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Background: Cognitive impairment (CI) cannot be diagnosed by magnetic resonance imaging (MRI). Functional magnetic resonance imaging (fMRI) paradigms, such as the immediate/delayed memory task (I/DMT), detect varying degrees of working memory (WM). Preliminary findings using I/DMT showed differences in blood oxygenation level dependent (BOLD) activation between impaired (MSCI, n = 12) and non-impaired (MSNI, n = 9) multiple sclerosis (MS) patients., Objectives: The aim of the study was to confirm CI detection based on I/DMT BOLD activation in a larger cohort of MS patients. The role of T2 lesion volume (LV) and Expanded Disability Status Scale (EDSS) in magnitude of BOLD signal was also sought., Methods: A total of 50 patients (EDSS mean ( m) = 3.2, disease duration (DD) m = 12 years, and age m = 40 years) underwent the Minimal Assessment of Cognitive Function in Multiple Sclerosis (MACFIMS) and I/DMT. Working memory activation (WMa) represents BOLD signal during DMT minus signal during IMT. CI was based on MACFIMS., Results: A total of 10 MSNI, 30 MSCI, and 4 borderline patients were included in the analyses. Analysis of variance (ANOVA) showed MSNI had significantly greater WMa than MSCI, in the left prefrontal cortex and left supplementary motor area ( p = 0.032). Regression analysis showed significant inverse correlations between WMa and T2 LV/EDSS in similar areas ( p = 0.005, 0.004, respectively)., Conclusion: I/DMT-based BOLD activation detects CI in MS. Larger studies are needed to confirm these findings.

Purpose: The vertical-occipital fasciculus (VOF), historically named as "the fasciculus occipitalis verticalis of Wernicke," has been recently brought to the attention of the neuroscience community. In this study, we delineated and quantified this tract with deterministic diffusion tensor imaging protocol., Methods: Five (all males aged 24-37 years) and 10 (7 males and 3 females aged 20-51 years) right-handed healthy subjects were studied with 1 and 2 mm DT-MRI data sets, respectively. The DTI attributes of this pathway along with its cortical representation (Brodmann areas) were presented in standard Montréal Neurological Institute space. Nearby pathways such as inferior fronto-occipital (IFOF) and inferior longitudinal fasciculi (ILF) were used as reference pathways., Results: The total volume of VOF has been found to be approximately .8-1% of whole brain in both data sets. The fractional anisotropy and axial diffusivity of this tract have been found to be relatively 10-15% lower than adjacent pathways such as IFOF and ILF in both data sets. Although IFOF and ILF showed somewhat leftward asymmetry in diffusivity, no right-left asymmetry has been observed in VOF., Conclusion: We believe that our work will pave the way for future imaging studies investigating VOF in different conditions such as stroke, traumatic brain injury, and multiple sclerosis., (Copyright © 2015 by the American Society of Neuroimaging.)

The major language pathways such as superior longitudinal fasciculus (SLF) pathways have been outlined by experimental and diffusion tensor imaging (DTI) studies. The SLF I and some of the superior parietal lobule connections of the SLF pathways have not been depicted by prior DTI studies due to the lack of imaging sensitivity and adequate spatial resolution. In the current study, the trajectory of the SLF fibers has been delineated on five healthy human subjects using diffusion tensor tractography on a 3.0-T scanner at high spatial resolution. We also demonstrate for the first time the trajectory and connectivity of the SLF fibers in relation to other language pathways as well as the superior parietal lobule connections of the language circuit using high spatial resolution DTI in the healthy adult human brain.

Previous neuroimaging studies have shown that working memory load has marked effects on regional neural activation. However, the mechanism through which working memory load modulates brain connectivity is still unclear. In this study, this issue was addressed using dynamic causal modeling (DCM) based on functional magnetic resonance imaging (fMRI) data. Eighteen normal healthy subjects were scanned while they performed a working memory task with variable memory load, as parameterized by two levels of memory delay and three levels of digit load (number of digits presented in each visual stimulus). Eight regions of interest, i.e., bilateral middle frontal gyrus (MFG), anterior cingulate cortex (ACC), inferior frontal cortex (IFC), and posterior parietal cortex (PPC), were chosen for DCM analyses. Analysis of the behavioral data during the fMRI scan revealed that accuracy decreased as digit load increased. Bayesian inference on model structure indicated that a bilinear DCM in which memory delay was the driving input to bilateral PPC and in which digit load modulated several parieto-frontal connections was the optimal model. Analysis of model parameters showed that higher digit load enhanced connection from L PPC to L IFC, and lower digit load inhibited connection from R PPC to L ACC. These findings suggest that working memory load modulates brain connectivity in a parieto-frontal network, and may reflect altered neuronal processes, e.g., information processing or error monitoring, with the change in working memory load. Hum Brain Mapp, 2012. © 2011 Wiley Periodicals, Inc., (Copyright © 2011 Wiley Periodicals, Inc.)

