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Diffusion Tensor Imaging (diffusion + tensor_imaging)
Terms modified by Diffusion Tensor Imaging Selected AbstractsIllustrative White Matter Fiber BundlesCOMPUTER GRAPHICS FORUM, Issue 3 2010Ron Otten Abstract Diffusion Tensor Imaging (DTI) has made feasible the visualization of the fibrous structure of the brain white matter. In the last decades, several fiber-tracking methods have been developed to reconstruct the fiber tracts from DTI data. Usually these fiber tracts are shown individually based on some selection criteria like region of interest. However, if the white matter as a whole is being visualized clutter is generated by directly rendering the individual fiber tracts. Often users are actually interested in fiber bundles, anatomically meaningful entities that abstract from the fibers they contain. Several clustering techniques have been developed that try to group the fiber tracts in fiber bundles. However, even if clustering succeeds, the complex nature of white matter still makes it difficult to investigate. In this paper, we propose the use of illustration techniques to ease the exploration of white matter clusters. We create a technique to visualize an individual cluster as a whole. The amount of fibers visualized for the cluster is reduced to just a few hint lines, and silhouette and contours are used to improve the definition of the cluster borders. Multiple clusters can be easily visualized by a combination of the single cluster visualizations. Focus+context concepts are used to extend the multiple-cluster renderings. Exploded views ease the exploration of the focus cluster while keeping the context clusters in an abstract form. Real-time results are achieved by the GPU implementation of the presented techniques. [source] Generalized Diffusion Tensor Imaging (GDTI): A Method for Characterizing and Imaging Diffusion Anisotropy Caused by Non-Gaussian DiffusionISRAEL JOURNAL OF CHEMISTRY, Issue 1-2 2003Chunlei Liu For non-Gaussian distributed random displacement, which is common in restricted diffusion, a second-order diffusion tensor is incapable of fully characterizing the diffusion process. The insufficiency of a second-order tensor is evident in the limited capability of diffusion tensor imaging (DTI) in resolving multiple fiber orientations within one voxel of human white matter. A generalized diffusion tensor imaging (GDTI) method was recently proposed to solve this problem by generalizing Fick's law to a higher-order partial differential equation (PDE). The relationship between the higher-order tensor coefficients of the PDE and the higher-order cumulants of the random displacement can be derived. The statistical property of the diffusion process was fully characterized via the higher-order tensor coefficients by reconstructing the probability density function (PDF) of the molecular random displacement. Those higher-order tensor coefficients can be measured using conventional diffusion-weighted imaging or spectroscopy techniques. Simulations demonstrated that this method was capable of quantitatively characterizing non-Gaussian diffusion and accurately resolving multiple fiber orientations. It can be shown that this method is consistent with the q-space approach. The second-order approximation of GDTI was shown to be DTI. [source] Deviation of Fiber Tracts in the Vicinity of Brain Lesions: Evaluation by Diffusion Tensor ImagingISRAEL JOURNAL OF CHEMISTRY, Issue 1-2 2003Yaniv Assaf Diffusion Tensor Imaging (DTI) is used to characterize the diffusion properties of deviated white matter caused by brain tumors. DTI was recently shown to be very helpful in delineating white matter both within brain lesions and surrounding them. Displacement of white matter fibers may be one of the consequences of tumor growth adjacent to white matter. The combination of white matter mapping with DTI and gray matter mapping using functional MRI, in some cases, facilitated assessment of the relation between the shifted cortical areas and the corresponding white matter tracts. We found that the fractional anisotropy extracted from DTI is increased by 38% in areas of non-edematous shifted white matter fibers. By contrast, trace apparent diffusion coefficient (ADC) values in those areas were found to be similar to contralateral side and normal control values. Analysis of the three diffusion tensor eigenvalues revealed that the increase in the fractional anisotropy is a result of two processes. The first is the increase in the diffusion parallel to the fibers,,1 (by 18%), and the second is the decrease in the diffusion perpendicular to fibers,,3 (by 34%) as compared with the contralateral side. These opposing changes cause an increase in the diffusion anisotropy but no change in the trace ADC. It is suggested that the pressure caused by the tumor may lead to an increase in white matter fiber tension, thus causing an increase in ,1. On the other hand, the same pressure causes increased fiber density per unit area, leading to a higher degree of restricted diffusion in the extracellular space and, hence, a reduction in ,3. [source] Fiber tracking using magnetic resonance diffusion tensor imaging and its applications to human brain developmentDEVELOPMENTAL DISABILITIES RESEARCH REVIEW, Issue 3 2003Richard Watts Abstract Diffusion tensor imaging is unique in its ability to noninvasively visualize white matter fiber tracts in the human brain in vivo. Diffusion is the incoherent motion of water molecules on a microscopic scale. This motion is itself dependent on the micro-structural environment that restricts the movement of the water molecules. In white matter fibers there is a pronounced directional dependence on diffusion. With white matter fiber tracking or tractography, projections among brain regions can be detected in the three-dimensional diffusion tensor dataset according to the directionality of the fibers. Examples of developmental changes in diffusion, tracking of major fiber tracts, and examples of how diffusion tensor tractography and functional magnetic resonance imaging