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Anne Willerslev, Xiao Q. Li, Michael Larsen; Characteristics Of Intravascular Blood On Spectral-domain Optical Coherence Tomography. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2184.
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The characteristics of intravascular blood on spectral-domain optical coherence tomography (SD-OCT) scans of retinal and choroidal blood vessels were examined in human subjects.
Examination of five healthy subjects and two patients with retinal or systemic disease using SD-OCT at 800 nm.
Healthy retinal vessels scanned at right angles to the line of observation demonstrated longitudinal tri-layer patterns and cross-sectional figure-of-eight patterns of high reflectivity. In central retinal artery occlusion with stagnant intravascular blood no reflection from the blood was seen. In hypoperfused retinal vessels in a patient with carotid artery occlusion the optical density of blood was lower than normal and homogeneous. The highly perfused choroidal vessels generally showed no reflectivity and figure-of-eight and longitudinal tri-layer patterns were only observed rarely, the visibility being enhanced by a translucent or atrophic pigment epithelium. The reflectivity of the streaming blood decreased with an increasing shift in the angle of observation away from the rectangular, and was absent when flow was directly toward or away from the point of observation.
The SD-OCT profile of the blood column in retinal and choroidal vessels varies in a biphasic manner with flow velocity, being lowest at high and low flow rates and highest at intermediate flow rates such as those typical of larger vessels of a healthy retina. Our observations agree with in vitro studies using SD-OCT and other optical modalities, ultrasonography and electrical conductivity measurements. Past results have been successfully modeled assuming that erythrocytes aggregate at low flow rates, a condition associated with low optical scatter, whereas erythrocytes disaggregate at higher flow rates and become spatially organized in a radial manner. At high flow rates and for flow along the line of observation, the signal is lost because of the Doppler frequency-shift
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