Use of a Biocompatible Fiducial Marker in Evaluating the Accuracy of CT Image Registration

Rationale and Objectives. Accurate registration of Computed Tomography images to the patient is crucial for computer-assisted surgery. Markers used in Roentgen Stereogrammetric Analysis can be located in a CT scan using a novel approach, and can also be located physically. RSA data act as ”ground truth” for the 3D marker locations. Methods. Two foam-bone phantoms were marked. The markers were scanned 7 times with RSA, 3 times with axial CT, and contacted 4 times with a coordinate measuring arm. Root-mean-square errors were derived for the registrations. Results. CT and RSA data register to 0.15 mm RMS error. CT and arm data register to 0.25 mm. The markers are biocompatible, and the coordinate measuring arm is usable in an operating room. Conclusions. Typical in vitro registration errors are about 2 mm. We have developed a marker that provides superior registration, and a procedure that can be used for in vivo studies.