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At least 487 records · Page 27Linked to original sources
PubMed1987

Nanovid tracking: a new automatic method for the study of mobility in living cells based on colloidal gold and video microscopy.

We describe a new automatic technique for the study of intracellular mobility. It is based on the visualization of colloidal gold particles by video-enhanced contrast light microscopy (nanometer video microscopy) combined with modern tracking algorithms and image processing hardware. The approach can be used for determining the complete statistics of saltatory motility of a large number of individual moving markers. Complete distributions of jump time, jump velocity, stop time, and orientation can be generated. We also show that this method allows one to study the characteristics of random motion in the cytoplasm of living cells or on cell membranes. The concept is illustrated by two studies. First we present the motility of colloidal gold in an in vitro system of microtubules and a protein extract containing a kinesin-like factor. The algorithm is thoroughly tested by manual tracking of the videotapes. The second study involves the motion of gold particles microinjected in the cytoplasm of PTK-2 cells. Here the results are compared to a study using the spreading of colloidal gold particles after microinjection.

Animals↗
PubMed1996

In vivo tracking of platelets: circulating degranulated platelets rapidly lose surface P-selectin but continue to circulate and function.

To examine the hypothesis that surface P-selectin-positive (degranulated) platelets are rapidly cleared from the circulation, we developed novel methods for tracking of platelets and measurement of platelet function in vivo. Washed platelets prepared from nonhuman primates (baboons) were labeled with PKH2 (a lipophilic fluorescent dye), thrombin-activated, washed, and reinfused into the same baboons. Three-color whole blood flow cytometry was used to simultaneously (i) identify platelets with a mAb directed against glycoprotein (GP)IIb-IIIa (integrin alpha 11b beta 3), (ii) distinguish infused platelets by their PKH2 fluorescence, and (iii) analyze platelet function with mAbs. Two hours after infusion of autologous thrombin-activated platelets (P-selectin-positive, PKH2-labeled), 95 +/- 1% (mean +/- SEM, n = 5) of the circulating PKH2-labeled platelets had become P-selectin-negative. Compared with platelets not activated with thrombin preinfusion, the recovery of these circulating PKH2-labeled, P-selectin-negative platelets was similar 24 h after infusion and only slightly less 48 h after infusion. The loss of platelet surface P-selectin was fully accounted for by a 67.1 +/- 16.7 ng/ml increase in the plasma concentration of soluble P-selectin. The circulating PKH2-labeled, P-selectin-negative platelets were still able to function in vivo, as determined by their (i) participation in platelet aggregates emerging from a bleeding time wound, (ii) binding to Dacron in an arteriovenous shunt, (iii) binding of mAb PAC1 (directed against the fibrinogen binding site on GPIIb-IIIa), and (iv) generation of procoagulant platelet-derived microparticles. In summary, (i) circulating degranulated platelets rapidly lose surface P-selectin to the plasma pool, but continue to circulate and function; and (ii) we have developed novel three-color whole blood flow cytometric methods for tracking of platelets and measurement of platelet function in vivo.

Animals↗
PubMed1996

Use of mathematically enhanced spectral analysis and spectral contrast techniques for the liquid chromatographic and capillary electrophoretic detection and identification of pharmaceutical compounds.

The use of mathematically enhanced ultraviolet/visible (UV/VIS) absorbance spectral analysis and spectral contrast software techniques in high performance liquid chromatography (HPLC) and micellar electrokinetic capillary electrophoresis (MECC) as an aid for the determination of peak homogeneity, identification, and tracking during method development was investigated. Various structurally similar pharmaceutical compounds, and compounds present as either cis/trans isomers, diastereomers, or enantiomers were used as test compounds to probe the limits of this technique. Two tricyclic antidepressants, nortriptyline and imipramine, were employed to study the effects of HPLC mobile phase composition and pH on the ability to identify and track peaks during method development. It was found that method changes altered the spectral matches used for identification, but not enough to cause incorrect peak identification. It was also shown using HPLC that the cis/trans isomers of doxepin and the diastereomers ephedrine and pseudoephedrine could be distinguished. The mathematically enhanced spectral analysis and spectral contrast software techniques were also employed with MECC. Peaks tracking during method development as pH and the concentration of surfactant changes is shown for a separation of various penicillin type antibiotics. It was shown that during chiral MECC (CMECC) analyses ephedrine/pseudoephedrine diastereomers as well as ephedrine enantiomers could be distinguished. The determination of enantiomers is possible in CMECC since enantiomers are eluted as diastereomeric complexes, as opposed to HPLC where they are eluted in their native state.

Antidepressive Agents, Tricyclic↗
PubMedDate not supplied

Dynamic scan-plane tracking using MR position monitoring.

