Abstract: A surgical navigation system for navigating a region of a patient that may include a non-invasive dynamic reference frame and/or fiducial marker, sensor tipped instruments, and isolator circuits. The dynamic reference frame may be placed on the patient in a precise location for guiding the instruments. The dynamic reference frames may be fixedly placed on the patient. Also the dynamic reference frames may be placed to allow generally natural movements of soft tissue relative to the dynamic reference frames. Also methods are provided to determine positions of the dynamic reference frames. Anatomical landmarks may be determined intra-operatively and without access to the anatomical structure.