Systems for characterizing tissue comprise: a tissue probe comprising a plurality of probe electrodes; a signal generator, a controller, and a user interface. The signal generator is in communication with the probe electrodes for delivering a drive signal to at least one probe electrode. The controller receives a recorded signal from one or more probe electrodes, the recorded signal resulting from delivery of the drive signal through tissue proximate the plurality of probe electrodes. The controller is configured to determine patient-to-patient differences when the tissue probe is proximate a known type of patient tissue and/or bodily fluid, and it produces tissue characterization information based on the recorded signal and the patient-to-patient differences. The user interface provides the tissue characterization information to an operator of the system. Methods of characterizing tissue are also provided.