Diffusive Gradients Research Articles

Differential impacts of sewage sludge and biochar on phosphorus-related processes: An imaging study of the rhizosphere

Recycling of phosphorus (P) from waste streams in agriculture is essential to reduce the negative environmental effects of surplus P and the unsustainable mining of geological P resources. Sewage sludge (SS) is an important P source; however, several issues are associated with the handling and application of SS in agriculture. Thus, post-treatments such as pyrolysis of SS into biochar (BC) could address some of these issues. Here we elucidate how patches of SS in soil interact with the living roots of wheat and affect important P-related rhizosphere processes compared to their BC counterparts. Wheat plants were grown in rhizoboxes with sandy loam soil, and 1 cm Ø patches with either SS or BC placed 10 cm below the seed. A negative control (CK) was included. Planar optode pH sensors were used to visualize spatiotemporal pH changes during 40 days of plant growth, diffusive gradients in thin films (DGT) were applied to map labile P, and zymography was used to visualize the spatial distribution of acid (ACP) and alkaline (ALP) phosphatase activity. In addition, bulk soil measurements of available P, pH, and ACP activity were conducted. Finally, the relative abundance of bacterial P-cycling genes (phoD, phoX, phnK) was determined in the patch area rhizosphere. Labile P was only observed in the area of the SS patches, and SS further triggered root proliferation and increased the activity of ACP and ALP in interaction with the roots. In contrast, BC seemed to be inert, had no visible effect on root growth, and even reduced ACP and ALP activity in the patch area. Furthermore, there was a lower relative abundance of phoD and phnK genes in the BC rhizosphere compared to the CK. Hence, optimization of BC properties is needed to increase the short-term efficiency of BC from SS as a P fertilizer.

Impact of microplastics on the in situ, high-resolution of key nutrient dynamics at the soil-water interface in rice fields

Introduction: Microplastics are characterized by their small size, widespread distribution, and durability, present a significant environmental risk. Despite their omnipresence in terrestrial and aquatic systems, the potential consequences on nutrient cycling remain under-investigated. Microplastics have emerged as a focal point of current research, presenting both a challenge and a frontier in environmental science.Methods: This study explores the effects of microplastics on the high-resolution, in situ distribution and exchange dynamics of key nutrients, nitrogen (N) and phosphorus (P), at the soil-water interface in rice paddies, utilizing the Diffusive Gradients in Thin-films (DGT) technique.Results: Our results reveal distinct spatial distribution patterns for N and P across the soil-water interface. Labile phosphorus (P) concentrations were significantly higher in the soil than in the overlying water, whereas DGT-NO3− concentrations exhibited the inverse trend. Different microplastic concentrations notably impacted DGT-NO3− (P = 0.022) and DGT-NH4+ (P = 0.033), with an increase between 27.79% and 150.68%. Moreover, different particle sizes significantly influenced NH4+. Interestingly, paddy soil acted as a “source” for labile P and a “sink” for NH4+ and NO3−.Discussion: These insights provide valuable insights into the interactions between microplastics and nutrient cycles at the soil-water interface, and assess the effects on nutrient migration and transformation. The outcomes of this study will contribute to an improved understanding of the broader ecological implications of microplastic pollution in agricultural settings. It will also provide a foundation for the development of strategies to manage and mitigate the impacts of microplastic pollution in agricultural soils, particularly in rice dominated agroecosystems.

Bioavailability of Cd in Agricultural Soils Evaluated by DGT Measurements and the DIFS Model in Relation to Uptake by Rice and Tea Plants

The elevated accumulation of cadmium (Cd) in rice (Oryza sativa L.) and tea (Camellia sinensis L.) grown in agricultural soils may lead to a variety of adverse health effects. This study collected and analyzed crop samples along with paired rhizosphere soil samples from 61 sites in Cd-contaminated regions in Anhui Province, China. The findings revealed that both the diffusive gradients in thin-films (DGT) and soil solution were capable of effectively predicting Cd contents in crops. Conventional chemical extraction methods were inappropriate to evaluate the bioavailability of Cd. However, the effective concentrations (CE) corrected by the DGT-induced fluxes in soils (DIFS) model exhibited the strongest correlation with crop Cd contents. Except for CE, various measurement methods yielded better results for predicting Cd bioavailability in tea compared to rice. Pearson’s correlation analysis and the random forest (RF) model identified the key influencing factors controlling Cd uptake by rice and tea, including pH, soil texture, and contents of zinc (Zn) and selenium (Se) in soils, which antagonize Cd. To reduce the potential health risk from rice and tea, the application of soil liming and/or Se-oxidizing bacteria was expected to be an effective management strategy.

