Water Molecular Diffusion Research Articles

Magnetic Resonance Imaging of the Liver

The purpose of this study was to measure potential changes of the apparent diffusion coefficient (ADC) in diffusion-weighted imaging of the liver before and after caloric challenge in correlation to the induced changes in portal vein flow. The study was approved by the local ethics committee. Each of 10 healthy volunteers underwent 4 measurements in a 1.5-T whole-body magnetic resonance scanner on 2 different days: a first scan after fasting for at least 8 hours and a second scan 30 minutes after intake of a standardized caloric either a protein- or carbohydrate-rich meal. Diffusion-weighted spin-echo echo-planar magnetic resonance images were acquired at b values of 0, 50, 150, 250, 500, 750, and 1000 s/mm. In addition, portal vein flow was quantified with 2-dimensional phase-contrast imaging (velocity encoding parallel to flow direction, 60 cm/s). Mean ADC values for regions of interest in 3 different slices were measured from b50 to b250 and from b500 to b1000 images. Carbohydrate- and protein-rich food intake both resulted in a substantial increase in the portal vein flow (fasting state, 638.6 ± 202.3 mL/min; after protein intake, 1322 ± 266.8; after carbohydrate intake, 1767 ± 421.6). The signal decay with increasingly strong diffusion weighting (b values from 0 to 1000 s/mm2) exhibited a triexponential characteristic, implying fast, intermediate, and slow-moving water-molecule proton-spin ensembles in the liver parenchyma. Mean ADC for high b values (b500-b1000) after fasting was 0.93 ± 0.09 × 10 mm/s; that after protein intake, 0.93 ± 0.11 × 10; and that after carbohydrate intake, 0.93 ± 0.08 × 10. For intermediate b values (b50-b250), the signal-decay constants were 1.27 ± 0.14 × 10 mm/s, 1.28 ± 0.15 × 10, and 1.31 ± 0.09 × 10, respectively. There was no statistically significant difference between fasting and caloric challenge. The postprandial increase in portal vein flow is not accompanied by a change of liver parenchymal ADC values. In clinical diffusion imaging, patients may be scanned without prescan food-intake preparations. To minimize interference of perfusion effects, liver-tissue molecular water diffusion should be quantified using high b values (≥500 s/mm) only.

Water diffusion in brain cortex closely tracks underlying neuronal activity

Neuronal activity results in a local increase in blood flow. This concept serves as the basis for functional MRI. Still, this approach remains indirect and may fail in situations interfering with the neurovascular coupling mechanisms (drugs, anesthesia). Here we establish that water molecular diffusion is directly modulated by underlying neuronal activity using a rat forepaw stimulation model under different conditions of neuronal stimulation and neurovascular coupling. Under nitroprusside infusion, a neurovascular-coupling inhibitor, the diffusion response and local field potentials were maintained, whereas the hemodynamic response was abolished. As diffusion MRI reflects interactions of water molecules with obstacles (e.g., cell membranes), the observed changes point to a dynamic modulation of the neural tissue structure upon activation, which remains to be investigated. These findings represent a significant shift in concept from the current electrochemical and neurovascular coupling principles used for brain imaging, and open unique avenues to investigate mechanisms underlying brain function.

Are we ready to image the incoherent molecular motion in our minds?

