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  • 1.
    Bielejewski, Michal
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Giesecke, Marianne
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Furó, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    On electrophoretic NMR. Exploring high conductivity samples2014In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 243, p. 17-24Article in journal (Refereed)
    Abstract [en]

    The performance of a new electrophoretic NMR (eNMR) method that uses a Carr-Purcell-Meiboom-Gill echo train with repeated electric field reversal is investigated. We show that this pulse sequence, with acronym CPMGER, yields strongly reduced artifacts from convective flow effects caused by the simultaneous presence of electroosmotic and thermal driving forces. We demonstrate the achieved improvements in various aqueous solutions. Ultimately, the method can be used for obtaining electrophoretic mobilities by eNMR without relying on uncharged reference molecules, otherwise a significant limitation for electrophoretic experiments performed with nuclei other than 1H.

  • 2.
    Dvinskikh, Sergey V.
    et al.
    KTH, Superseded Departments, Chemistry.
    Furo, Istvan
    KTH, Superseded Departments, Chemistry.
    Combining PGSE NMR with homonuclear dipolar decoupling2000In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 144, no 1, p. 142-149Article in journal (Refereed)
    Abstract [en]

    A new robust approach for combining multiple-pulse homonuclear decoupling and ROSE NMR is introduced for accurately measuring molecular diffusion coefficients in systems with nonvanishing static homonuclear dipolar couplings. Homonuclear decoupling suppresses dipolar dephasing during the gradient pulses but its efficiency and scaling factor for the effective gradient vary across the sample because of the large variation of the frequency offset caused by the gradient. The resulting artifacts are reduced by introducing a slice selection scheme. The method is demonstrated by F-19 PGSE NMR experiments in a lyotropic liquid crystal.

  • 3.
    Dvinskikh, Sergey V.
    et al.
    KTH, Superseded Departments, Chemistry.
    Furo, Istvan
    KTH, Superseded Departments, Chemistry.
    Cross-relaxation effects in stimulated-echo-type PGSE NMR experiments by bipolar and monopolar gradient pulses2000In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 146, no 2, p. 283-289Article in journal (Refereed)
    Abstract [en]

    Exchange of longitudinal spin polarization by dipolar cross relaxation between nonequivalent spins results in a modulation of the stimulated echo signal on increasing the encoding/decoding delays and in a multiexponential decap on increasing the diffusion time. These artifacts are suppressed by 180 degrees pulses inserted in the middle of the gradient encoding/decoding periods. The efficiency of the gradient encoding is preserved if bipolar gradient pulses are used instead of monopolar pulses. The behavior of the different pulse sequences is demonstrated by F-19 PGSE NMR experiments in a lyotropic liquid crystal in both isotropic micellar and oriented nematic phases.

  • 4.
    Dvinskikh, Sergey V.
    et al.
    KTH, Superseded Departments, Chemistry.
    Furo, Istvan
    KTH, Superseded Departments, Chemistry.
    Measurement of the principal values of the anisotropic diffusion tensor in an unoriented sample by exploiting the chemical shift anisotropy: F-19 PGSE NMR with homonuclear decoupling2001In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 148, no 1, p. 73-77Article in journal (Refereed)
    Abstract [en]

    NMR methods (S. V. Dvinskikh et al. J. Magn. Reson. 142, 102-110 (2000) and S. V. Dvinskikh and I. Furo, J. Magn. Reson. 144, 142-149 (2000)) that combine PGSE with dipolar decoupling are extended to polycrystalline solids and unoriented liquid crystals. Decoupling suppresses dipolar dephasing not only during the gradient pulses but also under signal acquisition so that the detected spectral shape is dominated by the chemical shift tensor of the selected nucleus. The decay of the spectral intensity at different positions in the powder spectrum provides the diffusion coefficient in sample regions with their crystal axes oriented differently with respect to the direction of the field gradient. Hence, one can obtain the principal values of the diffusion tensor. The method is demonstrated by F-19 PGSE NMR with homonuclear decoupling in a lyotropic lamellar liquid crystal.

