An imaging system for imaging a living organism that is treated with a radionuclide emitting positrons is provided. A portion of the emitted positrons create photons within said living organism. The living organism is placed between first and second detection systems, which are diametrically opposed. The first and second detection systems are comprised of a plurality of position sensitive detectors. A portion of said photons are detected within said detection systems. A multi-channel readout system is coupled to the position sensitive detectors. A display system is coupled to the multi-channel readout system and includes a processor which determines directions of the portion of said photons.