A fast coincidence preamplifier for solid state radiation detectors

We introduce a compact preclinical PET detector that combines the output from 64 SiPM channels, forming an 8×8 matrix of pixels capable of efficiently encoding event position, with good energy and time resolution, as well as depth of interaction information. The scintillator matrices used to characterize the detector are a 16×16 matrix comprised of 1.3×1.3×12mm3 LYSO crystals, and a 1.3×1.3×15mm3 GSO/LYSO phoswhich. Preliminary results regarding spatial resolution show that the detector has a resolvability index of 0.25, an energy resolution below 14% for the 511KeV peak and a good separation between the two different phoswich crystal layers. Due to the compactness and MR compatibility of this detector it is proposed as a candidate to substitute those based on the R8900 PS-PMT in a full ring system that could be inserted into the MR bore of a preclinical PET-MR imager.

A driftless gas proportional scintillation counter for muonic hydrogen X-ray spectroscopy under strong magnetic fields

The design of a positron emission tomography (PET) scanner is specially challenging since it should not compromise high spatial resolution, high sensitivity, high count-rate capability, and good energy and time resolution. The geometrical design of the system alongside the characteristics of the individual PET detector modules contributes to the overall performance of the scanner. The detector performance is mainly influenced by the characteristics of the photo-detector and the scintillation crystal. Although silicon photomultipliers (SiPMs) have already proven to be promising photo-detectors for PET, their performance is highly influenced by micro-cell structure and production technology. Therefore, five types of SiPMs produced by KETEK with an active area size of 1.2 × 1.2 mm2 were characterized in this study. The SiPMs differed in the production technology and had micro-cell sizes of 25, 50, 75, and 100 μm. Performance of the SiPMs was evaluated in terms of their breakdown voltage, temperature sensitivity, dark count rate, and correlated noise probability. Subsequently, energy resolution and coincidence time resolution (CTR) of the SiPMs were measured with five types of crystals, including two Ce:LYSO, two Ce:GAGG, and one Pr:LuAG. Two crystals with a geometry of 1.5 × 1.5 × 6 mm3 were available from each type. The best CTR achieved was ∼ 240 ps, which was obtained with the Ce:LYSO crystals coupled to the 50 μm SiPM produced with the trench technology. The best energy resolution for the 511 keV photo-peak was ∼ 11% and was obtained with the same SiPM coupled to the Ce:GAGG crystals.

The idea of a very sensitive positron emission tomography (PET) system covering a large portion of the body of a patient already dates back to the early 1990s. In the period 2000–2010, only some prototypes with long axial field of view (FOV) have been built, which never resulted in systems used for clinical research. One of the reasons was the limitations in the available detector technology, which did not yet have sufficient energy resolution, timing resolution or countrate capabilities for fully exploiting the benefits of a long axial FOV design. PET was also not yet as widespread as it is today: the growth in oncology, which has become the major application of PET, appeared only after the introduction of PET-CT (early 2000).The detector technology used in most clinical PET systems today has a combination of good energy and timing resolution with higher countrate capabilities and has now been used since more than a decade to build time-of-flight (TOF) PET systems with fully 3D acquisitions. Based on this technology, one can construct total body PET systems and the remaining challenges (data handling, fast image reconstruction, detector cooling) are mostly related to engineering. The direct benefits of long axial FOV systems are mostly related to the higher sensitivity. For single organ imaging, the gain is close to the point source sensitivity which increases linearly with the axial length until it is limited by solid angle and attenuation of the body. The gains for single organ (compared to a fully 3D PET 20-cm axial FOV) are limited to a factor 3–4. But for long objects (like body scans), it increases quadratically with scanner length and factors of 10–40 × higher sensitivity are predicted for the long axial FOV scanner. This application of PET has seen a major increase (mostly in oncology) during the last 2 decades and is now the main type of study in a PET centre. As the technology is available and the full body concept also seems to match with existing applications, the old concept of a total body PET scanner is seeing a clear revival. Several research groups are working on this concept and after showing the potential via extensive simulations; construction of these systems has started about 2 years ago. In the first phase, two PET systems with long axial FOV suitable for large animal imaging were constructed to explore the potential in more experimental settings. Recently, the first completed total body PET systems for human use, a 70-cm-long system, called PennPET Explorer, and a 2-m-long system, called uExplorer, have become reality and first clinical studies have been shown. These results illustrate the large potential of this concept with regard to low-dose imaging, faster scanning, whole-body dynamic imaging and follow-up of tracers over longer periods. This large range of possible technical improvements seems to have the potential to change the current clinical routine and to expand the number of clinical applications of molecular imaging. The J-PET prototype is a prototype system with a long axial FOV built from axially arranged plastic scintillator strips.This paper gives an overview of the recent technical developments with regard to PET scanners with a long axial FOV covering at least the majority of the body (so called total body PET systems). After explaining the benefits and challenges of total body PET systems, the different total body PET system designs proposed for large animal and clinical imaging are described in detail. The axial length is one of the major factors determining the total cost of the system, but there are also other options in detector technology, design and processing for reducing the cost these systems. The limitations and advantages of different designs for research and clinical use are discussed taking into account potential applications and the increased cost of these systems.

