Mean Magnetic Susceptibility Research Articles

Differentiating calcifications from cerebral microbleeds using quantitative susceptibility mapping.

To differentiate cerebral microbleeds (CMBs) and calcifications using quantitative susceptibility mapping (QSM). CMBs were visualized and located using QSM from susceptibility-weighted imaging data collected on a 3-T MR scanner. Calcifications of the pineal gland and the choroid plexus were localized first using CT. All calcifications and CMBs were assessed using QSM to evaluate their magnetic susceptibility. The distribution of the magnetic susceptibility for the CMBs was determined and the CT attenuation was correlated with the mean magnetic susceptibility for the calcifications. A total of 232 hypointense foci were selected from the QSM data: 121 were CMBs and 111 were calcifications. The mean magnetic susceptibility was -214 ± 112 ppb for the calcifications and 392 ± 204 ppb for the CMBs. The minimum value of magnetic susceptibility was 75 ppb for all the CMBs and the maximum value was -52 ppb for all the calcifications. The calcifications were clearly differentiable from the CMBs from the sign alone (p < 0.001). The magnetic susceptibility for the CMBs was 299 ± 133 ppb in the lobar subcortical white matter and 499 ± 220 ppb for deep CMBs in the basal ganglia, thalamus, and brainstem. There was a significant difference in the susceptibility between these two regions (p < 0.001). The sign of the magnetic susceptibility was sufficient to differentiate calcifications and CMBs. The concentration of calcium or iron can be determined from the susceptibility value itself. The deep CMBs had higher susceptibility on average than lobar bleeds. This study's ability to differentiate between CMBs and calcifications using QSM could enhance diagnostic accuracy, guiding more precise treatment decisions for stroke or tumor patients. The sign of magnetic susceptibility is sufficient to differentiate calcifications and CMBs. QSM can successfully differentiate calcifications from microbleeds. The concentration of calcium or iron can be determined from the susceptibility value itself.

Localized Changes in Dentate Nucleus Shape and Magnetic Susceptibility in Friedreich Ataxia.

The dentate nuclei of the cerebellum are key sites of neuropathology in Friedreich ataxia (FRDA). Reduced dentate nucleus volume and increased mean magnetic susceptibility, a proxy of iron concentration, have been reported by magnetic resonance imaging studies in people with FRDA. Here, we investigate whether these changes are regionally heterogeneous. Quantitative susceptibility mapping data were acquired from 49 people with FRDA and 46 healthy controls. The dentate nuclei were manually segmented and analyzed using three dimensional vertex-based shape modeling and voxel-based assessments to identify regional changes in morphometry and susceptibility, respectively. Individuals with FRDA, relative to healthy controls, showed significant bilateral surface contraction most strongly at the rostral and caudal boundaries of the dentate nuclei. The magnitude of this surface contraction correlated with disease duration, and to a lesser extent, ataxia severity. Significantly greater susceptibility was also evident in the FRDA cohort relative to controls, but was instead localized to bilateral dorsomedial areas, and also correlated with disease duration and ataxia severity. Changes in the structure of the dentate nuclei in FRDA are not spatially uniform. Atrophy is greatest in areas with high gray matter density, whereas increases in susceptibility-reflecting iron concentration, demyelination, and/or gliosis-predominate in the medial white matter. These findings converge with established histological reports and indicate that regional measures of dentate nucleus substructure are more sensitive measures of disease expression than full-structure averages. Biomarker development and therapeutic strategies that directly target the dentate nuclei, such as gene therapies, may be optimized by targeting these areas of maximal pathology. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Longitudinal Changes in Iron and Myelination Within Ischemic Lesions Associate With Neurological Outcomes: A Pilot Study.

