A method and apparatus are provided for determining and tracking location of a metallic object in a living body, and then directing a second modality such as ultrasound waves to the determined location. The metal detector may be a radar detector adapted to operate on a living body. The adaption may include disposing a transfer material having electromagnetic properties similar to the body between the radar detector and the living body, ECG gating the radar detector, and/or employing an optimal estimator with a model of expected stent movement in a living body. Applications include determination of extent of in-stent restenosis, performing therapeutic thrombolysis, or determining operational features of a metallic implant.