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Christian van Oterendorp, Viktoria Mans, Charlotte Fischer, Mohammed Khattab, Thomas Wecker; 12% fat milk as OCT contrast agent for ex vivo imaging.. Invest. Ophthalmol. Vis. Sci. 2016;57(12):474.
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© ARVO (1962-2015); The Authors (2016-present)
Contrast agents applicable for optical coherence tomography (OCT) imaging are rare. Among them, gold nanorods are best characterised but expensive. The intrascleral aqueous outflow tract can be visualised by OCT, however to reliably identify those vessels draining aqueous the application of a contrast agent is desireable. We tested 12% fat milk as a potential agent for this application.
OCT images were obtained with a spectral domain device for clinical use (Spectralis OCT, Heidelberg Engineering, Germany). To determine the reflectivity of candidate contrast agents, transparent plastic tubes of 5 mm diameter were filled with either balanced salt solution, black ink or high fat (12%) milk and scanned with the OCT device. Normalised 8-bit grey scale pixel values from inside the test tubes were compared between the liquids (n=8, ANOVA with Tukey post hoc testing). For an ex vivo eye imaging application the anterior chamber of bovine eyes was cannulated to perfuse the aqueous outflow tract with either BSS or milk. OCT volume scans were obtained from the intrascleral aqueous veins, using 30 frames averaging per B-scan. The same region was scanned before and after perfusion with milk. Normalised 8-bit grey value pixel intensity in aqueous veins was measured at different locations and the intensity shift after perfusion with milk was quantified (n=8, Wilcoxon matched pairs signed rank test).
In the test tubes 12% fat milk shows a significant increase in OCT reflectivity compared to BSS and ink (185±34, 0.8±1.5 and 0.9±1.0, respectively, p<0.0001). When applied to ex vivo imaging of aqueous veins in bovine eyes, the perfusion with milk led to a significant shift in the intraluminal reflectivity (normalised pixel intensity BSS: 4.6±3.2, milk: 138±27; p=0.0078) and, thus, allowed to distinguished between aqueous veins and blood vessels without connection to the anterior chamber. Despite the relatively high reflectivity of milk, no shadow was cast from the milk perfused vessels, leaving the images free of the vertical stripy shadows which are seen in blood perfused vessels.
For ex vivo applications 12% fat milk proofed a low-cost and effective contrast agent for OCT imaging. Although not directly transferrable to in vivo application the principle of using fatty emulsions as possible contrast agents might be worth further investigation.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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