Browsing by Subject "Anisotropy"
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Item Open Access A case of frontal neuropsychological and neuroimaging signs following multiple primary-blast exposure.(Neurocase, 2012-06) Hayes, Jasmeet Pannu; Morey, Rajendra A; Tupler, Larry ABlast-related traumatic brain injury (TBI) from the Afghanistan and Iraq wars represents a significant medical concern for troops and veterans. To better understand the consequences of primary-blast injury in humans, we present a case of a Marine exposed to multiple primary blasts during his 14-year military career. The neuropsychological profile of this formerly high-functioning veteran suggested primarily executive dysfunction. Diffusion-tensor imaging revealed white-matter pathology in long fiber tracks compared with a composite fractional-anisotropy template derived from a veteran reference control group without TBI. This study supports the existence of primary blast-induced neurotrauma in humans and introduces a neuroimaging technique with potential to discriminate multiple-blast TBI.Item Open Access Altered white matter microstructural organization in posttraumatic stress disorder across 3047 adults: results from the PGC-ENIGMA PTSD consortium.(Molecular psychiatry, 2021-08) Dennis, Emily L; Disner, Seth G; Fani, Negar; Salminen, Lauren E; Logue, Mark; Clarke, Emily K; Haswell, Courtney C; Averill, Christopher L; Baugh, Lee A; Bomyea, Jessica; Bruce, Steven E; Cha, Jiook; Choi, Kyle; Davenport, Nicholas D; Densmore, Maria; du Plessis, Stefan; Forster, Gina L; Frijling, Jessie L; Gonenc, Atilla; Gruber, Staci; Grupe, Daniel W; Guenette, Jeffrey P; Hayes, Jasmeet; Hofmann, David; Ipser, Jonathan; Jovanovic, Tanja; Kelly, Sinead; Kennis, Mitzy; Kinzel, Philipp; Koch, Saskia BJ; Koerte, Inga; Koopowitz, Sheri; Korgaonkar, Mayuresh; Krystal, John; Lebois, Lauren AM; Li, Gen; Magnotta, Vincent A; Manthey, Antje; May, Geoff J; Menefee, Deleene S; Nawijn, Laura; Nelson, Steven M; Neufeld, Richard WJ; Nitschke, Jack B; O'Doherty, Daniel; Peverill, Matthew; Ressler, Kerry J; Roos, Annerine; Sheridan, Margaret A; Sierk, Anika; Simmons, Alan; Simons, Raluca M; Simons, Jeffrey S; Stevens, Jennifer; Suarez-Jimenez, Benjamin; Sullivan, Danielle R; Théberge, Jean; Tran, Jana K; van den Heuvel, Leigh; van der Werff, Steven JA; van Rooij, Sanne JH; van Zuiden, Mirjam; Velez, Carmen; Verfaellie, Mieke; Vermeiren, Robert RJM; Wade, Benjamin SC; Wager, Tor; Walter, Henrik; Winternitz, Sherry; Wolff, Jonathan; York, Gerald; Zhu, Ye; Zhu, Xi; Abdallah, Chadi G; Bryant, Richard; Daniels, Judith K; Davidson, Richard J; Fercho, Kelene A; Franz, Carol; Geuze, Elbert; Gordon, Evan M; Kaufman, Milissa L; Kremen, William S; Lagopoulos, Jim; Lanius, Ruth A; Lyons, Michael J; McCauley, Stephen R; McGlinchey, Regina; McLaughlin, Katie A; Milberg, William; Neria, Yuval; Olff, Miranda; Seedat, Soraya; Shenton, Martha; Sponheim, Scott R; Stein, Dan J; Stein, Murray B; Straube, Thomas; Tate, David F; van der Wee, Nic JA; Veltman, Dick J; Wang, Li; Wilde, Elisabeth A; Thompson, Paul M; Kochunov, Peter; Jahanshad, Neda; Morey, Rajendra AA growing number of studies have examined alterations in white matter organization in people with posttraumatic stress disorder (PTSD) using diffusion MRI (dMRI), but the results have been mixed which may be partially due to relatively small sample sizes among studies. Altered structural connectivity may be both a neurobiological vulnerability for, and a result of, PTSD. In an effort to find reliable effects, we present a multi-cohort analysis of dMRI metrics across 3047 individuals from 28 cohorts currently participating in the PGC-ENIGMA PTSD working group (a joint partnership between the Psychiatric Genomics Consortium and the Enhancing NeuroImaging Genetics through Meta-Analysis consortium). Comparing regional white matter metrics across the full brain in 1426 individuals with PTSD and 1621 controls (2174 males/873 females) between ages 18-83, 92% of whom were trauma-exposed, we report associations between PTSD and disrupted white matter organization measured by lower fractional anisotropy (FA) in the tapetum region of the corpus callosum (Cohen's d = -0.11, p = 0.0055). The tapetum connects the left and right hippocampus, for which structure and function have been consistently implicated in PTSD. Results were consistent even after accounting for the effects of multiple potentially confounding variables: childhood trauma exposure, comorbid depression, history of traumatic brain injury, current alcohol abuse or dependence, and current use of psychotropic medications. Our results show that PTSD may be associated with alterations in the broader hippocampal network.Item Open Access Cocaine dependence does not contribute substantially to white matter abnormalities in HIV infection.