Combined quantitative susceptibility mapping and R2* relaxometry can distinguish iron and myelin components in ischemic lesions. We aimed to investigate whether longitudinal changes in magnetic susceptibility and R2* values within ischemic lesions were associated with neurological outcomes. In this single-center prospective study, we included patients, 20 to 90 years of age, who were consecutively admitted to the stroke care unit between August 2020 and March 2022 due to acute ischemic stroke. The participants underwent 2 instances of quantitative susceptibility mapping and R2* relaxometry scanning before and after stroke rehabilitation. We compared the changes in these quantitative measures across different subtypes of acute ischemic stroke. Multiple linear regression models were used to investigate the associations between the National Institutes of Health Stroke Scale scores and the mean magnetic susceptibility and R2* values in ischemic lesions. Among a total of 112 patients with acute ischemic stroke, 32 participants (aged 73.3±9.4 years; 20 men and 12 women) were evaluated. The median time from stroke onset to the first imaging was 5 days and that to the second imaging was 102 days. The changes in magnetic susceptibility values of branch atheromatous disease were higher than those of cardioembolism (mean difference, 0.018 [95% CI, 0.009-0.027] ppm; P<0.001) and lacunar (mean difference, 0.013 [95% CI, 0.005-0.020] ppm; P=0.004). Across all patients, the changes in National Institutes of Health Stroke Scale scores were associated with those of magnetic susceptibility values (coefficient, 0.311 [95% CI, 0.098-0.520]; P=0.017) but not with R2* values (coefficient, 0.114 [95% CI, -0.127 to 0.345]; P=0.291). The longitudinal changes in the magnetic susceptibility values within ischemic lesions were associated with neurological outcomes during the restorative stages poststroke in patients experiencing acute ischemic stroke. URL: https://www.umin.ac.jp/ctr/; Unique identifier: UMIN000050719.

Quantitative susceptibility mapping from basal ganglia and related structures: correlation with disease severity in progressive supranuclear palsy.

We examined whether mean magnetic susceptibility values from deep gray matter structures in patients with progressive supranuclear palsy (PSP) differed from those in patients with Parkinson's disease (PD) and healthy volunteers, and correlated with the PSP rating scale. Head of caudate nucleus, putamen, globus pallidus, substantia nigra and red nucleus were the regions of interest. Mean susceptibility values from these regions in PSP patients were estimated using quantitative susceptibility mapping. Correlations with clinical severity of disease as measured by the PSP rating scale were examined. The mean susceptibility values were also compared with those from healthy volunteers and age- and disease duration-matched patients with PD. Data from 26 healthy volunteers, 26 patients with PD and 27 patients with PSP, were analysed. Patients with PSP had higher mean susceptibility values from all regions of interest when compared to both the other groups. The PSP rating scale scores correlated strongly with mean susceptibility values from the red nucleus and moderately with those from the putamen and substantia nigra. The scores did not correlate with mean susceptibility values from the caudate nucleus or globus pallidus. In patients with PD, the motor deficits correlated moderately with mean susceptibility values from substantia nigra. In patients with PSP, mean susceptibility values indicating the severity of mineralization of basal ganglia and related structures correlate with disease severity, the correlation of red nucleus being the strongest. Further studies are warranted to explore whether mean susceptibility values could serve as biomarkers for PSP.

Age-dependent changes in brain iron deposition and volume in deep gray matter nuclei using quantitative susceptibility mapping

BackgroundMicrostructural changes in deep gray matter (DGM) nuclei are related to physiological behavior, cognition, and memory. Therefore, it is critical to study age-dependent trajectories of biomarkers in DGM nuclei for understanding brain development and aging, as well as predicting cognitive or neurodegenerative diseases. ObjectivesWe aimed to (1) characterize age-dependent trajectories of mean susceptibility, adjusted volume, and total iron content simultaneously in DGM nuclei using quantitative susceptibility mapping (QSM); (2) examine potential contributions of sex related effects to the different age-dependence trajectories of volume and iron deposition; and (3) evaluate the ability of brain age prediction by combining mean magnetic susceptibility and volume of DGM nuclei. MethodsMagnetic susceptibilities and volumetric values of DGM nuclei were obtained from 220 healthy participants (aged 10–70 years) scanned on a 3T MRI system. Regions of interest (ROIs) were drawn manually on the QSM images. Univariate regression analysis between age and each of the MRI measurements in a single ROI was performed. Pearson correlation coefficients were calculated between magnetic susceptibility and adjusted volume in a single ROI. The statistical significance of sex differences in age-dependent trajectories of magnetic susceptibilities and adjusted volumes were determined using one-way ANCOVA. Multiple regression analysis was used to evaluate the ability to estimate brain age using a combination of the mean susceptibilities and adjusted volumes in multiple DGM nuclei. ResultsMean susceptibility and total iron content increased linearly, quadratically, or exponentially with age in all six DGM nuclei. Negative linear correlation was observed between adjusted volume and age in the head of the caudate nucleus (CN; R2 = 0.196, p < 0.001). Quadratic relationships were found between adjusted volume and age in the putamen (PUT; R2 = 0.335, p < 0.001), globus pallidus (GP; R2 = 0.062, p = 0.001), and dentate nucleus (DN; R2 = 0.077, p < 0.001). Males had higher mean magnetic susceptibility than females in the PUT (p = 0.001), red nucleus (RN; p = 0.002), and substantia nigra (SN; p < 0.001). Adjusted volumes of the CN (p < 0.001), PUT (p = 0.030), GP (p = 0.007), SN (p = 0.021), and DN (p < 0.001) were higher in females than those in males throughout the entire age range (10–70 years old). The total iron content of females was higher than that of males in the CN (p < 0.001), but lower than that of males in the PUT (p = 0.014) and RN (p = 0.043) throughout the entire age range (10–70 years old). Multiple regression analyses revealed that the combination of the mean susceptibility value of the PUT, and the volumes of the CN and PUT had the strongest associations with brain age (R2 = 0.586). ConclusionsQSM can be used to simultaneously investigate age- and sex- dependent changes in magnetic susceptibility and volume of DGM nuclei, thus enabling a comprehensive understanding of the developmental trajectories of iron accumulation and volume in DGM nuclei during brain development and aging.

