Fig. 2.

Illustration of the layered tissue model and the segmentation preprocessing workflow. Multiple air cavities are allowed. An arrow represents a thinning ($T_{-}$) or thickening ($T_{+}$) operation between two adjacent regions. Two sample pathways are indicated, shown by black and blue arrows, respectively. The circled numbers indicate the processing order. The gaps inserted between layers can be removed in the postprocessing step to recover shared boundaries (such as the CSF/GM/WM surfaces here).