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Partha P. Mitra - One of the best experts on this subject based on the ideXlab platform.
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multiple wave vector extensions of the nmr pulsed field Gradient Spin echo diffusion measurement
Physical Review B, 1995Co-Authors: Partha P. MitraAbstract:Multiple wave-vector extensions of NMR pulsed-field-Gradient diffusion measurements are discussed in the context of diffractionlike effects of restricted diffusion. In the case of two independent wave vectors, it is shown that the dependence of the amplitude on the relative angle between the wave vectors carries information that is absent in the usual single-wave-vector amplitude. It is shown that a two-wave-vector measurement is sensitive to restricted diffusion even at small wave vectors, in contrast with the single-wave-vector case. It is proposed that the angular dependence noted above may be used to distinguish effects of restricted diffusion from those arising from a distribution of diffusion constants. © 1995 The American Physical Society.
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multiple wave vector extensions of the nmr pulsed field Gradient Spin echo diffusion measurement
Physical Review B, 1995Co-Authors: Partha P. MitraAbstract:Multiple wave-vector extensions of NMR pulsed-field-Gradient diffusion measurements are discussed in the context of diffractionlike effects of restricted diffusion. In the case of two independent wave vectors, it is shown that the dependence of the amplitude on the relative angle between the wave vectors carries information that is absent in the usual single-wave-vector amplitude. It is shown that a two-wave-vector measurement is sensitive to restricted diffusion even at small wave vectors, in contrast with the single-wave-vector case. It is proposed that the angular dependence noted above may be used to distinguish effects of restricted diffusion from those arising from a distribution of diffusion constants.
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time dependent diffusion of water in a biological model system
Proceedings of the National Academy of Sciences of the United States of America, 1994Co-Authors: Lawrence L Latour, Karel Svoboda, Partha P. Mitra, Christopher H SotakAbstract:Abstract Packed erythrocytes are ideally suited as a model system for the study of water diffusion in biological tissue, because cell size, membrane permeability, and extracellular volume fraction can be varied independently. We used a pulsed-field-Gradient Spin echo NMR technique to measure the time-dependent diffusion coefficient D(t) in packed erythrocytes. The long-time diffusion constant, D(eff), depends sensitively on the extracellular volume fraction. This may explain the drop in D(eff) during the early stages of brain ischemia, where just minutes after an ischemic insult the extra-cellular volume in the affected region of the brain is significantly reduced. Using an effective medium formula, we estimate the erythrocyte membrane permeability, in good agreement with measurements on isolated cells. From the short-time behavior of D(t), we determine the surface-to-volume ratio of the cells, approximately (0.72 micron)-1.
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diffusion propagator as a probe of the structure of porous media
Physical Review Letters, 1992Co-Authors: Partha P. Mitra, Pabitra N Sen, Lawrence M Schwartz, Pierre Le DoussalAbstract:We propose a simple ansatz that relates the diffusion propagator for the molecules of a fluid confined in a porous medium to the pore-space structure factor. Theoretical arguments and numerical simulations show that it works well for both periodic and disordered geometries. The ansatz allows us to deconvolve structural data from momentum dependent pulsed field Gradient Spin-echo data. © 1992 The American Physical Society.
P T Callaghan - One of the best experts on this subject based on the ideXlab platform.
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translational dynamics and magnetic resonance principles of pulsed Gradient Spin echo nmr
2011Co-Authors: P T CallaghanAbstract:1. Thermal Processes and Diffusion 2. Flow and dispersion 3. Quantum description of nuclear ensembles 4. Introductory Magnetic Resonance 5. Magnetic field Gradients and Spin echos 6. Restricted diffusion 7. Diffraction phenomena 8. Double wavevector encoding 9. Multidimensional PGSE NMR 10. Velocimetry 11. Translational Dynamics and Quantum Coherence 12. Tricks of the Trade
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locally anisotropic motion in a macroscopically isotropic system displacement correlations measured using double pulsed Gradient Spin echo nmr
Magnetic Resonance in Chemistry, 2002Co-Authors: P T Callaghan, M E KomloshAbstract:We propose a novel application of double pulsed Gradient Spin-echo NMR in which two pairs of Gradient pulses are used successively to encode the Spin magnetization. These pairs were applied with Gradient directions collinear and orthogonal, and the results were compared. The method can be used to detect local diffusion anisotropy even when the distribution of domain directors in the sample is isotropic. The degree of the difference between collinear and orthogonal echo attenuation responses indicates the nature of that local anisotropy. We applied this method to a polydomain lyotropic liquid crystal system, Aerosol OT–water, and detected the local diffusion anisotropy directly. Copyright © 2002 John Wiley & Sons, Ltd.