Abstract WP106: Hemispheric Comparison Of Magnetic Susceptibility 24-72 Hours After Reperfusion

Introduction: Magnetic susceptibility is a radiological contrast mechanism that may provide a measure of oxygenation and contribute to an understanding the pathophysiology of stroke. Currently, there are few studies that have explored magnetic susceptibility in ischemic tissue as a marker of tissue injury. Our study assesses day one ischemic tissue post-reperfusion for changes in magnetic susceptibility and evaluates its relationship with radiological markers of ischemic injury - apparent diffusion coefficient (ADC). Methods: In a prospective observational study, thirty-five ischemic stroke patients who underwent endovascular thrombectomy were scanned with MRI (24 – 72 hours after reperfusion) to obtain multi-echo Gradient Echo and DWI images. An experienced neuroradiologist manually delineated ischemic tissue ROIs (region of interest) on DWI images. Contralateral ROIs were obtained using an automated method. The cerebrospinal fluid and regions of haemorrhagic transformation were excluded from the ROIs. A Morphology Enabled Dipole Inversion (MEDI) pipeline was employed to generate Quantitative Susceptibility Mapping (QSM) images, and these were used to quantify magnetic susceptibility. Mean magnetic susceptibility and mean ADC values were measured in these ROIs, and these values were then correlated. Results: Mean magnetic susceptibility of the ischemic ROI was significantly higher than that of the contralateral ROI (0.71±11.72 ppb, -5.59±7.30 ppb; p = 0.003). Mean ADC values of the ROI in the ischemic hemisphere were significantly lower than those in the contralateral hemisphere (0.65±0.09 х 10 -3 mm 2 /s, 0.81±0.05 х 10 -3 mm 2 /s; p = 1.31 х 10 -11 ). No significant correlation between susceptibility and ADC was found (ρ = -0.278, p = 0.106). Conclusion: Magnetic susceptibility in the ischemic tissue is measurable and is elevated when compared to the normal tissue. This may be attributed to the increased oxygen extraction fraction in the ischemic tissue. Further voxel wise analysis and larger longitudinal multi-parametric analysis correlating magnetic susceptibility with other imaging measures of tissue injury over time will help characterise the significance of lesional magnetic susceptibility changes in ischemic tissue.

Higher magnetic susceptibility of globus pallidus in patients after macrocyclic GBCAs: assessment using quantitative susceptibility mapping.

