Pulsed Gradient Spin Echo Research Articles

Solvent self-diffusion dependence on the swelling degree of a hydrogel.

This article describes high-field nuclear magnetic resonance experiments using pulsed gradient spin echo methods to investigate water mobility inside homogeneously swollen polyacrylamide hydrogel beads. The NMR data permitted determining the solvent self-diffusion coefficient dependence on either the swelling time or the polymer volume fraction. The sensitivity to the structure of the hydrogel network could be tuned to a certain extent via controlling the diffusion probing time. Relaxation measurements have helped substantiate a theoretical description for these self-diffusion dependencies based upon a fast-exchange two-site model. A tortuosity-porosity dependence is extracted from the model and then compared to other known tortuosity regimes. The diffusion dependence on the degree of swelling obtained here corroborates the existence of a gel swelling-front observed during inhomogeneous solvent imbibition experiments. Finally, we stress that the NMR experimental results reported here are of great value on performing theoretical modeling of gel swelling via solvent imbibition.

Comprehensive Structural Assessment of Linear Block Polymers by NMR and SEC

Block polymers are an important class of materials offering unique and useful properties different from random polymers. Because of their tailored structure, these materials present synthetic challenges. For this reason, it is necessary to provide a thorough structural analysis to drive the synthetic effort. We describe an analytical methodology that includes size exclusion chromatography (SEC), quantitative 13C NMR, and 1H pulsed gradient spin echo (PGSE) NMR coupled with direct exponential curve resolution algorithm (DECRA) data analysis. The combination of these complementary techniques provides a comprehensive assessment of the chemical structure of the final polymeric material, including the detection and quantification of homopolymer formation, compositional heterogeneity with molecular weight, and monomer sequencing. We present work on two different linear block polymers: poly(styrene-b-allyl methacrylate) and poly[styrene-b-(styrene-alt-maleic anhydride)].

Choroid plexus cysts analyzed using diffusion-weighted imaging with short diffusion-time

IntroductionOscillating gradient spin-echo (OGSE) sequences can shorten diffusion times by replacing the long-lasting diffusion-sensitizing gradients used in pulsed gradient spin-echo (PGSE) methods with rapidly oscillating gradients. To obtain information regarding the internal structure of choroid plexus cysts that appear hyperintense on diffusion-weighted imaging (DWI), we investigated the apparent diffusion coefficient (ADC) values acquired with a shorter diffusion time using an OGSE sequence. Material and methodsTwenty-seven patients with choroid plexus cysts were scanned using a 3 T magnetic resonance scanner. DWI was performed with both OGSE and PGSE, with effective diffusion times (Δeff) of 6.5 and 35.2 ms, respectively. ADC values for choroid plexus cysts, white matter (WM), and cerebrospinal fluid (CSF) were measured. The ADC values obtained with the shorter and longer diffusion times were compared using the Wilcoxon signed-rank test. P < .05 was considered significant. ResultsThe ADC values of choroid plexus cysts and WM were significantly higher at the Δeff of 6.5 ms on OGSE than with the Δeff of 35.2 ms on PGSE. The ADC values of CSF were significantly lower at the Δeff of 6.5 ms on OGSE than with the Δeff of 35.2 ms on PGSE. The ADC values of choroid plexus cysts were lower than the ADC values of CSF with Δeff of 35.2 and 6.5 ms. ConclusionsThe dependence of ADC values on the diffusion time in choroid plexus cysts suggested spatially restricted diffusion. In measurements obtained with short diffusion times, the lower ADC values for choroid plexus cysts in comparison with the CSF indicated the presence of spatially restricted diffusion and increased cyst viscosity.

Time-dependent diffusion MRI to distinguish malignant from benign head and neck tumors.