  • 5. Dvinskikh, Sergey V.
    et al.
    Furo, Istvan
    KTH, Superseded Departments, Chemistry.
    Sandstrom, D.
    Maliniak, A.
    Zimmermann, H.
    Deuterium stimulated-echo-type PGSE NMR experiments for measuring diffusion: Application to a liquid crystal2001In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 153, no 1, p. 83-91Article in journal (Refereed)
    Abstract [en]

    The accessibility of molecular self-diffusion coefficients in anisotropic materials, such as liquid crystals or solids, by stimulated-echo-type H-2 PGSE NMR is examined. The amplitude and phase modulation of the signal in the stimulated-echo-type sequence by the static quadrupole coupling during the encoding/decoding delays is suppressed by adjusting the pulse flip angles and the phase cycle. For nuclei that experience both nonnegligible quadrupole and dipole couplings, the application of magic echoes during the evolution periods of stimulated echo is demonstrated as a helpful technique in the case of slow diffusion. These findings are demonstrated by experimental results in the thermotropic liquid crystal of partially deuterated 8CB. The obtained diffusion coefficients are also compared to data obtained by a H-1 homonuclear-decoupling-type PGSE NMR method in the same material.

  • 6. Dvinskikh, Sergey V.
    et al.
    Sandstrom, D.
    Frequency offset refocused PISEMA-type sequences2005In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 175, no 1, p. 163-169Article in journal (Refereed)
    Abstract [en]

    The popular PISEMA experiment is highly sensitive to the H-1 chemical shift dispersion and the choice of the H-1 carrier frequency. This is due to the off-resonance H-1 irradiation in the FSLG-CP sequence employed during the dipolar evolution period. In the modified approach described in this work, the interfering frequency offset terms are suppressed. In the new pulse schemes, conventional FSLG-CP is intercalated with 180 degrees pulses applied Simultaneously to both frequency channels, and with phases set orthogonal to those of the spin-lock fields. The technique is demonstrated on a nematic liquid-crystalline sample. Extensions to amplitude-modulated FSLG-CP recoupling under MAS are also presented.

  • 7.
    Dvinskikh, Sergey V.
    et al.
    KTH, Superseded Departments, Chemistry.
    Sitnikov, R.
    Furo, Istvan
    KTH, Superseded Departments, Chemistry.
    C-13 PGSE NMR experiment with heteronuclear dipolar decoupling to measure diffusion in liquid crystals and solids2000In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 142, no 1, p. 102-110Article in journal (Refereed)
    Abstract [en]

    A new PGSE NMR experiment, designed to measure molecular diffusion coefficients in systems with nonvanishing static dipolar coupling, is described. The fast static dipolar dephasing of the single-quantum C-13 coherences is removed by multiple-pulse heteronuclear decoupling. The resulting slow dephasing of the C-13 coherences allows for inserting appropriate gradient pulses into the pulse sequence. The presence of the large magnetic field gradient reduces the efficiency of the decoupling sequences which is compensated for by introducing a scheme of sequential slice selection across the sample. The method is demonstrated by F-19-decoupled C-13 PGSE NMR experiments in a lyotropic nematic and lamellar liquid crystal,

  • 8.
    Dvinskikh, Sergey V.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Szutkowski, Kosma
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    MRI profiles over very wide concentration ranges: Application to swelling of a bentonite clay2009In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 198, no 2, p. 146-150Article in journal (Refereed)
    Abstract [en]

    In MRI investigation of soils, clays, and rocks, mainly mobile water is detected, similarly to that in biological and medical samples. However, the spin relaxation properties of water in these materials and/or low water concentration may make it difficult to use standard MRI approaches. Despite these limitations, one can combine MRI techniques developed for solid and liquid states and use independent information on relaxation properties of water, interacting with the material of interest, to obtain true images of both water and material content. We present procedures for obtaining such true density maps and demonstrate their use for studying the swelling of bentonite clay by water. A constant time imaging protocol provides 1D mapping of the clay distribution in regions with clay concentration above 10 vol%. T-1 relaxation time imaging is employed to monitor the clay content down to 10(-3) vol%. Data provided by those two approaches are in good agreement in the overlapping range of concentrations. Covering five orders of magnitude of clay concentration, swelling of sodium-exchanged bentonite clays from pre-compacted pellets into a gel phase is followed in detail.