The increasing radiological awareness about intravoxel incoherent motion imaging (IVIM) is reflected in this month’s issue of Neuroradiology. Hauser et al. [1] following hard on the heels of previous work [2] contribute substantially to the accumulating evidence for the utility of IVIM in tissue characterization. Several studies in abdominal imaging, where the theoretical principles of IVIM are verified in vivo in a satisfactory way [3], spearheaded the translation of IVIM into clinical applications after some time of hibernation. In human tissue, diffusion-weighted imaging (DWI) detects the molecular motion, which includes the molecular diffusion of water as well as the blood microcirculation in the capillary network. The cardinal DWIderived parameter, apparent diffusion coefficient, has been adapted over time to investigate the tissue-ofinterest but is dependent on the choice of b values and is endowed with a lumped and nonspecific character. The separation of pure diffusion from flow-related molecules motion demands complex models to describe the signal decay in DWI after application of increasing “motion probing” gradient intensities. The parameters D (tissue diffusivity or pure diffusion coefficient), D* (pseudodiffusion coefficient or perfusion-related incoherent microcirculation coefficient), and f (microvascular volume or perfusion fraction), which were dubbed by Le Bihan et al. [4] as the hallmarks of IVIM-sensitized DWI, seem to adequately resolve the perfusion (microcirculation or net flow) from the true diffusion given a sufficient b value sampling and a biexponential curve fit analysis. Almost simultaneous to the premier presentation of the IVIM technique, considerable skepticism was voiced concerning the suitability of f, D*, and fD* to measure perfusion in the “classical” sense of the term [5]. The debate remains ongoing and probably will not be terminated since it all seems to be a matter of definition. Actually, the rather loosely used term perfusion implies the efficiency of blood to saturate the tissue with oxygen and nutrients as well as to desaturate it from waste products. The monitoring of exogenous tracers (gadolinium compounds) by MRI provides the well-known blood flow parameter, which is conceptually related to perfusion. Diverse applied models rely on several assumptions that oversimplify the physiological background, resulting in an apparently meaningful determination of blood volume, which is not perfusion or blood flow. In contrast, IVIM devotees, by measuring the phase effects of flowing blood (endogenous marker), provide new insights into the capillary microcirculation, which may be conceptually related to “classical” perfusion under several assumptions about capillary network structure, too [6, 7]. Remarkably, the cellular shape/structuring may cause pseudo-perfusion like “guided flow” (for example in the kidney medulla or in the white brain matter). The apparent “overestimation” of perfusion fraction f compared to dynamic contrast-enhanced MR perfusion is inevitably influenced by the choice of motion-probing gradient directions versus the directionality of the neurons in the white matter. The bottom line is that the terms should bemeticulously chosen to avoid confusing imprecision that only serve to please our ears. Thus, before any further work clarifies these issues, it would be advisable to denominate f strictly as fractional volume of capillary flow instead of perfusion fraction. Whether IVIM launch means that “the end is nigh” for the contrast-enhanced perfusion-weighted MRI, the answer is probably not. The compartmental water exchange in the DWI experiments is not adequately captured due to the short evolution time (≈100 ms) compared to the dynamic contrastenhanced MRI, which tracks the intraand extravascular as This is a Comment to Original Article doi:10.1007/s00234-013-1154-9

MSE-MRI sequence optimisation for measurement of bi- and tri-exponential T2 relaxation in a phantom and fruit

The transverse relaxation signal from vegetal cells can be described by multi-exponential behaviour, reflecting different water compartments. This multi-exponential relaxation is rarely measured by conventional MRI imaging protocols; mono-exponential relaxation times are measured instead, thus limiting information about of the microstructure and water status in vegetal cells. In this study, an optimised multiple spin echo (MSE) MRI sequence was evaluated for assessment of multi-exponential transverse relaxation in fruit tissues. The sequence was designed for the acquisition of a maximum of 512 echoes. Non-selective refocusing RF pulses were used in combination with balanced crusher gradients for elimination of spurious echoes. The study was performed on a bi-compartmental phantom with known T2 values and on apple and tomato fruit. T2 decays measured in the phantom and fruit were analysed using bi- and tri-exponential fits, respectively. The MRI results were compared with low field non-spatially resolved NMR measurements performed on the same samples.The results demonstrated that the MSE-MRI sequence can be used for up to tri-exponential T2 quantification allowing for estimation of relaxation times from a few tens of milliseconds to over a second. The effects of the crusher moment and the TE value on T2 measurements were studied both on the bi-compartmental phantom and on the fruit tissues. It was demonstrated that the sequence should be optimised with regard to the characteristics of the tissue to be examined by considering the effects of water molecular diffusion in the presence of both imaging gradients and gradients produced by susceptibility inhomogeneities.

Diffusion tensor imaging and proton magnetic resonance spectroscopy in brain tumor: Correlation between structure and metabolism.

