Diffusion tensor imaging of early relapsing-remitting multiple sclerosis with histogram analysis using automated segmentation and brain volume correction

Higher hippocampal diffusivity values in welders are associated with greater R2* in the red nucleus and lower psychomotor performance

INTRODUCTION

Chronic excessive welding exposure may be related to higher metal accumulation and structural differences in different subcortical structures. We examined how welding affected brain structures and their associations with metal exposure and neurobehavioral consequences.

METHODS

Study includes 42 welders and 31 controls without a welding history. Welding-related structural differences were assessed by volume and diffusion tensor imaging (DTI) metrics in basal ganglia, red nucleus (RN), and hippocampus. Metal exposure was estimated by both exposure questionnaires and whole blood metal levels. Brain metal accumulations were estimated by R1 (for Mn) and R2* (for Fe). Neurobehavioral status was assessed by standard neuropsychological tests.

RESULTS

Compared to controls, welders displayed higher hippocampal mean (MD), axial (AD), and radial diffusivity (RD) (p's < 0.036), but similar DTI or volume in other ROIs (p's > 0.117). Welders had higher blood metal levels (p's < 0.004), higher caudate and RN R2* (p's < 0.014), and lower performance on processing/psychomotor speed, executive function, and visuospatial processing tasks (p's < 0.046). Higher caudate and RN R2* were associated with higher blood Fe and Pb (p's < 0.043), respectively. RN R2* was a significant predictor of all hippocampal diffusivity metrics (p's < 0.006). Higher hippocampal MD and RD values were associated with lower Trail Making Test-A scores (p's < 0.025). A mediation analysis of both groups revealed blood Pb indirectly affected hippocampal diffusivity via RN R2* (p's < 0.041).

DISCUSSION

Welding-related higher hippocampal diffusivity metrics may be associated with higher RN R2* and lower psychomotor speed performance. Future studies are warranted to test the role of Pb exposure in these findings.

Central vein sign and diffusion MRI differentiate microstructural features within white matter lesions of multiple sclerosis patients with comorbidities

Introduction

The Central Vein Sign (CVS) has been suggested as a potential biomarker to improve diagnostic specificity in multiple sclerosis (MS). Nevertheless, the impact of comorbidities on CVS performance has been poorly investigated so far. Despite the similar features shared by MS, migraine and Small Vessel Disease (SVD) at T2-weighted conventional MRI sequences, ex-vivo studies demonstrated their heterogeneous histopathological substrates. If in MS, inflammation, primitive demyelination and axonal loss coexist, in SVD demyelination is secondary to ischemic microangiopathy, while the contemporary presence of inflammatory and ischemic processes has been suggested in migraine. The aims of this study were to investigate the impact of comorbidities (risk factors for SVD and migraine) on the global and subregional assessment of the CVS in a large cohort of MS patients and to apply the Spherical Mean Technique (SMT) diffusion model to evaluate whether perivenular and non-perivenular lesions show distinctive microstructural features.

Methods

120 MS patients stratified into 4 Age Groups performed 3T brain MRI. WM lesions were classified in "perivenular" and "non-perivenular" by visual inspection of FLAIR* images; mean values of SMT metrics, indirect estimators of inflammation, demyelination and fiber disruption (EXTRAMD: extraneurite mean diffusivity, EXTRATRANS: extraneurite transverse diffusivity and INTRA: intraneurite signal fraction, respectively) were extracted.

Results

Of the 5303 lesions selected for the CVS assessment, 68.7% were perivenular. Significant differences were found between perivenular and non-perivenular lesion volume in the whole brain (p < 0.001) and between perivenular and non-perivenular lesion volume and number in all the four subregions (p < 0.001 for all). The percentage of perivenular lesions decreased from youngest to oldest patients (79.7%-57.7%), with the deep/subcortical WM of oldest patients as the only subregion where the number of non-perivenular was higher than the number of perivenular lesions. Older age and migraine were independent predictors of a higher percentage of non-perivenular lesions (p < 0.001 and p = 0.013 respectively). Whole brain perivenular lesions showed higher inflammation, demyelination and fiber disruption than non perivenular lesions (p = 0.001, p = 0.001 and p = 0.02 for EXTRAMD, EXTRATRANS and INTRA respectively). Similar findings were found in the deep/subcortical WM (p = 0.001 for all). Compared to non-perivenular lesions, (i) perivenular lesions located in periventricular areas showed a more severe fiber disruption (p = 0.001), (ii) perivenular lesions located in juxtacortical and infratentorial regions exhibited a higher degree of inflammation (p = 0.01 and p = 0.05 respectively) and (iii) perivenular lesions located in infratentorial areas showed a higher degree of demyelination (p = 0.04).

