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At least 757 records · Page 42Linked to original sources
PubMed1992

Digital image analysis of optic nerve head pallor as a diagnostic test for early glaucoma.

We developed a computer-based technique to quantify optic nerve head pallor from videographically acquired digitized optic nerve images and tested the ability of pallor measurements to discriminate between normal eyes and eyes with early glaucoma. Corresponding pixel values from images obtained under 540 nm (green) and 640 nm (red) light with a videographic fundus camera were used to quantify optic nerve head pallor. A pallor density histogram was calculated for each eye, and contained values between 0 (red) to 1 (white). A measure of the distribution width of the histogram provided pallor measurements standardized to the measurements of the large veins of the disc. A database of one eye each of 44 normal controls and 70 patients with early open angle glaucoma was used to test the measurements for diagnostic sensitivity and specificity. These standardized pallor measurements did not perform better than absolute pallor measurements to discriminate between normal and glaucomatous eyes. The sensitivity and specificity of standardized pallor measurements (49% and 57%, respectively, for this database) were not as good as those for stereoscopic measurements of disc rim area in the same database (70% and 73%). Pallor measurements of this type do not appear to be sensitive or specific indicators of early glaucoma.

Aged↗
PubMed2000

Optical coherence tomography: an introduction to the technique and its use.

This report describes the new optical imaging technique of optical coherence tomography (OCT). OCT is capable of high-resolution, micrometer-scale, cross-sectional imaging of biological tissue. The OCT for ophthalmic application uses 843-nm, near-infrared light, which produces a longitudinal resolution of 10 to 20 microm and a penetration depth of a few millimeters. The scans are displayed in a false color representation scale on which warm colors represent areas of high optical reflectivity and cool colors represent areas of minimal or no reflectivity. A cross-sectional view similar to a histology section is obtained. The cornea, iris, and lens may be visualized as well as the retina and optic nerve. OCT has been used to investigate several ocular diseases. These include macular disease, genetic retinal disease, retinal detachment and retinoschisis, choroidal tumors, optic nerve disorders, and glaucoma.

Diagnostic Techniques, Ophthalmological↗
PubMed1989

[Computerized digital image analysis of optic nerve heads with a three-dimensional image analyzer, IMAGEnet and a comparison with the Optic Nerve Head Analyzer].

Computerized digital image analysis of the optic nerve heads of 17 eyes with various sizes of optic disc cupping was performed using two kinds of three dimensional image analyzers, the IMAGEnet and the Optic Nerve Head Analyzer (ONHA). Intraphotographic error variances of measurements with both instruments were evaluated by measuring each image of the optic discs twice. The mean coefficient of variation (CV) with the IMAGEnet for the vertical cup/disc ratio, the horizontal cup/disc ratio, the cup volume, the rim area, and the rim area/disc area ratio were 3.75%, 3.03%, 7.89%, 2.55% and 1.36%, respectively. With the ONHA, the mean CV for the total cup/disc ratio, the cup volume, the rim area, and the rim area/disc area ratio were 0.82%, 0.21%, 2.39%, and 1.56%, respectively. The value of the cup/disc ratio and the cup volume obtained by the IMAGEnet was smaller than those by the ONHA (p greater than 0.1). Conversely, the rim area and rim area/disc area ratio measured by the IMAGEnet were statistically significantly larger than those by the ONHA (p = 0.01). Statistically significantly positive correlation was demonstrated for measurements made by both instruments in all disc parameters (p less than 0.01). These results seem to indicate the high reliability of the two instruments, however, further investigation is needed for the evaluation of the accuracy of measurements.

Glaucoma↗
PubMed2002

Design of angle-tolerant multivariate optical elements for chemical imaging.

