Increasing normal-appearing grey and white matter magnetisation transfer ratio abnormality in early relapsing-remitting multiple sclerosis

Longitudinal microstructural MRI markers of demyelination and neurodegeneration in early relapsing-remitting multiple sclerosis: Magnetisation transfer, water diffusion and g-ratio

INTRODUCTION

Quantitative microstructural MRI, such as myelin-sensitive magnetisation transfer ratio (MTR) or saturation (MTsat), axon-sensitive water diffusion Neurite Orientation Dispersion and Density Imaging (NODDI), and the aggregate g-ratio, may provide more specific markers of white matter integrity than conventional MRI for early patient stratification in relapsing-remitting multiple sclerosis (RRMS). The aim of this study was to determine the sensitivity of such markers to longitudinal pathological change within cerebral white matter lesions (WML) and normal-appearing white matter (NAWM) in recently diagnosed RRMS.

METHODS

Seventy-nine people with recently diagnosed RRMS, from the FutureMS longitudinal cohort, were recruited to an extended MRI protocol at baseline and one year later. Twelve healthy volunteers received the same MRI protocol, repeated within two weeks. Ethics approval and written informed consent were obtained. 3T MRI included magnetisation transfer, and multi-shell diffusion-weighted imaging. NAWM and whole brain were segmented from 3D T1-weighted MPRAGE, and WML from T2-weighted FLAIR. MTR, MTsat, NODDI isotropic (ISOVF) and intracellular (ICVF) volume fractions, and g-ratio (calculated from MTsat and NODDI data) were measured within WML and NAWM. Brain parenchymal fraction (BPF) was also calculated. Longitudinal change in BPF and microstructural metrics was assessed with paired t-tests (α = 0.05) and linear mixed models, adjusted for confounding factors with False Discovery Rate (FDR) correction for multiple comparisons. Longitudinal changes were compared with test-retest Bland-Altman limits of agreement from healthy control white matter. The influence of longitudinal change on g-ratio was explored through post-hoc analysis in silico by computing g-ratio with realistic simulated MTsat and NODDI values.

RESULTS

In NAWM, g-ratio and ICVF increased, and MTsat decreased over one year (adjusted mean difference = 0.007, 0.005, and -0.057 respectively, all FDR-corrected p < 0.05). There was no significant change in MTR, ISOVF, or BPF. In WML, MTsat, NODDI ICVF and ISOVF increased over time (adjusted mean difference = 0.083, 0.024 and 0.016, respectively, all FDR-corrected p < 0.05). Group-level longitudinal changes exceeded test-retest limits of agreement for NODDI ISOVF and ICVF in WML only. In silico analysis showed g-ratio may increase due to a decrease in MTsat or ISOVF, or an increase in ICVF.

DISCUSSION

G-ratio and MTsat changes in NAWM over one year may indicate subtle myelin loss in early RRMS, which were not apparent with BPF or NAWM MTR. Increases in NAWM and WML NODDI ICVF were not anticipated, and raise the possibility of axonal swelling or morphological change. Increases in WML MTsat may reflect myelin repair. Changes in NODDI ISOVF are more likely to reflect alterations in water content. Competing MTsat and ICVF changes may account for the absence of g-ratio change in WML. Longitudinal changes in microstructural measures are significant at a group level, however detection in individual patients in early RRMS is limited by technique reproducibility.

CONCLUSION

MTsat and g-ratio are more sensitive than MTR to early pathological changes in RRMS, but complex dependence of g-ratio on NODDI parameters limit the interpretation of aggregate measures in isolation. Improvements in technique reproducibility and validation of MRI biophysical models across a range of pathological tissue states are needed.

Quantitative magnetization transfer imaging in relapsing-remitting multiple sclerosis: a systematic review and meta-analysis

Myelin-sensitive MRI such as magnetization transfer imaging has been widely used in multiple sclerosis. The influence of methodology and differences in disease subtype on imaging findings is, however, not well established. Here, we systematically review magnetization transfer brain imaging findings in relapsing-remitting multiple sclerosis. We examine how methodological differences, disease effects and their interaction influence magnetization transfer imaging measures. Articles published before 06/01/2021 were retrieved from online databases (PubMed, EMBASE and Web of Science) with search terms including 'magnetization transfer' and 'brain' for systematic review, according to a pre-defined protocol. Only studies that used human in vivo quantitative magnetization transfer imaging in adults with relapsing-remitting multiple sclerosis (with or without healthy controls) were included. Additional data from relapsing-remitting multiple sclerosis subjects acquired in other studies comprising mixed disease subtypes were included in meta-analyses. Data including sample size, MRI acquisition protocol parameters, treatments and clinical findings were extracted and qualitatively synthesized. Where possible, effect sizes were calculated for meta-analyses to determine magnetization transfer (i) differences between patients and healthy controls; (ii) longitudinal change and (iii) relationships with clinical disability in relapsing-remitting multiple sclerosis. Eighty-six studies met inclusion criteria. MRI acquisition parameters varied widely, and were also underreported. The majority of studies examined the magnetization transfer ratio in white matter, but magnetization transfer metrics, brain regions examined and results were heterogeneous. The analysis demonstrated a risk of bias due to selective reporting and small sample sizes. The pooled random-effects meta-analysis across all brain compartments revealed magnetization transfer ratio was 1.17 per cent units (95% CI -1.42 to -0.91) lower in relapsing-remitting multiple sclerosis than healthy controls (z-value: -8.99, P < 0.001, 46 studies). Linear mixed-model analysis did not show a significant longitudinal change in magnetization transfer ratio across all brain regions [β = 0.12 (-0.56 to 0.80), t-value = 0.35, P = 0.724, 14 studies] or normal-appearing white matter alone [β = 0.037 (-0.14 to 0.22), t-value = 0.41, P = 0.68, eight studies]. There was a significant negative association between the magnetization transfer ratio and clinical disability, as assessed by the Expanded Disability Status Scale [r = -0.32 (95% CI -0.46 to -0.17); z-value = -4.33, P < 0.001, 13 studies]. Evidence suggests that magnetization transfer imaging metrics are sensitive to pathological brain changes in relapsing-remitting multiple sclerosis, although effect sizes were small in comparison to inter-study variability. Recommendations include: better harmonized magnetization transfer acquisition protocols with detailed methodological reporting standards; larger, well-phenotyped cohorts, including healthy controls; and, further exploration of techniques such as magnetization transfer saturation or inhomogeneous magnetization transfer ratio.

Myelin content changes in Clinically Isolated Syndrome and Relapsing- Remitting Multiple Sclerosis: Associations with lesion type and severity of visuomotor impairment

BACKGROUND

Cognitive disturbances occur in patients with Relapsing Remitting Multiple Sclerosis (RR-MS) and Clinically Isolated Syndrome (CIS). The Multi-Echo-Spin-Echo (MESE) T2-weighted sequence quantifies demyelination, the pathological hallmark of MS, but has not been used for the documentation of the potential relationship between anatomically specific demyelinating changes and cognitive impairment in MS.

PURPOSE

To identify markers of regional demyelination in patients with RR-MS and CIS in relation to clinical variables and severity of cognitive impairment.

METHODS AND MATERIALS

37 RR-MS patients, 39 CIS patients and 52 healthy controls (HC) were examined using the MESE sequence. Long T2 and myelin water fraction (MWF) values were measured, serving as indices of intra/extracellular water content and myelin content, respectively, in focal white matter lesions and 12 normal appearing white matter (NAWM) areas of the patients and HC. A comprehensive neuropsychological assessment was administered to all patients.

