TY - JOUR. T1 - Presurgical Mapping of Verbal Language in Brain Tumors with Functional MR Imaging and MR Tractography. AU - Bizzi, Alberto. PY - 2009/11. Y1 - 2009/11. N2 - Functional magnetic resonance (fMR) imaging and diffusion MR tractography have emerged as valuable tools in the evaluation of verbal language in brain tumor patients, and have changed the way neurosurgeons look at patients with a mass in the dominant hemisphere. The techniques have obtained recognition as valuable presurgical clinical tools in the determination of hemispheric dominance and in the selection of candidates who may benefit from awake craniotomy. In the near future fMRI and diffusion MR Tractography may contribute to elucidate mechanisms of brain plasticity and may provide predictors of favorable postoperative clinical outcome. The functional anatomy of the language network and the role of fMR imaging and diffusion MR tractography in the evaluation of patients with a brain tumor are the focus of this ...
Objectives: An increased incidence in white matter abnormalities is among the most frequently reported brain change in patients with bipolar disorder. The objective of the present study was to examine white matter tract integrity, using diffusion tensor imaging (DTI), in bipolar patients and healthy comparison subjects.. Methods: Eleven DSM-IV bipolar I patients and 10 healthy age- and sex-matched controls were studied. DTI data were acquired on a 1.5 Tesla scanner. Fractional anisotropy (FA) and diffusivity (trace) were determined from axial images using region of interest (ROI) analyses. The ROIs were manually placed in the midline and forward projecting arms of the genu (anterior) and the midline of the splenium (posterior) of the corpus callosum.. Results: Bipolar patients had significantly higher FA in the midline of the genu compared with healthy controls. Regional white matter differences were also observed, with significantly lower FA in the genu than forward projecting regions in both ...
The purpose of the present study was to detail the childhood developmental course of different white matter (WM) characteristics. In a longitudinal diffusion tensor imaging (DTI) study of 159 healthy children between 4 and 11 years scanned twice, we used tract-based spatial statistics as well as delineation of 15 major WM tracts to characterize the regional pattern of change in fractional anisotropy (FA), mean (MD), radial (RD) and axial diffusivity (AD). We tested whether there were decelerations of change with increasing age globally and tract-wise, and also illustrated change along medial-to-lateral, posterior-to-anterior and inferior-to-superior gradients. We found a significant linear increase in global FA, and decrease in MD and RD over time. For mean AD, a weak decrease was observed. The developmental changes in specific WM tracts showed regional differences. Eight WM tracts showed non-linear development patterns for one or several DTI metrics, with a deceleration in change with age. Sex ...
A recent computational model of brain tumor growth, developed to better describe how gliomas invade through the adjacent brain parenchyma, is based on two major elements: cell proliferation and isotropic cell diffusion. On the basis of this model, glioma growth has been simulated in a virtual brain, provided by a 3D segmented MRI atlas. However, it is commonly accepted that glial cells preferentially migrate along the direction of fiber tracts. Therefore, in this paper, the model has been improved by including anisotropic extension of gliomas. The method is based on a cell diffusion tensor derived from water diffusion tensor (as given by MRI diffusion tensor imaging). Results of simulations have been compared with two clinical examples demonstrating typical growth patterns of low-grade gliomas centered around the insula. The shape and the kinetic evolution are better simulated with anisotropic rather than isotropic diffusion. The best fit is obtained when the anisotropy of the cell diffusion tensor is
BACKGROUND: To study early neurodevelopment in preterm infants, evaluation of brain maturation and injury is increasingly performed using diffusion tensor imaging, for which the reliability of underlying data is paramount. OBJECTIVE: To review the literature to evaluate acquisition and processing methodology in diffusion tensor imaging studies of preterm infants. MATERIALS ... read more AND METHODS: We searched the Embase, Medline, Web of Science and Cochrane databases for relevant papers published between 2003 and 2013. The following keywords were included in our search: prematurity, neuroimaging, brain, and diffusion tensor imaging. RESULTS: We found 74 diffusion tensor imaging studies in preterm infants meeting our inclusion criteria. There was wide variation in acquisition and processing methodology, and we found incomplete reporting of these settings. Nineteen studies (26%) reported the use of neonatal hardware. Data quality assessment was not reported in 13 (18%) studies. ...
