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Cherenkov light can improve the timing resolution of Positron Emission Tomography (PET) radiation detectors, thanks to its prompt emission. Coincidence time resolutions (CTR) of ~30 ps were recently reported when using 3.2 mm-thick Cherenkov emitters. However, sufficient detection efficiency requires thicker crystals, causing the timing resolution to be degraded by the optical propagation inside the crystal. We report on depth-of-interaction (DOI) correction to mitigate the time-jitter due to the photon time spread in Cherenkov-based radiation detectors. We simulated the Cherenkov and scintillation light generation and propagation in 3 × 3 mm2 lead fluoride, lutetium oxyorthosilicate, bismuth germanate, thallium chloride, and thallium bromide. Crystal thicknesses varied from 9 to 18 mm with a 3-mm step. A DOI-based time correction showed a 2-to-2.5-fold reduction of the photon time spread across all materials and thicknesses. Results showed that highly refractive crystals, though producing more Cherenkov photons, were limited by an experimentally obtained high-cutoff wavelength and refractive index, restricting the propagation and extraction of Cherenkov photons mainly emitted at shorter wavelengths. Correcting the detection time using DOI information shows a high potential to mitigate the photon time spread. These simulations highlight the complexity of Cherenkov-based detectors and the competing factors in improving timing resolution.

Energetic electrons traveling in a dispersive medium can produce Cerenkov radiation. Cerenkov photons' prompt emission, combined with their predominantly forward emission direction with respect to the parent electron, makes them extremely promising to improve radiation detector timing resolution. Triggering gamma detections based on Cerenkov photons to achieve superior timing resolution is challenging due to the low number of photons produced per interaction. Monte Carlo simulations are fundamental to understanding their behavior and optimizing their pathway to detection. Therefore, accurately modeling the electron propagation and Cerenkov photons emission is crucial for reliable simulation results. In this work, we investigated the physics characteristics of the primary electrons (velocity, energy) and those of all emitted Cerenkov photons (spatial and timing distributions) generated by 511 keV photoelectric interactions in a bismuth germanate crystal using simulations with Geant4/GATE. Geant4 uses a stepwise particle tracking approach, and users can limit the electron velocity change per step. Without limiting it (default Geant4 settings), an electron mean step length of ~250 μm was obtained, providing only macroscopic modeling of electron transport, with all Cerenkov photons emitted in the forward direction with respect to the incident gamma direction. Limiting the electron velocity change per step reduced the electron mean step length (~0.200 μm), leading to a microscopic approach to its transport which more accurately modeled the electron physical properties in BGO at 511 keV. The electron and Cerenkov photons rapidly lost directionality, affecting Cerenkov photons' transport and, ultimately, their detection. Results suggested that a deep understanding of low energy physics is crucial to perform accurate optical Monte Carlo simulations and ultimately use them in TOF PET detectors.

Machine learning has found unique applications in nuclear medicine from photon detection to quantitative image reconstruction. While there have been impressive strides in detector development for time-of-flight positron emission tomography, most detectors still make use of simple signal processing methods to extract the time and position information from the detector signals. Now with the availability of fast waveform digitizers, machine learning techniques have been applied to estimate the position and arrival time of high-energy photons. In quantitative image reconstruction, machine learning has been used to estimate various corrections factors, including scattered events and attenuation images, as well as to reduce statistical noise in reconstructed images. Here machine learning either provides a faster alternative to an existing time-consuming computation, such as in the case of scatter estimation, or creates a data-driven approach to map an implicitly defined function, such as in the case of estimating the attenuation map for PET/MR scans. In this article, we will review the abovementioned applications of machine learning in nuclear medicine.

Silicon Carbide MOSFETs have lower switching losses when compared to similarly rated Silicon IGBT, but exhibit faster switching edges, larger overshoots and increased oscillatory switching behaviour, resulting in greater electro-magnetic interference (EMI) generation. Active Gate Drivers (AGD) can help mitigate these issues while maintaining low switching losses. Numerous AGD topologies have been presented with varying capabilities in terms of timing resolution and output stage complexity. This paper presents an experimental investigation into the influence these capabilities have on the switching performance of an AGD driven high current module, with the goal of advising future AGD designers on the performance trade-offs between signal resolution and complexity. A 2.5 ns resolution 6-level AGD was utilised in combination with parameter sweeps and a genetic algorithm to determine gate voltage patterns that provided improved switching performance. Results indicate that higher resolution (2.5–5 ns) provided the greatest improvements in switching performance, even utilising the simplest considered gate driving patterns, with the use of more complex patterns offering minimal additional improvements. However, at lower timing resolutions (10–40 ns) a stronger set-point dependence degradation in switching performance is observed when using simpler gate patterns, which can be mitigated by utilising more complex patterns.

