Time-resolved Information Research Articles

Gamma knife surgery for arteriovenous malformations in the brain: integration of time-resolved contrast-enhanced magnetic resonance angiography into dosimetry planning

The aim of this study was to develop an algorithm for the integration of time-resolved contrast-enhanced magnetic resonance (MR) angiography into dosimetry planning for Gamma Knife surgery (GKS) of arteriovenous malformations (AVMs) in the brain. Twelve patients harboring brain AVMs referred for GKS underwent intraarterial digital subtraction (DS) angiography and time-resolved MR angiography while wearing an externally applied cranial stereotactic frame. Time-resolved MR angiography was performed on a 1.5-tesla MR unit (Achieva, Philips Medical Systems) using contrast-enhanced 3D fast field echo sequencing with stochastic central k-space ordering. Postprocessing with interactive data language (Research Systems, Inc.) produced hybrid data sets containing dynamic angiographic information and the MR markers necessary for stereotactic transformation. Image files were sent to the Leksell GammaPlan system (Elekta) for dosimetry planning. Stereotactic transformation of the hybrid data sets containing the time-resolved MR angiography information with automatic detection of the MR markers was possible in all 12 cases. The stereotactic coordinates of vascular structures predefined from time-resolved MR angiography matched with DS angiography data in all cases. In 10 patients dosimetry planning could be performed based on time-resolved MR angiography data. In two patients, time-resolved MR angiography data alone were considered insufficient. The target volumes showed a notable shift of centers between modalities. Integration of time-resolved MR angiography data into the Leksell GammaPlan system for patients with brain AVMs is feasible. The proposed algorithm seems concise and sufficiently robust for clinical application. The quality of the time-resolved MR angiography sequencing needs further improvement.

Off-Site Exposure to Respirable Aerosols Produced during the Disk-Incorporation of Class B Biosolids

Field experiments were conducted at a Class B biosolids land application site in central Arizona to measure, model, and source-track the off-site transport of aerosols emitted when biosolids were disk-incorporated into soils. Real-time PM10 monitoring provided time-resolved aerosol information sufficient for verifying both off-site concentration and off-site exposure time model results. Under the conditions considered and at a distance of 165 m from the aerosol source, biosolids disk-incorporation resulted in an intermittent exposure to biosolids-derived aerosol concentration between 15 and 40 μg∕ m3 and an inhalable biosolids dose between 2 and 8 μg . Transport modeling predicted that these doses will decrease with increasing wind speed. In addition, three DNA sequence-based biosolids source tracking methods were applied to aerosol samples and confirmed the presence of biosolids in aerosols at 5, 65, and 165 m from the aerosol source. Field measurements and modeling indicate that the nature of biosolids-...

Polarization dependence of vibrational coupling signals in femtosecond stimulated Raman spectroscopy

The polarization dependence of vibrational coupling signals seen in femtosecond stimulated Raman spectroscopy (FSRS) is investigated. Changing the polarization of a pulse used to impulsively excite coherent low frequency chlorine bending motion in CDCl(3) has a dramatic effect on the line shape of vibrational sidebands which arise from the anharmonic coupling of the pumped modes at 262 and 365 cm(-1) with the higher frequency symmetric stretching mode at 652 cm(-1). The asymmetric bend sideband (652+262 cm(-1)) changes sign and magnitude as the impulsive pulse polarization is rotated relative to the Raman pulses, while the symmetric bend sideband (652+365 cm(-1)) is relatively polarization independent. These experiments demonstrate the ability of FSRS to obtain time-resolved information on not only the vibrational coupling strength but also the symmetry of anharmonically coupled modes.

Translational and localised ionic motion in materials with disordered structures

Ionic materials with disordered structures may be crystalline, glassy or polymeric. Broad-band spectra of their ionic conductivities are found to display surprisingly similar features. With the help of linear response theory, time-resolved information on the ion dynamics has been extracted from such spectra. It has thus become evident that three kinds of ionic motion may be distinguished, all of them being collective and cooperative. These are vibrations, strictly localised displacements, and hops along diffusion pathways. The translational motion along diffusion pathways is well described in terms of a model called the MIGRATION concept, the acronym standing for MIsmatch Generated Relaxation for the Accommodation and Transport of IONs. The MIGRATION concept consists of a set of simple rules that are written in the form of rate equations. Model conductivity spectra can be derived from them. Strictly localised displacive movements may be performed by ions within voids provided by the structure. In our model, this situation requires a modification of one of the rate equations. As a result, we obtain the well-known features of the Nearly Constant Loss (NCL) behaviour. We present broad-band conductivity spectra of several ionic materials with disordered structures and discuss them in terms of our model treatment.