High angular diffusion tensor imaging estimation from minimal evenly distributed diffusion gradient directions.

Diffusion-weighted Imaging (DWI) is a non-invasive imaging technique based on Magnetic Resonance Imaging (MRI) principles to measure water diffusivity and reveal details of the underlying brain micro-structure. By fitting a tensor model to quantify the directionality of water diffusion a Diffusion Tensor Image (DTI) can be derived and scalar measures, such as fractional anisotropy (FA), can then be estimated from the DTI to summarise quantitative microstructural information for clinical studies. In particular, FA has been shown to be a useful research metric to identify tissue abnormalities in neurological disease (e.g. decreased anisotropy as a proxy for tissue damage). However, time constraints in clinical practice lead to low angular resolution diffusion imaging (LARDI) acquisitions that can cause inaccurate FA value estimates when compared to those generated from high angular resolution diffusion imaging (HARDI) acquisitions. In this work, we propose High Angular DTI Estimation Network (HADTI-Net) to estimate an enhanced DTI model from LARDI with a set of minimal and evenly distributed diffusion gradient directions. Extensive experiments have been conducted to show the reliability and generalisation of HADTI-Net to generate high angular DTI estimation from any minimal evenly distributed diffusion gradient directions and to explore the feasibility of applying a data-driven method for this task. The code repository of this work and other related works can be found at https://mri-synthesis.github.io/.

Enhanced As extraction from paddy soils with high As contamination risk by rice plant upon Si fertilization

Owing to flooded growing conditions and specific physiological characteristics, rice plant is more efficient in As uptake and accumulation, which provides a cost-effective and time-efficient pathway to deplete bioavailable As from paddy soils. In the present study, the enhancing effect of silicon (Si) fertilization on As extraction from heavily contaminated paddy soils by rice was explored Upon incorporation of one weak acid Si fertilizer (AcSF), soil As solubility was significantly promoted by 1.3–1.4-fold, while a slightly increase in porewater As was observed with alkaline soluble Si fertilizer Na2SiO3 (AlSF). With both Si fertilizers applied before transplanting, a relatively low Si/As molar ratio (<100) in soil porewater was obtained, As a result, soil As uptake by rice plant with Si fertilizers was enhanced by 37.2%–171.7% compared to control (CK). Notably, up to 91.6% of the total As in rice plant retained in root with Si fertilization, suggesting the importance of root removal. By harvesting the whole rice plant including roots, soil bioavailable As measured by diffusive gradients in thin films (DGT) declined by 26.9%–31.3% in AlSF treatments relative to CK. Total soil As depletion by the whole rice plant was significantly enhanced from 2.8% in CK to 7.0%–11.2% in Si fertilizer treatments. In this way, 197.5 mg As m−2-232.5 mg As m−2 could be eliminated from soil following one rice-growth season, which was 2.3–2.7-fold higher compared to CK. These results identified the effectiveness of soluble Si fertilizer in enhancing soil As depletion by rice from paddy soils with high As contamination risk, which could serve as a cost-effective strategy with little technical-restriction.

Assessment of interfacial turbulence treatment models for free surface flows

The modelling of complex free surface flows is challenging due to the mobility and deformability of the interface and air entrainment characteristics, which are highly affected by turbulence. With the framework of Reynolds averaged Navier–Stokes (RANS) models and the volume of fluid (VOF) method, turbulence quantities at the air–water interface tend to be over-estimated. In this study, interfacial turbulence treatment methods including the buoyancy modification model based on the simple gradient diffusion hypothesis (SGDH) and Egorov’s turbulence damping model are investigated. Furthermore, due to the unconditionally unstable characteristics of the standard k-ε turbulence model, the stabilized k-ε turbulence model is applied as a comparison. The turbulence attenuation performance using different interfacial turbulence treatment methods in the vicinity of the interface is compared and discussed for stratified flows and free overflow weirs for aerated and non-aerated nappe scenarios. The turbulence quantities and free surface profile under different flow conditions are validated against experimental data and an analytical model. The results show that for free surface waves, both the SGDH model and the turbulence damping model give strong improvements in turbulence production compared with the standard k-ε model. The SGDH model augments the turbulence kinetic energy (TKE) in the unstable stratification, leading to unphysical behaviour for the partially dispersed and separated flow.

