The system computer is located in the control room or equipment room. It controls the electrical unit, captures the signals and calculates the location and orientation of the sensors by using a unique real-time algorithm. The computer also acquires the scanned images from the scanner and adds annotations according to the sensors location and orientation. The annotation can also be plotted on an external monitor, e.g. an MRI-safe monitor in the scanner room. The tracking information can be sent via tcp/ip communication to 3rd party applications, or saved on the computer for retrospective analysis.