An MR-based method for tracking subject motion is presented. The technique identifies subject motion from the three-dimensional positions of three small samples attached to the subject in a fixed, triangular configuration. The updated positions of these samples relative to their initial positions determine a rigid body transformation. Applied to the MRI scan prescription via adaptive feedback controls, this transformation yields an updated MRI scan plane that tracks the prescribed imaging section as the subject moves. The scan-plane tracking procedure is demonstrated experimentally for two-dimensional imaging of a standard imaging phantom and the head of a human subject. Sets of images were acquired sequentially, with motion (translations and/or rotations) introduced between image frames. The scan-plane tracking system provides well registered image slices of the same section, adaptively compensating for the subject motion.

Artifacts↗
PubMed2007

[Ablation on the undersurface of a LASIK flap. Instrument and method for continuous eye tracking].

BACKGROUND: The risk of iatrogenic keratectasia after laser in situ keratomileusis (LASIK) increases with thinner posterior stromal beds. Ablations on the undersurface of a LASIK flap could only be performed without the guidance of an eye tracker, which may lead to decentration. A new method for laser ablation with flying spot lasers on the undersurface of a LASIK flap was developed that enables the use of an active eye tracker by utilizing a novel instrument. The first clinical results are reported. PATIENTS AND METHODS: Patients wishing an enhancement procedure were eligible for a modified repeat LASIK procedure if the flaps cut in the initial procedure were thick enough to perform the intended additional ablation on the undersurface leaving at least 90 microm of flap thickness behind. (1) The horizontal axis and the center of the entrance pupil were marked on the epithelial side of the flap using gentian violet dye. (2) The flap was reflected on a newly designed flap holder which had a donut-shaped black marking. (3) The eye tracker was centered on the mark visible in transparency on the flap. (4) Ablation with a flying spot Bausch & Lomb Technolas 217z laser was performed on the undersurface of the flap with a superior hinge taking into account that in astigmatic ablations the cylinder axis had to be mirrored according to the formula: axis on the undersurface=180 degrees -axis on the stromal bed. (5) The flap was repositioned. RESULTS: Detection of the marking on the modified flap holder and continuous tracking instead of the real pupil was possible in all of the 12 eyes treated with this technique. It may be necessary to cover the real pupil during ablation in order not to confuse the eye tracker. Ablation could be performed without decentration or loss of best spectacle-corrected visual acuity. Refractive results in minor corrections were good without nomogram adjustment. CONCLUSIONS: Using this novel flap holder with a marking that is tracked instead of the real pupil, centered ablations with a flying spot laser on the undersurface of a LASIK flap are feasible. Thus, the additional risk of iatrogenic keratectasia associated with stromal enhancement ablations is avoided.

Adolescent↗
PubMedDate not supplied

The role of molecular methods in evaluating biological treatment processes.

Methods derived from molecular biology provide powerful new tools to analyze biological treatment processes. Because molecular methods can be used to directly interrogate genetic information about the microbial community, they can provide the fine detail that is impossible with the blunt, nondiscriminating information usually obtained from more traditional measures such as biochemical oxygen demand and volatile suspended solids. Molecular methods allow tracking of critical groups of microorganisms, such as ammonia oxidizers, that comprise a small fraction of the total biomass. Molecular methods also allow tracking of specific metabolic reactions or other functions that are key to the satisfactory performance of a system. Despite their power, molecular methods do not provide sufficient information when used alone. Aggregated measures and quantitative modeling remain necessary to establish mass balances, quantify the function of the microbial community, and connect the results of molecular assays to practice. Several examples involving nitrifying bacteria in activated sludge illustrate the fine detail available with molecular methods and how they can be linked to traditional and quantitative analyses. Other manuscripts in this special issue also provide examples of the value of using molecular tools in combination with traditional methods.

Biomass↗
PubMed2006

Integrated analysis of established and novel microbial and chemical methods for microbial source tracking.

