Corpus callosal diffusivity predicts motor impairment in relapsing–remitting multiple sclerosis: A TBSS and tractography study

Improvement of the thalamocortical white matter network in people with stable treated relapsing-remitting multiple sclerosis over time

Advanced imaging techniques (tractography) enable the mapping of white matter (WM) pathways and the understanding of brain connectivity patterns. We combined tractography with a network-based approach to examine WM microstructure on a network level in people with relapsing-remitting multiple sclerosis (pw-RRMS) and healthy controls (HCs) over 2 years. Seventy-six pw-RRMS matched with 43 HCs underwent clinical assessments and 3T MRI scans at baseline (BL) and 2-year follow-up (2-YFU). Probabilistic tractography was performed, accounting for the effect of lesions, producing connectomes of 25 million streamlines. Network differences in fibre density across pw-RRMS and HCs at BL and 2-YFU were quantified using network-based statistics (NBS). Longitudinal network differences in fibre density were quantified using NBS in pw-RRMS, and were tested for correlations with disability, cognition and fatigue scores. Widespread network reductions in fibre density were found in pw-RRMS compared with HCs at BL in cortical regions, with more reductions detected at 2-YFU. Pw-RRMS had reduced fibre density at BL in the thalamocortical network compared to 2-YFU. This effect appeared after correction for age, was robust across different thresholds, and did not correlate with lesion volume or disease duration. Pw-RRMS demonstrated a robust and long-distance improvement in the thalamocortical WM network, regardless of age, disease burden, duration or therapy, suggesting a potential locus of neuroplasticity in MS. This network's role over the disease's lifespan and its potential implications in prognosis and treatment warrants further investigation.

A Novel Sensory Wave (P25) in Myelin Oligodendrocyte Glycoprotein-induced Experimental Autoimmune Encephalomyelitis Murine Model

Myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE) is a murine model for multiple sclerosis. This model is characterized by chronic and progressive demyelination, leading to impairment of motor function and paralysis. While the outcomes of the disease, including impaired motor function and immunological changes, are well-characterized, little is known about the impact of EAE on the electrophysiology of the motor and sensory systems. In this study, we assessed evoked potentials as a quantitative marker for in vivo monitoring of nervous system damage. Motor-evoked potentials (MEPs) and sensory-evoked potentials (SEPs) were first standardized in naïve C57BL mice and studied thoroughly in EAE mice. The duration of MEPs and the number of connotative potentials increased significantly alongside an increase in temporal SEP amplitudes. Moreover, a new SEP wave was identified in naïve animals, which significantly increased in MOG-induced EAE animals with no or mild symptoms (clinical score 0-2, 0-5 scale). This wave occurred ∼25 milliseconds poststimulation, thus named p25. P25 was correlated with increased vocalization and was also reduced in amplitude following treatment with morphine. As the EAE score progressed (clinical score 3-4, 0-5 scale), the amplitude of MEPs and SEPs decreased drastically. Our results demonstrate that desynchronized neural motor activity, along with hypersensitivity in the early stages of EAE, leads to a complete loss of motor and sensory functions in the late stages of the disease. The findings also suggest an increase in p25 amplitude before motor deficits appear, indicating SEP as a predictive marker for disease progression. PERSPECTIVE: This article assesses p25, a new sensory electrophysiology wave that correlates with pain-related behavior in MOG-induced EAE mice and appears prior to the clinical symptoms. Motor electrophysiology correlates with traditional motor behavior scoring and histology.

Associations between corpus callosum damage, clinical disability, and surface-based homologous inter-hemispheric connectivity in multiple sclerosis

Axonal damage in the corpus callosum is prevalent in multiple sclerosis (MS). Although callosal damage is associated with disrupted functional connectivity between hemispheres, it is unclear how this relates to cognitive and physical disability. We investigated this phenomenon using advanced measures of microstructural integrity in the corpus callosum and surface-based homologous inter-hemispheric connectivity (sHIC) in the cortex. We found that sHIC was significantly decreased in primary motor, somatosensory, visual, and temporal cortical areas in a group of 36 participants with MS (29 relapsing-remitting, 4 secondary progressive MS, and 3 primary-progressive MS) compared with 42 healthy controls (cluster level, p < 0.05). In participants with MS, global sHIC correlated with fractional anisotropy and restricted volume fraction in the posterior segment of the corpus callosum (r = 0.426, p = 0.013; r = 0.399, p = 0.020, respectively). Lower sHIC, particularly in somatomotor and posterior cortical areas, was associated with cognitive impairment and higher disability scores on the Expanded Disability Status Scale (EDSS). We demonstrated that higher levels of sHIC attenuated the effects of posterior callosal damage on physical disability and cognitive dysfunction, as measured by the EDSS and Brief Visuospatial Memory Test-Revised (interaction effect, p < 0.05). We also observed a positive association between global sHIC and years of education (r = 0.402, p = 0.018), supporting the phenomenon of "brain reserve" in MS. Our data suggest that preserved sHIC helps prevent cognitive and physical decline in MS.

Performance in information processing speed is associated with parietal white matter tract integrity in multiple sclerosis

Background

The Symbol Digit Modalities Test (SDMT) is most frequently used to test processing speed in patients with multiple sclerosis (MS). Functional imaging studies emphasize the importance of frontal and parietal areas for task performance, but the influence of frontoparietal tracts has not been thoroughly studied. We were interested in tract-specific characteristics and their association with processing speed in MS patients.

Methods

Diffusion tensor imaging was obtained in 100 MS patients and 24 healthy matched controls to compare seed-based tract characteristics descending from the superior parietal lobule [Brodman area 7A (BA7A)], atlas-based tract characteristics from the superior longitudinal fasciculus (SLF), and control tract characteristics from the corticospinal tract (CST) and their respective association with ability on the SDMT.

Results

Patients had decreased performance on the SDMT and decreased white matter volume (each p &lt; 0.05). The mean fractional anisotropy (FA) for the BA7A tract and CST (p &lt; 0.05), but not the SLF, differed between MS patients and controls. Furthermore, only the FA of the SLF was positively associated with SDMT performance even after exclusion of the lesions within the tract (r = 0.25, p &lt; 0.05). However, only disease disability and total white matter volume were associated with information processing speed in a linear regression model.

Conclusions

Processing speed in MS is associated with the structural integrity of frontoparietal white matter tracts.

Combined effects of cerebellar tDCS and task-oriented circuit training in people with multiple sclerosis: A pilot randomized control trial

Background: Balance and mobility impairments are frequent in people with multiple sclerosis, partly due to cerebellar dysfunctions. Task-oriented behavioural approaches were previously shown to promote physical function. The possibility exists that cerebellar transcranial direct current stimulation (ctDCS) applied during training, known to increase the excitability of the brain, can boost rehabilitation effects through modulation of cerebellum-brain inhibition. Objective: To test the efficacy of cerebellar ctDCS stimulation combined with motor training on mobility and balance in people with multiple sclerosis. Methods: 16 subjects were randomly assigned to receive real- or sham-ctDCS and task-oriented training daily over two weeks in a double-blind, randomised clinical pilot trial. Functional mobility, balance, walking performance and quality of life were tested before and after treatment and at two-week follow-up. Effects of cerebellar stimulation on psychological and executive functions were also recorded. Results: Walking performance, balance and quality of life improved for both groups at post-treatment assessment which was maintained at 2-weeks follow up. A two-way ANOVA revealed a significant time effect for balance and walking performance. A significant interaction effect of time–treatment (F = 3.12, df = 2,26; p = 0.03) was found for motor aspects of quality of life assessment in patients who received real-ctDCS. Conclusions: Task-oriented training improves balance and mobility in people with multiple sclerosis, but ctDCS does not boost motor training effects.

Quantitative mapping of the brain's structural connectivity using diffusion MRI tractography: A review

Diffusion magnetic resonance imaging (dMRI) tractography is an advanced imaging technique that enables in vivo reconstruction of the brain's white matter connections at macro scale. It provides an important tool for quantitative mapping of the brain's structural connectivity using measures of connectivity or tissue microstructure. Over the last two decades, the study of brain connectivity using dMRI tractography has played a prominent role in the neuroimaging research landscape. In this paper, we provide a high-level overview of how tractography is used to enable quantitative analysis of the brain's structural connectivity in health and disease. We focus on two types of quantitative analyses of tractography, including: 1) tract-specific analysis that refers to research that is typically hypothesis-driven and studies particular anatomical fiber tracts, and 2) connectome-based analysis that refers to research that is more data-driven and generally studies the structural connectivity of the entire brain. We first provide a review of methodology involved in three main processing steps that are common across most approaches for quantitative analysis of tractography, including methods for tractography correction, segmentation and quantification. For each step, we aim to describe methodological choices, their popularity, and potential pros and cons. We then review studies that have used quantitative tractography approaches to study the brain's white matter, focusing on applications in neurodevelopment, aging, neurological disorders, mental disorders, and neurosurgery. We conclude that, while there have been considerable advancements in methodological technologies and breadth of applications, there nevertheless remains no consensus about the "best" methodology in quantitative analysis of tractography, and researchers should remain cautious when interpreting results in research and clinical applications.

