1. Image processing device for processing a multi-dimensional data set of image data, in particular of three-dimensional medical volume image data, including a segmentation unit for a segmentation of an image object in said data set, said segmentation unit comprising: model-based segmentation means for performing a model-based segmentation of said data set for obtaining a multi-dimensional model representing a first approximation of said image object; data-driven segmentation means for performing a data-driven segmentation of said multidimensional data set for obtaining a multi-dimensional subset of said multi-dimensional data set representing a second approximation of said image object; optimizing means for adapting said model and said subset for optimizing a similarity value between said first and said second approximation; and selecting means for selecting said adapted model or said adapted subset as a segmentation of said image object.