Diffusion tensor magnetic resonance imaging in multiple sclerosis

Resting state sensorimotor functional connectivity in multiple sclerosis inversely correlates with transcallosal motor pathway transverse diffusivity

Recent studies indicate that functional connectivity using low-frequency BOLD fluctuations (LFBFs) is reduced between the bilateral primary sensorimotor regions in multiple sclerosis. In addition, it has been shown that pathway-dependent measures of the transverse diffusivity of water in white matter correlate with related clinical measures of functional deficit in multiple sclerosis. Taken together, these methods suggest that MRI methods can be used to probe both functional connectivity and anatomic connectivity in subjects with known white matter impairment. We report the results of a study comparing anatomic connectivity of the transcallosal motor pathway, as measured with diffusion tensor imaging (DTI) and functional connectivity of the bilateral primary sensorimotor cortices (SMC), as measured with LFBFs in the resting state. High angular resolution diffusion imaging was combined with functional MRI to define the transcallosal white matter pathway connecting the bilateral primary SMC. Maps were generated from the probabilistic tracking employed and these maps were used to calculate the mean pathway diffusion measures fractional anisotropy FA, mean diffusivity MD, longitudinal diffusivity lambda(1), and transverse diffusivity lambda(2). These were compared with LFBF-based functional connectivity measures (F(c)) obtained at rest in a cohort of 11 multiple sclerosis patients and approximately 10 age- and gender-matched control subjects. The correlation between FA and F(c) for MS patients was r = -0.63, P < 0.04. The correlation between all subjects lambda(2) and F(c) was r = 0.42, P < 0.05. The correlation between all subjects lambda(2) and F(c) was r = -0.50, P < 0.02. None of the control subject correlations were significant, nor were FA, lambda(1), or MD significantly correlated with F(c) for MS patients. This constitutes the first in vivo observation of a correlation between measures of anatomic connectivity and functional connectivity using spontaneous LFBFs.

Normal regional fractional anisotropy and apparent diffusion coefficient of the brain measured on a 3 T MR scanner

INTRODUCTION

We aim to establish norms of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) in 20 different regions of the brain in healthy human volunteers.

METHODS

Thirty-one individuals were examined for ADC and FA in 20 regions of the brain using a single-shot, spin echo, echo planar diffusion tensor imaging sequence with 32 directions at 3 T. FA and ADC maps were computed using the Philips PRIDE tool, and regions of interest were drawn at 20 different locations in the brain. Relationships of FA and ADC with age and gender were explored.

RESULTS

We found a negative correlation between age and FA in the inferior fronto-occipital fasciculus and forceps minor. There were no gender differences. The cerebral peduncle, the middle cerebellum, and cingulum had the highest variation in FA, while fornix, optic radiation, and optic tract had the highest variation in ADC.

CONCLUSION

We provide a table of normative FA and ADC measurements in 20 brain regions of potential clinical relevance to the diagnosis and monitoring of specific neurological diseases.

Abnormal anterior cingulum integrity in bipolar disorder determined through diffusion tensor imaging

BACKGROUND

Convergent evidence implicates white matter abnormalities in bipolar disorder. The cingulum is an important candidate structure for study in bipolar disorder as it provides substantial white matter connections within the corticolimbic neural system that subserves emotional regulation involved in the disorder.

AIMS

To test the hypothesis that bipolar disorder is associated with abnormal white matter integrity in the cingulum.

METHOD

Fractional anisotropy in the anterior and posterior cingulum was compared between 42 participants with bipolar disorder and 42 healthy participants using diffusion tensor imaging.

RESULTS

Fractional anisotropy was significantly decreased in the anterior cingulum in the bipolar disorder group compared with the healthy group (P=0.003); however, fractional anisotropy in the posterior cingulum did not differ significantly between groups.

CONCLUSIONS

Our findings demonstrate abnormalities in the structural integrity of the anterior cingulum in bipolar disorder. They extend evidence that supports involvement of the neural system comprising the anterior cingulate cortex and its corticolimbic gray matter connection sites in bipolar disorder to implicate abnormalities in the white matter connections within the system provided by the cingulum.

Functional cortical changes of the sensorimotor network are associated with clinical recovery in multiple sclerosis

OBJECTIVE

To assess the early cortical changes following an acute motor relapse secondary to a pseudotumoral lesion in MS patients, the longitudinal cortical functional correlates of clinical recovery, and the evolution over time of cortical reorganization.

METHODS

FMRI during the performance of a simple motor task were obtained from 12 MS patients (after a clinical attack involving the motor system secondary to a pseudotumoral lesion) and 15 matched controls. In six patients and five controls, a longitudinal fMRI study was also performed.

RESULTS

In patients, at baseline, the primary sensorimotor cortex (SMC) of the ipsilateral (contralesional) hemisphere was significantly more active during task performance with the impaired than the unimpaired hand. During task performance with the unimpaired hand, the ipsilateral cerebellum and several motor areas in the contralateral hemisphere were significantly more active. Pseudotumoral lesion volume was correlated with activation of the primary SMC bilaterally (r = -0.86 and -0.85) and the nine-hole peg test score with activation of the primary SMC of the affected hemisphere (r = 0.88). A recovery of function of the primary SMC of the affected hemisphere was found in the four patients with clinical improvement. In the two patients without clinical recovery, there was a persistent recruitment of the primary SMC of the unaffected hemisphere.

CONCLUSIONS

Pseudotumoral MS lesions affecting the motor system can determine short-term cortical changes characterized by the recruitment of pathways in the unaffected hemisphere. The regain of function of motor areas of the affected hemisphere seems to be a critical factor for a favorable recovery.

Imaging white matter diffusion changes with development and recovery from brain injury

PURPOSE

This study reviews the application of diffusion tensor imaging (DTI) to the study of developmental and pathological changes in brain white matter. The ability to measure and monitor such changes in vivo would provide important opportunities for charting disease progression and monitoring response to therapeutic intervention. This study first reviews the use of DTI in studying normal human brain development. It goes on to illustrate how DTI has been used to provide insights into recovery from damage in selected brain disorders.

CONCLUSIONS

It is concluded that potential clinical applications of DTI include: (i) monitoring pathological change, (ii) providing markers that predict recovery and allow for individual targeting of therapy, (iii) providing outcome measures, (iv) providing measures of potentially compensatory structural changes and (v) improving understanding of normal brain anatomy to aid in interpretation of the consequences of localized damage.