can be combined are provided. These techniques are complimentary and allow both the identification of the eloquent areas of the brain involved in specific functional tasks, and the connections between them. The noninvasive nature of magnetic resonance imaging will allow these techniques to be used in both longitudinal developmental and diagnostic studies. An overview of the technique and preliminary applications are presented, along with its current limitations. MRDD Research Reviews 2003;9:168,177. © 2003 Wiley-Liss, Inc. [source] MRI of late microstructural and metabolic alterations in radiation-induced brain injuriesJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2009Kevin C. Chan BEng Abstract Purpose To evaluate the late effects of radiation-induced damages in the rat brain by means of in vivo multiparametric MRI. Materials and Methods The right hemibrains of seven Sprague-Dawley rats were irradiated with a highly collimated 6 MV photon beam at a single dose of approximately 28 Gy. Diffusion tensor imaging (DTI), proton MR spectroscopy (1H-MRS), T2-weighted imaging, and T1-weighted imaging were performed to the same animals 12 months after radiation treatment. Results Compared with the contralateral side, a significantly higher percentage decrease in fractional anisotropy was observed in the ipsilateral fimbria of hippocampus (29%) than the external capsule (8%) in DTI, indicating the selective vulnerability of fimbria to radiation treatment. Furthermore, in 1H-MRS, significantly higher choline, glutamate, lactate, and taurine peaks by 24%, 25%, 87%, and 58%, respectively, were observed relative to creatine in the ipsilateral brain. Postmortem histology confirmed these white matter degradations as well as glial fibrillary acidic protein and glutamine synthetase immunoreactivity increase in the ipsilateral brain. Conclusion The microstructural and metabolic changes in late radiation-induced brain injuries were documented in vivo. These multiparametric MRI measurements may help understand the white matter changes and neurotoxicity upon radiation treatment in a single setting. J. Magn. Reson. Imaging 2009;29:1013,1020. © 2009 Wiley-Liss, Inc. [source] Retrograde Wallerian degeneration of cranial corticospinal tracts in cervical spinal cord injury patients using diffusion tensor imagingJOURNAL OF NEUROSCIENCE RESEARCH, Issue 10 2008Saurabh Guleria Abstract Diffusion tensor imaging (DTI) has the potential to reveal disruption of white matter microstructure in chronically injured spinal cords. We quantified fractional anisotropy (FA) and mean diffusivity (MD) to demonstrate retrograde Wallerian degeneration (WD) of cranial corticospinal tract (CST) in cervical spinal cord injury (SCI). Twenty-two patients with complete cervical SCI in the chronic stage were studied with DTI along with 13 healthy controls. Mean FA and MD values were computed for midbrain, pons, medulla, posterior limb of internal capsule, and corona radiata. Significant reduction in the mean FA and increase in MD was observed in the cranial CST in patients with SCI compared with controls, suggesting retrograde WD. Statistically significant inverse FA and MD changes were noted in corona radiata, indicating some restoration of spared white matter tracts. Temporal changes in the DTI metrics suggest progressing degeneration in different regions of CST. These spatiotemporal changes in DTI metrics suggest continued WD in injured fibers along with simultaneous reorganization of spared white matter fibers, which may contribute to changing neurological status in chronic SCI patients. © 2008 Wiley-Liss, Inc. [source] Characterization of White Matter Microstructure in Fetal Alcohol Spectrum DisordersALCOHOLISM, Issue 3 2009Susanna L. Fryer Background:, Exposure to alcohol during gestation is associated with CNS alterations, cognitive deficits, and behavior problems. This study investigated microstructural aspects of putative white matter abnormalities following prenatal alcohol exposure. Methods:, Diffusion tensor imaging was used to assess white matter microstructure in 27 youth (age range: 8 to 18 years) with (n = 15) and without (n = 12) histories of heavy prenatal alcohol exposure. Voxelwise analyses, corrected for multiple comparisons, compared fractional anisotropy (FA) and mean diffusivity (MD) between groups, throughout the cerebrum. Results:, Prenatal alcohol exposure was associated with low FA in multiple cerebral areas, including the body of the corpus callosum and white matter innervating bilateral medial frontal and occipital lobes. Fewer between-group differences in MD were observed. Conclusions:, These data provide an account of cerebral white matter microstructural integrity in fetal alcohol spectrum disorders and support extant literature showing that white matter is a target of alcohol teratogenesis. The white matter anomalies characterized in this study may relate to the neurobehavioral sequelae associated with gestational alcohol exposure, especially in areas of executive dysfunction and visual processing deficits. [source] In vivo diffusion tensor imaging of the human optic nerve: Pilot study in normal controlsMAGNETIC RESONANCE IN MEDICINE, Issue 2 2006C.A.M. Wheeler-Kingshott Abstract Diffusion tensor imaging (DTI) of the optic nerve (ON) was acquired in normal controls using zonally oblique multislice (ZOOM) DTI, which excites a small field of view (FOV) using a fast sequence with a shortened EPI echo train. This combines the benefit of low sensitivity to motion (due to the single-shot acquisition used), with the additional advantage of reduced sensitivity to magnetic field susceptibility artifacts. Reducing the bright signal from the fat and cerebrospinal fluid (CSF) surrounding the nerve are key requirements for the success of the presented method. Measurements of mean diffusivity (MD) and fractional anisotropy (FA) indices were made in a coronal section of the middle portion of the optic nerve (ON) in the right (rON) and left (lON) ONs. The average values across 10 healthy volunteers were FArON = 0.64 ± 0.09 and FAlON = 0.57 ± 0.10, and MDrON = (1173 ± 227) × 10,6 mm2 s,1 and MDlON = (1266 ± 170) × 10,6 mm2 s,1. Measurements of the principal eigenvalue of the DT and its orthogonal component were also in agreement with those expected from a highly directional structural organization. Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc. [source] Conventional DTI vs. slow and fast diffusion tensors in cat visual cortexMAGNETIC RESONANCE IN MEDICINE, Issue 5 2003Itamar Ronen Abstract Diffusion tensor imaging (DTI) uses water diffusion anisotropy in axonal fibers to provide a tool for analyzing and tracking those fibers in brain white matter. In the present work, multidirectional diffusion MRI data were collected from a cat brain and decomposed into slow and fast diffusion tensors and directly compared with conventional DTI data from the same imaging slice. The fractional anisotropy of the slow diffusing component (Dslow) was significantly higher than the anisotropy measured by conventional DTI while reflecting a similar directionality and appeared to account for most of the anisotropy observed in gray matter, where the fiber density is notoriously low. Preliminary results of fiber tracking based on the slow diffusion component are shown. Fibers generated based on the slow diffusion component appear to follow the vertical fibers in gray matter. DslowTI may provide a way for increasing the sensitivity to anisotropic structures in cortical gray matter. Magn Reson Med 49:785,790, 2003. © 2003 Wiley-Liss, Inc. [source] In vivo mapping of the fast and slow diffusion tensors in human brainMAGNETIC RESONANCE IN MEDICINE, Issue 4 2002Chris A. Clark Abstract Recent studies have shown that the diffusional signal decay in human brain is non-monoexponential and may be described in terms of compartmentalized water fractions. Diffusion tensor imaging (DTI), which provides information about tissue structure and orientation, typically uses b values up to 1000 s mm,2 so that the signal is dominated by the fast diffusing fraction. In this study b factors up to 3500 s mm,2 are utilized, allowing the diffusion tensor properties of the more slowly diffusing fraction to be mapped for the first time. The mean diffusivity (MD) of the slow diffusion tensor was found to exhibit strong white/gray matter (WM/GM) contrast. Maps depicting the principal direction of the slow tensor indicated alignment with the fast tensor and the known orientation of the WM pathways. Magn Reson Med 47:623,628, 2002. © 2002 Wiley-Liss, Inc. [source] Diffusion tensor MRI in rat models of invasive and well-demarcated brain tumorsNMR IN BIOMEDICINE, Issue 3 2008Sungheon Kim Abstract Diffusion tensor imaging (DTI) and its metrics, such as mean diffusivity (MD) and fractional anisotropy (FA), have been used to detect the extent of brain tumors and understand tumor growth and its influence on the surrounding tissue. However, there are conflicting reports on how DTI metrics can be used for tumor diagnosis. The physiological interpretation of these metrics in terms of tumor growth is also not clear. The objective of this study was to investigate the DTI parameters in two rat brain tumor models (9L and F98) with different patterns of aggressiveness by longitudinal monitoring of tumor growth and comparing the DTI parameters of these two tumor models. In addition to the standard DTI metrics, MD and FA, we measured other metrics representing diffusion tensor shape, such as linear and planar anisotropy coefficients (CL and CP), and orientational coherence measured by lattice index (LI), to characterize the two tumor models. The 9L tumor had higher FA, CL, and LI than the F98 tumor. F98 had a larger difference in anisotropies between tumor and peritumor regions than 9L. From the eigenvalues, it was found that the increase in CL and trace of the 9L tumor was due to an increase in the primary eigenvalue, whereas the increase in CP in the peritumor region was due to an increase in both primary and secondary eigenvalues and a decrease in tertiary eigenvalue. Our results indicate that shape-oriented anisotropy measures, such as CL and CP, and orientational coherence measures, such as LI, can provide useful information in differentiating these two tumor models and also differentiating tumor from peritumoral regions. Copyright © 2007 John Wiley & Sons, Ltd. [source] Diffusion tensor imaging in fixed brain tissue at 7.0 TNMR IN BIOMEDICINE, Issue 2 2003David N. Guilfoyle Abstract The purpose of this work is to assess the feasibility of performing quantitative in vitro brain tissue diffusion tensor imaging (DTI) measurements and to examine their comparability to in vivo measurements. DTI of fixed tissue at high field strength is potentially a very valuable investigative tool as very high spatial resolution can be achieved. DTI was applied to human and mouse brain fixed tissue samples as well as in vivo measurements of the mouse brain. T1 and T2 relaxography of the fixed tissue samples was also performed to provide further characterization of the tissue. All experiments were performed at 7,T. The fractional anisotropy (FA) of the human fixed brain tissue samples is found to be higher in the corpus callosum than in the occipital white matter region, consistent with in vivo measurements reported in the literature. Our FA measurements of the corpus callosum of a mouse brain are also found to be the same both in vitro and in vivo. This preliminary work supports the use of DTI in both fixed human and fixed animal brain tissue as a valid investigative tool. With the increased availability of brain banks in different brain disorders, DTI in fixed tissue may prove to be a very useful method for the study of white matter abnormalities. Copyright © 2003 John Wiley & Sons, Ltd. [source] Diffusion tensor imaging in spinal cord: methods and applications , a reviewNMR IN BIOMEDICINE, Issue 7-8 2002Chris A. Clark Abstract The spinal cord is a clinically eloquent site within the central nervous system, containing important sensorimotor tracts confined within a small cross-sectional area. Damage to the spinal cord may be caused by a wide