Showing papers on "Optical coherence tomography published in 1996"

Optical Coherence Tomography for Optical Biopsy Properties and Demonstration of Vascular Pathology

Abstract: Background Optical coherence tomography (OCT) is a recently developed medical diagnostic technology that uses back-reflected infrared light to perform in situ micron scale tomographic imaging. In this work, we investigate the ability of OCT to perform micron scale tomographic imaging of the internal microstructure of in vitro atherosclerotic plaques. Methods and Results Aorta and relevant nonvascular tissue were obtained at autopsy. Two-dimensional cross-sectional imaging of the exposed surface of the arterial segments was performed in vitro with OCT. A 1300-nm wavelength, superluminescent diode light source was used that allows an axial spatial resolution of 20 μm. The signal-to-noise ratio was 109 dB. Images were displayed in gray scale or false color. Imaging was performed over 1.5 mm into heavily calcified tissue, and a high contrast was noted between lipid- and water-based constituents, making OCT attractive for intracoronary imaging. The 20-μm axial resolution of OCT allowed small structural details...

Optical coherence tomography.

Abstract: This paper gives an introduction to optical coherence tomography (OCT), explains its basic principles, and discusses the information content of OCT images. Various interferometric techniques used in OCT are reviewed and a short survey of results obtained so far in different fields of application and possible future developments are presented.

Single mode fiber-optic catheter/endoscope for optical coherence tomography

Abstract: Summary form only given. In order to apply OCT for imaging of internal organ systems, a flexible, small diameter, catheter/endoscope, which is capable of delivering, focusing, scanning, and collecting a single-spatial-mode optical beam, must be constructed. In this summary, we describe the design and performance of a prototype single-mode fiber-optic scanning OCT catheter with a diameter of 1 mm. OCT imaging may be performed at 1.3-micron wavelengths using either a superluminescent laser diode source or a Kerr-lens mode-locked Cr:forsterite laser, which provides high powers for high-speed imaging. This device is an enabling technology for OCT and will permit micron scale, cross-sectional medical diagnostic imaging in tissues such as the vascular system, the gastrointestinal tract, the urinary tract, and the respiratory tract.

Optical coherence tomography and microscopy in gastrointestinal tissues

Abstract: Optical coherence tomography (OCT) and optical coherence microscopy (OCM) are novel techniques for noninvasive biomedical imaging based on low-coherence interferometry. OCT achieves high-spatial resolution ( 100 dB) in a fiber-optically integrated system which is suitable for application in minimally invasive diagnostics, including endoscopy. The technique of OCM combines the depth-ranging capability of OCT with the micron-scale resolution imaging capability of confocal microscopy to extend the available imaging depth of confocal microscopy up to several hundred micrometers deep in highly scattering tissues. The theoretical and technical bases for OCT and OCM imaging are described. Example OCT images are provided in gastrointestinal (GI) tissues to illustrate contrast between histological layers of the GI mucosa and differentiation of the mucosa from submucosa. Example OCM images revealing cellular-level microstructure up to several hundred micrometers deep in GI tissue are presented for the first time. The potential applications of OCT and OCM imaging in clinical diagnostic medicine are discussed.

Characterization of epiretinal membranes using Optical Coherence Tomography (OCT)

Abstract: OBJECTIVE To evaluate optical coherence tomography (OCT), a novel noncontact and noninvasive imaging technique, for the diagnosis and quantitative characterization of epiretinal membranes. METHODS Optical coherence tomography is similar to an ultrasound B-scan, except that light rather than sound is used, which enables higher resolution. Over a 2-year period, OCT was used to examine 186 eyes of 160 patients who had a diagnosis of an epiretinal membrane. Optical coherence tomograms were correlated with visual acuity, slit-lamp biomicroscopy, fluorescein angiography, and funds photography. RESULTS Based on OCT, the epiretinal membrane was clearly separated from the retina with focal points of attachment in 49 eyes and globally adherent (no observed separation) in 125 eyes. Globally adherent membranes were associated with the following features: macular pseudohole (32 eyes), a difference in optical reflectivity between the membrane and retina (65 eyes), and/or a visible membrane tuft or edge (92 eyes). The membrane was undetectable on OCT in 12 eyes. The membrane thickness (mean +/- standard deviation) was 61 +/- 28 microns in the 169 eyes in which the thickness could be measured with OCT. Mean central macular thickness measured with OCT correlated with visual acuity (R2 = 0.73). CONCLUSION Optical coherence tomography was able to provide a structural assessment of the macula that was useful in the preoperative and postoperative evaluation of epiretinal membrane surgery. Quantitative measurements and the assessment of membrane adherence with OCT may be useful in characterizing the surgical prognosis of eyes with an epiretinal membrane.

