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The benefits of measuring the time difference between the arrival of the two photons from positron annihilation was recognized from the very early days of PET imaging in the 1960s. However, at that time the scintillator light decay time and the timing of the electronics was insufficient to implement a measurement of time-of-flight (TOF) that could have a beneficial effect on the image quality....
This presentation will make an overview of the present clinical TOF PET imaging and its benefit brought about by lowering the TOF CTR slightly above 200 ps. These advantages will be even more apparent when pushing for ≤ 100 ps TOF PET CTR paving the ground for having a 10-ps TOF PET challenge.
The radiotracer principle, as first introduced by George Hevesy in 1923 [1], and supported by sophisticated radiation imaging systems, highly specific radiotracers, and mathematical modeling, has been a powerful tool with broad uses in biomedical research. Applications span animal models, and in vivo human imaging in many disease states and the tracer method has been used to interrogate and...
The paradigm shift in medicine from treatment of acute and/or advanced disease to very early diagnosis and even prevention in cancer, neurodegenerative as well as cardiac fields, puts more stringent requirements on PET imaging both in terms of sensitivity as well as specificity. Likewise, recent developments in Targeted Radionuclide Therapy (TRT) where theragnostic pairs are used to tailor a...
With the aging of the global population, neurodegenerative diseases such as Alzheimer's and Parkinson's are becoming more common. In addition, PET is a useful clinical tool for accurately visualizing the presence of biomarkers in the brain associated with various neurodegenerative diseases (e.g., amyloid-β plaques or microtubule-associated protein tau strands). However, the relatively high...
We are studying new detection concepts, methods, and system designs to advance time-of-flight (TOF) positron emission tomography (PET). In this talk we will describe three efforts in this direction. The first is a ‘radio-frequency-penetrable’ PET insert design that we are building for simultaneous brain TOF-PET/MRI of neurological disorders that employs novel design features to enable ~230...
Interest towards high sensitivity multiparametric imaging modalities has increased during the last years. In this context, high precision Positron Emission Tomography (PET) scanners have shown great potential. Two paths to further enhance PET sensitivity have been outlined: (i) including photon Time-of-Flight (TOF) information during the image reconstruction process; or (ii) increasing the...
We are conceiving a new imaging modality called Prompt Gamma Time Imaging (PGTI) to achieve the real time measurement of the proton range during particle therapy treatments. The goal of PGTI is to reconstruct an image of the vertex distribution of Prompt Gamma rays (PG) emitted from the patient, through the exclusive measurement of particle Time-Of-Flight (TOF). The start trigger is given by a...
J-PET is a multi-photon PET system prototype [1] enabling multi-photon and positronium imaging. The quality of these images relies strongly on the system's time resolution. In this presentation, we will explain the newly developed method of positronium imaging and present the first multi-photon [2] and in-vitro positronium images [3]. We will discuss the clinical motivation for improving the...
Extracellular vesicles (EVs) are nano- and micro-sized cell-derived entities, released from cells under physiological and pathological conditions [1]. EVs can be found in every biological fluid including blood, saliva, milk, or urine, serving as a liquid biopsy [2]. Their biological properties (cell-uptake, biocompatibility) [3], and chemical (composition, structure) or physical (size,...
The characterization of cancerous tissue alterations in magnetic resonance imaging (MRI) requires the acquisition of demanding gradient pulse sequences that use a high slew rate. This allows for a high temporal resolution both in the sensitivity to the movement of water molecules diffusion in tissues and to the kinetics of blood flow through vessels and capillaries, the principles of diffusion...
Recent developments have shown the potential of a time-of-flight measurement of individual photons using fast X-ray detectors to significantly reduce the adverse effects of scattered photons both in X-ray radiography and computed tomography (CT) without using anti-scatter grids. However, the improvements observed in simulations have yet to be confirmed experimentally using a system realistic...
PET technology has received several improvements in performance due to significant advances in instrumentation and software. Recent trends make use of the time-of-flight (ToF) information to increase the signal-to-noise ratio (SNR) in the reconstructed image and improve the location of the annihilation event. One of the most important components in ToF-PET instrumentation is the scintillation...
