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W. Gao, D. Cabrera DeBuc; Evaluating the Effect of Speckle Denoising on the Estimation of Optical Properties of Intraretinal Layers Using Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1396.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the effect of speckle denoising on the estimation of optical properties of intraretinal layers using Optical Coherence Tomography.
Speckle- free test Stratus OCT images from normal and pathological eyes were obtained after applying median filtering. Experiments were conducted on the OCT test images at 5%, 10% and 15% Gaussian additive noise level after applying a nonlinear complex diffusion filter. Automatic layer segmentation (RNFL, GCL+IPL, INL, OPL, ONL, IS/OS and RPE) was performed using a custom-built algorithm. The lateral coordinates and the diameters of the blood vessel shadows were first extracted in each OCT image by using the technique of blood vessel shadowgram. Relative light-backscattering and scattering coefficients of two particular layers characterized by low (ONL) and high light-backscatter ( ISOS) were calculated. The scattering coefficients were calculated using a finite difference method. For quantitative evaluation, we used the signal-to-mean square error ratio (S/MSE) and ratio measurements fo the scattering coefficients.
Our results showed a S/MSE improvement of 3%, 8% and 21% after applying the complex diffusion filter to the free-speckle test images with 5%(In5F), 10%(In10F) and 15%(In15F) Gaussian additive noise, respectively. The scattering coefficients for healthy and pathological eyes decreased when the noise level was increased from 5 to 15% for the low scattering structure (ONL). However, the scattering coefficients for the high scattering structure (ISOS) increased when a 15% noise level was added:
Our results suggets that the estimation of scattering coefficients is more affected as the noise level increases. The extracted scattering coefficients from OCT images could be useful not only for the identification of pathological changes in retinal tissue but also for therapeutic purposes. However, further experiments are needed to study the suppression of the speckle noise for accurate measurements of backscattering signal and scattering coefficient with the OCT technique.
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