Applied Magnetic Resonance最新文献

Sample preparation for metabolomics does not follow a standardized procedure, often involving various sampling and storage methods, with solvent storage, such as in ethanol, sometimes used when immediate freezing is not possible or feasible. While convenient, solvent storage raises concerns about passive metabolite extraction from tissues—a potentially valuable but overlooked process for isolating biomolecules. Thus, while chemical storage conditions are suboptimal for metabolomics analysis, there exists untapped potential for passive extraction of valuable metabolites. This study investigated the potential for metabolite diffusion into ethanol during storage of Thyone aurea, a little-known sea cucumber species endemic to the Western Coastlines surrounding Southern Africa. Samples from Saldanha Bay were collected during summer and winter and, due to the time lapse between collection and analysis, were stored in 100% ethanol. Untargeted analysis on the crude ethanolic storage extract using ¹H-NMR metabolomics and full-scan UPLC-QTOF-MS revealed significant metabolite diffusion, with compounds linked to energy metabolism, immune response, osmoregulation, and tissue integrity. Seasonal variation showed higher compound abundance in summer. These results underscore the potential impact of solvent storage during metabolomics studies and highlight the need to assess both storage solvents and tissues in such analyses. In addition, the presence of unidentifiable compounds suggests storage ethanolic extracts from T. aurea as a promising source of novel metabolites, warranting further research to explore its biochemical and therapeutic potential.

This review examines the theoretical frameworks underlying electron magnetic resonance (EMR) and optical spectroscopy, with particular focus on the historical development and applications of tensor operators in interpreting spectroscopic data. Our motivation is to establish unequivocally the legacy of K.W.H. Stevens as a brilliant scholar of his epoch. The evolution from physical Hamiltonians to effective spin Hamiltonians is delineated, focusing on systems exhibiting orthorhombic, monoclinic, and triclinic site symmetry, where precise theoretical formulations are essential for accurate data interpretation. It highlights J.R. Pilbrow's seminal contributions to EPR spectroscopy of 3d^N transition ions and his classification of low symmetry effects. A comprehensive assessment of tesseral tensor operators (TTO) and spherical tensor operators (STO), clarifying their relationship and appropriate applications in describing the zero-field splitting (ZFS) is provided. The key features of triclinic ZFS Hamiltonian are explained. The theoretical foundations of various Stevens-type operators, referred to as usual (USO), extended Stevens-type operators (ESO), and generalized extended Stevens-type operators (GESO) operators are examined, demonstrating that the selection of TTO versus STO should be guided by practical considerations rather than preconceived notion. The significance and wide usage of the USO and/or ESO is pointed out by referencing relevant books and reviews. The terminological inconsistencies identified in the recent literature, concerning, e.g. the key notions, distinctions between ZFS and crystal/ligand field (CF/LF) frameworks, and interchangeability of TTO versus STO formalisms, are discussed in the Appendix. The historical developments and key notions are elucidated to provide valuable insights in EMR, optical spectroscopies, magnetism and related areas.

The results of studies of NMR and spin relaxation in solids are systematized and discussed under the conditions when three or more nuclei of single species are simultaneously involved in the elementary event of their dipole interactions but not two nuclei as is ordinarily the case. Such interactions are clearly manifested in the magically oriented singly, doubly, and triply rotating frames (RFs). A number of effects in RFs NMR and spin relaxation are described which are explicitly specified by the many-spin homo-nuclear dipolar interactions. The studies were carried out by the method of direct recording of NMR in the strong effective magnetic field in the single magic-angle RF at comparatively low-resonance frequency. A modification of the standard coherent pulsed NMR spectrometer is described, which makes it capable to carry out similar measurements at the high frequency in a large polarizing magnetic field. In contrast to the low-frequency direct method, the measurements by the modified high-frequency one are carried out point-by-point by multiple repetitions of the experiment, much as the spin–lattice relaxation time is measured in the single-resonant RF in the standard continuous spin-locking experiments.