As previous studies reported, gadolinium deposits in globus pallidus (GP) and dentate nucleus (DN) after repeated administrations of gadolinium-based contrast agents (GBCAs) and a signal intensity (SI) increase on T1-weighted images were related to linear GBCAs, not macrocyclic GBCAs. To identify whether quantitative susceptibility mapping (QSM) could measure a subtle increase in magnetic susceptibility in DN and GP in patients after repeated administrations of gadoteric acid meglumine (Gd-DOTA). In this study, 50 patients with cerebral tumors who had received at least three injections of Gd-DOTA (GBCA group) and 50 individuals without a history of GBCA injections (non-GBCA group) were included. The image data for QSM and T1-weighted images were reviewed. Spearman rank correlation was used to estimate the associations between the values (magnetic susceptibility of QSM and SI ratios of T1-weighted images) and the number of Gd-DOTA injections. The mean magnetic susceptibility of GP in GBCA group was 0.136 ± 0.031 ppm, which was significantly higher than that in control group (0.114 ± 0.030 ppm) (P = 0.001). In the GBCA group (n = 50), we found a substantial positive correlation between magnetic susceptibility of GP and the number of Gd-DOTA injections according to Spearman rank correlation coefficient (ρ = 0.673, P = 0.0001). There was a modest but significant correlation between magnetic susceptibility of DN and the number of Gd-DOTA injections (ρ = 0.311, P = 0.028). In comparison to the control group, the magnetic susceptibility of GP in the GBCA group was significantly higher and had a substantial positive association with the number of Gd-DOTA injections.

Variation in Anisotropy of Magnetic Susceptibility with Depth in the Upper 1 km of the Earth’s Crust in Singhbhum Region (India) – First Results

Abstract In this paper the first results of anisotropy of magnetic susceptibility (AMS) studies carried out on 10 schist samples taken from different depths of a borehole in the vicinity of Singhbhum Shear Zone (SSZ) are presented. A cube of 8 cm3 volume was extracted from each borehole sample and its AMS was measured; the shallowest sample is from 112 m depth, while the deepest is from 850 m depth. In the depth vs. mean magnetic susceptibility (Km) plot, a sharp decrease in the Km values is noted in samples from 547 m and 588 m depths. Microstructural investigation of the different samples reveals presence of thick quartz veins in samples from the above mentioned depths vis-à-vis other samples. Petrographic studies also reveal presence of the mineral “allanite” in sample from 547 m depth, which contained a thick quartz vein. It is thus suggested that studies involving AMS investigation of borehole samples from the top 1 km depth of the region hold promise in mineral exploration studies.

An improved asymmetric susceptibility tensor imaging model with frequency offset correction.

To improve susceptibility tensor imaging (STI) reconstruction using the asymmetric STI model with the correction of non-bulk-magnetic-susceptibility (NBMS) effects. A frequency offset term was introduced into the asymmetric STI model to account for the bias between measured MRI frequency signals and conventional susceptibility tensor models because of NBMS contributions. Experiments were conducted to compare the proposed model with conventional STI, conventional STI with the proposed frequency offset correction, and asymmetric STI on simulation, ex vivo mouse brain, and in vivo human brain data. In the simulation where NBMS contributions are head rotation-invariant, the proposed method achieves the lowest errors in mean magnetic susceptibility (MMS) and magnetic susceptibility anisotropy (MSA) and is more robust to noise in the estimation of principal eigenvector (PEV). When considering the head orientation dependency of NBMS contributions, the proposed method shows advantages in estimating MSA and PEV. On the mouse and human brain data, the proposed method produces more reliable MSA maps and more consistent white matter fiber directions when referring to those from DTI than the compared STI methods. The proposed method can reduce the effects of NBMS-related frequency shifts on the susceptibility tensors in the brain white matter. This study inspires STI reconstruction from the perspective of better modeling the sources of frequency shifts.

Application of magnetic susceptibility and heavy metal bioaccessibility to assessments of urban sandstorm contamination and health risks: Case studies from Dunhuang and Lanzhou, Northwest China

Direct ingestion of sandstorm particles is an important pathway in human exposure to heavy metals. This study investigated the potential health risks of heavy metals transported in sandstorms from Dunhuang to Lanzhou in northwestern China using environmental magnetic parameters and metal bioaccessibilities in simulated gastric and intestinal tracts. The mean magnetic susceptibility of sandstorms in Lanzhou was 366.86 × 10−8 m3/kg, which was more than 5-fold higher than that of sandstorms in Dunhuang, indicating that these sandstorms continuously receive heavy metals with high magnetic mineral content along their pathways. Heavy metal concentrations in sandstorms were higher than background values and those in urban topsoil. Enrichment factors and pollution load indices showed that these heavy metals were derived from both natural and anthropogenic sources, with Cu, Zn, Pb, and Cd being strongly influenced by anthropogenic sources. The bioaccessibilities of Cd, Cu, Zn, and Pb in the sandstorms of Lanzhou were very high, ranging from 22.69% (Cu) to 50.86% (Pb) for gastric phase, and 12.07% (Pb)–22.11% (Cd) for interstinal phase, with the significant reduction in χlf of the physiologically-based extraction testing (PBET) treated sandstorms. The magnetic minerals are significant correlation with the concentrations of heavy metals in sandstorm and effect the release of heavy metals during human digestion process. The overall ecological risk posed by heavy metals contained in sandstorms was relatively low; however, the risk was moderate to high at individual sites. Ingestion posed the highest carcinogenic and non-carcinogenic risks for both adults and children, with the risk for children being higher.

