Figure 1. Simplified sensitivity distribution of a four-electrode impedance measurement applied to a uniform conductive cylinder. (a) The lead field produced by the current excitation electrodes (Ir refers to reciprocal current injection). (b) The field which would be produced if current were driven through voltage measurement electrodes. (c) Superimposed fields of the previous two lead fields. (d) Principled presentation of the sensitivity of the measurement setup in a few locations.