Dephasing relaxation and quantum entanglement are studied in a two-spin-1/2 system with the dipole–dipole interaction on a basis of the Lindblad equation in multiple-quantum NMR experiments. A multiple-quantum (MQ) NMR dynamics is investigated. It is shown that MQ NMR spectrum consists of only MQ NMR coherences of zeroth- and plus/minus-second orders. Intensities of MQ NMR coherences are calculated. Quantum correlations (entanglement) are also considered. The relationship between entanglement and the MQ NMR coherence of the second order is also investigated.

Recently, interest to the Ga–In binary alloy increased remarkably because of its new applications in biology, medicine, flexible robotics, and wearable electronics. We present detailed studies of the evolution of the ⁷¹ Ga and ¹¹⁵In NMR spectra within the temperature range between the complete melted and complete frozen states of the bulk Ga–In alloy aimed to find evidences for the liquid–liquid transition. The Ga–In alloy composition was close to the eutectic point for α-Ga. While the structural transformations were revealed in the supercooled pure gallium and some gallium alloys under nanoconfinement, they were not found in their bulk counterparts, in spite of being theoretically predicted for pure gallium. Changes in the lineshapes and line splitting were found for both gallium and indium isotopes between 277 and 268 K upon cooling and between 250 and 260 K upon warming. The resonance lines within these temperature ranges were deconvolved into two components. Measurements during additional thermal cycles and the analysis of the Knight shifts and intensities of the components proved the occurrence of the liquid–liquid-phase transitions.

NMR studies of spin–lattice relaxation were carried out for two gallium isotopes, ⁶⁹Ga and ⁷¹Ga, for an undoped semi-insulator GaAs crystal under the additional continuous magnetic saturation of the nuclear spin systems at the Larmor frequencies. The magnetization recovery after inversion was observed within the temperature range from 80 to 300 K using a Bruker Avance 400 pulse spectrometer. Two main contributions to relaxation due to the hyperfine coupling with the electron centers accompanied by spin diffusion and due to the spin–phonon interaction in the regular crystal lattice were separated by suppressing the first one. Both contributions to relaxation were found to be of the quadrupole nature and followed the temperature dependence predicted for quadrupole relaxation owing to the modulation by thermal phonons of the electric field gradients at nuclei. The results obtained are consistent with the suggestion that the quadrupole hyperfine coupling dominates for nuclei in the neighborhood of the electron centers and the rapid spin diffusion approximation is satisfied.

The food industry is creating a diverse range of plant-based alternatives to dairy products, due to the increasing demand from consumers for more sustainable, healthy, and ethical products. Since such products are often more expensive than conventional cow’s milk products, quick, accurate and low-cost instrumental method is necessary to prove the labelling claim. The objective of the research was to examine the use of low-field ¹H-NMR spectroscopy at 80 MHz to differentiate between vegan and non-vegan dairy products as well as among different botanical origins of vegan products. More than 100 samples of vegan and non-vegan products (yoghurt, milk, (cooking) cream, cottage cheese and condensed milk), which are representative of the German market, were investigated. Carbohydrate profile, in particular lactose, glucose, sucrose and galactose, extracted in aqueous phase, can be used to differentiate lactose-free, lactose-containing and plant surrogates. Supplementary information is hidden in fatty acids profile of the investigated products. Exploratory analysis based on principal component analysis (PCA) confirmed and supplemented findings of visual spectra interpretation. Low-field NMR can be a quicker and cheaper alternative to conventional techniques for food label control from both animal and botanical origin.

