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Marcel Trerice Bernucci, Conrad Merkle, Vivek Jay Srinivasan; Using a contrast agent to explain vascular scattering patterns in OCT angiography. Invest. Ophthalmol. Vis. Sci. 2017;58(8):5434.
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© ARVO (1962-2015); The Authors (2016-present)
OCT angiography has enabled high-resolution and depth-resolved imaging of retinal and choroidal vasculature without exogenous contrast. Yet, seemingly artefactual but repeatable patterns in OCT angiograms remain challenging to explain. In the choroid, below an intact retinal pigment epithelium (RPE), vessel lumens display low signal, with a relative signal increase beneath vessels. We hypothesize that by using a relatively isotropic scattering contrast agent with a symmetrical particle shape, for OCT angiography, we may explore to what extent these patterns result from the high scattering anisotropy and asymmetrical shape of red blood cells (RBCs).
A commercial 1300 nm spectral / Fourier domain OCT microscope was adapted as an ophthalmoscope for imaging the rat retina at a speed of 91 kHz. The cornea was exposed to a 1.5 mW beam with a diameter of 846 μm. The maximum sensitivity measured was 92 dB. Sprague-Dawley rats (n = 2) were anesthetized with isoflurane. Imaging was performed both before and after intravenous injection of Intralipid-20% (used as a contrast agent). The total injected volume was ~3% of the total blood volume. Pre- and post- contrast images were registered and compared on a point-by-point basis.
Pre-contrast OCT angiograms clearly show microvascular networks throughout the retina and choroid based on RBC scattering contrast (A). Post-contrast OCT angiograms better accentuate retinal capillaries, and particularly, highlight microvasculature in the choriocapillaris that was not previously seen (B). Notably, the contrast agent, more isotropically scattering than RBCs, enhances vessel lumens much more than the regions below vessels in the choroid.
The use of a contrast agent improves visualization of retinal and choroidal vasculature in OCT angiography. Moreover, choosing a relatively isotropic scattering contrast agent with symmetrical particle shape and comparing angiograms pre- and post-enhancement, patterns in OCT angiography that are specific to the scattering anisotropy and asymmetrical shape of RBCs were identified.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
Pre-contrast (A) and post-contrast (B) OCT angiograms show that signal inside the vessel is enhanced more than signal outside the vessel in the choroid.
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