Magnetic Susceptibility Effects Research Articles

Three-Dimensional MT Conductive Anisotropic and Magnetic Modeling Using A − ϕ Potentials Employing a Mixed Nodal and Edge-Based Element Method

Magnetotelluric (MT) sounding is a geophysical technique widely utilized in mineral resource surveys, where conductivity and magnetic permeability serve as essential physical parameters for forward modeling and inversion. However, the effects of conductive anisotropy and non-zero magnetic susceptibility are usually ignored. In this study, we present a three-dimensional (3D) MT modeling algorithm using Coulomb-gauged electromagnetic potentials, incorporating a mixed nodal and edge-based finite element method capable of simulating MT responses for conductive anisotropic and magnetic anomalies. Subsequently, the algorithm’s accuracy was validated in two steps: first, it was compared with analytical solutions for a 1D magnetic model; then, a comparison was made with previously published numerical results for a 3D generalized conductive anisotropic model. The results of two tests show that the maximum relative error is below 0.5% for both models. Furthermore, representative models were computed to comprehensively analyze the responses of MT. The findings illustrate the relationship between anisotropic parameters and electric fields and emphasize the significance of considering the impact of magnetic susceptibility in magnetite-rich regions.

Magnetic field-dependent thermopower: Insights into spin and quantum interactions

This study explores the impact of external magnetic fields on thermoelectric properties, focusing on the interplay of spin and quantum effects. Using gadolinium (Gd) as a case study, we observed anomalous magneto-thermopower trends, with a reduction in thermopower at ∼35 K and an enhancement at TC ≈ 293 K under high magnetic fields. Comprehensive temperature and field-dependent measurements, including specific heat capacity, magnetic susceptibility, and Hall effect, were performed to uncover the underlying mechanisms. We derived a relation for the total thermopower of an uncompensated ferromagnetic metal and calculated multi-band carrier characteristics, such as concentration and mobility, using the maximum entropy principle. Our findings reveal a ∼70 % suppression of the magnetic contribution to specific heat capacity under a 12 T field and a positive magnon-drag contribution to the total thermopower. Field-dependent Hall measurements indicate that the anomalous Hall effect is dominated by intrinsic contributions from Berry curvature. Additionally, transverse magnetoresistance data suggest anisotropic Fermi surfaces, domain movement, suppression of spin-flip effects, and Fermi surface modifications. First-principles calculations based on Density Functional Theory (DFT) further support these findings. These calculations reveal significant Berry curvature contributions, leading to an anomalous Hall conductivity of approximately 1260 S/cm at the Fermi level. The enhancement of thermopower near TC is primarily attributed to the suppression of magnon-drag and the imbalance in carrier mobility and relaxation times, driven by spin and quantum effects. These combined effects result in a ∼50 % increase in thermopower and a ∼150 % improvement in zT at 12 T. The notable peak in zT at cryogenic temperatures highlights a potential pathway for designing efficient thermoelectric materials for cryogenic cooling applications. Our results demonstrate the significance of field-dependent spin and quantum effects in enhancing thermoelectric performance, offering new directions for thermoelectric research and material design.

Effect of Specific Magnetic Susceptibility of AISI 304 and 08Kh18N10 Steels on Their Limiting Potentials in Chloride-Containing Environments

Effect of Specific Magnetic Susceptibility of AISI 304 and 08Kh18N10 Steels on Their Limiting Potentials in Chloride-Containing Environments

Assessing Weak Anion Binding to Small Peptides.

