P. Kowalski, P. Moskal, W. Wiślicki, L. Raczyński, T. Bednarski, P. Białas, J. Bułka, E. Czerwiński, A. Gajos, A. Gruntowski, D. Kamińska, Ł. Kapłon, A. Kochanowski, G. Korcyl, J. Kowal, T. Kozik, W. Krzemień, E. Kubicz, Sz. Niedźwiecki, M. Pałka, Z. Rudy, P. Salabura, N. G. Sharma, M. Silarski, A. Słomski, J. Smyrski, A. Strzelecki, A. Wieczorek, I. Wochlik, M. Zieliński, N. Zoń
Novel Positron Emission Tomography system, based on plastic scintillators, is developed by the J-PET collaboration. In order to optimize geometrical configuration of built device, advanced computer simulations are performed. Detailed study is presented of background given by accidental coincidences and multiple scattering of gamma quanta.
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A model is proposed to address issues on the precise background evaluation due to the complex data structure defined by the delayed coincidence method, which is widely used in reactor electron-antineutrino oscillation experiments. In this model, the effects from the muon veto, uncorrelated random background, coincident signal and background are all studied with the analytical solutions, simplifying the estimation of the systematic uncertainties of signal efficiency and accidental background rate determined by the unstable single rate. The result of calculation is validated numerically with a n…
The PandaX-II experiment employed a 580kg liquid xenon detector to search for the interactions between dark matter particles and the target xenon atoms. The accidental coincidences of isolated signals result in a dangerous background which mimic the signature of the dark matter. We performed a detailed study on the accidental coincidence background in PandaX-II, including the possible origin of the isolated signals, the background level and corresponding background suppression method. With a boosted-decision-tree algorithm, the accidental coincidence background is reduced by 70% in the dark ma…
The measurement of the time of flight of the two 511 keV gammas recorded in coincidence in a PET scanner provides an effective way of reducing the random background and therefore increases the scanner sensitivity, provided that the coincidence resolving time (CRT) of the gammas is sufficiently good. The best commercial PET-TOF system today (based in LYSO crystals and digital SiPMs), is the VEREOS of Philips, boasting a CRT of 316 ps (FWHM). In this paper we present a Monte Carlo investigation of the CRT performance of a PET scanner exploiting the scintillating properties of liquid xenon. We fi…
In this paper we present a general method for estimating rates of accidental coincidence between a pair of single photon detectors operated within their saturation regimes. By folding the effects of recovery time of both detectors and the detection circuit into an "effective duty cycle" we are able to accomodate complex recovery behaviour at high event rates. As an example, we provide a detailed high-level model for the behaviour of passively quenched avalanche photodiodes, and demonstrate effective background subtraction at rates commonly associated with detector saturation. We show that by p…
Positron Emission Tomography (PET) using time-of-flight information, which can greatly improve the quality of the reconstructed image, has recently become an exciting topic. In this work, 3.2mm*3.2mm*25mm finger-like LYSO crystals were used to make a 5*5 array, coupled to the Hamamatsu H8500 photomultiplier tube (PMT) as a detector. A fast leading-edge discriminator was designed for the LYSO-H8500 detector. Average coincidence time resolution FWHM of 330 ps was obtained for the LYSO detector with a reference BaF2 detector, whose time resolution for 511 keV γ-rays was FWHM 150 ps. Time resoluti…
In this paper we use detailed Monte Carlo simulations to demonstrate that liquid xenon (LXe) can be used to build a Cherenkov-based TOF-PET, with an intrinsic coincidence resolving time (CRT) in the vicinity of 10 ps. This extraordinary performance is due to three facts: a) the abundant emission of Cherenkov photons by liquid xenon; b) the fact that LXe is transparent to Cherenkov light; and c) the fact that the fastest photons in LXe have wavelengths higher than 300 nm, therefore making it possible to separate the detection of scintillation and Cherenkov light. The CRT in a Cherenkov LXe TOF-…
Modern PET systems reach a spatial resolution of 3-10 mm. A disadvantage of this technique is the diffusion of the positron before its decay with a typical range of ca. 1 mm (depending on its energy). This motion and Compton scattering of the 511 keV photons within the patient limit the performance of PET. We present a nuclear medical imaging technique, able to reach submillimeter spatial resolution in 3 dimensions with a reduced activity application compared to conventional PET. This 'gamma-PET' technique draws on specific positron sources simultaneously emitting an additional photon with the…
Improving PET scanner time-of-flight resolution using additional prompt photon
本研究提出利用额外瞬发光子信息改进PET三重符合事件的位置重建，结合正电子素寿命分布，并基于模拟数据验证了该方法能提升飞行时间分辨率。
We present results of simulations on the influence of photon propagation and the Cherenkov effect on the time resolution of LSO:Ce scintillators. The influence of the scintillator length on the coincidence time resolution is shown. Furthermore, the impact of the depth of interaction on the time resolution, the light output and the arrival time distribution at the photon detector is simulated and it is shown how these information can be used for time walk correction.
