Classification of bacterial contamination using image processing and distributed computing.

Disease outbreaks due to contaminated food are a major concern not only for the food-processing industry but also for the public at large. Techniques for automated detection and classification of microorganisms can be a great help in preventing outbreaks and maintaining the safety of the nations food supply. Identification and classification of foodborne pathogens using colony scatter patterns is a promising new label-free technique that utilizes image-analysis and machine-learning tools. However, the feature-extraction tools employed for this approach are computationally complex, and choosing the right combination of scatter-related features requires extensive testing with different feature combinations. In the presented work we used computer clusters to speed up the feature-extraction process, which enables us to analyze the contribution of different scatter-based features to the overall classification accuracy. A set of 1000 scatter patterns representing ten different bacterial strains was used. Zernike and Chebyshev moments as well as Haralick texture features were computed from the available light-scatter patterns. The most promising features were first selected using Fishers discriminant analysis, and subsequently a support-vector-machine (SVM) classifier with a linear kernel was used. With extensive testing we were able to identify a small subset of features that produced the desired results in terms of classification accuracy and execution speed. The use of distributed computing for scatter-pattern analysis, feature extraction, and selection provides a feasible mechanism for large-scale deployment of a light scatter-based approach to bacterial classification.

Radioprotection from radiation-induced lymphedema without tumor protection.

Lymphedema or tissue swelling from impaired lymph drainage commonly occurs after regional nodal dissection and/or radiation therapy for cancer control. Treatment options for this disabling and life-altering complication involve long-term labor-intensive commitments. Sentinel node biopsy can forestall removal of negative regional nodes, offering some protection against lymphedema, however, most preventive measures are elusive, ineffective, or unproven. Our goal was to determine whether the radioprotectant amifostine could prevent or retard the development of lymphedema in a rodent radiation therapy-dependent model yet not offer tumor protection from the therapeutic effects of radiation therapy. We pre-treated rats after unilateral radical groin dissection with the organic thiophosphate radioprotectant amifostine or placebo prior to single dose post-operative groin radiation therapy and monitored hindlimb volumes, wound scores, and tissue lymphostasis. In addition, we determined whether amifostine protected human MCF7 breast cancer cells exposed to a range of radiation therapy doses in an in vitro clonogenic assay and an in vivo MCF7 tumor xenograft model. Our findings indicate that amifostine markedly reduced the volume of limb lymphedema and dramatically improved wound healing and tissue lymphostasis in the rodent lymphedema model. The in vivo and in vitro studies further demonstrated that amifostine offered no MCF7 tumor protection from radiation therapy. These pre-clinical findings provide proof-of-principle to further delineate specific mechanisms underlying amifostine's beneficial effects, determine optimal amifostine-radiation therapy dosing regimens, and thereby expedite translation into clinical trials to reduce lymphedema incidence and severity in cancer patients at high lymphedema risk in whom radiation therapy is the recommended therapy.

Forward light scattering for arbitrary sharp-edged convex crystals in Fraunhofer and anomalous diffraction approximations.

Fraunhofer diffraction is a well-known physical model for describing forward light scattering from opaque particles much larger than the wavelength of the light. Analytical expressions exist for diffraction from circular- or rectangular-shaped apertures. An expression is derived for diffraction by apertures of a general polygonal shape. From this expression the exact solution for anomalous diffraction by arbitrary convex crystals is calculated. These expressions are useful in characterizing crystal size and shape, by laser diffraction instruments, when measured in a solution.

Influence of internal refractive index gradients on size measurements of spherically symmetric particles by phase Doppler anemometry.

A model based on geometric optics for predicting the response of interferometric (phase Doppler) instruments for size measurements of particles with radially symmetric but inhomogeneous internal refractive index profiles is developed. The model and results are important for applications in which heat or mass transfer from the particles or droplets is significant, for example, in liquid-fuel combustion. To quantify the magnitude of potential bias errors introduced by the classical assumption of uniform internal properties on phase Doppler measurements, we compute calibration curves for a sequence of times during the evaporation of a decane droplet immersed in an environment of T = 2000 K and p = 10 bars. The results reveal considerable effects on the relation between phase difference and droplet diameter caused by the refractive index gradients present. The model provides an important tool to assess sizing uncertainties that can be expected when applying conventional (based on uniform properties) phase Doppler calibration curves in spray combustion and similar processes.

Light scatter from polysilicon and aluminum surfaces and comparison with surface-roughness statistics by atomic force microscopy.

