Magnetization Recovery Curves Research Articles

Orbital disorder and ordering in NaTiSi2O6 : Si29 and Na23 NMR study

${\mathrm{NaTiSi}}_{2}{\mathrm{O}}_{6}$ is an exemplary compound, showing an orbital assisted spin-Peierls phase transition at ${T}_{c}=210$ K. We present the results of $^{29}\mathrm{Si}$ and $^{23}\mathrm{Na}$ nuclear magnetic resonance (NMR) measurements of ${\mathrm{NaTiSi}}_{2}{\mathrm{O}}_{6}$. The use of magic angle spinning (MAS) techniques unambiguously shows that only one dynamically averaged silicon site can be seen at $T$ $>\phantom{\rule{4pt}{0ex}}{T}_{c}$. At cooling, the $^{29}\mathrm{Si}$ MAS NMR spectrum shows interesting changes. Immediately below ${T}_{c}$, the spectrum gets very broad. Cooling further, it shows two broad lines of unequal intensities which become narrower as the temperature decreases. Below 70 K, two narrow lines have chemical shifts that are typical for diamagnetic silicates. The hyperfine couplings for the two sites are $^{29}\mathrm{H}$ ${}_{\text{hf}}=7.4$ kOe/${\ensuremath{\mu}}_{B}$ and 4.9 kOe/${\ensuremath{\mu}}_{B}$. In the paramagnetic state at high temperature, the spin-lattice relaxation of $^{29}\mathrm{Si}$ was found to be weakly temperature dependent. Below ${T}_{c}$ the Arrhenius-type temperature dependence of the relaxation rate indicates an energy gap $\mathrm{\ensuremath{\Delta}}$/${\mathrm{k}}_{B}=1000(50)$ K. In the temperature region from 120 to 300 K, the relaxation rate was strongly frequency dependent. At room temperature, we found a power law dependence ${T}_{1}^{\ensuremath{-}1}\phantom{\rule{3.33333pt}{0ex}}\ensuremath{\propto}\phantom{\rule{3.33333pt}{0ex}}{\ensuremath{\omega}}_{L}^{\ensuremath{-}0.65(5)}$. For 70 K $<$ $T$ $<$ 120 K, the relaxation appeared to be nonexponential, which we assigned to a relaxation due to fixed paramagnetic centers. Simulation of the magnetization recovery curve showed activation type temperature dependence of the concentration of these centers. The NMR spectrum of $^{23}\mathrm{Na}$ shows the line with typical shape for the central transition of a quadrupolar nucleus. A small frequency shift of $^{23}\mathrm{Na}$ resonance corresponds to a very small hyperfine coupling $^{23}\mathrm{H}$ ${}_{\text{hf}}=0.32$ kOe/${\ensuremath{\mu}}_{B}$. In addition, at $T$ $>\phantom{\rule{4pt}{0ex}}{T}_{c}$ the $^{23}\mathrm{Na}$ spectrum shows another Lorentzian shaped resonance which we attribute to the Na sites where the quadrupolar coupling is partly averaged by ionic motion.

Intracellular Water Lifetime as a Tumor Biomarker to Monitor Doxorubicin Treatment via FFC-Relaxometry in a Breast Cancer Model.

This study aims to explore whether the water exchange rate constants in tumor cells can act as a hallmark of pathology status and a reporter of therapeutic outcomes. It has been shown, using 4T1 cell cultures and murine allografts, that an early assessment of the therapeutic effect of doxorubicin can be detected through changes in the cellular water efflux rate constant kio. The latter has been estimated by analyzing the magnetization recovery curve in standard NMR T1 measurements when there is a marked difference in the proton relaxation rate constants (R1) between the intra- and the extra-cellular compartments. In cellular studies, T1 measurements were carried out on a relaxometer working at 0.5 T, and the required difference in R1 between the two compartments was achieved via the addition of a paramagnetic agent into the extracellular compartment. For in-vivo experiments, the large difference in the R1 values of the two-compartments was achieved when the T1 measurements were carried out at low magnetic field strengths. This task was accomplished using a Fast Field Cycling (FFC) relaxometer that was properly modified to host a mouse in its probe head. The decrease in kio upon the administration of doxorubicin is the result of the decreased activity of Na+/K+-ATPase, as shown in an independent test on the cellular uptake of Rb ions. The results reported herein suggest that kio can be considered a non-invasive, early and predictive biomarker for the identification of responsive patients immediately from the first doxorubicin treatment.