Evaluation of Coincidence Time Resolution in a liquid xenon detector with silicon photomultipliers
本研究探索在PET中结合液氙与硅光电倍增管以增强飞行时间分辨率，通过优化原型实现281 ps FWHM的符合时间分辨率，证明液氙可作为传统闪烁体的可行替代方案。
$Objective$. Obtaining the intrinsic dose distributions in particle therapy is a challenging problem that needs to be addressed by imaging algorithms to take advantage of secondary particle detectors. In this work, we investigate the utility of deep learning methods for achieving direct mapping from detector data to the intrinsic dose distribution. $Approach$. We performed Monte Carlo simulations using GATE/Geant4 10.4 simulation toolkits to generate a dataset using human CT phantom irradiated with high-energy protons and imaged with compact in-beam PET for realistic beam delivery in a single-…
Alleviating the trade-off between coincidence time resolution and sensitivity using scalable TOF-DOI detectors
提出一种名为xDetector的交叉堆叠PET探测器读出方案，通过正交堆叠一维探测器将闪烁体厚度减至约13 mm，在不损失灵敏度的同时缓解了TOF能力与灵敏度间的权衡，并具备DOI探测能力和可扩展性。
The positron-electron pair annihilation in two photons is known for its numerous applications using PET scanners. The decay of Positronium (Ps) from a standard sealed source in more than two photons is less likely but can be observed with a relatively simple setup. The main goal of this experiment was to verify momentum and total angular momentum conservation principles at subatomic level through the Ps annihilation. The two spin configurations of Ps are produced with a beta+ source. The decay modes are identified using gamma-ray spectroscopy techniques in a double and triple coincidence setup…
New detector approaches in Positron Emission Tomography imaging will play an important role in reducing costs, lowering administered radiation doses, and improving overall performance. PETALO employs liquid xenon as the active scintillating medium and UV-sensitive silicon photomultipliers for scintillation readout. The scintillation time in liquid xenon is fast enough to register time-of-flight information for each detected coincidence, and sufficient scintillation is produced with low enough fluctuations to obtain good energy resolution. The present simulation study examines a full-body-sized…
108 ps coincidence time resolution through optimized scintillators, photodetectors, readout electronics, and DOI-based timing correction in orthogonally stacked detector configurations
该研究提出正交堆叠的xDetector构型，通过优化闪烁体、光电探测器、读出电子学及三维相互作用CTR校正，使系统CTR达108.6 ps FWHM，较传统探测器提升10.3%，有望助力TOF-PET性能提升
This paper describes the characterization of crystal matrices and silicon photomultiplier arrays for a novel Positron Emission Tomography (PET) detector, namely the external plate of the EndoTOFPET-US system. The EndoTOFPET-US collaboration aims to integrate Time-Of-Flight PET with ultrasound endoscopy in a novel multimodal device, capable to support the development of new biomarkers for prostate and pancreatic tumors. The detector consists in two parts: a PET head mounted on an ultrasound probe and an external PET plate. The challenging goal of 1 mm spatial resolution for the PET image requir…
Coincidence-based reconstruction for reactor antineutrino detection in gadolinium-doped Cherenkov detectors
本研究提出一种基于符合的重建算法，利用IBD事件对的组合光重建顶点，在掺钆水及水基液体闪烁体探测器中显著提升顶点分辨率，并实现高效的本底排除。
The aim of this work is to show the potential capabilities of monolithic crystals coupled to large SiPM arrays, to be considered as detector blocks for PET scanners enabling Time Of Flight (TOF) capabilities. Monolithic blocks allow one to decode the 3D photon impact position. This approach, along with TOF information, can be of high interest in clinical Positron emission tomography (PET) applications where a typical ring configuration is used. In this manuscript, we evaluate an ASIC- based readout for digitizing all signals coming from analog photosensors. Validation results with one-to-one c…
In recent years, SiPM photoelectric devices have drawn much attention in the domain of time-of-flight-based positron emission tomography (TOF-PET). Using them to construct PET detectors with excellent coincidence time resolution (CTR) is always one of research focus. In this paper, a SiPM readout pre-amplifier based on common-base current amplifier structure followed by a Pole-Zero (PZ) compensation network is constructed, and the main factors that affect the timing performance of the PET detector are investigated. By experimental measurement, we found that the CTR is heavily related to the ba…
