Abstract: 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.