![]() For approximately >10 scattering particle the amplitude distribution for the linear representation of the OCT signal is assumed to follow a Rayleigh distribution 14. For samples with randomly positioned identical scattering particles within the sampling, or coherence volume V C defined below, the backscattered field phases are uniformly and randomly distributed between 0 and 2π 13. As a first step towards modelling the amplitude distribution from actual tissue, we start with an analysis of discrete random media (DRM). The amplitude distribution can also be fitted with a probability distribution function, from which the function shape parameters can be obtained. From the amplitude distribution, values for the mean, the standard deviation (σ), the variance (σ 2) and the contrast (c = σ/) can be calculated. Speckle, which from now on we will refer to as the OCT amplitude distribution, can be studied by analyzing the distribution of the amplitude values of a region of interest (ROI) in the OCT image. Here, we will focus on the characterization of static speckle as a measure for structural tissue properties. in flow channels or blood vessels) have been the focus of a large number of studies, in which flow information is usually obtained by quantifying the speckle de- or auto-correlation between successive scans of a fixed tissue location 11, 12. Hence, speckle contains information on the scattering particles that are in general smaller than the OCT resolution of approximately 5–20 µm. Speckle in OCT is the voxel-to-voxel fluctuation of the OCT amplitude caused by phase differences of the backscattered field due to the spatial distribution of the scattering particles in the sample 10. In addition to the amplitude and the attenuation coefficient, studies suggest that statistical measures of the speckle pattern in OCT images can be quantified as additional parameters to derive sub-resolution structural tissue properties, and potentially provide for a tool for tissue characterization in the clinic 8, 9. By carefully taking into account system parameters such as confocal point spread function and sensitivity roll-off, and the effects multiple scattering, we arrived at values for sample optical properties: backscattering coefficient ( µ b,NA) and scattering coefficient ( µ s) 7. In our previous work we proposed and validated a reliable approach to obtain the amplitude and attenuation coefficient from OCT data. ![]() Optical coherence tomography (OCT) is a technique which allows for measurement of tissue optical properties in a spatially confined region, corresponding to the OCT resolution OCT-signal parameters amplitude and attenuation are determined as a measure for sample optical properties. Yet, the relation between structural properties and optical properties is less understood. Therefore, clinical studies aim to quantify tissue optical properties for the purpose of tissue characterization 1, 2, 3, 4, 5, 6. As these changes will alter the interaction of light with the tissue, their quantification employing optical techniques could enable minimally-invasive detection, early-stage diagnosis, and monitoring of disease progression and treatment. Experimentally determined and theoretically calculated optical properties are compared and in good agreement.Ĭhanges in the structural properties of tissue, such as the size and organization of cells and cellular components, are important indicators of disease development and progression. We show that the OCT amplitude variance is sensitive to sub-resolution changes in size and organization of the scattering particles. We assume fully developed speckle and verify the validity of this assumption by experiments on controlled samples of silica microspheres suspended in water. Starting the calculations from the size and organization of the scattering particles, we analytically find expressions for the OCT amplitude mean, amplitude variance, the backscattering coefficient and the scattering coefficient. As a first step, we present a theoretical description of OCT speckle, relating the OCT amplitude variance to size and organization for samples of discrete random media (DRM). ![]() However, a rigorous theoretical framework relating OCT speckle statistics to structural tissue properties has yet to be developed. Speckle statistics could therefore be utilized in the characterization of biological tissues. Speckle, amplitude fluctuations in optical coherence tomography (OCT) images, contains information on sub-resolution structural properties of the imaged sample.
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