Changes In Magnetic Susceptibility Research Articles

A Late Holocene climate reconstruction from the high-altitude Lake Gölcük sedimentary records, Isparta (SW Anatolia)

AbstractA high-resolution multiproxy lake sediment dataset, comprising lithology, radiography, μXRF elemental, magnetic susceptibility (MS), δ13C, and δ18O measurements since ca. AD 400 is presented in this study. Changes in lithology, radiography, magnetic susceptibility (MS), δ13C, and δ18O reflect wet/dry climate periods, whereas variability in log(Ca/K) can reflect warm/cold climate periods. Analyses of the multiproxy results allow the distinction of several climate periods, which may be associated with climatic phenomena such as changes in North Atlantic Oscillation (NAO) and/or solar activity. The influence of NAO−/NAO+ (negative/positive) is suggested to be related with the southward/northward displacement of the storm tracks resulting from the NAO−/NAO+ phases. For solar activity, the influence is explained through a direct increase in solar heating leading to calcite precipitation. The Dark Ages Cold Period (DACP, AD 450–750) reflects cold-dry climate conditions at this site, indicative of a positive North Atlantic Oscillation (NAO+) and low solar activity. The Medieval Climate Anomaly (MCA, AD 950–1250) exhibits wet-dry-wet and warm-cold-warm climate conditions. The wet/dry periods likely are associated with NAO−/NAO+, respectively, and the warm/cold period may reflect relatively high/low solar activity. The Little Ice Age (LIA, AD 1400–1850) is characterized by dry and cold climate conditions, suggesting the influence of NAO+ and low solar activity. Comparison of the results of this study with local and regional results suggests a generally similar climate pattern, which is indicative of similar climate mechanisms. The contradictions can be associated with age-related uncertainties, orographic differences, and/or other regional teleconnections.

Investigation of contrast mechanisms for MRI phase signal-based proton beam visualization in water phantoms.

The low sensitivity and limitation to water phantoms of convection-dependent MRI magnitude signal-based proton beam visualization hinder its in vivo applicability in MR-integrated proton beam therapy. The purpose of the present study was, therefore, to assess possible contrast mechanisms for MRI phase signal-based proton beam visualization that can potentially be exploited to enhance the sensitivity of the method and extend its applicability to tissue materials. To assess whether proton beam-induced magnetic field perturbations, changes in material susceptibility or convection result in detectable changes in the MRI phase signal, water phantom characteristics, experiment timing, and imaging parameters were varied in combined irradiation and imaging experiments using a time-of-flight angiography pulse sequence on a prototype in-beam MRI scanner. Velocity encoding was used to further probe and quantify beam-induced convection. MRI phase signal-based proton beam visualization proved feasible. The observed phase difference contrast was evoked by beam-induced buoyant convection with flow velocities in the mm/s range. Proton beam-induced magnetic field perturbations or changes in magnetic susceptibility did not influence the MRI phase signal. Velocity encoding was identified as a means to enhance the detection sensitivity. Because the MRI phase difference contrast observed during proton beam irradiation of water phantoms is caused by beam-induced convection, this method will unlikely be transferable to tightly compartmentalized tissue wherein flow effects are restricted. However, strong velocity encoded pulse sequences were identified as promising candidates for the future development of MRI-based methods for water phantom-based geometric quality assurance in MR-integrated proton beam therapy.

