Retrospective intermodality registration techniques for images of the head: Surface-based versus volume-based

The primary objective of this slurry is to perform a blinded evaluation of two groups of retrospective image registration techniques, using as a gold standard a prospective marker-based registration method, and to compare the performance of one group with the other. These techniques have already bee n evaluated individually [27], In this paper, however, me End that by group ing the techniques as volume based or surface based, we can make some inter esting conclusions which were not visible in the earlier study, In order to ensure blindness, all retrospective registrations were performed by partic ipants who had no knowledge of the gold-standard results until after their results had been submitted, Image volumes of three modalities: X-ray comput ed tomography (CT), magnetic resonance (MR), and positron emission tomograp hy (PET) were obtained from patients undergoing neurosurgery at Vanderbilt University Medical Center on whom bone-implanted fiducial markers were moun ted.. These volumes had all traces of the markers removed and were provided via the Internet to project collaborators outside Vanderbilt, who then per formed retrospective registrations on the volumes, calculating transformati ons from CT to MR and/or From PET to MR, These investigators communicated t heir transformations, again via the Internet, to Vanderbilt, where the accu racy of each registration was evaluated, In this evaluation, the accuracy i s measured at multiple volumes of interest (VOI's). Our results indicate th at the volume-based techniques in this study tended to give substantially m ore accurate and reliable results than the surface-based ones for the CT-to -MR registration tasks, and slightly more accurate results for the PET-to-M R tasks, Analysis of these results revealed that the rotational component o f error was more pronounced for the surface-based group, It was also appare nt that all of the registration techniques we examined have the potential t o produce satisfactory results much of the time, but that visual inspection is necessary to guard against large errors.