Optical Coherence Tomography Angiography Overview
OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY BASIC PRINCIPLES
Based on optical coherence tomography (OCT).
Noninvasive method allowing for visualization of functional blood vessels in the eye producing a three-dimensional reconstruction of vascular networks.
Achieved by using variation in the OCT signal caused by moving red blood cells (RBCs).
To differentiate dynamic particles (predominantly RBCs) from static structural tissues of the eye, repeated scans are taken at the same location.
Produces a static map of the vascular network without providing any true information regarding blood flow or vascular leakage.
Provides ability to view optical coherence tomography angiography (OCTA) images with corresponding en-face images.
OCTA TECHNIQUES1
Phase signal-based OCTA technique
Phase variance
Measurement of phase variance between adjacent B-scans or the motion-contrast technique.
Quantifies axial blood flow parallel to the direction of the imaging acquisition device.
Intensity-based OCTA technique
Amplitude decorrelation
Performed through analysis of amplitude changes in the OCT signal.
Split-spectrum amplitude decorrelation angiography (SSADA) acts to partition the spectrum into smaller spectra and performs the repeated B-scan decorrelation separately for each subspectrum.
Improves the signal-to-noise ratio.
Speckle variance
Complex signal-based OCTA technique
OCT microangiography (OMAG) algorithm
Uses variations in both the intensity and phase information between sequential B-scans at the same position.
Coherent information used to calculate flow signal.
SPECTRAL-DOMAIN OCTA VERSUS SWEPT-SOURCE OCTA
