OCT-based angiography (OCTA) enables imaging of retinal microvasculature. However, involuntary movements of subjects prevent obtaining microvasculature with a large field of view (FOV) with high-dense spatial sampling. Meanwhile, a short duration for blood flow detection results in unstable vasculature contrast. By combining a Lissajous scan and a slow shift, Lissajous OCT enables compensating eye movements, and then the FOV will be extended while the spatial sampling density is preserved by the slow shift. The Lissajous scan allows a long blood flow detection duration. In vivo human eye microvasculature imaging using the convolutional Lissajous OCTA is investigated with several disease eyes.
Degree of polarization uniformity (DOPU) provides promising biomarkers of abnormalities in the retinal pigment epithelium (RPE) and is obtained by polarization-sensitive optical coherence tomography (OCT), which is not commercially available. A U-Net shape model was used to synthesize retinal DOPU from OCT with OCT angiography (OCTA) images. Sets of OCT, OCTA, and DOPU images from 175 subjects, 107 subjects, and 30 subjects were used for training, validation, and evaluation, respectively. RPE abnormalities were compared between True DOPU and synthesized DOPU. Healthy structure, RPE elevation, and RPE thickening were synthesized with high recall and precision. However, further improvements are required for RPE defect and hyperreflective retina foci synthesizing.
We propose a long-term stable model eye with three-layered retinal phantom. The layers are made of fluorosilicone which refractive index is 1.38 and includes fine particles of TiO2 or polystyrene. The particle mixing amount is determined with respect to haze for each layer to achieve OCT images resemble to those of human retina. Stable liquid of fluorinated oil is filled in vitreous-mimic cavity. In addition, high-temperature durability test indicates that the model eye has high stability for more than six years. We have successfully obtained OCT images of the model eye, which are comparable to those of human eyes.
In this research, we demonstrated a CNN-based DOPU estimation algorithm without polarization-sensitive OCT signals. The CNN was trained with pairs of retinal OCT (input) and DOPU (teaching) images. The recall and precision of RPE abnormal appearances between true DOPU and synthesized DOPU of pathological eyes were calculated. For normal eyes, the grader evaluated the soundness of the RPE appearance for true DOPU and synthesized DOPU. The recalls are relatively good (0.74-0.95), while the precisions highly depend on the types of abnormalities (0.37-0.98). Five RPE abnormalities are found in synthesized DOPU within 25 synthesized DOPU B-scans while there is no abnormality in the true DOPU.
KEYWORDS: Optical coherence tomography, 3D image processing, Retinal scanning, Motion estimation, 3D image reconstruction, Tissues, Retina, Range imaging, Prototyping, In vivo imaging
Three-dimensional motion-free imaging of retinal diseases is investigated. The Lissajous scan with the 3-mm scan width is repeated during the gradually shifting center of the scanning pattern. The lateral and axial motion amounts are estimated by using image correlation of OCT and OCTA en face images and the OCT intensity cross-sections, respectively. It results in an imaging area of 6.8 mm or more in diameter. Several eyes with retinal diseases have been scanned. The three-dimensional OCT images are well reconstructed without significant motion artifacts. Although some eyes exhibit severe eye motion, the three-dimensional structure of the retina is well reconstructed.
Increasing the field of view (FOV) of optical coherence tomography (OCT) for the high-resolution posterior eye imaging with a continuous scan is demonstrated. The combination of a Lissajous trajectory, which is designed for high-resolution imaging, and a slow drift was applied to scan the probing beam. The FOV is increased as the slow drift progresses. The motion artifacts are suppressed by motion estimation and correction in post-processing. The high-resolution, motion-free OCT and OCT angiography imaging with a FOV of over 6.75 mm is achieved.
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.
Optical coherence tomography (OCT) reveals the depth-resolved structure of the posterior eye non-invasively. However, artifacts caused by involuntary eye movement is one of the largest problems. Recently, we have demonstrated a motionartifact- free, high-resolution imaging technique based on Lissajous scanning pattern and advanced motion correction algorithm. Although this method works to a certain degree, the residual artifacts are still problematic for clinical applications.
In this study, we demonstrate the improvement of motion correction for en-face OCT imaging. The OCT signals are acquired with a Lissajous scanning pattern which has been modified from a standard Lissajous scan to enable OCT angiography (OCT-A) imaging. The lateral motion is estimated from several en-face images of OCT and OCT-A by using a motion estimation algorithm. Some diseased eyes exhibit abnormal patterns in OCT en-face images. Simultaneously using these images will enhance the motion estimation and will improve the motion correction at these abnormal regions. Motion-free imaging for retinal diseases is demonstrated.
Jones matrix optical coherence tomography (JM-OCT) is a functional extension of OCT. However, the clinical utility of JM-OCT is not widely accepted. Because of its hardware complexity and poorly established methods for clinical interpretation.
In this study, we propose the approaches to solve the above-mentioned problems. To reduce the hardware complexity, we employ encapsulated passive polarization delay module (PPD) and encapsulated polarization diversity detection module (PDD), and develop full-function JM-OCT and simplified JM-OCT. In addition, we developed a pixel wise segmentation method for JM-OCT.
The full-function JM-OCT which uses both PDD and PPD measures OCT, OCT angiography (OCTA), degree-of-polarization-uniformity (DOPU) and birefringence. The simplified JM-OCT which uses only PDD measures OCT, OCTA, and DOPU but not birefringence. In both JM-OCT systems, all the optical components are packed in a standard-sized retinal scanner.
A pixel-wise segmentation method for retinal pigment epithelium (RPE) and choroidal stroma exploits multiple types of images obtained by the JM-OCT. Attenuation coefficient, OCTA, and DOPU are combined to synthesize a new artificial contrast. By applying a simple threshold to it, the target tissue is segmented. After segmenting the RPE, an en face “melano-layer thickness map” is created.
A Normal subject and a pigment epithelial detachment (PED) subject are obtained by full-function JM-OCT and simplified JM-OCT. In PED subject, thickened RPE, hyper-reflective foci, and damaged RPE are correctly detected by RPE segmentation. In addition, created melano-layer thickness map has similar patterns to infrared fundus autofluorescence (NIR-AF), and it can contribute further interpretation of the NIR-AF.
TERS has emerged over the past decade as a powerful tool for Raman spectroscopy that shows high sensitivity and capability of nano-scale imaging with high spatial resolution. TERS utilizes a metallic nano-tip, which confines and enhances the propagating light into near-field in the close vicinity of the apex. Besides the nano-scale spatial resolution, polarization analysis in TERS is of tremendous advantage, as it allows one to study highly directional intrinsic properties of a sample at the nanoscale. In this study, we have developed a method to analyze the polarization of near-field light in TERS from the scattering pattern produced by the induced dipole in the metallic tip. Under dipole approximation, we measured the image of the dipole at a plane away from the focal plane, where the information about the direction of the dipole oscillation was intact. The direction of the dipole oscillation was determined from the defocused pattern, and then the polarization of near-field light was evaluated from the oscillation direction by calculating the intensity distribution of near-field light We used those evaluated tips to measure nano-images from single-walled carbon nanotubes and confirmed that the contrast of the TERS image depended on the oscillation direction of the dipole, which were also found in excellent agreement with the calculated TERS images, verifying that the polarization of the near-field was quantitatively estimated by our technique.
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