TY - JOUR. T1 - Does the use of hormonal contraceptives cause microstructural changes in cerebral white matter? Preliminary results of a DTI and tractography study. AU - De Bondt, Timo. AU - Van Hecke, Wim. AU - Veraart, Jelle. AU - Leemans, Alexander. AU - Sijbers, Jan. AU - Sunaert, Stefan. AU - Jacquemyn, Yves. AU - Parizel, Paul M.. PY - 2013/1/1. Y1 - 2013/1/1. N2 - Objective: To evaluate the effect of monophasic combined oral contraceptive pill (COCP) and menstrual cycle phase in healthy young women on white matter (WM) organization using diffusion tensor imaging (DTI). Methods: Thirty young women were included in the study; 15 women used COCP and 15 women had a natural cycle. All subjects underwent DTI magnetic resonance imaging during the follicular and luteal phase of their cycle, or in different COCP cycle phases. DTI parameters were obtained in different WM structures by performing diffusion tensor fibre tractography. Fractional anisotropy and mean diffusivity were calculated for ...
TY - JOUR. T1 - The DTI Challenge. T2 - Toward Standardized Evaluation of Diffusion Tensor Imaging Tractography for Neurosurgery. AU - Pujol, Sonia. AU - Wells, William. AU - Pierpaoli, Carlo. AU - Brun, Caroline. AU - Gee, James. AU - Cheng, Guang. AU - Vemuri, Baba. AU - Commowick, Olivier. AU - Prima, Sylvain. AU - Stamm, Aymeric. AU - Goubran, Maged. AU - Khan, Ali. AU - Peters, Terry. AU - Neher, Peter. AU - Maier-Hein, Klaus H.. AU - Shi, Yundi. AU - Tristan-Vega, Antonio. AU - Veni, Gopalkrishna. AU - Whitaker, Ross. AU - Styner, Martin. AU - Westin, Carl Fredrik. AU - Gouttard, Sylvain. AU - Norton, Isaiah. AU - Chauvin, Laurent. AU - Mamata, Hatsuho. AU - Gerig, Guido. AU - Nabavi, Arya. AU - Golby, Alexandra. AU - Kikinis, Ron. PY - 2015/11/1. Y1 - 2015/11/1. N2 - Diffusion tensor imaging (DTI) tractography reconstruction of white matter pathways can help guide brain tumor resection. However, DTI tracts are complex mathematical objects and the validity of tractography-derived ...
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Shiverer is an important model of central nervous system dysmyelination characterized by a deletion in the gene encoding myelin basic protein with relevance to human dysmyelinating and demyelinating diseases. Perfusion fixed brains from shiverer mutant (C3Fe.SWV Mbp^(shi)/Mbp^(shi)n = 6) and background control (C3HeB.FeJ, n = 6) mice were compared using contrast enhanced volumetric diffusion tensor magnetic resonance microscopy with a nominal isotropic spatial resolution of 80 mum. Images were accurately coregistered using non-linear warping allowing voxel-wise statistical parametric mapping of tensor invariant differences between control and shiverer groups. Highly significant differences in the tensor trace and both the axial and radial diffusivity were observed within the major white matter tracts and in the thalamus, midbrain, brainstem and cerebellar white matter, consistent with a high density of myelinated axons within these regions. The fractional anisotropy was found to be much less ...
