millimeters. This kind of a detector can be used in various fields, vis-a-vis, medical imaging, radioactive waste management, nuclear proliferation control, and various applications that deal with precisely identifying and locating radioactivity.

Improved direct detection of low-energy ions using a multipixel photon counter coupled with a novel scintillator

Recently, we described a direct low-energy ion detector for time-of-flight applications based on a single-photon avalanche diode (SPAD) array optically coupled to an LYSO (cerium-doped lutetium yttrium orthosilicate) scintillator. Here, we present a greatly improved version of the detector, developed through testing of a number of different scintillator and phosphor materials in combination with a commercially available SPAD array. The various scintillator materials have been characterized in terms of the achievable detection sensitivity and time response when used in conjunction with the SPAD array. Organic para-polyphenylene dyes, a relatively new class of scintillator for particle detection, were found to exhibit markedly improved performance relative to well-established scintillators such as LYSO crystal scintillators and P47 phosphors, both in terms of brightness and time response. The optimized detector has a time resolution of ∼2ns, an improvement of more than an order of magnitude over the original version, at the same time as achieving a five- to ten-fold improvement in detection sensitivity. Our approach points the way towards the development of a generic silicon-based ion detector technology to complement or replace the microchannel-plate (MCP) ion detectors in widespread use at present. Such a detector would remove the need for high voltages and high vacuum, and at the same time greatly reduce detector cost relative to MCP-based detectors.

Precision timing calorimeter for high energy physics

Scintillator based calorimeter technology is studied with the aim to achieve particle detection with a time resolution on the order of a few 10ps for photons and electrons at energies of a few GeV and above. We present results from a prototype of a 1.4×1.4×11.4cm3 sampling calorimeter cell consisting of tungsten absorber plates and Cerium-doped Lutetium Yttrium Orthosilicate (LYSO) crystal scintillator plates. The LYSO plates are read out with wave lengths shifting fibers which are optically coupled to fast photo detectors on both ends of the fibers. The measurements with electrons were performed at the Fermilab Test Beam Facility (FTBF) and the CERN SPS H2 test beam. In addition to the baseline setup plastic scintillation counter and a MCP-PMT were used as trigger and as a reference for a time of flight measurement (TOF). We also present measurements with a fast laser to further characterize the response of the prototype and the photo sensors. All data were recorded using a DRS4 fast sampling digitizer. These measurements are part of an R&D program whose aim is to demonstrate the feasibility of building a large scale electromagnetic calorimeter with a time resolution on the order of 10ps, to be used in high energy physics experiments.

Development of a Small-Sized, Flexible, and Insertable Fiber-Optic Radiation Sensor for Gamma-Ray Spectroscopy.

We fabricated a small-sized, flexible, and insertable fiber-optic radiation sensor (FORS) that is composed of a sensing probe, a plastic optical fiber (POF), a photomultiplier tube (PMT)-amplifier system, and a multichannel analyzer (MCA) to obtain the energy spectra of radioactive isotopes. As an inorganic scintillator for gamma-ray spectroscopy, a cerium-doped lutetium yttrium orthosilicate (LYSO:Ce) crystal was used and two solid-disc type radioactive isotopes with the same dimensions, cesium-137 (Cs-137) and cobalt-60 (Co-60), were used as gamma-ray emitters. We first determined the length of the LYSO:Ce crystal considering the absorption of charged particle energy and measured the gamma-ray energy spectra using the FORS. The experimental results demonstrated that the proposed FORS can be used to discriminate species of radioactive isotopes by measuring their inherent energy spectra, even when gamma-ray emitters are mixed. The relationship between the measured photon counts of the FORS and the radioactivity of Cs-137 was subsequently obtained. The amount of scintillating light generated from the FORS increased by increasing the radioactivity of Cs-137. Finally, the performance of the fabricated FORS according to the length and diameter of the POF was also evaluated. Based on the results of this study, it is anticipated that a novel FORS can be developed to accurately measure the gamma-ray energy spectrum in inaccessible locations such as narrow areas and holes.

Performances evaluation of a PET/CT device for treatments virtual simulation in radiotherapy

