A system for modulating delivery of a fluid medium to a selected site within a patient's body includes a syringe for injecting the fluid medium, a delivery catheter including a conduit for delivering the fluid medium from outside of the body to the selected site within the body, a medium reservoir configured to receive a portion of the fluid medium, and a flow diverter assembly disposed in a fluid medium flow path between the syringe and the delivery catheter. The syringe includes a chamber for receiving the fluid medium therein. The flow diverter assembly is configured to divert the portion of the fluid medium from the chamber of the syringe away from the delivery of the medium through the delivery catheter conduit during injecting with the syringe, and simultaneously increase medium fluid flow resistance with increasing pressure level of the fluid medium within the flow diverter assembly.