A system includes emission of a first plurality of radiation beams from respective ones of a first plurality of locations along a first arc, acquisition of a first plurality of projection images of a target based on the first plurality of radiation beams, emission of a second plurality of radiation beams from respective ones of a second plurality of locations along a second arc, acquisition of a second plurality of projection images of the target based on the second plurality of radiation beams, and generation of a three-dimensional image of the target based on the first plurality of projection images and the second plurality of projection images, wherein a density of the first plurality of locations along the first arc is less than the density of the second plurality of locations along the second arc.