Journal articles: 'Tensor dependent diffusion'

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Sajib, Saurav Z. K., Munish Chauhan, Oh In Kwon, and Rosalind J. Sadleir. "Magnetic-resonance-based measurement of electromagnetic fields and conductivity in vivo using single current administration—A machine learning approach." PLOS ONE 16, no. 7 (July 22, 2021): e0254690. http://dx.doi.org/10.1371/journal.pone.0254690.

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Diffusion tensor magnetic resonance electrical impedance tomography (DT-MREIT) is a newly developed technique that combines MR-based measurements of magnetic flux density with diffusion tensor MRI (DT-MRI) data to reconstruct electrical conductivity tensor distributions. DT-MREIT techniques normally require injection of two independent current patterns for unique reconstruction of conductivity characteristics. In this paper, we demonstrate an algorithm that can be used to reconstruct the position dependent scale factor relating conductivity and diffusion tensors, using flux density data measured from only one current injection. We demonstrate how these images can also be used to reconstruct electric field and current density distributions. Reconstructions were performed using a mimetic algorithm and simulations of magnetic flux density from complementary electrode montages, combined with a small-scale machine learning approach. In a biological tissue phantom, we found that the method reduced relative errors between single-current and two-current DT-MREIT results to around 10%. For in vivo human experimental data the error was about 15%. These results suggest that incorporation of machine learning may make it easier to recover electrical conductivity tensors and electric field images during neuromodulation therapy without the need for multiple current administrations.

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Hanyga, Andrzej, and Richard L. Magin. "A new anisotropic fractional model of diffusion suitable for applications of diffusion tensor imaging in biological tissues." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 470, no. 2170 (October 8, 2014): 20140319. http://dx.doi.org/10.1098/rspa.2014.0319.

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An anomalous anisotropic diffusion equation is constructed in which the order of the spatial pseudo-differential operator is generalized to be distributed with a directionally dependent distribution. A time fractional version of this equation is also considered. First, it is proved that the equation is positivity-preserving and properly normalized. Second, the existence of a smooth Green's function solution is proved. Finally, an expression for the diffusive flux density for this new fractional order process is calculated. This approach may find utility in modelling diffusion tensor imaging data in the white matter of the human brain where both the apparent diffusion coefficient and the order of the pseudo-differential operator are anisotropic.

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KOPIETZ, PETER. "THOULESS NUMBER AND SPIN DIFFUSION IN QUANTUM HEISENBERG FERROMAGNETS." Modern Physics Letters B 07, no. 27 (November 20, 1993): 1747–59. http://dx.doi.org/10.1142/s0217984993001788.

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Using an analogy between the conductivity tensor of electronic systems and the spin stiffness tensor of spin systems, we introduce the concept of the Thouless number g0 and the dimensionless frequency-dependent conductance g(ω) for quantum spin models. It is shown that spin diffusion implies the vanishing of the Drude peak of g(ω), and that the spin diffusion coefficient Ds is proportional to g0. We develop a new method based the Thouless number to calculate D s , and present results for D s in the nearest-neighbor quantum Heisenberg ferromagnet at infinite temperatures for arbitrary dimension d and spin S.

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Ben-Sira, Liat, Noam Goder, Haim Bassan, Shlomi Lifshits, Yaniv Assaf, and Shlomi Constantini. "Clinical benefits of diffusion tensor imaging in hydrocephalus." Journal of Neurosurgery: Pediatrics 16, no. 2 (August 2015): 195–202. http://dx.doi.org/10.3171/2014.10.peds13668.

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OBJECT The object of this study was to use diffusion tensor imaging (DTI) to evaluate and characterize white matter changes in hydrocephalus. METHODS The authors performed a retrospective analysis of DTI in a cohort of patients with hydrocephalus (n = 35), 19 of whom had both pre- and postsurgical imaging studies. These patient’s DTI values were compared with values extracted from age-dependent trend lines computed from a healthy subject group (n = 70, age span 14 months-14 years). Several DTI parameters in different regions of interest (ROIs) were evaluated to find the most sensitive parameters for clinical decision making in hydrocephalus. RESULTS Compared with healthy controls, patients with active hydrocephalus had a statistically significant change in all DTI parameters. The most sensitive and specific DTI parameter for predicting hydrocephalus was axial diffusivity (λ1) measured at the level of the corona radiata. Diffusion tensor imaging parameters correlated with several conventional radiological parameters in the assessment of hydrocephalus but were not superior to them. There was no convincing correlation between clinical disease severity and DTI parameters. When examining the pre- and postsurgical effect, it was found that DTI may be a sensitive tool for estimating tissue improvement. CONCLUSIONS This large-cohort study with a multidisciplinary approach combining clinical, neurological, radiological, and multiple DTI parameters revealed the most sensitive DTI parameters for identifying hydrocephalus and suggested that they may serve as an important tool for the disorder’s quantitative radiological assessment.

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Chen, Bin, Hua Guo, and Allen W. Song. "Correction for direction-dependent distortions in diffusion tensor imaging using matched magnetic field maps." NeuroImage 30, no. 1 (March 2006): 121–29. http://dx.doi.org/10.1016/j.neuroimage.2005.09.008.

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Mueller, Karsten, Alfred Anwander, Harald E. Möller, Annette Horstmann, Jöran Lepsien, Franziska Busse, Siawoosh Mohammadi, et al. "Sex-Dependent Influences of Obesity on Cerebral White Matter Investigated by Diffusion-Tensor Imaging." PLoS ONE 6, no. 4 (April 11, 2011): e18544. http://dx.doi.org/10.1371/journal.pone.0018544.

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Thiessen, Jonathan D., Trevor J. Vincent, Sheryl L. Herrera, and Melanie Martin. "Diffusion Tensor Metric Measurements as a Function of Diffusion Time in the Rat Central Nervous System." Magnetic Resonance Insights 5 (January 2012): MRI.S10692. http://dx.doi.org/10.4137/mri.s10692.

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MRI and Monte Carlo simulated data of pulsed gradient spin echo experiments were used to study the effects of diffusion time, gradient strength and b-value on diffusion tensor (DT) metrics using real and simulated fixed rat spines. Radial (λ⊥) in grey matter and simulation data, axial (λ||) in both grey and white matter in fixed rat spinal cords and mean diffusivity in all tissues showed a significant decrease with diffusion time at b = 1 μm2/ms. All diffusivities significantly decreased with b-value at g = 116 mT/m and at Δeff = 23 ms. The fractional anisotropy (FA) significantly increased with diffusion time at b = 1 μm2/ms in the simulation data and grey matter. FA significantly increased in white matter and simulation data and significantly decreased in grey matter with b-value at g = 116 mT/m and at Δeff = 23 ms. These data suggest that DTI metrics are highly dependent on pulse sequence parameters.

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Chanraud, Sandra, Michel Reynaud, Michèle Wessa, Jani Penttilä, Nikoleta Kostogianni, Arnaud Cachia, Eric Artiges, et al. "Diffusion Tensor Tractography in Mesencephalic Bundles: Relation to Mental Flexibility in Detoxified Alcohol-Dependent Subjects." Neuropsychopharmacology 34, no. 5 (July 9, 2008): 1223–32. http://dx.doi.org/10.1038/npp.2008.101.

