|
A color coded flow mapping method for ophthalmic applications of optical coherence tomography (OCT) is presented. The described algorithm was developed taking into account the specific changes in the interference signal caused by the characteristics of the biological fluid flow through the scanning plane. A key feature of the algorithm is the multistage analysis of fluctuations in the speckle pattern of OCT-images. Speckle pattern is identified by using the color reverse function, convolution, threshold limitation, morphological digital processing, convex hull generation, gradient based processing and image recoding. The interference signal intensity peaks caused by sharp changes of the optical properties at the boundaries of highly scattering layers (the retina has a multilayered structure) are smoothed out for the specklestructures mapping. The correlation coefficients of the same parts of the sequence of structural OCT-images are calculated not for pixel intensities, but for previously identified speckle pattern. The variance values between nonoverlapping parts of the same structural image are calculated also not for pixel intensities, but for previously identified speckle pattern. Absolute flow velocity quantitative evaluation is made by a standard way, i.e. taking into account the time intervals between acquisition moments of the corresponding parts of the interference signal.
|
