Whole-brain diffusion MR histograms differ between MS subtypes

Intracranial computed tomography histogram analysis detects changes in the setting of elevated intracranial pressure and normal imaging

BACKGROUND

Patients with idiopathic intracranial hypertension (IIH) have elevated intracranial pressure (ICP) of unclear etiology. This study evaluated the ability of quantitative intracranial Hounsfield unit (HU) histogram analysis to detect pathophysiological changes from elevated ICP in the setting of a normal head CT.

METHODS

Retrospective analysis of non-contrast-enhanced head CT images of IIH patients and matched controls. Following skull stripping, total intracranial CT voxels within the range of 0-70 HU were divided into seven 10 HU bins. A measurement of total intracranial HU was also calculated for each patient. Imaging studies for IIH patients were reviewed for features of IIH including transverse sinus stenosis (TSS). Histogram measures were compared between IIH and control groups and correlated with imaging and clinical data.

RESULTS

Fourteen IIH patients with CSF opening pressure ≥25 cm water, and 31 age-, sex-, and ethnicity-matched controls were included. Compared to controls, IIH patients had a significantly greater proportion of voxels in the 40-50, 50-60, and 60-70 HU bins (p = 0.003, 0.001, and 0.003, respectively) but similar proportion in the 0-10 HU range. Severity of TSS significantly correlated with total intracranial HU measures. 50-60 HU and 60-70 HU bins demonstrated high AUCs of 0.81 and 0.80, respectively, in differentiating IIH from normal status.

CONCLUSION

Idiopathic intracranial hypertension patients have a greater proportion of high intracranial HU voxels representing blood volume, which may be explained by TSS causing venous congestion. The pattern provides further insights into the pathophysiology of IIH and may be useful for detecting elevated ICP in the setting of normal head CT imaging.

Disentangling white-matter damage from physiological fibre orientation dispersion in multiple sclerosis

Multiple sclerosis leads to diffuse damage of the central nervous system, affecting also the normal-appearing white matter. Demyelination and axonal degeneration reduce regional fractional anisotropy in normal-appearing white matter, which can be routinely mapped with diffusion tensor imaging. However, the standard fractional anisotropy metric is also sensitive to physiological variations in orientation dispersion of white matter fibres. This complicates the detection of disease-related damage in large parts of cerebral white matter where microstructure physiologically displays a high degree of fibre dispersion. To resolve this ambiguity, we employed a novel tensor-valued encoding method for diffusion MRI, which yields a microscopic fractional anisotropy metric that is unaffected by regional variations in orientation dispersion. In 26 patients with relapsing-remitting multiple sclerosis, 14 patients with primary-progressive multiple sclerosis and 27 age-matched healthy controls, we compared standard fractional anisotropy mapping with the novel microscopic fractional anisotropy mapping method, focusing on normal-appearing white matter. Mean microscopic fractional anisotropy and standard fractional anisotropy of normal-appearing white matter were significantly reduced in both patient groups relative to healthy controls, but microscopic fractional anisotropy yielded a better reflection of disease-related white-matter alterations. The reduction in mean microscopic fractional anisotropy showed a significant positive linear relationship with physical disability, as reflected by the expanded disability status scale. Mean reduction of microscopic fractional anisotropy in normal-appearing white matter also scaled positively with individual cognitive dysfunction, as measured with the symbol digit modality test. Mean microscopic fractional anisotropy reduction in normal-appearing white matter also showed a positive relationship with total white-matter lesion load as well as lesion load in specific tract systems. None of these relationships between normal-appearing white-matter microstructure and clinical, cognitive or structural measures emerged when using mean fractional anisotropy. Together, the results provide converging evidence that microscopic fractional anisotropy mapping substantially advances the assessment of cerebral white matter in multiple sclerosis by disentangling microstructure damage from variations in physiological fibre orientation dispersion at the stage of data acquisition. Since tensor-valued encoding can be implemented in routine diffusion MRI, microscopic fractional anisotropy mapping bears considerable potential for the future assessment of disease progression in normal-appearing white matter in both relapsing-remitting and progressive forms of multiple sclerosis as well as other white-matter-related brain diseases.

Diffusion tensor imaging in multiple sclerosis at different final outcomes

OBJECTIVES

Methods to evaluate the relative contributions of demyelination vs axonal degeneration over the long-term course of MS are urgently needed. We used magnetic resonance diffusion tensor imaging (DTI) to estimate degrees of demyelination and axonal degeneration in the corpus callosum (CC) in cases of MS with different final outcomes.

MATERIALS AND METHODS

We determined DTI measures mean diffusivity (MD), fractional anisotropy (FA), and axial (AD) and radial (RD) diffusivities in the CC of 31 MS patients, of whom 13 presented a secondary progressive course, 11 a non-progressive course, and seven a monophasic course. The study participants were survivors from an incidence cohort of 254 attack-onset MS patients with 50 years of longitudinal follow-up. As reference, we included five healthy individuals without significant morbidity.

RESULTS

In patients with secondary progression, compared to all other groups, the corpus callosum showed increased RD and reduced FA, but no change in AD. None of the parameters exhibited differences among non-progressive and monophasic course groups and controls.

CONCLUSION

Increased RD was observed in secondary progressive MS, indicating significant myelin loss. Normal RD values observed in the clinically isolated syndrome and non-progressive groups confirm their benign nature. AD was not a characterizing parameter for long-term outcome. Demyelination revealed by increased RD is a distinguishing trait for secondary progression.

Double diffusion encoding MRI for the clinic

PURPOSE

The purpose of this study is to develop double diffusion encoding (DDE) MRI methods for clinical use. Microscopic diffusion anisotropy measurements from DDE promise greater specificity to changes in tissue microstructure compared with conventional diffusion tensor imaging, but implementation of DDE sequences on whole-body MRI scanners is challenging because of the limited gradient strengths and lengthy acquisition times.

