Recent progress and outlooks in rhodamine-based fluorescent probes for detection and imaging of reactive oxygen, nitrogen, and sulfur species.

Reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS) serve as vital mediators essential for preserving intracellular redox homeostasis within the human body, thereby possessing significant implications across physiological and pathological domains. Nevertheless, deviations from normal levels of ROS, RNS, and RSS disturb redox homeostasis, leading to detrimental consequences that compromise bodily integrity. This disruption is closely linked to the onset of various human diseases, thereby posing a substantial threat to human health and survival. Small-molecule fluorescent probes exhibit considerable potential as analytical instruments for the monitoring of ROS, RNS, and RSS due to their exceptional sensitivity and selectivity, operational simplicity, non-invasiveness, localization capabilities, and ability to facilitate in situ optical signal generation for real-time dynamic analyte monitoring. Due to their distinctive transition from their spirocyclic form (non-fluorescent) to their ring-opened form (fluorescent), along with their exceptional light stability, broad wavelength range, high fluorescence quantum yield, and high extinction coefficient, rhodamine fluorophores have been extensively employed in the development of fluorescent probes. This review primarily concentrates on the investigation of fluorescent probes utilizing rhodamine dyes for ROS, RNS, and RSS detection from the perspective of different response groups since 2016. The scope of this review encompasses the design of probe structures, elucidation of response mechanisms, and exploration of biological applications.

Novel D-π-A hemicyanine dye as photoinitiators for in situ hydrogel formation and DLP printing.

The field of biofabrication imposes stringent requirements on the polymerization activity and biosafety of photopolymeric hydrogel systems. In this investigation, we designed and synthesized four hemicyanine dyes with a D-π-A structure specifically tailored for biofabrication purposes. These novel dyes, incorporating carbazole (CZ), triphenylamine (TPA), anthracene (AN), and benzodithiophene (BDT) as electron donors, along with heterocyclic salt (IN) as electron acceptors, were prepared using a straightforward synthesis method. The absorption maxima of ANIN, CZIN, and TPAIN exceeded 500 nm, rendering them suitable co-initiators for the free radical photopolymerization of acrylates under green-red light exposure facilitated by light-emitting diodes (LEDs) and the co-initiator iodonium salt (ION). Notably, CZIN and TPAIN, due to their robust dye absorption and efficient electron transfer to ION, functioned as high-performance photosensitizers. Meanwhile, BDTIN, with its strong and broad absorption range (400-600 nm), enhanced the accuracy of visible light photopolymerization. These dyes exhibit characteristics such as facile synthesis, heightened photo stability, and non-toxicity and also demonstrate the ability to discern the alkalinity of a solution to some extent. Furthermore, we explored the application of these hemicyanine dyes in 3D printing, showing potential to enhance printing resolution in DLP 3D printing (digital light process 3D printing).

Highly Selective and Rapid "Turn-On" Fluorogenic Chemosensor for Detection of Salicylic Acid in Plants and Food Samples.

Salicylic acid (SA) is one of the chemical molecules, involved in plant growth and immunity, thereby contributing to the control of pests and pathogens, and even applied in fruit and vegetable preservation. However, only a few tools have ever been designed or executed to understand the physiological processes induced by SA or its function in plant immunity and residue detection in food. Hence, three Rh6G-based fluorogenic chemosensors were synthesized to detect phytohormone SA based on the "OFF-ON" mechanism. The probes showed high selectivity, ultrafast response time (<60 s), and nanomolar detection limit for SA. Moreover, the probe possessed outstanding profiling that can be successfully used for SA imaging of callus and plants. Furthermore, the fluorescence pattern indicated that SA could occur in the distal transport in plants. These remarkable results contribute to improving our understanding of the multiple physiological and pathological processes involved in SA for plant disease diagnosis and for the development of immune activators. In addition, SA detection in some agricultural products used probes to extend the practical application because its use is prohibited in some countries and is harmful to SA-sensitized persons. Interestingly, the as-obtained test paper displayed that SA could be imaged by ultraviolet (UV) and was directly visible to the naked eye. Given the above outcomes, these probes could be used to monitor SA in vitro and in vivo, including, but not limited to, plant biology, food residue detection, and sewage detection.

Rhodamine-based fluorescent sensors for the rapid and selective off-on detection of salicylic acid and their use in plant cell imaging.