The scintillation light distribution produced by photodetectors in positron emission tomography (PET) provides the depth of interaction (DOI) information required for high-resolution imaging. The goal of positioning techniques is to reverse the photodetector signal’s pattern map to the coordinates of the incident photon energy position. By considering the DOI information, monolithic crystals offer good spatial, energy, and timing resolution along with high sensitivity. In this work, a supervised deep neural network was used for the approximation of DOI and to assess through Monte Carlo (MC) simulations the performance on a small-animal PET scanner consisting of ten 50 × 50 × 10 mm3 continuous Lutetium-Yttrium Oxyorthosilicate doped with Cerium (LYSO: Ce) crystals and 12 × 12 silicon photomultiplier (SiPM) arrays. The scintillation position was predicted by a multilayer perceptron neural network with 256 units and 4 layers whose inputs were the number of fired pixels on the SiPM plane and the total deposited energy. A GEANT4 MC code was used to generate training and test datasets by altering the photons’ incident position, energy, and direction, as well as readout of the photodetector output. The calculated spatial resolutions in the X-Y plane and along the Z-axis were 0.96 and 1.02 mm, respectively. Our results demonstrated that using a multilayer perceptron (MLP)-based positioning algorithm in the detector modules, constituting the PET scanner, enhances the spatial resolution by approximately 18% while the absolute sensitivity remains constant. The proposed algorithm proved its ability to predict the DOI for depth under 7 mm with an error below 8.7%.

The SuperFGD detector will be a novel and important upgrade to the ND280 near detector for both the T2K and Hyper-Kamiokande projects. The main goal of the ND280 upgrade is to reduce systematic uncertainties associated with neutrino flux and cross-section modeling for future studies of neutrino oscillations using the T2K and Hyper-Kamiokande experiments. The upgraded ND280 detector will be able to perform a full exclusive reconstruction of the final state from neutrino-nucleus interactions, including measurements of low momentum protons, pions and for the first time, event-by event measurements of neutron kinematics. Precisely understanding the time resolution is critical for the neutron energy measurements and hence an important factor in reducing the systematic uncertainties. In this paper we present the results of time resolution measurements made with the SuperFGD prototype that consists of 9216 plastic scintillator cubes (cube size is 1 cm3) readout with 1728 wavelength-shifting (WLS) fibers along the three orthogonal directions. We used data from a muon beam exposure at CERN. A time resolution of 0.97 ns was obtained for one readout channel after implementing the time calibration with a correction for time-walk effects. The time resolution improves with increasing energy deposited in a scintillator cube, improving to 0.87 ns for large pulses. Averaging two readout channels for one scintillator cube further improves the time resolution to 0.68 ns implying that signals in different channels are not synchronous. In addition the contribution from the time sampling interval of 2.5 ns is averaged as well. Most importantly, averaging time values from N channels improves the time resolution by ∼ 1/√(N). For example, averaging the time from 2 scintillator cubes with 2 fibers each improves the time resolution to 0.47 ns which is much better than the intrinsic electronics time resolution of 0.72 ns in one channel due to the 2.5 ns sampling window. This indicates that a very good time resolution should be achievable for neutrons since neutron recoils typically interact with several scintillator cubes and in addition produce larger signal amplitudes than muons. Measurements performed with a laser and a wide-bandwidth oscilloscope in which the contribution from the electronics time sampling window was removed demonstrated that the time resolution obtained with the muon beam is not far from the theoretical limit. The intrinsic time resolution of a scintillator cube and one WLS fiber is about 0.67 ns for signals of 56 photo electrons which is typical for minimum ionizing particles.

