Continuous monitoring of retinal pigment epithelium (RPE) cell growth and functionality is imperative in both pre- and post- RPE transplantation phases. We propose a telecentric add-on scan lens design that is integrated with the probe arm of a polarization-sensitive optical coherence tomography (PS-OCT) system for in vitro retinal organoid imaging. The system can be switched to in vivo or in vitro imaging mode depending on the requirement. In the context of retinal imaging, the polarization information of the RPE layer and other layers, along with their conventional morphology, can be effectively contrasted using the in vivo mode. The add-on lens attachment enables a wide field of view retinal organoid growth monitoring and its functionality visualization. It includes a field flattener to compensate for field curvature. The comprehensive PS-OCT system provides a 12 mm x 12 mm field of view on the retina and can cover up to 15 mm x 15 mm on retinal organoids. The system successfully images young and mature retinal organoids, capturing well-defined layered structures and highly pigmented outer RPE boundaries using polarimetric entropy contrast. Intensity based segmentation on the cross-section image of retinal organoid is performed to retrieve the thickness heatmap which provides the insight of organoids’ growth statistics.
We used multi-contrast OCT (MC-OCT), which is capable of the simultaneous measurement of OCT angiography, degree of polarization uniformity and intensity OCT, to evaluate retinal pigment epithelium (RPE) changes. MC-OCT system was operated at an axial scan speed of 100,000 A-scans/s, using a swept-source laser at a central wavelength of 1,048 nm. From the dataset of MC-OCT, a pixel-wise segmentation method for RPE-melanin was developed and used to create RPE-melanin-specific contrast images to evaluate RPE-melanin changes. The RPE-melanin cross-sectional images were generated to evaluate the depth-resolved distribution of RPE-melanin. RPE-melanin thickness maps were created by counting the number of pixels with RPE-melanin at each A-line in the 3D dataset. An RPE-melanin thickness map represents the en face distribution of the thickness of RPE-melanin. We evaluated 37 eyes with age-related macular degeneration (AMD) with serous retinal pigment epithelium detachment, and 24 eyes with chronic Vogt-Koyanagi- Harada (VKH) disease. In these cases, RPE-melanin thickness maps showed similarities to the near infrared autofluorescence (NIR-AF; excitation 780 nm) images. In the eyes with AMD, focal RPE damages could be readily detected with RPE-melanin thickness map. RPE-melanin cross-sectional images were more sensitive for the damage at RPE-Bruch’s membrane band than intensity OCT images. In the eyes with VKH disease, RPE-melanin-specific contrast images clearly showed focal RPE-melanin accumulation at granular hyper NIR-AF lesions. In conclusion, this study demonstrated the clinical usefulness of RPE-melanin specific contrast OCT imaging for evaluating RPE changes in retinal diseases.
Fiber-based polarization-sensitive optical coherence tomography (PS-OCT) can measure cumulative Jones matrix that includes both the fiber-optic components of the interferometer and the sample. To derive a relative optic axis of the sample, a relative angle of the eigenpolarizations is often calculated on the Poincaré sphere. Here, we suggest a new approach using Jones formalism. This method is demonstrated for optic axis imaging of the inner retina and sclera in the posterior eye segment using PS-OCT with parallel detection of Jones-matrix elements.
We evaluated intraretinal RPE migration in AMD using multimodal imaging including polarimetric images. Depolarized
light images were computed using a PS-SLO. M-DOPU was calculated using multifunctional Jones-matrix OCT. RPE
migration was detected in 59 of 155 eyes. Focal similarities could be confirmed among en-face projection images of
minimum M-DOPU, depolarized light images, and NIR-AF images.
Polarization sensitive optical coherence tomography (PS-OCT) is a functional extension of OCT that contrasts the polarization properties of tissues. It has been applied to ophthalmology, cardiology, etc. Proper quantitative imaging is required for a widespread clinical utility. However, the conventional method of averaging to improve the signal to noise ratio (SNR) and the contrast of the phase retardation (or birefringence) images introduce a noise bias offset from the true value. This bias reduces the effectiveness of birefringence contrast for a quantitative study. Although coherent averaging of Jones matrix tomography has been widely utilized and has improved the image quality, the fundamental limitation of nonlinear dependency of phase retardation and birefringence to the SNR was not overcome. So the birefringence obtained by PS-OCT was still not accurate for a quantitative imaging.
The nonlinear effect of SNR to phase retardation and birefringence measurement was previously formulated in detail for a Jones matrix OCT (JM-OCT) [1]. Based on this, we had developed a maximum a-posteriori (MAP) estimator and quantitative birefringence imaging was demonstrated [2]. However, this first version of estimator had a theoretical shortcoming. It did not take into account the stochastic nature of SNR of OCT signal.
In this paper, we present an improved version of the MAP estimator which takes into account the stochastic property of SNR. This estimator uses a probability distribution function (PDF) of true local retardation, which is proportional to birefringence, under a specific set of measurements of the birefringence and SNR. The PDF was pre-computed by a Monte-Carlo (MC) simulation based on the mathematical model of JM-OCT before the measurement. A comparison between this new MAP estimator, our previous MAP estimator [2], and the standard mean estimator is presented. The comparisons are performed both by numerical simulation and in vivo measurements of anterior and posterior eye segment as well as in skin imaging. The new estimator shows superior performance and also shows clearer image contrast.
Quantitative evaluation of optical properties of choroid and sclera are performed by multifunctional optical coherence
tomography. Five normal eyes, five glaucoma eyes and one choroidal atrophy eye are examined. The refractive error was
found to be correlated with choroidal birefringence, polarization uniformity, and flow in addition to scleral birefringence
among normal eyes. The significant differences were observed between the normal and the glaucoma eyes, as for
choroidal polarization uniformity, flow and scleral birefringence. An automatic segmentation algorithm of retinal
pigment epithelium and chorioscleral interface based on multifunctional signals is also presented.
Optical coherence tomography (OCT) visualizes cross-sectional microstructures of biological tissues. Recent
developments of multifunctional OCT (MF-OCT) provides multiple optical contrasts which can reveal currently unknown
tissue properties. In this contribution we demonstrate multifunctional OCT specially designed for dermatological
investigation. And by utilizing it to measure four different body parts of in vivo human skin, three-dimensional scattering
OCT, OCT angiography, polarization uniformity tomography, and local birefringence tomography images were obtained
by a single scan. They respectively contrast the structure and morphology, vasculature, melanin content and collagen traits
of the tissue.
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