The scintillator bismuth germanate (BGO) has attractive properties for positron emission tomography (PET) systems such as high stopping power, high photo-fraction, and relatively low cost. However, its moderate scintillation light yield and slow rise and decay time compared to lutetium (yttrium) oxyorthosilicate (L(Y)SO) results in a degradation of coincidence timing resolution when scintillation photons are used for timing. Recently, it has been reported that the coincidence timing resolution of BGO can be improved by detecting Cerenkov photons, while scintillation photons still provide energy information. However, the measured coincidence timing spectrum showed much longer tails compared to the single Gaussian distribution. Because of this, TOF PET detectors based on BGO will perform worse than the full width at half maximum (FWHM) of the distribution, which is the most common metric for timing resolution, would suggest. From simulation studies, during the first few picoseconds, BGO generates ~16 Cerenkov photons per photoelectric interaction, following a 511 keV gamma ray interaction, while the probability of producing a scintillation photon during the first few picoseconds is very small. Therefore, when we configure a BGO crystal with dual-ended readout, the first arriving photons among the two opposing SiPMs are most likely Cerenkov photons, and by selecting the appropriate SiPM, an improvement in coincidence timing resolution can be achieved. In this study, both ends of a 3 × 3 × 20 mm3 BGO crystal were coupled to NUV-HD SiPMs. Trigger time differences from the dual-ended readout of BGO were widely distributed due to detecting a mixture of prompt Cerenkov and scintillation photons on both SiPMs. When using trigger times from only a single SiPM, the estimated coincidence timing resolution between two identical BGO detectors was 463 ps FWHM and 1463 ps FWTM. In contrast, when using trigger times from both SiPMs, the estimated coincidence timing resolution was 399 ps FWHM and 936 ps FWTM with no loss of events. Based on a recent report, high-bandwidth amplifiers were implemented and shown to further improve the estimated coincidence timing resolution to 331 ps FWHM and 923 ps FWTM. In summary, the coincidence timing resolution of BGO, most notably the FWTM, was significantly improved using time information from the dual-ended readout.

PurposeWe are investigating the use of promptly emitted Cerenkov photons to improve scintillation detector timing resolution for time-of-flight (TOF) positron emission tomography (PET). Bismuth germanate (BGO) scintillator was used in most commercial PET scanners until the emergence of lutetium oxyorthosilicate, which allowed for TOF PET by triggering on the fast and bright scintillation signal. Yet BGO is also a candidate to generate fast timing triggers based on Cerenkov light produced in the first few picoseconds following a gamma interaction. Triggering on the Cerenkov light produces excellent timing resolution in BGO but is complicated by the very low number of photons produced. A better understanding of the transport and collection of Cerenkov photons is needed to optimize their use for effective triggering of the detectors.MethodsWe simultaneously generated and tracked Cerenkov and scintillation photons with a new model of light transport that we have released in GATE V8.0. This crystal reflectance model was used to study photon detection and timing properties, building realistic waveforms as measured with silicon photomultipliers.ResultsWe compared the behavior and effect of detecting Cerenkov and scintillation photons at several levels, including detection time stamps, travel time, and coincidence resolving time in 3 × 3 × 20 mm3 BGO crystals. Simulations showed excellent agreement with experimental results and indicated that Cerenkov photons constitute the majority of the signal rising edge. They are therefore critical to provide early triggering and improved the coincidence timing resolution by 50%.Potential applicationsTo our knowledge, this is the first complete simulation of the generation, transport, and detection of the combination of Cerenkov and scintillation photons for TOF detectors. This simulation framework will allow for quantitative study of the factors influencing timing resolution, including the photodetector characteristics, and ultimately aid the development of BGO and other Cerenkov-based detectors for TOF PET.

Thallium bromide (TlBr) is a promising semiconductor detector material for positron emission tomography (PET) because it can offer very good energy resolution and 3D segmentation capabilities, and it also provides detection efficiency surpassing that of commonly used scintillators. Energy, timing, and spatial resolution were measured for thin (

The leading edge timing pick-off technique is the simplest timing extraction method for PET detectors. Due to the inherent time-walk of the leading edge technique, corrections should be made to improve timing resolution, especially for time-of-flight PET. Time-walk correction can be done by utilizing the relationship between the threshold crossing time and the event energy on an event by event basis. In this paper, a time-walk correction method is proposed and evaluated using timing information from two identical detectors both using leading edge discriminators. This differs from other techniques that use an external dedicated reference detector, such as a fast PMT-based detector using constant fraction techniques to pick-off timing information. In our proposed method, one detector was used as reference detector to correct the time-walk of the other detector. Time-walk in the reference detector was minimized by using events within a small energy window (508.5 - 513.5 keV). To validate this method, a coincidence detector pair was assembled using two SensL MicroFB SiPMs and two 2.5 mm × 2.5 mm × 20 mm polished LYSO crystals. Coincidence timing resolutions using different time pick-off techniques were obtained at a bias voltage of 27.5 V and a fixed temperature of 20 °C. The coincidence timing resolution without time-walk correction were 389.0 ± 12.0 ps (425 -650 keV energy window) and 670.2 ± 16.2 ps (250-750 keV energy window). The timing resolution with time-walk correction improved to 367.3 ± 0.5 ps (425 - 650 keV) and 413.7 ± 0.9 ps (250 - 750 keV). For comparison, timing resolutions were 442.8 ± 12.8 ps (425 - 650 keV) and 476.0 ± 13.0 ps (250 - 750 keV) using constant fraction techniques, and 367.3 ± 0.4 ps (425 - 650 keV) and 413.4 ± 0.9 ps (250 - 750 keV) using a reference detector based on the constant fraction technique. These results show that the proposed leading edge based time-walk correction method works well. Timing resolution obtained using this method was equivalent to that obtained using a reference detector and was better than that obtained using constant fraction discriminators.