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Li, J., W. Shi, M. Li, Z. Wang, H. He, J. Xian, B. Lv, and F. Yan. "Time-dependent diffusion tensor changes of optic nerve in patients with indirect traumatic optic neuropathy." Acta Radiologica 55, no. 7 (September 2014): 855–63. http://dx.doi.org/10.1177/0284185113506900.

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Kusumi, Ryosuke, Fumiko Kimura, and Tsunehisa Kimura. "Single Crystal Solid-State NMR of Magnetically Oriented Powder." Acta Crystallographica Section A Foundations and Advances 70, a1 (August 5, 2014): C1086. http://dx.doi.org/10.1107/s205327331408913x.

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Solid-state NMR spectroscopy is one of the most widely used methods for investigating crystal structures, along with the X-ray and neutron diffraction methods. Solid-state NMR can provide structural information including isotropic chemical shift, dipolar and quadrupolar couplings, spin diffusion, and chemical shift tensor. Among these, the chemical shift tensor is of particular significance because the electronic environment around a nucleus is directly reflected on the chemical shift tensor. However, full information of the chemical shift tensor, including principal values and axes, is difficult to obtain experimentally because a large single crystal is required for the measurement. On the other hand, we have proposed the use of a magnetically oriented microcrystal array (MOMA) as an alternative to a single crystal.[1,2] A MOMA is a composite in which microcrystals are aligned three-dimensionally, prepared by using a time-dependent magnetic field. We recently demonstrated that the13C chemical shift tensors of L-alanine crystal can be completely determined by application of the standard procedure in the single-crystal rotation method to a MOMA of L-alanine microcrystals,[3] as shown in Figure 1. The L-alanine MOMA produces sharp resonance peaks without resolution enhancement by magic angle spinning (MAS). In addition, we observed that the positions of the13C resonance peaks vary systematically as a function of the angle ψ that is the sample-rotation angle about the axis inclined by the magic angle with respect to the NMR magnetic field. From the ψ-dependence of the chemical shifts,13C chemical shift tensor was completely determined. We confirmed that the combination of MOMA with the single-crystal rotation method can be applied to other nuclei such as31P and15N. These results clearly show that the MOMA method is a powerful tool for obtaining full information of the chemical shift tensor from a microcrystalline powder without MAS.

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WEICHMAN, PETER B., and ROMAN E. GLAZMAN. "Passive scalar transport by travelling wave fields." Journal of Fluid Mechanics 420 (October 10, 2000): 147–200. http://dx.doi.org/10.1017/s0022112000001452.

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We study turbulent transport of passive tracers by random wave fields of a rather general nature. A formalism allowing for spatial inhomogeneity and anisotropy of an underlying velocity field (such as that caused by a latitudinally varying Coriolis parameter) is developed, with the aim of treating problems of large-scale ocean transport by long internal waves. For the special case of surface gravity waves on deep water, our results agree with the earlier theory of Herterich & Hasselmann (1982), though even in that case we discover additional, off-diagonal elements of the diffusion tensor emerging in the presence of a mean drift. An advective diffusion equation including all components of the diffusion tensor D plus a mean, Stokes-type drift u is derived and applied to the case of baroclinic inertia–gravity (BIG) waves. This application is of particular interest for ocean circulation and climate modelling, as the mean drift, according to our estimates, is comparable to ocean interior currents. Furthermore, while on the largest (100 km and greater) scales, wave-induced diffusion is found to be generally small compared to classical eddy-induced diffusion, the two become comparable on scales below 10 km. These scales are near the present limit on the spatial resolution of eddy-resolving ocean numerical models. Since we find that uz and Dzz vanish identically, net vertical transport is absent in wave systems of this type. However, for anisotropic wave spectra the diffusion tensor can have non-zero off-diagonal vertical elements, Dxz and Dyz, and it is shown that their presence leads to non-positive definiteness of D, and a negative diffusion constant is found along a particular principal axis. However, the simultaneous presence of a depth-dependent mean horizontal drift u(z) eliminates any potential unphysical behaviour.

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Liu, Cui Yin, Chun Yu Zhang, Hong Zhao Yuan, and Xi Long Qu. "The Comparison of Isotropic and Anisotropic Diffusion Techniques for Image Denoising." Applied Mechanics and Materials 34-35 (October 2010): 557–61. http://dx.doi.org/10.4028/www.scientific.net/amm.34-35.557.

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The non-linear diffusion techniques were proposed for overcome the linear diffusion defaults. The linear diffusion was a homogeneous diffusivity with a constant conductivity. In this diffusion process, the noise and the edges were smoothed in the image. In order to prevent the edge from being smoothed during the denoising, the nonlinear diffusion was proposed by Pereona and Malik. In this method, noise was smoothed Simultaneously with the edges blurred. In diffusion processes, the conductivity is dependent on the image local information. We analyzed the ineffectiveness of isotropic and extended the work into the tensor-based anisotropic diffusion. It would be desirable to rotate the flux towards the orientation of interesting features. We compare the difference of isotroic linear and non-linear anisotropic diffusivity, and considere how to design non-linear anisotropic conductivity based on the different requires of the image filtering.

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Göksel-Duru, Dilek, and Mehmed Özkan. "Application of Self-Organizing Artificial Neural Networks on Simulated Diffusion Tensor Images." Mathematical Problems in Engineering 2013 (2013): 1–13. http://dx.doi.org/10.1155/2013/690140.

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Diffusion tensor magnetic resonance imaging (DTMRI) as a noninvasive modality providing in vivo anatomical information allows determination of fiber connections which leads to brain mapping. The success of DTMRI is very much algorithm dependent, and its verification is of great importance due to limited availability of a gold standard in the literature. In this study, unsupervised artificial neural network class, namely, self-organizing maps, is employed to discover the underlying fiber tracts. A common artificial diffusion tensor resource, named “phantom images for simulating tractography errors” (PISTE), is used for the accuracy verification and acceptability of the proposed approach. Four different tract geometries with varying SNRs and fractional anisotropy are investigated. The proposed method, SOFMAT, is able to define the predetermined fiber paths successfully with a standard deviation of (0.8–1.9) × 10−3depending on the trajectory and the SNR value selected. The results illustrate the capability of SOFMAT to reconstruct complex fiber tract configurations. The ability of SOFMAT to detect fiber paths in low anisotropy regions, which physiologically may correspond to either grey matter or pathology (abnormality) and uncertainty areas in real data, is an advantage of the method for future studies.

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Concha, Luis, Donald W. Gross, B. Matt Wheatley, and Christian Beaulieu. "Diffusion tensor imaging of time-dependent axonal and myelin degradation after corpus callosotomy in epilepsy patients." NeuroImage 32, no. 3 (September 2006): 1090–99. http://dx.doi.org/10.1016/j.neuroimage.2006.04.187.

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Chaudhary, Umair J., and John S. Duncan. "Applications of Blood-Oxygen-Level-Dependent Functional Magnetic Resonance Imaging and Diffusion Tensor Imaging in Epilepsy." Neuroimaging Clinics of North America 24, no. 4 (November 2014): 671–94. http://dx.doi.org/10.1016/j.nic.2014.07.001.

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Ma, Liangsuo, Joel L. Steinberg, Lori Keyser-Marcus, Divya Ramesh, Ponnada A. Narayana, Randall E. Merchant, F. Gerard Moeller, and David X. Cifu. "Altered white matter in cocaine-dependent subjects with traumatic brain injury: A diffusion tensor imaging study." Drug and Alcohol Dependence 151 (June 2015): 128–34. http://dx.doi.org/10.1016/j.drugalcdep.2015.03.015.