Using Bismuth Germanate (BGO) scintillators coupled to general purpose analog Silicon Photomultipliers (SiPM) we have developed methods to improve the coincidence timing resolution of PET detectors with BGO in order to reach a timing resolution that can be used for time of flight (TOF) PET detection. TOF measurements have already been acquired using LYSO crystals, but the low cost of BGO along with its optical properties and favorable energy resolution make BGO an attractive option to reduce the overall cost of PET scanners without sacrificing image quality. Using an analog SiPM with a pre-amplifier at a higher voltage improves energy and timing resolution for BGO coincidence detection, but also introduces a much higher baseline noise level, which can obscure the start of the waveform. We have found this noise level can be significantly reduced by cooling the detectors to values below -30°C, allowing us to perform leading edge discrimination (LED) timing at much lower voltages. On average cooling the detectors to this point improves their timing resolution by around 300ps, and as much as 600ps. Using this setup our values are approaching the values necessary for time of flight PET detection. In this paper we will discuss the experimental setup in further depth and share promising initial timing and energy resolution results from our findings.

For the high luminosity upgrade of the LHC at CERN, ATLAS is considering the addition of a High Granularity Timing Detector (HGTD) in front of the end cap and forward calorimeters at |z|= 3.5 m and covering the region 2.4 <|η|< 4 to help reducing the effect of pile-up. The chosen sensors are arrays of 50 μm thin Low Gain Avalanche Detectors (LGAD). This paper presents results on single LGAD sensors with a surface area of 1.3×1.3 mm2 and arrays with 2×2 pads with a surface area of 2×2 mm2 or 3×3 mm2 each and different implant doses of the p+ multiplication layer. They are obtained from data collected during a beam test campaign in autumn 2016 with a pion beam of 120 GeV energy at the CERN SPS. In addition to several quantities measured inclusively for each pad, the gain, efficiency and time resolution have been estimated as a function of the position of the incident particle inside the pad by using a beam telescope with a position resolution of few μm. Different methods to measure the time resolution are compared, yielding consistent results. The sensors with a surface area of 1.3×1.3 mm2 have a time resolution of about 40 ps for a gain of 20 and of about 27 ps for a gain of 50 and fulfil the HGTD requirements. Larger sensors have, as expected, a degraded time resolution. All sensors show very good efficiency and time resolution uniformity.

Time-of-flight (TOF) information can improve the imaging quality of positron emission tomography (PET) camera by calculating the original positron-electron annihilation position. In this work, we measured the preliminary TOF resolution of non-TOF-optimized LYSO arrays for TOF PET using our PMT-Quadrant-Sharing (PQS) technology which has higher light collection efficiency (no external light guide). We investigated digital signal processing methods that may achieve better time resolution. Digital oscilloscope Tektronix DPO7054 was used to capture the waveforms. Three timing methods, Linear Fitting (LF) to the pulse rising time, Constant Fraction Discriminator (CFD) and Leading edge Discriminator (LD), were studied. A new Time-Energy (T-E) correction using Multivariate Least Mean Square Fit was applied to minimize time walk caused by the variation of signal shape. The time resolution as a function of the depth of interaction was also studied. The average block-to-block coincident timing resolution of 13×13 (4×4×20 mm3 detector pixel) array with fast PMT R9779 (51-mm diameter) was measured to be 432 ps (FWHM). Another 13×13 crystal array with ultrahigh spatial resolution 1.4×1.4×10 mm3 detector pixels coupling to small 19-mm diameter poor-timing XP1912 PMTs was also tested and achieved 551 ps. This study shows that our regular PQS detector blocks (without optimization for TOF) have good TOF time resolution suitable for TOF PET systems, in addition to higher spatial resolution and reducing PMT cost.

In this paper we report on our investigation of the CeBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> timing properties for Time-of-Flight (TOF) Positron Emission Tomography (PET). The TOF detection can significantly improve the signal-to-noise ratio in a reconstructed PET image and reduce the number of events necessary to do the reconstruction. In order to achieve TOF PET, a scintillator must have good timing resolution and good light output. We have investigated seven CeBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> samples of different height, ranging from 3 mm to 37 mm. Two Hamamatsu R4998 fast photomultipliers were used for most experiments. Each sample was measured against a common standard (LaBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> :5%Ce) and the average timing resolution was found to be about 166 ps (fwhm). The two reference (LaBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> :5%Ce) crystals measured against each other gave the timing resolution of 170 ps. The best time resolution of 108 ps (fwhm) was measured for two CeBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> samples (3 and 12 mm height). The longest sample (37 mm) provided 215 ps (fwhm). Two such samples working in coincidence would give about 252 ps timing resolution (fwhm, calculated). We have also measured TOF, where the source was moved between the two detectors and the change in a timing peak position was registered. The results show that a shift of 5 cm could be easily resolved by such a system.

