No, the catchment bassins have nothing to do with blood flow: they are defined on an algorithmic point of view (a shape analysis algorithm based on a watershed-like method, used to split folds into pieces using anatomical depth/curvature criterions).
It's a parcellation image: values in the image do not represent an anatomical or physiological measure, but are meant to distinguish between different regions (like a ROI): value 1 is the first region, value 2 a different region, and so on.
Denis