Multivariate optical elements (MOEs) are multilayer optical interference coatings with arbitrary spectral profiles that are used in multivariate pattern recognition to perform the task of projecting magnitudes of special basis functions (regression vectors) out of optical spectra. Because MOEs depend on optical interference effects, their performance is sensitive to the angle of incidence of incident light. This angle dependence complicates their use in imaging applications. We report a method for the design of angle-insensitive MOEs based on modification of a previously described nonlinear optimization algorithm. This algorithm operates when the effects of deviant angles of incidence are simulated prior to optimization, which treats the angular deviation as an interferent in the measurement. To demonstrate the algorithm, a 13-layer imaging MOE (IMOE, with alternating layers of high-index Nb2O5 and low-index SiO2) for the determination of Bismarck Brown dye in mixtures of Bismarck Brown and Crystal Violet, was designed and its performance simulated. For angles of incidence that range from 42 degrees to 48 degrees, the IMOE has an average standard error of prediction (SEP) of 0.55 microM for Bismarck Brown. This compares with a SEP of 2.8 microM for a MOE designed by a fixed-angle algorithm.

Journal Article↗
PubMed2004

Ground-based imaging differential optical absorption spectroscopy of atmospheric gases.

We describe a compact remote-sensing instrument that permits spatially resolved mapping of atmospheric trace gases by passive differential optical absorption spectroscopy (DOAS) and present our first applications of imaging of the nitrogen dioxide contents of the exhaust plumes of two industrial emitters. DOAS permits the identification and quantification of various gases, e.g., NO2, SO2, and CH2O, from their specific narrowband (differential) absorption structures with high selectivity and sensitivity. With scattered sunlight as the light source, DOAS is used with an imaging spectrometer that is simultaneously acquiring spectral information on the incident light in one spatial dimension (column). The second spatial dimension is scanned by a moving mirror.

Journal Article↗
PubMedDate not supplied

[Macular imaging with optical coherence tomography].

PURPOSE: Optical Coherence Tomography (OCT) is a novel noninvasive and noncontact imaging technique providing cross-sectional representations of the eye structures. OCT is analogous to Ultrasound B-scan, except that it analyzes the reflection of a 850 nm light wave. The aim of this study was to assess the potential of ocular coherence tomography for diagnosing and monitoring macular diseases. METHODS: Cross-sectional images were performed with the Zeiss-Humphrey OCT. Over one year period, we examined approximately 300 patients with idiopathic full thickness macular hole, lamellar hole, cystoid macular edema, choroidal new vessels, epiretinal membrane, diabetic maculopathy, and central serous chorioretinopathy. RESULTS: OCT can provide new information concerning the posterior pole diseases mentioned above. OCT can also be useful in thickness measurements. CONCLUSION: OCT allows tomographic analysis of macular diseases. The information obtained is different from that obtained by histologic study which is sometimes hard to interprete. OCT is mostly useful in studying internal layers of the retina. Further applications may be developed.

Choroid Diseases↗
PubMed1987

Magnetic resonance imaging of optic tract involvement in multiple sclerosis.

We studied two cases of optic tract involvement in multiple sclerosis with documentation by magnetic resonance imaging. In one, incongruous homonymous hemianopsia was accompanied by a decrease in visual acuity in one eye from chiasmal involvement. In the other, the involvement was restricted to the optic tract and the homonymous hemianoptic visual field defect was nearly congruous.

Adult↗
PubMed1998

Imaging of the optic disc in glaucoma: which way to go?

Less than 10 years ago, fundus photography was believed to be the only method to document optic disc changes in glaucoma. Since then, many sophisticated electronic devices have been developed to supersede conventional photography. At the moment, confocal laser scanning tomography, nerve fiber layer polarimetry, and optical coherence tomography are the most popular techniques. The current status of optic disc imaging in glaucoma can (in our very subjective opinion) be summarized as follows. Confocal laser scanning tomography is the most comprehensively tested electronic modality. It is perhaps the method of choice in major glaucoma centers. Nerve fiber layer polarimetry has forged ahead during the past 2 years and may become an alternative to confocal laser scanning tomography in the future. Optical coherence tomography is a fascinating technique, which may also become important in the future. Right now, however, it is still in the experimental stage. Conventional disc photography--despite all those new techniques--still has its place. Perhaps it is the method of choice in routine glaucoma practice, except those clinics that can afford one of the "high tech" machines.

