1. An imaging system for imaging a human subject, the imaging system comprising: a ring of positron emission tomography (PET) detectors including scintillators selected from the group consisting of lutetium yttrium oxyorthosilicate (LYSO), lutetium oxyorthosilicate (LSO), and lanthium bromide (LaBr) and optical sensors; a PET housing at least partially surrounding the ring of PET detectors and defining a patient aperture of at least 80 cm; and a coincidence detection processor or circuitry configured to identify substantially simultaneous 511 keV radiation detection events corresponding to electron positron annihilation events, the coincidence detection processor or circuitry being configured to identify substantially simultaneous 511 keV radiation detection events corresponding to electron positron annihilation events using a narrow energy window of about 15% FWHM or shorter and a narrow time window of about 10 ns or shorter.