Background Although diffusion tensor imaging has been a major research focus for Alzheimers disease in recent years, it remains unclear whether it has sufficient stability to have biomarker potential. To date, frequently inconsistent results have been reported, though lack of standardisation in acquisition and analysis make such discrepancies difficult to interpret. There is also, at present, little knowledge of how the biometric properties of diffusion tensor imaging might evolve in the course of Alzheimers disease. Methods The biomarker question was addressed in this study by adopting a standardised protocol both for the whole brain (tract-based spatial statistics), and for a region of interest: the midline corpus callosum. In order to study the evolution of tensor changes, cross-sectional data from very mild (N = 21) and mild (N = 22) Alzheimers disease patients were examined as well as a longitudinal cohort (N = 16) that had been rescanned at 12 months. Findings and Significance The results
As diffusion tractography is increasingly used to generate quantitative measures to address clinical questions, it is important to characterise the inter-session reproducibility and inter-subject variability of these measures. Here, we assess the reproducibility and variability of diffusion tractography measures using diffusion data from 8 subjects scanned 3 times. We used probabilistic tractography to define the cingulum bundle, pyramidal tracts, optic radiations and genu of the corpus callosum in each individual data set using three different methods of seed definition. Measures of mean fractional anisotropy (FA) and mean diffusivity (MD) along the tracts were more reproducible than measures of tract volume. Further, tracts defined using a two region of interest (ROI) approach were more reproducible than those defined using manually placed seed masks alone. For mean FA taken from tracts defined using the two ROI approach, inter-session coefficients of variation (CV) were all below 5% and inter-subject
Van Hecke W, Leemans A, Sage CA, Emsell L, Veraart J, Sijbers J, Sunaert S, Parizel PM. The effect of template selection on diffusion tensor voxel-based analysis results. NEUROIMAGE 55 (2) : 566 - 573(2011) PubMed ...
Diffusion-weighted imaging (DWI) tractography is a technique with great potential to characterize the in vivo anatomical position and integrity of white matter tracts. Tractography, however, remains an estimation of white matter tracts, and false-positive and false-negative rates are not available. The goal of the present study was to compare postmortem tractography of the dentatorubrothalamic tract (DRTT) by its 3D histological reconstruction, to estimate the reliability of the tractography algorithm in this specific tract. Recent studies have shown that the cerebellum is involved in cognitive, language and emotional functions besides its role in motor control. However, the exact working mechanism of the cerebellum is still to be elucidated. As the DRTT is the main output tract it is of special interest for the neuroscience and clinical community. A postmortem human brain specimen was scanned on a 7T MRI scanner using a diffusion-weighted steady-state free precession sequence. Tractography was
The convergence of the long-time apparent diffusion tensor of diffusion magnetic resonance imaging (dMRI) to the effective diffusion tensor obtained by mathematical homogenization theory was considered for two-compartment geometric models containing non-elongated cells of general shapes. A numerical study was conducted in two and three dimensions to demonstrate this convergence as a function of the diffusion time. ...
Introduction - The infarct border zone (BZ) consists of a mixture of fibrotic scar and viable myocardium and is important in ventricular arrhythmogenesis. Late gadolinium enhanced (LGE) MRI can be used to identify infarct and BZ, but the magnitude of microstructural remodeling within the BZ is incompletely characterized. Diffusion tensor MRI (DT-MRI) evaluates microstructural remodeling by quantifying cellularity (increases with decreasing tensor trace), fibrosis (increases with decreasing fractional anisotropy, FA), and tissue mode (increase in fiber disarray with decreasing mode). Our objective was to quantify microstructural remodeling in the BZ using DT-MRI.. Methods - Porcine infarcts were made by balloon occlusion of the LCx (N1=4) or RCA (N2=1); or microbead obstruction of the LAD (N3=3). Gd-DTPA was injected (0.1mmol/kg) on week 8 and circulated for 15 minutes before sacrifice. Normal pigs (N=5) served as controls. Excised hearts were imaged with LGE MRI (0.33×0.33×0.33-0.50mm) and ...
In this project we use GPU particle tracing to visualize 3D diffusion tensor fields. We can integrate and render about half a million particles at interactive rates, and we can select different visualization options like oriented particles of diffusion-dependent shape, stream lines or stream tubes. The proposed method provides an efficient and intuitive means to show the dynamics in diffusion tensor fields and it can thus be applied to explore the diffusion properties of biological tissue. ...