Proton magnetic resonance spectroscopy and diffusion tensor imaging are non-invasive techniques used to detect metabolites and water diffusion in vivo. Previous studies have confirmed a positive correlation of individual fractional anisotropy values with N-acetylaspartate/creatine and N-acetylaspartate/choline ratios in tumors, edema, and normal white matter. This study divided the brain parenchyma into tumor, peritumoral edema, and normal-appearing white matter according to MRI data, and analyzed the correlation of metabolites with water molecular diffusion. Results demonstrated that in normal-appearing white matter, N-acetylaspartate/creatine ratios were positively correlated with fractional anisotropy values, negatively correlated with radial diffusivities, and positively correlated with maximum eigenvalues. Maximum eigenvalues and radial diffusivities in peritumoral edema showed a negative correlation with choline, N-acetylaspartate, and creatine. Radial diffusivities in tumor demonstrated a negative correlation with choline. These data suggest that the relationship between metabolism and structure is markedly changed from normal white matter to peritumoral edema and tumor. Neural metabolism in the peritumoral edema area decreased with expanding extracellular space. The normal relationship of neural function and microstructure disappeared in the tumor region.

Contribution of perfusion in piffusion-weighted 1H-MRI of intrahepatic and subcutaneous hepatocellular carcinoma in rat

Hepatocellular carcinoma (HCC) and liver metastases are an increasing problem worldwide. Non-invasive methods for understanding of HCC growth mechanisms are highly desirable. A biexponential model for analysis of non-invasive diffusion-weighted 1 H magnetic resonance imaging (MRI) provides important information about neoplastic transformation in capillary liver tissue perfusion and water molecular diffusion. Fast and slow components of water apparent diffusion coefficient (ADC) were separated in the normal rat liver, intrahepatic, and subcutaneous HCCs. MRI was acquired with a Varian 9.4 T horizontal bore system. The fast component of ADC (ADC fast ), which contributes 38% to total signal in the intrahepatic HCC, was significantly lower compared to normal liver value, while the slow component of ADC did not differ in liver, intrahepatic, and subcutaneous HCCs. A decrease in ADC fast may be caused by restricted perfusion in abnormal tumor microvessels. Thus, a reported earlier decrease in ADC in HCC compared to normal liver was mostly due to a decreased in tumor perfusion rather than a decrease in water diffusion. Subcutaneous HCC showed a very limited vasculature development, which makes the tumor perfusion extremely poor and hypoxic. Simultaneous monitoring of water ADC changes in orthotopic and subcutaneous HCCs may be useful, but a possibility of location-based physiological and metabolic differences must be recognized. Keywords: hepatocellular carcinoma, 1 H-MRI, apparent diffusion coefficient, perfusion, tumor location.

Positive Semidefinite Generalized Diffusion Tensor Imaging via Quadratic Semidefinite Programming

The positive definiteness of a diffusion tensor is important in magnetic resonance imaging because it reflects the phenomenon of water molecular diffusion in complicated biological tissue environments. To preserve this property, we represent it as an explicit positive semidefinite (PSD) matrix constraint and some linear matrix equalities. The objective function is the regularized linear least squares fitting for the log-linearized Stejskal--Tanner equation. The regularization term is the heuristic nuclear norm of the PSD matrix, since we expect it to be of low rank. In this way, we establish a convex quadratic semidefinite programming (SDP) model, whose global solution exists. The optimal solution could be solved by three efficient methods. While there are two state-of-the-art solvers---SDPT3 and QSDP---for the primal problem, we design a new augmented Lagrangian based alternating direction method (ADM) for the dual problem. Sensitivity analyses on the coefficients of the optimal diffusion tensor and the ...

COMPLEXITY MEASURES AND NOISE EFFECTS ON DIFFUSION MAGNETIC RESONANCE IMAGING OF THE NEURON AXONS NETWORK IN THE HUMAN BRAIN

Diffusion Magnetic Resonance Imaging (dMRI) is a novel technique that mirrors the complex architecture of the neuron axons fiber networks in the human brain. Based on the dMRI scans, fractal dimensions (Box Counting and Multifractal Dimensions) are used to quantify the complexity of the neuron axons networks. The values of the fractal dimensions are calculated as a function of the intensity threshold τ in an effort to remove the effects of stochastic noise, always present in the molecular diffusion of water in the brain. It is shown that intermediate values of the noise threshold τ are better for estimating the complexity of the neuron network architecture, because for small τ the presence of stochastic noise often masks the underlying structure, while for τ > 0.6 important parts of the axon network structure are ignored. Calculations of the multifractal dimensions in healthy brains as a function of τ, give consistent scaling results in the medium intensity thresholds, where the neuron axons activity is better discerned. In these intermediate τ scales, deviations are recorded in the multifractal spectra of pathological brains, which indicate damaged network architectures.