Time-Resolved Fourier Transform Infrared Spectroscopy of Chemical Reactions in Solution Using a Focal Plane Array Detector

A Fourier transform infrared (FT-IR) microscope equipped with a single as well as a 64 x 64 element focal plane array MCT detector was used to measure chemical reaction taking place in a microstructured flow cell designed for time-resolved FT-IR spectroscopy. The flow cell allows transmission measurements through aqueous solutions and incorporates a microstructured mixing unit. This unit achieves lamination of the two input streams with a cross-section of 300 x 5 microm each, resulting in fast diffusion-controlled mixing of the two input streams. Microscopic measurement at defined positions along the outlet channel allows time-resolved information of the reaction taking place in the flow cell to be obtained. In this paper we show experimental results on the model reaction between formaldehyde and sulfite. Using the single-point MCT detector, high-quality FT-IR spectra could be obtained from a spot size of 80 x 200 microm whereas the FPA detector allowed recording light from an area of 260 x 260 microm focused on its 64 x 64 detector elements. Therefore, more closely spaced features could be discerned at the expense of a significantly lower signal-to-noise (S/N) ratio per spectrum. Multivariate curve resolution-alternating least squares was used to extract concentration profiles of the reacting species along the outlet channel axis.

Control of the yeast cell cycle with a photocleavable alpha-factor analogue.

The budding yeast Saccharomyces cerevisiae is widely used as a model organism for studying many biological processes and systems, particularly for understanding the cell cycle. The yeast peptide pheromone α-factor (WHWLQLKPGQPMY) activates the mating pathway in MATa cells, arresting the cell cycle in the G1 phase. This arrest is used as a tool for synchronizing yeast cultures and for investigating signaling events involved in the pathway and other processes related to morphogenesis and transcription. Herein we report the synthesis and activity of an α-factor analogue designed to control the on/off state of the mating signal. Incorporating a photocleavable residue at a flexible site in the peptide allowed UV degradation in situ to mimic the natural protease degradation of this signaling peptide. The control over the α-factor signal achieved serves as proof of concept for use of this analogue as a tool. It also and allows access to previously impractical experiments that will yield highly time-resolved information about the yeast cell cycle and mating pathway.

A Combined SAXS/WAXS/XAFS Setup Capable of Observing Concurrent Changes Across the Nano-to-Micrometer Size Range in Inorganic Solid Crystallization Processes

A novel combined SAXS/WAXS/XAFS setup for studying the self-assembly processes occurring during the crystallization of porous materials, such as ZnAlPO-34, is described. In a single experiment, it has been possible to obtain congruent and time-resolved information on aggregation processes in the synthesis gel, the incorporation process of Zn2+ ions in the framework, and the formation of the crystalline material.

Time-modulated type-II optical parametric oscillator: Quantum dynamics and strong Einstein-Podolsky-Rosen entanglement

We investigate semiclassical dynamics and quantum properties of light beams generated in time-modulated nondegenerate optical parametric oscillator (NOPO). Having in view production of continuous-variable (CV) entangled states of light beams we propose two experimentally feasible schemes of NOPO: (i) driven by continuously modulated pump field; (ii) under action of a periodic sequence of identical laser pulses. It is shown that the time modulation of pump field amplitude essentially improves the degree of CV entanglement in NOPO. On the whole the level of integral two-mode squeezing, which characterizes the degree of CV entanglement, goes below the standard limit established in an ordinary NOPO with monochromatic pumping. We develop semiclassical and quantum theories of these devices for both below- and above-threshold regimes of generation. Properties of CV entanglement for various operational regimes of the devices are discussed in the time domain in application to time-resolved quantum information technologies. Our analytical results are in well agreement with the results of numerical simulation and support a concept of CV entangled states of time-modulated light beams.