Joint subgrid velocity-scalar filtered mass density function method for compressible turbulent flows

In large eddy simulations (LESs) and scalar filtered mass density functions, a gradient diffusion model is generally used for subgrid-scale (SGS) scalar flux modeling. However, this hypothesis is known to generate evident errors under certain conditions, particularly when the counter-gradient scalar transport effect dominates. Herein, a joint subgrid velocity-scalar filtered mass density function (VSGSSFMDF) method is developed to address this problem. The exact FMDF transport equation is derived in detail. Based on the order of the magnitude analysis and simply Langevin model, the FMDF transport equation is modeled, and a system of stochastic differential equations is, thus, proposed. Theoretical derivation and analysis suggest that both the first- and second-order moments are consistent. A compressible mixing layer and hydrogen/air-reactive mixing layer are simulated to verify the proposed method. Based on the diffusion model, a direct numerical simulation and an LES are performed for comparative verification. A generally reasonable SGS velocity distribution is obtained using the proposed VSGSSFMDF method. Consequently, the counter-gradient scalar transport effect is effectively simulated using this method. Overall, the VSGSSFMDF produces better results than the SFMDF and LES in both cases, particularly in the reactive case.

Approaches to the antimicrobial susceptibility testing of Campylobacter to monitor the spread of antibiotic-resistant strains

Introduction. Campylobacteriosis is one of the most common diarrhea-associated infections over the world. The situation is getting worse along with increasing cases of the disease caused by the Campylobacter spp. pathogen resistant to antimicrobials (AMPs). Preventing the disease requires monitoring the spread of resistant Campylobacter strains isolated from both sick people and animals, food, and water. &#x0D; Aim of the study is to evaluate the results of the antimicrobial susceptibility testing of Campylobacter according to the requirements of the EUCAST and CLSI methodologies using Russia-made nutrient media. &#x0D; Materials and methods. Collected and freshly isolated strains of C. jejuni, C. coli, C. fetus and C. lari were used. Campylobacter cultures were subcultured on Campylobacter Agar Base (HiMedia), Preston laboratory-produced medium and iron-erythritol blood agar (Obolensk). Their sensitivity to AMPs was determined by three methods as ffollows: disc diffusion, gradient diffusion and microdilutions using Mueller-Hinton agar, and broth of two manufacturers (BD BBL and Obolensk) according to EUCAST and CLSI.&#x0D; Results. Using Russian-made and imported Mueller-Hinton agar and broth allowed obtaining identical results for AMPs susceptibility of Campylobacter spp. The campylobacter strains were attributed to the same susceptibility category by all three methods in frame of any methodology (EUCAST or CLSI) when interpreting results. Due to differences in cutoffs of MIC and inhibition zone diameters in the EUCAST and CLSI standards, there were some differences in the interpretation of the results.&#x0D; Limitations. Eight strains of four species Campylobacter were tested for their susceptibility to three antimicrobials by three methods according to EUCAST and CLSI methodology.&#x0D; Conclusion. The results obtained confirm the possibility of applying a complex of domestic nutrient media for cultivating and monitoring the spread of antibiotic resistant strains of Campylobacter spp. This is especially important in view of implementing the import substitution program.

Fractionation and speciation of metals in lakes formed by abandoned clay pits from industrial effluents (Santa Gertrudes, São Paulo, Brazil) using the diffusive gradient in thin films (DGT) technique

Environmental impacts caused by mining activities (mainly tailings and effluents) are presenting serious challenges for humanity worldwide. In Brazil, clay extraction activities in the Ceramic District of Santa Gertrudes (CDSG) have led to the formation of abandoned drainage wells causing environmental and human health concerns. In the 90's, it was discovered that in one of the production areas, known as the region of the lakes of Santa Gertrudes, several ceramic industries had contaminated lakes created by abandoned clay pits with industrial effluents containing toxic metals. In the present study, analysis of total and dissolved concentrations of Al, Cd, Co, Cu, Mn, Ni, Pb and Zn in the waters of these lakes were combined with the diffusive gradients in thin films (DGT) technique to assess the lability and bioavailability of the target elements, representing one of the first studies to investigate the real environmental impact of contamination caused by ceramic production wastes to an aquatic system. Furthermore, based on the total concentrations and main physicochemical characteristics of each lake, a speciation analysis was performed using the MINTEQ software which data was compared with other surface water systems. The results indicated the presence of metals associated with ceramic residues in total, dissolved and labile fractions. It was verified that Zn, Ni and Cu were the only target metals found in labile form and according to speciation were present in the form of “free” ions, and thus may present risk in terms of bioavailability, although the majority of the total concentrations are within the limits established by the national environmental agency.