Ab initio description of magnetic and critical properties of spin-glass pyrochlore NaSrMn2F7

In this study, I have investigated the magnetic and critical properties of manganese pyrochlore fluoride NaSrMn2F7, which exhibits a glass transition at Tf = 2.5 (K) due to charge disorder. A DFT + U + SOC framework is used in this paper to derive spin-Hamiltonian terms, including isotropic and anisotropic exchange interactions. An optimized geometry reveals a local distortion of the F–Mn–F angle along the ⟨111⟩ direction (95.48° and 84.51°), which is considered a weak bond disorder (δJ). Despite the complex structure of this material, first principle calculations show that its magnetic properties are only controlled by the nearest neighbor’s Heisenberg exchange interaction, and other interactions do not affect spin arrangements in the ground state. Thus, this material is considered a suitable candidate for studying electron correlation in spin glasses. Using a replica-exchange framework, Monte Carlo simulations indicate that with δJ=0, no phase transition is observed when magnetic susceptibility changes with temperature. The results demonstrate that the presence of local bond disorder serves as a perturbation, and the degeneracy of the energy manifold of the system persists if its effect is not taken into consideration. Based on δJ=0.13(meV) and the derived spin Hamiltonian, 2.6 (K) is obtained as the phase transition temperature.

Microstructural and functional impairment of the basal ganglia in Wilson's disease: a multimodal neuroimaging study.

Magnetic susceptibility changes in brain MRI of Wilson's disease (WD) patients have been described in subcortical nuclei especially the basal ganglia. The objectives of this study were to investigate its relationship with other microstructural and functional alterations of the subcortical nuclei and the diagnostic utility of these MRI-related metrics. A total of 22 WD patients and 20 healthy controls (HCs) underwent 3.0T multimodal MRI scanning. Susceptibility, volume, diffusion microstructural indices and whole-brain functional connectivity of the putamen (PU), globus pallidus (GP), caudate nucleus (CN), and thalamus (TH) were analyzed. Receiver operating curve (ROC) was applied to evaluate the diagnostic value of the imaging data. Correlation analysis was performed to explore the connection between susceptibility change and microstructure and functional impairment of WD and screen for neuroimaging biomarkers of disease severity. Wilson's disease patients demonstrated increased susceptibility in the PU, GP, and TH, and widespread atrophy and microstructural impairments in the PU, GP, CN, and TH. Functional connectivity decreased within the basal ganglia and increased between the PU and cortex. The ROC model showed higher diagnostic value of isotropic volume fraction (ISOVF, in the neurite orientation dispersion and density imaging model) compared with susceptibility. Severity of neurological symptoms was correlated with volume and ISOVF. Susceptibility was positively correlated with ISOVF in GP. Microstructural impairment of the basal ganglia is related to excessive metal accumulation in WD. Brain atrophy and microstructural impairments are useful neuroimaging biomarkers for the neurological impairment of WD.

Quantitative Evaluation of Oxygen Extraction Fraction Changes in the Monkey Brain during Acute Stroke by Using Quantitative Susceptibility Mapping.

The oxygen extraction fraction (OEF) indicates the brain's oxygen consumption and can be estimated by using the quantitative susceptibility mapping (QSM) MRI technique. Recent studies have suggested that OEF alteration following stroke is associated with the viability of at-risk tissue. In the present study, the temporal evolution of OEF in the monkey brain during acute stroke was investigated using QSM. Ischemic stroke was induced in adult rhesus monkeys (n = 8) with permanent middle cerebral artery occlusion (pMCAO) by using an interventional approach. Diffusion-, T2-, and T2*-weighted images were conducted on day 0, day 2, and day 4 post-stroke using a clinical 3T scanner. Progressive changes in magnetic susceptibility and OEF, along with their correlations with the transverse relaxation rates and diffusion indices, were examined. The magnetic susceptibility and OEF in injured gray matter of the brain significantly increased during the hyperacute phase, and then decreased significantly on day 2 and day 4. Moreover, the temporal changes of OEF in gray matter were moderately correlated with mean diffusivity (MD) (r = 0.52; p = 0.046) from day 0 to day 4. Magnetic susceptibility in white matter progressively increased (from negative values to near zero) during acute stroke, and significant increases were seen on day 2 (p = 0.08) and day 4 (p = 0.003) when white matter was significantly degenerated. However, significant reduction of OEF in white matter was not seen until day 4 post-stroke. The preliminary results demonstrate that QSM-derived OEF is a robust approach to examine the progressive changes of gray matter in the ischemic brain from the hyperacute phase to the subacute phase of stroke. The changes of OEF in gray matter were more prominent than those in white matter following stroke insult. The findings suggest that QSM-derived OEF may provide complementary information for understanding the neuropathology of the brain tissue following stroke and predicting stroke outcomes.