Discussion

Age and migraine have a relevant impact in reducing the percentage of perivenular lesions, particularly in the deep/subcortical WM. SMT may differentiate perivenular lesions, characterized by higher inflammation, demyelination and fiber disruption, from non perivenular lesions, where these pathological processes seemed to be less pronounced. The development of new non-perivenular lesions, especially in the deep/subcortical WM of older patients, should be considered a "red flag" for a different -other than MS- pathophysiology.

Diffusion Tensor Imaging Revealed Microstructural Changes in Normal-Appearing White Matter Regions in Relapsing–Remitting Multiple Sclerosis

Background

Axons and myelin sheaths are the physical foundation for white matter (WM) to perform normal functions. Our previous study found the metabolite abnormalities in frontal, parietal, and occipital normal-appearing white matter (NAWM) regions in relapsing–remitting multiple sclerosis (RRMS) patients by applying a 2D 1H magnetic resonance spectroscopic imaging method. Since the metabolite changes may associate with the microstructure changes, we used the diffusion tensor imaging (DTI) method to assess the integrity of NAWM in this study.

Method

Diffusion tensor imaging scan was performed on 17 clinically definite RRMS patients and 21 age-matched healthy controls on a 3.0-T scanner. DTI metrics including fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were extracted from 19 predefined regions of interest (ROIs), which were generated by removing a mask of manually drawn probabilistic lesion map from the Johns Hopkins University white-matter atlas. The mean values of FA, MD, AD, and RD were compared between different groups in the same ROIs.

Results

A probabilistic lesion map was successfully generated, and the lesion regions were eliminated from the WM atlas. We found that the RRMS patients had significantly lower FA in the entire corpus callosum (CC), bilateral of anterior corona radiata, and right posterior thalamic radiation (PTR). At the same time, RRMS patients showed significantly higher MD in the bilateral anterior corona radiata and superior corona radiata. Moreover, all AD values increased, and the bilateral external capsule, PTR, and left tapetum NAWM show statistical significance. What is more, all NAWM tracts showed increasing RD values in RRMS patients, and the bilateral superior corona radiata, the anterior corona radiata, right PTR, and the genu CC reach statistical significance.

Conclusion

Our study revealed widespread microstructure changes in NAWM in RRMS patients through a ready-made WM atlas and probabilistic lesion map. These findings support the hypothesis of demyelination, accumulation of inflammatory cells, and axonal injury in NAWM for RRMS. The DTI-based metrics could be considered as potential non-invasive biomarkers of disease severity.

Higher Hippocampal Mean Diffusivity Values in Asymptomatic Welders

Chronic high-level manganese (Mn)-induced neurotoxicity has been associated with Mn accumulation in the basal ganglia and higher risk for developing parkinsonism. Recent studies in Mn-exposed animals revealed Mn accumulation in the hippocampus, the presence of Aβ diffuse plaques, and deficits in associative learning, the latter being hallmarks of Alzheimer's disease (AD) or related disorders. This and recent evidence of hippocampal Mn accumulation in welders prompted us to test the hypothesis that welders with chronic Mn exposure would display changes in the hippocampus. Subjects with (welders; n = 42) or without (controls; n = 31) welding history were studied. Mn exposure was estimated by occupational questionnaires, whole blood Mn, and R1 imaging (estimate of short-term brain Mn accumulation). Hippocampal diffusion tensor imaging (DTI; estimate of microstructural brain changes) and volume were determined. Compared with controls, welders displayed no significant difference in hippocampal volume (p = .165). Welders, however, exhibited higher DTI hippocampal mean diffusivity (MD) values compared with controls (p = .035) that was evident particularly in older welders (>50 years, p = .002). Hippocampal MD was associated significantly with age in welders (R = 0.59; p < .001) but not in controls (p = .16). Moreover, higher hippocampal MD values (age adjusted) were associated with long-term cumulative Mn exposure (R = 0.36, p = .021). Welders with chronic exposure have higher MD values in the hippocampus that become greater with increasing age, a brain change that is similar to that observed in those at risk for AD. The current results suggest that Mn exposure, coupled with aging, may make welders more vulnerable to AD or AD-like changes.

