NMR study of tomato pericarp tissue by spin-spin relaxation and water self-diffusion

Pericarp tissues of tomato varieties Quest and Cameron were studied by low-field nuclear magnetic resonance (NMR) at a controlled temperature of 20°C. The spin-spin relaxation times and the water diffusion coefficients were measured with Carr-Parcell-Meiboom-Gill and pulsed field gradient multi-spin-echo (PFGMSE) NMR sequences. Four relaxing components were extracted from the spin-spin relaxation. The components withT ₂=11 ms,T ₂=65 ms,T ₂=430 ms andT ₂=1500 ms were related to the nonexchangeable protons and water proton in each cell compartment (i.e., cell wall-extracellular space, cytoplasm and vacuole, respectively). In contrast to the relative intensities, theT ₂ values appeared insensitive to variety and harvest period. The difference in relative intensity was related to the size of the pericarp cell. The water self-diffusion coefficients for each cell compartment were determined simultaneously with the PFGMSE sequence. The water self-diffusion coefficients for the vacuole and cytoplasm were not affected by the harvest date or variety. However, the water self-diffusion in the cell wall-extracellular space was significantly different between the two varieties.     

Estimation of water content and water mobility in the nucleus and cytoplasm of Xenopus laevis oocytes by NMR microscopy

NMR microscopy is a noninvasive approach for studying cell structure and properties. Spatially resolved measurement of the relaxation times T₁ and T₂ provided information on the water proton spin density and water mobility in different parts of Xenopus laevis oocytes. The spin-lattice relaxation time T₁ was determined using a saturation-recovery sequence and the common spin-echo sequence with increasing repetition times, while the transverse relaxation time T₂ was measured by means of the spin-echo sequence with varying echo times. From the relaxation times, the mole fractions of possible reorientational correlation times τ_c for different types of intracellular water were calculated according to a simple two-phase model. The values for T₁, T₂, and proton spin density (i.e., water content) are: nucleus ⪢ animal cytoplasm > vegetal cytoplasm. Based on the estimation of τ_c, nearly 90% of the nuclear water and 74.4% of the water of the animal pole was considered as free mobile water, whereas 55.5% of the water of the vegetal pole appeared as bound water.     

Molecular Diffusion in NMR Microscopy

The signal-to-noise ratio and the T₂ contrast in ¹H NMR microscopy are strongly affected by self-diffusion effects. Here, we investigate the free diffusion of water within imaging gradients. As a result we obtain an apparent relaxation time T₂ which in NMR microscopy is at least one order of magnitude smaller than the true T₂ value of water in the object. This apparent T₂ relaxation is considerably reduced by improving spatial resolution. We conclude that quantitative true T₂ values cannot be calculated from series of images with increasing echo time. Furthermore, from the knowledge of the apparent T₂, an optimum short echo time can be found in order to maximize signal-to-noise ratio. Our theoretical findings are confirmed by phantom experiments at 11.75 T field strength.     

Temperature dependence of spin diffusion coefficient and T2 for dilute 3He in solid 4He

Spin diffusion coefficients D and NMR line widths 1/T₂ have been measured as a function of temperature for ³He in solid ⁴He at fractional concentrations down to 10^-4. Minima are seen in D and T₂ and the existence of impuritons is confirmed.     

Quantitative NMR microscopy on intact plants

Quantitative high resolution images on intact young maize plants were acquired by using magnetization-prepared NMR microscopy. Although the spatial resolution is low compared with that of light microscopy, the calculated spin density and T₁ maps exhibit contrasts that are in excellent agreement with photomicrographic images. The T₂ map gives image contrasts that are not visible in a usual light microscopic image. The diffusion images show an anisotropic behavior of the water self-diffusion coefficient in the vascular bundles, which can be understood by the cell morphology in this plant section. This work demonstrates that quantitative imaging on intact plant systems is possible and that long total acquisition times are no obstacle. Furthermore, the different single parameter maps give a better insight into the morphology of plants under in vivo conditions.     

Solvent aided NMR microscopy of γ-irradiatedcis 1,4-polybutadiene

Cross-linked structure of γ-irradiatedcis 1,4-polybutadiene (PBi) was studied by NMR microscopy with the aid of deuterated benzene. After PBi was swollen (PBiS) in C₆D₆, the¹H NMR linewidth of the polymer was reduced from 4 to 2 kHz. The images show that the relaxation times,T ₁ andT ₂, of PBiS are longer than those of PBi. The simultaneous increase ofT ₁ andT ₂ implies that the molecular chains of PBi become more mobile upon swelling. The enhanced mobility of the molecular chains may provide a possibility of the increase in space resolution.     