TY - JOUR. T1 - More insights into early brain development through statistical analyses of eigen-structural elements of diffusion tensor imaging using multivariate adaptive regression splines. AU - Chen, Yasheng. AU - Zhu, Hongtu. AU - An, Hongyu. AU - Armao, Diane. AU - Shen, Dinggang. AU - Gilmore, John H.. AU - Lin, Weili. PY - 2014/1/1. Y1 - 2014/1/1. N2 - The aim of this study was to characterize the maturational changes of the three eigenvalues (λ1 ≥ λ2 ≥ λ3) of diffusion tensor imaging (DTI) during early postnatal life for more insights into early brain development. In order to overcome the limitations of using presumed growth trajectories for regression analysis, we employed Multivariate Adaptive Regression Splines (MARS) to derive data-driven growth trajectories for the three eigenvalues. We further employed Generalized Estimating Equations (GEE) to carry out statistical inferences on the growth trajectories obtained with MARS. With a total of 71 longitudinal datasets acquired ...
TY - JOUR. T1 - Independent and Combined Effects of Chronic HIV-Infection and Tobacco Smoking on Brain Microstructure. AU - Liang, Huajun. AU - Chang, Linda. AU - Chen, Rong. AU - Oishi, Kenichi. AU - Ernst, Thomas. PY - 2018/1/1. Y1 - 2018/1/1. N2 - HIV-infected individuals (HIV+) have 2-3 times higher prevalence of tobacco smoking than the general U.S. population. This study aims to evaluate the independent and combined effects of tobacco-smoking and HIV-infection on brain microstructure and cognition using a 2 × 2 design. 21 HIV + Smokers, 25 HIV + Nonsmokers, 25 Seronegative (SN)-Smokers and 23 SN-Nonsmokers were evaluated using diffusion tensor imaging. Fractional anisotropy (FA), mean (MD), radial (RD) and axial (AD) diffusivity were assessed in 8 major cerebral fiber tracts and 5 subcortical regions. Cognitive performance in 7 neurocognitive domains was also assessed. Compared to SN, HIV+ had higher AD in genu of corpus callosum (GCC, p = 0.002). Smokers also had higher diffusivities in ...
To our knowledge, this is the first study to examine cognitive function and white matter integrity in subjects with a history of heavy psychostimulant use and comorbid HIV infection, compared to healthy, matched control subjects. The main findings of the present study are that the patient group exhibited significantly lower white matter integrity, indicated by decreased FA values, in the four important white matter tracts of the anterior commissure, left and right anterior limb of the internal capsule, and the genu of the corpus callosum. With the exception of the anterior commissure, all tracts also showed a significant increase in MD and RD, suggesting that increases in axonal membrane permeability, for example by processes such as demyelination, may underlie the observed decrease in FA values. The patient group also displayed widespread neurocognitive impairment, which was significant in tasks that assess cognitive set-shifting, fine motor speed and verbal memory.. All subjects were recruited ...
Methods Inclusion criteria: Preterm birth , 33 weeks gestational age (GA), serial MRI and DTI, first scan ≤ 33 weeks post-menstrual age (PMA), second at TEA.. We studied 52 preterm infants, with a median GA at birth of 27+1 (24+ 3 - 32+ 6) weeks. DTI data were analysed using tract based spatial statistics (TBSS). Voxel based statistics was performed to assess the correlation between GA at birth and FA, corrected for PMA at scan.. ...
We analyzed the degree of genetic control over intersubject variability in the microstructure of cerebral white matter (WM) using diffusion tensor imaging (DTI). We performed heritability, genetic correlation and quantitative trait loci (QTL) analyses for the whole-brain and 10 major cerebral WM tra …
Imaging the heart is central to cardiac phenotyping, but in clinical practice, this has been restricted to macroscopic interrogation. Diffusion tensor cardiovascular magnetic resonance (DT-CMR) is a novel, noninvasive technique that is beginning to unlock details of this microstructure in humans in vivo. DT-CMR demonstrates the helical cardiomyocyte arrangement that drives rotation and torsion. Sheetlets (functional units of cardiomyocytes, separated by shear layers) have been shown to reorientate between diastole and systole, revealing how microstructural function facilitates cardiac thickening. Measures of tissue diffusion can also be made: fractional anisotropy (a measure of myocyte organization) and mean diffusivity (a measure of myocyte packing). Abnormal myocyte orientation and sheetlet function has been demonstrated in congenital heart disease, cardiomyopathy, and after myocardial infarction. It is too early to predict the clinical importance of DT-CMR, but such unique in vivo information ...
