1. A method of acquiring PET images of a patient comprising: obtaining a preliminary image of a patient; describing a spatial location of said patient using said preliminary image; for each line of response connecting a pair of oppositely disposed PET detectors, calculating a time coincidence window based on an intersection of said described spatial location with said line; detecting a pair of gamma photons produced by an annihilation event; determining whether the detection of said pair of gamma photons occurs within a calculated time coincidence window corresponding to a line of response of said annihilation event; accepting data relative to the detection of said pair of gamma photons only if the detection of said gamma photons occurs within said time coincidence window; calculating a spatial location of said annihilation event only if the event has been accepted; and, adding the calculated spatial location of said annihilation event to a stored distribution of calculated annihilation event spatial locations representing the radioactivity distribution in said patient.