Swept-source OCT angiography of the retinal vasculature using intensity differentiation-based optical microangiography algorithms

Abstract

Background and objective: To demonstrate the feasibility of using a 1,050-nm swept-source optical coherence tomography (SS-OCT) system to achieve noninvasive retinal vasculature imaging in human eyes.

Materials and methods: Volumetric data sets were acquired using a 1-µm SS-OCT prototype that operated at a 100-kHz A-line rate. A scanning protocol designed to allow for motion contrast processing, referred to as OCT angiography or optical microangiography (OMAG), was used to scan an approximately 3 × 3–mm area in the central macular region of the retina within approximately 4.5 seconds. An intensity differentiation-based OMAG algorithm was used to extract three-dimensional retinal functional microvasculature information.

Results: Intensity signal differentiation generated capillary-level resolution en face OMAG images of the retina. The parafoveal capillaries were clearly visible, thereby allowing visualization of the foveal avascular zone in healthy subjects.

Conclusion: The capability of OMAG to produce retinal vascular images was demonstrated using the 1-µm SS-OCT prototype. This technique has potential clinical value for studying retinal vasculature abnormalities.

Figure 1

The scanning protocols for OCT angiography used in the current study. (A) “x” indicates the fast axis in a B-scan and “y” indicates the slow scan axis, where at each y scan point, a cluster of repeated B-scans (4 times in the current study) are performed to extract the flow signal. (B) Top view of the OCT angiography scan pattern: cluster scans comprise of 4 repeated B-scans obtained at the same location.

Figure 2

A flowchart showing OMAG processing steps for generating a projected en face vasculature distribution image based on the acquired 3-D volumetric data.

Figure 3

Typical results of OMAG from a scan region of ~3×3 mm² in the right eye of a normal subject (#1). (A) A typical cross-sectional image showing the segmentation lines for the different layers including the inner retina (IR), middle retina (MR), outer retina (OR), choriocapillaris (CC) and choroid. The white arrows in (A) show the RPE layer. (B) OMAG flow image. (C) An en face OCT fundus image from the structural OCT signal and the red dotted line shows the location where (A) and (B) are obtained. (D) and (E) show the projected OMAG images for the retinal and choroidal layer, respectively. The scale bars show a distance of 500 µm. FAZ – foveal avascular zone.

Figure 4

Typical OMAG images for different lays of retina and choroid in the right eye of Subject #1. (A)–(C) include OMAG images from inner retina, middle retina and the whole retina; (D)–(F) include OMAG images from choriocapillaris, choroid and the whole choroid. In the combined images (C and F), a color coding scheme is used to indicate the blood vessels from different layers. For retina, inner retina = red = ~70 µm of the inner retina, middle retina = green = ~60 µm lying in the middle retina. For choroid, choriocapillaris = red = ~30 µm underneath RPE, choroid = green = ~250 µm underneath choriocapillaris. The scale bars in (A) show a distance of 500 µm which apply to all other images.

Figure 5

Color-coded OMAG images of a scanned region of ~3×3 mm² in the foveal region from three different normal subjects. Subjects #2–4 are shown for both the right (OD) (top row) and the left (OS) (bottom row) eyes. Color coding: inner retina = red = ~70 µm of the inner retina, middle retina = green = ~60 µm in the middle retina. The scale bars in the first image show a distance of 500 µm which apply to all other images.