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A. Szkulmowska, M. Szkulmowski, A. Kowalczyk, M. Wojtkowski; Retinal Blood Flow Analysis Using Spectral OCT: Joint Spectral and Time Domain OCT versus Phase-Resolved Doppler OCT. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1873. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To compare two Spectral OCT techniques for analysis of blood circulation in human retina: a new modification of OCT called joint Spectral and Time domain Optical Coherence Tomography (STdOCT) with well-known phase-resolved OCT. New STdOCT method is based on spectral interferogram registration in time increments.
Spectral OCT has been performed in vivo in 10 eyes of 5 healthy volunteers. Registered data have been processed in two different ways: using STdOCT and phase-resolved OCT. The velocity estimation of moving sample in STdOCT is derived from Doppler shifts arising during the spectral fringe signal registration in time, the phase-resolved OCT is based on direct, linear dependence between the phase difference of consecutive spectral fringe signals.
To prove the advantage of STdOCT we present cross-sectional images of human retina scanned through the region of optic disc with detailed two-dimensional maps of the flow velocity distribution. We demonstrate that the phase-resolved OCT underestimates the magnitude of flow velocities in bigger blood vessels where the signal registered by OCT is decreased. In case of smaller vessels (capillaries), blood flow is invisible in phase-resolved OCT, whereas in STdOCT it can be still measurable.
In vivo examination of human eye suffers from involuntary patient movement and signal decay caused by possible pathological changes in eye tissue. These two factors mainly deteriorate and even preclude velocity recovery in the phase-resolved OCT. Undesired movement as well as system unsteadiness introduce phase instabilities and relevant velocity error in measured signals. Accuracy and precision of velocity estimation are strongly influenced by signal-to-noise ratio (SNR), thus the signal decay seriously affects the reliability of phase-resolved OCT. Since velocity estimation in STdOCT is based not on phase information but on signal amplitude changing in time, STdOCT is more sensitive, accurate and precise under low SNR conditions than phase-resolved OCT. We believe that STdOCT enables quantitative analysis of blood circulation in human retina in more reliable manner than previously reported techniques.
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