  • 9. Dvinskikh, Sergey V.
    et al.
    Yamamoto, Kazutoshi
    Durr, Ulrich H. N.
    Ramamoorthy, Ayyalusamy
    Sensitivity and resolution enhancement in solid-state NMR spectroscopy of bicelles2007In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 184, no 2, p. 228-235Article in journal (Refereed)
    Abstract [en]

    Magnetically aligned bicelles are becoming attractive model membranes to investigate the structure, dynamics, geometry, and interaction of membrane-associated peptides and proteins using solution- and solid-state NMR experiments. Recent studies have shown that bicelles are more suitable than mechanically aligned bilayers for multidimensional solid-state NMR experiments. In this work, we describe experimental aspects of the natural abundance C-13 and N-14 NMR spectroscopy of DMPC/DHPC bicelles. In particular, approaches to enhance the sensitivity and resolution and to quantify radio-frequency heating effects are presented. Sensitivity of C-13 detection using single pulse excitation, conventional cross-polarization (CP), ramp-CP, and NOE techniques are compared. Our results suggest that the proton decoupling efficiency of the FLOPSY pulse sequence is better than that of continuous wave decoupling, TPPM, SPINAL, and WALTZ sequences. A simple method of monitoring the water proton chemical shift is demonstrated for the measurement of sample temperature and calibration of the radio-frequency-induced heating in the sample. The possibility of using N-14 experiments on bicelles is also discussed.

  • 10. Dvinskikh, Sergey V.
    et al.
    Zimmermann, H.
    Maliniak, A.
    Sandstrom, D.
    Heteronuclear dipolar recoupling in liquid crystals and solids by PISEMA-type pulse sequences2003In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 164, no 1, p. 165-170Article in journal (Refereed)
    Abstract [en]

    A pulse sequence is described for the recoupling of heteronuclear dipolar interactions under MAS. The method is similar to the PISEMA experiment, but employs a well-defined amplitude modulation of one of the two radio-frequency fields. The technique is used for measurements of H-1-C-13 dipolar couplings in unoriented solid and liquid-crystalline samples.

  • 11. Dvinskikh, Sergey V.
    et al.
    Zimmermann, H.
    Maliniak, A.
    Sandstrom, D.
    Measurements of motionally averaged heteronuclear dipolar couplings in MAS NMR using R-type recoupling2004In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 168, no 2, p. 194-201Article in journal (Refereed)
    Abstract [en]

    A novel MAS NMR approach is presented for the determination of heteronuclear dipolar couplings in unoriented materials. The technique is based on the proton-detected local field (PDLF) protocol, and achieves dipolar recoupling by R-type radio-frequency irradiation. The experiment, which is called R-PDLF spectroscopy, is demonstrated on solid and liquid-crystalline systems. For mobile systems, it is shown that the R-PDLF scheme provides better dipolar resolution as compared to techniques combining conventional separated local field (SLF) spectroscopy with R-type recoupling.

  • 12. Dvinskikh, Sergey V.
    et al.
    Zimmermann, H.
    Maliniak, A.
    Sandstrom, D.
    Separated local field spectroscopy of columnar and nematic liquid crystals2003In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 163, no 1, p. 46-55Article in journal (Refereed)
    Abstract [en]

    We are in this work comparing the efficiencies of various H-1-C-13 separated local field (SLF) experiments when applied to columnar and nematic liquid crystals. In particular, the performances of the conventional SLF, proton-detected local field (PDLF), and polarization inversion spin exchange at the magic angle (PISEMA) methods in terms of spectral resolution, robustness, and ability to measure long-range couplings are investigated. The PDLF sequence provides in most cases the best dipolar resolution. This is especially obvious for weakly coupled H-1-C-13 spin pairs.

  • 13.
    Furo, Istvan
    et al.
    KTH, Superseded Departments, Chemistry.
    Hedin, N.
    Noise reduction in quadrupolar echo spectra at short echo times2001In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 152, no 2, p. 214-216Article in journal (Refereed)
    Abstract [en]

    The phase cycling scheme Exorcycle embedded into the quadrupolar echo pulse sequence is presented as a tool for reducing ringing effects in broad quadrupolar spectra.

  • 14.
    Giesecke, Marianne
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Dvinskikh, Sergey V.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Furó, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Constant-time chemical-shift selective imaging2013In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 226, p. 19-21Article in journal (Refereed)
    Abstract [en]

    We demonstrate that chemical-shift-selective constant-time imaging (CTI) can be performed by simply inserting selective saturation into the original imaging pulse sequence. The performance of the proposed method is illustrated by 7Li CTI imaging in a battery model that contains both Li metal electrodes and an electrolyte containing a dissolved Li salt.

