Magnetic Resonance Spin-lattice Relaxation Rate Research Articles

Nuclear spin relaxation in aqueous paramagnetic ion solutions.

A Brownian shell model describing the random rotational motion of a spherical shell of uniform particle density is presented and validated by molecular dynamics simulations. The model is applied to proton spin rotation in aqueous paramagnetic ion complexes to yield an expression for the Larmor-frequency-dependent nuclear magnetic resonance spin-lattice relaxation rate T_{1}^{-1}(ω) describing the dipolar coupling of the nuclear spin of the proton with the electronic spin of the ion. The Brownian shell model provides a significant enhancement to existing particle-particle dipolar models without added complexity, allowing fits to experimental T_{1}^{-1}(ω) dispersion curves without arbitrary scaling parameters. The model is successfully applied to measurements of T_{1}^{-1}(ω) from aqueous manganese(II), iron(III), and copper(II) systems where the scalar coupling contribution is known to be small. Appropriate combinations of Brownian shell and translational diffusion models, representing the inner and outer sphere relaxation contributions, respectively, are shown to provide excellent fits. Quantitative fits are obtained to the full dispersion curve of each aquoion with just five fit parameters, with the distance and time parameters each taking a physically justifiable numerical value.

Continuous Matrix Product Operator Approach to Finite Temperature Quantum States.

We present an algorithm for studying quantum systems at finite temperature using continuous matrix product operator representation. The approach handles both short-range and long-range interactions in the thermodynamic limit without incurring any time discretization error. Moreover, the approach provides direct access to physical observables including the specific heat, local susceptibility, and local spectral functions. After verifying the method using the prototypical quantum XXZ chains, we apply it to quantum Ising models with power-law decaying interactions and on the infinite cylinder, respectively. The approach offers predictions that are relevant to experiments in quantum simulators and the nuclear magnetic resonance spin-lattice relaxation rate.

Solid state ¹H spin-lattice relaxation and isolated-molecule and cluster electronic structure calculations in organic molecular solids: the relationship between structure and methyl group and t-butyl group rotation.

We report ab initio density functional theory electronic structure calculations of rotational barriers for t-butyl groups and their constituent methyl groups both in the isolated molecules and in central molecules in clusters built from the X-ray structure in four t-butyl aromatic compounds. The X-ray structures have been reported previously. We also report and interpret the temperature dependence of the solid state (1)H nuclear magnetic resonance spin-lattice relaxation rate at 8.50, 22.5, and 53.0 MHz in one of the four compounds. Such experiments for the other three have been reported previously. We compare the computed barriers for methyl group and t-butyl group rotation in a central target molecule in the cluster with the activation energies determined from fitting the (1)H NMR spin-lattice relaxation data. We formulate a dynamical model for the superposition of t-butyl group rotation and the rotation of the t-butyl group's constituent methyl groups. The four compounds are 2,7-di-t-butylpyrene, 1,4-di-t-butylbenzene, 2,6-di-t-butylnaphthalene, and 3-t-butylchrysene. We comment on the unusual ground state orientation of the t-butyl groups in the crystal of the pyrene and we comment on the unusually high rotational barrier of these t-butyl groups.

An MRI digital brain phantom for validation of segmentation methods

Knowledge of the exact spatial distribution of brain tissues in images acquired by magnetic resonance imaging (MRI) is necessary to measure and compare the performance of segmentation algorithms. Currently available physical phantoms do not satisfy this requirement. State-of-the-art digital brain phantoms also fall short because they do not handle separately anatomical structures (e.g. basal ganglia) and provide relatively rough simulations of tissue fine structure and inhomogeneity. We present a software procedure for the construction of a realistic MRI digital brain phantom. The phantom consists of hydrogen nuclear magnetic resonance spin-lattice relaxation rate (R1), spin-spin relaxation rate (R2), and proton density (PD) values for a 24 × 19 × 15.5 cm volume of a "normal" head. The phantom includes 17 normal tissues, each characterized by both mean value and variations in R1, R2, and PD. In addition, an optional tissue class for multiple sclerosis (MS) lesions is simulated. The phantom was used to create realistic magnetic resonance (MR) images of the brain using simulated conventional spin-echo (CSE) and fast field-echo (FFE) sequences. Results of mono-parametric segmentation of simulations of sequences with different noise and slice thickness are presented as an example of possible applications of the phantom. The phantom data and simulated images are available online at http://lab.ibb.cnr.it/.