METHODS

A custom single-refocused DDE sequence was implemented on a 3T whole-body scanner. The DDE gradient orientation scheme and sequence parameters were optimized based on a Gaussian diffusion assumption. Using an optimized 5-min DDE acquisition, microscopic fractional anisotropy (μFA) maps were acquired for the first time in multiple sclerosis patients.

RESULTS

Based on simulations and in vivo human measurements, six parallel and six orthogonal diffusion gradient pairs were found to be the minimum number of diffusion gradient pairs necessary to produce a rotationally invariant measurement of μFA. Simulations showed that optimal precision and accuracy of μFA measurements were obtained using b-values between 1500 and 3000 s/mm² . The μFA maps showed improved delineation of multiple sclerosis lesions compared with conventional fractional anisotropy and distinct contrast from T₂ -weighted fluid attenuated inversion recovery and T₁ -weighted imaging.

CONCLUSION

The μFA maps can be measured using DDE in a clinical setting and may provide new opportunities for characterizing multiple sclerosis lesions and other types of tissue degeneration. Magn Reson Med 80:507-520, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Diffusion tensor imaging in multiple sclerosis: a tool for monitoring changes in normal-appearing white matter

Our objectives were to determine the reproducibility of diffusion tensor imaging (DTI) in volunteers and to evaluate the ability of the method to monitor longitudinal changes occurring in the normal-appearing white matter (NAWM) of patients with multiple sclerosis (MS). DTI was performed three-mo nthly for one year in seven MS patients: three relapsing-remitting (RRMS), three secondary progressive (SPMS) and one relapsing SP. They were selected with a limited cerebral lesion load. Seven age- and sex-matched controls also underwent monthly examinations for three months. Diffusivity and anisotropy were quantified over the segmented whole supratentorial white matter, with the indices of trace (Tr) and fractional anisotropy (FA). Results obtained in volunteers show the reproducibility of the method. Patients had higher trace and lower anisotropy than matched controls (P B-0.0001). O ver the follow-up, both Tr and FA indicated a recovery after the acute phase in RRMS and a progressive shift towards abnormal values in SPMS. A lthough this result is not statistically significant, it suggests that DTI is sensitive to microscopic changes occurring in tissue of normal appearance in conventional images and could be useful for monitoring the course of the disease, even though it was unable to clearly distinguish between the various physiopathological processes involved.

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

Diffusion tensor magnetic resonance imaging (DTI) reveals measurable abnormalities in normal-appear ing brain tissue (NA BT) in established multiple sclerosis (MS). However, it is unclear how early this occurs. Recent studies have employed whole brain histogram analysis to improve sensitivity, but concern exists regarding reliability of tissue/cerebrospinal fluid segmentation and possible intersubject brain volume differences, which can introduce partial volume error. To address this, 28 early relapsing-remitting MS subjects [median disease duration 1.6 years; median Expanded Disability Status Scale (EDSS) score 1.5] and 20 controls were compared with whole brain histogram analysis using an automated segmentation algorithm to improve reproducibility. Brain parenchymal volumes (BPV) were estimated for each subject in the analysis. The mean, peak height and peak location were calculated for DTI parameters [fractional anisotropy (FA), mean diffusivity and volume ratio]. A n increased FA peak height in MS subject NA BT was observed (P =0.02) accounting for age, gender and BPV. Removing BPV revealed additional abnormalities in NABT. The main conclusions are i) FA peak height is increased in NA BT in early MS, ii) partial volume edge effects may contribute to apparent NA BT histogram abnormalities, and iii) correction for brain volume differences should reduce potential partial volume edge effects.

Multi-site Study of Diffusion Metric Variability: Characterizing the Effects of Site, Vendor, Field Strength, and Echo Time using the Histogram Distance

MRI-based multi-site trials now routinely include some form of diffusion-weighted imaging (DWI) in their protocol. These studies can include data originating from scanners built by different vendors, each with their own set of unique protocol restrictions, including restrictions on the number of available gradient directions, whether an externally-generated list of gradient directions can be used, and restrictions on the echo time (TE). One challenge of multi-site studies is to create a common imaging protocol that will result in a reliable and accurate set of diffusion metrics. The present study describes the effect of site, scanner vendor, field strength, and TE on two common metrics: the first moment of the diffusion tensor field (mean diffusivity, MD), and the fractional anisotropy (FA). We have shown in earlier work that ROI metrics and the mean of MD and FA histograms are not sufficiently sensitive for use in site characterization. Here we use the distance between whole brain histograms of FA and MD to investigate within- and between-site effects. We concluded that the variability of DTI metrics due to site, vendor, field strength, and echo time could influence the results in multi-center trials and that histogram distance is sensitive metrics for each of these variables.

ADC histograms from routine DWI for longitudinal studies in cerebral small vessel disease: a field study in CADASIL

Diffusion tensor imaging (DTI) histogram metrics are correlated with clinical parameters in cerebral small vessel diseases (cSVD). Whether ADC histogram parameters derived from simple diffusion weighted imaging (DWI) can provide relevant markers for long term studies of cSVD remains unknown. CADASIL patients were evaluated by DWI and DTI in a large cohort study over a 6-year period. ADC histogram parameters were compared to those derived from mean diffusivity (MD) histograms in 280 patients using intra-class correlation and Bland-Altman plots. Impact of image corrections applied to ADC maps was assessed and a mixed effect model was used for analyzing the effects of scanner upgrades. The results showed that ADC histogram parameters are strongly correlated to MD histogram parameters and that image corrections have only limited influence on these results. Unexpectedly, scanner upgrades were found to have major effects on diffusion measures with DWI or DTI that can be even larger than those related to patients' characteristics. These data support that ADC histograms from daily used DWI can provide relevant parameters for assessing cSVD, but the variability related to scanner upgrades as regularly performed in clinical centers should be determined precisely for longitudinal and multicentric studies using diffusion MRI in cSVD.