(Journal of neurovirology, 2017-06) Cordero, Daniella M; Towe, Sheri L; Chen, Nan-Kuei; Robertson, Kevin R; Madden, David J; Huettel, Scott A; Meade, Christina SThis study investigated the association of HIV infection and cocaine dependence with cerebral white matter integrity using diffusion tensor imaging (DTI). One hundred thirty-five participants stratified by HIV and cocaine status (26 HIV+/COC+, 37 HIV+/COC-, 37 HIV-/COC+, and 35 HIV-/COC-) completed a comprehensive substance abuse assessment, neuropsychological testing, and MRI with DTI. Among HIV+ participants, all were receiving HIV care and 46% had an AIDS diagnosis. All COC+ participants were current users and met criteria for cocaine use disorder. We used tract-based spatial statistics (TBSS) to assess the relation of HIV and cocaine to fractional anisotropy (FA) and mean diffusivity (MD). In whole-brain analyses, HIV+ participants had significantly reduced FA and increased MD compared to HIV- participants. The relation of HIV and FA was widespread throughout the brain, whereas the HIV-related MD effects were restricted to the corpus callosum and thalamus. There were no significant cocaine or HIV-by-cocaine effects. These DTI metrics correlated significantly with duration of HIV disease, nadir CD4+ cell count, and AIDS diagnosis, as well as some measures of neuropsychological functioning. These results suggest that HIV is related to white matter integrity throughout the brain, and that HIV-related effects are more pronounced with increasing duration of infection and greater immune compromise. We found no evidence for independent effects of cocaine dependence on white matter integrity, and cocaine dependence did not appear to exacerbate the effects of HIV.Item Open Access Electrospun Scaffolds for Cartilage Tissue Engineering: Methods to Affect Anisotropy, Material and Cellular Infiltration(2011) Garrigues, Ned WilliamThe aim of this dissertation was to develop new techniques for producing electrospun scaffolds for use in the tissue engineering of articular cartilage. We developed a novel method of imparting mechanical anisotropy to electrospun scaffolds that allowed the production of a single, cohesive scaffold with varying directions of anisotropy in different layers by employing insulating masks to control the electric field. We improved the quantification of fiber alignment, discovering that surface fibers in isotropic scaffolds show similar amounts of fiber alignment as some types of anisotropic scaffolds, and that cells align themselves in response to this subtle fiber alignment. We improved previous methods to improve cellular infiltration into tissue engineering scaffolds. Finally, we produced a new material with chondrogenic potential consisting of native unpurified cartilage which was electrospun as a composite with a synthetic polymer. This work provided advances in three major areas of tissue engineering: scaffold properties, cell-scaffold interaction, and novel materials.
Item Open Access Enhancing imaging systems using transformation optics.(Opt Express, 2010-09-27) Smith, David R; Urzhumov, Yaroslav; Kundtz, Nathan B; Landy, Nathan IWe apply the transformation optical technique to modify or improve conventional refractive and gradient index optical imaging devices. In particular, when it is known that a detector will terminate the paths of rays over some surface, more freedom is available in the transformation approach, since the wave behavior over a large portion of the domain becomes unimportant. For the analyzed configurations, quasi-conformal and conformal coordinate transformations can be used, leading to simplified constitutive parameter distributions that, in some cases, can be realized with isotropic index; index-only media can be low-loss and have broad bandwidth. We apply a coordinate transformation to flatten a Maxwell fish-eye lens, forming a near-perfect relay lens; and also flatten the focal surface associated with a conventional refractive lens, such that the system exhibits an ultra-wide field-of-view with reduced aberration.Item Open Access Gender-specific structural abnormalities in major depressive disorder revealed by fixel-based analysis.(NeuroImage. Clinical, 2019-01-08) Lyon, Matt; Welton, Thomas; Varda, Adrina; Maller, Jerome J; Broadhouse, Kathryn; Korgaonkar, Mayuresh S; Koslow, Stephen H; Williams, Leanne M; Gordon, Evian; Rush, A John; Grieve, Stuart MBackground
Major depressive disorder (MDD) is a chronic disease with a large global impact. There are currently no clinically useful predictors of treatment outcome, and the development of biomarkers to inform clinical treatment decisions is highly desirable.Methods
In this exploratory study we performed fixel-based analysis of diffusion MRI data from the International Study to Predict Optimized Treatment in Depression with the aim of identifying novel biomarkers at baseline that may relate to diagnosis and outcome to treatment with antidepressant medications. Analyses used MR data from individuals with MDD (n = 221) and healthy controls (n = 67).Results
We show focal, gender-specific differences in the anterior limb of the internal capsule (males) and bilaterally in the genu of the corpus callosum (females) associated with diagnosis. Lower fibre cross-section in the tapetum, the conduit between the right and left hippocampi, were also associated with a decreased probability of remission. Analysis of conventional fractional anisotropy showed scattered abnormalities in the corona radiata, cerebral peduncles and mid-brain which were much lower in total volume compared to fixel-based analysis.Conclusions