range of pathologies, and can result in profound functional disability. Characterization of the structural integrity of the spinal cord can be assessed using diffusion tensor imaging methods. Development and application of this technique may improve our understanding of the nature and evolution of structural damage in spinal cord disease. Possible developments include improved detection of ischaemic lesions, clarification of the relationship between clinical disability and structural damage to the cord and monitoring of anti-inflammatory or neuroprotective therapies. In this review current technical aspects, clinical applications and the suggested future development of spinal cord diffusion imaging are discussed. Copyright © 2002 John Wiley & Sons, Ltd. [source] White matter abnormalities in bipolar disorder and schizophrenia detected using diffusion tensor magnetic resonance imagingBIPOLAR DISORDERS, Issue 1 2009Jessika E Sussmann Objectives:, Strong qualitative and quantitative evidence exists of white matter abnormalities in both schizophrenia and bipolar disorder (BD). Diffusion tensor imaging (DTI) studies suggest altered connectivity in both disorders. We aim to address the diagnostic specificity of white matter abnormalities in these disorders. Methods:, DTI was used to assess white matter integrity in clinically stable patients with familial BD (n = 42) and familial schizophrenia (n = 28), and in controls (n = 38). Differences in fractional anisotropy (FA) were measured using voxel-based morphometry and automated region of interest analysis. Results:, Reduced FA was found in the anterior limb of the internal capsule (ALIC), anterior thalamic radiation (ATR), and in the region of the uncinate fasciculus in patients with BD and those with schizophrenia compared with controls. A direct comparison between patient groups found no significant differences in these regions. None of the findings were associated with psychotropic medication. Conclusions:, Reduced integrity of the ALIC, uncinate fasciculus, and ATR regions is common to both schizophrenia and BD. These results imply an overlap in white matter pathology, possibly relating to risk factors common to both disorders. [source] Cognitive impairment and white matter damage in hypertension: a pilot studyACTA NEUROLOGICA SCANDINAVICA, Issue 4 2009K. Hannesdottir Objectives,,, Hypertension has been associated with impaired cognition. Diffusion tensor imaging (DTI) and magnetic resonance spectroscopy were applied to assess white matter abnormalities in treated vs untreated hypertension and if these correlated with neuropsychological performance. Methods,,, Subjects were 40 patients with medically treated hypertension (mean age 69.3 years), 10 patients with untreated hypertension (mean age 57.6 years) and 30 normotensive controls (mean age 68.2 years). Hypertension was defined as a previous diagnosis and taking hypertensive medication, or a resting blood pressure of >140/90 mmHg on the day of assessment. Results,,, Patients with treated hypertension performed worse on immediate (P = 0.037) as well as delayed memory tasks (P = 0.024) compared with normotensive controls. Cognitive performance was worse in untreated compared with treated hypertension on executive functions (P = 0.041) and psychomotor speed (P = 0.003). There was no significant correlation between cognition and any of the imaging parameters in treated hypertension. However, in untreated hypertension the results revealed a positive correlation between an executive functioning and attention composite score and DTI mean diffusivity values (P = 0.016) and between psychomotor speed and spectroscopy NAA/tCr levels (P = 0.015). Conclusions,,, These results suggest there is cognitive impairment in hypertension. Treated hypertension was associated with deficits in memory while untreated hypertension revealed a more ,subcortical' pattern of cognitive impairment. [source] Diffusion tensor magnetic resonance imaging in spinal cord injuryCONCEPTS IN MAGNETIC RESONANCE, Issue 3 2008Benjamin M. Ellingson Abstract Noninvasive assessment of spinal cord integrity following injury is critical for precise diagnosis, prognosis, and surgical intervention strategies. Diffusion weighted imaging and diffusion tensor imaging are more sensitive to the underlying spinal cord microstructure than traditional imaging techniques. As a result, diffusion imaging is emerging as the clinical technique for imaging the spinal cord after trauma, surgery or during progressive degenerative diseases. This review describes the basic physics of diffusion imaging using magnetic resonance, techniques used to visualize diffusion measurements, and expected changes in diffusion measurements following spinal cord injury. © 2008 Wiley Periodicals, Inc.Concepts Magn Reson Part A 32A: 219,237, 2008. [source] Analysis of b -value calculations in diffusion weighted and diffusion tensor imagingCONCEPTS IN MAGNETIC RESONANCE, Issue 1 2005Daniel Güllmar Abstract Diffusion weighted imaging has opened new diagnostic possibilities by using microscopic diffusion of water molecules as a means of image contrast. The directional dependence of diffusion has led to the development of diffusion tensor imaging, which allows us to characterize microscopic tissue geometry. The link between the measured NMR signal and the self-diffusion tensor is established by the so-called b matrices that depend on the gradient's direction, strength, and timing. However, in the calculation of b -matrix elements, the influence of imaging gradients on each element of the b matrix is often neglected. This may cause errors, which in turn leads to an incorrect extraction of diffusion coefficients. In cases where the imaging gradients are high (high spatial resolution), these errors may be substantial. Using a generic pulsed gradient spin-echo (PGSE) imaging sequence, the effects of neglecting the imaging gradients on the b -matrix calculation are demonstrated. By measuring an isotropic phantom with this sequence it can be analytically as well as experimentally shown that large deviations in single