Development of two-color laser system for high-resolution polarization spectroscopy measurements of atomic hydrogen.

We have developed a high-spectral-resolution laser system for two-photon pump, polarization spectroscopy probe (TPP-PSP) measurements of atomic hydrogen in flames. In the TPP-PSP technique, a 243-nm laser beam excites the two-photon 1S-2S transition, and excited n=2 atoms are then detected by polarization spectroscopy of the n=2 to n=3 transition using 656-nm laser radiation. The single-frequency-mode 243 and 656-nm beams are produced using injection-seeded optical parametric generators coupled with pulsed dye amplifiers. The use of single-mode lasers allows accurate measurement of signal line shapes and intensities even with significant pulse-to-pulse fluctuations in pulse energies. Use of single-mode lasers and introduction of a scheme to select nearly constant laser energies enable repeatable extraction of important spectral features in atomic hydrogen transitions.

Modeling and experimental verification of plasmas induced by high-power nanosecond laser-aluminum interactions in air.

It has been generally believed in literature that in nanosecond laser ablation, the condensed substrate phase contributes mass to the plasma plume through surface evaporation across the sharp interface between the condensed phase and the vapor or plasma phase. However, this will not be true when laser intensity is sufficiently high. In this case, the target temperature can be greater than the critical temperature, so that the sharp interface between the condensed and gaseous phases disappears and is smeared into a macroscopic transition layer. The substrate should contribute mass to the plasma region mainly through hydrodynamic expansion instead of surface evaporation. Based on this physical mechanism, a numerical model has been developed by solving the one-dimensional hydrodynamic equations over the entire physical domain supplemented by wide-range equations of state. It has been found that model predictions have good agreements with experimental measurement for plasma front location, temperature, and electron number density. This has provided further evidence (at least in the indirect sense), besides the above theoretical analysis, that for nanosecond laser metal ablation in air at sufficiently high intensity, the dominant physical mechanism for mass transfer from the condensed phase to the plasma plume is hydrodynamic expansion instead of surface evaporation. The developed and verified numerical model provides useful means for the investigation of nanosecond laser-induced plasma at high intensities.

An outbreak of Cryptosporidium hominis infection at an Illinois recreational waterpark.

Cryptosporidium has become increasingly recognized as a pathogen responsible for outbreaks of diarrhoeal illness in both immunocompetent and immunocompromised persons. In August 2001, an Illinois hospital reported a cryptosporidiosis cluster potentially linked to a local waterpark. There were 358 case-patients identified. We conducted community-based and waterpark-based case-control studies to examine potential sources of the outbreak. We collected stool specimens from ill persons and pool water samples for microscopy and molecular analysis. Laboratory-confirmed case-patients (n=77) were more likely to have attended the waterpark [odds ratio (OR) 16.0, 95% confidence interval (CI) 3.8-66.8], had pool water in the mouth (OR 6.0, 95% CI 1.3-26.8), and swallowed pool water (OR 4.5, 95% CI 1.5-13.3) than age-matched controls. Cryptosporidium was found in stool specimens and pool water samples. The chlorine resistance of oocysts, frequent swimming exposures, high bather densities, heavy usage by diaper-aged children, and increased recognition and reporting of outbreaks are likely to have contributed to the increasing trend in number of swimming pool-associated outbreaks of cryptosporidiosis. Recommendations for disease prevention include alteration of pool design to separate toddler pool filtration systems from other pools. Implementation of education programmes could reduce the risk of faecal contamination and disease transmission.

Gain-swept superradiance applied to the stand-off detection of trace impurities in the atmosphere.

We show that gain-swept superradiance can be used to detect low (parts per million) concentrations of various gases at distances on the order of kilometers, which is done by using pulse timing to create small regions of gain at positions that sweep toward a detector. The technique is far more sensitive than previous methods such as light detection and ranging or differential absorption light detection and ranging.

FAST CARS: engineering a laser spectroscopic technique for rapid identification of bacterial spores.

