Readout Electronics for a Novel Animal PET Scanner using Field Programmable Gate Arrays : System Definition, Implementation and Assessment

A digital FPGA-based data acquisition system for a novel preclinical PET detector developed at the University of Oslo will be described. The detector, called ComPET, employs an inventive geometry with 600 LYSO scintillator crystals interleaved with 400 wavelength-shifters, grouped into 4 modules and arranged in a rectangular fashion to attain high photon sensitivity and high spatial resolution with minimal shift-variance. By means of APDs and a custom analog front-end the detector response is converted to a digital output, its rising edge and width being a measure of the γ-photon arrival time and energy, respectively. An FPGA samples up to 84 of these channels with deserialisers clocked at up to 1 GHz, computes and stores the event photon arrival time, energy and location, provides a fan-in structure to collect data from these channels, and sends these over Ethernet to a data acquisition system. The system allows for coincidence- and energy-windows to be set for improved contrast resolution, can handle sustained event-rates of 100 Mevents/s with full 3D-readout, and is parametrised for ease of maintainability and flexibility.