1. A method, comprising: determining, with a processor, a permeability metric of a vascular tissue of interest based on a difference between a first time enhancement curve and second time enhancement curve corresponding to a first contrast material and a second contrast material flowing through the vascular tissue of interest, wherein the first and second contrast materials are different; and generating, with the processor, a signal indicative of the permeability metric, wherein the difference is an average on weighted differences between the first and second time enhancement curves, and the permeability metric is used to automatically determine a tumor grade.