1. A method of performing a medical procedure using a plurality of electrodes implanted within tissue of a patient, comprising: generating an electrical energy perturbation on at least one of the plurality of electrodes; and computing network resistances for each of at least three active ones of the electrodes in response to the electrical energy perturbation, wherein the network resistances represent the resistances between the respective active electrodes and a common node to which the active electrodes are connected in parallel.