b -matrix elements are generated. These deviations are obtained by applying the diffusion weighting in the readout direction of the imaging dimension in combination with relatively large imaging gradients. The systematic errors can be avoided by a full b -matrix calculation considering all the gradients of the sequence or by generating cross-term free signals using the geometric average of two diffusion weighted images with opposite polarity. The importance of calculating the exact b matrices by the proposed methods is based on the fact that more precise diffusion parameters are obtained for extracting correct property maps, such as fractional anisotropy, volume ratio, or conductivity tensor maps. © 2005 Wiley Periodicals, Inc. Concepts Magn Reson Part A 25A: 53,66, 2005 [source] Fiber tracking using magnetic resonance diffusion tensor imaging and its applications to human brain developmentDEVELOPMENTAL DISABILITIES RESEARCH REVIEW, Issue 3 2003Richard Watts Abstract Diffusion tensor imaging is unique in its ability to noninvasively visualize white matter fiber tracts in the human brain in vivo. Diffusion is the incoherent motion of water molecules on a microscopic scale. This motion is itself dependent on the micro-structural environment that restricts the movement of the water molecules. In white matter fibers there is a pronounced directional dependence on diffusion. With white matter fiber tracking or tractography, projections among brain regions can be detected in the three-dimensional diffusion tensor dataset according to the directionality of the fibers. Examples of developmental changes in diffusion, tracking of major fiber tracts, and examples of how diffusion tensor tractography and functional magnetic resonance imaging can be combined are provided. These techniques are complimentary and allow both the identification of the eloquent areas of the brain involved in specific functional tasks, and the connections between them. The noninvasive nature of magnetic resonance imaging will allow these techniques to be used in both longitudinal developmental and diagnostic studies. An overview of the technique and preliminary applications are presented, along with its current limitations. MRDD Research Reviews 2003;9:168,177. © 2003 Wiley-Liss, Inc. [source] Language lateralization in temporal lobe epilepsy using functional MRI and probabilistic tractographyEPILEPSIA, Issue 8 2008Sebastian Rodrigo Summary Purpose: Language functional magnetic resonance imaging (fMRI) is used to noninvasively assess hemispheric language specialization as part of the presurgical work-up in temporal lobe epilepsy (TLE). White matter asymmetries on diffusion tensor imaging (DTI) may be related to language specialization as shown in controls and TLE. To refine our understanding of the effect of epilepsy on the structure,function relationships, we focused on the arcuate fasciculus (ArcF) and the inferior occipitofrontal fasciculus (IOF) and tested the relationship between DTI- and fMRI-based lateralization indices in TLE. Methods: fMRI with three language tasks and DTI were obtained in 20 patients (12 right and 8 left TLE). The ArcF, a major language-related tract, and the IOF were segmented bilaterally using probabilistic tractography to obtain fractional anisotropy (FA) lateralization indices. These were correlated with fMRI-based lateralization indices computed in the inferior frontal gyrus (Pearson's correlation coefficient). Results: fMRI indices were left-lateralized in 16 patients and bilateral or right-lateralized in four. In the ArcF, FA was higher on the left than on the right side, reaching significance in right but not in left TLE. We found a positive correlation between ArcF anisotropy and fMRI-based lateralization indices in right TLE (p < 0.009), but not in left TLE patients. No correlation was observed for the IOF. Conclusions: Right TLE patients with more left-lateralized functional activations also showed a leftward-lateralized arcuate fasciculus. The decoupling between the functional and structural indices of the ArcF underlines the complexity of the language network in left TLE patients. [source] Molecular and diffusion tensor imaging of epileptic networksEPILEPSIA, Issue 2008Aimee F. Luat Summary Several studies have shown that seizure-induced cellular and molecular changes associated with chronic epilepsy can lead to functional and structural alterations in the brain. Chronic epilepsy, when medically refractory, may be associated with an expansion of the epileptic circuitry to involve complex interactions between cortical and subcortical neuroanatomical substrates. Progress in neuroimaging has led not only to successful identification of epileptic foci for surgical resection, but also to an improved understanding of the functional and microstructural changes in long-standing epilepsy. Positron emission tomography (PET), functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) are all promising tools that can assist in elucidating the underlying pathophysiology in chronic epilepsy. Studies using PET scanning have demonstrated dynamic changes associated with the evolution from acute to chronic intractable epilepsy. Among these changes are data to support the existence of secondary epileptogenesis in humans. MRI with DTI is a powerful tool which has the ability to characterize microstructural abnormalities in epileptic foci, and to demonstrate the white matter fibers and tracts participating in the epileptic network. In this review, we illustrate how PET and DTI can be applied to depict the functional and microstructural alterations associated with chronic epilepsy. [source] Intellectual abilities and white matter microstructure in development: A diffusion tensor imaging studyHUMAN BRAIN MAPPING, Issue 10 2010Christian K. Tamnes Abstract Higher-order cognitive functions are supported by distributed networks of multiple interconnected cortical and subcortical regions. Efficient cognitive processing depends on fast communication between these regions, so the integrity of the connections between them is of great importance. It