1. A method for detecting a roughness of a vessel situated in a living subject, comprising the steps of: providing a medical imaging modality; obtaining image data representing an image of an inner contour of a vessel wall of a vessel in the living subject using said imaging modality, said image containing image information representing a length associated with said inner contour; and supplying said image data to a processor and, in said processor, determining a dimensional value representing a complexity of said inner contour from said image information by analyzing said image information representing said length at increasingly finer resolutions and setting said dimensional value dependent on increase of said length, as said length represented by said image information increases upon analysis thereof at said increasingly finer resolutions, and making said dimensional value representing complexity of said contour available as an output from said processor at a display unit.