  • 15. Grebenkov, Denis
    et al.
    Nguyen, Van Dang
    Li, Jing-Rebecca
    Exploring diffusion across permeable barriers at high gradients. I. Narrow pulse approximation,2014In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 248, p. 153-163Article in journal (Refereed)
    Abstract [en]

    The adaptive variation of the gradient intensity with the diffusion time at a constant optimal b-value is proposed to enhance the contribution of the nuclei diffusing across permeable barriers, to the pulsed-gradient spin-echo (PGSE) signal. An exact simple formula the PGSE signal is derived under the narrow pulse approximation in the case of one-dimensional diffusion across a single permeable barrier. The barrier contribution to the signal is shown to be maximal at a particular b-value. The exact formula is then extended to multiple permeable barriers, while the PGSE signal is shown to be sensitive to the permeability and to the inter-barrier distance. Potential applications of the protocol to survey diffusion in three-dimensional domains with permeable membranes are illustrated through numerical simulations.

  • 16.
    Gudmundson, Erik
    et al.
    Dept. of IT, Uppsala University.
    Stoica, Petre
    Dept. of IT, Uppsala University.
    Li, Jian
    University of Florida.
    Jakobsson, Andreas
    Lund University.
    Rowe, Michael D.
    King's College London.
    Smith, John A. S.
    King's College London.
    Ling, Jun
    University of Florida.
    Spectral estimation of irregularly sampled exponentially decaying signals with applications to RF spectroscopy2010In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 203, no 1, p. 167-176Article in journal (Refereed)
    Abstract [en]

    The problem of estimating the spectral content of exponentially decaying signals from a set of irregularly sampled data is of considerable interest in several applications. for example in various forms of radio frequency spectroscopy. in this paper. we propose a new nonparametric iterative adaptive approach that provides a Solution to this estimation problem As opposed to commonly used methods in the field, the damping coefficient, or linewidth, is explicitly modeled. which allows for all Improved estimation performance Numerical examples Using both simulated data and data from NQR experiments Illustrate he benefits of the proposed estimator as compared to Currently available lion parametric methods.

  • 17.
    Hallberg, Fredrik
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Yushmanov, Pavel V.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Stilbs, Peter
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Sensitive and robust electrophoretic NMR: Instrumentation and experiments2008In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 192, no 1, p. 69-77Article in journal (Refereed)
    Abstract [en]

    Although simple as a concept, electrophoretic NMR (eNMR) has so far failed to find wider application. Problems encountered are mainly due to disturbing and partly irreproducible convection-like bulk flow effects from both electro-osmosis and thermal convection. Additionally, bubble formation at the electrodes and rf noise pickup has constrained the typical sample geometry to U-tube-like arrangements with a small filling factor and a low resulting NMR sensitivity. Furthermore, the sign of the electrophoretic mobility cancels out in U-tube geometries. We present here a new electrophoretic sample cell based on a vertically placed conventional NMR sample tube with bubble-suppressing palladium metal as electrode material. A suitable radiofrequency filter design prevents noise pickup by the NMR sample coil from the high-voltage leads which extend into the sensitive sample volume. Hence, the obtained signal-to-noise ratio of this cell is one order of magnitude higher than that of our previous U-tube cells. Permitted by the retention of the sign of the displacement-related signal phase in the new cell design, an experimental approach is described where bulk flow effects by electro-osmosis and/or thermal convection are compensated through parallel monitoring of a reference signal from a non-charged species in the sample. This approach, together with a CPMG-like pulse train scheme provides a superior first-order cancellation of non-electrophoretic bulk flow effects.

  • 18. Hedin, N.
    et al.
    Furo, Istvan
    KTH, Superseded Departments, Chemistry.
    Accurate intensities of broad NMR lines from composite pulse experiments2000In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 142, no 1, p. 32-36Article in journal (Refereed)
    Abstract [en]

    Accurate determination of integral intensities of broad lines is difficult when spin relaxation during the applied pulses cannot be neglected and/or when ringing of the tank circuit interferes with the signal. Here we present an extension of the analytical solution of the generalized Bloch equations (G. A. Morris and P. B. Chilvers, J. Magn. Reson. A 107, 236 (1994)), which is then used to evaluate the signal intensity obtained in a composite pulse experiment designed to cancel ringing effects. Comparing intensities of broad and narrow Br-81 spectral lines tests and proves the accuracy Of this approach.