REDUCING CSF PARTIAL VOLUME EFFECTS TO ENHANCE DIFFUSION TENSOR IMAGING METRICS OF BRAIN MICROSTRUCTURE

Technological advances over recent decades now allow for in vivo observation of human brain tissue through the use of neuroimaging methods. While this field originated with techniques capable of capturing macrostructural details of brain anatomy, modern methods such as diffusion tensor imaging (DTI) that are now regularly implemented in research protocols have the ability to characterize brain microstructure. DTI has been used to reveal subtle micro-anatomical abnormalities in the prodromal phase ofº various diseases and also to delineate "normal" age-related changes in brain tissue across the lifespan. Nevertheless, imaging artifact in DTI remains a significant limitation for identifying true neural signatures of disease and brain-behavior relationships. Cerebrospinal fluid (CSF) contamination of brain voxels is a main source of error on DTI scans that causes partial volume effects and reduces the accuracy of tissue characterization. Several methods have been proposed to correct for CSF artifact though many of these methods introduce new limitations that may preclude certain applications. The purpose of this review is to discuss the complexity of signal acquisition as it relates to CSF artifact on DTI scans and review methods of CSF suppression in DTI. We will then discuss a technique that has been recently shown to effectively suppress the CSF signal in DTI data, resulting in fewer errors and improved measurement of brain tissue. This approach and related techniques have the potential to significantly improve our understanding of "normal" brain aging and neuropsychiatric and neurodegenerative diseases. Considerations for next-level applications are discussed.

Magnetization transfer ratio relates to cognitive impairment in normal elderly

Magnetization transfer imaging (MTI) can detect microstructural brain tissue changes and may be helpful in determining age-related cerebral damage. We investigated the association between the magnetization transfer ratio (MTR) in gray and white matter (WM) and cognitive functioning in 355 participants of the Austrian stroke prevention family study (ASPS-Fam) aged 38-86 years. MTR maps were generated for the neocortex, deep gray matter structures, WM hyperintensities, and normal appearing WM (NAWM). Adjusted mixed models determined whole brain and lobar cortical MTR to be directly and significantly related to performance on tests of memory, executive function, and motor skills. There existed an almost linear dose-effect relationship. MTR of deep gray matter structures and NAWM correlated to executive functioning. All associations were independent of demographics, vascular risk factors, focal brain lesions, and cortex volume. Further research is needed to understand the basis of this association at the tissue level, and to determine the role of MTR in predicting cognitive decline and dementia.

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.

Depressive symptoms in multiple sclerosis from an in vivo study with TBSS

Clinically significant depression can impact up to 50% of patients with multiple sclerosis (MS) over a course of their life time, which is associated with an increased morbidity and mortality. In our study, fifteen relapsing-remitting MS (RRMS) patients and 15 age- and gender-matched normal controls were included. Diffusion tensor imaging (DTI) was acquired by employing a single-shot echo planar imaging sequence on a 3.0 T MR scanner and fractional anisotropy (FA) was performed with tract-based spatial statistics (TBSS) approach. Finally, widespread WM and GM abnormalities were observed in RRMS patients. Moreover, the relationships between the depressive symptoms which can be measured by Hamilton depression rating scale (HAMD) as well as clinical disabilities measured by the expanded disability status scale (EDSS) and FA changes were listed. There was a positive relation between EDSS and the FA changes in the right inferior parietal lobule, while negative relation was located in the left anterior cingulate cortex and hippocampus. Also a positive relation between HAMD and FA changes was found in the right posterior middle cingulate gyrus, the right hippocampus, the left hypothalamus, the right precentral gyrus, and the posterior cingulate which demonstrated a link between the depressive symptoms and clinically relevant brain areas in RRMS patients.