Pressure, temperature and lithological dependence of seismic and magnetic susceptibility anisotropy in amphibolites and gneisses from the central Scandinavian Caledonides

As a petrofabric indicator, anisotropy of magnetic susceptibility (AMS) can potentially be used to infer seismic properties of rocks, and in particular seismic anisotropy. To evaluate the link between AMS and seismic anisotropy we present laboratory measurements of elastic wave velocities and anisotropy of magnetic susceptibility (AMS) for eight samples from the deep drilling investigation forming a part of the Collisional Orogeny in the Scandinavian Caledonides (COSC) project. The samples consist of a representative suite of mid crustal, deformed rock types, namely felsic and biotite-rich gneisses, and amphibolites (mafic gneisses). Compressional (P) and shear (S) waves were measured at confining pressures from room pressure to 600 MPa and temperature from room condition to 600 °C. Seismic anisotropy changes with increasing temperature and pressure, where the effect of pressure is more significant than temperature. Increasing pressure, considering the range of samples, results in an increase in mean wave speed values from 4.52 to 7.86 km/s for P waves and from 2.75 to 4.09 km/s for S waves. Biotite gneiss and amphibolite exhibit the highest anisotropy with P wave anisotropy (AVp) in the ranges of ~9% to ~20%, and maximum S- wave anisotropy exceeds 10%. In contrast, Felsic gneisses are significantly less anisotropic, with AVp of <7% and AVs of <6%. Up to 20% anisotropy may be generated by microcracks at 600 MPa and 600 °C, which is likely originating from thermal expansion of anisotropic minerals. An agreement is found between AMS and seismic anisotropy, although this is only a case if mean magnetic susceptibility (kmean) ranges between ~1 × 10−5 to ~1 × 10−3 [SI]. Such kmean values are common in rocks dominated by paramagnetic matrix minerals. Based on our results we propose that such samples are the most likely to be useful for the prediction of seismic anisotropy based on their AMS.

Quantitative Susceptibility Mapping of Venous Vessels in Neonates with Perinatal Asphyxia.

Cerebral venous oxygen saturation can be used as an indirect measure of brain health, yet it often requires either an invasive procedure or a noninvasive technique with poor sensitivity. We aimed to test whether cerebral venous oxygen saturation could be measured using quantitative susceptibility mapping, an MR imaging technique, in 3 distinct groups: healthy term neonates, injured term neonates, and preterm neonates. We acquired multiecho gradient-echo MR imaging data in 16 neonates with perinatal asphyxia and moderate or severe hypoxic-ischemic encephalopathy (8 term age: average, 40.0 [SD, 0.8] weeks' gestational age; 8 preterm, 33.5 [SD, 2.0] weeks' gestational age) and in 8 healthy term-age controls (39.3 [SD, 0.6] weeks, for a total of n = 24. Data were postprocessed as quantitative susceptibility mapping images, and magnetic susceptibility was measured in cerebral veins by thesholding out 99.95% of lower magnetic susceptibility values. The mean magnetic susceptibility value of the cerebral veins was found to be 0.36 (SD, 0.04) ppm in healthy term neonates, 0.36 (SD, 0.06) ppm in term injured neonates, and 0.29 (SD, 0.04) ppm in preterm injured neonates. Correspondingly, the derived cerebral venous oxygen saturation values were 73.6% (SD, 2.8%), 71.5% (SD, 7.4%), and 72.2% (SD, 5.9%). There was no statistically significant difference in cerebral venous oxygen saturation among the 3 groups (P = .751). Quantitative susceptibility mapping-derived oxygen saturation values in preterm and term neonates agreed well with values in past literature. Cerebral venous oxygen saturation in preterm and term neonates with hypoxic-ischemic encephalopathy, however, was not found to be significantly different between neonates or healthy controls.

