Spin-lattice Relaxation Time Constants Research Articles

Strain-dependent ultrafast carrier dynamics and spin–lattice interaction in LaMnO3 films

We investigate the ultrafast carrier dynamics and spin–lattice interaction in strained and unstrained LaMnO3 films via temperature-dependent femtosecond transient optical spectroscopy. The transient reflectivity measurements show two characteristic relaxation processes in both types of films, which are attributed to electron–phonon coupling and phonon-assisted spin–lattice interaction, respectively. The carrier dynamics and coupling between lattice and spin system are well described with the three-temperature model; the spin–lattice relaxation time constant is dominated by the temperature-dependent spin specific heat. Both the electron–phonon coupling and the spin–lattice interaction are enhanced in the strained film, as a result of the modified band structure and orbital ordering under biaxial compressive strain. Our results reveal the critical role of strain in the photo-induced dynamical interactions in LaMnO3.

Biomarkers of Cartilage Composition.

Magnetic resonance imaging (MRI) has significantly advanced the understanding of osteoarthritis (OA) because it enables visualization of noncalcified tissues. Cartilage is avascular and nurtured by diffusion, so it has a very low turnover and limited capabilities of repair. Consequently, prevention of structural and detection of premorphological damage is key in maintaining cartilage health. The integrity of cartilage composition and ultrastructure determines its mechanical properties but is not accessible to morphological imaging. Therefore, various techniques of compositional MRI with and without use of intravenous contrast medium have been developed. Spin-spin relaxation time (T2) and spin-lattice relaxation time constant in rotating frame (T1rho) mapping, the most studied cartilage biomarkers, were included in the recent standardization effort by the Quantitative Imaging Biomarkers Alliance (QIBA) that aims to make compositional MRI of cartilage clinically feasible and comparable. Additional techniques that are less frequently used include ultrashort echo time with T2*, delayed gadolinium-enhanced MRI of cartilage (dGEMRIC), glycosaminoglycan concentration by chemical exchange-dependent saturation transfer (gagCEST), sodium imaging, and diffusion-weighted MRI.

Solid-State mathrm {^3He} NMR of the Superconducting Rubidium Endofulleride mathrm {Rb_3(^3He@C_{60})}

A new variant of the superconducting fulleride Rb_3C_{60} is presented, with ^3He atoms encapsulated in the C_{60} cages. The ^3He nuclei act as sensitive NMR probes embedded in the material. The superconducting and normal states are characterized by ^3He NMR. Evidence is found for coexisting vortex liquid and vortex solid phases below the superconducting transition temperature. A strong dependence of the spin–lattice relaxation time constant on spectral frequency is observed in the superconducting state, as revealed by two-dimensional NMR utilizing an inverse Laplace transform. Surprisingly, this phenomenon persists, in attenuated form, at temperatures well above the superconducting transition.

Quantitative 1H NMR method for analyzing primaquine diphosphate in active pharmaceutical ingredients

Thermal analysis, Fourier Transform IR, the isotropic chemical shift of 1H NMR in different solvents, their temperature dependence and spin-lattice relaxation time constant (T1), solution 1D and 2D NMR, and solid-state 13C and 31P NMR (magic angle spinning NMR) were employed to obtain full information and elucidate the structures of primaquine diphosphate (PQD) samples used for quality controlling malaria medicines. Additionally, a simple, rapid, specific, and reliable quantitative method (qNMR) was developed to determine the PQD level in the raw material of active pharmaceutical ingredients (APIs). The method was developed using ethylene carbonate (EC) as the internal standard and dimethylsulfoxide-d6 (DMSO-d6) as the NMR solvent. For the API qNMR, 1H NMR signals at 3.82 and 1.22 ppm were used. The qNMR methodology, through the linearity, range, LOD and LOQ, stability, precision, robustness, and accuracy, was validated within the requirements of guidelines. The accuracy of the qNMR was evaluated by comparing it to a pharmacopeial HPLC technique and there were no statistical differences (p > 0.05). The proposed qNMR method authentically supports and endorses the current pharmacopoeial methods used for determining the PQD content.

