1. An inspection system for a metal-reinforced concrete structure, comprising: (a) a radio frequency (RF) system configured to be movable with respect to a surface of the concrete structure while transmitting radio signals into the interior of the structure, and receiving reflected radio signals; and (b) a processor configured to process the reflected radio signals, so as to obtain a focused image of the reinforcement in least one selected region within the concrete structure, said image corresponding to the physical condition of the reinforcement.