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Biomedical subjects

I Furó

Publications and source records attributed to I Furó.

At least 19 recordsLinked to original sources
PubMed2006

NMR cryoporometry with octamethylcyclotetrasiloxane as a probe liquid. Accessing large pores.

Octamethylcyclotetrasiloxane is presented and investigated as probe liquid for NMR cryoporometry or DSC-based thermoporometry. This compound which may imbibe into both hydrophilic and hydrophobic pores is shown to exhibit a melting point depression that is larger than that for other cryoporometric probe materials such as cyclohexane. The transverse relaxation time differs by more than three orders of magnitude between the solid and liquid states, separated by a sharp phase transition. Hence, as demonstrated in controlled pore glasses, octamethylcyclotetrasiloxane can provide pore size distributions for materials with pore sizes up to the micrometer range.

Journal Article↗
PubMed2006

Inorganic salt hydrates as cryoporometric probe materials to obtain pore size distribution.

The depression of the melting temperature of Zn(NO3)2.6H2O was used to obtain the pore size distributions in controlled pore glasses. Measured by 1H NMR, the average value of the temperature depression DeltaT and the known average pore size yield K=DeltaT.d approximately 116 K.nm as the material-dependent factor for Zn(NO3)2.6H2O in the Gibbs-Thompson equation. The melting temperature is close to room temperature. Hence, this salt hydrate and some related other ones are better materials than water (K approximately 50 K.nm) for cryoporometric studies of systems with hydrophilic pores. The data also provide 46 mN/m for the solid-liquid surface tension of this salt hydrate.

Journal Article↗
PubMed2004

Diffusion-diffusion correlation and exchange as a signature for local order and dynamics.

We demonstrate the use of new two-dimensional nuclear magnetic resonance experiments in the examination of local diffusional anisotropy under conditions of global isotropy. The methods, known as diffusion-diffusion correlation spectroscopy and diffusion exchange spectroscopy, employ successive pairs of magnetic field gradient pulses, with signal analysis using two-dimensional inverse Laplace transformation. Diffusional anisotropy is measured for water molecules in a polydomain lamellar phase lyotropic liquid crystal, 40 wt % nonionic surfactant C10E3 (C10H21O(CH2CH2O)6H) in H2O.

Journal Article↗
PubMed2002

Anisotropic self-diffusion in thermotropic liquid crystals studied by 1H and 2H pulse-field-gradient spin-echo NMR.

The molecular self-diffusion coefficients in nematic and smectic-A thermotropic liquid crystals are measured using stimulated-echo-type 2H and 1H pulse-field-gradient spin-echo nuclear magnetic resonance (PGSE NMR) combined with multiple-pulse dipolar decoupling and slice selection. The temperature dependence of the principal components of the diffusion tensor in the nematic phase follows a simple Arrhenius relationship except in the region of nematic-isotropic phase transition where it reflects, merely, the decrease of the molecular orientational order. The average of the principal diffusion coefficients in the isotropic-nematic phase transition region is close to the diffusion coefficient in the isotropic phase. At the nematic-smectic-A phase transition the diffusion coefficients change continuously. The results in nematic phase are best described in terms of the affine transformation model for diffusion in nematics formed by hard ellipsoids. In the smectic-A phase the data are interpreted using a modified model for diffusion in presence of a periodic potential along the director.

Journal Article↗
PubMed2002

Molecular self-diffusion in a columnar liquid crystalline phase determined by deuterium NMR.

We report translational diffusion coefficients in a columnar phase of a discotic liquid crystal formed by a triphenylene-based compound. The experiments were performed using 2H stimulated-echo-type pulsed-field-gradient spin-echo NMR applied to a chain-deuterated sample. The diffusion coefficients were found in the range of 1x10(-14)-4x10(-14) m2/s, three orders of magnitude lower than in the isotopic phase of the same compound. This, together with the high activation energy obtained in columnar phase, indicates that the diffusion is dominated by solidlike jump processes.

