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J Ramella-Roman; Measurement of retina vascular flow across small and large vessel sizes. Invest. Ophthalmol. Vis. Sci. 2014;55(13):227.
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© ARVO (1962-2015); The Authors (2016-present)
The quantitative estimation of blood flow is an important tool for exploring the etiology, and the treatment of many diseases of the eye including diabetic retinopathy. Current imaging technique focus on limited ranges of vessel sizes. We introduce a novel retinal flow imaging system that combines Speckle Imaging and TRacking of Red blood cells (SITAR). The system provides not only quantitative values of flow but does so across multiple vessels sizes (250µm to 20 µm in diameter).
The SITAR imaging system consists of a fundus camera, a fast high sensitivity cooled CCD, and a laser light source, (520 nm). The RBC tracking system utilizes the same laser source as the speckle imaging system but requires amplitude modulation and coherence scrambling. Calibration and characterization of the system was conducted by imaging several micro-fluidic devices of different diameters. Physiologic flow velocities of whole human blood were observed and compared to Finite Element simulations of capillary flow. A self-calibration scheme is utilized to expand the values of flow rate to the full range under study.
Test conducted with SITAR in-vitro showed high accuracy of flow determination in small vasculature size (20 to 60 µm in diameter) where error between measured flow and predicted flow was less than 3%. When expanding to larger vessel (200µm in diameter) the error grew to up to 6%. An example of this scheme is shown in Fig. 1.
We propose the combination of two flow measuring techniques, Laser Speckle Contrast Imaging and red blood cell tracking to truly quantify flow on all retina vessels regardless of their size or location for the first time. We also propose a set of in vitro and measurements to explore the limit and strengths of the technique. We believe that this procedure (instrumentation and processing algorithms) will find use in a variety of clinical and research applications where ever the assessment of perfusion within superficial vascular beds is important.
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