Diffusion tensor imaging (DTI)-based white matter mapping in brain research: a review

Diffusion tensor imaging (DTI) has become one of the most popular MRI techniques in brain research, as well as in clinical practice. The number of brain studies with DTI is growing steadily and, over the last decade, has produced more than 700 publications. Diffusion tensor imaging enables visualization and characterization of white matter fascicli in two and three dimensions. Since the introduction of this methodology in 1994, it has been used to study the white matter architecture and integrity of the normal and diseased brains (multiple sclerosis, stroke, aging, dementia, schizophrenia, etc.). Although it provided image contrast that was not available with routine MR techniques, unique information on white matter and 3D visualization of neuronal pathways, many questions were raised regarding the origin of the DTI signal. Diffusion tensor imaging is constantly validated, challenged, and developed in terms of acquisition scheme, image processing, analysis, and interpretation. While DTI offers a powerful tool to study and visualize white matter, it suffers from inherent artifacts and limitations. The partial volume effect and the inability of the model to cope with non-Gaussian diffusion are its two main drawbacks. Nevertheless, when combined with functional brain mapping, DTI provides an efficient tool for comprehensive, noninvasive, functional anatomy mapping of the human brain. This review summarizes the development of DTI in the last decade with respect to the specificity and utility of the technique in radiology and anatomy studies.

Magnetic resonance imaging metrics and their correlation with clinical outcomes in multiple sclerosis: a review of the literature and future perspectives

Magnetic resonance imaging (MRI) has revolutionized the diagnosis and management of patients with multiple sclerosis (MS). Conventional MRI metrics are employed as primary endpoints in proof-of-concept clinical trials evaluating new drugs for MS and as secondary endpoints in definitive phase III trials. Metrics derived from non-conventional MRI techniques are now emerging and hold significant promise since they appear to be more correlated with the most disabling features of MS. However, none of these has been approved for use as a surrogate endpoint for accumulation of physical disability, which is the most important clinical endpoint of this disease. Taking into account the large numbers of patients needed, the extensive exposure to placebo, and the relatively long duration required for phase III clinical trials to show a meaningful effect on progression of disability, the need for a valid, reliable, and objective paraclinical marker of disease evolution cannot be overemphasized. This paper reviews the most up-to-date data regarding MRI techniques, their relationship with central nervous system pathology, as well as with clinical endpoints, and proposes future insights into the use of MRI metrics as surrogate endpoints in clinical trials of MS.

Regional differences in diffusion tensor imaging measurements: assessment of intrarater and interrater variability

BACKGROUND AND PURPOSE

Diffusion tensor imaging (DTI) has become a valuable tool in both the research and clinical evaluation of subjects. We sought to quantify interobserver and intraobserver variability of diffusivity and diffusion anisotropy measurements with regard to specific regions of interest (ROIs).

MATERIALS AND METHODS

The subject group consisted of 5 healthy control subjects and 7 study subjects (all males; 16-19 years old; mean age = 17.5 years), as part of a protocol for closed head injury. Two whole-brain DTI scans were acquired on a 3T scanner for each subject. Analysis was performed using a ROI approach. Two independent observers analyzed the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) indices in the corpus callosum, cortical spinal tract, internal capsules (ICs), basal ganglia, and centrum semiovale (CSO). Intraobserver and interobserver variability were calculated for the mean ADC, FA, and ordered eigenvalues of the diffusion tensor (lambda(1), lambda(2), and lambda(3)).

RESULTS

The overall kappa statistic for intraobserver variability for both observers showed slight-to-substantial agreement (kappa = 0.02-0.69), however FA values in the CSO showed only slight agreement. Interobserver agreement was also slight to substantial for these DTI measurements with high variability in FA values in the IC and CSO.

CONCLUSIONS

When one is comparing 2 DTI measurements, it is important to assess intraobserver and interobserver variability. We recommend caution in the analysis of DTI contrasts in the IC and CSO, because we have found the widest range of variability in measurements within these structures.

Longitudinal evaluation of clinically early relapsing-remitting multiple sclerosis with diffusion tensor imaging

Diffusion tensor imaging (DTI) parameters such as mean diffusivity (MD) and fractional anisotropy (FA) assess aspects of structural integrity within tissue. In relapsing-remitting (RR) multiple sclerosis (MS), abnormalities in normal appearing brain tissue (NABT) have been shown cross-sectionally. The evolution of these abnormalities over time is unclear. We present a longitudinal study investigating early RR MS subjects. The aims were to determine DTI changes over two years and assess the potential of DTI as a longitudinal quantitative marker at this stage of MS. Fifteen controls and 28 patients with RR MS (median disease duration 1.9 years; median EDSS 1.5) had DTI yearly for two years. NABT and whole brain tissue (NABT plus lesions) FA and MD histograms analysed. At baseline, differences in FA were noted between patients and controls (mean [p = 0.042] and peak height [p = 0.008]), while at two years differences in MD were observed (mean [p = 0.008] and peak location [p = 0.024]). However there were no significant DTI differences in longitudinal rates of change between patients and cohorts. In conclusion, although subtle NABT abnormalities were detected in early RR MS, the absence of longitudinal change suggests a limited role for global DTI assessment of NABT in following the early disease course.

Quantitative analysis of white matter on DTI images of patients with tinnitus: preliminary report

Tinnitus is defined as an unwanted auditory perception of internal origin, usually localized, and rarely heard by others. Persisting appearances of tinnitus are most commonly combined with diseases or damage in the inner ear or neuro-auditory pathway. Diffusion tensor magnetic resonance imaging (DTI) is a new imaging method with the capability of providing non-invasive information on tissue microstructure not available in routine clinical MRI images. Since white matter regions of the brain are an ordered structure due to the myelination and directionality of axons and have a high degree of anisotropy, the ability to detect changes in anisotropy can be extremely useful in the study of diseases such as tinnitus and multiple sclerosis, which are assumed to involve the demyelination of axons. While several studies investigated tinnitus using MRI, few studies tried to analyze neurological disorders quantitatively using DTI. In this study, the cerebral volume of white matter on DTI images of patients with tinnitus was measured using the semi-automated and intuitive menu based image processing tool (Human Analyzer, ETRI, Korea). Total number of ten patients with tinnitus including three women was examined.

Imaging of remyelination and neuronal health

Remyelination of axons that have been demyelinated due to multiple sclerosis (MS) may be a critical step in restoring the damaged axons and reversing the disease process. While it is possible to establish the presence of remyelination with microscopy of tissue samples, it is important to have noninvasive or minimally invasive methods to measure remyelination in living animals and humans. Such tools are critical to establishing the efficacy of agents purported to promote or enhance remyelination. This chapter reviews the technology of imaging of the brain, its application to MS, and the current state of imaging techniques for measuring remyelination and the health of the associated neurons in the setting of MS.

Compromised myelin integrity during psychosis with repair during remission in drug-responding schizophrenia

Functional connection among the information-processing (grey-matter) centres within the CNS are necessary for the coordinated processing of perception, affect, thought and behaviour. Myelinated neuronal bundles provide the links among such processing centres. Magnetic resonance diffusion tensor imaging (DTI) can assess the physical integrity of myelin. Using DTI, the authors assessed diffusivity (Dm) within whole brain in 14 controls and within 13 acutely psychotic, drug-free schizophrenics both before and after 28 d of antipsychotic drug treatment. Drug-responder schizophrenicss (D-RS) (n=8) were differentiated from poor responders (PR) (n=5) according to previously defined criteria. Differences of Dm at both baseline and following treatment were assessed using Dm distributional analyses and Statistical Parametric Software (SPM2). Impaired physical integrity of myelin, demonstrated by an increase (overall p<0.05) of Dm, was found in the D-RS patients, with multiple regions demonstrating p<0.0005 patient-control differences. The pathological increase in Dm was reduced (p<0.03) following treatment-associated reduction of psychotic symptoms by 84%. Dm of PR patients did not differ from controls at baseline or following subacute treatment. While the pathophysiology(ies) underlying psychosis in poorly responsive (PR) schizophrenics does not appear to be related to a disordered myelin, the findings are consistent with a partially reversible disorder of myelin integrity, and may underlie a dys-synchrony of information processing in a major subgroup of drug-responsive patients with schizophrenia. An antipsychotic drug-induced cascade may partially restore myelin integrity and functional connectivity concomitant with antipsychotic effects in such D-RS patients.

