We are exploring a scintillator-based detector with potential of high sensitivity, DOI capability and timing resolution in a single-side readout configuration. Our concept combines: 1) A design with 2+ crystal arrays stacked with relative offset, with inherent DOI information but good timing performance has not been shown with conventional light sharing readout. 2) Single crystal array with one-to-one coupling to the photodetector (PD) array, with good timing performance, but no DOI. We believe the combination, where the first layer of a staggered design is coupled one-to-one to a PD array may provide both DOI and timing. The concept is here evaluated through light transport simulations. Results show that: 1) In terms of DOI one-to-one readout of the first layer allows for accurate DOI extraction using a single threshold relative to the PD sum signal, for up to 4 layers. The number of PD pixels exceeding the threshold corresponds to the layer of interaction. The corresponding approach is not possible for the same geometries with a light sharing readout scheme. 2) When employing a low threshold of 2 optical photons the layered approach with one-to-one readout of the first layer improves timing close to the PD compared to single layer, due to reduced crystal thickness. Single detector timing resolution values of 91, 127, 151 and 164 ps were seen in the 4-layer design with unpolished pixels, compared to 148 ps for single array with one-to-one coupling. 3) For the layered design with light sharing readout, timing improves with increased PD pixel size, with an apparent tradeoff between spatial resolution and timing not observed for the one-to-one coupled counterpart. The combination of straightforward and accurate DOI determination, good timing performance and relatively simple design makes the proposed detector a promising candidate for brain dedicated DOI TOF-PET.
Purpose: Explaining why 90Y TOF-PET based equivalent uniform dose (EUD) using standard FDG reconstruction parameters has been shown to predict response. Methods: The hot rods insert of a Jaszczak deluxe phantom was partially filled with a 2.65 GBq 90Y - 300ml DTPA water solution resulting in a 100 Gy mean absorbed dose in the 6 sectors. A two bed 20min/position acquisition was performed on a 550ps- and on a 320ps- TOF-PET/CT and reconstructed with standard FDG reconstruction parameters, without and with additional filtering. The whole procedure was repeated on both PET after adding a 300ml of …
Aim: Investigate whether a time walk assessment derived from crystal light sharing and multi-photon time stamps can improved the TOF resolution. Method: Monte Carlo simulations were performed for SiPM (FBK-NUV-HD) coupled to conventional 4x4 mm2 pixelated LSO (0.2%Ca:Ce ) and also coupled to 8x4 mm2 pixelated LSO in which a triangular optical window allows light sharing between the two 4x4 mm2 sub-pixels depending on the DOI. A time walk estimation was modelled as a DOI dependent weighted sum of the time differences within the photons detection sequence. The DOI dependent weights were optimize…
We perform a parametric study of the newly developed time-of-flight (TOF) image reconstruction algorithm, proposed for the real-time imaging in total-body Jagiellonian PET (J-PET) scanners. The asymmetric 3D filtering kernel is applied at each most likely position of electron-positron annihilation, estimated from the emissions of back-to-back $γ$-photons. The optimisation of its parameters is studied using Monte Carlo simulations of a 1-mm spherical source, NEMA IEC and XCAT phantoms inside the ideal J-PET scanner. The combination of high-pass filters which included the TOF filtered back-proje…
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…
Modern TOF-PET scanner systems require high-speed computing resources for efficient data processing, monitoring and image reconstruction. In this article we present the data flow and software architecture for the novel TOF-PET scanner developed by the J-PET collaboration. We discuss the data acquisition system, reconstruction framework and image reconstruction software. Also, the concept of computing outside hospitals in the remote centers such as Świerk Computing Centre in Poland is presented.