MRI of Transcallosal White Matter Helps to Predict Motor Impairment in Multiple Sclerosis

Background Altered callosal integrity has been associated with motor deficits in patients with multiple sclerosis (MS), but its contribution to disability has, to the knowledge of the authors, not been investigated by using multiparametric MRI approaches. Purpose To investigate structural and functional interhemispheric MRI substrates of global disability at different milestones and upper limb motor impairment in MS. Materials and Methods In this cross-sectional study, healthy control patients and patients with MS (between January 1, 2008, and December 31, 2016) were retrospectively selected from our hospital database. Clinical assessment included Expanded Disability Status Scale (EDSS), nine-hole peg test, and digital finger tapping test. By using structural and resting-state functional MRI sequences, probabilistic tractography of hand corticospinal tract fibers, and transcallosal fibers between hand-motor cortices (hereafter, referred to as hand-M1), supplementary motor areas (SMAs), premotor cortices (PMCs), and voxel-mirror homotopic connectivity (VMHC) were analyzed. Random forest analyses identified the MRI predictors of clinical disability at different milestones (EDSS scores of 3.0, 4.0, 6.0) and upper limb motor impairment (nine-hole peg test and finger tapping test z scores < healthy control patients 5th percentile). Results One-hundred thirty healthy control patients (median age, 39 years; interquartile range, 31-50 years; 70 women) and 340 patients with MS (median age, 43 years; interquartile range, 33-51 years; 213 women) were studied. EDSS 3.0 predictors (n = 159) were global measures of atrophy and lesions together with damage measures of corticospinal tracts and transcallosal fibers between PMCs and SMAs (accuracy, 86%; P = .001-.01). For EDSS 4.0 (n = 131), similar predictors were found in addition to damage in transcallosal fibers between hand-M1 (accuracy, 89%; P = .001-.049). No MRI predictors were found for EDSS 6.0 (n = 70). Nine-hole peg test (right, n = 161; left, n = 166) and finger tapping test (right, n = 117; left, n = 111) impairments were predicted by damage in transcallosal fibers between SMAs and PMCs (accuracy range, 69%-77%; P = .001-.049). VMHC abnormalities did not explain clinical outcomes. Conclusion Structural, not functional, abnormalities at MRI in transcallosal premotor and motor white matter fibers predicted severity of global disability and upper limb motor impairment in patients with multiple sclerosis. The informative role of such predictors appeared less evident at higher disability levels. © RSNA, 2021 Online supplemental material is available for this article. See also the editorial by Barkhof and Pontillo in this issue.

Axonal loss in major sensorimotor tracts is associated with impaired motor performance in minimally disabled multiple sclerosis patients

Multiple sclerosis is a neuroinflammatory disease of the CNS that is associated with significant irreversible neuro-axonal loss, leading to permanent disability. There is thus an urgent need for in vivo markers of axonal loss for use in patient monitoring or as end-points for trials of neuroprotective agents. Advanced diffusion MRI can provide markers of diffuse loss of axonal fibre density or atrophy within specific white matter pathways. These markers can be interrogated in specific white matter tracts that underpin important functional domains such as sensorimotor function. This study aimed to evaluate advanced diffusion MRI markers of axonal loss within the major sensorimotor tracts of the brain, and to correlate the degree of axonal loss in these tracts to precise kinematic measures of hand and foot motor control and gait in minimally disabled people with multiple sclerosis. Twenty-eight patients (Expanded Disability Status Scale < 4, and Kurtzke Functional System Scores for pyramidal and cerebellar function ≤ 2) and 18 healthy subjects underwent ultra-high field 7 Tesla diffusion MRI for calculation of fibre-specific measures of axonal loss (fibre density, reflecting diffuse axonal loss and fibre cross-section reflecting tract atrophy) within three tracts: cortico-spinal tract, interhemispheric sensorimotor tract and cerebello-thalamic tracts. A visually guided force-matching task involving either the hand or foot was used to assess visuomotor control, and three-dimensional marker-based video tracking was used to assess gait. Fibre-specific axonal markers for each tract were compared between groups and correlated with visuomotor task performance (force error and lag) and gait parameters (stance, stride length, step width, single and double support) in patients. Patients displayed significant regional loss of fibre cross-section with minimal loss of fibre density in all tracts of interest compared to healthy subjects (family-wise error corrected p-value < 0.05), despite relatively few focal lesions within these tracts. In patients, reduced axonal fibre density and cross-section within the corticospinal tracts and interhemispheric sensorimotor tracts were associated with larger force tracking error and gait impairments (shorter stance, smaller step width and longer double support) (family-wise error corrected p-value < 0.05). In conclusion, significant gait and motor control impairments can be detected in minimally disabled people with multiple sclerosis that correlated with axonal loss in major sensorimotor pathways of the brain. Given that axonal loss is irreversible, the combined use of advanced imaging and kinematic markers could be used to identify patients at risk of more severe motor impairments as they emerge for more aggressive therapeutic interventions.

Altered task-induced cerebral blood flow and oxygen metabolism underlies motor impairment in multiple sclerosis

The neural mechanisms underlying motor impairment in multiple sclerosis (MS) remain unknown. Motor cortex dysfunction is implicated in blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) studies, but the role of neural-vascular coupling underlying BOLD changes remains unknown. We sought to independently measure the physiologic factors (i.e., cerebral blood flow (ΔCBF), cerebral metabolic rate of oxygen (ΔCMRO2), and flow-metabolism coupling (ΔCBF/ΔCMRO2), utilizing dual-echo calibrated fMRI (cfMRI) during a bilateral finger-tapping task. We utilized cfMRI to measure physiologic responses in 17 healthy volunteers and 32 MS patients (MSP) with and without motor impairment during a thumb-button-press task in thumb-related (task-central) and surrounding primary motor cortex (task-surround) regions of interest (ROIs). We observed significant ΔCBF and ΔCMRO2 increases in all MSP compared to healthy volunteers in the task-central ROI and increased flow-metabolism coupling (ΔCBF/ΔCMRO2) in the MSP without motor impairment. In the task-surround ROI, we observed decreases in ΔCBF and ΔCMRO2 in MSP with motor impairment. Additionally, ΔCBF and ΔCMRO2 responses in the task-surround ROI were associated with motor function and white matter damage in MSP. These results suggest an important role for task-surround recruitment in the primary motor cortex to maintain motor dexterity and its dependence on intact white matter microstructure and neural-vascular coupling.

Diffusion basis spectrum imaging provides insights into MS pathology

Objective

To use diffusion basis spectrum imaging (DBSI) to assess how damage to normal-appearing white matter (NAWM) in the corpus callosum (CC) influences neurologic impairment in people with MS (pwMS).

Methods

Using standard MRI, the primary pathologies in MS of axonal injury/loss, demyelination, and inflammation are not differentiated well. DBSI has been shown in animal models, phantoms, and in biopsied and autopsied human CNS tissues to distinguish these pathologies. Fifty-five pwMS (22 relapsing-remitting, 17 primary progressive, and 16 secondary progressive) and 13 healthy subjects underwent DBSI analyses of NAWM of the CC, the main WM tract connecting the cerebral hemispheres. Tract-based spatial statistics were used to minimize misalignment. Results were correlated with scores from a battery of clinical tests focused on deficits typical of MS.

Results

Normal-appearing CC in pwMS showed reduced fiber fraction and increased nonrestricted isotropic fraction, with the most extensive abnormalities in secondary progressive MS (SPMS). Reduced DBSI-derived fiber fraction and increased DBSI-derived nonrestricted isotropic fraction of the CC correlated with worse cognitive scores in pwMS. Increased nonrestricted isotropic fraction in the body of the CC correlated with impaired hand function in the SPMS cohort.

Conclusions

DBSI fiber fraction and nonrestricted isotropic fraction were the most useful markers of injury in the NAWM CC. These 2 DBSI measures reflect axon loss in animal models. Because of its ability to reveal axonal loss, as well as demyelination, DBSI may be a useful outcome measure for trials of CNS reparative treatments.

Paternal age contribution to brain white matter aberrations in autism spectrum disorder

AIM

Although advanced parental age holds an increased risk for autism spectrum disorder (ASD), its role as a potential risk factor for an atypical white matter development underlying the pathophysiology of ASD has not yet been investigated. The current study was aimed to detect white matter disparities in ASD, and further investigate the relationship of paternal and maternal age at birth with such disparities.

METHODS

Thirty-nine adult males with high-functioning ASD and 37 typically developing (TD) males were analyzed in the study. The FMRIB Software Library and tract-based spatial statistics were utilized to process and analyze the diffusion tensor imaging data.

RESULTS

Subjects with ASD exhibited significantly higher mean diffusivity (MD) and radial diffusivity (RD) in white matter fibers, including the association (inferior fronto-occipital fasciculus, right inferior longitudinal fasciculus, superior longitudinal fasciculi, uncinate fasciculus, and cingulum), commissural (forceps minor), and projection tracts (anterior thalamic radiation and right corticospinal tract) compared to TD subjects (Padjusted  < 0.05). No differences were seen in either fractional anisotropy or axial diffusivity. Linear regression analyses assessing the relationship between parental ages and the white matter aberrations revealed a positive correlation between paternal age (PA), but not maternal age, and both MD and RD in the affected fibers (Padjusted  < 0.05). Multiple regression showed that only PA was a predictor of both MD and RD.

CONCLUSION

Our findings suggest that PA contributes to the white matter disparities seen in individuals with ASD compared to TD subjects.

