The procedure of brainstem segmentation update with respect to the repetitive user interactions. (a) Initial segmentation with large errors, (b) initial segmentation with user interactions, (c) intermediate segmentation result based on the interactions shown in (b), (d) intermediate result with some additional user interactions, (e) updated segmentation result based on the interactions shown in (d), and (f) ground-truth segmentation. The red / blue dots represent the FG / BG interactions. Three different views in 3D space are shown in the top, middle, and bottom rows.