The Experts below are selected from a list of 186 Experts worldwide ranked by ideXlab platform

Enrico Gratton - One of the best experts on this subject based on the ideXlab platform.

  • Alpha Hemolysin Induces an Increase of Erythrocytes Calcium: A FLIM 2-Photon Phasor Analysis Approach
    2016
    Co-Authors: Susana Sanchez, Enrico Gratton, Vanesa Herlax
    Abstract:

    a-hemolysin (HlyA) from Escherichia coli is considered as the prototype of a family of toxins called RTX (repeat in toxin), a group of proteins that share genetic and structural features. HlyA is an important virulence factor in E. coli extraintestinal infections, such as meningitis, septicemia and urinary infections. High concentrations of the toxin cause the lysis of several cells such as erythrocytes, granulocytes, monocytes, endothelial and renal epithelial cells of different species. At low concentrations it induces the production of cytokines and apoptosis. Since many of the subcytolytic effects in other cells have been reported to be triggered by the increase of intracellular calcium, we followed the calcium concentration inside the erythrocytes while incubating with sublytic concentrations of HlyA. Calcium concentration was monitored using the calcium indicator Green 1, 2-photon excitation, and fluorescence lifetime imaging microscopy (FLIM). Data were analyzed using the Phasor Representation. In this report, we present evidence that, at sublytic concentrations, HlyA induces an increase of calcium concentration in rabbit erythrocytes in the first 10 s. Results are discussed in relation to the difficulties of measuring calcium concentrations in erythrocytes where hemoglobin is present, the contribution of the background an

  • Measurements of absolute concentrations of NADH in cells using the Phasor FLIM method
    Biomedical optics express, 2016
    Co-Authors: Michelle A. Digman, Leonel Malacrida, Enrico Gratton
    Abstract:

    We propose a graphical method using the Phasor Representation of the fluorescence decay to derive the absolute concentration of NADH in cells. The method requires the measurement of a solution of NADH at a known concentration. The Phasor Representation of the fluorescence decay accounts for the differences in quantum yield of the free and bound form of NADH, pixel by pixel of an image. The concentration of NADH in every pixel in a cell is obtained after adding to each pixel in the Phasor plot a given amount of unmodulated light which causes a shift of the Phasor towards the origin by an amount that depends on the intensity at the pixel and the fluorescence lifetime at the pixel. The absolute concentration of NADH is obtained by comparison of the shift obtained at each pixel of an image with the shift of the calibrated solution.

  • Spectral Phasor approach for fingerprinting of photo-activatable fluorescent proteins Dronpa, Kaede and KikGR
    Methods and applications in fluorescence, 2013
    Co-Authors: Francesco Cutrale, Anya Salih, Enrico Gratton
    Abstract:

    The Phasor global analysis algorithm is common for fluorescence lifetime applications, but has only been recently proposed for spectral analysis. Here the Phasor Representation and fingerprinting is exploited in its second harmonic to determine the number and spectra of photo-activated states as well as their conversion dynamics. We follow the sequence of photo-activation of proteins over time by rapidly collecting multiple spectral images. The Phasor Representation of the cumulative images provides easy identification of the spectral signatures of each photo-activatable protein.

  • laurdan fluorescence lifetime discriminates cholesterol content from changes in fluidity in living cell membranes
    Biophysical Journal, 2013
    Co-Authors: Ottavia Golfetto, Elizabeth Hinde, Enrico Gratton
    Abstract:

    Detection of the fluorescent properties of Laurdan has been proven to be an efficient tool to investigate membrane packing and ordered lipid phases in model membranes and living cells. Traditionally the spectral shift of Laurdan’s emission from blue in the ordered lipid phase of the membrane (more rigid) toward green in the disordered lipid phase (more fluid) is quantified by the generalized polarization function. Here, we investigate the fluorescence lifetime of Laurdan at two different emission wavelengths and find that when the dipolar relaxation of Laurdan’s emission is spectrally isolated, analysis of the fluorescence decay can distinguish changes in membrane fluidity from changes in cholesterol content. Using the Phasor Representation to analyze changes in Laurdan’s fluorescence lifetime we obtain two different Phasor trajectories for changes in polarity versus changes in cholesterol content. This gives us the ability to resolve in vivo membranes with different properties such as water content and cholesterol content and thus perform a more comprehensive analysis of cell membrane heterogeneity. We demonstrate this analysis in NIH3T3 cells using Laurdan as a biosensor to monitor changes in the membrane water content during cell migration.