To assess whether there was a relationship between these functional interactions and white matter microstructure across participants, we used tract-based spatial statistics (TBSS) to investigate local correlations between FA and ppTMS/spTMS MEP ratio effect size (16). We used MEP ratios with 6- and 12-ms IPLs from right hand response trials in the pre-SMA/M1 IPL experiment and the rIFG/M1 IPL experiment. Therefore, we had four different and uncorrelated regressors in the TBSS multiple regression analysis. Effects were reported as being significant at a one-tailed statistical threshold of P , 0.001 (uncorrected) and a cluster size of ,10 voxels (16). We found 2 clusters significantly correlated with the TMS effect in the pre-SMA/M1 experiment at an IPL of 6 ms. These clusters lay in dorsal white matter likely to connect pre-SMA, premotor, motor, and parietal areas. At an IPL of 12 ms, we found 6 clusters significantly correlated with pre-SMA/M1 interactions. Again, some of these clusters lay in ...
OBJECTIVE: Transverse relaxation time (T2) imaging provides the opportunity to examine membrane fluidity, which can affect a number of cellular functions. The objective of the present work was to examine T2 abnormalities in children with unmodified DSM-IV-TR bipolar disorder (BD) in bilateral cingulate-paracingulate (CPC) white matter. METHOD: A total of 21 children and adolescents with BD and 16 healthy control subjects underwent magnetic resonance imaging at 1.5 Tesla and were compared using a region-of-interest analysis. A post hoc diffusion tensor imaging (DTI) analysis was also performed on selected subjects. RESULTS: The T2 values were significantly decreased on the right-side of the subjects with BD compared with that of the control subjects. Hemispheric difference was also observed in the BD group, with decreased T2 on the right side compared with the left side. No significant difference was observed between left and right CPC T2 in control subjects. For participants who had both T2 and DTI
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Given an order-d tensor $\tensor A \in \R^{n \times n \times...\times n}$, we present a simple, element-wise sparsification algorithm that zeroes out all sufficiently small elements of $\tensor A$, keeps all sufficiently large elements of $\tensor A$, and retains some of the remaining elements with probabilities proportional to the square of their magnitudes. We analyze the approximation accuracy of the proposed algorithm using a powerful inequality that we derive. This inequality bounds the spectral norm of a random tensor and is of independent interest. As a result, we obtain novel bounds for the tensor sparsification problem. ...
Tractography is a three-dimensional modeling technique that has been used for approximately the past two decades to help visualize the structural connections between different parts of the brain. This method is based on diffusion magnetic resonance imaging (dMRI), which images the way in which water moves within the brain. Since we know that water flows in the path of least resistance, we can assume that this path represents the connections between cells in the brain - or in other words, that it represents axons and white matter tracts that connect neurons. This concept forms the basis of tractography and image-based white matter mapping. As the only non-invasive method of visualizing white matter tracts in living human subjects, its clinical and research applications have continued to expand. It is used clinically for planning surgeries in patients with brain tumors and epilepsy; and its potential is immense as its use as a diagnostic and prognostic tool in stroke, multiple sclerosis, ...
The ability of fiber tractography to delineate noninvasively the white matter fiber pathways of the brain raises possibilities for clinical applications and offers enormous potential for neuroscience. In the last decade, fiber tracking has become the method of choice to investigate quantitative MRI parameters in specific bundles of white matter....
Region of interest (ROI) analysis is a widely used method for the analysis of DTI data. An anatomically defined region-either based on anatomical borders or a geometrical shape-is used to extract DTI...
ORIGINAL ARTICLES Journal of Neurosurgical Sciences 2012 June;56(2):137-43. Predictive value of inferior fronto-occipital fasciculus (IFO) DTI-fiber tracking for determining the extent of resection for surgery of frontal and temporal gliomas preoperatively. Bertani G., Carrabba G., Raneri F., Fava E., Castellano A., Falini A., Casarotti A., Gaini S. M., Bello L. ...