Exploratory MRI measures after intravenous autologous culture-expanded mesenchymal stem cell transplantation in multiple sclerosis

Background

Mesenchymal stem cells (MSC) have immunomodulatory and neuro-protective properties and are being studied for treatment of multiple sclerosis (MS). Tractography-based diffusion tensor imaging (DTI), cortical thickness (Cth) and T2 lesion volume (T2LV) can provide insight into treatment effects.

Objective

The objective of this study was to analyse the effects of MSC transplantation in MS on exploratory MRI measures.

Methods

MRIs were obtained from 24 MS patients from a phase 1 open-label study of autologous MSC transplantation. DTI metrics were obtained in lesions and normal-appearing white matter motor tracts (NAWM). T2LV and Cth were derived. Longitudinal evolution of MRI outcomes were modelled using linear mixed effects. Pearson’s correlation was calculated between MRI and clinical measures.

Results

Lesional radial diffusivity (RD) and axial diffusivity (AD) decreased pre-transplant and showed no changes post-transplant. There were mixed trends in NAWM RD and AD pre/post-transplant. Transplantation stabilized T2LV growth. NAWM RD and AD correlated with Cth, T2LV and with leg and arm function but not with cognition. Lesional DTI demonstrated similar but less robust correlations.

Conclusions

Microstructural tissue integrity is altered in MS. DTI changes pre-transplant may be influenced by concomitant lesion accrual. Contributor to DTI stabilization post-transplant is multifactorial. DTI of major motor tracts correlated well with clinical measures, highlighting its sensitivity to clinically meaningful changes.

Diffusion tensor imaging and disability progression in multiple sclerosis: A 4-year follow-up study

OBJECTIVES

Diffusion tensor imaging (DTI) is sensitive technique to detect widespread changes in water diffusivity in the normal-appearing white matter (NAWM) that appears unaffected in conventional magnetic resonance imaging. We aimed to investigate the prognostic value and stability of DTI indices in the NAWM of the brain in an assessment of disability progression in patients with a relapsing-onset multiple sclerosis (MS).

METHODS

Forty-six MS patients were studied for DTI indices (fractional anisotropy (FA), mean diffusivity (MD), radial (RD), and axial (AD) diffusivity) in the NAWM of the corpus callosum (CC) and the internal capsule at baseline and at 1 year after. DTI analysis for 10 healthy controls was also performed at baseline. Simultaneously, focal brain lesion volume and atrophy measurements were done at baseline for MS patients. Associations between DTI indices, volumetric measurements, and disability progression over 4 years were studied by multivariate logistic regression analysis.

RESULTS

At baseline, most DTI metrics differed significantly between MS patients and healthy controls. There was tendency for associations between baseline DTI indices in the CC and disability progression (p < 0.05). Changes in DTI indices over 1 year were observed only in the CC (p < 0.008), and those changes were not found to predict clinical worsening over 4 years. Clear-cut association with disability progression was not detected for baseline volumetric measurements.

CONCLUSION

Aberrant diffusivity measures in the NAWM of the CC may provide additional information for individual disability progression over 4 years in MS with the relapsing-onset disease. CC may be a good target for DTI measurements in monitoring disease activity in MS, and more studies are needed to assess the related prognostic potential.

Brain imaging of locomotion in neurological conditions

Impaired locomotion is a frequent and major source of disability in patients with neurological conditions. Different neuroimaging methods have been used to understand the brain substrates of locomotion in various neurological diseases (mainly in Parkinson's disease) during actual walking, and while resting (using mental imagery of gait, or brain-behavior correlation analyses). These studies, using structural (i.e., MRI) or functional (i.e., functional MRI or functional near infra-red spectroscopy) brain imaging, electrophysiology (i.e., EEG), non-invasive brain stimulation (i.e., transcranial magnetic stimulation, or transcranial direct current stimulation) or molecular imaging methods (i.e., PET, or SPECT) reveal extended brain networks involving both grey and white matters in key cortical (i.e., prefrontal cortex) and subcortical (basal ganglia and cerebellum) regions associated with locomotion. However, the specific roles of the various pathophysiological mechanisms encountered in each neurological condition on the phenotype of gait disorders still remains unclear. After reviewing the results of individual brain imaging techniques across the common neurological conditions, such as Parkinson's disease, dementia, stroke, or multiple sclerosis, we will discuss how the development of new imaging techniques and computational analyses that integrate multivariate correlations in "large enough datasets" might help to understand how individual pathophysiological mechanisms express clinically as an abnormal gait. Finally, we will explore how these new analytic methods could drive our rehabilitative strategies.

Elevated body-mass index is associated with reduced white matter integrity in two large independent cohorts

Obesity has been associated with a variety of neurobiological alterations. Recent neuroimaging research has pointed to the relevance of brain structural and functional alterations in the development of obesity. However, while the role of gray matter atrophy in obesity has been evidenced in several well powered studies, large scale evidence for altered white matter integrity in obese subjects is still absent. With this study, we therefore aimed to investigate potential associations between white matter abnormalities and body mass index (BMI) in two large independent samples of healthy adults. Associations between BMI values and whole brain fractional anisotropy (FA) were investigated in two independent cohorts: A sample of n = 369 healthy subjects from the Münster Neuroimaging Cohort (MNC), as well as a public available sample of n = 1064 healthy subjects of the Humane Connectome Project (HCP) were included in the present study. Tract based spatial statistics (TBSS) analyses of BMI on whole brain FA were conducted including age and sex as nuisance covariates using the FMRIB library (FSL Version 5.0). Threshold-free cluster enhancement was applied to control for multiple comparisons. In both samples higher BMI was significantly associated with strong and widespread FA reductions. These effects were most pronounced in the corpus callosum, bilateral posterior thalamic radiation, bilateral internal capsule and external capsule, bilateral inferior longitudinal fasciculus and inferior fronto-occipital fasciculus. The association was found to be independent of age, sex and other cardiovascular risk factors. No significant positive associations between BMI and FA occurred. With this highly powered study, we provide robust evidence for globally reduced white matter integrity associated with elevated BMI including replication in an independent sample. The present work thus points out the relevance of white matter alterations as a neurobiological correlate of obesity.

How changes in brain activity and connectivity are associated with motor performance in people with MS

People with multiple sclerosis (MS) exhibit pronounced changes in brain structure, activity, and connectivity. While considerable work has begun to elucidate how these neural changes contribute to behavior, the heterogeneity of symptoms and diagnoses makes interpretation of findings and application to clinical practice challenging. In particular, whether MS related changes in brain activity or brain connectivity protect against or contribute to worsening motor symptoms is unclear. With the recent emergence of neuromodulatory techniques that can alter neural activity in specific brain regions, it is critical to establish whether localized brain activation patterns are contributing to (i.e. maladaptive) or protecting against (i.e. adaptive) progression of motor symptoms. In this manuscript, we consolidate recent findings regarding changes in supraspinal structure and activity in people with MS and how these changes may contribute to motor performance. Furthermore, we discuss a hypothesis suggesting that increased neural activity during movement may be either adaptive or maladaptive depending on where in the brain this increase is observed. Specifically, we outline preliminary evidence suggesting sensorimotor cortex activity in the ipsilateral cortices may be maladaptive in people with MS. We also discuss future work that could supply data to support or refute this hypothesis, thus improving our understanding of this important topic.

Impact of Gradient Number and Voxel Size on Diffusion Tensor Imaging Tractography for Resective Brain Surgery

OBJECTIVE

To explore quantitatively and qualitatively how the number of gradient directions (NGD) and spatial resolution (SR) affect diffusion tensor imaging (DTI) tractography in patients planned for brain tumor surgery, using routine clinical magnetic resonance imaging protocols.

METHODS

Of 67 patients with intracerebral lesions who had 2 different DTI scans, 3 DTI series were reconstructed to compare the effects of NGD and SR. Tractographies for 4 clinically relevant tracts (corticospinal tract, superior longitudinal fasciculus, optic radiation, and inferior fronto-occipital fasciculus) were constructed with a probabilistic tracking algorithm and automated region of interest placement and compared for 3 quantitative measurements: tract volume, median fiber density, and mean fractional anisotropy, using linear mixed-effects models. The mean tractography volume and intersubject reliability were visually compared across scanning protocols, to assess the clinical relevance of the quantitative differences.

RESULTS

Both NGD and SR significantly influenced tract volume, median fiber density, and mean fractional anisotropy, but not to the same extent. In particular, higher NGD increased tract volume and median fiber density. More importantly, these effects further increased when tracts were affected by disease. The effects were tract specific, but not dependent on threshold. The superior longitudinal fasciculus and inferior fronto-occipital fasciculus showed the most significant differences. Qualitative assessment showed larger tract volumes given a fixed confidence level, and better intersubject reliability for the higher NGD protocol. SR in the range we considered seemed less relevant than NGD.

CONCLUSIONS

This study indicates that, under time constraints of clinical imaging, a higher number of diffusion gradients is more important than spatial resolution for superior DTI probabilistic tractography in patients undergoing brain tumor surgery.

