Kinpui Chan

Three-dimensional and high-speed swept-source optical coherence tomography for in vivo investigation of human anterior eye segments

A two- and three-dimensional swept source optical coherence tomography (SS-OCT) system, which uses a ready-to-ship scanning light source, is demonstrated. The light source has a center wavelength of 1.31 mum, -3 dB wavelength range of 110 nm, scanning rate of 20 KHz, and high linearity in frequency scanning. This paper presents a simple calibration method using a fringe analysis technique for spectral rescaling. This SS-OCT system is capable of realtime display of two-dimensional OCT and can obtain three-dimensional OCT with a measurement time of 2 s. In vivo human anterior eye segments are investigated two- and three-dimensionally. The system sensitivity is experimentally determined to be 114 dB. The three-dimensional OCT volumes reveal the structures of the anterior eye segments, which are difficult to observe in two-dimensional OCT images.

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.

Automated segmentation of outer retinal layers in macular OCT images of patients with retinitis pigmentosa

To provide a tool for quantifying the effects of retinitis pigmentosa (RP) seen on spectral domain optical coherence tomography images, an automated layer segmentation algorithm was developed. This algorithm, based on dual-gradient information and a shortest path search strategy, delineates the inner limiting membrane and three outer retinal boundaries in optical coherence tomography images from RP patients. In addition, an automated inner segment (IS)/outer segment (OS) contour detection method based on the segmentation results is proposed to quantify the locus of points at which the OS thickness goes to zero in a 3D volume scan. The segmentation algorithm and the IS/OS contour were validated with manual segmentation data. The segmentation and IS/OS contour results on repeated measures showed good within-day repeatability, while the results on data acquired on average 22.5 months afterward demonstrated a possible means to follow disease progression. In particular, the automatically generated IS/OS contour provided a possible objective structural marker for RP progression.

Optical Coherence Tomography in the UK Biobank Study – Rapid Automated Analysis of Retinal Thickness for Large Population-Based Studies

Purpose To describe an approach to the use of optical coherence tomography (OCT) imaging in large, population-based studies, including methods for OCT image acquisition, storage, and the remote, rapid, automated analysis of retinal thickness. Methods In UK Biobank, OCT images were acquired between 2009 and 2010 using a commercially available “spectral domain” OCT device (3D OCT-1000, Topcon). Images were obtained using a raster scan protocol, 6 mm x 6 mm in area, and consisting of 128 B-scans. OCT image sets were stored on UK Biobank servers in a central repository, adjacent to high performance computers. Rapid, automated analysis of retinal thickness was performed using custom image segmentation software developed by the Topcon Advanced Biomedical Imaging Laboratory (TABIL). This software employs dual-scale gradient information to allow for automated segmentation of nine intraretinal boundaries in a rapid fashion. Results 67,321 participants (134,642 eyes) in UK Biobank underwent OCT imaging of both eyes as part of the ocular module. 134,611 images were successfully processed with 31 images failing segmentation analysis due to corrupted OCT files or withdrawal of subject consent for UKBB study participation. Average time taken to call up an image from the database and complete segmentation analysis was approximately 120 seconds per data set per login, and analysis of the entire dataset was completed in approximately 28 days. Conclusions We report an approach to the rapid, automated measurement of retinal thickness from nearly 140,000 OCT image sets from the UK Biobank. In the near future, these measurements will be publically available for utilization by researchers around the world, and thus for correlation with the wealth of other data collected in UK Biobank. The automated analysis approaches we describe may be of utility for future large population-based epidemiological studies, clinical trials, and screening programs that employ OCT imaging.

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].

Evaluation of Cultured Corneal Epithelial Cells and Epithelial Thickness by Full-Field Optical Coherence Tomography

The growth process of cultured corneal epithelial cells has been evaluated by full-field optical coherence tomography. Three different layers of the epithelium were discriminated and the thickness of corneal epithelium was quantitatively measured.

Three-dimensional investigation of in vivo anterior eye segments by swept-source optical coherence tomography with ready-for-shipping scanning light source

A two- and three- dimensional swept source optical coherence tomography (SS-OCT) system which uses a ready-to-ship scanning light source is demonstrated. The light source has the center wavelength of 1.31 μm, the -3 dB wavelength range of 110 nm, the scanning rate of 20 KHz and high linearity of frequency scanning. A simple calibration method using a fringe analysis technique for spectral rescaling is presented. This SS-OCT is capable of realtime display of two-dimensional OCT, and can take three-dimensional OCT with the measurement time of 2 s. In vivo human anterior eye segments are investigated both two- and three- dimensionally. The system sensitivity is experimentally determined as 113 dB.

Video-rate en-face OCT imaging by parallel heterodyne detection

We have demonstrated video-rate horizontal cross-sectional (en-face) OCT imaging using a parallel heterodyne detection technique. This technique is based on a dual-channel frequency synchronous detection technique that operates a pair of CCD cameras as two-dimensional heterodyne sensor arrays. Using this technique a series of full-field en-face OCT images are acquired at a rate of 100 frames/s during a single longitudinal scan. Results of en-face OCT imaging are reported.