Techniques for segmentation of organs and tumors and cells in image data include revising a position of a boundary by evaluating an evolution equation that includes differences of amplitude values for voxels on the boundary from a statistical metric of amplitude of voxels inside, and from a statistical metric of amplitude of voxels outside, for a limited region that lies within a distance r of the boundary. The distance r is small compared to a perimeter of the first boundary. Some techniques include determining a revised position of multiple boundaries by evaluating an evolution equation that includes differences in a first topographical distance from a first marker and a second topographical distance from a second marker for each voxel on the boundary, and also includes at least one other term related to boundary detection.