Fig 1. Region-of-interest technique for perfusion determination. Two ROIs are drawn on the average map (A) adjacent to each ventricle for a total of 8 PV ROI's. Two further ROIs are placed within the adjacent subcortical white matter defined by an imaginary line between the ventricle and overlying cortex for a total of 8 SC ROIs. The ROIs are subsequently projected onto the inherently coregistered maps for PV and SC CBF (B), CBV (C) and MTT (D) calculation.