1. A computer-implemented method for segmenting an object in a set of image data wherein a first shape has been grown inside the object based on a seed point, comprising: a processor configured to perform the following steps of: testing points on the first shape to determine a first set of one or more seed points; growing a second shape inside the object based on one of the seed points in the first set; and testing points on a perimeter of the second shape to determine a second set of one or more seed points; and growing a third shape inside the structure based on one of the seed points in the second set.