1. Segmentation of a 3D Brain Cortical Surface Using Watersheds
Kathleen Marty
12/10/02

2. Problem Statement
How can the cortical surface of the brain be segmented into “meaningful” areas? Anatomy: sulci and gyri
Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.

3. “Meaningful” Areas Defined
General labeling division between sulci and gyri
Specific labeling of individual sulci
White->sulci, Black->gyri
Colors->sulci, White->gyri

4. Motivation Why segment the cortical surface?
Obtain correspondences between brain models to compare them (i.e. registration)
Visualization

5. Segmentation Using Watersheds
Idea: Simulate rain falling. Each drop eventually descends into a “catchment basin.”
Watersheds: the ridges between the catchment basins
Each catchment basin corresponds to a different labeling
Watershed
Catchment Basins

6. Visualize Watersheds on a Cortical Surface
Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.

7. Watersheds Algorithm Sorting Step Flooding Step
Define each point by a height function
i.e. curvatures, geodesic/shortest distance from point to outside surface, etc.
Flooding Step
Each local minima is the base of a catchment basin
Flood the catchment basins based upon given height function to obtain labeling