1. A method for automatic 3D (three-dimensional) lesion segmentation, comprising the steps of: determining a 3D surface of a lesion in an original 3D volume space; transforming the 3D surface of the lesion to a spherical coordinate space; processing the 3D surface in the spherical coordinate space to determine a lesion surface in the spherical coordinate space which separates the lesion from surrounding normal structure; transforming the lesion surface in the spherical coordinate space to the original 3D volume space; and extracting a volume corresponding to the lesion from the original 3D volume space using the transformed lesion surface.