RESULTS

RR-MS patients showed widespread long T2 increases and MWF reductions in NAWM, compared to the respective values of HC (p < 0.001), which correlated with total lesion volume. Among RR-MS patients illness duration correlated negatively with MWF in right hemisphere frontal and periventricular NAWM areas (and positively with corresponding long T2 values). MWF values were lower in the CIS, as compared to the HC group, in the temporal, frontal and periventricular NAWM areas. Focal demyelinating lesions displayed variable higher T2 and lower MWF values, compared to NAWM, closely corresponding to their intensity on T1 sequences. Reduced MWF values and increased long T2 values in right periventricular NAWM were significantly associated with poor visuomotor performance.

CONCLUSION

The MESE sequence affords accurate estimation of myelin and water content in NAWM and focal lesions in RR-MS and CIS patients, by means of the MWF and long T2 values, respectively, providing a sensitive index of demyelination associated with visuomotor deficits.

Periventricular magnetisation transfer ratio abnormalities in multiple sclerosis improve after alemtuzumab

BACKGROUND

In multiple sclerosis (MS), disease effects on magnetisation transfer ratio (MTR) increase towards the ventricles. This periventricular gradient is evident shortly after first symptoms and is independent of white matter lesions.

OBJECTIVE

To explore if alemtuzumab, a peripherally acting disease-modifying treatment, modifies the gradient's evolution, and whether baseline gradients predict on-treatment relapses.

METHODS

Thirty-four people with relapsing-remitting MS underwent annual magnetic resonance imaging (MRI) scanning (19 receiving alemtuzumab (four scans each), 15 untreated (three scans each)). The normal-appearing white matter was segmented into concentric bands. Gradients were measured over the three bands nearest the ventricles. Mixed-effects models adjusted for age, gender, relapse rate, lesion number and brain parenchymal fraction compared the groups' baseline gradients and evolution.

RESULTS

Untreated, the mean MTR gradient increased (+0.030 pu/band/year) but decreased following alemtuzumab (-0.045 pu/band/year, p = 0.037). Within the alemtuzumab group, there were no significant differences in baseline lesion number (p = 0.568) nor brain parenchymal fraction (p = 0.187) between those who relapsed within 4 years (n = 4) and those who did not (n = 15). However, the baseline gradient was significantly different (p = 0.020).

CONCLUSION

Untreated, abnormal periventricular gradients worsen with time, but appear reversible with peripheral immunotherapy. Baseline gradients - but not lesion loads or brain volumes - may predict on-treatment relapses. Larger confirmatory studies are required.

Gray Matter Alterations in Early and Late Relapsing-Remitting Multiple Sclerosis Evaluated with Synthetic Quantitative Magnetic Resonance Imaging

Extensive gray matter (GM) involvement has been demonstrated in multiple sclerosis (MS) patients. This study was aimed to identify GM alterations in relapsing-remitting MS (RRMS) patients using synthetic quantitative MRI (qMRI). We assessed myelin volume fraction (MVF) in each voxel on the basis of R1 and R2 relaxation rates and proton density in 14 early and 28 late (disease duration ≤5 and >5 years, respectively) RRMS patients, and 15 healthy controls (HCs). The MVF and myelin volumes of GM (GM-MyVol) were compared between groups using GM-based spatial statistics (GBSS) and the Kruskal-Wallis test, respectively. Correlations between MVF or GM-MyVol and disease duration or expanded disability status scale were also evaluated. RRMS patients showed a lower MVF than HCs, predominantly in the limbic and para-limbic areas, with more extensive areas noted in late RRMS patients. Late-RRMS patients had the smallest GM-MyVol (20.44 mL; early RRMS, 22.77 mL; HCs, 23.36 mL). Furthermore, the GM-MyVol in the RRMS group was inversely correlated with disease duration (r = -0.43, p = 0.005). In conclusion, the MVF and MyVol obtained by synthetic qMRI can be used to evaluate GM differences in RRMS patients.

Emerging Magnetic Resonance Imaging Techniques and Analysis Methods in Amyotrophic Lateral Sclerosis

Objective markers of disease sensitive to the clinical activity, symptomatic progression, and underlying substrates of neurodegeneration are highly coveted in amyotrophic lateral sclerosis in order to more eloquently stratify the highly heterogeneous phenotype and facilitate the discovery of effective disease modifying treatments for patients. Magnetic resonance imaging (MRI) is a promising, non-invasive biomarker candidate whose acquisition techniques and analysis methods are undergoing constant evolution in the pursuit of parameters which more closely represent biologically-applicable tissue changes. Neurite Orientation Dispersion and Density Imaging (NODDI; a form of diffusion imaging), and quantitative Magnetization Transfer Imaging (qMTi) are two such emerging modalities which have each broadened the understanding of other neurological disorders and have the potential to provide new insights into structural alterations initiated by the disease process in ALS. Furthermore, novel neuroimaging data analysis approaches such as Event-Based Modeling (EBM) may be able to circumvent the requirement for longitudinal scanning as a means to comprehend the dynamic stages of neurodegeneration in vivo. Combining these and other innovative imaging protocols with more sophisticated techniques to analyse ever-increasing datasets holds the exciting prospect of transforming understanding of the biological processes and temporal evolution of the ALS syndrome, and can only benefit from multicentre collaboration across the entire ALS research community.

Normal-appearing grey and white matter T1 abnormality in early relapsing–remitting multiple sclerosis: a longitudinal study

Objective

To investigate the presence and evolution of T1 relaxation time abnormalities in normal-appearing white matter (NAWM) and grey matter (GM), early in the course of relapsing–remitting multiple sclerosis (MS).

Methods

Twenty-three patients with early relapsing–remitting MS and 14 healthy controls were imaged six monthly for up to three years. Mean follow-up was 26 months for MS patients and 24 months for controls. Dual-echo fast-spin echo and gradient-echo proton-density and T1-weighted data sets (permitting the calculation of a T1 map) were acquired in all subjects. GM and NAWM T1 histograms were produced and a hierarchical regression model was used to investigate changes in T1 over time.

Results

At baseline, significant patient-control differences were seen, both in NAWM (P = 0.001) and in GM (P = 0.01). At follow-up, there was no evidence for a serial change in either mean T1 or peak-location for either NAWM or GM. There was weak evidence for a decline in patient NAWM peak-height and also evidence for a decline in control GM peak-height.

Conclusion

There are significant and persistent abnormalities of NAWM and GM T1 in early relapsing-remitting MS. Further studies should address whether such T1 measures have a role in prognosis or therapeutic monitoring. Multiple Sclerosis 2007; 13:169–177. http://msj.sagepub.com

Brain Parenchymal Fraction in Healthy Adults-A Systematic Review of the Literature

Brain atrophy is an important feature of many neurodegenerative disorders. It can be described in terms of change in the brain parenchymal fraction (BPF). In order to interpret the BPF in disease, knowledge on the BPF in healthy individuals is required. The aim of this study was to establish a normal range of values for the BPF of healthy individuals via a systematic review of the literature. The databases PubMed and Scopus were searched and 95 articles, including a total of 9269 individuals, were identified including the required data. We present values of BPF from healthy individuals stratified by age and post-processing method. The mean BPF correlated with mean age and there were significant differences in age-adjusted mean BPF between methods. This study contributes to increased knowledge about BPF in healthy individuals, which may assist in the interpretation of BPF in the setting of disease. We highlight the differences between post-processing methods and the need for a consensus gold standard.