Large Eddy Simulation of Scalar Mixing in a Coaxial Confined Jet

The highly turbulent flow occurring inside gas-turbine combustors requires accurate simulation of scalar mixing if CFD methods are to be used with confidence in design. This has motivated the present paper, which describes the implementation of a passive scalar transport equation into an LES code, including assessment/testing of alternative discretisation schemes to avoid over/undershoots and excessive smoothing. Both second order accurate TVD and higher order accurate DRP schemes are assessed. The best performance is displayed by a DRP method, but this is only true on fine meshes; it produces similar (or larger) errors to a TVD scheme on coarser meshes, and the TVD approach has been retained for LES applications. The unsteady scalar mixing performance of the LES code is validated against published DNS data for a slightly heated channel flow. Excellent agreement between the current LES predictions and DNS data is obtained, for both velocity and scalar statistics. Finally, the developed methodology is applied to scalar transport in a confined co-axial jet mixing flow, for which experimental data are available. Agreement with statistically averaged fields for both velocity and scalar, is demonstrated to be very good, and a considerable improvement over the standard eddy viscosity RANS approach. Illustrations are presented of predicted time-resolved information e.g. time histories, and scalar pdf predictions. The LES results are shown, even using a simple Smagorinsky SGS model, to predict (correctly) lower values of the turbulent Prandtl number in the free shear regions of the flow, compared to higher values in the wall-affected regions. The ability to predict turbulent Prandtl number variations (rather than input these as in combustor RANS CFD models) is an important and promising feature of the LES approach for combustor flow simulation since it is known to be important in determining combustor exit temperature traverse

Ionic motion in materials with disordered structures

The dynamics of mobile ions in materials with disordered structures constitute a challengingly complicated many-particle process. Time-resolved information on the dynamics is obtained from spectra of the complex ionic conductivity, which span more than 17 decades on the frequency scale. Ionic crystals with structural disorder as well as ion-conducting glasses, melts and polymers are found to display similar characteristics of their complex conductivity spectra. The features observed in the spectra led us to formulate a set of simple rules for the ion dynamics. The rules may be written as rate equations, forming the so-called MIGRATION concept. The acronym stands for MIsmatch Generated Relaxation for the Accommodation and Transport of IONs. Ionic movements that remain localised are described by a modified version of the MIGRATION concept, which accounts for the NCL (Nearly Constant Loss) behaviour. In general, all aspects of the experimental conductivity spectra of disordered ionic materials are well reproduced by model spectra comprising MIGRATION-type, NCL-type and vibrational components.

Transient multi pulse method for the determination of N2O - interaction with ZSM-5 type zeolites

Multipulse experiments reveal qualitative and quantitative, time-resolved information about the interaction of N2O with ZSM-5 type zeolites under conditions of catalytic applications, like the mechanism of N2O decomposition, amount and reactivity of an atomic surface oxygen species.

A new method to quantify radial error of a motorized end-milling cutter/spindle system at very high speed rotations

The radial error motion of a machine tool cutter/spindle system is critical to the dimensional accuracy of the parts to be machined. The spindle's radial error motions can be measured by mounting a sphere target onto the spindle as a reference. A set of sensors is used to measure displacements of the reference sphere in various directions to determine spindle error motions. This measurement technique can be reliably carried out when the spindle is at rest or at low rotational speeds. However, at very high speeds, the reference sphere must be carefully centered and balanced to avoid introducing additional error motions. In addition, the sensors must be held with very rigid mounts in order to avoid measurement errors caused by vibrations. For high-speed end milling spindles, the spindle is operated with a cutter. The cutter must be removed when mounting a reference sphere. Because the cutter itself can introduce errors due to centering and unbalancing effects, the error motions measured by the reference sphere method do not include the error caused by the cutter. This paper introduces a new and practical method to provide an indicator of the radial error of a motorized end-milling cutter/spindle system at very high speed rotations without the need of a reference sphere. This indicator of the radial error is based on the size of the cutting marks produced by the end mill, which is attached to the spindle. The cutting marks are circular, and their diameters are related to the radial error of the cutter/spindle system. Quantitative precision analysis was carried out to confirm the accuracy and repeatability of this new measurement technique. This technique has been implemented in order to determine the effects of the spindle speed, the level of unbalanced mass, and the spindle stiffness on the cutter/spindle's radial error. The results reveal that the centrifugal force generated by the unbalanced mass is the main factor causing the increase in radial error. One way to compensate for the effect of unbalanced mass is to increase the spindle stiffness. Experimental results confirm that a higher front bearing preload can render the spindle stiffer, thus reducing the radial error of the cutter/spindle system. Finally, it should be pointed out that the proposed cutting mark measurement cannot replace the sphere method because it cannot provide time-resolved or angle-resolved information as those obtained from polar charts. However, the proposed cutting mark measurement can provide the characterization of the spindle with the cutter attached. As a result, both methods can complement each other to provide a more complete picture of the behavior of the cutter/spindle system at high speeds.

