Monte Carlo-based inverse model for calculating tissue optical properties. Part I: Theory and validation on synthetic phantoms

A flexible and fast Monte Carlo-based model of diffuse reflectance has been developed for the extraction of the absorption and scattering properties of turbid media, such as human tissues. This method is valid for a wide range of optical properties and is easily adaptable to existing probe geometries, provided a single phantom calibration measurement is made. A condensed Monte Carlo method was used to speed up the forward simulations. This model was validated by use of two sets of liquid-tissue phantoms containing Nigrosin or hemoglobin as absorbers and polystyrene spheres as scatterers. The phantoms had a wide range of absorption (0-20 cm(-1)) and reduced scattering coefficients (7-33 cm(-1)). Mie theory and a spectrophotometer were used to determine the absorption and reduced scattering coefficients of the phantoms. The diffuse reflectance spectra of the phantoms were measured over a wavelength range of 350-850 nm. It was found that optical properties could be extracted from the experimentally measured diffuse reflectance spectra with an average error of 3% or less for phantoms containing hemoglobin and 12% or less for phantoms containing Nigrosin.     

Monte Carlo-based inverse model for calculating tissue optical properties. Part II: Application to breast cancer diagnosis

The Monte Carlo-based inverse model of diffuse reflectance described in part I of this pair of companion papers was applied to the diffuse reflectance spectra of a set of 17 malignant and 24 normal-benign ex vivo human breast tissue samples. This model allows extraction of physically meaningful tissue parameters, which include the concentration of absorbers and the size and density of scatterers present in tissue. It was assumed that intrinsic absorption could be attributed to oxygenated and deoxygenated hemoglobin and beta-carotene, that scattering could be modeled by spheres of a uniform size distribution, and that the refractive indices of the spheres and the surrounding medium are known. The tissue diffuse reflectance spectra were evaluated over a wavelength range of 400-600 nm. The extracted parameters that showed the statistically most significant differences between malignant and nonmalignant breast tissues were hemoglobin saturation and the mean reduced scattering coefficient. Malignant tissues showed decreased hemoglobin saturation and an increased mean reduced scattering coefficient compared with nonmalignant tissues. A support vector machine classification algorithm was then used to classify a sample as malignant or nonmalignant based on these two extracted parameters and produced a cross-validated sensitivity and specificity of 82% and 92%, respectively.     

Sequential estimation of optical properties of a two-layered epithelial tissue model from depth-resolved ultraviolet-visible diffuse reflectance spectra

A method for estimating the optical properties of two-layered media (such as squamous epithelial tissue) over a range of wavelengths in the ultraviolet-visible spectrum is proposed and tested with Monte Carlo modeling. The method first used a fiber-optic probe with angled illumination and the collection fibers placed at a small separation (or=1000 microm) was used to detect diffuse reflectance preferentially from the bottom layer. A second Monte Carlo-based inverse model for a two-layered medium was applied to estimate the bottom layer optical properties, as well as the top layer thickness, given that the top layer optical properties have been estimated. The results of Monte Carlo validation show that this method works well for an epithelial tissue model with a top layer thickness ranging from 200 to 500 microm. For most thicknesses within this range, the absorption coefficients were estimated to within 15% of the true values, the reduced scattering coefficients were estimated to within 20% and the top layer thicknesses were estimated to within 20%. The application of a variance reduction technique to the Monte Carlo modeling proved to be effective in improving the accuracy with which the optical properties are estimated.     

Thermal properties and performance of carbon fiber-based ultra-high temperature ceramic matrix composites (Cf-UHTCMCs)

The thermophysical properties of carbon fiber-based ultra-high temperature ceramic matrix composites have been determined to aid designers who need these properties when considering using the composites in ultra-high temperature aerospace applications. The coefficient of thermal expansion (CTE) and thermal diffusivity of the composites were measured parallel and perpendicular to the ply direction; the thermal conductivity was measured using the laser-flash method and the heat capacity calculated from the relationship between the thermal diffusivity, density, and thermal conductivity. Both the CTE and thermal conductivity showed higher values across the ply and increased with increasing temperature as expected, whilst the thermal diffusivity showed higher values parallel to the ply and increased smoothly with temperature. In addition, two different but related oxyfuel torch tests, based on oxyacetylene and oxypropane, were used to evaluate the thermo-ablation behavior of the composites. The tests showed how good the composites were at withstanding the ultra-high temperatures, high heat fluxes, and gas velocities involved.     

Experimental Verification of the Lateral Periodicity of Axially Periodic Incoherent Fields Using the Lau Effect

Abstract

‘General’ objects, which are specially prepared to possess restricted spatial frequency spectra, have been used in the conventional Lau experiment to obtain experimental proof for the existence of lateral periodicity arising from axial periodicity, for a subclass of axially periodic wavefields in an incoherent situation.     