  • 19. Ivchenko, Nickolay V.
    et al.
    Hughes, C. E.
    Levitt, M. H.
    Application of cogwheel phase cycling to sideband manipulation experiments in solid-state NMR2003In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 164, no 2, p. 286-293Article in journal (Refereed)
    Abstract [en]

    Cogwheel phase-cycling schemes are applied to sideband suppression and sideband separation experiments in solid-state NMR. It is shown that cogwheel phase cycles lead to the elimination of most pulse imperfection effects, while using far fewer experimental signal acquisitions than conventional phase-cycling methods.

  • 20. Ivchenko, Nickolay V.
    et al.
    Hughes, C. E.
    Levitt, M. H.
    Multiplex phase cycling2003In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 160, no 1, p. 52-58Article in journal (Refereed)
    Abstract [en]

    We discuss a new class of phase cycling procedures, in which a set of individual phase-shifted transients are stored separately in the computer and processed afterwards to yield the separated NMR signals from two or more coherence transfer pathways. In the case of two-dimensional double-quantum spectroscopy, this multiplex acquisition procedure allows the acquisition of pure-absorption spectra in only 62.5% of the time needed by previous methods.

  • 21.
    Kharkov, Boris B.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Chizhik, V. I.
    Dvinskikh, Sergey V.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Low rf power high resolution H-1-C-13-N-14 separated local field spectroscopy in lyotropic mesophases2012In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 223, p. 73-79Article in journal (Refereed)
    Abstract [en]

    Efficiency of the proton detected (encoded) H-1-C-13-N-14 local field spectroscopy technique at low radiofrequency power is examined when applied to concentrated ionic lyotropic mesophases exhibiting heteronuclear and homonuclear dipolar couplings in kHz range. We demonstrate that highly resolved heteronuclear dipolar spectra can be obtained with limited radiofrequency power corresponding to decoupling B-1 field of 20 kHz and with superior spectral resolution and sensitivity provided by standard solution state probes. To maintain sufficiently large spectral window in indirect dimension, power level alternation scheme for homonuclear decoupling was introduced. In anisotropic mesophases of an ionic surfactant, pair-wise coupling constants in the three-spin system H-1-C-13-N-14 were accurately determined. Relative signs of heteronuclear dipolar couplings to nitrogen were obtained employing frequency selective decoupling.

  • 22. Li, Jing-Rebecca
    et al.
    Nguyen, Hang Tuan
    Nguyen, Van-Dang
    CEA Saclay Center, France.
    Haddar, Houssem
    Coatléven, Julien
    Le Bihan, Denis
    Numerical study of a macroscopic finite pulse model of the diffusion MRI signal2014In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 248, p. 54-65Article in journal (Refereed)
    Abstract [en]

    Diffusion magnetic resonance imaging (dMRI) is an imaging modality that probes the diffusion characteristics of a sample via the application of magnetic field gradient pulses. The dMRI signal from a heterogeneous sample includes the contribution of the water proton magnetization from all spatial positions in a voxel. If the voxel can be spatially divided into different Gaussian diffusion compartments with inter-compartment exchange governed by linear kinetics, then the dMRI signal can be approximated using the macroscopic Karger model, which is a system of coupled ordinary differential equations (ODEs), under the assumption that the duration of the diffusion-encoding gradient pulses is short compared to the diffusion time (the narrow pulse assumption). Recently, a new macroscopic model of the dMRI signal, without the narrow pulse restriction, was derived from the Bloch-Torrey partial differential equation (PDE) using periodic homogenization techniques. When restricted to narrow pulses, this new homogenized model has the same form as the Karger model. We conduct a numerical study of the new homogenized model for voxels that are made up of periodic copies of a representative volume that contains spherical and cylindrical cells of various sizes and orientations and show that the signal predicted by the new model approaches the reference signal obtained by solving the full Bloch-Torrey PDE in O(ε(2)), where ε is the ratio between the size of the representative volume and a measure of the diffusion length. When the narrow gradient pulse assumption is not satisfied, the new homogenized model offers a much better approximation of the full PDE signal than the Karger model. Finally, preliminary results of applying the new model to a voxel that is not made up of periodic copies of a representative volume are shown and discussed.

