Shielded surgical navigation system that determines the position and orientation of the tracked object with real and virtual dipoles

A surgical navigation system comprising:

• a transmitter assembly with at least one transmitter element capable of emitting electromagnetic energy, each said transmitter element, when emitting electromagnetic energy, being considered a real dipole;
• a correction sensor assembly with at least one sensor element capable of sensing electromagnetic energy is provided, wherein, relative to said transmitter assembly, said correction sensor assembly is at a fixed position and orientation so as to form a transmitter-correction sensor assembly;
• a tracker sensor assembly with at least one sensor element capable of sensing electromagnetic energy, wherein one of said transmitter-correction sensor assembly or said tracker sensor assembly is moveable relative to the other of said tracker sensor assembly or said transmitter-correction sensor assembly and one of said transmitter-correction sensor assembly or said tracker sensor assembly is part of a tracker attached to a surgical tool or to a marker attached to a patient;
• a shield formed of magnetically permeable material that is positioned so that the patient, said transmitter-correction sensor assembly and said tracker sensor assembly are located on one side of said shield, the patient is located close to said shield, said tracker sensor assembly is located further from said shield than the distance the patient is located from said shield and said transmitter-correction sensor assembly is located further from said shield than the distance said tracker sensor assembly is located from said shield and both said transmitter-correction sensor assembly and said tracker sensor assembly are moveable relative to said shield said;
• and
• a processor connected to said tracker sensor assembly to receive at least one measurement of electromagnetic field strength from said at least one tracker sensor assembly sensor element and to said correction sensor assembly to receive at least one measurement of electromagnetic field strength from said at least one correction sensor assembly sensor element and said processor being configured to:
• based on the at least one measurement of electromagnetic field strength from said at least one correction sensor assembly sensor element, determine the location of at least one virtual dipole, the at least one virtual dipole being located on the side of shield opposite the side on which said transmitter-correction sensor assembly is located;
• based on the location of the at least one real dipole, the location of the at least one virtual dipole and the at least one measurement of electromagnetic field strength of the at least one tracker sensor assembly sensor element, determine the position and orientation of said tracker sensor assembly relative to said transmitter assembly.