1. An image processing system comprising 3D image data processing means ( 10 ) of automatic mapping a 3-D Surface Model onto the surface of an object of interest in a 3-D image, for estimating a model-based 3-D segmentation surface, comprising visualizing means ( 60 ) and further comprising: means of interactive adaptation ( 20 ) of the segmentation surface to the actual surface of the object of interest including: means of interactive selection ( 40 ) of a 2D data plane (DP) that intersects the 3-D segmentation surface along a 2-D Model Curve (MC), said Data Plane having a user-selected orientation with respect to said surface, which is appropriate for the user to visualize a 2-D portion called Aberrant Curve (AC) of said Model Curve to be modified; means of interactive definition of a Guiding Curve (GC) in the 2-D Data Plane; means of interactive adaptation of said Aberrant Curve (AC) to said Guiding Curve (GC); and means of further automatically adapting the 3D segmentation surface within a neighborhood of the interactively adapted Aberrant Curve.