8 May 2014 SPADnet: a fully digital, scalable, and networked photonic component for time-of-flight PET applications
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The SPADnet FP7 European project is aimed at a new generation of fully digital, scalable and networked photonic components to enable large area image sensors, with primary target gamma-ray and coincidence detection in (Time-of- Flight) Positron Emission Tomography (PET). SPADnet relies on standard CMOS technology, therefore allowing for MRI compatibility. SPADnet innovates in several areas of PET systems, from optical coupling to single-photon sensor architectures, from intelligent ring networks to reconstruction algorithms. It is built around a natively digital, intelligent SPAD (Single-Photon Avalanche Diode)-based sensor device which comprises an array of 8×16 pixels, each composed of 4 mini-SiPMs 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. A few tens of sensor devices are tightly abutted on a single PCB to form a so-called sensor tile, thanks to TSV (Through Silicon Via) connections to their backside (replacing conventional wire bonding). The sensor tile is in turn interfaced to an FPGA-based PCB on its back. The resulting photonic module acts as an autonomous sensing and computing unit, individually detecting gamma photons as well as thermal and Compton events. It determines in real time basic information for each scintillation event, such as exact time of arrival, position and energy, and communicates it to its peers in the field of view. Coincidence detection does therefore occur directly in the ring itself, in a differed and distributed manner to ensure scalability. The selected true coincidence events are then collected by a snooper module, from which they are transferred to an external reconstruction computer using Gigabit Ethernet.
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Claudio Bruschini, Edoardo Charbon, Chockalingam Veerappan, Leo H. C. Braga, Nicola Massari, Matteo Perenzoni, Leonardo Gasparini, David Stoppa, Richard Walker, Ahmet Erdogan, Robert K. Henderson, Steve East, Lindsay Grant, Balázs Játékos, Ferenc Ujhelyi, Gábor Erdei, Emöke Lörincz, Luc André, Laurent Maingault, David Jacolin, L. Verger, Eric Gros d'Aillon, Peter Major, Zoltan Papp, Gabor Nemeth, "SPADnet: a fully digital, scalable, and networked photonic component for time-of-flight PET applications", Proc. SPIE 9129, Biophotonics: Photonic Solutions for Better Health Care IV, 912913 (8 May 2014); doi: 10.1117/12.2051952; https://doi.org/10.1117/12.2051952

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