Diffusion tensor imaging and tractography of the human language pathways: moving into the clinical realm

The functional correlates of anatomical derangements are of interest to the neurological clinician. Diffusion tensor tractography (DTT) is a relatively new tool in the arsenal of functional neuroimaging, by which to assess white matter tracts in the brain. While much import has been given to tracking corticospinal tracts in neurological disease, studying language pathway interconnections using DTT has largely remained in the research realm. Hardware and software advances have allowed this tool to ease into clinical practice, with several radiologists, neurologists, and neurosurgeons now familiar with its applications. DTT images, although visually appealing, are founded in mathematical equations and assumptions, and require a more than basic understanding of principles and limitations before they can be integrated into routine clinical practice. Cognitive pathways like that of language, that are normally hard to assess and especially more so when pathologically affected, have been at the receiving end of several opposing and often controversial hypotheses, and the past decade has seen the clarification, validation or rejection of several of these by the in vivo charting of functional connectivity using DTT. The focus of this review is to illustrate DTT of the language pathways with emphasis on practical considerations, clinical applications, and limitations.

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

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

White-matter abnormalities in the right posterior hemisphere in generalized anxiety disorder: a diffusion imaging study

BACKGROUND

Prior imaging studies have shown structural, functional and biochemical impairments in patients with generalized anxiety disorder (GAD), particularly in the right hemisphere. In this study we investigated, for the first time to the best of our knowledge, the white-matter microstructure organization in GAD.

METHOD

A total of 12 patients with DSM-IV GAD and 15 matched healthy controls underwent a magnetic resonance imaging session of diffusion weighted imaging, exploring white-matter water molecules by the means of apparent diffusion coefficients (ADCs). Regions of interests were placed in the frontal, parietal, temporal and occipital lobes and in the splenium and genu of the corpus callosum, bilaterally.

RESULTS

ADC measures were significantly greater in patients with GAD in the right splenium and right parietal cortex compared with healthy controls (p⩽0.002). No significant correlations between ADCs and age or clinical variables were found.

CONCLUSIONS

We provide evidence that GAD is associated with disrupted white-matter coherence of posterior right hemisphere regions, which may partly sustain the impaired cognitive regulation of anxiety. Future diffusion imaging investigations are expected to better elucidate the communication between the parietal cortex and other right hemisphere regions in sustaining the cognitive processing of social and emotional stimuli in patients with GAD.

Diffusion abnormality maps in demyelinating disease: correlations with clinical scores

BACKGROUND AND PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Diffusion MR imaging for monitoring treatment response

The objective of this article was to emphasize the use of diffusion-weighted imaging in the diagnosis and follow-up of several major disease contexts, as established in recent literature. In some of these diseases the diffusion changes are correlated with the clinical deficit and are potentially useful for early diagnosis and longitudinal evaluation, as well as in the context of pharmacologic trials. Diffusion magnetic resonance is a major advance in the continuing evolution of MR imaging. It provides contrasts and characterization between tissues at a cellular level that may imply differences in function as well as framework and have contributed to a better understanding of the pathophysiological mechanisms of several diseases.

Segmentation of multiple sclerosis lesions in MR images: a review

INTRODUCTION

Multiple sclerosis (MS) is an inflammatory demyelinating disease that the parts of the nervous system through the lesions generated in the white matter of the brain. It brings about disabilities in different organs of the body such as eyes and muscles. Early detection of MS and estimation of its progression are critical for optimal treatment of the disease.

METHODS

For diagnosis and treatment evaluation of MS lesions, they may be detected and segmented in Magnetic Resonance Imaging (MRI) scans of the brain. However, due to the large amount of MRI data to be analyzed, manual segmentation of the lesions by clinical experts translates into a very cumbersome and time consuming task. In addition, manual segmentation is subjective and prone to human errors. Several groups have developed computerized methods to detect and segment MS lesions. These methods are not categorized and compared in the past.

RESULTS

This paper reviews and compares various MS lesion segmentation methods proposed in recent years. It covers conventional methods like multilevel thresholding and region growing, as well as more recent Bayesian methods that require parameter estimation algorithms. It also covers parameter estimation methods like expectation maximization and adaptive mixture model which are among unsupervised techniques as well as kNN and Parzen window methods that are among supervised techniques.

CONCLUSIONS

Integration of knowledge-based methods such as atlas-based approaches with Bayesian methods increases segmentation accuracy. In addition, employing intelligent classifiers like Fuzzy C-Means, Fuzzy Inference Systems, and Artificial Neural Networks reduces misclassified voxels.

Segmentation of multiple sclerosis lesions in MR images: a review

INTRODUCTION

Multiple sclerosis (MS) is an inflammatory demyelinating disease that the parts of the nervous system through the lesions generated in the white matter of the brain. It brings about disabilities in different organs of the body such as eyes and muscles. Early detection of MS and estimation of its progression are critical for optimal treatment of the disease.

METHODS

For diagnosis and treatment evaluation of MS lesions, they may be detected and segmented in Magnetic Resonance Imaging (MRI) scans of the brain. However, due to the large amount of MRI data to be analyzed, manual segmentation of the lesions by clinical experts translates into a very cumbersome and time consuming task. In addition, manual segmentation is subjective and prone to human errors. Several groups have developed computerized methods to detect and segment MS lesions. These methods are not categorized and compared in the past.

RESULTS

This paper reviews and compares various MS lesion segmentation methods proposed in recent years. It covers conventional methods like multilevel thresholding and region growing, as well as more recent Bayesian methods that require parameter estimation algorithms. It also covers parameter estimation methods like expectation maximization and adaptive mixture model which are among unsupervised techniques as well as kNN and Parzen window methods that are among supervised techniques.

CONCLUSIONS

Integration of knowledge-based methods such as atlas-based approaches with Bayesian methods increases segmentation accuracy. In addition, employing intelligent classifiers like Fuzzy C-Means, Fuzzy Inference Systems, and Artificial Neural Networks reduces misclassified voxels.

Fractional anisotropy and mean diffusivity in the corpus callosum of patients with multiple sclerosis: the effect of physiotherapy

INTRODUCTION

Modulation of neurodegeneration by physical activity is an active topic in contemporary research. The purpose of this study was to investigate changes in the brain's microstructure in multiple sclerosis (MS) after facilitation physiotherapy.