Magnetic inhomogeneity in charge-ordered La1.885Sr0.115CuO4 studied by NMR

We report the inverse Laplace transform (ILT) analysis of the $^{139}$La nuclear spin-lattice relaxation rate $1/T_1$ in charge ordered La$_{1.885}$Sr$_{0.115}$CuO$_4$ ($T_{charge} \sim 80$K, $T_{c} \simeq T_{spin}^{neutron}=30$K), and shed new light on its magnetic inhomogeneity. We deduce the probability density function $P(1/T_{1})$ of the distributed $1/T_1$ (i.e. the histogram of distributed $1/T_1$) by taking the inverse Laplace transform of the experimentally observed nuclear magnetization recovery curve $M(t)$. We demonstrate that spin freezing sets in in some domains precisely below the onset of charge order at $T_{charge}$, but their volume fraction grows only gradually toward $T_{c}$. Nearly a half of the sample volume exhibits properties expected for canonical high $T_c$ cuprates without charge order even near $T_c$. Our findings explain why charge order does not suppress $T_c$ of La$_{1.885}$Sr$_{0.115}$CuO$_4$ as significantly as in La$_{1.875}$Ba$_{0.125}$CuO$_4$.

Saturation capability of short phase modulated pulses facilitates the measurement of longitudinal relaxation times of quadrupolar nuclei

The ability of various pulse types, which are commonly applied for distance measurements, to saturate or invert quadrupolar spin polarization has been compared by observing their effect on magnetization recovery curves under magic-angle spinning. A selective central transition inversion pulse yields a bi-exponential recovery for a diamagnetic sample with a spin-3/2, consistent with the existence of two processes: the fluctuations of the electric field gradients with identical single (W1) and double (W2) quantum quadrupolar-driven relaxation rates, and spin exchange between the central transition of one spin and satellite transitions of a dipolar-coupled similar spin. Using a phase modulated pulse, developed for distance measurements in quadrupolar spins (Nimerovsky et al., JMR 244, 2014, 107–113) and suggested for achieving the complete saturation of all quadrupolar spin energy levels, a mono-exponential relaxation model fits the data, compatible with elimination of the spin exchange processes. Other pulses such as an adiabatic pulse lasting one-third of a rotor period, and a two-rotor-period long continuous-wave pulse, both used for distance measurements under special experimental conditions, yield good fits to bi-exponential functions with varying coefficients and time constants due to variations in initial conditions. Those values are a measure of the extent of saturation obtained from these pulses. An empirical fit of the recovery curves to a stretched exponential function can provide general recovery times. A stretching parameter very close to unity, as obtained for a phase modulated pulse but not for other cases, suggests that in this case recovery times and longitudinal relaxation times are similar. The results are experimentally demonstrated for compounds containing 11B (spin-3/2) and 51V (spin-7/2). We propose that accurate spin lattice relaxation rates can be measured by a short phase modulated pulse (<1–2ms), similarly to the "true T1" measured by saturation with an asynchronous pulse train (Yesinowski, JMR 252, 2015, 135–144).

1H NMR T 1 Relaxation of Polymer/Montmorillonite Nanocomposites with Different Clay Contents and Degrees of Exfoliation: Magnetic Field Effects

Abstract The initial stage of the NMR 1H T 1 relaxation of well-defined polypropylene-montmorillonite nanocomposites was investigated at two different magnetic fields of 0.54 and 7.05 T. At 0.54 T, two periods can be distinguished during the first 30 ms after a saturation pulse train. Both periods scale linearly with the square root of the recovery time. The first period occurs during the first 1 ms and is attributed to direct dipolar relaxation of nuclei in immediate proximity to the clay. It is caused by paramagnetic impurities within the clay and is characterized by a magnetization recovery curve with a slope proportional to the concentration of these impurities. The second period occurs at 4 to 30 ms after saturation and is due to spin diffusion between the sink, formed by the initial relaxation at the clay surface, and the surrounding polymer matrix, which relaxes at a much slower rate. The second period is characterized by a magnetization recovery curve with a slope proportional to the effective surface area of the clay, from which a degree of exfoliation may be determined. At 7.05 T, only a single relaxation recovery period is observed. At this higher magnetic field, the direct relaxation is characterized by a substantially longer relaxation time so that it is not distinguished from the spin-diffusion process. As with the slope of the second period of the magnetization recovery at 0.54 T, the slope of the magnetization recovery curve at 7.05 T can be utilized to extract a degree of exfoliation.