Airborne contaminants, e.g., bacterial spores, are usually analyzed by time-consuming microscopic, chemical, and biological assays. Current research into real-time laser spectroscopic detectors of such contaminants is based on e.g., resonance fluorescence. The present approach derives from recent experiments in which atoms and molecules are prepared by one (or more) coherent laser(s) and probed by another set of lasers. However, generating and using maximally coherent oscillation in macromolecules having an enormous number of degrees of freedom is challenging. In particular, the short dephasing times and rapid internal conversion rates are major obstacles. However, adiabatic fast passage techniques and the ability to generate combs of phase-coherent femtosecond pulses provide tools for the generation and utilization of maximal quantum coherence in large molecules and biopolymers. We call this technique FAST CARS (femtosecond adaptive spectroscopic techniques for coherent anti-Stokes Raman spectroscopy), and the present article proposes and analyses ways in which it could be used to rapidly identify preselected molecules in real time.

Comparison of pharmacokinetic MRI and [18F] fluorodeoxyglucose PET in the diagnosis of breast cancer: initial experience.

It was the aim of this methodology-oriented clinical pilot study to compare the potential of dynamic MRI and 2-[18F]fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) for the detection and characterization of breast cancer. Fourteen women with suspicious breast lesions were examined. The MRI data were acquired with a turbo fast low-angle shot sequence and analyzed using a pharmacokinetic model. Emission data were detected in the sensitive 3D modus, iteratively reconstructed, and superimposed onto corresponding transmission images. In the 14 patients, 13 breast masses with a suspicious contrast enhancement and FDG uptake were detected. For these lesions, no statistically significant correlation between evaluated MR and PET parameters was found. Of the 9 histologically confirmed carcinomas, 8 were correctly characterized with MRI and PET. Two inflammatory lesions were concordantly classified as cancer. Moreover, dynamic MRI yielded another false-positive finding. In 6 patients, PET detected occult lymph node and/or distant metastases. Although both functional imaging techniques provide independent tissue information, the results concerning the diagnosis of primary breast lesions were almost identical. An advantage of PET, however, is its ability to localize lymph node involvement and distant metastases as an integral part of the examination.

Quantification of [(18)F]FDG uptake in the normal liver using dynamic PET: impact and modeling of the dual hepatic blood supply.

UNLABELLED: For quantification of hepatic [(18)F]FDG uptake, the dual blood supply to the liver must be considered. In contrast to the arterial input, however, the portal venous blood supply to the liver cannot be monitored directly by PET because of the inaccessibility of the portal vein on PET scans. In this study, we investigated whether the dual hepatic input can be predicted from the measurable arterial input. Moreover, we assessed the effect of different input models on the rate constants of the standard 3-compartment model describing regional uptake of FDG. METHODS: Dynamic FDG PET scanning was performed on 5 foxhounds. Activity concentrations in blood from the aorta and the portal vein were measured simultaneously using external circuits. After image reconstruction, time--activity courses were determined from the aorta and the liver. The venous input was approximated by convolving the arterial input with a notional system function describing the dispersion of the arterial input on its way through the gastrointestinal tract. On the basis of these data, 5 different hepatic input models, which pertain to a single-input as well as a dual-input scenario, were statistically compared with regard to the adequacy of the model fits to liver data and to differences in the estimated rate constants. RESULTS: Portal venous input to the liver could be approximated by convolving the arterial input function with a system function. From this function, a mean transit time of 25 s was computed for FDG to pass through the gastrointestinal tract. According to the statistical analysis, dual-input models were superior to their single-input counterparts. However, differences in the rate constants estimated for the 5 input models were in the same order as interindividual variations within the different model groups. For the dephosphorylation rate constant, a consistent value of 0.05 +/- 0.01 min(-1) was found. CONCLUSION: Dual-input models proved to be superior to single-input models with respect to the adequacy of FDG model fits to normal liver data. However, the hepatic blood supply may be approximated by the arterial input function as well, especially for the evaluation of liver lesions mainly fed by the hepatic artery.

X-ray reflectivity study of smectic wetting and prewetting at the free surface of isotropic liquid crystals.

We study the structures of free-surface-wetting layers above the isotropic to smectic-A transition of three liquid-crystal compounds that show different kinds of growth of the wetting film as the bulk transition is approached: layer-by-layer, continuous, and continuous with prewetting. The smectic-A surface phase of the layer-by-layer compound consists of well-defined layers and possesses a sharp boundary to the isotropic bulk phase, whereas in the two continuous compounds sinusoidal density oscillations with a continuously decaying amplitude are found. In the continuous case with prewetting, the wetting film below the prewetting transition does not show an essential difference to the continuous case without prewetting.