is known that white matter (WM) development is a slow process, continuing into adulthood. While the significance of cortical maturation for intellectual development is described, less is known about the relationships between cognitive functions and maturation of WM connectivity. In this cross-sectional study, we investigated the associations between intellectual abilities and development of diffusion tensor imaging (DTI) derived measures of WM microstructure in 168 right-handed participants aged 8,30 years. Independently of age and sex, both verbal and performance abilities were positively related to fractional anisotropy (FA) and negatively related to mean diffusivity (MD) and radial diffusivity (RD), predominantly in the left hemisphere. Further, verbal, but not performance abilities, were associated with developmental differences in DTI indices in widespread regions in both hemispheres. Regional analyses showed relations with both FA and RD bilaterally in the anterior thalamic radiation and the cortico-spinal tract and in the right superior longitudinal fasciculus. In these regions, our results suggest that participants with high verbal abilities may show accelerated WM development in late childhood and a subsequent earlier developmental plateau, in contrast to a steadier and prolonged development in participants with average verbal abilities. Longitudinal data are needed to validate these interpretations. The results provide insight into the neurobiological underpinnings of intellectual development. Hum Brain Mapp, 2010. © 2010 Wiley-Liss, Inc. [source] Microstructural status of ipsilesional and contralesional corticospinal tract correlates with motor skill in chronic stroke patientsHUMAN BRAIN MAPPING, Issue 11 2009Judith D. Schaechter Abstract Greater loss in structural integrity of the ipsilesional corticospinal tract (CST) is associated with poorer motor outcome in patients with hemiparetic stroke. Animal models of stroke have demonstrated that structural remodeling of white matter in the ipsilesional and contralesional hemispheres is associated with improved motor recovery. Accordingly, motor recovery in patients with stroke may relate to the relative strength of CST degeneration and remodeling. This study examined the relationship between microstructural status of brain white matter tracts, indexed by the fractional anisotropy (FA) metric derived from diffusion tensor imaging (DTI) data, and motor skill of the stroke-affected hand in patients with chronic stroke. Voxelwise analysis revealed that motor skill significantly and positively correlated with FA of the ipsilesional and contralesional CST in the patients. Additional voxelwise analyses showed that patients with poorer motor skill had reduced FA of bilateral CST compared to normal control subjects, whereas patients with better motor skill had elevated FA of bilateral CST compared to controls. These findings were confirmed using a DTI-tractography method applied to the CST in both hemispheres. The results of this study suggest that the level of motor skill recovery achieved in patients with hemiparetic stroke relates to microstructural status of the CST in both the ipsilesional and contralesional hemispheres, which may reflect the net effect of degeneration and remodeling of bilateral CST. Hum Brain Mapp, 2009. © 2009 Wiley-Liss, Inc. [source] Resting state sensorimotor functional connectivity in multiple sclerosis inversely correlates with transcallosal motor pathway transverse diffusivityHUMAN BRAIN MAPPING, Issue 7 2008Mark J. Lowe Abstract Recent studies indicate that functional connectivity using low-frequency BOLD fluctuations (LFBFs) is reduced between the bilateral primary sensorimotor regions in multiple sclerosis. In addition, it has been shown that pathway-dependent measures of the transverse diffusivity of water in white matter correlate with related clinical measures of functional deficit in multiple sclerosis. Taken together, these methods suggest that MRI methods can be used to probe both functional connectivity and anatomic connectivity in subjects with known white matter impairment. We report the results of a study comparing anatomic connectivity of the transcallosal motor pathway, as measured with diffusion tensor imaging (DTI) and functional connectivity of the bilateral primary sensorimotor cortices (SMC), as measured with LFBFs in the resting state. High angular resolution diffusion imaging was combined with functional MRI to define the transcallosal white matter pathway connecting the bilateral primary SMC. Maps were generated from the probabilistic tracking employed and these maps were used to calculate the mean pathway diffusion measures fractional anisotropy ,FA,, mean diffusivity ,MD,, longitudinal diffusivity ,,1,, and transverse diffusivity ,,2,. These were compared with LFBF-based functional connectivity measures (Fc) obtained at rest in a cohort of 11 multiple sclerosis patients and ,10 age- and gender-matched control subjects. The correlation between ,FA, and Fc for MS patients was r = ,0.63, P < 0.04. The correlation between all subjects ,,2, and Fc was r = 0.42, P < 0.05. The correlation between all subjects ,,2, and Fc was r = ,0.50, P < 0.02. None of the control subject correlations were significant, nor were ,FA,, ,,1,, or ,MD, significantly correlated with Fc for MS patients. This constitutes the first in vivo observation of a correlation between measures of anatomic connectivity and functional connectivity using spontaneous LFBFs. Hum Brain Mapp, 2008. © 2008 Wiley-Liss, Inc. [source] Asynchrony of the early maturation of white matter bundles in healthy infants: Quantitative landmarks revealed noninvasively by diffusion tensor imagingHUMAN BRAIN MAPPING, Issue 1 2008Jessica Dubois Abstract Normal cognitive development in infants follows a well-known temporal sequence, which is assumed to be correlated with the structural maturation of underlying functional networks. Postmortem studies and, more recently, structural MR imaging studies have described qualitatively the heterogeneous spatiotemporal progression of white