Choriocapillaris and Choroidal Microvasculature Imaging with Ultrahigh Speed OCT Angiography

We demonstrate in vivo choriocapillaris and choroidal microvasculature imaging in normal human subjects using optical coherence tomography (OCT). An ultrahigh speed swept source OCT prototype at 1060 nm wavelengths with a 400 kHz A-scan rate is developed for three-dimensional ultrahigh speed imaging of the posterior eye. OCT angiography is used to image three-dimensional vascular structure without the need for exogenous fluorophores by detecting erythrocyte motion contrast between OCT intensity cross-sectional images acquired rapidly and repeatedly from the same location on the retina. En face OCT angiograms of the choriocapillaris and choroidal vasculature are visualized by acquiring cross-sectional OCT angiograms volumetrically via raster scanning and segmenting the three-dimensional angiographic data at multiple depths below the retinal pigment epithelium (RPE). Fine microvasculature of the choriocapillaris, as well as tightly packed networks of feeding arterioles and draining venules, can be visualized at different en face depths. Panoramic ultra-wide field stitched OCT angiograms of the choriocapillaris spanning ∼32 mm on the retina show distinct vascular structures at different fundus locations. Isolated smaller fields at the central fovea and ∼6 mm nasal to the fovea at the depths of the choriocapillaris and Sattler's layer show vasculature structures consistent with established architectural morphology from histological and electron micrograph corrosion casting studies. Choriocapillaris imaging was performed in eight healthy volunteers with OCT angiograms successfully acquired from all subjects. These results demonstrate the feasibility of ultrahigh speed OCT for in vivo dye-free choriocapillaris and choroidal vasculature imaging, in addition to conventional structural imaging.本研究展示了利用光学相干断层扫描（optical coherence tomography, OCT）对正常人体受试者开展活体脉络膜毛细血管及脉络膜微脉管系统成像的研究成果。本研究研发了一款工作波长1060 nm、A扫描速率达400 kHz的超高速扫频OCT原型系统，用于实现眼球后部的三维超高速成像。光学相干断层扫描血管造影（OCT angiography, OCTA）无需引入外源性荧光染料，通过检测从视网膜同一位置快速重复采集的OCT强度断层图像间的红细胞运动对比度，即可实现三维血管结构成像。通过光栅扫描获取体素化断层OCT血管造影图像，并在视网膜色素上皮（retinal pigment epithelium, RPE）下方多个深度处对三维血管造影数据进行分割，即可可视化脉络膜毛细血管及脉络膜脉管系统的面扫OCT血管造影图。在不同面扫深度下，可清晰观测到脉络膜毛细血管的精细微脉管结构，以及密集排布的供血小动脉和引流小静脉网络。跨度覆盖视网膜约32 mm的脉络膜毛细血管全景超宽视场拼接OCT血管造影图，可显示不同眼底位置的特征性血管结构。针对黄斑中心凹及黄斑鼻侧约6 mm处的孤立小视野，在脉络膜毛细血管层及Sattler层深度下采集的OCT血管造影图，其脉管结构与组织学及电子显微腐蚀铸型研究中确立的解剖形态特征高度吻合。本研究对8名健康志愿者开展了脉络膜毛细血管成像，所有受试者均成功获取到合格的OCT血管造影图像。上述结果证明，除常规结构成像外，超高速OCT技术可用于实现无需外源性染色剂的活体脉络膜毛细血管及脉络膜脉管系统成像。