In this paper we compare Mixed-Integer Evolution Strategies (MI-ES) and standard Evolution Strategies (ES) when applied to find optimal solutions for artificial test problems and medical image processing problems. MI-ES are special instantiations of standard ES that can solve optimization problems with different objective variable types (continuous, integer, and nominal discrete). Artificial test problems are generated with a mixed-integer test generator. The practical image processing problem iss the detection of the lumen boundary in IntraVascular UltraSound (IVUS) images. Based on the experimental results, it is shown that MI-ES generally perform better than standard ES on both artifical and practical image processing problems. Moreover it is shown that MI-ES can effectively improve the parameters settings for the IVUS lumen detection algorithm. Categories and Subject Descriptors