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Salo, Ruth, Thomas E. Nordahl, Michael H. Buonocore, Yutaka Natsuaki, Christy Waters, Charles D. Moore, Gantt P. Galloway, and Martin H. Leamon. "Cognitive Control and White Matter Callosal Microstructure in Methamphetamine-Dependent Subjects: A Diffusion Tensor Imaging Study." Biological Psychiatry 65, no. 2 (January 2009): 122–28. http://dx.doi.org/10.1016/j.biopsych.2008.08.004.

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Forder, John R., Jonathan D. Bui, David L. Buckley, and Stephen J. Blackband. "MR imaging measurement of compartmental water diffusion in perfused heart slices." American Journal of Physiology-Heart and Circulatory Physiology 281, no. 3 (September 1, 2001): H1280—H1285. http://dx.doi.org/10.1152/ajpheart.2001.281.3.h1280.

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Myocardial tissue slices were isolated from the left ventricular free wall (7 slices) and left ventricular papillary muscle (3 slices) of New Zealand White male rabbits ( n= 4) and were subsequently superfused with a modified St. Thomas' Hospital cardioplegic solution at 19°C. The diffusion-weighted images were obtained with a 600-MHz nuclear magnetic resonance spectrometer using diffusion gradient b-values that ranged from 166 to 6,408 s/mm2; the apparent diffusion coefficient of water in the tissues were subsequently calculated. All of the tissue samples that were studied exhibited nonmonoexponential diffusion. Data from seven slices were mathematically fitted by a biexponential expression with a fast diffusion component of 0.72 ± 0.07 × 10−3 mm2/s, and a slow diffusion component of 0.060 ± 0.033 × 10−3 mm2/s. The fast component dominated the calculated apparent diffusion coefficient of the tissue, composed of 82 ± 3% of the overall diffusion-dependent signal decay. Thus myocardial tissue exhibits characteristics consistent with multiple compartments of diffusion. This work has important implications for myocardial diffusion tensor imaging, as well as the changes in diffusion that have been reported following myocardial ischemia.

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Song, Sheng-Kwei, Joong Hee Kim, Shiow-Jiuan Lin, Robert P. Brendza, and David M. Holtzman. "Diffusion tensor imaging detects age-dependent white matter changes in a transgenic mouse model with amyloid deposition." Neurobiology of Disease 15, no. 3 (April 2004): 640–47. http://dx.doi.org/10.1016/j.nbd.2003.12.003.

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WALLENBURG, MARIKA A., MIHAELA POP, MICHAEL F. G. WOOD, NIRMALYA GHOSH, GRAHAM A. WRIGHT, and I. ALEX VITKIN. "COMPARISON OF OPTICAL POLARIMETRY AND DIFFUSION TENSOR MR IMAGING FOR ASSESSING MYOCARDIAL ANISOTROPY." Journal of Innovative Optical Health Sciences 03, no. 02 (April 2010): 109–21. http://dx.doi.org/10.1142/s1793545810000976.

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We have recently proposed an optical method for assessing heart structure that uses polarized light measurement of birefringence as an indicator of tissue anisotropy. The highly aligned nature of healthy cardiac muscle tissue has a detectable effect on the polarization of light, resulting in a measurable phase shift ("retardance"). When this organized tissue structure is perturbed, for example after cardiac infarction (heart attack), scar tissue containing disorganized collagen is formed, causing a decrease in the measured retardance values. However, these are dependent not only on tissue anisotropy, but also on the angle between the tissue's optical anisotropy direction and the beam interrogating the sample. To remove this experimental ambiguity, we present a method that interrogates the sample at two different incident beam angles, thus yielding enough information to uniquely determine the true magnitude and orientation of the tissue optical anisotropy. We use an infarcted porcine heart model to compare these polarimetry-derived anisotropy metrics with those obtained with diffusion tensor magnetic resonance imaging (DT-MRI). The latter yields the anisotropy and the direction of tissue water diffusivity, providing an independent measure of tissue anisotropy. The optical and MR results are thus directly compared in a common ex vivo biological model of interest, yielding reasonable agreement but also highlighting some technique-specific differences.

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Baird, Abigail A., Mary K. Colvin, John D. VanHorn, Souheil Inati, and Michael S. Gazzaniga. "Functional Connectivity: Integrating Behavioral, Diffusion Tensor Imaging, and Functional Magnetic Resonance Imaging Data Sets." Journal of Cognitive Neuroscience 17, no. 4 (April 2005): 687–93. http://dx.doi.org/10.1162/0898929053467569.

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In the present study, we combined 2 types of magnetic resonance technology to explore individual differences on a task that required the recognition of objects presented from unusual viewpoints. This task was chosen based on previous work that has established the necessity of information transfer from the right parietal cortex to the left inferior cortex for its successful completion. We used reaction times (RTs) to localize regions of cortical activity in the superior parietal and inferior frontal regions (blood oxygen level-dependent [BOLD] response) that were more active with longer response times. These regions were then sampled, and their signal change used to predict individual differences in structural integrity of white matter in the corpus callosum (using diffusion tensor imaging). Results show that shorter RTs (and associated increases in BOLD response) are associated with increased organization in the splenium of the corpus callosum, whereas longer RTs are associated with increased organization in the genu.

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Schmidt, Manfred, Gregor Kasprian, Gabriele Amann, Dominik Duscher, and Oskar C. Aszmann. "Diffusion tensor tractography for the surgical management of peripheral nerve sheath tumors." Neurosurgical Focus 39, no. 3 (September 2015): E17. http://dx.doi.org/10.3171/2015.6.focus15228.

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OBJECT Peripheral nerve sheath tumors (PNSTs) are uncommon but bear a significant risk of malignancy. High-resolution MRI is the standard technique for characterizing PNSTs. However, planning the appropriate extent of resection and subsequent reconstructive strategies is highly dependent on the intraoperative findings because preoperative MRI evaluation can be insufficient. Diffusion tensor tractography (DTT) represents a recently developed advanced MRI technique that reveals the microstructure of tissues based on monitoring the random movement of water molecules. DTT has the potential to provide diagnostic insights beyond conventional MRI techniques due to its mapping of specific fibrillar nerve structures. Here, DTT was applied to evaluate PNSTs and to examine the usefulness of this method for the correct delineation of tumor and healthy nerve tissue and the value of this information in the preoperative planning of surgical interventions. METHODS In this prospective study, patients with the clinical symptoms of a PNST were investigated using DTT 3-Tesla MRI scans. Image data processing and tractography were performed using the FACT (fiber assessment by continuous tracking) algorithm and multiple-regions-of-interest approach. The surgical findings were then compared with the results of the DTT MRI scans. Preoperative fascicle visualization and the correlation with the intraoperative findings were graded. RESULTS In a 21-month period, 12 patients with PNSTs were investigated (7 female and 5 male patients with a mean age of 46.2 ± 19.2 years). All patients underwent surgical removal of the tumor. Schwannoma was the most common benign histopathological finding (n = 7), whereas 2 malignant lesions were detected. In 10 of 12 patients, good preoperative nerve fascicle visualization was achieved using DTT scans. In 9 of 10 patients with good preoperative fascicle visualization, good intraoperative correlation between the DTT scans and surgical anatomy was found. CONCLUSIONS DTT properly visualizes the peripheral nerve fascicles and their correct anatomical relation to PNST. DTT represents a promising new method for the preinterventional planning of nerve tumor resection.