Several in vivo quantitative MRI techniques have been proposed as surrogate measures to map iron content in the human brain. The majority of in vivo quantitative MRI iron mapping methods used the age-dependent iron content data based on postmortem data. In this work, we fused atlas-based human brain volumetry obtained on a large cohort of healthy adults using FreeSurfer with T(2) relaxation time measurements. We provide a brain atlas-based T(2) relaxation time map, which was subsequently used along with published postmortem iron content data to obtain a map of iron content in subcortical and cortical gray matter. We have also investigated the sensitivity of the linear model relating transverse relaxation rate with published iron content to the number of regions used. Our work highlights the challenges encountered on using the simple model along with postmortem data to infer iron content in several brain regions where postmortem iron data are scant (e.g., corpus callosum, amygdale)., (Copyright © 2011 Wiley Periodicals, Inc.)

In this work, we present a framework to fuse and quantify tissue microstructural attributes (e.g. diffusion, functional, relaxation and perfusion MRI) using high spatial resolution T1-weighted volumetric measurements. The proposed computational procedures can be implemented by utilizing advanced, image segmentation, registration and diffusion tensor image processing software. Feasibility of the framework is also demonstrated using in-house developed software and freely available software such as FreeSurfer for regional tissue segmentation, Advanced Normalization Tools (ANTs) for registration and DTIStudio for fiber tracking and diffusion tensor data processing. We also demonstrate the application of these methods in the provision of quality control measures to assess the fidelity of tissue segmentation and multi-modal MRI registration., (2010 Elsevier Ltd. All rights reserved.)

In this work we provide an up-to-date short review of computational magnetic resonance imaging (MRI) and software tools that are widely used to process and analyze diffusion-weighted MRI data. A review of different methods used to acquire, model and analyze diffusion-weighted imaging data (DWI) is first provided with focus on diffusion tensor imaging (DTI). The major preprocessing, processing and post-processing procedures applied to DTI data are discussed. A list of freely available software packages to analyze diffusion MRI data is also provided., (2010 Elsevier Ltd. All rights reserved.)

Microstructural metrics obtained using magnetic resonance imaging (MRI) such as transverse relaxation time and radial diffusivity have been used as in vivo markers of human brain tissue integrity. Considering the sensitivity of these parameters to some common biophysical contributors and their structural and spatial heterogeneity, we hypothesized that strong inter and intra-regional associations exist between these variables providing evidence to possible interplay between transverse relaxation time and radial diffusivity. To validate our hypothesis we obtained high resolution anatomical T1-weighted data and fused it with T2-relaxometry and diffusion tensor imaging (DTI) data on a cohort of healthy adults. The anatomical data were parcellated using FreeSurfer and then coaligned and fused with the T2 and DTI maps. Our data reveal some association between transverse relaxation and radial diffusivity that may help toward the interpretation and modeling of the biophysical contributors to the measured MRI metrics., (Copyright © 2011 Elsevier Inc. All rights reserved.)

In this communication, we extended a previously described and validated diffusion tensor imaging (DTI) method for segmenting whole brain cerebrospinal fluid (CSF) and gray and white matter (WM) tissue to provide regional volume and DTI metrics of WM tract and cortical and subcortical gray matter. This DTI-based regional segmentation was implemented using the statistical parametric mapping (SPM) toolbox and used the international consortium for brain mapping atlases and Montreal Neurological Institute brain templates. We used our DTI-based segmentation approach to calculate the left putamen volume in a cohort of 136 healthy right-handed males and females aged 15.8-62.8 years. We validated our approach by demonstrating its sensitivity to age-related changes of the putamen. Indeed, our method found that the putamen volume decreased with age (r = -0.30; P < 0.001) while the corresponding fractional anisotropy (FA) increased with advancing age (r = 0.5; P < 0.00001). It is then demonstrated, on a subset of our cohort (n = 31), that the putamen volume obtained by our method correlated with measurements obtained from FreeSurfer (r = 0.396, P < 0.05). Our novel approach increases the information obtained with a DTI examination by providing routine volumetry measure, thereby eliminating separate scans to obtain volumetry data. In addition, the labeled volumes obtained with our method have the potential to increase the accuracy of fiber tracking. In the future, this new approach can be automated to analyze large data sets to help discover noninvasive neuroimaging markers for clinical trials and brain-function studies in both health and disease., (Hum Brain Mapp, 2010. © 2010 Wiley-Liss, Inc.)