Assessment of cortical damage in early multiple sclerosis with quantitative T2 relaxometry

T2 relaxation time is a quantitative MRI in vivo surrogate of cerebral tissue damage in multiple sclerosis (MS) patients. Cortical T2 prolongation is a known feature in later disease stages, but has not been demonstrated in the cortical normal appearing gray matter (NAGM) in early MS. This study centers on the quantitative evaluation of the tissue parameter T2 in cortical NAGM in a collective of early MS and clinically isolated syndrome (CIS) patients, hypothesizing that T2 prolongation is already present at early disease stages and variable over space, in line with global and focal inflammatory processes in MS. Additionally, magnetization transfer ratio (MTR) mapping was performed for further characterization of the expected cortical T2 alteration. Quantitative T2 and MTR maps were acquired from 12 patients with CIS and early MS, and 12 matched healthy controls. The lesion-free part of the cortical volume was identified, and the mean T2 and MTR values and their standard deviations within the cortical volume were determined. For evaluation of spatial specificity, cortical lobar subregions were tested separately for differences of mean T2 and T2 standard deviation. We detected significantly prolonged T2 in cortical NAGM in patients. T2 prolongation was found across the whole cerebral cortex and in all individual lobar subregions. Significantly higher standard deviations across the respective region of interest were found for the whole cerebral cortex and all subregions, suggesting the occurrence of spatially inhomogeneous cortical damage in all regions studied. A trend was observed for MTR reduction and increased MTR variability across the whole cortex in the MS group, suggesting demyelination. In conclusion, our results suggest that cortical damage in early MS is evidenced by spatially inhomogeneous T2 prolongation which goes beyond demyelination. Iron deposition, which is known to decrease T2, seems less prominent.

Magnetization transfer ratio in lesions rather than normal-appearing brain relates to disability in patients with multiple sclerosis

Magnetization transfer ratio (MTR) is a semi-quantitative measure that seems to correlate with the degree of myelin loss and generally tissue destruction in multiple sclerosis (MS). Our objective was to comprehensively assess the MTR of lesions and normal appearing (NA) tissue separately in the white matter (WM), the cortex, the thalamus and the basal ganglia (BG) and determine their relative contribution to disability. In this cross-sectional study 71 patients were included (59 with relapsing-remitting MS, 12 with secondary progressive MS). We used a three-dimensional MTR sequence with high spatial resolution, based on balanced steady-state free precession. Mean MTR was calculated for lesions and NA tissue separately for each tissue type. Lesional MTR was lower than normal-appearing MTR in WM, cortex and thalamus. In the regression analysis, MTR of cortical lesions (β = -0.23, p = 0.05) and MTR of WML (β = -0.21, p = 0.08) were related by trend to the expanded disability status scale. MTR of WML significantly predicted the paced auditory serial-addition test (β = 0.35, p = 0.004). MTR of normal-appearing tissue did not relate to any outcome. Our results suggest that MTR of lesions in the white matter and cortex rather than of normal-appearing tissue relates to disability in patients with MS.

Comparison between balanced steady-state free precession and standard spoiled gradient echo magnetization transfer ratio imaging in multiple sclerosis: methodical and clinical considerations

Different pathological processes like demyelination and axonal loss can alter the magnetisation transfer ratio (MTR) in brain tissue. The standard method to measure this effect is to scan the respective tissue twice, one with and one without a specific saturation pulse. A major drawback of this technique based on spoiled gradient echo (GRE) sequences relates to its long acquisition time due to the saturation pulses. Recently, an alternative concept for MT imaging based on balanced steady state free precession (bSSFP) has been proposed. Modification of the duration of the radiofrequency pulses for imaging allows scanning MT sensitive and non-sensitive images. The steady-state character of bSSFP with high intrinsic signal-to-noise ratio (SNR) allows three-dimensional (3D) whole brain MTR at high spatial resolution within short and thus clinically feasible acquisition times. In the present study, both bSSFP-MT and 2D GRE-MT imaging were used in a cohort of 31 patients with multiple sclerosis (MS) to characterize different normal appearing (NA) and pathological brain structures. Under the constraint of identical SNR and scan time, a 3.4 times higher voxel size could be achieved with bSSFP. This increased resolution allowed a more accurate delineation of the different brain structures, especially of cortex, hippocampus and MS lesions. In a multiple linear regression model, we found an association between MTR of cortical lesions and a clinical measure of disability (r= -0.407, p=0.035) in the bSSFP dataset only. The different relaxation weighting of the base images (T2/T1 in bSSFP, proton density in GRE) had no effects besides a larger spreading of the MTR values of the different NA structures. This was demonstrated by the nearly perfect linearity between the NA matter MTR of both techniques as well as in the absolute MTR differences between NA matter and the respective lesions.

Imaging outcomes for trials of remyelination in multiple sclerosis

Trials of potential neuroreparative agents are becoming more important in the spectrum of multiple sclerosis research. Appropriate imaging outcomes are required that are feasible from a time and practicality point of view, as well as being sensitive and specific to myelin, while also being reproducible and clinically meaningful. Conventional MRI sequences have limited specificity for myelination. We evaluate the imaging modalities which are potentially more specific to myelin content in vivo, such as magnetisation transfer ratio (MTR), restricted proton fraction f (from quantitative magnetisation transfer measurements), myelin water fraction and diffusion tensor imaging (DTI) metrics, in addition to positron emission tomography (PET) imaging. Although most imaging applications to date have focused on the brain, we also consider measures with the potential to detect remyelination in the spinal cord and in the optic nerve. At present, MTR and DTI measures probably offer the most realistic and feasible outcome measures for such trials, especially in the brain. However, no one measure currently demonstrates sufficiently high sensitivity or specificity to myelin, or correlation with clinical features, and it should be useful to employ more than one outcome to maximise understanding and interpretation of findings with these sequences. PET may be less feasible for current and near-future trials, but is a promising technique because of its specificity. In the optic nerve, visual evoked potentials can indicate demyelination and should be correlated with an imaging outcome (such as optic nerve MTR), as well as clinical measures.

Quantitative texture analysis of brain white matter lesions derived from T2-weighted MR images in MS patients with clinically isolated syndrome

INTRODUCTION

This study investigates the application of texture analysis methods on brain T2-white matter lesions detected with magnetic resonance imaging (MRI) for the prognosis of future disability in subjects diagnosed with clinical isolated syndrome (CIS) of multiple sclerosis (MS).

METHODS

Brain lesions and normal appearing white matter (NAWM) from 38 symptomatic untreated subjects diagnosed with CIS as well as normal white matter (NWM) from 20 healthy volunteers, were manually segmented, by an experienced MS neurologist, on transverse T2-weighted images obtained from serial brain MR imaging scans (0 and 6-12 months). Additional clinical information in the form of the Expanded Disability Status Scale (EDSS), a scale from 0 to 10, which provides a way of quantifying disability in MS and monitoring the changes over time in the level of disability, were also provided. Shape and most importantly different texture features including GLCM and laws were then extracted for all above regions, after image intensity normalization.

RESULTS

The findings showed that: (i) there were significant differences for the texture futures extracted between the NAWM and lesions at 0 month and between NAWM and lesions at 6-12 months. However, no significant differences were found for all texture features extracted when comparing lesions temporally at 0 and 6-12 months with the exception of contrast (gray level difference statistics-GLDS) and difference entropy (spatial gray level dependence matrix-SGLDM); (ii) significant differences were found between NWM and NAWM for most of the texture features investigated in this study; (iii) there were significant differences found for the lesion texture features at 0 month for those with EDSS≤2 versus those with EDSS>2 (mean, median, inverse difference moment and sum average) and for the lesion texture features at 6-12 months with EDSS>2 and EDSS≤2 for the texture features (mean, median, entropy and sum average). It should be noted that whilst there were no differences in entropy at time 0 between the two groups, significant change was observed at 6-12 months, relating the corresponding features to the follow-up and disability (EDSS) progression. For the NAWM, significant differences were found between 0 month and 6-12 months with EDSS≤2 (contrast, inverse difference moment), for 6-12 months for EDSS>2 and 0 month with EDSS>2 (difference entropy) and for 6-12 months for EDSS>2 and EDSS≤2 (sum average); (iv) there was no significant difference for NAWM and the lesion texture features (for both 0 and 6-12 months) for subjects with no change in EDSS score versus subjects with increased EDSS score from 2 to 5 years.

