Previous studies in optoretinography often rely on AO-OCT systems to resolve individual cells or use intensity-based image processing to extract the dynamics of the retinal layer as an ensemble. For non-AO point-scan OCT, investigating tissue dynamics from obscure speckle patterns while preserving the spatial heterogeneity of signals remains challenging. Here, we developed phase-restoring subpixel image registration and unsupervised machine learning algorithms to accurately extract spatially-resolved OCT phase signals from the outer retina in rodents. In addition to observing light-evoked deformation of the photoreceptors outer segments, we discovered an optical signature of the retinal pigment epithelium (RPE) response to visual stimuli.
In-vivo imaging of the light-evoked responses of retinal cells in rodents can provide valuable insights into the correlation between optoretinography (ORG) signals and retinal degeneration. However, interpreting outer retina dynamics in rodents is challenging due to the limited resolution of optical coherence tomography, which often results in the superposition of outer retinal layers, such as the rod outer segment (ROS), retinal pigment epithelium (RPE), and Bruch’s membrane, within speckle patterns. Here, we present an automated, unbiased approach for extracting spatially-resolved outer retinal dynamics from complicated speckle patterns. Using this approach, we revealed the light-evoked dynamics of both ROS and RPE in rodents.
Small animals, such as rodents, are attractive options for investigating the intrinsic process of retinal degeneration. In this study, we used phase-sensitive optical coherence tomography to explore the comprehensive dynamics of rats’ outer retinas in response to visual stimuli. By calculating the temporal phase difference between different outer retinal bands, we revealed highly reproducible retinal dynamics, on the order of tens of nanometers, related to different parts of the outer retina. Our approach may pave the way for preclinical optoretinography study in small animals, facilitating clinical translations for the early detection of neurodegenerative diseases.
Recently, there has been vast interest in probing photoreceptor dynamics using optical coherence tomography (OCT). Most successful demonstrations implemented adaptive optics or digital adaptive optics to resolve individual cones or rods in human subjects. Here we use phase information to trace the photoreceptor response in rodents using an ultrahigh-resolution, phase-sensitive, spectral-domain OCT. Brown Norway rats (six to 14 weeks) were sedated using a ketamine and xylazine cocktail. Repeated scans were registered by a phase-restoring subpixel motion correction algorithm to isolate the bulk motion, and two hyperreflective bands (inner segment/outer segment junction – IS/OS; outer segment tip + retinal pigment epithelium + Bruch's membrane) were segmented automatically. As a result, two types of nanoscale signals (biphasic Type-I and monophasic Type-II) were detected with a clear separation in depth. We tested the repeatability, scotopic stimulus strength dependency, and photopic background intensity dependency. Besides, we demonstrated enface mapping of the ORG signals in a wide field of 20°, analogous to the multifocal electroretinogram but with a much higher resolution, revealing the spatial distribution of the outer retina function. This method could be extended to study animal models with photoreceptor degeneration and clinical studies to investigate early photoreceptor dysfunction with high spatiotemporal resolution.
KEYWORDS: Image registration, Optical coherence tomography, Image segmentation, Visualization, Tissues, Speckle pattern, Signal detection, Motion models, In vivo imaging, Image processing algorithms and systems
Phase-sensitive OCT can be used for imaging the photoreceptor deformations in response to the light stimulus or optoretinography (ORG). Here, we propose a phase-restoring subpixel image registration method and an automated signal extraction algorithm for optoretinography using phase-sensitive OCTs. We validated these methods in simulations, phantom experiments, and in-vivo optoretinogram imaging. Our image registration method yields better amplitude stability and higher phase accuracy compared with conventional approaches, and we found two types of signals (one monophasic and the other biphasic) simultaneously in rodent ORG imaging. These results can be beneficial to the ongoing preclinical/clinical ORG studies.
KEYWORDS: Optical coherence tomography, In vivo imaging, Adaptive optics, Signal detection, Optical signal processing, Human subjects, Head, Animal model studies
In recent years, there have been vast interests in probing photoreceptor dynamics using optical coherence tomography (OCT). Most of the successful demonstrations implemented adaptive optics or digital adaptive optics to resolve individual cones or rods in human subjects. Here we use phase information to trace the photoreceptor response in rodents using an ultrahigh-resolution, phase-sensitive, spectral-domain OCT. As a result, two types of nanoscale signals (monophasic and biphasic) were detected with a clear separation in depth. The monophasic signal is less susceptible to stimulus intensity and saturated from a 3% breach rate.
Phase-sensitive optical coherence tomography (OCT) enables label-free imaging of structural dynamics with nanoscopic sensitivity. However, the inevitable bulk tissue motions degrade the signal stability and introduce extra phase error. To suppress the motion-induced phase error, we propose a phase-restoring subpixel motion correction method for post-hoc motion correction in Fourier domain OCT, which enables translational shifts of complex-valued OCT images by arbitrary distance. Phantom and in-vivo rodent optoretinogram imaging experiments were conducted to demonstrate the advantages of the proposed method over conventional pixel-level method and the Fourier transform based method.
We investigated the correlation of the blood optical attenuation coefficient (OAC) and the blood glucose concentration (BGC). The blood OAC was measured in mouse retina in vivo through OCT angiography (OCTA). The arteries and veins presented a blood OAC change of ~0.05-0.07 mm-1 per 10 mg/dl and a significant elevation of blood OAC in diabetic mice was observed. Besides, the veins had a higher correlation coefficient between the measured blood OAC and BGC than that of the arteries. The blood OAC-BGC correlation suggests a concept of non-invasive OCTA-based glucometry, allowing a fast assessment of the blood glucose of specific vessels.
Complex decorrelation-based OCT angiography (OCTA) has the potential for quantitively monitoring hemodynamic activities. To improve the dynamic range and uncertainty for quantification, an adaptive spatial-temporal (ST) kernel was proposed. The ensemble size in decorrelation computation was enlarged by collecting samples in the spatial/ temporal dimensions. The spatial sub-kernel size was adaptively changed to suppress the bulk motion influence by solving a maximum entropy model. The improvement of dynamic range and uncertainty were validated by theoretical analyzation, numerical simulation, and in vitro/ in vivo experiments. Furthermore, proved by the in vivo experiments, the adaptive ST-kernel can also improve the separability between different stimuli and allow a reliable temporal analysis of the hemodynamic response.
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