Diffusion and solubility of hydrogen and water in periclase

Cylinders of synthetic periclase single crystals were annealed at 0.15–0.5 GPa and 900–1200 °C under water-saturated conditions for 45 min to 72 h. Infrared spectra measured on the quenched products show bands at 3,297 and 3,312 cm−1 indicating VOH− centers (OH-defect stretching vibrations in a half-compensated cation vacancy) in the MgO structure as a result of proton diffusion into the crystal. For completely equilibrated specimens, the OH-defect concentration, expressed as H2O equivalent, was calculated to 3.5 wt ppm H2O at 1,200 °C and 0.5 GPa based on the calibration method of Libowitzky and Rossmann (Am Min 82:1111–1115, 1997). This value was confirmed via Raman spectroscopy, which shows OH-defect-related bands at identical wavenumbers and yields an H2O equivalent concentration of about 9 wt ppm using the quantification scheme of Thomas et al. (Am Min 93:1550–1557, 2008), revised by Mrosko et al. (Am Mineral 96:1748–1759, 2011). Results of both independent methods give an overall OH-defect concentration range of 3.5–9 (+4.5/−2.6) ppm H2O. Proton diffusion follows an Arrhenius law with an activation energy Ea = 280 ± 64 kJ mol−1 and the logarithm of the pre-exponential factor logDo (m2 s−1) = −2.4 ± 1.9. IR spectra taken close to the rims of MgO crystals that were exposed to water-saturated conditions at 1,200 °C and 0.5 GPa for 24 h show an additional band at 3,697 cm−1, which is related to brucite precipitates. This may be explained by diffusion of molecular water into the periclase, and its reaction with the host crystal during quenching. Diffusion of molecular water may be described by logDH2O (m2 s−1) = −14.1 ± 0.4 (2σ) at 1,200 °C and 0.5 GPa, which is ~ 2 orders of magnitude slower than proton diffusion at identical P-T conditions.

The Diffusion Tensor Imaging Toolbox

During the past few years, The Journal of Neuroscience has published more than 30 articles that describe investigations that used Diffusion Tensor Imaging (DTI) and related techniques as a primary observation method. This illustrates a growing interest in DTI within the basic and clinical neuroscience communities. This article summarizes DTI methodology in terms that can be immediately understood by the neuroscientist who has little previous exposure to DTI. It describes the fundamentals of water molecular diffusion coefficient measurement in brain tissue and illustrates how these fundamentals can be used to form vivid and useful depictions of white matter macroscopic and microscopic anatomy. It also describes current research applications and the technique's attributes and limitations. It is hoped that this article will help the readers of this Journal to more effectively evaluate neuroscience studies that use DTI.

