In this paper, the purpose is to discuss the relationships among different voltage patterns on the surface so as to compare the noise sensitivity in the voltage measurements for two current patterns frequently used in electric current computed tomography (ECCT). The relationship between the voltage and current patterns on the boundary of homogeneity and concentrically symmetric inhomogeneity can be represented by a pseudo operatorR(σ) for a 32‐electrode system. Thus, using the eigencurrents and their corresponding eigenvalues forR,which are called characteristic resistances, any arbitrary voltage patterns can be synthesized. The two currents studied here are a set of spatial trigonometric patterns and a set of an “adjacent‐pair” patterns. Comparing the synthesized and experimentally measured surface voltages for the two current patterns, the sensitivity to noise for systems using these two types of current patterns may be obtained. Based upon the results, it is shown that the system with the trigonometric current patterns is better than the one with adjacent‐pair current patterns for producing the impedance images.