Classification of signal-time curves from dynamic MR mammography by neural networks.

The aim of this study was to test the performance of artificial neural networks for the classification of signal-time curves obtained from breast masses by dynamic MRI. Signal-time courses from 105 parenchyma, 162 malignant, and 102 benign tissue regions were examined. The latter two groups were histopathologically verified. Four neural networks corresponding to different temporal resolutions of the signal-time curves were tested. The resolution ranges from 28 measurements with a temporal spacing of 23s to just 3 measurements taken 1.8, 3, and 10 minutes after contrast medium administration. Discrimination between malignant and benign lesions is best if 28 measurement points are used (sensitivity: 84%, specificity: 81%). The use of three measurement points results in 78% sensitivity and 76% specificity. These results correspond to values obtained by human experts who visually evaluated signal-time curves without considering additional morphologic information. All examined networks yielded poor results for the subclassification of the benign lesions into fibroadenomas and benign proliferative changes. Neural networks can computationally fast distinguish between malignant and benign lesions even when only a few post-contrast measurements are made. More precise specification of the type of the benign lesion will require incorporation of additional morphological or pharmacokinetic information.

Interline Transfer CCD Camera for Gated Broadband Coherent Anti-Stokes Raman-Scattering Measurements.

Use of an interline transfer CCD camera for the acquisition of broadband coherent anti-Stokes Raman-scattering (CARS) spectra is demonstrated. The interline transfer CCD has alternating columns of imaging and storage pixels that allow one to acquire two successive images by shifting the first image in the storage pixels and immediately acquiring the second image. We have used this dual-image mode for gated CARS measurements by acquiring a CARS spectral image and shifting it rapidly from the imaging pixel columns to the storage pixel columns. We have demonstrated the use of this dual-image mode for gated single-laser-shot measurement of hydrogen and nitrogen CARS spectra at room temperature and in atmospheric pressure flames. The performance of the interline transfer CCD for these CARS measurements is compared directly with the performance of a back-illuminated unintensified CCD camera.

OH sensor based on ultraviolet, continuous-wave absorption spectroscopy utilizing a frequency-quadrupled, fiber-amplified external-cavity diode laser.

The development of an all-solid-state cw laser system for optical absorption measurements of the OH radical in the UV spectral range is described. The tunable output of a 1064-nm external-cavity diode laser is amplified by use of a Nd:doped, double-clad fiber amplifier. The amplified near-IR radiation is frequency doubled by a periodically poled lithium niobate crystal and then quadrupled in a beta-barium borate crystal. The design and operation of the system and measurements of OH absorption in the (2, 0) band of the A(2)?(+)- X(2)? electronic transition are discussed.

Comparison of rigid and elastic matching of dynamic magnetic resonance mammographic images by mutual information.

The present study aims at (i) the evaluation of the performance of a rigid and of an elastic matching algorithm for the coregistration of dynamic magnetic resonance (MR) images visualizing the female breast, and (ii) the evaluation of the mutual information (MI) as a matching criterion. To this end, ten patient data sets were analyzed. The comparison was performed with respect to the achieved increase in the MI and by visual inspection of the dynamic image series in a continuous film sequence ((cine mode). In most cases, the achieved increase in MI by elastic image registration is much higher than that achieved by rigid registration. Only for three of the ten data sets could the MI be increased by rigid image registration to a similar or even larger degree than by elastic image registration. Taking into account the results of the visual inspection of the rigid and elastic matched data sets, however, the elastic match leads to equal or better results for all data sets. Therefore, elastic matching is the gold standard for the registration of dynamic MR mammographic images of the female breast. The comparison of the increase in MI and the visual inspection further shows that the visual impression agrees in most cases with the result of the calculation of the MI. Therefore, the MI proves to be a suitable matching criterion for the type of data sets studied.

