Zhenguo Wang

Automated layer segmentation of macular OCT images using dual-scale gradient information

A novel automated boundary segmentation algorithm is proposed for fast and reliable quantification of nine intra-retinal boundaries in optical coherence tomography (OCT) images. The algorithm employs a two-step segmentation schema based on gradient information in dual scales, utilizing local and complementary global gradient information simultaneously. A shortest path search is applied to optimize the edge selection. The segmentation algorithm was validated with independent manual segmentation and a reproducibility study. It demonstrates high accuracy and reproducibility in segmenting normal 3D OCT volumes. The execution time is about 16 seconds per volume (480x512x128 voxels). The algorithm shows potential for quantifying images from diseased retinas as well.

Introduction to Swept Source OCT

Optical coherence tomography (OCT), first introduced in 1991, is an enabling optical, noninvasive imaging modality that provides cross-sectional visualization of biological tissues with resolutions one to two orders of magnitude better than conventional ultrasound [1]. Because the eye is optically accessible for visible and near-infrared light, ophthalmic OCT has been the most successful clinical application from the invention of OCT with an unparalleled combination of axial resolution (1–10 μm) and penetration depth (1–2 mm in tissue). This chapter presents a brief introduction of OCT, including the early time-domain OCT (TD-OCT) and the more recent Fourier-domain OCT (FD-OCT), which can be characterized into the two forms of spectral-domain OCT (SD-OCT) and swept source OCT (SS-OCT). Since the commercial launch of SD-OCT in 2006 by multiple manufacturers, including the world’s first Topcon 3D OCT-1000, the significant practical advantages of both higher speed and higher sensitivity of SD-OCT over TD-OCT [2–4] have led to a widespread use of OCT instruments in ophthalmology [5]. On the other hand, SS-OCT, which employs the state-of-the-art high-speed wavelength tuning laser (swept source) as well as digital data acquisition and processing technology, offers further advantages of overcoming the signal roll-off observed for SD-OCT at a deeper range along with an unprecedented A-scan rate for wider field-of-view structural OCT and OCT angiography imaging [6, 7]. With advances in commercial wavelength tuning lasers, the first clinical 1 μm SS-OCT machine, Topcon DRI OCT-1 Atlantis, became commercially available for retinal imaging in 2012 [8].