1. A method for segmenting an image representing a mass of a tissue, comprising: accessing digital image data representing an image including a tissue region; extracting from said digital image data a Region of Interest (ROI) surrounding the mass; transforming the ROI to polar space for obtaining a polar image of the ROI; calculating an edge strength of the mass from said polar image; calculating an expected gray level which corresponds with an edge of the mass by using Gaussian mixture; calculating an expected mass radius by using data from said expected gray level; assigning local cost to sub portions of said polar image as a weighted combination of the edge strength, expected gray level, and expected mass radius, wherein weight of the edge strength is larger in value than weight of the expected gray level; and finding a contour of the mass based on the assigned local costs.