Salicylic acid (SA) is a key hormone that regulates plant growth and immunity, and understanding the physiologic processes induced by SA enables the development of highly pathogen-resistant crops. Here, we report the synthesis of three new SA-sensors (R1-R3) from hydroxyphenol derivatives of a rhodamine-acylhydrazone scaffold and their characterization by NMR and HRMS. Spectroscopic analyses revealed that structural variations in R1-R3 resulted in sensors with different sensitivities for SA. Sensor R2 (with the 3-hydroxyphenyl modification) outperformed R1 (2-hydroxyphenyl) and R3 (4-hydroxyphenyl). The SA-detection limit of R2 is 0.9 µM with an ultra-fast response time (<60 s). In addition, their plant imaging indicated that designed sensor R2 is useful for the further study of SA biology and the discovery and development of new inducers of plant immunity.

Discovery and Structural Optimization of 1,2,3,4-Tetrahydro-ß-carbolines as Novel Reactive Oxygen Species Inducers for Controlling Intractable Plant Bacterial Diseases.

Nowadays, reactive oxygen species (ROS) have been acknowledged as promising bactericidal targets against pesticide-resistant bacteria. Herein, to further excavate more excellent ROS inducers, simple 1,2,3,4-tetrahydro-ß-carboline derivatives containing a 3-aminopropanamide moiety were prepared and assessed for their antibacterial potency. Notably, three promising compounds displayed significant antibacterial potency. Compound I29 exhibits excellent in vitro bioactivity, with an EC50 value of 5.73 µg/mL, and admirable in vivo activities (protective activity of 55.74% and curative activity of 65.50%) toward Xanthomonas oryzae pv. oryzae. Compound I16 has good activity in vitro, with an EC50 of 3.43 µg/mL, and outstanding bioactivities in vivo (protective activity of 92.50% and curative activity of 59.68%) against Xanthomonas axonopodis pv. citri. Compound I6 shows excellent in vitro bioactivity (EC50 = 2.86 µg/mL) and significant protective activity (94.02%) for preventing Pseudomonas syringae pv. actinidiae. Antibacterial mechanism investigations indicate that these compounds disrupt the balance of the redox system to kill bacteria. These simple 1,2,3,4-tetrahydro-ß-carboline derivatives are promising leads to the discovery of bactericidal agents.

Novel Sulfonamide Derivatives Containing a Piperidine Moiety as New Bactericide Leads for Managing Plant Bacterial Diseases.

Plant bacterial diseases are an intractable problem due to the fact that phytopathogens have acquired strong resistances for traditional pesticides, resulting in restricting the quality and yield of agricultural products around the world. To develop new agrochemical alternatives, we prepared a novel series of sulfanilamide derivatives containing piperidine fragments and assessed their antibacterial potency. The bioassay results revealed that most molecules displayed excellent in vitro antibacterial potency towards Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas axonopodis pv. citri (Xac). In particular, molecule C4 exhibited outstanding inhibitory activity toward Xoo with EC50 value of 2.02 µg mL-1, which was significantly better than those of the commercial agents bismerthiazol (EC50 = 42.38 µg mL-1) and thiodiazole copper (EC50 = 64.50 µg mL-1). A series of biochemical assays confirmed that compound C4 interacted with dihydropteroate synthase, and irreversibly damaged the cell membrane. In vivo assays showed that the molecule C4 presented acceptable curative and protection activities of 34.78% and 39.83%, respectively, at 200 µg mL-1, which were greater than those of thiodiazole and bismerthiazol. This study highlights the valuable insights for the excavation and development of new bactericides that can concurrently target dihydropteroate synthase and bacterial cell membranes.

Discovery of novel rost-4-ene derivatives as potential plant activators for preventing phytopathogenic bacterial infection: Design, synthesis and biological studies.

