Real-time position monitoring of invasive devices using magnetic resonance. 
Techniques which can be used to follow the position of invasive devices in real-time using magnetic resonance (MR) are described.  Tracking of an invasive device is made possible by incorporating one or more small RF coils into the device.  These coils detect MR signals from only those spins near the coil.  Pulse sequences which employ nonselective RF pulses to excite all nuclear spins within the field-of-view are used.  Readout magnetic field gradient pulses, typically applied along one of the primary axes of the imaging system, are then used to frequency encode the position of the receive coil(s).  Data are Fourier transformed and one or more peaks located to determine the position of each receiver coil in the direction of the applied field gradient.  Subsequent data collected on orthogonal axes permits the localization of the receiver coil in three dimensions.  The process can be repeated rapidly and the position of each coil can be displayed in real-time.