matter myelination. However, in vivo quantification of the maturation phases of fiber bundles is still lacking. We used noninvasive diffusion tensor MR imaging and tractography in twenty-three 1,4-month-old healthy infants to quantify the early maturation of the main cerebral fascicles. A specific maturation model, based on the respective roles of different maturational processes on the diffusion phenomena, was designed to highlight asynchronous maturation across bundles by evaluating the time-course of mean diffusivity and anisotropy changes over the considered developmental period. Using an original approach, a progression of maturation in four relative stages was determined in each tract by estimating the maturation state and speed, from the diffusion indices over the infants group compared with an adults group on one hand, and in each tract compared with the average over bundles on the other hand. Results were coherent with, and extended previous findings in 8 of 11 bundles, showing the anterior limb of the internal capsule and cingulum as the most immature, followed by the optic radiations, arcuate and inferior longitudinal fascicles, then the spinothalamic tract and fornix, and finally the corticospinal tract as the most mature bundle. Thus, this approach provides new quantitative landmarks for further noninvasive research on brain-behavior relationships during normal and abnormal development. Hum Brain Mapp, 2008. © 2007 Wiley-Liss, Inc. [source] Isotropic resolution diffusion tensor imaging with whole brain acquisition in a clinically acceptable timeHUMAN BRAIN MAPPING, Issue 4 2002Derek Kenton Jones Abstract Our objective was to develop a diffusion tensor MR imaging pulse sequence that allows whole brain coverage with isotropic resolution within a clinically acceptable time. A single-shot, cardiac-gated MR pulse sequence, optimized for measuring the diffusion tensor in human brain, was developed to provide whole-brain coverage with isotropic (2.5 × 2.5 × 2.5 mm) spatial resolution, within a total imaging time of approximately 15 min. The diffusion tensor was computed for each voxel in the whole volume and the data processed for visualization in three orthogonal planes. Anisotropy data were further visualized using a maximum-intensity projection algorithm. Finally, reconstruction of fiber-tract trajectories i.e., ,tractography' was performed. Images obtained with this pulse sequence provide clear delineation of individual white matter tracts, from the most superior cortical regions down to the cerebellum and brain stem. Because the data are acquired with isotropic resolution, they can be reformatted in any plane and the sequence can therefore be used, in general, for macroscopic neurological or psychiatric neuroimaging investigations. The 3D visualization afforded by maximum intensity projection imaging and tractography provided easy visualization of individual white matter fasciculi, which may be important sites of neuropathological degeneration or abnormal brain development. This study has shown that it is possible to obtain robust, high quality diffusion tensor MR data at 1.5 Tesla with isotropic resolution (2.5 × 2.5 × 2.5 mm) from the whole brain within a sufficiently short imaging time that it may be incorporated into clinical imaging protocols. Hum. Brain Mapping 15:216,230, 2002. © 2002 Wiley-Liss, Inc. [source] Generalized Diffusion Tensor Imaging (GDTI): A Method for Characterizing and Imaging Diffusion Anisotropy Caused by Non-Gaussian DiffusionISRAEL JOURNAL OF CHEMISTRY, Issue 1-2 2003Chunlei Liu For non-Gaussian distributed random displacement, which is common in restricted diffusion, a second-order diffusion tensor is incapable of fully characterizing the diffusion process. The insufficiency of a second-order tensor is evident in the limited capability of diffusion tensor imaging (DTI) in resolving multiple fiber orientations within one voxel of human white matter. A generalized diffusion tensor imaging (GDTI) method was recently proposed to solve this problem by generalizing Fick's law to a higher-order partial differential equation (PDE). The relationship between the higher-order tensor coefficients of the PDE and the higher-order cumulants of the random displacement can be derived. The statistical property of the diffusion process was fully characterized via the higher-order tensor coefficients by reconstructing the probability density function (PDF) of the molecular random displacement. Those higher-order tensor coefficients can be measured using conventional diffusion-weighted imaging or spectroscopy techniques. Simulations demonstrated that this method was capable of quantitatively characterizing non-Gaussian diffusion and accurately resolving multiple fiber orientations. It can be shown that this method is consistent with the q-space approach. The second-order approximation of GDTI was shown to be DTI. [source] Development of axonal pathways in the human fetal fronto-limbic brain: histochemical characterization and diffusion tensor imagingJOURNAL OF ANATOMY, Issue 4 2010Lana Vasung Abstract The development of cortical axonal pathways in the human brain begins during the transition between the embryonic and fetal period, happens in a series of sequential events, and leads to the establishment of major long trajectories by the neonatal period. We have correlated histochemical markers (acetylcholinesterase (AChE) histochemistry, antibody against synaptic protein SNAP-25 (SNAP-25-immunoreactivity) and neurofilament 200) with the diffusion tensor imaging (DTI) database in order to make a reconstruction of the origin, growth pattern and termination of the pathways in the period between 8 and 34 postconceptual weeks (PCW). Histological sections revealed that the initial outgrowth and formation of joined trajectories of subcortico-frontal pathways (external capsule, cerebral stalk,internal capsule) and limbic bundles (fornix, stria terminalis, amygdaloid radiation) occur by 10 PCW. As early as 11 PCW, major afferent fibers invade the corticostriatal junction. At 13,14 PCW, axonal pathways from the