BACKGROUND: Gradually aggravated disease caused by phytopathogenic bacteria severely restricts food security and crop yield, and few pesticides can relieve this severe situation. Thus, development and excavation of new agrochemicals with high bioactivity and novel action mechanism may be a feasible strategy to control intractable bacterial diseases. As a privileged molecular framework, steroid molecules exhibit diversiform bioactivities. Herein, a series of novel androst-4-ene derivatives were designed, synthesised and investigated for their antibacterial behaviour to excavate novel agrochemicals on the base of steroid molecules. RESULTS: Bioassay results indicated that target compounds displayed high bioactivities toward three destructive phytopathogenic bacteria, including Xanthomonas oryzae pv. oryzae (Xoo), Xanthomonas axonopodis pv. citri (Xac) and Pseudomonas syringae pv. actinidiae (Psa). Compound III19 displayed excellent in vitro antibacterial profiling (EC50  = 2.37 mg L-1 towards Xoo, EC50  = 2.10 mg L-1 towards Xac, EC50  = 9.50 mg L-1 towards Psa). Furthermore, compound III19 showed outstanding in vivo protective activities, with values of 81.81% and 58.75% towards kiwifruit bacterial canker and rice bacterial leaf blight, respectively. Analysis of the antibacterial mechanism disclosed that compound III19 enhanced host defence enzyme activities superoxide dismutase (SOD), peroxidase (POD), phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), and catalase (CAT) and increased the salicylate synthase content to induce host resistance. In addition, compound III19 increased the membrane permeability, destroyed the cell membrane and killed the bacteria. CONCLUSION: Given these profiles of target compounds, we highlight a new strategy for controlling intractable plant bacterial diseases by inducing plant resistance and targeting the bacterial cell membrane. © 2022 Society of Chemical Industry.

Application of dental pulp stem cells in oral maxillofacial tissue engineering.

In the maxillofacial area, soft and hard tissue abnormalities are caused by trauma, tumors, infection, and other causes that expose the maxillofacial region to the surface of the human body. Patients' normal physiological function and appearance are interfered with, and their mental health is adversely impacted, reducing their overall life quality. The pursuit of appropriate medical treatments to correct these abnormalities is thus vital. Autologous stem cell regeneration technology mainly focused on tissues has lately emerged as a significant problem in the medical community. Because of the capacity of dental pulp stem cells (DPSCs) to self-renew, the use of DPSCs from the human pulp tissues of deciduous teeth or permanent teeth has gained popularity among scientists as a stem cell-based therapy option. Aside from that, they are simple to extract and have minimal immunogenicity. As a result, bone tissue engineering may be a critical component in treating maxillofacial and periodontal bone abnormalities. DPSCs activity in maxillofacial and periodontal tissue-engineered bone tissue was investigated in this research.

Transcriptomic profiling of mice brain under Bex3 regulation.

BEX family genes are expressed in various tissues and play significant roles in neuronal development. A mouse model of Bex3 gene knock-out was generated in this study, using the CRISPR-Cas9 system. Transcriptomic analysis of the brain was performed to identify genes and pathways under Bex3 regulation. Essential biological functions under the control of Bex3 related to brain development were identified. Ninety-five genes were differentially expressed under Bex3-/- regulation, with 53 down and 42 up. Among down-regulated genes, LOC102633156 is a member of zf-C2H2, Xlr3a is an X-linked lymphocyte regulated gene, LOC101056144 is a hippocampal related gene, 2210418O10Rik and Fam205a3 are cortex related genes. Among the upregulated genes, Zfp967 is a zf protein, Tgtp2 is a T cell-specific regulator, Trpc2 is a neuron-related gene, and Evi2 is related to NF1. A total of 34 KEGG disease terms were identified under the Bex3-/- regulation. The most prominent is non-syndromic X-linked mental retardation, where Fgd1 is enriched. Similarly, IRF, MBD, SAND, zf-BED, and zf-C2H2 were significantly enriched transcription factors. A further study is required to confirm and explain each aspect that has been identified in this study.

Fabrication of Versatile Pyrazole Hydrazide Derivatives Bearing a 1,3,4-Oxadiazole Core as Multipurpose Agricultural Chemicals against Plant Fungal, Oomycete, and Bacterial Diseases.

Developing multipurpose agricultural chemicals is appealing in crop protection, thus eventually realizing the reduction and efficient usage of pesticides. Herein, an array of versatile pyrazole hydrazide derivatives bearing a 1,3,4-oxadiazole core were initially synthesized and biologically evaluated the antifungal, antioomycetes, and antibacterial activities. In addition, the pyrazole ring was replaced by the correlative pyrrole, thiazole, and indole scaffolds to extend the molecular diversity. The results showed that most of these hybrid compounds were empowered with multifunctional bioactivities, which are exemplified by compounds a1-a6, b1-b3, b7, b10, b13, and b18. For the antifungal activity, the minimal EC50 values could afford 0.47 (a2), 1.05 (a2), 0.65 (a1), and 1.32 µg/mL (b3) against the corresponding fungi Gibberella zeae (G. z.), Fusarium oxysporum, Botryosphaeria dothidea, and Rhizoctonia solani. In vivo pot experiments against corn scab (caused by G. z.) revealed that the compound a2 was effective with protective and curative activities of 90.2 and 86.3% at 200 µg/mL, which was comparable to those of fungicides boscalid and fluopyram. Further molecular docking study and enzymatic activity analysis (IC50 = 3.21 µM, a2) indicated that target compounds were promising succinate dehydrogenase inhibitors. Additionally, compounds b2 and a4 yielded superior anti-oomycete and antibacterial activities toward Phytophora infestins and Xanthomonas oryzae pv. oryzae with EC50 values of 2.92 and 8.43 µg/mL, respectively. In vivo trials against rice bacterial blight provided the control efficiency within 51.2-55.3% (a4) at 200 µg/mL, which were better than that of bismerthiazol. Given their multipurpose characteristics, these structures should be positively explored as agricultural chemicals.

