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Results for “Tomography, Optical Coherence”

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At least 19 recordsLinked to original sources
PubMed2004

Near-infrared dyes as contrast-enhancing agents for spectroscopic optical coherence tomography.

Optical coherence tomography (OCT) images of biological tissues often have low contrast. Spectroscopic optical coherence tomography (SOCT) methods have been developed to enhance contrast but remain limited because most tissues are not spectrally active in the frequency bands of laser sources commonly used in OCT. Near-infrared (NIR) dyes with absorption spectra features within the OCT source spectrum can be used for enhancing contrast in this situation. We introduce and demonstrate the use of NIR dyes as contrast agents for SOCT. Contrast-enhanced images are compared with fluorescence microscopy, demonstrating a link between SOCT and fluorescence imaging.

Apium↗
PubMed2000

[Optical coherence tomography].

Optical coherence tomography is a novel, noninvasive, noncontact and repetitive imaging technique which produces high depth resolution cross-sectional tomographs of ocular tissue. It's value is given by the possibility of achieving pseudo-histological images of the target tissue. It is optically based, analogue to ultrasound B-scan examination and similar to laser reflectometry. Optical coherence tomography involves shining low-level infrared light on a tissue specimen, an interferometer and a computerized imaging system. The most attractive applications of optical coherence tomography are the diseases of the retina such as: central serous retinopathy, macular hole, chronic macular edema, age-related macular degenerescence.

Diagnostic Techniques, Ophthalmological↗
PubMedDate not supplied

Measurement and imaging of birefringent properties of the human cornea with phase-resolved, polarization-sensitive optical coherence tomography.

Optical coherence tomography (OCT) is an emerging technology for high-resolution, noncontact imaging of transparent and scattering media. Polarization-sensitive optical coherence tomography (PS-OCT) is a functional extension of OCT that can image birefringent properties of a biological sample. PS-OCT was used to measure and image retardation and birefringent axis orientation of in vitro human cornea. We used a two-channel PS-OCT system employing a phase-sensitive recording of the interferometric signals in two orthogonal polarization channels. Using an algorithm based on a Hilbert transform, it is possible to calculate the retardation and the slow axis orientation of the sample with only a single A-scan per transversal measurement location. While the retardation information is encoded in the amplitude ratio of the two interferometric signals, the axis orientation is encoded entirely in their phase difference. We present maps of retardation and the distribution of slow axis orientation of the human cornea in longitudinal cross-sections and en face images obtained at the back surface of the cornea. The retardation increases in a radial direction and with depth; the slow axis varies in the transversal direction. Knowledge of the retardation and the slow axis distribution of the cornea might improve nerve fiber polarimetry for glaucoma diagnostics and could be useful for diagnosing different types of pathologies of the cornea.

Birefringence↗
PubMed2003

Macular hole: improved understanding of pathogenesis, staging, and management based on optical coherence tomography.

Optical coherence tomography (OCT) has improved the understanding and management of idiopathic macular hole. Images of precursor lesions and their progression demonstrate that antero-posterior as well as tangential traction are involved in macular hole formation. The staging of macular holes with biomicroscopic examination can be paralleled by optical coherence tomography staging with some modification. OCT is useful in differentiating simulating lesions and in allowing better counseling of patients regarding their disorder. Finally, OCT findings are prognostic of surgical success and can assist in evaluating the results of surgery.

Diagnosis, Differential↗
PubMedDate not supplied

Birefringence measurements in human skin using polarization-sensitive optical coherence tomography.

