Changes In Diffusion Properties Research Articles

Modification of the properties of coal electrode pitch

We considered the use of electrode pitch as a binding material and the ways of processing it in order to improve its operational properties as an electrode material. The existing methods of modifying electrode pitches do not sufficiently ensure the formation of the properties of electrode masses and, accordingly, the operational characteristics of self-igniting electrodes. Therefore, in this research, a technological method was developed aimed at improving these properties by modifying it with a surface-active substance. The modification with a surface-active substance made it possible to establish the structural and chemical modification of the electrode masses by evaluating, based on the structural changes, the main characteristics and physicochemical properties that determine their behavior in the process of carbonization of the working end of the self-igniting electrode. Phenol-formaldehyde resin was used as a surfactant. The results of the study showed that the use of phenol-formaldehyde resin as a modifier of electrode pitch allowed reducing the specific electrical resistance of carbon masses by 11% and increasing the tensile strength limits by 9% due to the change in diffusion properties in the "filler–binder" system. It was established that the modifier contributes to the intensification of the processes of association of supramolecular substances (graphitosomes); the relationship between the rheological parameters and the rational composition of the polydisperse system of organic pitch mass was revealed. It was proposed to add a modifier of up to 2% at the expense of medium-temperature pitch B1 in the composition of carbon masses. This made it possible to reduce the use of medium-temperature pitch, improve the operational properties of carbon graphite products and reduce the burden on the environment.

White matter markers and predictors for subject-specific rTMS response in major depressive disorder

Repetitive transcranial magnetic stimulation (rTMS) has established therapeutic efficacy for major depressive disorder (MDD). While translational research has focused primarily on understanding the mechanism of action of TMS on functional activation and connectivity, the effects on structural connectivity remain largely unknown especially when rTMS is applied using subject-specific brain targets. This study aims to use novel diffusion magnetic resonance imaging (dMRI) analysis to examine microstructural changes related to rTMS treatment response using a unique cohort of 21 patients with MDD treated using rTMS with subject-specific targets. White matter dMRI microstructural measures and clinical scores were captured before and after the full course of treatment. We defined disease-relevant fiber bundles connected to different subregions of the left prefrontal cortex and analyzed changes in diffusion properties as well as correlations between the changes of dMRI measures and the changes in Hamilton Depression Rating Scale (HAMD). No significant changes were observed in tracts connected to the TMS targets. rTMS significantly increased the extra-axonal free-water volume, fractional anisotropy and decreased the radial diffusivity in anterior-medial prefrontal fiber bundles but did not lead to raw changes in lateral prefrontal tracts. That said, the microstructural changes in the lateral prefrontal white matter were significantly correlated with treatment response. Moreover, pre-rTMS dMRI measures of the dorsal anterior cingulate cortex and lateral prefrontal cortex connections are correlated with changes in HAMD scores. Microstructural changes in the anterior-medial and lateral prefrontal white matter are potentially involved in treatment response to TMS, though further investigation is needed using larger datasets.

Neurobiological underpinnings of rapid white matter plasticity during intensive reading instruction

Diffusion MRI is a powerful tool for imaging brain structure, but it is challenging to discern the biological underpinnings of plasticity inferred from these and other non-invasive MR measurements. Biophysical modeling of the diffusion signal aims to render a more biologically rich image of tissue microstructure, but the application of these models comes with important caveats. A separate approach for gaining biological specificity has been to seek converging evidence from multi-modal datasets. Here we use metrics derived from diffusion kurtosis imaging (DKI) and the white matter tract integrity (WMTI) model along with quantitative MRI measurements of T1 relaxation to characterize changes throughout the white matter during an 8-week, intensive reading intervention (160 total hours of instruction). Behavioral measures, multi-shell diffusion MRI data, and quantitative T1 data were collected at regular intervals during the intervention in a group of 33 children with reading difficulties (7–12 years old), and over the same period in an age-matched non-intervention control group. Throughout the white matter, mean 'extra-axonal' diffusivity was inversely related to intervention time. In contrast, model estimated axonal water fraction (AWF), overall diffusion kurtosis, and T1 relaxation time showed no significant change over the intervention period. Both diffusion and quantitative T1 based metrics were correlated with pre-intervention reading performance, albeit with distinct anatomical distributions. These results are consistent with the view that rapid changes in diffusion properties reflect phenomena other than widespread changes in myelin density. We discuss this result in light of recent work highlighting non-axonal factors in experience-dependent plasticity and learning.