Gray Matter Atrophy Is Primarily Related to Demyelination of Lesions in Multiple Sclerosis: A Diffusion Tensor Imaging MRI Study

Objective: Cortical pathology, periventricular demyelination, and lesion formation in multiple sclerosis (MS) are related (Hypothesis 1). Factors in the cerebrospinal fluid close to these compartments could possibly drive the parallel processes. Alternatively, the cortical atrophy could be caused by remote axonal transection (Hypothesis 2). Since MRI can differentiate between demyelination and axon loss, we used this imaging modality to investigate the correlation between the pattern of diffusion parameter changes in the periventricular- and deep white matter and the gray matter atrophy.

Methods: High-resolution T1-weighted, FLAIR, and diffusion MRI images were acquired in 52 RRMS patients and 50 healthy, age-matched controls. We used EDSS to estimate the clinical disability. We used Tract Based Spatial Statistics to compare diffusion parameters (fractional anisotropy, mean, axial, and radial diffusivity) between groups. We evaluated global brain, white, and gray matter atrophy with SIENAX. Averaged, standard diffusion parameters were calculated in four compartment: periventricular lesioned and normal appearing white matter, non-periventricular lesioned and normal appearing white matter. PLS regression was used to identify which diffusion parameter and in which compartment best predicts the brain atrophy and clinical disability.

Results: In our diffusion tensor imaging study compared to controls we found extensive alterations of fractional anisotropy, mean and radial diffusivity and smaller changes of axial diffusivity (maximal p > 0.0002) in patients that suggested demyelination in the lesioned and in the normal appearing white matter. We found significant reduction in total brain, total white, and gray matter (patients: 718.764 ± 14.968, 323.237 ± 7.246, 395.527 ± 8.050 cm³, controls: 791.772 ± 22.692, 355.350 ± 10.929, 436.422 ± 12.011 cm³; mean ± SE), (p < 0.015; p < 0.0001; p < 0.009; respectively) of patients compared to controls. The PLS analysis revealed a combination of demyelination-like diffusion parameters (higher mean and radial diffusivity in patients) in the lesions and in the non-lesioned periventricular white matter, which best predicted the gray matter atrophy (p < 0.001). Similarly, EDSS was best predicted by the radial diffusivity of the lesions and the non-lesioned periventricular white matter, but axial diffusivity of the periventricular lesions also contributed significantly (p < 0.0001).

Interpretation: Our investigation showed that gray matter atrophy and white matter demyelination are related in MS but white matter axonal loss does not significantly contribute to the gray matter pathology.

Role of Oligodendrocyte Dysfunction in Demyelination, Remyelination and Neurodegeneration in Multiple Sclerosis

Oligodendrocytes (OLs) are the myelinating cells of the central nervous system (CNS) during development and throughout adulthood. They result from a complex and well controlled process of activation, proliferation, migration and differentiation of oligodendrocyte progenitor cells (OPCs) from the germinative niches of the CNS. In multiple sclerosis (MS), the complex pathological process produces dysfunction and apoptosis of OLs leading to demyelination and neurodegeneration. This review attempts to describe the patterns of demyelination in MS, the steps involved in oligodendrogenesis and myelination in healthy CNS, the different pathways leading to OLs and myelin loss in MS, as well as principles involved in restoration of myelin sheaths. Environmental factors and their impact on OLs and pathological mechanisms of MS are also discussed. Finally, we will present evidence about the potential therapeutic targets in re-myelination processes that can be accessed in order to develop regenerative therapies for MS.

Corpus Callosum Structural Integrity Is Associated With Postural Control Improvement in Persons With Multiple Sclerosis Who Have Minimal Disability

BACKGROUND

Improvement of postural control in persons with multiple sclerosis (PwMS) is an important target for neurorehabilitation. Although PwMS are able to improve postural performance with training, the neural underpinnings of these improvements are poorly understood.

OBJECTIVE

To understand the neural underpinnings of postural motor learning in PwMS.

METHODS

Supraspinal white matter structural connectivity in PwMS was correlated with improvements in postural performance (balancing on an oscillating surface over 25 trials) and retention of improvements (24 hours later).

RESULTS

Improvement in postural performance was directly correlated to microstructural integrity of white matter tracts, measured as radial diffusivity, in the corpus callosum, posterior parieto-sensorimotor fibers and the brainstem in PwMS. Within the corpus callosum, the genu and midbody (fibers connecting the prefrontal and primary motor cortices, respectively) were most strongly correlated to improvements in postural control. Twenty-four-hour retention was not correlated to radial diffusivity.

CONCLUSION

PwMS who exhibited poorer white matter tract integrity connecting the cortical hemispheres via the corpus callosum showed the most difficulty learning to control balance on an unstable surface. Prediction of improvements in postural control through training (ie, motor learning) via structural imaging of the brain may allow for identification of individuals who are particularly well suited for postural rehabilitation interventions.

ASSOCIATION ASSESSMENT BETWEEN DIFFUSION TENSOR MAGNETIC RESONANCE IMAGING INDICES AND CLINICAL DISABILITIES IN MS PATIENTS

Purpose: Diffusion tensor magnetic resonance imaging (DT-MRI) has the ability to gather information on tissue microstructure by using the indices that quantify the anisotropy of water diffusion in tissues. This study was designed to find out the impact of patient clinical disability on diffusion tensor (DT) indices. Method: In this paper, images were generated from the data acquired at 3T among 25 MS patients (mean age [Formula: see text] years old). DT indices including fractional anisotropy (FA), mean diffusivity (MD), relative anisotropy (RA), and volume ratio (VR) of multiple sclerosis (MS) lesions are calculated and the correlation between Kurtzke expanded disability status scale (EDSS) score and the values of DT indices of 25 MS patients lesions are obtained. The correlation comparison procedure is done between the EDSS scores and DT indices in MS lesions attained, respectively, from fluid attenuated inversion recovery (FLAIR) images and black holes of T1-weighted (T1-w) images. Results: EDSS scores and DT indices of MS lesions extracted from the black holes present in T1-w images are more correlated in comparison with those extracted from FLAIR images. It is found that MD has a significant correlation with EDSS in both types of images. The results of FLAIR image processing indicates that any increase in EDSS leads to decreasing FA and RA on one hand and increasing MD and VR on the other hand. The correlation between the identical size of lesions in different parts of brain with EDSS shows that the location of lesion in brain also has a correlation with EDSS. Conclusion: The results showed, MD is the best biomarker of clinical disability between these four DT indices. It is also concluded that the correlation between DT indices of frontal brain lesions and EDSS is higher than the other selected brain parts.

Cerebellar contribution to motor and cognitive performance in multiple sclerosis: An MRI sub-regional volumetric analysis

OBJECTIVE

To investigate the role of cerebellar sub-regions on motor and cognitive performance in multiple sclerosis (MS) patients.

METHODS

Whole and sub-regional cerebellar volumes, brain volumes, T2 hyperintense lesion volumes (LV), and motor performance scores were obtained from 95 relapse-onset MS patients and 32 healthy controls (HC). MS patients also underwent an evaluation of working memory and processing speed functions. Cerebellar anterior and posterior lobes were segmented using the Spatially Unbiased Infratentorial Toolbox (SUIT) from Statistical Parametric Mapping (SPM12). Multivariate linear regression models assessed the relationship between magnetic resonance imaging (MRI) measures and motor/cognitive scores.

RESULTS

Compared to HC, only secondary progressive multiple sclerosis (SPMS) patients had lower cerebellar volumes (total and posterior cerebellum). In MS patients, lower anterior cerebellar volume and brain T2 LV predicted worse motor performance, whereas lower posterior cerebellar volume and brain T2 LV predicted poor cognitive performance. Global measures of brain volume and infratentorial T2 LV were not selected by the final multivariate models.

CONCLUSION

Cerebellar volumetric abnormalities are likely to play an important contribution to explain motor and cognitive performance in MS patients. Consistently with functional mapping studies, cerebellar posterior-inferior volume accounted for variance in cognitive measures, whereas anterior cerebellar volume accounted for variance in motor performance, supporting the assessment of cerebellar damage at sub-regional level.

Patterns of white matter damage are non-random and associated with cognitive function in secondary progressive multiple sclerosis

In multiple sclerosis (MS), white matter damage is thought to contribute to cognitive dysfunction, which is especially prominent in secondary progressive MS (SPMS). While studies in healthy subjects have revealed patterns of correlated fractional anisotropy (FA) across white matter tracts, little is known about the underlying patterns of white matter damage in MS. In the present study, we aimed to map the SPMS-related covariance patterns of microstructural white matter changes, and investigated whether or not these patterns were associated with cognitive dysfunction. Diffusion MRI was acquired from 30 SPMS patients and 32 healthy controls (HC). A tensor model was fitted and FA maps were processed using tract-based spatial statistics (TBSS) in order to obtain a skeletonised map for each subject. The skeletonised FA maps of patients only were decomposed into 18 spatially independent components (ICs) using independent component analysis. Comprehensive cognitive assessment was conducted to evaluate five cognitive domains. Correlations between cognitive performance and (1) severity of FA abnormalities of the extracted ICs (i.e. z-scores relative to FA values of HC) and (2) IC load (i.e. FA covariance of a particular IC) were examined. SPMS patients showed lower FA values of all examined patterns of correlated FA (i.e. spatially independent components) than HC (p < 0.01). Tracts visually assigned to the supratentorial commissural class were most severely damaged (z = - 3.54; p < 0.001). Reduced FA was significantly correlated with reduced IC load (i.e. FA covariance) (r = 0.441; p < 0.05). Lower mean FA and component load of the supratentorial projection tracts and limbic association tracts classes were associated with worse cognitive function, including executive function, working memory and verbal memory. Despite the presence of white matter damage, it was possible to reveal patterns of FA covariance across SPMS patients. This could indicate that white matter tracts belonging to the same cluster, and thus with similar characteristics, tend to follow similar trends during neurodegeneration. Furthermore, these underlying FA patterns might help to explain cognitive dysfunction in SPMS.