METHODS

Eleven patients with MS were examined using motor and neuropsychological testing and multimodal MRI at the beginning of the study, with second baseline measurement after 1 month without any therapy, and after a 2-month period of facilitation physiotherapy. Eleven healthy controls were examined at the beginning of the study and after 1 month. Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (λ (ax)), and radial diffusivity (λ (rad)) were calculated for the whole corpus callosum (CC) in the midsagittal slice of T1W 3D MPRAGE spatially normalized images. Data were analyzed using linear mixed-effect models, paired, and two-sample tests.

RESULTS

At the baseline, patients with MS showed significantly lower values in FA (p < 0.001), and significantly higher values in MD (p < 0.001), λ (ax) (p = 0.003), and λ (rad) (p < 0.001) compared to control subjects. The FA, MD, λ (ax), and λ (rad) did not change between the first and second baseline examinations in either group. Differences 2 months after initiating facilitation physiotherapy were in FA, MD, and in λ (rad) significantly higher than differences in healthy controls (p < 0.001 for FA, p = 0.02 for MD, and p = 0.002 for λ (rad)). In MS patients, FA in the CC significantly increased (p < 0.001), MD and λ (rad) significantly decreased (p = 0.014 and p = 0.002), and thus approached the values in healthy controls.

CONCLUSION

The results of the study show that facilitation physiotherapy influences brain microstructure measured by DTI.

Diffusion imaging in multiple sclerosis: research and clinical implications

Multiple sclerosis (MS) is an inflammatory-demyelinating and neurodegenerative disease of the central nervous system (CNS) and the most frequent cause of non-traumatic disability in young and middle-age adults. Although conventional MRI (including T2-weighted, pre- and post-contrast T1-weighted scans) has had a huge impact on MS by enabling an earlier diagnosis, and by providing surrogate markers for monitoring treatment response, it is limited by the low pathological specificity and the low sensitivity to diffuse damage in normal-appearing white matter and gray matter. Diffusion weighted MRI is a quantitative technique able to overcome these limitations by providing markers more specific to the underlying pathologic substrates and more sensitive to the full extent of 'occult' brain tissue damage. This review describes diffusion studies in MS, discusses their pathophysiological implications and emphasizes their clinical relevance.

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.

MR relaxation in multiple sclerosis

This article provides an overview of relaxation times and their application to normal brain and brain and cord affected by multiple sclerosis. The goal is to provide readers with an intuitive understanding of what influences relaxation times, how relaxation times can be accurately measured, and how they provide specific information about the pathology of MS. The article summarizes significant results from relaxation time studies in the normal human brain and cord and from people who have multiple sclerosis. It also reports on studies that have compared relaxation time results with results from other MR techniques.

New imaging techniques in the diagnosis of multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) is a chronic disabling disorder histopathologically characterized by inflammation, demyelination and axonal loss. Conventional MRI has made most contributions to the diagnosis of MS. However, it is not sufficiently sensitive and specific to reveal the extent and severity of the damage in the disease. Other nuclear magnetic resonance (NMR) techniques including magnetic resonance spectroscopy, magnetization transfer imaging, diffusion weighted and diffusion tensor imaging, and functional MRI have provided additional information that improves the diagnosis and understanding of MS. Optical techniques including optical coherence tomography (OCT) and coherent anti-Stokes Raman scattering (CARS) microscopy have shown promise in diagnosis and mechanistic study of myelin diseases.

OBJECTIVE

To review new imaging techniques and their potential in diagnosis of MS.

METHOD

The principles of three imaging techniques (MRI, OCT and CARS) and their applications to MS studies are described. Their advantages and disadvantages are compared.

CONCLUSION

Conventional MRI remains a critical tool in the diagnosis of MS. Alternative NMR/MRI techniques have improved specificity for the detection of lesions and provided more quantitative information about MS. Optical techniques including OCT and CARS microscopy are opening up new ways for diagnosis and mechanistic study of myelin diseases.

Cerebral infarction associated with moyamoya disease: histogram-based quantitative analysis of diffusion tensor imaging -- a preliminary study

Moyamoya disease (MMD) is a rare disorder of unknown etiology in which terminal portions of the internal carotid arteries become steno-occlusive, with fine collateral "moyamoya vessels" formed secondarily, resulting in serial ischemic strokes throughout its clinical course. Whole-brain histogram (WBH) of diffusion tensor imaging (WBH-DTI) is an analytical tool whose feasibility has been ascertained in various pathologies. To elucidate whether WBH-DTI could detect any difference between ischemic MMD and normal controls, we examined 27 consecutive MMD patients without hemorrhage and 48 normal controls in this prospective study using a 3.0-T magnetic resonance scanner. WBHs of fractional anisotropy (FA) (WBH-FA) and mean diffusivity (MD) (WBH-MD) were compared among three groups: Group 1, MMD patients with infarct (n=15); Group 2, MMD patients without infarct (n=12); and Group 3, normal controls (n=48). Group 1 showed significantly higher peak height and significantly lower mean value on WBH-FA, as well as significantly lower peak height and significantly higher mean value on WBH-MD, compared with Groups 2 and 3. No significant difference was seen in parameters at either WBH-FA or WBH-MD between Groups 2 and 3. These results might reflect the pathological severity of each group, and WBH-DTI could feasibly detect differences between ischemic MMD with infarction and MMD without infarction and normal controls.

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.

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.

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.

The role of white matter for the pathophysiology of schizophrenia

Inter- and intra-hemispheric connectivity disturbances have been suggested to play a major role in schizophrenia. To this extent, diffusion weighted imaging (DWI) is a relatively new technique examining subtle white matter microstructure organization. DWI studies in schizophrenia strongly suggest that white matter communication is disrupted. This supports the hypothesis that there is a cortico-cortical and transcallosal altered connectivity in schizophrenia, which may be relevant for the pathophysiology and the cognitive disturbances of the disorder. Future longitudinal diffusion and functional imaging studies targeting brain communication together with genetic investigations should further characterize white matter pathology in schizophrenia and its relevance for the development of the illness.