This paper presents an analysis of the updated version of the Front-End Board (FEB) for the NectarCAM camera, developed for the Cherenkov Telescope Array Observatory (CTAO). The FEB is a critical component responsible for reading and converting signals from the camera's photo-multiplier tubes into digital data and generating module-level trigger signals. This study provides an overview of the design and performance of the new FEB version, including the use of an improved NECTAr3 chip with advanced features. The NECTAr3 chip contains a switched capacitor array for sampling signals at 1 GHz and a 12-bit analog-to-digital converter (ADC) for digitization upon receiving a trigger signal. The integration of the new NECTAr3 chip results in a significant reduction of NectarCAM's deadtime by an order of magnitude compared to the previous version. The paper also presents the results of laboratory testing, including measurements of timing performance, linearity, dynamic range, and deadtime, to characterize the new FEB's performance. [ABSTRACT FROM AUTHOR]

Energetic electrons traveling in a dispersive medium can produce Cerenkov radiation. Cerenkov photons’ prompt emission, combined with their predominantly forward emission direction with respect to the parent electron, makes them extremely promising to improve radiation detector timing resolution. Triggering gamma detections based on Cerenkov photons to achieve superior timing resolution is challenging due to the low number of photons produced per interaction. Monte Carlo simulations are fundamental to understanding their behavior and optimizing their pathway to detection. Therefore, accurately modeling the electron propagation and Cerenkov photons emission is crucial for reliable simulation results. In this work, we investigated the physics characteristics of the primary electrons (velocity, energy) and those of all emitted Cerenkov photons (spatial and timing distributions) generated by 511 keV photoelectric interactions in a bismuth germanate crystal using simulations with Geant4/GATE. Geant4 uses a stepwise particle tracking approach, and users can limit the electron velocity change per step. Without limiting it (default Geant4 settings), an electron mean step length of ∼250 μm was obtained, providing only macroscopic modeling of electron transport, with all Cerenkov photons emitted in the forward direction with respect to the incident gamma direction. Limiting the electron velocity change per step reduced the electron mean step length (∼0.200 μm), leading to a microscopic approach to its transport which more accurately modeled the electron physical properties in BGO at 511 keV. The electron and Cerenkov photons rapidly lost directionality, affecting Cerenkov photons’ transport and, ultimately, their detection.Results suggested that a deep understanding of low energy physics is crucial to perform accurate optical Monte Carlo simulations and ultimately use them in TOF PET detectors.

We have constructed and characterized a time-of-flight Positron Emission Tomography (TOF PET) camera called the Tachyon. The Tachyon is a single-ring Lutetium Oxyorthosilicate (LSO) based camera designed to obtain significantly better timing resolution than the ~ 550 ps found in present commercial TOF cameras, in order to quantify the benefit of improved TOF resolution for clinically relevant tasks. The Tachyon's detector module is optimized for timing by coupling the 6.15 × 25 mm2 side of 6.15 × 6.15 × 25 mm3 LSO scintillator crystals onto a 1-inch diameter Hamamatsu R-9800 PMT with a super-bialkali photocathode. We characterized the camera according to the NEMA NU 2-2012 standard, measuring the energy resolution, timing resolution, spatial resolution, noise equivalent count rates and sensitivity. The Tachyon achieved a coincidence timing resolution of 314 ps +/- ps FWHM over all crystal-crystal combinations. Experiments were performed with the NEMA body phantom to assess the imaging performance improvement over non-TOF PET. The results show that at a matched contrast, incorporating 314 ps TOF reduces the standard deviation of the contrast by a factor of about 2.3.

The thickness of the high-resistivity layer (active layer) is a crucial factor affecting the timing resolution of low gain avalanche diodes (LGADs). We studied the potential improvement of the timing resolution of charge particles based on LGADs with different active layer thicknesses. The Institute of High Energy Physics (IHEP) and the Novel Device Laboratory (NDL) jointly designed two types of LGAD sensors with active layer thicknesses of 33 and 50 $\mu \text{m}$. The timing resolution is given by contributions from the time walk, jitter, and nonuniform charge deposition (Landau term). The jitter and the Landau term contributions in the timing resolution are extracted by the combination of the ${^{90}{Sr}}$ beta source test and the picosecond laser test. The Landau contribution is found to be the dominant contribution for both types of LGAD sensors, and the Landau contribution of the 33 $\mu \text{m}$ sensor is lower than that of the 50 $\mu \text{m}$ sensor. Based on the experimental results, we perform the simulation for thinner active layer LGAD with the WeightField2 program. The timing resolution can be further improved by reducing the active layer thickness from 33 to 20 $\mu \text{m}$. [ABSTRACT FROM AUTHOR]

The AC-coupled Strip LGAD (Strip AC-LGAD) is a novel LGAD design that diminishes the density of readout electronics through the use of strip electrodes, enabling the simultaneous measurement of time and spatial information. The Institute of High Energy Physics has designed a long Strip AC-LGAD prototype with a strip electrode length of 5.7 mm and pitches of 150 μ m, 200 μ m, and 250 μ m. Spatial and timing resolutions of the long Strip AC-LGAD are studied by pico-second laser test and beta source tests. The laser test demonstrates that spatial resolution improves as the pitch size decreases, with an optimal resolution achieved at 8. 3 μ m. Furthermore, the Beta source test yields a timing resolution of 37.6 ps. [ABSTRACT FROM AUTHOR]

A signal tapping circuit has been designed to derive the fast timing signal from the Chevron type, 2 stage MCP having phosphor screen as a readout device. Using this, the timing property of the MCP-BaF2 system has been studied using the digital storage oscilloscope in which a timing resolution of ~ 500 ps has been obtained. The applicability of MCP with phosphor screen configuration for timing measurements has been demonstrated. [ABSTRACT FROM AUTHOR]