Enhanced electrooxidation of methanol,ethylene glycol,glycerol, and xylitol over a polypyrrole/manganese oxyhydroxide/palladium nanocomposite electrode

A small quantity of palladium metal (Pd, 5 wt%) nanoparticles supported by a polypyrrole/manganese oxyhydroxide (PPy/MOH) nanocomposite was developed and investigated as an electrocatalyst for the alcohol electrooxidation reaction in alkaline media. In voltammetric studies, the PPy/MOH/Pd catalyst, compared to C/Pd, exhibited improved electrocatalytic activity for methanol electrooxidation. The peak current density ratios (j ^f/j ^b) for the C/Pd and PPy/MOH/Pd nanocomposite electrodes were 0.67 and 2.43, respectively, indicating that the PPy/MOH/Pd nanocomposite electrode was much more resistant to catalytic poisoning. The electrooxidation of ethylene glycol (EG), glycerol, and xylitol was also tested using the PPy/MOH/Pd nanocomposite electrode. Among these alcohol electrooxidations, that of EG exhibited the maximum power density of 430 mA cm^?2. The intermediates formed during the electrooxidation reactions were removed by increasing the upper sweep potential from +0.2 to +1.0 V. The catalytic performance of the PPy/MOH nanocomposite is discussed in detail. The study results demonstrate that PPy/MOH acts as a superior catalytic supporting material for alcohol electrooxidation reactions in alkaline media.     

Synthesis of High-Performance Parallel Programs for a Class of ab Initio Quantum Chemistry Models

This paper provides an overview of a program synthesis system for a class of quantum chemistry computations. These computations are expressible as a set of tensor contractions and arise in electronic structure modeling. The input to the system is a a high-level specification of the computation, from which the system can synthesize high-performance parallel code tailored to the characteristics of the target architecture. Several components of the synthesis system are described, focusing on performance optimization issues that they address.     

Optimizing KTP and LiTaO3 channel waveguides forquasi-phase-matched second harmonic generation with high conversionefficiency

The conversion efficiency of quasi-phase-matched second harmonic generation (QPM-SHG) in waveguides can be enhanced significantly by optimizing the linear properties of the guiding structure. We describe here a method for fast and accurate computation of the modal properties of continuous, periodically poled, ferroelectric channel waveguides and a multiparameter optimization algorithm which we have used to maximize normalized internal SHG conversion efficiency. We present the phase-matching characteristics of these designs and discuss the possibility of high SHG conversion efficiency between lowest order transverse modes at the fundamental and second harmonic wavelengths near noncritically phase-matched regimes of operation     

Design of grasping methodologies for rotational assembly components

This article describes a design methodology for grasping assembly components. Three heuristics are developed. The first determines feasible grasping configurations based on component geometric information. The second heuristic determines feasible grasping configurations by including gripper functional attributes. The third heuristic generates the final set of grasping configurations by including the area available for grasping a component. An interactive program written in Fortran 77 is developed to capture the user inputs, and a sample application is described. The methodology does not assume an initial feeding state of the component to the robot. The grasping configurations generated (if more than one) provide the designer with alternate feasible feeding methods.     

Portable, Fiber-Based, Diffuse Reflection Spectroscopy (DRS) Systems for Estimating Tissue Optical Properties

Steady-state diffuse reflection spectroscopy is a well-studied optical technique that can provide a noninvasive and quantitative method for characterizing the absorption and scattering properties of biological tissues. Here, we compare three fiber-based diffuse reflection spectroscopy systems that were assembled to create a light-weight, portable, and robust optical spectrometer that could be easily translated for repeated and reliable use in mobile settings. The three systems were built using a broadband light source and a compact, commercially available spectrograph. We tested two different light sources and two spectrographs (manufactured by two different vendors). The assembled systems were characterized by their signal-to-noise ratios, the source-intensity drifts, and detector linearity. We quantified the performance of these instruments in extracting optical properties from diffuse reflectance spectra in tissue-mimicking liquid phantoms with well-controlled optical absorption and scattering coefficients. We show that all assembled systems were able to extract the optical absorption and scattering properties with errors less than 10%, while providing greater than ten-fold decrease in footprint and cost (relative to a previously well-characterized and widely used commercial system). Finally, we demonstrate the use of these small systems to measure optical biomarkers in vivo in a small-animal model cancer therapy study. We show that optical measurements from the simple portable system provide estimates of tumor oxygen saturation similar to those detected using the commercial system in murine tumor models of head and neck cancer.