There is growing interest in the effect of diffusion time on apparent diffusion coefficient (ADC) values in cancers; however, little evidence exists regarding its utility to differentiate malignant from benign head and neck tumors. To investigate the utility of ADC value changes in distinguishing between malignant and benign head and neck tumors using the different diffusion times obtained from oscillating gradient spin-echo (OGSE) and pulsed gradient spin-echo (PGSE) MRI sequences. Prospective. Thirty-one consecutive patients with suspected head and neck tumors and a phantom. 3T MRI with diffusion-weighted imaging (DWI) using OGSE (effective diffusion time: 4.3 msec) and PGSE (effective diffusion time: 82.6 msec) sequences and b-values of 0 and 700 s/mm2 . ADC values using OGSE (ADCOGSE ) and PGSE (ADCPGSE ) and relative ADC value changes between ADCOGSE and ADCPGSE . Wilcoxon test, Mann-Whitney test, and McNemar test. Relative ADC changes for each polyvinylpyrrolidone (PVP) and water in the phantom between OGSE and PGSE sequences were small (relative ADC change within 0.6%). Malignant tumors had significantly smaller ADCOGSE and ADCPGSE values than benign tumors (P < 0.001 and < 0.0001, respectively). Significantly larger relative ADC changes were observed in malignant compared with benign head and neck tumors (P < 0.0001). ADCPGSE values were significantly lower than ADCOGSE values in both malignant and benign head and neck tumors (0.97 vs. 1.28 × 10-3 mm2 /s: P < 0.0001 and 1.93 vs. 1.99 × 10-3 mm2 /s: P = 0.0056, respectively). Relative ADC change and ADCPGSE tended to have higher diagnostic performance than ADCOGSE , with area under the curve (AUC) values of 0.97, 0.96, and 0.89, respectively. ADC values obtained using the PGSE sequence were lower than those obtained with OGSE. This difference was larger for malignant than benign tumors, suggesting differences in tissue structure (diffusion hindrance) or cell permeability, revealed by changes in diffusion time. The results underline the potential importance of reporting diffusion time for interpretation of head and neck diffusion MRI. 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:88-95.

Magnetic resonance imaging of strain in elastic gels

Magnetic resonance imaging (MRI) can also be used for studying different material conditions, including strain, which is the subject of this study. A pair of pulsed magnetic field gradients combined with the spin-echo imaging sequence [pulsed-gradient spin-echo (PGSE)] enables the detection of small sample displacements that are induced in the time between the gradient pulses. The displacements are registered in the image phase shift, which is then processed by the phase unwarping algorithm and phase background correction. The processed phase shift can then be used to calculate sample displacements by multiplying it with the corresponding calibration constant. Finally, the strain tensor can be calculated from the map of sample displacements. In the study, the PGSE imaging method was tested on a gelatin sample. While being MRI scanned, the sample was deformed synchronously with the imaging sequence using a special MRI-compatible apparatus for inducing sample deformations. The apparatus was based on the use of compressed air that was directed via a nozzle on the surface of the sample in pulses controlled by transistor-transistor logic pulses of the spectrometer. With the 20 ms pulses of compressed air at a pressure of 0.5 bar, sample displacements of up to 300 μm were detected at the impact point of compressed air, while the detection threshold was at 0.7 μm. Results of the PGSE method were also compared with the tagging method. The study was performed in 2D; however, the method can be implemented also in 3D, thus enabling the measurement of the full strain tensor.

Understanding the behavior of mixtures of protic-aprotic and protic-protic ionic liquids: Conductivity, viscosity, diffusion coefficient and ionicity

We have investigated the physicochemical properties such as electrical conductivity, viscosity and diffusion coefficient for the binary mixtures of protic ionic liquids with aprotic ionic liquids and of protic with protic ionic liquids at 298.15 K. A significant enhancement in the electrical conductivity is observed for the binary mixtures of ionic liquids, as compared to those of the constituent pure ionic liquids and varied with the composition of the mixtures. The viscosity of binary mixtures of protic with aprotic ionic liquids, 1‑butyl‑3‑methylimidazoliumbis(trifluoromethylsulfonyl)imide [bmIm][NTf2], 1‑butyl‑1‑methylpyrrolidiumbis(trifluoromethylsulfonyl)imide [bmPyrr][NTf2] and 1,3-dimethylimidazolium methyl sulfate, [mmIm][CH3SO4] decreases with an increase in the composition of the [HmIm][CH3COO]. On the contrary, the viscosity for binary mixtures of protic with protic ionic liquid, 1‑methylpyrrolidium acetate [HmPyrr][CH3COO] and 4‑methylmorpholine acetate [HmMorph][CH3COO] increases upon the addition of 1‑methylimidazolium acetate [HmIm][CH3COO]. The self diffusion coefficients were determined for all the binary mixtures of ionic liquids by using Pulsed Gradient Spin Echo (PGSE) NMR method. Self diffusion coefficients of [bmIm][NTf2]-[HmIm][CH3COO], [bmPyrr][NTf2]-[HmIm][CH3COO], [mmIm][CH3SO4]-[HmIm][CH3COO] are enhanced, while those of [HmPyrr][CH3COO]-[HmIm][CH3COO] and [HmMorph][CH3COO]-[HmIm][CH3COO] decreases on addition of [HmIm][CH3COO]. This is converse in the case of viscosity. Furthermore, the above correlations were interpreted with the help of NMR spectroscopy on the basis of interactions of ions in the binary mixtures of ionic liquids. Finally, we have quantified the ionicity through the Nernst–Einstein equation and have confirmed the validity of the Walden rule for the binary mixture of ionic liquids.

