A method and apparatus generate an image in positron emission tomography (PET). The method and apparatus are configured to divide detected signals into sections at time intervals. The detected signals are emitted from tracers introduced into a target. The method and apparatus are also configured to generate unit signals for each of the sections by accumulating the divided signals at each respective section. The method and apparatus are further configured to classify the unit signals into groups based on characteristics of each of the unit signals, and generate the medical image of the target from the unit signals classified into the groups.