Since Hofmeister's seminal studies in the late 19th century, it has been known that salts and buffers can drastically affect the properties of peptides and proteins. These Hofmeister effects can be conceived of in terms of three distinct phenomena/mechanisms: water-salt interactions that indirectly induce the salting-out of a protein by water sequestration by the salt, and direct salt-protein interactions that can either salt-in or salt-out the protein. Unfortunately, direct salt-protein interactions responsible for Hofmeister effects are weak and difficult to quantify. As such, they are frequently construed of as being nonspecific. Nevertheless, there has been considerable effort to better specify these interactions. Here, we use pentapeptides to demonstrate the utility of the H-dimension of nuclear magnetic resonance (NMR) spectroscopy to assess anion binding using N-H signal shifts. We qualify binding using these, demonstrating the upfield shifts induced by anion association and revealing how they are much larger than the corresponding downfield shifts induced by magnetic susceptibility and other ionic strength change effects. We also qualify binding in terms of how the pattern of signal shifts changes with point mutations. In general, we find that the observed upfield shifts are small compared with those induced by anion binding to amide-based hosts, and MD simulations suggest that this is so. Thus, charge-diffuse anions associate mostly with the nonpolar regions of the peptide rather than directly interacting with the amide N-H groups. These findings reveal the utility of 1H NMR spectroscopy for qualifying affinity to peptides─even when affinity constants are very low─and serve as a benchmark for using NMR spectroscopy to study anion binding to more complex systems.

Ambient temperature 1H/13C NMR spectra of sodium 3-(trimethylsilyl)propane-1-sulfonate (DSS) in D2O referenced to external TMS: A discussion of these and closely related results. Corrections for the bulk magnetic susceptibility effect for aqueous NMR samples.

This study aimed to obtain the title spectra and verify the temperature dependence of δDSS of the HOD signal from D2O of the NMR sample. However, the analysis of the collected δX data, extended by the results of other closely related measurements reported in the literature, provided important guidelines for performing routine 1H/13C NMR spectra in aqueous solvents externally referenced to neat liquid TMS contained in a coaxial capillary. Therefore, it is recommended that the previously proposed correction of δX data thus determined, which is mainly due to the difference in volume magnetic susceptibility χv between the sample and the external standard used, usually called the bulk magnetic susceptibility (BMS) correction, has been increased by +0.05 ppm (7%). The new value of this correction, +0.73 ppm, based on NMR experiments carried out at a standard temperature of 25°C, was confirmed in a classical approach using critically reviewed χm, χM, and ρ data for TMS, D2O, and H2O. The BMS correction for H2O solutions is +0.75 ppm. Important issues concerning magnetic susceptibility measurements for D2O and H2O, coaxial bulb-ended inserts, and the geometry of two-tube NMR cells (shape factor αav) are also critically discussed here, partly from a historical perspective.

NMR Spectroscopic Investigations of the Performance Limiting Mechanisms of Lithium-Sulfur Batteries