Bioavailability Assessment of Heavy Metals and Organic Pollutants in Water and Soil Using DGT: A Review

In recent years, the diffusive gradients in the thin films (DGT) technique has also been increasingly applied to assess the bioavailability of heavy metals and organic pollutants in the soil. The combination of binding and diffusion phases made from different materials allows for the targeted determination of different target substances. This review briefly introduces the compositions and development of the DGT technique and analyzes the composition structure of DGT and the impact of environmental factors, such as pH, ion strength (IS), and dissolved organic matter (DOM), on the bioavailability evaluation of heavy metals and organic pollutants in soil. Finally, the application potential and broad application prospects of the DGT technique were expected. In addition, standardized DGT technique methods and calibration procedures are conducive to the establishment of a more stable and reliable measurement system to enhance the robustness of the DGT technique application in the soil.

Occurrence and distribution of PPCPs in water from two largest urban lakes of China: First perspective from DGT in-situ measurement

Pharmaceutical and personal care products (PPCPs) are an important group of emerging contaminants that may threaten organisms at trace concentrations. However, research on the occurrence of PPCPs in urban lakes in China is still scarce. In this study, 15 PPCPs in the Tangxun Lake and the Donghu Lake were collected using the diffusive gradients in thin-films (DGT) technique and analyzed by high performance liquid chromatography tandem-mass spectrometry (HPLC-MS/MS). Thirteen of the 15 targeted PPCPs were detected in the Tangxun Lake, and all PPCPs were detected in the Donghu Lake, with total concentrations ranging from 160 to 730 ng/L (average: 401 ng/L) and 187 to 1933 ng/L (average: 653 ng/L), respectively. Bisphenol A (BPA) was the dominant PPCP, followed by disinfectants in both lakes. The total concentrations of PPCPs in the Donghu Lake were higher than those in the Tangxun Lake. The spatial distribution characteristics of PPCPs in the two lakes were different, with higher total concentrations in the eastern part than in the western part of the Tangxun Lake spatially and higher in the north-western part than in the south-eastern part of the Donghu Lake. The results of the risk assessment showed that BPA and estrone posed high risks to the aquatic environment (RQ ≥ 1), while triclosan and estriol presented a medium risk (0.1 ≤ RQ < 1) in some sites. This study was the first attempt to apply DGT for providing vital data on the evaluation of the ecological risk of PPCPs in the two largest lakes in China, and attention should be paid to the long-term ecological effects caused by the occurrence of PPCPs in lakes.

Lithium Ion Battery Electrolytes Based on Deep Eutectic Solvents

Deep eutectic solvents (DESs) have emerged as an alternative to both common organic solvents and ionic liquids (ILs). DESs share physicochemical properties with ILs such as low vapor pressure, high thermal stability, while offering advantages such as low toxicity, lower cost, and ease of preparation. Moreover, DESs are attractive candidates for electrochemical applications due to their large voltage windows and solubility properties. DESs as a solvent class share a general composition of a hydrogen bond donor (HBD), typically a polyol, amide, or acid, and a hydrogen bond acceptor (HBA), usually a quaternary ammonium or phosphonium salt. At a specific molar composition of a HBD and HBA, the DES forms a eutectic mixture resulting in a large melting point depression.Despite being widely studied, the microscopic structures of DESs have remained largely uncharacterized. Herein, we present a multitechnique NMR study of ethaline (ethylene glycol + choline chloride). Pulsed field gradient diffusion, nuclear Overhauser effect spectroscopy (NOESY), 13C NMR relaxation experiments are deployed to sample a range of frequencies and modes of motion of the polyol and choline components of the DES. Generally, translational and rotational diffusion of polyols are more rapid than those of choline while short-range rotational motions observed from 13C relaxation indicate slow local motion of ethylene glycol at low choline chloride (ChCl) content.Additionally, we have investigated the solubility properties of several lithium salts (LiTFSI, LiFSI, LiBF4, and LiOAc) in these DESs and utilized the same suite of NMR techniques to understand how they act as solvents. One interesting observation is that the Li+ diffusivity exceeds that of the counterion for TFSI-, but not for FSI-. Finally, large changes in the structural organization of DESs that result from the presence of lithium salts may serve as a guide to the design of a new class of electrolytes for lithium-ion batteries.