First experimental proof of PET imaging based on multi-anode MCP-PMTs with Cherenkov radiator-integrated window
本研究开发了基于8×8阳极切伦科夫辐射体集成窗口MCP-PMT的双模块PET成像平台，实现103 ps FWHM的符合时间分辨率，首次完成模块级切伦科夫PET成像并验证了其可行性。
First ClearMind gamma detector prototype for TOF-PET imaging
本研究开发了首个 ClearMind TOF-PET 伽马探测器原型，通过在 PWO 晶体上直接沉积双碱光电阴极，实现了 350 ps 符合时间分辨率、4-5 mm 空间分辨率和 28% 探测效率，验证了其概念可行性。
Recent tests of a single module of the Jagiellonian Positron Emission Tomography system (J-PET) consisting of 30 cm long plastic scintillator strips have proven its applicability for the detection of annihilation quanta (0.511 MeV) with a coincidence resolving time (CRT) of 0.266 ns. The achieved resolution is almost by a factor of two better with respect to the current TOF-PET detectors and it can still be improved since, as it is shown in this article, the intrinsic limit of time resolution for the determination of time of the interaction of 0.511 MeV gamma quanta in plastic scintillators is…
PET provides in vivo molecular and functional imaging capability that is crucial to studying the interaction of plant with changing environment at the whole-plant level. We have developed a dedicated plant PET imager that features high spatial resolution, housed in a fully controlled environment provided by a plant growth chamber (PGC). The system currently contains two types of detector modules: 84 microPET R4 block detectors with 2.2 mm crystals to provide a large detecting area; and 32 Inveon block detectors with 1.5 mm crystals to provide higher spatial resolution. Outputs of the four micr…
Multi-Kernel TOF-PET Image Reconstruction Using ADMM
针对多核TOF-PET中不同符合时间分辨率成分导致的收敛不平衡问题，提出基于交替方向乘子法（ADMM）的分裂优化算法（TOF-decomp ADMM），通过分别优化快慢CTR对数似然项并在约束下平衡贡献，实现更稳定的收敛和更好的对比度-噪声权衡。
This work reports on a new reconstruction algorithm allowing to reconstruct the decays of ortho-positronium atoms into three photons using the places and times of photons recorded in the detector. The method is based on trilateration and allows for a simultaneous reconstruction of both location and time of the decay. Results of resolution tests of the new reconstruction in the J-PET detector based on Monte Carlo simulations are presented, which yield a spatial resolution at the level of 2 cm (FWHM) for X and Y and at the level of 1 cm (FWHM) for Z available with the present resolution of J-PET…
Photon number resolving detectors as evidence for the corpuscular nature of light
本文通过提出基于符合窗口内重合探测聚合的波动解释，并结合多路复用PNR探测器实验与经典振幅阈值模型比较，证明低SNR的PNR探测结果不能作为光的粒子性证据。
Imaging simulation of a dual-panel PET geometry with ultrafast TOF detectors
本研究通过Geant4模拟探究搭载超快TOF探测器的双面板PET的成像特性，分析不同TOF分辨率与探测效率下的成像表现，验证了该结构的可行性及相比传统方案的潜在优势。
Investigating the Timing Behavior of Compton Scattering in BGO for Time-of-Flight PET
本研究探讨BGO中康普顿散射对TOF-PET时间分辨的影响，发现InterCS事件显著降低时间分辨率，需采用时间感知的像素时间戳策略以维持性能。
Fast emitting nanocomposites for high-resolution ToF-PET imaging based on multicomponent scintillators
本文提出含氧化铪纳米颗粒的聚合物闪烁体并与BGO耦合形成多层结构，利用组分间能量共享激发快发光，使CTR较整块BGO提升25%。
Current clinical PET systems utilize detectors where the scintillator typically contains single elements of 3 - 6 mm width and about 20 mm height. While providing good TOF performance, this design limits the spatial resolution and causes radial astigmatism as the DOI remains unknown. We propose an alternative, aiming to combine the advantages of current detectors with the DOI capabilities shown for monolithic concepts, based on semi-monolithic scintillators (slabs). An array of 8 monolithic LYSO slabs of dimensions 3.9 x 32 x 19 mm3 was read out by a 64-channel photosensor containing digital S…
Towards polarization-enhanced PET: Study of random background in polarization-correlated Compton events
本研究探索利用湮灭光子偏振关联的康普顿散射来降低PET随机背景，实验表明在特定角度选择下，偏振关联事件的信号背景比优于传统单像素测量，且随偏振调制因子提升。
Light-Based Fast Timing in Bulk CsPbBr3 Crystals for TOF-PET and Proton Range Verification
本研究针对半导体探测器时间分辨率差的问题，提出利用CsPbBr3晶体中的切伦科夫光提升定时性能，经模拟与实验验证获得419 ps FWHM的符合时间分辨率，证实其在快速定时及三维定位方向的应用可行性。
Rethinking Timing Residuals: Advancing PET Detectors with Explicit TOF Corrections
本研究提出一种基于残差的物理校准方法，通过显式时间残差定义训练机器学习模型直接预测校正值，将PET探测器定时性能从371 ps提升至281 ps，并简化数据采集、减小模型规模。
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