CONCLUSIONS

The findings of this study provide evidence that texture features of T2 MRI brain white matter lesions may have an additional potential role in the clinical evaluation of MRI images in MS and perhaps may provide some prognostic evidence in relation to future disability of patients. However, a larger scale study is needed to establish the application in clinical practice and for computing shape and texture features that may provide information for better and earlier differentiation between normal brain tissue and MS lesions.

Reduced magnetisation transfer ratio in cognitively impaired patients at the very early stage of multiple sclerosis: a prospective, multicenter, cross-sectional study

OBJECTIVES

Cognitive impairment belongs to the core symptoms in multiple sclerosis (MS) and can already be present at the very early stages of the disease. The present study evaluated cognitive functioning after the first clinical presentation suggestive of MS and brain tissue damage in a non-lesion focused MRI approach by using magnetisation transfer imaging (MTI).

SETTING AND PARTICIPANTS

47 patients (15 men and 32 women; mean age: 31.17 years) after the first clinical event suggestive of MS were recruited in six different MS centres in Germany and underwent a neuropsychological test battery including tests for attention, memory and executive function as well as depression and fatigue. MTI and conventional MRI measures (T1/T2 lesion load) were assessed. In addition, Magnetisation Transfer Ratio (MTR) maps were calculated. Primary outcome measure was the investigation of cognitive dysfunction in very early MS in correlation to MRI data.

RESULTS

55.3% of patients with MS failed at least one test parameter. Specifically, 6% were reduced in working memory, 14.9% in focused attention, 25.5% in figural learning and up to 14.9% in executive function. When the sample was subdivided into cognitively impaired and preserved, MTR scores within the cognitively impaired subgroup were significantly lower compared with the preserved group (t(43)=2.346, p=0.02*). No significant differences between the two groups were found in T2-weighted and T1-weighted lesion volume.

CONCLUSIONS

After the first MS-related clinical event, 55.3% of patients showed distinct cognitive deficits. Cognitively impaired patients had significantly lower whole brain MTR, but no differences in focal brain lesion volumes supporting the idea that early cognitive deficits may be related to diffuse loss of brain tissue integrity.

Multiple sclerosis: altered thalamic resting-state functional connectivity and its effect on cognitive function

PURPOSE

To investigate, by using resting-state (RS) functional magnetic resonance (MR) imaging, thalamocortical functional connectivity (FC) and its correlations with cognitive impairment in multiple sclerosis (MS).

MATERIALS AND METHODS

All subjects provided written informed consent; the study protocol was approved by the university institutional review board for this HIPAA-compliant study. Forty-eight patients with relapsing-remitting MS and 24 control subjects underwent multimodal MR imaging, including diffusion-tensor imaging, three-dimensional (3D) T1-weighted imaging, and functional MR imaging at rest and a neuropsychological examination with the Paced Auditory Serial Addition Test (PASAT). Functional MR imaging data were analyzed with tools from FMRIB Software Library, by using the seed-based method to identify the thalamic RS network (RSN).

RESULTS

When compared with control subjects, patients showed gray matter and white matter atrophy, as well as diffusion-tensor imaging abnormalities (P < .01). Patients displayed significantly greater synchronization than control subjects in the cerebellum; basal ganglia; hippocampus; cingulum; and temporo-occipital, insular, frontal, and parietal cortices. They also exhibited significantly lower synchronization in the thalamus; cerebellum; cingulum; and insular, prefrontal, and parieto-occipital cortices (cluster level, P < .05, corrected for familywise error [FWE]). In patients, the PASAT score at 3 seconds significantly inversely correlated with the thalamus, cerebellum, and some cortical areas in all cerebral lobes; the PASAT score at 2 seconds significantly correlated, even more strongly, with all the aforementioned regions and, in addition, with the cingulum and the left hippocampus (cluster level, P < .05, corrected for FWE).

CONCLUSION

Thalamic RSN is disrupted in MS, and decreased performance in cognitive testing is associated with increased thalamocortical FC, thus suggesting that neuroplasticity changes are unable to compensate for tissue damage and to prevent cognitive dysfunction.

Insights from magnetic resonance imaging

Recent years have witnessed impressive advancements in the use of magnetic resonance imaging (MRI) for the assessment of patients with multiple sclerosis (MS). Complementary to the clinical evaluation, conventional MRI (cMRI) provides crucial pieces of information for the diagnosis of MS, the understanding of its natural history, and monitoring the efficacy of experimental treatments. Measures derived from cMRI present clear advantages over the clinical assessment, including their more objective nature and an increased sensitivity to MS-related changes. However, the correlation between these measures and the clinical manifestations of the disease remains weak, and this can be explained, at least partially, by the limited ability of cMRI to characterize and quantify the heterogeneous features of MS pathology. Quantitative MR-based techniques have the potential to overcome the limitations of cMRI. Magnetization transfer MRI, diffusion-weighted and diffusion tensor MRI with fiber tractography, proton magnetic resonance spectroscopy, T1 and T2 relaxation time measurement, and functional MRI are contributing to elucidate the mechanisms that underlie injury, repair, and functional adaptation in patients with MS. All conventional and nonconventional MR techniques will benefit from the use of high-field MR systems (3.0T or more).

Sample sizes for lesion magnetisation transfer ratio outcomes in remyelination trials for multiple sclerosis

BACKGROUND

Enhancing remyelination in MS might improve function and protect axons from future damage. Lesion magnetisation transfer ratio (MTR) is sensitive to myelin content, and may be a useful measure for trials evaluating potential remyelinating agents.

OBJECTIVE

Estimating sample sizes required for a parallel group, placebo-controlled trial in MS using change in mean MTR of all T2lesions as a primary outcome measure.

METHODS

The primary sample size calculation was derived from data from a natural history study of relapsing remitting MS (n=18). The MTR values observed in demyelinated and remyelinated lesions in an ex vivo study were used to estimate the effect of remyelination on lesion MTR. The ex vivo data were also used to independently calculate sample sizes in order to inform the robustness of the in vivo estimates.

RESULTS

Calculations suggest that 30% remyelination of T2 lesions could be detected with 80% power in 38 (95% confidence interval 12-96) patients per arm based on the in vivo data, and in 66 per arm based on the ex vivo data.

CONCLUSION

The sample sizes derived are in a range that makes MTR a feasible outcome measure for proof-of-concept trials of putative therapies achieving remyelination in MS lesions.

Gray Matter Pathology in MS: Neuroimaging and Clinical Correlations

It is abundantly clear that there is extensive gray matter pathology occurring in multiple sclerosis. While attention to gray matter pathology was initially limited to studies of autopsy specimens and biopsies, the development of new MRI techniques has allowed assessment of gray matter pathology in vivo. Current MRI techniques allow the direct visualization of gray matter demyelinating lesions, the quantification of diffuse damage to normal appearing gray matter, and the direct measurement of gray matter atrophy. Gray matter demyelination (both focal and diffuse) and gray matter atrophy are found in the very earliest stages of multiple sclerosis and are progressive over time. Accumulation of gray matter damage has substantial impact on the lives of multiple sclerosis patients; a growing body of the literature demonstrates correlations between gray matter pathology and various measures of both clinical disability and cognitive impairment. The effect of disease modifying therapies on the rate accumulation of gray matter pathology in MS has been investigated. This review focuses on the neuroimaging of gray matter pathology in MS, the effect of the accumulation of gray matter pathology on clinical and cognitive disability, and the effect of disease-modifying agents on various measures of gray matter damage.

Within-lesion differences in quantitative MRI parameters predict contrast enhancement in multiple sclerosis

PURPOSE

To investigate the relationship between quantitative magnetic resonance imaging (qMRI) and contrast enhancement in multiple sclerosis (MS) lesions. We compared maps of T1 relaxation time, proton density (PD), and magnetization transfer ratio (MTR) between lesions with and without contrast enhancement as quantified by the amount of T1 shortening postcontrast agent (CA).