Diffusion tensor imaging allows for visualization of white matter tracts by tractography. Methodology in this new magnetic resonance imaging (MRI) varies to match the desired use. In this study, methods of creating three-dimensional (3D) tracts were tested to analyze the corticospinal tract (CST) and somatosensory tract in post-stroke patients both before and after neurorehabilitation. Using an imaging software called FSL, I was able to superimpose the fractional anisotropy brain image with the T1 MRI image and create mask where the tracts have a higher probability of being found. The software then connected the tracts, producing a 3D visualizations of the tract which I then superimposed onto a 3D brain to show the tract in space. I found that the CST had the most reliable and reproducible results. However, the somatosensory tract results varied and I could not get a concrete methodology for this tract.
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A technique called high-definition fiber tractography (HDFT) provides a powerful new tool for tracing the course of nerve fiber connections within the brain-with the potential to improve the accuracy of neurosurgical planning and to advance scientific understanding of the brains structural and functional networks, reports a paper in the August issue of Neurosurgery, official journal of the Congress of Neurological Surgeons. The journal is published by Lippincott Williams & Wilkins, a part of Wolters Kluwer Health.
In this study, we propose a methodology to estimate 3D+time maps of left ventricular fibre strain from human structural and dynamic MRI data. A finite elem
This imaging technology, performed by neuroradiologists, can help our surgeons better determine the location of tumors for removal.
New visualization evidence from MRI study of the human brain demonstrated previously unidentified structural connections between the brainstem and the forebrain.
In this paper, we study the $l^k$-eigenvalues/vectors of a real symmetric square tensor. Specially, we investigate some properties on the related $l^k$-spectral radius of a real nonnegative symmetric square tensor.
The first high-resolution structural connection map of the human cerebral cortex was published earlier this month in the journal PLoS Biology. The study reveals regions that are highly connected and central, forming a structural core network [1]. Intriguingly, this core network consists of many areas that are more active when were at rest than when were engaged in a task that requires concentration. ...
The first high-resolution structural connection map of the human cerebral cortex was published earlier this month in the journal PLoS Biology. The study reveals regions that are highly connected and central, forming a structural core network [1]. Intriguingly, this core network consists of many areas that are more active when were at rest than when were engaged in a task that requires concentration. ...
Large I, Bridge H, Ahmed B, Clare S, Kolasinski J, Lam WW, Miller KL, Dyrby TB, Parker AJ, Smith JET, Daubney G, Sallet J Bell AH, Krug K, Individual differences in the alignment of structural and functional markers of the V5/MT complex in primates, Cerebral Cortex, 2016, Accepted. Donahue C, Sotiropoulos S, Jbabdi S, Hernandez-Fernandez M, Beherens T, Dyrby TB, Kennedy H, Knoblauch K, Coalson T, Glasser M, Van Essen D, Using Diffusion Tractography to Predict Cortical Connection Strength and Distance: A Quantitative Comparison with Tracers in the Monkey, Journal Neuroscience, 2016, Accepcted Innocenti GM, Dyrby TB, Winther-Andersen K , Rouillier EM, Caminiti R, The crossed projection to the striatum in two species of monkey and in humans: Behavioral and evolutionary significance, Cerebral Cortex accepted. Reislev NL, Dyrby TB, Siebner HR, Kupers R, Simultaneous assessment of white matter changes in microstructure and connectedness in the blind brain, Neural Plasticity, Article ID 795865, ...
SCI] Tractography-guided statistics(TGIS) in diffusion tensor imaging for the detection of gender difference of fiber integrity in the midsagittal and parasagittal corpora callosa ...
clearcoeff.m - absorbs the physical coefficient of the tensor train into its cores. conj.m - element-wise conjugation of a matrix in a TT representation. ctranspose.m - conjugate-transpose of a matrix in a TT representation. diag.m - mimics diag for matrices. If an input is ttclass matrix, returns a ttclass vector (matrix with 1 column) containing the diagonal. If an input is a vector, returns a diagonal matrix. dot.m - mimics the dot product operation for matrices. full.m - mimics the corresponding operation for sparse matrices. Computes all Kronecker products and returns full matrix. May result in out-of-memory errors for large matrices. hdot.m - the Hadamard dot product operation. ismatrix.m - returns true for non-empty TT objects. isnumeric.m - returns true for non-empty TT objects isreal.m - returns true for real-valued ttclass objects. kron.m - Kronecker product of tensor train representation of matrices. mean.m - mimics the corresponding operation for matrices. If the input is a ttclass ...