Cortical white-matter microstructure in schizophrenia. Diffusion imaging study

BACKGROUND

Several, although not all, of the previous small diffusion-weighted imaging (DWI) studies have shown cortical white-matter disruption in schizophrenia.

AIMS

To investigate cortical white-matter microstructure with DWI in a large community-based sample of people with schizophrenia.

METHOD

Sixty-eight people with schizophrenia and 64 healthy controls underwent a session of DWI to obtain the apparent diffusion coefficient (ADC) of white-matter water molecules. Regions of interest were placed in cortical lobes.

RESULTS

Compared with controls, the schizophrenia group had significantly greater ADCs in frontal, temporal and occipital white matter (analysis of covariance, P < 0.05).

CONCLUSIONS

Our findings confirm the presence of cortical white-matter microstructure disruption in frontal and temporo-occipital lobes in the largest sample of people with schizophrenia thus for studied with this technique. Future brain imaging studies, together with genetic investigations, should further explore white-matter integrity and genes encoding myelin-related protein expression in people with first-episode schizophrenia and those at high risk of developing the disorder.

Quantitative diffusion weighted imaging measures in patients with multiple sclerosis

Diffusion-weighted imaging (DWI) has been proposed as a sensitive measure of disease severity capable of detecting subtle changes in gray matter and white matter brain compartments in patients with multiple sclerosis (MS). However, DWI has been applied to the study of MS clinical subtypes in only a few studies. The objective of this study was to demonstrate the validity of a novel, fully automated method for the calculation of quantitative DWI measures. We also wanted to assess the correlation between whole brain (WB)-DWI variables and clinical and MRI measures of disease severity in a large cohort of MS patients. For this purpose we studied 432 consecutive MS patients (mean age 44.4+/-10.2 years), 16 patients with clinically isolated syndrome (CIS) and 38 normal controls (NC) using 1.5 T brain MRI. Clinical disease subtypes were as follows: 294 relapsing-remitting (RR), 123 secondary-progressive (SP) and 15 primary-progressive (PP). Mean disease duration was 12+/-10 years. Mean Expanded Disability Status Scale (EDSS) was 3.3+/-2.1. Brain parenchymal fraction (BPF), gray matter fraction (GMF) and white matter fraction (WMF) were calculated using a fully automated method. Mean parenchymal diffusivity (MPD) maps were created. DWI indices of peak position (PP), peak height (PH), MPD and entropy (ENT) were obtained. T2- and T1-lesion volumes (LV), EDSS, ambulation index (AI) and nine-hole peg test (9-HPT) were also assessed. MS patients had significantly lower BPF (d=1.26; p<0.001) and GMF (d=0.61; p=0.003), and higher ENT (d=1.2; p<0.0001), MPD (d=1.04; p<0.0001) and PH (d=0.47; p=0.045) than NC subjects. A GLM analysis, adjusted for age and multiple comparisons, revealed significant differences between different clinical subtypes for BPF, GMF, ENT, PH, PP, T2-LV and T1-LV (p<0.0001), WMF (p=0.001) and MPD (p=0.023). In RR and SP MS patients, ENT showed a more robust correlation with other MRI (r=0.54 to 0.67, p<0.0001) and clinical (r=0.31 to 0.36, p<0.0001) variables than MPD (r=0.23 to 0.41, p<0.001 for MRI and r=0.13 to 0.18; p=0.006 to p<0.001 for clinical variables). The GMF and BPF showed a slightly stronger relationship with all clinical variables (r=0.33 to 0.48; p<0.0001), when compared to both lesion and DWI measures. ENT (R2=0.28; p<0.0001) and GMF (R2=0.26; p<0.001) were best related with SP disease course. This study highlights the validity of DWI in discerning differences between NC and MS patients, as well as between different MS subtypes. ENT is a sensitive marker of overall brain damage that is strongly related to clinical impairment in patients with SP MS.

Cerebral atrophy and white matter disruption in chronic schizophrenia

Several magnetic resonance imaging (MRI) studies have shown cerebral atrophy in established schizophrenia, although not in all reports. Discrepancies may mostly be due to population and postprocessing differences. Recently, disruption of cortical white matter integrity has also been reported in chronic patients with schizophrenia. In this study we explored tridimensional (3D) cerebral volumes and white matter microstructure in schizophrenia with structural and diffusion magnetic resonance. Twenty-five patients with established schizophrenia and 25 1:1 matched normal controls underwent a session of MRI using a Siemens 1.5T-scanner. 3D brain volume reconstruction was performed with the semi-automatic software Amira (TGS, San Diego, CA), whereas the apparent diffusion coefficients (ADCs) of cortical white matter water molecules were obtained with in-house developed softwares written in MatLab (The Mathworks-Inc., Natick, MA). Compared to controls, patients with schizophrenia had significantly smaller gray matter intracranium and total brain volumes, increased 4th ventricle volumes, and greater temporal and occipital ADCs. Patients treated with typical antipsychotic medication (N = 9) had significantly larger right lateral and 4th ventricles compared to those on atypical antipsychotic drugs. Intracranial volumes significantly inversely correlated with left temporal ADC in patients with schizophrenia. Also, age correlated directly with right, left, and 3rd ventricle volumes and inversely with gray matter intracranium volumes in individuals with schizophrenia. This study confirmed the presence of cortical atrophy in patients with schizophrenia, especially in those on typical antipsychotic drugs, and the existence of white matter disruption. It also suggested that physiological aging effects on brain anatomy may be abnormally pronounced in schizophrenia.

Cerebral and cerebellar ADC values during a migraine attack

INTRODUCTION

We investigated the diffusion-weighted MRI changes, apparent diffusion coefficient (ADC) values, and conventional MRI findings in specific brain areas during migraine attacks in patients with and without aura.

