In this study we present a desktop swept-source optical coherence tomographic angiography (OCTA) system for a diverse range of ophthalmic applications. The system can achieve 500 kHz ultrafast imaging with a 75-degree field of view, assisted by a GPU-accelerated real-time cross-sectional and en face OCT/OCTA acquisition interface, a self-tracking method for motion correction, and an AI-based retinal layer segmentation algorithm. High-resolution and high-sensitivity OCTA images from different retinal disease types are demonstrated.
In this study, we present the development of sensorless adaptive optics swept-source optical coherence tomographic angiography (sAO-SS-OCTA) imaging system for mice. GPU-based real-time OCTA image acquisition and processing software was applied to guide wavefront correction using a deformable mirror. High-resolution OCTA images with high capillary resolution and contrast have been successfully acquired. 45-degree field of view high-resolution montaged OCTA image was also acquired.
In this study, we demonstrate a novel self-tracking method to suppress eye motions on wide-field optical coherence tomography angiography (OCTA) with a high scanning efficiency. GPU-based real-time OCTA image acquisition and processing software was developed to calculate the eye motion artifacts. An instantaneous motion index was introduced to evaluate the strength of motion artifact on en face OCTA images. Areas with suprathreshold motion and eye blinking artifacts can be rescanned in real-time.
Elevated intraocular pressure (IOP) is an important risk factor for glaucoma. However, the role of IOP in glaucoma progression, as well as retinal physiology in general, remains incompletely understood. We demonstrate the use of visible light optical coherence tomography to measure retinal responses to acute IOP elevation in Brown Norway rats. We monitored retinal responses in reflectivity, angiography, blood flow, oxygen saturation (sO2), and oxygen metabolism over a range of IOP from 10 to 100 mmHg. As IOP was elevated, nerve fiber layer reflectivity was found to decrease. Vascular perfusion in the three retinal capillary plexuses remained steady until IOP exceeded 70 mmHg and arterial flow was noted to reverse periodically at high IOPs. However, a significant drop in total retinal blood flow was observed first at 40 mmHg. As IOP increased, the venous sO2 demonstrated a gradual decrease despite steady arterial sO2, which is consistent with increased arterial-venous oxygen extraction across the retinal capillary beds. Calculated total retinal oxygen metabolism was steady, reflecting balanced responses of blood flow and oxygen extraction, until IOP exceeded 40 mmHg, and fell to 0 at 70 and 80 mmHg. Above this, measurements were unattainable. All measurements reverted to baseline when the IOP was returned to 10 mmHg, indicating good recovery following acute pressure challenge. These results demonstrate the ability of this system to monitor retinal oxygen metabolism noninvasively and how it can help us understand retinal responses to elevated IOP.
In this study, we demonstrate a novel scanning pattern for improving flow quantification in optical coherence tomography angiography (OCTA) with a high scanning efficiency. A bidirectional interleaved scan pattern was introduced to adjust the adjacent inter-scan time in order to achieve OCTA sensitivity to different flow speeds. This bidirectional scanning protocol uses a triangular function on the fast scanning direction, meaning that it takes the same time in completing B-scans at adjacent lateral positions, acquired in opposite directions. By applying this scheme, the duty cycle is increased to almost 100%. To improve the linear velocity range represented by OCTA signals, different inter-B-scan intervals (at least two) are required to visualize flow at different speeds. In our scanning protocol, the time between the first and second repetition is different than the time between second and third repetition, allowing a total of 3 different inter-scan times (1-2, 2-3 and 1-3) to be computed to improve flow quantification. A retinal OCTA of a healthy subject was acquired using our 400-kHz swept source OCT system. The volumetric scan was acquired in less than two seconds, potentially minimizing the prevalence of motion artifacts, which are more predominant in the scanning intervals most sensitive to slow speed flow. By averaging the three different images generated by 3 different inter-scan times, flow with large linear range (up to 5.2 mm/sec according to our prior calibration) is apparent on en face OCTA.
Phase wrapping is a crucial issue in Doppler optical coherence tomography (OCT) and restricts its automatic implementation for clinical applications that quantify total retinal blood flow. We propose an automated phase-unwrapping technique that takes advantage of the parabolic profile of blood flow velocity in vessels. Instead of inspecting the phase shift manually, the algorithm calculates the gradient magnitude of the phase shift on the cross-sectional image and automatically detects the presence of phase wrapping. The voxels affected by phase wrapping are corrected according to the determined flow direction adjacent to the vessel walls. We validated this technique in the rodent retina using a prototype visible-light OCT and in the human retina with a commercial infrared OCT system. We believe this signal processing method may well accelerate clinical applications of Doppler OCT in ophthalmology.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.