Substituent-controlled chemoselective synthesis of multi-substituted pyridones via a one-pot three-component cascade reaction.

An efficient and concise one-pot strategy for the synthesis of multisubstituted pyridones via a one-pot three-component cascade reaction catalyzed by Cs2CO3 under solvent-free conditions has been developed. The substituent-controlled chemoselective cycloaddition process involved steps including a Michael addition/ethanol elimination/intermolecular cyclization sequence utilizing anilines, diethyl acetylenedicarboxylate, and diethyl ethoxymethylenemalonate. In doing so, various 2-pyridone and 4-pyridone species (41 examples) could be obtained in good to excellent yields.

Construction of Fully Substituted 2-Pyridone Derivatives via Four-Component Branched Domino Reaction Utilizing Microwave Irradiation.

Microwave irradiation, four-component branched domino reaction of methyl acetoacetate/2,4-pentanedione, diethyl malonate, triethyl orthoformate and amines offering an extremely efficient strategy for the construction of fully substituted 2-pyridone derivatives under sustainable conditions is established. This self-sorting branched domino transformation is proposed to proceed separate through N-nucleophilic addition and imine-enamine tautomerization/condensation reaction generated from enamino ester and diethyl ethoxymethylenemalonate, and then would be subjected to an aza-ene reaction and intramolecular cyclization mechanism to afford the 2-pyridones with only water and ethanol as byproducts. The simple experimental procedure, high bond-forming efficiency, step and atom economy, inexpensive readily available starting materials, moderate to excellent yields, and good functional group compatibility are other noteworthy advantages of this method.

An Accurate Timing Alignment Method with Time-to-Digital Converter Linearity Calibration for High-Resolution TOF PET.

Accurate PET system timing alignment minimizes the coincidence time window and therefore reduces random events and improves image quality. It is also critical for time-of-flight (TOF) image reconstruction. Here, we use a thin annular cylinder (shell) phantom filled with a radioactive source and located axially and centrally in a PET camera for the timing alignment of a TOF PET system. This timing alignment method involves measuring the time differences between the selected coincidence detector pairs, calibrating the differential and integral nonlinearity of the time-to-digital converter (TDC) with the same raw data and deriving the intrinsic time biases for each detector using an iterative algorithm. The raw time bias for each detector is downloaded to the front-end electronics and the residual fine time bias can be applied during the TOF list-mode reconstruction. Our results showed that a timing alignment accuracy of better than ±25 ps can be achieved, and a preliminary timing resolution of 473 ps (full width at half maximum) was measured in our prototype TOF PET/CT system.

Tunable surface electron spin splitting with electric double-layer transistors based on InN.

Electrically manipulating electron spins based on Rashba spin-orbit coupling (SOC) is a key pathway for applications of spintronics and spin-based quantum computation. Two-dimensional electron systems (2DESs) offer a particularly important SOC platform, where spin polarization can be tuned with an electric field perpendicular to the 2DES. Here, by measuring the tunable circular photogalvanic effect (CPGE), we present a room-temperature electric-field-modulated spin splitting of surface electrons on InN epitaxial thin films that is a good candidate to realize spin injection. The surface band bending and resulting CPGE current are successfully modulated by ionic liquid gating within an electric double-layer transistor configuration. The clear gate voltage dependence of CPGE current indicates that the spin splitting of the surface electron accumulation layer is effectively tuned, providing a way to modulate the injected spin polarization in potential spintronic devices.

Determination of the surface band bending in In x Ga1-x N films by hard x-ray photoemission spectroscopy.

