Validated simulation for LYSO: Ce scintillator based PET detector modules built on fully digital SiPM arrays

In the recent years new digital photon counter devices (also known as silicon photomultipliers, SiPMs) were designed and manufactured to be used specifically in positron emission tomography (PET) scanners. These finely pixelated devices opened new opportunities in PET detector development, hence their application with monolithic scintillator crystals now are of particular interest. We worked out a simulation tool and a corresponding validation method to assist the optimization and characterization of such PET detector modules. During our work we concentrated on the simulation of SPADnet sensors and the LYSO:Ce scintillator material. Validation of our algorithms combines measurements and simulations performed on UV-excited detector modules. In this paper we describe the operation of the simulation method in detail and present the validation scheme for two demonstrative PET detector-like modules: one built of a scintillator with black-painted faces and another with polished faces. By evaluating the results we show that the shape deviation of the average light distributions is lower than 13%, and the pixel count statistics follow Poisson distribution for both measurement and simulation. The calculated total count values have less than 10% deviation from the measured ones

Toward the development of a fully CMOS Single-Photon Detector for PET systems: a Montecarlo simulator as an optimization tool to support the sensor design

A Zemax/Matlab Monte Carlo (MC) simulator of a gamma detector module for PET applications is presented. The simulator models the optical arrangement and the photodetector based on CMOS Single-Photon Avalanche Diodes (SPADs). The simulator serves as a tool for optimization of the detector configuration, as it allows the designers to evaluate different sensor configurations and find the one that maximizes the signal-to-noise ratio (SNR). Three sensor configurations have been tested, employing SPADs with a diameter of 8 µm, 16 µm and 32 µm. Results show that 16 um-wide devices lead to the best trade-off between fill factor and noise

A 5x5 SPADnet Digital SiPM Tile for PET Applications

SPADnet is a sensor platform for the detection and processing of gamma photons generated in a PET system. SPADnet uses the novel technique of deferred coincidence detection, whereas timestamps associated with gamma events and their energy are routed at high speed (up to 3.3 million events per second) over a 2Gbps network, along with synchronization information. In this work, we describe SPADnet's key building block, a tile of SPADnet-I chips. SPADnet-I is a 50 mm2, 8x16 pixel digital SiPM where each pixel includes an array of 720 SPADs and the logic to count photons and record their arrival time. A fill factor of 42.9% is achieved. A distributed adder provides the number of photons detected throughout the whole array every 10 ns. On-chip triggering logic monitors this value in real time to discriminate gamma events from dark counts. The chip features a 10.8% energy resolution and a CRT of 288ps when coupled to a 3x3x10 mm3 LYSO crystal. High spatial resolution is obtained by combining the data generated by each pixel to efficiently locate the gamma absorption in the 2D space even when coupled to large arrays of crystal needles as small as 1.12x1.12mm2. The tile is built on a 5x5 array of SPADnet-I sensors. A Xilinx Spartan6 FPGA controls the whole module and monitors the gamma activity across the 25 sensors. Here, the large amount of data generated for each detected gamma is processed in real time to extract energy, position and time-of-arrival. Pile-up detection and energy windowing are applied to the events, which are then fed to a network of tiles for coincidence detection. A centralized snooper recognizes coincidence pairs while thermal, Compton, and single events are discarded. The system is inherently scalable, as it enables single- or multi-rings of photonic modules for potentially large PET systems

SPADnet: A Fully Digital, Networked Approach to MRI Compatible PET Systems Based on Deep-Submicron CMOS Technology

This paper is the first comprehensive presentation of the SPADnet concept. SPADnet is a fully digital, networked MRI compatible time-of-flight PET system, exploiting the speed and integration density of deep-submicron CMOS technologies. The core technologies of SPADnet are a sensor tile comprising an array of 16x32 mini-SiPM pixels with in situ time-to-digital conversion, a multi-ring network to filter, carry, and process data produced by the sensors at 2Gbps, and a 130nm CMOS process enabling mass-production of photonic modules that are optically interfaced to scintillator crystals. The SPADnet photonic modules comprise 25 tightly packed sensor tiles; each module is networked in multiple rings, where coincidence pairs are identified and readily used in reconstruction algorithms, enabling scalable, MRI compatible preclinical PET systems for multi-modal imaging

SPADnet: Embedded Coincidence in a Smart Sensor Network for PET Applications

In this paper we illustrate the core technologies at the basis of the European SPADnet project (www.spadnet.eu), and present the corresponding first results. SPADnet is aimed at a new generation of MRI-compatible, scalable large area image sensors, based on CMOS technology, that are networked to perform gamma-ray detection and coincidence to be used primarily in (Time-of-Flight) Positron Emission Tomography (PET). The project innovates in several areas of PET systems, from optical coupling to single-photon sensor architectures, from intelligent ring networks to reconstruction algorithms. In addition, SPADnet introduces the first computational model enabling to study the full chain from gamma photons to network coincidence detection through scintillation events, optical coupling, etc