The proposed Electron-Ion Collider (EIC) will operate high-luminosity high-energy electron+proton and electron+nucleus collisions at the collision energies from 20 GeV to 141 GeV to solve several fundamental questions in the high energy and nuclear physics fields. Its instantaneous luminosity can reach 1 0 33 − 34 cm − 2 s − 1 and the bunching crossing rate is around 10 ns. The EIC project has received CD1 approval from the US DOE in 2021 and moves toward the machine design and preparation for construction. To realize various particle measurements with high precision at the future EIC, a low material-budget and high-granularity silicon vertex and tracking detector with fine spatial and momentum resolutions and nearly 4 π solid angle coverage is desired. The Monolithic Active Pixel Sensor (MAPS) and AC Coupled Low Gain Avalanche Diode (AC-LGAD) technologies stand out of several advanced technology options for the EIC silicon vertex and tracking detector subsystems. The MAPS technology has advanced features of low material budget, low power consumption, good radiation resistance and fine spatial resolution. The AC-LGAD technology can achieve fast timing resolution. Latest studies and progress of the EIC silicon vertex and tracking detector conceptual design, performance validations in simulation and ongoing MAPS and AC-LGAD R&D will be shown. Schedule and plan of the EIC project detector development will be discussed as well. • This paper introduces the latest design concept of the EIC project detector, which is expected to start construction in 2025. • Sub-percentage momentum resolution and better than 10 μ m spatial resolution can be achieved by the EIC vertex and tracking detector in a broad kinematic coverage, which meets most of the EIC detector requirements. • Two advanced silicon detector technologies have been selected for the EIC vertex and tracking detector, one is the Monolithic Active Pixel Sensor (MAPS), and the other one is the AC coupled Low Gain Avalanche Diode (AC-LGAD). • Better than 4. 5 μ m hit spatial resolution has been achieved by the new 65 nm MAPS prototype sensor with up to 1 0 15 1 MeV n e q cm−2 radiation dose. • Around 30 ps timing resolution has been achieved by the AC-LGAD prototype sensor. [ABSTRACT FROM AUTHOR]

Abstract The spatial, timing, and energy resolutions of a detector affect the image quality of a positron emission tomography (PET) system. These parameters are in turn dependent on various factors, such as the choice of scintillator, photodetectors, reflector material, and surface treatment (rough or polished) of the scintillators. In this study, we investigated the performances of sub-millimeter scintillator array, LYSO:Ce (polished and rough surfaces with BaSO 4 reflector or enhanced specular reflector (ESR)), a gadolinium aluminum gallium garnet (Ce:GAGG, rough surface with BaSO 4 reflector), and a new gadolinium fine aluminum gallate (Ce:GFAG, rough surface with BaSO 4 reflector) detectors. The outer dimension of each scintillator block was ∼ 12 × 12 mm with a 12 × 12 matrix of 0.9 × 0. 9 × 6 mm3 crystal elements. These blocks were optically coupled to a digital silicon photomultiplier (dSiPM, DPC-3200-22-44) with a 1 mm thick optical guide. Experiments were conducted at a sensor temperature of ∼ 15 °C, and a two-dimensional position histogram for 22Na gamma photons showed that all pixels were clearly resolved for all block detectors (peak-to-valley ratios ranging from 5.3 to 11.1). The average energy resolutions for the LYSO (ESR, rough), LYSO (ESR, polished), LYSO (BaSO 4 , rough), LYSO (BaSO 4 , polished), GAGG (BaSO 4 , rough), and GFAG (BaSO 4 , rough) arrays were measured as 11.3%, 10.2%, 18.7%, 10.3%, 10.0%, and 13.2% full width at half maximum (FWHM), respectively. The coincidence resolving times (with 3 × 3 × 5 mm3 LYSO crystal as reference) for the LYSO (ESR, rough), LYSO (ESR, polished), LYSO (B aSO 4 , rough), LYSO (BaSO 4 , polished), GAGG (BaSO 4 , rough), and GFAG (BaSO 4 , rough) arrays were 209 ps, 222 ps, 197 ps, 230 ps, 321 ps, and 276 ps, respectively. In conclusion, the new GFAG scintillator may be a promising candidate for future high-resolution time-of-flight (ToF) PET systems, considering the tradeoff between its performance and potential to be grown at a lower cost. [ABSTRACT FROM AUTHOR]

NectarCAM is a Cherenkov camera which is going to equip the Medium-Sized Telescopes (MST) of the northern site of the Cherenkov Telescope Array Observatory (CTAO). NectarCAM is equipped with 265 modules, each consisting of 7 photo-multiplier tubes (PMTs), a Front-End Board and a local camera trigger system used for data acquisition. This paper addresses the timing performance of NectarCAM which are crucial to reduce the noise in shower images and improve image cleaning as well as to discriminate between gamma-ray photons and cosmic-ray background and finally to allow coincidence identification with neighboring telescopes for stereoscopic operations. Verification tests of the system have been performed in a dark room using various light sources to illuminate the first NectarCAM unit. The resulting timing precision and accuracy of the trigger arrival relative to a laser source, of individual and multiple pixel signals have been studied and are shown to comply to CTAO requirements. [ABSTRACT FROM AUTHOR]

We characterized the single-photon timing response function of various silicon photomultipliers (SiPMs) over a broad (500-1100 nm) spectral range. We selected two SiPM manufacturers, and we investigated two active areas, i.e., a small (1-1.69 mm2) and a large (9 mm2) one, for each of them. We demonstrate that selected SiPMs are suitable for time-resolved diffuse optics (DO) applications where a very large detection area and sensitivity down to single photons are crucial to detecting the very faint return signal from biological tissues, like the brain, thus allowing replacement of photomultiplier tubes and opening the way to a novel generation of DO multichannel instrumentation. Due to our custom front-end electronics, we show the world's best single-photon timing resolution for SiPMs, namely, 57-ps full-width at half maximum for Hamamatsu 1.69 mm2 and 115 ps for Excelitas 9 mm2. Even further, we provide a thorough spectral investigation of the full single-photon timing response function, also detailing diffusion tails' time constants and dynamic range. The achieved insight and the reported performance open the way to a widespread diffusion of SiPMs not just in many-photon regimes (e.g., PET) but at single-photon counting regimes like DO as well.

