Ravi K. Ghanta

Ultrahigh-resolution ophthalmic optical coherence tomography

Here we present new technology for optical coherence tomography (OCT) that enables ultrahigh-resolution, non-invasive in vivo ophthalmologic imaging of retinal and corneal morphology with an axial resolution of 2–3 μm. This resolution represents a significant advance in performance over the 10–15-μm resolution currently available in ophthalmic OCT systems and, to our knowledge, is the highest resolution for in vivo ophthalmologic imaging achieved to date. This resolution enables in vivo visualization of intraretinal and intra-corneal architectural morphology that had previously only been possible with histopathology. We demonstrate image processing and segmentation techniques for automatic identification and quantification of retinal morphology. Ultrahigh-resolution OCT promises to enhance early diagnosis and objective measurement for tracking progression of ocular diseases, as well as monitoring the efficacy of therapy.

Ultrahigh-resolution optical coherence tomography using continuum generation in an air–silica microstructure optical fiber

We demonstrate ultrahigh-resolution optical coherence tomography (OCT) using continuum generation in an air-silica microstructure fiber as a low-coherence light source. A broadband OCT system was developed and imaging was performed with a bandwidth of 370 nm at a 1.3-mu;m center wavelength. Longitudinal resolutions of 2.5 microm in air and ~2 microm in tissue were achieved. Ultrahigh-resolution imaging in biological tissue in vivo was demonstrated.

Ultrahigh resolution in vivo versus ex vivo OCT imaging and tissue preservation

Summary form only given. Many previous studies have compared ex vivo OCT imaging to histopathology. While some tissues, such are arterial pathology or cartilage, are relatively stable post mortem, others, such as epithelial tissues, exhibit rapid degradation. It is therefore important to preserve these tissues with minimal changes in morphology. The goal of this study is to investigate the difference between in vivo and ex vivo OCT imaging and the effect of different preservation solutions on image quality using the hamster cheek pouch. The hamster cheek pouch was chosen because of its easy access and because it is a well established model for carcinogenesis and cancer progression. The advent of the ultrahigh resolution OCT imaging technology is important for this study because it enables changes in tissue morphology to be dearly visualized which may have been difficult to resolve with standard resolution OCT imaging.

OCT imaging of osteoarthritic cartilage: structure, polarization sensitivity, and clinical feasibility

This work demonstrates the feasibility of OCT for identifying early osteoarthritic pathology. In addition to structural abnormalities, changes in collagen fiber organization, an indicator of very early osteoarthritis, were assessed with a polarization sensitive OCT system. A portable, real time, modular OCT system, suitable for both laboratory and clinical settings, has been developed. Preliminary in vivo imaging results obtained during partial knee replacement surgery are discussed.

In-vivo optical biopsy of the human retina using optical coherence tomography

Using state of the art laser technology, third generation ophthalmologic optical coherence tomography (OCT) has been developed which enables ultrahigh resolution, non-invasive in vivo imaging of retinal morphology with an unprecedented axial resolution of 3 micrometers . This represents a quantum leap in performance over the 10-15 micrometers resolution currently available in ophthalmic OCT systems and, to our knowledge, is the highest resolution in vivo ophthalmologic imaging achieved to date. This resolution enables optical biopsy, i.e. the in vivo visualization of intraretinal architectural morphology which had previously only been possible with histopathology. Image processing and segmentation techniques are demonstrated for automatic identification and quantification of retinal morphology. Ultrahigh resolution ophthalmic OCT has the potential to enhance the sensitivity and specificity for early diagnosis of several ocular diseases, e.g. glaucoma, which requires precise imaging and measurement of retinal nerve fiber layer thickness, as well as improve monitoring of disease progression and efficacy of therapy.