Several microbes and chemicals have been considered as potential tracers to identify fecal sources in the environment. However, to date, no one approach has been shown to accurately identify the origins of fecal pollution in aquatic environments. In this multilaboratory study, different microbial and chemical indicators were analyzed in order to distinguish human fecal sources from nonhuman fecal sources using wastewaters and slurries from diverse geographical areas within Europe. Twenty-six parameters, which were later combined to form derived variables for statistical analyses, were obtained by performing methods that were achievable in all the participant laboratories: enumeration of fecal coliform bacteria, enterococci, clostridia, somatic coliphages, F-specific RNA phages, bacteriophages infecting Bacteroides fragilis RYC2056 and Bacteroides thetaiotaomicron GA17, and total and sorbitol-fermenting bifidobacteria; genotyping of F-specific RNA phages; biochemical phenotyping of fecal coliform bacteria and enterococci using miniaturized tests; specific detection of Bifidobacterium adolescentis and Bifidobacterium dentium; and measurement of four fecal sterols. A number of potentially useful source indicators were detected (bacteriophages infecting B. thetaiotaomicron, certain genotypes of F-specific bacteriophages, sorbitol-fermenting bifidobacteria, 24-ethylcoprostanol, and epycoprostanol), although no one source identifier alone provided 100% correct classification of the fecal source. Subsequently, 38 variables (both single and derived) were defined from the measured microbial and chemical parameters in order to find the best subset of variables to develop predictive models using the lowest possible number of measured parameters. To this end, several statistical or machine learning methods were evaluated and provided two successful predictive models based on just two variables, giving 100% correct classification: the ratio of the densities of somatic coliphages and phages infecting Bacteroides thetaiotaomicron to the density of somatic coliphages and the ratio of the densities of fecal coliform bacteria and phages infecting Bacteroides thetaiotaomicron to the density of fecal coliform bacteria. Other models with high rates of correct classification were developed, but in these cases, higher numbers of variables were required.

Animals↗
PubMed2004

[A novel method for continuously assessing the spatio-temporal properties of locomotor activity in mice].

OBJECTIVE: To develop a novel method for continuously assessing the spatio-temporal properties of locomotor activity of mice in an open field using a video-tracking system. METHODS: The locomotor tracks in the open field were recorded by video camera within 22 h, and analyzed by AnalyPower1.1 system that we developed recently. Total distance, distances traveled in different zones and their ratios to total distance; total time,times spent in different zones and their ratios to total time were used as indicators to assess the properties of locomotor activity. RESULTS: In free and wakeful state, the locomotor activity of mice presented obvious regional and temporal properties. Mice preferred to stay in home base (food and water zones), and frequently visited the peripheral zones but seldom the center zones within 22 h. On the other hand, mice were most active within the first 1 h, and then their activity obviously decreased. After their activity became stable, the mice showed the obvious circadian variation of the activity as they were more active in the night. CONCLUSION: The novel method we developed in this study can continuously assess the spatio-temporal properties of locomotor activity quantitatively and objectively.

Animals↗
PubMed2006

Uncertainty in diffusion tensor based fibre tracking.

BACKGROUND: Diffusion tensor imaging and related fibre tracking techniques have the potential to identify major white matter tracts afflicted by an individual pathology or tracts at risk for a given surgical approach. However, the reliability of these techniques is known to be limited by image distortions, image noise, low spatial resolution, and the problem of identifying crossing fibres. This paper intends to bridge the gap between the requirements of neurosurgical applications and basic research on fibre tracking uncertainty. METHOD: We acquired echo planar diffusion tensor data from both 1.5 T and 3.0 T scanners. For fibre tracking, an extended deflection-based algorithm is employed with enhanced robustness to impaired fibre integrity such as caused by diffuse or infiltrating pathological processes. Moreover, we present a method to assess and visualize the uncertainty of fibre reconstructions based on variational complex Gaussian noise, which provides an alternative to the bootstrap method. We compare fibre tracking results with and without variational noise as well as with artificially decreased image resolution and signal-to-noise. FINDINGS: Using our fibre tracking technique, we found a high robustness to decreased image resolution and signal-to-noise. Still, the effects of image quality on the tracking result will depend on the employed fibre tracking algorithm and must be handled with care, especially when being used for neurosurgical planning or resection guidance. An advantage of the variational noise approach over the bootstrap technique is that it is applicable to any given set of diffusion tensor images. CONCLUSIONS: We conclude that the presented approach allows for investigating the uncertainty of diffusion tensor imaging based fibre tracking and might offer a perspective to overcome the problem of size underestimation observed by existing techniques.

Adult↗
PubMed2005

Modeling and output tracking of transverse flux permanent magnet machines using high gain observer and RBF neural network.

This paper deals with modeling and adaptive output tracking of a transverse flux permanent magnet machine as a nonlinear system with unknown nonlinearities by utilizing high gain observer and radial basis function networks. The proposed model is developed based on computing the permeance between rotor and stator using quasiflux tubes. Based on this model, the techniques of feedback linearization and Hinfinity control are used to design an adaptive control law for compensating the unknown nonlinear parts, such as the effect of cogging torque, as a disturbance is decreased onto the rotor angle and angular velocity tracking performances. Finally, the capability of the proposed method in tracking both the angle and the angular velocity is shown in the simulation results.

Algorithms↗
PubMedDate not supplied

A robust time-varying identification algorithm using basis functions.