Metabolic voxel-based analysis of the complete human brain using fast 3D-MRSI: Proof of concept in multiple sclerosis

PURPOSE

To detect local metabolic abnormalities over the complete human brain in multiple sclerosis (MS) patients, we used optimized fast volumic echo planar spectroscopic imaging (3D-EPSI).

MATERIALS AND METHODS

Weighted mean combination of two 3D-EPSI covering the whole brain acquired at 3T in AC-PC and AC-PC+15° axial planes was performed to obtain high-quality metabolite maps for five metabolites: N-acetyl aspartate (NAA), glutamate+glutamine (Glx), choline (Cho), myo-inositol (m-Ins), and creatine+phosphocreatine (tCr). After spatial normalization, maps from 19 patients suffering from relapsing-remitting MS were compared to 19 matched controls using statistical mapping analyses to determine the topography of metabolic abnormalities. Probabilistic white matter (WM) T2 lesion maps and gray matter (GM) atrophy maps were also generated.

RESULTS

Two-group analysis of variance (ANOVA) (SPM8, P < 0.005, false discovery rate [FDR]-corrected P < 0.05 at the cluster level with age and sex as confounding covariates) comparing patients and controls matched for age and sex showed clusters of abnormal metabolite levels with 1) decreased NAA (around -15%) and Glx (around 20%) predominantly in GM within prefrontal cortices, motor cortices, bilateral thalami, and mesial temporal cortices in line with neuronal/neuro-astrocytic dysfunction; 2) increased m-Ins (around + 20%) inside WM T2 lesions and in the normal-appearing WM of temporal-occipital lobes, suggesting glial activation.

CONCLUSION

We demonstrate the ability to noninvasively map over the complete brain-from vertex to cerebellum-with a validated sequence, the metabolic abnormalities associated with MS, for characterizing the topography of pathological processes affecting widespread areas of WM and GM and its functional impact. J. Magn. Reson. Imaging 2016;44:411-419.

Multiple sclerosis

Due to its sensitivity to the different multiple sclerosis (MS)-related abnormalities, magnetic resonance imaging (MRI) has become an established tool to diagnose MS and to monitor its evolution. MRI has been included in the diagnostic workup of patients with clinically isolated syndromes suggestive of MS, and ad hoc criteria have been proposed and are regularly updated. In patients with definite MS, the ability of conventional MRI techniques to explain patients' clinical status and progression of disability is still suboptimal. Several advanced MRI-based technologies have been applied to estimate overall MS burden in the different phases of the disease. Their use has allowed the heterogeneity of MS pathology in focal lesions, normal-appearing white matter and gray matter to be graded in vivo. Recently, additional features of MS pathology, including macrophage infiltration and abnormal iron deposition, have become quantifiable. All of this, combined with functional imaging techniques, is improving our understanding of the mechanisms associated with MS evolution. In the near future, the use of ultrahigh-field systems is likely to provide additional insight into disease pathophysiology. However, the utility of advanced MRI techniques in clinical trial monitoring and in assessing individual patients' response to treatment still needs to be assessed.

Cerebral white matter fractional anisotropy and tract volume as measured by MR imaging are associated with impaired cognitive and motor function in pediatric posterior fossa tumor survivors

BACKGROUND

Disease and therapy cause brain damage and subsequent functional loss in pediatric patients with posterior fossa tumors. Treatment-related toxicity factors are resection in patients with pilocytic astrocytoma (PA) and, additionally, cranio-spinal irradiation together with chemotherapy in patients with medulloblastoma (MB). We tested whether damage to white matter (WM) as revealed by diffusion tensor MR imaging (DTI) correlated with specific cognitive and motor impairments in survivors of pediatric posterior fossa tumors.

PROCEDURES

Eighteen MB (mean age ± SD, 15.2 ± 4.9 y) and 14 PA (12.6 ± 5.0 y) survivors were investigated with DTI on a 3-Tesla-MR system. We identified fractional anisotropy (FA) of WM, the volume ratio of WM to gray matter and cerebrospinal fluid (WM/GM + CSF), and volume of specific frontocerebellar tracts. Ataxia was assessed using the International Cooperative Ataxia Rating Scale (ICARS), while the Wechsler Intelligence Scale for Children determined full-scale intelligence quotients (FSIQ). Amsterdam Neuropsychological Tasks (ANT) was used to assess processing speed. Handwriting automation was analyzed using a digitizing graphic tablet.

RESULTS

The WM/GM + CSF ratio correlated significantly with cognitive measures (IQ, P = 0.002; ANT baseline speed, P = 0.04; ANT shifting attention, P = 0.004). FA of skeletonized tracts correlated significantly with FSIQ (P = 0.008), ANT baseline speed (P = 0.028) and ANT shifting attention (P = 0.045). Moreover, frontocerebellar tract volumes correlated with both the FSIQ (P = 0.011) and ICARS (P = 0.007).

CONCLUSION

DTI provides a method for quantification of WM damage by tumor and by therapy-associated effects in survivors of pediatric posterior fossa tumors. DTI-derived WM integrity may be a representative marker for cognitive and motor deterioration.

Injury to white matter tracts in relapsing-remitting multiple sclerosis: A possible therapeutic window within the first 5 years from onset using diffusion-tensor imaging tract-based spatial statistics

DTI studies in multiple sclerosis (MS) reveal white matter (WM) injury that occurs with disease progression. In the present study we aimed to elucidate the relationship of microstructural WM damage in patients with varying periods of disease duration. DTI scans were acquired from 90 MS patients and 25 healthy controls. Patients were grouped to short (<1 year), moderate (1 up to 6 years) and long (6–10 years) disease duration periods. Statistical analyses of the fractional anisotropy (FA) data were performed using tract-based spatial statistics (TBSS). Whole-brain skeletal FA measurements showed a significant decrease between healthy controls and the short MS disease duration group, as well as between moderate disease duration and long disease duration groups, but failed to show a significant difference between short and moderate disease duration groups.

Voxelwise analysis revealed clusters of diffuse FA reductions in 40 WM tracts when comparing healthy controls and MS short disease duration group, with the point of maximal significant difference located in the left inferior longitudinal fasciculus.

Comparing short with long disease duration groups, progressive FA reduction was demonstrated across 30 WM tracts, with the point of maximal significant difference migrating to the body of the corpus callosum. A non-linear pattern of WM microstructure disruption occurs in RRMS. Alterations are seen early in the disease course within 1 year from onset, reach a plateau within the next 5 years, and only later additional WM changes are detected. An important period of a possible therapeutic window therefore exists within the early disease stage.

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A non-linear pattern of WM microstructure disruption occurs in patients with RRMS.

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WM disruption is identified within 1 year from disease onset.

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FA reduction is similar in patients with early and moderate disease duration periods.

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Different patterns of WM disruption occur in patients with longer disease duration.

Decoding diffusivity in multiple sclerosis: analysis of optic radiation lesional and non-lesional white matter

Objectives

Diffusion tensor imaging (DTI) has been suggested as a new promising tool in MS that may provide greater pathological specificity than conventional MRI, helping, therefore, to elucidate disease pathogenesis and monitor therapeutic efficacy. However, the pathological substrates that underpin alterations in brain tissue diffusivity are not yet fully delineated. Tract-specific DTI analysis has previously been proposed in an attempt to alleviate this problem. Here, we extended this approach by segmenting a single tract into areas bound by seemingly similar pathological processes, which may better delineate the potential association between DTI metrics and underlying tissue damage.

Method

Several compartments were segmented in optic radiation (OR) of 50 relapsing-remitting MS patients including T2 lesions, proximal and distal parts of fibers transected by lesion and fibers with no discernable pathology throughout the entire length of the OR.

Results

Asymmetry analysis between lesional and non-lesional fibers demonstrated a marked increase in Radial Diffusivity (RD), which was topographically limited to focal T2 lesions and potentially relates to the lesional myelin loss. A relative elevation of Axial Diffusivity (AD) in the distal part of the lesional fibers was observed in a distribution consistent with Wallerian degeneration, while diffusivity in the proximal portion of transected axons remained normal. A moderate, but significant elevation of RD in OR non-lesional fibers was strongly associated with the global (but not local) T2 lesion burden and is probably related to microscopic demyelination undetected by conventional MRI.

Conclusion

This study highlights the utility of the compartmentalization approach in elucidating the pathological substrates of diffusivity and demonstrates the presence of tissue-specific patterns of altered diffusivity in MS, providing further evidence that DTI is a sensitive marker of tissue damage in both lesions and NAWM. Our results suggest that, at least within the OR, parallel and perpendicular diffusivities are affected by tissue restructuring related to distinct pathological processes.

Functionally relevant white matter degradation in multiple sclerosis: a tract-based spatial meta-analysis

PURPOSE

To identify statistical consensus between published studies for distribution and functional relevance of tract white matter (WM) degradation in multiple sclerosis (MS).