The QIBA Profile for MRI-based Compositional Imaging of Knee Cartilage.

MRI-based cartilage compositional analysis shows biochemical and microstructural changes at early stages of osteoarthritis before changes become visible with structural MRI sequences and arthroscopy. This could help with early diagnosis, risk assessment, and treatment monitoring of osteoarthritis. Spin-lattice relaxation time constant in rotating frame (T1ρ) and T2 mapping are the MRI techniques best established for assessing cartilage composition. Only T2 mapping is currently commercially available, which is sensitive to water, collagen content, and orientation of collagen fibers, whereas T1ρ is more sensitive to proteoglycan content. Clinical application of cartilage compositional imaging is limited by high variability and suboptimal reproducibility of the biomarkers, which was the motivation for creating the Quantitative Imaging Biomarkers Alliance (QIBA) Profile for cartilage compositional imaging by the Musculoskeletal Biomarkers Committee of the QIBA. The profile aims at providing recommendations to improve reproducibility and to standardize cartilage compositional imaging. The QIBA Profile provides two complementary claims (summary statements of the technical performance of the quantitative imaging biomarkers that are being profiled) regarding the reproducibility of biomarkers. First, cartilage T1ρ and T2 values are measurable at 3.0-T MRI with a within-subject coefficient of variation of 4%-5%. Second, a measured increase or decrease in T1ρ and T2 of 14% or more indicates a minimum detectable change with 95% confidence. If only an increase in T1ρ and T2 values is expected (progressive cartilage degeneration), then an increase of 12% represents a minimum detectable change over time. The QIBA Profile provides recommendations for clinical researchers, clinicians, and industry scientists pertaining to image data acquisition, analysis, and interpretation and assessment procedures for T1ρ and T2 cartilage imaging and test-retest conformance. This special report aims to provide the rationale for the proposed claims, explain the content of the QIBA Profile, and highlight the future needs and developments for MRI-based cartilage compositional imaging for risk prediction, early diagnosis, and treatment monitoring of osteoarthritis.

Evaluation of fluorine-19 magnetic resonance imaging of the lungs using octafluorocyclobutane in a rat model.

PurposeTo test octafluorocyclobutane (OFCB) as an inhalation contrast agent for fluorine‐19 MRI of the lung, and to compare the image quality of OFCB scans with perfluoropropane (PFP) scansTheory and MethodsAfter normalizing for the number of signal averages, a theoretical comparison between the OFCB signal‐to‐noise ratio (SNR) and PFP SNR predicted the average SNR advantage of 90% using OFCB during gradient echo imaging. The OFCB relaxometry was conducted using single‐voxel spectroscopy and spin‐echo imaging. A comparison of OFCB and PFP SNRs was performed in vitro and in vivo. Five healthy Sprague‐Dawley rats were imaged during single breath‐hold and continuous breathing using a Philips Achieva 3.0T MRI scanner (Philips, Andover, MA). The scan time was constant for both gases. Statistical comparison between PFP and OFCB scans was conducted using a paired t test and by calculating the Bayes factor.ResultsSpin‐lattice (T1) and effective spin‐spin (T2∗) relaxation time constants of the pure OFCB gas were determined as 28.5 ± 1.2 ms and 10.5 ± 1.8 ms, respectively. Mixing with 21% of oxygen decreased T1 by 30% and T2∗ by 20%. The OFCB in vivo images showed 73% higher normalized SNR on average compared with images acquired using PFP. The statistical significance was shown by both paired t test and calculated Bayes factors. The experimental results agree with theoretical calculations within the error of the relaxation parameter measurements.ConclusionThe quality of the lung images acquired using OFCB was significantly better compared with PFP scans. The OFCB images had higher a SNR and were artifact‐free.