The HyPET project proposes a hybrid dedicated TOF-PET for prostate imaging, with pixelated detector blocks in the front layer and monolithic blocks in the back layer. In this work, four detector configurations have been experimentally evaluated for the rear detector layer. The detector configuration consists of LYSO monolithic blocks with the same size (25.4 mm × 25.4 mm) but different thicknesses (5, 7.5, 10, and 15 mm) coupled to the same SiPM array. Each detector configuration has been experimentally characterized in terms of time, energy and spatial resolution by scanning the crystal surface using a fan beam in steps of 0.25 mm. Regarding spatial resolution, the interaction position was estimated using a Neural Network technique. All resolutions except energy, which remains nearly constant at 17% for all cases, show better values for the 5 mm detector thickness. We have achieved spatial resolution values of FWHM of 1.02 ± 0.10, 1.19 ± 0.13, 1.53 ± 0.17, 2.33 ± 0.55 mm, for the 5, 7.5, 10, and 15 mm blocks, respectively. The detector time resolution obtained was 275 ± 26, 291 ± 21, 344 ± 48, and 433 ± 45 ps respectively, using the energy weighted average method for the time stamps.

A multiphase all‐digital crystal‐less clock generator (CLCG) with an interpolating digital controlled oscillator (DCO) that achieves an operating frequency of 500 MHz with 10‐phase outputs is proposed. The CLCG adopts a specific temperature coefficient of a time‐to‐digital convertor (TDC) to create a positive or negative temperature coefficient and compensates for the DCO frequency drift. A time amplifier (TA) can extend the timing resolution of the TDC and reduce the effects of process variations in order to tune the TA gains. The frequency compensator adopts the frequency difference between the ring oscillator and DCO to reduce the frequency drift. The frequency accuracy is 69 ppm/°C from − 20 to 80°C. The root mean square jitter and output phase noise are 3.86 ps and − 100.36 dBc/Hz at 1 MHz, respectively. The core area of the test chip is 350 × 420 μm2 in a 65‐nm CMOS process. At a supply voltage of 0.6 V, the power consumption is 1.8 mW for the 5 Gb/s clocking system. [ABSTRACT FROM AUTHOR]

A tin-loaded liquid scintillator has been developed for gamma spectroscopy and neutron detection. The scintillator was characterized in regard to energy resolution, pulse shape discrimination, neutron light output function, and timing resolution. The loading of tin into scintillators with low effective atomic number was demonstrated to provide photopeaks with acceptable energy resolution. The scintillator was shown to have reasonable neutron/gamma discrimination capability based on the charge comparison method. The effect on the discrimination quality of the total charge integration time and the initial delay time for tail charge integration was studied. To obtain the neutron light output function, the time-of-flight technique was utilized with a 252 Cf source. The light output function was validated with the MCNPX-PoliMi code by comparing the measured and simulated pule height spectra. The timing resolution of the developed scintillator was also evaluated. The tin-loading was found to have negligible impact on the scintillation decay times. However, a relatively large degradation of timing resolution was observed due to the reduced light yield. [ABSTRACT FROM AUTHOR]

Purpose: Newer high-performance time-of-flight (TOF) positron emission tomography (PET) systems have the capability to preserve diagnostic image quality with low count density, while maintaining a high raw photon detection sensitivity that would allow for a reduction in injected dose or rapid data acquisition. To assess this, we performed quantitative and visual assessments of the PET images acquired using a highly sensitive (23.3 cps/kBq) large field of view (25-cm axial) silicon photomultiplier (SiPM)-based TOF PET (400-ps timing resolution) integrated with 3 T-MRI in comparison to PET images acquired on non-TOF PET/x-ray computed tomography (CT) systems.Procedures: Whole-body 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) PET/CT was acquired for 15 patients followed by whole body PET/magnetic resonance imaging (MRI) with an average injected dose of 325 ± 84 MBq. The PET list mode data from PET/MRI were reconstructed using full datasets (4 min/bed) and reduced datasets (2, 1, 0.5, and 0.25 min/bed). Qualitative assessment between PET/CT and PET/MR images were made. A Likert-type scale between 1 and 5, 1 for non-diagnostic, 3 equivalent to PET/CT, and 5 superior quality, was used. Maximum and mean standardized uptake values (SUVmax and SUVmean) of normal tissues and lesions detected were measured and compared.Results: Mean visual assessment scores were 3.54 ± 0.32, 3.62 ± 0.38, and 3.69 ± 0.35 for the brain and 3.05 ± 0.49, 3.71 ± 0.45, and 4.14 ± 0.44 for the whole-body maximum intensity projections (MIPs) for 1, 2, and 4 min/bed PET/MR images, respectively. The SUVmean values for normal tissues were lower and statistically significant for images acquired at 4, 2, 1, 0.5, and 0.25 min/bed on the PET/MR, with values of - 18 ± 28 % (p < 0.001), - 16 ± 29 % (p = 0.001), - 16 ± 31 % (p = 0.002), - 14 ± 35 % (p < 0.001), and - 13 ± 34 % (p = 0.002), respectively. SUVmax and SUVpeak values of all lesions were higher and statistically significant (p < 0.05) for 4, 2, 1, 0.50, and 0.25 min/bed PET/MR datasets.Conclusion: High-sensitivity TOF PET showed comparable but still better visual image quality even at a much reduced activity in comparison to lower-sensitivity non-TOF PET. Our data translates to a seven times reduction in either injection dose for the same time or total scan time for the same injected dose. This "ultra-sensitivity" PET system provides a path to clinically acceptable extremely low-dose FDG PET studies (e.g., sub 1 mCi injection or sub-mSv effective dose) or PET studies as short as 1 min/bed (e.g., 6 min of total scan time) to cover whole body without compromising diagnostic performance. [ABSTRACT FROM AUTHOR]

