Applied Magnetic Resonance最新文献

Gallium alloys are widespread materials in microelectronics and are promising as components of nanocomposites for using in soft robotics, wearable electronics, and sensors. Here, we present NMR studies of the impact of a particular nanoconfinement on the phase diagram for the GaInSn eutectic alloy in a porous Al₂O₃ ceramic template with the middle pore size 11 nm. Measurements of the NMR spectra and Knight shifts were carried out for ⁷¹Ga, ⁶⁹Ga, and ¹¹⁵In isotopes from 180 to 310 K. The precipitation of gallium-rich segregates with crystalline structures of α- and β-Ga was found at cooling. The evolution of the NMR lines during cooling and warming evidenced the occurrence of the liquid–liquid-phase transition in the melt fraction with pronounced amount of indium. The results obtained for the GaInSn alloy embedded into the porous aluminum oxide ceramic were found to differ remarkably from the phase diagrams of the alloy confined within silica opal and glass porous matrices.

The purpose of this study was to evaluate the importance of automated lateral and medial temporal volume measurement technique for the early diagnosis of Alzheimer's disease (AD). A cross-sectional T1-weighted magnetic resonance image was obtained from 39 healthy adults and 39 patients with mild AD. The study demonstrates significant volume loss in the lateral temporal lobe (LTL) and medial temporal lobe (MTL) regions of the brain in early cases of AD, suggesting that volume loss could be used as a viable biomarker for mild AD diagnosis. Using a deep learning-based auto-segmentation network (CINet), the study accurately estimates the volumes of various LTL and MTL brain regions. Notably, higher volume loss is observed in the left MTL and LTL regions compared to the right, indicating an asymmetric impact in mild AD. The study underscores the significance of automated technique for AD diagnosis and monitoring disease progression, contributing valuable insights for potential early interventions.

The Lindblad equation for dissipative open systems is applied for an investigation of relaxation of multiple-quantum (MQ) NMR coherences in two-spin systems. We choose two examples of two-spin systems. One of them is the zigzag proton chain in a single crystal of hambergite in such an orientation that one of the two intra-chain dipolar coupling constants becomes zero. Then, the chain consists of well-isolated pairs of spins, with the spins of each pair coupled by the dipole–dipole interaction. The second example of a two-spin system is a single crystal of gypsum in which protons belong to water molecules. The MQ NMR dynamics with relaxation was investigated for different preparation times of the MQ NMR experiment.

The development of ecofriendly electrolytes for lithium-ion batteries is one of the actual tasks of modern electrochemistry. In particular, to this purpose, the highly concentrated ternary aqueous systems based on lithium acetate (LiOAc) have been actively investigated. Here, the diffusion coefficients of ⁷Li⁺ and ¹³³Cs⁺ cations, OAc^– anion, as well as water (¹H), in ternary aqueous solutions of cesium and lithium acetates in a range of temperature (– 15 ÷ 35 °C) have been measured using the PFG NMR method. A direct attempt to interpret the obtained dependences within the framework of the Stokes–Einstein model led to the fact that the calculated hydrodynamic radius of the Cs⁺ cation turned out to be noticeably smaller than its crystallographic one. An approach to describing the high rate of diffusion of cesium cations is proposed, based on taking into account the local viscosity near cations of both types. The use of the approach allowed us to calculate more correctly the hydrodynamic radii of cations, while remaining within the framework of the Stokes–Einstein model. As a result, it has been possible to describe the features of translational motion of components in a complex system that is interesting for electrochemical applications.

The gradient coils represent an indispensable constituent within magnetic resonance imaging systems. Their performance significantly impacts the quality of images, particularly the nonlinearity of the gradient magnetic field. Due to the presence of ferromagnetic materials surrounding the gradient coil in the permanent magnet system, the magnetic field of the gradient coil experiences influence. Consideration must be given to ferromagnetic materials during the design phase. The objective of this study is to design gradient coils that mitigates the impact of ferromagnetic materials on gradient field linearity. In this paper, the original coil structure is formulated utilizing the discrete trajectory method, while introducing mirrored current to elucidate the effects of ferromagnetic material. Through the integration of these two methods, gradient coil structures with excellent linearity are achieved. Ultimately, the optimal gradient coils are fabricated, and computational as well as experimental findings demonstrate concordance between measured nonlinear degree and efficiency of the gradient coils with theoretical calculations in the presence of ferromagnetic materials.

This article reports on the use of fluorocarbons as an imaging medium in MRI. The function of this medium is to uniformly fill the space intended for MR scanning and to provide a strong signal against which objects of interest can be visualized. In our case, such objects were coils used as signal sensors in MRI studies. The aim of the study is visualization of the conductors located inside of an MRI coil and, therefore, could not be visually assessed. To enable the conductor’s imaging, signal amplification from the imaging medium in the vicinity of the conductors was used. The physical phenomenon behind this effect is the fact that the magnetic field induced in the conductor by precessing spins, causing a current in it, which is recorded by the receiver, greatly increases with decreasing distance of the spins from the conductor. The fluorocarbons—octafluorocyclobutane gas—C₄F₈, as well as so-called dry water—perfluoro(2-methyl-3-pentanone)—CF₃CF₂C(O)CF(CF₃)₂ can be used as a visualization medium. In both cases, MRI scan is performed to detect fluorine nuclei (¹⁹F). The method is most effective in active mode—when the coil to be examined is connected to the receiver. The application of the conductor visualization method was shown for three types of two-channel quadrature coils. The ability to visualize the conductors separately for each channel, including volumetric reconstructions, and to construct coil sensitivity maps was demonstrated. ¹⁹F MR images of the coils were compared with their photographs, X-ray and proton MR images, and showed high correspondence.

