Showing papers on "Optical coherence tomography published in 1999"

Optical coherence tomography (OCT): a review

Abstract: This paper reviews the state of the art of optical coherence tomography (OCT), an interferometric imaging technique that provides cross-sectional views of the subsurface microstructure of biological tissue. Following a discussion of the basic theory of OCT, an overview of the issues involved in the design of the main components of OCT systems is presented. The review concludes by introducing new imaging modes being developed to extract additional diagnostic information.

In vivo ultrahigh-resolution optical coherence tomography.

Abstract: Ultrahigh-resolution optical coherence tomography (OCT) by use of state of the art broad-bandwidth femtosecond laser technology is demonstrated and applied to in vivo subcellular imaging. Imaging is performed with a Kerr-lens mode-locked Ti:sapphire laser with double-chirped mirrors that emits sub-two-cycle pulses with bandwidths of up to 350 nm, centered at 800 nm. Longitudinal resolutions of ~1mum and transverse resolution of 3mum, with a 110-dB dynamic range, are achieved in biological tissue. To overcome depth-of-field limitations we perform zone focusing and image fusion to construct a tomogram with high transverse resolution throughout the image depth. To our knowledge this is the highest longitudinal resolution demonstrated to date for in vivo OCT imaging.

Speckle in Optical Coherence Tomography

Abstract: Speckle arises as a natural consequence of the limited spatial-frequency bandwidth of the interference signals measured in optical coherence tomography (OCT). In images of highly scattering biological tissues, speckle has a dual role as a source of noise and as a carrier of information about tissue microstructure. The first half of this paper provides an overview of the origin, statistical properties, and classification of speckle in OCT. The concepts of signal-carrying and signal-degrading speckle are defined in terms of the phase and amplitude disturbances of the sample beam. In the remaining half of the paper, four speckle-reduction methods-polarization diversity, spatial compounding, frequency compounding, and digital signal processing-are discussed and the potential effectiveness of each method is analyzed briefly with the aid of examples. Finally, remaining problems that merit further research are suggested. © 1999 Society of Photo-Optical Instrumentation Engineers.

Macular hole formation: new data provided by optical coherence tomography.

Abstract: Objective To establish the sequence of events leading from vitreofoveal traction to full-thickness macular hole formation. Methods Both eyes of 76 patients with a full-thickness macular hole in at least 1 eye were examined by biomicroscopy and optical coherence tomography. Results Sixty-one fellow eyes had a normal macula. Optical coherence tomograms showed central detachment of the posterior hyaloid over the posterior pole in 19 cases (31%) and a perifoveal hyaloid detachment not detected on biomicroscopy in 26 cases (42%). In the 4 impending macular holes, optical coherence tomography disclosed various degrees of intrafoveal split or cyst, with adherence of the posterior hyaloid to the foveal center and convex perifoveal detachment. In the 14 stage 2 holes, eccentric opening of the roof of the hole was observed, and in the 24 stage 3 holes, the posterior hyaloid was detached from the entire posterior pole. Conclusions In fellow eyes of eyes with macular holes posterior hyaloid detachment begins around the macula, but the hyaloid remains adherent to the foveolar center, indicating the action of anteroposterior forces. This results in an intraretinal split evolving into a cystic space, and then to the disruption of the outer retinal layer and the opening of the foveal floor, thus constituting a full-thickness macular hole.

Determination of the depth-resolved Stokes parameters of light backscattered from turbid media by use of polarization-sensitive optical coherence tomography.

Abstract: Polarization-sensitive optical coherence tomography (PS-OCT) was used to characterize completely the polarization state of light backscattered from turbid media. Using a low-coherence light source, one can determine the Stokes parameters of backscattered light as a function of optical path in turbid media. To demonstrate the application of this technique we determined the birefringence and the optical axis in fibrous tissue (rodent muscle) and in vivo rodent skin. PS-OCT has potentially useful applications in biomedical optics by imaging simultaneously the structural properties of turbid biological materials and their effects on the polarization state of backscattered light. This method may also find applications in material science for investigation of polarization properties (e.g., birefringence) in opaque media such as ceramics and crystals.

Two-dimensional depth-resolved Mueller matrix characterization of biological tissue by optical coherence tomography.

Abstract: We built a polarization-sensitive optical coherence tomographic system and measured the two-dimensional depth-resolved full 4×4 Mueller matrix of biological tissue for what is believed to be the first time. The Mueller matrix measurements, which we made by varying the polarization states of the light source and the detector, yielded a complete characterization of the polarization property of the tissue sample. The initial experimental results indicated that this new approach reveals some tissue structures that are not perceptible in standard optical coherence tomography.