Tooth radiation dosimetry using an in vivo electron paramagnetic resonance (EPR) spectrometer serves as a triage method for victims in large-scale radiation emergencies, such as the Fukushima and Chernobyl accidents. However, the victim’s breathing and movement during in vivo measurements causes signal loss and uncertainty in the radiation-induced signal (RIS). This study aims to address these issues by developing a wearable resonator for a tooth. Using ANSYS High Frequency Structure Simulation (HFSS), the dimensions and configuration of an attachable surface coil were optimized by calculating the magnetic field distribution in the enamel volume of a 3D incisor model. The magnetic energy concentration on the tooth enamel was maximized by the attachable surface coil, which had a 5 mm inner diameter and a 0.7 mm trace width at a given microwave power. To assess the dosimetric performance, a 50-Gy irradiated tooth was measured by an optimized wearable resonator. The tooth measurement was conducted by employing homebuilt 1.15 GHz continuous-wave EPR spectroscopy. The configured wearable resonator produced a constant RIS amplitude with a ± 2.0% variation from an exposed tooth sample, even with a 2 mm movement along the central axis. In addition, secure fixation of the wearable resonator resulted in significant stability, showing a relatively low uncertainty of 1.2% in the RIS amplitude. The wearable resonator also achieved an ~ 8.4% increase in RIS amplitude by concentrating more magnetic energy on the tooth sample compared to a conventional rigid resonator. This enhancement improved the accuracy and sensitivity of in vivo tooth dosimetry. In conjunction with an automatic control circuit (ACC), the wearable resonator acquired undistorted in vivo EPR spectra; thereby, significantly reducing the need for manual intervention to reset the device due to the in vivo motion. This combination of the wearable resonator and ACC effectively established a motion compensation system for in vivo EPR tooth dosimetry.

Medical imaging plays a pivotal role in modern healthcare, with Magnetic Resonance Imaging (MRI) standing out for its exceptional resolution and non-ionizing nature. Diffusion-Weighted Imaging (DWI) has further enhanced the diagnostic capability of MRI by visualizing tissue microstructure, making it invaluable for early disease detection, but it cannot assess perfusion. IntraVoxel Incoherent Motion (IVIM) MRI addresses this gap by simultaneously quantifying both diffusion and perfusion, offering deeper insights into tissue characteristics. However, its clinical adoption remains limited due to challenges such as the lack of standardized algorithms, noise-related image degradation, and variability in parameter estimation. This review explores the evolution of IVIM MRI, its physiological models for parameter estimation, the impact of noise and denoising techniques on image quality, and different fitting approaches to improve accuracy and reliability. The exploration of these areas in this work aims to enhance the reliability of IVIM and facilitate its integration into clinical practice, ultimately improving diagnostic accuracy and patient outcomes across diverse medical conditions.

While gadolinium-enhanced magnetic resonance imaging (MRI) enables assessment of blood–brain barrier (BBB) integrity post-stroke, it presents inherent risks and limitations. We evaluated diffusion tensor imaging (DTI) as a contrast-free method for monitoring BBB integrity during ischemia–reperfusion (I/R) in a rat stroke model. Seventeen Sprague–Dawley rats underwent one-hour transient middle cerebral artery occlusion (MCAO). Serial MRI sequences, including DTI, perfusion-weighted imaging, and T1 mapping, were performed to monitor BBB permeability (BBBP) dynamics in regions initially identified as ischemic penumbra (IP) and ischemic core (IC) during MCAO. The fractional anisotropy (FA) ratio (rFA) was compared with BBBP changes throughout the observation period. In the IC, rFA values exhibited a 13% increase during ischemia, followed by a 10% decrease post-recanalization, and a 36% decline at 120 h post-reperfusion. Although BBBP in the IC decreased during ischemia and normalized post-reperfusion, persistent leakage was observed. The IP maintained stable rFA and BBB integrity throughout I/R. Strong negative correlations between rFA and BBBP were found in ischemic regions (IC: r = − 0.90, p < 0.001; IP: r = − 0.78, p = 0.007), with FA reductions at 24 h post-reperfusion predicting BBB disruption at 120 h. These findings suggest that DTI metrics correlate significantly with BBB integrity during I/R, indicating potential utility as a contrast-free monitoring tool for early detection of BBB impairment following stroke.