Extended application of diffusive gradients in thin films (DGT) in assessing arsenic bioavailability and human health risks in brownfield soils

The environmental and human health risks of arsenic (As) mainly depend on its bioavailability in the soil. However, precise determination of bioavailable As in situ is still challenging due to the complexity of soil types and hydrogeological conditions in polluted sites. Diffusive gradients in thin films (DGT) is one of the reliable analysis technology in the in situ analysis of bioavailable chemicals in waters, sediments and farmland soils. However, few studies have investigated the application of DGT in evaluating the bioavailability of heavy metals in brownfield soils. In this study, DGT was extended applied to evaluate the availability of As in 16 contaminated soil samples from seven brownfield sites. The correlation between the bioavailable As measured by DGT and the bioaccessible As determined by the Unified BRAGE method (UBM) assay was also analyzed. In addition, the human health risks were evaluated, and the DGT-based prediction model for bioavailable As was also developed (R2=0.852, P< 0.001). The results indicated that considering bioavailability in risk assessments can improve the accuracy of calculations for site-specific health risks and provide guidance for effective remediation. The study will demonstrate the effectiveness of DGT in characterizing bioavailable heavy metals in contaminated site soils and provide decision-making support for the soil remediation.

Treatment outcomes with benzylpenicillin and non-benzylpenicillin antibiotics, and the performance of the penicillin zone-edge test versus molecular detection of blaZ in penicillin-susceptible Staphylococcus aureus (PSSA) bacteraemia.

The blaZ gene encodes penicillinase, which inactivates penicillin. As there were reports on suboptimal sensitivity for the penicillin zone-edge test, a phenotypic method for blaZ detection, we investigated treatment outcomes in patients with penicillin-susceptible Staphylococcus aureus (PSSA) bacteraemia (phenotypically negative for penicillinase), subjecting isolates to molecular testing for blaZ retrospectively. A retrospective cohort study was conducted on 121 patients with a first episode of PSSA bacteraemia from 1 January 2012 to 31 October 2015 at Tan Tock Seng Hospital (TTSH), Singapore. Patients were grouped into IV benzylpenicillin and non-benzylpenicillin groups. The primary outcome was overall treatment failure, defined as either 30 day all-cause mortality and/or 90 day relapse. The penicillin (P10) zone-edge test was repeated on archived PSSA isolates, concurrently with penicillin MIC determination via gradient diffusion and PCR for blaZ. Among 121 patients, 57 patients (47.1%) received IV benzylpenicillin as the predominant antibiotic. There was no significant difference in overall treatment failure between treatment with the benzylpenicillin [7/57 (12.3%)] versus non-benzylpenicillin groups [12/64 (18.8%)] (P = 0.33) or cloxacillin/cefazolin [6/37 (16.2%)] (P = 0.59). For 112 PSSA isolates available for testing, repeat penicillin zone-edge testing was negative for penicillinase production, corroborating previous results. A single PSSA isolate with a negative penicillin zone-edge test was found to be positive for blaZ. We found no differences in overall treatment failure between patients with PSSA bacteraemia treated with benzylpenicillin, anti-staphylococcal β-lactams cefazolin/cloxacillin and other antimicrobials, when using the penicillin zone-edge test as the phenotypic method for blaZ screening.

Application of two-dimension, high-resolution evidences to reveal the biogeochemical process patterns of trace metals in reservoir sediments

Pollutions of trace metals (TMs) in reservoirs are blooming due to TMs were trapped efficiently in reservoir sediments by dams. Despite the mobilization of TMs in sediments have been well-documented, the patterns of biogeochemical processes occurred in sediments remain poorly understanding. Herein, a deep reservoir was selected to investigate the patterns of TMs biogeochemical processes in sediments by using high-resolution ZrO-Chelex-AgI diffusive gradient in thin films technique (HR-ZCA DGT) and the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). 2-dimension high-resolution (2D-HR) images showed significant differential spatial enrichment of TMs (V, Mn, Fe, Co, Zn and Sb) in sediments, indicating strong heterogeneity in sediments. Correlations of TMs within microniches (diameter < 1 mm) in horizontal were usually different even contrast with that in vertical profile, suggesting distinct biogeochemical process patterns occurred in vertical vs. in horizontal. Further analyses from 2D-HR images showed the distributions of TMs in microniches reflected their mobilization that was driven by microenvironmental conditions. In contrast, distributions in sediment vertical profile recorded the diagenesis in different deposition depth. The diagenesis in sediment vertical is continuously accumulated by the discrete, microniches mobilization of TMs in horizontal. Collectively, our findings evidenced that 2D-HR data is an update complement to 1-dimension data for better interpret the biogeochemical process patterns of TMs in sediments, that have implication for water management to metals pollution in reservoir ecosystems.

