A system comprising a probe having a proximal end, a distal end, and a radially expandable array of electrodes disposed near the distal end for circumferentially engaging a lumen wall of a body lumen, a variable frequency power source coupled to the array of electrodes such that, when the electrode array engages the lumen wall, an electrical circuit comprising the power source, selected electrodes of the array, and engaged lumen wall can be defined, and a processor coupled with the variable frequency power source, the processor comprising computer-readable media embodying software instructions configured to characterize an eccentric target material of the lumen wall by monitoring a characteristic of the electrical circuit as a frequency supplied by the variable frequency power source is varied between differing frequencies, wherein the processor is configured to characterize the target material using a tissue signature profile curve, within a frequency range, of impedance magnitude and phase angles of the circuit.
