Abstract: A method of assessing tissue vascular permeability for nanotherapeutics using non-labeled dextran can include: receiving a non-labeled, physiologically-tolerable dextran solution by a subject; acquiring a plurality of magnetic resonance images of a distribution of the dextran solution within at least one region of interest of the subject for a corresponding plurality of times; and assessing a tissue vascular permeability of the at least one region of interest to dextran particles in the dextran solution based on differences between the plurality of magnetic resonance images, wherein the dextran solution is a substantially mono-disperse solution of dextran particles of one size.