Characterization of susceptibility artifacts in magnetic resonance thermometry images during laser interstitial thermal therapy: dimension analysis and temperature error estimation

Objective. Laser interstitial thermal therapy (LITT) is a minimally invasive procedure used to treat a lesion through light irradiation and consequent temperature increase. Magnetic resonance thermometry imaging (MRTI) provides a multidimensional measurement of the temperature inside the target, thus enabling accurate monitoring of the damaged zone during the procedure. In proton resonance frequency shift-based thermometry, artifacts in the images may strongly interfere with the estimated temperature maps. In our work, after noticing the formation of the dipolar-behavior artifact linkable to magnetic susceptibility changes during in vivo LITT, an investigation of susceptibility artifacts in tissue-mimicking phantoms was implemented. Approach. The artifact was characterized: (i) by measuring the area and total volume of error regions and their evolution during the treatment; and (ii) by comparison with temperature reference provided by three temperature sensing needles. Lastly, a strategy to avoid artifacts formation was devised by using the temperature-sensing needles to implement a temperature-controlled LITT. Main results. The artifact appearance was associated with gas bubble formation and with unwanted treatment effects producing magnetic susceptibility changes when 2 W laser power was set. The analysis of the artifact’s dimension demonstrated that in the sagittal plane the dipolar-shape artifact may consistently spread following the temperature trend until reaching a volume 8 times bigger than the ablated one. Also, the artifact shape is quite symmetric with respect to the laser tip. An absolute temperature error showing a negative Gaussian profile in the area of susceptibility artifact with values up to 64.4 °C was estimated. Conversely, a maximum error of 2.8 °C is measured in the area not-affected by artifacts and far from the applicator tip. Finally, by regulating laser power, susceptibility artifacts formation was avoided, and appreciable thermal damage was induced. Significance. These findings may help in improving the MRTI-based guidance of thermal therapies.

Multimodal comparisons of QSM and PET in neurodegeneration and aging

Quantitative susceptibility mapping (QSM) has been used to study susceptibility changes that may occur based on tissue composition and mineral deposition. Iron is a primary contributor to changes in magnetic susceptibility and of particular interest in applications of QSM to neurodegeneration and aging. Iron can contribute to neurodegeneration through inflammatory processes and via interaction with aggregation of disease-related proteins. To better understand the local susceptibility changes observed on QSM, its signal has been studied in association with other imaging metrics such as positron emission tomography (PET). The associations of QSM and PET may provide insight into the pathophysiology of disease processes, such as the role of iron in aging and neurodegeneration, and help to determine the diagnostic utility of QSM as an indirect indicator of disease processes typically evaluated with PET. In this review we discuss the proposed mechanisms and summarize prior studies of the associations of QSM and amyloid PET, tau PET, TSPO PET, FDG-PET, 15O-PET, and F-DOPA PET in evaluation of neurologic diseases with a focus on aging and neurodegeneration.

East Asian hydroclimate responses to the Eocene-Oligocene transition in the Weihe Basin, central China