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Lee, Hyun-Ah, and Dae-Hyun Kim. "Brain Connectivity Affecting Gait Function after Unilateral Supratentorial Stroke." Brain Sciences 11, no. 7 (June 29, 2021): 870. http://dx.doi.org/10.3390/brainsci11070870.

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Gait dysfunction is a leading cause of long-term disability after stroke. The mechanisms underlying recovery of gait function are unknown. We retrospectively evaluated the association between structural connectivity and gait function in 127 patients with unilateral supratentorial stroke (>1 month after stroke). All patients underwent T1-weighted, diffusion tensor imaging and functional ambulation categorization. Voxel-wise linear regression analyses of the images were conducted using fractional anisotropy, mean diffusivity, and mode of anisotropy mapping as dependent variables, while the functional ambulation category was used as an independent variable with age and days after stroke as covariates. The functional ambulation category was positively associated with increased fractional anisotropy in the lesioned cortico-ponto-cerebellar system, corona radiata of the non-lesioned corticospinal tract pathway, bilateral medial lemniscus in the brainstem, and the corpus callosum. The functional ambulation category was also positively associated with increased mode of anisotropy in the lesioned posterior corpus callosum. In conclusion, structural connectivity associated with motor coordination and feedback affects gait function after stroke. Diffusion tensor imaging for evaluating structural connectivity can help to predict gait recovery and target rehabilitation goals after stroke.

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Mullins, Roger J., Su Xu, Jiachen Zhuo, Steve Roys, Edna F. R. Pereira, Edson X. Albuquerque, and Rao P. Gullapalli. "Postnatal Guinea Pig Brain Development, as Revealed by Magnetic Resonance and Diffusion Kurtosis Imaging." Brain Sciences 10, no. 6 (June 12, 2020): 365. http://dx.doi.org/10.3390/brainsci10060365.

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This study used in vivo magnetic resonance imaging (MRI) to identify age dependent brain structural characteristics in Dunkin Hartley guinea pigs. Anatomical T2-weighted images, diffusion kurtosis (DKI) imaging, and T2 relaxometry measures were acquired from a cohort of male guinea pigs from postnatal day (PND) 18–25 (juvenile) to PND 46–51 (adolescent) and PND 118–123 (young adult). Whole-brain diffusion measures revealed the distinct effects of maturation on the microstructural complexity of the male guinea pig brain. Specifically, fractional anisotropy (FA), as well as mean, axial, and radial kurtosis in the corpus callosum, amygdala, dorsal-ventral striatum, and thalamus significantly increased from PND 18–25 to PND 118–123. Age-related alterations in DKI measures within these brain regions paralleled the overall alterations observed in the whole brain. Age-related changes in FA and kurtosis in the gray matter-dominant parietal cerebral cortex and dorsal hippocampus were less pronounced than in the other brain regions. The regional data analysis revealed that between-age changes of diffusion kurtosis metrics were more pronounced than those observed in diffusion tensor metrics. The age-related anatomical differences reported here may be important determinants of the age-dependent neurobehavior of guinea pigs in different tasks.

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Segobin, S., L. Ritz, C. Lannuzel, C. Boudehent, F. Vabret, F. Eustache, H. Beaunieux, and A. L. Pitel. "FOC1-2THE POTENTIAL OF DIFFUSION TENSOR IMAGING TO IDENTIFY ALCOHOL DEPENDENT PATIENTS AT RISK OF DEVELOPING KORSAKOFF'S SYNDROME." Alcohol and Alcoholism 50, suppl 1 (September 2015): i35.4—i36. http://dx.doi.org/10.1093/alcalc/agv079.02.

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Song, Allen W., Todd Harshbarger, Tianlu Li, Keun-Ho Kim, Kamil Ugurbil, Susumu Mori, and Dae-Shik Kim. "Functional activation using apparent diffusion coefficient-dependent contrast allows better spatial localization to the neuronal activity: evidence using diffusion tensor imaging and fiber tracking." NeuroImage 20, no. 2 (October 2003): 955–61. http://dx.doi.org/10.1016/s1053-8119(03)00292-1.

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Zhang, Chao, A. Y. Morozova, V. P. Baklaushev, I. L. Gubsky, P. A. Melnikov, A. N. Gabashvily, Guowen Wang, et al. "Nanoparticles guided precise transplantation of varying numbers of mesenchymal stem cells into post–traumatic syrinx in spinal cord injury rat." NANOMEDICINE, no. 6 (December 30, 2018): 49–56. http://dx.doi.org/10.24075/brsmu.2018.084.

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Spinal cord injury (SCI) is a traumatic injury to the spinal cord which is not a consequence of the disease. Mesenchymal stem cells (MSCs) have gradually become one of the most used stem cells in research and clinic trial. Based on the previous reports employed the cells ranged from 4 • 105 to 1 • 106, the present study was performed to figure out the best number of MSCs for transplantation of the chronic SCI. Magnetic nanoparticles were used for proving the precise transplantation strategy. Using magnetic resonance imaging (MRI), diffusion tensor imaging (DTI), diffusion tensor tractography (DTT), and behavior testing evaluations, we focused the effect of varying numbers of MSCs on reducing lesion cavity and post–traumatic syrinx formation, suppressing glial scar formation, enhancing neuronal fibers remodeling, promoting axonal regeneration and sprouting, improving vascularization, ameliorating the neuronal factors expressional level, and function improvement. Magnetic nanoparticles were precisely transplanted into the post–traumatic syrinx (PTS). MSCs can restore function after chronic SCI through stimulating the regeneration and sprouting of the axons, reducing the formation of PTS. The effect of MSCs on PTS management and functional improvement post chronic SCI was cell number–dependent, and within the range of 4 • 105 to 1 • 106, 1 • 106 cells were proved to be the best dose.

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Peng, Huiling, Carmen M. Cirstea, Christina L. Kaufman, and Scott H. Frey. "Microstructural integrity of corticospinal and medial lemniscus tracts: insights from diffusion tensor tractography of right-hand amputees." Journal of Neurophysiology 122, no. 1 (July 1, 2019): 316–24. http://dx.doi.org/10.1152/jn.00316.2018.

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Reductions in sensory and motor activity following unilateral upper limb amputation during adulthood are associated with widespread, activity-dependent reorganization of the gray matter and white matter through the central nervous system. Likewise, in cases of congenital limb absence there is evidence that limited afferent or efferent activity affects the structural integrity of white matter pathways serving the affected side. Evidence that the structural integrity of mature sensory and motor tracts controlling the lost upper limb exhibits similar activity dependence is, however, sparse and inconsistent. Here we used diffusion tensor tractography to test whether amputation of the dominant right hand during adulthood ( n = 16) alters the microstructural integrity of the major sensory (medial lemniscus, ML) and motor (corticospinal tract, CST) pathways controlling missing hand function. Consistent with prior findings, healthy control subjects ( n = 27) exhibited higher fractional anisotropy (FA), an index of white matter microstructural integrity, within dominant left CST and nondominant right ML. Critically, in contrast to what might be expected if the microstructural organization of these tracts is activity dependent, these asymmetries persisted in amputees. Moreover, we failed to detect any differences in dominant left ML or CST between healthy control subjects and amputees. Our results are consistent with these white matter tracts being robust to changes in activity once mature or that continued use of the residual limb (in a compensatory fashion or with prosthesis) provides stimulation sufficient to maintain tract integrity. NEW & NOTEWORTHY We report that unilateral hand amputation in adults has no significant effects on the structure of major sensory or motor pathways contralateral to the amputation. Our results are consistent with the organization of these white matter tracts being robust to changes in activity once mature or that continued use of the residual limb (with or without a prosthesis) provides stimulation sufficient to maintain tract integrity.

