1. Image analyzing apparatus ( 100 ), comprising an input device ( 101 , 101 a, 101 b, 101 c, 101 d ); a processing device ( 102 ); an output device ( 103 ); wherein the input device ( 101 , 101 a, 101 b, 101 c, 101 d ) is adapted for receiving input data in form of clinical image data; geometric data; and boundary data; wherein the processing device ( 102 ) is adapted for generating flow pattern data from the geometric data and from the boundary data; wherein the processing device ( 102 ) is adapted for generating virtual image data from the generated flow pattern data; and wherein the processing device ( 102 ) is adapted for determining a plurality of characteristic locations ( 202 , 303 , 404 , 601 ) in the clinical image data and in the virtual image data for comparing the clinical image data and the virtual image data; wherein the output device ( 103 ) is adapted for providing a quality measure ( 204 , 213 , 222 , 227 ) at each of the plurality of characteristic locations ( 202 , 303 , 404 , 601 ); wherein the quality measure ( 204 , 213 , 222 , 227 ) indicates the quality of correspondence of the clinical image data and the virtual image data at each of the plurality of characteristic locations ( 202 , 303 , 404 , 601 ).