  • Calcium concentration on RRBC without stimulus.
    2013
    Co-Authors: Susana Sanchez, Enrico Gratton, Laura Bakás, Vanesa Herlax
    Abstract:

    Phasor Representation of FLIM data (A) and intensity image (B) of RRBC labeled with CaG-1 at 37°C. In the Phasor plot two areas of calcium concentration have been defined and color coded as red for 4–25 nM and yellow 25–80 nM. The pixels corresponding to the Phasors inside each colored circle in the Phasor plot (A) are highlight in the intensity image (B) with the corresponding color. The black line and the dots at the extremities correspond to the internal calibration curve described in Figure 3 and in the text.

Arjen N. Bader - One of the best experts on this subject based on the ideXlab platform.

  • Multi-component quantitative magnetic resonance imaging by Phasor Representation
    Scientific Reports, 2017
    Co-Authors: Frank J. Vergeldt, Alena Prusova, Herbert Van Amerongen, Farzad Fereidouni, Tom W J Scheenen, Arjen N. Bader
    Abstract:

    Quantitative magnetic resonance imaging (qMRI) is a versatile, non-destructive and non-invasive tool in life, material, and medical sciences. When multiple components contribute to the signal in a single pixel, however, it is difficult to quantify their individual contributions and characteristic parameters. Here we introduce the concept of Phasor Representation to qMRI to disentangle the signals from multiple components in imaging data. Plotting the Phasors allowed for decomposition, unmixing, segmentation and quantification of our in vivo data from a plant stem, a human and mouse brain and a human prostate. In human brain images, we could identify 3 main T _ 2 components and 3 apparent diffusion coefficients; in human prostate 5 main contributing spectral shapes were distinguished. The presented Phasor analysis is model-free, fast and accurate. Moreover, we also show that it works for undersampled data.

  • spectral Phasor analysis allows rapid and reliable unmixing of fluorescence microscopy spectral images
    Optics Express, 2012
    Co-Authors: Farzad Fereidouni, Arjen N. Bader, Hans C. Gerritsen
    Abstract:

    A new global analysis algorithm to analyse (hyper-) spectral images is presented. It is based on the Phasor Representation that has been demonstrated to be very powerful for the analysis of lifetime imaging data. In spectral Phasor analysis the fluorescence spectrum of each pixel in the image is Fourier transformed. Next, the real and imaginary components of the first harmonic of the transform are employed as X and Y coordinates in a scatter (spectral Phasor) plot. Importantly, the spectral Phasor Representation allows for rapid (real time) semi-blind spectral unmixing of up to three components in the image. This is demonstrated on slides with fixed cells containing three fluorescent labels. In addition the method is used to analyse autofluorescence of cells in a fresh grass blade. It is shown that the spectral Phasor approach is compatible with spectral imaging data recorded with a low number of spectral channels.

Farzad Fereidouni - One of the best experts on this subject based on the ideXlab platform.

  • Multi-component quantitative magnetic resonance imaging by Phasor Representation
    Scientific Reports, 2017
    Co-Authors: Frank J. Vergeldt, Alena Prusova, Herbert Van Amerongen, Farzad Fereidouni, Tom W J Scheenen, Arjen N. Bader
    Abstract:

    Quantitative magnetic resonance imaging (qMRI) is a versatile, non-destructive and non-invasive tool in life, material, and medical sciences. When multiple components contribute to the signal in a single pixel, however, it is difficult to quantify their individual contributions and characteristic parameters. Here we introduce the concept of Phasor Representation to qMRI to disentangle the signals from multiple components in imaging data. Plotting the Phasors allowed for decomposition, unmixing, segmentation and quantification of our in vivo data from a plant stem, a human and mouse brain and a human prostate. In human brain images, we could identify 3 main T _ 2 components and 3 apparent diffusion coefficients; in human prostate 5 main contributing spectral shapes were distinguished. The presented Phasor analysis is model-free, fast and accurate. Moreover, we also show that it works for undersampled data.

  • spectral Phasor analysis allows rapid and reliable unmixing of fluorescence microscopy spectral images
    Optics Express, 2012
    Co-Authors: Farzad Fereidouni, Arjen N. Bader, Hans C. Gerritsen
    Abstract:

    A new global analysis algorithm to analyse (hyper-) spectral images is presented. It is based on the Phasor Representation that has been demonstrated to be very powerful for the analysis of lifetime imaging data. In spectral Phasor analysis the fluorescence spectrum of each pixel in the image is Fourier transformed. Next, the real and imaginary components of the first harmonic of the transform are employed as X and Y coordinates in a scatter (spectral Phasor) plot. Importantly, the spectral Phasor Representation allows for rapid (real time) semi-blind spectral unmixing of up to three components in the image. This is demonstrated on slides with fixed cells containing three fluorescent labels. In addition the method is used to analyse autofluorescence of cells in a fresh grass blade. It is shown that the spectral Phasor approach is compatible with spectral imaging data recorded with a low number of spectral channels.