Reorganization of neural circuits in the blind on diffusion direction analysis

The neural reorganization of the visual cortex of early blind individuals was evaluated using voxel-by-voxel analysis of diffusion tensor images with regard to the diffusion direction, diffusion anisotropy and diffusivity. Reduced anisotropy and increased diffusivity was found mainly in the visual pathways of 18 early blind individuals as opposed to 25 sighted individuals. Alteration of the diffusion direction was detected not only in the visual pathways but also in nonvisual pathways such as the u fibers of the parietal lobe, the sagittal striatum, the pulvinar and the inferior and superior longitudinal fasciculi. The alteration of regional diffusion direction, reduced anisotropy and increased diffusivity in early blind individuals imply the neural reorganization for functional adaptation to the loss of visual input during the early development period.

Non-uniform gradient prescription for precise angular measurements using DTI

Diffusion Tensor Imaging (DTI) calculates a tensor for each voxel, representing the mean diffusive characteristics in volume-averaged tissue. Gradients that phase-encode spins according to the amount of their diffusion are usually applied uniformly over a sphere during a DTI procedure for minimal bias of tensor information. If prior knowledge of diffusion direction exists, the angular precision for determining the principle eigenvector of cylindrically-symmetric ("prolate") tensors can be improved by specifying gradients non-uniformly. Improvements in precision of 30-40% can be achieved using a restricted band of zenith angle values for gradient directions. Sensitivity to the a priori angular range of the principle eigenvector can be adjusted with the width of the band. Simulations and phantom data are in agreement; a preliminary validation is presented.

Disturbed structural connectivity in schizophrenia primary factor in pathology or epiphenomenon?

Indirect evidence for disturbed structural connectivity of subcortical fiber tracts in schizophrenia has been obtained from functional neuroimaging and electrophysiologic studies. During the past few years, new structural imaging methods have become available. Diffusion tensor imaging and magnetization transfer imaging (MTI) have been used to investigate directly whether fiber tract abnormalities are indeed present in schizophrenia. To date, findings are inconsistent that may express problems related to methodological issues and sample size. Also, pathological processes detectable with these new techniques are not yet well understood. Nevertheless, with growing evidence of disturbed structural connectivity, myelination has been in the focus of postmortem investigations. Several studies have shown a significant reduction of oligodendroglial cells and ultrastructural alterations of myelin sheats in schizophrenia. There is also growing evidence for abnormal expression of myelin-related genes in schizophrenia: Neuregulin (NRG1) is important for oligodendrocyte development and function, and altered expression of erbB3, one of the NRG1 receptors, has been shown in schizophrenia patients. This is consistent with recent genetic studies suggesting that NRG1 may contribute to the genetic risk for schizophrenia. In conclusion, there is increasing evidence from multiple sides that structural connectivity might be pathologically changed in schizophrenia illness. Up to the present, however, it has not been possible to decide whether alterations of structural connectivity are intrinsically linked to the primary risk factors for schizophrenia or to secondary downstream effects (ie, degeneration of fibers secondarily caused by cortical neuronal dysfunction)-an issue that needs to be clarified by future research.

Fractional anisotropy and mean diffusivity: comparison between 3.0-T and 1.5-T diffusion tensor imaging with parallel imaging using histogram and region of interest analysis

We performed a comparison study focusing on differences in fractional anisotropy (FA) and mean diffusivity (MD) between 3-T and 1.5-T diffusion tensor imaging (DTI) with parallel imaging. Thirty healthy volunteers underwent DTI with an eight-channel phased-array coil at both 3 T and 1.5 T. Histogram and region of interest (ROI) analyses were performed. Paired t tests were applied for statistical analysis. Signal-to-noise ratios of these regions were also measured. For histogram analysis, peak location of FA was significantly lower at 3 T than at 1.5 T (P = 0.04). Mean FA was significantly higher at 3 T than at 1.5 T (P = 0.002). Peak location of MD was significantly lower at 3 T than at 1.5 T (P < 0.001). Mean MD was significantly lower at 3 T than at 1.5 T (P < 0.001). In ROI analysis, FA was significantly larger at 3 T than at 1.5 T in the centrum semiovale (P < 0.001), middle cerebellar peduncle (P < 0.001), cerebral peduncle (P = 0.006), posterior limb of the internal capsule (P = 0.007), genu (P < 0.001) and splenium (P < 0.001). FA was significantly lower at 3 T than at 1.5 T in the globus pallidus (P < 0.001). MD was significantly smaller at 3 T than at 1.5 T in the globus pallidus (P = 0.007), thalamus (P < 0.001), centrum semiovale (P < 0.001), middle cerebellar peduncle (P < 0.001), cerebral peduncle (P = 0.01), posterior limb of the internal capsule (P < 0.001), genu (P = 0.01) and splenium (P < 0.001). Significant differences in FA and MD exist between 3 T and 1.5 T for whole-brain histogram analysis and ROI analysis.

Case control study of diffusion tensor imaging in Parkinson's disease

BACKGROUND

Preliminary work has shown that diffusion tensor MRI (DTI) may contribute to the diagnosis of Parkinson's disease (PD).

OBJECTIVES

We conducted a large, prospective, case control study to determine: (1) if fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values on DTI in the basal ganglia and substantia nigra are different between patients with PD and healthy controls; and (2) the predictive value of these parameters and their clinical utility.

METHODS

DTI imaging was carried out in patients with PD and controls. FA and ADC values were obtained from various brain structures on the DTI scan using the diffusion tensor taskcard. The structures studied were: caudate, putamen, globus pallidus, thalamus and substantia nigra.

RESULTS

151 subjects (73 PD patients, 41 men, 32 women; mean age 63.6 years) and 78 age and sex matched control subjects were studied. The FA value of the substantia nigra in patients with PD was lower compared with controls (0.403 vs 0.415; p = 0.001). However, no significant differences were demonstrated for FA or ADC values of other structures. Multiple regression analysis revealed that the clinical severity of PD correlated inversely with the FA value in the substantia nigra in patients with PD (regression coefficient -0.019). No single FA value had both a high positive and negative predictive power for PD.

