Biology subjects

Miller, D. A.

Publications and source records attributed to Miller, D. A..

3 recordsLinked to original sources

bioRxiv2021

Balanced-detection visible-light optical coherence tomography

Increases in speed and sensitivity enabled rapid clinical adoption of optical coherence tomography (OCT) in ophthalmology. Recently visible-light OCT (vis-OCT) achieved ultrahigh axial resolution, improved tissue contrast, and new functional imaging capabilities, demonstrating the potential to improve clincal care further. However, limited speed and sensitivity caused by the high relative intensity noise (RIN) in supercontinuum lasers impeded the clinical adoption of vis-OCT. To overcome these limitations, we developed balanced-detection vis-OCT (BD-vis-OCT), which uses two calibrated spectrometers to cancel noises common to sample and reference arms, including RIN. We analyzed the RIN to achieve a robust pixel-to-pixel calibration between the two spectrometers and showed that BD-vis-OCT enhanced system sensitivity by up to 22.2 dB. We imaged healthy volunteers at an A-line rate of 125 kHz and a field-of-view as large as 10 mm x 4 mm. We found that BD-vis-OCT revealed retinal anatomical features previously obscured by the noise floor.

bioengineering↗

bioRxiv2021

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

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.

bioengineering↗

bioRxiv2019

Associated habitat and suitability modeling of goldenseal (Hydrastis canadensis L.) in Pennsylvania: explaining and predicting species distribution in a northern edge of range state

Goldenseal (Hydrastis canadensis L.) is a well-known perennial herb indigenous to forested areas in eastern North America. Owing to conservation concerns including wild harvesting for medicinal markets, habitat loss and degradation, and an overall patchy and often inexplicable absence in many regions, there is a need to better understand habitat factors that help determine the presence and distribution of goldenseal populations. In this study, flora and edaphic factors associated with goldenseal populations throughout Pennsylvania--a state near the northern edge of its range--were documented and analyzed to identify habitat indicators and provide possible in situ stewardship and farming (especially forest-based farming) guidance. Additionally, maximum entropy (Maxent) modeling was applied to better predict where suitable habitat might be encountered more broadly and explain species absence from regions of the state (and the northeastern states). Habitat study results identified rich, mesic, woodland sites as being suitable for goldenseal. The most prevalent overstory tree associates on such sites were tulip-poplar (Liriodendron tulipifera L.) and sugar maple (Acer saccharum Marshall), and the most common understory associates were spicebush (Lindera benzoin L.), Virginia creeper (Parthenocissus quinquefolia (L.) Planch.), Jack-in-the-pulpit (Arisaema triphyllum (L.) Schott), mayapple (Podophyllum peltatum L.), wood fern (Drypoteris marginalis (L.) A. Gray), and rattlesnake fern (Botrypus virginianus (L.) Michx.). Loam soils were the most common textural class (average sand, silt, and clay ratio of 50:30:20) with an average pH of 6.2 and high variation in macronutrients. While such sites are widespread in the state, Maxent modeling suggested the present distribution in Pennsylvania is largely restricted by winter temperatures and bedrock type. The latter of these, in turn, is correlated in part with land use legacy (e.g., clearing for farming or livestock grazing), especially in southeast portions of the state.

ecology↗