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In magnetic resonance imaging, the application of a strong diffusion weighting suppresses the signal contributions from the less diffusion-restricted constituents of the brain's white matter, thus enabling the estimation of the transverse relaxation time T2 that arises from the more diffusion-restricted constituents such as the axons. However, the presence of cell nuclei and vacuoles can confound the estimation of the axonal T2, as diffusion within those structures is also restricted, causing the corresponding signal to survive the strong diffusion weighting. We devise an estimator of the axonal T2 based on the directional spherical variance of the strongly diffusion-weighted signal. The spherical variance T2 estimates are insensitive to the presence of isotropic contributions to the signal like those provided by cell nuclei and vacuoles. We show that with a strong diffusion weighting these estimates differ from those obtained using the directional spherical mean of the signal which contains both axonal and isotropically-restricted contributions. Our findings hint at the presence of an MRI-visible isotropically-restricted contribution to the signal in the white matter ex vivo fixed tissue (monkey) at 7T, and do not allow us to discard such a possibility also for in vivo human data collected with a clinical 3T system.

The effect of high concentration of magnetic nanoparticles (MNP) on Magnetic Resonance Imaging (MRI) transverse relaxation rates (R2=1/T2 and R2*=1/T2*) were studied using Monte Carlo (MC) simulations. Theoretical models assume that particle occupies a small volume fraction of the sample space. This work aims to test if available models based on Motional Averaged (MAR) and Static Dephasing Regimes (SDR) can still represent relaxation rates at large volume fractions. Furthermore, echo-time effects were tested on both gradient-echo and spin-echo sequences in order to examine if diffusion is involved. Findings will clarify if models need to be modified to take account of high particle concentration. This is especially important for application involving the clustering of nanoparticles inside tissues or being trap inside cells. Another important area is relaxation due to MNP administered through vesicles as a carrier medium. This is important to understand the relaxation mechanism caused by MNP in order to improve their design process.

Improved moisture stability is desired in cellulose biocomposites. In order to clarify nanostructural effects, a new approach is presented where water and polymer matrix mobilities are characteriied separately. Nanocornposites from cellulose nanofibers (CNF) in the xyloglucan (XG) biopolynier matrix are investigated at different hydration states Films of XG, CNF, and CNF/XG composites are subjected to detailed H-2 and C-13 NMR relaxation studies. Since the H-2 NMR. signal arises from heavy water and the C-13 signal from the polysaccharides, - molecular Water and polymer dynamics is for the first time investigated separately In the neat components, H-2 transverse relaxation (T-2), data are consistent. With water Clustering at the CNF fibril sulfaces, but bulk spread of moisture in XG. The-new method results in a description of water interaction with the nanoscale phases. At low hydration) water molecules at the CNF/XG interface exhibit higher water-mobility-than in neat CNF or XG, due to locally high Water concentration. At the same time, CNF-associated interphase segments of XG Slower NMR-dynamics that in teat XG., QC 20150615

PurposeTo determine whether Lorentzian or Gaussian intra-voxel frequency distributions are better suited for modeling data acquired with gradient-echo sampling of single spin-echoes for the simultaneous characterization of irreversible and reversible relaxation rates. Clinical studies (e.g., of brain iron deposition) using such acquisition schemes have typically assumed Lorentzian distributions.Theory and methodsTheoretical expressions of the time-domain spin-echo signal for intra-voxel Lorentzian and Gaussian distributions were used to fit data from a human brain scanned at both 1.5 Tesla (T) and 3T, resulting in maps of irreversible and reversible relaxation rates for each model. The relative merits of the Lorentzian versus Gaussian model were compared by means of quality of fit considerations.ResultsLorentzian fits were equivalent to Gaussian fits primarily in regions of the brain where irreversible relaxation dominated. In the multiple brain regions where reversible relaxation effects become prominent, however, Gaussian fits were clearly superior.ConclusionThe widespread assumption that a Lorentzian distribution is suitable for quantitative transverse relaxation studies of the brain should be reconsidered, particularly at 3T and higher field strengths as reversible relaxation effects become more prominent. Gaussian distributions offer alternate fits of experimental data that should prove quite useful in general. Magn Reson Med 74:51-62, 2015. © 2014 Wiley Periodicals, Inc.