Wetting behavior above the liquid-crystal-isotropic transition in a homologous series

An ellipsometric study of the wetting behavior at the free surface above the isotropic to nematic or isotropic to smectic-A transition of nine homologous compounds with even alkyl chain lengths n in the range from four to twenty carbon atoms is presented. All compounds show a pretransitional increase of the nematic or smectic surface coverage as the bulk isotropic to liquid-crystal transition is approached from above. The behavior of the nematic compounds (n=4 to 10) can be interpreted, within the framework of a Landau model, as complete wetting. In short nematic homologs the divergence of the nematic coverage is strongly reduced by a decrease of the nematic susceptibility of the isotropic phase. The elastic coefficient L of the Landau model shows a pronounced increase with increasing n, resulting in the occurrence of a discontinuous prewetting transition in the shortest smectic homolog (n=12) that is still describable by the nematic Landau model. In the longer smectic homologs (n=14 to 20), layering steps appear in the pretransitional increase of the coverage. The results indicate probable partial wetting for the longest homolog, whereas for the other smectic compounds the distinction between complete and partial wetting is difficult on the basis of ellipsometry.

Surface plasmon resonance study of the spreading of a liquid-crystal smectic- a droplet on a gold substrate.

We report a study of the spreading of liquid-crystal smectic- A droplets which completely wet a gold substrate. After the initial spreading of a molecular precursor layer, the droplets develop a complex terraced structure consisting of several monolayers and one bilayer spreading at different rates. During the late stage of spreading the droplet height decreases via a series of layer-by-layer shrinkages until a final state is reached which consists of a single dense monolayer.

[Diagnostic evaluation of the breast using PET: optimization of data acquisition and postprocessing]. / Mammadiagnostik mit PET: Optimierung der Datenakquisition und -nachverarbeitung.

PURPOSE: Development and evaluation of an optimized protocol for PET examinations of the female breast with 2-F-18-fluoro-2-deoxyglucose (F-18-FDG). METHODS: All PET measurements were performed with a whole-body PET system (ECAT EXACT HR+). In order to examine the women with the breasts freely pendant, a special extension for the patient table made of carbon layer composite was designed. After data acquisition in the 3D modus, emission data were sorted into 2D sinograms using the Fourier rebinning algorithm and reconstructed by means of an ultra-fast iterative 2D algorithm (HOSP). The reconstructed emission scans were superimposed onto the corresponding transmission images. The protocol presented was evaluated in examinations on 6 women with breast lesions after the administration of 150-220 MBq F-18-FDG. From two adjacent bed positions, emission and transmission data were acquired over periods of 20 min and 10 min, respectively. For comparison, dynamic magnetic resonance (MR) image series were acquired with a whole-body MR system (MAGNETOM SP 4000) using a double-breast coil. RESULTS AND CONCLUSION: Using the designed extension of the patient table, it was possible to examine corpulent women despite the limited patient port of the PET system in the prone position with the breasts freely pendant. Alongside a reduction in motion artifacts, this positioning also offers the possibility of making a direct comparison between PET and MR images. Despite the fact that the amount of F-18-FDG applied to the patient was markedly reduced, the combination of 3D data acquisition and iterative image reconstruction resulted in excellent quality of the emission scans. By super-positioning of iteratively reconstructed emission and transmission scans, anatomical localization of breast lesions visualized on the emission scans could be improved. The postprocessing of the PET data described was completed in 60 min, this meaning that the presented concept can readily be employed in clinical practice.

[Dynamic MR mammography. Multidimensional visualization of contrast medium enhancement in virtual reality]. / Dynamische MR-Mammographie. Multidimensionale Visualisierung der Kontrastmittelanreicherung in virtueller Realität.

BACKGROUND: The purpose of this study was the development of a method for fast and efficient analysis of dynamic MR images of the female breast. The image data sets were acquired with a saturation-recovery turbo-FLASH sequence which enables the detection of the kinetics of the contrast agent concentration in the whole breast with a high temporal and spatial resolution. In addition, a morphologic 3D-FLASH data set was acquired. METHODS: The dynamic image datasets were analyzed by a pharmacokinetic model which enables the representation of the relevant functional tissue information by two parameters. In order to display simultaneously morphologic and functional tissue information, we developed a multidimensional visualization system, which enables a practical and intuitive human-computer interface in virtual reality. DISCUSSIONS: The developed system allows the fast and efficient analysis of dynamic MR data sets. An important clinical application is the localization and definition of multiple lesions of the female breast.