During the past decades, the development of alternative energy sources has become increasingly important as the growing consumption of non-regenerative fossil energy poses a threat to the environment. Hence, developing of next-generation batteries featuring high capacity, reduced costs and improved safety, such as in lithium-sulfur batteries, is of utmost importance. The benefits of lithium-sulfur batteries have led to widespread efforts to understand the fundamentals of the sulfur redox chemistry that drives their operation, as capacity fade has been observed in almost all Li-S batteries.[1] Therefore, the involved local structural changes that correlate with the (electro)chemical processes need to be unveiled during the operation of Li-S batteries, suitably by in situ and in operando methods. This presentation will demonstrate the development and application of one such (operando) technique: nuclear magnetic resonance (NMR) spectroscopy. NMR spectroscopic measurements allow the probing of the structural changes in a battery during electrochemical cycling. In particular, the application of a non-invasive experimental set-up, which can follow the reaction inside the battery in operando is highly desirable as it provides real-time structural information compared to ex situ analysis.[2] Lithium-sulfur batteries contain various NMR-active nuclear isotopes, like 7Li, 6Li and 33S, which allow the following of the chemical reactions during the charge-discharge process. This includes the transition between elemental sulfur and polysulfides on the cathode side, the formation of the solid-electrolyte interface (SEI) and the metal plating and stripping on the anode side. Herein, we use for the first time a combination of lithium and sulfur in operando NMR spectroscopy to reveal a fundamental understanding of the reaction pathway of lithium-sulfur batteries during the cycling process.Lithium NMR spectroscopy is a powerful technique to apply to batteries, as demonstrated by many previous investigations on different lithium battery systems, since it enables the detection of the chemical environments of lithium species during electrochemical cycling and parasitic reactions in the cell.[3] The great advantage of in operando 7Li NMR spectroscopy is that the 7Li signals of the lithium anode and the deposited metal differ due to the bulk magnetic susceptibility effects and the surface area, bringing the skin depth effect into play. Thus, this method enables a time-resolved and quantitative evaluation of the electrochemical metal deposition during electrochemical cycling. Therefore, it is possible to investigate a critical problem that reduces the cell performance – the formation of lithium dendrites. This lithium deposition is particularly problematic if it occurs uncontrolled and inhomogeneous and the exact mechanism of nucleation and propagation of dendrites is not yet fully understood.[4] The developed technique helps to understand this deposition to improve the safety during cycling. The interpretation of the electrolyte signal in the in operando 7Li spectra is much more difficult because of the overlapping signals. Therefore, in situ 33S and 6Li NMR spectroscopy supports the identification and quantification of (poly-)sulfides during the charge-discharge-process. 33S NMR experiments are rarely reported since 33S is a quadrupolar nucleus characterized by a low natural abundance and magnetogyric ratio, resulting in a very low receptivity. Nevertheless, the developed 33S NMR technique allows the detection of the formation Li2S under in operando conditions.[5] Additional in operando 6Li NMR experiments allow to follow the (poly-)sulfide formation as the spectra yield much sharper lines in asymmetric lithium environments in comparison to 7Li NMR experiments.[6] Thus, these techniques provide complementary results to the 7Li NMR spectroscopic studies and help to elucidate the sulfur redox mechanism in lithium-sulfur batteries.Our developed in situ NMR spectroscopic set-up is a powerful analytical method since real-time qualitative and quantitative detection of different sulfur and lithium species is crucial for understanding the electrochemical process in sulfur batteries. The first time, a combination of in operando lithium and sulfur NMR spectroscopy is presented, providing new insights at the molecular level that are essential for accelerating the development of lithium-sulfur battery technologies.[1] H. Wang, N. Sa, et al., The Journal of Physical Chemistry C 2017, 121, 6011–6017.[2] J. B. Richter, et al., Chemical Communications 2019, 55, 6042–6045.[3] R. Bhattacharyya, et al., Nat Mater 2010, 9, 504–510.[4] A. B. Gunnarsdóttir, et al., J Mater Chem A Mater 2020, 8, 14975–14992.[5] R. Musio, in Annu Rep NMR Spectrosc, 2006, pp. 1–88.[6] L. A. Huff, et al., Surf Sci 2015, 631, 295–300.

An ultra-low field SQUID magnetometer for measuring antiferromagnetic and weakly remanent magnetic materials at low temperatures.

A novel setup for measuring magnetic fields of antiferromagnets (i.e., quadrupolar or higher-order magnetic fields) and generally weakly remanent magnetic materials is presented. The setup features a highly sensitive superconducting quantum interference device magnetometer with a magnetic field resolution of ∼ 10fT and non-electric temperature control of the sample space for a temperature range of 1.5-65K with a non-electric sample movement drive and optical position encoding. To minimize magnetic susceptibility effects, the setup components are degaussed and realized with plastic materials in sample proximity. Running the setup in magnetically shielded rooms allows for a well-defined ultra-low magnetic background field well below 150 nT in situ. The setup enables studies of inherently weak magnetic materials, which cannot be measured with high field susceptibility setups, optical methods, or neutron scattering techniques, giving new opportunities for the research on, e.g., spin-spiral multiferroics, skyrmion materials, and spin ices.