MATERIALS AND METHODS

In 17 patients with relapsing-remitting MS (RRMS), 15 with progressive MS (PMS), and 17 healthy controls, T1, PD, and MTR were measured at 3T and T1-mapping was repeated after CA administration. Manually drawn MS-lesions (3D-FLAIR) were labeled as enhancing if post-CA T1-shortening exceeded mean T1-shortening in normal-appearing white matter (NAWM) by at least 2 standard deviations. Precontrast T1, PD, and MTR were compared in enhancing lesions, nonenhancing lesions, NAWM, and gray matter.

RESULTS

Precontrast T1, PD, and MTR differed significantly between enhancing and nonenhancing lesions in RRMS and PMS patients (all P < 0.01). In PMS patients, PD of NAWM, enhancing, and nonenhancing lesions and MTR and T1 of gray matter differed significantly from RRMS and controls. Only MTR of gray matter differed between RRMS and controls.

CONCLUSION

Contrast enhancement in MS quantified by relative T1 shortening may be predicted by precontrast abnormalities of T1, PD, and MTR and likely represents blood-brain barrier damage.

Blood-brain barrier permeability of normal appearing white matter in relapsing-remitting multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) affects the integrity of the blood-brain barrier (BBB). Contrast-enhanced T1 weighted magnetic resonance imaging (MRI) is widely used to characterize location and extent of BBB disruptions in focal MS lesions. We employed quantitative T1 measurements before and after the intravenous injection of a paramagnetic contrast agent to assess BBB permeability in the normal appearing white matter (NAWM) in patients with relapsing-remitting MS (RR-MS).

METHODOLOGY/PRINCIPAL FINDINGS

Fifty-nine patients (38 females) with RR-MS undergoing immunomodulatory treatment and nine healthy controls (4 females) underwent quantitative T1 measurements at 3 tesla before and after injection of a paramagnetic contrast agent (0.2 mmol/kg Gd-DTPA). Mean T1 values were calculated for NAWM in patients and total cerebral white matter in healthy subjects for the T1 measurements before and after injection of Gd-DTPA. The pre-injection baseline T1 of NAWM (945±55 [SD] ms) was prolonged in RR-MS relative to healthy controls (903±23 ms, p = 0.028). Gd-DTPA injection shortened T1 to a similar extent in both groups. Mean T1 of NAWM was 866±47 ms in the NAWM of RR-MS patients and 824±13 ms in the white matter of healthy controls. The regional variability of T1 values expressed as the coefficient of variation (CV) was comparable between the two groups at baseline, but not after injection of the contrast agent. After intravenous Gd-DTPA injection, T1 values in NAWM were more variable in RR-MS patients (CV = 0.198±0.046) compared to cerebral white matter of healthy controls (CV = 0.166±0.018, p = 0.046).

CONCLUSIONS/SIGNIFICANCE

We found no evidence of a global BBB disruption within the NAWM of RR-MS patients undergoing immunomodulatory treatment. However, the increased variation of T1 values in NAWM after intravenous Gd-DTPA injection points to an increased regional inhomogeneity of BBB function in NAWM in relapsing-remitting MS.

Multicentre imaging measurements for oncology and in the brain

Multicentre imaging studies of brain tumours (and other tumour and brain studies) can enable a large group of patients to be studied, yet they present challenging technical problems. Differences between centres can be characterised, understood and minimised by use of phantoms (test objects) and normal control subjects. Normal white matter forms an excellent standard for some MRI parameters (e.g. diffusion or magnetisation transfer) because the normal biological range is low (<2-3%) and the measurements will reflect this, provided the acquisition sequence is controlled. MR phantoms have benefits and they are necessary for some parameters (e.g. tumour volume). Techniques for temperature monitoring and control are given. In a multicentre study or treatment trial, between-centre variation should be minimised. In a cross-sectional study, all groups should be represented at each centre and the effect of centre added as a covariate in the statistical analysis. In a serial study of disease progression or treatment effect, individual patients should receive all of their scans at the same centre; the power is then limited by the within-subject reproducibility. Sources of variation that are generic to any imaging method and analysis parameters include MR sequence mismatch, B(1) errors, CT effective tube potential, region of interest generation and segmentation procedure. Specific tissue parameters are analysed in detail to identify the major sources of variation and the most appropriate phantoms or normal studies. These include dynamic contrast-enhanced and dynamic susceptibility contrast gadolinium imaging, T(1), diffusion, magnetisation transfer, spectroscopy, tumour volume, arterial spin labelling and CT perfusion.

Clinical correlates of grey matter pathology in multiple sclerosis

Traditionally, multiple sclerosis has been viewed as a disease predominantly affecting white matter. However, this view has lately been subject to numerous changes, as new evidence of anatomical and histological changes as well as of molecular targets within the grey matter has arisen. This advance was driven mainly by novel imaging techniques, however, these have not yet been implemented in routine clinical practice. The changes in the grey matter are related to physical and cognitive disability seen in individuals with multiple sclerosis. Furthermore, damage to several grey matter structures can be associated with impairment of specific functions. Therefore, we conclude that grey matter damage - global and regional - has the potential to become a marker of disease activity, complementary to the currently used magnetic resonance markers (global brain atrophy and T2 hyperintense lesions). Furthermore, it may improve the prediction of the future disease course and response to therapy in individual patients and may also become a reliable additional surrogate marker of treatment effect.

Comprehensive brain analysis with automated high-resolution magnetization transfer measurements

PURPOSE

To enhance the reliability and spatial resolution of magnetization transfer ratio (MTR) measurements for interrogation of subcortical brain regions with an automated volume of interest (VOI) approach.

MATERIALS AND METHODS

A 3D magnetization transfer (MT) sequence was acquired using a scan-rescan imaging protocol in nine healthy volunteers. VOI definition masks for the MTR measurements were generated using FreeSurfer and compared to a manual region of interest (ROI) approach. (The longitudinal stability of MTR was monitored using agar gel phantom over a 5-month period.) Intraclass correlation coefficients (ICCs), coefficients of variation (CVs), and instrumental standard deviation (ISD) were determined.

RESULTS

CVs ranged from 1.29%-2.64% (automated) vs. 1.30%-3.40% (manual). ISDs ranged from 0.62-1.10 pu (automated) vs. 0.68-1.67 pu (manual). The SD of the running difference was 1.70% for the phantom scans. The Bland-Altman method indicated interchangeability of the automated VOI and manual ROI measurements.

CONCLUSION

The automated VOI approach for MTR measurement yielded higher ICCs, lower CVs, and lower ISDs compared to the manual method, supporting the utility of this strategy. These results demonstrate the feasibility of obtaining reliable MTR measurements in hippocampus and other critical subcortical regions.

Prevalence of grey matter pathology in early multiple sclerosis assessed by magnetization transfer ratio imaging

The aim of the study was to assess the prevalence, the distribution and the impact on disability of grey matter (GM) pathology in early multiple sclerosis. Eighty-eight patients with a clinically isolated syndrome with a high risk developing multiple sclerosis were included in the study. Forty-four healthy controls constituted the normative population. An optimized statistical mapping analysis was performed to compare each subject's GM Magnetization Transfer Ratio (MTR) imaging maps with those of the whole group of controls. The statistical threshold of significant GM MTR decrease was determined as the maximum p value (p<0.05 FDR) for which no significant cluster survived when comparing each control to the whole control population. Using this threshold, 51% of patients showed GM abnormalities compared to controls. Locally, 37% of patients presented abnormalities inside the limbic cortex, 34% in the temporal cortex, 32% in the deep grey matter, 30% in the cerebellum, 30% in the frontal cortex, 26% in the occipital cortex and 19% in the parietal cortex. Stepwise regression analysis evidenced significant association (p = 0.002) between EDSS and both GM pathology (p = 0.028) and T2 white matter lesions load (p = 0.019). In the present study, we evidenced that individual analysis of GM MTR map allowed demonstrating that GM pathology is highly heterogeneous across patients at the early stage of MS and partly underlies irreversible disability.

