Higher Diffusivity Values Research Articles

Evaluation of white matter properties in sinus vein thrombosis with diffusion tensor imaging

Objective: Brain MRI findings in sinus vein thrombosis have been well described in many studies. However, to our knowledge, there is no diffusion tensor imaging (DTI) study in these cases in the literature. The main purpose of this article is to examine white matter integrity in sinus vein thrombosis and to better understand the possible underlying white matter damage. Materials and Methods: Our retrospective study is a neuroimaging study including 1.5 T MRI and brain diffusion tensor imaging (DTI) to evaluate the white matter integrity of patients with sinus vein thrombosis and healthy controls. White matter DTI abnormalities were evaluated according to ROI. DTI findings of cases and healthy controls were compared. Results: In cases with sinus vein thrombosis, higher apparent diffusion coefficiency (ADC) values were detected in cingulum, middle cerebellar peduncle, optic radiatio compared to healthy controls. Decreased fractional anisotrophy (FA) values were detected in cingulum, corona radiata, corpus callosum splenium, anterior limb of internal capsule, posterior limb of internal capsule, optic radiatio and corticospinal tract. High radial diffusivity (RD) values were detected in cingulum, corona radiata, superior longitudinal fasciculus, anterior limb of internal capsule, posterior limb of internal capsule, middle cerebellar peduncle, optic radiatio and corticospinal tract. Low axial diffusivity (AD) values were detected in cingulum, posterior limb of internal capsule and corticospinal tract. Conclusion: Our findings may suggest intercellular edema and axon and myelin damage in white matter tracts in sinus thrombosis. DTI findings may be useful in quantitatively monitoring the response to treatment.

Cluster-based prognostication in glioblastoma: Unveiling heterogeneity based on diffusion and perfusion similarities.

While the association between diffusion and perfusion magnetic resonance imaging (MRI) and survival in glioblastoma is established, prognostic models for patients are lacking. This study employed clustering of functional imaging to identify distinct functional phenotypes in untreated glioblastomas, assessing their prognostic significance for overall survival. A total of 289 patients with glioblastoma who underwent preoperative multimodal MR imaging were included. Mean values of apparent diffusion coefficient normalized relative cerebral blood volume and relative cerebral blood flow were calculated for different tumor compartments and the entire tumor. Distinct imaging patterns were identified using partition around medoids (PAM) clustering on the training dataset, and their ability to predict overall survival was assessed. Additionally, tree-based machine-learning models were trained to ascertain the significance of features pertaining to cluster membership. Using the training dataset (231/289) we identified 2 stable imaging phenotypes through PAM clustering with significantly different overall survival (OS). Validation in an independent test set revealed a high-risk group with a median OS of 10.2 months and a low-risk group with a median OS of 26.6 months (P = 0.012). Patients in the low-risk cluster had high diffusion and low perfusion values throughout, while the high-risk cluster displayed the reverse pattern. Including cluster membership in all multivariate Cox regression analyses improved performance (P ≤ 0.004 each). Our research demonstrates that data-driven clustering can identify clinically relevant, distinct imaging phenotypes, highlighting the potential role of diffusion, and perfusion MRI in predicting survival rates of glioblastoma patients.

Frontal interhemispheric structural connectivity, attention, and executive function in children with perinatal stroke.

Perinatal stroke affects ∼1 in 1000 births and concomitant cognitive impairments are common but poorly understood. Rates of Attention Deficit/Hyperactivity Disorder (ADHD) are increased 5–10× and executive dysfunction can be disabling. We used diffusion imaging to investigate whether stroke‐related differences in frontal white matter (WM) relate to cognitive impairments. Anterior forceps were isolated using tractography and sampled along the tract. Resulting metrics quantified frontal WM microstructure. Associations between WM metrics and parent ratings of ADHD symptoms (ADHD‐5 rating scale) and executive functioning (Behavior Rating Inventory of Executive Function (BRIEF)) were explored. Eighty‐three children were recruited (arterial ischemic stroke [AIS] n = 26; periventricular venous infarction [PVI] n = 26; controls n = 31). WM metrics were altered for stroke groups compared to controls. Along‐tract analyses showed differences in WM metrics in areas approximating the lesion as well as more remote differences at midline and in the nonlesioned hemisphere. WM metrics correlated with parental ratings of ADHD and executive function such that higher diffusivity values were associated with poorer function. These findings suggest that underlying microstructure of frontal white matter quantified via tractography may provide a relevant biomarker associated with cognition and behavior in children with perinatal stroke.