  • 23.
    Lindh, Erik L.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. Innventia AB, Sweden.
    Stilbs, Peter
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Site-resolved H-2 relaxation experiments in solid materials by global line-shape analysis of MAS NMR spectra2016In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 268, p. 18-24Article in journal (Refereed)
    Abstract [en]

    We investigate a way one can achieve good spectral resolution in H-2 MAS NMR experiments. The goal is to be able to distinguish between and study sites in various deuterated materials with small chemical shift dispersion. We show that the H-2 MAS NMR spectra recorded during a spin-relaxation experiment are amenable to spectral decomposition because of the different evolution of spectral components during the relaxation delay. We verify that the results are robust by global least-square fitting of the spectral series both under the assumption of specific line shapes and without such assumptions (COmponent-REsolved spectroscopy, CORE). In addition, we investigate the reliability of the developed protocol by analyzing spectra simulated with different combinations of spectral parameters. The performance is demonstrated in a model material of deuterated poly(methacrylic acid) that contains two H-2 spin populations with similar chemical shifts but different quadrupole splittings. In H-2-exchanged cellulose containing two H-2 spin populations with very similar chemical shifts and quadrupole splittings, the method provides new site-selective information about the molecular dynamics.

  • 24. Lips, O.
    et al.
    Privalov, A. E.
    Dvinskikh, Sergey V.
    Fujara, F.
    Magnet design with high B-0 homogeneity for fast-field-cycling NMR applications2001In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 149, no 1, p. 22-28Article in journal (Refereed)
    Abstract [en]

    The design, construction, and performance of a low-inductance solenoidal coil with high B-0 homogeneity for fast-field-cycling NMR is presented. It consists of six concentric layers. The conductor width is varied to minimize the B-0 inhomogeneity in the volume of the sample. This is done using an algorithm which takes the real shape of the conductor directly into account. The calculated coil geometry can be manufactured easily using standard computerized numeric control equipment, which keeps the costs low. The coil is liquid cooled and produces a B-0 field of 0.95 T at 800 A. The field inhomogeneity in a cylindrical volume (diameter 5 mm, length 10 mm) is about 10 ppm, and the inductance is 190 muH. Switching times below 200 mus can be achieved. During 6 months of operation the coil has shown good stability and reliability.

  • 25.
    Nguyen, Van Dang
    et al.
    Ecole Polytechnique, France.
    Grebenkov, Denis
    Le Bihan, Denis
    Li, Jing-Rebecca
    Numerical study of a cylinder model of diffusion MRI signal for neuronal dendrite trees2015In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 252, p. 103-113Article in journal (Refereed)
    Abstract [en]

    We study numerically how the neuronal dendrite tree structure can affect the diffusion magnetic resonance imaging (dMRI) signal in brain tissue. For a large set of randomly generated dendrite trees, synthetic dMRI signals are computed and fitted to a cylinder model to estimate the effective longitudinal diffusivity DL in the direction of neurites. When the dendrite branches are short compared to the diffusion length, DL depends significantly on the ratio between the average branch length and the diffusion length. In turn, DL has very weak dependence on the distribution of branch lengths and orientations of a dendrite tree, and the number of branches per node. We conclude that the cylinder model which ignores the connectivity of the dendrite tree can still be adapted to describe the apparent diffusion coefficient in brain tissue.

  • 26.
    Nguyen, Van Dang
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computational Science and Technology (CST).
    Jansson, Johan
    KTH, School of Electrical Engineering and Computer Science (EECS), Computational Science and Technology (CST).
    Tran, Hoang Trong An
    CMAP, Polytechnique, France.
    Hoffman, Johan
    KTH, School of Electrical Engineering and Computer Science (EECS), Computational Science and Technology (CST).
    Li, Jing-Rebecca
    CMAP, Ecole Polytechnique, France.
    Diffusion MRI simulation in thin-layer and thin-tube media using a discretization on manifolds2019In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 299, p. 176-187Article in journal (Refereed)
    Abstract [en]

    The Bloch-Torrey partial differential equation can be used to describe the evolution of the transverse magnetization of the imaged sample under the influence of diffusion-encoding magnetic field gradients inside the MRI scanner. The integral of the magnetization inside a voxel gives the simulated diffusion MRI signal. This paper proposes a finite element discretization on manifolds in order to efficiently simulate the diffusion MRI signal in domains that have a thin layer or a thin tube geometrical structure. The variable thickness of the three-dimensional domains is included in the weak formulation established on the manifolds. We conducted a numerical study of the proposed approach by simulating the diffusion MRI signals from the extracellular space (a thin layer medium) and from neurons (a thin tube medium), comparing the results with the reference signals obtained using a standard three-dimensional finite element discretization. We show good agreements between the simulated signals using our proposed method and the reference signals for a wide range of diffusion MRI parameters. The approximation becomes better as the diffusion time increases. The method helps to significantly reduce the required simulation time, computational memory, and difficulties associated with mesh generation, thus opening the possibilities to simulating complicated structures at low cost for a better understanding of diffusion MRI in the brain.