Diffusion of Rodlike Polymers: Pulsed Gradient Spin Echo NMR of Poly(γ-stearyl-α,l-glutamate) Solutions and the Importance of Helix Stability.

Many natural and synthetic polymers and particles have a rodlike shape, leading to important and intriguing solution behavior, such as high intrinsic viscosities and liquid crystalline phases. Much of what is known about suspensions of rods has been learned by studying helical polypeptides, even though such molecules are not perfectly rigid, smooth cylinders. Previous optical tracer self-diffusion studies of poly(γ-benzyl-α,l-glutamate) (PBLG) revealed that the molecule initially resists topological constraints imposed by neighboring molecules, but diffusion strongly decreases as concentration rises beyond a certain number density. In contrast, the tracer self-diffusion coefficient of truly rigid tobacco mosaic virus begins decreasing immediately with concentration. We used pulsed gradient spin echo NMR to measure another polypeptide, poly(γ-stearyl-α,l-glutamate) (PSLG), to gain physical insight into the question of polypeptide diffusion in crowded isotropic solutions. The PSLG molecule, with long alkyl sidechains, is semiflexible like PBLG but does not exhibit the same ability to evade topological constraints. Instead, PSLG follows a simple exponential decay, D/ DKR = A e(-κν/ν*) + B, where DKR is the Kirkwood-Riseman expectation for rod diffusion, ν is the number density of rods, ν* is the Onsager expectation for the number density at the onset of liquid crystal formation, A = 1 ± 0.1, B = 0.1 ± 0.01, and κ = 4.5 ± 0.5. The results emphasize the importance of helix stability when choosing rodlike polypeptides as model systems, particularly with regard to the chain ends.

Electrophoretic nuclear magnetic resonance measurement of electroosmotic flow and dispersion in hydrating cement paste

This research analyzes the effect of an applied electric current on the dynamic displacement behavior of hydrogen ions in a hydrating cement paste confined in a closed cell. Electroosmotic flow (EOF) and dispersion in hydrating cement pastes is measured via the nuclear magnetic resonance (NMR) pulsed gradient spin echo technique (PGSE). The dynamic PGSE NMR measurements indicate changes in pore structure after the application of the electric field. Micro CT scan imaging experiments confirmed that gaseous and fluid pore pressure is sufficient to cause particle rearrangement, consolidation, and void formation at relatively low voltages when the electroosmotic pressure approaches its maximum in a medium closed to external flow. Such phenomena may also result where blocked pores present restrictions in a medium otherwise open to flow.

Influence of Diffusion Time on the Diffusion Coefficients of Gases in Polymers Determined by Pulsed Gradient Spin Echo NMR

The diffusive behavior of pure and mixed 13CO2, methane, and ethylene in poly(4,4′-hexafluoroisopropylidene diphthalic anhydride-2,3,5,6-tetramethyl-1,4-phenylenediamine) membranes is investigated using a pulsed gradient spin echo NMR method. Also, proton and 13C spin–lattice and spin–spin relaxation times are measured. In all cases, the relaxation times of sorbed gases are well described assuming a single component, indicating that gas molecules in the membrane recognize one environment. If there is more than one, they are in fast exchange between them, and average values of relaxation times are observed. The diffusion coefficient of 13CO2 is independent of the diffusion time, exhibiting a Fickian behavior in all cases. Meanwhile, those of methane and ethylene vary with the diffusion time, and data analysis was performed considering their non-Fickian behavior. The diffusion coefficient of methane increases in the presence of 13CO2 and ethylene, suggesting that the sieving properties of the glassy polyimi...

