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Vivek Jay Srinivasan, Conrad Merkle, Marcel Bernucci, Conor Leahy; Contrast-enhanced OCT angiography of the choriocapillaris. Invest. Ophthalmol. Vis. Sci. 2016;57(12):453. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Though Optical Coherence Tomography (OCT) angiography can clearly image the choriocapillaris in cases of Retinal Pigment Epithelium (RPE) atrophy, methods that assess the choriocapillaris beneath an intact RPE are lacking. To address these limitations, we use Intralipid-20% (FDA-approved for intravenous parenteral nutrition in humans) as a contrast agent to fill under-perfused vessels and enhance scattering signal in vessels beneath an intact RPE. By combining contrast enhancement with a long imaging wavelength and a customized image processing technique for further vessel enhancement, we image the choriocapillaris in the rat retina with a level of detail approaching that of histology.
A 1300 nm spectral / Fourier domain OCT ophthalmoscope was adapted for imaging the rat retina at a speed of 92,000 axial scans per second. The axial and transverse resolutions were approximately 7 microns in air. Sprague-Dawley rats (n = 3) were anesthetized with isoflurane. Imaging was performed both before and after intravenous injection of Intralipid-20% (used here as a contrast agent). The total injected volume was ~2.5% of the total blood volume. A Hessian-based algorithm was used for scale-dependent enhancement vessels in the angiograms.
Pre-contrast OCT angiograms clearly show the microvascular networks throughout the retina (A), as well as large vessels in the choroid (B, depth is color-coded). Post-contrast OCT angiograms better accentuate the retinal capillaries (C), and particularly, highlight microvasculature in the choriocapillaris that was not previously visualized (D, depth is color-coded).
Here we demonstrate the value of exogenous contrast enhancement for OCT angiography of microvasculature, particularly in the choriocapillaris. While the results show that contrast enhancement provides a clear benefit in imaging Sprague-Dawley rats, future work is required to test the benefits in more highly pigmented eyes. These methods will improve the monitoring of early age-related macular degeneration in experimental models, and potentially also in human subjects.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Retinal (A) and choroidal (B) maximum intensity projection (MIP) angiograms without contrast agent. Only the large choroidal vessels are visible in B). Retinal (C) and choroidal (D) MIP angiograms after injection of 2 mL kg-1 of the contrast agent, Intralipid-20%. The choriocapillaris is more prominent in post-contrast angiogram.
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