In a method and a magnetic resonance system for determining the position and/or orientation of the image plane of slice image exposures of a vessel region in a contrast agent bolus examination, in particular in the region of the aorta bifurcation or the aorta arch, wherein the image plane traverses the vessel region in the longitudinal section, initially a group of slice image exposures disposed essentially orthogonal to the vessel is automatically acquired from different planes of the vessel region lying parallel to one another, and the image regions showing the vessel region are automatically determined within the orthogonal slice image exposures in an image-processing device, and using the determined image regions the spatial position of the vessel region is determined. The position and/or orientation of the image plane disposed essentially orthogonal to the planes of the slice image exposures and traversing the vessel region in the longitudinal section is determined automatically using the position information, such that the image plane lies in the center of the vessel region.