1. A method for brain tumor segmentation in multi-parametric 3D magnetic resonance (MR) images, comprising: pre-processing an input multi-parametric 3D MR image; classifying each voxel in the pre-processed multi-parametric 3D MR image, determining and assigning a classification probability that the voxel is part of a brain tumor; labeling voxels if their classification probabilities are higher than a selected threshold; obtaining initial label information for image segmentation using only labeled voxels; constructing a graph based representation for the pre-processed image to be segmented; and generating the segmented brain tumor image using the initial label information and graph based representation.