A surgical navigation system includes a CT scanner that takes a plurality
of x-ray images of a patient. A patient tracker including locators is
attached to the patient, and a registration appendage is removably
secured to the patient tracker in a known position and orientation. The
registration appendage includes radio-opaque markers arranged in a
predetermined geometric pattern. The registration appendage is viewable
in a CT scan in situations where the locators of the patient tracker are
outside of a field of view of the CT scanner.