The Eocene-Oligocene transition (EOT) at ∼34 Ma marked a significant global cooling on Earth when the ice cover in the Antarctic was formed. How the regional hydroclimate responded to this global cooling event has been extensively investigated, but the specific processes in the Asian monsoon dominated regions are still elusive, due to the lack of independent and detailed timescales. Moreover, previous sedimentary records are mainly from the Asian interior and the influence of tectonic deformation/uplifts in northeastern Tibetan Plateau on the deposit records has not been effectively separated. Here, we present a high-resolution hydroclimate record from a fluvial-lacustrine sequence in the Weihe Basin, central China, which is dated from ∼34.9 to 31.5 Ma by a high-resolution magnetostratigraphy with age controls of mammal fossil assemblages and apatite fission track (AFT) chronometry. This record shows a remarkable hydroclimatic shift occurred at ∼33.7 Ma, as manifested by a sedimentary environment change from lakeshore to lake-delta. The associated significant changes in sediment grain size and magnetic susceptibility exhibit responses of regional drying to the EOT and the Early Oligocene Glacial Maximum (EOGM). In addition, spectral analyses of the time series of paleoenvironmental proxies reveal that the hydroclimate also varied at orbital frequencies with relatively persistent eccentricity cycles (∼100 kyr), accompanied by precession (∼20 kyr) and obliquity (∼ 40 kyr) cycles after the formation of the Antarctic ice sheet at ∼33.2 Ma. Our results suggest that the monsoon-like paleoclimate variations in the mid-latitude northern Hemisphere during the EOT were partly modulated by high-latitude temperature and insolation variations.

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.

The Influence of Sewage Sludge and Fly Ash Fertilization on the Total Number of Bacteria (TNB) and Bradyrhizobium Species in Soybean Agroecosystem

The aim of this study was to determine the impact of different chemical properties in soil, including changes in magnetic susceptibility and the impact of humic substances from sewage sludge and fly ash on the microbial community in the soybean agroecosystem. A field experiment was carried out using the random plot method on Cambisol with a texture of silt loam. The experiment consisted of 24 plots (six treatments and four replications) using different dozes of sewage sludge and fly ash. The following physicochemical and chemical analyses were performed in the soil samples: pH in KCl, conductivity (λ), total content of heavy metal, magnetic measurements and fractional composition of organic matter. The TNB and the number of the species of Bradyrhizobium in the field cultivation of the soybean variety Lissabon were evaluated using the spread plate method. The total content of heavy metals (Cu, Zn, Cd, Ni, Pb, Cr, Hg, Fe) in the analyzed treatments showed a significant difference between them. The study of the magnetic parameter χ indicated a significant differentiation between treatments from 34.0 to 65.8 × 10−8·m3·kg−1. High correlation coefficients between χ and Fe (r = 0.789), Zn (r = 0.653), Cr (r = 0.617) and TOC (r = 0.949) indicated that the source of these elements was external organic matter. Biological tests (TNB and species of Bradyrhizobium) in different experimental treatments indicated significant relationships between them and showed the resistance of the microbial community in the field cultivation of Lissabon soybean to heavy metal contamination from sewage sludge and fly ash. The study confirmed that external organic matter, such as sewage sludge, can be used as an alternative to natural fertilizers for soybean production.

Spatial patterns of elevated magnetic susceptibility in progressive apraxia of speech

PurposeProgressive apraxia of speech (PAOS) is a neurodegenerative disorder affecting the planning or programming of speech. Little is known about its magnetic susceptibility profiles indicative of biological processes such as iron deposition and demyelination. This study aims to clarify (1) the pattern of susceptibility in PAOS patients, (2) the susceptibility differences between the phonetic (characterized by predominance of distorted sound substitutions and additions) and prosodic (characterized by predominance of slow speech rate and segmentation) subtypes of PAOS, and (3) the relationships between susceptibility and symptom severity. MethodsTwenty patients with PAOS (nine phonetic and eleven prosodic subtypes) were prospectively recruited and underwent a 3 Tesla MRI scan. They also underwent detailed speech, language, and neurological evaluations. Quantitative susceptibility maps (QSM) were reconstructed from multi-echo gradient echo MRI images. Region of interest analysis was conducted to estimate susceptibility coefficients in several subcortical and frontal regions. We compared susceptibility values between PAOS and an age-matched control group and performed a correlation analysis between susceptibilities and an apraxia of speech rating scale (ASRS) phonetic and prosodic feature ratings. ResultsThe magnetic susceptibility of PAOS was statistically greater than that of controls in subcortical regions (left putamen, left red nucleus, and right dentate nucleus) (p < 0.01, also survived FDR correction) and in the left white-matter precentral gyrus (p < 0.05, but not survived FDR correction). The prosodic patients showed greater susceptibilities than controls in these subcortical and precentral regions. The susceptibility in the left red nucleus and in the left precentral gyrus correlated with the prosodic sub-score of the ASRS. ConclusionMagnetic susceptibility in PAOS patients was greater than controls mainly in the subcortical regions. While larger samples are needed before QSM is considered ready for clinical differential diagnosis, the present study contributes to our understanding of magnetic susceptibility changes and the pathophysiology of PAOS.