Using tissue microstructure and multimodal MRI to parse the phenotypic heterogeneity and cellular basis of autism spectrum disorder.

Identifying the brain bases for phenotypic heterogeneity in Autism Spectrum Disorder (ASD) will advance understanding of its pathogenesis and improve its clinical management. We compared Diffusion Tensor Imaging (DTI) indices and connectome measures between 77 ASD and 88 Typically Developing (TD) control participants. We also assessed voxel-wise associations of DTI indices with measures of regional cerebral blood flow (rCBF) and N-acetylaspartate (NAA) to understand how tissue microstructure associates with cellular metabolism and neuronal density, respectively. Autism Spectrum Disorder participants had significantly lower fractional anisotropy (FA) and higher diffusivity values in deep white matter tracts, likely representing ether reduced myelination by oligodendrocytes or a reduced density of myelinated axons. Greater abnormalities in these measures and regions were associated with higher ASD symptom scores. Participant age, sex and IQ significantly moderated these group differences. Path analyses showed that reduced NAA levels accounted significantly for higher diffusivity and higher rCBF values in ASD compared with TD participants. Reduced neuronal density (reduced NAA) likely underlies abnormalities in DTI indices of white matter microstructure in ASD, which in turn are major determinants of elevated blood flow. Together, these findings suggest the presence of reduced axonal density and axonal pathology in ASD white matter. Greater pathology in turn accounts for more severe symptoms, lower intellectual ability, and reduced global efficiency for measures of white matter connectivity in ASD.

Regional microstructural alteration of the corpus callosum in preclinical Alzheimer’s disease

AbstractBackgroundWhile previous studies consistently reported regional microstructural changes of the cerebral white matter (WM) in Alzheimer’s disease (AD) dementia and mild cognitive impairment (MCI), little information is available for such changes in the preclinical stage of AD. We first aimed to investigate regional microstructural alteration of the WM in cognitively normal (CN) older adults with amyloid‐beta (Aβ) deposition. We also tried to develop a prediction model for Aβ positivity in CN using information on WM microstructural alteration and clinical variables that can be easily obtained in memory clinics.MethodSeventy‐five CN older adults from the Korean Brain Aging Study for the Early diagnosis and prediction of Alzheimer’s disease (KBASE) cohort were included in the analyses. All Participants underwent comprehensive clinical and neuropsychological assessment, T1 MRI, diffusion tensor imaging (DTI), and [11C]PiB‐PET. All CN subjects were divided into Aβ positive (CN+) and negative (CN‐) based on the level of cerebral Aβ retention on [11C]PiB‐PET. Multivariate stepwise logistic regression analyses were conducted to develop Aβ positivity prediction models.ResultWhen compared to CN‐, CN+ showed high mean diffusivity (MD) value of the genu of the corpus callosum (CC_genu) (F(1,73) = 6.357, p = 0.014, Figure 1). The area under the curve (AUC) of the receiver operating characteristics curve for the Aβ positivity prediction model only using MD of the CC_genu was 0.653 [confidence interval (CI) = 0.511‐0.794]. Model with MD of the CC_genu, age, and word list recall and constructional recall test scores were finally selected. The AUC of the final model was 0.851 [CI = 0.765‐0.937] (Figure 2).ConclusionThe findings indicate that microstructural alteration of the CC_genu occurs even in the stage of preclinical AD. When taken together with episodic memory scores commonly available in clinical practice, information about such regional WM microstructural alteration can be used to screen preclinical AD.

