An apparatus and method for determining a position of a point source arranged in a Positron Emission Tomography (PET) scanner apparatus. The apparatus includes processing circuitry configured to obtain list-mode data generated from a PET scan of the point source, determine a plurality of lines-of-response (LORs) from the obtained list-mode data, determine intersecting pairs of LORs from the determined plurality of LORs, determine corresponding coordinates of intersection points of the determined intersecting pairs of LORs, and determine the position of the point source based on the determined coordinates of the intersections points.