Cognitive impairment and whole brain diffusion in patients with neuromyelitis optica after acute relapse

The objective of this study investigated cognitive impairments and their correlations with fractional anisotropy (FA) and mean diffusivity (MD) in patients with neuromyelitis optica (NMO) without visible lesions on conventional brain MRI during acute relapse. Twenty one patients with NMO and 21 normal control subjects received several cognitive tests to assess cognitive function. Head diffusion tensor imaging (DTI) of all patients with NMO were collected with a 3-T MR system. Correlations of cognitive test scores and whole brain FA and MD were examined by voxel-based analysis. Region-of-interest analysis was applied to the significantly correlated regions which the most frequently appeared. We found that NMO patients without visible brain lesions had significantly impaired learning and memory, decreased information processing speed, and damaged attention compared with normal control subjects. These impaired cognitive domains were significantly correlated with FA and MD in local regions of corpus callosum, anterior cingulate and medial frontal cortex. In corpus callosum of NMO patients, mean FA was significantly lower and mean MD higher than normal control subjects. Our findings suggest that cognitive impairments in learning and memory, information processing speed and attention occur in NMO patients without visible brain lesions during acute relapse. The impairments in immediate and short-term memory in NMO patients may be due to information encoding deficits in the process of information acquisition. The corpus callosum of such patients may have local microscopic damages that play a role in cognitive impairments during acute relapse.

Imaging biomarkers in multiple sclerosis

Recent years have witnessed impressive advances in the use of magnetic resonance imaging (MRI) for the assessment of patients with multiple sclerosis (MS). Complementary to the clinical evaluation, conventional MRI provides crucial pieces of information for the diagnosis of MS. However, the correlation between the burden of lesions observed on conventional MRI scans and the clinical manifestations of the disease remains weak. The discrepancy between clinical and conventional MRI findings in MS is explained, at least partially, by the limited ability of conventional MRI to characterize and quantify the heterogeneous features of MS pathology. Other quantitative MR-based techniques, however, have the potential to overcome such a limitation of conventional MRI. Indeed, magnetization transfer MRI, diffusion tensor MRI, proton MR spectroscopy, and functional MRI are contributing to elucidate the mechanisms that underlie injury, repair, and functional adaptation in patients with MS. Such techniques are likely to benefit from the use of high-field MR systems and thus allow in the near future providing additional insight into all these aspects of the disease. This review summarizes how MRI is dramatically changing our understanding of the factors associated with the accumulation of irreversible disability in MS and highlights the reasons why they should be used more extensively in studies of disease evolution and clinical trials.

Texture analysis: a review of neurologic MR imaging applications

Texture analysis describes a variety of image-analysis techniques that quantify the variation in surface intensity or patterns, including some that are imperceptible to the human visual system. Texture analysis may be particularly well-suited for lesion segmentation and characterization and for the longitudinal monitoring of disease or recovery. We begin this review by outlining the general procedure for performing texture analysis, identifying some potential pitfalls and strategies for avoiding them. We then provide an overview of some intriguing neuro-MR imaging applications of texture analysis, particularly in the characterization of brain tumors, prediction of seizures in epilepsy, and a host of applications to MS.

A comparative assessment of cerebral white matter by magnetization transfer imaging in early- and adult-onset multiple sclerosis patients matched for disease duration

A more favorable clinical course in early-onset (EO) multiple sclerosis (MS) than adult-onset (AO) disease is reported. Our aim was to assess white matter with/without lesions by magnetization transfer (MT) imaging in EO and AO MS patients matched for duration of the disease. Relapsing-remitting MS patients with disease onset at age < or =18 years and >18 years (n = 11 for each) were matched according to sex, age, disease duration, and 22 sex-and age-matched healthy subjects were studied with MT imaging. MT ratios (MTR) of manually outlined ROIs from T1-hypointense, T1-isointense lesions and perilesional normal appearing white matter (NAWM) as well as NAWM of the left frontal lobe of the patients and healthy subjects were calculated. MTR differences between two patient groups and control subjects, and correlation of MTR with EDSS, disease onset age, disease duration and relapse rate were analyzed statistically. In comparison with NAWM of the patients and healthy subjects, the greatest MTR reductions were observed in T1-hypointense lesions followed by T1-isointense lesions and perilesional NAWM, respectively, in EO and AO MS. Both groups' NAWM MTR were reduced; greater and more significantly in EO patients. No correlation was found between MTR of any ROI and EDSS, duration of the disease, disease onset age, or relapse rate. Although normalization does not occur, abnormality of white matter in MS decreases as distance from the lesions increases. Greater NAWM abnormality in EO MS may relate to inherent myelin abnormalities and different repair/reorganization processes in this particular group.

TI-relaxation time changes over five years in relapsing-remitting multiple sclerosis

The pathological effects of multiple sclerosis are not confined to lesions; tissues that appear normal on conventional magnetic resonance imaging scans are also affected, albeit subtly. One imaging technique that has proven sensitive to such effects is T1-relaxation time measurement, with previous work demonstrating abnormalities in normal-appearing white matter and grey matter. In this work we investigated the evolution of T1-relaxation time changes in normal-appearing white matter and grey matter in relapsing—remitting multiple sclerosis. Three- and five-year follow-up data from 35 people with clinically early (a mean of 1.6 years from first clinical event) relapsing—remitting multiple sclerosis and 15 healthy controls were analysed. T1-relaxation time histograms were extracted from normal-appearing white matter and grey matter, and mean, peak height and peak location values were estimated. T1-relaxation time peak height declined in the multiple sclerosis normal-appearing white matter and grey matter, but not the control group (rate difference p = 0.024 in normal-appearing white matter, in normal-appearing grey matter p = 0.038); other T1-relaxation time changes were not significantly different between groups. Changes in T1-relaxation time measures did not correlate with increases in brain T2-weighted lesion loads or Expanded Disability Status Scale scores. These results suggest that the processes underlying changes in normal-appearing white matter and grey matter T1-relaxation times are not immediately linked to white matter lesion formation, and may represent more diffuse but progressive sub-clinical pathology in relapsing—remitting multiple sclerosis.

Bimonthly assessment of magnetization transfer magnetic resonance imaging parameters in multiple sclerosis: a 14-month, multicentre, follow-up study

This study was performed to assess the temporal evolution of damage within lesions and the normal-appearing white matter, measured using frequent magnetization transfer (MT) MRI, in relapsing-remitting multiple sclerosis (RRMS). The relationship of MT ratio (MTR) changes with measures of lesion burden, and the sample sizes needed to demonstrate a treatment effect on MTR metrics in placebo-controlled MS trials were also investigated. Bimonthly brain conventional and MT MRI scans were acquired from 42 patients with RRMS enrolled in the placebo arm of a 14-month, double-blind trial. Longitudinal MRI changes were evaluated using a random effect linear model accounting for repeated measures, and adjusted for centre effects. The Expanded Disability Status Scale (EDSS) score remained stable over the study period. A weak, but not statistically significant, decrease over time was detected for normal-appearing brain tissue (NABT) average MTR (-0.02% per visit; p = 0.14), and MTR peak height (-0.15 per visit; p = 0.17), while average lesion MTR showed a significant decrease over the study period (-0.07% per visit; p = 0.03). At each visit, all MTR variables were significantly correlated with T2 lesion volume (LV) (average coefficients of correlation ranging from -0.54 to -0.28, and p-values from <0.001 to 0.02). At each visit, NABT average MTR was also significantly correlated with T1-hypointense LV (average coefficient of correlation = -0.57, p < 0.001). The estimation of the sample sizes required to demonstrate a reduction of average lesion MTR (the only parameter with a significant decrease over the follow-up) ranged from 101 to 154 patients to detect a treatment effect of 50% in a 1-year trial with a power of 90%. The steady correlation observed between conventional and MT MRI measures over time supports the hypothesis of axonal degeneration of fibres passing through focal lesions as one of the factors contributing to the overall MS burden.