Liver fibrosis: An intravoxel incoherent motion (IVIM) study

To characterize longitudinal changes in molecular water diffusion, blood microcirculation, and their contributions to the apparent diffusion changes using intravoxel incoherent motion (IVIM) analysis in an experimental mouse model of liver fibrosis. Liver fibrosis was induced in male adult C57BL/6N mice (22-25 g; n = 12) by repetitive dosing of carbon tetrachloride (CCl(4) ). The respiratory-gated diffusion-weighted (DW) images were acquired using single-shot spin-echo EPI (SE-EPI) with 8 b-values and single diffusion gradient direction. True diffusion coefficient (D(true) ), blood pseudodiffusion coefficient (D(pseudo) ), and perfusion fraction (P(fraction) ) were measured. Diffusion tensor imaging (DTI) was also performed for comparison. Histology was performed with hematoxylin-eosin and Masson's trichrome staining. A significant decrease in D(true) was found at 2 weeks and 4 weeks following CCl(4) insult, as compared with that before insult. Similarly, D(pseudo) values before injury was significantly higher than those at 2 weeks and 4 weeks after CCl(4) insult. Meanwhile, P(fraction) values showed no significant differences over different timepoints. For DTI, significant decrease in ADC was observed following CCl(4) administration. Fractional anisotropy at 2 weeks after CCl(4) insult was significantly lower than that before insult, and subsequently normalized at 4 weeks after the insult. Liver histology showed collagen deposition, the presence of intracellular fat vacuoles, and cell necrosis/apoptosis in livers with CCl(4) insult. Both molecular water diffusion and blood microcirculation contribute to the alteration in apparent diffusion changes in liver fibrosis. Reduction in D(true) and D(pseudo) values resulted from diffusion and perfusion changes, respectively, during the progression of liver fibrosis. IVIM analysis may serve as valuable and robust tool in detecting and characterizing liver fibrosis at early stages, monitoring its progression in a noninvasive manner.

Long-term evolution of diffusion tensor indices after temporary experimental ischemic stroke in rats

Diffusion tensor (DT) imaging measures the random molecular diffusion of water in vivo and provides information on the microstructure of tissue. Ischemic brain damage leads to tissue disorganization and structural lost. We aimed to evaluate these changes in a rat model of focal stroke from the hyperacute to chronic phase by utilizing several DT indices. Adult male Wistar rats, subjected to temporary focal cerebral ischemia by suture occlusion of the middle cerebral artery for 90min, and sham controls were serially imaged at 4.7Tesla. DT scans were collected repeatedly during the hyperacute (2 and 3.5h), acute (1, 2, and 3days), subacute (4, 7, and 14days), and chronic (4, 6, and 8weeks) phases. We measured the evolution of DT indices (mean diffusivity (MD), axial diffusivity (λ║), radial diffusivity (λ┴), and fractional anisotropy (FA)) in the cortex, subcortex, and corpus callosum of the ischemic hemisphere. In the hyperacute phase, MD, λ║, and λ┴ reduced with no change in FA. From the acute to subacute phase, MD, λ║, and λ┴ normalized and thereafter increased, whereas FA decreased in all the tissues. In the chronic phase, MD, λ║, and λ┴ continued to rise, whereas FA normalized in the corpus callosum and subcortex, but remained low in the cortex. We described structural tissue changes in ischemic rat brain longitudinally utilizing DT analysis. DT indices reveal different individual patterns reflecting different facades and phases of tissue injury. The use of several DT indices may improve accuracy in estimating the age of the brain injury and in detecting ongoing pathological events.

Water Diffusion in Silica Glass and Wet Oxidation of Si: An Interpretation for the High Speed of Wet Oxidation

It has been postulated that the molecular water, H2O, is mobile but the hydroxyl water, OH, is immobile in silica glass. Further, it has been theorized that H2O and OH are held in a strict equilibrium. This study investigates the behavior of H2O in the oxidation of silicon: It was found that the strict equilibrium was not held, and fast-moving H2O was found to cause silicon oxidation. It is suggested that the diffusion of molecular water, which can diffuse faster than oxygen and has not been directly observed in a normal water diffusion study in silica glass, is responsible for the faster oxidation of silicon in wet oxidation than in dry (oxygen) oxidation. Some indirect evidence for such fast moving molecular water is presented.

Obsidian hydration dating by infrared spectroscopy: method and calibration

Low temperature (90–190 °C) hydrothermal experiments have been conducted on seven obsidians where composition of the glass varies significantly in the concentration of structural water within the unhydrated bulk material. Infrared transmission spectroscopy was used to track the diffusion of molecular water into the glass surface as a function of time and temperature. Long-term (60–360 days) hydration sequences at 90 °C show a t 0.6 time dependence for the mass uptake of molecular water that forms the hydration layer. The structural water concentration of the unhydrated bulk obsidian is highly correlated with the pre-exponential and activation energy and may be used to estimate the Arrhenius constants. In addition, secondary ion mass spectrometry (SIMS) hydrogen profiling of Napa Glass Mountain obsidian hydrated at 90 °C reveals that the early stages of diffusion exhibit a dynamic behavior that includes a fluctuating hydrogen concentration and a changing diffusion coefficient that slows with time.

