All-optical encoding of PET detector signals

Typical PET scanners use many electronic readout channels and dedicated electronic coincidence processing boards that contribute significantly to system complexity and costs. We have developed a method of optically encoding position, energy, and arrival time of annihilation photon interactions in PET detectors with fast coherent optical pulse (100 ps FWHM) trains from telecommunications-grade lasers, and propose a method that, if successful, will enable multiplexing the entire system output to a single optical fiber output channel. This will allow the elimination of much of the currently used processing electronics, achieving coincidence time resolutions of 300 ps FWHM while decreasing system complexity. We constructed a single channel proof of concept system using fast 10 Gbps off-the-shelf optical components and a silicon photomultiplier (SiPM) coupled to an LSO:Ce crystal. Using this system we demonstrated the encoding of position, energy, and arrival time into four coherent optical pulses. We measured extremely low timing jitter for the optical pulses (3 ps) and collected preliminary ¹³⁷Cs energy spectra (energy resolution ~17% FWHM at 662 keV - not optimized yet) with all-optical pulse encoding. Optical encoding and multiplexing could greatly facilitate the construction of high resolution PET scanners with thousands of detector channels.