Three-dimensional quantitative imaging of retinal and choroidal blood flow velocity using joint Spectral and Time domain Optical Coherence Tomography

Abstract

Recently, joint Spectral and Time domain Optical Coherence Tomography (joint STdOCT) has been proposed to measure ocular blood flow velocity. Limitations of CCD technology allowed only for two-dimensional imaging at that time. In this paper we demonstrate fast three-dimensional STdOCT based on ultrahigh speed CMOS camera. Proposed method is straightforward, fully automatic and does not require any advanced image processing techniques. Three-dimensional distributions of axial velocity components of the blood in human eye vasculature are presented: in retinal and, for the first time, in choroidal layer. Different factors that affect quality of velocity images are discussed. Additionally, the quantitative measurement allows to observe a new interesting optical phenomenon - random Doppler shift in OCT signals that forms a vascular pattern at the depth of sclera.

Quantitative lateral and axial flow imaging with optical coherence microscopy and tomography

“…The most straightforward approach is to evaluate the local phase difference between time samples, from which the Doppler frequency is then obtained. In joint spectral and time domain OCT, Fourier transformations are performed along both time and wavenumber dimensions, yielding the spatially resolved Doppler spectrum [14,19,20]. At each location, the Doppler shift is estimated as the frequency corresponding to the maximum magnitude position or to the center of mass using circular statistics [21].…”

In vivo human retinal and choroidal vasculature visualization using differential phase contrast swept source optical coherence tomography at 1060 nm

“…Smart scanning protocols enhance sensitivity to the smaller signals expected from the microvasculature by increasing the time separation between two OCT depth scans and relying on the acquired phase 10 or joint intensity and phase information 11,12 of 800 nm spectral domain (SD)-OCT signals for contrast. The proposed motion contrast method by Wang 11 can visualize the microvasculature using Hilbert and Fourier analyses of the OCT signal; however, these also highlight highly reflective stationary regions.…”

“…The proposed motion contrast method by Wang 11 can visualize the microvasculature using Hilbert and Fourier analyses of the OCT signal; however, these also highlight highly reflective stationary regions. 2D Fourier analysis of the OCT signals along the wavenumber and time axes can provide structural and motion information for mapping the blood flow velocity within retinal capillaries 12 .…”

Differential intensity contrast swept source optical coherence tomography for human retinal vasculature visualization

“…Although D-OCT captures the regions of high-velocity blood flow, such as in major vessels, it is unable to capture slow flow in retinal capillaries 11 or deep flows such as the choroidal circulation due to limited phase sensitivity and small time separation between two successive A-scans. Smart scanning protocols enhance sensitivity to the smaller signals expected from the microvasculature by increasing the time separation between two OCT depth scans and relying on the acquired phase [12][13][14][15] of OCT signals for contrast. However, these methods [13][14][15] such as PC-OCT 12 are highly sensitive to the phase instability of the system and environment by relying on the phase information.…”

“…Smart scanning protocols enhance sensitivity to the smaller signals expected from the microvasculature by increasing the time separation between two OCT depth scans and relying on the acquired phase [12][13][14][15] of OCT signals for contrast. However, these methods [13][14][15] such as PC-OCT 12 are highly sensitive to the phase instability of the system and environment by relying on the phase information. The required bulk motion removal 16 and timing-induced phase error correction algorithms 17 as well as extra optical module 17 add to the complexity of the phase sensitive swept source (SS)-OCT software and hardware.…”