Quantitative analysis of cerebral images using an elastically deformable atlas: theory and validation

A method of anatomical localization by elastically deforming a three-dimensional atlas to match the anatomic brain image volume of a subject is described. The anatomic atlas is modeled as an elastic object and the matching process is formulated as a minimization of the cost function, cost equals cost(deformation) - cost(similarity). The system uses a multiresolution deformation scheme to accelerate and improve the convergence of the matching process. To validate the system, six deformed versions of an atlas were generated. The atlas was then matched to its deformed versions. The accuracy of the matches was evaluated by determining the correspondence of several cortical and subcortical regions. The system on average matched the centroid of a region to within 1 mm of its true position and fit a region to within 11% of its true volume. The mean overlap between the matched and true regions, defined by the ratio between the volume of their intersection and the volume of their union, was 66% ((sigma) equals 16%). Each match was performed three times and the results in all six cases were reproducible. The results of the preliminary validation of the elastic matching technique are promising and show that the method can account for local shape differences in brain anatomy.