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

Use of a Biocompatible Fiducial Marker in Evaluating the Accuracy of CT Image Registration R. E. Ellis? S. Toksvig-Larseny M. Marcacciz D. Caramella M. Faddaz ? Department of Computing and Information Science Queen's University at Kingston, Ontario, Canada y Department of Orthop dic Surgery University Hospital, Lund, Sweden z Biomechanics Laboratory Rizzoli Orthop dics Institute, Bologna, Italy Department of Radiology University of Pisa, Pisa, Italy Abstract In order to numerically assess registration procedures, comparisons must be made to a reliable common metrological standard. One such standard is a ducial marker that can be found in all measuring modalities that are used in the registration. In a study of reliability and accuracy, we show that small markers used in Roentgen Stereogrammetric Analysis (RSA) can be located in a Computed Tomography (CT) scan and can also be located physically by a pointing device. The CT processing is unusual because the markers are smaller than a single slice; however, the beam spread of a CT machine permits interpolation of the centers of the markers in three dimensions. For foam-bone phantoms, the ducial markers can be used to register CT and RSA data to within 0.15 mm RMS error. The CT scans can then be registered to the pointer data to within 0.25 mm RMS error. This is a basic technology that can be used to assess various registration methods, especially those in computer-assisted surgery or other image-guided procedures.