Investigation of the Li-ion conduction behavior in the Li10GeP2S12 solid electrolyte by two-dimensional T1-spin alignment echo correlation NMR

Li10GeP2S12 (LGPS) is the fastest known Li-ion conductor to date due to the formation of one-dimensional channels with a very high Li mobility. A knowledge-based optimization of such materials for use, for example, as solid electrolyte in all-solid-state batteries requires, however, a more comprehensive understanding of Li ion conduction that considers mobility in all three dimensions, mobility between crystallites and different phases, as well as their distributions within the material. The spin alignment echo (SAE) nuclear magnetic resonance (NMR) technique is suitable to directly probe slow Li ion hops with correlation times down to about 10−5 s, but distinction between hopping time constants and relaxation processes may be ambiguous. This contribution presents the correlation of the 7Li spin lattice relaxation (SLR) time constants (T1) with the SAE decay time constant τc to distinguish between hopping time constants and signal decay limited by relaxation in the τc distribution. A pulse sequence was employed with two independently varied mixing times. The obtained multidimensional time domain data was processed with an algorithm for discrete Laplace inversion that does not use a non-negativity constraint to deliver 2D SLR–SAE correlation maps. Using the full echo transient, it was also possible to estimate the NMR spectrum of the Li ions responsible for each point in the correlation map. The signal components were assigned to different environments in the LGPS structure.

Optimising magnetic resonance sampling patterns for parametric characterisation

Sampling strategies are often central to experimental design. Choosing efficiently which data to acquire can improve the estimation of parameters and reduce the acquisition time. This work is focused on designing optimal sampling patterns for Nuclear Magnetic Resonance (NMR) applications, illustrated with respect to the best estimate of the parameters characterising a lognormal distribution. Lognormal distributions are commonly used as fitting models for distributions of spin-lattice relaxation time constants, spin-spin relaxation time constants and diffusion coefficients. A method for optimising the choice of points to be sampled is presented which is based on the Cramér–Rao Lower Bound (CRLB) theory. The method’s capabilities are demonstrated experimentally by applying it to the problem of estimating the emulsion droplet size distribution from a pulsed field gradient (PFG) NMR diffusion experiment. A difference of <5% is observed between the predictions of CRLB theory and the PFG NMR experimental results. It is shown that CLRB theory is stable down to signal-to-noise ratios of ∼10. A sensitivity analysis for the CRLB theory is also performed. The method of optimizing sampling patterns is easily adapted to distributions other than lognormal and to other aspects of experimental design; case studies of optimising the sampling scheme for a fixed acquisition time and determining the potential for reduction in acquisition time for a fixed parameter estimation accuracy are presented. The experimental acquisition time is typically reduced by a factor of 3 using the proposed method compared to a constant gradient increment approach that would usually be used.

Long-lived states detect interactions between small molecules and diamagnetic metal ions

Long-lived states of nuclear spin order were used for the first time to probe interactions between molecules and diamagnetic metal ions. Proton spin states with lifetimes twice as long as the spin-lattice relaxation time constants of the same nuclei were promoted on the methoxyphenyl and tolyl substituents of a 1,3,4-oxadiazole derivative. The transient interaction of this oxadiazole derivative with silver(I) ions significantly speeds up the relaxation rate constants of proton long-lived states. The interactions between silver and organic compounds lead to the formation of coordination polymers that can be used for the preparation of bio-compatible materials.