Fixel-based analysis appeared to identify different underlying abnormalities than conventional tensor-based metrics, with almost no overlap between significant regions. We show that MDD is associated with gender specific abnormalities in the genu of the corpus callosum (females) and in the anterior limb of the internal capsule (males), as well as gender-independent differences in the tapetum that predict remission. Diffusion MRI may play a key role in future guidance of clinical decision-making for MDD.Item Open Access Global versus tract-specific components of cerebral white matter integrity: relation to adult age and perceptual-motor speed.(Brain structure & function, 2015-09) Johnson, Micah A; Diaz, Michele T; Madden, David JAlthough age-related differences in white matter have been well documented, the degree to which regional, tract-specific effects can be distinguished from global, brain-general effects is not yet clear. Similarly, the manner in which global and regional differences in white matter integrity contribute to age-related differences in cognition has not been well established. To address these issues, we analyzed diffusion tensor imaging measures from 52 younger adults (18-28) and 64 older adults (60-85). We conducted principal component analysis on each diffusion measure, using data from eight individual tracts. Two components were observed for fractional anisotropy: the first comprised high loadings from the superior longitudinal fasciculi and corticospinal tracts, and the second comprised high loadings from the optic radiations. In contrast, variation in axial, radial, and mean diffusivities yielded a single-component solution in each case, with high loadings from most or all tracts. For fractional anisotropy, the complementary results of multiple components and variability in component loadings across tracts suggest regional variation. However, for the diffusivity indices, the single component with high loadings from most or all of the tracts suggests primarily global, brain-general variation. Further analyses indicated that age was a significant mediator of the relation between each component and perceptual-motor speed. These data suggest that individual differences in white matter integrity and their relation to age-related differences in perceptual-motor speed represent influences that are beyond the level of individual tracts, but the extent to which regional or global effects predominate may differ between anisotropy and diffusivity measures.Item Open Access Highly parallel acoustic assembly of microparticles into well-ordered colloidal crystallites.(Soft Matter, 2016-01-21) Owens, Crystal E; Shields, C Wyatt; Cruz, Daniela F; Charbonneau, Patrick; López, Gabriel PThe precise arrangement of microscopic objects is critical to the development of functional materials and ornately patterned surfaces. Here, we present an acoustics-based method for the rapid arrangement of microscopic particles into organized and programmable architectures, which are periodically spaced within a square assembly chamber. This macroscale device employs two-dimensional bulk acoustic standing waves to propel particles along the base of the chamber toward pressure nodes or antinodes, depending on the acoustic contrast factor of the particle, and is capable of simultaneously creating thousands of size-limited, isotropic and anisotropic assemblies within minutes. We pair experiments with Brownian dynamics simulations to model the migration kinetics and assembly patterns of spherical microparticles. We use these insights to predict and subsequently validate the onset of buckling of the assemblies into three-dimensional clusters by experiments upon increasing the acoustic pressure amplitude and the particle concentration. The simulations are also used to inform our experiments for the assembly of non-spherical particles, which are then recovered via fluid evaporation and directly inspected by electron microscopy. This method for assembly of particles offers several notable advantages over other approaches (e.g., magnetics, electrokinetics and optical tweezing) including simplicity, speed and scalability and can also be used in concert with other such approaches for enhancing the types of assemblies achievable.Item Open Access Self-assembly of polymer-grafted anisotropic nanoparticles(2021) Lee, BrianWhile anisotropic nanoparticles provide unique building blocks for self-assembling useful nanodevices and nanomaterials ranging from plasmonic sensors to chiral metamaterials, controlling their self-assembly process to achieve targeted structure remains challenging. Recently, surface functionalization of nanoparticles with polymer grafts was shown to be a powerful strategy for tuning the orientation-dependent interactions of the nanoparticles. This technique allows modulation of the interaction between nanoparticles as grafted polymers can provide both repulsive interactions arising from their steric hindrance as well as attractive interactions due to their adsorption to the particle surfaces. Utilizing this approach, experiments have successfully assembled nanoparticles into large structures with highly uniform interparticle orientations. However, many challenges remain in fabricating desired nanostructures with the polymer-grafted anisotropic nanoparticles. First, much of the underlying physics governing assembly of such nanoparticles is not well understood and is difficult to discern using experimental techniques due to the nanoscopic nature of the self-assembly process. Second, the relevant parameter space that affects the particle assembly is vast and investigation of such large parameter space is costly in terms of both time and expenses. Third, computationally investigating the behavior of anisotropic