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segmental motion of entangled random coil polymers studied by pulsed Gradient Spin echo nuclear magnetic resonance
Journal of Chemical Physics, 1998Co-Authors: M E Komlosh, P T CallaghanAbstract:Pulsed Gradient Spin echo nuclear magnetic resonance (NMR) is used to investigate polymer mean-squared segmental displacements in semidilute solutions of high molar mass polystyrene in deuterio-toluene. Nine molar masses from 1 to 20 million daltons are studied at a fixed concentration of 5% w/v, and a range of concentrations from 5% to 20% at fixed molar mass of 3 million daltons. The distance and time scales accessed are 20 to 1000 nm and 10 to 3000 ms, respectively. Evidence for intrachain Spin diffusion is found and its effect corrected for. The time dependence of mean-squared segmental displacements is fitted to the predictions of the Doi–Edwards model and tube disengagement times and tube diameters obtained.
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earth s field nmr in antarctica a pulsed Gradient Spin echo nmr study of restricted diffusion in sea ice
Journal of Magnetic Resonance, 1998Co-Authors: P T Callaghan, C D Eccles, T G Haskell, P J Langhorne, Joseph D. SeymourAbstract:We report on the use in Antarctica of a nuclear magnetic resonance spectrometer which utilizes the terrestrial magnetic field. Free induction decay data are used to obtain estimates of brine content, in samples of sea ice extracted from the annual ice of McMurdo Sound, in the vicinity of Cape Evans, Ross Island. Pulsed Gradient Spin echo experiments were performed on these samples in which the orientation of the Gradient with respect to the ice growth axis was varied and the separation time between the Gradient pulses was varied. Anisotropic restricted diffusion effects are apparent and we use these to tentatively model the brine pocket morphology. Copyright 1998 Academic Press.
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an earth s field nuclear magnetic resonance apparatus suitable for pulsed Gradient Spin echo measurements of self diffusion under antarctic conditions
Review of Scientific Instruments, 1997Co-Authors: P T Callaghan, C D Eccles, Joseph D. SeymourAbstract:We describe an earth’s field nuclear magnetic resonance apparatus which can be used to carry out pulsed Gradient Spin echo (PGSE) diffusion measurements. The instrument is portable and incorporates automated process control, allowing direct measurement of the Larmor precession. The use of a common clock for pulse sequencing, excitation pulse synthesis, and detection, results in a phase stability sufficient for accurate signal averaging. The analysis of PGSE data under the conditions of a weak detection field is discussed and measurements of diffusion are presented under both New Zealand and Antarctic conditions. The Antarctic results include an example of restricted diffusion of brine water in McMurdo Sound sea ice.
Olle Soderman - One of the best experts on this subject based on the ideXlab platform.
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restricted self diffusion of water in a highly concentrated w o emulsion studied using modulated Gradient Spin echo nmr
Journal of Magnetic Resonance, 2002Co-Authors: Daniel Topgaard, Carin Malmborg, Olle SodermanAbstract:Restricted diffusion of water in a highly concentrated w/o emulsion was studied using pulsed field Gradient Spin echo techniques. The standard two-pulse version of this technique, suitable for analysis in the time domain, fails to investigate the short time-scale for diffusion inside a single emulsion droplet with radius 0.7 mum. With a pulse-train technique, originally introduced by Callaghan and Stepisnik, shorter time-scales are accessible. The latter approach is analyzed in the frequency domain and yields frequency dependent diffusion coefficients. Predictions for the outcome of the experiment were calculated in the time domain using the Gaussian phase distribution and the pore hopping formalism expressions for the echo attenuation. The results of these calculations were transformed to the frequency domain via a numerical inverse integral transform in order to compare with the experimental results. (C) 2002 Elsevier Science (USA). (Less)
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structure determination of a highly concentrated w o emulsion using pulsed field Gradient Spin echo nuclear magnetic resonance diffusion diffractograms
Langmuir, 1999Co-Authors: Bjorn Hakansson, Ramon Pons, Olle SodermanAbstract:Diffraction-like effects have been observed by applying pulsed-field-Gradient Spin−echo (PFG-SE) NMR to a highly concentrated W/O emulsion, made from the nonionic surfactant C12E4 (CH3(CH2)11(OCH2CH2)4OH), n-decane, and brine (1 wt % NaCl(aq) solution). The q-space plots of the PFG-SE NMR data show one pronounced maximum and the shoulder of a second maximum in the attenuation curve of the NMR signal of water. Such peaks are often referred to as diffraction-like peaks, because of the close analogy of their origin to the origin of peaks observed in scattering experiments. In this paper it is suggested that the peak positions in the “diffusion diffractograms” can be related to the structure of the emulsion, i.e., to the three-dimensional packing of the (nonspherical) emulsion droplets. Furthermore, the characteristic distances in the emulsion system, in this case related to the average size of an emulsion droplet, can be determined from the positions of the diffraction-like peaks. This can be achieved withou...
Peter J Basser - One of the best experts on this subject based on the ideXlab platform.
