Methods and algorithms for optical coherence tomography-based angiography: a review and comparison

Abstract

Optical coherence tomography (OCT)-based angiography is increasingly becoming a clinically useful and important imaging technique due to its ability to provide volumetric microvascular networks innervating tissue beds in vivo without a need for exogenous contrast agent. Numerous OCT angiography algorithms have recently been proposed for the purpose of contrasting microvascular networks. A general literature review is provided on the recent progress of OCT angiography methods and algorithms. The basic physics and mathematics behind each method together with its contrast mechanism are described. Potential directions for future technical development of OCT based angiography is then briefly discussed. Finally, by the use of clinical data captured from normal and pathological subjects, the imaging performance of vascular networks delivered by the most recently reported algorithms is evaluated and compared, including optical microangiography, speckle variance,phase variance, split-spectrum amplitude decorrelation angiography, and correlation mapping. It is found that the method that utilizes complex OCT signal to contrast retinal blood flow delivers the best performance among all the algorithms in terms of image contrast and vessel connectivity. The purpose of this review is to help readers understand and select appropriate OCT angiography algorithm for use in specific applications.

Visualization of micro-capillaries using optical coherence tomography angiography with and without adaptive optics

“…In order to improve the contrast between static (non-vascular) and non-static (perfused) tissue, the technique has been extended by comparing information (such as recorded B-scans) at the same tissue location that was recorded at different time points. After processing these signals, using a variety of methods, the result is a vasculature map of the retina which is comparable to state-of-the-art fluorescence angiography [6]. Thus the technique is often referred to as optical coherence angiography or optical coherence tomography angiography (OCTA) [7][8][9][10].…”

Highly efficient eigen decomposition based statistical optical microangiography

“…This created image is taken as a surrogate for the ground truth, from which a binary vascular mask is generated ( Figure 4E) by using a binary operation through adaptive Hessian filter (18). Finally, the SNR, image contrast and vessel connectivity were calculated according to the definitions described in (3). Note that for the metric of vessel connectivity, the lower value indicates a better vessel connection that an algorithm can deliver to an angiogram.…”

“…Since the tissue signal X t dominates X, it can be obtained through the eigenvector decomposition of the signal correlation matrix ˆX C , which can be estimated by Eq. [3],…”

“…Assuming the speckle signal due to tissue components and that due to moving particles are not correlated, the multivariate statistics (12) can be applied to express the measured signals in multi-dimensional spaces in terms Original Article Highly efficient eigen decomposition based statistical optical microangiography of their spatial and temporal frequency components ( Figure 1B). Since the bio-tissue is heterogeneous, its OCT signal contains band-limited frequency components (typically Gaussian distribution) centered at zero frequency (3,16). In this case, a high-pass filtering should be amendable to separate the OCT signal due to moving blood cells from the static tissue components ( Figure 1C), examples of which include differentiation OMAG (9) and feature space OMAG (17).…”

Artefacts Removal from Optical Coherence Tomography Angiography

“…In [12], the authors provided a review and comparison of various algorithms for optical coherence tomography angiography, including split-spectrum amplitudedecorrelation angiography, correlation matching OCT, optical microangiography, speckle variance, and phase variance methods. In [6], the authors postulated that optic nerve head (ONH) blood flow may be associated with glaucoma development and proposed the use of Split-spectrum amplitude-decorrelation angiography (SSADA) method [7] together with flow index and vessel density for glaucoma detection.…”