Investigation of thermal property of spark plasma sintered Ti-Zr-Ta shape memory alloys

There is increasing demand for the performance improvement of novel shape memory alloys (SMAs), such as the Ti-Zr-based systems. The effects of fabrication parameters and material compositions are critical to the thermal properties of the alloys. This study is designed to investigate the effects of ternary Ta additions on the thermal properties of spark plasma sintered (SPSed) novel Ti-Zr based SMAs for high temperature applications. The SPSed Ti-Zr/Ta specimens were characterized for their microstructural and crystallographic features using scanning electron microscopy (SEM) incorporated with Energy Dispersive X-ray Spectroscopy (EDS), and X-ray powder diffractometry (XRD). Thermal property measurements were conducted using the Laser Flash technique to obtain the thermal diffusivity behaviour, while the phase transformation properties were determined by the differential scanning calorimetry (DSC). The presence of both alpha martensite, and beta structures were revealed by the SEM/EDX and XRD respectively. High thermal diffusivity values were obtained, and they show an increasing trend with temperature. The DSC measurement revealed high reversible martensitic transformation (above 200 deg Celcius) for all the alloys, a two-stage phase transformation in the binary alloy, and a single-phase transformation event in the ternary alloys. A downward parabolic gradient of the specific heat and thermal conductivity with respect to temperature was recorded in the alloys, thus revealing an interaction between phonon-mediated and electron-mediated thermal transport processes. Two-stage phase transformations, noticed in the binary alloy indicate the reversible transformation events of alpha-Ti and alpha-Zr phases at different temperatures to-and-fro the austenite phase, whereas, in the ternary phase the single transformation event indicates the presence of only alpha-Ti phase. These results further strengthen the understanding of material atomic compositions effect on the thermal behaviour of the as-sintered alloys. The high thermal diffusivity and high martensitic transformation behaviour of the Ti-Zr/Ta alloys suggest they can be suitable candidates for high temperature applications in the aerospace technologies.

Estimating vertical mixing in the deep north Aegean Sea using argo data corrected for conductivity sensor drift

Successive CTD profiles of an Argo float trapped within a deep (~1250 m) sub-basin of the North Aegean Sea during 2014–2015 enabled identification of deep-water ventilation episodes and inference of a bulk (budget-based) vertical eddy diffusivity during the period that followed these events. Independent effective eddy diffusivity profiles were computed under the assumption that the turbulent exchange of heat, salt and buoyancy through each isobath below 400 m will balance the rate of change of the corresponding variable's content of the water volume within the basin below that depth. The initially estimated thermal, saline and density diffusivity profiles were significantly different from each other. Assuming turbulence was the dominant mixing process between the intermediate and deep water masses led to identification of conductivity sensor drift rate of 4.6 × 10−6 S m−1 day−1. After correcting the sensor's drift, bulk eddy diffusivities Kρ,KS and KT were found to span (2–30) × 10−3 m2 s−1, in close agreement below 400 m depth. These estimates are at least one order of magnitude higher than eddy diffusivities based on a finescale internal-wave strain parameterization. Enhanced boundary mixing and double diffusion are examined as candidates to explain the high effective diffusivity values. A hypsometric correction appears to provide sufficient diapycnal transport along the boundaries to reproduce bulk buoyancy transports.

Effect of microwave power on drying kinetics, structure, color, and antioxidant activities of corncob