Associations between age and brain microstructure in older community-dwelling men and women: the Rancho Bernardo Study

Cytoarchitectural brain changes during normal aging remain poorly characterized, and it is unclear whether patterns of brain aging differ by sex. This study used restriction spectrum imaging to examine associations between age and brain microstructure in 147 community-dwelling participants (aged 56-99 years). Widespread associations with age in multiple diffusion compartments, including increased free water, decreased restricted and hindered diffusion, and reduced neurite complexity, were observed in the cortical gray matter, the white matter tracts, and the hippocampus. Age differences in cortical microstructure were largely independent of atrophy. Associations were mostly global, although foci of stronger effects emerged in the fornix, anterior thalamic radiation and commissural fibers, and the medial temporal, orbitofrontal, and occipital cortices. Age differences were stronger and more widespread for women than men, even after adjustment for education, hypertension, and body mass index. Restriction spectrum imaging may be a convenient, noninvasive tool for monitoring changes in diffusion properties that are thought to reflect reduced cellular fractions and neurite density or complexity, which occur with typical aging, and for detecting sex differences in patterns of brain aging.

On the role of surface deformation in the oxidation of NiCr alloys at 340–600 °C

The effect of surface deformation on selective oxidation is studied on a Ni-30Cr alloy prepared by grinding (SiC paper) vs. polishing (diamond suspensions), and oxidized in air at 340−600 °C. Imaging and subsurface composition profiling by transmission electron microscopy are combined to investigate the relationships between microstructure, diffusion and oxidation. The depth of deformed material is found to be critical to selective oxidation. Atypical Cr depletion profiles reflect an abrupt change in diffusion properties between the severely deformed subsurface and the bulk. The relative contributions of grain boundary, dislocation and bulk diffusion to the Cr flux are examined based on short-circuit diffusion theory.

Short-term plasticity following motor sequence learning revealed by diffusion magnetic resonance imaging.

Current noninvasive methods to detect structural plasticity in humans are mainly used to study long‐term changes. Diffusion magnetic resonance imaging (MRI) was recently proposed as a novel approach to reveal gray matter changes following spatial navigation learning and object‐location memory tasks. In the present work, we used diffusion MRI to investigate the short‐term neuroplasticity that accompanies motor sequence learning. Following a 45‐min training session in which participants learned to accurately play a short sequence on a piano keyboard, changes in diffusion properties were revealed mainly in motor system regions such as the premotor cortex and cerebellum. In a second learning session taking place immediately afterward, feedback was given on the timing of key pressing instead of accuracy, while participants continued to learn. This second session induced a different plasticity pattern, demonstrating the dynamic nature of learning‐induced plasticity, formerly thought to require months of training in order to be detectable. These results provide us with an important reminder that the brain is an extremely dynamic structure. Furthermore, diffusion MRI offers a novel measure to follow tissue plasticity particularly over short timescales, allowing new insights into the dynamics of structural brain plasticity.

Sensing phases of water via nitrogen-vacancy centres in diamond

Ultra-thin layers of liquids on a surface behave differently from bulk liquids due to liquid-surface interactions. Some examples are significant changes in diffusion properties and the temperature at which the liquid-solid phase transition takes place. Indeed, molecular dynamics simulations suggest that thin layers of water on a diamond surface may remain solid even well above room temperature. However, because of the small volumes that are involved, it is exceedingly difficult to examine these phenomena experimentally with current technologies. In this context, shallow NV centres promise a highly sensitive tool for the investigation of magnetic signals emanating from liquids and solids that are deposited on the surface of a diamond. Moreover, NV centres are non-invasive sensors with extraordinary performance even at room-temperature. To that end, we present here a theoretical work, complemented with numerical evidence based on bosonization techniques, that predicts the measurable signal from a single NV centre when interacting with large spin baths in different configurations. In fact, by means of continuous dynamical decoupling, the polarization exchange between a single NV centre and the hydrogen nuclear spins from the water molecules is enhanced, leading to differences in the coherent dynamics of the NV centre that are interpreted as an unambiguous trace of the molecular structure. We therefore propose single NV centres as sensors capable to resolve structural water features at the nanoscale and even sensitive to phase transitions.