Standard deviations of MR signal intensities show a consistent trend during imaging follow-ups for glioblastoma patients when corrected for non-biological heterogeneity due to hardware and software variation

IntroductionGlioblastoma multiforme (GBM) has a poor prognosis in spite of advanced MRI guided treatments today. Routine MRI using conventional T1 or advanced permeability based MRI of GBM often does not adequately represent changing tumor phases or overall survival. In this work, region of interest (ROI) based tissue MR standard deviation (SD) is demonstrated as an important MRI variable that could be a potential biomarker of GBM heterogeneity and radioresistance. Materials and methodsMRI characterization is often qualitative and lacks reproducibility. Using standardized MRI phantoms we have normalized retrospective records of 12 radioresistant GBM patients that underwent radiation therapy (RT) with concomitant and adjuvant temozolomide (TMZ) chemotherapy followed by serial MR imaging with gadolinium contrast. Results and discussionWe have identified key variables like hardware, software and protocol variation and have standardized those using test phantoms at five MR systems. We suggest GBM growth during the treatment period can be linked to normalized MRI signal and its fluctuations from session to session and from magnet to magnet by using an ROI derived standard deviation that corresponds to heterogeneity of the tumor MRI signal and changes in magnetic susceptibility. The time period observed in our patient group for peak standard deviations is approximately halfway through the tumor course and may correspond to a growth of more aggressive MES subtype of cells. To model the GBM heterogeneity we performed in vitro T1 weighted inversion recovery MRI experiments at 3 T for porous media of silicate particles in 1% aq solution of Gadavist and linked SD with particle size and local gadolinium volume within porous media. Such in vitro models mimic the increased SD in radioresistant GBM and as a novel contribution suggest that finer texture with high surface area might arise approximately halfway through the overall survival duration in GBM. ConclusionStandard deviation as a measure of magnetic susceptibility may be collectively linked to the changes in texture, cell fractions (biological) and trapped contrast media (vascular as well as artifactual consequences) and should be evaluated as a potential biomarker of GBM aggressiveness than the overall MRI signal intensity from a GBM.

HALO: A software tool for real-time head alignment in the MR scanner.

MRI studies in human subjects often require multiple scanning sessions/visits. Changes in a subject's head position across sessions result in different alignment between brain tissues and the magnetic field which leads to changes in magnetic susceptibility. These changes can have considerable impacts on acquired signals. Head ALignment Optimization (HALO), a software tool was developed by the authors for active head alignment between sessions. HALO provides real-time visual feedback of a subject's current head position relative to the position in a previous session. The tool was evaluated in a pilot sample of seven healthy human subjects. HALO was shown to enable subjects to actively align their head positions to the desired position of their initial sessions. The subjects were able to improve their head alignment significantly using HALO and achieved good alignment with their first session meeting stringent criteria similar to that used for within-run head motion (less than 2 mm translation or 2 degrees rotation in any direction from the desired position). Moreover, we found a negative correlation between the post-alignment rotation and similarity in inter-session BOLD patterns around the air-tissue interface near sinus which further highlighted the impact of tissue-field alignment on BOLD data quality. Utilization of HALO in longitudinal studies may help to improve data quality by ensuring the consistency of susceptibility gradients in brain tissues across sessions. HALO has been made publicly available.