The Compressed Baryonic Matter (CBM) experiment has decided to use the Multi-gap Resistive Plate Chambers(MRPC) technology to build its Time-Of-Flight (TOF) wall. CBM-TOF requires a rate capability over 20 kHz/cm 2 for inner region. A 10-gap pad-MRPC assembled with low resistive glass is designed to construct this area. The prototypes, which consist of 10×0.22 mm gas gaps and 2×8 20 mm×20 mm readout pads, require fewer electronic channels compared to the strip design. A timing resolution of around 60 ps and an efficiency above 98% were obtained in a cosmic test and a beam test taken in 2014 October GSI beam time. The results show that the real-size prototypes fulfill the requirements of the CBM-TOF. [ABSTRACT FROM AUTHOR]

In this work we present and discuss the use of state-of-the-art Geiger-mode APDs, also known as single-photon avalanche diodes (SPADs), for the detection of minimum ionizing particles (MIPs) with best-in-class timing resolution. The SPADs were implemented in standard CMOS technology and integrated with on-chip quenching and recharge circuitry. Two devices in coincidence allowed to measure the time-of-flight of 180 GeV/c momentum pions with a coincidence time resolution of 22 ps FWHM (9.4 ps Gaussian sigma). This result paves the path for new generation of cheap plug-and-play trackers with extremely high spatial and timing resolution, meant to be used in beam test facilities. [ABSTRACT FROM AUTHOR]

The PICOSEC Micromegas detector is a precise timing gaseous detector based on a Cherenkov radiator coupled to a semi-transparent photocathode and a Micromegas amplifying structure. First single-pad prototypes demonstrated a time resolution below σ = 25 ps, however, to make the concept appropriate to physics applications, several developments are required. The objective of this work was to achieve an equivalent time resolution for a 10 × 10 cm 2 area PICOSEC Micromegas detector. The prototype was designed, produced and tested in the laboratory and successfully operated with a 80 GeV/c muon beam. Preliminary results for this device equipped with a CsI photocathode demonstrated a time resolution below σ = 25 ps for all measured pads. The time resolution was reduced to be below σ = 18 ps by decreasing the drift gap to 180 μ m and using dedicated RF amplifier cards as new electronics. The excellent timing performance of the single-channel proof of concept was not only transferred to the 100-channel prototype, but even improved, making the PICOSEC Micromegas detector more suitable for large-area experiments in need of detectors with high time resolutions. • 10 × 10 cm 2 PICOSEC MM detector successfully operated with a 80 GeV/c muon beam • Timing performance of a single-channel detector transferred to a 100-channel device • Time resolution of σ = 18 ps achieved for the 10 × 10 cm 2 PICOSEC MM detector [ABSTRACT FROM AUTHOR]

Purpose: Our purpose is to investigate the timing resolution in edge-on silicon strip detectors for photon-counting spectral computed tomography. Today, the timing for detection of individual x-rays is not measured, but in the future, timing information can be valuable to accurately reconstruct the interactions caused by each primary photon., Approach: We assume a pixel size of 12 × 500    μ m 2 and a detector with double-sided readout with low-noise CMOS electronics for pulse processing for every pixel on each side. Due to the electrode width in relation to the wafer thickness, the induced current signals are largely dominated by charge movement close to the collecting electrodes. By employing double-sided readout electrodes, at least two signals are generated for each interaction. By comparing the timing of the induced current pulses, the time of the interaction can be determined and used to identify interactions that originate from the same incident photon. Using a Monte Carlo simulation of photon interactions in combination with a charge transport model, we evaluate the performance of estimating the time of the interaction for different interaction positions., Results: Our simulations indicate that a time resolution of 1 ns can be achieved with a noise level of 0.5 keV. In a detector with no electronic noise, the corresponding time resolution is ∼ 0.1    ns ., Conclusions: Time resolution in edge-on silicon strip CT detectors can potentially be used to increase the signal-to-noise-ratio and energy resolution by helping in identifying Compton scattered photons in the detector., (© 2023 The Authors.)

Positron emission tomography (PET) is a molecular imaging modality that provides information at the molecular level. This system is composed of radiation detectors to detect incoming coincident annihilation gamma photons emitted from the radiopharmaceutical injected into a patient's body and uses these data to reconstruct images. A major trend in PET instrumentation is the development of time-of-flight positron emission tomography (ToF-PET). In ToF-PET, the time information (the instant the radiation is detected) is incorporated for image reconstruction. Therefore, precise and accurate timing recording is crucial in ToF-PET. ToF-PET leads to better localization of the annihilation event and thus results in overall improvement in the signal-to-noise ratio (SNR) of the reconstructed image. Several factors affect the timing performance of ToF-PET. In this article, the background, early research and recent advances in ToF-PET instrumentation are presented. Emphasis is placed on the various types of scintillators, photodetectors and electronic circuitry for use in ToF-PET, and their impact on timing resolution is discussed. [ABSTRACT FROM AUTHOR]