CSF contamination contributes to apparent microstructural alterations in mild cognitive impairment

Diffusion MRI is used widely to probe microstructural alterations in neurological and psychiatric disease. However, ageing and neurodegeneration are also associated with atrophy, which leads to artefacts through partial volume effects due to cerebrospinal-fluid contamination (CSFC). The aim of this study was to explore the influence of CSFC on apparent microstructural changes in mild cognitive impairment (MCI) at several spatial levels: individually reconstructed tracts; at the level of a whole white matter skeleton (tract-based spatial statistics); and histograms derived from all white matter. 25 individuals with MCI and 20 matched controls underwent diffusion MRI. We corrected for CSFC using a post-acquisition voxel-by-voxel approach of free-water elimination. Tracts varied in their susceptibility to CSFC. The apparent pattern of tract involvement in disease shifted when correction was applied. Both spurious group differences, driven by CSFC, and masking of true differences were observed. Tract-based spatial statistics were found to be robust across much of the skeleton but with some localised CSFC effects. Diffusivity measures were affected disproportionately in MCI, and group differences in fornix microstructure were exaggerated. Group differences in white matter histogram measures were also partly driven by CSFC. For diffusivity measures, up to two thirds of observed group differences were due to CSFC. Our results demonstrate that CSFC has an impact on quantitative differences between MCI and controls. Furthermore, it affects the apparent spatial pattern of white matter involvement. Free-water elimination provides a step towards disentangling intrinsic and volumetric alterations in individuals prone to atrophy.

•

We examine the effect of CSFC on perceived microstructural alterations in MCI.

•

We correct for CSFC with free-water elimination and assess at three spatial levels.

•

The pattern of individual tract involvement is shifted due to CSFC.

•

TBSS is robust to CSFC in much of the skeleton.

•

Group differences in white matter diffusion histograms are partly driven by CSFC.

Diffusion tensor MRI alterations of subcortical deep gray matter in clinically isolated syndrome

BACKGROUND

Abnormalities in the gray matter (GM) of the brain parenchyma are present early in the course of multiple sclerosis.

OBJECTIVES

To quantify white matter (WM) and subcortical deep GM (SDGM) alterations in patients with clinically isolated syndrome (CIS) using diffusion tensor imaging (DTI).

MATERIALS AND METHODS

45 CIS patients and 52 healthy controls (HC) were scanned on 3T MRI. Mean diffusivity (MD) and fractional anisotropy (FA) were calculated, in addition to the estimation of structural brain volume and lesion measurements.

RESULTS

FA was significantly lower in CIS patients in the whole brain (p<0.001), total SDGM (p<0.001), normal appearing (NA) GM (p=0.016), thalamus (p=0.029) putamen (p=0.036), caudate (p=0.041) and accumbens nuclei (p=0.041) compared to HC. No DTI MD or volumetric differences were detected in the brain parenchyma between CIS and HC groups. Normalized lateral ventricular volume was higher in CIS patients compared to HC (p=0.033). A significant association was detected between the increased T2 lesion number and volume and decreased FA of the NAWM (p=0.036), but not with FA of NAGM or SDGM structures.

CONCLUSIONS

Diffuse DTI alterations of GM structures, not associated with lesion formation, are present in CIS patients.

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.

Extra-hippocampal subcortical limbic involvement predicts episodic recall performance in multiple sclerosis

BACKGROUND

Episodic memory impairment is a common but poorly-understood phenomenon in multiple sclerosis (MS). We aim to establish the relative contributions of reduced integrity of components of the extended hippocampal-diencephalic system to memory performance in MS patients using quantitative neuroimaging.

METHODOLOGY/PRINCIPAL FINDINGS

34 patients with relapsing-remitting MS and 24 healthy age-matched controls underwent 3 T MRI including diffusion tensor imaging and 3-D T1-weighted volume acquisition. Manual fornix regions-of-interest were used to derive fornix fractional anisotropy (FA). Normalized hippocampal, mammillary body and thalamic volumes were derived by manual segmentation. MS subjects underwent visual recall, verbal recall, verbal recognition and verbal fluency assessment. Significant differences between MS patients and controls were found for fornix FA (0.38 vs. 0.46, means adjusted for age and fornix volume, P<.0005) and mammillary body volumes (age-adjusted means 0.114 ml vs. 0.126 ml, P<.023). Multivariate regression analysis identified fornix FA and mammillary bodies as predictor of visual recall (R(2) = .31, P = .003, P = .006), and thalamic volume as predictive of verbal recall (R(2) = .37, P<.0005). No limbic measures predicted verbal recognition or verbal fluency.

CONCLUSIONS/SIGNIFICANCE

These findings indicate that structural and ultrastructural alterations in subcortical limbic components beyond the hippocampus predict performance of episodic recall in MS patients with mild memory dysfunction.