Red blood cell magnetophoresis as a function of oxygen partial pressure

Red blood cell (RBC) magnetophoresis is a function of the concentration of dissolved oxygen (O2) in normal RBCs measured by cell tracking velocimetry (CTV). The hemoglobin (Hb) magnetic susceptibility changes from diamagnetic (when fully oxygenated, oxyHb) to paramagnetic (when fully deoxygenated, deoxyHb) resulting in a small shift in the normal RBC diamagnetic susceptibility from lower to higher than that of water (-9.05 × 10-6). To date, the RBC magnetophoretic motion analyses have been limited to only two quaternary states of the Hb-O2 complexes, fully oxygenated RBCs (i.e. 100 % O2 saturation of Hb inside RBCs) and fully deoxygenated RBCs (0 % O2 saturation of Hb inside RBCs). In this work, the RBC magnetophoretic velocity is measured at small pO2 intervals for the entire physiological range of 0–160 mmHg. The changes in the RBC magnetophoresis as a function of the O2 partial pressure in solution (pO2) agreed with the theoretical predictions based on the RBC-O2 equilibrium curve (OEC, measured by Hemox Analyzer and Blood Oxygen Binding System, BOBS™) and the Adair O2-Hb cooperative binding theory. The results provide a scientific basis for future designs of a “magnetic filter” based on the precise control of the RBC magnetic moment by carefully controlling the pO2 of the RBC suspension.

Clinical correlates of R1 relaxometry and magnetic susceptibility changes in multiple sclerosis: a multi-parameter quantitative MRI study of brain iron and myelin

ObjectivesThe clinical impact of brain microstructural abnormalities in multiple sclerosis (MS) remains elusive. We aimed to characterize the topography of longitudinal relaxation rate (R1) and quantitative susceptibility (χ) changes, as indices of iron and myelin, together with brain atrophy, and to clarify their contribution to cognitive and motor disability in MS.MethodsIn this cross-sectional study, voxel-based morphometry, and voxel-based quantification analyses of R1 and χ maps were conducted in gray matter (GM) and white matter (WM) of 117 MS patients and 53 healthy controls. Voxel-wise between-group differences were assessed with nonparametric permutation tests, while correlations between MRI metrics and clinical variables (global disability, cognitive and motor performance) were assessed both globally and voxel-wise within clusters emerging from the between-group comparisons.ResultsMS patients showed widespread R1 decrease associated with more limited modifications of χ, with atrophy mainly involving deep GM, posterior and infratentorial regions (p < 0.02). While R1 and χ showed a parallel reduction in several WM tracts (p < 0.001), reduced GM R1 values (p < 0.001) were associated with decreased thalamic χ (p < 0.001) and small clusters of increased χ in the caudate nucleus and prefrontal cortex (p < 0.02). In addition to the atrophy, χ values in the cingulum and corona radiata correlated with global disability and motor performance, while focal demyelination correlated with cognitive performance (p < 0.04).ConclusionsWe confirmed the presence of widespread R1 changes, involving both GM and WM, and atrophy in MS, with less extensive modifications of tissue χ. While atrophy and χ changes are related to global and motor disability, R1 changes are meaningful correlates of cognition.Key Points• Compared to healthy controls, multiple sclerosis patients showed R1 and χ changes suggestive of iron increase within the basal ganglia and reduced iron and myelin content within (subnuclei of) the thalamus.• Thalamic volume and χ changes significantly predicted clinical disability, as well as pulvinar R1 and χ changes, independently from atrophy.• Atrophy-independent R1 and χ changes, suggestive of thalamic iron and myelin depletion, may represent a sensitive marker of subclinical inflammation.