MATERIALS AND METHODS

By systematically searching online databases, tract-based spatial statistics studies were identified that compared fractional anisotropy (FA; a marker for WM integrity) in MS patients to healthy control subjects, correlated FA in MS patients with physical disability, or correlated FA in MS patients with cognitive performance. Voxelwise meta-analysis was performed by using the Signed Differential Mapping method for each comparison. Moderating effects of mean age, mean physical disability score, imager magnet strength, lesion load, and number of diffusion directions were assessed by means of meta-regression.

RESULTS

Meta-analysis was performed on data from 495 patients and 253 control subjects across 12 studies. MS diagnosis was significantly associated with widespread lower tract FA (nine studies; largest cluster, 4379 voxels; z = 7.1; P < .001). Greater physical disability was significantly associated with lower FA in the right posterior cingulum, left callosal splenium, right inferior fronto-occipital fasciculus, and left fornix crus (six studies; 323 voxels; z = 1.7; P = .001). Impaired cognition was significantly associated with lower FA in the callosal genu, thalamus, right posterior cingulum, and fornix crus (seven studies; largest cluster, 980 voxels; z = 2.5; P < .001).

CONCLUSION

WM damage is widespread in MS with differential and only minimally overlapping distributions of low FA that relates to physical disability and cognitive impairment. The higher number of clusters of lower FA in relation to cognition and their higher z scores suggest that cerebral WM damage may have a greater relevance to cognitive dysfunction than physical disability in MS, and that low anterior callosal and thalamic FA have specific importance to cognitive status.

Tract-based spatial statistics of the olfactory brain in patients with multiple sclerosis

PURPOSE

To investigate diffusion tensor abnormalities, e.g. fractional anisotropy (FA), mean diffusivity (MD), and radial diffusivity (RD), in olfactory structures of multiple sclerosis (MS) patients using diffusion tensor imaging (DTI).

METHODS

Institutional review board-approved prospective study on 30 MS patients and 12 healthy controls investigated with MRI including DTI. Central olfactory structures were labelled on each patient's and healthy contro''s DTI volume. The diffusion tensor was determined in the central olfactory structures in MS patients. Tract-based spatial statistics (TBSS) was used to quantify the streamlines outgoing from the olfactory structures and to quantify changes in FA, MD, and RD within olfactory structures. These brain changes were correlated with olfactory function measured as TDI (Threshold, Discrimination, Identification) scores in patients and compared to our own reference group of 30 healthy volunteers.

RESULTS

Central olfactory structures in the MNI (Montreal Neurological Institute) data volume comprise 4808 voxels (4808 mm(3)). TFCE (Threshold-free cluster enhancement) and cluster analysis of patients identified a total of 127 voxels in one cluster with a significantly decreased FA (p<0.05) and none for MD and RD within olfactory structures compared to healthy controls. The correlation with the age-normalised Identification subscore of the TDI score increased the significant number of voxels with decreased FA to 208 voxels, with increased MD to 370 and with increased RD 364 voxels at the same region.

CONCLUSION

The decrease in FA and increase of MD and RD correlate with the degree of identification impairment of olfactory function in MS patients and clusters of abnormalities were identified on a MNI data volume.

Differentiation of edema and glioma infiltration: proposal of a DTI-based probability map

Conflicting results on differentiating edema and glioma by diffusion tensor imaging (DTI) are possibly attributable to dissimilar spatial distribution of the lesions. Combining DTI-parameters and enhanced registration might improve prediction. Regions of edema surrounding 22 metastases were compared to tumor-infiltrated regions from WHO grade 2 (12), 3 (10) and 4 (18) gliomas. DTI data was co-registered using Tract Based Spatial Statistics (TBSS), to measure Fractional Anisotropy (FA) and Mean Diffusivity (MD) for white matter only, and relative changes compared to matching reference regions (dFA and dMD). A two-factor principal component analysis (PCA) on metastasis and grade 2 glioma was performed to explore a possible differentiating combined factor. Edema demonstrated equal MD and higher FA compared to grade 2 and 3 glioma (P < 0.001), but did not differ from glioblastoma. Differences were non-significant when corrected for spatial distribution, since reference regions differed strongly (P < 0.001). The second component of the PCA (PCA-C2) did differentiate edema and low-grade tumor (sensitivity 91.7%, specificity 86.4%). PCA-C2 scores were plotted voxel-wise as a probability-map, discerning distinct areas of presumed edema or tumor infiltration. Correction of spatial dependency appears essential when differentiating glioma from edema. A tumor-infiltration probability-map is presented, based on supplementary information of multiple DTI parameters and spatial normalization.

Altered inter-subregion connectivity of the default mode network in relapsing remitting multiple sclerosis: a functional and structural connectivity study

Background and Purpose

Little is known about the interactions between the default mode network (DMN) subregions in relapsing-remitting multiple sclerosis (RRMS). This study used diffusion tensor imaging (DTI) and resting-state functional MRI (rs-fMRI) to examine alterations of long white matter tracts in paired DMN subregions and their functional connectivity in RRMS patients.

Methods

Twenty-four RRMS patients and 24 healthy subjects participated in this study. The fiber connections derived from DTI tractography and the temporal correlation coefficient derived from rs-fMRI were combined to examine the inter-subregion structural-functional connectivity (SC-FC) within the DMN and its correlations with clinical markers.

Results

Compared with healthy subjects, the RRMS patients showed the following: 1) significantly decreased SC and increased FC in the pair-wise subregions; 2) two significant correlations in SC-FC coupling patterns, including the positive correlation between slightly increased FC value and long white matter tract damage in the PCC/PCUN-MPFC connection, and the negative correlations between significantly increased FC values and long white matter tract damage in the PCC/PCUN-bilateral mTL connections; 3) SC alterations [log(N track) of the PCC/PCUN-left IPL, RD value of the MPFC-left IPL, FA value of the PCC/PCUN-left mTL connections] correlated with EDSS, increases in the RD value of MPFC-left IPL connection was positively correlated to the MFIS; and decreases in the FA value of PCC/PCUN-right IPL connection was negatively correlated with the PASAT; 4) decreased SC (FA value of the MPFC-left IPL, track volume of the PCC/PCUN-MPFC, and log(N track) of PCC/PCUN-left mTL connections) was positively correlated with brain atrophy.

Conclusions

In the connections of paired DMN subregions, we observed decreased SC and increased FC in RRMS patients. The relationship between MS-related structural abnormalities and clinical markers suggests that the disruption of this long-distance “inter-subregion” connectivity (white matter) may significantly impact the integrity of the network's function.

Diffusion tensor MRI as a biomarker in axonal and myelin damage

Diffusion tensor imaging has been used extensively as a research tool to understand the structural changes associated with white matter pathology. Using water diffusion as the basis to construct anatomic details, diffusion tensor imaging offers the potential to identify structural and functional adaptations before gross anatomical changes, such as lesions and tumors, become apparent on conventional MRI. Over the past 10 years, further parameters, such as axial and radial diffusivity, have been developed to characterize white matter changes specific to axons and myelin. In this paper, the potential application and outstanding issues on the use of diffusion tensor imaging directional diffusivity as a biomarker in axonal and myelin damage in neurological disorders will be reviewed.

Cognitive functions in multiple sclerosis: impact of gray matter integrity

OBJECTIVES

Our aim was to investigate the impact of gray matter (GM) integrity on cognitive performance in multiple sclerosis (MS), and its relationship with white matter (WM) integrity and presence of lesions.

METHODS

Sixty-seven patients with MS and 26 healthy controls underwent voxel-based analysis of diffusion tensor images (DTI) in GM and tract-based spatial statistics (TBSS) from WM to identify the regional correlations between cognitive functions and integrity. Lesion probability mapping (LPM) was generated for correlation analysis with cognition. Multiple linear regression analyses were used to identify the imaging measures associated with cognitive scores.

RESULTS

Compared with controls, patients showed abnormal DTI indices in several GM regions and in most WM tracts. Impairment in DTI indices in specific GM regions was associated with worse performance of distinct cognitive functions. Those regions showed anatomical correspondence with cognitively relevant tracts in TBSS and LPM. The combination of regional GM and WM DTI and lesion volume accounted for 36-51% of the variance of memory and attention scores. Regional GM DTI explained less than 5% of that variance.

CONCLUSION

GM and WM integrity of specific networks influences cognitive performance in MS. However, GM damage assessed by DTI only adds a small increment to the explained variance by WM in predicting cognitive functioning.

Intra-individual variability in information processing speed reflects white matter microstructure in multiple sclerosis

Slowed information processing speed is commonly reported in persons with multiple sclerosis (MS), and is typically investigated using clinical neuropsychological tests, which provide sensitive indices of mean-level information processing speed. However, recent studies have demonstrated that within-person variability or intra-individual variability (IIV) in information processing speed may be a more sensitive indicator of neurologic status than mean-level performance on clinical tests. We evaluated the neural basis of increased IIV in mildly affected relapsing–remitting MS patients by characterizing the relation between IIV (controlling for mean-level performance) and white matter integrity using diffusion tensor imaging (DTI). Twenty women with relapsing–remitting MS and 20 matched control participants completed the Computerized Test of Information Processing (CTIP), from which both mean response time and IIV were calculated. Other clinical measures of information processing speed were also collected. Relations between IIV on the CTIP and DTI metrics of white matter microstructure were evaluated using tract-based spatial statistics. We observed slower and more variable responses on the CTIP in MS patients relative to controls. Significant relations between white matter microstructure and IIV were observed for MS patients. Increased IIV was associated with reduced integrity in more white matter tracts than was slowed information processing speed as measured by either mean CTIP response time or other neuropsychological test scores. Thus, despite the common use of mean-level performance as an index of cognitive dysfunction in MS, IIV may be more sensitive to the overall burden of white matter disease at the microstructural level. Furthermore, our study highlights the potential value of considering within-person fluctuations, in addition to mean-level performance, for uncovering brain–behavior relationships in neurologic disorders with widespread white matter pathology.