Gray- and white-matter changes 1 year after first clinical episode of multiple sclerosis: MR imaging

PURPOSE

To assess, by means of magnetic resonance (MR) imaging, the longitudinal changes in white matter (WM) and gray matter (GM) in a cohort of patients with clinically isolated syndrome (CIS) who were followed up for 1 year.

MATERIALS AND METHODS

This prospective, HIPAA-compliant study was approved by the institutional review board. Written informed consent was obtained from all the participants. Changes in GM and WM integrity were respectively investigated by using three-dimensional T1-weighted and diffusion-tensor (DT) imaging sequences and by applying voxel-based morphometry (VBM) and tract-based spatial statistics (TBSS) analyses. Thirty-four consecutive patients (21 women, 13 men; mean age, 32.8 years ± 7.7 [standard deviation]) who had CIS were recruited. All the patients underwent a neurologic and an MR examination at baseline and 12 months later; the MR examination consisted of three-dimensional T1-weighted dual-echo turbo spin-echo DT imaging. VBM and TBSS were used to analyze GM volume and WM fractional anisotropy, respectively.

RESULTS

After 1 year, multiple sclerosis (MS) was diagnosed in 33 (97%) of 34 patients with CIS. Longitudinal volumetric analysis revealed a significant (P < .001) reduction in global GM volume. The VBM analysis showed the development of regional GM atrophy involving several cortical and subcortical regions in both hemispheres (P < .05). No significant longitudinal change in global or regional WM fractional anisotropy was otherwise observed.

CONCLUSION

WM damage was detectable early and involved most fiber tracts in patients with MS, but it did not worsen significantly during the 1st year after clinical onset. In contrast, GM damage was not detectable at the time of clinical onset, but a significant decrease in cortical and deep GM volume was observed at 1 year.

Twenty-five pitfalls in the analysis of diffusion MRI data

Obtaining reliable data and drawing meaningful and robust inferences from diffusion MRI can be challenging and is subject to many pitfalls. The process of quantifying diffusion indices and eventually comparing them between groups of subjects and/or correlating them with other parameters starts at the acquisition of the raw data, followed by a long pipeline of image processing steps. Each one of these steps is susceptible to sources of bias, which may not only limit the accuracy and precision, but can lead to substantial errors. This article provides a detailed review of the steps along the analysis pipeline and their associated pitfalls. These are grouped into 1 pre-processing of data; 2 estimation of the tensor; 3 derivation of voxelwise quantitative parameters; 4 strategies for extracting quantitative parameters; and finally 5 intra-subject and inter-subject comparison, including region of interest, histogram, tract-specific and voxel-based analyses. The article covers important aspects of diffusion MRI analysis, such as motion correction, susceptibility and eddy current distortion correction, model fitting, region of interest placement, histogram and voxel-based analysis. We have assembled 25 pitfalls (several previously unreported) into a single article, which should serve as a useful reference for those embarking on new diffusion MRI-based studies, and as a check for those who may already be running studies but may have overlooked some important confounds. While some of these problems are well known to diffusion experts, they might not be to other researchers wishing to undertake a clinical study based on diffusion MRI.

Brain-water diffusion coefficients reflect the severity of inherited prion disease

OBJECTIVE

Inherited prion diseases are progressive neurodegenerative conditions, characterized by cerebral spongiosis, gliosis, and neuronal loss, caused by mutations within the prion protein (PRNP) gene. We wished to assess the potential of diffusion-weighted MRI as a biomarker of disease severity in inherited prion diseases.

METHODS

Twenty-five subjects (mean age 45.2 years) with a known PRNP mutation including 19 symptomatic patients, 6 gene-positive asymptomatic subjects, and 7 controls (mean age 54.1 years) underwent conventional and diffusion-weighted MRI. An index of normalized brain volume (NBV) and region of interest (ROI) mean apparent diffusion coefficient (ADC) for the head of caudate, putamen, and pulvinar nuclei were recorded. ADC histograms were computed for whole brain (WB) and gray matter (GM) tissue fractions. Clinical assessment utilized standardized clinical scores. Mann-Whitney U test and regression analyses were performed.

RESULTS

Symptomatic patients exhibited an increased WB mean ADC (p = 0.006) and GM mean ADC (p = 0.024) compared to controls. Decreased NBV and increased mean ADC measures significantly correlated with clinical measures of disease severity. Using a stepwise multivariate regression procedure, GM mean ADC was an independent predictor of Clinician's Dementia Rating score (p = 0.001), Barthel Index of activities of daily living (p = 0.001), and Rankin disability score (p = 0.019).