The H1 Nuclear Magnetic Resonance Spin-Lattice Relaxation Rate of Some Hydrated Synthetic and Natural Sands

The hydrogen nuclear magnetic resonance (NMR) spin-lattice relaxation rate [Formula: see text] of three fully hydrated natural sands was measured and compared to that for a fully hydrated synthetic sand as a function of applied magnetic field and particle diameter [Formula: see text]. [Formula: see text] values increased with decreasing particle diameter for both natural and synthetic sands. The increase in [Formula: see text] became greater with decreasing magnetic field strength. The field dependent [Formula: see text] data allowed the prediction of [Formula: see text] at the Earth’s magnetic field [Formula: see text]. Measurable [Formula: see text] differences were observed between the three natural sands, as well as the natural and a synthetic sand. The difference in [Formula: see text] of the natural sands can not be attributed to the geometric characteristics of the grains, as these were identical within experimental error. The [Formula: see text] differences can be attributed to trace paramagnetic impurities in the grains which influence the surface relaxation component of [Formula: see text]. These results show that it is unwise to predict aquifer characteristics based on [Formula: see text] values from nuclear magnetic resonance sounding without knowledge of the paramagnetic impurities in the sand grains. Furthermore, the results emphasize that laboratory measurements of [Formula: see text] should be performed at [Formula: see text].

Ion transport and diffusion in nanocrystalline and glassy ceramics

In the present paper we review experimental studies on ion transport and diffusion in nanocrystalline and glassy ceramics of LiNbO3 and LiAlSi2O6 and report on new ones on LiBO2 using the measurement of dc conductivities and 7Li nuclear magnetic resonance spin-lattice relaxation rates. Nanocrystalline ceramics, with an average particle size of 50 nm and less, often show an enhanced diffusivity compared to their microcrystalline (μm-sized) counterparts. This increase is due to the large fraction of atoms or ions located in the interfacial regions. A key for understanding the structure-mobility relations in nanocrystalline ceramics is to clarify the microscopic structure of the grain boundaries and also the morphology of the grain boundary network. In this context it is useful to study not only the ion transport properties of the nano- and microcrystalline materials but also those of the corresponding glassy forms. Such comparative studies gave strong evidence that in some cases the interfacial regions are of amorphous structure. For example, this was recently shown for nanocrystalline lithium niobate which was prepared by high-energy ball milling.

Critical slowing down of the spin dynamics in antiferromagnetic rings

Abstract We report 1 H nuclear magnetic resonance spin–lattice relaxation rates T 1 −1 vs. T at different magnetic field values, for molecular antiferromagnetic (AFM) rings with S Total =0 singlet ground state. New results in {CsFe8}, {Cr8} and {Fe6} are compared with previous results in {Fe6} and {Fe10}. In all cases a strong enhancement of T 1 −1 was observed with a maximum occurring at some temperature T 0 which is found to be field dependent. It is shown that the critical enhancement appears to be a robust universal feature in these AFM rings for which a general theory is still lacking.

Heisenberg spin triangles in{V6}-type magnetic molecules: Experiment and theory

We report the results of systematic experimental and theoretical studies of two closely related species of magnetic molecules of the type ${{\mathrm{V}}_{6}},$ where each molecule includes a pair of triangles of exchange-coupled vanadyl $({\mathrm{VO}}^{2+},$ spin $s=1/2)$ ions. The experimental studies include the temperature dependence of the low-field susceptibility from room temperature down to 2 K, the dependence of the magnetization on magnetic field up to 60 T for several low temperatures, the temperature dependence of the magnetic contribution to the specific heat, and the ${}^{1}\mathrm{H}$ and ${}^{23}\mathrm{Na}$ nuclear magnetic resonance spin-lattice relaxation rates ${1/T}_{1}.$ This body of experimental data is accurately reproduced for both compounds by a Heisenberg model for two identical uncoupled triangles of spins; in each triangle, the spins interact via isotropic antiferromagnetic exchange, where two of the three V-V interactions have exchange constants that are equal and an order of magnitude larger than the third; the ground-state eigenfunction has total spin quantum number $S=1/2$ for magnetic fields below a predicted critical field ${H}_{c}\ensuremath{\approx}74\mathrm{T}$ and $S=3/2$ for fields above ${H}_{c}.$