Magnetization transfer ratio abnormalities reflect clinically relevant grey matter damage in multiple sclerosis

BACKGROUND

In multiple sclerosis, grey matter (GM) damage appears more clinically relevant than either white matter damage or lesion load.

OBJECTIVE

We investigated if normal-appearing white matter (NAWM) and grey matter tissue changes assessed by magnetization transfer ratio were associated with long-term disability.

METHODS

Sixty-nine people were assessed 20 years after presentation with a clinically isolated syndrome (CIS) [28 still CIS, 31 relapsing-remitting multiple sclerosis, 10 secondary progressive multiple sclerosis], along with 19 healthy subjects. Mean magnetization transfer ratio, peak height (PH) and peak location of the normalized magnetization transfer ratio histograms were determined in NAWM and grey matter, as well as, white matter and GM Fraction (GMF) and T(2)-weighted lesion load.

RESULTS

Median expanded disability status scale for multiple sclerosis patients was 2.5 (range 1-8). GM-PH, and less so, NAWM mean and peak location, were lower in multiple sclerosis patients (P = 0.009) versus controls, relapsing-remitting multiple sclerosis versus CIS (P = 0.008) and secondary progressive multiple sclerosis versus relapsing-remitting multiple sclerosis (P = 0.002). GM-PH (as well as GMF) correlated with expanded disability status scale (r(s) = -0.49; P = 0.001) and multiple sclerosis functional score (r(s) = 0.51; P = 0.001). GM-PH independently predicted disability with similar strength to the associations of GMF with clinical measures.

CONCLUSION

Grey matter damage was related to long-term disability in multiple sclerosis cohort with a relatively low median expanded disability status scale. Markers of intrinsic grey matter damage (magnetization transfer ratio) and tissue loss offer clinically relevant information in multiple sclerosis.

Thalamic involvement and its impact on clinical disability in patients with multiple sclerosis: a diffusion tensor imaging study at 3T

BACKGROUND AND PURPOSE

Several studies suggest that grey matter involvement may play a role in multiple sclerosis (MS) pathology. Diffusion tensor imaging (DTI) at 3T was used to investigate the presence of damage to the normal-appearing thalamus in MS and its relationship with disability.

MATERIALS AND METHODS

Twenty-four patients with relapsing-remitting (RR, n = 13, age = 41.7 +/- 6.1, Expanded Disability Status Scale [EDSS] score = 2.2 +/- 1.2) and secondary-progressive (n = 11, age = 46.9 +/- 9.6, EDSS = 5.9 +/- 1.0) MS and 24 age- and sex-matched healthy volunteers were studied. Fractional anisotropy (FA) and mean diffusivity (MD) were measured in regions of interest of normal-appearing thalamus. We examined group differences in MD and FA and correlations between DTI-derived metrics and clinical or imaging measures of disease.

RESULTS

Patients with MS had higher thalamic FA (P < .0001) and MD (P = .035) than volunteers. MD values correlated with the Paced Auditory Serial Addition Task (r = -0.43, P = .034) and motor EDSS (r = 0.47, P = .021) scores. In patients with RRMS, MD values correlated with global EDSS (r = 0.75, P = .003) and motor EDSS (r = 0.68, P = .010). Correlations were found between MD values and T1 and T2 lesion load (r = 0.58, P < .05) and brain parenchymal fraction (r = -0.46, P < .05).

CONCLUSIONS

DTI was able to detect abnormalities in normal-appearing thalamus of patients with MS. The strength of association between thalamic DTI measures and functional impairment was in the same range as those seen with standard MR imaging disease measures. The assessment of the integrity of the thalamus with DTI is a promising metric as a marker of disease for future studies.

Magnetization transfer MR imaging in multiple sclerosis

We introduce the fundamental aspects of MT, of MT MR imaging, and the respective analysis techniques. We then review the applications of MT MR imaging to multiple sclerosis. Finally we review the technique's contribution to our understanding of this disease.

Grey matter magnetization transfer ratio independently correlates with neurological deficit in secondary progressive multiple sclerosis

Although there is substantial brain grey matter pathology in secondary progressive multiple sclerosis (MS), there has been limited investigation of its contribution to disability.This study investigated the correlation of magnetization transfer ratio (MTR) measures taken from brain grey matter, normal appearing white matter (NAWM) and lesions with neurological deficit and disability in 113 people with secondary progressive MS. In order to adjust for the potential effects of focal white matter lesions and global brain atrophy, T2 lesion volume and normalized brain volume (NBV) were also calculated for each subject. Clinical measures included the expanded disability status scale (EDSS) and the multiple sclerosis functional composite (MSFC) scores. Linear regression analysis was used to assess the age- and gender-adjusted correlation of MTR histogram mean, peak height and peak location with the MSFC and individual component measures. Logistic regression analysis was used to determine whether imaging measures could be used to predict if subjects were in the higher disability group (EDSS > or = 6.5).Significant correlations were detected between MSFC composite and mean MTR in (i) normal appearing white matter (NAWM; r = 0.327, p < 0.0001), (ii) grey matter (r = 0.460, p < 0.0001) and (iii) lesions (r = 0.394, p < 0.0001). Although NBV and T2 lesion volume correlated significantly with MSFC, grey matter histogram mean emerged as the best predictor of MSFC score. None of the MRI measures significantly predicted higher EDSS.These results suggest that brain grey matter pathology plays an important role in determining neurological impairment. The apparent paucity of correlation between MRI measures and EDSS is likely to represent the relative insensitivity of the latter measure in this study group.

Grey matter pathology in clinically early multiple sclerosis: evidence from magnetic resonance imaging

In multiple sclerosis (MS) it is emerging that the most visible element of pathology, white matter (WM) lesions, represents only a fraction of the disease burden borne by the brain; non-lesional WM is also damaged, as is the grey matter (GM). Evidence is also accruing that GM damage may be a major determinant of longer-term outcomes in MS, and that such damage occurs from the earliest clinical stages of the disease. In this review, we focus on the early stages of relapse onset MS, considering the nature, extent and evolution of GM pathology, as determined using magnetic resonance imaging.

Magnetic resonance techniques to quantify tissue damage, tissue repair, and functional cortical reorganization in multiple sclerosis

A dramatic paradigm shift is taking place in our understanding of the pathophysiology of multiple sclerosis (MS). An important contribution to such a shift has been made possible by the advances in magnetic resonance imaging (MRI) technology, which allows structural damage to be quantified in the brains of patients with MS and to be followed over the course of the disease. Modern quantitative MR techniques have reshaped the picture of MS, leading to the definition of the so- called "axonal hypothesis" (i.e., changes in axonal metabolism, morphology, or density are important determinants of functional impairment in MS). Metrics derived from magnetization transfer and diffusion-weighted MRI enable us to quantify the extent of structural changes occurring within T2-visible lesions and normal-appearing tissues (including gray matter), with increased pathological specificity over conventional MRI to irreversible tissue damage; proton MR spectroscopy adds valuable pieces of information on the biochemical nature of such changes. Finally, functional MRI can provide new insights into the role of cortical adaptive changes in limiting the clinical consequences of MS-related irreversible structural damage. Our current understanding of the pathophysiology of MS is that this is not only a disease of the white matter, characterized by focal inflammatory lesions, but also a disease involving more subtle and diffuse damage throughout the white and gray matter. The inflammatory and neurodegenerative components of the disease process are present from the earliest observable phases of the disease, but appear to be, at least partially, dissociated. In addition, recovery and repair play an important role in the genesis of the clinical manifestations of the disease, involving both structural changes and plastic reorganization of the cortex. This new picture of MS has important implications in the context of treatment options, since it suggests that agents that protect against neurodegeneration or promote tissue repair may have an important role to play alongside agents acting on the inflammatory component of the disease.

