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Christian van Oterendorp, Hanna Gottschalk, Christoph Russmann, Hans Hoerauf; Parameters influencing signal strength in lipid emulsion-based OCT-angiography.. Invest. Ophthalmol. Vis. Sci. 2018;59(9):2854.
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© ARVO (1962-2015); The Authors (2016-present)
Lipid emulsions (LE) can be used as contrast agents for OCT imaging. Similar to blood they induce a highly fluctuating scatter of the OCT signal, which enables the application of OCT-angiography (OCTA) for their detection. We investigated the influence of LE concentration and flow on the signal generated by a commercial OCTA device in vitro. Using a prototype add-on lens, we also used LE based OCTA for aqueous angiography in ex vivo pork and bovine eyes.
The anaesthetic substance propofol (10mg/ml) was used as LE for all experiments. Polyethylene tube phantoms of 1 mm inner diameter were filled with various dilutions of propofol (range: 1-100%). Morphological OCT B-scans and OCTA scans were obtained using a Zeiss Angioplex device (Carl Zeiss Meditec, Jena, Germany) equipped with a prototype add-on lens. The tubes were connected to a flow pump and the OCTA B-scan signal was measured at different flow velocities and simultaneously with a no-flow tube. For ex vivo-aqueous angiography pork and bovine eye’s anterior chamber was perfused with undiluted propofol. OCTA B-scan and en face-images of the aqueous outflow tract were obtained.
Application of OCTA allowed for direct detection of the contrast agent at no-flow conditions. OCTA signal intensity was linearly correlated with the logarithmic LE concentration (R2=0.98) and with the signal intensity of the conventional OCT B-scan (R2=0.98) at different concentrations. Compared to the no-flow signal the application of flow did not lead to significant changes of the OCTA signal intensity over a flow velocity range of 0.009 to 9 mm/s (flow/no-flow OCTA signal intensity coefficient not significantly different from 1; one-sample t test with multiple comparison correction; p>0.05). Only the highest flow velocity applied (18 mm/s) showed a significant decrease in OCTA signal intensity for all 4 concentrations tested (p=0.01). In LE-perfused pork and bovine eyes OCTA visualised the intra- and episcleral aqueous outflow tract and produced 2D en face-images of the scan area. For depth resolved images, custom made post-processing algorithms of the OCTA B-scans had to be applied.
A lightly modified commercial OCTA device can be used for detection of LE as contrast agent. In tube phantoms, the LE propofol produced a strong OCTA signal independent from the presence of flow. This is presumably due to Brownian movement of the lipid micelles.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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