mapped using the mr signal received by an external coil when using a small circular microcoil positioned on the device or probe the method of the present invention determines the position and orientation of interventional access devices and surgical probes based on phase patterns in the mr signal around the small circular microcoil positioned on the device or probe the microcoil may be connected electrically to the mr system or signals from the coil may be coupled optically or inductively to a transducer which is electrically connected to the mr scanner the latter embodiments provide some electrical isolation between the patient and the scanner one can configure the system so that it is possible to separately receive signals from different coils at the same time that said when using microcoils phase images are derived from the signal from each microcoil in the method of the invention accurate position and orientation information can be obtained over a circular area of at least 4 microcoil diameters moreover since only a sample of the information is needed to position and orient the catheter highly redundant localization information is available and global correlations can be used to identify the phase patterns the present invention will now be described further with particular reference to certain non limiting embodiments and to the accompanying drawings in fig1 to 4 in the method of the invention the sensitivity field of a circular microcoil is evaluated the theory of reciprocity states that the sensitivity field of an mr receive coil is equivalent to the magnetic field produced.