Brain hemorrhage is a critical medical condition that is likely to cause long-term disabilities and death. Timely and precise emergency care, incorporating the accurate interpretation of computed tomography (CT) images, plays a crucial role in the effective management of a hemorrhagic stroke. However, conventional artificial intelligence methods are capable enough to detect the presence or absence of hemorrhage but fail to detect multiple types of hemorrhage with high accuracy. To address this, the paper introduces an innovative Deep Learning based approach that automatically detects, segments, and classifies subtypes of intracranial hemorrhages. The proposed model is trained and evaluated on two different datasets. It is initially trained on a dataset of CT images from the Radiological Society of North America (RSNA) brain CT hemorrhage database, which contained 752,803 head non-contrast computer tomography images obtained from 2,200 patients. Furthermore, the model's performance is validated using a real-time CT dataset collected from a diagnostic lab, comprising 15,000 CT scan images from 176 patients. The proposed model surpasses standard benchmarks for detection and classification, achieving exceptional metrics. It showcases overall segmentation accuracy with a Dice score and Jaccard Index of 0.99 and 0.88 respectively, while the classification metrics include an accuracy of 0.99, precision, recall, and F1 score of 0.97, 0.98, and 0.97 respectively. When two expert radiologists independently assessed the predicted hemorrhage locations and subtypes, ensuring uniform specificity levels, they determined the observed rate of false positives per patient was less. These results validate its applicability as a dependable clinical decision support tool.

Spin exchange caused by the exchange interaction during bimolecular collisions of paramagnetic particles in dilute solutions causes several effects: broadens the resonance lines of the EPR spectrum, changes the resonance frequencies, changes the shape of the resonance lines of the spectrum, and causes the effect of the exchange narrowing of the spectrum. The well-established belief is that the dipole–dipole interaction between paramagnetic particles only broadens the resonance lines. According to the new paradigm of spin exchange, the dipole–dipole interaction causes effects similar to the effects of spin exchange. In this article, a detailed quantitative analysis of the effect of the dipole–dipole interaction on the shape of the EPR spectra of dilute solutions of paramagnetic particles is carried out for the model system. It is shown that the contribution of the dipole–dipole interaction to the spin coherence transfer between particles makes it possible to more accurately determine the rate of spin exchange and, as a result, the rate of bimolecular collisions of molecules from the analysis of the shape of the EPR spectra. An experimental protocol is proposed that definitely highlights the contribution of the dipole–dipole interaction to the transfer of spin coherence.

To respond to the increasing demand for hyaluronic acid (HA) in dietary supplements (DSs) and nutricosmetics marketed for the treatment of osteoarthritis or moistening, it is essential to have an accurate and reliable method for its analysis in the final products. The study aimed to develop and validate alternative method for the quality control of HA in DSs using low-field (LF) and high-field (HF) nuclear magnetic resonance (NMR) spectroscopy at 80 MHz and 600 MHz, respectively. Moreover, chondroitin sulphate (CH), another active ingredient in DSs, can be simultaneously quantified. The ¹H-NMR methods have been successfully validated in terms of limit of detection (LOD) and limit of quantitation (LOQ), which were found to be 0.1 mg/mL and 0.2 mg/mL (80 MHz) as well as 0.2 mg/mL and 0.6 mg/mL (600 MHz). Recovery rates were estimated to be between 92 and 120% on both spectrometers; precision including sample preparation was found to be 4.2% and 8.0% for 600 MHz and 80 MHz, respectively. Quantitative results obtained by HF and LF NMR were comparable for 16 DSs with varying matrix. HF NMR experiments at 70 ℃ serve as a simple and efficient quality control tool for HA and CH in multicomponent DSs. Benchtop NMR measurements, upon preceding acid hydrolysis, offer a cost-effective and cryogen-free alternative for analyzing DSs in the absence of CH and paramagnetic matrix components.

The local specific absorption rate (SAR) is a key safety indicator in high-field MRI. Constructing a specific model for each patient is important for accurate estimation of local SAR. The aim of this study is to construct subject-specific knee models based on low-field images for realizing accurate local SAR estimation in high-field MRI systems (3T and 1.5T). The proposed method used two U-Net networks for tissue segmentation of knee joint and the classification results of the two networks were merged to generate the final models. Muscle has high dielectric properties and large volume, which have an important influence on the electromagnetic field distribution. To improve the accuracy of muscle segmentation, a U-Net making use of boundary information was used to segment muscle alone to overcome the problem of inhomogeneous intensity at the edge of the muscle region. Other tissues were segmented by another U-Net, which used a weighted loss function to mitigate the adverse influence of class imbalances between tissues. The proposed method was compared with other methods using manual delineation as the standard. Its muscle segmentation performance was better than that of the comparison methods. On the other hand, local SAR in 3T using models constructed by these methods was also evaluated through electromagnetic simulation separately. It was shown that the maximum SAR_10g of the models constructed by the proposed method was much closer to that of manual delineation on the whole. These results validated the availability of the proposed method.