Adaptive spectroscopic visible-light optical coherence tomography for human retinal oximetry

Abstract

Alterations in the retinal oxygen saturation (sO2) and oxygen consumption are associated with nearly all blinding diseases. A technology that can accurately measure retinal sO2 has the potential to improve ophthalmology care significantly. Recently, visible-light optical coherence tomography (vis-OCT) showed great promise for noninvasive, depth-resolved measurement of retinal sO2 as well as ultra-high resolution anatomical imaging. We discovered that spectral contaminants (SC), if not correctly removed, could lead to incorrect vis-OCT sO2 measurements. There are two main types of SCs associated with vis-OCT systems and eye conditions, respectively. Their negative influence on sO2 accuracy is amplified in human eyes due to stringent laser power requirements, eye motions, and varying eye anatomies. We developed an adaptive spectroscopic vis-OCT (Ads-vis-OCT) method to iteratively remove both types of SCs. We validated Ads-vis-OCT in ex vivo bovine blood samples against a blood-gas analyzer. We further validated Ads-vis-OCT in 125 unique retinal vessels from 18 healthy subjects against pulse-oximeter readings, setting the stage for clinical adoption of vis-OCT.

Multiple forward scattering reduces the measured scattering coefficient of blood in visible-light optical coherence tomography

“…We performed leastsquares fitting using Eq. 4 to measure sO 2 using the ratio of the oxygen-dependent coefficients [64] and estimate the SSF. The fitting (R 2 = 0.98) in Fig.…”

“…7 plots experimental vis-OCT measurements of ex vivo blood phantoms. All A-line reconstruction included correction for roll-off and background biases as previously reported [64, 66]. Fig.…”

“…Although there are a handful of ways to extract μ sHbO 2 ( avg ) from this equation, we elected to compute a depth-average of Eq. 11, which we empirically found robust against noise [64]. The starting measurement depth is z 0 and the depth range is Δ z .…”

Green multi-SLED source for high-resolution visible OCT

“…The two integrated combi-2 SLED modules are operated by multi-channel EBD10200 driver boards, allowing individual current control and individual fast on/off modulation of each SLED channel. This means that each SLED channel from 486 nm to 511 nm can be also operated individually, for example for performing spectroscopic OCT measurements [2] or for other imaging modalities. The individual current adjustment of each SLED channel also allows, to some extent, doing some spectral shaping of the combined optical spectrum.…”

“…However, more relevant might be a higher scattering contrast in biological tissue, which means that different types of tissue may show a larger difference in the scattering of light, therefore allowing for a better discrimination of different tissue layers and thus better visualization of microvascular or neural layers in the retina, which may translate into larger clinical benefits for non-invasive OCT imaging [1,2]. VIS-OCT and wavelengths in the range of 500-600 nm may allow for retinal oxygen saturation measurements [1,2] while VIS-OCT with wavelengths slightly below 500 nm may also utilize absorption information of endogenous chromophores, for example macular pigments such as lutein or zeaxanthin [3].…”