The Effects of Wearing a 3-Ply or KN95 Face Mask on Cerebral Blood Flow and Oxygenation.

BackgroundThe SARS‐CoV‐2 virus has impacted life in many ways, one change being the use of face masks. Their effect on MRI‐based measurements of cerebral oxygen levels with quantitative susceptibility mapping (QSM) and cerebral blood flow (CBF) is not known.PurposeThis study investigated whether wearing a face mask leads to changes in CBF and cerebral venous oxygen saturation measured with MRI.Study TypeRepeated‐measures cohort study.PopulationA total of 16 healthy volunteers (eight male, eight female; 22–36 years) were recruited for the 3‐ply study. Ten of the 16 participants (five male, five female; 23–36 years) took part in the KN95 study.Field Strength/SequenceA 3 T, single‐delay 3D gradient‐and spin‐echo pseudo‐continuous arterial spin labeling (pCASL) scan for CBF quantification, and gradient‐echo for QSM and oxygenation quantification.AssessmentGray matter CBF and magnetic susceptibility were assessed by masking the pCASL CBF map and the QSM map to the T1‐weighted gray matter tissue segmentation. Venous oxygenation was determined from venous segmentation of QSM maximum intensity projections.Statistical TestsPaired Student's t‐tests and Cohen's d effect sizes were used to compare the face mask and no face mask scans for gray matter CBF, gray matter magnetic susceptibility, and cerebral venous oxygen saturation. Standard t‐tests were used to assess whether the order of scanning with and without a mask had any impact. A statistical cut off of P < 0.05 was used.ResultsThe 3‐ply masks increased gray matter CBF from an average of 43.99 mL/(100 g*min) to 46.81 mL/(100 g*min). There were no significant changes in gray matter magnetic susceptibility (P = 0.07), or cerebral venous oxygen saturation (P = 0.36) for the 3‐ply data set. The KN95 masks data set showed no statistically significant changes in gray matter CBF (P = 0.52) and magnetic susceptibility (P = 0.97), or cerebral venous oxygen saturation (P = 0.93).Data ConclusionThe changes in blood flow and oxygenation due to face masks are small. Only CBF increased significantly due to wearing a 3‐ply mask.Evidence Level2Technical EfficacyStage 3

Effect of Normal Breathing on the Movement of CSF in the Spinal Subarachnoid Space.

Forced respirations reportedly have an effect on CSF movement in the spinal canal. We studied respiratory-related CSF motion during normal respiration. Six healthy subjects breathed at their normal rate with a visual guide to ensure an unchanging rhythm. Respiratory-gated phase-contrast MR flow images were acquired at 5 selected axial planes along the spine. At each spinal level, we computed the flow rate voxelwise in the spinal canal, together with the associated stroke volume. From these data, we computed the periodic volume changes of spinal segments. A phantom was used to quantify the effect of respiration-related magnetic susceptibility changes on the velocity data measured. At each level, CSF moved cephalad during inhalation and caudad during expiration. While the general pattern of fluid movement was the same in the 6 subjects, the flow rates, stroke volumes, and spine segment volume changes varied among subjects. Peak flow rates ranged from 0.60 to 1.59 mL/s in the cervical region, 0.46 to 3.17 mL/s in the thoracic region, and 0.75 to 3.64 mL/s in the lumbar region. The differences in flow rates along the canal yielded cyclic volume variations of spine segments that were largest in the lumbar spine, ranging from 0.76 to 3.07 mL among subjects. In the phantom study, flow velocities oscillated periodically during the respiratory cycle by up to 0.02 cm/s or 0.5%. Respiratory-gated measurements of the CSF motion in the spinal canal showed cyclic oscillatory movements of spinal fluid correlated to the breathing pattern.

A Preliminary Study of Alterations in Iron Disposal and Neural Activity in Ischemic Stroke.

