1. A computer-implemented method for vertebra segmentation comprising: providing an image of a plurality of vertebrae; determining a seed in each of at least two adjacent vertebrae in the image; mapping a unit square to the seeds in the image as corresponding shape constraints on a segmentation; evolving the shape constraints to determine the segmentation of the adjacent vertebrae, wherein evolutions of the shape constraints interact; and outputting a segmented image indicating a location of the vertebra.