Conduction-electron mediated 1H nuclear spin-lattice relaxation in Ti45Zr38Ni17H x icosahedral quasicrystals

Nuclear magnetic resonance spin-lattice relaxation rates for 1H in quasicrystalline Ti45Zr38Ni17H x are presented as a function of temperature and hydrogen concentration x. The temperature dependence demonstrates that the relaxation is via interaction with conduction electrons. The relaxation rate is extremely sensitive to hydrogen content, with the rate changing by a factor of as much as two for samples that differ in x

Proton spin-lattice relaxation at low temperature in the ferromagnetic spin ring Cu6

We report H1 nuclear magnetic resonance spin-lattice relaxation rate (NSLR) measurements as a function of temperature (1.5–4.2 K) and as a function of applied magnetic field (0.2–8.2 T) in the molecular magnet [(PhSiO2)6Cu6(O2SiPh)6] in short Cu6. The results are explained in terms of a simple model whereby the NSLR is driven by the fluctuations of the local hyperfine field due to the reorientation of the total spin of the molecule in its ground state. From the analysis of the data, we infer the temperature and field dependence of the characteristic rate of the fluctuations of the total magnetization of the Cu6 ring in its ground state.

The role of proton nuclear magnetic resonance spin-lattice relaxation centers in the strong absorption transition at 210 nm in fused silica

The performance of fused silica for deep ultraviolet optical applications is adversely affected by a radiation-induced absorbance centered at 210 nm which is attributed to the formation of E′ centers. In this work, the 1H nuclear magnetic resonance spin-lattice relaxation rates, 1/T1 of various types of unirradiated fused silica were shown to be correlated to variations in the transmission at 210 nm (T210) that occurs upon irradiation. High concentrations of spin-lattice relaxation centers correlate with the ability to withstand larger numbers of 248 nm laser pulses before a sudden drop in T210, known as the strong-absorption transition (SAT), occurs. If irradiation is halted prior to the SAT, higher concentrations of these centers also correlate with faster rates of partial T210 recovery. We propose that these centers are diamagnetic defects consisting of an adjacent pair of silanol groups that release mobile hydrogen upon irradiation. This hydrogen can reversibly passivate E′ centers, thus accounting for the differences in partial recovery rates of T210 prior to SAT. We also propose the onset of the SAT corresponds to the consumption of all the irradiation susceptible silanol pair defects, after which no partial recovery of T210 is observed when laser irradiation has ceased.

Non-invasive determination of tumor oxygen tension and local variation with growth

Purpose : The objective was to develop and demonstrate a novel noninvasive technique of measuring regional pO 2 in tumors. The method is based on measuring 19F nuclear magnetic resonance spin-lattice relaxation rate ( R 1 = 1 T 1 ) of perfluorocarbon (PFC) emulsion discretely sequestered in a tumor. Methods and Materials : We have examined pO 2 in the Dunning prostate tumor R3327-AT1 implanted in a Copenhagen rat.Oxypherol blood substitute emulsion was administered intravenously and became sequestered in tissue. Proton magnetic resonance imaging (MRI) showed tumor anatomy and correlated 19F MRI indicated the distribution of perfluorocarbon. Fluorine-19 spectroscopic relaxometry was used to measure P02 in the tumor and repeated measurements over a period of 3 weeks showed the variation in local pO 2 during tumor growth. Results : Perfluorocarbon initially resided in the vascularized peripheral region of the tumor: 19F nuclear magnetic resonance R 1 indicated pO 2 ∼ 75 torr in a small tumor (∼1 cm) in an anesthetized rat. As the tumor grew, the sequestered PFC retained its original distribution. When the tumor had doubled in size the residual PFC was predominantly in the core of the tumor and the p02 of this region was ∼-1 torr indicating central tumor hypoxia. Conclusion : We have demonstrated a novel noninvasive approach to monitoring regional tumor pO 2. Given the critical role of oxygen tension in tumor response to therapy this may provide new insight into tumor physiology, the efficacy of various therapeutic approaches, and ultimately provide a clinical technique for assessing individual tumor oxygenation.