Optical coherence tomography enables cross-sectional imaging of tissue structure to depths of around 1.5 mm, at high-resolution and in real time. Incorporation of polarization sensitivity (PS) provides an additional contrast mechanism which is complementary to images mapping backscattered intensity only. We present here polarization-sensitive optical coherence tomography (OCT) images of human skin in vivo, demonstrating the ability of the technique to visualize and quantify the birefringent properties of skin. Variation in normal skin birefringence according to anatomical location is demonstrated, and discussed in relation to collagen distribution at each location. From measurements on a sample of five human volunteers, mean double-pass phase retardation rates of 0.340+/-0.143, 0.250+/-0.076, and 0.592+/-0.142 deg/microm were obtained for the dorsal hand, temple, and lower back regions, respectively. We demonstrate how averaging the Stokes parameters of backscattered light over a range of axial and lateral dimensions results in a reduction of speckle-induced noise. Examples of PS-OCT images from skin sites following wound healing and repair are also presented and discussed.

Adult↗
PubMed2006

Inverse scattering for rotationally scanned optical coherence tomography.

Optical coherence tomography of luminal structures, such as for intravascular or gastrointestinal imaging, is performed by using a fiber-optic catheter as a beam-delivery probe. The interrogating beam is scanned angularly by rotating the fiber around a fixed central axis. Because the beam is focused only at a fixed distance from the center of the fiber, only scatterers near this distance are resolved. We present a solution of the inverse scattering problem that provides an estimate of the susceptibility of the sample for an angularly scanned Gaussian beam focused at a fixed distance from the origin. This solution provides quantitatively meaningful reconstructions while also extending the volume of the sample that is resolvable by the instrument.

Algorithms↗
PubMed2006

Imaging growth dynamics of tumour spheroids using optical coherence tomography.

Optical coherence tomography (OCT) was used to monitor the dynamics of tumour spheroid formation by the hanging drop method. In contrast to microscopy, the estimates obtained using OCT for the volume of the spheroid, were consistent with the measured changes in cell number as a function of time. The OCT images also revealed heterogeneous structures in the spheroids of approximately 200 microm diameter. These corresponded to the necrotic regions identified by fluorescence of propidium iodide stained cells.

Cell Count↗
PubMed2005

Visualization of neointima formation by optical coherence tomography.

Optical coherence tomography (OCT) has recently been proposed as a high-resolution imaging method. Our male patient, who had been treated with a coronary stent, died due to acute leukemia. Coronary artery images using intravascular ultrasound (IVUS) and OCT were obtained postmortem. We also compared the image of neointima formation after stent implantation evaluated by histopathological examination with that evaluated by IVUS and OCT. OCT visualized well-apposed stent struts and neointima formation, which could not be visualized completely by IVUS. OCT may be useful for monitoring structural changes after stent implantation.

Coronary Stenosis↗
PubMedDate not supplied

New method for evaluation of in vivo scattering and refractive index properties obtained with optical coherence tomography.

Optical coherence tomography (OCT) provides more parameters than pure morphology does. In a recent paper [A. Knuettel and M. Boehlau-Godau, J. Biomed. Opt. 5(1) 83-92 (2000)] we have shown that the refractive index (RI) can be evaluated in a localized manner in skin tissue under in vivo conditions. Based on a theory, originally developed for light detecting and ranging applications [L. Thrane et al., J. Opt. Soc. Am. A 17(3) 484-490 (2000)], the parameter mean scattering angle (MSA) could be derived in addition to RI. The effects of hydration on MSA and RI have been evaluated in vitro in pigskin and in vivo in human skin with our OCT scanner SkinDex 300. These parameters may have a viable impact in (cosmetic) skin research and clinical diagnoses. To the best of our knowledge, this is the first time that (multiple) scattering of light has been quantified through the observation of a new scattering parameter under in vivo conditions.

Adult↗
PubMed2005

Possible histopathologic correlates of dermoscopic features in pigmented melanocytic lesions identified by means of optical coherence tomography.