MRI phantom for tissue simulation with respect to diffusion coefficient and kurtosis - Validation with injection of liposomal theranostics

This study presents gelatine-based and agar-based phantoms with an addition of glycerol, safflower oil, silicone oil and cellulose microcrystalline with a potential to cover the entire range of tissue diffusion coefficients and kurtosis values. Forty types of phantoms were prepared and examined for NMR relaxation times T₁ and T₂ and diffusional metrics D, K and ADC. Wide ranges of values of D (0.0003–0.0031 mm²s⁻¹), K (0.00–7.24) and ADC (0.0002–0.0031 mm²s⁻¹) were observed. Two of the phantoms closely mimic muscle and cortical gray matter with respect to water diffusion parameters. Although many of the presented phantoms display both D and K values within the range of human tissues, they match different tissues with respect to D and K. The imaging results for the gray matter simulating phantom injected with the liposomal solution, bear a resemblance to the particle size effect described in the literature. The phantoms presented in this work are simple in preparation and affordable tissue-simulating materials to be used primarily in development of diffusion kurtosis-based MRI methods and possibly in a preliminary assessment of MRI contrast agents. Further adjustments of the chemical compositions could potentially lead to development of new types of phantoms mimicking diffusional properties of more kinds of soft tissues.     

Complementary use of T2-weighted and postcontrast T1- and T21-weighted imaging to distinguish sites of reversible and irreversible brain damage in focal ischemic lesions in the rat brain

The evolution of a photochemically induced cortical infarct was monitored using T₂-, postcontrast (GdDOTA) T₁-, and postcontrast (DyDTPA-BMA) T₂¹-weighted NMR imaging techniques. Data acquired with these different NMR imaging types were compared, both qualitatively and quantitatively. The T₂¹-weighted NMR images after sprodiamide injection (DyDTPA-BMA) were perfusion-weighted images that allowed the differentiation between several infarct-related areas in terms of different degrees of perfusion deficiency. No quantitative information on cerebral blood flow (CBF) was obtained. A clear distinction was made between areas with a complete lack of CBF located in the core of the lesion and temporary CBF insufficiencies in the rim surrounding this core. Concomitant observations on T₂-weighted and postcontrast T₁-weighted images revealed the same temporary rim characterized by an increased water content, and an intact blood-brain barrier (BBB), as well as by reduced perfusion. This rim appeared within the first hours after infarct induction, reached a maximum 24 h later, and lasted between 3–5 days, when its size gradually decreased until complete disappearance. These observations suggest the existence of an area at risk. Only on postcontrast T₁-weighted images, the core of the lesion remained visible during the whole experimental period (10 days) and reflected in all likelihood the irreversibly damaged ischemic central core. The combined application of different NMR imaging techniques when studying focal cerebral infarctions in the rat brain allowed us to distinguish, in terms of NMR characteristics, zones of reversible from irreversible brain damage and to estimate the severity of the damage. This might offer an appropriate experimental setup for the screening of cerebroprotective compounds.     

Study of γ-irradiation crosslinking ofcis-1,4-polybutadiene by NMR microscopy

Crosslink properties of ψ-irradiatedcis-1,4-polybutadiene (PB) were studied by NMR microscopy. Spin density images of the irradiated bulk materials show that crosslinking at the ?CH= atom dominates and the segments between two crosslinks are still flexible enough to twist, forming a dense material.T ₁ andT ₂ weighted images of these bulk materials show that theT ₁/T ₂ ratio increases upon irradiation. This is an indication of the increase of stiffness upon irradiation.¹H spin density images of the irradiated PB swollen in C₆D₆ show that the dimension of the cavities formed by irradiation is greater than the space resolution of the experiment.     

Diffusion and NMR spin lattice relaxation of 1H in α′ TaHx and NbHx

The concentration and temperature dependence of the self diffusion coefficient, D, of H in Group V transition metals Nb and Ta has been measured for the α^' phase. The nuclear magnetic resonance spin lattice relaxation time, T₁, was measured in Ta only. A pulsed field gradient, NMR spin echo technique was utilized to measure D. In both systems, the activation energy increases with hydrogen concentration while the pre-exponential factor is not strongly concentration dependent. The diffusion results are compared with published values of the macroscopic diffusion coefficient, $\text{D}{}^1$, obtained from Gorsky effect measurements. Values of the thermodynamic factor [$\text{(}\text{ρ}\text{kT}\text{)(}\text{?μ}\text{(?ρ)}$] are found for selected ρ and T, where μ is the chemical potential and ρ is the density of hydrogen atoms. These values agree with known determinations of the same factor obtained from the Gorsky effect relaxation strengths, but the agreement with results from solubility measurements is less satisfactory. NMR relaxation is partitioned into conduction electron (T^?1_1e) and dipolar (T^?1_1d) relaxation rates. The observed x dependence of ($\text{D}\text{T}{}_{\mathrm{1d}}$) is inconsistent with random occupancy of tetrahedral sites, and it is suggested that a repulsive interaction exists between H atoms on nearest neighbor sites.     