METHODS

Included in the study were 22 patients (2 male, 20 female) aged between 17 and 49 years who were diagnosed as having migraine according to the diagnostic criteria of the International Headache Society. Also included in the study were 18 age- and sex-matched healthy volunteers. Hyperintense lesions were evaluated in conventional MR images. Heavily diffusion-weighted images, ADC maps, and segmented ADC maps generated for regional ADC (rADC) measurements, were also studied. ADC values from specific brain areas were used with appropriate region of interests (ROI).

RESULTS

Migraine with aura was diagnosed in 13 patients and migraine without aura was diagnosed in 9 patients. A total of 23 hyperintense lesions within the periventricular white matter and deep white matter were detected in five patients (21.8%). All of these hyperintense lesions were seen in migraine patients with aura. In only one patient did a hyperintense lesion show an increased diffusion pattern on diffusion-weighted images and ADC maps. One hyperintense lesion was detected in the control group (5.5%). There was no significant difference in ADC values between the migraine and control groups.

CONCLUSION

T2-weighted hyperintense lesions were significantly more frequent in migraine patients especially in those with aura than in the control group. No diffusion alterations in diffusion-weighted images were detected in the infra- and supratentorial brain areas during migraine attacks in patients with and without aura.

Structural and functional surrogates of cognitive impairment at the very early stage of multiple sclerosis

Following our previous reports based on parametric MRI methods (T(2)-weighted MRI, statistical mapping analysis of magnetization transfer ratio images and functional MRI) applied to a population of 18 patients with clinically isolated syndrome suggestive of multiple sclerosis, we have reviewed the possible structural and functional surrogates of MS that could explain the subtle cognitive impairment related to attention and working memory deficits evaluated with paced auditory serial addition test (PASAT). We propose that the brain substrates underlying cognitive impairment observed at the very early stage of MS are multifactorial. Several components could influence PASAT performances in patients: i) the extent of diffuse white matter damage, ii) the location of visible and non visible lesions, iii) the connectivity efficiency between distant brain functional areas involved in working memory processes and iv) the cortical reorganization. Nevertheless, individually, each of these parameters may have few influences on PASAT performance in patients. Using a multiregression model built with independent MR parameters, a very good evaluation of PASAT scores has been obtained in this limited number of patients explaining 90% of the variance. In conclusion, the different aspects of tissue and functional pathological brain underpinnings must be accounted to monitor accurately new therapeutic strategies for the treatment of early cognitive deficits related to MS.

Secondary progressive multiple sclerosis: current knowledge and future challenges

The secondary progressive phase of multiple sclerosis (MS), which is characterised by a steady accrual of fixed disability after an initial relapsing remitting course, is not clearly understood. Although there is no consensus on the mechanisms underlying such a transition to the progressive phase, epidemiological and neuroimaging studies indicate that it is probably driven by the high prevalence of neurodegenerative compared with inflammatory pathological changes. This notion is lent support by the limited efficacy of available immunomodulating and immunosuppressive treatment strategies, which seems to be further decreased in the late stages of secondary progressive MS. No established clinical or paraclinical predictors of the transition from relapsing remitting to secondary progressive MS have been described. However, the use of quantitative MRI-derived measures is warranted to monitor natural history studies and therapeutic trials of secondary progressive MS with increased reliability. In view of the small effects of immunomodulating and immunosuppressive treatments in preventing the transition to secondary progression, the development of treatments promoting neuroaxonal repair remains an important goal in this disease.

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.

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.

MRI evidence for multiple sclerosis as a diffuse disease of the central nervous system

The classical view of MS as a chronic inflammatory demyelinating disease leading to the formation of focal central nervous system (CNS) white matter (WM) lesions has been recently challenged by pathological studies and by the extensive application of modern MRI-based techniques. There is now overwhelming evidence supporting the following statements: MS causes widespread tissue damage in the normal-appearing white matter (NAWM) of the brain and spinal cord, whose extent and severity is more strictly associated to the clinical manifestations of the disease than the extent of focal pathology. Discrete, macroscopic lesions are just the tip of the iceberg of MS pathology. Grey matter (GM) damage is a consistent feature of all MS phenotypes, which is progressive from the start of the relapsing-remitting phase of the disease. As is the case for WM, GM damage is also a mixture of focal lesions and diffuse pathology. High-field strength MR scanners are improving our ability to image focal GM lesions and modern MR-based techniques are enabling us to quantify in vivo the extent and severity of GM pathology, which have been shown to correlate only moderately with the amount of WM changes. At least part of GM pathology in MS is not secondary to retrograde degeneration of fibers traversing WM lesions. The neurodegenerative component of the disease is not a late phenomenon and it is not completely driven by inflammatory demyelination. In fact, neurodegeneration occurs very early in the course of MS and the correlation between MRI measures of inflammation and neurodegeneration is weak in all disease phases. The interplay of inflammation and neurodegeneration is a complex and still poorly understood phenomenon. At least part of MS-related neurodegeneration is not directly driven by Wallerian degeneration. Functional cortical changes can be seen in virtually all MS patients and are likely to play a central role in the ability of the MS brain to respond to tissue injury and, hence, limit the functional consequences of structural damage. MS disability is not just the result of tissue destruction but rather a balance between tissue destruction, tissue repair and adaptive cortical reorganization. All of this calls for the concept of MS as a focal, inflammatory demyelinating, WM disease to be reexamined and to start viewing MS as a diffuse CNS disease with an important neurodegenerative component. This is central for identifying novel and effective treatment strategies.