We have chosen to establish the Compton Suppression Spectrometer (CSS) for low activity environmental samples with a high purity germanium (HPGe) primary detector and a removable plug-in detector (NaI(Tl)) surrounded with a cylindrical annulus guard detector (NaI(Tl)). Monte Carlo simulation with PENELOPE (PENetration and Energy LOss of Positrons and Electrons) is used to determine the optimal geometry of the CSS. To verify a correlation between experiment and simulation, the energy distribution of 137 Cs and 60 Co point sources is measured and simulated for each condition. The CSS parameters are studied to determine optimal detector geometry and Compton Suppression Factor (CSF). The timing resolution of the CSS was found to be 44 ns (FWHM), which is an outstanding result in the semiconductor-based gamma-ray spectrometry. All measured values of CSF agree within 5% with the values obtained from the simulation. The optimum geometry and CSF values are discussed. [ABSTRACT FROM AUTHOR]

Ce doped Gd 2 SiO 5 (GSO) is a scintillator which has relatively fast decay time, high density, high light output, and is used for commercial PET systems. However as time-of-flight (TOF) PET systems become more popular in clinical diagnostic, GSO seems less attractive, because its performance is thought to be insufficient for use in TOF-PET application. Although the timing resolution of the GSO combined with photomultiplier tube (PMT) is known to be inappropriate for TOF-PET system, the performance of GSO coupled to silicon photomultipliers (Si-PM) has not been reported to date. In addition, GSO possesses a variety of decay times depending on its Ce concentration. We measured basic performance of GSOs with different Ce concentrations and then coupled them to Si-PMs to measure the precise timing resolution using a high bandwidth digital oscilloscope. The decay time of GSO with 0.4 mol% Ce were longer (63±4 ns) compared with those with 1.0 mol% (40±2 ns) and 1.5 mol% (33±1 ns). With a Si-PM, the photo-peak channels were almost the same for GSOs with 0.4 mol% Ce and those with 1.5 mol% Ce, but the GSO with 1.0 mol% Ce was ~25% higher. Energy resolutions of these three GSOs were ~13% full-width at half-maximum (FWHM) for 662 keV gamma photons without correcting for saturation effects. When coupled to Si-PMs, the timing resolution for GSO with 1.5 mol% Ce (decay time 33 ns) was 549 ps FWHM, almost good enough to use for TOF-PET system. The combination of GSO with 1.5 mol% Ce with Si-PM will be an interesting combination to realize low cost TOF-PET systems. [ABSTRACT FROM AUTHOR]

Time-of-flight positron emission tomography requires high timing resolution. In this paper, we determined the influence of scintillation properties on the detector timing resolution for crystals with non-negligible optical transit timespread. In addition to intrinsic scintillation properties, such as the light yield, decay time constant, and scintillation rise time, we also studied the relation between the timing resolution and extrinsic scintillation properties, such as the dimensions of the crystal, the absorption probability of the reflector, the dwell time of photons inside the reflector during the reflection process, and the crystal polish. For this purpose, we developed ray-tracing software. The crystals simulated in this paper are LSO:Ce, LYSO:Ce, LSO:Ce,0.2%Ca, LYSO:0.11%Ce,0.2%Mg, and LYSO:0.2%Ce,0.2%Ca, with dimensions 3 \times 3 \times 5~\mm^3, 3 \times 3 \times 10~\mm^3, 3 \times 3 \times 20~\mm^3, and 4 \times 4 \times 22~\mm^3. We furthermore studied the optical transit timespread of photons inside polished and etched crystals, which explains the differences in timing resolution. [ABSTRACT FROM AUTHOR]

A detailed characterization of doped paraterphenyl (p-Terphenyl) neutron detectors was obtained by means of γ-sources and a 252 Cf fission chamber. The intrinsic timing resolution, the energy resolution up to 2 MeV ee , and the electron-equivalent energy calibration were determined using γ-sources. The neutron time-of-flight spectrum from the spontaneous fission of 252 Cf provided information on the proton energy calibration, the light output function, and the intrinsic neutron detection efficiency between 0 and 8 MeV for a threshold of 250 keV. Measurements of the latter were also performed using monoenergetic neutron beams. The applied experimental methods were cross-checked using two BC501A scintillation detectors, which were previously calibrated at the Physikalisch-Technische Bundesanstalt in Braunschweig, Germany. Results were compared to Monte-Carlo simulations performed using NRESP7 and NEFF7 codes. [ABSTRACT FROM AUTHOR]

Single-crystal chemical vapor-deposited diamond (sCVD) was investigated for its ability to act as fission-fragment detector. In particular we investigated timing and energy resolution for application in a simultaneous time-of-flight and energy measurement to determine the mass of the detected fission fragment. Previous tests have shown that poly-crystalline chemical vapor deposited (pCVD) diamonds provide sufficient timing resolution, but their poor energy resolution did not allow complete separation between very low-energy fission fragments, α-particles and noise. Our present investigations prove artificial sCVD diamonds to show similar timing resolution as pCVD diamonds close to 100 ps. Improved pulse-height resolution allows the unequivocal separation of fission fragments, and the detection efficiency reaches 100%, but remains with about a few percent behind requirements for fragment-mass identification. With high-speed digital electronics a timing resolution well below 100 ps is possible. However, the strongly varying quality of the presently available diamond material does not allow application on a sufficiently large scale within reasonable investments. [ABSTRACT FROM AUTHOR]