Introduction The Big Bore PET/CT is the model which offers the widest opening of tunnel (a diameter of 85 cm) due to the absence of external septa. The use of bulky restraint systems like those used in radiotherapy is possible. Therefore the Big Bore is presented like the PET/CT dedicated to virtual simulation of radiation treatment. Few studies have been conducted on performances evaluation of the PET/CT Big Bore. Besides, none bears to pay particular attention to the absence of external septa. The purpose of this study is to compare the Big Bore performances to the standard model TF 16, used as a reference in this work, to assess the impact of the tunnel enlargement on the quantification and the target volumes definition in radiotherapy. Meanwhile, this study offers to carry out new tests, more specific to the characteristics of the PET/CT Big Bore. Material and methods The Big Bore is composed of 28336 crystals of 4 × 4 × 22 mm 3 Cerium doped Lutetium Yttrium Orthosilicate (LYSO) spread over 44 rings of 90 cm diameter. Wide bore opening is 85 cm. The axial (〚FOV〛_ax) and transverse (〚FOV〛_tr) fields of view axial are 18 cm and more than 67.6 cm, respectively. It doesn't have any septa and can operate in 3-dimensional (3D) mode. The coincident window width is 3.8 ns. The energy is greater than 440 keV. The electronic system allows using the Time Of Flight (TOF). The CT scanner is the Brillance 16 slice. In comparison, PET/CT Gemini TF 16 has same characteristics except a wide bore opening of 70 cm because of presence of external septa of 7.5 cm. The performances of both PET/CT are evaluated using ‘‘classical” experiments found in literature: the NEMA NU 2-2007 Protocol, measurement of intrinsic radioactivity from LYSO and evaluation of temporal and energy resolutions. The original experiment, created for this work, consists on assessment of an external radioactivity source influence, over multiple distances, on the image quality of test phantom. Results The preliminary results of the first experiment underline that the absence of external septa has an influence on the image quality. Carrying out other experiments would permit to characterize the phenomenon in depth. Conclusion This study proposes the performances evaluation of the Big Bore. Results of the different experiments are being processed and will be presented.

A prototype MR insertable brain PET using tileable GAPD arrays

The aim of this study was to develop a prototype magnetic resonance (MR)-compatible positron emission tomography (PET) that can be inserted into a MR imager and that allows simultaneous PET and MR imaging of the human brain. This paper reports the initial results of the authors' prototype brain PET system operating within a 3-T magnetic resonance imaging (MRI) system using newly developed Geiger-mode avalanche photodiode (GAPD)-based PET detectors, long flexible flat cables, position decoder circuit with high multiplexing ratio, and digital signal processing with field programmable gate array-based analog to digital converter boards. A brain PET with 72 detector modules arranged in a ring was constructed and mounted in a 3-T MRI. Each PET module was composed of cerium-doped lutetium yttrium orthosilicate (LYSO) crystals coupled to a tileable GAPD. The GAPD output charge signals were transferred to preamplifiers using 3 m long flat cables. The LYSO and GAPD were located inside the MR bore and all electronics were positioned outside the MR bore. The PET detector performance was investigated both outside and inside the MRI, and MR image quality was evaluated with and without the PET system. The performance of the PET detector when operated inside the MRI during MR image acquisition showed no significant change in energy resolution and count rates, except for a slight degradation in timing resolution with an increase from 4.2 to 4.6 ns. Simultaneous PET/MR images of a hot-rod and Hoffman brain phantom were acquired in a 3-T MRI. Rods down to a diameter of 3.5 mm were resolved in the hot-rod PET image. The activity distribution patterns between the white and gray matter in the Hoffman brain phantom were well imaged. The hot-rod and Hoffman brain phantoms on the simultaneously acquired MR images obtained with standard sequences were observed without any noticeable artifacts, although MR image quality requires some improvement. These results demonstrate that the simultaneous acquisition of PET and MR images is feasible using the MR insertable PET developed in this study.

Optical fiber-based gamma-ray spectroscopy with cerium-doped lutetium yttrium orthosilicate crystal

A fiber-optic radiation sensor (FORS), which is composed of an inorganic scintillator, a plastic optical fiber (POF), a photomultiplier tube (PMT), and a multichannel analyzer (MCA), was developed for gamma-ray energy spectroscopy. In this study, we selected a cerium-doped lutetium yttrium orthosilicate (LYSO:Ce) as the sensitive element of the FORS and found that LYSO:Ce with dimensions of 3 × 3 × 15mm3 gives the best performance in obtaining a gammaray energy spectrum. The FORS allows us to measure the energy spectra of Co-60, Na-22, and Cs-137.

Study and optimization of positioning algorithms for monolithic PET detectors blocks

We are developing a PET insert for existing MRI equipment to be used in clinical PET/MR studies of the human brain. The proposed scanner is based on annihilation gamma detection with monolithic blocks of cerium-doped lutetium yttrium orthosilicate (LYSO:Ce) coupled to magnetically-compatible avalanche photodiodes (APD) matrices. The light distribution generated on the LYSO:Ce block provides the impinging position of the 511 keV photons by means of a positioning algorithm. Several positioning methods, from the simplest Anger Logic to more sophisticate supervised-learning Neural Networks (NN), can be implemented to extract the incidence position of gammas directly from the APD signals. Finally, an optimal method based on a two-step Feed-Forward Neural Network has been selected. It allows us to reach a resolution at detector level of 2 mm, and acquire images of point sources using a first BrainPET prototype consisting of two monolithic blocks working in coincidence. Neural networks provide a straightforward positioning of the acquired data once they have been trained, however the training process is usually time-consuming. In order to obtain an efficient positioning method for the complete scanner it was necessary to find a training procedure that reduces the data acquisition and processing time without introducing a noticeable degradation of the spatial resolution. A grouping process and posterior selection of the training data have been done regarding the similitude of the light distribution of events which have one common incident coordinate (transversal or longitudinal). By doing this, the amount of training data can be reduced to about 5% of the initial number with a degradation of spatial resolution lower than 10%.