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Hueper, Katja, Dagmar Hartung, Marcel Gutberlet, Faikah Gueler, Holger Sann, Bettina Husen, Frank Wacker, and Dania Reiche. "Assessment of impaired vascular reactivity in a rat model of diabetic nephropathy: effect of nitric oxide synthesis inhibition on intrarenal diffusion and oxygenation measured by magnetic resonance imaging." American Journal of Physiology-Renal Physiology 305, no. 10 (November 15, 2013): F1428—F1435. http://dx.doi.org/10.1152/ajprenal.00123.2013.

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Diabetes is associated with impaired vascular reactivity and the development of diabetic nephropathy. In a rat model of streptozotocin-induced diabetic nephropathy, the effects of systemic nitric oxide (NO) synthesis inhibition on intrarenal diffusion and oxygenation were determined by noninvasive magnetic resonance diffusion tensor imaging and blood O2 level-dependent (BOLD) imaging, respectively. Eight weeks after the induction of diabetes, 21 rats [ n = 7 rats each in the untreated control group, diabetes mellitus (DM) group, and DM with uninephrectomy (DM UNX) group] were examined by MRI. Diffusion tensor imaging and BOLD sequences were acquired before and after NO synthesis inhibition with N-nitro-l-arginine methyl ester (l-NAME). In the same rats, mean arterial pressure and vascular conductance were determined with and without the influence of l-NAME. In control animals, NO synthesis inhibition was associated with a significant increase of mean arterial pressure of 33.8 ± 4.3 mmHg ( P < 0.001) and a decrease of vascular conductance of −17.8 ± 2.0 μl·min−1·100 mmHg−1 ( P < 0.001). These changes were attenuated in both DM and DM UNX groups with no significant difference between before and after l-NAME measurements in DM UNX animals. Similarly, l-NAME challenge induced a significant reduction of renal transverse relaxation time (T2*) at MRI in control animals, indicating reduced renal oxygenation after l-NAME injection compared with baseline. DM UNX animals did not show a significant T2* reduction after NO synthesis inhibition in the renal cortex and attenuated T2* reduction in the outer medulla. MRI parameters of tissue diffusion were not affected by l-NAME in all groups. In conclusion, BOLD imaging proved valuable to noninvasively measure renal vascular reactivity upon NO synthesis inhibition in control animals and to detect impaired vascular reactivity in animals with diabetic nephropathy.

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Brang, David, Zack Taich, Steven A. Hillyard, and Vilayanur S. Ramachandran. "Task dependent anatomical connections underlie multisensory processing." Seeing and Perceiving 25 (2012): 8. http://dx.doi.org/10.1163/187847612x646316.

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Our senses interact in daily life through multisensory integration, facilitating perceptual processes and behavioral responses. Numerous multisensory regions have been identified in humans and animals, raising the question of whether a single mechanism can support the dynamic range of experiences and behaviors multisensory processing engenders. The most common neural mechanisms proposed to underlie multisensory processing include anatomical connections directly linking early sensory areas, indirect connections to higher-order multisensory regions, and functional connectivity between cortical areas. Here we examine the relationship between white matter connectivity, as assessed with diffusion tensor imaging and individual differences in two divergent forms of multisensory processing: the redundant-target effect (RTE), in which subjects’ behavior is facilitated by congruent multisensory information, and the sound-induced illusory flash (SIIF) paradigm, in which incongruent multisensory information elicits a novel percept. Behavioral results demonstrated strong intra-subject reliability of the RTE and SIIF paradigms, but no correlation in performance between the two tasks. Consistent with this behavioral finding, we identified distinct anatomical networks underlying these two forms of multisensory processing. Using a whole-brain analysis and contrasting anatomical models of multisensory processing, increased behavioral performance on the RTE was associated with increased connectivity between the superior parietal lobe and early sensory regions. Conversely, increased incidence of illusion on the SIIF paradigm was associated with increased connectivity directly between early auditory and visual areas. These results implicate a broad network of anatomical connections involved in task-dependent multisensory processes.

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Farinas, Angel F., Isaac V. Manzanera Esteve, Alonda C. Pollins, Nancy L. Cardwell, Mark D. Does, Richard D. Dortch, and Wesley P. Thayer. "Diffusion Tensor Tractrography Visualizes Partial Nerve Laceration Severity as Early as 1 Week After Surgical Repair in a Rat Model Ex Vivo." Military Medicine 185, Supplement_1 (January 2020): 35–41. http://dx.doi.org/10.1093/milmed/usz360.

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Abstract Background: Previous studies in our laboratory have demonstrated that a magnetic resonance imaging method called diffusion tensor imaging (DTI) can differentiate between crush and complete transection peripheral nerve injuries in a rat model ex vivo. DTI measures the directionally dependent effect of tissue barriers on the random diffusion of water molecules. In ordered tissues such as nerves, this information can be used to reconstruct the primary direction of diffusion along fiber tracts, which may provide information on fiber tract continuity after nerve injury and surgical repair. Methods: Sprague-Dawley rats were treated with different degrees of partial transection of the sciatic nerve followed by immediate repair and euthanized after 1 week of recovery. Nerves were then harvested, fixed, and scanned with a 7 Tesla magnetic resonance imaging to obtain DTIand fiber tractography in each sample. Additional behavioral (sciatic function index, foot fault asymmetry) and histological (Toluidine blue staining) assessments were performed for validation. Results: Tractography yielded a visual representation of the degree of injury that correlated with behavioral and histological evaluations. Conclusions: DTI tractography is a noninvasive tool that can yield a visual representation of a partial nerve transection as early as 1 week after surgical repair.

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Li, Q. I., Abby Y. Ding, Ran Wei, Wendy Kong, Sylvia Lam, Xiao F. Zhang, Siew E. Chua Ed X. Wu, and Grainne M. McAlonan. "Poster #28 GENDER-DEPENDENT DIFFERENCES IN THE NEURAL RESPONSES TO FEAR ACQUISITION: A VOXEL-BASED DIFFUSION TENSOR IMAGING (DTI) STUDY." Schizophrenia Research 136 (April 2012): S290—S291. http://dx.doi.org/10.1016/s0920-9964(12)70861-7.

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Chou, Lot-Kei, and Siu-Long Lei. "Tensor-Train Format Solution with Preconditioned Iterative Method for High Dimensional Time-Dependent Space-Fractional Diffusion Equations with Error Analysis." Journal of Scientific Computing 80, no. 3 (June 25, 2019): 1731–63. http://dx.doi.org/10.1007/s10915-019-00994-3.

