Irregular motion recovery in fluorescein angiograms

Fluorescein angiography is a common procedure in ophthalmic practice, mainly to evaluate vascular retinopathies and choroidopathies from sequences of ocular fundus images. In order to compare the images, a reliable overlying is essential. This paper proposes some methods for the recovery of irregular motion in fluorescein angiograms (FA). The overlying is done by a three step procedure: detection of relevant points, matching points from different images and estimation of the assumed linear geometric transformation. A stochastic model (closely related to the general linear model) allows to fuse the second and third steps, Two different estimators of the geometric transformation are proposed and tested with real FAs. Images from choroido-retinal diseases have been analysed: diabetic retinopathy, vein occlusions and choroidal neovascular membrane. Results have been evaluated using a different number of relevant points with different spatial arrangements. Registration accuracy is evaluated as the mean squared error between real and transformed relevant point locations for those points not used to estimate the transformation. (C) 1997 Elsevier Science B.V.