A new registration algorithm for estimating and discriminating average shapes of sets of corneal topographies.

In this study we present a method to build 3D corneal atlases of different populations using a registration step based on inter-surface volume minimization. First the construction method is presented. It is based on a global factor computation in order to minimize the volume between several surfaces. Then the significance of the choice of the matching step is shown with the comparison of two atlases expected to be nearly identical: male vs. female corneas. Finally two atlases are presented and compared, for two different populations: right myopic and hyperopic eyes. Our study demonstrates that the matching step is crucial to correctly compare two surfaces, and shows two clinical applications of this method.

Quantitative in vivo MRI measurement of cortical development in the fetus.

Normal brain development is associated with expansion and folding of the cerebral cortex following a highly orchestrated sequence of gyral-sulcal formation. Although several studies have described the evolution of cerebral cortical development ex vivo or ex utero, to date, very few studies have characterized and quantified the gyrification process for the in vivo fetal brain. Recent advances in fetal magnetic resonance imaging and post-processing computational methods are providing new insights into fetal brain maturation in vivo. In this study, we investigate the in vivo fetal cortical folding pattern in healthy fetuses between 25 and 35 weeks gestational age using 3-D reconstructed fetal cortical surfaces. We describe the in vivo fetal gyrification process using a robust feature extraction algorithm applied directly on the cortical surface, providing an explicit delineation of the sulcal pattern during fetal brain development. We also delineate cortical surface measures, including surface area and gyrification index. Our data support an exuberant third trimester gyrification process and suggest a non-linear evolution of sulcal development. The availability of normative indices of cerebral cortical developing in the living fetus may provide critical insights on the timing and progression of impaired cerebral development in the high-risk fetus.

Contour detection of the cornea from OCT radial images.

In this paper, we present a new approach for contour detection in the frame of OCT images of the cornea. With the aim of detecting upper and lower curves that define the cornea in radial slices, we have elaborated a three step specific method. The first step consists in finding epithelium and endothelium points (we call them anchor points). Then the image is preprocessed to enhance the contrast and to reduce speckle. In the final step both anchor points are used as starting points for the algorithm: we trace the contour of the cornea pixel by pixel from these two points with a weight criterion. Taking into account geometrical knowledge of the cornea enhances the robustness of the technique. We validate our approach on a bank of scans including low quality images.