1. A method of estimating a position distribution of radiation emission, the method comprising: acquiring a previously stored timing resolution of each of a pair of detectors; obtaining a time difference between radiations detected by the pair of detectors; generating a probability of radiation emission for a position based on the time difference and on the timing resolution of each of the pair of detectors; and generating an image using the generated probability of radiation emission, wherein the generating of the probability of radiation emission comprises generating an asymmetrical probability distribution function (PDF); wherein the pair of detectors comprises a first and a second detector; a width of the PDF in a direction toward the first detector from a center of the PDF is stretched based on a timing resolution of the first detector; and a width of the PDF in a direction toward the second detector from the center of the PDF is stretched based on a timing resolution of the second detector; wherein a width of the asymmetrical PDF in a direction toward the first detector among the pair of detectors having larger timing resolution from a center of the PDF is stretched to compensate for the larger timing resolution of the first detector.