Rapid acquisition of in vivo biological images by use of optical coherence tomography.

Abstract: The development of techniques for high-speed image acquisition in optical coherence tomography (OCT) systems is essential for suppressing motion artifacts when one is imaging living systems. We describe a new OCT system for performing micrometer-scale, cross-sectional optical imaging at four images/s. To achieve OCT image-acquisition times of less than 1 s, we use a piezoelectric fiber stretcher to vary the reference arm delay. A Kerr-lens mode-locked chromium-doped forsterite laser is employed as the low-coherence source for the highspeed OCT system. Dynamic, motion-artifact-free in vivo imaging of a beating Xenopus laevis (African frog) heart is demonstrated.

Self-phase-modulated Kerr-lens mode-locked Cr:forsterite laser source for optical coherence tomography.

Abstract: An all-solid-state Kerr-lens mode-locked Cr:forsterite laser operating at 1.28 μm is demonstrated as a shortcoherence-length, high-average-power source for optical coherence tomographic (OCT) imaging. We achieve ultrahigh resolution by spectrally broadening the laser pulses, using self-phase modulation in a dispersion-shifted single-mode fiber. OCT imaging with a resolution of 6 μm and a dynamic range of 115 dB is achieved.

Imaging of coronary artery microstructure (in vitro) with optical coherence tomography

Abstract: OCT achieves high-resolution and image differentiation of vascular tissues to a degree that has not been previously possible with any method except excisional biopsy. Thus, OCT represents a promising new diagnostic technology for intracoronary imaging, which could permit the in vivo evaluation of critical vascular pathology.

Catheter-Based Optical Imaging of a Human Coronary Artery

Abstract: Optical coherence tomography (OCT) is a recently developed technology that uses infrared light to generate micrometer-scale cross-sectional images ( Science. 1991;254:1178-1181). We recently demonstrated the feasibility of using OCT for assessing atherosclerotic plaque microstructure ( Circulation. 1996;93:1206-1213) at resolutions of 4 to 16 …

Imaging Congenital Optic Disc Pits and Associated Maculopathy Using Optical Coherence Tomography

Abstract: Objective: To elucidate the anatomy of congenital optic disc pits with and without maculopathy using optical coherence tomography. Setting: All patients were examined, photographed, and scanned at the New York Eye and Ear Infirmary. Patients: Ten eyes of eight consecutive patients with congenital optic disc pits were studied. Three eyes had associated serous macular detachment (group 1), four had evidence of resolved detachment (group 2), and three had no clinical macular pathologic lesion (group 3). Methods: Optical coherence tomography, a new, noninvasive, noncontact, imaging technology capable of producing cross-sectional images of the retina in vivo with high resolution ( Results: Communication between a schisis cavity or subretinal space and the optic nerve pit was imaged in all eyes in group 1. No such communication could be identified in groups 2 and 3. Cystic degeneration and schisis were imaged in the peripapillary retina, macula, or both in all eyes of groups 1 and 2 and in one patient in group 3. A direct communication between the subretinal space and vitreous cavity could not be identified in any eye. Conclusions: Schisis formation plays an integral role in the development of serous retinal detachment in the presence of congenital optic disc pits. Our findings are consistent with the theory that the optic disc pit acts as a conduit for fluid flow between the schisis cavity or subretinal space and the subarachnoid space.

