We present the results of a study on the application of registration and pixel-level fusion techniques to retinal images. The images are of different modalities (color, fluorescein angiogram), different resolutions, and taken at different times (from a few minutes during an angiography examination to several years between two examinations). We propose a new registration method based on global point mapping with blood vessel bifurcations as control points and a search for control point matches that uses local structural information of the retinal network. Three transformation types (similarity, affine, and second-order polynomial) are evaluated on each image pair. Fourteen pixel-level fusion techniques have been tested and classified according to their qualitative and quantitative performance. Four quantitative fusion performance criteria are used to evaluate the gain obtained with the grayscale fusion.

We present a new method to register high and low resolution color images of the retina as well as high resolution angiographies. The registration method is based on global point mapping with blood vessel bifurcations as control points. We also present results of various image fusion algorithms to determine the most appropriate one. Registration and fusion quality assessment is also discussed.

We explore the feasibility of reconstructing some 3D surface information of the human fundus present in a sequence of fluorescein angiograms. The angiograms are taken during the same examination with an uncalibrated camera. The camera is still and we assume that the natural head/eye micro movement is large enough to create the necessary view change for the stereo effect. We test different approaches to calculate the fundamental matrix and the disparity map. A careful medical analysis of the reconstructed 3D information indicates that it represents the 3D distribution of the fluorescein within the eye fundus rather than the 3D retina surface itself because the latter is mainly a translucent medium. Qualitative evaluation is presented and compared with the 3D information perceived with a stereoscope. This preliminary study indicates that this approach could provide a simple way to extract 3D fluorescein information without the use of a stereo image acquisition setup.

Abstract

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