nanoparticles is difficult as calculation of their interaction energies is computationally expensive due to the lack of analytical expressions for these energies.In this dissertation, I tackle these challenges in self-assembly of anisotropic nanoparticles through computational modeling, focusing specifically on polymer-grafted nanocubes and DNA-grafted nanorods. For both systems, computational methods and analytical models for efficiently calculating the interaction energies between the anisotropic nanoparticles are first developed. Using such methods as well as advanced Monte Carlo simulations and atomistic calculations, free-energy landscapes describing the assembly of these anisotropic nanoparticles are obtained. Analysis of the free-energy landscapes demonstrates that understanding the interplay between the different interaction components of the systems as well as their dependencies on the relative configurations of the assembled particles is crucial. Specifically for the nanocubes, the competition between the attractive interactions between the inorganic particle cores lead to face-face type of configurations while the repulsive interactions due to the polymer corona induce edge-edge configurations. For the DNA-grafted nanorods, the competition between attractive and repulsive interactions interplay with the chirality of the bridging DNA to induce chiral assembly of the nanorods. Based on these results, material design rules for assembling both the nanocubes and the nanorods into desired configurations are suggested. These results were not only in agreement with many previous experimental studies but also provided the underlying mechanism that explain such assembly behaviors. In summary, the results presented in this dissertation should both aid in fabrication of nanodevices with precisely controlled particle assemblies as well as provide efficient computational methods for future investigation of anisotropic nanoparticles.
Item Open Access Signal Improvement and Contrast Enhancement in Magnetic Resonance Imaging(2015) Han, YiThis thesis reports advances in magnetic resonance imaging (MRI), with the ultimate goal of improving signal and contrast in biomedical applications. More specifically, novel MRI pulse sequences have been designed to characterize microstructure, enhance signal and contrast in tissue, and image functional processes. In this thesis, rat brain and red bone marrow images are acquired using iMQCs (intermolecular multiple quantum coherences) between spins that are 10 μm to 500 μm apart. As an important application, iMQCs images in different directions can be used for anisotropy mapping. We investigate tissue microstructure by analyzing anisotropy mapping. At the same time, we simulated images expected from rat brain without microstructure. We compare those with experimental results to prove that the dipolar field from the overall shape only has small contributions to the experimental iMQC signal. Besides magnitude of iMQCs, phase of iMQCs should be studied as well. The phase anisotropy maps built by our method can clearly show susceptibility information in kidneys. It may provide meaningful diagnostic information. To deeply study susceptibility, the modified-crazed sequence is developed. Combining phase data of modified-crazed images and phase data of iMQCs images is very promising to construct microstructure maps. Obviously, the phase image in all above techniques needs to be highly-contrasted and clear. To achieve the goal, algorithm tools from Susceptibility-Weighted Imaging (SWI) and Susceptibility Tensor Imaging (STI) stands out superb useful and creative in our system.
Item Open Access The architecture of cross-hemispheric communication in the aging brain: linking behavior to functional and structural connectivity.(Cereb Cortex, 2012-01) Davis, Simon W; Kragel, James E; Madden, David J; Cabeza, RobertoContralateral recruitment remains a controversial phenomenon in both the clinical and normative populations. To investigate the neural correlates of this phenomenon, we explored the tendency for older adults to recruit prefrontal cortex (PFC) regions contralateral to those most active in younger adults. Participants were scanned with diffusion tensor imaging and functional magnetic rresonance imaging during a lateralized word matching task (unilateral vs. bilateral). Cross-hemispheric communication was measured behaviorally as greater accuracy for bilateral than unilateral trials (bilateral processing advantage [BPA]) and at the neural level by functional and structural connectivity between contralateral PFC. Compared with the young, older adults exhibited 1) greater BPAs in the behavioral task, 2) greater compensatory activity in contralateral PFC during the bilateral condition, 3) greater functional connectivity between contralateral PFC during bilateral trials, and 4) a positive correlation between fractional anisotropy in the corpus callosum and both the BPA and the functional connectivity between contralateral PFC, indicating that older adults' ability to distribute processing across hemispheres is constrained by white matter integrity. These results clarify how older adults' ability to recruit extra regions in response to the demands of aging is mediated by existing structural architecture, and how this architecture engenders corresponding functional changes that allow subjects to meet those task demands.