Optical encoding and multiplexing of PET coincidence events

We have developed a method of optically encoding position, energy, and arrival time of annihilation photon interactions in PET detectors with fast optical pulse (130 ps FWHM) trains, and demonstrated it in a two-channel coincidence setup. Two LSO-SiPM detector channels were optically encoded and multiplexed down to one optical fiber readout channel, and custom software was used to decode coincidences in the resulting pulse trains and calculate coincidence timing resolution. Timing resolution of ~168 ps FWHM was achieved using pulse height discrimination, indicating that optical encoding introduces little timing jitter, and showing promise for use in time-of-flight (ToF) PET imaging. We have demonstrated what is essentially two-channel optically multiplexed coincidence detection with only a single digitizer. This technique has the potential to eliminate the need for coincidence processing electronics for every detector channel, thereby reducing the complexity of high-resolution PET scanners with thousands of readout channels. It could eventually replace bulky electronic multiplexing and readout schemes with only a few optical fibers.