Nowadays, the performance in Time-of-Flight (TOF) for Positron Emission Tomography (PET) detectors, which boosts the effective sensitivity of the system, is reaching the technological limit imposed by the scintillator crystal and photosensors used. Increasing the axial length of a PET scanner improves the solid angle coverage, thus allowing to boost the sensitivity. This are the so-called...
In Positron Emission Tomography (PET), depending on the scintillator type and geometry, many events undergo Compton interactions before photoelectric absorption. If these interactions are not properly identified, an image blurring is observed. In this report, the main components of the scatter ring of a Compton-PET system for mice brain imaging with high timing and spatial resolution are...
In positron emission tomography, dense Cherenkov radiators provide an
opportunity for high gamma detection efficiency and excellent CTR.
However, because only a few tens of Cherenkov photons follow a gamma
interaction in the radiator, the detection efficiency and the energy
resolution of a pure Cherenkov detector are an issue. We study gamma
detection efficiency and CTR of PbF$_2$ based...
This study is performed within the scope of the SwissPix project, which aims at developing a new photo-sensor for Positron Emission Tomography with ~10 ps FHWM timing resolution, capable of exploiting the prompt nature of Cherenkov radiation. Using Monte Carlo simulations, we estimated the physical limits of timing resolution for two possible detector geometries: a radiator of 3x3x3 mm$^3$...
Accurate time estimation utilizing (semi-)prompt photons can benefit Time-of-Flight Positron Emission Tomography. However, we are limited to fewer detected photons with current state-of-the-art ultra-fast detectors, ultimately resulting in the pursuit of every single photon.
In the lab, this quest starts with light production (Cherenkov photons, quantum confinement luminescence etc),...
Recent SiPM developments and improved front-end electronics have opened new doors in TOF-PET with a focus on prompt photon detection. For instance, the relatively high Cherenkov yield of Bismuth-Germanate (BGO) upon 511keV gamma interaction has triggered a lot of interest, especially for its use in total-body PET scanners due to the crystal’s relatively low production costs. However, the...
Nanophotonics - the control of the flow of light on the nanoscale - had immense impact on technology in recent years, with example spanning from solar cells and LEDs to the telecommunication industry.
We will discuss the prospects of nanophotonics for the development of future scintillators.
In particular, I will focus on two recent experiments:
1. At MIT, we observed a ten-fold...
Since many decades scintillating crystals have been used for radiation detectors such as high resolution electromagnetic calorimeters and positron emission tomographs. Significant progress has been made in the field of inorganic scintillators in the understanding of their scintillation properties, radiation hardness and production methods over the last 30 years. In addition many applications...
Ultrafast emission processes are required to further improve the coincidence time resolution (CTR) of time-of-flight PET detectors. Extensive research efforts are underway in trying to generate and detect so-called prompt photons having much faster emission dynamics than conventional scintillation. In this contribution, we provide an analysis on key aspects to better model and understand the...
Time-of-flight positron emission tomography (TOFPET) is currently one of the key directions in medical imaging enabling substantially higher spatial resolution and lower radiation dose for patients. This trend requires new scintillators with faster response and currently results in the substitution of BGO by LYSO:Ce as the scintillator of choice in TOFPETs. The scintillator material represents...
In this contribution we extend the current understanding of the different energy-transfer mechanisms present in state-of-the-art Lu(2−x)YxSi2O5:Ce scintillators. We present results of a photon emission mechanism known as optical stimulated luminescence (OSL), able to efficiently trap a fraction of the energy deposited in the material. OSL competes with the non-radiative energy transfer to...
A semi-monolithic scintillator crystal consists of a monolithic block segmented in only one direction in different pieces called slabs. This approach is intended to combine the benefits of both pixelated and monolithic crystals, which are usually employed in PET detectors, preserving the good timing resolution of pixelated crystals, and the high sensitivity and good spatial resolution of...
