The accuracy of optical coherence tomography angiography (OCTA) based blood flow velocimetry is affected by Axial Velocity Gradient (AVG) when the scanning beam is not perpendicular to the blood flow. We have developed two methods to eliminate the effect of AVG on amplitude decorrelation, where the AVG term is cancelled according to the established analytical model of dynamic light scattering (DLS) using two OCTA signals acquired with different spatial resolutions. We verified both solutions with flow phantom experiments. The effectiveness and limitations of both methods are discussed.
Optical Coherence Tomography Angiography (OCTA), a functional extension of Optical Coherence Tomography (OCT), is capable of imaging blood flow signals non-invasively at the capillary level without the need for dye injection. However, widespread usage of OCTA is hindered by the trade-off between transverse sampling rate and Signal to Noise Ratio (SNR). To achieve a clinically applicable field of view, capillary fine details are commonly sacrificed due to under-sampling. In addition, the image contrast of capillaries suffers from 'thin line' motion artifacts. We introduce spectrally extended line field OCTA (SELF-OCTA) that tackles the above-mentioned issues with parallel transverse sampling and increased allowable light exposure. We show that SELF-OCTA provides significantly improved sampling density and image contrast for microvasculature compared with the standard OCTA technique.
We have developed a novel scanning protocol based on Spectrally Extended Line Field OCTA (SELF-OCTA) to realize 4 interscan times ranging from 0.54 ms to 5.4 ms without increasing A-scan repetitions at the same position. Based on the linear model, we further developed signal processing methods to realize high dynamic range blood flow map by concatenating the dynamic range of 3 interscan time: 0.54 ms, 1.35 ms and 2.70 ms. The differential OCTA signals provided by different interscan times help with flow dynamic range extension and blood flow evaluation.
KEYWORDS: Angiography, Optical coherence tomography, Skin, Signal to noise ratio, Eye, Signal processing, In vivo imaging, Functional imaging, Blood vessels, 3D visualizations
We introduce spectrally extended line field (SELF) technique to address some of limitations with the current OCTA, such as relatively small field of view, limited flow dynamic range, and motion artifacts. SELF-OCT acquires signals from multiple transverse positions simultaneously, providing an advantage in the transverse sampling rate. In addition, the allowable light exposure is higher so that there is more sensitivity budget for wide-field and functional imaging. We demonstrate that SELF technique enables improvement in field of view or transverse sampling density, flow dynamic range, sensitivity to slow flow, and motion tracking and correction in the human skin and retina in vivo.
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