Optical coherence tomography (OCT) is a novel non-invasive imaging technique for in vivo histologic characterization of tissues. Besides pure morphology, additional functional parameters of the tissue investigated can be evaluated at the same time, such as the refractive index and the scattering coefficient. The purpose of our study is to correlate in vivo the dermoscopic structures that first appear in the melanocytic pigmented lesion (pigment network and brown globules) using this new method, with the histopathologic correlates, in order to improve their characterization and achieve easier recognition and inter-observer reproducibility. We concentrated in particular on the pigment network and the brown globules, as these are dermoscopic parameters of great diagnostic importance in melanocytic lesions. Moreover, as these parameters are the histopathologic equivalents of structures located at the level of the dermo-epidermal junction, they enable a correct evaluation to be made using OCT, that at present has only a few millimetres penetration power. The results of our trial, performed using the histopathological preparation as an evaluation gold standard, show that in selected cases OCT allows an in vivo correlation to be made between surface dermoscopic parameters and histopathologic correlates, in particular the pigment network and brown globules. The resolution is not high enough to reveal the morphology of the single cells, but it is possible to evaluate the architecture of a lesion.

Adult↗
PubMed2006

Automatic recovery of the optic nervehead geometry in optical coherence tomography.

Optical coherence tomography (OCT) uses retroreflected light to provide micrometer-resolution, cross-sectional scans of biological tissues. OCT's first application was in ophthalmic imaging where it has proven particularly useful in diagnosing, monitoring, and studying glaucoma. Diagnosing glaucoma is difficult and it often goes undetected until significant damage to the subject's visual field has occurred. As glaucoma progresses, neural tissue dies, the nerve fiber layer thins, and the cup-to-disk ratio increases. Unfortunately, most current measurement techniques are subjective and inherently unreliable, making it difficult to monitor small changes in the nervehead geometry. To our knowledge, this paper presents the first published results on optic nervehead segmentation and geometric characterization from OCT data. We develop complete, autonomous algorithms based on a parabolic model of cup geometry and an extension of the Markov model introduced by Koozekanani, et al. to segment the retinal-nervehead surface, identify the choroid-nervehead boundary, and identify the extent of the optic cup. We present thorough experimental results from both normal and pathological eyes, and compare our results against those of an experienced, expert ophthalmologist, reporting a correlation coefficient for cup diameter above 0.8 and above 0.9 for the disk diameter.

Algorithms↗
PubMed2005

Spectral domain second-harmonic optical coherence tomography.

Optical coherence tomography (OCT) provides micrometer-scale structural imaging by coherent detection of backscattered light. Molecular contrast in OCT has been demonstrated using transient absorption, coherent anti-Stokes Raman scattering, and second-harmonic (SH) generation. The sensitivity of molecular contrast signals can be enhanced by use of Fourier domain techniques. We have constructed a spectrometer-based Fourier domain SH-OCT system for simultaneous acquisition of the fundamental and SH signals. We report a >30 dB increase in SH sensitivity over a similar time domain SH-OCT system and demonstrate contrast between cartilage and bone using collagen as the contrast agent.

Equipment Design↗
PubMed2005

Localized measurement of optical attenuation coefficients of atherosclerotic plaque constituents by quantitative optical coherence tomography.

Optical coherence tomography (OCT) is a novel, high-resolution diagnostic tool that is capable of imaging the arterial wall and plaques. The differentiation between different types of atherosclerotic plaque is based on qualitative differences in gray levels and structural appearance. We hypothesize that a quantitative data analysis of the OCT signal allows measurement of light attenuation by the local tissue components, which can facilitate quantitative spatial discrimination between plaque constituents. High-resolution OCT images (at 800 nm) of human atherosclerotic arterial segments obtained at autopsy were histologically validated. Using a new, simple analysis algorithm, which incorporates the confocal properties of the OCT system, the light attenuation coefficients for these constituents were determined: for diffuse intimal thickening (5.5 +/- 1.2 mm(-1)) and lipid-rich regions (3.2 +/- 1.1 mm(-1)), the attenuation differed significantly from media (9.9 +/- 1.8 mm(-1)), calcifications (11.1 +/- 4.9 mm(-1) ) and thrombi (11.2 +/- 2.3 mm(-1)) (p < 0.01). These proof of principle studies show that simple quantitative analysis of the OCT signals allows spatial determination of the intrinsic optical attenuation coefficient of atherosclerotic tissue components within regions of interest. Combining morphological imaging by OCT with the observed differences in optical attenuation coefficients of the various regions may enhance discrimination between various plaque types.