Core-level and valence band spectra of In x Ga1-x N films were measured using hard x-ray photoemission spectroscopy (HX-PES). Fine structure, caused by the coupling of the localized Ga 3d and In 4d with N 2s states, was experimentally observed in the films. Because of the large detection depth of HX-PES (∼20 nm), the spectra contain both surface and bulk information due to the surface band bending. The In x Ga1-x N films (x = 0-0.21) exhibited upward surface band bending, and the valence band maximum was shifted to lower binding energy when the mole fraction of InN was increased. On the other hand, downward surface band bending was confirmed for an InN film with low carrier density despite its n-type conduction. Although the Fermi level (EF) near the surface of the InN film was detected inside the conduction band as reported previously, it can be concluded that EF in the bulk of the film must be located in the band gap below the conduction band minimum.

Engineering and performance (NEMA and animal) of a lower-cost higher-resolution animal PET/CT scanner using photomultiplier-quadrant-sharing detectors.

UNLABELLED: The dedicated murine PET (MuPET) scanner is a high-resolution, high-sensitivity, and low-cost preclinical PET camera designed and manufactured at our laboratory. In this article, we report its performance according to the NU 4-2008 standards of the National Electrical Manufacturers Association (NEMA). We also report the results of additional phantom and mouse studies. METHODS: The MuPET scanner, which is integrated with a CT camera, is based on the photomultiplier-quadrant-sharing concept and comprises 180 blocks of 13 × 13 lutetium yttrium oxyorthosilicate crystals (1.24 × 1.4 × 9.5 mm(3)) and 210 low-cost 19-mm photomultipliers. The camera has 78 detector rings, with an 11.6-cm axial field of view and a ring diameter of 16.6 cm. We measured the energy resolution, scatter fraction, sensitivity, spatial resolution, and counting rate performance of the scanner. In addition, we scanned the NEMA image-quality phantom, Micro Deluxe and Ultra-Micro Hot Spot phantoms, and 2 healthy mice. RESULTS: The system average energy resolution was 14% at 511 keV. The average spatial resolution at the center of the field of view was about 1.2 mm, improving to 0.8 mm and remaining below 1.2 mm in the central 6-cm field of view when a resolution-recovery method was used. The absolute sensitivity of the camera was 6.38% for an energy window of 350-650 keV and a coincidence timing window of 3.4 ns. The system scatter fraction was 11.9% for the NEMA mouselike phantom and 28% for the ratlike phantom. The maximum noise-equivalent counting rate was 1,100 at 57 MBq for the mouselike phantom and 352 kcps at 65 MBq for the ratlike phantom. The 1-mm fillable rod was clearly observable using the NEMA image-quality phantom. The images of the Ultra-Micro Hot Spot phantom also showed the 1-mm hot rods. In the mouse studies, both the left and right ventricle walls were clearly observable, as were the Harderian glands. CONCLUSION: The MuPET camera has excellent resolution, sensitivity, counting rate, and imaging performance. The data show it is a powerful scanner for preclinical animal study and pharmaceutical development.

A Real Time Coincidence System for High Count-Rate TOF or Non-TOF PET Cameras Using Hybrid Method Combining AND-Logic and Time-Mark Technology.

A fully digital FPGA-based high count-rate coincidence system has been developed for TOF (Time of Flight) and non-TOF PET cameras. Using a hybrid of AND-logic and Time-mark technology produced both excellent timing resolution and high processing speed. In this hybrid architecture, every gamma event was synchronized by a 125 MHz system clock and generating a trigger associated with a time-mark given by an 8-bit high-resolution TDC (68.3 ps/bin). AND-logic was applied to the synchronized triggers for the real-time raw sorting of coincident events. An efficient FPGA based Time-mark fine-sort algorithm is used to select all the possible coincidence events within the preset coincidence time window. This FPGA-based coincidence system for a modular PET camera offers reprogrammable flexibility and expandability, so the coincidence system is easily employed, regardless of differences in the scale of the PET camera detector setup. A distributed processing method and pipeline technology were adopted in the design to obtain very high processing speed. In this design, both prompt and time-delayed accidental coincidences are simultaneously processed in real time. The real-time digital coincidence system supports coincidence in 2 to 12 detector module setups, capable of processing 72 million single events per second with no digital data loss and captures multiple-event coincidence for better imaging performance evaluation. The coincidence time window-size and time-offset of each coincidence event pair can be programmed independently in 68.3 ps increments (TDC LSB) during the data acquisition in different applications to optimize the signal-to-noise ratio. The complex coincidence system is integrated in one circuit board with 1.5 Gbps fiber optic interface. We demonstrated the system performance using the actual circuit and Monte Carlo simulations.