Diagnostic Imaging↗
PubMed2004

Dynamic in vivo imaging and cell tracking using a histone fluorescent protein fusion in mice.

BACKGROUND: Advances in optical imaging modalities and the continued evolution of genetically-encoded fluorescent proteins are coming together to facilitate the study of cell behavior at high resolution in living organisms. As a result, imaging using autofluorescent protein reporters is gaining popularity in mouse transgenic and targeted mutagenesis applications. RESULTS: We have used embryonic stem cell-mediated transgenesis to label cells at sub-cellular resolution in vivo, and to evaluate fusion of a human histone protein to green fluorescent protein for ubiquitous fluorescent labeling of nucleosomes in mice. To this end we have generated embryonic stem cells and a corresponding strain of mice that is viable and fertile and exhibits widespread chromatin-localized reporter expression. High levels of transgene expression are maintained in a constitutive manner. Viability and fertility of homozygous transgenic animals demonstrates that this reporter is developmentally neutral and does not interfere with mitosis or meiosis. CONCLUSIONS: Using various optical imaging modalities including wide-field, spinning disc confocal, and laser scanning confocal and multiphoton excitation microscopy, we can identify cells in various stages of the cell cycle. We can identify cells in interphase, cells undergoing mitosis or cell death. We demonstrate that this histone fusion reporter allows the direct visualization of active chromatin in situ. Since this reporter segments three-dimensional space, it permits the visualization of individual cells within a population, and so facilitates tracking cell position over time. It is therefore attractive for use in multidimensional studies of in vivo cell behavior and cell fate.

Animals↗
PubMed2002

Blood capillary distribution correlates with hemodynamic-based functional imaging in cerebral cortex.

Our study concerns the mechanisms that underlie functional imaging of sensory areas of cortex using hemodynamic-based methods such as optical imaging of intrinsic signals, functional magnetic resonance imaging and positron emission tomography. In temporal cortex of chinchilla, we have used optical imaging of intrinsic signals evoked by acoustic stimulation to define the functionally responsive area and then made (scanning electron microscopy) observations of the corresponding capillary networks prepared by corrosion cast methods. We report that intrinsic signals associated with auditory cortex correlate directly with discrete capillary beds. These capillary beds, within the cortical surface layers, are distributed across the cortex in a non-uniform fashion. Within cortex both the arterial supply and the capillary network contain various flow control structures. Our study suggests a causal relationship between the metabolic demands of local neuronal activity and both the density of the capillary network and the placement of the control structures. Such relationships will affect the ultimate spatial resolution obtainable by hemodynamic-based functional brain imaging studies. These relationships will also affect quantitative comparisons of activity levels in different areas of cortex.

Acoustic Stimulation↗
PubMed2002

The application of interferometry to optical astronomical imaging.

In the first part of this review we survey the role optical/infrared interferometry now plays in ground-based astronomy. We discuss in turn the origins of astronomical interferometry, the motivation for its development, the techniques of its implementation, examples of its astronomical significance, and the limitations of the current generation of interferometric arrays. The second part focuses on the prospects for ground-based astronomical imaging interferometry over the near to mid-term (i.e. 10 years) at optical and near-infrared wavelengths. An assessment is made of the astronomical and technical factors which determine the optimal designs for imaging arrays. An analysis based on scientific capability, technical feasibility and cost argues for an array of large numbers of moderate-sized (2 m class) telescopes rather than one comprising a small number of much larger collectors.

Astronomy↗
PubMed2000

A comparison study of linear reconstruction techniques for diffuse optical tomographic imaging of absorption coefficient.

