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Conrad Merkle, Vivek Jay Srinivasan; Imaging microvascular hemodynamics in the rat retina and choroid with dynamic contrast OCT. Invest. Ophthalmol. Vis. Sci. 2016;57(12):2195.
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© 2017 Association for Research in Vision and Ophthalmology.
Despite the prevalence of imaging techniques to measure hemodynamics in larger vessels, quantitative measurements of hemodynamics in capillaries in the retina and choroid have traditionally been challenging. Here a new imaging technique called Dynamic Contrast Optical Coherence Tomography (DyC-OCT) is used in the rat eye for the first time to study microvascular hemodynamics in vivo. The aims are 1) To study differences in microvascular hemodynamics between the inner and outer plexiform layers using DyC-OCT and 2) To show that DyC-OCT can quantify transit characteristics within the choroid.
A Thorlabs 1325 nm spectral/Fourier domain OCT system was used to image Sprague Dawley rat eyes in vivo under isoflurane anesthesia. DyC-OCT uses a bolus of Intralipid 20%, an FDA-approved nutritional supplement for intravenous use in humans, injected via the tail vein as a contrast agent to cause a transient increase in OCT signal within the vasculature. This change is recorded by acquiring repeated OCT B-scans at the region of interest and can be thought of as the depth-resolved OCT analogue of fluorescein/ICG angiography. A model is then applied to quantify transit characteristics such as arrival time, peak time, and FWHM of the bolus signal. Arrival time distributions in different layers are obtained and compared using a 2-sided t-test followed by the Bonferroni correction.
Figure A shows the arrival times of the Intralipid tracer overlaid on the mean log-intensity OCT image and demonstrates imaging of microvascular hemodynamics across the inner retina and into the choroid. Mean arrival time and standard deviations for different layers of the eye are shown in Figure B with statistically significant differences.
Arrival times in the choroid and choriocapillaris are imaged by DyC-OCT and shown to be significantly different from arrival times in the inner retina. DyC-OCT provides a new way to image depth-resolved hemodynamics, and will potentially enable the isolation of changes in specific layers that are differentially affected in disease.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
This figure shows quantitative, depth-resolved measurements of tracer arrival times on top of the log-intensity OCT signal (A). Mean and standard deviations of arrival times from different layers of the eye are shown and tested for statistical significance (B). Inner Plexiform Layer (IPL), Outer Plexiform Layer (OPL), and Choriocapillaris (CC).
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