Synthesis and Characterization of Isosorbide-Based Polyurethanes Exhibiting Low Cytotoxicity Towards HaCaT Human Skin Cells.

The synthesis of four samples of new polyurethanes was evaluated by changing the ratio of the diol monomers used, poly(propylene glycol) (PPG) and D-isosorbide, in the presence of aliphatic isocyanates such as the isophorone diisocyanate (IPDI) and 4,4′-methylenebis(cyclohexyl isocyanate) (HMDI). The thermal properties of the four polymers obtained were determined by DSC, exhibiting Tg values in the range 55–70 °C, and their molecular structure characterized by FTIR, 1H, and 13C NMR spectroscopies. The diffusion coefficients of these polymers in solution were measured by the Pulse Gradient Spin Echo (PGSE) NMR method, enabling the calculation of the corresponding hydrodynamic radii in diluted solution (1.62–2.65 nm). The molecular weights were determined by GPC/SEC and compared with the values determined by a quantitative 13C NMR analysis. Finally, the biocompatibility of the polyurethanes was assessed using the HaCaT keratinocyte cell line by the MTT reduction assay method showing values superior to 70% cell viability.

7Li NMR diffusion studies in micrometre-space for perovskite-type Li0.33La0.55TiO3 (LLTO) influenced by grain boundaries

Perovskite-type oxide solid electrolyte Li0.33La0.55TiO3 (LLTO) samples are known to have high ionic conductivities and grain-boundary resistances from AC impedance spectroscopy. In addition, the existence of domain structures has been shown by transmission electron microscopy and other techniques. In this study Li+ migration in tetragonal and cubic samples (t- and c-LLTO) was studied in micrometre space by pulsed-gradient spin-echo (PGSE) NMR from the room temperature up to 100 °C. The grain-boundary effects appeared clearly in the 7Li echo attenuation plots, which were not linear and included at least two components. Previously, we reported that the Li+ diffusion in inorganic solid electrolytes (garnets, NASICON, sulfides) distributes widely in time and space, illustrated by the dependences of the measuring parameters such as observation time (Δ) and pulsed-field gradient (PFG) strength (g). In addition to the complexities of parameter dependent Li+ diffusion, grain-boundary disturbance effects were observed for Li+ diffusion phenomena in LLTO samples. We indicated that a unique DLi value could be estimated from the linear echo attenuation plot at convergent measuring conditions with long Δ and large g for garnets and NASICON. The LLTO samples showed curved echo attenuation plots at the convergent measuring conditions, which were analysed by two components to give two Li+ diffusion constants (DLi-fast and DLi-slow). These values are consistent with the tracer diffusion constants measured at higher temperatures (>150 °C). For c-LLTO, DLi-fast and DLi-slow showed good correspondences with the bulk ionic conductivity (σbulk) and grain-boundary ionic conductivity (σgb), respectively. The Li carrier numbers estimated from DLi-fast and σbulk for c- and t-LLTO showed similar values, whereas those estimated from DLi-slow and σgb for c-LLTO were smaller by approximately one-order of magnitude.

Ionic Conductivity, Diffusion Coefficients, and Degree of Dissociation in Lithium Electrolytes, Ionic Liquids, and Hydrogel Polyelectrolytes.

The conductive and diffusional behavior of electrolytes in media with different dielectric and viscoelastic properties is investigated. A revised model to separate the contribution of dissociated and nondissociated species to the diffusion coefficients determined with NMR is proposed. Impedance spectroscopy is used to measure the ionic conductivity of lithium salts in aqueous medium, ionic liquids in aprotic solvents, and hydrogel polyelectrolytes. The diffusion coefficients of the species of interest in those systems are determined with multinuclear pulsed-gradient spin-echo (PGSE) NMR. The results are analyzed using the revised model. It is shown that the degree of ionization could be determined directly from measurements of ionic conductivity and diffusion coefficients in very different types of electrolytes and in a wide range of concentrations. Furthermore, these findings support the original Arrhenius hypothesis about electrolytes and show that the assumption of a complete dissociation is not required to describe their conductive behavior. The reduced conductivity observed in hydrogels, at or near swelling equilibrium, compared to that in solutions could be attributed mainly to the hindered ionic mobility caused by the network structure.

