Calibrating intensity values of optical coherence tomography (OCT) images helps to extract valuable tissue information, such as the attenuation coefficient. To achieve this, knowledge of focus position and Rayleigh length is crucial. We study the potential of obtaining the focus position from an OCT scan acquired with a single focus setting using the system’s longitudinal chromatic aberration. Different focus positions for sub-spectrum reconstructed OCT images are realized by taking advantage of the chromatic focal shift. Ratios of these sub-spectral images are used to estimate the focus position. High-resolution B-scan reconstruction is demonstrated by coherently combining sub-spectrum confocal function corrected B-scans, followed by OCT attenuation coefficient imaging. Additionally, we present an approach to experimentally identify the chromatic focal shift from OCT data itself.
The accurate measurement of blood hematocrit levels in ocular vessels holds significant clinical value by saving time, minimizing discomfort, and reducing the use of single-use cuvettes, which generates significant biohazardous waste. We present a novel approach for non-invasive measurement of blood hematocrit levels in retinal vasculature using a modified full-field fundus imaging system centered around two isosbestic wavelengths. To aid in the selection of bandpass filters, we developed a detailed Monte-Carlo simulation of our imaging system applied to retinal vasculature. We also present this model as a tool to analyze the images coming from the Fundus camera, which helps us understand what tissue and system parameters affect our in-vivo measurements. We present the analysis methods employed for data from a clinical trial data and demonstrate the trends between the optical densities of the collected images and our Monte Carlo simulations.
With the growing demand for vital signs monitoring using wearables, there is a gap between what is offered and the desire for clinical accuracy. Advancements in electronic miniaturization, materials and signal processing have increased possibilities for wearable technology. Optical sensing using photoplethysmography (PPG) is prominent within the field of wearable healthcare due to the non-invasive and versatile nature of the modality. Different aspects related to cardiovascular health can be screened and monitored with PPG, such as oxygen saturation (SPO2), heart rate (HR), heart rate variability (HRV) and possibly blood pressure. Although the principles and possibilities for vital sign monitoring with PPG are present, there is only sparse evidence of clinically relevant signals from commercial optical sensors. Furthermore, there is still a big challenge regarding motion artifact within a wearable device. Currently three wavelengths are commonly used within commercial wearables; green (550nm), red (660nm) and infrared (850nm). There is increased research on including shorter wavelengths (blue) potentially providing increased robustness to motion artifacts during wear.
Within this study, the design challenges for a universal wearable optic patch for improved signal accuracy were investigated. A dual-photodiode and multi-wavelength flexible wearable optic patch was fabricated using hybrid printed electronics. The design was evaluated as a function of patch-skin contact pressure during motion. Our preliminary results show a more robust PPG signal with increased patch-skin contact pressure. In addition, this study demonstrates the capability of our wearable and flexible optical patch at measuring simultaneous multi-wavelength PPG.
Polarization-sensitive optical coherence tomography (PS-OCT) is used to investigate changes in fiber structures in the eyes of myopia, wet age-related macular degeneration (wAMD), and glaucoma patients. A depth-multiplexed fiber-based PS-OCT system is used to extract local optic axis orientations of birefringent structures in the eye locally in 3D in vivo. For healthy volunteers, birefringent structures include the retinal nerves, Henle’s fiber layer, and sclera. Scleral collagen architecture is observed to be altered in myopia patients. In wAMD patients fibrosis orientation and volume can be extracted using this technique.
We present experimental results using ex-vivo human blood in a setup built to mimic the scattering and flow properties of retinal vasculature. This system controls sources of imaging variability to assist with extracting the core physical principles required to better understand in-vivo OCT, doppler OCT, and SLO data. The setup consists of a flow system which is able to manipulate the blood oxygenation level/flow velocity and interchangeable silicone-elastomer capillaries which acts as an optical window to the flow medium. Here, we reproduce the well-known hour-glass profile in an OCT B-scan cross-section of our phantom capillary, typically seen in small-diameter vasculature.
We present a new experimental setup specialized in creating retinal models with real human blood flow that controls or measure many sources of imaging variability. This will assist with extracting the core physical principles required to better understand in-vivo OCT, doppler OCT, and spectroscopic SLO data, to build better retinal imaging devices.
Our setup consists of two components, developed simultaneously. The first component is a flow system with the calibration methods needed to drive human whole blood through a closed-loop system. Controls include fluid pressure/flow rate (via pump speed) and the oxygenation level of the blood (via a gas exchange component). This results in a flow characterized by sensors measuring blood oxygenation saturation, temperature, pH, and flow rate through our model eye.
The second setup component is the model eye. We have created silicone elastomer-based phantoms with flow channel diameters matching typical vasculature dimensions of a human retina (50 – 150 µm). These phantoms are embedded in a custom-built housing which mimics the optics of the eye. This makes the flow medium running through the phantom’s capillary easily accessible by any optical measurement technique for analysis. The optical scattering properties of the model eye, as well as phantom geometry, can be manipulated at fabrication to suit the requirements of the experiments being performed, and can be easily interchanged in the flow system.
We present initial results on imaging the flow channel with an intralipid scattering medium and human whole-blood using an optical coherence tomography (OCT) setup built for ophthalmic applications. The goal of this research project is to quantify blood flow velocity from the dynamic OCT speckle patterns seen in sequential flow-channel images (Doppler OCT).
Accurate determination of the attenuation coefficients of retinal structures would allow for quantitative tissue characterization and can be calculated from OCT data. This requires compensating for the system’s confocal function. We present measurement series for extraction of the focal plane and apparent Rayleigh length from the ratios of OCT images acquired through a range of different focus depths. The optimal combination of focus depths is determined for intralipid and titanium oxide phantoms with different scatterer concentrations and the confocal-function-corrected attenuation coefficients are calculated. We further demonstrate good reproducibility in a multi-layered titanium oxide phantom and apply this method to in-vivo retinal data.
The attenuation coefficient can be calculated from OCT data, but accurate determination requires compensating for the confocal function. We present detailed measurement series for extraction of the focal plane and the apparent Rayleigh length from the ratios of OCT images acquired with different focus depths and compare these results with alternative approaches. The optimal focus depth difference is determined for intralipid and titanium oxide phantoms with different scatterer concentrations and the attenuation coefficients corrected for the confocal function are calculated. We further demonstrate good reproducibility of the determined attenuation coefficient of layers with identical scatter concentrations in a multi-layered titanium oxide phantom.
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.