How to segment sub-class tissues in BrainWeb simulated brain models?

This is Mu-Lan Jen writing from The University of Texas MD Anderson Cancer Center. Recently, we’re implementing our simulation onto the discrete anatomical model. However, we noticed that vessel component is consisted by a mixture of arteries and veins, which we would like to have them separate in our work. Do you have any sub-class vessel model available? Or, would you mind to provide the recommended way to segment these two sub-class tissues?