SPT and Imaging FCS Provide Complementary Information on the Dynamics of Plasma Membrane Molecules

The dynamics of biomolecules in the plasma membrane is of fundamental importance to understanding cellular processes. Cellular signaling often starts with extracellular ligand binding to a membrane receptor, which then transduces an intracellular signal. Ligand binding and receptor-complex activation often involve a complex rearrangement of proteins in the membrane, which results in changes in diffusion properties. Two widely used methods to characterize biomolecular diffusion are single-particle tracking (SPT) and imaging total internal reflection fluorescence correlation spectroscopy (ITIR-FCS). Here, we compare the results of recovered diffusion coefficients and mean-square displacements of the two methods by simulations of free, domain-confined, or meshwork diffusion. We introduce, to our knowledge, a new method for the determination of confinement radii from ITIR-FCS data. We further establish and demonstrate simultaneous SPT/ITIR-FCS for direct comparison within living cells. Finally, we compare the results obtained by SPT and ITIR-FCS for the receptor tyrosine kinase MET. Our results show that SPT and ITIR-FCS yield complementary information on diffusion properties of biomolecules in cell membranes.

FV 9. Diffusion Tensor Imaging in Neuromuscular diseases - A novel method for quantification of muscle degeneration in myopathy patients

Introduction The field of rare Myopathy diseases lacks in non-invasive, however quantifiable methods for evaluating states of diseases as well as monitoring disease progress and therapies. Therefore Diffusion Tensor Imaging (DTI) for non-invasive indirect representation of muscle fibre structure of human skeletal muscles, is a very promising tool for investigating and quantifying disease dependent structural changes, which cannot be observed using conventional imaging methods. DTI provides indirect measures of diffusion quantity and microstructure properties of skeletal muscles by fractional anisotropy (FA) and mean diffusivity (MD). Although there is raising evidence of this method in healthy control groups, little is known about disease dependent changes in diffusion properties. Aims In the current study we sought to investigate, whether differences between healthy control subjects and patients with Glycogen storage disease type V (also known as McArdle disease), a metabolic disorder, can be quantified by using DTI as a non-invasive method. Specifically we were interested in defining parameters (e.g. FA or MD) that provide evidence for this disease and could therefore maybe used as an indirect marker for early disease stages. Methods Conventional T1 weighted images as well as muscle diffusion weighted images were acquired from upper limbs of 12 healthy control subjects as well as from 5 (??) McArdle patients. Using a 3T Philips Achieva 3T x-Series MR with a 16 CH Sense XL-Torso coil, a 450 × 284 × 372 mm[c] FOV was imaged in approximately 20 min. All data analysis, including tractography for muscle separation and quantification was conducted, using Matlab based toolbox ExploreDTI. Results Given the 12 healthy subject, we were able to generate norm values for the applied study setup. These norm values, including FA as well as MD, were created for six separate thigh muscles (M. vastus lateralis, M. Vastus medialis, M. biceps femoris, M. rectus femoris, M. Semitendinosus and M. Semimembranosus). Some of the McArdle patients showed partially significant deviations from these norm-values, mostly in the distribution of given FA-values. Conclusion/outlook In this study we present diffusion dependent norm-values for six thigh muscles measured in a healthy population. Furthermore we provide first evidence, that myopathy specific changes in Glycogen storage disease type V could be observed non-invasively using diffusion tensor imaging approaches. Further research should focus more specifically on different types of glycogen storage disease to provide predictive measures for type and progress of the disease.