CONCLUSIONS

We demonstrated in a large, prospective, case control study that the FA value in the substantia nigra on DTI was lower in PD compared with healthy controls, and correlated inversely with the clinical severity of PD. Further longitudinal studies would be helpful to assess the clinical utility of serial FA measurements of the substantia nigra in objective quantification of disease progression and monitoring of the therapeutic response.

Diffusion-tensor MR imaging and tractography: exploring brain microstructure and connectivity

Diffusion magnetic resonance (MR) imaging is evolving into a potent tool in the examination of the central nervous system. Although it is often used for the detection of acute ischemia, evaluation of directionality in a diffusion measurement can be useful in white matter, which demonstrates strong diffusion anisotropy. Techniques such as diffusion-tensor imaging offer a glimpse into brain microstructure at a scale that is not easily accessible with other modalities, in some cases improving the detection and characterization of white matter abnormalities. Diffusion MR tractography offers an overall view of brain anatomy, including the degree of connectivity between different regions of the brain. However, optimal utilization of the wide range of data provided with directional diffusion MR measurements requires careful attention to acquisition and postprocessing. This article will review the principles of diffusion contrast and anisotropy, as well as clinical applications in psychiatric, developmental, neurodegenerative, neoplastic, demyelinating, and other types of disease.

Primary granulomatous angiitis of the central nervous system: findings of magnetic resonance spectroscopy and fractional anisotropy in diffusion tensor imaging prior to surgery. Case report

Primary granulomatous angiitis of the central nervous system (CNS) is extremely rare. Its preoperative diagnosis is difficult as the condition displays nonspecific features on routine neuroimaging investigations. In this paper, the authors report findings of magnetic resonance (MR) spectroscopy and fractional anisotropy (FA) with diffusion tensor MR imaging in a case of granulomatous angiitis of the CNS. A 30-year-old man presented with morning headaches and grand mal seizures. An MR image revealed a mass resembling glioblastoma in the right temporal lobe. Magnetic resonance spectroscopy showed a high choline/creatine (Cho/Cr) ratio indicative of a malignant neoplasm, accompanied by a slight elevation of glutamate and glutamine. The FA value was very low, which is inconsistent with malignant glioma. The mass was totally removed surgically. Histologically, the peripheral lesion of the mass consisted of a rough accumulation of fat granule cells, infiltration of inflammatory cells, and distribution of capillary vessels. Some vessels within the lesion were replaced by granulomas. The histological diagnosis was granulomatous angiitis of the CNS. The MIB-1-positive rate of the granuloma was approximately 5%. Both MR spectroscopy and FA were unable to accurately diagnose granulomatous angiitis of the CNS prior to surgery; however, elevated Cho/Cr and glutamate and glutamine shown by MR spectroscopy may indicate the moderate proliferation potential of the granuloma and the inflammatory process, respectively, in this condition. Although the low FA value in the present case enabled the authors to rule out a diagnosis of glioblastoma, FA values in inflammatory lesions require careful interpretation.

Representing diffusion MRI in 5-D simplifies regularization and segmentation of white matter tracts

We present a new five-dimensional (5-D) space representation of diffusion magnetic resonance imaging (dMRI) of high angular resolution. This 5-D space is basically a non-Euclidean space of position and orientation in which crossing fiber tracts can be clearly disentangled, that cannot be separated in three-dimensional position space. This new representation provides many possibilities for processing and analysis since classical methods for scalar images can be extended to higher dimensions even if the spaces are not Euclidean. In this paper, we show examples of how regularization and segmentation of dMRI is simplified with this new representation. The regularization is used with the purpose of denoising and but also to facilitate the segmentation task by using several scales, each scale representing a different level of resolution. We implement in five dimensions the Chan-Vese method combined with active contours without edges for the segmentation and the total variation functional for the regularization. The purpose of this paper is to explore the possibility of segmenting white matter structures directly as entirely separated bundles in this 5-D space. We will present results from a synthetic model and results on real data of a human brain acquired with diffusion spectrum magnetic resonance imaging (MRI), one of the dMRI of high angular resolution available. These results will lead us to the conclusion that this new high-dimensional representation indeed simplifies the problem of segmentation and regularization.

Restless legs syndrome is a common finding in multiple sclerosis and correlates with cervical cord damage

In this prospective study, we estimated the prevalence of restless legs syndrome (RLS) in multiple sclerosis (MS) patients, and compared the extent of brain and cervical cord damage between patients with and without RLS using conventional and diffusion tensor magnetic resonance imaging (MRI). Eighty-two consecutive MS patients were evaluated. Each patient underwent a medical history interview, a neurological examination and brain/cervical cord MRI. Global and regional dual-echo lesion load (LL), number of cervical cord lesions, mean diffusivity (MD) and fractional anisotropy (FA) histograms metrics of the normal-appearing tissues of the brain and cervical cord were assessed. Thirty subjects had RLS; they showed a higher Expanded Disability Status Scale score than patients without. No difference between the two groups was found in whole brain, cerebellar and brainstem T(2)-LLs; MD and FA histograms derived metrics of the normal appearing brain tissues; basal ganglia MD; number of cervical cord lesions and cord MD histograms derived metrics. Cervical cord average FA was significantly reduced in MS patients with RLS compared to those without. RLS symptoms are very common in MS. This form of RLS should be considered as symptomatic. Higher disability and cervical cord damage represent a significant risk factor for RLS in MS patients.

Handedness and the brain: a review of brain-imaging techniques

The author reviewed brain-imaging studies on human handedness reported in major academic journals for the last 12 years, classified them as having anatomical or functional interest, and attempted to determine consensus on findings and limitations among the studies. Present reviews suggest that there have been fewer functional than anatomical examinations into handedness and that findings from those studies have not been necessarily consistent, that participants' degree of handedness has not been consistent between left-handed and right-handed people, and that much more brain-imaging study is anticipated to examine functional and anatomical differences of handedness based on genetic and environmental models.

Fractional anisotropy correlates with auditory simple reaction time performance

During the last two decades, modern imaging studies focused intensively on the broad field of reaction time paradigms and significantly enhanced the understanding of behavioral performance. However, interindividual variations of simple reaction time (SRT) have been barely investigated. In this study, we intended to identify neural correlates of interindividual variation in auditory SRT (aSRT) employing the Poffenberger paradigm with auditory stimuli, in order to investigate neural processing speed performance. We conducted a whole-head voxel based morphometry analysis of fractional anisotropy (FA) in 19 healthy, right handed subjects. Simple regression analysis between FA and interindividual aSRT measures was performed for each voxel. Significant positive correlation (R(2): 0.44/0.78 min/max) for FA vs. individual mean aSRT was found in the right central cerebellum dorso-cranial of the dentate nucleus. A significant correlation (R(2): 0.453/0.633 min/max) was also detected between FA and the hand performance index, which characterizes the intraindividual RT difference between left and right hand, within the precentral portion of the pyramidal tract in the left hemisphere. Fast right handed response correlated with high local FA values located within neural structures participating in right hand control. Against the background of only right handed participants in our study, the hypothesis of local myelination as one basic condition influencing reaction time performance is strongly supported. The presented results identify brain areas involved in the processing speed of the aSRT tasks. We propose that the presented findings are due to an influence of participants' right hand preference on both FA and aSRT measures.