We extend a recently developed time invariant (TIV) model order search criterion named the optimal parameter search algorithm (OPS) for identification of time varying (TV) autoregressive (AR) and autoregressive moving average (ARMA) models. Using the TV algorithm is facilitated by the fact that expanding each TV coefficient onto a finite set of basis sequences permits TV parameters to become TIV. Taking advantage of this TIV feature of expansion parameters exploits the features of the OPS, which has been shown to provide accurate model order selection as well as extraction of only the significant model terms. Another advantage of the new algorithm is its ability to discriminate insignificant basis sequences thereby reducing the number of expansion parameters to be estimated. Due to these features, the resulting algorithm can accurately estimate TV AR or ARMA models and determine their orders. Indeed, comparison via computer simulations of AR models between the proposed method and one of the well-known iterative methods, recursive least squares, shows the greater capability of the new method to track TV parameters. Furthermore, application of the new method to experimentally obtained renal blood flow signals shows that the new method provides higher-resolution time-varying spectral capability than does the short-time Fourier transform (STFT), concomitant with fewer spurious frequency peaks than obtained with the STFT spectrogram.

Algorithms↗
PubMed1990

[Computer-assisted contour detection in a complete heart cycle by levocardiography with adaptive raster tracking--validation of the method].

A method for computer-assisted edge detection in a full heart cycle of the left ventricular cineangiogram is presented. Left ventricular cineangiograms were acquired in the 30 degrees RAO position on cinefilms with 50 frames/s. A selected heart cycle was digitized with a spatial resolution of 512 x 512 pixels and a grey-value range from 0 to 255. In the first frame of the heart cycle a raster was calculated from contour points marked by an operator. The raster was automatically adapted to the left ventricular contour in the following frames. The contour points were determined on the adaptive raster by a gradient method. The automatic calculation of all contours of the systolic contraction was possible in 28 of 30 cineangiograms, operator interaction was necessary in two cineangiograms. The calculation of the diastolic contours requested operator interaction in 4 of 30 cineangiograms. The mean deviation of the calculated from the true contours ranged from -1.2 +/- 1.9 mm to 0.9 +/- 2.9 mm. The correlation coefficients between volumes calculated from the computer-determined and manually drawn contours ranged from r = 0.98 to r = 1.0 at beginning of systole, midsystole, endsystole, middiastole, and enddiastole with a standard error of the estimate between 2.8 ml and 5.2 ml. A repeated automatic determination of the contours after an independent remarking of the starting points resulted in a linear correlation of the calculated volumes with a correlation coefficient of r = 1.0 and a standard error of the estimate between 1.3 ml and 4.7 ml. The correlation coefficient for the ejection fraction was r = 0.99 with a standard error of the estimate of 1.9%.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2004

Spatiotemporal motion boundary detection and motion boundary velocity estimation for tracking moving objects with a moving camera: a level sets PDEs approach with concurrent camera motion compensation.

The purpose of this study is to investigate a method of tracking moving objects with a moving camera. This method estimates simultaneously the motion induced by camera movement. The problem is formulated as a Bayesian motion-based partitioning problem in the spatiotemporal domain of the image quence. An energy functional is derived from the Bayesian formulation. The Euler-Lagrange descent equations determine imultaneously an estimate of the image motion field induced by camera motion and an estimate of the spatiotemporal motion undary surface. The Euler-Lagrange equation corresponding to the surface is expressed as a level-set partial differential equation for topology independence and numerically stable implementation. The method can be initialized simply and can track multiple objects with nonsimultaneous motions. Velocities on motion boundaries can be estimated from geometrical properties of the motion boundary. Several examples of experimental verification are given using synthetic and real-image sequences.

Algorithms↗
PubMed2006

Ultrasonic tracking of acoustic radiation force-induced displacements in homogeneous media.

The use of ultrasonic methods to track the tissue deformation generated by acoustic radiation force is subject to jitter and displacement underestimation errors, with displacement underestimation being primarily caused by lateral and elevation shearing within the point spread function (PSF) of the ultrasonic beam. Models have been developed using finite element methods and Field II, a linear acoustic field simulation package, to study the impact of focal configuration, tracking frequency, and material properties on the accuracy of ultrasonically tracking the tissue deformation generated by acoustic radiation force excitations. These models demonstrate that lateral and elevation shearing underneath the PSF of the tracking beam leads to displacement underestimation in the focal zone. Displacement underestimation can be reduced by using tracking beams that are narrower than the spatial extent of the displacement fields. Displacement underestimation and jitter decrease with time after excitation as shear wave propagation away from the region of excitation reduces shearing in the lateral and elevation dimensions. The use of higher tracking frequencies in broadband transducers, along with 2D focusing in the elevation dimension, will reduce jitter and improve displacement tracking accuracy. Relative displacement underestimation remains constant as a function of applied force, whereas jitter increases with applied force. Underdeveloped speckle (SNR < 1.91) leads to greater levels of jitter and peak displacement underestimation. Axial shearing is minimal over the tracking kernel lengths used in acoustic radiation force impulse imaging and thus does not impact displacement tracking.

Acoustics↗