1. A nuclear image system for updating an original nuclear image, the nuclear image system comprising: a data memory for storing the original three-dimensional nuclear image; a nuclear radiation detector, which is movable along a freely variable path, for measuring nuclear radiation, in order to obtain nuclear radiation values; a tracking system for tracking the nuclear radiation detector while measuring the nuclear radiation, so that detector coordinates are obtained which indicate a posture of the tracked nuclear radiation detector in relation to an image coordinate system of the nuclear image; a nuclear data input configured to receive the nuclear radiation values from the nuclear radiation detector and the detector coordinates from the tracking system, and to associate the nuclear radiation values with the respective detector coordinates; and an image updating module including an updating rule for changing the original nuclear image on the basis of the nuclear radiation values and the detector coordinates, wherein the image updating module is configured to generate an updated three-dimensional nuclear image by applying the updating rule to the original nuclear image.