Single Photon Avalanche Diodes (SPAD) are known for their excellent timing performance which enables Time of Flight capabilities in positron emission tomography (PET). However, current array architectures juxtapose the SPAD with its ancillary electronics at the expense of a poor fill factor of the SPAD array. The 3D vertical integration of SPADs and readout electronics represents a solution to the aforementioned problem. Compared to systems with external electronics readout, 3D vertical integration reduces the SPAD interconnect parasitic capacitance while greatly increasing the photosensitive area and improving overall performances. This paper presents the implementation of two SPAD structures designed for PET. The SPAD structures are designed using Teledyne DALSA high voltage (HV) CMOS technology targeted for a 3-dimensional single photon counting module (3DSPCM). SPAD with two types of guard ring (diffusion-based and virtual guard ring) are designed, fabricated and characterized. All structures are based on a p + anode in an n-well cathode and are implemented along with active quenching circuits for proper characterization. The results show that the contact distribution and the anode-cathode spacing impact the dark count rate (DCR). The design of SPADs with a diffusion guard ring have a DCR down to 3~\s^- 1\mu \m^-2 at room temperature, afterpulsing probability of < 2\% , timing resolution of 27 ps FWHM and PDE of 49% at 480 nm. [ABSTRACT FROM PUBLISHER]

Scintillation properties of LSO:Ce, LSO:Ce,0.2%Ca, LYSO:Ce, LYSO:0.11%Ce,0.2%Mg, and LYSO:0.2%Ce,0.2%Ca were studied for application in time-of-flight positron emission tomography. To find the scintillation material with the best timing performance among those, we measured intrinsic scintillation pulse shapes–defined as the number of photons emitted per unit time at the ionization track as a function of time - by means of 100 ps x-ray excitation in the temperature range from 193 K to 373 K, from which intrinsic rise and decay time constants were derived. Photoelectron yields were measured by 662 keV gamma excitation. From these scintillation properties we calculated the corresponding lower bound on the timing resolution for each material. [ABSTRACT FROM PUBLISHER]

To increase contrast in positron emission tomography (PET) images, researchers are investigating detectors that reach below the nanosecond timing resolution. This allows a tight coincidence window which reduces random coincidence counts in the acquired data, as well as to include time-of-flight information into the reconstruction algorithms. With this goal in mind, single photon avalanche diode (SPAD) arrays have been under study for their excellent timing performances. However, their spurious dark counts can blur the start of PET signals where timing information is the most precise and create false starts in the acquisition system, introducing dead time. To minimize these problems in digital SPAD systems using a single time to digital converter (TDC) per PET channel, dark count discriminator circuits are required to reduce timing errors and increase the triggering efficiency in presence of dark counts. This paper compares the performance of a probabilistic and a novel delay line based dark count discriminator. Simulations of a SPAD array investigate the impact of dark counts on triggering efficiency and coincidence timing. Results show that the probabilistic discriminator provides excellent event recovery with regard to dark counts at the cost of some coincidence timing resolution. On the other hand, the delay line discriminator maintains the peak coincidence timing resolution but does not provide as much efficiency at high dark count rate levels. [ABSTRACT FROM PUBLISHER]

The scintillator is one of the key building blocks that critically determine the physical performance of PET detectors. The quest for scintillation crystals with improved characteristics has been crucial in designing scanners with superior imaging performance. Recently, it was shown that the decay time constant of high lutetium content Lu1.8Gd0.2SiO_5\!\!:Ce (LGSO) scintillators can be adjusted by varying the cerium concentration from 0.025 mol% to 0.75 mol%, thus providing interesting characteristics for phoswich detectors. The high light output (90%–120% NaI) and the improved spectral match of these scintillators with avalanche photodiode (APD) readout promise superior energy and timing resolutions. Moreover, their improved mechanical properties, as compared to conventional LGSO (Lu0.4Gd1.6SiO_5\!\!:Ce), make block array manufacturing readily feasible. To verify these assumptions, new phoswich block arrays made of LGSO-90%Lu with low and high mol% Ce concentrations were fabricated and assembled into modules dedicated to the LabPET scanner. Typical crystal decay time constants were 31 ns and 47 ns, respectively. Phoswich crystal identification performed using a digital pulse shape discrimination algorithm yielded an average 8% error. At 511 keV, an energy resolution of 17–21% was obtained, while coincidence timing resolution between 4.6 ns and 5.2 ns was achieved. The characteristics of this new LGSO-based phoswich detector module are expected to improve the LabPET scanner performance. The higher stopping power would increase the detection efficiency. The better timing resolution would also allow the use of a narrower coincidence window, thus minimizing the random event rate. Altogether, these two improvements will significantly enhance the noise equivalent count rate performance of an all LGSO-based LabPET scanner. [ABSTRACT FROM PUBLISHER]

This paper presents a novel approach towards incorporating photonic crystals (PhCs) into optical Monte Carlo (MC) simulations. This approach affords modeling the full diffractive nature of PhCs including their reflection and transmission behavior as well as the manipulation of the photon trajectories through light scattering. The main purpose of this tool is to study the impact of PhCs on the light yield and timing performance of scintillator-based detectors for positron emission tomography (PET). To this end, the PhCs are translated into look-up tables and implemented into the optical MC algorithm. Our simulations are validated in optical experiments using PhC samples fabricated with electron beam lithography. The experimental results indicate that the simulations match the measurements within the accuracy of the experiments. The application of the combined simulation technique to a PET detector module predicts an increase of the total light yield by up to 23% for PhC coatings versus the reference without PhCs. Timing calculations reveal an improvement of the coincident resolving time by up to 6%. The results underline the potential of PhCs to improve light yield and timing of PET detector modules. [ABSTRACT FROM PUBLISHER]