Establishing and Comparing the Normal apparent Diffusion Coefficient Values of Fetal Organs and Placenta Using 1.5 Tesla and 3.0 T MRI at Various Gestational Age.

Diffusion-weighted imaging (DWI) is the random Brownian motion of water molecules within a tissue voxel. The apparent diffusion coefficient (ADC) is a quantitative parameter calculated from the DWI that directly reflects the mobility of water molecules in biological tissues. The objective of this study was to establish and compare the normal reference ADC values of fetal organs and the placenta using 1.5 T and 3.0 T MRI at various gestational ages. This was a retrospective and prospective observational study. This study included one hundred and three (103) singleton pregnancies for each magnetic field strength. Diffusion-weighted imaging was performed using single-shot spin-echo-planar imaging (EPI) in the axial plane of the fetal head-trunk with a slice thickness of 4mm and diffusion gradient values of b = 0 and b = 700-800 s/mm2. The mean ADC values of cerebral WM areas were significantly higher than the deep grey areas in the brain. The white-matter regions, lung, and placenta showed a positive and significant correlation with increasing gestational age in both field strengths. A statistically weak negative correlation was observed between increasing gestational age and ADC measurements obtained in the thalamus, cerebellum, pons, and kidney. This study gives the reference values for both 1.5T and 3T MRI of vital organs. The current study shows that diffusion-weighted MRI can offer a promising technique to evaluate the structural development of fetal organs and can potentially act as a biomarker for predicting the functionality of the fetal organs in abnormalities.

Frequency-dependent diffusion kurtosis imaging in the human brain using an oscillating gradient spin echo sequence and a high-performance head-only gradient

Measuring the time/frequency dependence of diffusion MRI is a promising approach to distinguish between the effects of different tissue microenvironments, such as membrane restriction, tissue heterogeneity, and compartmental water exchange. In this study, we measure the frequency dependence of diffusivity (D) and kurtosis (K) with oscillating gradient diffusion encoding waveforms and a diffusion kurtosis imaging (DKI) model in human brains using a high-performance, head-only MAGNUS gradient system, with a combination of b-values, oscillating frequencies (f), and echo time that has not been achieved in human studies before. Frequency dependence of diffusivity and kurtosis are observed in both global and local white matter (WM) and gray matter (GM) regions and characterized with a power-law model ∼Λ*fθ. The frequency dependences of diffusivity and kurtosis (including changes between fmin and fmax, Λ, and θ) vary over different WM and GM regions, indicating potential microstructural differences between regions. A trend of decreasing kurtosis over frequency in the short-time limit is successfully captured for in vivo human brains. The effects of gradient nonlinearity (GNL) on frequency-dependent diffusivity and kurtosis measurements are investigated and corrected. Our results show that the GNL has prominent scaling effects on the measured diffusivity values (3.5∼5.5% difference in the global WM and 6∼8% difference in the global cortex) and subsequently affects the corresponding power-law parameters (Λ, θ) while having a marginal influence on the measured kurtosis values (<0.05% difference) and power-law parameters (Λ, θ). This study expands previous OGSE studies and further demonstrates the translatability of frequency-dependent diffusivity and kurtosis measurements to human brains, which may provide new opportunities to probe human brain microstructure in health and disease.

Estimating axon radius using diffusion-relaxation MRI: calibrating a surface-based relaxation model with histology.