Monomerisation of [Rh2(1,3-Bis-(Diphenylphosphino)-Propane)2(μ2-Cl)2] Detected by Pulsed Gradient Spin Echo Spectroscopy and 31P Nmr Monitoring of Metathesis Experiments

A pulsed gradient spin echo experiment on [Rh2(1,3-bis-(diphenylphosphino)-propane)2(μ2-Cl)2] complex has been conducted in order to shed light on the supposed monomerisation process of [Rh2(diphosphine)2(μ2-Cl)2] complexes in solution. Such a process should generate a 14-electron [Rh(diphosphine)Cl] complex, which has only been postulated to date. Metathesis experiments on [Rh2(1,3-bis-(diphenylphosphino)-propane)2(μ2-Cl)2] and [Rh2(bis[2-(diphenylphosphino)phenyl]ether)2(μ2-Cl)2] complexes, analysed by 31P NMR, reveal that monomerisation of [Rh2(diphosphine)2(μ2-Cl)2] complexes is not restricted to the case of 1,3-bis-(diphenylphosphino)propane.

Mass Transfer Parameters and Ionic Association of Dual-Cation Electrolyte for Hybrid Capacitor System

[Introduction] Hybrid capacitors, which combine an activated carbon (AC) electrode with a large-capacity faradic (psuedocapacitive or battery) electrode, are the focus on an increase in energy density of electric double layer capacitors (EDLCs). One representative faradic electrode material for such hybrid systems is lithium titanate (Li4Ti5O12, LTO), which was used as a negative electrode in one of the first hybrid systems1) and has been extensively investigated since then 2). In this connection, we have reported a dual-cation electrolyte system composed of lithium tetrafluoroborate (LiBF4) and spiro-(1,1’)-bipyrrolidium tetrafluoroborate (SBPBF4) dissolved in propylene carbonate (PC), where the latter cation gives high ionic conductivity in the PC-based electrolytes3). The dual-cation electrolyte system raised rate capability of LTO/AC hybrid capacitors to a level comparable to EDLCs, thanks to the enhancement of LTO reaction kinetic. Still, the detailed mechanism of improved rate capability by dual-cation system has not been completely understood. The difficulty of the analysis lies in the electrolyte containing multiple ion spices, whose contribution to the rate capability cannot be simply divided into individuals.The purpose of this study was to evaluate the contribution of individual ionic species by using pulsed gradient spin-echo (PGSE) NMR technique. Specifically, by determining the self-diffusion coefficient of dual cation electrolyte system, we attempted to break down the ionic conductivity of the whole electrolyte system into individual ionic species and to calculate a carrier number of ions. [Experimental]Electrolytes used in this report were prepared by dissolving 1 M LiBF4 and x M SBPBF4 in PC (0<x<3). All the electrolyte was prepared by mixing components with magnetic stirrer overnight in the Ar-filled glove box. PGSE-NMR was conducted to determine self-diffusion coefficients of Li+(7Li), SBP+(1H) and BF4 -(19F) in electrolytes with maximum gradient strength of 13.5 T/m at different durations. The interval between pulse gradients was set as 50 ms. Ionic conductivity of prepared electrolytes was measured by electrochemical impedance spectroscopy (EIS). [Results and discussion]Self-diffusion coefficients of different ions obtained from PGSE-NMR were plotted in Figure 1, with different concentration of SBPBF4 (0, 1, 2, and 3 M) in the 1 M LiBF4/PC electrolyte. Diffusion coefficients for all three ions decreased with an increment of added SBPBF4 concentration, while the value of SBP+ is higher compared to other two ions, especially Li+, in all cases. Based on obtained self-diffusion coefficients, we calculated the transport number t x of ions (x = Li+, SBP+, or BF4 -) according to the following equation(1) t x = N x D x /(N[Li+]D[Li+] + N[BF4 -] D[BF4 -] + N[SBP+] D[SBP+]) (1)where N x and D x is a concentration and self-diffusion coefficient of corresponding ions, respectively. Using this t x, we further calculated ionic conductivity of each ion by simply multiplying electrolyte ionic conductivity by t x. The evaluated values are shown in Figure 2. Like diffusion coefficients shown in Figure 1, Li+ ionic conductivity decreased with an increment of SBPBF4 concentration. Interestingly, cations ionic conductivity, which is sum of Li+ and SBP+, kept increased with an addition of SBPBF4. In order to discuss cations dissociation in electrolytes with presentence of SBPBF4, we evaluated number of carrier for Li+ based on the peak shifts observed in 7Li NMR spectra and theory of Haven ratio where degree of dissociation is considered as λEIS/λNMR. Here again, with a SBPBF4 concentration increase, number of Li+ carrier decreased, while number of SBP+ carrier increased. In conclusion, a dual-cation electrolyte (Li+ and SBP+) decreases Li+ ionic conductivity and its number of carrier, however, increases the two parameters for the SBP+. The present result suggests that the presence of highly conductive and dissociated SBP+ accelerates charge compensation of LTO reaction, and thus enhanced its rate capability. [References]1) G.G. Amatucci et al., J. Electrochem. Soc., 148 (8) A930 (2001).2) K. Naoi et al., Acc. Chem. Res., 46 (5), 1075 (2013).3) T. Ueda et al., 5th International Conference on Advanced Capacitors (ICAC 2016), 2O-03, Otsu, Japan (2016). Figure 1