Abstract TP60: T1 Rho Magnetic Resonance Imaging Can Detect and Quantify Acute Ischemic Stroke in Humans

Introduction: Establishing a timeline of acute ischemic stroke (AIS) onset is critically important for selecting time-sensitive treatments. However, there is currently no accepted imaging method for reliably dating stroke onset. T1 Rho MR is an investigative imaging modality for quantifying the spin lattice relaxation time constant in a rotating frame. T1 Rho is sensitive to chemical exchange, and in acute stroke, has been shown in animal models to increase linearly in the first 6 hours after onset of cerebral infarction, making it possible to accurately date onset. Hypothesis: We hypothesize that a rapid non-contrast T1 Rho MR sequence can be used to detect and quantify AIS in humans. Methods: AIS patients (n=11) underwent 3.0T brain MR scans in the late acute to subacute period after onset (mean 56 hours). The infarct volume was identified on DWI and infarct regions of interest (ROIs) were mapped onto the contralateral side to serve as within-subject controls. Infarct and control ROIs were co-registered with T1 Rho maps and compared using a Student t-test. Results: T1 Rho infarct volume correlated well to DWI volume and mean T1 Rho intensity values in the infarct, were significantly higher compared to controls (p&lt;0.004, mean difference 37ms, std 19.3). When inter-individual T1rho values were plotted against time from stroke onset, we found that they remained stable. Conclusion: T1 Rho MR is feasible, and can detect and quantify AIS in humans. Further, T1 Rho values in the infarct bed were stable in the late acute to early subacute time period, consistent with animal studies that show T1rho values to undergo predictable change only in the first 6 hours after infarct onset. Further studies are needed to determine if T1rho in humans has a predicable rate of change in the early acute phase, that can one day be used as a quantifiable surrogate of stroke onset and thus inform stroke therapy when time of onset is unknown.

Application of 13C NMR cross-polarization inversion recovery experiments for the analysis of solid dosage forms

Solid-state nuclear magnetic resonance (ssNMR) is a powerful and unique method for analyzing solid forms of the active pharmaceutical ingredients (APIs) directly in their original formulations. Unfortunately, despite their wide range of application, the ssNMR experiments often suffer from low sensitivity and peaks overlapping between API and excipients. To overcome these limitations, the crosspolarization inversion recovery method was successfully used. The differences in the spin-lattice relaxation time constants for hydrogen atoms T1(H) between API and excipients were employed in order to separate and discriminate their peaks in ssNMR spectra as well as to increase the intensity of API signals in low-dose formulations. The versatility of this method was demonstrated by different examples, including the excipients mixture and commercial solid dosage forms (e.g. granules and tablets).

Solution and Solid State Nuclear Magnetic Resonance Spectroscopic Characterization of Efavirenz

Samples of efavirenz (EFZ) were evaluated to investigate the influence of the micronization process on EFZ stability. A combination of X-ray diffraction, thermal analysis, FTIR, observations of isotropic chemical shifts of 1H in distinct solvents, their temperature dependence and spin-lattice relaxation time constants (T1), solution (1D and 2D) 13C nuclear magnetic resonance (NMR), and solid-state 13C NMR (CPMAS NMR) provides valuable structural information and structural elucidation of micronized EFZ and heptane-recrystallized polymorphs (EFZ/HEPT). This study revealed that the micronization process did not affect the EFZ crystalline structure. It was observed that the structure of EFZ/HEPT is in the same form as that obtained from ethyl acetate/hexane, as shown in the literature. A comparison of the solid-state NMR spectra revealed discrepancies regarding the assignments of some carbons published in the literature that have been resolved.

Errors in quantitative T1rho imaging and the correction methods.

The spin-lattice relaxation time constant in rotating frame (T1rho) is useful for assessment of the properties of macromolecular environment inside tissue. Quantification of T1rho is found promising in various clinical applications. However, T1rho imaging is prone to image artifacts and quantification errors, which remains one of the greatest challenges to adopt this technique in routine clinical practice. The conventional continuous wave spin-lock is susceptible to B1 radiofrequency (RF) and B0 field inhomogeneity, which appears as banding artifacts in acquired images. A number of methods have been reported to modify T1rho prep RF pulse cluster to mitigate this effect. Adiabatic RF pulse can also be used for spin-lock with insensitivity to both B1 RF and B0 field inhomogeneity. Another source of quantification error in T1rho imaging is signal evolution during imaging data acquisition. Care is needed to affirm such error does not take place when specific pulse sequence is used for imaging data acquisition. Another source of T1rho quantification error is insufficient signal-to-noise ratio (SNR), which is common among various quantitative imaging approaches. Measurement of T1rho within an ROI can mitigate this issue, but at the cost of reduced resolution. Noise-corrected methods are reported to address this issue in pixel-wise quantification. For certain tissue type, T1rho quantification can be confounded by magic angle effect and the presence of multiple tissue components. Review of these confounding factors from inherent tissue properties is not included in this article.

