A method is for determining a respiratory phase is based on receiving tomographic raw data on the basis of a spiral scan of an examination region of a patient, the examination region including at least part of the torso and/or abdomen of the patient. Slice image pairs are reconstructed on the basis of the tomographic raw data, wherein a slice image pair includes two slice images having a first interval at an identical position along a predefined axis. The position refers to the position of the examination region. This enables determining of differences between reference positions of the examination region in two slice images respectively of a slice image pair and determining a respiratory phase on the basis of the differences. The differences correspond in each case to the change in the anatomy of the examination region, wherein this change occurs during the first interval.