AbstractIn this study, the effect of microwave drying (MWD) at four power levels (180, 300, 600, and 900 W) on kinetics, structure, color parameters, and antioxidant activity of corncob (CCB) was evaluated. Hot air‐dried (HAD) and freeze‐dried (FD) CCBs were used as controls. Drying conditions significantly affected the physicochemical characteristics as well as bioactivities of CCB. For MWD products, direct absorption of electromagnetic energy by water molecules greatly accelerated the evaporation process, leading to a faster dehydration with a very high moisture diffusivity value. Additionally, the application of microwave markedly enhanced disintegration of cellular components manifested in lowered values of structural and color attributes for MWD CCBs, which facilitated the liberation of bound polyphenols into fractions of free phenolic compounds and intensified the ultrasound‐assisted extraction of antioxidants. The presence of rutin, protocatechuic acid, gallic acid, caffeic acid, chlorogenic acid, and quercetin was responsible for high bioactivity of MWD CCB. However, thermal‐ and oxidation‐induced degradation of thermolabile polyphenols was responsible for the loss of antioxidant activity at higher (600 and 900 W) and lower (180 W) microwave powers. CCB dried using 300 W microwave power was the best drying process with the highest content of bioavailable antioxidants and antioxidant activity.Practical applicationsUsing lignocellulosic plant part as a source of functional food or nutritional compounds requires intensive studies on the nutritional quality of products as well as bioavailabilities of such compounds. As most of the antioxidant compounds remain bound to cellulose and hemicellulose in seed, cob, and peel, techniques that promote the disintegration of bound polymeric complexes improve the bioactivity of these products. The present research highlights the potential benefits of microwave drying for the improvement in the bioactivity of corncob (CCB). The presence of several key phenolic compounds suggests a potential application of CCB in medicinal, cosmetic, and food industries.

Interdiffusion at Room Temperature in Cu-Ni(Fe) Nanolaminates

The decomposition of a one-dimensional composition wave in Cu-Ni(Fe) nanolaminate structures is quantified using X-ray diffraction to assess kinetics of the interdiffusion process for samples aged at room temperature for 30 years. Definitive evidence for growth to the composition modulation within the chemical spinodal is found through measurement of a negative interdiffusivity for each of sixteen different nanolaminate samples over a composition wavelength range of 2.1–10.6 nm. A diffusivity value Ď of 1.77 × 10−24 cm2·s−1 is determined for the Cu-Ni(Fe) alloy system, perhaps the first such measurement at a ratio of melt temperature to test temperature that is greater than 5. The anomalously high diffusivity value with respect to bulk diffusion is attributed to the nanolaminate structure that features paths for short-circuit diffusion through interlayer grain boundaries.

Mathematical modeling and numerical simulation of the mitotic spindle orientation system

The mitotic spindle orientation and position is crucial for the fidelity of chromosome segregation during asymmetric cell division to generate daughter cells with different sizes or fates. This mechanism is best understood in the budding yeast Saccharomyces cerevisiae, named the spindle position checkpoint (SPOC). The SPOC inhibits cells from exiting mitosis until the mitotic spindle is properly oriented along the mother-daughter polarity axis. Despite many experimental studies, the mechanisms underlying SPOC regulation remains elusive and unexplored theoretically. Here, a minimal mathematical is developed to describe SPOC activation and silencing having autocatalytic feedback-loop. Numerical simulations of the nonlinear ordinary differential equations (ODEs) model accurately reproduce the phenotype of SPOC mechanism. Bifurcation analysis of the nonlinear ODEs reveals the orientation dependency on spindle pole bodies, and how this dependence is altered by parameter values. Partial differential equation (PDEs) model as well as linear stability analysis indicate that diffusion play no major role using experimental high diffusion values. These results provide for systems understanding on the molecular organization of spindle orientation system via mathematical modeling. The presented mathematical model is easy to understand and, within the above mentioned context, can be used as a base for further development of quantitative models in asymmetric cell-division.

Characterization of unsaturated diffusivity of tight sandstones using neutron radiography

Water flow in unsaturated tight sandstones plays a significant role in the area of the secondary and enhanced hydrocarbon recovery as well as the geological storage of carbon dioxide and nuclear wastes. Although a few non-destructive techniques, such as nuclear magnetic resonance, magnetic resonance imaging and X-ray imaging, can be used to capture fluid transport in sub-micron pores, great challenges exist due to the presence of iron or the use of the contrast agents (e.g. cesium chloride and salts), resulting in inaccurate results or alteration of the wetting behavior of the porous media. In addition, models for describing diffusivity and water transport in unsaturated tight sandstones are also limited. In this work, the neutron radiography facility at China Advanced Research Reactor was used to determine water content profiles during the water imbibition in two types of tight sandstones: silty sandstone and coarse grained sandstone. The diffusivity was determined separately by three methods, including Matano’s method, Meyer-Warwick method and a fractal method, which was introduced as probably the first attempt to relate the microstructure observed by the high resolution X-ray computed tomography (CT) with the unsaturated diffusivity function for the tested tight sandstones. The air-entry value and the fractal dimension used in the fractal model were calculated based on the results of mercury intrusion porosimetry and CT data, respectively. The results from neutron images illustrate that the fractal model can give a reasonable description of the diffusivity function for the tested sandstones. Meyer-Warwick model produces a little bit higher diffusivity value at low water content range. The fractal model works better for the silty sandstone. Results also show that the value of water diffusivity increases with the increase in volumetric water content for both tested tight sandstones. This work shows that neutron radiography offers a feasible and more reliable way for characterizing fluid flow in other tight geo-materials and the fractal model also provides an easier way to give a quantitative description of the diffusivity than the core-flooding or centrifuge drainage experiment.