CONCLUSIONS

Brain volume loss in inherited prion diseases is accompanied by increased cerebral apparent diffusion coefficient (ADC), correlating with increased disease severity. The association between gray matter ADC and clinical neurologic status suggests this measure may prove a useful biomarker of disease activity in inherited prion diseases.

Clinically isolated syndrome suggestive of multiple sclerosis: voxelwise regional investigation of white and gray matter

PURPOSE

To quantify white matter (WM) and gray matter (GM) damage in patients who presented with clinically isolated syndrome (CIS), which is suggestive of multiple sclerosis (MS), by combining volume-based morphometry (VBM) and tract-based spatial statistics (TBSS).

MATERIALS AND METHODS

This prospective HIPAA-compliant study was approved by the institutional review board. Written informed consent was obtained from all participants. In this study, 34 consecutive patients (21 women, 13 men; mean age, 31.7 years +/- 7.7 [standard deviation]) who presented with CIS were recruited. The magnetic resonance (MR) examination included dual-echo fast spin-echo, three-dimensional T1, and diffusion-tensor imaging. Sixteen matched healthy volunteers served as control subjects. T2 lesion volumes were assessed with a semiautomatic technique. VBM and TBSS were used for the GM and WM analyses, respectively, to compare regional GM volumes and fractional anisotropy (FA) values in the two groups.

RESULTS

TBSS analysis revealed a pattern of diffuse FA reductions in patients with CIS at the cluster level (P < .05). Regions of decreased FA involved most of the WM pathways, including the corticospinal tracts, corpus callosum, and superior and inferior longitudinal fasciculi. There were no significant differences between the two groups in terms of global GM, WM, or cerebrospinal fluid volume or in terms of regional GM volume.

CONCLUSION

Diffuse WM damage not accompanied by any change in GM or WM volume is observed in patients with CIS. This suggests that WM involvement plays a relevant role in the early phases of MS. Subsequently detected GM damage may be secondary to WM alterations.

Apparent Diffusion Coefficient Histograms in the Follow-up of Relapsing-Remitting Multiple Sclerosis

Diffusion-weighted (DW) magnetic resonance (MR) imaging in addition to conventional magnetic resonance MR images provide valuable information in multiple sclerosis (MS). Increased diffusivity measured with diffusion-weighted imaging (DWI) has been demonstrated in normal appearing brain tissue in MS. So far, longitudinal changes taking place in whole-brain histograms in patients with active relapsing-remitting MS have not been evaluated. The aim of this study was to evaluate how apparent diffusion coefficient (ADC) histograms are altered during the follow-up of active relapsing-remitting MS patients. Nine patients were studied twice by MRI with a three-month interval. All patients had active newly diagnosed MS with two to three relapses during the year preceding the first MRI, and interferon-beta treatment was initiated after obtaining the first image. ADC histograms were produced after removing extracranial tissues and cerebrospinal fluid from the images. Additionally, brain volume index (BVI) and lesion volume on FLAIR images were measured. Five patients had signs of disease activity in the follow-up MRI. In the four patients without signs of disease activity the change in ADC histogram parameters was less than 2%. In patients with disease activity both increase (one case) and decrease (four cases) in histogram parameters were detected. Changes in BVI or lesion volume did not significantly correlate with histogram changes. The number of new T2-lesions showed a positive correlation with mean (r=0.79, P=0.014) and upper quartile (r=0.77, P=0.021) value change. Alterations in disease activity lead to histogram changes; both shifts to lower values and shifts to higher values are possible. The histogram changes are mostly related to subtle inflammatory changes in normal appearing brain tissue during inflammatory activity and their resolution during less active inflammatory conditions.

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.

Diffusion-tensor MR imaging of cortical lesions in multiple sclerosis: initial findings

PURPOSE

To prospectively perform a direct measurement of fractional anisotropy (FA) and mean diffusivity (MD) in cortical lesions of patients with multiple sclerosis (MS).