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Wang, Yi-Xiang J., Xian-Lun Zhu, Min Deng, Deyond Y. W. Siu, Jason C. S. Leung, Queenie Chan, Danny T. M. Chan, Calvin Hoi Kwan Mak, and Wai S. Poon. "The use of diffusion tensor tractography to measure the distance between the anterior tip of the Meyer loop and the temporal pole in a cohort from Southern China." Journal of Neurosurgery 113, no. 6 (December 2010): 1144–51. http://dx.doi.org/10.3171/2010.7.jns10393.

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Object Anterior temporal lobe resection plus amygdalohippocampectomy can cause damage to the anterior portion of the optic radiation, also known as the Meyer loop, resulting in homonymous superior quadrantanopia. Magnetic resonance diffusion tensor tractography (DTT) of the Meyer loop can help in surgical planning. In this study, the distance of the anterior tip of the Meyer loop to the temporal lobe pole (ML-TP) in the Southern Chinese population was assessed. Methods The authors studied 16 Southern Chinese individuals (8 men and 8 women; mean age 45.6 years, range 21–60 years). Diffusion tensor images were obtained with a 3-T MR imaging system using a single-shot spin echo echo planar imaging sequence. Two trained operators, one neurosurgeon (Operator A) and one radiologist (Operator B), carried out the DTT analysis with software iPlan (BrainLAB) and FiberTrak (Philips). Results For the 32 temporal lobes, the intraclass correlation coefficient (ICC) of the 2 operators' results using iPlan was 0.96, while that of Operator A using iPlan and Operator B using FiberTrak was 0.75. The ICC of Operator B using iPlan and FiberTrak was 0.81. The ML-TP distance of normal lobes (30 lobes [2 lobes that previously underwent surgery were excluded]) was 36.3 ± 5.5 mm (range 26.6–48.9 mm), 36.3 ± 5.3 mm (range 26.8–48.2 mm), and 35.9 ± 6.4 mm (range 20.8–48.4 mm) for Operator A using iPlan, Operator B using iPlan, and Operator B using FiberTrak, respectively (p > 0.05). Conclusions The 2 operators reached good agreement on ML-TP distance measurement using DTT. The DDT results can be more software dependent than operator dependent. The measurement with FiberTrak demonstrated larger range and standard deviation than measurement with iPlan.

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Breu, Markus, Jiangyang Zhang, Michael Porambo, Mikhail V. Pletnikov, Katharina Goeral, Mihir Kakara, Michael V. Johnston, and Ali Fatemi. "Diffusion Tensor Imaging Abnormalities in the Cerebral White Matter Correlate with Sex-Dependent Neurobehavioral Deficits in Adult Mice with Neonatal Ischemia." Developmental Neuroscience 38, no. 2 (2016): 83–95. http://dx.doi.org/10.1159/000442943.

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Background: Neonatal white matter injury (NWMI) is the leading cause of cerebral palsy in prematurely born children. In order to develop a test bed for therapeutics, we recently reported a mouse model of NWMI by using a modified Rice-Vannucci model of neonatal ischemia on postnatal day 5 (P5) in CD-1 mice. We have previously shown that these mice illustrate initial neuroinflammation and oligodendroglial differentiation arrest followed by long-term dysmyelination, periventricular astrogliosis and axonal injury, resembling human NWMI. The objective of this study was to determine the sex-dependent long-term effects of neonatal brain injury on neurobehavioral and advanced in vivo neuroimaging indices in this mouse model, and to correlate these variables with histopathology. Methods: After right common artery ligation on P5, in vivo T2-weighted imaging and diffusion tensor imaging (DTI) were performed on ligated and control animals at 4 and 8 weeks. Common sets of regions of interest were used to compare fractional anisotropy (FA) values between ischemic and control mice. Behavioral testing (open field, startle response and grip strength) was performed at adult age. Finally, the animals were sacrificed for immunohistochemical (IHC) assessment of major white matter tracts. Results: DTI revealed significant sex-dependent changes in FA values ipsi- and contralateral to the ligation. Behavioral testing showed decreased reaction to acoustic stimuli in males but not females. Similarly, increased number of rearings and lack of novelty-induced habituation in the open field were encountered only in the male subgroup. Several regional correlations were found between FA values and these behavioral alterations. IHC studies revealed degeneration of mature oligodendrocytes and damage of white matter tracts in ligated animals, as previously reported in this model, and showed regional correlation with in vivo FA values and behavioral alterations. Conclusions: Our findings suggest structural sex-dependent long-term abnormalities after neonatal ischemia. These changes lead to behavioral deficits resembling common problems of patients with cerebral palsy.

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Nishioka, Christopher, Hsiao-Fang Liang, Chen-Fang Chung, and Shu-Wei Sun. "Disease stage-dependent relationship between diffusion tensor imaging and electrophysiology of the visual system in a murine model of multiple sclerosis." Neuroradiology 59, no. 12 (August 24, 2017): 1241–50. http://dx.doi.org/10.1007/s00234-017-1904-1.

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Mascioli, Giulia, Simone Salvolini, Gian Luca Cavola, Mara Fabri, Alfonso Giovannini, Cesare Mariotti, Luca Salvolini, and Gabriele Polonara. "Functional MRI Examination of Visual Pathways in Patients with Unilateral Optic Neuritis." Radiology Research and Practice 2012 (2012): 1–7. http://dx.doi.org/10.1155/2012/265306.

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The relations between brain areas involved in vision were explored in 8 patients with unilateral acute optic neuritis using functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI). In all patients monocular stimulation of affected and unaffected eye elicited significantly different activation foci in the primary visual cortex (V1), whereas the foci evoked in the middle temporal visual area (area V5) were similar in size and in delay of blood-oxygen-level-dependent response. DTI analysis documented lower white matter anisotropy values and reduced fibre reconstruction in the affected compared with the unaffected optic nerves. The preserved activation of area V5 observed in all our patients is an interesting finding that suggests the notion of a different sensitivity of the optic pathways to inflammatory changes.

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Holloway, C. R., G. Cupples, D. J. Smith, J. E. F. Green, R. J. Clarke, and R. J. Dyson. "Influences of transversely isotropic rheology and translational diffusion on the stability of active suspensions." Royal Society Open Science 5, no. 8 (August 2018): 180456. http://dx.doi.org/10.1098/rsos.180456.

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Suspensions of self-motile, elongated particles are a topic of significant current interest, exemplifying a form of ‘active matter’. Examples include self-propelling bacteria, algae and sperm, and artificial swimmers. Ericksen's model of a transversely isotropic fluid (Ericksen 1960 Colloid Polym. Sci. 173 , 117–122 ( doi:10.1007/bf01502416 )) treats suspensions of non-motile particles as a continuum with an evolving preferred direction; this model describes fibrous materials as diverse as extracellular matrix, textile tufts and plant cell walls. Director-dependent effects are incorporated through a modified stress tensor with four viscosity-like parameters. By making fundamental connections with recent models for active suspensions, we propose a modification to Ericksen's model, mainly the inclusion of self-motility; this can be considered the simplest description of an oriented suspension including transversely isotropic effects. Motivated by the fact that transversely isotropic fluids exhibit modified flow stability, we conduct a linear stability analysis of two distinct cases, aligned and isotropic suspensions of elongated active particles. Novel aspects include the anisotropic rheology and translational diffusion. In general, anisotropic effects increase the instability of small perturbations, while translational diffusion stabilizes a range of wave-directions and, in some cases, a finite range of wavenumbers, thus emphasizing that both anisotropy and translational diffusion can have important effects in these systems.