Ionic transport in glassy materials

Abstract A brief survey is given of some of the currently unresolved issues in the field of ionic conduction in glassy materials. An outline is then given of a recent microscopic model for ionic transport - the diffusion-controlled relaxation model - which can account for the behaviour of the a. c. conductivity and nuclear magnetic resonance spin-lattice relaxation rate observed experimentally in ionically conducting glasses.

Delineation of conformational dynamics in solution from1H and3H nuclear magnetic resonance spin–lattice relaxation rates

Nuclear magnetic resonance relaxation analysis has been carried out on 1H and 3H nuclei within the succinyl moiety of the following tripeptides: (i) succinyl-L-Prolyl-L-alanine: (ii)[2,3–2H]-succinyl-L-prolyl-L-alanine; (iii)[2,3–3H]-succinyl-L-prolyl-L-alanine. 1H–1H and 3H–3H dipolar relaxation terms were evaluated by measuring non-selective, single-selective and double-selective spin–lattice relaxation rates, yielding complete delineation of motional and conformational features. Rotamer fractional populations were calculated and used for unambiguously assigning all J couplings. Correlation times for both principal and internal reorientational motions could be evaluated at 0.33 and 0.09 ns, respectively, at 298 K. 3H n.m.r. relaxation investigations were shown to provide a very suitable aid to delineation of conformational dynamics in solution.

Oxygen-sensitive 19F NMR imaging of the vascular system in vivo

The fluorine nuclear magnetic resonance spin-lattice relaxation rate ( 1 T 1 ) of the perfluorochemical blood substitute perfluorotripropylamine (FTPA) is very sensitive to oxygen tension. This presents the possibility of measuring blood oxygen tension by 19F MR imaging. We obtained oxygen-sensitive 19F NMR images of the circulatory system of rats infused with emulsified FTPA. Blood oxygenation was assessed under conditions of both air- and 100% O 2-breathing. T 1 relaxation times were derived from MR images using a partial saturation pulse sequence. The T 1 times were compared with a phantom calibration curve to calculate average blood pO 2 values in the lung, liver, and spleen. The results showed marked, organ-specific increases in blood oxygen tension when the rat breathed 100% O 2 instead of air.

Hemoglobin-water interactions in normal and sickle erythrocytes by proton magnetic resonance T1 ϱ measurements

The dependence of the water proton magnetic resonance spin-lattice relaxation rate ( T 1 ϱ −1) in the rotating frame on the strength of the spin-locking ( H 1) field has been investigated for packed oxy and deoxy normal and sickle erythrocytes at temperatures from 9 to 40 °C. The T 1 ϱ −1 of oxy or deoxy normal erythrocytes shows no dependence on H 1 up to ~7 G at any temperature studied. On the other hand, T 1 ϱ −1 decreases from about 40 s −1 to 15 s −1 ( H 1 from 0 to ~7 G) for deoxygenated packed sickle cells at 40 °C. The magnitude of this variation of T 1 ϱ −1 with H 1 decreases with decreasing temperature. Oxy packed sickle cells also show a dependence of T 1 ϱ −1 on H 1 but the magnitude is <10% of that of the deoxygenated samples. These results suggest that water proton T 1 ϱ −1 measurements are a sensitive probe of hemoglobin S polymerization and provide a novel technique for the study of slow water motions in these systems. The T 1 ϱ −1 results are compared with low frequency T 1 −1 results of other investigators on hemoglobin S solutions. Analysis of the data suggests that water proton motions with correlation times of the order of 10 −5 s are present in the deoxygenated sickle cell samples at temperatures above 10 °C.