Pixelated PET systems produce higher count rates as they integrate several detecting channels per detector module. An increased data flow from the detectors posses higher needs on the bandwidth requirements. We aim to optimize the bandwidth usage efficiency by filtering on the fly the detected events with non valid energies. PET systems with a SiPM-ASIC readout scheme are being extensively used to get enhanced images on Time-Of-Flight PET scanners. These kind of digital readout systems are specially interesting for the application of on-line processing techniques given the ease of access to ea…
We propose PET scanners using low atomic number media that undergo a persistent local change of state along the paths of the Compton recoil electrons. Measurement of the individual scattering locations and angles, deposited energies, and recoil electron directions allows using the kinematical constraints of the 2-body Compton scattering process to perform a statistical time-ordering of the scatterings, with a high probability of precisely identifying where the gamma first interacted in the detector. In these cases the Line-of-Response is measured with high resolution, determined by the underly…
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…
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…
Monolithic crystals are examined as an alternative to segmented scintillator arrays in positron emission tomography (PET). Monoliths provide good energy, timing and spatial resolution including intrinsic depth of interaction (DOI) encoding. DOI allows reducing parallax errors (radial astigmatism) at off-center positions within a PET ring. We present a novel DOI-estimation approach based on the supervised machine learning algorithm gradient tree boosting (GTB). GTB builds predictive regression models based on sequential binary comparisons (decision trees). GTB models have been shown to be imple…
High-resolution Time-Of-Flight PET with Depth-Of-Interaction becomes feasible: a proof of principle
在本文中，我们证明了闪烁体表面的适当处理的选择，以及用于原始数据分析的适当光电探测器电子器件和特定算法，允许实现能量、时间和DOI分辨率之间的最佳权衡，从而强烈支持具有所需特征和性能的前列腺TOF-PET探针的可行性，所述探针与MRI兼容。在数量上，这意味着1.5mm x 1.5mm x 10 mm的探测器元件，同时实现约11.5%的能量分辨率、约150 ps的飞行时间分辨率和甚至低于1 mm的DOI分辨率。我们强调，这样的时间分辨率允许显著增加噪声等效计数率，从而提高图像质量和病变检测能力。这些个别值对应于其他小组迄今为止获得的最佳值，但我们同时获得了所有这些值。在我们看来，这一原理证明为具有前所未有的功能和性能的TOF-PET MRI兼容探头的可行性铺平了道路，不仅是前列腺放射性示踪剂成像的创新，而且可能也适用于其他器官。
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 TOF-PET scanner systems require high-speed computing resources for efficient data processing, monitoring and image reconstruction. In this article we present the data flow and software architecture for the novel TOF-PET scanner developed by the J-PET collaboration. We discuss the data acquisition system, reconstruction framework and image reconstruction software. Also, the concept of computing outside hospitals in the remote centers such as Świerk Computing Centre in Poland is presented.
Time-Of-Flight (TOF) is a noble technique that is used in Positron Emission Tomography (PET) imaging worldwide. The scintillator based imaging system that is being used around the world for TOF-PET is very expensive. Multi-gap Resistive Plate Chambers (MRPCs) are gaseous detectors which are easy to fabricate, inexpensive and have excellent position and timing resolution. They can be used as a suitable alternative to highly expensive scintillators. For the sole purpose of TOF-PET, a pair of 18 cm $\times$ 18 cm, 5 gap, glass-based MRPC modules have been fabricated. Our main aim was to determine…
A novel method for the line-of-response and time-of-flight reconstruction in TOF-PET detectors based on a library of synchronized model signals
本文提出了一种新的闪烁体探测器命中时间和命中位置重建方法。该方法基于检测器信号与存储在针对闪烁点的一组明确定义的位置配准的同步模型信号库中的结果的比较。命中位置被重建为对应于来自库的与测量信号最相似的信号的命中位置。相互作用的时间被确定为所测量的信号与库中最相似的信号之间的相对时间。测量信号和模型信号的相似度被定义为在多维测量空间中表示测量信号和模型信号的点之间的距离。该方法的新颖性还在于所提出的模型信号同步的方式，使得能够直接确定从湮灭点到检测器的湮灭量子的飞行时间（TOF）之间的差异。使用通过J-PET探测器的双带原型和作为湮灭伽马量子源的$^{22}$ Na钠同位素获得的实验数据来验证所介绍的方法。探测器由尺寸为5 mm x 19 mm x 300 mm的塑料闪烁体带制成，在两侧光学连接到光电倍增管，利用所介绍的方法，建立了空间分辨率约为1.3 cm（$σ$），飞行时间分辨率约为125 ps（$σ$）的空间分辨率和飞行时间分辨率。
PETALO (a Positron Emission Tof Apparatus based on Liquid xenOn) is a new approach for Positron Emission Tomography scanners, based on liquid xenon. The PETALO detector aims at capturing the light produced by the scintillation in LXe taking advantage of its uniform response and continuity. This strategy will lead to a geometrical distortion free behavior compared to other PET detectors. To this end, the sensors chosen for the light readout are SiPMs, which provide large area, high gain and very low noise. In order to take advantage of the unique PETALO detector characteristics a read-out archi…
Rethinking Timing Residuals: Advancing PET Detectors with Explicit TOF Corrections
