Abstract: A gamma camera system for which a predetermined resolution is sought includes a collimator having at least one opening in which the largest cross-section adjacent the detector is greater than twice the intrinsic resolution of the detector so that plural beams pass through each opening giving plural points of impact on the detector. The detector is displaced by successive steps, the successive steps being of the order of magnitude of a predetermined image resolution. Information collected by the detector is processed by storing locating information corresponding to the impact points for each position of the opening during displacement, and processing the information to reconstruct the radiation volume density function of radiation emitted by the radiation source.