Systems and methods are provided for identifying and locating a plurality of RFID markers implanted within a target tissue region within a patient's body. A probe is provided that may receive signals from the RFID markers. The RFID markers modulate signals from the respective markers based on code sequences opening and closing respective switches of the markers to modulate the backscatter signals. The probe processes the signals to separate the signals based at least in part on the code sequences to identify each of the plurality of markers.