  • 27.
    Nguyen, Van Dang
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Leoni, Massimiliano
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Dancheva, Tamara
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Jansson, Johan
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Hoffman, Johan
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Wassermann, Demian
    Li, Jing-Rebecca
    Portable simulation framework for diffusion MRI2019In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 309, article id 106611Article in journal (Refereed)
    Abstract [en]

    The numerical simulation of the diffusion MRI signal arising from complex tissue micro-structures is helpful for understanding and interpreting imaging data as well as for designing and optimizing MRI sequences. The discretization of the Bloch-Torrey equation by finite elements is a more recently developed approach for this purpose, in contrast to random walk simulations, which has a longer history. While finite elements discretization is more difficult to implement than random walk simulations, the approach benefits from a long history of theoretical and numerical developments by the mathematical and engineering communities. In particular, software packages for the automated solutions of partial differential equations using finite elements discretization, such as FEniCS, are undergoing active support and development. However, because diffusion MRI simulation is a relatively new application area, there is still a gap between the simulation needs of the MRI community and the available tools provided by finite elements software packages. In this paper, we address two potential difficulties in using FEniCS for diffusion MRI simulation. First, we simplified software installation by the use of FEniCS containers that are completely portable across multiple platforms. Second, we provide a portable simulation framework based on Python and whose code is open source. This simulation framework can be seamlessly integrated with cloud computing resources such as Google Colaboratory notebooks working on a web browser or with Google Cloud Platform with MPI parallelization. We show examples illustrating the accuracy, the computational times, and parallel computing capabilities. The framework contributes to reproducible science and open-source software in computational diffusion MRI with the hope that it will help to speed up method developments and stimulate research collaborations.

  • 28.
    Pagès, Guilhem
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Dvinskikh, Sergey V.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Furó, István
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Suppressing magnetization exchange effects in stimulated-echo diffusion experiments2013In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 234, p. 35-43Article in journal (Refereed)
    Abstract [en]

    Exchange of nuclear magnetization between spin pools, either by chemical exchange or by cross-relaxation or both, has a significant influence on the signal attenuation in stimulated-echo-type pulsed field gradient experiments. Hence, in such cases the obtained molecular self-diffusion coefficients can carry a large systematic error. We propose a modified stimulated echo pulse sequence that contains T-2-filters during the z-magnetization store period. We demonstrate, using a common theoretical description for chemical exchange and cross-relaxation, that these filters suppress the effects of exchange on the diffusional decay in that frequent case where one of the participating spin pools is immobile and exhibits a short T-2. We demonstrate the performance of this experiment in an agarose/water gel. We posit that this new experiment has advantages over other approaches hitherto used, such as that consisting of measuring separately the magnetization exchange rate, if suitable by Goldman-Shen type experiments, and then correcting for exchange effects within the framework of a two-site exchange model. We also propose experiments based on selective decoupling and applicable in systems with no large T-2 difference between the different spin pools. (C) 2013 The Authors. Published by Elsevier Inc. All rights reserved.

  • 29. Price, W. S.
    et al.
    Stilbs, Peter
    KTH, Superseded Departments, Chemistry.
    Jonsson, B.
    Soderman, O.
    Macroscopic background gradient and radiation damping effects on high-field PGSE NMR diffusion measurements2001In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 150, no 1, p. 49-56Article in journal (Refereed)
    Abstract [en]

    The effects of macroscopic background gradients due to susceptibility differences at the sample interfaces and of radiation damping on pulsed-gradient spin-echo (PGSE) experiments are examined. Both phenomena can lead to the seemingly strange effect of the echo signal growing as the gradient strength increases at low applied gradient strengths. For a freely diffusing species, background gradients manifest themselves as slight concave or convex inflections in the linearized PGSE attenuation curve, depending on the polarity of the applied gradient, The various means of overcoming macroscopic background gradient problems, including bipolar gradients, and their efficacy are examined experimentally and discussed. The effects of radiation damping can also result in the attenuation curve being nonlinear but, different from the effect of background gradients, the nonlinearity does not change with the polarity of the applied gradient. The vulnerability of the stimulated echo-based PGSE sequence and variations of Hahn-based PGSE sequences is investigated. Both background gradients and radiation damping have serious implications for accurate diffusion measurement determination.