Transverse expansion of Bjorken flow in (1+1D) relativistic ideal-magnetohydrodynamics with magnetization

We study the evolution of magnetized quark gluon plasma (QGP) in the magneto hydrodynamic (MHD) framework. The fluid under investigation has a non-zero magnetization with infinite electrical conductivity. We solve the coupled Maxwell and conservation equations in (1+1D) transverse flow. We assume that the motion of fluid is longitudinally boost-invariant along beam line.In this study, we consider two different scenarios. First, we consider an ideal relativistic plasma with massless particles and infinite electrical conductivity with a constant magnetic susceptibility (χm). Thus, we solve the coupled Maxwell and conservation equations, and obtain the transverse fluid velocity, the energy density and the magnetic field as functions of both space and time. We investigate the effects of magnetic susceptibility (χm) on the evolution of thermodynamic quantities. Then, we solve the coupled Maxwell and conservation equations with a temperature-dependent magnetic susceptibility and a realistic equation of state given by lattice-QCD data [43,44]. We find the evaluation of temperature, energy density, the magnetic field, and the transverse fluid velocity. We improve our previous study [21] to include a nonzero magnetization, the transverse relativistic velocity ux2≠0, and a realistic equation of state.We realize the effects of non-zero magnetization on the fluid quantities are rather small. Besides, our work shows a fluid with a realistic equation and a temperature-dependent magnetic susceptibility behaves like a conformal fluid with a small constant magnetic susceptibility.

Operando benchtop NMR reveals reaction intermediates and crossover in redox flow batteries

Redox flow batteries (RFBs) provide a promising battery technology for grid-scale energy storage. High-field operando NMR analyses of RFBs have yielded useful insight into their working mechanisms and helped improve battery performance. Nevertheless, the high cost and large footprint of a high-field NMR system limit its implementation by a wider electrochemistry community. Here, we demonstrate an operando NMR study of an anthraquinone/ferrocyanide-based RFB on a low-cost and compact 43 MHz benchtop system. The chemical shifts induced by bulk magnetic susceptibility effects differ remarkably from those obtained in high-field NMR experiments, due to the different orientations of the sample relative to the external magnetic field. We apply Evans method to estimate the concentrations of paramagnetic anthraquinone radical and ferricyanide anions. The degradation of 2,6-dihydroxy-anthraquinone (DHAQ) to 2,6-dihydroxy-anthrone and 2,6-dihydroxy-anthranol has been quantified. We further identified the impurities commonly present in the DHAQ solution to be acetone, methanol and formamide. The crossover of DHAQ and impurity molecules through the sseparation Nafion® membrane was captured and quantified, and a negative correlation between the molecular size and crossover rate was established. We show that a benchtop NMR system has sufficient spectral and temporal resolution and sensitivity for the operando study of RFBs, and anticipate a broad application of operando benchtop NMR methods for studying flow electrochemistry targeted for different applications.

Minimizing magnetic resonance image geometric distortion at 7 Tesla for frameless presurgical planning using skin-adhered fiducials.

