Apparatus for analyzing brain MRI, is disclosed. The apparatus comprises an input for receiving a first and a second MRI scans at the beginning and end of a predetermined time interval post contrast administration； a subtraction map former for forming a subtraction map from said first and said second MRI scans by analyzing said scans to distinguish between two primary populations, a slow population, in which contrast clearance from the tissue is slower than contrast accumulation, and a fast population in which clearance is faster than accumulation； and an output to provide an indication of distribution of said two primary populations, wherein said predetermined time period is at least twenty minutes.
