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Mircea Mujat, Youbo Zhao, Nicusor Iftimia, R Daniel Ferguson; Ocular blood flow imaging and quantification. Invest. Ophthalmol. Vis. Sci. 2018;59(9):5873.
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© ARVO (1962-2015); The Authors (2016-present)
To test a new approach for vascular (retinal and choroidal) imaging and flow quantification that enables hemodynamic studies in animals and human subjects. Microgravity-induced ocular functional and structural alterations have been experienced by astronauts in long-duration space travel. It is hypothesized that weightlessness-induced fluid shift, possibly associated with elevated intracranial pressure, may play a critical role. Comprehensive hemodynamic studies as proposed here may help elucidate these ocular changes.
The instrument combines Optical Coherence Tomography (OCT) as a platform and Line-scanning Doppler Flowmetry (LSDF). OCT provides 3D structural information and precise local flow parameters while the wide-field semi-quantitative LSDF technique aids in visualizing global blood flow patterns and in identifying specific locations. Net choroid blood flow quantification is then performed at these locations using circular OCT scans. Standard Doppler OCT and speckle-variance OCT are used for local 3D mapping and quantification of blood flow.
LSDF provides visualization and mapping of retinal and choroidal blood vessels in different Doppler frequency ranges, therefore, differentiating between slow, medium, and fast flow. Large area maps of blood vessels are obtained and enable identification of and navigation to key landmark locations for flow quantification using OCT. OCT raster scans are acquired with B-scan repetition (5). Average of repeated B-scans provides noise reduction, while inter-frame speckle variance provides 3D visualization of the blood vessels. Layer segmentation can be used to generate thickness maps for RNFL, retina, and choroid. Circular scans at specific locations provide quantitative flow values and enable calculation of the total blood flow into the retina and choroid. Examples are shown in Fig. 1.
Our preliminary retinal and choroidal imaging demonstrations (performed at safe light levels for retinal imaging under a NASA human subjects protocol) have clearly shown the potential of this these two complementary imaging modalities to map retinal and choroidal blood vessels. An advanced diagnostic imaging system is fundamental to understanding hemodynamic processes in the eye.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
OCT reflectivity (top) and Doppler image (center) showing choroidal (left) and retinal (right) flow. Bottom row shows medium speed LSDF image (left) and choroid OCT reflectivity map (right). Box - OCT scan position.
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