MRI in multiple sclerosis: what's inside the toolbox?

Magnetic resonance imaging (MRI) has played a central role in the diagnosis and management of multiple sclerosis (MS). In addition, MRI metrics have become key supportive outcome measures to explore drug efficacy in clinical trials. Conventional MRI measures have contributed to the understanding of MS pathophysiology at the macroscopic level yet have failed to provide a complete picture of underlying MS pathology. They also show relatively weak relationships to clinical status such as predictive strength for clinical progression. Advanced quantitative MRI measures such as magnetization transfer, spectroscopy, diffusion imaging, and relaxometry techniques are somewhat more specific and sensitive for underlying pathology. These measures are particularly useful in revealing diffuse damage in cerebral white and gray matter and therefore may help resolve the dissociation between clinical and conventional MRI findings. In this article, we provide an overview of the array of tools available with brain and spinal cord MRI technology as it is applied to MS. We review the most recent data regarding the role of conventional and advanced MRI techniques in the assessment of MS. We focus on the most relevant pathologic and clinical correlation studies relevant to these measures.

Evaluation of white matter in patients with multiple sclerosis through diffusion tensor magnetic resonance imaging

OBJECTIVE: To study the white matter of patients with multiple sclerosis (MS) with diffusion tensor magnetic resonance (MR) imaging (DTI). METHOD: Forty patients with clinical-laboratorial diagnosis of relapsing-remitting MS and 40 age- and sex-matched controls, who underwent conventional and functional (DTI) MR imaging, were included in the study. The DTI sequences resulted in maps of fractional anisotropy (FA) and regions of interest were placed on the plaques, peri-plaque regions, normal-appearing white matter (NAWM) around the plaques, contralateral normal white matter (CNWM) and normal white matter of the controls (WMC). The FA values were compared and the statistical treatment was performed with the Mann-Whitney U test. RESULTS: The mean FA in plaques was 0.268, in peri-plaque regions 0.365, in NAWM 0.509, in CNWM 0.552 and in WMC 0.573. Statistical significant differences in FA values were observed in plaques, peri-plaque regions and in NAWM around the plaques when compared to the white matter in the control group. There was no significant difference between the FA values of the CNWM of patients with MS and normal white matter of controls. CONCLUSION: Patients with MS show difference in the FA values of the plaques, peri-plaques and NAWM around the plaques when compared to the normal white matter of controls. As a result, DTI may be considered more efficient than conventional MR imaging for the study of patients with MS.

Cell-oriented analysis in vivo using diffusion tensor imaging for normal-appearing brain tissue in multiple sclerosis

There have been several methods proposed so far using diffusion tensor imaging (DTI) for the assessment of normal-appearing brain tissue (NABT) injury in multiple sclerosis (MS). However, for these methods, the analyses of the NABT injury at the cellular level, wherein histological examinations can be used, still present challenging problems. We developed a method of segregating NABT into the following anatomical structures using lambda chart analysis associated with a two-dimensional Gaussian deconvolution of diffusion characteristic functions: 1) structures primarily composed of small neurons and glia; 2) structures primarily composed of large neurons; 3) structures primarily composed of short axons; and 4) structures primarily composed of long axons. Each segregated structure that had a distinctive diffusion characteristic was subjected to the statistical inference of DTI-derived parameters for 14 patients with conventional relapsing-remitting MS (RRMS) and 20 age-matched healthy volunteers. In all of the structures, the trace values were significantly higher and the fractional anisotropy values were significantly lower in the RRMS patients than in the healthy volunteers. Furthermore, the volume fractions of the structures primarily composed of short axons markedly decreased, whereas those of the structures primarily composed of small neurons and glia markedly increased. These results suggest that axonal loss and glial proliferation predominantly occurred in the subcortical white matter and adjacent deep cortical layer, namely, the juxtacortical region. This cell-oriented analysis of NABT injury using DTI confirmed in vivo the histological observation that the juxtacortical region is the most vulnerable site in MS.

Assessing "occult" cervical cord damage in patients with neuropsychiatric systemic lupus erythematosus using diffusion tensor MRI

BACKGROUND

Whereas focal and diffuse brain damage on conventional MRI is seen in patients with neuropsychiatric systemic lupus erythematosus (NSLE), the spinal cord seems to be rarely involved. Diffusion tensor (DT) MRI provides information on the patterns of tissue disruption of the central nervous system, which may go undetected by conventional MRI.

OBJECTIVE

To quantify the extent of otherwise "occult" injury of the cervical cord in NSLE, and to improve our understanding of its nature.

SUBJECTS AND METHODS

Conventional and DT MRI scans of the cervical cord and brain were acquired from 11 patients with NSLE and 10 healthy controls. Histograms of mean diffusivity (MD) and fractional anisotropy (FA) of the cervical cord and brain were analysed. Measures of cervical cord and brain atrophy and focal lesion loads were computed.

RESULTS

Only one patient had a single focal lesion of the cord whereas all had multiple brain lesions on conventional MRI scans. Cord and brain volumes did not differ between patients and controls. Mean peak height of the cervical cord MD histogram (p = 0.0001) and average brain FA (p = 0.001) were significantly lower in patients than in controls. Average cord MD was correlated with average brain MD (r = 0.69, p = 0.01) and FA (r = -0.81, p = 0.002).

CONCLUSION

DT MRI shows mild and otherwise "occult" cord damage in NSLE, which might be secondary to Wallerian degeneration of long tract fibres passing trough damaged areas of the brain.

Inflammatory demyelination and neurodegeneration in early multiple sclerosis

A number of recent magnetic resonance imaging studies have challenged the classical view of multiple sclerosis (MS) as a "two-stage" disease where an early inflammatory demyelinating phase with focal macroscopic lesions formed in the white matter (WM) of the central nervous system is followed by a late neurodegenerative phase, which is believed to be a mere consequence of repeated inflammatory insults and irreversible demyelination. These studies have consistently shown the presence of diffuse normal-appearing WM damage, marked gray matter involvement and significant cortical functional reorganization, as well as the occurrence of the neurodegenerative component of MS from the earliest clinical stages of the disease with only a partial relation to MRI markers of inflammatory demyelination. The present review argues that MS can no longer be viewed as a "two-stage" disease, which suggests that the two pathological components are dissociated in time, but rather as a "simultaneous two-component" disease, where the relative contributions of the various pathological processes of the disease to the development of "fixed" disability, their relationship and their evolution over time need to be clarified. This new view of MS should inform the development of future research protocols to define its actual physiopathology and prompt the institution of early treatment which should ideally target not only inflammatory demyelination, but also the neurodegenerative aspects of the disease, as well as promote neuroprotection and enhance reparative mechanisms and adaptive functional reorganization of the cortex.