Nuclear magnetic relaxation by self-diffusion in solid lithium:T 1-frequency dependence

We report on measurements of the⁷Li nuclear spin relaxation timeT ₁ in solid lithium as a function of temperature (?170°C≦T≦+180°C) and Larmor frequency (450kHz≦v _Li≦31.5 MHz). Using a relaxation model developed by Wolf and Cavelius and combining it with Seeger's diffusion formalism, the diffusion parameters for mono-and divacancy migration were evaluated by a least squares fit to the newly obtainedT ₁ data as well as to previousT _1? measurements. The result for the self-diffusion coefficientD ^SD is given byD ^SD=D ₁₀·exp(?Q ₁/RT)·[1+D ₂₁·exp(?Q ₂₁/RT)], withD ₁₀=0.038 cm²s^?1,Q ₁=12.0 kcal mol^?1,D ₂₁=250,Q ₂₁=4 kcal mol^?1 andR=1.98₅·10^?3 kcal mol^?1 degree^?1. Due to the flexibility of Seeger's formula, which contrasts with the standard Arrhenius interpretation of diffusion, discrepancies between earlier high- and low-frequency NMR investigations were eliminated. Furthermore, an excellent agreement with available results from tracer experiments was achieved by taking into account the theoretical predictions of the isotope effect and the vacancy correlation factor.     

Diffusion measurements by microscopic NMR imaging

Proton NMR images of the brains of living mice with voxel sizes as small as 80 × 80 × 500 μm were acquired at 9.3 T by the 2D FT spin-echo method. Using gradients of 3.75 G/cm, images with pixel dimensions below 50 μm were of low sensitivity because of degradation of the echo due to diffusion and flow. In the absence of bulk flow, this decrease in image intensity as image pixel size is decreased can be used to measure the local self-diffusion coefficient of water (D_H2O) in small samples. By this method, D_H2O at 22°C was estimated to be 2.59, 2.13, 1.59, and 0.84 × 10⁻⁵ cm²/s in pure water, 10% gelatin, mouse skeletal muscle, and rat liver, respectively.     

2H nuclear magnetic resonance study of deuterated water dynamics in perfluorosulfonic acid ionomer Nafion

We have employed deuteron nuclear magnetic resonance (NMR) spectroscopy in order to study the dynamics of the deuterated water (D₂O) molecules introduced into a perfluorosulfonic acid ionomer Nafion (NR-211) film. According to the ²H NMR spectral analysis, the deuterated water molecules at low temperatures occupied either relatively rigid or mobile sites up to the temperature T_M=240 K where all the deuterated water molecules became mobile. The temperature-dependent NMR linewidths sensitively reflected the motional narrowing of the rigid and mobile sites, and the NMR chemical shift reflected significant changes in the hydrogen bonds of the deuterated water. While a slow- to fast-limit motional transition was manifested at T_M in the laboratory-frame NMR spin–lattice relaxation, the rotating-frame spin–lattice relaxation indicated no bulk liquid water state down to 200 K.     

Emulation of petroleum well-logging D-T2 correlations on a standard benchtop spectrometer

An experimental protocol is described that allows two-dimensional (2D) nuclear magnetic resonance (NMR) correlations of apparent diffusion coefficient D_app and effective transverse relaxation time T_2,eff to be acquired on a bench-top spectrometer using pulsed field gradients (PFG) in such a manner as to emulate D_app − T_2,eff correlations acquired using a well-logging tool with a fixed field gradient (FFG). This technique allows laboratory-scale NMR measurements of liquid-saturated cored rock to be compared directly to logging data obtained from the well by virtue of providing a comparable acquisition protocol and data format, and hence consistent data processing. This direct comparison supports the interpretation of the well-logging data, including a quantitative determination of the oil/brine saturation. The D − T₂ pulse sequence described here uses two spin echoes (2SE) with a variable echo time to encode for diffusion. The diffusion and relaxation contributions to the signal decay are then deconvolved using a 2D numerical inversion. This measurement allows shorter relaxation time components to be probed than in conventional diffusion measurements. A brief discussion of the numerical inversion algorithms available for inverting these non-rectangular data is included. The PFG-2SE sequence described is well suited to laboratory-scale studies of porous media and short T₂ samples in general.     