Evaluation of focal defects in the nerve fiber layer using optical coherence tomography

Abstract: OBJECTIVE To analyze glaucomatous eyes with known focal defects of the nerve fiber layer (NFL), relating optical coherence tomography (OCT) findings to clinical examination, NFL and stereoscopic optic nerve head (ONH) photography, and Humphrey 24-2 visual fields. DESIGN Cross-sectional prevalence study. PARTICIPANTS The authors followed 19 patients in the study group and 14 patients in the control group. INTERVENTION Imaging with OCT was performed circumferentially around the ONH with a circle diameter of 3.4 mm using an internal fixation technique. One hundred OCT scan points taken within 2.5 seconds were analyzed. MAIN OUTCOME MEASURES Measurements of NFL thickness using OCT were performed. RESULTS In most eyes with focal NFL defects, OCTs showed significant thinning of the NFL in areas closely corresponding to focal defects visible on clinical examination, to red-free photographs, and to defects on the Humphrey visual fields. Optical coherence tomography enabled the detection of focal defects in the NFL with a sensitivity of 65% and a specificity of 81%. CONCLUSION Analysis of NFL thickness in eyes with focal defects showed good structural and functional correlation with clinical parameters. Optical coherence tomography contributes to the identification of focal defects in the NFL that occur in early stages of glaucoma.

Optical coherence tomography with the "Spectral Radar" - Fast optical analysis in volume scatterers by short coherence interferometry

Abstract: We present a sensor for acquisition of cross-sectional images of volume scatterers, we call it 'spectral radar'. Medical and technical applications are possible. The sensor is a modified Michelson interferometer, with a broad bandwidth light source. The scattering amplitude a(z) along one vertical axis from the surface into the bulk can be measured within one exposure. No reference arm scanning is necessary. Measurement results of stationary and non stationary scattering phantoms, human skin and of a fish eye in vitro are shown.

Simultaneous measurement of thicknesses and refractive indices of multiple layers by a low-coherence confocal interference microscope.

Abstract: We propose a novel technique for simultaneous measurement of layer thicknesses and refractive indices of multiple layers. It is based on a combination of a confocal microscope and low-coherence interferometry. We derived an expression for the geometrical thickness and the refractive index of each layer from both tracing of a marginal ray accepted by a microscope objective and optical path matching conditions. Experimental verification of this method is illustrated by several samples that have a maximum of 13 layers. The geometrical thicknesses and refractive indices thus derived agreed well with those measured by a micrometer or cited from the literature.

Observation of light propagation in volume scatterers with 10 11 -fold slow motion

Abstract: An optical method is introduced for observation of temporally and spatially resolved frames that show how light propagates in diffusely scattering materials. The method permits videos with 100-fs resolution in time to be produced. The method utilizes short-coherence interferometry. The source of information is the speckle contrast. The temporal and spatial evolution of the multiple scattering process is demonstrated for several biological and industrial samples. A major objective of the method is to investigate the conditions for optimum coherence and optimum apertures to achieve high resolution in the short-coherence interferometry. One important result is that during the propagation a sharp photon horizon evolves, which is useful for the morphological analysis of volume scatterers.

Sources of contrast in confocal reflectance imaging.

Abstract: The relationship between optical properties and image contrast in confocal imaging is investigated A Monte Carlo simulation has been developed to analyze the effects of changes in scattering, index of refraction, and absorption in a three-layer medium Contrast was calculated from the computed signal-to-background ratios for changes in tissue optical properties Results show that the largest source of contrast is changes in refractive index

Imaging developing neural morphology using optical coherence tomography

Abstract: Imaging technologies offer numerous possibilities to investigate the processes involved in neural development. The optical coherence tomography (OCT) technology is analogous to ultrasound backscatter microscopy except reflections of light are detected rather than sound. The OCT technology combines high-resolution in vivo imaging in a diode-based benchtop instrument capable of micron-scale resolution in transparent and non-transparent biological specimens. In this paper, we examine the potential of using OCT for the investigation of developing neural morphology. To demonstrate the capabilities of this technique in assessing neural development, we have chosen to image early normal and abnormal neural morphology in a common developmental biology model, Xenopus laevis. In vivo images clearly identify gross and subtle differences in neural structure and may offer an alternative to the costly and time-consuming process of repeated histological preparation for neural developmental studies. Because imaging can be performed rapidly and repeatedly, the morphological changes of single specimens can be followed throughout development. To illustrate the future potential of this technique, a state-of-the-art Cr 4+ :forsterite modelocked laser is used as a broad bandwidth light source to image individual cells in a developing specimen.

