Axial and horizontal registration guided speckle suppression in single-line HD mode for retinal optical coherence tomography images

Abstract

We propose an image registration method to suppress the speckle noise in retinal optical coherence tomography(OCT) adapted to single-line HD mode hardware implementation. In single-line HD mode, multiple cross-section images at the same straight scan line are obtained repeatedly and rapidly for averaging the speckle noise. Not like static objects, cross-section retinal images are often blurred by direct averaging due to unintentional eye/head motions in axial and horizontal directions. An image registration method which combines regularized dynamic programming algorithm with hill-climbing algorithm is demonstrated to correct axial and lateral motion shifts efficiently. The unaligned images are discarded automatically using a criterion based on probability densities of image gray levels. Finally, an adaptive gamma correction method is adopted to adjust the contrast of averaged OCT image for better retinal feature visualization. The experimental results of the algorithm based on our lab-built OCT setup show the improvement of image quality. The method is automatic and rapid which is potential to be applied in the OCT imaging with micro-motion targets.