Alfred R. Fuller

Cellular resolution volumetric in vivo retinal imaging with adaptive optics–optical coherence tomography

Ultrahigh-resolution adaptive optics-optical coherence tomography (UHR-AO-OCT) instrumentation allowing monochromatic and chromatic aberration correction was used for volumetric in vivo retinal imaging of various retinal structures including the macula and optic nerve head (ONH). Novel visualization methods that simplify AO-OCT data viewing are presented, and include co-registration of AO-OCT volumes with fundus photography and stitching of multiple AO-OCT sub-volumes to create a large field of view (FOV) high-resolution volume. Additionally, we explored the utility of Interactive Science Publishing by linking all presented AO-OCT datasets with the OSA ISP software.

Adaptation of a support vector machine algorithm for segmentation and visualization of retinal structures in volumetric optical coherence tomography data sets

Recent developments in Fourier domain-optical coherence tomography (Fd-OCT) have increased the acquisition speed of current ophthalmic Fd-OCT instruments sufficiently to allow the acquisition of volumetric data sets of human retinas in a clinical setting. The large size and three-dimensional (3D) nature of these data sets require that intelligent data processing, visualization, and analysis tools are used to take full advantage of the available information. Therefore, we have combined methods from volume visualization, and data analysis in support of better visualization and diagnosis of Fd-OCT retinal volumes. Custom-designed 3D visualization and analysis software is used to view retinal volumes reconstructed from registered B-scans. We use a support vector machine (SVM) to perform semiautomatic segmentation of retinal layers and structures for subsequent analysis including a comparison of measured layer thicknesses. We have modified the SVM to gracefully handle OCT speckle noise by treating it as a characteristic of the volumetric data. Our software has been tested successfully in clinical settings for its efficacy in assessing 3D retinal structures in healthy as well as diseased cases. Our tool facilitates diagnosis and treatment monitoring of retinal diseases.

Correction of motion artifacts and scanning beam distortions in 3D ophthalmic optical coherence tomography imaging

The ability to obtain true three-dimensional (3D) morphology of the retinal structures is essential for future clinical and experimental studies. It becomes especially critical if the measurements acquired with different instruments need to be compared, or precise volumetric data are needed for monitoring and treatment of retinal disease. On the other hand, it is well understood that optical coherence tomography (OCT) images are distorted by several factors. Only limited work has been performed to eliminate these problems in ophthalmic retinal imaging, perhaps because they are less evident in the more common 2D representation mode of time-domain OCT. With recent progress in imaging speed of Fourier domain - OCT (Fd-OCT) techniques, however, 3D OCT imaging is more frequently being used, thereby exposing problems that have been ignored previously. In this paper we propose possible solutions to minimize and compensate for artifacts caused by subject eye and head motion, and distortions caused by the geometry of the scanning optics. The first is corrected by cross-correlation based B-scan registration techniques; the second is corrected by incorporating the geometry of the scanning beam into custom volume rendering software. Retinal volumes of optical nerve head (ONH) and foveal regions of healthy volunteer, with and without corrections, are presented. Finally, some common factors that may lead to increased distortions of the ophthalmic OCT image such as refractive error or position of the subjects head are discussed.

Real-time procedural volumetric fire

We present a method for generating procedural volumetric fire in real time. By combining curve-based volumetric free-form deformation, hardware-accelerated volumetric rendering and Improved Perlin Noise or M-Noise we are able to render a vibrant and uniquely animated volumetric fire that supports bi-directional environmental macro-level interactivity. Our system is easily customizable by content artists. The fire is animated both on the macro and micro levels. Macro changes are controlled either by a prescripted sequence of movements, or by a realistic particle simulation that takes into account movement, wind, high-energy particle dispersion and thermal buoyancy. Micro fire effects such as individual flame shape, location, and flicker are generated in a pixel shader using three- to four-dimensional Improved Perlin Noise or M-Noise (depending on hardware limitations and performance requirements). Our method supports efficient collision detection, which, when combined with a sufficiently intelligent particle simulation, enables real-time bi-directional interaction between the fire and its environment. The result is a three-dimensional procedural fire that is easily designed and animated by content artists, supports dynamic interaction, and can be rendered in real time.