High resolution in vivo intra-arterial imaging with optical coherence tomography

Abstract: Background—Optical coherence tomography (OCT) is a new method of catheter based micron scale imaging. OCT is analogous to ultrasound, measuring the intensity of backreflected infrared light rather than sound waves. Objective—To demonstrate the ability of OCT to perform high resolution imaging of arterial tissue in vivo. Methods—OCT imaging of the abdominal aorta of New Zealand white rabbits was performed using a 2.9 F OCT imaging catheter. Using an ultrashort pulse laser as a light source for imaging, an axial resolution of 10 µm was achieved. Results—Imaging was performed at 4 frames/second and data were saved in either super VHS or digital format. Saline injections were required during imaging because of the signal attenuation caused by blood. Microstructure was sharply defined within the arterial wall and correlated with histology. Some motion artefacts were noted at 4 frames/second. Conclusions—In vivo imaging of the rabbit aorta was demonstrated at a source resolution of 10 µm, but required the displacement of blood with saline. The high resolution of OCT allows imaging to be performed near the resolution of histopathology,oVering the potential to have an impact both on the identification of high risk plaques and the guidance of interventional procedures. (Heart 1999;82:128‐133)

Real-time in vivo imaging of human gastrointestinal ultrastructure by use of endoscopic optical coherence tomography with a novel efficient interferometer design.

Abstract: We report on the design and initial clinical experience with a real-time endoscopic optical coherence tomography (EOCT) imaging system. The EOCT unit includes a high-speed optical coherence tomography interferometer, endoscope-compatible catheter probes, and real-time data capture and display hardware and software. Several technological innovations are introduced that improve EOCT efficiency and performance. In initial clinical studies using the EOCT system, the esophagus, stomach, duodenum, ileum, colon, and rectum of patients with normal endoscopic findings were examined. In these initial investigations, EOCT imaging clearly delineated the substructure of the mucosa and submucosa in several gastrointestinal organs; microscopic structures such as glands, blood vessels, pits, villi, and crypts were also observed.

Optimal interferometer designs for optical coherence tomography

Abstract: We introduce a family of power-conserving fiber-optic interferometer designs for low-coherence reflectometry that use optical circulators, unbalanced couplers, and (or) balanced heterodyne detection. Simple design equations for optimization of the signal-to-noise ratio of the interferometers are expressed in terms of relevant signal and noise sources and measurable system parameters. We use the equations to evaluate the expected performance of the new configurations compared with that of the standard Michelson interferometer that is commonly used in optical coherence tomography (OCT) systems. The analysis indicates that improved sensitivity is expected for all the new interferometer designs, compared with the sensitivity of the standard OCT interferometer, under high-speed imaging conditions.

Optical coherence tomography: high-resolution imaging in nontransparent tissue

Abstract: Optical coherence tomography (OCT) is a method of high-resolution imaging originally developed for the transparent tissue of the eye. Recently, the technology has been advanced toward the difficult challenge of imaging in nontransparent tissue. In the paper, three topics are addressed. First, the principles behind OCT imaging are discussed. Second, the difficulties associated with OCT imaging in nontransparent tissue are outlined. Finally, the feasibility of OCT for medical imaging is discussed. Specifically, OCT demonstrates its greatest potential in situations where conventional biopsy is either dangerous or ineffective.

Power-efficient nonreciprocal interferometer and linear-scanning fiber-optic catheter for optical coherence tomography

Abstract: A nonreciprocal fiber-optic interferometer is demonstrated in an optical coherence tomography (OCT) system. The increased power efficiency of this system provides a 4.1-dB advantage over standard Michelson implementations. In addition, a new linear-scanning fiber-optic catheter is demonstrated that avoids the rotary optical junction that is required in circumferential scanning systems. These advancements have permitted the clinical implementation of OCT imaging in the human gastrointestinal tract.

Characterization of dentin and enamel by use of optical coherence tomography

Abstract: Optical coherence tomographic images of human dentin and enamel are obtained by use of polarization-sensitive optical coherence tomography. A birefringence effect in enamel (lambda = 856 nm) and light propagation along dentinal tubules are observed. The group index of refraction for both dentin and enamel was measured at 1.50 +/- 0.02 and 1.62 +/- 0.02, respectively.

High resolution in-vivo intraarterial imaging with optical coherence tomography

Abstract: High resolution imaging of intraarterial structure is necessary for the identification of high risk coronary plaque. OpticalCoherence Tomography (OCT), a recently developed technology, is a compact, fiber optic based imaging modality withresolutions between 2 — 20 im and real time image acquisition rates. Previous in vitro studies have demonstrated the capability of OCT to identify plaque morphology and distinguish plaques with high lipid content. This work demonstratesthe feasibility for OCT imaging of in-vivo intraarterial structures. We demonstrate the detection of microstructural detail andthe effects ofblood on imaging. Saline injections were required during imaging to reduce the signal attenuation of blood.An axial resolution of 10 im was achieved. Microstructure within the arterial wall was sharply defined and correlated withhistology. OCT shows potential to assist in the risk stratification of plaques and the guidance of interventional procedures,such as stent deployment.Key Words: optical coherence tomography, OCT, atherosclerosis, stent, plaque, coronary artery

Combined scanning optical coherence and two-photon-excited fluorescence microscopy.