MATERIALS AND METHODS

The study was approved by the institutional review board and was HIPAA compliant; informed consent was obtained. Magnetic resonance (MR) images, including double inversion-recovery (DIR), phase-sensitive inversion-recovery (PSIR), and diffusion-tensor images, were acquired from nine MS patients with cortical lesions (five women, four men; median age, 47 years) and nine age- and sex-matched volunteer control subjects. Following nonlinear elastically constrained image registration for aligning diffusion-weighted images to DIR images, maps of FA and MD were computed for each subject. Cortical lesions were identified on DIR images and validated by using PSIR images. The diffusion-tensor imaging maps were then overlaid on the coregistered DIR images, and mean FA and MD values were measured in regions of interest drawn on the cortical lesions. Differences between normal gray matter (GM) and cortical lesions were evaluated by using the generalized estimating equation. FA and MD histograms of whole brain and GM (global analysis) in healthy control subjects and MS patients were also computed for comparison with those in previously published studies.

RESULTS

FA and MD values were significantly higher in cortical lesions compared with similar regions in healthy control subjects. Histogram peak FA was significantly decreased and peak MD was significantly increased in patients relative to control subjects.

CONCLUSION

DIR and PSIR combined with nonlinear image registration allowed direct focal measurement of FA and MD in cortical lesions.

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.

Altered diffusion tensor in multiple sclerosis normal-appearing brain tissue: cortical diffusion changes seem related to clinical deterioration

PURPOSE

To investigate normal-appearing white (NAWM) and cortical gray (NAGM) matter separately in multiple sclerosis (MS) in vivo using diffusion tensor imaging (DTI).

MATERIALS AND METHODS

In 64 MS patients (12 primary progressive [PP], 38 relapsing remitting [RR], 14 secondary progressive [SP]) and 20 healthy controls, whole-brain apparent diffusion coefficient (ADC) and fractional anisotropy (FA) maps were acquired. A stimulated echo acquisition mode (STEAM) DTI sequence was used with minimal geometrical distortion in comparison to echo-planar imaging (EPI). NAWM and NAGM were identified using conventional magnetic resonance (MR) images, allowing a cautious assessment of FA in cortex.

RESULTS

Histogram analyses showed significant global FA decreases and ADC increases in MS NAWM compared to control WM. MS cortical NAGM had no significant global ADC increase, but FA was decreased significantly. In regional analyses, nearly all NAWM regions-of-interest (ROIs) had significantly increased ADC compared to controls, but FA was not changed. In nearly all cortical NAGM ROIs, ADC was significantly increased and FA significantly reduced. In multiple linear regression analyses in RR/SPMS patients, NAGM-ADC histogram peak height was associated more strongly with clinical disability than T2 lesion load.

CONCLUSION

Tissue damage occurs in both NAWM and cortical NAGM. The cortical damage appears to have more clinical impact than T2 lesions.

Principal component and linear discriminant analysis of T1 histograms of white and grey matter in multiple sclerosis

Twenty-three relapsing remitting multiple sclerosis (RRMS) patients and 14 controls were imaged to produce normal-appearing white and grey matter T1 histograms. These were used to assess whether histogram measures from principal component analysis (PCA) and linear discriminant analysis (LDA) out-perform traditional histogram metrics in classification of T1 histograms into control and RRMS subject groups and in correlation with the expanded disability status score (EDSS). The histograms were classified into one of two groups using a leave-one-out analysis. In addition, the patients were scanned serially, and the calculated parameters correlated with the EDSS. The classification results showed that the more complex techniques were at least as good at classifying the subjects as histogram mean, peak height and peak location, with PCA/LDA having success rates of 76% for white matter and 68%/65% for grey matter. No significant correlations were found with EDSS for any histogram parameter. These results indicate that there is much information contained within the grey matter as well as the white matter histograms. Although in these histograms PCA and LDA did not add greatly to the discriminatory power of traditional histogram parameters, they provide marginally better performance, while relying only on data-driven feature selection.

Novel diffusion anisotropy indices: An evaluation

PURPOSE

To systematically evaluate diffusion anisotropy (DA) using newly defined indices based on the diffusion deviation and mean diffusivity approach.

MATERIALS AND METHODS

Measures of amplitude, area, and volume of the DA index (DAI) were measured and compared with regard to their sensitivity to changes in DA, susceptibility to noise in the original diffusion-weighted (DW) images, and contrast-to-noise ratio (CNR) in homogenous regions. Simulations were performed under different levels of noise and DA. Human DTI data were acquired from eight normal volunteers.

RESULTS

Indices of area and volume measures provided improved resolution for characterizing the DA compared to the eigenvalue ratio. The amplitude measure showed consistent performances with good CNR and less susceptibility to noise in the original data.

