Using an entropy similarity measure to enhance the quality of DSA images with an algorithm based on template matching

The reduction of motion artifacts arising in DSA requires registration of mask- and contrast image prior to subtraction. An algorithm has been developed consisting of a) partitioning an interactively chosen region-of-interest (ROI) and exclusion of low-contrast partitions, b) assignment of homologous landmarks or control points, c) estimation of parameters of an affine transformation and application of the transformation on the mask image (inside the ROI), and d) subtraction of contrast- and corrected mask image. For assigning homologous landmarks, we use the entropy as similarity measure and compare the results to other frequently used measures.