Compact gamma detectors based on FBK SiPMs for a Ps Time Of Flight apparatus

Silicon Photomultipliers (SiPMs) are single-photon detectors currently used in many applications as a valid alternative to Photomultiplier Tubes (PMTs). In fact, SiPMs present several advantages compared to PMTs, in terms of size, ruggedness, insensitivity to magnetic fields and voltage supply.In this work, we evaluated the use of SiPMs produced by FBK (Fondazione Bruno Kessler)-AdvanSid (Trento, Italy) in Positronium Time Of Flight (Ps TOF) technique. The aim of this technique is the study of the energy of Ps emitted by porous media for advanced experiments in the field of antimatter physics and, in the future, for open porosities characterization.The TOF spectrometer in operation at the positron beam of the University of Trento (Italy) is based on five gamma detectors composed of NaI(Tl) scintillators coupled to PMTs. We compared the performance of one of these standard detectors against a detector formed by two 4 × 4 mm2 SiPMs coupled to a 4 × 4 × 30 mm3 LYSO (Cerium-doped Lutetium Yttrium Orthosilicate) scintillator. The LYSO+SiPM detector was characterized for timing and energy resolution as well as for the background emission level.It is shown that SiPMs, thanks to their small size and versatility, can be coupled successfully to small scintillators, obtaining more compact detectors with respect to the NaI(Tl)+PMT detectors. The design of an array of detectors with wide angular acceptance and spatial resolution is discussed in order to improve the performances of Ps-TOF setups.

Development of brain PET using GAPD arrays

In recent times, there has been great interest in the use of Geiger-mode avalanche photodiodes (GAPDs) as scintillator readout in positron emission tomography (PET) detectors because of their advantages, such as high gain, compact size, low power consumption, and magnetic field insensitivity. The purpose of this study was to develop a novel PET system based on GAPD arrays for brain imaging. The PET consisted of 72 detector modules arranged in a ring of 330 mm diameter. Each PET module was composed of a 4 × 4 matrix of 3 × 3 × 20 mm(3) cerium-doped lutetium yttrium orthosilicate (LYSO) crystals coupled with a 4 × 4 array three-side tileable GAPD. The signals from each PET module were fed into preamplifiers using a 3 m long flat cable and then sent to a position decoder circuit (PDC), which output a digital address and an analog pulse of the interacted channel among 64 preamplifier signals transmitted from four PET detector modules. The PDC outputs were fed into field programmable gate array (FPGA)-embedded data acquisition (DAQ) boards. The analog signal was then digitized, and arrival time and energy of the signal were calculated and stored. The energy and coincidence timing resolutions measured for 511 keV gamma rays were 18.4 ± 3.1% and 2.6 ns, respectively. The transaxial spatial resolution and sensitivity in the center of field of view (FOV) were 3.1 mm and 0.32% cps/Bq, respectively. The rods down to a diameter of 2.5 mm were resolved in a hot-rod phantom image, and activity distribution patterns between the white and gray matters in the Hoffman brain phantom were well imaged. Experimental results indicate that a PET system can be developed using GAPD arrays and the GAPD-based PET system can provide high-quality PET imaging.

Ultra-High Resolution LYSO PQS-SSS Heptahedron Blocks for Low-Cost MuPET

We developed and built a solid detector ring for a new murine positron emission tomography (MuPET) system. We use cerium-doped lutetium yttrium orthosilicate (LYSO) crystals and regular round 19 mm photomultipliers (PMTs) arranged in a quadrant-sharing (PQS) configuration. The detector system comprised 180 PQS-SSS heptahedron-shaped blocks distributed in 6 subrings. Each block comprised a 13 × 13 crystal array with nominal dimensions of 19 × 19 × 10 mm3. To form a zero-gap solid ring, the rectangular blocks were ground into heptahedron-shaped blocks with a taper angle of 6° on the edge crystals and optical surfaces. The two edge crystals were 1.76 mm wide, and the inner crystals were 1.32 mm wide. We explored the possibility of increasing the detector's performance by implementing new design, materials, and production techniques; testing the detector's performance; and measuring the detector's timing resolution. List-mode data were acquired using a Ga-68 source, in-house high-yield pileup-event recovery electronics, and data-acquisition software. Four randomly selected blocks were used to evaluate the quality of the detector and our mass-production method. The four blocks' performances were quite similar. A typical block had a packing fraction of 95%, a peak-to-valley ratio of 2.4, a light collection efficiency of 78%, and an energy resolution of 14% at 511 keV, and all 169 of the block's crystal detectors were clearly decoded. Using a single crystal in coincidence with a block, the average coincidence timing resolution was found to be 430 ps (full width at half maximum). A block-to-block coincidence timing resolution of 530 ps is expected. Our PQS-SSS heptahedron block design indicates that it is feasible to construct a high resolution (~1.2 mm) MuPET detector ring using round 19 mm PMTs instead of the more expensive position-sensitive PMTs or solid-state detectors.