3D OCT imaging in clinical settings : toward quantitative measurements of retinal structures

The acquisition speed of current FD-OCT (Fourier Domain - Optical Coherence Tomography) instruments allows rapid screening of three-dimensional (3D) volumes of human retinas in clinical settings. To take advantage of this ability requires software used by physicians to be capable of displaying and accessing volumetric data as well as supporting post processing in order to access important quantitative information such as thickness maps and segmented volumes. We describe our clinical FD-OCT system used to acquire 3D data from the human retina over the macula and optic nerve head. B-scans are registered to remove motion artifacts and post-processed with customized 3D visualization and analysis software. Our analysis software includes standard 3D visualization techniques along with a machine learning support vector machine (SVM) algorithm that allows a user to semi-automatically segment different retinal structures and layers. Our program makes possible measurements of the retinal layer thickness as well as volumes of structures of interest, despite the presence of noise and structural deformations associated with retinal pathology. Our software has been tested successfully in clinical settings for its efficacy in assessing 3D retinal structures in healthy as well as diseased cases. Our tool facilitates diagnosis and treatment monitoring of retinal diseases.

Towards building an anatomically correct solid eye model with volumetric representation of retinal morphology

An accurate solid eye model (with volumetric retinal morphology) has many applications in the field of ophthalmology, including evaluation of ophthalmic instruments and optometry/ophthalmology training. We present a method that uses volumetric OCT retinal data sets to produce an anatomically correct representation of three-dimensional (3D) retinal layers. This information is exported to a laser scan system to re-create it within solid eye retinal morphology of the eye used in OCT testing. The solid optical model eye is constructed from PMMA acrylic, with equivalent optical power to that of the human eye (~58D). Additionally we tested a water bath eye model from Eyetech Ltd. with a customized retina consisting of five layers of ~60 μm thick biaxial polypropylene film and hot melt rubber adhesive.

Development of quantitative diagnostic observables for age-related macular degeneration using Spectral Domain OCT

We report on the development of quantitative, reproducible diagnostic observables for age-related macular degeneration (AMD) based on high speed spectral domain optical coherence tomography (SDOCT). 3D SDOCT volumetric data sets (512 x 1000 x 100 voxels) were collected (5.7 seconds acquisition time) in over 50 patients with age-related macular degeneration and geographic atrophy using a state-of-the-art SDOCT scanner. Commercial and custom software utilities were used for manual and semi-automated segmentation of photoreceptor layer thickness, total drusen volume, and geographic atrophy cross-sectional area. In a preliminary test of reproducibility in segmentation of total drusen volume and geographic atrophy surface area, inter-observer error was less than 5%. Extracted volume and surface area of AMD-related drusen and geographic atrophy, respectively, may serve as useful observables for tracking disease state that were not accessible without the rapid 3D volumetric imaging capability unique to retinal SDOCT.

Comparison of real-time visualization of volumetric OCT data sets by CPU-slicing and GPU-ray casting methods

We describe and compare two volume visualization methods for Optical Coherence Tomography (OCT) retinal data sets. One of these methods is CPU-slicing, which is previously reported and used in our visualization engine. The other is GPU-ray casting. Several metrics including image quality, performance, hardware limitations and perception are used to grade the abilities of each method. We also discuss how to combine these methods to make a scalable volume visualization system that supports advanced lighting and dynamic volumetric shadowing techniques on a broad range of hardware. The feasibility of each visualization method for clinical application as well as potential further improvements are discussed.

Application of adaptive optics: optical coherence tomography for in vivo imaging of microscopic structures in the retina and optic nerve head

Two deformable mirrors (2DM) were used in an adaptive optics - optical coherence tomography (AO-OCT) system to image in vivo microscopic retinal structures of healthy and diseased retinas. As a result, multiple morphological structures not previously seen in vivo have been visualized. Among those presented are three-dimensional representations of the fovea and optic nerve head (ONH), revealing cellular structures and micro-vasculature. Drusen in macular degeneration and photoreceptor dystrophies are also presented. Different methods for displaying volumetric AO-OCT data to facilitate visualization of certain morphological details are compared.