MR diffusion changes correlate with ultra-structurally defined axonal degeneration in murine optic nerve

Diffusion weighted imaging (DWI) and diffusion tensor imaging (DTI) are widely used to investigate central nervous system (CNS) white matter structure and pathology. Changes in principal diffusivities parallel and perpendicular to nerve fibers or axonal tracts have been associated with axonal pathology and de/dysmyelination respectively. However, the ultra-structural properties and the pathological alterations of white matter responsible for diffusivity changes have not been fully elucidated. We examined the relationship between the directional diffusivities and ultra-structural properties in mouse optic nerve using healthy animals, and mice with optic neuritis (ON) that exhibited marked inflammatory changes and moderately severe axonal pathology. Progressive axonal degeneration in ON resulted in a 23% reduction of parallel diffusivity as detected by diffusion MRI (P<10(-5)), but no change in perpendicular diffusivity. Parallel diffusion changes were highly correlated with the total axolemmal cross-sectional area in the pre-chiasmal portion of the optic nerve (r=0.86, P<0.001). This study provides quantitative evidence that reduced parallel diffusivity in the optic nerve correlates significantly with axolemmal cross-sectional area reductions. MRI-based assessment of axonal degeneration in murine ON is feasible and potentially useful for monitoring of neuro-protective therapies in preclinical trials in animals.

fMRI changes in relapsing-remitting multiple sclerosis patients complaining of fatigue after IFNbeta-1a injection

If fatigue in multiple sclerosis (MS) is related to an abnormal activation of the sensorimotor brain network, the activity of such a network should vary with varying fatigue. We studied 22 patients treated with interferon beta 1a (IFNbeta-1a; Avonex, Biogen, Cambridge, MA) with no fatigue (10) and with reversible fatigue (12). fMRI examinations were performed: 1) the same day of IFNbeta-1a injection (no fatigue; entry), 2) the day after IFNbeta-1a injection (fatigue; time 1), and 3) 4 days after IFNbeta-1a injection (no fatigue; time 2). Patients performed a simple motor task with the right, clinically unaffected hand. At time 1, compared with entry and time 2, MS patients with reversible fatigue showed an increased activation of the thalamus bilaterally. In MS patients without fatigue thalamus was more activated at entry than at time 1. In both groups at entry the primary SMC and the SMA were more activated than at times 1 and 2. At entry and time 1, when compared to patients with reversible fatigue, those without showed increased activations of the SII. Conversely, patients with reversible fatigue had increased activations of the thalamus and of several regions of the frontal lobes. An abnormal recruitment of the fronto-thalamic circuitry is associated with IFNbeta-1a-induced fatigue in MS patients.

Comparison of breast cancer detection by diffusion-weighted magnetic resonance imaging and mammography

PURPOSE

Breast cancer-detecting ability of diffusion-weighted magnetic resonance imaging (DW-MRI) was investigated by comparing the breast cancer detection rates of DW-MRI and mammography (MMG).

MATERIALS AND METHODS

The subjects were 48 women who had breast cancer (53 cancer lesions) who underwent DW-MRI before surgery. Altogether, 41 lesions were invasive ductal carcinoma (IDC), 7 were noninvasive ductal carcinoma (NIDC) and 5 were "others."

RESULTS

The breast cancer detection rates by MMG and DW-MRI were 84.9% and 94.3% (P < 0.001), respectively. In each classification of histology and size, the detection rate by DW-MRI was higher than that by MMG. In relation to the mammary gland density, the detection rates of fatty, scattered, heterogeneously dense, and extremely dense mammary glands were 100%, 100%, 92.0%, and 83.3%, respectively. The mean apparent diffusion coefficient values of the histologic types were 1.07 +/- 0.17 x 10(-3), 1.50 +/- 0.24 x 10(-3), 1.12 +/- 0.25 x 10(-3), and 2.01 +/- 0.29 x 10(-3) mm(2)/s for IDC, NIDC, others, and normal breast, respectively, showing that the values of IDC and NIDC were significantly different from that of the normal breast (P < 0.001 each). A significant difference was also noted between IDC and NIDC (P < 0.001).

CONCLUSION

DW-MRI may be useful for detecting breast cancer in a wide age group of women, including young women with dense mammary glands.

The contribution of diffusion-weighted MR imaging in multiple sclerosis during acute attack

PURPOSE

The aims of the study are firstly, to determine the difference in diffusion-weighted imaging (DWI) in normal appearing white matter (NAWM) between patients with acute multiple sclerosis (MS) and controls; secondly, to determine whether there is a correlation between EDSS scores and DWI in acute plaques and also NAWM.

MATERIALS AND METHOD

Out of 50 patients with acute MS attack, 35 patients had active plaques with diffuse or ring enhancement on postcontrast images. Eighteen healthy volunteers constituted the control group. While 26 of 35 had relapsing-remitting, 9 had secondary progressive MS. Apparent diffusion coefficients (ADC) of the active plaques, NAWM at the level of centrum semiovale and occipital horn of lateral ventricle in the patients and NAWM in control group were measured. ADC values of active plaques were compared with WM of the patients and the control group. The relationship of ADC value of active plaques and WM in MS with expanded disability status scale (EDSS) was investigated by using Mann-Whitney U-test.

RESULTS

Of 63 plaques totally, 26 and 37 of the active plaques had diffuse and ring enhancement, respectively. There was no statistically significant difference between ADC value of active plaques and EDSS (p>0.05). However, there was a statistically significant difference between ADC value of WM occipital horn and EDSS (p<0.05). ADC value of active plaques were higher than WM in both groups (p<0.001). The difference between ADC value of WM at the centrum semiovale (p<0.05) and occipital horns (p<0.001) in patients and controls was statistically significant. There was no statistically significant difference between EDSS scores, ADC value at centrum semiovale and WM around occipital horn and active plaques in subgroups (p>0.05).

CONCLUSION

Apparently normal tissue in MS patients may show early abnormalities when investigated carefully enough, and there is an even though moderate correlation between EDSS and ADC values and early alterations of ADC value are starting in the occipital white matter along the ventricles. This has to be verified in larger series.

Diffusion tensor MRI in multiple sclerosis

During the last 10 years, thanks to the development of sophisticated acquisition schemes and the application of novel image analysis and postprocessing, diffusion tensor (DT) magnetic resonance imaging (MRI) has increasingly been applied to the study of multiple sclerosis (MS). DT MRI proved to be able to detect and quantify tissue damage within and outside T2-visible MS lesions. In addition, DT MRI has been shown to be sensitive to the evolution of MS damage over short-term periods of time, and therefore holds promise to provide us with in vivo correlates of MS clinical severity, as well as predictors of long-term disease evolution. Recent developments of the technique, such as DT tractography, are likely to improve dramatically our understanding of the mechanisms associated to the accumulation of MS disability. Unresolved issues to be addressed include the definition of the actual features underlying diffusion changes in MS and the potential of DT MRI in the differential diagnosis between MS and other demyelinating conditions. The best acquisition and postprocessing strategies for DT MRI studies of MS also remain a matter of debate. Moreover, the precision and accuracy of DT MRI scans in detecting longitudinal, MS-related changes need to be further investigated. This is a pivotal issue for a future application of DT MRI to the monitoring of MS evolution in large-scale clinical trials and, possibly, in individual patients.