Absence of diffuse cervical cord tissue damage in early, non-disabling relapsing-remitting MS: a preliminary study

BACKGROUND

Magnetization transfer (MT) magnetic resonance imaging (MRI) can provide quantitative information about the severity of tissue damage in the cervical cord of patients with multiple sclerosis (MS). MT MRI-derived measures of cord damage are correlated with the severity of disease-related locomotor disability.

OBJECTIVES

The objective of this study was to investigate whether MT MRI-detectable cervical cord damage is present in early relapsing-remitting (RR) MS.

SUBJECTS AND METHODS

We studied 23 patients with 'early' RR MS (i.e., with a disease duration shorter than 5 years) and 10 age-matched healthy control subjects. During a single session, the following sequences were acquired using a 1.5 T scanner: (a) brain dual-echo turbo spin echo; (b) cervical cord fast short-tau inversion recovery; (c) cervical cord gradient echo, without and with MT pulse. Brain T2 lesion volume was measured. Cervical cord lesions were counted and normalized histograms of cord MT ratio (MTR) were produced.

RESULTS

One or more cervical cord lesions were found in nine patients (39%). The average cord MTR and the mean histogram peak height values did not differ between patients and controls. There was no significant correlation between brain T2 lesion volume and cervical cord MTR histogram-derived metrics.

CONCLUSIONS

Cervical cord tissue damage seems to be limited to macroscopic lesions in patients with early, non-disabling RR MS. Longitudinal studies are warranted to define the dynamics of MS-related cord damage accumulation over time later on in the course of the disease.

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

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

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.

Magnetisation transfer ratio in the normal appearing white matter predicts progression of disability over 1 year in early primary progressive multiple sclerosis

BACKGROUND

Progression rates in primary progressive multiple sclerosis (PPMS) vary widely and brain magnetisation transfer imaging (MTI) has potential as an early prognostic indicator. We investigated the predictive value of MTI and the longitudinal changes developing over 1 year in early PPMS.

AIMS

To determine (1) whether baseline brain MTI parameters in early PPMS predict clinical changes over 1 year, independent of brain volume and (2) whether a change in magnetisation transfer (MT) parameters occurs over 1 year, independent of atrophy.

METHODS

30 patients with PPMS within 5 years of symptom onset and 15 controls underwent MT and volumetric imaging studies, at baseline and at 1 year. Patients underwent clinical assessment using the Expanded Disability Status Scale (EDSS) and Multiple Sclerosis Functional Composite (MSFC), including the timed walk subtest (TWT). Normalised MT histograms were generated for whole brain, normal appearing brain tissue (NABT) and normal appearing white and grey matter (NAWM and NAGM) segments. Multiple regression analyses were performed to investigate whether baseline MTR parameters predicted clinical change over 1 year, adjusting for baseline brain volume. MTR changes over 1 year were assessed using paired t tests.

RESULTS

In patients, lower baseline NAWM MTR predicted greater deterioration in EDSS and MSFC, particularly in walking ability measured by the TWT, independent of NAWM baseline volume (p = 0.001). NAGM MTR mean (p<0.001), and to a lesser extent NAWM mean (p = 0.011) and lesion MTR (p = 0.03), decreased over 1 year.

CONCLUSIONS

NAWM MTR may provide information on short term clinical prognosis in early PPMS. MTI is sensitive to brain tissue changes over 1 year in early PPMS, which were primarily seen in the NAGM.

[Future of non conventional MR techniques in MS]

Although conventional magnetic resonance imaging (MRI) is used for diagnosing multiple sclerosis (MS) and monitoring disease activity and course, the correlation between conventional MRI data and clinical findings remains weak. This "clinical-MRI paradox" could be partly due to the lack of MRI specificity related to the heterogeneous pathological substrates of MS and to its inability to quantify the extent of damage in the normal-appearing tissue. Recently, non-conventional MRI techniques, including magnetization transfer MRI, diffusion tensor MRI, and proton MR spectroscopy have been applied to improve our understanding of the pathophysiology of MS. These techniques may provide information about structural and biochemical changes occurring within and outside macroscopic MS lesions (inflammation, demyelination, axonal loss), in particular in the normal-appearing white and grey matter. These techniques could also significantly improve our ability to monitor inflammatory demyelination and axonal injury. In the same way, functional MRI gives us the potential substrate to assess the mechanisms of adaptive cortical reorganization, which may limit the irreversible consequences of MS tissue injury.

Magnetization transfer magnetic resonance imaging of the brain, spinal cord, and optic nerve

Magnetic resonance imaging is highly sensitive in revealing CNS abnormalities associated with several neurological conditions, but lacks specificity for their pathological substrates. In addition, MRI does not allow evaluation of the presence and extent of damage in regions that appear normal on conventional MRI sequences and that postmortem studies have shown to be affected by pathology. Quantitative MR-based techniques with increased pathological specificity to the heterogeneous substrates of CNS pathology have the potential to overcome such limitations. Among these techniques, one of the most extensively used for the assessment of CNS disorders is magnetization transfer MRI (MT-MRI). The application of this technique for the assessment of damage in macroscopic lesions, in normal-appearing white and gray matter, and in the spinal cord and optic nerve of patients with several neurological conditions is providing important in vivo information-dramatically improving our understanding of the factors associated with the appearance of clinical symptoms and the accumulation of irreversible disability. MT-MRI also has the potential to contribute to the diagnostic evaluation of several neurological conditions and to improve our ability to monitor treatment efficacy in experimental trials.

Magnetization Transfer MRI in Multiple Sclerosis

In multiple sclerosis (MS), conventional magnetic resonance imaging (cMRI) has proved to be sensitive for detecting lesions and their changes over time. However, cMRI is not able to characterize and quantify the tissue damage within and outside such lesions. Magnetization transfer (MT) MRI is a quantitative technique with the potential to overcome this limitation and, as a consequence, to provide additional information about the nature and the extent of tissue damage associated to this disease. During the last 10 years, MT MRI indeed has allowed us to quantify the structural changes occurring within and outside lesions visible on cMRI scans, thus providing a more accurate in vivo picture of the heterogeneity of MS and, as a consequence, improving our ability to monitor the evolution of the disease. The application of MT MRI to the study of MS has contributed to change our understanding of how MS causes irreversible disability by showing that MS is more than an inflammatory-demyelinating condition of the white matter of the central nervous system.

A magnetization transfer MRI study of deep gray matter involvement in multiple sclerosis

BACKGROUND/PURPOSE

Gray matter involvement in multiple sclerosis (MS) is of growing interest with respect to disease pathogenesis. Magnetization transfer imaging (MTI), an advanced MRI technique, is sensitive to disease in normal appearing white matter (NAWM) in patients with MS.

DESIGN/METHODS

We tested if MTI detected subcortical (deep) gray matter abnormalities in patients with MS (n= 60) vs. age-matched normal controls (NL, n= 20). Magnetization transfer ratio (MTR) maps were produced from axial proton density, conventional spin-echo, 5 mm gapless slices covering the whole brain. Region-of-interest-derived MTR histograms for the caudate, putamen, globus pallidus, thalamus, and NAWM were obtained. Whole brain MTR was also measured.

RESULTS

Mean whole brain MTR and the peak position of the NAWM MTR histogram were lower in patients with MS than NL (P < .001) and mean whole brain MTR was lower in secondary progressive (SP, n= 10) than relapsing-remitting (RR, n= 50, P < .001) patients. However, none of the subcortical gray matter nuclei showed MTR differences in MS vs. NL, RR vs. SP, or SP vs. NL.

CONCLUSIONS

The MTI technique used in this cohort was relatively insensitive to disease in the deep gray matter nuclei despite showing sensitivity for whole brain disease in MS. It remains to be determined if other MRI techniques are more sensitive than MTI for detecting pathology in these areas.