The objective of our research is to develop an ultrasound, time-of-flight triangulation based system for real-time, intraoperative 3-dimensional tracking of minimally invasive surgical instruments. We have chosen to first apply this technology towards tracking catheters used in endovascular aortic stent-grafting. To demonstrate the feasibility of this concept, we have developed a system involving a custom catheter based transducer and performed an experiment in excised porcine tissue with a model aorta.