Elastic matching of dynamic MR mammographic images.

Dynamic magnetic resonance imaging (MRI) carried out with paramagnetic contrast media has been proven to increase sensitivity and specificity in the detection of breast cancer. Due to movements of the patients and changes in the shape of the breasts during the measurement period, a coregistration (matching) of the acquired data volumes is necessary to obtain higher accuracy for the localization of lesions. In this study, an algorithm for the elastic matching of dynamic MRI volume data is presented. The approach includes automatic feature extraction along with the analysis of corresponding features between the data sets. The matching is actually slice-oriented, even though information on displacement vectors in adjacent slices is taken into account. An extension of the procedure to fully three-dimensionally (3D) matching is straight forward. Up until now, the approach has been applied to 20 dynamic MRI studies. The matching time for two image data sets with 256 x 256 x 15 voxels each was about 4 min using a PC (Pentium Pro, 200MHz).

Experimental investigation of saturated polarization spectroscopy for quantitative concentration measurements.

Polarization-spectroscopy (PS) line shapes and signal intensities are measured in well-characterized hydrogen-air flames operated over a wide range of equivalence ratios. We use both low (perturbative) and high (saturating) pump beam intensities in the counterpropagating pump-probe geometry. The effects of saturation on the line-center signal intensity and the resonance linewidth are investigated. The PS signal intensities are used to measure relative OH number densities in a series of near-adiabatic flames at equivalence ratios (phi) ranging from 0.5 to 1.5. The use of saturating pump intensities minimizes the effect of pump beam absorption, providing more accurate number density measurements. When calibrated to the calculated OH concentration in the phi = 0.6 flame, the saturated PS number density measurements probing the P(1)(2) transition are in excellent agreement with OH absorption measurements, equilibrium calculations of OH number density, and previous saturated degenerate four-wave mixing OH number density measurements.

Development of high-resolution n(2) coherent anti-stokes Raman scattering for measuring pressure, temperature, and density in high-speed gas flows.

Mean and instantaneous measurements of pressure, temperature, and density have been acquired in an optically accessible gas cell and in the flow field of an underexpanded sonic jet by use of the high-resolution N(2) coherent anti-Stokes Raman scattering (CARS) technique. This nonintrusive method resolves the pressure- and temperature-sensitive rotational transitions of the nu = 0 ? 1 N(2) Q-branch to within Domega = 0.10 cm(-1). To extract thermodynamic information from the experimental spectra, theoretical spectra, generated by a N(2) spectral modeling program, are fit to the experimental spectra in a least-squares manner. In the gas cell, the CARS-measured pressures compare favorably with transducer-measured pressures. The precision and accuracy of the single-shot CARS pressure measurements increase at subatmospheric conditions. Along the centerline of the underexpanded jet, the agreement between the mean CARS P/T/rho measurements and similar quantities extracted from a Reynolds-averaged Navier-Stokes computational fluid dynamic simulation is generally excellent. This CARS technique is able to capture the low-pressure and low-temperature conditions of the M = 3.4 flow entering the Mach disk, as well as the subsonic conditions immediately downstream of this normal shock.

Experimental investigation of saturated degenerate four-wave mixing for quantitative concentration measurements.

Degenerate four-wave mixing (DFWM) line shapes and signal intensities are measured experimentally in well-characterized hydrogen-air flames operated over a wide range of equivalence ratios. We use both low (perturbative) and high (saturating) beam intensities in the phase-conjugate geometry. Resonances in the A 2Sigma+ -X 2II (0,0) band of OH are probed with multiaxial-mode laser radiation. The effects of saturation on the line-center signal intensity and the resonance linewidth are investigated. The DFWM signal intensities are used to measure OH number densities in a series of near-adiabatic flames at equivalence ratios ranging from 0.5 to 1.5. Use of saturating pump intensities minimizes the effects of beam absorption, providing more-accurate number density measurements. The saturated DFWM results are in excellent agreement with OH absorption measurements and equilibrium calculations of OH number density. The polarization dependence of the P(1)(2) and R(2)(1) resonances is investigated in both laser intensity regimes. There is a significant change in relative reflectivities for different polarization configurations when saturated.