7T MRI offers significant benefits to spatial and contrast resolution compared to lower field strengths. This superior image quality can help better delineate targets in stereotactic neurosurgical procedures; however, the potential for increased geometric distortions at 7T has impaired its widespread use for these applications. Image geometric distortions can be due to distortions of B0 arising from tissue magnetic susceptibility effects or inherent field inhomogeneities, and nonlinearity of the magnetic field gradients. The purpose of this study was to investigate the use of 7T MRI for neurosurgical frameless stereotactic navigation procedures. Image geometric distortions at the skin surface in 7T images were minimized and compared to results from clinical 3T frameless imaging protocols. A 3D-printed grid phantom filled with oil was designed to perform a fine calibration of the 7T imaging gradients, and an oil-filled head phantom with internal targets was used to determine ground truth (from computed tomography [CT]) positioning errors. Three volunteers and the head phantom were imaged consecutively at 3T and 7T. Ten skin-adhesive fiducial markers were placed on each subject's exposed skin surface at standard clinical placement locations for frameless procedures. Imaging sequences included MPRAGE (three bandwidths at 7T: 400, 690, and 1020Hz/pixel, and one at 3T: 400Hz/pixel), T2 SPACE, and T2 SPACE FLAIR acquisitions. An additional GRE field map was acquired on both scanners using a multi-echo GRE sequence. Custom Matlab code was used to perform additional distortion correction of the images using the unwrapped field maps. Fiducial localization was performed with 3D Slicer, with absolute fiducial positioning errors determined in phantom experiments following rigid registration to the CT images. For human experiments, 3T and 7T images were registered and relative differences in fiducial locations were compared using two-tailed paired t-tests. Phantom measurements at 7T yielded gradient distance scaling errors of 1.1%, 2.2%, and 1.0% along the x-, y-, and z-axes, respectively. These system miscalibrations were traced back to phantom manufacturing deviations in the sphericity of the vendor's gradient calibration phantom. Correction factors along each gradient axis were applied, and afterward, geometric distortions of less than 1mm were obtained in the 7T MR head phantom images for the 1020Hz/pixel bandwidth MPRAGE sequence. For the human subjects, four fiducial locations were excluded from the analysis due to patient positioning differences. Differences between 3T and 7T MPRAGE with low/medium/high bandwidth were 2.2/2.6/2.3mm, respectively, before the correction, reducing to 1.6/1.3/1.0mm after the correction (p<0.001). T2 SPACE and T2 SPACE FLAIR yielded a similar pattern when the correction was applied, decreasing from 2.1 to 0.8mm, and 2.6 to 1.0mm, respectively. 7T MRI can be used to perform frameless presurgical planning with skin-adhesive fiducials. Geometric distortions can be reduced to a clinically relevant level (errors<∼1mm) with no significant susceptibility-related distortions, by using high receiver bandwidth, ensuring gradients are properly calibrated, and placing skin fiducials in areas where distortions from patient positioning are minimal.

Synthesis, structural and physical properties of new ternary metal-rich phosphides M3Ge2P (M = Mo and W)

We report on the successful synthesis of two new ternary metal-rich phosphides Mo3Ge2P and W3Ge2P, and on their structural, electrical, magnetic, thermal and electronic properties. Mo3Ge2P is thermally stable below 1500 ​°C, while W3Ge2P decomposes initially at 1110 ​°C and finally evolves into W, Ge, and P above 1360 ​°C. They adopt a non-centrosymmetric orthorhombic structure with space group C2v16—Ama2 (No. 40). In the unit cell with content Z ​= ​4, Mo (W) atoms are located at two inequivalent sites, respectively 4b (Mo1/W1) and 8c (Mo2/W2) Wyckoff positions, Ge and P atoms occupy 8c and 4b positions, respectively. The structure is made up of networks organized by edge-shared (Mo1/W1)3P3 planar six-membered rings and edge-shared (Mo2/W2)3Ge3 chair-form six-membered rings. Both compounds exhibit weak magnetism and metallic conduction with electron-dominant charge carriers at high temperatures, as revealed by magnetic susceptibility, electrical resistivity and Seebeck effect. Sommerfeld coefficient γ and Sommerfeld-Wilson ratio Rw were derived as 8.87 ​mJ ​mol−1 ​K−2, 1.69 for Mo3Ge2P and 9.85 ​mJ ​mol−1 ​K−2, 1.78 for W3Ge2P, indicating weak electron-electron correlation in the system. Analyses on thermal conductivity (κ) suggest a considerable phonon contribution κL to the total one in these metallic materials. First-principles calculations demonstrate that the Mo-4d (W-5d) orbital electrons dominate the band structures and density of states near the Fermi level.

NMR Susceptibility and Magnetization of DNA Bases, Nucleotides and Their Derivatives with C2Fe+, A DFT Study

DNA strands and their bases are in the cells in every creature. They essential for growth, metabolism regulation and carrying genetic information bases to new generations. The bases of DNA are working with 0 and 1 system. In this theoretical research, first, by using Gaussian program, NMR susceptibility of DNA bases and their C2Fe+ attached varieties are determined. In the next step, with effect of magnetic field (H) and NMR susceptibility of these compounds, their resulted Magnetization (M) is calculated. These resulted magnetizations not only can be considered as a method to make a new (0) and (1) system for DNA bases but also can be used as creating certain signals to mark of DNA bases and their compounds which are attached to C2Fe+.