Thermodynamic properties of a charged particle in non-uniform magnetic field

We solve the Schrödinger equation for a charged particle in the non-uniform magnetic field by using the Nikiforov–Uvarov method. We find the energy spectrum and the wave function, and present an explicit relation for the partition function. We give analytical expressions for the thermodynamic properties such as mean energy and magnetic susceptibility, and analyze the entropy, free energy and specific heat of this system numerically. It is concluded that the specific heat and magnetic susceptibility increase with external magnetic field strength and different values of the non-uniformity parameter, in the low temperature region, while the mentioned quantities are decreased in high temperature regions due to increasing the occupied levels at these regions. The non-uniformity parameter has the same effect with a constant value of the magnetic field on the behavior of thermodynamic properties. On the other hand, the results show that transition from positive to negative magnetic susceptibility depends on the values of non-uniformity parameter in the constant external magnetic field.

Structural deformation in Kaladawan of North Altun orogenic belt, NW China: Constraints from magnetic and EBSD fabrics

The North Altyn Tagh ductile shear zone is well exposed in the Kaladawan area of North Altun orogenic belt. The deformed rocks provide clues to the deformation conditions and the tectonic evolution of the North Altun orogen. This study investigated structural deformation in Kaladawan of North Altun orogenic belt using magnetic fabric and electronic backscattered diffraction (EBSD) quartz fabric in order to reveal the dynamic and kinematic characteristics of the North Altyn Tagh ductile shear zone. We conducted detailed field investigations and collected oriented samples to analyse magnetic and EBSD fabrics. The mean magnetic susceptibility (Km) value for the Kaladawan rocks is low, indicating that paramagnetic and diamagnetic minerals are the principal carriers of magnetic susceptibility. The corrected degree of anisotropy (Pj), magnetic lineation (L), magnetic foliation (F), shape parameter (T), and oblateness of the magnetic susceptibility ellipsoid (E) show that the deformation in the central part of a transect across Kaladawan is weak indicating elongated prolate strain, whereas the deformation in the north and south is strong indicating oblate strain. The anisotropic magnetic susceptibility (AMS) principal ellipsoidal axis K1 (magnetic lineation) trends mainly WNW–ESE and are oriented with variable magnetic foliation attitudes, whereas the AMS principal axis K3 (pole to magnetic foliation) trends NNE–SSW. Deformation under different conditions generated two types of quartz c‐axis fabric style: type A (point maximum) and type B (Y maximum plus crossed girdles). Fabric thermometry analyses suggest that the quartz fabrics formed at a medium temperature of 400–500°C. According to previous zircon U–Pb data from Kaladawan, deformation of the North Altyn Tagh ductile shear zone took place between 478.1 and 427.3 Ma. The ductile shear can be interpreted as a tectonic response to dextral oblique convergence between the Tarim and Central Altun blocks.

Structural Setting, Paleomagnetism, and Magnetic Fabric of Miocene Plutons in a Transpressional Sinistral Shear Zone, Tonalá, Chiapas, Mexico: Evidence of Shortening During Magma Emplacement

AbstractWe studied the structure, paleomagnetism, and magnetic fabric of Miocene granitoids intruded along the left‐lateral, transpressional, Tonalá shear zone in Chiapas, southern Mexico. Magmatic fabrics delineate patterns of regional folding striking parallel to the shear zone, suggesting syn‐magmatic shortening. Magnetic susceptibility fabrics are well developed, and mean magnetic susceptibility averages 18.6 × 10−3 SI. The magnetic fabric of the plutons is controlled primarily by MD and finer PSD magnetite, which also carries the magnetic remanence. The orientations of macroscopic mineral fabrics and magnetic susceptibility fabrics are consistently parallel in protomylonites, but their coincidence is good to poor in granitoids that preserve magmatic fabrics. Most site mean directions are NW‐NE directed of moderate positive inclination (or antipodal), but on a local scale site, mean directions are very discordant. The overall mean direction, omitting highly discordant sites, is of Decl. = 359.6° and Incl. = +41.9° (k = 14.4, α95 = 8.1°, N = 24 sites); it is nearly concordant with the North America reference direction, and the slight difference may indicate a gentle, north‐side down regional tilt. High directional dispersion is interpreted to reflect relative rotation about local vertical to sub‐vertical axes of plutons, or parts of plutons, along the shear zone, with some rotations interpreted to be caused by progressive deformation within the shear zone. Paleomagnetic and AMS data from the protomylonite rocks are interpreted to have been affected by the distortional strain, which accommodated shape and volume change in the rock. We suggest that the introduction of granitic magma into middle crustal levels critically enhanced the crustal response to shortening within the shear zone, possibly due to melt compressibility.

