Patent ID: 7646899

Claim:
A method for determining an orientation of a base to which a fiducial marker is detachably mounted, wherein the base has an axis of symmetry, a b , representing the orientation, a threaded portion at a first end threaded into a portion of a human anatomy at a predetermined location, and an engagement portion at a second end opposing the first end, and wherein the fiducial marker has an axis of symmetry, a m , and is detachably mounted to the engagement portion of the second end of the base, comprising of the steps of: determining the axis of symmetry for the fiducial marker; and choosing the determined axis of symmetry of the fiducial marker as the axis of symmetry of the base, wherein the determining step comprises the steps of: a. acquiring an image having the fiducial marker from the portion of the human anatomy; b. segmenting the fiducial marker into a plurality of voxels from the acquired image; c. estimating the centroid of the fiducial marker from the segmented fiducial marker image; d. estimating the axis of symmetry of the fiducial marker at the estimated centroid; e. simulating an image of the fiducial marker at the estimated centroid and the estimated axis of symmetry; f. registering the simulated image of the fiducial marker with the acquired image of the fiducial marker so as to obtain a registered centroid and a registered axis of symmetry of the fiducial marker in the acquired image; g. updating the estimated centroid and the estimated axis of symmetry of the fiducial marker to the registered centroid and the registered axis of symmetry of the fiducial marker, respectively; h. repeating steps (e)-(g) until both differences between the estimated centroid and the registered centroid and differences between the estimated axis of symmetry and the registered axis of symmetry are substantially small; and i. choosing the last registered axis of symmetry as the axis of symmetry of the fiducial marker.