Effects of index-mismatch-induced spherical aberration in pump–probe microscopic image formation

Pump--probe fluorescence microscopy has been demonstrated to be a powerful tool for obtaining three-dimensional, time-resolved information in bioimaging applications. However, the use of this technique can be complicated by the fact that the different wavelengths used to achieve pump--probe microscopy can result in wavelength-dependent spherical aberration, thus limiting the usefulness of the technique. We address this issue by investigating the effects of refractive-index-mismatch-induced spherical aberration on pump--probe image formation. We model the effects by considering pump--probe imaging performed with an objective with a numerical aperture of 0.75 focusing through an oil-water interface. Our results show that spherical aberration has the greatest effect in degrading an axial point-spread function. In addition to signal loss, the redistribution of signal strength along the axial direction results in broadening of the FWHM of the plane response function. The inclusion of confocal detection tends to improve image resolution but at a significant loss of signal strength.

Dynamic flow-through approaches for metal fractionation in environmentally relevant solid samples

In recent decades, batchwise equilibrium-based single or sequential extraction schemes have been consolidated as analytical tools for fractionation analyses to assess the ecotoxicological significance of metal ions in solid environmental samples. However, taking into account that naturally occurring processes always take place under dynamic conditions, recent trends have been focused on the development of alternative methods aimed at mimicking environmental events more correctly than their classical extraction counterparts. The present review details the state-of-the-art and the fundamental principles of automated, miniaturized strategies for on-line metal fractionation studies in solid substrates based on the concepts of stirring chambers, rotating coiled columns and packed microcartridges, mostly exploiting the attractive features of continuous-flow analysis, and of the first and second generations of flow-injection analysis. Special attention is also paid to a novel, robust, non-invasive approach for on-site continuous sampling of soil solutions, capitalizing on flow-through microdialysis, which presents itself as an appealing complementary approach to the conventional lysimeter experiments. In addition, a critical comparison between the time-resolved analytical information provided by these novel dynamic extraction procedures and that of the traditional schemes is given and thoroughly discussed in the bulk of the text.

Morphology development of a polystyrene/polymethylmethacrylate blend during start-up of uniaxial elongational flow

The morphology development of a polystyrene/polymethylmethacrylate blend has been investigated during uniaxial elongational flow. For this purpose linear conservative dichroism measurements are used to gather time-resolved information and scanning electron microscopy is performed on quenched samples. With the former technique the evolution of the droplet deformation in a semiconcentrated blend is studied in real time, whereas the latter technique was used for imaging individual droplets after the elongation. It is shown that the droplet deformation is affine for the conditions under investigation and that it is possible to predict the evolution of the dichroism by existing theories and the assumption of affine deformation. It has also been verified whether rheological measurements can be used to deduce morphological information during elongational flow, as this method has been succesfully applied previously in simple shear flow.

Automated Sequential Injection-Microcolumn Approach with On-Line Flame Atomic Absorption Spectrometric Detection for Implementing Metal Fractionation Schemes of Homogeneous and Nonhomogeneous Solid Samples of Environmental Interest

An automated sequential injection (SI) system incorporating a dual-conical microcolumn is proposed as a versatile approach for the accommodation of both single and sequential extraction schemes for metal fractionation of solid samples of environmental concern. Coupled to flame atomic absorption spectrometric detection and used for the determination of Cu as a model analyte, the potentials of this novel hyphenated approach are demonstrated by the ability of handling up to a 300 mg sample of a nonhomogeneous sewage amended soil (viz., CRM 483). The three steps of the endorsed Standards, Measurements, and Testing sequential extraction method have been also performed in a dynamic fashion and critically compared with the conventional batchwise protocols. The ecotoxicological relevance of the data provided by both methods with different operationally defined conditions is thoroughly discussed. As compared to traditional batch systems, the developed SI assembly offers minimal risks of sample contamination, the absence of metal re-distribution/readsorption, and dramatic saving of operational times (from 16 h to 40-80 min per partitioning step). It readily facilitates the accurate manipulation of the extracting reagents into the flow network and the minute, well-defined injection of the desired leachate volume into the detector. Moreover, highly time-resolved information on the ongoing extraction is given, which is particularly relevant for monitoring fast leaching kinetics, such as those involving strong chelating agents. On-line and off-line (for Cu, Pb, and Zn) single extraction schemes are also proven to constitute attractive alternatives for fast screening of metal pollution in solid samples and for predicting the current, rather than the potential, element bioavailability by the assessment of the readily mobilizable metal forms.

