A method for determining the position and/or orientation of a catheter or other interventional access device or surgical probe using phase patterns in a magnetic resonance (MR) signal. In the method of the invention, global two-dimensional correlations are used to identify the phase pattern around individual microcoils, which is unique for each microcoil's position and orientation. In one embodiment the position and orientation of a catheter tip can be reliably tracked using low resolution MR scans clinically useful for real-time interventional MRI applications. In a further embodiment, the invention provides real-time computer control to track the position of endovascular devices and interventional treatment systems, including surgical tools and tissue manipulators, devices for in vivo delivery of drugs, angioplasty devices, biopsy and sampling devices, devices for delivery of RF, thermal, microwave or laser energy or ionizing radiation, and internal illumination and imaging devices, such as catheters, endoscopes, laparoscopes, and related instruments.