Quantitative Optical Spectroscopy Research Articles

Effect of the Architecture of Fiber-Optic Probes Designed for Soluble Solid Content Prediction in Intact Sugar Beet Slices.

Sugar beet is the second biggest world contributor to sugar production and the only one grown in Europe. One of the main limitations for its competitiveness is the lack of effective tools for assessing sugar content in unprocessed sugar beet roots, especially in breeding programs. In this context, a dedicated near infrared (NIR) fiber-optic probe based approach is proposed. NIR technology is widely used for the estimation of sugar content in vegetable products, while optic fibers allow a wide choice of technical properties and configurations. The objective of this research was to study the best architecture through different technical choices for the estimation of sugar content in intact sugar beet roots. NIR spectral measurements were taken on unprocessed sugar beet samples using two types of geometries, single and multiple fiber-probes. Sugar content estimates were more accurate when using multiple fiber-probes (up to R2 = 0.93) due to a lesser disruption of light specular reflection. In turn, on this configuration, the best estimations were observed for the smallest distances between emitting and collecting fibers, reducing the proportion of multiply scattered light in the spectra. Error of prediction (RPD) values of 3.95, 3.27 and 3.09 were obtained for distances between emitting and collecting fibers of 0.6, 1.2 and 1.8 µm respectively. These high RPD values highlight the good predictions capacities of the multi-fiber probes. Finally, this study contributes to a better understanding of the effects of the technical properties of optical fiber-probes on the quality of spectral models. In addition, and beyond this specificity related to sugar beet, these findings could be extended to other turbid media for quantitative optical spectroscopy and eventually to validate considered fiber-optic probe design obtained in this experimental study.

Mathematical model to interpret localized reflectance spectra measured in the presence of a strong fluorescence marker.

Quantification of multiple fluorescence markers during neurosurgery has the potential to provide complementary contrast mechanisms between normal and malignant tissues, and one potential combination involves fluorescein sodium (FS) and aminolevulinic acid-induced protoporphyrin IX (PpIX). We focus on the interpretation of reflectance spectra containing contributions from elastically scattered (reflected) photons as well as fluorescence emissions from a strong fluorophore (i.e., FS). A model-based approach to extract μa and μ′s in the presence of FS emission is validated in optical phantoms constructed with Intralipid (1% to 2% lipid) and whole blood (1% to 3% volume fraction), over a wide range of FS concentrations (0 to 1000 μg/ml 1000 μg/ml ). The results show that modeling reflectance as a combination of elastically scattered light and attenuation-corrected FS-based emission yielded more accurate tissue parameter estimates when compared with a nonmodified reflectance model, with reduced maximum errors for blood volume (22% versus 90%), microvascular saturation (21% versus 100%), and μs′ (13% versus 207%). Additionally, quantitative PpIX fluorescence sampled in the same phantom as FS showed significant differences depending on the reflectance model used to estimate optical properties (i.e., maximum error 29% versus 86%). These data represent a first step toward using quantitative optical spectroscopy to guide surgeries through simultaneous assessment of FS and PpIX.

Comparison of electron energy-loss and quantitative optical spectroscopy on individual optical gold antennas

AbstractUsing a rather large set of different individual metallic optical antennas, we compare directly measured electron energy-loss spectra with measured quantitative optical extinction and scattering cross-section spectra on the identical antennas. All antenna resonances lie near 1.4 µm wavelength. In contrast to other reports, we find identical resonance positions for electrons and photons to within the experimental errors. We discuss possible artifacts which can lead to seemingly different resonance positions in experiments. Our experimental results agree well with complete numerical calculations of both sorts of spectra.

Visible light optical spectroscopy is sensitive to neovascularization in the dysplastic cervix

Neovascularization in cervical intraepithelial neoplasia (CIN) is studied because it is the precursor to the third most common female cancer worldwide. Diffuse reflectance from 450-600 nm was collected from 46 patients (76 sites) undergoing colposcopy at Duke University Medical Center. Total hemoglobin, derived using an inverse Monte Carlo model, significantly increased in CIN 2+ (N=12) versus CIN 1 (N=16) and normal tissues (N=48) combined with P<0.004. Immunohistochemistry using monoclonal anti-CD34 was used to quantify microvessel density to validate the increased hemoglobin content. Biopsies from 51 sites were stained, and up to three hot spots per slide were selected for microvessel quantification by two observers. Similar to the optical study results, microvessel density was significantly increased in CIN 2+ (N=16) versus CIN 1 (N=21) and normal tissue (N=14) combined with P<0.007. Total vessel density, however, was not significantly associated with dysplastic grade. Hence, our quantitative optical spectroscopy system is primarily sensitive to dysplastic neovascularization immediately beneath the basement membrane, with minimal confounding from vascularity inherent in the normal stromal environment. This tool could have potential for in vivo applications in screening for cervical cancer, prognostics, and monitoring of antiangiogenic effects in chemoprevention therapies.