Purpose– The coincidence time resolution (CTR) values can be improved by increasing photostatistics, which in the PET detector occurs with a high light yield (LY) of scintillation crystals. The two main contributors to the LY are the intrinsic LY of the scintillation crystal and the light transfer efficiency, which depend on crystal material, dimensions, and wrapping conditions. We report on a...
Scintillating materials suffer degradation while in operation due to defects induced in the process. Lattice defects could severely impact detector efficiency via non-radiative transfer of electron excitation. Like most materials for this kind of applications, there is a strong performance-structure relationship. An understanding of the defect formation process is therefore important in the...
— In order to achieve superior timing for time-of-flight positron emission tomography, combined with high detection efficiency and cost-effectiveness, we probe the applicability of BaF2 in metascintillators driven by timing of cross-luminescence photon production. Building on simulation study of energy sharing and analytic multi-exponential scintillation pulse and sensitivity characteristics,...
There is a desire to continue reducing the time resolution of scintillator based detectors without sacrificing the space resolution to further improve the image resolution of current ToF PET scanners. Unfortunately, we have reached a limit of finding one ideal single crystal candidate that can achieve both aims. Current commercial LSO and LYSO crystal detector can offer time resolution...
In the field of time-of-flight positron emission tomography (PET-TOF), the time resolution of the scintillationbased detector is an essential feature. Recent studies have shown that some materials have fast emissions in the vacuum ultraviolet (VUV) region.
To acquire the fast-rising signals of these emissions, we are using optimized Coincidence Time Resolution (CTR) test boards with two...
The novel concept of metascintllator, topologies consisting of heterogeneous scinitllating and light-guiding materials has been proved to achieve an equivalent CTR of 200ps for BGO-based set and 140ps for LYSO-based set even with an non-optimized configuration. In this work, we evaluate a novel architecture: The principle is to slice a slow scintillator (BGO or LYSO) monolithic in thin slabs,...
Lutetium-based scintillators (LSO, LYSO, LGSO) are commonly used for TOF-PET, representing the better compromise between stopping power, light yield, energy and time resolution. However, the limit in the improvement of time performances of these materials has been reached, and new technologies to break the current boundaries are being investigated. Heterostructured scintillators are gaining...
In recent years the need for ultrafast detection of ionizing radiation is being pushed particularly by high energy physics and medical imaging. It requires detection systems involving scintillating materials able to produce quasiprompt photons. To achieve that, there are several concepts currently being pursued, one of them being exploitation of quantum confinement effect in nanoparticles....
Radiation detection is of outmost importance in fundamental scientific research and applications including medical diagnostics, homeland security, environmental monitoring, and non-destructive inspection in industrial manufacturing. Lead halide perovskites (LHP) are rapidly emerging as high-Z materials for next generation of solution processable scintillators and photoconductors for ionizing...
Nanocrystals like ZnO:Ga or CsPbBr$_3$ were identified as potential scintillators for fast timing applications, including medical imaging techniques such as TOF-PET (time-of-flight positron emission tomography) or TOF-CT (time-of-flight computed tomography). Both feature sub-nanosecond scintillation decays which is a crucial property for this type of application.
However, such materials with...
In the quest for optimized time-of-flight scintillation detectors, an important physical barrier is the statistical variation of photon production, propagation, extraction and detection. While nothing can be done for the isotropic production of scintillation light, we simulate a way to alter propagation and extraction of optical photons from the scintillator, using photonic crystal (PhC) slabs...
II-VI semiconductor nanocrystals (NCs) are known to show very good optical fluorescence quantum yields. As direct band gap semiconductors they also exhibit a fast excitonic emission in the order of a few tens of ns. In addition, because of their reduced size, multiple excitation generation are favoured, resulting in a significantly faster emission which can be attractive for the scintillation...
Colloidal nanocrystals combine the flexibility of solution-processed materials with the enhanced stability of inorganic semiconductors. They are typically composed of heavy-metal chalcogenides and have a high fluorescence quantum efficiency, which makes them suitable for the detection of high-energy photons and subsequent conversion into visible radiation.