Purpose: To investigate the utility of diffusion tensor tractography at 1mm slice thickness to map and quantify the whole trajectory of different cortico-ponto-cerebellar pathways of the healthy adult human brain., Materials and Methods: This work was approved by the local Institutional Review Board, and was Health Insurance Portability and Accountability Act (HIPAA) compliant. Five healthy right-handed men (age range, 24-37 years) were studied and written informed consent was obtained. Diffusion tensor imaging data acquired with 1-mm slice thickness at a 3.0 Tesla (T) clinical MRI scanner were prepared and analyzed using tractography methods to reconstruct the cortico-ponto-cerebellar pathways which included the fronto-ponto-cerebellar, parieto-ponto-cerebellar, occipito-ponto-cerebellar, and temporo-ponto-cerebellar tracts., Results: We demonstrate the feasibility of tractographic mapping and quantification of the four cortico-ponto-cerebellar system components based on their cortical connections in the healthy human brain using DTI data with thin 1-mm sections., Conclusion: In vivo quantification of different cortico-ponto-cerebellar pathways based on cortical connection is feasible, using 1-mm slices at 3.0T.

Mapping the human brain frontostriatal pathways using noninvasive diffusion tensor imaging (DTI) has been hampered by the inadequate imaging sensitivity, poor spatial resolution, lower tensor anisotropy within gray matter, increased partial volume averaging effects and poor signal-to-noise ratio. We investigated for the first time the utility of high spatial resolution DTI-based fiber-tractography using the fiber assignment by continuous tracking (FACT) to reconstruct and quantify bilaterally the prefronto-caudo-thalamic connections within the human brain at 3T. Five healthy right-handed men (age range 24-37 years) were studied. We traced the anterior thalamic radiation and prefronto-caudo-thalamic pathways bilaterally and measured the volume of each tract and the corresponding diffusion tensor metrics in all subjects. The anterior thalamic radiation tract volume and corresponding fractional anisotropy (FA) were significantly larger bilaterally than prefronto-caudate pathway, whereas the mean diffusivity (D(av)) values were similar (p>0.7). For both anterior thalamic radiation and prefronto-caudate pathway the tract volume and corresponding DTI metrics (FA, D(av)) were not significantly different between the two hemispheres (p>0.2). Our DTI acquisition protocol and analysis permitted the reconstruction of the connectivity of the caudate with the thalamus as well as with the prefrontal cortex and allowed tracking of the whole trajectory of the prefronto-caudo-thalamic pathway., (Copyright (c) 2010 Elsevier B.V. All rights reserved.)

In this study of a cohort of 33 young and middle-age adults (19-59 years) we report simultaneous measurements of normal age-related changes in the caudate nuclei volume, diffusion tensor metrics, and T(2) relaxation time. Both the absolute caudate volume and its ratio relative to the total intracranial volume decreased rapidly with age in both men and women (r = -0.55; P < 0.001). The fractional diffusion tensor anisotropy of the caudate nuclei increased with age in both males and females (r = 0.48; P = 0.005). The corresponding age correlations of the caudate axial (r = 0.17; P = 0.35), transverse (r = -0.12; P = 0.50), mean diffusivities (r = 0.018; P = 0.92), and T(2) relaxation times (r = 0.194; P = 0.28) were weaker and did not reach statistical significance (P > 0.05). Our preliminary findings warrant further studies on the older and aging adults and indicate that caudate diffusion tensor imaging-derived metrics can be used as surrogates in modeling the neuronal substrates of gray matter atrophy., (2007 Wiley-Liss, Inc)

We used a diffusion tensor imaging-based whole-brain tissue segmentation to characterize age-related changes in (a) whole-brain grey matter, white matter, and cerebrospinal fluid relative to intracranial volume and (b) the corresponding brain tissue microstructure using measures of diffusion tensor anisotropy and mean diffusivity. The sample, a healthy cohort of 119 right-handed males and females aged 7-68 years. Our results demonstrate that white matter and grey matter volumes and their corresponding diffusion tensor anisotropy and mean diffusivity follow nonlinear trajectories with advancing age. In contrast, cerebrospinal fluid volume increases linearly with age.

Fractional anisotropy (FA) and relative anisotropy (RA) are the two most commonly used scalar measures of anisotropy in diffusion tensor (DT) MRI. While a few published studies have shown that FA has superior noise immunity relative to RA, no theoretical basis has been proposed to explain this behavior. In the current study, the diffusion tensor invariants were used to derive a simple analytical expression that directly relates RA and FA. An analysis based on that analytical expression demonstrated that the FA images have a higher signal-to-noise ratio (SNR) than RA for any value of tensor anisotropy RA or FA > 0. This theoretical behavior was verified using both Monte Carlo simulations and bootstrap analysis of DT-MRI data acquired in a spherical water phantom and normal human subjects., (Copyright 2004 Wiley-Liss, Inc.)

