A Comprehensive & Systematic Study of Coincidence Time Resolution and Light Yield Using Scintillators of Different Size and Wrapping

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Time based readout of a silicon photomultiplier (SiPM) for Time Of Flight Positron Emission Tomography (TOF-PET)

Time of flight (TOF) measurements in positron emission tomography (PET) are very challenging in terms of timing performance, and should achieve ideally less than 100ps FWHM precision. We present a time-based differential technique to read out SiPMs that has less than 25ps rms electronic jitter. The novel readout is a fast front end circuit (NINO) based on a first stage differential current mode amplifier with 20input resistance. Therefore the amplifier inputs are connected differentially to the SiPM’s anode and cathode ports. The leading edge of the output signal provides the time information, while the trailing edge provides the energy information. Based on a Monte Carlo photon-generation model, SPICE simulations were run with a 3x3mm2 SiPM-model, read out with a differential current amplifier. The results of these simulations are presented here and compared with experimental data obtained with a 3x3x15mm3 LSO crystal coupled to a SiPM. The measured time coincidence precision is interpreted by the combined Monte Carlo/ SPICE simulation, as well as by Poisson statistics

Quantum Systems for Enhanced High Energy Particle Physics Detectors

Developments in quantum technologies in the last decades have led to a wide range of applications, but have also resulted in numerous novel approaches to explore the low energy particle physics parameter space. The potential for applications of quantum technologies to high energy particle physics endeavors has however not yet been investigated to the same extent. In this paper, we propose a number of areas where specific approaches built on quantum systems such as low-dimensional systems (quantum dots, 2D atomic layers) or manipulations of ensembles of quantum systems (single atom or polyatomic systems in detectors or on detector surfaces) might lead to improved high energy particle physics detectors, specifically in the areas of calorimetry, tracking or timing

A Novel Time-Based Readout Scheme for a Combined PET-CT Detector Using APDs

This paper summarizes CERN R&D work done in the framework of the European Commission's FP6 BioCare Project. The objective was to develop a novel "time-based" signal processing technique to read out LSO-APD photodetectors for medical imaging. An important aspect was to employ the technique in a combined scenario for both computer tomography (CT) and positron emission tomography (PET) with effectively no tradeoffs in efficiency and resolution compared to traditional single mode machines. This made the use of low noise and yet very high-speed monolithic front-end electronics essential so as to assure the required timing characteristics together with a high signal-to-noise ratio. Using APDs for photon detection, two chips, traditionally employed for particle physics, could be identified to meet the above criteria. Although both were not optimized for their intended new medical application, excellent performance in conjunction with LSO-APD sensors could be derived. Whereas a measured energy resolution of 16% (FWHM) at the 511 keV photo peak competes favorably with that of 'classical' PMTs, the coincidence time resolution of 1.6 ns FWHM with dual APD readout is typically lower. This is attributed to the stochastic photon production mechanism in LSO and the photon conversion characteristic of the photo diode, as well as to the fluctuations in photon conversion, albeit the APD's superior quantum efficiency. Also in terms of CT counting speed, the chosen readout principle is limited by the intrinsic light decay in LSO (40 ns) for each impinging X-ray

Machine learning-based events classification in heterostructured scintillators

Time-of-flight positron emission tomography (TOF PET) faces the challenge of improving time resolution while maintaining high detector efficiency. Heterostructured scintillators, which consist of multiple layers of different scintillating materials with complementary properties, have emerged as a promising solution. These scintillators rely on the energy sharing mechanism, where the incoming 511 keV γ-ray can be fully stopped in the heavy material while the recoil photoelectron can escape and deposit some of its energy in the fast emitter (shared events) [1], [2]. Accurate event classification is crucial to fully leverage this concept. A well-established method is to correlate the amplitude and integrated charge of the pulse and apply a coordinate transformation, but it is not easily scalable to more complex systems [1]. In this study, we use the hierarchical clustering method to distinguish events based on the deposited energy in a BGO & plastic heterostructured scintillator. We compared the two methods by evaluating the CTR of the events coming from the corresponding classes of events. The results were found to be compatible, indicating the effectiveness of the proposed clustering method for event classification in heterostructured scintillators

A Systematic Study to Optimize SiPM Photo-Detectors for Highest Time Resolution in PET

We report on a systematic study of time resolution made with three different commercial silicon photomultipliers (SiPMs) (Hamamatsu MPPC S10931-025P, S10931-050P, and S10931-100P) and two LSO scintillating crystals. This study aimed to determine the optimum detector conditions for highest time resolution in a prospective time-of-flight positron emission tomography (TOF-PET) system. Measurements were based on the time over threshold method in a coincidence setup using the ultrafast amplifier-discriminator NINO and a fast oscilloscope. Our tests with the three SiPMs of the same area but of different SPAD sizes and fill factors led to best results with the Hamamatsu type of 50×50×μm2 single-pixel size. For this type of SiPM and under realistic geometrical PET scanner conditions, i.e., with 2×2×10×mm3 LSO crystals, a coincidence time resolution of 220 ±4 ps FWHM could be achieved. The results are interpreted in terms of SiPM photon detection efficiency (PDE), dark noise, and photon yield

Enhancing Timing Performance of Heterostructures with Double-Sided Readout

Heterostructured scintillators are gaining ground as a possible solution to the trade-off between the high sensitivity and fast timing of detectors for time-of-flight positron emission tomography (TOF-PET). They consist of stacks of alternating layers of two materials with complementary properties: high stopping power and ultrafast timing. The fast emitter improves the timing performance of the detector. However, layering is a limiting factor for the best achievable time resolution, as it worsens light transport. This effect can be mitigated by increasing light collection and retrieving the depth-of-interaction (DOI) information. The double-sided readout can meet both requirements.In this work, we use high-frequency electronics in a double-sided readout configuration with a 3x3x20mm3BGO&EJ232; heterostructure. By selecting the photopeak events, we were able to achieve a DOI resolution of 6.4±0.5mm3. The improvement in coincidence time resolution (CTR), compared to the single-sided readout, is 18% for all photopeak events (from 256±8 to 211±6ps) and 36% when considering only photopeak events that share the energy between the two materials (from 200±6 to 128±4ps)

Comparison of timing and DOI performance of light-sharing TOF-PET modules with different readout electronics

Time resolution plays a key role in positron emission tomography (PET) by enhancing the signal-to-noise ratio and ultimately improving the quality of the image. In previous studies, an array of 16 LYSO crystals (measuring 3.1x3.1x15 mm$^3$) coupled to Hamamatsu S13361-3050AE-04 SiPMs and readout by a custom-made NINO board achieved a coincidence time resolution (CTR) below 160 ps. However, the spatial resolution of the array was affected by parallax error due to the unknown depth of interaction (DOI) of the incident gamma-ray photon. The DOI information was successfully extracted with 3 mm resolution using a light-sharing mechanism and the NINO board. Nevertheless, the board is not commercially available and cannot be scaled to a full PET detector. To address this limitation, this study examines the commercially available TOFPET2 ASIC (application specific integrated circuits) from PETsys Electronics S.A. using light-sharing DOI-capable modules and compares it to the custom-made NINO board. The SiPM array coupled to the matrix of 16 LYSO crystals using TOFPET2 PETsys demonstrates a DOI resolution of 3.6 ± 0.3 mm and a CTR value of 224 ± 3 ps. This approach is scalable to a full PET detector. Finally, potential paths to further improve DOI resolution and CTR are discussed