In this presentation, I will...
To improve timing coincidence resolution to the time scale of few tens of picoseconds in future generations of TOF-PET, among others, scintillator material producing more light in subnanosecond time scale is needed. Semiconductors with Wannier exciton emission in quantum confinement regime are an option as their radiative lifetimes can be shortened down to subnanosecond time scale thanks to...
This presentation will present the opportunities offered by nanophotonics to improve the performance of detectors including results obtained from the ATTRACT-Photoquant project [1] that aimed at demonstrating that recent nanophotonics innovations such as metalenses and more generally metamaterials could allow a breakthrough in single-photon time resolution. Silicon photomultipliers are...
Silicon photomultiplier (SiPM) consisting of single photon avalanche diode (SPAD) array has been widely used in many types of applications, those requires photon counting capability. Dynamic range of SiPM, which is one of the representative characteristics, is generally limited by the number of SPADs composing the SiPM. Its dynamic range can be expanded by using small size SPAD, e.g., 10, 15,...
Fast timing performance is of paramount importance in a number of time-resolved medical applications, including TOF-PET, FLIM and Raman. The EPFL AQUA lab has explored several strategies to increase the performance of miniature all-solid-state silicon detectors in the form of single-photon avalanche diodes (SPADs), also known as Geiger-mode APDs. SPADs feature an exquisite timing performance...
Optimization of the timing resolution in the scintillation light readout has been one of the most important challenges in the SiPM field since the beginning of their development. Several sensor parameters contribute to the timing performance achieved in the application. The latest iteration of the NUV-HD SiPM technology developed at FBK feature PDE in excess of 60% at 410 nm, DCR around 60...
Inorganic scintillators are widely used for fast timing applications in time-of-flight (TOF) positron emission tomography (PET), time tagging of soft and hard X-ray photons at advanced light sources and photon counting computed tomography (CT). As the best coincidence time resolution (CTR) achievable is proportional to the square root of the scintillation decay time it is worth studying fast...
Recent developments in semiconductor pixel detectors allow for a new generation of positron-emission tomography (PET) scanners that, in combination with advanced image reconstruction algorithms, will allow for a few hundred microns spatial resolutions. Such novel scanners will pioneer ultra-high-resolution molecular imaging, a field that is expected to have an enormous impact in several...
We present an overview of the TOFHIR2 ASIC design and experimental results on the timing performance. TOFHIR2 will be used in the front-end readout of the barrel section of the new MIP Timing Detector (BTL) developed for the HL-LHC upgrade of the CMS experiment. The BTL sensors are based on LYSO:Ce scintillation crystals coupled to SiPMs.
Novel front-end designs have shown to push the timing performance of scintillators and silicon-photomultipliers (SiPMs) used in PET applications, such that their physical limits regarding timing performance can be established. Using an electronic high-frequency (HF) readout concept, we determine the contribution of a commercial application-specific integrated circuit (TOFPET2 ASIC by PETsys...
Time-of-flight Positron Emission Tomography (TOF-PET) scanning is a molecular imaging procedure for early diagnosis and even prevention in cancer disease. Standard PET scanners are mainly built by modules consisting of scintillation crystals optically coupled to photo-detectors with fast readout electronics. Pushing the limits of the readout system will improve tomographic...
State-of-the-art (SoA) electronic readout for silicon photomultiplier (SiPM)-based scintillation detectors that demonstrate experimental limits in achievable coincidence time resolution (CTR) leverage low noise, high frequency signal processing to facilitate a single photon time response that is near the limit of the SiPM's architecture. This readout strategy can optimally exploit fast...
Good energy and timing resolutions are key parameters for new generations of PET detectors. In particular, the implementation of detectors with minimum electronics, potentially only passive components, is desired. This will improve the cost but more importantly the power consumption of the final scanner, which will further reduce requirements for cooling and
space.
In this work, we...