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limits to flow detection in pulsed Gradient Spin echo nmr
bioRxiv, 2020Co-Authors: Nathan H Williamson, Michal E Komlosh, Dan Benjamini, Peter J BasserAbstract:Velocity detection with single pulsed Gradient Spin echo (PGSE) NMR is known to be limited by diffusion smearing the phase coherence and obscuring dispersive attenuation. We present an equation for the lowest detectable velocity with phase contrast velocimetry which incorporates the signal-to-noise ratio. We show how to best sample q-space when approaching this limit. We confirm that the apparent diffusion/dispersion coefficient can be used to infer fluid velocity for Peclet number Pe > 1. When measuring flow in biological systems we determined that with realistic experimental protocols the limits are roughly 1 {micro}m/s for velocimetry and 300 {micro}m/s for diffusometry.
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observation of microscopic diffusion anisotropy in the Spinal cord using double pulsed Gradient Spin echo mri
Magnetic Resonance in Medicine, 2008Co-Authors: Michal E Komlosh, Martin J Lizak, Ferenc Horkay, Raisa Z Freidlin, Peter J BasserAbstract:A double-pulsed Gradient Spin echo (d-PGSE) filtered MRI sequence is proposed to detect microscopic diffusion anisotropy in heterogeneous specimen. The technique was developed, in particular, to characterize local microscopic anisotropy in specimens that are macroscopically isotropic, such as gray matter. In such samples, diffusion tensor MRI (DTI) produces an isotropic or nearly isotropic diffusion tensor despite the fact that the medium may be anisotropic at a microscopic length scale. Using d-PGSE filtered MRI, microscopic anisotropy was observed in a "gray matter" phantom consisting of randomly oriented tubes filled with water, as well as in fixed pig Spinal cord, within a range of b-values that can be readily achieved on clinical and small animal MR scanners. These findings suggest a potential use for this new contrast mechanism in clinical studies and biological research applications.
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detection of microscopic anisotropy in gray matter and in a novel tissue phantom using double pulsed Gradient Spin echo mr
Journal of Magnetic Resonance, 2007Co-Authors: Michal E Komlosh, Ferenc Horkay, Raisa Z Freidlin, Uri Nevo, Yaniv Assaf, Peter J BasserAbstract:A double Pulsed Gradient Spin Echo (d-PGSE) MR experiment was used to measure and assess the degree of local diffusion anisotropy in brain gray matter, and in a novel “gray matter” phantom that consists of randomly oriented tubes filled with water. In both samples, isotropic diffusion was observed at a macroscopic scale while anisotropic diffusion was observed at a microscopic scale, however, the nature of the resulting echo attenuation profiles were qualitatively different. Gray matter, which contains multiple cell types and fibers, exhibits a more complicated echo attenuation profile than the phantom. Since microscopic anisotropy was observed in both samples in the low q regime comparable to that achievable in clinical scanner, it may offer a new potential contrast mechanism for characterizing gray matter microstructure in medical and biological applications.
Tatsuya Umecky - One of the best experts on this subject based on the ideXlab platform.
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direct measurements of ionic mobility of ionic liquids using the electric field applying pulsed Gradient Spin echo nmr
Journal of Physical Chemistry B, 2009Co-Authors: Tatsuya Umecky, Yuria Saito, Hajime MatsumotoAbstract:Ionic mobilities of the ionic liquids, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)amide,1-ethyl-3-methylimidazolium fluorosulfonyl-(trifluoromethylsulfonyl)amide, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) -amide, were measured using the electric field applying pulsed Gradient Spin-echo NMR technique. Observed mobilities were more than 1 order of magnitude greater than the values estimated from the diffusion coefficients measured under the equilibrium state without the electric field. Electric field dependence of the ionic mobility showed that the high mobility appeared above the threshold of the field strength with keeping the constant values. This indicates that the ions are orientated by the application of the electric field may be due to the dielectric polarization.
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self diffusion coefficients of 1 butyl 3 methylimidazolium hexafluorophosphate with pulsed field Gradient Spin echo nmr technique
Fluid Phase Equilibria, 2005Co-Authors: Tatsuya Umecky, Mitsuhiro Kanakubo, Yutaka IkushimaAbstract:Abstract The self-diffusion coefficients of the cation and anion species in 1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF6], were independently determined over a wide temperature range by observing 1H and 19F nuclei with the pulsed-field Gradient Spin-echo NMR technique. The self-diffusion measurements were carried out for two samples of [BMIM][PF6], of which one was synthesized in our laboratory and the other was purchased commercially (97%). There has been a relatively large difference observed in the self-diffusion coefficients between the two samples. It has become apparent that a small amount of impurity significantly affects the transport phenomena in the ionic liquid. On the basis of the hydrodynamic model, moreover, the self-diffusion coefficients of [BMIM][PF6] were discussed in terms of intermolecular interactions.