Optical Coherent Tomography with Electrically Tunable Semiconductor Laser Using FMCW Techniques

Abstract: Imaging of highly scattering objects in scattering media can play an important part in assessing melanoma in human skin. The technique to be presented is based on frequency modulated continuous waves using a coherent tunable semiconductor laser irradiating a Michelson interferometer. The electrically tunable laser is characterized and the procedure to linearize the instantaneous frequency with time is described. The temporal point spread function of dilute milk is measured. Finally the performance of our imaging system is demonstrated on 2D-images of solid scattering phantoms and of an eye of a pig.

Optical Coherence Tomography of age-related macular degeneration and choroidal neovascularization

Abstract: Objective: The authors used optical coherence tomography (OCT), a new technique for cross-sectional imaging of the retina, to morphologically study eyes with nonexudative and exudative age-related macular degeneration (AMO). In patients with untreated exudative AMO, OCT was compared with fluorescein angiography in the identification and classification of choroidal neovascularization (CNV). Methods: Optical coherence tomography imaging is analogous to ultrasound, except that the use of light rather than sound enables higher longitudinal resolution with a noncontact and noninvasive measurement. Optical coherence tomography was performed on 391 patients with the clinical diagnosis of AMO and was compared with conventional clinical examination to establish the cross-sectional morphology of different lesions and to develop a classification scheme for CNV. Optical coherence tomograms and fluorescein angiograms then were reviewed and correlated independently in 90 eyes of 86 patients who had exudative AMO without previous laser treatment. Results: Pigmentary changes, soft drusen, and detachments of the neurosensory retina and retinal pigment epithelium all had distinct presentations on OCT. Subretinal and intraretinal fluid caused changes in retinal thickness or elevation that could be quantified directly from the images. Choroidal neovascularization was evident in the tomograms as a thickening and fragmentation of a reflective layer, which corresponded to the retinal pigment epithelium and choriocapillaris. Changes in the reflection from this layer were observed during the progression of neovascularization, and after laser photocoagulation treatment. Classic CNV consistently presented with well-defined boundaries on OCT, whereas occult CNV had a variable cross-sectional appearance. Conclusions: Optical coherence tomography was useful in quantitatively evaluating subretinal and intraretinal fluid, assessing possible subfoveal involvement of neovascularization, and in monitOring CNV before and after laser photocoagulation. Optical coherence tomography was unable to detect CNV beneath serous pigment epithelial detachments. Optical coherence tomography may have potential in accurately defining the boundaries in a subset of angiographically occult CNV. Ophthalmology 1996;103:1260-1270

Time-resolved transillumination and optical tomography

Abstract: In response to an invitation by the editor-in-chief, I would like to present the current status of time domain imaging With exciting new photon diffusion techniques being developed in the frequency domain and promising optical coherence tomography, time-resolved transillumination is in constant evolution and the subject of passionate discussions during the numerous conferences dedicated to this subject The purpose of time-resolved optical tomography is to provide noninvasive, high-resolution imaging of the interior of living bodies by the use of nonionizing radiation Moreover, the use of visible to near-infrared wavelength yields metabolic information Breast cancer screening is the primary potential application for time-resolved imaging Neurology and tissue characterization are also possible fields of applications Time-resolvedtransillumination and optical tomography should not only improve diagnoses, but the welfare of the patient As no overview of this technique has yet been presented to my knowledge, this paper briefly describes the various methods enabling time-resolved transillumination and optical tomography The advantages and disadvantages of these methods, as well as the clinical challenges they face are discussed Although an analytic and computable model of light transport through tissues is essential for a meaningful interpretation of the transillumination process, this paper will not dwell on the mathematics of photon propagation

Endoscopic optical coherence tomography

Abstract: We present advances in OCT technology that will enable in vivo OCT imaging of internal organ systems such as the cardiovascular system, the urinary tract, and the gastrointestinal tract. These advances include improvements in image acquisition speed to avoid motion artifacts, and the development of an OCT compatible catheter-endoscope for access to internal organ systems. A fast scanning OCT system has recently been constructed. This system employs a high power (200 mW) chromium doped forsterite laser as the low coherence source and a piezoelectric fiber stretcher to induce reference arm optical path length delay. The fast scanning system acquires OCT images with an acquisition rate of four images per second, an axial resolution of 15 /spl mu/m, and a signal to noise ratio of 112 dB.

Macular disease and optical coherence tomography.