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Intra-individual variability (IIV) predicts neurologic status in multiple sclerosis (MS).

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Diffusion tensor imaging (DTI) was used to study the neural correlates of IIV in MS.

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IIV was significantly related to DTI metrics in many white matter regions.

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Compared to mean response speed, IIV may be more sensitive to disease burden in MS.

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Evaluating IIV may be important for characterizing brain–behavior relationships.

Bayesian scalar-on-image regression with application to association between intracranial DTI and cognitive outcomes

Diffusion tensor imaging (DTI) measures water diffusion within white matter, allowing for in vivo quantification of brain pathways. These pathways often subserve specific functions, and impairment of those functions is often associated with imaging abnormalities. As a method for predicting clinical disability from DTI images, we propose a hierarchical Bayesian "scalar-on-image" regression procedure. Our procedure introduces a latent binary map that estimates the locations of predictive voxels and penalizes the magnitude of effect sizes in these voxels, thereby resolving the ill-posed nature of the problem. By inducing a spatial prior structure, the procedure yields a sparse association map that also maintains spatial continuity of predictive regions. The method is demonstrated on a simulation study and on a study of association between fractional anisotropy and cognitive disability in a cross-sectional sample of 135 multiple sclerosis patients.

Assessing the correlation between grey and white matter damage with motor and cognitive impairment in multiple sclerosis patients

Background

Multiple sclerosis (MS) is characterized by demyelinating and degenerative processes within the central nervous system. Unlike conventional MRI,new advanced imaging techniques improve pathological specificity and better highlight the relationship between anatomical damage and clinical impairment.

Objective

To investigate the relationship between clinical disability and both grey (GM) and white matter (WM) regional damage in MS patients.

Methods

Thirty-six relapsing remitting-MS patients and 25 sex- and age-matched controls were enrolled. All patients were clinically evaluated by the Expanded Disability Status Scale and the Multiple Sclerosis Functional Composite (MSFC) scale, which includes the 9-hole peg test (9HPT), the timed 25-feet walking test (T25FW) and the paced auditory serial addition test (PASAT). All subjects were imaged by a 3.0 T scanner: dual-echo fast spin-echo, 3DT1-weighted and diffusion-tensor imaging (DTI) sequences were acquired. Voxel-based morphometry (VBM) and tract-based spatial statistics (TBSS) analyses were run for regional GM and WM assessment, respectively. T2 lesion volumes were also calculated, by using a semi-automated technique.

Results

Brain volumetric assessment of GM and DTI measures revealed significant differences between patients and controls. In patients, different measures of WM damage correlated each-other (p<0.0001), whereas none of them correlated with GM volume. In patients, focal GM atrophy and widespread WM damage significantly correlated with clinical measures. In particular, VBM analysis revealed a significant correlation (p<0.05) between GM volume and 9HPT in cerebellum and between GM volume and PASAT in orbito-frontal cortex. TBSS showed significant correlations between DTI metrics with 9HPT and PASAT scores in many WM bundles (p<0.05), including corpus callosum, internal capsule, posterior thalamic radiations, cerebral peduncles.

Conclusions

Selective GM atrophy and widespread WM tracts damage are associated with functional impairment of upper-limb motion and cognition. The combined analysis of volumetric and DTI data may help to better understand structural alterations underlying physical and cognitive dysfunction in MS.

A novel approach with "skeletonised MTR" measures tract-specific microstructural changes in early primary-progressive MS

We combined tract-based spatial statistics (TBSS) and magnetization transfer (MT) imaging to assess white matter (WM) tract-specific short-term changes in early primary-progressive multiple sclerosis (PPMS) and their relationships with clinical progression. Twenty-one PPMS patients within 5 years from onset underwent MT and diffusion tensor imaging (DTI) at baseline and after 12 months. Patients' disability was assessed. DTI data were processed to compute fractional anisotropy (FA) and to generate a common WM "skeleton," which represents the tracts that are "common" to all subjects using TBSS. The MT ratio (MTR) was computed from MT data and co-registered with the DTI. The skeletonization procedure derived for FA was applied to each subject's MTR image to obtain a "skeletonised" MTR map for every subject. Permutation tests were used to assess (i) changes in FA, principal diffusivities, and MTR over the follow-up, and (ii) associations between changes in imaging parameters and changes in disability. Patients showed significant decreases in MTR over one year in the corpus callosum (CC), bilateral corticospinal tract (CST), thalamic radiations, and superior and inferior longitudinal fasciculi. These changes were located both within lesions and the normal-appearing WM. No significant longitudinal change in skeletonised FA was found, but radial diffusivity (RD) significantly increased in several regions, including the CST bilaterally and the right inferior longitudinal fasciculus. MTR decreases, RD increases, and axial diffusivity decreases in the CC and CST correlated with a deterioration in the upper limb function. We detected tract-specific multimodal imaging changes that reflect the accrual of microstructural damage and possibly contribute to clinical impairment in PPMS. We propose a novel methodology that can be extended to other diseases to map cross-subject and tract-specific changes in MTR.

DTI Measurements in Multiple Sclerosis: Evaluation of Brain Damage and Clinical Implications

Diffusion tensor imaging (DTI) is an effective means of quantifying parameters of demyelination and axonal loss. The application of DTI in Multiple Sclerosis (MS) has yielded noteworthy results. DTI abnormalities, which are already detectable in patients with clinically isolated syndrome (CIS), become more pronounced as disease duration and neurological impairment increase. The assessment of the microstructural alterations of white and grey matter in MS may shed light on mechanisms responsible for irreversible disability accumulation. In this paper, we examine the DTI analysis methods, the results obtained in the various tissues of the central nervous system, and correlations with clinical features and other MRI parameters. The adoption of DTI metrics to assess the outcome of prognostic measures may represent an extremely important step forward in the MS research field.

Tracking cerebral white matter changes across the lifespan: insights from diffusion tensor imaging studies

Delineating the normal development of brain white matter (WM) over the human lifespan is crucial to improved understanding of underlying WM pathology in neuropsychiatric and neurological conditions. We review the extant literature concerning diffusion tensor imaging studies of brain WM development in healthy individuals available until October 2012, summarise trends of normal development of human brain WM and suggest possible future research directions. Temporally, brain WM maturation follows a curvilinear pattern with an increase in fractional anisotropy (FA) from newborn to adolescence, decelerating in adulthood till a plateau around mid-adulthood, and a more rapid decrease of FA from old age onwards. Spatially, brain WM tracts develop from central to peripheral regions, with evidence of anterior-to-posterior maturation in commissural and projection fibres. The corpus callosum and fornix develop first and decline earlier, whilst fronto-temporal WM tracts like cingulum and uncinate fasciculus have protracted maturation and decline later. Prefrontal WM is most vulnerable with greater age-related FA reduction compared with posterior WM. Future large scale studies adopting longitudinal design will better clarify human brain WM changes over time.

MRI in multiple sclerosis: a review of the current literature

PURPOSE OF REVIEW

This review summarizes the recent data pertaining to the use of magnetic resonance imaging (MRI) in assessing brain and spinal cord involvement in multiple sclerosis (MS).

RECENT FINDINGS

Using MRI as a tool, investigators have made progress recently in understanding the substrate and mechanisms underlying the development and evolution of focal lesions and diffuse damage in MS. The application of refined MRI sequences has markedly improved the characterization of focal lesions, in particular cortical lesions. Promising improvements have been made to clarify the pathological specificity and sensitivity of MRI techniques by performing combined histopathologic-MRI correlation studies. The use of high-field (3 T) and ultra-high-field (UHF; >3 T) MRI has further facilitated the detection of both gray matter and white matter microstructural damage, and elucidated the topographic relationship of overt damage to venous blood vessels. The development of advanced MRI postprocessing tools has led to additional progress in detecting clinically relevant regional gray matter and white matter damage.

SUMMARY

MRI continues to play a pivotal role in the investigation of MS. Ongoing advances in MRI technology should further expand the current understanding of pathologic disease mechanisms and improve diagnostic, prognostic, and monitoring ability in patients with MS.

Clinical applications of imaging disease burden in multiple sclerosis: MRI and advanced imaging techniques

This review will address the critical role of radiographic techniques in monitoring multiple sclerosis disease course and response to therapeutic interventions using conventional imaging. We propose an algorithm of obtaining a contrast-enhanced brain MRI 6 months after starting a disease-modifying therapy, and considering a gadolinium-enhancing lesion on that scan to indicate suboptimal response to therapy. New or enlarging T2 lesions should be followed on scans at 6-month intervals to assess for change, and the presence of one or more enhancing lesions on a 6- or 12-month scan, or two or more new or enlarging T2 lesions on a 12-month scan should prompt consideration of therapy change. New techniques such as PET imaging, magnetic resonance spectroscopy, magnetic resonance relaxometry, iron-sensitive imaging and perfusion MRI will also be overviewed, with their potential roles in monitoring disease course and activity.

