Peripapillary Retinal Thickness Maps in the Evaluation of Glaucoma Patients: A Novel Concept

Purpose. To show how peripapillary spectral domain optical coherence tomography (SDOCT) retinal thickness (RT) maps can complement retinal nerve fiber layer (RNFL) thickness maps in the evaluation of glaucoma patients. Methods:. After a complete eye exam with standard fundus photography and visual field testing, normal and glaucomatous eyes were imaged with an experimental SDOCT system. From SDOCT images, RNFL thickness and RT maps were constructed and then correlated with disc photography and visual field testing. Results:. Two normal eyes of 2 patients and 5 eyes of 4 glaucoma patients were imaged. Although both RNFL and RT maps correlated well with visual field defects, glaucomatous arcuate defects were sometimes more easily identified in the RT maps. Conclusions:. To our knowledge, this is the first paper to show that peripapillary SDOCT RT maps may provide important supplemental information to RNFL thickness maps in the evaluation of glaucoma patients

Models for Metal Hydride Particle Shape, Packing, and Heat Transfer

A multiphysics modeling approach for heat conduction in metal hydride powders is presented, including particle shape distribution, size distribution, granular packing structure, and effective thermal conductivity. A statistical geometric model is presented that replicates features of particle size and shape distributions observed experimentally that result from cyclic hydride decreptitation. The quasi-static dense packing of a sample set of these particles is simulated via energy-based structural optimization methods. These particles jam (i.e., solidify) at a density (solid volume fraction) of 0.665+/-0.015 - higher than prior experimental estimates. Effective thermal conductivity of the jammed system is simulated and found to follow the behavior predicted by granular effective medium theory. Finally, a theory is presented that links the properties of bi-porous cohesive powders to the present systems based on recent experimental observations of jammed packings of fine powder. This theory produces quantitative experimental agreement with metal hydride powders of various compositions.Comment: 12 pages, 12 figures, 2 table

Ultra-high resolution Fourier domain optical coherence tomography for old master paintings

In the last 10 years, Optical Coherence Tomography (OCT) has been successfully applied to art conservation, history and archaeology. OCT has the potential to become a routine non-invasive tool in museums allowing cross-section imaging anywhere on an intact object where there are no other methods of obtaining subsurface information. While current commercial OCTs have shown potential in this field, they are still limited in depth resolution (> 4 μm in paint and varnish) compared to conventional microscopic examination of sampled paint cross-sections (~1 μm). An ultrahigh resolution fiber-based Fourier domain optical coherence tomography system with a constant axial resolution of 1.2 μm in varnish or paint throughout a depth range of 1.5 mm has been developed. While Fourier domain OCT of similar resolution has been demonstrated recently, the sensitivity roll-off of some of these systems are still significant. In contrast, this current system achieved a sensitivity roll-off that is less than 2 dB over a 1.2 mm depth range with an incident power of ~1 mW on the sample. The high resolution and sensitivity of the system makes it convenient to image thin varnish and glaze layers with unprecedented contrast. The non-invasive 'virtual' cross-section images obtained with the system show the thin varnish layers with similar resolution in the depth direction but superior clarity in the layer interfaces when compared with conventional optical microscope images of actual paint sample cross-sections obtained microdestructively

Medical optics and biotechnology; (170.4500) Optical coherence tomography; (170.3880) Medical and biological imaging

Abstract: We have developed a dual-beam Fourier domain optical Doppler tomography (FD-ODT) system to image zebrafish (Danio rerio) larvae. Two beams incident on the zebrafish with a fixed angular separation allow absolute blood flow velocity measurement to be made regardless of vessel orientation in a sagittal plane along which the heart and most of the major vasculature lie. Two spectrometers simultaneously acquire spectra from two interferometers with a typical (maximum) line rate of 18 (28) kHz. The system was calibrated using diluted milk and microspheres and a 0.5-mm thick flow cell. The average deviation from the set velocity from 1.4 to 34.6 mm/s was 4.1%. Three-dimensional structural raster videos were acquired of an entire fish, and through the head, heart, and upper tail of the fish. Coarse features that were resolved include the telencephalon, retina, both heart chambers (atrium and ventricle), branchial arches, and notochord. Other fine structures within these organs were also resolved. Zebrafish are an important tool for high-throughput screening of new pharmacological agents. The ability to generate high-resolution three-dimensional structural videos and accurately measure absolute flow rates in major vessels with FD-ODT provides researchers with additional metrics by which the efficacy of new drugs can be assessed

Bandwidth dependence of the heterodyne efficiency in low coherence interferometry

The effect of radiation bandwidth on the heterodyne detection process is discussed. We show that, although neglected in current formalisms, the spectral changes induced by the scattering process are decreasing the heterodyne detection efficiency. This effect depends on the bandwidth of the radiation used

Optical Characterization Of Porous Membranes

Multiple light scattering techniques are intensively investigated as potential characterization tools for a broad range of applications. We are reporting on the noninvasive characterization of filters used in processes such as slurries filtering for CMP. Filters are soft porous membranes characterized by their pore size distribution and thickness, and a noncontact, nondestructive optical procedure to measure these properties is highly desirable. Due to their internal inhomogeneity, porous media strongly scatter light and, therefore, a specific procedure needs to be developed. In this work, low coherence interferometry is used to investigate light propagation in the filter and obtain the reflectivity as a function of optical pathlength for backscattered photons. This can be subsequently related to the optical properties of the sample using analytical and/or numerical models, and the porosity of the sample can be determined. In the case of filters with thicknesses much larger than the wavelength, a diffusion approximation for light propagation is used to infer the porosity information. For thinner membranes, numerical methods are used to describe the intermediate low-scattering regime that can not be represented analytically. As a direct result of the measurement, the thickness of the filter is determined independent of porosity

Evidence of scattering anisotropy effects on boundary conditions of the diffusion equation

We present experimental evidence that the diffusion process close to the boundary is fundamentally different from the bulk diffusion in the sense that it is affected by the scattering properties of the individual centers. Systematic measurements show a nontrivial behavior of the extrapolation length ratio on the scattering anisotropy of individual particles. The results are compared with other works and are supported by an independent Monte Carlo simulation. A simple analytical model that emphasizes the influence of the last scattering event successfully describes the results

Optical Pathlengths In Dental Caries Lesions

The average pathlength of light inside dental enamel and incipient (i.e. white spot) lesions is measured and compared, in order to quantitatively confirm the prediction that incipient lesions have higher scattering coefficients that sound enamel. The technique used, called optical pathlength spectroscopy (OPS), provides experimental access to the pathlength distribution of light inside highly scattering samples. This is desirable for complex biological materials, where current theoretical models are very difficult to apply. To minimize the effects of surface reflections the average pathlength is measured in wet sound enamel and white spots. We obtain values of 367 μm and 272 μm average pathlength for sound enamel and white spots respectively. We also investigate the differences between open and subsurface lesions, by measuring the change in the pathlength distribution of light as they go from dry to wet