Longitudinal development in the preterm thalamus and posterior white matter: MRI correlations between diffusion weighted imaging and T2 relaxometry.

Infants born prematurely are at increased risk of adverse neurodevelopmental outcome. The measurement of white matter tissue composition and structure can help predict functional performance. Specifically, measurements of myelination and indicators of myelination status in the preterm brain could be predictive of later neurological outcome. Quantitative imaging of myelin could thus serve to develop biomarkers for prognosis or therapeutic intervention; however, accurate estimation of myelin content is difficult. This work combines diffusion MRI and multi‐component T2 relaxation measurements in a group of 37 infants born very preterm and scanned between 27 and 58 weeks equivalent gestational age. Seven infants have longitudinal data at two time points that we analyze in detail. Our aim is to show that measurement of the myelin water fraction is achievable using widely available pulse sequences and state‐of‐the‐art algorithmic modeling of the MR imaging procedure and that a multi‐component fitting routine to multi‐shell diffusion weighted data can show differences in neurite density and local spatial arrangement in grey and white matter. Inference on the myelin water fraction allows us to demonstrate that the change in diffusion properties of the preterm thalamus is not solely due to myelination (that increase in myelin content accounts for about a third of the observed changes) whilst the decrease in the posterior white matter T2 has no significant component that is due to myelin water content. This work applies multi‐modal advanced quantitative neuroimaging to investigate changing tissue properties in the longitudinal setting. Hum Brain Mapp 37:2479–2492, 2016. © The Authors Human Brain Mapping Published by Wiley Periodicals, Inc..

White matter and memory in healthy adults: Coupled changes over two years

Numerous cross-sectional studies have used diffusion tensor imaging (DTI) to link age-related differences in white matter (WM) anisotropy and concomitant decrements in cognitive ability. Due to a dearth of longitudinal evidence, the relationship between changes in diffusion properties of WM and cognitive performance remains unclear. Here we examine the relationship between two-year changes in WM organization and cognitive performance in healthy adults (N=96, age range at baseline=18–79 years). We used latent change score models (LCSM) to evaluate changes in age-sensitive cognitive abilities — fluid intelligence and associative memory. WM changes were assessed by fractional anisotropy (FA), axial diffusivity (AD), and radial diffusivity (RD) in WM regions that are considered part of established memory networks and exhibited individual differences in change. In modeling change, we postulated reciprocal paths between baseline measures and change factors, within and between WM and cognition domains, and accounted for individual differences in baseline age. Although baseline cross-sectional memory performance was positively associated with FA and negatively with RD, longitudinal effects told an altogether different story. Independent of age, longitudinal improvements in associative memory were significantly associated with linear reductions in FA and increases in RD. The present findings demonstrate the sensitivity of DTI-derived indices to changes in the brain and cognition and affirm the importance of longitudinal models for evaluating brain-cognition relations.

Longitudinal Changes in Diffusion Properties in White Matter Pathways of Children With Tuberous Sclerosis Complex

BackgroundAbnormal white matter development in patients with tuberous sclerosis complex, a multisystem hamartomatous disorder caused by aberrant neural proliferation and axonal maturation, may be associated with poorer neurocognitive outcomes. The purpose of this study is to identify predictors of longitudinal changes in diffusion properties of white matter tracts in patients with tuberous sclerosis complex. MethodsDiffusion magnetic resonance imaging was carried out in 17 subjects with tuberous sclerosis complex (mean age, 7.2 ± 4.4 years) with at least two magnetic resonance imaging scans (mean number of days between scans, 419.4 ± 105.4). There were 10 males; 5 of 17 had autism spectrum disorder and 10 of 17 had epilepsy. Regions of interest were placed to delineate the internal capsule/corona radiata, cingulum, and corpus callosum. The outcomes were mean change in apparent diffusion coefficient and fractional anisotropy. Data were analyzed using Pearson's correlation and multiple linear regression analyses. ResultsGender was a significant predictor of mean change in apparent diffusion coefficient in the left internal capsule, right and left cingulum bundles, and corpus callosum and a significant predictor of mean change in fractional anisotropy in the corpus callosum. Epilepsy was a significant predictor of mean change in apparent diffusion coefficient in the left internal capsule. Autism spectrum disorder was not predictive of diffusion changes in any of the studied pathways. ConclusionClinical variables, including gender and epilepsy, have an effect on the development of white matter pathways. These variables should be taken into consideration when counseling tuberous sclerosis complex patients and in future imaging studies in this population.