Single-shot nuclear magnetization recovery curves with force-gradient detection.

We measure the spin-lattice relaxation time as a function of sample temperature in GaAs in a real-time single-shot inversion recovery experiment using spin force gradients acting on a magnetic tipped cantilever. After inverting 69Ga spins localized near the magnet with a single 20 ms adiabatic rapid passage sweep, the spins' magnetization recovery was passively tracked by recording the cantilever's frequency change, which is proportional to the longitudinal component of the spins' magnetization. The cantilever's frequency was recorded for a time 3*T1 for sample temperatures ranging from 4.8 to 25 K. The temperature dependence was observed for the 69Ga quadrupolar relaxation interaction.

Rapid T1 mapping of mouse myocardium with saturation recovery look‐locker method

Dynamic contrast-enhanced MRI using gadolinium or manganese provides unique characterization of myocardium and its pathology. In this study, an electrocardiography (ECG) triggered saturation recovery Look-Locker method was developed and validated for fast cardiac T(1) mapping in small animal models. By sampling the initial portion of the longitudinal magnetization recovery curve, high temporal resolution (∼ 3 min) can be achieved at a high spatial resolution (195 × 390 μm2) in mouse heart without the aid of parallel imaging or echo-planar imaging. Validation studies were performed both in vitro on a phantom and in vivo on C57BL/6 mice (n = 6). Our results showed a strong agreement between T(1) measured by saturation recovery Look-Locker and by the standard saturation recovery method in vitro or inversion recovery Look-Locker in vivo. The utility of saturation recovery Look-Locker in dynamic contrast-enhanced MRI studies was demonstrated in manganese-enhanced MRI experiments in mice. Our results suggest that saturation recovery Look-Locker can provide rapid and accurate cardiac T(1) mapping for studies using small animal models.

TH‐D‐201C‐02: Rapid T1 Mapping of Myocardium and Left Ventricle Blood for Small Animals Using Saturation Recovery Look‐Locker Method

Purpose: Dynamic contrast enhanced MRI (DCE‐MRI) has been increasingly used to delineate cardiac patho‐physiological conditions such as tumor and infarction. The time course of contrast agent in tissue and blood is required for quantitative analysis. However the sampling of contrast agent dynamics is challenging for small animal models because of the fast heart beat and blood circulation. Current study aims to develop and validate a rapid T1 mapping method for simultaneous quantification of myocardium and blood contrast agent concentrations in small animal DCE‐MRI studies. Method and Materials: An ECG‐triggered saturation recovery Look‐Locker (SRLL) method was developed for T1 estimation by sampling the initial portion of the longitudinal magnetization recovery curve. Monte‐Carlo simulations were conducted for error analysis and parameter optimization. Validation was performed on both phantom and mouse heart in vivo (n=7). SRLL and keyhole sampling scheme was also jointly applied in a manganese enhanced MRI experiment to show its practical utility. Results: Simulations showed that SRLL can provide accurate T1 estimation despite of heart rate fluctuation and field inhomogeneity. This was validated in both phantom and in vivo mouse heart by a strong agreement between T1 measured by SRLL and by the standard inversion recovery Look‐Locker method. The myocardium and blood T1 values were also consistent with the literature. No significant changes in SRLL measured T1 were found by the application of keyhole method. In the manganese enhanced MRI experiment T1 continuously decreased during MnCl2 injection and remained unchanged during the 15 min post infusion period. Conclusion: Our results indicate that SRLL can provide a robust measurement of myocardium and blood T1 in mice at high spatial (195×390 μm2) and temporal (3 min) resolutions. The application of keyhole can further reduce the imaging time to less than 2 min.