NMR in well logging and hydrocarbon exploration

Nuclear magnetic resonance (NMR) has become a versatile tool for the evaluation of underground hydrocarbon reservoirs. Formation attributes such as rock porosity and rock pore size distributions, as well as the relative concentrations of water, oil and gas, can be inferred from subsurface NMR. The hydrogen NMR signal encodes porosity as amplitude, pore sizes as relaxation times and fluid properties as a mixture of relaxation and diffusion rates. The paper describes the basic operating principles for NMR on cable (wireline), NMR on a drill string (logging-while-drilling) and NMR for downhole fluid sampling. The geometry of the borehole requires a magnet that projects its field into the surrounding rock, implying a grossly inhomogeneous field distribution. Experience shows that even under these circumstances, saturation-recovery and Carr-Purcell-Meiboom-Gill sequences can work well and yield meaningfulT ₁ andT ₂ information.     

Single-shot diffusion imaging at 2.0 tesla

A single-shot echo-planar diffusion imaging sequence (IVIM-EPI: intra-voxel incoherent motion echo-planar imaging) is presented, which is immune from the motion artifacts which may seriously impair images obtained using other diffusion imaging sequences. For a static water phantom, the measured value of diffusion constant (D = 2.30 × 10⁻⁹ m² s⁻¹ at T = 298 K) shows excellent agreement with that obtained using a multipulse spin-echo technique and with literature values. Single-shot diffusion imaging can now be used reliably to make dynamic time-course studies with excellent time resolution.     

1H NMR study of the α phase of Mg2NiHx system

Hydrogen behavior in the α phase of Mg₂NiH_x system was studied by ¹H NMR. ¹H NMR spectra and spin-lattice relaxation times, T₁ and T_1ρ, of Mg₂NiH_0.22 were measured in the temperature range between 100 and 480 K. The drastic change in the linewidth is observed between 170 and 340 K, and ¹H rigid lattice is observed below 170 K, from which it is deduced that the hydrogen atoms are randomly distributed in α-Mg₂NiH_x. The relaxation mechanism for t₁ is the paramagnetic one, while the T_1ρ value is determined partially by hydrogen diffusion. The hydrogen diffusion rate has been determined from the linewidth and the T_1ρ value. The paramagnetic relaxations observed in T₁ and T_1ρ have been discussed relating to the hydrogen diffusion.     

The effect of ultrasound treatment on the interaction of brine with pork meat proteins

The objective of the study is to elucidate the effect of ultrasound treated salt solution on curing of pork meat. The interactions of salt (NaCl) solutions of 3 and 25% with the proteins of pork meat are studied. High intensity ultrasound operating at 20 kHz was used. The differential scanning calorimetry (DSC), NMR spin-spin relaxation time, unfrozen water and water diffusion coefficient measurements were carried out in meat cured with ultrasound treated and untreated salt solutions. The effect of ultrasonication was most evident from measured spin-spin relaxation times T₂₁, the rate of chemical exchange of water protons k and the amount of unfrozen water W_unf in the meat. The measured diffusion coefficient of water D_w in meat cured with ultrasound treated and control salt solution did not show significant difference. The nuclear magnetic resonance (NMR) relaxation data, differential scanning calorimetry (DSC) and the diffusion coefficient data reliably show that the possible action of ultrasound to salt solution was manifested on the first 2 days of the experiment with a 3% salt solution.     

Investigation of proton diffusion in Nafion®117 membrane by electrical conductivity and NMR

The proton dynamics in Nafion ^®117 is investigated by comparison of the diffusion coefficient D_NMR estimated from PFG-NMR with that of D_σ estimated from electrical conductivity. At high water content region, D_σ is about two times higher than D_NMR as a result of Grotthuss mechanism. At low water content region, D_σ and D_NMR are in good agreement with each other. Both of the diffusion coefficients decrease steeply at low water content region. It can be explained as a result of the percolation transition due to the isolation of ion clusters, which is suggested by the recent small angle X-ray scattering data.     

NMR studies of hydrogen diffusion in hydrogen uranyl phosphate tetrahydrate (HUP)

¹H NMR spin-lattice relaxation times, T₁ (Zeeman) and T_1ϱ (rotating frame) and spin-spin relaxation times, T₂, and ³¹P NMR solid-echoes are reported for phase I and II of hydrogen uranyl phosphate tetrahydrate (HUP) at temperatures in the range 200–323 K. The spectral density functions extracted from the measured relaxation times for phases I and II are consistent with a 2D diffusion mechanism for hydrogen motion. ³¹P second moments determined from the solid-echoes show that all the hydrogens diffuse rapidly in phase I, and that the hydrogen-bond site nearest to the phosphate oxygen is not occupied in phase II. The mechanism for diffusion in phase II is discussed.