Contralateral interictal spikes are related to tapetum damage in left temporal lobe epilepsy.

In temporal lobe epilepsy (TLE), the epileptogenic focus is focal and unilateral in the majority of patients. A key characteristic of focal TLE is the presence of subclinical epileptiform activity in both the ictal and contralateral "healthy" hemisphere. Such interictal activity is clinically important, as it may reflect the spread of pathology, potentially leading to secondary epileptogenesis. The role played by white matter pathways in this process is unknown. We compared three interhemispheric white matter tracts (anterior commissure, fornix, and tapetum) to determine the pathway most associated with the presence of contralateral interictal spikes. Forty patients with unilateral left or right TLE were categorized based on the presence or absence of contralateral interictal spikes. Analyses of variance (ANOVAs) were run on diffusion properties from each tract. The analyses revealed that patients with left TLE and with bilateral interictal spikes had lower fractional anisotropy (FA) and higher mean diffusivity (MD) in the tapetum. Patients with right TLE did not show this effect. No significant associations with bilateral activity were observed for the other tracts. Blood oxygen level-dependent (BOLD) functional connectivity data revealed that homotopic lateral, not mesial, temporal areas were reliably correlated in bilateral patients, independent of ictal side. Our results indicate that, among the tracts investigated, only the tapetum was associated with contralateral epileptiform activity, implicating this structure in seizures and possible secondary epileptogenesis. We describe two mechanisms that might explain this association (the interruption of inhibitory signals or the toxic effect of carrying epileptiform signals toward the healthy hemisphere), but also acknowledge other rival factors that may be at work. We also report that patients with TLE with bilateral spikes had increased lateral bitemporal lobe connectivity. Our current results can be seen as bringing together important functional and structural data to elucidate the basis of contralateral interictal activity in focal, unilateral epilepsy. A PowerPoint slide summarizing this article is available for download in the Supporting Information section here.

FMEM: Functional mixed effects modeling for the analysis of longitudinal white matter Tract data

Many longitudinal imaging studies have collected repeated diffusion tensor magnetic resonance imaging data to understand white matter maturation and structural connectivity pattern in normal controls and diseased subjects. There is an urgent demand for the development of statistical methods for the analysis of diffusion properties along fiber tracts and clinical data obtained from longitudinal studies. Jointly analyzing repeated fiber-tract diffusion properties and covariates (e.g., age or gender) raises several major challenges including (i) infinite-dimensional functional response data, (ii) complex spatial–temporal correlation structure, and (iii) complex spatial smoothness. To address these challenges, this article is to develop a functional mixed effects modeling (FMEM) framework to delineate the dynamic changes of diffusion properties along major fiber tracts and their association with a set of covariates of interest and the structure of the variability of these white matter tract properties in various longitudinal studies. Our FMEM consists of a functional mixed effects model for addressing all three challenges, an efficient method for spatially smoothing varying coefficient functions, an estimation method for estimating the spatial–temporal correlation structure, a test procedure with local and global test statistics for testing hypotheses of interest associated with functional response, and a simultaneous confidence band for quantifying the uncertainty in the estimated coefficient functions. Simulated data are used to evaluate the finite sample performance of FMEM and to demonstrate that FMEM significantly outperforms the standard pointwise mixed effects modeling approach. We apply FMEM to study the spatial–temporal dynamics of white-matter fiber tracts in a clinical study of neurodevelopment.