Diffusion tensor MRI (DT-MRI) is a promising modality for in vivo mapping of the organization of deep tissues. The most commonly used DT-MRI invariant maps are the mean diffusivity, mu(D), relative anisotropy (RA), and fractional anisotropy (FA). Because of the computational burden, anisotropy maps are generally computed offline. The availability of a simple procedure to compute RA, FA, and mu(D) online would make DT-MRI more useful in clinical applications that require immediate feedback. In this study, analytical expressions that relate the commonly used tensor anisotropy measures obtained from the decoded and diagonalized DT with those obtained from the first and second moments of the measured diffusion-weighted (DW) data are derived. Specifically, it is shown that for the principal icosahedron encoding scheme, RA is related to the mean and standard deviation (SD) of the DW measurements that can be computed online. Since FA is commonly used as an anisotropy measure, an analytical expression relating RA and FA was derived from the tensor invariants. These results were validated using both Monte Carlo simulations and high-resolution, normal whole-brain DT-MRI measurements acquired with different b-factors, encoding schemes, and signal-to-noise ratio (SNR) levels. The bias introduced by the rotationally variant encoding schemes into the diffusion measures is also investigated., (Copyright 2003 Wiley-Liss, Inc.)

Diffusion tensor MRI provides unique directional diffusion information that can be used to estimate the patterns of white matter connectivity in the human brain. In this study, the behavior of an algorithm for white matter tractography is examined. The algorithm, called TEND, uses the entire diffusion tensor to deflect the estimated fiber trajectory. Simulations and imaging experiments on in vivo human brains were performed to investigate the behavior of the tractography algorithm. The simulations show that the deflection term is less sensitive than the major eigenvector to image noise. In the human brain imaging experiments, estimated tracts were generated in corpus callosum, corticospinal tract, internal capsule, corona radiata, superior longitudinal fasciculus, inferior longitudinal fasciculus, fronto-occipital fasciculus, and uncinate fasciculus. This approach is promising for mapping the organizational patterns of white matter in the human brain as well as mapping the relationship between major fiber trajectories and the location and extent of brain lesions., (Copyright 2003 Wiley-Liss, Inc.)

Chronic cocaine and alcohol use impart significant stress on biological and cognitive systems, resulting in changes consistent with an allostatic load model of neurocognitive impairment. The present study measured potential markers of allostatic load in individuals with comorbid cocaine/alcohol use disorders (CUD/AUD) and control subjects. Measures of brain white matter (WM), telomere length, and impulsivity/attentional bias were obtained. WM (CUD/AUD only) was indexed by diffusion tensor imaging metrics, including radial diffusivity (RD) and fractional anisotropy (FA). Telomere length was indexed by the telomere to single copy gene (T/S) ratio. Impulsivity and attentional bias to drug cues were measured via eye-tracking, and were also modeled using the Hierarchical Diffusion Drift Model (HDDM). Average whole-brain RD and FA were associated with years of cocaine use (R2 = 0.56 and 0.51, both p < .005) but not years of alcohol use. CUD/AUD subjects showed more anti-saccade errors (p < .01), greater attentional bias scores (p < .001), and higher HDDM drift rates on cocaine-cue trials (Bayesian probability CUD/AUD > control = p > 0.99). Telomere length was shorter in CUD/AUD, but the difference was not statistically significant. Within the CUD/AUD group, exploratory regression using an elastic-net model determined that more years of cocaine use, older age, larger HDDM drift rate differences and shorter telomere length were all predictive of WM as measured by RD (model R2 = 0.79). Collectively, the results provide modest support linking CUD/AUD to putative markers of allostatic load. [ABSTRACT FROM AUTHOR]

The human limbic system is composed of gray and white matter structures which have been known to have a role in core processes such as motivation, memory, emotion, social behavior, self-awareness as well as certain primitive instincts. Multiple functional studies investigated some of these brain tasks in human brain limbic system. However, the underlying fine fiber pathways of the limbic system including the trajectory of the stria terminalis have not been delineated separately by prior diffusion weighted imaging. The ability to trace the underlying fiber anatomy noninvasively using diffusion tensor tractography (DTT) would be helpful to study the neurophysiology of these tracts in different functions in future functional studies. Few studies have focused on the stria terminalis using diffusion tensor tractography. Yet, the trajectory of the stria terminalis and some fine subtrajectories of the fornix have not been elucidated by prior DTT studies. We decided to further investigate these fine neuronal trajectory using tractography and high spatial resolution diffusion tensor imaging on 3T. Fifteen healthy right-handed men (age range 24–37 years) were studied. We delineated the detailed trajectories of the stria terminalis and fornix bilaterally in fifteen normal adult human brains. Using a high resolution DTT technique, we demonstrate for the first time, the trajectory of stria terminalis as well as detailed precommissural and postcommissural connectivity of the forniceal columns. [ABSTRACT FROM AUTHOR]