We compare, through simulations, the performance of four linear algorithms for diffuse optical tomographic reconstruction of the three-dimensional distribution of absorption coefficient within a highly scattering medium using the diffuse photon density wave approximation. The simulation geometry consisted of a coplanar array of sources and detectors at the boundary of a half-space medium. The forward solution matrix is both underdetermined, because we estimate many more absorption coefficient voxels than we have measurements, and ill-conditioned, due to the ill-posedness of the inverse problem. We compare two algebraic techniques, ART and SIRT, and two subspace techniques, the truncated SVD and CG algorithms. We compare three-dimensional reconstructions with two-dimensional reconstructions which assume all inhomogeneities are confined to a known horizontal slab, and we consider two 'object-based' error metrics in addition to mean square reconstruction error. We include a comparison using simulated data generated using a different FDFD method with the same inversion algorithms to indicate how our conclusions are affected in a somewhat more realistic scenario. Our results show that the subspace techniques are superior to the algebraic techniques in localization of inhomogeneities and estimation of their amplitude, that two-dimensional reconstructions are sensitive to underestimation of the object depth, and that an error measure based on a location parameter can be a useful complement to mean squared error.

Algorithms↗
PubMed2006

Method of images in optical discrete systems.

We show that optical wave propagation in discrete boundary geometries can be effectively analyzed using the method of images. Such semi-infinite and finite discrete systems include, for example, waveguide arrays as well as coupled resonator optical waveguides. In the linear domain, the diffraction properties of one- and two-dimensional bounded array structures are considered in detail. The possibility of using the method of images to numerically investigate nonlinear semi-infinite lattices is also discussed.

Journal Article↗
PubMed1990

MR imaging of optic nerve lesions: value of gadopentetate dimeglumine and fat-suppression technique.

Eleven patients with known or suspected optic nerve lesions and eight normal subjects were examined with spin-echo technique at 1.5 T with unenhanced T1-weighted imaging, IV gadopentetate-dimeglumine-enhanced T1-weighted imaging, and enhanced T1-weighted imaging with fat suppression. Two pathologically proved and four presumed optic nerve meningiomas demonstrated significant enhancement and were best seen with the fat-suppression technique. None of the three presumed optic nerve gliomas nor the optic nerves of normal subjects demonstrated qualitative enhancement. We conclude that the use of a fat-suppression technique with gadopentetate dimeglumine enhancement improves delineation of enhancing optic nerve lesions. This technique should be useful for evaluating other anatomic regions where enhancing tissue marginates fat.

Adipose Tissue↗
PubMed2003

Fluorescence imaging of physiological activity in complex systems using GFP-based probes.

Genetically encoded probes for the optical imaging of excitable cell activity have been constructed by fusing fluorescent proteins to functional proteins that are involved in physiological signaling systems, such as those that control membrane potential, free calcium and cyclic nucleotide concentrations and pH. Using specific promoters and targeting signals, the probes are introduced into an intact organism and directed to specific tissue regions, cell types, and subcellular compartments, thereby extracting specific signals more efficiently and in a more relevant physiological context than before. Optical imaging using genetically encoded probes has enabled us to decipher spatio-temporal information coded in complex tissues.

Animals↗
PubMed2003

Modification of the Heidelberg retinal flowmeter to record pattern and flicker induced blood flow changes.

PURPOSE: We tested a prototype stimulator interfaced with a commercially available scanning laser ophthalmoscope designed to measure retinal capillary perfusion (Heidelberg Retina Flowmeter (HRF)). The add-on stimulator optically superimposed the image of a monitor display on to the subject's retina coaxially with the imaging optics of the HRF. The purpose of the study was to determine if flicker and pattern stimulation presented in this manner could evoke changes in retinal perfusion that could be measured by the HRF. METHODS: The prototype stimulator projected 55 degrees visual angle circular fields of homogeneous flicker, alternating checkerboard, and multi-focal m-sequence hexagonal patterns on the retina of 10 human subjects during acquisition of images by the HRF. RESULTS: Images were successfully acquired and processed. HRF perfusion values during flicker and pattern stimulation were not significantly different from control values. CONCLUSIONS: Results of the present study and a previously published study showing a flicker-induced increase in the HRF perfusion values are contradictory. Retinal perfusion measured by the HRF were not affected by flicker and pattern stimulation delivered through the prototype device. These data are not consistent with a large flicker or pattern induced increase in retinal perfusion. The instrumental modification appears promising. However, the raster scan stimulation technique or some other aspect of stimulation or image acquisition may account for the different results in the present study and previous studies in our laboratory and in the laboratories of other investigators.

Adult↗