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Ou Tan, Ranjith Konduru, Xinbo Zhang, Srinivas R. Sadda, David Huang; Dual Angle Scan Protocol for Doppler Optical Coherence Tomography of Retinal Blood Flow. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1715.
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Doppler optical coherence tomography (OCT) with the circumpapillary double-circular scan pattern is a novel method of measuring retinal blood flow. To obtain reliable blood flow measurement from a vessel, the Doppler angle between the vessel and the OCT beam cannot be too close (<5°) to perpendicular. For some eyes, it may not be possible to obtain an adequate Doppler angle for all vessels using a single angle of approach for the OCT beam. The purpose of this study was to test a scan protocol where 2 different OCT beam approaches are used.
Patient’s Doppler scans were retrieved from advance imaging for glaucoma study between 2009.3 and 2010.4. Two scan protocols were tested in this study. In the "single-angle" protocol 5 Doppler scans were acquired at a single beam angle. In the "dual-angle" protocol, 3 scans were obtained with the OCT beam passing through the superonasal portion of the pupil and 3 scans through the inferonasal portion. Scans were performed in a single session. The Doppler OCT images were processed by a software algorithm which automatically identifies arteries and veins and computes their positions, diameters, and flows. Human graders then reviewed each identified vessel and made manual corrections as necessary. Total retinal blood flow was obtained by adding flow from all veins. Flow values from an eye were deemed acceptable only if greater than half of the venous cross-sectional area met criteria for acceptable Doppler angle (>3°) and angle variability (Coefficient variance<0.5).
Seventeen eyes (10 normal, 7 glaucoma suspect and glaucoma) were scanned with the single angle scan protocol and 19 (7 normal, 12 glaucoma suspect and glaucoma) eyes were scanned with the dual angle scan protocol. Four eyes were scanned with both protocols. The acceptability rate of single-angle protocol scans was 58%, while the acceptability rate of dual-angle protocol was 74%. The acceptability of dual-angle protocol is significantly higher than single-angle protocol (p=0.046).
The dual-angle scan protocol improved the yield of acceptable cases for computing total retinal blood flow values with Doppler OCT.
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