Using monoexponential models, magnetic resonance (MR) parameters transverse relaxation time (T2) and apparent diffusion coefficient (ADC) have been used to non–invasively assess cell density, which characteristically increases with brain tumor malignancy. Multiexponential models of T2 and ADC may allow for a more accurate evaluation of cell density than the traditionally used monoexponential model. To better understand how cell density affects multicomponent T2 and ADC, tumor models with a range of cell densities were created by suspending astrocytoma cells in agarose at different densities. T2 was measured using a Carr–Purcell–Meiboom–Gill (CPMG) sequence with 64 echo times. ADC was measured using a diffusion–weighted sequence with 32 b–values. Three models were used to fit the data and determine the T2 values, ADC values, and associated fractions: monoexponential, biexponential, non–negative least squares (NNLS). Spearman Rank was used to test the correlation with cell density. Both the monoexponential T2 and ADC were significantly negatively correlated with cell density. The biexponential model identified two T2 components, short and long. Both T2 components’ values and fractions were significantly correlated to cell density. The biexponential model identified two ADC components, slow and fast. Both ADC components’ values were significantly correlated with cell density, but not the fractions. The NNLS model identified up to three T2 and three ADC components. For the NNLS identified T2s, the components were labeled short, medium, and long. Both the NNLS short and medium T2 values and fractions were significantly correlated with cell density. For the NNLS identified ADCs, the components were labeled slow, intermediate, and fast. Only the fast fraction was significantly correlated with cell density.The NNLS components obtained from samples of packed cells were further evaluated by washing the samples with a gadolinium contrast agent (Gd–DTPA) to shorten the T2 assoc

The magnetic properties of cobalt ferrite-silica nanocomposites with different concentrations (15, 30, and 50 wt %) and sizes (7, 16, and 28 nm) of ferrite particles have been studied by static magnetization measurements and Mossbauer spectroscopy. The results indicate a superparamagnetic behavior of the nanoparticles, with weak interactions slightly increasing with the cobalt ferrite content and with the particle size. From high-field Mossbauer spectra at low temperatures, the cationic distribution and the degree of spin canting have been estimated and both parameters are only slightly dependent on the particle size. The magnetic anisotropy constant increases with decreasing particle size, but in contrast to many other systems, the cobalt ferrite nanoparticles are found to have an anisotropy constant that is smaller than the bulk value. This can be explained by the distribution of the cations. The weak dependence of spin canting degree on particle size indicates that the spin canting is not simply a surface phenomenon but also occurs in the interiors of the particles. (c) 2006 American Institute of Physics.

Apparatus has been designed and constructed that incorporates the experimental techniques for achieving high signal-to-noise ratios and sufficiently long relaxation times, in order to obtain a gradient magnetometer with a differential sensitivity of 0.1 milligamma/ft. The apparatus consists of two magnetic resonance sensors operated in a self oscillating mode and spaced eighteen inches apart. The resonance medium (cesuim vapor) is contained in vacuum, wall-coated cells. The field differential is obtained by means of phase comparison of the two simultaneously observed cesium resonances. In preliminary tests in the laboratory ambient magnetic fields, required signal-to-noise ratios have been shown to be attainable. Techniques have been developed for producing cesium resonance cells with stable longitudinal relaxation times in excess of 150 ms. An analysis of the useful sensitivity of gradient magnetometers in the presence of wave noise was carried out. It is shown that the full sensitivity of 0.1 milligamma/ft. can be used with appropriate orientation of the gradient device and/or with signal processing. (Author)

© 2019, Springer Nature B.V. The work introduces the original and efficient approach toward hydrophilization of Gd(III) complex with hydrophobic octa-2,3,9,10,16,17,23,24-n-butoxyphthalocyanine (1H 2 ). It consists in the solvent-mediated self-assembly of the preliminary synthesized octa-2,3,9,10,16,17,23,24-n-butoxyphthalocyaninatogadolinium(III) acetate 1GdOAc into the colloid species followed by their hydrophilization through the polyelectrolyte deposition. Small-angle X-ray scattering, TEM, and DLS measurements of the aqueous colloids reveal the disk-like colloid species formation with the greatest size value about 40 nm. Deposition of polystyrene sulfonate layer onto the surface of nanocolloids does not prevent their partial aggregation in aqueous solutions. The phthalocyaninate ligand is the reason for specific electrochemical behavior of the colloids, which is affected by the nanoparticulate form of the complex. The magnetic behavior of the complex reveals it as pure paramagnetic, while magnetic relaxation behavior of the colloids points to some specificity. The r 2 /r 1 ratio measured at 0.47 T is higher (2.6) than the ratios commonly reported for Gd(III) complexes, coming to 36.8 at 11.75 T. Thus, the synthesized colloids are more efficient as T 2 - than T 1 -contrasting agents at magnetic field strengths above 1.4 T. [Figure not available: see fulltext.].

