1. A system for imaging a region of interest comprising: a positron emission tomography (PET) scanner comprising at least one detector configured for detection of temporally coincident photons; a collimation assembly, having a plurality of apertures, placed such that the collimation assembly is closer to the region of interest than the at least one detector; an image creator configured to detect a set of pairs of coincident photons at the detector associated with the PET scanner to determine a corresponding set of lines of response for the set of pairs of coincident photons, determine which of the plurality of apertures that a photon of a pair of coincident photons passed through from the line of response corresponding to the pair of coincident photons, reject at least one line of response of the set of respective lines of response according to the relationship of each line of response to the plurality of apertures, and generate an image of the region of interest from the plurality of lines of response that have not been rejected.