The Effects of Magnetic Susceptibility on Controlled-Source Audio-Frequency Magnetotellurics

The Effects of Magnetic Susceptibility on Controlled-Source Audio-Frequency Magnetotellurics

Imaging white matter microstructure with gradient-echo phase imaging: Is ex vivo imaging with formalin-fixed tissue a good approximation of the in vivo brain?

PurposeEx vivo imaging is a commonly used approach to investigate the biophysical mechanism of orientation‐dependent signal phase evolution in white matter. Yet, how phase measurements are influenced by the structural alteration in the tissue after formalin fixation is not fully understood. Here, we study the effects on magnetic susceptibility, microstructural compartmentalization, and chemical exchange measurement with a postmortem formalin‐fixed whole‐brain human tissue.MethodsA formalin‐fixed, postmortem human brain specimen was scanned with multiple orientations to the main magnetic field direction for robust bulk magnetic susceptibility measurement with conventional quantitative susceptibility imaging models. White matter samples were subsequently excised from the whole‐brain specimen and scanned in multiple rotations on an MRI scanner to measure the anisotropic magnetic susceptibility and microstructure‐related contributions in the signal phase and to validate the findings of the whole‐brain data.ResultsThe bulk isotropic magnetic susceptibility of ex vivo whole‐brain imaging is comparable to in vivo imaging, with noticeable enhanced nonsusceptibility contributions. The excised specimen experiment reveals that anisotropic magnetic susceptibility and compartmentalization phase effect were considerably reduced in the formalin‐fixed white matter specimens.ConclusionsFormalin‐fixed postmortem white matter exhibits comparable isotropic magnetic susceptibility to previous in vivo imaging findings. However, the measured phase and magnitude data of the fixed white matter tissue shows a significantly weaker orientation dependency and compartmentalization effect. Alternatives to formalin fixation are needed to better reproduce the in vivo microstructural effects in postmortem samples.

Comparison of Lanthanide Macrocyclic Complexes as 23Na NMR Sensors.

Nuclear magnetic resonance (NMR) agents, composed of paramagnetic lanthanide ions (Ln3+) complexed with negatively charged cyclic chelating agents (Che(n+3)-) forming polyanionic lanthanide complexes (LnChen-), perturb sodium-23 (23Na) signals, a phenomenon which depends sodium ions (Na+) exchanging with LnChen-. We analyzed 23Na shiftability and broadening due to hyperfine and bulk magnetic susceptibility (BMS) effects that arise from LnChen- designs using selective Ln3+ ions (i.e., thulium, Tm3+; gadolinium, Gd3+; and europium, Eu3+) and macrocyclics derived from 1,4,7,10-tetraazacyclododecane (cyclen) [i.e., with phosphonate (DOTP8-) and carboxylate (DOTMA4-) arms] and 1,4,7-triazacyclononane (TACN) [i.e., with phosphonate (NOTP6-) arms]. All LnChen- complexes showed downfield shifts, but Gd3+ and Tm3+ agents, respectively, were dominated by BMS and hyperfine effects, in good agreement with theory. While 23Na shiftability and broadening were minimally affected by pH and competing cations (K+, Ca2+, and Mg2+) within physiological ranges, the 23Na shiftability and broadening were most sensitive to LnChen- concentration in relation to the interstitial Na+ level in vivo. Greatest 23Na shiftability and broadening were obtained with Tm3+ and Gd3+ agents, respectively. While BMS contribution to shiftability was most impacted by the number of unpaired electrons on Ln3+, negative charge on LnChen- regulated Na+ exchange for line broadening. In brain tumor models, TmDOTP5- with 23Na-NMR has been used previously to separate Na+ in intracellular, blood, and interstitial pools, while evidence here shows that GdDOTP5- can distinguish Na+ within intracellular and extracellular (i.e., blood and interstitial) pools. Given the biological importance of Na+ in vivo, future macrocyclic designs of LnChen- should be sought for 23Na-NMR biomedical applications.

Quantitative MRI analysis of structural changes in tomato tissues resulting from dehydration.

