a method for calculating perfusion data , such as blood volume or blood flow from 2 - d angiography data or dsa sequences , is proposed . an angiography scene is recorded using specific acquisition parameters to generate the 2 - d angiography data or dsa sequences with administration of contrast agent based on a multiplicity of individual angiography images . a region of interest is defined suitable for comparison purposes . the volume segments are defined by the region of interest . the time / contrast curve is determined in the volume segments . perfusion data for calculating the relative perfusion data is ascertained . the perfusion data is compared and the relative perfusion data is calculated . the calculated relative perfusion data is not specified in terms of absolute physical quantities , but is provided simply as ratios , such as left / right or before / after .