Widespread effects of hyperintense lesions on cerebral white matter structure

OBJECTIVE

Hyperintense lesions are a common finding on neuroimaging and are associated not only with aging, medical illness, and some invasive medical procedures, but also with neurologic and psychiatric morbidity. We hypothesized that hyperintense lesions are associated with alterations in white matter structure beyond the visible lesion boundaries as assessed with diffusion tensor imaging (DTI).

SUBJECTS AND METHODS

Eighty-two neurologically intact older individuals completed brain MRI with DTI. DTI scans were analyzed using regions of interest placed in normal-appearing white matter to measure fractional anisotropy and diffusivity in the white matter of the frontal lobe, the genu of the corpus callosum, and the internal capsule. Hyperintense lesions volumes were measured separately in subcortical gray matter and anterior white matter through a semiautomated segmentation program. The relationship between lesion volumes and DTI measures was examined while controlling for patient age, patient sex, and total cerebral volume.

RESULTS

Greater anterior white matter lesion volumes were associated with higher diffusivity and lower anisotropy in the white matter of the dorsolateral prefrontal cortex and with higher diffusivity of the internal capsule and white matter lateral to the anterior cingulate cortex. Gray matter lesion volumes were associated with higher diffusivity in the genu of the corpus callosum and the internal capsule.

CONCLUSION

Ischemic hyperintense lesions are associated with widespread effects on the structure of the frontal lobe white matter and central white matter structures. This may reflect effects of lesions on neural circuits or identification of white matter changes that have not yet become visible on conventional MRI.

Diffusion-Tensor Imaging at 3 T

OBJECTIVE

Fractional anisotropy (FA) is a powerful measure to study the integrity of the cerebral white matter in vivo. However, because clinical FA assessments are frequently based on single slice evaluations, intra- and interindividual comparisons are highly dependent on image alignment. We attempted to develop an observer-independent, fully automated technique for quantitative FA assessment.

MATERIALS AND METHODS

We employed whole brain diffusion tensor imaging at 3 T with an echo planar imaging sequence (isotropic spatial resolution 1.8 mm) on 4 patients (2x Alzheimer disease, 1x microangiopathy, 1x paraneoplastic disease) and 2 normal control groups (group "young," age 19-32 years; group "old," age 59-69 years). The images were spatially normalized to the standard brain template of the Montreal Neurologic Institute. We introduced a fractional anisotropy index (FAI) as a single measure for the mean tissue anisotropy in certain brain regions of interest. The regions of interest were defined by masks in relation to the Montreal Neurologic Institute coordinate space. We varied the spatial extent of the masks. Confidence intervals of the FAIs for both control groups were calculated.

RESULTS

We found the resulting FAIs to be highly robust against considerable mask variations (product-moment correlation: r > 0.97). The FAIs of the 4 patients presented with neurologic conditions associated with white matter alterations significantly fell outside the confidence intervals for normal FA.

CONCLUSION

FAIs based on mean fractional anisotropy values obtained from isotropic whole-head high-field diffusion tensor imaging by fully automated algorithms represent a robust and observer-independent measure for the comparative assessment of white matter integrity, ideally suited for further statistical treatments.

The pathogenesis of the white matter abnormalities in phenylketonuria. A multimodal 3.0 tesla MRI and magnetic resonance spectroscopy (1H MRS) study

OBJECTIVE

To gain insights into the nature and pathogenesis of white matter (WM) abnormalities in PKU.

METHODS

Thirty-two patients with phenylalanine hydroxylase deficiency (21 with early and 11 with late diagnosis and treatment) and 30 healthy controls underwent an integrated clinical, neuroimaging (3.0 T MRI, diffusion-weighted imaging (DWI), diffusion tensor imaging (DTI)) and neurochemical (1H MRS) investigation.

RESULTS

All patients had white matter abnormalities on T2-weighted (T2W) and fluid-attenuated inversion recovery (FLAIR) scans; parietal white was consistently affected, followed by occipital, frontal and temporal white matter. T1-weighted hypointense alterations were also found in 8 of 32 patients. DWI hyperintense areas overlapped with those detected on T2W/FLAIR. The apparent diffusion coefficient (ADC) was reduced and correlated inversely with severity of white matter involvement. Fractional anisotropy index, eigenvalues lambda(min), lambda(middle), lambda(max) obtained from DTI data, and the principal brain metabolites assessed by 1H MRS (except brain phenylalanine (Phe)) were normal. Brain Phe peak was detected in all but two subjects. Brain and blood Phe were strictly associated. Blood Phe at the diagnosis, patient's age, and concurrent brain Phe independently influence white matter alteration (as expressed by conventional MRI or ADC values).

CONCLUSIONS

(a) MRI abnormalities in phenylketonuria are the result of a distinctive alteration of white matter suggesting the intracellular accumulation of a hydrophilic metabolite, which leaves unaffected white matter architecture and structure. (b) White matter abnormalities do not seem to reflect the mechanisms involved in the derangement of mental development in PKU. (c) Our data do not support the usefulness of conventional brain MRI examination in the clinical monitoring of phenylketonuria patients.

Normal-appearing white and grey matter damage in MS. A volumetric and diffusion tensor MRI study at 3.0 Tesla

The aims of this study were to improve, using a 3.0 Tesla (T) scanner and diffusion tensor (DT) magnetic resonance imaging (MRI) with sensitivity encoding, our understanding of: 1) the possible pathological substrates of normal-appearing white matter (NAWM) and grey matter (GM) damage in multiple sclerosis (MS) and 2) the factors associated to WM and GM atrophy in this condition. Conventional and DT MRI of the brain were acquired from 32 relapsing-remitting (RR) MS patients and 16 controls. Lesion load, WM (WMV), overall GM (GMV), and neocortical GM (NCV) volumes were measured. NAWM mean diffusivity (MD) and fractional anisotropy (FA), and GM MD were calculated. GMV and NCV were lower (p < or = 0.001) in MS patients than controls, whereas WMV did not differ significantly. MS patients had higher NAWM and GM average MD and lower NAWM average FA (p < or = 0.001) than controls. Moderate correlations were found between intrinsic lesion and tissue damage with both GM volumetric and diffusivity changes (-0.41 < or = r < or = 0.42, p < or = 0.04). DT MRI and volumetry measurements at 3.0 T confirm the presence of NAWM and GM abnormalities in RRMS patients. Although histopathology was not available, axonal and neuronal damage and consequent reactive glial proliferation are the most likely substrates of the changes observed.