Frank J. Vergeldt - One of the best experts on this subject based on the ideXlab platform.

  • Multi-component quantitative magnetic resonance imaging by Phasor Representation
    Scientific Reports, 2017
    Co-Authors: Frank J. Vergeldt, Alena Prusova, Herbert Van Amerongen, Farzad Fereidouni, Tom W J Scheenen, Arjen N. Bader
    Abstract:

    Quantitative magnetic resonance imaging (qMRI) is a versatile, non-destructive and non-invasive tool in life, material, and medical sciences. When multiple components contribute to the signal in a single pixel, however, it is difficult to quantify their individual contributions and characteristic parameters. Here we introduce the concept of Phasor Representation to qMRI to disentangle the signals from multiple components in imaging data. Plotting the Phasors allowed for decomposition, unmixing, segmentation and quantification of our in vivo data from a plant stem, a human and mouse brain and a human prostate. In human brain images, we could identify 3 main T _ 2 components and 3 apparent diffusion coefficients; in human prostate 5 main contributing spectral shapes were distinguished. The presented Phasor analysis is model-free, fast and accurate. Moreover, we also show that it works for undersampled data.

Ionel Vechiu - One of the best experts on this subject based on the ideXlab platform.

  • Power quality improvement using an advanced control of a four-leg multilevel converter
    2015 IEEE 16th Workshop on Control and Modeling for Power Electronics (COMPEL), 2015
    Co-Authors: Ionel Vechiu, Quentin Tabart, Aitor Etxeberria
    Abstract:

    In this paper, the transient operation of a Three-Level Neutral Point Clamped (3LNPC) four-leg inverter equipped with an innovative control strategy able to improve the power quality in renewable energy based weak grids is investigated. The 3LNPC four-leg inverter is controlled to manage a Hybrid Energy Storage System in order to satisfy the energy/power demand in a weak grid and simultaneously to balance the AC voltage during unbalanced 3-phase loads. The proposed control strategy uses a special designed offset for the DC power/energy division and the decomposition of the supply three-phase voltage and current into symmetrical components using Phasor Representation for voltage balance. Real time simulations and experimental tests have been performed using a RT-LAB simulator, a 3LNPC converter prototype and an experimental MicroGrid in order to prove the effectiveness of the proposed system in a weak grid context.

  • Transient operation of a four-leg inverter for autonomous applications with unbalanced load
    IEEE Transactions on Power Electronics, 2010
    Co-Authors: Ionel Vechiu, Octavian Curea, Haritza Camblong
    Abstract:

    In this paper, the transient operation of a four-leg inverter equipped with an innovative control strategy under unbalanced load conditions is investigated. The inverter is proposed for transformerless hybrid power system applications, in order to provide simultaneous supply of three-phase and single-phase AC loads with balanced voltage and constant frequency. The four-leg inverter is controlled to ensure balanced voltage by means of a control strategy based on the decomposition of the supply three-phase voltage and current into instantaneous positive, negative, and homopolar sequence components using Phasor Representation. These three sequences are controlled independently in their own reference frames as DC signals. The implementation derived for the controller design is also described. The transient operation performance of the proposed control strategy has been tested in simulations with an average model and experimentally using a laboratory prototype.

  • Control of four leg inverter for hybrid power system applications with unbalanced load
    Energy Conversion and Management, 2007
    Co-Authors: Ionel Vechiu, Haritza Camblong, Gerardo Tapia, Brayima Dakyo, Octavian Curea
    Abstract:

    Abstract This paper proposes an improved control strategy for a three phase, four leg inverter used for the simultaneous supply of three phase and single phase AC loads in a transformerless hybrid power system (HPS) application. First, the mathematical model of the inverter is obtained by using the average technique, which allows converter systems to be rapidly and accurately simulated. Then, two control strategies are described. The first one uses the conventional dq0 frame rotating with the angular frequency ω (ω = 314 rad/s) and PI (proportional integral) controllers to ensure voltage and current regulation. The second one is an improved control strategy based on the decomposition of the supply three phase voltage and current into instantaneous positive, negative and homopolar sequence components using Phasor Representation. These three sequences are controlled independently in their own reference frames as DC signals. The positive sequence is regulated by the PI controllers in a positive reference frame, which rotates counterclockwise, while the negative sequence is regulated by the PI controllers in a negative reference frame, which rotates clockwise at the same angular frequency. Since the proposed strategy uses Phasor Representation, the actually superposed Phasors of the homopolar sequence are spatially displaced at 120°. Then, using a negative reference frame system, the obtained DC signals are regulated by the PI controllers. Simulation results show the validity of the innovative control strategy.