Abstract: We demonstrate simultaneous imaging by optical coherence microscopy (OCM) and two-photon-excited (TPE) fluorescence microscopy. A mode-locked Ti:sapphire laser is focused and scanned in three dimensions through a fixed sample, generating both backscattered light and fluorescence light, which are independently detected. Both imaging modes provide rapid en-face imaging with submicrometer resolution. High-power delivery into the sample yields an OCM sensitivity in excess of 130 dB at 100-kHz pixel rates. Simultaneous imaging of cell nuclei with OCM and TPE is demonstrated in live drosophila embryos.

Monte Carlo simulation of an optical coherence tomography signal in homogeneous turbid media

Abstract: The Monte Carlo technique with angle biasing is used to simulate the optical coherence tomography (OCT) signal from homogeneous turbid media. The OCT signal is divided into two categories: one is from a target imaging layer in the medium (Class I); the other is from the rest of the medium (Class II). These two classes of signal are very different in their spatial distributions, angular distributions and the numbers of experienced scattering events. Multiply scattered light contributes to the Class I signal as well as the Class II signal. The average number of scattering events increases linearly with the probing depth. The Class II signal decays much more slowly than the Class I signal whose decay constant is close to the total attenuation coefficient of the turbid medium. The effect of the optical properties of the medium on the Class I signal decay is studied.

Spatially resolved spectral interferometry for determination of subsurface structure

Abstract: We describe an instrument capable of obtaining two-dimensional images of subsurface structure in real time with no moving parts. The technique is based on spectral interferometry and uses an imaging spectrograph to obtain spatially resolved spectra. A test sample consisting of microscope coverslips and a Ronchi grating was measured, illustrating the system’s depth resolution of 38 ?m and transverse resolution of at least 12.7 ?m. The technique is readily adaptable to endoscopic delivery as well as three-dimensional real-time image acquisition.

Dispersion effects in partial coherence interferometry: implications for intraocular ranging

Abstract: In nondispersive media, the minimum distance that can be resolved by partial coherence interferometry (PCI) and optical coherence tomography (OCT) is inversely proportional to the source spectral bandwidth. Dispersion tends to increase the signal width and to degrade the resolution. We analyze the situation for PCI ranging and OCT imaging of ocular structures. It can be shown that for each ocular segment an optimum source bandwidth yielding optimum resolution exists. If the resolution is to be improved beyond this point, the group dispersion of the ocular media has to be compensated. With the use of a dispersion compensating element, and employing a broadband superluminescent diode, we demonstrate a resolution of 5 μm in the retina of both a model eye and a human eye in vivo. This is an improvement by a factor of 2-3 as compared to currently used instruments. © 1999 Society of Photo-Optical Instrumentation Engineers.

High resolution imaging of normal and osteoarthritic cartilage with optical coherence tomography.

Abstract: Objective. We describe optical coherence tomography (OCT), a high resolution micron scale imaging technology, for assessment of osteoarthritic articular cartilage microstructure. OCT is analogous to ultrasound, measuring the intensity of backreflected infrared light rather than acoustical waves. Methods. OCT imaging was performed on over 100 sites on 20 normal and osteoarthritic cartilage specimens in vitro. Results. Microstructures that were identified included fibrillations, fibrosis, cartilage thickness, and new bone growth at resolutions between 5 and 15 μm. In addition, the polarization sensitivity of imaging suggested a diagnostic role of polarization spectroscopy. Conclusion. OCT represents an attractive new technology for intraarticular imaging due to its high resolution (greater than any available clinical technology), ability to be integrated into small arthroscopes, compact portable design, and relatively low cost.

