A method is provided for measuring a permeability of a subject's blood-brain barrier to water. The method includes acquiring, with an magnetic resonance imaging (“MRI”) system, a first T1 map of the subject over at least a selected region-of-interest (“ROI”) including a brain of the subject and waiting a delay period selected to allow an affect of the contrast agent on the longitudinal relaxation period to change. The method then includes acquiring, after expiration of the delay period and with the MRI system, a second T1 map of the subject over at least the selected ROI and determining, using the first T1 map and the second T1 map, a fractional volume of vascular compartments in the ROI and a permeability surface area product in the ROI. The method includes creating, using the determined fractional volume and permeability surface area product, a map of water exchange rate in the ROI.
