A semiconductor structure includes a wafer, at least one nonmetal oxide layer, a pad, a passivation layer, an isolation layer, and a conductive layer. The activation request is received when one or more alert conditions are satisfied. The longitudinal legs of the noble metal box are held in a stretched position by tension springs. The adjustable element is moveably disposed on the substrate and is moved corresponding to the reflective element. The injection rate of the contrast medium varies with time according to the variable pattern for maintaining a state in which the image contrast achieved by the contrast medium approximates an optimum level.