Algorithms↗
PubMed2001

[Optical coherence tomography].

Optical coherence tomography has become an established method for imaging retinal diseases. It is now an accepted method for making quantitative measurements in studies on the cause and course of macular holes, vitreoretinal traction, pigment epithelial detachment, macular edema, and diabetic retinopathy. Its potential benefit in the evaluation of age-related macular degeneration and a variety of other diseases is currently under investigation. In clinical practice optical coherence tomography images add information to the biomicroscopic findings and results of other imaging techniques or functional testing and can significantly help in making critical decisions. Its future role in routine clinical practice will depend on further technical development and the results of long-term studies.

Humans↗
PubMed1998

New technology for high-speed and high-resolution optical coherence tomography.

Optical coherence tomography (OCT) is an optical imaging technique that is capable of performing micron-scale, cross-sectional imaging of internal microstructure in biological systems. OCT is analogous to ultrasound B mode imaging except that it uses light rather than sound and performs imaging by measuring the back-scattered intensity of light from structures in tissue. We describe recent advances in OCT technology including the application of short pulse solid state lasers based on Ti: Al2O3 and Cr: Mg2SiO4 to enable high-resolution, high-speed imaging as well as the development of OCT catheter/endoscope delivery to permit imaging of internal organ systems. OCT enables the nonexcisional, in situ, real-time imaging of tissue microstructure and is thus a powerful and promising technique for optical biopsy.

Animals↗
PubMed2003

Dispersion in a grating-based optical delay line for optical coherence tomography.

Optical coherence tomography (OCT) is a high-resolution imaging technology based on low-coherence interferometry. When OCT imaging is performed in biological tissue, dispersion almost inevitably occurs. We quantify the group-velocity dispersion that a grating-based optical delay line may induce and its contribution to the axial point-spread function of OCT. Among the practical reasons for modeling the dispersion in grating-based optical delay line is that, at maximum compensation, it can provide insight into the dispersive properties of tissues.

Computer Simulation↗
PubMed2003

[Optical coherence tomography].

Optical coherence tomography (OCT) is a novel technique for two and three-dimensional imaging of tissues at a histological level. The technique is based on optical technology and commercially available fiber-optic components that may be adapted for use in conventional endoscopes or intravascular catheters. OCT is a non-invasive technique, which does not utilize ionizing radiation, and it may within a few seconds provide in vivo images ("optical biopsies") of tissues in cases where excisional biopsy is hazardous or impossible, or when repeated examinations are required. OCT has numerous potential clinical applications, and the technique is currently used in ophthalmology, where it may improve diagnosis and therapeutic control of various eye diseases. Detection and characterization of skin tumors and other dermatological diseases is another area where OCT has tremendous clinical potential. In the field of cardiology, intravascular OCT may be capable to contribute to early diagnosis of vulnerable atherosclerotic lesions. The OCT technique is also being developed in other clinical areas and is expected to become integrated in a range of clinical situations in the future.

Coronary Disease↗
PubMed2000

Imaging of the oral cavity using optical coherence tomography.

Optical coherence tomography is a new method for noninvasively imaging internal tooth and soft tissue microstructure. The intensity of backscattered light is measured as a function of depth in the tissue. Low coherence interferometry is used to selectively remove the component of backscattered signal that has undergone multiple scattering events, resulting in very high resolution images (< 15 microns). Lateral scanning of the probe beam across the biological tissue is then used to generate a 2-D intensity plot, similar to ultrasound images. This imaging method provides information that is currently unobtainable by any other means, making possible such diverse applications as diagnosis of periodontal disease, caries detection, and evaluation of restoration integrity. This chapter presents an overview of this exciting new imaging technique and its current application to dental diagnosis.

Dental Caries↗