This paper introduces an adaptive method that significantly improves visualization quality of reconstructed strains in phase-sensitive optical coherence elastography (OCE). The strain is estimated by finding axial gradients of interframe phase variations and the phase-variation gradients are estimated over a certain scale. The noise level of the so-found strain maps heavily depends on the chosen scale that is used for gradient estimation. Choosing a scale that is too small or too large can degrade the results of elastographic visualization. In real conditions the spatial strain distribution usually is essentially inhomogeneous. Obtaining the best results in different areas of OCT scans requires utilization of different scales, although usually some fixed “compromise” scale over the entire OCT image is used to estimate phase-variation gradients. To improve the quality of strain maps in phase-sensitive OCE, we propose a method of automatic adaptive selection of this scale depending on the level of local strain in the visualized area. The proposed method is elucidated using on both numerically simulated and real OCT scans which are characterized by significant spatial inhomogeneity of strains.
Computer vision approaches have grown exponentially in recent years. Training AI models often requires annotated data. To increase effectiveness of this procedure one can use semi-automatic semantic annotation tools where some simplified approaches (based either on some pretrained models or visible features parameters) are implemented and manually tuned to isolate specific objects. OCT-signals contain information-bearing specific speckle structure and signal attenuation patterns. The parameters of these patterns corresponds to tangible tissue properties (such as scatterers spatial distributions), therefore can be used to construct semi-automatic semantic annotation tools. Using OCT-signal simulation approaches we evaluate the parameters of speckle patterns and attenuation coefficients and propose novel semantic annotation tools for OCT scans. We demonstrate the performance of semi-automatic 3D segmentation and annotation. This tool can be used as a supportive tool for AI applications as well as independent tool for semi-automatic scans segmentations and further characterization.
KEYWORDS: Optical coherence tomography, Monte Carlo methods, Computer simulations, Angiography, Tissues, Spectral models, Signal processing, Aberration correction, 3D modeling, Retina
Computationally efficient realistic spectral model of OCT-scan formation with easily accounted scatterer motions is considered. Its applications related to OCT-beam corrections, optimization of angiographic and elastographic processing are discussed.
Numerical simulations of signal formation in optical coherence tomography (OCT) is a useful tool for understanding and evaluation of the actively developing novel modalities in OCT including, but not limited to elastography, angiography and high-resolution OCT-imaging based on digital refocusing. Numerical simulation of OCT signals allows one to simulate OCT scans using highly controllable parameters characterizing the tissue, e.g., position of the scatterers, their scattering properties, evolution of the scatterer positions (due to straining, Brownian motions or flows). In real or physical phantom experiments sufficiently fine control of these parameters is very complicated or even impossible, therefore the numerical simulations are preferable. We developed a full-wave model for simulations of OCT scans taking into account beam focusing/defocusing and motion of scatterers. This full-wave model can be used for studying OCT signal formation and its analysis in phase-sensitive OCT. Here we present an example of such a computational study of OCT-based angiography with numerical refocusing.
Numerical beam refocusing in OCT is used to increase lateral resolution in the out-of-focus areas for strongly focused beams. However, this approach is based on overlapping lateral scanning in the assumption of the same scatterers positions. In the presence of scatterer motions the numerical refocusing approach can fail. It limit the applicability of the numerical refocusing approach to such based on scatterer motion evaluation modalities as angiography and elastopgraphy. Due to hard controlling phantom experiments we evaluate the influence of motion of scatterers on numerical beam refocusing on the base of numerical simulated OCT scans. The motions of the scatterers are well controlled in the numerical model and its effect on the numerical refocusing approach can be quantified. For this study, a full-wave model for simulating images in spectral-domain optical coherence tomography (OCT) with rigorous accounting for the beam-focusing effects is used.
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