NMR of Liquid 3He in Pores of a Clay Sample

In the present work a new method for studying porous media by nuclear magnetic resonance of liquid 3He has been proposed. This method has been demonstrated by an example of a clay mineral sample. For the first time the integral porosity of the clay sample has been measured. For investigated samples the value of the integral porosity is in the range of 10–30%. The inverse Laplace transform of the 3He longitudinal magnetization recovery curve has been carried out and the distribution of the relaxation times T 1 has been obtained.

Evolution of Clay Morphology in Polypropylene/Montmorillonite Nanocomposites upon Equibiaxial Stretching: A Solid-State NMR and TEM Approach

Solid-state NMR and TEM were used to quantitatively examine the evolution of clay morphology upon equibiaxial stretching of polypropylene/montmorillonite (PP−MMT) nanocomposites up to a stretch ratio (λ = final length/initial length) of 3.5. 1H spin−lattice relaxation times were measured by the saturation−recovery sequence. For the nanocomposites, initial portions of the magnetization recovery curves (≤∼20 ms) were found to depend on √t, indicative of diffusion-limited relaxation and in agreement with calculations based on estimates of the spin-diffusion barrier radius surrounding the paramagnetic centers in the clay, the electron−nucleus coupling constant, and the spin-diffusion coefficient. Initial slopes of these magnetization recovery curves directly correlated with the fraction of clay/polymer interface. New clay surface was exposed as a near linear function of strain. Long-time portions of the magnetization recovery curves yielded information on the average interparticle separations, which decreased slowly before reaching a plateau at λ = ∼2.5 as particles aligned. TEM images supported these findings and were used to define and quantify degrees of exfoliation and homogeneity from the NMR data. Exfoliation, defined as (platelets/stack)−1, increased from 0.38 (unstretched) to 0.80 at λ = 3.5 for PP−MMT nanocomposites stretched at 150 °C and 16 s−1. A lower stretch temperature, 145 °C, which is slightly below melting onset, led to an exfoliation degree of 0.87 at λ = 2.8, consistent with the ability of higher melt viscosities to allow for higher shear stress transfer. Exposure of new clay surface is attributed to aggregate breakup and orientation at low strains (λ ≤ ∼2) and to platelets sliding apart at higher strains.

Structural characterization of sputtered hydrogenated amorphous carbon films by solid state nuclear magnetic resonance

Solid state nuclear magnetic resonance (NMR) methods have been used to investigate the effect of H content on the structure of sputtered hydrogenated amorphous carbon a-C:H films. Carbon-13 NMR spectra of a-C:H consist of two broad peaks at 135 and 40 ppm, which correspond to the sp2 and sp3 carbons, respectively. Surprisingly, the sp2/sp3 carbon ratio (2.0±0.3) is relatively independent of the H content in the range of 13%–35%. Hence, all a-C:H films contain approximately 66% graphitelike sp2 carbon. Cross polarization and spectral editing experiments reveal that the nonprotonated (quaternary) sp3 carbon fraction reaches as high as 30% at low H concentrations of 13%–23%. As the H content exceeds 23%, however, quaternary carbon bonds are terminated by H atoms to form protonated sp3 carbons, such as methylene (CH2) and methine (CH). Our results show that the hardness of a-C:H correlates with the quaternary carbon fraction rather than the sp2/sp3 ratio, as commonly believed. We also report the first extensive studies of both H1 and C13 spin-lattice relaxation for sputtered a-C:H. Relaxation data for hydrogen and carbon indicate that the unpaired electrons are probably equally distributed among sp2 and sp3 carbons. Moreover, the number of unpaired electrons in the a-C:H samples is relatively independent of H content, as revealed by spin counting experiments. C13 and H1 magnetization recovery curves for samples with H content up to 28% can be fitted with a single exponential, which is in contrast to the biexponential behavior reported for plasma-enhanced chemical vapor deposition (PECVD) a-C:H films. Hence, our results for sputtered a-C:H films do not support the model of proton-rich and proton-deficient regions proposed for PECVD carbon.