Magnetic signature of sewage polluted river sediments

The present study was designed to characterize the magnetic proxy for sewage-related pollution from river sediments. A suite of mineral magnetic analyses including low-field magnetic susceptibility, isothermal remanent magnetization (IRM) acquisition and demagnetization, back-field IRM treatment, and thermal demagnetization of composite IRMs are carried out for topsoil samples collected from river sediments in Daejeon, South Korea. A 350-m long in situ profile of magnetic susceptibility shows a background mean magnetic susceptibility of 22.4 ± 5.6 × 10−5 SI. The coercivity spectra display dual peaks of lower- and higher-coercivity fractions. The predominance of magnetic signal with maximum unblocking temperatures of 580 °C points to magnetite as the sole magnetic mineral. Hence the lower- and higher-coercivity fractions correspond to coarse-grained and fine-grained magnetite, respectively. Extraordinarily high magnetic susceptibility was observed from BTC02, near to the sewage discharge point. However, its mineral magnetic properties and particle morphologies are not different to those of other soil samples. Then, it is apparent that a high magnetic susceptibility simply reflects the high concentration of magnetites in BTC02. It is likely that a continuous discharge of heavy metal enriched water at the discharging point concentrated significant amount of magnetic particles. It is fortunate that anomalously high magnetic susceptibility (by implication heavy metal concentrations) diminished only several meters away from the discharge point. Perhaps, influences of anthropogenic magnetite were diluted as the high magnetic phases were washed away from the water cycles along the river. In practice, it can be proposed that a periodic replacement of soils near the sewage discharge point is efficient to reduce the heavy metal concentrations.

Anisotropy of magnetic susceptibility analysis in Tunas Formation cores (Permian), Claromecó Basin, Buenos Aires, Argentina: Its relation to depositional and post-depositional conditions

Anisotropy of magnetic susceptibility (AMS) has been used as an important tool to study magnetic fabrics and as a basis of interpretation of depositional conditions and post-depositional processes in sedimentary successions. This contribution presents results of standard AMS and magnetic mineralogy analysis performed in core samples from the PANG 0003 well, located at the Claromecó Basin, Buenos Aires province, Argentina. The sedimentary sequence analyzed has been assigned to the Tunas Formation (Permian), upper Pillahuincó Group, southwestern of the Gondwana boundary. Additionally, obtained results were compared with previous Tunas Formation outcrop data at the Sierras Australes and Claromecó Basin area.Measured AMS parameters vary with depth, reflecting changes in postdepositional conditions such as mechanical compaction and the influence of tectonic stress. Analyses of the mean magnetic susceptibility, thermomagnetic properties and petrographic studies indicate that paramagnetic minerals as Fe-phyllosilicates are the main contributors for the AMS of this sequence. Obtained AMS parameters are mainly characterized by triaxial to oblate AMS ellipsoids and shortening directions (Kmin) with a tendency to cluster in vertical positions, parallel to the bedding plane poles, assigned to sedimentary or weak deformed magnetic fabrics. By contrast, toward the base of the sequence, strongly oblate AMS ellipsoid shapes and Kmin axes that migrate to horizontal positions indicate a high deformation degree product of tectonic stress. The presented results are consistent with geological, AMS and paleomagnetic data from Tunas Formation outcrops and confirm that deformation degree was gradually attenuated upwards in the sequence, to the younger strata and toward the foreland Claromecó basin. The study of AMS parameters and magnetic mineralogy have proven to be important tools to interpret the processes that acted during the burial history of Tunas Formation, increasing the knowledge about the evolution of the Claromecó Basin.

Diffusion-regularized susceptibility tensor imaging (DRSTI) of tissue microstructures in the human brain.