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Faust, Katharina, and Peter Vajkoczy. "Distinct displacements of the optic radiation based on tumor location revealed using preoperative diffusion tensor imaging." Journal of Neurosurgery 124, no. 5 (May 2016): 1343–52. http://dx.doi.org/10.3171/2015.3.jns141584.

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OBJECT Visual field defects (VFDs) due to optic radiation (OR) injury are a common complication of temporal lobe surgery. The authors analyzed whether preoperative visualization of the optic tract would reduce this complication by influencing the surgeon’s decisions about surgical approaches. The authors also determined whether white matter shifts caused by temporal lobe tumors would follow predetermined patterns based on the tumor’s topography. METHODS One hundred thirteen patients with intraaxial tumors of the temporal lobe underwent preoperative diffusion tensor imaging (DTI) fiber tracking. In 54 of those patients, both pre- and postoperative VFDs were documented using computerized perimetry. Brainlab’s iPlan 2.5 navigation software was used for tumor reconstruction and fiber visualization after the fusion of DTI studies with their respective magnetization-prepared rapid gradient-echo (MP-RAGE) images. The tracking algorithm was as follows: minimum fiber length 100 mm, fractional anisotropy threshold 0.1. The lateral geniculate body and the calcarine cortex were employed as tract seeding points. Shifts of the OR caused by tumor were visualized in comparison with the fiber tracking of the patient’s healthy hemisphere. RESULTS Temporal tumors produced a dislocation of the OR but no apparent fiber destruction. The shift of white matter tracts followed fixed patterns dependent on tumor location: Temporolateral tumors resulted in a medial fiber shift, and thus a lateral transcortical approach is recommended. Temporopolar tumors led to a posterior shift, always including Meyer’s loop; therefore, a pterional transcortical approach is recommended. Temporomesial tumors produced a lateral and superior shift; thus, a transsylvian-transcisternal approach will result in maximum sparing of the fibers. Temporocentric tumors also induced a lateral fiber shift. For those tumors, a transsylvian-transopercular approach is recommended. Tumors of the fusiform gyrus generated a superior (and lateral) shift; consequently, a subtemporal approach is recommended to avoid white matter injury. In applying the approaches recommended above, new or worsened VFDs occurred in 4% of the patient cohort. Total neurological and surgical morbidity were less than 10%. In 90% of patients, gross-total resection was accomplished. CONCLUSIONS Preoperative visualization of the OR may help in avoiding postoperative VFDs.

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Taylor, Paul A., and Bharat Biswal. "Geometric analysis of the b-dependent effects of Rician signal noise on diffusion tensor imaging estimates and determining an optimal b value." Magnetic Resonance Imaging 29, no. 6 (July 2011): 777–88. http://dx.doi.org/10.1016/j.mri.2011.02.031.

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Yang, Fei Fei, Shu Guang Yuan, and David T. Yew. "Use of Functional Magnetic Resonance Imaging (Blood Oxygenation Level-Dependent Imaging, Diffusion Tensor Imaging and Magnetic Resonance Spectroscopy) in Brain Development Research." Neuroembryology and Aging 5, no. 1-2 (2008): 56–59. http://dx.doi.org/10.1159/000116733.

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Bai, Lijun, Yin Tao, Dan Wang, Jing Wang, Chuanzhu Sun, Nongxiao Hao, Shangjie Chen, and Lixing Lao. "Acupuncture Induces Time-Dependent Remodelling Brain Network on the Stable Somatosensory First-Ever Stroke Patients: Combining Diffusion Tensor and Functional MR Imaging." Evidence-Based Complementary and Alternative Medicine 2014 (2014): 1–7. http://dx.doi.org/10.1155/2014/740480.

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Different treatment interventions induce distinct remodelling of network architecture of entire motor system. Acupuncture has been proved to be of a promising efficacy in motor recovery. However, it is still unclear whether the reorganization of motor-related brain network underlying acupuncture is related with time since stroke and severity of deficit at baseline. The aim of study was to characterize the relation between motor-related brain organization following acupuncture and white matter microstructural changes at an interval of two weeks. We demonstrated that acupuncture induced differential reorganization of motor-related network for stroke patients as time-lapse since stroke. At the baseline, acupuncture can induce the increased functional connectivity between the left primary motor cortex (M1) and the right M1, premotor cortex, supplementary motor area (SMA), thalamus, and cerebellum. After two-week recovery, the increased functional connectivity of the left M1 was more widely distributed and primarily located in the insula, cerebellum, basal ganglia, and SMA. Furthermore, a significant negative relation existed between the FA value in the left M1 at the baseline scanning and node centrality of this region following acupuncture for both baseline and two-week recovery. Our findings may shed a new insight on understanding the reorganization of motor-related theory underlying motor impairments after brain lesions in stroke patients.

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Moeller, Frederick Gerard, Khader M. Hasan, Joel L. Steinberg, Larry A. Kramer, Donald M. Dougherty, Rafael M. Santos, Ignacio Valdes, Alan C. Swann, Ernest S. Barratt, and Ponnada A. Narayana. "Reduced Anterior Corpus Callosum White Matter Integrity is Related to Increased Impulsivity and Reduced Discriminability in Cocaine-Dependent Subjects: Diffusion Tensor Imaging." Neuropsychopharmacology 30, no. 3 (December 22, 2004): 610–17. http://dx.doi.org/10.1038/sj.npp.1300617.

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Conti, Alfredo, Giovanni Raffa, Francesca Granata, Vincenzo Rizzo, Antonino Germanò, and Francesco Tomasello. "Navigated Transcranial Magnetic Stimulation for “Somatotopic” Tractography of the Corticospinal Tract." Operative Neurosurgery 10, no. 4 (July 25, 2014): 542–54. http://dx.doi.org/10.1227/neu.0000000000000502.

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Abstract BACKGROUND: Diffusion tensor imaging tractography provides 3-dimensional reconstruction of principal white matter tracts, but its spatial accuracy has been questioned. Navigated transcranial magnetic stimulation (nTMS) enables somatotopic mapping of the motor cortex. OBJECTIVE: We used motor maps to reconstruct the corticospinal tract (CST) by integrating elements of its somatotopic organization. We analyzed the accuracy of this method compared with a standard technique and verified its reliability with intraoperative subcortical stimulation. METHODS: We prospectively collected data from patients who underwent surgery between January 2012 and October 2013 for lesions involving the CST. nTMS-based diffusion tensor imaging tractography was compared with a standard technique. The reliability and accuracy between the 2 techniques were analyzed by comparing the number of fibers, the concordance in size, and the location of the cortical end of the CST and the motor area. The accuracy of the technique was assessed by using direct subcortical stimulation. RESULTS: Twenty patients were enrolled in the study. nTMS-based tractography provided a detailed somatotopic reconstruction of the CST. This nTMS-based reconstruction resulted in a decreased number of fibers (305.1 ± 231.7 vs 1024 ± 193, P < .001) and a significantly greater overlap between the motor cortex and the cortical end-region of the CST compared with the standard technique (90.5 ± 8.8% vs 58.3 ± 16.6%, P < .001). Direct subcortical stimulation confirmed the CST location and the somatotopic reconstruction in all cases. CONCLUSION: These results suggest that nTMS-based tractography of the CST is more accurate and less operator dependent than the standard technique and provides a reliable anatomic and functional characterization of the motor pathway.

