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Mircea Mujat, Yang Lu, Daniel Ferguson, Nicusor Iftimia; Calibration of laser Doppler flowmetry. Invest. Ophthalmol. Vis. Sci. 2020;61(7):2540.
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Despite decades of research and the introduction of several advanced systems for measurement of blood flow, retinal blood flow Doppler imaging diagnostics have not yet achieved wide-spread adoption. In laser Doppler flowmetry (LDF), the results are given in arbitrary units (Volume and Flow) or Hz (Velocity) since the conversion factor to the correct parameters claimed to be measured were rather elusive so far. We demonstrate here a method to enable quantitative measurement of the blood velocity by determining the calibration factor, the conversion from Hz to mm/s directly in the living eye and for each measurement session, eliminating this way the uncertainties associated with standard LDF.
Two imaging modalities: line-scanning Doppler flowmetry (LSDF) and optical coherence tomography (OCT) are combined in the same instrument to provide complementary aspects of ocular blood flow. The wide-field LSDF technique enables visualization and mapping of retinal and choroidal blood vessels without additional contrast agents and over large areas. Doppler OCT quantifies precise local flow parameters and provides the proper calibration factors for LSDF.
Parallel scanning in LSDF enables orders of magnitude speed increase as compared to LDF which in turn affords imaging much larger areas and visualization of much faster flow. Retinal and choroidal flow is mapped non-invasively without the use of fluorescein or indocyanine green. Simultaneously, Doppler OCT at specific locations provides quantitative flow values. We show here that the calibration factor from frequency to absolute velocity can be obtained locally with Doppler OCT every time the LDF measurement is performed, therefore removing subjective factors related to the operator and the subject. The technique has been demonstrated on microfluidic devices covering a velocity range of 1 – 100 mm/s precisely controlled with a syringe pump and it is currently being applied to imaging human retina/choroid.
Ultra-wide mapping of retinal and choroidal blood flow has been demonstrated using LSDF  and correct quantification of the blood velocity is enabled here by the use of Doppler OCT. Such an advanced diagnostic imaging system will help understanding hemodynamic processes in the eye as a response to disease or treatment.1. M. Mujat, et al., “Visualizing the vasculature of the entire human eye posterior hemisphere without a contrast agent”, Biomed. Opt. Express, 10(1), 167-180, (2019)
This is a 2020 ARVO Annual Meeting abstract.
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