Single-beam laser Doppler measurements of flow velocity are only sensitive to the velocity component parallel to the optical axis. We describe a simple modification to a standard Doppler optical coherence tomography (OCT) system using a single sample beam that provides velocity information from multiple angles within the beam. By introducing a glass plate midway into the OCT beam path, the sample beam is divided into several components, each with a different group delay and each providing a separate interferogram with its own effective Doppler angle. By combining the Doppler shift measured in each of these component interferograms, the flow velocity vector is fully determined.
We present a fiber-based, low-coherence interferometer that significantly reduces phase noise by incorporating a second, narrowband, continuous-wave light source as a phase reference. By incorporating this interferometer into a Doppler OCT system, we demonstrate significant velocity noise reduction in reflective and scattering samples using processing techniques amenable to real-time implementation. We also demonstrate 90% suppression of velocity noise in a flow phantom.
Increased regurgitant blood flow has been linked to endocardial cushion defects and resultant congenital heart diseases (CHDs). Prenatal alcohol exposure (PAE) has been shown to alter early blood flow resulting in abnormal endocardial cushions and CHDs. Compounds, including folic acid (FA), mitigate PAE effects and prevent CHDs, but few studies have assessed their effects on blood flow. We modeled binge drinking in quail embryos at gastrulation. Embryos were exposed to ethanol alone, FA (3.2 μg/egg) alone, and the two simultaneously. We quantified in cardiac looping stages (equivalent to 4 weeks of human gestation) regurgitant blood flow with Doppler optical coherence tomography (OCT) and endocardial cushion volumes using OCT imaging. Incidences of abnormal body curvature and heart rates were also measured. Embryos exposed to ethanol showed significantly increased regurgitant blood flow compared to controls, while embryos given FA with ethanol had significantly reduced regurgitant blood flow but did not return to control levels. Ethanol exposure led to significantly smaller, abnormal endocardial cushions and the addition of FA improved their size, but they remained smaller than controls. Abnormal body curvatures after PAE were reduced in incidence but not fully prevented by FA. FA supplementation partially alleviated PAE induced abnormal cardiovascular function and morphology. Normal blood flow and endocardial cushions are both required to produce a healthy four-chambered heart. These findings support that FA supplementation should begin early in pregnancy to prevent heart as well as neural tube defects. Investigations into the efficacy of combinations of compounds to prevent PAE-induced defects is warranted.
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