Coexistence of antiferromagnetism and superconductivity in CeCo(In 0.9Cd 0.1) 5: A spin lattice relaxation study

We present an In(1) NQR study on the heavy-fermion (HF) compound CeCo(In 1− x Cd x ) 5 ( x = 0.10 ) . Bulk measurements indicate that Cd doping acts as an electronic tuning agent in CeCoIn 5, and that superconductivity (SC) and antiferromagnetism (AFM) may coexist at ambient pressure for 0.05 < x < 0.15 . For x = 0.10 , the nuclear spin lattice relaxation rate shows a broad peak at the Néel temperature T N = 2.8 K , with a subsequent onset of SC at T c ≃ 1.2 K . Our results provide strong evidence for microscopic coexistence of these two ground states. The nuclear magnetization recovery curves in both the ordered and mixed states reveal a single T 1 -component, which suggests a homogeneous nature of the Ce-4f 1 electronic state.

Bayesian image decomposition applied to relaxographic imaging

AbstractT1 relaxographic imaging is a precise and accurate way to characterize tissue. A number of fast MRI acquisition techniques allow both spatial and magnetization recoveries to be well sampled in reasonable imaging times. However, two limitations common to the analysis of relaxographic imaging data are (1) the assumption of single exponential behavior for each image voxel and (2) the treatment of each pixel as an independent entity. The first assumption disregards tissue heterogeneity known to be present and reduces the information content that can be extracted. The latter assumption reduces both the modeling stability and the accuracy of extracted parameters. A new method that overcomes these limitations is presented here. The method, Bayesian Image Decomposition, recovers individual tissue type magnetization recovery curves and their corresponding tissue‐specific relaxographic images (i.e. segmented images) from a series of inversion recovery images. The general form of the decomposition is given together with its specific implementation to longitudinal relaxographic imaging. The method is validated by comparison of the results with those of the standard method and by comparison across data sets. A specific advantage of the new method is the ability to determine fractional contributions of tissue subtypes to each image voxel. © 2005 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 15;2–9, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.20033

Components and fractions for differently bound water molecules of dipalmitoylphosphatidylcholine–water system as studied by DSC and 2H-NMR spectroscopy

Differently bound water molecules of dipalmitoylphosphatidylcholine (DPPC)–H 2O system were investigated with differential scanning calorimetry (DSC). According to a method previously reported by us, the ice-melting DSC curves of the DPPC–H 2O samples of varying water contents were deconvoluted into multiple components, and the ice-melting enthalpies for the individual deconvoluted components were used to estimate average molar ice-melting enthalpies for freezable interlamellar and bulk waters, respectively. With these average molar ice-melting enthalpies, the numbers of differently bound water molecules of the DPPC–H 2O system were calculated at varying water contents and were used to construct a water distribution diagram of this system. Furthermore, to evaluate the reliability of the present DSC deconvolution method, 2H-NMR T 1 measurements of DPPC– 2H 2O system were carried out at 5 °C of the gel phase temperature, and components and fractions for differently bound water ( 2H 2O) molecules were estimated from the analysis of nonexponential magnetization recovery curves.

Proton spin–lattice relaxation study of the hydration of self-stressed expansive cement

Proton spin–lattice relaxation, compressive strength, and water tightness measurements have been undertaken in order to study the hydration process and the mechanical properties of Portland cement modified with a calcium sulfoaluminate-based expansive additive (EXPAD). The compression strength of the modified cement was more than 70% higher while water permeability was about 60% smaller than in the unmodified cement. Magnetization–recovery curves analysis allowed for a time-resolved monitoring of both the increase of the internal surface as well as the formation of solid products during the hydration. A significant difference between the hydration kinetics of modified and unmodified cement was observed.

Multinuclear NMR/NQR study of HgBa 2CuO 4+ xF y superconductors with different oxygen and fluorine content

We have measured 63,65Cu NMR/NQR spectra, 199Hg and 19F NMR spectra and spin-lattice relaxation rate on a series of powder HgBa 2CuO 4+ x F y samples with different oxygen and fluorine content. Comparison of 63Cu and 199Hg relaxation data to numerical calculations for several types of the order parameter symmetry gives the best coincidence with the d-wave symmetry. 19F NMR line width and relaxation rate are strongly influenced by the magnetic flux-line motion. The 19F magnetization recovery curve is described by a stretched exponential function. The 19F spin-lattice relaxation strongly depends on the fluorine content evidencing that at higher doping level part of F atoms occupy the apical O2 position.