A quantitative magnetic resonance imaging (MRI) analysis at 1.5T of the effects of different dehydration regimes on transverse relaxation parameters measured in tomato tissue is presented. Multi-exponential T2 maps have been estimated for the first time, providing access to spatialized microstructural information at voxel scale. The objective was to provide a better understanding of the changes in the multi-exponential transverse relaxation parameters induced by dehydration in tomato tissues and to unravel the effects of microstructure and composition on relaxation parameters. The results led to the hypothesis that the multi-exponential relaxation signal reflects cell compartmentation and tissue heterogeneity, even at the voxel scale. Multi-exponential relaxation times provided information about water loss from specific cell compartments and seem to indicate that the dehydration process mainly affects large cells. By contrast, total signal intensity showed no sensitivity to variations in water content in the range investigated in the present study (between 95% [fresh tissue] and 90% [after dehydration]). The variation in relaxation times resulting from water loss was due to both changes in solute concentration and compartment size. The comparative analysis of the two contrasted tissues in terms of microporosity demonstrated that magnetic susceptibility effects, caused by the presence of air in the placenta tissue, significantly impact the effective relaxation and might be the dominant effect in the variations observed in relaxation times in this tissue.

Predictive value of thrombus susceptibility for cardioembolic stroke by quantitative susceptibility mapping.

The hypointense blooming signal of thrombi on susceptibility-weighted imaging (SWI), known as the susceptibility vessel sign (SVS), is predictive of cardioembolic stroke. The SVS originates from the local magnetic susceptibility effect; thus, the susceptibility value of thrombi may provide useful information in discriminating stroke etiology. We aim to utilize quantitative susceptibility mapping (QSM) to assess thrombus's susceptibility value in acute ischemic stroke patients and explore the relationship of thrombus susceptibility with cardioembolic stroke. From 2018 to 2020, 132 consecutive acute ischemic stroke patients with middle cerebral artery occlusion were recruited within 48 hours of onset. All patients underwent a three-dimensional multi-echo SWI scan using a 3 Tesla magnetic resonance imaging scanner. The SVS presence and the diameter of the SVS-related hypointense signal were assessed on SWI. QSM was applied to compute the susceptibility value of the thrombus. The receiver operating characteristic (ROC) methodology was used to define the optimal cutoff value of the susceptibility in QSM and the diameter on SWI for predicting cardioembolic stroke. The SVS was identified in 93 (70.5%) patients with symptomatic middle cerebral artery occlusion and was significantly associated with cardioembolism. The hyperintense signal on QSM in the corresponding middle cerebral artery occlusion was present in 116 (87.9%) patients. ROC analysis indicated that thrombus susceptibility had a greater area under the curve than that of the SVS diameter (0.88 vs. 0.70, P<0.001) and that the optimal cutoff value of thrombus susceptibility for cardioembolism was 0.35 ppm. Multivariate analysis demonstrated that thrombus susceptibility (≥0.35 ppm) was an independent predictor of cardioembolic stroke (odds ratio =20.75; 95% CI, 7.19-59.87; P<0.001), with sensitivity, specificity, a positive predictive value, and a negative predictive value of 85.2%, 80.8%, 75.4%, and 88.7%, respectively, while the SVS presence showed sensitivity, specificity, a positive predictive value, and a negative predictive value of 90.7%, 43.6%, 87.2%, and 52.7%, respectively. Thrombus susceptibility provides superior diagnostic performance over the SVS for discriminating between cardioembolism and other stroke subtypes. Quantitative susceptibility measurements of thrombi may help predict cardioembolic stroke in patients with acute middle cerebral artery occlusion.

Quantification of magnetic susceptibility fingerprint of a 3D linearity medical device.