Role of Diffusion-weighted Magnetic Resonance Imaging in Cervical Cancer for Prediction and Monitoring of Chemo-radiotherapy Response

Objectives: To investigate the possibility of DWI as an imaging bio marker and evaluate its role in prediction and monitoring of chemoradiotherapy response in cervical carcinoma. Methods: 30 carcinoma cervix patients undergoing radiation for Carcinoma Cervix were examined with routine pelvic MRI and DWI before chemoradiation, following EBRT and on completion of brachytherapy. Based on the response on conventional MRI patients were categorized into complete, good and partial response groups. Analysis of variance (ANOVA) and Student t test (two tailed, independent) were used to compare the ADC, size and volume parameters between response groups and therapeutic times. Pearson's correlation test was calculated between ADC parameters and tumor size and volume response. Results: Cervical cancer demonstrated serial increase in tumor ADC values with corresponding decrease in tumor diameters and volumes during the therapy (all p values <0.001). significant and moderate positive linear correlation was found between the tumor ADC values and final size and volume responses at pre-treatment, post EBRT and post-treatment. Tumors with high diffusion values responded better to therapy than with low diffusion values. Patients with greater post EBRT tumor ADC changes and greater size and volume responses responded better to therapy. The pretreatment tumor ADC values, post EBRT ADC changes were found to be correlating well with the final outcome. However ADC mapping was less useful in predicting the extension and staging of carcinoma. Conclusion: DWI and its quantitative parameter, ADC has a potential role in the prediction, assessment and monitoring of cervical cancer treatment response to chemo radiation therapy.

Modification of Ohnaka back diffusion equation

The first and simplest analytical model for a binary alloy came from Gulliver-Scheil, considering a constant partition coefficient at the interface during solidification without back diffusion in solid. Later, Brody-Flemings proposed an approximate analytical model, taking into account one dimensional diffusion of solute in solid during solidification in plate-like dendrite arms for parabolic growth. However, this model does not work well at high back diffusion values. Ohnaka modified this back diffusion parameter. The Ohnaka model works well at the low and high back diffusion values but it underestimates between them. In this paper, Voller-Ohnaka back diffusion model is modified further to predict concentration profiles more accurately than all others analytical models for the parabolic growth rate.

Water vapor sorption and diffusion in wheat straw particles and their impact on the mass transfer properties of biocomposites

ABSTRACTThis work intends to decipher the role of hydrophilic fillers, wheat straw fibers (WSF), on the water vapor transfer properties (sorption and diffusion) of biocomposites based on poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate), (PHBV) as matrix. Transfer in biocomposites, measured using dynamical vapor sorption measurement, is correlated to the transfer properties of each individual constituent and to the specific structural arrangements induced by the presence of particles inside the matrix. Increasing amounts of WSF particles in the PHBV matrix lead to an increase of the water vapor sorption (WVS) of the resulting composites. This is attributed to the high sorption of hydrophilic WSF as compared to that of the neat PHBV matrix. Water vapor diffusion in composites (around 0.13 × 10−11 m2 s−1 at 20°C whatever the filler content) is always lower than in the neat matrix (0.26 × 10−11 m2 s−1) although wheat straw displays high diffusivity values (1.84 × 10−11 m2 s−1). Such unexpected behavior is related to (1) changes of structure and properties of the WSF particle once embedded in the PHBV matrix, (2) changes in the polymer matrix structure and properties in contact with fibers, and also (3) to the representativeness of the filler diffusivity, which is difficult to appraise. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43329.