Purpose The study aimed to evaluate the postrehabilitation changes in deep gray matter (DGM) nuclei, corticospinal tract (CST), and motor cortex area, involved in motor tasks in patients with ischemic stroke. Methods Three patients participated in this study, who had experienced an ischemic stroke on the left side of the brain. They underwent a standard rehabilitation program for four consecutive weeks, including transcranial direct current stimulation (tDCS), neuromuscular electrical stimulation (NMES), and occupational therapy. The patients' motor ability was evaluated by Fugl-Meyer assessment-upper extremity (FMA-UE) and Wolf motor function test (WMFT). Multimodal magnetic resonance imaging (MRI) was acquired from the patients by a 3 Tesla machine before and after the rehabilitation. The magnetic susceptibility changes were examined in DGM nuclei including the bilateral caudate (CA), putamen (PT), globus pallidus (GP), and thalamus (TH) using quantitative susceptibility mapping (QSM). Functional MRI (fMRI) in the motor cortex areas was acquired to evaluate the postrehab functional motor activity. The three-dimensional corticospinal tract (CST) was reconstructed using diffusion-weighted imaging (DWI) and diffusion tensor tractography (DTT), and the fractional anisotropy (FA) was measured along the tract. Ultimately, the relationship between the structural and functional changes was evaluated in CST and motor cortex. Results Postrehabilitation FMA-UE and WMFT scores increased for all patients compared to the prerehabilitation. QSM analysis revealed increasing in susceptibility values in GP and CA in all patients at the ipsilesional hemisphere. By fMRI analysis, the ipsilesional hemisphere demonstrated an increase in functional activity in motor areas for all 3 patients. In the ipsilesional hemisphere, the fractional anisotropy (FA) was increased in CST in two patients, while the mean diffusivity (MD) was decreased in CA in a patient, in PT and TH in another patient, and in PT in two patients. Conclusion This preliminary study demonstrates that the magnetic susceptibility may decrease at some ipsilesional DGM nuclei after tDCS, NMES, and occupational therapy for patients with ischemic stroke, suggesting a drop in the level of iron deposition, which may be associated with an increase in the level of activity in motor cortex after rehabilitation.

Detailed luminescence dating of dust mass accumulation rates over the last two glacial-interglacial cycles from the Irig loess-palaeosol sequence, Carpathian Basin

Mineral dust records distant from dust sources are crucial in establishing wider atmospheric dust loads in the past. However, detailed, independent chronologies for loess-palaeosol sequences distant from local dust sources are still rare in Europe. In this study we present a high-resolution OSL and pIRIR290 chronology and multi-proxy investigation of the Irig loess-palaeosol sequence (LPS), Vojvodina, Serbia. Our results show that 4–11 μm quartz is a reliable dosimeter only up to ~59 ka (179 Gy), after which the OSL ages underestimate the expected ages based on stratigraphy. The pIRIR290 signal displays generally good luminescence behaviour and resultant ages show good agreement with the expected stratigraphic ages, although with apparent 15 kyr and 35 kyr age underestimations at the L2-S2 and S2-L3 boundaries, respectively. The calculated dust mass accumulation rates (MAR) reveal large fluctuations during the last two glacial-interglacial cycles. During the penultimate glacial, the highest MARs were observed between 171 and 181 ka, subsequently decreasing rapidly during MIS 5. During the last glacial period, dust MARs display maximum values during MIS 2 and MIS 4, while the lowest dust input was observed during the Holocene, followed by MIS 3. Dust MAR and grain-size shifts appear to lead changes in magnetic susceptibility by several kyr. Our results imply that changes in dust availability and wind dynamics occurred prior to changes in climate-controlled soil moisture conditions at the Irig LPS. Moreover, our results reveal a close coupling of the dust MAR and grain-size variations during the Mid-Late Pleistocene. These patterns suggest that the Irig site is likely representative of regional dust dynamics, which separates it from more source proximal loess sites, such as those close to major rivers, which are likely more affected by local dust availability and river discharge.