The preamplifier based on the ASIC NINO for the Time of Flight system (TOF) of MPD/NICA was developed and tested. The signal is read from both sides of the strip of the multi gap Resistive Plate Chamber (MRPC). In total there are around 14000 channels of electronics. To measure time of flight of secondary particles from collision of heavy ions on the collider NICA the Time over Threshold (ToT) method is used. According to the bench tests the preamplifier board showed stable work and good time resolution <10 ps for one channel. It was also tested at the test beam facility of the Nuclotron. The time resolution of the TOF detector which used the described preamplifier was reached ∼42 ps.

Positron emission tomography (PET) is one of the most promising techniques for hadron therapy monitoring. This method uses imaging of the annihilation photons resulting from positron emitting isotopes produced during patient irradiation in hadron therapy. In order to maximize the sensitivity, in-beam PET is the preferred option, which requires a partial ring configuration. The usage of partial ring PET systems causes image artefacts and low quality images due to incomplete data. The inclusion of Time-of-flight (TO F) information into the reconstruction algorithm provides better image quality for PET systems. Therefore, a PET system with very good time and spatial resolution is necessary for hadron therapy monitoring. The Resistive-Plate-Chambers (RPCs), providing very good time and spatial resolution might be used for the quality control of hadron therapy. However, they have lower sensitivity than crystal-based systems. The objective of this study is the comparison of the performance of two TOF-PET systems, a RPC-based PET system currently under investigation by the TERA group and a commercially available crystal-based PET system, with respect to their feasibility of being applied to monitor cancer treatment with ion- and proton-beams. Various Monte-Carlo simulations were performed using GATE to evaluate the performance of both systems following NEMA protocols. Furthermore, a set of sources emulating the annihilation photons from β+-emitters produced after proton pencil beam irradiation on a PMMA target were obtained. These sources were employed to study the capability to reproduce the proton beam path and the distal edge position. Finally, we calculated the activity distribution produced by carbon ions on the basis of one field of a real treatment plan. The results obtained indicate that a RPC-based system has five times lower sensitivity, similar spatial resolution and about two times higher scatter fraction compared to the crystal-based system. The low sensitivity obtained by the RPC-based system is not sufficient to determine range deviations.

Single-photon detectors are employed to measure faint light signals with high detection efficiency and time resolution. Silicon photomultipliers (SiPMs) are arrays of Single-photon avalanche diodes (SPADs), each one with its quenching resistor; they are connected in parallel giving a signal proportional to the number of detected photons. They offer the typical advantages of solid-state detectors (e.g. ruggedness, low power consumption, small size), high detection efficiency, good time resolution [1] and very good photon-number resolving capabilities. In FBK we produce SiPMs and SPADs with detection efficiency peaked for blue/ultraviolet light (called NUV technology) [2], or green-red light detection (RGB technology), with different geometries. The former are typically employed in a large number of applications exploiting scintillators [3]. Looking for the maximization of the photo-detection efficiency (PDE), e.g. increasing the fill-factor (FF) of the SiPM cell, noise components such as afterpulsing and optical crosstalk between cells (i.e. the correlated noise) become important issues. Recently, we developed new NUV-SiPMs, with high detection efficiency and with different solutions to reduce the noise of the detectors, both at a technological level [4] and a cell-layout level. Here we show the performance of this new NUV-SiPM, produced at FBK, employing a new silicon substrate, with a reduced minority-carriers lifetime, and new SiPM with trenches between cells and high cell density.

A fiber optic two-color pyrometer has been developed at the Institute of Heat Transfer and Air Conditioning at RWTH Aachen to measure temperatures at surfaces with low emissivities with a high time and space resolution. A fused silica fiber is used to transmit the radiation to the pyrometer from measuring positions with limited optical access. The two-color principle allows accurate measurements of absolute temperatures of surfaces with unknown emissivities if the assumption of a gray body behavior at the measurement wavelengths is valid. The minimum temperature which can be measured with the pyrometer is limited due to the small radiation energy at low temperatures given by Planck's law, the emissivity of the body and the size of measurement area. At present temperatures of low emissivity metallic surfaces with sizes of 0.4 mm can be measured down to 250 degree(s)C. A new application to measure temperatures during high speed turning required a time resolution above the maximum of 2 microsecond(s) . To enhance the time resolution of the pyrometer the electronics was modified and a 30 MHz data acquisition board has been applied to the system. With this configuration a nanosecond time resolution is possible but the minimum measurable temperature increases. Different aspects for the limitation of the time resolution will be discussed. A new set-up with a nanosecond spark-flashlight will be described for the test of the transient response of the pyrometer and some test measurements will be presented.

A time-to-amplitude converter for use with a pulsed accelerator