Water Mobility within Compacted Clay Samples: Multi-Scale Analysis Exploiting 1H NMR Pulsed Gradient Spin Echo and Magnetic Resonance Imaging of Water Density Profiles.

1H NMR pulsed gradient spin echo attenuation and water density profile analysis by magnetic resonance imaging are both used to determine the mobility of water molecules confined within a porous network of compacted kaolinite clay sample (total porosity of ∼50%). These two complementary experimental procedures efficiently probe molecular diffusion within time scales varying between milliseconds and few hours, filling the gap between the time scale of diffusion dynamics measured by traditional quasi elastic neutron scattering and through-diffusion methods. Furthermore, magnetic resonance imaging is a nondestructive investigation tool that is able to assess the effect of the local structure on the macroscopic mobility of the diffusing probe.

Inferring diameters of spheres and cylinders using interstitial water.

Most early methods to infer axon diameter distributions using magnetic resonance imaging (MRI) used single diffusion encoding sequences such as pulsed gradient spin echo (SE) and are thus sensitive to axons of diameters > 5 μm. We previously simulated oscillating gradient (OG) SE sequences for diffusion spectroscopy to study smaller axons including the majority constituting cortical connections. That study suggested the model of constant extra-axonal diffusion breaks down at OG accessible frequencies. In this study we present data from phantoms to test a time-varying interstitial apparent diffusion coefficient. Diffusion spectra were measured in four samples from water packed around beads of diameters 3, 6 and 10 μm; and 151 μm diameter tubes. Surface-to-volume ratios, and diameters were inferred. The bead pore radii estimates were 0.60±0.08 μm, 0.54±0.06 μm and 1.0±0.1 μm corresponding to bead diameters ranging from 2.9±0.4 μm to 5.3±0.7 μm, 2.6±0.3 μm to 4.8±0.6 μm, and 4.9±0.7 μm to 9±1 μm. The tube surface-to-volume ratio estimate was 0.06±0.02 μm-1 corresponding to a tube diameter of 180±70 μm. Interstitial models with OG inferred 3-10 μm bead diameters from 0.54±0.06 μm to 1.0±0.1 μm pore radii and 151 μm tube diameters from 0.06±0.02 μm-1 surface-to-volume ratios.

Changes in the ADC of diffusion-weighted MRI with the oscillating gradient spin-echo (OGSE) sequence due to differences in substrate viscosities.

Compared with the conventional pulsed gradient spin-echo (PGSE) sequence, diffusion-weighted imaging (DWI) with the oscillating gradient spin-echo (OGSE) sequence can shorten the diffusion time by changing the frequency. The purpose was to investigate whether n-alkanes are suitable as isotropic phantoms for estimating the diffusion coefficient with the OGSE sequence. We investigated changes in the apparent diffusion coefficient (ADC) due to differences in the viscosities of nine n-alkane phantoms with different numbers of carbon atoms from C8H18 to C16H34 using OGSE and PGSE sequences at 21°C. Effective diffusion times of 4.3, 5.1, 6.5, 9.3, 20, 40, and 60ms were used. The T2 relaxation times of each n-alkane phantom were measured using quantitative synthetic magnetic resonance imaging (MRI). Circular regions of interest were placed manually within the alkane phantoms on ADC and T2 maps. In each alkane phantom, changes in mean ADC values were almost constant with changes in diffusion times. Viscosities and ADC values showed inverse proportionality, as expected theoretically. The ADC values of alkanes do not depend on diffusion times. The n-alkanes can be useful phantoms for assessing the accuracy of clinical protocols of DWI with the OGSE sequence.

