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 pairs into each of a plurality of spatially defined virtual frames based on time-of-flight information; 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.