1. A positron emission tomography (PET) system comprising: a memory configured to continuously record detected coincident event pairs detected by PET detectors; a subject support configured to support a subject and move in a continuous movement through a field of view of the PET detectors; a categorizing unit configured to categorize the recorded coincident event pairs into each of a plurality of spatially defined virtual frames, wherein the detected events of some of the detected coincident event pairs are located in two different virtual frames and the categorizing unit allocates the coincident event pair to one of the two virtual frames based on at least one of time-of-flight information and a projected location of an annihilation event which produced the event pair; and a reconstruction unit configured to reconstruct the categorized coincident pairs of each virtual frame into a frame image and combine the frame images into a common elongated image.