Diffusion-weighted MR imaging of fetal lung maturation in sheep: effect of prenatal cortisone administration on ADC values

To assess changes in diffusion properties in the fetal lung after cortisone administration with diffusion-weighted imaging (DWI) in fetal sheep. DWI was performed on 11 pregnant sheep with singleton pregnancies on a 1.5-T MRI scanner. Four animals received cortisone injections before baseline imaging. Seven animals served as controls. Apparent diffusion coefficient (ADC) was measured on DWI in the fetal lungs by two independent readers. The Pearson test was used to correlate ADC and gestational age. A t-test was performed to compare differences in ADC values at the baseline and follow-up images within and between groups. Inter-rater reliability was calculated. In the cortisone group, ADC values increased about 10 % between the baseline and follow-up images (P = 0.039). Comparing the cortisone and control groups, ADC values of the baseline images did not differ; whereas in the follow-up imaging, ADC values were significantly higher in the cortisone group (P = 0.024). Lung ADC values did not correlate with gestational age (P = 0.970). Inter-rater reliability was high (0.970, P = 0.000). In this experimental model, MR-DWI can detect cortisone-induced changes in diffusion properties of the fetal lung. • Corticosteroids are frequently administered antenatally to prevent fetal lung immaturity at birth • DWI can detect changes in the fetal lung after corticosteroid administration • Changes can be detected as early as 5 days after treatment • Fetal MRI may offer a non-invasive method of monitoring lung maturation.

Ex vivo diffusion tensor MRI of human hearts: Relative effects of specimen decomposition

Recently, diffusion tensor MRI has been utilized as a tool to reconstruct, with high resolution, the three-dimensional myofiber orientation of hearts ex vivo. However, because of limited availability of human hearts, it is common to recover specimens postmortem, after some degree of decomposition has occurred. In this study, we describe the ability to reconstruct local fiber orientation within a unique set of human hearts using diffusion tensor MRI; relative effects of specimen decomposition were also assessed. The mean diffusivity, fractional anisotropy, and principal eigenvalues (E1, E2, and E3) were measured in hearts with varying postmortem intervals from 0 to 27 days (n = 17), and local fiber orientations were reconstructed. Mean diffusivities and principal eigenvalues nonlinearly increased as a function of postmortem interval, while fractional anisotropies nonlinearly decreased. There were good correlations between postmortem intervals and changes in diffusion properties after linear transformation of the data (R(2) > 0.7). Thus, we determined that there were regional discontinuities in the reconstruction of local fiber orientation in hearts where postmortem intervals were greater than 3 days. Therefore, any delay in tissue fixation after death (if not properly preserved using organ transplantation techniques) will compromise measurement of fiber orientation and delineation of diseased pathology, e.g., based, in part, on fractional anisotropy.

Diffusion tensor imaging of liver fibrosis in an experimental model

To characterize changes in diffusion properties of liver using diffusion tensor imaging (DTI) in an experimental model of liver fibrosis. Liver fibrosis was induced in Sprague-Dawley rats (n = 12) by repetitive dosing of carbon tetrachloride (CCl(4)). The animals were examined with a respiratory-gated single-shot spin-echo echo-planar DTI protocol at 7 T before, 2 weeks after, and 4 weeks after CCl(4) insult. Apparent diffusion coefficient (ADC), directional diffusivities (ADC(//) and ADC(⊥)), and fractional anisotropy (FA) were measured. Liver histology was performed with hematoxylin-eosin staining and Masson's trichrome staining. Significant decrease (P < 0.01) in ADC was found at 2 weeks (0.86 ± 0.09 × 10(-3) mm(2)/s) and 4 weeks (0.74 ± 0.09 × 10(-3) mm(2)/s) following CCl(4) insult, as compared with that before insult (0.97 ± 0.08 × 10(-3) mm(2)/s). Meanwhile, FA at 2 weeks (0.18 ± 0.03) after CCl(4) insult was significantly lower (P < 0.01) than that before insult (0.26 ± 0.05), and subsequently normalized at 4 weeks (0.26 ± 0.07) after the insult. Histology showed collagen deposition, presence of intracellular fat vacuoles, and cell necrosis/apoptosis in livers with CCl(4) insult. DTI detected the progressive changes in water diffusivities and diffusion anisotropy of liver tissue in this liver fibrosis model. ADC and FA are potentially valuable in detecting liver fibrosis at early stages and monitoring its progression. Future human studies are warranted to further verify the applicability of DTI in characterizing liver fibrosis and to determine its role in clinical settings.