Optical coherence tomography of macular holes

Abstract: OBJECTIVE: To study the characteristics and clinical application value of the optical coherence tomography (OCT) of macular holes. METHOD: A total of 35 patients with the clinical diagnosis of macular hole were examined with OCT between September and December 1998. OCT imaging was conducted through a dilated pupil, and the OCT images were analyzed and measured. RESULTS: Of the 35 patients examined with OCT, there were pseudohole and epimacular membrane in one eye, vitreofoveal traction in one eye, macular holes in 36 eyes, and 3 patients had macular hole in bilateral eyes. In 4 eyes, there were partial-thickness macular holes, and the defect of partial thickness of neural epithelium in the fovea without halo of retinal detachment was shown in the OCT image. In 32 eyes, there were full-thickness holes; the OCT displayed complete losing of the whole thickness of the neural epithelium in the fovea, sharp edge of the hole and the halo of retinal detachment around the hole. Sometimes nonreflective cavities could be seen within the retina, and the retinal thickness around the hole was increased. According to Gass stage classification of macular hole, there were 2 eyes with impending hole, 3 eyes in stage 2, 15 eyes in stage 3 and 6 eyes in stage 4. 4 eyes underwent vitrectomy. The OCT imaging after the surgery demonstrated the closure of hole and the disappearance of halo surrounding the hole. Through quantitative measurement, the diameter of the hole was (565.88 +/- 40.35) microm, the diameter of the halo was (1,338.76 +/- 147.57) microm, and the retinal thickness surrounding the hole was (391.87 +/- 18.97) microm. The sizes of the hole and the halo and the retinal thickness around the hole were correlated with the vision. CONCLUSION: OCT is a novel noninvasive, noncontact imaging technique. It is helpful in the diagnosis and differential diagnosis of the macular hole; the progress of the hole can be quantitatively estimated, and it is also helpful in selection of operation and assessment of operative therapeutic effects.

Polarization sensitive optical coherence tomography of the rabbit eye

Abstract: A polarization-sensitive optical coherence tomography (PSOCT) system was used to acquire depth-resolved images of the Stokes parameters of light backreflected from ex vivo rabbit eyes. The light backreflected from the eye interferes with that from the reference arm and is coherently detected in two orthogonal polarization channels. The two signals are digitized and the four Stokes parameters (I, Q, U, and V) of the backreflected light are computed for light backreflected from each longitudinal/lateral position in the eye. From the measured Stokes parameters, an estimate of the relative phase retardation between the two orthogonal polarizations can be determined. Two eyes were enucleated, imaged within 6-h postmortem and histology performed. Images of the Stokes parameters of light backreflected from the corneal stroma show significant local variations in the polarization state, possibly due to local changes in stromal structure. Depth-resolved Stokes parameter images of light backreflected from the retina were also acquired. A birefringent layer was observed at the position consistent with the known location of the nerve fiber layer (NFL). The local thickness of the birefringent layer determined with PSOCT was in good agreement with values determined histologically.

Dynamic range of optical reflectometry with spectral interferometry

Abstract: I present an optical reflectometry (OR) technique with spectral interferometry (SIOR) that realizes high dynamic range compared with a conventional OR system using the delayed heterodyne technique (DHOR), and report on the application of this system to noninvasive in vivo measurements of the structure of the skin and the nail of an index finger. The theoretically derived dynamic range of SIOR is m/4-times superior to that of DHOR, where m is the number of independent image pixels. A dynamic range of 105 db was experimentally realized, which is comparable to the theoretically expected dynamic range of 112 db.

Differential phase contrast in optical coherence tomography.

Abstract: We report on a modification of optical coherence tomography (OCT) that allows one to measure small phase differences between beams traversing adjacent areas of a specimen. The sample beam of a polarization-sensitive low-coherence interferometer is split by a Wollaston prism into two components that traverse the object along closely spaced paths. After reflection at the various sample surfaces, the beams are recombined at the Wollaston prism. Any phase difference encountered between the two beams is converted into a change of polarization state of the recombined beam. This change is measured, and the resulting signals are converted to differential phase-contrast OCT images. The first images obtained from simple test objects allowed us to determine path-difference gradients with a resolution of the order of 5×10-5.

Phase-Domain Processing of Optical Coherence Tomography Images

Abstract: In optical coherence tomography (OCT), images are usually formed from the envelope of the measured interference signal. Computation of the absolute magnitude of the signal for measurement of the envelope is a nonlinear process that destroys phase information. This study explores the idea of recording and processing the phase of the OCT interference signal before calculation of the magnitudes for display. Processing the partially coherent OCT signals in the complex domain provides the opportunity to correct phase aberrations responsible for speckle noise in OCT images. We describe an OCT system that incorporates a quadraturedemodulation scheme for accurate recording of the phase and amplitude of OCT signals from single or multiple detectors. A speckle-reduction technique that works in the complex domain, called the zeroadjustment procedure (ZAP), is investigated as an example of complex-domain processing. After demonstrating its speckle-correction properties mathematically and in numerical simulations, we apply ZAP to OCT images of living skin. The results show that ZAP reduces speckle contrast in regions where scatterer density is high and expands the range of gray values in the image. However, as presently implemented, ZAP tends to blur sharp boundaries between image features. © 1999 Society of Photo-Optical Instrumentation Engineers. [S1083-3668(99)01501-4]

Three-Dimensional Reconstruction of Blood Vessels from in vivo Color Doppler Optical Coherence Tomography Images

Abstract: Purpose: Current laser treatment for vascular disorders such as port wine stains can have incomplete or unacceptable results. A customized treatment strategy based on knowledge of t