Koozekanani Dara, Boyer Kim L, Roberts Cynthia
Biomedical Engineering Program, Signal Analysis and Machine Perception Laboratory, Department of Electrical Engineering, College of Medicine, The Ohio State University, Columbus, OH 43210-1272, USA.
IEEE Trans Med Imaging. 2003 Dec;22(12):1519-36. doi: 10.1109/TMI.2003.817753.
Optical coherence tomography (OCT) is a new ophthalmic imaging modality generating cross sectional views of the retina. OCT systems are essentially Michelson interferometers that form images in 1.5 s by directing a superluminescent diode (SLD) beam over the retinal surface. Involuntary eye motions frequently cause incorrect locations to be imaged. This motion may leave no obvious artifacts in the scan data and can easily go undetected. For glaucoma monitoring especially, knowing the measurement path, typically a circle concentric with the nerve head, is crucial. The commercially available OCT system displays a near-infrared video of the retina showing the SLD beam. This paper presents a prototype system to detect the nerve head and SLD beam in the video, and report the true scan path relative to the nerve head. Low image contrast and limited resolution make the reliable detection of retinal features difficult. In an adaptive model construction phase, the system directly detects retinal vasculature and the nerve head and incrementally builds a model of the current subject's vascular pattern relative to the optic disk. The nerve head identification is multitiered, using a novel dual eigenspace technique and a geometric comparison of detected vessel positions and nerve head hypotheses. In its operational phase, a correspondence is achieved between the currently detected vasculature and the model. Using subjects not included in training, the system located the optic nerve head to within 5 pixels (0.07 optic disk diameters, an error well below clinical significance) in 99.75% of 2800 video fields. In current clinical practice, motions as large as 1-2 disc diameters may go undetected, so this is a vast improvement.
光学相干断层扫描（OCT）是一种新型眼科成像方式，可生成视网膜的横截面视图。OCT系统本质上是迈克尔逊干涉仪，通过将超发光二极管（SLD）光束投射到视网膜表面，在1.5秒内形成图像。非自主眼球运动经常导致成像位置错误。这种运动可能在扫描数据中不留下明显伪影，并且很容易未被检测到。特别是对于青光眼监测，了解测量路径（通常是与视盘同心的圆）至关重要。市售的OCT系统会显示视网膜的近红外视频，展示SLD光束。本文提出了一种原型系统，用于在视频中检测视盘和SLD光束，并报告相对于视盘的真实扫描路径。低图像对比度和有限分辨率使得可靠检测视网膜特征变得困难。在自适应模型构建阶段，该系统直接检测视网膜血管系统和视盘，并逐步构建当前受试者相对于视盘的血管模式模型。视盘识别是多层次的，使用了一种新颖的双特征空间技术以及检测到的血管位置与视盘假设的几何比较。在其操作阶段，在当前检测到的血管系统与模型之间建立对应关系。使用未包含在训练中的受试者，该系统在2800个视野中的99.75%中将视神经头定位在5个像素以内（0.07个视盘直径，误差远低于临床意义）。在当前临床实践中，高达1 - 2个视盘直径的运动可能未被检测到，所以这是一个巨大的改进。