Noninvasive Method for the Assessment of Dermal Uptake of Pesticides Using Attenuated Total Reflectance Infrared Spectroscopy

Dermal absorption of pesticides is a primary exposure route for agricultural workers, but is not well characterized. Current measurement techniques are either invasive, such as tape-stripping, or require extensive sample preparation or analysis time, such as urinary metabolite monitoring or wipe sampling followed by gas chromatography analysis. We present the application of a noninvasive, spectroscopic approach for the measurement of pesticide absorption into skin. Attenuated total reflectance infrared spectroscopy (ATR-IR) was used to monitor directly the absorption of two pesticides--captan and azinphos-methyl--in ten volunteers over 20 min under occlusive conditions. We found substantial variability in absorption across subjects. Our results were comparable to those measured by the more traditional method of wipe-sampling followed by extraction and gas chromatography analysis. Multivariate data analysis, in the form of multivariate curve resolution (MCR), is a novel addition to this type of experiment, yielding time-resolved information unachievable by standard methods. These data are potentially more informative than the monitoring of blood or urinary metabolites because they can be acquired in essentially real-time, allowing observations of pesticide absorption on a rapid timescale rather than over hours or days.

E104 Time-Resolved Three-Dimensional Phase-Contrast MRI による脳動脈瘤内血流可視化

The purpose of our study was to visualize hemodynamics in a silicon vascular model with a middle cerebral aneurysm using Time-Resolved Three-Dimensional Phase-Contrast MR Imaging (4D-Flow). We created a realistic silicon model of a right middle cerebral artery bifurcation aneurysm. We ran an aqueous solution of glycerol as a flowing fluid through the silicon vessel model with a pulsatile pump. The 4D-Flow technique is based on a radiofrequency-spoiled gradient-echo sequence and it encodes flow velocity in three orthogonal directions. This technique was carried out using 1.5T MR scanner with a voxel size of 0.88x0.88x3mm, 20 phases during one cardiac cycle, and imaging time of 48min. Time-resolved images of three-dimensional streamlines clearly demonstrated that the aneurysm had three-dimensional complex vortex flows within it during systolic phase. A helical flow at the left aspect of the aneurysm was seen along the aneurysmal wall. The point where the helical flow reversed direction was coincident with the bleb. Flow rate of the bleb was low. In our model the 4D-Flow technique provided us with time-resolved three-dimensional hemodynamic information about the intracranial aneurysm and the adjacent parent artery.

New developments in MRA: time-resolved MRA

For many clinical questions, less invasive angiography methods have at least in part already replaced digital subtraction angiography (DSA) as a routine diagnostic procedure. However, temporal resolution achievable with DSA is still indispensable in some patients. Recent advances in MR hardware performance and imaging techniques permit sub-second frame rate MR angiographies to be performed using a rapidly repeated fast T1 weighted gradient echo sequence during administration of a contrast bolus, and subsequent complex subtraction in k-space to emphasise the difference in phase between stationary tissue and contrast-enhanced blood. This technique allows two-dimensional projection angiograms to be obtained at a temporal frame rate of three images per second and with a spatial in-plane resolution of about one square millimetre. This time-resolved information is important for (a) the detection and follow-up of arteriovenous malformations, including their arterial feeders, the size of the nidus and their venous drainage patterns, (b) the demonstration of dural arteriovenous fistulas, recognised as an early filling of a dural sinus during the early arterial phase, and (c) the characterization of the vascularisation of brain tumours. With regards to vascular malformations, the direction of venous drainage and therefore the most pressing clinical questions concerning the need for therapeutic intervention can be ascertained. This technique is the only MR imaging method able to provide dynamic information on the cerebral vasculature. It therefore constitutes a helpful adjunct to the imaging armentarium in many clinical situations.

Combined in situ attenuated total reflection infrared and UV–vis spectroscopic study of alcohol oxidation over Pd/Al 2O 3

In situ attenuated total reflection (ATR) infrared and UV–vis spectroscopy are combined to yield simultaneous time-resolved information on dissolved reaction products, adsorbed species, and the catalyst during the oxidation of ethanol and 2-propanol on a 5% Pd/Al 2O 3 catalyst. The oxidation is initiated by change from hydrogen- to oxygen-saturated solvent flow. 2-Propanol oxidation is observed only in the transient period, whereas ethanol oxidation is also observed in the steady state. This may be ascribed to overoxidation of the catalyst in the former case. In a mixture of the two alcohols the same thing is observed. Competitive adsorption in the steady state may explain this behavior. For ethanol oxidation ethyl acetate is also observed during the transient period. The UV–vis spectra reveal a fast reversible change of the catalyst with switching between hydrogen and oxygen and a slow irreversible change during ethanol oxidation. The latter is ascribed to the change in Pd particle structure, which hardly affects, however, catalyst activity on the time scale of about 1 h.