In vivo volumetric imaging of human retinal circulation with phase-variance optical coherence tomography

Abstract

We present in vivo volumetric images of human retinal micro-circulation using Fourier-domain optical coherence tomography (Fd-OCT) with the phase-variance based motion contrast method. Currently fundus fluorescein angiography (FA) is the standard technique in clinical settings for visualizing blood circulation of the retina. High contrast imaging of retinal vasculature is achieved by injection of a fluorescein dye into the systemic circulation. We previously reported phase-variance optical coherence tomography (pvOCT) as an alternative and non-invasive technique to image human retinal capillaries. In contrast to FA, pvOCT allows not only noninvasive visualization of a two-dimensional retinal perfusion map but also volumetric morphology of retinal microvasculature with high sensitivity. In this paper we report high-speed acquisition at 125 kHz A-scans with pvOCT to reduce motion artifacts and increase the scanning area when compared with previous reports. Two scanning schemes with different sampling densities and scanning areas are evaluated to find optimal parameters for high acquisition speed in vivo imaging. In order to evaluate this technique, we compare pvOCT capillary imaging at 3x3 mm(2) and 1.5x1.5 mm(2) with fundus FA for a normal human subject. Additionally, a volumetric view of retinal capillaries and a stitched image acquired with ten 3x3 mm(2) pvOCT sub-volumes are presented. Visualization of retinal vasculature with pvOCT has potential for diagnosis of retinal vascular diseases.

Keywords: (110.4500) Optical coherence tomography; (120.3890) Medical optics instrumentation; (170.0110) Imaging systems; (170.4470) Ophthalmology.

Fig. 1

Schematic of the Fourier-domain OCT instrument. The CMOS (Complementary Metal Oxide Semiconductor) camera is driven by a LabVIEW operating program on a workstation computer through a frame grabber. Subjects can see a green dot from the fixation target through the dichroic beamsplitter. SLD: Superluminescent diode.

Fig. 2

Fundus color photograph of a normal human subject with OCT scanning locations. (a) Scanning 3x3 mm² of a parafoveal region. (b) Scanning 1.5x1.5 mm² of a perifoveal region.

Fig. 3

Fourier domain optical coherence tomography of the in vivo human retina. (a) Intensity image of a single B-scan. (b) Phase image of the same single B-scan as (a). (c) Average intensity image of five B-scans. (d) Phase-variance processed image using phase data from the same five B-scans phase data as (c). The scanning size of the lateral direction is 3 mm and the sampling density of the lateral direction is 6 μm. Scale bar: 500 μm.

Fig. 4

In vivo human retinal vasculature images with a normal subject. The size of imaging is 3x3 mm². (a) Fluorescein angiography. (b) Projection image of phase-variance OCT retinal layers. The numbers of A-scans and B-scans are 500 and 200, respectively. The imaging acquisition time is 3.6 seconds. Scale bar: 500μm.

Fig. 5

Human retinal images of phase-variance OCT data processing over 1.5 mm. (a) Average intensity imaging of three B-scans from a single BM-scan. (b) Phase-variance image. (c) Combined image of average intensity (a) and red color-coded phase-variance imaging (b). Media 1 shows the composite image over the 1.5x1.5 mm² scanning area. The imaging acquisition time of a single BM-scan containing three B-scans is approximately 10 ms. Scale bar: 250 μm.

Fig. 6

In vivo human retinal micro-capillary network. Image size is 1.5x1.5 mm². (a) Fluorescein angiography. (b) Projection view of retinal contributions to pvOCT. The numbers of A-scans and B-scans are 375 and 360, respectively. (c) RGB depth color-coded projection view of retinal pvOCT data. Upper right shows depth scale bar with red color denoting a top layer, green showing capillaries as an intermediate vascular bed, and finally blue represents micro-capillaries as a deeper vascular plexus layer. The imaging acquisition time of pvOCT is 3.5 seconds. Scale bar: 250 μm. Media 2 shows C-scan fly through of the three-dimensional pvOCT data set.

Fig. 7

Three-dimensional depth color-coded image of pvOCT, using the same data presented in Fig. 6 (c).

Fig. 8

Large field of view stitched pvOCT imaging overlaid on a fundus FA. (a) Fluorescein angiography. (b) Depth color-coded imaging with the ten volumes. Total image acquisition time for ten volumetric images is approximately 35 seconds.