A New Statistics-Based Online Baseline Restorer for a High Count-Rate Fully Digital System.

The goal of this work is to develop a novel, accurate, real-time digital baseline restorer using online statistical processing for a high count-rate digital system such as positron emission tomography (PET). In high count-rate nuclear instrumentation applications, analog signals are DC-coupled for better performance. However, the detectors, pre-amplifiers and other front-end electronics would cause a signal baseline drift in a DC-coupling system, which will degrade the performance of energy resolution and positioning accuracy. Event pileups normally exist in a high-count rate system and the baseline drift will create errors in the event pileup-correction. Hence, a baseline restorer (BLR) is required in a high count-rate system to remove the DC drift ahead of the pileup correction. Many methods have been reported for BLR from classic analog methods to digital filter solutions. However a single channel BLR with analog method can only work under 500 kcps count-rate, and normally an analog front-end application-specific integrated circuits (ASIC) is required for the application involved hundreds BLR such as a PET camera. We have developed a simple statistics-based online baseline restorer (SOBLR) for a high count-rate fully digital system. In this method, we acquire additional samples, excluding the real gamma pulses, from the existing free-running ADC in the digital system, and perform online statistical processing to generate a baseline value. This baseline value will be subtracted from the digitized waveform to retrieve its original pulse with zero-baseline drift. This method can self-track the baseline without a micro-controller involved. The circuit consists of two digital counter/timers, one comparator, one register and one subtraction unit. Simulation shows a single channel works at 30 Mcps count-rate with pileup condition. 336 baseline restorer circuits have been implemented into 12 field-programmable-gate-arrays (FPGA) for our new fully digital PET system.

The System Design, Engineering Architecture, and Preliminary Results of a Lower-Cost High-Sensitivity High-Resolution Positron Emission Mammography Camera.

A lower-cost high-sensitivity high-resolution positron emission mammography (PEM) camera is developed. It consists of two detector modules with the planar detector bank of 20 × 12 cm(2). Each bank has 60 low-cost PMT-Quadrant-Sharing (PQS) LYSO blocks arranged in a 10 × 6 array with two types of geometries. One is the symmetric 19.36 × 19.36 mm(2) block made of 1.5 × 1.5 × 10 mm(3) crystals in a 12 × 12 array. The other is the 19.36 × 26.05 mm(2) asymmetric block made of 1.5 × 1.9 × 10 mm(3) crystals in 12 × 13 array. One row (10) of the elongated blocks are used along one side of the bank to reclaim the half empty PMT photocathode in the regular PQS design to reduce the dead area at the edge of the module. The bank has a high overall crystal packing fraction of 88%, which results in a very high sensitivity. Mechanical design and electronics have been developed for low-cost, compactness, and stability purposes. Each module has four Anger-HYPER decoding electronics that can handle a count-rate of 3 Mcps for single events. A simple two-module coincidence board with a hardware delay window for random coincidences has been developed with an adjustable window of 6 to 15 ns. Some of the performance parameters have been studied by preliminary tests and Monte Carlo simulations, including the crystal decoding map and the 17% energy resolution of the detectors, the point source sensitivity of 11.5% with 50 mm bank-to-bank distance, the 1.2 mm-spatial resolutions, 42 kcps peak Noise Equivalent Count Rate at 7.0-mCi total activity in human body, and the resolution phantom images. Those results show that the design goal of building a lower-cost, high-sensitivity, high-resolution PEM detector is achieved.

Monte Carlo Simulation Study on the Time Resolution of a PMT-Quadrant-Sharing LSO Detector Block for Time-of-Flight PET.

We developed a detailed Monte Carlo simulation method to study the time resolution of detectors for time-of-flight positron emission tomography (TOF PET). The process of gamma ray interaction in detectors, scintillation light emission and transport inside the detectors, the photoelectron generation and anode signal generation in the photomultiplier tube (PMT), and the electronics process of discriminator are simulated. We tested this simulation method using published experimental data, and found that it can generate reliable results. Using this method, we simulated the time resolution for a 13 × 13 detector block of 4 × 4 × 20 mm(3) lutetium orthosilicate (LSO) crystals coupled to four 2-inch PMTs using PMT-quadrant-sharing (PQS) technology. We analyzed the effects of several factors, including the number of photoelectrons, light transport, transit time spread (TTS), and the depth of interaction (DOI). The simulation results indicated that system time resolution of 360 ps should be possible with currently available fast PMTs. This simulation method can also be used to simulate the time resolution of other detector design method.