Longitudinal diffusion changes in cerebral hemispheres after MCA infarcts

Diffusion tensor imaging can be used in vivo to assess the longitudinal and regional microstructural changes occurring after middle cerebral artery (MCA) infarcts in humans. Nine patients were investigated 1 week (D7), 1 (M1), 3 (M3), and 6 months (M6) after the occurrence of an isolated MCA infarction. First, an overall analysis was performed using histograms of mean diffusivity (MD) and fractional anisotropy (FA) in each hemisphere. Thereafter, the regional pattern of diffusion changes was investigated voxel by voxel with statistical parametric mapping 99. In the hemisphere ipsilateral to the infarction, histogram analysis revealed a significant decrease in FA between D7 and M6 associated with a progressive increase in MD from D7 to M3. Remote from the MCA territory, the voxel by voxel analyses detected a significant increase in MD within the thalamus at M3 and M6 and a reduction in FA along the pyramidal tract at M6. In the contralateral hemisphere, between D7 and M6, a significant hemispheric atrophy was observed in association with a global reduction in anisotropy, in the absence of distinctive regional diffusion changes. These results suggest that micro- and macrostructural tissue modifications can be detected with diffusion tensor imaging in regions remote from the ischemic area in both hemispheres.

Multisequence magnetic resonance imaging study of neuropsychiatric systemic lupus erythematosus

OBJECTIVE

To investigate the relationship between magnetization transfer imaging (MTI), diffusion-weighted imaging (DWI), proton magnetic resonance spectroscopy (H-MRS), and T2 relaxometry findings in patients with primary neuropsychiatric systemic lupus erythematosus (NPSLE).

METHODS

The study group consisted of 24 female patients (mean age 36 years [range 23-65]) who had had a variety of neuropsychiatric symptoms that were judged to be due to NPSLE according to the criteria of the American College of Rheumatology. Patients with current active disease were excluded from participation. Quantitative MTI, DWI, H-MRS, and T2 relaxometry data were acquired in all patients, and the correlation coefficients were calculated.

RESULTS

MTI results reflecting a decrease in homogeneity of cerebral parenchyma correlated significantly with H-MRS results representing axonal damage. MTI results also correlated significantly with DWI results reflecting increased diffusivity in the cerebral parenchyma. Finally, MTI results reflecting decreased cerebral homogeneity correlated significantly with increased T2 relaxation time, associated with either edema or gliosis. Increased T2 relaxation time correlated significantly with DWI results reflecting increased diffusivity. With the exception of the correlation between H-MRS and MTI findings, there was no significant correlation between H-MRS results and any other parameter.

CONCLUSION

The selected study parameters represent different biologic features in the human brain and can be informative with regard to different pathologic processes in NPSLE. The demonstrated associations between MTI, DWI, H-MRS, and T2 data in patients with a history of NPSLE suggest that there is one pathogenesis and/or common neuropathologic outcome in NPSLE despite differences in clinical presentation.

Magnetic resonance imaging and spectroscopy in assessing 3-nitropropionic acid-induced brain lesions: an animal model of Huntington’s disease

Huntington's disease (HD) is an inherited neurodegenerative disease, in which there is progressive motor and cognitive deterioration, and for which the pathogenesis of neuronal death remains controversial. Mitochondrial toxins like 3-nitropropionic acid (3-NP) and malonate, functioning as the inhibitors of the complex II of mitochondrial respiratory chain, have been found to effectively induce specific behavioral changes and selective striatal lesions in rats and non-human primates mimicking those in HD. Furthermore, several kinds of transgenic mouse models of HD have been recently developed, and used in the development and assessment of novel treatments for HD. In the past, most studies evaluating the animal models for HD were based on histological changes or in vitro neuronal cultures. With the emergence of advanced magnetic resonance technologies, non-invasive magnetic resonance imaging (MRI) and spectroscopy provide more detail of cerebral alterations, including the changes of cerebral structure, function and metabolites. These studies support the hypothesis that mitochondrial dysfunction with increased excitation of N-methyl-D-aspartate (NMDA) receptors can replicate the neurobehavioral changes, selective brain injury and neurochemical alterations in HD. The present review focuses on our work as well as that of others regarding 3-NP-induced neurotoxicity and other animal models of HD. Using both conventional and advanced MRI and spectroscopy, we summarize the pathogenesis and possible therapeutic strategies in chemical and transgenic models of HD. The results show magnetic resonance techniques to be powerful techniques in the evaluation of pathogenesis and therapeutic intervention for both chemical and transgenic models of HD.

The evolution of the apparent diffusion coefficient in the pediatric brain at low and high diffusion weightings

PURPOSE

To evaluate the evolution of the apparent diffusion coefficient (ADC) with age for different degrees of diffusion weighting using a clinically feasible approach.

MATERIALS AND METHODS

Data was acquired using separate scans with b values in the range typically used for clinical studies (100-900 seconds/mm(2)) and higher b values (1800-3000 seconds/mm(2)). The ADC was calculated for each of the data sets by fitting the data to a monoexponential function.

RESULTS

The results from 50 children aged three years and less showed some deviations from literature values derived using a full biexponential fit, with these differences reflecting the approximations inherent in this approach. The values obtained with this technique appear to be reproducible but the resulting "institutional values" are comparable to those from other centers only if identical measurement criteria are used.

CONCLUSION

A significant decline in both components of the ADC during the first few months of life was observed; in addition, the attenuated slow ADC values seen in adult white matter were only present at birth in early myelinating regions. The subsequent development of the slow ADC in white matter suggests that it is associated with myelination or processes associated with axonal development.

Multislice T1 relaxation time measurements in the brain using IR-EPI: Reproducibility, normal values, and histogram analysis in patients with multiple sclerosis

PURPOSE

To perform T(1) measurements using inversion recovery (IR) echoplanar imaging (EPI) to evaluate reproducibility, normal values, and T(1) histogram analysis as a measure of disease progression in multiple sclerosis (MS) patients.

MATERIALS AND METHODS

Multislice IR-EPI was performed in 10 controls and 36 MS patients. Region-of-interest (ROI) and T(1) histogram analysis were performed on T(1) maps and compared to hypointense T(1) lesions and brain atrophy in MS patients.

RESULTS

Coefficient of variation (COV) varied from 1.6% to 4.9%. Callosal normal (appearing) white matter (N(A)WM) showed the lowest and cortical gray matter the highest T(1) values. T(1) histogram analysis in controls showed a sharp WM peak centered on a T(1) value of 729 msec (range = 679-765) with extension into a shoulder of higher T(1) values. In MS patients, a shift toward higher T(1) values (mean = 788 msec, range = 700-957) with a lower relative peak amplitude was present, predominantly resulting from T(1) prolongation in NAWM. T(1) histogram parameters strongly related to hypointense T(1) lesion volume and brain atrophy in MS patients.

