1. A method of spatially segmenting an anatomical structure from 3-D medical image data, comprising: receiving the 3-D medical image data, and a plurality of grid locations from within a section of the 3-D medical data, the section including a sub-portion of the anatomical structure; determining a first seed selection, based on the grid locations and the section; determining a 2-D or thin slab-like region of interest having a 2-D shape, including the first seed selection, from the grid locations and from an expected maximum aspect ratio of the anatomical structure, selected so that the interior of the shape will include all of the anatomical structure appearing in the section within the region of interest; determining a partial segmentation of the anatomical structure within the section, based on the first seed selection, comprising moving a boundary of the first seed selection outward from an initial position of the first seed selection boundary, the boundary constrained to remain within the region of interest, and excluded from locations outside the region of interest; determining a second seed selection, based on the location of the partial segmentation within the 3-D medical image data; and determining a 3-D segmentation of the anatomical structure, based on the second seed selection and the 3-D medical image data.