Tract-specific analysis for investigation of Alzheimer disease: a brief review

Magnetic resonance diffusion tensor imaging is a noninvasive technique that can identify white matter tracts by evaluating bulk diffusion of water in three dimensions and can thus describe the microarchitectural characteristics of local brain tissue. Several recent reports have shown that mapping of diffusion parameters is potentially useful for speculating about the pathology of Alzheimer disease (AD). These reports have employed image-analysis approaches, including region-of-interest measurement, voxel-based analysis, tract-based spatial statistics, and tract-specific analysis (TSA). The present review focuses on TSA to investigate AD. An overview of the changes in diffusion properties of AD measured using TSA is presented and discussed.

Microstructural changes in patients with progressive supranuclear palsy: A diffusion tensor imaging study

To determine whether progressive supranuclear palsy (PSP) is associated with specific diffusion tensor imaging (DTI) patterns of diffusivity, anisotropy, and coherence in functionally relevant brain areas. In all, 17 PSP patients and 17 controls were scanned using a 3 T magnetic resonance imaging (MRI) scanner. Patients were assessed in the off-medication condition using the Hoehn and Yahr staging and the United Parkinson's Disease Rating Scale, motor subscale (UPDRS-III). Diffusion information were analyzed in relation to disease severity and subtypes. Numerous changes in diffusion properties were identified in the subcortical areas. In the midbrain, fractional anisotropy (FA) decreased and MD (mean diffusivity) increased with disease progression. UPDRS-III scores correlated positively with both FA in the caudate and MD in the pons. DTI analysis of disease subtypes demonstrated significant differences between PSP-Parkinsonism and Steele-Richardson-Olszewski syndrome in axial diffusivity values in the putamen and globus pallidus, as well as in intervoxel diffusion coherence values in the middle cerebellar peduncle. Our findings, cautiously interpreted, demonstrate the advantage of using a functional imaging technique to aid in the specificity of defining more precisely the pathological processes taking place in white and gray matter regions in PSP.

Changes in MR Diffusion Properties during Active Muscle Contraction in the Calf

To elucidate changes in the diffusion properties of muscle fiber between rest and active contraction. In 10 healthy adult volunteers (4 men, 6 women), we obtained diffusion tensor (DT) images (b=500 s/mm(2)) of bilateral calves using a 1.5-tesla clinical magnetic resonance (MR) imager. We first simultaneously scanned both calves at rest, then obtained scans of bilateral calves with plantar flexion of the right ankle using the same imaging parameters. We measured fractional anisotropy (FA) and lambda(1), lambda(2), and lambda(3) in the gastrocnemius medialis (GCM) and anterior tibialis (AT) muscles of both calves by seeding the region of interest at the thickest part, then calculated the right-to-left ratio of the FA and eigenvalues in each muscle and compared each ratio between rest and contraction by paired t-test. In the GCM, the FA ratio increased from 1.05 at rest to 1.17 after contraction, and contraction elevated the lambda1 and 2 ratios from 0.99 in resting muscles to 1.06 (lambda(1)) and 1.07 (lambda(2)). In contrast, the AT showed a decrease of the lambda(1) ratio from 0.99 at rest to 0.96 at elongation and of the lambda(2) ratio, from and 1.01 at rest to 0.94 at elongation. Statistically significant differences were observed in the FA (P<0.05), lambda1 and lambda2 (P<0.01) in the GCM, and the lambda1 and lambda2 (P<0.05) in the AT. The higher FA and lambda(1) and lambda(2) values of muscles at contraction than rest presumably reflect complicated changes, including microscopic morphological changes of the diffusion-restricting factor, focal temperature, and perfusion. We found that change in perfusion could affect the AT, and changes in focal perfusion and temperature could influence the GCM.