1. A method comprising: performing a first T2-weighted imaging (T2WI) on a subject; injecting said subject with a contrast agent after performing said first T2WI; waiting a predetermined period of time before performing a second T2WI on said subject; co-registering said first T2WI and said second T2WI; trimming said co-registered first T2WI and said co-registered second T2WI; determining a ΔR 2 map based on each pixel of said trimmed first T2WI and corresponding pixels of said trimmed second T2WI; and constructing a three-dimensional (3D) map based on said ΔR 2 map.