Detection of Iron Nanoparticles using Nuclear Magnetic Resonance Relaxometry and Inverse Laplace Transform

Department of Bioindustrial Machinery Engineering College of Agriculture and Life Sciences, Chonbuk National University, 567 Baekje-daero, Deokjin-gu, Jeonju-si 561-756, Republic of Korea Received: November 14th, 2014; Revised: November 24th, 2014; Accepted: November 26th, 2014 Purpose: Rapid detection of bacteria is very important in agricultural and food industries to prevent many foodborne illnesses. The objective of this study was to develop a portable nuclear magnetic resonance (NMR)-based system to detect foodborne pathogens (E. coli). This study was focused on developing a method to detect low concentrations of magnetic nanoparticles using NMR techniques. Methods: NMR relaxometry was performed to examine the NMR properties of iron nanoparticle mixtures with different concentrations by using a 1 T permanent magnet magnetic resonance imaging system. Exponential curve fitting (ECF) and inverse Laplace transform (ILT) methods were used to estimate the NMR relaxation time constants, T1 and T2, of guar gum solutions with different iron nanoparticle concentrations (0, 10-3, 10-4, 10-5, 10-6, and 10-7 M). Results: The ECF and ILT methods did not show much difference in these values. Analysis of the NMR relaxation data showed that the ILT method is comparable to the classical ECF method and is more sensitive to the presence of iron nanoparticles. This study also showed that the spin-spin relaxation time constants acquired by a Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence are more useful for determining the concentration of iron nanoparticle solutions comparwith the spin-lattice relaxation time constants acquired by an inversion recovery pulse sequence. Conclusions: We conclude that NMR relaxometry that utilizes CPMG pulse sequence and ILT analysis is more suitable for detecting foodborne pathogens bound to magnetic nanoparticles in agricultural and food products than using inversion recovery pulse sequence and ECF analysis.

An NMR thermometer for cryogenic magic-angle spinning NMR: The spin-lattice relaxation of 127I in cesium iodide

The accurate temperature measurement of solid samples under magic-angle spinning (MAS) is difficult in the cryogenic regime. It has been demonstrated by Thurber et al. (J. Magn. Reson., 196 (2009) 84-87) [10] that the temperature dependent spin-lattice relaxation time constant of 79Br in KBr powder can be useful for measuring sample temperature under MAS over a wide temperature range (20–296 K). However the value of T 1 exceeds 3 min at temperatures below 20 K, which is inconveniently long. In this communication, we show that the spin-lattice relaxation time constant of 127I in CsI powder can be used to accurately measure sample temperature under MAS within a reasonable experimental time down to 10 K.

Solvent-induced anomeric diastereoselectivity switching using a single glycosyl donor

Highly diastereoselective glycosylation reactions have been developed; however, not all glycosylation reactions are diastereoselective and these reactions have probably not been reported. For some fucosylation reactions, unusually low or abnormally opposite selectivities have been demonstrated. In the present study, the fucosylation reaction of long-chain hydrocarbon alcohols, ethyl 9-hydroxynonanoate and decanol using a series of the 2- O-benzyl-protected fucopyranosyl donors were investigated. The resulting products demonstrated the solvent-induced diastereoselectivity switching using diethyl ether (Et 2O) or dichloromethane (CH 2Cl 2). Practical α-selectivities were observed using ether solvents. In contrast, practical β-selectivities were observed using CH 2Cl 2. The anomeric diastereoselectivity switching was similarly observed in the alcohol galactosylation reaction. The larger spin-lattice relaxation time constant ( T 1) actually indicated that molecular motion of ethyl 9-hydroxynonanoate was more vigorous in Et 2O than in CH 2Cl 2, suggesting its dissociation in Et 2O and association in CH 2Cl 2. The bulkiness of the associated alcohols is most likely responsible for the observed diastereoselectivity.