Purpose-SiPM is a highly used photosensor in PET systems, however, its detector capacitance needs to be compensated for fast timing. Two capacitance compensation technique has been proposed, active compensation using an op-amp, and passive compensation using a balun transformer. In this study, we evaluated the performance of two compensation technique by measuring the CTR with the same...
Purpose
Timing resolution of leading edge discriminators is affected by the time-walk caused by the uncertainty of interaction energy, thus several methods for time-walk compensation have been proposed. Most of the correction methods use the integral of the signal as a parameter for energy, while some studies tried amplitude or slew rate as a parameter for energy. In this study, we tested...
MOLECUBES detectors use monolithic scintillation crystals. This detector architecture demands high-speed readout because all pixels of the photodetector must be processed when an event occurs. An often used approach is integration of the current pulses generated by every pixel, but such circuitry quickly becomes bulky, power consuming and expensive. Alternative approaches are often integrated...
Challenges in modern physics experiments and medical imaging call for continuous boosting of various specifications of detector instrumentation. While spatial and timing resolution, power consumption and data-rate reduction are among parameters, which require constant improvements, new signal analysis and feature extraction methods have to be developed in parallel to aid the performance...
Compton cameras can determine the origin distribution of emitted photons by exploiting Compton scattering kinematics and electronic collimation. The detectors operate in time coincidence and thus, good timing resolution is essential to reduce the amount of random coincidences by applying narrow coincidence windows. Backscattering constitutes an important source of image degradation, in...
The effective sensitivity of a PET system can be increased by improving its time-of-flight (TOF) resolution. For that purpose, new detectors are being developed, including detectors that use not only scintillation but also Cerenkov photons, and detectors consisting of two different scintillators. Such systems have events with different coincidence time resolution (CTR), i.e. different...
The PET-detector time resolution (DTR) using BGO can be improved by using not only scintillation, but also Cerenkov photons. Geant4/GATE Monte Carlo simulations were performed for 511 keV photon interactions in a BGO crystal of 3 x 3 x 20 mm3. In 13720 interaction events, the electrons, scintillation and Cerenkov photons were followed until the photons entered the SiPM, where immediate...
The benefits of time-of-flight (TOF) in positron emission tomography (PET) have long been recognized and later clearly demonstrated in terms of sensitivity and image contrast-to-noise ratio. However, the impact on spatial resolution is generally considered negligible, if not detrimental due to the trade-offs that must be made to optimize the detector coincidence time resolution (CTR). As...
Coincidence detection of the two 511 keV annihilation photons from positron-emitting radiotracers provides an unrivaled mechanism for sensitive, specific, and quantitative molecular imaging in living objects. In positron emission tomography (PET), a large number of coincident 511 keV photons must be collected with sufficient angular sampling to provide the data needed for tomographic...
Most developments in AI for medical imaging target the (semi-)automated analysis of images, these techniques have however also large potential for improving and accelerating the acquisition and for making the scanner lower cost. In monolithic detectors with SiPM array readout positioning can be improved by using a dedicated network for improving the estimation of the transverse position (about...
In the framework of the UTOFPET project, a new TOF-PET detector prototype has been developed to provide uncompromised beyond-state-of-the-art performance. The proposed technology is based on a monolithic LYSO scintillator coupled to a matrix of 16 x 16 SiPMs which is well known to be capable of a high intrinsic spatial resolution but is typically not considered the best solution for providing...
Monolithic scintillation crystals can be used for PET detectors, offering good spatial resolution and depth-of-interaction decoding capabilities. Gamma time estimation however often suffers from the spread of scintillation light, leading to an increased influence of dark counts and other statistical fluctuations in analog SiPMs. Digitizing the SiPM waveforms enables us to perform an accurate...
Computationally expensive physics simulations involving Monte Carlo runs form the backbone of designing improved medical imaging detectors. We show initial results, from an EU-sponsored grant, leveraging uncertainty quantification (UQ) techniques to drastically reduce simulation time with negligible loss in fidelity. We outline the use of embedding such UQ techniques within a machine learning...