Influence of the Window Thermal Diffusivity on the Silicon Wafer Temperature in a Rapid Thermal System

The heating of a silicon wafer in a rapid thermal process is studied by numerical simulation. In the model, the equations of conservation of mass and energy are solved with the finite-volume method and the determination of the solutions of the radiative transfer equation is based on the Monte-Carlo method. The results of numerical simulations, without optimization and in steady state, show a close relationship between the thermal profiles of the silicon wafer and the ones of the quartz window. By introducing a high thermal diffusivity value for the window, the homogeneity of the wafer temperature is improved by 54%. The effect of heat storage by the quartz window on the temperature profile of the silicon substrate is hence well appreciated. Finally, a selection of materials is proposed for the implementation of the high diffusivity infrared window.

A Method for the Estimation of the Interface Temperature in Ultrasonic Joining

Ultrasonic joining of copper foil to 1100 aluminum sheet at nominal joining temperatures of 298 K to 413 K (25 °C to 140 °C) for 1.25 second caused significant copper diffusion into the aluminum sheet, indicating very high diffusivity (D) values of 1.54 × 10−13 to 2.22 × 10−13 m2/s. The D values reflect high excess vacancy concentrations caused by the rapid plastic deformation in the joining surfaces. A method is presented to estimate the actual values of interface temperature from the diffusion data and expected values of vacancy concentrations. The estimated values of interface temperature were about 390 to 410 deg below the equilibrium melting point of aluminum, and in agreement with reported experimental values.

Revising the exceptionally high thermal diffusivity of spider silk

The outstanding mechanical properties of spider silk have been widely studied, but measuring its thermal transport properties is actually a challenge, since the silk fibers are very thin (few micrometers in diameter). Recently, an exceptionally high thermal diffusivity value for the dragline silk has been reported, 70mm2s−1, similar to the best thermal conducting metals. In this work, by means of a lock-in thermography setup specially designed to measure thermal diffusivity of very thin filaments, we have measured the thermal diffusivity of spider dragline silk. The value we have obtained, 0.20±0.01mm2s−1, is 400 times lower than the previously reported result and falls within the typical diffusivity range of biomaterials (0.1–0.3mm2s−1).

Empirical Green’s function estimation for lossy systems: analysis of the volume of relevance for the origin of ambient fluctuations

From a theoretical perspective, perfect Green's function recovery in diffusive systems is based on cross-correlation of time-series measured at distinct locations arising from background fluctuations from an infinite set of uncorrelated sources, either naturally occurring or engineered. Clearly such a situation is impossible in practice, and a relevant question to ask, then, is how does an imperfect set of noise sources affect the quality of the resulting empirical Green's function (EGF)? We narrow down this broad question by exploring the effect of source location and make no distinction between whether the noise sources are natural or man made. Following the theory of EGF recovery, the only requirement is that the sources are uncorrelated and endowed with the same (or nearly so) frequency spectrum and amplitude. As such, our intuition suggests that noise sources proximal to the observation points are likely to contribute more to the Green's function estimate than distal ones. However, in what manner and over what spatial extent our intuition is less clear. Thus, in this short note we specifically ask the question, ‘Where are the noise sources that contribute most to the Green's function estimate in heterogeneous, lossy systems?’ We call such a region the volume of relevance (VoR). Our analysis builds upon recent work on 1-D homogeneous systems by examining the effect of heterogeneity, dimensionality and receiver location in both one and two dimensions. Following the strategy of previous work in the field, the analysis is conducted out of mathematical convenience in the frequency domain although we stress that the sources need not be monochromatic. We find that for receivers located symmetrically across an interface between regions of contrasting diffusivity, the VoR rapidly shifts from one side of the interface to the other, and back again, as receiver separation increases. For the case where the receiver pair is located on the interface itself, the shifting is less rapid, and for moderate-to-high diffusivity contrasts, the VoR remains entirely on the more diffusive side over receiver separations up to two to three skin depths based on the high-diffusivity value. Finally, because diffusivity plays a role analogous to resistivity in electromagnetic induction problems, our results suggest that the VoR for the latter is dominated by the air region when the receivers are located on the Earth's surface—a finding that demonstrates the minimal impact of subsurface noise sources for EGF estimation from surface-based electromagnetic geophysical experiments.