Transverse relaxation and self-diffusion of molecules in a glyceryl monooleate (monoolein)-D2O system was studied using pulsed 1H NMR in a range of water concentrations from 10 to 30 wt % and a range of temperatures from 20 to 90°C. It was noted that self-diffusion is described by one or two self-diffusion coefficients, depending on the temperature and concentration of water, while NMR-relaxation has a complex form. It was determined that with a reduction in the transverse magnetization, a component that has a form similar to Gaussian and relaxation times of 70 to 250 j, s is observed at certain temperatures and concentrations of water, confirming the formation of structures in which glyceryl monooleate molecules (GM) are characterized by anisotropic rotational mobility. It was demonstrated that the ranges of the concentrations of water and temperature in which this component is observed correspond to liquid-crystalline phase for lamellar and inverse hexagonal structural organizations of lipids, according to the state diagram obtained by X-ray diffraction. In the state diagram areas corresponding to micellar and cubic structures (characterized by the isotropic rotation of GM molecules in the time scale of NMR), multiexponential decays of magnetization with average relaxation times were noted in the range of 10 to 200 ms. A number of features were discovered with the use of NMR: specimens always contain structures with isotropic rotational mobility in the presence of structures characterized by anisotropic rotational mobility; a change in the fraction of the structures with anisotropic rotational mobility takes place slowly over 5-15 K, not abruptly. Our conclusions regarding the polymorphism of a GM-D2O system in the presence of anisotropic structures was confirmed by an analysis of the transverse NMR relaxation in an egg phosphatidylcholine-D2O system, for which the presence of only lamellar liquid-crystalline structure is confirmed by 31P NMR. © Pleiades Publishin

The article introduces transverse relaxation rates of water protons in the aqueous hydrophilic colloids synthesized on the basis of the oleate-coated iron oxide nanoparticles (17. nm) with non-ionic and cationic surfactants, triblock copolymers, polyethyleneimine (PEI) and 4,5-dihydroxybenzene-1,3-disulfoacid disodium salt (Tiron) as hydrophilic components. The IR spectroscopy, atomic force and transmission electron microscopy, along with dynamic light scattering data were obtained to evaluate the content of the hydrophilic coating, the clustering of iron oxide nanoparticles within the hydrophilic covering and the aggregation of hydrophilic nanoclusters. The analysis of the obtained results together with transverse relaxation rates under various concentration, counter-ion and temperature conditions reveals the particular importance of the water molecules diffusion in the outer hydrophilic layer versus the nearest to the iron oxide core layer. The obtained results reveal the counter ion binding with the charged hydrophilic iron oxide colloids as a route to affect the water transverse relaxation rates by biorelevant anionic substrates such as adenosine triphosphates. © 2013 Elsevier B.V.

Transverse relaxation and self-diffusion of molecules in a glyceryl monooleate (monoolein)-D2O system was studied using pulsed 1H NMR in a range of water concentrations from 10 to 30 wt % and a range of temperatures from 20 to 90°C. It was noted that self-diffusion is described by one or two self-diffusion coefficients, depending on the temperature and concentration of water, while NMR-relaxation has a complex form. It was determined that with a reduction in the transverse magnetization, a component that has a form similar to Gaussian and relaxation times of 70 to 250 j, s is observed at certain temperatures and concentrations of water, confirming the formation of structures in which glyceryl monooleate molecules (GM) are characterized by anisotropic rotational mobility. It was demonstrated that the ranges of the concentrations of water and temperature in which this component is observed correspond to liquid-crystalline phase for lamellar and inverse hexagonal structural organizations of lipids, according to the state diagram obtained by X-ray diffraction. In the state diagram areas corresponding to micellar and cubic structures (characterized by the isotropic rotation of GM molecules in the time scale of NMR), multiexponential decays of magnetization with average relaxation times were noted in the range of 10 to 200 ms. A number of features were discovered with the use of NMR: specimens always contain structures with isotropic rotational mobility in the presence of structures characterized by anisotropic rotational mobility; a change in the fraction of the structures with anisotropic rotational mobility takes place slowly over 5-15 K, not abruptly. Our conclusions regarding the polymorphism of a GM-D2O system in the presence of anisotropic structures was confirmed by an analysis of the transverse NMR relaxation in an egg phosphatidylcholine-D2O system, for which the presence of only lamellar liquid-crystalline structure is confirmed by 31P NMR. © Pleiades Publishin

The article introduces transverse relaxation rates of water protons in the aqueous hydrophilic colloids synthesized on the basis of the oleate-coated iron oxide nanoparticles (17. nm) with non-ionic and cationic surfactants, triblock copolymers, polyethyleneimine (PEI) and 4,5-dihydroxybenzene-1,3-disulfoacid disodium salt (Tiron) as hydrophilic components. The IR spectroscopy, atomic force and transmission electron microscopy, along with dynamic light scattering data were obtained to evaluate the content of the hydrophilic coating, the clustering of iron oxide nanoparticles within the hydrophilic covering and the aggregation of hydrophilic nanoclusters. The analysis of the obtained results together with transverse relaxation rates under various concentration, counter-ion and temperature conditions reveals the particular importance of the water molecules diffusion in the outer hydrophilic layer versus the nearest to the iron oxide core layer. The obtained results reveal the counter ion binding with the charged hydrophilic iron oxide colloids as a route to affect the water transverse relaxation rates by biorelevant anionic substrates such as adenosine triphosphates. © 2013 Elsevier B.V.