In a method and x-ray device to determine a three-dimensional target image data set showing at least one partial region of interest of an acquisition region, wherein the image data of the three-dimensional target image data set are reconstructed from two-dimensional projection images acquired from various projection directions, first projection images are acquired without a collimation of the radiation source from first projection directions and a three-dimensional overview image data set of the acquisition region is reconstructed from the first projection images. The partial region of interest is selected in the overview image data set. Second projection images are acquired, with collimation at the partial region, from second projection directions, the second projection directions differing from the first projection directions. The target image data set showing the acquisition region and the partial region of interest is reconstructed from all first and second projection images.