Ratnarajah, Nagulan and Simmons, Andy and Davydov, Oleg and Hojjatoleslami, Ali (2010) A Novel White Matter Fibre Tracking Algorithm Using Probabilistic Tractography and Average Curves. Medical Image Computing and Computer-Assisted Intervention, 6361 . pp. 666-673. ISSN 0302-9743. (doi:https://doi.org/10.1007/978-3-642-15705-9_81 ) (The full text of this publication is not currently available from this repository. You may be able to access a copy if URLs are provided ...
I am a neuroradiologist with expertise in the imaging of the brain, neck, and spine. My interests lie in the advanced imaging of brain tumors using diffusion tensor, perfusion, spectroscopic and functional MRI. I work closely with the neurosurgeons, neurologists, and radiation oncologists at Memorial Sloan Kettering to bring the most advanced standard and experimental treatments to our patients.
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Model selection in tensor decomposition is important for real applications if the rank of the original data tensor is unknown and the observed tensor is noisy ...
在TensorFlow神经网络中的激活函数中,tf.tanh函数用于计算x元素的双曲正切值,该参数x可以是一个Tensor或者是具有 float16,float32,double,complex64或complex128类型的SparseTensor;tf.tanh函数返回一个Tensor或 SparseTensor,它们分别与x具有相同的类型。_来自TensorFlow官方文档,w3cschool编程狮。
Prader-Willi Syndrome (PWS) is a genetic disorder characterized by infantile hypotonia, hyperphagia, hypogonadism, growth hormone deficiency, intellectual disability, and severe emotional and behavioral problems. The brain mechanisms that underpin these disturbances are unknown. Diffusion tensor imaging (DTI) enables in vivo investigation of the microstructural integrity of white matter pathways. To date, only one study has used DTI to examine white matter alterations in PWS. However, that study used selected regions of interest, rather than a whole brain analysis. In the present study, we used diffusion tensor and magnetic resonance (T 1-weighted) imaging to examine microstructural white matter changes in 15 individuals with PWS (17-30 years) and 15 age-and-gender-matched controls. Whole-brain voxel-wise statistical analysis of FA was carried out using tract-based spatial statistics (TBSS). Significantly decreased fractional anisotropy was found localized to the left hemisphere in individuals ...
In this article, we discuss the theoretical background for diffusion weighted imaging and diffusion tensor imaging. Molecular diffusion is a random process involving thermal Brownian motion. In biological tissues, the underlying microstructures restrict the diffusion of water molecules, making diffusion directionally dependent. Water diffusion in tissue is mathematically characterized by the diffusion tensor, the elements of which contain information about the magnitude and direction of diffusion and is a function of the coordinate system. Thus, it is possible to generate contrast in tissue based primarily on diffusion effects. Expressing diffusion in terms of the measured diffusion coefficient (eigenvalue) in any one direction can lead to errors. Nowhere is this more evident than in white matter, due to the preferential orientation of myelin fibers. The directional dependency is removed by diagonalization of the diffusion tensor, which then yields a set of three eigenvalues and eigenvectors, ...
BACKGROUND AND PURPOSE: Traumatic axonal injury is a primary brain abnormality in head trauma and is characterized by reduction of fractional anisotropy (FA) on diffusion tensor imaging (DTI). Our hypothesis was that patients with mild traumatic brain injury (TBI) have widespread brain white matter regions of reduced FA involving a variety of fiber bundles and show fiber disruption on fiber tracking in a minority of these regions. MATERIALS AND METHODS: Ethics committee approval and informed consent were obtained. Twenty-one patients with mild TBI were investigated (men:women, 12:9; mean age +/- SD, 32 +/- 9 years). In a voxel-based comparison with 11 control subjects (men:women, 8:3; mean age, 37 +/- 9 years) using z score analysis, patient regions with abnormally reduced FA were defined in brain white matter. MR imaging, DTI, and fiber tracking characteristics of these regions were described and analyzed using Pearson correlation, linear regression analysis, or the chi(2) test when appropriate.