thalamus and basal forebrain approach the deep moiety of the cortical plate, causing the first lamination. The period between 15 and 18 PCW is dominated by elaboration of the periventricular crossroads, sagittal strata and spread of fibers in the subplate and marginal zone. Tracing of fibers in the subplate with DTI is unsuccessful due to the isotropy of this zone. Penetration of the cortical plate occurs after 24,26 PCW. In conclusion, frontal axonal pathways form the periventricular crossroads, sagittal strata and ,waiting' compartments during the path-finding and penetration of the cortical plate. Histochemistry is advantageous in the demonstration of a growth pattern, whereas DTI is unique for demonstrating axonal trajectories. The complexity of fibers is the biological substrate of selective vulnerability of the fetal white matter. [source] Neuroimaging of cortical development and brain connectivity in human newborns and animal modelsJOURNAL OF ANATOMY, Issue 4 2010Gregory A. Lodygensky Abstract Significant human brain growth occurs during the third trimester, with a doubling of whole brain volume and a fourfold increase of cortical gray matter volume. This is also the time period during which cortical folding and gyrification take place. Conditions such as intrauterine growth restriction, prematurity and cerebral white matter injury have been shown to affect brain growth including specific structures such as the hippocampus, with subsequent potentially permanent functional consequences. The use of 3D magnetic resonance imaging (MRI) and dedicated postprocessing tools to measure brain tissue volumes (cerebral cortical gray matter, white matter), surface and sulcation index can elucidate phenotypes associated with early behavior development. The use of diffusion tensor imaging can further help in assessing microstructural changes within the cerebral white matter and the establishment of brain connectivity. Finally, the use of functional MRI and resting-state functional MRI connectivity allows exploration of the impact of adverse conditions on functional brain connectivity in vivo. Results from studies using these methods have for the first time illustrated the structural impact of antenatal conditions and neonatal intensive care on the functional brain deficits observed after premature birth. In order to study the pathophysiology of these adverse conditions, MRI has also been used in conjunction with histology in animal models of injury in the immature brain. Understanding the histological substrate of brain injury seen on MRI provides new insights into the immature brain, mechanisms of injury and their imaging phenotype. [source] Prospects for progress in diagnostic imagingJOURNAL OF INTERNAL MEDICINE, Issue 4 2000E. J. Potchen Abstract. Potchen EJ (Michigan State University, Michigan, USA). Prospects for progress in diagnostic imaging (Internal Medicine in the 21st Century). J Intern Med 2000; 247: 411,424. New fast-imaging MRI systems designed specifically for cardiac magnetic resonance enable new applications of noninvasive vascular imaging. The use of functional MRI and diffusion tensor imaging to map brain function and structure offers a new dimension to an understanding of the human condition. Clinical applications of functional MRI will influence many specialties including surgery, education, and rehabilitation. Functional imaging has the potential to visualize the regional concentration of specific proteins. This imaging at the level of molecules may be possible by use of a contrast material whose signal is changed by local enzymatic activity. The three-dimensional digital data collected in modern imaging techniques allow for virtual endoscopy in the respiratory, alimentary, and cardiovascular systems. Virtual endoscopy may replace many of the more invasive diagnostic methods in the near future. The measurement of clinical decision-making through observer performance studies better informs both the physician and the patient on how to improve upon the quality of clinical practice. These prospects for progress reinforce diagnostic imaging as a cornerstone in medical informatics. The history of creating images used in medicine reveals the invention of diagnostic tools which may provide new information but premature use can result in improper application of a poorly understood technology. Research into the use of new technology may be as important as the technology itself in improving the human condition. [source] In vivo vascular hallmarks of diffuse leukoaraiosisJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2010Jinsoo Uh PhD Abstract Purpose: To characterize multiple patterns of vascular changes in leukoaraiosis using in vivo magnetic resonance imaging (MRI) techniques. Materials and Methods: We measured cerebral blood flow (CBF), cerebrovascular reactivity (CVR), and blood,brain-barrier (BBB) leakage in a group of 33 elderly subjects (age: 72.3 ± 6.8 years, 17 males, 16 females). Leukoaraiosis brain regions were identified in each subject using fluid-attenuated inversion-recovery (FLAIR) MRI. Vascular parameters in the leukoaraiosis regions were compared to those in the normal-appearing white matter (NAWM) regions. Vascular changes in leukoaraiosis were also compared to structural damage as assessed by diffusion tensor imaging. Results: CBF and CVR in leukoaraiosis regions were found to be 39.7 ± 5.2% (P < 0.001) and 52.5 ± 11.6% (P = 0.005), respectively, of those in NAWM. In subjects who did not have significant leukoaraiosis, CBF and CVR in regions with high risk for leukoaraiosis showed a slight reduction compared to the other white matter regions. Significant BBB leakage was also detected (P = 0.003) in leukoaraiosis and the extent of BBB leakage was positively correlated with mean diffusivity. In addition, CVR in NAWM was lower than that in white matter of subjects without significant leukoaraiosis. Conclusion: Leukoaraiosis was characterized by reduced CBF, CVR, and a leakage in the BBB. J. Magn. Reson. Imaging 2010;32:184,190. © 2010 Wiley-Liss, Inc. [source] | ||||||||||||||||||||||||||||||||||