Abstract: Optical coherence tomography (OCT) is a new diagnostic tool for high-resolution cross-sectional imaging of the retina. By measuring the "echo" delay time of light as it reflects from tissue at different ranges and by performing multiple axial scans in the transverse direction, OCT generates two-dimensional images detailing retinal architecture. OCT is a powerful new modality because it has a longitudinal resolution of 10 microns in the retina, which is superior to other currently available imaging techniques. Examinations are exceptionally tolerable for patients because OCT is noninvasive, the probe beam is near-infrared and thus not very bright, and scan acquisition time is only 2.5 seconds. OCT appears to be a useful device for evaluating a variety of retinal diseases, including macular holes, macular edema, and central serous chorioretinopathy.

Ultrasound biomicroscopy of the anterior segment.

Abstract: Background New imaging technologies are revolutionizing the understanding and treatment of a wide variety of ocular disorders. Confocal scanning laser ophthalmoscopy, ultrasound biomicroscopy, confocal scanning laser polarimetry, color doppler imaging of blood flow, and optical coherence tomography are providing important information regarding disease pathophysiology, diagnosis, progression, and treatment. Methods High frequency (50 MHz), high resolution ultrasound biomicroscopy of the anterior segment was obtained in a wide variety of disorders of the anterior segment. Tissue resolution is approximately 50 microns and the penetration depth is 5 mm. Results Ultrasound biomicroscopy is capable of imaging the comea, iris, anterior chamber, anterior chamber angle, posterior chamber, and ciliary body with great detail. The structures surrounding the posterior chamber, previously hidden from clinical observation, can be imaged and their normal anatomic relationships assessed. The various forms of angle closure glaucoma, such as pupillary block and plateau iris configuration, can be differentiated. The concave iris found in pigment dispersion and its response to treatment can be assessed. Visualization of anterior segment anatomy in eyes with opaque media is possible. Conclusions Ultrasound biomicroscopy assists in the management of eyes with disorders of the anterior segment. Future applications of this technology will yield important information regarding accommodation, normal ocular physiology and disease pathophysiology.

Spectroscopic optical coherence tomography

Abstract: Summary form only given. Implementations of OCT, which take advantage of the spectral bandwidth of low coherence sources for tissue spectroscopy, have not yet been reported. We describe a novel technique for depth-resolved coherent backscatter spectroscopy, which is an extension of OCT technology. Our system incorporates an OCT scanner illuminated by a superluminescent diode (SLD) at 1.3-/spl mu/m center wavelength. In the low-coherence interferometer, a scanning reference mirror generates the temporal cross-correlation function of light reflected from the reference mirror, and that backscattered from the sample arm target. A separate helium-neon interferometer is utilized for digital correction of artifacts in the low-coherence interferometer output due to nonlinearities in the reference arm retroreflector stage velocity. The low-coherence interferometric signal is digitally demodulated and filtered to obtain the complete complex envelope of the interferometric signal, which is required for the spectroscopic technique. Using this system, low-coherence interferograms with accurate sampling intervals and high dynamic range (>98 dB) are acquired.

Current imaging of the optic disk and retinal nerve fiber layer.

Abstract: The optic nerve head and the retinal nerve fiber layer (RNFL) are the sites of clinically detectable glaucomatous tissue damage. Photographic techniques are used to document the optic disk and the RNFL to monitor patients with suspected primary open-angle glaucoma or to follow-up patients already suffering from this disease. New techniques such as laser scanning tomography (LST), scanning laser polarimetry, and optical coherence tomography have been introduced to quantify structural alterations with the aim of early detection of optic nerve or RNFL damage prior to functional loss. These novel, additional diagnostic tools are currently being evaluated in clinical practice. While scanning laser polarimetry and optical coherence tomography are discussed elsewhere in this volume, articles on LST and conventional techniques are considered here. Imaging and computed data processing allow for three-dimensional in vivo measurements in the range of micrometers. With regard to the structure of the optic nerve head, this aspect in the evaluation of the optic disk can be based on quantitative topographic data. We expect "topometry" to become an important additional tool in the early diagnosis and follow-up of patients with glaucoma. However, computed parameter readings should always be evaluated in a clinical context. The goal is to improve, combine, and integrate all the different diagnostic approaches to improve patient care for the benefit of those suffering from glaucoma.