Plasticity of the corticospinal tract in early blindness revealed by quantitative analysis of fractional anisotropy based on diffusion tensor tractography

Early visual deprivation may induce plastic changes, not only in the visual system, but also in the remaining sensory systems, secondary to altered experience in these spared modalities. Most of previous studies were focused on the plasticity of cortical areas of sensory modalities, but little attention was paid to the plasticity of motor system and white matter fiber tracts. Our purpose is to investigate the plasticity of the corticospinal tract (CST) in early blindness by tract-based quantitative analysis of fractional anisotropy (FA). Diffusion tensor imaging was performed in 17 early blind and 17 gender- and age-matched sighted subjects. The entire CST of each subject was reconstructed and the average FA of the tract was analyzed. To validate the results derived from the entire CST, we further analyzed a segment of the CST between the lowest slice of the cerebral peduncle and the uppermost slice of the lateral ventricle, in which the fibers are coherently arranged and the anatomical correspondence of the CST across subjects is established. On comparison with matched sighted participants, the average FA of the CST was significantly increased in the early blind men, but not in the early blind women. In conclusion, the plasticity of the CST is present in the early blind men, which might be related to the changes of motor experience during critical developmental period of the CST. This study also supports the perspective that experience-dependent plasticity occurs not only in the cortical areas but also in the white matter fiber tracts.

Global White Matter Analysis of Diffusion Tensor Images Is Predictive of Injury Severity in Traumatic Brain Injury

Conventional clinical neuroimaging is insensitive to axonal injury in traumatic brain injury (TBI). Immunocytochemical staining reveals changes to axonal morphology within hours, suggesting potential for diffusion-weighted magnetic resonance (MR) in early diagnosis and management of TBI. Diffusion tensor imaging (DTI) characterizes the three-dimensional (3D) distribution of water diffusion, which is highly anisotropic in white matter fibers owing to axonal length. Recently, DTI has been used to investigate traumatic axonal injury (TAI), emphasizing regional analysis in more severe TBI. In the current study, we hypothesized that a global white matter (WM) analysis of DTI data would be sensitive to TAI across a spectrum of TBI severity and injury to scan interval. To investigate this, we compared WM-only histograms of a scalar, fractional anisotropy (FA), between 20 heterogeneous TBI patients recruited from Detroit Medical Center, including six mild TBI (GCS 13-15), and 14 healthy age-matched controls. FA histogram parameters were correlated with admission GCS and posttraumatic amnesia (PTA). In all cases, including mild TBI, patients' FA histograms were globally decreased compared with control histograms. The shape of the TBI histograms also differed from controls, being more peaked and skewed. The mean FA, kurtosis and skewness were highly correlated suggesting a common mechanism. FA histogram properties also correlated with injury severity indexed by GCS and PTA, with mean FA being the best predictor and duration of PTA (r = 0.64) being superior to GCS (r = 0.47). Therefore, in this heterogeneous sample, the FA mean accounted for 40% of the variance in PTA. Increased diffusion in the short axis dimension, likely reflecting dysmyelination and swelling of axons, accounted for most of the FA decrease. FA is globally deceased in WM, including mild TBI, possibly reflecting widespread involvement. FA changes appear to be correlated with injury severity suggesting a role in early diagnosis and prognosis of TBI.

Correlation of magnetization transfer and diffusion magnetic resonance imaging in multiple sclerosis

The aim of this study was to correlate diffusion to magnetization transfer (MT) magnetic resonance imaging (MRI) results in multiple sclerosis (MS), in order to establish if the former technique provides complementary information. Magnetization transfer ratio (MTR) and apparent diffusion coefficient (ADC) were measured in 156 different regions of interest (ROIs) of 14 MS patients, where 84 corresponded to T1 hypointense lesions, 60 to T1 isointense lesions and 12 to regions of normal appearing white matter (NAWM). MTR mean value was higher for T1 isointense than for T1 hypointense lesions, and lower when compared to NAWM. ADC mean value for T1 isointense lesions was higher than for NAWM, but lower than for T1 hypointense lesions. A significant negative correlation was found between ADC and MTR for hypointense lesions (Pearson's r = -0.758, P < 0.001), whereas this correlation was much weaker for T1 isointense lesions (Pearson's r= -0.256, P = 0.049). There was no correlation between ADC and MTR for NAWM. The fact that ADC and MTR show a strong correlation only for T1 hypointense lesions indicates that, when tissue integrity is not severely compromised, as in the case of T1 isointense lesions or NAWM, ADC and MTR might be sensitive to different pathological processes.

Detection of traumatic axonal injury with diffusion tensor imaging in a mouse model of traumatic brain injury

Traumatic axonal injury (TAI) is thought to be a major contributor to cognitive dysfunction following traumatic brain injury (TBI), however TAI is difficult to diagnose or characterize non-invasively. Diffusion tensor imaging (DTI) has shown promise in detecting TAI, but direct comparison to histologically-confirmed axonal injury has not been performed. In the current study, mice were imaged with DTI, subjected to a moderate cortical controlled impact injury, and re-imaged 4-6 h and 24 h post-injury. Axonal injury was detected by amyloid beta precursor protein (APP) and neurofilament immunohistochemistry in pericontusional white matter tracts. The severity of axonal injury was quantified using stereological methods from APP stained histological sections. Two DTI parameters--axial diffusivity and relative anisotropy--were significantly reduced in the injured, pericontusional corpus callosum and external capsule, while no significant changes were seen with conventional MRI in these regions. The contusion was easily detectable on all MRI sequences. Significant correlations were found between changes in relative anisotropy and the density of APP stained axons across mice and across subregions spanning the spatial gradient of injury. The predictive value of DTI was tested using a region with DTI changes (hippocampal commissure) and a region without DTI changes (anterior commissure). Consistent with DTI predictions, there was histological detection of axonal injury in the hippocampal commissure and none in the anterior commissure. These results demonstrate that DTI is able to detect axonal injury, and support the hypothesis that DTI may be more sensitive than conventional imaging methods for this purpose.

Neuroimaging in multiple sclerosis

Conventional magnetic resonance imaging (MRI) has routinely been used to improve the accuracy of multiple sclerosis (MS) diagnosis and prognosis. Metrics derived from conventional MRI are now routinely used to detect therapeutic effects and extend clinical observations. However, conventional MRI measures, such as the use of lesion volume and count of gadolinium-enhancing and T2 lesions, have insufficient sensitivity and specificity to reveal the true degree of pathological changes occurring in MS. They cannot distinguish between inflammation, edema, demyelination, Wallerian degeneration, and axonal loss. In addition, they do not show a reliable correlation with clinical measures of disability and do not provide a complete assessment of therapeutic outcomes. Recent neuropathologic studies of typical chronic MS brains reveal macroscopic demyelination in cortical and deep gray matter (GM) that cannot be detected by currently available MRI techniques. Therefore, there is a pressing need for the development of newer MRI techniques to detect these lesions. Newer metrics of MRI analysis, including T1-weighted hypointense lesions, central nervous system atrophy measures, magnetization transfer imaging, magnetic resonance spectroscopy, and diffusion tensor imaging, are able to capture a more global picture of the range of tissue alterations caused by inflammation and neurodegeneration. At this time, they provide the only proof--albeit indirect--that important occult pathology is occurring in the GM. However, evidence is increasing that these nonconventional MRI measures correlate better with both existing and developing neurological impairment and disability when compared to conventional metrics.