Journal Article↗
PubMed2001

Measurement of the principal values of the anisotropic diffusion tensor in an unoriented sample by exploiting the chemical shift anisotropy: (19)F PGSE NMR with homonuclear decoupling.

NMR methods (S. V. Dvinskikh et al., J. Magn. Reson. 142, 102-110 (2000) and S. V. Dvinskikh and I. Furó, 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 (19)F PGSE NMR with homonuclear decoupling in a lyotropic lamellar liquid crystal.

Journal Article↗
PubMed2001

Deuterium stimulated-echo-type PGSE NMR experiments for measuring diffusion: application to a liquid crystal.

The accessibility of molecular self-diffusion coefficients in anisotropic materials, such as liquid crystals or solids, by stimulated-echo-type (2)H 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 (1)H homonuclear-decoupling-type PGSE NMR method in the same material.

Journal Article↗
PubMed2000

Accurate intensities of broad NMR lines from composite pulse experiments.

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 (81)Br spectral lines tests and proves the accuracy of this approach.

Bromine↗
PubMed2000

13C PGSE NMR experiment with heteronuclear dipolar decoupling to measure diffusion in liquid crystals and solids.

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 (13)C coherences is removed by multiple-pulse heteronuclear decoupling. The resulting slow dephasing of the (13)C 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 (19)F-decoupled (13)C PGSE NMR experiments in a lyotropic nematic and lamellar liquid crystal.

Carbon Isotopes↗
PubMed2000

Combining PGSE NMR with homonuclear dipolar decoupling.

A new robust approach for combining multiple-pulse homonuclear decoupling and PGSE 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 (19)F PGSE NMR experiments in a lyotropic liquid crystal.

Calibration↗
PubMed1986

Combined 1H-NMR and vacuum dehydration study of rat muscles.

Combined NMR and the vacuum dehydration method were used to study the state of water in rat muscle. Comparative studies were carried out on muscles of young and old mature white rats. The spin-lattice relaxation time was measured as a function of water content. The single-exponential behaviour of the relaxation process indicates a normal fast-exchange process between the different fractions. The more elaborate analysis demonstrates the failure of the original fast-exchange model. It is proved that structural changes take place in the macromolecule/ion/bound water system of the muscle even at the beginning of dehydration. All the muscle water seems to be necessary to maintain the normal natural state of the muscle's molecular structure.

Age Factors↗
PubMed1986

In vitro 1H NMR "mapping" of human intervertebral discs.

Human intervertebral discs were investigated by 1H NMR in vitro. The measured parameters of samples differently located in discs give the "maps" of discs. The spin-lattice relaxation-time maps show similar structure to dry matter and bound water maps, which might mean the future possibility to detect certain disc processes via accurate T1 images.

Adult↗
PubMed1986

1H nuclear magnetic resonance study of intervertebral discs. A preliminary report.

In vitro 1H pulse nuclear magnetic resonance (NMR) studies on human intervertebral disc tissues were performed to establish the characteristics of relaxation processes. The spin-lattice relaxation time, bound water and dry matter content were measured. Biopsy material from fresh cadavers was taken from different discs along the spinal column and from different sectors of some single discs. It is suggested that the measured parameters correlate with the biomechanical behavior of discs, which in turn is influenced by function, by exposure to physical stresses, or by aging.

Adolescent↗
PubMed1986

Freezing-thawing hysteresis. I. NMR detection in human lens.

Human eye lenses were investigated by 1H-NMR as a function of temperature around freezing. Wide hysteresis in line intensity and relaxation time has been found. The hysteresis behavior of the phase transition presents a useful possibility for investigating the structure of water in these materials.

Body Water↗
PubMed1986

Freezing-thawing hysteresis. II. Investigation of human ocular tissues.

The freezing-thawing behavior of cataractous eye lenses and corneas was investigated by 1H-NMR. The corneas have shown hysteresis similarly to the normal lens. No hysteresis could be demonstrated in cataractous lenses. The transparency of lens seems to be correlated with the existence of the freezing-thawing hysteresis.

Body Water↗