Host and adsorbate dynamics in silicates with flexible frameworks: Empirical force field simulation of water in silicalite

Molecular dynamics simulations are performed on the pure silica zeolite silicalite (MFI framework code), maintaining via a new force field both framework flexibility and realistic account of electrostatic interactions with adsorbed water. The force field is similar to the well-known "BKS" model [B. W. H. van Beest et al., Phys. Rev. Lett. 64, 1955 (1990)], but with reduced partial atomic charges and reoptimized covalent bond potential wells. The present force field reproduces the monoclinic to orthorhombic transition of silicalite. The force field correctly represents the hydrophobicity of pure silica silicalite, both the adsorption energy, and the molecular diffusion constants of water. Two types of adsorption, specific and weak unspecific, are predicted on the channel walls and at the channel intersection. We discuss molecular diffusion of water in silicalite, deducing a barrier to crossing between the straight and the zigzag channels. Analysis of the thermal motion shows that at room temperature, framework oxygen atoms incurring into the zeolite channels significantly influence the dynamics of adsorbed water.

Age‐related differences in multiple measures of white matter integrity: A diffusion tensor imaging study of healthy aging

Diffusion tensor imaging (DTI) measures diffusion of molecular water, which can be used to calculate indices of white matter integrity. Early DTI studies of aging primarily focused on two global measures of integrity; the average rate (mean diffusivity, MD) and orientation coherence (fractional anisotropy, FA) of diffusion. More recent studies have added measures of water movement parallel (axial diffusivity, AD) and perpendicular (radial diffusivity, RD) to the primary diffusion direction, which are thought to reflect the neural bases of age differences in diffusion (i.e., axonal shrinkage and demyelination, respectively). In this study, patterns of age differences in white matter integrity were assessed by comparing younger and healthy older adults on multiple measures of integrity (FA, AD, and RD). Results revealed two commonly reported patterns (Radial Increase Only and Radial/Axial Increase), and one relatively novel pattern (Radial Increase/Axial Decrease) that varied by brain region and may reflect differential aging of microstructural (e.g., degree of myelination) and macrostructural (e.g., coherence of fiber orientation) properties of white matter. In addition, larger age differences in FA in frontal white matter were consistent with the anterior-posterior gradient of age differences in white matter integrity. Together, these findings complement other recent studies in providing information about patterns of diffusivity that are characteristic of healthy aging.

Liver Cirrhosis: Intravoxel Incoherent Motion MR Imaging—Pilot Study

To retrospectively evaluate a respiratory-triggered diffusion-weighted (DW) magnetic resonance (MR) imaging sequence combined with parallel acquisition to allow the calculation of pure molecular-based (D) and perfusion-related (D*, f) diffusion parameters, on the basis of the intravoxel incoherent motion (IVIM) theory, to determine if these parameters differ between patients with cirrhosis and patients without liver fibrosis. The institutional review board approved this retrospective study; informed consent was waived. IVIM DW imaging was tested on three alkane phantoms, on which the signal-intensity decay curves according to b factors were logarithmically plotted. Ten b factors (0, 10, 20, 30, 50, 80, 100, 200, 400, 800 sec/mm(2)) were used in patients. Patients with documented liver cirrhosis (cirrhotic liver group, n = 12) and patients without chronic liver disease (healthy liver group, n = 25) were included. The mean liver D, D*, and f values were measured and compared with the apparent diffusion coefficient (ADC) computed by using four b values (0, 200, 400, 800 sec/mm(2)). Liver ADC and D, f, and D* parameters were compared between the cirrhotic liver group and healthy liver group. Means were compared by using the Student t test. Signal-intensity decay curves were monoexponential on phantoms and biexponential in patients. In vivo, mean ADC values were significantly higher than D in the healthy liver group (ADC = 1.39 x 10(-3) mm(2)/sec +/- 0.2 [standard deviation] vs D = 1.10 x 10(-3) mm(2)/sec +/- 0.7) and in the cirrhotic liver group (ADC = 1.23 x 10(-3) mm(2)/sec +/- 0.4 vs D = 1.19 x 10(-3) mm(2)/sec +/- 0.5) (P = .03). ADC and D* were significantly reduced in the cirrhotic liver group compared with those in the healthy liver group (respective P values of .03 and .008). Restricted diffusion observed in patients with cirrhosis may be related to D* variations, which reflect decreased perfusion, as well as alterations in pure molecular water diffusion in cirrhotic livers.

