Plug-and-play TOF-PET Module Readout Based on TDC-on-FPGA and Gigabit Optical Fiber Network

Positron Emission Tomography (PET) scanner technology requires the use of a large number of PET detector modules that work in a parallel and synchronous manner. Moreover, system modularity is a desirable feature, that enables technology reutilization for different PET applications and geometries. Additionally, Time-of-Flight (TOF) PET requires a synchronization error, between the modules, below hundred picoseconds in order not to degrade the system level coincidence-resolving-time significantly. In a modular approach, every PET detector module, which typically is composed of a photodetector coupled to a scintillator, includes mixed-signal electronics and a data transmission system. If a host-based architecture is chosen for connecting all the modules to a central acquisition unit, a significant complexity is added at interconnection level and the modularity is reduced. This work aims to a full flexible and fast prototyping solution, where all the estimation methods are integrated in a Field Programmable Gate Array (FPGA), and the analog part is built with off-the-shelf components. An exploration and solution of module connection is proposed in order to reduce complexity and allowing full modularity. Every module hosts a FPGA that includes the data transmission resources and a multi-channel and high-performance Time-to-Digital Converter (TDC), with single-shoot channel precision below 12.5 ps r.m.s. In this way, it performs not only the timing measurement but also position and energy estimation, as well as independent data transmission. Furthermore, the connections are realized using optical fibers driven by Gigabit Transceivers (GT). In this way, we guarantee a physical link up to 8 Gb/s that makes feasible to sustain a global measure rate of 300 Mega measures per second. Moreover, the optical fiber link guaranties null electromagnetic interference that affects the analog stages or other sensitive parts.