Susceptibility tensor imaging (STI) has been proposed as an alternative to diffusion tensor imaging (DTI) for non-invasive in vivo characterization of brain tissue microstructure and white matter fiber architecture, potentially benefitting from its high spatial resolution. In spite of different biophysical mechanisms, animal studies have demonstrated white matter fiber directions measured using STI to be reasonably consistent with those from diffusion tensor imaging (DTI). However, human brain STI is hampered by its requirement of acquiring data at more than 10 head rotations and a complicated processing pipeline. In this paper, we propose a diffusion-regularized STI method (DRSTI) that employs a tensor spectral decomposition constraint to regularize the STI solution using the fiber directions estimated by DTI as a priori. We then explore the high-resolution DRSTI with MR phase images acquired at only 6 head orientations. Compared to other STI approaches, the DRSTI generated susceptibility tensor components, mean magnetic susceptibility (MMS), magnetic susceptibility anisotropy (MSA) and fiber direction maps with fewer artifacts, especially in regions with large susceptibility variations, and with less erroneous quantifications. In addition, the DRSTI method allows us to distinguish more structural features that could not be identified in DTI, especially in deep gray matters. DRSTI enables a more accurate susceptibility tensor estimation with a reduced number of sampling orientations, and achieves better tracking of fiber pathways than previous STI attempts on in vivo human brain.

Magnetic and Thermodynamic Properties of a Nanowire with Rashba Spin–Orbit Interaction

In this work, we have considered ballistic nanowires in the presence of gate-controlled Rashba spin–orbit interaction and an in-plane magnetic field. First, the energy expression of the nanowires was obtained. Then, the analytical relations for the mean energy, free energy, specific heat, entropy and magnetic susceptibility of the system were derived. It is found that the specific heat and magnetic susceptibility show peak structure in the presence of spin–orbit and magnetic field. The peak position of specific heat depends on the Rashba constant, Zeeman splitting parameter and the angle between magnetic field and the wire axis (θ). The peak of magnetic susceptibility disappears with increasing magnetic field and decreasing θ.

Magnetic properties of pseudotachylytes from western Jämtland, central Swedish Caledonides

Abstract. Fault kinematics can provide information on the relationship and assembly of tectonic units in an orogen. Magnetic fabric studies of faults where pseudotachylytes form have recently been used to determine direction and sense of seismic slip in prehistoric earthquakes. Here we apply this methodology to study magnetic fabrics of pseudotachylytes in field structures of the Köli Nappe Complex (central Swedish Caledonides), with the aim to determine fault kinematics and decipher the role of seismic faulting in the assembly of the Caledonian nappe pile. Because the pseudotachylyte veins are thin, we focused on small (ca. 0.2 to 0.03 cm3) samples for measuring the anisotropy of magnetic susceptibility. The small sample size challenges conventional use of magnetic anisotropy and results acquired from such small specimens demand cautious interpretation. Importantly, we find that magnetic fabric results show inverse proportionality among specimen size, degree of magnetic anisotropy and mean magnetic susceptibility, which is most likely an analytical artifact related to instrument sensitivity and small sample dimensions. In general, however, it is shown that the principal axes of magnetic susceptibility correspond to the orientation of foliation and lineation, where the maximum susceptibility (k1) is parallel to the mineral lineation, and the minimum susceptibility (k3) is dominantly oriented normal to schistosity. Furthermore, the studied pseudotachylytes develop distinct magnetic properties. Pristine pseudotachylytes preserve a signal of ferrimagnetic magnetite that likely formed during faulting. In contrast, portions of the pseudotachylytes have altered, with a tendency of magnetite to break down to form chlorite. Despite magnetite breakdown, the altered pseudotachylyte mean magnetic susceptibility is nearly twice that of altered pseudotachylyte, likely originating from the Fe-rich chlorite, as implied by temperature-dependent susceptibility measurements and thin-section observations. Analysis of structural and magnetic fabric data indicates that seismic faulting occurred during exhumation into the upper crust, but these data yield no kinematic information on the direction and sense of seismic slip. Additionally, the combined structural field and magnetic fabric data suggest that seismic faulting was postdated by brittle E–W extensional deformation along steep normal faults. Although the objective of finding kinematic indicators for the faulting was not fully achieved, we believe that the results from this study may help guide future studies of magnetic anisotropy with small specimens (&lt;1 cm3), as well as in the interpretation of magnetic properties of pseudotachylytes.