Methods and apparatus are provided for obtaining a representation of the distribution of electrical impedance within a multiphase flow with an electrically continuous or discontinuous principle flow contained within an electrically conductive solid ring electrode, including providing a plurality of mutually spaced electrical contacts mounted at the outside wall of the ring and electrically contacting with the ring, applying currents or voltages to the ring from the electrical contacts, generating a more homogeneous electric field distribution within the material, measuring voltage or current distribution alone the ring from other electrical contacts, relatively intensifying the imaging sensitivity at the central area of the sensing domain using a /2 angle sensing strategy and reconstructing the representation of the impedance distribution using CG method with an error processing strategy.