NMR Study of the Dissolution of Core-Crystalline Micelles

Short fragments of the core-crystalline micelles formed by a sample of poly(ferrocenyldimethylsilane)-block-poly(isoprene) (PFS-b-PI) block copolymer (BCP) underwent self-seeding in decane when heated above its dissolution temperature. Variable temperature (VT) 1H NMR and diffusion-ordered pulsed-gradient spin–echo (DOSY) NMR were used to monitor the behavior of micelles that dissolved as a function of increasing temperature. We examined a sample of micelle fragments of PFS65-b-PI637 characterized by Ln = 39 nm and Lw/Ln = 1.13. The PI corona had high mobility and gave a 1H NMR signal in both micellar and unimer forms. In contrast, the PFS component could only be detected for the dissolved unimer. We found from 1H NMR that essentially all the BCP molecules were incorporated into the micelles at temperatures up to and including 50 °C, at the limit of NMR detection. Both PFS and PI resonances could be detected between 70 and 100 °C, and the integration ratio of the PFS-to-PI peaks increased with temperature...

Oscillating gradient diffusion kurtosis imaging of normal and injured mouse brains.

Recent advances in diffusion MRI employ multiple diffusion encoding schemes with varying diffusion direction, weighting, and diffusion time to investigate specific microstructural properties in biological tissues. In this study, we examined time-dependent diffusion kurtosis contrast in adult mouse brains and in neonatal mouse brains after hypoxic-ischemic (HI) injury. In vivo diffusion kurtosis maps were acquired with a short diffusion time using an oscillating gradient spin echo (OGSE) sequence at 100Hz and with a relatively long diffusion time (20ms) using a pulsed gradient spin echo (PGSE) sequence. In the adult mouse brain, we found that the cortex and hippocampus showed larger differences between OGSE kurtosis and PGSE kurtosis than major white matter tracts. In neonatal mouse brains with unilateral HI injury, the OGSE kurtosis map overall provided stronger edema contrast than the PGSE kurtosis map, and the differences between OGSE and PGSE kurtosis measurements in the edema region reflected heterogeneity of injury. This is the first in vivo study that has demonstrated multi-direction OGSE kurtosis contrasts in the mouse brain. Comparing PGSE and OGSE kurtosis measures may provide additional information on microstructural changes after ischemic stroke.

Non-uniform lithium-ion migration on micrometre scale for garnet- and NASICON-type solid electrolytes studied by 7Li PGSE-NMR diffusion spectroscopy

The migration behaviours of Li+ in three garnet- and one NASICON-type solid oxide electrolytes were studied on the micrometre scale by pulsed-gradient spin-echo (PGSE) 7Li NMR diffusion spectroscopy to clarify common and specific characteristics of each electrolyte. In these solid electrolytes, clear evidences of grain boundary effects in the diffusion of Li+ were not observed. The Li+ diffusion constants were dependent on parameters such as observation time (Δ) and pulsed field gradient (PFG) strength (g) for all the studied inorganic solid electrolytes. For low Δ values, Li+ ions underwent collisions and diffractions with diffraction distance Rdiffraction [μm]. The apparent Li+ diffusion constants (Dapparent [m2 s-1]) exhibited distributions in a wide range. In this paper, we introduced the apparent diffusion radius, rradius [μm], and compared it with Rdiffraction and mean square displacement (MSD) [μm]; the lengths of these distances were of the micrometre order (10-6 m). The relations between the values of rradius, Rdiffraction and MSD suggested that the migration behaviours of Li+ on the micrometre scale were complicated. Using high Δ and high g values, we obtained an equilibrated value of DLi. The temperature dependences of the number of carrier ions were estimated from the DLi values and ionic conductivities in the four solid oxide electrolytes. For simple comparison and reference, the data of DLi and ionic conductivity of LiPF6 in 1 M solution of propylene carbonate were added.