In situ forming implants (ISFI) allow for precise placement of a drug eluting depot into the body, using a simple injection. However, the properties of the injection sites can alter the drug release profile in situ. Diffusion weighted imaging (DWI) provides a method for non-invasively and nondestructively tracking changes in the implant diffusivity in situ. Using DWI, we have characterized the diffusivity profile of ISFIs made using a poly(lactic-co-glycolic) acid polymer, loaded with the mock drug fluorescein. The ability to characterize the diffusivity profile of implants in situ, will provide the necessary tools for improving the rational design of implants.