CONCLUSION

These indices are rotationally invariant without the requirement of eigenvalue sorting. At low anisotropy, all indices have a similar CNR. For larger DA, the first index (the deviation tensor divided by the DT) shows improved sensitivity, contrast-to-noise ratio (CNR), and noise immunity compared to the other indices.

Functional implications of hippocampal volume and diffusivity in mild cognitive impairment

Hippocampal atrophy has been related to mild cognitive impairment (MCI) and early Alzheimer disease (AD), but the diagnostic significance of cross-sectionally determined hippocampal volumes is still ambiguous. Diffusion-Tensor-Imaging (DTI) in MCI patients revealed an association of microstructural changes in hippocampal areas with verbal memory decline. MRI volumetry and DTI were combined to investigate 18 MCI patients attending a memory clinic, and 18 carefully age- and gender-matched healthy controls. Neuropsychological testing, high resolution T1-weighted volume MRI scans, and DTI scans with regions-of-interest in hippocampal areas were applied. Left hippocampal volume was significantly lower (-11%, P = 0.02) in MCI patients than in control subjects. No significant differences were found for the right hippocampus (-4%). Mean diffusivity (MD) was significantly elevated in MCI patients vs. controls in left (+10%, P = 0.002) and right hippocampal areas (+13%, P = 0.02). Hippocampal volume and MD values were not significantly correlated. Combining left hippocampal volume and MD measures showed that lower left hippocampal volumes were associated with poor verbal memory performance particularly when co-occurring with high MD values. No comparable associations could be found regarding the right hippocampal formation and with respect to non-verbal memory function. The results demonstrate that microstructural abnormalities as revealed by DTI are very sensitive early indicators of hippocampal dysfunction. The combination of macro- and microstructural parameters in hippocampal areas could be promising in early detection of neurodegenerative processes.

Unbiased segmentation of diffusion-weighted magnetic resonance images of the brain using iterative clustering

Segmentation of diffusion-weighted echo-planar imaging (DW-EPI) is challenging because of concerns regarding spatial resolution and distortion. Methods commonly used require manual input and often need thresholding measures to segment white matter (WM), gray matter (GM) and cerebrospinal fluid (CSF). This may introduce operator bias and misclassification error. When comparing patients with a diffuse disease process-such as multiple sclerosis (MS)--with healthy controls, although information from all images may be biased due to disease effect, this is more so if the data set employed to perform segmentation is also used as a measured outcome for the study, for example, fractional anisotropy maps. Presented in this work is an unbiased method for segmenting DW-EPI data sets using the b=0 and single-shot inversion recovery EPI into WM, GM and CSF. The method employs an iterative clustering technique to account for partial volume effects and signal variation caused by radiofrequency inhomogeneity. The technique is evaluated with both real and synthetic brain data and results compared with statistical parametric mapping (SPM02). With synthetic brain data, where a gold standard of segmentation exists, the presented method showed less misclassification compared to SPM02. The unbiased method proposed may provide a more accurate methodology of segmentation in the analysis of DWI-EPI images in conditions such as MS.

Diffusion Tensor Magnetic Resonance Imaging in Multiple Sclerosis

Multiple sclerosis (MS), a demyelinating disease, occurs principally in the white matter (WM) of the central nervous system. Conventional magnetic resonance imaging (MRI) is sensitive to some, but not all, brain changes associated with MS. Diffusion-weighted imaging (DWI) provides information about water diffusion in tissue and diffusion tensor MRI (DT-MRI) about fiber direction, allowing for the identification of WM abnormalities that are not apparent on conventional MRI images. These techniques can quantitatively characterize the local microstructure of tissues. MS-associated disease processes lead to regions characterized by an increased amount of water diffusion and a decrease in the anisotropy of diffusion direction. These changes have been found to produce different patterns in MS patients presenting different courses of the disease. Changes in water diffusion may allow examination of the type, appearance, enhancement, and location of lesions not readily visible by other means. Ongoing studies of MS are integrating conventional MRI and DT-MRI measures with connectivity-based regional assessment, aiming to provide a better understanding of the nature and the location of WM lesions. This integration and the development of novel image-processing and visualization techniques may improve the understanding of WM architecture and its disruption in MS. This article presents a brief history of DWI, its basic principles and applications in the study of MS, a review of the properties and applications of DT-MRI, and their use in the study of MS. In addition, this article illustrates the methodology for the analysis of DT-MRI in ongoing studies of MS.