Optical-scatter measurements from polysilicon and aluminum surfaces were performed by using 632.8-nm illumination at 45 deg and 488-nm illumination at 76.8 deg. Scatter was recorded up to 60 deg from the specular beam by using a concentric ring photodetector. The results are compared with surface statistics derived from atomic force microscopy. Quantitative predictions of the scatter were derived from power spectral density curves and angle-resolved-scattering theory. The agreement was fair for polysilicon samples with rms surface roughnesses of ~18 and 42 nm and aluminum with 17-nm rms roughness but poor for other samples. The discrepancy is attributed primarily to internal scatter within the measuring instrument.

Synthesis of integral transform solutions for the reconstruction of particle-size distributions from forward-scattered light.

Five integral transform solutions to the Fredholm integral equation that describes the forward-scattering properties of the distributions of spherical particles in the Fraunhofer diffraction regime have been studied. We have systematically reformulated the family of solutions, including four derivations by three other research groups and one developed as part of this work, using a standardized notation. This synthesis elucidates the mathematical interrelationships and fosters an understanding of the inversion performance of the five solutions. Finally a series of numerical experiments was carried out to demonstrate the relative performance of the techniques when applied to identical sets of simulated forward-scattering signatures.

Optical particle sizing: an introduction by the feature editors.

This issue of Applied Optics features 36 papers on topics related to particle sizing by optical methods. The contributions to this special issue derive primarily, though not exclusively, from papers presented at the Second International Congress on Optical Particle Sizing held in Tempe, Arizona, on 5-9 March 1990. The congress was the second in what we hope will be a continuing series of international meetings, held at 3-year intervals, on topics related to particle-size measurements by optical techniques. The 1990 Congress built on the successful First International Congress held in Rouen, France, in 1987. A third Congress is planned for 1993 in Yokohama, Japan.

General solution to the inverse near-forward-scattering particle-sizing problem in multiple-scattering environments: theory.

A general solution to the problem of measuring the size distribution of large particles in optically thick media by using small-angle light scattering is presented. The approach is general in the sense that no assumption of the form of the particle-size distribution function is required, although the particles must be distributed uniformly throughout the medium. The method is based on a successive order, discrete ordinates approach for modeling multiple-scattering phenomena and requires that the particle field be interrogated by using an array of near-forward input light angles. The scattering redistribution matrix is thereby determined, which permits a numerical inversion of the problem to obtain the single-scattering signature. Finally, conventional inverse scattering methods are used to reconstruct the particle-size distribution from the near-forward (single-scattering) light-scattering pattern.

Adaptive Fraunhofer diffraction particle sizing instrument using a spatial light modulator.

Integration of a magnetooptic spatial light modulator into a Fraunhofer diffraction particle sizing instrument is proposed and demonstrated theoretically and experimentally. The concept gives the instrument the ability to reconfigure a detector array on-line and thereby adapt to the measurement context.

Light scattering signatures of individual spheres on optically smooth conducting surfaces.

The differential (angle-resolved) light scattering characteristics of spheres deposited on an optically smooth polished nickel surface were studied. In the experimental work a He-Ne laser beam (632.8 nm) illuminated individual polystyrene spheres of diameters 0.50, 1.09, 2.02, and 4.10 microm. The laser beam was directed onto the surface at 45 degrees angle of incidence and focused to 15-microm l/e(2) diameter. A ring/wedge photodiode detector array centered about the specularly reflected beam collected the light scattered into twenty one ring-shaped elements ranging from ~17 degrees to 62 degrees from the specular direction. For comparison with experiment a theoretical model which partially uncoupled the scattering by the surface and the particle was developed based on extensions of Lorenz-Mie theory. The scattering measurements showed reasonable agreement with the model and indicated that the formulation can be adapted for first-order predictions of light scattering by spherical particles on optically smooth surfaces.

Laser technique for simultaneous particle-size and -velocity measurements.

A laser technique for simultaneous determination of particle size and velocity is proposed and the requisite theoretical analysis presented. The method utilizes light scattering or fluorescence signatures from individual particles passing through parallel laser beams to specify completely the particle trajectory, including two velocity components and the traverse position, in the plane perpendicular to the laser beams. The incident-laser-intensity history of the particle can then be calculated, which allows the particle size to be unambiguously determined from absolute light-scattering or fluorescence measurements.

Intensity distribution properties of a Gaussian laser beam focus.

A generalized method for determining the properties of a Gaussian laser beam focus including waist radius, position, and intensity distribution is presented. Of significance to in situ laser diagnostic methods is a unique analysis of illuminated area as a function of intensity in a plane of the laser beam. The results apply for nontruncating diffraction-limited optical systems and are important in determination of the optical sampling volume of laser instruments for particulate and gaseous species analysis.