Diffusion tensor imaging correlates with cytopathology in a rat model of neonatal hydrocephalus

BackgroundDiffusion tensor imaging (DTI) is a non-invasive MRI technique that has been used to quantify CNS abnormalities in various pathologic conditions. This study was designed to quantify the anisotropic diffusion properties in the brain of neonatal rats with hydrocephalus (HCP) and to investigate association between DTI measurements and cytopathology.MethodsDTI data were acquired between postnatal day 7 (P7) and P12 in 12 rats with HCP induced at P2 and in 15 age-matched controls. Animals were euthanized at P11 or P22/P23 and brains were processed with immunohistochemistry for glial fibrillary acidic protein (GFAP), ionized calcium-binding adaptor molecule (Iba-1), and luxol fast blue (LFB) to assess astrocytosis, microglial reactivity and degree of myelination, respectively.ResultsHydrocephalic rats were consistently found to have an abnormally low (at corrected p-level of <0.05) fractional anisotropy (FA) value and an abnormally high mean diffusivity (MD) value in the cerebral cortex (CX), the corpus callosum (CC), and the internal capsule (IC). Immunohistochemical analysis demonstrated trends of increasing astrocyte and microglial reactivity in HCP rats at P11 that reached statistical significance at P22/P23. A trend toward reduced myelination in the HCP rats was also found at P22/P23. Correlation analysis at P11 for the CC demonstrated statistically significant correlations (or trends) between the DTI measurement (the decreased FA and increased MD values) and the GFAP or Iba-1 rankings. The immunohistochemical rankings in the IC at P22/P23 were also significantly correlated or demonstrated a trend with both FA and MD values.ConclusionsThis study demonstrates the feasibility of employing DTI on the brain in experimental hydrocephalus in neonatal rats and reveals impairments in multiple regions of interest in both grey and white matter. A strong correlation was found between the immunohistochemical results and the changes in anisotropic diffusion properties.

Relationships between induced polarization relaxation time and hydraulic properties of sandstone

We investigated electrical and physical–chemical properties of six sandstone samples with contrasting mineralogical characteristics and with hydraulic conductivity varying in a wide range. The electrical data were obtained from time domain spectral induced polarization (IP) measurements. We inverted the IP decays to relaxation time distributions, and then compared the modal relaxation times with the dominant pore throat diameters obtained from the Mercury Injection Capillary Pressure (MICP) data. We found a positive logarithmic relationship between the relaxation time and the pore throat diameter. Also, we found the normalized chargeability (an integral IP parameter) to be positively correlated with the clay content. These two results suggest that the polarization of our sandstones is controlled by the pore throat distribution, and by the clay content. The logarithmic relationship contradicts previous theories, and is not universal. Adopting an approach of Kruschwitz and her co-workers, we calculated the effective diffusivity from IP and MICP data, and we found the effective diffusivity values ranging from 2.9 × 10−13 to 1.6 × 10−10 m2 s−1. High diffusivity values, typical of surface diffusion, were obtained for clean sandstones. Low diffusivity values were obtained for clayey sandstones, and they were one to two orders of magnitude lower than those characteristic of the surface diffusion. We proposed two mechanisms to explain the ‘slow’ diffusion: (1) the effect of surface tortuosity of pore throats filled with clay minerals and (2) the effect of pore geometry. These two effects represent an obstacle in assessing the pore throat diameter and hydraulic conductivity of sandstones with large specific surface and clay content on the basis of spectral IP measurements. However, we believe that the sandstones featuring ‘slow’ diffusion can be discriminated based on the integral polarization parameters, and that the relaxation time remains a valuable parameter for assessing hydraulic properties of clean sandstones.