Mossy fiber sprouting in pilocarpine-induced status epilepticus rat hippocampus: A correlative study of diffusion spectrum imaging and histology

Mossy fiber sprouting (MFS) is the main characteristic of temporal lobe epilepsy (TLE), which is highly correlated with the frequencies of recurrent seizures as well as degrees of severity of TLE. A recent MRI technique, referred to as diffusion spectrum imaging (DSI), can resolve crossing fibers and investigate the intravoxel heterogeneity of water molecular diffusion. Being able to achieve higher accuracy in depicting the complex fiber architecture, DSI may help improve localization of the seizure-induced epileptic foci. In this study, two indices of DSI, which represented the mean diffusivity (MSL) and diffusion anisotropy (DA), were proposed. A correlative study between diffusion characteristics and the severity of MFS was investigated in the pilocarpine-induced status epilepticus (SE) rat model. Nine SE rats and five control rats were studied with MRI and histological Timm's staining. For MSL, no significant correlation was found in the dentate gyrus (DG), r = − 0.36; p = 0.2017, and positive correlation was found in cornu ammonis (CA3), r = 0.62; p = 0.0174. The correlation between DA and Timm's score showed positive correlation in DG, r = 0.71; p = 0.0047, and negative correlation in CA3, r = − 0.63; p = 0.0151. Our results were compatible with the previous reports on fiber architecture alterations in DG and CA3 subregions. In conclusion, the histological correspondence of DSI indices was demonstrated. With DSI indices, longitudinal follow-up of hippocampal fiber architecture can be achieved to elucidate the pathophysiology of TLE, which might be helpful in disease localization.

MR tractography for stroke

The diffusion-tensor imaging (DTI) technique records the anisotropy of water molecular diffusion. By postprocessing the DTI data, one can acquire in vivo information about neuronal pathways. This process is now well known as MR tractography. This technique can depict the major fiber bundles, including the sensory tracts, pyramidal tracts, and visual pathways. To test whether tractography is reproducible and reliable, we used this technique to document the presence of acute tiny infarcts located in the supratentorial brain. We analyzed the data of 14 patients who presented to our institute with sensorimotor symptoms. There was an excellent correlation between the location of the infarct as assessed by tractography and clinical symptoms. Therefore, this study showed that MR tractography reliably depicts the sensorimotor tracts. Next, we applied the technique to patients with evolving symptoms after admission to hospital. We specifically assessed the change in the tract–infarct relationship over time. The data showed that, in most cases when there was symptomatic progression, the distance between the tract and the infarct border depicted on diffusion-weighted images (DWI) diminished. Finally, we studied whether the use of tractography could help predict a patient's prognosis. To simplify the analysis, we specifically focused on patients with lenticulostriate artery (LSA) infarcts. We analyzed the correlation between the extent of CST involvement within the infarcts and the severity of motor deficits. The data indicated that the tractographic technique could be useful in predicting a patient's outcome. Furthermore, combining this information with the apparent diffusion coefficient (ADC) and perfusion data may further refine the accuracy of the outcome prediction.

High-temperature treatment of hydrogen loaded GeO 2:SiO 2 glasses for photonic device fabrication

High-temperature treatment of hydrogen loaded silica- and germanium doped silica glass, also referred to as OH flooding, has been studied. The removal mechanism of hydroxyl groups in silica glass, during OH flooding, occurs by formation and diffusion of molecular hydrogen, while in germanium doped silica the main diffusion mechanism is attributed to diffusion of molecular water. UV exposure of OH flooded and non-treated germanium doped silica samples, from a ArF laser at 193 nm, show large changes in the asymmetric stretching vibration of Si–O–Si bridges, indicating compaction of the glass network. In addition, the thermal relaxation kinetics of the UV induced compaction are found to be similar for non-treated samples and OH flooded samples.