Quantitative optical spectroscopy can identify long-term local tumor control in irradiated murine head and neck xenografts

Noninvasive and longitudinal monitoring of tumor oxygenation status using quantitative diffuse reflectance spectroscopy is used to test whether a final treatment outcome could be estimated from early optical signatures in a murine model of head and neck cancer when treated with radiation. Implanted tumors in the flank of 23 nude mice are exposed to 39 Gy of radiation, while 11 animals exposed to sham irradiation serve as controls. Diffuse optical reflectance is measured from the tumors at baseline (prior to irradiation) and then serially until 17 days posttreatment. The fastest and greatest increase in baseline-corrected blood oxygen saturation levels are observed from the animals that show complete tumor regression with no recurrence 90 days postirradiation, relative to both untreated and treated animals with local recurrences. These increases in saturation are observed starting 5 days posttreatment and last up to 17 days posttreatment. This preclinical study demonstrates that diffuse reflectance spectroscopy could provide a practical method far more effective than the growth delay assay to prognosticate treatment outcome in solid tumors and may hold significant translational promise.

American Gastroenterological Association (AGA) Institute Technology Assessment on Image-Enhanced Endoscopy

This document presents the official recommendations of the American Gastroenterological Association (AGA) Institute Technology Assessment on "Image-Enhanced Endoscopy." It was approved by the Clinical Practice and Economics Committee on August 3, 2007, and by the AGA Institute Governing Board September 27, 2007.

Charge states and quantitative infrared spectroscopy of electrically active oxygen centers in gallium arsenide

Oxygen-doped gallium arsenide crystals have been investigated by Fourier transform infrared spectroscopy. Samples with the Fermi level at about 0.4eV below the conduction band exhibit under thermal equilibrium conditions both stable states of electrically active oxygen Ooc, identified optically by the associated local vibrational modes at 730 and 715cm−1. Based on the analysis of compensating centers in the material and comparative Hall measurements, the charge states +1 and −1, respectively, are assigned to these bands. This result favors the (AsGa)2–OAs (two arsenic antisites and one off-center substitutional oxygen atom) microscopic model for the Ooc defect, presented recently, and is in disagreement with the earlier isolated OAs models. Systematic investigations related to the quantitative optical spectroscopy of this center using optically induced conversion experiments confirm that the absorption strengths of the two bands differ by 15%. A calibration factor of 3.6×1016cm−1 is suggested for the band at 730cm−1, derived indirectly from the variation of the +1 and −1 charge states with the carbon acceptor concentration.

Optical imaging of the cervix.

Recent advances in fiber optics, sources and detectors, imaging, and computer-controlled instrumentation have stimulated a period of unprecedented growth in the development of photonics technologies for a wide variety of diagnostic and therapeutic clinical applications. These include the application of quantitative optical spectroscopy and imaging for the detection of precancerous lesions in the uterine cervix, a topic of interest at the Second International Conference on Cervical Cancer, which was held April 11-14, 2002. Investigators have applied the Littenberg method of emerging technology assessment to new optical methods used to detect cervical neoplasia. Currently, such technologies as fluorescence spectroscopy (the combination of fluorescence and diffuse reflectance spectroscopy), tri-modal spectroscopy, and light-scattering spectroscopy that probe the spectral characteristics of tissue are being investigated. Optical technologies that create images of subcellular structure without biopsy subsequent to pathology that currently are under investigation include in vivo confocal imaging and optical coherence tomography. Numerous small studies have demonstrated the potential of these optical technologies. What remains to be elucidated are the fundamental biophysical origins of variations in remitted optical signals between normal and dysplastic tissue. Large multicenter randomized controlled trials are needed to confirm the detection and imaging capabilities of optical technology. Furthermore, the development of contrast agents that could boost detection with these technologies is needed, and basic biologic characterization of signals should be pursued. Applying the Littenberg assessment will help ensure that superior, not simply alternative, technologies are implemented.

A Survey for Pulsating Hot B Subdwarfs in the Northern Hemisphere

We present the final results of a survey to search for pulsating hot B subdwarf (sdB) stars. We picked our candidates on the basis of their values of Teff and log g, as estimated from available quantitative optical spectroscopy. With the help of a three-channel photometer, we gathered white-light light curves using a uniform sampling time of 10 s for a total of 74 stars. Our survey had a yield of ~5.4%, leading to the discovery of detectable luminosity variations in four objects: PG 1047+003, KPD 2109+4401, KPD 1930+2752, and PG 0014+067. For the light curves of the other 70 stars, we derive upper limits on the amplitudes of possible periodic signals (in the period window 20-1000 s) that range from ~0.05% of the mean brightness of the star at an apparent magnitude of y ~ 12 to ~0.20% at y ~ 15. We use our survey results as well as those of others to discuss the location and extent of the empirical instability strip for pulsating sdB stars in the log g-Teff diagram. We also address the question of the coexistence of pulsators and nonvariable stars in the same region of that diagram.

Active nitrogen atoms in an atmospheric pressure flowing Ar-N2 microwave discharge

The flowing afterglow of an Ar-N2 mixed gas plasma gives rise to the recombination of nitrogen atoms according to the reaction N(4S)+N(4S)+(Ar-N2)KB(V') to N2(B3 pi g,v')+(Ar-N2) N2(B3 pi g,v') to N2(A3 Sigma uv")+hv (first positive system). Quantitative optical spectroscopy measurements of the emission spectra of the N2(B3 pi g-A3 Sigma u) transition have allowed determination of the total KB and individual KB(v') rates of atomic nitrogen recombination into excited N2 molecules in the B3 pi g state with upper vibrational levels v' between 1 and 12. The active nitrogen atoms are produced by dissociation of N2 molecules in a surface-wave-induced microwave discharge (2450 MHz) sustained in an open-ended dielectric tube. The discharge is operated at atmospheric pressure and the absorbed microwave power is about 200 W for a 5 cm discharge length.