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.
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.
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.
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.