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Sylvia Desissaire, Florian Beer, Matthias Salas, Florian Schwarzhans, Mitsuro Sugita, Bernhard Baumann, Georg Fischer, Clemens Vass, Michael Pircher, Christoph K Hitzenberger; B-scan imaging along retinal vessels using OCT with tracking. Invest. Ophthalmol. Vis. Sci. 2019;60(9):1277.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate retinal vessels along their trace using an OCT system with retinal tracking and arbitrary scanning patterns and to retrieve structural and hemodynamic information.
A spectral domain OCT system operating at 860nm and at 70kHz A-scan rate is used for imaging. The achieved resolution is 4.2 μm axially and 20 μm laterally. The setup includes a line scanning laser ophthalmoscope (LSLO) for retinal tracking. It operates at 790 nm and at a frame rate of 60 Hz. In order to record B-scans along a vessel, interpolation points on the vessel are manually selected on the LSLO image and a corresponding path for the OCT beam is automatically calculated. Depending on the targeted area, 1024 or 2048 A-scans per B-scan are used. 200 to 300 B-scans repeated at the same position are acquired per measurement. From the recorded data sets, averaged intensity images and Doppler images (phase difference between adjacent A-scans) are calculated. Arteries and veins of different caliber and from different subjects (5) were imaged.
In the averaged intensity tomograms, the vessel wall can be clearly distinguished from other tissues (Fig. 1(B)). In the center of the vessel reduced intensity is observed that may be due to the orientation and deformation of red blood cells in shear flow. Segmentation allows retrieving the vessel caliber. For the imaged artery in Fig 1, the caliber ranges from (135 ± 6) μm close to the nerve head to (115 ± 8) μm at a location 4.5 mm away from the nerve head. Doppler tomograms show strongly varying phase signals along the vessel mainly due to the varying angle (Doppler angle) between vessel and imaging beam. It should be noted that even small angle changes result in comparatively large variations in the phase signal. At 1.5 mm away from the nerve head, variations of 10° in angle result in deviation of around 60° on the phase signal. The arbitrary pattern allows for investigations of dynamic changes associated with the cardiac cycle. Representative images indicating the differences between diastolic and systolic phases are shown in Fig 1(C)-(D).
Retinal vessels could be imaged along their trace using an OCT system with retinal tracking. In these images the vessel can clearly be distinguished from other tissues especially in the averaged intensity images. Time-resolved information on variations of blood flow velocity during the heart beat cycle can be obtained from the Doppler tomograms.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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