Speckle images of the vessels and hydrodynamic phantoms in optical coherence tomography

The results of a study of a series of sequential images of a vessel and a hydrodynamic phantom of biological tissues obtained using a Spectral Domain Optical Coherence Tomography (SP OCT) are presented. Acquired data were processed and histograms of speckle distributions were created. They demonstrated differences in the intensity distribution for three different areas of the OCT image: (1) free space, (2) wall of the vessel, and (3) the flow of scatterers. Using an optimization algorithm the histograms were approximated by various distribution functions, best result was demonstrated by the beta distribution with the determination coefficient R2 ~ 0.95. The resulting distributions quantitatively demonstrate effect of tissue heterogeneity. They show significant differences in the values of the shape and scale parameters, corresponding to the obtained beta distribution parameters, which were α ~ 1.7, β ~ 20.5 for free space, α ~ 3.1, β ~ 5.5 for the wall region of the phantom, α ~ 2.6, β ~ 1.7 for the flow of the scattering liquid. Variance matrices of the OCT images, which show correlation of speckles between adjacent pixels and those of the successive images were also obtained. Brighter areas of the variance matrix indicate a dynamic speckle structure in OCT images, while low brightness of the areas indicates static speckle structure, on the contrary.