Nuclear magnetic resonance and electron spin resonance of amorphous hydrogenated carbon

The temperature dependences of the and magnetization recovery and spin-lattice relaxation times as well as the NMR spectra have been studied between 300 K and 4 K. The observed short and nearly temperature independent proton and spin-lattice relaxation times demonstrate that the dominant spin-lattice relaxation mechanism is spin diffusion to paramagnetic impurities. The fact that the magnetization recovery curves clearly deviate from the single-exponential form expected for the case of spin diffusion and randomly distributed paramagnetic centres demonstrates that the paramagnetic centres aggregate in clusters. Superparamagnetic freezing effects expected for such an inhomogeneous distribution are indeed seen below 50 K in the temperature dependence of the electron spin-resonance (ESR) intensity, the NMR spectra and the SQUID magnetization measurements which show a distinct magnetic hysteresis loop.

23Na Nuclear Spin-Lattice Relaxation in Dehydrated Zeolite NaY

Abstract The spin-lattice relaxation time T1 of 23Na-NMR in dehydrated zeolite NaY has been measured from 26 to 300 K. The magnetization recovery curve is not single-exponential at all measured temperatures and T1 -1 increases in proportion to the square of temperature above 200 K. The result is analyzed with a theory of the Raman process based on covalency. The value of T1 is compared with that of NaX in which the concentration of Na is about 2 times larger than in NaY.

13C and 1H spin-lattice relaxation in amorphous hydrogenated carbon

The temperature dependences of the 13C and 1H magnetization recovery and spin-lattice relaxation times have been measured in amorphous hydrogenated carbon ( a-C : H). The observed short and nearly temperature independent proton and 13C spin-lattice relaxation times demonstrate that the dominant spin-lattice relaxation mechanism is spin diffusion to paramagnetic impurities. The fact that the magnetization recovery curves clearly deviate from the single exponential form demonstrates that the paramagnetic centers aggregate in clusters so that the unpaired electron distribution in a-C : H is strongly inhomogeneous.

Dynamics of sodium ions in NaClO4 complexed in poly(propylene-oxide): A 23Na nuclear magnetic resonance study

Amorphous poly(propylene oxide), PPO (molecular weights, 425 and ∼106), complexed with NaClO4 salt has ionic conductivities as high as 10−5 S/cm at room temperature. In an attempt to directly study the dynamics of the Na+ ions, (I=3/2) nuclear magnetic resonance (NMR) spin-lattice relaxation times, T1, and spin–spin relaxation times, T2, at a resonance frequency of 77.0 MHz have been measured over the temperature range from 150 to 390 K. A range of salt compositions [(PPO)nNaClO4; n=8–30] have been investigated. In addition, the glass transition temperature for each sample is reported. The recovery of equilibrium magnetization following a π/2 pulse is biexponential as expected for a spin I=3/2 system in the viscous liquid region. Below Tg a better fit to the magnetization recovery curve can be obtained if Kohlrausch–Williams–Watts (KWW) functions are used in place of the exponential functions. At low temperature the molecular motion has slowed to the point where a common spin temperature is not achieved by ionic diffusion. Two T2 values are observed over a limited temperature region near the T1 minimum. In the remaining low temperature region only the T2 associated with the central transition could be determined because the large 23Na quadrupole coupling constant made detection of the satellite transitions impossible. There is no evidence from the NMR relaxation time data for two Na+ populations. The experimental spin-lattice relaxation times can be analyzed to determine the correlation time for the ionic motion as a function of reciprocal temperature. The correlation time data display a distinct change in behavior at Tg which is interpreted as an indication of a crossover between two ionic transport mechanisms. Plots of T1 as a function of Tg/T indicate that dynamics for T&amp;gt;Tg are largely determined by the flexibility of the polymer host (the α process) whereas a different process dominates for T&amp;gt;Tg (presumably the β process). A comparison of correlation times derived from NMR relaxation times and ionic conductivities show a marked difference especially in the region of Tg. The conductivity decreases rapidly while the sodium ion motion continues with a correlation time ∼10−6 s through the glass transition.