Institute of Imaging and Computer Vision (LfB), RWTH Aachen University（成像与计算机视觉研究所（LfB），亚琛工业大学）；Department of Physics of Molecular Imaging Systems (PMI), Institute for Experimental Molecular Imaging, RWTH Aachen University（分子成像系统物理系（PMI），实验分子成像研究所，亚琛工业大学）；Institute of High Energy Physics (HEPHY), Austrian Academy of Sciences（高能物理研究所（HEPHY），奥地利科学院）；Hyperion Hybrid Imaging Systems GmbH（Hyperion混合成像系统有限公司）
Measurement of the Time-of-Flight (TOF) of the 511 keV gammas brings an important reduction of statistical noise in the PET image, with higher precision time measurements producing clearer images. Scintillating crystals are used to convert the 511 keV annihilation photon to an electron of ~511 KeV energy via the photoelectric effect; it is necessary to determine with precision the position and time of this conversion within the scintillating crystal. We propose using an array of crystals cut into a specific geometry discussed below; these crystals are read out by an array of strip SiPMs. This …
Presice measurements of the photons conversion points in the scintillators are required to achieve a high spatial resolution of the PET system. I have developed a new method of reconstruction of the depth-of-interaction information for PET detectors with dual-side readout. The depth-of-interaction and energy resolutions from Monte-Carlo simulations are presented in this paper. The new method allows to reach depth-of-interaction resolution that is about 0.4~mm ($σ$) [or about 1.0~mm (FWHM)] for 10-mm long LYSO scintillator. If the precise measurement of the primary photon energy is not a high p…
PETALO (Positron Emission TOF Apparatus based on Liquid xenOn) exploits the unique characteristics of liquid xenon as a scintillator for use in a PET detector. Here initial simulation studies are detailed which highlight the potential of such a detector and outline the steps taken in the reconstruction of 511 keV gamma rays and in the full PET image reconstruction. In particular, a neural network-based approach is conceived in order to tag gamma rays that are poorly reconstructed due to Compton scattering. It is found that though a significant fraction of events undergo Compton scattering, not…
The Multigap Resistive Plate Chambers (MRPCs) provide excellent timing as well as position resolutions at relatively low cost. Therefore, they can be used in medical imaging applications such as PET where precise timing is a crucial parameter of measurement. We have designed and fabricated several six-gap glass MRPCs and extensively studied their performance. In this paper, we describe the fabrication and characterization of the detector, the electronics and the data acquisition system of the setup. We present here the result of our Time Of Flight (TOF) experiment using a radioactive source Na…
108 ps coincidence time resolution through optimized scintillators, photodetectors, readout electronics, and DOI-based timing correction in orthogonally stacked detector configurations
Central Research Laboratory, Hamamatsu Photonics K. K.（滨松光子株式会社中央研究实验室）
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…
The potential of photon detectors to achieve precise timing information is of increasing importance in many domains, PET and CT scanners in medical imaging and particle physics detectors, amongst others. The goal to increase by an order of magnitude the sensitivity of PET scanners and to deliver, via time-of-flight (TOF), true space points for each event, as well as the constraints set by future particle accelerators require a further leap in time resolution of scintillator-based ionizing radiation detectors, reaching eventually a few picoseconds resolution for sub MeV energy deposits. In spit…
For TOF positron emission tomography (TOF PET) detectors, time-to-digital converters (TDCs) are essential to resolve the coincidence time of the photon pairs. Recently, an efficient TDC structure called ring-oscillator-based (RO-based) Vernier TDC using carry chains was reported by our team. The method is very promising due to its low linearity error and low resource cost. However, the implementation complexity is rather high especially when moving to multi-channels TDC designs, since this method calls for a manual intervention to the initial fitting results of the compilation software. In thi…
We have developed a new laser-based time calibration system for the MEG II timing counter dedicated to timing measurement of positrons. The detector requires precise timing alignment between $\sim\,$500 scintillation counters. In this study, we present the calibration system which can directly measure the time offset of each counter relative to the laser-synchronized pulse. We thoroughly tested all the optical components and the uncertainty of this method is estimated to be 24 ps. In 2017, we installed the full system into the MEG II environment and performed a commissioning run. This method s…