In vivo ultrahigh-resolution, functional optical coherence tomography

Summary form only given.Optical coherence tomography (OCT), has been extensively evaluated as a possible diagnostic tool for high-speed, noninvasive, high-resolution in vivo and in situ imaging in a variety of medical fields. Based on low coherence interferometry, the axial resolution of OCT is limited by the bandwidth of the light source, usually a superluminescent diode, to typically 10-15 /spl mu/m. This is approximately one order of magnitude better than any other conventional technique. However many of the early changes associated with diseases are still below its detection limit. Recent developments of femtosecond Kerr-lens mode-locking of Ti:sapphire solid-state lasers have established a generation of powerful low-coherence light sources for OCT.

Ultrahigh resolution retinal imaging with optical coherence tomography

Summary form only given. Current clinical practice calls for the development of techniques to diagnose retinal disease in its early stages, when treatment is most effective and significant irreversible damage can either be prevented or delayed. At 10-/spl mu/m axial resolution, optical coherence tomography (OCT) already provides more detailed structural information than any other conventional imaging technique. However the detection of many of the early changes associated with diseases, such as age-related macular degeneration, glaucoma, and diabetic retinopathy, can require more accurate quantitation of retinal structure than is possible with standard resolution OCT. The axial resolution of OCT in clinical ophthalmic systems is limited to 10-15 /spl mu/m by the bandwidth of superluminescent diodes light sources used for imaging. The paper presents the development and application of a third-generation ophthalmic OCT system, with 3-/spl mu/m axial resolution, for in vivo quantitative structural and functional imaging of the retina.

Ultrahigh-resolution in vivo versus ex vivo OCT imaging and tissue preservation

Many studies have been performed which compare ex-vivo OCT imaging to histopathology in a wide range of tissues and organ systems. While some tissues, such as arterial pathology or cartilage, are relatively stable post mortem, others, such as epithelial tissues, exhibit rapid degradation. It is important to preserve these tissues with minimal changes in morphology relative to their in vivo state in order to enable meaningful ex vivo OCT imaging studies. In this paper, we investigate the differences between in vivo and ex vivo OCT imaging and the effect of different tissue preservation solutions on tissue degradation and image quality. Ultrahigh resolution OCT imaging was preformed using a Ti:Al2O3 light source with 2 micrometers axial and 5 micrometers transverse resolution, using the hamster cheek pouch as a model for epithelial tissue. Tissue preservation solutions examined included: low temperature saline, room temperature saline, phosphate buffered sucrose, University of Wisconsin solution, and 10% formalin. Results of in vivo versus ex vivo ultrahigh resolution OCT imaging indicate that changes in optical properties and image degradation occur on a rapid time scale (in minutes) for all preservation solutions except formalin.

Ultrahigh resolution optical coherence tomography for quantitative topographic mapping of retinal and intraretinal architectural morphology

Quantitative, three-dimensional mapping of retinal architectural morphology was achieved using an ultrahigh resolution ophthalmic OCT system. This OCT system utilizes a broad bandwidth titanium-sapphire laser light source generating bandwidths of up to 300 nm near 800 nm center wavelength. The system enables real-time cross-sectional imaging of the retina with ~3 micrometers axial resolution. The macula and the papillomacular axis of a normal human subject were systematically mapped using a series of linear scans. Edge detection and segmentation algorithms were developed to quantify retinal and intraretinal thicknesses. Topographic mapping of the total retinal thickness and the total ganglion cell/inner plexiform layer thickness was achieved around the macula. A topographic mapping quantifying the progressive thickening of the nerve fiber layer (NFL) nasally approaching the optic disk was also demonstrated. The ability to create three-dimensional topographic mapping of retinal architectural morphology at ~3 micrometers axial resolution will be relevant for the diagnosis of many retinal diseases. The topographic quantification of these structures can serve as a powerful tool for developing algorithms and clinical scanning protocols for the screening and staging of ophthalmic diseases such as glaucoma.

Ultrahigh resolution, functional optical coherence tomography using state of the art femtosecond laser technology

Using state of the art femtosecond laser technology, in vivo optical coherence tomography imaging with subcellular level resolution is achieved, enabling optical biopsy, the in situ visualization of biological tissue at the level of histopathology. Spectroscopic OCT allows the extraction of spatially resolved functional or biochemical properties.