Axon radius is a potential biomarker for brain diseases and a crucial tissue microstructure parameter that determines the speed of action potentials. Diffusion MRI (dMRI) allows non-invasive estimation of axon radius, but accurately estimating the radius of axons in the human brain is challenging. Most axons in the brain have a radius below one micrometer, which falls below the sensitivity limit of dMRI signals even when using the most advanced human MRI scanners. Therefore, new MRI methods that are sensitive to small axon radii are needed. In this proof-of-concept investigation, we examine whether a surface-based axonal relaxation process could mediate a relationship between intra-axonal T2 and T1 times and inner axon radius, as measured using postmortem histology. A unique in vivo human diffusion-T1-T2 relaxation dataset was acquired on a 3T MRI scanner with ultra-strong diffusion gradients, using a strong diffusion-weighting (i.e., b = 6,000 s/mm2) and multiple inversion and echo times. A second reduced diffusion-T2 dataset was collected at various echo times to evaluate the model further. The intra-axonal relaxation times were estimated by fitting a diffusion-relaxation model to the orientation-averaged spherical mean signals. Our analysis revealed that the proposed surface-based relaxation model effectively explains the relationship between the estimated relaxation times and the histological axon radius measured in various corpus callosum regions. Using these histological values, we developed a novel calibration approach to predict axon radius in other areas of the corpus callosum. Notably, the predicted radii and those determined from histological measurements were in close agreement.

Determination of the Isotopic Composition of Aqueous Mercury in a Paddy Ecosystem Using Diffusive Gradients in Thin Films.

Measuring the isotopic composition of Hg in natural waters is challenging due to the ultratrace level of aqueous Hg (ng L-1). At least 5 ng of Hg mass is required for Hg isotopic analysis. Given the low Hg concentration in natural waters, a large volume of water (>10 L) is typically needed. The conventional grab sampling method is time-consuming, laborious, and prone to contamination during transportation and preconcentration steps. In this study, a DGT (diffusive gradients in thin films) method based on aminopropyl and mercaptopropyl bi-functionalized SBA-15 nanoparticles was developed and extended to determine the concentration and isotopic composition of aqueous Hg for the first time. The results of laboratory analysis showed that Hg adsorption by DGT induces ∼ -0.2‰ mass-dependent fractionation (MDF) and little mass-independent fractionation (MIF). The magnitude of MDF exhibits a dependence on the diffusion-layer thickness of DGT. Since Hg-MDF can occur in a broad range of environmental processes, monitoring the δ202Hg of aqueous Hg using the DGT method should be performed with caution. Field results show consistent MIF signatures (Δ199Hg) between the DGT and conventional grab sampling method. The developed DGT method serves as a passive sampling method that effectively characterizes the MIF of Hg in waters to understand the biogeochemical cycle of Hg at contaminated sites.

The potential of electromyography, diagnostic transcranial magnetic stimulation, and multiparametric magnetic resonance imaging in the combinatory assessment of facial nerve disorders: a literature review and clinical case series

Facial neuropathy (FN) is a complex multicausal problem that, with a seemingly obvious clinical picture, might be challenging to diagnose. Up to 5% of FN cases could be caused by neoplastic or otogenic processes, necessitating an interdisciplinary approach to its treatment by various specialties and in some cases a surgical intervention. In addition, in the early stages of FN, it is difficult to predict its outcomes. Therefore, beyond usual neurological exam and widely used electromyography (EMG), other additional diagnostic tools are used to ensure extended diagnosis, including cancer awareness.&#x0D; In this paper we have analyzed the principles, role and value of computed tomography, magnetic resonance imaging (MRI), diagnostic transcranial magnetic stimulation combined with EMG, and ultrasound assessment with a high-frequency linear transducer in acute FN. We present our own clinical cases of pediatric patients with FN, who were assessed with EMG and multiparametric MRI including diffusion tensor imaging. These cases illustrate both the abnormalities found in the typical course of Bell's palsy, as well as the abnormalities in neoplasm-associated FN that clinically fully mimic the Bell's palsy. Based on the world experience in multiparametric MRI, including the use of extended protocols in the Pediatric Research and Clinical Center for Infectious Diseases, in case of suspected FN, the most important are high-resolution structural submillimeter sequences based on the gradient echo (SSFP) and diffusion tensor imaging (DTI). Measurement and assessment of fractional anisotropy at the motor nuclei of the facial nerves in the pons look promising for further research. The paper is the first to describe a modified combination diagnostic approach to Bell's palsy with the use of diagnostic transcranial magnetic stimulation with round coil, supramaximal stimulation with identification of the motor evoked response threshold (minimal inducer power to register a reproducible evoked motor response of 50-100 mV in amplitude) in the occipito-parietal area of the ipsilateral muscle.