Manganese enhanced MRI (MEMRI): neurophysiological applications

Manganese ion (Mn(2+)) is a calcium (Ca(2+)) analog that can enter neurons and other excitable cells through voltage gated Ca(2+) channels. Mn(2+) is also a paramagnetic that shortens the spin-lattice relaxation time constant (T(1)) of tissues where it has accumulated, resulting in positive contrast enhancement. Mn(2+) was first investigated as a magnetic resonance imaging (MRI) contrast agent approximately 20 years ago to assess the toxicity of the metal in rats. In the late 1990s, Alan Koretsky and colleagues pioneered the use of manganese enhanced MRI (MEMRI) towards studying brain activity, tract tracing and enhancing anatomical detail. This review will describe the methodologies and applications of MEMRI in the following areas: monitoring brain activity in animal models, in vivo neuronal tract tracing and using MEMRI to assess in vivo axonal transport rates.

Local mobility in grafted polydimethylsiloxane melts

Spin–lattice relaxation time constants, T 1, were studied for low-molecular-weight linear and grafted polydimethylsiloxane over a wide temperature and frequency range. Quantitative evaluations of proton T 1 measurements indicated two relaxation processes: anisotropic rotation of methyl groups around the Si–C bond (low temperature process) and motions of the PDMS side-chains connected with the glass transition (high temperature process). Additional analyses of the T 1 relaxation dispersion profiles revealed specific local segment fluctuation times, which are characteristic of the coherent motions in the grafted polymer chains.

Long-lived states to sustain hyperpolarized magnetization.

Major breakthroughs have recently been reported that can help overcome two inherent drawbacks of NMR: the lack of sensitivity and the limited memory of longitudinal magnetization. Dynamic nuclear polarization (DNP) couples nuclear spins to the large reservoir of electrons, thus making it possible to detect dilute endogenous substances in magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI). We have designed a method to preserve enhanced ("hyperpolarized") magnetization by conversion into long-lived states (LLS). It is shown that these enhanced long-lived states can be generated for proton spins, which afford sensitive detection. Even in complex molecules such as peptides, long-lived proton states can be sustained effectively over time intervals on the order of tens of seconds, thus allowing hyperpolarized substrates to reach target areas and affording access to slow metabolic pathways. The natural abundance carbon-13 polarization has been enhanced ex situ by almost four orders of magnitude in the dipeptide Ala-Gly. The sample was transferred by the dissolution process to a high-resolution magnet where the carbon-13 polarization was converted into a long-lived state associated with a pair of protons. In Ala-Gly, the lifetime T(LLS) associated with the two nonequivalent H(alpha) glycine protons, sustained by suitable radio-frequency irradiation, was found to be seven times longer than their spin-lattice relaxation time constant (T(LLS)/T(1) = 7). At desired intervals, small fractions of the populations of long-lived states were converted into observable magnetization. This opens the way to observing slow chemical reactions and slow transport phenomena such as diffusion by enhanced magnetic resonance.

Long‐lived States in Multiple‐Spin Systems

Long-lived spin states are excited in molecules featuring more than two isolated coupled spins, including amino acids. The figure shows the exponential recovery with the longest time-constant in aspartic acid, T1max=5.842±0.004 s, and of the decay of the long-lived state, TLLS=10.9±0.2 s). An improvement in spin memory by a factor 2 compared to longitudinal spin-lattice relaxation time constants is obtained for most systems.