CONCLUSIONS

IR-EPI provides a reproducible method to obtain T(1) values in the brain. Regional variation in T(1) values is present in N(A)WM of volunteers and MS patients. Since T(1) histogram parameters reflect changes in NAWM and correlate with conventional measures of disease burden in MS patients, T(1) histogram analysis may provide a global measure of disease progression in MS.

Replicability of diffusion tensor imaging measurements of fractional anisotropy and trace in brain

PURPOSE

To evaluate within-scanner and between-scanner reliability of fractional anisotropy (FA) and trace (sum of the diagonal elements of the diffusion tensor) as measured by diffusion tensor imaging (DTI).

MATERIALS AND METHODS

Ten young healthy adults were scanned on three separate days, on two different systems made by the same manufacturer. One scan was acquired at one site, and two scans were acquired on two different occasions on another scanner at another site. Three levels of analysis were used to compare the DTI metrics: 1) a voxel-by-voxel analysis of all supratentorial brain (gray matter + white matter + cerebrospinal fluid) and of supratentorial white matter; 2) a slice-by-slice analysis of supratentorial white matter; and 3) a single-region analysis of the corpus callosum.

RESULTS

The voxel-by-voxel analysis of all supratentorial brain found that FA and trace measures and correlations were equivalently and significantly higher within than across scanners. For supratentorial white matter, FA was similar within and across scanners, whereas trace demonstrated across-scanner bias. A similar pattern was observed for the slice-by-slice comparison. For the single-region analysis of the corpus callosum, within-scanner FA and trace measures were highly reproducible for FA (CV = 1.9%) and trace (CV = 2.6%), but both DTI measures showed a systematic mean bias across scanners (CV = 4.5% for FA and CV = 7.5% for trace).

CONCLUSION

These estimates of measurement variation and scanner bias can be used to predict effect sizes for longitudinal and multisite studies using diffusion tensor imaging.

Directional diffusion in relapsing-remitting multiple sclerosis: A possible in vivo signature of Wallerian degeneration

PURPOSE

To examine the role of directional dependence of the apparent diffusion coefficients in the evaluation of normal-appearing brain regions of patients with relapsing-remitting multiple sclerosis.

MATERIALS AND METHODS

The role of diffusion tensor eigenvalues was investigated in the normal-appearing brain regions for 18 patients with relapsing-remitting multiple sclerosis and 15 age-matched normal controls.

RESULTS

The isotropic apparent diffusion was increased in all regions. However, reduced anisotropy was significant only in regions with high anisotropy, including the corpus callosum and the internal capsule, and was due to increased diffusion tensor eigenvalues corresponding to diffusion transverse to the fibers without significant increase along the fibers. This characteristic pattern of changes in diffusion tensor eigenvalues has been observed previously in cases of Wallerian degeneration. Low-anisotropy regions corresponded to gray matter and gray/white interface regions. Since fiber tract orientations are not determined for regions of low anisotropy, this characteristic pattern of diffusion change is not detectable in these regions.

CONCLUSION

Examination of diffusion tensor eigenvectors may provide insight into the changes observed in diffusion and a signature of Wallerian degeneration in the normal-appearing white matter of relapsing-remitting multiple sclerosis patients.

The use of quantitative magnetic-resonance-based techniques to monitor the evolution of multiple sclerosis

Conventional MRI can improve accuracy in the diagnosis of multiple sclerosis (MS) and monitor the efficacy of experimental treatments. However, conventional MRI provides only gross estimates of the extent and nature of tissue damage associated with this disease. Other quantitative magnetic-resonance-based techniques have the potential to overcome the limitations of conventional MRI and, as a consequence, to improve our understanding of the natural history of MS. Magnetisation-transfer, diffusion-weighted, and functional MRI--as well as proton magnetic-resonance spectroscopy--are helping us to elucidate the mechanisms that underlie injury, repair, and functional adaptation in patients with MS. These techniques are substantially changing our understanding of how MS causes irreversible disability and should be used more extensively in clinical trials and in studies of disease progression.

Age-related changes in conventional, magnetization transfer, and diffusion-tensor MR imaging findings: study with whole-brain tissue histogram analysis

PURPOSE

To investigate the influence of aging on conventional magnetic resonance (MR) imaging-, magnetization transfer MR imaging-, and diffusion-tensor MR imaging-derived measurements.

MATERIALS AND METHODS

Dual-echo T1-weighted magnetization transfer and diffusion-tensor MR images of the brain were obtained in 89 healthy subjects. Normalized brain parenchymal volume (NBV) was measured by using a fully automated technique. Magnetization transfer ratio (MTR), apparent diffusion coefficient (ADC), and fractional anisotropy (FA) histograms were created for the whole brain (MTR values) or for a large representative portion of it (ADC and FA values). Bivariate correlations were assessed by using the Spearman rank correlation coefficient. A stepwise selection procedure was used to identify the combination of variables that were most influenced by subject age in a multivariate regression model.

RESULTS

Significant correlations were found between subject age and the following variables: number of hyperintense areas in the brain at T2-weighted MR imaging (r = 0.63, P <.001), NBV (r = -0.79, P <.001), mean ADC (r = 0.34, P =.001), ADC peak height (r = -0.34, P =.001), and FA peak height (r = -0.57, P <.001). NBV correlated significantly with number of hyperintense areas (P <.001), MTR peak height (P <.001), mean ADC (P =.001), ADC peak height (P =.001), and FA peak height (P <.001). The final multivariable regression model included NBV and number of hyperintense areas at T2-weighted MR imaging as independent predictors of subject age.

CONCLUSION

In addition to the extent of T2-weighted MR imaging hyperintense areas and the measurement of NBV, diffusion-tensor MR imaging provides additional in vivo information about microstructural age-related brain tissue changes.