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Afonso, Marco Martins, Andrea Mazzino, and Paolo Muratore-Ginanneschi. "Eddy diffusivities of inertial particles under gravity." Journal of Fluid Mechanics 694 (February 7, 2012): 426–63. http://dx.doi.org/10.1017/jfm.2011.562.

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AbstractThe large-scale/long-time transport of inertial particles of arbitrary mass density under gravity is investigated by means of a formal multiple-scale perturbative expansion in the scale-separation parameter between the carrier flow and the particle concentration field. The resulting large-scale equation for the particle concentration is determined, and is found to be diffusive with a positive definite eddy diffusivity. The calculation of the latter tensor is reduced to the resolution of an auxiliary differential problem, consisting of a coupled set of two differential equations in a $(6+ 1)$-dimensional coordinate system (three space coordinates plus three velocity coordinates plus time). Although expensive, numerical methods can be exploited to obtain the eddy diffusivity, for any desirable non-perturbative limit (e.g. arbitrary Stokes and Froude numbers). The aforementioned large-scale equation is then specialized to deal with two different relevant perturbative limits: (i) vanishing of both Stokes time and sedimenting particle velocity; (ii) vanishing Stokes time and finite sedimenting particle velocity. Both asymptotics lead to a greatly simplified auxiliary differential problem, now involving only space coordinates and thus easily tackled by standard numerical techniques. Explicit, exact expressions for the eddy diffusivities have been calculated, for both asymptotics, for the class of parallel flows, both static and time-dependent. This allows us to investigate analytically the role of gravity and inertia on the diffusion process by varying relevant features of the carrier flow, such as the form of its temporal correlation function. Our results exclude a universal role played by gravity and inertia on the diffusive behaviour: regimes of both enhanced and reduced diffusion may exist, depending on the detailed structure of the carrier flow.

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Boyd, Lara A., Eric D. Vidoni, and Janis J. Daly. "Answering the Call: The Influence of Neuroimaging and Electrophysiological Evidence on Rehabilitation." Physical Therapy 87, no. 6 (June 1, 2007): 684–703. http://dx.doi.org/10.2522/ptj.20060164.

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Functional recovery after brain damage or disease is dependent on the neuroplastic capability of the cortex and the nonaffected brain. Following cortical injury in the motor and sensory regions, the adjacent spared neural tissues and related areas undergo modifications that are required in order to drive more normal motor control. Current rehabilitation models seek to stimulate functional recovery by capitalizing on the inherent potential of the brain for positive reorganization after neurological injury or disease. This article discusses how neuroimaging and electrophysiological data can inform clinical practice; representative data from the modalities of functional magnetic resonance imaging, diffusion tensor imaging, magnetoencephalography, electroencephalography, and positron emission tomography are cited. Data from a variety of central nervous system disease and damage models are presented to illustrate how rehabilitation practices are beginning to be shaped and informed by neuroimaging and electrophysiological data.

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Fieremans, Els, Gregory Lemberskiy, Jelle Veraart, Eric E. Sigmund, Soterios Gyftopoulos, and Dmitry S. Novikov. "In vivomeasurement of membrane permeability and myofiber size in human muscle using time-dependent diffusion tensor imaging and the random permeable barrier model." NMR in Biomedicine 30, no. 3 (October 7, 2016): e3612. http://dx.doi.org/10.1002/nbm.3612.

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Sun, Shu-Wei, Sheng-Kwei Song, Michael P. Harms, Shiow-Jiuan Lin, David M. Holtzman, Kalpana M. Merchant, and John J. Kotyk. "Detection of age-dependent brain injury in a mouse model of brain amyloidosis associated with Alzheimer's disease using magnetic resonance diffusion tensor imaging." Experimental Neurology 191, no. 1 (January 2005): 77–85. http://dx.doi.org/10.1016/j.expneurol.2004.09.006.

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Thomas, Cibu, Linda Moya, Galia Avidan, Kate Humphreys, Kwan Jin Jung, Mary A. Peterson, and Marlene Behrmann. "Reduction in White Matter Connectivity, Revealed by Diffusion Tensor Imaging, May Account for Age-related Changes in Face Perception." Journal of Cognitive Neuroscience 20, no. 2 (February 2008): 268–84. http://dx.doi.org/10.1162/jocn.2008.20025.

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An age-related decline in face processing, even under conditions in which learning and memory are not implicated, has been well documented, but the mechanism underlying this perceptual alteration remains unknown. Here, we examine whether this behavioral change may be accounted for by a reduction in white matter connectivity with age. To this end, we acquired diffusion tensor imaging data from 28 individuals aged 18 to 86 years and quantified the number of fibers, voxels, and fractional anisotropy of the two major tracts that pass through the fusiform gyrus, the pre-eminent face processing region in the ventral temporal cortex. We also measured the ability of a subset of these individuals to make fine-grained discriminations between pairs of faces and between pairs of cars. There was a significant reduction in the structural integrity of the inferior fronto-occipital fasciculus (IFOF) in the right hemisphere as a function of age on all dependent measures and there were also some changes in the left hemisphere, albeit to a lesser extent. There was also a clear age-related decrement in accuracy of perceptual discrimination, especially for more challenging perceptual discriminations, and this held to a greater degree for faces than for cars. Of greatest relevance, there was a robust association between the reduction of IFOF integrity in the right hemisphere and the decline in face perception, suggesting that the alteration in structural connectivity between the right ventral temporal and frontal cortices may account for the age-related difficulties in face processing.

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Schwarb, Hillary, Curtis L. Johnson, Michael R. Dulas, Matthew D. J. McGarry, Joseph L. Holtrop, Patrick D. Watson, Jane X. Wang, Joel L. Voss, Bradley P. Sutton, and Neal J. Cohen. "Structural and Functional MRI Evidence for Distinct Medial Temporal and Prefrontal Roles in Context-dependent Relational Memory." Journal of Cognitive Neuroscience 31, no. 12 (December 2019): 1857–72. http://dx.doi.org/10.1162/jocn_a_01454.

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Declarative memory is supported by distributed brain networks in which the medial-temporal lobes (MTLs) and pFC serve as important hubs. Identifying the unique and shared contributions of these regions to successful memory performance is an active area of research, and a growing literature suggests that these structures often work together to support declarative memory. Here, we present data from a context-dependent relational memory task in which participants learned that individuals belonged in a single room in each of two buildings. Room assignment was consistent with an underlying contextual rule structure in which male and female participants were assigned to opposite sides of a building and the side assignment switched between buildings. In two experiments, neural correlates of performance on this task were evaluated using multiple neuroimaging tools: diffusion tensor imaging (Experiment 1), magnetic resonance elastography (Experiment 1), and functional MRI (Experiment 2). Structural and functional data from each individual modality provided complementary and consistent evidence that the hippocampus and the adjacent white matter tract (i.e., fornix) supported relational memory, whereas the ventromedial pFC/OFC (vmPFC/OFC) and the white matter tract connecting vmPFC/OFC to MTL (i.e., uncinate fasciculus) supported memory-guided rule use. Together, these data suggest that MTL and pFC structures differentially contribute to and support contextually guided relational memory.

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Journal articles on the topic 'Tensor dependent diffusion'

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