  • 30. Price, W. S.
    et al.
    Stilbs, Peter
    KTH, Superseded Departments, Chemistry.
    Soderman, O.
    Determination of pore space shape and size in porous systems using NMR diffusometry. Beyond the short gradient pulse approximation2003In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 160, no 2, p. 139-143Article in journal (Refereed)
    Abstract [en]

    The influence of finite length gradient pulses on NMR diffusion experiments on liquids confined to diffuse between two parallel planes is investigated. It is experimentally verified that the pore size decreases when determined using finite gradient pulses if the results are analyzed within the short gradient pulse approximation. The results are analyzed using the matrix formulation. The observed minima in the echo decay profiles are considerably less sharp than theoretical analysis would indicate and we suggest that this is due to the presence of a distribution of pore sizes in the sample. In addition, effects due to the presence of background gradients are discussed. It is argued that effects due to the finite length gradient pulses are relatively minor and in realistic applications the effects due to inhomogeneities in pore sizes and effects due to background gradients will constitute more serious problems in pore size determinations by means of NMR diffusometry.

  • 31.
    Stilbs, Peter
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    RECORD processing: A robust pathway to component-resolved HR-PGSE NMR diffusometry2010In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 207, no 2, p. 332-336Article in journal (Refereed)
    Abstract [en]

    It is demonstrated that very robust spectral component separation can be achieved through global least-squares CORE data analysis of automatically or manually selected spectral regions in complex NMR spectra in a high-resolution situation. This procedure (acronym RECORD) only takes a few seconds and quite significantly improves the effective signal/noise of the experiment as compared to individual frequency channel fitting, like in the generic HR-DOSY approach or when using basic peak height or integral fitting. Results from RECORD processing can be further used as starting value estimates for subsequent CORE analysis of spectral data with higher degree of spectral overlap.

  • 32. Szutkowski, Kosma
    et al.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Effective and accurate single-shot NMR diffusion experiments based on magnetization grating2008In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 195, no 2, p. 123-128Article in journal (Refereed)
    Abstract [en]

    Current single-shot diffusion methods based on magnetization gratings suffer from low sensitivity due to small rf tip angles and, consequently, from inefficient use of the total equilibrium magnetization. Here, we propose and illustrate the use of a slightly modified form of the magnetization encoding scheme OUFIS for single-shot diffusion experiments. In a detailed theoretical and experimental analysis, we compare the performance of the proposed method to other encoding schemes such as the one-phase or two-phase DANTE and conclude that the OUFIS-based experiment is a superior one. The primary reason is that this scheme allows one to use a larger total pulse area. Hence, one can encode a far larger portion of the initial magnetization into a frequency grating before the onset of various nonlinear effects. In the experimental illustration, we present a single-shot measurement of multicomponent diffusion.

  • 33.
    Yushmanov, Pavel
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    Furo, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Industrial NMR Centre.
    A temperature-jump design for conventional NMR probes2006In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 181, no 1, p. 148-153Article in journal (Refereed)
    Abstract [en]

     The design and performance of a simple probe insert for temperature-jump experiments in conventional NMR probes is described. The insert uses the output from conventional NMR amplifiers for heating conductive aqueous samples with a rate of 30-80 K/s for 200 W radiofrequency power. The observed dependence of the heating rate on sample conductivity is explained by the dominance of dielectric heating. Factors governing the temperature gradient within the sample are discussed.

  • 34.
    Yushmanov, Pavel V.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Furó, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    A rapid-mixing design for conventional NMR probes2005In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, Vol. 175, no 2, p. 264-270Article in journal (Refereed)
    Abstract [en]

    A simple stopped-flow design for rapid mixing of two liquids within the NMR probe is presented. The device uses no switches or relays but exploits instead the torque exerted by the magnetic field on a current-leading-coil to open and close the start and stop valves. Two serially arranged tangential jet mixer blocks provide a homogeneous mixture with, depending on conditions and requirements, a filling time in the 50-100 ms range and a subsequent stabilization time in the range of 10-40 ms as tested by mixing various combinations of liquids and observing their 1H NMR spectrum. Factors influencing the mixing process are analyzed.

1 - 34 of 34
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