1. A method for determining a tissue parameter of tissue that is determinable from passage of a contrast agent through the tissue based on a series of temporally consecutive two-dimensional digital subtraction angiography x-ray images showing propagation of the contrast agent in the tissue over time and a vascular system present in a region of the tissue, the method comprising: locating at least some of the vessels of the vascular system, the locating comprising segmenting in the x-ray images; assigning pixels showing segmented vessels an interpolation intensity determined by interpolation from intensities of at least some pixels bordering the segmented vessel, so that x-ray images from which vessels have been eliminated result; and determining tissue parameters for at least some of the pixels of the series of x-ray images from which the vessels have been eliminated.