Non-lesional white matter changes in pediatric multiple sclerosis and monophasic demyelinating disorders

OBJECTIVE

To analyze diffusion tensor imaging (DTI) derived metrics between patients with childhood onset multiple sclerosis (MS), monophasic demyelinating illnesses, and healthy controls.

BACKGROUND

Monophasic demyelinating illnesses can be indistinguishable clinically and radiologically, utilizing standard MRI studies. DTI studies in adults implicate the involvement of normal-appearing white matter (NAWM) in MS.

METHODS

Subjects with DTI studies (15 directions, 1.5 Tesla (GE), 3x3x3 mm, interpolated to 1.5x1.5x3 mm) were retrospectively identified. We studied three groups: childhood onset MS (n=18), monophasic illness (eight with acute disseminated encephalomyelitis (ADEM), seven with clinically isolated syndrome (CIS)) and age-matched controls. DTI had been obtained within one month of symptom onset for patients with ADEM and within a median of 20 months for the MS group. DTI measures were determined using a semi-automated method from standardized regions of interest (ROI) containing central fibers of the corpus callosum genu and internal capsule.

RESULTS

The MS group had significantly lower fractional anisotropy (FA) values compared to controls (p<0.001), with increased radial diffusivity (RD) and decreased axial diffusivity (AD). In the monophasic group FA was smaller than the controls (p=0.01) with increased RD and no difference in AD.

CONCLUSIONS

This retrospective analysis provides evidence that NAWM is affected in pediatric MS and monophasic demyelinating disease, with a potentially novel pattern demonstrating reduced AD in pediatric MS. Further larger scale confirmatory studies are needed to address whether the demonstrated DTI changes could be used as a biomarker in pediatric patients presenting with an initial demyelinating event.

Corpus callosum damage predicts disability progression and cognitive dysfunction in primary-progressive MS after five years

We aim to identify specific areas of white matter (WM) and grey matter (GM), which predict disability progression and cognitive dysfunction after five years in patients with primary-progressive multiple sclerosis (PPMS). Thirty-two patients with early PPMS were assessed at baseline and after five years on the Expanded Disability Status Scale (EDSS), and EDSS step-changes were calculated. At year five, a subgroup of 25 patients and 31 healthy controls underwent a neuropsychological assessment. Baseline imaging consisted of dual-echo (proton density and T2-weighted), T1-weighted volumetric, and diffusion tensor imaging. Fractional anisotropy (FA) maps were created, and fed into tract-based spatial statistics. To compensate for the potential bias introduced by WM lesions, the T1 volumes underwent a lesion-filling procedure before entering a voxel-based morphometry protocol. To investigate whether FA and GM volume predicted EDSS step-changes over five years and neuropsychological tests scores at five years, voxelwise linear regression analyses were performed. Lower FA in the splenium of the corpus callosum (CC) predicted a greater progression of disability over the follow-up. Lower FA along the entire CC predicted worse verbal memory, attention and speed of information processing, and executive function at five years. GM baseline volume did not predict any clinical variable. Our findings highlight the importance of damage to the interhemispheric callosal pathways in determining physical and cognitive disability in PPMS. Disruption of these pathways, which interconnect motor and cognitive networks between the two hemispheres, may result in a disconnection syndrome that contributes to long-term physical and cognitive disability.

Diffusion abnormality maps in demyelinating disease: correlations with clinical scores

BACKGROUND AND PURPOSE

Magnetic resonance imaging (MRI) has been explored as a noninvasive tool to assess pathology in multiple sclerosis (MS) patients. However, the correlation between classical MRI measures and physical disability is modest in MS. The diffusion tensor imaging (DTI) MRI technique holds particular promise in this regard. The present study shows brain regions where FA and individual diffusivities abnormalities are present and check their correlations with physical disability clinical scores.

METHODS

Eight patients and 12 matched healthy controls were recruited. The Multiple Sclerosis Functional Composite was administered. For MR-DTI acquisitions, a Genesis Signa 1.5 T MR system, an EP/SE scanning sequence, 25 gradient directions were used.

RESULTS

Tract Based Spatial Statistics (TBSS) group comparisons showed reduced FA and increased individual diffusivities in several brain regions in patients. Significant correlations were found between FA and: EDSS, 9-HPT(NON)DOM and 25 FW score; between λ2 and: P100 (r&l), 9-HPT(NON)DOM and 25 FW; between λ3 and: 9-HPT(NON)DOM and 25 FW score.

CONCLUSIONS

Fractional anisotropy and individual radial diffusivities proved to be important markers of motor disabilities in MS patients when the disease duration mean and the disability scores values range are relatively high.

Fundamental differences in callosal structure, neurophysiologic function, and bimanual control in young and older adults

Bimanual actions involve coordinated motion but often rely on the movements performed with each hand to be different. Older adults exhibit differentially greater variability for bimanual actions in which each hand has an independent movement goal. Such actions rely on interhemispheric communication via the corpus callosum, including both facilitatory and inhibitory interactions. Here, we investigated whether age differences in callosal structure and interhemispheric function contribute to this selective movement difficulty. Participants performed 3 force production tasks: 1) unimanual, 2) bimanual simultaneous, and 3) bimanual independent. Older adults had significantly greater interhemispheric facilitation during voluntary muscle activation. We also report a fundamental shift with age in the relationship between callosal tract microstructural integrity and interhemispheric inhibition (IHI). Specifically, older adults with relatively greater callosal tract microstructural integrity have less IHI. Furthermore, greater IHI was related to poorer bimanual performance (assessed by dominant hand force variability) in older adults on all tasks, whereas this relationship was only observed in young adults for the bimanual independent condition. These findings indicate changes in interhemispheric communication with advancing age such that older adults may rely on bilateral cortical cooperation to a greater extent than young adults for manual actions.

Transcallosal sensorimotor fiber tract structure-function relationships

Recent studies have demonstrated neuroanatomically selective relationships among white matter tract microstructure, physiological function, and task performance. Such findings suggest that the microstructure of transcallosal motor fibers may reflect the capacity for interhemispheric inhibition between the primary motor cortices, although full characterization of the transcallosal inhibitory sensorimotor network is lacking. Thus, the goal of this study was to provide a comprehensive description of transcallosal fibers connecting homologous sensorimotor cortical regions and to identify the relationship(s) between fiber tract microstructure and interhemispheric inhibition during voluntary cortical activity. To this end, we assessed microstructure of fiber tracts connecting homologous sensorimotor regions of the cortex with diffusion tensor imaging. We also assessed interhemispheric inhibition by eliciting the ipsilateral silent period (iSP) within the same participants. We mapped mutually exclusive transcallosal connections between homologous sensorimotor regions and computed quantitative metrics of each fiber tract. Paralleling work in non-human primates, we found the densest interhemispheric sensorimotor connections to be between the medial motor areas. Additionally, we provide a midsagittal callosal atlas in normalized Montreal Neurological Institute (MNI) space for future studies to use when investigating callosal fiber tracts connecting primary and secondary sensorimotor cortices. Finally, we report a strong, positive relationship (r = 0.76) between strength of interhemispheric inhibition (iSP) and microstructure of interhemispheric fibers that is specific to tracts connecting the primary motor cortices. Thus, increased fiber microstructure in young adults predicts interhemispheric inhibitory capacity.

Multiple white matter tract abnormalities underlie cognitive impairment in RRMS

Diffusion tensor imaging (DTI) is a sensitive tool for detecting microstructural tissue damage in vivo. In this study, we investigated DTI abnormalities in individuals with relapsing remitting multiple sclerosis (RRMS) and examined the relations between imaging-based measures of white matter injury and cognitive impairment. DTI-derived metrics using tract-based spatial statistics (TBSS) were compared between 37 individuals with RRMS and 20 healthy controls. Cognitive impairment was assessed with three standard tests: the Symbol Digit Modalities Test (SDMT), which measures cognitive processing speed and visual working memory, the Rey Auditory Verbal Learning Test (RAVLT), which examines verbal memory, and the Paced Auditory Serial Addition Test (PASAT), which assesses sustained attention and working memory. Correlations between DTI-metrics and cognition were explored in regions demonstrating significant differences between the RRMS patients and the control group. Lower fractional anisotropy (FA) was found in RRMS participants compared to controls across the tract skeleton (0.40 ± 0.03 vs. 0.43 ± 0.01, p<0.01). In areas of reduced FA, mean diffusivity was increased and was dominated by increased radial diffusivity with no significant change in axial diffusivity, an indication of the role of damage to CNS myelin in MS pathology. In the RRMS group, voxelwise correlations were found between FA reduction and cognitive impairment in cognitively-relevant tracts, predominantly in the posterior thalamic radiation, the sagittal stratum, and the corpus callosum; the strongest correlations were with SDMT measures, with contributions to these associations from both lesion and normal-appearing white matter. Moreover, results using threshold-free cluster enhancement (TFCE) showed more widespread white matter involvement compared to cluster-based thresholding. These findings indicate the important role for DTI in delineating mechanisms underlying MS-associated cognitive impairment and suggest that DTI could play a critical role in monitoring the clinical and cognitive effects of the disease.