The study investigates the numerical modelling as well as experimental validation of magnetic susceptibility effects with respect to a 3D linearity phantom used for the quantification of MR image distortions. Magnetic field numerical simulations based on finite difference methods were conducted to generate the susceptibility (χ) model of the MRID3D phantom. Experimental data was acquired and analyzed for eight different MR scanners to include a wide range of scanning parameters. Distortion vector fields were generated by applying a harmonic analysis based on finite elements methods. Phantom scans for the same setup but with opposite polarities of the frequency encoding gradient were processed in conjunction with the susceptibility modelling to separately quantify three field components due to gradient non-linearities (GNL), B0 inhomogeneities and χ perturbations. The numerical modelling showed a significant range of χ value of up to 8.23ppm, with a mean value of 2.9ppm. The χ perturbations were found to be mostly present at the end plates of the cylindrical phantom design. The simulations also showed that setup rotations of up to 10° introduced only negligible variations in the χ model of less than 0.1ppm. This allows for a straightforward practical implementation of the modelling as a single lookup table. After correcting for the χ perturbations, the B0 inhomogeneities were derived and found to be in good agreement with either the MR system manufacturer specifications or experimental data available in the literature. It is possible to accurately model the magnetic susceptibility signature of a 3D linearity device and remove it as a post-processing correction step. This is important as the procedure unlocks the ability of determining both the GNL field and B0 map of the scanner without the need of extra acquisitions or phantoms.

Measuring compartmental [formula omitted]-orientational dependence in human brain white matter using a tiltable RF coil and diffusion-[formula omitted] correlation MRI

The anisotropy of brain white matter microstructure manifests itself in orientational-dependence of various MRI contrasts, and can result in significant quantification biases if ignored. Understanding the origins of this orientation-dependence could enhance the interpretation of MRI signal changes in development, ageing and disease and ultimately improve clinical diagnosis. Using a novel experimental setup, this work studies the contributions of the intra- and extra-axonal water to the orientation-dependence of one of the most clinically-studied parameters, apparent transverse relaxation T2. Specifically, a tiltable receive coil is interfaced with an ultra-strong gradient MRI scanner to acquire multidimensional MRI data with an unprecedented range of acquisition parameters. Using this setup, compartmental T2 can be disentangled based on differences in diffusional-anisotropy, and its orientation-dependence further elucidated by re-orienting the head with respect to the main magnetic field B→0. A dependence of (compartmental) T2 on the fibre orientation w.r.t. B→0 was observed, and further quantified using characteristic representations for susceptibility- and magic angle effects. Across white matter, anisotropy effects were dominated by the extra-axonal water signal, while the intra-axonal water signal decay varied less with fibre-orientation. Moreover, the results suggest that the stronger extra-axonal T2 orientation-dependence is dominated by magnetic susceptibility effects (presumably from the myelin sheath) while the weaker intra-axonal T2 orientation-dependence may be driven by a combination of microstructural effects. Even though the current design of the tiltable coil only offers a modest range of angles, the results demonstrate an overall effect of tilt and serve as a proof-of-concept motivating further hardware development to facilitate experiments that explore orientational anisotropy. These observations have the potential to lead to white matter microstructural models with increased compartmental sensitivity to disease, and can have direct consequences for longitudinal and group-wise T2- and diffusion-MRI data analysis, where the effect of head-orientation in the scanner is commonly ignored.

Crossover from Kondo to Fermi-liquid behavior induced by high magnetic field in 1T−VTe2 single crystals

The magnetic and magnetotransport properties of metallic $1T\text{\ensuremath{-}}{\mathrm{VTe}}_{2}$ single crystals were investigated at temperatures from 1.3 to 300 K and in magnetic fields up to 35 T. Upon applying a high magnetic field, it is found that the electrical resistivity displays a crossover from the logarithmic divergence of the single-impurity Kondo effect to the Fermi liquid behavior at low temperatures. The Brillouin scale of the negative magnetoresistivity above the Kondo temperature ${T}_{\mathrm{K}}$ = 12 K indicates that the Kondo features originate from intercalated V ions, with $S$ = 1/2. Both magnetic susceptibility and Hall effect show an anomaly around ${T}_{\mathrm{K}}$. By using the modified Hamann expression we successfully describe the temperature-dependent resistivity under various magnetic fields, which shows the characteristic peak below ${T}_{\mathrm{K}}$ due to the splitting of the Kondo resonance.